Optimizing the inclination angle of the swirl chamber in dry powder inhalers for improved carrier particle retention

This study investigated the effect of the inclination angle of the swirl chamber in a dry powder inhaler (DPI) on the retention of carrier particles. It was found that a small inclination angle can retain most carrier particles within the chamber by promoting constant collisions with the wall. However, care must be taken to avoid a large inclination angle, which can result in a stronger siphoning effect at the top of the swirl chamber. Two DPIs, Cyclohaler® and an in-house DPI, were studied using Euler/Lagrangian simulations to determine the optimal inclination angle for two inhalation pressure drops (2 and 4 kPa) and two carrier sizes (46 and 83 µm). The preferred outcome is for most carriers to remain in the swirl chamber while most drugs leave the inhaler. For an inclination angle of 5° and a carrier size of 46 µm, more than 50% of drugs escaped while less than 3% of carriers escaped. Experimental studies using a next generation impactor (NGI) confirmed the simulation results. This novel finding provides guidance for preventing carrier lactose particles from leaving DPIs.