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The stability of phospholipid and biomimetic polymer vesicles

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Title: The stability of phospholipid and biomimetic polymer vesicles
Author(s): Flores, Courtney
Advisor(s): Zilles, Julie L.
Department / Program: Civil & Environmental Eng
Discipline: Environ Engr in Civil Engr
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): phospholipids biomimetic polymers phospholipid vesicles biomimetic polymer vesicles PMOXA-PDMS-PMOXA Aquaporin Z (AqpZ) aquaporin biomimetic membranes
Abstract: Biomimetic membranes are a novel alternative that may address issues inorganic scaling, biofouling, and membrane vulnerability to chemicals currently plaguing membranes. They mimic cell membranes and incorporate membrane proteins, such Aquaporin Z (AqpZ). PMOXA-PDMS-PMOXA (ABA) triblock co-polymers have demonstrated similar properties as phospholipids and incorporate AqpZ. Previous research conducted on AqpZ:ABA vesicles showed permeabilities exceeding commercial RO membranes and high selectivity. These properties make biomimetic materials promising for RO, but investigation of their long-term chemical and physical stability under water treatment conditions is needed to assess their feasibility for use in desalination membranes. In order to investigate the stability of biomimetic materials, phospholipid and biomimetic polymer vesicles at pH 7.2 were prepared with and without AqpZ using film-hydration techniques and stored at room temperature. Their formation was confirmed by Transmission Electron Microscopy. Size and uniformity were measured using Dynamic Light Scattering. Stopped-flow testing was used to monitor vesicle permeability and for selectivity measurements. Phospholipid and ABA polymer vesicles remained stable in size, uniformity, and permeability over the course of several months in conditions typical in water treatment. Fluorescence leakage assays on vesicles were inconclusive. The incorporation of AqpZ into lipid vesicles improved their permeabilities over lipid-only vesicles up to 200 days, but these effects diminished over time. This implies limited protein stability. Vesicles with AqpZ showed fluctuations in size and permeability over time. Lipid-AqpZ vesicles demonstrated high selectivity of monovalent ions and slightly lower selectivity of divalent ions. Varying salinity levels in PBS did not affect vesicle selectivity or time stability over 5 weeks. Vesicles prepared in artificial seawater fluctuated in size, uniformity, and permeability over time. These vesicles in seawater also showed lower rejection of NaCl. Seawater effects were likely caused by Ca2+ ions. Lipid and polymer vesicles show great potential for the use of biomimetic materials in desalination membranes, as demonstrated by their long-term stability and high selectivity under water treatment conditions and various salinity levels, and their increased permeabilities with AqpZ addition. Material constraints prevented a thorough assessment of ABA3 and AqpZ, so more stability tests are needed to better characterize their long-term stability over time and in desalination conditions. It is not clear what effects seawater might have on a planar, supported lipid bilayer, nor have its effects on polymer membranes been thoroughly evaluated, although initial experiments suggest resistance rupture by Ca2+ ions. If membranes made with these materials are feasible for use in RO membranes, their low operating energy requirements will likely promote widespread applicability in water treatment.
Issue Date: 2012-06-27
URI: http://hdl.handle.net/2142/32032
Rights Information: Copyright 2012 Courtney Flores
Date Available in IDEALS: 2012-06-27
Date Deposited: 2012-05
 

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