Biomedical Engineering Reference
In-Depth Information
interactions.between.charged.elements.on.the.surface.of.the.iber.jet..First,.polymers.will.
be. surveyed. as. iber-forming. materials.. Later,. other. materials,. such. as. metals,. ceramics,.
and.glass,.will.be.considered.as.iber.precursors.
Electrospinning.gained.substantial.attention.due.mainly.to.its.potential.for.fabricating.
highly.porous.ibrous.membranes.with.the.iber.diameters.in.the.range.of.micro-.to.nano-
scale..Interestingly,.the.ranges.of.iber.diameters.that.can.be.achieved.are.two.to.three.orders.
of.magnitude.smaller.than.those.formed.by.conventional.iber.production..Moreover,.the.
electrospun.ibers.can.have.many.different.morphologies,.such.as.porous-surface,
3-7
.core-
sheath,
1,8
.and.side-by-side
9
.structure..The.extremely.unique.characteristics.of.electrospun.
nanoibers.make.them.very.useful.in.a.wide.range.of.advanced.applications,.such.as.non-
wovens.for.iltration,
10
.membranes.for.aerosol.puriication,
1
,.thin.coatings.for.defense.and.
protection,
12
.structures.incorporated.in.composites,
13
.and.tissue.scaffold,.wound.healing,.
and.drug.delivery.devices.in.biomedical.applications.
14,15
In.the.past.several.years,.the.usage.of.electrospun.iber.mats.for.biomedical.applications.
has.attracted.a.great.deal.of.attention.because.the.iber.mats.have.been.considered.suitable.
substrates.for.tissue.engineering,
16-19
.wound.dressing,
20,21
.and.immobilized.enzymes.
22-25
.
In. addition,.they.have.also.been.used.as.barriers.for.the.prevention.of.post-operative-in-
duced.adhesion
26,27
.and.vehicles.for.controlled.drug.or.gene.delivery.
28-32
.In.tissue.engineer-
ing,.the.electrospun.ibers.can.mimic.the.nanoibrous.features.of.an.extracellular.matrix.
(ECM).with.suitable.mechanical.properties..They.should.also.be.able.to.promote.cell.adhe-
sion,.spreading,.and.proliferation.
33
.For.wound.dressing,.the.nanoibrous.scaffold.should.
not.only.serve.as.a.substrate.for.tissue.regeneration,.but.also.may.deliver.suitable.bioactive.
agents,.including.drugs.(e.g.,.antibiotic.agent),.in.a.controlled.manner.during.healing.
33
23.2 ElectrospinningProcessandVariables
In.the.electrospinning.process,.a.high.voltage.is.used.to.create.a.strong.electrostatic.ield.
across.a.conductive.capillary.attached.to.a.reservoir.containing.a.polymer.solution.or.melt.
and.a.screen.collector..Upon.increasing.the.electrostatic.ield.strength.up.to.a.critical.value,.
charges.on.the.surface.of.a.pendant.drop.destabilize.its.shape,.from.partially.spherical.to.
conical,.known.as.the.Taylor.cone..Beyond.a.critical.value.at.which.the.electrostatic.ield.
strength. overcomes. the. surface. tension. of. polymer. solution. or. melt,. a. charged. polymer.
jet.is.eventually.ejected.from.the.apex.of.the.cone..The.iber.jet.undergoes.an.instability.
and.elongation.process,.which.allows.the.jet.to.become.very.long.and.thin..When.the.jet.
travels,.the.solvent.evaporates.or.solidiies.to.inally.leave.ultra-ine.ibers.on.the.collector..
For. a. typical. electrospinning. setup,. the. following. are. required:. (1). a. polymer. reservoir.
attached.to.a.capillary.or.needle,.(2).a.high-voltage.power.supply,.and.(3).a.screen.collector,.
as.shown.in.Figure 23.1.
Although.conceptually.a.simple.process,.electrospinning.has.signiicant.challenges..A.
number.of.parameters.can.greatly.inluence.the.formation.and.structure.of.the.obtained.
ibers..In.principle,.these.parameters.can.be.divided.into.two.major.ones:.system.param-
eters.and.process.parameters..By.appropriately.varying.all.or.some.of.these.parameters,.
ibers.are.successfully.electrospun..To.understand.the.electrospinning.process,.the.differ-
ent.parameters.that.affect.the.process.have.to.be.considered.
