Keenan Research Centre for Biomedical Science, St. Michael's Hospital , Toronto, Canada.
Institute for Biomedical Engineering, Science and Technology (iBEST), a partnership between Ryerson University and St. Michael's Hospital , Toronto, Canada.
Anal Chem. 2016 Apr 5;88(7):3982-9. doi: 10.1021/acs.analchem.6b00225. Epub 2016 Mar 21.
We present a simple microfluidic system that generates water-in-water, aqueous two phase system (ATPS) droplets, by passive flow focusing. ATPS droplet formation is achieved by applying weak hydrostatic pressures, with liquid-filled pipette tips as fluid columns at the inlets, to introduce low speed flows to the flow focusing junction. To control the size of the droplets, we systematically vary the interfacial tension and viscosity of the ATPS fluids and adjust the fluid column height at the fluid inlets. The size of the droplets scales with a power law of the ratio of viscous stresses in the two ATPS phases. Overall, we find a drop size coefficient of variation (CV; i.e., polydispersity) of about 10%. We also find that when drops form very close to the flow focusing junction, the drops have a CV of less than 1%. Our droplet generation method is easily scalable: we demonstrate a parallel system that generates droplets simultaneously and improves the droplet production rate by up to one order of magnitude. Finally, we show the potential application of our system for encapsulating cells in water-in-water emulsions by encapsulating microparticles and cells. To the best of our knowledge, our microfluidic technique is the first that forms low interfacial tension ATPS droplets without applying external perturbations. We anticipate that this simple approach will find utility in drug and cell delivery applications because of the all-biocompatible nature of the water-in-water ATPS environment.
我们提出了一种简单的微流控系统，通过被动流聚焦生成水包水、双水相体系（ATPS）液滴。通过施加较弱的静水压力，将充满液体的移液管尖端作为入口处的流体柱，将低速流动引入流聚焦结，从而实现 ATPS 液滴的形成。为了控制液滴的大小，我们系统地改变了 ATPS 流体的界面张力和粘度，并调整了流体入口处的流体柱高度。液滴的大小与两相 ATPS 中粘性应力的比值呈幂律关系。总体而言，我们发现液滴的尺寸变化系数（CV；即多分散性）约为 10%。我们还发现，当液滴非常接近流聚焦结形成时，液滴的 CV 小于 1%。我们的液滴生成方法易于扩展：我们展示了一个并行系统，可以同时生成液滴，并将液滴的生成速率提高一个数量级。最后，我们通过包封微颗粒和细胞展示了我们的系统在水包水乳液中包封细胞的潜在应用。据我们所知，我们的微流控技术是第一种在不施加外部扰动的情况下形成低界面张力 ATPS 液滴的技术。我们预计，由于水包水 ATPS 环境的全生物相容性，这种简单的方法将在药物和细胞输送应用中找到实用价值。
