Harnessing machine mechanisms to continuously reprogram metamaterials

Mechanical metamaterials have yielded properties not accessible to their monolithic counterparts, but these properties are often fixed post fabrication. Tunable properties are desired in many applications, including robotics, aerospace, and healthcare. Machine metamaterials employ elements and mechanisms of machine design to implement a diverse range of internal motions in metamaterials to drastically and continuously alter their architectures and, consequently, properties in situ. The adaptations are quick and reversible over numerous cycles, consume little energy, and induce minimal mechanical stress and strain. Machine metamaterials can be made from various materials, including ceramics and glasses, promising transparent reprogrammable materials for extreme environments. Here, we showcase the emergence of this relatively simple but potent concept in the recent literature. We then use hypothetical metamaterial examples to illustrate their promising future to reprogram properties, bridge the gap across different length scales, facilitate modular assembly, and implement sensing, actuation, computation, and reprogrammable inhomogeneities.