Nylon thread made into artificial muscles

Using simple re-purposed nylon filament, MIT researchers have created heat-activated artificial muscles(Credit: Felice Frankel and Seyed Mohammad Mirvakili/MIT)

Using a combination of ordinary nylon thread and conductive ink, MIT scientists have created artificial muscles that can perform many of the motions found in natural muscle tissue. The researchers believe that the new flexing devices could be used in a range of applications, from robotics and artificial limbs to powered flexible components for use in the automobile and aviation industries.

Created by manipulating nylon fibers in a relatively simple manufacturing process, the new material responds to heat by contracting in length and expanding in girth. In this way, when a heat source is applied, such as using conductive ink that warms the nylon filaments when a voltage is applied, the researchers have demonstrated that the new "muscles" are capable of reliable performance even after at 100,000 bending cycles, and able to bend and spring back at over 17 times per second.

To make this artificial muscle, the cross-section of the nylon thread first needed to be specifically shaped using a rolling mill to compress its cross-section from round to rectangular or square. Then, by painting conductive ink on one side and making it heat up, the fiber bends in that direction. By altering the direction of this heating, the researchers found that they could also make the material produce more intricate motions, including moving in circles and figures-of-eight.

Other attempts at making artificial muscles from polymer fishing line using twisted coils of filament have been able to emulate basic straight-line muscle activity that could stretch and retract in greater amounts, as well as hold and release more energy than natural muscles. But these devices needed linear actuators to move them, so were slower and more energy intensive than the new MIT versions. And though other research, such as using carbon nanotubes combined with rubber, could provide more than a million linear contraction cycles, they are far too expensive for common applications.

"This method is novel and elegant, with very good experimental data supported by appropriate physics-based models," said Geoffrey Spinks, a professor at the University of Wollongong Australia, who was not connected with this research. "This is a simple idea that works really well. The materials are inexpensive. The manufacturing method is simple and versatile. The method of actuation is by simple electrical input. The bending actuation performance is impressive in terms of bending angle, force generated, and speed."

Other uses for these new fibers, say the researchers, may include clothes that automatically adjust to the shape of the body when an electrical charge is applied, thereby offering true "one-size-fits-all" garments, that would also markedly improve comfort and fit. The scientists even suggest that in the manner of Back to the Future, the MIT fibers could be used in shoelaces that tighten themselves or adjust their shape during each step for ultimate shoe performance.

The devices may also offer such things as self-adjusting biomedical devices, smart vehicle panels that constantly alter their aerodynamic shape in response to speed, or automatic systems for solar panels where heat radiated from the panels maintain the aim of the panels towards the sun.

The results of this work were recently published in the journal Advanced Materials.

The short video below shows the new fibers in action.

Source: MIT

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