Biomedical Engineering Reference
In-Depth Information
stem. cells. (hMSC). in. a. pattern. to. encourage. cardiac. regeneration.. The. hMSC. cells. have.
been. shown. to. inhibit. apoptosis. of. endothelial. cells. in. hypoxic. conditions,. increase.
survival,.and.stimulate.angiogenesis.(Pittenger.1999)..Printing.hMSC.in.close.proximity.
with. HUVEC. cells. would. allow. for. the. hMSC. cells. to. stabilize. the. neovasculature.
(Giordano.and.Galderisi.2006)..Patterns.were.created.to.encourage.vascularization,.with.
signiicant.improvement.in.cell.proliferation.observed.versus.patches.that.were.randomly.
seeded.with.cells..Additionally,.rats.suffering.from.myocardial.infarction.showed.marked.
improvement.of.heart.function.with.the.administration.of.the.printed.cardiac.patch.versus.
the.randomly.seeded.patch.(Gaebel.et.al..2011;.Gruene.et.al..2011)..Integration.with.the.host.
myocardium.was.also.seen.
Femtosecond.pulses.have.been.used.to.transfer.cells.(Kaji.et.al..2007;.Uchugonova.et.al..
2008)..Due.to.the.extremely.short.timescale,.very.small.areas.of.the.print.ribbon.are.ener-
gized,.allowing.for.the.transfer.of.single.cells.as.was.shown.with.mouse.NIH3T3.ibroblasts.
(Hosokawa.et.al..2004)..Consistent.regeneration.of.ilopodia.was.seen,.and.re-adherence.
was.seen.in.around.4.h;.80%.successful,.nondestructive.transfer.was.achieved..This.level.of.
print.control.with.cells.will.likely.be.vital.for.future.development.in.3D.printing.of.tissue.
constructs.and.for.the.study.of.spatial.cell-cell.interactions.
13.5 Trends and Future Prospects
Controlled. printing. to. various. depths. (e.g.,. x-y. μms). has. been. demonstrated. with. cells.
(Nahmias.et.al..2005;.Patz.et.al..2005)..Additionally,.layering.methods.have.been.used.to.
create.3D.constructs..Currently,.the.ield.of.tissue.engineering.is.limited.to.fabrication.of.thin.
tissues..However,.thick.tissues.are.critical.for.any.sort.of.functional.complex.organ.growth,.
and.a.major.hurdle..One.of.the.primary.issues.is.the.inability.for.in.vivo.cells.to.survive.
far.from.a.capillary.structure.(Frerich.et.al..2001;.Cassell.2002;.Nomi.et.al..2002;.Secomb.
and.Pries.2002;.Gridley.2007)..This.is.due.to.diffusion-based.limitations.on.the.availability.
of. nutrients. and. the. removal. of. waste. products,. as. well. as. enabling. cell. signaling. and.
communication.(Secomb.and.Pries.2002;.Gridley.2007;.Ko.et.al..2007)..A.vascular.system.
is. critical. in. the. growth. and. maintenance. of. all. major. tissues. (Ko. et. al.. 2007).. In. vivo,.
blood.vessels.are.formed.in.two.processes:.angiogenesis,.which.involves.a.branching.of.
capillaries.from.preexisting.blood.vessels,.and.vasculogenesis,.wherein.undifferentiated.
endothelial.cells.assemble.the.vessel.in.situ.(Ko.et.al..2007)..In.vitro,.aspects.of.this.process.
have. been. accomplished.. Branched. networks. of. cells. have. been. created. with. the. aid. of.
preformed.paths..Lumens.(Kaihara.et.al..2000;.Egginton.and.Gerritsen.2003;.Wu.et.al..2004).
and. contiguous. vessel. walls. (Sieminski. et. al.. 2004). have. also. been. created. with. similar.
assisted. methods.. Currently. however,. the. best. efforts. have. only. yielded. microvessel.
networks.that.are.not.as.effective.as.those.grown.in.vivo.(Sieminski.et.al..2002,.2004)..Since.
blood. vessel. formation. depends. on. both. complex. biochemical. cues. as. well. as. physical.
and. structural. factors,. similar. factors. need. to. be. simulated. in. vitro. to. accomplish. true.
vasculogenesis.in.tissue.engineering.(Black.et.al..1998)..Vessel.networks.have.been.created,.
but.their.functionality.is.lacking..Additionally,.the.creation.of.useful.capillary.beds.is.not.
even.this.advanced..Macroscale.blood.vessels.have.been.created.in.bioreactors;.yet,.issues.
remain. in. controlling. growth. and. creating. capillaries. (Patan. et. al.. 2001a,b;. Borges. et. al..
2003;.Kulkarni.et.al..2004;.Kannan.et.al..2005)..Bioreactors.are.certainly.necessary.for.the.
creation.of.tissues.in.vitro.(Niklason.et.al..2002;.Barron.et.al..2003;.McCulloch.et.al..2004;.
