Off-center motion of a trapped elastic capsule in a microfluidic channel with a narrow constriction,Soft Matter

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Off-center motion of a trapped elastic capsule in a microfluidic channel with a narrow constriction
Soft Matter ( IF 2.9 ) Pub Date : 2017-10-18 00:00:00 , DOI: 10.1039/c7sm01425b
Zheng Yuan Luo _{1,

2,

3,

4} , Bo Feng Bai _{1,

2,

3,

4}

Affiliation

Owing to their significance in capsule-related engineering and biomedical applications, a number of studies have considered the dynamics of elastic capsules flowing in constricted microchannels. However, these studies have focused on capsules moving along the channel centerline. In the present study, we numerically investigate the transient motion of an elastic capsule in a microfluidic channel with a rectangular constriction, which is initially trapped at the constriction inlet while off the channel centerline (i.e., on the channel bottom-wall). Under the push of the surrounding flow, the capsule can squeeze into the constriction, but only if the capsule deformability or the constriction size is sufficiently large. We find that the critical capillary number leading to the penetration of the capsule into the constriction is larger for off-centerline capsules compared to centered capsules. The centered capsule is stationary at the steady state when it remains stuck at the constriction; in contrast, the off-centerline capsule is not stationary but exhibits a tank-treading motion, i.e., its overall shape maintains a nonspherical shape with a protrusion into the constriction while its membrane exhibits a continuous rotation. Further, we examine the dependence of the capsule motion type, capsule deformation degree and membrane tension distribution on the capillary number (measuring the effects of flow strength and membrane mechanics) and constriction geometries (including the constriction height and width). Finally, we discuss the mechanism governing the capsule motion by analyzing the hydrodynamic forces acting on the capsule. The shear force acting on the capsule top owing to the fluid flow in the gap between the capsule top and the channel top-wall is the main source inducing the membrane tank-treading rotation.

中文翻译：

狭窄狭窄的微流体通道中捕获的弹性胶囊的偏心运动

由于它们在与胶囊有关的工程和生物医学应用中的重要性，许多研究已经考虑了在狭窄的微通道中流动的弹性胶囊的动力学。但是，这些研究集中在沿通道中心线移动的胶囊上。在本研究中，我们通过数值研究弹性胶囊在具有矩形收缩的微流体通道中的瞬态运动，该运动最初被捕获在收缩入口处，而偏离通道中心线（即，位于通道底墙上）。在周围流动的推动下，胶囊可以挤入狭窄处，但前提是胶囊的可变形性或狭窄处尺寸足够大。我们发现，与中心胶囊相比，偏离中心线的胶囊导致毛细管渗入缩颈的临界毛细管数更大。当居中的胶囊保持卡在颈缩处时，它在稳态下是静止的。相反，偏心线囊不是固定的，而是表现出坦克踩踏运动，即，其整体形状保持非球形，并在缩颈中突出，而其膜呈现出连续的旋转。此外，我们检查了胶囊运动类型，胶囊变形程度和膜张力分布对毛细管数（测量流动强度和膜力学的影响）和收缩几何形状（包括收缩高度和宽度）的依赖性。最后，我们通过分析作用在胶囊上的流体动力来讨论控制胶囊运动的机理。由于在囊顶与通道顶壁之间的间隙中的流体流动而作用在囊顶上的剪切力是引起膜罐踩踏旋转的主要来源。

更新日期：2017-11-15

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