February 24, 2014

Researchers Create Muscles from Fishing Line, Thread

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Twisting together a bundle of polyethylene fishing lines, whose total diameter is only about ten times larger than a human hair, produces a coiled polymer muscle that can lift 16 pounds. Operated in parallel, similar to how natural muscles are configured, 100 of these polymer muscles could lift about 1,600 pounds, Baughman said. Photograph courtesy of UT Dallas.

An international team of researchers led by The University of Texas at Dallas (UT Dallas) has discovered that ordinary fishing line and sewing thread can be cheaply converted to powerful artificial muscles. In a paper published February 21 in the journal Science, the researchers explained that the powerful muscles are produced by twisting and coiling high-strength polymer fishing line and sewing thread. The muscles could be used for applications such as robots, exoskeletons, and prostheses, said corresponding author Ray Baughman, PhD, the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas and director of the UT Dallas Alan G. MacDiarmid NanoTech Institute.

According to the researchers, the new muscles can lift 100 times more weight and generate 100 times higher mechanical power than a human muscle of the same length and weight. Per weight, they can generate 7.1 horsepower per kilogram, about the same mechanical power as a jet engine. The muscles are powered thermally by temperature changes, which can be produced electrically, by the absorption of light or by the chemical reaction of fuels. Twisting the polymer fiber converts it to a torsional muscle that can spin a heavy rotor to more than 10,000 revolutions per minute. Subsequent twisting, so that the polymer fiber coils like a heavily twisted rubber band, produces a muscle that dramatically contracts along its length when heated, and returns to its initial length when cooled. If coiling is in a different twist direction than the initial polymer fiber twist, the muscles expand when heated instead.

Compared to natural muscles, which contract by only about 20 percent, these new muscles can contract by about 50 percent of their length. The muscle strokes also are reversible for millions of cycles as the muscles contract and expand under heavy mechanical loads.

“The application opportunities for these polymer muscles are vast,” said Baughman. “Today’s most advanced humanoid robots, prosthetic limbs and wearable exoskeletons are limited by motors and hydraulic systems, whose size and weight restrict dexterity, force generation, and work capability.”

On the opposite extreme, independently operated coiled polymer muscles having a diameter less than a human hair could bring lifelike facial expressions to humanoid companion robots for the elderly and dexterous capabilities for minimally invasive robotic microsurgery. Also, they could power miniature “laboratories on a chip,” as well as devices for communicating the sense of touch from sensors on a remote robotic hand to a human hand.

The polymer muscles are normally electrically powered by resistive heating using the metal coating on sewing thread or by using metal wires that are twisted together with the muscle. For other applications, however, the muscles can be self-powered by environmental temperature changes, said Carter Haines, a UT Texas materials science and engineering doctoral candidate and lead author of the study.

“We have woven textiles from the polymer muscles whose pores reversibly open and close with changes in temperature,” said Haines. “This offers the future possibility of comfort-adjusting clothing.” The research team also has demonstrated the feasibility of using environmentally powered muscles to automatically open and close the windows of greenhouses or buildings in response to ambient temperature changes, thereby eliminating the need for electricity or noisy and costly motors.

Scientists at UT Dallas’ Tech Institute teamed with scientists from universities in Australia, South Korea, Canada, Turkey, and China to accomplish the advances.

Editor’s note: This story was adapted from materials provided by UT Dallas.

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