Tulip-Shaped Pattern Imprinting for Omni-Phobic Surfaces Using Partially Cured Photopolymer

Abstract

Functional films with hydrophobic, oleophobic, anti-fouling, anti-icing, anti-bacterial and low reflectance properties can be produced by patterning nano- or micro-structures on films via nano imprint lithography. Here, an omni-phobic surface showing both hydrophobicity and oleophobicity was obtained without chemical surface treatment by increasing the surface roughness and deforming the pattern morphology using only nano imprint lithography and the oxygen-inhibited curing properties of polyurethane acrylate (PUA) resin. A tulip-shaped pattern imprinting process was designed in which microscale patterns were fabricated using a porous polydimethylsiloxane (PDMS) mold with high oxygen transmission. During ultraviolet (UV) curing, a curing inhibiting layer was formed by reaction with oxygen. Next, a PDMS pad was used for the pressurized curing of the curing inhibition layer to modify the micro scale structures. Finally, final curing of the deformed pattern was performed using ultra high-power UV light. The deformation of the pattern into tulip-like shapes with increased surface roughness was confirmed by microscopy, and contact angle measurement was performed to confirm omni-phobicity. The final cured imprinted samples showed water and oil contact angles reaching 169.2° and 115°, respectively; thus, the omni-phobic surface could be demonstrated by a tulip-shaped pattern imprinting process.

Microstructured Surfaces for Reducing Chances of Fomite Transmission via Virus-Containing Respiratory Droplets

“…For surface designing, we considered the structural stability and robust particle capture ability of the surface for high-touch environmental applications, as presented in Figure . On the basis of a surface topography inspired by the structure of natural surfaces, ,− we proposed the design of interconnected microcavity architectures to enhance the mechanical robustness of the microstructures while entrapping the particles within their cavity from external mechanical contact. We developed a V-shaped microcavity as an additional design feature to ensure the insertion of the directional particle aggregates into the microcavities driven by contact line depinning and the low CAH of the evaporating droplets (related to surface chemistry θ Y ).…”

“…For the proof-of-concept, we designed a hexagonal microwall without a structure gradient (hexawall) and an inverted pyramidal microwall with a structure gradient (ipyrawall), considering the structural requirements described in Figure B. Our interconnected hexawall (α = 90°) and ipyrawall (α = ∼125°) were fabricated through the UV-NIL process (Figure A,B and see the “Materials and Methods” section), , which are highly compatible with the roll-to-roll (R2R) printing for scalable manufacturing of functional surfaces (Figure C). Additionally, the transparency of our microcavity surfaces as shown in Figure D, is compatible with optical sensing technologies (e.g., surface-enhanced Raman spectroscopy-based biosensor) and other in practical applications (e.g., touch screens) …”

“…As the first component of our surface design, the microstructure consisted of an interconnected cavity with a low contact area that captured the particles, which could help prevent high-touch surface contamination in the healthcare environment. The interconnected microcavity architecture also enhanced the mechanical robustness, as observed for various natural structures including springtail skin and honeycomb, ,− and maintained the robust particle capture stability from external mechanical contact. Additional design features were considered to ensure directional particle aggregates driven by low contact angle hysteresis (CAH) of the droplets and structural gradient of surfaces to minimize particle residues for extremely low touch transfer.…”

“…Here, we proposed a robust particle capture surface that allows the directional particle aggregation of microdroplets by controlling the 3D geometry and surface chemistry of the substrate for low contact transfer from the fomites contaminated by respiratory droplets. Although we focused on the low efficacy of transfer from the contaminated microstructured surfaces to other clean surfaces in this study, we expect that the microcavity surfaces will help limit the contact transfer of various pathogens from contaminated objects (i.e., hands) to recipient surfaces due to their small contact area (∼0.21 for hexawall and ∼0.015–0.03 for ipyrawall). , The efficient particle capturing ability of the microcavity structures not only prevents fomite-based transmission but also may be utilized to preconcentrate target analytes, which may be useful for the environmental monitoring or Raman spectroscopy of pathogens, including SARS-CoV-2. − In addition to the mechanical and chemical stability of surfaces observed after spray cleaning (Figure S10) and the ability to capture particles even without cleaning (Figures S11–13), our engineered surfaces are highly compatible with large-scale manufacturing techniques. ,, For example, we have applied a R2R imprinting process to achieve scalable high-throughput fabrication of interconnected microcavity surfaces (Figure C). With cost-effective large-scale fabrication, our microstructured surfaces will find a wider range of applications in various fields.…”

“…The PUA and PDMS resins were cured with ultraviolet (UV) light (λ = 365 nm) for a few seconds and in an oven at 100 °C for 1h, respectively. In this study, the microstructured surfaces were replicated using UV nanoimprint lithography as described earlier. , …”