The method of depositing CeO2 nanoparticles onto a DPPC monolayer affects surface tension behaviour

Abstract

Abstract Studies using Langmuir-Wilhelmy balance (LWB) systems have demonstrated that engineered nanoparticles (NPs) can disrupt the surface tension behaviour of model lung surfactants. However, the majority of such studies used approaches that do not accurately mimic in vivo deposition at the air-liquid interface of inhaled particles – using instead NP suspensions. The present study investigated for the first time the effect of the mode of delivery of NPs to the interface on the compression surface pressure (Π) – mean molecular area (Mma) isotherms of surfactant monolayers, using an LWB. A novel system to deposit a well characterised aerosol of cerium oxide nanoparticles (CeO2NPs) on a dipalmitoylphosphatidylcholine (DPPC) monolayer was developed. The effects of depositing CeO2NPs from an aerosol were compared with two alternative approaches used in the literature: CeO2NPs suspended in chloroform and deposited on a DPPC monolayer and mixtures of CeO2NPs and DPPC in chloroform deposited directly on the subphase. Experiments were undertaken using a physiologically relevant subphase and temperature, 37\u202f°C, with additional experiments at 21\u202f°C. In each case Langmuir-Blodgett films were imaged using scanning electron microscopy and the distribution of cerium mapped using time of flight – secondary ion mass spectrometry. The results clearly demonstrate that mode of delivery has a differential effect on surface tension behaviour and that caution should be exercised in the use of solvent deposition techniques because of effects on NP agglomeration state and the pattern of distribution of NP agglomerates, which may not accurately reflect the behaviour in vivo of inhaled particles. The study findings therefore suggest that aerosol deposition techniques are to be preferred, however, there are issues that need to be investigated further, including the effect of control air exposures, and also a need to explore the effects of cycling and the use of more complete lung surfactant models, before such a recommendation can be confirmed.