Nitinol

When a limb is rendered immobile for long periods of time, its muscles will inevitably begin to atrophy. A new implant could help keep that from happening, however, by mechanically stretching and compressing those muscles.

A German research team has prototyped an extraordinary heating/cooling system that stresses and unloads nickel-titanium "muscle wires" to create heated and cooled air at twice the efficiency of a heat pump or three times the efficiency of an air conditioner.