Repair of Rat Calvarial Bone Defect by Using Exosomes of Umbilical Cord–Derived Mesenchymal Stromal Cells Embedded in Chitosan/Hydroxyapatite Scaffolds

Purpose: To seek out the bone regeneration effect of human umbilical cord-mesenchymal stem cell (hUC-MSC)-derived exosomes of loaded chitosan/hydroxyapatite (CS/HA) scaffold in a rat calvarium bone regeneration model.
Materials and methods: The hUC-MSC exosomes were purified and characterized. The scaffolds were prepared by a freeze-drying method. Animals were divided into five groups, and the CS/HA/exosome (CS/HA/Exo) scaffolds were transplanted to 5 × 2-mm critical-sized calvarial bone defects for repair in rats. All animals were sacrificed at the postoperative sixth week. Immunohistochemical and histologic analyses were performed.
Results: Scanning electron microscopy (SEM) images showed that the exosomes were round-shaped vesicles with bounded membrane, and the diameter of the exosomes was 83.728 ± 27.269 nm. Histologic analysis showed that mean new bone volumes were statistically significantly higher in the CS/HA/Exo group (1.83 ± 0.54, P_{CS/Exo-CS/HA/Exo} = .000), and other new bone volumes in the other groups were statistically significant compared with the control (CS/Exo 1.50 ± 0.14 mm³; CS 1.20 ± 0.43 mm³; control 1.06 ± 0.10 mm³; and CS/HA 1.43 ± 0.66 mm³).
Conclusion: The CS/HA/Exo combination is a novel treatment for bone defect repair to induce bone formation. The CS scaffold can significantly promote bone regeneration compared with the control. Moreover, the combination with HA and exosomes is promising for applications in bone tissue regeneration.