Fabrication of monodisperse droplets and microcapsules using microfluidic chips: a review of methodologies and applications

Microfluidics has been applied in the preparation of monodisperse droplets and microcapsules due to its high encapsulation efficiency, its ability to create uniform particle sizes, and its capacity to control core-shell ratio and structure. To bring to the fore methodologies for the fabrication and application of monodisperse microcapsules using microfluidics, we present a review of the design, structure, materials, and surface modification techniques of various microfluidic chips. The review also covers fabrication methods, operating parameters and regulation methods of single and multiple monodisperse emulsion droplets fabricated from various microfluidic devices. Our findings show that particle size of monodisperse droplets depend mainly on microchannel characteristic size and flow rate, with particle size increasing with larger microchannel but decreasing with higher continuous phase flow rate. We additionally reviewed and compared various fabrication methods for monodisperse microcapsules, such as interfacial polymerization, free-radical polymerization, ionic cross-linking, and solvent evaporation. We further reviewed and examined the application of monodisperse microcapsules in biology applications, food engineering, composite materials development and pharmaceutical industry. We found that high-throughput microfluidics for scale-up monodisperse microcapsule preparation towards uniform degradation and targeted release properties of monodisperse microcapsules would be key innovative direction for future applications.