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Structural hierarchy of the gecko adhesive system. Images (a,b) provided by Mark Moffett. (a) Ventral view of a tokay gecko (Gekko gecko) climbing a vertical glass surface. (b) Ventral view of the foot of a tokay gecko, showing a mesoscale array of seta-bearing scansors (adhesive lamellae). (c) Microscale array of setae are arranged in a nearly grid-like pattern on the ventral surface of each scansor. In this scanning electron micrograph, each diamond-shaped structure is the branched end of a group of four setae clustered together in a tetrad. (d ) Cryo-SEM image of a single gecko seta (image by S. Gorb and K. Autumn). Note individual keratin fibrils comprising the setal shaft. (e) Nanoscale array of hundreds of spatular tips of a single gecko seta. ( f ) Synthetic spatulae fabricated from polyimide at UC Berkeley in the laboratory of Ronald Fearing using nanomoulding (Campolo et al. 2003).
Source publication
If geckos had not evolved, it is possible that humans would never have invented adhesive nanostructures. Geckos use millions of adhesive setae on their toes to climb vertical surfaces at speeds of over 1ms-1. Climbing presents a significant challenge for an adhesive in requiring both strong attachment and easy rapid removal. Conventional pressure-s...
Contexts in source publication
Context 1
... single seta (figure 1d ) of the tokay gecko ( figure 1a) is approximately 110 mm in length and 4.2 mm in diameter (Ruibal & Ernst 1965;Russell 1975;Williams & Peterson 1982). Setae are similarly oriented and uniformly distributed in arrays (figure 1c) on approximately 20 leaf-like scansors of each toe (figure 1b). ...
Context 2
... the unloaded state, gecko setae are recurved proximally (towards the animal's body), with the tips bearing the spatular nanoarrays misaligned with the substrate. (In figure 1d, the left edge of the figure represents the approximate orientation of a vertical surface relative to an unloaded seta during climbing.) When the toes of the gecko are planted, the setae bend out of this resting state, flattening the stalks between the toe and the substrate such that their tips point distally (away from the animal's body). ...
Similar publications
The study of the adhesion of millions of setae on the toes of geckos has been advanced in recent years with the emergence of new technology and measurement methods. The theory of the mechanism of adhesion by van der Waals forces is now accepted and broadly understood. However, this paper presents limitations of this theory and gives a new hypothesi...
Conventional pressure sensitive adhesives (PSAs) are fabricated from soft viscoelastic materials that satisfy Dahlquist's criterion for tack with a Young's modulus (E) of 100 kPa or less at room temperature and 1 Hz. In contrast, the adhesive on the toes of geckos is made of beta-keratin, a stiff material with E at least four orders of magnitude gr...
Citations
... [3][4][5][6][7][8][9] One of the driving forces for this is that dispersion interactions have been found to be responsible for many important chemical phenomena, including ligand binding, 10,11 catalytic reaction processes, 12,13 stacking in 2D materials 14,15 and, at macroscopic scales, the adhesion of geckos to walls. 16,17 In particular, for non-covalent interactions (NCIs), the necessity of dispersion effects cannot be overstated for correctly predicting the properties and behavior of molecules. However, for theoretical models to include dispersion effects, the models must explicitly include electron correlations within the computation. ...
In light of the recent discrepancies reported between fixed node diffusion Monte Carlo and local natural orbital coupled cluster with single, double, and perturbative triples [CCSD(T)] methodologies for non-covalent interactions in large molecular systems [Al-Hamdani et al., Nat. Commun. 12, 3927 (2021)], the applicability of CCSD(T) is assessed using a model framework. The use of the semi-empirical π-space only Pariser–Parr–Pople (PPP) model for studying large molecules is critically examined and is shown to recover both bandgap closure as system size increases and long range dispersive behavior of r⁻⁶ with increasing separation between monomers. Since bandgap closure in systems with long-range Coulomb interactions is problematic for perturbative methods, such as CCSD(T), this model, therefore, serves as a testing ground for such methods, enabling them to be benchmarked with high-order CC methods, which are not possible with ab initio Hamiltonians. Using the PPP model, coupled cluster methodologies, CCSDTQ and CCSDT(Q), are then used to benchmark CCSDT and CCSD(T) methodologies for non-covalent interactions in large one- and two-dimensional molecular systems up to the dibenzocoronene dimer. We show that CCSD(T) demonstrates no signs of overestimating the interaction energy for these systems. Furthermore, by examining the Hartree–Fock HOMO–LUMO gap of these large molecules, the perturbative treatment of the triples contribution in CCSD(T) is not expected to cause problems for accurately capturing the interaction energy for system sizes up to at least circumcoronene.
... 3-9 One of the driving forces for this is that dispersion interactions have been found to be responsible for many important chemical phenomena, including ligand binding, 10,11 catalytic reaction processes, 12,13 2D materials 14,15 and, at macroscopic scales, the adhesion of geckos to walls. 16,17 Particularly for non-covalent interactions (NCI), the necessity of dispersion effects cannot be overstated for correctly predicting the properties and behavior of molecules. However, for theoretical models to include dispersion effects, the models must explicitly include electron correlations within the computation. ...
In light of the recent discrepancies reported between fixed node diffusion Monte Carlo and local natural orbital coupled cluster with single, double and perturbative triples (CCSD(T)) methodologies for non-covalent interactions in large molecular systems [Al-Hamdani et al., Nat. Comm., 2021, 12, 3927], the applicability of CCSD(T) is assessed using a model framework. The use of the Pariser-Parr-Pople (PPP) model for studying large molecules is critically examined and is shown to recover both bandgap closure as system size increases and long range dispersive behavior of r^-6 with increasing separation between monomers, in corollary with real systems. Using the PPP model, coupled cluster methodologies, CCSDTQ and CCSDT(Q), are then used to benchmark CCSDT and CCSD(T) methodologies for non-covalent interactions in large one- and two-dimensional molecular systems up to the dibenzocoronene dimer. We show that CCSD(T) demonstrates no signs of overestimating the interaction energy for these systems. Furthermore, by examining the Hartree-Fock HOMO-LUMO gap of these large molecules, the perturbative treatment of the triples contribution in CCSD(T) is not expected to cause problems for accurately capturing the interaction energy for system sizes up to at least circumcoronene.
... To address these key issues, many works on creating reversible adhesives are focused on controlling the contact geometry or the elastic properties of adhesive materials. For example, micropillars with various geometries and aspect ratios can be patterned on the adhesive layer to tune adhesion strength and toughness [15][16][17][18][19][20][21]. Controlling adhesive geometry or stiffness also tunes crack dynamics and adhesion performance. ...
Metamaterial design approaches, which integrate structural elements into material systems, enable the control of uncommon behaviours by decoupling local and global properties. Leveraging this conceptual framework, metamaterial adhesives incorporate nonlinear cut architectures into adhesive films to achieve unique combinations of adhesion capacity, release, and spatial tunability by controlling how cracks propagate forward and in reverse directions during separation. Here, metamaterial adhesive designs are explored with triangular cut features while integrating hierarchical and secondary cut patterns among primary nonlinear cuts. Both cut geometry and secondary cut features tune adhesive force capacity and energy of separation. Importantly, the size and spacing of cut features must be designed around a critical length scale. When secondary cut features are greater than a critical length, cracks can be steered in multiple directions, going both forward and backwards within a primary attachment element. This control over crack dynamics enhances the work of separation by a factor of 1.5, while maintaining the peel force relative to a primary cut. If hierarchical cut features are too small or too compliant, they interact and do not distinctly modify crack behaviour. This work highlights the importance of adhesive length scales and stiffness for crack control and attachment characteristics in adhesive films.
This article is part of the theme issue ‘Origami/Kirigami-inspired structures: from fundamentals to applications’.
... These structures are renowned for their exceptional adhesive properties, even on rough surfaces [11][12][13]. They are inspired by biological attachment systems, such as those found in geckos [14]. Gecko-like fibrillar structures are typically fabricated using elastic polymer fibrils through techniques like soft lithography or molding [15]. ...
This study presents a numerical investigation into the adhesion strength of micro fibrillar structures, incorporating statistical analysis and the effects of excessive pre–load leading to fibril buckling. Fibrils are modeled as soft cylinders using the Euler–Bernoulli beam theory, with buckling conditions described across three distinct states, each affecting the adhesive properties of the fibrils. Iterative simulations analyze how adhesion strength varies with pre–load, roughness, number of fibrils, and the work of adhesion. Roughness is modeled both in fibril heights and in the texture of a rigid counter surface, following a normal distribution with a single variance parameter. Results indicate that roughness and pre–load significantly influence adhesion strength, with excessive pre–load causing substantial buckling and a dramatic reduction in adhesion. This study also finds that adhesion strength decreases exponentially with increasing roughness, in line with theoretical expectations. The findings highlight the importance of buckling and roughness parameters in determining adhesion strength. This study offers valuable insights into the complex adhesive interactions of fibrillar structures, offering a scalable solution for rapid assessment of adhesion in various rough surface and loading scenarios.
... Examples of such processes include soldering, welding, fertilizer packaging, fine particle transporting, etc. In nature, adhesion is successfully used by some living organisms to move on inclined surfaces [14,15], by bacteria to attach living organs [16][17][18], etc. As a rule, easily deformable bodies with a small elastic modulus are prone to good adhesion. ...
This study contributes to the understanding of the adhesive properties in normal contacts, providing valuable information on the influence of various factors on adhesive strength and energy dissipation. The adhesive normal contact between a steel spherical indenter and a soft sheet of elastomer is studied experimentally. The dependencies of contact strength and mechanical energy dissipation in the complete indentation–detachment cycle on the indentation depth, the velocity of the indenter, its radius, thickness, and elastic modulus of the elastomer, the specific work of adhesion, as well as the roughness of the indenter surface, were analyzed. Experimental results are compared with simulations using the boundary element method (BEM), and the reasons leading to discrepancies between experiments and simulations are analyzed. It is shown that over a wide range of experimental parameters, the rate of mechanical energy dissipation can be estimated with sufficient accuracy using a simple empirical relation.
... Adhesive pads have evolved multiple times, including multiple clades of arthropods (Federle, 2006;Buscher and Gorb, 2021) and lizards. The pads of lizards, including geckos, anoles, and some skinks, are considered dry fibrillar adhesives; a novel example of naturally occurring biological nanotechnology (Autumn and Gravish, 2008). Using very small (<150 mm long) hair-like structures called setae (Ruibal and Ernst, 1965;Garner and Russell, 2021), pad bearing lizards adhere to surfaces using van der Waals forces and/or contact electrification (Autumn et al., 2002;Izadi et al., 2014). ...
Introduction
Similar 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.
Methods
Using 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.
Results
We found multiple examples of significant parallel differences in toe pad morphology and support for a model of early burst morphological evolution.
Discussion
Our 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.
... Many arthropods and vertebrates have developed the ability to attach to and move across various surfaces (such as plants and rocks) by utilizing their specialized feet, providing engineers with innovative solutions to the technical systems requiring fast connection and release. 1,2 Studies on the biological attachment devices that consider topographic features of substrate surfaces, such as slopes, 3 roughness, 4-7 compliance, [8][9][10] slipperiness, 11,12 or discontinuity, 12,13 have not only elucidated the morphological and functional intelligence of animals 11,[14][15][16][17][18][19] but also contributed to the development of advanced artificial adhesive systems [20][21][22][23][24][25] and novel methodology for biomimetic research. [26][27][28] Nevertheless, many functional advantages of the biological attachment systems remain unclear. ...
Dynamic attachment is indispensable for animals to cope with unexpected disturbances. Minor attention has been paid to the dynamic performance of insects’ adhesive pads. Through experiments pulling whole grasshoppers off a glass rod at varying speeds, surprising findings emerged. The feet did not always maintain contact but released and then reconnected to the substrate rapidly during leg extension, potentially reducing the shock damage to pads. As the pulling speeds increased from 1 to 400 mm/s, the maximum forces of single front tarsus insects and entire tarsi insects were nearly proportional to the 1/3 power of pulling speeds by 0.11 and 0.29 times, respectively. The force of some individuals could be even 800 times greater than their weight, which is unexpectedly high for smooth insect pads. This work not only helps us to understand the attachment intelligence of animals but is also informative for artificial attachment in extreme situations.
... The ventral side of each toe of the gecko is characterized by a series of arc-shaped folds, which are formed by proteinaceous setae measuring approximately 100 µm in length and 5 µm in diameter. These setae, numbering around 5000 per square millimeter, further split into spatula-shaped nanofibers at their tips, which can create a cup-like adhesive structure that maximizes the contact area [29,30]. Thus, a hierarchical and finely divided adhesive system is formed for the gecko. ...
... The remarkable adhesive capability of geckos allows them to exhibit an exceptional climbing performance in various environments, which is attributed to the van der Waals forces generated by the countless setae structures [31]. The adhesion structure of a gecko's foot has been confirmed to possess unique advantages, including the mechanisms of van der Waals forces, anisotropy, strong attachment, controllable detachment, anti-adhesiveness to itself, and self-cleaning properties [29][30][31][32]. By referring to the adhesion structure, it can be used in the design of a robot attachment system. ...
... By referring to the adhesion structure, it can be used in the design of a robot attachment system. the attachment state and detachment state of gecko feet [33]; (c) The microscopic structure of gecko feet [30]. (b) the attachment state and detachment state of gecko feet [33]; (c) The microscopic structure of gecko feet [30]. ...
This paper presents a study on bioinspired rigid-flexible coupling adaptive compliant motion control of a robot gecko with hybrid actuation for space stations. The biomimetic robot gecko is made of a rigid trunk, four motor-driven active legs with dual-degree-of-freedom shoulder joints, and four pneumatic flexible pleated active attachment–detachment feet. The adaptive impedance model consists of four input parameters: the inertia coefficient, stiffness coefficient, damping coefficient, and segmented expected plantar force. The robot gecko is equipped with four force sensors mounted on its four feet, from which the normal force of each foot can be sensed in real-time. Based on the sensor signal, the variable stiffness characteristics of the feet in different states are analyzed. Furthermore, an adaptive active compliance control strategy with whole-body rigidity–flexibility-force feedback coupling is proposed for the robot gecko. Four sets of experiments are presented, including open-loop motion control, static anti-interference experiment, segmented variable stiffness experiment, and adaptative compliant motion control, both in a microgravity environment. The experiment results indicated that the presented control strategy worked well and the robot gecko demonstrates the capability of stable attachment and compliant detachment, thereby normal impact and microgravity instability are avoided. It achieves position tracking and force tracking while exhibiting strong robustness for external disturbances.
... There are a number of areas in which adhesion finds practical application, including soldering, painting, granulation, packaging of fertilizers, mechanical manipulation by macroscopic and microscopic objects, etc. [1,2]. Adhesive interaction is used by biological organisms for moving and attaching to surfaces: from microscopic bacteria [3,4] to amphibians and reptiles [5,6]. Recently, adhesive contacts have been the object of intensive experimental (e.g., [7][8][9]), theoretical [9,10] and numerical [8,[11][12][13] studies. ...
... Due to the fact that transparent rubber TARNAC CRG N3005 was used as a substrate (5) in the experiment, direct observation of the contact area was possible, which was carried out using a Conrad USB digital camera with a physical resolution of 1600 × 1200 pixels (located at the position (7)). Number (6) in the left panel of figure shows the tilt mechanism, which allowed us to change substrate orientation; this is important for experiments with a tangential motion of indenter. (4), which is connected with a force sensor (3), and the transparent elastomer sheet (5) with all-round LED illumination (8). ...
An experimental study of the process of friction between a steel spherical indenter and a soft elastic elastomer, with a strongly pronounced adhesive interaction between the surfaces of the contacting bodies, is presented. We consider sliding of the indenter at low speed (quasi-static contact) for different indentation depths. The forces, displacements and contact configuration as functions of time were recorded. The most important finding is that under conditions of uni-lateral continuous sliding, the tangential stress in the contact area remains constant and independent on the indentation depth and details of loading. We suggest a simple numerical model in which the elastic substrate is considered as a simple elastic layer (thus reminding a two-dimensional elastic foundation), although with in-plane elastic interactions. It is found that this model leads to the dynamic scenarios which qualitatively resemble the experimentally observed behavior of the considered system.
... Kinematic adjustment of the limbs could occur at multiple levels: at the whole limb, at the foot level or at the level of the toes. The hierarchy of the gecko adhesive system has been well studied [11,[17][18][19][20], but the contribution of higher units of hierarchy, toes, feet, limbs and indeed the whole body, has received less attention. ...
Many climbing animals use direction-dependent adhesives to attach to vertical or inclined surfaces. These structures adhere when activated via a pull but detach when pushed. Therefore, a challenge arises when a change in climbing direction causes external forces such as gravity to change its acting orientation upon the lizard. To investigate how specialized climbers adjust, we studied kinematics and dynamics of six Hemidactylus frenatus geckos climbing head-up and head-down a vertical racetrack. We found that limbs functionally swap their adhesive role: feet above the centre of mass (COM) generated adhesive forces, feet below the COM compressive forces, both equal in magnitude across directions. To investigate how lizards perform this swap, despite the constraint of their direction-dependent adhesives, we analysed kinematic adjustments across multiple smaller levels of hierarchy: limbs, feet and toes. All levels contributed: the hindfoot angle was reoriented realigning the adhesive structure, the hindlimb centre range of motion was further protracted and the hindfoot toe spreading was reduced. Notably, all three variables were adjustments of hindlimbs, suggesting that they make a more flexible contribution in upward versus downward climbing, while forelimbs may be anatomically or functionally constrained. The relevance of multilevel dynamic adjustments might inform the development of performant gaits for legged climbing robots.
