Vitrification of oocytes: from basic science to clinical application.

Vitrification is a physical process by which a liquid is transformed into a solid of amorphous glass form. It was only at the end of the nineteenth century (1898) that Gustav Heinrich Johann Apollon Tammann pointed out that a large number of substances can be obtained as glasses and suggested that this property might be universal (Tammann, Zeitschrift for Physikalische Chemie; 25: 441-479, 1898). Basically, vitrification is the supercooling of a liquid to a temperature at which the viscosity is so high that it can be defined as being at a solid state. The understanding of the vitrification process has been deepened over the years and has been applied for cryopreservation and currently is the method of choice for preserving oocytes and embryos.