胸大動脈壁内コラーゲン線維の2軸等方引張負荷下リアルタイム変形挙動観察

抄録

Since collagen fibers are crucial in determining the mechanical properties of the aorta at large strain levels, they may affect aortic rupture profoundly. In this study, we observed change in collagen fiber direction in the aortic media under equibiaxial stretch. The media of porcine thoracic aorta was sliced into 50 or 100-μm-thick sections perpendicular to the radial direction and stretched under a microscope equipped with birefringent imaging system to measure slow axis azimuth θ (circumferential direction is taken as 0°) as an index of the direction of collagen fibers. At no-load state, collagen fibers sharply oriented in the circumferential direction in sub-intimal specimens. The distribution of the orientation became broad as one goes toward adventitia, and had two symmetric peaks in sub-adventitial specimens. The differences between the two peaks were 2.9° and 40.0° for sub-intimal and sub-adventitial sides, respectively. The collagen fiber direction corresponded to the long axis of the cell nuclei, indicating that the collagen fibers were oriented in the long axis of cell direction. Standard deviation of the collagen fiber angle in each specimen was 19°±7° (mean±SD, n=6) at no-load state. By applying the equibiaxial stretch to the mid-medial specimens, the standard deviation of the fiber angle decreased gradually to 13°±6° (n=6) just before failure, indicating that more collagen fibers oriented in the circumferential direction. It has been reported that cracks of specimens obtained from porcine thoracic aortas always run in circumferential direction at rupture. The direction of collagen fibers might be a determinant factor for the aortic failure.