Formation of monodisperse calcium alginate microbeads by rupture of water-in-oil-in-water droplets with an ultra-thin oil phase layer

This paper reports a novel formation method of monodisperse calcium alginate microbeads from water-in-oil-in-water (W/O/W) droplets with an ultra-thin oil phase layer. W/O/W droplets containing sodium alginate in an internal aqueous phase were formed as a template of calcium alginate microbeads using a microfluidic device. The ultra-thin oil phase layer of the W/O/W droplets was ruptured by an osmotic pressure difference between the internal and external aqueous phase. Immediately after the rupture, polyanionic alginate in the internal aqueous phase was cross-linked with calcium ion diffused from the external aqueous phase, and monodisperse and spherical calcium alginate microbeads were formed.