What’s just a bit thicker than a human hair and has ten times the capability of a human muscle? Polymer-coated carbon nanotube yarn. Researchers at the University of Texas at Dallas created this yarn using carbon nanotubes coated with a polymer and coiled with a diameter of about 140 microns.
Passing a voltage through the fiber causes the muscle yarn to expand or contract. Previous similar fibers have to do both actions. That is, they expand and then contract in a bipolar movement. The polymer coating allows for unipolar fibers, critical to using the fibers as artificial muscles.