https://www.scientificamerican.com/article/a-new-twist-on-artificial-muscles/

Even as electronics have shrunk more and more, motors, hydraulics and other gadgets used to drive motion have stubbornly resisted the trend. It is difficult to make and assemble minuscule mechanisms that can provide the forces and handle the stresses needed to drive exceptionally small moving parts. This week in Science, several teams of researchers present studies describing advances in making small artificial muscles—all of which use tiny twisted fibers to store and release energy. The fibers could be employed in everything from miniature robots to valves in medical devices.

These fibers, which often include lightweight polymers such as nylon or high-density polyethylene, can be more powerful, based on their weight, than human muscles. As they contract, some can lift more than 1,000 times their own mass, says Sameh Tawfick, a mechanical engineer at the University of Illinois at Urbana-Champaign. The fibers enable engineers to store a lot of energy in a small space, which “lets them do things they can’t otherwise do,” notes Tawfick, who co-authored a perspective on the studies published in the same issue of Science.