Biomechanics Laboratory, Department of Mechanical Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, 466-8555, Japan.
Department of Mechanical Systems Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan.
Biomech Model Mechanobiol. 2018 Apr;17(2):577-587. doi: 10.1007/s10237-017-0979-2. Epub 2017 Nov 13.
Although elucidation of the mechanism of aortic aneurysm rupture is important, the characteristics of crack initiation and propagation sites remain unknown. To determine the microscopic properties of these sites, the characteristics of local strains and constituents at crack initiation and propagation sites were investigated during biaxial stretching of porcine thoracic aortas (PTAs). PTAs were sliced into approximately 50-[Formula: see text]-thick sections, and the center of the sections was made especially thin using our previously developed technique. Alpha-elastin and cell nuclei were fluorescently labeled as indices of local elastin density and as a strain marker, respectively. Birefringence and second harmonic generation (SHG) light images were used to determine local collagen distributions. The specimens were then stretched biaxially with a laboratory-made tensile tester under a fluorescent microscope equipped with a birefringence imaging system. Local strains were calculated from the local displacement of the cell nuclei. The degree of alignment and density of local collagen fibers were measured from retardance and SHG images. The strain distributions, specifically the first and second principal, and maximum shear strains, fluorescent intensity of [Formula: see text]-elastin, and degree of alignment of collagen fibers, showed insignificant differences between the crack initiation sites and other sites. The retardance and intensity of SHG light at the crack initiation sites were significantly lower than those at other sites for all ([Formula: see text]) specimens. Cracks tended to propagate along the local direction of the collagen fibers. These results indicate that the local density and direction of collagen fibers play an important role in aorta rupture.
虽然阐明主动脉瘤破裂的机制很重要，但裂纹起始和扩展部位的特征仍不清楚。为了确定这些部位的微观特性，在猪胸主动脉（PTAs）的双向拉伸过程中，研究了裂纹起始和扩展部位的局部应变和成分的特征。PTAs 被切成约 50-[Formula: see text]-厚的切片，并且使用我们之前开发的技术使切片的中心特别薄。α-弹性蛋白和细胞核被荧光标记为局部弹性蛋白密度和应变标记物的指标。双折射和二次谐波产生（SHG）光图像用于确定局部胶原分布。然后，将标本在荧光显微镜下用实验室制造的拉伸试验机进行双向拉伸，该显微镜配备有双折射成像系统。从细胞核的局部位移计算局部应变。从延迟和 SHG 图像测量局部胶原纤维的取向程度和密度。应变分布，特别是第一和第二主应变以及最大剪切应变、[Formula: see text]-弹性蛋白的荧光强度和胶原纤维的取向程度，在裂纹起始部位和其他部位之间没有明显差异。在所有 ([Formula: see text]) 标本中，裂纹起始部位的延迟和 SHG 光的强度均明显低于其他部位。裂纹倾向于沿着胶原纤维的局部方向扩展。这些结果表明，胶原纤维的局部密度和方向在主动脉破裂中起着重要作用。
