Skin banking methodology: An evaluation of package format,cooling and warming rates,and storage efficiency

The two major skin packaging formats for transplantable human skin, flat — folded and rolled — cylindrical, were evaluated with respect to the control of cooling rate, warming rate, and storage efficiency. Experiments were performed with six amounts of skin ranging from 7.6 × 20 cm (0.17 ft²) up to 7.6 × 120 cm (1.00 ft²).Contrary to previously published statements, when skin packaged in either of the two formats is cooled at an uncontrolled rate in a low temperature (?70 °C) mechanical refrigerator or dry-ice chest, the smaller skin dimensions cool too rapidly (up to ?24 °C min^?1), while the packets containing larger skin dimensions exhibit prolonged exothermic temperature plateaus (8–44 min), allowing the possibility of significant crystallization damage to the cells. On the other hand, controlled-rate cooling of ?1 °C min^?1 can be obtained using a temperature-feedback controlled-rate freezer along with a flat skin packet geometry. Much less control is obtained if a cylindrical skin packet geometry is used with a controlled-rate freezer.Skin processed in the flat format is capable of being warmed by water immersion about 10 times more quickly than equivalent amounts of skin processed in the rolled format. The longer warming times associated with the cylindrical package format (3.5–25 min, depending upon the amount of skin per packet) result from extended endothermic temperature plateaus in the subzero region, which have been shown to damage skin cells and reduce their subsequent viability. The short warming times (0.25–3.5 min) associated with the flat skin package format are devoid of such complications, since they are within the needed warming rate of 50 °C–70 °C min^?1.Package geometry affects the storage requirements of transplantable skin. The flat format possesses a two- to threefold advantage in storage efficiency. Capital equipment and liquid nitrogen usage for storage is drastically decreased if a flat package format is chosen.