Preparation of Monodisperse Calcium Alginate Micro-/Nanospheres via Shirasu Porous Glass Membrane Emulsification Followed by Classification Using Microfiltration Membranes

Monodisperse calcium alginate micro-/nanospheres were developed via ionic cross-linking of alginate polymers in water-in-oil emulsion droplets prepared using a direct membrane emulsification technique with Shirasu porous glass (SPG) membranes. By changing the concentration of the alginate polymers in the dispersed phase and the pore size of the membrane, we obtained monodisperse calcium alginate micro-/nanospheres with tunable sizes because each micro-/nanosphere was formed in each droplet. However, the monodispersity decreased when SPG membranes with pores of smaller than 0.5 μm were used because they contained larger microspheres from the coalescence of the emulsion droplets. To remove such larger microspheres for achieving an excellent monodispersity, classification using microfiltration membranes was performed. After serial classifications with membranes of 1.2, 0.8, and 0.45 μm pore sizes, the resulting fraction showed an average diameter of 0.22 μm and CV of 21%, starting from an original with an average diameter of 0.35 μm and CV of 59%.