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Kyoto University’s research team recently announced that they successfully used freeze-drying techniques in animal experiments to fertilize rat sperm and eggs that had been stored in refrigerators for five years and produce baby rats.
Freeze-drying, also known as sublimation drying, is a drying method in which after the object to be dried is rapidly frozen, the ice therein is sublimated into water vapor under high vacuum conditions. Sperm can be stored at minus 200 degrees Celsius with liquid nitrogen, but the cost is high, so researchers have been hoping to get a new cheap and easy way to preserve sperm.
The research team rapidly chilled the rat's sperm after special treatment. After drying for about 4 hours under vacuum, the freeze-dried state was successfully achieved. Researchers recently used artificial insemination to fertilize rats' lyophilized sperm and rats' eggs that had been stored in refrigerators for five years, and then transplanted the fertilized eggs into the fallopian tubes of female rats, and finally delivered pups.
Experiments conducted by the research team using multiple rats showed that the birth rate of pups was 10% to 15%, which was the same as the probability of artificial insemination using unfrozen sperm.
The team also succeeded in experiments using mouse freeze-dried sperm that had been stored for 3 years, and confirmed that freeze-dried mouse sperm can be stored for approximately 3 months at 25 degrees Celsius.
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The freeze-drying method is different from the above drying method. The drying of the product is basically performed at a temperature of 0° C. or lower, that is, the product is frozen until the later stage, in order to further reduce the residual moisture content of the product, the product is allowed to rise to Temperature above 0°C, but generally does not exceed 40°C.
Freeze-drying is to contain a large amount of water, pre-cooling and freezing into solids, and then sublimate the water vapor under vacuum conditions, and the material itself remains in the frozen ice shelf, so its volume will not change after drying. Loose pores absorb heat during sublimation. The temperature of the product itself is lowered to slow down the speed of sublimation. In order to increase the speed of sublimation and shorten the drying time, the product must be properly heated. The entire drying is performed at a lower temperature.
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