A surface double network composite hydrogel with a three-layer structure imitating a caterpillar, a preparation method thereof and a repeatable programmable biomimetic deformation application

Abstract

The application discloses a surface double-network composite hydrogel with a three-layer structure similar to a flat worm, which comprises a graphene-containing polyacrylamide hydrogel matrix layer, and a poly-N-isopropyl acrylamide gel network thin layer formed on one side of the graphene-containing polyacrylamide hydrogel matrix layer and a poly-sodium methacrylate gel network thin layer formed on the other side of the graphene-containing polyacrylamide hydrogel matrix layer. The application forms a gel double-network structure with photothermal response and pH response on the surface of the two sides of the matrix gel, which is similar to the body structure of a flat worm in nature, in which the back skin and the belly skin sandwich the body. The application can present different initial shapes by adjusting the pH, so as to endow the application with various photothermal response complex driving modes under different initial shapes, and finally realizes the repeatable programming of the photothermal response complex deformation.

Description

TECHNICAL FIELD

[0001] The present application relates to functional polymer materials, and in particular to a surface double-network composite hydrogel with a three-layer structure simulating a flatworm and a preparation method thereof and a repeatable programmable biomimetic deformation application. BACKGROUND

[0002] Stimuli-responsive shape-changing hydrogels are a kind of very promising intelligent biomimetic materials, which have a very broad application prospect in the fields of soft robots, biomedical devices, artificial muscles, intelligent multifunctional valves, flexible sensors, etc. The research on complex deformation of stimuli-responsive shape-changing hydrogels initially focused on the development of a single driving mode. This kind of hydrogel can produce a predetermined deformation under a specific external stimulus. Although this kind of hydrogel performs well in some application scenarios, its function is relatively limited. With the development of technology and the increase of application demand, the design of stimuli-responsive shape-changing hydrogels has begun to develop towards more complex and regulated driving modes. This kind of hydrogel can obtain rich types of stimulus response and various designs of deformation. In recent years, in particular, based on the construction of anisotropic structures (such as oriented structures, gradient structures, layered structures and patterned structures, etc.), the complex deformation of stimuli-responsive shape-changing hydrogels can be programmed and designed, and more complex and controllable biomimetic deformation functions can be achieved. However, this kind of programming design of complex deformation of stimuli-responsive shape-changing hydrogels has been completed at the time of gel formation, so it can only be programmed and designed once. If different complex deformation properties are needed, new gels need to be reprogrammed and prepared, which is time-consuming and laborious, and seriously limits its further application. SUMMARY

[0003] Therefore, the present application provides a surface double-network composite hydrogel with a three-layer structure simulating a flatworm, which solves the problems of single deformation mode and poor repeatable programmable driving performance of existing stimuli-responsive shape-changing hydrogels.

[0004] In one aspect of the present application, a surface double-network composite hydrogel with a three-layer structure simulating a flatworm is adopted, which comprises a graphene-containing polyacrylamide hydrogel base layer, and the graphene-containing polyacrylamide hydrogel base layer forms a poly-N-isopropyl acrylamide gel network thin layer on one side and a poly-sodium methacrylate gel network thin layer on the other side.

[0005] Preferably, the thickness of the graphene-containing polyacrylamide hydrogel base layer is 0.5±0.05 mm, and the thickness of the poly-N-isopropyl acrylamide gel network thin layer and the poly-sodium methacrylate gel network thin layer is 0.1±0.01 mm.

[0006] Another aspect of the present application adopts a preparation method of a surface double network composite hydrogel with a worm-like three-layer structure, comprising the following steps: placing a graphene-containing polyacrylamide hydrogel base layer into a poly-N-isopropyl acrylamide prepolymer solution, standing for a period of time, taking out, placing into a mold, performing first ultraviolet light irradiation polymerization on one side, taking out, washing, drying, placing into a polymethacrylic acid sodium prepolymer solution, standing for a period of time, taking out and placing into a mold, and performing second ultraviolet light irradiation polymerization on the other side to obtain a worm-like structure hydrogel.

[0007] Preferably, the time of the two ultraviolet light irradiation polymerizations is 15 min.

[0008] Preferably, the graphene-containing polyacrylamide hydrogel base layer is prepared by the following method: taking 200 mg of acrylamide and 8 mg of N,N-methylene acrylamide, placing into 2 mL of a water-soluble graphene dispersion solution with a mass concentration of 0.5 wt%, mixing uniformly, placing into a refrigerator for cold storage, adding 140 μL of an ammonium persulfate solution with a mass concentration of 4.0 wt% and 14 μL of tetramethyl ethylenediamine into the mixed solution, rapidly shaking uniformly, injecting into a mold, sealing, and polymerizing at 4℃ for 2 h to obtain the graphene-containing polyacrylamide hydrogel base layer.

[0009] Preferably, the poly-N-isopropyl acrylamide gel prepolymer solution comprises 3000 mg of N-isopropyl acrylamide, 120 mg of N,N-methylene acrylamide, 120 mg of azobis isobutyl imidazole hydrochloride and 30 mL of deionized water.

[0010] Preferably, the polymethacrylic acid sodium prepolymer solution comprises 1285.5 mg of acrylamide, 214.5 mg of sodium methacrylate, 45 mg of N,N-methylene acrylamide, 30 mg of azobis isobutyl imidazole hydrochloride and 30 mL of deionized water.

[0011] Another aspect of the present application also provides an application of the surface double network composite hydrogel with a worm-like three-layer structure in the preparation of a repeatable programming photo-thermal response complex deformation driver.

[0012] Another aspect of the present application also provides an application of the surface double network composite hydrogel with a worm-like three-layer structure in the preparation of a complex bionic driving-self-sensing dual-function synergistic driver.

[0013] The method provided by the application is based on the fact that the ultraviolet light is sharply attenuated in the gel due to the high light absorption efficiency of graphene, and a thin layer of UV-polymerized gel second network can only be formed on the surface of the substrate, and accordingly two different second gel networks of poly N-isopropyl acrylamide (PNIPAM) and poly methyl acrylic acid sodium (PMAA-Na) can be formed on the two surfaces of the substrate gel, so that the double-network structure of the gel with photothermal response and pH response is formed on the surface of the substrate gel on the two surfaces, which is just like the structure of the worm body structure in which the back skin and the ventral skin clasp the body. Unlike the initial shape of the existing shape-changing hydrogel which cannot be changed after the gel is formed, the "imitation worm structure" hydrogel can present different initial shapes based on the adjustment of pH, so as to give various different photothermal response complex driving modes under different initial shapes, and finally realize the repeatable programming of the photothermal response complex deformation.

[0014] Further, the surface double-network composite hydrogel FLH of the imitation worm three-layer structure of the application can change the conductivity in real time during the deformation process of poly methyl acrylic acid sodium (PMAA-Na), and the deformation process of the gel can be sensed and presented in real time by the self-electric signal, so that the gel can be applied in the bionic complex driving-self-sensing double-function synergistic driver. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a preparation schematic diagram of the "imitation worm structure" hydrogel (FLH) of the application;

[0016] Figure 2 It is the light transmittance of the PAAm-G hydrogel with different graphene contents under different wavelengths (a) and the light transmittance of the PAAm-G hydrogel with different thicknesses and different graphene contents under 365 nm ultraviolet light (b);

[0017] Figure 3 It is the surface morphology of (a) PAAm-G, (b) the surface containing PNIPAM, and (c) the surface containing PMAA-Na;

[0018] Figure 4 It is a scanning electron microscope image of the cross section of the FLH hydrogel;

[0019] Figure 5 It is (a) the Raman white light picture and (b) the Raman spectrum imaging of the cross section of the FLH hydrogel;

[0020] Figure 6 It is (a) the contact angle change curve of the two surfaces of the FLH hydrogel (FLH-1 is the surface containing PNIPAM, and FLH-2 is the surface containing PMAA-Na); (b) the contact angle change curve of the PAAm-G hydrogel;

[0021] Figure 7 (a) equilibrium bending shape and angle at different pH; (b) equilibrium bending angle curve at different pH; (c) cycle test between pH = 2 and pH = 12 (scale 5mm);

[0022] Figure 8 (a) equilibrium swelling angle at different temperature under initial condition of pH = 4.6 (b) bending process in hot water at 40℃; (c) recovery process in cold water at 20℃ (scale 5mm);

[0023] Figure 9 (a) bending and (b) recovery process of FLH hydrogel under NIR irradiation at pH = 4.6 and 8W / cm 2

[0024] Figure 10 (a) bending and (b) recovery process of FLH hydrogel under NIR irradiation at pH = 4.6 and 8W / cm 2

[0025] Figure 11 DETAILED DESCRIPTION

[0026] The principles and features of the present application are described below in conjunction with the attached drawings, in which the examples are used to explain the present application, but not to limit the scope of the present application.

[0027] The chemical raw materials used in the embodiments of the present application are shown in Table 1.

[0028] Table 1: Raw material details

[0029]

[0030]

[0031] Embodiment 1: A preparation method of a surface double network composite hydrogel with a flatworm three-layer structure, comprising the following steps:

[0032] S101: Preparation of the base hydrogel

[0033] ​​​AAm (monomer, 200 mg) and BIS (cross-linker, 8 mg) were weighed and placed in 2 mL of a diluted water-soluble graphene dispersion with a mass concentration of 0.5 wt%. After mixing, the mixture was placed in a 4°C refrigerator. 140 μL of ammonium persulfate solution (oxidant, 4.0 wt%) and 14 μL of TEMED (reducing agent) were added to the mixed solution. After rapid shaking, the mixture was injected into a mold containing 0.5 mm thick silicone rubber that had also been refrigerated at 4°C. After sealing, low-temperature polymerization was carried out in a 4°C refrigerator for 2 hours. After the polymerization process was completed, the mixture was immersed in a large amount of deionized water for 24 hours and washed to obtain a graphene-containing polyacrylamide hydrogel (PAAm-G).

[0034] Preparation of S102 PNIPAM prepolymer solution

[0035] Weigh 3000 mg of NIPAM (monomer), 120 mg of BIS (cross-linker), 120 mg of AIBA (initiator) and 30 mL of deionized water, and store the mixture in a refrigerator and away from light.

[0036] Preparation of S103 PMAA-Na prepolymer solution

[0037] Weigh 1285.5 mg AAm (monomer), 214.5 mg MMA-Na (monomer), 45 mg BIS (cross-linker), 30 mg AIBA (initiator), and 30 mL deionized water, mix them, and refrigerate the mixture and protect it from light.

[0038] Preparation of S104 "Flatworm-like" Hydrogel (FLH)

[0039] The PAAm-G hydrogel prepared by S101 was placed in the PNIPAM prepolymer solution and allowed to soak for 6 hours, keeping it away from light. Finally, the PAAm-G hydrogel was taken out and placed in a 0.5mm thick silicone rubber mold, and one side was irradiated with 365nm UV light for 15 minutes. After that, the gel was taken out and placed in a large amount of deionized water for 24 hours to remove unreacted compounds; after taking it out and drying the water, it was placed in the PMAA-Na prepolymer solution and allowed to soak for 6 hours, keeping it away from light. After that, the soaked gel was placed in a 0.5mm thick silicone rubber mold, and the other side was irradiated with 365nm UV light for 15 minutes. After that, a "flatworm structure" hydrogel (FLH) was obtained.

[0040] Example 2: The difference between Example 2 and Example 1 is that in step S101, graphene dispersions of different mass concentrations are added, and a UV spectrophotometer is used to study the gradient transmittance of the graphene content and the thickness of the hydrogel. Figure 2As can be seen in a, when the thickness of PAAm-G is 0.5 mm and the content of graphene is 0.1-0.2wt%, there is more than 1% transmittance under the irradiation of 365 nm ultraviolet light; when the content is 0.1-0.4wt%, there is more than 1% transmittance under the irradiation of 808 nm infrared light. It shows that under this thickness, more than 0.2wt% content of graphene is needed to ensure the formation of a surface thin layer of the second gel network. Figure 2 b The transmittance of PAAm-G under 365 nm ultraviolet light at different thicknesses and various graphene contents is shown in the table. When the content of graphene is 0.5wt%, the transmittance is about 4%, the formed thin layer is also the required thickness, and under this content of graphene, the photo-thermal conversion effect also meets the initial driving design. The severe attenuation of ultraviolet light in the gel caused by the high light absorption efficiency of graphene leads to the formation of a 0.1 mm thin layer on the surface of the second network of UV-polymerized gel, so the content of 0.5wt% water-soluble graphene is finally selected.

[0041] Example Three: Characterization test of the "flatworm structure" hydrogel (FLH) prepared in Example One

[0042] (1) The microstructure of FLH hydrogel was characterized by scanning electron microscopy (SEM), and the results are shown in Figure 3 Compared with PAAm-G base gel, the surface microstructure of FLH hydrogel can be observed to have a more dense pore structure than the single network PAAm-G base gel, indicating that two different double network gel structures have been formed on the surface of the base gel respectively. It shows that the surface gel double network structure has been successfully obtained. As shown in Figure 4 The microstructure of the cross-section of FLH hydrogel can be divided into three parts: PAAm and PNIPAM double network thin layer (FLH-1), PAAm network layer (FLH-0) and PAAm and PMAA-Na double network thin layer (FLH-2). It can be observed that the surface layers on the upper and lower sides have a thickness of about 0.1 mm, which has a different morphology than other parts. The side proves that the composition on the upper and lower sides has changed. This difference in structure makes FLH hydrogel have an anisotropic structure, increases the modulus and driving performance of FLH hydrogel, and in addition, it is observed that the network structure from the surface to the inside is in a transition state, forming a double network gradient structure.

[0043] (2) The cross-section of FLH hydrogel was analyzed by Raman (Raman) image, as shown in Figure 5 The results show that the water-soluble graphene is uniformly distributed in the hydrogel, forming the FLH hydrogel with stable composition in Example One.

[0044] (3) The contact angles of two surfaces of FLH hydrogel were tested (FLH-1 with PNIPAM surface, FLH-2 with PMAA-Na surface), and the results are shown in Figure 6 , the hydrophilicity of PMAA-Na gel network decreased from 63° to 39° within 0-8s; while the hydrophilicity of PNIPAM side changed greatly, decreasing from 73° to 71° within 0-8s, almost no change. The curves of FLH-1 and FLH-2 further illustrate the difference between the two surfaces, proving the difference of the two surfaces of the double network structure of FLH hydrogel. The two double network surfaces are denser than the gel network of the single matrix hydrogel, so the contact angle of the two surfaces of FLH hydrogel is larger than that of the matrix hydrogel (PAAm-G) and changes more slowly.

[0045] (4) Study on the pH response performance of FLH hydrogel

[0046] As shown in Figure 7 a, the same FLH hydrogel (size 2x12x5mm 3 ) was placed in solutions with different pH values, and after waiting for 2h for complete swelling, the central angle of the gel was measured as its equilibrium swelling angle. The results show that there is an angle of 0° between pH=4-5, as shown in Figure 7 b, at pH=4.6, the equilibrium swelling angle is 0°, and the shape is a straight strip. When pH<4.6, the FLH hydrogel bends to the side containing the PMAA-Na second network, and the positive bending can reach 160°; when pH>4.6, the FLH hydrogel bends to the side containing the PNIPAM second network, and the negative bending can reach 267°. As can be seen, the various states of FLH hydrogel under different pH conditions can be used as the initial state for driving deformation, providing a basis for programming design of the initial state of hydrogel. In addition, the FLH hydrogel was subjected to a cycle test to verify its stability and durability. The same FLH hydrogel (size 2x12x5mm 3 ) was repeatedly placed in solutions with pH=2 and pH=12, and each time it stayed in the solution for 1h, and after reaching the equilibrium swelling state, its central angle was measured and repeated for 10 times. As shown in Figure 7 c, after 10 cycles, it can be observed that it can reach a recovery degree of 96% of the initial state, proving that the hydrogel has good durability and stability.

[0047] (5) Test of thermal response performance of FLH hydrogel

[0048] When pH=4.6, the FLH hydrogel (size 2x12x5mm 3 ) is a straight strip, as shown in Figure 8a, the bending angle of FLH hydrogel changes from 0° to 360° as the water temperature increases from 20℃ to 40℃. In addition, the driving and recovery processes of FLH hydrogel in 40℃ hot water and 20℃ cold water are recorded respectively. As shown in Figure 8 b, the FLH hydrogel in 40℃ constant temperature hot water realizes the bending change from 0° to 360° within 80s driven by the shrinkage of the second PNIPAM network. After the completion of the bending driving, the FLH hydrogel is quickly placed in 20℃ constant temperature cold water. The recovery rate of FLH hydrogel is from fast to slow, and finally reaches the equilibrium state Figure 8 c).

[0049] (6) Test of photo-thermal response performance of FLH hydrogel

[0050] In order to study the bending and folding performance of FLH hydrogel under the irradiation of area light source and point light source, the following experimental design is designed and carried out. First, a strip-shaped FLH hydrogel with a size of 2×12×5mm 3 is selected as the experimental sample. Then, the near-infrared light with an irradiation intensity of 2.4W / cm 2 is applied. Under the full coverage of near-infrared light, the diameter of area light source is 13mm, as shown in Figure 9 a and 9b, the FLH hydrogel in initial state is straight strip-shaped at pH=4.6, and it bends from 0° to 360° within 74s. Then, the near-infrared light is immediately removed, and the FLH hydrogel returns to the initial state in about 170s. After returning to the initial state, the same experimental sample is used, and the near-infrared light with an irradiation intensity of 0.6W / cm 2 is applied. The experimental sample is locally irradiated, and the diameter of the irradiation area of near-infrared light is 2mm. The side containing the second PNIPAM network begins to shrink under the irradiation, and the unirradiated part remains unchanged, thus showing the bending phenomenon. The bending angle of FLH hydrogel can change from 0° to 90° in about 25s Figure 9 c). When the near-infrared light is removed, the experimental sample returns to the original straight strip shape in about 60s Figure 9 d). This shows that the prepared FLH hydrogel has excellent photo-thermal response performance.

[0051] (7) Repeatedly programmable bionic application of FLH hydrogel

[0052] By using the various different initial states of FLH hydrogel which can be repeatedly programmed, various bionic driving based on remote control of near-infrared light is realized, such as "put", "hook", "lift", "top" and other bionic actions.

[0053] As shown in Figure 10In the initial state of the FLH hydrogel in the positive bending, the actions of "put" and "hook" can be realized. First, one end of a 1.2 mm long FLH hydrogel is fixed, the whole FLH hydrogel experimental sample is completely immersed in a liquid environment with pH = 2, and a ring-shaped weight is put on the sample. The weight is lifted by the hydrogel sample, and a high platform is placed directly below it to simulate the scene when the object is actually taken and put. Then, a near-infrared surface light source (light source diameter of 5 mm) with a power of 4.0 W / cm 2 is used for dynamic irradiation. The hydrogel needs to be deformed from top to bottom to drive, and the deformation needs to be uniform and effective. When the deformation reaches a certain degree, the weight is put down. When the near-infrared light source is removed, the FLH hydrogel sample returns to the initial state, and the action of "put" is completed. It can be observed that in this bionic driving, the deformation rate and recovery rate of the hydrogel are high, and the action can be completed efficiently.

[0054] (8) Bionic driving of FLH hydrogel - self-sensing collaborative application

[0055] Based on the basic performance of FLH hydrogel sensing, a device with self-sensing intelligent delivery system is developed to lift or lift the weight. For example Figure 11 When there is no near-infrared surface light source irradiation, the initial state of the bionic device is in the state of reverse bending. When the surface light source is irradiated, the device begins to deform and lifts the weight. At this time, the resistance will decrease sharply, and the amplitude of the current signal fluctuation will increase. At this time, the current signal is at the peak value. When the near-infrared surface light source is removed, the current gradually returns to the initial state. In this way, based on the change of the electric signal, the driving process of the device can be observed in real time, the self-driving and self-sensing are cooperated, and the future collaborative design development in the field of flexible sensor is realized.

[0056] In summary, the preparation method of the "bionic worm structure" hydrogel provided by the present application uses water-soluble graphene-polyacrylamide (PAAm-G) composite hydrogel as the matrix, and two different second gel networks of poly N-isopropyl acrylamide (PNIPAM) and poly methyl methacrylate sodium (PMAA-Na) are formed on the two surfaces of the matrix gel, respectively. The gel double network structure with photothermal response and pH response is formed on the surface of the matrix gel on both sides, which is just like the worm body structure with the back skin and the abdominal skin clamping the body. Unlike the initial shape of the existing shape-changing hydrogel which cannot be changed after gelation, the "bionic worm structure" hydrogel can present different initial shapes by adjusting the pH, thereby giving it various complex driving modes of photothermal response under different initial shapes, and finally realizing the repeatable programming of photothermal response complex deformation.

[0057] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A surface double network composite hydrogel mimicking the structure of a three-layered worm, characterized in that, The surface double network composite hydrogel of the imitation flatworm three-layer structure comprises a graphene-containing polyacrylamide hydrogel base layer, which forms a poly-N-isopropyl acrylamide gel network thin layer on one side and a poly-sodium methacrylate gel network thin layer on the other side, and is prepared by the following steps: placing the graphene-containing polyacrylamide hydrogel base layer in a poly-N-isopropyl acrylamide prepolymer solution, soaking for a period of time, taking out and placing in a mold, performing first ultraviolet light polymerization on one side, taking out, washing, drying, placing in a poly-sodium methacrylate prepolymer solution, soaking for a period of time, taking out and placing in a mold, and performing second ultraviolet light polymerization on the other side to obtain the imitation flatworm structure hydrogel.

2. The surface double network composite hydrogel with a worm-like three-layer structure according to claim 1, characterized in that, The graphene-containing polyacrylamide hydrogel base layer has a thickness of 0.5±0.05 mm, and the poly-N-isopropyl acrylamide gel network thin layer and the poly-sodium methacrylate gel network thin layer each have a thickness of 0.1±0.01 mm.

3. A method for preparing a surface double network composite hydrogel of the worm-like three-layer structure according to claim 1 or 2, characterized by, The surface double network composite hydrogel of the imitation flatworm three-layer structure comprises a graphene-containing polyacrylamide hydrogel base layer, which forms a poly-N-isopropyl acrylamide gel network thin layer on one side and a poly-sodium methacrylate gel network thin layer on the other side, and is prepared by the following steps: placing the graphene-containing polyacrylamide hydrogel base layer in a poly-N-isopropyl acrylamide prepolymer solution, soaking for a period of time, taking out and placing in a mold, performing first ultraviolet light polymerization on one side, taking out, washing, drying, placing in a poly-sodium methacrylate prepolymer solution, soaking for a period of time, taking out and placing in a mold, and performing second ultraviolet light polymerization on the other side to obtain the imitation flatworm structure hydrogel.

4. The method according to claim 3, wherein the method is characterized by, Each of the two ultraviolet light polymerization times is 15 min.

5. The method according to claim 3, wherein the method is characterized by, The graphene-containing polyacrylamide hydrogel base layer is prepared by the following method: taking 200 mg of acrylamide and 8 mg of N,N-methylene acrylamide, placing them in 2 mL of a water-soluble graphene dispersion solution with a mass concentration of 0.5 wt%, mixing uniformly, placing them in a refrigerator for cold storage, adding 140 µL of an ammonium persulfate solution with a mass concentration of 4.0 wt% and 14 µL of tetramethyl ethylenediamine to the mixed solution, rapidly shaking uniformly, injecting into a mold, sealing, and polymerizing at 4℃ for 2 h to obtain the graphene-containing polyacrylamide hydrogel base layer.

6. The method for preparing a flatworm-mimicking three-layer surface double-network composite hydrogel according to claim 3, characterized in that: The poly-N-isopropyl acrylamide gel prepolymer solution comprises 3000 mg of N-isopropyl acrylamide, 120 mg of N,N-methylene acrylamide, 120 mg of azobisdimethylamino propylammonium chloride, and 30 mL of deionized water.

7. The method according to claim 3, wherein the method is characterized by, The poly-sodium methacrylate prepolymer solution comprises 1285.5 mg of acrylamide, 214.5 mg of sodium methacrylate, 45 mg of N,N-methylene acrylamide, 30 mg of azobisdimethylamino propylammonium chloride, and 30 mL of deionized water.

8. Use of the surface double network composite hydrogel of the imitation flatworm three-layer structure according to claim 1 or 2 in the preparation of a repeatable programming photo-thermal response complex deformation driver.

9. Use of the surface double network composite hydrogel of the imitation flatworm three-layer structure according to claim 1 or 2 in the preparation of a complex bionic driving-self-sensing dual-function synergistic driver.

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