Release and antibacterial activity of allyl isothiocyanate/β-cyclodextrin complex encapsulated in electrospun nanofibers

ColloidsandSurfacesB:Biointerfaces120(2014)125–131

ContentslistsavailableatScienceDirect

Colloids

and

Surfaces

B:

Biointerfaces

jou rn a l h om ep ag e :w w w . e l s e v i e r . c o m / l o c a t e / c o l s u r f b

Release

and

antibacterial

activity

of

allyl

isothiocyanate/

␤-cyclodextrin

complex

encapsulated

in

electrospun

nanofibers

Zeynep

Aytac

_,

_Sema

_Y.

_Dogan

_,

_Turgay

_Tekinay

_,

_Tamer

_Uyar

a_{InstituteofMaterialsScience&Nanotechnology,BilkentUniversity,Ankara06800,Turkey} b_{UNAM-NationalNanotechnologyResearchCenter,BilkentUniversity,Ankara06800,Turkey} c_{GaziUniversity,LifeSciencesApplicationandResearchCenter,Ankara06830,Turkey} d_{GaziUniversity,PolatlıScienceandLiteratureFaculty,Ankara06900,Turkey}

a

r

t

i

c

l

e

i

n

f

o

Received21December2013

Receivedinrevisedform19March2014 Accepted13April2014

Availableonline22May2014 Keywords: Electrospinning Nanofibers Allylisothiocyanate ␤-Cyclodextrin Release Antibacterialactivity

a

b

s

t

r

a

c

t

Allylisothiocyanate(AITC)isknownasanefficientantibacterialagentbutithasaveryhigh volatil-ity.Herein,AITCandAITC/␤-cyclodextrin(CD)-inclusioncomplex(IC)incorporatedinpolyvinylalcohol (PVA)nanofiberswereproducedviaelectrospinning.SEMimageselucidatedthatincorporationofAITC andAITC/␤-CD-ICintopolymermatrixdidnotaffectthebead-freefibermorphologyofPVAnanofibers. 1_{H-NMRand headspaceGC-MSanalysesrevealedthatverylow amountof AITCwas remainedin} PVA/AITC-NFbecauseoftherapidevaporationofAITCduringtheelectrospinningprocess. Neverthe-less,muchhigheramountofAITCwaspreservedinthePVA/AITC/␤-CD-IC-NFduetotheCDinclusion complexation.ThesustainedreleaseofAITCfromnanofiberswasevaluatedat30◦C,50◦Cand75◦Cvia headspaceGC–MS.WhencomparedtoPVA/AITC-NF,PVA/AITC/␤-CD-IC-NFhasshownhigher antibac-terialactivityagainstEscherichiacoliandStaphylococcusaureusduetothepresenceofhigheramountof AITCinthissamplewhichwaspreservedbyCD-IC.

©2014ElsevierB.V.Allrightsreserved.

1. Introduction

Electrospinningisawidelyusedmethodtoproducefunctional nanofibersfromvarietyofmaterialsincludingpolymers,inorganic materialsandcompositestructures[1,2].Generallyelectrospinning is a room temperature process in which the polymer solution isexposed toelectrostatic field and theelectrifiedjetis drawn towardtothegroundedcollectoranddepositedonthecollector asa fibrousweb. Asthesolventevaporates duringtheprocess, nanofibrousmaterialswithuniquepropertieshavingveryhigh sur-faceareatovolumeratioandnanoporousstructuresareproduced [1,2].Theuniquepropertiesenableelectrospunnanofiberstobe usedinwounddressing,tissuescaffold,drugdelivery,food pack-aging,filtration,energy,catalysis,sensors,etc.[1,2].Owingtothe roomtemperatureandambientprocessconditionsthatprovide protectionforthebioactivecompoundsinelectrospunnanofibers,

∗ Correspondingauthorat:InstituteofMaterialsScience&Nanotechnology (UNAM),UNAM,BilkentUniversity,06800Ankara,Turkey.Tel.:+903122903571; fax:+903122664365.

E-mailaddresses:tamer@unam.bilkent.edu.tr,tameruyar@gmail.com(T.Uyar).

electrospinningisusedforproductionoffunctionalnanofibers con-tainingactiveagentslikeantioxidants[3,4],flavors/fragrances[5,6] andantibacterialagents[7].

Activeagentsloadedelectrospunnanofibersmaybeusefulin food packaging [3,4,7–11] and biomedical applications[12–14] asreportedintheliterature.Vega-Lugoetal.madecomparison intermsofreleasecharacteristicsoffreeAITCandAITC/_␤-CD-IC includingsoyproteinnanofiberswithchangingrelativehumidity andtheyalsostudiedtheeffectofAITCamountonthereleaseof AITC fromAITC includingpolylacticacidnanofibersin different relative humidity [8]. In another related study, Ge et al. pro-ducedmaterialsforfoodpackagingapplicationsbyimmobilizing glucoseoxidaseenzymeinpolyvinylalcohol/chitosan/teaextract electrospunnanofibrousmembrane[9].Inastudyconductedby ourresearchgroup,polylacticacidnanofibersincorporatedwith inclusioncomplexoftriclosanandcyclodextrinswereproduced viaelectrospinning[7].Ina studyofPérez-Masiá etal.,aphase changing material was encapsulated in electrospun zein fibers for the possible application as smart packaging materials [10]. Withregardstobiomedicalapplications,Mattanaveeetal.(2009) prepared different biomolecules immobilized electrospun poly-caprolactonenanofiberswiththepurposeofusingthemintissue http://dx.doi.org/10.1016/j.colsurfb.2014.04.006

Fig.1.Chemicalstructureof(a)allylisothiocyanate,(b)␤-CD;schematicrepresentationof(c)␤-CD,(d)formationofAITC/␤-CD-ICand(e)electrospinningofnanofibers fromPVA/AITC/␤-CD-ICsolution.

engineering [12]. Merrell et al. obtained curcumin-antioxidant agent-loadedelectrospunpolycaprolactonenanofibersfordiabetic wounddressingapplications[13].InthestudyofUnnithanetal.,an antibacterialelectrospunnanofibersthatareintendedtobeused aswounddressingmaterialwereproducedbyelectrospinningof a drug– ciprofloxacinHCl –including solutionof dextran and polyurethane[14].

Cyclodextrins (CD) are cyclic oligosaccharides (Fig. 1b) and ableto form inclusion complex (IC)with variety of molecules. CDhave␣-(1-4)linkagesformingatruncated-coneshaped struc-ture(Fig.1c).␣-CD,␤-CDand␥-CDhaving6,7,8glucopyranose units are the most common CD types [15,16]. Owing to their hydrophobiccavity, CD are ableto formhost–guest complexes viaweakforces,suchasvanderWaalsinteractions,dipole–dipole interactions,andhydrogenbondingwithmoleculesin appropri-atepolarityand dimension.ICof CDwithaguestmoleculehas advantages likeproviding higher solubility,higherthermal sta-bility and bioavailability of hydrophobic guests; controlling of volatility,masking offunpleasant odors,and controllingrelease of drugs and flavors [15–17]. CD are widely used in pharma-ceutical,cosmetics, biotechnology, agriculture,textile,chemical, environmental protection industries [15–17]. There also exist studies concerning application of CD in active food packaging [18–20] and biomedical applications [21–23] in the literature. Inthefoodpackagingstudies,CD wereincorporatedwith poly-mersin free formtocaptureundesired molecules in thefoods like cholesterol [18], hexanal and cholesterol [19] or in guest molecule-CD-ICformtoreleaseanantimicrobialagent (trans-2-hexenal)[20].ICofCDand varioustypesofdrugsareprepared and theseCD-drug-ICcouldbeused in biomedicalapplications [21–23].

Allyl isothiocyanate (AITC) (Fig. 1a) is a major pungent, an antimicrobialcompoundfoundincabbage,horseradish,mustard, wasabiaandusedinfoodpackaging[24],andbiomedical applica-tions[25,26].ICofAITCwithCDwasinvestigatedintheliterature [27,28].InastudyofLietal.,releaserateofICofAITCand␣-CD andICofAITCand␤-CDwasinvestigatedagainstrelativehumidity [27].Inanotherstudy,Ohtaetal.studiedonthedecompositionand thermodynamicpropertiesofinclusioncomplexationofAITCand CD(␣-CDand␤-CD)[28].

AITC could be used in food packaging applications by incorporating it into polymeric films [29] or fibers [8]. Plack-ett et al. investigated the effect of CD type in the release behavior of AITC from AITC/CD-IC incorporated into polylactic acid–polycaprolactone films [29]. Vega-Lugo et al. studied the release ofAITC fromonlyAITC and AITC/␤-CD-ICincludingsoy proteinnanofibersatdifferentrelativehumidity[8].

Inthisstudy,AITCencapsulatedinelectrospunpolyvinyl alco-hol(PVA)nanofibersweregeneratedbytwomethods.PVAasa nanofibermatrixwaschosensincePVAisasuitablepolymertype forfoodpackagingapplicationsshownintheliteratureby incorpo-ratingdifferentmoleculesorbacteriaintoPVAfilms[30]andfibers [5,31]duetoitshightensilestrength,flexibility,highoxygenand barrierproperties.FreeAITCandinclusioncomplexofAITCwith ␤-CD(AITC/␤-CD-IC)(Fig.1d)preparedinaqueoussolutionwas incorporatedintoPVAsolution;thenPVA/AITCandPVA/AITC/ ␤-CD-ICnanofiberswereproducedviaelectrospinning(Fig.1e).The resultingnanofibrouswebswerecharacterizedbySEM,XRD,and

1_{H-NMR.Therelease of AITCfromnanofiberswasmeasuredat}

30◦C,50◦Cand75◦CbyheadspaceGC–MS.Theantibacterial activ-ities of nanofibers were tested against Escherichia coli (E. coli) andStaphylococcusaureus(S.aureus)accordingtocolonycounting method.

2. Materialsandmethods 2.1. Materials

Polyvinyl alcohol (PVA, Mw∼85.000–146.000g/mol, Sigma

Aldrich,87–89%hydrolyzed),allylisothiocyanate(AITC,95%,Sigma Aldrich),beta-cyclodextrin(␤-CD,WackerChemieAG,Germany), deuterateddimethylsulfoxide(DMSO-d6,deuterationdegreemin 99.8% for NMR spectroscopy,Merck) werepurchased and used as-receivedwithoutanyfurtherpurification.Distilledwaterwas suppliedfromMilliporeMilli-Qultrapurewatersystem.

2.2. Preparationofsolutions

AITCcontainingPVAnanofiberswerepreparedbyincorporating AITCintoPVAsolutionsviatwomethods.Inthefirstmethod,free

Z.Aytacetal./ColloidsandSurfacesB:Biointerfaces120(2014)125–131 127

Table1

Thepropertiesofthesolutionsusedforelectrospinningandmorphologicalcharacteristicsoftheresultingelectrospunnanofibers(thefibersizeisreportedasthe aver-age±standarddeviationand100fiberswereanalyzedforeachcase).

Solutions PVAa_{(g/kg,w/v) ␤-CD}b (g/kg,w/w) AITCb (g/kg,w/w) Viscosity (Pas) Conductivity (␮S/cm) Averagefiber diameter(nm) Fiberdiameter range(nm) Fibermorphology

PVA 75 – – 0.177 470 290±65 140–580 Bead-freenanofibers

PVA/AITC 75 – 40 0.267 487 210±45 120–330 Bead-freenanofibers

PVA/AITC/␤-CD-IC 75 227 40 0.194 523 235±90 90–540 Bead-freenanofibers

a_{Withrespecttosolvent(water).} b_{Withrespecttopolymer(PVA).}

AITC(4%,w/w,withrespecttopolymer)wasdispersedin aque-oussolutionandthen7.5%PVA(w/v)wasputintothissolution. Thesolution(PVA/AITCsolution)wasstirredatroomtemperature overnightandfinallyitwaselectrospun(PVA/AITC-NF).Inthe sec-ondmethod,4%AITC(w/w,withrespecttopolymer)wasdispersed inaqueoussolution,then␤-CDwasaddedtogiveamolarratio of2:1(AITC:␤-CD)andresulting solutionwasstirred overnight at room temperature and white, turbidsolution was obtained. Finally,7.5%PVA(w/v)wasadded(PVA/AITC/␤-CD-ICsolution), andPVA/AITC/␤-CD-ICsolutionwasstirred6hmoreatroom tem-peratureandelectrospun(PVA/AITC/␤-CD-IC-NF).Forcomparison, wehavealsoelectrospunPVAaqueoussolution(7.5%,w/v)without AITCorAITC/␤-CD-IC.Table1summarizesthecompositionsofthe solutionsusedfortheelectrospinningofthenanofibers.

2.3. Electrospinning

PVA,PVA/AITCandPVA/AITC/_␤-CD-ICsolutionswereseparately loadedinto3mLplasticsyringe(metallicneedlewith0.8mminner diameter)andthenelectrospunbyusingthehorizontal electro-spinning setup.The solutions were pumped through a syringe pump(WPI,SP101IZ)at1mL/hrate.Cylindricalmetalcovered withaluminumfoilwasusedasacollector.Theelectricfield(15kV) wasappliedfromahighvoltagepowersupply(AUSeries, Matsu-sadaPrecisionInc.)andthetip-to-collectordistancewas10cm. Experimentswereperformedat24–25◦Cunder17–20%humidity. 2.4. Characterizationandmeasurements

The viscosityof PVA, PVA/AITC and PVA/AITC/␤-CD-IC solu-tionsweredeterminedbyAntonPaarPhysicaMCR301rheometer equippedwithacone/plate accessory(spindletype CP40-2)at aconstantshearrateof100s−1,at25◦Candtheconductivityof solutionswasmeasuredbyInolab®_{Multi720-WTWatroom}

tem-perature.

The morphologies of the electrospun PVA-NF, PVA/AITC-NF and PVA/AITC/␤-CD-IC-NF wereexaminedby scanningelectron microscopy (SEM, FEI—Quanta 200 FEG). Prior to taking SEM images,nanofibersamplesmountedonmetalstubswith double-sidedadhesivetapewerecoatedwith5nmAu/Pd(PECS-682)to minimizecharging.Diametersofthenanofibersweremeasured directlyfromtheSEMimages(n≥100)andaveragefiberdiameter (AFD)wascalculated.

Thecrystalline structureof PVA-NF, ␤-CD,PVA/AITC-NF and PVA/AITC/␤-CD-IC-NFwere recordedby X-raydiffraction (XRD, PANalyticalX’Pertpowderdiffractometer)applyingCuK␣ radia-tionina2range7.5–30◦.

Theprotonnuclearmagneticresonance(1_{H-NMR)spectrawere}

recorded onBrukerDPX-400in DMSO-d6 at400MHzat 25◦C. 30mg/mLofAITC,PVA-NF,␤-CD,PVA/AITC-NFandPVA/AITC/ ␤-CD-IC-NFweredissolvedinDMSO-d6toexaminethepresenceof AITCinthesamplesandstoichiometryofPVA/AITC/␤-CD-IC-NF. Integration of the chemical shifts (_ı) given in parts per mil-lion(ppm)of thesampleswascalculatedbyusingMestReNova software.

The cumulative amount of AITC released from PVA/AITC-NF and PVA/AITC/␤-CD-IC-NF were determined for 240minby headspace gaschromatography–massspectrometry (GC–MS)of AgilentTechnologies7890Agaschromatographcoupledtoan Agi-lentTechnologies5975CinertMSDwithatriple-axisdetector.The capillarycolumnusedwasHP-5MS(Hewlett-Packard,Avondale, PA)(30m×0.25mmi.d.,0.25␮mfilmthickness).Theheadspace GC–MSexperiments wereperformedwitha CTCPAL auto sam-pler.20mgofPVA/AITC-NFandPVA/AITC/␤-CD-IC-NFtakenfrom thealuminumfoilwereplacedin20mLheadspaceglassvials.The vialswereagitatedat500rpmat30◦C,50◦Cand75◦Cof incuba-tiontemperatureand20%relativehumidity.Heliumwasusedas carriergaswasataflowrateof1.2mL/min.500␮Lofvaporwas injectedtotheheadspaceGC–MSbyusingaheadspaceinjector (MSH02-00B,volume:2.5mL,scale:60mm).Thesyringe temper-aturewas50◦C.Oventemperaturewasheldat50◦Cfor1minand increasedto200◦Cattherateof20◦C/minandheldatthis tem-peraturefor3min.Thermaldesorptionwasconductedinthesplit mode(20:1).HeadspaceGC–MSanalyseswerecarriedoutinthe completeselectedionmonitoringmode(SIM).Flavor2andNIST 0.5librarieswereusedtodecideAITCpeak.Therelease experi-mentwasperformedintriplicateandtheresultswerereportedas average±standarddeviation.

The antibacterial activity of PVA/AITC-NF and PVA/AITC/ ␤-CD-IC-NF was assessed by colony counting method against Gram-negativeE.coliandGram-positiveS.aureusbacteria.200␮L oftheE.coliandS.aureusgrownovernightwereinoculatedinto 10mLofLuria–Bertani(LB)brothandnanofibersweresterilized byUVirradiationandputintotheflasks.About1mgofnanofiber samplesandcontrolswereincubatedat37◦Candstirred100rpm for24h.Samplesfromeachflaskandcontrolswereseriallydiluted, 100␮LofeachwasspreadontoLBagarandcolonieswerecounted andphotographedafter24h.Allexperimentswereperformedin triplicateandreportedasaverage±standarddeviation.

3. Resultsanddiscussion

3.1. Morphologyanalysisofnanofibers

As an aim toward producing PVA nanofibers (NF) encapsu-latingAITC,freeAITC andinclusioncomplexofAITC with␤-CD (AITC/␤-CD-IC)wasincorporatedintoPVAnanofibers (PVA/AITC-NFandPVA/AITC/␤-CD-IC-NF)byusingelectrospinningtechnique. ThemorphologicalcharacterizationofPVA-NF,PVA/AITC-NFand PVA/AITC/␤-CD-IC-NFwascarriedoutviaSEM.SEMimagesand averagefiberdiameter(AFD)alongwithfiberdistributionsofthe nanofibersaredepictedin Fig.2.In thecase ofelectrospinning of pristinePVA solution,bead-free anduniformPVA-NF having AFDof290±65nmwasobtained.Then,weincorporatedAITCand AITC/␤-CD-ICintoPVAsolutionandthenelectrospinningwas per-formedinordertoobtainfunctional nanofibers.Asclearlyseen fromSEMimages,theincorporationofAITCorAITC/␤-CD-ICdid notcauseanynotablechangeinthemorphologyoftheelectrospun nanofibers.TheAFDofPVA/AITC-NFandPVA/AITC/␤-CD-IC-NFwas veryclosetoeachotherwhichwere210±45nmand235±90nm,

Fig.2. SEMimagesandfiberdiameterdistributionswithaveragefiberdiameter(AFD)oftheelectrospunnanofibersobtainedfromsolutionsof(a)PVA,(b)PVA/AITC,(c) PVA/AITC/␤-CD-IC.

respectively.Thesenanofiberswereslightlythinnerthanthe PVA-NF. The slight variations of fiber diameters observed for the nanofibersampleswerepossiblyduetodifferencesinviscosityand conductivityofthesolutions[1,2,32].Theviscosity,conductivity andAFDvaluesofPVA,PVA/AITCandPVA/AITC/␤-CD-ICsolutions areshowninTable1.PVA/AITCandPVA/AITC/␤-CD-ICsolutions havehigherviscosityandhigher conductivitycompared toPVA solution.

3.2. Crystallinestructureofnanofibers

XRD was performed for PVA-NF, ␤-CD, PVA/AITC-NF and PVA/AITC/␤-CD-IC-NFandthediffractionpatternsaredepictedin Fig.3.AITCisaliquidcompoundatroomtemperature,sowedid notrunXRDanalysisforpureAITC.PVAisasemi-crystalline poly-merandtheXRDofPVA-NFhasshownabroaddiffractionataround 2∼19.6◦[33].XRDpatternofPVA/AITC-NFwassimilartoPVA-NF, thusPVAkeepsitssemi-crystallinestructureafterincorporationof AITC.Thecage-typepackingcrystalstructureobservedinCD gener-allytransformintochannel-typepackinginCD-IC.Theas-received ␤-CDhasacage-typepackinganditscharacteristicdiffraction pat-ternisgiveninFig.3.Thechannel-typepackingof␤-CDhassalient characteristicpeakat2∼12◦[6].Here,thepeakat2∼12◦inXRD patternofPVA/AITC/_␤-CD-IC-NFwasobservedandweconcluded thattheICformationbetweenAITCand␤-CDinPVA/AITC/ ␤-CD-IC-NFwaspresent.Inaddition,thecage-typepackingof␤-CDpattern

wasabsentinthefibersampleandthismaysupporttheAITC/ ␤-CD-ICformationaswell.

3.3. AITCcontentinnanofibers

PVA/AITC-NF and PVA/AITC/␤-CD-IC-NF were tested by 1

H-NMRtodeterminethestoichiometryofAITC/␤-CD-ICandwhether

Z.Aytacetal./ColloidsandSurfacesB:Biointerfaces120(2014)125–131 129

Fig.4. 1_{H-NMRspectraofAITC,PVA,␤-CDandAITCcontainingPVAnanofibers.}

AITC was present in PVA/AITC-NF and PVA/AITC/␤-CD-IC-NF (Fig.4).ThepeaksforAITCwereobservedataround4.2,5.3,and 5.9ppmcorrespondingtotheprotonsofAITC[34].The stoichiom-etryofAITCand␤-CD-ICinPVA/AITC/␤-CD-IC-NFwasdetermined

as0.68:1.00(AITC:␤-CD)byintegratingthepeakratioofthe charac-teristicchemicalshiftsofAITC(5.3ppm)and␤-CD(5.7ppm).Thus, initialmolarratioof2:1forAITC:␤-CDwhichwasusedtoobtain AITC/␤-CD-ICwaspreservedsubstantially.So,PVA/AITC/ ␤-CD-IC-NFstillcontainedsomeofAITCinthefibersamplewhereaswe couldnotobserveanypeakofAITCinPVA/AITC-NF.Therefore,we deducedthatextremelylowquantityofAITCexistinPVA/AITC-NF. ThepossiblereasonforthissituationisevaporationofAITC dur-ingtheelectrospinningofsolutionsinceAITCisahighlyvolatile substance.Infact,wewereabletosmellAITCheavilyduring elec-trospinningofPVA/AITC-NF.Inbrief,1_{H-NMRstudyshowedthat}

␤-CDpreventedevaporationofAITCtosomeextentduring electro-spinningprocessandhighloadingofAITCinPVA/AITC/␤-CD-IC-NF wasachievedcomparedtoPVA/AITC-NF.

3.4. ThereleasestudyofAITCfromnanofibers

The application of AITC is somehow restricted because of its highly volatile nature, unpleasant odor and hydrophobic nature[27].Here, wehaveincorporatedAITC/␤-CD-ICintoPVA polymer solution, and PVA/AITC/␤-CD-IC-NF were obtainedvia electrospinning.Foracomparativestudy,wehavealsoproduced PVA/AITC-NFwithoutCD-IC.Therehavebeenreportsin the lit-eratureabouttheapplicationofCDinfoodpackagingmaterials tocontrolthedeliveryofactivecompounds[8,20,27,29].Here,we haveevaluatedthereleasebehaviorofAITCfromPVA/AITC-NFand PVA/AITC/␤-CD-IC-NFatthreedifferenttemperatures(30◦C,50◦C and75◦C)byusingheadspaceGC–MS(Fig.5).

ThecumulativeamountofAITCreleasedat30◦C,50◦Cand75◦C (for240min) fromPVA/AITC-NFwereminimalandsignificantly muchlowerthanthatofPVA/AITC/␤-CD-IC-NFsample.Itisevident thatverysmallamountofAITCwaspresentinthePVA/AITC-NF sampleasalsoconfirmedby1_{H-NMRstudieswhichwecouldnot}

even detectAITC inthis sample.In thecase ofPVA/AITC/ ␤-CD-IC-NF,theamountofAITCwassignificantandthereleaseofAITC fromthenanofibersamplewasincreasedgraduallywithtimeand finally becameconstant. Hence,we have successfully produced PVA/AITC/␤-CD-IC-NFwithasustainedreleasebehaviorofAITC. Inaddition,asthetemperaturewasincreasedfrom30◦Cto75◦C, theamountofAITCreleasedwasalsoincreasedobviouslyforboth PVA/AITC-NFand PVA/AITC/_␤-CD-IC-NFsamples.Thisis related withthehigherdiffusioncoefficientofmoleculesathigher tem-peratures [35]. Athigher temperatures, the motionof polymer chainsincreases,sothemovementofactivemoleculethroughthe amorphous partsof thepolymeris favored [36]. Moreover,the incrementinthereleaseofAITCfromPVA/AITC/␤-CD-IC-NFwas muchclearerthanPVA/AITC-NF.Inshort,headspaceGC-MSresults clearlyconfirmedthattheevaporationofAITCwashinderedby CD-ICandmuchhigheramountofAITCwasencapsulatedinthePVA nanofiberswhenAITCwascomplexedwith␤-CD.

3.5. Antibacterialactivityofnanofibers

AITC,themajorpungentcompoundinplants,hasbeenreported tohavestrongantimicrobialactivityinbothliquidandvaporforms. Here,wehavetestedtheantibacterialactivityofPVA/AITC-NFand PVA/AITC/␤-CD-IC-NFbycolony countingmethodagainst Gram negativeE.coliandGrampositiveS.aureusbacteria.Fig.6ashows representativeimagesofbacteriacoloniestreatedby PVA/AITC-NF and PVA/AITC/␤-CD-IC-NF; and Fig. 6b shows the effect of PVA/AITC-NFandPVA/AITC/␤-CD-IC-NFonthegrowthinhibition rateofE.coliandS.aureus.Thegrowthinhibitionrate(%)of bacte-riawascalculatedbyassumingthatplateswithoutnanofibershave 100% growth.PVA/AITC-NFand PVA/AITC/␤-CD-IC-NFexhibited 31.98% and 94.41% antibacterialactivity againstE.coli whereas

Fig.5.CumulativereleaseofAITCfromPVA/AITC-NFandPVA/AITC/␤-CD-IC-NFat30◦_C,50◦_Cand75◦_{C(n=3).Theerrorbarsinthefigurerepresentthestandarddeviation}

(SD).

antibacterial activity against S. aureus was 53.55% and 99.82%, respectively.ItwasobviousPVA/AITC/␤-CD-IC-NFsample (includ-ingabout0.0107mg AITC accordingto NMR result)hasshown muchbetterantibacterialactivitywhencomparedtoPVA/AITC-NF. ThisismostlikelyduetothepresenceofhigheramountofAITCin PVA/AITC/␤-CD-IC-NFwhichwaspreservedbyCD-IC.Inthecase ofPVA/AITC-NF,someantibacterialactivityagainstE.coliandS.

aureuswasobservedsinceverylowlevelofAITCwaspresentin thissampleasitwasdetectedbyheadspaceGC–MSanalysis. More-over,theelectrospinningprocessinwhichveryhighvoltageswere appliedhasnonegativeeffectontheantibacterialpropertyofAITC encapsulatedinPVA/AITC-NFandPVA/AITC/␤-CD-IC-NF.In addi-tion,thedifferenceintheantibacterialactivityofbothnanofiber samplesagainstE.coliandS.aureusmaybecausedbythedifference

Fig.6.(a)ExemplaryimagesofcoloniesofEscherichiacoli,Staphylococcusaureus;E.coliandS.aureuscoloniestreatedbyPVA/AITC-NF;E.coliandS.aureuscoloniestreated byPVA/AITC/␤-CD-IC-NF;(b)growthinhibitionrate(%)ofE.coliandS.aureusinPVA/AITC-NFandPVA/AITC/␤-CD-IC-NF(n=3).Theerrorbarsinthefigurerepresentthe standarddeviation(SD).

Z.Aytacetal./ColloidsandSurfacesB:Biointerfaces120(2014)125–131 131 betweencellwallcompositionoftwobacteria,whichareGram

negativeandGrampositive,respectively.Gramnegativebacteria haveasemi-permeable barrierthatdeceleratespassingof com-pounds[37].

4. Conclusion

Inthisstudy,weperformedtheelectrospinningoffunctional PVAnanofibersincorporatingAITCandAITC/␤-CD-IC.SEMimages showedthatthebead-freefibermorphologyofPVAnanofibersdid notchangeaftertheincorporationofAITCandAITC/␤-CD-ICinto polymermatrix.Weobservedthattheextremelylowquantityof AITCexistinPVA/AITC-NFduetothequickevaporationofAITC duringtheelectrospinningofPVA/AITCsolutionsinceAITChasa highlyvolatilenature.On thecontrary,much higheramountof AITCwasencapsulatedinthePVA/AITC/␤-CD-IC-NFsampledue tothecyclodextrin inclusioncomplexation. Hence,PVA/AITC/ ␤-CD-IC-NFhasshownimprovedantibacterialactivityagainstE.coli and S. aureus when compared to PVA/AITC-NF without CD-IC. Inbrief,newlydevelopedPVA/AITC/␤-CD-IC-NFwithhigh load-ingefficiency,sustainedrelease behaviorandconsiderably high antibacterialactivitymayhavepotentialsforactivefoodpackaging andbiomedicalapplications.

Acknowledgments

Dr. Uyar acknowledges The Scientific and Technological Research Council of Turkey (TUBITAK) (Project no. 111M459) and EU FP7-PEOPLE-2009-RG Marie Curie-IRG (NANOWEB, PIRG06-GA-2009-256428) and The Turkish Academy of Sciences—Outstanding Young Scientists Award Program (TUBA-GEBIP) for funding the research. Z. Aytac thanks to TUBITAK (Projectno.111M459)forthePh.D.scholarship.Dr.Tekinaythanks GaziUniversityScientificResearchProjectUnitfortheirsupport. References

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