Multi-scale structural basis of mechanical behavior in porcine aorta and pulmonary artery

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The aorta and pulmonary artery perform distinct physiological functions and therefore exhibit different mechanical behaviors. However, the multi-scale structural determinants of these differences remain incompletely understood. In this study, uniaxial tensile testing was combined with ex vivo two-photon microscopy to characterize the mechanical properties and wall structure of the porcine aortas and pulmonary arteries. Statistical mediation analysis was used to identify the structural parameters underlying their mechanical differences. Compared with the pulmonary arteries, the aortas exhibit significantly higher initial modulus and tangent modulus in both the longitudinal and circumferential directions, as well as higher circumferential tensile strength. Mediation analysis further shows that these differences are governed by multi-scale structural features. Specifically, the lower initial modulus of the pulmonary arteries is associated with a smaller medial proportion and lower straightness of medial collagen fibers. The lower adventitial collagen content in the pulmonary arteries may contribute to their reduced longitudinal tangent modulus, whereas the higher adventitial composition partly offsets the difference in circumferential tangent modulus between the two vessels. In addition, the lower circumferential tensile strength of the pulmonary arteries is partly explained by reduced full-thickness collagen content. These findings establish a multi-scale structural basis for vessel-specific mechanical behavior and provide insights into vascular modeling and tissue-engineered graft design.