Biomedical Engineering Reference
In-Depth Information
composite surfaces when compared to the controls,
b
Ti6Al4V were found to be the most appropriate
materials for use in a corneal bioreactor system
[13]
.
Some polymers, including polytetrafluoroethylene
(PTFE), were found to be cytotoxic to human corneal
fibroblasts after autoclaving.
In 2002, Rivard et al.
[14]
reported on the devel-
opment of a new spinal implant system that did not
induce fusion. Because the spinal implant system
was made from metal and the PEEK polymer, which
would likely generate PEEK particulate debris, the
authors designed a rabbit study in which 50 million
(per surgical site
d
a “worst case scenario”) PEEK
particles (40
-glucoronidase activity and osteoblastic production
of Type I collagen and osteocalcin were similar to
levels detected on Ti6Al4V. Lin et al.
[11]
evaluated
a GPEEK (PEEK and 10% random, chopped E-glass
fibers) composite material using human-derived
osteoblast-like cell cultures. In these experiments, the
surface roughness of the GPEEK composite varied
between 3, 6, and 9
m. Based on the analysis of cell
yield (sixfold increase), osteocalcin production, and
levels of alkaline phosphatase, the authors concluded
that all the rough GPEEK surfaces were found to
promote proliferation and continued functioning of
osteoblast-like cells (MG63
d
human osteoblast-like
cell line) over the 5-day duration of exposure. Lin et al.
[11]
further concluded, “Overall, this study demon-
strates that GPEEK supported proliferation of osteo-
blast-like cells and provided a favorable environment
for the continued production of osteocalcin in vitro”.
In 2002, Katzer et al.
[12]
performed two inde-
pendent cytotoxicity and mutagenicity test series on
PEEK (381G PEEK resin), one using the bacterium
Salmonella typhimurium
m
m average size) would be injected into
the spinal canal of rabbits at both lumbar and
thoracic sites. The amount, size, and shape of the
wear debris were based on mechanical wear tests that
simulated the outcome of the spinal implant system
after 5
e
10 years of implantation. Injecting the PEEK
particulate would give the authors an opportunity to
characterize the inflammatory response by histology
in neural tissues of the rabbit, which might be
inflamed by particulate debris generated by the
intended spinal implant device. Rivard et al.
[14]
reported that the inflammatory response decreased
over a 12-week period. Although PEEK is not
resorbable, phagocytosis with particle transport to
adjacent lymph nodes and the lungs may have
occurred with time, thereby explaining the decrease
in inflammation at 12 weeks. Specimens examined
by histology at 12 weeks demonstrated an increase in
connective tissue thickness surrounding the spinal
cord at the injection site, which may be explained by
the encapsulation with connective tissue of larger
particles that could not be phagocytosed (40
m
(Ames Test) and the other
using mammalian cells (Chinese hamster fibro-
blasts, V-79) to determine if PEEK was cytotoxic.
Mutagenicity results are discussed in Section 8.2.
Katzer et al.
[12]
reported that “the results of the
incubation of polyetheretherketone (PEEK) fiber
material with seven different genotype variants of
Salmonella typhimurium
bacterium showed no
mutagenic or cytotoxic activity of the test mate-
rial”. 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]
. 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
m
mis
larger than a macrophage but smaller than a foreign
body giant cell). It is important to point out here that
injection of smaller PEEK particulate might have
generated a different result. Many authors consider
the host response to 50-
m particulate approxi-
mately equal to the host response to the bulk
biomaterial, with a maximum inflammatory host
response occurring when particulate is in the 0.5- to
1-
m
g/ml)
[12]
. Thus, the authors concluded that
the PEEK material produced no evidence of cyto-
toxicity
[12]
.
Orwin et al.
[13]
have shown that PEEK has no
inhibitory effects on the growth of human corneal
stromal fibroblasts (HCF) cultured in a bioreactor for
up to 7 days. In their study, several materials were
evaluated for potential use in a bioreactor system for
a tissue-engineered cornea. Two types of cytotoxicity
tests were performed using HCF: a 24-h cytotoxicity
test based on the ASTM standard F813-01 and
a 7-day growth inhibition test
m
m size range
[2]
. Although transmitted and
polarized light microscopy revealed fibrous connec-
tive tissues with an attendant chronic inflammatory
response to birefringent PEEK particulate in peri-
dural tissues, neither necrosis nor swelling of the
nerve roots or spinal cords was associated with the
injection of the PEEK particulate. Thus, the authors
concluded that PEEK particulate was well tolerated
by neural tissues
[14]
.
m
[13]
. PEEK and
