Mechanical metamaterials exhibit properties and functionalities that cannot be realized in conventional materials. Originally, the field focused on achieving unusual (zero or negative) values for familiar mechanical parameters, such as density, Poisson's ratio or compressibility, but more recently, new classes of metamaterials — including shape-morphing, topological and nonlinear metamaterials — have emerged. These materials exhibit exotic functionalities, such as pattern and shape transformations in response to mechanical forces, unidirectional guiding of motion and waves, and reprogrammable stiffness or dissipation. In this Review, we identify the design principles leading to these properties and discuss, in particular, linear and mechanism-based metamaterials (such as origami-based and kirigami-based metamaterials), metamaterials harnessing instabilities and frustration, and topological metamaterials. We conclude by outlining future challenges for the design, creation and conceptualization of advanced mechanical metamaterials.

机械超常材料表现出常规材料无法实现的特性和功能。最初，该领域专注于为熟悉的机械参数（例如密度，泊松比或可压缩性）获得不同寻常的（零或负）值，但最近出现了新型超材料，包括形状变形，拓扑和非线性超材料。这些材料展现出奇特的功能，例如响应机械力的图案和形状转换，运动和波浪的单向引导以及可重新编程的刚度或耗散性。在本综述中，我们确定了导致这些特性的设计原则，并特别讨论了基于线性和基于机理的超材料（例如基于折纸和基于折纸的超材料），利用不稳定和挫败感的超材料，以及拓扑超材料。最后，我们概述了高级机械超材料的设计，创建和概念化方面的未来挑战。