Calcification assessment of bioprosthetic heart valve tissues using an improved in vitro model

Calcification is a recurrent problem in patients suffering from heart valve disease and it is the main cause of failure in biological heart valve prostheses. The development of reliable calcification tests that consider both the material properties of the prostheses and the fluid composition is of paramount importance for the effective testing and subsequent selection of new cardiovascular implants. In this article, a fast, reliable, and highly reproducible method for the assessment of the calcification potential of biomaterials was developed. The developed method simulated closely the chemical environment in vivo, where the supersaturation levels of calcium and phosphate remain constant. Seeded hydroxyapatite (HAP) crystal growth experiments were used as the reference system and compared to the mineralization kinetics and extent of frozen untreated bovine and porcine pericardium, and glutaraldehyde-fixed bovine pericardium. Untreated pericardial patches did not calcify in the supersaturated calcium phosphate solutions whereas glutaraldehyde-fixed bovine pericardial patches mineralized at the same conditions. The present work suggested that the loose collagenous serosa side of the pericardium mineralized at lower rates compared to its dense collagenous fibrous side. Concordant with these findings, the mineralization of bioprostheses may also be attributed, to the structural deterioration of collagen-rich tissues, induced by chemical treatment used to control in vivo structural stability and immunomodulation of the implants.