Polymers - Orthopaedic Biomaterials in Research and Practice - page 146

Table 6.2 Primary engineering properties of polymers

Tensile
“ultimate
strength”
(MPa)

Maximum
tensile
elongation
(%)

Glass
transition
temperature
(°C)

Tensile
“modulus”
(GPa)

Melting
temperature
(°C)

Density
(g/cm 3 ) Polymer

PE a °
HD 0.94-0.97 1.05-1.09 22-31 10-120 −110 135

UHMW 0.93-0.95 0.94-1.05 39 420-525

PMMA (in situ) 1.17-1.20 1.6-2.6 25-48 5-10 105 Amorphous

70 b

PS 0.92 2.0-2.5 100 50-100 90-100 Amorphous

PVC
Flexible 1.19-1.28 0.02-0.05 16-28 170-400 −40 Amorphous

Rigid 1.35-1.55 0.015 15-40 2-30 80-90 Amorphous

SR 1.34 0.004 10-12 700-800 −105 Amorphous

PEEK 1.23-1.84 2.70-138 51.0-

2070

0.3-150 145 335

PLLA 1.2-1.4 8.50 900 25 56 170

a

HD, high density; UHMW = 2 × 10 6 molecular weight.

b

Minimum compressive strength.

one manufacturer may have values of mechanical properties signifi-
cantly different from that from another manufacturer. Specifications for
these materials tend to be methods to describe their composition and
properties rather than discrete compositions that will lead to specific
properties. Thus, the bioengineering literature refers routinely to these
materials by their specific manufacturer's grade and composition desig-
nation. Even this is no assurance of uniformity of properties: resin com-
pounders routinely make minor changes in their grade compositions and
processing from time to time, without changing the grade designation.
In addition, there are no medical grades of most polymers, since the rate
of use in medical devices is almost always below the minimum required
for commercial production of a specific grade: 5,000,000 lb/year. For
this reason, many medical device manufacturers compound their own
primary resins, especially of low-volume polymers.

PROBLEM 6.3
Rank UHMWPE, PMMA, cortical bone (CRB), and cancellous bone
(CNB) in increasing order of

A. Stiffness (modulus)

B. Strength (ultimate)

ANSWER:
(Refer to Figure 5.12, and assume that CRB has a density of 2 g/cm 3 and
CNB has a density of 0.3 g/cm 3 )