polymeric micelles: authoritative aspects for drug delivery

This article was downloaded by: [Istanbul Universitesi Kutuphane ve Dok]On: 21 December 2014, At: 10:00Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Designed Monomers and PolymersPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tdmp20

Polymeric micelles: authoritativeaspects for drug deliverySushant S. Kulthe a , Yogesh M. Choudhari a , Nazma N. Inamdar a

& Vishnukant Mourya aa Government College of Pharmacy , Aurangabad , 431005 ,Maharashtra , IndiaPublished online: 02 Jul 2012.

To cite this article: Sushant S. Kulthe , Yogesh M. Choudhari , Nazma N. Inamdar & VishnukantMourya (2012) Polymeric micelles: authoritative aspects for drug delivery, Designed Monomers andPolymers, 15:5, 465-521, DOI: 10.1080/1385772X.2012.688328

To link to this article: http://dx.doi.org/10.1080/1385772X.2012.688328

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/loi/tdmp20

http://www.tandfonline.com/action/showCitFormats?doi=10.1080/1385772X.2012.688328

http://dx.doi.org/10.1080/1385772X.2012.688328

http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/page/terms-and-conditions

REVIEW

Polymeric micelles: authoritative aspects for drug delivery

Sushant S. Kulthe, Yogesh M. Choudhari, Nazma N. Inamdar and Vishnukant Mourya*

Government College of Pharmacy, Aurangabad 431005 Maharashtra, India

The generation of supramolecular architectures with well-defined structures and functional-ities is recently garnering attraction. Self-assemblage of amphiphilic polymers leads to theformation of polymeric micelles that demonstrate unique set of characteristics such asexcellent biocompatibility, low toxicity, enhanced blood circulation time, and solubilizationof poorly water-soluble drugs. In this article, we provide an up-to-date review on importantaspects of polymeric micelles. Critical factors for solubilization of hydrophobic drugs inthe micellar core are discussed. Polymeric micelles can be used as ‘smart’ drug carriers fortargeting certain areas of the body. Here, we have especially emphasized on the recentdevelopments in the targetability of certain tissues such as cancerous tissues using poly-meric micelles. Different stimuli exploited for creating stimuli-sensitive micelles are dis-cussed comprehensively. Application of polymeric micelles in the photodynamic therapy isalso meticulously described.

Keywords: polymeric micelles; solubilization; targeting; stimuli-sensitivity; photodynamictherapy

Introduction

Mysterious are the nature’s ways of creating the materials of great complexicity and function-ality from simple ones with variety of arrangements starting from the biological membrane tonacre. With the hope to use nature’s tricks to an advantage, the very large effort in polymerscience has been applied to get the molecules which will assemble spontaneously or withstimulus to structures that can be employed in science. One such assembly of interest is amicelle and more particularly a polymeric micelle. The field of polymeric micelles is expand-ing its roots from academic settings into industrial one adopting it for preclinical and clinicaldrug development. With more players embracing this technology, more innovative researchon polymeric micelles spanning basic science as development of newer polymers and theirmicelles with characterization to application part as for drug solubilization, drug targeting viavarious routes of drug administration and targeting of nucleic acid drugs is expected.

Micelles: formation and features

The amphiphilic molecules or surfactant monomers that possess a polar head and a lipophilictail show concentration dependent variation in the physicochemical properties. The changesin physicochemical properties are associated with the orientation and aggregation of amphi-philic molecules in solution resulting in the formation of structures called micelles. Micelles

*Corresponding author. Email: [email protected]

Designed Monomers and PolymersVol. 15, No. 5, September 2012, 465–521

ISSN 1568-5551 online� 2012 Taylor & Francishttp://dx.doi.org/10.1080/1385772X.2012.688328http://www.tandfonline.com

Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

are dynamic structures that are in continuous equilibrium with free monomers, wherein mono-mers are constantly exchanged between micelles and intermicellar solution. Due to this to andfro motion of molecules or the exchange phenomenon, surfactant molecules reside in themicelle form for a definite time called the surfactant residence time [1]. An average numberof monomers forming micelle at any given time is termed as the aggregation number.Micelles are generally made up of 50–200 monomers. The radius of a spherical micelle isalmost the same as the length of a fully extended surfactant monomer, which mostly is 1–3 nm, and thus micelles lie in the colloidal range. Molecular size and geometrical features ofthe surfactants determine size of the micelle [2]. Micelle formation in aqueous solution ismainly governed by the effective interaction between the hydrophobic parts of the surfactants.The major driving force behind self-association is the decrease of free energy of the system.Decrease in energy of the system is a result of removal of hydrophobic fragments from theaqueous surroundings with the formation of a micelle core stabilized with hydrophilic blocksexposed into water. The change in free energy for the micellization process is described as:

�G�mic ¼ RT lnðCMCÞ

where R is the gas constant, T is the temperature of the system and CMC is the criticalmicelle concentration [3].

The effective interactions resulting in micellization are opposed by repulsive interactionsbetween the head groups and an interaction associated with residual alkyl chain-water mole-cule contacts at the micelle surface.

The most important factor affecting the process of micelle formation or self-assembly isthe size of the hydrophobic domain in the amphiphilic molecule [4]. Other factors of impor-tance are the conditions of the system as solvent, concentration of amphiphiles, temperature,etc. These micelles are microheterogeneous, in that they internally have a hydrophobic coreand externally a hydrophilic surface. The assembly formation starts only when a certain mini-mum concentration is crossed by the amphiphilic molecules, called as critical micelle concen-tration. At low concentrations in a medium, the amphiphilic molecules exist separately, andare so small that they appear to be subcolloidal. Below the CMC, the concentration of amphi-phile undergoing adsorption at the air–water interface increases as the total concentration ofthe amphiphile is increased. Finally at CMC, the interface as well as the bulk phase is satu-rated with monomers. Any further amphiphile added in excess of CMC results in the aggrega-tion of monomers in the bulk phase, such that the free energy of the system is reduced [1,5].The temperature below which amphiphilic molecules exist as unimers and above which asaggregates is the critical micellization temperature (CMT). This self-assembly is initiatedeither at a given temperature by increasing the concentration beyond the CMC or at a givenconcentration by increasing the temperature beyond the CMT.

Polymeric micelles

Amphiphilic block or graft copolymers behave in the same manner as that of conventionalamphiphiles. In solution, attachment of a water-soluble polymer to an insoluble polymer leadsto the formation of micelles of amphiphilic block copolymers resulting in structural and flowcharacteristics of the polymer that differ from either parent polymer. A major differencebetween the micelles of conventional surfactant monomers and polymeric surfactants is thatthere usually is a covalent linkage in individual polymeric surfactant molecules within thehydrophobic core that does not allow dynamic exchange of monomers between free solution

466 S.S. Kulthe et al.

Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

and the micellar pseudo-phase. This confers rigidity and stability to the polymeric micelles[6]. The diameter of polymeric micelle ranges from 10 to 100 nm.

These supramolecular structures are generated as a result of delicate balance betweenstrong covalent bonds that hold the molecular building blocks together and the reversibleintermolecular forces that assemble them. Factors controlling the size of the polymericmicelles include molecular weight of the amphiphilic block copolymer, aggregation numberof the amphiphiles, relative proportion of hydrophilic and hydrophobic chains, quantity ofsolvent trapped inside the micellar core, and the preparation process [7,8]. The radius of anentire micelle is designated as Rm and that of the core as Rc.

In aqueous medium, amphiphilic block copolymers can principally self-assemble intospherical micelles, worm-like or cylindrical micelles, and polymer vesicles or polymersomes.Main factor governing the morphology of micelles is the hydrophilic–hydrophobic balance ofthe block copolymer defined by the hydrophilic volume fraction, f. For amphiphilic blockcopolymers with value of f� 35%, polymer vesicles are formed, whereas for value of f> 45%,spherical micelles are formed. Other controlling experimental factors are degree of swelling ofthe corona, concentration, temperature, pH, ionic strength, and sample preparation [9–11]. Forconvenience, amphiphilic diblock polymers are said to be those polymers for which the molec-ular mass is in the range 5000–30,000Da in contrast with surfactants for which the molecularmass is in the range 100–500Da [12]. Besides higher molecular weights, amphiphilic blockcopolymers are complex structures. Thus, in dilute solutions they yield monomolecularmicelles and micelles of various shapes at different concentrations [13]. By using amphiphilesof more complicated molecular design, e.g. star copolymers or by varying the experimentalconditions for self-assembly more complex morphologies such as crew-cut micelles, multicom-partment micelles, toroids, etc. may be obtained which may have great influence on their appli-cation performance of interfacial activity, viscosity, and emulsification [14–17].

Attractive features of polymeric micelles

Polymeric amphiphiles have received increasing attention because of their special physico-chemical and morphological characteristics in water, and possibility to generate ‘applicationsuitable’ polymers. Suitable amphiphilic block copolymers are easily obtainable via controlledsynthesis by varying the block ratio, the total molecular weight, the chemical structure, andconjugation with biomolecules. Size and morphology of the polymeric micelles developedfrom amphiphilic polymers can readily be controlled through adjusting the structure of amphi-philic copolymers as the factors controlling size of the polymeric micelles include molecularweight of amphiphilic block copolymer, aggregation number of amphiphiles, relative propor-tion of hydrophilic and hydrophobic chains, quantity of solvent trapped inside the micellarcore, and the preparation process.

The colloidal dimensions of micelles render them suitable for sterilization by simple filtra-tive process with no special aseptic processing. The micellar core produces a hydrophobicdomain. Thus, polymeric micelles are used for solubilization of hydrophobic moieties in thecore region through hydrophobic interactions and/or ionic interactions. Most of the drugsbeing poorly water-soluble can be easily incorporated into the core of polymeric micelles toovercome solubility problems [18,19]. Solubility enhancement usually is associated with bet-terment of oral bioavailability of the hydrophobic drugs [20,21]. Incorporation of the druginto block copolymer micelles results in the in vitro stabilization of drug as it is protectedfrom various destructive agents in aqueous environment. Also, the hydrophilic shell of poly-meric micelles is thought to disguise the drug in vivo and prevent its interaction with bloodproteins, cells, and tissues which otherwise might lower the plasma drug concentration [22].

Designed Monomers and Polymers 467

Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Mostly, the hydrophobic segments exhibit low glass transition temperatures (ca. 40 °C). Thisfeature allows incorporation of thermolabile agents into polymeric micelles at compatible tem-peratures [23]. Surfactant micelles tend to disintegrate upon dilution triggering lysis of cellmembranes. Polymeric micelles are considerably more stable toward dilution than surfactantmicelles and hence, exhibit minimal cytotoxicity. The hydrophilic shell and the nanoscopicsize prevent mechanical clearance of micelles by filtration or in the spleen [24]. This is bene-ficial for prolonging the blood circulation of drug. Also, the shell stabilizes the micelle, inter-acts with the plasma proteins and cell membranes and its nature controls biodistribution ofthe carrier. Mostly, the shell is made up of chains of hydrophilic, biocompatible polymerssuch as poly(ethylene oxide) (PEO), etc. [25]. It also favors the particular absorption in gas-trointestinal system. Along with these features, low toxicity and faster rate of clearance ofpolymeric micelles from the body make them suitable for intravenously administered drugdelivery systems [26]. Additionally, there is no need of modification of chemical structure ofthe drugs [27]. Thus, owing to the exciting facets offered by polymeric micelles, they arepotential drug delivery carriers, especially when the micelles are made from suitable biode-gradable polymers having low risk of chronic accumulation in the body [28,29].

The size of polymeric micelles is typical of a virus. Nanoscopic size minimizes the riskof embolism in capillaries, contrary to larger drug carriers [30]. It also avoids renal filtrationand reticuloendothelial system (RES) uptake, and so can circulate in the blood for long peri-ods of time, eventually passing through capillaries that are disrupted near tumor growth [31–34]. Polymeric micelles thus provide targeting of the loaded drug. End-functionalization ofblock copolymers with sugars and peptides on the periphery yield an array of micelles thatcan be used for the receptor-mediated targeted drug and gene delivery. Immunomicelles,another means of targeting, are prepared by covalently attaching monoclonal antibody mole-cules to a surfactant or polymeric micelles demonstrate high binding specificity and target-ability [35,36]. Polymeric micelles are employed as ‘intelligent drug carriers’ through use ofstimuli-sensitive (pH and temperature) copolymers, etc. and are investigated for controlleddrug delivery [37].

Limitations

The industrial growth of polymeric micelles is hindered by high cost of preparation and the dif-ficulty in drug loading [38]. When the polymer is sufficiently hydrophilic it can be dissolveddirectly along with the drug to yield drug-loaded polymeric micelles. But this method, which issuitable for highly hydrophilic polymers, usually is associated with low drug loading. For mostother amphiphilic polymers, an organic solvent is used to solubilize polymer and poorly water-soluble drug. Drug loading in polymeric micelles is then effected by emulsification or dialysistechniques. However, emulsification usually involves use of chlorinated solvents which are notsafe. Dialysis process often requires more than 36 h for efficient loading and replenishment ofwater at regular intervals. Nevertheless, the above-mentioned limitations can be overcome byemploying a simple and cost-effective method in which water/tert-butanol mixture is used fordissolving drug as well as polymer and then lyophilizing it. Drug-loaded polymeric micellesare obtained by redispersing lyophilized product in a suitable vehicle [39–41].

Owing to extreme dilutions by blood upon intravenous injections of micellar solution,polymeric micelles are prone to deformation and disassembly which may lead to leakage andburst release of loaded drugs. However, this limitation can now be overcome by improvedinteraction of the drug and polymer via chemical conjugation or by cross-linking of the shell[42,43]. The loss of hydrophilic and hydrophobic balance upon increased loading of hydro-phobic drug into the core region also has been related to decreased stability of the polymeric


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

micelles. Drugs or copolymers prone to hydrolytic cleavage in aqueous systems may as wellpose stability problems. However, lyophilized polymeric micelle formulations have shown topossess improved long-term stability for intravenously administered preparations [44–46].

Polymers used for micelle preparation

Polymers for preparation of micelles can either be amphiphilic or nonamphiphilic in nature.Moreover, amphiphilic copolymers can be block copolymers or graft copolymers. Theseamphiphilic block or graft copolymers are usually biodegradable and also offer excellent bio-compatibility. From the era of emergence of polymeric micelles, most of the research focushave been on the synthesis of diblock and triblock copolymers [22]. Recently, some studieshave been conducted for producing tetrablock and pentablock copolymers also. A blockcopolymer molecule contains two or more polymer chains attached at their ends. Linear blockcopolymers comprise two or more polymer chains in sequence, whereas a starblock copoly-mer comprises more than two linear block copolymers attached at a common branch point[47,48]. Polymers containing at least three homopolymers attached at a common branchingpoint have been termed mixed arm block copolymers, although they can also be viewed asmultigraft copolymers [47]. Synthesis of block copolymers is reviewed by Zhou et al. [49].Relatively fewer studies concerning the micellization of graft copolymers have been con-ducted. A graft copolymer is one which comprises a polymer chain as a backbone andanother polymer chain as side ‘grafted’ part. These copolymers usually demonstrate propertiesof both, i.e. polymeric backbones as well as of the grafts. Copolymerization of styrene with aPEO macromonomer in water to form a unimolecular graft copolymer having tendency tomicellize is reported [50]. Synthesis of polystyrene-graft-polyolefin elastomer copolymer, hav-ing micellization ability, through Friedel–Crafts alkylation reaction was reported by Guo andFang [51]. In a recent report, amylopectin was hydrophobically modified by grafting poly(lactic acid) chains to provide a biodegradable amphiphilic polysaccharide with micellizationproperties [52]. Table 1 shows different possible structures of amphiphilic copolymers withrepresentative example of each class.

Usually when the length of a hydrophilic block exceeds to some extent than that of ahydrophobic one, spherical micelles are formed from self-assemblage of amphiphilic diblockor triblock copolymers in aqueous solutions. Whereas if the length of a hydrophilic block istoo large, copolymers exist in water as individual molecules (unimers) and molecules withlengthy hydrophobic blocks develop various structures. Different backbone structures that areused for constructing amphiphilic polymers have been presented in Figure 1 and their exam-ples in Table 2. Certain other types of polymers have also found applications in micelle prep-aration. Dendritic macromolecules are investigated by some researchers for generation ofmicelles. Dendrimers are nanoscale macromolecules with high density of surface functional-ities, well-defined structures, and molecular weights [96]. Inner core cavity and a great num-ber of end groups justify the development of dendritic molecules as a new model of potentialamphiphilic polymers for micelle preparation [97]. On this basis, a series of drug-incorporateddendritic micelles from linear-dendritc macromolecules having increased biocompatibility andbiodegradability have been reported [98]. Yet another variant class of polymer for micellepreparation is a new group of polymers, viz. hyperbranched polymers. Hyperbranched poly-mers are highly active nano-structured materials with a large number of end groups whoseproperties can be tailored for different applications [99,100]. Amin and others prepared poly-esteramide and poly(urea-urethane) hyperbranched amphiphilic polymers that could be usedas carriers for hydrophobic drugs [101]. Of late, a multifunctional unimolecular micelle madeof a hyperbranched amphiphilic block copolymer was synthesized and characterized for can-cer-targeted drug delivery and imaging [102].


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Table

1.Possiblestructures

ofam

phiphilic

copo

lymers.

Typ

esof

micelle-formingcopo

lymers

Representationof

structurea

Examples

ofcopo

lymers

Ref.

Block

copo

lymers

Di-blockAAAAAAABBBBBB

Poly(styrene)-b-PEO

[53]

Tri-block

AAAABBBBBAAAA

PEO-b-PPO-b-PEO

[54]

Tetra-block

ABCA

PEG-b-poly(L-histid

ine)-b-poly(L-lactic

acid)-b-PEG

[55]

Penta-block

ABABA

DMAEMA-b-M

MA-b-D

MAEMA-b-M

MA-b-D

MAEMA

[56]

2-(dim

ethy

lamino)ethy

lmethacrylate(D

MAEMA),methy

lmethacrylate(M

MA)

Star-block(seven-arm

)Poly(L-lactid

e-star

block-N-isoprop

ylacrylamide)

[57]

Graftcopo

lymers

Stearic

acid-grafted-chitosanoligosaccharide

[43]

a A-hydrophilicunitandB/C-hydrophobic

unit.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Interesting studies over nonamphiphilic block copolymers have revealed that such poly-mers can also be used for micelle preparation based on an indirect method of micellization.In this, molecularly dissolved nonamphiphilic copolymers are converted into amphiphiliccopolymers in situ by certain stimuli as temperature, pressure, pH, or salt formation [103]. Inthis context, Yoshida reported micelle preparation from poly(vinylphenol)-b-polystyrene in1,4-dioxane (a non-selective solvent) in the presence of 1,4-butanediamine [103]. Micelleswith UV absorbents at their coronas prepared using poly(vinylphenol)-b-poly{4-(2-hydrox-ybenzophenoxymethyl)styrene-co-styrene} di-block copolymer were reported by Yoshida andOhta [104]. The polymer did not self-assemble in 1,4-dioxane, but in the presence of α,ω-dia-mine formed micelles with an UV absorbent at the corona. The micelles were formed by thehydrogen bond cross-linking between the poly(vinylphenol) blocks via the diamine.

Methods of preparation

Polymeric micelles are generally prepared by either of the two methods – direct dissolutionof the polymer in an appropriate solvent (direct dissolution is usually followed by stepwisedialysis) or addition of a precipitating solvent for one block. Micellization leads to the forma-tion of ordered structures in which the contact between the insoluble block and the solvent isminimized.

Figure 1. Common polymeric backbones used for constructing micellar systems.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

The first method is most commonly used for the formation of micelles of block copoly-mers whose total molecular weight is low and the length of the insoluble block is short. Tofacilitate dissolution, stirring, thermal, or ultrasound treatments have been used. Block copoly-mers in a selective solvent (a thermodynamically good solvent for one block, but a nonsol-vent for the other) form a micellar structure through the association of the insoluble segments

Table 2. Various polymers used for micelle preparation.

Polymers Examples of polymers Ref.

Chitosan derivatives All trans retinoic acid-chitosan [58]N-Phthaloylcarboxymethylchitosan [24]Oleoyl-carboxymethyl chitosan [59]N-palmitoyl chitosan [38]Linoleic acid modified chitosan [60]N-octyl-N-dimethyl chitosan and N-octyl-N-trimethylchitosan

[61]

Linoleic acid-carboxymethyl chitosan [62]N-octyl-N,O-carboxymethyl chitosan [63]Chitosan-graft-PCL [64]Stearic acid-grafted chitosan oligosaccharide [65]PEG conjugated N-octyl-O-sulfate chitosan [66]

Polyacrylate derivatives Poly(benzyl methacrylate)-b-poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)

[67]

Poly(2-ethylhexyl acrylate)-b-poly(acrylic acid) [68]Poly(tert-butyl acrylate)-b-poly(2-vinylpyridine) [69]Poly(n-butyl acrylate)-b-poly(acrylic acid) [70]Poly(2-ethylhexyl acrylate)-b-poly(methyl methacrylate)-b-poly(acrylic acid)

[71]

Poly[(ethylene oxide)-b-2-(dimethylamino)ethylmethacrylate-b-2-(diethylamino) methacrylate]

[72]

Polycaprolactonederivatives

PEO-b-PCL [73–76]PCL-b-PEG-b-PCL [77]PEG-PCL-PEG [78]PCL-b-poly(methacrylic acid) [79]Poly(ɛ-caprolactone)-poly(ethyl ethylene phosphate) [80]PCL-b-poly(2-(dimethylamino) ethyl methacrylate) [81]N-phthaloylchitosan-g-PCL [82]Poly(ethyleneglycol)-b-poly(ɛ-caprolactone-co-trimethylenecarbonate)

[83]

Dendritic poly(ether-amide)-PCL-PIPAAm [84]

Polylactide (PLA)derivatives

PEG-Poly(D,L-lactide) [85,86]Poly(aspartic acid)-b-PLA [87]PLA-b-PEO [88]Poly(glutamic acid-alt-PEG)-graft-poly(ɛ-caprolactone-co-lactide)

[89]

Poly(VP)-b-poly(D,L-lactide) [39,90]Poly(L-histidine)-b-poly(L-lactide)-b-PEG [91]Poly(N-isopropylacrylamide-co-methacryl acid)-g-poly(D,L-lactide)

[92]

Poly(p-Dioxanone-co-L-Lactide)-b-PEG [93]

Polyacrylamidederivatives

Polyisobutylene-b-poly(N,N-dimethylacrylamide) [94]Polyacrylamide hydrophobically modified withdihexylacrylamide

[95]


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[105]. Cao and others prepared polystyrene-poly(methacrylic acid) (PS-PMA) block copoly-mer micelles by directly adding the polymer to 80:20 v/v dioxane:water followed by a step-wise dialysis to pure aqueous buffer [106].

The micelles become spherical and stable with a monodisperse type of size distributionwhen an appropriate solvent for a particular polymer and processing condition is chosen.Improper solvent combination and/or processing conditions may lead to a precipitate or anuncontrolled growth of structures that will eventually aggregate and come out of the solution.

The second method depends on formation of molecularly dissolved chains of polymer in anonselective solvent. To induce micellization in the molecularly dissolved chains, a selectivesolvent for one of the blocks and precipitant for the other may be added. In nonselective sol-vents, the polystyrene–polybutadiene (PS–PB) chains were molecularly dissolved and bothblocks adopted a stretched conformation due to intersegmental repulsion [107]. In n-decane, aselective solvent for the PB block, aggregated PS–PB chains forming spherical micelles wereobserved above the CMC. But, addition of a precipitating solvent does not imply literally,rather it indicates changing the system such that the selective solvent conditions for a particularpolymer are produced. Change in temperature, ionic strength, or pH of the system can be usedfor this purpose. In this context, formation of poly(2-vinylpyridine)-b-PEO micelles in aqueoussolution by titration from highly acidic to highly alkaline pH has been demonstrated [108].

The search for effective micellization conditions depends upon solubility of the individualblock of the copolymer. The size of final micelle may depend on the preparation protocol for agiven polymer. The selection of solvents, employment of dialysis procedure, thermal treatment,etc. may all influence the formation of micelles. For a series of PEO-b-poly(ɛ-caprolactone)(PCL) samples, it was observed that spherical micelles were formed upon self-assemblyinduced from either dimethylformamide or tetrahydrofuran [109]. Whereas for the same set ofpolymer precursors, large wormlike micelles were formed in solutions prepared from acetone.Therefore, simple modification in the experimental method of micelle preparation may be usedto alter the shape of the micelles. As per Tian and his group, the micelle properties are very sta-ble once the micelle resides in a solvent that is a strong nonsolvent for the core [110].

Drug loading into micelles

Ringsdorf’s group in early 1980s first proposed the use of block copolymer micelles as drugdelivery vehicles [111,112]. Since then many researchers have emphasized on the develop-ment of polymeric micellar systems for drug delivery using different techniques.

Both, chemical conjugation and physical entrapment techniques can be used for loadingof drugs into the core or the shell region of polymeric micelles. Incorporation of drug in theouter shell is usually avoided as the drug molecules (mostly hydrophobic) might interact withthe outer shell and lead to undesired aggregate formation. Also the minimization of hydropho-bic interactions between drug carriers and components of the biological system (such as pro-teins and cells) is an important key to targeting, since these hydrophobic interactions mayconsiderably reduce contribution of diffusive and convectional transport through intracellularchannels or intercellular junctions of endothelia on which the enhanced permeability andretention (EPR) effect is based (discussed later). The outer shell serves the function of shield-ing and prevents the hydrophobic interactions that would occur if the drug is incorporated inthe outer shell [113].

Factors that influence drug loading

The loading efficiency of the micellar carrier is an indication of the amount of drug that can beincorporated per micelle. The factor of prime importance is the compatibility between the drug


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

and the core-forming block. But stability and degradation of micelles in aqueous medium alsoaffects the drug loading efficiency and drug release characteristics, which are very importantfor the application of amphiphilic block copolymer micelles in drug delivery [114,115]. Thelength and nature of the core and corona forming blocks also is an important parameter [116].The larger is the hydrophobic block, the larger is the core size and greater is its ability to entraphydrophobic drugs. While an increase in the length of the hydrophilic block is associated withan increase in the CMC. Thus, the quantity of the drug entrapped in micelle drops.

Several other factors that control the drug loading efficiency into the polymeric micellesinclude molecular weight of the copolymer, concentration of the copolymer, the nature andconcentration of the drug, and finally, the method of preparation of the polymeric micellardrug delivery system [117,118].

Different approaches for preparation of drug-loaded polymeric micelles

Drug-loaded polymeric micelles can be prepared mainly by three common approaches: directdissolution, solvent evaporation, and dialysis. Direct dissolution of the amphiphilic copolymerand drug in water is the simplest technique of preparing drug-loaded polymeric micelles. Ator above CMC, copolymer and the drug self-assemble in water to form drug-loaded micelles.To enhance drug loading, this technique can be combined with an increase in temperature oralternately a thin evaporated film of drug can be prepared before the addition of copolymer.

In solvent evaporation or solution-casting technique, volatile organic solvents like metha-nol, ethanol, acetone, acetonitrile, or others are used to dissolve the copolymer and the drug.A thin film of copolymer and drug is obtained after the solvent is removed by evaporation(mostly by rotary evaporator). Drug-loaded polymeric micelles are obtained by reconstitutionof film with water or aqueous buffers. Methoxy PEO-b-PCL micelles were used for theencapsulation of cyclosporine A (CyA) by a cosolvent evaporation method [119]. The cosol-vent composition was varied by changing the type of organic cosolvent (using acetone, aceto-nitrile, and tetrahydrofuran), the ratio of organic to aqueous phase, and their order ofaddition. Manipulation of the self-assembly conditions such as organic to aqueous phase ratioand order of phase addition in this method may be used to improve the efficiency of hydro-phobic drug encapsulation in polymeric nanocarriers and average diameter of assembledstructures. Addition of acetone to water at low organic to aqueous phase ratio leads to a smal-ler average diameter for self-assembled structures and is shown to be more efficient for CyAencapsulation. The higher encapsulation capacity for CyA despite smaller size may beattributed to the formation of compact micelles under this condition.

When the core forming blocks are long and more hydrophobic, the two above mentionedtechniques are unsuitable. Micelles from such copolymers have more potential to solubilizelarge amounts of poorly water-soluble drugs. In these cases, the dialysis technique has beenused to prepare drug-loaded micelles. Solutions of the drug and the polymer in organic sol-vent are placed in the dialysis bag and the solvent is exchanged with water by immersing baginto water, inducing micelle assembly [120,121]. Although highly effective, dialysis is a time-consuming process for preparation of polymeric micelles.

Table 3 summarizes some studies demonstrating use of different preparation approachesof polymeric micelles.

Properties and characterization of micelles

Critical micelle concentration

CMC is the key parameter for the formation and the static stability of polymeric micelles. Inaqueous media, amphiphilic polymers can exist in the form of micelles when the


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Table3.

Examples

ofpreparationof

polymeric

micellesby

differentapproaches.

Preparatio

nmetho

dandpo

lymersused

Loadeddrug

/probe

Com

ment

Ref.

Directdissolution

Chitosan-Pluronic

Indo

methacin

Aided

bysonicatio

n[122

]Mon

ometho

xyPEG-PCL

Hon

okiol

Dissolutio

nassisted

byultrasou

nd[123

]Polox

amineT1107

(Tetronic)

Triclosan

After

dissolving

polymer,system

equilib

ratedfor24

hto

allow

micelle

form

ation

[124

]

PEG-poly(aspartic

acid)

Cisplatin

Polym

eranddrug

dissolvedin

distilled

water

andreactedfor72

h[125

]

Solventevap

oration

Metho

xyPEG-poly(D,L-lactic

acid)

Triptolide

Stirredat

300rpm

[126

]1,2-distearoyl-sn-glycero-3-ph

osph

oethanolam

ine-

N-m

etho

xyPEG

Rapam

ycin,5-fluo

rocytosine,am

photericin

BSolvent

evaporated

underhigh

vacuum

toprod

uceathin

film

[127

]

PEO-b-PCL

Curcumin

Vigorou

slystirredandthen

vacuum

applied

forremov

alof

organicsolvent.

[128

]

α,β-Poly(aspartic

acid)-g-octadecyl-g-PEG

Metho

trexate,

oleano

licacid,po

doph

yllotoxin

Organic

solventevaporated

undervacuum

toprod

uceapo

lymer

film

[129

,130

]

Dialysis

N-phthaloylchito

san-g-po

lyviny

lpyrrolid

one

Predn

ison

eacetate

Vigorou

sstirring

follo

wed

dialysis

[131

]Dextran

andhydroxypropylcellulose

hydrop

hobically

mod

ified

bygraftin

gpo

lyox

yethylenecetylether

CyA

Dialyzedfor48

h[132

]

PCL-b-PEO

Fluorescein-5-carbo

nylazidediacetate

Dim

ethy

lformam

ideremov

edby

dialysis

againstwater

for24

hwith

atleasteigh

tchanges

[133

]

PCL-b-PEO

Benzo[a]pyreneandcell-trackerCM-D

iI,17β-

Estradiol,Neurotrop

hicAgentsFK50

6andL-

685,81

8

Solutionstirredov

ernigh

tanddialyzed

againstMilliQ

water

inthedark

[74–76

]


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

concentration is higher than CMC, and when diluted below this concentration, the micellesmay collapse. Thus, CMC is said to be an apparent measure of polymeric micellar thermody-namic stability [134,135]. At CMC or slightly above the CMC, loose aggregates of micellescontaining a little water in the core are formed [136]. With an increase in polymer concentra-tion above CMC, the residual solvent is excluded from the core; the micellar structurebecomes more compact with reduction in the micelle size, and develops into stable structures.The CMC of the polymeric solution and the kind of aggregates the copolymers can form isdependent on the competition between the enthalpic interaction and the entropic effect in thesolution [137,138]. Below CMC, the entropic effects dominate over the enthalpic interaction,whereas the enthalpic contributions are dominant over the entropic effects above CMC, whichmakes the rapid aggregation of copolymers to form aggregates with particular properties.

To discriminate CMC of polymeric micelles from the CMC of surfactant micelles, theterm critical association concentration (CAC) is sometimes employed for polymeric micelles.The enhanced stability of polymeric micelles as compared with conventional surfactants (withCMC 10�3–10�4M) in water is owing to their lower CMC values (10�6–10�7M) [136,139].Conventional surfactants have much higher CMC values as compared with polymeric surfac-tants and the resultant micelles may be destabilized earlier and collapse. In order to obtainstable polymeric micelles, the degree of hydrophobicity for the core-forming block must becontrolled.

Factors affecting CMC are the hydrophilic and hydrophobic block length of the copoly-mer, branching parameter, temperature, salt concentration, pH, etc. The CMC of the drugloaded micelles is also influenced by the drug solubility, drug interaction with polymers, andthe drug loading content [140].

Generally, an increase in the number of hydrophilic units in the block copolymers leadsto an increase in the CMC [141,142]. An increase in the hydrophilicity improves the aqueoussolubility of polymer and hence lowers the tendency for the polymeric surfactants to formmicelles and thereby increases the CMC [143].

Usually, the CMC is found to increase as the length of the core forming block decreases[116]. Soga et al. observed that the CMC as well as the CMT decreased with increasinghydrophobic block lengths in poly(N-(2-hydroxypropyl) methacrylamide lactate)-b-PEGcopolymer micelles, which can be attributed to the greater hydrophobicity of the block withincreasing molecular weight [144]. Similarly, Gadelle et al. and Kozlov et al. also have dem-onstrated that as the length of the hydrophobic block increases, the CMC decreases[145,146]. With an effort to determine the effect of hydrophobic tail architecture on self-assembling behavior, different architectures of linear, branched, starlike, and dendritic tailswere selected for comparison by Cheng and Cao [147]. They used the branching parameterof the tail to characterize the tail architectures and showed that the self-assembly of linear tailcopolymer had the lowest CMC, with almost a spherical shape of the micelle. It was foundthat the CMC is inversely proportional to the branching parameter and, as CMC is a result ofcompetition between entropy and enthalpy contributions, tails with a low branching parameterhave lower configurational entropy and lose less configurational entropy in the process ofaggregation.

The thermodynamics of micelle formation have been obtained from the temperaturedependence of the CMC [148,149]. Thurn et al. were able to demonstrate the temperature-dependent micellization of Pluronic F127 [150]. CMC of Pluronic F127 decreased largely onincreasing temperature due to the temperature-dependent difference in the solvation of ethyl-ene oxide and propylene oxide blocks.

The effect of salt concentration on CMC has been studied by Elisseeva et al. [151]. CMCof Pluronic F127 was strongly influenced by the salt concentration and the presence of 0.1M


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

sodium chloride decreased the CMC of Pluronic F127 by a factor of 2. Sodium chloridebecause of the salting-out effect decreases the solvent quality of the polymer aqueous solutionwith respect to the ethylene oxide blocks of the F127 molecules.

The dependence of the conformation and hydrophilicity of the Tetronic T904 unimers andmicelles on CMC has been shown by Alvarez-Lorenzo and others [152]. For Tetronic atpH < 5.8, the diprotonated form predominates over the nonprotonated one. The deprotoniza-tion of the central diamine group was essential for micellization, which was an endothermicentropy-driven process owing to hydrophobic interactions between the poly(propylene oxide)chains. With decrease in pH of the solutions, the CMC values were elevated and size of themicelles decreased as the positively charged amine groups repelled each other making theaggregation more difficult.

Different methods can be employed for the determination of CMC, and it has been fre-quently observed that the reported CMC value is influenced by the choice of the method.Therefore, a more feasible definition of CMC than the earlier one would be the concentrationat which a sufficient number of micelles are formed and detected by a given method[120,153]. Most commonly used methods include surface tensiometry and fluorescent probetechniques. Some other methods include conductivity, solubilization experiments, osmotome-try, differential scanning calorimetry, chromatography, small angle neutron scattering (SANS),small angle X-ray scattering, and nuclear magnetic resonance (NMR). Recently, a method hasbeen developed to determine the CMC of polydisperse block copolymer micelles of lowCMC by static light scattering [4,154]. Few of these methods are discussed.

Surface tensiometry

In surface tensiometry, surface tension of aqueous solutions is measured over a wide range ofconcentration. The method detects completion of the Gibb’s monolayer at the air/water inter-face, and is a secondary indicator of the onset of micellization. CMC is located as the pointat which the surface tension becomes essentially independent of concentration. Hence, CMCcan be given as the value at which the surface tension stops decreasing and reaches a plateauwhen a graph of surface tension is plotted as a function of the logarithm of concentration.The surface tension measurements are very sensitive to the presence of hydrophobic impuri-ties, and only an impurity level of the order of 0.1% of the surfactant may well cause a dras-tic deviation from the normally obtained curve. In the case of polydisperse block copolymers,more difficulty arises in the determination of an effective CMC value as the polydispersecopolymers show a more gradual decrease in the surface tension when plotted againstconcentration.

El-Ghazawy et al. [155] used drop volume tensiometry to measure the surface tension ofaliphatic polyester surfactants. The surface tension isotherms were then used to determineCMC of these surfactants.

Fluorescence probe

The hydrophobic fluorescence probes that are sensitive to changes in the vicinal polarity areused to determine CMC. Amongst various fluorescent probes used, pyrene (a highly hydro-phobic condensed aromatic hydrocarbon) is the most widely used molecule. Pyrene is sensi-tive to the polarity of the surrounding environment and its partitioning into the hydrophobiccore is observed upon steadily increasing the polymer concentration from extremely low tohigh [156]. The fluorescence spectrum of pyrene at the low concentration possesses a vibra-tional band structure that exhibits a strong sensitivity to the polarity of the pyrene environ-


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

ment [156,157]. As pyrene partitions preferentially toward the hydrophobic core it experi-ences a nonpolar environment and results in an increase in the fluorescence intensity, a redshift in the excitation spectra and a change in the vibrational fine structure of the emissionspectra. Based upon these changes, pyrene was used to measure the CAC for poly(styrenesulfonate)/dodecyltrimethylammonium bromide through quenching, vibrational fine structureshifts (I1/I3), and time-dependent fluorescence [158,159]. For CMC determination, the I1/I3ratio (the intensity ratio between the first and third highest energy emission peaks, which ismeasured at a constant excitation wavelength and variable emission wavelengths correspond-ing to I1 and I3) can be used. A drastic change in the slope of the plot of the fluorescence ofpyrene, the I1/I3 ratio from emission spectra against concentration signifies the onset of mic-ellization [160]. Colombani et al. characterized poly(n-buyl acrylate)-b-poly(acrylic acid)diblock copolymer micelles in aqueous solution using fluorescence correlation spectroscopy(FCS) and pyrene fluorescence spectroscopy [161]. FCS and steady-state pyrene fluorescencespectroscopy revealed a very low apparent CMC (nearly 10�8mol/L), in the absence andpresence of added salt at high pH.

During the determination, concentration of pyrene used should be very low (10�7M) sothat a change in slope can be precisely detected [162]. Changes in anisotropy of fluorescentprobes have also been associated with the onset of micellization [163,164]. Pyrene has beenused by many research groups for CMC determination of the polymeric micelles; few exam-ples include micelles formed from methoxy PEG-PCL, [165] β-Cyclodextrin-poly(γ-benzyl L-glutamate), [166] β-cyclodextrin-poly(L-leucine), [167] PEG-b-poly(2-hydroxyethyl methacry-late-g-PCL), [168] PEG-b-PCL, [169], and Tetronic-PCL-heparin [170].

Other fluorescent probes used to determine CMC are naphthalene, [171] phenanthrene,[172] 9-chloromethyl anthracene, [173] Nile red, [174], and 1,6-diphenyl-1,3,5-hexatriene[175].

Light scattering

Light scattering (static or dynamic) can be used to detect the start of micellization only if theCMC falls within the sensitivity of the scattering method which is unusual for aqueous poly-meric solutions [176]. In static light scattering, for a series of samples of varying concentra-tions, the scattering intensity at different scattering angles is collected. Under favorablecircumstances, the concentration dependence of excess light scattering intensity (excess overcopolymer solution) can be used to determine the CMC. The results are recapitulated in a so-called Zimm-plot and from reciprocal of the scattering intensity extrapolated to zero concen-tration, the angular dependence of scattering intensity, and concentration dependence of scat-tering intensity information about the molecular weight, size, and intermolecular interactions(via a second virial coefficient B), respectively, is extracted. For a given system, static anddynamic light scattering (DLS) experiments can be combined together which reveals informa-tion about the micellar size, shape, and aggregation number, Nagg. The surfactant theory insmall molecules can be used to relate Nagg to the concentration from:

Nagg ¼ 2ðC=CMCÞ1=2

where C is the surfactant/copolymer concentration [177]. This equation is valid for simplemicelle morphologies like spheres, rods, and vesicles.

Chen et al. [178] studied the effect of the architecture of graft copolymers on CAC anddetermined CAC of the copolymers by light intensity measurement. CAC of the copolymerwas defined as the concentration at which the light intensity abruptly increased.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Pyrene method or light scattering may yield different results for the CMC of drug loadedmicelles owing to the formation of a secondary micelle structures during drug loading (associ-ation of few primary micelles). Usually, only primary micelles are formed as the polymerconcentration is gradually increased from low to high concentration in the pyrene method.Conversely, secondary micelle structures can be formed during drug loading by dialysis meth-ods. Due to additional interactions between polymers, the CMC of these secondary micellesmay be lower than the values obtained from the pyrene method.

Conductivity measurement

Poly(aspartic acid)-g-octadecylamine-g-polyethylene glycol (PASP-g-OD-g-PEG) solutionswith an increasing concentration were prepared and used to measure the conductivity [129].In deionized water, the copolymer possessed a negative charge as a result of partial ionizationof the carboxylic acid groups of PASP. Hence, a correlation between the conductivity of thePASP-g-OD-g-PEG solution with the concentration of the solution was observed. At aspecific copolymer concentration, a change in slope was detected in the conductivity curves.The conductivity value increased with the increase in polymer concentration on the whole;however, it increased more gradually when the concentration was above the specific concen-tration. The copolymer concentration corresponding to the turning point in plots was noted asCMC.

Small angle neutron scattering (SANS)

The polymer volume fractions in the core and the corona can be calculated using SANS andthe core-corona form factor can then be used to extract information about the micelle sizeand micelle aggregation number [179,180]. Ramzi et al. used neutron experiments to deriveinformation on change in the size of the core and the micelle’s aggregation number as a func-tion of time [181].

Gel permeation chromatography (GPC)

If the polymeric micelles are sufficiently stable to travel through the size exclusion columnduring their elution, then GPC can be employed for CMC determination of such systems. Assingle polymer chains and micellar copolymer chain fractions produce distinct elution vol-umes in aqueous milieu, GPC can be suitably used for measurements of CMC alongwithmolecular weight and aggregation number of the micellar system [182]. Yang and others stud-ied the aggregation behavior of the PLA/PEG diblock copolymers in aqueous medium withaqueous GPC [183].

Size, shape, and polydispersity index (PDI) determination

Size of polymeric micelles falls in the colloidal range. DLS/photon correlation spectroscopyaffords characterization of micellar size (hydrodynamic diameters) and PDI [184]. DLS offersthe Rh from the mode corresponding to micellar diffusion obtained from the intensity distribu-tion of relaxation times and the time dependence of the light intensity fluctuations is analyzedin order to yield information about the diffusion coefficient. The Rh can then be calculatedusing the diffusion coefficient from the Stokes-Einstein equation. By DLS, change in the sizeof micelles can also be determined. It was shown that the addition of a low molecular weightsurfactant such as sodium dodecyl sulfate (1%w/v) can destroy the polymeric micelle struc-


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

ture and bring about a complete shift of the mean diameter from approximately 50–3 nm[185].

Static light scattering also provides the data on association number of the micelles [186].Static light scattering experiments provide information for the thermodynamic radius ofmicelles.

PDI indicates the degree of the dispersity of the prepared polymer micelles [187]. PDI ofmicelles is obtained by examining the micellar solution with quasi-elastic light scatteringtechnique. Monodisperse micelles produce blue color from light scattering which indicatesgood micellar preparation, as contrasted with the white color shown by aggregates [188]. PDIof the micelles is also obtained from DLS measurements. Accordingly, PDI of the disulfide-linked dextran-b-PCL diblock copolymer micelles was found to be 0.1–0.2, signifying almostmonodisperse micelle preparation, when determined by DLS by Zhong and his coworkers[189].

Other methods that are also frequently employed for determination of micellar size andshape include scanning electron microscopy (SEM) [190], transmission electron microscopy(TEM) [191,192], and atomic force microscopy (AFM) [193]. Although SEM enjoys highresolution, its use is hindered by the fact that the sample should be able to withstand highvacuum and be conductive (which is done by coating gold on their surface). However, aque-ous samples cannot withstand the high vacuum of an electron microscope and water lossoccurs leading to microstructure changes. Therefore, sample preparation necessitates somespecial treatment before it is subjected to electron microscopy examination. Freeze fracturehas shown promise to overcome these problems [194]. AFM permits the visualization ofpolymeric micelles at atmospheric pressure without gold coating and hence overcomes thelimitations of SEM [195]. SEM or AFM reveal information regarding size distribution whenmicelles attached chemically to surfaces are presented. Direct visualization of block copoly-mer micelles either in the dried state or directly in situ within a liquid cell can be achievedby AFM. The microstructure of colloidal systems can be visualized with the high-magnifica-tion power of the electron microscope.

More recently developed cryo-TEM technique has increasingly started gaining importancefor characterization of shape of polymeric micelles in aqueous medium. Cryo-TEM imagingof poly(n-butyl acrylate)-b-poly(acrylic acid) at different salt concentrations revealed sphericalshape of these micelles [70]. Size characterization of drug-loaded polymeric micelles wasdone using asymmetrical flow field-flow fractionation and the structure of assemblies wasdetermined by SANS [196].

Microviscosity of the micellar core

The micellar core viscosity can affect the micellar physical stability and drug release from themicelles. Fluorescence probe techniques have played a crucial role in obtaining microstruc-tural information in micelles [197]. Microviscosity (intrinsic viscosity or microfluidity) definesthe viscosity of the probe environment in the interior of aggregate and is different from thatof the bulk solvent medium. Microviscosity of the hydrophobic core can be determined byusing fluorescent probes such as dipyme (1,1′-dipyrenyl methyl ether), DPH (1,6-diphenyl-1,3,5-hexatriene), and others. For example, the intramolecular excimer formation of dipyme isan attractive tool for studying hydrophobic microenvironments and the extent of excimeremission is dependent on the local friction imposed by the environment. As a result, measure-ment of the monomer to excimer intensity ratio, IM/IE provides information about the micro-viscosity experienced by the probe. Dipyme is sensitive to both polarity and viscositychanges in its local environment [198]. The micellar microviscosity afforded by Pluronic and


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Tetronic PEO-PPO block copolymer aqueous solutions has been investigated by fluorescencespectroscopy by Nivaggioli et al. [199].

1H NMR also provides information on the viscosity of the micellar core. The copolymersare usually dissolved in D2O and in a solvent where micelle formation is not expected, andwhere all the peaks proper to the hydrophilic and hydrophobic part of the polymer can bedetected (e.g. CDCl3). In D2O, the presence of micelles with highly inner viscous state resultsin a restricted motion of the protons within the micellar core as demonstrated by the weaksignals associated with the hydrophobic part of the copolymer [200]. Highly viscous stateswere found to exist in PEO-poly(DL-lactic acid) [163] and PEO-poly(β-benzyl L-aspartate)micelles [134].

DSC experiments showed that methoxy PEG-poly(hexyl-substituted lactides) (mPEG-PHLA) block copolymer presents a bulk microstructure containing mPEG domains segregatedfrom the PHLA domains [174].

Stability of polymeric micelles

The stability of polymeric micelles can be defined in terms of thermodynamic and kinetic sta-bility. Polymeric micelles are said to be thermodynamically stable when the polymer concen-tration in water is above their CMC.

The exchange rate of single polymer chain between the micelles and bulk determines thekinetic stability of a micellar system [116,201]. In vitro and in vivo stability of polymericmicelles depends on the CMC values of micelle forming polymers, the strength of van derWaals interactions between hydrophobic blocks forming the core, and the molecular size ofthe hydrophilic block of the polymer [202].

Upon intravenous injection, polymeric micelles are subject to extreme dilution in the cir-culation and hence when these are to be used as drug delivery vehicles, it is important toknow the CMC [203]. The CMC value should be sufficiently low so that the polymericmicellar drug carriers remain stable during circulation in the bloodstream [204]. This isimportant as the micellar drug carrier will get sufficient time for drug delivery and accumulateat the target site [136]. Kinetic stability is also important as it reflects the rate at which aphysically entrapped drug is released from the micellar carrier. Polymeric micelles from someblock copolymers are said to be kinetically stable apparently because of the presence of mul-tiple sites capable of hydrophobic interaction within each polymer molecule [182]. However,it has been observed that most other polymeric micelles are often destabilized in the presenceof blood components leading to premature drug release [205]. The micellar disassembly isgoverned by the magnitude of the interactions in the micellar core which are dependent onthe crystalline or amorphous state of the core-forming polymer, solvent in the micellar core,hydrophilic and hydrophobic balance of the copolymer, and presence of loaded hydrophobiccompound [113,201]. Therefore, to improve the thermodynamic and the kinetic stability ofdrug-loaded micelles several strategies have emerged that include enhanced compatibility ofthe drug and polymer [74,206], cross-linking of the micelle core/corona [207,208], prepara-tion of stereocomplex micelles [209,210], and reduction in CMC by altering the polymer[211,212].

Improved stability of polymeric micelles has been reported after the introduction of aro-matic groups that helps lowering the CMC and also strengthens the interactions inside themicellar core through π–π-stacking. Hennink et al. recently were able to show the effect ofthe presence of an aromatic end group on the micelle stability [206]. They loaded docetaxeland paclitaxel into oligomeric micelles composed of methoxyPEG750-b-oligo(ɛ-caprolac-tone)5 having a hydroxyl, benzoyl, or naphthoyl end group. Both taxanes contain several


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

aromatic rings, which may form π–π interactions with the aromatic rings in the micellar core.It was concluded that the presence of an aromatic end group on the core forming block isnecessary to improve the loading and enhance the stability of the formulation of taxanes, indi-cating the importance of a good compatibility between the loaded drug and the micellar core.

The importance of core cross-linking of the polymeric micelles to enhance stability hasbeen demonstrated by Bronich et al. wherein they prepared polymeric micelles withcross-linked ionic cores by using block ionomer complexes of PEO-b-PMA and divalentmetal cations [213]. The drug-loaded micelles were stable in aqueous dispersions exhibitingno aggregation or precipitation for a prolonged period of time.

The dissociation of self-assembled polymeric micelles into unimers below the CMC inbody fluids accelerates the release of any incorporated drug, which results in drug loss atunwanted tissues or organs [203]. To tackle this problem, cross-linking is a powerfulapproach to stabilize micelles because such structures can hold self-assembled polymericmicelles [214,215]. Generally, two methods of cross-linking have been used: one is cross-linking of the micellar shells and the other is preparation of core cross-linked micelles. Theshell cross-linked micelles lead to formation of stable nanosized hollow particles by removalof the cores after cross-linking and then hydrophilic drugs can be encapsulated inside[216,217]. Hence, reversibly shell cross-linked micelles based on triblock copolymer com-posed of poly(aliphatic ester), polyphosphoester, and PEG demonstrating improved physicalstability were reported [218].

The core cross-linking can increase the stability of the micellar structures without affect-ing the drug loading capacity, leading to the sequential control of the hydrophobic drugrelease. Henselwood and Liu prepared poly(2-cinnamoylethyl methacrylate)-b-poly(acrylicacid) micelles with the cinnamoyl moieties cross-linked by UV irradiation [219]. The intro-duction of thiol groups into the core blocks as effective means for preparing the core cross-linked micelles using PEG-b-poly(L-lysine) was demonstrated by Kataoka and Harada [220].

The stereocomplexes are characterized by higher physical and chemical stabilities[221,222]. It has been reported that the kinetic stability of polymeric micelles greatlyimproved through the formation of stereocomplex cores. On this basis, monodisperse stereo-complex PLA-PEG micelles through the self-assembly of equimolar mixtures of the blockcopolymer in water were prepared [223]. It was demonstrated that in an aqueous environ-ment, the core of PLA based polymeric micelles can crystallize in a stereocomplex configura-tion and that these polymeric micelles exhibited enhanced kinetic stability. Chen et al.synthesized the block copolymers of enantiomeric poly(L-lactide)-PEG and poly(D-lactide)-poly(ethylene–glycol) and prepared a series of stereocomplex micelles of enantiomeric PLA-PEG copolymers loaded rifampin and having different length of PLA chains [210]. Therelease rate of rifampin decreased as contents of PLA segment were increased due to higherstereocomplex crystallization and better stability of the polymer micelles.

Reduction in CMC has been correlated to improved stability of polymeric micelles. Thereduction in CMC can be achieved by either of the two approaches: adjusting the sizes of theblocks such that the polymer becomes more hydrophobic or adjusting the nature of the hydro-phobic block. Higher hydrophobicity can be achieved with introduction of a larger hydropho-bic block or a smaller hydrophilic block, thereby resulting in a reduced CMC value [224].Alteration in the nature of the hydrophobic block is possible by means of chemical modifica-tion of the hydrophobic block, e.g. by introducing aromatic groups on the block [225].

Reulen and Merkx have shown the potential of using Förster resonance energy transferimaging technique in assessing stability of micelles [226]. In their study, Förster resonanceenergy transfer between the fluorescent proteins ECFP and EYFP was used to investigate thelipid exchange behavior of protein-functionalized micelles of cysteine-functionalized


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

PEG2000-distearoylphosphatidyl-ethanolamine. It was concluded that functionalization ofPEGylated phospholipids with donor and acceptor fluorescent domains provides a straightfor-ward approach to study the stability of protein-functionalized micelles with respect to protein-lipid transfer.

Applications of polymeric micelles

Solubilization of drug molecules

The poorly water-soluble drugs or contrast agents may be entrapped within the hydrophobiccore or linked covalently to the surface of polymeric micelles to improve their aqueous solu-bility. Solubilization is controlled by characteristics of the drug as well as those of the micel-lar systems. The molecular weight and partition coefficient of the drug are importantparameters, while hydrophobic block length of the micelle is also equally important. Some-times, steric hindrance and interaction of drug and polymer may lead to an unfavorable aggre-gation process. Thus, selection of an amphiphilic polymer for solubilization of drug is acritical issue and requires an indepth understanding for the selectivity of micellar systemswhich is achieved by studying various types of intermolecular interactions for solubilizationof drug in a given micellar system [227–229]. In pharmaceutical industry, micellar solubiliza-tion finds important application for enhancement of solubility and bioavailability of drugs. Itis noted that nearly half of the approved active pharmaceutical ingredients are poorly water-soluble and show very low bioavailability. Polymeric micellar solubilization may realize theirusage [230,231] (Table 4).

Solubilization of drug in polymeric micelles is expressed by the partitioning of the drugdescribed as the ratio of molar drug concentration in the micelle to the molar concentration ofdrug in the aqueous phase. The extent of solubilization depends upon the micellization pro-cess, the compatibility between the drug and the core-forming block, chain length of thehydrophobic block, concentration of polymer, and temperature [248]. It is observed thatamphiphilic polymers can solubilize drugs even when micelles are not formed. Above CMC,there is a sharp increase in the solubility of drug as it gets more space to occupy in the aggre-gates of the hydrophobic part of micelle. The occupancy of core region by drug leads to anincreased Rc of the micelle. It is worth mentioning that the core region has limited capacityfor accommodation, for instance, Pluronic P85 has a core region which is 13% of the wholemicelle weight [249]. An increase in solubility is usually observed when there is a highdegree of compatibility between the drug and the core-forming block of the micelles [250].The influence on solubilization capacity of hydrophobic block length has been examined forgriseofulvin in polyoxyethylene and polyoxybutylene copolymer micelles with varying num-ber of hydrophobic block lengths and hydrophilic block lengths sufficient for formation ofspherical micelles. It was found that the solubilization capacity was dependent on the hydro-phobic block length upto a particular extent (15 units of hydrophobic block), after which thesolubilization capacity became independent of the same [251]. Zhang et al. showed that thechitosan derivatives of high methylation degree, medium-sized long-chain acyl group (C14),and large molecular weight had the best effect in loading CyA [252]. The effect of hydropho-bic block length of diblock and triblock polyurethane surfactants on solubilization of toluenehas been reported by Dong and coworkers [253].

A temperature dependent transition in micellar shape has been quoted in literature. Indilute aqueous solutions, compact micelles turned to wormlike micelles with an increase intemperature from 25 to 40 °C for polyoxyethylene-b-polyoxybutylene copolymers. This shapetransition phenomenon was attributed to the increase in number of unimers per micelle. An


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Table4.

Examples

ofim

prov

ementin

solubilityof

drug

susingpo

lymeric

micellarsystem

.

Drug

Amph

iphilic

polymer

Com

ment

Ref.

Aceclofenac

Mixed

micellesof

Pluronic

L81

andP12

3Mixed

micellesincreasedaqueou

ssolubilityby

abou

t10

0tim

esalon

gwith

spon

taneou

ssolubilizationof

drug

[232

]

Amph

otericin

BPEG-poly(lactide)

Freeze-driedmicellesshow

edsustainedrelease

[44]

Biphalin

PluronicP85

Higherpeak

effect

andlong

eractiv

ityin

BBB

transport

[233

]Cam

ptothecin

PluronicP10

5,d-α-tocoph

eryl

PEG

1000

succinate

Increasedmicellarstability;increasedcytotoxicity

[234

]

Cisplatin

PEG-poly(glutam

icacid)block

copo

lymers

Enh

ancedin

vivo

antitum

oractiv

ity;im

prov

edtherapeutic

indices

[27]

Cyclosporin

AMetho

xy-poly(ethy

lene

glycol)-hexy

l-substituted

poly

(lactid

es)

500-fold

increase

inwater

solubilityof

drug

[235

]

Docetaxel

PEO-b-poly(styreneox

ide)

and

PEO-b-poly(bu

tylene

oxide)

Enh

ancedsolubilityandlong

-term

stability

forlyop

hilized

micelles

[23]

Dox

orub

icin

Poly(L-histid

ine)-b-PEG/poly

(L-lactid

e)-b-PEG

pH-sensitiv

emicelles

[91]

Efavirenz

PluronicF12

7andTetronic

T90

4The

aqueou

ssolubilityof

thedrug

was

increasedmorethan

8400

times

[236

]

Fenofi

brate

PEG-b-PCL

Amou

ntof

feno

fibrateencapsulated

depend

edon

PCLblocksize

[121

]Halop

eridol

PluronicP85

5-fold

increase

insolubility

[237

]Hyd

rochlorothiazide

PluronicP10

3,P12

3andF12

7Solub

ility

ofdrug

sign

ificantly

enhanced

byincreasing

copo

lymer

concentration/saltconcentration/temperature

[238

]

Ibup

rofen

N-palmito

ylchito

san

pHandtemperature-sensitiv

emicelles

[38]

Indo

methacin

Cho

lesteryl-bearing

Carbo

xymethy

lcellulose

pH-sensitiv

e;controlleddrug

release

[239

]

Megestrol

PluronicF12

7/L61

Enh

ancedbioavailability

[240

]Morph

ine

PluronicF12

7Drugsolubilized

with

prolon

geddeliv

ery

[241

]Nim

esulide

Tetron

icT90

4Spo

ntaneous

micellarsolubilizationof

drug

[242

]Nystatin

Pluronics

F68

,F98

,P10

5,F12

7Increasedsolubility

[243

]

(Con

tinued)


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Table

4.(Con

tinued)

Drug

Amph

iphilic

polymer

Com

ment

Ref.

Octaethylpo

rphine,

mesotetraph

enylpo

rphine

PluronicandPEG-

distearoylph

os-

phatidylethano

lamine

Dem

onstratedthat

micelle

core

may

besuitableforon

edrug

while

beingun

suitableforanother

[227

]

Paclitaxel

N-octyl-O

-sulfate

chito

san

Improv

edbioavailabilityandredu

cedtoxicity

[244

]Propo

fol

PluronicF68

,F12

7Highersolubility

[245

]Tanespimycin

PEO-b-poly(D,L-lactid

e)15

0-fold

increase

insolubility

[246

]Tim

olol

maleate

PluronicF12

7Abo

ut2.4-fold

improv

edbioavailability

[247

]


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

investigation about the effect of micelle shape (spherical and wormlike) on the aqueous solu-bility of three drugs: griseofulvin, spironolactone, and carbamazepine was conducted by Att-wood and his research team. Griseofulvin and spironolactone were solubilized to a greaterextent than the more water-soluble drug, carbamazepine. The change in shape was responsiblefor greater solubilization of the drugs [254]. Contrarily, the process of solubilization can alsoinfluence micelle geometry. This feature has been elaborately discussed by Nagarajan in hisreview [255]. Thus, designing block copolymers with proper composition and structure toform micelles with high solubilization capacity for poorly water-soluble drugs can lead to theformulation of efficient drug delivery systems. The potential of polymeric micelles as promis-ing drug delivery systems for overcoming the problems of poor water solubility and poor bio-availabilty becomes quite evident.

Polymeric micelles may act as a carrier for transporting poorly water-soluble compoundsacross the intestinal mucosa by endocytosis. In general, cells take up materials such asmicelles by folding the cell membrane inwardly, surrounding the materials to be ingested.The material is then engulfed in small bubble-like endocytic vesicles. This is called the endo-cytosis that allows supramolecular assemblies to sneak into intracellular regions avoiding thecell-membrane transporters. Another mechanism involves release of hydrophobic compoundby the action of lipases on the polymeric micelles. The released compound is then transportedacross the mucosal barrier, with increased permeability, using the normal physiological con-stituents [256–258].

A reverse transporter associated with P-glycoprotein may inhibit absorption of drugs byactively pumping drug out of gut wall cells back into the intestinal lumen. Inhibition of P-glycoprotein and of gut wall metabolism may lead to enhanced drug absorption. Kabanovet al. showed the effectiveness of Pluronic block copolymers as polymeric inhibitors of P-gly-coprotein that sensitized multidrug resistant tumors to doxorubicin, paclitaxel, and vinblastine,and thereby led to efficient uptake of these drugs [259]. The intestinal absorption of CyA wassignificantly improved by monomethoxy PEG-poly(lactide) micelles and was found compara-ble to that of Sandimmun Neoral® when a comparative study was conducted by Liu and hiscoworkers [260]. A 15–250-fold higher uptake efficiency of particles �100 nm in diameter bythe gastrointestinal tract was noted than that of the micrometer-sized particles [132]. PEG-b-poly(alkyl acrylate-co-methacrylic acid) micelles entrapping fenofibrate exhibited enhancedoral bioavailability as compared to fenofibrate suspension [261]. Han et al. studied the phar-macokinetics and biodistribution of Pluronic P123 micelles loaded with paclitaxel [262]. Theeffective solubilization of paclitaxel by the micellar core resulted in an increased bioavailabil-ity of the drug. Our group has recently demonstrated the applicability of Pluronic L81 andP123 mixed micelles for effective solubilization of aceclofenac [232]. The resultant mixedmicelles bestowed very small sizes (around 20 nm) and high solubilization potential (about4.7mg/mL) making them potential candidates for passive targeting of drugs.

Polymeric micelles provide safer alternatives for parenteral administration of poorlywater-soluble drugs. Aliabadi et al. evaluated PEO-b-PCL micelles to reduce the renal uptakeand nephrotoxicity of CyA [263]. Compared to Sandimmune® (Cremophor EL based com-mercial formulation), polymeric micelles reduced kidney uptake of CyA by 2.6-fold andincreased CyA levels in blood by 2.1-fold [264]. Hashida et al. demonstrated that all-transretinoic acid (ATRA) incorporated in PEG-b-poly(aspartic acid) micelles showed the largestblood concentration when compared with inherent ATRA or ATRA in liposomes [265,266].Almost 2mg/mL of paclitaxel was loaded in poly(N-(2-hydroxypropyl) methacrylamide lac-tate)-b-PEG micelles [267]. The large solubilization capacity of micelles for paclitaxel, simplepreparation method, size of around 60 nm, and size stability demonstrated make thesemicelles an attractive vehicle for parenteral paclitaxel delivery.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Recent developments in drug delivery reveal the applicability of polymeric micelles forwater-soluble drugs as well. Trilayered polymeric micelles from PEG-b-PLA copolymerserved as containers for hydrophilic compounds and were incorporated into hydrogels ascross-linking agents. Resulting hydrogel could be used for releasing hydrophilic compoundsin a sustained manner owing to degradation of copolymer and collapse of the micelle[268,269].

Targeting: general considerations and approaches

The site of action of the drug is mostly at distant locations from the site of administration.Drug has to take a complicated path to reach at the desired site, during which it might bedestroyed or distributed to many unwanted tissues. This usually is associated with increasedside-effects on the body. Also it results in subtherapeutic concentration of drug at targetorgans. Thus, drug targeting is a major issue for avoiding all the related problems.

Factors important for targeting related to polymeric micelles

Some of the factors of polymeric micelles that govern drug targeting include size, chainlength, drug content, stability and degradation of micelles in aqueous solutions, andhydrophobic inner core.

Owing to their characteristic size, the polymeric micelles may represent suitable targetingvehicles utilizing EPR effect through passive targeting (discussed later) [270]. Their sizeusually is small enough to extravasate the small gaps in endothelial lining of blood vessels.Usually, particles larger than 200 nm in diameter are hardly able to traverse the narrow gapsin the leaky vasculature. Also particles larger than 200 nm are immediately recognized as for-eign products in blood and results in instant removal through the RES [271]. Therefore, theparticles should be small enough (<200 nm) to avoid such exclusion [272]. Thus, sizebecomes an important parameter that needs consideration for targeting. Fenretinide, an anti-cancer agent, was encapsulated in PEG-poly(benzyl aspartate) block copolymer micelles byHashida and his coworkers [273]. They observed the mean particle size of drug encapsulatedpolymeric micelles to be around 173 nm. These micelles were able to accumulate in tumorand inhibit the tumor growth, providing promising and effective carrier of fenretinide for tar-geted cancer chemotherapy.

The chain length of each block is an important factor that determines micelle-formingcharacters such as the aggregation behavior of the polymer [274]. Opanasopit et al. showedthe importance of block chain length in their work, wherein PEG-poly(β-benzyl L-aspartate)block copolymer micelles were used for loading of camptothecin [275]. They observed thechain lengths to influence the incorporation efficiency and stability of polymeric micelles.Several block copolymers were synthesized with variation in PEG and aspartic acid units andby esterification of these polymers with different groups as benzyl, lauryl, and n-butyl. Inchain length variations, 5–27 Bz-69 coded polymer showed a higher camptothecin incorpora-tion than 12–50 Bz-63, 12–26 Bz-64, and 5–52 Bz-67. (The block copolymers were codedby chain lengths of the PEG and polyaspartate, the name of the hydrophobic group, anddegree of esterification. 5–27 Bz-69 implies a block copolymer composed of the PEG blockof molecular weight of 5000, the polyaspartate block possessing 27 units of aspartic acid, and69% of the aspartic acid residue that was esterified to the benzyl aspartate residue.) Amongthe higher camptothecin incorporations, 5–27 Bz-69 showed higher micelle stability than12–50 Bz-63 and 12–26 Bz-64. This suggested that the balance between the hydrophobic andhydrophilic chains affected the stability of micelles.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

The effect of drug content influencing the targeting efficacy has been demonstrated byKataoka et al. for the adriamycin-incorporated polymeric micelles. The in vivo antitumoractivities of two polymeric micelle samples composed of identical chain lengths of both thePEG and the poly(aspartic acid) chains, but different drug contents were compared [113].Adriamycin incorporated in the inner core (both by chemical conjugation and physical entrap-ment) was quantitatively measured using a synthetic method, and effects of the adriamycincontents on micelle stability and in vivo antitumor activity were analyzed. They found thephysically entrapped adriamycin to be responsible for in vivo antitumor activity.

Kwon and Vakil have shown the effect of micellar stability for efficient targeting throughthe preparation of mixed polymeric micelles formed from PEG-b-PCL and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxy PEG. They proposed the micelles to possess highthermodynamic stability and suitable as long circulating carriers in the context of antineoplas-tic and antibiotic drug delivery [276]. The hydrolytic degradation of poly(lactic acid)-PluronicF127-poly(lactic acid) nanoparticles has been reported by Xiong et al. [277,278]. They notedthat the hydrolytic degradation of the amphiphilic block copolymers affected the sizes andmorphologies of these nanoparticles.

The extent of hydrophobic interactions of the core region of the polymeric micelles withthe drug determines the strength with which the micelle system holds the drug within its core.

Different approaches toward targeting

Drug targeting can be classified as active targeting and passive targeting [279]. Targeting viapolymeric micelles is usually achieved by one of the following approaches; the EPR effect, stim-uli-sensitivity, or by complexing specific targeting ligand molecules to the micelle surface [36].

EPR effect

The greatest difficulty in effective treatment against cancer is the nonselective distribution ofdrug to healthy cells. Blood vessels of most of the normal tissues have an intact endotheliallayer which restricts macromolecules or other nanoparticles from the tissue and only allowsthe diffusion of small molecules. Contrarily, because of the fast growth of tumor tissue, theendothelial layer of blood vessels in tumor is often porous, and both small and large mole-cules have access to the malignant tissue. Owing to their nanoscopic size, polymeric micellespassively accumulate at the interstitial spaces of various pathological sites by extravasatingleaky capillaries (especially of solid tumors). They also have been shown to distribute tosome of the cytoplasmic organelles and infarct tissues, infected areas, inflammatory sites thathave compromised barrier function [30,280]. This in turn helps in reducing the volume of dis-tribution of the drug as the polymeric micellar drug carriers cannot pass through walls of nor-mal blood vessels, thereby resulting in decreased side-effects of the drug. For effectivetherapy, drug carriers must be able to avoid uptake by the fixed macrophages. Polymericmicelles have the ability to escape uptake by the fixed macrophages of liver and spleen, i.e.by the mononuclear phagocyte system. In tumor neovasculature, there is a poorly developedlymphatic drainage system that leads to enhanced retention of polymeric micelles within thesolid tumor as micelles are not efficiently cleared. This feature allows prolonged circulationof polymeric micelles in the circulatory system upon administration [281]. Owing to thesecharacteristics, it is possible to achieve passive drug targeting using polymeric micelles.

The hyperpermeability of tumors associated with the EPR effect is based on excessiveproduction and secretion of vascular permeability factors stimulating extravasation withincancerous tissue. Commonly secreted chemicals include vascular endothelial growth factorbradykinins, nitric oxide, prostaglandins, enzyme collagenase, and peroxynitrite [282,283].


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

EPR effect depends upon the pore cut-off size of blood vessels. It has been demonstratedthat the pore cut-off size for different tumors is different. This leads to variable permeabilitythrough different tumors. The small size of polymeric micelles allows easy penetrability eventhrough very small cut-off sizes of the tumors which could be of the order of even lesser than200 nm [139]. Efficacy of micelle accumulation depends on tumor type (cut-off size of tumorvasculature) and can be controlled by varying the molecular size of PEG blocks in PEG-PEconjugates [270].

EPR effect is also associated with the concentration of drug in plasma and the molecularweight of polymers or drug-copolymer conjugates. The plasma drug concentration mustalways remain higher for effective therapy. It is well-established that the EPR effect is effec-tive only with macromolecules which can avoid the renal clearance (generally larger than40 kDa). It has been shown that there is an increase in EPR with an increase in molecularweight above some critical size, because it is usually hard to maintain the drug concentrationin the tumor greater than the plasma drug concentration for long periods for low-molecular-weight drugs [284].

Vetvicka and his associates formulated a micellar drug delivery system designed to pro-long the blood circulation time and maximize the efficiency of the EPR effect. They prepareddoxorubicin conjugated PEO-b-poly(allyl glycidyl ether) micellar system that circulated forlong time and released doxorubicin efficiently at the tumor site because of the acidic pH pre-vailing at the tumor site. This also led to destabilization and disruption of the micellar systemgenerating free diblock unimers that could be excreted [285]. Watanabe et al. developed poly-meric micelles composed of various PEG-poly(aspartate ester) block copolymers incorporat-ing camptothecin. The stability of the formulation was found to strongly depend on theamount of benzyl esters and length of the PEG. The drug-loaded micelles delivered the drugto tumor sites owing to the EPR effect [225]. The EPR effect has been exploited to advantageby other research groups also [125,270].

Stimuli-sensitivity

For ideal drug targeting, there should not be any drug release from the micelle during circula-tion. Only after the polymeric micelles accumulate at the targeted tissue, the drug should bereleased by means of some internal environmental trigger such as pH, particular enzyme, etc.or by an external trigger including temperature, light, or ultrasound (Figure 2).

Depending on the stimulus applied varied responses may be observed including disruptionof the structure, changes in shape, volume, permeation rates, hydration state, swelling/collaps-ing, hydrophilic/hydrophobic surface, or conformational changes. Destabilization of micellesas a result of stimulation by either physiological or external trigger is termed as ‘stimuli-sensitivity’ or ‘environmental sensitivity’ of the micelles [286]. Release of drug from themicellar system is dependent on the exploitation of differences that exist in normal tissuesand pathological tissues. Such a release mechanism from polymeric micelles is also termed as‘ON-OFF release,’ ‘intelligent delivery,’ or ‘smart delivery’ by other researchers.

The origin of various stimuli for destabilization of micelles can be explained taking intoconsideration the pathophysiological changes that occur in a diseased state of body. Variousstimuli-sensitive polymeric micellar systems used for targeting are discussed hereunder.

pH-sensitive polymeric micelles

There are a number of pH gradients that exist in normal and pathophysiological states insidethe body. pH-sensitive polymeric micelles exploit these differences in pH for targeting. In


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

tumors and inflammatory tissues a mildly acidic pH is encountered (pH around 6.8). This is aslightly low value as compared with the pH of blood and normal tissues (pH around 7.4).Micelles can also be taken up into the cell by the process of endocytosis and may as wellenter cell organelles as endosomes, lysosomes, etc. The pH value inside these organelles isnearly 5.5 [91].

The decreased pH in pathological areas such as tumors, infarcts, and inflammatory siteshas been related to hypoxia, hydrolysis of ATP in hypoxic conditions and massive cell death,and decreased pH in endosomes and lysosomes to the change in proton concentration alongwith the presence of enzymes. Most of the tumors are poorly perfused and hence an alteredmetabolic pathway with subsequent glycolysis is being followed, leading to elevation in thelevels of lactic acid within the interstitia and in effect lowering the pH value at that particularsite [287–289]. This served as the basis for the development of pH-sensitive polymericmicelles. For example, negatively charged oligo/poly(nucleic acids) can be delivered intracel-lularly by complexing them with cationic polymers. Once into endosomes, these are deproto-nated causing disruption of endosomal membrane and releasing nucleic acids in the cytosol[290].

In experimental animals and humans, pH 7.0–6.8 is the natural pH range used for target-ing the solid tumors. Upon oral or intravenous administration of glucose, the extracellulartumor pH may reduce by 0.2–0.4 pH units. If required, sometimes, glucose can be adminis-tered for lowering pH for the treatment of patients [291].

Two main approaches that have been used for developing pH-sensitive systems are:involvement of a titrable group into the copolymer and inclusion of labile linkages that aredestabilized in acidic conditions. Incorporation of titrable groups such as amines and carbox-ylic acids into the backbone of the copolymer leads to an alteration of the solubility of thepolymer upon protonation. This in effect may disrupt the micellar structure. Acid degradablelinkages can be constructed using linkers such as hydrazone, acetal, imine, etc. that arecleaved at a pH nearly 5.5. Inclusion of acid-labile linkages, such as benzoic imine linkage,in polymeric structures has shown to cause change in micellar integrity or complete

Figure 2. Important stimuli that can be exploited for destabilization of polymeric micelle.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

destruction of the micellar structure when these polymers encounter low-pH environment.However, the imine linkage is unstable at physiological conditions and is less frequently usedin designing of drug delivery systems. To overcome the problem associated with imine linkerit can be conjugated to other group. PEGylation via the benzoic imine linker has been suc-cessfully used for constructing self-assembling stealth amphiphilic polycation synthesizedfrom poly-L-lysine-grafted-cholic acid. The benzoic imine group provided a physiologicallystable pH responsive polymer that responded at very slight acidic condition, i.e. pH about 6.8[286,292].

Systems respond to pH changes if they have ionisable blocks with a pKa value between 3and 10 in their backbone. Block copolymers having basic groups such as L-histidine, pyri-dine, tertiary amine, and acidic groups such as carboxylic acids and phosporic acids are pHsensitive [290]. Many researchers are further trying to explore tumor-targetability via use ofpH-responsive polymeric micelles. Some significant examples are shown in Table 5.

Thermosensitive polymeric micelles

Most of the primary tumors can directly be excised using heat such that the cancer cells arekilled by the high temperatures (>43 °C) of sufficient time duration [299]. Alternately, suchtumors can indirectly be sensitized by mild hyperthermia [300,301]. During the excision ther-apy, certain tissues experience only mild hyperthermia (40–43 °C), which is insufficient tocause tissue necrosis in that stipulated time interval. Thus, regions of tissue experiencing mildhyperthermia may be benefited from combined treatment with therapeutics that can respond tomodest increases in temperature [302]. Also, as most of the pathological areas (noticeably mostof the tumors) demonstrate distinct hyperthermia the thought of developing temperature-sensi-tive micellar carriers for drug delivery has emerged as an interesting onset toward targeting.

Hyperthermia is thought to preferentially increase tumor blood flow and tumor microvas-cular permeability and thereby increase drug accumulation at the tumor tissue [303]. Hyper-thermia is associated with altered fluidity and stability of cellular membranes or inhibition ofDNA-repair enzymes and thereby able to exert certain antitumor effects on tumors [304].When combined with chemotherapies, hyperthermia can synergetically kill malignant tumorcells [305,306]. Temperature changes can be internal, e.g. hyperthermia during inflammation,or can be from an external source. Moreover, there exist various means to heat the requiredarea in the body. Heat can be generated inside target tissues by locally applied ultrasound orby locally applied high frequency causing the oscillation of target-accumulated magneto-sen-sitive micelles.

The thermosensitivity of polymeric micelles is the phenomenon where the carrier under-goes a change in structure with an increase in temperature, leading to the deposition of thedrug and easier drug absorption by cells. Temperature-sensitive polymeric micelles can bemade by assembling them with amphiphilic copolymers, in which one of the blocks demon-strates thermosensitive properties. At a certain temperature, these polymers produce a volumephase transition associated with a sudden change in the solvation state. This transition temper-ature is termed as critical solution temperature. Polymers solubilized upon heating possess anupper critical solution temperature, and those which become insoluble possess lower criticalsolution temperature (LCST). With regard to the thermal targeting strategy, LCST is the mostimportant physical parameter that governs the performance of a thermosensitive material forits application in drug delivery [290]. Below the LCST, the polymer is well soluble in waterdue to extensive formation of hydrogen bonds between polymer and water molecules. How-ever, the network of hydrogen bonds collapses to exclude water molecules from the polymerat a temperature above the LCST, eventually leading to aggregation and precipitation of the


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Table

5.Acid-sensitive

drug

-loadedpo

lymeric

micellarsystem

s.

pH-sensitiv

eam

phiphilic

blockcopo

lymer

Abb

reviation

ReasonforpH

-sensitiv

ityRef.

Loa

ding

ofdo

xorubicin(adriamycin)

PEO-b-poly(allylglycidyl

ether)

PEO-b-PAGE

Hyd

razone

bond

[285

]Stearic

acid-g-chitosanoligosaccharide

CSO-SA

Atlow

pH,theam

inogrou

psarepartially

orcompletelyionized

[42]

Poly(L-lactic

acid)-b-PEG

PLLA-PEG

Acid-labile

hydrazon

ebo

ndandacis-acon

itylbo

nd,used

forthe

conjug

ationof

doxo

rubicinto

theterm

inal

endof

PLLA

[293

]

Poly(L-histid

ine)/PEG

andpo

ly(L-lactic

acid)/PEG

Poly(His)/PEG

and

(PLLA)/PEG

Poly(His)prom

oted

pH-ind

uced

destabilizatio

nandendo

somal

drug

release

[294

,295

]

Poly(L-glutamic

acid)-b-PPO-b-Poly(L-glutamic

acid)

andPoly(ethy

lene

glycol)-b-po

ly(propy

lene

oxide)

PLGA-b-PPO-b-

PLGA,andPEG-b-

PPO

Chang

eof

conformationof

PLGA

atlower

pH[296

]

RGD-decorated

PEO-b-PCL

GRGDS-PEO-b-

PBCL

[297

]

Cross-linkedpo

ly(ethyleneox

ide)-b-poly(methacrylic

acid)

PEO-b-PMA

Protonatio

nof

carbox

ylic

grou

psof

PMA

chains

inthemicelles

[213

]

PEG-poly(aspartate-hy

drazon

e-adriam

ycin)

(PEG-p(A

sp-H

yd-

ADR))

Cleavageof

acid-sensitiv

ehy

drazon

ebo

ndsin

late

endo

somes

and/or

lysosomes

inthecells

with

pHvalues

arou

nd5.0

[256

]

Loa

ding

ofpo

doph

yllotoxin

Poly(aspartic

acid)-g-octadecylamine-g-po

lyethy

lene

glycol

PASP-g-O

DA-g-PEG

Protonatio

nor

deproton

ationof

carbox

ylgrou

psin

backbo

ne[130

]

Loa

ding

ofpa

clita

xel

Hyd

rotrop

icpo

lymerscontaining

acrylic

acid

moieties

–Acrylic

acid

moieties

[298

]


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

polymer [307]. Exact properties of thermosensitive polymeric micelles can be adjusted bychemical modifications of both hydrophobic and hydrophilic blocks in such a way that themicelle can destabilize at temperatures above LCST and release the drug dissolved in itshydrophobic core The main mechanism of thermosensitive polymeric micelles is that duringtheir circulation through the heated malignant tissues, where local temperature is above itsLCST, the outer shell of the micelles transfers into a hydrophobic structure and is subse-quently absorbed into cells mediated by hydrophobic interaction. Consequently, a highenough level of drug to kill the cancer cells can be achieved when the anticancer drug loadedinside the micelles accumulate at malignant tissues. Thermo-targeted polymeric micelles canbe applied on a wide spectrum of tumors notably improving their clinical applications [308].One of the most widely studied polymer for thermoresponsiveness is poly(N-isopropylacryl-amide) (PIPAAm). PIPAAm is well-known to exhibit a reversible phase transition across itsLCST in aqueous medium. This polymer is water-soluble and hydrophilic, existing in anextended conformation, below its LCST but undergoes a phase transition to insoluble, hydro-phobic aggregates above 32 °C [309]. The thermoresponsive properties and structures of thepolymeric micelles depend upon the molecular structure of a single modified PIPAAm chainthat is the building block of the micellar assembly. The thermoresponsive character, especiallythe LCST, of polymeric micelles of the modified PIPAAm chains is not always consistentwith that of PIPAAm. The LCST of PIPAAm is independent of the molecular weight and theconcentration, but can be changed by shifting the hydrophilic/hydrophobic balance [310].

On these backgrounds, many research groups have focused on the development of ther-mosensitve polymeric micelles. A block copolymer, poly(N-isopropylacrylamide-coacryla-mide)-b-poly(D,L-lactide) with the LCST of 41 °C was synthesized and used as the carrier fordelivery of docetaxel by Liu et al. [311]. The polymer formed micelles and the hydrated outershell prevented micelles from being aggregated and also enabled them to escape from nonse-lective scavenging by the RES to gain a longer plasma half-life at the physiological tempera-ture. It was observed that hyperthermia greatly enhanced the targeting efficacy of drug-loadedmicelles and also helped in reduction of toxicity of drug. They further compared the cytotox-icity of the docetaxel-loaded micelle with conventional docetaxel formulation as a control for-mulation in different cancer cell lines and the antitumor efficacy in Lewis lung carcinoma-bearing C57BL/6 mice [312]. The results revealed reduced toxicity of docetaxel-loadedmicelle and higher docetaxel concentration in tumor than that of the conventional docetaxelformulation. A significantly higher antitumor efficacy was observed in mice treated withdocetaxel-loaded micelles accompanied by hyperthermia. Nakayama et al. demonstrated theeffect of varying chain lengths and effects of terminal functional groups, especially surfacepolarity and hydrophobicity, on thermoresponses of the PIPAAm-b-poly(benzyl methacrylate)polymeric micelles [67]. The micelle surface chemistry was found to significantly influencemicellar thermoresponse, which depended on PIPAAm chain lengths. The LCST shifted dras-tically to lower temperatures with micelles having hydrophobic phenyl groups. The magnitudeof these LCST shifts increased with decreasing molecular weight of the PIPAAm chains.

Santis et al. were the first to report the preparation of PEGylated and thermosensitivepolyion complex micelles having a coacervate core formed by two strong oppositely andpermanently charged polyelectrolyte block copolymers of poly(sodium 2-acrylamido-2-methyl-propanesulfonate)-b-PIPAAm and poly[(3-acrylamidopropyl)-trimethylammonium chloride]-b-PEO under stoichiometric charge neutralization conditions and polyelectrolyte chain lengthmatching [313].

In general, incorporation of hydrophobic groups into PIPAAm chains decreases the LCSTand hence, usually a slightly different value as compared with that of the PIPAAm is obtained[314].


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Besides PIPAAm, poly(N,N-diethylacrylamide) also possesses a LCST of about 32 °C andis considered as an alternative thermosensitive water-soluble polymer to replace PIPAAm dueto its lower toxicity [315]. Bian et al. synthesized poly(styrene-b-N,N-diethylacrylamide) withcontrolled molecular weight and narrow polydispersity [316]. The aqueous micellar solutionunderwent a reversible aggregation transition at around the LCST of poly(N,N-diethylacryla-mide) block chains comprising the outer shell.

Soga et al. studied thermosensitivity of poly(N-(2-hydroxypropyl) methacrylamide lac-tate)-b-PEG. Polymeric micelles were formed with approximately 50 nm diameter by heatingaqueous polymer solution from below to above the CMT. With an increase in hydrophobicblock length the CMC as well as the CMT decreased, which can be attributed to the greaterhydrophobicity of the thermosensitive block with increasing molecular weight [144]. It wasfound that micelles showed a controlled instability due to hydrolysis of the lactic acid sidechains in the thermosensitive block. Rijcken et al. showed that poly(N-(2-hydroxyethyl)-meth-acrylamide-oligolactates)-b-PEG hydrolyzed more rapidly than poly(N-(2-hydroxypropyl)methacrylamide-oligolactates) [317]. Thus, rapidly degrading thermosensitive polymericmicelles could possess attractive features for targeted drug delivery than slow degrading poly-meric micelles. Of late, a new class of thermoresponsive polymer, 2-hydroxy-3-butoxypropylstarch was synthesized [318]. The polymer self-assembled into micelles below the LCST,while above the LCST micelles aggregated into more polar and larger objects. Many otherexamples of PIPAAm and other polymers-based thermosensitive polymeric micelles havebeen reported. Some examples are depicted in Table 6.

Dual-responsive polymeric micelles

To improve the targeting and treatment efficacy, efforts have been emphasized on the prepara-tion of dual-responsive polymeric micelles, the micelles responding to temperature as well as

Table 6. Examples of thermoresponsive polymeric micelles.

Thermoresponsive block and examplesof amphiphilic polymers LCST Loaded drug Ref.

PIPAAm derivativesPIPAAm-b-poly(l-alanine) Slightly lower than

32.4 °CAdriamycin [319]

PIPAAm-b-oligo(methyl methacrylate) 34 °C Prednisolone [320]Poly(t-butyl acrylate)-b-PIPAAm 33.8 °C Naproxen [321]PIPAAm-b-poly(styrene-alternate-maleic anhydride)-

b-PS33.5–35 °C Folic acid [322]

(β-Cyclodextrin-(PIPAAm)4) 33.5 °C – [323]PIPAAm-g-poly(2-(N-carbazolyl)ethyl acrylate) 31.5 °C Methotrexate [324]Poly(L-lactide-star block-N-isopropylacrylamide) around 33 °C Methotrexate [57]PIPAAm-g-polyphosphazene near 30 °C – [325,326]Poly(benzyl methacrylate)-b-PIPAAm-co-N,N-

dimethylacrylamide)32 °C – [67]

Cholic acid, conjugated with amine-terminatedPIPAAm

31.5 °C Indomethacin [327]

PluronicChitosan-Pluronic – Indomethacin [122]

Poly(2-(dimethylamino) ethyl methacrylate)PCL-b-poly(2-(dimethylamino) ethyl methacrylate) – Aspirin [81]


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

pH changes. Accordingly, a pentablock copolymer was synthesized by the coupling of pH-sensitive poly(β-amino ester) to thermosensitive biodegradable PCL-PEG-PCL [328]. Aninteresting dual-stimuli-responsive polymer has been based on acid-labile acetal linkages thatprovide an effective mechanism of polymer biodegradation in an acidic medium. Poly(N-(2-hydroxypropyl) methacrylamide dilactate)-b-PEG was synthesized by Soga et al. [267]. Thispolymer formed polymeric micelles which gradually dissolved due to hydrolysis of the lacticacid side groups. The characteristic destabilization of the polymeric micelles was used for thegeneration of controlled release of paclitaxel. At pH 8.8 and 37 °C, paclitaxel-loaded micellesdestabilized within 10 h due to the hydrolysis of the lactic acid side group of the copolymer.

Usually, the combination of a thermoresponsive monomer like IPAAm with a pH-respon-sive monomer yields double-responsive copolymers [329]. Yin et al. synthesized a randomcopolymer of IPAAm and propylacrylic acid that showed a sharp phase transition in responseto temperature and pH [330]. Zhang et al. reported nanoparticles assembled from poly(IPA-Am-co-acrylic acid)-b-PCL, which demonstrated dual-responsiveness to both thermo and pHin a suitable window for targeted anticancer drug delivery [331]. An amphiphilic star blockcopolymer comprising of poly(methyl methacrylate)-b-poly(IPAAm-co-N,N-dimethylamino-ethylmethacrylate) was synthesized and micelles were constructed [332]. Dual-response origi-nated from the thermo-sensitivity of PIPAAm and the pH-sensitivity from poly(N,N-dimethylaminoethylmethacrylate). In vitro drug release study revealed that methotrexaterelease was hastened by the thermo-trigger at pH 7.4, as well as the pH-trigger at 37 °C.

Block copolymers containing a hydrophilic N,N-dimethylacrylamide block and doublyresponsive blocks of N-isopropylacrylamide and N-acryloylvaline were prepared [333]. Thesecopolymers demonstrated reversible pH- and temperature-induced unimer-to-micelle transi-tion. Within a specified range of pH and temperature, the micelles could be ‘locked’ by inter-polyelectrolyte complexation of anionic N-acryloylvaline segments with those of a cationicpoly([ar-vinylbenzyl]trimethylammonium chloride). When the temperature was lowered toroom temperature, the polymeric micelles remain ‘locked’ in their multimeric structures whichremained stable in aqueous solution at temperature below CMT.

PEG-b-poly(trans-N-(2-ethoxy-1,3-dioxan-5-yl)acrylamide) dual-responsive micelles wereconstructed and loaded with hydrophobic Nile red by Huang and coworkers [334]. The poly-meric micelles were stable at pH 7.4 and the release of Nile red upon dissociation of themicelles was provoked by the acid-triggered hydrolysis of the orthoester groups in mildlyacidic environment.

Other stimuli-sensitive polymeric micelles

Thiol-responsive (redox-responsive) systems. Redox sensitive systems are fascinating as theseare susceptible toward disassembly in specific disease locations, where the redox environmentis significantly different from the normal body cells. A redox potential difference existsbetween the reducing intracellular space and oxidizing extracellular space [335,336]. Thereducing environment near cancer cells due to the over-expression of several peptides likeglutathione (the intracellular concentration of which is many folds greater than extracellularconcentration) provides an opportunity to utilize these conditions for targeting [337,338]. Forexample, the interconversion of thiols and disulfides has been exploited to synthesize variousbioconjugated polymers. The disulfide bonds are sufficiently stable in the circulation and inthe extracellular environment and are rapidly cleaved under a reductive environment throughintracellular thiol-disulfide exchange reactions [339,340]. The presence of reducing agents orthe exchange of disulfide in the presence of other thiols can convert disulfide bonds reversiblyto thiols. Thus, polymers containing disulfide bonds can be considered as thiol- as well as


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

redox-responsive. Wang et al. recently reported synthesis of reversibly cross-linked triblockcopolymer PCL-b-poly(2,4-dinitrophenylthioethyl ethylene phosphate)-b-PEG [218]. Afterdeprotection, core-shell-corona micelles were formed in aqueous milieu from the resultant tri-block copolymer bearing thiol groups. The cross-linkages were cleaved intracellularly toresult in enhanced drug release and cytotoxicity. Thayumanavan and others generated nonco-valent polymeric assemblies between a surfactant complexed with a disulfide containing poly-electrolyte that could be disassembled via glutathione exposure [341]. The disassembly was aresult of the polyvalent interaction between the polyelectrolyte and surfactant changing to amonovalent interaction through a reductive disulfide bond cleavage reaction. PEG-poly(aminoacid)s polymeric micelles with disulfide-cross-linked shells via thiol-reducible bonds wereconstructed [342]. The reducing conditions prevalent in most of the cancerous tissues trig-gered the release of anticancer drugs preferentially at the tumor site. Redox-responsive corecross-linked PEO-b-poly(N-isopropylacrylamide-co-N-acryloxysuccinimide) micelles weredeveloped by Zhang et al. [343]. Recently, disulfide-linked star PEG-(N-acetyl cysteine) con-jugates tailored to release the drug under intracellular glutathione levels were prepared [344].Terpolymers with thiol- and pH-responsive properties demonstrating membrane-disruptivecharacteristics were synthesized by copolymerization of a pyridyl disulfide containing acryloylmonomer with methacrylic acid and butyl acrylate by Bulmus et al. [345]. The terpolymerswere used in delivery of biomolecules.

Ultrasound-sensitive systems

The application of the external ultrasound to control drug delivery and release from micellarcarriers is based on accumulation of these systems in required areas and making the arealeaky by local application of external ultrasound. Ultrasonic waves can be focused and trans-mitted through a medium, thus allowing the waves to be directed to and/or focused on a par-ticular volume of tissue. The waves can induce either thermal or mechanical effects, whilemicellar systems can be designed to respond either to the elevation in temperature or to themechanical effects of ultrasonic waves, or to both. Due to its noninvasive nature, and no needof surgery for insertion, these systems are currently gaining attraction. Ultrasound has beenshown to facilitate the delivery of chemotherapeutic agents into tumors and facilitate the heal-ing of wounds and bone fractures [346–349].

Ultrasound has been exploited to trigger the release of drugs from micellar carriers. Doxo-rubicin encapsulated in micelles was released using ultrasound to provide high local concen-trations at the tumor site [350]. After systemic administration of micelle-encapsulateddoxorubicin in rats bearing tumors and application of 70 kHz ultrasound, results showed thattumor volume was significantly reduced.

The group of Husseini has been engaged in the development of ultrasound-based poly-meric micelles and their characterization to optimize the effects of drug for better efficiency.Polymeric micelles incorporating doxorubicin have been prepared that released the drug afterultrasonication [351]. They showed that the DNA damage induced by doxorubicin deliveredto human leukemia cells (HL-60) from Pluronic P105 micelles was at an optimum after cellswere exposed to ultrasound, when comparatively studied with and without the application ofultrasound [352]. The percentage of drug released was highest at 20 kHz ultrasound anddecreased with increasing ultrasound frequency despite much higher power densities when anultrasonic exposure chamber with real-time fluorescence detection was used to measure ultra-sound-activated drug release from P105 micelles under continuous wave or pulsed ultrasound[353]. The thermodynamic characteristics of ultrasound-activated release of doxorubicin fromP105 micelles were observed [354]. They further investigated the degradation kinetics of


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

stabilized P105 micelles for several hours following a two-hour application of ultrasound at70 and 476 kHz [355]. At both frequencies, the degradation appeared to be at a statisticallysignificantly higher rate compared to samples that were not exposed to ultrasound. Lately, thegroup presented an artificial neural network model that attempted to predict the dynamicrelease of doxorubicin from P105 micelles under different ultrasonic power densities at20 kHz [356]. The developed model could be used in optimizing the ultrasound applicationfor targeted drug release at the tumor site by controlling power density and ultrasound dura-tion via model predictive control. Their investigations over ultrasound-activated micellar drugdelivery have been summarized in a recent review [357].

Tumor imaging becomes quite essential when effective drug targeting via tumor irradia-tion by ultrasound is considered. Hence, multifunctional nanoparticles that could target tumor,act as long-lasting ultrasound contrast agents, and augment drug delivery of ultrasound-medi-ated carriers were developed [358].

The mechanisms controlling acoustic activation of drug uptake from Pluronic micelleswere described by Marin et al. from their study over Pluronic micelles [359]. Acoustically-triggered drug release from micelles was related to higher concentration of free drug in theincubation medium and also increased uptake of the micellar-encapsulated drug because ofdisruption of cell membranes. Still further studies on ultrasound-sensitive systems and themechanisms controlling drug release from such systems represent an important part ofresearch on stimuli-sensitive micellar carriers. To design an ultrasound-sensitive system,assessing the destruction thresholds of echogenic carriers with clinical ultrasound is a majorchallenge [360].

Magnetically-sensitive systems

Systems in which the rate of drug release is controlled by oscillating or heating the carrier inresponse to the external electromagnetic field are said to be magnetically responsive [361].Iron oxide nanoparticles possess specific magnetic properties in the presence of an externalmagnetic field making them an attractive platform as contrast agents for magnetic resonanceimaging (MRI) (one of the best noninvasive methodologies in clinical science for evaluatinganatomy and physiology of tissues) and because of their superparamagnetic properties theyare commonly referred to as superparamagnetic iron oxide nanoparticles (SPIONs). The mag-netic and optical properties of these magnetic particles, upon loading into micelles, werefound to remain unchanged and these nanocomposites have shown good in vivo biocompati-bility as well. The concept of magnetic targeting toward the intended tissues under the influ-ence of external magnetic field using such nanocomposites has received increasedconsideration recently. Hong et al. constructed PEG-PCL micelles and folate was used as atargeting ligand to functionalize the micelles which contained the MRI contrast agent SPIONsand doxorubicin [362]. These micelles demonstrated better targeting response to the hepaticcarcinoma cells, Bel 7402 cells, in vitro than their nontargeted counterparts. Ai et al. alsohave shown great potential of combining MRI and drug delivery functions in cancer treatment[363]. PEG-PLA polymeric micelles with a cyclic pentapeptide c(Arg-Gly-Asp-D-Phe-Lys) asa targeting ligand to detect the delivery of SPIONs and doxorubicin-loaded micelles into thetumor vascular endothelia cells were formulated. Gang et al. targeted gemcitabine-loadedmagnetic PCL nanoparticles in pancreatic cancer xenograft mouse model using external mag-nets [364]. Manganese ferrite-SPIONs were synthesized and solubilized with the help ofmethoxy PEG-b-poly(ɛ-caprolactone) micelles in water [365]. Mn-SPIONs inside polymericmicelles were found to strongly improve the contrast between small lesions and normaltissues. Guthi et al. have developed a multifunctional micelle system to which a lung cancer-


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

targeting peptide has been attached, and encapsulated with SPIONs and doxorubicin for MRIand therapeutic delivery, respectively [366]. The multifunctional micelles modified with tar-geting peptide demonstrated improved lung cancer targeting. Hence, the usefulness of mag-neto-responsive micellar systems not only in targeted drug delivery but also for diagnosticapplications like imaging has been very well established.

Photo-responsive systems

Photo-responsive systems comprise of macromolecules that change their properties when irra-diated with light of suitable wavelength [367,368]. Frequently, an incorporated chromophoreinto the structure of the hydrophobic block along the polymer backbone or side chainsundergo structural alterations in response to light of particular wavelength, disturbing thehydrophilic/lipophilic balance of the polymer and ultimately leading to micellar disruption[369,370]. An important advantage of photo-sensitive micellar systems is that light-irradiationis a relatively straight-forward, noninvasive mechanism to induce responsive behavior. Light-responsive systems are attractive as materials responding to electromagnetic radiations, mainlyto the UV, visible and near-infrared range, can be developed and applied at well enclosedsites in the body [371]. Various synthetic approaches to photoresponsive polymers and theirproperties have been reviewed by Yu and Kobayashi [372].

Decorated shell cross-linked reverse polymer micelles constituted of poly(dimethylamino-ethyl methacrylate)-b-poly(methyl methacrylate-random-coumarin methacrylate) and respon-sive to light were reported by Babin et al. [373]. Jiang et al. prepared amphiphilic blockcopolymer micelles whose core-shell structure was disrupted upon irradiation with differentwavelengths of light [374,375]. Jing et al. reported a facile approach for the preparation oflight-responsive monomethoxy PEG-b-poly(5-methyl-5-(2-nitro-benzoxycarbonyl)-1,3-dioxan-2-one) copolymer micelles containing a light-sensitive linkage [376]. Photolysis of the2-nitrobenzyl ester side-groups on the hydrophobic block of these micelles could be dissoci-ated by UV irradiation to release their payload. Photosolvolysis of hydrophobic groups hasbeen used in hydrophilic PEO copolymer micellar solutions with polymethacrylate bearingpyrene moiety in the side group as hydrophobic block [377]. Pyrene from the copolymer wasthen being separated using UV-light irradiation that increased the hydrophilicity of the hydro-phobic block by formation of PMA causing micellar dissociation.

Triple-responsive (multi-responsive) polymeric micelles

Newer strategies combine sensitivities to different stimuli in designing a highly efficient mul-tistimuli responsive targeted polymeric micellar system. Klaikherd and his group reported atriple stimuli sensitive block copolymer assembly that could respond to changes in tempera-ture, pH, and redox potential [378]. The block copolymer comprised of an acid-sensitivetetrahydropyran-protected 2-hydroxyethyl methacrylate as the hydrophobic part and a temper-ature-sensitive PIPAAm as the hydrophilic part with an intervening disulfide bond. The devel-oped structures were sensitive not only to a single stimulus, but responded simultaneously tothe presence of multiple stimuli.

Less frequently used stimuli

Some reports over materials that change on receiving stimuli from electric field (electro-responsive) [379], changes in glucose concentration (sugar-responsive) [380], and presence ofenzymes [381] as well have been reported. Examples of stimuli-sensitive nanocarriers fortargeting are reviewed by Torchilin [382], and stimuli-sensitive materials by Roy et al. [383].


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

Complexing targeting ligand molecules to micelles

One of the best approaches to enhance cellular internalization of polymeric micelles at desiredtarget tissue is attachment of cell-specific ligands on the surface of these polymeric micelles.Thus, covalent attachment of cell specific ligands, e.g. monoclonal antibodies [384], sugars[385], folate residues [386], and peptides [387] on the surface of polymeric micelles has beenpursued to enhance drug delivery to various cells.

Monoclonal antibodies

Immunomicelles can be prepared by covalently attaching an antibody to a surfactant or poly-meric micelles. Attachment of antibodies to micelle surface provides the broadest opportuni-ties in terms of diversity of targets. Thus, many groups are trying to exploit theseopportunities by preparing ‘immunomicelles’ [36,136]. To demonstrate the effectiveness ofusing immunomicelles in tumor targeting, Sawant et al. solubilized paclitaxel and camptothe-cin in mixed micelles of PEG-PE and vitamin E [388]. The mixed micelles were modifiedwith antinucleosome monoclonal antibody 2C5 (mAb 2C5), which can specifically bringmicelles to tumor cells in vitro. These mixed micelles and mAb 2C5-immunomicelles demon-strated significantly higher in vitro cytotoxicity against various cancer cell lines.

Lee et al. prepared PEG-PE-based immunomicelles modified with monoclonal antibodiesby using PEG-PE conjugates with the free PEG terminus activated with p-nitrophenylcarbonylgroup [389]. Targeted immunomicelles were prepared by incubating the corresponding anti-body with doxorubicin-loaded p-nitrophenylcarbonyl-PEG-PE-containing micelles at pHaround 8. The lipid fragments of this PEG derivative could firmly incorporate into the micellecore, while the p-nitrophenylcarbonyl group could interact, in response to pH, with amino-groups of various antibodies, their fragments, or other peptides, thus increasing tumor speci-ficity. In most AB-type block copolymer syntheses that have the PEG chain for polymericmicelles, a chemically unreactive functional group such as methoxy is used as the PEG termi-nal. Synthesis of aldehyde group-terminated (on the PEG side) PEG-PLA block copolymershas been reported by Scholz et al. [33]. Polymeric micelles that had antibodies as targetingligands on their surface by utilizing this aldehyde group shown potential for active targetingof tumors.

Gao et al. have demonstrated the cytotoxicity of micellar paclitaxel and free drug using astandard MTS test [390]. At paclitaxel concentration of 40 ng/ml, free drug killed <2% ofcancer cells in the culture, whereas activity of paclitaxel in plain micelles was slightly higherkilling about 5% of cancer cells. Paclitaxel-loaded immunomicelles killed more than 50% ofcancer cells. Thus, paclitaxel-loaded 2C5-immunomicelles provided more efficient killing ofcancer cells compared to the free drug or paclitaxel in plain micelles.

Sugars

One of the key players in cell-involved biorecognition is sugar, and perhaps one of the mostfascinating routes in cellular-specific drug targeting comes via sugar-mediated deliverythrough glyco-receptors on the cellular plasma membrane [391,392]. Glycoreceptor binding toa particular sugar often occurs in a regioselective manner [393]. Thus, a block copolymerhaving a glucose or galactose residue at the chain end of one of the block in a regioselectivemanner was synthesized by Yasugi et al. [85]. PEG-PLA block copolymer having a site spe-cifically protected-sugar group at the PEG chain end using a metalated protected sugar as aninitiator was synthesized. Polymer micelles having sugar residues on the surface were thenprepared by dialyzing an N,N-dimethylacetamide solution of the sugar-bearing PEG-PLA


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

block copolymer against water. A galactose-bearing PEG-PLA micelle was confirmed toselectively attach to RCA-1 lectin (RCA-1 is one of the well-studied plant lectins which spe-cifically recognize a β-D-galactose residue). Nagasaki et al. in another study synthesized sev-eral types of sugar-installed PEG-PLA block copolymers which formed polymeric micelles inaqueous media [385]. Specific recognition of lectin proteins with the sugar molecules on themicelle surface was observed. Both the galactose- and lactose-installed micelles specificallyinteracted with RCA-1; on the other hand, the mannose-installed micelle interacted specifi-cally with Con A. These polymer micelles were expected to have wide utility in the field ofdrug targeting as glyco-receptor-directed carrier systems.

Folate residues

Membrane folate receptors (FRs), including FR-α and FR-β, are glycosylphosphatidylinositol-anchored glycoproteins. FR-α expression is amplified in over 90% of ovarian carcinomas andat varying frequencies in other epithelial cancers. FR-β is expressed in a nonfunctional formin neutrophils and in a functional form in activated macrophages and in myeloid leukemias[394]. In contrast, most normal tissues lack expression of either of the FR isoform. Folate isa high affinity ligand for the FRs upon derivatization via one of its carboxyl group and hasbeing widely studied due to its small size and ease of availability for tumor-specific drugdelivery [395]. Upon attaching the folate molecules onto the surface layer of polymericmicelles, FR-mediated endocytosis of micelles is attainable. In this regard, Kim et al. pre-pared poly(His-co-Phe)-b-PEG and PLLA-b-PEG-folate pH-sensitive micelles [396]. Acceler-ated doxorubicin release from these polymeric micelles triggered by an early endosomal pHof 6.0 was observed. When this triggered release was combined with active targeting via FR-mediated endocytosis, the polymeric micelles were able to effectively kill drug-sensitive ovar-ian cancer cells as well as drug-resistant counterpart cells. Recently, micellar docetaxel formu-lation using folic acid-conjugated D-α-tocopheryl polyethylene glycol succinate 2000 fortargeted delivery was reported and showed an enhanced cellular uptake with in vitro therapeu-tic effects [397]. Amphiphilic hyperbranched block copolymer with a dendritic Boltorn® H40core, a hydrophobic poly(L-lactide) inner shell, and a hydrophilic methoxy PEG and folate-conjugated PEG outer shell was synthesized by Prabaharan et al. [398]. Doxorubicin encapsu-lated polymeric micelles were prepared and it was observed that the cellular uptake of thedoxorubicin-loaded and folate-conjugated micelles was higher than doxorubicin-loaded,folate-free micelles because of the folate-receptor mediated endocytosis. It resulted in highercytotoxicity against the 4T1 mouse mammary carcinoma cell line. Yang et al. synthesized thefolate-conjugated copolymer, folate-PEG-PCL, and fabricated micelles of the same with theencapsulation of a potent multidrug resistance modulator, FG020326 [399]. Cytotoxicity stud-ies indicated that folate-functionalized and FG020326-loaded micelles resensitized humanKBv200 cells treated with vincristine approximately five times more than their folate-freecounterparts. Similarly, folate-modified chitosan micelles with enhanced tumor targeting werealso recently developed [400].

In a little different study, Bae et al. [401] were able to significantly increase cancer treat-ment efficacy and safety of the polymeric micelles by optimizing the number of ligands onthe micelle surface. Using precise synthesis, folate concentration on the surface of themicelles was controlled for two different amphiphilic block copolymers that self-assembledinto spherical micelles, folate-PEG-poly(aspartate-hydrazone-adriamycin) with γ-carboxylicacid activated folate and methoxy PEG-poly(aspartate-hydrazone-adriamycin) without folate.Interestingly, folate conjugation could not significantly improve the tumor accumulation ofthe micelles as liver accumulation was seen. However, when folate concentration was


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

adjusted to achieve minimum ligand–receptor interaction, folate-conjugated micelles showedan effective cancer treatment efficiency that was 5-fold broader than free adriamycin as wellas the micelles without folate conjugation.

Many studies have been performed in which folic acid has been applied as a targetingligand in both the tumor imaging diagnosis and cancer chemotherapy. But the combination oftwo strategies is little reported. In a more advanced study, Hong et al. accommodated doxoru-bicin and MRI contrast agent superparamagnetic iron oxide in the core of PEG-PCL micelleswith a folate targeting ligand attached to the distal ends of PEG [362]. The prepared micellesserved dual purpose with better targeting tropism, in vitro, toward the hepatic carcinoma cellsthan their nontargeting counterparts, and showed a great potential in diagnostic imaging.

Peptides

For tumor targeting, cancer-specific peptides are also very appropriate, as peptides can easilybe derivatized and engineered to achieve better in vivo stability and tissue specificity. Xionget al. conjugated an arginine-glycine-aspartic acid (RGD) containing peptide as a ligand torecognize adhesion molecules overexpressed on the surface of metastatic cancer cells, overthe surface of PEO-b-PCL micelles [387]. These micelles proved to be good ligand-targetedcarriers for enhanced drug delivery to metastatic tumor cells. Musacchio et al. used the over-expression of Peripheral Benzodiazepine Receptor (PBR) in certain cancers for targeting suchcancers [402]. Selective ligands to the PBR may induce apoptosis and cell cycle arrest.Hence, PBR-targeted PEG-PE micellar drug delivery system loaded with paclitaxel was pre-pared that demonstrated significantly enhanced toxicity against some cancerous cells. Lately,multifunctional RGD-functionalized polymeric micelles coencapsulating doxorubicin andcombretastatin A4 were shown to have prolonged blood circulation and preferential accumu-lation in solid tumor [403]. In B16-F10 tumor-bearing mice, these micelles demonstratedexcellent antitumor efficacy and low side-effects.

Photodynamic therapy

Photodynamic therapy (PDT) is a minimally invasive treatment, considered as an alternativeto classical therapies such as surgery, radiotherapy, and chemotherapy, that combines a photo-sensitiser or a photosensitising agent with photoirradiation by a specific type of light to killcancer cells (particularly tumors of oesophagus, bladder, and melanoma). After the adminis-tration of the photosensitiser, the directed nonthermal light (635–760 nm) onto the abnormaltissue where the drug has preferentially accumulated leads to the formation of an excited pho-tosensitizer. Upon activation, the photosensitiser transfers its excess energy to molecular oxy-gen, directly or through an indirect mechanism via formation of intermediate radical species,to produce the highly reactive cytotoxic singlet oxygen that causes irreversible oxidativedestruction at the target site [404–407]. PDT induces both apoptosis and necrosis leading tolight-induced cell death of the subcellular organelles and other biomolecules. Although PDTwas originally developed for cancer therapy, its potential for application has been substan-tially extended to many other clinical applications such as the treatment of hardening arteries,age-related macular degeneration, and sun induced precancerous skin lesions and woundinfections [408,409].

Some desirable properties of a photosensitizer molecule are its nontoxic nature in theabsence of light irradiation, photostability, ability to absorb in the red region of spectrum withhigh extinction molar coefficient, target specificity, minimal tendency toward self-aggregation,and capability to be rapidly eliminated from the body. The pharmacokinetic properties of the


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

photosensitizer play a critical role in achieving the desired biological response. Photosensitiz-ers such as phthalocyanine and porphyrin derivatives have been mostly explored for systemicadministration in PDT [410].

pH-responsive micelles of N-isopropylacrylamide, methacrylic acid, and octadecyl acrylatecopolymers were prepared and loaded with aluminum chloride phthalocyanine (AlClPc) byTaillefer et al. [411]. The micelles exhibited higher cytotoxicity against EMT-6 mouse mam-mary cells in vitro than control Cremophor EL formulation. However, the polymeric micellesshowed rapid clearance and relatively poor retention in blood because of the amphiphilic nat-ure of the PIPAAm corona with relatively marginal stealth properties. To minimize clearance,Taillefer and coworkers in their further investigation increased the hydrophilicity of N-isopro-pylacrylamide copolymer by synthesizing different pH-sensitive copolymers bearing N-vinyl-2-pyrrolidone (VP) [412]. AlClPc was loaded in the PIPAAm copolymeric micelles bydialysis. On comparing the biodistribution and in vivo photodynamic activity of the copoly-mer micelles and control Cremophor EL formulations in Balb/c mice bearing intradermalEMT-6 tumors, similar AlClPc tumor uptake was observed. However, the micelles exhibitedgreater activity in vivo than Cremophor EL formulations at an AlClPc subtherapeutic dose.The decrease in clearance of the micelles was accompanied by preferential accumulation ofthe drug at the target site. Sibata et al. verified complete loading of zinc(II) phthalocyanine(ZnPc) in PEG-5000-distearoyl-phosphatidylethanolamine micelles by absorbance measure-ments, steady state, and time-resolved fluorescence measurements [413]. This system pro-vided a better stability of the incorporated drug, with a narrow size distribution pattern of itsparticles and a lower photobleaching quantum yield. Silicon phthalocyanine Pc 4, a highlyhydrophobic second-generation photosensitizer, was encapsulated in biocompatible micellesof PEG-b-poly-ɛ-caprolactone and in vitro PDT studies in MCF-7c3 human breast cancer cellswere conducted [414]. Studies revealed efficient intracellular uptake of the micelle-formulatedPc 4 in cells, and significant cytotoxic effect of the formulation upon photoirradiation.

Hioka et al. solubilized a benzoporphyrin derivative using Pluronic P123 for PDT [415].The behavior of the photosensitizer varied with differing polymer concentration. Above theCMC of the polymer, the photosensitizer was present in its monomeric form in the core of themicelle while aggregates were formed in water below the CMC. Aggregated structures possesslow quantum yields of light absorption and cause significantly less singlet oxygen production.Li et al. investigated the formulation of hydrophobic protoporphyrin IX (PpIX) with methoxyPEG-b-PCL micelles and compared their PDT response to that of free PpIX [416]. Fluores-cence microscopy revealed that the subcellular localization of free PpIX and PpIX formulatedin micelles was similar. However, the cellular uptake and photocytotoxicity of PpIX in RIF-1cells from micelles was markedly increased than free PpIX signifying the potential of thesemicelles in drug delivery systems for hydrophobic photodynamic sensitizers.

Conclusions and future perspectives

Owing to their salient properties, polymeric micelles are emerging as important pharmaceuti-cal drug carriers. The most pertinent trait of block copolymer micelles for drug delivery istheir ability to form prominent core-shell structures. Poorly water-soluble drugs can easily beloaded in the hydrophobic core of the polymeric micelles, thus providing an opportunity toenhance bioavailability of such drugs. Importantly, stable polymeric micelles possessing anexcellent ability to carry a variety of poorly water-soluble drugs can effectively be used totarget certain pathological areas in the body with compromised vasculature such as tumorsand infarcts owing to their size and the EPR effect. Targeting can also be achieved byattaching specific ligands or specific antibodies onto their surface. Thus, widespread use of


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

polymeric micelles can be expected, particularly in the field of drug delivery for the cytotoxicagents.

So long as the mystery about micelle stability in the blood is resolved, formulation ofpolymeric micelles to maximize drug efficacy will remain challenge. Still, when comparedwith other novel drug delivery systems, the development of polymeric micelles appears to bequite promising. The development of stimuli-sensitive micelles exploiting the properties ofpolymeric micelles to improve the selective drug delivery via physiological triggers appearsto be quite exhilarating field of research. Intensive efforts in this field of research would defi-nitely foster polymeric micelles as one of the major vehicles in the field of site-specific drugdelivery.

References[1] Zana R. Introduction to surfactants and surfactant self-assemblies. In: Dynamics of surfactant self-

assemblies – micelles, microemulsions, vesicles, and lyotropic phases. Zana R, editors. BocaRaton, FL: Taylor & Francis; 2005. 2–36.

[2] Rangel-Yagui CO, Pessoa JA, Tavares LC. Micellar solubilization of drugs. Journal of Pharmacyand Pharmaceutical Sciences. 2005;8:147–63.

[3] Adams ML, Lavasanifar A, Kwon GS. Amphiphilic block copolymers for drug delivery. Journal ofPharmaceutical Sciences. 2003;92:1343–55.

[4] M. Malmsten, Micelles. In: Surfactants and Polymers in Drug Delivery. Marcel Dekker, New York(2002).19–50.

[5] Y. Moroi, Dissolution of amphiphiles. In: Micelles: Theoretical and Applied Aspects, PlenumPress, New York (1992).25–40.

[6] Hickok RS, Wedge SA, Hansen AL, Morris KF, Billiot FH, Warner IM. Pulsed field gradientNMR investigation of solubilization equilibria in amino acid and dipeptide terminated micellar andpolymeric surfactant solutions. Magnetic Resonance in Chemistry. 2002;40:755–61.

[7] Jones MC, Leroux JC. Polymeric micelles a new generation of colloidal drug carriers. EuropeanJournal of Pharmaceutics and Biopharmaceutics. 1999;48:101–11.

[8] Trubetskoy VS, Torchilin VP. Polyethyleneglycol-based micelles as carriers for delivery of thera-peutic and diagnostic agents. STP Pharma Sciences. 1996;6:79–86.

[9] Zarafshani Z, Akdemir O, Lutz JF. A ‘‘click’’ strategy for tuning in situ the hydrophilic-hydropho-bic balance of AB macrosurfactants. Macromolecular Rapid Communications. 2008;29:1161–6.

[10] Erhardt R, Boker A, Zettl H, Kaya H, Pyckhout-Hintzen W, Krausch G, Abetz V, Muller AHE.Janus micelles. Macromolecules. 2001;34:1069–75.

[11] Forster S, Plantenberg T. From self-organizing polymers to nanohybrid and biomaterials. Ange-wandte Chemie International Edition. 2002;41:688–714.

[12] Jacquin M, Muller P, Cottet H, Crooks R, Theodoly O. Controlling the melting of kinetically fro-zen poly(butyl acrylate-b-acrylic acid) micelles via addition of surfactant. Langmuir.2007;23:9939–48.

[13] Cao Y, Li H. Micellar solutions of CMC amphipathic copolymers. Polymer International.2003;52:869–75.

[14] Lutz JF, Pfeifer S, Zarafshani Z. In situ functionalization of thermoresponsive polymeric micellesusing the “click” cycloaddition of azides and alkynes. QSAR & Combinatorial Science.2007;26:1151–8.

[15] Liu H, Xu J, Jiang J, Yin J, Narain R, Cai Y, Liu S. Syntheses and micellar properties of well-defined amphiphilic AB2 and A2B Y-shaped miktoarm star copolymers of ɛ-caprolactone and 2-(dimethylamino)ethyl methacrylate. Journal of Polymer Science Part A: Polymer Chemistry.2007;45:1446–62.

[16] Zhang YX, Liu SP, Du LB, Zhang DQ, Chen JY, Jiang M. Synthesis and characterization of fluo-rocarbon-containing, hydrophobically associative poly (acrylic acid-co-Rf-poly (ethylene glycol)macromonomer). Journal of Applied Polymer Science. 2002;84:1035–47.

[17] Kline SR. Polymerization of rodlike micelles. Langmuir. 1999;15:2726–32.[18] Miyata K, Christie RJ, Kataoka K. Polymeric micelles for nano-scale drug delivery. Reactive &

Functional Polymers. 2011;71:227–34.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[19] Mourya VK, Inamdar NN, Nawale RB, Kulthe SS. Polymeric micelles: general considerations andtheir applications. Indian Journal of Pharmaceutical Education and Research. 2011;45:128–38.

[20] Varma MV, Panchagnula RV. Enhanced oral paclitaxel absorption with vitamin E-TPGS: effect onsolubility and permeability in vitro, in situ and in vivo. European Journal of Pharmaceutical Sci-ences. 2005;25:445–53.

[21] Bromberg L. Polymeric micelles in oral chemotherapy. Journal of Controlled Release.2008;128:99–112.

[22] Kabanov AV, Alakhov VY. Micelles of amphiphilic block copolymers as vehicles for drug delivery.In: Amphiphilic block copolymers: self-assembly and applications. Alexandris P, Lindman B, edi-tors. Amsterdam: Elsevier Science; 2000. 352–76.

[23] Elsabahy M, Perron M, Bertrand N, Yu G, Leroux JC. Solubilization of docetaxel in poly(ethyleneoxide)-block-poly(butylene/styrene oxide) micelles. Biomacromolecules. 2007;8:2250–7.

[24] Peng X, Zhang L. Formation and morphologies of novel self-assembled micelles from chitosanderivatives. Langmuir. 2007;23:10493–8.

[25] Yokoyama M. Novel passive targetable drug delivery with polymeric micelles. In: Biorelated poly-mers and gels: controlled release and applications in biomedical engineering. Okano T, editors. SanDiego, CA: Academic Press; 1998. 193–231.

[26] Zhang C, Qu G, Sun Y, Wu BX, Yao Z, Guo Q, Ding Q, Yuan S, Shen Z, Ping Q, Zhou H. Phar-macokinetics, biodistribution, efficacy and safety of N-octyl-O-sulfate chitosan micelles loaded withpaclitaxel. Biomaterials. 2008;29:1233–41.

[27] Nishiyama N, Okazaki S, Cabral H, Miyamoto M, Kato Y, Sugiyama Y, Nishio K, Matsumura Y,Kataoka K. Novel cisplatin-incorporated polymeric micelles can eradicate solid tumors in mice.Cancer Research. 2003;63:8977–83.

[28] Jiang M, Wu Y, Heb Y, Nie J. Micelles formed by self-assembly of hyperbranched poly[(amine-ester)-co-(D, L-lactide)] (HPAE-co-PLA) copolymers for protein drug delivery. Polymer Interna-tional. 2009;58:31–9.

[29] Mahmud A, Xiong XB, Aliabadi HM, Lavasanifar A. Polymeric micelles for drug targeting. Jour-nal of Drug Targeting. 2007;15:553–84.

[30] Kwon GS, Okano T. Polymeric micelles as new drug carriers. Advanced Drug Delivery Reviews.1996;21:107–16.

[31] Harada A, Kataoka K. Block copolymer micelles as long-circulating drug vehicles. Advanced DrugDelivery Reviews. 1995;16:295–309.

[32] Harada A, Kataoka K. Formation of polyion complex micelles in an aqueous milieu from a pair ofoppositely-charged block copolymers with poly(ethylene glycol) segments. Macromolecules.1995;28:5294–9.

[33] Scholz C, Iijima M, Nagasaki Y, Kataoka K. A novel reactive polymeric micelle with aldehydegroups on its surface. Macromolecules. 1995;28:7295–7.

[34] Juillerat-Jeanneret L, Schmitt F. Chemical modification of therapeutic drugs or drug vector systemsto achieve targeted therapy: Looking for the grail. Medicinal Research Reviews. 2007;27:574–90.

[35] Kataoka K, Harada A, Nagasaki Y. Block copolymer micelles for drug delivery: Design, character-ization and biological significance. Advanced Drug Delivery Reviews. 2001;47:113–31.

[36] Torchilin VP. Targeted polymeric micelles for delivery of poorly soluble drugs. Cellular andMolecular Life Sciences. 2004;61:2549–59.

[37] Seo DH, Jeong Y, Kim DG, Jang MJ, Jang MK, Nah JW. Methotrexate-incorporated polymericnanoparticles of methoxy poly(ethylene glycol)-grafted chitosan. Colloids and Surfaces B: Biointer-faces. 2009;69:157–63.

[38] Jiang GB, Quan D, Liao K, Wang H. Novel polymer micelles prepared from chitosan graftedhydrophobic palmitoyl groups for drug delivery. Molecular Pharmaceutics. 2006;3:152–60.

[39] Fournier E, Dufresne MH, Smith DC, Ranger M, Leroux JC. A novel one-step drug-loading proce-dure for water-soluble amphiphilic nanocarriers. Pharmaceutical Research. 2004;21:962–8.

[40] Kwon GS, Naito M, Yokoyama M, Okano T, Sakurai Y, Kataoka K. Physical entrapment of adri-amicin in AB block copolymer micelles. Pharmaceutical Research. 1995;12:192–5.

[41] La SB, Okano T, Kataoka K. Preparation and characterization of the micelle-forming polymericdrug indomethacin-incorporated poly(ethylene oxide)-poly(β-benzyl l-aspartate) block copolymermicelles. Journal of Pharmaceutical Sciences. 1996;85:85–90.

[42] Ye YQ, Yang FL, Hu FQ, Du YZ, Yuan H, Yu HY. Core-modified chitosan-based polymericmicelles for controlled release of doxorubicin. International Journal of Pharmaceutics.2008;352:294–301.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[43] Hu FQ, Wu XL, Du YZ, You J, Yuan H. Cellular uptake and cytotoxicity of shell crosslinked stea-ric acid-grafted chitosan oligosaccharide micelles encapsulating doxorubicin. European Journal ofPharmaceutics and Biopharmaceutics. 2008;69:117–25.

[44] Yang ZL, Li XR, Yang KW, Liu Y. Amphotericin B-loaded poly(ethylene glycol)-poly(lactide)micelles: Preparation, freeze-drying, and in vitro release. Journal of Biomedical Materials Research.2008;85A:539–46.

[45] Huh KM, Lee SC, Cho YW. Hydrotropic polymer micelle system for delivery of paclitaxel. Jour-nal of Controlled Release. 2005;101:59–68.

[46] Burkersroda FV, Gref R, Gopferich A. Erosion of biodegradable block copolymers made of poly(DL-lactic acid) and poly(ethylene glycol). Biomaterials. 1997;18:1599–607.

[47] Hamley IW. Introduction to block polymers. In: Developments in block copolymer science andtechnology. Hamley IW, editors. Chichester: Wiley; 2004. 1–30.

[48] Erdogan T, Bernaerts KV, Van Renterghem LM, Du Prez FE, Goethals EJ. Preparation of starblock co-polymers by combination of cationic ring opening polymerization and atom transfer radi-cal polymerization. Designed Monomers and Polymers. 2005;8:705–14.

[49] Zhou J, Wang L, Ma J. Recent research progress in the synthesis and properties of amphiphilicblock co-polymers and their applications in emulsion polymerization. Designed Monomers andPolymers. 2009;12:19–41.

[50] Maniruzzaman M, Kawaguchi S, Ito K. Micellar copolymerization of styrene with a poly(ethyleneoxide) macromonomer in water to a unimolecular graft copolymer micelle. Designed Monomersand Polymers. 2000;3:255–61.

[51] Guo Z, Fang Z. Effects of the competition between grafting reaction and decomposition on themiscibility and rheological behaviors of PS/POE blends in the presence of AlCl3. Polymer-PlasticsTechnology and Engineering. 2009;48:1185–90.

[52] Lu HW, Zhang LM, Wang C, Chen RF. Preparation and properties of new micellar drug carriersbased on hydrophobically modified amylopectin. Carbohydrate Polymers. 2011;83:1499–506.

[53] Bronstein LM, Chernyshov DM, Timofeeva GI, Dubrovina LV, Valetsky PM, Khokhlov AR. Inter-action of polystyrene-block-poly(ethylene oxide) micelles with cationic surfactant in aqueous solu-tions. Metal colloid formation in hybrid systems. Langmuir. 2000;16:3626–32.

[54] Michels B, Waton G, Zana R. Dynamics of micelles of poly(ethylene oxide)-poly(propyleneoxide)-poly(ethylene oxide) block copolymers in aqueous solutions. Langmuir. 1997;13:3111–8.

[55] Oh KT, Lee ES. Cancer-associated pH-responsive tetracopolymeric micelles composed of poly(eth-ylene glycol)-b-poly(L-histidine)- b-poly(L-lactic acid)-b-poly(ethylene glycol). Polymers forAdvanced Technologies. 2008;19:1907–13.

[56] Hadjiantoniou NA, Christoforou TK, Loizou E, Porcar L, Patrickios CS. Alternating amphiphilicmultiblock copolymers: Controlled synthesis via raft polymerization and aqueous solution charac-terization. Macromolecules. 2010;43:2713–20.

[57] Wei H, Zhang XZ, Chen WQ, Cheng SX, Zhuo RX. Self-assembled thermosensitive micellesbased on poly(L-lactide-star block-N-isopropylacrylamide) for drug delivery. Journal of BiomedicalMaterials Research. 2007;83A:980–9.

[58] Fattahi A, Golozar MA, Varshosaz J, Sadeghi HM, Fathi M. Preparation and characterization ofmicelles of oligomeric chitosan linked to all-trans retinoic acid. Carbohydrate Polymers.2012;87:1176–84.

[59] Li Y, Zhang S, Meng X, Chen X, Ren G. The preparation and characterization of a novel amphi-philic oleoyl-carboxymethyl chitosan self-assembled nanoparticles. Carbohydrate Polymers.2011;83:130–6.

[60] Chen XG, Lee CM, Park HJ. O/W emulsification for the self-aggregation and nanoparticle forma-tion of linoleic acid modified chitosan in the aqueous system. Journal of Agriculture and FoodChemistry. 2003;51:3135–9.

[61] Zhang C, Ding Y, Ping Q, Yu L. Novel chitosan-derived nanomaterials and their micelle-formingproperties. Journal of Agriculture and Food Chemistry. 2006;54:8409–16.

[62] Tan YL, Liu CG. Self-aggregated nanoparticles from linoleic acid modified carboxymethyl chito-san: Synthesis, characterization and application in vitro. Colloids and Surfaces B: Biointerfaces.2009;69:178–82.

[63] Huo M, Zhang Y, Zhou J, Zou A, Li J. Formation, microstructure, biodistribution and absence oftoxicity of polymeric micelles formed by N-octyl-N,O-carboxymethyl chitosan. Carbohydrate Poly-mers. 2011;83:1959–69.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[64] Duan K, Zhang X, Tang X, Yu J, Liu S, Wang D, Li Y, Huang J. Fabrication of cationic nanomi-celle from chitosan-graft-polycaprolactone as the carrier of 7-ethyl-10-hydroxy-camptothecin. Col-loids and Surfaces B: Biointerfaces. 2010;76:475–82.

[65] Hu FQ, Liu LN, Du YZ, Yuan H. Synthesis and antitumor activity of doxorubicin conjugated stea-ric acid-g-chitosan oligosaccharide polymeric micelles. Biomaterials. 2009;30:6955–63.

[66] Qu G, Yao Z, Zhang C, Wu X, Ping Q. PEG conjugated N-octyl-O-sulfate chitosan micelles fordelivery of paclitaxel: In vitro characterization and in vivo evaluation. European Journal of Phar-maceutical Sciences. 2009;37:98–105.

[67] Nakayama M, Okano T. Polymer terminal group effects on properties of thermoresponsive poly-meric micelles with controlled outer-shell chain lengths. Biomacromolecules. 2005;6:2320–7.

[68] Kriz J, Pletil J, Tuzar Z, Pospisil H, Brus J, Jakes J, Masar B, Vlcek P, Doskocilova D. Interfaceaffected polymer dynamics: NMR, SANS, and DLS study of the influence of shell-core interactionson the core chain mobility of poly(2-ethylhexyl acrylate)-block-poly(acrylic acid) micelles in water.Macromolecules. 1999;32:397–410.

[69] Prochazka K, Martin TJ, Munk P, Webber SE. Polyelectrolyte poly(tert-butyl acrylate)-block-poly(2-vinylpyridine) micelles in aqueous media. Macromolecules. 1996;29:6518–25.

[70] Colombani O, Ruppel M, Burkhardt M, Drechsler M. Structure of micelles of poly(n-butyl acry-late)-block-poly(acrylic acid) diblock copolymers in aqueous solution. Macromolecules.2007;40:4351–62.

[71] Kriz J, Masar B, Pletil J, Tuzar Z, Pospisil H, Doskocilova D. Three-layer micelles of an ABCblock copolymer: NMR, SANS, and LS study of a poly(2-ethylhexyl acrylate)-block-poly(methylmethacrylate)-block-poly(acrylic acid) copolymer in D2O. Macromolecules. 1998;31:41–51.

[72] Liu S, Weaver JVM, Tang Y, Billingham NC, Armes SP, Tribe K. Synthesis of shell cross-linkedmicelles with pH-responsive cores using ABC triblock copolymers. Macromolecules.2002;35:6121–31.

[73] Geng Y, Discher DE. Hydrolytic degradation of poly(ethylene oxide)-block-polycaprolactone wormmicelles. Journal of the American Chemical Society. 2005;127:12780–1.

[74] Soo PL, Luo L, Maysinger D, Eisenberg A. Incorporation and release of hydrophobic probes inbiocompatible polycaprolactone-block-poly(ethylene oxide) micelles: Implications for drug delivery.Langmuir. 2002;18:9996–10004.

[75] Soo PL, Lovric J, Davidson P, Maysinger D, Eisenberg A. Polycaprolactone-block-poly(ethyleneoxide) micelles: A nanodelivery system for 17β-estradiol. Molecular Pharmaceutics.2005;2:519–27.

[76] Allen C, Yu Y, Maysinger D, Eisenberg A. Polycaprolactone-b-poly(ethylene oxide) block copoly-mer micelles as a novel drug delivery vehicle for neurotrophic agents FK506 and L-685,818. Bio-conjugate Chemistry. 1998;9:564–72.

[77] Hu Y, Zhang L, Cao Y, Ge H, Jiang X, Yang C. Degradation behavior of poly(ɛ-caprolactone)-b-poly(ethylene glycol)-b-poly(ɛ-caprolactone) micelles in aqueous solution. Biomacromolecules.2004;5:1756–62.

[78] Gong CY, Shi S, Dong PW, Kan B, Gou ML, Wang XH, Li XY, Luo F, Zhao X, Wei YQ, QianZY. Synthesis and characterization of PEG-PCL-PEG thermosensitive hydrogel. International Jour-nal of Pharmaceutics. 2009;365:89–99.

[79] Lee SC, Kim KJ, Jeong YK, Chang JH, Choi J. pH-induced reversible complexation of poly(ethyl-ene glycol) and poly(ɛ-caprolactone)-b-poly(methacrylic acid) copolymer micelles. Macromole-cules. 2005;38:9291–7.

[80] Wang YC, Liu XQ, Sun TM, Xiong MH, Wang J. Functionalized micelles from block copolymerof polyphosphoester and poly(ɛ-caprolactone) for receptor-mediated drug delivery. Journal of Con-trolled Release. 2008;128:32–40.

[81] Zhou J, Wang L, Ma J, Wang J, Yu H, Xiao A. Temperature- and pH-responsive star amphiphilicblock copolymer prepared by a combining strategy of ring-opening polymerization and reversibleaddition- fragmentation transfer polymerization. European Polymer Journal. 2010;46:1288–98.

[82] Huang Y, Li L, Fang Y. Self-assembled particles of N-phthaloylchitosan-g-polycaprolactone molec-ular bottle brushes as carriers for controlled release of indometacin. Journal of Materials Science:Materials in Medicine. 2010;21:557–65.

[83] Danhier F, Magotteaux N, Ucakar B, Lecouturier N, Brewster M, Preat V. Novel self-assemblingPEG-p-(CL-co-TMC) polymeric micelles as safe and effective delivery system for paclitaxel. Euro-pean Journal of Pharmaceutics and Biopharmaceutics. 2009;73:230–8.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[84] Yang Z, Xie J, Zhou W, Shi W. Temperature sensitivity and drug encapsulation of star-shapedamphiphilic block copolymer based on dendritic poly(ether-amide). Journal of Biomedical Materi-als Research. 2009;89:988–1000.

[85] Yasugi K, Nakamura T, Nagasaki Y, Kato M, Kataoka K. Sugar-installed polymer micelles: Syn-thesis and micellization of poly(ethylene glycol)-poly(d,l-lactide) block copolymers having sugargroups at the PEG chain end. Macromolecules. 1999;32:8024–32.

[86] Jule E, Nagasaki Y, Kataoka K. Surface plasmon resonance study on the interaction between lac-tose-installed poly(ethylene glycol)-poly(d,l-lactide) block copolymer micelles and lectins immobi-lized on a gold surface. Langmuir. 2002;18:10334–9.

[87] Arimura H, Ohya Y, Ouchi T. The formation of biodegradable polymeric micelles from newly syn-thesized poly(aspartic acid)-block-polylactide AB-type diblock copolymers. Macromolecular RapidCommunications. 2004;25:743–7.

[88] Stepaek M, Uchman M, Prochazka K. Self-assemblies formed by four-arm star copolymers withamphiphilic diblock arms in aqueous solutions. Polymer. 2009;50:3638–44.

[89] Xun W, Wang HY, Li ZY, Cheng SX, Zhang XZ, Zhuo RX. Self-assembled micelles of novel graftamphiphilic copolymers for drug controlled release. Colloids and Surfaces B: Biointerfaces.2011;85:86–91.

[90] Benahmed A, Ranger M, Leroux JC. Novel polymeric micelles based on the amphiphilic diblockcopolymer poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide). Pharmaceutical Research.2001;18:323–8.

[91] Yin H, Bae YH. Physicochemical aspects of doxorubicin-loaded pH-sensitive polymeric micelleformulations from a mixture of poly(L-histidine)-b-poly(L-lactide)- b-poly(ethylene glycol). Euro-pean Journal of Pharmaceutics and Biopharmaceutics. 2009;71:223–30.

[92] Huang CK, Lo CL, Chen HH, Hsiue GH. Multifunctional micelles for cancer cell targeting, distri-bution imaging, and anticancer drug delivery. Advanced Functional Materials. 2007;17:2291–7.

[93] Bhattarai N, Bhattarai SR, Yi HK, Lee JC, Khil MS, Hwang PH, Kim HY. Novel polymericmicelles of amphiphilic triblock copolymer poly(p-dioxanone-co-L-lactide)-block-poly(ethylene gly-col). Pharmaceutical Research. 2003;20:2021–7.

[94] Martinez-Castro N, Zhang M, Pergushov DV, Müller AHE. Anionic polymerization of N,N-dimeth-ylacrylamide with thienyllithium and synthesis of block co-polymers of isobutylene and N,N-dim-ethylacrylamide by site transformation of chain ends. Designed Monomers and Polymers.2006;9:63–79.

[95] Volpert E, Selb J, Candau F. Associating behaviour of polyacrylamides hydrophobically modifiedwith dihexylacrylamide. Polymer. 1998;39:1025–33.

[96] Quanming L, Guohua J, Kangkang T. Dendrimers in drug-delivery applications. Designed Mono-mers and Polymers. 2010;13:301–24.

[97] Chang Y, Kim C. Synthesis and Photophysical Characterization of Amphiphilic Dendritic–Linear–Dendritic Block Copolymers. Journal of Polymer Science Part A: Polymer Chemistry.2001;39:918–26.

[98] Namazi H, Jafarirad S. Application of hybrid organic/inorganic dendritic ABA type triblockcopolymers as new nanocarriers in drug delivery systems. International Journal of Polymeric Mate-rials. 2011;60:603–19.

[99] Gao C, Yan D. Hyperbranched polymers: from synthesis to applications. Progress in Polymer Sci-ence. 2004;29:183–275.

[100] Guohua J, Wenxing C, Wei X. Environmental-sensitive hyperbranched polymers as drug carriers.Designed Monomers and Polymers. 2008;11:105–22.

[101] Amin A, Rehim MA, Mohamed H. Modification of some hyperbranched polyols with oligo (eth-yleneoxide) units on the way to new applications. Polymer-Plastics Technology and Engineering.2008;47:1250–5.

[102] Xiao Y, Hong H, Javadi A, Engle JW, Xu W, Yang Y, Zhang Y, Barnhart TE, Cai W, Gong Sha-oqin. Multifunctional unimolecular micelles for cancer-targeted drug delivery and positron emis-sion tomography imaging. Biomaterials. 2012;33:3071–82.

[103] Yoshida E. TEM observation of nonamphiphilic copolymer micelles. Colloid and Polymer Sci-ence. 2007;285:941–5.

[104] Yoshida E, Ohta M. Preparation of micelles having a UV absorbent at their coronas using a ’non-amphiphilic’ di-block co-polymer. Designed Monomers and Polymers. 2005;8:501–13.

[105] Bates FS, Fredrickson GH. Block copolymer thermodynamics: theory and experiment. AnnualReview of Physical Chemistry. 1990;41:525–57.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[106] Cao T, Munk P, Ramireddy C, Tuzar Z, Webber SE. Fluorescence studies of amphiphilic poly(methacrylic acid)-block-polystyrene-block-poly-(methacrylic acid) micelles. Macromolecules.1991;24:6300–5.

[107] Tsunashima Y, Hirata M, Kawamata Y. Diffusion motions and microphase separation of styrene-butadiene diblock copolymer in solution. 1. Extremely dilute solution region. Macromolecules.1990;23:1089–96.

[108] Prochazka K, Martin TJ, Webber SE, Munk P. Onion type micelles in aqueous media. Macromol-ecules. 1996;29:6526–30.

[109] Giacomelli C, Borsali R. Morphology of poly(ethylene oxide)-block-polycaprolatone blockcopolymer micelles controlled via the preparation method. Macromolecular Symposium.2006;245–246:147–53.

[110] Tian M, Qin A, Ramireddy C, Webber SE, Munk P, Tuzar Z, Prochazka K. Hybridization ofblock copolymer micelles. Langmuir. 1993;9:1741–8.

[111] Hirano T, Klesse W, Ringsdorf H. Polymeric derivatives of activated cyclophosphamide as drugdelivery systems in anti-tumor chemotherapy- Pharmacologically active polymers. MacromolecularChemistry and Physics. 1979;180:1125–31.

[112] Gros L, Ringsdorf H, Schupp H. Polymeric antitumor agents on a molecular and on a cellularlevel? Angewandte Chemie (International Edition in English). 1981;20:305–25.

[113] Yokoyama M, Fukushima S, Uehara R, Okamoto K, Kataoka K, Sakurai Y, Okano T. Character-ization of physical entrapment and chemical conjugation of adriamycin in polymeric micelles andtheir design for in vivo delivery to a solid tumor. Journal of Controlled Release. 1998;50:79–92.

[114] He F, Li SM, Vert M, Zhuo RX. Enzyme-catalyzed polymerization and degradation of copolymersprepared from ɛ-caprolactone and poly(ethylene glycol). Polymer. 2003;44:5145–51.

[115] Chen HL, Bei JZ, Wang SG. Hydrolytic degradation of polyester-polyether block copolymerbased on polycaprolactone/poly(ethylene glycol)/polylactide. Polymers for Advanced Technolo-gies. 2000;11:180–4.

[116] Allen C, Maysinger D, Eisenberg A. Nano-engineering block copolymer aggregates for drugdelivery. Colloids and Surfaces B: Biointerfaces. 1999;16:3–27.

[117] Bromberg L, Magner E. Release of hydrophobic compounds from micellar solutions of hydropho-bically modified polyelectrolytes. Langmuir. 1999;15:6792–8.

[118] Patrick LS, Laibin L, Maysinger D, Eisenberg A. Incorporation and release of hydrophobic probesin biocompatible polycaprolactone-block-poly(ethylene oxide) micelles: Implications for drugdelivery. Langmuir. 2002;18:9996–10004.

[119] Aliabadi HM, Elhasi S, Mahmud A, Gulamhusein R, Mahdipoor P, Lavasanifar A. Encapsulationof hydrophobic drugs in polymeric micelles through co-solvent evaporation: The effect of solventcomposition on micellar properties and drug loading. International Journal of Pharmaceutics.2007;329:158–65.

[120] Gohy JF. Block copolymer micelles. Advances in Polymer Science. 2005;190:65–136.[121] Jette KK, Law D, Schmitt EA, Kwon GS. Preparation and drug loading of poly(ethylene glycol)-

block-poly(-caprolactone) micelles through the evaporation of a cosolvent azeotrope. Pharmaceuti-cal Research. 2004;21:1184–91.

[122] Park KM, Bae JW, Joung YK, Shin JW, Park KD. Nanoaggregate of thermosensitive chitosan-Pluronic for sustained release of hydrophobic drug. Colloids and Surfaces B: Biointerfaces.2008;63:1–6.

[123] Gou M, Zheng X, Men K, Zhang J, Wang B, Lei L, Wang X, Zhao Y, Luo F, Chen L, Zhao X,Wei Y, Qian Z. Self-assembled hydrophobic honokiol loaded MPEG-PCL diblock copolymermicelles. Pharmaceutical Research. 2009;26:2164–73.

[124] Chiappetta DA, Degrossi J, Teves S, D’Aquino M, Bregni C, Sosnik A. Triclosan-loaded polox-amine micelles for enhanced topical antibacterial activity against biofilm. European Journal ofPharmaceutics and Biopharmaceutics. 2008;69:535–45.

[125] Nishiyama N, Kato Y, Sugiyama Y, Kataoka K. Cisplatin-loaded polymer-metal complex micellewith time-modulated decaying property as a novel drug delivery system. Pharmaceutical Research.2001;18:1035–41.

[126] Xu L, Chen H, Xu H, Yang X. Anti-tumour and immuno-modulation effects of triptolide-loadedpolymeric micelles. European Journal of Pharmaceutics and Biopharmaceutics. 2008;70:741–8.

[127] Vakil R, Knilans K, Andes D, Kwon GS. Combination antifungal therapy involving amphotericinB, rapamycin and 5-fluorocytosine using PEG-phospholipid micelles. Pharmaceutical Research.2008;25:2056–64.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[128] Ma Z, Haddadi A, Molavi O, Lavasanifar A, Lai R, Samuel J. Micelles of poly(ethylene oxide)-b-poly(e-caprolactone) as vehicles for the solubilization, stabilization, and controlled delivery ofcurcumin. Journal of Biomedical Materials Research. 2008;86A:300–10.

[129] Jiang T, Wang Z, Tang L, Mo F, Chen C. Polymer micellar aggregates of novel amphiphilic bio-degradable graft copolymer composed of poly (aspartic acid) derivatives: Preparation, character-ization, and effect of pH on aggregation. Journal of Applied Polymer Science. 2006;99:2702–9.

[130] Jiang T, Wang Z, Chen C, Mo F, Xu Y, Tang L, Liang J. Poly(aspartic-acid) derivatives as poly-meric micelle drug delivery systems. Journal of Applied Polymer Science. 2006;101:2871–8.

[131] Bian F, Jia L, Yu W, Liu M. Self-assembled micelles of N-phthaloylchitosan-g-polyvinylpyrroli-done for drug delivery. Carbohydrate Polymers. 2009;76:454–9.

[132] Francis MF, Cristea M, Yang Y, Winnik FM. Engineering polysaccharide-based polymericmicelles to enhance permeability of cyclosporin A across Caco-2 cells. Pharmaceutical Research.2005;22:209–19.

[133] Savi R, Azzam T, Eisenberg A, Maysinger D. Assessment of the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles under biological conditions: A fluorogenic-based approach. Lang-muir. 2006;22:3570–8.

[134] Kwon GS, Naito M, Yokoyama M, Okano T, Sakurai Y, Kataoka K. Micelles based on AB blockcopolymers of poly(ethylene oxide) and poly(β-benzyl L-aspartate). Langmuir. 1993;9:945–9.

[135] Dowling KC, Thomas JK. A novel micellar synthesis and photophysical characterization ofwater-soluble acrylamide-styrene block copolymers. Macromolecules. 1990;23:1059–64.

[136] Torchilin VP. Structure and design of polymeric surfactant-based drug delivery systems. Journalof Controlled Release. 2001;73:137–72.

[137] Bourov GK, Bhattacharya A. Brownian dynamics simulation study of self-assembly of amphi-philes with large hydrophilic heads. Journal of Chemical Physics. 2005;122:044702.

[138] Suek NW, Lamm MH. Computer simulation of architectural and molecular weight effects on theassembly of amphiphilic linear-dendritic block copolymers in solution. Langmuir.2008;24:3030–6.

[139] Gao Z, Anatoly NL, Singhal A, Torchilin VP. Diacyllipid-polymer micelles as nanocarriers forpoorly soluble anticancer drugs. Nano Letters. 2002;2:979–82.

[140] Bae YH, Yin H. Stability issues of polymeric micelles. Journal of Controlled Release.2008;131:2–4.

[141] Schick MJ, Gilbert AH. Effect of urea, guanidinium chloride, and dioxane on the c.m.c. ofbranched-chain nonionic detergents. Journal of Colloid Science. 1965;20:464–72.

[142] Rosen MJ, Cohen AW, Dahanayake M, Hua X. Relationship of structure to properties in surfac-tants. 10. Surface and thermodynamic properties of 2-dodecyloxypoly(ethenoxyethanol)s,C12H25(OC2H4)xOH, in aqueous solution. Journal of Physical Chemistry. 1982;86:541–5.

[143] Al-Sabagh AM. Surface and thermodynamic properties of p-alkylbenzene polyethoxylated andglycerated sulfonate derivative surfactants. Colloids and Surfaces A: Physicochemical and Engi-neering Aspects. 1998;134:313–20.

[144] Soga O, Nostrum CF, Ramzi A, Visser T, Soulimani F, Frederik PM, Bomans PH, Hennink WE.Physicochemical characterization of degradable thermosensitive polymeric micelles. Langmuir.2004;20:9388–95.

[145] Gadelle F, Koros WJ, Schechter RS. Solubilization of aromatic solutes in block copolymers. Mac-romolecules. 1995;28:4883–92.

[146] Kozlov MY, Melik-Nubarov NS, Batrakova EV, Kabanov AV. Relationship between Pluronicblock copolymer structure, critical micellization concentration and partitioning coefficients of lowmolecular mass solutes. Macromolecules. 2000;33:3305–13.

[147] Cheng L, Cao D. Effect of tail architecture on self-assembly of amphiphiles for polymericmicelles. Langmuir. 2009;25:2749–56.

[148] Quintana JR, Villacampa M, Munoz M, Andrio A, Katime IA. Micellization of a polystyrene-block-poly(ethylene/propylene) copolymer in n-alkanes. 1. Thermodynamic study. Macromole-cules. 1992;25:3125–9.

[149] Quintana JR, Villacampa M, Katime IA. Micellization of a polystyrene-b-poly(ethylene/propylene)block copolymer in n-dodecane/1,4-dioxane mixtures. 1. Thermodynamics of micellization. Mac-romolecules. 1993;26:601–5.

[150] Thurn T, Couderc S, Sidhu J, Bloor DM, Penfold J, Holzwarth JF, Wyn-Jones E. Study of mixedmicelles and interaction parameters for ABA triblock copolymers of the type EOm-POn-EOm andionic surfactants: Equilibrium and structure. Langmuir. 2002;18:9267–75.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[151] Elisseeva OV, Besseling NA, Koopal LK, Cohen MA. Influence of NaCl on the behavior ofPEO-PPO-PEO triblock copolymers in solution, at interfaces, and in asymmetric liquid films.Langmuir. 2005;21:4954–63.

[152] Alvarez-Lorenzo C, Gonzalez-Lopez J, Fernandez-Tarrio M, Sandez-Macho I, Concheiro A.Tetronic micellization, gelation and drug solubilization: Influence of pH and ionic strength. Euro-pean Journal of Pharmaceutics and Biopharmaceutics. 2007;66:244–52.

[153] Elias HG. Nonionic micelles. Journal of Macromolecular Science-Chemistry. 1973;7:601–22.[154] Khougaz K, Gao Z, Eisenberg A. Determination of the critical micelle concentration of block

copolymer micelles by static light scattering. Macromolecules. 1994;27:6341–6.[155] El-Ghazawy RA, Raheem RA, Al-Sabagh AM. Surface activity-thermodynamic properties and

light scattering studies for some novel aliphatic polyester surfactants. Polymers for AdvancedTechnologies. 2004;15:244–50.

[156] Kalyanasundaram K, Thomas JK. Environmental effects on vibronic band intensities in pyrenemonomer fluorescence and their application in studies of micellar systems. Journal of the Ameri-can Chemical Society. 1977;99:2039–44.

[157] Dong DC, Winnik MA. The Py scale of solvent polarities. Canadian Journal of Chemistry.1984;62:2560–5.

[158] Abuin EB, Scaiano JC. Exploratory study of the effect of polyelectrolyte surfactant aggregates onphotochemical behavior. Journal of the American Chemical Society. 1984;106:6274–83.

[159] Almgren M, Hansson P, Mukhtar E, Van Stam J. Aggregation of alkyltrimethylammonium surfac-tants in aqueous poly(styrenesulfonate) solutions. Langmuir. 1992;8:2405–12.

[160] Shin IL, Kim SY, Lee YM, Cho CS, Sung YK. Methoxy poly(ethylene glycol)-ɛ-caprolactoneamphiphilic block copolymeric micelle containing indomethacin 1. Preparation and characteriza-tion. Journal of Controlled Release. 1998;51:1–11.

[161] Colombani O, Ruppel M, Schubert F, Zettl H, Pergushov DV, Muller AHE. Synthesis of poly(n-butyl acrylate)-block-poly(acrylic acid) diblock copolymers by ATRP and their micellization inwater. Macromolecules. 2007;40:4338–50.

[162] Chen YW, Alexandridis P, Su CK, Patrickios CS, Hertler WR, Hatton TA. Effect of block sizeand sequence on the micellization of ABC triblock methacrylic acid polyampholytes. Macromole-cules. 1995;28:8604–11.

[163] Zhang X, Jackson JK, Burt HM. Development of amphiphilic diblock copolymers as micellar car-riers of taxol. International Journal of Pharmaceutics. 1996;132:195–206.

[164] Zhang X, Jackson JK, Burt HM. Determination of surfactant micelle concentration by a novelfluorescence depolarization technique. Journal of Biochemical and Biophysical Methods.1996;31:145–50.

[165] Shi B, Fang C, Xian M, Yan Y, Shoukuan Z, Yuan F, Pei Y. Stealth MePEG-PCL micelles:Effects of polymer composition on micelle physicochemical characteristics, in vitro drug release,in vivo pharmacokinetics in rats and biodistribution in S180 tumor bearing mice. Colloid and Poly-mer Science. 2005;283:954–67.

[166] Wu QH, Liang F, Wei TZ, Song XM, Liu DL, Zhang GL. Synthesis and micellization of anamphiphilic biodegradable β-cyclodextrin/poly(γ-benzyl L-glutamate) copolymer. Journal of Poly-mer Research. 2010;17:183–90.

[167] Zhang G, Liang F, Song X, Liu D, Li M, Wu Q. New amphiphilic biodegradable b-cyclodextrin/poly(L-leucine) copolymers: Synthesis, characterization, and micellization. Carbohydrate Poly-mers. 2010;80:885–90.

[168] Zhang W, Li Y, Liu L, Sun Q, Shuai X, Zhu W, Chen Y. Amphiphilic toothbrushlike copolymersbased on poly(ethylene glycol) and poly(ɛ-caprolactone) as drug carriers with enhanced properties.Biomacromolecules. 2010;11:1331–8.

[169] Mohanty AK, Dilnawaz F, Mohanty C, Sahoo SK. Etoposide-loaded biodegradable amphiphilicmethoxy (poly ethylene glycol) and poly (e-caprolactone) copolymeric micelles as drug deliveryvehicle for cancer therapy. Drug Delivery. 2010;17:330–42.

[170] Lee JS, Go DH, Bae JW, Lee SJ, Park KD. Heparin conjugated polymeric micelle for long-termdelivery of basic fibroblast growth factor. Journal of Controlled Release. 2007;117:204–9.

[171] Eckert AR, Webber SE. Naphthalene-tagged copolymer micelles based on polystyrene-alt-maleicanhydride-graft-poly(ethylene oxide). Macromolecules. 1996;29:560–7.

[172] Teng Y, Morrison ME, Munk P, Webber SE, Prochazka K. Release kinetics studies of aromaticmolecules into water from block polymer micelles. Macromolecules. 1998;31:3578–87.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[173] Zhang Y, Jin T, Zhuo R. Methotrexate-loaded biodegradable polymeric micelles: Preparation,physicochemical properties and in vitro drug release. Colloids and Surfaces B: Biointerfaces.2005;44:104–9.

[174] Trimaille T, Mondon K, Gurny R, Moller M. Novel polymeric micelles for hydrophobic drugdelivery based on biodegradable poly(hexyl-substituted lactides). International Journal of Pharma-ceutics. 2006;319:147–54.

[175] Mikhail AS, Allen C. Poly(ethylene glycol)-b-poly(ɛ-caprolactone) micelles containing chemicallyconjugated and physically entrapped docetaxel: Synthesis, characterization, and the influence ofthe drug on micelle morphology. Biomacromolecules. 2010;11:1273–80.

[176] Astafieva I, Zhong X, Eisenberg FA. Critical micellization phenomena in block polyelectrolytesolutions. Macromolecules. 1993;26:7339–52.

[177] Zhang L, Eisenberg A. Formation of crew-cut aggregates of various morphologies from amphi-philic block copolymers in solution. Polymers for Advanced Technologies. 1998;9:677–99.

[178] Yao JH, Mya KY, Li X, Parameswaran M, Xu Q, Loh KP, Chen Z. Light scattering and lumines-cence studies on self-aggregation behavior of amphiphilic copolymer micelles. Journal of PhysicalChemistry B. 2008;112:749–55.

[179] Lin Y, Alexandridis P. Small-angle neutron scattering characterization of micelles formed by poly(dimethylsiloxane)-graft-polyether copolymers in mixed polar solvents. Journal of Physical Chem-istry B. 2002;106:12124–32.

[180] Soni SS, Sastry NV, Aswal VK, Goyal PS. Micellar structure of silicone surfactants in water fromsurface activity, SANS and viscosity studies. Journal of Physical Chemistry B.2002;106:2606–17.

[181] Ramzi A, Rijcken CJF, Veldhuis T, Schwahn D, Hennink WE, Nostrum C. Core-shell structure ofdegradable, thermosensitive polymeric micelles studied by small-angle neutron scattering. Journalof Physical Chemistry B. 2008;112:784–92.

[182] Yokoyama M, Sugiyama T, Okano T, Sakurai Y, Naito M, Kataoka K. Analysis of micelle forma-tion of an adriamycin-conjugated poly(ethylene glycol)-poly(aspartic acid) block copolymer bygel permeation chromatography. Pharmaceutical Research. 1993;10:895–9.

[183] Yang L, Qi X, Liu P, Ghazoui AE, Li S. Aggregation behavior of self-assembling polylactide/poly(ethylene glycol) micelles for sustained drug delivery. International Journal of Pharmaceutics.2010;394:43–9.

[184] Nagasaki Y, Okada T, Scholz C, Iijima M, Kato M, Kataoka K. The reactive polymeric micellebased on an aldehyde-ended poly(ethylene glycol)/poly(lactide) block copolymer. Macromole-cules. 1998;31:1473–9.

[185] Yokoyama M, Miyauchi M, Yamada N, Okano T, Sakurai Y, Kataoka K, Inoue S. Characteriza-tion and anticancer activity of the micelle-forming polymeric anticancer drug adriamycin-conju-gated poly(ethylene glycol)-poly (aspartic acid) block copolymer. Cancer Research.1990;50:1693–700.

[186] Booth C, Attwood D. Effects of block architecture and composition on the association propertiesof poly(oxyalkylene) copolymers in aqueous solution. Macromolecular Rapid Communications.2000;21:501–27.

[187] Cao T, Yin W, Webber SE. Poly(2-vinylnaphthalene-alt-maleic acid)-graft-polystyrene as a photo-active polymer micelle and stabilizer for polystyrene latexes. Macromolecules. 1994;27:7459–64.

[188] Webber SE. Polymer micelles: An example of self-assembling polymers. Journal of PhysicalChemistry B. 1998;102:2618–26.

[189] Sun H, Guo B, Li X, Cheng R, Meng F, Liu H, Zhong Z. Shell-sheddable micelles based on dex-tran-ss-poly(ɛ-caprolactone) diblock copolymer for efficient intracellular release of doxorubicin.Biomacromolecules. 2010;11:848–54.

[190] Kim SY, Shin IG, Lee YM, Cho CS, Sung YK. Methoxy poly(ethylene glycol) and ɛ-caprolac-tone amphiphilic block copolymeric micelle containing indomethacin. II. Micelle formation anddrug release behavior. Journal of Controlled Release. 1998;51:13–22.

[191] Yu BG, Okano T, Kataoka K, Kwon G. Polymeric micelles for drug delivery: Solubilization andhaemolytic activity of amphotericin B. Journal of Controlled Release. 1998;53:131–6.

[192] Del-real A, Garcóa-Garduño MV, Castaño VM. Transmission electron microscopy observations ofmicelle structure in a vinyl acetate-based microemulsion. International Journal of Polymeric Mate-rials. 1998;42:319–26.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[193] Kohori F, Sakai K, Aoyagi T, Yokoyama M, Sakurai Y, Okano T. Preparation and characterizationof thermally responsive block copolymer micelles comprising poly(N-isopropylacrylamide-b-D,L-lactide). Journal of Controlled Release. 1998;55:87–98.

[194] Mueller-Goymann CC. Drug delivery: Liquid crystals. In: Encyclopedia of pharmaceutical tech-nology. Swarbrick J, editors. New York, NY: Informa Healthcare; 2001. 1115–31.

[195] Allemann E, Leroux JC, Gurny R. Biodegradable nanoparticles of poly(lactic acid) and poly(lac-tic-co-glycolic acid) for parenteral administration. In: Pharmaceutical dosage forms: disperse sys-tems. Lieberman H, Rieger M, Banker G, editors. New York, NY: Marcel Dekker; 1998. 163–93.

[196] Kang DY, Kim MJ, Kim ST, Oh KS, Yuk SH, Lee S. Size characterization of drug-loaded poly-meric core/shell nanoparticles using asymmetrical flow field-flow fractionation. Analytical andBioanalytical Chemistry. 2008;390:2183–8.

[197] Winnik MA, Pekcan O, Croucher MD. Fluorescence techniques in the study of polymer colloid.In: Scientific methods for the study of polymer colloids and their applications. Candau F. Otte-will RH, editors. Dordrecht: Kluwer Academic; 1990. 225–46.

[198] Winnik FM, Davidson AR, Hamer GR, Kitano H. Amphiphilic poly(N-isopropylacrylamides) pre-pared by using a lipophilic radical initiator- synthesis and solution properties in water. Macromol-ecules. 1992;25:1876–80.

[199] Nivaggioli T, Tsao B, Alexandridis P, Hatton TA. Microviscosity in Pluronic and Tetronic poly(ethylene oxide)-poly(propylene oxide) block copolymer micelles. Langmuir. 1995;11:119–26.

[200] Bahadur P, Sastry NV, Rao YK, Riess G. Interaction studies of styreneethylene oxide blockcopolymers with ionic surfactants in aqeuous solution. Colloids and Surfaces. 1988;29:343–58.

[201] Kwon GS. Polymeric micelles for delivery of poorly water-soluble compounds. Critical Reviewsin Therapeutic Drug Carrier Systems. 2003;20:357–403.

[202] Torchilin VP. Polymeric micelles as pharmaceutical carriers. In: Polymers in drug delivery.Uchegbu IF Schatzlein AG, editors. Boca Raton, (FL): Taylor & Francis; 2006. 111–30.

[203] Liu J, Zeng F, Allen C. In vivo fate of unimers and micelles of a poly(ethylene glycol)-block-poly(caprolactone) copolymer in mice following intravenous administration. European Journal ofPharmaceutics and Biopharmaceutics. 2007;65:309–19.

[204] Yang C, Attia ABE, Tan JPK, Ke X, Gao S, Hedrick JL, Yang YY. The role of non-covalentinteractions in anticancer drug loading and kinetic stability of polymeric micelles. Biomaterials.2012;33:2971–9.

[205] Lo CL, Huang CK, Lin KM, Hsiue GH. Mixed micelles formed from graft and diblock copoly-mers for application in intracellular drug delivery. Biomaterials. 2007;28:1225–35.

[206] Carstens MG, Jong PH, Nostrum CF, Kemmink J, Verrijk R, Leede LG, Crommelin DA, HenninkWE. The effect of core composition in biodegradable oligomeric micelles as taxane formulations.European Journal of Pharmaceutics and Biopharmaceutics. 2008;68:596–606.

[207] Tao Y, Xu J, Chen M, Bai H, Liu X. Core cross-linked hyaluronan-styrylpyridinium micelles as anovel carrier for paclitaxel. Carbohydrate Polymers. 2012;88:118–24.

[208] Thurmond KB, II, Kowalewski T, Wooley KL. Water-soluble knedel-like structures: the prepara-tion of shell-cross-linked small particles. Journal of the American Chemical Society.1996;118:7239–40.

[209] Kataoka K, Kwon GS, Yokoy M. Block copolymer micelles as vehicles for drug delivery. Journalof Controlled Release. 1993;24:119–32.

[210] Chen L, Xie Z, Hu J, Chen X, Jing X. Enantiomeric PLA-PEG block copolymers and their ste-reocomplex micelles used as rifampin delivery. Journal of Nanoparticle Research. 2007;9:777–85.

[211] Gaucher G, Dufresne M, Sant VP, Kang N, Maysinger D, Leroux JC. Block copolymer micelles:Preparation, characterization and application in drug delivery. Journal of Controlled Release.2005;109:169–88.

[212] Mahmud A, Xiong XB, Lavasanifar A. Novel self-associating poly(ethylene oxide)-block-poly(1-caprolactone) block copolymers with functional side groups on the polyester block for drug deliv-ery. Macromolecules. 2006;39:9419–28.

[213] Kim JO, Kabanov AV, Bronich TK. Polymer micelles with cross-linked polyanion core for deliv-ery of a cationic drug doxorubicin. Journal of Controlled Release. 2009;138:197–204.

[214] Zhang L, Bernard J, Davis TP, Barner-Kowollik C, Stenzel MH. Acid-degradable core-crosslinkedmicelles prepared from thermosensitive glycopolymers synthesized via RAFT polymerization.Macromolecular Rapid Communications. 2008;29:123–9.

[215] Rosler A, Vandermeulen WM, Klok HA. Advanced drug delivery devices via self-assembly ofamphiphilic block copolymers. Advanced Drug Delivery Reviews. 2001;53:95–108.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[216] Murthy KS, Ma Q, Clark CG, Remsen EE, Wooley KL. Fundamental design aspects of amphi-philic shell-crosslinked nanoparticles for controlled release applications. Chemical Communica-tions. 2001;773–4.

[217] Huang H, Remsen EE, Kowalewski T, Wooley KL. Nanocages derived from shell cross-linkedmicelle templates. Journal of the American Chemical Society. 1999;121:3805–6.

[218] Wang YC, Li Y, Sun TM, Xiong MH, Wu J, Yang YY, Wang J. Core–shell–corona micelle stabi-lized by reversible cross-linkage for intracellular drug delivery. Macromolecular Rapid Communi-cations. 2010;31:1201–6.

[219] Henselwood F, Liu G. Water-soluble nanospheres of poly(2-cinnamoylethyl methacrylate)-block-poly(acrylic acid). Macromolecules. 1997;30:488–93.

[220] Kakizawa Y, Harada A, Kataoka K. Glutathione-sensitive stabilization of block copolymermicelles composed of antisense DNA and thiolated poly(ethylene glycol)-block-poly(L-lysine): apotential carrier for systemic delivery of antisense DNA. Biomacromolecules. 2001;2:491–7.

[221] Hu J, Tang Z, Qiu X, Pang X, Yang Y, Chen X, Jing X. Formation of flower- or cake-shaped ste-reocomplex particles from the stereo multiblock copoly(rac-lactide)s. Biomacromolecules.2005;6:2843–50.

[222] Stager J, Domb A. Biopolymer stereocomplexes. Advanced Drug Delivery Reviews.2003;55:549–83.

[223] Kang N, Perron ME, Prud’homme RE, Zhang Y, Gaucher G, Leroux JC. Stereocomplex blockcopolymer micelles: Core-shell nanostructures with enhanced stability. Nano Letters.2005;5:315–9.

[224] Carstens MG, Bevernage JJL, Van Nostrum CF, Van Steenbergen MJ, Flesch FM, Verrijk R, DeLeede LGJ, Crommelin DJA, Hennink WE. Small oligomeric micelles based on end group modi-fied mPEG-oligocaprolactone with monodisperse hydrophobic blocks. Macromolecules.2007;40:116–22.

[225] Watanabe M, Kawano K, Yokoyama M, Opanasopit P, Okano T, Maitani Y. Preparation of cam-ptothecin-loaded polymeric micelles and evaluation of their incorporation and circulation stability.International Journal of Pharmaceutics. 2006;308:183–9.

[226] Reulen S, Merkx M. Exchange kinetics of protein-functionalized micelles and liposomes studiedby Förster resonance energy transfer. Bioconjugate Chemistry. 2010;21:860–6.

[227] Sezgin Z, Yuksel N, Baykara T. Preparation and characterization of polymeric micelles for solubi-lization of poorly soluble anticancer drugs. European Journal of Pharmaceutics and Biopharma-ceutics. 2006;64:261–8.

[228] Bugrin VS, Kozlov MY, Baskin II, Melik-Nubarov NS. Intermolecular interactions governing sol-ubilization in micelles of poly(alkylene oxide) surfactants. Polymer Science Series A.2007;49:463–72.

[229] El-Saeed SM, Farag RK, Abdul-Raouf ME, Abdel-Azim A. Synthesis and characterization ofnovel crude oil dispersants based on ethoxylated schiff base. International Journal of PolymericMaterials. 2008;57:860–77.

[230] Chiappetta DA, Sosnik A. Poly(ethylene oxide)-poly(propylene oxide) block copolymer micellesas drug delivery agents: Improved hydrosolubility, stability and bioavailability of drugs. EuropeanJournal of Pharmaceutics and Biopharmaceutics. 2007;66:303–17.

[231] Chi SC, Yeom D, Kim SC, Park ES. A polymeric micellar carrier for the solubilization of biphe-nyl dimethyl dicarboxylate. Archives of Pharmacal Research. 2003;26:173–81.

[232] Kulthe SS, Inamdar NN, Choudhari YM, Shirolikar SM, Borde LC, Mourya VK. Mixed micelleformation with hydrophobic and hydrophilic Pluronic block copolymers: Implications for con-trolled and targeted drug delivery. Colloids and Surfaces B: Biointerfaces. 2011;88:691–6.

[233] Witt KA, Huber JD, Egleton RD, Davis TP. Pluronic P85 copolymer enhances opioid peptideanalgesia. Journal of Pharmacology and Experimental Therapeutics. 2002;303:760–7.

[234] Gao Y, Li LB, Zhai G. Preparation and characterization of Pluronic/TPGS mixed micelles for sol-ubilization of camptothecin. Colloids and Surfaces B: Biointerfaces. 2008;64:194–9.

[235] Mondon K, Zeisser-Labouèbe M, Gurny R, Möller M. Novel Cyclosporin A formulations usingMPEG–hexyl-substituted polylactide micelles: A suitability study. European Journal of Pharma-ceutics and Biopharmaceutics. 2011;77:56–65.

[236] Chiappetta DA, Hocht C, Taira C, Sosnik A. Oral pharmacokinetics of the anti-HIV efavirenzencapsulated within polymeric micelles. Biomaterials. 2011;32:2379–87.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[237] Kabanov AV, Ckekhonin VP, Alakhov V, Batrakova EV, Lebedev AS, Melik-Nubarov NS, Arzha-kov S, Levashov AV, Morozov GV, Severin ES, Kabanov VA. The neuroleptic activity of haloper-idol increases after its solubilization in surfactant micelles. FEBS Letters. 1989;258:343–5.

[238] Kadam Y, Yerramilli U, Bahadur A, Bahadur P. Micelles from PEO–PPO–PEO block copolymersas nanocontainers for solubilization of a poorly water soluble drug hydrochlorothiazide. Colloidsand Surfaces B: Biointerfaces. 2011;83:49–57.

[239] Yang L, Kuang J, Wang J, Li Z, Zhang LM. Loading and in vitro controlled release of indometh-acin using amphiphilic cholesteryl-bearing carboxymethylcellulose derivatives. MacromolecularBioscience. 2008;8:279–86.

[240] Alakhov V, Pietrzynski G, Patel K, Kabanov A, Bromberg L, Hatton TA. Pluronic block copoly-mers and Pluronic poly(acrylic acid) microgels in oral delivery of megestrol acetate. Journal ofPharmacy and Pharmacology. 2004;56:1233–41.

[241] Dumortier G, Groissord JL, Zuber M, Couarraze G, Chaumeil JC. Rheological study of a thermo-reversible morphine gel. Drug Development and Industrial Pharmacy. 1991;17:1255–65.

[242] Parekh P, Singh K, Marangoni DG, Bahadur P. Micellization and solubilization of a model hydro-phobic drug nimesulide in aqueous salt solutions of Tetronic® T904. Colloids and Surfaces B:Biointerfaces. 2011;83:69–77.

[243] Croy SR, Kwon GS. The effects of Pluronic block copolymers on the aggregation state of nysta-tin. Journal of Controlled Release. 2004;95:161–71.

[244] Mo R, Jin X, Li N, Ju C, Sun M, Zhang C, Ping Q. The mechanism of enhancement on oralabsorption of paclitaxel by N-octyl-O-sulfate chitosan micelles. Biomaterials. 2011;32:4609–20.

[245] Momot KI, Kuchel PW, Deo P, Whittaker D. NMR study of the association of propofol with non-ionic surfactants. Langmuir. 2003;19:2088–95.

[246] Xiong MP, Yanez JA, Kwon GS, Davies NM, Forrest ML. A cremophor-free formulation for tan-espimycin (17-AAG) using PEO-b-PDLLA micelles: Characterization and pharmacokinetics inrats. Journal of Pharmaceutical Sciences. 2009;98:1577–86.

[247] El-Kamel AH. In vitro and in vivo evaluation of Pluronic F127- based ocular delivery system fortimolol maleate. International Journal of Pharmaceutics. 2002;241:47–55.

[248] Lee H, Zeng F, Dunne M, Allen C. Methoxy poly(ethylene glycol)-block-poly(δ-valerolactone)copolymer micelles for formulation of hydrophobic drugs. Biomacromolecules. 2005;6:3119–28.

[249] Kabanov AV, Alakov VY. Pluronic block copolymers in drug delivery: From micellar nanocon-tainers to biological response modifiers. Critical Reviews in Therapeutic Drug Carrier Systems.2002;19:1–73.

[250] Liu JB, Xiao YH, Allen C. Polymer-drug compatibility: a guide to the development of deliverysystems for the anticancer agent, ellipticine. Journal of Pharmaceutical Sciences. 2004;93:132–43.

[251] Ribeiro ME, Cavalcante IM, Ricardo NM, Mai SM, Attwood D, Yeates SG, Booth C. Solubilisa-tion of griseofulvin in aqueous micellar solutions of diblock copolymers of ethylene oxide, 1,2-butylene oxide with lengthy B blocks. International Journal of Pharmaceutics. 2009;369:196–8.

[252] Chen X, Ding S, Qu G, Zhang C. Synthesis of novel chitosan derivatives for micellar solubiliza-tion of cyclosporine A. Journal of Bioactive and Compatable Polymers. 2008;23:563–78.

[253] Dong Y, Jin Y, Wei D. Surface activity and solubilization of a novel series of functional polyure-thane surfactants. Polymer International. 2007;56:14–21.

[254] Zhou Z, Chaibundit C, D’Emanuele A, Lennon K, Attwood D, Booth C. Solubilisation of drugsin worm-like micelles of block copolymers of ethylene oxide and 1,2-butylene oxide in aqueoussolution. International Journal of Pharmaceutics. 2008;354:82–7.

[255] Nagarajan R. Solubilization of hydrocarbons and resulting aggregate shape transitions in aqueoussolutions of Pluronic (PEO-PPO-PEO) block copolymers. Colloids and Surfaces B: Biointerfaces.1999;16:55–72.

[256] Bae Y, Fukushima S, Harada A, Kataoka K. Design of environment-sensitive supramolecularassemblies for intracellular drug delivery: polymeric micelles that are responsive to intracellularpH change. Angewandte Chemie International Edition. 2003;42:4640–3.

[257] Van Hasselt PM, Janssens GEPJ, Slot TK, Van der Ham M, Minderhoud TC, Talelli M, Akker-mans LM, Rijcken CJF, Van Nostrum CF. The influence of bile acids on the oral bioavailabilityof vitamin K encapsulated in polymeric micelles. Journal of Controlled Release. 2009;133:161–8.

[258] Zastre J, Jackson J, Burt H. Pharmaceutical Research. 2004;21:1489.[259] Sharma AK, Zhang L, Li S, Kelly DL, Alakhov VY, Batrakova EV, Kabanov AV. Prevention of

MDR development in leukemia cells by micelle-forming polymeric surfactant. Journal of Con-trolled Release. 2008;131:220–7.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[260] Zhang Y, Li X, Zhou Y, Wang X, Fan Y, Huang Y, Liu Y. Preparation and evaluation of poly(eth-ylene glycol)-poly(lactide) micelles as nanocarriers for oral delivery of cyclosporine A. NanoscaleResearch Letters. 2010;5:917–25.

[261] Sant VP, Smith D, Leroux JC. Enhancement of oral bioavailability of poorly water-soluble drugsby poly(ethylene glycol)-block-poly(alkyl acrylate-co-methacrylic acid) self-assemblies. Journal ofControlled Release. 2005;104:289–300.

[262] Han LM, Guo J, Zhang LJ, Wang QS, Fang XL. Pharmacokinetics and biodistribution of poly-meric micelles of paclitaxel with Pluronic P123. Acta Pharmacologica Sinica. 2006;27:747–53.

[263] Aliabadi HM, Brocks DR, Lavasanifar A. Polymeric micelles for the solublization and delivery ofcyclosporine A: pharmacokinetics and biodistribution. Biomaterials. 2005;26:7251–9.

[264] Aliabadi HM, Elhasi S, Brocks DR, Lavasanifar A. Polymeric micellar delivery reduces kidneydistribution and nephrotoxic effects of cyclosporine A after multiple dosing. Journal of Pharma-ceutical Sciences. 2008;97:1916–26.

[265] Kawakami S, Opanasopit P, Yokoyama M, Chansri N, Yamamoto T, Okano T, Yamashita F,Hashida M. Biodistribution characteristics of all-trans retinoic acid incorporated in liposomes andpolymeric micelles following intravenous administration. Journal of Pharmaceutical Sciences.2005;94:2606–15.

[266] Chansri N, Kawakami S, Yokoyama M, Yamamoto T, Charoensit P, Hashida M. Anti-tumor effectof all-trans retinoic acid loaded polymeric micelles in solid tumor bearing mice. PharmaceuticalResearch. 2008;25:428–34.

[267] Soga O, Van Nostrum CF, Fens M, Rijcken CJF, Schiffelers RM, Storm G, Hennink WE. Ther-mosensitive and biodegradable polymeric micelles for paclitaxel delivery. Journal of ControlledRelease. 2005;103:341–53.

[268] Uchida Y, Murakami Y. Trilayered polymeric micelle: A newly developed macromolecular assem-bly that can incorporate hydrophilic compounds. Colloids and Surfaces B: Biointerfaces.2010;79:198–204.

[269] Uchida Y, Murakami Y. Successful preferential formation of a novel macromolecular assembly—Trilayered polymeric micelle—That can incorporate hydrophilic compounds: The optimization offactors affecting the micelle formation from amphiphilic block copolymers. Colloids and SurfacesB: Biointerfaces. 2011;84:346–53.

[270] Lukyanov AN, Gao Z, Mazzola L, Torchilin VP. Polyethylene glycol-diacyllipid micelles demon-strate increased acculumation in subcutaneous tumors in mice. Pharmaceutical Research.2002;19:1424–9.

[271] Grislain L, Couvreur P, Lenaerts V, Roland M, Deprez-Decampeneere D, Speiser P. Pharmacoki-netics and distribution of a biodegradable drug-carrier. International Journal of Pharmaceutics.1983;15:335–45.

[272] Remant Bahadur KC, Aryal S, Bhattarai SR, Khil MS, Kim HY. Amphiphilic triblock copolymerbased on poly(p-dioxanone) and poly(ethylene glycol): Synthesis, characterization, and aqueousdispersion. Journal of Applied Polymer Science. 2007;103:2695–702.

[273] Okuda T, Kawakami S, Higuchi Y, Satoh T, Oka Y, Yokoyama M, Yamashita F, Hashida M.Enhanced in vivo antitumor efficacy of fenretinide encapsulated in polymeric micelles. Interna-tional Journal of Pharmaceutics. 2009;373:100–6.

[274] Sayyah SM, Abd El-Salam HM, Azzam EMS. Surface activity of monomeric and polymeric (3-alkyloxy aniline) surfactants. International Journal of Polymeric Materials. 2005;54:541–55.

[275] Opanasopit P, Yokoyama M, Watanabe M, Kawano K, Maitani Y, Okano T. Block copolymerdesign for camptothecin incorporation into polymeric micelles for passive tumor targeting. Phar-maceutical Research. 2004;21:2001–8.

[276] Vakil R, Kwon GS. Poly(ethylene glycol)-b-poly(ɛ-caprolactone) and PEG-phospholipid form sta-ble mixed micelles in aqueous media. Langmuir. 2006;22:9723–9.

[277] Xiong XY, Tam KC, Gan LH. Synthesis and aggregation behavior of pluronic f127/poly(lacticacid) block copolymers in aqueous solutions. Macromolecules. 2003;36:9979–85.

[278] Xiong XY, Tam KC, Gan LH. Hydrolytic degradation of Pluronic F127/poly(lactic acid) blockcopolymer nanoparticles. Macromolecules. 2004;37:3425–30.

[279] Yokoyama M, Okano T. Targetable drug carriers: Present status and a future perspective.Advanced Drug Delivery Reviews. 1996;21:77–80.

[280] Lukyanov AN, Torchilin VP. Micelles from lipid derivatives of water-soluble polymers as deliv-ery systems for poorly soluble drugs. Advanced Drug Delivery Reviews. 2004;56:1273–89.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[281] Vlerken LE, Vyas TK, Amiji MM. Poly(ethylene glycol)-modified nanocarriers for tumor-targetedand intracellular delivery. Pharmaceutical Research. 2007;24:1405–14.

[282] Maeda H, Greish K, Fang J. The EPR effect and polymeric drugs: A paradigm shift for cancerchemotherapy in the 21st century. Advances in Polymer Science. 2006;193:103–21.

[283] Matsumura Y. Poly(amino acid) micelle nanocarriers in preclinical and clinical studies. AdvancedDrug Delivery Reviews. 2008;60:899–914.

[284] Jagur-Grodzinski J. Polymers for targeted and/or sustained drug delivery. Polymers for AdvancedTechnologies. 2008;19:1–12.

[285] Vetvicka D, Hruby M, Hovorka O, Etrych T, Vetrik M, Kovar L, Kovar M, Ulbrich K, Rihova B.Biological evaluation of polymeric micelles with covalently bound doxorubicin. BioconjugateChemistry. 2009;20:2090–7.

[286] Gillies ER, Fréchet JM. Development of acid-sensitive copolymer micelles for drug delivery. Pureand Applied Chemistry. 2004;76:1295–307.

[287] Kim MS, Hwang SJ, Han JK, Choi EK, Park HJ, Kim JS, Lee DS. pH-responsive PEG-poly(b-amino ester) block copolymer micelles with a sharp transition. Macromolecular Rapid Communi-cations. 2006;27:447–51.

[288] Rodriguez-Hernandez J, Checot F, Gnanou Y, Lecommandoux S. Toward ‘smart’ nano-objects byself-assembly of block copolymers in solution. Progress in Polymer Science. 2005;30:691–724.

[289] Sethuraman VA, Lee MC, Bae YH. A biodegradable pH-sensitive micelle system for targetingacidic solid tumors. Pharmaceutical Research. 2008;25:657–66.

[290] Schmaljohann D. Thermo- and pH-responsive polymers in drug delivery. Advanced Drug Deliv-ery Reviews. 2006;58:1655–70.

[291] Lee ES, Gao Z, Kim D, Park K, Kwon IC, Bae YH. Super pH-sensitive multifunctional poly-meric micelle for tumor pHe specific TAT exposure and multidrug resistance. Journal of Con-trolled Release. 2008;129:228–36.

[292] Gu J, Cheng WP, Liu J, Lo SY, Smith D, Qu X, Yang Z. pH-triggered reversible “stealth” poly-cationic micelles. Biomacromolecules. 2008;9:255–62.

[293] Yoo HS, Lee EA, Park TG. Doxorubicin-conjugated biodegradable polymeric micelles havingacid-cleavable linkages. Journal of Controlled Release. 2002;82:17–27.

[294] Mohajer G, Lee ES, Bae YH. Enhanced intercellular retention activity of novel pH-sensitive poly-meric micelles in wild and multidrug resistant MCF-7 cells. Pharmaceutical Research.2007;24:1618–27.

[295] Oh KT, Lee ES, Kim D, Bae YH. l-Histidine-based pH-sensitive anticancer drug carrier micelle:Reconstitution and brief evaluation of its systemic toxicity. International Journal of Pharmaceutics.2008;358:177–83.

[296] Lin J, Zhu J, Chen T, Lin S, Cai C, Zhang L, Zhuang Y, Wang XS. Drug releasing behavior ofhybrid micelles containing polypeptide triblock copolymer. Biomaterials. 2009;30:108–17.

[297] Xiong XB, Mahmud A, Uludag H, Lavasanifar A. Multifunctional polymeric micelles forenhanced intracellular delivery of doxorubicin to metastatic cancer cells. Pharmaceutical Research.2008;25:2555–66.

[298] Kim S, Kim JY, Huh KM, Acharya G, Park K. Hydrotropic polymer micelles containing acrylicacid moieties for oral delivery of paclitaxel. Journal of Controlled Release. 2008;132:222–9.

[299] Dewhirst MW, Viglianti BL, Lora-Michiels M, Hanson M, Hoopes PJ. Adverse temperature levelsin the human-proceedings of the WHO conference. International Journal of Hyperthermia.2003;19:267–94.

[300] Kampinga HH. Cell biological effects of hyperthermia alone or combined with radiation or drugs:A short introduction to newcomers in the field. International Journal of Hyperthermia.2006;22:191–6.

[301] Falk MH, Issels RD. Hyperthermia in oncology. International Journal of Hyperthermia.2001;17:1–18.

[302] Dreher MR, Liu W, Michelich CR, Dewhirst MW, Chilkoti A. Thermal cycling enhances theaccumulation of a temperature-sensitive biopolymer in solid tumors. Cancer Research.2007;67:4418–24.

[303] Chilkoti A, Dreher MR, Meyer DE, Raucher D. Targeted drug delivery by thermally responsivepolymers. Advanced Drug Delivery Reviews. 2002;54:613–30.

[304] Gaber MH, Wu NZ, Hong K, Huang SK, Dewhirst MW, Papahadjopoulos D. Thermosensitiveliposomes: Extravasation and release of contents in tumor microvascular networks. InternationalJournal of Radiation Oncology Biology Physics. 1996;36:1177–87.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[305] Riehemann K, Schmitt O, Ehlers EM. The effects of thermochemotherapy using cyclophospha-mide plus hyperthermia on the malignant pleural mesothelioma in vivo. Annals of Anatomy.2005;187:215–23.

[306] Dewhirst MW, Prosnitz L, Thrall D, Prescott D, Clegg S, Charles C, MacFall J, Rosner G, Sam-ulski T, Gillette E, LaReu S. Hyperthermic treatment of malignant diseases: Current status and aview toward the future. Seminars in Oncology. 1997;24:616–25.

[307] Schild HG. Poly(N-isopropylacrylamide): Experiment, theory and application. Progress in Poly-mer Science. 1992;17:163–249.

[308] Kong G, Dewhirst MW. Review- hyperthermia and liposomes. International Journal of Hyperther-mia. 1999;15:345–70.

[309] Heskins M, Guillet JE. Solution properties of poly(N-isopropylacrylamide). Journal of Macromo-lecular Science-Chemistry. 1968;A2:1441–55.

[310] Fujishige S, Kubota K, Ando I. Phase transition of aqueous solutions of poly(N-isopropylacrylam-ide) and poly(N-isopropylmethacrylamide). Journal of Physical Chemistry. 1989;93:3311–3.

[311] Yang M, Ding YT, Zhang LY, Qian XP, Jiang XQ, Liu BR. Novel thermosensitive polymericmicelles for docetaxel delivery. Journal of Biomedical Materials Research. 2007;81A:847–57.

[312] Liu B, Yang M, Li R, Ding Y, Qian X, Yu L, Jiang X. The antitumor effect of novel docetaxel-loaded thermosensitive micelles. European Journal of Pharmaceutics and Biopharmaceutics.2008;69:527–34.

[313] Santis SD, Ladogana RD, Diociaiuti M, Masci G. Pegylated and thermosensitive polyion complexmicelles by self-assembly of two oppositely and permanently charged diblock copolymers. Macro-molecules. 2010;43:1992–2001.

[314] Takei YG, Aoki T, Sanui K, Ogata N, Okano T, Sakurai Y. Temperature-responsive bioconjugates.2. Molecular design for temperature-modulated bioseparations. Bioconjugate Chemistry.1993;4:341–6.

[315] Luo S, Ling C, Hu X, Liu X, Chen S, Han M, Xia J. Thermoresponsive unimolecular micelleswith a hydrophobic dendritic core and a double hydrophilic block copolymer shell. Journal ofColloid and Interface Science. 2011;353:76–82.

[316] Bian F, Xiang M, Yu W, Liu M. Preparation and self-assembly behavior of thermosensitive poly-meric micelles comprising poly(styrene-b-N,N-diethylacrylamide). Journal of Applied PolymerScience. 2008;110:900–7.

[317] Rijcken CJF, Veldhuis TFJ, Ramzi A, Meeldijk JD, Nostrum CF, Hennink WE. Novel fastdegradable thermosensitive polymeric micelles based on PEG-block-poly(N-(2-hydroxyethyl)methacrylamide-oligolactates). Biomacromolecules. 2005;6:2343–51.

[318] Ju B, Yan D, Zhang S. Micelles self-assembled from thermoresponsive 2-hydroxy-3-butoxypropylstarches for drug delivery. Carbohydrate Polymers. 2012;87:1404–9.

[319] Qiao P, Niu Q, Wang Z, Cao D. Synthesis of thermosensitive micelles based on poly(N-isopropyl-acrylamide) and poly(l-alanine) for controlled release of adriamycin. Chemical Engineering Jour-nal. 2010;159:257–63.

[320] Li W, Tu W, Cao D. Synthesis of thermoresponsive polymeric micelles of PNIPAAm-b-OMMAas a drug carrier for loading and controlled release of prednisolone. Journal of Applied PolymerScience. 2009;111:701–8.

[321] Li G, Guo L, Ma S. Self-assembly and drug delivery behaviors of thermo-sensitive poly(t-butylacrylate)-b-poly (N-isopropylacrylamide) micelles. Journal of Applied Polymer Science.2009;113:1364–8.

[322] Qu T, Wang A, Yuan J, Gao Q. Preparation of an amphiphilic triblock copolymer with pH- andthermo-responsiveness and self-assembled micelles applied to drug release. Journal of Colloid andInterface Science. 2009;336:865–71.

[323] Zhang ZX, Liu X, Xu FJ, Loh XJ, Kang ET, Neoh KG, Li J. Pseudo-block copolymer based onstar-shaped poly(N-isopropylacrylamide) with β-cyclodextrin core and guest-bearing PEG: Con-trolling thermoresponsivity through supramolecular self-assembly. Macromolecules.2008;41:5967–70.

[324] Liu Y, Wu J, Meng L, Zhang L, Lu X. Self-assembled, fluorescent polymeric micelles of a graftcopolymer containing carbazole for thermo-controlled drug delivery in vitro. Journal of Biomedi-cal Materials Research Part B: Applied Biomaterials. 2008;85B:435–43.

[325] Zhang ZX, Qiu LY, Zhu KJ, Jin Y. Thermosensitive micelles self-assembled by novel N-isopro-pylacrylamide oligomer grafted polyphosphazene. Macromolecular Rapid Communications.2004;25:1563–7.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[326] Liyan Q, Jianxiang Z, Yi J, Kangjie Z. Thermosensitive self-assembly behaviors of novel amphi-philic polyphosphazenes. Chinese Science Bulletin. 2005;50:1453–5.

[327] Kim IS, Jeong Y, Lee YH, Kim SH. Drug release from thermo-responsive self-assembled poly-meric micelles composed of cholic acid and poly(N-isopropylacrylamide). Archives of PharmacalResearch. 2000;23:367–73.

[328] Tomlinson R, Klee M, Garrett S, Heller J, Duncan R, Brocchini S. Pendent chain functionalizedpolyacetals that display pH-dependent degradation: A platform for the development of novel poly-mer therapeutics. Macromolecules. 2002;35:473–80.

[329] Dong LC, Hoffman AS. A novel-approach for preparation of pH-sensitive hydrogels for entericdrug delivery. Journal of Controlled Release. 1991;15:141–52.

[330] Yin X, Hoffman AS, Stayton PS. Poly(N-isopropylacrylamide-co-propylacrylic acid) copolymersthat respond sharply to temperature and pH. Biomacromolecules. 2006;7:1381–5.

[331] Zhang LY, Guo R, Yang M, Jiang XQ, Liu BR. Thermo and pH dual-responsive nanoparticles foranti-cancer drug delivery. Advanced Materials. 2007;19:2988–92.

[332] Liu Y, Cao X, Luo X, Le Z, Xu W. Self-assembled micellar nanoparticles of a novel star copoly-mer for thermo and pH dual-responsive drug release. Journal of Colloid and Interface Science.2009;329:244–52.

[333] Lokitz BS, York AW, Stempka JE, Treat ND, Li Y, Jarrett WL, McCormick CL. Aqueous RAFTsynthesis of micelle-forming amphiphilic block copolymers containing N-acryloylvaline. Dualmode, temperature/ ph responsiveness, and “locking” of micelle structure through interpolyelectro-lyte complexation. Macromolecules. 2007;40:6473–80.

[334] Huang X, Du F, Cheng J, Dong Y, Liang D, Ji S, Lin SS, Li Z. Acid-sensitive polymeric micellesbased on thermoresponsive block copolymers with pendent cyclic orthoester groups. Macromole-cules. 2009;42:783–90.

[335] Koo AN, Min KH, Lee HJ, Lee SU, Kim K, Kwon IC, Cho SH, Jeong SY, Lee SC. Tumor accu-mulation and antitumor efficacy of docetaxel-loaded core-shell-corona micelles with shell-specificredox-responsive cross-links. Biomaterials. 2012;33:1489–99.

[336] Saito G, Swanson JA, Lee KD. Drug delivery strategy utilizing conjugation via reversible disul-fide linkages: Role and site of cellular reducing activities. Advanced Drug Delivery Reviews.2003;55:199–215.

[337] Li J, Huo M, Wang J, Zhou J, Mohammada JM, Zhang Y, Zhu Q, Waddad AY, Zhang Q. Redox-sensitive micelles self-assembled from amphiphilic hyaluronic aciddeoxycholic acid conjugates fortargeted intracellular delivery of paclitaxel. Biomaterials. 2012;33:2310–20.

[338] Meng FH, Hennink WE, Zhong Z. Reduction-sensitive polymers and bioconjugates for biomedi-cal applications. Biomaterials. 2009;30:2180–98.

[339] Raina S, Missiakas D. Making and breaking disulfide bonds. Annual Review of Microbiology.1997;51:179–202.

[340] Gilbert HF. Thiol/disulfide exchange equilibria and disulfide bond stability. Methods in Enzymol-ogy. 1995;251:8–28.

[341] Ghosh S, Yesilyurt V, Savariar EN, Irvin K, Thayumanavan S. Redox, ionic strength, and pH sen-sitive supramolecular polymer assemblies. Journal of Polymer Science Part A: Polymer Chemistry.2009;8:1052–60.

[342] Koo AN, Lee HJ, Kim SE, Chang JH, Park C, Kim C, Park JH, Lee SC. Disulfide-cross-linkedPEG-poly(amino acid)s copolymer micelles for glutathione-mediated intracellular drug delivery.Chemical Communications. 2008;48:6570–2.

[343] Zhang J, Jiang X, Zhang Y, Li Y, Liu S. Facile fabrication of reversible core cross-linked micellespossessing thermosensitive swellability. Macromolecules. 2007;40:9125–32.

[344] Navath RS, Wang B, Kannan S, Romero R, Kannan RM. Stimuli-responsive star poly(ethyleneglycol) drug conjugates for improved intracellular delivery of the drug in neuroinflammation.Journal of Controlled Release. 2010;142:447–56.

[345] Bulmus V, Woodward M, Lin L, Murthy N, Stayton P, Hoffman A. A new pH-responsive andglutathione-reactive, endosomal membrane-disruptive polymeric carrier for intracellular deliveryof biomolecular drugs. Journal of Controlled Release. 2003;93:105–20.

[346] Mitragotri S, Blankschtein D, Langer R. Ultrasound-mediated transdermal protein delivery. Sci-ence. 1995;269:850–3.

[347] Rapoport NY, Christensen DA, Fain HD, Barrows L, Gao Z. Ultrasound-triggered drug targetingof tumors in vitro and in vivo. Ultrasonics. 2004;42:943–50.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[348] Mitragotri S, Kost J. Low-frequency sonophoresis: A review. Advanced Drug Delivery Reviews.2004;56:589–601.

[349] Mitragotri S. Healing sound: The use of ultrasound in drug delivery and other therapeutic applica-tions. Nature reviews: Drug discovery. 2005;4:255–60.

[350] Nelson JL, Roeder BL, Carmen JC, Roloff F, Pitt WG. Ultrasonically activated chemotherapeuticdrug delivery in a rat model. Cancer Research. 2002;62:7280–3.

[351] Husseini GA, Diaz de la Rosa MA, Gabuji T, Zeng Y, Christensen DA, Pitt WG. Release ofdoxorubicin from unstabilized and stabilized micelles under the action of ultrasound. Journal ofNanoscience and Nanotechnology. 2007;7:1–6.

[352] Husseini GA, Fayoumi RIE, O’Neill KL, Rapoport NY, Pitt WG. DNA damage induced bymicellar-delivered doxorubicin and ultrasound: Comet assay study. Cancer Letters.2000;154:211–6.

[353] Husseini GA, Myrup GD, Pitt WG, Christensen DA, Rapoport NY. Factors affecting acousticallytriggered release of drugs from polymeric micelles. Journal of Controlled Release. 2000;69:43–52.

[354] Husseini GA, Stevenson-Abouelnasr D, Pitt WG, Assaleh KT, Farahat LO, Fahadi J. Kinetics andthermodynamics of acoustic release of doxorubicin from non-stabilized polymeric micelles. Col-loids and Surfaces A: Physicochemical and Engineering Aspects. 2010;359:18–24.

[355] Husseini GA, Pitt WG, Christensen DA, Dickinson DJ. Degradation kinetics of stabilized Pluron-ic micelles under the action of ultrasound. Journal of Controlled Release. 2009;138:45–8.

[356] Husseini GA, Abdel-Jabbar NM, Mjalli FS, Pitt WG, Al-Mousa A. Optimizing the use of ultra-sound to deliver chemotherapeutic agents to cancer cells from polymeric micelles. Journal of theFranklin Institute. 2011;348:1276–84.

[357] Husseini GA, Pitt WG. The use of ultrasound and micelles in cancer treatment. Journal of Nano-science and Nanotechnology. 2008;8:2205–15.

[358] Rapoport N, Gao Z, Kennedy A. Multifunctional nanoparticles for combining ultrasonic tumorimaging and targeted chemotherapy. Journal of the National Cancer Institute. 2007;99:1095–106.

[359] Marin A, Muniruzzaman M, Rapoport N. Acoustic activation of drug delivery from polymericmicelles: Effect of pulsed ultrasound. Journal of Controlled Release. 2001;71:239–49.

[360] Smith DA, Porter TM, Martinez J, Huang S, MacDonald RC, McPherson DD, Holland CK.Destruction thresholds of echogenic liposomes with clinical diagnostic ultrasound. Ultrasound inMedicine and Biology. 2007;33:797–809.

[361] Sukhorukov GB, Rogach AL, Garstka M, Springer S, Parak WJ, Munoz-Javier A, Kreft O, Skir-tach AG, Susha AS, Ramaye Y, Palankar R, Winterhalter M. Multifunctionalized polymer micro-capsules: novel tools for biological and pharmacological applications. Small. 2007;3:944–55.

[362] Hong G, Yuan R, Liang B, Shen J, Yang X, Shuai X. Folate-functionalized polymeric micelle ashepatic carcinoma-targeted, MRI-ultrasensitive delivery system of antitumor drugs. BiomedicalMicrodevices. 2008;10:693–700.

[363] Ai H, Flask C, Weinberg B, Shuai XT, Pagel MD, Farrell JD, Gao JM. Magnetite-loaded polymericmicelles as ultrasensitive magnetic-resonance probes. Advanced Materials. 2005;17:1949–52.

[364] Gang J, Park SB, Hyung W, Choi EH, Wen J, Kim HS, Shul YG, Haam S, Song SY. Magneticpoly epsilon-caprolactone nanoparticles containing Fe3O4 and gemcitabine enhance anti-tumoreffect in pancreatic cancer xenograft mouse model. Journal of Drug Targeting. 2007;15:445–53.

[365] Lu J, Ma S, Sun J, Xia C, Liu C. Manganese ferrite nanoparticle micellar nanocomposites asMRI contrast agent for liver imaging. Biomaterials. 2009;30:2919–28.

[366] Guthi JS, Yang SG, Huang G, Li S, Khemtong C, Kessinger CW, Peyton M, Minna JD, BrownKC, Gao J. MRI-visible micellar nanomedicine for targeted drug delivery to lung cancer cells.Molecular Pharmaceutics. 2009;7:32–40.

[367] Dai S, Ravi P, Tam KC. Thermo- and photo-responsive polymeric systems. Soft Matter.2009;5:2513–33.

[368] Kumar GS, Neckers DC. Photochemistry of azobenzene-containing polymers. Chemical Reviews.1989;89:1915–25.

[369] Irie M. Photoresponsive polymers. Advances in Polymer Science. 1990;94:27–67.[370] Natansohn A, Rochon P. Photoinduced motions in azo-containing polymers. Chemical Reviews.

2002;102:4139–75.[371] Alvarez-Lorenzo C, Bromberg L, Concheiro A. Light-sensitive intelligent drug delivery systems.

Photochemistry and Photobiology. 2009;85:848–60.[372] Yu H, Kobayashi T. Photoresponsive block copolymers containing azobenzenes and other chro-

mophores. Molecules. 2010;15:570–603.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[373] Babin J, Lepage M, Zhao Y. Decoration of shell cross-linked reverse polymer micelles usingATRP: A new route to stimuli-responsive nanoparticles. Macromolecules. 2008;41:1246–53.

[374] Jiang J, Tong X, Zhao Y. A new design for light-breakable polymer micelles. Journal of theAmerican Chemical Society. 2005;127:8290–1.

[375] Jiang J, Tong X, Morris D, Zhao Y. Toward photocontrolled release using light-dissociable blockcopolymer micelles. Macromolecules. 2006;39:4633–40.

[376] Xie Z, Hu X, Chen X, Mo G, Sun J, Jing X. A novel biodegradable and light-breakable diblockcopolymer micelle for drug delivery. Advanced Engineering Materials. 2009;11:B7–B11.

[377] Tong X, Wang G, Soldera A, Zhao Y. How can azobenzene block copolymer vesicles be dissoci-ated and reformed by light?. Journal of Physical Chemistry B. 2005;109:20281–7.

[378] Klaikherd A, Nagamani C, Thayumanavan S. Multi-stimuli sensitive amphiphilic block copolymerassemblies. Journal of the American Chemical Society. 2009;131:4830–8.

[379] Bajpai A, Shulka S, Bhanu S, Kankane S. Responsive polymers in controlled drug delivery. Pro-gress in Polymer Science. 2008;33:1088–118.

[380] Jin Q, Lv LP, Liu GY, Xu JP, Ji J. Phenylboronic acid as a sugar- and pH-responsive trigger totune the multiple micellization of thermo-responsive block copolymer. Polymer.2010;51:3068–74.

[381] Carstens MG, Nostrum CF, Verrijk R, De Leede LGJ, Crommelin DJA, Hennink WE. A mecha-nistic study on the chemical and enzymatic degradation of PEG-oligo(ɛ-caprolactone) micelles.Journal of Pharmaceutical Sciences. 2008;97:506–18.

[382] Torchilin V. Multifunctional and stimuli-sensitive pharmaceutical nanocarriers. European Journalof Pharmaceutics and Biopharmaceutics. 2009;71:431–44.

[383] Roy D, Cambre JN, Sumerlin BS. Future perspectives and recent advances in stimuli-responsivematerials. Progress in Polymer Science. 2010;35:278–301.

[384] Vinogradov S, Batrakova E, Li S, Kabanov A. Polyion complex micelles with protein-modifiedcorona for receptor-mediated delivery of oligonucleotides into cells. Bioconjugate Chemistry.1999;10:851–60.

[385] Nagasaki Y, Yasugi K, Yamamoto Y, Harada A, Kataoka K. Sugar-installed block copolymermicelles: Their preparation and specific interaction with lectin molecules. Biomacromolecules.2001;2:1067–70.

[386] Leamon CP, Weigl D, Hendren RW. Folate copolymer-mediated transfection of cultured cells.Bioconjugate Chemistry. 1999;10:947–57.

[387] Xiong XB, Mahmud A, Uludag H, Lavasanifar A. Conjugation of arginine-glycine-aspartic acidpeptides to poly(ethylene oxide)-b-poly(ɛ-caprolactone) micelles for enhanced intracellular drugdelivery to metastatic tumor cells. Biomacromolecules. 2007;8:874–84.

[388] Sawant RR, Sawant RM, Torchilin VP. Mixed PEG–PE/vitamin E tumor-targeted immunomicellesas carriers for poorly soluble anti-cancer drugs: Improved drug solubilization and enhancedin vitro cytotoxicity. European Journal of Pharmaceutics and Biopharmaceutics. 2008;70:51–7.

[389] Lee ES, Na K, Bae YH. Doxorubicin loaded pH-sensitive polymeric micelles for reversal of resis-tant MCF-7 tumor. Journal of Controlled Release. 2005;103:405–18.

[390] Gao Z, Lukyanov AN, Chakilam AR, Torchilin VP. PEG-PE/phosphatidylcholine mixed immu-nomicelles specifically deliver encapsulated taxol to tumor cells of different origin and promotetheir efficient killing. Journal of Drug Targeting. 2003;11:87–92.

[391] Goto M, Yura H, Chang CW, Kobayashi A, Shinoda T, Maeda A, Kojima S, Kobayashi K,Akaike TJ. Lactose-carrying polystyrene as a drug carrier-investigation of body distribution toparenchymal liver-cells using I-125 labeled lactose-carrying polystyrene. Journal of ControlledRelease. 1994;28:223–33.

[392] Dwek RA. Glycobiology: toward understanding the function of sugars. Chemical Reviews.1996;96:683–720.

[393] Mammen M, Choi SK, Whitesides GM. Angewandte Chemie (International Edition in English).Polyvalent interactions in biological systems: Implications for design and use of multivalentligands and inhibitors. 1998;37:2754–94.

[394] Elwood PC. Molecular cloning and characterization of the human folate-binding protein cDNAfrom placenta and malignant tissue culture (KB) cells. Journal of Biological Chemistry.1989;264:14893–901.

[395] Kim SH, Jeong JH, Mok H, Lee SH, Kim SW, Park TG. Folate receptor targeted delivery ofpolyelectrolyte complex micelles prepared from ODN-PEG-folate conjugate and cationic lipids.Biotechnology Progress. 2007;23:232–7.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

[396] Kim D, Lee ES, Oh KT, Gao ZG, Bae YH. Doxorubicin-loaded polymeric micelle overcomesmultidrug resistance of cancer by double-targeting folate receptor and early endosomal pH. Small.2008;4:2043–50.

[397] Mi Y, Liu Y, Feng SS. Formulation of Docetaxel by folic acid-conjugated D-a-tocopheryl polyeth-ylene glycol succinate 2000 (Vitamin E TPGS2k) micelles for targeted and synergistic chemother-apy. Biomaterials. 2011;32:4058–66.

[398] Prabaharan M, Grailer JJ, Pilla S, Steeber DA, Gong S. Amphiphilic multi-arm-block copolymerconjugated with doxorubicin via pH-sensitive hydrazone bond for tumor-targeted drug delivery.Biomaterials. 2009;30:5757–66.

[399] Yang X, Deng W, Fu L, Blanco E, Gao J, Quan D, Shuai X. Folate-functionalized polymericmicelles for tumor targeted delivery of a potent multidrug-resistance modulator FG020326. Jour-nal of Biomedical Materials Research. 2008;86A:48–60.

[400] Zhua H, Liu F, Guo J, Xue J, Qian Z, Gu Y. Folate-modified chitosan micelles with enhancedtumor targeting evaluated by near infrared imaging system. Carbohydrate Polymers.2011;86:1118–29.

[401] Bae Y, Nishiyama N, Kataoka K. In vivo antitumor activity of the folate-conjugated pH-sensitivepolymeric micelle selectively releasing adriamycin in the intracellular acidic compartments. Bio-conjugate Chemistry. 2007;18:1131–9.

[402] Musacchio T, Laquintan V, Latrof A, Trapani G, Torchilin VP. PEG-PE micelles loaded with pac-litaxel and surface-modified by a PBR-ligand: Synergistic anticancer effect. Molecular Pharmaceu-tics. 2009;6:468–79.

[403] Wang Y, Yang T, Wang X, Dai W, Wang J, Zhang X, Li Z, Zhang Q. Materializing sequentialkilling of tumor vasculature and tumor cells via targeted polymeric micelle system. Journal ofControlled Release. 2011;149:299–306.

[404] Wilson BC. Photodynamic therapy for cancer: Principles. Canadian Journal of Gastroenterology.2002;16:393–6.

[405] Dougherty TJ, Gomer CJ, Henderson BW, Jori G, Kessel D, Korbelik M, Moan J, Peng Q. Pho-todynamic therapy. Journal of the National Cancer Institute. 1998;90:889–905.

[406] Dolmans DE, Fukumura D, Jain RK. Photodynamic therapy for cancer. Nature Reviews Cancer.2003;3:380–7.

[407] Bechet D, Couleaud P, Frochot C, Viriot ML, Guillemin F, Barberi-Heyob M. Nanoparticles asvehicles for delivery of photodynamic therapy agents. Trends in Biotechnology. 2008;26:612–21.

[408] Meisel P, Kocher T. Photodynamic therapy for periodontal diseases: state of the art. Journal ofPhotochemistry and Photobiology B: Biology. 2005;79:159–70.

[409] Demidova TN, Hamblin MR. Photodynamic therapy targeted to pathogens. International Journalof Immunopathology and Pharmacology. 2004;17:245–54.

[410] Chen JX, Wang HY, Li C, Han K, Zhang XZ, Zhuo RX. Construction of surfactant-like tetra-tailamphiphilic peptide with RGD ligand for encapsulation of porphyrin for photodynamic therapy.Biomaterials. 2011;32:1678–84.

[411] Taillefer J, Jones MC, Brasseur N, Lier JE, Leroux JC. Preparation and characterization of pH-responsive polymeric micelles for the delivery of photosensitizing anticancer drugs. Journal ofPharmaceutical Sciences. 2000;89:52–62.

[412] Garrec DL, Taillefer J, Lier JEV, Lenaerts V, Leroux JC. Optimizing pH-responsive polymericmicelles for drug delivery in a cancer photodynamic therapy model. Journal of Drug Targeting.2002;10:429–37.

[413] Sibata MN, Tedesco AC, Marchetti JM. Photophysicals and photochemicals studies of zinc(II)phthalocyanine in long time circulation micelles for photodynamic therapy use. European Journalof Pharmaceutical Sciences. 2004;23:131–8.

[414] Master AM, Rodriguez ME, Kenney ME, Oleinick NL, Gupta AS. Delivery of the photosensitizerPc 4 in PEG–PCL micelles for in vitro PDT studies. Journal of Pharmaceutical Sciences.2010;99:2386–98.

[415] Hioka N, Chowdhary RK, Chansarkar N, Delmarre D, Sternberg E, Dolphin D. Studies of a ben-zoporphyrin derivative with Pluronics. Canadian Journal of Chemistry. 2002;80:1321–6.

[416] Li B, Moriyama EH, Li F, Jarvi MT, Allen C, Wilson BC. Diblock copolymer micelles deliverhydrophobic protoporphyrin ix for photodynamic therapy. Photochemistry and Photobiology.2007;83:1505–12.


Dow

nloa

ded

by [

Ista

nbul

Uni

vers

itesi

Kut

upha

ne v

e D

ok]

at 1

0:00

21

Dec

embe

r 20

14

polymeric micelles: authoritative aspects for drug delivery

Documents