Upstream swimming in microbiological flows

TL;DR

This paper models microswimmer behavior in non-Newtonian flows, revealing how fluid properties influence upstream migration and swimmer orientation, with implications for microbial sorting.

Contribution

It introduces a new model for microswimmer dynamics in non-Newtonian fluids, highlighting the effects of shear-thickening/thinning and viscoelastic stresses on migration and orientation.

Findings

Swimmers migrate faster in shear-thickening fluids.

Viscoelastic stresses reorient swimmers upstream at the centerline.

Proposes a microbial sorting mechanism based on swimming speed.

Abstract

Interactions between microorganisms and their complex flowing environments are essential in many biological systems. We develop a model for microswimmer dynamics in non-Newtonian Poiseuille flows. We predict that swimmers in shear-thickening (-thinning) fluids migrate upstream more (less) quickly than in Newtonian fluids and demonstrate that viscoelastic normal stress differences reorient swimmers causing them to migrate upstream at the centreline, in contrast to well-known boundary accumulation in quiescent Newtonian fluids. Based on these observations, we suggest a sorting mechanism to select microbes by swimming speed.