A major barrier to the clinical utilization of microfluidically generated water-in-oil droplets is the cumbersome washing steps required to remove the non-biocompatible organic oil phase from the droplets. In this paper, we report an on-chip magnetic water-in-water droplet generation and manipulation platform using a biocompatible aqueous two-phase system of a polyethylene glycol–polypropylene glycol–polyethylene glycol triblock copolymer (PEG–PPG–PEG) and dextran (DEX), eliminating the need for subsequent washing steps. By careful selection of a ferrofluid that shows an affinity toward the DEX phase (the dispersed phase in our microfluidic device), we generate magnetic DEX droplets in a non-magnetic continuous phase of PEG–PPG–PEG. We apply an external magnetic field to manipulate the droplets and sort them into different outlets. We also perform scaling analysis to model the droplet deflection and find that the experimental data show good agreement with the model. We expect that this type of all-biocompatible magnetic droplet microfluidic system will find utility in biomedical applications, such as long-term single cell analysis. In addition, the model can be used for designing experimental parameters to achieve a desired droplet trajectory.

中文翻译：

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磁性水包水滴微流控：系统实验和定标数学分析

临床上利用微流体产生的油包水液滴的主要障碍是从液滴中除去非生物相容性有机油相所需的繁琐的洗涤步骤。在本文中，我们报告了使用生物相容性水相两相系统（聚乙二醇-聚丙二醇-聚乙二醇三嵌段共聚物（PEG-PPG-PEG）和右旋糖酐）的片上磁性水包水产生和处理平台（DEX），无需后续清洗步骤。通过仔细选择对DEX相（我们的微流体设备中的分散相）具有亲和力的铁磁流体，我们在PEG-PPG-PEG的非磁性连续相中生成磁性DEX液滴。我们施加外部磁场来操纵液滴并将其分类到不同的出口中。我们还进行了定标分析以对液滴的变形进行建模，并发现实验数据与该模型显示出良好的一致性。我们希望这种类型的全生物相容性磁滴微流体系统将在生物医学应用（例如长期单细胞分析）中找到实用性。另外，该模型可以用于设计实验参数以获得期望的液滴轨迹。