Unraveling hagfish slime

TL;DR

This study models the rapid unraveling of hagfish slime threads using viscous hydrodynamics, demonstrating that viscous drag can explain the quick deployment crucial for predator defense.

Contribution

It introduces a physical model showing viscous hydrodynamics as a key factor in slime unraveling, advancing understanding beyond chemical reaction explanations.

Findings

Unraveling occurs within hundreds of milliseconds under physiological conditions.

Pinned skeins unravel faster, aiding rapid deployment.

The model provides a framework for future experimental validation.

Abstract

Hagfish slime is a unique predator defense material containing a network of long fibrous threads each ~ 10 cm in length. Hagfish release the threads in a condensed coiled state known as thread cells, or skeins (~ 100 microns), which must unravel within a fraction of a second to thwart a predator attack. Here we consider the hypothesis that viscous hydrodynamics can be responsible for this rapid unraveling, as opposed to chemical reaction kinetics alone. Our main conclusion is that, under reasonable physiological conditions, unraveling due to viscous drag can occur within a few hundred milliseconds, and is accelerated if the skein is pinned at a surface such as the mouth of a predator. We model a single thread cell unspooling as the fiber peels away due to viscous drag. We capture essential features by considering one-dimensional scenarios where the fiber is aligned with streamlines in either uniform flow or uniaxial extensional flow. The peeling resistance is modeled with a power-law dependence on peeling velocity. A dimensionless ratio of viscous drag to peeling resistance appears in the dynamical equations and determines the unraveling timescale. Our modeling approach is general and can be refined with future experimental measurements of peel strength for skein unraveling. It provides key insights into the unraveling process, offers potential answers to lingering questions about slime formation from threads and mucous vesicles, and will aid the growing interest in engineering similar bioinspired material systems.