Biomedical Engineering Reference
In-Depth Information
21.8.1 Cytotoxicity
DLC and TiN-coated surfaces were studied for their Cytotoxicity effects using
the direct contact, test on extract and agar over lay techniques as per the interna-
tional standard ISO 10993: Part 5. All these coatings passed the test and hence
could be classifi ed as non-cytotoxic material.
Cytocompatibility studies of DLC, TIN on titanium, and UHMWPE were
carried out with bare Titanium and UHMWPE, respectively, as controls. L-929
mouse fi broblast cells, osteoblast cells and endothelial cells were used for DLC-
coated samples, while L-929 mouse fi broblast cells were used for TiN samples.
Both qualitative and quantitative analysis indicates that DLC-coated Ti showed
improved cytocompatibility (Kumari et al., 2002).
For better endothelialisation, cells should attach, adhere, spread and prolifer-
ate to give a confl uent monolayer. The studies indicated that initial number of
cells attached and area of spreading of cells are signifi cantly increased on DLC
and TiN coated samples compared to the corresponding uncoated surfaces. Adhe-
sion pattern of thickly populated endothelial cells on DLC makes it suitable for
vascular application.
21.8.2 Hemocompatbility
The blood compatibility of DLC and TiN coatings was assessed using a number of
in vitro
tests using human blood collected from healthy individual voluntary
donors. The tests were chosen from the guidelines given in the standard ISO
10993: Part 4. The hemocompatbility assessment studies included estimation of
consumption of blood components during exposure to whole blood, effect of the
materials on the activation of coagulation factors and effect of the material on the
complement activation characteristics.
The samples are exposed to whole blood for 30 minutes under agitation using
an environmental shaker thermo stabilized at 35 ° C
2 ° C. The count of various
formed elements of blood before and after the study were compared to arrive at
the blood cell consumption profi les (Krishnan et al., 2002).
The platelet consumption showed a marginal reduction in the coated samples
compared to the bare metal surfaces (see Figure 21.9). Quantifi cation of platelet
adhesion using radio labeled platelets confi rmed this. The WBC consumption was
more or less unaffected by the presence of the coating (see Figure 21.10).
The coated surfaces also had lower levels of adsorption of high molecular
weight proteins, correlating with the lower platelet adhesion on the coated
surfaces. High molecular weight proteins may consist of adhesive proteins that
can mediate cell adhesion and thrombus formation. No signifi cant platelet
function abnormality was induced due to the material contact; however, the mild
activation of platelets seems to have induced a change in plasma coagulation.
The observed effect of the materials on plasma proteins on exposure of platelet-
poor plasma has shown no signifi cant clotting abnormality (Krishna Prasad
et al., 2006).
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