Experimental measurements of particle deposition in the human nasal airway.

Intranasal drug delivery is a promising non-invasive method for administering both local and systemic medications. While previous studies have extensively investigated the effects of particle size, airflow dynamics, and deposition locations on deposition efficiency, limited attention has been given to the thickness of deposited particles, which can significantly affect drug dissolution, absorption and therapeutic efficacy. This study evaluated the deposition behaviour of three lactose powders in a silicone nasal airway replica under varying flow rates (15, 35, and 55 L/min) using optical coherence tomography (OCT). The main conclusion of these findings is that the anterior region of the nasal airway is the most effective site for capturing particles, exhibiting the highest deposition thickness and particle number density across all conditions. Specifically, deposition thickness exceeded 150 µm in some anterior regions, particularly under high flow rates, reaching up to 230 µm at 55 L/min for the most cohesive particle type (ML001). At 55 L/min, more cohesive particles, such as ML001, formed thicker clusters with deposition thickness 15-24 % greater than less cohesive particles like SV003 and SV010. Larger particles (SV010, D50 = 109 µm) mainly deposited in the anterior region, while smaller particles (SV003, D50 = 61 µm) showed a more uniform distribution, with deposition at location 1 about 10 % thicker than at location 2. Localised flow patterns, including recirculation zones, were identified as critical contributors to particle accumulation, as demonstrated by complementary computational fluid dynamics (CFD) simulations.