Micrometer-sized, electrically morphing metamaterial-robots (MetaBots)*

Auxetic mechanical metamaterials provide an unparalleled platform for designing soft microrobots stemming from their large degrees of freedom, negative Poisson's ratio, and easy fabrication. Here, we demonstrate electrically programmable, micrometer-sized metamaterial-based robots (MetaBots) that could form three-dimensional (3D) surfaces from two-dimensional patterns, cycle among different shapes, and locomote in a biocompatible solvent. These MetaBots have a hierarchical structure: the repeating panels are linked by origami-based splay hinges, which are controlled by applying voltage to atomically thin surface electrochemical actuators. When we apply a voltage, the local expansions of the unit cells alter the local Gaussian curvature of the MetaBot, allowing it to reconfigure into a 3D surface. By locally actuating different subsets of the splay hinges, we can transform the MetaBot into a rich class of 3D shapes that we characterize using confocal fluorescence microscopy. Furthermore, by applying a phase delay between actuating the different hinge subsets, we break both the spatial and temporal symmetry, and drive the MetaBots to locomote in a biocompatible solution. These MetaBots could open the door to a variety of applications, including microscopic robots with distributed control, tunable optical metasurface, and medical microrobotics.