Release of Insulin from Calcium Carbonate Microspheres with and without Layer-by-Layer Thin Coatings

The release of insulin from insulin-containing CaCO3 microspheres was investigated. The microspheres were prepared by mixing aqueous solutions of CaCl2 and Na2CO3 in the presence of insulin. The surface of the insulin-containing CaCO3 microspheres was coated with a layer-by-layer thin film consisting of poly(allylamine hydrochloride) and poly(styrene sulfonate) to regulate the release kinetics of insulin. The release rate of insulin from the coated CaCO3 microspheres was significantly suppressed compared with that of uncoated CaCO3 microspheres, and depended on the thickness of the films. Rhombohedral calcite crystals of CaCO3 formed from the microspheres during the release of insulin, suggesting that the CaCO3 microspheres dissolved and recrystallized during the release of insulin.