Microencapsulation and Function of Islets Sample Clauses

Microencapsulation and Function of Islets. Microencapsulation of islets involves three steps, namely: (a) generation of microcapsules enclosing islets, by droplet-formation, followed by chelation in a solution of calcium chloride to form a solid gel, (b) additional coatings of the resulting gelled spheres with two outer coatings consisting of polylysine and alginate membrane, (c) liquefaction of the original core gel with a solution of sodium citrate. The three steps are separated by washings in normal saline. To produce microcapsules containing only one or two islets/capsule, we set the pressure on the alginate flow at 1 psi and the air flow rate at 7 cc/mm, using a 22 gauge needle fitted to a 2cc syringe and a chelating solution of 1.11% calcium chloride, pH 7.4. The resulting capsules measure between 500-800 micro-M in diameter. There had been suggestions that the liquefaction of the inner solid gel may compromise the structural support of the microcapsules. We therefore examined the function of islets enclosed in microcapsules that had not been subjected to liquefaction of the inner core (solid microcapsules), with that of islets contained in liquefied microcapsules (islets in hollow microcapsules) . It was found that islets in fresh hollow microcapsules responded better to a glucose challenge than those contained in fresh solid microcapsules; albeit, culture of the latter prior to use, enhanced the response of their enclosed islets to glucose stimulation. These findings are contained in a paper to be published in the Journal of Surgical Research in June 1998 (preprint enclosed).