Mechanism of Biomineralization of Bovine Pericardium Tissue

Abstract

Pathologic biomineralization is the major cause of failure of tissue derived heart valve bioprosthesis (Schoen, 1989). The formation of calcified deposits in the cardiovascular system is a very important process and if its mechanism is properly understood, it may greatly affect the technology of long-lasting bioprosthesis. The present study was to investigate the mechanism of in vitro mineralization of de-endotheliazed, glutaraldehyde-treated bovine pericardium (BP), the essential component of BP bioprostheses. The primary question is: does the mineralization in vitro proceed as surface (extrinsic) process (Tomazic et al, 1991) or as a subsurface (intrinsic) process recorded in vivo (Schoen et al., 1985)? The BP mineralization in vitro was investigated by using a diffusion cell with two compartments that contained calcium phosphate solutions of different concentrations, separated by de-endotheliazed BP membrane. Diffusion of Ca and P through the membrane was monitored over extended periods under specified thermodynamic conditions. This permitted predicting which calcium phosphate compound could form at the membrane/solution interface (extrinsic mineralization), but more complexity occurs within the membrane corresponding to intrinsic mineralization. The analysis of transport of Ca and P through the BP membrane indicated the retention of Ca and P at/within membrane. Histology, scanning electron microscopy (SEM) and energy dispersive x-ray microanalysis (EDX) provided good evidence of subsurface mineralization, in addition to surface mineralization. The latter was not documented by histology, only with EDX. The EDX data compiled by line scan analyses indicated the Ca/P heterogeneity of the early precursor formed in the membrane environment that was indicated by Ca and P x-ray mapping of subsurface calcified regions.