Biomedical Engineering Reference
In-Depth Information
Table 1.1
Material properties of various poly(lactide-
co
- glycolides) [5] .
Comonomer proportion (mol%)
Polymer properties
Diglycolide
L
,
L
- dilactide
rac
-
Dilactide
T
g
( ° C)
T
m
( ° C)
E
(GPa)
σ
B
(MPa)
ε
B
(%)
0
100
0
57
174
3.6
58
2.1
0
84
16
55
124
0
75
25
60
-
3.4
46
1.6
0
50
50
60
-
3.3
46
3.2
0
25
75
59
-
2.8
41
2.9
0
0
100
59
-
3.2
48
8.7
100
0
0
36
228
7.0
15.0
90
10
0
37
200
7 5
2 5
0
4 4
-
5 0
5 0
0
4 4
-
2 5
7 5
0
5 2
-
7 5
0
2 5
4 3
-
2 5
0
7 5
5 4
-
tensile strength (
B
). These properties are of similar magnitude to those found
within human hard tissues (bones, ligaments, tendons) [36], and are useful for the
biomaterial applications mentioned in Section 1.1.1 .
Polyglycolide is of high crystallinity, 40-55%, and has a relatively high melting
point of 228 °C. The glass transition temperature is 36 °C. Polyglycolide is insoluble
in most organic solvents with the exception of highly fl uorinated solvents, which
must be taken into account when processing materials. Upon copolymerization
with dilactides, amorphous materials are produced if the diglycolide content is less
than 25%. The glass transition temperature rises from 36 ° C to 54 ° C as the amount
of dilactide monomers are incorporated into the polymer. Poly(l - lactide) has
slightly lower crystallinity of 37%;
T
g
σ
174 ° C. Incorporation of
rac
-dilactide as a comonomer gradually decreases the crystallinity and at 25%
rac
-
dilactide content amorphous polymers result. Poly(d , l-lactide) with a glass transi-
tion temperature of 65 °C is completely amorphous. The bacterially produced
poly(3-hydroxybutyrate) is highly crystalline at 60-80% and has
T
g
=
57 ° C and
T
m
=
10 ° C and
T
m
of 179 °C. The modulus is 3.5 GPa. As shown in Table 1.2, incorporation of
3-hydroxyvaleric acid as comonomer leads to a softer and more elastomeric mate-
rial [37] .
Materials comprised of the other major groups of poly(hydroxycarboxylic acid)
are considerably softer and more elastic. The polyetherester polydioxanone has a
melting point of 115 °C and a glass transition temperature in the range of
=
10 -
0 °C. The crystallinity is approximately 55%. Polydioxanone has a lower modulus
(1.5 GPa) than the polylactide materials, and loses mechanical strength at a higher
rate during hydrolytic degradation. Poly(
−
ε
- caprolactone)
is
a
semicrystalline
