Influence of Infill Density on the Degradation and Tribological Performance of FDM-Printed PLA for Biomedical Applications

This study investigates the influence of physiological body fluids on the mass stability and tribological performance of polylactic acid (PLA) samples produced by Fused Deposition Modeling (FDM) 3D printing. Body fluid exposure was simulated using Dulbecco’s Modified Eagle Medium (DMEM) under controlled conditions. Black PLA filament was printed with three infill densities (15%, 20%, and 90%) and immersed in DMEM for 7 days at 37 ± 1 °C. Mass measurements revealed that lower infill densities resulted in significantly higher mass loss, with the 15% infill samples exhibiting the greatest reduction (5.07%), while the 90% infill samples showed negligible change (0.17%). Tribological testing using a CSM nanotribometer under loads of 5 mN, 500 mN, and 1000 mN demonstrated that infill density critically affects friction and wear behavior. The 90% infill samples exhibited the lowest wear volumes and the most stable tribological response, while the 15% infill samples showed degradation-dominated contact behavior. Although the friction measurements for the 15% infill samples were consistent, their interpretation should be approached with caution due to pronounced surface deterioration and debris-mediated sliding. This behavior is attributed to structural weakening caused by immersion in DMEM, which promoted material degradation and influenced the tribological response. These findings confirm the critical role of structural density in wear resistance. To the best of our knowledge, this is the first study to systematically investigate the combined effect of hydrolytic degradation and tribological behavior of FDM-printed PLA as a function of infill density under simulated physiological conditions. These findings provide a scientific basis for optimizing infill density in the design of PLA-based surgical instrument guides, where both degradation resistance and tribological performance under body fluid exposure are essential. The findings should be interpreted within the limitations of the experimental design.