Bipolar electrostatic charge and mass distributions of powder aerosols – Effects of inhaler design and inhaler material

Abstract This study investigated the effect of modifying the Aerolizer® inhaler design and material on bipolar charging of a powder aerosol. The modified inhalers included various grid configurations, mouthpiece lengths, air inlet sizes, and were also constructed of different materials (acrylonitrile butadiene styrene, acetal, low density polyethylene, nylon, polypropylene, and stainless steel). The novel BOLAR™ (Dekati Ltd., Kangasala, Finland) was used to characterise bipolar charge and mass distributions. All of the tested inhalers showed spray-dried mannitol powder carried significantly different positive and negative charges that had higher magnitudes than the measured net charge. The estimated elementary charges per particle indicated the aerosols carried significant levels of charge that may potentially influence particle deposition in the lungs. Increasing the grid voidage decreased the magnitude of charging, as did reducing the air inlet size, whereas mouthpiece length had no obvious effect. The observed effects on charging due to modifications to the inhaler design could be explained by a difference in the level of contacts due to impaction between the particles and the inhaler internal surface. Bipolar charge of mannitol did not differ when dispersed by inhalers constructed of different materials. This could be attributed to various potential factors such as the very brief contact time between the powder and the inhaler material, as well as coating of the inhaler interior by the powder which effectively renders the surface to be mannitol-like. Overall, the comparable q / m profiles across all the inhaler designs and inhaler materials indicated charging correlated with the mass distributions and modifications to the inhaler did not affect the qualitative bipolar charge characteristics of mannitol powder.