Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming

TL;DR

This study uses lattice Boltzmann simulations to explore how hydrodynamic interactions influence the behavior of run-and-tumble particles under confinement, revealing effects like self-assembled pumping and upstream flux without chiral swimming.

Contribution

It demonstrates the impact of hydrodynamics on confined run-and-tumble particles, including the formation of a pump and upstream flow, extending understanding of active matter in fluid environments.

Findings

Hydrodynamics minimally affect sedimentation steady states.

A self-assembled pump forms when run length exceeds confinement length.

Particles in channels exhibit upstream flux independent of chirality.

Abstract

We simulate by lattice Boltzmann the nonequilibrium steady states of run-and-tumble particles (inspired by a minimal model of bacteria), interacting by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic interactions barely perturb the steady state found without them, but for particles in a harmonic trap such a state is quite changed if the run length is larger than the confinement length: a self-assembled pump is formed. Particles likewise confined in a narrow channel show a generic upstream flux in Poiseuille flow: chiral swimming is not required.