Biomedical Engineering Reference
In-Depth Information
standards. Both the coated and uncoated materials passed the systemic toxicity,
sensitization, and intracutaneous reactivity.
Intramuscular implantation was carried out for studying the effects under
various time periods. Skeletal muscle around the coated and uncoated implants
was grossly normal at all time periods. There was no evidence of necrosis or
infl ammation in any specimen. Good healing pattern was observed around both
coated and uncoated samples. The light microscopic observations of the various
parameters established that the tissue response around both coated and uncoated
implants were similar to each other and showed evidence of repair at all time
periods. There was no evidence of chronic infl ammation in any specimen
(Mohanty et al., 2002).
21.8.4 Large Animal Experiments
Two series of large animal experiments were conducted with the DLC and TiN-
coated materials. The animal experiments were carried out in sheep with the
authorization of the Institute's Animal Ethics Committee and the concerned
national agency regulating experiments in animals. The international guiding
principles for biomedical research involving animals of the Council for the Inter-
national Organisation of Medical Sciences (CIOMOS) were adhered to during
the animal experiments (Howard, 1985).
The fi rst series was aimed at studying the blood compatibility characteristics
of DLC coatings. Circular shaped buttons were implanted in the
inferior vena
cava
(IVC) of sheep. The response to DLC-coated commercially-pure titanium
(CP Ti + DLC) as the test material was compared against to that of commercially-
pure titanium (CP Ti) as control. The buttons are harvested after two hours of
implantation and the area of thrombus formed on the surface is assessed. The
location of the control and test samples were interposed every experiment to
eliminate the effect of implantation site on the results.
Microphotographs (20X) of the explanted samples scanned and digitized to
assess the area of the thrombus on the samples using stereo zoom microscope
(Nikon Corporation, Japan) and digital microscopy documentation system (DC
120, Kodak Corporation, USA). From these images, the area of the thrombus was
estimated using image processing techniques (see Figure 21.11). The area of
thrombus averaged over a set of six experiments was found to be marginally more
on the bare CP titanium surface over the DLC-coated surface, but the differences
were not statistically signifi cant. The thrombus area estimation was validated
using radio labeling technique.
The second series of large animal experiments were carried out as part of
qualifi cation of TiN coating on Ti6Al4V alloy for use in artifi cial heart valves.
Sheep were chosen as the model based on the previous experience in heart valve
evaluation (Bhuvaneshwar et al., 1996). Adult sheep in the weight range 35 to
50 Kg have heart size suitable for implantation of #23 mm size heart valve. Surgery
was carried out under general anesthesia through a left thorocotomy in the fourth
intercostals space. Cardiopulmonary bypass was established and the animal
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