Controlled propulsion of wheel-shape flaky microswimmers under rotating magnetic fields

Effective propulsion of untethered micro-/nanorobots at low Reynolds numbers can offer possibilities for promising biomedical applications. Diverse locomotion modes have been proposed for propulsion at a small scale, and rolling is an alternative method which is significantly effective. Here, we demonstrate mass produced magnetic wheel-shape flaky microswimmers fabricated via a simple and cost-effective method. Locomotion behaviors under vertical rotating magnetic fields were studied, and the propulsion mechanisms were analyzed. They exhibited two modes to swim forward as tumbling and rolling, which relied on the actuating field and the fluid. The rolling microswimmers could be propelled and steered precisely and a high velocity can be easily reached. Forward velocity and transition frequency within diverse fields and fluids were analyzed, and side slip effects when rolling at a camber angle were also observed. Such microswimmers synthesized in bulk with alternative locomotion modes and excellent swimming performances may have potential in low Reynolds number fluids.