Impact of biodegradation on the mechanical and fatigue properties of 3D-printed PLA bone scaffolds

A proper degradation rate of bone scaffolds ensures optimal mechanical support and effective tissue regeneration. The present study examines the degradation effects of simulated body fluids (SBF) on the compressive and fatigue strength of 3D-printed PLA bone scaffolds. Scaffolds with varying surface-to-volume (S/V) ratios and identical porosity (60 %) were immersed in Hanks' solution for a maximum period of 30 days. Static and dynamic compression tests were performed at different immersion times to assess how S/V ratio influences the degradation process. CT images showed that scaffold pore structure remained interconnected after biodegradation, with no significant change in strut thickness or dry weight. Results also indicated that while the compressive strength and modulus of scaffolds remained largely unchanged during biodegradation, their fatigue resistance reduced significantly. This reduction in fatigue resistance was attributed to the embrittlement of PLA material caused by crystalline phase changes during degradation. Microscopic images and X-ray analysis revealed the brittle fracture of scaffolds at the diagonal shear plane and the presence of SBF's salts within the scaffold material. Scaffolds with higher S/V ratios exhibited a greater decrease in fatigue resistance. The failure cycle of scaffolds with S/V ratios of 3.4, 2.4, and 1.9 mm^-1 decreased by 77 %, 76 %, and 60 %, respectively after 30 days of biodegradation. Higher S/V ratios increased the surface exposure to the corrosive media. This resulted in higher water absorption, which subsequently intensified the embrittlement of the scaffolds.