Alginate/aminopropyl-silicate/alginate (Alg/AS/Alg) membrane was prepared on Ca-alginate gel beads by a sol-gel process. The membrane has ≡Si-O-Si≡ bonds as well as electrostatic bonds between amino groups of AS and carboxyl groups of alginate. Permeability and stability were investigated for the membrane. Furthermore, rat islets encapsulated in the membrane (499±32μm in diameter, 1000 islets/recipient) were transplanted to the peritoneal cavities of the mice with streptozotocin-induced diabetes. Our data show that the membrane had the molecular weight cut-off point of between 70 and 150kDa, and hardly inhibited the permeation of glucose and insulin. The Alg/AS/Alg microcapsule was more stable than the well-known Alg/poly-L-lysine (PLL)/Alg microcapsule. After 30 days of soaking in stimulated body fluid, the percentages of intact microcapsule were 98.4±0.5 (mean±SEM)% and 88.0±1.5% (p<0.001) for the Alg/AS/Alg and Alg/PLL/Alg microcapsules, respectively. The maximum maintenance period of normoglycemia was 105 days without administration of immunosuppressive drugs.
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