Fabrication of directional nanopillars with high-aspect-ratio using a stretching imprint process with a microcavity mold

Facile Nanoimprinting of Robust High-Aspect-Ratio Nanostructures for Human Cell Biomechanics

High-aspect-ratio and hierarchically nanostructured surfaces are common in nature. Synthetic variants are of interest for their specific chemical, mechanic, electric, photonic, or biologic properties but are cumbersome in fabrication or suffer from structural collapse. Here, we replicated and directly biofunctionalized robust, large-area, and high-aspect-ratio nanostructures by nanoimprint lithography of an off-stoichiometric thiol-ene-epoxy polymer. We structured-in a single-step process-dense arrays of pillars with a diameter as low as 100 nm and an aspect ratio of 7.2; holes with a diameter of 70 nm and an aspect ratio of >20; and complex hierarchically layered structures, all with minimal collapse and defectivity. We show that the nanopillar arrays alter mechanosensing of human hepatic cells and provide precise spatial control of cell attachment. We speculate that our results can enable the widespread use of high-aspect-ratio nanotopograhy applications in mechanics, optics, and biomedicine.

Replication of Mesoscale Pore One-dimensional Nanostructures: Surface-induced Phase Separation of Polystyrene/Poly(vinyl alcohol) (PS/PVA) Blends

Mesoscale pore one-dimensional (1D) nanostructures, or vertically aligned porous nanostructures (VAPNs), have attracted attention with their excellent hydrophobic properties, ultra-high surface area, and high friction coefficient, compared to conventional vertically aligned nanostructures (VANs). In this study, we investigate the replication of VAPNs produced by the thermal nanoimprint process using anodic aluminum oxide (AAO2) templates (100 nm diameter). Polystyrene/poly(vinyl alcohol) (PS1/PVA) blends, prepared by the advanced melt-mixing process with an ultra-high shear rate, are used to investigate the formation of porosity at the nanometer scale. The results reveal that domain size and mass ratios of PVA precursors in the PS matrix play a dominant role in the interfacial interaction behavior between PS1-PVA-AAO2, on the obtained morphologies of the imprinted nanostructures. With a PVA nanodomain precursor (PS1/PVA 90/10 wt%), the integration of PVA nanodroplets on the AAO2 wall due to the hydrogen bonding that induces the phase separation between PS1-PVA results in the formation of VAPNs after removal of the PVA segment. However, in the case of PVA microdomain precursors (PS1/PVA 70/30 wt%), the structure transformation behavior of PS1 is induced by the Rayleigh instability between PVA encapsulated around the PS1 surfaces, resulting in the PS1 nanocolumns transforming into nanopeapods composed of nanorods and nanospheres.