Maximal period of cryopreservation with the Bicell biofreezing vessel for rat tracheal isografts.

Objective: The maximal period of cryopreservation for the trachea is still unsolved. We assessed the maximal period of cryopreservation using the Bicell biofreezing vessel as an easy and cheap slow-freezing instrument for viable tracheal grafts in 95 rats.

Methods: Each isograft was harvested from 17 donor rats, immersed in the preservative solution, and stored in a Bicell device in a deep freezer at -80 degrees C. The tracheal isografts were then randomly assigned to 9 groups according to cryopreservation periods ranging from 0 to 12 months. Included in the 9 groups were 2 subgroups (n = 6 per subgroup) that were observed immediately after being thawed and 1 month after heterotopic transplantation into the omentum after being thawed. Four subgroups (n = 6 per subgroup) were added according to the cryopreservation period for 1, 3, 6, and 12 months to evaluate the graft morphology 3 months after being thawed and transplanted heterotopically.

Results: A prolonged period of cryopreservation had a degenerative effect on both the epithelium and cartilage. One month after transplantation, degeneration was more pronounced in the cartilage than in the epithelium, as characterized by the viable chondrocyte ratio and the epithelial score of isografts undergoing cryopreservation for more than 9 months. Three months after transplantation, the morphology of the epithelium and cartilage in isografts undergoing cryopreservation for less than 3 months was better preserved, whereas the morphology of both deteriorated in isografts undergoing cryopreservation for more than 6 months.

Conclusions: We conclude that the permissible period of cryopreservation to maintain tracheal isograft viability in this simple system using a Bicell biofreezing vessel is 3 months.