2, Harvard Medical School, Boston, Massachusetts, United States
Microbot propulsion is challenging due to the reversible nature of microscale fluid transport. Recently, it has been shown that methods that break flow-field symmetry using a nearby surface can lead to net translation. Here, we demonstrate that coupling between rotating wheel-shaped bots and nearby walls can be enhanced through surface topography. In this, magnetic microwheels are assembled from individual colloidal particles via an in-plane rotating magnetic field. Upon reorientation of the magnetic field rotation plane, microwheels roll along flat walls, translating at differing velocities depending on wheel size, symmetry, and rotational frequency. We find here that frequencies associated with surface spatial periodicity during microwheel rolling on textured surfaces can lead to significant (~5x) microwheel translation velocity enhancements. These are observed when the spatial and rotational frequencies approach each other, a phenomenon that can be described with a simple hydrodynamic mobility model.