Tree frog-inspired nanopillar arrays for enhancement of adhesion and friction

Effect of bionic hexagonal texture on squeezing films inside soft contacts with high adhesion and high friction

To understand the mechanisms of high friction and high adhesion in bioinspired textured surfaces under wet conditions, the evolution behavior of squeezing films across lubricated interfaces is experimentally investigated using optical interferometry. The results show that the splitting of the continuous large-scaled liquid film into numerous isolated micro zones is an important function of the hexagonal texture. Both the orientation and the size of the hexagonal texture have noticeable effects on the drainage rate: either downscaling the hexagonal texture or orienting the texture with two sides of each micro-hexagon parallel to the inclining direction could accelerate the draining process. While the draining process is completed, residual micro-droplets turn out to be entrapped within the contact regions of single hexagonal micro-pillars. The entrapped micro-droplets gradually shrink as the hexagonal texture downsizes. Moreover, a novel geometrical shape for the micro-pillared texture is proposed to improve the drainage efficiency.

Research status and development trend of frog-inspired robots

The frog-inspired robots with amphibious locomotion ability have greatest application prospects and practical value in the fields of resource exploration and environmental reconnaissance. Although frog-inspired robots have been of interest over many years, research on frog-inspired amphibious robots is still in its infancy. Since the locomotion mechanism is the basis for the research of frog-inspired amphibious robots, the research methods of the single motion mechanism of frogs are firstly inductive analyzed, and a reference scheme is proposed to inspire the research on the amphibious motion mechanism. Then, we collect and introduce a systematic discussion of the research status of frog-inspired robots according to the locomotion mode. The characteristics of the robots are analyzed from the aspects of design concept, structural characteristics, driving method, and motion performance. Finally, the technical challenges faced by the research on the frog-inspired robots are analyzed, and the development trend is predicted. The authors hope that this study can provide an informative reference for future research in the direction of frog-inspired amphibious robot.

Robust and Elevated Adhesion and Anisotropic Friction in a Bioinspired Bridged Micropillar Array

Bioinspired structured adhesives have promising applications in the fields of robotics, electronics, medical engineering, and so forth. The strong adhesion and friction as well as the durability of bioinspired hierarchical fibrillar adhesives are essential for their applications, which require fine submicrometer structures to stay stable during repeated use. Here, we develop a bioinspired bridged micropillars array (BP), which realizes a 2.18-fold adhesion and a 2.02-fold friction as compared to that of poly(dimethylsiloxane) (PDMS) original micropillar arrays. The aligned bridges offer BP strong anisotropic friction. The adhesion and friction of BP can be finely regulated by changing the modulus of the bridges. Moreover, BP shows strong adaptability to surface curvature (ranging from 0 to 800 m^-1), excellent durability over 500 repeating cycles of attachment/detachment, and self-cleaning ability. This study presents a novel approach for designing robust structured adhesives with strong and anisotropic friction, which may find applications in areas such as climbing robots and cargo transportation.

Mathematical model and nanoindentation properties of the claws of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae)

Scanning electron microscopy (SEM) was used to observe the macroscopic, microscopic, and cross‐sectional structures of the claws of Cyrtotrachelus buqueti Guer (Coleoptera: Curculionidae), and a mathematical model of a claw was used to investigate the structure–function relationships. To improve the quality of the SEM images, a non‐local means (NLM) algorithm and an improved NLM algorithm were applied. After comparison and analysis of five classical edge‐detection algorithms, the boundaries of the structural features of the claw were extracted based on a B‐spline wavelet algorithm, and the results showed that the variable curvature of the beetle claw enhances its adhesion force and improves its strength. Adhesion models of the claw were established, and the mechanical properties of its biomaterials were measured using nanoindentation. Considering that the presence of water can affect the hardness and Young's modulus, both ‘dry’ and ‘wet’ samples were examined. For the dry samples, the hardness and Young's modulus were 0.197 ± 0.074 GPa and 1.105 ± 0.197 GPa, respectively, whereas the respective values for the wet samples were both lower at 0.071 ± 0.030 GPa and 0.693 ± 0.163 GPa. This study provides data that can inform the design of climbing robots.