Controlled release of multiple actives after encapsulation in a microenvironment is significant for various biological and chemical applications such as controlled drug delivery and transplantation of encapsulated cells. However, traditional systems often lack efficient encapsulation and release of multiple actives, especially when incorporated substances must be released at a targeted location. Here, we present a straightforward approach to release multiple actives at a prescribed position in microfluidic systems; one or two actives are encapsulated in water-in-oil-in-water emulsion droplets, followed by controlled release of the actives via an alternating current electric field. An electric field-induced compression due to Maxwell–Wagner interfacial polarization overcomes the disjoining pressure at the thin shell and leads to the thinning and rupture of the oil layer of the droplets, resulting in the release of the encapsulated actives to the suspending medium. This technique is feasible for encapsulation and release of various reagents in terms of ion species and ion concentrations. Moreover, polymer nanoparticles and yeast cells can also be included in the droplets and then be released at targeted locations. This versatile method should be well-suited for targeted delivery of various active ingredients such as functional chemical reagents and biological cells.

It is becoming more difficult to use bulk mixing and bi-fluid micromixing in multi-step continuous-flow reactions, multicomponent reactions, and nanoparticle synthesis because they typically involve multiple reactants. To date, most micromixing studies, both passive and active, have focused on how to efficiently mix two fluids, while micromixing of three or more fluids together (multi-fluid mixing) has been rarely explored. This study is the first on tri-fluid mixing in microchannels. We investigated tri-fluid mixing in three microchannel models: a straight channel, a classical staggered herringbone mixing (SHM) channel, and a three-dimensional (3D) X-crossing microchannel. Numerical simulations and experiments were jointly conducted. A two-step experimental process was performed to determine the tri-fluid mixing efficiencies of these microchannels. We found that the SHM cannot significantly enhance mixing of three streams especially for a Reynolds number (Re) higher than 10. However, the 3D X-crossing channel based on splitting-and-recombination (SAR) showed effective tri-mixing performance over a wide Re range up to 275 (with a corresponding flow rate of 1972.5 μL min⁻¹), thereby enabling high microchannel throughput. Furthermore, this tri-fluid micromixing process was used to synthesize a kind of Si-based nanoparticle. This achieved a narrower particle size distribution than traditional bulk mixing. Therefore, SAR-based tri-fluid mixing is an alternative for chemical and biochemical reactions where three reactants need to be mixed.