INTRODUCTION
Mechanical metamaterials (1–16) represent a type of artificial materials usually consisting of periodic microstructures whose architectures are carefully designed to offer mechanical properties that surpass those of conventional materials. These architected metamaterials mainly leverage the spatial motions, extreme deformations, multiple equilibrium states, and shape morphing of microstructures to obtain exotic properties and/or functionalities, such as zero/negative values of Poisson’s ratios (17–20), thermal expansion coefficients (21–24) and swelling ratios (25, 26), reprogrammable stiffness and/or dissipation (27–33), controlled acoustic wave propagation (34, 35), and tailorable multistability (9, 36, 37). The latter property (i.e., tailorable multistability) is of rapidly increasing interests because of promising potentials for applications in information processing (38–41), recyclable energy absorption (42, 43), and soft robotic