Engineering Vascularized Bone Graft With Osteogenic and Angiogenic Lineage Differentiated Bone Marrow Mesenchymal Stem Cells

Tissue-engineered bone provides a promising method for the rehabilitation of acquired bone defects and congenital deformities. However, generating a vascular supply to the engineered graft remains a major challenge. We report a novel strategy to engineer vascularized bone grafts with osteogenic and angiogenic lineage differentiated marrow mesenchymal stem cells (MSCs). MSCs were expanded to form an osteogenic cell sheet using a continuous culture method and a scraping technique under osteogenic culture conditions. Another portion of MSCs was directed to differentiate into highly proliferative endothelial progenitor cells (EPCs), which were then seeded onto the cell sheets. Cell sheet-EPC complexes were implanted subcutaneously in nude mice. Cell sheets without EPCs were also implanted as a control. The mice were sacrificed, and the samples were harvested for evaluation consisting of micro-CT scanning, histological analysis and scanning electronic microscopy 4 and 8 weeks after implantation. The results showed that cell sheets were composed of viable cells and extracellular matrix and showed apparent mineralization. The obtained EPCs could express the specific antigen marker of CD31 and form capillary-like structures in vitro. The osteogenic cell sheet-EPC complexes yielded well-vascularized bone grafts 4 and 8 weeks after implantation. Both bone density and vascular density were significantly higher in the cell sheet-EPC complex group than in the control group. The results demonstrated that the introduction of EPCs could not only generate a vascular network but also increase bone formation for cell sheet-based bone engineering. These findings suggest that the strategy of engineering bone grafts with osteogenic and angiogenic lineage differentiated MSCs has great potential for clinical applications to repair large bone defects.