Biomedical Engineering Reference
In-Depth Information
7.5 Examples of Si
3
N
3
±Si
3
N
4
and Si
3
N
4
±CoCr bearing couples under
development or in process of approval for applications in total hip arthroplasty
and total knee arthroplasty. (Courtesy of Amedica Corp., Salt Lake City, UT.)
engines (Riley, 2000). This extensive research and development work has
resulted in the ability to produce Si
3
N
4
with attractive mechanical properties and
high reliability. Dense Si
3
N
4
produced by optimized methods with an elongated
grain microstructure, referred to as `in situ toughened' Si
3
N
4
, can have a flexural
strength of 1 GPa and a fracture toughness of 10±12MPa m
1/2
, values that are far
superior to those of Al
2
O
3
. Testing of Si
3
N
4
±Si
3
N
4
and Si
3
N
4
±CoCr bearings
has shown wear rates that are comparable to those of Al
2
O
3
±Al
2
O
3
bearings (Bal
et al., 2008, 2009a). Si
3
N
4
is biocompatible, and elicits no adverse biological
response in vivo (Howlett et al., 1989; Kue et al., 1999). These properties may
allow the use of Si
3
N
4
bearing couples in THA and TKA which retain the
advantages of CoCr, but with the low wear rates associated with ceramic-on-
ceramic bearings.
7.4.2 Ceramic composites
Al
2
O
3
-based composites have been developed in an attempt to retain the high
hardness and low wear of Al
2
O
3
, but to improve the fracture toughness and
strength. ZrO
2
-toughened Al
2
O
3
(ZTA) is a composite material consisting of 20
