Electrospun Nanomaterials Implementing Antibacterial Inorganic Nanophases

16 Pages·2017·3.18 MB·English

applied
sciences
Review
Electrospun Nanomaterials Implementing
Antibacterial Inorganic Nanophases
NicolettaDitaranto1 ,FrancescoBasoli2,MarcellaTrombetta2,NicolaCioffi1,*
andAlbertoRainer2,*
1 DipartimentodiChimica,UniversitàdegliStudidiBari“AldoMoro”,viaOrabona4,70125Bari,Italy;
[email protected]
2 DipartimentodiIngegneria,UniversitàCampusBio-MedicodiRoma,ViaÁlvarodelPortillo21,
00128Roma,Italy;[email protected](F.B.);[email protected](M.T.)
* Correspondence:nicola.cioffi@uniba.it(N.C.);[email protected](A.R.);
Tel.:[phone](N.C.);[phone](A.R.)
(cid:1)(cid:2)(cid:3)(cid:1)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:1)
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)
Received:2August2018;Accepted:7September2018;Published:13September2018
Abstract: Electrospinningisaversatile,simple,andlowcostprocessforthecontrolledproductionof
fibers.Inrecentyears,itsapplicationtothedevelopmentofmultifunctionalmaterialshasencountered
increasingsuccess. Inthispaper,webrieflyoverviewthegeneralaspectsofelectrospinningandthen
wefocusontheimplementationofinorganicnanoantimicrobials,e.g.,nanosizedantimicrobialagents
inelectrospunfibers. Themostrelevantcharacteristicssoughtinnanoantimicrobialssupportedon
(ordispersedinto)polymericmaterialsareconciselydiscussedaswell. Theinterestingliterature
issuedinthelastdecadeinthefieldofantimicrobialelectrospunnanomaterialsiscriticallydescribed.
A classification of the most relevant studies as a function of the different approaches chosen for
incorporatingnanoantimicrobialsinthefinalmaterialisalsoprovided.
Keywords: Electrospinning;antimicrobial;metalnanoparticles;nanofibers
1. Electrospinning: Generalities
Electrospinningisaneasyfabricationmethodinwhichelectrostaticforcesareusedtoproduce
finefibers. Foritsversatility,simplicity,andlowcost,electrospinninghasattractedtheinterestofmany
researchersfascinatedbythepossibilitytofabricatefiberswithbothmicroandnano-sizedstructural
featuresbyfinelytuningprocessparameters. Forthesereasons,electrospinninghasbeenextensively
reviewed with respect to its setup, applications, advantages, and prospective developments [1,2].
Even though the origin of electrospinning can be traced back to the first years of the twentieth
century[1,3–7],theterm“electrospinning”isratherrecent. Infact,itwasusedforthefirsttimein1995
byR.H.Renekerandcoworkersintwodifferentscientificarticles[8,9].
Theelectrospinningfabricationprocesscanbebrieflysummarizedasfollows. Ahighvoltage
(generallyintheorderofafewtensofkilovolts)isappliedbetweenanextrusionsystem(i.e.,aneedle
orspinneret)andacollector. Apolymericsolutionisfedatasetflowratetothespinneretwhere,
undertheforceexertedbtheelectricfield,itstartselongatingformingacharacteristiccone-shaped
tip(Taylor’scone)[10,11]. Whensurfacetensionisovercomebyelectrostaticforces, ajetofliquid
is ejected from the Taylor cone, and reaches the collector in the form of a solid nonwoven web,
withsolventevaporatingduringflight[12]. Lateralinstabilitiesinthechargedtravellingjetresultina
whippingmotionthatfurthercontributestofiberelongation[13](seeFigure1). Athoroughanalysis
ofthephysicalphenomenabehindtheelectrospinningprocessandadetaileddescriptionofthemain
experimentalsetupscanbefoundinReference[14].
Appl.Sci.2018,8,1643;doi:10.3390/app8091643 www.mdpi.com/journal/applsci
Appl.Sci.2018,8,1643 2of16
Appl. Sci. 2018, 8, x FOR PEER REVIEW 2 of 16

Figure 1. A typical electrospinning set-up, comprising: (i) A spinneret containing the polymeric
Figure 1. A typical electrospinning set-up, comprising: (i) A spinneret containing the polymeric
solution;(ii)aDChighvoltagesupply;and(iii)agroundedcollector.Achargedjetofpolymersolution
solution; (ii) a DC high voltage supply; and (iii) a grounded collector. A charged jet of polymer
isextsroalcutteiodnf irso emxtrtahcetesdp firnonme rtehtet sippin(wneirthet atipty (pwiictahl ac otynpeicsahl acponee, isnhathpee, iinns tehte) ainnsdet)r eaancdh reesacthhees ctohlel ector
withcaotlylepctiocra lwwithh iap tpyipnigcaml wohtiiopnp.ing motion.
TheTehleec terloecstproinspniinnnginpg rporcoecsesssi sisa faffefecctteedd bbyy tthhrreeee cclalasssesse sofo fpapraamraemteerste, risn,cliundcilnugd isnoglutsioonlu tion
propeprrtoipeesr(teie.sg .(,e.cgo.,n ccoenncternattriaotnio,nv, ivsicsocossitiyty,,s suurrffaaccee tteennssioionn, ,cocnodnudcuticvtiitvyi, tayn,da nsdolvseonlvt evnaptovra pproersspurrees),s ure),
procepsrsopceasrsa mpaertaemrse(tee.rgs .,(seo.gl.u, tsioonlutfieoend freaetde ,raaptpe,l iaepdpvlioeldta gvoel,tnagoez,z lneo-ztoz-lec-otlol-eccotlolercdtoisr tadnisctea)n,caen),d aanmd bient
ambient parameters (e.g., humidity and temperature). Seyedmahmoud et al. have demonstrated the
parameters(e.g.,humidityandtemperature). Seyedmahmoudetal. havedemonstratedthefeasibility
feasibility of applying statistical methods to gain a quantitative and systematic insight about the
ofapplyingstatisticalmethodstogainaquantitativeandsystematicinsightabouttheeffectsofprocess
effects of process parameters on the resulting fiber properties [15,16].
parametersontheresultingfiberproperties[15,16].
Electrospinning has been the subject of many different setup modifications that have been
Electrospinning has been the subject of many different setup modifications that have been
implemented over the years to accommodate different application needs. In fact, besides the more
implementedovertheyearstoaccommodatedifferentapplicationneeds. Infact,besidesthemore
conventional randomly oriented fiber mats, a variety of morphologies and structures can be
conveanchtiioevneadl brayn pduormpolsyeloyr ciehnantegdinfigb there meleacttsr,oaspvinarniientgy coofnmditoiorpnhs oanlodg bieys maonddifsytirnugc tthuer esestcuapn (eb.ge.,a tchhei eved
bypusrppinonseerleyt cahnadn tghien cgoltlhecetoerle, catmroosnpgi notnhienrgs) c[o17n]d. itionsandbymodifyingthesetup(e.g.,thespinneret
andthecoMllaetc mtoorr,pahmoloonggy o(it.eh.e, frisb)e[r1 a7l]ig.nment and pattern) can be influenced by the collector geometry.
MIn aotrdmeor rtpo hporolodguyce( ia. er.a,nfidboemrlayl iogrniemnteendt naonnd-wpoavtetenr nm)act,a an sbtaetiicn flpluaennarc etadrgbeyt tish ethceo clolencvteonrtigoenoaml etry.
choice, whereas to obtain aligned fibers, collection is performed around a rotating cylindrical target
Inordertoproducearandomlyorientednon-wovenmat,astaticplanartargetistheconventional
[18,19]. In different designs, a series of parallel electrodes have been used to generate aligned fibers
choice,whereastoobtainalignedfibers,collectionisperformedaroundarotatingcylindricaltarget[18,
[20,21]. For more specific applications, collectors have been designed with customized geometries to
19]. Indifferentdesigns,aseriesofparallelelectrodeshavebeenusedtogeneratealignedfibers[20,21].
obtain specific orientations or patterns, such as a knife-edge rotating disk to collect highly aligned
Formorespecificapplications,collectorshavebeendesignedwithcustomizedgeometriestoobtain
fibers [22], or the use of grid-shaped collectors to create patterned nanofibrous mats [23].
specificorTiheen tsaptiinonnesreotr wpaast taelrsno st,hseu scuhbjaescta okf nvaifreio-euds gmeordoitfaictaintigondsi stakrgtoetcinogll espctechifiigch alpypallicigatnioednsfi. Obenres [22],
ortheofu stheeo fmgarjiodr- sahdavpaendcecso lilne cteolercstrtooscprienantiengp aitst errenperdesnenatneodfi bbyro uthsem ianttsro[d2u3c].tion of the coaxial
Tcohnefisgpuirnantieorne tiwn as20a0ls3o t[2h4e],s uebnjeabctlionfg vathrieo upsromdoudctiifiocna tioofn scotarreg-sehteinllg mspiecrcoifiarccahpitpecltiucaretiso nws.itOh neof
themcaojmorpaardtmvaenncteeds ipnroepleecrttireoss. pFiunrnthinerg iinscrreempreensteanl timedprboyvethmeeinntstr (oi.deu., cttriioaxniaolf stphiennceoraext)i ahlacvoen lfiedg utor ation
in200th3e[ 2fa4b],riecnaatibolni nogf tmheupltirloadyeurcetdio fniboefr csotrrue-csthureelsl m[2i5c]r owairtchh ittheec tpuoresssibwiliitthy ctoom inpdaerptmenednetnetdlyp truonpee rties.
thickness, degradation rate, and diffusion properties of each layer for advanced drug delivery
Furtherincrementalimprovements(i.e.,triaxialspinneret)haveledtothefabricationofmultilayered
applications.
fiber structures [25] with the possibility to independently tune thickness, degradation rate, and
In 2008, Liu et al. [26] demonstrated the possibility to fabricate electrospun nano-fibers by a
diffusionpropertiesofeachlayerforadvanceddrugdeliveryapplications.
needless setup. Using an aerated polymer solution, they managed to produce continuous and
In 2008, Liu et al. [26] demonstrated the possibility to fabricate electrospun nano-fibers by a
uniform nanofibers. In fact, insufflation of gas inside a vessel containing the polymer solution led to
needltehses fsoermtuapt.ioUns oinf gbuabnblaeesr oante tdhep osolylumtieorn ssoulrufaticoen, ,ththate ycomuladn gaigveed ritsoe ptor othdeu ecxetrcaocntitoinnu oof unsanaonfdibuernsi form
nanoufipboenr s.theIn afpapclti,caitniosnu fflofa taio npootefngtiaasl. iTnhsied ekeay vaedsvsaenltacgoenst aoinf itnhgis thnoevpelo ldyemsiegrn,s ocalullteido nbulebdbleto the
formationofbubblesonthesolutionsurface,thatcouldgiverisetotheextractionofnanofibersupon
theapplicationofapotential. Thekeyadvantagesofthisnoveldesign,calledbubbleelectrospinning,
isrepresentedbytheeasinesstoovercomethesurfacetensionofthesmallbubbles,andthescalability
Appl.Sci.2018,8,1643 3of16
oftheprocess, whichhasthepotentialforthemass-productionofnanofibers. Moreover, different
from classical electrospinning, in which spinnability mainly depends on the solution properties,
inbubble-electrospinningitmainlydependsonthesizeofthebubbles[27].
Electrospun meshes are characterized by high surface-to-volume ratio, dimensions ranging
fromtensofnanometerstomicrometers,highporosity,andvariableporesizedistribution,showing
morphological similarities to the natural extracellular matrix (ECM). Hence, one of the main
applicationsforelectrospunfibershasbeenasscaffoldsfortissueengineering.
Additionally, the possibility to modify fiber surface and the ease of incorporating molecules
or nanoparticles of interest in the solution to be electrospun further enhanced their range of
application, including drug delivery systems [28–30], water treatment [31,32], energy conversion
and storage [33,34], biosensing devices [35], gas sensors [36,37], electronics [38], as sorbents in
microextractiontechniques[39],aschromatographicphases[40],asseparators,concentrators,ormixers
inmicrofluidicsystems[41–43].
2. Nanoantimicrobials
Inthelasttwodecades,antimicrobialnanomaterials—conciselyaddressedasnanoantimicrobials
(NAMs)—haverisenatremendousinterestinbothfundamentalandapplication-orientedresearch[44].
The continuous search for new agents capable of preventing the growth of pathogens and
other undesired microorganisms, urged by the increased worldwide concern about antimicrobial
resistance[45],hasstimulatedamassivedevelopmentofnewmaterialsandprocessesimplementing
NAMs[46–48]. Thisclassofbioactivematerialsisbeingusedinformulations,technologicalsolutions,
andcommercialproducts,whichareavailablefortheconsumer[49].
AmongthedifferentinorganicNAMs,nanomaterialscomposedoftransitionmetalssuchasAg,
Cu, Zn, and their oxides are the most diffused, since they provide a wide-range biocidal activity,
andontheotherside,theyarewelltoleratedbyhumanbeingsatconcentrationlevelsthatareeffective
alreadytowardsthegrowthofseveralmicroorganisms[48]. Acomprehensiveoverviewonreal-life
applications of NAMs is provided by References [44,50–57]. Silver-based NAMs are definitively
the most investigated. This is due to the concurrence of different causes. Firstly, silver provides
an efficient biocidal effect toward a broad range of microorganisms; and secondly, the general
lack of solubility that silver salts and compounds show in several aqueous media (for instance
chloride-containingfluids)intrinsicallybufferstheconcentrationofbioactiveionicspeciesthatcanbe
releasedbyAgnanophases,thusprolongingtheirbiocidaleffects. Finally,thenumberofsynthetic
routestocoinagemetalnanophasesisenormous;thisguaranteesaneasyaccesstonanosilverbiocidal
agents,andsupportstheproductionofanalmostinfinitenumberofgoodsimplementingAg-NAMs.
Suchawideandindiscriminatediffusionofactivenanomaterialsisrisinganincreasingconcernabout
theirenvironmentaltoxicity,andparticularlytherisksrelatedtotheNAMsactiontowardsnon-target
organisms[58]. Inthisrespect,engineerednano-sizedagentswhichareprotected,encapsulated,orin
anycase,preventedfromdirectreleaseintocontactmediaarebyfarthemostinterestingNAMs. Since
2004[59],weproposedtheinclusionofcoppernanoparticlesintowaterinsolublepolymersasoneof
thebestroutestogainacontrolledbioactivityfromNAMs. Inotherwords,NAMsshouldbebetter
usedasnano-reservoirsinacompositematerial,providingatunablereleaseofbioactivespecies(such
asmetalions),ratherthanbeingjustadded(asentirenanophases)tothesystemwherethebiocidal
effectissought. ThemostimportantrequisitefortheresultingmaterialistoprotecttheNAMsfrom
beingdirectlyreleasedintothecontactsolution,butontheotherside,theinorganicnanophaseshasto
retainpartofitsreactivity,inordertoundergothecorrosionandionicreleaseprocesses,whichsupport
thefinalbiocidaleffects[60].
Morerecently,wehavefurtherexploredthisapproach,combiningmicroscopyandanalytical
spectroscopytechniques,demonstratingthataproperNAMadhesionorencapsulationinpolymer
coatingspreventsthereleaseofentirenanoparticles[61],pavingthewaytothedevelopmentofefficient
andsafeNAMs[62].
Appl.Sci.2018,8,1643 4of16
Withthisinmind,webelievethatthecombinationofNAMswithinnovativepolymersynthesis
and/or processing technologies, such as the electrospinning technique, affording a high level of
morphologicalandcompositioncontrolovertheresultingmaterial,willrepresentapropersolution
forafurtherstepinthediffusionandexploitationoftheseagents.
3. Electrospun(Nano)MaterialsImplementingAntibacterialProperties
Theadvantageofusingantimicrobialpolymerstofighttheincreasingresistanceagainstclassical
antibioticsarisesfromthepossibilityofsynergisticallycombiningthesematerialsandapplyingthem
indifferentphysicalforms(e.g.,coatings,films,emulsionsandfibers). Polymerfibersproducedvia
electrospinningareamongthemostefficientandcosteffectivesystemsfortwomainreasons: Inthe
first place, because of their huge surface area-to-volume ratio; and secondly, the polymers can be
implemented with antimicrobial functionalities before or after electrospinning. This provides the
opportunitytodesignandmodifythefibersinthesmartestwaytospecificallytargetdifferenttypes
ofmicroorganisms.
Antimicrobial polymers can be classified into two categories. The first one includes all those
polymerswithinherentantimicrobialorantisepticproperties,thatcanbedirectlyappliedorusedina
varietyofsubstrates,namelytextiles,metalmaterialsorplasticsones. Thesecondcategorycontains
inertpolymersincorporatingadditionalantimicrobialphases/agentsthatarereleasedovertime.
Thefirstclasscomprisesnaturalandsyntheticpolymers,includingpolypeptides. Antimicrobial
peptidesarenaturallyassociatedtothedefensesystemofmicroorganismsandhumans[63],andare
generallycationicspecieswithanoverallnetpositivecharge. Basedonthosestructures,synthetic
amphiphilicpolymershavebeendesignedtomimictheantimicrobialpeptides[64,65]. Whilemany
antimicrobialpeptideshavebeendescribed,theirlarge-scaleproductionisexpensive,theirinvivo
stabilityisgenerallypoorandrelativelylittleinvestigated[66,67].
Electrospunnanofibrousmembranesofnaturalpolymershaverecentlydrawnmuchattention
asnovelmaterialsinbiomedicalapplications,suchaswounddressing,tissueengineering,anddrug
delivery. While the use of bio-based materials as precursors for electrospinning seemed to be an
excellentsolutiontoaddressalltheraisedconcerns,manydifficultiesaroseontheactualpractical
side. Infact,naturalpolymersareusuallydifficulttobeelectrospun,thereforethestartingsolutionis
frequentlycomposedbyasyntheticpolymerinblendwiththenaturalone. Anotherpossibleapproach
istochemicallymodifythenaturalpolymer,chitosanprocessingrepresentsaclassicexampleofthis
approach. Chitosanisaninherentlyantimicrobialnaturalpolymerbeinghighlyactiveagainstboth
gram-positiveandgram-negativebacteria. Thus,itwouldbeanexcellentcandidatefortheproduction
ofantimicrobialnanofibers[68]. Anyhow,purechitosancannotbemerelyelectrospunintonanofibers,
andthisleadtotheneedofblendingchitosanintothestartingsolutionwithotherpolymers(e.g.,
polyethylene oxide, polyvinyl alcohol, polycaprolactone) even though this dilution could lead to
loweringthebiocidalpropertiesoftheasmadenanofibrousmembranes. Aninterestingoverviewof
differentnaturalelectrospunnanofibersforantibacterialuses,includingausefullistofpurepolymers
andtheirblendssuccessfullyprocessedbyelectrospinning,isgivenbyVineisetal. andBshenaet
al.[69,70].
Thesecondclassofantimicrobialnanofibersisbyfarthemostinvestigated,sincedifferentactive
agentsaswellasdifferentstrategieshavebeenexplored. Mostcommonly,biocides(e.g.,antibiotics,
ammoniumsalts,cyclodextrins,chlorhexidine,metal,ormetaloxidenanoparticles,etc.) areattached
toorencapsulatedintosupportingfibers,bymeansofdifferentpreparationapproaches. Themost
straightforwardoneconsistsinanchoringtheactiveagentontothesurfaceofpre-synthesizedfibers.
This approach, however, provides little control over the release rate, that is usually characterized
byaburst. Alternatively,theactivematerialcanbeencapsulatedinsidethefibereitherbyblending
theactiveagentinthepolymersolutionbeforeelectrospinningorbyfirstlyencapsulatingtheactive
agent into nanostructures to be dispersed in the electrospinning solution. Additionally, precursor
compounds can be blended in the solution to be electrospun, and conversion to their active form
Appl.Sci.A2p0p1l.8 S,c8i., 21061483, 8, x FOR PEER REVIEW 5 of5 1o6f 16
Additionally, precursor compounds can be blended in the solution to be electrospun, and
canbepcoenrvfoerrsmioend taos athpeior sta-cetlievcet rfoosrpmi ncnainn gbetr epaetrmfoermnte.dT haes sea appopstr-oealecchtreossparineneinffge cttrievaetminenptr.o Tvhideisne ga
sustainaepdprroealecahsees oafret heeffaeccttiivvee iang epnrot,vrideignugl aat esdusbtayinitesd drieflfeuassieo noft hthroe uagchtivteh eagpeonlty, mreegrumlataetdr ixb,yb iytst he
degraddaitfifounsioonf tthhreomugaht rthixe, poorlybmyear cmoamtrbixi,n bayt itohne dtheegrraedoaf.tiMono orfe thsoe pmhaitsrtiixc, aotre bdya ap cpormobaicnhaetisoanl tshoerfoeoref.s ee
More sophisticated approaches also foresee the use of a multi-axial electrospinning setup, in order to
theuseofamulti-axialelectrospinningsetup,inordertoconfinetheactiveagentinthecoreofthe
confine the active agent in the core of the obtained fibers, enhancing the control over the achievable
obtainedfibers,enhancingthecontrolovertheachievablereleaseprofiles(seeFigure2).
release profiles (see Figure 2).
Manytypologiesofantibacterialnanofibershavebeenproducedbytheelectrospinningtechnique,
Many typologies of antibacterial nanofibers have been produced by the electrospinning
basedontheincorporationofdifferentbiocides,asextensivelyreviewedinReference[71],wherea
technique, based on the incorporation of different biocides, as extensively reviewed in Reference
very comprehensive explanatory table is reported. As meaningful examples, we could focus on
[71], where a very comprehensive explanatory table is reported. As meaningful examples, we could
antibioftoiccsusi nocno rapnotirbaiotitoicns (inncuomrpeorroautiosnh y(ndurmoperhoiulisc haynddrohpyhdilrico panhdo bhiycdarnotpihboiobticic asnhtiabvioetibces ehnavues ebdee)n[ 71]
andcyculsoedde) x[7tr1i]n aensdi nccylculosdioenxtr[7in2e–s7 i5n]cliunstioona [p7o2l–y7m5] einritco sao pluotlyiomne.rAic tstoelnuttiioonn.h Aatstetnotiboen thaakse tno tboe tthaekednr ug
concenttor atthieo ndr,uags caonnceexnctreastsiown,i alls panro ebxacbeslsy wleilal dprtoobacbhlayn legaeds ttoo cphaonlygmes etro eploelcytmroesr peilencntraobsipliintyn,aabnilditya, s a
conseqaunedn caes ,ao cnonfisbeeqrusemncoe,r ponh ofilboegrsy ,mdourephtoolcohgya,n dguees ttoo cshoalnugtieos ntop sroolputeirotnie psraopsecrotineds uasc tciovnitdyu,cvtiivsictoys, ity,
viscosity, and surface tension.
andsurfacetension.

FigureF2i.guVrea rio2.u sVmareiothuos dsmoetfhiondcso rpofo rainticnogrpboiroatciindge sbiinotcoideesle ctinrotos puelnecntraonspoufinb ernsa.no(1fi)bebrlse. nd(1in) g/
dispersbiolenndoifntgh/ediascpteirvseioang eonf ttihne thaectpivoel yamgeenrt soinlu tthioen pporliyomretro esolelucttrioons ppinrinoirn gto; (2el)eccotrnofispnienmnienng;t o(2f)t he
activeacgoennfitnienmtehnet coofr ethoef tahcetivfieb eargtehnrt oiung hthceo -caoxreia loef lethcetr ofisbpeirn nthinrogu;g(h3 )ceon-caaxpiasl uellaetcitornos/paidnnsoinrgp;t i(o3n) of
encapsulation/adsorption of the active agent in nanostructures before dispersion in the
theactiveagentinnanostructuresbeforedispersionintheelectrospinningsolution;(4)conversionof
electrospinning solution; (4) conversion of a precursor to active agent in the nanofibers after
aprecursortoactiveagentinthenanofibersafterelectrospinning;and(5)attachmentoftheactive
electrospinning; and (5) attachment of the active agent onto the nanofibers after electrospinning.
agent onto the nanofibers after electrospinning. Reprinted from Reference [71], Copyright 2014,
Reprinted from Reference [71], Copyright 2014, with permission from John Wiley and sons.
withpermissionfromJohnWileyandsons.
Another relevant drawback comes from the burst release associated to the loading of high drug
Anotherrelevantdrawbackcomesfromtheburstreleaseassociatedtotheloadingofhighdrug
amounts. Indeed, as soon as fibers are submerged into an aqueous solution, antibiotics will tend to
amountlesa.cIhn doeuetd ,raapsisdolyo.n Tahsifis bbeerhsaavrieors upbrmoveorkgeesd ain rteodaunceadq ufueonuctsiosnoalulittyio no,f atnhtei bnioantiocfsibweirl lmteenmdbtroanleea ch
outrapaidglayi.nTsth bisacbteerhiaav biyo rrpelreoavsionkge salal rtheed uancetidbifoutniccst iionn aa lvietyryo sfhthoret ntaimneo fifrbaemrem wemithboruatn geuaagraainntseteibnagc tae ria
byreleapsrionlognagleldth ceoavnertaibgieo tpicesriiond.a Tvoe rayvsohido rbtutirmst erferlaeamsee, wdiitffheoreunttg sueat-ruapnst eheainvge abeperno luosnegde: dCcooavxeiarla ge
period.elTeoctarovsopiidnnbiungrs trteeclehansiqeu,ed iffaelrleonwtss ett-ou pscrheaavtee bae enpuoslyemd:erC oa(ex.iga.l, elepcotlryocsapprinolnaicntogntee ch[n76iq] ue
allowsptoolycr(leaactteic-acop-gollyycmoleicr a(eci.dg)., [p77o]l,y pcoalpyr(olalcatcict oanceid[)7 [67]8]p, oployl(yla(mcteitch-ycol -mgleythcaoclriyclaatcei)d/n)y[l7o7n] ,[p79o]l, ya(nladc tic
acid)[7p8o],lyp(oL-llya(cmtideeth-cyol-cmapertholaaccrtyonlaet)e )[/8n0y])l osnhe[7at9h] ,athnadt peonlcya(pLs-ulalcattied eth-ceo -acnatpibroiolaticct o(ne.eg).,[ 8g0e])ntsahmeaytchint,h at
ampicillin, tetracycline hydrochloride) component into the core section of the nanofibers. Another
encapsulatetheantibiotic(e.g.,gentamycin,ampicillin,tetracyclinehydrochloride)componentinto
common approach for a sustained release of the antibiotics is to adsorb or encapsulate the drug in a
thecoresectionofthenanofibers. Anothercommonapproachforasustainedreleaseoftheantibiotics
istoadsorborencapsulatethedruginananostructuresuchashydroxyapatitenanoparticlesbefore
dispersing it in the polymer solution [81–83]. This approach does not allow a high drug payload,
butstillprovidesasufficientantibacterialactivity. Amongtheothers,potentantimicrobialmaterials
Appl.Sci.2018,8,1643 6of16
thathavebeeninvestigatedinconjunctionwithpolymersarethequaternaryammoniumsalts(QACs)
andN-substitutedhalamines[84]. ThestrategyofpreparingantimicrobialpolymersbasedonQACsis
veryattractive,becausetertiaryor/andsecondaryaminogroupsprovideconvenientreactivemoieties
tobeproperlymodified.
OneoftheapproachesistopermanentlyattachtheactiveQACsagentsbymeansofcoupling
agents,suchasalkoxysilanes,toavarietyofdifferentsubstratesthroughcovalentinteractions[85–88].
Besides,othermethodsincludetheuseofammoniumsaltsderivativesasmonomersinaquaternization
reactionorsimplyaddingamixtureofthemtodifferentpolymersolutions. Acomprehensivereview
byJaegeretal.[89]discussedthemultiplesyntheticroutesofvariouschargedpolymersystemsthat
havequaternaryammoniummoieties.
Recently, some concerns have been raised over possible drawbacks in the use of
nanoparticles/nanomaterials (including nanosized antimicrobial agents) and synthetic antibiotics.
Ithasbeenpointedoutthattheycouldbeofsomehazardtotheenvironment,couldhavecollateral
effectsonhumanhealth,and/orcouldpossiblycreatebacterialresistanceissues. Ontheotherhand,
is strictly demanding an effective prevention of infections caused by biofilm-forming pathogens.
Toaddressthoseissues,manyengineerednanofibrousmembranescontainingmetaland/ormetal
oxidesnanoparticleshavebeenproposed,mainlybasedontheuseofsilver,copper,andzinc,thanks
totheirwell-establisheddisinfectantproperties. Itisgenerallyacceptedthattheeffectofmetalsina
nanoparticlesformisduebothtothereleaseofmetalionsandtothedirectcontactwiththebacterial
cellmembranes; anyhow, metalnanoparticlespresenttheadvantageofactingasactivereservoirs.
Inthiscontext,thedecreasedamountofmetal,combinedwiththeencapsulation/stabilizationinto
electrospunfibers,isexpectedtoproduceenvironmentallysustainablematerials,nontoxicforhuman
health,withreducednanotoxicologyissues[90].
InclusionofMetalNanophasesasBiocides
Silverhaslongbeenknownasaneffectiveantibacterialagentandithasbeenusedinvarious
applicationsthankstoitschemicalversatility. Copperandcopperoxide,aswell,possessantimicrobial
propertiesthathavebeenknownforcenturiesonthemacroscale[91].Withtheprogressoftechnological
applications,thecostcontrolremainsakeyfactorwhenconsideringthescaleupandthewiderange
ofapplicationsonalargescale. Forthisreason,cheapermetals(copper,zinc,iron,titanium)have
increasinglybecometheselectedmetalstoconferantimicrobialproperties,inplaceoforincombination
withsilver. Amongothers,electrospunnanofibermaterialshavebeenproducedincorporatingmetal
nanostructuresbydifferentstrategiesandwithvariouspolymers,accordingtothefinalapplication.
Oneofthewidespreadmethodsconsistsofasaltsolutionmixedwithapolymeronetoobtain
thefinalelectrospinningmixture(blending). Inthisconditionsthemetalspeciesarestabilizedinthe
nanoparticle form by means of the polymer itself, acting both as reductant and as capping agent.
Followingthisapproach,Quiròsatal[92]obtainedAg-,Zn-andCu-poly(vinylpyrrolidone)(PVP)
compositematsatdifferentcopperloadings,withgoodantibacterialperformancesagainstE.coliand
S.aureus.
Thesameapproachhasbeenreportedusingpoly(vinylalcohol)(PVA),asoneofthemostusedand
desirablematerialforbiomedicalapplications. Itshighlyfavorableproperties,suchasbiocompatibility,
nontoxicity,andbioadhesivecharacteristicsmakeitagoodcandidatetobemodifiedwithbiocidal
nanophasesinclusion. AstheincorporationofAgsaltsintoeasilyelectrospinnablepolymersmatrices
produces an even particles distribution, many papers have been published on the AgNPs/PVA
system [93–95]. Typically, the polymer acts as stabilizer of the nanocomposite fibers and also has
good reductant capabilities to yield Ag nanoparticles directly formed during the electrospinning
process[96]. Insomecases,post-treatmentprocessesarerequired,likeaddingasecondreductant[97]
oracombinationofUVirradiationand/orheattreatment/calcination[98,99]. Thisapproachcould
bealsobeneficialfromtheapplicationpointofview. Forinstance,Celebiogluetal.[97]reportedon
theinfluenceofAgNPssizeand/orasecondcomponentontheantimicrobialeffect(seeFigure3).
AAppppll.. SSccii.. 22001188,, 88,, xx FFOORR PPEEEERR RREEVVIIEEWW 77 ooff 1166
Appl.Sci.2018,8,1643 7of16
ttrreeaattmmeenntt//ccaallcciinnaattiioonn [[9988,,9999]].. TThhiiss aapppprrooaacchh ccoouulldd bbee aallssoo bbeenneeffiicciiaall ffrroomm tthhee aapppplliiccaattiioonn ppooiinntt ooff
vviieeww.. FFoorr iinnssttaannccee,, CCeelleebbiioogglluu eett aall.. [[9977]] rreeppoorrtteedd oonn tthhee iinnfflluueennccee ooff AAggNNPPss ssiizzee aanndd//oorr aa sseeccoonndd
WhileccooJmimnppeootnnaeenln.tt[ 9oo6nn] ttshhteue daaninettdiimmhiicocrrwoobbidiaaillf feeeffrffeeecncttt ((rsseeedee u FFciigignuugrreec o33)n).. d WWithihoiilnlee s JJicinna neetta afaflle.. c[[9t966t]h] essttmuuddoiieredpd h hhooolwowg dydiifofffeferrAeenngtt- PVA
nanorfireebddeuurccsiinn(Fgg i cgcoounnrddeiit4tiio)o.nnss ccaann aaffffeecctt tthhee mmoorrpphhoollooggyy ooff AAgg--PPVVAA nnaannooffiibbeerrss ((FFiigguurree 44))..

FigurFFeiigg3uu.rrTeeh 33e.. TpThhheoe tppohhgoorttaoopggrhraasppohhfss a oonff t aainbntatiicbbtaaeccrttieearrliiaatlel tstetesisnttiignnggo foofnf nananannooofiffbiibbrroroouuusss mmmaaatttsss ttthhhaaattt wwweeerrreee pppeeerrfrfofoorrmmrmeedde d aaggaaagiinansisntt st(a)
E.col(i(aaa))n EEd.. cc(ooblli)i aaSnn.dda u((bbr)e) u SSs.. . aauRurreeepuusrs.i. nRRteeeppdrriinfnrttoeedmd ffr[ro9om7m] , [[9C977o]],p, CCyoorpipgyyhrritigg2hh0tt 1 22400,114w4,, iwwthiitthph eppreemrrmmisiissssisoiioonnn f ffrrrooommm EEElllssseeevvviieieerr.r. .

Figure4. Onthe(left): TEMofPVAnanofiberselectrospunfrom12wt%PVAsolutionscontaining
1wt%ofAgNO :(a)Notrefluxed,(b)refluxedat80◦Cfor1h,and(c)refluxedat80◦Cfor2h.Onthe
3
(right):TEMofPVA(polyvinylalcohol)nanofiberselectrospunfrom12wt%PVAsolutionscontaining
1 wt% of AgNO after being annealed at (a) 50 ◦C, (b) 80 ◦C, and (c) 110 ◦C for 14 h. Reprinted
3
from[96],Copyright2007,withpermissionfromElsevier.
Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 16
Figure 4. On the (left): TEM of PVA nanofibers electrospun from 12 wt% PVA solutions containing 1
wt% of AgNO3: (a) Not refluxed, (b) refluxed at 80 °C for 1 h, and (c) refluxed at 80 °C for 2 h. On the
(right): TEM of PVA (polyvinyl alcohol) nanofibers elect rospun from 12 wt% PVA solutions
Appl.Sci.201c8o,n8ta,i1n6i4n3g 1 wt% of AgNO3 after being annealed at (a) 50 °C, (b) 80 °C, and (c) 110 °C for 14 h. 8of16
Reprinted from [96], Copyright 2007, with permission from Elsevier.
ElectErolescptruonspCunu -CPuV-APVfiAb efirbserhs ahvaeveb ebeenenp prroodduucceedd iinn ccoonnjujunnctciotino nwiwthi tChuCCul2C [1l200[]1 0o0r ]cooprpceor pper
acetataece[1ta0t1e ]t[o10o1b]t aitno PoVbAta-ipnr otPeVctAe-dprcootpecpteerd nacnoopppearr ticnlaenso.pAadrtdicilteios.n aAlldy,dmitiioxneadllym, etmalixneadn omstreutaclt ures
nanostructures have been produced, like CuO-ZnO, and have been included in PVA. The
havebeenproduced,likeCuO-ZnO,andhavebeenincludedinPVA.Thecombinationoftwometals
combination of two metals was demonstrated to be effective as enhanced adsorption and
wasdemonstratedtobeeffectiveasenhancedadsorptionandantimicrobialefficiencywereobtained
antimicrobial efficiency were obtained with these nanocomposite fibers [102]. Along with the
withthesenanocompositefibers[102]. Alongwiththeantimicrobialresults,theauthorsalsoproposed
antimicrobial results, the authors also proposed a mechanism responsible for the bactericidal action
amechanismresponsibleforthebactericidalactionofthosenanofibers(seeFigure5).
of those nanofibers (see Figure 5).

FigurFeig5u.re( a5). C(ao) mCpomarpaatrivateivpe loptlort erperperseesenntitningg tthhee aannttiibbaaccteteriraila lacatcivtiitvyi tyof oCfuCOu-ZOn-OZ n(COZ() CloZa)dleoda ded
nanofinbaneorsfibweristh wditihff edrieffnertecnot nccoenncetrnattriaotinosnsa gagaaininsstt GGFFPP--EE.. ccoollii ((GG−−) a)nadn dS. Sa.uraeuurse u(Gs+()G; +(b)); P(bro)pPorsoepdo sed
mechmaneicshmaniosfmb oafc tbearcitceirdicaildaalc taicotnionC ZCZn annanoofifbibeerrss;; aanndd ((cc)) FFluluoorersecsecnecnec sepsepcterac trdaepdicetpinicgt itnhge RthOeS ROS
generation with different concentrations of CZ nanofibers. Reprinted from [102], Copyright 2017,
generationwithdifferent concentrations ofCZnanofibers. Reprinted from[102], Copyright2017,
with permission from Elsevier.
withpermissionfromElsevier.
One of the major applications for electrospun fibers has long been in the filtration field and
One of the major applications for electrospun fibers has long been in the filtration field and
polyacrylonitrile (PAN) has been the most used, due to its high mechanical strength and chemical
polyacrylonitrile(PAN)hasbeenthemostused,duetoitshighmechanicalstrengthandchemical
stability. One of the drawbacks in the filtration process is the rapid fouling by bacteria, negatively
stability. Oneofthedrawbacksinthefiltrationprocessistherapidfoulingbybacteria,negatively
affecting the permeability and the throughput of the membrane. Moreover, PAN or composite
affectcienlglultohsee/PpAerNm feibaebrisl iatyre awniddetlhy eemthprlooyuegdh ipnu btioomfetdhiecaml deemvibcreas,n we.heMre othreeo bvaecrt,erPiaAl Nconotrrocl oism apn osite
celluliosssuee/.P IAn Nthifis breesrpseacrt,e CwuiNdPesly aenmd pAlgoNyPesd minayb iaodmd ead cilceaalr dbeevniecfeits w,whehne reemtbheeddbeadc tienr ieallecctoronstprouln isan
issue.PIAnNth ainsdre cseplleuclto,sCe ufiNbePrss. aAndddAitigoNnaPllsy,m ina ythaisd cdasae,c ltehaer bbleenndeifintg waphpernoaecmh bise dthdee mdoinst einlevcetsrtoigspatuend; PAN
andcseilllvuelro saenfidb ecorsp.pAerd dsaitlitos n[a1l0ly3,–i1n05t]h, isocr asper,eftohrembelde nZdninOg-CaupOp-rNoaPcsh [i1s0t6h],e mareo stinicnlvuedsetdig ainte dth;es ilver
electrospinning solution. An interesting alternative is represented by the cellulose nanofibers,
andcoppersalts[103–105],orpreformedZnO-CuO-NPs[106],areincludedintheelectrospinning
because the high number of –OH groups offers a location for fibers functionalization, thus regulating
solution. An interesting alternative is represented by the cellulose nanofibers, because the high
the nanophases upload and their release. Gouda et al. [107] published a comprehensive paper about
numberof–OHgroupsoffersalocationforfibersfunctionalization,thusregulatingthenanophases
carboxymethyl cellulose functionalized with copper, iron, and zinc NPs. They reported on the
uploadandtheirrelease. Goudaetal.[107]publishedacomprehensivepaperaboutcarboxymethyl
cellulosefunctionalizedwithcopper,iron,andzincNPs. Theyreportedonthedifferentmorphology
accordingtothedifferentMeNPs(Figure6),alongwithcompositenanofibersreleasepropertiesand
theirexcellentantibacterialactivity.
Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 16
Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 16
different morphology according to the different MeNPs (Figure 6), along with composite nanofibers
release properties and their excellent antibacterial activity.
Appl.Sdcii.ff2e0r1e8n,t8 ,m16o4r3phology according to the different MeNPs (Figure 6), along with composite nanofibers9 of16
release properties and their excellent antibacterial activity.

FFiigguurrFeei g66u.. rOOe nn6. ttOhhene (t(lhleeef f(ttl))e::f TTt)EE: MTME Miimm iamaggaeegsse oso ffo CfC CMMMCCC e eellleeeccctttrrrooossspppuuunnn n nnaaannnoofoifibfiebbree (rra ()(a aa))n adann CddM CCCMM-MCCN--MMPsNN ePlPessc teerloleesccptturronos sppuunn
nanofibers CuNPs (b), FeNPs (c) and ZnNPs (d). On the (right): SEM images of CMC electrospun
nnaannoofifibbeerrss CCuuNNPPss ((bb)),, FFeeNNPPss ((cc)) aanndd ZZnnNNPPss ((dd)).. OOnn tthhee ((rriigghhtt)):: SSEEMM iimmaaggeess ooff CCMMCC eelleeccttrroossppuunn
nanofiber (a) and CMC-MNPs electrospun nanofibers CuNPs (b), FeNPs (c) and ZnNPs (d).
nnaannoofifibbeerr (a()a)a nadnCd MCCM-MC-NMPNsePlse cetrloecsptruonspnuann onfiabneorsfiCbeurNs PCsu(bN),PFse N(bP)s, (Fce)NanPds Z(nc)N Pansd(d )Z.nRNepPrsi n(tded).
Reprinted by permission from [107], Springer Nature, Copyright 2017.
bRyeppreirnmteidss bioyn pferrommis[s1i0o7n] ,fSropmrin [g1e0r7]N, Sapturrine,gCero Npyartiugrhet, 2C0o1p7y.right 2017.
The attachment and core-sheath preparation methods are far less common and usually involve a
TThhee aattttaacchhmmeenntt aanndd ccoorree--sshheeaatthh pprreeppaarraattiioonn mmeetthhooddss aarree fafar rlelesss scocommmmoonn anandd usuusaulalyll yinivnovlovlev ea
two or three-step procedure. Nevertheless, they provide electrospun nanofibers with worthy
atwtow opoeror frothrtmrheraeen-esc-etse tapes p apnprtorimocecidcerduourbeira.e l. NmNeaevtevereriatrhltshe. leIelnse ssp,s a,rtthtihceueyly arpp, rwroovhviedinde ea peeplleleiccctatrrtoioossnppsuu innn vnonalavnneo ocffioibbaeteirnrssg sww [1iitt0hh8 ] wworoo rrtthhyy
ppeerrffoobrrammrraaiennrcc eem aaessm aabnnrattniimmesii cc[rr1oo0b9b]ii,aa llt hmmosaaett eemrriieaatllhsso.. dIIsnn oppffaaerrrtt iigccouuolladar r,,r ewwsuhhleetsnn. Maappopprelliioccvaaettrii,oo nnthsse iinnmvvuooltllivv-seet eccpoo aapttriionncggessd u[[11re00 88]] oorr
bbaarrrriieeorrff memrese mtmhbebr rpaaonnsesesisb[ i1[li01t9y0] 9,t]ot, httuohnsoees meth eem tmheotahdteosrdioasfl fseo prffrgeoorp oegrdtoireoesds a unrledtss .umMlotsro.p rheMoolovoregery,o,t vhbeyer ,ma ctuthinletg i-m sotnue plptiop-ssrtto-escpyen dpthureroseciseo dffuerrse
tohfefeprsod sitfshfieebr eiplniotty spstaiobraitlmuitneyte etrtosh . etSuhmni eaa ttte hareli.a [ml1s0ap8tr]e orrpeiapelorstr itpeersdo aopnned rAtmige-soP raApnNhdo nlmoangooyrf,pibbheyorlsao cogtbiynta,g ibnoyend a pscotoiasnktg-ins oygn ne tlphecoetssritos-sspdyuinfnfte hreesnist
pdaifrfaemrfeibenetter srp sian.rtaoSm hsiielvtaeetrr san.l i.Strh[a1it e0a 8st]o alrule.t pi[o1on0r,8 tae]n drde opwnoerrAtee gsdu- PboAsneN qAugenn-aPtnlAyo Nfipeb rnefoarsrnmooifbnibtgae airn sre eoddbustcaotiianoknei dnre gsaocetalikoenicnt. rgIon se Fpleiugcuntrroefi sbpeurns
ifnibtoerss7i litvnheteor S nsEiiMltvr aecrthe anrsiaotcrltauetrteii zosanot,ilouantni oodfn wt,h aeonrseed s fwiubbeerrssee iqssu ureebpnsoetlrqytuepdee,n wrtflhyoer prmee irintf ogisr amevriienddgeun atc ttriheoadntu trcheteai oicnntfi loruenea.ncIctnei ooFnfi .gs iIulnvr eeFri 7gtuhree
salt concentration and reaction time on the adsorption effect and crystallization ability of silver ions.
S7E tMhe cShEaMra ccthearriazcatteiorinzaotfiotnh oosfe thfiobseer sfiibserresp ios rrteepdo,rwtehde, rwehiteirse eivt iids eenvtidthenatt tthheati nthfleu iennfclueeonfcsei lovfe srilsvaeltr
Then, the subsequent silver reduction step is a further independent parameter.
csoalntc ceonntcraentitornatiaonnd arneda crteiaocntiotinm teimoen otnh ethaed asdosrportipotnionef efeffcetcat nadndc rcyrystsatlallilzizaatitoionna abbiliiltityy ooff ssiillvveerr iioonnss..
TThheenn,, tthhee ssuubbsseeqquueenntt ssiillvveerr rreedduuccttiioonn sstteepp iiss aa ffuurrtthheerr iinnddeeppeennddeenntt ppaarraammeetteerr..

Figure 7. SEM images of pretreating PAN (polyacrylonitrile) nanofibers in Ag NO3 solution at
different soaking times, different concentrations, and different reduction reaction time. Reprinted
from [108], Copyright 2015, with permission from Elsevier.

FFiigguurree 77..S ESEMMim imagaegseosf porf eptrreeattrienagtiPnAgN P(ApNoly (apcorylyloancrityrliolen)intrainleo)fi nbaenrsofinibAergs NinO 3Asgo luNtOio3n saotlduitfifoenre natt
sdoifafkeirnegntt ismoaeks,indgif fteimreenst, cdoinfcfeernetnrat tcioonnsc,eanntrdatdioifnfes,r eanntdr eddiuffcetrieonnt rreeadcuticotniotnim reea.cRtieopnr intitmede. frRoempr[i1n0te8d],
Cfroopmy r[i1g0h8t],2 C01o5p,ywriigthhtp 2e0r1m5i, swsiiotnh fpreormmEislssieovni efrr.om Elsevier.
Appl.Sci.2018,8,1643 10of16
Anincreasedstabilizationofthenanophasesintothemembranesisalwaysbeneficialandcould
be obtained by means of encapsulation approach, in order to avoid loosely attached nanoparticles
tobedispersedintheenvironment. Fewpapershavebeenpublishedsofarfollowingthismethod,
which allows also a controlled release of metal species [110,111]. In particular, Quiròs et al. [110]
reportedhowsilverandcopperNPssupportedinsepioliteandsilicaactasreservoirsabletoaffect
microorganismgerminationandgrowth,andtoreducefungalmetabolicactivity.
Table 1 reports a summary with some representative studies dealing with electrospun
antimicrobialfibersembeddingmetalnanoparticles.
Table 1. Some representative studies where electrospun antibacterial nanofibers incorporate
metalnanoparticles.
AntibacterialAgent ElectrospunPolymerComposite References
CuNPs,CuONPs Coppersalt+PVP [92]
CommercialCuO+PHBV [109]
Supportedcoppersalt+CA [110]
Cu/CuOx+PAN [103,104,111]
Coppersalt+PVA [100,101]
Coppersalt+CMC [107]
Coppersalt+PVDF [112]
Coppersalt+PU [113,114]
AgNPs Silversalt+PVP [92,93]
Supportedsilversalt+CA [105,110]
Silversalt+PAN [108]
Silversalt+PVA [94–99]
OtherMe/MeoxidesNPs Coppersalt+zincsalt+PVA [102]
Zincsalt+CMC [107]
Ironsalt+CMC [107]
Nomatterthepreparationmethod,alltheabovementionedcompositeelectrospunnanofibershave
beenprovedtoexertgoodantibacterialpropertiesagainstmanyGram-positive[70,92,97,99,102–108,113,114]
and Gram-negative [70,92,97,99,102,103,105–108,113,114] species, as well as antifungal effect [70,108–110].
Thedetailedanalysisontheantibacterialmechanismsinvolvedandtheoverviewonthedifferentantimicrobial
testsisbeyondtheaimofthisreview;nevertheless,thereadersinterestedinthetopiccanreferto[115–120].
4. Conclusions
Inthelastdecades,greatadvanceshavebeenachievedintheunderstandingoftheelectrospinning
process,intermsofinstrumentaldevelopmentandperspectiveapplications. Asaresult,itisnow
possible to easily produce uniform nanofibers from most synthetic polymers and many natural
polymers in the lab scale and also for industrial needs. Moreover, numerous biocides have been
successfully incorporated into nanofibers to obtain electrospun mats potentially used as medical
implants,scaffolds,wounddressings,textiles,orasfiltermedia. Amongothers,differentinorganic
nanomaterialscomposedoftransitionmetalswereconsidered,thankstotheirwiderangeofbiocidal
activityandbecausetheirionsarewelltoleratedbyhumanbeingsatconcentrationlevelsthatare
effectivetowardsseveralmicroorganisms.
Despitethesignificantadvances,severalissuesstillneedtobefurtheraddressedinantibacterial
nanofibers,mainlyrelatedtothecontrolledreleaseoftheantibacterialagentsfromthenanofibers.
Withthisinmind,webelievethatthecombinationofmetalnanoparticleswithinnovativepolymer
synthesisand/orprocessingtechnologies,suchastheelectrospinningtechnique,affordingahighlevel
ofmorphologicalandcompositioncontrolovertheresultingmaterial,willrepresentapropersolution
forafurtherstepinthediffusionandexploitationoftheseagents.