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Journal of Particle Science and Technology 3 (2017) 71-77

Journal of

Particle Science and Technology

J | P | S | T

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H I G H L I G H T S G R A P H I C A L A B S T R A C T

A R T I C L E I N F O A B S T R A C T

I R O S T

Gamma irradiation induced surface modification of silk fabrics for antibacterial application

Sahar S. El Sayed, Amal A. El-Naggar*, Sayeda M. Ibrahim

Department of Radiation Chemistry, National Center for Radiation Research and Technology, P. N. 13759, Cairo, Egypt

• Fabricswerecarriedoutbycoatingwith silver nanoparticles (AgNPs)stabilizedwithpolyvinylpyrrolidone(PVP)throughγ-irradiation.

• The AgNPs-coated silk fabricsdemonstrated an excellentantibacterial activity against thetested bacteria, Escherichia coliandStaphylococcus aureus.

• This work offers potentials toproduce specific AgNPs-coatedantimicrobial silk for variousapplicationsinthetextileindustry.

Article history:Received29March2017Revised7June2017Accepted4November2017

Keywords:SilkSilvernanoparticleAntibacterialactivitySurfacemodificationγ-Irradiation

Silk fabrics were modified by a treatment of silver nitrate solution (AgNO3) andpolyvinylpyrrolidone (PVP) as a stabilizer then exposure to γ-irradiation to createantibacterialproperties.Effectsoftheabsorbeddoseontreatedfabricswereinvestigated.Thescanningelectronmicroscopy(SEM)andX-raydiffraction(XRD)patternswereusedtoconfirmthepresenceofsilvernanoparticles(AgNPs)onthefabric.ThetreatedfabricsshouldhaveenhancedthermalstabilityduetothepresenceofAgNPs.Thetreatedsilkfabricwasexaminedforitsantibacterialactivitytowardvarioustypesofbacteria.TheAgNPs-treatedsilkfabricsdemonstratedexcellentantibacterialactivityagainstthetestedbacteria,Escherichia coliandStaphylococcus aureus.ThisworkopensthedoorforproductionofspecificAgNPs-silkasatypeoftextileintheantibacterialdomain.

* Corresponding author. Tel.: +202-22749298 ; fax: +202-22749298 ; E-mail address: [email protected]: 10.22104/JPST.2017.2090.1074

S. S. El Sayed et al. / Journal of Particle Science and Technology 3 (2017) 71-77

1. Introduction

Asanaturalproteinfiber, silkpossesses a structurevery similar to human skin with smooth, breathable,soft, non-itching and antistatic characteristics [1];however, bacteria can easily adhere and grow onsilk fabric causing deformation and degradation[2]. So, it is necessary to produce a silk fiber havingantimicrobialactivitywhichcanbeusedinawiderangeofapplications.Theantimicrobialfinishingcanbeusedfor fabrics andclothes used inhospital andcrowdedpublicareasortextilesthatareleftwetforalongperiodoftimebetweenprocessingsteps.Finally,theuseofthisfinishinginintimateapparel,underwearandsockscanpreventunpleasantodors[3].As advances in nanotechnology have been made,

numerous nanomaterials with various structuresand unique properties have been fabricated [4-9].Researchers have recently become interesting in theimmobilizationoffiberswithnanomaterialstoproducemultifunctional textiles. Since the silver nanoparticle(AgNP)isatypicalnanomaterialwithbroad-spectrumantibacterialeffectsonbothGram-negativeandGram-positive bacteria [10,11], it has been utilized to treatsilk fibers for antimicrobial properties [12-15]. Theantimicrobial properties of silver particles have beenexploited for a long time in biomedical textiles as itsbroad-spectrum action is particularly significant inpreventing polymicrobial colonization associatedwith hospital-acquired infections [16,17]. Silver hasrevealed bactericidal activity against a wide range ofGram-positive and Gram-negative bacteria, namelyPseudomonas aeruginosa, S. aureus, Staphylococcus epidermidis, E. coli and Klebsiella pneumonia [18].TheAgNPs interactwith the bacterialmembrane andare able to penetrate inside the cell.ThemechanismsofinteractioninvolveAgNPsattachingtobacterialcellmembranes, which increase permeability and disturbrespiration.Another advantage ofAgNPs is that theyareeasilyembeddedintothefibers’polymericmatrices[19,20].Various polymers, such as polyamide, polyvinyl-

pyrrolidone, and polyacrylic acid, were employedto functionalize the silk surface [21-23] to produce ahydrophiliccharactertoincreasetheadsorptionamountofAg+,whichsubsequentlyreducedtoAgNPs[11,24].Antibacterialfabricscanbeusedtomakebandages,

gauze,bedsheets,andsurgicalclothes[25,26].

MohammadMirjaliliet al.impartedanantimicrobialfinishingtocellulosefabricusingananosilversolution[27].The surface characteristicsof these fabricshavebeen studiedby scanningelectronmicroscopy (SEM)whichindicatedsilvernanoparticleswerewelldispersedonthefabricsurface.Anantibacterialtest,usingGram-negative bacteria (Escherichia coli), was used toestimatethebiologicalactivityofthetreatedfabrics.Wasif A. I. and Laga S. K. studied antimicrobial

finishing on cotton woven fabric using a nano silversolutionasanantimicrobialagentagainstGrampositive(Staphylococcus aureus) and Gram-negative bacteria(Escherichia coli), at various concentrations in thepresenceofpolyvinylalcohol(PVOH)[28].Theyfoundthatthehighertheconcentrationofantimicrobialagentthe larger the zone of inhibition in the cases of bothGram-positive and Gram-negative bacteria. Variousproperties like tensilestrength,bending length,creaserecoveryangle,andzoneofinhibitionwerealsostudied.In this study, we prepared silk fabrics treated with

AgNPs via γ-ray irradiation. SEM, XRD, and TGAwere used to confirm the properties of these treatedfabrics.The antimicrobial finishwas applied tomakesilkfabricsmoresuitableforindustrialapplications.

2. Experimental

2.1. Materials

Silver nitrate, crystal, andACS,M.W. 169.87, wasobtained from GAMMA, Laboratory Chemicals.Polyvinylpyrolidone(PVP),M.W.40000,wassuppliedfromUniversalFineChemicalsPVT.LTD, India.Allthematerialswereusedwithoutfurtherpurification.Silkfabric was kindly supplied byAl Khateeb Company,Akhmen,Egypt.

2.2. Treatment of silk fabric

Approximately 60 g of washed silk fabrics wereirradiated in 500ml of 3mMAgNO3 solution usingthe stabilizer of 1.0% Polyvinylpyrrolidone (PVP) inthedoserangefrom5to20kGyofgammairradiationat the National Center for Radiation Research andTechnology,Cairo,Egypt.Afterwards,sampleswererinsedwithwateranddried

at40°Cfor40min.Asimilarprocedurewasappliedfor40repeatedwashes.

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3. Characterizations

Samples (silk treatedwithAgNPs)weredigested inconc.Nitricacid69%(Anular)andH2O2ina5:1ratiousingaMicrowaveDigesterInstrument,Milestone1200Miga,Italy[29].TheAgelementwasestimatedusinganAtomicAbsorptionSpectrometer,ThermoScientificE3000series,England.Tensile(tensilestrengthand%elongation-at-break)propertiesweredeterminedusingaMecmesin,(Model10-1)UK,equippedwithsoftwareandacrossheadspeedof50mm/min.Allmechanicalparameters were directly calculated. The samples fortensile measurements were dumbbell shaped witha width of 4mm and length of 50mm. The surfacemorphologyofthemodifiedsilkfabricsincomparisonwithunmodifiedsilkfabricswasexaminedbySEM.Themicrographswere takenwith a JSM-5400 instrumentmanufactured by Joel, Japan.AnXRDexperiment ofthesampleswasperformedatroomtemperatureusingaPhilipsPW1390diffractometer(30kV,10mA)withcopper target irradiation at a scanning rate of 80/minina2Өrangeof400-900oC.ThermalcharacteristicsofAgNPs treated silk fabricswere determined from thethermogravimetricanalysis(TGA)data,usingaTGA-30apparatus(atShimadzu,Kyoto,Japan),ataheatingrateof10oC/min.inair,overatemperaturerangefromroomtemperatureto600oC.

4. Antibacterial activity testing

A disk diffusion test, according to the Kirby Baurmethod[30],wasappliedtoidentifythebacterialeffectthroughthemeasurementsofbacterialbroth.Aknownquantityofbacteriawasgrownovernightonagar(solidgrowth media) plates. The samples were placed inPetri-dishes and then incubated for 24 hr at 30-32oC.Theinhibitionzonewasthenmeasuredincmfromonesideof thesquaresample.Bothpositiveandnegativebacteria,Escherichia ColiandStaphylococcus aurous,weretested.

5. Results and discussions

5.1. Measurement of silver content on the treated silk fabrics

Theamountofsilvercontentonthetreatedsilkfabricswascalculated.Figure1showstherelationshipbetween

theabsorbeddoseandsilvercontent.TheresultsobtainedfromthisfigureindicatethatthecontentofAgNPsonthesilkfabricsincreasesastheabsorbeddoseincreasesupto10kGythentendstoleveloff.AmaximalvalueoftheAgNPscontentonfabricswasfoundtobe177ppmforthesilkfabricsina3mMAgNO3solutionirradiatedwithanabsorbeddoseof10kGy.

Fig. 1. Relationship between the content of AgNPs on the silkfabricsandirradiationdose.

TheformationofAg+ionswasaresultofsilkfabricstreatedwiththeAgNO3solution.TheseAg+ionswerereduced to Ag atoms and simultaneously depositedonthesilkfabrics.TheinteractionbetweenfibersandmetallicAgNPsstabilizedbyPVPpolymercausedtheformation of a chemical bond between the silver andalcoholic groups of silk and resulted in the physicaladsorptionofAgNPsonthefabricsurface[31].

5.2. Mechanical properties

Mechanical properties of the treated silk fabrics interms of tensile strength (TS) and elongation (E,%)in the dose range from 0 to 20 kGy were plotted inFigures2and3.Theresultsshowthattensilestrengthandelongationatbreak(%)oftheAgNPstreatedsilkfabricsareslightlyaffectedatthedoses(5-20kGy)incomparison with the control silk fabrics. The resultsshowedthattensilestrength(TS)oftheAgNPstreatedsilkfabricsirradiatedwith5kGyexhibitslightlylowertensilestrengththanthecontrolsilkfabricasshowninFigure2.Whereas,thestrainvalueofthetreatedfabricat the samedosewasmore than that of theuntreatedfabricasshowninFigure3.Theresultsobtainedfromthis figure indicate that the treatment process did notalterthemechanicalpropertiesofthesilkfabric.

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5.3. Scanning electron microscopy (SEM) of untreated and treated silk fabrics

Thesurfacemorphologyofuntreatedandtreatedsilkfabricsirradiatedtodifferentdoses(5and10kGy)wasinvestigatedbySEM(Figure4a,b,andc).(a)showsthesurfacemorphologyofuntreatedfabric,whichappearedsmoothandhomogeneous.Figure4(b,andc)illustratesthe surface morphology of silk fabric treated withsilverNPs,which appeared roughand full of particleaggregatesduetotheimbeddingofAgNPs.Itwasnotedthatafterirradiationto5kGyinAgNO3solution,someoftheAgNPswereagglomeratedandthereforecausedthe formation of large nanoparticles dispersed on thefabricsurface.Astheirradiationdoseincreasedfrom5kGyto10kGy,theaggregationoftheAgNPsincreases[32].TolimitthesideeffectsofAgNPsaggregation,a

Fig. 4. SEM of untreated and AgNPs-treated silk fabrics withdifferentgammairradiationdoses,a)Originalsilkfabric,b)5kGy,c)10kGy.

low irradiation dosewith efficientAgNPs productionis preferred for obtaining homogeneously dispersedAgNPs on the surface.

5.4. XRD of untreated and treated silk fabrics

XRD patterns of untreated and treated silk fabricswithAgNPs are shown in Figure 5 (a, b and c).Thesilkfabricshadacrystallinepeaklocatedat2Ө=20.28o

[33].Figure(5a)showsthereisnosignificantchangein this peak after the treatment; this suggests that thegammairradiationandAgNPsattachmentdonotalterthestructureofthesilkfibers.(Figure5bandc)showsfournewpeaksat2Өvaluesof38.4oC,44.6oC,64.7oCand77.5oCweredetected,whichwereattributedtothediffraction peaks of the (111), (200), (220) and (311)planes of silver NPs, respectively [34]. The XRDpattern clearly indicates that AgNPs were depositeddirectlyonthesilksurfaceandthesilkfabricstreatedwith AgNPs were successfully prepared using silvernitratebyradiation.

5.5. Thermogravimetric analysis (TGA) of untreated and treated silk fabrics

Thermalbehaviorofuntreatedandtreatedsilkfabricsinatemperaturerangefromroomtemperatureto600oCatallgammairradiationdoses(5-20kGy)areshowninFigure6.Itcanbeseenthatthethermaldecomposition

Fig. 2. EffectofdifferentirradiationdoseonthetensilestrengthatbreakofuntreatedsilkfabricandAgNPs-treatedoneswithdifferentgammairradiationdoses.

Fig. 3.Effectofdifferentirradiationdoseontheelongation(%)atbreakofuntreatedsilkfabricandAgNPs-treatedsilkfabricswithdifferentgammairradiationdoses.

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Fig. 7.AntibacterialeffectsoftheuntreatedandAgNPs-treatedsilkfabricsonE.coli(A)Gram-negativebacteria.

Fig. 8. AntibacterialeffectsoftheuntreatedandAgNPs-treatedsilkfabricsonS. aureus(B)Gram-positivebacteria.

Fig. 5. XRDpatternsofuntreated(a)andAgNPs-treatedsilkfabricwithdifferentgammairradiationdoses(bandc).

of both the untreated and treated silk fabrics passesthrough three stages upon heating from roomtemperature to 600oC.All the curves show an initialstage of weight loss below 100oC, which can beascribedtotheeliminationofadsorbedwaterfromthefabrics.Inthesecondstageattemperaturesfrom100-290oC,allsamplesagainshowweightloss,whichmaybeattributedtothedegradationofsidechaingroupsofsilkfibroinproteins[35].Thethirdstageofweightlossfrom300 to 600oCmaybe caused by the breakdownofthemainchainsofsilkfibers[35].Moreover,itwasfoundthatthermalstabilityincreasesastheirradiationdoseincreasesupto10kGy.Forexample,ataconstanttemperatureof350oCweight loss% is30%and19%at an irradiation dose of 5 and 10 kGy, respectively.Sincecarboxylgroupsonthesidechainsofsilkproteinsare expected to be the binding sites of AgNPs, itsattachmentmaypossiblyprotect the side chains fromthermaldegradation[36-38].

Fig. 6. TGA curves of untreated and AgNPs-treated silk fabricwithdifferentgammairradiationdoses.

5.6. Antibacterial activity testing

Figures 7 and 8 show the antibacterial effects ofuntreatedandAgNPs-treatedsilkfabrics(5and10kGy)on E.coli(A)Gram-negativeandS. aureus(B)Gram-positivebacteria.E. coliandS. aureuswereselectedasmodel bacteria to explore the antimicrobial effects ofthemodified silk fabric in the zone of inhibition testsincetheyaretypicalGram-negativeandGram-positivebacteria,respectively.Inthisstudy[39],noclearzoneoccursoneithertheE. coliandS. aureusagarplatesfortheuntreatedsilkfabric.Incontrast,allAgNPs-treatedfabrics have obvious inhibition zones. The resultsobtained from these figures signified the followingfeatures:(a)theuntreatedsilkfabric(control)exhibitedno inhibitionzone indicatingnoantibacterialactivity;(b) treatment of a constant concentration of silvernitrate(3mM)irradiatedto5and10kGyrenderedthefabricantibacterialirrespectiveofthebacteriaused,(c)resistance of themodified fabric to E.coli (A)Gram-negativebacteria isgreater than that for theS. aureus(B)Gram-positivebacteriaasevidencedbycomparingthe inhibitionzoneforallusedbacteria.TheseresultsstronglyprovethatAgNPs-treatedsilkfabricspossessthe capability to kill both Gram-negative and Gram-positivebacteria.

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6. Conclusions

The preparation of the treated fabric depends onthe gamma irradiation doses in the presence of PVPpolymerandsilverions.GammairradiationdosescausesignificantaggregationofAgNPsonthefabric.AgooddistributionofAgNPsonthesilkfabricsurface,exhibitedinSEM images,proves theexistingofAgNPson thesilkfabrics.TheXRDdatarevealthatthesynthesizedtreated fabric possess good crystalline structures.ThepresenceofAgNPsgreatlychangedthepatternoftheTGA curve, and may be due to the attachedAgNPsprotectingthesilkfibersfromdegradation.TheresidueweightobservedintheTGAexperimentfurtherprovesthesuccessfulsynthesisofAgNPsonthefibersurface.The antimicrobial activity including bacterial growthinhibitionandbactericidaleffectsoftheAgNPs-coatedsilk is demonstrated in the zone of inhibition. Basedon the data, it can be concluded that AgNPs-coatedsilk,whichpossessesexcellentantibacterialactivity,isdirectlyfabricatedwithagammairradiated-assistedinsitusynthesisapproachusingdegummedsilkfibersandaAgNO3 solution as rawmaterials.Thiswork offersthe potential to produce treated antimicrobial silk forapplicationsincludingclothingandindustrialtextiles.

Acknowledgements

WewouldliketosincerelythanktheDepartmentofRadiation Chemistry National Center for RadiationResearch and Technology. Authors also gratefullyacknowledgetheAtomicEnergyAuthorityCairo,Egyptforitssupportofthisworkandforthecooperationofitsstaffworkingintheradiationsource.References

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