Figure 4.3
10
1
10 1
Elastic Modulus [MPa]
10
0
10
–1
10
–2
0.8
0.6
1.0 1.2
BNCgelatin
Gelatin
BNC
Fracture Stress [MPa]
BNCgelatin
Gelatin
10
0
10
–1
10
–3
0.0 0.2
ED
0.4
C Con
(a)
centration [M]
10 –2
0.0 0.2
ED
0.4
C Con
0.6
(b)
0.8
centration [M]
1.0 1.2
78
Bacterial Cellulose
Figure 4.3
Effect. of. cross-linker. EDC. concentration. on. the. compressive. elastic. modulus. (a). and. the.
compressive.fracture.stress.(b).of.BNC-gelatin.DN.gel.and.gelatin.gel..The.compression.was.
performed.perpendicular.to.the.stratified.structure.of.the.BNC-gelatin.gel..Concentration.of.
gelatin.in.feed:.30.wt%..(Reproduced.with.permission.of.Nakayama.et.al..2004.)
Effect of Water Content
Since. the. mechanical. property. of. hydrogel. is. changed. by. its. water. content.
(i.e., swelling. degree),. the. effect. of. the. degree. of. swelling,. q,. on. the. . elastic.
. modulus. and. fracture. stress. of. BNC-gelatin. DN. gel. was. investigated.
(Figures 4.4a. and. 4.4b).. As. shown. in. the. figures,. both. the. elastic. modulus.
and. fracture. stress. decrease. with. an. increase. in. the. degree. of. swelling,. q,.
following. a. power. law. relation.. The. fracture. stress. of. BNC-gelatin. DN. gel.
is.4–18 times.greater.than.that.of.gelatin.gel.over.the.same.degree.of.swelling.range..Also,.the.elastic.modulus.of.the.BNC-gelatin.DN.gel.is.2–8.times.
greater. than. that. of. gelatin. gel.. Both. values. decrease. less. sensitively. with.
increasing.swelling.for.the.DN.gels..Thus,.despite.its.high.water.content.of.up.
to.70.wt%,.BNC-gelatin.DN.gel.exhibits.a.high.mechanical.strength.of.5.MPa.
in.fracture.stress.and.4.MPa.in.elastic.modulus;.both.are.almost.equivalent.to.
those.of.articular.cartilage.(McCutchen.1978).
BNC-PAAm DN gel
Effect of DN
A.great.improvement.in.the.mechanical.properties.of.BNC.gel.is.obtained.
through. combination. with. poly(acrylamide). (PAAm). (BNC-PAAm). using.
the.DN.technique,.which.sustains.not.only.high.compression,.but.also.high.
. elongation..By.controlling.the.water.content.of.the.BNC.gel.prior.to.polymerization.of.the.second.(PAAm).network,.a.ligament-like,.tough.BNC-PAAm.
DN.gel.with.a.tensile.strength.of.40.MPa.was.successfully.obtained.
10
1
10 1
Elastic Modulus [MPa]
10
0
10
–1
10
–2
0.8
0.6
1.0 1.2
BNCgelatin
Gelatin
BNC
Fracture Stress [MPa]
BNCgelatin
Gelatin
10
0
10
–1
10
–3
0.0 0.2
ED
0.4
C Con
(a)
centration [M]
10 –2
0.0 0.2
ED
0.4
C Con
0.6
(b)
0.8
centration [M]
1.0 1.2
78
Bacterial Cellulose
Figure 4.3
Effect. of. cross-linker. EDC. concentration. on. the. compressive. elastic. modulus. (a). and. the.
compressive.fracture.stress.(b).of.BNC-gelatin.DN.gel.and.gelatin.gel..The.compression.was.
performed.perpendicular.to.the.stratified.structure.of.the.BNC-gelatin.gel..Concentration.of.
gelatin.in.feed:.30.wt%..(Reproduced.with.permission.of.Nakayama.et.al..2004.)
Effect of Water Content
Since. the. mechanical. property. of. hydrogel. is. changed. by. its. water. content.
(i.e., swelling. degree),. the. effect. of. the. degree. of. swelling,. q,. on. the. . elastic.
. modulus. and. fracture. stress. of. BNC-gelatin. DN. gel. was. investigated.
(Figures 4.4a. and. 4.4b).. As. shown. in. the. figures,. both. the. elastic. modulus.
and. fracture. stress. decrease. with. an. increase. in. the. degree. of. swelling,. q,.
following. a. power. law. relation.. The. fracture. stress. of. BNC-gelatin. DN. gel.
is.4–18 times.greater.than.that.of.gelatin.gel.over.the.same.degree.of.swelling.range..Also,.the.elastic.modulus.of.the.BNC-gelatin.DN.gel.is.2–8.times.
greater. than. that. of. gelatin. gel.. Both. values. decrease. less. sensitively. with.
increasing.swelling.for.the.DN.gels..Thus,.despite.its.high.water.content.of.up.
to.70.wt%,.BNC-gelatin.DN.gel.exhibits.a.high.mechanical.strength.of.5.MPa.
in.fracture.stress.and.4.MPa.in.elastic.modulus;.both.are.almost.equivalent.to.
those.of.articular.cartilage.(McCutchen.1978).
BNC-PAAm DN gel
Effect of DN
A.great.improvement.in.the.mechanical.properties.of.BNC.gel.is.obtained.
through. combination. with. poly(acrylamide). (PAAm). (BNC-PAAm). using.
the.DN.technique,.which.sustains.not.only.high.compression,.but.also.high.
. elongation..By.controlling.the.water.content.of.the.BNC.gel.prior.to.polymerization.of.the.second.(PAAm).network,.a.ligament-like,.tough.BNC-PAAm.
DN.gel.with.a.tensile.strength.of.40.MPa.was.successfully.obtained.