Calcification of Trileaflet Polyurethane Heart Valve

Heart valve disease is a common type of cardiac disease that causes a large number of mortalities worldwide. Patients with severe heart valve problems are required to undergo heart valve replacement surgeries. Mechanical and bioprosthetic heart valves are the current available prostheses for patients in need of a heart valve replacement surgery. Mechanical heart valves are susceptible to thromboembolism and thrombosis and bioprosthetic valves have a limited life-span because of leaflet wear and calcification. Different polyurethane valves were suggested as an alternative material. However, prior results indicated that tested polyurethanes failed due to calcification. The mechanism for polyurethane calcification is not yet completely understood. Kou Imachi et al. [2], suggested that the calcification is due to entrapment of blood proteins and/or phospholipids in microgaps in the polymer and subsequent attraction of Ca ion, leading to formation of calcium phosphate (Ca₃(PO₄)₂). Bisphosphonates (BP), which are considered to enhance the calcification resistance of polymers once covalently bonded to the material, indicated promising results in some studies. Focus of the present study is the trileaflet polyurethane valve, originally developed in the design of the AbioCor^® replacement heart, and has demonstrated excellent durability and hemocompatibility in clinical evaluation. Over the past three years, this valve has been modified and its potential as a replacement valve have been studied [1]. Valve hemodynamic analysis showed that it is comparable to bioprosthetic valve in terms of fluid flow, pressure drop and regurgitation [1]. In order to ensure the suitability of the trileaflet polyurethane valve as a replacement valve its fatigue and calcification resistance are studied. The purpose of this paper is to simulate calcification of trileaflet polyurethane valves in an in vitro accelerated test and compare that with that of tissue valves. Furthermore the effect of bisphosphonate modified polyurethane on calcification is studied.