Thermal post-processing driven surface smoothing of 3D-printed PLA-Hydroxyapatite scaffolds for bone tissue engineering

PLA-Hydroxyapatite bone scaffolds play a significant role in bone tissue repair and regeneration due to their excellent biocompatibility and degradability. The widespread application of selective laser sintering (SLS) technology has met the demand for patient-specific customization. However, adjacent particles in SLS-produced implants often exhibit incomplete fusion at their contact edges, resulting in the rough surface. The rough surface can induce robust immune responses in adjacent tissues via complement activation and inflammatory cell recruitment, leading to inflammation and fibrosis and posing challenges for clinical applications. In this study, a thermal treatment method was proposed to solve the problem. By exploiting the rheological responsiveness of PLA-Hydroxyapatite composites to temperature, the scaffold was heated at temperatures near its rheological transition, enabling surface tension-driven fusion of the melt interfaces and achieving a smooth surface. However, elevated temperatures intensified molecular thermal motion in PLA-Hydroxyapatite, leading to large-scale depolymerization and gravitational collapse of the scaffold. To explore the mechanism, a thermofluidic coupled phase-field simulation was employed to determine the critical conditions for scaffold remelting and reshaping, as well as gravitational collapse. Cell adhesion and proliferation, demonstrated that appropriate thermal treatment not only reduced friction between the scaffold and human tissues but also promoted osseointegration. This work significantly enhanced the biocompatibility and osseointegration capability of the scaffold, offering safer and more effective clinical treatments for bone defect repair and tissue engineering applications.