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dc.contributor.authorHopkinson, David P.en_US
dc.date.accessioned2014-03-14T20:20:13Z
dc.date.available2014-03-14T20:20:13Z
dc.date.issued2007-12-06en_US
dc.identifier.otheretd-12122007-120204en_US
dc.identifier.urihttp://hdl.handle.net/10919/30064
dc.description.abstractBilayer lipid membranes (BLMs) are formed from phospholipid molecules which self-assemble into a lipid bilayer with 4 to 9 nm thickness when submerged in an aqueous solution. This is due to their amphiphilic nature, meaning that one part of the molecule is hydrophilic, or attracted to water, and one part is hydrophobic, or repelled by water. They are the primary structural component of cell membranes in living organisms and therefore are useful for modeling the properties of cell membranes since they share many of the same chemical and physical properties. The objective of this dissertation is to investigate the maximum pressure that can be withstood by a BLM formed over a porous substrate, which will be referred to as the failure pressure. This work represents the first time that this quantity has been measured and reported. The failure pressure is investigated in several complementary ways, including mechanical, electrical, and optical measurements and modeling. The phospholipids that are tested include 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylcholine (SOPC) and mixtures of SOPC and cholesterol (CHOL), which was chosen because cholesterol is known to increase the strength of SOPC BLMs. A new test methodology was developed to measure the failure pressure of BLMs. A custom test fixture was used to pressurize BLMs while measuring the applied pressure with a high degree of precision and repeatability. The BLMs were tested in an electrolyte solution over substrates that contained a single pore and also substrates that contained an array of many pores. SOPC BLMs were tested over single pore substrates with pore sizes ranging from 5 to 20 microns, and this resulted in failure pressures from 67 to 19 kPa, respectively. For single pore tests, the addition of 50 mol% cholesterol to SOPC resulted in a 56% higher failure pressure on average than SOPC alone. For multi pore substrates, SOPC BLMs were tested using pore sizes between 0.05 and 10 microns, which yielded bulk failure pressures of 380 to 1.5 kPa, respectively. For multi pore tests, SOPC/CHOL-50 mol% resulted in a 47% higher bulk failure pressure on average. A model was developed to predict the pressurization curve of BLMs and was applied to both the single and multi pore tests. It was found that the failure pressure of BLMs follows a distribution which was well modeled by a Weibull distribution with a positive skew. Parameters such as the Weibull shape parameter were determined by fitting the model to the experimental pressurization curves and it was found that the shape of the Weibull distribution was nearly the same for every pore size. Using the pressurization model it was estimated that the percentage of failed BLMs that were pressurized over a multi pore substrate ranged from 4% to 33%. The model also coupled the bulk failure pressure of BLMs formed over multiple pores to the failure pressure of a single BLM, showing that the bulk failure pressure of multiple BLMs is smaller than the failure pressure of a single BLM because it represents the failure of only the weakest BLMs in a group. Electrical impedance was measured before and after pressurization of the BLMs, and these measurements were modeled by assuming that the BLMs act as a resistor and a capacitor configured in parallel. In general, the impedance magnitude dropped by two to three orders of magnitude after BLM pressurization, which was a result BLMs failing and opening conductive pathways through the subsequently empty pores. It was found that normalized conductance values for SOPC BLMs were between G / A = 4 x 10^-12 and 2 x 10^-8 S/cm^2, and normalized capacitance values varied between C / A = 3 x 10^-14 and 1 x 10^-10 F/cm^2. In the literature these values ranged from G / A = 10^-1 to 10^-9 S/cm^2 and C / A = 10^-6 to 10^-8 F/cm^2, having a wide range of values due to the many variations of experimental test procedures. Visual images of BLMs were produced using fluorescence microscopy. Images were recorded before and after pressurization of SOPC BLMs formed over a multi pore substrate. As predicted by the pressurization model, it was found that some but not all BLMs fail after pressurization. It was also found that BLMs fail over the center of a pore, and leave remnants around the perimeter of the pore.en_US
dc.publisherVirginia Techen_US
dc.relation.hasparthopkinson_etd_2007.pdfen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectfluorescenceen_US
dc.subjectimpedanceen_US
dc.subjectpressureen_US
dc.subjectfailureen_US
dc.subjectbilayer lipid membraneen_US
dc.titleMeasurements and Modeling of the Failure Pressure of Bilayer Lipid Membranesen_US
dc.typeDissertationen_US
dc.contributor.departmentMechanical Engineeringen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineMechanical Engineeringen_US
dc.contributor.committeechairLeo, Donald J.en_US
dc.contributor.committeememberVlachos, Pavlos P.en_US
dc.contributor.committeememberInman, Daniel J.en_US
dc.contributor.committeememberCase, Scott W.en_US
dc.contributor.committeememberDe Vita, Raffaellaen_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-12122007-120204/en_US
dc.date.sdate2007-12-12en_US
dc.date.rdate2008-01-12
dc.date.adate2008-01-12en_US


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