Spiders teach scientists how to create a completely novel liquid-solid material
Look closely at an active spider’s web and you will notice that it always retains its shape. Even after trapping an insect, a spider’s orb web can reel in the stretched thread to regain the web’s tension. This phenomenon is something that has fascinated scientists for decades. The tiny and seemingly incredible forces of physics at work in a spider’s web were baffling; only now are scientists beginning to uncover the truth. Fritz Vollrath, coordinator for the EU-funded SABIP (Silks as Biomimetic Ideals for Polymers) project has discovered that a web consists of both the silk spun by a spider and microscopic glue droplets that sit on the silk thread. These droplets are not made by the spider itself. Instead, the spider coats the thread with a thin layer of sticky material that then absorbs water from the atmosphere. The glue swells, becomes unstable, then it forms droplets, Vollrath explains. The droplets are mainly used to capture prey, but they can also reel in the silk filament keeping the whole web under tension. One tiny droplet, which measures about a tenth of a millimetre across, can reel in over 20 cm of thread packing it tightly inside the droplet. The thread can then be reeled in and out again many times. Remarkably, the silk-droplet combination behaves like both a solid and a liquid, leading the Oxford- based SABIP team and its collaborators at Paris’ Pierre and Marie Curie University to baptise it ‘liquid wire’. ‘When the spider’s web thread is stretched it’s like a particularly stretchy solid owing to its molecular nanosprings, but when it is compressed it switches its behaviour to that of a liquid, shrinking with no apparent limit while exerting a constant tension,’ says Vollrath. ‘This really is a novel class of materials. A complex silk composite that people never thought possible,’ adds Herve Elettro, key researcher of the Paris team who focussed his PhD on this discovery. Understanding this unique behaviour has lead the team researchers to create synthetic silk with the same properties as a spider’s web using a nylon thread and sugar solution. Moreover, this synthetic silk is produced at ambient temperatures, without any harsh chemicals and is easily recyclable. ‘Now we are tackling the question of what we can do with this material. Can we upscale it? Does it have to be integrated into something? The technology is so new and we’re at the phase of exploring the possibilities where such small forces could be used,’ Vollrath continues. A second PhD student is currently working in the Paris team on exploring ideas for novel devices based on this discovery, funded principally by French Research funding. ‘EU funding, and the mixing of French and Anglo-Saxon academic cultures encouraged by the EU, was key to our fantastic discovery and the creation of synthetic liquid-wire,’ concludes Vollrath. For more information please see: CORDIS project website Oxford Silk Group website
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