Figure 9.1
182
Bacterial Cellulose
(diameter up to.20.μm).with.lower.mechanical.properties,.whereas.the.structure.on.the.upper.surface.is.denser.(mesh.diameter.<.1.μm).and.. carries.aggregated.fibers.(Helenius.et.al..2006;.Tang.et.al..2010)..These.structural.features.
are.strongly.influenced.by.the.bacterial.strain,.the.composition.of.the.culture.
medium,.and.the.culture.conditions..In.addition,.the.features.can.be.modified.
by.adding.solid.or.solubilized.components.during.biosynthesis.or.by.applying.postprocessing.steps.(Andersson.et.al..2010;.Baeckdahl.et.al..2008;.Bodin.
et.al..2010;.Klemm.et.al..2011;.Tang.et.al..2010;.Wan.et.al..2007).
The.layered.structure.of.the.BNC.hydrogel.body.causes.a.location-dependent.differential.ingrowth.of.cells.upon.in.vitro.cell.culture.or.in.vivo.after.
implantation..Indeed,.Helenius.et.al..(2006).observed.an.immigration.of.cells.
on.the.wide-meshed.layer.on.the.bottom.of.the.BNC.fleece,.whereas.no.cells.
infiltrated.the.dense.network.on.the.upper.surface.after.implantation.of.BNC.
into.rats.for.12.weeks.
Our.own.in.vitro.results.confirmed.these.findings,.in.that.human.chondrocytes.seeded.on.the.upper.surface.of.the.BNC.hydrogels.in.serum-free.
Dulbecco’s.Modified.Eagle.Medium.(DMEM).and.subjected.to.a.chemotactic.
gradient.by.10%.fetal.calf.serum.(FCS).in.transwell.inserts.for.24.h.entered.
the.BNC,.but.only.migrated.to.the.border.region.between.the.bottom.and.the.
middle.layer.of.the.hydrogel.(Figure 9.1a)..In.contrast,.chondrocytes.were.not.
able.to.enter.the.material.at.the.upper.surface,.even.during.cultivation.up.to.
7. days. (Figure 9.1b).. The. precise. reasons. for. this. differential. behavior. and.
the.influence.of.the.specific.cell.type.investigated.are.currently.the.subject.of.
intense.discussion.(Backdahl.et.al..2006;.Helenius.et.al..2006;.Wan.et.al..2007).
Current. efforts. are. directed. at. improving. the. network. structure. of. BNC.
and.thereby.optimizing.the.immigration.and.distribution.of.the.cells.within.
the.bulk.material..One.approach.described.an.opening.of.the.BNC.structure.
by.incorporation.of.solid.porogen.particles.during.biosynthesis.(Baeckdahl.
et. al.. 2008). and. subsequent. leaching. of. the. particles. in. order. to. obtain. a.
(a)
(b)
100 µm
100 µm
Figure 9.1
(See color insert.).Histological.cross-section.of.the.lower.(a).and.upper.(b).surface.of.a.BNC.
hydrogel.seeded.with.human.chondrocytes.in.a.transwell.system.with.serum.gradient.for.24 h..
While. the. more. porous. lower. surface. enables. cell. ingrowth. up. to. 70. μm,. the. upper. surface.
restricts.cell.. migration.into.the.bulk.staining.with.hematoxylin.and.eosin.
182
Bacterial Cellulose
(diameter up to.20.μm).with.lower.mechanical.properties,.whereas.the.structure.on.the.upper.surface.is.denser.(mesh.diameter.<.1.μm).and.. carries.aggregated.fibers.(Helenius.et.al..2006;.Tang.et.al..2010)..These.structural.features.
are.strongly.influenced.by.the.bacterial.strain,.the.composition.of.the.culture.
medium,.and.the.culture.conditions..In.addition,.the.features.can.be.modified.
by.adding.solid.or.solubilized.components.during.biosynthesis.or.by.applying.postprocessing.steps.(Andersson.et.al..2010;.Baeckdahl.et.al..2008;.Bodin.
et.al..2010;.Klemm.et.al..2011;.Tang.et.al..2010;.Wan.et.al..2007).
The.layered.structure.of.the.BNC.hydrogel.body.causes.a.location-dependent.differential.ingrowth.of.cells.upon.in.vitro.cell.culture.or.in.vivo.after.
implantation..Indeed,.Helenius.et.al..(2006).observed.an.immigration.of.cells.
on.the.wide-meshed.layer.on.the.bottom.of.the.BNC.fleece,.whereas.no.cells.
infiltrated.the.dense.network.on.the.upper.surface.after.implantation.of.BNC.
into.rats.for.12.weeks.
Our.own.in.vitro.results.confirmed.these.findings,.in.that.human.chondrocytes.seeded.on.the.upper.surface.of.the.BNC.hydrogels.in.serum-free.
Dulbecco’s.Modified.Eagle.Medium.(DMEM).and.subjected.to.a.chemotactic.
gradient.by.10%.fetal.calf.serum.(FCS).in.transwell.inserts.for.24.h.entered.
the.BNC,.but.only.migrated.to.the.border.region.between.the.bottom.and.the.
middle.layer.of.the.hydrogel.(Figure 9.1a)..In.contrast,.chondrocytes.were.not.
able.to.enter.the.material.at.the.upper.surface,.even.during.cultivation.up.to.
7. days. (Figure 9.1b).. The. precise. reasons. for. this. differential. behavior. and.
the.influence.of.the.specific.cell.type.investigated.are.currently.the.subject.of.
intense.discussion.(Backdahl.et.al..2006;.Helenius.et.al..2006;.Wan.et.al..2007).
Current. efforts. are. directed. at. improving. the. network. structure. of. BNC.
and.thereby.optimizing.the.immigration.and.distribution.of.the.cells.within.
the.bulk.material..One.approach.described.an.opening.of.the.BNC.structure.
by.incorporation.of.solid.porogen.particles.during.biosynthesis.(Baeckdahl.
et. al.. 2008). and. subsequent. leaching. of. the. particles. in. order. to. obtain. a.
(a)
(b)
100 µm
100 µm
Figure 9.1
(See color insert.).Histological.cross-section.of.the.lower.(a).and.upper.(b).surface.of.a.BNC.
hydrogel.seeded.with.human.chondrocytes.in.a.transwell.system.with.serum.gradient.for.24 h..
While. the. more. porous. lower. surface. enables. cell. ingrowth. up. to. 70. μm,. the. upper. surface.
restricts.cell.. migration.into.the.bulk.staining.with.hematoxylin.and.eosin.