Nature-inspired reentrant surfaces

Reentrant feature widely exists in natural structures ranging from mushroom, overhang, undercut, trapezoid, sphere, spatula and taper to sharp edge, and has triggered a biomimetic design revolution of functional surfaces for extreme repellency to fluid foulants, directional fluid navigation, and strong adaptive adhesion. In this Review, we discuss how the bionic introduction of reentrant feature on a surface mediates fluid wetting, contact line motion, as well as solid adhesion. We briefly introduce nature-inspired design principles from representative reentrant surfaces on the springtail, gecko, and pitcher plant. Through quantitatively associating microscopic structural parameters of reentrant feature, including angle, shape, diameter, thickness, sharpness and anisotropy, with macroscopically visible wetting and adhesion properties, we evaluate how the design of reentrant feature can enable exceptional superomniphobicity, strong adaptive adhesion, and directional fluidic navigation, promising an effective guidance for the creation of superomniphobic surface, fluid-navigation surface, adhesive surface or their combinations. The realization of the reentrant surfaces benefits from the rapid development of cuttingedge manufacturing technologies, such as 3D printing, lithography, microfluidics, self-assembly, and template-assisted soft replication. We finally provide potential applications of reentrant surfaces, as well as scientific and technological challenges and opportunities.