Secret of always-taut spider threads inspires new material

Plastic filament reeling and unreeling inside an oil droplet as the thread extends and contracts
Scientists from the University of Oxford and the Pierre and Marie Curie University, in Paris have taken inspiration from spider webs to create a hybrid wire technology that could be used in applications such as microfabrication of complex structures, reversible micro-motors, or self-tensioned stretchable systems.

Pulling on a sticky thread in a spider’s web and letting it snap back reveals that the thread never sags but always stays taut - even when stretched to many times its original length. This is because any loose thread is immediately spooled inside the tiny droplets of watery glue that coat and surround the core gossamer fibres of the web's capture spiral.

The researchers studied the details of this ‘liquid wire’ technique in spiders’ webs and used it to create composite fibres which extend like a solid and compress like a liquid. The team says that these novel insights may lead to new bio-inspired technology.

Professor Fritz Vollrath of the Oxford Silk Group in the Department of Zoology at Oxford University said: “The thousands of tiny droplets of glue that cover the capture spiral of the spider’s orb web do much more than make the silk sticky and catch the fly. Each drop packs enough punch in its watery skins to reel in loose bits of thread. This winching behaviour is used to excellent effect to keep the threads tight at all times.”

The novel properties observed and analysed by the scientists rely on a subtle balance between fibre elasticity and droplet surface tension. The team was also able to recreate this technique in the laboratory using oil droplets on a plastic filament. This artificial system behaved just like the spider's natural winch silk, with spools of filament reeling and unreeling inside the oil droplets as the thread extended and contracted.

Dr Hervé Elettro, a doctoral researcher at the Jean Le Rond D'Alembert Institute, Pierre and Marie Curie University, said: “Spider silk has been known to be an extraordinary material for around 40 years, but it continues to amaze us. While the web is simply a high-tech trap from the spider's point of view, its properties have a huge amount to offer the worlds of materials, engineering and medicine.”

Author
Tom Austin-Morgan

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