U.S. and Australian researchers are putting a different twist on textile spinning to help create a new class of artificial muscles made from highly twisted fibers ranging from carbon nanotubes to nylon thread and common fishing line.

“We call these actuating fibers ‘artificial muscles’ because they mimic the fiber-like form factor of natural muscles,” says Dr. Carter Haines, associate research professor at the Alan G. MacDiarmid NanoTech Institute at the University of Texas at Dallas. The name may evoke the idea of humanoid robots, but the researchers say they are excited about their potential use for applications such as in next-generation intelligent textiles.

When heated and cooled, spiral-shaped artificial muscles expand and contract back and forth. Source: University of Texas at DallasWhen heated and cooled, spiral-shaped artificial muscles expand and contract back and forth. Source: University of Texas at DallasWhat the UT researchers and their colleagues at the University of Wollongong in Australia have done is to twist the muscle yarns so that like their wooly counterparts, they can be woven, sewn and knitted into textiles.

Previously, UT researchers developed a method to draw out “forests” of nanotubes into sheets of aligned fibers, similar to carded wool, and then twist the sheets into yarns. Next, the group turned to more conventional polymer fibers such as nylon sewing thread and fishing line, which consist of many individual molecules aligned along the fiber’s length. Twisting the thread or fishing line orients these molecules into helices, producing torsional — or rotational — artificial muscles that can spin a heavy rotor more than 100,000 revolutions per minute, researchers say.

However, these yarns could expand or contract only so far. “The coiled artificial muscles we initially made from fishing line and sewing thread were limited in the amount they could expand and contract along their length,” Haines says. “Because of their geometry — like a phone cord — they could only contract so far before the coils began to collide with one another.”

The solution was to form the coiled actuators into spirals. “The advantage to the spiral shape is that now our muscle can contract into a flat state, expand out in the other direction, and return to its original length, all without getting stuck on itself,” says research associate Dr. Na Li. Experiments to date have been proof-of-concept, but have already shown that heating and cooling can be used to drive this back-and-forth motion across a giant range. This type of telescoping actuator can produce over an 8,600% change in length, compared to around 70% for previous coils, the researchers say.

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