Undulatory swimming in shear-thinning fluids: Experiments with C. elegans

TL;DR

This study experimentally examines how shear-thinning fluids affect the swimming behavior of C. elegans, revealing modifications in flow fields without changing swimming speed or kinematics, and highlighting enhanced local vorticity and circulation.

Contribution

It provides new experimental insights into the effects of shear-thinning rheology on microorganism swimming, complementing recent theoretical and numerical studies.

Findings

Shear-thinning modifies velocity fields around the swimmer.

Swimming speed and kinematics remain unchanged.

Local vorticity and fluid velocity near the tail increase.

Abstract

The swimming behaviour of microorganisms can be strongly influenced by the rheology of their fluid environment. In this manuscript, we experimentally investigate the effects of shear-thinning viscosity on the swimming behaviour of an undulatory swimmer, the nematode Caenorhabditis elegans. Tracking methods are used to measure the swimmer's kinematic data (including propulsion speed) and velocity fields. We find that shear-thinning viscosity modifies the velocity fields produced by the swimming nematode but does not modify the nematode's speed and beating kinematics. Velocimetry data show significant enhancement in local vorticity and circulation and an increase in fluid velocity near the nematode's tail compared to Newtonian fluids of similar effective viscosity. These findings are compared to recent theoretical and numerical results.