Direct 3D printing of two bio-inspired new microstructure-based adhesives using a custom-made elastomer resin. Springtail-gecko-inspired microstructures are designed for three simultaneous functionalities: top-surface liquid super-repellency, side-surface liquid-repellency, and strong dry adhesion. Next, octopus-gecko-inspired microstructures are designed for high adhesion on both underwater and dry conditions on synthetic skin.
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 has been implemented using two-photon polymerization [ ]. A custom aliphatic urethane acrylate-based elastomer is used as the 3D printing material. We demonstrate two designs 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 for the first time. 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.
In our another study, we focus on increasing adhesion performance of gecko-inspired adhesives. We design bio-inspired composite microfibers for strong and reversible adhesion to smooth surfaces. The proposed microfibrillar patterns are composed of PDMS fibers decorated with vinylsiloxane mushroom shaped tips, which are additionally coated with an extremely soft and thin terminal layer of silicone based pressure sensitive adhesive. We demonstrated that mushroom tips coated with thin adhesive terminal layers can greatly enhance the adhesion through their optimal shape and enhanced load sharing. A high adhesion strength of 300 kPa together with superior durability on smooth surfaces are achieved, outperforming monolithic fibers by 35 times [ ].