The next artificial muscle, for either robotics or medical applications, will need to be strong, and it will need to be flexible. Right now, carbon nanotubes reign supreme as the strongest artificial muscle, while materials such as spider silk come in as close possible seconds. But now a new material breakthrough has entered the artificial muscle arena, and it could beat its competitors down. And this muscle is made out of fishing line, of all things.
How do you get muscle out of a fishing line? First, you have to create tension that can be released.
It's a simple process that goes by an equally simple moniker: "twist insertion."
One end of a high-strength polymer fiber (like a 50 pound test-line, for example, available at pretty much any sporting goods store) is held fast, while the other is weighted and twisted. Twist a little and the line becomes an artificial "torsional" muscle that exerts energy by spinning. Twist a lot, however, and something interesting happens: the cord coils over on itself, creating an ordered series of stacking loops.
When you do this to a piece of fishing line, researchers discovered, it turns into an artificial tensile muscle that can contract, just like our own muscles, i09 says. To test the fishing line's strength, the researchers applied hot and cold temperatures—a standard means of testing material properties—which caused the artificial muscle to contract and relax. In this way, they could coax four interwoven artificial muscles into lifting 30-pound weights, for example. Sewing thread, they also found, demonstrates similar properties when treated this way.
After performing a number of tests, the researchers found that the artificial muscles could "generate about seven horsepower of mechanical power per kilogram of polymer fiber," i09 writes. The study authors put this into perspective: that means the fishing line can "lift loads over 100 times heavier than can human muscle of the same length and weight" and can perform mechancial work about equivalent to that of a jet engine.