A hierarchically EGCG-coated black phosphorus/PI scaffold for vascularized bone regeneration in large infectious area

Effective repair of large-scale bone defects remains challenging in orthopedic device applications due to the persistent implant-associated infection and insufficient osseointegration. In this study, the multifunctional composite scaffold (PB@EG) was fabricated by first reinforcing a polyimide (PI) matrix with black phosphorus nanosheets (BPNS) prepared via liquid-phase exfoliation. The resulting composite was subsequently fabricated into a hierarchical porous architecture, featuring interconnected macropores (100-200 µm) and micropores (10-50 µm), using a dual-size salt leaching method. The process was finalized with a surface coating of epigallocatechin-3-gallate (EGCG). Under 808 nm near-infrared irradiation, the nanosheet phase exhibited on-demand photothermal antibacterial activity, and the EGCG coating further enhanced the antimicrobial property against S. aureus and E. coli in vitro. In addition, the EGCG coating promoted macrophage polarization toward an M2 pro-healing phenotype as well as enhanced endothelial tube formation. Together with phosphate released from the nanosheets, this pro-angiogenic microenvironment promoted matrix mineralization in vitro. In vivo safety evaluation of supernatant extracts from the scaffold revealed no histopathological abnormalities in major organs consistent with acceptable systemic biocompatibility. In summary, the antibacterial, immunomodulatory, pro-angiogenic, and osteogenic functions indicate that PB@EG is a promising scaffold for vascularized bone regeneration in large infected defects.