Artificial muscles could find use in a wide range of applications, including prosthetic limbs, robotics, exoskeletons, or pretty much any situation in which hydraulics or electric motors just aren't a practical means of moving objects. Scientists have been working on such muscles for a number of years, using materials like vanadium dioxide, graphene, carbon nanotubes and dielectric elastomers. Now, however, some of those same scientists have discovered that very powerful artificial muscles can be made from much more down-to-earth materials – regular polymer fishing line, and metal-coated nylon sewing thread.
The research was led by The University of Texas at Dallas, but involved the input of partnering universities in Australia, South Korea, Canada, Turkey and China.
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To make the muscles, the team started by attaching one end of a piece of fishing line to the tip of a power drill, with the other end hanging below it, held in place by an attached heavy weight. A piece of the thread hung with the line, joined to it along one side. As the drill was powered up and its end started spinning, the line initially responded by twisting along its length. Once it had twisted as much as it could, it then proceeded to bunch up into a series of coils, like a land-line telephone receiver cord.
The scientists then heated that coiled line with a hair dryer, causing the coils to set permanently – even once the weight was removed, the line remained coiled.
A variety of sizes of the artificial muscles, with a pencil for scale (Photo: University of Texas at Dallas)
When heat is subsequently applied to one of those lines, it will respond by coiling tighter, thus contracting like a muscle. According to a recently-published paper on the research, "Extreme twisting produces coiled muscles that can contract by 49 percent, lift loads over 100 times heavier than can human muscle of the same length and weight, and generate 5.3 kilowatts of mechanical work per kilogram [2.2 lb] of muscle weight, similar to that produced by a jet engine."
While the heat could be applied electrically (via the metal in the thread), it could also take the form of exposure to light, or a chemical reaction. This means that the muscles wouldn't necessarily require an electrical power source, and could be used for things like automatically opening and closing window shutters based on time of day or air temperature.
The paper was published on Feb. 21, in the journal Science. The following video, from Australian project partner the ARC Centre of Excellence for Electromaterials Science, illustrates the production process – it also shows how a number of the artificial muscles could be weaved together, for extra power.