GOALI: A GOALI Study of the Stability of Monolayers, Bilayers, and Multivesicular Lipsomes

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ABSTRACT CTS-9634050 It is planned to pattern model biomembranes onto solid substrates via functionalized silane self assembled monolayers ("patterned SAMs") produced by microcontact printing on oxidized silicon or mica. The free ends of the silanes will be functionalized with specific reactive groups such as thiol-coupled gold colloids or ligand-receptor pairs such as biotinated lipid-streptavidin to anchor an otherwise free-floating bilayer at a pattern of discrete points. The unfunctionalized part of the substrate will be treated with a second silane terminated with a neutral group to prevent adhesion to the substrate. Bilayers incorporating biotinated or gold-colloid lipids will be deposited on these functionalized surfaces either by adsorption from vesicle solution or by Langmuir-Blodgett or Langmuir-Schaefer deposition, to bind to the SAM layer at discrete points. Alternatively, we can lithographically pattern a substrate via plasma-enhanced chemical vapor deposition of silicon oxide, then apply monolayers of functionalized silanes to anchor bilayers. The idea is to create the bilayer equivalent of a Langmuir monolayer in which we can study the morphology and interactions of nearly free-floating membranes with the Surface Forces Apparatus, fluorescence and Brewster angle microscopy (BAM), and AFM. In addition to studying membrane properties, patterning membranes is a first step toward biofunctionalizing semiconductors with a micronresolution technique similar to and compatible with microlithography for use in biosensors. An important part of this project is to study the long-term stability of surfactant and lipid structures on surfaces (2D assembly) and in solution (3D assembly). It is still not known whether many surfactant structures, such as circular or stripe domains in monolayers, or unilamellar vesicles in solution, are true equilibrium structures. This question is particularly important to creating membrane-based biosensors that require long-term stability and our GO ALI project of predicting drug release from the DepoTech Co.'s multivesicular liposomes (MVL). It is proposed to study these effects at the air-water interface in monolayers by constructing a completely sealed Langmuir trough to provide temperature and environment control. The surface pressure will be measured using a novel floating wire sensor the monolayers will be viewed by fluorescence microscopy and BAM. It is planned to investigate the long-term stability of domain structures at the airwater interface by continuously monitori.ng. Concurrent with these studies, freeze-fracture electron microscopy will be used to examine a novel multivesicular liposome (DepoFoam) drug delivery system in collaboration with the Depotech Co. The MVL are made from a water-organic-water double emulsion process and the structure is similar to a gas-liquid foam. The goal is to determine the effects of processing conditions, drug composition, and the progression to equilibrium on drug-release properties.