R&D Profile: Low Cost Fabrication of Free-Standing Polymer Membranes with Micro- and Nanopores for Mimicking Biosystems: S. Park, Louisiana State University, US
The ability to mimic micro- and nanostructures existing in biosystems is of great interest because it provides tools and platforms for many fundamental biophysical studies and technological applications.
Overview courtesy of S. Park, Louisiana State University, US
The ability to mimic micro- and nanostructures existing in biosystems is of great interest because it provides tools and platforms for many fundamental biophysical studies and technological applications. One interesting structure is artificial membranes with perforated micro- and nanoscale pores as the model architecture of cell membranes. Cell membranes, selectively permeable layer, consist of a lipid bilayer and various proteins and separate the cytoplasm from the outer extracellular environment. As a model architecture of the cell membrane, a planar lipid bilayer architecture which is formed in mechanically stable, free-standing membranes and facilitates an access from the both sides will provide a more flexible platform to elucidate the cell functions, such as chemical and mechanical stability of the cell membrane, transportation through ion channels, and signaling and regulation functions of membrane proteins.
We presented at Nanotech 2008 in Boston a fast and high-throughput process to produce free-standing membranes in SU-8 polymer with perforated pores down to sub-micron diameter by combining nanoimprint lithography with a sacrificial layer technique. First, a double resist layer, lift-off resist as a sacrificial layer and SU-8 as the membrane layer, was spin-coated on a substrate. Pore structures were defined using nanoimprint lithography. After oxygen plasma treatment for window opening and UV-curing of the SU-8 layer, a fully-released, free-standing SU-8 membrane was achieved by selectively dissolving the sacrificial layer. The smallest pore size that we produced with this method was 0.5 µm in diameter. We also achieved large area membranes up to 4 inch diameter fully covered with 5 µm pores. Then, the feasibility of using the SU-8 membrane with perforated pores to mimic a cell membrane was examined by studying the adsorption behavior of lipid vesicles to the membrane surface. We found that lipid vesicles selectively adsorb at the pore sites in the membrane and that the adsorption behavior strongly depends on the quality of imprinted patterns, surface treatment with poly-L-lysine-grafted-(polyethylene glycol), and viscosity of the lipid solution.
One advantage of using the fabricated SU-8 membrane is that it is mechanically stable to be free-standing and can be used as a modular component to build a fluidic system. Currently, we are developing processes to produce integrated fluidic systems with the SU-membrane that can be used to study cell membranes by sandwiching between two other microchips and also to reduce the pore size of the membrane to the real nanometer regime. This project is highly interdisciplinary and is one of the on-going research projects in the Dr. Park’s research group, with the long-term research goal of developing low cost technologies to produce micro- and nanostructured tools and platforms that can control, manipulate, and mimic biosystems.
(left) Photograph and scanning electron micrographs of free-standing SU-8 membranes with perforated pores and (right) fluorescence micrographs after adsorption of lipid vesicles on the SU-8 membrane with and without PLL-g-PEG treatment on the membrane surface.
