3D-printed BaTiO₃-modified PCL/β-TCP scaffolds with multimodal optimization for enhanced critical-size bone...

Critical-size bone defects (CSDs) remain a major clinical challenge. Although three-dimensional (3D) printing enables precise structural control and defect-specific scaffold fabrication, conventional polymer-based scaffolds often exhibit insufficient mechanical strength and limited osteogenic activity. In this study, poly(ε-caprolactone)/β-tricalcium phosphate (PCL/β-TCP) scaffolds containing 0, 1, 2, 4, or 8 wt% barium titanate (BaTiO₃, BT) were fabricated by direct ink writing. Their rheology, microstructure, mechanical properties, local electromechanical response, cytocompatibility, angiogenesis-related activity, osteogenic differentiation, and bone regeneration in vivo were evaluated. All formulations exhibited suitable printability and regular porous structures. Moderate BT incorporation increased surface roughness and mechanical strength, with compressive strength remaining within the range of human cancellous bone. Piezoresponse force microscopy confirmed a detectable but mild local piezoelectric response. However, its direct osteogenic contribution was not isolated from other BT-related material effects and requires further verification. All scaffolds exhibited good cytocompatibility. PTB4 showed the most favorable biological performance, including enhanced MC3T3-E1 cell proliferation, increased ALP-positive area, greater mineralized deposition, and more pronounced VEGF-related fluorescence in HUVECs. After 12 weeks in a rat calvarial critical-size defect model, PTB4 exhibited significantly higher bone volume fraction and bone mineral density than the blank and PT groups. Histological and immunohistochemical analyses showed more extensive new bone formation, collagen deposition, and stronger osteogenesis-angiogenesis coupling. Overall, PTB4 achieved the best balance among printability, mechanical compatibility, cytocompatibility, angiogenesis-related activity, and osteogenic performance, supporting low-dose BT modification as a promising strategy for safe, printable scaffolds for critical-size craniofacial and oral bone defect repair.