  Collective control of mobile microrobotic swarms is indispensable for their
potential high-impact applications in targeted drug delivery, medical
diagnostics, parallel micromanipulation, and environmental sensing and
remediation. Lack of on-board computational and sensing capabilities in current
microrobotic systems necessitates use of physical interactions among individual
microrobots for local physical communication and cooperation. Here, we show
that mobile microrobotic swarms with well-defined collective behavior can be
designed by engineering magnetic interactions among individual units.
Microrobots, consisting of a linear chain of self-assembled magnetic
microparticles, locomote on surfaces in response to a precessing magnetic
field. Control over the direction of precessing magnetic field allows
engineering attractive and repulsive interactions among microrobots and, thus,
collective order with well-defined spatial organization and parallel operation
over macroscale distances (~1 cm). These microrobotic swarms can be guided
through confined spaces, while preserving microrobot morphology and function.
These swarms can further achieve directional transport of large cargoes on
surfaces and small cargoes in bulk fluids. Described design approach,
exploiting physical interactions among individual robots, enables facile and
rapid formation of self-organized and reconfigurable microrobotic swarms with
programmable collective order.
