Metamaterials that learn to change shape

Learning how to change shape is a fundamental strategy in the adaptation and evolution of living organisms, from cells to tissues and animals. Human-made materials can also exhibit advanced shape-morphing capabilities but lack the ability to learn. Here we build metamaterials that can learn complex shape-changing responses using a contrastive learning scheme. By being shown examples of the target shape changes, our metamaterials are able to learn those shape changes by progressively updating their internal learning degrees of freedom—the local stiffnesses. Unlike traditional materials that are designed once and for all, our metamaterials have the ability to forget and learn new shape changes in sequence, to learn several shape changes that break reciprocity, and to learn multistable shape changes, which in turn allows them to perform reflex gripping actions and locomotion. Our findings establish metamaterials as an exciting platform for physical learning, which in turn opens avenues for the use of physical learning to design adaptive materials and robots.