Everyday fibres used to create artificial muscles

Researchers are using fibres from fishing line and sewing thread to create inexpensive artificial muscles that could be used in medical devices, humanoid robots, prosthetic limbs, or woven into fabrics.

In a study published in Science, international researchers, including University of British Columbia Electrical and Computer Engineering professor John Madden and PhD candidate Seyed Mohammad Mirvakili, detail how they created inexpensive artificial muscles that generate far more force and power than human or animal muscles of the same size.

‘In terms of the strength and power of the artificial muscle, we found that it can quickly lift weights 100 times heavier than a same-sized human muscle can, in a single contraction,” Madden said in a statement. “It also has a higher power output for its weight than that of an automobile combustion engine.”

Artificial muscles have been made out of materials like metal wires and carbon nanotubes in the past but researchers and device makers have found these artificial muscles expensive to fabricate and difficult to control.

Madden and his colleagues from from universities in Australia, South Korea, the USA, Turkey and China used high-strength polymer fibres made from polyethylene and nylon that were twisted into tight coils to create an artificial muscle that could contract and relax.

The muscles are powered thermally by temperature changes, which can be produced electrically, by the absorption of light or by the chemical reaction of fuels. 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 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 about 20 per cent, these new muscles can contract by about 50 per cent of their length. The muscle strokes are reversible for millions of cycles as the muscles contract and expand under heavy mechanical loads. 

This system has so far been demonstrated by using such muscles to manipulate surgical forceps.

Research partner Dr Ray Baughman, the Robert A. Welch Distinguished Chair in Chemistry at the University of Texas at Dallas, said the muscles could be used for applications where superhuman strengths are sought, such as with robots or exoskeletons.

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 16 pounds. Operated in parallel, similar to how natural muscles are configured, a hundred of these polymer muscles could lift about 0.8 tons, Baughman said.

Similarly, 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.