Comparative hygroscopic aerosol particle sizing measurements of the hygroscopic growth of inhaled pharmaceutical ingredients†

Abstract

The size distribution of an inhaled pharmaceutical aerosol generated by a nebulizer is a critical parameter influencing the deposition and therapeutic effect of the medication. Relative humidity (RH) can alter size distribution by promoting particle growth through condensation, depending on the hygroscopicity of the formulation. In this study, we evaluate the effect of RH on mannitol, trehalose, salbutamol, and tobramycin aerosols using the Comparative Hygroscopic Aerosol Particle Sizing (CHAPS) technique under varying RH conditions, ranging from ambient to physiological levels. The results demonstrate that RH significantly influences the aerosol particle size, with particle growth becoming more pronounced as RH exceeds 95%. The findings confirm that understanding the relationship between geometric radial growth factors (rGFs) from single droplet size measurements and the aerodynamic rGF is essential for more accurate prediction of plume size distribution, especially at lower RH levels. We also demonstrate consistency between the size distributions measured by CHAPS and a Next Generation Impactor (NGI), with CHAPS providing higher resolution in size and time and data on actuation-by-actuation variability in size distribution and aerosol dose.