Molecular dynamics simulation of structural changes of lipid bilayers induced by shock waves: Effects of incident angles

Unsteady and nonequilibrium molecular dynamics simulations of the response of dipalmitoylphosphatidylcholine (DPPC) bilayers to the shock waves of various incident angles are presented. The action of an incident shock wave is modeled by adding a momentum in an oblique direction to water molecules adjacent to a bilayer. We thereby elucidate the effects of incident shock angles on (i) collapse and rebound of the bilayer, (ii) lateral displacement of headgroups, (iii) tilts of lipid molecules, (iv) water penetration into the hydrophobic region of the bilayer, and (v) momentum transfer across the bilayer. The number of water molecules delivered into the hydrophobic region is found to be insensitive to incident shock angles. The most important structural changes are the lateral displacement of headgroups and tilts of lipid molecules, which are observed only in the half of the bilayer directly exposed to a shock wave for all incident shock angles studied here. As a result, only the normal component of the added oblique momentum is substantially transferred across the bilayer. This also suggests that the irradiation by shock waves may induce a jet-like streaming of the cytoplasm toward the nucleus.