Numerical investigations of translocation characteristics of nano-silica lunar dust across pulmonary surfactant monolayer

Abstract

The interactions between nano-silica lunar dust (NSLD) on the moon surface and pulmonary surfactant (PS) monolayer will pose risks to astronaut health in future manned lunar exploration missions, but the specifics of these interactions are unknown. This study investigates them using the coarse-grained molecular dynamics method considering different sizes (5, 10, and 15 nm) and shapes (sphere, ellipsoid, and cube), with special focus on the unique morphology of NSLDs with bugles. The key findings are as follows: (1) The 10 nm and 15 nm NSLDs embed in the PS monolayer through the major sphere of spherical-type, major ellipsoid of ellipsoidal-type, or one edge of cubic-type NSLDs upon contact the PS monolayer. (2) Adsorbed NSLDs cause a higher S_z value (AS_z > 0.84), while embedded NSLDs cause a lower S_z value (0.47 < AS_z < 0.83) that decreases with an increase in the number of bulges. (3) The embedding process absorbs 50-342 dipalmitoylphosphatidylcholine (DPPC) molecules, reducing the PS monolayer area by 0.21%-6.05%. NSLDs with bulges absorb approximately 9-126 additional DPPC molecules and cause a 0.05%-3.22% reduction in the PS monolayer area compared to NSLDs without bulges. (4) NSLDs move obliquely or vertically within the PS monolayer, displaying two distinct stages with varying velocities. Their movement direction and speed are influenced by the increasing complexity of NSLD with more bulges on them. In general, larger NSLDs with sharper shapes and increasing complex morphology of more bulges cause more significant damages to the PS monolayer. These findings have implications for safeguarding astronaut health in future manned lunar exploration missions.

Keywords: Coarse-grained molecular dynamics; Nano-silica lunar dust; Pulmonary surfactant monolayer; Translocation.