Microencapsulation of crystalline insulin or islets of Langerhans: an insulin diffusion study

Microcapsules containing insulin crystals or islets of Langerhans were made by extruding a mixture of insulin crystals or islets and sodium alginate into a calcium chloride solution, and then coating it with poly-l-lysine. When these microcapsules were incubated at 37 degrees C, insulin could be detected readily in the medium, indicating that the microcapsular membrane is permeable to insulin. The efficiency of insulin encapsulation with crystalline insulin declined as the concentration in the sodium alginate mixture increased. Over 90% of the entrapped insulin was released after 3 days of incubation at 37 degrees C, indicating that the rate of insulin release from the microcapsules requires modification if the microcapsules are to be used as a long-term insulin delivery system. The amount of insulin secreted by the encapsulated islets was not significantly different from that of unencapsulated islets, suggesting the islets were not affected by the modified encapsulation process.