In a Texas laboratory, a toy mechanical arm just the length of an index finger perches, folded up, at the edge of an empty glass bowl. A young man in a lab coat squirts a volatile fluid, methanol, into the bowl. Moments later, the arm jerks and then hesitantly reaches forward. Although clumsy and slow, the gesture is a remarkable one never previously achieved in any lab: The arm moves when parts of its structure contract in response to reactions triggered by local chemical fuel—much as our own limbs do.
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