Biocompatibility and immunologic properties of pericardial tissue stabilized by dye-mediated photooxidation

Bovine and porcine pericardial tissues stabilized by dye-mediated photooxidation have found application as bioprosthetic heart valve material.

To help predict clinical performance, a series of tests were performed to assess the biocompatibility and immunologic properties of these materials.

Photooxidized bovine or porcine pericardium sterilized with an iodine-based solution were found to be non-cytotoxic, non-hemolytic, and non-mutagenic. Oil or saline extracts of these tissues passed tests for intracutaneous toxicity (irritation), acute systemic toxicity, and subchronic toxicity. Histopathology of 90-day implants of these tissues in the rabbit model demonstrated no significant macroscopic reaction and only slight microscopic response. Using a rabbit model to assess immune response, both bovine and porcine pericardial tissues elicited low levels of antibody. Furthermore, tissue photooxidation or iodine sterilization did not increase the overall level of antibodies. Glutaraldehyde-treated tissue also elicited low antibody levels which were higher than photooxidized tissue-induced levels. Absorption studies indicated that the photooxidation process may generate new epitopes, possibly collagen cross-links. Using the juvenile sheep model to assess in vivo performance, bioprosthetic valves made with photooxidized tissue were implanted and allowed to serve as functional implants for up to two years. Upon explant, the photooxidized pericardial leaflets were found to be non-calcific and partially covered with a layer of host cells. Histological cross-sections stained with von Willebrand's factor confirmed this layer as endothelial cells.