Nanomechanics of phospholipid bilayer failure under strip biaxial stretching using molecular dynamics

Abstract

The current study presents a nanoscale in silico investigation of strain rate dependency of membrane (phospholipid bilayer) failure when placed under strip biaxial tension with two planar areas. The nanoscale simulations were conducted in the context of a multiscale modelling framework in which the macroscale damage (pore volume fraction) progression is delineated into pore nucleation (number density of pores), pore growth (size of pores), and pore coalescence (inverse of nearest neighbor distance) mechanisms. As such, the number density, area fraction, and nearest neighbor distances were quantified in association with the stress–strain behavior. Deformations of a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer were performed using molecular dynamics to simulate mechanoporation of a neuronal cell membrane due to injury, which in turn can result in long-term detrimental effects that could ultimately lead to cell death. Structures with 72 and 144 phospholipids were subjected to strip biaxial tensile deformations at multiple strain rates. Formation of a water bridge through the phospholipid bilayer was the metric to indicate structural failure. Both the larger and smaller bilayers had similar behavior regarding pore nucleation and the strain rate effect on pore growth post water penetration. The applied strain rates, planar area, and cross-sectional area had no effect on the von Mises strains at which pores greater than 0.1 nm2 were detected (0.509 ± 7.8%) or the von Mises strain at failure (εfailure = 0.68 ± 4.8%). Additionally, changes in bilayer planar and cross-sectional areas did not affect the stress response. However, as the strain rate increased from 2.0 × 108 s−1 to 1.0 × 109 s−1, the yield stress increased from 26.5 MPa to 66.7 MPa and the yield strain increased from 0.056 to 0.226.