3D-Printable Toe-joint Design of Prosthetic Foot

The toe joint is one of the important design factors for prosthetic foot. The toe joint provides feeling of springiness in toe-off step and its stiffness affects the ankle kinematics in robotic prosthesis during gait cycle. Moreover, since human toe joints exhibit nonlinear toe torque-angle behavior, these nonlinear characteristics should be considered when the prosthetic foot is designed to mimic human gait behavior more naturally. To implement nonlinear toe joint behavior without additional mechanical components such as actuators, sensors and electronic circuits, the structural foot design should be considered. In this study, the auxetic structure with negative Poisson’s ratio was applied to the toe joint design and bending space was considered for stable bending deformation of prosthetic foot. Finite element analysis was performed to analyze the designed toe joint behavior. The mechanical properties of onyx material which is a short carbon fiber reinforced nylon filament were applied in the FE simulation, considering 3D printing manufacturing. The torque-angle graph for toe joint from a result of FEA was compared with the human toe torque-angle behavior. Consequently, the nonlinear toe stiffness characteristics were implemented through a structured single-part prosthetic design.