Three-dimensional model for surface accumulation of chiral and nonchiral microswimmers.

Persistent motion of microswimmers near boundaries is known to result in surface accumulation. A way to control surface accumulation is by reducing the contact surface area between swimmers and surface by modifying its topography, typically through the application of microscale structures. In this work, we introduce a three-dimensional (3D) phenomenological model of a microswimmer navigating a volume bounded by a top and bottom surface. We describe the swimmer-surface interaction with an effective near-surface alignment force, and study numerically the effect of surface textures, modeled by convex obstacles, on the surface accumulation of chiral and nonchiral microswimmers. We find that, depending on the angular velocity of the swimmer, and the alignment force, convex obstacles can either hinder or enhance surface accumulation. We discuss potential applications to sorting of microswimmers by their angular velocity.