Characterization of ultrastructural damage of valves cryopreserved under standard conditions

Cryopreserved allograft valves are increasingly being used as valvular replacements. This study was conducted to characterize the ultrastructural damage on the allograft valves obtained by a current standard protocol of valve procurement, antibiotic exposure, and cryopreservation, as a basis for future studies on allograft valve preservation. Materials used were seven aortic and seven pulmonary fresh porcine valves, which were cryopreserved according to the requirements of the American and European Associations of Tissue Banks. The samples were randomly assigned into four groups: (1) fresh, untreated; (2) fresh, treated with antibiotics for 24 h.; (3) treated with antibiotics and exposed to dimethyl sulfoxide (without freezing); and (4) treated with antibiotics, exposed to dimethyl sulfoxide, and then cryopreserved and stored until the study. All tissue samples were processed simultaneously for routine light microscopy and transmission electron microscopy. Fresh-untreated, antibiotic-treated, and dimethyl sulfoxide-exposed valves showed adequate preservation of cellular components. However, after cryopreservation significant damage was observed in fibroblasts with signs of apoptotic cellular injury. Our observation suggests that apoptosis occurs during valve processing. This apoptotic process may be related to various factors, including chemical injury or hypoxia.