Dynamics of a model microswimmer in an anisotropic fluid

Several recent experiments investigate the orientational behavior of self-propelled bacteria and colloidal particles in anisotropic fluids such as nematic liquid crystals. Correspondingly, we study theoretically the dynamics of a simple model microswimmer in a uniaxially anisotropic fluid. The behavior of both puller- and pusher-type swimmers in the anisotropic fluid is analyzed. Depending on the propulsion mechanism as well as the relative magnitude of different involved viscosities, we find alignment of the microswimmer parallel or perpendicular to the anisotropy axis. The observed swimmer reorientation results from the hydrodynamic coupling between the self-induced fluid flow and the anisotropy of the host fluid. Our theoretical predictions are found to be in qualitative agreement with recent experiments on swimming bacteria in nematic liquid crystals. They support the objective of utilizing the anisotropy of a surrounding fluid to guide individual swimmers and self-propelled active particles along a requested path, enabling controlled active transport.