Multifunctional stimuli-responsive POM-based ionized water gel with sensing, fluorescence and antibacterial properties as well as preparation method and application of multifunctional stimuli-responsive POM-based ionized water gel

Abstract

The invention discloses a preparation method of multifunctional stimuli-responsive POM-based hydrogel with conductive sensing, fluorescent and antibacterial properties, which comprises the following steps: 1) dispersing Na2WO4 in water, adjusting the pH value to 7-7.5, heating to 80-100 DEG C, adding an Eu (NO3) 3 aqueous solution, heating for 45-60 minutes, cooling to room temperature, filtering, and growing white crystals, namely lanthanide polyacid POM; and 2) uniformly dispersing the ionic liquid in a solvent, sequentially adding lanthanide polyacid POM, acrylamide, N, N '-methylene bisacrylamide and ammonium persulfate, uniformly dispersing, and finally adding a catalyst, thereby obtaining the water-soluble polymer. The hydrogel has relatively high sterilization efficiency; meanwhile, the material also has excellent conductivity, and can be further applied to human body wearable sensors; in addition, the material has excellent fluorescence performance, shows reversible light-emitting switch characteristics under HCl / NH3 stimulation, is an ideal choice for information safety storage, and has wide application prospects in the aspects of flexible sensors, biological tissue engineering, biomimetic materials, electronic skin and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functionalized lanthanide polyoxometalates, and specifically relates to a lanthanide polyoxometalate with fluorescent properties, and further forms a multifunctional stimulus-responsive POM-based ionic hydrogel with conductive sensing, fluorescence and antibacterial properties through a one-pot free radical polymerization method with a positively charged ionic liquid and acrylamide. Due to the addition of ionic liquid, the system can not only improve the dispersibility and biocompatibility of POM, but also improve the antibacterial efficiency and conductive properties of the hydrogel, and at the same time explore its practical application potential, which provides a valuable reference for further applications in the future. Background Art

[0002] In order to adapt to changes in the environment, the skin of animals can convert external stimuli such as pressure, temperature, humidity, and light sources into characteristic bioelectric signals, and the bioelectric signals are transmitted to the brain through neural pathways to produce intelligent perception. For example, chameleons can control their color and shape when stimulated by external stimuli, which shows that camouflage can be well achieved through color changes. Electronic skin (E-skin) has similar flexibility, mechanical properties, and tactile perception as animal and plant skin, and has attracted widespread attention in the fields of wearable smart health monitoring, tactile sensors, soft robots, and information encryption. As a polymer with a three-dimensional network structure with swelling properties, hydrogel has become an ideal candidate for E-skin wearable sensors, with unique advantages such as high mechanical properties, conductivity, flexibility, and transparency. Notably, ion-conductive hydrogels (ICHs) combine the conductivity and softness of tissue-like materials to mimic the mechanical and sensory properties of human skin, and are considered to be promising materials to replace traditional rigid metal conductors in the manufacture of human motion sensors. In recent years, hydrogel wearable sensors have achieved multifunctional applications by displaying changes in electrical and optical signals in response to various external stimuli. As the demand for sensors increases, hydrogels are essential for flexibility, high stretchability, transparency, and conductivity. In addition to the above properties, antibacterial properties are a key part of wearable sensors and can significantly improve the practicality of these sensors.

[0003] Imidazolium ionic liquids (ILs) are molten salts composed of asymmetric cations and anions. They have good non-volatility, antibacterial properties, thermal stability, and electrochemical properties, making them ideal candidates for conductive hydrogels. The addition of ILs to the hydrogel network not only inherits its inherent advantages, but also makes the hydrogel have higher solubility and conductivity. In recent years, ion-conductive hydrogels have received extensive attention in the field of multifunctional sensors. For example, Yan et al. reported the preparation of fully physically cross-linked PNIPAM ion gels using a binary solvent system consisting of water / ionic liquid (H2O / IL). The hydrogen-bonded imidazole, urea, and hydrophobic alkyl segments of ILs provide additional non-covalent interactions to enhance the mechanical properties, self-recovery, and adhesion properties of the ion gels. In addition, ILs also endow PNIPAM ion gels with ionic conductivity, enabling them to be used as flexible sensors for human motion monitoring. Zeng et al. introduced the cross-linking of modified imidazolium ion cellulose and acrylic acid to form imidazolium ion cellulose / polyacrylic acid hydrogel (ILHPMC / PAA). Due to the introduction of epoxidized imidazolium ionic liquid, this hydrogel has high conductivity, flexibility, stretchability, biocompatibility and antibacterial properties, providing ideas for wearable ion conductive sensing. The above studies show that ion gel can improve the mechanical properties and conductivity of hydrogel by introducing ionic liquid into the hydrogel network.

[0004] However, most reported hydrogel-based flexible wearable sensors can only display a single electrical output, which limits their multifunctional applications. It is noteworthy that when combined with ionic hydrogels, photochromic materials can exhibit excellent optical properties and are widely used in information storage, anti-counterfeiting, optical sensing, and sensors. At present, common photochromic materials mainly include quantum dots, organic dyes, lanthanide complexes, etc. The general method for preparing photochromic hydrogels is to introduce these photochromic materials into hydrogels through non-covalent interactions or chemical bonds. Compared with organic photochromic materials, inorganic photochromic materials have the advantages of simple preparation, low cost, good chemical stability, and good photochromic cycle stability. Among various inorganic photochromic materials, well-defined lanthanide polyoxometalates (POMs) play an important role in the construction of photochromic compounds. Interestingly, POMs have received great attention in many fields due to their diverse structures and special physicochemical properties, mainly including biomedicine, biosensors, photothermal therapy, and information security storage. When POMs are combined with lanthanide ions, they can provide unique functionalities by combining surface bridging or terminal oxygen atoms, such as europium (Eu) with two Lindqvist-type [W5O 18 ] 6- Anionic synthesis of lanthanide polyoxometalates ([EuW 10 O 36 ] 9-), showing excellent fluorescence properties. Therefore, the development of fluorescent photochromic hydrogels that dynamically respond to external stimuli is of great significance for the preparation of advanced sensors and luminescent materials.

[0005] In summary, this application uses N,N'-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator to prepare a new polyacrylamide-co-1-butyl-3-vinyl-1H-imidazol-3-ium bromide ion hydrogel network under ultrasonic activation. The ionic liquid is introduced into the main chain of the PAM hydrogel through covalent bonds, which greatly improves the conductivity of the hydrogel. Lanthanide POM ([EuW 10 O 36 ] 9- ) are also uniformly dispersed in the hydrogel matrix, and obvious red fluorescence is observed under ultraviolet irradiation. The multifunctional lanthanide luminescent hydrogel has significant advantages. First, the preparation method of the multifunctional hydrogel is simple, mainly one-step free radical polymerization. Second, the multifunctional hydrogel has high transparency, sensing performance and antibacterial properties. Finally, EuW 10 The introduction of makes the hydrogel have excellent luminescence performance in the specific information encryption transmission process. Therefore, this multifunctional lanthanide luminescent hydrogel not only realizes simple synthesis, but also provides a new idea for the preparation of ion luminescent hydrogel as wearable sensors and information protection. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art, provide a lanthanide polyoxometalate with fluorescent properties, and further form a multifunctional stimulus-responsive POM-based ionic hydrogel with conductive sensing, fluorescence and antibacterial properties through a one-pot free radical polymerization method with a positively charged ionic liquid and acrylamide. Due to the addition of ionic liquid, the system can not only improve the dispersibility and biocompatibility of POM, but also improve the antibacterial efficiency and conductive properties of the hydrogel. At the same time, its practical application potential is explored, which provides a valuable reference for further applications in the future.

[0007] The present invention also provides a preparation method and application of the multifunctional stimulus-responsive POM-based ionic hydrogel having conductive sensing, fluorescence and antibacterial properties.

[0008] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a multifunctional stimulus-responsive POM-based hydrogel with conductive sensing, fluorescence and antibacterial properties comprises the following steps: 1) Preparation of lanthanide polyacid POM: Disperse Na2WO4 in water, adjust the pH value to between 7-7.5, then transfer to a water bath at 80-100℃, gradually add Eu(NO3)3 aqueous solution, heat for 45-60min, cool to room temperature, filter, and white crystals will grow on the bottom in about 5 days, which is lanthanide polyacid POM (EuW 10 ,[EuW 10 O 36 ] 9- ); 2) Preparation of multifunctional stimuli-responsive POM-based ionic hydrogels (PAM / PIL / EuW 10 ): The ionic liquid is evenly dispersed in the solvent, and lanthanide polyacid POM, acrylamide (AM), N,N'-methylenebisacrylamide (MBA), and ammonium persulfate (APS) are added, ultrasonically dispersed evenly, and finally a catalyst is added to form a multifunctional stimulus-responsive POM-based ionic hydrogel.

[0009] Specifically, in step 1), the pH value can be adjusted to between 7 and 7.5 using glacial acetic acid. In step 1), the mass ratio of Eu(NO3)3 to Na2WO4 can be 1:6-9.

[0010] Specifically, in step 2), the solvent is a binary solvent, preferably a mixture of ethylene glycol and water in a volume ratio of 1:3-5. Further, in step 2), the ionic liquid can be 1-butyl-3-vinyl-1H-imidazole-3-ium bromide (abbreviated as IL, a common commercial product, Shanghai Macklin Biochemical Technology Co., Ltd, China); the catalyst can be N,N,N',N'-tetramethylethylenediamine (TEMED) and the like.

[0011] Further preferably, in step 2), the mass ratio of the ionic liquid, lanthanide polyacid POM, acrylamide, N,N'-methylenebisacrylamide, ammonium persulfate and catalyst can be 70-80:6-10:80-100:1-2:2-4:1.

[0012] The invention provides a multifunctional stimulation-responsive POM-based hydrogel prepared by the preparation method.

[0013] The multifunctional stimulus-responsive POM-based hydrogel of the present invention has excellent antibacterial properties, and thus provides its application in antibacterial aspects.

[0014] The multifunctional stimulus-responsive POM-based hydrogel of the present invention has strong red fluorescence under ultraviolet light irradiation, thus providing its application in information security storage.

[0015] The multifunctional stimulus-responsive POM-based hydrogel of the present invention has conductivity, thus providing its application in flexible electronic sensors (such as wearable sensors for human body, etc.), biological tissue engineering, bionic materials, electronic skin, etc.

[0016] The multifunctional stimuli-responsive POM-based hydrogel of the present invention, the first step is to first synthesize a Weakley-type POM with fluorescent properties, and then perform one-pot free radical polymerization with an ionic liquid (1-butyl-3-vinyl-1H-imidazol-3-ium bromide) and acrylamide to form a hydrogel. The second step is to use the multifunctional stimuli-responsive POM hydrogel obtained above for flexible electronic sensors and information security storage. Finally, due to the positively charged ionic liquid in the multifunctional stimuli-responsive POM-based hydrogel, the hydrogel is added to the bacterial suspension, and the bacterial cell wall shows obvious wrinkling, collapse and severe damage, indicating the effect of the ionic hydrogel on the integrity of the cell wall. This antibacterial ability is attributed to the fact that the cations of the ionic liquid absorb negatively charged bacteria through electrostatic interactions, and interact with the cell wall, causing severe damage, destroying the cell structure, promoting and inducing cytoplasmic leakage, and ultimately leading to bacterial cell death. Therefore, the multifunctional stimuli-responsive POM hydrogel can also be used for antibacterial purposes.

[0017] The multifunctional stimulus-responsive POM-based hydrogel described in the present invention embeds lanthanide polyoxometalates into the hydrogel three-dimensional network. The formed multifunctional stimulus-responsive hydrogel has excellent electrical conductivity and fluorescence properties and has broad application prospects in flexible sensors, biological tissue engineering, bionic materials, electronic skin, etc. Compared with traditional hydrogels, the addition of ionic liquids significantly improves the mechanical properties, electrical conductivity and antibacterial properties of the hydrogel. The multifunctional stimulus-responsive hydrogel not only has excellent sensing performance, but also exhibits reversible luminescence switching characteristics under HCl / NH3 stimulation, making it an ideal choice for secure information storage. In addition, IL and EuW 10 Incorporation into a hydrogel matrix not only reduces their toxicity but also significantly improves their antibacterial properties. Notably, due to the above excellent properties, the multifunctional stimuli-responsive hydrogels can be used as wearable sensors for detecting changes in strain and pressure as well as for encrypted information transmission.

[0018] The present invention forms a multifunctional POM-based ionic hydrogel by introducing lanthanide POM and ionic liquid into a hydrogel substrate, and the obtained multifunctional stimulus-responsive POM-based ionic hydrogel has excellent electrical conductivity, fluorescence and antibacterial properties. In addition, due to the addition of ionic liquid, the system can not only improve the dispersibility and biocompatibility of POM, but also improve the antibacterial efficiency and electrical conductivity of the hydrogel. At the same time, its practical application potential is explored, which provides a valuable reference for further applications in the future.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) The introduction of the positively charged ionic liquid of the present invention improves the electrical conductivity and antibacterial properties of the hydrogel and also improves the dispersibility of POM.

[0020] 2) The multifunctional POM-based ionic hydrogel prepared by the present invention has a high bactericidal efficiency and can maintain the antibacterial effect for a certain period of time.

[0021] 3) The multifunctional POM-based ionic hydrogel prepared by the present invention also has excellent conductivity and can be further applied to wearable human sensors.

[0022] 4) The lanthanide POM synthesized in the present invention has strong fluorescence properties. When introduced into the ionic hydrogel, it has strong red fluorescence under the irradiation of ultraviolet light, which can realize information security storage. The multifunctional POM-based ionic hydrogel prepared by the present invention has excellent fluorescence properties and exhibits reversible luminescence switching characteristics under the stimulation of HCl / NH3, which is an ideal choice for information security storage. We firmly believe that the obtained functionalized POM-based ionic hydrogel material has great application prospects in sensors and information security storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the synthesis route of multifunctional stimulus-responsive POM-based ionic hydrogel; Figure 2 FT-IR spectra of different hydrogel samples; Figure 3 SEM images of different hydrogels (a) PAM, (b) PAM / PIL and (c) PAM / PIL / EuW 10 ; Figure 4 In (a) EuW 10 and PAM / PIL / EuW 10 Excitation spectrum of hydrogel, (b) EuW 10 and PAM / PIL / EuW 10 Emission spectra of hydrogels; Figure 5 Among, (a) PAM, PAM / PIL, PAM / PIL / EuW 10 Rheological test of hydrogel at a fixed strain of 1% and room temperature of 25 °C. (b) PAM / PIL / EuW when the strain amplitude increases 10 Modulus changes of hydrogels; Figure 6 (a) PAM / PIL / EuW 10GF value of hydrogel sensor, (bc) PAM / PIL / EuW 10 Relative resistance changes of hydrogel as sensor at different stretching rates (1-5 mm / s) and different strains (1, 100, 150, 200, 250%); Figure 7 (a) PAM / PIL / EuW 10 Hydrogels for HCl / NH3 and Fe 3+ / EDTA 2- Stimulating advanced information encryption and decryption, PAM / PIL / EuW 10 Hydrogel in HCl / NH3(b) and Fe 3+ / EDTA 2- (c) Emission spectra under stimulation; Figure 8 Different hydrogel materials for E. coli and S. aureus Antibacterial optical photograph. Specific implementation methods The present invention is further described below by means of specific examples, but the protection scope of the present invention is not limited thereto.

[0025] In the following examples, the raw materials used are all common commercial products that can be directly purchased, or can be prepared using conventional techniques in the art.

[0026] Room temperature refers to 25±5°C.

[0027] Embodiment 1: A method for preparing a multifunctional stimulus-responsive POM-based hydrogel with conductive sensing, fluorescence and antibacterial properties, comprising the following steps (for specific synthesis route, see Figure 1 ): 1) Preparation of lanthanide polyacid POM: Add Na2WO4 (8.30 g) to 20 mL of water, stir and disperse evenly, and adjust the pH value of the solution to between 7-7.5 with glacial acetic acid. Then place the Na2WO4 aqueous solution in a 90 ℃ water bath, and gradually add Eu(NO3)3 aqueous solution (obtained by dispersing 1.1 g Eu(NO3)3 in 2 mL H2O). Heat for 60 min, cool to room temperature, filter, and white crystals will grow on the bottom after 5 days, which is lanthanide polyacid POM (EuW 10 ,[EuW 10 O 36 ] 9- ); 2) Preparation of multifunctional stimuli-responsive POM-based ionic hydrogels (PAM / IL / EuW 10): Weigh 1.15 g of ionic liquid 1-butyl-3-vinyl-1H-imidazol-3-ium bromide into a binary solvent of ethylene glycol-water (2 mL: 8 mL) and stir to make it dispersed evenly. Then add lanthanide polyacid POM ([EuW 10 O 36 ] 9- , 0.13 g), then acrylamide (AM, 1.42 g), N,N'-methylenebisacrylamide (MBA, 0.025 g), and ammonium persulfate (APS, 0.05 g) were added in sequence, and ultrasonic dispersion was performed for 20 min. Finally, 20 μL of catalyst N,N,N',N'-tetramethylethylenediamine (TEMED) was added to form a multifunctional stimuli-responsive POM-based ionic hydrogel (PAM / PIL / EuW 10 ).

[0028] At the same time, for comparison, an ionic hydrogel (PAM / PIL, i.e., without adding EuW) is provided. 10 ), specifically as follows: Weigh 1.15g of ionic liquid 1-butyl-3-vinyl-1H-imidazol-3-ium bromide and add it to the binary solvent of ethylene glycol-water (2mL:8 mL), stir to make it dispersed evenly. Then add acrylamide (AM, 1.42 g), N,N'-methylenebisacrylamide (MBA, 0.025 g), and ammonium persulfate (APS, 0.05 g) in sequence, and disperse evenly by ultrasonication for 20 min. Finally, add 20 μL of catalyst N,N,N',N'-tetramethylethylenediamine (TEMED) to form ionic hydrogel (PAM / PIL).

[0029] At the same time, for comparison, the preparation method of PAM hydrogel is also provided. The difference from ionic hydrogel (PAM / PIL) is that no ionic liquid IL is added during the preparation process.

[0030] Embodiment 2: Characterization of different hydrogel samples by near infrared spectroscopy: In order to better verify their structure and composition, the Fourier transform infrared spectroscopy (FT-IR) of different hydrogels is shown in Figure 2 .

[0031] In order to verify its structure and composition, FT-IR of different hydrogel samples was as follows. Figure 2 As shown. At 3440 cm -1 There is a broad and strong peak at 1668 and 1615 cm, which is caused by the stretching vibration of OH. -1 The characteristic peaks at 2933 and 2873 cm are attributed to the C=O stretching and NH in-plane bending of the -CONH2 group in AM. -1The vibration bands at 1562 cm -1 The characteristic vibration of the imidazole ring NH main chain was observed at , proving that IL was successfully introduced into the hydrogel. 10 After that, at 941 cm -1 The characteristic peak at is attributed to EuW 10 v(WO on the skeleton d ) tensile vibration.

[0032] Embodiment 3: The cross-sections of different hydrogel samples were characterized by scanning electron microscopy (SEM, JSM-4800, Hitachi, Japan). After freeze-drying, gold was sputtered onto the surface of the hydrogel samples before observation. The general accelerating voltage was 10 kV. Figure 3 The freeze-dried PAM, PAM / PIL and PAM / PIL / EuW are given. 10 SEM image of hydrogel. Figure 3 It can be clearly seen that all the hydrogels present an interconnected three-dimensional porous network structure. Compared with pure PAM hydrogel, Figure 3 The PAM / PIL hydrogel in (b) has a tightly connected pore structure, which is due to the fact that IL is inserted into AM as a physical cross-linking point after copolymerization to form PAM-co-PIL chains, thereby enriching the existence of molecular interactions between IL and the polymer matrix. Figure 3 c, PAM / PIL / EuW 10 The pore structure of the hydrogel is more ordered and interconnected, and the pore size decreases after the addition of POM, indicating that the interaction between POM and the hydrogel network is enhanced. This is attributed to the interaction between the imidazolium cation in the IL and the EuW 10 The electrostatic interaction between [EuW 10 O 36 ] 9- This electrostatic interaction not only enhances the strength of the polymer network but also helps EuW 10 Uniform dispersion in the hydrogel network.

[0033] Embodiment 4: Evaluation of the fluorescence properties of lanthanide polyacid POM and multifunctional stimuli-responsive POM-based ionic hydrogels: The fluorescence properties of the hydrogels were measured by fluorescence spectroscopy (FLS980), with an excitation wavelength of 276 nm and an emission wavelength of 591 nm.

[0034] Given EuW 10 With excellent photoluminescence performance, adding EuW 10The hydrogel has good luminescence properties. 10 and PAM / PIL / EuW 10 Fluorescence experiments were performed on hydrogels. The excitation and emission spectra are shown in Figure 4 .like Figure 4 As shown in a, EuW 10 A broad excitation band centered at 310 nm can be seen, while PAM / PIL / EuW 10 A broad excitation band centered at 270 nm can be observed for the hydrogel, which is assigned to the ligand-to-metal charge transfer (LMCT) transition. This is due to the transfer of the O→W (LMCT) state to Eu 3+ Ionic 5 D0 emission state, indicating that the energy is from [EuW 10 O 36 ] 9- Transfer to EU 3+ Excited state of ions, leading to PAM / PIL / EuW 10 Eu appears in the emission spectrum of the hydrogel 3+ Strong luminescence emission peak. Eu 3+ Ion emission begins 5 D0 excited state, terminated in 7 F j In addition, EuW 10 Some narrow excitation bands in the range of 350-500 nm are attributed to Eu 3+ ff transition of ions, such as 362 nm ( 7 F0→ 5 D4), 385 nm ( 7 F0→ 5 G2), 395 nm ( 7 F0→ 5 L6), 418 nm ( 7 F0→ 5 D3) and 467 nm( 7 F0→ 5 D2). Figure 4 From b, we can see that PAM / PIL / EuW 10 The emission spectrum of the hydrogel shows four characteristic peaks at 579 nm, 593 nm, 620 nm, 647 nm and 700 nm, which belong to EuW 10 of 5 D0→ 7 F0, 5 D0→ 7 F1, 5 D0→ 7 F2, 5 D0→ 7F3 and 5 D0→ 7 F4 transition. The results show that in PAM / PIL / EuW 10 In hydrogel, EuW 10 Dispersed in the gel network, the network structure has a great influence on EuW 10 The luminescence performance was not significantly affected.

[0035] Embodiment 5: Rheological evaluation of multifunctional stimuli-responsive POM-based ionic hydrogels: To measure the rheological properties of the hydrogels, a rotational rheometer (DHR2, USA) was used. The viscoelastic modulus of the hydrogels was determined by measuring the storage modulus (G′) and loss modulus (G′′) of the hydrogels. The experiments were measured at 25 °C by applying a 1% strain in the range of 0.1 to 100 Hz. The hydrogel samples were made into disks and analyzed using a parallel plate geometry with a diameter of 20 mm, and the gap between the plates was adjusted to 1 mm. All hydrogel samples were prepared in the same mold, and the same group of hydrogel samples were measured three times under the same conditions.

[0036] Hydrogels usually gel at an appropriate frequency. The storage modulus (G') represents the elastic properties, and the loss modulus (G") represents the viscosity. The measurement results of different hydrogels are shown in Figure 5 .like Figure 5 As shown in Figure a, within the detection frequency range, G′ is greater than G", indicating that the elastic property is dominant and exhibits typical gelation characteristics. Figure 5 As shown in (b), compared with other hydrogels, PAM / PIL / EuW 10 The intersection of G′ and G" of the hydrogel moves backward, indicating that PAM / PIL / EuW 10 The hydrogel has higher mechanical properties. This is mainly due to the positively charged imidazolium cations and the negatively charged EuW 10 There is a strong electrostatic interaction between them, which makes the dynamic network more compact. As the second cross-linking network, the electrostatic interaction is a dynamic physical interaction. This is also proved by the rheological properties of the hydrogel.

[0037] Embodiment 6: Evaluation of the sensing performance of multifunctional stimulus-responsive POM-based ionic hydrogels: The resistance change of the hydrogel sensing was recorded by an electrochemical workstation (CHI660E, Chenhua, Shanghai, China). For human motion detection, the sensor was directly adhered to the skin of the volunteer, and the sensor was connected to the electrochemical workstation with a wire, and all the sensing performances were recorded on the electrochemical workstation. The current signal of the strain sensor was recorded under an external voltage of 1.0 V. To measure the sensing signal generated by the actuation behavior, the two ends of the composite hydrogel were connected with a copper wire to collect the real-time current in a similar manner.

[0038] Sensitivity factor (GF) is an important parameter that reflects the sensitivity of strain sensors. The calculation formula is GF= (Δ R / R 0 ) / ε, where Δ R is the resistance change, R 0 is the initial resistance, and ε is the applied strain. Figure 6 .

[0039] like Figure 6 As shown in Figure a. Under a tension of 0-150%, the GFs of the multifunctional stimuli-responsive POM-based ion hydrogel sensors reached 0.25 and 0.43, respectively. The hydrogel sensor also showed a stable response to different stretching rates. Figure 6 As shown in (b), at different stretching rates (1, 2, 3, 4, 5 mm / s), the strain sensing resistance remains basically unchanged and there is no obvious hysteresis, indicating that the hydrogel has good stability and excellent speed response. Figure 6 Figure c shows that the relative resistance change of the ionic hydrogel sensor during continuous loading-unloading increases with increasing strain at 50%, 100%, 150%, 200%, and 250% strain.

[0040] Embodiment 7: Evaluation of the fluorescence properties of multifunctional stimuli-responsive POM-based ionic hydrogels: using HCl / NH3 and Fe 3+ / EDTA 2- Acts as an "eraser" and "restorer" to achieve reversible erasure and restoration of information.

[0041] In recent years, anti-counterfeiting materials and related information encryption and decryption technologies have attracted much attention. Among them, lanthanide fluorescent hydrogel has great potential as a reliable information encryption and decryption medium, thereby enhancing the security of anti-counterfeiting and information output. 10 Hydrogel in HCl / NH3 and Fe 3+ / EDTA 2- Inspired by this, PAM / PIL / EuW 10 Hydrogels can be used as useful information carriers, "HCl / Fe 3+ ” and “NH3 / EDTA 2- " act as an "eraser" and "restorer" to hide / recover information. Figure 7 As shown in a, choose HCl or Fe 3+ As ink in PAM / IL / EuW 10Draw "123" or "Hydrogel" on the hydrogel. This information is only visible under UV light. NH3 or EDTA 2- This information can be hidden and is invisible even under UV light. The corresponding fluorescence intensity is Figure 7 The emission spectra shown in bc show that in the presence of HCl and Fe 3+ In the presence of , the fluorescence is completely quenched.

[0042] Embodiment 8: Since the problem of bacterial infection caused by long-term wear of sensors cannot be ignored, there is an urgent need to develop a hydrogel that can inhibit bacterial growth.

[0043] Evaluation of the antibacterial properties of multifunctional stimuli-responsive POM-based ionic hydrogels: plate colony counting method was used to detect the antibacterial effects of different hydrogels on Escherichia coli E. coli and Staphylococcus aureus S. aureus First, take out 1 mL of frozen bacterial solution and add it to a centrifuge tube containing 50 mL of LB liquid culture medium. Incubate it overnight (12 h) in a shaker at 37 °C and 220 rad / min. Dilute the culture solution into a 96-well plate and measure the optical density (OD) of 100 µL of solution in each well at 600 nm using a microplate reader. 600 ). When OD 600 When the value is 0.5, the bacterial concentration is 10 8 CFU / mL. Dilute the bacterial solution to a concentration of 10 5 CFU / mL, 500 μL of bacterial solution and 100 mg of hydrogel sample were added to a 24-well plate and cultured in a 37 ℃ bacterial incubator for 10 min. Then, 100 μL of bacterial solution was applied to an agar plate and cultured in a 37 ℃ bacterial incubator for 16 h. The results are shown in Figure 8 .

[0044] like Figure 8 As shown in the figure, the bacterial suspension was co-cultured with different hydrogels at 37 °C to evaluate the bacterial survival rate. Compared with the control group, PAM, PAM / PIL and PAM / PIL / EuW 10 Hydrogel against Escherichia coli E. coli and Staphylococcus aureus S. aureus The survival rate of PAM / PIL is low. E. coli and S. aureus The bacterial survival rates of PAM / PIL / EuW10 were 91.96% and 99.89% respectively. E. coli and S. aureusThe bacterial survival rates of PAM / PIL hydrogels were 84.07% and 97.69%, respectively. It is worth noting that after adding IL, the bacterial survival rate of PAM / PIL hydrogels almost reached the highest. 10 The antibacterial activity of the hydrogel is slightly weaker than that of the PAM / PIL hydrogel. This is mainly due to the broad-spectrum antibacterial effect of the cations in the imidazolium ionic liquid. 10 The hydrogel has excellent biosafety, electrical conductivity and antibacterial properties. The cationic sites in the ionic hydrogel may interact electrostatically with the bacterial cell wall or cell membrane. In this process, some cations from the polymer fragments interact with the bacterial membrane or cell wall, and the remaining cations may rearrange. Subsequently, the hydrophobic fragments of the ionic hydrogel may extensively penetrate the hydrophobic cell membrane, leading to the destruction and disintegration of the phospholipid bilayer, resulting in intracellular cytoplasmic leakage.

[0045] In summary, the present invention focuses on how to improve sensing performance and information security storage, and develops a POM-based ionic hydrogel with high conductivity, excellent fluorescence performance and good antibacterial performance. First, acrylamide, lanthanide polyoxometalate (EuW 10 ) and cationic imidazolium-type ionic liquid (1-butyl-3-vinylimidazolium-1-bromide) as raw materials, a multifunctional lanthanide luminescent hydrogel with high conductivity, photochromism and good antibacterial properties was prepared by a one-pot free radical polymerization method. The prepared multifunctional stimulus-responsive POM-based hydrogel not only has excellent sensing performance, but also exhibits reversible luminescence switching behavior under HCI / NH3 stimulation. This reversible luminescence switching property makes the hydrogel a good candidate for secure information storage. In addition, the information security storage application of the multifunctional stimulus-responsive POM-based hydrogel has also been explored, which provides a valuable reference for its further application in future information security. The present invention utilizes imidazolium-type ionic liquid and Weakley-type POM (EuW 10 ) and prepared the polyionic liquid hydrogel with a network structure by ultrasound-assisted free radical polymerization. The synthetic route of the prepared multifunctional stimuli-responsive hydrogel is as follows: hydrogel substrate solution + [EuW 10 O 36 ] 9- + 1-butyl-3-vinylimidazol-1-ium bromide → multifunctional stimuli-responsive hydrogel, in which [EuW 10 O 36 ] 9- It is a lanthanide polyoxometalate. That is, the imidazolium ionic liquid and the Weakley POM (EuW 10) and the polyionic liquid hydrogel with a mesh structure was prepared by ultrasound-assisted free radical polymerization. That is, ionic liquids and polyoxometalates are introduced into the hydrogel matrix, and higher conductivity and fluorescence properties are also given. Due to the conductive properties of ionic liquids and the fluorescent properties of POM, the multifunctional stimulus-responsive hydrogel is endowed with stronger conductive and fluorescent effects. In addition, the hydrogel of the present invention also has efficient antibacterial properties, which is mainly due to the fact that the cationic sites in the ionic hydrogel may electrostatically interact with the bacterial cell wall or cell membrane, and then widely penetrate the hydrophobic cell membrane, resulting in the destruction and disintegration of the phospholipid bilayer and the leakage of intracellular cytoplasm, and finally cell lysis leading to bacterial death. Due to the above-mentioned excellent properties, the multifunctional stimulus-responsive POM-based hydrogel of the present invention can also be used as a wearable sensor for detecting changes in strain and pressure and for encrypted information transmission. This study provides a new strategy for designing and manufacturing multifunctional stimulus-responsive hydrogels for wearable sensors, advanced information encryption and antibacterial activity.

Claims

1. A method for preparing a multifunctional stimulus-responsive POM-based hydrogel with conductive sensing, fluorescence and antibacterial properties, characterized in that: The steps include: 1) Preparation of lanthanide polyacid POM: Disperse Na2WO4 in water, adjust the pH value to between 7-7.5, then heat to 80-100℃, add Eu(NO3)3 aqueous solution, heat for 45-60min, cool to room temperature, filter, and grow white crystals, which are lanthanide polyacid POM; 2) Preparation of multifunctional stimulus-responsive POM-based ionic hydrogel: The ionic liquid is evenly dispersed in a solvent, lanthanide polyacid POM, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate are added, dispersed evenly, and finally a catalyst is added to form a multifunctional stimulus-responsive POM-based ionic hydrogel.

2. The method for preparing the multifunctional stimulus-responsive POM-based hydrogel according to claim 1, characterized in that: In step 1), the pH value is adjusted to between 7 and 7.5 with glacial acetic acid.

3. The method for preparing the multifunctional stimulus-responsive POM-based hydrogel according to claim 1, characterized in that: In step 1), the mass ratio of Eu(NO3)3 to Na2WO4 is 1:6-9.

4. The method for preparing the multifunctional stimulus-responsive POM-based hydrogel according to claim 1, characterized in that: In step 2), the solvent is composed of a mixture of ethylene glycol and water in a volume ratio of 1:3-5.

5. The method for preparing the multifunctional stimulus-responsive POM-based hydrogel according to claim 1, characterized in that: In step 2), the ionic liquid is 1-butyl-3-vinyl-1H-imidazol-3-ium bromide; and the catalyst is N,N,N',N'-tetramethylethylenediamine.

6. The method for preparing the multifunctional stimulus-responsive POM-based hydrogel according to claim 1, characterized in that: In step 2), the mass ratio of the ionic liquid, lanthanide polyacid POM, acrylamide, N,N'-methylenebisacrylamide, ammonium persulfate and catalyst is 70-80:6-10:80-100:1-2:2-4:

1.

7. A multifunctional stimulus-responsive POM-based hydrogel prepared by the preparation method according to any one of claims 1 to 6.

8. Application of the multifunctional stimulus-responsive POM-based hydrogel according to claim 7 in antibacterial applications.

9. Application of the multifunctional stimulus-responsive POM-based hydrogel according to claim 7 in information security storage.

10. Application of the multifunctional stimulus-responsive POM-based hydrogel according to claim 7 in flexible electronic sensors, biological tissue engineering, bionic materials, and electronic skin.

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