Fluidic torque–enabled object manipulation by microrobot collectives

Microscale systems experience strong viscous interactions because of the low-Reynolds-number regime in which they exist. This means that fluidic manipulation and actuation of passive objects can be enabled and influenced by the individual spin rate of microscale robots, the number of microrobots, and their positions relative to the objects. We explore these parameter spaces and find that the fluidic torque generated by a magnetic microrobot collective can be exploited to apply bidirectional torque to concentric ring structures and demonstrate this through physical experiments and numerical simulations. Additionally, we demonstrate how the fluidic torque of the microrobots can be exploited to actuate gear trains, rotate comparatively large three-dimensional objects, dynamically self-assemble internally driven ring structures, and absorb and expel large numbers of circular objects. Last, we show emergent behaviors where the microrobot collective's morphology and method of locomotion changes as a function of the spin rate of the microrobots and the size and shape of the surrounding objects.