Scaffold-Free Bone Marrow-Derived Mesenchymal Stem Cell Sheets Enhance Bone Formation in a Weight-Bearing Rat Critical Bone Defect Model

Researchers have been exploring alternative methods for bone tissue engineering, as current management of critical bone defects may be a significant challenge for both patient and surgeon with conventional surgical treatments associated with several potential complications and drawbacks. Recent studies have shown mesenchymal stem cell sheets may enhance bone regeneration in different animal models. We investigated the efficacy of implanted scaffold-free bone marrow-derived mesenchymal stem cell (BMSC) sheets on bone regeneration of a critical bone defect in a weight-bearing rat model. BMSCs were isolated from the femora of male Sprague-Dawley rats 5-6 weeks of age and cell sheets were produced on temperature-responsive culture dishes. Nine male Sprague-Dawley rats 6-8 weeks of age were utilized. A bilateral femoral critical bone defect was created with a bridge plate serving as internal fixation. One side was randomly selected and BMSC sheets were implanted into the bone defect (BMSC group), with the contralateral side receiving no treatment (control). Rats were anesthetized and radiographs were performed at 2-week intervals. At the 8-week time point, rats were euthanized, femurs harvested, and microcomputed tomography and histological analysis was performed. We found a statistically significant increase in new bone formation and bone volume fraction compared with the control. Histomorphometry analysis revealed a larger percent of newly formed bone and a higher total histological score. Our results suggest that scaffold-free BMSC sheets may be used in the management of large weight-bearing bone defects to complement a different surgical technique or as a standalone approach followed by internal fixation. However, further research is still needed.