Studies on small (< 350 mu m) alginate-poly-L-lysine microcapsules. V. Determination of carbohydrate and protein permeation through microcapsules by reverse-size exclusion chromatography

wMembrane molecular weight (MW) cut-off is a critical factor for immunoprot ection of transplanted microencapsulated cells as well as for graft surviva l. Our goal was to study dextran and protein permeation through small (<350 mu m in diameter) alginate-poly-L-lysine microcapsules made with an electr ostatic system. Microcapsules were packed into a column, and gel-sieving ch romatography was performed with proteins and dextrans of known MW. The obje ctives of this study were (1) to validate this approach for the assessment of the MW cut-off of <350 mu m-in-diameter microcapsules and (2) to evaluat e the effect on MW cut-off of changes in experimental conditions. Elution p rofiles of proteins suggest that the MW cut-off of our small microcapsules lies between 14,500 and 44,000 Da whereas dextrans greater than or equal to 19,000 concentration from 0.02 to 0.08% reduced the MW cut-off. Increasing the PLL MW from 11.6 to 69.6 kDa induced no change in the MW cut-off. The results also show that the method can be used to discriminate between adsor ption and absorption and that insulin diffuses freely across the microcapsu le membrane. This method will be useful in establishing the ideal MW cut-of f, in optimizing microcapsule characteristics, and in performing routine qu ality controls. (C) 2000 John Wiley & Sons, Inc.