Programmable and resilient metamaterials with anisotropic and non-linear mechanical responses composed exclusively of stiff constituents

Recently, significant progress has been made in the field of flexible bulk metamaterials composed of soft and elastic materials, unlocking the potential for achieving programmable non-linear mechanical responses, such as shape morphing, energy absorption, and information processing. However, the majority of these metamaterials utilize expensive hyperelastic materials and require complex fabrication processes. Additionally, constructing eco-friendly stiff constituents for these metamaterials remains challenging due to their limited elastic limit strains (<0.1). Here, we propose a systematic design strategy by combining curved beams with chiral metastructures to generate a family of three-dimensional programmable resilient mechanical metamaterials without relying on flexible or hyperelastic constituents. These tiled metamaterials demonstrate robust, anisotropic and non-linear resilience under large elastic compression strains (>0.75), while exhibiting a programmable effective modulus reduction of nearly 6 orders of magnitude compared to the native stiff components. Furthermore, leveraging their stable resilience under high-frequency stimuli, we successfully developed a meter-scale soft robot capable of traversing complex narrow scenarios on demand without the need for flexible materials or sophisticated pipelines. We anticipate that these mechanical metamaterials could serve as a universal platform for programmable active dampers, modular flexible robots, and medical rehabilitation equipment at various scales.