| Summary: | A lack of affordable energy storage and return (ESR) prosthetic feet compels amputees in low and middle income countries (LMIC) to adopt feet that do not meet the performance of ESR feet distributed in high-income countries. The GEAR Lab at MIT developed the LLTE design framework that systematically alters the geometry and stiffness of a foot to design ESR feet using a low cost material (Nylon 6/6) that enables close replication of able-bodied gait. LLTE-optimized foot prototypes have been tested in a long-term field trial in India and in gait labs in the United States. The feet demonstrated robustness to use for activities of daily living in India, and as good or better biomechanical performance and user satisfaction than commercial carbon fiber feet sold in the United States. However, these prototypes were not designed to be commercial products, but rather to demonstrate the viability of the LLTE design framework. The prototypes were CNC machined, resulting in a cost of >$200 per foot (a significant expense for many individuals in LMIC) and were only compatible with a single attachment system, thus limiting the potential for adoption by LMIC distributors, each with their own unique attachment system. This thesis aims to translate these proof-of-concept prototypes to commercial products by making the foot mass-manufacturable, easily adoptable by major distribution networks, and incorporating a few upgrades: improved aesthetics, coronal compliance, and a sandal toe.
The upgraded foot described in this thesis is comprised of a mass-manufacturable keel encased in a Polyurethane foam overmold resembling a biological footwith a ruggedized sole and two swappable attachment modules. The swappable attachment modules can be easily fastened to the foot to facilitate dissemination through the major distribution networks in LMIC. The first module ensures compatibility with the Bhagwan Mahavir Viklang Sahayta Samiti (BMVSS) attachment system, while the second module makes the foot compatible with both the ICRC attachment system and a pyramid adaptor. An upgraded architecture with a c-channel cross-section (to facilitate injection molding)was incorporated into the LLTE design framework and an optimization for a 60 kg person with a size 7 foot was run. The resulting optimized design has an LLTE value of ~0.1 and is thus expected to retain the high performance of previously tested LLTE prototypes.
The mass-manufacturable keel was mechanically tested to validate that it behaved as predicted, and over-molded by Vibram to result in a final prototype. The prototypes will be ISO tested and then used in a field trial to compare their performance to existing LMIC feet. Following the field trial, a sizing system for a product line (with a finite amount of feet) will be developed such that a large percentage of the population can be prescribed a foot that is either optimal or close-to-optimal for them. Commercialization of this upgraded foot would offer amputees an affordable ESR option that can readily be adopted by major distribution networks in LMIC.
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