Shape memory polymer / stimulus responsive hydrogel bifunctional synergistic biomimetic driving material and preparation method thereof

Abstract

The application discloses a preparation method of a shape memory polymer / stimulus response hydrogel bifunctional synergistic biomimetic driving material, uses polyurethane as a shape memory layer, combines a stimulus response composite hydrogel with the polyurethane by using a cellulose-based material and ultraviolet curing UV glue to form a double-layer structure driving material, and the method is simple and the process is controllable. The double-layer structure driving material prepared by the method can be used to design a variety of initial shape drivers with high fixing rate, so that the same driver has multiple driving modes; on the other hand, the driver with various initial shapes can be reversibly driven under the condition that the critical temperature of the polyurethane is not triggered, and the light-thermal response or pH response is realized based on the stimulus response mechanism of the driving layer, so that excellent shape memory-stimulus response driving bifunctional synergy is finally realized.

Description

Technical Field

[0001] This invention relates to novel composite materials, and more particularly to a bifunctional biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel and its preparation method. Background Technology

[0002] Hydrogel-driven materials can exhibit shape changes in response to external stimuli, and complex actuation behaviors can be achieved through structural design, making them promising for applications in smart valves, artificial muscles, and intelligent robots. Hydrogel-driven materials can achieve single / multiple response actuation under various stimuli (temperature, pH, ionic strength, magnetic field, light, etc.). By constructing anisotropic structures (layered structures, gradient structures, oriented structures), and based on programmable structural design, even more complex and varied actuation behaviors can be achieved with hydrogel-driven materials.

[0003] In recent years, researchers have started from the fabrication structure and used photomask method to prepare the initial shape of various stripes, thereby realizing the shape change corresponding to the pattern. At present, the complex actuation of hydrogel driving materials is mainly a single driving mode (that is, there is only one driving mode corresponding to the structure design of the driving material), which makes it difficult to realize that the same driving material has various complex and variable driving behaviors. Moreover, the driving behavior of programmable hydrogel driving materials depends on the initial network structure and requires a lot of time to operate.

[0004] Chen et al. (Lu H et al., 2020) prepared a hydrogel-driven material by combining shape memory hydrogel with driving hydrogel, which can achieve dual-function synergy and drive based on driving hydrogel under various initial shapes. However, it has problems such as low shape memory hydrogel modulus, need to improve its fixation rate, complex operating conditions, and poor controllability of initial shape.

[0005] Therefore, it is necessary to study a bifunctional biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel and its preparation method. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing a bifunctional synergistic biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel, which solves the problems of low modulus and low fixation rate of existing shape memory hydrogels.

[0007] This invention provides a method for preparing a bifunctional biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel, comprising the following steps: applying adhesive to the surface of polyurethane, then pressing and fixing the cellulose-based material in UV adhesive, and then polymerizing the stimulus-responsive hydrogel prepolymer in a mold above the cellulose-based material to obtain the bifunctional biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel.

[0008] Preferably, the cellulose-based material is soft yarn or napkin paper.

[0009] Preferably, the polyurethane is prepared by the following method: 5g of polycaprolactone diol is weighed and melted in a vacuum drying oven at 100°C. Then, 10mL of butyl acetate solvent, 734μL of hexamethylene diisocyanate, 156μL of polyhexamethylene diisocyanate and 25μL of dibutyltin dilaurate are added in sequence and stirred until fully mixed. The mixture is then poured onto an aluminum sheet covered with a silicone rubber mold and cured in an oven at 60°C for 2 hours, and then dried in a vacuum drying oven at 80°C for 6 hours.

[0010] Preferably, the stimulus-responsive hydrogel is a photothermal-responsive hydrogel or a pH-responsive hydrogel.

[0011] Preferably, the pH-responsive hydrogel prepolymer is prepared by dissolving 85 mg acrylamide, 15 mg sodium methacrylate, and 5 mg methylenebisacrylamide in 1 mL of deionized water, and then adding 4 μL of tetramethylethylenediamine and 40 μL of 4 wt% ammonium persulfate solution under low temperature conditions and stirring until homogeneous.

[0012] Preferably, the photothermal responsive hydrogel prepolymer is prepared by mixing 100 mg N-isopropylacrylamide, 5 mg methylenebisacrylamide, 300 μL of 10 wt% MXene aqueous solution, and 700 μL of 2 wt% XLS nanoclay, placing the mixture at low temperature, and then adding 4 μL of tetramethylethylenediamine and 40 μL of 4 wt% ammonium persulfate solution in sequence and stirring rapidly until homogeneous.

[0013] Preferably, the polymerization time is 6 hours and the polymerization temperature is 4°C.

[0014] Another aspect of the present invention provides a bifunctional synergistic biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel.

[0015] This invention provides a method for preparing a bifunctional synergistic biomimetic actuating material based on shape memory polymer / stimulus-responsive hydrogel. Using polyurethane SMP as the shape memory layer, a cellulose-based material and UV-curable adhesive are used to bond the stimulus-responsive composite hydrogel to the polyurethane to form a bilayer actuating material. The method is simple and the process is controllable. The bilayer actuating material prepared using this method allows for the design of actuators with multiple initial shapes and high fixation rates, enabling the same actuator to have multiple actuation modes. Furthermore, actuators with various initial shapes can perform reversible actuation without triggering the polyurethane's critical temperature, and achieve photothermal or pH responses based on the stimulus-response mechanism of the actuating layer, ultimately achieving excellent shape memory-stimulus-responsive actuation synergy.

[0016] Furthermore, the bilayer structure driving material prepared using this method exhibits high fixation rate and resilience, and strong remote driving capability, solving the problem of low fixation rate and poor controllability of initial shape in shape memory hydrogels due to their low modulus. Moreover, the shape memory / pH-responsive bifunctional synergistic biomimetic driving material prepared using this method demonstrates synergistic driving capability at different pH levels, achieving shape memory / pH-responsive bifunctional synergistic driving, thus addressing the limitation of application range caused by the low response temperature and difficulty in controlling photothermal properties of polyurethane SMP. Attached Figure Description

[0017] Figure 1 Infrared spectral images of PAAm hydrogel and PAA composite hydrogel prepared in Example 1;

[0018] Figure 2 Scanning electron microscope images of PAAm hydrogel (a) and PAA composite hydrogel (b) prepared in Example 1;

[0019] Figure 3 Cross-sectional scanning electron microscope images of the bifunctional biomimetic driving material (a) and cellulose-based napkin (b) prepared in Example 3;

[0020] Figure 4 a is the tensile curve of PAA composite hydrogel prepared in Example 1, polyurethane SMP in Example 2, and bifunctional biomimetic driving material in Example 3. Figure 4 b represents the stress-strain curve of the PAA composite hydrogel;

[0021] Figure 5 a represents a bar graph showing the fixation rate of the bifunctional biomimetic driving material prepared in Example 3 under bending, folding, and spiral shapes; Figure 5 b represents its bending and fixing cycle diagram; Figure 5 c represents its w-bending and fixing cycle diagram; Figure 5 d represents its spiral fixed cycle diagram;

[0022] Figure 6 The equilibrium bending angle (a), bending angle curve (b) in solution (pH=11), recovery process behavior (c) and cycle test diagram (d) of the bifunctional biomimetic driving material prepared in Example 3 are shown in solutions with different pH values.

[0023] Figure 7 The driving behavior of the spiral bifunctional biomimetic driving material prepared in Example 3 in solutions with pH=3 and pH=11 (scale bar is 6mm);

[0024] Figure 8The diagram shows the preparation of the polyurethane SMP in Example 2, the MXene / PNIPAM composite hydrogel in Example 4, and the bifunctional biomimetic driving material in Example 5.

[0025] Figure 9 XPS spectrum (a) and XRD spectrum (b) of the MXene / PNIPAM composite hydrogel in Example 4;

[0026] Figure 10 a is a cross-sectional electron microscope image of the overall bifunctional biomimetic driving material prepared in Example 5; 10b is a cross-sectional electron microscope image of the cellulose-based cloud-like yarn in the bifunctional biomimetic driving material;

[0027] Figure 11 a is a tensile curve of the polyurethane SMP of Example 2, the MXene / PNIPAM composite hydrogel of Example 4, and the bifunctional biomimetic driving material of Example 5. Figure 11 b represents the stress-strain curve of the MXene / PNIPAM composite hydrogel;

[0028] Figure 12 The bifunctional biomimetic actuation material of Example 5 at 4.0 W / cm 2 Bending (a) and recovery (b) processes under NIR irradiation; with an infrared laser power of 0.2 W / cm². 2 The bending (c) and recovery (d) process diagrams are shown, with a spot diameter of 1 mm and a scale bar of 10 mm.

[0029] Figure 13 The bending (a) and recovery (b) processes of the bifunctional biomimetic driving material in Example 5 under arc-shaped conditions and NIR irradiation at 4.0 W / cm² are shown; and the bending process under obtuse angle conditions and NIR irradiation at 0.2 W / cm² is also shown. 2 The bending (c) and (d) recovery processes, with a spot diameter of 1 mm and a scale of 10 mm;

[0030] Figure 14 The bifunctional biomimetic driving material of Example 5, in its initial state as an "S" shape, operates at 4.0 W / cm². 2 Driven and recovered processes under NIR irradiation (scale bar: 10mm);

[0031] Figure 15 The diagram shows the simulated motion behavior of the dual-function biomimetic drive material in Example 5, which is shaped like a hook, when lifting a heavy object (point light source: 0.2W, diameter: 2mm, scale bar: 10mm).

[0032] Figure 16 This is a diagram illustrating the motion behavior of the dual-function biomimetic drive material in Example 5, which grasps and releases heavy objects in a gripper shape (scale bar is 10mm).

[0033] Figure 17 Figure 5 shows the study of the closing drive behavior of a bifunctional biomimetic driving material for a biomimetic orchid (scale bar is 10mm). Detailed Implementation

[0034] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0035] The reagents and raw materials used in the following examples were all purchased from reputable companies. The main component of the UV adhesive is acrylate. The pH solution was prepared by mixing 0.1 mol / L Na2HPO4 solution and 0.1 mol / L NaH2PO4 solution to prepare a buffer solution with pH=7. The pH was then adjusted with HCl and NaOH to obtain solutions with pH=3, pH=5, pH=9 and pH=11.

[0036] Example 1: A method for preparing sodium methacrylate-polyacrylamide composite hydrogel, comprising the following steps:

[0037] Preparation of polyacrylamide (PAAm) hydrogel: Weigh 100 mg of acrylamide monomer into 1 mL of deionized water, add 4 mg of methylenebisacrylamide (crosslinking agent BIS), shake well, then add 4 μL of tetramethylethylenediamine and 40 μL of 4 wt% ammonium persulfate solution, mix well, place in a mold, cover with a glass slide and wait for gel formation, then demold and soak in a large amount of deionized water to obtain PAAm hydrogel.

[0038] Preparation of pH-responsive hydrogel: Weigh 85 mg acrylamide (AAm), 15 mg sodium methacrylate (SMA), and 5 mg methylenebisacrylamide (crosslinking agent BIS) and dissolve them in 1 mL of deionized water. Then, place the mixture in the refrigerator compartment to cool to 4 °C. Next, add 4 μL of tetramethylethylenediamine (TEMED) and 4 wt% ammonium persulfate solution (APS, 40 μL). Stir the prepolymer solution quickly until it is homogeneous to obtain the prepolymer solution. Pour it into a mold and seal it. React at 4 °C for 6 h to obtain PAA composite hydrogel.

[0039] The PAAm hydrogel and PAA composite hydrogel prepared in Example 1 were tested:

[0040] (1) As Figure 1 Infrared spectroscopy results showed that the characteristic peaks of symmetric and asymmetric stretching of the amino groups in PAAm hydrogel were in the range of 3000-3500 cm⁻¹. -1The peak at the red line is broad. Compared to the PAAm spectrum, the FT-IR curve of the red line (PAA composite hydrogel) retains both the amino characteristic peak of PAAm and the carboxyl characteristic peak of sodium methacrylate, indicating that the PAA composite hydrogel was successfully prepared.

[0041] (2) Figure 2 SEM results showed that both PAAm hydrogel and PAA composite hydrogel have porous structures. However, the pores in the PAAm network structure are of different sizes and have thick pore walls. The PAA composite hydrogel, which is doped with SMA, has a denser pore structure and thinner pore walls. This indicates that the PAA composite hydrogel has a large specific surface area, which is beneficial for its higher efficiency in binding with water and its higher swelling performance.

[0042] (3) Further, the effect of sodium methacrylate content (0, 5 mg, 10 mg, 15 mg, 20 mg) on ​​the swelling properties of the composite hydrogel was studied. The experimental results showed that when the composite hydrogel formulation was SMA=15, the PAA composite hydrogel prepared in this embodiment had the maximum swelling ratio of 18.54 and the largest difference in swelling ratio. Its length changed significantly at pH=11 and pH=3, and its volume changed up to four times, which can provide a great driving force for the preparation of driving materials.

[0043] Example 2: A method for preparing polyurethane shape memory polymer, comprising the following steps:

[0044] First, weigh 5g of polycaprolactone diol (PCL) and melt it in a vacuum drying oven at 100℃. Then, add 10mL of butyl acetate solvent, 734μL of hexamethylene diisocyanate, 156μL of polyhexamethylene diisocyanate, and 25μL of dibutyltin dilaurate (catalyst DBTDL) in sequence. Mix thoroughly on a magnetic stirrer, then pour it onto an aluminum sheet covered with a 100μm silicone rubber mold and cure it in an oven at 60℃ for 2 hours. Finally, dry it in a vacuum drying oven at 80℃ for 6 hours to obtain polyurethane shape memory polymer (SMP).

[0045] Example 3: Preparation of a bifunctional synergistic biomimetic driving material of shape memory polymer / pH-responsive hydrogel, including the following steps:

[0046] A layer of UV adhesive was uniformly coated on the polyurethane prepared by the method in Example 2. Smooth, patternless cellulose-based napkin paper was combined with shape memory polymer. The napkin paper was fixed with UV adhesive cured by ultraviolet light. The pH-responsive hydrogel prepolymer liquid from Example 1 was then poured onto the surface of the napkin paper. The mold was covered and polymerized at 4°C for 6 hours. After demolding, the napkin paper was soaked in a large amount of deionized water to remove unreacted compounds and obtain a bifunctional synergistic biomimetic driving material.

[0047] (1) As Figure 3Cross-sectional electron microscopy images show that the bilayer composite driving material of this embodiment was successfully prepared. A cellulose-based napkin paper is used as an interlayer to tightly connect the composite hydrogel and the polyurethane SMP. The napkin paper is fixed with UV adhesive, achieving a tight bond with the polyurethane SMP. Simultaneously, the hydrogel penetrates the cellulose-based napkin paper, forming numerous hydrogen bonds to achieve a strong mechanical interlock. Furthermore, the large porous structure and excellent hydrophilicity of the cellulose-based napkin paper contribute significantly to the increase in the swelling rate of the hydrogel.

[0048] Furthermore, EDS-mapping was used to characterize the cross-section of this composite driving material. The results showed that the distribution of C, O, and Na elements from top to bottom exhibited a stratified pattern. The elements were uniformly distributed in the upper hydrogel, indicating a strong and uniform bond between the hydrogel and the cellulose-based napkin, while the SMA was also uniformly distributed within the hydrogel. However, no elements were distributed in the polyurethane SMP portion, indicating that the hydrogel was not incorporated into the dense structure of the polyurethane SMP, but only existed at the napkin and the interface.

[0049] (2) Tensile tests were performed on PAA composite hydrogel, polyurethane SMP, and bilayer driven materials. For example... Figure 4 The results show that, compared with the tensile strength of 41±0.4 kPa of PAA composite hydrogel, the tensile strength of the composite driving material in this embodiment can reach 2.6±0.3 MPa, which is 6.34 times that of PAA composite hydrogel.

[0050] (3) The shape fixation rate of the dual-functional synergistic biomimetic actuation material prepared in this embodiment was tested. The dual-functional synergistic biomimetic actuation material of this embodiment was softened by immersing it in hot water, allowing it to be designed into actuation materials with curved, folded, and spiral shapes, such as... Figure 5 The results showed that the angle fixation rates of the material before and after swelling were 98.3%, 95.6%, and 93.1%, respectively. Furthermore, a shape memory cyclic test was conducted on this composite driving material. After five cycles, the fixation rates for bending, folding, and spiraling remained at 90.54%, 89.4%, and 82.9%, respectively, indicating that the shape memory performance of this driving material remained at a high level and its cyclic performance was excellent.

[0051] (4) pH response behavior test of the bifunctional synergistic biomimetic driving material prepared in this embodiment.

[0052] The results are as follows Figure 6As shown in Figure a, we tested the final angle of the driving material under different pH solutions. The driving material was placed in solutions of different pH values ​​and allowed to fully swell. The angle measured after 2 hours was taken as the final angle. The results show that the equilibrium angle of the driving material at pH = 3 is 0°, which is taken as the initial state of the driving material. Its bending angle increases with increasing pH. When the pH is greater than 7, the bending angle of the driving material is greater than 360°. Therefore, when this material is placed in a solution at pH = 11, the hydrogel begins to swell, and its initial driving state is a straight strip-shaped driving material movement.

[0053] In addition, the specific driving process of the driving material was measured, such as... Figure 6 As shown in b, in a buffer solution with pH = 3, the initial angle of the driving material is 0°. As the PAA hydrogel swells, -COOH groups in the PAA hydrogel form -COO groups. - The functional groups gradually close the driving material, increasing the bending angle. After 14 minutes of swelling, the bending angle of the driving material is 360°, and the driving speed is 25.71° / min. Throughout the driving process, the shape of the driving material changes from a straight strip to a circle. Figure 6 As shown in c, after complete activating at pH=11, the activating material was returned to the pH=3 solution for recovery. Compared to the activating process, the contraction rate was significantly reduced, with the contraction process lasting 28 minutes and an average recovery rate of 12.86° / min.

[0054] Other examples Figure 6 The d-cycle test showed that the driving material has good durability. During five tests, with the solution pH continuously changed from 3 to 11, the bending angle of the driving material did not change significantly.

[0055] (5) The synergistic driving behavior of the bifunctional synergistic biomimetic driving material prepared in this embodiment was tested. The driving material was designed into different shapes and placed in a pH solution to respond to the driving action. The straight driving material was immersed in a 39°C water bath for 5 seconds, and then a temporary shape was quickly designed under external force. After cooling, the driving material in the designed temporary shape was placed in a pH=3 solution. After the hydrogel swelled, the shape at this point was the initial shape of the driving material's response. The driving process of the driving material was observed by changing the pH of the solution. For example... Figure 7As shown, the initial actuator is a loose spiral shape, approximately 540°, with a relatively large interlayer spacing. Placed in a buffer solution at pH 11, after 10 minutes of pH response, due to the swelling of the hydrogel, the polyurethane SMP moves towards the center. This actuator exhibits a significant decrease in length, a narrowing of the interlayer spacing, and a gradual increase in the spiral angle from the initial 540° to approximately 900°. In contrast, the actuation process of a spiral actuator containing a hydrogel is quite different. The actuation process of this spiral actuator can be divided into two processes: unwinding and rewinding. First, the actuator unwinds, unfolding into a straight strip within 3 minutes, then reverses the spiral. After 10 minutes, the spiral angle of this actuator is approximately 400°. Furthermore, the actuating material can be designed into various initial shapes such as arcs or right angles, demonstrating that the same actuating material can achieve actuation in various complex temporary shapes and has multiple actuation modes.

[0056] In summary, the hydrogel actuation layer in this embodiment is a pH-responsive bifunctional synergistic biomimetic actuation material. Sodium methacrylate / polyacrylamide hydrogel was selected as the actuation response layer, and a polyurethane SMP-PAA bilayer composite actuation material was prepared based on the excellent hydrophilicity and organic solvent affinity of napkin paper. This actuation material exhibits high controllability of its initial shape and can be actuated under pH response. Furthermore, this actuation material was designed in "arc-shaped," "obtuse-angled," and spiral shapes, enabling reversible actuation in pH solutions, achieving multiple complex actuation functions from the same material. This solves the problem that existing polyurethane materials have low shape transition temperatures, requiring reversible actuation under critical power infrared light control, which limits the application of actuation materials.

[0057] Example 4: Preparation of MXene / PNIPAM composite hydrogel, including the following steps:

[0058] First, 200 mg of nano-clay XLS was weighed into 10 mL of deionized water and shaken to prepare a 2 wt% nano-clay XLS solution. Then, 100 mg of n-isopropylacrylamide (NIPAM), 5 mg of methylene bisacrylamide (BIS), and 300 μL of 10 wt% MXene aqueous solution were added to 700 μL of a 2 wt% nano-clay XLS mixed solution and mixed well. The solution was then placed in the refrigerator and cooled to 4 °C. 4 μL of tetramethylethylenediamine (TEMED) and 4 wt% ammonium persulfate solution (APS, 40 μL) were added sequentially and stirred rapidly to obtain a prepolymer solution. The prepolymer solution was injected into a mold with a built-in thickness of 0.2 mm and sealed. The reaction was carried out at 4 °C for 6 h. Finally, the solution was purified by soaking in a large amount of deionized water for 48 h to wash away unreacted compounds and obtain the MXene / PNIPAM composite hydrogel.

[0059] Due to the low MXene content, the Ti2p doublet at 440–470 eV in the total XPS spectrum is weak, with bond energies at 454.58 eV and 458.28 eV, respectively. Figure 9 The XPS and XLS spectra show that the blank PNIPAM hydrogel exhibits characteristic peaks of nano-clay XLS, while the MXene / PNIPAM composite hydrogel with the same nano-clay XLS content shows peak enhancement around 8°, which is a characteristic peak of MXene, indicating that MXene in this composite hydrogel retains its original crystal structure. These characterizations demonstrate that the MXene / PNIPAM composite hydrogel has been successfully prepared.

[0060] Example 5: Preparation of a bifunctional synergistic biomimetic driving material of shape memory polymer / photothermal responsive hydrogel, including the following steps:

[0061] A small amount of UV adhesive was applied to the polyurethane SMP prepared in Example 2. Cellulose-based soft yarn was cut to a suitable size and placed on the UV adhesive. It was pressed to ensure full absorption of the UV adhesive and then cured with UV light, thereby tightly bonding the cellulose-based soft yarn to the polyurethane SMP. A 0.2mm silicone rubber mold of suitable size was cut and placed on the soft yarn. The MXene / PNIPAM hydrogel prepolymer prepared in Example 4 was poured into the mold, covered with a glass slide, and reacted at 4°C for 6 hours. The hydrogel-driven material was then demolded and purified by soaking in a large amount of deionized water for 48 hours to remove unreacted compounds, thus obtaining a bifunctional synergistic biomimetic driving material.

[0062] (1) The morphology and structure of the driving material were characterized by scanning electron microscopy (SEM). Figure 10As shown, the exposed cellulose-based cloud-like yarn in the middle layer bonds the upper porous hydrogel and the lower dense and smooth polyurethane SMP layer, thus successfully constructing a bilayer SMP-MXene / PNIPAM hydrogel actuation material with cellulose-based cloud-like yarn as the middle layer. A dense transition layer exists between the composite hydrogel and the polyurethane SMP. The interface between the cellulose-based cloud-like yarn and the polyurethane SMP is a cured UV adhesive, while the surface of the UV adhesive is a denser hydrogel network formed by the composite hydrogel infused with cloud-like yarn. Because the nano-clay XLS in the hydrogel contains a large number of hydroxyl groups, it forms numerous hydrogen bonds and physical-mechanical interlocks with cellulose, achieving tight adhesion. In this actuation material system, the cloud-like yarn is not solely part of the actuation or memory layer, and the incorporation of the cellulose-based cloud-like yarn does not affect its performance. Therefore, the entire actuation material can still be considered a bilayer actuation material. The MXene in the composite hydrogel, as a photothermal conversion component, can endow the actuation material with remote light-controlled actuation. Comparing the Ti element distribution in the EDS-mapping energy dispersive spectra of the MXene / PNIPAM composite hydrogel and the undoped pure PNIPAM hydrogel, it can be seen from the figure that MXene is fully and uniformly dispersed in the PNIPAM hydrogel.

[0063] (2) Tensile tests were performed on the MXene / PNIPAM composite hydrogel, polyurethane SMP, and composite driving material, respectively, and their stress-strain curves are shown below. Figure 11 As shown, the tensile strength of the MXene / PNIPAM composite hydrogel is 55±0.8 kPa. After being combined with polyurethane SMP (5.2±0.3 MPa), the tensile strength of the driving material is 2.8±0.5 MPa, indicating a significant improvement in tensile strength, which is 50.9 times that of the composite hydrogel. Furthermore, compared to the 200% elongation at break of the polyurethane SMP, the elongation at break of the driving material in the wet state is close to 420%, showing a significant increase.

[0064] (3) The bending and folding behavior of the driving material prepared in Example 5 under critical power infrared light was studied. Figure 12 As shown in a, at 4.0 W / cm 2 Under near-infrared light, the driving material gradually bends, completing the actuation from 0° to 360° within 22 seconds. Figure 12 b recorded the recovery process of the driving material. Within the first 180 seconds, the bending angle recovered 73.6%. After approximately 420 seconds, the hydrogel swelling nearly reached equilibrium, and the driving material could recover to 0°. (See image for details.) Figure 12As shown in Figure c, when the near-infrared light power is 0.2W and the spot diameter is 1mm, local irradiation of the driving material causes the composite hydrogel at the irradiated location to shrink, while the unirradiated driving material remains in its original state, thus exhibiting a bending phenomenon. The bending angle of the driving material can fold from 0° to 90° within 9 seconds. After the near-infrared light is removed, the driving material recovers 77.3% within the first 60 seconds. After a 6.5-minute water absorption and swelling process, the driving material can return to its original straight strip shape. Figure 12 d). This indicates that the near-infrared critical power of this composite driving material is 5 W / cm². 2 Under near-infrared light irradiation at a light intensity lower than this, the composite actuation material can undergo reversible actuation recovery.

[0065] (4) Study the synergistic driving behavior of composite driving materials under different temporary shapes.

[0066] The linear driving material was immersed in a 39°C water bath for 5 seconds, and then a temporary shape was quickly designed under external force. After cooling, the driving material in the designed temporary shape was placed in 20°C water and allowed to swell with hydrogel before photothermal response testing was performed.

[0067] like Figure 13 a and Figure 13 As shown in b, we designed the driving material as a temporary arc shape and recorded its performance at 4.0 W / cm². 2 The shape change process under infrared light irradiation. Observation shows that the arc-shaped driving material gradually shrinks, eventually bending into a circle, and after about 4 minutes of hydrogel water absorption and expansion, it finally returns to the temporary shape (arc-shaped) designed before the response. In addition, the driving material is fixed in an obtuse angle shape of about 123° ( Figure 13 (c-13d) Using a point light source to illuminate the bending point, the material was driven to bend, reducing the bending angle from 123° to 21° within 9 seconds, at a bending speed of 34° / s. After 7 minutes, the material returned to near equilibrium, with an angle of 118°, still maintaining an obtuse angle shape.

[0068] Furthermore, based on the contraction and closure actuation of the arc-shaped actuating material under near-infrared light, we designed the actuating material to be "S"-shaped. In this case, the curved portions of the upper and lower parts of the actuating material, composed of hydrogel and polyurethane SMP, have opposite directions, thus exhibiting both inward bending and outward expansion actuation behaviors. For example... Figure 14 The recorded images show that at 4.0 W / cm 2When the driving material is irradiated with near-infrared light, the MXene / PNIPAM composite hydrogel responds to the near-infrared light by contracting, driving the polyurethane SMP. The upper part bends and gradually closes, while the lower part bends and gradually unfolds. After 140 seconds of irradiation by a near-infrared surface light source, the upper part of the "S"-shaped driving material is completely closed, and the lower part's bending angle is approximately 0°, indicating an unfolded state. The "S" gradually transforms into a shape resembling the number "9". At this point, the temperature of the polyurethane SMP has not yet reached its critical temperature. After the NIR light is turned off, the "9"-shaped driving material gradually absorbs water and recovers, eventually returning to its designed "S" shape.

[0069] The results above demonstrate that the same driving material can have various initial shapes, and based on these initial shapes, remote optical control can be used to achieve various complex driving methods.

[0070] (5) Investigate the driving behavior of this driving material under suspended heavy load conditions, such as Figure 15 As shown, when the laser power is 0.2W and the diameter is 2mm, the biomimetic actuating material responds rapidly and can suspend a heavy object and move upwards. After the light source is removed, the actuating material moves rapidly downwards under the influence of the weight, but after a brief period of falling motion, the actuating material itself hinders its continued downward movement, subsequently moving according to its own recovery mechanism. The composite actuating material and the weight weigh 33.3mg and 1.0792g respectively, enabling it to lift an object 32.4 times its own weight.

[0071] (6) Study the grasping and releasing behavior of robots driven by "gripper" materials, such as Figure 16 The results show that after contacting the target object, the gripper was sequentially illuminated by an infrared light source, causing the three arms to gradually close and grasp the weight. After the light source was turned off, the gripper moved upwards with the aid of external force, maintaining the gripping state for 13 seconds. Once the driving material absorbed water and the gripper opened slightly, the weight was no longer firmly held, allowing the gripper to open and release the weight. The driving material had a mass of 15.3 mg, and the weight of the object was 944.8 mg, which is 61.8 times the weight of the driving material itself.

[0072] (7) Research biomimetic "orchid" shaped drive materials to simulate the vine growth and petal closing behavior of flowers in nature. For example... Figure 17The results show that the actuating material was designed as a combination of four petals and two spiral-shaped dendrobium orchids. When infrared light irradiated the spiral-shaped actuating material's "vines," the "vines" gradually tightened and lengthened, mimicking the behavior of vines climbing tree trunks in nature. When a surface light source irradiated the petals, the actuating material quickly responded by closing inwards, and the vines continued to extend. After the infrared light was removed, the orchid gradually opened until swelling reached equilibrium. This biomimetic application demonstrates that the dual-function synergistic biomimetic actuating material exhibits high fixation and recovery rates, and its shape fixation method is simple and quick, expanding the application of hydrogel actuating materials in the field of soft robotics.

[0073] In summary, the preparation method of the bifunctional biomimetic actuation material provided by this invention utilizes cellulose-based materials (cloud yarn, napkin paper) and UV-curable adhesives to prepare a bifunctional synergistic biomimetic material by combining polyurethane SMP and stimulus-responsive hydrogel. This allows the same actuation material to possess multiple complex actuation capabilities while having various initial shapes. The actuation materials with various initial shapes can be reversibly actuated without triggering the critical temperature of the polyurethane SMP, and photothermal and pH responses are achieved based on the stimulus-response mechanism of the actuation layer, realizing excellent shape memory-stimulus-responsive actuation synergy.

[0074] Furthermore, the shape memory / photothermal responsive bifunctional synergistic biomimetic actuation material prepared using this method exhibits high fixation rate and recovery force, and strong long-range actuation capability, solving the problem of low fixation rate and poor controllability of initial shape due to the low modulus of shape memory hydrogels. Moreover, the shape memory / pH responsive bifunctional synergistic biomimetic actuation material prepared using this method demonstrates actuation capability at different pH levels, achieving synergistic actuation of shape memory and pH response, thus addressing the limitation of application range caused by the low response temperature and difficulty in controlling photothermal properties of polyurethane SMP.

[0075] The above description is only a preferred embodiment of the present invention and is 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 scope of protection of the present invention.

Claims

1. A method for preparing a bifunctional synergistic biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel, characterized in that... Includes the following steps: Apply adhesive to the polyurethane surface, then press and fix the cellulose-based material onto the UV adhesive. Next, place the stimulus-responsive hydrogel prepolymer into a mold above the cellulose-based material and polymerize to form an adhesive, thus obtaining a shape memory polymer / stimulus-responsive hydrogel dual-function synergistic biomimetic driving material. The polyurethane is prepared by the following method: Weigh 5 g of polycaprolactone diol and melt it in a 100℃ vacuum drying oven. Then, add 10 mL of butyl acetate solvent, 734 μL of hexamethylene diisocyanate, 156 μL of polyhexamethylene diisocyanate, and 25 μL of dibutyltin dilaurate, and stir until fully mixed. Pour the mixture onto an aluminum sheet covered with a silicone rubber mold, cure it in a 60℃ oven for 2 h, and then dry it in a 80℃ vacuum drying oven for 6 h. The stimulus-responsive hydrogel is a photothermal-responsive hydrogel or a pH-responsive hydrogel; the pH-responsive hydrogel prepolymer solution is obtained by dissolving 85 mg acrylamide, 15 mg sodium methacrylate, and 5 mg methylenebisacrylamide in 1 mL of deionized water, and then adding 4 µL of tetramethylethylenediamine and 40 µL of ammonium persulfate solution with a mass fraction of 4 wt% under 4°C conditions and stirring until homogeneous. The photothermal responsive hydrogel prepolymer was prepared by mixing 100 mg N-isopropylacrylamide, 5 mg methylenebisacrylamide, 300 µL of 10 wt% MXene aqueous solution, and 700 µL of 2 wt% XLS nanoclay, and then placing the mixture at 4 °C. Next, 4 µL of tetramethylethylenediamine and 40 µL of 4 wt% ammonium persulfate solution were added sequentially and the mixture was rapidly stirred until homogeneous.

2. The method for preparing a shape memory polymer / stimulus-responsive hydrogel bifunctional synergistic biomimetic driving material according to claim 1, characterized in that, The cellulose-based material is cloud-soft yarn or napkin paper.

3. The method for preparing a shape memory polymer / stimulus-responsive hydrogel bifunctional synergistic biomimetic driving material according to claim 1, characterized in that, The polymerization time was 6 hours and the polymerization temperature was 4°C.

4. A bifunctional synergistic biomimetic driving material of shape memory polymer / stimulus-responsive hydrogel prepared by the method according to any one of claims 1 to 3.

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