Anti-freezing multifunctional hydrogel sensor and preparation method and application thereof

Abstract

The present application relates to the technical field of hydrogel, and particularly relates to an anti-freezing multifunctional hydrogel sensor and a preparation method and application thereof, wherein the preparation method comprises the following steps: polyvinyl alcohol, oxidized sodium carboxymethyl cellulose and gelatin are first added into a water solution of magnesium chloride or a hydrated salt thereof, a precursor hydrogel is constructed by directional freezing in a liquid nitrogen environment, and the precursor hydrogel is placed in a water-glycerol binary solution of sodium citrate or a hydrated salt thereof to obtain a composite hydrogel. Compared with the prior art, the present application solves the technical problem that the ion conductivity, mechanical strength and biocompatibility of the traditional hydrogel are difficult to balance by the synergistic effect of multi-component design and step-by-step modulation of specific ion salt-water mediated polymer chain bonding, and breaks through the difficulty that the performance of the hydrogel is reduced and fails in an extreme environment; the present application can realize multi-modal recognition of strain / pressure / temperature, and has high sensitivity and high stability of strain sensing performance in indoor, underwater and lower than -70 DEG C environments.

Description

Technical Field

[0001] This invention relates to the field of hydrogel technology, and in particular to an antifreeze multifunctional hydrogel sensor, its preparation method, and its application. Background Technology

[0002] Flexible sensors have garnered significant attention in fields such as electronic skin, human-computer interaction, and biosensors due to their superior flexibility and conductivity. They can accurately convert external stimuli into measurable electrical signals, facilitating the monitoring of complex human movements and enabling multimodal information transmission. Furthermore, their ability to seamlessly integrate into biological tissues holds immense potential in medical rehabilitation, motion detection, intelligent robot integration, and biomedicine. Among these, conductive hydrogels composed of polymer networks are considered highly promising candidates for flexible sensors due to their tunable physical and electrochemical properties.

[0003] For a wide range of applications, an ideal hydrogel flexible sensor not only needs to generate stable and persistent sensing signals in all weather conditions, but also needs to be safe and reliable for human use. Therefore, hydrogels must possess the following characteristics: high conductivity and sensing sensitivity, robust mechanical properties and fatigue resistance, tolerance to different environments, and excellent biocompatibility. Based on the synergy of these functions, hydrogels can stably acquire minute signal differences over long periods while meeting the needs of real-world scenarios, and achieve long-term safe human interaction.

[0004] However, traditional polymer hydrogels often struggle to achieve integrated construction with multiple properties. Polymer systems inherently suffer from poor electrical conductivity and weak mechanical properties; in the constructed hydrogels, a large amount of free water is lost or freezes with changes in ambient temperature, causing structural damage and performance degradation, thus failing to meet practical requirements.

[0005] While strategies based on directional freezing, ion-conducting fillers, and the Hofmeister effect have achieved significant improvements in individual performance metrics such as sensing sensitivity, conductivity, and mechanical properties in recent years, these strategies suffer from issues such as decreased toughness due to internal inhomogeneities or cell death due to high ion salt concentrations. This often results in a trade-off between the prepared hydrogels' sensing performance, mechanical properties, and biocompatibility. These shortcomings limit the application of hydrogels in a wide range of scenarios and hinder the further development of flexible hydrogel sensors. Therefore, achieving multi-dimensional performance integration of hydrogel sensors using simple and low-cost strategies remains a pressing technical challenge in this field.

[0006] For example, existing technology CN120518824A describes a method for preparing ion-sensitive hydrogels and their application in flexible sensing, but the overall mechanical strength is low and it does not consider use in different environments. Existing technology CN 120309805A uses ion liquids to construct ion-sensing hydrogels, but the use of ultraviolet catalysis may pose potential biocompatibility risks due to catalyst residues. Existing technology CN120518970A introduces MXene nanosheets into polyacrylamide hydrogels to construct strain-sensing hydrogels, but this also carries the risk of toxic reagent residues and the problem of adapting to multiple environments. Therefore, although significant breakthroughs have been made in the research of hydrogel sensing, research on multifunctional integrated hydrogel sensors with high environmental tolerance based on "mechanical enhancement-multidimensional sensing-biofriendliness" has not yet been reported. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art by providing a freeze-resistant multifunctional hydrogel sensor, its preparation method, and its application. Through the stepwise modulation synergistic effect of multi-component design and ion salt-water mediated polymer chain bonding, it solves the technical problem of balancing ionic conductivity, mechanical strength, and biocompatibility in traditional hydrogels, and overcomes the problem of performance degradation and failure of hydrogels in extreme environments. It can realize multimodal recognition of strain / pressure / temperature, and can achieve high sensitivity and high stability strain sensing in indoor, underwater, and below -70°C environments.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] The first aspect of this invention provides a method for preparing an antifreeze multifunctional hydrogel sensor, comprising the following steps:

[0010] S1. Add polyvinyl alcohol, sodium carboxymethyl cellulose oxide, and gelatin to an aqueous solution of magnesium chloride or its hydrated salt, heat and stir, so that magnesium chloride or its hydrated salt can break the hydrogen bond entanglement between polymer chains through hydration, promote uniform dispersion of components, and obtain a uniformly mixed precursor solution.

[0011] S2. Pour the precursor solution into a mold and perform directional freezing in a liquid nitrogen environment to rapidly freeze the precursor solution and construct a precursor hydrogel with a directional and dense structure.

[0012] S3. The precursor hydrogel is placed in a water-glycerol binary solution of sodium citrate or its hydrated salt for immersion and strengthening. Sodium citrate or its hydrated salt promotes the strengthening of inter-polymer chain bonding by inhibiting hydration, and the water-glycerol binary solvent provides water retention and antifreeze properties, resulting in a composite hydrogel with high mechanical strength, ionic conductivity and antifreeze properties.

[0013] S4. Connect the composite hydrogel to wires and electrical signal detection equipment to assemble it into a flexible sensor for strain, pressure or temperature sensing.

[0014] Further, in S1, the mass ratio of polyvinyl alcohol, sodium carboxymethyl cellulose oxide, and gelatin is 1:0.05-0.3:0.05-0.3;

[0015] In the aqueous solution of magnesium chloride or its hydrated salt, the mass ratio of water to magnesium chloride or its hydrated salt is 1:0.02-0.4.

[0016] Furthermore, in S3, the mass ratio of water to glycerol in the water-glycerol binary solvent is 1:0.5-1.5;

[0017] The mass ratio of the water-glycerol binary solvent to sodium citrate or its hydrated salt is 1:0.02-0.25.

[0018] Further, in S3, the mass ratio of the water-glycerol binary solution of sodium citrate or its hydrated salt to the precursor hydrogel is 1:0.02-0.1.

[0019] Furthermore, in S1, the heating and stirring temperature is 50-100℃, and the stirring time is 30-90 minutes;

[0020] In S2, the directional freezing time is 10-40 minutes;

[0021] In S3, the soaking time for strengthening is 12-48 hours.

[0022] A second aspect of the present invention provides an antifreeze multifunctional hydrogel sensor obtained by the preparation method described above, wherein the antifreeze multifunctional hydrogel sensor has a directional dense structure.

[0023] Furthermore, the antifreeze multifunctional hydrogel sensor is a strain-type flexible sensor, which obtains the resistance change signal by the change in ion conduction path when the hydrogel is stretched.

[0024] or,

[0025] The pressure-type flexible sensor obtains the resistance change signal by detecting the change in ion conductivity path when the hydrogel is compressed.

[0026] or,

[0027] A temperature-sensitive flexible sensor obtains the resistance change signal by measuring the change in ionic conductivity in a hydrogel with temperature.

[0028] The third aspect of the present invention provides an application of the above-mentioned antifreeze multifunctional hydrogel sensor, which is used as a wearable sensor for human motion monitoring, pressure detection, and temperature sensing, and can be used indoors, underwater or in extreme environments below -70°C.

[0029] At the mechanistic level, this invention first constructs a composite network (PVA / OCMC-Na / Gel) based on a PVA main framework. After hydration with magnesium chloride or its hydrated salt, it undergoes rapid directional freezing in a liquid nitrogen environment, followed by immersion in a water-glycerol binary solution of sodium citrate or its hydrated salt to strengthen the composite hydrogel. PVA serves as the main framework, providing the mechanical strength of the main body; OCMC-Na provides hydrophobic groups and metal ion coordinating groups, and forms a Schiff base reversible bond with Gel, enhancing the hydrogel's toughness; on the other hand, free ions with salt-dissolving effects (such as Cl-)... - This introduces free water, alleviating localized aggregation of polymer chains, promoting the uniform formation of crystal nuclei under directional freezing, and achieving the construction of an anisotropic framework; in the water-glycerol binary solution of sodium citrate or its hydrated salt, free salting-out effect ions (such as Ct) 3- The citrate ion (a component of the hydrogel) further strengthens the bonding of polymer chains on the oriented framework by inhibiting hydration, thereby improving the mechanical properties and anisotropy of the hydrogel. Free ions also form conductive pathways within the hydrogel, enhancing its conductivity as they migrate. The anisotropic structure allows for rapid strain response, increasing the hydrogel's strain sensitivity, thus enabling its assembly into wearable sensors to detect various strain movements of the body. This multidimensional coordination mode and water-mediated interchain bonding modulation achieve effective performance enhancement at low ion salt concentrations, contributing to excellent biocompatibility. Furthermore, the hydrogel possesses a synergistic salt-water-glycerol system and strong internal bonding, maintaining stability under high / low temperature conditions and enabling effective strain sensing underwater and in cryogenic environments.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) Based on polyvinyl alcohol, sodium carboxymethyl cellulose oxide and gelatin, the present invention uses a directional freezing method to crosslink hydrogels, so that the interior of the composite hydrogel has a multi-dimensional coordination environment of physical crosslinking, Schiff base bonding and ion coordination, which is conducive to the uniform dissipation of internal stress and improves the strength of hydrogels; the coordination with ions can further construct internal conductive paths and enhance the conductivity of hydrogels; at the same time, the directional structure is also conducive to generating large signal changes under strain, which is beneficial to improving the sensing sensitivity.

[0032] (2) This invention utilizes a multi-component design and the synergistic effect of ion salt-water mediated stepwise modulation with salt-dissolution / salting-out effects to prepare an antifreeze multifunctional hydrogel (PCG-x). This effectively solves the technical problem of poor performance integration in traditional hydrogel sensors and overcomes the challenge of mutual constraints between mechanical strength, ionic conductivity, and biocompatibility in traditional hydrogel materials. The prepared PCG-x can provide a stress strength of 4.9 MPa at 739% elongation and has a strength of 4.2 mS / cm. -1 The high ionic conductivity and -92.1℃ antifreeze properties of the hydrogel greatly enhance its reliability in practical sensing applications, enabling it to maintain stable signal changes during frequent deformation in all weather conditions. In vivo compatibility tests also show that PCG-x hydrogel can remain in vivo for a long time without causing adverse symptoms such as rejection or inflammation, ensuring safety for long-term use.

[0033] (3) The present invention enhances the conductivity of hydrogel based on ion-conductive filler and enables hydrogel sensor to sense different stimuli. It is assembled into a multi-mode sensor by connecting it with an electrical signal detection device with wires. It can identify the strain generated by the body, external pressure and temperature changes, effectively solving many problems of current sensing hydrogel.

[0034] (4) The hydrogel sensor provided by this invention has an ionic salt-water-glycerol synergistic system, which realizes enhanced locking of internal moisture and has the ability to be used in special scenarios such as high temperature / low temperature and underwater. This hydrogel can be worn to achieve high sensitivity and high stability strain sensing in indoor, underwater and below -70℃ environments;

[0035] (5) The hydrogel sensor provided by this invention can be applied to all-weather motion monitoring and information interaction devices, including wearable sensors made of hydrogel, and has a relatively simple structure. Because hydrogel itself has multifunctional integration and high environmental tolerance, it can reduce the use of additional components and the limitations of usage conditions, avoid the complex multi-layer design in traditional sensors, and improve the integration and wide applicability of the product. Attached Figure Description

[0036] Figure 1 This invention relates to a method for preparing the antifreeze multifunctional hydrogel.

[0037] Figure 2 SEM images of the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Example 3 before and after immersion in salting-out solution for reinforcement.

[0038] Figure 3 Stress-strain curves of the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Examples 1-4;

[0039] Figure 4 EIS curves of the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Examples 1-4;

[0040] Figure 5 The graph shows the actual electrical conductivity of the antifreeze multifunctional hydrogel prepared in Example 3 and the change in bulb brightness with stretching.

[0041] Figure 6 DSC curves of the antifreeze multifunctional hydrogels prepared in Comparative Examples 1-2 and Example 3;

[0042] Figure 7 The results of basketball activity monitoring in Example 1 are used;

[0043] Figure 8 The results are from the monitoring of different finger bending amplitudes in the dry ice environment in Application Example 2.

[0044] Figure 9 The results of cytotoxicity testing are for the antifreeze multifunctional hydrogels prepared in Comparative Example 1 and Examples 1, 3, and 4. Detailed Implementation

[0045] The preparation method of the antifreeze multifunctional hydrogel sensor in this invention is described in [reference needed]. Figure 1 Wherein, 'a' corresponds to the endpoint of the traditional technical path, namely, the inherent defects in the final product performance due to the disorder of the initial structure; 'b' corresponds to the ion-water mediated stepwise modulation strategy of first dispersing, then orienting, and finally strengthening in this invention. The initially disordered mixture is woven into a structurally robust and high-performance functional material through precise control of physicochemical processes. Specifically: polyvinyl alcohol (PVA), sodium oxidized carboxymethyl cellulose (OCMC-Na), and gelatin are added to an aqueous solution of magnesium chloride or its hydrated salt and heated and stirred until uniformly mixed. A precursor hydrogel is then directionally frozen and oriented in a liquid nitrogen environment, and strengthened in a water-glycerol binary solution of sodium citrate or its hydrated salt to obtain a composite hydrogel. The composite hydrogel is then connected to wires and electrical signal detection devices to assemble a flexible sensor for strain, pressure, or temperature sensing.

[0046] In practice, the water includes deionized water or distilled water.

[0047] In a specific implementation, the mass ratio of polyvinyl alcohol, sodium carboxymethyl cellulose oxide, and gelatin in the preparation method of the antifreeze multifunctional hydrogel sensor is 1:(0.05-0:3):(0.05-0.3).

[0048] In specific implementation, preferably, the ratio of polyvinyl alcohol (PVA), sodium oxidized carboxymethyl cellulose (OCMC-Na), and gelatin is fixed at 1:0.1:0.1.

[0049] In specific implementation, the mass ratio of water to magnesium chloride or its hydrated salt is 1:(0.02-0.4), preferably 1:0.17.

[0050] In practice, the temperature at which the component is heated and stirred with an aqueous solution of magnesium chloride or its hydrated salt is 50-100℃.

[0051] In practice, the stirring time is 30-90 minutes.

[0052] In practice, the liquid nitrogen directional freezing time is 10-40 minutes.

[0053] In specific implementation, the mass ratio of water to glycerol in the water-glycerol binary solvent is 1:(0.5-1.5), preferably, the volume ratio of water to glycerol is 1:1.

[0054] In specific implementation, the mass ratio of the water-glycerol binary solvent to sodium citrate or its hydrated salt is 1:(0.02-0.25).

[0055] In specific implementation, the mass ratio of the water-glycerol binary solution of sodium citrate or its hydrated salt to the precursor hydrogel is 1:(0.02-0.1).

[0056] In specific implementation, the sodium citrate or its hydrated salt is soaked in a water-glycerol binary solution for 12-48 hours.

[0057] Specifically, the key raw material is sodium carboxymethyl cellulose oxide, which is prepared by dissolving and mixing sodium carboxymethyl cellulose and sodium periodate separately, reacting them under acidic conditions, adding ethanol to precipitate the precipitate, washing with ethanol, centrifuging three times, and drying in an oven.

[0058] In practice, the solvent for the solution is deionized water.

[0059] In specific implementation, the mass fraction of the sodium carboxymethyl cellulose solution is 2-10 wt%.

[0060] In practice, the sodium periodate solution has a mass fraction of 2-10 wt%.

[0061] In specific implementation, the volume ratio of the sodium carboxymethyl cellulose solution to the sodium periodate solution is 1:(0.25-1).

[0062] In practice, the additive for the acidic conditions is hydrochloric acid or sulfuric acid.

[0063] In practice, the volume of the hydrochloric acid or sulfuric acid is 100-300 μL.

[0064] In practice, the reaction time is 3-6 hours.

[0065] In practice, the drying temperature is 30-45 ℃.

[0066] In practice, the drying time is 8-12 hours.

[0067] The present invention also provides the application of the antifreeze multifunctional hydrogel described in the above technical solution or the antifreeze multifunctional hydrogel described in the above technical solution in flexible sensors.

[0068] Specifically, the antifreeze multifunctional hydrogel can be used as a wearable temperature, pressure, and strain sensor.

[0069] It should be noted that the first embodiment of the present invention provides an antifreeze multifunctional hydrogel, comprising a polyvinyl alcohol hydrogel, a sodium carboxymethyl cellulose oxide and gelatin composite network dispersed in the polyvinyl alcohol hydrogel, and ionic salts, water, and glycerol in the composite hydrogel. The ionic salts are used to stepwise regulate the interactions between polymer chains.

[0070] This implementation method utilizes the differences in hydration effects of different salt ions to stepwise regulate the interaction between polymer chains and free water molecules, promoting the formation of a highly uniform and oriented composite network in the polymer system. Ions with salt-dissolving effects first alleviate the aggregation phenomenon within the polymer chains, constructing a highly oriented and uniform framework during directional freezing; ions with salting-out effects further expel excess free water molecules from the framework, promoting further bonding and strengthening of the framework; and water-glycerol replacement enhances the overall water retention and freeze resistance. This strategy enables the prepared hydrogel to provide a stress strength of 4.9 MPa at 739% elongation and exhibits a strength of 4.2 mS / cm. -1 Its high ionic conductivity, -92.1℃ antifreeze performance, and excellent biocompatibility effectively solve the technical problem of poor performance integration in traditional hydrogels, and break through the problem of mutual constraints between mechanical strength, ionic conductivity and biocompatibility in traditional hydrogel materials.

[0071] It should be noted that the water that can be used in the embodiments of the present invention includes deionized water, distilled water, etc.

[0072] It should also be noted that ionic salts with salt-dissolving effect are applicable to this invention. Ions with salt-dissolving effect will first break the hydrogen bonds between polymer chains, introduce more free water molecules, form more uniform crystallization sites during directional freezing, and construct a highly oriented uniform framework.

[0073] It should be noted that the second embodiment of the present invention provides a method for preparing the multifunctional, environmentally resistant hydrogel of the first embodiment. Polyvinyl alcohol, sodium carboxymethyl cellulose oxide and gelatin are mixed evenly with an aqueous solution of magnesium chloride or its hydrated salt, poured into a mold and directionally frozen in liquid nitrogen, and then reinforced by immersion in an aqueous-glycerol binary solution of sodium citrate or its hydrated salt.

[0074] It should be noted that since the function of magnesium chloride or its hydrated salt is to break the uneven hydrogen bond entanglement of polymer chains, polyvinyl alcohol, sodium carboxymethyl cellulose oxide and gelatin components need to be added to the aqueous solution of magnesium chloride or its hydrated salt, rather than adding magnesium chloride or its hydrated salt to the solution-gel mixture formed by polyvinyl alcohol, sodium carboxymethyl cellulose oxide and gelatin for adjustment.

[0075] There are no particular limitations on the temperature and time for heating and stirring, as long as uniform mixing is achieved. Those skilled in the art can adjust the time according to the suitability of the reactants. In some preferred embodiments, the stirring temperature is 90-100°C and the stirring time is 30-90 minutes.

[0076] There is no particular limitation on the freezing time, as long as it achieves firm freezing. Those skilled in the art can adjust it adaptively according to the actual situation. In some preferred embodiments, the freezing time is 10-40 minutes.

[0077] There is no particular limitation on the soaking time of the water-glycerol binary solution of sodium citrate or its hydrated salt, as long as uniform strengthening is achieved. Those skilled in the art can adjust the time according to the actual situation. In some preferred embodiments, the soaking time is 12-48 hours.

[0078] It should be noted that the third embodiment of the present invention provides the application of the multifunctional, environmentally resistant hydrogel of the first embodiment in multimodal monitoring and multi-environment sensing.

[0079] Multi-mode monitoring scenarios include monitoring human movement (such as swallowing, finger movements, running, shooting, etc.), pressure changes (such as writing, etc.), and temperature changes (such as cold water, hot water, etc.), and can obtain relevant information in real time.

[0080] Multi-environment sensing scenarios are built based on wearable sensors, including environments such as tap water, seawater, and extremely low temperatures, to meet the actual needs of different fields.

[0081] The multi-mode monitoring equipment to which this invention can be applied includes wearable sensors, pressure sensors, and temperature sensors.

[0082] The specific monitoring principle of wearable sensors is as follows: (1) They can generate electrical signals corresponding to "points" when the fingers are bent for a short time, and "strokes" when the fingers are bent for a long time. This allows for the efficient transmission of complex information such as "SOS", "FDU", and "CALL". (2) When placed on the throat, different volumes can be distinguished by analyzing the waveform, and swallowing actions can also be monitored. (3) When placed on different parts such as the wrist, the differences in technical movements in complex sports such as basketball can be distinguished based on different waveforms, which is beneficial for further analysis of technical characteristics.

[0083] The pressure sensor works on the principle that hydrogel is compressible and can generate a changing waveform in response to the pressure applied during writing, thereby sensing the pressure.

[0084] When a temperature sensor measures temperature changes, it works by recognizing the difference in transmission rate of ions at different temperatures. This difference in resistance signals is generated in water at different temperatures, which is then used to determine the temperature difference.

[0085] The multi-environment sensing scenario is based on wearable sensors and further constructs swimming motion recognition in tap water, information transmission of finger movements in seawater, and gesture information communication under freezing conditions. The main principles are: (1) Wearable sensors are attached to the legs and perform leg kicking movements in tap water to output waveforms for rapid movement changes; (2) Wearable sensors are attached to the fingers and generate corresponding "point" electrical signals for short-term bending of the fingers in seawater environment, while long-term bending represents "sweeping", thereby efficiently transmitting complex information such as "UP", "DOWN", "HELP"; (3) Wearable sensors are attached to different fingers and generate corresponding high / low triangular wave electrical signals for different degrees of bending in an environment of -76.6℃, and generate flat wave output signals for no bending, thereby transmitting different complex gesture communication information.

[0086] In this embodiment of the invention, the material exhibits excellent biosafety in cellular experiments, without inducing significant toxic reactions, demonstrating good biocompatibility. This characteristic provides a reliable guarantee for its application in the biomedical field and further broadens its potential application scenarios.

[0087] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0088] Example 1

[0089] Preparation of multifunctional, environmentally resistant hydrogels

[0090] Weigh 0.203 g of MgCl2·6H2O and dissolve it in 6 g of water, stirring until completely dissolved. Then add 0.1 g of sodium carboxymethyl cellulose oxide (OCMC-Na) and stir at 50 °C for 20 minutes. Next, add 1.0 g of polyvinyl alcohol (PVA), raise the temperature to 90 °C, and stir for 60 minutes to obtain precursor solution A. Add 0.1 g of gelatin to 3 g of water and stir at 50 °C for 20 minutes to obtain precursor solution B. Mix precursor solutions A and B and continue stirring for 20 minutes. Then allow to stand to eliminate air bubbles to obtain hydrogel precursor solution. Pour the hydrogel precursor solution into a mold and immerse one end of the mold in liquid nitrogen for 15 minutes to completely freeze the precursor solution and achieve preliminary cross-linking, obtaining the precursor hydrogel. The precursor hydrogel was immersed in 200 mL of a water-glycerol mixed solution containing 5.86 g Na3Ct·2H2O (water to glycerol volume ratio of 1:1) and allowed to stand for 24 h to obtain a multifunctional, environmentally resistant hydrogel, named PCG-0.1.

[0091] Example 2

[0092] Preparation of multifunctional, environmentally resistant hydrogels

[0093] Same as Example 1, except that 0.406 g of MgCl2·6H2O was weighed. The resulting multifunctional, environmentally resistant hydrogel was named PCG-0.2.

[0094] Example 3

[0095] Preparation of multifunctional, environmentally resistant hydrogels

[0096] Same as Example 1, except that 1.015 g of MgCl2·6H2O was weighed. The resulting multifunctional, environmentally resistant hydrogel was named PCG-0.5.

[0097] Example 4

[0098] Preparation of multifunctional, environmentally resistant hydrogels

[0099] Same as Example 1, except that 2.03 g of MgCl2·6H2O was weighed. The resulting multifunctional, environmentally resistant hydrogel was named PCG-1.0.

[0100] Comparative Example 1

[0101] The only difference from Example 1 was the absence of MgCl2·6H2O. The resulting hydrogel was named PCG.

[0102] Comparative Example 2

[0103] Compared to Example 1, the difference lies in the absence of MgCl2·6H2O, OCMC-Na, and Gel. The resulting hydrogel was named PVA.

[0104] Verification Example 1

[0105] Performance testing

[0106] Figure 2 SEM images of the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Example 3 before and after immersion in salting-out solution for reinforcement. Figure 2 As can be seen from Figure a, the comparative example exhibits internal aggregation after directional freezing, which also leads to the continued presence of non-uniform morphology such as pores even after salting-out enhancement; from Figure 2 As can be seen from Figure b, after the salt-soluble ions are deagglomerated, Example 3 can form a uniform porous structure after directional freezing. This is beneficial for further uniform enhancement of salting out, resulting in a directional and compact structure.

[0107] Figure 3 The stress-strain curves are for the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Examples 1-4. All Examples 1-4 showed enhanced stress-strain properties compared to the Comparative Example, with Example 3 exhibiting the strongest mechanical properties, providing a stress strength of 4.9 MPa at 739% elongation.

[0108] Figure 4 The EIS curves of the antifreeze multifunctional hydrogels prepared in Comparative Example 2 and Examples 1-4 are shown. All Examples 1-4 exhibited reduced impedance compared to the comparative examples, indicating improved conductivity. Among them, Example 3 showed an ionic conductivity of 4.2 mS / cm. -1 .

[0109] Figure 5 The graph shows the actual conductivity of the antifreeze multifunctional hydrogel prepared in Example 3 and the change in bulb brightness with stretching. The bulb can be lit at a low voltage of 4V and dims as the hydrogel is stretched, indicating that the hydrogel not only has good conductivity, but also increases resistance when stretched, showing responsiveness to strain, indicating its potential to be made into a flexible strain sensor.

[0110] Figure 6 The DSC curves of the antifreeze multifunctional hydrogels prepared in Comparative Examples 1-2 and Example 3 are shown. The glass transition temperature of Example 3 is as low as -92.1℃, indicating that it has the ability to work in cold environments.

[0111] Application Example 1

[0112] Ionized hydrogels for motion monitoring

[0113] The hydrogel from Example 3 was placed at the wrist joint, with electrodes connected to both ends. Simulations of basketball shooting, dribbling, and passing movements were performed to obtain the resistance change rate for each movement. Recording the resistance change rate and time yielded response data for different movements. Figure 7 As shown.

[0114] Application Example 2

[0115] Ionic hydrogels for motion detection under freezing conditions

[0116] The hydrogel from Example 3 was placed on the fingertips of a freeze-proof glove, with electrodes connected to both ends. In an extremely cold dry ice environment at -76.6°C, the fingers were bent and extended with gradually increasing amplitude. The resulting relative resistance change signal corresponding to the amplitude change indicates that the hydrogel prepared in this invention still possesses good reliability for monitoring human movement in extremely cold environments. Figure 8 As shown.

[0117] Figure 9 The results of cytotoxicity testing of the antifreeze multifunctional hydrogels prepared in Comparative Example 1 and Examples 1, 3, and 4 are shown. Live / Dead staining showed that green live cells were the main component in each group from 24 to 72 h, with very few red dead cells. The PCG and 0.1-1.0 groups were comparable to the control, with intact cell morphology and increased density over time. No dose-dependent toxicity was observed, indicating that the material has good cell compatibility.

[0118] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a freeze-resistant multifunctional hydrogel sensor, characterized in that, Includes the following steps: S1. Add polyvinyl alcohol, sodium carboxymethyl cellulose oxide, and gelatin to an aqueous solution of magnesium chloride or its hydrated salt, heat and stir, so that magnesium chloride or its hydrated salt can break the hydrogen bond entanglement between polymer chains through hydration, promote uniform dispersion of components, and obtain a uniformly mixed precursor solution. S2. Pour the precursor solution into a mold and perform directional freezing in a liquid nitrogen environment to rapidly freeze the precursor solution and construct a precursor hydrogel with a directional and dense structure. S3. The precursor hydrogel is placed in a water-glycerol binary solution of sodium citrate or its hydrated salt for immersion and strengthening. Sodium citrate or its hydrated salt promotes the strengthening of inter-polymer chain bonding by inhibiting hydration, and the water-glycerol binary solvent provides water retention and antifreeze properties, resulting in a composite hydrogel with high mechanical strength, ionic conductivity and antifreeze properties. S4. Connect the composite hydrogel to wires and electrical signal detection equipment to assemble it into a flexible sensor for strain, pressure or temperature sensing.

2. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S1, the mass ratio of polyvinyl alcohol, sodium carboxymethyl cellulose oxide, and gelatin is 1:0.05-0.3:0.05-0.

3.

3. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S1, the mass ratio of water to magnesium chloride or its hydrated salt in the aqueous solution is 1:0.02-0.

4.

4. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S3, the mass ratio of water to glycerol in the water-glycerol binary solvent is 1:0.5-1.5; The mass ratio of the water-glycerol binary solvent to sodium citrate or its hydrated salt is 1:0.02-0.

25.

5. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S3, the mass ratio of the water-glycerol binary solution of sodium citrate or its hydrated salt to the precursor hydrogel is 1:0.02-0.

1.

6. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S1, the heating and stirring temperature is 50-100℃, and the stirring time is 30-90 minutes.

7. The method for preparing an antifreeze multifunctional hydrogel sensor according to claim 1, characterized in that, In S2, the directional freezing time is 10-40 minutes; In S3, the soaking time for strengthening is 12-48 hours.

8. A freeze-resistant multifunctional hydrogel sensor obtained by the preparation method according to any one of claims 1 to 7, characterized in that, The antifreeze multifunctional hydrogel sensor has a directional dense structure.

9. The antifreeze multifunctional hydrogel sensor according to claim 8, characterized in that, The aforementioned antifreeze multifunctional hydrogel sensor is a strain-type flexible sensor that obtains resistance change signals by detecting changes in the ion conduction path when the hydrogel is stretched. or, The pressure-type flexible sensor obtains the resistance change signal by detecting the change in ion conductivity path when the hydrogel is compressed. or, A temperature-sensitive flexible sensor obtains the resistance change signal by measuring the change in ionic conductivity in a hydrogel with temperature.

10. An application of the antifreeze multifunctional hydrogel sensor as described in claim 8, characterized in that, The antifreeze multifunctional hydrogel sensor, as a wearable sensor, is used for human motion monitoring, pressure detection, and temperature sensing, and can operate indoors, underwater, or in extreme environments below -70°C.

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