The increasing demands for adaptive interfacial control across harsh conditions, from deep-space microgravity to deep-sea hydrostatic pressure, have propelled bioinspired structural adhesion/friction materials (SAFMs) into a transformative scientific frontier. Guided by nature’s evolutionary masterstrokes, the hierarchical fibrillar architecture of the gecko enables anisotropic van der Waals adhesion, and the muscular-hydrodynamic suction synergies of the octopus have engineered interfaces with unprecedented environmental adaptability. Despite breakthroughs in robotics and biomedicine, synthetic SAFMs persistently lag behind their biological counterparts in three dimensions: structural hierarchy fidelity, dynamic stability under cross-media disturbance, and adaptability to concurrent multiple environments. Through a comparative analysis of biotic/abiotic mechanisms, we demonstrate how current state-of-the-art synthetic systems, which are often limited by single-environment optimization or manufacturing-compromised structural hierarchies, fail to match the robustness of natural systems. To overcome these barriers, we propose a codesigned framework that integrates multiple mechanism synergies, multiple functional material networks, and bioinspired fabrication technologies. By bridging these domains, the framework aims to realize multiple environmentally adaptive bioinspired adhesions/frictions that transcend current application silos from space environments that are tolerant of robotics for lunar exploration to self-adjusting biomedicine devices for health monitoring.

With the development of human spaceflight, the impact of the microgravity environment in space stations on the work and life of astronauts has received increasing attention. For astronauts, establishing stable and switchable attachments to multiple surfaces in an orbiting space station is important and yet a great challenge. Here, inspired by the variable stiffness structures of biological adhesion organs with different functional directions, a multi-modulus adhesive unit is designed. The low-modulus adhesive layer provides good adaptability by mimicking the soft bottom of the rock-climbing loach suction cups and the setae on the gecko’s toes; the high-modulus flat substrate provides good stiffness to suppress deformation; the elasticity adaption layer reduces preload required for attachment to uneven surfaces like gecko muscular tissues, and the detachment switch made from nylon rope allows switching the adhesion force by adjusting the angle of force. Experiments in simulated microgravity environments demonstrate the ability of the adhesive shoes to rapidly generate strong and switchable adhesion and friction on rough surfaces, and tests in China's space station show that adhesive shoes based on multi-mechanism adhesion are a viable option for lower limb muscle exercising.

The crawling process of snakes is known to have fascinating tribological phenomena, whereas investigations on their frictional properties depending on patterned cuticles are insufficient. In this study, we have designed and fabricated biomimetic microstructures inspired by the geometric microunits of Achalinus spinalis cuticle using polyurethane acrylate (PUA) material and performed its tribological analysis. The micro-morphology of this Achalinus-inspired textured polymer surface (AITPS) is characterized by the closely and evenly quasi-rectangular microgrooves, periodically arranged along certain orientations. We have compared the frictional performance of our fabricated AITPS with other competitive microstructure, using a smooth steel ball and commercial clay as an interacting surface. After performing massive friction tests with steel ball and clay, AITPS still maintains good resistance reduction performed compared to the patterned surface with straight microgrooves, which is most likely due to the reduction of actual contact areas at the frictional interface.

Adhesion achieved through feet setae is fundamental for gecko agilely maneuvering. Although diverse hypotheses have been proposed, none of them thoroughly explains the setae function, implying a kind of hybrid-mechanism-based adhesion in geckos. In addition to van der Waals interactions and capillary force, the electrostatic attraction that emerges from triboelectrification was suggested as a component of setae adhesion. Nevertheless, the contribution by electrostatic attraction to the total setae attachment is still controversial. In this study, we analyzed the occurrence of electrostatic attraction at gecko setae through experiments and model analyses. By touching the substrates with only ~1/70^th of the foot area, freely wall-climbing geckos developed tribocharge at their feet setae with a density of ~277 pC/mm², generating electrostatic attractions with a strength of ~4.4 mN/mm². From this perspective, the adhesion driven by triboelectrification could account for about 1% of total adhesion. Model analyses at spatula level indicated a similar result showing that the electrostatic force might account for ~3% of the adhesion that facilitates wall-climbing in geckos. The low contribution of the electrostatic force partly explains why geckos always face difficulty in maneuvering onto those substrates (e.g., teflon) where they could easily develop tribocharge but difficultly generate van der Waals force. However, long-range electrostatic forces may play other roles in a distance range where the van der Waals interaction cannot function. These findings not only add to our understanding of the mechanism of gecko adhesion, but also will help us advance gecko-inspired fibular adhesives.

Geckos’ ability to move on steep surfaces depends on their excellent adhesive structure, timely adjustments on locomotor behaviors, and elaborates control on reaction forces. However, it is still unclear how they can generate a sufficient driving force that is necessary for locomotion, while ensuring reliable adhesion on steep inclines. We measured the forces acting on each foot and recorded the contact states between feet and substrates when geckos encountered smooth inclination challenges ranging from 0° to 180°. The critical angles of the resultant force vectors of the front and hind-feet increased with respect to the incline angles. When the incline angle became greater than 120°, the critical angles of the front- and hind-feet were similar, and the averages of the critical angles of the front- and hind-feet were both smaller than 120°, indicating that the complicated and accurate synergy among toes endows gecko’s foot an obvious characteristic of “frictional adhesion” during locomotion. Additionally, we established a contact mechanical model for gecko’s foot in order to quantify the contribution of the frictional forces generated by the heel, and the adhesion forces generated by the toes on various inclines. The synergy between multiple contact mechanisms (friction or adhesion) is critical for the reliable attachment on an inclined surface, which is impossible to achieve by using a single-contact mechanism, thereby increasing the animal’s ability to adapt to its environment.

Hypothesis on electrostatic attraction mechanisms involving the hairy adhesion of climbing animals has been a matter of controversy for several years. The detection of tribocharge and forces at attachment organs of animals is a practical method of clarifying the dispute with respect to electrostatic attraction in the attachment of animals. Nonetheless, the tribo-electrification is rarely examined in the contact-adhesion of animals (especially in their free and autonomous attachment) due to the lack of available devices. Therefore, the present study involves establishing a method and an apparatus that enables synchronous detection of tribocharge and contact forces to study tribo-electrification in the free locomotion of geckos. A type of a combined sensor unit that consists of a three-dimensional force transducer and a capacitor-based charge probe is used to measure contact forces and tribocharge with a magnitude corresponding to several nano-Coulombs at a footpad of geckos when they climb vertically upward on an acrylic oligomer substrate. The experimental results indicate that tribocharge at the footpads of geckos is related to contact forces and contact areas. The measured charge allows the expectation of an exact attraction with magnitude corresponding to dozens of newtons per square meter and provides a probability of examining tribo-electrification in animal attachment from a macro level.

Many animals have the natural ability to move on various surfaces, such as those having different roughness and slope substrates, or even vertical walls and ceilings. Legged animals primarily attach to surfaces using claws, soft and hairy pads, or combinations of them. Recent studies have indicated that the frictional forces generated by these structures not only control the movement of animals but also significantly increase the reliability of their attachment. Moreover, the frictional forces of various animals have opposite characteristics and hierarchical properties from toe-to-toe and leg-to-leg. These opposite frictional forces allow animals to attach securely and stably during movement. The coordination of several attachment (adhesion) modes not only helps animals adhere, which would be impossible in single mode, but also increases the overall stability of the attachment (adhesion) system. These findings can help the design of highly adaptable feet for bionic robots in the near future.