REActiv: Rugged prosthetic feet for active users

What it does

REActiv low-cost feet facilitate desired walking performance as good or better than costly commercial carbon fiber feet. They meet international standards for safety and have a life-like covering with a high-wear sole for rugged terrain and barefoot walking.

Your inspiration

Globally, 80% of amputees reside in regions where high-performance feet are prohibitively expensive or access to certified prosthetists and fitting time is limited. Current low-cost options do not meet the mobility and social needs of high-activity users. Replicating able-bodied walking and biological appearance is vital in these regions due to severe disability stigmas. Traction and durability are critical for walking barefoot in homes and on farm fields. Thus, a simple, robust foot that can be mass-manufactured at low cost and that enables amputees to walk with an inconspicuous, able-bodied-like gait with minimal fitting time is essential.

How it works

REActiv feet are designed using our novel Lower Leg Trajectory Error (LLTE) Framework, which quantitatively connects mechanical design (foot shape and stiffness) to biomechanical performance. REActiv feet are made of low-cost nylon plastic. They enable near able-bodied lower leg motion through energy storage and return (ESR), which is clinically recommended for active users. The foot acts like a spring, bending to store energy. As the loading moves towards the toe, the spring extends back to neutral, releasing stored energy, aiding the user with forward movement. The predictive design of REActiv feet means any patient of varying mass and size can receive a foot that maximizes their walking performance and comfort with minimal in-clinic iterative fitting. The cosmetic overmold of the foot was developed with Vibram, the global leader in shoe sole design, to ensure REActiv feet are aesthetically pleasing and provide durability for long-term rugged terrain use.

Design process

To ensure REActiv feet meet the needs of users, they were created in collaboration with the Jaipur Foot Organization, the largest global distributor of prosthetic feet. We interviewed 74 stakeholders (users, clinicians, manufacturers, and distributors) in India to construct a holistic techno-socioeconomic analysis. Stakeholder feedback prioritized replication of able-bodied walking, leading to the development of the LLTE Framework. User testing of LLTE-optimized REActiv feet (published in Nature Scientific Reports in 2022) showed they have more energy storage and as good or better replication of able-bodied walking, and strong user preference, compared to industry-standard carbon fiber feet. A given foot design can work for a range of body masses and sizes, which supports a finite, tractable product line of REActiv feet. The cost and size range of REActiv feet fit within Jaipur Foot’s current provision model. The REActiv foot meets international (ISO) safety, loading, and fatigue standards, is compatible with prosthesis attachment methods globally, and is mass-manufacturable. An ongoing pre-production field trial in India with Jaipur Foot will be used to validate that all stakeholders' needs were met and to elucidate the benefits of the REActiv foot over existing low-cost feet.

How it is different

REActiv feet are the most technologically advanced passive prosthetic feet ever made. They can stand up to the tough conditions of low-resource settings, be inexpensively mass-manufactured, and be quickly provided in clinical settings. REActiv feet are an accessible, low-cost product that enables walking performance similar to industry-standard carbon fiber prosthetic feet, which typically cost 10-20X more. Using the LLTE framework, REActiv feet are quantitatively designed to user body characteristics and mobility needs, providing users near-able-bodied walking performance without extensive, iterative, and costly design and fitting processes. Achieving a good fit requires time and resources often not available in low-resource settings; in contrast, a near-optimal REActiv foot can be provided by a technician simply using a person’s body mass and height. REActiv feet will transform access to comprehensive amputee care for active users in low-resource settings.

Future plans

REActiv feet are on the path to becoming a scalable, sustainable, and affordable product that meets the unique needs of users in low-resource settings. We're developing a product line by examining the trade-offs between biomechanical performance (best if optimized for each user) and practical considerations that may benefit from fewer sizes (manufacturing cost, distribution capacity, etc.). This will ensure that the feet can be adopted sustainably, while providing the best possible patient care. REActiv feet will be commercialized through Vibram and Jaipur Foot. Over 30,000 patients per year may soon have their mobility transformed.

Awards

National Science Foundation CAREER Award (2017); US Department of Defense PRORP grant (2017); DeFlorez Award, MIT (2019); Thomas Sheridan Prize, MIT (2019); Best Paper Award in ASME IDETC MR Conference (2021); A core project in attracting $36 million of philanthropic funding to MIT (2019 and 2024).