How infill percentage affects the ultimate strength of 3d-printed transtibial sockets during initial contact

Abstract

BACKGROUND: 3D printing is becoming more popular across many industries. The first step to safely introducing 3D printed sockets in to prosthetics is to conduct strength testing on these sockets. PURPOSE: This study tests how changing the infill percentage (the percentage of material between the internal and external socket wall) affects the strength of 3D-printed transtibial sockets. METHODS: A Fused Deposition Modelling (FDM) printer was used to print a total of nine transtibial (TT) sockets (three sockets at 30% infill, three sockets at 40% infill, and three sockets at 50%) using polylactic acid (PLA). A strength-testing apparatus measured, in Newtons (N), the maximum load the 3D-printed transtibial sockets could withstand at initial contact of the gait cycle. RESULTS: Based on the specific criteria outlined in this research project, all nine sockets exceeded the 4480N threshold set by ISO Standard 10328. Eight out of nine sockets failed at approximately double the force required with one socket (socket #2) failing at 5360N. Seven out of nine sockets failed at the medial popliteal region and two out of nine sockets failed at lateral mid socket region. Differences in infill percentage from 30%, 40%, 50% did not appear to influence strength of sockets. CONCLUSION: Strength of 3D-printed TT sockets needs rigorous testing to be deemed safe for patient use. More definitive research and a higher number of samples are required to investigate how a larger range of infill percentage can affect strength. Until all the requirements of ISO Standard 10328 are satisfied, the safety of using 3D-printed TT sockets in clinical practice are uncertain.