Encapsulation of individual pancreatic islets by sol-gel SiO2: a novel procedure for perspective cellular grafts.

Pancreatic rat islets are encapsulated by a siliceous layer deposited on the surface of single islets upon reaction with gaseous siliceous precursors. The process preserves original islet dimensions and does not suppress viability or function. The encapsulated material is homogeneously distributed on the islet surface, and layer thickness can be controlled in the 0.1-2.0 microm interval. Dynamic perfusion experiments with glucose stimulation were carried out in both encapsulated and non-encapsulated islets. Results were treated according to a kinetic model presented here for the analysis of perfusion data; the model tested by literature data, was used to substantiate the diffusion features of the siliceous layer, which does not affect mass transfer of insulin but which modifies the texture of the islet surface tissue. The clinical potential of silica encapsulation was demonstrated by in vivo experiments using encapsulated islets transplanted into diabetic rats. Transplantation was carried out in both inbred and outbred rats and indicated prolonged restoration of normal glycaemia levels and protection from immunological attack.

Entrapment of viable microorganisms by SiO2 sol-gel layers on glass surfaces: trapping, catalytic performance and immobilization durability of Saccharomyces cerevisiae.

Yeast cells are immobilized into SiO2-sol layers coating glass sheets, starting from a SiO2-sol dispersion of viable cells and using the dip-coating method for deposition on the glass surface. The trapped biocatalyst survives experimental working-up and displays kinetic behavior excluding mass transport interference during sucrose degradation. The morphological and other physical features of SiO2-sol layers do not exclude viability and cell reproduction: prolonged contacts between immobilized system and substrate favour discharge of bud cells in solution. The phenomenon is suppressed by coating the SiO2-sol layer with a film composed of triethoxysilane and diethoxymethylsilane. This fact is attributed to the mechanical features of this film, which displays a tensile strength sufficient to contrast the tensile stress exerted by cell reproduction.