Is vitrification an alternative to standard cryopreservation (slow cooling)?
Conventional methods of cryopreservation have been developed to accomodate the consequences of ice formation. Vitrification is a process which, by combining the use of concentrated solutions with rapid cooling avoids the formation of ice. Samples reach low temperatures in a glassy state, which has the molecular structure of a viscous liquid and is not crystalline. This method has the potential advantages of being rapid and not requiring controlled rate cooling equipment. Good survival of mammalian embryos and oocytes have been reported by vitrification. However, this approach is still experimental and the high levels of additives that are necessary to achieve vitrification are potentially cytotoxic. There are many disadvantages
The technique is highly operator dependent:- the timing of the processing steps are critical and require a high level of training, in contrast to slow freezing.
It is known that vitrified solutions tend to devitrify, i.e. to crystallise into ice, during long term storage or thawing leading to a loss of viability. Long term viability of vitrified samples is not guaranteed. Slowly frozen samples have been demonstrated to be viable following 50 years storage, and potentially many thousands of years are possible..
Rapid cooling is often achieved by direct exposure to a cryogen; this carries the potential of contamination from organisms present in the liquid nitrogen, this means that the process should not be used with therapeutic cells.
Vitrification is limited to cell suspensions cooled in small volumes, it is not anticipated that the technique will be readily applicable to larger volumes such as cryovials, bags, matrix tubes, microtitre plates etc. A further point made by people in this field is that if you slow freeze 200 straws they are all identical and quality control can be carried out by thawing a small number of straws. However, if you vitrify 200 straws you essentially carry out 200 experiments and QC is impossible.
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