Surface analytical techniques in solid-state particle characterization for predicting performance in dry powder inhalers

The pulmonary route is of interest for both ef fective local therapy for respiratory and lung diseases, such as asthma, chronic obstructive pulmonary disease and cystic fibrosis, and systemic administration of drugs, such as proteins and peptides. Dry powder inhalers (DPIs) are devices through which a dry powder formulation of drug is delivered via the pulmonary route. The DPIs are highly efficient but complicated systems, the performance of which relies on many aspects, including aerodynamic diameter of the powder formulation, particle density, bulk density, surface morphology and composition, particle shape, interparticulate cohesive forces between drug particles and interparticulate adhesive forces between drug and carrier particles. Among them, surface morphology of both drug particles and carrier particles within the formulation is a very important factor in determining the interparticulate contact area and forces, aerosolization efficiency and subsequent lung deposition. Techniques that have been applied to study surface properties of solidstate particles in DPIs include atomic force microscopy, micro-and nanothermal analysis, inverse gas chromatography and X-ray photoelectron spectroscopy. This paper reviews different aspects of DPIs, with emphasis on their surface properties and influence on aerosol performance, and the techniques that are utilized to examine their surface properties.