Gecko Toe Research Articles

Switchable adhesion of gecko-inspired hierarchically wedge-mushroom-shaped surface

The outstanding adhesion ability of gecko is mainly attributed to its sophisticated hierarchical adhesive structures. The relationship between structure and function of gecko adhesion has been attracting scientific research interests. However, studies on the effect of the structural hierarchy on the interfacial switchable adhesion remain limited. In the present paper, a gecko toe-inspired hierarchically wedge-mushroom-shaped adhesive is fabricated. The first level is NdFeB particles decorated asymmetrical wedges, mimicking the lamellar structures on gecko toe. The asymmetry of the wedge can guarantee the anisotropic adhesion in different directions. The second level is the mushroom-shaped fibrils on the sloping surface of the wedges, mimicking gecko seta arrays. The mushroomed fibrils can be used to enhance the normal interfacial adhesion. The fabricated hierarchical adhesive possesses the adhesion advantages of both the wedge- and mushroom-shaped structures. Switchable adhesion can be realized both by loading-dragging-pulling (LDP) mode and actuation of external magnetic field. Specially, the switchable adhesion achieved under the control of magnetic field can overcome the drawback of shear induced adhesion limit of normal direction in LDP mode. Furthermore, the fabricated hierarchical adhesive can realize releasing ultra-light objects and highly efficient self-cleaning ability. The hierarchical adhesive inspired by gecko demonstrated in this study may have potential applications in the fields of micro /nano manufacturing and flexible devices.

Developmental Patterns Underlying Variation in Form And Function Exhibited by House Gecko Toe Pads.

Adhesive toe pads have evolved numerous times over lizard evolutionary history, most notably in geckos. Despite significant variation in adult toe pad morphology across independent origins of toe pads, early developmental patterns of toe pad morphogenesis are similar among distantly related species. In these distant phylogenetic comparisons, toe pad variation is achieved during the later stages of development. We aimed to understand how toe pad variation is generated among species sharing a single evolutionary origin of toe pads (house geckos-Hemidactylus). We investigated toe pad functional variation and developmental patterns in three species of Hemidactylus, ranging from highly scansorial (H. platyurus), to less scansorial (H. turcicus), to fully terrestrial (H. imbricatus). We found that H. platyurus generated significantly greater frictional adhesive force and exhibited much larger toe pad area relative to the other two species. Furthermore, differences in the offset of toe pad extension phase during embryonic development results in the variable morphologies seen in adults. Taken together, we demonstrate how morphological variation is generated in a complex structure during development and how that variation relates in important functional outcomes.

Detachment Behavior of Gecko Toe in Functional Strategies for Bionic Toe

Detachment Behavior of Gecko Toe in Functional Strategies for Bionic Toe

Early burst of parallel evolution describes the diversification of gecko toe pads

IntroductionSimilar traits appearing in distantly related organisms have intrigued scientists for generations. While anole lizards of the Caribbean are often touted as a classic example of repeated evolution, the adhesive toe pads of gecko lizards are an equally striking yet underappreciated example of relatedly evolved traits. The strikingly diverse toe pads of gecko lizards (Gekkota) have been gained and lost multiple times throughout the clade’s evolutionary history. In addition, distantly related genera have repeatedly evolved remarkably similar morphologies. This complicated combination of divergent and repeated evolution represents a useful system for understanding the evolution of complex structures, including repeated adaptation.MethodsUsing geometric morphometrics, we evaluated parallel morphological differences across families and expanded existing approaches fitting models of trait evolution to use geometric morphometric data. Adapting the use of phylogenetic independent contrasts for shape data, we conducted a node height test to investigate how toe pad shape has evolved across geckos.ResultsWe found multiple examples of significant parallel differences in toe pad morphology and support for a model of early burst morphological evolution.DiscussionOur results suggest the diversification of Gekkotan toe pads included repeated parallel changes from padless ancestral morphologies to derived pad bearing morphologies. This morphological diversification occurred rapidly early in the diversification of gecko families and genera and slowed more recently, during diversification within genera.

Machine Learning-Based Shear Optimal Adhesive Microstructures with Experimental Validation.

Bioinspired fibrillar structures are promising for a wide range of disruptive adhesive applications. Especially micro/nanofibrillar structures on gecko toes can have strong and controllable adhesion and shear on a wide range of surfaces with residual-free, repeatable, self-cleaning, and other unique features. Synthetic dry fibrillar adhesives inspired by such biological fibrils are optimized in different aspects to increase their performance. Previous fibril designs for shear optimization are limited by predefined standard shapes in a narrow range primarily based on human intuition, which restricts their maximum performance. This study combines the machine learning-based optimization and finite-element-method-based shear mechanics simulations to find shear-optimized fibril designs automatically. In addition, fabrication limitations are integrated into the simulations to have more experimentally relevant results. The computationally discovered shear-optimized structures are fabricated, experimentally validated, and compared with the simulations. The results show that the computed shear-optimized fibrils perform better than the predefined standard fibril designs. This design optimization method can be used in future real-world shear-based gripping or nonslip surface applications, such as robotic pick-and-place grippers, climbing robots, gloves, electronic devices, and medical and wearable devices.

Biomimetic multi-organisms providing a new dawn for intelligent soft robots

Designing more intelligent bio-inspired soft robots to effectively convert output stimulus into controllable and programmable deformations and motions is highly desirable. This Preview reviews the recent breakthroughs in biomimetic multi-organisms that achieve soft climbing robots with intelligent locomotion. Designing more intelligent bio-inspired soft robots to effectively convert output stimulus into controllable and programmable deformations and motions is highly desirable. This Preview reviews the recent breakthroughs in biomimetic multi-organisms that achieve soft climbing robots with intelligent locomotion. Gecko-and-inchworm-inspired untethered soft robot for climbing on walls and ceilingsSun et al.Cell Reports Physical ScienceJanuary 17, 2023In BriefA synergy of biological principles is harnessed by Sun et al. for a bioinspired, untethered soft robot with hierarchical plantar microstructures and flexible actuators. The robot can emulate the dynamic attachment/detachment of the gecko toe and the striding gait of the inchworm and can climb on walls and ceilings with a magnetic-field-assisted photo-driven strategy. Full-Text PDF Open Access

Phase Change Hydrogels for Bio‐Inspired Adhesion and Energy Exchange Applications

AbstractThe adhesion strategies of the gecko's toe through surface adaptation of spatulas to increase contact area and the snail's epiphragm via dehydration‐induced solidification to lock interfaces are combined to design a class of adhesion‐switchable hydrogels. The hydrogels are made via incorporating CH3COONa·3H2O salt (SA) into polyacrylamide (PAM) aqueous networks to construct supersaturated and stimuli‐responsive phase change materials (PAM‐SA). The crystallization dramatically strengthens the mechanical properties, and tensile Young's moduli are 340.7 and 0.1 MPa for crystalline C‐PAM‐SA‐120% and soft PAM hydrogel. As a result, PAM‐SA‐120% shows excellent adhesive performance (adhesion strength, 348 kPa) compared with PAM hydrogel adhesive (adhesion strength, 7 kPa). The stimuli‐induced crystallization from H‐PAM‐SA‐120% phase change hydrogels releases thermal controllably, which can be utilized for thermochromic materials and thermotherapy.

Dancing feet and gecko toes

Groove is a feeling On the dance floor, the warmth of a “disco inferno” can certainly be felt, even when its flames are invisible. At least that’s what a recent study on inaudible bass and dancing found. Dance floor science is one subject of study at LIVELab, a unique fusion of performance hall and research facility, which is part of the McMaster Institute for Music and the Mind. Centered on exploring the interplay of science and the arts, LIVELab has the capability to manipulate acoustics in real time while recording the motion and physiological responses of both performers and audience members. Recently, LIVELab hosted an electronic music concert to study whether deep bass contributes to groove, even if inaudible. Every 2.5 min of the continuous 55 min concert, the researchers dropped a beat so low— 8–37 Hz—that it was below the range of human hearing. The lucky dance floor participants,

Dancing feet and gecko toes

Dancing feet and gecko toes

Reversible Adhesive Bio-Toe with Hierarchical Structure Inspired by Gecko

The agile locomotion of adhesive animals is mainly attributed to their sophisticated hierarchical feet and reversible adhesion motility. Their structure-function relationship is an urgent issue to be solved to understand biologic adhesive systems and the design of bionic applications. In this study, the reversible adhesion/release behavior and structural properties of gecko toes were investigated, and a hierarchical adhesive bionic toe (bio-toe) consisting of an upper elastic actuator as the supporting/driving layer and lower bionic lamellae (bio-lamellae) as the adhesive layer was designed, which can adhere to and release from targets reversibly when driven by bi-directional pressure. A mathematical model of the nonlinear deformation and a finite element model of the adhesive contact of the bio-toe were developed. Meanwhile, combined with experimental tests, the effects of the structure and actuation on the adhesive behavior and mechanical properties of the bio-toe were investigated. The research found that (1) the bending curvature of the bio-toe, which is approximately linear with pressure, enables the bio-toe to adapt to a wide range of objects controllably; (2) the tabular bio-lamella could achieve a contact rate of 60% with a low squeeze contact of less than 0.5 N despite a ±10° tilt in contact posture; (3) the upward bending of the bio-toe under negative pressure provided sufficient rebounding force for a 100% success rate of release; (4) the ratio of shear adhesion force to preload of the bio-toe with tabular bio-lamellae reaches approximately 12, which is higher than that of most existing adhesion units and frictional gripping units. The bio-toe shows good adaptability, load capacity, and reversibility of adhesion when applied as the basic adhesive unit in a robot gripper and wall-climbing robot. Finally, the proposed reversible adhesive bio-toe with a hierarchical structure has great potential for application in space, defense, industry, and daily life.

Near-infrared responsive gecko-inspired flexible arm gripper

Inspired by the microstructure of gecko toes, a drivable bionic gecko toe adhesion surface with double-layer structure was designed and fabricated. The driving ability is derived from the volume shrinkage of the dehydrated hydrogel after the driving hydrogel layer is irradiated by near-infrared light (808 nm) (the temperature of the single-layer hydrogel can be increased from 17.9 °C to 107 °C within 30s, and the curling angle can be curled by 0°–180°, similar to the folded state.), and another layer with a microstructure similar to gecko toes can withstand a maximum shear force of 22.4N/cm−2. The different properties of the two layers are combined together to achieve a reversible transition of adhesion/desorption similar to the gecko walking process. The double-layer structure of the drivable bionic gecko toe adhesion surface was structurally optimized to prepare a four-arm gripper that could grasp/release only by unilateral irradiation. This bilayer-structured bionic gecko toe adhesion surface has great design potential, and in the future, it is hoped that it can provide insights into the preparation of large-actuated remote-controlled robots and fast-actuated soft robots.

Polyvinyl chloride gel based electro-active switchable bio-inspired adhesive

Controlled attachment and detachment mechanisms of geckos have been the focus of attention for decades. Although great progress has been made in the fabrication of biomimetic adhesive materials, dynamically switchable adhesion is still challenging. In this work, inspired by the active muscular locomotion of gecko toes, a novel switchable electro-active adhesive based on polyvinyl chloride (PVC) gel was successfully prepared, including PVC gel active backing layer and a passive PVC fibrillar adhesive layer.The performance of PVC gel actuator, adhesive, and electro-active adhesive are stable. Due to the active backing layer and adhesive layer are all made by PVC gel, the strong bonding between two layers was achieved. Compared with reported reversible adhesive, it exhibited greater adhesion force and response speed.Furthermore, a flexible gripper was made, and the grasping test was successfully carried out.This work provides a new technology for micro/nano manipulation, transfer printing, and climbing robot applications.

Effect of the Structural Characteristics on Attachment-Detachment Mechanics of a Rigid-Flexible Coupling Adhesive Unit.

The terminal toes of adhesive animals are characterized by rigid-flexible coupling, and their structure–function relationship is an urgent problem to be solved in understanding bioinspired adhesive systems and the design of biomimetic adhesive units. In this paper, inspired by the rigid-flexible coupling adhesive system of the gecko toe, a rigid-flexible coupling adhesive unit was designed, the interface strength of the adhesives under different preloads was tested, and the model and analysis method of the compression and peeling process of the rigid-flexible coupling adhesive unit was established. Meanwhile, combined with the experimental test, the effect of the coupling mechanism of the rigid-flexible structure on the interfacial stress and the final peeling force during the compression and peeling process of the adhesive unit was studied. The research found that the length of the adhesive unit L has no apparent effect on the normal peel force of the system within a specific range, and the normal peeling force increases linearly with the increase in the compression force P; while the influence of the inclination angle θ0 of the adhesive unit and the thickness of the rigid backing layer hb on the final normal peeling force of the system presents nonlinear characteristics, when the inclination angle θ0 of the adhesive unit is 5°, and the thickness of the rigid backing layer hb is 0.2 mm or 0.3 mm, the normal peel force and the ratio of adhesion force to preload the system reaches its maximum value. Compared with the flexible adhesive unit, the compressed zone formed by the rigid-flexible coupling adhesive unit during the same compression process increased by 6.7 times, while under the same peeling force, the peel zone increased by 8 times, and the maximum normal tensile stress at the peeling end decreased by 20 times. The rigid-flexible coupling mechanics improves the uniformity of the contact stress during the compression and peeling process. The research results provide guidelines for the design of the rigid-flexible coupling adhesive unit, further providing the end effector of the bionic wall-climbing robot with a rigid-flexible coupled bionic design.

An easy-coating, versatile, and strong soy flour adhesive via a biomineralized structure combined with a biomimetic brush-like polymer

The development of a formaldehyde-free soy flour adhesive with good coating ability, mildew resistance, and flame retardancy while maintaining high bond strength, is urgent but presents a challenge. Inspired by the strong adhesive performance derived from the brush-like structure of gecko toes, a brush-like polymer with a catechol group was synthesized to improve the adhesive behavior of soy flour adhesives. Prompted by the high strength derived from the biomineralized structure of oysters, Ca3(PO4)2 was sedimented on soy protein and combined with the brush-like polymer to construct a biomineralized structure, which endowed the resultant adhesive with mildew resistance and flame retardancy while maintaining high bond strength. The dry and wet shear strengths of the bonded plywood by the resultant adhesive increased by 118.8 % and 750 % relative to those of the unmodified adhesive. Moreover, the resultant adhesive possessed outstanding coating performance, superior mildew resistance (no mildew for 7 d), and high toughness (4.05 J of the work of adhesion). The limiting oxygen index of the resultant adhesive was increased from 26.4 % to 30.1 %. Thus, developing a system combined with a bioinspired biomineralized strategy and a brush-like polymer can potentially offer a template for the fabrication of hydrogels, functionalized surfaces, and composite materials.

Switchable Adhesion on Curved Surfaces Mimicking the Coordination of Radial-Oriented Spatular Tips and Motion of Gecko Toes.

Bio-inspired structured adhesives have promising applications in many fields, like biomedicine, robotics, and aerospace. However, achieving robust and switchable adhesion in structured adhesives on non-planar surfaces remains highly challenging. Inspired by the gripping and rolling motions of gecko toes, a strong and switchable adhesive, which comprises a pillar array with radial-oriented spatular tips and is named as PROST, is developed. PROST possesses a robust adhesion on flat surfaces and doubles its adhesion on curved surfaces. Moreover, in situ and fast adhesion switching of PROST on flat/curved surfaces in dry and wet conditions has been realized by solvent stimulation, mimicking the bending locomotion of gecko toes. The work here provides a new strategy for designing controllable adhesion on curved substrates.

Gecko inspired reversible adhesion via quantum dots enabled photo-detachment

• High efficiency photo driven reversible adhesion smart surface inspired by gecko. • The smart surface could increase up to 88.5 °C in 60 s trigger by MoO 3 dots. • The mechanism of the reversible process were discussed. Inspired by the detachment behavior of gecko toe valgus, a reversible dry adhesive surface was developed, which is composed of polydimethylsiloxane (PDMS) micropillar arrays and MoO 3-x quantum dots (MoO 3-x QDs). The reversibility of adhesion is caused by the thermal expansion of the overall structure of the PDMS micropillar array due to the thermal response of MoO 3-x QDs to external stimuli. Under infrared laser irradiation, the interface temperature of MoO 3-x -PDMS surface increased from 20 °C to 88.5 °C in 60 s. The MoO 3-x QDs-induced photothermal conversion facilitate the reduction of the real contact fraction between the bio-inspired micropillar arrays and the opposing/target surface, resulting in a significant decrease in adhesion. This work demonstrates a new strategy for realizing remote control of smart adhesives or surfaces. The mechanism elucidated in this work may find a broad application, such as in climbing robots, micro-manipulation/micro-selection in advanced manufacturing, active self-cleaning surface for solar panels, fibrillar dry adhesives and touch sensitive grippers in outer space explorations, and more.

Cytoskeleton Markers in the Spinal Cord and Mechanoreceptors of Thick-Toed Geckos after Prolonged Space Flights.

Spaceflight may cause hypogravitational motor syndrome (HMS). However, the role of the nervous system in the formation of HMS remains poorly understood. The aim of this study was to estimate the effects of space flights on the cytoskeleton of the neuronal and glial cells in the spinal cord and mechanoreceptors in the toes of thick-toed geckos (Chondrodactylus turneri GRAY, 1864). Thick-toed geckos are able to maintain attachment and natural locomotion in weightlessness. Different types of mechanoreceptors have been described in the toes of geckos. After flight, neurofilament 200 immunoreactivity in mechanoreceptors was lower than in control. In some motor neurons of flight geckos, nonspecific pathomorphological changes were observed, but they were also detected in the control. No signs of gliosis were detected after spaceflight. Cytoskeleton markers adequately reflect changes in the cells of the nervous system. We suggest that geckos’ adhesion is controlled by the nervous system. Our study revealed no significant disturbances in the morphology of the spinal cord after the prolonged space flight, supporting the hypothesis that geckos compensate the alterations, characteristic for other mammals in weightlessness, by tactile stimulation.

A tough, anti-mildew and anti-counterfeiting soybean protein adhesive enhanced by gecko-inspired functional fiber and bio-based epoxide

The development of efficient and sustainable formaldehyde-free adhesives has become an important strategy to solve the problems of environmental pollution, resource depletion and clean production. It is a promising and challenging task to prepare multifunctional adhesives with high adhesive strength from soybean protein (SP), an abundant and sustainable biomaterial that is largely produced from agricultural waste. Inspired by gecko toe, carboxylated paper fiber (CPF) anchored by MOFs (namely UiO66-NH2@CPF) was constructed as micro-nano structure reinforcing phase, and resveratrol-based epoxide (RE) was employed as crosslinking agent to formulate a series of SP-based green adhesives. In particular, plywood bonded with SP/RE13/UiO66-NH2@CPF1.5 presented the maximum dry/wet shear strength to 2.52 MPa and 1.43 MPa, which increased by 90.9% and 457% compared to that of adhesive made with SP alone, respectively. SP/RE13/UiO66-NH2@CPF1.5 displayed a 92.02% residual rate (in water at 60 °C for 6 h), showing excellent bonding strength and water resistance. More importantly, SP/RE13/UiO66-NH2@CPF1.5 successfully inhibited the invasion of mold, enabling to extend its shelf time to 12 h. In addition, it showed excellent fluorescent properties, exposing great potential in anti-counterfeiting of wood-based composite materials and information transmission. The development of SP-based adhesives improved the added value of industrial by-products, which not only met the demand for green and sustainable development, but also contributed to clean production by providing environmental and economic benefits along with excellent performance.

And thereby hangs a tail: morphology, developmental patterns and biomechanics of the adhesive tails of crested geckos (Correlophus ciliatus).

Among the most specialized integumentary outgrowths in amniotes are the adhesive, scale-like scansors and lamellae on the digits of anoles and geckos. Less well-known are adhesive tail pads exhibited by 21 gecko genera. While described over 120 years ago, no studies have quantified their possible adhesive function or described their embryonic development. Here, we characterize adult and embryonic morphology and adhesive performance of crested gecko (Correlophus ciliatus) tail pads. Additionally, we use embryonic data to test whether tail pads are serial homologues to toe pads. External morphology and histology of C. ciliatus tail pads are largely similar to tail pads of closely related geckos. Functionally, C. ciliatus tail pads exhibit impressive adhesive ability, hypothetically capable of holding up to five times their own mass. Tail pads develop at approximately the same time during embryogenesis as toe pads. Further, tail pads exhibit similar developmental patterns to toe pads, which are markedly different from non-adhesive gecko toes and tails. Our data provide support for the serial homology of adhesive tail pads with toe pads.

Strategic strengthening of the interfacial transition zone (ITZ) between microfiber and cement paste matrix with carbon nanofibers (CNFs)

The interfacial transition zone (ITZ) governs the mechanical properties and durability of fiber-reinforced cement-based composites. It has been reported that strategic strengthening of the ITZ by simple coating of carbon nanofibers (CNFs) on microfibers resulted in a 22% enhancement of the fiber/matrix bond. In the current study, ingenious methods were used to characterize such CNF-reinforced ITZ (CNF-ITZ). Results show that strategic application of CNFs greatly densified the ITZ with much reduced voids and defects. A distinctive hairy microstructure, resembling the setae on the toes of geckos, and less portlandite were found in the CNF-ITZ. The indentation hardness and indentation modulus were enhanced in both the radial and the tangential directions. The resulting CNF-reinforced ITZ is tougher and stronger with improved mechanical properties against deformation and cracking, which leads to enhanced fiber/matrix bond and elevated load transfer efficiency between fiber and matrix.