Haslach Henry W, Leahy Lauren N, Fathi Parinaz, Barrett Joshua M, Heyes Amanda E, Dumsha Thomas A, McMahon Eileen L
Department of Mechanical Engineering, University of Maryland, College Park, MD, 20742, USA.
Cardiovasc Eng Technol. 2015 Dec;6(4):501-18. doi: 10.1007/s13239-015-0245-7. Epub 2015 Sep 23.
Aortic dissection and rupture may involve circumferential shear stress in the circumferential-longitudinal plane. Inflation of bovine descending aortic ring specimens provides evidence of such shear from the non-uniform circumferential distortion of radial lines drawn on the circumferential-radial ring face. Delamination without tensile peeling induces cracks that propagate nearly circumferentially in the circumferential-longitudinal plane from the root of a radial cut representing rupture initiation in a ring. Translational shear deformation tests of small rectangular aortic wall blocks in the circumferential and longitudinal direction measure the consequences of such shear on substructures in the aortic wall, in particular the collagen fibers. The two directions of shear deformation produce no statistical difference in the shear stress response of the wall. Possibly, the interfiber connections between collagen fibers are put into tension by either translational shear deformation so that the stress measured reflects the tensile response of these connections. Wall rupture may involve failure of these connections; such failure is supported by the voids parallel to the collagen fibers observed in a histological study after translational shear. Further, interstitial fluid is redistributed by shear as evidenced by the measured weight loss of a set of specimens during the translational shear of blocks. Because the mass changes, mathematical modeling of aortic tissue in vitro as incompressible is an approximation. These observations suggest that no simple modification of classical rupture theories, whether based on energy functions, stress or strain, suffices to predict the rupture of hydrated soft biological tissue that has complex substructures.
主动脉夹层和破裂可能涉及周向 - 纵向平面内的周向剪切应力。牛降主动脉环标本的膨胀通过绘制在周向 - 径向环面上的径向线的不均匀周向变形提供了这种剪切的证据。无拉伸剥离的分层会产生裂纹，这些裂纹在周向 - 纵向平面内从代表环破裂起始的径向切口根部几乎沿周向扩展。小矩形主动脉壁块在周向和纵向的平移剪切变形试验测量了这种剪切对主动脉壁亚结构，特别是胶原纤维的影响。两个方向的剪切变形在壁的剪切应力响应上没有统计学差异。可能是，胶原纤维之间的纤维间连接通过平移剪切变形而处于拉伸状态，因此测量到的应力反映了这些连接的拉伸响应。壁破裂可能涉及这些连接的失效；在平移剪切后的组织学研究中观察到的与胶原纤维平行的空隙支持了这种失效。此外，剪切会使间质液重新分布，这在块体平移剪切过程中一组标本的测量重量损失中得到了证明。由于质量发生变化，将体外主动脉组织数学建模为不可压缩是一种近似。这些观察结果表明，无论是基于能量函数、应力还是应变的经典破裂理论，都没有简单的修正足以预测具有复杂亚结构的水合软生物组织的破裂。
