Comparison of the effects of hydrogel and normal saline as carriers of MSC on fracture healing in a rat long bone fracture model.

BACKGROUND: Mesenchymal stem cells (MSCs) are used in cell therapy to enhance healing in long bone fractures, where nonunion is highly likely to occur. However, only a few studies have been conducted on carriers that should be used for more effective cell delivery. This study compared the use of hydrogel and normal saline as carriers for enhancing fracture healing when injecting MSC in a long bone fracture rat model. METHODS: Wistar rats were classified according to the carrier used for MSC injection: Groups C (normal saline) and H (hydrogel). MSCs were administered to the fracture site via direct injection method. The long bone specimens were harvested at 2 and 6 weeks after fracture. Western blot analysis was used to assess the expression of chemokines associated with MSC recruitment (stromal cell-derived factor 1 [SDF-1], monocyte chemoattractant protein-1 [MCP-1]), and osteogenesis (bone morphogenetic protein-2 [BMP-2], transforming growth factor-beta 1 [TGF-β1]) at 2 and 6 weeks post-fracture, respectively. Bone volume [BV], percentage bone volume [PBV] and bone marrow density [BMD]) were evaluated using micro-computed tomography (CT). MSC survival was monitored using fluorescence imaging up to 2 weeks post-fracture. RESULTS: Group H demonstrated higher SDF-1 and MCP-1 levels at 2 weeks post-fracture compared with group C. No significant differences in protein expression levels of osteogenesis-related chemokines were observed between the two groups at 6 weeks post-fracture. Micro-CT showed higher BV, PBV and BMD in group H compared with group C at 6 weeks post-fracture. Signals of MSCs injected into fracture site lasted longer in group H until 2 weeks post-fracture and showed higher radiance efficiency in each period than in group C. CONCLUSIONS: Compared with using normal saline, using hydrogel significantly enhanced fracture healing in the early phase and formed more new bones at higher densities in the late phase. Injected MSCs were more concentrated around the fracture site and survived longer with hydrogel use than with normal saline use. LEVEL OF EVIDENCE: Level V.