When most of us walk over uneven ground, our feet respond to the dips and humps by flexing the ankle and moving the toes. Prosthetic feet typically don't do so, often resulting in falls. An experimental new model, however, uses a tripod-like assembly to react more like a real foot.

The device is being developed at Stanford University, by a team consisting of Assoc. Prof. Steven Collins, grad student Vincent Chiu and postdoctoral researcher Alexandra Voloshina.

Actually a complete lower-leg prosthesis, its foot incorporates three rubber contact points – two front "toes" and one rear "heel." As the wearer walks, integrated sensors detect the pressure (or lack of it) exerted on these points as the foot hits the ground. Utilizing electric motors, the toes/heel respond by independently moving up or down – in this way, they shift pressure between one another to maintain ground contact in the dips, while not letting the foot get tipped off-balance on the humps.

Additionally, an inertial measurement unit (an accelerometer/gyroscope combo) in the prosthesis is continuously able to determine where the foot is within the walking stride. This information is important, as it's used to dictate the manner in which the foot responds to the various terrain irregularities it encounters, plus it lets the toes spring the foot up at the end of each stride.

While the current version of the device has been successfully tested on a volunteer amputee, it was initially developed using a computerized and motorized emulator rig. That setup simulated a human walking gait, and provided feedback on how changes in the prosthesis would be perceived by a human user.

"One of the things we're excited to do is translate what we find in the lab into lightweight and low power and therefore inexpensive devices that can be tested outside the lab," says Collins. "And if that goes well, we'd like to help make this a product that people can use in everyday life."

A paper on the research was recently published in the journal IEEE Transactions on Biomedical Engineering.

The prototype can be seen in use, in the video below.

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