A high and low temperature resistant conductive antibacterial hydrogel and its preparation method and application

Abstract

This invention discloses a high- and low-temperature resistant conductive antibacterial hydrogel, its preparation method, and its applications. The preparation method includes the following steps: dissolving a high-molecular-weight alcohol polymer in a low-freezing-point mixed solution, then adding a silver salt solution at 85℃~95℃ for reaction, followed by a freeze-thaw treatment of the resulting hydrogel precursor solution to obtain the high- and low-temperature resistant conductive antibacterial hydrogel. The preparation process provided by this invention is simple and the conditions are mild. The prepared high- and low-temperature resistant conductive antibacterial hydrogel maintains good mechanical properties, conductivity, and stability within a temperature range of -30℃ to 70℃, with an elongation at break of up to 440%, a tensile strength of up to 0.75 MPa, good compression resilience (rapid recovery under 60% compressive strain), and good inhibitory and bactericidal effects against Escherichia coli and Staphylococcus aureus. It can be applied to flexible sensing, biosignal acquisition, optical sensing, and imaging under extreme conditions.

Description

Technical Field

[0001] This invention relates to the field of multifunctional flexible conductive polymer materials technology, specifically to a high and low temperature resistant conductive antibacterial hydrogel, its preparation method, and its application. Background Technology

[0002] Hydrogels are a class of polymers with hydrophilic groups, belonging to the category of network structures that can swell in water but are insoluble in water. Composed of a 3D polymer network and a large amount of water, they possess both "soft" and "wet" properties, sharing many structural and compositional similarities with biological soft tissues (organs, muscles, skin). They offer advantages such as environmental friendliness, biocompatibility, resistance to biofouling, and the ability to sense external stimuli, leading to their wide application in cell culture, tissue engineering, biosensing, controlled drug release, soft robotics, and flexible wearables. Currently, to meet the demands of more complex applications, extensive research has been conducted on the functional modification of hydrogels, such as mechanically enhanced hydrogels, environmentally responsive hydrogels (temperature-responsive, pH-responsive, light-, force-responsive, ion-soluble, redox-responsive, magnetic-field-responsive, electric-field-responsive, ultrasound-responsive, etc.), conductive hydrogels, self-healing hydrogels, self-adhesive hydrogels, and antibacterial hydrogels. Furthermore, interdisciplinary and cross-domain collaborative research on multifunctional hydrogels (MFHs) integrating intelligent environmental response, complex driven deformation, and patterning functions is becoming a significant development trend.

[0003] Conductive hydrogels, possessing biocompatibility, a flexible three-dimensional network structure, conductivity, and unique functionalities, have attracted widespread attention in the fields of flexible sensing and bioelectronics. They are considered one of the ideal interface materials for achieving perfect compatibility between the human body and bioelectronics in applications such as biosimulation and artificial neural networks, thus drawing significant industry interest. Conductive hydrogels have broad application prospects in flexible wearable electronics, energy storage, energy conversion, and electrochemical biosensors. Their conductive, soft, transparent, and biocompatible properties offer a natural advantage in combining with flexible electronics.

[0004] Most hydrogels are currently ion-conductive, and research on conductive hydrogels is relatively scattered and has not yet formed a systematic study. The main problems in practical applications are: (1) poor mechanical properties, especially insufficient tensile properties, which cannot meet the requirements of flexible sensing and smart wearable sensing in scenarios with large deformation such as human movement; (2) in sub-zero low temperature environments, water freezes, the hydrogel material becomes hard and brittle, and loses its flexibility; when exposed to air or in environments above room temperature, water evaporates, the hydrogel material loses water and shrinks, and collapses and shrunken; (3) ion-conductive hydrogel materials will lose conductivity due to the lack of freely moving ions when water freezes at low temperatures or evaporates at high temperatures; (4) when used for biosignal acquisition, especially in the case of body-tight testing, there are health risks such as microbial contamination. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high- and low-temperature resistant conductive antibacterial hydrogel, its preparation method, and its applications. The preparation method is simple and the conditions are mild. The prepared conductive antibacterial hydrogel can maintain good mechanical properties, conductivity, and stability within a temperature range of -30℃ to 70℃, and has antibacterial and antimicrobial effects. It can be used for flexible sensing and biosignal acquisition under extreme conditions.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first aspect of this invention provides a method for preparing a high and low temperature resistant conductive antibacterial hydrogel, comprising the following steps:

[0008] (1) Dissolve the high molecular weight alcohol polymer in a low freezing point mixed solution to obtain a pregel solution;

[0009] (2) Add silver salt solution to the pregel solution obtained in step (1) at 85℃~95℃ and react to obtain hydrogel precursor solution;

[0010] (3) The hydrogel precursor solution obtained in step (2) is subjected to freeze-thaw treatment to obtain the high and low temperature resistant conductive antibacterial hydrogel.

[0011] This invention utilizes the numerous hydrogen bonds formed between the active ingredients in a low-freezing-point mixed solution and water molecules to stabilize the water, preventing freezing at low temperatures and evaporation at high temperatures within a wide temperature range of -30℃ to 70℃. By leveraging the reducing properties of the polyols in the low-freezing-point mixed solution and the polymer, silver salt solution is reduced to silver nanoparticles (AgNPs). The polymer also acts as a dispersant and stabilizer, preventing the silver nanoparticles from agglomerating, thus achieving antibacterial and conductive properties. During freezing, the polymer chains form numerous hydrogen bonds with the low-freezing-point mixed solution, inducing the formation of crystalline regions within the polymer and acting as physical cross-linking points for the silver nanoparticles. These physical cross-linkings endow the hydrogel with excellent mechanical properties and adjustability. The preparation process provided by this invention is simple and operates under mild conditions, making it applicable to flexible sensing, biosignal acquisition, optical sensing, and imaging under extreme conditions.

[0012] Further, in step (1), the high molecular weight alcohol polymer is selected from one or more of polyvinyl alcohol (PVA), polyethylene glycol (PEG), polypropylene glycol (PPG) and polybutylene glycol (PBD).

[0013] Further, in step (1), the average molecular weight of the high molecular weight alcohol polymer is 20,000-150,000.

[0014] Furthermore, in step (1), the degree of alcoholysis of the high molecular weight alcohol polymer is 87%-89% (mol / mol).

[0015] Further, in step (1), the high molecular weight alcohol polymer is preferably polyvinyl alcohol, and the polyvinyl alcohol is preferably of type 1788. Further, in step (1), the low freezing point mixed solution is a mixed solution of one or more polyols and water.

[0016] Furthermore, the polyol is ethylene glycol, glycerol, propylene glycol, butylene glycol, etc.

[0017] Further, in step (1), the mass ratio of water to polyol in the low freezing point mixed solution is 1:9-9:1.

[0018] Further, in step (1), the low freezing point mixed solution is preferably a mixed solution of glycerol and water.

[0019] In a binary mixture of water and glycerol, hydrogen bonds form between water molecules and the hydroxyl groups in glycerol. Both PVA and glycerol are rich in hydroxyl groups, resulting in a large number of hydrogen bonds in the prepared hydrogel. These numerous hydrogen bonds firmly lock water molecules in, giving it a low freezing point and evaporation rate, thus providing excellent antifreeze and moisture retention properties. The freezing point of the binary mixture of water and glycerol can be adjusted by changing the mixing ratio of the two components.

[0020] Further, in step (1), the mass ratio of the low freezing point mixed solution to the high molecular weight alcohol polymer is 100:(5-20).

[0021] Further, in step (1), the high molecular weight alcohol polymer is dissolved in a low freezing point mixed solution at 50℃~95℃.

[0022] In a specific embodiment, in step (1), the high molecular weight alcohol polymer is uniformly dissolved in a low freezing point mixed solution under heating and stirring conditions to obtain a pregel solution.

[0023] Furthermore, the heating temperature is preferably 80℃~90℃.

[0024] Furthermore, the stirring speed is 70-80 rpm, and the stirring time is 4-5 hours.

[0025] Furthermore, in step (2), the silver salt solution is an aqueous solution of silver salt.

[0026] Further, in step (2), the silver salt solution is selected from one or more of silver ammonia solution, silver nitrate solution, silver oxalate solution, silver chloride solution and silver bromide solution, preferably silver ammonia solution.

[0027] Further, in step (2), the mass ratio of silver ions in the pregel solution to silver salt solution is (30-70):(0.2-1.5), preferably (30-70):(0.3-1.3), and more preferably (30-70):(0.6-1.3).

[0028] Further, in step (2), the silver ammonia solution is prepared from silver nitrate, water and ammonia, and the mass ratio of the pregel solution to silver nitrate is (30-70):(0.5-2), preferably (40-60):(1-2).

[0029] In a specific embodiment, in step (2), a silver salt solution is added to the pregel solution obtained in step (1) at 85℃~95℃ with stirring, and the reaction is maintained for a period of time to ensure that all silver ions are reduced to uniformly dispersed elemental silver particles, and a hydrogel precursor solution is obtained.

[0030] Furthermore, the stirring speed is 70-80 rpm, and the stirring time is 2-3 hours.

[0031] Further, in step (3), the conditions for the freeze-thaw process are: freezing at -25℃ to -20℃ and thawing at 0℃ to 70℃.

[0032] In a specific embodiment, in step (3), the hydrogel precursor solution is left to stand overnight to degas and remove bubbles, then poured into a mold and subjected to a freeze-thaw process to obtain the high and low temperature resistant conductive antibacterial hydrogel.

[0033] Furthermore, the mold is a national standard mechanical performance testing mold or other mold of the required shape.

[0034] The second aspect of the present invention provides a conductive antibacterial hydrogel resistant to high and low temperatures prepared by the method described in the first aspect.

[0035] The conductive antibacterial hydrogel provided by this invention maintains good mechanical properties, conductivity, and stability within a temperature range of -30℃ to 70℃. Its elongation at break can reach 440%, its tensile strength can reach 0.75 MPa, and it has good compression resilience, recovering rapidly under 60% compressive strain. It also has good inhibitory and bactericidal effects on Escherichia coli and Staphylococcus aureus.

[0036] The third aspect of this invention provides the application of the high and low temperature resistant conductive antibacterial hydrogel described in the second aspect in sensors and biosignal acquisition, which can be applied to flexible sensing, optical sensing and imaging under extreme conditions, such as flexible strain sensors and flexible temperature sensors.

[0037] The beneficial effects of this invention are:

[0038] 1. This invention utilizes the large number of hydrogen bonds formed between the effective components in the low freezing point mixed solution and water molecules to stabilize the water, so that it does not freeze at low temperatures and does not evaporate at high temperatures within a wide temperature range of -30℃ to 70℃, while maintaining good mechanical properties and morphology.

[0039] 2. This invention utilizes the reducing properties of low freezing point mixed solutions and polyols (such as ethylene glycol, glycerol, and high molecular weight alcohol polymers) to reduce silver salt solutions to silver nanoparticles. At the same time, the high molecular weight alcohol polymers also act as dispersants and stabilizers, preventing the silver particles from agglomerating and ensuring uniform distribution, thereby achieving antibacterial and conductive properties.

[0040] 3. In the preparation method of the present invention, during the cyclic freezing process, the polymer chains of the high molecular weight alcohol polymer form a large number of hydrogen bonds with the low freezing point mixed solution, and induce the formation of crystalline regions of the high molecular weight alcohol polymer, as well as the physical cross-linking effect of silver nanoparticles. These physical cross-linkings endow the hydrogel with good mechanical properties and adjustability.

[0041] 4. The preparation process provided by this invention is simple and the conditions are mild, and it can be applied to flexible sensing, biosignal acquisition, optical sensing and imaging under extreme conditions. Attached Figure Description

[0042] Figure 1 This is a physical diagram of the reaction in step (2) of Example 1.

[0043] Figure 2 Images of hydrogel samples in different forms.

[0044] Figure 3 This is a photograph of a typical PVA hydrogel frozen in place, as shown in Comparative Example 1.

[0045] Figure 4 The figures show the test results of the antifreeze properties and moisturizing abilities of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1. Among them, (a) is a data graph of temperature and humidity changes in an indoor open environment, (b) is a data graph of the weight change rate of the hydrogel samples of Examples 1-3 and Comparative Example 1 in an indoor open environment, (c) is a comparison of the appearance of the hydrogel sample of Example 1 and the PVA hydrogel sample without glycerol, (d) is a data graph of the weight change rate of the hydrogel samples of Examples 1-3 and Comparative Example 1 under 70℃ oven conditions, (e) is a data graph of the weight change rate of the hydrogel samples of Examples 1-3 and Comparative Example 1 under -30℃ freezing conditions, and (f) is a physical image showing the antifreeze properties of the hydrogel sample of Example 1.

[0046] Figure 5The figures show the mechanical property test results of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1; where (a) is the stress-strain curve of the tensile test (the curves are from bottom to top Comparative Example 1, Example 1, Example 2, and Example 3), (b) is the stress-strain curve of the compression test (the curves are from bottom to top Comparative Example 1, Example 1, Example 2, and Example 3), (c) is the data graph of elastic modulus, (d) is the physical image of the tensile and compression test, (e) is the data table of elastic modulus of different human tissues, (f) is the physical image of the hydrogel sample of Example 1 after being cut and subjected to ultimate compression, and (g) is the physical image of the light transmittance test.

[0047] Figure 6 The figures show the (strain sensing) conductivity test results of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1; where (a) is the data graph of the resistance change and tensile strain sensitivity of the hydrogel sample in Comparative Example 1 within a 200% stretch range, (b) is the data graph of the resistance change and tensile strain sensitivity of the hydrogel sample in Example 1 within a 200% stretch range, (c) is the data graph of the resistance change and tensile strain sensitivity of the hydrogel sample in Example 2 within a 200% stretch range, (d) is the data graph of the resistance change and tensile strain sensitivity of the hydrogel sample in Example 3 within a 200% stretch range, and (e) is the data graph of the resistance change and tensile strain sensitivity of the hydrogel sample in Example 3 within a 200% stretch range. The following are physical images of the hydrogel samples collected synchronously during stretching and compression: (f) shows the resistance change and compressive strain sensitivity of the hydrogel sample in Comparative Example 1 within a 60% compression range; (g) shows the resistance change and compressive strain sensitivity of the hydrogel sample in Example 1 within a 60% compression range; (h) shows the resistance change and compressive strain sensitivity of the hydrogel sample in Example 2 within a 60% compression range; (i) shows the resistance change and compressive strain sensitivity of the hydrogel sample in Example 3 within a 60% compression range; (j) shows the strain test results of the hydrogel sample in Example 3 used for different bending angles of the finger; and (k) shows the response and recovery time of the hydrogel sample in Example 1 used as a hydrogel flexible strain sensor.

[0048] Figure 7The graphs show the (temperature sensing) conductivity test results of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1. Among them, (a) is the resistance change graph of the hydrogel samples of Examples 1-3 and Comparative Example 1 in the temperature range of -30℃ to 70℃, (b) is the resistance change graph and TCR graph of the hydrogel sample of Comparative Example 1 in the temperature range of -20℃ to 25℃, (c) is the resistance change graph and TCR graph of the hydrogel sample of Example 1 in the temperature range of -20℃ to 25℃, (d) is the resistance change graph and TCR graph of the hydrogel sample of Example 2 in the temperature range of -20℃ to 25℃, and (e) is the resistance change graph and TCR graph of the hydrogel sample of Example 3 in the temperature range of -20℃ to 25℃.

[0049] Figure 8 The figures show the antibacterial performance test results of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1; where (a) is the test result of the inhibition zone method and (b) is the test result of the shaking culture method. Detailed Implementation

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0053] Example 1

[0054] A method for preparing a high- and low-temperature resistant conductive antibacterial hydrogel (PVA-glycerol-Ag0.5 organohydrogel) includes the following steps:

[0055] (1) At 85°C, 4g of polyvinyl alcohol was dissolved in 10.4mL of water and 28mL of glycerol (GL), and stirred at 80rpm for 4h to obtain a pregel solution.

[0056] (2) Add silver ammonia solution to the pregel solution obtained in step (1) at 85℃. The silver ammonia solution is prepared by 0.5g AgNO3, 1mL H2O and 0.6mL ammonia water. Stir at 80rpm for 2h to obtain hydrogel precursor solution.

[0057] (3) The hydrogel precursor solution obtained in step (2) was left to stand overnight to degas and remove bubbles, then poured into a mold and subjected to a freeze-thaw treatment. The solution was frozen at -20°C for 5 hours and thawed at room temperature for 2 hours. This process was repeated twice to obtain the high and low temperature resistant conductive antibacterial hydrogel.

[0058] Figure 1 This is a physical reaction diagram of step (2) in Example 1, from... Figure 1 Ag can be seen in + The process of being restored.

[0059] Figure 2 The images show actual samples of hydrogels in different forms, demonstrating that the hydrogels prepared by this invention can be made into different forms using different molds.

[0060] Example 2

[0061] A method for preparing a high- and low-temperature resistant conductive antibacterial hydrogel (PVA-glycerol-Ag1.0 organohydrogel) includes the following steps:

[0062] (1) At 85°C, 4g of polyvinyl alcohol was dissolved in 9.8mL of water and 28mL of glycerol (GL), and stirred at 80rpm for 4h to obtain a pregel solution.

[0063] (2) Add silver ammonia solution to the pregel solution obtained in step (1) at 85℃. The silver ammonia solution is prepared by 1.0gAgNO3, 1mLH2O and 1.2mLammonia water. Stir at 80rpm for 2h to obtain hydrogel precursor solution.

[0064] (3) The hydrogel precursor solution obtained in step (2) was left to stand overnight to degas and remove bubbles, then poured into a mold and subjected to a freeze-thaw treatment. The solution was frozen at -20°C for 5 hours and thawed at room temperature for 2 hours. This process was repeated twice to obtain the high and low temperature resistant conductive antibacterial hydrogel.

[0065] Example 3

[0066] A method for preparing a high- and low-temperature resistant conductive antibacterial hydrogel (PVA-glycerol-Ag2.0 organohydrogel) includes the following steps:

[0067] (1) At 85°C, 4g of polyvinyl alcohol was dissolved in 9.0mL of water and 28mL of glycerol (GL), and stirred at 80rpm for 4h to obtain a pregel solution.

[0068] (2) Add silver ammonia solution to the pregel solution obtained in step (1) at 85℃. The silver ammonia solution is prepared by 2.0gAgNO3, 1mLH2O and 2.0mLammonia water. Stir at 80rpm for 2h to obtain hydrogel precursor solution.

[0069] (3) The hydrogel precursor solution obtained in step (2) was left to stand overnight to degas and remove bubbles, then poured into a mold and subjected to a freeze-thaw treatment. The solution was frozen at -20°C for 5 hours and thawed at room temperature for 2 hours. This process was repeated twice to obtain the high and low temperature resistant conductive antibacterial hydrogel.

[0070] Comparative Example 1

[0071] A method for preparing a PVA hydrogel (PVA-glycerol organohydrogel) includes the following steps:

[0072] (1) At 85°C, 4g of polyvinyl alcohol was dissolved in 12.0mL of water and 28mL of glycerol (GL), and stirred at 80rpm for 4h to obtain a pregel solution.

[0073] (2) The pregel solution obtained in step (1) was left to stand overnight to degas and remove bubbles, then poured into a mold and subjected to a freeze-thaw treatment. The solution was frozen at -20°C for 5 hours and thawed at room temperature for 2 hours. This process was repeated twice to obtain a hydrogel.

[0074] Figure 3 This is a photograph of a regular PVA hydrogel without glycerol that has been frozen.

[0075] Test Example 1

[0076] The stability of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1 in high and low temperature environments was tested using the following methods:

[0077] Hydrogel samples were stored in an open indoor environment for 34 days, frozen at -30℃ for 30 days, and dried in an oven at 70℃ for 16 hours. The state and weight changes of the hydrogel samples were recorded to characterize their antifreeze properties and moisturizing ability.

[0078] The method for calculating the rate of change in weight is as follows:

[0079] Weight rate (%) = (W0 - W) t ) / W0*100%

[0080] Where W0 is the initial weight (g) of the sample, W t It is the weight (g) after a certain storage time.

[0081] Test results are as follows Figure 4 As shown, Figure 4 (a) records the changes in ambient temperature and humidity of the hydrogel sample stored in an open indoor environment for 34 days. Figure 4 As shown in (b), in an open indoor environment (20–34℃, 42–91% RH), the sample weight change rate is mainly affected by humidity. This is because PVA and glycerol have hydrophilic and hygroscopic properties, and the indoor temperature fluctuation is relatively small. The weight change rates of the four hydrogel samples all remained within 6.5%, exhibiting good moisturizing properties. Conversely, from... Figure 4 As can be seen in (c), the PVA hydrogel without glycerol loses about 80% of its mass and becomes shriveled and brittle due to the loss of moisture.

[0082] The hydrogel samples were dried in a 70℃ oven for 16 hours, and the weight change rate of the hydrogel samples was recorded. The data are as follows: Figure 4 As shown in Figure (d), the mass of the hydrogel sample basically no longer decreased after drying for 5 hours, and the mass loss rate decreased with the increase of AgNPs content. The maximum mass loss was about 5.5%, and the minimum was only about 1.5%, highlighting its excellent moisturizing performance and stability.

[0083] Hydrogel samples were stored at -30℃ for 30 days for freeze-thaw testing, and the weight change rate of the hydrogel samples was recorded. The data are as follows: Figure 4 As shown in (e), the weight of the hydrogel sample increases slowly due to moisture absorption, and the rate of weight increase decreases with increasing AgNP content. This is because the increased number of physical cross-linking points of AgNPs makes the sample structure more compact, thus reducing water absorption. Furthermore, the hydrogel sample of Example 1, after being frozen at -30°C for 30 days, still maintains good flexibility and tensile strength, and can be bent under its own weight, exhibiting remarkable softness. After more than 5 consecutive torsions and tensile deformations exceeding 200%, no damage was observed. Figure 4 As shown in (f).

[0084] The tests conducted under the three different conditions demonstrated that the hydrogel samples prepared by this invention possess excellent antifreeze, heat resistance, and moisturizing properties. They can maintain good morphology and performance under extreme environments of -30℃ and 70℃, meeting the application needs of daily and special scenarios.

[0085] Test Example 2

[0086] The mechanical properties of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1 were tested. The stress-strain test method was as follows:

[0087] Dumbbell-shaped samples were selected for tensile testing at a speed of 20 mm / min; cylindrical samples were selected for compression testing at a speed of 5 mm / min. The calculation method is as follows:

[0088]

[0089]

[0090] Where: σ is the tensile / compressive stress (MPa); F is the force (N) borne during tension / compression;

[0091] A is the cross-sectional area of ​​the sample (m²) 2 ); δ represents tensile / compressive strain (%);

[0092] L is the clamping distance during tension / compression (mm); L0 is the initial clamping distance (mm).

[0093] Generally, the tensile strength at break and the elongation at break of a material are negatively correlated, because increasing the strength of a material often reduces its tensile properties. However, as... Figure 5 As shown in Figure (a), the hydrogel sample prepared by this invention exhibits increased stress (tensile strength) and strain (elongation) in tensile tests with increasing AgNPs content. This is because the AgNPs obtained by the reduction method are uniformly dispersed in the hydrogel substrate. On one hand, they act as physical crosslinking points, enhancing the tensile properties of the three-dimensional gel network; on the other hand, AgNPs, as nanoparticles, possess small particle size and large specific surface area, effectively dispersing stress and thus improving tensile strength. The stress-strain curves from the tensile tests show that AgNPs significantly improve the tensile strength of the sample, increasing the tensile strength at break from approximately 2.82 kPa to 0.751 MPa, a more than 260-fold increase; the elongation at break increases from 285% to 440%, a 1.5-fold increase. Figure 5 As shown in (f), the sample exhibits good toughness during cutting and does not break even under the ultimate compression at 99% deformation (14.019 MPa), indicating good crosslinking strength.

[0094] According to Hooke's Law, within the elastic limit of an object, stress is directly proportional to strain, and the ratio is the elastic modulus (E). This can be expressed as... Figure 5 The slope of the initial linear region (tensile strain ε = 10–20%) of the stress-strain curve in (b) is calculated. Figure 5As shown in (c), the tensile elastic moduli (E = σ / ε) of the four hydrogel samples are 0.99 kPa, 49.81 kPa, 74.38 kPa, and 170.76 kPa, respectively. The elastic modulus reflects the hardness of a material; the higher the elastic modulus, the less easily the material deforms. Materials with an elastic modulus in the order of kPa and below are defined as "ultrasoft materials." By changing the AgNPs content, the range from "ultrasoft materials" to general soft materials can be achieved, and their elastic modulus can match that of most biological tissues in the human body (e.g., ...). Figure 5 (as shown in (e)). The preparation method of the present invention does not contain harmful substances such as chemical cross-linking agents, and the cross-linking molding conditions are mild and the speed is suitable. Cells can be uniformly mixed into the gel precursor solution. By adjusting the elastic modulus, different cell differentiations can be induced. The prepared hydrogel can be used as an ideal scaffold material for 3D cell and tissue culture.

[0095] Most optical fibers currently in use are silicon fibers or high-modulus polycarbonate fibers, which often damage soft tissues. Therefore, the "ultra-softness" and high light transmittance of the hydrogel prepared in this invention are noteworthy. Figure 5 As shown in (c) and (g), a laser can enter from one end of a straightened or bent hydrogel and exit from the other end, as... Figure 5 As shown in (i) and (ii), after splicing 2-3 hydrogel segments together, it was found that the propagation of the laser was significantly hindered at the interface, as shown in... Figure 5 As shown in (iii) and (iv). Combining the "ultra-softness" of hydrogels, the hydrogels prepared in this invention can be used as flexible optical fiber materials in biomedical fields such as optical sensing and imaging.

[0096] Test Example 3

[0097] The conductivity properties of the high and low temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1 were tested. The test method was as follows:

[0098] The resistance change of different hydrogel samples was tested within a 200% tensile range. The tensile strain sensitivity of the gel samples was evaluated by the sensitivity coefficient (GF), where GF = [(R-R0) / R0] / ε, R is the real-time resistance under tensile strain, R0 is the initial resistance when the strain is 0%, and ε is the tensile strain.

[0099] On the one hand, PVA is a polyelectrolyte rich in hydroxyl groups, which can dissociate in an aqueous environment, releasing a large number of protons (H+). + Therefore, PVA hydrogels possess a certain degree of ionic conductivity. For example... Figure 6As shown in Figure (a), the hydrogel sample of Comparative Example 1 exhibits a linear increase in electrical resistance with tensile strain over a relatively large tensile strain range of 0% to 125%, with GF = 3.5141 (R). 2 =0.989); Further stretching causes the PVA polymer chain segments to break, disrupting the conductive network and causing fluctuations in the increasing resistance trend. However, in the hydrogel sample provided by this invention, uniformly distributed AgNPs tunnel through each other to form a conductive network, thus the addition of AgNPs significantly improves conductivity. The resistance change of the sample containing AgNPs is mainly affected by the content and distribution of AgNPs. For example... Figure 6 As shown in (b), (c), and (d), the resistance of the hydrogel sample increases with the increase of the average distance between AgNPs during stretching. Within the tensile strain range of 0% to 125%, the resistance of the hydrogel sample in Example 1 fluctuates drastically with almost no linear region, while the resistance of the hydrogel sample in Example 2 is GF = 2.1920 (R). 2 =0.993), the GF of the hydrogel sample in Example 3 was 2.5072 (R = 0.993). 2 =0.969), and the comparison showed that the hydrogel sample of Example 2 had the best linear fit of the "tensile strain-resistance change" curve (R = 0.969). 2 =0.993), indicating that within a certain tensile strain range, an appropriate AgNPs content can improve the stability of the linear change in sample resistance. When assembled into a flexible strain sensor, high linearity is beneficial for the design of the back-end acquisition circuit and data processing. Compared with hydrogel strain sensors reported in related literature, the hydrogel prepared in this invention has higher tensile strain sensitivity.

[0100] The resistance changes of different hydrogel samples were tested within a 60% compression range, and the test results are as follows: Figure 6 As shown in (f), (g), (h), and (i), the resistance of the hydrogel samples of Comparative Example 1 and Example 1 decreases linearly with the compression process, and their compression sensitivity coefficients (GF) are -1.370 (R0). 2 =0.990), -0.001(R) 2 =0.996). The hydrogel samples of Examples 2 and 3 exhibited negative pressure sensitivity during compression. Their GF values ​​decreased with increasing compressive strain, meaning they were more sensitive at low compression levels. Their maximum compressive sensitivity coefficients (GF) were -13.967 (0%–5%), respectively. 2 =0.983), -11.129 (0% ~ 7%, R 2=0.985). This is because as the AgNP content increases, the spacing between uniformly distributed AgNPs in the hydrogel sample becomes smaller. Compression shortens the axial distance of the hydrogel sample and makes the AgNPs more densely packed, forming a good conductive path, and the resistance drops rapidly. Afterward, due to the formation of the conductive path, the effect of compression on the resistance of the hydrogel sample is small, but the resistance still decreases linearly with compression within this range. The compression sensitivity coefficient (GF) of the hydrogel samples in Examples 2 and 3 decreased to -0.1369 (25%~60%, R 2 =0.969), -0.0368 (25% ~ 60%, R 2 =0.992).

[0101] The above tests show that the resistance of the hydrogel sample increases under tension and decreases under compression, exhibiting a linear correlation within a certain strain range. To verify its application in the field of flexible wearables, a hydrogel sample from Example 3, with an elastic modulus similar to that of human muscle and cartilage tissue, was used to fabricate a gel strain sensor to monitor repetitive motion signals of the finger at different bending angles (30°, 60°, 90°). Figure 6 As shown in (j), when the finger is bent, the gel strain sensor is stretched, and its relative resistance changes rapidly. When the finger returns to its original position, the relative resistance change rapidly decreases and recovers, indicating that the gel strain sensor has high sensitivity. In continuous repeatability tests, its relative resistance change shows good stability and repeatability (occasional small fluctuations are caused by deviations in the volunteer's finger bending action), indicating that the gel strain sensor has excellent electrical signal stability. Furthermore, its relative resistance change is positively correlated with the finger bending angle (tensile strain) and... Figure 6 The results shown in (d) are consistent. Figure 6 As shown in (k), during the monitoring of a finger bending at 30°, the response time and recovery time of the gel strain sensor are both less than 200ms, which is limited by the back-end signal acquisition frequency (0.1s / time, 10Hz), but is sufficient to realize the recognition and monitoring of high-frequency human motion.

[0102] Test Example 1 demonstrated that the hydrogel provided by this invention maintains good flexibility, tensile strength, and quality stability under extreme environments of -30℃ and 70℃. Furthermore, its conductivity changes were tested within the temperature range of -30℃ to 70℃. The test results are as follows... Figure 7As shown in (a), AgNPs can significantly improve the conductivity of samples in sub-zero temperature environments. Hydrogel samples containing AgNPs maintain good conductivity even at -30℃; furthermore, as temperature increases, charge carriers increase and sample resistance decreases, indicating that the hydrogel sample also possesses temperature responsiveness. Further, the temperature responsiveness of hydrogel samples with different AgNPs contents is evaluated using the temperature coefficient of resistance (TCR), TCR = [(R-R0) / R0] / ΔT, where R is the instantaneous resistance at the test temperature, R0 is the initial resistance, and ΔT is the temperature difference. Figure 7 As shown in (b), (c), (d), and (e), the TCR of the hydrogel samples of Comparative Example 1, Example 1, Example 2, and Example 3 in the temperature range of -20℃ to 25℃ was -1.842%℃. -1 (R 2 =0.987), -1.739%℃ -1 (R 2 =0.959), -1.772%℃ -1 (R 2 =0.986), -0.019%℃ -1 (R 2 =0.998), it can be observed that the TCR decreases with increasing AgNPs content in the hydrogel sample, and the TCR value of the hydrogel sample in Example 3 drops sharply, only one percent of that of the hydrogel sample in Example 2. This is because a large number of AgNPs form a stable conductive path inside the hydrogel, and its relative resistance change is less affected by temperature changes. Therefore, hydrogel samples with different AgNPs contents can be selected according to different application requirements.

[0103] Test Example 4

[0104] The mechanical properties, conductivity, and elastic modulus of hydrogel samples can be adjusted by regulating the AgNP content. AgNPs are also a safe and efficient antibacterial agent. Therefore, the antibacterial properties of the high- and low-temperature resistant conductive antibacterial hydrogels prepared in Examples 1-3 and the PVA hydrogel prepared in Comparative Example 1 were tested. *Escherichia coli* [CMCC(B)44102] was used as a representative of Gram-negative bacteria, and *Staphylococcus aureus* [CMCC(B)26003] was used as a representative of Gram-positive bacteria. Both were purchased from Nanjing Lezhen Biotechnology Co., Ltd. The antibacterial properties were tested using the inhibition zone method (inhibition rate PI) and the shaking culture method (inhibition rate R). The calculation methods are as follows:

[0105] Inhibition rate PI = d i / d h *100%

[0106] Where d id is the diameter of the antibacterial zone. h The sample diameter is in mm.

[0107] Antibacterial rate R = (BC)B * 100%

[0108] Where B represents the colony count in the control group and C represents the colony count in the test group.

[0109] The inhibition zone method was used to preliminarily determine the antibacterial properties of the hydrogel samples. The test results are as follows: Figure 8 As shown in Figure (a), position 1 corresponds to the hydrogel sample of Example 1, position 2 corresponds to the hydrogel sample of Example 1, position 3 corresponds to the hydrogel sample of Example 2, and position 4 corresponds to the hydrogel sample of Example 3. It can be seen that the hydrogel sample of Example 3 exhibits a clear inhibition zone. The inhibition rates (PI) against *E. coli* and *S. aureus*, calculated by measuring the diameter of the inhibition zone, were 389.59% and 419.97%, respectively. After 28 days, the inhibition zone showed no significant change, indicating a very significant and stable antibacterial effect. Notably, after 7 days, a ring-shaped "silver film" appeared on the upper surface of the hydrogel sample of Example 3 and the surrounding culture medium surface. According to Fajans' rules, unreduced Ag in the gel sample... + The Ag is mainly adsorbed around AgNPs, therefore the positively charged Ag in the hydrogel sample of Example 3 + Under the influence of Coulomb attraction, AgNPs are attracted by the negatively charged E. coli and S. aureus, and AgNPs aggregate to form a ring-shaped "silver film", which exhibits a long-lasting and significant antibacterial effect.

[0110] The antibacterial rate (R) of hydrogel samples was quantitatively tested using the shaking culture method. The test results are as follows: Figure 8 As shown in (b), no colonies were detected in any of the hydrogel samples containing AgNPs, so the colony count was recorded as "<1" for antibacterial rate calculation. The antibacterial rates against E. coli and S. aureus were ≥99.56% and ≥99.76%, respectively, showing significant antibacterial effects. The hydrogel samples of Example 1 and Example 2, which did not show obvious inhibition zones, exhibited antibacterial rates of over 99% against both Gram-negative E. coli and Gram-positive S. aureus, thus demonstrating safe and highly effective antibacterial properties. Furthermore, the inhibitory effect on S. aureus was slightly higher than that on E. coli.

[0111] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high and low temperature resistant conductive antibacterial hydrogel, characterized in that, Includes the following steps: (1) Dissolve a high molecular weight alcohol polymer in a low freezing point mixed solution to obtain a pregel solution; the high molecular weight alcohol polymer is polyvinyl alcohol; the low freezing point mixed solution is a mixed solution of one or more polyols with water, wherein the polyol is ethylene glycol, glycerol, propylene glycol or butanediol; (2) Add silver salt solution to the pregel solution obtained in step (1) at 85 ℃~95 ℃ and react to obtain hydrogel precursor solution; (3) The hydrogel precursor solution obtained in step (2) is subjected to freeze-thaw treatment to obtain the high and low temperature resistant conductive antibacterial hydrogel.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the low freezing point mixed solution to the high molecular weight alcohol polymer is 100:(5-20).

3. The preparation method according to claim 1, characterized in that, In step (1), the average molecular weight of the high molecular weight alcohol polymer is 20,000-150,000.

4. The preparation method according to claim 1, characterized in that, In step (1), the high molecular weight alcohol polymer is dissolved in a low freezing point mixed solution at 50 ℃~95 ℃.

5. The preparation method according to claim 1, characterized in that, In step (2), the silver salt solution is selected from one or more of silver ammonia solution and silver nitrate solution.

6. The preparation method according to claim 5, characterized in that, In step (2), the mass ratio of silver ions in the pregel solution to those in the silver salt solution is (30-70):(0.2-1.5).

7. The preparation method according to claim 1, characterized in that, In step (3), the freezing-thawing conditions are: freezing at -25 ℃ to -20 ℃ and thawing at 0 ℃ to 70 ℃.

8. The conductive antibacterial hydrogel resistant to high and low temperatures prepared by the method according to any one of claims 1-7.

9. The application of the high and low temperature resistant conductive antibacterial hydrogel as described in claim 8 in a sensor.

10. The application of the high and low temperature resistant conductive antibacterial hydrogel of claim 8 in the preparation of biosignal acquisition products.

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