Calcification of polyurethane-based biomaterials implanted subcutaneously in rats: role of porosity and fluid absorption in the mechanism of mineralization

The object of this study was to investigate the mineralization of polyurethane in the rat subcutaneous environment, in comparison to collageneous biomaterials, which would facilitate investigation of the calcification mechanism in implantable biomaterials. This model was compared to an in vitro model of non-spontaneous formation of calcium phosphate precipitate. To study the role of porosity/fluid absorption capacity, various biomaterials such as polyurethane, hydrophilic polyurethane foam, Type I collagen sponges, and bioprosthetic heart valve tissue were examined in in vitro and in vivo models. In view of the exceedingly low levels of polyurethane calcification, it seems that the rat subcutaneous model is not suitable for routine studies of the mechanism of polyurethane calcification. The calcification extent of both collageneous and hydrophilic polyurethane, was found to be in good correlation with the water absorption capacity of these biomaterials. It is suggested that the water capacity of the biomaterial determines the bulk level of calcification, which in turn is generated and propagates via the inherent affinity sites of the biomaterial to Ca²⁺.