Microdroplet-mediated exosome delivery system for the therapeutic management of radiation-induced bone damage

Radiation-induced skeletal deterioration and bone loss remain major clinical challenges. Although exosomes derived from human bone marrow-derived mesenchymal stromal cells (hBMSCs) (MSC-Exos) are promising cell-free therapeutics, their limited stability and low delivery efficiency hinder translational application. Here, we developed an innovative microdroplet-based exosome delivery platform (MD/Exos) and systematically evaluated its protective effects under irradiation-induced stress. MSC-Exos were successfully isolated and characterized using transmission electron microscopy and western blot analysis. Fluorescence imaging and confocal microscopy confirmed efficient uptake of MSC-Exos by both macrophages and hBMSCs. MD/Exos were fabricated by encapsulating exosomes within bovine serum albumin-stabilized microdroplets. Cytocompatibility assays showed that MD/Exos exhibited no detectable cytotoxicity toward macrophages. Functionally, MD/Exos significantly enhanced the viability, metabolic activity, and cytoskeletal integrity of irradiated hBMSCs. Notably, MD/Exos markedly promoted osteogenic differentiation after irradiation, as evidenced by increased alkaline phosphatase activity, enhanced mineralized matrix deposition, and upregulated osteogenesis-related gene expression. In parallel, MD/Exos modulated macrophage responses to radiation by suppressing aberrant multinucleated giant-cell formation and reducing pro-inflammatory cytokine expression. In vivo, administration of MD/Exos in an irradiation-induced bone injury model significantly attenuated bone loss and promoted bone regeneration, as evidenced by preserved bone microstructure, reduced osteoclast activity, and downregulated tumor necrosis factor-alpha (TNF-α) expression. Further in vivo cytokine analysis indicated that MD/Exos treatment significantly reduced pro-inflammatory cytokines compared to irradiated controls. Collectively, these findings demonstrate that MD/Exos represent a biocompatible and efficient exosome delivery platform capable of mitigating irradiation-induced cellular dysfunction, enhancing osteogenesis, and modulating immune-bone crosstalk. This study highlights the therapeutic potential of MD/Exos as a novel strategy for the prevention and treatment of radiation-induced bone loss.