Much of the design of robots today focus on copying the bodies of humans and other creatures. Researchers from MIT have found an unusual property of spider silk that would mean the ultrastrong material is useful for artificial muscle needed for robotic twisting or pulling motions. The team discovered that the spider silk responds “very strongly” to changes in humidity.
Above a certain amount of relative humidity in the air, the fibers will suddenly contract and twist. The fiber exerts enough force to be competitive with other materials used in actuators.
The property is called supercontraction and describes the phenomena where the fibers suddenly shrink in response to changes in moisture. The team discovered that the threads not only contract, but they also twist at the same time providing a strong torsional force.
The discovery was a happy accident initially according to the team. The team was conducting an experiment where weight was suspended on spider dragline silk to create a pendulum. When the weighted silk was enclosed in a chamber where humidity could be controlled, the pendulum weight started to rotate.
This was entirely out of expectation to the team. That contraction and rotation was seen as something that could be interesting for use in robotics. Ultimately, the spider silk could be harnessed to build humidity-driven soft robots or smart fabrics. The contraction starts at about 70% humidity says the team.