Bioactive 3D-bioprinted scaffolds with endothelial progenitor cells and Zn2+-enhanced SFMA/HisMA/nHAP for healing of infected bone defect

Infected bone defects remain one of the greatest challenges in orthopedics, as bacterial contamination and insufficient vascularization severely compromise regeneration. Here, we report the development of a multifunctional 3D-bioprinted scaffold composed of zinc ion (Zn 2+ ) functionalized silk fibroin methacryloyl (SFMA), histidine methacryloyl (HisMA), and nano-hydroxyapatite (nHAP), further loaded with endothelial progenitor cells (EPCs) to promote simultaneous antibacterial, angiogenic, and osteogenic responses. The photocrosslinkable SFMA/HisMA bio-ink reinforced with nHAP provided mechanical stability, controlled swelling and degradation, while Zn 2+ coordination endowed strong antibacterial activity against E. coli and S. aureus . EPCs adhered and proliferated on the scaffolds, markedly enhancing osteogenic differentiation, angiogenesis while suppressing oxidative stress, as evidenced by increased expression of OCN, RUNX2, COL1, OPN, VEGF and inhibited lipid and mitochondrial ROS levels. Proteomic profiling further revealed that EPC-loaded scaffolds orchestrate osteoblast protein expression, promoting immunoregulation and extracellular matrix (ECM) reconstruction to accelerate tissue regeneration. In a murine femoral infected defect model, EPC-loaded scaffolds suppressed pro-inflammatory cytokines, stimulated angiogenesis, and supported robust new bone formation, leading to accelerated defect repair confirmed by μCT and histological analyses. Together, these findings demonstrate that the EPC-loaded Zn 2+ functionalized SFMA/HisMA/nHAP scaffold integrates antibacterial defence with vascular and osteogenic stimulation, offering a promising translational strategy for the treatment of complex infected bone defects.