Cryopreservation of skin using an insulated heat sink box stored at -70 degrees C

The cooling of skin to a temperature of -70 degrees C was carried out by two methods: programmed controlled-rate (PCR) cooling at -1 degree C min-1 to -70 degrees C, and variable-rate cooling to -70 degrees C in an insulated heat sink box (IHSB). The IHSB was constructed of polystyrene and contained two aluminum heat sinks placed one on each side of flat packets of skin. The IHSB containing skin was cooled in a -70 degrees C constant-temperature refrigerator. When using the IHSB, the insulation provides a slow cooling rate while the paired heat sinks provide even heat flow across the top and bottom surfaces of the flat skin packets, minimizing the duration and potential damaging effects of the exothermic temperature plateau which occurs at the freezing point. When followed by 24-hr storage at -70 degrees C and warming at about 316 degrees C min-1, the IHSB cooling method was equivalent to the PCR method in generating a suitably slow cooling rate of -1 to -2 degrees C min-1, and maintaining about 80% of normal skin cell glucose metabolism. The development of the IHSB cooling system provides a method for the simple, cost-efficient cryopreservation of small amounts of autograft skin, such as those remaining from surgical procedures, and can also provide an allograft skin banking capability to any facility possessing a -70 degrees C refrigerator.