(527h) Understanding the Effect of Engineered Carbon Nanodiamonds on the Reversible Collapse of Lung Surfactant Monolayers

Lung surfactants [LSs] are a complex mixture of lipids and proteins lining the air-water interface of the alveolar wall of our lungs. LSs help in reducing the energy required for breathing by lowering the surface tension of water. This makes it easier for the alveoli to expand with inspiration. LSs also act as a barrier against any foreign particle capable of entering the alveoli of the lungs. At present, Engineered Carbon Nanodiamonds [ECNs] are being considered for drug delivery and the respiratory tract is a lucrative route for this purpose. This in turn raises the question of their compatibility with LS mixtures, which would certainly come in contact with the nanoparticles. Therefore, any possible changes in the properties of the LSs because of its interaction with ECNs must be carefully scrutinized. In this report, we try to understand the effect of ECNs on the reversible collapse of the LSs at high compressions. Reversible collapse is a particularly important property of LSs that allows material to be retained near the surface at high compressions. This can be observed in the form of bright folded structures with fluorescent microscopy. The retained material is then capable of spreading back on the surface and minimizing the loss of surfactants. Here, multiple compositions were tested with fluorescent microscopy to evaluate the effect of electrostatics and lipid tail saturation on the collapse mechanism of LS. Under the microscope, model mixtures of dipalmitoyl phosphatidyl choline (DPPC)-dipalmitoyl phosphatidyl glycerol (DPPG) and DPPC-palmitoyl oleoyl glycerol (POPG), tagged with Texas red dye, revealed the formation of folded collapse features. Upon immediate exposure to ECN, this feature was still retained in both the samples. However, the DPPC-DPPG mixture collapsed irreversibly after four days of exposure to ECNs. This was observed as bright specs on the surface that are believed to be vesicles and are incapable of spreading back to the surface. Interestingly, this was not observed in the case of the DPPC-POPG mixture, which continued to collapse with the formation folded features. Therefore, unsaturation in the lipid mixture may be a crucial component, capable of countering any potential negative impact by the ECNs on the LS mixture at higher compressions.