Micropipette aspiration, optical tweezers, rheometry, or ecktacytometry have been used to study the shape recovery of healthy human Red Blood Cells (RBCs) and measure associated relaxation times of the order of 100–300 ms. These measurements are in good agreement with the Kelvin–Voigt model, which describes the cell as a visco-elastic material, predicting that its relaxation time only depends on cell intrinsic properties. However, such mechanical solicitation techniques are far from being relevant regarding RBC solicitation in vivo. In this paper, we report for the first time the existence of two different behaviors of the RBC shape recovery while flowing out of a microfluidic constricted channel. The calculation of the viscous stress corresponding to the frontier between the two recovery modes confirms that the RBC resistance to shear $\mu$ is the elastic property dominating the transition between the two recovery behaviors. We also quantified associated recovery times ${\tau }_r$ and report values as low as 4 ms—which is almost two decades smaller than the typical RBC relaxation time—at high viscosity and flow velocity of the carrier fluid. Although we cannot talk about relaxation time because the cell is never at rest, we believe that the measured shape recovery time arises from the coupling of the cell intrinsic deformability and the hydrodynamic stress. Depending on the flow conditions, the cell mechanics becomes dominant and drives the shape recovery process, allowing the measurement of recovery times of the same order of magnitude than relaxation times previously published. Finally, we demonstrated that the measurement of the shape recovery time can be used to distinguish Plasmodium falciparum (causing malaria) infected RBCs from healthy RBCs.

中文翻译：

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从微流体狭窄处流出的红细胞的双重形状恢复。

微量移液管抽吸，光镊，流变仪或颈动脉流式细胞仪已用于研究健康人红细胞（RBC）的形状恢复，并测量相关的松弛时间，范围为100–300 ms。这些测量结果与Kelvin-Voigt模型非常吻合，该模型将细胞描述为粘弹性材料，预测其弛豫时间仅取决于细胞的固有特性。但是，这样的机械招标技术与体内RBC招标无关。。在本文中，我们首次报道了从微流体收缩通道流出时RBC形状恢复的两种不同行为。对应于两种恢复模式之间的边界的粘性应力的计算证实了RBC的抗剪力$\mu$是决定两个恢复行为之间过渡的弹性属性。我们还量化了相关的恢复时间${\tau }_{\mathrm{[R}}$并且在载流体的高粘度和高流速下，其报告值低至4 ms（比典型的RBC弛豫时间小了近二十年）。尽管由于电池从未处于静止状态而无法谈论松弛时间，但我们认为测得的形状恢复时间是由电池固有的可变形性与流体动力应力的耦合引起的。取决于流动条件，电池力学成为主导，并驱动形状恢复过程，从而使恢复时间的测量值与先前公布的松弛时间相同。最后，我们证明了形状恢复时间的测量可用于区分恶性疟原虫（引起疟疾）感染的RBC与健康RBC。