Spider silk’s resistance to twisting explained in new study
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Chinese and British researchers investigating a curious property of dragline spider silk have found that by yielding to dissipate potential energy within its silk, a spider can stabilise itself against spinning.
Dragline silk is used to create the outer rim and ‘spokes’ of spider webs, and is used as a lifeline when spiders need to safely drop a distance. The material has attracted the interest of scientists for decades due to its strength, stretchiness and thermal conductivity, although little research has been done into another mechanical property: how it responds to twisting.
“Spider silk is very different from other, more conventional materials,” said Dr Dabiao Liu, a researcher at Huazhong University of Science and Technology, China. “We find that the dragline from the web hardly twists, so we want to know why.”
The researchers used a torsion pendulum to study dragline silk from two species of golden silk orb weaver spiders. Silk was collected from captive spiders and suspended in a cylinder – to protect the system from disturbances – while small weights were used to mimic the spider.
A rotating turntable twisted the silk, and a high-speed camera recorded the oscillations of the silk thread.
Unlike wire, synthetic fibres or human hair, the researchers found that spider silk deforms slightly when it is twisted, releasing more than 75 per cent of its potential energy. This causes its oscillations to decelerate rapidly. The silk partially ‘snaps back’ after twisting.
Within a thread of spider silk is a core of fibrils: very slender fibres. Each fibril has segments of amino acids in sheets and looping chains. The researchers suggest that, under torsion, the sheets and chains are deformed. While the sheets recover their original shapes, the chains remain partially deformed. This may be what causes the thread to stabilise quickly after twisting
A better understanding of how this material resists twisting could lead to novel biomimetic fibres which could be used in parachute chords, helicopter rescue ladders and even violin strings.
“If we understood how spider silk achieves this, then maybe we could incorporate the properties into our own synthetic ropes,” said Professor David Dunstan, who works at Queen Mary University of London’s School of Physics and Astronomy.
“This spider silk is displaying a property that we simply don’t know how to recreate ourselves, and that is fascinating.”