Low-Cost, Passive Prosthetic Foot Helps Users Walk with Natural Gait

MIT researchers have developed a new prosthetic foot that is low-cost and can be customized to help a wearer walk with a normal gait.

Most of the time, current prosthetic limb functionality is focused on giving users more robotic and bionic features to provide natural movement. Unfortunately, this kind of innovation usually comes at a high financial cost to the user.

Researchers at MIT have gone in the other direction, developing a simple, passive prosthetic foot that is low-cost and can be customized to an individual to allow him or her to walk naturally. Mechanical engineers at the university have developed the foot, which can be tuned to a user depending on his or her body weight and size. This allows a person to walk with a natural gait when using the prosthetic, they said.

MIT prosthetic foot
MIT researchers have developed a low-cost prosthetic foot that can be customized to help those wearing it walk with a normal gait. (Image source: MIT researchers)

Taking a Stroll

“[Walking] is something so core to us as humans, and for this segment of the population who have a lower-limb amputation, there’s just no theory for us to say, ‘Here’s exactly how we should design the stiffness and geometry of a foot for you, in order for you to walk as you desire,’” said Amos Winter, associate professor of mechanical engineering at MIT and part of the research team in an MIT press release. “Now we can do that. And that’s super powerful,” he added.

Researchers based the prosthetic on a design framework that provides a quantitative way to predict a user’s biomechanical performance, or walking behavior, based on the mechanical design of the prosthetic foot.

According to the MIT release, the team was inspired to develop the foot after an experience Winter had soon after joining the MIT faculty. He spent time in Jaipur, India, with an organization that donates simple prosthetics to the local population.

Heavy Feet

“They’ve been making this foot for over 40 years, and it’s rugged, so farmers can use it barefoot outdoors, and it’s relatively life-like, so if people go in a mosque and want to pray barefoot, they’re likely to not be stigmatized,” he is quoted in the release. “But it’s quite heavy, and the internal structure is made all by hand, which creates a big variation in product quality,” he said.

While the foot lived up to the job it needed to do for people wearing it, Winter realized that there could be improvements in its quality and design, which the organization asked him to provide.

“At that point, we started asking ourselves, ‘how should we design this foot as engineers?’” said Winter. “’How should we predict the performance, given the foot’s stiffness and mechanical design and geometry? How should we tune all that to get a person to walk the way we want them to walk?’” The result is the prosthetic designed by the MIT team, which reported on their work in the ASME Journal of Mechanical Design.

Relationships

The team took a different approach to designing a foot than is typical by studying the relationship between the foot and the lower leg. Instead of designing a prosthetic foot to replicate the motions of an able-bodied foot, the team aimed to design a prosthetic that would produce lower-leg motions similar to those of an able-bodied person’s lower leg as they walk.

“This really opened up the design space for us,” Winter said. “We can potentially drastically change the foot, so long as we make the lower leg do what we want it to do in terms of kinematics and loading, because that’s what a user perceives.”

Through their modeling and experimentation, the team figured out how to produce a prosthetic foot that generates leg motions similar to able-bodied walking, they said. They produced several prototype feet from machined nylon—chosen for its energy-storage capability—for volunteers in India who agreed to test them.

“What’s cool is, this behaves nothing like an able-bodied foot—there’s no ankle or metatarsal joint—it’s just one big structure, and all we care about is how the lower leg is moving through space,” Winter said. “Most of the testing was done indoors, but one guy ran outside, he liked it so much. It puts a spring in your step.”

Partner

The team already has found a commercial partner for its prosthetic in an Italian company called Vibram, which manufactures rubber outsoles. Vibram is designing a life-like covering for the team’s prosthesis that also should give the foot some traction over muddy or slippery surfaces, researchers said.

The next step for the team is to test the prosthetic and covering on volunteers in India this spring, and move forward from there, they added in the MIT release.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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