Spider silk twists like muscle
5 Mar 2019 by Evoluted New Media
The presence of an amino acid in spider silk causes its fibres to contract and twist when exposed to humidity changes.
Researchers at MIT discovered that this process, called supercontraction, is based on the folding of proline, an amino acid used in the biosynthesis of proteins.
Dabiao Liu, joint author of the findings, said: “Spider dragline silk is a protein fibre. It’s made of two main proteins, called MaSp1 and MaSp2.”
The proline, crucial to the twisting reaction, is found within MaSp2. When water molecules interact with it they disrupt its hydrogen bonds in an asymmetrical way that causes the reaction.
The rotation only goes in one direction, and takes place at a threshold of about 70 percent relative humidity. Researchers think the supercontraction may be a natural response for the spider to sense its prey through vibrations.
This property of the spider silk makes a new class of materials possible and may be replicated in synthetic material. The twisting mechanism exerts enough force to potentially be used as actuators in mechanical devices.
Anna Tarakanova at MIT said: “Silk’s unique propensity to undergo supercontraction and exhibit a torsional behaviour in response to external triggers such as humidity can be exploited to design responsive silk-based materials that can be precisely tuned at the nanoscale.”
Applications include hygroscopic artificial muscles in soft robots and sensors, smart textiles, and green energy generators.
MIT researchers worked with collaborators at Queen Mary University of London and two China-based institutions. They reported their findings in Science Advances.
