Engineering L-Arg@ZIF-8 nanoparticles to modulate the immune–osteogenic–angiogenic microenvironment for accelerated bone fracture healing

Abstract Bone fracture healing requires coordinated regulation of osteogenesis, angiogenesis, and immune homeostasis within a dynamically evolving microenvironment. However, current biomaterials rarely integrate these three regulatory dimensions. Herein, we engineered L-arginine–loaded zeolitic imidazolate framework-8 (L-Arg@ZIF-8) nanoparticles to remodel the immune–osteogenic–angiogenic microenvironment and accelerate fracture healing. L-Arg@ZIF-8 nanoparticles exhibited uniform morphology, positive surface charge, and stable L-Arg incorporation, enabling efficient cellular uptake and sustained bioactivity. Using two physiologically relevant 3D co-culture spheroid models (osteoblast–macrophage and osteoblast–endothelial), we demonstrated that L-Arg@ZIF-8 promotes osteogenic differentiation, endothelial activation and the upregulation of angiogenic markers, and strengthens osteogenesis–angiogenesis coupling. Bulk transcriptomic profiling further revealed activation of regenerative pathways, including PI3K–Akt and Wnt signaling, along with coordinated modulation of cytokine–receptor interactions and immune-related remodeling programs. In vivo, L-Arg@ZIF-8 markedly accelerated fracture repair in a rat rib fracture model, characterized by enhanced callus formation, increased bone mineral density, greater trabecular thickness, and a significantly elevated mineral apposition rate. Histological and immunofluorescence analyses confirmed upregulation of key osteogenic markers (OPN, OSX) at the fracture site. Together, these findings demonstrate that L-Arg@ZIF-8 functions as a bioengineered microenvironment-modulating nanoplatform that orchestrates immune regulation, osteogenesis, and angiogenesis to promote efficient fracture healing. This strategy offers a promising therapeutic avenue for translational management of complex fractures.