Lipid bilayer membranes have a native (albeit small) permeability for water molecules. Under an external load, provided that the bilayer structure stays intact and does not suffer from poration or rupture, a lipid membrane deforms and its water influx/efflux is often assumed negligible in the absence of osmolarity. In this work we use boundary integral simulations to investigate the effects of water permeability on the hydrodynamics of an inextensible membrane under a mechanical load, such as the viscous stress from an external flow deforming an inextensible membrane in free space or pushing it through a confinement. Incorporating the membrane permeability into the framework of Helfrich free energy for an inextensible, elastic membrane (a vesicle), we illustrate that, in the absence of an osmotic stress gradient, the semipermeable vesicle is affected by water influx/efflux over a sufficiently long time or under a strong confinement. Our simulations quantify the conditions for water permeation to be negligible in terms of the timescales, flow strength, and confinement. These results shed light on how microfluidic confinement can be utilized to estimate membrane permeability.

中文翻译：

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流动和约束下半透不可伸展膜的流体动力学

脂质双层膜对水分子具有天然的（尽管很小）渗透性。在外部负载下，如果双层结构保持完整并且不会发生穿孔或破裂，脂质膜会变形，并且在没有渗透压的情况下，它的水流入/流出通常可以忽略不计。在这项工作中，我们使用边界积分模拟来研究透水性对机械载荷下不可伸展膜的流体动力学的影响，例如来自外部流动的粘性应力使自由空间中的不可伸展膜变形或推动它通过限制。将膜渗透性纳入不可延伸的弹性膜（囊泡）的 Helfrich 自由能框架，我们说明，在没有渗透应力梯度的情况下，半透性囊泡在足够长的时间内或在强限制下受到水流入/流出的影响。我们的模拟量化了水渗透的条件，在时间尺度、流动强度和限制方面可以忽略不计。这些结果阐明了如何利用微流体限制来估计膜通透性。