ABSTRACT
Continuum finite element material models used for traumatic brain injury lack local injury parameters necessitating nanoscale mechanical injury mechanisms be incorporated. One such mechanism is membrane mechanoporation, which can occur during physical insults and can be devastating to cells, depending on the level of disruption. The current study investigates the strain state dependence of phospholipid bilayer mechanoporation and failure. Using molecular dynamics, a simplified membrane, consisting of 72 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) phospholipids, was subjected to equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial tensile deformations at a von Mises strain rate of 5.45 × 108 s-1, resulting in velocities in the range of 1 to 4.6 m·s-1. A water bridge forming through both phospholipid bilayer leaflets was used to determine structural failure. The stress magnitude, failure strain, headgroup clustering, and damage responses were found to be strain state-dependent. The strain state order of detrimentality in descending order was equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial. The phospholipid bilayer failed at von Mises strains of .46, .47, .53, .77, and 1.67 during these respective strain path simulations. Additionally, a Membrane Failure Limit Diagram (MFLD) was created using the pore nucleation, growth, and failure strains to demonstrate safe and unsafe membrane deformation regions. This MFLD allowed representative equations to be derived to predict membrane failure from in-plane strains. These results provide the basis to implement a more accurate mechano-physiological internal state variable continuum model that captures lower length scale damage and will aid in developing higher fidelity injury models.
Subject(s)
Biomechanical Phenomena , Lipid Bilayers/chemistry , Molecular Dynamics Simulation , Phosphatidylcholines/chemistry , Algorithms , Models, Theoretical , Phospholipids/chemistryABSTRACT
An interatomic potential for sulfur has been developed using the bond order addition to the modified embedded-atom method (MEAM-BO). In order to correctly model the interaction between molecules, dispersion forces have been included via the DFT-D3 modification. It is demonstrated that this semiempirical classical potential correctly reproduces the behavior of the S2 dimer, various cyclic sulfur rings, the molecular solids α-, ß-, and γ-sulfur, and a number of theoretical, high symmetry sulfur structures. This potential will serve as a useful tool in the atomistic modeling of sulfur and, ultimately, in the modeling of sulfur containing organic compounds using this updated MEAM-BO formalism.
ABSTRACT
In this paper, we develop a new modified embedded atom method (MEAM) potential that includes the bond order (MEAM-BO) to describe the energetics of unsaturated hydrocarbons (double and triple carbon bonds) and also develop improved parameters for saturated hydrocarbons from those of our previous work. Such quantities like bond lengths, bond angles, and atomization energies at 0 K, dimer molecule interactions, rotational barriers, and the pressure-volume-temperature relationships of dense systems of small molecules give a comparable or more accurate property relative to experimental and first-principles data than the classical reactive force fields REBO and ReaxFF. Our extension of the MEAM potential for unsaturated hydrocarbons (MEAM-BO) is a step toward developing more reliable and accurate polymer simulations with their associated structure-property relationships, such as reactive multicomponent (organic/metal) systems, polymer-metal interfaces, and nanocomposites. When the constants for the BO are zero, MEAM-BO reduces to the original MEAM potential. As such, this MEAM-BO potential describing the interaction of organic materials with metals within the same MEAM formalism is a significant advancement for computational materials science.