Biomedical Engineering Reference
In-Depth Information
10.3 ImportanceofNano/MicrofibrousScaffolds
Many.extracellular.proteins.have.a.ibrous.structure.with.diameters.on.the.low.or.submi-
crometer.scales..For.example,.collagen.is.the.most.abundant.ECM.protein.in.the.human.
body,.and.it.has.a.ibrous.structure.with.iber.bundle.diameters.varying.from.50.to.500.nm,.
depending. on. the. site. and. species. (Hay,. 1991).. In. the. native. tissues,. the. structural. ECM.
proteins. are. one. to. two. orders. of. magnitude. smaller. than. the. cells,. and. therefore,. the.
cells.are.in.direct.contact.with.many.ECM.ibers..It.is.now.well.known.that.many.biologi-
cally.active.molecules,.extracellular.matrix.components,.and.cells.interact.with.each.other.
using.functional.groups.on.the.nanoscale..It.is.therefore.a.useful.approach.to.mimic.the.
ibrous.nature.of.the.extracellular.matrix.when.fabricating.scaffolds.(Barnes.et.al.,.2007)..
Nanoibers.have.a.high.surface-to-volume.ratio,.which.enhances.the.number.of.cells.that.
adhere.to.the.surface.(Ma.and.Langer,.1999)..Cell.migration,.proliferation,.and.differentia-
tion.follow.adhesion.(Palecek.et.al.,.1997),.and.it.is.expected.that.these.reactions.will.be.
much.higher.on.nanoibrous.scaffolds.than.on.foams.or.ilms..As.a.result,.nanoibers.have.
attracted.the.attention.of.many.researchers.who.considered.them.as.potential.scaffolds.for.
applications.such.as.tissue.engineered.vasculature.(Xu.et.al.,.2004;.Lee.et.al.,.2007),.bone.
(Sui.et.al.,.2007;.Cui.et.al.,.2007),.nerve.(Yang.et.al.,.2005;.Schnell.et.al.,.2007),.and.tendon.
and.ligament.(Lee.et.al.,.2005;.Sahoo.et.al.,.2006).
10.4 FabricationofNano/MicrofibrousScaffolds
Since. ibrous. scaffolds. with. nanometric. iber. diameters. have. been. found. to. be. satisfac-
tory. for. various. tissue. engineering. applications,. extensive. research. toward. developing.
processes. for. the. fabrications. of. these. ibrous. structures. is. being. conducted.. The. main.
methods. used. in. the. fabrication. of. ibrous. scaffolds. are. self-assembly,. template. synthe-
sis,.drawing.and.extrusion,.phase.separation,.wet.spinning,.and.electrospinning..Each.of.
these.procedures.leads.to.ibers.with.different.dimensions.and.organizations.
In. the. case. of. self-assembly,. atoms. and. molecules. arrange. themselves. through. weak.
and.noncovalent.interactions,.and.it.is.known.as.a.bottom-up.method.since.the.built-up.
nanoscale. ibers. are. formed. starting. from. smaller. molecules.. It. yields. ibers. with. small.
dimensions.(less.than.100.nm.wide.and.up.to.a.few.micrometers.long),.and.it.offers.novel.
properties.and.functionalities.that.cannot.be.achieved.by.conventional.organic.synthesis.
(Hasseinkhan. et. al.,. 2006).. The. main. disadvantage. of. this. method. is. its. complexity,. in.
addition.to.being.a.long.and.extremely.elaborate.process.with.low.productivity.(Ma.et.al.,.
2005).
Another.fabrication.method.is.template.synthesis..As.the.name.implies,.a.nanoporous.
membrane.is.used.as.a.mold.or.template.in.order.to.obtain.the.material.of.interest.in.the.
form.of.solid.nanoibrous.or.hollow-shaped.tubules..This.method.uses.a.polymer.solution.
to.be.extruded.through.a.porous.membrane.by.application.of.pressure..Fibers.are.formed.
when.the.extruded.polymer.comes.into.contact.with.a.precipitating.solution.(Feng.et.al.,.
2002).. Fiber. diameter. depends. on. the. pore. size. of. the. template. used,. and. it. varies. from.
a.few.to.a.hundred.nanometers..Many.materials,.like.metals,.polymers,.and.carbon,.can.
be.utilized.as.templates.for.iber.fabrication;.however,.this.method.is.limited.in.that.the.
length.of.nanoibers.can.only.be.a.few.micrometers.
