Calcium Phosphate Nanoparticle-Immobilized Macrophage-Derived Extracellular Vesicle Nanohybrid Facilitates Diabetic Bone Regeneration

Diabetes significantly hinders bone regeneration, and existing tissue engineering therapies struggle to improve the hyperglycemia-induced inflammatory microenvironment, resulting in unbalanced bone remodeling. M2-macrophage-derived extracellular vesicles (M2EVs) possess inherent immunomodulatory properties and promote stem cell differentiation; however, their therapeutic potential in diabetic bone regeneration is significantly limited by poor stability and insufficient osteoinductive capacity. Inspired by biomineralization, a calcium phosphate nanoparticle-immobilized macrophage-derived small extracellular vesicle nanohybrid (M2EV@CaP) is developed by in situ growth of inorganic nanocrystals on M2EV surfaces. In the nanohybrid system, the chemically inert CaP-nanoparticle-reinforced shell provides structural protection for M2EV, inhibiting vesicle aggregation caused by membrane protein denaturation/cross-linking or lipid phase transition through physical barrier. More importantly, M2EV@CaP provides bioavailable calcium/phosphorus ion reservoirs and signaling molecules for bone regeneration and releases responsively under inflammation-induced acidic conditions. In vitro, M2EV@CaP significantly enhances macrophage polarization toward a reparative M2 phenotype, and promotes stem cell osteogenic differentiation under high-glucose inflammatory conditions by activating the CA²⁺-Akt signaling axis. In vivo, hydrogel-assisted delivery of M2EV@CaP significantly promotes bone regeneration in diabetic rat calvarial defects through immunomodulation and osteoinduction. This study proposes a nanohybridization strategy based on inorganic nanoparticles reinforcing biostructures, offering a promising extracellular vesicle therapy for complex pathological conditions.