Numerical design and experimental validation of a 3D-printed composite energy-storage-and-return prosthetic foot

The currently available prosthetic feet for amputees with high ambulation potential are difficult to access by the majority of amputees due to their high cost. This is especially since the majority of amputations are found among people with low economic status. This is because such prostheses are mostly made by a time-consuming approach (i.e., lamination) and expensive materials (i.e., carbon fiber composites). Relying on additively manufactured composites can possibly lead to low-cost, yet high-functioning prostheses to serve potentially active amputees. This work aimed to develop continuous fiber-reinforced additively manufactured prostheses and validate their ability to store and return elastic energy, which indicates their comfort and responsiveness. Mechanical tests replicating the critical stages of the gait cycle were performed on the prostheses, which enabled the estimation of the Energy Storage and Return (ESR) capability. Test results were assessed based on pre-defined design criteria and allowed iterating upon different designs until the criteria were met. Finite element simulations were performed and validated experimentally to allow more efficient design iterations. The versatility of 3D printing was utilized to introduce new design solutions despite their geometrical complexity, which enabled solving for the limited functionality observed in the material. Eventually, four designs were prototyped and tested, with the final one completely meeting the design criteria, reaching a stiffness of 74 and 43 N/mm, and an energy return of 88 % and 79 % under the heel and forefoot loading conditions, respectively. This work thus demonstrates the potential of 3D-printed prosthetic feet with qualified ESR performance.