Physical limitations of the rapid freezing method

Abstract

Throughout the recorded history of biological freezing, it has generally been recognized that one may differentiate between rapid and slow freezing, although it has not always been realized how compelling is the distinction which can be drawn between the two on the basis of the markedly different distribution of ice crystals and the differing mechanism of cell injury which may result. In order, therefore, to discuss the physical limitations of rapid freezing, the term must be defined and differentiated from slow freezing. This paper thus becomes primarily a discussion of slow and rapid freezing from which the limitations of the rapid freezing method should become self evident. Possibly the single most important concept in biological freezing as well as the most difficult for the biologist to assimilate is the following: despite the collective and individual complexity of living cells, freezing in a biological matrix represents nothing more than the removal of all available water and its isolation into inert foreign bodies, the ice crystals. Freezing is a wholly physical phenomenon obeying known and simple laws and, tempting though it may be to imbue biological freezing with the same mysterious complexity that surrounds the cells themselves, it is quite unnecessary. The transfer of water out of solution into ice crystals is a very straightforward phenomenon and is, in effect, simply dehydration with the removed water sequestered locally in the tissue rather than entirely removed. From this dual event—dehydration with foreign body formation—stem all the physiological and biochemical events subsequent to freezing (Meryman 1956).