Biomedical Engineering Reference
In-Depth Information
10.5.3 Cardiac Muscle Tissue Engineering
The. heart. is. the. center. of. the. circulation. system. and. distributes. blood. throughout. the.
body.. The. function. of. the. heart. is. vital. to. supply. oxygen. and. nutrients. to,. and. remove.
waste.products.from,.the.body.via.the.blood.in.order.to.maintain.the.balance.that.is.nec-
essary.to.sustain.life.(Vander.et.al.,.1994)..Strong.muscular.contractions.in.the.ventricles.
pump. blood. out. of. the. heart. and. into. the. circulatory. system.. These. muscular. contrac-
tions.are.produced.by.the.muscle.tissue.that.makes.up.the.walls.of.the.ventricles..Healthy.
heart.muscle.wall.is.composed.of.three.layers:.a.muscular.sheet,.the.myocardium,.lined.
on.either.side.by.two.collagenous.membranes.(containing.type.I.and.type.III.collagen.and.
elastin);. the. endocardium,. which. is. populated. by. endothelial. cells;. and. the. epicardium,.
also. called. visceral. pericardium. (van. de. Graaff,. 1998).. The. myocardium. is. the. layer. of.
functional.beating.muscle.that.consists.of.ibroblasts.and.highly.oriented.cardiomyocytes.
(muscle.ibers).in.a.matrix.of.collagen..The.cardiomyocytes.are.connected.end.to.end.in.
the.longitudinal.direction.and.side.by.side.in.the.transverse.direction.(Parker.and.Ingber,.
2007).. Collagen. types. I. and. III. are. the. predominant. interstitial. collagens. in. the. myocar-
dium. that. generate. structural. integrity. for. the. adjoining. cardiomyocytes,. providing. the.
means.by.which.myocyte.shortening.is.translated.into.overall.ventricular.pump.function..
Basement.membrane.components.include.laminin,.entactin,.ibronectin,.collagen.type.IV,.
and.ibrillin,.and.proteoglycans.include.chondroitin.sulfate,.dermatan.sulfate,.and.hepa-
ran. sulfate. (Kassiri. and. Khokha,. 2005).. The. cardiomyocytes. facilitate. conduction. of. the.
electrical.signals.needed.to.initiate.contractile.movement.in.order.to.pump.blood.out.of.
the.ventricles.(Vander.et.al.,.1994)..The.elementary.myocardial.functional.units.are.not.lone.
cardiomyocytes,.but.rather.are.multicellular.assemblies.of.these.highly.oriented.cells..The.
cardiomyocytes.are.connected.with.intercalated.discs.that.integrate.individual.electrical.
activation.and.contraction.into.a.pumping.action..Gap.junctions.in.these.intercalated.discs.
allow.the.action.potential.to.travel.through.the.membranes.of.the.myocytes,.thus.facilitat-
ing.signal.propagation.and.a.synchronized.contractile.pulse.(Vander.et.al.,.1994).
Heart.failure,.stemming.from.cardiovascular.diseases,.is.the.number.one.cause.of.death.
in.industrialized.countries..About.5.million.people.in.the.United.States.have.heart.failure,.
and. the. number. is. growing;. heart. failure. contributes. to. or. causes. about. 300,000. deaths.
each. year.. The. inability. of. the. heart. to. deliver. suficient. blood. to. meet. the. body's. meta-
bolic. requirements. leads. to. heart. failure.. The. most. common. causes. are. coronary. artery.
disease.and.hypertension.(high.blood.pressure),.which.damage.the.myocardium..Damage.
to.any.part.of.the.intricate.structure.of.the.heart,.though,.can.impair.cardiac.performance.
and. result. in. heart. failure;. examples. include. diseases. of. the. heart. valves,. the. electrical.
conduction.system,.or.external.pressure.around.the.heart,.due.to.constriction.of.the.peri-
cardial. sac. in. which. the. heart. is. located. (Jawad. et. al.,. 2007).. Congenital. heart. disease. is.
also.a.considerable.problem.worldwide,.affecting.approximately.1%.of.infants.(Wu.et.al.,.
2006)..Congenital.heart.defects.such.as.atrial.septal.defect,.ventricular.septal.defect,.double.
outlet.ventricles,.and.hypoplastic.left.heart.syndrome.are.associated.with.aplastic,.defec-
tive,. or. necrotic. myocardial. structures,. where. patch. closure,. correction. of. the. defect,. or.
revascularization.is.usually.required.(Koidis.et.al.,.2002)..Although.the.currently.available.
prostheses.are.adequate.for.restoring.ventricular.geometry.and.maintaining.ventricular.
pressure,.and.thus.may.be.life.saving,.they.do.not.actively.adapt.to.the.physiological.envi-
ronment.and.mechanical.demands,.as.they.are.nonliving.materials..When.implanted.into.
the. immature. heart. of. a. child,. these. materials. do. not. grow. with. the. pediatric. patient..
Therefore,.these.prostheses.have.limited.durability.and.are.prone.to.infection,.immuno-
logic.reactivity,.and.thrombosis,.which.often.requires.repeated.operations.(Mirensky.and
