What is vitrification?
Vitrification is one of many cell-freezing methods used to preserve oocytes and embryos. The method is currently used worldwide and is considered to be the easy and safe freezing technique. Vitrification safely cryopreserves oocytes and embryos for the long term, theoretically without significant deterioration. The method plays an important role in stopping time for oocytes and embryos in order to preserve fertility and treat sterility.
History of vitrification
- 1949
- Polge
- Successful cryopreservation for a chicken’s spermatozoa with glycerol--Discovery of cryoprotectant
- 1972
- Whittingham
- First successful cryopreservation of a mouse embryo by slow freezing
- 1977
- Willadsen
- Establishment of a simplified slow freezing method
- 1983
- Trounson
- First reported case of human pregnancy/delivery with a cryopreserved embryo
- 1985
- Rall，Fahy
- First successful embryo freezing by a vitrification method
- 1991
- Kuwayama
- Successful vitrification of a bovine embryo by the 16-step method
- 1999
- Kuwayama
- First successful vitrification of a human oocyte by the minimum volume cooling (MVC) technique
- 2000
- Kuwayama
- Establishment of Cryotop Method
- 2003, 2004
- Kuwayama
- First successful pregnancy/delivery with cryopreserved oocyte in the United States, South America, and Europe
- 2012
- Kuwayama
- Establishment of Cryotec Method
Mechanism of vitrification
As it is often said that approximately 60 % of the human body is made from water, cells contain plenty of water. Water is the only substance in nature for which the volume increases when it is solidified.
Mechanism of Vitrification
As it is often said that approximately 60 percent of the human body is water, it is no surprise that cells contain plenty of water.
Water is peculiar in that it is the only substance in nature that increases in volume when solidified. In a process called ice crystal formation, as thermal energy decreases and the activity of water molecules is reduced, molecules bind to each other to form a uniform mesh-like structure. Unlike spermatozoa, oocytes have a high water content, and as a result, it has long been considered extremely difficult to cryopreserve oocytes due to the danger of cell membrane-rupture caused by excessive expansion during ice crystal formation.
The vitrification method replaces the water within cells with a solution containing substances called cryoprotectants or cryoprotective agents. These agents dehydrate cells by means of a difference in osmotic pressure.
The cryoprotectants penetrate water molecules to inhibit the formation of ice crystals, and oocytes and embryos are quickly submerged, as-is, in ultra-low temperature liquid nitrogen (minus 196 degrees Celsius). This process of a substance losing its fluidity while remaining a liquid is called vitrification. As all substances lose the energy to move at minus 196 degrees Celsius, they can be semi-permanently preserved without experiencing an improvement or deterioration in quality.
