203
Bacterial Nanocellulose Biomaterials with Controlled Architecture
customizable. implants. and. scaffolds. for. tissue. engineering,. especially.
since.cell.response.to.a.material.directly.correlates.to.nanoscale.topography.
(Stevens. and. George. 2005).. This. can. be. attained. by. using. electric. fields. to.
control.the.movement.of.G. xylinus.at.the.nanoscale.level.to.create.custom.
cellulose.networks.(Sano.et.al..2010)..By.carefully.controlling.the.electrokinetic.forces,.bacterial.motion.can.be.directed.while.the.organisms.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.. This. nanoscale. control. provides. the. ability. to.
develop.and.affect.the.macroscale.tissue.properties.by.controlling.the.direction.of.fiber.orientation..Using.electrokinetic.forces,.structures.can.be.tailored.
to.have.the.desired.mechanical.properties.for.a.variety.of.tissue.engineering.
and.implantable.device.applications.
Electrokinetics.is.the.result.of.several.effects.that.occur.once.a.particle.is.
introduced.to.a.fluid..In.theory,.an.object.in.a.fluid.will.form.an.electrical.
double. layer. composed. of. ions.. The. first. layer,. or. surface. charge,. is. composed.of.either.all.positive.or.all.negative.ions..The.second.layer,.or.diffuse.
layer,.forms.in.the.fluid.by.surface.charge.attraction..When.an.external.force,.
such. as. an. electric. field,. is. applied. on. a. particle. in. a. fluid,. the. motion. of.
the.particle.moves.toward.a.region.of.opposite.charge.as.a.result.of.the.diffuse.layer.combined.with.the.Coulombic.force..The.net.forces.on.the.particle.
are.known.as.electrokinetic.forces.and.can.be.identified.as.electroosmosis.
and.electrophoresis..Electroosmosis.is.the.response.of.the.fluid.to.an.electric.
field.and.typically.can.affect.the.motion.of.a.particle.within.the.fluid,.while.
electrophoresis.is.the.motion.of.charged.particle.in.a.uniform.electric.field..
The electrokinetic.velocity.can.be.calculated.using.Huckel’s.equation,.where.
the.μ eo .and.μ ep .are.the.electroosmotic.and.electrophoretic.mobilites.and.E
.is.
the.magnitude.of.the.applied.electric.field.(Tandon.et.al..2008):
.
V ek = ( µ +
eo
µ ep ) E .
The. weavers. of. BNC,. G. xylinus, are. 1–2. μm. in. length. and. therefore. can.
feel.the.effects.of.electrokinetics..Furthermore,.their.size.assists.with.electrokinetics. having. a. stronger. effect. than. Brownian. motion. and. negligible.
effects. from. gravity. (Pohl. 1978).. With. electrokinetics,. the. phenomena. of.
electro. phoresis. can. play. a. dominant. role. in. precise. control. over. bacteria. .
cells. and. has. been. utilized. to. align. bacterial. cellulose. fiber. orientation,. as.
seen. in. Figure 10.2.. Using. low. direct. current. (DC). fields. in. the. range. of.
0.25–1. V/cm,. bacterial. cells. continue. to. secrete. cellulose. nanofibrils. and.
result. in. fiber. alignment,. with. their. electrophoretic. mobility. estimated. to.
be. 4.68. ×. 10 -9 . m 2 ⋅V/s.. As. electric. fields. are. increased. above. this. threshold,.
cellulose.production.slows.down.or.halts.due.to.rapid.velocities.that.impede.
metabolic.processes.
Bacterial Nanocellulose Biomaterials with Controlled Architecture
customizable. implants. and. scaffolds. for. tissue. engineering,. especially.
since.cell.response.to.a.material.directly.correlates.to.nanoscale.topography.
(Stevens. and. George. 2005).. This. can. be. attained. by. using. electric. fields. to.
control.the.movement.of.G. xylinus.at.the.nanoscale.level.to.create.custom.
cellulose.networks.(Sano.et.al..2010)..By.carefully.controlling.the.electrokinetic.forces,.bacterial.motion.can.be.directed.while.the.organisms.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.. This. nanoscale. control. provides. the. ability. to.
develop.and.affect.the.macroscale.tissue.properties.by.controlling.the.direction.of.fiber.orientation..Using.electrokinetic.forces,.structures.can.be.tailored.
to.have.the.desired.mechanical.properties.for.a.variety.of.tissue.engineering.
and.implantable.device.applications.
Electrokinetics.is.the.result.of.several.effects.that.occur.once.a.particle.is.
introduced.to.a.fluid..In.theory,.an.object.in.a.fluid.will.form.an.electrical.
double. layer. composed. of. ions.. The. first. layer,. or. surface. charge,. is. composed.of.either.all.positive.or.all.negative.ions..The.second.layer,.or.diffuse.
layer,.forms.in.the.fluid.by.surface.charge.attraction..When.an.external.force,.
such. as. an. electric. field,. is. applied. on. a. particle. in. a. fluid,. the. motion. of.
the.particle.moves.toward.a.region.of.opposite.charge.as.a.result.of.the.diffuse.layer.combined.with.the.Coulombic.force..The.net.forces.on.the.particle.
are.known.as.electrokinetic.forces.and.can.be.identified.as.electroosmosis.
and.electrophoresis..Electroosmosis.is.the.response.of.the.fluid.to.an.electric.
field.and.typically.can.affect.the.motion.of.a.particle.within.the.fluid,.while.
electrophoresis.is.the.motion.of.charged.particle.in.a.uniform.electric.field..
The electrokinetic.velocity.can.be.calculated.using.Huckel’s.equation,.where.
the.μ eo .and.μ ep .are.the.electroosmotic.and.electrophoretic.mobilites.and.E
.is.
the.magnitude.of.the.applied.electric.field.(Tandon.et.al..2008):
.
V ek = ( µ +
eo
µ ep ) E .
The. weavers. of. BNC,. G. xylinus, are. 1–2. μm. in. length. and. therefore. can.
feel.the.effects.of.electrokinetics..Furthermore,.their.size.assists.with.electrokinetics. having. a. stronger. effect. than. Brownian. motion. and. negligible.
effects. from. gravity. (Pohl. 1978).. With. electrokinetics,. the. phenomena. of.
electro. phoresis. can. play. a. dominant. role. in. precise. control. over. bacteria. .
cells. and. has. been. utilized. to. align. bacterial. cellulose. fiber. orientation,. as.
seen. in. Figure 10.2.. Using. low. direct. current. (DC). fields. in. the. range. of.
0.25–1. V/cm,. bacterial. cells. continue. to. secrete. cellulose. nanofibrils. and.
result. in. fiber. alignment,. with. their. electrophoretic. mobility. estimated. to.
be. 4.68. ×. 10 -9 . m 2 ⋅V/s.. As. electric. fields. are. increased. above. this. threshold,.
cellulose.production.slows.down.or.halts.due.to.rapid.velocities.that.impede.
metabolic.processes.