Evaluation of xenogenic extracellular matrix scaffolds for use in tissue engineered vascular grafts

Existing synthetic vascular grafts have unacceptably high failure rates when replacing below knee arteries. In vitro endothelialisation is an emerging procedure that has been shown to enhance the patency rates of below knee synthetic vascular grafts. Here autologous endothelial cells are harvested and cultured on the lining of the graft prior to implantation. The technique is limited by the narrow time frame availalble for culture and the finite cells obtainable following harvest. As well as this, existing synthetic materials are poor cellular substrates and must be combined with coatings to promote cellular growth and attachment. The most common coated graft used clinically is fibrin-coated polytetrafluoroethylene (ePTFE). The study aim was to compare the endothelialisation of fibrin-coated ePTFE with emerging novel extracellular matrix (ECM) scaffolds, which we hypothesise will provide a superior substrate for cell growth by mimicking the in vivo environment more closely. We also construct and verify a novel subatmospheric bioreactor in order to enhance the proliferation of cultured cells. Finally, we examine the culturing of endothelial cells inside the lumen of small diameter ECM vascular grafts. Our Results showed that cells remained viable and produced von Willebrand factor on all substrates tested. There was no difference in adhesion rates between ECM scaffolds and fibrin-coated ePTFE (p = 1.00). Endothelial cells proliferated fastest on ECM scaffolds when compared to all other materials tested (p <0.001). When seeded scaffolds were exposed to subatmospheric pressures in a closed bioreactor a mechanical strain was exerted on the construct. This was shown to alter cellular morphology and enhance cellular proliferation. We found we could rapidly form a confluent endothelial lining on the luminal surface of small diameter ECM grafts. In conclusion, ECM bioscaffolds offer a superior substrate for promoting rapid endothelialisation compared to existing fibrin-coated ePTFE by combining firm cellular anchorage and rapid cell expansion. Proliferation rates were positively influenced by a subatmospheric bioreactor. This work suggests that ECM materials are promising scaffolds for use in small vessel tissue engineering.