ChBE Seminar Series: Marjorie Longo
Tuesday, March 4, 2008
11:00 a.m.-12:00 p.m.
Room 2110 Chemical & Nuclear Engineering Bldg.
Professor Jeffery Klauda
Domain in the Membrane: Lipid Domains in Bilayers and Monolayer Microbubble Shells
Presented by Marjorie Longo
Department of Chemical Engineering and Materials Science
Nanometer-scale domains within the plane of the cell plasma membrane, referred to as membrane rafts, have been a topic of considerable interest in the scientific community. As a model for the plasma membrane, lipid membranes formed from multiple lipid components can laterally separate into coexisting phases, or domains, with distinct compositions. Theoretical frameworks link domain interfacial line tension (γ) to characteristics that may help us to understand membrane rafts: critical nuclei size (rc), nucleation rate (J), and when combined with bending parameters, pattern formation. Our goal was then to quantitatively determine γ values in these three ternary systems. We mapped γ (in pN range) with cholesterol concentration for the three ternary lipid mixtures and symmetric vs. asymmetric domains by applying classical theory of nucleation to nucleation data attained by atomic force microscopy (AFM). Domain nucleation is followed by domain growth, in which we were able to identify growth regimes (diffusion-limited and reaction-limited). Micron-scale phase coexistence (domains) in multi-component lipid monolayers, rather than bilayers, has also been a topic of interest to the scientific community. Our interest has been in understanding multi-component monolayers on the surface of micron-scale bubbles (microbubbles) used as coatings for medical ultrasound contrast agents (UCAs). We find that these lipid/lipo-polymer shells often display phase separated domains that are seen to play a role in bubble collapse, component squeeze-out and gas transport resistance. Recently our focus has been on coating of monodisperse (1 μm +/- 0.1 μm) microbubbles formed by microfluidics (flow-focusing) and mixing behavior in lipid/lipo-polymer shells.