Characteristics of poly-L-ornithine-coated alginate microcapsules

Poly-L-Lysine (PLL) is the most widely used biomaterial for providing perm-selectivity in alginate ,microcapsules for islet transplantation. We had previously reported that Poly-L-Ornithine (PLO) is less immunogenic than PLL, and in the present study, we have compared the physical characteristics of PLO- and PLL-coated hollow alginate microcapsules. Microspheres made with 1.5% alginate were divided into 2 groups that were first coated with either 0.1% PLO or PLL, followed by a second coating with 0.25% alginate. After liquefaction of the inner alginate core with sodium citrate, the microcapsules were washed with saline and used for experiments. Pore size exclusion studies were performed with FITC-labeled lectins incubated with encapsulated pig islets followed by examination for fluorescence activity. Mechanical strength was assessed by an osmotic pressure test and by 36h of mechanical agitation of microcapsules with inert soda lime beads. The pore size exclusion limit of microcapsules after 20 min of coating was significantly smaller with PLO. While the mean +/- SEM diameter of PLL-coated microcapsules increased from 718 +/- 17 to 821 +/- 17 mu m(p < 0.05) during 14 days incubation at 37 degrees C, the PLO group did not change in size. Also, PILL group had a higher percentage of broken capsules (52.7 +/- 4.9%) compared to 3.1 +/- 2.05% for PLO capsules (p < 0.0001, n = 6). We conclude that PLO-coated alginate microcapsules are mechanically stronger and provide better perm-selectivity than PLL-coated microcapsules. (c) 2005 Elsevier Ltd. All rights reserved.