99
Bacterial Cellulose Surface Modifications
investigated.the.ability.of.an.Acetobacter xylinum.ATCC.10245.strain.to.incorporate.glucosamine.and.N-acetylglucosamine.into.exopolymers..The.study.
showed.that.glucose.resulted.in.the.highest.production.of.exopolymer.among.
the.carbon.sources.used..The.exopolymers.synthesized.with.glucosamine.or.
N-acetylglucosamine.as.the.main.carbon.source.were.found.to.contain.glucose.and.glucosamine.or.N-acetylglucosamine..The.author.suggested.that,.
probably,. cellulose. synthase. and. other. enzymes. involved. in. . cellulose. synthesis. have. broad. specificities.. Preliminary. analysis. of. the. fibers. obtained.
(cellulose.and.the.new.copolymers).by.environmental.SEM.suggested.similar.gross.morphology.(e.g.,.diameter.and.surface.. smoothness)..Kobayashi.et.
al.. (2006). produced. a. cellulose-chitin. hybrid. polysaccharide. by. enzymatic.
polymerization,.using.a.chitinase.and.a.cellulase.from.Trichoderma viride..The.
molecular.weight.(MW).values.of.the.cellulose-chitin.hybrid.polysaccharides.
reached.4030.and.2840.Da,.which.correspond.to.22 and.16.saccharide.units,.
ring.chitin.and.cellulose..The.obtained.cellulose-chitin.hybrid.polysaccharide.did.not.exhibit.a.crystalline.structure.and.was.hydrolyzed.in.vitro.by.
lysozyme..Also,.Phisalaphong.and.Jatupaiboon.(2008).obtained.a.nanostructured.BNC-chitosan.composite.by.supplementing.the.BNC.culture.medium.
with.low.molecular.weight.chitosan.during.biosynthesis.by.A. xylinum..The.
BNC-chitosan. films. presented. improved. mechanical. properties. and. water.
absorption.capacity,.significantly.denser.fibril.structure,.smaller.pore.diameter,. and. greater. surface. area. compared. with. those. of. native. BNC. films..
However,. no. significant. influence. in. the. water. vapor. transmission. rates.
(indicative.of.the.water.vapor.permeability),.crystallinity,.and.antimicrobial.
activity.were.observed.
The. use. of. BNC. is. currently. expanding. as. an. excellent. biomaterial. with.
a. 3D. nanonetwork. for. scaffold. preparation. in. the. tissue. engineering. field..
However,. BNC. is. not. enzymatically. degradable. in. the. human. body.. As. a.
consequence,. biodegradability. has. become. an. essential. limiting. factor. in.
BNC.applications.as.a.scaffold.material.in.tissue.engineering.
rides.may.give.rise.to.derivatives.with.altered.chemical.and.physical.properties,. namely. concerning. chain. flexibility. and. extension,. crystallinity,.
physical.interactions.with.other.biopolymers,.and,.most.importantly,.hydrolytic. lability. ,. which. may. provide. a. basis. for. biomaterials. with. increased.
. biodegradability..Periodate.oxidation.is.characterized.by.the.specific.cleavage.
of.the.C2–C3.bond.of.the.glucopyranoside.ring,.and.this.cleavage.results.in.
the.formation.of.two.aldehyde.groups.per.glucose.unit..2,3-dialdehyde.cellulose.degrades.at.physiological.pH.in.vivo,.and.in.vitro.it.can.be.degraded.into.
glycolic.acid.and.2,4-dihydroxybutyric.acid..For.a.review.of.the.fundamental.
aspects.of.periodate.oxidation,.see.Kristiansen.et.al..(2010).and.Perlin.(2006).
Li. et. al.. (2009). produced. biodegradable. 2,3-dialdehyde. cellulose. BNC.
from. BC. by. periodate. oxidization.. While. this. chemical. treatment. maintained.the.original.3D.nanonetwork.structure,.the.obtained.scaffold.could.
Bacterial Cellulose Surface Modifications
investigated.the.ability.of.an.Acetobacter xylinum.ATCC.10245.strain.to.incorporate.glucosamine.and.N-acetylglucosamine.into.exopolymers..The.study.
showed.that.glucose.resulted.in.the.highest.production.of.exopolymer.among.
the.carbon.sources.used..The.exopolymers.synthesized.with.glucosamine.or.
N-acetylglucosamine.as.the.main.carbon.source.were.found.to.contain.glucose.and.glucosamine.or.N-acetylglucosamine..The.author.suggested.that,.
probably,. cellulose. synthase. and. other. enzymes. involved. in. . cellulose. synthesis. have. broad. specificities.. Preliminary. analysis. of. the. fibers. obtained.
(cellulose.and.the.new.copolymers).by.environmental.SEM.suggested.similar.gross.morphology.(e.g.,.diameter.and.surface.. smoothness)..Kobayashi.et.
al.. (2006). produced. a. cellulose-chitin. hybrid. polysaccharide. by. enzymatic.
polymerization,.using.a.chitinase.and.a.cellulase.from.Trichoderma viride..The.
molecular.weight.(MW).values.of.the.cellulose-chitin.hybrid.polysaccharides.
reached.4030.and.2840.Da,.which.correspond.to.22 and.16.saccharide.units,.
ring.chitin.and.cellulose..The.obtained.cellulose-chitin.hybrid.polysaccharide.did.not.exhibit.a.crystalline.structure.and.was.hydrolyzed.in.vitro.by.
lysozyme..Also,.Phisalaphong.and.Jatupaiboon.(2008).obtained.a.nanostructured.BNC-chitosan.composite.by.supplementing.the.BNC.culture.medium.
with.low.molecular.weight.chitosan.during.biosynthesis.by.A. xylinum..The.
BNC-chitosan. films. presented. improved. mechanical. properties. and. water.
absorption.capacity,.significantly.denser.fibril.structure,.smaller.pore.diameter,. and. greater. surface. area. compared. with. those. of. native. BNC. films..
However,. no. significant. influence. in. the. water. vapor. transmission. rates.
(indicative.of.the.water.vapor.permeability),.crystallinity,.and.antimicrobial.
activity.were.observed.
The. use. of. BNC. is. currently. expanding. as. an. excellent. biomaterial. with.
a. 3D. nanonetwork. for. scaffold. preparation. in. the. tissue. engineering. field..
However,. BNC. is. not. enzymatically. degradable. in. the. human. body.. As. a.
consequence,. biodegradability. has. become. an. essential. limiting. factor. in.
BNC.applications.as.a.scaffold.material.in.tissue.engineering.
rides.may.give.rise.to.derivatives.with.altered.chemical.and.physical.properties,. namely. concerning. chain. flexibility. and. extension,. crystallinity,.
physical.interactions.with.other.biopolymers,.and,.most.importantly,.hydrolytic. lability. ,. which. may. provide. a. basis. for. biomaterials. with. increased.
. biodegradability..Periodate.oxidation.is.characterized.by.the.specific.cleavage.
of.the.C2–C3.bond.of.the.glucopyranoside.ring,.and.this.cleavage.results.in.
the.formation.of.two.aldehyde.groups.per.glucose.unit..2,3-dialdehyde.cellulose.degrades.at.physiological.pH.in.vivo,.and.in.vitro.it.can.be.degraded.into.
glycolic.acid.and.2,4-dihydroxybutyric.acid..For.a.review.of.the.fundamental.
aspects.of.periodate.oxidation,.see.Kristiansen.et.al..(2010).and.Perlin.(2006).
Li. et. al.. (2009). produced. biodegradable. 2,3-dialdehyde. cellulose. BNC.
from. BC. by. periodate. oxidization.. While. this. chemical. treatment. maintained.the.original.3D.nanonetwork.structure,.the.obtained.scaffold.could.