Development and applications of mass transport systems based on biomimetic lipid membranes

Abstract

Due to its ubiquitous nature and importance in numerous physiological phenomena, research on mass transport across the biological cell membrane has been widely investigated, stimulating the development of various model cell membrane systems based on bottom-up approaches. However, previous model cell membrane systems generally exhibit poor stability and require laborious fabrication steps and sophisticated analysis tools. Therefore, the development of a novel model cell membrane system for effective mass transport study is necessary. In this dissertation, mass transport systems based on biomimetic lipid membranes were developed, and their potential for use in various applications was demonstrated. By spontaneous self-assembly of phospholipids at the oil/water interface, a stable freestanding planar lipid bilayer with millimeter-scale size could be constructed in a simple and reproducible manner. Next, the application of the developed mass transport system to permeability assay for lipophilic drug compounds was explored. Real-time transport curves for six lipophilic drug compounds could be obtained, and by applying an integrated transport model considering both permeation through the lipid bilayer and partitioning to the oil phase, membrane permeability and membrane retention fraction for individual compounds could be calculated. In addition, by incorporating protein nanopores into the lipid membrane, chiral selective transport of amino acids through protein pores was also investigated. Transport of total 13 kinds of amino acids depending on their enantiomeric forms could be successfully measured with the highest observed permeation selectivity of 15.63 for glutamine. These results provide a comprehensive structure-selectivity relationship in amino acid transport through protein pores for the first time, where it is discovered that hydrogen bond propensity of the amino acid side chain and molecular size of the amino acid determine the extent of chiral selective transport of amino acids. Further investigations using steered molecular dynamics simulations elucidate the molecular mechanism behind the enantioselective transport of amino acids in our system. This dissertation is expected to provide an effective strategy to build a biomimetic membrane-based system optimized for various mass transport studies, as well as pave the way to find novel applications with broad interests in both academia and industry.