Janus bilayer coating of functional quaternized chitosan and borate bioactive glass for antibacterial protection and osseointegration.

Peri-implant infection and insufficient osseointegration remain leading causes of implant failure, yet existing surface strategies address these challenges sequentially rather than concurrently. A hierarchically organized bilayer coating was developed on titanium by integrating an electrospun quaternized chitosan and poly(vinyl alcohol) nanofibrous base with an electrosprayed overlayer of borate bioactive glass nanospheres encapsulated within a quaternized chitosan shell. The Si-free ternary 70B₂O₃-25CaO-5K₂O composition, synthesized via a surfactant-directed sol-gel route, yields monodisperse spherical nanoparticles; shell encapsulation reduces cumulative boron release to 78.2% over 14 days and suppresses burst release to 0.33% at 2 h, sustaining ion delivery within the cytocompatible and osteogenically active range. Broad-spectrum bactericidal activity against a clinically representative polymicrobial peri-implant panel was achieved through synergistic contact killing and borate dissolution derived ionic perturbation. Among formulations evaluated, B40 comprising 40 wt% quaternized chitosan and 5 wt% bioactive glass simultaneously maximized infection control and osteogenic maturation in primary human mesenchymal stem cells, producing superior metabolic activity, cytoskeletal organization, collagen expression, and matrix mineralization. Surface cationic charge density and controlled borate ion flux are identified as coupled regulators of antibacterial and osteogenic responses, establishing a rational drug-free framework for multifunctional implant surface engineering.