Biomedical Engineering Reference
In-Depth Information
materials.have.been.performed.using.electrospun.poly(ethylene-
co
-vinyl.alcohol).(EVOH).
ibrous. mats,. for. example. (Kenawy. et. al.. 2003).. It. was. shown. in. this. study. that. smooth.
muscle.cells.and.ibroblasts.could.be.successfully.cultured.in.vitro.
Porosity.is.another.parameter.critical.to.tissue.engineering.applications..This.includes.
the.density.of.pores.and.the.iber.mat.pore.size.(Sill.and.von.Recum.2008)..Both.of.these.
factors. attribute. to. how. a. cell. migrates. and. invades. the. scaffold. (Cima. et. al.. 1991,. Wei.
and.Ma.2004,.Rezwan.et.al..2006)..Determining.porosity.for.the.electrospun.scaffold.has.
been. shown. theoretically. by. Eichhorn. and. Sampson. to. depend. upon. the. iber. width..
They.determined.that.the.mean.pore.radius.increases.with.iber.width..The.explanation.
provided. for. this. paradox. is. that. the. nanoiber. meshes. with. diameters. less. than. 100.nm.
behave.as.a.2D.sheet.rather.than.a.3D.scaffold..Electrospun.scaffolds.are.referred.to.as.2D.
stacked.networks.(Eichorn.and.Sampson.2005)..This.is.still.biologically.relevant.because.
the. basal. laminae. that. line. all. epithelial. cell. sheets. and. tubes. are. 2D. mats. (Sill. and. von.
Recum.2008)..Although.iber.width.may.be.large,.by.increasing.the.number.of.layers.one.
can.actually.decrease.the.mean.pore.radius..An.example.of.an.application.for.smaller.and.
less.pores.would.be.barrier.applications.that.include.skin.and.endothelium.(Sill.and.von.
Recum.2008)..An.application.that.would.require.larger.and.an.abundance.of.pores.would.
include.bone.regeneration.(Yoshimoto.et.al..2002)..Thus,.smaller.and.fewer.pores.are.not.
always.advantageous.if.cells.need.to.iniltrate.and.move.around.inside.the.scaffold..Thus,.
3D.scaffolds.are.necessary.for.this.and.require.that.pores.be.much.larger.in.radius.(on.the.
order. of. microns).. An. example. of. this. would. be. a. chondrogenesis. application. in. which.
chondrocytes.are.seeded.onto.PCL.scaffolds.with.10.μm.pores.(Gorsline.et.al..2006).
Surface. modiications. are. sometimes. necessary. when. considering. tissue-engineering.
applications.. By. attaching. bioactive. molecules. to. the. surface. of. nanoibrous. scaffolds,.
enhanced. control. of. cellular. function. can. be. achieved.. Examples. of. these. molecules.
include.ibronectin.(Sitterley.2008),.gelatin.(Ma.et.al..2005),.perlecan.(Casper.et.al..2007),.
acrylic. acid. (Park. et. al.. 2007),. and. the. RGD. peptide. sequence. (Kim. and. Park. 2006).. For.
example,.by.grafting.an.RGD.sequence.to.the.surface.of.a.nanoibrous.scaffold,.it.is.pos-
sible.to.strengthen.cell.attachment,.spreading,.and.proliferation,.all.of.which.are.vital.for.
engineering.a.functional.tissue.(Ho.et.al..2005)..In.addition,.it.is.possible.to.incorporate.
materials.into.the.scaffold,.such.as.gold,.in.order.to.make.them.conductive..For.example,.
gold.nanowires.have.been.integrated.into.alginate.scaffolds.in.order.to.improve.the.thera-
peutic.potential.of.cardiac.patches.(Dvir.et.al..2011).
14.4.2 Nanofiber-Based Drug Delivery
Electrospinning.has.been.examined.for.drug.delivery.purposes.because.there.is.promise.
for.site-speciic.delivery.of.drugs.(Kenawy.et.al..2009)..A.couple.of.examples.of.electrospun.
nanoibers. for. drug. delivery. have. been. shown. in. Table. 14.6.. Both. biodegradable. and.
nonbiodegradable.materials.can.be.used.as.delivery.vessels.(Zheng.et.al..2003,.Yu.et.al..
2009)..However,.biodegradable.materials.are.desired.because.there.is.no.need.to.explant.
the.scaffold..The.issue.with.this.is.that.the.drug.may.be.released.as.the.material.begins.
to.degrade..Therefore,.careful.attention.must.be.paid.to.these.rates.so.that.the.drug.can.
undergo. controlled. release. and. not. be. dumped. locally. altogether.. Typical. materials.
studied. for. this. application. include:. ɛ-caprolactone. and. ethyl. ethylene. phosphate.
(PCLEEP),.polycaprolactone.(PCL),.and.various.combinations.of.PLGA,.PEG,.and.PLA,.to.
name.a.few.(Sill.and.von.Recum.2008)..In.terms.of.drug.types,.there.are.several.that.have.
been.studied.for.controlled.release.using.electrospun.scaffolds..These.include.antibiotics,.
anticancer. drugs,. proteins,. and. DNA. (Agarwal. et. al.. 2008,. Sill. and. von. Recum. 2008)..
