The potential of using cell microencapsulation in successful clinical applications can be realized only if several requirements encountered during the development process are optimized such as the use of an appropriate biocompatible polymer to form the mechanically and chemically stable semi-permeable matrix, production of uniformly sized microcapsules, use of an appropriate immune-compatible polycations cross-linked to the encapsulation polymer to stabilized the capsules, selection of a suitable cell type depending on the situation.