FIG. 1.

Flow focusing using two dispersed phases and one immiscible continuous phase forms core-shell beads. Beads are pinched off at the intersection with mineral oil that has been acidified with acetic acid. As the acid diffuses into the beads, it causes the breakdown of the calcium carbonate particles. The released calcium ions then crosslink the alginate, causing the beads to gel. This bead formation method, in which the crosslinking ions are mixed with alginate in an insoluble form and then chemically released, is called internal gelation. This method produces a core-shell structure in which the shell is composed of alginate, and the core is composed of Matrigel^®+ collagen + alginate in which cells are encapsulated.