Elastic modulus of free-standing lipid bilayer

In the current study, molecular dynamics (MD), finite element (FE) method, and genetic algorithm are employed to compute Young’s modulus of free-standing DPPC lipid bilayer. MD method is utilized to simulate loading of a free-standing DPPC lipid bilayer under an indenter. Indentation experiment is also simulated with FE method where genetic algorithm controls value of Young’s modulus in FE simulation and finds the best value for it. The best value means the value results in a force–depth curve which agrees well with the curve obtained from MD simulation. While simulating indentation with MD method two distinct regimes are distinguished in force–depth curve before rupture of the bilayer. The first regime shows elastic response of the bilayer to indentation and it is shown that force–depth curve can be fitted with a cubic polynomial in this regime. The second regime starts at the point which the force–depth curve changes from convex to concave. This point is an inflection point and would be regarded as yield point of the bilayer. Slope of the curve decreases with indentation depth in this regime which shows changes in internal structure of the bilayer. Also we investigate effects of indenter’s shape and indentation speed on computed Young’s modulus and show rate-dependent behavior of free-standing lipid bilayer.