Electrothermal response three-layer hydrogel actuator and preparation method thereof
By using a three-layer hydrogel actuator, combined with a flexible heater consisting of polyvinyl alcohol, lithium magnesium silicate, nano-silica, and silver nanowires, a multi-response hydrogel actuator under multiple environmental stimuli was achieved. This solves the problem of single actuation conditions in existing actuators and improves their performance in specific application areas.
Patent Information
- Application Number
- CN202511089065.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-05
- Publication Date
- 2025-11-11
AI Technical Summary
Existing hydrogel actuators mainly consist of a driving layer and a rigid layer, and their actuation conditions are limited, which affects their application potential in underwater robots, grippers, valve switches and other fields.
The hydrogel actuator employs a three-layer structure, comprising a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer, a silver nanowire flexible heater, and a polyimide film. By introducing polyvinyl alcohol, lithium magnesium silicate, and nano-silica, the mechanical properties are improved, and the silver nanowire flexible heater is used to convert external thermal stimulation into electrical signal stimulation, thereby achieving multiple responses.
This improves the controllability and responsiveness of hydrogel actuators, enabling them to perform bending motions under various environmental conditions, thus enriching their application scenarios, especially in the fields of underwater robots, grippers, and valve switches.
Smart Images
Figure CN120921782A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of intelligent drive technology, and in particular to an electrothermal responsive three-layer hydrogel actuator, and also to a method for preparing the three-layer hydrogel actuator. Background Technology
[0002] Hydrogels are polymers rich in water and have a three-dimensional network structure. Currently, hydrogels are widely used in food preservation, biomedicine, and tissue engineering. Hydrogel actuators are devices made of hydrogels that can respond to specific environments. They show great application potential in fields such as soft robotics, drug delivery, and intelligent sensing. The power of such responsive actuators usually comes from the heterogeneous structure of two layers of hydrogel. Under different conditions, the difference in swelling and deswelling of the heterogeneous structure drives it to perform bending and other movements.
[0003] However, conventionally fabricated hydrogel actuators mainly consist of a driving layer and a rigid layer. The driving layer receives and responds to environmental stimuli by contracting or swelling, while the rigid layer does not have a responsive capability and serves as a support. This causes the contraction motion of the driving layer hydrogel to evolve into the bending motion of a bilayer heterogeneous hydrogel. The problem with this bilayer hydrogel is that it can only rely on one of the active hydrogel layers for response, resulting in a relatively simple actuation condition, which limits its application potential in underwater robots, grippers, valve switches, and other fields. Summary of the Invention
[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electrothermal responsive three-layer hydrogel actuator and its preparation method.
[0005] A method for preparing an electrothermal responsive three-layer hydrogel actuator includes the following steps:
[0006] (1) Dissolve N-isopropylacrylamide in deionized water, then add polyvinyl alcohol, lithium magnesium silicate and nano silica in sequence, mix well, add crosslinking agent and ammonium persulfate, mix well and remove foam, add initiator, pour into mold for polymerization to obtain poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer.
[0007] (2) A silver nanowire layer is obtained by screen printing, a flexible ribbon cable is connected to the silver nanowire layer and bonded between two polyurethane films, and a silver nanowire flexible heater is obtained by hot pressing.
[0008] (3) The polyimide film is placed in an alkaline solution, taken out and dried, and then the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer prepared in step (1) is pressed onto one surface of the polyimide film. The silver nanowire flexible heater obtained in step (2) is pressed onto the other surface of the polyimide film and rolled to obtain a three-layer hydrogel actuator.
[0009] As a further improvement to the above scheme, in step (1), the amount of deionized water is equivalent to 2 to 4 times that of N-isopropylacrylamide; the mass ratio of N-isopropylacrylamide, polyvinyl alcohol, lithium magnesium silicate and nano silica is 1:0.1 to 0.25:0.2 to 0.3:0.2 to 0.3.
[0010] As a further improvement to the above scheme, in step (1), the amount of the crosslinking agent is 0.5% to 1.5% of N-isopropylacrylamide; the amount of the ammonium persulfate is 0.3% to 1% of N-isopropylacrylamide; the amount of the initiator is 0.7% to 2% of N-isopropylacrylamide; the crosslinking agent includes N,N′-methylenebisacrylamide; and the initiator includes N,N,N',N'-tetramethylethylenediamine.
[0011] As a further improvement to the above scheme, the specific operation of adding the initiator in step (1) is as follows: use a pipette to measure the initiator and add it to the solution to remove foam, stir under ice water bath conditions to form a pregel solution, pour the pregel solution into the mold, and after standing for a period of time, a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer with a thickness of 3-6 mm is obtained.
[0012] As a further improvement to the above scheme, in step (2), the mass ratio of the silver nanowire ink to N-isopropylacrylamide is 0.1 to 0.3:1; the thickness of the polyurethane film is 50 to 100 μm; the hot pressing temperature is 120 to 150 °C, and the hot pressing time is 8 to 12 min.
[0013] As a further improvement to the above scheme, in step (2), the method of obtaining the silver nanowire layer by screen printing is specifically operated as follows: place the silver nanowire ink on the edge of the screen printing stencil, use a squeegee to scrape the silver nanowire ink from one side of the pattern to the other side, keep the squeegee in line contact with the stencil during the printing process, apply uniform force and uniform speed, and put the substrate with printed ink into an oven at 60-100°C to bake it and solidify it to obtain the silver nanowire layer.
[0014] As a further improvement to the above scheme, in step (3), the thickness of the polyimide film 2 is 15-100 μm; the polyimide film is placed in an alkaline solution and heated at 50-80°C for 3-8 minutes; the alkaline solution is a 5% sodium hydroxide solution; in this invention, the alkaline solution is conducive to etching the surface of the polyimide film under a heating environment.
[0015] As a further improvement to the above scheme, after drying, the tissue adhesive is applied to the surface of the polyimide film to form a mesh-like adhesive layer, and then the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer obtained in step (1) is oriented and laminated onto the surface of the polyimide film to connect the two.
[0016] As a further improvement to the above scheme, an epoxy adhesive coating is applied to the other surface of the polyimide film. The silver nanowire flexible heater obtained in step (2) is aligned with the epoxy adhesive coating and rolled to obtain a three-layer hydrogel actuator. The epoxy adhesive coating is a two-component flexible epoxy adhesive obtained by mixing epoxy resin main agent and curing agent in a 1:1 ratio. The thickness of the epoxy adhesive coating is 10-15 μm.
[0017] As a further improvement to the above scheme, the three-layer hydrogel actuator obtained by step (3) is placed in an electrically powered environment or a hot water environment, and the hydrogel actuator performs bending motion; in the electrically powered environment, a voltage of 5 to 10V is applied; the temperature of the hot water is greater than 32°C.
[0018] A three-layer hydrogel actuator, prepared by the aforementioned method, comprises a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer, a silver nanowire flexible heater, and a polyimide film located between the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer and the silver nanowire flexible heater; wherein the silver nanowire flexible heater comprises two polyurethane films, a silver nanowire layer located between the two polyurethane films, and flexible wiring laid on the silver nanowire layer.
[0019] As a further improvement to the above scheme, the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer is bonded and fixed on one side of the polyimide film, and the silver nanowire flexible heater is bonded and fixed on the other side of the polyimide film; the silver nanowire layer is bonded and fixed between the two polyurethane films.
[0020] Compared with the prior art, the beneficial effects of the present invention are:
[0021] This invention introduces polyvinyl alcohol, lithium magnesium silicate, and nano-silica into poly(N-isopropylacrylamide) hydrogel, significantly improving the mechanical and thermal response properties of the hydrogel. The introduction of a silver nanowire flexible heater converts the external thermal stimulation required by the hydrogel actuator into an electrical signal stimulation, significantly improving the controllability of the hydrogel actuator.
[0022] The preparation method of this invention is simple and easy to operate. The resulting hydrogel actuator has a three-layer structure, good mechanical properties, and exhibits good, rapid, and stable response to both temperature and current. This enriches the actuation conditions. The temperature response is derived from the thermal shrinkage property of poly(N-isopropylacrylamide), while the current response is derived from the Joule heating property of the silver nanowire flexible heater. The hydrogel actuator prepared by this invention can play a better role in underwater robots, grippers, valve switches, and other fields, showing excellent application prospects. Attached Figure Description
[0023] Figure 1 The diagram shown is a schematic diagram of a three-layer hydrogel actuator provided in Embodiment 3 of the present invention.
[0024] Explanation of main component symbols
[0025] 1. Poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer; 2. Polyimide film; 3. Polyurethane film; 4. Silver nanowire layer; 5. Flexible cable.
[0026] The above description of the main component symbols, together with the accompanying drawings and specific embodiments, provides a more detailed explanation of the present invention. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.
[0028] The specific embodiments of the present invention will be described in detail below.
[0029] Example 1
[0030] This embodiment provides a method for preparing an electrothermally responsive three-layer hydrogel actuator, which includes the following steps:
[0031] (1) Add 400 mg N-isopropylacrylamide and 3 ml deionized water to a beaker in sequence. After stirring magnetically for 30 min to dissolve completely, add 80 mg polyvinyl alcohol, 80 mg lithium magnesium silicate, and 80 mg nano silica. After stirring magnetically for 2 h to dissolve completely, add 4 mg N,N′-methylenebisacrylamide and 15 mg ammonium persulfate. After stirring magnetically to mix evenly, treat with an ultrasonic cleaner for 30 min to remove foam. Accurately measure 7.8 mg N,N,N',N'-tetramethylethylenediamine with a pipette and add it to the beaker. Place the beaker in an ice-water bath and continue stirring for 10 min to form a pregel solution. Pour the pregel solution into a mold with a depth of 3 mm and let it stand for 25 min to obtain a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 with a thickness of 3 mm.
[0032] In this embodiment, the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 contains poly(N-isopropylacrylamide) as a thermoresponsive polymer. Its molecular chain contains both hydrophilic amide groups and hydrophobic isopropyl groups. When the external temperature is higher than the lower critical dissolution temperature (≈32°C) of poly(N-isopropylacrylamide), the hydrophilic effect of the amide groups dominates. The hydrogen bonding between the amide groups and water molecules causes the hydrogel to absorb a large amount of water, thereby causing the hydrogel to expand. When the external temperature is lower than its lower critical dissolution temperature, the hydrophobic effect of the isopropyl groups dominates. The water inside the hydrogel is expelled, and the hydrogel shrinks, thus realizing the response of the hydrogel actuator to temperature stimulation.
[0033] In this embodiment, polyvinyl alcohol (PVA), lithium magnesium silicate, and nano-silica are introduced into poly(N-isopropylacrylamide) hydrogel to improve its mechanical and thermal response properties. PVA is a water-soluble synthetic polymer with a backbone rich in hydroxyl groups, giving it excellent hydrophilicity, film-forming properties, and chemical modifiability. PVA forms a stable hydrogel network through physical or chemical crosslinking, and its numerous hydroxyl groups allow for structural regulation and functional modification. Furthermore, PVA exhibits good biocompatibility, high mechanical strength, and unique environmental responsiveness. Lithium magnesium silicate is a layered nanoclay with a negatively charged lamellar structure, high specific surface area, and excellent dispersion, thickening, and thixotropic properties. It readily forms a transparent colloid in water and can be functionalized through ion exchange or surface modification, enhancing its performance and improving its responsiveness. Nano-silica improves dispersibility, strengthens the mechanical properties of the PVA hydrogel, and enhances its thermal response.
[0034] (2) Lay a 100μm thick polyurethane film 3 flat on the screen printing table, place the screen printing screen above the substrate, with a gap of 2-5mm between the substrate and the screen, place 50mg of silver nanowire ink on the edge of the screen, and use a squeegee to scrape the silver nanowire ink from one side of the pattern to the other side. During the printing process, the squeegee and the screen should maintain line contact, and the force and speed should be uniform. Place the substrate with the printed ink in an oven at 70℃ to bake it and cure it to obtain the silver nanowire layer 4. Connect the flexible ribbon cable 5 to the silver nanowire layer 4. Cut the substrate with the ink and the substrate used for encapsulation into rectangles. Lay the two polyurethane films 3 together to strengthen the connection of the flexible ribbon cable 5. Use a hot press to hot press at 130℃ for 10min to obtain the silver nanowire flexible heater.
[0035] In this embodiment, a silver nanowire layer 4 is obtained through screen printing, and a flexible ribbon cable 5 is encapsulated within the silver nanowire layer 4 to form a heat source layer. While responding to current stimulation, the external thermal stimulation is converted into an electrical signal stimulation, thereby improving the controllability of the hydrogel actuator. The introduced silver nanowires are one-dimensional nanomaterials with a high aspect ratio. They combine the excellent electrical and thermal conductivity, flexibility, and surface plasmon resonance of silver, making them easy to process into a transparent conductive network, thus enabling the hydrogel actuator to respond to current stimulation.
[0036] (3) The 100 μm thick polyimide film 2 is placed in a 5% sodium hydroxide solution and heated at 60°C for 5 min to etch the surface of the polyimide film 2. After taking it out, it is placed in an oven at 70°C to dry. The tissue adhesive is dotted on the surface of the polyimide film 2 to form a mesh adhesive layer. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 obtained in step (1) is oriented and laminated on the surface of the polyimide film 2 to connect the two. A 15 μm thick epoxy adhesive coating is applied to the surface of the polyimide film 2 using a syringe. The epoxy adhesive coating is a two-component flexible epoxy adhesive obtained by mixing epoxy resin main agent and curing agent in a 1:1 ratio. The silver nanowire flexible heater obtained in step (2) is aligned with the epoxy adhesive coating and rolled for a period of time to obtain a three-layer hydrogel actuator.
[0037] In this embodiment, the hydrogel actuator obtained by step (3) is designed into a long strip shape. When a 5V voltage is applied or placed in deionized water at 70°C, the hydrogel actuator performs bending motion.
[0038] The hydrogel actuator prepared by the method of this embodiment is elongated and has a three-layer structure consisting of a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1, a polyimide film 2, and a silver nanowire flexible heater. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 serves as the driving layer and can respond to temperature stimulation. The polyimide film 2 serves as the rigid layer and provides support. The silver nanowire flexible heater serves as the heat source layer and can respond to current stimulation. When the hydrogel actuator of this embodiment is placed in an electrically powered or hot water environment, it will shrink or expand in volume, causing the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 to bend, thereby realizing the bending movement of the hydrogel actuator in response to environmental stimulation.
[0039] Example 2
[0040] This embodiment provides a method for preparing an electrothermally responsive three-layer hydrogel actuator, which includes the following steps:
[0041] (1) Add 400 mg N-isopropylacrylamide and 3 ml deionized water to a beaker in sequence. After stirring magnetically for 30 min to dissolve completely, add 40 mg polyvinyl alcohol, 100 mg lithium magnesium silicate, and 40 mg nano silica. After stirring magnetically for 2 h to dissolve completely, add 6 mg N,N′-methylenebisacrylamide and 15 mg ammonium persulfate. After stirring magnetically to mix evenly, treat with an ultrasonic cleaner for 30 min to remove foam. Accurately measure 9 mg N,N,N',N'-tetramethylethylenediamine with a pipette and add it to the beaker. Place the beaker in an ice-water bath and continue stirring for 10 min to form a pregel solution. Pour the pregel solution into a mold with a depth of 4.5 mm and let it stand for 25 min to obtain a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 with a thickness of 6 mm.
[0042] (2) Lay a 50μm thick polyurethane film 3 flat on the screen printing table, place the screen printing screen above the substrate, with a 2-5mm gap between the substrate and the screen, place 70mg of silver nanowire ink on the edge of the screen, and use a squeegee to scrape the silver nanowire ink from one side of the pattern to the other. During the printing process, the squeegee and the screen should maintain line contact, and the force and speed should be uniform. Place the substrate with the printed ink in a 70℃ oven to bake and cure it to obtain the silver nanowire layer 4. Connect the flexible ribbon cable 5 to the silver nanowire layer 4. Cut the substrate with the ink and the substrate used for encapsulation into rectangles. Lay the two polyurethane films 3 together to strengthen the connection of the flexible ribbon cable 5. Use a hot press to hot press at 130℃ for 10min to obtain the silver nanowire flexible heater.
[0043] (3) The 50 μm thick polyimide film 2 is placed in a 5% sodium hydroxide solution and heated at 60°C for 5 min to etch the surface of the polyimide film 2. After taking it out, it is placed in an oven at 70°C to dry. The tissue adhesive is dotted on the surface of the polyimide film 2 to form a mesh adhesive layer. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 obtained in step (1) is oriented and laminated on the surface of the polyimide film 2 to connect the two. A 10 μm thick epoxy coating is applied to the surface of the polyimide film 2 with a syringe. The epoxy coating is a two-component flexible epoxy adhesive obtained by mixing epoxy resin main agent and curing agent in a 1:1 ratio. The silver nanowire flexible heater obtained in step (2) is aligned with the epoxy coating and rolled for a period of time to obtain a three-layer hydrogel actuator.
[0044] In this embodiment, the hydrogel actuator obtained by step (3) is designed into a long strip shape. When an 8V voltage is applied or placed in deionized water at 55°C, the hydrogel actuator performs bending motion.
[0045] Example 3
[0046] Please see Figure 1 This embodiment provides a three-layer hydrogel actuator prepared using the method of Example 1 or Example 2, comprising a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1, a silver nanowire flexible heater, and a polyimide film 2 located between the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 and the silver nanowire flexible heater. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 is bonded and fixed to one side of the polyimide film 2, and the silver nanowire flexible heater is bonded and fixed to the other side of the polyimide film 2.
[0047] When stimulated by temperature, the three-layer hydrogel actuator performs a bending motion. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 responds to thermal stimulation, and its response mechanism is as follows: The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 contains poly(N-isopropylacrylamide), a thermoresponsive polymer. When the external temperature is higher than the lower critical dissolution temperature of poly(N-isopropylacrylamide), poly(N-isopropylacrylamide) swells, while when the external temperature is lower than the lower critical dissolution temperature of poly(N-isopropylacrylamide), poly(N-isopropylacrylamide) contracts. The difference between the contraction and swelling of poly(N-isopropylacrylamide) causes the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 to bend, thereby enabling the hydrogel actuator to perform a bending motion in response to environmental thermal stimulation.
[0048] The hydrogel actuator of this embodiment has a three-layer structure consisting of a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1, a polyimide film 2, and a silver nanowire flexible heater. The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer 1 acts as a driving layer in response to temperature stimulation, the polyimide film 2 acts as a rigid layer to provide support, and the silver nanowire flexible heater acts as a heat source layer in response to current stimulation, thereby realizing multiple responses of the hydrogel actuator and enriching the actuation conditions.
[0049] The silver nanowire flexible heater includes two polyurethane films 3, a silver nanowire layer 4 located between the two polyurethane films 3, and a flexible cable 5 laid on the silver nanowire layer 4. The silver nanowire layer 4 is bonded and fixed between the two polyurethane films 3. In this embodiment, based on the aforementioned design, the flexible cable 5 is encapsulated, thereby reinforcing the connection between the flexible cable 5 and the silver nanowire layer 4.
[0050] When stimulated by an electric current, the three-layer hydrogel actuator undergoes a bending motion. The flexible ribbon cable 5 conducts electricity, working in conjunction with the transparent conductive network formed by the silver nanowire layer 4 to enable the hydrogel actuator to respond to electrical stimulation. Simultaneously, the flexible silver nanowire heater converts external thermal stimulation into electrical signal stimulation, thereby improving the controllability of the hydrogel actuator.
[0051] In summary, the hydrogel actuator of this embodiment has the following advantages: it has multiple responsiveness, can respond to both current and external temperature environmental conditions, and can achieve nearly 360° large-angle reversible bending. It can play a better role in underwater robots, grippers, valve switches and other fields, and overcome the defects of single actuation conditions.
[0052] The above embodiments are merely preferred embodiments of the present invention. Any simple modifications, alterations, and substitutions made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.
Claims
1. A method for preparing an electrothermal responsive three-layer hydrogel actuator, characterized in that, Includes the following steps: (1) Dissolve N-isopropylacrylamide in deionized water, then add polyvinyl alcohol, lithium magnesium silicate and nano silica in sequence, mix well, add crosslinking agent and ammonium persulfate, mix well and remove foam, add initiator, pour into mold for polymerization to obtain poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer. (2) A silver nanowire layer is obtained by screen printing, a flexible ribbon cable is connected to the silver nanowire layer and bonded between two polyurethane films, and a silver nanowire flexible heater is obtained by hot pressing. (3) The polyimide film is placed in an alkaline solution, taken out and dried, and then the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer prepared in step (1) is pressed onto one surface of the polyimide film. The silver nanowire flexible heater obtained in step (2) is pressed onto the other surface of the polyimide film and rolled to obtain a three-layer hydrogel actuator.
2. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1, characterized in that, In step (1), the amount of deionized water used is equivalent to 2 to 4 times that of N-isopropylacrylamide; the mass ratio of N-isopropylacrylamide, polyvinyl alcohol, lithium magnesium silicate and nano silica is 1:0.1 to 0.25:0.2 to 0.3:0.2 to 0.
3.
3. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 2, characterized in that, In step (1), the amount of the crosslinking agent is 0.5% to 1.5% of N-isopropylacrylamide; the amount of the ammonium persulfate is 0.3% to 1% of N-isopropylacrylamide; the amount of the initiator is 0.7% to 2% of N-isopropylacrylamide; the crosslinking agent includes N,N′-methylenebisacrylamide; and the initiator includes N,N,N',N'-tetramethylethylenediamine.
4. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1, characterized in that, In step (1), the specific operation of adding the initiator is as follows: use a pipette to measure the initiator and add it to the solution to remove foam. Stir under ice-water bath conditions to form a pregel solution. Pour the pregel solution into the mold and let it stand for a period of time to obtain a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer with a thickness of 3-6 mm.
5. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1, characterized in that, In step (2), the mass ratio of the silver nanowire ink to N-isopropylacrylamide is 0.1 to 0.3:1; the thickness of the polyurethane film is 50 to 100 μm; the hot pressing temperature is 120 to 150 °C, and the hot pressing time is 8 to 12 min.
6. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1, characterized in that, In step (2), the method for obtaining the silver nanowire layer by screen printing is as follows: place the silver nanowire ink on the edge of the screen printing stencil, use a squeegee to scrape the silver nanowire ink from one side of the pattern to the other side, keep the squeegee in line contact with the stencil during the printing process, apply uniform force and speed, and place the printed ink substrate in an oven at 60-100°C to bake it and solidify it to obtain the silver nanowire layer.
7. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1, characterized in that, In step (3), the thickness of the polyimide film 2 is 15-100 μm; the polyimide film is placed in an alkaline solution and heated at 50-80°C for 3-8 minutes; the alkaline solution is a 5% sodium hydroxide solution; in this invention, the heating environment facilitates the etching of the surface of the polyimide film 2 by the alkaline solution. After drying, tissue adhesive is applied to the surface of the polyimide film to form a mesh-like adhesive layer. Then, the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer obtained in step (1) is oriented and laminated onto the surface of the polyimide film to connect the two. An epoxy coating is applied to the other surface of the polyimide film. The silver nanowire flexible heater obtained in step (2) is aligned with the epoxy coating and rolled to obtain a three-layer hydrogel actuator. The epoxy coating is a two-component flexible epoxy adhesive obtained by mixing epoxy resin main agent and curing agent in a 1:1 ratio; the thickness of the epoxy coating is 10-15 μm.
8. The method for preparing the electrothermal responsive three-layer hydrogel actuator according to claim 1 or 7, characterized in that, The three-layer hydrogel actuator obtained after step (3) is placed in an electrically powered environment or a hot water environment, and the hydrogel actuator performs bending motion; in the electrically powered environment, a voltage of 5 to 10V is applied; the temperature of the hot water is greater than 32°C.
9. A three-layer hydrogel actuator, prepared by the method described in any one of claims 1 to 8, characterized in that, The invention includes a poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer, a silver nanowire flexible heater, and a polyimide film located between the poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer and the silver nanowire flexible heater; wherein the silver nanowire flexible heater includes two polyurethane films, a silver nanowire layer located between the two polyurethane films, and flexible wiring laid on the silver nanowire layer.
10. The three-layer hydrogel actuator according to claim 9, characterized in that, The poly(N-isopropylacrylamide)-polyvinyl alcohol hydrogel layer is bonded and fixed on one side of the polyimide film, and the silver nanowire flexible heater is bonded and fixed on the other side of the polyimide film. The silver nanowire layer is bonded and fixed between two polyurethane films.