Fabrication of Free-Standing Polymer Membranes via Imprint Lithography and Selective Immobilization of Lipid Vesicles at Micropores in the Membrane

This study presents fabrication of free-standing, perforated membranes in polymer with the pore diameter down to 500 nm via novel imprint lithography and use of the membrane to selectively immobilize lipid vesicles at the micropores in the membrane. For the fabrication, a combination of imprint lithography and a sacrificial layer technique was employed in order to get a clean, fully released, and mechanically stable membrane with perforated pores. Si molds with microscale pillar structures fabricated via photolithography were used to define patterns in SU-8 resist layer which was spin-coated on lift-off resist (LOR) used as a sacrificial layer. This was followed by a UV curing process to achieve enough mechanical strength in the SU-8 layer to be fee-standing. Release of the SU-8 layer from the LOR sacrificial layer by lift-off results in the free-standing, perforated membranes with pore diameter down to sub-micrometer range. Prior to the application of lipid vesicles, the SU-8 membrane surface was treated with poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) which prevents non-specific adsorption of the lipid vesicles on the membrane surface. As a result, lipid vesicles were found to selectively adsorb at the pore sites in the membrane, as observed with an evanescence fluorescence microscope. This result indicates that the perforated polymer membranes with micro- and nanoscale pores have potential as a platform for fundamental study of biological systems.