Investigating and characterising tubular scaffolds for small-diameter artificial blood vessels manufactured by using TPU and combining Solvent Electrospinning and Melt-Electrowriting techniques.

Cardiovascular diseases (CVDs) are the main cause of death worldwide. Autologous vessels, such as the saphenous vein, are nowadays the gold standard grafts for the surgical treatment of CVDs for small-diameter vessels. However, the procedure doesn’t go without drawbacks, like their limited availability and the incidence of post-operative complications. Alternative vessels sources have been taken into consideration leading to the investigation of tissue-engineered vascular grafts (TEVGs). Currently, polymers like Dacron and ePTFE are used to fabricate vessels substitutes that are successfully applied for large diameter vessels (d > 7 mm) replacement. When it comes to small diameter grafts (d < 5 mm), however, the failure rate of these synthetic grafts becomes significantly higher. Failures are mainly associated with thrombosis and stenosis caused by the lack of re-endothelialization of the substitute and its compliance mismatch with the native vessel. From here comes the need for a synthetic vascular graft that mimics the mechanical properties of the native vessel and induces the formation of an endothelial monolayer on the luminal side of the prosthesis. In this study we developed the manufacturing process of a bilayered tubular vascular graft using thermoplastic polyurethane (TPU). The bilayered hierarchical structure has been obtained by combining Solvent Electrospinning (SES) and Melt-Electrowriting (MEW). The SES layer on the luminal side of the graft is meant to promote endothelial cells (ECs) adhesion and the development of a continuous endothelium. The outer MEW layer provides structural support, and its mechanical properties can be tuned based on the fibers geometry deposition. The morphology and mechanical behaviour of the manufactured tubular scaffolds have been characterized and compared with poly-caprolactone (PCL) grafts with analogous bilayered structure, showing a significant improvement in their mechanical properties. The study confirms the potential of this novel composite scaffold in vascular tissue engineering.