Biomedical Engineering Reference
In-Depth Information
7.3 Mutagenesis (Genotoxicity)
controls, the authors found the maximum numbers of
exudate cells and Ia-positive macrophages on day 7
[15]
. The percentage of Ia-positive macrophages
varied according to the specific polymer present in the
cages after 7 days, with PEEK generating one of the
highest levels of Ia-positive macrophages on day 7
[15]
. By day 14, the percentage of Ia-positive macro-
phages decreased with individual exudates, showing
19
e
32% Ia-positive cells depending on the type of
material
[15]
. Only in the case of polydimethylsiloxane
(PDMS) did the percentage of Ia-positivemacrophages
remain the same when compared with control empty
cage macrophages
[15]
. The authors found evidence to
support their hypothesis that polymer composition
influenced the cellular response following implanta-
tion, but the clinical significance of these findings is not
clear.
Jockish et al. implanted cylinders (3 mm diameter,
10 mm length) of PEEK (Victrex 450G) as well as
30% CFR-PEEK (Victrex 450CA30) into the para-
vertebral muscles of rabbits according to ASTM
F981. Half of the rabbits were euthanized with
explantation of the PEEK implants at 8 weeks with
the other half euthanized and explanted at 12 weeks.
Histopathological examination pursuant to Table 1 of
ASTM F981 revealed normal muscle tissue with no
adverse tissue response, no visible infection, few
PEEK particulates, and a mild chronic inflammatory
response with macrophages and foreign body giant
cells. Lymphocytes, plasma cells, and eosinophils
were not frequently found
[16]
. The tissue response
was comparable to UHMWPE. The researchers'
second phase study used CFR-PEEK as internal
fixation devices for transverse midshaft femoral
osteotomies in canines. The results of this analysis
demonstrated the material to be effective in
promoting fracture healing with a nonspecific foreign
body response shown to the fracture fixation plates
and infrequent particulate debris
[16]
.
In 2002, Katzer et al.
[12]
performed two inde-
pendent cytotoxicity and mutagenicity test series on
PEEK, one using the bacterium
typhimurium
(Ames Test) and the other using mammalian cells
(Chinese hamster fibroblasts, V-79). Katzer et al.
[12]
reported that “the results of the incubation of poly-
etheretherketone (PEEK) fiber material with seven
different genotype variants of
S
.
Salmonella typhimu-
rium
bacterium showed no mutagenic or cytotoxic
activity of the test material”. In tests in which the
PEEK raw material was finely cut and applied
directly to the agar plate, there was no evidence of
cytotoxic or mutagenic effects
[12]
. When mutage-
nicity tests were conducted with PEEK
e
dimethyl
sulfoxide (DMSO) extracts, extracts from the PEEK
material did not release any substances that caused
cells to mutate
[12]
. Further investigation of the toxic
reaction to PEEK revealed that the number of
surviving colonies per 10
5
surviving cells lay within
or below the range of the solvent control even in the
presence of high PEEK concentrations (5.0
g/ml)
[12]
. Thus the authors concluded that the PEEK
material produced no evidence of cell damage
[12]
.
m
7.4 Immunogenesis
There is no evidence that PEEK is associated with
immunogenesis.
7.5 Soft Tissue Response
The intramuscular tissue response to PEEK was
investigated by Williams et al.
[5]
over a period of 30
weeks. It was shown to elicit a minimal response from
the muscular tissue with no evidence of significant
irritation of the tissues. Petillo et al.
[15]
studied the
inflammatory response of an unspecified grade of
PEEK using a stainless steel cage implant system in
rats and evaluated the early cellular response to
implantation of a variety of polymeric biomaterials in
this system after 4, 7, and 14 days. The authors
examined the cellular components of the inflammatory
exudate of the cages, as macrophages may initiate
a wide spectrum of responses upon interaction with
a foreign material. The authors sought to test the
hypothesis that chemically different polymers
(including PEEK) could differentially activate
macrophages. For all materials tested, including empty
7.6 Osteocompatibility of PEEK
Devices
As mentioned earlier, the best way to understand
biocompatibility is to study the interaction between
the host and the biomaterial. Thus, as Dr Jonathon
Black
[2]
has indicated, biocompatibility is the
“biological performance in a specific application that
is judged suitable for that site/situation”. For this
reason, the interaction (and therefore the observed
