Department of Modern Mechanical Engineering, School of Creative Science and Engineering, Waseda University, Tokyo, Japan; Department of Integrative Bioscience and Biomedical Engineering, Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.
Department of Integrative Bioscience and Biomedical Engineering, Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.
J Mech Behav Biomed Mater. 2023 Oct;146:106028. doi: 10.1016/j.jmbbm.2023.106028. Epub 2023 Jul 15.
The aortic wall exhibits a unique elastic behavior, periodically expanding in aortic diameter by approximately 10% during heartbeats. This elastic behavior of the aortic wall relies on the distinct yet interacting mechanical properties of its three layers: intima, media, and adventitia. Aortic aneurysms develop as a result of multifactorial remodeling influenced by mechanical vulnerability of the aortic wall. Therefore, investigating the mechanical response of the aneurysmal wall, in conjunction with changes in microstructural parameters on both the intimal and adventitial sides, may offer valuable insights into the mechanisms of aortic aneurysm development or rupture. This study aimed to develop a biaxial tensile testing system to measure the mechanical properties of both sides of the tissue to gain insights concerning the interactions in anisotropic layered tissue. The biaxial tensile test set-up consisted of four motors, four cameras, four load cells, and a toggle switch. Porcine ascending aortas were chosen as the test subject. Graphite particles with diameters of approximately 5-11 [μm] were randomly applied to both sides of the aorta. Strain measurements were obtained using the stereo digital-image correlation method. Because stretching a rectangular specimen with a thread inevitably concentrates and localizes stress, to reduce this effect the specimen's shape was investigated using finite element analysis. The finite element analysis showed that a cross-shaped specimen with diagonally cut edges would be suitable. Therefore, we prepared specimens with this novel shape. This test system showed that mechanical response of the aortic tissue was significantly different between the intimal and adventitial side in the high-strain range, due to the disruption of collagen fibers. The adventitia side exhibited a smaller elastic modulus than the intimal side, accompanied by disruption of collagen fibers in the adventitia, which were more pronounced in the longitudinal direction. In contrast, in the mid-strain range, the elastic modulus did not differ between the intimal and adventitial sides, irrespective of longitudinal or circumferential direction, and collagen fibers were not disrupted but elongated. A biaxial tensile test system, which measures the mechanical properties of both sides of biological tissues and the shape of the specimen for reducing the concentration of stress at the chuck region, was developed in this study. The biaxial tensile testing system developed here is useful for better understanding the influences of mechanical loads and tissue degeneration on anisotropic, layered biological tissues.
主动脉壁具有独特的弹性行为，在心跳过程中其直径周期性地扩张约 10%。主动脉壁的这种弹性行为依赖于其三个层的独特但相互作用的机械特性：内膜、中膜和外膜。主动脉瘤是由于主动脉壁的机械脆弱性受多种因素影响而发生的重塑的结果。因此，研究动脉瘤壁的机械响应，以及内膜和外膜两侧微观结构参数的变化，可能有助于深入了解主动脉瘤发展或破裂的机制。本研究旨在开发一种双向拉伸测试系统，以测量组织两侧的力学性能，从而深入了解各向异性分层组织的相互作用。双向拉伸测试系统由四个电机、四个相机、四个负载单元和一个拨动开关组成。选择猪的升主动脉作为测试对象。将直径约为 5-11μm 的石墨颗粒随机施加到主动脉的两侧。使用立体数字图像相关方法获得应变测量值。由于用线拉伸矩形试样不可避免地会集中和局部化应力，为了减少这种影响，使用有限元分析研究了试样的形状。有限元分析表明，具有对角切割边缘的十字形试样将是合适的。因此，我们准备了具有这种新颖形状的试样。该测试系统表明，由于胶原纤维的破坏，在高应变范围内，主动脉组织的力学响应在内膜侧和外膜侧之间有显著差异。外膜侧的弹性模量小于内膜侧，同时外膜侧的胶原纤维被破坏，在纵向方向上更为明显。相比之下，在中应变范围内，无论在纵向还是周向方向，内膜侧和外膜侧的弹性模量都没有差异，胶原纤维没有被破坏，而是被拉长。本研究开发了一种双向拉伸测试系统，该系统可测量生物组织两侧的力学性能，并可对试样的形状进行调整以减少夹头区域的应力集中。这里开发的双向拉伸测试系统有助于更好地理解机械载荷和组织退化对各向异性、分层生物组织的影响。
