mechanical heart valves require patients to be on blood thinners for the rest of their life, bovine and porcine heart valves are most similar to human heart valves in size and shape and they have very good reliability without requiring the patient to continue taking blood thinners.
It is fascinating that we can't reproduce the mechanical properties of a small biological valve, even a dead one (they are 'killed' before they are implanted).
When they finally do figure it out, imagine all the various applications to improve the longevity of ... well, everything.
We can't even design water pipes and valves that don't degrade over time. Limescale builds up and clogs the works. There's only a tiny amount of minerals in water, and yet that happens. Blood -- as they say -- is much thicker than water, and contains components specifically designed to clot. It's not wonder that this is a tricky problem to solve.
There is also a difference in failure modes. Natural valves degrade performance overtime due to calcification of the valve, giving you warning and time to make decisions over replacement. Mechanical valves fail catastrophically by either remaining stuck open or having the valve plate shatter. If you ever stop hearing your valve click you need to get to a hospital ASAP
