Functional integration is an inherent characteristic for multiscale structures of biological materials. In this contribution, we first investigate the liquid-solid adhesive forces between water droplets and superhydrophobic gecko feet using a high-sensitivity micro-electromechanical balance system. It was found, in addition to the well-known solid-solid adhesion, the gecko foot, with a multiscale structure, possesses both superhydrophobic functionality and a high adhesive force towards water. The origin of the high adhesive forces of gecko feet to water could be attributed to the high density nanopillars that contact the water. Inspired by this, polyimide films with gecko-like multiscale structures were constructed by using anodic aluminum oxide templates, exhibiting superhydrophobicity and a strong adhesive force towards water. The static water contact angle is larger than 150° and the adhesive force to water is about 66 μN. The resultant gecko-inspired polyimide film can be used as a "mechanical hand" to snatch micro-liter liquids. We expect this work will provide the inspiration to reveal the mechanism of the high-adhesive superhydrophobic of geckos and extend the practical applications of polyimide materials.

Solid-liquid-vapor interfaces dominated by the three-phase contact line, usually performing as the active center in reactions, are important in biological and industrial processes. In this contribution, we provide direct three-dimensional (3D) experimental evidence for the inside morphology of interfaces with either Cassie or Wenzel states at micron level using X-ray micro-computed tomography, which allows us to accurately "see inside" the morphological structures and quantitatively visualize their internal 3D fine structures and phases in intact samples. Furthermore, the in-depth measurements revealed that the liquid randomly and partly located on the top of protrusions on the natural and artificial superhydrophobic surfaces in Cassie regime, resulting from thermodynamically optimal minimization of the surface energy. These new findings are useful for the optimization of classical wetting theories and models, which should promote the surface scientific and technological developments.

Cracks are Janus-faced, which cause material failure on one hand and serve as a powerful approach for material processing on the other. To predict cracks and control them in a desired manner, foundational fracture mechanisms are continuously being pursued, based on simplified modes of planar cracks. In reality, cracks usually occur in a three-dimensional (3D) irregular manner. Prediction of 3D fractures is of particular significance for understanding the fundamental fracture mechanisms. However, controlling cracks in typical 3D modes is rare. Here we report that controllable 3D helical cracks on heterogeneous spindle knots are induced by biaxial thermal stresses. The thermal expansion mismatch between the tough core and brittle shell during the heating process generates biaxial stresses in the axial and circumferential directions. Surface cleavage and interface delamination driven by the release rate of elastic strain energy are harmonized due to the unique spindle geometry and cooperate to produce a 3D helical crack. This finding is helpful for understanding complex cracking mechanisms and provides a promising prospect for controlling or eliminating 3D cracks.

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Solid-liquid-vapor interfaces dominated by the three-phase contact line,u sually performing as the active center in reactions,a re important in biological and industrial processes.Inthis contribution, we providedirect three-dimensional (3D) experimental evidence for the inside morphology of interfaces with either Cassie or Wenzel states at micron level using X-ray micro-computed tomography,w hich allows us to accurately "see inside" the morphological structures and quantitatively visualizet heir internal 3D fine structures and phases in intact samples.F urthermore,t he in-depth measurements revealed that the liquid randomly and partly located on the top of protrusions on the natural and artificial superhydrophobic surfaces in Cassie regime,r esulting from thermodynamically optimal minimization of the surface energy. These new findings are useful for the optimization of classical wetting theories and models,which should promote the surface scientific and technological developments.