Trajectory of microswimmers in square and rectangular channels

In both natural and microfluidic systems, microswimmers are often seen in confined environments. In this work we study hydrodynamic interactions between model microswimmers, namely squirmers, with confining channels using numerical simulations based on lattice Boltzmann method. The numerical approach is complemented with an analytical mathematical framework based on far field approximations. We first show that the motion of microswimmers in microfluidic channels of square and rectangular cross sections show a diverse and complex behaviour in a three dimensional channel. We propose to understand the complexity of the 3D trajectories of the microswimmers as that resulting from the superposition of two dimensional trajectories induced by a pair of confining walls. We then analyse the hydrodynamic collision process between a microswimmer and a passive particle and show that the collision results in a net displacement of the passive particle. Finally we study the hydrodynamic collision between a pair of microswimmers that occurs inside a micro-channel and the consequent modification to their trajectories.