Biomedical Engineering Reference
In-Depth Information
consists.of.dendrites,.an.axon,.and.a.cell.body.(Schmidt.and.Leach,.2003)..A.gray.matter.
localized.in.the.center.of.the.spinal.cord.is.composed.of.the.cell.bodies.of.excitatory.neu-
rons,.glial.cells,.and.blood.vessels..The.gray.matter.is.surrounded.by.white.matter,.which.
provides.protection.and.insulation.of.the.spinal.cord..White.matter.consists.of.axons.and.
glial.cells,.such.as.oligodendrocytes,.astrocytes,.and.microglia..Oligodendrocytes.myeli-
nate.the.axons.in.the.CNS,.while.astrocytes.are.active.in.the.blood-nerve.barrier,.separat-
ing. the. CNS. from. blood. proteins. and. cells.. Fascicles,. axons. in. bundles,. come. out. from.
the.white.matter.and.then.exit.the.encasing.bone.of.the.spinal.column..Following.travel.
through.the.PNS-CNS.transition.zone,.nerves.enter.the.PNS.
Nervous.system.injuries.may.result.in.permanent.functional.disabilities,.and.thus.have.
a. signiicant. impact. on. the. patient's. quality. of. life.. In. severe. damage. of. the. peripheral.
nervous.system,.self-regeneration.of.the.tissue.is.dificult,.and.it.is.almost.impossible.in.
the.central.nervous.system.(Meek.et.al.,.2002;.Schmidt.and.Leach,.2003)..For.that.reason,.
the. repair. of. the. damaged. tissue. in. the. nervous. system. is. complicated.. Surgical. inter-
ventions. (end-to-end. anastomosis). are. used. for. small. nerve. gaps. (Sanghvi. et. al.,. 2004);.
however,. for. long. gaps. (longer. than. 5. mm). the. common. treatment. is. to. use. autografts..
The.inherent.drawbacks.of.autografts,.such.as.limited.supply,.permanent.loss.of.the.nerve.
function.at.the.donor.site,.and.the.requirement.of.a.second.surgery,.are.great.challenges.
for.researchers.and.compel.them.to.investigate.alternative.treatments.(Millesi,.1991;.Terzis.
et.al.,.1997).
The.rapidly.developing.alternative,.nerve.tissue.engineering,.aims.to.restore.the.function.
of.damaged.neural.tissue.through.use.of.native.cells.and.cell.carriers..The.cells.commonly.
used.in.nerve.tissue.engineering.are.mature.neurons,.stem.cells,.and.supportive.cells,.such.
as.Schwann.cells,.astrocytes,.and.oligodendrocytes..The.construct.developed.by.nerve.tis-
sue.engineering.should.imitate.the.anatomic.structure.of.the.nervous.system.for.proper.
performance.. When. the. native. architecture. of. the. nerve. tissue. is. considered,. it. becomes.
apparent.that.a.directional.cell.growth.is.a.prerequisite.for.functional.nerve.regeneration..
The. desired. physical. properties. of. a. cell. carrier. are. biodegradability,. high. porosity,. and.
also. a. cell. guiding. tool,. such. as. an. internal. oriented. matrix. with. appropriate. chemical.
structure.(ECM.proteins,.especially.laminin,.for.nerve.tissue)..Topographical.cues.for.cell.
migration.could.serve.to.mimic.the.native.nerve.fascicles.(Hudson.et.al.,.1999)..The.guid-
ance.needed.for.the.tissue-engineered.nerve.construct.may.be.achieved.by.the.use.of.ilms.
with.patterned.surfaces,.or.longitudinally.oriented.microchannels.and.ibrous.scaffolds.
Fibrous.scaffolds.to.be.used.in.nerve.regeneration.could.be.produced.by.electrospinning.
and.self-assembly.(Table 10.2)..Since.they.are.inherently.porous.and.have.a.high.surface.
area-to-volume.ratio,.these.ibrous.scaffolds.promote.attachment,.survival,.and.growth.of.
cells.(Chiu.et.al.,.2005)..An.architecture.similar.to.ECM.makes.ibrous.scaffolds.a.promis-
ing.tool.for.nerve.tissue.engineering..The.ideal.scaffold.should.be.biocompatible.to.avoid.
inlammatory. response,. be. biodegradable,. and. have. appropriate. mechanical. properties.
to.provide.the.support.required.for.proper.healing.(Hudson.et.al.,.1999)..The.material.of.
the.cell.carrier.is.a.very.important.determinant.in.achieving.a.scaffold.suitable.for.nerve.
tissue. engineering.. The. degradation. rate. and. mechanical. properties. of. synthetic. poly-
mers. such. PLLA,. PLGA,. PHBV,. and. PCL. can. be. controlled. by. chosing. the. appropriate.
compound,. and. as. such,. they. are. very. suitable. for. tissue. engineering.. Natural. materi-
als.such.as.PHBV,.collagen,.gelatin,.chitosan,.and.especially.laminin.have.speciic.physi-
cal. properties. and. biomolecular. recognition. sites. as. in. native. tissue.and,. therefore,.they.
have.been.increasingly.investigated.as.ibrous.scaffolds.for.nerve.tissue.regeneration.(Cao.
et.al.,.2009)..Blends.of.polymers.have.also.been.extensively.used.in.nerve.tissue.engineer-
ing.to.achieve.the.desired.scaffold.properties..For.instance,.natural.polymers.lack.proper.
