Liquid phase and vapour phase cryogenic storage are two distinct approaches to maintaining biological samples at cryogenic temperatures in a liquid nitrogen storage tank. The choice between them has significant implications for cross-contamination risk, temperature consistency, and regulatory compliance in HFEA-licensed IVF facilities.
In liquid phase storage, samples are submerged directly in liquid nitrogen at -196 degrees Celsius. The temperature is consistent and is the coldest achievable with liquid nitrogen at atmospheric pressure. However, liquid nitrogen is not sterile. Any pathogen present in the tank, however rare, can theoretically be carried from one sample to another in the liquid. Several cases of viral transmission between samples in shared liquid phase storage have been documented in the scientific literature, and the HFEA has progressively strengthened its guidance on closed carrier systems and vapour phase storage for human reproductive material.
In vapour phase storage, samples are held above the liquid nitrogen surface in cold nitrogen gas at temperatures typically between -140 and -190 degrees Celsius. This is above -130 degrees Celsius, the glass transition temperature, only at the very top of a poorly designed system, a well-engineered vapour phase tank maintains temperatures well below -130 degrees Celsius at all storage levels. Cross-contamination risk between samples is eliminated, as there is no liquid medium to carry pathogens.
The CryoBank Series maintains temperatures as low as -190 degrees Celsius in vapour phase mode at its highest storage points, providing full protection below the glass transition threshold while eliminating cross-contamination risk. For HFEA-licensed IVF programmes storing human embryos and gametes, vapour phase storage in a correctly specified and monitored tank is now the recommended approach.
