Bistable Networks Enable Complex Shape Changes.

The ability to change a surface's profile allows biological systems to effectively manipulate and blend into their surroundings. To mimic this behavior, Mechanical metamaterials can be pre-programmed during fabrication for complex single deformations. Multi-stability has enabled metamaterials with programmable mechanical properties and complex shape changes. However, these multi-stable structures either have a limited number of stable states or no method of achieving the complexity of the profiles available in prefabricated structures from their large state space. Here we show that by coupling bistable elements in a periodic array, we can navigate a vast and otherwise degenerate state space, allowing us to encode targeted and varied shape transformations. We decouple shape programming force from holding force, so low force actuation is amplified into stable and large displacement shape changes. This subset of scale-independent, additively manufactured metamaterials harnesses shearing to enable asymmetry. They can be automatically rewritten after fabrication to generate complicated 2D profiles and laminated to form 3D surfaces. For successful navigation between profiles with no mechanical frustration, we have developed an inverse shape matching strategy and physically demonstrate the results using an automatic material encoding machine. Our work opens new opportunities in microdevices, tactile displays, manufacturing, and robotic systems.