Programmable Modular Acoustic Microrobots.

Microrobots have emerged as promising tools for biomedical and in vivo applications, leveraging their untethered actuation capabilities and miniature size. Despite extensive research on diversifying multi-actuation modes for single types of robots, these tiny machines tend to have limited versatility while navigating different environments or performing specific tasks. To overcome such limitations, self-assembly microstructures with on-demand reconfiguration capabilities have gained recent attention as the future of biocompatible microrobotics, as they can address drug delivery, microsurgery, and organoid development processes. Reversible modular reconfiguration structures require specific arrangements of particles that can assume several shapes when external fields are applied. We show how magnetic interaction can be used to assemble cylindrical microrobots into modular microstructures with different shapes. The motion actuation of the formed microstructure happens due to an external acoustic field, which generates responsive forces in the air bubbles trapped in the inner cavity of the robots. An external magnetic field can also steer these structures. We illustrate these capabilities by assembling the robots into different shapes that can swim and be steered, showing the potential to perform biomedical applications. Furthermore, we confirm the biocompatibility of the cylindrical microrobot used as the building blocks of our microstructure. Exposing Chinese Hamster Ovary cells to our microrobots for 24 hours demonstrates cell viability when in contact with the microrobot.