Sewing Thread, Fishing Line Used To Create Powerful Artificial Muscles
February 21, 2014

Sewing Thread, Fishing Line Used To Create Powerful Artificial Muscles

Lawrence LeBlond for - Your Universe Online

Fishing line and sewing thread both have their own unique practical qualities, but when the two are combined they can do so much more, according to a new international study led by researchers from the Alan G. MacDiarmid NanoTech Institute at The University of Texas at Dallas.

In a paper published today in the journal Science, researchers from UT Dallas, the University of British Columbia (UBC), and others from Australia, South Korea, Turkey and China have shown the strength of common fishing line and sewing thread as artificial muscles. The results of the study offer a wide range of implications for the materials, including medical devices, humanoid robots, prosthetic limbs or stronger fabrics.

The study details how these common materials can easily and inexpensively be utilized to create powerful artificial muscles that generate far more force than any human or animal muscle of equal size.

The newly created muscles have been shown to lift a hundred times more weight and generate a hundred times higher mechanical power than the same length and weight of human muscle. Per weight, the artificial muscles can generate 7.1 horsepower per kilogram, which is the equivalent of the mechanical power produced by a jet engine, according to the researchers.

"In terms of the strength and power of the artificial muscle, we found that it can quickly lift weights 100 times heavier than a same-sized human muscle can, in a single contraction," John Madden, a professor of Electrical and Computer Engineering at UBC, said in a statement. "It also has a higher power output for its weight than that of an automobile combustion engine."

The powerful muscles are produced by twisting and coiling the high-polymer fishing line and sewing thread together. The muscles are then powered thermally, which is accomplished by electrical force, by the absorption of light, or by chemical reaction of fuels. Twisting the fiber converts it to a torsional muscle that can spin a heavy rotor to more than 10,000 rpm. Additional twisting makes the fiber coil act like a heavily twisted rubber band, producing a muscle that contracts along its length when heated and returns to its initial length when cooled. However, if the coiling is in a different twist direction than the initial fiber twist, the muscles will expand when heated and retract when cooled.

Compared to natural muscles, which contract by about 20 percent, the new polymer fiber muscles can contract by about 50 percent. The muscle strokes also are reversible for millions of cycles as the muscles contract and expand under heavy mechanical loads, according to the study findings.

"The application opportunities for these polymer muscles are vast," said corresponding author Dr. Ray Baughman, the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas and director of the NanoTech Institute. "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."

The practicalities of these artificial muscles are wide. Baughman noted that applications such as humanoids and exoskeletons could make use of the technology, giving them superhuman strength. He explained that by twisting together a bundle of polyethylene fishing lines, roughly ten times the thickness of a human hair, a polymer muscle is produced that can lift 16 pounds. In similar fashion, if a hundred of these bundles were to be twisted together, it would result in a powerful muscle that could lift as much as 1600 pounds.

While these artificial muscles are shown to be powerful lifters, they have other practical purposes as well. On the opposite extreme, single strands of the polymer muscles that have much less of a diameter than a human hair could be used to give humanoid robots life-like facial expressions or perhaps power miniature “laboratories on a chip.”

Carter Haines, lead author of the study from UT Dallas, explained that the polymer muscles are generally electrically powered by resistive heating using the metal coating on commercially available sewing thread. But for other applications, the muscles may be self-powered by environmental temperature changes.

"We have woven textiles from the polymer muscles whose pores reversibly open and close with changes in temperature. This offers the future possibility of comfort-adjusting clothing," said Haines, who earned an undergraduate physics degree from UT Dallas and is now a doctoral student in materials science and engineering.

The team also demonstrated the feasibility of using environmentally powered muscles to automatically open and close windows in greenhouses or other buildings in response to ambient temperature changes, thereby eliminating the need for electricity or costly, noisy motors.

The UBC researchers noted that artificial muscles have, in the past, been successfully created using metal wires and carbon nanotubes. However, researchers and device makers have found that these types of artificial muscles are quite expensive to fabricate and difficult to control.