Optimum warming rates to maintain glucose metabolism in porcine skin cryopreserved by slow cooling.

The optimum warming rate for cryopreserved skin (dimensions: 7.6 cm X 20 cm X 0.38 mm thick) folded double in a flat package format was tested using a recently developed quantitative assay of skin cell metabolism. The assay measured the metabolic conversion of glucose to carbon dioxide by intact partial-thickness skin. Skin cooled at a constant, controlled rate of -1 degree C min-1 to a temperature of -100 degrees C, and then rapidly transferred to -196 degrees C for overnight storage, could be optimally warmed at rates of 95-260 degrees C min-1 by immersion in 10-20 degrees C water. The amount of metabolic activity remaining in skin warmed at rates within this optimal range was 76-78% of normal. Slightly less than maximal metabolic activity, 71-75% of normal, resulted from warming rates of 292-458 degrees C min-1, obtained by immersion in 25-37 degrees C water. Skin metabolism remaining after warming rates of 30-53 degrees C min-1 (3-5 degrees C water) was 52-70% of normal, while that remaining after rates of 501-882 degrees C (40-65 degrees C water) was 0-47% of normal. These experiments establish practical upper and lower limits for post-cryopreservation warming rates employed to maintain skin cell metabolism, and the cellular viability which depends upon that metabolism.