Liquid cryogenic is a term used to describe any substance that exists in liquid form at extremely low temperatures, typically below minus 150 degrees Celsius. In laboratory and clinical settings, liquid nitrogen is by far the most widely used cryogenic liquid, valued for its inertness, availability, and boiling point of minus 195.8 degrees Celsius at atmospheric pressure. Other cryogenic liquids include liquid helium (minus 268.9 degrees Celsius) and liquid argon (minus 185.9 degrees Celsius), though these are not routinely used in biological sample preservation.
Cryogenic refrigeration in the context of IVF and biobanking refers to maintaining biological samples in a thermally arrested state using either direct liquid nitrogen immersion, liquid phase storage at minus 196 degrees Celsius, or vapour phase storage at temperatures between minus 150 and minus 190 degrees Celsius. At these temperatures, all enzymatic reactions, metabolic processes, and molecular diffusion effectively cease. Theoretical models based on the Arrhenius equation suggest that samples stored correctly at minus 196 degrees Celsius should remain viable for centuries, a conclusion supported by the longest documented storage intervals currently reported in human reproductive medicine.
Vapour phase cryogenic refrigeration is increasingly preferred for long-term embryo and oocyte storage because it eliminates cross-contamination risk between samples while maintaining temperatures sufficiently low to prevent ice recrystallisation. This requires storage dewars with sealed, self-pressurising liquid nitrogen reservoirs that generate vapour phase above the liquid surface. The HFEA advises UK fertility clinics to assess cross-contamination risk management in their quality management systems, and vapour phase storage is one accepted engineering control. Cryolab supplies both vapour phase and liquid phase cryogenic storage dewars to clinical and research customers at cryolab.co.uk/storage-vessels/.
