Accumulation of Microswimmers due to Their Collisions with a Surface

TL;DR

This paper presents a kinematic model explaining how microswimmers accumulate near surfaces due to collisions and rotational Brownian motion, aligning well with experimental density distributions across various microorganisms.

Contribution

The study introduces a simple kinematic model that captures microswimmer-surface interactions and explains accumulation phenomena observed in experiments.

Findings

Model reproduces experimental density distributions

Microswimmers travel parallel after surface collision

Rotational Brownian motion facilitates escape from surface

Abstract

In this letter we propose a kinematic model to show how collisions with a surface and rotational Brownian motion give rise to the accumulation of micro-swimmers near a surface. In this model, an elongated microswimmer invariably travels parallel to the surface after hitting it from any incident angle. It then swims away from the surface after some time, facilitated by rotational Brownian motion. Simulations based on this model reproduce the density distributions measured for the small bacteria E. coli and Caulobacter crescentus, as well as for the much larger bull spermatozoa swimming in confinement.