Characterization of supported membranes on topographically patterned polymeric elastomers and their applications to microcontact printing

This article describes the fluorescence microscopy and imaging ellipsometry-based characterization of supported phospholipid bilayer formation on elastomeric substrates and its application in microcontact printing of spatially patterned phospholipid bilayers. Elastomeric stamps, displaying a uniformly spaced array of square wells (20, 50, and 100 mum linear dimensions), are prepared using poly(dimethyl)siloxane from photolithographically derived silicon masters. Exposing elastomeric stamps, following UV/ozone-induced oxidation, to a solution of small unilamellar phospholipid vesicles results in the formation of a 2D contiguous, fluid phospholipid bilayers. The bilayer covers both the elevated and depressed regions of the stamp and exhibits a lateral connectivity allowing molecular transport across the topographic boundaries. Applications of these bilayer-coated elastomeric stamps in microcontact printing of lipid bilayers reveal a fluid-tearing process wherein the bilayer in contact regions selectively transfers with 75-90% efficiency, leaving behind unperturbed patches in the depressed regions of the stamp. Next, using cholera-toxin binding fluid POPC bilayers that have been asymmetrically doped with ganglioside Gm1 ligand in the outer leaflets, we examine whether the microcontact transfer of bilayers results in the inversion of the lipid leaflets. Our results suggest a complex transfer process involving at least partial bilayer reorganization and molecular re-equilibration during (or upon) substrate transfer. Taken together, the study sheds light on the structuring of lipid inks on PDMS elastomers and provides clues regarding the mechanism of bilayer transfer. It further highlights some important differences in stamping fluid bilayers from the more routine applications of stamping in the creation of patterned self-assembled monolayers.