Freezing containers are specialized devices designed to regulate the cooling rate of biological samples—typically contained in cryovials—as they transition from ambient or refrigerated conditions to ultra-low temperatures. Their primary function is to prevent cryoinjury by maintaining a controlled, reproducible cooling profile, most commonly approximately −1 °C per minute, which allows cellular dehydration to occur before intracellular ice formation becomes lethal. These devices fall into two broad categories: passive freezing containers, which rely on thermal engineering to achieve a nominal cooling rate without active control, and controlled-rate freezers, which actively regulate chamber temperature according to a programmable profile.

Applications and Comparative Performance

Passive containers are well established for small-scale cryopreservation of robust cell lines, peripheral blood mononuclear cells, plant cells, and protoplasts. They are also used for the initial freezing of haematopoietic progenitor cell products before long-term liquid-nitrogen storage; recent evidence indicates that passive freezing can be equivalent to controlled-rate freezing for hematopoietic progenitor cell engraftment, making it an acceptable alternative for initial cryopreservation in that setting.

Controlled-rate freezers are preferred where reproducibility, documentation, and the handling of sensitive or larger-volume products are required. They accommodate cryobags and larger volumes that cannot be frozen reproducibly in passive containers, and they provide the audit trail necessary for regulated manufacturing. For leukapheresis material from healthy donors, direct comparisons have concluded that only controlled-rate freezing enabled the full retention of certain quality attributes. Variability between runs is also reduced with controlled-rate systems compared with passive containers.