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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.

Background: Aortic dissection is a devastating condition, beginning with a tear through from intima to the medial layer, leading to splitting of aortic layers and creating the false and true lumen with a septum (or flap). Little is known about the properties of the dissection flap. Aim: To determine the time-dependent (creep) biomechanical behaviour and biochemical properties of the dissection flap. Methods: 15 descending thoracic aorta samples were obtained from patients undergoing elective surgery for chronic dissected aneurysms. Creep was measured using a non-destructive ball indentation technique utilising a stainless-steel ball over 5 hours. Images were obtained using a long focal distance objective microscope. Remaining tissues were used to determine elastin and glycosaminoglycan (GAG) levels. Results: The elastic modulus (tissue stiffness) was 64.68 ± 11 kPa and 55.1 ± 9.5 kPa for the flap and true aortic wall respectively. Over 5 hours, the central deformation of the flap tissue was found to be 0.52 ± 0.07 mm as compared to 0.67 ± 0.07 mm for the true aortic wall (p < 0.05). Elastin levels were 126.8 ± 37.25 mg/mg for the flap and 79.82 ± 19.64 mg/mg for the true aortic wall (p < 0.05). The GAG levels were 4.2 mg/mg ± 0.9 mg/mg for the flap and 3.0 ± 0.5 mg/mg (p < 0.05). Conclusion: The dissection flap exhibits reduced time-dependent deformation and has higher levels of elastin and GAG relative to the aortic wall. These findings may help develop bespoke surgical treatments based on the unique biomechanical and biochemical properties that have been identified.

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