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.