An electrostatic co-assembled extracellular vesicles infused hydrogel for bone regeneration in aged defects.

Age-related bone defects remain challenging due to the reduced osteogenic capacity of aged bone marrow mesenchymal stem cells (A-BMSCs). An injectable hydrogel incorporating extracellular vesicles (EVs) from young BMSCs (Y-EVs) was designed to enhance bone regeneration. The hydrogel, composed of star-PEG-KA7 and polyphosphate-gelatin (P-GA, generated by conjugating imidazole-modified polyphosphate (PolyP-Im) with gelatin (GA), encapsulates Y-EVs to form the P-GA/KA7@Y-EVs system. In vitro, Y-EVs promoted osteogenic differentiation and alleviated senescence in A-BMSCs, while the hydrogel provided injectability, biocompatibility, and sustained release. In vivo, P-GA/KA7@Y-EVs significantly improved cranial bone regeneration in aged rats, surpassing Y-EVs or hydrogel alone. Transcriptomic and microRNA analyses indicated that Y-EVs rejuvenated A-BMSCs by modulating PI3K-Akt, TGF-β, and MAPK pathways, supported by gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) enrichment. This EVs-infused bioactive hydrogel offers a minimally invasive and effective strategy for age-related bone regeneration.