Biomedical Engineering Reference
In-Depth Information
biological.stimuli..These.2D.methods.can.be.miniaturized.using.selective.surface.modi-
ication. through. microfabrication. techniques. and. enable. the. control. of. cell-cell. contacts.
on.geometrically.deined.2D.surfaces..Controlling.the.degree.of.cell-cell.contact.is.useful.
in.cell.biology.studies.and.tissue.engineering.because.cell-cell.communications.in.aggre-
gates. play. a. signiicant. role. in. controlling. the. cell. behavior.. One. example. is. in. embry-
onic. stem. cell. (ESC). proliferation. and. differentition.
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. Variety. of. technologies,. such. as.
microtopography,
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.microfabricated.stencils,
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.microcontact.printing,
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.and.layer-by-layer.
deposition,
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.have.been.established.for.ESC.patterning.on.2D.surfaces..One.approach.uses.
poly(ethylene.glycol).(PEG).hydrogel.microarrays.for.uniform.cell.seeding.and.embryoid.
body.(EB).formation,
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.and.this.approach.was.further.used.to.generate.spatially.and.tem-
porally.synchronized.beating.human.EBs.
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.Moreover,.homogeneous.EBs.obtained.from.
the.microwell.can.be.used.to.direct.EB-mediated.differentiation.
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.Another.approach.used.
microfabricated.parylene-C.stencils.to.pattern.cocultures.in.both.static.and.dynamic.con-
ditions.by.using.several.stencils.sequentially.with.different.surface.properties.
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12.2.1 Photolithography
Photolithography. is. a. well-established. and. widely. used. method. for. patterning. cells. on.
a. surface.
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. In. this. process,. materials. that. interact. with. cells. are. patterned. selectively. by.
the.transfer.of.patterns.from.a.photomask.to.photosensitive.polymers.prepared.on.a.sub-
strate.. Typically,. photoresist. is. used. as. photosensitive. materials. patterned. by. ultraviolet.
(UV).exposure.and.selectively.removed.on.the.exposed.(or.unexposed).area..After.depos-
iting. cell-adhesive. (or. repellent). materials. on. the. substrate,. the. patterned. photoresist. is.
removed. to. leave. the. material. of. interest. selectively.. This. so-called. lift-off. process. is. an.
effective. way. to. selectively. pattern. cells. on. a. surface.. Recently,. direct. patterning. of. cell.
interacting. materials. has. been. investigated. to. overcome. low. biocompatibility. of. the. lift-
off.process.using.photoresist..Patterning.of.vitronectin,
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.hexamethyldisilazane.(HMDS),
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.
cell-adhesive.proteins,
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.and.PEG
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.can.eliminate.photoresist.during.the.selective.surface.
modiication.for.cell.studies..Karp.et.al..demonstrated.cell.patterning.using.photocross-
linkable. chitosan.
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. They. prepared. the. polymer. ilms. on. a. slide. glass. and. exposed. UV.
light. to. crosslink. chitosan,. then. washed. out. uncrosslinked. chitosan. to. leave. patterns. of.
crosslinked.polymer..Using.this.approach,.cardiomyocytes.were.cultured.on.the.glass.sur-
face.between.chitosan.lane.patterns,.and.osteoblasts.were.localized.within.the.patterns..In.
another.interesting.example,.Yamazoe.et.al..selectively.converted.albumin.surfaces.to.cell.
adhesive.through.UV.exposure.(Figure 12.1).
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.UV.irradiation.changed.the.contact.angle.of.
the.albumin.from.85°.to.23°,.which.successfully.applied.to.selective.attachment.of.mouse.
ibroblast.cells.on.the.UV-irradiated.region.
12.2.2 Microcontact Printing
Compared.with.the.photolithography.technique,.microcontact.printing.(µCP).can.trans-
fer. self-assembled. monolayers. (SAMs). from. a. soft. elastomeric. stamp,. typically. made. of.
polydimethylsiloxane.(PDMS),.onto.another.substrate.without.any.exposure.steps.
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.For.
example,. methyl-terminated. alkanethiol. SAMs. facilitated. protein. adsorption,. leading. to.
increased.cell.adhesion,.while.PEG-modiied.alkanethiol.SAMs.prevented.cell.adhesion..
Other.mechanisms.can.also.be.adapted.to.use.with.microstamps.for.creating.structures..
Khademhosseini.and.colleagues.used.the.direct.contact.of.a.PDMS.stamp.on.a.thin.poly-
mer.ilm.to.generate.patterns.by.using.capillary.forces.(Figure 12.2).
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.Wet.polymers.coated.
on.a.substrate.and.pressed.by.a.PDMS.stamp.move.spontaneously.into.a.void.space,.which.
