Lyophilization (from the Greek. lyo - dissolve and philia - prone) - drying in vacuum pre-frozen biological products, thermolabile compounds and food products. Used as a laboratory method in Microbiology for preservation for a long period of bacteria, viruses, with the aim of creating "museums of cultures in histochemistry for fixation and preservation of histological preparations. Widely used in the medical industry for production of therapeutic, prophylactic and diagnostic preparations - of vaccine and serum, antibiotics, canned blood products (dry plasma for transfusion, blood substitutes), and for creating "banks" dry drugs (gonokocchi, homology, homosexual)used in surgical operations. Lyophilized preparations can be stored for a long time; they are insensitive to fluctuations in temperature during storage, easily translated to the native state after the introduction of solvent (water, Fiziol. the solution).
Lyophilization consists of pre-freezing and freeze-drying. Preservation of the drug is made by freezing the hardening liquid phase (environment); practically suspended all biochemical, chemical and physical processes. For microbiological and viral preparations environment are selected so as to prevent the possible collapse of individual cells solidification of the solution and the formation of ice. Such environments are typically consist of a combination of crystalloid and colloid (for example, saharoso-gelatina environment).
Tissue preparations require special selection modes freezing because of the introduction of any media under such drugs are usually unacceptable. The main requirement to the modes of freezing of tissue preparations is to avoid mechanical damage cell membranes and shells formed by ice crystals, as well as to have prevented fractionation solutions inside and outside the cells observed in slow freezing of complex protein and salt solutions. Final temperature in the freezing should be below the point of hardening the most fusible fraction of the drug. At very high speeds freezing, achievable only in a thin slices or finely sprayed liquid crystallization does not occur and the water goes into solid (amorphous) state without crystallization (vitrification). In this way manage to get histological and tissue preparations, fully restoring native properties after deconservation.
In labs freezing produce mixtures of ice with salt, dry ice with alcohol or acetone, in liquid nitrogen; in industry use low-temperature refrigeration cabinets with forced air circulation, gel with brine, cooled to low temperature. The greatest speed of freezing reach at fast cooling of thin films or slices, put in contact low-melting liquid (for example, isopentane), cooled by liquid nitrogen.
In the drying process water is removed by sublimation (ice goes directly into vapor, without a liquid phase). Drying is in layers. With the purpose of reduction of terms of dried by freezing liquid drugs tend to get thin layers and large surface; this bottle or bottle material slowly rotate around a horizontal axis in the tub with the cooling mixture. This material is covered on the sides of the vessel. Primary obtained by freezing, the structure must not be violated during drying. For this, the temperature of the drug in the drying process should be below the melting point of the most fusible fraction of the drug. Drying is carried out in special apparatuses under vacuum (residual pressure less than 10-1-10-3 mm RT. Art.). The absence of air continuously pumped vacuum pump ensures the smooth flow of vapor from the surface evaporation to the absorber (chemical or cold traps). In connection with the absorption of large quantities of heat by evaporation of ice temperature drying of the material is maintained at the required level is low without special cooling.
The ultimate goal lyophilization - a drug with a low residual moisture content (less than 1 % by weight of dry residue). The drying process consists of the removal of free water from drug and dried - removal-bound water. Associated water is bad, so the final drying is carried out at higher temperatures (20 degrees and above) and improvement of the vacuum in the system. In some cases, at this stage use special chemical absorbers (P2O5) and high-vacuum diffusion pumps in addition to pumps and sinks that are used at the stage of removal of free water. Dried medications stored in sealed ware - bottles, cans, sealed to prevent moisture in contact with moist air. Histological specimens after drying impregnated with paraffin under vacuum and store in paraffin blocks.
Cm. also Drying.