Scalable air-assisted microfluidic system for core–shell alginate beads: Design, experimental characterization, and industrial validation

An innovative, scalable microfluidic technology is presented for producing core–shell alginate microcapsules using a coaxial air-assisted droplet generation system. Designed for industrial applicability, the device employs three concentric capillaries to co-flow sunflower oil (core), sodium alginate (shell), and pressurized air (continuous phase), enabling precise control over droplet breakup via Rayleigh–Plateau instability. The influence of air flow rate (1–16 ln min -1 ) on bead size and uniformity was investigated through single- and multi-nozzle configurations. Results indicate that increasing air flow reduces average droplet size (D 50 from 334.7 μm to 64.6 μm) while affecting polydispersity (span from 0.65 to 2.42). A four-nozzle parallelized system was validated for mass production, maintaining high encapsulation uniformity (D 50 ∼122 μm, span ∼1.59) with no significant nozzle-to-nozzle variability. Encapsulation efficiency reached ∼64%, constrained by maximum core flow and jet instability. Rheological characterization confirmed the shear-thinning behavior of the alginate solution, with surfactant addition reducing viscosity. Compared to traditional bulk emulsification or immiscible-phase methods, the proposed approach offers a clean, low-cost, oil-free pathway to core–shell microcapsules with high monodispersity and scalability. Potential applications span food, pharmaceutical, and biotechnological fields, especially where high-throughput encapsulation of labile or hydrophobic actives is required. • Modular air-assisted nozzle enables scalable industrial core–shell bead production. • Oil-free air phase reduces washing steps and eases food-grade compliance. • One-to-four flow splitter parallelizes low-cost nozzles for high throughput. • Four-nozzle scale-up keeps median size ≈122 μm with span ≈1.59 at doubled flows. • No nozzle-to-nozzle bias confirms robust scale-up for continuous manufacturing.