A bionic ankle so natural, it's worth a happy dance

An artificial ankle created at the MIT Media Lab is made of chips and sensors that work together to adjust ankle stiffness, power, and position. One wearer was able to dance the rumba.

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The inventor wearing two of his own creations. Bryce Vickmark/MIT

The problem with many prosthetics that amputees use to replace lost legs and feet is that they don't provide a natural gait, which could contribute to osteoarthritis as patients age.

A bionic ankle designed by Hugh Herr, an associate professor of media arts and sciences at MIT, could overcome that problem. The artificial joint he's created consists of two microprocessors and six "environmental sensors." These work in concert to "adjust ankle stiffness, power, position, and damping thousands of times per second," according to an MIT News release.

The ankle activates at two key points. When the heel strikes the ground, the onboard computers adjust the stiffness in the joint. Next, algorithms create varying degrees of power based on the terrain to propel a wearer up and forward.

The effect can be akin to a power boost. When Herr first tried out a bionic leg his research group at the MIT Media Lab created, he said: "It was as profound as when you're walking through the airport and you hit the moving walkway. When you get off and return to normal walking, you're like, 'Walking is really strenuous and slow.' That's what it was like going from our powered system to passive conventional systems. So I knew there was magic there clinically."

In addition to creating a more natural gait and being more comfortable to wear, the computerized ankle also takes less time to adapt to. "Often, within minutes, a patient is walking around, even running around," Herr told MIT News.

Herr, who lost both his legs after a climbing accident in 1982, has been working on prostheses that mimic our natural movements for years. His company, Biom, has also produced an artificial knee that uses magnetism to control iron particles suspended in oil between steel plates to stiffen or relax as needed.

The first model of Herr's bionic ankle was released in 2011, and the current version, called the Biom T2 System, was brought to market in July of last year. It's gained recent attention because it was showcased during a TED talk last month that highlighted how smoothly the technology works. The ankle was used by Adrianne Haslet-Davis -- a professional dancer whose leg was partially amputated after the 2013 Boston Marathon bombings -- to dance the rumba. You can watch the moving performance below at 17:00.

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