Robot makers have long sought to replace the puny electric motors and heavy hydraulic actuators that drive most of their machines with something more musclelike. One possibility is shape memory alloys, metals that contract when an electric current heats them to a certain temperature and return to their original shape as they cool. But such alloys switch shapes slowly, making them hard to use as artificial muscles. Mechanical engineers Stephen Mascaro of North Dakota State University and Harry Asada of MIT have a potential solution: fluid-filled tubes containing wires made of a shape memory alloy. The fluid speeds the alloy's cooling, so it changes shape in only .15 seconds-more than an order of magnitude faster than previous systems. Asada hopes to use the networks to replace the electric motors used for seat and mirror adjustments in cars, but eventually the technology could bulk up robots with lifelike muscles.

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