Materials Science and Engineering C 36 (2014) 146–151

Contents lists available at ScienceDirect

Materials Science and Engineering C

j ourna l homepage: www.e lsev ie r .com/ locate /msec

Preparation, characterization, and antibacterial activity studies ofsilver-loaded poly(styrene-co-acrylic acid) nanocomposites

Cunfeng Song a,b, Ying Chang a, Ling Cheng a, Yiting Xu a, Xiaoling Chen c,⁎, Long Zhang a,Lina Zhong a, Lizong Dai a,⁎a Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005, Chinab Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Chinac Department of Endodontics, Xiamen Stomatology Hospital, Teaching Hospital of Fujian Medical University, Xiamen 361003, China

⁎ Corresponding authors. Tel.: +86 592 2186178; fax:E-mail addresses: tinachen0628@163.com (X. Chen), l

0928-4931/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.msec.2013.11.042

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 June 2013Received in revised form 24 October 2013Accepted 28 November 2013Available online 7 December 2013

Keywords:Antibacterial agentSoap-free emulsion polymerizationSilverNanocomposites

A simplemethod for preparing a new type of stable antibacterial agentwas presented.Monodisperse poly(styrene-co-acrylic acid) (PSA) nanospheres, serving as matrices, were synthesized via soap-free emulsion polymerization.Field-emission scanning electronmicroscopymicrographs indicated that PSA nanospheres have interesting surfacemicrostructures and well-controlled particle size distributions. Silver-loaded poly(styrene-co-acrylic acid) (PSA/Ag-NPs) nanocomposites were prepared in situ through interfacial reduction of silver nitrate with sodium borohy-dride, and further characterized by transmission electronmicroscopy andX-ray diffraction. Their effects on antibac-terial activity including inhibition zone, minimum inhibitory concentration (MIC), minimum bactericidalconcentration (MBC), and bactericidal kinetics were evaluated. In the tests, PSA/Ag-NPs nanocomposites showedexcellent antibacterial activity against both gram-positive Staphylococcus aureus and gram-negative Escherichiacoli. These nanocomposites are considered to have potential application in antibacterial coatings on biomedical de-vices to reduce nosocomial infection rates.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Uses of biomedical devices are always associatedwith a risk of infec-tion. Surface bacterial infestation to biomedical devices, such as cathe-ters, dental materials, wound and burn dressings, and implants, couldbe resistant to immune defense mechanisms, and then result in seriousinfection [1]. The presence of antibacterial agents is an effective strategyto keep biomedical devices away from the infestation of detrimentalbacteria. Antibacterial agents need to combine desirable attributes, forinstance, excellent antibacterial activity, environmental safety, low tox-icity, and ease of fabrication [2].

German obstetrician C. S. F. Crede introduced 1% silver nitrate solu-tion as an eye solution for the prevention of Gonococcal ophthalmianeonatorum in 1884, which is perhaps the first scientifically document-edmedical use of silver [3,4]. From then on, silver is well known to havestrong antibacterial effects, broad-spectrum biocidal activity, and lowtoxicity to mammalian cell. The mechanism of silver's antibacterialproperty may involve free silver ions (Ag+) uptake [5–7]. Firstly, dueto the high affinity with thiol groups presented in the cysteine residues,Ag+ ions can interactwith respiratory enzymes. Thiswill lead to disrup-tion of the mitochondrial respiratory chain [8]. Furthermore, the

+86 592 2183937.zdai@xmu.edu.cn (L. Dai).

ghts reserved.

mitochondrial dysfunction interrupts ATP synthesis, and induces DNAdamage. Finally, apoptosis may occur and program cell death [9]. Inmedical applications, silver in the form of nanoparticles is a promisingalternative to silver salts and bulk metal, because salts may possessquick and uncontrolled silver release while the bulk metal is a sluggishand inefficient releasing system [10].

In order to prepare highly stable silver nanoparticle dispersions forpractical purposes, inorganic matrices including silica glass [11], zeolite,apatite [12–14], zirconium phosphate [15,16], etc. are usually used toovercome unwanted agglomeration of the colloids. The sol–gel derivedsilica glass powders containing colloidal silver were reported to be usedas antibacterial agents of composite resin for dental restoration [17].Commercial silver-zeolites could serve as antibacterial agents againstoral bacteria even under anaerobic conditions [18]. Recently, many re-searches focused on the preparation of polymeric matrices with silvernanoparticles as well as the studies of their antibacterial activity[19–24]. Varun Sambhy et al. presented amethod of fabricating dual ac-tion antibacterial composites consisted of a cationic polymermatrix andembedded silver bromide nanoparticles [2]. Colloidal silver could alsobe deposited onto surface-functional porous poly(ethylene glycoldimethacrylate-co-acrylonitrile) microspheres, owing to the high affin-ity between silver and nitrile group on the surface of the microspheres[25].

In this paper, monodisperse nanospheres were served as polymericmatrices to prepare antibacterial agents for the first time. We synthe-sized poly(styrene-co-acrylic acid) (PSA) nanospheres via soap-free

Fig. 1. FE-SEMmicrographs and hydrodynamic size distributions of PSA nanospheres: AA/St: (a, b) 5 wt.%; (c, d) 10 wt.%; (e, f) 15 wt.%; (g, h) 25 wt.%.

147C. Song et al. / Materials Science and Engineering C 36 (2014) 146–151

emulsion polymerization. Using silver nitrate (AgNO3) as a precursorand sodium borohydride (NaBH4) as an oxidizing agent, silver nanopar-ticles were deposited onto the surfaces of PSA nanospheres. The obtain-ed polymer/silver nanocomposites (PSA/Ag-NPs) are expected to havepotential applications as antibacterial agents in biomedical devices.Preparation, characterization, and antibacterial activity of PSA/Ag-NPs

nanocomposites were studied and discussed in detail. The parametersof additives (antibacterial agents, antioxidant, wetting agents, etc.),such as size and content, play important roles in the final performanceof materials [26–28]. Therefore, controlling the size of antibacterialagents, just as what we have done in this paper (through the controlover the size of matrix), becomes meaningful.

Fig. 2. FITR of PSA nanospheres. Fig. 4. XRD of PSA/Ag-NPs nanocomposites.

148 C. Song et al. / Materials Science and Engineering C 36 (2014) 146–151

2. Materials and methods

2.1. Preparation of monodisperse poly(styrene-co-acrylic acid) (PSA)nanospheres

Monodisperse PSA nanospheres were prepared by soap-free emul-sion polymerization of styrene (St) and acrylic acid (AA) in water ac-cording to the method as described in the literature [29,30]. Briefly, acertain amount of AA (0.1, 0.2, 0.3, and 0.5 g) and 45 mL of H2O wereinitially charged into a three-necked flask. After the feeding AA beingfully dissolved, 2.0 g of styrene was added. The solution was vigorouslystirred for 30 min at room temperature under nitrogenous atmosphere.0.04 g of KPS, dissolved in 5 mL of H2O, was injected into the solutionunder stirring. Then the emulsion was heated to 75 °C and preservedfor 12 h. The products were washed with ultrapure water extensivelyand dispersed in water finally.

2.2. Synthesis of PSA/Ag-NPs nanocomposites

The fabrication of PSA/Ag-NPs nanocomposites was described as fol-lows: 20 mL of aqueous PSA dispersion (0.3 mg/mL) was mixed with0.5 mL of 10 mM AgNO3 in a 50 mL one-necked flask. The mixture dis-persion was stirred for 5 h with a magnetic bar at room temperature. Itwas followed by adding 10 mMNaBH4 into the dispersion and continu-ously stirring in an icewater bath for another 2 h. The attachedAg+ ionswere reduced by NaBH4, which led to the deposition of Ag nuclei andnanoparticles onto PSA surfaces. The resulting PSA/Ag-NPs nanocom-posites were washed with ultrapure water several times and collectedfor the further examination.

Fig. 3. TEM micrographs: (a) PSA nanospheres (AA/St: 15 wt.%); (b) PSA/Ag-

2.3. Characterization of PSA nanospheres and PSA/Ag-NPs nanocomposites

The morphologies of PSA nanospheres and PSA/Ag-NPs nanocom-posites were characterized via field-emission scanning electronmicros-copy (FE-SEM) (LEO1530, LEO, Germany) and transmission electronmicroscopy (TEM) (JEM-2100, JEOL, Japan). The hydrodynamic size ofPSA nanospheres were analyzed by dynamic light scattering (DLS)using a Zetasizer (Mastersizer 2000,Malvern, UK). Fourier transform in-frared spectrophotometry (FTIR) (Nicolet iS10, Thermo Nicolet, USA)was used to study the surface properties of PSA nanospheres. Thephase characteristics of Ag in the nanocomposites were observed by se-lected area electron diffraction (SAED) (JEM-2100, JEOL, Japan) and X-ray diffraction (XRD) (X'pert PRO, PANalytical B.V., Netherlands)measurement.

2.4. Antibacterial assays

2.4.1. Bacterial cultureGram-positive Staphylococcus aureus (S. aureus, CMCC 26003) and

gram-negative Escherichia coli (E. coli, CMCC 44103) were cultured inLB broth at 37 °C overnight until the optical density of culture mediumreached 2.0 at 600 nm, which indicated the content of bacteria approx-imately reached 109 CUF/mL.

2.4.2. Inhibition zone testFreshly grown bacteria were diluted by LB broth to an approximate

concentration of 2 × 107 CUF/mL of S. aureus or E. coli. 100 μL of thisstock solution was plated on LB agar plate. 20 μL of PSA nanospheres,PSA/Ag-NPs nanocomposites and control solutionswas respectively im-pregnated onto paper discs (6 mm diameter). The paper discs were

NPs nanocomposites; The inset is SAED of PSA/Ag-NPs nanocomposites.

Fig. 5. Inhibition zones (1. Control; 2. PSA nanoparticles (AA/St: 15 wt.%); 3. 100 μg/mL; 4.200 μg/mL of PSA/Ag-NPs nanocomposites) in the LB agar dishes inoculatedwith differentbacteria: (a) S. aureus; (b) E. coil.

Table 2MIC test of various concentrations of PSA/Ag-NPs nanocomposites against S. aureus andE. coil.a

Concentrations of PSA/Ag-NPs(μg/mL)

S. aureus E. coil

12.5 + +25 − +50 − −100 − −200 − −1000 − −a “+” for bacteria growth, “−” for no bacteria growth.

149C. Song et al. / Materials Science and Engineering C 36 (2014) 146–151

placed on surface of the inoculated agar plates and incubated at 37 °Cfor 24 h. Colonies were visualized and images of the plates were cap-tured [31–33]. A vernier caliper with an error of 0.1 mm was used tomeasure the size of inhibition zone.

2.4.3. Minimum inhibitory concentration (MIC) testPSA/Ag-NPs nanocomposites, at concentrations of 12.5, 25, 50, 100,

200, 1000 μg/mL, were added to the test tubes with the bacterial sus-pension which contained approximately 2 × 105 CUF/mL of S. aureusor E. coli. TheMICwasmeasured using a LBmediumbrothmicrodilutionmethod [34,35] at the concentration of which no bacterial growth wasobserved in the test tube after it was incubated at 37 °C for 24 h.

2.4.4. Minimum bactericidal concentration (MBC) testMBC is defined as the minimum concentration (μg/mL) of an anti-

bacterial agent at which 99.9% of bacteria are killed [36]. An appropriatevolume of a solution containing approximately 2 × 105 CUF/mL ofS. aureus or E. coli in LB brothwas added to sterile glass tubes. PSA nano-sphere and PSA/Ag-NPs nanocomposites were tested in triplicate re-spectively at final concentrations of 50, 100, 200, 1000 μg/mL. Thetubes were incubated at 37 °C with shaking at 250 rpm for 24 h.100 μL aliquots taken from the tubes were plated on LB agar plates.The plates were incubated at 37 °C for 24 h, and then bacterial colonieswere counted.

2.4.5. Bactericidal kinetics testThe effect of PSA/Ag-NPs nanocomposites on thebacteria-growth ki-

netics in liquid media was studied. 10 mL of a solution containing ap-proximately 2 × 105 CUF/mL of S. aureus or E. coli in LB broth wasadded to sterile glass tubes. Then these tubes were kept in an incubatedshaker at 37 °C. When LB-strains broths were added to the tubes, theinitial time was set as zero. 10 μL aliquots were withdrawn from eachtube at certain time intervals. The solution was diluted 10 times. Afterthat, 100 μL of the diluted solution was plated on LB agar plates. Theplates were incubated at 37 °C for 24 h, and then bacterial colonieswere counted [37].

Table 1Correlation of the size of inhibition zone with various concentrations of PSA/Ag-NPsnanocomposites.a

Concentrations of PSA/Ag-NPs(μg/mL)

Inhibition zone of S. aureus(mm)

Inhibition zone of E. coli(mm)

100 7.6 7.1200 9.1 8.4

a Size of inhibition zone ≥7 mm is effective.

3. Results and discussions

3.1. Characterization of PSA nanospheres and PSA/Ag-NPs nanocomposites

Monodisperse poly(styrene-co-acrylic acid) nanospheres were syn-thesized by soap-free emulsion polymerization. Fig. 1 showed FE-SEMmicrographs and hydrodynamic size distribution of PSA nanospheresprepared with different amount of AA. These results indicated thatthese nanospheres have interesting surface microstructures. Therewere many smart bulgings, which were uniformly distributed on thesurface of the nanospheres. Due to these bulgings, the increased surfacearea could effectively improve the absorption of Ag+. From Fig. 1, well-controlled particle size distributions could also been observed. Themean size of PSA (AA/St: 5, 10, 15, 25 wt.%) were ca. 424.1 ± 9.9,315.4 ± 8.2, 289.9 ± 5.9, and 282.1 ± 5.6 nm, respectively. The parti-cle size of PSA nanospheres was inversely proportional to the feed AAamount. To explain this phenomenon, a hypothesis was proposed thatthe presence of higher amount of ionic functional emulsifyingmonomercaused the larger number of formed primary particles, whereas thequantities of St used in all formulations were constant [38].

FTIR spectroscopy was used to study the surface properties of PSAnanospheres. Fig. 2 displayed FTIR spectra of PSA nanospheres. In thespectrum, several characteristic peaks were detected. The peaks at1601 cm−1 arose from C_C skeletal vibration of St, and the peaks ataround 1709 cm−1 corresponded to C_O stretching vibration of car-boxyl groups from AA.

PSA (AA/St: 15 wt.%) was chosen to prepare PSA/Ag-NPs nanocom-posites. TEM micrographs of PSA nanospheres and PSA/Ag-NPs nano-composites were shown in Fig. 3. From the micrographs, the core–shell structure of PSA nanospheres (Fig. 3a) and PSA covered with Agnanoparticles (Fig. 3b) could be seen clearly. In the SAED, as shown inthe inset, rings were indexed according to the reflections of (111),(200), (220), and (311) crystalline planes of cubic phase of Ag (JCPDScard No. 04-0783), which confirmed that Ag was successfully deposited[39]. Besides, the XRD pattern also provided evidence of the well-defined Ag crystallization. As shown in Fig. 4, sharp peaks at2θ = 38.1° (111), 44.3° (200), 64.4° (220), and 77.3° (311) wereobserved.

3.2. Antibacterial studies

PSA/Ag-NPs nanocomposites exhibited antibacterial activity in thetest of inhibition zone. As for S. aureus and E. coli, a zone directly aroundPSA/Ag-NPs coated paper disc could be viewed, whereas there was noclear zone around PSA coated paper disc and the control, as presentedin Fig. 5. Bare PSA nanospheres (AA/St: 15 wt.%),with the concentrationup to 1000 μg/mL, had not yet shown antibacterial activity against ei-ther the bacteria. This indicated that the growth inhibition was causedby Ag nanoparticles rather than PSA nanospheres. The bactericidal ac-tion of PSA/Ag-NPs nanocomposites caused the release of Ag+ ironsand its diffusion into the agar layer, which blocked the growth of bacte-rial colonies in the agar medium [40]. The sizes of the inhibition zonesfor PSA/Ag-NPs nanocomposites were measured and listed in Table 1.

Fig. 6.MBC test of different bacteria with PSA nanoparticles (AA/St: 15 wt.%) and various concentrations of PSA/Ag-NPs nanocomposites: (a) S. aureus and (b) E. coil.

150 C. Song et al. / Materials Science and Engineering C 36 (2014) 146–151

With the increasing concentration of PSA/Ag-NPs nanocomposites, theinhibition zone became wide.

As shown in Table 2, the MIC value of PSA/Ag-NPs nanocompositesagainst E. coli was 50 μg/mL, however, that value against S. aureus wasonly 25 μg/mL. As is well known, a lower MIC value corresponds to ahigher antibacterial effectiveness [41–43]. Hence, the bacteriostatic ef-fect for S. aureus was more noticeable than that for E. coli.

The presence of PSA/Ag-NPs nanocomposites on the LB agar plateswas able to kill the both types of the bacteria (Fig. 6). However, forPSA nanospheres (AA/St: 15 wt.%), uncontrollable bacterial prolifera-tion was shown. It is obvious that, comparing with PSA/Ag-NPs nano-composites, PSA nanospheres (AA/St: 15 wt.%) were ineffective forboth types of the bacteria, even at 1000 μg/mL. E. coli was completelykilled when the LB agar plates contained 200 μg/mL PSA/Ag-NPs nano-composites. PSA/Ag-NPs nanocomposites showed an antibacterial ac-tivity against S. aureus at a much lower MBC value (100 μg/mL). Onereasonmight be that the anionic surface of PSA/Ag-NPs nanocompositesincreased their association with the positive charged bacterial surface.This reasonwas consistentwith another report [44], which demonstrat-ed cationic PEI-coated Ag@MESs were more effective in slowing thegrowth of gram-negative E. coli.

Furthermore, the kinetics of antibacterial activity of PSA/Ag-NPsnanocomposites against S. aureus and E. coli were investigated, as

Fig. 7. Kinetics of antibacterial activity of PSA/Ag-NPs nanocom

shown in Fig. 7. Colony-forming of aliquot corresponded to the numberof live bacteria in each suspension at the time of withdrawing aliquot.Thus, a plot of colony-forming units (CFU/mL) of strains versus timewas constructed. As shown in Fig. 7, all the curves dropped steeply atthe initial stage, which meant that the initial bactericidal efficiency ofPSA/Ag-NPs nanocomposites was high [2]. In the case of S. aureus,when the concentration of PSA/Ag-NPs reached 100 μg/mL, all the ini-tially inoculated bacteria were sterilized within 390 min. The concen-tration was increased to 200 μg/mL, the sterilizing time was shortenedto 180 min. However, all the initially inoculated E. coliwere killed with-in 390 min only if the concentration of PSA/Ag-NPs reached 200 μg/mL.PSA/Ag-NPs nanocomposites, which resulted in a remarkable decreasein the number of bacteria, performed a higher bactericidal efficiencyagainst S. aureus than against E. coli at a lower equivalent concentration.However, increasing the concentration of PSA/Ag-NPs nanocompositesaccelerated the elimination of both the two bacteria.

Commercial nanocrystalline silver-coated dressings (Acticoat™)were reported to reduce infection in wound therapy [45,46]. In theabove experiments, PSA/Ag-NPs nanocomposites exhibited significantantibacterial effects and broad-spectrum biocidal activity. Therefore,PSA/Ag-NPs nanocomposites are expected todevelop antibacterial coat-ings on biomedical devices, which are broadly used in medical treatingprocesses.

posites against different bacteria: (a) S. aureus; (b) E. coil.

151C. Song et al. / Materials Science and Engineering C 36 (2014) 146–151

4. Conclusions

Monodisperse poly(styrene-co-acrylic acid) (PSA) nanospheres,serving as matrices, were synthesized via soap-free emulsion polymer-ization. FE-SEM micrographs indicated that PSA nanospheres have in-teresting surface microstructures and well-controlled particle sizedistributions. Their silver nanocomposites (PSA/Ag-NPs)were preparedin situ through controlled interfacial reduction. Themerits of thematrixcan help us to control the size of the nanocomposites. Structural studiesand XRD analysis clearly revealed the formation of Ag nanoparticles onthe PSAmatrices. The antibacterial activity of PSA/Ag-NPs nanocompos-ites against Gram-positive S. aureus and gram-negative E. coliwas stud-ied. Due to their excellent antibacterial activity, these nanocompositesare desirable to own potential application in developing antibacterialcoatings on biomedical devices, such as wound and burn dressings,catheters, and temporary implants.

Acknowledgments

This work was financially supported by the Special Program for KeyResearch of Chinese National Basic Research Program (2011CB612303);the Nation Natural Science Foundation of China (51173153, U1205113)and Xiamen Science and Technology Committee (No. 3502Z20120015).Authors are also grateful to Fujian Provincial Key Laboratory of FireRetardant Materials.

References

[1] V.M. Ragaseema, S. Unnikrishnan, V. Kalliyana Krishnan, L.K. Krishnan, Biomaterials33 (2012) 3083–3092.

[2] V. Sambhy, M.M. MacBride, B.R. Peterson, A. Sen, J. Am. Chem. Soc. 128 (2006)9798–9808.

[3] X. Chen, H.J. Schluesener, Toxicol. Lett. 176 (2008) 1–12.[4] S. Silver, L.T. Phung, G. Silver, J. Ind. Microbiol. Biotechnol. 33 (2006) 627–634.[5] C. Marambio-Jones, E.M.V. Hoek, J. Nanoparticle Res. 12 (2010) 1531–1551.[6] L. Bo, W. Yang, M. Chen, J. Gao, Q. Xue, Chem. Biodivers. 6 (2009) 111–116.[7] S. Bajpai, M. Bajpai, L. Sharma, Des. Monomers Polym. 14 (2011) 383–394.[8] P. AshaRani, G. LowKahMun,M.P.Hande, S. Valiyaveettil, ACSNano. 3 (2008) 279–290.[9] Y.H. Hsin, C.F. Chen, S. Huang, T.S. Shih, P.S. Lai, P.J. Chueh, Toxicol. Lett. 179 (2008)

130–139.[10] G. Vertelov, Y.A. Krutyakov, O. Efremenkova, A.Y. Olenin, G. Lisichkin, Nanotechnol-

ogy 19 (2008) 355707.[11] M. Kawashita, S. Tsuneyama, F. Miyaji, T. Kokubo, H. Kozuka, K. Yamamoto, Bioma-

terials 21 (2000) 393–398.[12] T. Syafiuddin, T. Igarashi, H. Shimomura, H. Hisamitsu, N. Goto, J. Showa Univ. Dent.

Soc. 13 (1993) 443–449.

[13] T. Syafiuddin, T. Igarashi, T. Toko, H. Hisamitsu, N. Goto, J. Showa Univ. Dent. Soc. 15(1995) 119–125.

[14] K. Kawahara, K. Tsuruda, M. Morishita, M. Uchida, Dent. Mater. 16 (2000) 452–455.[15] K. Yoshida, M. Tanagawa, M. Atsuta, J. Biomed. Mater. Res. 47 (1999) 516–522.[16] M. Tanagawa, K. Yoshida, S. Matsumoto, T. Yamada, M. Atsuta, Caries Res. 33 (1999)

366–371.[17] M. Kawashita, S. Tsuneyama, F. Miyaji, T. Kokubo, H. Kozuka, K. Yamamoto, Bioma-

terials 21 (2000) 393–398.[18] K. Kawahara, K. Tsuruda, M. Morishita, M. Uchida, Dent. Mater. 16 (2000) 452–455.[19] R. Wang, L. Wang, L. Zhou, Y. Su, F. Qiu, D. Wang, J. Wu, X. Zhu, D. Yan, J. Mater.

Chem. 22 (2012) 15227–15234.[20] J.J. Lin, W.C. Lin, R.X. Dong, S.H. Hsu, Nanotechnology 23 (2012) 065102.[21] M.M. da Silva Paula, C.V. Franco, M.C. Baldin, L. Rodrigues, T. Barichello, G.D. Savi, L.F.

Bellato, M.A. Fiori, L. da Silva, Mater. Sci. Eng. C 29 (2009) 647–650.[22] J. An, X. Yuan, Q. Luo, D. Wang, Polym. Int. 59 (2010) 62–70.[23] A.S. Nair, N.P. Binoy, S. Ramakrishna, T.R.R. Kurup, L.W. Chan, C.H. Goh, M.R. Islam, T.

Utschig, T. Pradeep, ACS Appl. Mater. Interfaces 1 (2009) 2413–2419.[24] P. Singh, A. Srivastava, R. Kumar, J. Polym. Sci. A Polym. Chem. 50 (2012)

1503–1514.[25] J.W. Kim, J.E. Lee, S.J. Kim, J.S. Lee, J.H. Ryu, J. Kim, S.H. Han, I.S. Chang, K.D. Suh, Poly-

mer 45 (2004) 4741–4747.[26] H. Ismail, H.D. Rozman, R.M. Jaffri, Z.A. Ishak, Eur. Polym. J. 33 (1997)

1627–1632.[27] J.W. Bae, W. Kim, S.H. Cho, S.H. Lee, J. Mater. Sci. 35 (2000) 5907–5913.[28] J. Douce, J.-P. Boilot, J. Biteau, L. Scodellaro, A. Jimenez, Thin Solid Films 466 (2004)

114–122.[29] H. Dong, F. Yan, H. Ji, D.K.Y. Wong, H. Ju, Adv. Funct. Mater. 20 (2010) 1173–1179.[30] R. Yan, Y. Zhang, X. Wang, J. Xu, D. Wang, W. Zhang, J. Colloid Interface Sci. 368

(2012) 220–225.[31] F.C. Yang, K.H. Wu, J.W. Huang, D.N. Horng, C.F. Liang, M.K. Hu, Mater. Sci. Eng. C 32

(2012) 1062–1067.[32] A.J. Kora, R. Manjusha, J. Arunachalam, Mater. Sci. Eng. C 29 (2009) 2104–2109.[33] H. Nakashima, H. Takahashi, M. Kameko, H. Saito, J. Infect. Chemother. 18 (2012)

970–972.[34] A. Panacek, M. Kolar, R. Vecerova, R. Prucek, J. Soukupova, V. Krystof, P. Hamal, R.

Zboril, L. Kvitek, Biomaterials 30 (2009) 6333–6340.[35] M.S. Tamboli, M.V. Kulkarni, R.H. Patil, W.N. Gade, S.C. Navale, B.B. Kale, Colloids

Surf. B: Biointerfaces 92 (2012) 35–41.[36] H. Lu, L. Fan, Q. Liu, J. Wei, T. Ren, J. Du, Polym. Chem. 3 (2012) 2217–2227.[37] H. Kong, J. Jang, Biomacromolecules 9 (2008) 2677–2681.[38] D. Polpanich, P. Tangboriboonrat, A. Elaïssari, Colloid Polym. Sci. 284 (2005)

183–191.[39] K. Kim, H.S. Kim, H.K. Park, Langmuir 22 (2006) 8083–8088.[40] K. Chaloupka, Y. Malam, A.M. Seifalian, Trends Biotechnol. 28 (2010) 580–588.[41] R. Prucek, J. Tucek, M. Kilianova, A. Panacek, L. Kvitek, J. Filip, M. Kolar, K.

Tomankova, R. Zboril, Biomaterials 32 (2011) 4704–4713.[42] B. Chudasama, A.K. Vala, N. Andhariya, R.V. Upadhyay, R.V. Mehta, Nano Res. 2

(2010) 955–965.[43] S. Dutta, A. Shome, T. Kar, P.K. Das, Langmuir 27 (2011) 5000–5008.[44] M. Liong, B. France, K.A. Bradley, J.I. Zink, Adv. Mater. 21 (2009) 1684–1689.[45] P. Muangman, C. Chuntrasakul, S. Silthram, S. Suvanchote, R. Benjathanung, S.

Kittidacha, S. Rueksomtawin, J. Med. Assoc. Thail. 89 (2006) 953–958.[46] J.B. Wright, K. Lam, A.G. Buret, M.E. Olson, R.E. Burrell, Wound Repair Regen. 10

(2002) 141–151.