Artificial muscles made out of fishing line and sewing thread can lift a hundred times more weight than human muscle.
By twisting and coiling high-strength polymer fishing line and sewing thread, an international team led by The University of Texas at Dallas has managed to create artificial muscles that can generate 7.1 horsepower per kilogram – about the same mechanical power as a jet engine.
The new muscles can lift a hundred times more weight and generate a hundred times higher mechanical power than the same length and weight of human muscle and are powered thermally by temperature changes, which can be produced electrically, by the absorption of light or by the chemical reaction of fuels.
"The application opportunities for these polymer muscles are vast," said corresponding author Dr Ray Baughman, director of the university’s Alan G MacDiarmid NanoTech Institute.
"Today's most advanced humanoid robots, prosthetic limbs and wearable exoskeletons are limited by motors and hydraulic systems, whose size and weight restrict dexterity, force generation and work capability."
A paper published in the journal Science today reports that twisting the polymer fibre converts it to a torsional muscle that can spin a heavy rotor to more than 10,000 revolutions per minute.
Subsequent additional twisting, so that the polymer fibre coils like a heavily twisted rubber band, produces a muscle that dramatically contracts along its length when heated, and returns to its initial length when cooled.
If coiling is in a different twist direction than the initial polymer fibre twist, the muscles instead expand when heated.
Compared to natural muscles, which contract by only about 20 per cent, these new muscles can contract by about 50 per cent of their length and the muscle strokes are also reversible for millions of cycles as the muscles contract and expand under heavy mechanical loads.
Twisting together a bundle of polyethylene fishing lines, whose total diameter is only about 10 times larger than a human hair, produces a coiled polymer muscle that can lift 16lb. Operated in parallel, similar to how natural muscles are configured, a hundred of these polymer muscles could lift about 0.8 tonnes, Baughman said.
On the opposite extreme, independently operated coiled polymer muscles having a diameter less than a human hair could bring life-like facial expressions to humanoid companion robots for the elderly and dexterous capabilities for minimally invasive robotic microsurgery, according to Baughman.
They could also power miniature "laboratories on a chip," as well as devices for communicating the sense of touch from sensors on a remote robotic hand to a human hand.
The polymer muscles are normally electrically powered by resistive heating using the metal coating on commercially available sewing thread or by using metal wires that are twisted together with the muscle, but for other applications, however, the muscles can be self-powered by environmental temperature changes, said Carter Haines, lead author of the study.
"We have woven textiles from the polymer muscles whose pores reversibly open and close with changes in temperature. This offers the future possibility of comfort-adjusting clothing," said Haines, a doctoral student in materials science and engineering.
The research team also has demonstrated the feasibility of using environmentally powered muscles to automatically open and close the windows of greenhouses or buildings in response to ambient temperature changes, thereby eliminating the need for electricity or noisy and costly motors.
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