(Summary description)Freeze dryer is one of the drying methods, the purpose is to store items. The damage, decay, and deterioration of items are mainly caused by external and internal factors. The external factors are the effects of air, water, temperature, organisms, etc.; the internal factors are mainly the metabolism of biological substances themselves. If the effects of external and internal factors can be reduced to a lower level, the object can be kept unchanged for a certain period of time. Freeze dryers are now widely used in chemistry, pharmaceutical industry, food industry and scientific research, especially in biological medicines containing biologically active substances. What is the difference between freeze drying and conventional drying?

Drying is a very old operation, but the heating and drying of powders and biological products often causes irreversible agglomeration of particles, especially in the preparation of ultrafine powders, the nanoparticles in the liquid phase will coalesce into difficult-to-disperse agglomerates after drying. This is mainly because moisture is emitted from the pores between the particles during the ordinary drying process, and the surface tension causes extremely high additional pressure, which compacts the particles together into agglomerates. The use of a freeze dryer can avoid this problem. Freeze drying is to freeze the gel or blood to be dried into a solid, and then under reasonable conditions, the water is vaporized and removed by sublimation. The gasification process will not affect the agglomeration state of solid particles, so the original particles can be kept intact without being compressed and agglomerated. In addition, the freeze dryer is very suitable for processing biological products, such as blood, because it does not have high-temperature operations. Prevent the deterioration of biological products.

The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the dried product compared to the one before drying. The freeze-drying method is basically carried out below 0°C, that is, the product is carried out in a frozen state. Only when the residual moisture content of the product is reduced in the later stage, the product is allowed to rise to a temperature above 0°C, but generally does not exceed 40°C. Under vacuum conditions, when the water vapor is directly sublimated, the drug remains in the frozen ice shelf, forming a sponge-like loose porous structure, so the volume is almost unchanged after being dried by a freeze dryer. Before using again, just add water for injection and it will dissolve immediately.

There are various drying methods in freeze dryers, such as sun-drying, boil-drying, drying, spray drying and vacuum drying, etc., but ordinary drying methods are usually carried out at temperatures above 0°C or higher. The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the dried product compared to the one before drying. The freeze-drying method is basically carried out below 0°C, that is, the product is carried out in a frozen state. Only when the residual moisture content of the product is reduced in the later stage, the product is allowed to rise to a temperature above 0°C, but generally does not exceed 40°C. In the freeze dryer under vacuum conditions, when the water vapor is directly sublimated, the medicine remains in the frozen ice shelf, forming a sponge-like loose porous structure, so its volume is almost unchanged after drying. Before using again, just add water for injection and it will dissolve immediately. Compared with conventional methods, freeze dryers have the following advantages:

　　 1. Many heat-sensitive substances will not be denatured or inactivated.
　　2. When drying at low temperature, the loss of some volatile components in the substance is very small.
　　3. During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot proceed, so the original properties can be maintained.
　　4. Because it is dried in a frozen state, the volume is almost unchanged, and the original structure is maintained without concentration.
　　5. Since the water in the material exists in the form of ice crystals after pre-freezing, the dissolved inorganic salt substances originally dissolved in the water are evenly distributed in the material

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• Time of issue:2021-03-12 16:24
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