Engineering Spatially Localized Bioactive Microenvironments in Assembly Implants for Spatially Extended Bone Ingrowth

The repair of large segmental bone defects requires implants that combine structural stabilization with biological regulation. Here, we developed a bioadaptive modular implant integrating porous titanium (Ti) alloy for structural reinforcement with spatially localized β-tricalcium phosphate (β-TCP) modules for bioactive regulation. Using a gelatin methacryloyl (GelMA)-based diffusion-confined model, we identified spatial differences in β-TCP-associated calcium distribution and corresponding position-dependent changes in hBMSC proliferation, adhesion, osteogenic differentiation, and Wnt/β-catenin-related signaling. The proximal region showing the strongest biological responses was used as a model-derived spatial reference for organizing β-TCP-containing modules. In a rabbit femoral segmental defect model, the Ti alloy/β-TCP assembly implant showed greater bone formation and ingrowth than porous Ti alloy controls. Histology further revealed that newly formed bone was preferentially associated with β-TCP-containing regions and extended into adjacent porous Ti structures. These findings demonstrate a proof-of-concept for translating experimentally characterized spatial biological responses into the spatial organization of structural and bioactive implant components.