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Yarns woven from carbon nanotubes can contract like muscles at extremely high speeds to lift large weights. These carbon nanotube muscles can lift loads 200 times greater than natural muscles the same size. Videos made by researchers at the University of Texas at Dallas show the nanotube yarns lifting loads as much as 50,000 times greater than their own weight.

Artificial muscles might be used as actuators in robotics and surgical tools, and drive tiny motors and flywheels. The nanotube muscles can be powered by electricity, but they also contract in response to light and certain chemicals. And they work at temperatures as high as 2,500 degrees Celsius, an extreme that reduces other strong actuating materials to a molten puddle. And unlike previous carbon nanotube muscles, these materials require no packaging or battery-like electrolytes to function. The yarns are described today in the journal Science.

Individual carbon nanotubes are stronger than steel, highly conductive, have great optical properties, and so on—you’ve heard the hype. But single nanotubes are not so useful. For many years, when researchers tried to build things out of them, they had trouble getting these properties to scale from single tubes to larger structures. One problem is the tendency for nanotubes to form spaghetti-like tangles, where each point of tube-to-tube contact can compromise strength. But over the past few years materials scientists have been learning how to straighten out these tangles and build large, useful things.

The trick in this case is a set of yarn-weaving techniques developed by Ray Baughman at the University of Texas at Dallas. His group starts by growing a vertical forest of carbon nanotubes, then dragging a roller over the top. As the tubes are pulled, they come together in a thin, stretchy sheet. The nanotubes in the sheet are all lined up like spaghetti in a box, and this alignment helps maintain their individual strength on a collective level. To make the nanotube muscles, the Texas researchers coat this sheet with a filler material that expands dramatically when heated. Then they weave the sheet into yarns with different twisting configurations. When the yarns are heated, the filler expands dramatically, and the yarn will contract in a way that’s determined by its coiling configuration.

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