Freezing rate critical

The freezing of a product is a very important step. The structure in the frozen product decides whether the product can be freeze-dried at all and under which conditions it can be done. For this reason, the consequences of the freezing rate, layer thickness of the product and excipients are discussed in some detail. The second main point is the measurement and control of the two drying phases the main and secondary drying and the third concentrates on the residual moisture content, its measurement and the consequences during storage of the dry product. There will be critical opinions that some of the processes are unilaterally represented. aim was to show the, hmrts and the advantages ot certain procedures to enable the reader to decide whether the ideas of the quoted authors, or my own can be applied to his tasks. 

Beirowski, J., Inghelbrecht, S., Arien, A., and Gieseler, H., Freeze-drying on nanosuspension, 1 Freezing rate versus formulation design as critical factors to preserve the original particle size reduction, 7. Pharm. Sci., 2011,100,1958-1968. 

To survive freezing, a cell must be cooled in such a way that it contains little or no freezable water by the time it reaches the temperature at which internal ice formation becomes possible. Above that temperature, the plasma membrane is a barrier to the movement of ice crystals into the cytoplasm. The critical factor is the cooling rate. Even in the presence of external ice, most cells remain unfrozen, and hence, supercooled, 10 to 30 degrees below their actual freezing point (-0.5 °C in mammalian cells). Supercooled cell water has a higher chemical potential than that of the water and ice in the external medium, and as a consequence, it tends to flow out of the cells osmotically and freeze externally (Figure 1). 

With this start-up the most critical machine data are to check No remaining ice, cooling and heating working, and leak rate acceptable. The procedure takes some time, but minimizes problems occuring during the freeze drying process. 

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