Hydrodynamic analysis of flagellated bacteria swimming in corners of rectangular channels

The inuence of nearby solid surfaces on the motility of bacteria is of fundamental importance as these interactions govern the ability of the microorganisms to explore their environment and formsessile colonies. Reducing biofouling in medical implants and controlling the transport of bacterialcells in a microfluidic device are two applications that could benefit from a detailed understandingof swimming in microchannels. In this study, we investigate the self-propelled motion of a modelbacterium, driven by rotating a single helical flagellum, in such an environment. In particular,we focus on the corner region of a large channel modelled as two perpendicular sections of no-slipplanes joined with a rounded corner. We numerically solve the equations of Stokes flow using theboundary element method to obtain the swimming velocities at different positions and orientationsrelative to the channel corner. From these velocities, we construct many trajectories to ascertainthe general behavior of the swimmers. Considering only hydrodynamic interactions between thebacterium and the channel walls, we show that some swimmers can become trapped near the cornerwhile moving, on average, along the axis of the channel. This result suggests that such bacteriamay be found at much higher densities in corners than in other parts of the channel. Anotherimplication is that these corner accumulating bacteria may travel quickly through channels sincethey are guided directly along the corner and do not turn back or swim transversely across the channel