An Optical Method for the Study of Aerosol Generation in Dry Powder Inhalers

Dry powder inhalers (DPIs) are portable, breath-actuated devices used for respiratory drug delivery. They have been the subject of intense research and development activity over the last 15 years, however, no systematic study of the effects of geometry on aerosol generation in DPIs has been reported in the literature. In particular, the first stage process — powder fluidisation — has hardly been studied in the context of DPI applications. The short time scales and the complexities of the air/powder interactions during the conversion of a powder bed into an aerosol present a challenging environment for experimental study. This paper reports an optical technique for the study of powder fluidisation inside a simplified, optically transparent DPI metering chamber geometry. We describe a system based on digital image analysis of high-speed video recordings of the transient powder-airflow interactions. Using diffuse backlighting we have generated black-on-white images of the interaction of frictional, cohesionless particles with an air jet flow. Image-processing techniques were subsequently applied to determine several aspects of the time-dependent properties that describe the development of the bed during the aeration of the powder. The paper concludes by pointing out how the proposed method could be used to improve understanding of the limitations associated with current DPI metering chamber configurations and help forward design of improved DPIs.