Spray drying of mannitol carrier particles with defined morphology and flow characteristics for dry powder inhalation

This study was dealing with the spray drying of tailored mannitol particles as carriers in dry powder inhalation formulations. A self-constructed spray tower equipped with a laminar rotary atomizer was used to generate very narrow particle-size distributions. A design of experiments with rotation speed and drying temperature as factors was applied for the preparation of a broad set of different mannitol particles. Drying parameters affected particle properties like particle size, particle shape, surface roughness, and flowability significantly. Here, rotation speed was mainly affecting droplet and therefore particle size. Further, it was found that the inner particle temperature, and so the pressure inside the early particle shell, plays an important role during particle formation as emerging water vapor at higher temperatures served for indented particles and rough surface structures. Lower drying temperatures resulted in spherical and smooth particles as the inner temperature remained below the boiling temperature. The occurrence of these particle properties could further be related to mannitol carrier particle flow dynamics as large indented carriers were found to be less flowable than small spherical ones. In general, it was possible to control particle properties by the parameters of the spray drying process.