The remarkable ability of geckos to climb and run rapidly on walls and ceilings has recently received considerable interest from many researchers. Significant progress has been made in understanding the attachment and detachment mechanisms and the fabrication of articulated gecko-inspired adhesives and structured surfaces. This article reviews the direct experiments that have investigated the properties of gecko hierarchical structures, i.e., the feet, toes, setae, and spatulae, and the corresponding models to ascertain the mechanical principles involved. Included in this review are reports on gecko-inspired surfaces and structures with strong adhesion forces, high ratios of adhesion and friction forces, anisotropic hierarchical structures that give rise to directional adhesion and friction, and “intelligent” attachment and detachment motions.

Quartz crystal microbalance (QCM) is a nondestructive technique in investigating the physical properties of solid-liquid interfacial layer in situ. It has the capability of quantifying the extremely tiny force change occurring on the interface by measuring the frequency shift $\Delta f$ and the energy dissipation change $\Delta \mathrm{D}$ (or the half-bandwidth variation $\Delta \Gamma$ ). The quantitative analysis of QCM results greatly depends on the theoretical models, whose development could generally expand the comprehension of the properties at the interfaces and the application of QCM. In the paper, the progresses on the theory and applications of QCM are reviewed. The commonly used theoretical models for a single layer in the gas/liquid phase are essential for QCM in the fields of biosensor application, surface chemistry study, and interfacial rheology, such as the adsorption of proteins, the polymer and surfactants, and the viscoelastic properties of the interfacial liquid layer. The advanced models, incorporating the effects of boundary slip, surface roughness, microstructure, and micro/nanoscale confinement, are helpful for a better understanding and description of how these factors influence the various interfacial processes occurring on the solid-liquid interface, e.g., interfacial rheology and adsorption. The establishments of nanocell and the corresponding theoretical model make QCM a potential technique in studying the dynamic behavior of micro/nanoscale flow coupling with various surface effects by connecting a micro/nanofluidic channel to the nanocell.

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.