Confinement-induced motion of ciliates

TL;DR

This paper demonstrates how the interaction between metachronal waves and channel geometry enables ciliates to swim in confined spaces, revealing new swimming behaviors and dynamics not observed in bulk fluid.

Contribution

It introduces a model incorporating metachronal waves and channel corrugation, showing how confinement influences ciliate swimming and can induce direction reversal.

Findings

Resonance between metachronal wave and channel corrugation enables swimming.

Ciliates can reverse swimming direction in confined channels.

Oscillatory and ballistic swimming regimes are identified.

Abstract

The time dynamics of flagellar and ciliary beating is often neglected in theories of microswimmers, with the most common models prescribing a time-constant actuation of the surrounding fluid. By explicitly introducing a metachronal wave, coarse-grained to a sinusoidal surface slip velocity, we show that a spatial resonance between the metachronal wave and the corrugation of a confining cylindrical channel enables a ciliate to swim even when it cannot move forward in a bulk fluid. Using lubrication theory, we reduce the problem to the Adler equation that reveals an oscillatory and ballistic swimming regime. Interestingly, a ciliate can even reverse its swimming direction in a corrugated channel compared to the bulk fluid.