title: Water-in-Water Droplets by Passive Microfluidic Flow Focusing.
abstract: 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.
authors.affiliation: 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.
authors.forename: Byeong-Ui
authors.initials: BU
authors.lastname: Moon
authors.affiliation: 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.
authors.forename: Niki
authors.initials: N
authors.lastname: Abbasi
authors.affiliation: 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.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Jones
authors.affiliation: 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.
authors.forename: Dae Kun
authors.initials: DK
authors.lastname: Hwang
authors.affiliation: 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.
authors.forename: Scott S H
authors.initials: SS
authors.lastname: Tsai
mesh_terms: D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D010316:Particle Size; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water