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

Grafting of encapsulated living cells has the po- tential to cure a wide variety of diseases. Large-scale appli- cation of the technique, however, is hampered by insuffi- cient 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 re- sponses 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 alg- inate-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 alg- inate-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 cap- sules can be successfully deleted by chemically crosslinking biocompatible molecules on the surface of alginate-PLL cap- sules. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 1219 -1227, 2003