Call it one small step for material science, one giant leap for origami. Researchers have created the first heat-reactive polymer material that can not only remember its current shape but also memorize new ones. The material—which currently requires high temperatures to change shape and reset its memory—could lead to a new generation of reusable self-folding materials that could be useful for everything from medical implants to shape-shifting electronics.
Self-folding materials aren’t new. The first generation of shape memory polymers folded into a single predetermined shape whenever they were heated. Later generations could be triggered by other stimuli, such as light, electrical charges, or a magnetic field. But they all relied on a property known as elasticity. When cool, their stringy polymers coil up. They straighten out into a new shape when heated, and then they bend right back to the default shape once they cool off again. In this way, they keep a “memory” of their original shape.
But elastic shape memory materials can only memorize two or three shapes. A 2005 Science paper offered a possible route to hundreds or even thousands: Rather than elasticity—the tendency for a material to come back to the same shape—the paper demonstrated a way to trigger a change in a material's plasticity, that is its ability to be reshaped. "The question was ... can we incorporate these two shape-shifting behaviors in one polymer?" says Tao Xie, a chemical engineer at the State Key Laboratory of Chemical Engineering in Hangzhou, China.
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