#131 Cryobiology (English)

Cryobiology

Cryobiology is the study of the effect of low temperatures on living things. In nature, freezing temperatures have been used to figure out different organism's coping mechanisms.

Bacteria

Some bacteria have been able to survive after being frozen in ice for thousands of years. Some bacteria produce proteins that are used for ice formation on the surface of plants and fruits. This causes injuries to the epithelium which is the cells that line the outermost layer of an organism and allows the bacteria to gain access to the nutrients in the plant tissues.

Plants

Plants go through hardening, which is when plants become tolerant to the effects of freezing for weeks to months. There are three stages in this process. Firstly, carbohydrates are moved to the roots of the plant and the permeability of the cell membrane increases. Once these two changes have occurred the plant will be able to tolerate temperatures from -5°C to -10°C. The second stage is when cell membranes are chemically altered to allow plants to survive temperatures around -20°C. In the final stage, vitrification will occur. Vitrification is to convert something into glass or a glassy substance by heat and fusion. With water, vitrification is rapid cooling where the temperature drops rapidly in megakelvin per second. When vitrification occurs, instead of crystallizing, a solution would be in a state like a 'solid liquid' which occurs at a certain temperature range known as the glass transition temperature, which differs for different types of material.

Animals

Vitrification has also been used in animals. A rabbit kidney was vitrified to -135°C. Once it was re-warmed and transplanted into the rabbit, it was able to keep the rabbit alive as the only functioning kidney. Vitrification has also been used to preserve human egg cells which were later fertilized and grew into a normal functioning human. Human gametes can survive at -196°C for ten years under controlled laboratory conditions after cryopreservation.

Risks

The main risks to cells during cryopreservation include:

1.    Extracellular ice formation- when tissues are cooled, water migrates out of cells and ice forms. Too much of this ice can cause damage to cell membranes due to crushing. However, some tissues and organisms can tolerate this

2.    Intracellular ice formation- if intercellular ice forms, it is almost always fatal to cells

3.    Dehydration- the movement of water to the outside of the cell causes dehydration which could potentially cause damage

How to Prevent Risks

1.    Slow freezing- Intercellular freezing can be prevented if cooling is slow enough to allow water to leave the cell. The rate of cooling varies but is around 1°C for most mammals but varies for other types of cells.

2.    Vitrification- See above

References:

https://en.wikipedia.org/wiki/Cryobiology
http://www.merriam-webster.com/dictionary/vitrified
http://www.scienceclarified.com/Co-Di/Cryobiology.html
http://www.scienceclarified.com/knowledge/Cryopreservation.html

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