Nylon fiber has a new powerful new application; it can be used to make artificial muscle fibers, according to the MIT Department of Mechanical Engineering. Muscles expand and contract and previous artificial muscles do that as well. Real muscles, however, also bend, and that capability has apparently been missing with most other materials used in for artificial muscles. Some exotic material such as carbon nanotube yarns can bend, but are expensive and hard to make, plus they have poor life cycle of fewer than 1,000 cycles.

And now nylon may have solved the problem with a solution that is both plentiful and inexpensive. We recently covered another technology that uses nylon to create artificial muscles. The MIT researchers use an approach that involves two factors: shaping and heating. Twisted nylon filament, compared to natural muscle fiber, had already been demonstrated to extend and retract further as well as store and release more energy.

The MIT researchers took advantage of nylon’s fast heating but slower cool down times. According to Seyed Mirvakili, a doctoral candidate in the Department of Mechanical Engineering, “The cooling rate can be a limiting factor,” Mirvakili says. “But I realized it could be used to an advantage.” Selective heating of one side of the fiber “causes that side to begin contracting faster than the heat can penetrate to the other side, and thus can produce a bending motion in the fiber. You need a combination of these properties: high strain [the pull of the shrinking motion] and low thermal conductivity.”

In testing  the researchers found the material maintains performance for at least 100,000 bending cycles and can bend and retract at least 17 times per second. Ian Hunter, the George N. Hatsopoulos Professor in the Department of Mechanical Engineering, said eventual applications could include clothing that adjust to body sizes, shoes that self-tighten, and medical devices such as self-adjusting catheters. Much work remains to be done on the further development of nylon fibers as artificial muscles, but the work at MIT is attracting attention worldwide as “a simple idea that works really well.”