Aix Marseille Université, Centre National de la Recherche Scientifique, Laboratoire Adhésion et Inflammation Unité Mixte de Recherche 7333, Inserm UMR1067, 13009 Marseille, France.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):20808-13. doi: 10.1073/pnas.1210236109. Epub 2012 Dec 3.
At the cellular scale, blood fluidity and mass transport depend on the dynamics of red blood cells in blood flow, specifically on their deformation and orientation. These dynamics are governed by cellular rheological properties, such as internal viscosity and cytoskeleton elasticity. In diseases in which cell rheology is altered genetically or by parasitic invasion or by changes in the microenvironment, blood flow may be severely impaired. The nonlinear interplay between cell rheology and flow may generate complex dynamics, which remain largely unexplored experimentally. Under simple shear flow, only two motions, "tumbling" and "tank-treading," have been described experimentally and relate to cell mechanics. Here, we elucidate the full dynamics of red blood cells in shear flow by coupling two videomicroscopy approaches providing multidirectional pictures of cells, and we analyze the mechanical origin of the observed dynamics. We show that contrary to common belief, when red blood cells flip into the flow, their orientation is determined by the shear rate. We discuss the "rolling" motion, similar to a rolling wheel. This motion, which permits the cells to avoid energetically costly deformations, is a true signature of the cytoskeleton elasticity. We highlight a hysteresis cycle and two transient dynamics driven by the shear rate: an intermittent regime during the "tank-treading-to-flipping" transition and a Frisbee-like "spinning" regime during the "rolling-to-tank-treading" transition. Finally, we reveal that the biconcave red cell shape is highly stable under moderate shear stresses, and we interpret this result in terms of stress-free shape and elastic buckling.
在细胞尺度上，血液的流动性和质量传输取决于血流中红细胞的动力学，特别是它们的变形和取向。这些动力学受细胞流变学特性的控制，如内部粘度和细胞骨架弹性。在细胞流变学因遗传、寄生虫入侵或微环境变化而改变的疾病中，血流可能会严重受损。细胞流变学和流动之间的非线性相互作用可能会产生复杂的动力学，这些动力学在很大程度上仍未得到实验探索。在简单剪切流中，仅通过两种运动，“翻滚”和“坦克履带”，已在实验中进行了描述，并与细胞力学有关。在这里，我们通过耦合两种提供细胞多向图片的视频显微镜方法来阐明红细胞在剪切流中的全动力学，并分析观察到的动力学的力学起源。我们表明，与普遍的看法相反，当红细胞翻转进入流动时，它们的取向由剪切率决定。我们讨论了“滚动”运动，类似于滚动的轮子。这种运动允许细胞避免能量成本高的变形，是细胞骨架弹性的真实特征。我们突出了一个滞后循环和两个由剪切率驱动的瞬态动力学：在“坦克履带-翻转”过渡期间的间歇性状态和在“滚动-坦克履带”过渡期间的 Frisbee 样“旋转”状态。最后，我们揭示了在适度的剪切应力下双凹红细胞形状非常稳定，我们根据无应力形状和弹性屈曲来解释这个结果。
