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 36 h 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 μm (p<0.05p<0.05) during 14 days incubation at 37 °C, the PLO group did not change in size. Also, PLL 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=6p<0.0001,n=6). We conclude that PLO-coated alginate microcapsules are mechanically stronger and provide better perm-selectivity than PLL-coated microcapsules.