Hydrodynamics of ciliate swimming revealed by individual ciliary motions

Ciliate, such as Paramecium, can swim in surrounding liquid by beating thousands of cilia. In 1971, Blake introduced a mathematical model of swimming microorganism, called as squirmer, and it has been widely used in fluid mechanical researchers. In the original squirmer model, the tips of cilia formed a ciliary envelope, and the displacement and stretch of the envelope surface was modeled by surface squirming velocities. The model was successful in describing the flow field external to the envelope. However, it could not describe the flow field inside the envelope, i.e. between the cell surface and the ciliary envelope. In this study, therefore, we develop a model of ciliate with hundreds of cilia, and analyze its swimming using a boundary element method. We found that the swimming is strongly affected by the existence of cilia. Especially, the swimming efficiency was found to be much smaller in the present model compared to the original squirmer model. These findings provide a fundamental basis in modeling a swimming ciliate.