Osteoimmunomodulation unveiled: Enhancing bone regeneration with 3D-printed PLLA/β-TCP/CS scaffolds

Bone tissue engineering shows great potential for repairing large segmental bone defects; however, the immune response to biological scaffolds remains a critical factor influencing bone regeneration. Despite this, there is a paucity of studies investigating the effects of biomaterial components and their degradation products on macrophage polarization and the subsequent process of bone regeneration. This study investigates the role of macrophages in osteogenesis and angiogenesis induced by PLLA(Poly-L-Lactic Acid)/β-TCP(β-Tricalcium Phosphate)/CS(Calcium Sulfate) bone scaffolds in vitro and in vivo. Various PLLA/β-TCP/CS scaffolds were fabricated via 3D printing and characterized for their physicochemical properties. The effect of P/T15/S15 (PLLA/β-TCP/CS scaffold containing 15 % β-TCP and 15 % CS) on macrophage polarization and the secretion of VEGF and BMP-2 was assessed in vitro. Additionally, the conditioned medium derived from macrophages stimulated with P/T15/S15 was evaluated for its effects on the migration and osteogenic differentiation of bone marrow-derived stem cells (BMSCs), as well as the angiogenic potential of human umbilical vein endothelial cells (HUVECs). In vivo, the relationship between macrophage polarization and osteogenesis was examined in a rabbit tibia segmental defect model. The results demonstrated that the 3D-printed P/T15/S15 scaffold exhibited favorable physicochemical properties and compatibility with BMSCs and RAW264.7 macrophages, while not disrupting BMSC apoptosis. P/T15/S15 promoted polarization of M0 macrophages towards the M2 phenotype, resulting in an increased secretion of the anti-inflammatory cytokine IL-10, as well as growth factors such as VEGF and BMP-2. However, it did not suppress TNF-α levels. Additional, the conditioned medium derived from P/T15/S15-stimulated macrophages significantly enhanced the osteogenesis of BMSCs, their migration, and the angiogenesis of HUVECs. In the rabbit model, P/T15/S15 facilitated bone regeneration by promoting macrophage polarization towards the M2 phenotype and reducing inflammation. This study highlights that P/T15/S15 regulates macrophage polarization, enhances osteogenesis and angiogenesis, and positions itself as a promising candidate for bone tissue engineering through osteoimmunomodulation.