A Novel Strategy To Engineer Small-diameter Vascular Grafts From Marrow-derived Mesenchymal Stem Cell Sheet

Vascular graft engineered from autologous cells based on tissue engineering strategy is the ideal substitute of the artery severely affected by atherosclerosis or after carotid artery resection due to tumor invasion. Vascular tissue engineering is one of the focal points in tissue engineering, which involves scaffolds, seed cells and methods.Objective:To fabricate tissue-engineered vascular graft with enough strength and favorable contour for clinical application. In details:1.To explore how to construct a completely biological TEVG assembled with autologous mesenchymal stem cells (MSCs), avoiding the use of exogenous biomaterials.2. To identify whether MSCs have an antithrombogenic property to prevent thrombosis as endothelial cells.3. To establish strategy of generating small-diameter tissue-engineered vascular graft in vitro. 4. To observe the patency and differentiation ability of the tissue-engineered vascular graft in vivo.Methods and results:Rabbit bone marrow mesenchymal stem cells (MSCs) were cultured continuously to form a cell sheet with proper mechanical strength and handling property, and the result of platelet adhesion assay indicated that MSCs had an antithrombogenic property to prevent thrombosis as endothelial cells. The cell sheet was composed of 5-7 layers of cells with a thickness of about 50μm. Electron microscopy showed that confluent MSCs arranged in an organized way on the bottom side of the sheet, and a fine matrix filament secretion could be observed on the surface side. Tissue-engineered vascular graft (TEVG) was fabricated by rolling the MSC sheet around a mandrel. The in vitro TEVG had certain mechanical strength, but the structure need improve. Furthermore, TEVGs were implanted into the common carotid artery (CCA) defects of rabbits. The results showed that the TEVGs remained patent 4 weeks after implantation without stenosis, thrombus formation, or inflation. Electron microscopy showed that the implanted TEVGs endothelialized in vivo. We also found that the TEVG can remodel itself in the mechanical environment in vivo and the structure was similar to that of the native artery. Conclusions:These results indicated that MSCs have an antithrombogenic property to prevent thrombosis as endothelial cells, and formed a cell sheet after continuous culture for a few days, with three-dimensional extracellular matrix. A completely biological TEVG could be assembled with autologous MSCs. The in vivo TEVGs had excellent patency and integrated well with the native vessel. We also observed that several layers of collagen and connective fibers had deposited circularly around the graft, which was obviously different from the structure of the TEVG in vitro and resembled the native artery instead. This suggests that the TEVGs can remodel themselves in the mechanical environment in vivo. Cell sheet strategy provides a novel approach to construct small-diameter vascular graft. TEVGs are useful for revascularization in humans, which would reduce the occurrence of complications caused by foreign materials and we believe that this novel strategy has great potential in future clinical application.