Biomedical Engineering Reference
In-Depth Information
this chapter, Invibio has commercialized and released
Pitch-based CFR-PEEK OPTIMA in 2009 under the
trade name MOTIS
. MOTIS is intended for ortho-
pedic bearings against metal and ceramic counterfaces.
For all-polymer bearings, such as those currently under
consideration for artificial discs, PAN-based CFR-
PEEK (LT1CA30) is preferred based on pin-on-disc
(
Fig. 16.8
) as well as spine wear simulator data
[66]
.
MOTIS is produced under the same ISO quality
system as unfilled PEEK OPTIMA and is backed by
a Food and Drug Administration (FDA) master file.
Invibio has adopted a “no change” policy that freezes
the material production process at its current speci-
fications. Technical specifications for MOTIS are
available from the Invibio website (
http://www.
invibio.com
).
Figure 16.12
Ti-coated, Mathys RM PEEK-OPTIMA
image contrast finger joint. Image courtesy of Mathys
Medical Ltd.
a reported wear rate of 0.26 mm
3
/million cycles,
although varied lubricant uptake in control samples
prevented an accurate determination of wear. The
inferior wear performance of virgin PEEK relative to
UHMWPE was attributed to the lack of fiber rein-
forcement and was consistent with Wang et al.'s
previous observations of neat PEEK vs. historical
UHMWPE in a hip simulator
[10]
.
In an analytical study, Yeoman et al.
[63]
explored
the influence of bearing materials on a meta-
carpophalangeal joint design. UHMWPE, stainless
steel, and PEEK were considered as potential mate-
rial candidates. The authors concluded that the finite
element analysis results confirm the safety of their
design.
The possibility of an all-polymer prosthesis was
first introduced by Bradley and co-workers in the
1990s
[64]
. They prospectively studied 63 TKRs in
which the femoral component was polyacetal and 138
TKRs in which the femoral component was conven-
tional cobalt chrome. The tibial and patellar compo-
nents were of UHMWPE. Patients were followed up
for at least 10 years. In the polyacetal group, a number
of patients died or were revised, for reasons unrelated
to the presence of polyacetal. There were neither
instances of femoral component fracture nor failure
by wear. One postmortem specimen, retrieved at
9 years after surgery, showed no measurable poly-
acetal wear and negligible PE wear
[65]
.
16.8 Summary and Concluding
Remarks
In mature implant fields with established and
successful alternatives, such as total joint replace-
ments, it is onlywith the challenges of new designs and
niche applications, such as with hip resurfacing and
finger joints, that PEEK biomaterials can offer an
attractive opportunity. Although hip resurfacing
designs are encouraging and in various stages of clin-
ical evaluation, it will still be many years, perhaps
a decade ormore, before these novel approaches can be
judged superior to their successful historical prede-
cessors.Whenmedical device engineers are facedwith
unusual size and dimensional constraints that limit
their design options for a bearing surface, PEEK
biomaterials may be considered as a feasible alterna-
tive to conventional orthopedic bearing materials.
Acknowledgments
The authors thank Doruk Baykal, Drexel Univer-
sity, for his editorial assistance with this chapter. The
authors also thank Richard Field for his valuable
collaboration on the MITCH PCR cup and for
providing access to radiographic images.
16.7 MOTIS: Medical Grade CFR-
PEEK for Bearing Applications
References
In response to growing interest in bearing applica-
tions of medical grade PEEK and based on the
expanding scientific literature
[15
e
18]
summarized in
[1] H. Voss, K. Friedrich, On the wear behaviour of
short-fibre-reinforced PEEK composites, Wear
116 (1987) 1
e
18.
