Experimental observation of the asymmetric instability of intermediate-reduced-volume vesicles in extensional flow.
Experimental observation of the asymmetric instability of intermediate-reduced-volume vesicles in extensional flow.
复制标题
DOI：
10.1039/c5sm03004h
复制
发表时间：
2016-04-20
期刊：
影响因子：
3.4
通讯作者：
Muller SJ
中科院分区：
文献类型：
--
作者：
Dahl JB;Narsimhan V;Gouveia B;Kumar S;Shaqfeh ES;Muller SJ
囊泡提供了一个有吸引力的模型系统，以了解活细胞在机械力作用下的变形。这些简单，封闭的脂质双层膜是适合互补的理论，数值和实验分析。最近的一项研究[Narsimhan，Spann，Shaqfeh，Journal of Fluid Mechanics，2014，750，144]预测，中等纵横比的囊泡在拉伸流中不对称地延伸。在对囊泡形状进行无限小的扰动后，囊泡伸展成不对称的哑铃状，其两端由圆柱形线分开。虽然已经观察到并表征了拉伸流中高纵横比囊泡的对称拉伸[Kantsler，塞格雷，Steinberg，Physics Review Letters，2008，101，048101]，并且在Narsimhan等人的数值模拟中进行了概括，不对称拉伸的实验观察还没有报道。在这项工作中，我们提出了从微流体交叉槽实验观察这种不稳定性，沿着仔细表征的流场，囊泡形状，囊泡弯曲模量的结果。这种形状转变的发生取决于两个无量纲参数：减少的体积（囊泡非球面性的量度）和毛细管数（粘性力与弯曲力的比率）。我们观察到，每一个中间减少体积囊泡延伸形成一个哑铃形状，这确实是不对称的。对于子集的中间减少的体积制度，我们可以捕获实验，我们提出了一个实验相图的不对称囊泡拉伸，这是一致的预测Narsimhan等人。
Vesicles provide an attractive model system to understand the deformation of living cells in response to mechanical forces. These simple, enclosed lipid bilayer membranes are suitable for complementary theoretical, numerical, and experimental analysis. A recent study [Narsimhan, Spann, Shaqfeh, Journal of Fluid Mechanics, 2014, 750, 144] predicted that intermediate-aspect-ratio vesicles extend asymmetrically in extensional flow. Upon infinitesimal perturbation to the vesicle shape, the vesicle stretches into an asymmetric dumbbell with a cylindrical thread separating the two ends. While the symmetric stretching of high-aspect-ratio vesicles in extensional flow has been observed and characterized [Kantsler, Segre, Steinberg, Physics Review Letters, 2008, 101, 048101] as well as recapitulated in numerical simulations by Narsimhan et al., experimental observation of the asymmetric stretching has not been reported. In this work, we present results from microfluidic cross-slot experiments observing this instability, along with careful characterization of the flow field, vesicle shape, and vesicle bending modulus. The onset of this shape transition depends on two non-dimensional parameters: reduced volume (a measure of vesicle asphericity) and capillary number (ratio of viscous to bending forces). We observed that every intermediate-reduced-volume vesicle that extends forms a dumbbell shape that is indeed asymmetric. For the subset of the intermediate-reduced-volume regime we could capture experimentally, we present an experimental phase diagram for asymmetric vesicle stretching that is consistent with the predictions of Narsimhan et al.