  Inhalation drug delivery has seen a swift rise in the use of dry powder
inhalers (DPIs) to treat chronic respiratory conditions. However, universal
adoption of DPIs has been restrained due to their low efficiencies and
significant drug losses in the mouth-throat region. Aerosol efficiency of DPIs
is closely related to the fluid-dynamics characteristics of the inhalation flow
generated from the devices, which in turn are influenced by the device design.
In-vitro and particle image velocimetry (PIV) have been used in this study to
assess the aerosol performance of a model carrier formulation delivered by DPI
devices and to investigate their flow characteristics. Four DPI device models,
with modification to their tangential inlets and addition of a grid, have been
explored. Similar aerosol performances were observed for all four device
models, with FPF larger than 50%, indicating desirable lung deposition. A high
swirling and recirculating jet-flow emerging from the mouthpiece of the DPI
models without the grid was observed, which contributed to particle deposition
in the throat. DPI models where the grid was present showed a straightened
outflow without undesired lateral spreading, that reduced particle deposition
in the throat and mass retention in the device. These findings demonstrate that
PIV measurements strengthen in-vitro evaluation and can be jointly used to
develop high-performance DPIs.
