Compromised elastin network load transfer in aging human aorta.

Elastic fibers are essential for passive arterial load bearing and must withstand billions of loading cycles throughout life. Although arterial stiffening is a hallmark of cardiovascular aging, how elastin mechanical function evolves with aging in humans remains poorly understood. This study investigated age-dependent changes in the mechanical properties and microstructure of purified human aortic elastin networks. Purified elastin networks were obtained from human thoracic aortas (17 in total; 9 males, 8 females; ages 26-92 years). Uniaxial tensile testing was performed, and tangent modulus at 1.1 stretch was calculated from Cauchy stress-stretch responses. Elastin microstructure was examined using multiphoton microscopy, histology, and scanning electron microscopy (SEM), combined with quantitative image analysis. Elastin tangent modulus decreases significantly with aging in male subjects (p < 0.05). Multiphoton imaging revealed progressive reduction in fiber straightness with age (p < 0.05 in males), with young elastin networks characterized by straight, continuous fibers that primarily reoriented under load, whereas older networks exhibited increased waviness, fragmentation, and loss of load-bearing fibers. Histological analysis further demonstrated a significant age-related reduction in lamellar length in males (p < 0.05), indicating increased network discontinuity. SEM further demonstrated pronounced ultrastructural deterioration in older male samples, with elastic fibers appearing fragmented and frayed compared to the continuous and organized fibers in younger males. These microstructural alterations were consistent with diminished mechanical engagement of elastin fibers under tensile loading in the older male samples. In contrast, female samples did not exhibit consistent age-dependent deterioration in either mechanical or microstructural metrics. STATEMENT OF SIGNIFICANCE: This study provides direct experimental evidence linking age-related microstructural degradation of isolated human elastin networks to impaired mechanical function. Using purified elastin from naturally aged human thoracic aortas, we demonstrate that aging in males is associated with increased elastin fragmentation, fiber waviness, reduced lamellar continuity, and diminished mechanical stiffness, whereas female elastin networks exhibit relative structural and functional preservation. These findings identify deterioration of elastin network integrity as a potential mechanobiological contributor to arterial aging and stiffening. By integrating biomechanics with multiscale imaging of aged human tissues, this work advances understanding of elastin's role in vascular biomechanics and suggests potential sex-specific differences in elastin aging.