“The new nylon-based system, by contrast, uses cheap material and a simple manufacturing process, and demonstrates very good cycling longevity. It all comes down to how the nylon fibers are shaped. Some polymer fiber materials, including highly oriented nylon, have an unusual property: When heated, “they shrink in length but expand in diameter,” Mirvakili says, and this property has been harnessed to make some linear actuator devices. But to turn that linear shrinking motion into bending typically requires a mechanism such as a pulley and a takeup reel, adding extra size, complexity, and expense. The MIT team ‘s advance was to directly harness the motion without requiring extra mechanical parts.”