The fabrication technique for hollow gel microparticles using microbubble templates

Hollow gel microparticles with shells composed of functional polymer gels are expected to be useful in the production of food additives or anti-reflective films for liquid crystal displays. However, few studies have addressed methods for the simple and efficient production of hollow gel microparticles. Hollow gel microparticles would be expected to find widespread applications if they could be fabricated more easily. In this study, we succeeded in fabricating hollow gel microparticles simply by atomizing a gas-supersaturated aqueous sodium alginate solution into aqueous calcium chloride solution. The gas-supersaturated aqueous sodium alginate solution was prepared by gas pressurization; following a rapid pressure decrease, the excess dissolved gas appeared as microbubbles in the atomized droplets. When the atomized droplets, with encapsulated microbubbles, came into contact with the aqueous calcium chloride solution, the droplets were converted to a gel by ionic crosslinking between sodium alginate and calcium ions, and any remaining bubbles were trapped inside the droplets. With this method, we can fabricate calcium alginate hollow gel microparticles of less than 100 μm with multi-voids. Furthermore, these hollow structures can be controlled by changing the compression pressure, which changes the amount of dissolved gas in the liquid.