212
Bacterial Cellulose
while. they. extrude. cellulose. networks.. The. manipulation. of. electrokinetic.
forces. acting. upon. a. bacterial. cell. can. produce. complex. cellulose. patterns.
on.the.nanoscale.not.achievable.in.static.culture..The.ability.to.control.the.
direction.of.fiber.orientation.could.be.readily.expanded.to.weave.structures.
of. multiple. fiber. layers. by. changing. the. orientation. of. the. applied. electric.
field.for.each.layer..Using.this.method,.these.structures.could.be.tailored.to.
have.the.desired.mechanical.properties.for.a.variety.of.applications,.including. tissue. engineering,. microelectromechanical. systems. (MEMS),. textiles,.
and.electronics.
BNC Scaffolds with Microvessels
Of.fundamental.importance.to.the.survival.of.most.engineered.tissue.structures.is.gas.and.nutrient.exchange..In.nature,.this.is.accomplished.by.virtue.
of. microcirculation. feeding. oxygen. and. nutrients. to. tissues. and. removing.
waste.at.the.capillary.level..Gas.exchange.in.most.engineered.tissue.scaffolds.
is.accomplished.by.passive.diffusion.(<1.mm.distances).or.actively.by.elution.
of. oxygen. from. specific. material. types. of. fibers. (Harrison. et. al.. 2007).. The.
architecture.for.microcirculation.is.difficult.to.fabricate,.particularly.since.the.
cross-sectional.dimension.of.a.capillary.is.only.about.5–10.μm.in.diameter..
The.existing.manufacturing.processes.were.not.developed.to.create.a.network.
of.microscopic.blood.vessels..Currently.there.are.no.known.tissue.engineering.
scaffolds.with.microcirculation.designed.into.the.structure.for.gas.exchange..
As.a.result,.the.scaffolding.for.tissues.and.organs.is.limited.in.size.and.shape..
In.addition.to.gas.exchange,.engineered.tissue.scaffolds.must.exhibit.mechanical.properties.comparable.to.the.native.tissues.they.are.intended.to.replace..
This.is.true.because.the.cells.that.populate.native.tissues.sense.physiologic.
strains,.which.can.help.to.control.tissue.growth.and.function.
We.created.a.BNC.scaffold.with.200–300.μm.cylindrical.channels.for.the.
purpose. of. endothelializing. the. walls. of. the. microchannels. (Figure 10.13)..
The. channels. were. created. by. growing. BNC. around. an. array. of. 300. μm.
silica.capillaries..It.was.shown.that.we.could.endothelialize.these.channels.
deep.within.a.thick.scaffold.using.human.umbilical.vein.endothelial.cells.
(HUVEC)..For.this.purpose,.HUVECs.were.seeded.statically.onto.purified.
BNC.and.incubated.for.24.h.at.37°C.and.5%.carbon.dioxide.and.then.exposed.
to.pulsatile.media.flow.for.36.h..After.harvest.and.fixation.of.the.material,.
one. hundred. 5. μm. . sections. were. sliced. in. a. microtome.. Cross-sectional.
. hematoxylin. and. eosin. staining. revealed. a. confluent. layer. of. endothelial.
cells. at. each. section.. This. result. has. implications. in. the. development. of.
larger.volumes.of.BNC.for.engineered.. tissues.since.those.volumes.can.now.
be.. perfused.with.oxygenated.media.
Bacterial Cellulose
while. they. extrude. cellulose. networks.. The. manipulation. of. electrokinetic.
forces. acting. upon. a. bacterial. cell. can. produce. complex. cellulose. patterns.
on.the.nanoscale.not.achievable.in.static.culture..The.ability.to.control.the.
direction.of.fiber.orientation.could.be.readily.expanded.to.weave.structures.
of. multiple. fiber. layers. by. changing. the. orientation. of. the. applied. electric.
field.for.each.layer..Using.this.method,.these.structures.could.be.tailored.to.
have.the.desired.mechanical.properties.for.a.variety.of.applications,.including. tissue. engineering,. microelectromechanical. systems. (MEMS),. textiles,.
and.electronics.
BNC Scaffolds with Microvessels
Of.fundamental.importance.to.the.survival.of.most.engineered.tissue.structures.is.gas.and.nutrient.exchange..In.nature,.this.is.accomplished.by.virtue.
of. microcirculation. feeding. oxygen. and. nutrients. to. tissues. and. removing.
waste.at.the.capillary.level..Gas.exchange.in.most.engineered.tissue.scaffolds.
is.accomplished.by.passive.diffusion.(<1.mm.distances).or.actively.by.elution.
of. oxygen. from. specific. material. types. of. fibers. (Harrison. et. al.. 2007).. The.
architecture.for.microcirculation.is.difficult.to.fabricate,.particularly.since.the.
cross-sectional.dimension.of.a.capillary.is.only.about.5–10.μm.in.diameter..
The.existing.manufacturing.processes.were.not.developed.to.create.a.network.
of.microscopic.blood.vessels..Currently.there.are.no.known.tissue.engineering.
scaffolds.with.microcirculation.designed.into.the.structure.for.gas.exchange..
As.a.result,.the.scaffolding.for.tissues.and.organs.is.limited.in.size.and.shape..
In.addition.to.gas.exchange,.engineered.tissue.scaffolds.must.exhibit.mechanical.properties.comparable.to.the.native.tissues.they.are.intended.to.replace..
This.is.true.because.the.cells.that.populate.native.tissues.sense.physiologic.
strains,.which.can.help.to.control.tissue.growth.and.function.
We.created.a.BNC.scaffold.with.200–300.μm.cylindrical.channels.for.the.
purpose. of. endothelializing. the. walls. of. the. microchannels. (Figure 10.13)..
The. channels. were. created. by. growing. BNC. around. an. array. of. 300. μm.
silica.capillaries..It.was.shown.that.we.could.endothelialize.these.channels.
deep.within.a.thick.scaffold.using.human.umbilical.vein.endothelial.cells.
(HUVEC)..For.this.purpose,.HUVECs.were.seeded.statically.onto.purified.
BNC.and.incubated.for.24.h.at.37°C.and.5%.carbon.dioxide.and.then.exposed.
to.pulsatile.media.flow.for.36.h..After.harvest.and.fixation.of.the.material,.
one. hundred. 5. μm. . sections. were. sliced. in. a. microtome.. Cross-sectional.
. hematoxylin. and. eosin. staining. revealed. a. confluent. layer. of. endothelial.
cells. at. each. section.. This. result. has. implications. in. the. development. of.
larger.volumes.of.BNC.for.engineered.. tissues.since.those.volumes.can.now.
be.. perfused.with.oxygenated.media.