ABSTRACT

Several reviews of the biophysical principles of cryobiology have been published recently and the interested reader is referred particularly to Mazur (1) for a detailed discussion or to Pegg (2) for an introductory account. In this chapter the science of cryopreservation will be approached in a more practical and applied way. We know that freezing living cells is normally lethal, a fact that is put to practical use in cryosurgery. But we also know that cooling slows the chemical processes both of life and of decay and this has lead to the idea that “suspended animation” might be achieved by cooling. Successful preservation will then depend on reducing the destructive action of ice but allowing the protective effect of low temperatures, such that any damaging effects are greatly outweighed by the protective effects. This is a complicated matter: many structures and processes are temperature-dependent and cooling has complex effects that combine to create conditions that are far removed from normal physiology. When cells are cooled much below 0°C, the effects are normally dominated by the freezing of water, which typically constitutes at least 80% of tissue mass. It was generally thought that the ice crystals were directly responsible for damage rather than the concentration of solutes in the progressively diminishing liquid phase as cooling proceeded.