Disorder-induced persistent random motion and trapping of microswimmers

TL;DR

This study uses simulations to explore how microswimmers move in disordered environments, revealing complex trapping behaviors and differences based on swimmer type and interactions.

Contribution

It demonstrates that hydrodynamic interactions alone can cause effective diffusion and trapping of microswimmers in porous media, with a novel analysis of pushers and pullers.

Findings

Pushers and pullers become localized via trapping mechanisms.

Microswimmers exhibit hopping-and-trapping dynamics.

Trapping probabilities depend on swimmer type and interactions.

Abstract

Microorganisms ofter move in confined, disordered environments, where hydrodynamic couplings can modify their transport behavior. Using extensive finite-element simulations, we investigate the dynamics of microswimmers -- modeled as squirmers -- in two-dimensional disordered porous media by resolving the full hydrodynamic interactions. We reveal that the deterministic coupling between activity, hydrodynamics, and disorder is sufficient to generate effective diffusive transport. Strong pushers and pullers become localised in the porous medium either by trapping at corners or dynamic trapping, depending on swimmer type and obstacle packing fraction. Squirmers can escape from dynamic traps, leading to a prominent ``hopping-and--trapping'' dynamics. Strikingly, we find a pusher-puller asymmetry in the trapping probability that can be reversed by short-range swimmer-obstacle interactions, highlighting the sensitivity of transport to near-field effects.