Biomedical Engineering Reference
In-Depth Information
and. differentiation. factors,. to. target. locations.. The. third. one. is. the. tissue. engineering.
approach,. in. which. cells. are. grown. in. 3D. scaffolds. (Langer. et. al.,. 1993).. The. use. of. cell.
suspensions.or.tissue-inducing.substances.is.considered.when.the.defects.are.small,.well.
contained,. or. not. suitable. for. implanting. a. 3D. structure.. To. engineer. tissues. with. prac-
tical. size. and. predetermined. shapes,. the. irst. two. approaches. are. not. appropriate.. The.
main. principle. of. the. tissue. engineering. strategy. is. to. seed. a. porous,. biodegradable. 3D.
cell.carrier.(scaffold,.matrix).with.cells,.add.signaling.molecules.like.growth.factors,.cul-
ture.the.construct.in.a.medium.for.growing.and.proliferation.of.cells,.and.then.implant.it.
into.the.defect.area.to.grow.a.new.tissue..It.is.expected.that.the.cells.of.the.natural.tissue.
would.also.attach.to.the.scaffold,.proliferate,.differentiate,.and.get.organized,.forming.a.
normal,.healthy.tissue.while.the.scaffold.itself.degrades..At.the.end,.healthy.tissue.ills.the.
defect. site. and. no. artiicial. matrix. remains.. Scaffolds,. cells,. and. signaling. biomolecules.
are.the.main.components.of.tissue.engineering.devices..All.of.these.components.play.very.
important.roles.during.tissue.regeneration..The.extracellular.matrix.(ECM).is.a.microen-
vironment.composed.of.parenchymal.cells.(functional.cells),.mesenchymal.cells.(support.
cells),. and. structural. materials.. Every. tissue. and. organ. in. our. body. is. formed. in. these.
microenvironments..The.body.serves.as.a.bioreactor,.which.applies.biomechanical.forces.
and.provides.biochemical.signals.to.the.cells.and.the.ECM.to.develop.and.maintain.tissue.
and.organs.(Barnes.et.al.,.2007)..In.the.tissue.engineering.approach,.the.biological.way.of.
tissue.formation.in.the.body.is.mimicked.by.taking.place.in.a.porous.matrix.
A.scaffold.is.one.of.the.essential.components.of.tissue.engineering.since.it.provides.3D.
support. for. the. cells,. as. ECM. does.. In. vitro,. cells. do. not. grow. in. a. way. to. ill. a. volume.
if. there. is. no. 3D. support.. Porous. scaffolds. provide. some. place. for. cell. attachment. and.
viability.through.transport.of.nutrients.and.metabolites,.and.allow.cell.expansion.and.tis-
sue.organization..There.are.some.requirements.for.proper.scaffolds..First,.they.should.be.
biocompatible,.and.therefore.should.not.cause.any.adverse.responses,.such.as.allergic.and.
carcinogenic.reactions.in.the.body..They.must.have.an.interconnected,.highly.porous.struc-
ture.with.a.high.surface.area.for.cell.adhesion.and.reorganization,.for.transport.of.nutri-
ents.and.removal.of.metabolic.waste,.and.for.homogeneous.cell.distribution.throughout.
the.scaffold..They.should.have.adequate.mechanical.strength.to.withstand.the.pressures.
and.mechanical.forces.applied.by.the.biological.system..The.degradation.rate.of.the.scaf-
fold.should.be.in.accordance.with.the.tissue.growth;.when.the.tissue.is.totally.regenerated,.
the. scaffold. should. be. almost. fully. degraded.. A. suitable. surface. chemistry. is. extremely.
important.for.cell.attachment,.proliferation,.and.differentiation.(Ma,.2004a;.Stevens.et.al.,.
2008.).The.material.of.the.scaffold.should.be.easily.processed.to.achieve.the.desired.shapes.
and.sizes..Finally,.the.scaffold.should.have.some.speciic.properties.for.speciic.tissue.engi-
neering.applications,.such.as.osteoconductivity.for.bone,.electrical.conductivity.for.nerve,.
and.contraction.for.myocardial.tissue.engineering.
Various. materials. have. been. studied. as. potential. scaffolds.. Some. metals. are. good.
choices. for. load-bearing. implants. since. they. have. superior. mechanical. properties.
(Catledge.et.al.,.2004)..Recently,.porous.titanium.(Ti).and.titanium.alloys.were.used.as.
scaffold. biomaterials. for. bone. tissue. engineering,. but. they. are. not. degradable. in. the.
body..Inorganic.materials.are.also.used.in.bone.tissue.engineering.studies.(Hench.and.
Polak,.2002)..Ceramics.such.as.hydroxyapatite.(HAp),.Bioglass,.A-W.glass.ceramics,.and.
β-tricalcium.phosphate.(β-TCP).closely.mimic.bone.tissues..They.are.osteoconductive.or.
osteoinductive,.and.enhance.the.absorption.of.bone.ECM.proteins,.resulting.in.improved.
osteoblast.adhesion.(Ducheyne.and.Qiu,.1999;.Dieudonné.et.al.,.2002;.Smith.et.al.,.2004)..
