Bioactive 3D-bioprinted scaffolds with endothelial progenitor cells and Zn ²⁺ -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 (Zn²□) 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 Zn²□ coordination endowed strong antibacterial activity against E. coli and S. aureus. EPCs adhered and proliferated on the scaffolds, and in co-culture with bone marrow stromal cells (BMSCs) markedly enhanced osteogenic differentiation, as evidenced by increased expression of OCN, RUNX2, COL1, and OPN. Proteomic profiling further revealed that EPC-loaded scaffolds modulated osteoblast protein expression patterns consistent with both immunoregulation and active extracellular matrix reconstruction to promote tissue regeneration. In a murine femoral infected defect model, EPC-loaded scaffolds suppressed pro-inflammatory cytokines (IL-6, TNF-α), 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 Zn²□ 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.