A varying-swirl design concept for dry powder inhalers

The de-agglomeration potential of a dry powder inhaler (DPI) strongly affects its aerosol performance. Typically, a swirling flow is employed for the entrainment and de-agglomeration of drug powder into the inhalation air flow. Here, we propose a novel design concept that passively modifies the DPI swirling-flow, and thereby the de-agglomeration process, in order to achieve higher lung deposition. The essence of this design is a varying inner cross-section of the pipe-shaped device, realised in the form of converging and diverging circular sections placed after the tangential inlets in the device. An improved aerosol performance was shown for this device, with the fine particle fraction reaching 68.4% of the emitted dose, compared with 66.8% from that of the baseline device. This was found to be a direct effect of the modified flow characteristics generated within the device and thereafter emerging from its mouthpiece. These flow characteristics were determined from computational fluid dynamics simulations and particle image velocimetry measurements. Adaptations of this DPI design concept were achieved through the use of a honeycomb grid placed either after the device tangential inlets, or at the device mouthpiece exit. When placed after the inlets, a 10.4% reduction in the fine particle fraction was observed, as the air flow was straightened due to the influence of the grid which significantly reduced the flow-swirl before the flow entered the converging–diverging sections. Whereas, when placed at the mouthpiece exit, the flow-straightening effect of the grid resulted in reduced lateral spreading of the emitted aerosol but did not significantly affect throat deposition.