Macro- and Micro-mechanical Properties of the Ovine Aorta: Correlation with Regional Variations in Collagen, Elastin and Glycosaminoglycan Levels

Aortic diseases are a significant cardiovascular health problem and occur in different ways across the vascular tree. Investigation of the mechanical properties of the aorta is important for better understanding of aortic diseases. In this study, the biomechanical and biochemical properties of the ovine aorta have been comprehensively mapped across different regions from the ascending to the abdominal aorta. We have determined the mechanical properties at the macro- (via tensile testing) and at the micro-scale (via oscillatory nanoindentation). Uniaxial tensile testing was conducted on circumferential strips for the ascending, upper thoracic region and upper abdominal region to determine physiological elastic modulus, tangent modulus at 0.5 strain, and the maximum elastic modulus. Nanoindentation was conducted on the medial layer (tissue cross-section) and intimal and adventitial face (longitudinal orientation) to determine the shear storage ( G ′) and shear loss modulus ( G ″). All of the measured mechanical properties increased with distance from the heart. For example, G ′ increased by 237.1% and 275.3% for the intimal face and adventitial face, respectively. In parallel, collagen, glycosaminoglycans (GAG) and elastin levels were also measured across the entire length of the ovine aorta. The mechanical properties correlated with increasing collagen, and decreasing GAG and elastin. Collagen increased by 147.2% whereas GAG (−120.3%) and elastin decreased (−78.2%). These findings have relevance for developing mechanistic insight into aortic aneurysms and dissections.