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.

In this study, we proposed a high-throughput separation strategy of the binary colloid mixture by dielectrophoresis (DEP) induced around large-scale bipolar electrode arrays embedded in microfabricated fluidic networks via a thorough numerical investigation. The usage of a floating electrode (FE) eliminates the need of external Ohmic connection to individual array units, therefore potentially steering the faddish design of new microdevice structures. Diffuse charge dynamics within the induced double layer at opposite ends of every FE permit a sinusoidal electric field to penetrate throughout the whole device, as long as the imposed field frequency is beyond the reciprocal resistor-capacitor time constant at the electrode/electrolyte interface. In this special device configuration, FEs interconnect multiple microchannels arranged in parallel. Pockets embedded on the sidewalls of fluidic channels help create strong field gradients at the tip of FEs and sharp pocket/channel junctions, improving the trapping performance of incoming bioparticles subjected to positive-DEP (pDEP) force, while latex beads experiencing negative-DEP (nDEP) stress are electrically squeezed to the midchannel and finally exit as a series of co-flowing thin streams with unequal translatory velocity. Taking the synergy of DEP force, induced-charge electro-osmosis, alternating-current electrothermal streaming, pressure-driven flow, and buoyancy effect into consideration, a numerical model is established to account for motion trajectories of micro-entities in full-scale three-dimensional space using the Lagrange particle track algorithm, as well as testing the feasibility of the device design in separation of the binary mixture containing yeast cells and polystyrene beads. Applying suitable voltage parameters of frequency O(1) MHz and electric field strength O(10) V/mm, highly efficient DEP separation is theoretically achievable under inlet flow velocity on the order of O(1) mm/s, where most of incoming yeasts are captured by pDEP within these five parallel branching channels, while polystyrene spheres are repelled by nDEP away from the FE array to form slim beams co-flowing into the outlet according to the calculation results. The microfluidic separation device exploiting the FE array offers great potential to build up scalable electrokinetic platforms for high-throughput on-chip sample treatment.

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.