Nematode Locomotion in Unconfined and Confined Fluids

TL;DR

This study combines a curvature-based model with hydrodynamic simulations to analyze how C. elegans nematodes swim in confined and unconfined fluids, revealing enhanced speed and navigation under confinement.

Contribution

It introduces a novel curvature-based description combined with bead models to accurately evaluate nematode locomotion in different fluid confinements.

Findings

Nematodes swim twice as fast under strong confinement.

Confinement improves navigation due to increased transverse resistance.

Optimal gait resembles high-viscosity swimming patterns.

Abstract

The millimeter-long soil-dwelling nematode {\it C. elegans} propels itself by producing undulations that propagate along its body and turns by assuming highly curved shapes. According to our recent study [PLoS ONE \textbf{7}, e40121 (2012)] all these postures can be accurately described by a piecewise-harmonic-curvature (PHC) model. We combine this curvature-based description with highly accurate hydrodynamic bead models to evaluate the normalized velocity and turning angles for a worm swimming in an unconfined fluid and in a parallel-wall cell. We find that the worm moves twice as fast and navigates more effectively under a strong confinement, due to the large transverse-to-longitudinal resistance-coefficient ratio resulting from the wall-mediated far-field hydrodynamic coupling between body segments. We also note that the optimal swimming gait is similar to the gait observed for nematodes swimming in high-viscosity fluids. Our bead models allow us to determine the effects of confinement and finite thickness of the body of the nematode on its locomotion. These effects are not accounted for by the classical resistive-force and slender-body theories.