FACTORS INFLUENCING THE ADEQUACY OF MICROENCAPSULATION OF RAT PANCREATIC-ISLETS

The observation that only a portion of all alginate-polylysine microca psules are overgrown after implantation suggests that physical imperfe ctions of individual capsules, rather than the chemical composition of the material applied, are responsible for inducing insufficient bioco mpatibility and thereby fibrotic overgrowth of those capsules. We rece ntly developed a lectin binding assay that allows for quantifying the portion of inadequately encapsulated islets, and demonstrated that ina dequately encapsulated islets induce a fibrotic response associated wi th graft failure. The present study investigates factors influencing t he adequacy of encapsulation of pancreatic islets, We applied our lect in binding assay and found that the number of inadequate, and particul arly incomplete, capsules is influenced by the following factors. (1) A capsule diameter of 800 mu m is associated with a lower percentage o f inadequate capsules than smaller (500 mu m and 600 mu m) or larger ( 1800 mu m) capsules. (2) A high rather than low guluronic acid content of the alginate is associated with a lower percentage of inadequate c apsules, This can be explained, at least in part, by smaller ranges of swelling and subsequent shrinkage during the encapsulation procedure. (3) An increase in viscosity caused by applying a higher alginate con centration compensates for a low guluronic acid content, This effect o f increased viscosity cannot be explained by a reduced range of swelli ng and shrinkage during the encapsulation procedure. We conclude that alginates with a high guluronic acid content and a viscosity near the filtration limit are preferable in order to minimize the number of ina dequate capsules.