Journal of Colloid and Interface Science 315 (2007) 389–395www.elsevier.com/locate/jcis

A versatile strategy to fabricate hydrogel–silver nanocomposites andinvestigation of their antimicrobial activity

V. Thomas a, Murali Mohan Yallapu b,1, B. Sreedhar c, S.K. Bajpai a,∗

a Department of Chemistry, Polymer Research Laboratory, Govt. Model Science College, Jabalpur, MP 482001, Indiab Department of Polymer Science & Technology, Sri Krishnadevaraya University, Anantapur, AP 515003, India

c Inorganic and Physical Chemistry, Indian Institute of Chemical Technology, Tarnaka, Hyderabad, AP 500007, India

Received 16 April 2007; accepted 25 June 2007

Available online 17 August 2007

Abstract

In this study, hydrogel–silver nanocomposites have been synthesized by a unique methodology, which involves formation of silver nanoparti-cles within swollen poly (acrylamide-co-acrylic acid) hydrogels. The formation of silver nanoparticles was confirmed by transmission electronmicroscopy (TEM) and surface plasmon resonance (SPR) which was obtained at 406 nm. The TEM of hydrogel–silver nanocomposites showed al-most uniform distribution of nanoparticles throughout the gel networks. Most of the particles, as revealed from the particle-size distribution curve,were 24–30 nm in size. The X-ray diffraction pattern also confirmed the face centered cubic (fcc) structure of silver nanoparticles. The nanocom-posites demonstrated excellent antibacterial effects on Escherichia coli (E. coli). The antibacterial activity depended on size of the nanocomposites,amount of silver nanoparticles, and amount of monomer acid present within the hydrogel–silver nanocomposites. It was also found that immersionof plain hydrogel in 20 mg/30 ml AgNO3 solution yielded nanocomparticle–hydrogel composites with optimum bactericidal activity.© 2007 Elsevier Inc. All rights reserved.

Keywords: Hydrogel; Silver nanoparticles; Surface plasmon resonance; Nanocomposites; E. coli; Transmission electron microscopy; Silver nitrate;Antibacterial activity; Scanning electron microscopy; Colony-forming unit

1. Introduction

The design and development of nanoparticles and nanostruc-tural materials have opened a new era for constructing well-designed nanostructures that have been considered as a novelclass of materials for catalytic, optical, electronic, and bio-medical applications [1]. It is widely renowned that nano-sizedmetal particles such as silver, gold, and copper are highly toxicto microorganisms [2–6], exhibiting strong biocidal effects onas many as 16 species of bacteria including Escherichia coli [7].Nanoparticles have an extremely large relative surface area,thus increasing their contact with bacteria or fungi, and vastlyimproving their bactericidal and fungicidal effectiveness. Silvernanoparticles show excellent antimicrobial activity by binding

* Corresponding author.E-mail address: mnlbpi@rediffmail.com (S.K. Bajpai).

1 Current address: Department of Biomedical Engineering ND4-20, LernerResearch Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.

0021-9797/$ – see front matter © 2007 Elsevier Inc. All rights reserved.doi:10.1016/j.jcis.2007.06.068

both to microbial DNA, preventing bacterial replication, and tothe sulfhydryl groups of the metabolic enzymes of the bacterialelectron transport chain causing their inactivation [8,9]. Hence,nanosilver particles have been applied to a wide range of health-care products such as burn dressings, scaffold, skin donor andrecipient sites, water purification systems, and medical devices[10–14]. Most recently, it has been demonstrated that silvernanoparticles undergo a size-dependent interaction with HIV-Ivirus via preferential binding to the gp120 glycoprotein knobs,thus inhibiting the virus from binding to the host cells [15].

Multipurpose systems are required to exhibit superior an-tibacterial activity toward germs on contact without releas-ing any toxic biocides. Ongoing research efforts, on three-dimensional network hydrogels, suggest that huge free spaceavailable between the cross-linked networks in the swollenstage behaves as nanoreactors for generating the nanoparti-cles [16]. These hydrogel nanoreactors offer a platform fornucleation and growth of nanocrystals, which eventually leadto nanoparticle formation. Further, gel–nanoparticle systems

390 V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395

have opened a new skylight for different applications in bio-medical engineering and these approaches are most effectiveand safe because they are compatible with most of biolog-ical molecules, cells, tissues, etc. Current studies have ex-ploited in situ synthesis of metal nanoparticles within theswollen hydrogel networks [17] and the resulting products areleading to new hybrid or composite systems that have ver-satile applications in bioengineering and biomedical fields.The most advanced feature of this novel approach is thatwe can alter the size and morphology of the nanoparticlesby changing the monomer and crosslinker concentrations inthe gel formulations. Well-defined gold nanoparticles embed-ded inside thermosensitive hydrogel matrices were reportedby Wang et al. [18,19]. In their work, the templates of gelnetworks were prepared using a combination of two crosslink-ers, namely N,N -methylenebisacrylamide (MBA) and N,N -cystaminebisacrylamide (CBA). CBA is highly responsible incontrolling the morphology of the nanoparticles by control-ling the crosslinking density of the networks. In another study,Zhang et al. [20] produced polymeric microgels which can actas versatile nanoreactors for semiconductor, metal, and mag-netic nanoparticles. Recently, microgel formulations based onN -isopropylacrylamide with nanoparticles have been effec-tively employed for photonic, electronic, and electroanalyticalapplication purposes [21–23]. Hydrogels have also been em-ployed for magnetic nanoparticle entrapment and the result-ing ferronanohydrogel composite properties have been stud-ied [24]. Gels constructed with methyl methacrylate (MMA)and ethylenedimethacrylate (EDMA) have been utilized as tem-plates to control the size and morphology of Pd nanoparticles.The developed microgel–metal nanoclusters are appropriatefor catalysis applications [25]. More recently, silver nanopar-ticles of ∼35 nm are embedded in a novel hydrogel systembased on poly(vinyl alcohol)/poly(styrene)-co-poly(ethyleneglycol methacrylate) [PVA/PS-PEGMA] [26]. A recent studydemonstrates that hydrogels are capable of producing nanosil-ver particles about ∼4 nm in size [27]. In these studies, dif-ferent strategies have been followed to prepare hydrogel–silvernanocomposites. These include (1) polymerization of monomerin the presence of initiator-funtionalized metal nanoparticles;(2) shrinking of a swollen gel in acetone followed by itsreswelling in solution of metal nanoparticles and then again itsshrinking in acetone, thus finally resulting in the formation ofnanoparticle-loaded gels; (3) surfactant-free emulsion polymer-ization (SFEP) to encapsulate metal nanoparticles within largerspherical hydrogel particles; and (4) mixing a colloidal solutionof metal nanoparticles with aqueous polymer solution, followedby solvent evaporation. However, the method used in our studyis very simple and economic and does not involve the use oforganic solvents. The use of organic solvents and other toxicreagents, harsh synthesis conditions, limit their use in preparinghydrogel/silver nanocomposites for biomedical applications.Contrary to this, we hereby report a universal approach forsynthesizing nanocomposites. In the present work, we havereported a novel approach for synthesizing Ag nanoparticlescontaining poly(acrylamide-co-acrylic acid) hydrogels and in-vestigated their antimicrobial activity against E. coli.

The antibacterial property of silver has been studied by anumber of microbiologists. For example, Deitch et al. [28] eval-uated the antibacterial activity of silver nylon fabrics on thegrowth of S. aureus and C. albicans to develop these fabricsas wound dressings. In another study, Sondi and Salopek-Sondi[7] evaluated the antimicrobial activity of silver nanoparticlesagainst E. coli. The results confirmed that the treated E. colicells were damaged, showing pit formation on bacterial cellwalls. Recently, Jain and co-workers [10] tested the bacter-ial action of silver nanoparticle-coated polyurethane foam andsuggested its use as an antibacterial water filter. In anotherwork, Hu et al. [29] treated cotton fabrics with a suspensionof silver oxide in chitosan and studied its antibacterial actionagainst S. aureus. Attempts have also been made to coat urinarycatheters with silver compounds to prevent infection [30]. Apartfrom silver, polycationic groups like alkylammonium have alsobeen employed to provide antimicrobial surfaces [31].

The real significance of this work is that if the surfaceof medical prostheses is grafted with polymeric chains, thenthis proposed novel approach may be used to incorporate Agnanoparticles into the grafted polymer network, followed bycitrate reduction, to yield devices with Ag-impregnated antimi-crobial surfaces.

2. Experimental

2.1. Materials

The two monomers used in this study, namely acrylamide(AAm) and acrylic acid (AAc), and the crosslinking agentN,N -methylenebisacrylamide were obtained from HiMediaLaboratories, Mumbai, India. The salts silver nitrate (AgNO3),trisodium citrate (SC), and potassium persulfate (KPS) wereobtained from E. Merck, Mumbai, India, and used as received.Standard cultures of the organisms were provided by the De-partment of Biotechnology. Nutrient broth and Nutrient andm-Endo agars were obtained from HiMedia Chemicals, In-dia. Double-distilled water was used throughout the investiga-tions.

2.2. Synthesis of poly(acrylamide-co-acrylic acid) hydrogels

The hydrogel disks were prepared by carrying out free rad-ical aqueous copolymerization of AAm and AAc using MBAas the crosslinker and KPS as the initiator. In brief, in order toprepare a sample (HG2), 14.08 mM AAm, 5.55 mM AAc and0.32 mM crosslinker MBA were dissolved in water and the finalvolume was made 5 ml. Then, 0.11 mM KPS was dissolved andthe whole reaction mixture was transferred in the test tube (in-ternal diameter 1.5 cm) and kept in an electric oven (Tempstar,India) at 60 ◦C for a period of 2 h. After the polymerization wasover, the test tube was broken and the resulting almost trans-parent hydrogels were cut into slices of same thickness. Thehydrogels were equilibrated in the distilled water for a periodof 2 days to remove the unreacted monomers, crosslinker, andinitiator and finally dried in a dust-free vacuum chamber till thegels attained constant weight. A blank poly (AAm) hydrogel,

V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395 391

HG1, was also prepared by employing the same conditions andcomposition, without AAc.

2.3. Synthesis of hydrogel–Ag nanoparticle composites

The hydrogel disk was equilibrated in the distilled waterfor 24 h followed by its immersion in solution of silver ni-trate (10 mg AgNO3 in 30 ml distilled water) for another 24 h.Then the disk was taken out and put in trisodium citrate solu-tion (20 mg dissolved in 30 ml water) for another 24 h to reduceAg+ ions into silver nanoparticles within the swollen gel. Thedark brown-cum-black color of the disk indicated formation ofsilver nanoparticles. The disk was dried in an electric oven,grinded, and finally sieved with mesh size No. 350 to yield finehydrogel–Ag nanoparticle composites.

2.4. Characterization

The Fourier transformation infrared (FTIR) spectra of plainand silver nanoparticle-loaded hydrogel samples were recordedon a FTIR spectrophotometer (Shimadzu 8400 S) using KBr.Absorption measurements were carried out on a Systron-ics 2201 UV–visible spectrophotometer for well-dispersedhydrogel–silver nanocomposite solutions (1 mg/1 ml) in thewavelength range 400–800 nm. XRD analyses for hydrogel–silver nanocomposites were performed with a Rikagu diffrac-tometer (Cu radiation, λ = 0.1546 nm) running at 40 kV and40 mA. The nanocomposite structural and morphological vari-ations were observed by using a JOEL JSM 840A (Japan)scanning electron microscope (SEM). Scanning electron mi-croscope specimens were prepared by placing 2–3 drops of thehydrogel–silver nanocomposite solution on a silicon wafer anddried in air. Transmission electron microscopy (TEM) imagesof the samples were recorded using a Tecnai F 12 TEM instru-ment. TEM samples were prepared by dispersing 2–3 drops ofgel–silver nanoparticle solution on a copper grid and dried atroom temperature after removal of excess solution using a filterpaper.

2.5. Microbial experimentation

Microbial experimentation was done to find the effect of sil-ver hydrogel particles on gram-negative bacteria E. coli. Forthis purpose approximately 108 colony-forming units (CFU) ofE. coli were cultured on a Nutrient agar plate supplementedwith silver hydrogel particles. Plates, free of silver hydrogelparticles, were used as a control set. The plates were incubatedfor 24 h at 37 ◦C and the numbers of colonies were counted.

3. Results and discussion

3.1. Fabrication of hydrogel–Ag nanoparticles

During the past two decades, a number of different ap-proaches have been employed to obtain better stabilization ofnanoparticles using various polymers, block copolymers, star

Fig. 1. Formation of silver nanoparticles within the swollen co-polymeric net-work.

polymers and dendrimers, microgels, hydrogels, and so on. Re-cently, as noted in the Introduction, there is a lot of interestin producing nanoparticles in the hydrogel networks since theyhave enormous valuable applications in bio-related fields. But,most of the hydrogels and microgels employed for this pur-pose must follow either controlled polymerization paths or havewell-organized networks through the gel structure, which mayincrease the cost of the nanoparticle–hydrogel hybrid materi-als. In contrast, we have developed a facile in situ approach ofnanoparticle synthesis using a conventional hydrogel. The em-ployed hydrogel networks in this study are random copolymersof acrylamide and acrylic acid repeating units throughout thegel macromolecular chains that are constructed with variouscrosslinking junctions. This macromolecular gel network willserve effectively as nanoreactors for silver nanoparticle prepa-ration.

Fig. 1 depicts a clear scheme for the formation of silvernanoparticles within the swollen co-polymeric network. Whena fully swollen hydrogel disk is put in the aqueous AgNO3 solu-tion, there occurs an ion exchange between Ag+ ions present inthe outer solution and H+ ions present within the gel phase. Af-ter equilibrium is attained, the hydrogel disk is transferred intotrisodium citrate solution. This results in a reduction of Ag+

392 V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395

Fig. 2. Photographs of (a) hydrogel, (b) hydrogel–silver nitrate salt composite, (c) and hydrogel–silver nanoparticle composite, respectively.

ions to silver nanoparticles within the swollen network. In thisway an almost uniformly distributed array of silver nanopar-ticles is obtained within the polymer network. Fig. 2 clearlydescribes the change in physical appearance of the hydrogeldisk during the process of formation of silver nanoparticleswithin the network. The hydrogel turns slightly brown due tothe presence of Ag nanoparticles. The most advanced featuresof this methodology are that the formed silver nanoparticlesprovided excellent stability over a longer period of time (at least6 months) inside the hydrogel networks through the carboxylategroups of co-polymeric chains.

3.2. FTIR, UV–vis spectral, and XRD analysis

Using FTIR spectra the formation of Ag nanoparticles insidethe gels was evaluated (figures are not shown). The charac-teristic features of the spectrum of Ag nanoparticle–hydrogelcomposites are almost very similar to those of plain polymer.For example, a broad peak corresponding to –COOH of acrylicacid as well as –NH stretching of acrylamide is observed inthe range 3400–3600 cm−1; a peak corresponding to the car-bonyl group of the amide moiety of the AAm unit is observedat 1691 cm−1 while a characteristic peak at 1726 cm−1 arisesfrom the carbonyl group C=O of poly(acrylic acid) chains.The N–H bending vibration band appeared at 1610 cm−1 forthe plain hydrogel sample but in the case of the Ag–hydrogelnanocomposite it is shifted to 1629 cm−1 in the spectrum. Theinteraction between the nitrogen function of the polymer sup-port and the metal atoms generally results in a blue shift ofthe band corresponding to the nitrogen functions in the FTIRspectra [32]. Therefore, FTIR spectroscopy provides concreteevidence about the mode of binding of Ag atoms with polymersupport in the matrix.

Further, to confirm the formation of silver nanoparticles inthe hydrogel, we carried out UV–visible absorption studies. InFig. 3, a strong characteristic absorption peak around 406 nmis noted for the silver nanoparticles in the gel nanocompos-ite due to the surface plasmon resonance effect. However, theplain poly(acrylamide-co-acrylic acid) hydrogel did not showany such peak. Recently, Mohan et al. [16] produced silvernanoparticles (∼3 nm) within the poly(N -isopropylacrylamide-

Fig. 3. UV–vis spectra of hydrogel (black) and hydrogel–silver nanocomposite(red).

co-sodium acrylate) hydrogels, which have also shown a well-defined surface plasmon resonance around 400 nm. Fig. 4demonstrates the XRD pattern of the silver nanoparticles in thehydrogel networks. In the XRD of hydrogel–silver nanocom-posites, the peaks exhibited at 38.0◦, 44.28◦, 64.46◦, and 77.40◦are assigned to reflections through (111), (200), (220), and(311) planes of the face centered cubic (fcc) of silver nanopar-ticles, respectively. However, poly(acrylamide-co-acrylic acid)hydrogel did not show any such peaks. Therefore, it is very clearthat hydrogel nanocomposite consists of silver nanoparticles.

3.3. Electron microscopy analysis

Scanning electron microscopy images of plain poly(acryl-amide-co-acrylic acid) hydrogel and hydrogel–silver nanocom-posite are depicted in Fig. 5. In Fig. 5A, there can be observeda clear and flat surface of the plain hydrogel. On the other hand,silver nanoparticles are clearly visible not only on the surfaceof the hydrogel–silver nanocomposites (Fig. 5B) but also insidethe networks as is visible in the cross-sectional view in Fig. 5C.

V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395 393

Fig. 4. X-ray diffraction pattern of (A) hydrogel and (B) hydrogel–silver nano-composite.

Fig. 5. (A) SEM image of HG1 hydrogel, (B) silver nanoparticles on the surfaceof HG1, and (C) silver nanoparticles in the hydrogel networks of HG1 (crosssection). Bar indicates 1 µm in all the SEM images.

The reason for the presence of silver nanoparticles inside thegel networks may be attributed to the fact that when silver ions,present on the surface of the swollen gel, are reduced by sodiumcitrate, the silver nanoparticles, so produced, increase the gelporosity, thus providing a pathway for reducing agents to enterinto the bulk to produce nanoparticles. We could not judge the

Fig. 6. (A) TEM image of HG2 (inset SAED pattern) and (B) silver nanoparti-cles distribution in the HG2 hydrogel.

particle size from the SEM analysis because the study was doneon dry nanocomposite sample.

Fig. 6A shows the TEM image of the silver nanoparticlesprepared within the hydrogel with 4.16 mM monomer acid inthe feed mixture. The image indicates nearly uniform distri-bution of silver nanoparticles. In addition, a typical selectedarea electron diffraction (SAED) pattern of a collection of sil-ver nanoparticles is also shown (see inset). The pattern appearsto be a little diffused due to smaller particle size, but three dif-fraction rings are clearly visible and they can be indexed to theface-centered cubic structure of silver as follows. The strongestring and the one closest to the center is probably a combina-tion of the {111} and {200} reflections. The second ring islikely the {222} reflection whereas the outermost and the weak-est third ring are either the {420} and/or the {422} reflections.Almost similar results have also been reported elsewhere [33].The size distributions were obtained by measuring the diame-ter of 35 particles in an arbitrarily chosen area of TEM image(see Fig. 6B). As can be seen, nearly 40% of particles have anaverage diameter of 26 nm and moreover, the distribution curveappears to be more or less symmetrical with all the nanopar-

394 V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395

Fig. 7. Photographs showing bacterial colonies in petri plates containing nano-composites with (A) 0.00 and (B) 5.55 mM acrylic acid.

ticles falling within the narrow range of 12–42 nm. One moreinteresting feature is that the nanoparticles do not seem to formaggregates. This may be due to excellent stabilization of silvernanoparticles by carboxylate anions present in the gel macro-molecular chains.

3.4. Antibacterial property of Ag–hydrogel nanocomposites

As noted in earlier sections, the formation of silver nanopar-ticles within the swollen hydrogel is mainly due to an ion-exchange process. So, it is expected that the sample, preparedwith a higher content of monomer acid in the feed mixture,should contain more silver nanoparticles, and hence shoulddemonstrate greater antibacterial properties. In order to inves-tigate this, we examined the antibactericidal property of twosamples, prepared with 0.00 and 5.55 mM acrylic acid in thefeed mixture, (i.e., samples HG1 and HG2, respectively) underidentical conditions. Fig. 7 clearly demonstrates that formationof bacterial colonies in the presence of nanocomposite HG2 isalmost negligible whereas more population of bacterial coloniesappears in the presence of sample HG1. This may simply beattributed to the fact that Ag nanoparticles are present in lessnumber in the sample HG1 and hence the sample HG1 is inca-pable in retarding the growth of bacterial colonies to a great ex-tent while the sample HG2, which contains a sufficient numberof silver nanoparticles, shows great potential for reducing thebacterial growth under similar conditions. The results also sup-port the proposed mechanism that ion exchange between Ag+ions present in the external AgNO3 solutions and H+ ions pro-duced due to ionization of –COOH groups within the swollenphase is a key factor for the entrapment of Ag+ ions within thepolymer network. Here it is worth noting that the presence ofsilver nanoparticles within the sample HG1 (i.e., without con-taining monomer acid) shows that silver ions, to some extent,must have entered into the swollen network and later on werereduced by sodium citrate. However, the presence of –COO−groups (due to acrylic acid as in sample HG2) becomes a ma-jor driving force for Ag+ ions to enter into the swollen networkthrough Ag+–H+ ion-exchange process. Hence, it may be con-cluded that composition of monomer acid in the feed mixture is

Fig. 8. Photographs of growth of bacterial colonies is the petri dishes containing(A) 200 and (B) 100 µm sized particles.

a key factor governing the bactericidal property of the resultingnanocomposites.

3.5. Effect of particle size on biocidal action

It is expected that size of the Ag hydrogel particles should in-fluence their antibacterial action because change in particle sizeresults in change in surface area which is in contact with thebacterial species. To investigate this, hydrogel–silver nanocom-posites of 100 and 200 µm sized particles were tested for theirantibacterial action against E. coli. The results, as depicted inFig. 8, clearly indicate that 100 µm sized particles show greatertendency to inhibit growth of bacterial colonies as comparedto the particles with size 200 µm. There are nearly 200 CFUsin the control set while this number reduces to 53 and 93 forthe petri dishes containing Ag–hydrogel particles with diameter100 and 200 µm, respectively. Thus, it can be seen that 200 µmsized hydrogel–Ag composite particles are able to reduce thebacterial growth up to 50% while 100 µm sized particles re-duce the colonies growth upto 75% as compared to the controlset. The results may simply be attributed to the fact that 100 µmsized particles possess greater surface area and hence they are incontact with a greater number of bacteria, thus inhibiting theirgrowth more effectively. Therefore it may be inferred that smallsized particles are preferable for obtaining greater inhibition ofbacterial colony growth.

3.6. Effect of silver content on bacterial action

The amount of silver nanoparticles within the hydrogel canbe varied by immersing plain hydrogel disks in silver nitratesolutions of different concentrations followed by citrate reduc-tion. This will of course affect the bactericidal action of Aghydrogel nanocomposites. To investigate this, plain hydrogelsamples HG2 were dipped in silver nitrate solutions, varyingin concentration from 10 to 30 mg/30 ml. A definite amountof nanocomposites so obtained was tested for their antibacte-rial action against E. coli. The results as depicted in Fig. 9clearly indicate that as the concentration of AgNO3 solutionsincreases the antibacterial activity of resulting nanocomposites

V. Thomas et al. / Journal of Colloid and Interface Science 315 (2007) 389–395 395

Fig. 9. Photograph showing growth of bacterial colonies in (A) silver-free con-trol plate; and in plates containing Ag–hydrogel particles, prepared by immer-sion in AgNO3 solution of concentration (B) 10, (C) 20, and (D) 30 mg per30 ml water.

also increases. It is clear that for the nanocomposites, preparedby immersion in 20 and 30 mg/30 ml solutions of AgNO3,the growth of bacterial colonies is almost nil, thus suggest-ing a fair bactericidal activity of their nanocomposites. Thisindicates that optimal concentration of AgNO3 solutions to ob-tain fair antibacterial activity of Ag hydrogel nanocompositesis 20 mg/30 ml. It is also evident that the hydrogel–silvernanocomposites, prepared with 10 mg/30 ml AgNO3 solution,are not so effective in inhibiting bacterial growth.

4. Summary

From the results of the above study it may be concludedthat silver nanoparticles can be produced within the swollenpolymer network. The developed silver–hydrogel nanocompos-ite demonstrates fair antibacterial activity against E. coli. Theirbacterial action depends on size of the particles, amount of sil-ver nanoparticles within the hydrogel, and amount of monomeracid in the feed mixture. The formation of Ag nanoparticleswith in the gel takes place due to entrapment of Ag+ ionsinto the swollen hydrogel network via Ag+–H+ ion-exchangemechanism, followed by citrate reduction. The X-ray diffrac-tion analysis confirms the fcc structure of Ag nanoparticles.In the next part of the study, we propose to graft monomeronto the surface of urinary catheters and then incorporate sil-ver nanoparticles to finally study the antibacterial action of thecatheter surface.

Acknowledgment

The authors thank Dr. O.P. Sharma, Head of the Departmentof Chemistry, Govt. Model Science College (Jabalpur), India,for providing facilities to work.

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