Jayaprakash K S, Sen A K
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
Biomicrofluidics. 2019 May 14;13(3):034108. doi: 10.1063/1.5096937. eCollection 2019 May.
Encapsulation of microparticles in droplets has profound applications in biochemical assays. We investigate encapsulation of rigid particles (polystyrene beads) and deformable particles (biological cells) inside aqueous droplets in various droplet generation regimes, namely, squeezing, dripping, and jetting. Our study reveals that the size of the positive (particle-encapsulating) droplets is larger or smaller compared to that of the negative (empty) droplets in the dripping and jetting regimes but no size contrast is observed in the squeezing regime. The size contrast of the positive and negative droplets in the different regimes is characterized in terms of capillary number and stream width ratio (i.e., ratio of stream width at the throat to particle diameter ). While for deformable particles, the positive droplets are always larger compared to the negative droplets, for rigid particles, the positive droplets are larger in the dripping and jetting regimes for but smaller in the jetting regime for . We exploit the size contrast of positive and negative droplets for sorting across the fluid-fluid interface based on noninertial lift force (at ), which is a strong function of droplet size. We demonstrate sorting of the positive droplets encapsulating polystyrene beads and biological cells from the negative droplets with an efficiency of ∼95% and purity of ∼65%. The proposed study will find relevance in single-cell studies, where positive droplets need to be isolated from the empty droplets prior to downstream processing.
将微粒包裹于液滴中在生化分析领域有着广泛的应用。我们研究了在各种液滴生成模式下，即挤压、滴落和喷射模式下，刚性颗粒（聚苯乙烯微珠）和可变形颗粒（生物细胞）在水滴内部的包裹情况。我们的研究表明，在滴落和喷射模式下，包裹有颗粒的正向液滴的尺寸相较于空的负向液滴更大或更小，但在挤压模式下未观察到尺寸差异。不同模式下正向和负向液滴的尺寸差异通过毛细管数和流宽比（即喉部流宽与颗粒直径的比值）来表征。对于可变形颗粒，正向液滴总是比负向液滴大；而对于刚性颗粒，在毛细管数为[具体数值1]时，正向液滴在滴落和喷射模式下更大，但在毛细管数为[具体数值2]时，正向液滴在喷射模式下更小。我们利用正向和负向液滴的尺寸差异，基于非惯性升力（在[具体条件]下）在流体 - 流体界面进行分选，非惯性升力是液滴尺寸的强函数。我们展示了从负向液滴中分选包裹聚苯乙烯微珠和生物细胞的正向液滴，分选效率约为95%，纯度约为65%。本研究所提出的方法在单细胞研究中具有重要意义，在单细胞研究中，需要在下游处理之前将正向液滴与空的负向液滴分离。
