Effect of Geometry and Degradation Environment on In Vitro Degradation of FFF-Printed PLA/PHB Structures

Biodegradable polymers based on poly(lactic acid) (PLA) and polyhydroxybutyrate (PHB) are widely investigated for biomedical engineering applications, particularly for temporary implants and tissue scaffolds fabricated by additive manufacturing. However, their degradation behavior is influenced not only by material composition, but also by manufacturing-related parameters, geometric design, and environmental conditions. This study investigates the in vitro degradation behavior of PLA/PHB structures fabricated using fused filament fabrication (FFF). Degradation was evaluated under two model environmental conditions over a 45 day period. Changes in specimen mass and the evolution of degradation medium pH were monitored as a function of exposure time, specimen geometry, and infill density. The results revealed a progressive degradation process, with pH values decreasing to approximately 2.7–4.1 in physiological saline solution and increasing to 8.9–9.7 in urea solution, depending on specimen geometry and infill density. After 45 days of exposure, the relative mass loss reached approximately 25–32% for type A specimens and 29–41% for type B specimens. The results revealed distinct differences between degradation environments and specimen geometries, while differences related to infill density partially overlapped within the investigated range. The findings indicate that the degradation behavior of additively manufactured PLA/PHB structures cannot be interpreted solely based on material composition, but should be considered in the context of manufacturing strategy and structural design. These results provide useful insights for the design of biodegradable polymer components with more predictable degradation behavior.