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Mechanical parameters modulated by the MOUS are insensitive to different overlapping pattern suggesting that endovascular procedure can be performed with less attention to the overlapping pattern.

Objective: Mechanical properties of healthy, aneurysmal, and atherosclerotic arterial tissues are essential for assessing the risk of lesion development and rupture. Strain energy density function (SEDF) has been widely used to describe these properties, where material constants of the SEDF are traditionally determined using the ordinary least square (OLS) method. However, the material constants derived using OLS are usually dependent on initial guesses. Methods: To avoid such dependencies, Bayesian inference-based estimation was used to fit experimental stress-stretch curves of 312 tissue strips from 8 normal aortas, 19 aortic aneurysms, and 21 carotid atherosclerotic plaques to determine the constants, C 1 , D 1 , and D 2 of the modified Mooney-Rivlin SEDF. Results: Compared with OLS, material constants varied much less with prior in the Bayesian inferencebased estimation. Moreover, fitted material constants differed amongst distinct tissue types. Atherosclerotic tissues associated with the biggest D 2 , an indicator of the rate of increase in stress during stretching, followed by aneurysmal tissues and those from normal aortas. Histological analyses showed that C 1 and D 2 were associated with elastin content and details of the colla

Objective: Fibre structures and pathological features, e.g., inflammation and glycosaminoglycan (GAG) deposition, are the primary determinants of aortic mechanical properties. This study is designed to quantify the association of tissue ultimate strength and stretch with the structural percentage of different components, in particular, GAG, and local fibre structure. Methods: Thoracic aortic aneurysm (TAA) tissues from 8 patients were collected. Ninety-six tissue strips of thickened intima, media and adventitia were prepared for uni-extension tests and histopathological examination. Area ratios of collagen, elastin, macrophage and GAG and collagen fibre dispersion were quantified. Results: Collagen, elastin and GAG were layer-dependent and the inflammatory burden in all layers was low. The local GAG ratio was negatively associated with the collagen ratio (r2=0.173, p<0.05), but positively with elastin (r2=0.037, p<0.05). Higher GAG deposition resulted in larger local collagen dispersion in media and adventitia, but not in intima. The ultimate stretch in axial and circumferential directions was exclusively associated with elastin ratio (Axial: r2=0.186, p=0.04; Circumferential: r2=0.175, p=0.04). Multivariate analysis showed that collagen and GAG were both associated with ultimate strength in the circumferential direction, but not with the axial direction (Collagen: slope=27.3, GAG: slope=-18.4, r2=0.438, p=0.002). Conclusions: GAG may play important roles in TAA material strength. Its deposition was found to be associated positively with the local collagen dispersion and negatively with ultimate strength in circumferential direction.

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