Department of Chemical Engineering, Columbia University, New York, NY, USA.
Lab Chip. 2018 Nov 6;18(22):3371-3378. doi: 10.1039/c8lc00526e.
Microfluidic gradient generators are used to study the movement of living cells, lipid vesicles, and colloidal particles in response to spatial variations in their local chemical environment. Such gradient driven motions are often slow (less than 1 μm s-1) and therefore influenced or disrupted by fluid flows accompanying the formation and maintenance of the applied gradient. Even when external flows are carefully eliminated, the solute gradient itself can drive fluid motions due to combinations of gravitational body forces and diffusioosmotic surface forces. Here, we develop a microfluid gradient generator based on the in situ formation of biopolymer membranes and quantify the fluid flows induced by steady solute gradients. The measured velocity profiles agree quantitatively with those predicted by analytical approximations of relevant hydrodynamic models. We discuss how the speed of gradient-driven flows depends on system parameters such as the gradient magnitude, the fluid viscosity, the channel dimensions, and the solute type. These results are useful in identifying and mitigating undesired flows within microfluidic gradient systems.
微流控梯度发生器用于研究活细胞、脂质体和胶体颗粒在其局部化学环境空间变化下的运动。这种梯度驱动的运动通常很慢（小于 1μm/s），因此会受到伴随梯度形成和维持的流体流动的影响或干扰。即使仔细消除外部流动，由于重力体力和扩散渗透表面力的组合，溶质梯度本身也会驱动流体运动。在这里，我们开发了一种基于原位形成生物聚合物膜的微流梯度发生器，并定量分析了由稳定溶质梯度引起的流体流动。测量的速度分布与相关流体力学模型的分析近似值预测的速度分布定量吻合。我们讨论了梯度驱动流的速度如何取决于系统参数，如梯度幅度、流体粘度、通道尺寸和溶质类型。这些结果有助于识别和减轻微流控梯度系统内的不期望流动。
