Spider silk inspires new super-stretchy nano-wire

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Scientists have created five synthetic ‘liquid wires’ that mimic the mechanics of spiders’ silk.

The sticky surface of silk produced by Australian Golden Orb Weavers is, like most spider webs, designed to glue insects down long enough for them to become a meal. But a new study has found that the glue is the reason webs can be stretched to many times its original length while still remaining taut.

The discovery could result in a breakthrough in wire technology for micro-fabrication.

The study, led by Hervé Elettro from France’s Université Pierre et Marie Curie with colleagues from Oxford University, analysed capture silk – webbing designed to immobilise prey – which can be stretched to three times its web length without breaking and still returns to its original state, with no sagging, when relaxed.

“This stretchiness confers spider silk a strength tenfold that of a natural or synthetic rubber,” says Elettro.

Its secret lies, he discovered, in the way the web spools inside the droplets of glue as a sort of “liquid wire”.

“It’s actually quite interesting for me, on the spider biology side of things, how they achieve that,” says Douglas Little, a physicist at Macquarie University in Sydney, Australia, who works with spider silk but was not involved in the study.

“The more you shrink the silk or move the end points closer together, the more the silk buckles and then starts to coil within the droplet.

“At that point, the surface tension of the liquid almost is taking over, keeping the entire structure taut and under tension.”

With an understanding of the mechanics of the silk, Elettro’s team put together five synthetic versions.

The best results came from a polyurethane filament brushed in silicone oil droplets, with a maximum extension of a remarkable 1,500%.

Normally, a thin polyurethane thread buckles under pressure, but when it’s given a coating of oil, “the thread instantly turns into a liquid wire seemingly adjusting its length so as to remain taut whatever the contraction”, Elettro says.

The research suggests virtually any material could be used to make a similar bio-inspired hybrid like the liquid wires described.

The study was published in the Proceedings of the National Academy of Sciences.

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