Cell-Free Yet Cell-Based Tissue Engineered Vascular Graft

Cardiovascular disease (CVD) is currently the leading cause of death worldwide resulting in 647,000 annual deaths in the United States alone. A common treatment is revascularization to bypass arterial blockages from CVD; however, currently clinical options are associated with a high failure rate1. The field of tissue engineering holds promise, and several groups have been working towards the development of an appropriate tissue engineered vascular graft. This dissertation focused on the development and in vivo testing of three different graft options: (1) custom silk (Antheraea assama (AA) and Bombyx mori (BM)) functionalized with macrophage attractant (C-C motif chemokine ligand 2, CCL2) loaded microparticles or (2) cellular secretions (conditioned media, CM), and (3) BM silk functionalized with extracellular vesicles (EVs). Each graft was assessed after 1 week and 8 weeks for patency and remodeling in a rat model. All graft types showed increased acute patency after 1 week in comparison to blank controls (scaffold only, no payload); however, graft failure due to stenosis was observed in the CCL2 and CM groups after 8 weeks. An increased macrophage presence and higher occurrence of stenosis was observed in response to both the CCL2 and CM functionalized scaffolds when compared to the EV group. Additionally, an increased occurrence of stenosis was observed in response to the inclusion of AA silk compared to BM silk possibly due to the increased RGD binding sites present within the AA silk fibroin. Overall, results have shown a more complete and positive remodeling response to BM silk treated with EVs characterized by increased patency, neotissue formation, extracellular matrix deposition, and a reduction in stenosis. The three TEVGs tested in this dissertation, particularly the EV functionalized BM silk scaffold, show promising potential for future studies and translation. The development of a TEVG which leverages the positive remodeling effects of cellular secretions, yet is cell-free, offers a lower risk of immune rejection and more easily translatable arterial graft option in comparison to previous cell-based options. A successful TEVG technology has the potential to improve the outcomes of small diameter revascularization including the 371,000 coronary bypass surgeries performed in the US annually.