Wooden robot arm is powered by plastic muscles

A polymer that changes shape when heated can lift objects 5000 times its own weight, with potential applications in robotics. Shape-memory polymers flip between their normal state, where molecules are flexible and disordered, and their deformed state, where the molecules bind after being stretched. Once in the stretched, deformed state, the polymer can be unstretched – resuming its "normal" state – by applying heat or light. However, traditional shape-memory polymers don't store significant amounts of energy while being stretched – meaning they don't release much energy while unstretching, which limits their use in tasks that involve lifting or moving objects. Zhenan Bao at Stanford University in California and her colleagues have now produced a shape-memory polymer that does store and release appreciable amounts of energy.