Design of 3D printable prosthetic foot to implement nonlinear stiffness behavior of human toe joint based on finite element analysis

Hui-Jin Um,Hak-Sung Kim,Heon-Su Kim,Pilwon Hur,Woolim Hong

doi:10.1038/s41598-021-98839-3

Abstract

Toe joint is known as one of the critical factors in designing a prosthetic foot due to its nonlinear stiffness characteristic. This stiffness characteristic provides a general feeling of springiness in the toe-off and it also affects the ankle kinetics. In this study, the toe part of the prosthetic foot was designed to improve walking performance. The toe joint was implemented as a single part suitable for 3D printing. The various shape factors such as curved shape, bending space, auxetic structure, and bending zone were applied to mimic human foot characteristics. The finite element analysis (FEA) was conducted to simulate terminal stance (from heel-off to toe-off) using the designed prosthetic foot. To find the structure with characteristics similar to the human foot, the optimization was performed based on the toe joint geometries. As a result, the optimized foot showed good agreement with human foot behavior in the toe torque-angle curve. Finally, the simulation conditions were validated by comparing with human walking data and it was confirmed that the designed prosthetic foot structure can implement the human foot function.

Highlights

Toe joint is known as one of the critical factors in designing a prosthetic foot due to its nonlinear stiffness characteristic
The ankle and toe joint were implemented by using series elastic actuators and they found that adding the toe joint could reduce the energy consumption in the prosthetic foot[10]
We proposed the 3D printable foot structure by using short carbon fiber reinforced polymer to mimic human foot characteristics, especially the toe stiffness

Summary

Introduction

Toe joint is known as one of the critical factors in designing a prosthetic foot due to its nonlinear stiffness characteristic. Human subjects testing has shown that greater energy storage and return could be obtained with a lower stiffness setting[14] All of these studies attempted to mimic the human gait behavior by implementing a human-like toe joint in the prosthetic foot. Their designs were complex to be manufactured and had challenges implementing nonlinear stiffness characteristics. To find the structure with characteristics similar to the human foot, the optimization was performed based on the toe joint geometries Simulation results such as toe/ankle kinematics, and COP were compared with human data to validate the FEA conditions

Methods

Results

Conclusion