Durability of sodium sulfate-treated polylysine-alginate microcapsules

Chelated hollow microcapsules are unstable under in vitro conditions becaus e of their hygroscopic nature. Nongel inducing cations, such as Na+, stabil ize the outer membrane of the alginate-polylysine-alginate microcapsules le ading to more stable beads. We made different batches of empty capsules wit h a mean +/- SEM diameter of 607 +/- 11 microns, and found that within 1 we ek of incubating these capsules in normal saline at 37 degreesC, they incre ased to 718 +/- 10 microns (p < 0.05, n = 5). In initial experiments, we ma de different batches of capsules and divided them into two groups. One grou p was left untreated (control) whereas the other was treated with 6 mM Na2S O4 for 30 min, before Incubation in saline at 37<degrees>C. Control capsule s increased in weight and size, before beginning to melt in less than 1 wee k. In contrast, treated capsules rapidly lost weight and remained intact du ring 1 month of follow-up. In perifusion experiments, we found no deleterio us effect of sodium sulfate treatment on the function of islets enclosed in the capsules. (C) 2000 John Wiley & Sons, Inc. J Biomed Mater Res 54: 396- 399, 2001.