Prosthetic arm

3d printed limb

Prosthetic arms require a lot of moving parts, which can make them heavy, clumsy and expensive.

3-D printers can change that, because of how efficiently they use materials. A titanium arm built at the Oak Ridge National Laboratory in Tennessee weighs just four pounds, half the weight of the average human arm, and has just $75 of materials.

First published August 18, 2014: 2:48 PM ET