Figure 2.6
Oxygen and
carbondioxide outlet
with a filter (blue)
Bacteria
Cellulose network
Growth media
Oxygen supply inlet
Silicon plug
Silicon tubing
Glass tube
Metallic plug
33
Effect of Cultivation on BNC Biomaterials
Figure 2.6
(See color insert.).Tube.bioreactor.setup.for.production.of.BNC.vascular.grafts..The.bacteria,.illustrated.with.black.dots,.produce.the.cellulose.network,.illustrated.in.beige,.around.the.silicon.tube.
BNC.is.an.attractive.material.for.vascular.grafts.due.to.its.unique.properties.
(great.mechanical.strength,.high.water.content.[approximately.99%],.good.integration.into.host.tissue,.and.flexibility.of.production.in.various.shapes)..The.major.
challenge.is.to.achieve.the.biomechanical.properties.required.for.long-term.use.
as.vascular.grafts..The.strain.G. xylinus.(ATCC 700178).is.grown.in.a.medium.
containing. D-fructose,. yeast. extract,. (NH 4 ) 2 SO 4 ,. KH 2 PO 4 ,. MgSO 4 ·7H 2 O,. CSL,.
trace.metal.solution,.and.vitamin.solution,.and.the.pH.is.set.to.5.5..Previous.
studies.with.the.tube.bioreactor.have.shown.that.G. xylinus synthesizes.different.cellulose.layers.with.different.densities,.that.is,.a.. density.gradient.can.be.
seen.in.the.BNC.tube.produced.(Bäckdahl.et.al..2011)..At.the.interface.between.
these.layers.there.is.a.tendency.toward.detachment.(i.e., delamination)..The.
production.of.two.layers.is.desired,.since.they.mimic.two.different.types.of.
extracellular.matrix.(ECM).in.native.connective.tissue.(Bäckdahl.et.al..2011).
There. is. a. clear. difference. between. the. two. layers;. the. cellulose. network.
closer.to.the.lumen.is.denser.and.more.ordered,.whereas.the.layer.far.away.
from.the.lumen.(i.e.,.closer.to.the.cultivation.medium).is.less.ordered.and.loose..
The.. density.gradient.in.the.nanocellulose.tube.network.produced.can.be.clearly.
seen. (Figure 2.7).. Cross. sections. of. cellulose. vascular. grafts. produced. after.
4 days.of.cultivation.(Figure 2.7A,.magnification.×77).and.after.7.days.of.cultivation.(Figure 2.7B,.magnification.×130).clearly.show.a.density.change.in.the.
cellulose.network..The.red.ring.(Figure 2.7A).represents.a.close-up.(Figure 2.7C,.
. magnification.×5000).at.the.interface.between.the.two.layers.
Oxygen and
carbondioxide outlet
with a filter (blue)
Bacteria
Cellulose network
Growth media
Oxygen supply inlet
Silicon plug
Silicon tubing
Glass tube
Metallic plug
33
Effect of Cultivation on BNC Biomaterials
Figure 2.6
(See color insert.).Tube.bioreactor.setup.for.production.of.BNC.vascular.grafts..The.bacteria,.illustrated.with.black.dots,.produce.the.cellulose.network,.illustrated.in.beige,.around.the.silicon.tube.
BNC.is.an.attractive.material.for.vascular.grafts.due.to.its.unique.properties.
(great.mechanical.strength,.high.water.content.[approximately.99%],.good.integration.into.host.tissue,.and.flexibility.of.production.in.various.shapes)..The.major.
challenge.is.to.achieve.the.biomechanical.properties.required.for.long-term.use.
as.vascular.grafts..The.strain.G. xylinus.(ATCC 700178).is.grown.in.a.medium.
containing. D-fructose,. yeast. extract,. (NH 4 ) 2 SO 4 ,. KH 2 PO 4 ,. MgSO 4 ·7H 2 O,. CSL,.
trace.metal.solution,.and.vitamin.solution,.and.the.pH.is.set.to.5.5..Previous.
studies.with.the.tube.bioreactor.have.shown.that.G. xylinus synthesizes.different.cellulose.layers.with.different.densities,.that.is,.a.. density.gradient.can.be.
seen.in.the.BNC.tube.produced.(Bäckdahl.et.al..2011)..At.the.interface.between.
these.layers.there.is.a.tendency.toward.detachment.(i.e., delamination)..The.
production.of.two.layers.is.desired,.since.they.mimic.two.different.types.of.
extracellular.matrix.(ECM).in.native.connective.tissue.(Bäckdahl.et.al..2011).
There. is. a. clear. difference. between. the. two. layers;. the. cellulose. network.
closer.to.the.lumen.is.denser.and.more.ordered,.whereas.the.layer.far.away.
from.the.lumen.(i.e.,.closer.to.the.cultivation.medium).is.less.ordered.and.loose..
The.. density.gradient.in.the.nanocellulose.tube.network.produced.can.be.clearly.
seen. (Figure 2.7).. Cross. sections. of. cellulose. vascular. grafts. produced. after.
4 days.of.cultivation.(Figure 2.7A,.magnification.×77).and.after.7.days.of.cultivation.(Figure 2.7B,.magnification.×130).clearly.show.a.density.change.in.the.
cellulose.network..The.red.ring.(Figure 2.7A).represents.a.close-up.(Figure 2.7C,.
. magnification.×5000).at.the.interface.between.the.two.layers.