Enhancing Physiological Realism in Nasal Spray Deposition Studies: Synthetic Mucus Properties and Interactions with Saline Solutions and Stereolithography Resin

This study investigated the role of synthetic mucus coatings in enhancing the physiological relevance of in vitro nasal spray deposition assessments using 3D-printed nasal cavity models. Synthetic mucus solutions, representing normal (0.25% w/v xanthan gum) and diseased (1% w/v xanthan gum) nasal conditions, were developed to mimic the viscoelastic properties of human nasal mucus. Their physical properties, including viscosity, surface tension, contact angle, and adhesivity on dry and synthetic mucus-coated stereolithography (SLA) surfaces, were systematically characterized. Comparative experiments evaluated the behavior of saline drops and liquid films on dry versus synthetic mucus-coated SLA surfaces at inclinations of 30°, 45°, and 60°. Observational deposition experiments using anatomically accurate nasal models were conducted under a 45° backward-tilted head position with gentle sniff airflow across uncoated, 0.25% w/v mucus-coated, and 1% w/v mucus-coated surfaces. Synthetic mucus coatings significantly influenced saline spray deposition patterns. On uncoated surfaces, deposition consisted of scattered droplets and limited film formation, mainly in the anterior and turbinate regions. In contrast, synthetic mucus coatings facilitated broader and more uniform liquid distribution due to diffusion and lubrication effects. These findings highlight the value of synthetic mucus coatings for better simulating nasal environments, offering insights to optimize nasal spray formulations and delivery devices.