In situ characterization of aerosol deposition in dry powder inhalers using optical coherence tomography.

This study employs high-resolution Optical Coherence Tomography (OCT) to characterize aerosol deposition within a model Dry Powder Inhaler (DPI). Deposition was examined for five in-house formulations containing different mass fractions of coarse lactose carrier (SV010), fine lactose (LH300), and Salbutamol Sulphate (SS), and for two commercial formulations, namely Aridol® (mannitol) and Pulmicort Flexhaler™ (budesonide). Experiments were performed at dispersion flow rates of 30 LPM and 50 LPM to evaluate the influence of formulation composition and aerodynamic conditions. Three-dimensional OCT mapping revealed that the in-house formulations, comprising over 90% (w/w) coarse excipients, deposited predominantly as discrete clusters of particles distributed across the DPI surface. Increasing flow rate led to reduced average cluster size while increasing cluster density. Deposition thickness increased with SS content, from 94 ± 24 µm for SV010 (0% SS) to 205 ± 18 µm for formulation F12 (4.5% SS), while the addition of fine lactose produced thicker depositions than the coarse carrier alone but thinner than formulations with the same fraction of SS without fines. Thickness distribution analysis demonstrated broad, formulation- and flow-dependent profiles with distinct modal values, providing a more comprehensive understanding of deposition behaviour than mean or peak measures. Both in-house and commercial formulations exhibited strong peripheral loading, with more than 70% of total deposited volume confined within the first 10% of radial distance from the swirl-chamber edge. Overall, the results demonstrate the potential of OCT as a diagnostic tool for quantifying spatially resolved deposition relevant to DPI design and formulation-device optimization.