Preparation of uniformly sized alginate microspheres using the novel combined methods of microchannel emulsification and external gelation

The purpose of this study was to prepare alginate (ALG) microspheres with narrow size distribution using a combination of microchannel (MC) emulsification technique and external gelation method. ALG solution was dispersed as water-in-oil (W/O) emulsion droplets in iso-octane containing 5 wt% Span 85 as the immiscible continuous phase via MC emulsification technique using hydrophobic MC array. The MC array used in this experiment is a grooved-type MC consisting of 1070 channels fabricated on a 25 mm × 28 mm silicon microchip. The monodisperse W/O emulsion droplets generated from the MCs were in the mean particle diameter (dav) range of 18–22 μm and coefficient of variation (CV) of 5–26% at the ALG concentrations of 0.5–3.0 wt% and flow rates of 0.05–0.4 mL/h. The dav of the emulsion droplets hardly changed below a dispersed phase threshold flow rate of 0.2 mL/h but gradually became smaller when the dispersed phase concentration was increased. The resulting emulsion droplets were then congealed to form rigid ALG gel particles by reacting them with calcium chloride (CaCl2) solution. Gelation of the ALG droplets by calcium ion (Ca2+) resulted in shrinkage of its dav, forming uniformly sized ALG microspheres with an average diameter of 6.2 μm and a CV of below 10% at the ALG concentration of 3 wt%.