Preclinical Assessment of a Compliance Matched Biopolymer Vascular Graft

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PROJECT ABSTRACT Cardiovascular diseases represent the leading cause of death worldwide and are currently responsible for 32% of all reported deaths before the start of the COVID-19 pandemic. The increase in cardiovascular disease prominence has placed increasing levels of demand for cardiac bypass grafting (CABG), which is now the most common cardiac surgery in the world. Despite CABG interventions with autologous tissues are viewed as one of the most effective treatment options, their failure of rate remains as high as 42.8%, with only 50% to 60% maintaining patency after 10 years. Vascular engineering research has sought to develop tissue engineered vascular grafts (TEVG) in the form of acellular or cellularized constructs as an alternative solution. Despite decades of research advancements, very few TEVGs have reached clinical studies, and there are no clinically approved TEVGs currently in use. Here we seek to advance our understanding of how TEVGs are infiltrated by the host’s cells when stimulated by three different isoforms of the protein Transforming Growth Factor Beta, and the impact this treatment can have on cellular remodeling of the TEVGs. Aim 1: Investigate native vascular tissue stromal cell migration onto and proliferation within a TEVG that is compliance matched and TGFβ isoform loaded in a 3D culture system. We will test the hypothesis that compliance matched TEVGs containing TGFβ2 loaded microparticles can modulate the rates of explanted native vascular tissue cellular migration and proliferation onto an adjoined TEVG at significantly higher levels than delivery of two alternative TGFβ isoforms utilizing a 3D culture system. Native rat arterial tissues will be canulated and placed into the 3D culture system adjoined to a compliance matched TEVGs. The acellular TEVGs will initially be manufactured to carry PLGA microparticles (MPs) loaded with TGFβ isoforms (TGFβ-1, -2, -3, respectively) to provide a controlled release of TGFβ from the intimal layer of the TEVGs. We will assess early and late term cellular migration and proliferation onto the TEVG scaffolds as a function of culture time and TGFβ isoform release across a selection of release rates and dosages. We will quantify these results using multiphoton intravital imaging of the specialized 3D biaxial TEVG culture system. Aim 2: Assess the cellular remodeling of the compliance matched TGFβ isoform loaded TEVGs through intravital 2-photon imaging. To investigate the subsequent ECM remodeling of the compliance matched TEVGs carrying TGFβ isoform loaded MPs in 3D culture, we will utilize intravital imaging of explanted native rat abdominal aortas adjoined to TEVGs in culture as before. In this supplemental aim, we will utilize the 2-photon imaging system to quantify ECM remodeling via collagen/elastin content though second harmonic generation (SHG, collagens) and 2-photon excited fluorescence (2PEF, elastin) signals. We will assess scaffold matrix remodeling by relative SHG and 2PEF levels as a function of culture time and the respective TGFβ isoform delivered. Aim 3: Investigate the impact of progressive biaxial biomechanical stimulation of the TGFβ isoform loaded TEVGs by assessing cellular migration, proliferation, and remodeling of the TEVGs by infiltrating stromal cells. We will utilize another feature of our custom-built bioreactors (biaxial biomechanical loading) to impose controlled pulsatile pressures and axial stretches upon the TEVGs to determine if this biomechanical stimulation synergizes with the TGFβ isoform delivery to enhance cellular activity. As before, the native rat aorta tissues will be adjoined to the TEVGs, this time exposed to a selection of progressive biaxial biomechanical conditioning scenarios. Cellular migration, proliferation, and remodeling of the TEVGs will be assessed with our intravital 2-photon intravital imaging system as before, and TEVG remodeling will be determined by the relative SHG and SPEF signal generation at various locations throughout the scaffolds as before. We will assess these measures as a function of culture time and levels of biaxial biomechanical loading in combination with TGFβ isoform delivery to determine how each uniquely impacts cellular remodeling outcomes.