Biomedical Engineering Reference
In-Depth Information
28.2 Antimicrobial Nanomaterials
Product-enhancing.nanomaterials.function.through.a.wide.variety.of.mechanisms..Many.
metal-oxide.nanomaterials.have.unique.light.absorption.properties,.making.them.amenable.
to.photocatalytic.applications.and/or.absorption.of.harmful.spectral.components,.typically.
ultraviolet. light. (Frederix. et. al.. 2003,. Han. et. al.. 2007,. Karunakaran. et. al.. 2010,. Yuan. et. al..
2010,.Nair.et.al..2011)..These.properties.have.been.well.exploited.in.sunscreen.lotions,.most.
often.using.titanium.or.zinc.oxide.nanoparticles..In.the.realm.of.antimicrobial.textiles,.metal.
nanoparticles.(including.silver,.gold,.copper,.and.others).have.been.shown.to.render.a.high.
degree.of.resistance.to.bacterial.and.fungal.growth.(Anyaogu.et.al..2008,.Mahapatra.et.al..
2008,.Gao.et.al..2009,.Ren.et.al..2009,.Dastjerdi.and.Montazer.2010,.Rafi.et.al..2010)..The.mode.
of.microbial.killing.for.these.particles.includes.the.production.of.reactive.oxide.species.(Kim.
et.al..2007,.Hwang.et.al..2008).and.possible.cell.membrane.damage.(Sondi.and.Salopek-Sondi.
2004,.Choi.et.al..2008,.Smetana.et.al..2008)..Of.the.commonly.used.metals,.silver.has.been.
the.most.widely.used,.in.the.form.of.nanoparticles,.silver.threads,.and.even.woven.silver.
meshes..One.way.of.measuring.antimicrobial.activity.is.to.perform.“zone.of.clearing”.tests,.
in.which.a.sample.of.material.is.placed.on.a.petri.dish.coated.with.bacteria.or.fungus..If.
the. material. has. antimicrobial. activity,. one. typically. observes. a. circular. area. around. the.
material.in.which.the.bacteria/fungus.cannot.grow..By.contrast,.the.bacteria/fungus.in.the.
remainder.of.the.petri.dish.has.grown.into.a.thick.mat..Most.zone.of.clearing.tests.measure.
the.radial.size.of.the.zone,.which.is.an.indicator.of.the.material's.antimicrobial.activity,.and.
its.ability.to.diffuse.outward..An.example.of.zone.of.clearing.results.is.shown.in.Figure.28.1.
In. the. case. of. pharmaceutical. antibiotics,. diffusion. is. necessary. to. deliver. the. antimi-
crobial.components.to.the.target.fungi/bacteria..For.instance,.nanoscale.textiles,.such.as.
those.produced.from.electrospinning.techniques,.can.be.loaded.with.traditional.antibiotic.
compounds.to.inhibit.bacterial.growth.(Soscia.et.al..2010)..An.example.of.bacterial.growth.
inhibition.by.antibiotic-loaded.nanoibers.is.shown.in.Figure.28.2.
For. antimicrobial. textiles. and. materials,. diffusion. and. leaching. has. a. twofold. effect..
First,.leaching.eventually.results.in.depletion.of.the.antimicrobial.activity,.and.second,.it.
presents.a.signiicant.route.of.environmental.exposure.
Antimicrobial.nanomaterials.are.typically.grouped.into.two.main.categories,.inorganic.
antimicrobial.nanomaterials.and.nanomaterials.used.as.antimicrobial.agent.delivery.vehi-
cles..Although.there.is.growing.interest.in.the.development.of.novel.antimicrobial.nanoma-
terials,.silver-based.nanomaterials.are.still.considered.the.“gold.standard”.and.are.typically.
Figure 28.1
Antimicrobial. zone. of. clearing. test. results. for. 4.mm. diameter. disks. loaded. with. various. nanomaterials.
(scale. bar. in. last. panel.=.5.mm).. Lighter. colored. areas. around. the. disks. are. areas. where. bacteria. are. not.
growing,. while. darker. areas. in. the. background. indicate. areas. where. bacteria. are. growing.. Materials. that.
have.higher.eficacy.and/or.diffuse.farther.into.the.agar.plate.will.have.larger.zones.of.clearing,.as.seen.in.
the.irst.two.panels.
