Capsule permeability via polymer and protein ingress/egress

Static incubation tests, where microcapsules and beads are contacted with p olymer and protein solutions, have been developed for the characterization of permselective materials applied for bioartificial organs and drug delive ry. A combination of polymer ingress, detected by size-exclusion chromatogr aphy, and protein ingress/egress, assessed by gel electrophoresis, provides information regarding the diffusion kinetics, molar mass cutoff(MMCO) and permeability. This represents an improvement over existing permeability mea surements that are based on the diffusion of a single type of solute. Speci fically, the permeability of capsules based on alginate, cellulose sulfate, polymethylene-co-guanidine were characterized as a function of membrane th ickness. Solid alginate beads were also evaluated. The MMCO of these capsul es was estimated to be between 80 and 90 kDa using polymers, and between 11 6-150 kDa with proteins. Apparently, the globular shape of the proteins (ra dius of gyration (R-g) of 4.2-4.6 nm) facilitates their passage through the membrane, comparatively to the polysaccharide coil conformation (R-g of 6. 5-8.3 nm). An increase of the capsule membrane thickness reduced these valu es. The MMCO of the beads, which do not have a membrane limiting their perm selective properties, was higher, between 110 and 200 kDa with dextrans, an d between 150 and 220 kDa with proteins. Therefore, although the permeabili ty estimated with biologically relevant molecules is generally higher due t o their lower radius of gyration, both the MMCO of synthetic and natural wa ter-soluble polymers correlate well, and can be used as in vitro metrics fo r the immune protection ability of microcapsules and microbeads. This artic le shows, to the authors' knowledge, the first reported concordance between permeability measures based on model natural and biological macromolecules . (C) 2000 John Wiley & Sons, Inc.