| The exact mechanisms involved in the pathogenesis of aortic aneurysms of the human ascending aorta (AA) are unknown. It is believed that the remodeling capabilities of the endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) combined with abnormal and non-uniform shear and tissue stresses, generated by a perturbed hemodynamics produced by a diseased aortic valve, are the precursors in the disease progression. In this work, we hypothesize that local remodeling of the dilated AA exists and is valve type dependent. However, very little data exists on the local mechanical and structural properties of healthy and dilated AA. A detailed description of these tissues will provide valuable clues about the progression of the disease and help identify the mechanisms involved. The regional analysis has revealed a significant location dependency in stiffness, thickness and collagen content in healthy and dilated BAV-T1 AA tissues. However, these natural regional variations were not evident in dilated TAV tissues, which suggests a loss of the natural heterogeneity with dilation. On average, collagen content and thickness have shown differences between dilated TAV and BAV-T1 tissues, which suggests two distinct remodeling processes. Regional variations in the density and orientation of the VSMCs have also been found in pig AA. The outer curvature has a higher cell density with cells tilting towards the axial direction in response to higher tissue stresses in this quadrant. Although, VSMCs activation with phenylephrine had a significant effect on the stiffness of the pig AA, which was independent of location or direction. Local remodeling often occurs after an aortic arch reconstruction surgery because of compliance mismatch between the native AA and the replacement material. Since no study has carefully quantified this degree of mismatch in the repaired AA, such an investigation was needed. We have found significant differences in stiffness and anisotropy between replacement materials and native tissues. Knowledge of the anisotropy is important when placing patch materials to minimize mismatch. Making surgeons aware of these mechanical differences can aid in surgical decision-making and hopefully inspire the design of new materials or techniques. |
