Shear thinning effect on liquid foam distribution in heterogeneously constricted in vitro airway models

Treating diseased lung regions using inhalation therapy is often limited due to airway constrictions and obstructions that significantly reduce aerosol deposition efficiency. Intratracheal administration of liquid foams is a potential strategy to improve pulmonary drug delivery to these affected airway regions. Here, we use effective viscosity measurements and in vitro small-airway models to examine how shear thinning effects in the foam can be leveraged to achieve a more uniform distribution within heterogeneously constricted or partially obstructed airways. We find that a foamed solution based on the formulation of Tacholiquin® exhibited a 5.75-fold decrease in effective viscosity across a shear rate range spanning 970 to 14'500 s^-1. As a result, the foam volume penetrating through the constricted airway models was up to 154% higher compared with air, depending on the cross-sectional area of the constrictions. This proof-of-concept study represents a first step towards understanding the transport mechanics of liquid foams towards future pulmonary delivery applications.