Journal of Colloid and Interface Science 318 (2008) 217–224www.elsevier.com/locate/jcis

First successful design of semi-IPN hydrogel–silver nanocomposites:A facile approach for antibacterial application

P.S.K. Murthy a,1, Y. Murali Mohan a,1,2,∗, K. Varaprasad a, B. Sreedhar b, K. Mohana Raju a,∗

a Department of Polymer Science and Technology, Sri Krishnadevaraya University, Anantapur 515003, Indiab Inorganic and Physical Chemistry, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, India

Received 19 August 2007; accepted 8 October 2007

Available online 19 November 2007

Abstract

Semi-IPN hydrogels in which poly(vinyl pyrrolidone) (PVP) chains were physically dispersed throughout poly(acrylamide) (PAM) gel net-works were synthesized. These semi-IPN hydrogel networks can act as excellent nanoreactors for producing and stabilizing metal nanoparticles.The current methodology allows us to entrap metal nanoparticles throughout hydrogel networks via PVP chains. An optimized semi-IPN hydro-gel formulation was found to produce silver nanoparticles, ca. 3–5 nm. The synthesized semi-IPN hydrogel–silver nanocomposites were fullycharacterized by using UV–vis, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmis-sion electron microscopy (TEM). The developed semi-IPN hydrogel–silver nanocomposite (SHSNC) was evaluated for preliminary antibacterialapplications.© 2007 Elsevier Inc. All rights reserved.

Keywords: Hydrogel network; Composite hydrogel; Antibacterial activity; Silver nanoparticles

1. Introduction

In the last decade, the synthesis and stabilization of metalnanosystems have been very interesting subjects of nanoscienceand nanotechnology [1] and these nanosystems have poten-tial applications in photonic, electronic, catalytic, chemical,and biosensor areas because of their size effects compared tothose of bulk metal and molecular compounds [2–9]. Due tothe lack of sufficient chemical and physical stability of metalnanoparticles, their development to real world applications hasbeen restricted to some extent. To receive a better stabiliza-tion or dispersion of metal nanoparticles in aqueous media,various protective agents had been used and these agents alsoplay a wonderful role in controlling the nanostructures of theparticles [1,7,10–14]. For this purpose, various polymeric sta-

* Corresponding authors.E-mail addresses: yallapm@ccf.org (Y. Murali Mohan),

kmrmohan@yahoo.com (K. Mohana Raju).1 Equal contribution from P.S.K. Murthy and Y. Murali Mohan.2 Present address: Department of Biomedical Engineering, Lerner Research

Institute, Cleveland Clinic, Cleveland, OH 44195, USA.

bilizating agents including natural and synthetic polymers, den-drimers, latex particles, microgels, and hydrogels have beenstudied exclusively [1,7,15–21].

Recent trends demonstrate that macroscopic gels are be-coming most promising as templates/nanoreactors for in situsynthesis of smaller size nanoparticles and this strategy hasbrought up a new concept in hybrid or composite systems inchemistry and engineering science [19,20,22–24]. Notewor-thy of hydrogel template methodology is that one can con-trol the size and morphology of the nanoparticles by varyingthe amount of monomer, cross-linker, and functionality of gelnetworks [22–24]. Similarly, microgel formulations based onN -isopropylacrylamide (NIPAM) in conjunction with nanopar-ticles are employed for electroanalytical applications [25].Ferro-nanohydrogel composites in which magnetic nanopar-ticles are entrapped inside the hydrogel have been studied re-cently [26]. Gels constructed with methyl methacrylate (MMA)and ethylene glycol dimethacrylate (EGDMA) have been em-ployed to control the size and morphology of the Pd nanopar-ticles [7]. A study by Saravanan et al. [27] has shown thatpoly(acrylamide) hydrogels are effective for the production ofnano-sized silver particles (∼4 nm). A few studies that deal

0021-9797/$ – see front matter © 2007 Elsevier Inc. All rights reserved.doi:10.1016/j.jcis.2007.10.014

218 P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224

Scheme 1. Schematic representation of in situ semi-IPN hydrogel–silver nanocomposites (SHSNC).

with metal nanoparticles, especially silver, gold, and copper,have exhibited antibacterial activity on microorganisms [28–31]. Among these nanoparticles, nanosilver displays reasonableantimicrobial activity [32–34]. Perhaps, it is the size-dependentinteraction with HIV-I virus via gp-120 glycoprotein knobsthat is responsible for the inhibition of virus binding to thecells [35]. Silver nanoparticles are considered as nontoxicand environmentally friendly antibacterial materials, but dueto their poor binding characteristic with surfaces, their utilityhas been restricted. Therefore, polymer-stabilized nanoparticlesand nanoparticles embedded in hydrogel networks are outstand-ing approaches for antibacterial applications [23,24,36,37].

Although a number of hydro-, micro-, and nanogel systemswere utilized as templates to produce metal nanoparticles, thereis no report found in the literature for silver nanoparticle syn-thesis employing semi-IPN gels until today (see, for exam-ple, reviews) [38,39]. Therefore, we herein report gel–silvernanoarchitectures as promising antibacterial materials, in whichsilver nanoparticles embedded in poly(acrylamide)/poly(vinylpyrrolidone) semi-IPN hydrogels extend good stability throughpoly(vinyl pyrrolidone)-interpenetrated polymer chains (Sche-me 1), whereas in earlier processes [19,21–24] the availablefunctional groups of hydrogel networks provide stability. Thedeveloped nanocomposites were evaluated by using UV–vis,FT-IR spectroscopy, X-ray diffraction (XRD), thermogravimet-ric analysis (TGA), scanning electron microscopy (SEM), andtransmission electron microscopy (TEM).

2. Experimental

2.1. Materials

Acrylamide (AM), N ,N -methylenebisacrylamide (MBA),N ,N ,N ′,N ′-tetramethylethylenediamine (TMEDA), ammoni-um persulfate (APS), poly(vinyl pyrrolidone) (PVP) (MW40,000), silver nitrate (AgNO3), and sodium borohydride(NaBH4) were purchased from Aldrich Chemical CompanyInc. (Milwaukee, WI). All chemicals were used without furtherpurification. Double-distilled water was used for the prepa-ration of all solutions in this study. To synthesize semi-IPN

Table 1Semi-IPN hydrogel formulation composition

Semi-IPNhydrogelcode

Concentration in the feed mixture of gel networks

AAm(mM)

PVP(mg)

MBA

(mM)×10−5APS

(mM) ×10−3TMEDA

(mM) ×10−5

1 14.08 0 6.48 2.19 6.312 14.08 50 6.48 2.19 6.313 14.08 100 6.48 2.19 6.314 14.08 150 6.48 2.19 6.315 14.08 200 6.48 2.19 6.316 14.08 200 3.24 2.19 6.317 14.08 200 4.68 2.19 6.318 14.08 200 1.62 2.19 6.319 14.08 200 8.1 2.19 6.31

10 14.08 200 9.72 2.19 6.3111 14.08 200 6.48 1.64 6.3112 14.08 200 6.48 2.73 6.3113 14.08 200 6.48 3.28 6.3114 14.08 200 6.48 2.19 6.3115 14.08 200 6.48 2.19 3.1516 14.08 200 6.48 2.19 4.7317 14.08 200 6.48 2.19 7.8918 14.08 200 6.48 2.19 9.47

hydrogel–silver nanocomposites, PVP (5 g/100 ml), MBA(1 g/100 ml), APS (5 g/100 ml), TMEDA (1 g/100 ml), sil-ver nitrate (AgNO3) (8.493 g/500 ml), and sodium borohydrate(1.8915 g/500 ml) solutions were made in double-distilled wa-ter.

2.2. Preparation of hydrogel

Poly(acrylamide)/poly(vinyl pyrrolidone) (PAM/PVP) semi-IPN hydrogels were synthesized by employing free radicalpolymerization using N ,N -methylenebisacrylamide as cross-linker and ammonium persulfate/N ,N ,N ′,N ′-tetramethyl-ethylenediamine as redox-initiating pair. PAM/PVP semi-IPNhydrogels were prepared by first mixing AM (1 g) with dif-ferent amounts (0, 0.05, 0.10, 0.15, 0.20 g) of PVP. A num-ber of series of semi-IPN hydrogels were synthesized by us-ing AM = 1 g and PVP = 0.20 g and varying the cross-linker, ammonium persulfate, and TMEDA concentrations (Ta-ble 1).

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2.3. Preparation of semi-IPN hydrogel–silver nanocomposites

For this, dry semi-IPN hydrogel disks were equilibrated withwater for 3 days and these disks were immediately transferredto a beaker containing 50 ml of AgNO3 aqueous solution andthen allowed to equilibrate for 1 day. In this step, the silverions are being exchanged from solution to the gel networks.These semi-IPN hydrogel-loaded silver salts were then finallytransferred to a beaker containing 50 ml of NaBH4 aqueoussolution and kept in the beaker for 2 h in order to reducethe silver ions into silver nanoparticles. The obtained silvernanoparticles in the semi-IPN hydrogels are often termed assemi-IPN hydrogel–silver nanocomposites (SHSCN) or semi-IPN hydrogel–silver nanohybrids (SHSNC) in the forthcomingsections.

The prepared semi-IPN hydrogels (Section 2.2) with differ-ent concentrations of PVP, MBA, APS, and TMEDA were em-ployed for producing the semi-IPN hydrogel–silver nanocom-posites. The resulting nanocomposite is termed SHSNC withthe semi-IPN hydrogel code number as the suffix.

2.4. Characterization

UV–vis spectra of semi-IPN hydrogel–silver nanocompos-ites (10 mg in 1 ml of distilled water) were carried out on aShimadzu (Kyoto, Japan) 160A UV spectrophotometer. X-raydiffraction measurements were recorded using a Rikagu diffrac-tometer (Cu radiation, λ = 0.1546 nm) running at 40 kV and40 mA. The thermal stabilities of the semi-IPN and SHSNCwere evaluated by using the Mettler Toledo 851e thermal sys-tem (Zurich, Switzerland) at a heating rate of 10 ◦C/min undernitrogen atmosphere (flow rate, 10 ml/min). The dry semi-IPNhydrogel (coated with a thin layer of palladium gold alloy) andthe semi-IPN hydrogel–silver nanocomposites were studied formorphological variations by using a JEOL JSM 840A (Tokyo,Japan) scanning electron microscope. Transmission electronmicroscopy images for semi-IPN hydrogel–silver nanocompos-ites were recorded using a Tecnai F 12 transmission electronmicroscope operating at an acceleration voltage of 15 kV. ForTEM measurements, samples were prepared by dropping 10–20 µl of finely grinded SHSNC solution on a copper grid anddried at room temperature after removing excess solution usingfilter paper.

2.5. Swelling studies [19]

Completely dried semi-IPN hydrogels of the same weightwere equilibrated in distilled water at 30 ◦C for 3 days. Thesesemi-IPN hydrogels were treated first with Ag salt and subse-quently with NaBH4 solutions as explained in the experimentalsection. The equilibrium swelling capacity or swelling ratio (Q)of the gels was calculated employing Q = We/Wd, where We

is the weight of water in the swollen hydrogel and Wd is the dryweight of the pure hydrogel.

2.6. Antibacterial activity

Nutrient agar medium was prepared by mixing peptone(5.0 g), beef extract (3.0 g), and sodium chloride (NaCl) (5.0 g)in 1000 ml distilled water and the pH was adjusted to 7.0. Fi-nally, agar (15.0 g) was added to the solution. The agar mediumwas sterilized in a conical flask at a pressure of 15 lbs for30 min. This medium was transferred into sterilized petri dishesin a laminar air flan. After solidification of the media, bacil-lus culture was streaked on the solid surface of the media.To this inoculated petri dish, one drop of gel particle solution(20 mg/10 ml distilled water) was added using 50-µl tip andincubated for 2 days at 37 ◦C in the incubation chamber.

3. Results and discussion

Because of the outstanding applications of hydrogel–metalnanocomposites in biological and medical fields, we have de-signed a facile way of producing silver nanoparticles insidethe hydrogel networks. For this purpose, we have developed anumber of formulations to obtain well-suitable network hydro-gel systems that can be effectively used for obtaining highlydispersed and or very small silver nanoparticles. These hy-drogel networks were prepared following simultaneous freeradical cross-linking polymerization [40,41]. In this process,acrylamide was polymerized in the presence of PVP to obtainPAM/PVP semi-IPN hydrogels where the PVP chains are ran-domly distributed throughout the cross-linked networks. In Ta-ble 1 is seen the hydrogel templates synthesized with differentcompositions of PVP, cross-linker (MBA), initiator (APS), andactivator (TMEDA). Most of the developed semi-IPN hydro-gels in this investigation have not shown considerable effectson the formation of silver nanoparticles but there is a signif-icant effect on the properties of the resulting final SHSNCs.Special interest in choosing PVP as an interpenetrating polymerin our hydrogels is due to its protecting, reducing, and nucleat-ing characteristics for metal nanoparticles [10,42]. Therefore,the combination of hydrogel with PVP would be a more opti-mal strategy that is highly suitable for producing nanoparticles.Fig. 1 illustrates the formation of silver nanoparticles within theswollen semi-IPN hydrogel networks. In this way, a highly dis-tributed array of silver nanoparticles was obtained within thesemi-IPN hydrogel polymer network.

Fig. 2 shows the influence of various formulations on theswelling characteristics of hydrogels, hydrogel-loaded silvernitrate, and hydrogel–silver nanoparticle composites. Consid-erable variation in the swelling capacity of semi-IPN hydrogelswas noted when the hydrogels were modified or loaded with Agsalt and Ag nanoparticles. The order of swelling capacity val-ues was found as semi-IPN hydrogel < Ag-semi-IPN hydrogel< semi-IPN hydrogel–silver nanocomposite. The gels treatedwith silver salt result in gel networks with Ag+ ions loadedthroughout the gel. These ions present in the electrostaticallyneutral gels (acrylamide gels) are responsible for a moderateincrement of the swelling behavior of Ag-loaded semi-IPNs.The gels containing silver ions treated with a reducing agent(sodium borohydrate) yield silver nanoparticles inside the gels.

220 P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224

Fig. 1. Photographs of (a) semi-IPN hydrogel, (b) silver ion-loaded semi-IPN hydrogel, and (c) semi-IPN hydrogel–silver nanocomposites (SHSNC).

Fig. 2. Swelling pattern of semi-hydrogel, silver ion-loaded semi-IPN hydrogel, and hydrogel–silver nanocomposites.

The formed silver nanoparticles having different amounts of Agnanoparticle surface charges (different sizes of the AgNPs) in-side the gel cause expansion of the hydrogel networks [19].

The immobilization of silver nanoparticles throughout thehydrogel networks is due to a strong localization of particleswithin the gel networks. The formation of the silver nanoparti-cles in the hydrogel networks was indicated by the appearanceof a brown color (Fig. 1). This can be due to the adsorption ofsilver nanoparticles through either nitrogen atoms and/or oxy-

gen atoms present in the semi-IPN hydrogel macromolecularchains. The presence of embedded silver nanoparticles withinthe gel macromolecular networks is confirmed by using UV–visspectral studies. As presented in Fig. 3, all the UV–vis spectra ofsilver nanoparticles embedded in semi-IPN gel networks haveshown a distinct characteristic absorption peak around 410 nm.This must be due to the characteristic surface plasmon reso-nance effect of quantum-size silver nanoparticles present in thehydrogel networks. With increase of PVP content in the hy-

P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224 221

Fig. 3. UV–vis spectra of semi-IPN hydrogel–silver nanocomposites preparedfrom semi-IPN hydrogel codes 1–4.

drogel composition, the silver salt loading probably increases,resulting in more silver nanoparticle formation (reduction reac-tion) in the gel structure which in turn progressively increasesthe absorption in the UV–vis spectra (Fig. 3). UV–vis spectralinformation for other all formulations is provided as supportinginformation I. In all the UV–vis spectra of semi-IPN hydrogel–silver nanohybrids, there are no peaks identified around 335 and560 nm, indicating the complete absence of Ag nanoparticleaggregation or Agn clusters [43,44]. From the UV–vis spectralanalysis of SHSNC, it is very clear that the silver nanoparticlesformed inside the semi-IPN hydrogel networks are highly sta-ble and well dispersed in nature. This supports that the silvernanoparticles are synthesized in the semi-IPN hydrogel nanore-actors, i.e., the semi-IPN hydrogel networks acting as nanoreac-tors for silver nanoparticles that grew between the gel networks.In our current methodology, we used PVP for the formationof semi-IPN networks in the poly(acrylamide) gels. Therefore,we believe that PVP chains promote the silver nanoparticle sta-bilization to a greater extent when compared to conventionalhydrogel systems. Further, it is proved by TEM studies in thecoming sections.

The formation of silver nanoparticles in the semi-IPN hydro-gels has been demonstrated by X-ray diffraction studies. XRDdata indicate well-defined characteristic patterns of the silvernanoparticles present in the hydrogel. The observed diffractionpeaks of semi-IPN hydrogel–silver nanohybrids are found at38.1, 44.26, 64.50, and 77.42 θ and assigned to (111), (200),(220), and (311) planes of fcc silver particles, respectively (fig-ures are not shown) [19,23]. But, their hydrogels did not possesssuch peaks in their X-ray diffraction (figure not shown). In addi-tion, a clear variation has been observed in TGA experiments,that semi-IPN hydrogel–silver nanocomposites exhibit excel-lent thermal stability than semi-IPN hydrogels. In detail, semi-IPN hydrogels followed two degradation steps and 82 wt%degradation of the hydrogel chains occurred below 460 ◦C butin the case of semi-IPN hydrogel–silver composite it is notedas three degradation steps and only a 45% weight loss below

Fig. 4. Semi-IPN hydrogel 15 (black) and SHSNC 15 (red). (For interpretationof the references to color in this figure legend, the reader is referred to the webversion of this article.)

460 ◦C (Fig. 4). The weight loss difference between the semi-IPN and SHSNC represents the presence of silver nanoparticles(weight percent) in the SHSNC. In this particular sample, it isnoted that there is a 3.71 wt% of silver nanoparticle content inthe SHSNC.

Scanning electron microscope images of pure poly(acryl-amide)/poly(vinyl pyrrolidone) semi-IPN hydrogel and semi-IPN hydrogel–silver nanoparticle hybrids are shown in Fig. 5.Figs. 5a and 5b showed a clear and flat surface for the semi-IPN hydrogels, whereas silver salt-loaded semi-IPN hydrogelsshowed a shrunken surface throughout the gel (Fig. 5c). How-ever, there is a pinpoint variation in the case of silver nanopar-ticles formed in the gel networks. Figs. 5d–5f illustrate theformation of defined nanostructures over all the hydrogel net-works. This indicates that clear silver nanoparticles are formedalong with the PVP chains rather than just entrapment in the gelnetworks. The use of poly(vinyl pyrrolidone) in the networks isto keep stabilized the formed nanoparticles in the gel networks.We also proved that silver nanoparticles not only formed on thesurfaces of hydrogels but also uniformly distributed throughoutthe hydrogel networks (supporting information II).

It is quite common that the control or alignment of nanopar-ticles can be achieved by modifying the hydrogel network ar-chitectures [19]. A number of different structural constructionsof gel networks can be obtained by varying the polymer, cross-linker, initiator, and or activator concentrations in the synthesisof the hydrogel. Supporting information III clearly demon-strates that most of the formulations resulted in aggregativesilver nanoparticles when they are extracted from the gels. Afteroptimizing various parameters in the semi-IPN gel formula-tions, a fine composition was found to achieve well-dispersednanoparticles in the hydrogel networks, i.e., high MBA con-centration was used for the hydrogel preparation. In Fig. 6,the TEM image demonstrates a highly uniform distribution ofsilver nanoparticles. It is possible that the silver nanoparticlesformed in the cross-linked networks are spherical, highly dis-

222 P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224

Fig. 5. SEM pictures of (a, b) semi-IPN hydrogel 6, (c) semi-IPN hydrogel 6 loaded with silver salt, and (d–f) SHSNC 6.

persed, and low nanometer in size. Moreover, from the selectedarea of the TEM image, the electron diffraction (SAED) patternof silver nanoparticles is clearly visible as three diffraction ringsand they are definitely attributed to the face-centered cubicstructure of silver nanoparticles. The brightest ring and the oneclosest to the center is a combination of the {111} and {200}reflections. The second ring belongs to {222} reflection and theweakest third ring is due to either {420} and/or {422} reflec-tions. This clearly represents that highly dense semi-IPN hydro-gel networks favor silver nanoparticle formation because thatcomposition permits the establishment of inter- and intramolec-ular attractions between the semi-IPN hydrogel networks due toless free space in the hydrogel networks. This ultimately helpsnot only in controlling the size of the nanoparticles but also pro-vides better stabilization of them for longer periods. In this en-vironment, the PVP chains in the networks are highly compactin nature and give enough stability to the silver nanoparticles.A hypothetical schematic diagram is shown in Fig. 7 for bet-ter understanding how the nanoparticles are being stabilized inthe highly dense semi-IPN hydrogel networks and the aggre-

Fig. 6. TEM image of silver nanoparticles obtained from SHSNC 10.

gates inside of the loosely cross-linked semi-IPN hydrogel net-works. In the slightly cross-linked semi-IPN hydrogels the PVPchains are in a relaxed state. The silver nanoparticles formedin most of these networks are in an aggregative pattern since

P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224 223

the PVP chains present in these networks may not provide ex-tensive stability to the formed nanoparticles. Recently, MuraliMohan et al. [19] synthesized hydrogel networks with differentcross-link densities and succeeded in obtaining ∼3 nm silvernanoparticles in those nanocarriers. Further, it is also possibleto produce different metal nanoparticles in the NIPAM-basednanogels with a different approach for controlling the size andparticle distributions [16]. The results from our study are ingood agreement with the results of the above literature [16,19,20,24]. But there are no reports found in the literature for pro-ducing nanoparticles in the networks using semi-IPN hydrogelsand it will be the first report [38,39]. In our opinion, the de-signed semi-IPN hydrogels are excellent nanoreactors for thesynthesis of metal and semiconducting nanoparticles.

(a)

(b)

Fig. 7. Schematic illustration of nanoparticle stabilization pattern in thesemi-IPN hydrogel networks.

At the same time, the poly (acrylamide) hydrogels alsoshowed highly distributed silver nanostructures but the nanopar-ticles are much less in number according to the TEM images(supporting information IV). The particle size is found between10 and 15 nm. More recently, Saravanan et al. [27] synthe-sized silver nanoparticle-immobilized polyacrylamide hydrogelnanocomposites. In their study, they produced silver nanoparti-cles of about 5 nm in size. Their results also demonstrate thatpolyacrylamide gels are capable of obtaining small nanopar-ticles but the number of particles is much less. In fact, thereis no significant peak observed in the UV–vis spectra for ourpoly(acrylamide) gel sample containing silver nanoparticles.The possible reason might be that the absorption of silvernanoparticles was obscured by the polymeric chains. More orless, semi-IPN hydrogels containing 50 mg of PVP showedsimilar results. But all the remaining compositions with PVPand with different formulations exhibited aggregated nanopat-terns as explained above. This behavior demonstrates that purepoly(acrylamide) and PAM-PVP 50 mg gels only gave a verylow number of particles whereas the remaining gel networksprovide a sufficient number for the synthesis of silver nanopar-ticles.

The task of the current study also includes testing the devel-oped semi-IPN hydrogel–silver nanocomposites for the purposeof antibacterial activity. A most advanced feature of these gel–silver nanocomposites is that the silver nanoparticles embeddedthroughout the networks come out with time in aqueous me-dia. Therefore, the nanoparticles escape from the gel networkswith time and interact with the bacteria. Because of a gooddispersion of silver nanoparticles in semi-IPN hydrogels, i.e.,SHSNC 10, we have evaluated the antibacterial activity for thissample. Fig. 8 illustrates the antibacterial effect of pure semi-IPN hydrogels and semi-IPN hydrogel–silver nanocompositeson E. coli. As expected the number of colonies grown surround-ing the semi-IPN hydrogel–Ag nanocomposite was found to bealmost nil whereas the pure semi-IPN hydrogel did not showany effect on E. coli. Therefore, we conclude that the semi-IPNhydrogel–silver nanocomposites are excellent antibacterial ma-terials.

Fig. 8. Photograph of pure semi-IPN hydrogel 10 and semi-IPN hydrogel–Ag nanocomposite (SHSNC 10) on E. coli.

224 P.S.K. Murthy et al. / Journal of Colloid and Interface Science 318 (2008) 217–224

4. Conclusion

In conclusion, we have demonstrated a highly facile and sim-ple methodology for preparing hydrogel–silver nanocompos-ites. For this, a number of poly(acrylamide)/poly(vinyl pyrroli-done) (PAM/PVP) semi-IPN hydrogels were formulated byvarying the poly(vinyl pyrrolidone), cross-linker, initiator, andactivator concentrations. It is clearly illustrated that the sil-ver nanoparticles are being formed not only on the surfaceof semi-IPN hydrogels but also throughout the networks. Anoptimal formulation was achieved with higher MBA concentra-tions that ultimately lead to obtaining highly dispersed silvernanoparticles in hydrogel networks. The developed nanocom-posite swelling properties are dependent on the internal networkstructure. The nanocomposites are confirmed by using spectral,thermal, and electron microscopy methods. They are confirmedas excellent antibacterial materials.

Acknowledgment

The authors thank the Defence Res. & Dev. Organization andMinistry of Defence, Govt. of India, New Delhi for the financialsupport.

Supporting information

Supplementary data for this article may be found in the on-line version at DOI: 10.1016/j.jcis.2007.10.014.

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