Some years ago we so the success of this prosthetic leg, made in laser sintered polyamide in a EOS machine. The project was accomplished by Design Study "Breun, the Fraunhofer IPA and EOS GmbH (http://www.eos.info/en/applications/medical/prostheses/design-study-breuninger.html)
As we see in the video, the leg has no motors, hydraulics or any other active component; it only works on reaction forces from the material thanks to the clever design of different sections, playing with the material properties and proper thickness.
The leg was customized to fit the man's remaining femoral portion of his limb.
What I like most is the satisfaction in his face at the end of the video.