Biomedical Engineering Reference
In-Depth Information
Lim. et. al.. 2005a,b).. More. speciically,. it. has. been. shown. that. cells. initially. undergo.
increased. cytoskeletal. organization. and. ilopodia. formation. when. compared. with.
cells.cultured.on.lat.controls,.but.this.initial.attachment.phase.is.short.lived.and.ibro-
blasts. begin. to. dedifferentiate. and. undergo. anoikis. (adhesion-mediated. apoptosis).
as. a. result. of. reduced. adhesion. and. cellular. spreading.. Similarly,. Berry. et. al.. (2006).
showed.that.three-dimensional.(3D).constructs.with.phase-separated.polymer.features.
of.a.similar.dimension.also.reduced.adhesion.in.bone.marrow-derived.osteoprogenitor.
populations.
Reducing.the.height.of.nanoprotrusion.features.to.<34.nm.has.been.shown.in.multiple.
cell.types.to.return.the.frequency.of.focal.adhesion.formation.to.that.of.cells.cultured.on.
planar. control. substrates. (Lamers. et. al.. 2010),. with. accompanying. upregulations. in. pro-
teins.critical.to.cytoskeletal.dynamics.(Dalby.et.al..2002d).
Lim.et.al..(2005a,b).have.further.demonstrated.the.increased.incidence.of.mature.focal.
adhesion.plaque.formation.in.osteoblasts.cultured.on.nanoislands.that.approach.11.nm.in.
height..It.can.be.inferred.that.the.effects.of.feature.height.on.integrin.clustering.are.dis-
ruptive.at.heights.>34.nm.and.that.features.with.z-dimensions.<34.nm.are.insuficient.to.
disrupt.integrin.clustering.(Sjostrom.et.al..2009),.which.may.be.as.a.result.of.clogging.of.
the.nanofeatures.in.a.protein-rich.environment..Conversely,.substrates.possessing.nano-
protrusions.with.heights.<34.nm.may.provide.subtle.cues.for.the.enhancement.of.cellular.
spreading.and.are.reported.to.increase.cellular.adhesion.(Lim.et.al..2005a,b).by.providing.
tactile.stimuli.for.ilopodial.extensions.(Dalby.et.al..2004b).
Perturbation. of. integrin. clustering. on. nanoprotrusion. arrays. with. heights. >34.nm. is.
related.to.feature.width.and.density;.however,.this.disruption.of.cell.adhesion.is.observ-
able. in. many. cell. types. on. a. wide. variety. of. polymeric. substrates. fabricated. by. various.
methods. (Dalby. et. al.. 2002b,c,d,. 2004b).. The. ability. of. raised. features. to. prevent. cellular.
contact.with.the.basal.“planar”.substrate.and.to.reduce.cellular.adhesion.is.dependent.on.
protrusion.diameter.and.density..Although.nanoprotrusion.height.is.critical.in.the.regula-
tion.of.focal.adhesion.formation.in.vitro,.feature.diameter.and.the.edge-edge.spacing.also.
dictate.whether.adherent.cells.become.exclusively.localized.to.the.feature.apexes.or.con-
tact.the.basal.substrate..When.protrusion.height.and.density.are.suficient.to.prevent.cell.
contact.with.the.underlying.substrate,.parameters.that.need.to.be.deined.for.individual.
cell.types,.the.inluence.of.the.nanoprotrusion.diameter.and.edge-edge.spacing.become.
the.deining.factors.in.the.regulation.of.integrin.clustering.and.focal.adhesion.formation.
(Sjostrom.et.al..2009).
To. facilitate. integrin. clustering. in. cells. suspended. on. an. array. of. nanoprotrusion,. the.
feature.diameter.or.width.must.exceed.73.nm..This.has.been.veriied.by.studies.making.
use.of.pillar.arrays.>400.nm.in.height..Here.the.nanoprotrusion.height.and.density.was.
suficient.to.isolate.cells.from.the.underlying.planar.substrate..Reducing.the.pillar.diam-
eter.to.<73.nm.and.increasing.the.edge-edge.distance.to.300.nm.markedly.reduced.cellular.
adhesion. (Kim. et. al.. 2005;. Lee. et. al.. 2008),. again. indicating. that. an. interprotrusion. dis-
tance.of.>73.nm.inhibits.focal.adhesion.formation.at.the.bridging.site.between.two.adjacent.
nanoprotrusions..This.was.identiied.by.Sjostrom.and.colleagues,.who.noted.a.reduction.
in. cellular. spreading. and. focal. adhesion. formation. when. skeletal. stem. cells. were. cul-
tured.on.nanopillar.arrays.with.an.edge-edge.spacing.approaching.73.nm.(Sjostrom.et.al..
2009)..This.effect.has.again.been.demonstrated.in.a.study.of.cardiomyoblast.adhesion.on.
nanoscale. dots.. Here. the. authors. noted. reduced. focal. adhesion. formation. on. substrates.
with. dot. sizes. of. 100. and. 200.nm;. this. effect. was. reversed,. however,. on. 50.nm. dots. (Pan.
et.al..2012)..For.a.schematic.explanation.see.Figure.20.5.
