Development of subsieve-size capsules and application to cell therapy

Reduction in the diameter of cell-enclosing capsules has a practical application in cell therapy as it induces beneficial effects such as higher molecular exchangeability between the enclosed cells and the ambient environment, as well as higher mechanical stability and biocompatibility. Subsieve-size capsules are capsules of less than 100 microm in diameter, which are approximately one tenth the size of conventional cell-enclosing microcapsules. Such small capsules can be prepared using the emulsion system obtained via the jetting process in which a cell-suspending polymer solution is extruded into an ambient coflowing water-immiscible liquid from a needle several hundred micrometers in diameter. The capsule size can be controlled by changing the velocity of the polymer solution and the ambient water-immiscible liquid. The emulsification process does not significantly affect viability of mammalian cells enclosed in the resultant subsieve-size capsules. In this chapter we will review the technique of subsieve-size capsule production and the effects of diameter reduction on the enclosed cells and properties of the capsules.