A cryogenic freezer, specifically a controlled-rate freezer, is active equipment that cools a sample from ambient temperature to cryogenic temperature at a precisely programmed rate. It performs the initial freeze. It does not store samples long term. A cryogenic storage vessel, whether a liquid nitrogen dewar, LN2 storage tank, or vacuum insulated cryogenic storage tank, is a passive vessel that maintains samples already at cryogenic temperature at -196 degrees Celsius indefinitely.
In a slow-cooling protocol, the sample passes through the controlled-rate freezer first, then moves to the storage vessel. In a vitrification protocol, the sample goes directly from the vitrification device into liquid nitrogen and then into the storage vessel: no controlled-rate freezer is involved in the embryo or oocyte workflow. The ESHRE guidelines on cryopreservation cover both protocols and the equipment requirements for each. A clinic planning both sperm banking and embryo vitrification needs both types of equipment. A clinic offering only vitrification needs storage infrastructure but not a controlled-rate freezer for embryo work.
