Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 77–83

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

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Modification of chitosan by using samarium for potential use in drugdelivery system

1386-1425/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.saa.2013.09.132

⇑ Corresponding author. Tel.: +62 21 7863516x6207; fax: +62 21 7863515.E-mail address: ekusrini@che.ui.ac.id (E. Kusrini).

Eny Kusrini a,⇑, Rita Arbianti a, Nofrijon Sofyan b, Mohd Aidil A. Abdullah c, Fika Andriani a

a Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI, 16424 Depok, Indonesiab Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus Baru UI, 16424 Depok, Indonesiac Department of Chemical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu Darul Iman, Malaysia

h i g h l i g h t s

� Chitosan–Sm complexes weresynthesized by the impregnationmethod.� Chitosan combined with Sm3+ ions

produced a drug carrier material withfluorescence properties.� The addition of Sm3+ ions into

chitosan affects its physical andchemical properties.� The Sm3+ ion is used as an indicator of

drug release with ibuprofen as amodel drug.� Chitosan–Sm 25 wt.% showed the

highest efficiency of ibuprofenadsorption (33.04%).

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 November 2012Received in revised form 16 September2013Accepted 29 September 2013Available online 7 October 2013

Keywords:ChitosanDrug deliveryIbuprofenFluorescenceSamarium

a b s t r a c t

In the presence of hydroxyl and amine groups, chitosan is highly reactive; therefore, it could be used as acarrier in drug delivery. For this study, chitosan–Sm complexes with different concentrations of samar-ium from 2.5 to 25 wt.% have been successfully synthesized by the impregnation method. Chitosan com-bined with Sm3+ ions produced a drug carrier material with fluorescence properties; thus, it could also beused as an indicator of drug release with ibuprofen (IBU) as a model drug. We evaluated the spectroscopicand interaction properties of chitosan and Sm3+ ions, the interaction of chitosan–Sm matrices with IBU asa model drug, and the effect of Sm3+ ions addition on the chitosan ability to adsorb the drug. The resultshowed that the hypersensitive fluorescence intensity of chitosan–Sm (2.5 wt.%) is higher than the oth-ers, even though the adsorption efficiency of chitosan–Sm 2.5 wt.% is lower (29.75%) than that of chito-san–Sm 25 wt.% (33.04%). Chitosan–Sm 25 wt.% showed the highest efficiency of adsorption of ibuprofen(33.04%). In the release process of ibuprofen from the chitosan–Sm–IBU matrix, the intensity of orangefluorescent properties in the hypersensitive peak of 4G5/2 ?

6H7/2 transition at 590 nm was observed.Fluorescent intensity increased with the cumulative amount of IBU released; therefore, the release ofIBU from the Sm-modified chitosan complex can be monitored by the changes in fluorescent intensity.

� 2013 Elsevier B.V. All rights reserved.

Introduction

Indonesia produces large amount of biological wastes, includingshrimp waste, crab shells, and ox bones. Shrimp waste is promising

material having a high sales value because it contains protein,carotenoids, and chitin [1]. Chitin compounds in biological wasteare part of a class of polysaccharides that can be converted tochitosan by deacetylation. Chitosan shows excellent potential asa biomaterial because of its biocompatibility in the mammalianbody; it is a polymer biomaterial that is biodegradable and non-toxic to mammalian cells [2]. Due to these properties, therefore,

78 E. Kusrini et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 77–83

it has the possibility to be used as a potential drug carrier in thedrug delivery process. As such, the carrier material is used to mod-ify the drug release profile, drug adsorption, and drug distributionin the body so that the medications would work optimally. In addi-tion, the drug carrier is also used to encapsulate the drug to be re-leased so that the drug is active only in targeted areas in the body.In this instance, as a drug carrier, chitosan is expected to encapsu-late the drug so that the drug will be released only in accordancewith the target disease in the mammalian body.

Use of chitosan as a drug carrier has been widely reported [3–10]. The cationic character in the amine groups of chitosan hasresponsibility in its application as drug delivery system [3]. Chito-san has higher nitrogen content compared to that of chitin, thuschitosan would be a better chelating agent compared to chitin[4]. Chitosan can be modified by combining it with other chemi-cals, such as N-Succinyl, glutaraldehyde, and glycyrrhetinic acid,for use as drug carriers for certain diseases [5–10]. Additionally,the use of lanthanide ions in drug carriers has also been widelystudied [11–13]. These lanthanide ions emit fluorescent lightcaused by excitation of electrons. Emission color, referred to asfluorescence, can be used as an indicator of drug release in drugcarrier systems. In the drug delivery system, lanthanide ions canfunction as sensors; their characteristic fluorescent intensitychange could be used to identify drug release in the drug deliveryprocess.

When ibuprofen (IBU) is dissolved in aqueous solution, it willform the carboxylic group having a negative charge, whereas chito-san will have a positive charged. Thus, it is expected that IBU andchitosan will interact through an electrostatic bonding and orhydrogen bonding [14]. IBU is frequently used as a model drugfor the purpose of sustained, controlled drug delivery and con-trolled release. This would enable straightforward measurementsof release times, primarily because the IBU possess short biologicalhalf-life (2 h), conducive to pharmacological activity and has suit-able molecule size (1.0–0.6 nm) [12]. However, IBU is an anti-steroidal antiflammatory drug and has an amphiphilic propertythat may lead to stomach injury and or gastric irritation. Hence,encapsulation of the IBU by using chitosan or modified chitosanwould reduce disorder effects and painful condition, especially tominimize the undesirable effects and prolong its anti-inflammatorycharacter.

In this study, chitosan was combined with samarium ion(Sm3+); lanthanide-type ion that emits orange fluorescent lightwith the transition region 4G5/2 ?

6H7/2 at a wavelength of590 nm. Introducing of samarium (Sm) in chitosan was expectedto increase chitosan ability to adsorb IBU as model drug. Basedon the FTIR, fluorescence spectrophotometry, UV–Vis and SEM–EDX characterizations, we would have the idea about the interac-tion, morphological change and performance of the Sm-modifiedchitosan used in drug delivery system. Therefore, contributions ofthis study would be the use of chitosan as carriers in the drugdelivery systems that is natural, nontoxic, biodegradable, and safe.Drug release from chitosan–Sm in dissolution media can be moni-tored by changes in the fluorescence of Sm3+ ion contained therein.

Materials and method

Materials

Chitosan medical grade powder with deacetylation degree of90.77%, off white, viscosity of 18 cps, moisture content of 6.61%,ash content of 0.73%, protein content of 60.5%, pH 7–8 and molec-ular weight from 20,000 to 300,000 Mw was purchased from PTBiotech Surindo (West Java, Indonesia). Sm(NO3)3�6H2O was pur-chased from Sigma Aldrich (Wisconsin, USA). Distilled water,

ethanol, methanol, KH2PO4, NaOH, HCl, and lactic acid were pur-chased from PT Merck Tbk Indonesia. All materials in the studywere used without any further purification.

Synthesis of chitosan–Sm

The chitosan–Sm was synthesized by impregnation method[15]. The Sm(NO3)3�6H2O with weight variations of 0.05, 0.1, 0.2,0.3 and 0.5 g was dissolved in 100 mL of distilled water and addedto chitosan (2 g). The solution was stirred with a magnetic stirrer at500 rpm for 6 h and was filtered with a vacuum filter. The residueformed was washed with distilled water and was dried in an ovenat 60 �C for 4 h. The resulting chitosan–Sm complex was crushedand weighed according to the mass. The yields of chitosan–Smwith Sm loading (2.5, 5, 10, 15, 25 wt.%) were 1.38, 1.21, 1.67,1.94 and 2.05 g, respectively.

Synthesis of chitosan–Sm–IBU

The chitosan–Sm–IBU matrices were prepared in accordancewith literature [13]. Each of chitosan–Sm (0.4 g) was added into50 mL of ethanol containing IBU of 3 g. The mixture was stirredwith a magnetic stirrer for 24 h before subsequently separatedby centrifugation and the obtained precipitate was dried in an ovenat 60 �C for 12 h. The resulting chitosan–Sm–IBU was crushed andweighed according to mass. The yields of chitosan–Sm–IBU withSm loading from 2.5 to 25 wt.% were 0.4002, 0.4005, 0.4167,0.4155 and 0.42 g, respectively.

Preparation of drug adsorption and release system

The experiments were carried out in a beaker containing meth-anol (25 mL) by mixing a 25 mg of chitosan–Sm–IBU with concen-tration variations of Sm loading from 2.5 to 25 wt.%. The solutionwas stirred and allowed to still for 24 h at room temperature. Eachof sample solutions was then filtered, and IBU content was mea-sured by using UV–Vis spectrophotometer.

The drug release system was prepared by adding 10 mg ofchitosan–Sm–IBU to five variations of the Sm loading in 50 mL ofphosphate buffer (pH 7.4) in a sealed container. All the drug releasesystems of chitosan–Sm–IBU were stored in an incubator at 37 �C.Sampling of the systems was performed by taking 5 mL from eachof the systems once per hour for 24 h. The UV–Vis adsorption spec-tral values were measured on a UV–Vis-spectrophotometer. Thedrug IBU adsorbed and released in vitro was performed in triplicatein order to obtain an accurate value during measurement. The fluo-rescence properties of all the samples were performed by using aspectrophotometer. For this measurement, the chitosan–Sm andchitosan–Sm–IBU were firstly dissolved in a lactic acid solution 5%.

Physical measurements

FTIR spectra were recorded on a Perkin–Elmer system 2000 FTIRspectrophotometer in the range of 4000–400 cm�1 by using theconventional KBr pellet method for solid samples. SEM–EDX mea-surements were performed by using the JEOL JSM-6360LA electronmicroscope at 20 kV and 30 mA. The loading amount of IBU in thematerials was performed using the UV–Vis spectrophotometer(HITACHI U-2810) with a wavelength of 280 nm. Fluorescenceproperties of synthesized materials were characterized by usingthe HITACHI F-2000 fluorescence spectrophotometer with an exci-tation wavelength of 295 nm and an emission wavelength of594 nm. All characterizations were carried out at roomtemperature.

Fig. 2. FTIR spectra of chitosan, IBU and chitosan–Sm–IBU, where a = chitosan,b = ibuprofen, c = chitosan–Sm–IBU 2.5 wt.%, d = chitosan–Sm–IBU 5 wt.%, e = chito-san–Sm–IBU 10 wt.%, f = chitosan–Sm–IBU 15 wt.%, g = chitosan–Sm–IBU 25 wt.%.

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Results and discussion

Characterization of materials

FTIR studies of chitosan, chitosan–Sm, and chitosan–Sm–IBUFunctional groups usually contain multiple bonds or lone pairs

of electrons that make them very reactive. As has been stated ear-lier, the amine and hydroxyl groups of chitosan are very reactive tocoordinate with the metallic ion, such as lanthanide ion.

The FTIR spectra for chitosan, IBU, chitosan–Sm and chitosan–Sm–IBU are displayed in Figs. 1 and 2. The characteristic absorp-tion band at 3383 cm�1 is assigned to the stretching vibration ofthe N–H group bonded to the O–H group, and the peaks at 1659and 1600 cm�1 are attributed to the bands of amide I and II. Theabsorption band of N–H at 1600 cm�1 is more intense comparedto the band at 1639 cm�1, indicating that the deacetylation processis more effective [16]. Since the deacetylation occurred, the absorp-tion band at 1659 cm�1 decreases, whereas the absorption band at1600 cm�1 increases, indicating the presence of amine group inchitosan [4]. In our study, the absorption band at 1600 cm�1 inchitosan is shifted to 1594–1597 cm�1, indicating coordination ofSm3+ with amine group. Both the amine and hydroxyl functionalgroups in chitosan are the most reactive and can bind Sm3+ ions.Bonding between the hydroxyl group and the Sm3+ ions leads tofrequency changes from 3383 cm�1 (free chitosan) to 3388, 3379,3377, 3373 and 3380 cm�1, for the chitosan–Sm matrices from2.5 to 25 wt.%, respectively. A new absorption band at 1619–1631 cm�1 is observed. This band is expected to be the bonding be-tween chitosan and samarium ions. The amine or acetamidegroups at C2 in chitosan are also associated with the samariumions. The interaction between chitosan and samarium ion is shownin Fig. 3A.

Indication of the adsorption of IBU onto the surface of chitosan–Sm was characterized by the appearance of carboxyl groups on thechitosan–Sm–IBU for five variations of Sm3+ ion concentrations,with a slight decrease in transmittance percentage. The band as-signed to the vibration of –COOH at 1714 cm�1 is clearly observedin the IBU spectrum. It is also observed that the intensity of bandabsorption of –COOH group for the chitosan–Sm–IBU is decreasedand shifted to a higher wavenumber (1717–1722 cm�1). Theabsorption bands of quaternary carbon atom at 1463 and1508 cm�1, tertiary carbon atom at 1322 cm�1, hydroxyl bendingvibration at 1420 cm�1 and C–H band at 2956 and 2925 cm�1 areobserved in the IBU spectrum. In all of the chitosan–Sm–IBU spec-tra displayed the quaternary carbon atom, tertiary carbon atom,

Fig. 1. FTIR spectra of chitosan and chitosan–Sm, where a = chitosan, b = chitosan–Sm 2.5 wt.%, c = chitosan–Sm 5 wt.%, d = chitosan–Sm 10 wt.%, e = chitosan–Sm15 wt.%, f = chitosan–Sm 25 wt.%.

hydroxyl bending vibration, and C–H band are similar with theabsorption peaks observed in the IBU. Thus, it is confirmed thatthe IBU is adsorbed onto the surface of chitosan–Sm. The OHgroups in chitosan are important for bonding drug molecules[13]. These groups cause the formation of hydrogen bonds so thatthe absorption peaks appeared at 2951–2957 cm�1. The intensityof IBU molecule aromatic ring is observed in all of the chitosan–Sm–IBU, which is decreased and signified by the peak appearingat 780 cm�1. New absorption peak at about of 964–967 cm�1 isalso observed. The vibration of Sm–O bond at 466–468 cm�1 is ob-served for all of chitosan–Sm–IBU spectra. The absorption peak ofthe secondary hydroxyl group in chitosan (1032 cm�1) and chito-san–Sm (1033 cm�1) is quite similar. However, in all of the chito-san–Sm–IBU spectra, this peak is shifted to 1021–1022 cm�1. It isconfirmed that the IBU drug is bonded with chitosan through hy-droxyl group of chitosan.

The bands at 2890 and 1383 cm�1 in chitosan are assigned tothe C–H stretching vibration in polymeric backbone and C–H bend-ing, respectively. These peaks in all of chitosan–Sm spectra areslightly shifted to 2886–2894 cm�1 and 1383–1385 cm�1. Theband at 1428 cm�1 in chitosan is attributed to the stretching vibra-tion of C–N group. This peak is shifted to lower frequencies at1424–1425 cm�1 for all the chitosan–Sm. Thus, the addition ofSm3+ ions into chitosan also affects the absorption peaks of theother functional groups present in the chitosan, namely C–H, C–O, and C–N. Upon complexation between Sm3+ and chitosan, theabsorption peaks of functional groups in chitosan are shifted tolower frequencies. It could be argued that the addition of Sm3+ ionsinto chitosan affects its physical and chemical properties.

Morphology and composition of chitosan, chitosan–Sm, and chitosan–Sm–IBU

The morphologies of chitosan, chitosan–Sm, and chitosan–Sm–IBU were characterized by using SEM (Fig. S1a–c). SEM of purechitosan reveals a flat structure and porous rods morphology. InFig. S1b, chitosan–Sm appears rougher than that of pure chitosanand some porous are covered by the samarium metal ions. Withthe addition of IBU into chitosan–Sm, the morphology of chito-san–Sm–IBU becomes dense and more rugged than that of chito-san–Sm because a number of IBU on the surface of chitosan forma clot as can be seen in Fig. S1c. The SEM micrograph of chito-san–Sm–IBU also reveals that the samarium metal ions and IBUuniformly spread over the surface of chitosan forming ruggedmicrostructure, indicating the presence of adsorbed ibuprofenmolecules on the surface of chitosan. The ibuprofen drug is more

Fig. 3. Possible molecule structure of chitosan and Sm (A) and possible interaction between IBU and chitosan (B). The dashed line (—) shows the hydrogen bonding.

Table 1Efficiency adsorption of ibuprofen by the chitosan and chitosan–Sm.

Sm loading(wt/wt.%)

Sample Concentrationof IBU (mg/mL)

Efficiency adsorption (%)

0 Chitosan–IBU 15.97 26.612.5 Chitosan–Sm–IBU 17.85 29.755 Chitosan–Sm–IBU 19.51 32.5110 Chitosan–Sm–IBU 19.75 32.9215 Chitosan–Sm–IBU 19.82 33.0325 Chitosan–Sm–IBU 19.82 33.04

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efficiently encapsulated in the chitosan–Sm matrices. In furtherstudy, to evaluate the loading characteristic, drug of 60 mg/mLwas loaded into chitosan–Sm with various concentration (2.5–25 wt.%). The results show that the encapsulation efficiency of drugin the chitosan–Sm matrices increases with increasing concentra-tion of samarium (Table 1).

Identification of chemical contents in pure chitosan, selectedsamples of chitosan–Sm 25 wt.%, and chitosan–Sm–IBU wasperformed with by using EDX. Images of the EDX results areshown in Fig. S2a–c. The selected results of EDX for thechitosan–Sm 25 wt.% confirm the presence of Sm3+ ions in

chitosan. Based on the EDX result, the mass of Sm3+ ions on thesurface of chitosan is 2.75%, whereas the Sm3+ ion attached ontothe surface of chitosan–Sm–IBU is 1.31%. This number decreasewhen compared with the Sm3+ ions in chitosan–Sm material. Thisdecrease is expected to be due to the replacement of the samar-ium metal ions by the IBU molecules. IBU is adsorbed onto thesurface of chitosan by impregnation method (Fig. S2a–c). Thehydroxyl groups on the surface of chitosan would act as the reac-tion sites and form hydrogen bonding with the carboxyl group ofIBU (Fig. 3B). Possible molecule structure interaction betweenthe Sm-modified chitosan and IBU as model drug is illustratedin Fig. 4.

Fluorescence properties of chitosan, chitosan–Sm, and chitosan–Sm–IBU

Fluorescence properties of chitosan–Sm and chitosan–Sm–IBUwere measured by using a fluorescence spectrophotometer. Inthe process of measurement, the emission wavelength was deter-mined according to the characteristics of the Sm3+ ions. Fluores-cence spectra for the chitosan–Sm and chitosan–Sm–IBU can beseen in Figs. 5 and 6. In all of the chitosan–Sm and chitosan–Sm–IBU samples, the hypersensitivity peak in the 4G5/2 ?

6H7/2

Fig. 4. Possible molecule structure and interaction between chitosan–Sm and IBU.The dashed line (—) shows the hydrogen bonding between the hydroxyl group ofchitosan and carboxyl group of IBU molecules.

Fig. 5. Fluoresence spectra of the modified of chitosan–Sm with different concen-tration of Sm3+ ion, where a = chitosan–Sm 2.5 wt.%, b = chitosan–Sm 5 wt.%,c = chitosan–Sm 10 wt.%, d = chitosan–Sm 15 wt.%, e = chitosan–Sm 25 wt.%.

Fig. 6. Fluoresence spectra of chitosan–Sm–IBU matrices at different concentrationof Sm3+ ion, where a = chitosan–Sm 2.5 wt.%, b = chitosan–Sm 5 wt.%, c = chitosan–Sm 10 wt.%, d = chitosan–Sm 15 wt.%, e = chitosan–Sm 25 wt.%.

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transition is contained in the emission wavelength of 590 nm. Thisfinding is consistent with that proposed by Bünzli and Piguet [17]in which orange luminescence properties of Sm3+ ions can be seenin the transition region 4G5/2 ?

6H7/2 at an emission wavelength of590 nm. Based on Figs. 5 and 6, it is observed that the emissionintensity of the chitosan–Sm changes with the Sm3+ ion concentra-tion. This change is expected to be due to the difference in energytransfer occurred in Sm3+ ions in the matrix. The lowest concentra-tion of Sm loading in chitosan–Sm (2.5 wt.%) has the highesthypersensitive fluorescence intensity (4930 a.u.). The highest con-centration of Sm loading in chitosan–Sm (25 wt.%) exhibits thehypersensitive fluorescence intensity at 4130 a.u, whereas the restshow hypersensitive fluorescence intensity from 3618 to 3970 a.u.These fluorescence properties of chitosan–Sm with various Smloading could be used as an indication of its potential for applica-tions in drug delivery/carrier systems. Relationship between thedrug adsorption and release of IBU as a model drug in the chito-san–Sm will be discussed in the following section.

Drug adsorption and release system

For this application, the drug IBU loading matrix was preparedby impregnation method to accommodate the drug IBU insidethe Sm-modified chitosan. During the process, the IBU moleculeswill be released through the diffusion mechanism. The hydroxylgroups from the chitosan will form hydrogen bonding with the car-boxyl group of IBU molecules since the IBU is adsorbed onto thesurface of matrices. In the release process, the solvent enters theIBU molecules via their pores. The IBU drug is then slowly dis-solved into the buffer solution from the surface and diffuses fromthe system.

Adsorption of IBU molecules onto the Sm-modified chitosancomplexes was performed by the incubation method. For thisstudy, the addition of IBU molecules into the chitosan–Sm materialwas carried out in accordance with the literature [10]. We notedthat selected drug IBU would physically stick to the Sm-modifiedchitosan or be adsorbed onto the surface of chitosan–Sm [18]. Inaddition, interaction of the IBU molecules with the chitosan–Smcomplex can also take place by hydrogen bonding between theOH group from chitosan and carboxylic groups from IBU moleculeswhen the IBU is adsorbed onto the surface of chitosan (Fig. 4). Dur-ing the process, chitosan–Sm complex will encapsulate the IBUmolecules so that the rate of diffusion of IBU molecules can be con-trolled and monitored.

Determination of IBU content in the chitosan–Sm by UV–Visspectrophotometer was conducted to determine the adsorptionefficiency of IBU molecules in the chitosan–Sm complex and the ef-fect of Sm3+ ions addition on chitosan adsorption of IBU molecules.The adsorption efficiency of IBU molecules in the chitosan–Smcomplex is greater than the adsorption of IBU molecules by purechitosan (Table 1). The adsorption of IBU molecules by the Sm-freechitosan is about 26.61%. Adsorption efficiency increases withincreasing concentrations of Sm3+ ions contained in the chitosan.These results indicate that Sm3+ ions affect chitosan ability to ad-sorb IBU molecules.

Chitosan–Sm–IBU with the Sm loading of 25 wt.% has adsorp-tion efficiency of IBU molecules of 33.04%. This amount is almostthe same with the adsorption efficiency of IBU (33.03%) by thechitosan–Sm–IBU with Sm3+ loading of 15 wt.%. This signifies thatthe Sm3+ loading in chitosan in the range of15–25 wt.% is optimumfor the IBU adsorption onto the chitosan–Sm matrices. Duringadsorption of IBU molecules onto pure chitosan and chitosan–Sm, the carboxyl groups contained in the IBU form bonds with

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the hydroxyl groups from chitosan (Figs. 3B and 4). The addition ofSm3+ ions into chitosan will create bonding between the ions andthe hydroxyl and amine groups of the chitosan (Fig. 3A). This willthen increase the bond strength in these groups and thus theywould become more reactive to bind the drug molecules. In addi-tion, the modification of chitosan with the addition of Sm3+ ionswill increase its reactivity, as noted by the increase in adsorptionefficiency of IBU with the increasing content of Sm3+ ions in thechitosan.

Determination of the IBU release profile of chitosan–Sm–IBU isnecessary to understand the difference in profiles of pure chitosanwith chitosan–Sm with various Sm loading. In addition, determina-tion of the IBU release profile of the chitosan–Sm–IBU complex wasperformed to understand the influence of the presence of Sm3+ ionson the rate of IBU release from chitosan–Sm–IBU matrices. IBUrelease profiles from the chitosan–Sm–IBU matrices are shown inFig. 7. The IBU adsorption pattern was conducted in triplicate.Standard deviation for each measurement in various Sm loadingfrom 0 to 25 wt.% is 0.00043, 0.00099, 0.02607, 0.00073, 0.00171and 0.00037, respectively. The in vitro release tests of IBU in thechitosan–Sm–IBU matrices were performed at pH 7.4, which isthe condition in the intestinal fluid, for 24 h. In general, the drugrelease from chitosan occurs through a diffusion mechanism thatswells the chitosan matrix [18].

In Fig. 7, it can be seen that the drug release profiles for purechitosan and chitosan–Sm–IBU with five concentration variationsof Sm3+ ions are quite similar. For all the drug release profiles,IBU is released slowly, reaching 50% in 8 hand perfectly separatingin 24 h. Based on the graph in Fig. 7, it can be observed that the re-lease mechanism of IBU from pure chitosan and chitosan–Sm–IBUdepends on the diffusion mechanism. In this process, IBU mole-cules diffused slowly from pure chitosan and chitosan–Sm–IBUmatrices. The drug release of IBU from both matrices begins withthe swelling of chitosan–Sm as a drug coating material, followedby a slow diffusion of IBU molecules into the dissolution mediumof the phosphate buffer pH 7.4 [13]. IBU diffusion is possible be-cause of differences in the concentrations of IBU in the dissolutionmedia of phosphate buffer pH 7.4 and the IBU in the chitosan–Sm.The slow rate of drug release of IBU could due to the strong hydro-gen bonding and interaction between IBU molecules and the func-tional groups of the chitosan. Based on the graph, it can also beobserved that the release of IBU from the chitosan–Sm–IBU matri-ces is slower than the release of IBU from pure chitosan. This couldbe due to the presence of Sm3+ ions that increase the reactivity of

Fig. 7. Drug release profile of ibuprofen in the chitosan–Sm–IBU complex, where0 = chitosan, a = chitosan–Sm–IBU 2.5 wt.%, b = chitosan–Sm–IBU 5 wt.%, c = chito-san–Sm–IBU 10 wt.%, d = chitosan–Sm–IBU 15 wt.%, e = chitosan–Sm–IBU 25 wt.%.Standard deviation with confidence level of 95.0% for each measurement in variousSm loading from 0 to 25 wt.% are 0.00043, 0.00099, 0.02607, 0.00073, 0.00171 and0.00037, respectively.

hydroxyl groups of chitosan, thus producing a strong hydrogenbond between hydroxyl groups from chitosan and the carboxylgroup of IBU. For all variations, the drug release profile continuesto rise to reach an equilibrium point after 12 h. This finding is con-sistent with the human digestive system time of 8 h. IBU releasedfrom the chitosan–Sm–IBU matrices in the phosphate buffer at pH7.4 enters the matrices of pure chitosan and chitosan–Sm–IBU.These matrices expand and swell causing IBU molecules diffuseinto the phosphate buffer until the concentration of IBU in thephosphate buffer is the same as the concentration of IBU in thepure chitosan and chitosan–Sm–IBU matrices at the time ofsynthesis.

The addition of Sm3+ ions into chitosan was intended to allowthe drug release from chitosan–Sm–IBU could be monitoredthrough the changes in fluorescent intensity. The relationship be-tween these intensity changes and the cumulative amount of IBUreleased from the chitosan–Sm–IBU matrices is shown in Fig. 8.Fluorescent intensity of the drug release samples was measuredaccording to the characteristics of Sm3+ ions, which emit fluores-cence with the 4G5/2 ?

6H7/2 transition at 590 nm and the excita-tion wavelength of 295 nm. Based on Fig. 8, it can be seen thatthe fluorescent intensity for all variations of the chitosan–Sm–IBU matrices increases with the cumulative amount of IBU releasedfrom the chitosan–Sm–IBU matrices. This finding is similar to theresults reported by Yang et al. [13]. When IBU molecules are ad-sorbed onto the surface of chitosan, hydrogen bonding occurs be-tween the hydroxyl group of chitosan and the carboxyl group ofIBU causes the Sm3+ ions bonding with the hydroxyl groups inchitosan to weaken [13]. Therefore, fluorescent intensity of theSm3+ ions in the matrices of chitosan–Sm–IBU will be weakened.In the process of drug release, IBU slowly detaches from the matri-ces indicated by weakening of the bond between chitosan hydroxylgroup and IBU carboxyl group. At the same time, the bond betweenthe Sm3+ions and hydroxyl groups in chitosan will rebound. Thiswill cause the fluorescent intensity to increase with the cumulativeamount of IBU released from the chitosan–Sm–IBU matrices.

At the beginning, the cumulative release pattern of IBU (below40%) from the chitosan–Sm are similar. Later on, the patternchanges after the cumulative release of IBU is greater than 45%.This may be due to the similar surface as well as interaction be-tween IBU and chitosan and/or chitosan–Sm. The Sm-modifiedchitosan (2.5 wt.%) gives the highest intensity compared to theothers chitosan–Sm (Fig. 8). The cumulative release of IBU (5%)from chitosan–Sm (2.5 wt.%) occurs at a fluorescence intensity of4221 a.u., then slightly increases and reaches 4366 a.u. for thecumulative release of IBU (38.7%). Furthermore, increasing thecumulative release of IBU until 90.8% take place at a fluorescence

Fig. 8. Comparison of fluorescence intensity for drug release activity, wherea = chitosan–Sm–IBU 2.5 wt.%, b = chitosan–Sm–IBU 5 wt.%, c = chitosan–Sm–IBU10 wt.%, d = chitosan–Sm–IBU 15 wt.%, e = chitosan–Sm–IBU 25 wt.%.

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intensity of 6431 a.u. On the other hand, the cumulative release ofIBU from chitosan–Sm 25 wt.% gradually increases and reaches47.3% at a fluorescence intensity of 2952 a.u. After that, the cumu-lative release of IBU is faster and sharper compared to that of theothers of matrices, even though it still occurs below of that thechitosan–Sm 2.5 wt.%. Finally, the cumulative release of IBU(100%) takes place at fluorescence intensities of 6653; 5701;4857; 5261 and 6100 a.u., respectively for the chitosan–Sm (2.5–25 wt.%) (see again Fig. 8). It is found that the lowest concentrationof Sm loading in chitosan–Sm (2.5 wt.%) has the hypersensitivefluorescence intensity higher than the others, even though theadsorption efficiency of chitosan–Sm 2.5 wt.% is lower (29.75%)compared to the chitosan–Sm 25 wt.% (33.04%).

Conclusion

The chitosan–Sm complexes with different concentrations ofSm from 0 to 25 wt.% have been successfully synthesized by theimpregnation method. The concentration variation of Sm loadingin chitosan was introduced to understand the influence of Sm3+

ion content on chitosan ability to adsorb a drug and the drug re-lease process. The addition of Sm3+ ions into chitosan enhancesits ability to adsorb IBU molecules as a model drug. The resultsshow that the hypersensitive fluorescence intensity of chitosan–Sm (2.5 wt.%) is higher than the others, even though its adsorptionefficiency is lower (29.75%) compared to that of chitosan–Sm25 wt.% (33.04%). Chitosan and Sm could be used to modify a drugrelease profile, drug adsorption, and drug distribution in the bodyso that medications will work optimally and can be monitored.Fluorescence properties of the Sm3+ ions could be used to indicateIBU release from the chitosan–Sm–IBU matrices; the change influorescent intensity takes place in the hypersensitive peak at590 nm. Chitosan–Sm 25 wt.% demonstrated the highest adsorp-tion efficiency of IBU (33.04%). Based on bioactivity of chitosanand fluorescent properties of Sm3+ ions, chitosan–Sm complexeswould be promising for potential applications in the field of drugdelivery and disease therapy.

Acknowledgements

This study was supported by Hibah Fundamental DIKTI, Minis-try of Education and Culture Republic of Indonesia.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2013.09.132.

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