Markle D R, Evans E A, Hochmuth R M
Biophys J. 1983 Apr;42(1):91-8. doi: 10.1016/S0006-3495(83)84372-0.
Force relaxation and permanent deformation processes in erythrocyte membrane were investigated with two techniques: micropipette aspiration of a portion of a flaccid cell, and extension of a whole cell between two micropipettes. In both experiments, at surface extension ratios less than 3:1, the extent of residual membrane deformation is negligible when the time of extension is less than several minutes. However, extensions maintained longer result in significant force relaxation and permanent deformation. The magnitude of the permanent deformation is proportional to the total time period of extension and the level of the applied force. Based on these observations, a nonlinear constitutive relation for surface deformation is postulated that serially couples a hyperelastic membrane component to a linear viscous process. In contrast with the viscous dissipation of energy as heat that occurs in rapid extension of a viscoelastic solid, or in plastic flow of a material above yield, the viscous process in this case represents dissipation produced by permanent molecular reorganization through relaxation of structural membrane components. Data from these experiments determine a characteristic time constant for force relaxation, tau, which is the ratio of a surface viscosity, eta to the elastic shear modulus, mu. Because it was found that the concentration of albumin in the cell suspension strongly mediates the rate of force relaxation, values for tau of 10.1, 40.0, 62.8, and 120.7 min are measured at albumin concentrations of 0.0, 0.01, 0.1, and 1.% by weight in grams, respectively. The surface viscosity, eta, is calculated from the product of tau and mu. For albumin concentrations of 0.0, 0.01, 0.1, and 1% by weight in grams, eta is equal to 3.6, 14.8, 25.6, and 51.9 dyn s/cm, respectively.
对部分松弛细胞进行微吸管抽吸，以及在两个微吸管之间拉伸整个细胞。在这两个实验中，当表面延伸率小于3:1且延伸时间小于几分钟时，残余膜变形的程度可忽略不计。然而，保持较长时间的延伸会导致显著的力松弛和永久变形。永久变形的大小与延伸的总时间段和施加力的水平成正比。基于这些观察结果，假设了一种表面变形的非线性本构关系，该关系将超弹性膜成分与线性粘性过程串联耦合。与粘弹性固体快速延伸或材料在屈服点以上的塑性流动中以热的形式出现的粘性能量耗散不同，在这种情况下，粘性过程代表通过结构膜成分的松弛进行永久分子重组产生的耗散。这些实验数据确定了力松弛的特征时间常数τ，它是表面粘度η与弹性剪切模量μ的比值。因为发现细胞悬浮液中白蛋白的浓度强烈介导力松弛的速率，所以在白蛋白重量浓度分别为0.0%、0.01%、0.1%和1%时，测得的τ值分别为10.1、40.0、62.8和120.7分钟。表面粘度η由τ和μ的乘积计算得出。对于白蛋白重量浓度为0.0%、0.01%、0.1%和1%的情况，η分别等于3.6、14.8、25.6和51.9达因·秒/厘米。
