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Photo by Kat Schleicher Photo by John Nienhuis

PUTTING THE BRAIN IN CHARGE OF PROSTHETIC LOWER LIMBS By Chris Jenkins

After more than two decades’ worth of work on devices to help amputees, Dr. Barbara Silver-Thorn is perhaps more enthusiastic than ever about new developments in the field. “Oh, there’s really exciting stuff happening as far as prosthetics right now,” says Silver-Thorn, an associate professor of biomedical and mechanical engineering.

While new electronic interfaces that allow amputees to control complex prosthetic arms with signals from their brains tend to get the most attention from the public, similar technology also is quietly making its way to prosthetic legs. Lower-limb prosthetics and orthotics are a primary research area for Silver-Thorn, and she currently is collaborating with a team that includes Dr. Philip Voglewede, P.E., assistant professor of mechanical engineering, and Dr. Scott Beardsley, assistant professor of biomedical engineering, on the development of a motorized ankle for a prosthetic leg. While typical prosthetic legs have a passive mechanical ankle, the system under development at Marquette uses an active powered ankle with a motor. The motor lifts the prosthetic foot’s toes upward while the user is taking a step, keeping the foot from scraping the ground. The motor also simulates the way calf muscles naturally push off during walking, a function that can enhance a user’s endurance for longer distances, increasing their activity level. Voglewede’s early versions of the ankle used sensors on the prosthetic foot to make it function. Silver-Thorn and others now are researching the possibility of using signals that amputees’ brains still send to the severed muscles to make the ankle perform even better. “Even though their limb is gone, they often still can perceive their phantom limb, toes or ankles,” Silver-Thorn says. Silver-Thorn developed a test protocol and collected initial data from lower-limb amputees to demonstrate that sensors in a prosthetic socket can read the electrical activity still generated by severed muscles. “We optimized muscle sensor locations ... and then had amputee subjects visualize ‘pushing off’ with their phantom foot-ankle, as they had done with their intact limb prior to amputation,” Silver-Thorn says. “The objective of this protocol was to see if minimal training might result in robust muscle control signals that were similar to that for the intact or sound limb.” Using data she acquired and computer code she wrote, Silver-Thorn continues to collaborate with Voglewede, Beardsley and undergraduate students to develop a preliminary algorithm to control the ankle during walking — and even to guide it through more complex activities, such as climbing stairs. The group has submitted a proposal for federal funding to advance this part of the project. (Voglewede’s initial work to develop his active foot-ankle received federal support.) And while it isn’t the only research she’s conducting — she’s also working on a study of hockey players’ skating techniques in a partnership with a sporting goods manufacturer, and helping prepare the next generation of STEM teachers through her work with the Noyce Scholar program — her work with amputees is especially meaningful. Through her research, Silver-Thorn hopes to develop new technology and find ways to make it cost-effective for people in need. “There are some really cool things out there,” she says. “There’s a small population that can benefit in general, and an even smaller population that can afford it. You hate to have quality of life be a function of cost.”

Photo by Kat Schleicher

It's Silver-Thorn’s collaboration with several other professors that puts Marquette right in the middle of it.

Collaboration with Dr. Barbara Silver-Thorn (top left) has opened up new possibilities for using residual muscle signals to guide the movement of the powered prosthetic ankle developed by Dr. Philip Voglewede (above).

A multidisciplinary team is developing an algorithm to control the ankle during walking, even climbing stairs.

marquette university college of engineering

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Marquette Engineer 2013  

Marquette Engineer 2013