Study of composite elastic elements for transfemoral prostheses: the MyLeg project

A foot prosthesis has the function of replacing the corresponding amputated limb. Everything from the design to the use of a leg prosthesis involves a long and complex process that includes several areas of study. The complexity of the process also stems from the need to provide a prosthetic device that is suitable for that specific user. The most common foot prostheses commercially available are the ESR feet. ESR stands for Energy-Storing-and-Releasing. They are characterized by elastic elements in composite material with the function of storing energy. The design of these prostheses requires optimization not only from the point of view of mechanical strength, but also in terms of stiffness, being characterized by elastic elements. In this thesis, a systematic design methodology is presented. It has been developed to allow the speeding up of the design part and reduce prototyping, with the consequence of reducing development time and costs. To validate the methodology, a new model of ESR prostheses characterized by a spherical ankle joint has been optimized for five different weight categories, produced and clinically tested. However, an ESR prosthesis is optimized for a specific stiffness. Daily activities, such as walking on a flat or inclined surface, or going up and down stairs, require different stiffness. For this reason, the next step that was taken in this thesis was to develop an ESR foot with variable stiffness. Once again, the design methodology was used for its development. Several versions of the same design have been prototyped, tested and improved from one version to the next, moving from a manually adjusted version to a semi-active one. The final version of the foot obtained is a semi-active variable stiffness ESR foot characterized by a spherical ankle that allows adaptations to the ground conditions. Immediate future study concerns clinical tests with users.