CCL2-functionalized composite scaffolds enhance bone regeneration via synergy of osteogenesis and angiogenesis

Background: Chemokine (C-C motif) ligand 2 (CCL2) enhances bone regeneration when integrated into a composite scaffold and show promise for clinical applications in persistent bone defects. Methods: A composite biodegradable scaffold was fabricated using 3D bioprinting with a polylactic acid-glycolic acid copolymer (PLGA) and β-tricalcium phosphate (β-TCP). Gelatin methacrylate (GelMA) hydrogel was used as carrier of CCL2 to enable prolonged release. The scaffolds were immersed in GelMA solution with or without CCL2. In vitro experiments were conducted to analyze the kinetics of CCL2 release and its influence on the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSC). Scaffolds PLGA/β-TCP (PT), GelMA/PLGA/β-TCP (GPT), and CCL2-conjugated GelMA/PLGA/β-TCP (CGPT) were implanted into a rat femoral defect model (n = 8) and analyzed to evaluate bone mass regeneration at 4 and 8 weeks. Results: CGPT exhibited a prolonged release period lasting 30 days. In vitro, CCL2 significantly promoted BMSCs proliferation (p < 0.05) and the formation of mineralized nodules, and it markedly increased tube formation in HUVECs. In the femoral defect model, bone mineral density and volume fraction in the CGPT group increased compared to the controls (PT, GPT, and control) after implantation. Histological analysis revealed enhanced new bone formation, and integration of the scaffold with surrounding tissue in this group. The expression of osteogenic markers (runt-related transcription factor 2 (Runx2), osteocalcin (OCN), and osteopontin (OPN)) and the angiogenic factor vascular endothelial growth factor (VEGF) significantly increased at the defect site within the CGPT group. Conclusions: Scaffolds made from a composite of GelMA-infused 3D-printed PLGA/β-TCP incorporated with CCL2 greatly enhance osteogenesis and angiogenesis to facilitate bone healing.