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This study investigates the fundamental physical properties of aerosols emitted from pressurised metered dose inhalers (pMDIs) using currently employed propellants and low global warming potential (GWP) alternatives.
The study found that the net surface charges for all propellants were positive, however, hydrofluoroolefin (HFO) 1234ze generated near-neutral charges of both polarities, with HFO being the least bipolar propellant. The droplet diameter and velocity for the different propellants fell into multiple groups. For example, the two low GWP propellant droplets were larger at short distances from the actuator.
This information will guide the use of excipients to achieve desirable performance of products reformulated using these propellants. The study also highlighted the influence of valve and actuator’s material components on the net charges developed, indicating that device sub-assembly components play an important role during pMDI re-formulation and development.
The study concludes that differences in aerosol droplet surface charge were observed for HFO 1234ze. Moreover, low GWP propellants droplets were larger at short distances from the actuator. These may determine relevant differences in aerosol deposition, which can be balanced by formulation composition.
