Bovine pericardium for heart valve bioprostheses:in vitro andin vivo characterization of new chemical treatments

Abstract

This study is aimed at investigating the bovine pericardium treated with different chemical procedures applied to prevent dystrophic calcification; decellularization of the fresh pericardium (samples B and C); fixation of the pericardium with glutaraldehyde (samples A, B, C, D and E); detoxification with aminoacids (samples A and B) and storage in a solution of benzoic acid esters. Pericardial sacs were harvested and delivered to the laboratories to be submitted to the chemical treatments. The samples E have been treated as the samples D but before the implantation they were exposed to the surgical lamp in order to promote some drying. The samples were tested for their mechanical properties and shrinkage temperature (at 1 week and after 36 months). Thein vivo tests were performed by means of implantation in a paravertebral subcutaneous position in rats. At the explant (2, 4 and 8 weeks) the samples were submitted to histological assay and the calcium content determined by spectroscopic atomic absorption. All the samples showed loss of tensile strength and elongation at 36 months (except for the sample A), as well as a moderate diminution of the shrinkage temperature. The histology showed that the decellularized samples (B, C) were thicker than the others and the collagen fibres were extensively homogenated. The cell colonization was macrophagic for the samples A and D while it was also composed of giant cells in the samples B, C and E at 8 weeks. The von Kossa's staining was positive only for the samples D and E after 4 weeks of implantation. The calcium content of the samples D was 285.3 mg/g at 8 weeks while in E it was 44.4 mg/g dry tissue at 4 weeks; for the remaining samples the calcium content did not increase with the time (2.1–2.3 mg/g at 8 weeks). In conclusion, the pericardium decellularization and detoxification associated with its storage in a glutaraldehyde-free solution is a promising method in order to realize more durable pericardial bioprostheses. The investigated tissue treatments applied to the bovine pericardium permit removal of the calcium nucleation sites, and hence the avoidance of the severe drawback of the aldehyde crosslink, but at the same time maintain the necessary and well known tissue stability.