Miniature pneumatic artificial muscle based on phase transition hydrogel driver and preparation method and application of miniature pneumatic artificial muscle

Abstract

The invention discloses a micro pneumatic artificial muscle based on a phase transition hydrogel driver and a preparation method and application thereof, and belongs to the technical field of polymer functional materials. The method comprises the following steps: (1) taking octyl acrylate and acrylamide as monomers, dissolving the monomers, beta-cyclodextrin and a cross-linking agent in a dimethylformamide dispersion liquid of sea squirt cellulose nanocrystals, and then adding a photoinitiator to obtain a pre-polymerized liquid; carrying out light curing and solvent replacement on the pre-polymerized liquid to obtain hydrogel with a pipeline-shaped structure; and (2) connecting one end of the hydrogel with the pipeline-shaped structure with the air cavity, and sealing the other end of the hydrogel to obtain the micro pneumatic artificial muscle based on the phase change hydrogel driver. The method has the advantages of convenient process, mild reaction and wide and easy materials. The miniature pneumatic artificial muscle prepared based on the method has the characteristics of adjustable mechanical properties independent of water permeation and high driving speed, and has a wide application prospect in miniature bionic soft robot equipment.

Description

Technical Field

[0001] The invention relates to the technical field of polymer functional materials, and in particular to a micro-pneumatic artificial muscle based on a phase-change hydrogel driver, and a preparation method and application thereof. Background Art

[0002] Pneumatic artificial muscles have the advantages of fast response, high stroke and high driving force, and are considered to be the most promising soft actuators. However, the driving source of pneumatic artificial muscles is heavily dependent on bulky equipment such as compressors and pumps, which limits their miniaturized applications. In addition, the current pneumatic artificial muscle materials do not contain water and do not achieve the bionic function of natural muscles in structure.

[0003] Recent micro-pneumatic artificial muscles are designed around the idea of ​​achieving internal air pressure changes through external stimuli, which usually include two directions: using internal fluids to produce pressure changes and using actuator materials to change pressure changes. The design of internal fluids includes: liquid-gas phase transition fluids, combustion reactions, chemical reactions that produce gases, and swelling / de-swelling, etc. Liquid-gas phase transition fluids are the most widely used method because these low-boiling point liquids can vaporize after heating, produce high-pressure expansion, and can liquefy after cooling to achieve reversible drive. However, liquid vaporization requires a lot of time and consumes considerable energy. Another method is to use smart membrane materials as pneumatic artificial muscles. A typical example is a dielectric elastomer membrane. By applying voltage on both sides of the membrane, the membrane material can be expanded in the in-plane direction, resulting in a decrease in the internal air pressure of the system to achieve drive.

[0004] The inventor disclosed a preparation method and application of shape memory hydrogel in a Chinese patent with publication number CN112940288A. The preparation method of the invention includes the following steps: step 1, dissolving acrylamide, acrylic acid, and acrylamide adamantane in a certain amount ratio in a dispersion of cyclodextrin-grafted sea squirt cellulose nanocrystals, incubating at 55 ° C for 2 h, cooling in an ice water bath, adding initiator ammonium persulfate, injecting the dispersion into a mold, and polymerizing at 55 ° C for 5 h to obtain a single cross-linked hydrogel; step 2, subjecting the single cross-linked hydrogel obtained in step 1 to a series of continuous orientation operations to obtain a spiral hydrogel; step 3, soaking the spiral hydrogel obtained in step 2 in a fixing solution for 24 h to obtain a shape memory hydrogel. The shape memory hydrogel has two chiral helical structures, which can respectively realize telescopic deformation in opposite directions under the stimulation of ethanol water solvent circulation. However, the driving process of this hydrogel material used as artificial muscle is realized in a swollen state, and its elastic modulus is low, resulting in low driving force and working capacity of the artificial muscle. At the same time, the shape memory hydrogel imitates the movement patterns of cucumber tendrils in nature through the shape memory effect, including climbing, winding and spiral contraction movements, but the driving speed is very slow, reaching a maximum of 17.9% / s, which limits its scope of application.

[0005] In the Chinese invention patent with publication number CN116426005A, the inventor provides a temperature-responsive hydrogel artificial muscle and its preparation method and application. The method comprises: dissolving N-isopropyl acrylamide, 3-sulfopropyl methacrylate potassium salt, acrylamide, a crosslinking agent, an initiator and a promoter in proportion in a sulfuric acid-hydrolyzed aqueous dispersion of sea squirt cellulose nanocrystals to obtain a mixed solution; then injecting the mixed solution into a mold for polymerization to obtain a chemically crosslinked hydrogel; continuously orienting the chemically crosslinked hydrogel to obtain a spiral hydrogel; immersing the spiral hydrogel in a zirconium salt solution to obtain a hydrogel artificial muscle. The hydrogel artificial muscle can achieve telescopic deformation through temperature stimulation and can be applied to soft actuator robots. However, it is still limited by the driving speed, which only reaches 0.7% / s, which limits its application.

[0006] In addition, the inventor disclosed a hydration-programmable shape memory artificial muscle and its preparation method and application in a Chinese patent with publication number CN117820555A. The preparation method includes the following steps: (1) in a solution environment, polyvinyl alcohol, sea squirt cellulose nanocrystals and polymerized monomers composed of acrylamide, acrylic acid and N,N'-methylenebisacrylamide are mixed and incubated to obtain a polymer precursor dispersion; (2) an initiator is added to the polymer precursor dispersion, and a fibrous hydrogel material is formed through polymerization reaction to obtain a shape memory artificial muscle. The raw materials of this method are widely available, the process is simple and fast, and the prepared shape memory artificial muscle has ultra-high elongation at break and toughness, and can realize shape programming and recovery process under high pre-stretching ratio and constant stress. When used in bionic structures, the antagonistic movement of artificial arms is realized. However, this artificial muscle shrinks to -60% strain within 3 s when heated to 120 °C, and the driving speed is still low, which is also limited in practical applications.

[0007] In summary, hydrogel materials have the biomimetic advantages of biological tissues due to their rich water content, but traditional hydrogel actuators achieve shape changes through swelling / de-swelling, a process that requires water molecules to penetrate the hydrogel network, thus limiting the rapid actuation of hydrogel actuators. Improving the actuation speed of artificial muscles is an urgent problem to be solved, which is of great significance for expanding the application of artificial muscles. Summary of the invention

[0008] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for preparing a micro-pneumatic artificial muscle based on a phase change hydrogel actuator with convenient process and mild reaction is provided, comprising the following steps: (1) Using octyl acrylate and acrylamide as monomers, the monomers, β-cyclodextrin and a crosslinking agent are dissolved in a dimethylformamide dispersion of ascidian cellulose nanocrystals, and then a photoinitiator is added to obtain a prepolymer solution; the prepolymer solution is photocured and solvent replaced to obtain a hydrogel with a tubular structure; (2) One end of the tubular hydrogel is connected to the air cavity and the other end is sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

[0009] Preferably, in step (1), the proportion of octyl acrylate to monomers is 6.7 mol.%-33.3 mol.%.

[0010] Preferably, in step (1), the proportion of monomers in the prepolymer solution is 20 wt.%-30 wt.%.

[0011] Preferably, in step (1), the molar ratio of β-cyclodextrin to octyl acrylate is 0-1:1.

[0012] Preferably, in step (1), the ratio of the cross-linking agent to the prepolymer solution is 1 wt.%-3 wt.%.

[0013] Those skilled in the art can select a suitable crosslinking agent based on the type of polymer raw material. Among them, N,N'-methylenebisacrylamide is a particularly suitable type for the preparation of the present invention. N,N'-methylenebisacrylamide can form stable covalent bonds during the polymerization process, connecting individual polymer chains together to form a tough three-dimensional network structure. Its presence ensures the effective connection of each chain segment and enhances the stability and mechanical strength of the overall structure.

[0014] Further preferably, the crosslinking agent includes at least one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and trimethylolpropane triacrylate.

[0015] Preferably, in step (1), the concentration of the dimethylformamide dispersion of the ascidian cellulose nanocrystals is 0.1 wt.%-0.3 wt.%.

[0016] Preferably, in step (1), the ratio of the photoinitiator to the prepolymer solution is 1 wt.%-3 wt.%.

[0017] The reaction conditions of photocuring are mild, and it can initiate polymerization under light irradiation at room temperature to form a stable polymer network. Photocuring allows precise control of the curing position of the material in a complex three-dimensional space, and is very suitable for making hydrogels with highly complex internal structures. Those skilled in the art can also select appropriate photoinitiators and curing times based on the type of polymer raw materials and the scale of production. As presented in one or more embodiments of the present invention, I2959 is a particularly suitable type of photoinitiator selection due to its superior water solubility, light absorption properties, high photopolymerization efficiency and good biocompatibility.

[0018] Further preferably, the photoinitiator includes at least one of 2-hydroxy-1-(4-(2-hydroxyethoxy)phenyl)-2-methyl-1-propanone (I2959), 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), and phenyl-2,4,6-trimethylbenzoyl lithium phosphite (LAP).

[0019] The hydrogel with a tubular structure can be synthesized by placing reactants in a transparent tubular mold, or by using other suitable processing methods in the art to form a tubular structure.

[0020] In the second aspect of the present invention, a micro-pneumatic artificial muscle based on a phase change hydrogel actuator with fast driving speed and adjustable mechanical properties is provided, wherein the micro-pneumatic artificial muscle comprises a tubular hydrogel structure and an air cavity, and is manufactured by the preparation method of the first aspect of the present invention.

[0021] Based on the above technical scheme, the design concept and principle of the present invention are to use octyl acrylate and acrylamide as monomers, dissolve them with β-cyclodextrin and a cross-linking agent in a dimethylformamide dispersion of sea squirt cellulose nanocrystals, and prepare hydrogels by a photocuring process, so that the hydrogels with tubular structures can achieve the regulation of mechanical properties without relying on water exchange with the outside world. This is caused by the switching between the hydrophobic interaction inside the hydrogel and the host-guest interaction. At room temperature, the hydrophobic chains of the side groups of the hydrogel polymer chains will form strong hydrophobic interactions after solvent replacement, increase the hydrophobic cross-linking inside the hydrogel network, and enhance the mechanical properties of the hydrogel. When the hydrogel is heated, these hydrophobic groups will form host-guest interactions with the free cyclodextrin inside the hydrogel network, resulting in the opening of hydrophobic cross-linking and the reduction of the mechanical properties of the hydrogel, realizing the thermal stimulation phase transition of the hydrogel from microphase separation to homogeneous phase.

[0022] Therefore, the micro-pneumatic artificial muscle can achieve a phase transition effect when heated, and the microphase separation generated by hydrophobic association cross-linking is transformed into a homogeneous hydrogel generated by host-guest interaction, which leads to a decrease in the modulus of the hydrogel and an increase in toughness. When the hydrogel with a tubular structure is sealed at one end, the other end is pressurized and filled with fluid, and the hydrogel can be expanded. During expansion, the radial expansion strain is greater than the axial expansion strain. The air pressure-volume curve of the hydrogel with a tubular structure when pressurized and expanded will decrease with increasing temperature, that is, the critical pressure decreases. When the hydrogel is connected to the air cavity, the hydrogel is pressurized to a state close to the critical pressure through the change of the air cavity volume at low temperature, and the hydrogel is in a high-pressure and small-volume steady state; when the hydrogel is heated, the hydrogel causes the modulus to decrease through phase transition, and the internal pressure exceeds the critical pressure. At this time, the hydrogel triggers sudden instability, realizes rapid expansion of the volume, and finally reaches a low-pressure and large-volume steady state.

[0023] In the third aspect of the present invention, there is provided an application of the micro-pneumatic artificial muscle based on the phase change hydrogel actuator according to the second aspect of the present invention, specifically, an application as an artificial muscle in the preparation of a robot.

[0024] Preferably, the robot includes a diving robot and a rolling robot.

[0025] Further preferably, the inner diameter of the tubular structured hydrogel is 1-3 mm, the outer diameter is 3-6 mm, and the internal volume of the air cavity is 0.5-5 mL.

[0026] The hydrogel with a tubular structure has adjustable mechanical properties that are independent of water penetration. After being connected to a miniaturized air cavity, it can remain stable after pressurization until external thermal stimulation triggers the hydrogel to suddenly become unstable, causing the actuator to expand rapidly. The air cavity can adopt a sealed but variable volume syringe pump structure. In application, the micro-pneumatic artificial muscle can be driven by external thermal stimulation after separating the compressor and air pump and other equipment. First, the air cavity is pressurized at room temperature, at which time the hydrogel actuator is in a high-pressure and small-volume steady state; after the hydrogel is heated, its volume expands rapidly. This is because the modulus of the hydrogel decreases and the toughness increases after heating, and the internal air pressure is higher than the critical pressure of the actuator, thereby triggering sudden instability, causing the hydrogel to reach a low-pressure and large-volume steady state and complete the drive. Phase transition hydrogel can use a mechanism without water participation to achieve the switching of hydrogel mechanical properties. Therefore, the combination of phase transition hydrogel and pneumatic artificial muscle makes miniaturized bionic soft robot devices possible.

[0027] For diving robots, the micro-pneumatic artificial muscles will sink in cold water after being pre-pressurized, while in hot water, the robot will sink first and then float up quickly because the actuator rapidly expands in an unstable manner in a short period of time. For rolling robots, the micro-pneumatic artificial muscles will expand in response to heat after being pre-pressurized, which will drive the robot to roll, allowing the robot to roll a long distance in a short period of time.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides a method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator, which has the advantages of convenient process, mild reaction and wide and easy use of materials.

[0029] The invention provides a micro-pneumatic artificial muscle based on a phase-change hydrogel driver, which has adjustable mechanical properties independent of water penetration and fast driving speed.

[0030] The present invention provides an application of a micro-pneumatic artificial muscle based on a phase-change hydrogel driver, which has broad application prospects in miniaturized bionic soft robotic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A physical picture of the rapid expansion of a hydrogel actuator with a tube-like structure; Figure 2 A physical picture of a submersible robot diving in cold water and surfacing in hot water; Figure 3 This is a photo of the rolling robot rolling after thermal stimulation. DETAILED DESCRIPTION

[0032] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0033] In the following embodiments: A transparent pipe mold with an inner diameter of 2 mm and an outer diameter of 5 mm was used.

[0034] Example 1 A method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator, comprising the following steps: (1) 0.077 g acrylamide, 82 μL octyl acrylate, 0.448 g β-cyclodextrin, and 0.012 g N, N'-methylenebisacrylamide were dissolved in 0.8 g dimethylformamide dispersion (0.2 wt.%) of ascidian cellulose nanocrystals, and then 0.01 g photoinitiator I2959 was added to obtain a prepolymer solution. The prepolymer solution was injected into a transparent tube mold, exposed to ultraviolet light at room temperature for 2 h, and then immersed in water for solvent replacement for 3 days to obtain a hydrogel with a tube structure. (2) One end of the tubular hydrogel was connected to an air cavity with an initial volume of 6 mL and the other end was sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

[0035] Example 2 A method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator, comprising the following steps: (1) 0.077 g acrylamide, 82 μL octyl acrylate, 0.448 g β-cyclodextrin, and 0.012 g N, N'-methylenebisacrylamide were dissolved in 0.8 g dimethylformamide dispersion (0.2 wt.%) of ascidian cellulose nanocrystals, and then 0.01 g photoinitiator I2959 was added to obtain a prepolymer solution. The prepolymer solution was injected into a transparent tube mold, exposed to ultraviolet light at room temperature for 2 h, and then immersed in water for solvent replacement for 3 days to obtain a hydrogel with a tube structure. (2) One end of the tubular hydrogel was connected to an air cavity with an initial volume of 1 mL and the other end was sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

[0036] Example 3 In this embodiment, after 0.9 mL of compressed gas was injected into the air cavity of the micro-pneumatic artificial muscle prepared in Example 1, the hydrogel with the tubular structure was heated to 70°C. Figure 1 As shown, the hydrogel radially expanded by 350% within 10 s, the expansion rate reached 200% / s, and its working capacity reached 27.2 J / kg.

[0037] The micro pneumatic artificial muscle prepared in Example 1 was integrated into a diving robot, and its effect in practical application was studied. Figure 2 As shown in the figure, the submersible robot is placed in 20 ℃ water and stays at the bottom of the water. When the ambient temperature changes to 70 ℃, the submersible robot quickly floats up within 3 s under the same operation. This is because it expands rapidly in hot water, which increases the buoyancy of the submersible robot and enables it to float up.

[0038] Example 4 The air cavity of the micro-pneumatic artificial muscle prepared in Example 2 was pressurized with 0.3 mL and then used to prepare a rolling robot. Figure 3 As shown in the figure, when the hydrogel is heated to 70 °C, the hydrogel expands radially by 210% within 10 seconds, and the expansion rate reaches 130% / s. The expansion of the hydrogel under thermal response will drive the robot to roll, so that the robot rolls forward 8.3 cm within 6 seconds.

[0039] Example 5 (1) 0.126 g acrylamide, 26.5 μL octyl acrylate, 0.144 g β-cyclodextrin, and 0.012 g N,N'-methylenebisacrylamide were dissolved in 0.8 g dimethylformamide dispersion (0.3 wt.%) of ascidian cellulose nanocrystals, and then 0.01 g photoinitiator I2959 was added to obtain a prepolymer solution. The prepolymer solution was injected into a transparent tube mold, exposed to ultraviolet light at room temperature for 2 h, and then immersed in water for solvent replacement for 3 d to obtain a hydrogel with a tube structure. (2) One end of the tubular hydrogel was connected to an air cavity with an initial volume of 6 mL and the other end was sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

[0040] Example 6 (1) 0.065 g acrylamide, 96 μL octyl acrylate, 0.522 g β-cyclodextrin, and 0.012 g N, N'-methylenebisacrylamide were dissolved in 0.8 g dimethylformamide dispersion (0.1 wt.%) of ascidian cellulose nanocrystals, and then 0.01 g photoinitiator I2959 was added to obtain a prepolymer solution. The prepolymer solution was injected into a transparent tube mold, exposed to ultraviolet light at room temperature for 2 h, and then immersed in water for solvent replacement for 3 days to obtain a hydrogel with a tube structure. (2) One end of the tubular hydrogel was connected to an air cavity with an initial volume of 6 mL and the other end was sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

[0041] In summary, compared to the traditional hydrogel actuator that achieves shape change through swelling / de-swelling, the micro-pneumatic artificial muscle of the present invention can achieve mechanical property regulation without relying on water exchange with the outside world by switching between hydrophobic interaction and host-guest interaction inside the hydrogel. At room temperature, the hydrophobic chains of the side groups of the hydrogel polymer chain will form strong hydrophobic interactions after solvent replacement, increase the hydrophobic cross-linking inside the hydrogel network, and enhance the mechanical properties of the hydrogel. When the hydrogel is heated, these hydrophobic groups will form host-guest interactions with the free cyclodextrin inside the hydrogel network, resulting in the opening of hydrophobic cross-linking and the reduction of the mechanical properties of the hydrogel, realizing the thermal stimulation phase transition of the hydrogel from microphase separation to homogeneous phase.

[0042] After integrating the micro-pneumatic artificial muscle into the robot, the air cavity is first pressurized at room temperature, at which point the hydrogel actuator is in a high-pressure, small-volume steady state. The diving robot can dive in cold water, but in hot water, the hydrogel is heated, the modulus decreases and the toughness increases, and the internal air pressure is higher than the critical pressure of the actuator, triggering sudden instability, causing the hydrogel to reach a low-pressure, large-volume steady state, and its volume expands rapidly, with an expansion rate of 200% / s, resulting in an increase in the robot's buoyancy and completing the floating drive. The rolling robot can rely on the expansion of the hydrogel to make its center of gravity unstable, thereby achieving rolling, and rolling forward 8.3 cm in 6 seconds.

[0043] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a micro pneumatic artificial muscle based on a phase change hydrogel actuator, characterized in that: The steps include: (1) Using octyl acrylate and acrylamide as monomers, the monomers, β-cyclodextrin and a crosslinking agent are dissolved in a dimethylformamide dispersion of ascidian cellulose nanocrystals, and then a photoinitiator is added to obtain a prepolymer solution; the prepolymer solution is photocured and solvent replaced to obtain a hydrogel with a tubular structure; (2) One end of the tubular hydrogel is connected to the air cavity and the other end is sealed to obtain a micro pneumatic artificial muscle based on a phase change hydrogel actuator.

2. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the proportion of octyl acrylate to monomers is 6.7 mol.%-33.3 mol.%.

3. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the proportion of monomers in the prepolymer solution is 20 wt.%-30 wt.%.

4. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the molar ratio of β-cyclodextrin to octyl acrylate is 0-1:

1.

5. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the ratio of the crosslinking agent to the prepolymer solution is 1 wt.%-3 wt.%; the crosslinking agent includes at least one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and trimethylolpropane triacrylate.

6. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the concentration of the dimethylformamide dispersion of the ascidian cellulose nanocrystals is 0.1 wt.%-0.3 wt.%.

7. The method for preparing a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator according to claim 1, characterized in that: In the step (1), the ratio of the photoinitiator to the prepolymer solution is 1 wt.%-3 wt.%; the photoinitiator includes at least one of 2-hydroxy-1-(4-(2-hydroxyethoxy)phenyl)-2-methyl-1-propanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and phenyl-2,4,6-trimethylbenzoyl lithium phosphite.

8. A micro pneumatic artificial muscle based on a phase-change hydrogel actuator, characterized in that: The structure includes a tubular structure of hydrogel and an air cavity, and is made by the preparation method described in any one of claims 1-7.

9. An application of a micro-pneumatic artificial muscle based on a phase-change hydrogel actuator as claimed in claim 8, characterized in that: Application as artificial muscle in the preparation of robots.

10. The application of the micro-pneumatic artificial muscle based on the phase-change hydrogel actuator according to claim 9, characterized in that: The robots include diving robots and rolling robots; the inner diameter of the tubular structure hydrogel is 1-3 mm, and the outer diameter is 3-6 mm; the internal volume of the air cavity is 0.5-5 mL.

Images