A tree frog toe pad structure wet-state adhesive gel and its preparation method and application

Abstract

The present application relates to the technical field of biomimetic functional gel. More particularly, it relates to a wet-state adhesive gel imitating tree frog toe pad structure and its preparation method and application. The preparation of the adhesive gel comprises the following steps: S1, spin coating photoresist on an anodic aluminum oxide substrate, after curing, exposing, developing and drying, an anodic aluminum oxide template with a micron-level hexagonal pattern is obtained; mixing anionic monomer, cationic monomer, photoinitiator and crosslinking agent to prepare a polyampholyte gel prepolymer solution; S2, in an inert atmosphere, the polyampholyte gel prepolymer solution is added dropwise on the anodic aluminum oxide template, and after photopolymerization, a patterned gel is formed on the surface of the anodic aluminum oxide template, which is immersed in a stripping solution containing sodium chloride and phosphoric acid to complete the stripping of the anodic aluminum oxide template; S3, cleaning the residual photoresist to obtain an adhesive gel with a tree frog toe pad micro-nano structure.

Description

Technical Field

[0001] This invention relates to the field of biomimetic functional gel technology. More specifically, it relates to a wet adhesive gel with a structure inspired by the toe pads of a tree frog, its preparation method, and its applications. Background Technology

[0002] Anti-slip performance is the core guarantee for crawling robots to achieve stable operation in complex unstructured terrain. In recent years, related research has continued to deepen in four dimensions: biomimetic mechanisms, material design, motion control, and environmental adaptation, forming a multidisciplinary technical system. Research draws inspiration from biological anti-slip prototypes such as gecko dry adhesion, octopus negative pressure adsorption, snail mucus adsorption, goat hoof-shaped gripping, and caterpillar claw-spine gripping, developing biomimetic anti-slip structures such as mushroom-shaped / shovel-shaped microstructures, composite hooves, claw-spine tracks, and biomimetic toe hook arrays, taking into account the adaptability of gripping and detachment on multiple interfaces such as dry, wet, rough, and steep slopes; at the same time, the friction characteristics and stress distribution of the contact surface are optimized by using anti-slip materials such as flexible polymers, surface micro-nano textures, and composite wear-resistant pads to improve the material's adaptability and durability to different surfaces.

[0003] The concept of achieving superior anisotropic adhesion in wet surfaces by introducing patterned materials into the feet of crawling robots has attracted widespread attention in the field. Existing research focuses on constructing biomimetic structures resembling tree frog toe pads on material surfaces to achieve anisotropic adhesion in wet environments. However, current surface patterned adhesion materials still face significant technical limitations: Firstly, existing materials are mostly easily moldable hydrophobic materials such as PDMS, PVS, PCL, and PU. When these materials are used for wet surface adhesion, their surfaces need to be hydrophilized first, but hydrophilization modification is prone to failure, leading to difficulties in achieving long-term anisotropic adhesion on wet surfaces and poor overall adhesion performance. Secondly, existing patterned gel materials used for anisotropic adhesion on wet surfaces have surface structure sizes ranging from micrometers to millimeters, also exhibiting insufficient wet surface adhesion performance. This limitation severely restricts the large-area preparation and practical application of such materials.

[0004] Therefore, developing a technical solution that can construct tree frog-inspired toe pad micro / nano structures on gel surfaces in a one-step process and achieve long-term stable anisotropic adhesion properties still has important research value and practical application significance. Summary of the Invention

[0005] To address the aforementioned problems, the first objective of this invention is to provide a method for preparing a wet adhesive gel with a tree frog-inspired toe pad structure. This method first constructs a hexagonal micropillar pattern on an anodic aluminum oxide substrate, and then utilizes the photopolymerization effect of a zwitterionic gel prepolymer to form a biomimetic structure with periodically arranged hexagonal micropillars composed of nanopillars. The entire process is simple and easy to operate.

[0006] A second objective of this invention is to provide a tree frog-inspired toe pad structure wet adhesive gel prepared using the method described above. This adhesive gel has a biomimetic structure of periodically arranged hexagonal micropillars composed of nanopillars, which can achieve strong shear and easy peeling anisotropic adhesion properties on wet surfaces.

[0007] A third objective of this invention is to provide a tree frog-inspired toe pad structure wet adhesive gel for use in crawling robots. This adhesive gel is obtained through photopolymerization of anionic and cationic monomers, and its structure comprises periodically arranged hexagonal micropillars, each composed of nanopillars of equal height.

[0008] The fourth objective of this invention is to provide an application of the wet adhesive gel with the tree frog toe pad structure described above in the preparation of a crawling robot.

[0009] In the context of crawling robot applications, the wet surface referred to in this invention refers to a surface covered by a thin layer of liquid such as liquid water film, oil-water mixture, condensate, or biological mucus, or a solid interface in a high-humidity environment. This represents a typical harsh working condition where robots are most prone to slipping. Such interfaces form a lubricating film due to the liquid, significantly reducing the coefficient of friction and disrupting conventional anti-slip effects such as dry adhesion and mechanical gripping. These surfaces are commonly found on rain-soaked ground, damp rock faces, underwater / near-water structures, condensation pipes, moist vegetation leaves, and moist cavities within minimally invasive medical procedures. They are also a key research focus for current research on biomimetic anti-slip mechanisms, anti-slip materials, and adaptive anti-slip control for wet surfaces.

[0010] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0011] This invention discloses a method for preparing a wet adhesive gel with a structure mimicking the toe pad of a tree frog, comprising the following steps:

[0012] S1. Photoresist is spin-coated onto an anodized aluminum substrate, cured, exposed, developed, and dried to obtain an anodized aluminum template with micron-scale hexagonal patterns.

[0013] Anionic monomers, cationic monomers, photoinitiators, and crosslinking agents are mixed to prepare a zwitterionic gel prepolymer solution.

[0014] S2. In an inert atmosphere, a zwitterionic gel prepolymer is dropped onto an anodized aluminum template. After photopolymerization, a patterned gel is formed on the surface of the anodized aluminum template. The template is then immersed in a release solution containing sodium chloride and phosphoric acid to complete the peeling off of the anodized aluminum template. The patterned gel is composed of uniform nanopillars extending axially along a micron-scale hexagonal pattern.

[0015] S3. Clean the remaining photoresist to obtain an adhesive gel with a micro-nano structure that mimics the toe pads of a tree frog. The adhesive gel has a biomimetic structure of periodically arranged hexagonal micro-pillars composed of nanopillars.

[0016] Inspired by the polygonal micropillar structure composed of nanopillars in the toe pads of tree frogs, this invention simultaneously synthesizes the adhesive gel and fabricates a micro / nano structure resembling the surface of a tree frog's toe pad. Specifically, the gel possesses a biomimetic pattern of hexagonal micropillars composed of uniform nanopillars, eliminating the need for further modification with adhesive molecules and hydrophilic treatment. The resulting adhesive gel exhibits strong frictional and easily peelable anisotropic adhesion properties on wet surfaces, with shear strength far exceeding peel strength, making it suitable for crawling robots.

[0017] It should be noted that the photomask used in the exposure of this invention is divided into a light-transmitting area and an opaque area. The light-transmitting area is a regular hexagon with a side length of 18-20 μm, and the opaque area is the boundary area used to separate the regular hexagons. The light-transmitting area and the opaque area are repeated. After photolithography using the above photomask, only the opaque area retains photoresist, while the light-transmitting area does not have photoresist. The light-transmitting area still exposes the anodic aluminum oxide substrate. Thus, the light-transmitting area can facilitate the inflow of zwitterionic gel prepolymer, which then penetrates into the pores of the anodic aluminum oxide to form a biomimetic pattern of hexagonal micropillars composed of uniform nanopillars.

[0018] Furthermore, the anionic monomer is selected from sodium p-styrenesulfonate and / or sodium 2-acrylamido-2-methylpropanesulfonate.

[0019] Furthermore, the cationic monomer is selected from acryloyloxyethyltrimethylammonium chloride and / or (3-acrylamidopropyl)trimethylammonium chloride.

[0020] Furthermore, the photoinitiator is selected from α-ketoglutaric acid.

[0021] Furthermore, the crosslinking agent is selected from N,N-dimethylbisacrylamide.

[0022] Furthermore, the molar ratio of the anionic monomer to the cationic monomer is 1-1.2.

[0023] Experiments show that the molar concentrations of chloride and sodium ions in the release solution must match those in the zwitterionic gel prepolymer solution; otherwise, the shear strength of the adhesive gel will be affected. In one specific embodiment, the ratio of the molar concentrations of chloride and sodium ions in the release solution to those in the zwitterionic gel prepolymer solution is 0.15-0.2, that is, the ratio of the molar concentrations of chloride ions in the release solution to those in the zwitterionic gel prepolymer solution is 0.15-0.2, and the ratio of the molar concentrations of sodium ions in the release solution to those in the zwitterionic gel prepolymer solution is 0.15-0.2.

[0024] Furthermore, the concentration of sodium chloride in the release solution is 0.20-0.26 mol / L. If the concentration of sodium chloride is too high or too low, it will reduce the shear strength of the adhesive gel.

[0025] Furthermore, the photoresist is P4620, the spin coating speed is 3000-4000 r, the spin coating acceleration is 800-1000 r / s, and the spin coating time is 60 s.

[0026] Furthermore, the curing temperature is 100-120℃, and the curing time is 70-90s.

[0027] Furthermore, the exposure wavelength is 350nm and the exposure time is 8-13s.

[0028] Furthermore, the developing solution used is 300MIF developer, and the developing time is 180-230s.

[0029] Furthermore, the surface pore size of the anodic aluminum oxide is 100-400 nm, and the pore depth is 0.5-20 μm, preferably 2-5 μm.

[0030] Furthermore, in the micron-scale hexagonal pattern, the side length of the hexagons is 18-20 μm, and a boundary with a width of 2-5 μm is reserved between adjacent hexagons.

[0031] Furthermore, according to every 4cm 2 Add 4-5 ml of zwitterionic gel prepolymer solution to the anodic aluminum oxide template.

[0032] Furthermore, the light source used for photopolymerization has a wavelength of 365 nm and a light intensity of 4 mW / cm². 2 The photopolymerization time for ultraviolet light is 10-13 hours.

[0033] Furthermore, step S3 further includes ultrasonically cleaning the patterned gel in acetone for 5 seconds, then transferring it to deionized water for another 5 seconds, repeating this process at least 5 times to remove the photoresist. Performing this cleaning operation ensures effective removal of the photoresist pillars without damaging the microstructure of the patterned gel due to excessive acetone cleaning.

[0034] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0035] This invention discloses a tree frog-inspired toe pad structure wet adhesive gel for crawling robots, which is prepared using the preparation method described above.

[0036] Furthermore, the adhesive gel is a biomimetic structure of hexagonal micropillars composed of periodically arranged nanopillars;

[0037] The size of the nanopillars is influenced by the micropores on the surface of the anodized aluminum oxide (i.e., surface pore diameter and pore depth). The height of the nanopillars is 0.5-20 μm, preferably 2-5 μm, and the diameter of the nanopillars is 100-400 nm.

[0038] In the hexagonal micro-pillar biomimetic surface, the side length of the hexagons is 18-20 μm, the height of the micro-pillars is the same as that of the nano-pillars, and the boundary width between adjacent hexagons is 2-5 μm.

[0039] To achieve the third objective mentioned above, the present invention adopts the following technical solution:

[0040] This invention discloses a tree frog-inspired toe pad structure wet adhesive gel for crawling robots. The adhesive gel is obtained by photopolymerization of anionic and cationic monomers as raw materials. Its structure has periodically arranged hexagonal micropillars, each of which is composed of nanopillars of equal height.

[0041] The hexagonal micropillar has a side length of 18-20 μm and a boundary width of 2-5 μm between adjacent hexagons.

[0042] The height of the nanopillar is 0.5-20 μm, and the diameter of the nanopillar is 100-400 nm.

[0043] The anionic monomer is selected from sodium p-styrene sulfonate and / or sodium 2-acrylamido-2-methylpropanesulfonate;

[0044] The cationic monomer is selected from acryloyloxyethyltrimethylammonium chloride and / or (3-acrylamidopropyl)trimethylammonium chloride.

[0045] To achieve the fourth objective mentioned above, the present invention adopts the following technical solution:

[0046] This invention discloses the application of the adhesive gel described above in the preparation of crawling robots.

[0047] The beneficial effects of this invention are as follows:

[0048] This invention discloses a method for constructing a strong shear-resistant, easily peelable adhesive gel inspired by the toe pads of tree frogs. The method first involves constructing a hexagonal micron-shaped column pattern on the surface of anodic aluminum oxide (AAO) using photolithography. Then, a zwitterionic hydrogel prepolymer is poured onto the surface, and the gel is obtained by ultraviolet light polymerization. The polymerized gel is then immersed in a phosphoric acid / sodium chloride solution to detach the gel from the anodic aluminum oxide surface. After washing away the photoresist residue on the gel surface, an adhesive pattern with strong friction and easy peelability on a wet surface is constructed on the gel surface.

[0049] By selecting anodic alumina templates with different pore sizes and depths (e.g., pore sizes of 100 nm, 200 nm, 300 nm, 400 nm, etc., and pore depths of 0.5 μm, 1 μm, 2 μm, 5 μm, 20 μm), the column diameter of the nanopillar structure on the gel surface can be precisely controlled at the nanoscale (e.g., 100 nm, 200 nm, 300 nm, 400 nm, etc.) and the column height at the microscale (e.g., 0.5 μm, 1 μm, 2 μm, 5 μm, 20 μm, etc.). The prepared micro / nano-structured adhesive gel exhibits excellent adhesion to wet surfaces with strong shear strength and easy peeling. This is mainly manifested in the ability to achieve strong shear strength on wet surfaces without pre-pressure, while simultaneously achieving separation from the wet surface with minimal peeling strength. Attached Figure Description

[0050] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0051] Figure 1 The images are electron microscope (EM) images of the anodic aluminum oxide template with micron-scale hexagonal patterns prepared in Example 1 of the present invention at different magnification ratios, wherein each EEM image is magnified in situ from left to right.

[0052] Figure 2 Electron micrographs of gel materials prepared at different sodium chloride concentrations are shown, where a is Example 1, b is Example 2, c is Example 3, d is Comparative Example 1, and e is Comparative Example 2.

[0053] Figure 3 The electron microscope images (corresponding to nanopillar diameter of 400 nm and pillar height of 5 μm) of the gel material with tree frog-inspired micro / nano structures on the surface prepared in Example 4 of the present invention are magnified in situ from left to right.

[0054] Figure 4 This is an optical image of the wet shear force test in Example 1.

[0055] Figure 5 This is an optical image of the peel strength test in Example 1.

[0056] Figure 6 The images show the application of the prepared adhesive gel to the feet of a flexible robot for climbing. Among them, a is a photo of climbing on a wet acrylic surface at an angle of 80°, b is a photo of climbing on a wet acrylic ball surface, c is a photo of climbing on a wet bamboo surface, and d is a photo of climbing on a wet leaf surface.

[0057] Figure 7 Images of a flexible robot climbing without adhesive gel. Detailed Implementation

[0058] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] A method for preparing a gel with a micro / nano structure resembling a tree frog's toe pad includes the following steps:

[0061] (1) Preparation of anodized aluminum oxide (AAO) substrates with micron-scale hexagonal patterning on the surface:

[0062] a. Place the anodized aluminum substrate in acetone and ultrasonically clean it for 300 s. The substrate should be 2cm*2cm*0.5mm in size, with a surface pore diameter of 400 nm and a pore depth of 2 μm. Then, dry it with nitrogen gas. Use double-sided tape to attach the cleaned anodized aluminum substrate to a glass slide with dimensions of 2.2cm*2.2cm*1mm.

[0063] b. Spin-coat P4620 photoresist onto the surface of anodized aluminum in the yellow light area. The spin-coating speed is 4000 r, the spin-coating acceleration is 1000 r / s, and the spin-coating time is 60 s. Then heat at 110℃ for 80 s to cure the photoresist and store it away from light.

[0064] c. A micron-sized hexagonal mask, designed in step b, is overlaid onto the anodic aluminum oxide substrate obtained in step b in the yellow light region. A photolithography step is then performed with an exposure wavelength of 350 nm and an exposure time of 13 s. The mask size is 2 cm * 2 cm, and it is divided into a transparent area and an opaque area. The transparent area consists of regular hexagons with a side length of 20 μm, while the opaque area is the boundary separating adjacent regular hexagons, with a width of 2 μm. The transparent and opaque areas are arranged in a repeating pattern.

[0065] d. After exposure, the anodized aluminum substrate is developed in a 300 MIF developer for 230 seconds, immersed in deionized water for 80 seconds, rinsed with deionized water for 30 seconds, dried with N2, and then heated at 110°C for 80 seconds to dry for later use. The photoresist remains in the opaque areas of the mask, while the anodized aluminum substrate in the transparent areas is exposed, thus obtaining an anodized aluminum template with a micron-scale hexagonal pattern. The microstructure is as follows: Figure 1 As shown.

[0066] (2) Preparation of zwitterionic gel prepolymer: Add 5.3609 g sodium p-styrene sulfonate, 5.8101 g acryloyloxyethyltrimethylammonium chloride, 18.2625 mg photoinitiator α-ketoglutaric acid, and 7.7085 mg crosslinking agent N,N-dimethylbisacrylamide to a two-necked flask, add deionized water to 20 ml, and purge with nitrogen for 30 min to obtain zwitterionic gel prepolymer.

[0067] (3) Place the anodic aluminum oxide template obtained in step (1) at the bottom of the photochemical reactor and purge the photochemical reactor with nitrogen for 5 minutes to fill it with nitrogen.

[0068] (4) Take 4 ml of zwitterionic gel prepolymer and drop it onto the anodic aluminum oxide template. Then, at a wavelength of 365 nm and an intensity of 4 mW / cm², apply the solution to the template. 2 Photopolymerization was carried out under ultraviolet light for 12 hours.

[0069] (5) Prepare the release solution: Add 0.71 g sodium chloride and 5 g phosphoric acid to 40 g water, then add water to 50 g. The concentration of sodium chloride is 0.24 mol / L.

[0070] (6) Gel template removal: The gel that has been photopolymerized in step (4) is scraped clean around the template to expose the bright aluminum. The gel is then soaked in the release solution for 10 h to separate the gel from the anodic aluminum template.

[0071] (7) Photoresist cleaning of gel surface: The obtained gel is sonicated in acetone for 5s, then quickly transferred to deionized water and sonicated for 5s. This process is repeated 5 times to obtain a gel material with a tree frog-like micro-nano structure on the surface. A biomimetic hydrogel surface with a micro-nano hierarchical structure is obtained. The micron-level hexagonal units in the hexagonal micron column biomimetic surface are arranged periodically. The side length of the hexagon is 18-20μm, and the boundary width between adjacent hexagons is 2-5μm. Each micron hexagonal unit is composed of densely packed nanopillars with a diameter of 400 nm and a height of 2 μm.

[0072] Wet shear force test

[0073] In this invention, the shear force test adopts the lap shear test, and all peel force tests are conducted using Markovnikov. 10. ESM301 test bench. Remove the sample from the release solution prepared in step (5). Cut the sample size to 2 cm * 0.5 cm. Overlap a portion of the sample area (0.5 cm * 0.5 cm) onto a glass surface with 0.5 μl of water droplets on it without pre-pressure. During the test, clamps on the upper and lower parts of the tensile testing machine hold the sample that is not overlapped on the glass. The upper end of the tensile testing machine clamps the glass and stretches it upward at a speed of 30 mm / min. Take the maximum value of force / area (0.5 cm * 0.5 cm) from the obtained displacement-force curve and record it as the shear strength.

[0074] Test graph as shown Figure 4 As shown, the wet shear strength of the gel with the tree frog-inspired micro / nano structure reaches 0.69 ± 0.08 N / cm. 2 .

[0075] Peel strength test

[0076] In this invention, all peel force tests were conducted using Markovnikov. 10. ESM301 test bench. Samples were cut to 2 cm long and 0.5 cm wide. A portion of the sample (0.5 cm long, 0.5 cm wide) was overlapped without pre-pressure onto a glass surface with 0.5 μl of water droplets. During the test, one end of the unoverlapped sample was secured with PI tape, and the sample was stretched upwards at a speed of 30 mm / min. The maximum value of the force / width (0.5 cm) in the resulting displacement-force curve was recorded as the peel strength.

[0077] Test graph as shown Figure 5 As shown, the gel with the tree frog-inspired micro / nano structure has a peel strength of 0.09 ± 0.003 N / cm.

[0078] Example 2

[0079] The sodium chloride concentration in the release solution was changed to 0.26 mol / L, while other processes and testing procedures remained the same as in Example 1. The resulting gel had a similar structure to that of Example 1; the surface structure electron micrograph is shown below. Figure 2 Photo b. The wet shear strength of the gel reaches 0.53 ± 0.07 N / cm. 2 The peel strength reached 0.013±0.005N / cm.

[0080] Example 3

[0081] The sodium chloride concentration in the release solution was changed to 0.20 mol / L, while other processes and testing procedures remained the same as in Example 1. The resulting gel had a similar structure to that of Example 1; the surface structure electron micrograph is shown below. Figure 2 Photo c. The wet shear strength of the gel reaches 0.47 ± 0.09 N / cm. 2 The peel strength reached 0.012±0.007 N / cm.

[0082] Comparative Example 1

[0083] The sodium chloride concentration in the release solution was changed to 0.33 mol / L, while other processes and testing procedures remained the same as in Example 1. The wet shear strength reached 0.22 ± 0.05 N / cm. 2 The peel strength reached 0.008±0.003 N / cm.

[0084] Comparative Example 2

[0085] The sodium chloride concentration in the release solution was changed to 0.16 mol / L, while other processes and testing procedures remained the same as in Example 1.

[0086] The wet shear strength reaches 0.17 ± 0.10 N / cm. 2 The peel strength reached 0.007±0.002N / cm.

[0087] Figure 2 Electron micrographs of the gel materials prepared in Examples 1-3 and Comparative Examples 1-2. Figure 2 In the image above (d), the micron-sized hexagons are no longer regular. The magnified in-situ image in the upper left corner shows that the nanopillars have been destroyed and fused together, no longer possessing a nanopillar structure. Combined with the adhesion data mentioned above, it can be seen that excessively high sodium chloride concentrations disrupt the micro / nano structure, leading to a significant decrease in tangential adhesion. Conversely, excessively low NaCl concentrations cause the Na+ in the gel to... + and Cl - Precipitation, intensified internal aggregation, from Figure 2 As can be seen in the image above, the micron-sized hexagons contract inwards and become concave. The magnified image in the upper left corner shows severe aggregation of the nanopillars, which no longer exhibit a uniform and flat distribution. Combined with the adhesion test data, it can be seen that excessively low sodium chloride concentrations disrupt the micro-nano structure, leading to a significant decrease in tangential adhesion. Therefore, in the aforementioned zwitterionic gel prepolymer system, when the NaCl concentration in the release solution is between 0.20 and 0.26 mol / L, the nanopillar structure is well-ordered and exhibits high shear strength.

[0088] Example 4: Effect of anodic aluminum oxide substrate on the micro-sodium structure of gel surface

[0089] Gel preparation was performed using anodic aluminum oxide with a column diameter of 200 nm and different pore depths of 0.5 μm, 1 μm, 2 μm, 5 μm, and 20 μm. The remaining procedures were the same as in Example 1. This resulted in a hexagonal micropillar biomimetic surface composed of periodically arranged nanopillars with column heights of 0.5 μm, 1 μm, 2 μm, 5 μm, and 20 μm. Shear strength and peel strength were tested on these surfaces, and the results are shown in Table 1. Nanopillars with heights of 2-5 μm exhibited superior adhesion with strong shear strength and easy peeling.

[0090] Table 1

[0091]

[0092] Gel preparation was performed using anodic aluminum oxide with different surface pore sizes of 100 nm, 200 nm, 300 nm, and 400 nm, and a pore depth of 5 μm. The remaining procedures were the same as in Example 1. This resulted in a biomimetic pattern of hexagonal micropillars composed of periodically arranged nanopillars with diameters of 100 nm, 200 nm, 300 nm, and 400 nm. An electron microscopy image of a sample with a nanopillar diameter of 400 nm and a height of 5 μm is shown below. Figure 3 As shown in Table 2, shear strength and peel strength tests were performed on the nanopillars. Nanopillars with diameters in the 100-400 nm range exhibit superior adhesion with strong shear strength and easy peeling.

[0093] Table 2

[0094]

[0095] Example 5: Effect of water loss of micro / nanostructured gel on shear strength and peel strength

[0096] The gel material of Example 4 (taking a nanopillar diameter of 200 nm and a nanopillar height of 5 μm as an example) was subjected to different water loss conditions through drying. The gel material of Example 4 without drying was recorded as having a water loss of 0%. Samples with water losses of 14%, 20%, and 30% were prepared sequentially and tested according to the testing procedure of Example 1. The results are shown in Table 3. The gel material prepared by this invention can maintain excellent adhesion with strong shear and easy peeling even with a water loss of up to 20%, indicating that the gel material has high stability even in a future drying environment.

[0097] Table 3

[0098]

[0099] Example 6: Shear strength and peel strength of micro / nanostructured gel on glass at different contact angles

[0100] The gel material prepared in Example 4 (taking a nanopillar diameter of 200 nm and a nanopillar height of 5 μm as an example) was adhered to glass with different contact angles and tested according to the test procedure in Example 1. The results are shown in Table 4.

[0101] Table 4

[0102]

[0103] Example 7: Testing shear strength and peel strength on different substrates

[0104] The gel material prepared in Example 4 (taking a nanopillar diameter of 400 nm and a nanopillar height of 5 μm as an example) was subjected to shear strength and peel strength tests on the following different substrates. The results are shown in Table 5, indicating that the gel can exhibit significant strong shear and weak peel on polydimethylsiloxane film, polyimide film, acrylic, stainless steel, aluminum, iron, copper, bamboo, leaves, and tree trunks.

[0105] Table 5

[0106]

[0107] Example 8: Application to the feet of a flexible robot

[0108] The adhesion gel prepared in Example 4 (taking a nanopillar diameter of 400 nm and a nanopillar height of 5 μm as an example) was adhered to the foot of the flexible robot. Figure 6 Figure a demonstrates the entire process of a flexible robot climbing a wet acrylic surface at an 80° angle. First, water droplets are sprayed onto the acrylic surface. The flexible robot, with adhesive gel attached to its feet, is placed at the bottom of the slope, and its deformation drive is activated to initiate climbing. After 3 seconds, it peels off its front legs, using its hind legs for support. From 3 to 9 seconds, the front legs extend and adhere to the wet surface, providing support. From 9 to 15 seconds, the hind legs peel off, lift, and retract. After 15 to 18 seconds, the legs adhere to the wet surface, completing one climbing cycle. Similarly, flexible robots with adhesive gel attached to their feet can freely climb on wet acrylic spheres, wet bamboo surfaces, and wet leaf surfaces (see Figure a). Figure 6 (middle bd). Comparison Figure 7 The flexible robot whose feet were not covered with the adhesive hydrogel slid off directly when placed at 30° and 80° respectively.

[0109] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a wet adhesive gel with a tree frog toe pad structure, characterized in that, Includes the following steps: S1. Photoresist is spin-coated onto an anodized aluminum substrate, cured, exposed, developed, and dried to obtain an anodized aluminum template with micron-scale hexagonal patterns. Anionic monomers, cationic monomers, photoinitiators, and crosslinking agents are mixed to prepare a zwitterionic gel prepolymer solution. S2. In an inert atmosphere, the zwitterionic gel prepolymer is dropped onto the anodic aluminum oxide template. After photopolymerization, a patterned gel is formed on the surface of the anodic aluminum oxide template. The template is then immersed in a release solution containing sodium chloride and phosphoric acid to complete the peeling off of the anodic aluminum oxide template. S3. Clean the remaining photoresist to obtain an adhesive gel with a micro-nano structure that mimics the toe pads of a tree frog. The adhesive gel has a biomimetic structure of periodically arranged hexagonal micro-pillars composed of nanopillars. The anionic monomer is selected from sodium p-styrene sulfonate and / or sodium 2-acrylamido-2-methylpropanesulfonate; The cationic monomer is selected from acryloyloxyethyltrimethylammonium chloride and / or (3-acrylamidopropyl)trimethylammonium chloride; The molar concentrations of chloride and sodium ions in the release solution are respectively 0.15-0.2 compared to the molar concentrations of chloride and sodium ions in the zwitterionic gel prepolymer solution. The concentration of sodium chloride in the release solution is 0.20-0.26 mol / L.

2. The preparation method according to claim 1, characterized in that, The photoinitiator is selected from α-ketoglutaric acid; The crosslinking agent is selected from N,N-methylenebisacrylamide; The molar ratio of the anionic monomer to the cationic monomer is 1-1.

2.

3. The preparation method according to claim 1, characterized in that, The photoresist is photoresist P4620; The curing temperature is 100-120℃, and the curing time is 70-90s; The exposure wavelength is 350nm, and the exposure time is 8-13s; The developing solution used is 300MIF, and the developing time is 180-230s.

4. The preparation method according to claim 1, characterized in that, The surface pore size of the anodic aluminum oxide is 100-400 nm, and the pore depth is 0.5-20 μm; The hexagonal pattern at the micrometer level has a side length of 18-20 μm, and a boundary with a width of 2-5 μm is reserved between adjacent hexagons.

5. The preparation method according to claim 1, characterized in that, According to every 4cm 2 Add 4-5 ml of zwitterionic gel prepolymer solution dropwise to the anodized aluminum template. The light source used for photopolymerization has a wavelength of 365 nm and a light intensity of 4 mW / cm². 2 The photopolymerization time for ultraviolet light is 10-13 hours.

6. A tree frog-inspired toe pad structure wet adhesive gel for crawling robots, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The adhesive gel according to claim 6, characterized in that, The adhesive gel is a hexagonal micropillar biomimetic structure composed of periodically arranged nanopillars; The height of the nanopillar is 0.5-20 μm, and the diameter of the nanopillar is 100-400 nm. In the hexagonal micro-pillar biomimetic surface, the side length of the hexagons is 18-20 μm, and the boundary width between adjacent hexagons is 2-5 μm.

8. A tree frog-inspired toe pad structure wet adhesive gel for crawling robots, characterized in that, The adhesive gel is obtained by photopolymerization of anionic and cationic monomers as raw materials. Its structure has periodically arranged hexagonal micropillars, each of which is composed of nanopillars of equal height. The hexagonal micropillar has a side length of 18-20 μm and a boundary width of 2-5 μm between adjacent hexagons. The height of the nanopillar is 0.5-20 μm, and the diameter of the nanopillar is 100-400 nm. The anionic monomer is selected from sodium p-styrene sulfonate and / or sodium 2-acrylamido-2-methylpropanesulfonate; The cationic monomer is selected from acryloyloxyethyltrimethylammonium chloride and / or (3-acrylamidopropyl)trimethylammonium chloride.

9. The use of the adhesive gel as described in any one of claims 6-8 in the preparation of a crawling robot.

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