Undulatory swimming in viscoelastic fluids

TL;DR

This study experimentally investigates how fluid elasticity affects the swimming behavior of C. elegans, revealing that elasticity hampers propulsion speed and is linked to molecular stretching near flow hyperbolic points.

Contribution

First experimental analysis of nematode swimming in viscoelastic fluids showing fluid elasticity reduces propulsion speed and elucidates the underlying flow-molecular interactions.

Findings

Fluid elasticity reduces swimming speed by 35%.

Self-propulsion decreases with increasing elastic stresses.

Molecular stretching near hyperbolic flow points influences propulsion.

Abstract

The effects of fluid elasticity on the swimming behavior of the nematode \emph{Caenorhabditis elegans} are experimentally investigated by tracking the nematode's motion and measuring the corresponding velocity fields. We find that fluid elasticity hinders self-propulsion. Compared to Newtonian solutions, fluid elasticity leads to 35% slower propulsion speed. Furthermore, self-propulsion decreases as elastic stresses grow in magnitude in the fluid. This decrease in self-propulsion in viscoelastic fluids is related to the stretching of flexible molecules near hyperbolic points in the flow.