Biocompatibility and surface structure of chemically modified immunoisolating alginate‐PLL capsules

Abstract Grafting of encapsulated living cells has the potential to cure a wide variety of diseases. Large‐scale application of the technique, however, is hampered by insufficient biocompatibility of the capsules. A major factor in the biocompatibility of capsules is inadequate covering of the inflammatory poly‐ L ‐lysine (PLL) on the capsules' surface. In the present study, we investigate whether tissue responses against alginate‐PLL capsules can be reduced by crosslinking the surface of the capsules with heparin or polyacrylic acid. Our transplant study in rats shows a tissue response composed of fibroblasts and macrophages on alginate‐PLL‐alginate and alginate‐PLL‐heparin capsules that was completely absent on alginate‐PLL‐polyacrylic acid capsules. Atomic force microscopy analyses of the capsules demonstrates that the improved biocompatibility of alginate‐PLL‐capsules by polyacrylic acid coating should not only be explained by a more adequate binding of PLL but also by the induction of a smoother surface. This study shows for the first time that biologic responses against capsules can be successfully deleted by chemically crosslinking biocompatible molecules on the surface of alginate‐PLL capsules. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 1219–1227, 2003