Spider silk, already known as one of the most durable materials with their weight, has another unusual property which can lead to the emergence of new types of artificial muscles or robotic actuators, the researchers found. Elastic fibers, as it turned out, are very responsive to humidity changes. Above a certain level of relative humidity they shrink and curl, with enough power to compete with other materials, which are investigated as actuators — that is, devices that move to implement a certain activity, like a control valve.
The results were presented in the journal Science Advances in the work of a Professor of MIT’s Markus Buehler.
Spider silk is the strongest material
Researchers not long ago discovered an amazing property of spider silk called supersymmet, when a thin fiber can suddenly shrink in response to changes in humidity. New conclusion is that threads are not only compressed but also twisted at the same time, creating a strong torsional strength. “This is a new phenomenon,” says Buhler.
“We found it by accident”, confirmed by his colleagues. “We wanted to study the effect of humidity on the dragline spider silk”. For this they have hung a load of silk to create a kind of pendulum, and put him in a cell, where they can monitor the relative humidity inside. “When we increased the humidity, the pendulum began to rotate. This was unexpected”.
The team has investigated a number of other materials, including human hair, but found no such twisting movements in other experiments. However, the first phenomenon has already tried to apply (in theory) to the artificial muscles.
“This could be very interesting for the community of robotics”, says bühler, referring to a new way of handling certain types of sensors or control devices. “You can manipulate the movements very precisely, controlling humidity”.
Spider silk is already known for its exceptional balance of strength and weight, its flexibility and elasticity. Several groups of scientists around the world are working to reproduce these properties in synthetic versions of fibre-based protein.
Although the purpose of this torsional force, from the point of view of a spider is unknown, scientists believe that supersymmet in response to moisture can be a way to make sure that the network is stretched when it is morning dew, which can damage it and reduce susceptibility to vibration, due to which the spider feels its prey.
“We found no biological sense” in this twisting motion, says bühler. But thanks to the combination of laboratory experiments and molecular modeling via computer, they were able to determine how the mechanism of twisting. It turns out that it is based on minimizing a particular form of construction a protein called Proline.
The study of this basic mechanism required detailed molecular modeling. “We tried to find the molecular mechanism that our colleagues found in the lab. And we found a potential mechanism based on the Proline”. They showed that the structure of the Proline leads to a twisting in the simulation.
“The dragline cobwebs is a protein fiber. It consists of two main proteins, MaSp1 and MaSp2”. Proline is needed for the reaction twisting found in MaSp2, and when the water molecules interact with him, they destroy his hydrogen bond is asymmetric, which causes torsion. The rotation occurs in one direction only and at a relative humidity of 70%.
“The protein has a built-in symmetry of rotation,” says Buhler. And because of his power torsion, it makes possible “a new class of materials”. Maybe it will reproduce in a synthetic material and create a new polymeric material, which be repeating this behavior.
“The unique ability of silk to be superstitio and show rotational behavior in response to external triggers such as moisture, can be used to develop sensitive materials based on silk, which can be accurately configured to the nanoscale. Potential applications range from soft robots, and humidity sensors to smart textiles and generators of clean energy”.