Summary

Glass beads (GBs) are ideal to be used as model carriers in dry powder inhalers as they can be selectively surface modified without altering other physico-chemical properties. In this study, GBs in the size range of 400-600 µm were silanised with agents varying in their functional groups thus conferring a broad range of hydrophobicity to the carrier surface, which was determined via contact angle (CA) measurements. Additionally the surface energy (SE) of the carrier particles was measured. Modified and untreated GBs were blended with spray dried budesonide (BUD), serving as a hydrophobic model drug to form interactive mixtures for inhalation. This study expands knowledge gained from the previous study by correlating aerodynamic performance and drug loading to carrier surface characteristics. On the one hand, surface modification had a substantial effect on the actual surface coverage (ASC) as it showed a direct positive correlation to the measured CA. On the other hand, aerodynamic performance was altered by the chemical surface properties of the carrier as a high degree of hydrophilicity (low CA) led to the highest fine particle fraction (FPF). The SEs of not only the carrier but also the API proved to have an impact on both output parameters.