Cover Image, Volume 54, Issue 17

Ordinary polymer fibers can be converted into high performance artificial muscles simply by twisting the fibers to form coils. Heating causes large length contraction of the coiled fiber, which is driven by untwisting of the fiber. The process is reversed on cooling. On page 1278 of Issue 54, Volume 13 (DOI: 10.1002/polb.24035 ) Geoffrey Spinks and colleagues explore the scaling relationships for the torsional actuation of twisted fibers and find that the amount of rotation is independent of fiber diameter and is determined only by the anisotropic volume expansion and the amount of twist inserted into the fiber. A simple geometric model successfully predicts the torsional stroke and torque generated.