Figure 4.9
85
Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network
Biodegradation of DN gels after implantation into Subcutaneous Tissue
Materials.for.artificial.cartilage.are.required.to.be.not.only.tough,.but.also.
resistant. to. biodegradation,. which. is. a. phenomenon. whereby. a. material.
implanted.in.a.living.body.deteriorates.over.time.by.biological.mechanisms..
The. biodegradation. properties. of. the. BNC-PDMAAm. and. BNC-gelatin.
gels,. along. with. some. other. DN. gels. such. as. PAMPS-PAAm. gel. and.
PAMPS-PDMAAm. gel,. were. tested. by. implanting. them. in. the. subcutaneous.tissue.of.mature.female.Japanese.white.rabbits..In.each.rabbit,.the.skin.
incision. was. well. healed. without. any. infection,. and. the. body. weight. was.
not. reduced. over. the. 6-week. period.. In. each. rabbit,. no. sign. of. inflammation.or.infection,.including.redness.of.the.skin,.effusion,.and.abscess,.was.
observed. at. the. implantation. site. at. the. time. of. sacrifice.. The. surface. of.
all. BNC-PDMAAm. DN. gel. specimens. became. rough,. although. they. were.
smooth.before.implantation.(Figure 4.9a)..All.BNC-gelatin.DN.gel.specimens.
were.mildly.deformed,.and.a.part.of.the.specimen.was.absorbed.(Figure 4.9b)..
Concerning. PAMPS-PAAm. and. PAMPS-PDMAAm. DN. gel. specimens,. no.
obvious.changes.were.found.on.the.gel.specimens.(Azuma.et.al..2007).
The. BNC-PDMAAm. DN. gel. specimens. did. not. show. any. significant.
changes.in.their.mechanical.properties.or.water.content.after.implantation.
(Table 4.3).. In. the. BNC-gelatin. DN. gel. specimens. (Table 4.3),. the. ultimate.
stress. was. dramatically. reduced. from. 4.30. to. 1.98. MPa. after. implantation.
(p.<.0.0001)..The.tangent.modulus.was.also.reduced,.from.2.50.to.1.18.MPa,.
on.average,.after.implantation..There.were.no.significant.differences.in.the.
strain.at.failure..The.water.content.was.significantly.increased.from.78.00%.
to.86.33%.after.implantation.(p.=.0.0002).
Regarding.the.mechanical.properties.of.other.DN.gels.without.BNC—for.
example,.in.PAMPS-PAAm.DN.gel.specimens.(Azuma.et.al..2007),.the.ultimate.stress.was.extremely.high.(average.11.40.MPa).and.the.water.content.
was.90%.before.implantation,.which.is.the.strongest.in.the.ultimate.stress.
(a)
(b)
Figure 4.9
(a). Gross. observations. of. the. BNC-PDMAAm. DN. gel. specimens. before. implantation. (left).
and.6.weeks.after.implantation:.immediately.before.harvest.(middle).and.after.harvest.(right)..
The.surface.of.all.specimens.became.rough,.although.they.were.smooth.before.implantation..
(b). Gross. observations. of. the. BNC-gelatin. DN. gel. specimens. before. implantation. (left). and.
6 weeks.after.implantation.immediately.before.harvest.(middle).and.after.harvest.(right)..All.
specimens.were.mildly.deformed.and.a.part.of.the.specimen.was.absorbed..(Reproduced.with.
permission.of.Azuma.et.al..2007.)
85
Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network
Biodegradation of DN gels after implantation into Subcutaneous Tissue
Materials.for.artificial.cartilage.are.required.to.be.not.only.tough,.but.also.
resistant. to. biodegradation,. which. is. a. phenomenon. whereby. a. material.
implanted.in.a.living.body.deteriorates.over.time.by.biological.mechanisms..
The. biodegradation. properties. of. the. BNC-PDMAAm. and. BNC-gelatin.
gels,. along. with. some. other. DN. gels. such. as. PAMPS-PAAm. gel. and.
PAMPS-PDMAAm. gel,. were. tested. by. implanting. them. in. the. subcutaneous.tissue.of.mature.female.Japanese.white.rabbits..In.each.rabbit,.the.skin.
incision. was. well. healed. without. any. infection,. and. the. body. weight. was.
not. reduced. over. the. 6-week. period.. In. each. rabbit,. no. sign. of. inflammation.or.infection,.including.redness.of.the.skin,.effusion,.and.abscess,.was.
observed. at. the. implantation. site. at. the. time. of. sacrifice.. The. surface. of.
all. BNC-PDMAAm. DN. gel. specimens. became. rough,. although. they. were.
smooth.before.implantation.(Figure 4.9a)..All.BNC-gelatin.DN.gel.specimens.
were.mildly.deformed,.and.a.part.of.the.specimen.was.absorbed.(Figure 4.9b)..
Concerning. PAMPS-PAAm. and. PAMPS-PDMAAm. DN. gel. specimens,. no.
obvious.changes.were.found.on.the.gel.specimens.(Azuma.et.al..2007).
The. BNC-PDMAAm. DN. gel. specimens. did. not. show. any. significant.
changes.in.their.mechanical.properties.or.water.content.after.implantation.
(Table 4.3).. In. the. BNC-gelatin. DN. gel. specimens. (Table 4.3),. the. ultimate.
stress. was. dramatically. reduced. from. 4.30. to. 1.98. MPa. after. implantation.
(p.<.0.0001)..The.tangent.modulus.was.also.reduced,.from.2.50.to.1.18.MPa,.
on.average,.after.implantation..There.were.no.significant.differences.in.the.
strain.at.failure..The.water.content.was.significantly.increased.from.78.00%.
to.86.33%.after.implantation.(p.=.0.0002).
Regarding.the.mechanical.properties.of.other.DN.gels.without.BNC—for.
example,.in.PAMPS-PAAm.DN.gel.specimens.(Azuma.et.al..2007),.the.ultimate.stress.was.extremely.high.(average.11.40.MPa).and.the.water.content.
was.90%.before.implantation,.which.is.the.strongest.in.the.ultimate.stress.
(a)
(b)
Figure 4.9
(a). Gross. observations. of. the. BNC-PDMAAm. DN. gel. specimens. before. implantation. (left).
and.6.weeks.after.implantation:.immediately.before.harvest.(middle).and.after.harvest.(right)..
The.surface.of.all.specimens.became.rough,.although.they.were.smooth.before.implantation..
(b). Gross. observations. of. the. BNC-gelatin. DN. gel. specimens. before. implantation. (left). and.
6 weeks.after.implantation.immediately.before.harvest.(middle).and.after.harvest.(right)..All.
specimens.were.mildly.deformed.and.a.part.of.the.specimen.was.absorbed..(Reproduced.with.
permission.of.Azuma.et.al..2007.)