Biobanks are making headlines worldwide, and that means cryopreservation is in the news more than ever before. But let’s take a step back: what exactly is cryopreservation . . . and why is it so fundamental to biobanking? The term “cryopreservation” is derived from the Greek word kryos, which means cold. Simply put, cryopreservation for biobanking purposes is a method of preserving biological samples (tissue or cells) in a vitrified state (a rapid version of freezing that prevents the formation of ice crystals by taking a sample to the amorphous ice phase, circumnavigating the hexagonal ice phase) for the purposes of long term storage. Because the temperatures used for cryopreservation are so low, all the water inside the cells of a sample is either vitrified or removed by osmosis. As a result, when a sample is cryopreserved, all of its metabolic processes have ceased. Essentially, it is “frozen in time.” The advantages of cryopreservation for sample storage include:
Since most identified metabolic processes stop at temperatures below the glass transition phase (the transformation from liquid to a glassy state), cryopreservation reduces the risk of microbial contamination or cross contamination with other tissue or cell samples.
- Likewise, in the vitrified sample itself, the risk of morphological and/or genetic changes is significantly reduced since metabolic processes have stopped. Preserving below the glass transition phase enables access to samples for future needs.
- Cryopreservation techniques are well-established, and there’s a long history of reliable methods and documented outcomes.
The list goes on, but it’s clear to anyone in the biobanking industry that cryopreservation is an extremely effective method for the storage of biological samples. But don’t misunderstand: It is not trouble-free. The process of sample preparation requires a researcher to determine conditions that will optimize sample viability and recovery, ensuring the samples are guided safely through the vitrification and de-vitrification processes to avoid (as much as possible) the formation of ice structures. Samples undergo tremendous stress during the freezing and vitrification processes. Over the years, research scientists have developed many techniques to help abate the impact of these processes, including the development of cryoprotectants (which first occurred in 1949, see Polge et al. Nature 164: 666 ) and the birth of controlled rate freezers to assist in the path to vitrification. Today, there are more sample preparation protocols then sample types being stored, each with its own pros and cons. But, stay tuned . . . I’ll dive into those details in a future blog post.