Variations in stiffness and structure of the human aorta along its length.

This study investigates the regional mechanical, structural, and morphological properties of the human aorta using fresh tissues from 10 middle-aged and elderly donors (62 ± 11 years old, 30% female). Four locations were analyzed: descending thoracic aorta (TA), supraceliac aorta (SC), infrarenal aorta (IFR), and distal abdominal aorta (dAA). Planar biaxial testing revealed location-specific stiffness, with distal regions exhibiting significantly reduced stretch at physiological stress levels. At 75 kPa, the circumferential stretch decreased from 1.24 in the TA to 1.12 in the dAA, while longitudinal stretch declined from 1.18 to 1.12. Elastin density in the medial layer showed a marked reduction, decreasing from 23.5% in the TA to 8.9% in the dAA, accompanied by thinning and fragmentation of elastic lamellae distally. Glycosaminoglycans were primarily localized near the intima and exhibited a consistent density (~ 5-6%) across all locations. Morphometric analysis revealed a progressive decrease in wall thickness in load-free conditions from 3.10 mm in the TA to 2.77 mm in the dAA, while stress-free configurations highlighted greater residual stresses in distal segments. Constitutive modeling using four common constitutive relations, including a four-fiber family model, provided parameters for computational simulations, with the four-fiber model offering the best fit. These findings provide quantitative insights into location-specific variations in the human aorta, advancing our understanding of its biomechanical and structural heterogeneity and informing computational models and therapeutic approaches.