Durability of sodium sulfate-treated polylysine-alginate microcapsules

Chelated hollow microcapsules are unstable under in vitro conditions because of their hygroscopic nature. Nongel inducing cations, such as Na+, stabilize the outer membrane of the alginate‐polylysine‐alginate microcapsules leading to more stable beads. We made different batches of empty capsules with a mean ± SEM diameter of 607 ± 11 microns, and found that within 1 week of incubating these capsules in normal saline at 37°C, they increased to 718 ± 10 microns (p < 0.05, n = 5). In initial experiments, we made different batches of capsules and divided them into two groups. One group was left untreated (control) whereas the other was treated with 6 mM Na2SO4 for 30 min, before incubation in saline at 37°C. Control capsules increased in weight and size, before beginning to melt in less than 1 week. In contrast, treated capsules rapidly lost weight and remained intact during 1 month of follow‐up. In perifusion experiments, we found no deleterious effect of sodium sulfate treatment on the function of islets enclosed in the capsules. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res 54: 396–399, 2001