The influence of actuator materials and nozzle designs on electrostatic charge of pressurised metered dose inhaler (pMDI) formulations.

Purpose: To investigate the influence of different actuator materials and nozzle designs on the electrostatic charge properties of a series of solution metered dose inhaler (pMDI) aerosols.

Methods: Actuators are manufactured with two different nozzle designs (flat and cone) using five different materials selected from the triboelectric series (Nylon, Polyethylene terephthalate, Polyethylene – High density, Polypropylene copolymer and Polytetrafluoroethylene). The electrostatic charge profiles of pMDI formulations containing beclomethasone dipropionate (BDP) as model drug, in HFA-134a propellant, with different concentrations of ethanol were studied with different actuator designs. Electrostatic measurements were taken using a modified electrical low-pressure impactor (ELPI) and the deposited drug mass was assayed chemically using HPLC.

Results: The charge profiles of HFA 134a propellant alone have shown strong electronegativity with all actuator materials and nozzle designs, at an average of –1531.34 pC ± 377.34. The presence of co-solvent ethanol significantly reduced the negative charge magnitude of HFA 134a, with 15% ethanol producing a net charge close to neutral for all actuator designs. BDP reduces the suppressing effect of ethanol on the negative charging property of the propellant. For all tested formulations, the flat nozzle design shown no significant differences between different actuator materials, where for the cone designs the net charge profile ranking follows the triboelectric series.  

Conclusion: The electrostatic charging profiles arising from a solution pMDI formulation containing BDP and ethanol as co-solvent can be significantly influenced by the actuator material, nozzle design and formulation components. Ethanol concentration appears to have the most significant impact. Furthermore, it has been shown that BDP interactions with ethanol and HFA could have an influence on the electrostatic charge of the aerosol. By choosing a different combination of actuator materials and orifice design, the fine particle fractions of the formulation can be altered.