Gradient nanofibrous chitosan/poly ɛ-caprolactone scaffolds as extracellular microenvironments for vascular tissue engineering

One of the major challenges of tissue-engineered small-diameter blood vessels is restenosis caused by thrombopoiesis. The goal of this study was to develop a 3D gradient heparinized nanofibrous scaffold, aiding endothelial cells lined on the lumen of blood vessel to prevent thrombosis. The vertical graded chitosan/poly ɛ-caprolactone (CS/PCL) nanofibrous vessel scaffolds were fabricated with chitosan and PCL by sequential quantity grading co-electrospinning. To mimic the natural blood vessel microenvironment, we used heparinization and immobilization of vascular endothelial growth factor (VEGF) in the gradient CS/PCL. The quantity of heparinized chitosan nanofibers increased gradually from the tunica adventitia to the lumen surfaces in the gradient CS/PCL wall of tissue engineered vessel. More heparin reacted to chitosan nanofiber in gradient CS/PCL than in uniform CS/PCL nanofibrous scaffolds. Antithrombogenic properties of the scaffolds were enhanced by the heparinization of these scaffolds, as shown by activated partial thromboplastin time and platelet adhesion assay. Compared to the uniform CS/PCL scaffold, the release of VEGF from the gradient CS/PCL was more stable and sustained, and the burst release of VEGF was reduced approximately 42.5% within the initial 12 h. The adhesion and proliferation of human umbilical vein endothelial cells (HUVEC) were enhanced on the gradient CS/PCL scaffold. Furthermore, HUVEC grew and formed an entire monolayer on the top side of the gradient CS/PCL scaffold. Therefore, use of vertical gradient heparinized CS/PCL nanofibrous scaffolds could provide an approach to create small-diameter blood vessel grafts with innate properties of mammalian vessels of anticoagulation and rapid induction of re-endothelialization.