Bioinspired elastomeric structural adhesives can provide reversible and controllable adhesion on dry/wet and synthetic/biological surfaces for a broad range of commercial applications. Shape complexity and performance of the existing structural adhesives are limited by the used specific fabrication technique, such as molding. To overcome these limitations by proposing complex 3D microstructured adhesive designs, a 3D elastomeric microstructure fabrication approach is implemented using two‐photon‐polymerization‐based 3D printing. A custom aliphatic urethane‐acrylate‐based elastomer is used as the 3D printing material. Two designs are demonstrated with two combined biological inspirations to show the advanced capabilities enabled by the proposed fabrication approach and custom elastomer. The first design focuses on springtail‐ and gecko‐inspired hybrid microfiber adhesive, which has the multifunctionalities of side‐surface liquid super‐repellency, top‐surface liquid super‐repellency, and strong reversible adhesion features in a single fiber array. The second design primarily centers on octopus‐ and gecko‐inspired hybrid adhesive, which exhibits the benefits of both octopus‐ and gecko‐inspired microstructured adhesives for strong reversible adhesion on both wet and dry surfaces, such as skin. This fabrication approach could be used to produce many other 3D complex elastomeric structural adhesives for future real‐world applications.
Various functional complex 3D patterned surfaces with micro‐ or nanostructures have been developed and their superior performances over non‐patterned smooth surfaces proven. However, it is challenging to mass‐produce such complex micro‐/nanopatterned surfaces, which limits their commercialization drastically. Although roll‐to‐roll (R2R) manufacturing using flexible molds has been implemented for mass‐production of such functional surfaces, the poor mold repeatability issue has not been resolved yet. Here, a strategy to significantly improve the repeatability of the micropatterned flexible silicone molds over 1000 cycles against highly adhesive polyurethane acrylates (PUAs) in UV light curing based R2R systems by using a two‐step curing process is reported. The mold repeatability is drastically increased from 10s of cycles to over 1000 cycles through the proposed strategy in spite of the complicated 3D undercut geometry and high tackiness of the microstructure. This two‐step process would enable scaled‐up production of micro‐/nanostructured adhesives, such as gecko‐inspired microfiber adhesives as demonstrated in this study, as well as various other functional micro‐/nanostructured surfaces by enhancing the flexible mold lifetime.
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