Tissue engineered vascularized periosteal flap enriched with MSC/EPCs for the treatment of large bone defects in rats

Vascularized periosteal flaps are used for complex cases if the reconstruction of large bone defects is necessary in modern trauma and orthopedic surgery. In this study, we combined this surgical procedure with β-TCP scaffold and mesenchymal stem cells (MSCs) + endothelial progenitor cells (EPCs) as a tissue engineering approach to obtain optimum conditions for bone healing in rats. A critical size femoral defect was created in 80 rats allocated into 4 groups. Defects were treated according to the following protocol: i) vascularized periosteal flap alone; ii) vascularized periosteal flap + β-TCP scaffold; iii) vascularized periosteal flap + β-TCP scaffold + ligated vascular pedicle; and ii) vascularized periosteal flap + β-TCP scaffold + MSCs/EPCs. After 8 weeks, femur bones were extracted and analyzed for new bone formation, vascularization, proliferation and inflammatory processes and strength. Bone mineral density (BMD) and biomechanical stability at week 8 were highest in group 4 (flap + β-TCP scaffold + MSCs/EPCs) compared to all the other groups. Stability was significantly higher in group 4 (flap + β-TCP scaffold + MSCs/EPCs) in comparison to group 3 (ligated flap + β-TCP scaffold). BMD was found to be significantly lower in group 3 (ligated flap + β-TCP scaffold) compared to group 1 (flap) and group 4 (flap + β-TCP scaffold + MSCs/EPCs). The highest density of blood vessels was observed in group 4 (flap + β-TCP + MSCs/EPCs) and the values were significantly increased in comparison to group 3 (ligated flap), but not to group 1 (flap) and group 2 (flap + β-TCP). The highest amounts of proliferating cells were observed in group 4 (flap + β-TCP scaffold + MSC/EPCs). The percentage of proliferating cells was significantly higher in group 4 (flap + β-TCP scaffold + MSCs/EPCs) in comparison to all the other groups after 8 weeks. Our data thus indicate that critical size defect healing could be improved if MSCs/EPCs are added to β-TCP scaffold in combination with a periosteal flap. Even after 8 weeks, the amount of proliferating cells was increased. The flap blood supply is essential for bone healing and the reduction of inflammatory processes.