74
Bacterial Cellulose
calcification,. resistance. to. biodegradation,. and. low. friction.. Hydrogels—
three-dimensional. hydrophilic. polymer. networks. in. which. a. large. amount.
of.water.is.interposed—may.be.suitable.for.this.purpose..Due.to.their.unique.
properties,.a.wide.range.of.medical,.pharmaceutical,.and.prosthetic.applications.have.been.proposed.(Gong.et.al..2001,.2003;.Kakugo.et.al..2002;.Osada.
and.Matsuda.1995;.Osada.et.al..1992)..However,.most.of.them.lack.mechanical.
toughness,.and.only.a.few.applications.have.been.accomplished.
Bacterial.nanocellulose.(BNC).is.one.such.hydrogel..BNC.is.an.extracellular.
cellulose,.produced.by.Acetobacter,.consisting.of.a.hydrophobic.ultrafine.fiber.
network.stacked.in.a.stratified.structure.(Hestrin.and.Schramm.1954)..Due.
to.this.unique.structure,.it.is.mechanically.anisotropic,.with.a.high.tensile.
modulus.along.the.fiber.layer.direction,.but.a.low.compressive.modulus.in.
perpendicular.to.the.stratified.direction..Water.is.easily.squeezed.out.of.BNC.
gel.through.slight.compression.and.it.does.not.recover.swelling.because.of.
hydrogen-bond.formation.between.the.cellulose.fibrils.
In.this.chapter,.a.BNC-based.biocompatible.hydrogel.with.high.mechanical.
strength.and.reversible.swelling.after.repeated.compression.cycles.is.reported,.
developed.by.combining.BNC.with.natural.polymers.such.as.gelatin,.as.well.
as.synthetic.ones.such.as.polyacrylamide,.using.the.technique.known.as.the.
double.network.(Gong.et.al..2003)..These.gels.exhibit.high.compressive.fracture.stress.comparable.to.cartilage.and.high.tensile.strength.comparable.with.
ligament.or.tendon..In.addition,.some.biological.properties.of.these.gels,.such.
as.resistance.to.wear,.biodegradation,.and.biological.interactions.within.the.
living.body,.are.discussed.
The. detailed. procedure. for. the. preparation. of. BNC. gel. (Takai. et. al.. 1975),.
gelatin.gel.and.BNC-gelatin.double-network.(DN).gel.(Nakayama.et.al..2004),.
BNC-PAAm. and. BNC-PDMAAm. DN. gel. (Hagiwara. et. al.. 2010),. basic. biomechanical.and.wear.properties.(Baily.2003;.Gong.et.al..2003;.McKellop.et.al..
1981;.Ueno.et.al..2002;.Yasuda.et.al..2005),.and.implantation.of.DN.gel.specimens.
into.subcutaneous.tissue.(Azuma.et.al..2007;.Ministry.of.Health,.Labour.and.
Welfare,.Japan.2003;.Tanabe.et.al..2008).can.be.found.in.articles.referenced.here.
Mechanical Properties of BNC Gels
BNC-gelatin DN gel
Effect of DN
Due.to.this.unique.structure,.BNC.shows.mechanical.anisotropy,.with.a.high.
sive.modulus.(0.007.MPa).perpendicular.to.the.stratified.direction..BNC.contains.90%.water;.however,.the.water.is.easily.squeezed.out.and.hydrogen-bond.
formation.between.cellulose.fibers.avoids.reswelling.(Figure 4.1,.column.1)..
Bacterial Cellulose
calcification,. resistance. to. biodegradation,. and. low. friction.. Hydrogels—
three-dimensional. hydrophilic. polymer. networks. in. which. a. large. amount.
of.water.is.interposed—may.be.suitable.for.this.purpose..Due.to.their.unique.
properties,.a.wide.range.of.medical,.pharmaceutical,.and.prosthetic.applications.have.been.proposed.(Gong.et.al..2001,.2003;.Kakugo.et.al..2002;.Osada.
and.Matsuda.1995;.Osada.et.al..1992)..However,.most.of.them.lack.mechanical.
toughness,.and.only.a.few.applications.have.been.accomplished.
Bacterial.nanocellulose.(BNC).is.one.such.hydrogel..BNC.is.an.extracellular.
cellulose,.produced.by.Acetobacter,.consisting.of.a.hydrophobic.ultrafine.fiber.
network.stacked.in.a.stratified.structure.(Hestrin.and.Schramm.1954)..Due.
to.this.unique.structure,.it.is.mechanically.anisotropic,.with.a.high.tensile.
modulus.along.the.fiber.layer.direction,.but.a.low.compressive.modulus.in.
perpendicular.to.the.stratified.direction..Water.is.easily.squeezed.out.of.BNC.
gel.through.slight.compression.and.it.does.not.recover.swelling.because.of.
hydrogen-bond.formation.between.the.cellulose.fibrils.
In.this.chapter,.a.BNC-based.biocompatible.hydrogel.with.high.mechanical.
strength.and.reversible.swelling.after.repeated.compression.cycles.is.reported,.
developed.by.combining.BNC.with.natural.polymers.such.as.gelatin,.as.well.
as.synthetic.ones.such.as.polyacrylamide,.using.the.technique.known.as.the.
double.network.(Gong.et.al..2003)..These.gels.exhibit.high.compressive.fracture.stress.comparable.to.cartilage.and.high.tensile.strength.comparable.with.
ligament.or.tendon..In.addition,.some.biological.properties.of.these.gels,.such.
as.resistance.to.wear,.biodegradation,.and.biological.interactions.within.the.
living.body,.are.discussed.
The. detailed. procedure. for. the. preparation. of. BNC. gel. (Takai. et. al.. 1975),.
gelatin.gel.and.BNC-gelatin.double-network.(DN).gel.(Nakayama.et.al..2004),.
BNC-PAAm. and. BNC-PDMAAm. DN. gel. (Hagiwara. et. al.. 2010),. basic. biomechanical.and.wear.properties.(Baily.2003;.Gong.et.al..2003;.McKellop.et.al..
1981;.Ueno.et.al..2002;.Yasuda.et.al..2005),.and.implantation.of.DN.gel.specimens.
into.subcutaneous.tissue.(Azuma.et.al..2007;.Ministry.of.Health,.Labour.and.
Welfare,.Japan.2003;.Tanabe.et.al..2008).can.be.found.in.articles.referenced.here.
Mechanical Properties of BNC Gels
BNC-gelatin DN gel
Effect of DN
Due.to.this.unique.structure,.BNC.shows.mechanical.anisotropy,.with.a.high.
sive.modulus.(0.007.MPa).perpendicular.to.the.stratified.direction..BNC.contains.90%.water;.however,.the.water.is.easily.squeezed.out.and.hydrogen-bond.
formation.between.cellulose.fibers.avoids.reswelling.(Figure 4.1,.column.1)..