The overall goal of the proposed program is to improve two major problem areas with present-day central flow/bileaflet pyrolytic carbon valves and to accomplish these improvements with minimal changes in the material and no changes in valve design. The two problem areas are (1) increased thrombogenicity compared to tissue bioprostheses; (2) sensitivity of the carbon material to surface mechanical damage, cavitational erosion in particular. We propose to achieve this goal by further development in Phase II of chemical vapor deposited (CVD) diamond coatings deposited on standard, polished, pyrolytic carbon-coated heart valve parts, as initially demonstrated in Phase I of this program. The Phase I studies conducted by Giner, Inc. have shown that samples that were formed with a thin interlayer between the carbon substrate and diamond enhance the quality and adhesion of the diamond film to the substrate. Also in a preliminary evaluation, using a modified Lee-White method with fresh bovine blood, it was shown that these diamond-coated pyrolytic carbon coupons exhibited a greater time to fibrin formation compared to a standard polished, pyrolytic carbon-coated heart valve leaflet. These encouraging results suggest the development studies initiated in Phase I should be extended to the diamond coating and evaluation of complete carbon heart valves in Phase II.
The Specific Aims for Phase II are: 1) Continue studies to improve diamond deposition and adhesion directly on pyrolytic carbon-coated heart valve components using an adhesion enhancer as an interlayer on the carbon, 2) Characterize the deposited films for uniformity of deposition, surface morphology, hermicity and durability, and 3) Compare, through in vitro and in vivo testing, the blood material interactions of the diamond-coated and standard commercial carbon heart valve materials.
Diamond coating is expected to increase the longevity of heart valves. The estimated market for 1990 for pyrolytic carbon valves is approximately $100M. The total market for all types of valves is approximately $330M/yr. Any improvement in technology, as the one proposed, is bound to impact a large percentage of the above dollar volume. Also, successful development of diamond coating as a biomaterial will find use in numerous other biomedical applications.
