Drying parameters

By choosing the excipient type and concentration, and by varying the spray-drying parameters, control was achieved over the physical properties of the dry chitosan powders. The in vitro release of betamethasone showed a dose-dependent burst followed by a slower release phase that was proportional to the drug concentration in the range 14-44% w/w [200]. 

Doner, T., Dundrarova, D., Teparicharova, I., Orozeva, M., Bustandzieva, R Mitor, B. Choice of cryoprotective media and freeze-drying parameters of bovine corona-virus and respiratory syncytial virus. IV. International School Cryobiology and Freeze-Drying p. 31,32, Sofia, 1989... 

Dawson, P. J., Hockley, D. J. Scanning microscopy (SEM) of freeze-dried preparationes relationship of morphology to freeze-drying parameters. Developments in Biological Standardization Vol. 74, p. 185-192. Acting Editors Joan C. May, F. Brown S. Karger AG, CH-4009 Basel (Switzerland), 1992... 

A detailed discussion of the properties of aerogels can be found in several recent review articles (51—55) and the references therein. This section provides a physical basis for these properties by focusing on the microstructure of an aerogel. The intent is to provide a bridge between the two previous sections, which discuss the preparative and drying parameters that affect microstructure, and the next one, which outlines the potential applications made possible by unique structural features. The emphasis is on silica aerogels because they have been the most extensively characterized. 

Effect of Basic Drying Parameters of Granulated Aminoplast upon Its... 

Effect of Spray Drying Parameters on Polyvinyl Chloride Resin Particle Size Distribution and Plastisol Rheology... 

The physical size of the resulting spray-dried particles is dictated by the mass of solute in each droplet and depends on both the size of the droplets atomized into the hot air stream and the concentration of the feed solution. More dilute solutions permit the formation of larger droplets, while more concentrated solutions require smaller droplets. The appropriate feed concentrations and atomization conditions must also be practical to be commercially viable. For example, doubling the feed concentration halves the amount of water, energy, and time required to produce a unit of drug powder. Typically, the spray-drying parameters can be adjusted to produce particles within the size range needed for alveolar deposition. 

Because the influence of drying parameters is not the same for all materials, optimal drying conditions vary depending on the final objective volatile retention, preservation of enzymatic activity and avoidance of protein denaturation, fat oxidation or crystallisation. Furthermore, some interactive influences may appear between components, an effect that is positive for protection of labile compounds by a network of polymers as polysaccharides, gums, proteins (Dumoulin and Bimbenet 1998). The phenomena may vary between centre and surface of drops, with some possible segregation by internal movement in the drop. 

While examination of the final product is essential to ensure that the lyophilization process performs consistently and as intended, the monitoring of freeze-drying parameters also ensures that they are maintained within an acceptable range and provides an additional degree of assurance that the process is under control. 

Compared to many other pharmaceutical processes, freeze-drying is intrinsically more complex. This is because process parameters and product characteristics are inherently interdependent. The freeze-drying parameters affect the product being freeze-dried, but the converse is also true. A marked impact on the course of freeze-drying may be caused by the chemical composition of the solution and sub-... 

The thermodynamic and structural properties of the frozen product The effects of the programmable freeze-drying parameters on dependent process variables... 

The purpose of prospective validation of cycle limits is to implement planned deviations around the target cycle by changing the programmable operating parameters in order to examine the impact of these variations on dependent freeze-drying parameters and on product properties. 

Examination of the reproducibility of the freeze-drying parameters, to show that the process and the equipment can be maintained within a state of control... 

Maelkki Nikkilae, Aalto and Heinonen [31, 32] stress the importance of the raw material quality of onions. Stieger [33] has investigated the suitablity of various strawberry varieties. Processes for flavour preservation have been thoroughly examined with cultivated mushrooms, leading to an illumination of the most important freeze drying parameters [34[. 

Having estimated the optimum primary drying parameters, a pilot study should be performed. It is not good practice to carry out such a study either in an incompletely filled drier or by filling up shelves partly with empty vials. The reliability of pressure and temperature measurements should be checked at this stage. It has sometimes been found that the (apparent) product temperature exceeds the shelf temperature. Since this is an obvious physical impossibility, such an anomaly is due to faulty calibration of the thermocouple probe. 

A convenient method of continuously monitoring the gas for H2O content is to measure the dew point using a commercially available dew-point meter. Certain meters, working on a conductance or capacitance principle, can be set to control the input, or drying, parameters, or to trigger alarms if a certain limiting value is exceeded. 

That will determine the choice of the spraying mode and drying parameters, including the liquid feed composition. 

Supprung, P. and Noomhorm, A., Optimization of drum drying parameters for low amylose rice (kdmll05) starch and flour. Drying Technol., 21, 1781, 2003. 

Comparison of Optimal Drying Parameters for Zn-Bacitracin in a Jet-Spouted Bed Dryer and Spray Dryer... 

Possibility of a frequent control, adjustment, and changes of drying parameters in many points of the dryer connected with the control of product quality changes. 

The influence of drying parameters (e.g., range of water removal, change of temperature, time) on changes of product quality and marking of the critical values of these parameters. 

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