The aim of this work is to understand the mixing behaviour of mechanically modified glass beads as model carriers in DPIs and spray dried salbutamol sulphate as model active pharmaceutical ingredient (API) particles. Regardless of what glass beads were used a 100% surface coverage could not be achieved although the amount of API weighed in was calculated for a 100% surface coverage. The actual surface coverage reached for the mechanicallymodified glass beads was about 75% compared to a 32% actual surface coverage for the untreated glass beads. By preparing adhesive mixtures with different calculated surface coverage, the calculated coverage and the actual coverage could be correlated for all the distinct glass beads used and linear equations with different slopes could be set.Based on these correlations comparable mixtures with 30% ± 5% actual surface coverage could be prepared. The evaluation of the fine particle fractions (FPF)showedthat the FPF is varying for the differently modified glass beads and dependent on the surfacecharacteristics of the glass beads. For mechanically modifiedglass beads the FPF can be correlated with the surface roughness and the specific surface area of the glass beads.The higher the surface roughness and the higher the specific surface area of the glass beads the higher the FPF.
This study shows that by understanding the mixing behaviour of mechanically modified glass beads, comparable mixtures with defined actual surface coverage can be prepared. As a result the performance of the differently modified glass beads can be compared.