Believe it or not, 3D printers are used for more than making chocolate. The University of Pennsylvania, for example, has put a RepRap open-source 3D printer to work making blood vessel networks (though they're also made of sugar).

Scientists currently have the ability to create small samples of organ tissue, but not yet the blood vessel networks that feed full-size organs. This is where researchers from Penn and MIT are trying to help using the RepRap. "The printer builds up the walls of a mold, then draws the sugar across it in filaments. When the sugar has hardened, researchers pour cells suspended in a gel into the mold, surrounding the filaments. After the gel solidifies, the researchers dissolve the sugar, which flows out of the tissue through the vessels it created." Early tests using the networks have been promising.

The researchers maintain that "this 3D printing method makes it easy to experiment with different [blood vessel] network designs," so it's not yet a solution to the challenge of feeding full-scale organs, but it's an interesting step in the right direction.

For more details visit Penn's website.