Monodisperse water-in-oil-in-water emulsions generation for synthesising alginate hydrogel microspheres via locally hydrophobic modification to PMMA microchannels

The inherent hydrophobic poly(methyl methacrylate) (PMMA) will show hydrophilic property due to the impurity or fabrication process in the practical use, which limits its application in water-in-oil (W/O) emulsions, e.g. hydrogel microparticles synthesised using water-in-oil-in-water (W/O/W) emulsions as precursors. In this paper, we propose an easy-to-use method for hydrophobic modification of PMMA channels by coating liquid poly(dimethylsiloxane) (PDMS) at arbitrarily chosen locations, thus making the hydrophilic PMMA channel wall hydrophobic and increasing the water contact angle from 67.1 ± 1.3° to 108.7 ± 1.1°. Monodisperse W/O/W emulsions can be easily produced using the modified PMMA devices, whereas, only water plug, which sticking to the channel walls, can be formed even with the aid of surfactant. As a verification, hydrogel microspheres were synthesised using W/O/W emulsions as precursors. Furthermore, fluorescent microparticles were encapsulated in alginate hydrogel microspheres to demonstrate the cells encapsulation process, which will be benefit to cells culture and analysis.