Addressing all these bottlenecks, we present here a method for generating surfactant-free, ultraviolet (UV) light curable core–shell microcapsules in a fully hydrophilic PDMS microfluidic device. Furthermore, the shell material of the existing solutions has been often limited to alginate, a salt of alginic acid and sodium or calcium. Reducing the amount of surface treatments in a microfluidic device significantly simplifies the fabrication process of the devices. Villard, “ Reconstruction of directed neuronal networks in a microfluidic device with asymmetric microchannels,” Methods in Cell Biology ( Elsevier, 2018), Vol. Hydrophilic treatment is used for the water-based counterpart. Tan, “ Negative pressure induced droplet generation in a microfluidic flow-focusing device,” Anal. In general, hydrophobic treatment is employed when oil-based liquids are used to wet the microchannel. The applied treatment accordingly depends on the interfacial tension of the bulk liquid flowing through each microchannel. The dual surface treatment is required for the complete wetting of the microchannels to ensure a steady and reliable liquid flow within each microchannel. Kwon, “ Liquid-capped encoded microcapsules for multiplex assays,” Lab Chip 17, 429– 437 (2017). and dual hydrophobic/hydrophilic surface treatment of polydimethylsiloxane (PDMS) devices. Middelberg, “ Controlled generation of ultrathin-shell double emulsions and studies on their stability,” ChemPhysChem 18, 1393– 1399 (2017). Ekanem, “ Double emulsion production in glass capillary microfluidic device: Parametric investigation of droplet generation behaviour,” Chem. However, the challenges for this approach are with the breaking and misalignment of glass capillary devices 7,14 7. Microfluidics has been a viable option for generating microcapsules. Nguyen, “ On-demand droplet merging with an AC electric field for multiple-volume droplet generation,” Anal. These methods, however, require the use of additional equipment for electric field generation. Zhao, “ Biomimetic enzyme cascade reaction system in microfluidic electrospray microcapsules,” Sci. On the contrary, smaller microcapsules can be obtained through electro-spraying with a strong electric field. Lin, “ Magnetic liquid marbles: Toward “lab in a droplet,”” Adv. Nguyen, “ Liquid marbles as biochemical reactors for the polymerase chain reaction,” Lab Chip 19, 3220– 3227 (2019). Liquid marbles, a liquid droplet coated with hydrophobic powder, are also constrained by their relatively large size. This makes them unsuitable for certain enzyme-related research. Collier, “ Shear-driven redistribution of surfactant affects enzyme activity in well-mixed femtoliter droplets,” Anal. However, surfactants may affect chemical processes, such as enzymatic activities in the droplet. Tadros, Surfactants in Agrochemicals ( Marcel Dekker, 1994), p. Surfactants are accordingly needed to ensure interfacial stability by reducing interfacial tension between the different liquid layers. Emulsion-based methods generate double emulsions through homogenization or ultrasonification of two liquid phases. Weitz, “ Controllable monodisperse multiple emulsions,” Angew. Garti, “ Double emulsions-Scope, limitations and new achievements,” Colloids Surf., A 123-124, 233– 246 (1997), frontiers in Colloid Chemistry an International Festschrift to Professor Stig E. The current production methods include emulsion-based, 3,4 3. Nabavi, “ Microfluidic production of multiple emulsions,” Micromachines 8, 75 (2017). van Hest, “ Preparation of biodegradable liquid core PLLA microcapsules and hollow PLLA microcapsules using microfluidics,” Macromol. These microcapsules serve as miniature containers for the storage and delivery of substances. Core–shell microcapsules play a significant role in research and commercial products.

Capillary microspheres core shell