Collective motions of microorganisms in geometric confinement

The ways in which microorganisms behave in their confined environment remain unclear. To understand the dynamics of microorganisms swimming in geometric confinement, a fictitious domain method is applied to study the collective motions of squirmers in viscoelastic fluids confined by circular chambers at low Reynolds numbers. It is observed that both pushers and pullers accumulate near the walls, which is enhanced by fluid elasticity. The results show that wall accumulations slow down their swimming speeds. At high concentrations, the pullers not only form significant multilayer structures near the boundary but also aggregate into clusters in the central area. It seems both behaviors compete with each other. Upon further analysis, it is found that the squirmer orientations incline toward the walls, strengthened by fluid elasticity. It is believed that this is connected with the wall accumulations.