Quasi-two-dimensional bacterial swimming around pillars: enhanced trapping efficiency and curvature dependence

TL;DR

This study combines experiments and simulations to explore how quasi-two-dimensional environments influence bacterial trapping around pillars, revealing increased trapping efficiency and curvature-dependent effects due to hydrodynamic interactions.

Contribution

It demonstrates the universal enhancement of hydrodynamic attractions in quasi-two-dimensional systems and elucidates the role of obstacle curvature in bacterial trapping.

Findings

Trapping efficiency increases with quasi-two-dimensionality.

Hydrodynamic attraction is universally enhanced in quasi-2D.

Obstacle curvature controls trapping effectiveness.

Abstract

Microswimmers exhibit more diverse behavior in quasi-two dimensions than in three dimensions. Such behavior remains elusive due to the analytical difficulty of dealing with two parallel solid boundaries. The existence of additional obstacles in quasi-two dimensional systems further complicates the analysis. Combining experiments and hydrodynamic simulations, we investigate how the spatial dimension affects the interactions between microswimmers and obstacles. We fabricated microscopic pillars in quasi-two dimensions by etching glass coverslips and observed bacterial swimming among the pillars. Bacteria got trapped around the circular pillars and the trapping efficiency increased as the quasi-two-dimensionality was increased or as the curvature of the pillars was decreased. Numerical simulations of the simplest situation of a confined squirmer showed anomalous increase of hydrodynamic attractions, establishing that the enhanced interaction is a universal property of quasi-two-dimensional microhydrodynamics. We also demonstrated that the local curvature of the obstacle controls the trapping efficiency by experiments with elliptic pillars.