Sorting of chiral microswmmers

Abstract

Microscopic swimmers, for example chemotactic bacteria and cells, are capable of directed motion by exerting a force on their environment. In some cases, including bacteria and spermatozoa swimming near boundaries, or many asymmetrical artificial microswimmers, the driving force and propulsion direction are misaligned. In those situations a torque acting on the microswimmers arises, resulting in motion with a well-defined chirality which is circular in two dimensions and helicoidal in three dimensions. In this thesis, I demonstrate with numerical simulations in two dimensions, how the chirality of the circular motion can couple to chiral features present in the microswimmer environment. I show that by employing static chiral pattern of elliptical obstacles in their environment, microswimmers can be separated on the basis of their motion parameters. In particular, levogyre and dextrogyre microswimmers as small as 50nm can be separated and selectively trapped in chiral flowers of ellipses. Patterned microchannels can be used as funnels to rectify the microswimmer motion, as sorters to separate microswimmers based on their linear and angular velocities, and as sieves to trap microswimmers with specific parameters. I also demonstrate that these results can be extended to helicoidal motion in three dimensions.