Effects of the mouthpiece and chamber of Turbuhaler® on the aerosolization of API-only powder formulations.

Powder dispersion in dry powder inhalers (DPIs) is affected by powder formulations as well as the design of a device. This paper conducted a numerical investigation based on the coupled computational fluid dynamics (CFD) and discrete element method (DEM) to evaluate the changes of the design of a commercial DPI device Turbuhaler® on the aerosolization of an API-only formulation. Six different designs were proposed by modifying the mouthpiece and chamber of the original geometry which was reconstructed from a CT-scan of the Turbuhaler, and their performances in terms of powder deposition in the device and fine powder fraction (FPF) were evaluated. The resistance of the device was observed to vary with different designs. For the change of the mouthpiece, the device with a cylindrical mouthpiece had the least resistance and the lowest FPF emitted among all the devices, confirming the important role of the spiral mouthpiece on powder dispersion. Reducing the mouthpiece size caused more powder deposition in the inhaler due to higher airflow velocity, but FPF emitted increased compared to the original design as more powder dispersion occurred inside the mouthpiece. The half-length mouthpiece design reduced device resistance to increase airflow velocity and average collision energy, resulting in an increase in FPF loaded but a decrease in the number of collisions. For the change of the chamber, the domed chamber design increased the powder dispersion time and thus enhanced the frequency and energy of particle collisions, which eventually led to an increase in FPF loaded. At fixed flow rates, the powder dispersion efficiency was a function of the device resistance with higher device resistance causing an increase in the FPF loaded. However, it is important for the patient's attainable pressure drop to be considered in this context. Correlations between the aerosolization efficiency and the ratio of the average collision energy and cohesion energy were established based on model-predicted quantities.