In my exercise physiology class we are discussing the amazing work that the human heart performs over a lifetime, even over a single day. My text book says that the fluid output of the heart exceeds that of a household faucet turned wide open (Katch, McArdle, Katch). With the invention of the 3-D printers I wonder what are the limitation to making biological machines that have the ability to regenerate cells. A simple example would be a 2-chamber heart like pump only the size of a car engine. Instead of electricity or fossil fuel a hose would feed it nutrients. Is this outlandish? has anyone heard of any recent projects in this area? what are some limitations you see?