87
Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network
The.present.study.suggested.that.each.unique.DN.gel.tested.in.this.study.has.
its.own.degradation.properties.within.the.living.body..It.is.important.to.know.
precisely.the.characteristics.of.each.material.when.considering.its.mechanical.
application..In.addition,.if.the.reasons.for.each.characteristic.in.these.m . aterials.
could.be.clarified.in.the.near.future,.this.will.be.useful.to.improve.DN.gels.
not. only. for. the. development. of. artificial. cartilage,. but. also. to. apply. them.
to. other. implants.. Therefore. further. studies. should. be. conducted. to. fully.
clarify.the.biodegradation.properties.of.the.four.unique.DN.gels.
Finally,. the. development. of. artificial. cartilage. is. one. main. goal. of. this.
study..According.to.Eisenberg.and.Grodzinsky.(1985),.the.compressive.stress.
and. the. tangent. modulus. of. the. knee. joint. cartilage. are. 0.06–0.21MPa. and.
0.26–1.37.MPa,.respectively,.depending.on.the.sodium.chloride.(NaCl).concentration. of. the. water.. Concerning. the. human. knee. cartilage,. Athanasiou.
et al.. (1991). reported. that. the. aggregate. modulus. averaged. 0.71. MPa.. The.
ultimate. . compressive. stress. of. the. BNC-based. DN. hydrogels. tested. in. the.
present.study.is.greater.than.that.of.the.previously.described.natural.cartilage..The.tangent.modulus.of.the.BNC-PDMAA.DN.gel.is.comparable.with.
that.of.the.previously.described.natural.cartilage..This.study.implied.that.the.
tested.BNC-PDMAA.gel.along.with.other.DN.gels,.except.for.the.BNC-gelatin.
DN.gel,.are.potential.materials.that.may.meet.the.requirements.of.artificial.
cartilage..However,.potential.materials.for.artificial.cartilage.also.have.to.be.
durable. to. endure. repetitive. stress,. resistant. to. wear,. and. resistant. to. biodegradation.within.the.living.body.
Biological responses of DN gels after implantation
into Muscle and Subcutaneous Tissue
Although.BNC-PDMAAm.and.BNC-gelatin.DN.are.unique.gels.that.include.
natural.polymers,.it.is.important.to.evaluate.what.kind.of.tissue.reaction.
is. induced. by. implantation. of. these. gel. materials. in. the. living. body. and.
how. strong. the. reaction. is. in. order. to. consider. application. of. these. DN.
gels. for. clinical. implants. as. a. replacement. for. natural. cartilage.. For. this.
purpose,.the.pellet.implantation.test.into.the.muscle.and.the.subcutaneous.
implantation.test.with.massive.material,.which.can.evaluate.local.reaction.
in.the.muscle.or.subcutaneous.tissue.around.the.implanted.material,.were.
investigated.(Iyakushin-Hatsu.2003)..This.study,.composed.of.macroscopic.
observations,.was.conducted.on.rabbits.using.the.sub. cutaneous.implantation. test. with. massive. material. and. histological. examinations. using. the.
ous.tissue,.according.to.the.international.guideline.for.biological.evaluation.of.the.safety.of.biomaterials.(Iyakushin-Hatsu.2003;.Tanabe.et.al..2008).
The.implanted.BNC-PDMAAm.DN.gels.induced.strong.inflammation.at.
each.period.(Tanabe.et.al..2008)..Currently.these.materials.are.difficult.to.apply.
as.clinical.implants..Around.the.BNC-gelatin.DN.gel,.which.was.composed.of.
two.natural.polymers,.inflammation.was.very.mild.at.1.week,.but.significantly.
Tough Bacterial Nanocellulose Hydrogels Based on the Double-Network
The.present.study.suggested.that.each.unique.DN.gel.tested.in.this.study.has.
its.own.degradation.properties.within.the.living.body..It.is.important.to.know.
precisely.the.characteristics.of.each.material.when.considering.its.mechanical.
application..In.addition,.if.the.reasons.for.each.characteristic.in.these.m . aterials.
could.be.clarified.in.the.near.future,.this.will.be.useful.to.improve.DN.gels.
not. only. for. the. development. of. artificial. cartilage,. but. also. to. apply. them.
to. other. implants.. Therefore. further. studies. should. be. conducted. to. fully.
clarify.the.biodegradation.properties.of.the.four.unique.DN.gels.
Finally,. the. development. of. artificial. cartilage. is. one. main. goal. of. this.
study..According.to.Eisenberg.and.Grodzinsky.(1985),.the.compressive.stress.
and. the. tangent. modulus. of. the. knee. joint. cartilage. are. 0.06–0.21MPa. and.
0.26–1.37.MPa,.respectively,.depending.on.the.sodium.chloride.(NaCl).concentration. of. the. water.. Concerning. the. human. knee. cartilage,. Athanasiou.
et al.. (1991). reported. that. the. aggregate. modulus. averaged. 0.71. MPa.. The.
ultimate. . compressive. stress. of. the. BNC-based. DN. hydrogels. tested. in. the.
present.study.is.greater.than.that.of.the.previously.described.natural.cartilage..The.tangent.modulus.of.the.BNC-PDMAA.DN.gel.is.comparable.with.
that.of.the.previously.described.natural.cartilage..This.study.implied.that.the.
tested.BNC-PDMAA.gel.along.with.other.DN.gels,.except.for.the.BNC-gelatin.
DN.gel,.are.potential.materials.that.may.meet.the.requirements.of.artificial.
cartilage..However,.potential.materials.for.artificial.cartilage.also.have.to.be.
durable. to. endure. repetitive. stress,. resistant. to. wear,. and. resistant. to. biodegradation.within.the.living.body.
Biological responses of DN gels after implantation
into Muscle and Subcutaneous Tissue
Although.BNC-PDMAAm.and.BNC-gelatin.DN.are.unique.gels.that.include.
natural.polymers,.it.is.important.to.evaluate.what.kind.of.tissue.reaction.
is. induced. by. implantation. of. these. gel. materials. in. the. living. body. and.
how. strong. the. reaction. is. in. order. to. consider. application. of. these. DN.
gels. for. clinical. implants. as. a. replacement. for. natural. cartilage.. For. this.
purpose,.the.pellet.implantation.test.into.the.muscle.and.the.subcutaneous.
implantation.test.with.massive.material,.which.can.evaluate.local.reaction.
in.the.muscle.or.subcutaneous.tissue.around.the.implanted.material,.were.
investigated.(Iyakushin-Hatsu.2003)..This.study,.composed.of.macroscopic.
observations,.was.conducted.on.rabbits.using.the.sub. cutaneous.implantation. test. with. massive. material. and. histological. examinations. using. the.
ous.tissue,.according.to.the.international.guideline.for.biological.evaluation.of.the.safety.of.biomaterials.(Iyakushin-Hatsu.2003;.Tanabe.et.al..2008).
The.implanted.BNC-PDMAAm.DN.gels.induced.strong.inflammation.at.
each.period.(Tanabe.et.al..2008)..Currently.these.materials.are.difficult.to.apply.
as.clinical.implants..Around.the.BNC-gelatin.DN.gel,.which.was.composed.of.
two.natural.polymers,.inflammation.was.very.mild.at.1.week,.but.significantly.