Researchers at Vanderbilt University in Tennessee has developed amputees a bionic "to walk without the leg-dragging gait characteristic of conventional artificial legs". Unlike the average peg-leg, the Vanderbilt leg has motors in the knee and ankle to actively move like the real thing. Sensors and microprocessors predict what the user is about to do and the leg moves accordingly. The leg itself is also pretty light on power, running for up to three days (or 14 kilometers) on a single charge.
The Vanderbilt leg is seen above worn by Craig Hutto, left, and Professor Michael Goldfarb, who is leading the team at VU. The leg itself has been in development for always seven years now, and packs in quite a bit of tech. From Vanderbilt: The device uses the latest advances in computer, sensor, electric motor and battery technology to give it bionic capabilities: It is the first prosthetic with powered knee and ankle joints that operate in unison. It comes equipped with sensors that monitor its user's motion. It has microprocessors programmed to use this data to predict what the person is trying to do and operate the device in ways that facilitate these movements.