Lithographically\nDefined Macroscale Modulation of\nLateral Fluidity and Phase Separation Realized via Patterned Nanoporous\nSilica-Supported Phospholipid Bilayers

Abstract

Using lithographically\ndefined surfaces consisting of hydrophilic\npatterns of nanoporous and nonporous (bulk) amorphous silica, we show\nthat fusion of small, unilamellar lipid vesicles produces a single,\ncontiguous, fluid bilayer phase experiencing a predetermined pattern\nof interfacial interactions. Although long-range lateral fluidity\nof the bilayer, characterized by fluorescence recovery after photobleaching,\nindicates a nominally single average diffusion constant, fluorescence\nmicroscopy-based measurements of temperature-dependent onset of fluidity\nreveals a locally enhanced fluidity for bilayer regions supported\non nanoporous silica in the vicinity of the fluid–gel transition\ntemperature. Furthermore, thermally quenching lipid bilayers composed\nof a binary lipid mixture below its apparent miscibility transition\ntemperature induces qualitatively different lateral phase separation\nin each region of the supported bilayer: The nanoporous substrate\nproduces large, microscopic domains (and domain-aggregates), whereas\nsurface texture characterized by much smaller domains and devoid of\nany domain-aggregates appears on bulk glass-supported regions of the\nsingle-lipid bilayer. Interestingly, lateral distribution of the constituent\nmolecules also reveals an enrichment of gel-phase lipids over nanoporous\nregions, presumably as a consequence of differential mobilities of\nconstituent lipids across the topographic bulk/nanoporous boundary.\nTogether, these results reveal that subtle local variations in constraints\nimposed at the bilayer interface, such as by spatial variations in\nroughness and substrate adhesion, can give rise to significant differences\nin macroscale biophysical properties of phospholipid bilayers even\nwithin a single, contiguous phase.