Abstract:

Shape morphing is vital to locomotion in microscopic organisms but has been challenging to achieve in sub-millimetre robots. By overcoming obstacles associated with miniaturization, we demonstrate microscopic electronically configurable morphing metasheet robots. These metabots expand locally using a kirigami structure spanning five decades in length, from 10 nm electrochemically actuated hinges to 100 μm splaying panels making up the ~1 mm robot. The panels are organized into unit cells that can expand and contract by 40% within 100 ms. These units are tiled to create metasheets with over 200 hinges and independent electronically actuating regions that enable the robot to switch between multiple target geometries with distinct curvature distributions. By electronically actuating independent regions with prescribed phase delays, we generate locomotory gaits. These results advance a metamaterial paradigm for microscopic, continuum, compliant, programmable robots and pave the way to a broad spectrum of applications, including reconfigurable micromachines, tunable optical metasurfaces and miniaturized biomedical devices.

Fig. 1 a, Redox reactions drive bending in an atomically thin SEA made of a platinum strip capped on one side by a titanium film. b, Microsplay origami linkage that converts the out-of-plane bending of SEAs into panel splay. c, A unit cell whose area actively expands and contracts under actuation. d, A metabot sheet capable of adopting a variety of shapes on the basis of which unit cells are electrically activated. Two lead wires are connected to one panel of the metasheet and the electrical signal is spread throughout the structure via hinges and panels. e, An optical microscopy image of a metabot with 96 panels. The lengths of the central hinge lc and the side hinge ls are 6 μm and 3 μm, respectively. The lateral length of the triangular building block L is 80 μm while the length of the small triangular panel p is 20 μm. f, A scanning transmission electron microscopy image of an actuator cross-section showing the platinum and titanium. g, A false-coloured SEM image of a microsplay hinge. Here, the SEAs appear bright yellow and the panels are coloured orange. h, A false-coloured SEM image of a metabot sheet. Holes on panels are used to provide etchants access to the sacrificial layer to enable rapid release. i, An optical image of a millimetre-scale metabot sheet. j, An optical image showing a millimetre-scale metasheet placed on a US quarter dollar coin. The expanded region shows an SEM image of the metabot that has conformally adopted its shape to the contours of the body of the Statue of Liberty displayed on the coin. k, An SEM image of a metasheet adopting a variety of folds and kinks generated under critical-point drying.

Fig. 2  a, Schematic of a hinge design with a passive signal wire that can be used to separately address other hinges. In this particular case signal 1 is used to actuate linkage 1 and signal 2 is passed through the first linkage to actuate linkage 2. b, An optical image of a fabricated metabot where the interior and exterior parts of the sheet are independently controlled by different electrical signals. c, Shape morphing and elastic energy calculations from a simulation of the metabot in a Unity3D engine. Shown is an energy landscape representing the sum of elastic energies corresponding to all of the hinges in the metabot versus the target angles for the outer and inner central hinges (CH). Also shown are the shapes adopted by the simulated sheets at four different points in the parameter space. d–f, Confocal fluorescence microscopy images of small cap (d), plane (e) and saddle (f) shapes formed from the same pattern with different actuated areas represented by the blue regions in the insets. The corresponding Gaussian (K) and mean (H) curvatures are plotted on the right.

DOI: 10.1038/s41563-024-02007-7