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Muscle, Heal Thyself


By Cynthia Lee

Published Jul 1, 2008 8:00 AM

It's too early to think about bulking up with the artificial muscles that scientists like Qibing Pei of UCLA's Materials Science and Engineering Department in the Henry Samueli School of Engineering and Applied Science have been working on for years. But researchers are fantasizing that the rubber-like material, called electroactive polymers, may one day power small, energy-efficient robots, turn your shoes into power generators that can keep your iPod or cell phone going, power your car windows and adjust your car seats, and help keep a weak heart pumping.

Oh, and one more super-powered thing: When it tears, an artificial muscle heals itself.

Here's how it works: When electricity is run through a thin film of the polymer, it expands. When the voltage stops, it contracts. Even better, it also works in reverse: If some mechanical force is applied to change the shape of the material, it unleashes a small current of electricity.

Paul Brochu, a graduate student on Pei's team, is looking into how a flag made of the material might generate electricity as it flaps in the wind. Scientists in Japan are developing a wave energy generator that will use the force of water to push against the "muscle" to generate electricity. Theoretically, shoes with polymer soles could generate electricity when you walk to power your iPod or other mobile devices.

And these abilities have piqued the interest of the private sector and even the military. General Motors, for one, is working with Pei and his graduate students in the hope that polymers may one day be used to make small actuators for various automobile components.

Until recently, there was one serious hitch. The constant expanding and contracting caused the material to fatigue and short out. "Once the material shorted," Pei explains, "the whole device was dead. That made it very unpredictable." But the UCLA scientist has overcome that problem by making the artificial muscle self-healing.

Using carbon nanotubes as electrodes, Pei and his team, which includes Wei Yuan, a graduate student in Pei's research group, recently demonstrated that when a defect occurs in the material, it can be electrically isolated. The high electrical field, in effect, destroys the conducting material around the defect. The area in which the defect is located does become isolated, and function is affected a little bit. But the rest of the muscle still works — in effect, it heals itself.

"Without this self-healing concept, the artificial muscle could die suddenly, unpredictably," says Pei, who first published his research in the February 2004 issue of Advanced Materials. "Using our method, it will slowly fade and wear out, but much more gracefully."

After all, even superheroes grow old.



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