Ecole Nationale Supérieure des Mines de Saint-Etienne, CIS-EMSE, SAINBIOSE, F-42023 Saint Etienne, France; INSERM, U1059, F-42000 Saint Etienne, France; Université de Lyon, SAINBIOSE, F-42000 Saint Etienne, France; Laboratoire de Tribologie et Dynamique des Systèmes, CNRS UMR 5513, Université de Lyon, Ecole Centrale Lyon, France.
Laboratoire de Tribologie et Dynamique des Systèmes, CNRS UMR 5513, Université de Lyon, Ecole Centrale Lyon, France.
J Mech Behav Biomed Mater. 2018 Jan;77:718-726. doi: 10.1016/j.jmbbm.2017.08.014. Epub 2017 Aug 12.
Biomechanics of the extracellular matrix in arteries determines their macroscopic mechanical behavior. In particular, the distribution of collagen fibers and bundles plays a significant role. Experimental data showed that, in most arterial walls, there are preferred fiber directions. However, the realignment of collagen fibers during tissue deformation is still controversial: whilst authors claim that fibers should undergo affine deformations, others showed the contrary. In order to have an insight about this important question of affine deformations at the microscopic scale, we measured the realignment of collagen fibers in the adventitia layer of carotid arteries using multiphoton microscopy combined with an unprecedented Fourier based method. We compared the realignment for two types of macroscopic loading applied on arterial segments: axial tension under constant pressure (scenario 1) and inflation under constant axial length (scenario 2). Results showed that, although the tissue underwent macroscopic stretches beyond 1.5 in the circumferential direction, fiber directions remained unchanged during scenario 2 loading. Conversely, fibers strongly realigned along the axis direction for scenario 1 loading. In both cases, the motion of collagen fibers did not satisfy affine deformations, with a significant difference between both cases: affine predictions strongly under-estimated fiber reorientations in uniaxial tension and over-estimated fiber reorientations during inflation at constant length. Finally, we explained this specific kinematics of collagen fibers by the complex tension-compression interactions between very stiff collagen fibers and compliant surrounding proteins. A tensegrity representation of the extracellular matrix in the adventitia taking into account these interactions was proposed to model the motion of collagen fibers during tissue deformation.
动脉细胞外基质的生物力学决定了其宏观力学行为。特别是胶原纤维和束的分布起着重要作用。实验数据表明，在大多数动脉壁中，存在着优先的纤维方向。然而，在组织变形过程中胶原纤维的重新排列仍然存在争议：尽管有些作者声称纤维应该经历仿射变形，但另一些作者则表明相反。为了深入了解微观尺度上仿射变形的这一重要问题，我们使用多光子显微镜结合一种前所未有的基于傅里叶的方法，测量了颈动脉外膜中胶原纤维的重新排列。我们比较了两种宏观加载方式下的重新排列：在恒压下的轴向拉伸（情况 1）和在恒轴向长度下的膨胀（情况 2）。结果表明，尽管组织在环向方向上经历了超过 1.5 的宏观拉伸，但在情况 2 加载过程中纤维方向保持不变。相反，在情况 1 加载时，纤维强烈地沿着轴向重新排列。在这两种情况下，胶原纤维的运动都不符合仿射变形，两种情况之间存在显著差异：在单轴拉伸时，仿射预测严重低估了纤维的重新取向，而在恒长度膨胀时，仿射预测又高估了纤维的重新取向。最后，我们通过非常硬的胶原纤维和顺应性周围蛋白之间复杂的拉压相互作用，解释了胶原纤维的这种特定运动学。提出了一种考虑到这些相互作用的外膜细胞外基质的 tensegrity 表示法，以模拟组织变形过程中胶原纤维的运动。
