From: Proceedings 10th World Congress of Cryosurgery
The cause and prevention fractures in cryopreserved tissues

November 1998
M Wusteman and D Pegg (The authors gratefully acknowledge the British Heart Foundation for its financial support for this work.) Medical Cryobiology Unit, Department of Biology, University of York, UK

Background: Macroscopic fractures are frequently found in vascular tissue (arteries, veins, cardiac valves) following cryopreservation. These can render the tissue useless for transplantation. Preliminary experiments with rabbit artery indicated that their incidence is independent of cryoprotectant concentration and cooling rate to -80'C. This study was carried out to establish more precisely the conditions under which the fractures appear in order to establish their cause and find a means of prevention.

Method: Rabbit common carotid artery, an established model for the small elastic artery required for vascular reconstructive surgery, was used to establish the stage of the cryopreservation process at which the fractures were formed. Physico chemical properties of the frozen tissue were characterized and the effects of different cooling and rewarming regimes on fracture incidence were assessed in order to elucidate the mechanism responsible.

Results: The results of this study suggest that fractures in cryopreserved tissue result from thermal stresses created during rapid rewarming of the vitreous material that is produced by the freezeconcentration of the aqueous phase. Relatively slow rewarming to -100C reduced these stresses and prevented fractures occurring without any apparent detrimental effect on post thaw function.

Conclusion: Cryopreserved vascular conduits can be retrieved without fractures by modifying the thawing process to minimize thermal stresses in the tissues.


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