Feasibility of prosthetic knee construction using 3D printed lattice structures
Moser, Timothy Long
The World Health Organization (WHO) estimated in 2005 that 30 million people in the developing world need a prosthetic. Estimates indicate this figure will double by 2050, yet only 5% of amputees have access to prosthetic options [1,2]. With nearly one in five South African citizens currently living below the international poverty value of R28.27 a day  (approximately $1.90) it can be assumed that there is a significant need within the country for low-cost, lower-limb prosthetics. Through the development 3D printed prosthetics, the amputee community has received bespoke, low-cost devices in turn improving quality of life. Through open-source sharing, 3D printing volunteers around the world have produced 3D printed prosthetics and have enabled individuals in developing countries to regain functionality, mobility, and to assimilate into their communities. However, current research of a 3D printed prosthetics is focused on feet, arms, and hands while 3D printed knee joint (PKJ) solutions are limited. In this research report, a low-cost, single-axis PKJ is designed specifically for fused filament fabrication (FFF) 3D printing and implements a conformable lattice structure. Literature review was performed to outline design considerations that must be met when developing a PKJ and identifies best practices for FFF 3D printing. The PKJ assembly was first modeled in Autodesk Fusion 360 software for both visualization and dimensioning of the design. nToplogy software was utilized to generate lattice structures within the PKJ and was used to characterize the lattice by its stiffness. The characterization model allows for specific optimization of the lattice parameters based off the user’s weight to create structure properties such as responsive or cushioned. Furthermore, this report simulated the designed PKJ against industry load requirements and experimentally tested 3D printed prototypes. Simulation data indicated no part failure, however, experimental testing of the 3D printed parts demonstrated failures unforeseen through simulation via layer delamination and bolt shear tear-out. This report demonstrated successful fabrication of complex lattice structures via FFF 3D printing despite the relative manufacturing limitations of FFF when compared to other 3D printing processes. While this research project’s designed PKJ failed to meet performance requirements, this report serves to transfer knowledge and motivate the prosthetic research community to develop a PKJ that can be produced with a low-cost desktop printer.
A research report submitted in partial fulfilment of the requirements for a Master of Science in Engineering in the Faculty of Engineering and Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, 2022