Biomedical Engineering Reference
In-Depth Information
(a)
(b)
Figure 14.3
SEM.images.of.electrospun.alginate.nanoibers.before.(a).and.after.(b).crosslinking.with.calcium.chloride.
last.30.years..The.two.main.drawbacks.of.this.method.are.that.the.melts.must.be.kept.at.
elevated.temperatures.and.that.the.polymer.needs.to.cool.over.the.capillary.to.collector.
distance.for.ibers.to.suficiently.form.(Sill.and.von.Recum.2008)..However,.melt.electros-
pinning.is.appealing.because.it.avoids.organic.solvents,.and.there.is.no.question.of.proper.
solvent.evaporation.and.potential.toxicity.of.solvent.residue.retained.within.the.nanoibers.
(McCann.et.al..2006).
Due.to.the.high.viscosity.and.lack.of.conductivity.of.polymer.melts,.limited.types.of.poly-
mers.have.been.tried.for.melt.electrospinning.(Table.14.3)..From.Table.14.3.we.can.see.that.
most.melt.electrospinning.processes.produce.micron-sized.nanoibers..In.order.to.achieve.
nanoscale. ibers,. we. need. to. precisely. control. the. air. temperature. surrounding. the. iber.
and.macromolecular.structure.throughout.the.melt.electrospinning.process..The.molecular.
weight.has.a.dramatic.effect.on.the.iber.diameter..The.higher.the.molecular.weight,.the.
larger.the.iber.diameter.will.be..The.tacticity.also.affects.the.iber.diameter.(Lyons.et.al..
2004)..Melt.electrospinning.allows.direct.deposition.of.nanoibers.onto.cells,.which.serves.
as.the.electrode.(Dalton.et.al..2006b),.and.enables.patterned.electrospinning.(Dalton.et.al..
2008)..In.addition,.melt.electrospinning.is.easy.to.scale.up.to.improve.production.rate.
14.2.5 Core-Shell electrospinning
Concentric. or. core-shell. electrospinning. is. a. technique. that. can. fabricate. scaffolds. of.
blended. polymers.. Typically,. one. polymer. remains. on. the. outer. sheath. while. the. other.
resides.in.the.inner.core..This.is.possible.by.choosing.two.polymer.solutions.that.phase.
separate.as.the.solvent.is.evaporated.and.by.using.two.coaxially.aligned.capillaries.(Sun.
et.al..2003,.Tran.et.al..2011)..An.advantage.of.this.technique.is.that.the.inner.core.is.protected,.
depending.upon.the.application..In.terms.of.nanobiotechnology,.a.core-shell.structure.of.
ibers.has.the.potential.to.protect.the.structural.integrity.and.bioactivity.of.encapsulated.
proteins.(Zhang.et.al.2004,.Jiang.et.al..2006,.Dai.et.al..2010).
14.2.6 Fabrication of Aligned Nanofibers
Randomly.oriented.nanoibers.are.typically.applied.in.iltration,.tissue.scaffolding,.implant-
ing.coating.ilms,.and.wound.dressings.(Huang.et.al..2003,.Rho.et.al..2006,.Gopal.et.al..2007)..
However,.it.is.also.important.to.realize.that.aligned.nanoibers.increase.the.capability.of.the.
