Measurements and Modeling of the Failure Pressure of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine Bilayer Lipid Membranes Formed over a Single Pore

Numerous methods have been developed for measuring mechanical properties of bilayer lipid membranes (BLMs) such as the Young’s modulus, strength, bending modulus, and others. This paper introduces a new method for measuring the maximum pressure that can be withstood by BLMs formed over a porous substrate. This quantity, referred to as the failure pressure, has not been reported in the literature previously. In this series of experiments a BLM is formed across a single pore and is then pressurized until failure. This experiment is performed on 1-Stearoyl-2-Oleoylsn-Glycero-3-Phosphocholine (SOPC) lipid bilayers formed over a polycarbonate substrate with a single pore ranging from 5 to 20 μm in diameter. A trend of increasing failure pressure with decreasing pore size is observed, with failure pressures falling between 67 and 19 kPa, respectively. The same set of experiments is repeated for BLMs that are formed from a mixture of SOPC and 50 mol% cholesterol (CHOL) and this is found to increase the failure pressure by 56% on average. A plate model, a planar membrane model, and a spherical membrane model are used to show that the behavior of the BLMs is more membrane-like than plate-like, with a relationship between failure pressure Pf and pore size a of Pf ∝ 1/a. Also a quantitative model of the characteristic pressure curve from this experiment is developed based on the pressurization and flow of fluid in the test fixture. This model accurately reproduces the pressure curve of a BLM which includes an initial increase in pressure when the BLM is well formed across a pore, followed by a sharp drop in pressure after the BLM fails. Electrical impedance is also measured before and after pressurization of the BLM. It is found that the magnitude of electrical impedance drops by three orders of magnitude after pressurization, indicating that the BLM has failed and has opened a conductive pathway through the pore.