Effects of 3D confinements on the trajectories of microswimmers

Ciliary beating generates fluid flows that determine the direction of microswimmers at low Reynolds numbers. The trajectories of microswimmers can be significantly influenced by confinement (i.e. the presence of walls), and the degree of confinement: strong versus weak. We numerically study this problem by confining a squirmer in 3D channels under different conditions: (i) no confinement, (ii) weak confinement, (iii) strong confinement. Our results show that the presence of confinement effects can result in a more directed trajectory compared to no confinement. In weak 3D confinement, pusher type squirmers (e.g. E.coli) exhibit oscillatory trajectories spanning the entire cross-section of the channel. However, the puller (e.g. Chlamydomonas) and neutral (e.g. Volvox) type squirmers show directed motion near to the centerline of the channels. In this work, we carry out a detailed study of parameters that can influence squirmer trajectories: (a) type of squirmer, (b) size of channel, (c) aspect ratio of channel and (d) ratio of squirmer size to channel size. Our goal is to group all the above parameters into a landscape of energy injection vs energy dissipation and develop comprehensive phase diagrams that quantify trajectories of microswimmers.