制备含有纳米银粒子的聚乙烯醇水凝胶及纳米银加量对抗菌性能的影响

HaijunYu,1,2XiaoyiXu,1,2XuesiChen,1TianchengLu,1,2PeibiaoZhang,1XiabinJing1StateKeyLaboratoryofPolymerPhysicsandChemistry,ChangchunInstituteofAppliedChemistry,ChineseAcademyofSciences,Changchun130022,People’sRepublicofChina2GraduateSchoolofChineseAcademyofSciences,Beijing100039,People’sRepublicofChina

Received20April2006;accepted14May2006DOI10.1002/app.24835

PublishedonlineinWileyInterScience(www.interscience.wiley.com).ABSTRACT:Thepoly(vinylalcohol)/poly(N-vinylpyr-rolidone)(PVA–PVP)hydrogelscontainingsilvernanopar-ticleswerepreparedbyrepeatedfreezing–thawingtreat-ment.Thesilvercontentinthesolidcompositionwasintherangeof0.1–1.0wt%,thesilverparticlesizewasfrom20to100nm,andtheweightratioofPVAtoPVPwas70:30.Theinfluenceofsilvernanoparticlesontheproper-tiesofPVA–PVPmatrixwasinvestigatedbydifferentialscanningcalorimeter,infraredspectroscopyandUV–visspectroscopy,usingPVA–PVPfilmscontainingsilverpar-ticlesasamodel.Themorphologyoffreeze-driedPVA–PVPhydrogelmatrixanddispersionofthesilvernanoparticlesin

thematrixwasexaminedbyscanningelectronmicroscopy.Itwasfoundthatathree-dimensionalstructurewasformedduringtheprocessoffreezing–thawingtreatmentandnose-riousaggregationofthesilvernanoparticlesoccurred.Waterabsorptionproperties,releaseofsilverionsfromthehydro-gelsandtheantibacterialeffectsofthehydrogelsagainstEscherichiacoliandStaphylococcusaureuswereexaminedtoo.Itwasprovedthatthenanosilver-containinghydrogelshadanexcellentantibacterialability.Ó2006WileyPeriodicals,Inc.

JApplPolymSci103:125–133,2007

1Keywords:silver;hydrogel;antibiotic;wounddressing

INTRODUCTION

Despitemajoradvancesinburnwoundmanagementandothersupportivecareregimens,infectionre-mainstheleadingcauseofmorbidityinthether-mallyinjuredpatients,andthesearchfordifferenttreatmentsandnewideasiscontinuing.1Silvermetalandsilverionshavebeenknownaseffectiveanti-microbialagentsforalongtime,Theapplicationofsilver-bindingmembraneshasrecentlybeensug-gestedtofurtherreducethesilvertoxicity,toretardthemovementofsilverions,andtominimizesilverabsorptionatahealingwound.2–4Therehavebeenseveralkindsofsilver-containingmaterialsthatcanbeusedforwounddressing.Forexample,silversulfadiazinecontainingchitosan-basedwounddressing,5–7dendrimer–silvercomplexesandnanocomposites,8nanosilver/celluloseacetatecom-positefibers,andsilvernylondressingswereallprovedtobeantibacterial.9,10Besideanantibioticability,however,theprincipalfunctionofawounddressingistoprovideanoptimalhealingenviron-ment,e.g.,isolationfromtheexternalenvironment,

Correspondenceto:X.Jing(xbjing@ciac.jl.cn).

Contractgrantsponsor:NationalNaturalScienceFounda-tionofChina;contractgrantnumbers:20274048,50373043.Contractgrantsponsor:ChineseAcademyofSciences;con-tractgrantnumber:KJCX2-SW-H07.

C2006WileyPeriodicals,Inc.V

JournalofAppliedPolymerScience,Vol.103,125–133(2007)

completecoverageofthewoundsurfacetoprevent

furthercontaminationorinfection,andmaintenanceofamoistmicroenvironmentnexttothewoundsur-face.11Hydrogelsconsistofthree-dimensionalhydro-philicpolymernetworksinwhichalargeamountofwaterisinterposed.Becauseoftheiruniqueproper-ties,awiderangeofmedical,pharmaceutical,andprostheticapplicationshavebeenproposedforthem.12Sohydrogelwounddressingsarebetterchoicethanfabricsorfilmsforburninjurytreatment.Manypolymerscanbeusedtopreparehydrogels,suchaspoly(vinylalcohol)(PVA)andpoly(vinylpyr-rolidone)(PVP).PVAisawell-knownbiologicallyfriendlypolymerandhasbeendevelopedforbiomed-icalapplicationssuchasartificialpancreas,13–15syn-theticvitreousbody,16wounddressing,artificialskin,andcardiovasculardevice.17,18PVPisoneofthemostwidelyusedpolymersinmedicinebecauseofitssolu-bilityinwateranditsextremelylowcytotoxicity.19ArecentworkdescribedthetopicalapplicationofPVPontotheskinfortransdermaldeliveryofdrugs.20CombinationofthepropertiesofPVAandPVPinPVA–PVPblendshasledtothepreparationofnewbiomaterials.21,22Inourpreviousstudy,23physicallycrosslinkedPVA–PVPhydrogelswithperfectme-chanicalpropertieswerepreparedbycyclicfreezing–thawingtreatment.

Inthispaper,therefore,greatattemptsaremadetoincorporatesilvernanoparticlesintoPVA–PVPhy-drogelstocombinethegoodmechanicalstrengthof

126PVA–PVPhydrogelwounddressingandthepower-fulantibacterialabilityofnanosilvertogether.Theformulationandpropertiesofthisnovelwounddress-ing,theinvitroreleaseprofilesofthesilverionsfromthehydrogelandtheantibacterialactivityagainstGram-negativeEscherichiacoli(E.coli)andGram-posi-tiveStaphylococcusaureus(S.aureus)arereported.EXPERIMENTAL

Materials

Polyvinalalcohol(PVA)withahydrolysisdegreeof99.0–99.8%(molecularweight¼7.3Â104–7.7Â104)wassuppliedbyShanghaiChemicalReagentCom-pany¼3.6(Shanghai,Â105China).PVP(molecularweight)waspurchasedfromBASFChemicalCo.(Ludwigshafen,Germany).Thesepolymerswereusedwithoutfurtherpurification.Silvernitrate(AgNO3),sodiumcitrateandallotherreagentswereofanalyticalgradeandusedwithoutfurtherpurifi-cation.Distilledwaterwasusedassolventinallexperiments.

Preparations

Preparationofsilversols

ThesilvernanoparticleswerepreparedbysodiumcitratereductionofAgNO3.24Typically,18mgofAgNO3wasdissolvedin100mLofdistilledwaterandbroughttoboiling.Twomillilitersof1%solu-tionoftrisodiumcitratewasadded,andthesolutionwaskeptonboilingfor$1h.TheAgsolpreparedwasgreenishyellow.

PreparationofAg/PVA–PVPcompositehydrogelsAPVA–PVPaqueoussolutionwasaddedintothepreparedAgsol.ThetotalconcentrationofPVAandPVPwas$12wt%andthePVA-to-PVPweightratiowas70:30.TheweightcontentsofsilverwithrespecttothePVA–PVPamountusedwere0.1,0.2,0.4,0.8,and1.0wt%,respectively.Themixtureso-lutionwasputintothewellsofa24-wellplateandwasfrozenat(À208Cfor12handthenthawedat258Cfor12h.Thistreatmentwasrepeatedforthreetimesandhydrogeldisksofabout3mminthicknesswereobtained.Thetotalsolidcontentinthehydro-gelswas12wt%.

PreparationofAg/PVA–PVPcompositefilmsToinvestigatetheinteractionbetweensilverandPVA–PVPmatrix,nanosilver/PVA–PVPcomposite

YUETAL.

filmswerepreparedasmodelsforAg/PVA–PVPhy-drogels.ThemixturesolutionswerepreparedbythesamemethodasforAg/PVA–PVPhydrogelsbutthetotalconcentrationofPVAandPVPwas$1wt%.Thenthemixturesolutionswerecastontoglassslidesanddriedinvacuumfor24hat608Ctoobtainthecompositefilmsofca.100mminthickness.Characterization

Structureandmorphology

UV–VisspectraofthesilversolsandtheAg/PVA–PVPfilmswerecollectedusingaUV-2400spectro-photometer(2100,Shimadzu,Kyoto,Japan)withaslitwidthof2.0nm.Thesizedistributionofthesil-vernanoparticleswasmeasuredusingatransmissionelectronmicroscope(TEM-20100TOEL,Tokyo,Japan)andadynamiclightscatteringinstrument(DLS)withaverticallypolarizedHe–Nelaser(DAWNEOS,WyattTechnology,SantaBarbara,CA)atafixedscatteringangleof908andataconstanttemperatureof258C.ThestructuresoftheAg/PVA–PVPfilmswerecharac-terizedbyFouriertransforminfraredspectroscopy(FTIR,BrukerVertex70,Ettlingen,Germany).Adiffer-entialscanningcalorimeter(DSC-7,Perkin–Elmer,Nor-walk,CT)wasemployedtodetectthecrystallinestatusinthenanoAg/PVA–PVPfilmsoverthetemperaturerangeof50–2408Catascanningrateof108C/minundernitrogenprotection.Thesurfaceandcrosssec-tionmorphologyofthefreeze-driednanoAg/PVA–PVPhydrogelswasexaminedusingafieldemissionscanningelectronmicroscope(FE-SEM,FEI/Philips,Hillsboro,OR).Watertake-up

Thepreparedhydrogelplateswereimmersedindis-tilledwaterof200-foldsmassat378Cfor24h,23thentheyweretakenoutandweighedafterremovalofthefreewateronthesurfaceswithfilterpaper.Theequilibriumswelling-ratio(ESR)wascalculatedby

ESRð%Þ¼ðWeÀWdÞ=WdÂ100%

whereWewastheweightoftheswollengelinequi-libriumstateandWdwasthesolidweightinthehydrogel.

Releaseofsilverionsfromthehydrogels

TheinvitroreleaseprofilesofsilverionsfromthehydrogelswereobtainedbythemethoddevelopedbyRadheshKumar.25Briefly,thehydrogelsof0.3gwasstoredinaflaskcontaining10mLaqueousme-dium(9.5mLdistilledwaterþ0.5mL0.1NHNO3)at378Candtheflaskwasoscillatedatafrequencyof

PVA–PVPHYDROGELSCONTAININGSILVERNANOPARTICLES127

Figureticlesprepared1TypicalbysodiumTEMmicrographcitratereductionofthesilverofAgNOnanopar-3.

60rpminarotaryshaker.HNO3wasaddedtopro-tectthereleasedAgþionsfrombeingreducedtome-tallicsilver.Theconcentrationsofsilverionsreleasedfromthehydrogelsintothewaterweremeasuredusinganinductivelycoupledplasmaatomicabsorb-ancespectrometer(SPS-1500VR,SeikoInstruments,Tokyo,Japan).

AntibacterialPVA–PVPhydrogels

abilityofthenanoAg/AntibacterialtestwasperformedbymodifiedKirbyBauertechniqueandLBbrothmethod.26Followingtwomicroorganismswereused:S.aureusstrain209,ATCC25,923,whichisGram-positiveandcanexistonthebodysurfaceofmammals;E.coli,ATCC25,922,whichisGram-negativeandisawidespreadintestinalparasiteofmammals.Thebacteriawerecultivatedat378CinsterilizedLBbroth(peptone10g,yeastextract5g,NaNO310g,distilledwater1000mL)at90rpminarotaryshakerfor16h.InthemodifiedKirbyBauermethod,adropletof50mLbacteriamediumwasdispensedontoanagarplate,thenthehydrogeldiskswereplacedandtheincuba-tionwascontinuedfor24hat378C.IntheLBbrothmethod,thehydrogeldisksof0.3gwereputintheflasks,whichcontained10mLaqueousmediumat378Candwereoscillatedatafrequencyof60rpmforperiodsrangingfrom1to96h.Then3.0mLoftheaboveaqueoussolutionwasmixedwith3.0mL

ofthebacteriamedium,theincubationwascontin-uedforanother6h.CulturewithpureLBbrothservedascontrol.Theopticaldensity(OD)ofthebacterialbrothmediumat600nmwasmeasuredbyaUV–visspectrophotometer.TheinhibitionratiosforthenanoAg/PVA–PVPhydrogelswerecalcu-latedasfollows:

Inhibitionratioð%Þ¼100À100

ÂðAtÀA0Þ=ðAconÀA0Þ

whereA0wastheODforbacterialbrothmediumbeforeincubation;AtandAconweretheODsforhydrogelandcontrolsampleafter6hincubation,respectively.

RESULTSANDDISCUSSION

Silvernanoparticles

Thesilvernanoparticleswerepreparedasananosil-versolorasilvercolloidbyreducingAgNO3withsodiumcitrate.TheirTEMimageisshowninFigure1.Theiraveragesizeisabout100nm.Theirsurfacesaresmooth.Figure2showstheirdiameterdistribu-tiondeterminedbyDLS,rangingover30–170nmwithanaverageof100nm.AtypicalabsorptionspectrumofthesilvercolloidalsolutionisshowninFigure3(a).AccordingtoRef.27,thisbandisassignedtothesurfaceplasmonabsorption(SPR)ofthenanosilverparticles.Itpeaksat425nmandhasabandwidthathalfmaximumof$130nm,whichisanindicationoftheparticlesizedistribution.

Figuredetermined2SizebyDLSdistributionmeasurement.

ofthesilvernanoparticles128Figuresol3UV–visabsorptionspectraofas-preparedsilver(b–e).inwater(a)andnanoAg/PVA–PVPcompositefilms(e)1.0Silverwt%.

contents:(b)0.2wt%;(c)0.4wt%;(d)0.8wt%;Ag/PVA–PVPcompositefilms

Toinvestigatepossibleinteractionsbetweenthesil-vernanoparticlesandthePVA–PVPmatrixintheAg/PVA–PVPcompositehydrogelsandtounder-standtheinfluenceofthesilvernanoparticlesonthestructureandperformanceofthehydrogels,compos-ite,Ag/PVA–PVPfilmswerepreparedinthepres-entstudyasamodelofAg/PVA–PVPhydrogels.Thesamemixturesolutionswereusedforbothcom-positefilmsandcompositehydrogels.Therefore,themodelfilmshavethesamesolidcompositionasthecompositehydrogels.Becausethereisnointerfer-enceofwaterinthemodelfilms,theycanbeeasilycharacterizedbyvarioustechniques.

Figure3alsoshowstheUV–visspectraoftheAg/PVA–PVPcompositefilms.TheSPRbandsoftheAg/PVA–PVPcompositefilmsshowdifferentpeakpositionsandpeakwidths.Forthefilmscontaining0.2,0.4,0.8,and1.0wt%ofnanosilver,thebandspeakat410,419,425,and443nm,respectively.ComparedwithFigure3(a)forthepuresilvercolloi-dalsolution,thefirsttwoshowblue-shiftswhiletheothertwoshowred-shifts.Amongthefourcompos-itefilms,onlytheonecontaining1.0wt%ofsilvershowscomparablebandwidth(160nm)tothecol-loidalsolution,therestthreegivenarrowerbandwidths(70–130nm).IthasbeenprovedthatPVAandPVParebothgoodstabilizingagentsforsilvernanoparticles.27,28Sotheblue-shiftsandthenar-rowerwidthsoftheSPRbandscanbeexplainedasthesmallersizeandmoreuniformsizedistribution

YUETAL.

ofthesilvernanoparticlesinthefirsttwocompositefilmsandthered-shiftsandwiderwidthindicatetheoppositevariations,whichcanbeinducedbyag-glomerationoftheAgnanoparticlesand/orchangeofthedielectricpropertiesofthesurroundingenvi-ronment.29Thiscanbefurtherexplainedbyconsid-eringtheinteractionsbetweenthenanosilverandthePVA–PVPmatrixinthefollowingdiscussions.AsseeninFigure4,anincreaseofthesilvercon-tentintheAg/PVA–PVPcompositefilmsleadstoenhancementofthe1145cmÀ1bandforthefilmscontaining0.1and0.2wt%ofnanosilverandtoweakeningofthesamebandforthefilmscontainingmorenanosilver.ThisbandcanbeassignedtoCÀÀOstretchingvibrationofPVA.ItisameasureoftheinteractionbetweenPVPandPVA.Itsenhancementandweakeningwithsilver-contentrevealinvolve-mentofthenanosilverintheinteractionbetweenPVPandPVA.

TheDSCtracesofpurePVA–PVPandnanoAg/PVA–PVPcompositefilmswithvariouscontentsofsilverareshowninFigure5.Themeltingtempera-tures(Tm),glasstransitiontemperatures(Tg)andmeltingenthalpies(DHm)ofthevarioussamplesarelistedinTableI.Sureenough,theTm,Tg,andDHmallshowsimilarvariationswithincreasingnanosil-vercontent,i.e.,increasing(TgandDHm)ordecreas-ing(Tm)forthefilmscontaining0.1,0.2and0.4wt%ofnanosilverandchangingreverselyforthosefilmscontainingmorenanosilver.ItisnoticedthatallAg/PVA–PVPfilmsshowmoreDHmthanthePVA–PVPfilm.TheseresultsdifferfromthatreportedbyZ.H.Mbheleetal.29Intheirstudy,incorporationofsilverparticles,withaveragediameterof5nm,intothePVAmatrixledtoadramaticdecreaseinTmandincreasein

FigurePVA–PVP4FTIR0.2,0.4,0.8,compositespectraand1.0wtfilmsofpurePVA–PVPandnanoAg/%).

withdifferentAgcontents(0.1,PVA–PVPHYDROGELSCONTAININGSILVERNANOPARTICLES129

FigurePVA–PVP5DSC(ForcompositecurvesfilmsofpurewithvariousPVA–PVPcontentsandnanoAg/ofsilverHeatingclarity,ratecurves108C/min).

arepresentedintherange180–2308C.Tgbothbymorethan208Cbutdidnotaffectcrystallin-ityinPVA.TheyexplainedtheobservedeffectsasthereducedmobilityofthePVAchainsattachedtothesur-faceoftheAgnanoparticles.ToexplaintheaboveresultsofUV–vis,FTIR,andDSCobservations,wehavetoconsiderthepossibleinteractionsintheAg/PVA–PVPsystems,i.e.,thosebetweenPVAandPVP,betweenPVAandnanosilver,andbetweenPVPandnanosilver.Inthepreviouswork,23weprovedthatthecrystallinityofPVAinPVA–PVPhydrogelsdecreasedwithincreasingPVPcontent,becauseoftheinterfer-enceofPVPtothecrystallizationofPVA.ItseemsthatthePVPhasstrongerinteractionthanthePVAdoeswiththesilverparticles.WhensilverparticlesareaddedintothePVA–PVPmatrix,theyinteractwiththePVPmoleculespreferentially,theinteractionbetweenPVAandPVPmoleculesisweakened,whichresultsintheimprovementofthecrystallinityofPVAinthecomposite(indicatedbytheincreaseofDHm).Ontheotherhand,interactionsbetweenthesilverparticles

MeltingandGlassEnthalpyTransition(DHTABLEMeltingI

m),PeakTemperature(Tm),andAg/PVA–PVPTemperatureComposite(Tg)ofFilms

PurePVA–PVP

Ag(wt%)

Tg(8C)Tm(8C)DHm(J/g)088.3216.425.50.188.7215.431.60.290.621333.10.495208.928.30.887.1210.4321

88.6

214.7

34

FigurenanoAg/PVA–PVP6WaterabsorptionabilityofpurePVA–PVPtentsofsilver.

compositehydrogelswithvariouscon-andandthePVAmoleculesstillexist,somobilityofthePVAchainsattachedtothesurfacesoftheAgparticlesisreduced.29Whensilvercontentis0.4wt%,thelowestTmandhighestTgareobtained.Furtherincrementofthesilvercontentresultsinaggregationofthesilvernano-particles,weakeningoftheirinteractionswithbothPVAandPVP,andenhancementoftheinteractionbetweenPVPandPVA.ThisisinaccordancewiththeFTIRdata.Onthebasisoftheaboveresults,wecandrawaconclusionthatsilverparticlescouldbeequablydis-persedinthePVA–PVPhydrogelmatrixduetotheirinteractionwiththePVA–PVPmatrix.Therefore,PVA–PVPhydrogelcouldbeusedasaneligiblesil-vernanoparticlecarriertopreparesilver-containinghydrogelsusedforwounddressing.Ag/PVA–PVPcompositehydrogelsWaterabsorption

Besidesgoodmechanicalproperties,ahydrogelwounddressinghastoabsorbtheexudatesonthewoundsurfaceandprovideawetenvironmentforthewound.Sothewaterabsorbingandkeepingabil-ityofhydorgelsisveryimportant.Water-take-upabilityoftheAg/PVA–PVPhydrogelsisshowninFigure6.Itcanbefoundthatallhydrogelsshowaswellingratioashighas40folds,whichisenoughforhydrogelwounddressings.Theincorporationofthenanosilverinthehydrogeldoesnotinfluencethewaterabsorptionability.SEManalysis

Itiswellknownthataporoussurfaceisimportantforthetransportofoxygenfromoutsidetoinsideof

130YUETAL.

Figure7SEMimagesofpurePVA–PVPandnanoAg/PVA–PVPcompositehydrogels.(a)surfaceimageofPVA–PVPhydrogelplate;(b)surfaceimageof0.1wt%Ag/PVA–PVPhydrogelplate;(c)surfaceimageof0.8wt%Ag/PVA–PVPhydrogelplate;(d)cross-sectionimageof0.1wt%Ag/PVA–PVPhydrogelplate;(e)cross-sectionimageof0.8wt%Ag/PVA–PVPhydrogelplate.

PVA–PVPHYDROGELSCONTAININGSILVERNANOPARTICLES131

thewounddressing,andathree-dimensionalnet-workstructureiscrucialtoabsorbingandkeepinglargeamountofwaterinhydrogelmaterials.Weexaminedthesurfaceandcross-sectionalmorpholo-giesofAg/PVA–PVPcompositehydrogelsbySEM.AsshowninFigure7,poroussurfacemorphologyandthree-dimensionalnetworkstructureinthecrosssectionareformedinbothPVA–PVPandAg/PVA–PVPhydrogels.Nodistinguisheddifferenceisfoundforthehydrogelswithdifferentsilvercontents.Noseriousaggregationofthenanoparticlesisobservedevenwhenthesilvercontentisupto1wt%.ThiscanbeexplainedasastablenetworkstructureformedinthehydrogelsandthestronginteractionbetweenthesilverparticlesandthePVAandPVPmoleculesaswehavediscussedintheprevioussection.InvitroreleaseofsilverionsfromthehydrogelsTheantimicrobialactivityofsilverisdependentonthesilvercationAgþ,whichbindsstronglytoelec-tron-donatinggroupsinbiologicalmoleculescon-tainingsulfur,oxygenornitrogen.Hencethesilver-basedantimicrobialpolymershavetoreleasetheAgþtoapathogenicenvironmenttobeeffective.InthisworkthesilverreleasemodeldevelopedbyRadheshKumarwasemployed,andatomicabsorp-tionspectroscopy(AAS)wasusedforthequantita-tivedeterminationofthesilverionreleasedfromthehydrogels.25FiveAg/PVA–PVPhydrogelsampleswithsilvercontentsof0.1,0.2,0.4,0.8,and1.0wt%withrespecttototalPVA–PVPweightwereused.Thedurationof96hwasselectedforthereleaseexperimenttostudythewholereleaseprocessofthesilverions.AsshowninFigure8(A),thereleaseofsilverionsfromthehydrogelsisveryquickatthebeginningandthenbecameslowerandslower.Thesilverionreleaseshowsdependencetosomeextentonthesilvercontentinthehydrogels.Forexample,theamountofsilverionsreleasedinthefirst12hincreaseswithincreasingsilvercontentinthehydro-gels,being0.20,0.45,1.35,3.76,and6.26ppmforthesamplescontaining0.1,0.2,0.4,0.8,and1.0wt%ofsilvercontent,respectively.Whenthesilverioncon-centrationreleasedisplottedagainstsquarerootofincubationtimeh1/2[Fig.8(B)],linearrelationshipsareobtained,exceptfortheinitialstagesofsoaking.Thisindicatesthatthereleaseofsilverionsiscon-trolledbytheinterdiffusionoftheionswithinthehydrogel.30Invitroantibacterialeffect

UsingamodifiedKirbyBauertechnique,thebacteri-cidaleffectsoftwoAg/PVA–PVPhydrogelsandpurePVA–PVPhydrogelwereevaluatedcompara-

Figurecomposite8SilvertheconcentrationconcentrationhydrogelsionreleaseofsilverwithionvariousprofilesreleasedcontentsofnanoAg/PVA–PVPversusoftime;silver:(B)(A)thetime.%;(n)(&0.1)1.0wtwtof%.

%;silver(!)ion0.8wtreleased%;(~versus)0.4wtsquare%;(l)root0.2wtoftively.26After24hincubationat378C,theAg/PVA–PVPhydrogelsshowedantibacterialeffectonGram-positiveS.aureusandGram-negativeE.coli.Thediameterofinhibitionzoneforthe1.0wt%Ag/PVA–PVPhydrogelisslightlylargerthanthatforthe0.2wt%Ag/PVA–PVPsample(seeFig.9).Asacontrol,thepurePVA–PVPhydrogelshowednoinhibitionability.Elementalsilverhasbeenbelievedtofunctionantimicrobiallyeitherasareleasesystemforsilverionsorasacontact-activematerial.31Inthepresentstudy,theAg/PVA–PVPhydrogelsseemtobeonlycontact-active.Thediffusingabilityofthesil-verionsonagarplatemighthavebeenlimitedbytheformationofsecondarysilvercompounds,whichisthelimitationoftheKirbyBauertechniqueasaquantitative32tooltodeterminetheantimicrobialac-tivity.Therefore,LBmediummethodwasintro-

132ducedtodeterminetheantimicrobial26activityofAg/PVA–PVPhydrogelsquantitatively.PurePVA–PVPhydrogelandfourAg/PVA–PVPsamples(Agwt%¼0.1,0.2,0.4,and1.0,respectively)weretested.AsshowninFigure10,theantibioticabilitytoE.coli,expressedasinhibitionratio,wasenhancedwithincreasingsilvercontentinthehydrogels.Whenthesilvercontentwas1.0wt%,theinhibitionratioreachedupto90%.

CONCLUSIONS

ThePVA–PVPhydrogelscontainingsilvernanopar-ticleswerepreparedthroughrepeatedfreezing–

FigureS.(b)aureus9(B)AntibacterialaftertestresultsforE.coli(A)andPVP0.2wt%Ag/PVA–PVP24hincubation.hydrogel;(a)(c)PVA–PVP1.0wt%hydrogel;issue,hydrogel.whichisavailable[Colorfigureatwww.interscience.wiley.com.]

canbeviewedintheAg/PVA–onlineYUETAL.

Figureabilityhydrogelsto10E.Quantitativeincoli6hofduration.

thepureevaluationPVA–PVPofandinvitroAg/PVA–PVPinhibitionthawingtreatment.Thesilvercontentwithrespecttothepolymersusedwasintherangeof0.1–1.0wt%.Thesilverparticlesizewasfrom20to100nmasmeasuredbyTEMandSDLS.ByusingPVA–PVPfilmscontainingsilverparticlesasamodel,theinflu-enceofsilvernanoparticlesonthepropertiesofPVA–PVPmatrixwasinvestigatedbyUV–vis,DSC,andFTIR,themorphologyoffreeze-driedPVA–PVPhydrogelmatrixanddispersionofthesilvernano-particlesinthematrixwasexaminedbySEM.Itwasfoundthatathree-dimensionalstructurewasformedduringtheprocessoffreezing–thawingtreatmentandnoseriousaggregationofthesilvernanopar-ticlesoccurred.Waterabsorptionproperties,thereleaseofsilverionsfromthehydrogelswereinves-tigated,andtheantibacterialeffectsofthehydrogelsagainstE.coliandS.aureuswereexaminedbymodi-fiedKBmethodandLBbrothmethod.Itwasprovedthatthenanosilver-containinghydrogelshadanexcellentantibacterialperformance.

WethankProfessorShanChenofNortheastNormalUniversityinChinaforprovidingthemicroorganismsS.aureusandE.coli.

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