Most chemical reactions are accompanied by a change of molecular shape. Impressively, evolution has harnessed this effect to generate mechanical power for biological 'devices', for example, in muscles, where the bending of myosin upon release of adenosine diphosphate is used to drive one fibre past another. In stark contrast, science has produced very few artificial analogues. In most cases, chemical transformations contribute to man-made mechanical devices only at the crudest level, by supplying a source of heat, or electrical energy, or indiscriminant swelling. Current work on nanodevices is changing this situation at the molecular level, but problems in linking such devices together to achieve larger-scale motion have inhibited progress. On page 778 of this issue, Irie and colleagues describe a breakthrough in this area — a light-induced chemical transformation that bends crystals without shattering them.
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