Efficient mucosal delivery remains a major challenge for the reason of the respiratory tract mucus act as a formidable barrier to nanocarriers by trapping and clearing foreign particulates.The surface property of nanoparticles determines their retention and penetration ability within the respiratory tract mucus.However,the interaction between nanoparticles and mucus,and how these interactions impact distribution has not been extensively investigated.In this study,polymeric nanoparticles loaded with a baicalein-phospholipid complex were modified with two kinds of polymers,mucoadhesive and mucus-penetrative polymer.Systematic investigations on the physicochemical property,mucus penetration,transepithelial transport,and tissue distribution were performed to evaluate the interaction of nanoparticles with the respiratory tract.Both nanoparticles had a similar particle size and good biocompatibility,exhibited a sustained-release profile,but showed a considerable difference in zeta potential.Interestingly,mucus-penetrative nanoparticles exhibited a higher diffusion rate in mucus,deeper penetration across the mucus layer,enhanced in vitro cellular uptake,increased drug distribution in airways,and superior local distribution and bioavailability as compared to mucoadhesive nanoparticles.These results indicate the potential of mucus-penetrative nanoparticles in design of a rational delivery system to improve the efficiency of inhaled therapy by promoting mucus penetration and increasing local distribution and bioavailability.