Bitbol M
Biophys J. 1986 May;49(5):1055-68. doi: 10.1016/S0006-3495(86)83734-1.
Two modes of behavior of single human red cells in a shear field have been described. It is known that in low viscosity media and at shear rates less than 20 s-1, the cells rotate with a periodically varying angular velocity, in accord with the theory of Jeffery (1922) for oblate spheroids. In media of viscosity greater than approximately 5 mPa s and sufficiently high shear rates, the cells align themselves at a constant angle to the direction of flow with the membrane undergoing tank-tread motion. Also, in low viscosity media, as the shear rate is increased, more and more cells lie in the plane of shear, undergoing spin with their axes of symmetry aligned with the vorticity axis of the shear field in an orbit "C = 0" (Goldsmith and Marlow, 1972). We have explored this latter phenomenon using two experimental methods. First, the erythrocytes were observed in the rheoscope and their diameters measured. Forward light scattering patterns were correlated with the red cell orientation mode. Light flux variations after flow onset or stop were measured, and the characteristic times of erythrocyte orientation and disorientation were assessed. The characteristic time of erythrocyte orientation in Orbit C = 0 is proportional to the inverse of the shear rate. The corresponding coefficient of proportionality depends on the suspending medium viscosity eta o. The disorientation time tau D, after flow has been stopped, is such that the ratio tau D/eta o is independent of the initial applied shear stress. However, tau D is much shorter than one would expect if pure Brownian motion were involved. The proportion of erythrocytes in orbit C = 0 was also measured. It was found that this proportion is a function of both the shear rate and eta o. At low values of eta o, the proportion increases with increasing shear rate and then reaches a plateau. For higher values of eta o (5 to 10 mPa s), the proportion of RBC in orbit C = 0 is a decreasing function of the shear stress. A critical transition between orbit C = 0 and parallel alignment was observed at high values of eta o, when the shear stress is on the order of 1 N/m2. Finally, the effect of altering membrane viscoelastic properties (by heat or diamide treatment) was tested. The proportion of oriented cells is a steep decreasing function of red cell rigidity.
已经描述了单个人类红细胞在剪切场中的两种行为模式。众所周知，在低粘度介质中且剪切速率小于20 s-1时，细胞会以周期性变化的角速度旋转，这与杰弗里（1922年）关于扁球体的理论一致。在粘度大于约5 mPa s的介质中以及足够高的剪切速率下，细胞会与流动方向成恒定角度排列，其膜进行坦克履带式运动。此外，在低粘度介质中，随着剪切速率的增加，越来越多的细胞位于剪切平面内，以其对称轴与剪切场的涡度轴对齐的方式在“C = 0”轨道中自旋（戈德史密斯和马洛，1972年）。我们使用两种实验方法探索了后一种现象。首先，在流变仪中观察红细胞并测量其直径。前向光散射模式与红细胞取向模式相关。测量了流动开始或停止后的光通量变化，并评估了红细胞取向和去取向的特征时间。在轨道C = 0中红细胞取向的特征时间与剪切速率的倒数成正比。相应的比例系数取决于悬浮介质的粘度ηo。流动停止后的去取向时间τD使得τD/ηo的比值与初始施加的剪切应力无关。然而，τD比如果涉及纯布朗运动时预期的要短得多。还测量了轨道C = 0中红细胞的比例。发现该比例是剪切速率和ηo两者的函数。在ηo值较低时，该比例随剪切速率的增加而增加，然后达到平稳状态。对于较高的ηo值（5至10 mPa s），轨道C = 0中红细胞的比例是剪切应力的递减函数。在高ηo值下，当剪切应力约为1 N/m2时，观察到轨道C = 0与平行排列之间的临界转变。最后，测试了改变膜粘弹性性质（通过加热或二酰胺处理）的效果。取向细胞的比例是红细胞刚性的陡峭递减函数。
