Purpose: To study the effect of particle size, air flow and inhaler type on the dispersion of spray dried mannitol powders into aerosols.
Methods: Mannitol powders were prepared by spray drying. The solid state properties of the powders were determined by laser diffraction, X-ray powder diffraction, scanning electron microscopy, freeze fracture, Karl Fischer titration and gas pycnometry. The powders were dispersed using Rotahaler and Dinkihalerg, connected to a multistage liquid impinger at different air flows.
Results: Three crystalline mannitol powders with primary particle size (MMD) 2.7, 5.0, 7.3 microm and a similar polydispersity were obtained. The particles were spherical with a density of 1.5 g/cm3 and a moisture content of 0.4 wt.%. At an air flow of 30 L/min all the powders were poorly dispersed by both inhalers. With the Rotahaler increasing the flow (60-120 L/min) increased the fine particle fraction (FPF) in the aerosols for the 2.7 microm powder, and decreased the FPF for the 7.3 microm powder; whereas the FPF for 5.0 microm powder was unaffected. With the Dinkihaler, all the powders were near complete dispersion at > or = 60 L/min.
Conclusions: The FPF in the mannitol powder aerosols was determined by an interplay of the particle size, air flow and inhaler design.