Dynamic Interactions of Titanium Dioxide Nano-Pollutants with a Lung Surfactant Model: A Nonlinear Interfacial Rheology Study

TiO2 nanoparticles are highly produced nanomaterials from industry and commonly found in the air we breathe, but their interactions with lung surfactants and impairing lung functions have not well understood. In this study, effects of two crystalline structures of TiO2 nanoparticles, i.e., anatase and rutile, with their various sizes, shapes, surface charges and concentrations, interacting with a single-component model of pulmonary surfactant, were studied. Nonlinear interfacial rheology was used to quantitatively distinguish effects of nanoparticles at different stages of breathing cycles. Oscillation studies which simulated the breathing cycles in different human ages showed that both crystalline structures of TiO2 nanoparticles made nanoparticles-dipalmitoyl phosphatidylcholine (DPPC) system more viscous, dissipative and irreversible during the oscillations, thus affecting the normal operation of lung surfactant. At the least concentration of nanoparticles studied, i.e., 0.01 wt %, the anatase ones significantly affected the expansion part of the cycle, whereas the rutile ones affected both expansion and compression phases. Interactions between DPPC and TiO2 nanoparticles under dynamic conditions of breathing cycles were affected by the crystalline structures and concentrations of nanoparticles and breathing conditions, with key factors including physical properties, such as sizes, shapes, and zeta potentials of nanoparticles. These results are crucial for understanding the adverse effects of nanosized pollutants in the lungs and applying drug delivery into lungs.