The effects of matrix anisotropy and shear flow on endothelial cells [electronic resource] : developing a small-diameter vascular graft to regulate endothelial function
Keywords: Chemical Engineering

The development of atherosclerosis, a chronic inflammatory disease of the arteries, can usually be attributed to specific regions of the blood vessel. In the straight segments of an artery, endothelial cells (ECs) align with the unidirectional blood flow which commonly occurs in these simple geometries. The elongated and aligned ECs are generally found to have a healthy, athero-resistant phenotype. In contrast, branches or curved vessel geometries have regions of disturbed flow, characterized by low shear stress and high shear stress gradients. In these regions of complicated flow patterns, ECs are non-aligned and have a cobblestone cellular morphology. The non-aligned ECs elicit biological properties that promote atherosclerosis, as the location of atherosclerotic fatty plaque is often found at these bends, branches, or bifurcations. Therefore, this correlation highly suggests that the morphology and biological function are inextricably linked in ECs. The ability to regulate both EC morphology and motility, with the aim to influence EC biology, might be highly beneficial in the prevention or treatment of vascular disease. In this dissertation, anisotropic matrices of collagen nanofibrils were fabricated with a simple flow processing technique and used to investigate fundamental cell-matrix interactions with ECs. The aligned fibrils were able to regulate both the morphology and biology of ECs, thereby suggesting the nanofibrillar collagen can be a useful tool to maintain vascular homeostasis. The ECs elongated and organized their actin cytoskeleton along the direction of the aligned collagen fibrils, as demonstrated by organized actin, microtubule networks, and focal adhesions. The nanofibrillar collagen also promoted increased cellular migration along the direction of the nanofibrils. The quantification of monocyte adhesion and expression level of adhesion molecules, known testing indicators of atherosclerosis development, suggested the aligned nanofibrils also promoted an athero-resistant phenotype in the ECs. ECs are subject to biophysical cues in vivo, either in the form of surface topography (provided by the basement membrane of the ECM) or the hemodynamic effects of blood flow. The combination of these cues regulate the organization and immunogenicity of ECs and is representative of the in vivo environment. Therefore, we also investigated the endothelial behavior when both types of cues (topography and flow) were simultaneously present. At physiological levels of high shear stress (14-17 dynes/cm2), the matrix-aligned ECs were able to resist reorientation despite shear flow perpendicular to the matrix direction. The anisotropic collagen matrix could preserve the alignment and elongation of ECs as well as promote an athero-resistant phenotype after exposure to antagonistic perpendicular flow. The ability of the anisotropic nanofibrillar collagen to regulate cell morphology and especially EC immunogenicity highlights its potential in the treatment of vascular diseases. Therefore, an aligned conduit of collagen nanofibrils was fabricated to address the need for a small-diameter vascular graft capable of regulating cellular function. The vascular graft was designed to have a mechanical integrity comparable to that of native vessels and was able to regulate EC attachment, morphology, and phenotype. In addition, the aligned collagen grafts could support an anti-thrombogenic surface modification, providing short-term patency in the carotid artery model of Sprague-Dawley rats.