Microfluidic techniques help expand applications for all-aqueous emulsion droplets

All-aqueous droplets attract attention for a wide range of biomedical applications for their biocompatibility, selective separation, and ability to facilitate rapid mass transfer.

Factors, such as ultra-low interfacial tension and large effective interfacial interface thicknesses, make it difficult to reliably generate precise droplets. The field of microfluidics offers a versatile path forward.

Zhou et al. provided a review of microfluidics-based techniques for generating all-aqueous droplets. The authors have highlighted current and emerging techniques for droplet generation, giving insight into how these methods accommodate this type of droplet formation in addition to discussing the stabilization methods that complement droplet generation.

“Most of the recent studies focused on the formation of biomaterials from the templates of all-aqueous emulsion droplets,” said author Liqiu Wang. “At present, we are interested in developing new microfluidics-based techniques to further improve the quality of all-aqueous emulsions and produce next-generation all-aqueous biomaterials.”

One such innovation, the “oil-droplet chopper” method, introduces an additional dispersed oil phase to produce oil-in-water droplets that perturb the aqueous jet to break into droplets of an aqueous two-phase system (ATPS). The all-aqueous droplets and oil choppers are separated in-channel using their difference in density.

Another, called transient double emulsion, involves water-in-oil-in-water (W1/O/W2) transient double emulsion droplets are first generated using droplet microfluidics by introducing an additional middle oil phase, and then the unstable W1/O/W2 droplets dewet into oil-in-water and ATPS droplets in a controllable manner, followed by the separation of ATPS droplets from oil droplets.

The team is now working on developing new microfluidics-based techniques to further improve the quality of all-aqueous emulsion droplets and use them as templates to engineer advanced biomaterials.

Source: “Progress in all-aqueous droplets generation with microfluidics: Mechanisms of formation and stability improvements,” by Chunmei Zhou, Pingan Zhu, Ye Tian, Rui Shi, and Liqiu Wang, Biophysics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0054201 .