Self-induced double-layer magnetic hydrogel actuator, preparation method and application thereof

Abstract

The application discloses a double-layer magnetic hydrogel driver capable of self-sensing, a preparation method and application thereof, and belongs to the technical field of intelligent materials.The magnetic hydrogel driver is prepared by the following steps: synthesizing PNaAMPS hydrogel by a free radical polymerization method with AMPSNa monomers, freeze-drying, ball-milling to obtain nano-microsphere powder, adding nano-clay and hard magnetic neodymium iron boron to the nano-microsphere powder as cross-linking points to prepare the magnetic hydrogel as a first-layer driver; and then preparing Paam hydrogel containing lithium chloride on the surface of the first-layer magnetic hydrogel by a photopolymerization method to serve as a second-layer sensing layer.When an external magnetic field is applied, the driver layer can quickly respond to drive the sensing layer to realize rapid bending deformation.Because the ionic gel has good conductivity, the resistance change can be generated under the bending deformation.The double-layer magnetic hydrogel driver has the advantages of good ductility, fast response speed and the like, has good sensing feedback capacity to magnetic and force signals, and has the advantages of simple preparation process, good cycle stability and the like, and the hydrogel driver can be applied to intelligent grabbing and the like.

Description

Technical Field

[0001] This invention relates to the field of intelligent driving materials and intelligent deformation hydrogel sensors, and in particular to a self-sensing double-layer magnetic hydrogel actuator, its preparation method, and its application. Background Technology

[0002] Hydrogels are three-dimensional networks composed of cross-linked hydrophilic polymer chains with high water content. Their excellent extensibility, biocompatibility, high structural flexibility, and intelligent responsiveness make them an important branch of biomaterials. Especially in soft actuators, hydrogel actuators containing stimulus-responsive polymers undergo rapid volume changes in response to environmental stimuli, converting received energy into mechanical motion and exhibiting gentle and flexible movements similar to those of living organisms. Classified by external stimuli, hydrogel actuators can respond to environmental conditions such as temperature, pH, ion concentration, electric field, magnetic field, and light. Magnetic actuators, due to their advantages of remote control, fast response speed, and real-time control, have significant application potential in the biomedical field. Hard magnetic materials, compared to soft magnetic materials, have higher remanent magnetization after magnetization and can achieve complex deformations through magnetic torque, leading to their widespread application in soft actuators.

[0003] However, most currently reported soft actuators cannot achieve self-sensing of deformation; these deformations can only be observed with the naked eye. This limits their ability to handle certain specialized applications, such as minimally invasive surgery in confined spaces where minute deformations cannot be directly observed. In such cases, the self-sensing capability of the soft actuator becomes crucial. Furthermore, some self-sensing soft actuators suffer from slow response times and poor mechanical properties. Therefore, developing a hydrogel actuator with fast response times, strong mechanical properties, and self-sensing capabilities is essential. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a self-sensing bilayer magnetic hydrogel actuator that meets the requirement of achieving self-sensing functionality during actuation. Another technical problem this invention aims to solve is to provide a method for preparing a self-sensing bilayer magnetic hydrogel actuator. A further technical problem this invention aims to solve is to provide an application of the aforementioned self-sensing bilayer magnetic hydrogel actuator.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A self-sensing bilayer magnetic hydrogel actuator, wherein the self-sensing bilayer magnetic hydrogel actuator has a bilayer structure and comprises:

[0007] The magnetically driven layer is a hard magnetic hydrogel containing microsphere gel and nano-clay, capable of undergoing complex and repeatable bending deformation under the influence of a magnetic field; and

[0008] The sensing layer is made of polyacrylamide hydrogel containing lithium chloride, which is formed on the magnetically driven layer through topological entanglement. It has ionic conductivity and can generate resistance changes under bending deformation. The sensing layer is connected to the wire to collect the changing resistance signal.

[0009] The magnetic drive layer has a nanosphere size of 50–1000 nm; the magnetic drive layer has a thickness of 0.5–1 mm; and the sensing layer has a thickness of 0.5–1 mm.

[0010] The preparation method of the self-sensing bilayer magnetic hydrogel actuator is as follows:

[0011] 1) Add deionized water, acrylamide monomer, crosslinking agent, and nano-clay to the reaction vessel and stir magnetically for 1-2 hours to obtain a homogeneous solution;

[0012] 2) Add sodium 2-acrylamide-2-methylpropanesulfonate monomer, crosslinking agent, initiator and deionized water to the reaction vessel and mix evenly. Pour the mixture into the prepared mold, protect it with inert gas, introduce ultraviolet light to cure it, freeze dry it in a freeze dryer, grind the freeze-dried particles into fine powder in a planetary mill, and then filter it with a standard sieve to obtain microsphere gel powder.

[0013] 3) Add the microsphere gel powder obtained in step 2) to the solution obtained in step 1) to obtain a hydrogel prepolymer containing nanospheres, mix and stir evenly with a planetary stirrer, and then store in an environment of 2-8℃ for several days.

[0014] 4) Add neodymium iron boron as magnetic particles to the hydrogel prepolymer of step 3), add thermal initiator, mix and stir with a planetary stirrer, pour into a mold, control the thickness of the magnetic hydrogel, and place in a drying oven to cure, to obtain the first layer of magnetic hydrogel, namely the magnetic driving layer.

[0015] 5) Add acrylamide monomer, crosslinking agent, lithium chloride powder and photoinitiator to the reaction vessel, and obtain a uniform solution by magnetic stirring. Inject the solution onto the surface of the first layer of magnetic hydrogel obtained in step 4). Under ultraviolet light irradiation, a polymerization reaction occurs to obtain the second layer of polyacrylamide hydrogel containing lithium chloride, i.e., the sensing layer. The two layers are tightly bonded together by topological entanglement, and finally a self-sensing bilayer magnetic hydrogel actuator is obtained.

[0016] In step 1), the concentration of acrylamide monomer is 4-4.2M, the concentration ratio of crosslinking agent methylenebisacrylamide to acrylamide monomer is 0.1-0.2%, and the mass ratio of nano-clay to the total weight of acrylamide monomer and deionized water is 2-2.5%.

[0017] In step 2), the concentration of sodium 2-acrylamide-2-methylpropanesulfonate monomer is 1-1.2M, the concentration ratio of crosslinking agent MBAA to sodium 2-acrylamide-2-methylpropanesulfonate monomer is 4-4.2%, and the concentration ratio of initiator α-ketoglutarate to sodium 2-acrylamide-2-methylpropanesulfonate monomer is 0.1-0.15%.

[0018] In step 2), the mold consists of two glass plates and a 9mm silicone spacer, and the inert gas used for protection is argon.

[0019] In step 3), the concentration of nanospheres is 1-4%.

[0020] In step 4), the mass ratio of neodymium iron boron to acrylamide monomer and deionized water is 0.5-50%, the mass ratio of thermal initiator azobisisobutyronitrile to acrylamide and deionized water is 0.1-0.2%, and the temperature of the drying oven is 75°C.

[0021] In step 5), the concentration of acrylamide monomer is 2.8–3 M, the concentration of MABA is 0.2–0.3%, the concentration of photoinitiator TPO is 0.5–0.6%, and the concentration of LiCl is 2.3–2.4 M.

[0022] The application of the self-sensing double-layer magnetic hydrogel actuator in the preparation of a gripper that can sense the size of an object involves cutting the double-layer magnetic hydrogel actuator into a cross shape or multi-lobed shape and assembling it into a gripper, which can be quickly bent or clamped under the action of a magnetic field higher than 100mT.

[0023] This invention utilizes sodium 2-acrylamide-2-methylpropanesulfonate monomer to synthesize PNaAMPS hydrogel via free radical polymerization, followed by freeze-drying and ball milling to obtain nanosphere gel powder. Then, using the nanospheres as crosslinking points, nano-clay and neodymium iron boron (NdFeB) hard magnetic particles are added via free radical polymerization to prepare a magnetic hydrogel, serving as the first layer of the magnetic actuator. Finally, a polyacrylamide hydrogel containing Li ions is prepared on top of the first layer of magnetic hydrogel using free radical polymerization, forming the second sensing layer. When subjected to an external magnetic field, the magnetic hydrogel layer responds rapidly, causing the sensing layer to undergo rapid bending deformation. Due to the excellent conductivity of ionomers, resistance changes can occur under bending deformation. This invention's bilayer magnetic hydrogel actuator has advantages such as good extensibility and fast response speed, exhibiting excellent sensing and feedback capabilities for both magnetic and force signals. Furthermore, the preparation process is simple, and the cycle stability is good. This hydrogel actuator can be used in intelligent grasping and other applications.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The self-sensing double-layer magnetic hydrogel actuator of the present invention includes a magnetic driving layer and a sensing layer, which enables the actuator to initially sense the external environment and has good sensing and feedback capabilities for magnetic and force signals.

[0026] 2) It adopts a magnetic field driving method, which enables remote control and improves response speed; the addition of hard magnetic particles neodymium iron boron gives it editable magnetic domains, which can achieve complex deformation under the action of magnetic torque, thus improving operability;

[0027] 3) The addition of microsphere gel powder and nano-clay increased the viscosity of the prepolymer by altering the rheological properties of the material, thereby improving the mechanical properties of the actuator. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process for fabricating a self-sensing bilayer magnetic hydrogel actuator.

[0029] Figure 2 This is a graph showing the relationship between the relative resistance change and tensile strain of a bilayer magnetic hydrogel actuator.

[0030] Figure 3a This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator under minute tensile strain.

[0031] Figure 3b This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator under normal tensile strain.

[0032] Figure 3c This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator under large tensile strain.

[0033] Figure 3d This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator during stage hold-load cycles within the 0-100% tensile strain range.

[0034] Figure 3e This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator during a 20% tensile strain cycle test.

[0035] Figure 4a This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator when it is bent at different angles under the influence of a magnetic field.

[0036] Figure 4b This is a graph showing the relative resistance change of a bilayer magnetic hydrogel actuator under cyclic testing at a bending angle of 45° in a magnetic field.

[0037] Figure 5a This is a schematic diagram of the human hand-like structure and deformation principle fabricated by a double-layer magnetic hydrogel actuator.

[0038] Figure 5b This is a graph showing the resistance changes of different fingers in a human hand-like structure fabricated using a double-layer magnetic hydrogel actuator as they bend. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and examples, but these examples are only for illustrating the present invention and do not limit the scope of protection of the present invention.

[0040] Example 1: Preparation method of self-sensing bilayer magnetic hydrogel actuator

[0041] like Figure 1 As shown, the microsphere gel powder was first prepared. 22.92 g of sodium 2-methyl-2-acrylamidopropanesulfonate was added to a sealed container of electronic solder paste equipped with a stirrer. Deionized water was added until the total net weight of both was 100 g. The mixture was magnetically stirred at room temperature until clear. Then, 0.616 g of N,N'-methylenebisacrylamide and 0.015 g of α-ketoglutaric acid were added sequentially, and stirring continued until the solution was homogeneous. The solution was poured into a mold made of a glass plate and a 9 mm silicone rubber gasket, and a strength of 2.5 mW cm⁻¹ was used. -2 The hydrogel was cured under 365nm ultraviolet light in an argon atmosphere for 8 hours, and then freeze-dried in a freeze dryer for 2 days. The freeze-dried particles were then ground into fine powder in a planetary mill for 12 hours, and then filtered through a standard sieve (50 mesh) to obtain microsphere gel powder, which was stored in a dry container for later use.

[0042] Next, the magnetically driven layer was prepared: the first layer, a magnetic hydrogel. 28.432 g of acrylamide was added to a sealed container of electronic solder paste equipped with a stirrer. Deionized water was added until the total net weight was 100 g. The mixture was magnetically stirred at room temperature until clear. Then, 0.616 g of N,N'-methylenebisacrylamide and 2 g of synthetic magnesium lithium silicate (nanoclay) were added sequentially. The mixture was magnetically stirred at room temperature for 1 hour to obtain a homogeneous solution. 2 g of the previously prepared microsphere gel powder was added, and the mixture was stirred at 2000 RPM for 2 minutes using a planetary stirrer. The mixture was then stored at 2–8 °C for two days to allow the microsphere gel to fully swell. Further, 10 g of neodymium iron boron powder and 0.1 g of azobisisobutyronitrile were added, and the mixture was stirred at 2000 RPM for 2 minutes using a planetary stirrer, followed by degassing for 30 seconds to obtain a magnetic hydrogel paste. Place it in a prepared square mold, which consists of two glass plates and a 1mm silicone spacer. After fixing the edges with clips, place it in a 75℃ drying oven to cure for 1-2 hours to obtain the first layer of magnetic hydrogel.

[0043] Finally, the sensing layer is integrated onto it. In an electronic solder paste sealed container equipped with a stirrer, 20g of acrylamide, 10g of lithium chloride, 0.04g of N,N'-methylenebisacrylamide, and 0.2g of TPO are dissolved sequentially in 70mL of deionized water and magnetically stirred at room temperature until a homogeneous solution is obtained. The first layer of magnetic hydrogel is placed in a square mold, which consists of two glass plates and a 2mm silicone spacer. The solution is poured into the mold, the edges are fixed with clips, and then it is irradiated under ultraviolet light for 20 minutes to obtain a self-sensing double-layer magnetic hydrogel actuator. Figure 1 As shown.

[0044] Example 2: Preparation method of self-sensing bilayer magnetic hydrogel actuator 2

[0045] like Figure 1 As shown, the microsphere gel powder was first prepared. 27.5 g of sodium 2-methyl-2-acrylamidopropanesulfonate was added to a sealed container of electronic solder paste equipped with a stirrer. Deionized water was added until the total net weight of both was 100 g. The mixture was magnetically stirred at room temperature until clear. Then, 0.647 g of N,N'-methylenebisacrylamide and 0.026 g of α-ketoglutaric acid were added sequentially, and stirring continued until the solution was homogeneous. The solution was poured into a mold made of a glass plate and a 9 mm silicone rubber gasket, and a strength of 2.5 mW cm⁻¹ was used. -2 The hydrogel was cured under 365nm ultraviolet light in an argon atmosphere for 8 hours, and then freeze-dried in a freeze dryer for 2 days. The freeze-dried particles were then ground into fine powder in a planetary mill for 12 hours, and then filtered through a standard sieve (50 mesh) to obtain microsphere gel powder, which was stored in a dry container for later use.

[0046] Next, the magnetically driven layer was prepared: the first layer, a magnetic hydrogel. 29.854 g of acrylamide was added to a sealed container of electronic solder paste equipped with a stirrer, and deionized water was added until the total net weight was 100 g. The mixture was magnetically stirred at room temperature until clear. Then, 1.295 g of N,N'-methylenebisacrylamide and 2.5 g of synthetic magnesium lithium silicate (nanoclay) were added sequentially, and the mixture was magnetically stirred at room temperature for 1 hour to obtain a homogeneous solution. 2 g of the previously prepared microsphere gel powder was added, and the mixture was stirred at 2000 RPM for 2 minutes using a planetary stirrer. The mixture was then stored at 2–8 °C for two days to allow the microsphere gel to fully swell. Further, 25 g of neodymium iron boron powder and 0.2 g of azobisisobutyronitrile were added, and the mixture was stirred at 2000 RPM for 2 minutes using a planetary stirrer, followed by degassing for 30 seconds to obtain a magnetic hydrogel paste. Place it in a prepared square mold, which consists of two glass plates and a 1mm silicone spacer. After fixing the edges with clips, place it in a 75℃ drying oven to cure for 1-2 hours to obtain the first layer of magnetic hydrogel.

[0047] Finally, the sensing layer is integrated onto it. In an electronic solder paste sealed container equipped with a stirrer, 20g of acrylamide, 10.15g of lithium chloride, 0.04g of N,N'-methylenebisacrylamide, and 0.2g of TPO are dissolved sequentially in 70mL of deionized water and magnetically stirred at room temperature until a homogeneous solution is obtained. The first layer of magnetic hydrogel is placed in a square mold, which consists of two glass plates and a 2mm thick silicone spacer. The solution is poured into the mold, the edges are fixed with clips, and then it is irradiated under ultraviolet light for 20 minutes to obtain a self-sensing double-layer magnetic hydrogel actuator.

[0048] Example 3: Detection of tensile strain using a self-sensing double-layer magnetic hydrogel actuator.

[0049] An experimental platform was built using a tensile testing machine and an impedance analyzer (WK6500B) to study its response to tensile strain. The sample to be tested was cut into a strip 12 mm long with a cross-sectional area of ​​2 mm × 2 mm, and connected to the impedance analyzer on both sides by wires. Figure 2 During the test, the AC frequency of the impedance analyzer was set to 100kHz, the AC voltage to 100mV, and the sampling frequency to once every 100ms, resulting in the image shown. Figure 2As can be seen, the resistance increases continuously as the sample is stretched. The sensitivity coefficients at each tensile strain stage were calculated using linear fitting. It can be seen that the sensitivity coefficient increases continuously during the stretching process: 1.41 at 50% tensile strain, 2.32 at 100% tensile strain, and 3.06 at 200% tensile strain. A linear relationship also exists under larger tensile strains (200%-400%), indicating that it can measure not only small tensile strains under low tensile strain conditions but also a wide range of high tensile strains.

[0050] Figure 3a Figures 3b and 3c show the resistance tests of the samples under repeated tensile stress. As can be seen from the figures, the resistance increases when tensile strain is applied, and returns to its initial position when the tensile strain is released. The entire process exhibits a linear relationship, and the resistance signal is very stable. Furthermore, the resistance varies significantly under different strain levels, demonstrating that it maintains a good and stable resistance response regardless of whether it is under low tensile strain (1%-7%), ordinary tensile strain (10%-40%), or large tensile strain (50%-300%). Figure 3d The test involved a phased holding load cycle from 0 to 100% tensile strain, with each holding time approximately 25 seconds. It can be observed that there is a significant shift in resistance between each loading phase, and no significant overshoot occurs during the holding phase. Figure 3e The test involved 400 tensile strain cycles at 20% tensile strain. It can be seen that while the relative resistance change ΔR / R0 increases with the number of tensile cycles, the increase is very slight, indicating a certain degree of fatigue resistance and repeatability. Overall, this bilayer magnetic hydrogel actuator possesses excellent response performance and stable durability as a sensor.

[0051] Example 4: Integrated testing of drive and sensing in a self-sensing dual-layer magnetic hydrogel actuator

[0052] The sample to be tested was cut into a strip 30 mm long with a cross-sectional area of ​​5 mm × 2 mm. It was fixed to a clean, vertical surface with insulating tape, and connected to an impedance analyzer on both sides via wires. A magnet with a magnetic field strength of 100 mT was gradually brought closer to the strip to attract it and cause it to bend. The resistance signal change was obtained as shown in Figure 4a. It can be seen that as the magnet slowly approaches, the strip responds rapidly within a very short time, bending from 0° to 60°, and maintaining and outputting a stable resistance signal at each bending angle. Figure 4bA bending angle of 45° was selected, and 20 bending cycles were conducted using a magnet. It can be seen that during the 20 bending cycles, although the relative resistance change ΔR / R0 increases and fluctuates with the increase in the number of bends, the amplitude is small, and the resistance signal does not show obvious overshoot, proving that the double-layer magnetic hydrogel actuator has a certain degree of operational stability and durability.

[0053] Example 5: Testing the bending signals of different fingers using a human hand-like structure made of a self-sensing double-layer magnetic hydrogel actuator.

[0054] The sample to be tested is cut into the shape of a human hand, such as... Figure 5a As shown, all five fingers are connected to an impedance analyzer via wires, with the thumb serving as a control group and left unmagnetized. The other four fingers are then saturated with magnetization. Figure 5a The deformation principle shown indicates that the magnetization direction of the deformed fingers is along the plane of the palm, while the magnetization direction of the undeformed fingers is perpendicular to the palm. When an external magnetic field is applied perpendicularly to the palm, the deformed fingers bend, thus aligning with the direction of the applied magnetic field. Using this principle, we were able to achieve different degrees of bending of the four fingers after applying an external magnetic field, while simultaneously obtaining... Figure 5b The images show the resistance changes of different fingers. As can be seen from the images, the ring finger shows the largest resistance change, followed by the index and middle fingers, while the little finger shows the smallest resistance change. This corresponds to the ring finger having the largest bending angle under the applied magnetic field, with the index and middle fingers also showing corresponding bending. The little finger has the smallest bending angle, while the thumb, being unmagnetized, shows no bending and its resistance change is zero. This demonstrates that the humanoid hand fabricated using this double-layer magnetic hydrogel actuator can reflect the degree of finger bending through changes in resistance signals.

[0055] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A self-induction enabled double-layer magnetic hydrogel actuator, characterized in that, The self-sensing double-layer magnetic hydrogel driver is a double-layer structure, comprising: a magnetic driving layer, which is a hard magnetic hydrogel containing microsphere gel and nanoclay, and can be repeatedly bent and deformed under the action of a magnetic field; and a sensing layer, which is a polyacrylamide hydrogel containing lithium chloride, and is formed on the magnetic driving layer by topological entanglement, has ionic conduction effect and can generate resistance change under bending deformation, and is connected with a wire for collecting the changed resistance signal. The preparation method of the self-sensing double-layer magnetic hydrogel driver comprises the following steps: 1) adding deionized water, acrylamide monomer, crosslinking agent and nanoclay into a reaction container, and stirring for 1-2 hours by magnetic force to obtain a uniform solution; 2) adding 2-acrylamide-2-methylpropanesulfonic acid sodium monomer, crosslinking agent, initiator and deionized water into a reaction container, mixing uniformly, pouring into a prepared mold, protecting by inert gas, introducing ultraviolet light for curing, freezing and drying in a freeze dryer, grinding the frozen and dried particles into fine powder in a planetary grinding machine, and then filtering the fine powder by a standard sieve to obtain microsphere gel powder; 3) adding the microsphere gel powder obtained in step 2) into the solution obtained in step 1) to obtain a nanometer microsphere-containing hydrogel prepolymer, and mixing and stirring uniformly by a planetary stirrer, and then storing in an environment of 2-8℃ for several days; 4) adding neodymium iron boron as magnetic particles into the hydrogel prepolymer of step 3), adding a thermal initiator, mixing and stirring by a planetary stirrer, pouring into a mold, controlling the thickness of the magnetic hydrogel, and then placing in a drying oven for curing to obtain a first layer of magnetic hydrogel, i.e., the magnetic driving layer; 5) adding acrylamide monomer, crosslinking agent, lithium chloride powder and photoinitiator into a reaction container, stirring by magnetic force to obtain a uniform solution, pouring the solution onto the surface of the first layer of magnetic hydrogel obtained in step 4), and generating a polymerization reaction under ultraviolet light to obtain a second layer of polyacrylamide hydrogel containing lithium chloride, i.e., the sensing layer; the two layers are tightly combined together by topological entanglement to finally obtain the self-sensing double-layer magnetic hydrogel driver. 2.The self-induction enabled double-layer magnetic hydrogel actuator according to claim 1, wherein: The particle size of the nanometer microspheres in the magnetic driving layer is 50-1000 nm. The thickness of the magnetic driving layer is 0.5-1 mm, and the thickness of the sensing layer is 0.5-1 mm. 3.The self-induction enabled double-layer magnetic hydrogel actuator according to claim 1, wherein: In step 1), the concentration of the acrylamide monomer is 4-4.2 M, the concentration ratio of the crosslinking agent methylene bisacrylamide to the acrylamide monomer is 0.1-0.2%, and the mass ratio of the nanoclay to the total weight of the acrylamide monomer and deionized water is 2-2.5%.

4. The self-induction enabled double-layer magnetic hydrogel actuator of claim 1, wherein: In step 2), the concentration of the 2-acrylamide-2-methylpropanesulfonic acid sodium monomer is 1-1.2 M, the concentration ratio of the crosslinking agent MBAA to the 2-acrylamide-2-methylpropanesulfonic acid sodium monomers is 4-4.2%, and the concentration ratio of the initiator α-ketoglutaric acid to the 2-acrylamide-2-methylpropanesulfonic acid sodium is 0.1-0.15%.

5. The self-induction enabled double-layer magnetic hydrogel actuator of claim 1, wherein: In step 2), the mold is a spacer plate made of two glass plates and a 9 mm layer of silica gel, and the inert gas used for protection is argon. 6.The self-induction enabled double-layer magnetic hydrogel actuator according to claim 1, wherein: In step 3), the concentration of the nanometer microspheres is 1-4%.

7. The self-induction enabled double-layer magnetic hydrogel actuator of claim 1, wherein: In step 4), the mass ratio of neodymium iron boron to the total weight of acrylamide monomer and deionized water is 0.5-50%, the mass ratio of thermal initiator azobisisobutyronitrile to the total weight of acrylamide and deionized water is 0.1-0.2%, and the temperature of the drying oven is 75℃. 8.The self-induction enabled double-layer magnetic hydrogel actuator according to claim 1, wherein: In step 5), the concentration of acrylamide monomer is 2.8-3M, the concentration of MBAA is 0.2-0.3%, the concentration of photoinitiator TPO is 0.5-0.6%, and the concentration of LiCl is 2.3-2.4M.

9. Use of the self-induction enabled double-layer magnetic hydrogel actuator according to claim 1 for the preparation of a gripper capable of sensing the size of an object, characterized in that: After the double-layer magnetic hydrogel driver is cut into a cross shape or a multi-petal shape and assembled into a gripper, the gripper can be quickly bent or gripped under the action of a magnetic field higher than 100mT.

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