Biomedical Engineering Reference
In-Depth Information
Figure 16.4
Wear performance of PEEK composites
and historical, gammaeair sterilized UHMWPE in
a cylinder-on-flat (knee-like) wear simulator. Adapted
from Ref.
[10]
.
Figure 16.3
Polished carbon fibers at the worn bearing
surface of invitro tested CFR-PEEK. The scanning elec-
tron microscopy image was provided courtesy of
Invibio.
a control. Under the higher stress, cylinder-on-flat
loading condition, the PEEK composites exhibited
higher wear
diameter and were tested in Vitallium (CoCr alloy)
metal shells. Gamma
e
air sterilized UHMWPE liners
(with a nominal dose of ~25 kGy) were evaluated as
controls. Zirconia heads (Prozyr: Desmarquest,
France) were used as the counterface. Five composite
cups and three controls were tested in an MTS hip
simulator to 10 million cycles, representing approx-
imately one decade of use for a typical elderly
patient. Bovine calf serum was used as the lubricant.
Under these conditions, the CFR-PEEK exhibited
two orders of magnitude less wear than the control
(0.39
rates
than the historical
control
(
Fig. 16.4
).
Under the lower stress hip simulator test condi-
tions, all the PEEK composites had substantially
lower wear rates than the historical control, with the
lowest wear observed between 30% pitch CFR-
PEEK against zirconia (
Fig. 16.5
). In contrast,
unreinforced PEEK wore at six times the rate of the
control UHMWPE.
The results of this study underscored the
importance of fiber reinforcement on lower stress,
conforming contact applications and provided
further basis for exploring the composite PEEK
5.4 mm
3
/million cycles, for
the composite and control, respectively). The authors
attributed the “exceptional” wear performance of
zirconia against CFR-PEEK in the hip simulator for
the effective load transfer and interfacial strength of
the PEEK and carbon fibers
[11]
.
Wang et al.
[10]
carried out a more comprehensive
tribological investigation of PEEK composites for
both hip and knee bearing applications. CFR-PEEK
formulations were injection molded using 150 G
resin blended with 20
e
30 w/w% discontinuous PAN
or pitch fibers. The polymers were tested against
CoCr alloy, zirconia, and alumina ceramic counter-
faces. The suitability for hip applications was tested
using the MTS hip simulator, whereas the suitability
for knee applications was evaluated using a multidi-
rectional cylinder-on-flat wear tester that resulted in
line contact conditions. Testing was performed up to
5 million cycles and with bovine calf serum as
lubricant. Once again, UHMWPE sterilized with
25 kGy of gamma radiation in air was used as
0.09 vs. 35.4
Figure 16.5
Wear performance of PEEK composites
and historical, gammaeair sterilized UHMWPE materials
in a hip simulator. Adapted from Ref.
[10]
.
