True microrobots, in contrast with externally controlled microparticles, must harvest or carry their own source of energy, as well as their own (preferably programmable) microcontroller of actuators for locomotion, using information acquired from their own sensors. We demonstrate here, for the first time, that microrobotic smartlets, hitherto buoyancy divers, can also be equipped to navigate in 2D on surfaces, with onboard control responding to both sensor information and their internal electronic program. Fabricating modular microrobots, with all dimensions of 1 mm and below, has been difficult to achieve because of competing demands for the limited surface area and the challenges of integrating and interconnecting the diverse functionalities of energy harvesting, actuation, sensing, communication, docking, and control. A novel high‐density heterogeneous integration, via soft‐substrate micro flip‐chip bonding of custom CMOS and LED microchiplets onto fold‐up polymer surfaces, compatible with roll‐up isotropic ambient light harvesting, now makes this possible. Fabricating electrolytic bubble actuators on multiple cube faces and connecting them to a custom sensor‐controlled onboard microchiplet (lablet) allow the smartlets to locomote on wet surfaces, changing direction in response to both timed programmed control as well as programmed response to locally sensed signals. Such locomoted robotic microcubes can also move to and selectively dock with other modules via patterned surfaces. This is powered by ambient light in natural aqueous media on smooth surfaces.
Bandari et al. (Sun,) studied this question.