Hydroxypropyl guar-guanidinium complex hydrogel, its preparation method and application

Abstract

The application provides a hydroxypropyl guar gum-zwitterionic composite hydrogel and a preparation method and application thereof. Hydroxypropyl guar gum, acrylamide, SBMA, lithium salt, a crosslinking agent, a photoinitiator are uniformly mixed, and then a borax aqueous solution is added and uniformly mixed to obtain a precursor solution; the precursor solution is subjected to one-time photocuring under ultraviolet light irradiation to obtain a double-network hydrogel; the double-network hydrogel is soaked in an SBMA aqueous solution, and after soaking is completed, secondary photocuring is performed to obtain a triple-network hydrogel, and the triple-network hydrogel is obtained. The application utilizes electrostatic interaction to provide a reversible energy dissipation channel in the deformation process, and constructs an ion conduction path through an ion component to improve the adhesion and sensing output stability. On the premise of not significantly sacrificing the soft deformable characteristics, the mechanical toughness, interface adhesion, low-temperature stability and sensing output and other performance are synergistically improved to meet the application requirements of wearable flexible sensing and related intelligent devices.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and functional hydrogels, and relates to a hydroxypropyl guar gum-zwitterionic composite hydrogel, its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

[0003] Hydrogels have attracted widespread attention in fields such as flexible electronics, sensing, and functional interfaces due to their softness, deformability, and responsiveness to external stimuli. Wearable flexible sensing materials used in human contact applications typically require both good mechanical adaptability and stable signal output capabilities.

[0004] To address this, dual-network hydrogels have been developed. By introducing a rigid covalent network and a flexible or reversible cross-linked network, the strength and toughness are significantly improved through energy dissipation mechanisms to meet the aforementioned requirements. However, in existing dual-network systems, the limited interaction between network components and insufficient control over connection points may restrict the structural stability and functional retention of the material under repeated deformation or complex stimuli. For example, a study disclosed a guar gum-based self-healing hydrogel strain sensor, where the core interaction of the CMGG / PAA system comes from carboxyl-hydrogen bonds / ion association and chain entanglement. When its water content is high, it is prone to embrittlement and a sharp drop in conductivity due to aqueous phase crystallization at low temperatures, which is a common challenge for hydrogel sensors in outdoor / cold chain / winter wear scenarios. Another study disclosed a sodium alginate-P (SBMA-co-AAm) hydrogel with a conductivity of only 0.058–0.26 S / m, which also requires a reaction at 60 ℃ for 4 h.

[0005] To address the needs for adhesion, freeze resistance, and functional integration, current strategies typically employ the introduction of ionic components, reversible physical interactions, or surface functionalization to enhance interfacial interactions, resistance to environmental interference, and sensing output. However, these strategies may still face the following challenges in practical applications: adhesion performance degrades at sweat / wet interfaces and under dynamic stretching conditions; during freeze-resistant modification and ion conductivity enhancement, aqueous systems are prone to restricted ion migration or network instability at low temperatures; and the introduction of antibacterial functions is difficult to balance with long-term stability and durability. This makes it difficult for materials to simultaneously meet the synergistic requirements of "high toughness—strong adhesion—low-temperature stability—stable sensing."

[0006] Therefore, there is an urgent need to provide a functional hydrogel and its preparation method that can achieve synergistic improvement in mechanical toughness, interfacial adhesion, low-temperature stability and sensing output without significantly sacrificing soft and deformable properties, so as to meet the application needs of wearable flexible sensing and related smart devices. Summary of the Invention

[0007] The purpose of this invention is to address the difficulty in simultaneously achieving optimal performance in mechanical toughness, interfacial adhesion, low-temperature stability, and stable electrical signal output of existing wearable / flexible sensing hydrogels. This invention provides a hydroxypropyl guar gum (HPG)-zwitterionic composite hydrogel, its preparation method, and its applications. This strategy utilizes electrostatic interactions to provide reversible energy dissipation channels during deformation and constructs ion conduction pathways through ionic components to improve adhesion and sensing output stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a method for preparing a three-network hydroxypropyl guar gum-zwitterionic composite hydrogel based on electrostatic interactions, comprising: Hydroxypropyl guar gum, acrylamide, SBMA, lithium salt, crosslinking agent, and photoinitiator are mixed evenly, and then borax aqueous solution is added and mixed evenly to obtain a precursor solution. The precursor solution was photocured once under ultraviolet light irradiation to obtain a dual-network hydrogel. The dual-network hydrogel was immersed in an SBMA aqueous solution. After immersion, it was subjected to a second photocuring to obtain a triple-network hydrogel.

[0009] The three-network construction logic of this invention is as follows: HPG is used as the polysaccharide backbone, AAm is used to construct the covalent main network, and SBMA is introduced to form a composite network with the ionic components. Then, through "immersion-secondary photopolymerization", zwitterionic networks are further generated in the original network, thereby realizing the construction of the three-network structure.

[0010] A second aspect of the present invention provides a three-network hydroxypropyl guar gum-zwitterionic composite hydrogel based on electrostatic interactions prepared by the above method, comprising: A covalently cross-linked network formed by AAm radical polymerization; A dynamic cross-linked network formed by HPG and borax (the reversible effect is beneficial for post-damage reconstruction); A zwitterionic network formed by the secondary polymerization of SBMA; It may also contain Li introduced by lithium salts. + To establish ion conduction pathways and regulate low-temperature stability.

[0011] After the three-network construction, the material exhibits a continuous three-dimensional porous structure. Compared with the two-network, the three-network sample has a denser pore structure, which is attributed to the increased cross-linking points / physical entanglement and enhanced chain aggregation due to the electrostatic interaction between zwitterionic groups.

[0012] A third aspect of this invention provides the application of the aforementioned electrostatically interactive three-network hydroxypropyl guar gum-zwitterionic composite hydrogel in the manufacture of wearable flexible sensors, wearable flexible electronic devices, or flexible ion-conducting elements. The hydrogel can be used as a flexible strain sensing material for real-time monitoring of human motion and exhibits stable electrical signal output at different strain levels; it can also be used in flexible devices / wearable devices requiring adhesion fixation and low-temperature stable operation.

[0013] Traditional PAA carboxyl adhesion is often significantly affected by pH, ionic strength, and competitive hydration at the wetting interface. The adhesion of this invention originates from "zwitterionic groups / multi-point physical interaction + dynamic network bonding and reconstruction," thus exhibiting good adhesion to various substrates (wood / pigskin / steel / glass, etc.). Furthermore, it maintains close contact with the skin during cyclical movement, making it suitable for manufacturing wearable flexible sensors.

[0014] Beneficial effects of the present invention (1) Highly stable ionic conductivity and tunable electrical properties: With the concentration of LiCl increasing from 1 mol·L -1 Increased to 5 mol·L -1 The hydrogel impedance decreased and the conductivity decreased from 6.26 S·m. -1 Increased to 9.76 S·m -1 ; 3 mol·L can be selected based on overall performance, for example. -1 Li + Concentration is used in three-network systems.

[0015] (2) Excellent antifreeze ability: With the development of Li + As the concentration increases, the DSC crystallization peak gradually weakens or even becomes indistinct, the frozen / unfrozen boundary shifts to lower temperatures, and the unfrozen range widens, demonstrating the regulatory effect of lithium salts on inhibiting aqueous phase crystallization and reducing freezing temperature.

[0016] (3) Significant moisture retention and environmental stability: After being placed at 23 ℃ and 55% relative humidity for 7 days, the three-network sample can still maintain an initial moisture content of over 90%; and after being placed in the air for 7 days, the mechanical properties are almost unchanged, providing a basis for stable electrical / sensing output.

[0017] (4) Strong self-healing ability: After the fracture interface is bonded and left to stand, the dynamic borate ester bond, hydrogen bond and electrostatic interaction can be gradually reconstructed at the interface; the fracture stress can be restored to about 96% (0.78 MPa) after self-healing for about 120 min, and the self-healing efficiency reaches 96%.

[0018] (5) Improved adhesion performance and repeated skin adhesion: The three-network hydrogel can adhere to various substrates such as wood, pigskin, steel plate, and glass, and the overall adhesion strength on the same substrate is higher than that of the two-network; and it can maintain close contact with the skin even after five consecutive cycles of actions such as finger bending.

[0019] (6) Excellent antibacterial / anti-biofouling properties: the antibacterial rate against E. coli and S. aureus can reach 97% and 99%, respectively; the mechanism is related to the strong hydration layer constructed by SBMA reducing non-specific adsorption, weakening the initial adhesion of bacteria and inhibiting biofilm formation.

[0020] (7) Feasibility of flexible sensing applications: The electrical signal output is stable under different strain levels, and the resistance change is positively correlated with the strain. It can be used for real-time monitoring of human activities such as wrists / fingers. The signal has periodicity and repeatability, which reflects the potential of wearable flexible sensing applications. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 The figures show the water retention / moisturizing properties and durability of the hydrogel. (a) shows the water retention performance after 10 h at 23 ℃ and 55% relative humidity; (b) shows the water retention performance after 7 days under the same conditions; and (c) shows the HAS / S-Li3... + Mechanical properties of the hydrogel after 7 days of exposure: (d) is the electrochemical impedance spectroscopy, and (e) is the conductivity.

[0023] Figure 2 Figures show the test results of the hydrogel adhesion performance. (a) is a schematic diagram of the adhesion test, (b) is the adhesion force-displacement curve of HAS-Li+ 3 on different substrates, (c) is the adhesion strength of HAS-Li+ 3 on different substrates, (d) is a physical image of the hydrogel adhesion on various substrates, (e) is the adhesion force-displacement curve of HAS / S-Li+ 3 on different substrates, and (f) is the adhesion strength of HAS / S-Li+ 3 on different substrates.

[0024] Figure 3The diagram shows the antibacterial effect of the hydrogel. (a) is a photograph of the colony formation of Escherichia coli and Staphylococcus aureus, (b) is a statistical graph of the antibacterial rate of Escherichia coli, and (c) is a statistical graph of the antibacterial rate of Staphylococcus aureus. The schematic diagram of the antibacterial mechanism is used to illustrate the antibacterial action pathway of the hydrogel. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0027] Currently, HPG-boron ester dynamic networks suffer from insufficient long-term load-bearing and shape retention capabilities (prone to creep / relaxation), and their conductivity and structural stability are often limited under large deformation cycles. PAAm (or PAAm-co-PSBMA) covalent networks, on the other hand, have weak energy dissipation and self-healing capabilities, making them more susceptible to irreversible damage during repeated stretching. Furthermore, using only zwitterionic monomers often faces the common problem of "weak polymer bulk mechanics." Therefore, this invention uses a PAAm-co-PSBMA covalent network to provide a continuous load-bearing framework, ensuring structural integrity during large deformation and cycling processes. The HPG-boron ester dynamic network serves as a reversible "sacrificial bond / energy-dissipating unit," preferentially breaking and dissipating energy under stress, and reconstructing after unloading, thereby improving toughness, fatigue resistance, and self-healing. This results in a hydrogel with the following properties: high and adjustable conductivity, freeze-thaw resistance and low-temperature electrical stability, strong self-healing, strong moisture retention / environmental stability, adhesion and re-attachability, antibacterial / anti-biofouling properties, and stable sensing output under large deformation cycles. This solves the problem of high strain range stability that is often difficult to achieve with existing hydrogels.

[0028] Therefore, this invention mainly proposes a method for preparing a three-network hydroxypropyl guar gum-zwitterionic composite hydrogel based on electrostatic interactions, comprising: Hydroxypropyl guar gum, acrylamide, SBMA, lithium salt, crosslinking agent, and photoinitiator are mixed evenly, and then borax aqueous solution is added and mixed evenly to obtain a precursor solution. The precursor solution was photocured once under ultraviolet light irradiation to obtain a dual-network hydrogel. The dual-network hydrogel was immersed in an SBMA aqueous solution. After immersion, it was subjected to a second photocuring to obtain a triple-network hydrogel.

[0029] The key components of the three-network hydrogel described in this invention include: hydroxypropyl guar gum (HPG), acrylamide (AAm), zwitterionic monomer SBMA, and lithium salt (providing Li). + The solution contains, preferably, LiCl or LiBr, a crosslinking agent N,N′-methylenebisacrylamide (MBAA), a photoinitiator I2959, and a borax (preferably sodium tetraborate) solution as the boron source. HPG and borax form a reversible dynamic crosslinking network of borate esters in the aqueous phase; AAM and SBMA undergo free radical copolymerization under UV initiation and form a covalent crosslinking network under the action of MBAA; subsequently, a third network is generated in situ within the original two networks through "immersion adsorption-secondary photopolymerization," resulting in a dense three-network hydrogel.

[0030] The amount of monomers used affects the properties of the hydrogel. Therefore, this invention has studied the amount of each monomer. Preferably, in the precursor solution, the mass fraction of hydroxypropyl guar gum is 0.1~3.0 wt%, the mass fraction of acrylamide is 5~25 wt%, the mass fraction of SBMA is 0.5~15 wt%, and the concentration of lithium salt is 1~5.0 mol·L⁻¹. -1 This invention introduces Li + (e.g., LiCl) establishes a strong solvating ionic environment and inhibits aqueous phase crystallization, which is manifested in DSC as a weakening of the crystallization peak, a downward shift of the frozen / unfrozen boundary, and a widening of the unfrozen region. Simultaneously, through Li... + Concentration adjustment can reduce conductivity from 6.26 S·m -1 Increased to 9.76 S·m -1 (1 to 5 mol·L) -1 The impedance is significantly reduced.

[0031] The amount of borax solution used affects the performance of the hydrogel. Therefore, this invention investigated the amount of borax solution used. Preferably, the borax solution is an aqueous solution of sodium tetraborate, with an effective concentration of 0.05~1.0 wt% in the precursor solution. Unlike CMGG / PAA, whose viscoelastic dissipation mainly comes from hydrogen bonding / ionic association and is prone to irreversible network damage accumulation under repeated large deformations, the system of this invention simultaneously possesses: dynamic borate ester bonds (reversible reconstruction, providing dissipation / repair); synergistic effect of zwitterionic electrostatic interaction and hydrogen bonding (improving interface recovery and network stability), and exhibits self-healing with fracture stress recovery to approximately 96% (0.78 MPa) after about 120 min, and a self-healing efficiency of 96%.

[0032] The present invention does not impose any special limitation on the type of crosslinking agent. Preferably, the crosslinking agent is N,N′-methylenebisacrylamide (MBAA), and its amount is 0.01~0.30 mol% of the total amount of AAM and SBMA to obtain a better crosslinking effect.

[0033] The present invention does not impose any special limitation on the type of photoinitiator. Preferably, the photoinitiator is I2959, and its amount is 0.02~0.30 wt% of the total mass of the precursor solution, so as to better initiate the photopolymerization reaction.

[0034] Unlike simple blending for hydrogel preparation, this invention employs a "dual-network / triple-network" architecture: a dual-network consisting of a dynamic HPG-borate ester network and a PAAm-co-PSBMA covalent network; a third SBMA network is then introduced through "immersion adsorption-secondary photopolymerization," increasing crosslinking points / entanglements and enhancing chain aggregation through zwitterionic electrostatic interactions, thus resulting in a denser pore structure. Preferably, the primary photocuring time is 1-10 min or 6 min; preferably, the secondary photocuring time is 1-10 min or 6 min, to obtain a triple-network structure with superior performance.

[0035] The concentration of the SBMA aqueous solution affects the formation of the third network. Therefore, this invention investigated the concentration of the SBMA aqueous solution. Preferably, the concentration of the SBMA aqueous solution is 0.5~6.0 mol·L⁻¹. - ¹, the soaking time is 0.5~48 h. In this invention, SBMA is not just an aid for "conductivity / adhesion", but rather inhibits biofilm formation by forming a strong hydration layer, reducing non-specific adsorption, weakening the initial adhesion of bacteria, and so on; and the antibacterial rate against E. coli and S. aureus can reach 97% and 99%, respectively.

[0036] This invention also includes post-treatment of the three-network hydrogel to further improve its performance. Preferably, the obtained three-network hydrogel is immersed in deionized water and the water is changed to remove unreacted monomers and residual small molecules. One of the most common failures of traditional wearable hydrogel sensors is: water loss → increased modulus / embrittlement → signal drift. The system of this invention can maintain an initial water content of >90% after being placed at 23 °C and 55% RH for 7 days, and its mechanical properties are almost unchanged after being placed in air for 7 days, providing a basis for stable signal output.

[0037] More specifically, it includes the following steps: (1) Preparation of precursor solution Hydroxypropyl guar gum, acrylamide, SBMA, and lithium salt (providing Li) + Crosslinking agent MBAA and initiator I2959 are added to deionized water in a set ratio and fully dissolved under stirring conditions; then borax aqueous solution is added and stirring is continued until a uniform and stable precursor solution is formed.

[0038] (2) Preparation of dual-network hydrogels The precursor solution is poured into a mold and photo-initiated polymerization is carried out under ultraviolet light irradiation, so that acrylamide and SBMA undergo free radical copolymerization and form a covalent cross-linked network under the action of a cross-linking agent. At the same time, HPG and borax complex to form a borate ester dynamic network, thereby obtaining a dual-network hydrogel.

[0039] (3) Construction of three-network hydrogels The double-network hydrogel obtained in step (2) is immersed in an aqueous SBMA solution, allowing the SBMA monomers to penetrate into the double network under the drive of the concentration gradient. The immersed hydrogel is then subjected to UV light for photocuring, allowing the penetrated SBMA to polymerize in situ within the gel, forming a third network, thus obtaining a triple-network hydrogel. If necessary, a small amount of I2959 or MBAA can be added to the immersion solution to improve the efficiency of the third network formation.

[0040] (4) Post-processing (optional) The obtained three-network hydrogel was soaked in deionized water and the water was changed to remove unreacted monomers and residual small molecules for later use.

[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0042] Example 1 This embodiment provides a dual-network ion-conducting hydrogel, HAS-Li3. + The preparation of LiCl (3 g) specifically includes the following steps: 1) Preparation of precursor solution: Weigh 4 g of 0.5 wt% HPG aqueous solution, 4 g of AAM, 3 g of LiCl, 4 g of SBMA, 0.02 g of MBAA, 0.05 g of I2959, and 15 g of deionized water, and mix them thoroughly; then add 0.5 g of 2 wt% borax solution and continue stirring to obtain a uniform and stable precursor solution.

[0043] 2) Photocuring: The precursor solution is injected into the mold and cured under ultraviolet light (wavelength 365 nm, intensity 6 mW / cm²). 2 After irradiation and curing for 6 min, a dual-network ion-conducting hydrogel, HAS-Li3, was obtained. + .

[0044] Example 2 Unlike Example 1, in step 1), 1g, 4g, and 5g of LiCl were used, respectively. The other steps were the same as in Example 1 to prepare the dual-network matrix HAS-Li1. + (LiCl=1 g), HAS-Li4 + (LiCl=4 g) and HAS-Li5 + (LiCl=5 g).

[0045] Example 3 This embodiment provides a three-network hydrogel HAS / S-Li3 + The construction of the gel (using the gel obtained in Example 1 as the matrix) specifically includes the following steps: 1) Preparation of dual-network matrix: HAS-Li3 was prepared according to Example 1. + Dual-network hydrogel.

[0046] 2) SBMA infiltration enrichment: The obtained HAS-Li3 + The hydrogel was soaked in a 26.7 wt% SBMA aqueous solution for 3 hours, allowing SBMA monomers to permeate and accumulate in the gel under the drive of the concentration gradient.

[0047] 3) Secondary photocuring to construct the third network: Remove the soaked hydrogel (the surface free solution can be gently wiped away), and then place it under ultraviolet light (wavelength 365 nm, intensity 6 mW / cm²). 2 Irradiation for 6 min initiated in-situ polymerization of SBMA enriched within the gel, forming a third network, resulting in the three-network hydrogel HAS / S-Li3. + .

[0048] Comparative Example 1 This comparative example provides the preparation of a dual-network hydrogel (lithium salt-free) HAS, specifically including the following steps: 1) Preparation of precursor solution: Weigh 4 g of 0.5 wt% HPG aqueous solution, 4 g of AAM, 4 g of SBMA, 0.02 g of MABA, 0.05 g of I2959, and 15 g of deionized water, and mix and stir until uniform; then add 0.5 g of 2 wt% borax solution.

[0049] 2) Photocuring: The precursor solution is injected into a mold and irradiated under ultraviolet light (wavelength 365 nm, intensity 6 mW / cm²). 2 After curing for 6 min, a dual-network hydrogel HAS (HPG–borate ester dynamic network + PAAm-co-PSBMA covalent network) was obtained.

[0050] Comparative Example 2 This comparative example provides a hydrogel HA-Li that does not contain the zwitterionic monomer SBMA. 3+ The preparation method was used to compare with samples containing SBMA to verify the antibacterial properties of the zwitterionic structure of SBMA on the hydrogel.

[0051] 1) Preparation of precursor solution: Weigh 4 g of 0.5 wt% HPG aqueous solution, 4 g of AAM, 3 g of LiCl, 0.02 g of MBAA, 0.05 g of I2959, and 19 g of deionized water, and mix them thoroughly; then add 0.5 g of 2 wt% borax solution and continue stirring to obtain a uniform and stable precursor solution.

[0052] 2) Photocuring: The precursor solution is injected into the mold and cured under ultraviolet light (wavelength 365 nm, intensity 6 mW / cm²). 2 After curing by irradiation for 6 min, hydrogel HA-Li was obtained. 3+ .

[0053] Performance testing (1) Moisturizing and antifreeze stability of hydrogels: The control hydrogel, glycerol-based hydrogel, and PBAS-Li hydrogel were placed in a constant temperature and humidity environment (23 ℃, 55% relative humidity) for static aging. Samples were taken and weighed at 10 h and 7 d to examine the mass retention of the samples over time. The water retention capacity of the hydrogels was characterized by the mass retention rate (or water retention rate), and the calculation formula is as follows: Water retention rate = ; in, w t$m$ is the mass measured after the sample is placed under constant temperature and humidity conditions for $t$ time. 、w $m_0$ is the initial mass at the start of the test (usually referring to the mass of the hydrogel just prepared / dried gently on the surface).

[0054] (2)Thermal transition properties of the hydrogel: The thermal transition behavior of the hydrogel was obtained by DSC 204 F1 test. Weigh about 5 - 10 mg of the sample and place it in the calorimeter cell, and set the heating program to -100 °C to 30 °C with a heating rate of 5 °C·min -1 .

[0055] The HAS / S-Li⁺ 3 hydrogel is expected to achieve a wide range of applications in low-temperature environments due to its excellent anti-freezing properties. As an amphoteric ion monomer, SBMA contains both positive and negative charge groups in its molecule and is a suitable component for constructing an anti-freezing hydrogel network; meanwhile, the introduction of LiCl can inhibit the crystallization of the water phase by weakening the hydrogen bonds between water molecules, thus achieving the anti-freezing effect.

[0056] From Figure 1 in (a), it can be seen that the water retention rates of the three are close (about 100%) at the initial stage (0 h); as time extends (to 10 h), the water retention rates slightly decrease, but the decrease amplitudes of HAS-Li₃ + and HAS / S-Li₃ + are small (and still remain at a relatively high level finally), while the decrease of HAS is relatively obvious. It shows that within a short period (10 h), the water retention properties of HAS-Li₃ + and HAS / S-Li₃ + are better. From Figure 1 in (b), it can be seen that the water retention rate is close to 100% at the initial stage (0 days); as the number of days increases (to 7 days), the water retention rates of all three decrease, but the water retention rate of HAS / S-Li₃ + is always higher than that of HAS and HAS-Li₃ + , and the decrease amplitude is the smallest. It indicates that under long-term (7-day) storage, the water retention durability of HAS / S-Li₃ + is more prominent. From Figure 1 in (c), it can be seen that the stress-strain curve of HAS / S-Li₃ + after 7 days is overall higher than that at the initial stage (0 days), and at the same strain, the stress of HAS / S-Li₃ + after 7 days is higher. It shows that after 7 days of exposure, the mechanical properties (such as tensile strength and toughness) of the hydrogel do not decrease, indicating its good durability and still having good mechanical response after long-term storage.

[0057] Furthermore, to characterize the electrical properties after the introduction of ionic salts, electrochemical impedance spectroscopy (EIS) was used to analyze HAS-Li at different LiCl concentrations+ The impedance response. For example... Figure 1 As shown in (d), as the LiCl concentration increases from 1 mol·L⁻¹, - ¹ Increased to 5 mol·L - ¹, the impedance curve shifts overall towards lower impedance, indicating a gradual increase in the system's ionic conductivity. Correspondingly, Figure 1 (e) shows that the conductivity is 6.26 S·m - ¹ Increased to 9.76 S·m - ¹ indicates that increasing the concentration of ionic salts significantly promotes charge transport. This trend mainly stems from the fact that the introduction of LiCl increases the concentration of mobile ions within the hydrogel and constructs more continuous ion conduction channels in the aqueous network, thereby reducing system resistance and improving overall conductivity. It is worth noting that HAS / S-Li3… + Li + Concentration and HAS-Li3 + Its conductivity remains consistent with that of HAS-Li3 + The results are essentially equivalent, indicating that the secondary introduction of the PSBMA third network did not weaken the ion conduction pathway. Considering the balance between overall mechanical and electrical properties, 3 mol·L⁻¹ was selected. - ¹ Li as a three-network system + The concentration can maintain a high level of ionic conductivity while ensuring good mechanical stability, thus meeting the basic requirements of electrical performance for subsequent flexible sensing applications.

[0058] Figure 2 The image shows the test results for the adhesion properties of the hydrogel. The adhesion strength of the composite hydrogel was obtained through an lap shear test using a universal testing machine. (The image shows a 20 × 20 × 3 mm...) 3 A hydrogel was sandwiched between two substrates of the same material (e.g., paper, pigskin, glass, and steel plate) to create a stable adhesion interface before mechanical loading was applied. Experiments were conducted at 5 mm / min. -1 A shear peeling force is applied at a tensile speed, and the maximum load-bearing capacity is collected in real time. Adhesion strength is defined as the peak load corresponding to the failure of the specimen in the initial adhesive region.

[0059] Figure 2 (a) shows a structure where a hydrogel is sandwiched between substrates of the same material (such as paper, pigskin, glass, or steel plate). The arrows indicate the applied shear peeling force, simulating the mechanical loading process at the actual adhesion interface. Figure 2 As shown in (b), HAS-Li+ 3 exhibits the highest adhesion to paper and the lowest to glass. From... Figure 2 As can be seen from (c), HAS-Li3 + The adhesion strength is highest in paper and lowest in glass. Figure 2 From (e), we can see that HAS / S-Li3 + The adhesion is highest in paper and lowest in glass. Figure 2 From (f) in the figure, we can see that HAS / S-Li3 + The adhesion strength is highest in paper and lowest in glass. Figure 2 (d) shows the actual adhesion state of the hydrogel to paper, pigskin, steel plate and glass substrate, which intuitively verifies the experimental phenomenon that "hydrogel can stably adhere to substrates of different materials".

[0060] Figure 3 (a) in the text represents different samples (control (blank), HA-Li) 3+ HAS-Li 3+ HAS / S-Li 3+ (Photographs of colony formation of Escherichia coli and Staphylococcus aureus) Figure 3 (b) and (c) show the antibacterial rate statistics, and the schematic diagram of the antibacterial mechanism is used to illustrate the antibacterial pathway of the hydrogel. Among them, HA-Li 3+ Contains only HPG, AAM, and LiCl, but no SBMA; and HA-Li 3+ Compared to HAS-Li containing SBMA 3+ and HAS / S-Li 3+ The significantly improved antibacterial rate indicates that the zwitterionic groups of SBMA can impart / enhance the antibacterial ability of the hydrogel by constructing a stable hydration layer, reducing non-specific adsorption, and weakening initial bacterial adhesion. The initial colony concentration was 1×10⁻⁶. 6 CFU / mL.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 hydroxypropyl guar gum-zwitterionic composite hydrogel, characterized in that, include: Hydroxypropyl guar gum, acrylamide, SBMA, lithium salt, crosslinking agent, and photoinitiator are mixed evenly, and then borax aqueous solution is added and mixed evenly to obtain a precursor solution. The precursor solution was photocured once under ultraviolet light irradiation to obtain a dual-network hydrogel. The dual-network hydrogel was immersed in an SBMA aqueous solution. After immersion, it was subjected to a second photocuring to obtain a triple-network hydrogel.

2. The method for preparing the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, In the precursor solution, the mass fraction of hydroxypropyl guar gum is 0.1–3.0 wt%, the mass fraction of acrylamide is 5–25 wt%, the mass fraction of SBMA is 0.5–15 wt%, and the concentration of lithium salt is 1–5.0 mol·L⁻¹. - ¹.

3. The preparation method of the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The borax solution is an aqueous solution of sodium tetraborate, with an effective concentration of 0.05~1.0 wt% in the precursor solution.

4. The preparation method of the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The crosslinking agent is N,N′-methylenebisacrylamide (MBAA), and its dosage is 0.01~0.30 mol of the total amount of AAM and SBMA.

5. The method for preparing the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The photoinitiator is I2959, and its amount is 0.02~0.30 wt% of the total mass of the precursor solution.

6. The method for preparing the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The time for one photocuring cycle is 1~10 min or 6 min; Alternatively, the secondary photocuring time may be 1-10 min or 6 min.

7. The method for preparing the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The concentration of the SBMA aqueous solution is 0.5~6.0 mol·L⁻¹. -1 Soaking time is 0.5~48 h.

8. The method for preparing the hydroxypropyl guar gum-zwitterionic composite hydrogel as described in claim 1, characterized in that, The resulting three-network hydrogel was immersed in deionized water and the water was changed to remove unreacted monomers and residual small molecules.

9. The hydroxypropyl guar gum-zwitterionic composite hydrogel prepared by the method according to any one of claims 1-8.

10. The application of the hydroxypropyl guar gum-zwitterionic composite hydrogel of claim 9 in the manufacture of wearable flexible sensors, wearable flexible electronic devices or flexible ion-conducting elements.

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