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MIT Technology Review

Ridiculously Elastic Conductive Fibers for Stretchable Circuits

New kinds of flexible, bendable, and twistable electronic devices could benefit from conducting wires that can stretch to many times their length.

July 23, 2015

It’s hard to know exactly how technologists might use electrically conductive fibers that can perform at a high level even when stretched to 15 times their length. But it’s possible the fibers, unveiled today by an international group of researchers, could help open new applications in robotics, find use in exoskeletons, make their way into new kinds of textiles, or bring power to sensor arrays that monitor the structural health of important curved surfaces like those on the outside of aircraft.

A microscope image shows how carbon nanotubes buckle when the fibers stretch and relax, which preserves their high conductivity.

Lots of progress has been made in recent years toward new kinds of electronic devices that can bend, flex, and stretch. But the creators of the new fibers say there is still a need for better elastic conducting materials to serve as wires, sensors, and for use in deformable energy storage devices and displays.

The new fibers, made by wrapping carbon nanotube sheets (see “Light-as-Air, Heatproof Nanotube Muscles”) around a rubber core, are relatively inexpensive and straightforward to manufacture, says Ray Baughman, a professor of chemistry and director of the Nanotech Institute at the University of Texas at Dallas. Baughman, who led the research, says they could be particularly useful for things like extendable robotic arms, or as the basis of sensor arrays that monitor the state of aircraft that “morph” to adapt to changing flight conditions.

To make them, the researchers first stretched rubber fibers to 15 times their length, before wrapping the nanotube sheets around them. When they released the stress, the individual nanotubes buckled, like accordions. When stretched again, the sheets buckled, in a different way, to account for the circumference of the rubber core shrinking as the fiber elongated. The degree to which they can stretch without losing their high conductivity is a vast upgrade over any previously demonstrated elastic conductor, according to Baughman.

One potential application of these fibers is super-stretchy charger cords for consumer electronics, says Baughman. He says next he’d like to put the new stretchy materials into textiles that could perform various electrical functions. No word yet on whether that will include pants that stretch when they sense that their wearer has put on a few pounds.