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To develop a novel type of immunoisolation membrane for a microcapsule-shaped bioartificial pancreas, we attempted to use a sol–gel synthesized silicate. An aminopropyl-silicate membrane derived from 3-aminopropyltrimethoxysilane and tetramethoxysilane was formed on Ca-alginate gel beads via electrostatic interaction. The positively charged amino groups remaining on the surface of the resultant gel beads were neutralized by immersion in an aqueous Na-alginate solution. From measurements of the partition coefficients and effective diffusivities of different substances to the gel beads, it was found that the aminopropyl-silicate membrane prepared under optimized composition of silicon alkoxide precursors successfully rejected γ-globulin, giving good permeability to substances having a low molecular weight. Islets could be encapsulated within the newly developed microcapsules while retaining their ability …