Figure 9.2
184
Bacterial Cellulose
(a)
(b)
(c)
Figure 9.2
Scanning.electron.micrographs.showing.the.effect.of.sodium.hydroxide.concentration.on.the.
network. morphology. of. BNC. during. autoclaving. conditions.. Treating. BNC. hydrogels. with.
(a) 1 M.and.(b).2.M.sodium.hydroxide.solution.has.no.detectable.effects.on.the.network.structure. ,.
while.(c).treatment.with.4.M.sodium.hydroxide.solution.leads.to.shrinking.of.hydrogels.and.a.
dense.structure..Pictures.showing.the.cross-section.of.BNC.after.freeze-drying.
(Barud. et. al.. 2007).. BNC. thus. withstands. the. heat. treatment. necessary.
(scale.bar.=.5.µm).for.sterilization.techniques.such.as.dry.heat.sterilization.
(>140°C). or. autoclaving. . (121°C),. the. latter. representing. the. most. important.
and.practical.technique..It is.possible.to.sterilize.hydrogels.in.the.initial.wet.
or.freeze-dried.state.(. aerogels).without.reswelling.of.the.network.structure..
The.latter.aspect.seems.to.be.very.important.for.the.long-term.storage.and.
stability.of.BNC.materials..In.addition,.it.is.important.to.note.that.steam.sterilization.has.no.detectable.effect.on.the.integrity.and.network.structure.of.
BNC.in.the.wet.or.dry.state.
Instead.of.water,.aqueous.sodium.hydroxide.can.also.be.used.as.the.fluid.
phase.for.sterilization.of.BNC.hydrogels,.thereby.combining.sterilization.of.
the.material.with.purification.and.removal.of.pyrogens..BNC.can.be.treated.
with.aqueous.sodium.hydroxide.solution.under.autoclaving.conditions.up.
to.a.concentration.of.3.M.without.any.shrinking.and.structural.changing.of.
the.material.(Figure 9.2).
Alternatively,.BNC.can.theoretically.be.sterilized.by.treatment.with.ethylene.oxide..To.ensure.contact.of.the.complete.BNC.structure.with.the.toxic.
gas,.the.material.must.be.in.a.dry.state.and,.for.releasing.toxic.substances,.
an.adapted.gas.emission.time.must.follow..However,.there.are.currently.no.
studies. on. the. effects. of. ethylene. oxide. treatment. on. BNC. (e.g.,. chemical.
modification).and.thus.potential.adverse.effects.of.the.highly.reactive.gas.on.
the.BNC.structure.cannot.be.completely.excluded.
In. contrast,. gamma. sterilization. performed. under. standardized. conditions.(≥25.kGy).does.not.cause.any.macroscopically.detectable.changes.of.the.
hydrogel.integrity,.although.systematic.investigations.concerning.the.effects.
of.gamma.sterilization.on.the.features.of.BNC.are.currently.unavailable.
Controlled Biotechnological Production of BNC
As.already.mentioned,.BNC.is.biotechnologically.produced.from.low.molecular.weight.sugars.such.as.glucose..For.its.application.as.a.biomaterial,.it.is.
184
Bacterial Cellulose
(a)
(b)
(c)
Figure 9.2
Scanning.electron.micrographs.showing.the.effect.of.sodium.hydroxide.concentration.on.the.
network. morphology. of. BNC. during. autoclaving. conditions.. Treating. BNC. hydrogels. with.
(a) 1 M.and.(b).2.M.sodium.hydroxide.solution.has.no.detectable.effects.on.the.network.structure. ,.
while.(c).treatment.with.4.M.sodium.hydroxide.solution.leads.to.shrinking.of.hydrogels.and.a.
dense.structure..Pictures.showing.the.cross-section.of.BNC.after.freeze-drying.
(Barud. et. al.. 2007).. BNC. thus. withstands. the. heat. treatment. necessary.
(scale.bar.=.5.µm).for.sterilization.techniques.such.as.dry.heat.sterilization.
(>140°C). or. autoclaving. . (121°C),. the. latter. representing. the. most. important.
and.practical.technique..It is.possible.to.sterilize.hydrogels.in.the.initial.wet.
or.freeze-dried.state.(. aerogels).without.reswelling.of.the.network.structure..
The.latter.aspect.seems.to.be.very.important.for.the.long-term.storage.and.
stability.of.BNC.materials..In.addition,.it.is.important.to.note.that.steam.sterilization.has.no.detectable.effect.on.the.integrity.and.network.structure.of.
BNC.in.the.wet.or.dry.state.
Instead.of.water,.aqueous.sodium.hydroxide.can.also.be.used.as.the.fluid.
phase.for.sterilization.of.BNC.hydrogels,.thereby.combining.sterilization.of.
the.material.with.purification.and.removal.of.pyrogens..BNC.can.be.treated.
with.aqueous.sodium.hydroxide.solution.under.autoclaving.conditions.up.
to.a.concentration.of.3.M.without.any.shrinking.and.structural.changing.of.
the.material.(Figure 9.2).
Alternatively,.BNC.can.theoretically.be.sterilized.by.treatment.with.ethylene.oxide..To.ensure.contact.of.the.complete.BNC.structure.with.the.toxic.
gas,.the.material.must.be.in.a.dry.state.and,.for.releasing.toxic.substances,.
an.adapted.gas.emission.time.must.follow..However,.there.are.currently.no.
studies. on. the. effects. of. ethylene. oxide. treatment. on. BNC. (e.g.,. chemical.
modification).and.thus.potential.adverse.effects.of.the.highly.reactive.gas.on.
the.BNC.structure.cannot.be.completely.excluded.
In. contrast,. gamma. sterilization. performed. under. standardized. conditions.(≥25.kGy).does.not.cause.any.macroscopically.detectable.changes.of.the.
hydrogel.integrity,.although.systematic.investigations.concerning.the.effects.
of.gamma.sterilization.on.the.features.of.BNC.are.currently.unavailable.
Controlled Biotechnological Production of BNC
As.already.mentioned,.BNC.is.biotechnologically.produced.from.low.molecular.weight.sugars.such.as.glucose..For.its.application.as.a.biomaterial,.it.is.