Poly(ethylene glycol)

Abstract

The demands placed on a material to be used for microencapsulation are stringent. The material should (1) be stable in the physiological environment over several years, (2) not engender any cytotoxicity, (3) be permselective so as to be immunoprotective and yet allow nutrient and metabolite access, and (4) be biocompatible so as not to elicit an inflammatory or fibrotic response from the host. Of the wide range of materials used, ionically coacervated microcapsules of alginate and poly(1-lysine) (PLL) have shown promise. O'Shea and Sun (1986) demonstrated rat islet survival times of 2 to 3 months, and occasionally of 1 year, in mice, using alginate/PLL/alginate trilayered microcapsules. The xenografts apparently failed as a result of over-growth with fibroblast-like and macrophage-like cells upon the microcapsules. This cellular overg-rowth is due to a nonspecific foreign body reaction elicited by the microcapsules and is by no means restricted to alginate/PLL/alginate microcapsules. Roberts et al, using HEMA-MMA copolymers for microencapsulation, also reported seeing up to a 10 μJim thick layer of cellular overgrowth after 4 weeks in vivo (Roberts et al 1991).