Flagellar swimmers oscillate between pusher- and puller-type swimming

TL;DR

This study reveals that flagellated microswimmers like algae and sperm oscillate between pusher and puller flow signatures, affecting their hydrodynamic interactions, which oscillate over time and diminish with distance.

Contribution

The paper demonstrates that flagellar microswimmers switch between pusher and puller modes, a dynamic not previously characterized, using experimental beat patterns and flow computations.

Findings

Flagellated microswimmers oscillate between pusher and puller types.

Hydrodynamic interactions oscillate in time and are comparable to swimming fluctuations.

Inertia attenuates flow oscillations beyond 100 micrometers.

Abstract

Self-propulsion of cellular microswimmers generates flow signatures, commonly classified as pusher- and puller-type, which characterize hydrodynamic interactions with other cells or boundaries. Using experimentally measured beat patterns, we compute that flagellated alga and sperm oscillate between pusher and puller. Beyond a typical distance of 100 um from the swimmer, inertia attenuates oscillatory micro-flows. We show that hydrodynamic interactions between swimmers oscillate in time and are of similar magnitude as stochastic swimming fluctuations.