High-throughput preparation of monodisperse biocompatible core-shell capsules by 3D-Printed Microfluidics

• Biocompatible core-shell capsules on the millimeter scale are prepared by 3D-printed microfluidic devices . • The effects of flow rates, channel hydrophobicity and fluid viscosity on capsule formation are systematically studied. • A trunk-branch microfluidic structure is adopted for multi-unit parallel devices to scale up the production capacity. • The prepared capsules possess distinct core-shell structure, uniform size and tunable strength. Capsules with a core–shell structure, which are capable of loading various actives and controlling their release, are used in various fields. Here, the controlled preparation of biocompatible core–shell capsules on the millimeter scale is systematically investigated. In the 3D-printed microfluidic channels, the inner oil phase is sheared into uniform oil droplets by the viscous drag of the outer alginate phase and then the flow tip is pulled off the nozzle to form uniform core–shell capsules by the gravitation force. The phase diagrams of capsule formation are explored in terms of flow rates, device hydrophobicity and alginate viscosity, which are consistent with the force analysis. To scale up the capsule production, a trunk-branch structure with twelve parallelized units is developed to increase the output by twelve times without any scale-up effects. The core–shell capsules possess tunable size, uniform size distribution and adjustable strength, showing great potentials for their practical applications.