Tightly coiled fibers could be used as artificial muscles in prosthetic limbs

Researchers from the Massachusetts Institute of Technology have found a way to coil contrasting materials together to create a lightweight and durable fiber that pulls and contracts like muscles. 

This mechanism could be used to replace artificial muscles made of heavy, slow-responding hydraulic systems and motors in prosthetic limbs and robots.

By coiling together two materials with different rates of thermal expansion, a stretchy cyclic copolymer elastomer and a stiffer thermoplastic polyethylene, the researchers created a single fiber that contracted and coiled after being stretched. 

The coiling and pulling action was possible because one of the fibers had a faster expansion rate, meaning that when the material was heated up, it expanded more quickly. 

Where one of the polymers wants to expand, it’s held back by the other material causing it to coil up tightly like the tendrils of a cucumber that help pull the plant up out of the ground. 

When the newly-created coil was picked up by one of the researchers, the warmth of their hands caused the fibers to curl up even more. 

A slight increase, even one degree Celsius in temperature, caused the coil to tighten. When the temperature decreased, the coil resumed its original length. 

Even after 10,000 tries, the coil kept its shape and was able to contract and relax without any problems. 

The new fiber mechanism has many exciting implications and can range from a few micrometers in width to a few millimeters. The fibers could measure hundreds of meters long, and a single fiber is able to lift 650 times its own weight. 

Some prosthetic limbs weigh as much as 30 pounds, but having a lightweight and fast responding alternative to those cumbersome systems could revolutionize prosthetics and robotics. 

The findings were published in the journal Science. 

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By Kay Vandette, Earth.com Staff Writer 

Image Credit: Minerva Studio