Silica sol-gel encapsulation of pancreatic islets

We developed a biocomposite material containing silica ceramic. The sol-gel technology in which ceramic materials are polymerized from liquid solutions at room temperature and physiologic pH can be used to produce ceramics that have a determined pore size and that contain living organisms or cells. Capsules were stable to extreme acid and base conditions as well as to trypsin in vitro for 6 months. We used insulin-secreting murine islet cells as the first mammalian material for encapsulation. Two approaches to generating successful encapsulation of islets were used: drop-tower sphere generation and emulsion. Sphere diameters of less than 1 mm were associated with positive insulin secretory capacity as documented by a static batch incubation technique. Average pore sizes were 161 A for drop-tower spheres and 105 A for emulsion spheres. Capsules allowed the passage of insulin and cytokines but not the passage of antibody. Implantation of encapsulated islets did not result in fibrosis of the capsule in vivo, and retrieval of capsules after 1 month in vivo documented continued insulin secretory capacity. Further in vivo experiments documented increased survival of transplant recipients despite failure to achieve normoglycemia in all but a few cases. Silica sol-gel encapsulation provides a potentially useful alternative for encapsulation of cells for transplantation or drug delivery, and further work is warranted to develop this potentially useful approach for the treatment of diabetes mellitus.