A biomimetic surface for use in micro crawling robots and its preparation method

Abstract

This invention discloses a biomimetic surface for use in micro crawling robots and its preparation method, belonging to the field of biomimetic technology. It employs MEMS photolithography to prepare a silicon-based template and uses polydimethylsiloxane to replicate the structure to obtain the biomimetic surface for micro crawling robots. Based on the structure of a tree frog's foot, this invention prepares an anisotropic, high-friction biomimetic surface. Compared to a bare surface, this biomimetic surface has a 10-fold increased coefficient of friction. When this biomimetic plane is bonded to the leg structure of a micro robot, actual testing shows that the micro robot's maximum speed without the biomimetic plane can reach 25 times its body length per second, while with the biomimetic plane, its maximum speed can reach 50 times its body length per second or even higher, representing a 100% increase in speed and a significant performance improvement.

Description

Technical Field

[0001] This invention belongs to the field of bionics technology, and in particular relates to a bionic surface for use in micro crawling robots and its preparation method. Background Technology

[0002] In the field of micro-robotics, patent CN202210474806.9 describes a walking wheel using a high-friction silicone wheel. The propeller pressure acts on the high-friction silicone wheel, generating sufficient friction to prevent the robot from slipping. Patent CN202122146812.5 describes a roller friction support component that uses elastic deformation to make the friction support surface fit more tightly against the roller, thereby improving friction. Patent CN202120558926.8 describes a crawling frame movably mounted on one side of the first crawling leg, which, together with an anti-slip sleeve, facilitates increased friction and improves stability. Patent CN202022559390.X describes a rubber layer with grooves that provide significant friction; even because its hardness is less than that of the tire surface, the raised parts of the grooves may intersect with the tire tread pattern, further increasing friction. However, most existing high-friction surfaces used in robots and other equipment achieve high friction based on increased pressure, or use existing rubber layers, anti-slip sleeves, and other technologies, which cannot fully support the robot's movement. Summary of the Invention

[0003] Currently, no one has introduced biomimetic planes into the field of micro-robotics to achieve high-friction surfaces. To address the aforementioned technical problems, this invention proposes a biomimetic surface for micro-crawling robots. Specifically targeting crawling robots that rely on friction for motion, this invention designs a biomimetic high-friction anisotropic plane with a structure resembling a tree frog's foot, which can significantly improve the crawling speed of existing crawling robots.

[0004] To achieve the above objectives, this invention provides a biomimetic surface for use in micro crawling robots. This biomimetic surface is formed by axially stretching a closely spaced hexagonal groove, resulting in a structure with a long side of 100 μm, a short side of 60 μm, a vertices of 60°, a groove width of 20 μm, and a depth of 50 μm. This biomimetic surface possesses an anisotropic coefficient of friction and high friction characteristics in humid environments. The biomimetic surface of this invention features an anisotropic surface pattern. On such a surface, water flow in the axial direction is smoother, achieving a critical friction state over a wider range; however, water flow in the lateral direction encounters greater resistance in some grooves perpendicular to the direction of movement, causing water to overflow onto the upper surface of the hexagonal prisms, thus disrupting the critical friction state. This structure exhibits high axial friction and low lateral friction, which is highly beneficial for the high-speed forward movement and flexible turning of micro surveying robots, enhancing the robot's maneuverability and adaptability to different surfaces. Furthermore, the present invention utilizes air plasma to introduce highly oxygen-containing functional groups, which reduces the surface tension of water molecules and accelerates the transport speed of water molecules in this process.

[0005] Tree frogs can adhere to and inhabit damp, smooth surfaces; they can also rapidly leap to escape predators thanks to the high coefficient of friction between their feet and tree bark. This frictional characteristic is clearly related to the unique micro-nano structure of their foot surface, as well as the suitable elastic modulus and surface chemical composition of the tree frog's feet. This invention, through studying the micro-nano structure of the tree frog's feet, concludes that maintaining the critical frictional state under various pressures and surfaces by controlling the water flow rate within the micro-nano grooves is key to improving friction. An anisotropic high-friction biomimetic structure was designed, and a silicon wafer template was fabricated using MEMS photolithography. Further, polydimethylsiloxane (PDMS) was used to replicate the structure to obtain a high-friction biomimetic surface. Finally, a polymer coating was formed on the robot's shell and the biomimetic surface, which was then bonded to the robot using UV adhesive for application.

[0006] Compared to hard materials, most soft materials, due to their lower elastic modulus, can better adhere to complex surfaces and generate greater van der Waals forces, thus producing higher friction. The classic polymer material PDMS (Dow Corning Sylgard 184 silicone rubber) can have its elastic modulus controlled by adjusting the ratio of the polymer prepolymer (SYLGARD 184-A) to the initiator (SYLGARD 184-B) (typically 10:1 by mass). Furthermore, its suitable chemical composition makes it suitable for surface modification using air plasma. Its abundant oxygen-containing functional groups can fully react upon contact with air plasma, dissociating more hydroxyl and carboxyl groups, thus endowing the PDMS biomimetic surface with excellent hydrophilicity. This allows water molecules to easily spread and flow on it, resulting in a wider critical friction threshold. By changing the shape of the groove, the present invention enables water to experience different resistances when moving in the groove in different directions, thereby controlling the range of critical friction in different directions and further realizing the regulation of the anisotropic frictional ability of such surfaces.

[0007] A method for preparing a biomimetic surface for use in a micro crawling robot includes the following steps: preparing a silicon-based template using MEMS photolithography, and obtaining a biomimetic surface for use in a micro crawling robot by secondary replication of the structure using polydimethylsiloxane.

[0008] Furthermore, the method for preparing the biomimetic surface used in the micro crawling robot specifically includes the following steps:

[0009] (1) Processing using MEMS photolithography: A silicon wafer pre-coated with photoresist is exposed by laser direct writing to form a pre-designed geometric pattern. Then, the exposed area is dissolved by developing solution to form a unique positive photoresist film structure. The positive photoresist film structure is transferred to the silicon wafer and silicon-based template is formed by ICP etching technology.

[0010] (2) A fluorinated layer with high electron density was formed by vacuum evaporation of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane on the surface of a silicon-based template, resulting in a silicon-based template with a fluorinated layer. To prevent polydimethylsiloxane (PDMS Dow Corning SYLGARD 184 silicone rubber), prepolymer (SYLGARD 184-A):initiator (SYLGARD 184-B) = 10:1 (mass ratio) from forming chemical bonds with SiO2 on the surface of the silicon-based template, making it difficult to peel off, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane was used to deposit a fluorinated layer on the surface of the silicon-based template under high temperature and vacuum (80℃, 10... 3 Vacuum evaporation is performed under Pa) to form a fluorinated layer with high electron density;

[0011] (3) After obtaining the silicon-based template with a fluorinated layer, PDMS monomer and curing agent are mixed and allowed to stand to obtain a prepolymer solution. The silicon-based template with the fluorinated layer is impregnated with the prepolymer solution, heat-treated, polydimethylsiloxane is removed, and the silicon-based template is peeled off to obtain a PDMS negative mold with an unfluorinated biomimetic anisotropic high-friction surface. Preferably, after obtaining the silicon-based template with a fluorinated layer, PDMS monomer (SYLGARD 184-A) and curing agent (SYLGARD 184-B) are uniformly mixed at a mass ratio of 10:1 and placed in a vacuum dish with a pressure of 100 kPa for 15 minutes to eliminate bubbles generated during thorough stirring. Subsequently, the prepolymer solution that has been defoamed is introduced into a culture dish containing the silicon-based template and placed in a vacuum dish with a pressure of 100 kPa for 15 minutes to ensure that the prepolymer solution can fully penetrate the micro-nano structure on the silicon-based template and further defoam. After low-pressure treatment, the entire culture dish was placed in an oven with a pre-set temperature of 60°C and waited for 8 hours before being removed. The PDMS was then completely removed with a scalpel, and the silicon template was peeled off to obtain a PDMS negative mold with an unfluorinated biomimetic anisotropic high-friction surface.

[0012] (4) The surface of the polydimethylsiloxane (PDMS) negative mold was cleaned using air plasma. The fluorination steps of the silicon-based template were repeated on the PDMS negative mold to obtain the PDMS negative mold. After curing, the biomimetic surface and the negative mold were peeled off. The biomimetic surface was then cleaned using air plasma to obtain a biomimetic surface for use in micro crawling robots. In this step, the surface of the PDMS negative mold was cleaned using air plasma to introduce a large number of hydroxyl groups on the surface, thereby increasing the thickness of the fluorinated layer formed in the next fluorination process and preventing the phenomenon that the bonding between the PDMS biomimetic surface and the PDMS negative mold is too strong and difficult to peel off. After the above steps, the fluorination steps of the silicon-based template were repeated on the PDMS negative mold to obtain a PDMS negative mold with a biomimetic anisotropic high-friction surface. Similarly, after two defoaming processes as in the preparation of the PDMS negative mold, it was placed in an oven at 60°C for curing for 8 hours. After curing, the cured PDMS block was carefully longitudinally cut with a knife to locate the interface between the negative mold and the PDMS biomimetic surface, which was formed by the fluorinated layer. After carefully peeling off a portion, anhydrous ethanol was squeezed into the resulting gaps, and the biomimetic surface was successfully separated from the negative mold. Then, through the same air plasma cleaning process, the surface was chemically modified with high oxygen-containing functional groups to reduce the surface tension of water on it and enhance its hydrophilicity, thus obtaining the final PDMS biomimetic anisotropic high-friction surface, i.e., the biomimetic surface.

[0013] Furthermore, in step (1), the photoresist is S1813 reagent; the developer is NMD developer.

[0014] Furthermore, in step (2), the vacuum evaporation temperature is 80°C and the vacuum degree is 10. 3 Pa.

[0015] Furthermore, in step (3), the mass ratio of PDMS monomer to curing agent is 10:1;

[0016] The settling time is 15 minutes, and the air pressure during settling is 100 kPa.

[0017] When impregnating a silicon-based template with a fluorinated layer with prepolymer solution, the processing time is 15 min and the air pressure is 100 kPa.

[0018] The heat treatment time is 60℃ for 8 hours.

[0019] Furthermore, in step (4), the curing temperature is 60°C and the curing time is 8 hours.

[0020] A method for applying a biomimetic surface to a micro crawling robot involves coating the biomimetic surface with cyanoacrylate adhesive and curing it with ultraviolet light to form an adhesive interface with the micro crawling robot. Since PDMS is difficult to bond using traditional UV adhesives, this invention introduces a polymer (cyanoacrylate adhesive) film on top to prevent the chemical components of PDMS from affecting the polymerization of the UV adhesive. Afterward, UV adhesive can be applied normally, and polymerization can be rapidly initiated by ultraviolet light to form a strong adhesive interface with a multi-layered structure of robot shell-UV adhesive-polymer film-PDMS. When this adhesive interface is bonded to the leg structure of a micro robot, actual testing shows that the micro robot can reach a maximum speed of 25 times its body length per second without the biomimetic surface, while with the biomimetic surface introduced, its maximum speed can reach 50 times its body length per second or even higher, representing a 100% increase in speed and a significant performance improvement.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] (1) Based on the foot structure of the tree frog, the present invention prepares an anisotropic high friction biomimetic surface, which has a friction coefficient that is 10 times higher than that of a bare surface;

[0023] (2) This invention uses laser direct writing to complete exposure and development + ICP plasma etching + PDMS casting method, and completes the preparation of biomimetic plane by surface hydrophilic and hydrophobic chemical modification. This biomimetic plane is applied to the leg structure of a micro robot with friction as the motion principle, which can significantly improve its motion performance. The maximum speed can reach 50 times the body length per second or even higher. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 The images show micrographs of the biomimetic surface in Example 1 and a schematic diagram of the chemical composition after plasma modification, where a) is a micrograph and b) is a schematic diagram of the chemical composition after plasma modification.

[0026] Figure 2 The images are of the preparation method in Example 1, where a) is a comparison of the effects before and after the defoaming process, the first image from left to right in a) is before defoaming, the second image is the defoaming and standing process, and the third image is after defoaming; b) is the 60℃ curing process; c) is the plasma surface modification process; and d) is an optical photograph of the biomimetic surface.

[0027] Figure 3 A comparison of the friction coefficients of a surface made of biomimetic surface, PDMS plane, and robot shell material in Example 1;

[0028] Figure 4 This is a speed-power frequency relationship graph after the biomimetic surface of Example 1 is applied to the robot. The ordinary plane refers to the result measured directly on the robot's bare shell.

[0029] Figure 5 This is the laser direct-write exposure and development image of the biomimetic surface in Example 1;

[0030] Figure 6 This is an electron microscope image of the biomimetic surface ICP etching in Example 1. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] Example 1

[0037] A method for preparing a biomimetic surface for use in micro crawling robots

[0038] (1) Processing using MEMS photolithography: A silicon wafer pre-coated with photoresist is exposed by laser direct writing to form a pre-designed geometric pattern (a regular hexagon with a long side of 100μm, a short side of 60μm, a vertices of 60°, a trench width of 20μm, and a depth of 50μm). Then, the exposed area is dissolved by developing solution to form a unique positive photoresist film structure. The positive photoresist film structure is transferred to the silicon wafer and a silicon-based template is formed using ICP etching technology.

[0039] (2) To prevent polydimethylsiloxane (PDMS (Dow Corning SYLGARD 184 silicone rubber), prepolymer (SYLGARD184-A): initiator (SYLGARD 184-B) = 10:1, mass ratio) from forming chemical bonds with SiO2 on the surface of the silicon-based template, thus making it difficult to peel off, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane was used on the surface of the silicon-based template under high temperature and vacuum (80℃, 10... 3 Vacuum evaporation is performed under Pa) to form a fluorinated layer with high electron density;

[0040] (3) After obtaining the silicon-based template with a fluorinated layer, PDMS (Dow Corning SYLGARD 184 silicone rubber) monomer (SYLGARD 184-A) and curing agent (SYLGARD 184-B) were uniformly mixed at a mass ratio of 10:1 and placed in a vacuum dish with a pressure of 100 kPa for 15 min to eliminate bubbles generated during thorough stirring. Then, the defoamed prepolymer was introduced into the culture dish containing the silicon-based template and placed in a vacuum dish with a pressure of 100 kPa for 15 min to ensure the prepolymer could fully penetrate the micro-nano structure on the silicon-based template and further defoam. After the low-pressure treatment, the entire culture dish was placed in an oven pre-set at 60°C and left for 8 h. The PDMS was then completely removed using a scalpel, and the silicon-based template was peeled off to obtain a PDMS negative mold with an unfluorinated biomimetic anisotropic high-friction surface.

[0041] (4) The PDMS negative mold was placed in a plasma cleaner. After the air pressure was reduced to 10 kPa, air plasma was introduced for surface modification for 10 minutes to introduce a large number of hydroxyl groups on the surface, so as to increase the thickness of the fluorinated layer formed in the next fluorination process and prevent the phenomenon that the bonding between the PDMS biomimetic surface and the PDMS negative mold is too strong and difficult to peel off. After the above steps, the fluorination steps of the silicon-based template were repeated on the PDMS negative mold to obtain a PDMS negative mold with a biomimetic anisotropic high friction surface. Similarly, after two defoaming processes as in the preparation of the PDMS negative mold, it was placed in an oven at 60°C for curing for 8 hours. After curing, the whole piece of PDMS obtained by curing was carefully cut longitudinally with a knife to find the interface between the negative mold and the PDMS biomimetic surface generated by the fluorinated layer. After carefully peeling off a part, anhydrous ethanol was squeezed into the gaps, and the biomimetic surface was successfully separated from the negative mold. Then, through the same air plasma cleaning process, the surface is modified with chemical components containing high oxygen functional groups to reduce the surface tension of water on it and enhance its hydrophilicity, thus obtaining the final PDMS biomimetic anisotropic high friction surface, i.e., biomimetic surface.

[0042] One drop (50 μL) of unpolymerized cyanoacrylate adhesive was added to the back of the aforementioned biomimetic surface using a dropper and spread evenly using a spotting tube. After being exposed to air for 30 minutes, the cyanoacrylate was fully polymerized. Then, a layer of approximately 100 μm of uncured UV adhesive was applied using a dropper. The UV adhesive-coated surface was then bonded to the surface of the robot shell to be bonded, and polymerization was quickly initiated using ultraviolet light to form a strong bonding interface of robot shell-UV adhesive-polymer film-PDMS multilayer structure.

[0043] Since PDMS is difficult to bond using traditional UV adhesives, this invention introduces a coating composed of high-molecular-weight cyanoacrylate adhesive to prevent the chemical components of PDMS from affecting the polymerization of UV adhesives. After this, UV adhesive can be applied normally, and polymerization is initiated by ultraviolet light to form an adhesive interface. This adhesive interface is then bonded to the leg structure of a microrobot. Actual tests show that the microrobot can reach a maximum speed of 25 times its body length per second without a biomimetic plane, while with the introduction of a biomimetic plane, its maximum speed can reach 50 times its body length per second or even higher, representing a 100% increase in speed and a significant performance improvement.

[0044] See the micrograph of the biomimetic surface and the schematic diagram of the chemical composition of the plasma-modified surface in Example 1. Figure 1 Where a) is a microscope photograph, and b) is a schematic diagram of the chemical composition of plasma modification; photographs of the preparation method in Example 1 are shown below. Figure 2 The figures are as follows: a) shows the comparison of the effects before and after the defoaming process; from left to right, the first image in a) is before defoaming, the second image is the defoaming and standing process, and the third image is after defoaming; b) shows the 60℃ curing process; c) shows the plasma surface modification process; and d) shows an optical photograph of the biomimetic surface. The friction coefficient of the biomimetic surface, PDMS plane, and robot shell material used in Example 1 was tested. The test method is as follows: The prepared biomimetic high-friction surface and the control samples (plane PDMS and robot shell material) were cut into small pieces of the same size. The surfaces of the test samples were ensured to be clean and free of impurities and contaminants. A metal plate was placed on the test platform of the friction coefficient tester, and a force sensor was connected to the tester. The test samples and control samples were installed on the upper and lower supports of the tester, respectively. Using a metal friction probe, the test was run for 100 seconds at a test speed of 0.01 mm / s and a pressure of 1 N. Before the test, the test environment was kept at a constant temperature and humidity (25℃, approximately 40% RH) to minimize errors caused by environmental changes. Start the testing instrument and begin the test, recording data during the process, including the frictional force between the test samples and the test time. After the test, clean the test samples to prepare for the next test. For the anisotropic frictional force of the samples, the direction with the highest frictional force is defined as the 0° angle, and the friction coefficient is compared from both the 0° and 90° directions during the test. To assess the biomimetic surface's adaptability to humid environments, two drops (approximately 50 μL) of deionized water are added to the surface using a dropper to characterize its friction coefficient on wet surfaces. Calculate the coefficient of friction based on the test data. The coefficient of friction is calculated by dividing the frictional force between the test samples by the pressure applied to the test samples during the test. See the results below. Figure 3 ,Depend on Figure 3It can be seen that the coefficient of friction of the biomimetic surface is increased by 10 times compared with the bare surface. The relationship between the robot's crawling speed and power supply frequency after the biomimetic surface was introduced was tested using the following method: An experimental platform was built, using a mat as the ground, and a square wave AC power supply was used. Displacement under different frequencies and current parameters was measured using a ruler over a certain period of time. The speed-power supply frequency relationship graph after the biomimetic surface was applied to the robot in Example 1 is shown below. Figure 4 The result of direct measurement of the exposed shell of the robot in ordinary flat surfaces; see the laser direct writing exposure and development pattern of the biomimetic surface in Example 1. Figure 5 Example 1: Electron microscope image of biomimetic surface ICP etching. Figure 6 .

[0045] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a biomimetic surface for use in micro crawling robots, characterized in that, Includes the following steps: (1) Processing using MEMS photolithography: A silicon wafer pre-coated with photoresist is exposed by laser direct writing to form a pre-designed geometric pattern. Then, the exposed area is dissolved by developing solution to form a positive photoresist film structure. The positive photoresist film structure is transferred to the silicon wafer and a silicon-based template is formed by ICP etching technology. (2) A fluorinated layer is formed by vacuum evaporation of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane on the surface of a silicon-based template, thus obtaining a silicon-based template with a fluorinated layer. (3) After obtaining the silicon-based template with the fluorinated layer, the polydimethylsiloxane monomer and the curing agent are mixed and allowed to stand to obtain a prepolymer liquid. The silicon-based template with the fluorinated layer is impregnated with the prepolymer liquid, heat-treated, the polydimethylsiloxane is removed, and the silicon-based template is peeled off to obtain a polydimethylsiloxane female mold with an unfluorinated biomimetic anisotropic high friction surface. (4) Clean the surface of the polydimethylsiloxane negative mold with air plasma, repeat the fluorination step of the silicon template on the dimethylsiloxane negative mold to obtain the polydimethylsiloxane negative mold, cure it to obtain a biomimetic surface that is slightly attached to the negative mold, peel the biomimetic surface from the negative mold, clean the biomimetic surface with air plasma to obtain a biomimetic surface for use in micro crawling robots. In step (3), the mass ratio of polydimethylsiloxane monomer to curing agent is 10:1; The settling time is 15 minutes, and the air pressure during settling is 100 kPa. When impregnating a silicon-based template with a fluorinated layer with prepolymer solution, the processing time is 15 min and the air pressure is 100 kPa. The heat treatment time is 60℃ for 8 hours; In step (4), the curing temperature is 60℃ and the curing time is 8h; The biomimetic surface used in the micro crawling robot is formed by axially stretching a closely spaced regular hexagonal groove to create a structure with a long side of 100 μm, a short side of 60 μm, a vertices of 60°, a groove width of 20 μm, and a depth of 50 μm.

2. The method for preparing a biomimetic surface for use in a micro crawling robot according to claim 1, characterized in that, In step (1), the photoresist is S1813 reagent; the developer is NMD developer.

3. The method for preparing a biomimetic surface for use in a micro crawling robot according to claim 1, characterized in that, In step (2), the vacuum evaporation temperature is 80℃ and the vacuum degree is 10. 3 Pa.

4. A method for applying biomimetic surfaces to a micro crawling robot, characterized in that, The biomimetic surface described in claim 1 is coated with cyanoacrylate adhesive and then cured with ultraviolet light to form an adhesive interface with the micro crawling robot.

Images