Directed Flow of Micromotors through Alignment Interactions with Micropatterned Ratchets.

To achieve control over naturally diffusive, out-of-equilibrium systems composed of self-propelled particles, such as cells or self-phoretic colloids, is a long-standing challenge in active matter physics. The inherently random motion of these active particles can be rectified in the presence of local and periodic asymmetric cues given that a nontrivial interaction exists between the self-propelled particle and the cues. Here, we exploit the phoretic and hydrodynamic interactions of synthetic micromotors with local topographical features to break the time-reversal symmetry of particle trajectories and to direct a macroscopic flow of micromotors. We show that the orientational alignment induced on the micromotors by the topographical features, together with their geometrical asymmetry, is crucial in generating directional particle flow. We also show that our system can be used to concentrate micromotors in confined spaces and identify the interactions leading to this effect. Finally, we develop a minimal model, which identifies the key parameters of the system responsible for the observed rectification. Overall, our system allows for robust control over both temporal and spatial distribution of synthetic micromotors.