Chemists have gotten a lot of mileage out of the Nobel Prize-winning, light-activated motor molecules invented in Ben L. Feringa’s lab at the University of Groningen. Feringa has used them to create molecule-sized cars that scoot along a surface, and others have incorporated them into polymers or used them to drill holes in cancer cells (see page 24). Feringa’s group has now managed to get these molecule-sized machines to flex some muscle. His team created a water-soluble version of the motor that assembles into fibers. In the presence of calcium ions, these fibers organize into macroscale strings made mostly of water that flex in response to ultraviolet light. They can even lift a small weight: a 400-mg piece of paper (Nat. Chem. 2017, DOI: 10.1038/nchem.2887). As with previous versions of Feringa’s motors, these molecules rotate via isomerization around a double bond when hit with UV light. The motor molecules pack closely together in the self-assembled fibers and expand a little bit in the presence of the light, causing the string to bend. “You amplify a tiny motion from the molecular level all the way up to the macroscopic level,” Feringa notes. While others have made artificial muscles using molecular machines covalently linked to polymers, this is the first time that such muscular systems have been assembled entirely from small molecules.