Empirical Validation of an Auxetic Structured Foot With the Powered Transfemoral Prosthesis

The toe joint has been studied since it plays a critical role in human ambulation, such as stability, energy storage and propulsion. Despite its critical role, only a few studies have used and tested toe-jointed feet in powered prosthetic walking. In previous studies, we proposed 3D printable prosthetic feet with auxetic structures that provide human-like toe joint properties, termed a flat-toe (FT) foot and a curved-toe (CT) foot. The numerical simulation revealed that these feet could mimic the function of the biological toe joint, but they have not yet been validated in an empirical manner. In this study, we conducted a walking experiment with three subjects (i.e., two able-bodied and one amputee) using a powered prosthesis and two custom-designed prosthetic feet: the FT foot and CT foot. To evaluate the given feet, several metrics (e.g., joint kinematics/kinetics, ground reaction forces, and gait symmetry) were utilized. According to the results, the CT foot exhibited greater toe flexion, resulting in an earlier heel-off, a later toe-off, and a longer push-off duration when compared to the FT foot. Furthermore, less ground reaction forces were measured from both the prosthesis and intact sides, and a more symmetric gait was achieved with the CT foot. Another interesting finding was that the CT foot affected the user's thigh kinematics, leading to an improved gait phase estimation while walking. We concluded that the CT foot allowed for a more natural roll-over, resulting in better consistency and symmetry while walking with the powered prosthesis.