MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 72

TABLE 3.4. Mechanical Properties of Different Synthetic Biopolymers which could be Used
as Hard Tissue Replacement

Materials Elastic modulus (GPa) Tensile strength (MPa)

HDPE 0.88 35

PTFE 0.5 27.5

PA 2.1 67

PMMA 2.55 59

PET 2.85 61

PEEK 8.3 139

PS 2.65 75

The combination of modulus and strength properties of most of the polymers,
as summarized in Table 3.4, do not meet the lower bound requirement of natural
cortical bone (Table 3.2 ).
Low stiffness (E-modulus) and high wear rate does not permit their use as
load-bearing hard tissue applications (such as bone, teeth, joint, and so on). Hence,
a new approach to the design of implanted biomaterials with tailor-made proper-
ties is attempted for various polymer biocomposite materials 63 . The polymer bio-
composite materials consist of one or more reinforcing phases (ceramics, metals
and polymers) in a polymer matrix. These composites are considered as an alter-
native choice to overcome various shortcomings of homogeneous polymers. Be-
sides signifi cant improvement in creep, fatigue resistance and other mechanical
properties, one major advantage of polymer biocomposites 64 is their radio trans-
parency and non-magnetic features. Such combinations of properties allows them
to be scanned by various modern imaging and modern diagnostic methods, like
computer tomography (CT) and magnetic resonance imaging (MRI). This feature
has broadened the application area of polymeric materials to cranial implants
as well.

3.5.1 Polymer-Polymer Composites

Polymer-polymer composite has important commercial implications, as new ma-
terials are being developed for various hard tissue replacements (acetabular cup,
knee replacement). Examples of few new polymer-polymer composites include
CF/UHMWPE, PET/PU, CF/C, CF/PEEK, CF/PMMA, PS/CF, etc 65 . One attrac-
tive aspect of the composite approach is the ability to control properties via
several variables. Important variables that can be adjusted to control properties
include:

a) type of continuous phase matrix,
b) type of polymer particles,
c) particle size distribution and
d) number of reinforcing phases 66 .