Geckos have the extraordinary ability to prevent their sticky feet from fouling while running on dusty walls and ceilings. Understanding gecko adhesion and self-cleaning mechanisms is essential for elucidating animal behaviours and rationally designing gecko-inspired devices. Here we report a unique self-cleaning mechanism possessed by the nano-pads of gecko spatulae. The difference between the velocity-dependent particle-wall adhesion and the velocity-independent spatula-particle dynamic response leads to a robust self-cleaning capability, allowing geckos to efficiently dislodge dirt during their locomotion. Emulating this natural design, we fabricate artificial spatulae and micromanipulators that show similar effects, and that provide a new way to manipulate micro-objects. By simply tuning the pull-off velocity, our gecko-inspired micromanipulators, made of synthetic microfibers with graphene-decorated micro-pads, can easily pick up, transport, and drop-off microparticles for precise assembling. This work should open the door to the development of novel self-cleaning adhesives, smart surfaces, microelectromechanical systems, biomedical devices, and more.

Gecko adhesion has inspired the fabrication of various dry adhesive surfaces, most of which are developed to be used under atmospheric conditions. However, applications of gecko-inspired surfaces can be expanded to vacuum and even space environment due to the characteristics of van der Waals interactions, which are always present between materials regardless of the surrounding environment. In this paper, a controllable, anisotropic dry adhesion in vacuum is demonstrated with gecko-inspired wedged dry adhesive surfaces fabricated using an ultraprecision diamond cutting mold. The adhesion and friction properties of the wedge-structured surfaces are systematically characterized in loading-pulling mode and loading-dragging-pulling mode. The surfaces show significant anisotropic adhesion (P ad ≈ 10.5 kPa vs P ad ≈ 0.7 kPa) and friction (P f ≈ 50 kPa vs P f ≈ 30 kPa) when actuated in gripping and releasing direction, respectively. The wedge-structured surfaces in vacuum show comparable properties as exposed in atmosphere. A three-legged gripper is designed to pick up, hold, and release a patterned silicon wafer in vacuum. The study demonstrates a green, high-yield, and low-cost method to fabricate a reliable and durable mold for gecko inspired anisotropic dry adhesive surfaces and the potential application of dry adhesive surface in vacuum.

The gecko exhibits remarkably swift and reliable climbing ability on most surfaces in nature. Numerous studies have been conducted to determine the underlying mechanisms of gecko adhesion in order to realise controllable gecko-inspired handling applications. This paper, reviews recent developments in the field of gecko-inspired dry adhesive surfaces from fabrication to application. First, the gecko adhesion progress, from the adhesive tools and the source of adhesion to the underlying mechanisms of tuning contact area and peeling behavior, is introduced. Then, the design and fabrication of gecko-inspired dry adhesive surfaces are comprehensively reviewed according to the three features of gecko adhesion, namely adaptability, controllability, and self-cleaning. Further, existing test methods for adhesion, friction and anisotropy are summarised, and the influences of test conditions such as the stiffness of test system, the area of the samples and the experimental environment are discussed. Finally, applications of robots and grippers based on the flexibly controllable adhesion and friction of gecko-inspired dry adhesive surfaces as well as novel controllable functional adhesive surfaces are introduced, and the associated control mechanisms are summarised.

Forces acted on legs of water-walking arthropods with weights in dynes are of great interest for entomologist, physicists, and engineers. While their floating mechanism has been recognized, the in vivo leg forces stationary have not yet been simultaneously achieved. In this study, their elegant bright-edged leg shadows are used to make the tiny forces visible and measurable based on the updated Archimedes' principle. The force was approximately proportional to the shadow area with a resolution from nanonewton to piconewton/pixel. The sum of leg forces agreed well with the body weight measured with an accurate electronic balance, which verified updated Archimedes' principle at the arthropod level. The slight changes of vertical body weight focus position and the body pitch angle have also been revealed for the first time. The visualization of tiny force by shadow is cost-effective and very sensitive and could be used in many other applications.

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