Red blood cells flowing through capillaries assume a wide variety of different shapes owing to their high deformability. Predicting the realized shapes is a complex field as they are determined by the intricate interplay between the flow conditions and the membrane mechanics. In this work we construct the shape phase diagram of a single red blood cell with a physiological viscosity ratio flowing in a microchannel. We use both experimental in vitro measurements as well as 3D numerical simulations to complement the respective other one. Numerically, we have easy control over the initial starting configuration and natural access to the full 3D shape. With this information we obtain the phase diagram as a function of initial position, starting shape and cell velocity. Experimentally, we measure the occurrence frequency of the different shapes as a function of the cell velocity to construct the experimental diagram which is in good agreement with the numerical observations. Two different major shapes are found, namely croissants and slippers. Notably, both shapes show coexistence at low (<1 mm s⁻¹) and high velocities (>3 mm s⁻¹) while in-between only croissants are stable. This pronounced bistability indicates that RBC shapes are not only determined by system parameters such as flow velocity or channel size, but also strongly depend on the initial conditions.

中文翻译：

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在微通道中流动的红血球的形状双稳态的数值-实验观察†

流过毛细血管的红细胞由于其高度的可变形性而呈现出多种不同的形状。预测实现的形状是一个复杂的领域，因为它们是由流动条件和膜力学之间复杂的相互作用决定的。在这项工作中，我们构建了具有生理粘度比的单个红细胞在微通道中流动的形状相图。我们都使用体外实验测量和3D数值模拟，以补充各自的内容。从数字上讲，我们可以轻松控制初始启动配置，并自然访问完整的3D形状。有了这些信息，我们就可以得到作为初始位置，起始形状和细胞速度的函数的相图。在实验上，我们测量不同形状的出现频率作为细胞速度的函数，以构建与数值观察结果非常吻合的实验图。发现了两种不同的主要形状，即羊角面包和拖鞋。值得注意的是，两种形状在低速（<1 mm s ^-1）和高速度（> 3 mm s ^-1）下都共存。），而只有羊角面包是稳定的。这种明显的双稳性表明，RBC形状不仅由系统参数（例如流速或通道大小）决定，而且还强烈取决于初始条件。