Xu Xiaojuan, Yang Fan, Yu Yue, Xin Yuan-Feng, Tong Jianhua
Institute for Biomedical Engineering and Nano Science, Shanghai East Hospital, Tongji University School of Medicine, 500 Zhennan Road, Shanghai, 200331, People's Republic of China.
School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai, People's Republic of China.
Biomech Model Mechanobiol. 2025 Apr;24(2):441-454. doi: 10.1007/s10237-024-01917-4. Epub 2024 Dec 26.
Hypertension and bicuspid aortic valve (BAV) are key clinical factors that may affect local biomechanical properties of ascending thoracic aortic aneurysms (ATAAs). This study sought to investigate regional differences in biaxial mechanical properties of the ATAAs for the hypertensive patients with BAV. Fresh ATAA samples were harvested from 16 hypertensive patients (age, 66 ± 9 years) undergoing elective aortic surgery. Biaxial extension tests were employed to characterize region-specific biaxial mechanical behaviors of the hypertensive BAV-ATAAs. A material model was used to fit biaxial experimental data to obtain model parameters in different regions. Histological analysis was performed to investigate the underlying aortic microstructure and to determine percentages of elastic and collagen fibers. Mechanical behaviors of the hypertensive BAV-ATAAs were nonlinear and anisotropic for most specimens from anterior, lateral and posterior regions. Under the equibiaxial stresses, the ATAA tissues in the lateral region had significantly lower extensibility and significantly higher stiffness in both circumferential and longitudinal directions when compared with the posterior and medial regions. The material model was able to fit regional biaxial data well. Histology showed that laminar structures of elastic fibers were mainly disrupted in the anterior and lateral regions in which, however, pronounced collagen fiber hyperplasia was observed. Moreover, there was a strong positive correlation between circumferential aortic stiffness and patient age in the anterior and lateral regions. Our results suggest that elastic properties in the lateral and anterior regions are more deteriorated than those in the posterior and medial regions for the hypertensive BAV-ATAAs. Thus, the outer curvature of the ATAA wall should be regarded as special quadrants that may be highly susceptible to microstructural changes and may have a substantial impact on aneurysm growth.
高血压和二叶式主动脉瓣（BAV）是可能影响升主动脉瘤（ATAAs）局部生物力学特性的关键临床因素。本研究旨在调查患有BAV的高血压患者ATAAs双轴力学特性的区域差异。从16例接受择期主动脉手术的高血压患者（年龄66±9岁）中获取新鲜的ATAA样本。采用双轴拉伸试验来表征高血压BAV-ATAAs区域特异性的双轴力学行为。使用材料模型拟合双轴实验数据以获得不同区域的模型参数。进行组织学分析以研究主动脉的潜在微观结构并确定弹性纤维和胶原纤维的百分比。对于大多数来自前、侧和后区域的标本，高血压BAV-ATAAs的力学行为是非线性和各向异性的。在等双轴应力下，与后和内侧区域相比，外侧区域的ATAA组织在周向和纵向方向上的伸展性明显更低，刚度明显更高。该材料模型能够很好地拟合区域双轴数据。组织学显示，弹性纤维的层状结构主要在前部和外侧区域被破坏，然而，在这些区域观察到明显的胶原纤维增生。此外，在前部和外侧区域，主动脉周向刚度与患者年龄之间存在很强的正相关。我们的结果表明，对于高血压BAV-ATAAs，外侧和前部区域的弹性特性比后部和内侧区域更差。因此，ATAA壁的外曲率应被视为特殊象限，可能极易受到微观结构变化的影响，并且可能对动脉瘤的生长产生重大影响。
