Interaction of microswimmers in viscoelastic liquid crystals

Swimming bacteria successfully colonize complex non-Newtonian environments exemplified by viscoelastic media and liquid crystals. While there is a significant body of research on microswimmer motility in viscoelastic liquids, the motion in anisotropic fluids still lacks clarity. This paper studies how individual microswimmers (e.g., bacteria) interact in a mucus-like environment modeled by a visco-elastic liquid crystal. We have found that an individual swimmer moves faster along the same track after the direction reversal, in faithful agreement with the experiment. This behavior is attributed to the formation of the transient tunnel due to the visco-elastic medium memory. We observed that the aft swimmer has a higher velocity for two swimmers traveling along the same track and catches up with the leading swimmer. Swimmers moving in a parallel course attract each other and then travel at a close distance. A pair of swimmers launched at different angles form a "train”: after some transient, the following swimmers repeat the path of the "leader”. Our results shed light on bacteria penetration in mucus and colonization of heterogeneous liquid environments.