Improvement of in vivo stability of alginate-polylysine capsules.

Dextran (MW 70,000) and rat islets were encapsulated in alginate-polylysine membrane. The capsules were further coated with tolylene 2,4-diisocyanate. Both of positive and negative charges were detected on the surface of alginate-polylysine capsules, which were absent after coating the capsules with tolylene 2,4-diisocyanate. In the peritoneal cavity, alginate-polylysine capsules were entrapped by the peritoneum, and 89% of dextran was leaked out of the capsules. Alginate-polylysine capsules coated with tolylene 2,4-diisocyanate were present freely in the peritoneal cavity and no leakage of dextran from the capsules were detected. Insulin release from the encapsulated islets was almost the same in both of tolylene 2,4-diisocyanate-coated and uncoated capsules. This study demonstrates that in vivo stability of capsules is dependent on the charge on the surface and can be improved by coating with tolylene 2,4-diisocyanate.