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Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers.

Nylon fibers of different weights can be coiled into "artificial muscles."

PHOTOGRAPH BY CARTER HAINES

Jane J. Lee

National Geographic

Published February 20, 2014

All it takes is a little twist, and fishing line and nylon carpet fibers may soon star as the latest in high-technology clothing and industry, report scientists. The secret isn't in complex manufacturing or exotic materials, but in coils given to the line.

A team led by researchers from the University of Texas, Dallas, has come up with a way to take polyethylene fishing line and nylon threads and turn them into fibers capable of lifting nearly a ton or rotating to produce as much horsepower, pound for pound, as a jet engine.

The coiled threads, called artificial muscles, promise technologies ranging from heat-sensing drapes to coats that tighten their pores on a chilly day to keep wearers warm. They may also serve as the "muscles" for futuristic prosthetics or give robots more human facial expressions, the researchers suggest.

The technique to turn these everyday objects into next-gen material is so easy that high school students can do it, says materials scientist Ray Baughman of the University of Texas, Dallas, senior author of the report in the journal Science.

The trick is to take high-strength threads, such as fishing line, and twist them until they coil, explains Baughman. The researchers set the coils in place using heat so that they don't unravel. Then, they report, simple changes in temperature can make the coil contract or relax.

"It is a very clever idea," says Qibing Pei, a materials scientist at the University of California, Los Angeles, in an email. "A remarkable new function is obtained from 'old' technologies," adds Pei, who was not involved in the study.

From Exotic to Everyday

Artificial muscles aren't a new concept. And researchers have gone through some very exotic materials—like carbon nanotubes infused with paraffin wax or shape-memory metal wires—in their quest.

But they have all had problems, says Baughman. Some can't change shape enough to get any meaningful work done. Others can't hold their form for enough contraction-relaxation cycles to be useful. Some artificial muscles simply have too short a life-span.

But these new muscles, say the study authors, don't have those problems. They can also be added together for bigger and bigger tasks.

Just one of the artificial muscles, made from polyethylene fishing line that is about ten times the diameter of a human hair, can lift about 16 pounds (7.3 kilograms). A hundred of them arranged together could lift 0.8 tons (0.7 tonnes).

And because of their corkscrew shape, they can be used to rotate motors. Some of them are so good at producing mechanical power that their output—7.1 horsepower per 2.2 pounds (a kilogram)—rivals that produced by a jet engine.

They're also very cheap to produce, Baughman adds, since you can find most of the materials you need at the hardware store.

Artificial muscles made out of carbon nanotubes cost about $4,000 to $5,000 for two pounds (a kilogram) of material. Researchers paid only $5 for the same amount of polyethylene fishing line or nylon fiber.

Old Materials, New Technology

"The ultimate goal is to make textiles that [result in] comfort-adjusting clothing," says Baughman. A shirt infused with these artificial muscles could contract in cold weather, keeping a person warm, and expand in warm weather, creating pores to keep you cool.

Baughman and colleagues have managed to use their new muscle threads to open and close window shutters in response to outside temperatures. This could replace the loud, expensive motors used to adjust window blinds in buildings and greenhouses, Baughman explains.

The key challenge "will be how to administer the temperature change in compact, reliable, and energy-efficient schemes," says UCLA's Pei. "Given the outstanding track record of the group, I expect these to be demonstrated soon."

Follow Jane J. Lee on Twitter.

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