Rugged Cosmetic Prosthetic Foot

2016-2018

As part of my PhD project, I developed a simulation based prosthetic foot design framework that creates customized passive prostheses to enable users to best replicate natural walking motions.

This framework was used to create affordable, high-performant, mass-manufacturable prostheses for emerging markets' users that were field piloted in India in 2017 and 2018. These field pilot were conducted along a successful clinical study showing that our plastic, energy storage and return (ESR), optimized feet performed as well as conventional carbon fiber ESR feet for less than one twentieth of the costs and development time.

With these effort, we designed mass-manufacturable, and affordable energy-storage and return prostheses that are being field tested with our partners in India. We used the LLTE to design a single part foot with a life-like cosmetic cover that can be mass produced in India. We are currently conducting clinical trials with the help of the BMVSS. Subjects will use our prototype feet for all their activities of daily living over a month-long period, and their feedback will be used to further refine our design. In the future, we will apply the LLTE to other ambulatory tasks such as running and ascending stairs, to create high performance, multi-purpose, low-cost prosthetic feet that can be mass produced in India and throughout low and middle income countries.

This work was funded by the MIT Tata center and the US department of defense orthotics & prosthetics outcomes research program. It was presented at the International Society of Prosthetics and Orthotics (ISPO) in 2019. More details can be found below, on the GEAR Lab's webiste and in the following papers.

Contributions

Human Centered Design

Multi-Material Structural Analysis

Manufacturing

Field Pilots

Collaborations

W. Brett Johnson

Vibram Corporation

Awards

MIT Thomas Sheridan Prize for Excellence in Human Machine Interaction Research (2019)

Patent No. US2020/0375763A1

The need for affordable, high performant feet

More than 80% of the lower limb amputee population live in low and middle income countries accounting for more than 30 million people. Only 10% have access to prosthetic devices but most emerging markets' amputee use inadequate limbs that require significantly more effort to walk, exhibit unnatural walking motions and are subject to social stigmas preventing them from employment and independent living. There is a gap between the high performance prosthetic feet in the United States that cost thousands of dollars and the affordable prostheses available in the low and middle income that lack quality, durability, and performance.

Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS), one of the largest distributor of these affordable prosthetic feet, started a collaboration with us, at the Global Engineering and Research Lab at MIT, to design an updated version of their Jaipur Foot. The original Jaipur Foot’s success was due to its lifelike look, flexibility, low-cost of $10 and extreme durability. The goal of this project was to create a foot that would be much lighter, can be mass-manufactured, meets international testing standards, is compatible with other prosthetic equipment, and matches the durability of the current foot.

High-end carbon prosthesis (Variflex, Ossur)

Affordable wood and rubber foot (Jaipur Foot)

Free-body diagram of the prosthetic foot and lower leg during a step

Integrating a single-part foot design into a rugged overmold for high durability and life-like aesthetics.

Through our partnered NGO in India, we conducted extensive user and stakeholder interviews as well as multiple prototype testing to understand the user’s perception and walking pattern on prosthetic limbs as well aslocal manufacturing, cultural and distribution constraints. This information enabled us to develop a novel design metric called the lower leg trajectory error (LLTE).

The LLTE value predicts the performance of any given passive prosthetic foot design before building it by combining structural and biomechanical analyses of the amputee's lower leg. The LLTE value evaluates how closely a prosthetic foot can enable the user to replicate a target walking pattern. Namely, it compares the prosthetic side predicted lower leg trajectory during a step to a reference set of target lower leg motion when the prosthetic foot is subject to reference walking loads. The LLTE value is a single value score that provides a quantitative understanding of how the mechanical design of the passive prosthetic foot affects the user’s walking pattern gait.

Extensive field testing demonstrated the durability and high performance of our rugged cosmetic foot.

A set of user-specific prosthetic feet made out of Nylon 6/6 were designed using the LLTE framework to replicated able-body flat ground walking pattern. Nylon 6/6 was chosen as it has high strain energy density characterisitics, is easy to manufacture, low viscous dissipation and is low-cost. These prototype ESR prosthetic feet have a material cost in the order of tens of dollars.

These LLTE optimal prosthetic feet prototypes were tested and validated in a motion lab and in the field with below-knee prosthetic users. Through gait testing, the LLTE prosthetic feet enabled closer replication of the target walking motion and loading, increased energy storage and return, and higher user preference scores than control carbon fiber feet. In addition, extensive user testing in India suggested that the LLTE prosthetic feet increased the walking speed of users and reduced walking effort.