A double-layer hydrogel soft actuator with pH response and a preparation method thereof

Abstract

The application provides a double-layer hydrogel soft driver with pH response and a preparation method thereof, two groups of hydrogel pre-polymerization solutions containing and not containing graphene oxide are prepared respectively, and the two groups of hydrogel pre-polymerization solutions are made into the double-layer hydrogel soft driver through a mold. Based on the fact that the composition of one of the gel layers of the double-layer hydrogel soft driver contains appropriate content of graphene oxide, the mechanical property target of the double-layer hydrogel soft driver is achieved, and the sensitivity of the double-layer hydrogel soft driver to the stimulation is not affected. The double-layer hydrogel soft driver has good mechanical property, can bend when the pH is 13 and restore the original state when the pH is 1, and meets the requirement of giving consideration to the mechanical property and the response sensitivity of the hydrogel driver.

Description

Technical Field

[0001] This invention relates to the field of flexible intelligent actuation materials technology, and in particular to a pH-responsive bilayer hydrogel soft actuator and its preparation method. Background Technology

[0002] Hydrogels possess a unique three-dimensional network structure, typically exhibiting distinctive reactivity and swelling behavior in response to changes in external conditions. As one of the most important smart materials, hydrogel actuators can convert various external stimuli (such as light, heat, electricity, pH, and chemicals) into controllable and reversible shape transformations. Compared to other polymer actuators, hydrogel actuators possess "soft" and "wet" properties, much like living organisms, thus showing excellent application prospects in soft robotics, artificial muscles, and drug delivery. However, currently, there is no hydrogel actuator that combines both mechanical properties and pH-responsive behavior. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention provides a pH-responsive bilayer hydrogel soft actuator and its preparation method. Under pH stimulation, the hydrogel soft actuator can produce bending deformation and recovery deformation, thereby achieving synergy between mechanical properties and stimulus response behavior.

[0004] The specific details of the invention are as follows:

[0005] In a first aspect, the present invention provides a method for preparing a pH-responsive bilayer hydrogel soft actuator, the method comprising the following steps:

[0006] S1. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator to the aqueous dispersion of graphene oxide, and adjust the pH to alkaline. Stir to obtain hydrogel prepolymerization solution A.

[0007] S2. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator to deionized water and stir to obtain hydrogel prepolymerization solution B.

[0008] S3. Inject the hydrogel prepolymerization solution A into the cavity of the mold and let it stand at room temperature for 20-30 minutes to obtain the first hydrogel layer.

[0009] S4. Inject hydrogel prepolymer solution B into the mold cavity above the first hydrogel layer, and let it stand at room temperature for 20-30 minutes to obtain a double-layer hydrogel prepolymer.

[0010] S5. Transfer the mold containing the bilayer hydrogel prepolymer to a constant temperature environment of 60°C, let it stand for 10-12 hours, remove the mold, soak the bilayer hydrogel prepolymer in deionized water to remove unreacted substances, and obtain the bilayer hydrogel soft actuator.

[0011] Optionally, in step S1, the mass percentage of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer in the hydrogel prepolymerization solution A is 45% to 75%.

[0012] The mass of the graphene oxide is 0.1% to 0.3% of the mass of the monomer;

[0013] The mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the mass of the monomer;

[0014] The mass of the ammonium sulfate initiator is 0.1% of the mass of the monomer;

[0015] The rest is water.

[0016] Optionally, in step S1, the graphene oxide dispersion aqueous solution is obtained by dissolving graphene oxide nanoparticles in deionized water and then ultrasonically dispersing them uniformly.

[0017] Optionally, in step S1, adjusting the pH to alkaline includes: adjusting the pH using ammonia, wherein the pH value is 10 to 12.

[0018] Optionally, the pH value is 10.

[0019] Optionally, in step S2, the mass percentage of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer in the hydrogel prepolymerization solution B is 45% to 75%.

[0020] The mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the mass of the monomer;

[0021] The mass of the ammonium sulfate initiator is 0.1% of the mass of the monomer;

[0022] The rest is water.

[0023] Optionally, in step S3, the mold is made by placing two hollow silicone rubber gaskets on transparent glass and then sealing them with another transparent glass plate.

[0024] Optionally, in step S5, the constant temperature environment is provided by a constant temperature chamber.

[0025] In a second aspect, the present invention provides a pH-responsive bilayer hydrogel soft actuator obtained by the preparation method described in the first aspect above.

[0026] Optionally, the bilayer hydrogel soft actuator has pH-responsive capability, bending at an ambient pH of 13 and returning to its original position at an ambient pH of 1.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention provides a method for preparing a pH-responsive bilayer hydrogel soft actuator. By introducing graphene oxide into the first hydrogel layer constituting the soft actuator, the mechanical properties of the actuator are enhanced. Simultaneously, the two-layer hydrogel structure of the soft actuator is prepared by controlling the contents of methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator. This actuator exhibits good mechanical properties and can bend at pH 13 and return to its original shape at pH 1, achieving a balance between mechanical performance and responsiveness. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart illustrating the preparation method of the pH-responsive bilayer hydrogel soft actuator provided in an embodiment of the present invention is shown.

[0031] Figure 2 A schematic diagram of the mold provided in an embodiment of the present invention is shown;

[0032] Figure 3 A schematic diagram of the fabrication process of the pH-responsive bilayer hydrogel soft actuator provided in an embodiment of the present invention is shown.

[0033] Figure 4 The diagram shows the pH response deformation of the pH-responsive bilayer hydrogel soft actuator provided in an embodiment of the present invention.

[0034] Figure 5 The stress-strain curve of the pH-responsive bilayer hydrogel soft actuator provided in the embodiment of the present invention is shown. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0036] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0037] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0038] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0039] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] In a first aspect, the present invention provides a method for preparing a pH-responsive bilayer hydrogel soft actuator. Figure 1 A flowchart illustrating the preparation method of the pH-responsive bilayer hydrogel soft actuator provided in this embodiment of the invention is shown, as follows: Figure 1 As shown, the preparation method includes the following steps:

[0041] S1. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator to the aqueous dispersion of graphene oxide, and adjust the pH to alkaline. Stir to obtain hydrogel prepolymerization solution A.

[0042] S2. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator to deionized water and stir to obtain hydrogel prepolymerization solution B.

[0043] S3. Inject the hydrogel prepolymerization solution A into the cavity of the mold and let it stand at room temperature for 20-30 minutes to obtain the first hydrogel layer.

[0044] S4. Inject hydrogel prepolymer solution B into the mold cavity above the first hydrogel layer, and let it stand at room temperature for 20-30 minutes to obtain a bilayer hydrogel prepolymer.

[0045] S5. Transfer the mold containing the bilayer hydrogel prepolymer to a constant temperature environment of 60°C, let it stand for 10-12 hours, remove the mold, soak the bilayer hydrogel prepolymer in deionized water to remove unreacted substances, and obtain the bilayer hydrogel soft actuator.

[0046] In specific implementation, this invention, while controlling the graphene oxide content, prepares two sets of hydrogel prepolymer solutions containing / without graphene oxide, respectively. These two sets of prepolymer solutions are then molded into a bilayer hydrogel soft actuator, thus achieving the fabrication of the bilayer hydrogel soft actuator. Because one of the gel layers constituting the bilayer hydrogel soft actuator contains an appropriate amount of graphene oxide, the mechanical properties of the bilayer hydrogel soft actuator are enhanced without affecting its overall sensitivity to stimuli. Furthermore, by controlling the content of methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator during the preparation process, the components in the hydrogel molecules are ordered to combine, resulting in a more regular bilayer hydrogel structure.

[0047] Based on this, in the hydrogel prepolymer solution A prepared in step S1, the mass percentage of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer is 45% to 75%; the mass of the graphene oxide is 0.1% to 0.3% of the monomer mass; the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the monomer mass; the mass of the ammonium sulfate initiator is 0.1% of the monomer mass; and the remainder is water.

[0048] As a preferred condition, in the hydrogel prepolymerization solution A, the mass ratio of the methacrylic acid monomer is 15% to 30% (1.5 ml to 3 ml), the mass ratio of the acryloyloxyethyltrimethylammonium chloride monomer is 30% to 45% (3 ml to 4.5 ml), the mass of the graphene oxide is 0.1% to 0.3% (0.006 g to 0.036 g) of the monomer mass, the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the monomer mass, the mass of the ammonium sulfate initiator is 0.1% of the monomer mass, and the remainder is water.

[0049] As a further preferred condition, in the hydrogel prepolymerization solution A, the mass ratio of the methacrylic acid monomer is 30% (3 ml), the mass ratio of the acryloyloxyethyltrimethylammonium chloride monomer is 30% (3 ml), the mass of the graphene oxide is 0.25% (0.03 g) of the monomer mass, the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the monomer mass, the mass of the ammonium sulfate initiator is 0.1% of the monomer mass, and the remainder is water.

[0050] Furthermore, in step S1, the graphene oxide dispersion aqueous solution is prepared by dissolving graphene oxide nanoparticles in deionized water and ultrasonically dispersing them for a time controlled between 15 min and 30 min to ensure uniform dispersion of the graphene oxide nanoparticles.

[0051] Further, in step S1, adjusting the pH to alkaline includes: adjusting the pH using ammonia, wherein the pH value is 10 to 12.

[0052] Furthermore, as a preferred condition, using ammonia to adjust the pH and controlling the pH value to 10 can ensure that the hydrogel prepolymer solution A achieves a better crosslinking effect when stirred.

[0053] Furthermore, through experimental investigation, this invention has found that the crosslinking effect of graphene nanoparticles, methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium sulfate initiator is better at 20°C than at other temperatures. Therefore, magnetic stirring can be selected, and the temperature of the stirred object can be controlled at 20°C through the temperature setting function of the magnetic stirrer, thereby ensuring the reaction between the components in the hydrogel prepolymerization solution A. Electrostatic interaction occurs between the carboxyl groups on GO (graphene oxide) and the quaternary amino groups of DAC (acryloyloxyethyltrimethylammonium chloride), while hydrogen bonds are formed between methacrylic acid and GO (graphene oxide), resulting in an orderly combination of components in the formed hydrogel molecules and a more regular structure.

[0054] Further, in step S2, in the hydrogel prepolymerization solution B, the mass ratio of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer is 45% to 75%; the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the mass of the monomers; the mass of the ammonium sulfate initiator is 0.1% of the mass of the monomers; and the remainder is water.

[0055] As a preferred condition, in the hydrogel prepolymerization solution B, the mass ratio of the methacrylic acid monomer is 15% to 30% (1.5 ml to 3 ml), the mass ratio of the acryloyloxyethyltrimethylammonium chloride monomer is 30% to 45% (3 ml to 4.5 ml), the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the mass of the monomers, the mass of the ammonium sulfate initiator is 0.1% of the mass of the monomers, and the remainder is water.

[0056] As a further preferred condition, in the hydrogel prepolymerization solution B, the mass ratio of the methacrylic acid monomer is 30% (3 ml), the mass ratio of the acryloyloxyethyltrimethylammonium chloride monomer is 30% (3 ml), the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the mass of the monomers, the mass of the ammonium sulfate initiator is 0.1% of the mass of the monomers, and the remainder is water.

[0057] Furthermore, in step S3, the mold is made by placing two hollow silicone rubber gaskets on transparent glass and then sealing them with another transparent glass plate.

[0058] In practice, Figure 2 A schematic diagram of a mold provided in an embodiment of the present invention is shown, as follows: Figure 2 As shown, the mold is made by sealing two hollow silicone rubber gaskets placed between two transparent glass plates, with the hollow dimensions of the silicone rubber gaskets being 40mm × 5mm × 2mm. It should be noted that this invention does not limit the specific size and shape of the mold; any size and shape can be selected according to actual needs. Figure 3 This diagram illustrates the fabrication process of a pH-responsive bilayer hydrogel soft actuator according to an embodiment of the present invention. Figure 3 As can be seen from the above, the mold provided in this embodiment of the invention consists of two hollow silicone rubber gaskets placed on a transparent glass plate. After injecting hydrogel prepolymer solution A and hydrogel prepolymer solution B into the hollow silicone gaskets, it is then sealed with another transparent glass plate to obtain a mold containing a double layer of hydrogel prepolymer.

[0059] Furthermore, during the experiments conducted in this embodiment of the invention, it was found that the bilayer hydrogel prepolymer formed in the above process, when used as a bilayer hydrogel soft actuator, did not show a significant response to changes in environmental pH. This may be because uneven internal cross-linking exists within the bilayer hydrogel prepolymer. Therefore, through extensive experimental verification, this embodiment of the invention found that further placing the bilayer hydrogel prepolymer formed in the above process in a constant temperature environment of 60°C allows for more thorough cross-linking under suitable temperature conditions. Specifically, in step S5, the 60°C constant temperature environment is provided by a constant temperature chamber.

[0060] In a second aspect, the present invention provides a pH-responsive bilayer hydrogel soft actuator obtained by the preparation method described in the first aspect above.

[0061] Furthermore, the bilayer hydrogel soft actuator has pH-responsive capability, bending at an ambient pH of 13 and returning to its original position at an ambient pH of 1.

[0062] Figure 4 The diagram illustrates the pH response deformation of a pH-responsive bilayer hydrogel soft actuator provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the bilayer hydrogel soft actuator exhibits bending deformation in an alkaline solution at pH 13, and the degree of bending gradually increases with the increase of response time. When transferred to an acidic solution at pH 1, the soft actuator gradually returns to its original shape.

[0063] To enable those skilled in the art to more clearly understand the present invention, the following embodiments will be used to provide a detailed description of a pH-responsive bilayer hydrogel soft actuator and its preparation method.

[0064] Example 1

[0065] The bilayer hydrogel actuator in this embodiment, abbreviated as MDG1, is prepared as follows:

[0066] Step (1): Dissolve 0.006g of graphene oxide in 4ml of deionized water and ultrasonically disperse for 1h to obtain a uniform graphene oxide dispersion.

[0067] Step (2): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to the graphene oxide dispersion under magnetic stirring. Adjust the pH to 10 with ammonia water and finally remove the dissolved oxygen in the solution to obtain hydrogel prepolymer A.

[0068] Step (3): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to deionized water under magnetic stirring. Finally, remove the dissolved oxygen contained in the solution to obtain hydrogel prepolymer solution B.

[0069] Step (4): Place two layers of silicone rubber gaskets with a hollowed-out center of 40mm×5mm×2mm on a transparent glass plate, and seal them with another transparent glass plate to make a mold;

[0070] Step (5): Inject the hydrogel prepolymer solution A obtained in step (2) into the mold of step (4) and let it stand for 30 minutes;

[0071] Step (6): Inject the hydrogel prepolymer solution B obtained in step (3) into the mold cavity above the prepolymer solution A after standing in step (5), and let it stand for 30 minutes to obtain a double-layer hydrogel prepolymer.

[0072] Step (7): The bilayer hydrogel prepolymer obtained in step (6) is subjected to further in-situ free radical polymerization reaction under constant temperature heating at 60℃. After demolding, it is soaked in deionized water to remove unreacted substances, thereby obtaining the bilayer hydrogel soft actuator.

[0073] Example 2

[0074] The bilayer hydrogel actuator in this embodiment, abbreviated as MDG2, is prepared as follows:

[0075] Step (1): Dissolve 0.012g of graphene oxide in 4ml of deionized water and ultrasonically disperse for 1h to obtain a uniform graphene oxide dispersion.

[0076] Step (2): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to the graphene oxide dispersion under magnetic stirring. Adjust the pH to 10 with ammonia water and finally remove the dissolved oxygen in the solution to obtain hydrogel prepolymer A.

[0077] Step (3): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to oxygen-deionized water under magnetic stirring. Finally, remove the dissolved oxygen in the solution to obtain hydrogel prepolymer solution B.

[0078] Step (4): Place two layers of silicone rubber gaskets with a hollowed-out center of 40mm×5mm×2mm on a transparent glass plate, and seal them with another transparent glass plate to make a mold;

[0079] Step (5): Inject the hydrogel prepolymer solution A obtained in step (2) into the mold of step (4) and cool it;

[0080] Step (6): Inject the hydrogel prepolymer solution B obtained in step (3) into the mold cavity above the prepolymer solution A after cooling in step (5), and let it stand to obtain a double-layer hydrogel prepolymer.

[0081] Step (7): The bilayer hydrogel prepolymer obtained in step (6) is subjected to further in-situ free radical polymerization under constant temperature heating. After demolding, it is soaked in deionized water to remove unreacted substances, thereby obtaining a bilayer hydrogel soft actuator.

[0082] Example 3

[0083] The bilayer hydrogel actuator in this embodiment, abbreviated as MDG3, is composed of the following substances by mass fraction:

[0084] Step (1): Dissolve 0.024g of graphene oxide in 4ml of deionized water and ultrasonically disperse for 1h to obtain a uniform graphene oxide dispersion.

[0085] Step (2): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to the graphene oxide dispersion under magnetic stirring. Adjust the pH to 10 with ammonia water and finally remove the dissolved oxygen in the solution to obtain hydrogel prepolymer A.

[0086] Step (3): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to oxygen-deionized water under magnetic stirring. Finally, remove the dissolved oxygen in the solution to obtain hydrogel prepolymer solution B.

[0087] Step (4): Place two layers of silicone rubber gaskets with a hollowed-out center of 40mm×5mm×2mm on a transparent glass plate, and seal them with another transparent glass plate to make a mold;

[0088] Step (5): Inject the hydrogel prepolymer solution A obtained in step (2) into the mold of step (4) and cool it;

[0089] Step (6): Inject the hydrogel prepolymer solution B obtained in step (3) into the mold cavity above the prepolymer solution A after cooling in step (5), and let it stand to obtain a double-layer hydrogel prepolymer.

[0090] Step (7): The bilayer hydrogel prepolymer obtained in step (6) is subjected to free radical polymerization under constant temperature heating. After demolding, it is soaked in deionized water to remove unreacted substances, thereby obtaining a bilayer hydrogel soft actuator.

[0091] Example 4

[0092] The bilayer hydrogel actuator in this embodiment, abbreviated as MDG4, is composed of the following mass fractions of substances:

[0093] Step (1): Dissolve 0.03g of graphene oxide in 4ml of deionized water and ultrasonically disperse for 1h to obtain a uniform graphene oxide dispersion.

[0094] Step (2): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to the graphene oxide dispersion under magnetic stirring. Adjust the pH to 10 with ammonia water and finally remove the dissolved oxygen in the solution to obtain hydrogel prepolymer A.

[0095] Step (3): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to oxygen-deionized water under magnetic stirring. Finally, remove the dissolved oxygen in the solution to obtain hydrogel prepolymer solution B.

[0096] Step (4): Place two layers of silicone rubber gaskets with a hollowed-out center of 40mm×5mm×2mm on a transparent glass plate, and seal them with another transparent glass plate to make a mold;

[0097] Step (5): Inject the hydrogel prepolymer solution A obtained in step (2) into the mold of step (4) and cool it;

[0098] Step (6): Inject the hydrogel prepolymer solution B obtained in step (3) into the mold cavity above the prepolymer solution A after cooling in step (5), and let it stand to obtain a double-layer hydrogel prepolymer.

[0099] Step (7): The bilayer hydrogel prepolymer obtained in step (6) is subjected to in-situ free radical polymerization under constant temperature heating. After demolding, it is soaked in deionized water to remove unreacted substances, thereby obtaining a bilayer hydrogel actuator.

[0100] Example 5

[0101] The bilayer hydrogel actuator in this embodiment, abbreviated as MDG5, is composed of the following substances by mass fraction:

[0102] Step (1): Dissolve 0.036g of graphene oxide in 4ml of deionized water and ultrasonically disperse for 1h to obtain a uniform graphene oxide dispersion.

[0103] Step (2): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to the graphene oxide dispersion under magnetic stirring. Adjust the pH to 10 with ammonia water and finally remove the dissolved oxygen in the solution to obtain hydrogel prepolymer A.

[0104] Step (3): Weigh 3 ml of monomer methacrylic acid, 3 ml of acryloyloxyethyltrimethylammonium chloride, 0.018 g of crosslinking agent N,N'-methylenebisacrylamide and 0.01 g of initiator ammonium persulfate and add them sequentially to oxygen-deionized water under magnetic stirring. Finally, remove the dissolved oxygen in the solution to obtain hydrogel prepolymer solution B.

[0105] Step (4): Place two layers of silicone rubber gaskets with a hollowed-out center of 40mm×5mm×2mm on a transparent glass plate, and seal them with another transparent glass plate to make a mold;

[0106] Step (5): Inject the hydrogel prepolymer solution A obtained in step (2) into the mold of step (4) and cool it;

[0107] Step (6): Inject the hydrogel prepolymer solution B obtained in step (3) into the mold cavity above the prepolymer solution A after cooling in step (5), and let it stand to obtain a double-layer hydrogel prepolymer.

[0108] Step (7): The bilayer hydrogel prepolymer obtained in step (6) is subjected to in-situ free radical polymerization under constant temperature heating. After demolding, it is soaked in deionized water to remove unreacted substances, thereby obtaining the bilayer hydrogel actuator.

[0109] Figure 5 The stress-strain curve of a pH-responsive bilayer hydrogel soft actuator provided in an embodiment of the present invention is shown, as follows: Figure 5As shown, the tensile stress of the bilayer hydrogel soft actuator prepared in Example 1 is 72.64 kPa and the tensile strain is 103.71%; the tensile stress of the bilayer hydrogel soft actuator prepared in Example 2 is 246.4 kPa and the tensile strain is 201.59%; the tensile stress of the bilayer hydrogel soft actuator prepared in Example 3 is 284.78 kPa and the tensile strain is 357.66%; the tensile stress of the bilayer hydrogel soft actuator prepared in Example 4 is 366.97 kPa and the tensile strain is 602.58%; and the tensile stress of the bilayer hydrogel soft actuator prepared in Example 5 is 204.64 kPa and the tensile strain is 272.12%. This demonstrates that the bilayer hydrogel soft actuators prepared in these embodiments possess excellent mechanical properties. Furthermore, they can bend at an ambient pH of 13 and return to their original shape at an ambient pH of 1, achieving a balance between mechanical performance and response sensitivity in hydrogel actuators.

[0110] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0111] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0112] The foregoing has provided a detailed description of a pH-responsive bilayer hydrogel soft actuator and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a pH-responsive bilayer hydrogel soft actuator, characterized in that, The preparation method includes the following steps: S1. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium persulfate initiator to the aqueous dispersion of graphene oxide, and adjust the pH to alkaline, with a pH value of 10-12. Stir to obtain hydrogel prepolymerization solution A. S2. Add methacrylic acid monomer, acryloyloxyethyltrimethylammonium chloride monomer, N,N'-methylenebisacrylamide crosslinking agent, and ammonium persulfate initiator to deionized water and stir to obtain hydrogel prepolymerization solution B; S3. Inject the hydrogel prepolymerization solution A into the cavity of the mold and let it stand at room temperature for 20-30 minutes to obtain the first hydrogel layer. S4. Inject hydrogel prepolymer solution B into the mold cavity above the first hydrogel layer, and let it stand at room temperature for 20-30 minutes to obtain a double-layer hydrogel prepolymer. S5. Transfer the mold containing the bilayer hydrogel prepolymer to a constant temperature environment of 60 ℃, let it stand for 10h to 12h, remove the mold, soak the bilayer hydrogel prepolymer in deionized water to remove unreacted substances, and obtain the bilayer hydrogel soft actuator. In the hydrogel prepolymerization solution A and the hydrogel prepolymerization solution B, the mass percentage of the methacrylic acid monomer is 15% to 30%, and the mass percentage of the acryloyloxyethyltrimethylammonium chloride monomer is 30% to 45%.

2. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In the hydrogel prepolymerization solution A, the mass of the graphene oxide is 0.1% to 0.3% of the total mass of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer. The mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the total mass of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer; The mass of the ammonium persulfate initiator is 0.1% of the total mass of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer; The rest is water.

3. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In step S1, the graphene oxide dispersion aqueous solution is obtained by dissolving graphene oxide nanoparticles in deionized water and then ultrasonically dispersing them uniformly.

4. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In step S1, adjusting the pH to alkaline includes: adjusting the pH using ammonia.

5. The method for preparing a pH-responsive bilayer hydrogel soft actuator according to claim 4, characterized in that, The pH value is 10.

6. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In the hydrogel prepolymerization solution B, the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.3% of the total mass of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer; The mass of the ammonium persulfate initiator is 0.1% of the total mass of the methacrylic acid monomer and the acryloyloxyethyltrimethylammonium chloride monomer; The rest is water.

7. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In step S3, the mold is made by placing two hollow silicone rubber gaskets on transparent glass and then sealing them with another transparent glass plate.

8. The method for preparing the pH-responsive bilayer hydrogel soft actuator according to claim 1, characterized in that, In step S5, the constant temperature environment is provided by a constant temperature chamber.

9. A pH-responsive bilayer hydrogel soft actuator obtained by the preparation method according to any one of claims 1-8.

10. The pH-responsive bilayer hydrogel soft actuator according to claim 9, characterized in that, The bilayer hydrogel soft actuator is pH-responsive, bending at an ambient pH of 13 and returning to its original shape at an ambient pH of 1.

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