The importance of glutaraldehyde pretreated bioprosthetic heart valves fabricated from bovine pericardium or porcine aortic valves is well realized in the management of valvular heart diseases. But, calcification limits the durability and is the most frequent cause of failure of these bioprosthetic heart valves. Various research groups in the world are actively involved in describing, understanding, and preventing calcification of bioprosthetic heart valves. Since there is no satisfactory clinical means for preventing or treating this disorder, attempts are made to improve the anticalcification properties of the replacement valves in the preparation stage itself. Research in this area is very active, and many newer approaches are made to mitigate the problem. An attempt has been made in the present article to review various theories put forward to explain the causative factors involved and mechanistic aspects of biocalcification and to present various strategies attempted for the prevention of calcification with the special feature on the work done in the area in our laboratory.
Calcification limits the functional lifetime of cardiac valve substitutes fabricated from glutaraldehyde preserved bovine pericardium. Host factors, mainly younger age, and implant factors, mainly glutaraldehyde cross-linking, are implicated in the calcification process. Glutaraldehyde cross-linking is believed to activate the potential sites in the tissues for biocalcification. In the present work, we investigated the possibility of using alginate azide (AA) instead of glutaraldehyde for the preservation of pericardial tissues in order to enhance the durability of bioprosthetic heart valves. Grafting with poly(GMA-BA) copolymer to the alginate azide cross-linked pericardial (AACPC) tissue was carried out to obtain better stability, strength, and anticalcification properties. The strength property and thermal stability of the AA cross-linked tissues were studied. Calcification studies in rat subdermal models reveal that AA cross-linking reduces the calcification to negligible levels. After 30 days implantation, the calcium content was found to be 10.4 +/- 1.2 and 6.1 +/- 0.3 micrograms mg-1 for untreated AACPC and polymer grafted AACPC, respectively, compared to a value of 100 +/- 1.2 micrograms mg-1 calcium recorded for control glutaraldehyde cross-linked pericardial (GCPC) tissues.
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