| As mentioned above, pyrolytic carbon has been used for making artificial heart valves. These actually consist of thick pyrolytic carbon coatings deposited onto graphite. Up until 1996, pyrolytic carbon heart valves consisted of silicon-alloyed pyrolytic carbon (containing from 3-8wt% silicon). The silicon was added to improve properties such as stiffness, hardness and wear resistance. Its addition had no adverse affect on biocompatibility. In 1996, a pure carbon implant material was introduced onto the market, also developed by Dr. Bokros and his team. An improved material was made possible due to a newly developed production process, which was both tougher and stronger then the silicon alloyed variant. It had the added advantage that is was more biocompatible as it did not contain silicon carbide inclusions, which could possible compromise the thromboresistance of the carbon. Deposition of Pyrolytic Carbon Coatings for Heart Valves Pyrolytic carbon coatings are made by co-depositing carbon and silicon carbide onto suitable substrates using chemical vapour deposition processes. Deposition is carried out in a fluidised bed furnace, fed with silicon carrier gas and a hydrocarbon. | 
Goodfellow
