ABSTRACT
Higher order emulsions are used in a variety of different applications in biomedicine, biological studies, cosmetics, and the food industry. Conventional droplet generation platforms for making higher order emulsions use organic solvents as the continuous phase, which is not biocompatible and as a result, further washing steps are required to remove the toxic continuous phase. Recently, droplet generation based on aqueous two-phase systems (ATPS) has emerged in the field of droplet microfluidics due to their intrinsic biocompatibility. Here, a platform to generate all-aqueous double and triple emulsions by introducing pressure-driven flows inside a microfluidic hybrid device is presented. This system uses a conventional microfluidic flow-focusing geometry coupled with a coaxial microneedle and a glass capillary embedded in flow-focusing junctions. The configuration of the hybrid device enables the focusing of two coaxial two-phase streams, which helps to avoid commonly observed channel-wetting problems. It is shown that this approach achieves the fabrication of higher-order emulsions in a poly(dimethylsiloxane)-based microfluidic device, and controls the structure of the all-aqueous emulsions. This hybrid microfluidic approach allows for facile higher-order biocompatible emulsion formation, and it is anticipated that this platform will find utility for generating biocompatible materials for various biotechnological applications.