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High-Strength Muscle-Emulating Nanotech Yarn Developed

Scanning electron microscope image of carbon nanotube yarn (University of Texas at Dallas)

Scanning electron microscope image of carbon nanotube yarn (University of Texas at Dallas)

Engineers and materials scientists from the U.S., Canada, Brazil, Australia, China, and Korea developed a super-strong yarn based on carbon nanotubes with the contracting ability of muscles. The team led by Ray Baughman of University of Texas in Dallas published its findings in this week’s issue of the journal Science (paid subscription required).

The yarn devised by Baughman and colleagues are made of carbon nanotubes, which are cylinders with layers of graphite similar to that found in lead pencils, only 10,000 times smaller than the diameter of a human hair, yet also by weight some 100 times stronger than steel. The researchers then infuse the nanotubes with paraffin wax, like that found in candles, and twist the strands into a coiled yarn about twice the width of a human hair.

When heat is added to the wax-filled yarn, with either an electric current or a flash of light, it causes the wax to expand and untwist, and the volume of the yarn to increase, that in turn causes the yarn length to contract. When the heating stops and the yarn cools, the opposite action occurs: the volume of yarn decreases and yarn length increases. This set of actions is similar to a child’s finger cuff toy, designed to trap a person’s fingers in both ends of a helically woven cylinder. To escape the trap, you push your fingers together, contracting the tube’s length and expanding its volume and diameter.

These properties enable the yarn to behave much like muscle contractions, only with much greater power. The researchers demonstrated the yarn’s contraction power density of 4.2 kilowatts per kilogram, which is four times the power-to-weight ratio of common internal combustion engines. “The artificial muscles that we’ve developed,” says Baughman, “can provide large, ultrafast contractions to lift weights that are 200 times heavier than possible for a natural muscle of the same size.”

Because the yarn-muscles can be woven, sewn, braided and knotted, they could be built into self-powered intelligent materials and textiles that respond to changes in temperature or ambient environmental conditions, providing protection against excess heat or toxic chemicals. Materials made from these yarn-muscles could also be deployed to regulate flow valves in response to detected chemicals, or adjust window blinds in response to air temperatures.

“Because of their simplicity and high performance,” notes Baughman, “these yarn-muscles could be used for such diverse applications as robots, catheters for minimally invasive surgery, micromotors, mixers for microfluidic circuits, tunable optical systems, microvalves, positioners, and even toys.” Baughman tells more about the team’s research in the following video.

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