Osteoimmunomodulation of astragalus-calcium silicate scaffolds-activated M2 macrophage-derived miR-218-rich exosome for enhanced bone regeneration

Abstract

Current therapeutic strategies for bone defects, including autografts, allografts, and conventional biomaterial scaffolds, are limited by donor site morbidity, immune rejection, and insufficient vascularization. Moreover, the complex inflammatory microenvironment in bone defects often impairs healing outcomes, necessitating the development of advanced biomaterials with enhanced immunomodulatory and regenerative capabilities. This study investigates the therapeutic potential of extracellular vesicles derived from Astragalus-modified calcium silicate (AstCS)-stimulated M2 macrophages (AstCSM2EVs) in bone regeneration. The AstCSM2EVs demonstrated superior immunomodulatory capabilities by effectively polarizing macrophages toward the M2 phenotype, characterized by significant downregulation of pro-inflammatory cytokines (IL-1β, TNF-α) and concurrent upregulation of anti-inflammatory mediators (IL-4, IL-10). Notably, AstCSM2EVs exhibited enhanced angiogenic potential, evidenced by increased endothelial tube formation and elevated VEGF secretion, while simultaneously promoting osteogenic differentiation of mesenchymal stem cells through upregulated expression of key markers including ALP, BSP, and OC. Mechanistic investigations revealed that AstCSM2EVs modulated these regenerative processes primarily through miR-218-5p-mediated regulation of multiple signaling pathways, including NOD-like receptor and ECM-receptor interaction pathways. In a rabbit femoral defect model, local administration of AstCSM2EVs significantly enhanced bone regeneration, demonstrated by increased bone volume fraction and improved trabecular architecture, while effectively suppressing local inflammation. These findings establish AstCSM2EVs as a promising therapeutic agent for bone regeneration, highlighting their multifaceted roles in immunomodulation, angiogenesis, and osteogenesis. This research introduces an innovative approach that combines extracellular vesicles (EV) with immunomodulatory tissue engineering strategies to improve the treatment of bone defects.