Microencapsulation of erythrocytes in Eudragit-RL-coated calcium alginate

Abstract

Human erythrocytes have been encapsulated in calcium alginate gel beads (approx. 2 mm diameter) which were subsequently coated with a water-insoluble cationic polyacrylate, Eudragit RL. Stained histological sections as well as scanning and transmission electron micrographs clearly showed the presence of a dense capsule wall, approx. 60 μm thick after 60 min of exposure to an aqueous emulsion of Eudragit, surrounding a sponge-like alginate core. Eudragit beads could withstand greater compressive forces before mechanical failure than uncoated beads. The effect of alginate concentration, coating time and ionic strength on the compressive load at failure, indicated the likelihood that coating involved ionic interactions between the polycationic Eudragit and the polyanionic alginate. Encapsulated erythrocytes continued to consume glucose but at a rate one-third higher than normal which was attributed to an under estimate in the number of immobilized cells or to an actual increase in cell metabolism due to immobilization. Alginate/Eudragit encapsulated erythrocytes also continued to reversibly bind oxygen even after 21 days storage at 4°C. Although in vivo stability and biocompatibility remain at question, this system is a model of that required to encapsulate pancreatic islets for the treatment of insulin-dependent diabetes.