Spider silk, already known as one of the mostdurable materials with its weight, has another unusual property, which can lead to the emergence of new types of artificial muscles or robotic drives, scientists have found. Elastic fibers, as it turned out, react very strongly to changes in humidity. Above a certain level of relative humidity, they suddenly shrink and twist, applying enough force to compete with other materials that are being researched as actuators — that is, devices that move to perform some kind of activity, like valve control.
The results of the work were presented in the journal Science Advances in the work of MIT Professor Marcus Bühler.
Web - the strongest material
Researchers have recently discoveredSpider silk's amazing property called super-compressibility, when fine fibers can suddenly shrink in response to changes in moisture. The new conclusion is that the threads are not only compressed, but twisted simultaneously, creating a strong twisting force. “This is a new phenomenon,” says Buhler.
"We discovered it by chance," confirm it.Colleagues. "We wanted to study the effect of moisture on the spider silk dragline." To do this, they suspended the load on silk to create a kind of pendulum, and placed it in a chamber where they could control the relative humidity inside. “When we increased the humidity, the pendulum began to rotate. We did not expect this. ”
The team checked a number of other materials, includingincluding human hair, but did not detect such twisting movements in other experiments. However, the first phenomenon has already tried to apply (in theory) to artificial muscles.
"It can be very interesting for the communityrobotics, ”says Bühler, referring to a new way of controlling certain types of sensors or control devices. "You can manipulate the movements very precisely by controlling the humidity."
Spider silk is already known for its exceptionalratio of strength and weight, its flexibility and elasticity. Several groups of scientists around the world are working to reproduce these properties in a synthetic version of protein-based fibers.
Although the purpose of this twisting force, from the pointSpider's point of view, it is not known, scientists believe that super-compressibility in response to moisture can be a way to make sure that the network is stretched when morning dew appears on it, which can damage it and reduce its susceptibility to vibration, due to which the spider feels its prey.
"We did not find any biological meaning" inthis twisting motion, says Bühler. But thanks to a combination of laboratory experiments and molecular modeling using a computer, they were able to determine how the twisting mechanism works. It turns out that it is based on the folding of a certain type of building protein called proline.
The study of this basic mechanismrequired detailed molecular modeling. “We tried to find the molecular mechanism of what our colleagues discovered in the laboratory. And we did find a potential mechanism based on proline. ” They showed that it is the structure of proline that leads to twisting in modeling.
“The dragline of the web is a protein fiber. It consists of two major proteins, MaSp1 and MaSp2. ” Proline, necessary for the twisting reaction, was found in MaSp2, and when the water molecules interact with it, they destroy its hydrogen bonds asymmetrically, causing torsion. Rotation occurs only in one direction and at a relative humidity of 70%.
"The protein has a built-in rotation symmetry",says Buhler. And thanks to its torsional strength, it makes possible a “whole new class of materials”. It may be possible to reproduce it in synthetic material and create a new polymeric material that would repeat this behavior.
"The unique ability of silk to be exposedsupercompression and rotational behavior in response to external triggers, such as moisture, can be used to develop sensitive silk-based materials that can be fine-tuned at the nano level. Potential applications range from soft robots and humidity sensors to smart fabrics and clean energy generators. ”
It may be that other natural materials have this property, but they have not yet been discovered. And what use do you see? Tell us in our chat.