Design Optimisation of Novel Pharmaceutical Actuator Using Optical Diagnostics

Pharmaceutical metered dose inhalers (MDIs) are drug delivery devices that are designed to produce self-propelled aerosols for inhalation therapies. Conventional MDI actuators use configurations based on a “two-orifice-and-sump” design. This promotes partial expansion of the propellant as a pre-atomisation stage. The final aerosol contains large numbers of respirable particles (1–5μm), but the aerosol plume velocity tends to be very high (50–100m/s). The KOS Vortex Nozzle Assembly (VNA) is an innovative actuator concept, which enables a measure of control of plume velocity. The device utilises a combination of a vortex chamber and a Bernoulli horn to reduce the plume velocity whilst increasing the respirable fraction of drug particles. The aerosol generation process in all MDIs, including the KOS VNA, inevitably leads to a certain amount of internal and external drug deposition, which represents an inefficiency of the drug delivery technology that can threaten dose uniformity. This paper reports the findings of an experimental study using optical diagnostics to investigate the primary atomization mechanism and external drug deposition in the VNA. High-speed video imaging is used to document the developing aerosol plume in the near-orifice and mouthpiece regions as well as the flow regime inside the vortex chamber using transparent versions of the VNA manufactured by means of rapid prototyping. We consider how the improved understanding of the flow processes resulting from this study supports measurements of fine-particle fractions and mouthpiece deposition. We also discuss how this type of fundamental investigation using optical diagnostics can be used to drive design improvements to identify VNA geometries with improved aerosol properties and reduced external drug deposition.