Design and Mechanical Characterization of a Variable Stiffness ESR Foot Prosthesis.

In this article, we present MyFlex-ϵ, an ESR foot prosthesis equipped with a light and manually adjustable mechanism that allows for varying its stiffness in the sagittal plane, along with a systematic approach to calculate its rotation-stiffness curves. Through a design of experiment conducted numerically using a two-dimensional (2D) finite element (FE) model, calibrated experimentally, we determined a geometric parameter whose variation alters the sagittal plane stiffness of a prosthesis originally designed with invariable stiffness, MyFlex-δ. After building the mechanism and integrating it into MyFlex-δ to obtain MyFlex-ϵ, we determined the displacement-force curves of the latter through tests equivalent to the static tests specified in ISO 10328. Based on the experimental results, we built and calibrated the 2D FE model of MyFlex-ϵ to determine its rotation-stiffness curves in the sagittal plane. Comparing the rotation-stiffness curves obtained with the most compliant setting to the stiffest setting, we found stiffness variations of 119%, 122%, 138%, and 162% at plantarflexion angles of -5° and -2.5°, and dorsiflexion angles of 7.5° and 15°, respectively.