In-drop capillary spooling of spider capture thread inspires hybrid fibers with mixed solid-liquid mechanical properties

TL;DR

This paper investigates the unique solid-liquid mechanical behavior of spider capture silk, revealing how buckling within droplets causes shape switching, and demonstrates the creation of programmable hybrid fibers inspired by this natural mechanism.

Contribution

It uncovers the physics behind the liquid-like behavior of spider capture silk and introduces a method to create programmable hybrid solid-liquid fibers.

Findings

Capture silk acts as a stretchy solid in extension.

It behaves as a liquid in compression, shrinking without limit.

Engineered liquid wires mimic natural shape-switching behavior.

Abstract

An essential element in the web-trap architecture, the capture silk spun by ecribellate orb spiders consists of glue droplets sitting astride a silk filament. Mechanically this thread presents a mixed solid-liquid behavior unknown to date. Under extension, capture silk behaves as a particularly stretchy solid, owing to its molecular nanosprings, but it totally switches behavior in compression to now become liquid-like: It shrinks with no apparent limit while exerting a constant tension. Here, we unravel the physics underpinning the unique behavior of this "liquid wire" and demonstrate that its mechanical response originates in the shape-switching of the silk filament induced by buckling within the droplets. Learning from this natural example of geometry and mechanics, we manufactured programmable liquid wires that present previously unidentified pathways for the design of new hybrid solid-liquid materials. This article is available in open access with supplementary materials on the PNAS website.