Vitrification

Vitrification is a process of converting a material into a glass-like amorphous solid which is free of any crystalline structure, either by the quick removal or addition of heat or by mixing with an additive. For example when sucrose is cooled slowly it results in crystal sugar (or "rock candy"), but when cooled rapidly it can form syrupy "cotton candy" or lollipops.

When the starting material is solid, vitrification usually involves heating the substances to very high temperatures. Many ceramics are produced in such a manner. Vitrification may also occur naturally when lightning strikes sand, where the extreme and immediate heat can create fine fingers of glass. Ordinary soda-lime glass, used in windows and drinking containers, is created by the addition of soda and lime (calcium oxide) to silicon dioxide. Without these additives silicon dioxide will (with slow cooling) form sand or quartz crystal, not glass.

Vitrification can also occur when starting with a liquid such as water, usually through very rapid cooling or the introduction of agents that suppress the formation of ice crystals. This is in contrast to ordinary freezing which results in ice crystal formation. Additives used in cryobiology or produced naturally by organisms living in polar regions are called cryoprotectants.

Arctic frogs and other reptiles naturally produce glycerol in their livers to reduce ice formation. Arctic insects often produce sugars as cryoprotectants.

Applications

Vitrification is being researched as a technique to improve the disposal and long term storage of nuclear waste or other hazardous wastes. In particular the goal is to allow waste materials to be more easily segregated and compacted. Ethylene glycol is used as automotive antifreeze and propylene glycol has been used to reduce ice crystals in ice cream (making it more smooth).

For years glycerol has been used in cryobiology as a cryoprotectant for blood cells and bull sperm, allowing storage at liquid nitrogen temperature. But glycerol cannot be used for organs. Much progress has been made at Twenty-First Century Medicine to discover cryoprotectant mixtures which may one day allow for storage of whole human organs at liquid nitrogen temperature. This would allow banking of human and xenobiotic organs -- such as kidneys, livers and hearts -- which could be used for transplant.

In the context of cryonics, especially in preservation of the human brain, vitrification of tissue is thought to be necessary to prevent destruction of the tissue or information encoded in the brain. Currently, vitrification techniques have only been applied to brains by Alcor and to the upper body by the Cryonics Institute, but research is in progress by both organizations to apply vitrication to the whole body.

Reference

• Steven Ashle, Divide and Vitrify, June 2002, Scientific American

External links

• Vitrification in Cryonics
• CRYOBIOLOGY 48(1):22-35 (2004)