Biomedical Engineering Reference
In-Depth Information
This. is. to. accommodate. the. mechanical. stress. bearing. of. tissue. and. the. magnitude. of.
exercise.the.tissue.is.accustomed.to.
As. mentioned. earlier,. scaffolds. with. high. mechanical. strength,. lexibility. and. optical.
transparency,.and.optimal.degradation.properties.and.biocompatibility.are.critical.to.the.
success.of.tissue-engineered.devices.(Grifith.and.Naughton.2002)..Early.attempts.in.tissue.
engineering.focused.on.building.microvascular.networks.that.have.been.characterized.with.
design.rules.and.scaling.laws.(Jiang.et.al..1994,.Huang.et.al..1996,.Kaazempur-Mofrad.et.al..
2001,.Emerson.et.al..2006,.Janakiraman.et.al..2006);.several.have.fabricated.PDMS.scaffolds.
for.seeding.endothelial.cells.to.realize.synthetic.capillary.networks..These.demonstrations.
are.useful.for.in.vitro.models.for.drug.discovery.and.safety.testing.and.for.artiicial.organ.
assist. devices.. However,. as. previously. discussed,. though. PDMS. is. biocompatible,. the.
fact.that.it.is.not.degradable.makes.it.unsuitable.for.implantable.applications.that.require.
long-term.resorption.and.host.integration..In.addition,.many.existing.studies.have.shown.
(Hu. et. al.. 2004,. Chen. et. al.. 2006,. Sui. et. al.. 2006). that. the. relative. instability. of. surface.
properties.and.permeation.and.absorption.of.organic.molecules.make.it.challenging.to.use.
PDMS.as.a.useful.tissue.engineering.platform..Therefore,.several.biodegradable.polymers,.
such. as. PLGA. (King. et. al.. 2004),. and. silk. ibroin. have. been. explored. for. applications. as.
scaffolding.materials.
Most. biodegradable. polymers. suffer. from. a. short. half-life. resulting. from. rapid. degra-
dation.upon.implantation,.exceedingly.high.stiffness,.and.limited.chemical.moieties.(Poirier.
et.al..1995)..While.some.of.the.aforementioned.polymers.have.been.considered.as.potential.
tissue. engineering. materials,. they. share. one. or. more. of. the. aforementioned. drawbacks..
However,. in. addition. to. the. classical. materials,. a. few. newly. developed. biodegradable.
elastomers.have.presented.new.options.for.material.selection.for.scaffolding.materials.
PGS.is.a.biodegradable.elastomer.that.is.biocompatible,.inexpensive,.and.can.be.easily.
polymerized.from.glycerol.and.sebacic.acid..As.glycerol.and.polymers.containing.sebacic.
acid.have.been.approved.for.medical.applications.use,.PGS.is.a.desirable.substrate.for.tissue.
engineering..Biocompatibility.studies.show.superior.cellular.response.and.morphology.of.
PGS.compared.to.PLGA,.which.has.been.observed.to.cause.inlammatory.responses.when.
implanted.in.bulk.form..Microfabrication.studies.demonstrate.that.PGS.is.easy.to.process.
(Duffy.et.al..1998),.and.it.has.proven.to.be.a.suitable.material.for.microluidic.scaffolds.for.
endothelialization.and.hepatocyte.culture,.as.well.as.for.numerous.other.applications.
Another.newly.developed.class.of.elastomeric.poly(ester.amides).known.as.APS.(Bettinger.
et.al..2008).has.been.introduced.to.address.the.rapid.erosion.of.PGS.during.degradation.
process..The.material.provides.a.high.degree.of.tunability.based.on.physiologic.processes.
for.its.mechanical.and.degradation.properties..The.balance.of.hydrolytic.and.enzymatic.
degradation.rates.can.be.adjusted.across.wide.ranges.based.upon.the.speciic.composition.
of. the. APS. polymer,. and. therefore. it. has. been. invoked. as. a. potential. scaffold. for. tissue.
engineering.(Wang.et.al..2010).
22.2.2 Micro- and Nanofabrication Technology
As. tissues. constantly. receive. internal. and. external. stimuli. from. their. surroundings,. a.
dynamic.3D.balance.is.maintained,.and.thus.the.surface.properties.of.scaffolds.and.spatial.
arrangements.are.another.topic.of.interest.for.research..It.has.been.shown.that.the.chemical.
and. mechanical. environment. of. the. growth. site. control. the. adhesion. and. migration. of.
cells,. as. well. as. the. rate. of. regeneration.. In. Koegler. and. Grifith. (2004),. by. varying. the.
patterning. and. the. coating. concentration. on. the. surface. of. scaffolds,. cell. behavior. was.
observed.to.change.drastically.
