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Many kinds of biological cells can be successfully cryopreserved by imposing a specific freeze-thaw procedure yielding a maximum survival rate for the respective type of cell. The tools cost frequently applied to achieve the desired freezing protocol are the variation of cooling and warming rates and the addition of cryoprotective agents. More recently, interest has been attracted to the use of certain polymers as cryo-additives (see e.g., 29, 38, 39, 59). An important difference as compared to the more commonly used low molecular weight (LMW) compounds like glycerol, certain alcohols or dimethyl sulfoxyde (Me2SO) is that polymers do not generally penetrate the cell membrane. This may constitute an important advantage if the macromolccular compound is non-toxic and hence does not have to be removed prior to retransfusion or reimplantation of the cryopreserved material. Under these circumstances so-called one-step preservation procedures (25) can be applied, circumventing time-consuming and expensive dilution processes for washing out the agent as usually required for Me2SO or glycerol. |
