Characterization of the nanostructure, crystallinity and specific surface of lactose based inhaler powders: Small-and Wide-Angle X-ray scattering (SWAXS) studies

Verena Wahl, Andreas Zimmer, Johannes Khinast, Amrit Paudel, Peter Laggner

The aim of this work was to implement simultaneous the small- and wide- angle X-ray scattering (SWAXS) technique in the characterization of dry powder inhaler (DPI) carriers and formulation. SWAXS data were used to identify changes in crystallinity and inner structure (specific surface) of diverse inhalable lactose micro-particles originating from particle surface manipulation process. During the wet surface processing of carrier material a high amount of fines were produced identified as a mixture of α-lactose monohydrate and anhydrous lactose by a detailed analysis via SWAXS. Furthermore, to envisage the impact of environmental factors relevant to the processing, packaging and storage on the formulation attributes and performance selected lactose based commercial DPI formulations were exposed to accelerated storage conditions and microstructural evolution was investigated by SWAXS at regular time intervals. It was shown that during the storage of two commercial DPI products at different relative humidities, the specific surface of the formulation decreased significantly while no differences in the crystallographic pattern were noticeable. To prove the results, complementary techniques were implemented in the study (e.g. differential scanning calorimetry). Combined small- and wide- angle X-ray scattering seems to be a promising technique to identify changes in the particulate and the solid-states of DPI formulations and to predict physical stability.

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