Vitrification is the process of flash-freezing a cell, such as an egg. Vitrification uses liquid nitrogen to quickly cool cells to -196ºC (at a cooling rate of 15,000°C/min). This speed ensures that water molecules inside the cell don’t have time to form potentially damaging ice crystals, making it the more effective method for freezing eggs, which have a high proportion of water.

What is vitrification?

Vitrification is a cryopreservation technique that employs rapid freezing of liquid or cells so that they become glass-like (from the Latin vitreum for “glass” ). While traditional cryopreservation uses slow freezing at a controlled rate until cells reach -196º Celsius (-321°F), vitrification immerses cells directly in liquid nitrogen for near-instantaneous freezing without ice crystal formulation.

Vitrification for fertility preservation

Vitrification is typically used to freeze eggs and embryos for later use, preserving the chances of fertility for an extended period of time. This is especially useful for patients with cancer, endometriosis, or those who anticipate having children later in life.

The rapid freezing method has been found to be superior to slow freezing for eggs and embryos because those larger cells contain more water, and the ice crystals that can form during slow freezing have the ability to damage or compromise cells. Studies have found that vitrification has led to improved oocyte survival rates, fertilization, and embryonic development in vitro.

Vitrification is not typically used for sperm freezing. Sperm are small and don’t contain as much water, so they’re less likely to produce ice crystals — plus vitrification carries the risk of contamination and sperm damage. The technique is also less efficient, whereas traditional slow freezing allows for the cryopreservation of large sample volumes simultaneously.

History of vitrification

The development of kinetic vitrification is credited to Father Basile J. Luyet, a professor of biology at Saint Louis University. His research showed that rapidly cooled solutions could become so viscous that they solidified without forming ice crystals, transforming into a transparent glass-like state. In the 1950s, experiments on vitrifying chick hearts proved to be semi-successful, followed by successful mouse embryo vitrification in 1985.
Meanwhile, various freezing solutions were being tested and compared regarding their potential toxicity to embryos. A decade later, vitrification was proposed as a potential technology for the cryopreservation of human oocytes, embryos, and blastocysts, leading to a full-blown industry by the mid-2000s.