From agglomerates to aerosols: airflow–particle dynamics and impact-driven deagglomeration in dry powder inhaler

Dry powder inhalers (DPIs) transform adhesive/cohesive formulations into respirable aerosols for pulmonary drug delivery, yet the transient pathways by which powder agglomerates mobilize, break up, and disperse within devices remain insufficiently understood and quantified. Here, we used Symbicort Turbuhaler as a representative DPI to elucidate dispersion mechanism. A coupled CFD–DEM model was developed on a reconstructed geometry, and validated against pressure–flow characteristics and aerodynamic performance across 30–90 L min−1. The validated model resolved airflow–particle dynamics and transient deagglomeration. Inhalation flow mobilized the static powder bed, and particle–wall impacts promoted deagglomeration. Spiral channel in the mouthpiece served as the dominant impact region for breakup, where particle–wall impacts increased sharply and adhesive contacts disrupted progressively. Higher flow rates increased particle velocity, drag force, and, importantly, particle–wall impacts, producing faster and more extensive deagglomeration. A design study supported this mechanism: shortening the spiral reduced wall impacts and lowered aerodynamic performance. In summary, these results identify particle–wall impact, driven by swirl-inducing geometry and inhalation flow, as a primary mechanism governing the dispersion of adhesive agglomerates in DPIs.