Bone-Targeting Microspheres Enable Sustained Release of CD301b⁺ Macrophage-Derived Small Extracellular Vesicles to Promote Bone Repair

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

• Level A · Stronger Clinical Evidence
• Level B · Emerging clinical evidence with positive signals
• Level C · Early human research exploring benefits
• Level D · Scientific groundwork from lab and animal studies
• Emerging · Emerging topic under active research

Abstract (original English)

Rationale Large bone defects often exceed the body's intrinsic capacity for self-repair. Successful bone healing depends on a coordinated immune transition alongside tightly coupled angiogenesis and osteogenesis, in which macrophages play a key regulatory role. Therefore, ideal bone-regenerative materials should integrate immunomodulatory, pro-angiogenic, and osteogenic functions. Methods and results Small extracellular vesicles (sEVs) from CD301b + macrophages (CD301b⁺-sEVs) are isolated by ultracentrifugation for inclusion in a bone-targeting microsphere system fabricated by microfluidic technology through dynamic Schiff-base cross-linking of alendronate-functionalized succinylated chitosan with oxidized sodium alginate allowing pH-responsive release of CD301b⁺-sEVs. Transcriptome sequencing and comprehensive in vitro studies reveal that CD301b⁺-sEVs possess the ability to modulate immune homeostasis by promoting macrophage polarization toward the pro-repair M2 phenotype, upregulate angiogenic factors that can enhance vascularization as seen by HUVEC sprouting assay, and contain RNA that stimulate osteogenic differentiation of BMSCs through activation of the Akt/GSK-3β/β-catenin signaling pathway. Preclinical studies with a rat calvaria model show that microspheres loaded with CD301b + -sEVs significantly promote bone regeneration in comparison to microsphere controls. Conclu

Evidence level

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

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