Effect of powder polydispersity on aerosol generation

Purpose. We investigated the effect of primary powder polydispersity on the generation of pharmaceutical powder aerosols, using mannitol and bovine serum albumin (BSA) as the model compounds. Methods. Primary powders with different polydispersity but comparable physical and mass median aerodynamic diameter (MMAD) were obtained from spray drying. The polydispersity, i.e. the width of the particle size distribution, of the primary powder was measured by the span. Span = [particle diameter at 90% cumulative size] - [particle diameter at 10% cumulative size] / [particle diameter at 50% cumulative size]. A small span indicates a narrow size distribution. Solid state properties and the aerosol behaviour of the powders were determined. Results. For both compounds, dispersion of the smaller span powder generated more fine particles below the MMAD of the primary powder, but the increase was less apparent at high air flows or with a high dispersion efficiency inhaler. With the Dinkihaler(R), however, the smaller span powder of BSA, but not of mannitol, was found to experience less impaction loss and capsule and device retention. This could be due to the BSA powder being more cohesive, as it was amorphous and had a higher residual moisture content than that of mannitol. Conclusions. The present study has demonstrated that the amount of fines available in the aerosol could be modified by the primary powder polydispersity.