TABLe 4.3
Changes.in.the.Mechanical.Properties.and.the.Water.Content.of.
Each.DN.Hydrogel.Due.to.Implantation..Before:.Specimens.
before.Implantation;.After:.Specimens.Harvested.6.Weeks.after.
Implantation..(Reproduced.with.permission.of.Azuma.et.al..2007.)
BNC-PDMAAm
BNC-Gelatin
Tangent.modulus.(MPa)
Before
1.70.(0.70)
2.50.(1.10)
After
1.00.(0.60)
1.18.(1.10)
p-value
N.S.
N.S.
Ultimate.stress.(MPa)
Before
1.90.(0.28)
4.30.(0.35)
After
2.17.(0.35)
1.98.(0.52)
p-value
N.S.
<0.0001
Strain.at.failure.(m/m)
Before
0.37.(0.03)
0.33.(0.04)
After
0.40.(0.06)
0.40.(0.11)
p-value
N.S.
N.S.
Water.content.(%)
Before
85.00.(0.71)
78.00.(2.30)
After
85.17.(0.75)
86.33.(0.75)
p-value
N.S.
0.0002
86
Bacterial Cellulose
among.the.four.DN.gels—the.mechanical.parameters.except.for.the.tangent.
modulus.and.the.water.content.did.not.change.after.implantation,.although.
the.modulus.was.significantly.reduced..In.contrast,.the.PAMPS-PDMAAm.
DN.gel,.which.is.highly.resistant.to.wear.in.pin-on.flat.wear.testing.(Yasuda.
et.al..2005),.the.ultimate.stress.and.the.tangent.modulus.were.significantly.
increased.with.a.significant.reduction.of.the.water.content.after.implantation.
(Azuma.et.al..2007).
These.results.suggest.that.degradation.properties.of.BNC-based.DN.hydrogels.and.some.other.conventional.DN.hydrogels.within.the.living.body.were.
extremely.different,.depending.on.the.properties.of.the.polymers.contained.
in.each.hydrogel..Concerning.the.mechanical.deterioration.observed.in.each.
DN. hydrogel,. two. mechanisms. are. considered:. biodegradation. and. simple.
degradation. of. the. polymer. network. that. would. occur. over. time.. In. the.
BNC-gelatin.DN.gel,.the.ultimate.stress.dramatically.decreased.after.implantation. with. the. obvious. deformation. of. the. gel. specimens,. while. obvious.
deterioration. was. not. observed. in. the. BNC-PDMAAm. DN. gel.. These. facts.
indicate.that.the.structure.composed.of.gelatin.was.greatly.deteriorated.by.
biological.mechanisms,.although.the.increase.in.the.water.content.may.also.
be.a.possible.cause.of.the.mechanical.reduction..In.the.BNC-PDMAAm.DN.
gel,. however,. the. surface. of. all. specimens. became. rough,. although. it. was.
smooth.before.implantation..Therefore.the.structure.of.the.cellulose.appeared.
to.deteriorate.more.slowly.than.gelatin..It.can.be.speculated.that.the.structure.of.PDMAAm.in.this.gel.material.might.compensate.for.the.deterioration.
of.the.second.structure.of.cellulose,.at.least.during.the.6-week.period..It.is.
important.to.clarify.these.mechanisms.in.the.future.