The current status of tissue cryopreservation

Cryopreservation plays an important role ill tissue banking and will assume even greater importance when tissue engineering becomes an everyday realit y. For some tissue grafts, living cells are unnecessary and adequate preser vation methods are usually available. For other tissues living and function ing cells are needed and preservation methods are much less advanced. The b asic requirements for cell recovery can usually be defined if a few basic b iophysical properties of the cell are known and some standard measurements of the effect of cryobiological variables are carried out. The problems in tissue cryopreservation are not usually due to difficulties in preserving t he living cells per se, but arise from the properties of the integrated cel l/matrix systems upon which tissue function almost always depends. Some exa mples of such difficulties are described. It is concluded that the formatio n of ice, through both direct and indirect effects, is probably fundamental to these difficulties, and this is why vitrification seems to be the most likely way forward. However, two major problems still to be overcome are cr yoprotectant toxicity and recrystallization during rewarming. Less obvious, and certainly less well understood is chilling injury - damage caused by r eduction in temperature per se; this may yet turn out to be of fundamental importance.