title: Microfluidic preparation of water-in-oil-in-water emulsions with an ultra-thin oil phase layer.
abstract: We developed a novel microfluidic device to prepare monodisperse water-in-oil-in-water (W/O/W) emulsions with an ultra-thin (<1 microm) oil phase layer. This microfluidic device was composed of two microchannel junctions, one of which had a step structure, and a uniformly hydrophobic surface for effective oil removal from W/O/W droplets. At the first junction, an internal aqueous phase was transformed into slug-shaped water-in-oil (W/O) droplets by a flow-focusing mechanism. At the second junction equipped with the step structure, the preformed slug-shaped W/O droplets were introduced into an external aqueous phase and were transformed into spherical W/O droplets. In the downstream area of the second junction, the W/O droplets were released from the hydrophobic surface of the microchannel into the external aqueous phase by inertial lift force and were transformed into W/O/W droplets. During this process, most of the oil phase was effectively removed from the W/O droplets: the bulk of the oil phase flowed along the hydrophobic surface of the microchannel. The thickness of the oil phase layer of the resulting W/O/W droplets was ultra-thin, less than 1 microm. The volume of the internal aqueous phase of the W/O/W droplets reflected that of the W/O droplets and was controlled by the flow rates of the internal aqueous phase and oil phase during W/O droplet formation. We successfully demonstrated encapsulation of water-soluble molecules and polymer particles into the prepared W/O/W emulsion.
authors.affiliation: Organ Development Research Laboratory, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Saeki
authors.forename: Shinji
authors.initials: S
authors.lastname: Sugiura
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kanamori
authors.forename: Seigo
authors.initials: S
authors.lastname: Sato
authors.forename: Sosaku
authors.initials: S
authors.lastname: Ichikawa
mesh_terms: D045424:Complex Mixtures / Q000737:chemistry; D003198:Computer Simulation; D017076:Computer-Aided Design; D004655:Emulsions / Q000138:chemical synthesis; D004867:Equipment Design; D019544:Equipment Failure Analysis; D044085:Microfluidics / Q000295:instrumentation* / Q000379:methods*; D008956:Models, Chemical; D009821:Oils / Q000737:chemistry*; D044367:Phase Transition; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water / Q000737:chemistry*
chemical_list: D045424:Complex Mixtures; D004655:Emulsions; D009821:Oils; D014867:Water