BMP-2-driven osteo-organoid formation retains key osteogenic-support features and promotes bone repair following total-body irradiation

Irradiation stress causes persistent skeletal injury by disrupting marrow homeostasis, stromal function, and bone repair. However, the temporal remodeling of the native bone microenvironment and the capacity of a biomaterial-induced osteogenic environment to sustain regeneration under systemic irradiation remain unclear. Using 6 Gy total body irradiation (TBI), we characterized time-resolved changes in the native femur and evaluated BMP-2-loaded hyaluronic acid methacryloyl (BMP-2/HAMA)-induced osteo-organoids relative to their corresponding non-irradiated controls. TBI caused progressive femoral deterioration, including trabecular bone loss, persistent B-cell depletion, neutrophil-associated myeloid expansion, Type-H endothelial-cell decline, and accumulation of senescence-associated mesenchymal stromal cells (MSCs). Single-cell RNA sequencing further resolved mature B-cell loss and enrichment of inflammatory and mature neutrophil states. In osteo-organoids, irradiation delayed but did not abolish tissue maturation. By 6 weeks, irradiated osteo-organoids approached the tissue and cellular features of non-irradiated osteo-organoids at the mature 3-week stage, while the MSC-associated stromal compartment remained relatively stable. Osteo-organoid-derived MSCs exhibited less pronounced irradiation-associated dysfunction and retained clonogenic, osteogenic, and immunomodulatory capacities. In an irradiation-impaired femoral defect model, BMP-2/HAMA enhanced mineralized tissue formation, mechanical competence, and gait function. These findings support BMP-2/HAMA as a biomaterial-assisted strategy for functional bone regeneration under irradiation-impaired conditions.