Effect of humidity on the stiffness and hysteresis of composite 3D Printed paediatric prosthetic foot coupon samples

This research investigates the impact of ageing and humidity on the mechanical properties, specifically stiffness and hysteresis, of composite 3D printed paediatric prosthetic foot coupon samples. Understanding these effects is essential for ensuring the durability and performance of 3D Printed prosthetic devices in varying environmental conditions. A Markforged Mark 2 (Markforged Inc., Massachusetts) 3D printer was used to fabricate samples from Onyx, reinforced with carbon fibre. Compression testing was conducted, adapted from the ISO 10328 standard to evaluate the samples under conditions that simulate real-world use. Microscopy analysis was used for visual inspection of the samples post-testing. Results indicate that both stiffness and hysteresis properties of the composite samples deteriorate significantly with increased humidity exposure. Stiffness of the samples decreased by approximately 30% after 90 days, and hysteresis efficiency declined from 83% to 72%, reflecting a reduction in energy return capability. These findings highlight the importance of understanding how the mechanical properties of composite 3D printed paediatric prosthetic components change over time, especially under varying environmental conditions. The observed reductions in stiffness and hysteresis efficiency demonstrate the negative impacts on prosthetic performance and durability, and the effect this could have on the end user. This research also emphasises the necessity of investigating methods to maintain the initial mechanical properties, such as developing protective coatings or improved material formulations, to ensure the long-term reliability and effectiveness of paediatric prosthetic devices.