Physical and biological aspects of renal vitrification

Cryopreservation would potentially very much facilitate the inventory control and distribution of laboratory-produced organs and tissues. Although simple freezing methods are effective for many simple tissues, bioartificial organs and complex tissue constructs may be unacceptably altered by ice formation and dissolution. Vitrification, in which the liquids in a living system are converted into the glassy state at low temperatures, provides a potential alternative to freezing that can in principle avoid ice formation altogether. The present report provides a brief overview of the problem of renal vitrification. We report here the detailed case history of a rabbit kidney that survived vitrification and subsequent transplantation, a case that demonstrates both the fundamental feasibility of complex system vitrification and the obstacles that must still be overcome, of which the chief one in the case of the kidney is adequate distribution of cryoprotectant to the renal medulla. Medullary equilibration can be monitored by monitoring urine concentrations of cryoprotectant, and urine flow rate correlates with vitrification solution viscosity and the speed of equilibration. By taking these factors into account and by using higher perfusion pressures as per the case of the kidney that survived vitrification, it is becoming possible to design protocols for equilibrating kidneys that protect against both devitrification and excessive cryoprotectant toxicity.