Platelet responses to silicon-alloyed pyrolytic carbons.

Pyrolytic carbon (PYC) containing approximately 7 wt % silicon is used in most clinical mechanical heart valves where it has demonstrated a high level of blood compatibility. The Si, present as SiC, is included since it is believed to enhance durability. However, it has been suggested that SiC reduces PYC blood compatibility. In the present study, PYC valve leaflets were prepared with low, conventional, and high levels of Si. The in vitro responses of human platelets to these materials were then quantified. Platelet responses were consistent with previous reports: Adherent platelets were extremely well spread, closely followed submicron contours, and formed very few aggregates or microthrombi-like structures. No significant differences with respect to the Si concentrations were observed for platelets adherent per unit area and the numbers of thrombi-like structures. Some differences were observed with platelet morphologies and the material surface covered with platelets, although these did not vary consistently with respect to Si concentration. These results indicate that lowering (or raising) the Si alloy concentration in PYC over a reasonable range (0.54-13.5 wt % as examined here) is unlikely to improve or otherwise alter the in vivo blood compatibility of this important clinical material.