Influence of heterogeneity or shape on the locomotion of a caged squirmer
Influence of heterogeneity or shape on the locomotion of a caged squirmer
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DOI：
10.1017/jfm.2023.450
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发表时间：
2023-07-12
影响因子：
3.7
通讯作者：
Nganguia，H.
中科院分区：
文献类型：
--
作者：
Aymen，U.;Palaniappan，D.;Nganguia，H.
新型给药系统的发展正在给现代医学带来革命性的变化，这得益于对微生物游动的研究。本文研究了一种封闭在粘性液滴中的模型微生物（蠕动器），研究了介质非均质性和几何形状对蠕动器推进速度的影响。我们首先考虑蠕动器和液滴是球形的（没有形状效应），并推导出控制问题的方程的精确解。对于具有纯切向表面速度的蠕动器，蠕动器总是能够在液滴内部移动（即使液滴由于非均质介质的大流体阻力而停止移动）。在表面速度中加入径向模态，建立了共游速度存在的新条件（其中蠕动体和液滴以相同的速度运动）。接下来，为了探究几何对推进力的影响，我们考虑在牛顿流体中的蠕动体和液滴。对于具有纯切向表面速度的蠕动器，数值模拟显示蠕动器的速度与形状、液滴大小和粘度对比有很强的依赖性。研究发现，当液滴尺寸和蠕动器偏心距较小时，粘度对比较大时，蠕动速度最大。对于共同游泳，我们的研究结果揭示了各种因素之间复杂而重要的相互作用，这些因素共同产生了蠕动者的推进速度。综上所述，我们的研究为未来药物输送系统的有效设计提供了几个考虑因素。
The development of novel drug delivery systems, which are revolutionizing modern medicine, is benefiting from studies on microorganisms’ swimming. In this paper we consider a model microorganism (a squirmer) enclosed in a viscous droplet to investigate the effects of medium heterogeneity or geometry on the propulsion speed of the caged squirmer. We first consider the squirmer and droplet to be spherical (no shape effects) and derive exact solutions for the equations governing the problem. For a squirmer with purely tangential surface velocity, the squirmer is always able to move inside the droplet (even when the latter ceases to move as a result of large fluid resistance of the heterogeneous medium). Adding radial modes to the surface velocity, we establish a new condition for the existence of a co-swimming speed (where squirmer and droplet move at the same speed). Next, to probe the effects of geometry on propulsion, we consider the squirmer and droplet to be in Newtonian fluids. For a squirmer with purely tangential surface velocity, numerical simulations reveal a strong dependence of the squirmer's speed on shapes, the size of the droplet and the viscosity contrast. We found that the squirmer speed is largest when the droplet size and squirmer's eccentricity are small, and the viscosity contrast is large. For co-swimming, our results reveal a complex, non-trivial interplay between the various factors that combine to yield the squirmer's propulsion speed. Taken together, our study provides several considerations for the efficient design of future drug delivery systems.