Phase behavior, collapse transitions, and permeability of natural and synthetic monolayers

Binary disaturated phosphatidylcholine(PC)/PEG-lipid systems have been widely used in bilayer and monolayer studies for the production of liposomes/vesicles and lipid-coated microbubbles both with applications in biomedical research. In this study, surface pressure (pi)-A isotherms, pi vs. 2D isothermal surface compressibility (ks) plots, molecular area vs. composition, and fluorescence images of Langmuir monolayers of DMPC, DPPC, and DSPC mixed with DSPE-PEG2000 were used to construct binary pi-composition (XDSPE-PEG2000) phase diagrams that showed syntectic, eutectic, peritectic, and monotectic phase transformations. We statistically characterize the chain length dependence of the collapse/shedding mechanisms during the dissolution of microbubbles coated with monolayers of disaturated PC/DSPE-PEG2000. We also obtain the gas transport resistance of the PC/DSPE-PEG2000 shell coating dissolving microbubbles under controlled conditions by modeling the dissolution of air microbubbles in an aqueous media. Combining the monolayer and microbubble dissolution results, we show how acyl chain condensation in DSPE-PEG2000, not present in the previously studied systems, dramatically impacts the dissolution behavior in this mixed system.;Furthermore, we propose a novel design for drug delivery by conjugating lipid-coated microbubbles and vesicles via DNA hybridization. Lastly, we used our experience on model lipid monolayer systems to explain the phase behavior and obtain surface tension measurements of microbubbles generated in seawater collected offshore.