Interfacial rheology for the assessment of potential health effects of inhaled carbon nanomaterials at variable breathing conditions

Lung surface is the first line of contact between inhaled carbon nanomaterials, CNMs, and the organism, so this is the place where pulmonary health effects begin. The paper analyzes the influence of several CNMs (single- and multi-walled nanotubes with various surface area: 90–1,280 m(2)/g and aspect ratio: 8–3,750) on the surface-active properties of the lung surfactant, LS, model (Survanta). Effects of CNM concentration (0.1–1 mg/ml) and surface oscillation rate were determined using the oscillating drop method at simulated breathing conditions (2–10 s per cycle, 37 °C). Based on the values of apparent elasticity and viscosity of the interfacial region, new parameters: S(ε) and S(μ) were proposed to evaluate potential effect of particles on the LS at various breathing rates. Some of tested CNMs (e.g., COOH- functionalized short nanotubes) significantly influenced the surfactant dynamics, while the other had weaker effects even at high particle concentration. Analysis of changes in S(ε) and S(μ) provides a new way to evaluate of a possible disturbance of the basic functions of LS. The results show that the expected pulmonary effects caused by inhaled CNMs at variable breathing rate depend not only on particle concentration (inhaled dose) but also on their size, structure and surface properties.