Programmable mechanical metamaterials with tunable Poisson's ratio and morphable stiffness

Mechanical metamaterials have gained significant attention in recent years due to their extraordinary and counterintuitive properties, while current designs are still lacking in flexibility in tuning their mechanical performance. Here, we create a type of metamaterials which exhibit the characteristics of complex alternations between positive and negative Poisson's ratios under a unidirectional loading. Moreover, the mechanical metamaterial not only demonstrates stiffness anisotropy but also possesses excellent load-bearing capacity in specific directions despite its lightweight nature. Our approach exploits origami and kirigami technique to design morphable polyhedral modules which are utilized to construct two and three-dimensional periodic mechanical metamaterials. The design principle in this work can be employed to create various polyhedral modules as well as mechanical metamaterials. The proposed metamaterials are promising candidates for constructing lightweight and high-strength metamaterials and will inspire more in intelligent materials and soft robots.