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Jaipur Foot gets makeover by MIT
July 15, 2018, 4:40 pm

In recent years, prosthetic limbs have taken great strides in technological advancements giving amputees a range of bionic options, including artificial knees controlled by microchips, sensor-laden feet driven by artificial intelligence, and robotic hands that users can manipulate with their minds. But such high-tech advancements have come with an equally high price-tag that makes them unaffordable for many amputees.

Now MIT engineers with funding from the Tata Center for Technology and Design in India have developed a simple, low-cost, passive prosthetic foot that they can be tailored to fit individual amputees. By inputting a user's body weight and size, the researchers can tune the shape and stiffness of the prosthetic foot so that user’s walk resembles that of an able-bodied person. If mass-produced the new foot is expected to cost at least ten times less than existing products.

In 2012, Jaipur Foot, a manufacturer of passive prosthetic foot in India, which donates more than 28,000 prosthetics each year to amputees in India and other countries in the developing world, approached MIT with their problem. For over 40 years the organization had been making artificial foot that was rugged enough to be worn by farmers toiling in their fields while being relatively life-like in appearance so that wearers were not stigmatized. But the foot, which was hand-made from wood was heavy and the quality was not consistent.

On receiving, Jaipur Foot’s request to design a better, lighter foot that could be mass-produced at low cost, the MIT team first looked at ways to quantitatively relate a prosthesis' mechanical characteristics to a user's walking performance — a fundamental relationship that had never before been fully codified.

Instead of designing a prosthetic foot to replicate the motions of an able-bodied foot, the team looked to design a structure that would produce lower-leg motions similar to those of an able-bodied person's lower leg as they walk.

To do this, the researchers consulted an existing dataset comprising measurements of steps taken by an able-bodied walker with a given body size and weight. With each step, previous researchers had recorded the ground reaction forces and the changing center of pressure experienced by a walker's foot as it rocked from heel to toe, along with the position and trajectory of the lower leg.

The team then developed a mathematical model of a simple, passive prosthetic foot, which describes the stiffness, possible motion, and shape of the foot. They plugged into the model the ground reaction forces from the dataset, which they could sum up to predict how a user's lower leg would translate through a single step. With their model, they then tuned the stiffness and geometry of the simulated prosthetic foot to produce a lower-leg trajectory that was close to the able-bodied swing.

The team then sought to identify an ideal shape for a single-part prosthetic foot that would be simple and affordable to manufacture. The researchers mixed and matched various shapes to eventually evolve a model with the lowest possible lower leg trajectory error. By tuning the stiffness and shape of this model to match a person’s body weight and size the researchers were able to produce a prosthetic foot that could generate leg motions similar to able-bodied walking. The prostheses were made from machined nylon, a material chosen for its energy-storage capability, and tested out on several volunteer amputees in India.

The team has now partnered with Vibram, an Italian company that manufactures rubber outsoles — flexible hiking boots and running shoes that look like feet. The company is designing a life-like covering for the team's prosthesis, that will also give the foot some traction over muddy or slippery surfaces. The researchers plan to test the prosthetics and coverings on volunteers in India this spring.

A common passive foot in the US market made of carbon fiber costs anywhere between $1,000 to $10,000, by contrast the custom-designed nylon Jaipur Foot could be available for a less than a tenth of that price. The simple prosthetic foot design can also be a much more affordable and durable option for populations such as soldiers who want to return to active duty or veterans who want to live an active lifestyle.


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