Abstract
Understanding interactions between inhaled nanoparticles and lung surfactants (LS) present at the air-water interface in the lung, is critical to assessing the toxicity of these nanoparticles. Specifically, in this work, we assess the impact of engineered carbon nanoparticles (ECN) on the ability of healthy LS to undergo reversible collapse, which is essential for proper functioning of LS. Using a Langmuir trough, multiple compression-expansion cycles are performed to assess changes in the surface pressure vs. area isotherms with time and continuous cyclic compression-expansion. Further, theoretical analysis of the isotherms is used to calculate the ability of these lipid systems to retain material during monolayer collapse, due to interactions with ECNs. These results are complemented with fluorescence images of alterations in collapse mechanisms in these monolayer films. Four different model phospholipid systems, that mimic the major compositions of LS, are used in this study. Together, our results show that the ECN does not impact the mechanism of collapse. However, the ability to retain material at the interface during monolayer collapse, as well as re-incorporation of material after a compression-expansion cycle is altered to varying extent by ECNs and depends on the composition of the lipid mixtures.
Highlights
Langmuir monolayers at the air-water interface, demonstrate several 2-D phases and phase transitions, ranging from gas-like phase to more condensed phases, when compressed laterally [1].if the monolayer film is compressed beyond its stability limit, a transition from 2-D to 3-D structure occurs
While our fluorescence images after the first compression cycle shows that engineered carbon nanoparticles (ECN) do not impact the mechanism of monolayer collapse, a detailed analysis of the surface pressure area (Π-A) isotherms over five consecutive compression/expansion cycles show that lipid mixtures containing ECN show a difference in material loss and material re-incorporation between the different lipid systems
We find that when interacting with phospholipid mixtures containing saturated lipids only, ECN causes a net positive effect on monolayer collapse by improving the adsorption of material from the subphase
Summary
If the monolayer film is compressed beyond its stability limit, a transition from 2-D to 3-D structure occurs This transition from 2-D to 3-D, referred to as monolayer collapse, occurs at a constant surface pressure. Monolayer collapse has been a subject of interest, especially for biological lung surfactant mixtures that are present at the air-water interface in alveoli of lungs and helps reduce the work of breathing by maintaining near zero surface tension during compression, while maintaining a stable film during monolayer collapse. Folds “unfold” upon expansion, allowing the collapsed material to be re-incorporated into the monolayer, making the collapse reversible. These folds are formed perpendicular to the axis of compression (or parallel to the barriers used for compression), and are Molecules 2020, 25, 714; doi:10.3390/molecules25030714 www.mdpi.com/journal/molecules
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