Measurement protocol for planar lipid bilayer viscoelastic properties

This paper describes how to estimate planar lipid bilayer´s elasticity module E and surface tension sigma by means of measuring its breakdown voltage and using Dimitrov´s viscoelastic model of electric field-induced breakdown of lipid bilayers. Planar lipid bilayers (BLMs) were made of two components: 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC) and 1-palmitoyl 2-oleoyl phosphatidylserine (POPS) in five different compositions. Folding method for forming planar lipid bilayers in the salt solution of 100 mM KCl was used. Breakdown voltages U_br and membrane life times t_br were measured by means of applying linear rising voltage signals of seven different slopes. Specific capacitances c_BLM of bilayers were measured with charge pulse method. Then Dimitrov´s viscoelastic model was fitted to measured data allowing for estimation of elasticity module and surface tension of the lipid bilayer. Our results show that onecomponent bilayers composed from POPS were more stable and thus having higher breakdown voltages and elasticity moduli then bilayers composed of POPC. Surface tension values were similar regardless of the membrane composition. Values of the elasticity (E) and surface tension (sigma) are comparable to those published in the literature. We conclude that the protocol used, though time consuming, is an alternative to other methods used for determination of bilayer´s mechanical properties.