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Modification of Flow Properties of Pharmaceutically Relevant Materials Due to Thin Film Nanosmearing


Flow properties modification with nano-sized powders has been receiving a lot of attention in recent years. For this reason, a comparison study was undertaken to characterize the effects of nano-sized fumed silica (SiO2) additives on the flow and shear properties of pharmaceutically relevant powders. Several blends with various concentrations of active ingredient and excipients were prepared with and without silica.

The resulting blends were characterized by utilizing two very different characterization techniques: an avalanching method, the gravitation displacement rheometer (GDR), which is used to study the powders under gravity-driven flow conditions, and the rotational shear cell, introduced as a part of the FT4 powder rheometer, which studies the powders in a consolidated state.

This study demonstrated significant correlation between these two characterization methods; the ranges of applicability for each technique were determined and the parameters of interest resulting from each technique were established. Some discrepancies observed between the methods could be attributed to the differences in the state of powder consolidation for each technique; compressibility studies performed with the FT4 powder rheometer supported this finding. When a density study was performed, there was a near perfect linear correlation observed between the values of aerated bulk density, conditioned density in the FT4 powder rheometer and dilated density of the GDR, suggesting that a critical dilated density may exist for any powder/blend, which could be a material property describing the flow properties of the material.

The mechanism of the described flow properties modification was also of great interest; for that reason, the investigation of surface properties of powder particles was performed with several methods: inductively coupled plasma mass spectroscopy (ICPMS), scanning electron microscopy with X-ray microanalysis/energy dispersive spectroscopy (SEM/EDS) and x-ray diffraction. It was found that flow enhancer particles (SiO2) smeared the surface of the powder particles when subjected to shear, leaving a thin nano-layer of coating and, while not completely coating the particle, drastically changing its surface properties. Changes in these surface characteristics due to mixing under shear were found to alter the primary function of components in the blend.

The results of chemical analysis clearly showed that mixing nano-sized flow enhancers into a blend under shear altered the relative surface composition of particles, resulting in different electronic patterns and microscopic structures of particle surfaces. The results of this study provide substantial insight into the powder flow behavior and the methods of characterizing this behavior. The manner in which powders flow will determines the quality of the final product, such as tablet’s drug content, weight and hardness and is, therefore, of great interest and importance.

Address Goals

This activity addresses the primary strategic goal of discovery by focusing on understanding the nano-scale mechanisms that control flow of powder ingredients and blends. This topic, which is a component of the larger area of powder rheology, remains one of the great underdeveloped challenges in material science. This activity also addresses the development of research infrastructure in two independent ways, first by generating methods for modifying the flow properties of powders, which are of great importance in a myriad of industrial processes, and second by promoting the development of better methods for characterizing powder flow properties. Such methods are of great importance in product development, process optimization, and quality control in many industries that use powders as their main ingredients.