Multimodal X-ray and laser diagnostics for pressurized metered dose inhaler sprays

Pressurized metered-dose inhaler sprays (pMDIs) are a prevalent means of delivering drugs to the lungs. Their performance depends strongly on the properties of the drug particles produced from the evaporation of droplets in the spray. The flow contains multiple species and phases and exhibits multiple modes of spray breakup. The rich physics in this environment and the large number of variables make experimental measurements challenging. We demonstrate how laser diagnostics and X-ray diagnostics can be combined to obtain new insights that were not possible using any single technique. X-ray radiography, fluorescence, and ultra small angle X-ray scattering measurements performed at the Advanced Photon Source at Argonne National Laboratory were combined with laser scattering data from Monash University to estimate average droplet composition and species evaporation rates for solution-based pMDIs containing ipratropium bromide in an ethanol co-solvent with two hydrofluoroalkane propellants. Our approach exploits the relative sensitivities of these different methods to droplet composition and density. Evaporation rate of the less volatile components in the droplets are much more significant in the near field than previously expected. The methodology demonstrates the value of combining X-ray and traditional optical diagnostics to obtain novel insight into complex multi-phase flows.