Failure Characteristics of Bilayer Lipid Membranes (BLMs) Formed over a Single Pore
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Failure Characteristics of Bilayer Lipid Membranes (BLMs) Formed over a Single Pore David Hopkinson, and Donald J. Leo Mechanical Engineering, Virginia Tech, 310 Durham Hall, Blacksburg, VA, 24061 ABSTRACT A new methodology has been developed to measure the maximum pressure that can be withstood by a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated to pressurize BLMs in very fine increasing increments until they fail. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylocholine (SOPC) BLMs formed over polycarbonate substrates with a single pore ranging from 5 to 20 µm in diameter. Failure pressure was found to be inversely proportional to pore diameter. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and 50 mol% cholesterol (CHOL). The presence of cholesterol was found to increase the failure pressure of the BLMs by 56% on average. A model of the characteristic pressure curve from this experiment was developed based on the pressurization and flow of fluid through a porous substrate. The model was found to accurately fit the experimental pressure curves. INTRODUCTION Bilayer lipid membranes (BLMs) are formed from phospholipid molecules which selfassemble into a lipid bilayer with 4 to 8 nm thickness when submerged in an aqueous solution due to their amphiphilic nature [1]. They are the primary structural component of cell membranes in living organisms and therefore are useful for modeling the properties of cells since they share many of the same chemical and physical properties. Researchers are showing an increasing interest in integrating biological or biologically-inspired components into engineering materials and systems, such as a biomimetic actuator that has been developed by researchers at Virginia Tech [2]. In order to successfully integrate a BLM into an engineering application it is necessary to quantify the mechanical properties of the membrane. Investigators in biomechanics have long been interested in studying the mechanical behavior of spherical shells of BLMs, known as vesicles, because they resemble the spherical shape of cell membranes. The micropipet aspiration technique that was pioneered by Mitchison and Swann and has been developed extensively by Evans and Needham is among the best established methods for measuring the mechanical properties of vesicles [3,4]. Several other methods have also been adopted to test BLMs such as atomic force microscopy, magnetic twisting cytometry, and cytoindentation [5]. The purpose of this research is to measure and analyze the maximum pressure that can be withstood by a BLM formed over a porous substrate, which is an aspect of mechanical characterization that has not been explored by other methods in the literature. In this paper BLMs are formed over a substrate containing a single pore, ranging in size from 5 to 20 µm diameter, and the BLMs are pressurized until failure. BLMs are pressurized using a custom test fixture with a stepper mo
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