Visualizing powder de-agglomeration upon impact with simultaneous flowing charge behaviour

Abstract

The effectiveness of the dry powder inhaler (DPI) in treating respiratory diseases lies in its ability to deliver consistent and reliable drug dosage with each actuation. From aerosolization upon actuation to throat impaction, the deagglomeration with subsequent detachment of the drug from the carrier particles depend on the interaction forces, including electrostatic contributions, between the particles themselves or with the inhaler wall and the extent of which could depend on the surface roughness of the carrier particles. In this study, we have simultaneously investigated the contributions of the electrostatic forces while visualizing the de-agglomeration and impaction behaviours of carrier powders in an impaction throat model using a non-contact vibrating capacitive probe and a high speed camera respectively. Rough and smooth carrier particles were obtained by spray drying and then aerosolized at 60 L/min in the model. Higher flowing charges were observed for the rough aerosolized carrier particles while experiencing rebound or limited agglomerate fracture upon impaction. On the other hand, smooth particles were broken up upon impaction resulting in a 'plume-like' re-entrainment. Further analyses revealed that the increased moisture sorption on the larger specific surface area of the rough particles would have facilitated the accumulation of surface charges that could in turn contribute to the cohesiveness of the rough particles. Combined high speed imaging with electrostatic monitoring has proved to be useful in investigating the mechanisms of powder de-agglomeration upon impaction.