Biomedical Engineering Reference
In-Depth Information
22.2.1  Functions and requirements of Synthetic Scaffolds
One.of.the.most.essential.requirements.for.a.functional.scaffold.is.its.biocompatibility,.and.
many.factors.are.used.to.evaluate.it:
•. Does. the. scaffold. interact. naturally. with. the. existing. cells. and. tissues. without.
triggering.immune.responses?
•. Does.the.scaffold.activate.the.blood.clotting.mechanism?
•. Does.the.scaffold.disturb.tissue.functions?
Besides. the.aforementioned.points,. the.shape,.size,.chemical. reactivity,. and. degradation.
by. products. are. also. considered. evaluation. factors. in. determining. the. biocompatibility.
of. scaffolds. (Velema. and. Kaplan. 2006).. Several. examples. of. common. scaffold. materials.
are. poly(dimethylsiloxane). (PDMS),. poly(lactic. acid). (PLA),. and. poly(lactic-co-glycolic.
acid). (PLGA);. each. is. generally. considered. a. biocompatible. scaffolding. material. and. is.
FDA-approved.for.some.applications.
Another.property.of.implants.and.scaffolds.that.may.be.important.is.that.these.medical.
devices.would.be.completely.replaced.by.differentiated.and.functional.cells.over.time..In.
such.cases,.the.biodegradation.properties.of.scaffolds.are.very.important.factors.in.mate-
rial.selection..It.is.generally.best.for.the.scaffolds.to.biodegrade.into.harmless.fragments,.or.
to.be.completely.bioresorbed,.meaning.that.all.degradation.residues.are.resorbable.by.the.
body.through.processes.like.metabolization..One.major.concern.that.often.rises.from.bio-
degradable.materials.is.the.immune.responses.triggered.from.degradation.residues..For.
example,.poly(α-hydroxy.acid).groups.often.degrade.into.acidic.residues,.causing.severe.
local.inlammation..Therefore,.much.work.had.been.put.into.designing.new.biodegradable.
polymers.with.more.bioresorbable.monomers,.and.iller.materials,.which.help.control.the.
production.and.release.of.inlammation-inducing.particles.(Hutmacher.et.al..2001).
Controlling.the.degradation.rate.of.the.polymer.is.considered.both.the.most.important.
as. well. as. the. most. dificult. factor. in. designing. biodegradable. medical. devices.. The.
degradation. rate. is. to. be. timed. perfectly. so. that. as. the. scaffold. degrades,. the. space,.
strength,. and. function. of. the. scaffold. would. be. replaced. by. newly. generated. tissue..
Adverse.effects.may.appear.even.if.the.degradation.rate.is.only.timed.slightly.off..With.a.
scaffold.that.degrades.too.quickly,.the.growing.tissue.is.likely.to.suffer.from.premature.
exposure. to. weight,. and. the. growth. may. be. seriously. disturbed.. If,. on. the. other. hand,.
the. degradation. rate. is. lower. than. the. tissue. regeneration. rate,. tissue. growth. would. be.
restricted.and.suppressed.by.limited.space.and.would.suffer.from.stress.shielding,.leaving.
the.tissue.without.the.necessary.mechanical.stimulation.during.growth..Therefore,.tuning.
the. scaffolds. with. proper. degradation. rate. via. material. selection,. scaffold. design,. and.
triggered.degradation.mechanisms.has.been.a.major.focus.in.implantable.medical.device.
design.for.the.past.decade.
Biodegradable. scaffolds. are. designed. and. created. for. two. main. purposes:. assisting.
cell. seeding,. migration,. and. differentiation,. and. serving. as. a. structural. support. while.
regeneration.takes.place..The.latter.indicates.that.the.mechanical.properties.of.scaffolds.
and. that. of. the. designated. tissue. should. be. relatively. similar.. The. stiffness. of. the.
scaffold. is. very. important. in. the. regenerating. tissue. for. supporting. and. for. assisting.
tissue. regeneration.. It. is. particularly. important. in. assisting. the. proliferation. and.
differentiation.of.cells.(Androjna.et.al..2007)..The.elasticity.of.the.scaffolds.is.also.critical.
to. the. activities. and. functions. of. the. tissues.. While. a. scaffold. for. bone. regeneration. is.
nonelastic. and. rigid,. scaffolds. for. regeneration. of. tendon. and. muscle. are. more. elastic..
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