By Patrycja Sztachelski
Spider silk contains resilient fibers that contract and twist upon changes in humidity, a significant finding for medical innovation because the silk can exert enough force to possibly serve as an actuator, or a device that moves to perform some activity: in this case, the silk could serve as robotic muscle.
Researchers have discovered the property of supercontraction, in which the fibers in spider silk can shrink as a result of changes in moisture. Simultaneously, though, the threads twist, which produces a strong torsional force. MIT Professor and head of the Department of Civil and Environmental Engineering, Markus Buehler believes that this discovery “could be very interesting for the robotics community”, explaining that “it’s very precise in how you can control these motions by controlling the humidity”.
Although researchers are not sure of the biological purpose of this twisting force as it relates to adaptive functions of the spider, they have successfully determined how the twisting mechanism occurs. Furthermore, they have found that it depends on the folding of proline, a specific kind of protein building block.
Essentially, spider silk is a protein fiber, and it’s composed of the two main proteins MaSp1 and MaSp2. Additionally, “the proline, crucial to the twisting reaction, is found within MaSp2, and when water molecules interact with it they disrupt its hydrogen bonds in an asymmetrical way that causes the rotation. The rotation only goes in one direction, and it takes place at a threshold of about 70 percent relative humidity”.
Researchers are hopeful that the properties of spider silk can be replicated in synthetic materials, and transfer to various useful applications, including humidity-driven soft robots and sensors, smart textiles, and green energy generators.
Massachusetts Institute of Technology. (2019, March 1). Spider silk could be used as robotic muscle: Unusual property of the ultrastrong material could be harnessed for twisting or pulling motions. ScienceDaily. Retrieved March 8, 2019 from www.sciencedaily.com/releases/2019/03/190301160907.htm