Biomedical Engineering Reference
In-Depth Information
Biodegradable.PLA,.PGA,.and.PLGA.are.FDA-approved.materials.that.have.been.widely.
used.in.drug.delivery,.tissue.engineering,.and.regenerative.medicine..The.generation.of.
acidic.degradation.products.limits.the.applications.of.these.materials.in.vivo..This.factor.
further. drives. people. to. seek. other. biodegradable. polymers. to. produce. electrospun.
nanoibers.. PCL,. which. has. been. used. in. FDA-approved. drug. delivery. devices,. sutures,.
and. implants,. is. an. excellent. alternative. biodegradable. material. for. in. vivo. applications..
Commercially. available. synthetic. nanoibers. for. 3D. cell. culture. include. UltraWeb.
polyamide.surfaces.from.Corning,.PCL.nanoiber.inserts.from.Nanoiber.Solutions,.and.
optically.transparent.nanoiber.inserts.distributed.by.Sigma-Aldrich.
14.2.3.2 Natural Polymers
Natural.polymers.such.as.collagen,.ibronectin,.elastin,.laminin,.and.glycosaminoglycans.
are. the. major. components. of. extracellular. matrix. (ECM).. ECM. is. a. web-like,. ibrous.
matrix,. which. provides. biological,. structural,. and. mechanical. cues. and. support. for.
cells. organizing. into. functional. tissues. in. vivo.. Electrospun. nanoibers. resemble. the.
nanoibrous. structure. of. ECMs.. Electrospinning. of. ECM. proteins,. such. as. collagen,.
ibronectin,. elastin,. and. laminin,. have. provided. valuable. approaches. to. mimicking.
ECM.. Additionally,. polysaccharides. (e.g.,. alginate,. chitosan). have. been. electrospun. into.
nanoibers.as.well.with.the.aid.of.PEO,.which.are.low.in.cost,.compared.to.ECM.proteins.
and.can.easily.be.chemically.modiied.with.ECM.or.its.individual.proteins..Considering.
the.high.performance.in.mechanical.strength.and.elasticity,.silk.has.been.electrospun.into.
nanoibers.from.HFP.(Zarkoob.1998).or.from.an.aqueous.solution.in.the.presence.of.PEO.
(Jin.et.al..2002,.Vepari.and.Kaplan.2007).
Compared. to. synthetic. polymers,. electrospun. natural. polymeric. nanoibers. are. not.
very. stable. upon. hydration.. Various. crosslinking. strategies. have. been. tried. including.
glutaraldehyde,. formaldehyde,. hexamethylene. diisocyanate,. adipic. acid. hydrazide,.
epichlorohydrin,.and.other.epoxy.compounds.(Lu.et.al..2006,.Bhattarai.and.Zhang.2007)..
However,. these. crosslinking. strategies. have. the. potential. for. cytotoxicity.. Recently,.
1-ethyl-3-(3-dimethylaminopropyl)carbodiimidehydrochloride. (EDC). has. been. used.
to. crosslink. natural. nanoibers,. which. are. free. of. toxic. effects. (Sell. et. al.. 2010).. After.
electrospinning,.most.natural.polymers.form.nanoiber.meshes.similar.to.the.morphology.
of. electrospun. synthetic. polymers. (Figure. 14.3a).. After. crosslinking. under. hydration,.
the. electrospun. natural. polymeric. matrix. exhibits. ECM-like. morphology,. which. better.
recapitulates.the.structure.of.ECM.than.synthetic.polymers.(Figure.14.3b).
Examples.of.natural.polymers.that.have.successfully.been.electrospun.into.nanoibers.
are.listed.in.Table.14.2..HFP.is.the.most.used.solvent.for.electrospinning.of.natural.poly-
mers.. PEO. is. frequently. used. to. increase. the. viscosity. of. aqueous. solutions. in. order. to.
make.natural.polymers.electrospinnable..Natural.polymers.have.been.electrospun.alone.
or.blended.with.other.synthetic.or.natural.polymers.in.order.to.produce.nanoibers.with.
diverse.morphological,.biological,.and.mechanical.properties..More.detailed.information.
regarding.electrospinning.of.natural.polymers.can.be.found.in.a.review.(Sell.et.al..2010).
14.2.4 Melt electrospinning
Another. alternative. to. dissolving. a. polymer. in. a. solution. prior. to. electrospinning. is.
directly.electrospinning.from.a.melt,.which.is.known.as.melt.electrospinning..Although.
the.irst.melt.electrospinning.technique.was.reported.in.1981,.the.progress.has.been.very.
slow.. Only. several. dozen. papers. on. melt. electrospinning. were. published. during. the.
