Structural Design of Hydrogel Particles by Phase Separation in Aqueous Droplets

Abstract

Microfluidics is a powerful tool to precisely control the structure of colloidal materials. A microfluidic process to fabricate monodisperse hydrogel microcapsules having a large aqueous core using phase separation in aqueous droplets was developed. Specifically, hydrogel microcapsules were prepared by the formation of aqueous two-phase system droplets with dextran-rich core and tetra-PEG-rich shell, and subsequent cross-linking reaction in the shell. This process enabled to produce hydrogel microcapsules in the absence of radical initiators and external energies such as heat and ultraviolet light. The diameter and shell thickness of the microcapsules could be modulated independently by changing flow rates and monomer concentrations upon droplet formation. In addition, tuning the rate of polymerization was found to be an important parameter to determine the phase-separated structure of the hydrogel particles. In this review, the experimental procedures and the representative results are reported and key points to produce well-defined hydrogel materials are discussed.