2) hollow metal ball, an alloy (metal composite) cage, anda Teflon base Pyrolite carbon
3)Minimal regurgitation - This means that the amount of blood lost upstream as the valve closes is small. For example, closure regurgitation through the mitralvalve would result in some blood loss from the left ventricle to the left atrium as the mitral valve closes. Some degree of valvular regurgitation is inevitable and natural (Fixme: Give indicative value).However, several heart valve pathologies (e.g. rheumaticendocarditis) may lead to clinically significant valvular regurgitation. A desirable characteristic of heart valve prostheses is that regurgitationis minimal over the full range of physiological heart function (i.e. complete functional envelope of cardiac output vs. heart rate).
Minimal transvalvular pressure gradient - Whenevera fluid flows through a restriction, such as a valve, a pressure gradient arises over the restriction. This pressure gradient is a result of the increased resistance to flow through the restriction. Naturalheart valves have a low transvalvular pressure gradient as they present little obstruction to the flow through themselves, normally less than 16 mmHg. A desirable characteristic of heart valve prosthesesis that their transvalvular pressure gradient is as small as possible.
Non-thrombogenic - As natural heart valves are lined with an endothelium continuous with the endothelium lining the heartchambers they are not normally thrombogenic. This is important as should thrombus form on the heart valve leaflets and become seeded with bacteria, so called "bacterial vegetations" will form....