Endothelialization Using Protein Substrates and Hydrogels for Aortic Valve Applications

Aortic valve disease is currently the leading cause of cardiovascular morbidity in the United States.1 In 2003, approximately 290,000 patients required heart valve replacement and that number is estimated to continue to rise as the average age of the population continues to increase.2 However, the current valve replacement options have multiple limitations. Tissue engineering hopes to address these shortcomings by providing a viable valve that more closely mimics the native valve, structurally and functionally.3 An ideal valve replacement should contain endothelial and interstitial cells, with the ability to remodel the extra-cellular matrix. While tissue-engineered heart valves are not uncommon in the field, retaining an adequate monolayer of endothelial cells on the scaffold surface remains an unresolved challenge. Without a functional endothelial layer, the implant can become thrombogenic, initiate an immune response, and become incapable of conducting necessary communications with the underlying interstitial cells. The focus of this series of studies is to create a seeding method that optimizes the adherence and uniformity of endothelial cells on an acellular heart valve scaffold. This study has three approaches to maximize endothelial cell adhesion: the use of protein substrates, the application of hydrogels, and dynamic seeding. First, protein substrates – laminin and fibronectin – were applied to samples of decelled bovine pericardium and seeded with endothelial cells in static conditions. In the next study, hydrogels – PureCol, Q.Gel, and fibrin glue – were applied to the surfaces of tissue samples followed by the aforementioned protein substrates and finally seeded statically with endothelial cells. A novel rotating device was then used to dynamically seed the decelled native valve. Finally the seeded valve was analyzed in vitro for cellular retention by exposing the valve to physiological shear stress in the heart valve bioreactor. The use of substrates in combination with fibrin glue has shown to increase endothelial cell adhesion on bovine pericardium in proof-of-concept studies. A rotating device for valve seeding applications has shown positive results for uniform and confluent endothelial cell coverage. These studies will serve as a reference for future endothelialization studies as the field of cardiovascular tissue engineering strives to develop permanent solutions for patients with valve or vascular diseases