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Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved April 19, 2016 (received for review February 12, 2016)
Significance
The spiraling capture threads of spider orb webs are covered with thousands of tiny glue droplets whose primary function is to entrap insects. In this paper we demonstrate that the function of the drops goes beyond that of gluing prey for they also play a role in the mechanical properties of these fibers—usually ascribed solely to the complex molecular architecture of the silk. Indeed, each of the droplets can spool and pack the core silk filament, thus keeping the thread and the whole web under tension. We demonstrate that this effect is the result of the interplay between elasticity and capillarity by making a fully artificial drops-on-fiber compound as extensible as capture thread is.
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.
Footnotes
- ↵1To whom correspondence should be addressed. Email: arnaud.antkowiak{at}upmc.fr.
Author contributions: S.N. and A.A. designed research; H.E., S.N., F.V., and A.A. performed research; H.E., S.N., and A.A. analyzed data; and H.E., S.N., F.V., and A.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1602451113/-/DCSupplemental.
Freely available online through the PNAS open access option.
Spider-silk–inspired hybrid liquid–solid fibers
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