A functional approach towards the design, development, and test of an affordable dynamic prosthetic foot

Humanitarian actors involved in physical rehabilitation, such as the International Committee of the Red Cross (ICRC), usually provide their beneficiaries with lower-limb prostheses comprising Solid Ankle Cushion Heel (SACH) feet as these are considered appropriate (price, durability, low profile to fit a majority of patients, appearance) and reliable for all ambulation levels. However, individuals in low-resource settings having higher ambulation abilities would greatly benefit from dynamic prosthetic feet with improved biomechanics and energy storage and release. Some attempts tried to address this increasing need (e.g. Niagara Foot) but most products proposed by large manufacturers often remain unaffordable and unsuitable to the context of low-resource settings. The design requirements and a price target were defined in partnership with the ICRC according to their initial assessment and used as a starting point for the development process and related technological choices. Numerical simulation and modeling were used to work on the design and to determine the required materials properties (mechanical, chemical, wear), and a cost modeling tool was used to select suitable materials and relevant processing routes (price vs. performance). A prosthetic foot comprising an internal keel made of composite materials, a filling foam, and a cosmetic shell with a foot shape was developed. Manufacturing processes meeting the cost criteria were identified and prototype feet were produced accordingly. These were successfully tested using a compression testing system before gait analyses were performed in the laboratory with non-amputees wearing testing boots. After validation in laboratory conditions, the prototype foot was tested in the field (Vietnam) with 11 trans-tibial unilateral amputees, who showed an increased mobility compared with the SACH foot. The collaboration of different research fields led to the development of a prosthetic foot which met the technical requirements determined by the ICRC's specific needs in its field of operation. The materials and selected production processes led to a manufacturing cost of less than 100 USD per part.