Material Selection and Structural Redesign of a 3D Printed Four Bar Mechanism for Prosthetic Joint Motion

Abstract

Material selection for a printed joint mechanism depends on structural response, recovery and assembly conditions. This study combines an exploratory comparison of polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) specimens with the redesign of a four bar mechanism intended to demonstrate prosthetic joint motion. Fourteen distinct structural loading conditions and four spring conditions were analyzed at applied masses of 0.5 and 1.0 kg. Recorded displacement and uncalibrated voltage endpoints were retained separately. Apparent stiffness, paired displacement differences and origin constrained spring fits were calculated without treating loading levels as replicates. At 1.0 kg, the PLA plate and unrestrained double arch displaced 8.26 and 3.57 mm, respectively. ABS plate displacement exceeded PLA by 33.7%, whereas the corresponding difference for unrestrained arches was 10.4%. Fitted spring stiffness was 216.4 N/m for ABS and 380.9 N/m for PLA. ABS showed approximately 1 mm residual shortening, compared with 3–4 mm for PLA. A prototype combined ABS moving components, PLA supports, 4 mm interlink separation and shaft and pin location. Qualitative observations indicated smoother motion and no visible powder during the demonstration. The results support component level screening and assembly redesign; calibrated measurements, repeated tests and quantified wear remain necessary for prosthetic performance assessment.