Spider silk has been spun into everything from violin strings and electrical wires to biodegradable shoes and winter coats.

Soon, it may be turned into artificial muscles or robotic actuators, thanks to a team of MIT engineers.

One of the strongest materials for its weight, spider silk apparently reacts strongly to changes in humidity.

Exceed a certain level of dampness in the air, and the fibers suddenly contract and twist, exerting a similar amount of force as a machine component controlling a valve.

“It’s a new phenomenon,” study author Markus Buehler, head of MIT’s Department of Civil and Environmental Engineering, said in a statement.

 

The cylindrical chamber allows for precise control of humidity while testing the contraction and twisting of spider silk fibers.

 

Well, not entirely new…

Researchers previously discovered a property of spider silk called supercontraction, in which the fibers suddenly shrink in response to changes in moisture.

Buehler’s team, however, revealed an additional twisting action, providing a strong torsional force.

“We found this by accident initially,” according to study co-author Dabiao Liu, an associate professor at Huazhong University of Science and Technology in Wuhan, China.

To study the influence of humidity on spider dragline silk, Liu & Co. created a sort of pendulum by suspending a weight from the silk and enclosing it in a chamber where they could control the dampness inside.

“When we increased the humidity, the pendulum started to rotate,” he explained. “It was out of our expectation. It really shocked me.”

 

Scanning electron microscope images show filaments of spider dragline silk.

 

Various other materials—including human hair—yielded not such twisting motions.

“This could be very interesting for the robotics community,” Buehler said, proposing this precise phenomenon as a way of controlling certain kinds of sensors or devices.

Researchers believe supercontraction may be a way to ensure the web is pulled tight in morning dew, protecting it from damage and maximizing responsiveness to vibrations that signal incoming prey.

“This kind of twisting motion might be found in other materials that we haven’t looked at yet,” Buehler said.

The full results were published last week in the journal Science Advances.