Biomedical Engineering Reference
In-Depth Information
Table 3.2.2-1 Mechanical properties of biomedical polymers
Polymer
Water absorption
(%)
Bulk modulus
(GPa)
Tensile strength
(MPa)
Elongation at break
(%)
T
g
(K)
T
m
(K)
Polyethylene
0.001-0.02
0.8-2.2
30-40
130-500
160-170
398-408
Polypropylene
0.01-0.035
1.6-2.5
21-40
100-300
243-270
433-453
Polydimethyl-siloxane
0.08-0.1
3-10
50-800
148
233
Polyurethane
0.1-0.9
1.5-2
28-40
600-720
200-250
453-523
*
Polytetrafluoro-ethylene
0.01-0.05
1-2
15-40
250-550
293-295
595-600
Polyvinyl-chloride
0.04-0.75
3-4
10-75
10-400
250-363
423
*
Polyamides
0.25-3.5
2.4-3.3
44-90
40-250
293-365
493-540
Polymethyl-methacrylate
0.1-0.4
3-4.8
38-80
2.5-6
379-388
443
*
Polycarbonate
0.15-0.7
2.8-4.6
56-75
8-130
418
498-523
Polyethylene-terephthalate
0.06-0.3
3-4.9
42-80
50-500
340-400
518-528
*
[
decomposition temperature
to crystallize or to exhibit secondary interactions such as
hydrogen bonding. The crystallinity and secondary in-
teractions can give polymers additional strength. In gen-
eral, increasing molecular weight corresponds to
increasing physical properties; however, since melt vis-
cosity also increases with molecular weight, process-
ability will decrease and an upper limit of useful molecular
weights is usually reached. Mechanical properties of some
polymeric biomaterials are presented in
Table 3.2.2-1.
Synthesis
Methods of synthetic polymer preparation fall into two
categories: addition polymerization (chain reaction) and
condensation polymerization (stepwise growth)
(
Fig. 3.2.2-2
). (Ring opening is another type of poly-
merization and is discussed in more detail later in the
section on degradable polymers.) In addition polymeri-
zation, unsaturated monomers react through the stages of
A Free radical polymerization - poly(methyl methacrylate)
CH
3
CH
3
O
O
R"
+
CH
2
C
C
R"
CH
2
C
C
O
O
CH
3
CH
3
B Condensation polymerization - poly(ethyleneterephthalate)
O
O
(n+1)
n
HO
CH
2
CH
2
+
OH
CH
3
O
C
C
O
CH
3
O
O
2n
CH
2
HO
CH
2
CH
2
O
C
C
O
CH
3
CH
2
OH
+
CH
3
OH
n
Fig. 3.2.2-2 (A) Polymerization of methyl methacrylate (addition polymerization). (B) Synthesis of PET (condensation polymerization).
