Figure 2.1
21
Effect of Cultivation on BNC Biomaterials
Figure 2.1
(See c
olor i
nsert.).An.artificial.blood.vessel.synthesized.by.the.bacteria.G. xylinus.
replacement.for.their.own.autologous.grafts..Today.it.is.possible.to.replace.large.
arteries.with.synthetic.grafts.(e.g.,.Dacron,.expanded.polytetra. fluoroethylene.
[ePTFE],.and.polyurethane)..However,.these.materials.give.poor.performance.
for. small. (less. than. 6. mm). grafts. due. to. the. formation. of. thrombosis. and.
occlusion. (Hess. et. al.. 1985).. New. materials. that. are. not. thrombogenic. and.
have. mechanical. properties. that. mimic. the. native. blood. vessel. are. needed..
Nanocellulose.produced.by.G. xylinus.is.a.biomaterial.that.has.gained.interest.in.the.field.of.tissue.engineering.owing.to.its.unique.properties.(i.e.,.great.
mechanical.strength,.high.water.content,.and.the.. ability.to.be.shaped.into.3D.
structures. during. biosynthesis).. Cultivation. can. be. done. in. the. presence. of.
molds.and.porogens.of.different.sizes.and.shapes,.. making.it.possible.to.design.
desirable.scaffold.geometries.(Bäckdahl.et.al..2008;.Bodin.et.al..2007)..Several.
generations.of.bioreactors.have.been.designed.and.constructed.to.grow.BNC.
tubes..Bioreactors.have.been.designed.and.. fermentation.conditions.developed.
that.allow.the.growth.of.tubes.in.various.diameters.and.lengths.(1–10.mm.in.
diameter,.4–30.cm.in.length).as.well.as.in.various.shapes..Several.techniques.
to.alter.the.porosity.of.BNC.are.currently.under.investigation.
The.fabrication.process.of.BNC.vascular.grafts.is.very.unique.because.the.
material. synthesis. and. product. formation. take. place. simultaneously.. The.
biomechanical. performance,. including. rupture. pressure. and. compliance.
along.with.biological.response.(endothelialization,.blood.compatibility,.etc.),.
is.dependent.on.the.morphology.of.the.fibrillar.network..The.network.formation.is.affected.by.cellulose.assembly.and.bacteria.motion,.proliferation.rate,.
and.other.factors..An.understanding.of.the.effects.of.cultivation.conditions.
on.BNC.network.formation.is.therefore.of.great.importance.
21
Effect of Cultivation on BNC Biomaterials
Figure 2.1
(See c
olor i
nsert.).An.artificial.blood.vessel.synthesized.by.the.bacteria.G. xylinus.
replacement.for.their.own.autologous.grafts..Today.it.is.possible.to.replace.large.
arteries.with.synthetic.grafts.(e.g.,.Dacron,.expanded.polytetra. fluoroethylene.
[ePTFE],.and.polyurethane)..However,.these.materials.give.poor.performance.
for. small. (less. than. 6. mm). grafts. due. to. the. formation. of. thrombosis. and.
occlusion. (Hess. et. al.. 1985).. New. materials. that. are. not. thrombogenic. and.
have. mechanical. properties. that. mimic. the. native. blood. vessel. are. needed..
Nanocellulose.produced.by.G. xylinus.is.a.biomaterial.that.has.gained.interest.in.the.field.of.tissue.engineering.owing.to.its.unique.properties.(i.e.,.great.
mechanical.strength,.high.water.content,.and.the.. ability.to.be.shaped.into.3D.
structures. during. biosynthesis).. Cultivation. can. be. done. in. the. presence. of.
molds.and.porogens.of.different.sizes.and.shapes,.. making.it.possible.to.design.
desirable.scaffold.geometries.(Bäckdahl.et.al..2008;.Bodin.et.al..2007)..Several.
generations.of.bioreactors.have.been.designed.and.constructed.to.grow.BNC.
tubes..Bioreactors.have.been.designed.and.. fermentation.conditions.developed.
that.allow.the.growth.of.tubes.in.various.diameters.and.lengths.(1–10.mm.in.
diameter,.4–30.cm.in.length).as.well.as.in.various.shapes..Several.techniques.
to.alter.the.porosity.of.BNC.are.currently.under.investigation.
The.fabrication.process.of.BNC.vascular.grafts.is.very.unique.because.the.
material. synthesis. and. product. formation. take. place. simultaneously.. The.
biomechanical. performance,. including. rupture. pressure. and. compliance.
along.with.biological.response.(endothelialization,.blood.compatibility,.etc.),.
is.dependent.on.the.morphology.of.the.fibrillar.network..The.network.formation.is.affected.by.cellulose.assembly.and.bacteria.motion,.proliferation.rate,.
and.other.factors..An.understanding.of.the.effects.of.cultivation.conditions.
on.BNC.network.formation.is.therefore.of.great.importance.