Boundary accumulations of active rods in microchannels with elliptical cross-section

Abstract: Many motile microorganisms and bio-mimetic micro-particles have been successfully modeled as active rods - elongated bodies capable of self-propulsion. A hallmark of active rod dynamics under confinement is their tendency to accumulate at the walls. Unlike passive particles, which typically sediment and cease their motion at the wall, accumulated active rods continue to move along the wall, reorient, and may even escape from it. The dynamics of active rods at the wall and those away from it result in complex and non-trivial distributions. In this work, we examine the effects of wall curvature on active rod distribution by studying elliptical perturbations of tube-like microchannels, that is, the cylindrical confinement with a circular cross-section, common in both nature and various applications. By developing a computational model for individual active rods and conducting Monte Carlo simulations, we discovered that active rods tend to concentrate at locations with the highest wall curvature. We then investigated how the distribution of active rod accumulation depends on the background flow and orientation diffusion. Finally, we used a simplified mathematical model to explain why active rods preferentially accumulate at high-curvature locations.