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Nylon Fibers Given Muscle-Like Bending Properties

Nylon fibers

Nylon fibers (Daplaza, Wikimedia Commons)

23 November 2016. Research engineers designed a process that gives ordinary nylon fibers the ability to bend and flex like artificial muscles. Doctoral candidate Seyed Mirvakili and mechanical engineering professor Ian Hunter at Massachusetts Institute of Technology describe their discovery in today’s issue of the journal Advanced Materials (paid subscription required).

Mirvakili and Hunter study characteristics of synthetic fibers to devise solutions for medical devices and other applications using fibers that respond to their environment. Many current approaches for these solutions, however, involve exotic or expensive materials, like yarns made from carbon nanotubes. These nanotech yarns have a long lifetime, but today are still too expensive. Other metal alloys can bend and return to their original shape, say the authors, but are not durable enough for everyday use.

In earlier work, Mirvakili and Hunter found ordinary nylon fiber, twisted into coils, could simulate some properties of human muscle. Nylon is an inexpensive polymer, easy to produce, and with a long life cycle. They found nylon could be configured to extend and retract in linear actions like human muscles, storing energy to a greater extent than natural muscle fibers.

The ability to direct nylon fibers to bend like human muscles, however, remained a challenge. Mirvakili and Hunter began with applying heat, which would then contract the nylon when it cooled. They discovered just heat alone was not enough, but directing the heat to one side of the fiber would bend the fiber in a desired direction. Taking the process further, the researchers found they could bend nylon fibers into complex shapes, including figure-eights, and movements.

While Mirvakili and Hunter started with ordinary nylon fishing line, they had to change the shape of the fiber and other properties to get the desired responses. They compressed the fiber’s shape to change its cross section from round to rectangular. They also experimented with different heat sources, including heat converted from electricity or chemical reactions, as well as laser beams.

In other tests, the researchers used a conductive paint that when exposed to an electric current heated a section of the fiber, causing the non-painted portion of the fiber to bend in the desired direction. In addition, their fibers lasted through more than 100,000 bending cycles, at speeds of more than 17 bending cycles per second.

The authors foresee the bendable nylon fibers used in medical devices, such as prosthetic devices or self-adjusting catheters to better fit the patient’s blood vessels or organs. Other potential applications are clothes or shoes that adjust to fit the wearers, or solar panels that respond to heat to keep directly facing the sun’s rays.

The following video tells more about this research.

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