Microfluidic Generation of All‐Aqueous Double and Triple Emulsions

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.

Deformable and Robust Core–Shell Protein Microcapsules Templated by Liquid–Liquid Phase‐Separated Microdroplets

“…The formation of LLPS (two-phase, Figure 5a) or multiphase-LLPS (Figure 5b) systems from microgel precursors provided a simple and facile approach to generating all-aqueous emulsion without direct on-chip generation that usually required additional setups. [6][7][8]37,[52][53][54][55] Previously, the fusion of core-shell structures was reported in water-oil-water double emulsion or RNAprotein hollow condensates; [84,85] this present study extends the fusion phenomena to crowder-protein-crowder all-aqueous interfaces and has the potential to inspire the explanation of the fusion of hollow-like structures or multiphase condensates from other materials (Figure 5b). On the one hand, the formation of Janus and core-shell microgels (Figure 1) was achieved by gelatin/PEG LLPS and by the sol-gel transition (gelation) of gelatin.…”

“…[6,20] Developing all-aqueous emulsions from oil-free microgel precursors is a facile and simple approach that complements existing methods such as electrospray, 3D printing, glass capillary microfluidics, or hydrostatic pressure microfluidics. [6][7][8]37,[52][53][54][55] Here, we report robust, deformable, and smart gelatin microcapsules from GRAS materials which were processed via a onestep method in a 2D microfluidic device under mild gelation conditions and their potential usage scenarios in healthcare for cargo release and controlled degradability. Specifically, the minimization of surface energy in a liquid-liquid phase-separated system can drive the self assembly of the microcapsules from ECM-substituting protein, which makes the microcapsule production scalable, accessible, and controllable for medical applications with improved biocompatibility, bioactivity, and biomimicry.…”

Droplet Microfluidics for Food and Nutrition Applications

“…These all-aqueous droplets are expected to find many food applications, as their compositions are biocompatible, and their structures can be finely tuned, as recently shown in [ 67 ], where double and even triple all-aqueous emulsions based on PEG and dextran were produced using a hybrid PDMS/glass capillary microfluidic device. However, one of the main concerns related to all-aqueous systems produced by microfluidics is the ease of droplet formation in the absence of an appreciable interfacial tension, which implies that shear forces need to be tailored precisely.…”

Exploring New Horizons in Liquid Compartmentalization via Microfluidics

“…Higher order emulsions are difficult to generate using w/w microfluidics; only a few examples are known of higher-order emulsions. 65 − 68 Combining ATPS with classical w/o microfluidics makes it possible to increase the stability and complexity of the emulsions and obtain more flexibility in choice of materials.…”