Spider silk could be used to make robotic muscles
Spider dragline silk twists and contracts in high humidity, an effect which could be replicated to build robotic components.
Spider silk's newly-discovered ability to twist could provide new possibilities for robotic components. The findings could be used to build artificial muscles or moving parts that open and close valves.
A team of researchers, led by Professor Markus Buehler at Massachusetts Institute of Technology, discovered the surprising effect when studying how spider silk contracts in humid air. They dangled a pendulum from a thread of spider dragline silk, the strong fibres that make up the outer rim and spokes of the webs, expecting it to become almost half the length and twice as wide in response to damp air.
They also found that when the air passed 70 per cent humidity, the pendulum started to spin. The silk twisted by over 300 degrees every millimetre, providing enough force that the researchers believe it could be used in robotic systems to twist components.
The exact reason for the twisting motion is unclear, but the researchers think it might help to make webs stronger. If a spider weaves a web overnight, the dragline silk would contract and twist in the morning dew, pulling the whole web tight. Also, spiders use the vibrations in the web to catch prey that has stumbled into it, and tension in the threads would make them hum like a plucked string.
The team has identified the source of the threads' ability to twist in a molecule called proline, a building block of one of the proteins that make up dragline silk. When water molecules interact with proline, they disrupt the structure of the protein, causing it to twist in one direction.
Dr Anna Tarakanova, assistant professor at the University of Connecticut, who worked on this study, thinks that the possibilities go beyond opening valves. "Potential applications are diverse: from humidity-driven soft robots and sensors, to smart textiles and green energy generators," she explained.
This doesn't mean that factories are going to be harvesting spider silk for robotic components any time soon: the team believe that, now that proline has been identified as the key ingredient, the twisting effect could be reproduced in synthetic materials.