By Stefan Schneid and Dr. Henning Gieseler
Division of Pharmaceutics
University of Erlangen, Germany
In a freeze drying process, mass transfer and product temperature are dependent upon the resistance of the product matrix to water vapor flow (Rp). Rp is influenced by numerous factors such as nature of the product, solute concentration, and freezing properties, and differs between formulations and process conditions used. The objective of the study described in this article was to characterize product resistance as a function of dry layer thickness for various sucrose solutions using SMART Freeze-Dryer technology. This new approach employs manometric temperature measurement (MTM) for the optimization of a lyophilization process during the first laboratory experiment. A pressure rise experiment is performed at user predefined intervals to determine the vapor pressure of ice at the sublimation interface (Pice) and the product resistance. Using steady-state heat and mass transfer theory, product temperature at the sublimation interface (Tp) and several additional derivative parameters are calculated. In addition, it is also possible to obtain temperature and resistance data for an entire batch during preexisting freeze-drying cycles, and to evaluate effects of material and process variations.