Preparation and application of cross-linked network hydrogel material under action of freeze-thaw cycle

Abstract

The invention discloses preparation and application of a cross-linked network hydrogel material under the action of freeze-thaw cycles, and relates to the technical field of application materials, the prepared hydrogel material comprises a main chain monomer, a comonomer, a cross-linking agent, an initiator, a moisturizing enhancer and a pH regulator; the composite material further comprises phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres and a hyperbranched synergistic network. According to the preparation method disclosed by the invention, novel additive components with structure guidance and function synergy capability, such as the phosphorylated lignin nanoparticles, the benzothiazole chitin derivative, the modified porous carbon microspheres and the hyperbranched synergy network, are introduced, so that the mechanical flexibility and the water retention and frost resistance of the hydrogel at the temperature of-20 DEG C or below are effectively improved; and the electric responsiveness, intelligent release regulation and control and stable construction of a multi-scale channel structure of the material are also realized, and the problems of strong mobility, unstable structure and single function of the existing anti-freezing additive are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of applied materials, in particular to the preparation and application of cross-linked network hydrogel materials under freeze-thaw cycles. Background Art

[0002] As a flexible material with a high water content and a three-dimensional cross-linked network structure, hydrogel has been widely used in fields such as tissue engineering, soft electronics, drug controlled release, and cryogenic buffering due to its excellent biocompatibility, adjustable mechanical properties, and good environmental responsiveness. In recent years, in order to improve the comprehensive performance of hydrogels in low temperature, complex mechanical or multifunctional scenarios, researchers have generally adopted a double-network hydrogel design strategy that combines a freeze-thaw cycle-induced physical cross-linking structure with a chemical covalent cross-linking network, in order to achieve a balance between strength and flexibility of the material. However, the double-network hydrogels constructed in the existing technology still have the following major problems: First, most hydrogel systems exhibit significant embrittlement and hardening at temperatures below -10°C. The fundamental reason is the lack of a stable water-retaining framework and antifreeze mechanism within the material. Commonly used additives to improve antifreeze properties, such as glycerol, urea, salts, or polyethylene glycol, rely on lowering the freezing point and limiting crystal formation. However, these ingredients suffer from defects such as easy migration, rapid failure, and mechanical property degradation, making it difficult to maintain long-term material stability.

[0003] Secondly, in order to enhance the environmental response and intelligent sensing capabilities of hydrogels, studies have attempted to introduce conductive fillers or functional nanoparticles, such as carbon nanotubes, graphene oxide or metal ions. Although this has improved the functionality to a certain extent, such additives are prone to aggregation or biotoxicity reactions in hydrogels, and lack a synergistic construction mechanism with the three-dimensional network structure, making it difficult to balance flexibility, responsiveness and safety.

[0004] Therefore, existing technologies urgently need to develop a hydrogel material that can maintain softness and functional stability in low-temperature environments and has a multiple network collaborative construction mechanism, and it is necessary to break through the existing bottleneck through an additive system with controllable structure, stable interface and highly integrated functions. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides the preparation and application of a cross-linked network hydrogel material under freeze-thaw cycles to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a cross-linked network hydrogel material under freeze-thaw cycle conditions. The hydrogel material comprises the following specific components: Main chain monomers, comonomers, cross-linking agents, initiators, moisturizing enhancers and pH adjusters; The hydrogel material further comprises additives, which specifically include: Phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres, and hyperbranched synergistic networks.

[0007] To further optimize this technical solution, the mass fractions of the specific components are as follows: The main chain monomer is 40-60 parts; The comonomer is 10-20 parts; The cross-linking agent is 0.05-0.5 parts; The initiator is 0.1-0.5 parts; Moisturizing enhancer is 5-20 parts; The pH adjuster is 1-5 parts.

[0008] To further optimize this technical solution, the mass fractions of the additives are as follows: 3-10 parts of phosphorylated lignin nanoparticles; 2-8 parts of benzothiazole chitosan derivative; Modified porous carbon microspheres are 1-5 parts; The hyperbranched cooperative network is 0.5-2 copies.

[0009] To further optimize this technical solution, the specific components include: The main chain monomer is polyvinyl alcohol (PVA), which is a linear polymer with a repeating structural unit of [-CH2CH(OH)-]. The comonomer is acrylamide AAm, which is a small molecule monomer containing polymerizable double bonds and amide groups; The cross-linking agent is N,N'-methylenebisacrylamide MBAA, which has two double bonds in its molecular structure; The initiators are ammonium persulfate APS and N,N,N',N'-tetramethylethylenediamine TEMED. APS is a thermal initiator and TEMED is an accelerator, which form free radicals at room temperature. The moisturizing enhancer is glycerin, which, as a triol, contains three hydroxyl groups in its molecule; The pH regulator is triethanolamine TEA, which is an organic alkaline compound used to adjust the pH value of the hydrogel material.

[0010] Further optimizing this technical solution, the phosphorylated lignin nanoparticles use lignin from natural plant sources as raw material, and undergo a phosphating reaction under alkaline conditions using a phosphating agent to introduce phosphate functional groups into the lignin molecular chain; Subsequently, the modified lignin is treated with high-energy ultrasound and high-shear homogenization to control the particle size within the range of 30-100 nm, thereby obtaining nanoparticles with uniform particle size distribution.

[0011] Further optimizing the technical solution, the benzothiazole chitosan derivative is synthesized by amidation reaction of high-purity chitosan with a deacetylation degree ≥80% and 2-aminobenzothiazole in the presence of a carbodiimide condensation agent; This reaction covalently grafts the benzothiazole ring onto the chitin backbone through an amide bond. The resulting product retains the multi-hydroxyl / amino active sites of chitin and introduces a new thiazole electron conjugation system.

[0012] Further optimizing the technical solution, the modified porous carbon microspheres are formed into primary carbon spheres by hydrothermal carbonization of a glucose solution at 180-200°C for 6-8h; Then, thermal activation was performed under nitrogen protection to obtain a porous structure with a specific surface area greater than 300 m² / g and a pore size concentrated in the range of 20-50 nm; Subsequently, biological amino acids such as L-lysine or L-histidine are used to undergo covalent or ion adsorption with the active sites on the microsphere surface to achieve amino acid functionalization coating.

[0013] The technical solution is further optimized. The hyperbranched synergistic network is a hyperbranched polyamide-polyester synergistic network, which is prepared by a gradual polycondensation reaction with adipoyl chloride and lactic acid under solvent method conditions with pentaerythritol as the core initiator. The molecular structure contains a large number of terminal carboxyl groups -COOH, amino groups -NH2 and ester bond bridging units, presenting a highly branched molecular network.

[0014] Further optimizing the technical solution, the preparation method of the hydrogel material comprises the following specific steps: S1. Preparation of main chain monomer and comonomer compound system; S2, cross-linking agent and moisturizing enhancer compound addition; S3, simultaneous pretreatment activation of pH regulator and initiator; S4, multi-stage synergistic dispersion of additives; S5, mold forming and freeze-thaw cycle induced cross-linking structure construction; S6. Drying and stabilization treatment.

[0015] The application of cross-linked network hydrogel materials under freeze-thaw cycles is based on the above-mentioned hydrogel materials and includes the following specific application scenarios: Scenario A: The prepared hydrogel material is cut into an appropriate size and shape and implanted into the desired contact interface or embedded into a supporting frame structure. The proportion of phosphorylated lignin nanoparticles is adjusted as needed to achieve a buffering response with different elastic modulus ranges at low temperatures. Scenario B: Before the preparation step S4, the target release substance is uniformly premixed with a solution and loaded into the system. During the polymerization and freeze-thaw formation process, the target molecule is physically embedded or chemically adsorbed into the internal network nodes. When the material is exposed to external physiological fluids or water environment, it is slowly released in an orderly manner according to the osmotic gradient or pH value. The release rate is controlled by adjusting the cross-linker content. Scenario C: The prepared hydrogel material is thinned and integrated as a sensing membrane onto a flexible circuit board, with the peripheral electrode structure formed by screen printing or conductive ink. Scenario D: The prepared hydrogel material is refrigerated and then applied directly to the skin or wound surface. The material absorbs exudate and slowly releases a cooling sensation, effectively alleviating local swelling and micro-inflammatory reactions.

[0016] Compared with the prior art, the present invention provides the preparation and application of cross-linked network hydrogel materials under freeze-thaw cycles, which has the following beneficial effects: The preparation and application of cross-linked network hydrogel materials under freeze-thaw cycles, by introducing new additives with structural guidance and functional synergy such as phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres and hyperbranched synergistic networks, not only effectively improves the mechanical flexibility and water retention and antifreeze properties of the hydrogel below -20°C, but also realizes the electrical responsiveness, intelligent release regulation and stable construction of multi-scale channel structures of the material, overcoming the problems of strong migration, structural instability and single function of existing antifreeze additives, and has broad application potential and promotion value in the fields of extreme environment response, flexible electronics and biomedical materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of the composition of the cross-linked network hydrogel material under freeze-thaw cycle proposed by the present invention; Figure 2 This is a schematic flow chart of the method for preparing a cross-linked network hydrogel material under freeze-thaw cycles proposed in the present invention. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it constitute a separate or selective embodiment that is mutually exclusive with other embodiments.

[0022] Example 1: Reference Figures 1 and 2 , which is the first embodiment of the present invention, provides a preparation method for a cross-linked network hydrogel material under freeze-thaw cycle, wherein the hydrogel material comprises the following specific components: Main chain monomers, comonomers, crosslinking agents, initiators, moisturizing enhancers and pH adjusters.

[0023] In this embodiment, the mass fractions of the specific components are as follows: The main chain monomer is 40 parts; The comonomer is 10 parts; The cross-linking agent is 0.05 parts; The initiator is 0.1 parts; Moisturizing enhancer is 5 parts; The pH adjuster is 1 part.

[0024] Among the specific components: The main chain monomer is polyvinyl alcohol (PVA), a linear polymer with a repeating structural unit of [-CH2CH(OH)-]. During freeze-thaw cycles, PVA rearranges its chain segments to form numerous crystalline domains, which serve as physical crosslinks to construct a three-dimensional network structure. Its excellent hydrophilicity gives the hydrogel excellent water content and swelling properties. Furthermore, the PVA molecular chains can form hydrogen or covalent bonds with a variety of functional substances, facilitating subsequent functionalization design.

[0025] The comonomer is acrylamide (AAm), a small molecule containing polymerizable double bonds and amide groups. During freeze-thaw cycles, AAm initiates polymerization, forming a cross-linked branched network within the system and enhancing mechanical properties. The amide groups form hydrogen bonds with PVA segments, further enhancing the gel's elasticity and toughness. Furthermore, the presence of AAm can modulate the gel's swelling ratio and network density.

[0026] The crosslinker is N,N'-methylenebisacrylamide (MBAA), which has two double bonds in its molecular structure. Through free radical-initiated polymerization, MBAA forms covalent crosslinks between multiple chain segments, imparting enhanced stability and mechanical strength to the gel. The synergistic effects of freeze-thaw crosslinking and chemical crosslinking create a dual network structure, enhancing fatigue resistance.

[0027] The initiators are ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED) (APS: 0.05 parts, TEMED: 0.05 parts). APS acts as a thermal initiator, and TEMED acts as an accelerator, generating free radicals at room temperature. This initiation system effectively stimulates the polymerization of double-bonded monomers such as AAm, forming an initial chemical crosslinking network that provides the framework for the formation of freeze-thaw crosslinks. This system has high initiation efficiency and reacts rapidly at low temperatures, facilitating stable subsequent freeze-thaw cycles.

[0028] The moisturizing enhancer is glycerol, a triol containing three hydroxyl groups. As a hydrophilic small molecule, glycerol forms stable hydrogen bonds with water, enhancing the gel's water absorption and freeze resistance. During freeze-thaw cycles, glycerol inhibits the formation and growth of ice crystals, reduces damage to the polymer network, and maintains the stability of the gel's mechanical properties.

[0029] The pH adjuster is triethanolamine (TEA), an organic alkaline compound used to adjust the pH of hydrogel materials. Controlling the pH environment of the polymerization reaction promotes uniform polymerization of monomers, improving the uniformity of the network structure and the stability of the final gel. In certain functionalized reaction systems, TEA can also act as a complexing agent to regulate the activity of functional groups.

[0030] The above components show obvious synergistic relationship during the formation of freeze-thaw cross-linked hydrogel: PVA acts as the main chain to provide the main structure, and physical cross-linking points are formed by freeze-thaw induction; AAm introduces chemical cross-linking to improve network density and controllability; MBAA ensures multi-point connectivity and a stable three-dimensional network; The APS / TEMED system activates free radical reactions and promotes cross-linking to form a network; Glycerol inhibits ice crystal growth and ensures the integrity of the gel under repeated freeze-thaw cycles; TEA optimizes the reaction environment of the system and improves the polymerization stability of the system.

[0031] The above basic system provides a good chemical environment and structural foundation for the subsequent introduction of additives, ensuring that the additives can be fully embedded and achieve functional synergy.

[0032] The hydrogel material further comprises additives, which specifically include: Phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres, and hyperbranched synergistic networks.

[0033] In this embodiment, the mass fractions of the additives are as follows: phosphorylated lignin nanoparticles were 3 parts; benzothiazole chitosan derivative is 2 parts; Modified porous carbon microspheres are 1 part; The hyperbranched collaborative network is 0.5 copies.

[0034] The phosphorylated lignin nanoparticles (PLNPs) are made from natural plant-derived lignin. Phosphate groups are introduced into the lignin molecular chains using a phosphating agent (such as phosphorus oxychloride (POCl3) or phosphoric anhydride) under alkaline conditions. High-energy ultrasonic treatment and high-shear homogenization are then applied to control the particle size of the modified lignin to within 30-100 nm, resulting in nanoparticles with a uniform size distribution.

[0035] The abundant phosphate groups (-PO3H2) and phenolic hydroxyl structures (-OH) on the PLNP surface can form multiple hydrogen bonds and esterification reaction sites with the hydroxyl groups of PVA and the amide groups of AAm in the hydrogel system, constructing a highly cross-linked dynamic network. The porous structure of the nanoparticles restricts the migration of water molecules, buffers nucleation during freezing, and significantly inhibits the embrittlement of the hydrogel at low temperatures. The phosphate structure also imparts flame retardancy to the material. Dynamic hydrogen bonding allows for local network reconstruction after freeze-thaw damage, imparting a degree of self-healing capability. Unlike conventional nano-silica and graphene oxide, PLNP possesses the multiple properties of biodegradability, thermal stability, and ion chelation, forming a "multifunctional composite reinforcement" model that overcomes the single-function nature of traditional additives.

[0036] The benzothiazole chitin derivative is synthesized by an amidation reaction between high-purity chitin with a deacetylation degree of ≥80% and 2-aminobenzothiazole in the presence of a carbodiimide condensing agent (such as EDC). This reaction covalently grafts the benzothiazole ring onto the chitin backbone via an amide bond. The resulting product retains the chitin's multiple hydroxyl / amino active sites while introducing a new thiazole-based electronic conjugation system.

[0037] Benzothiazole groups can capture reactive oxygen species (ROS), significantly enhancing the antioxidant properties of hydrogels. Their aromatic structure has strong binding ability with microbial membrane proteins, exhibiting excellent antibacterial properties, making them particularly suitable for biomedical hydrogel systems. Residual amino groups in the grafted structure can form hydrogen bonds with the hydrogel backbone (such as PVA), helping to build a secondary physical network and enhance overall mechanical strength. The benzothiazole ring can also chelate with metal ions such as Cu²⁺ and Zn²⁺, giving the hydrogel intelligent responsiveness. Compared to traditional unmodified chitosan, benzothiazole chitin derivatives possess enhanced functional expansion capabilities; combining antibacterial, metal responsiveness, and mechanical enhancement, they are suitable for applications with complex functional requirements, such as implantables and wound dressings.

[0038] The modified porous carbon microspheres are hydrothermally carbonized in a glucose solution at 180-200°C for 6-8 hours to form primary carbon spheres. Thermal activation (KOH as an activator) under nitrogen protection results in a porous structure with a specific surface area greater than 300 m² / g and pore sizes concentrated between 20 and 50 nm. Subsequently, bio-amino acids such as L-lysine or L-histidine are covalently or ionically adsorbed onto the active sites on the microsphere surface, achieving amino acid functionalization.

[0039] The mesoporous structure of the microspheres serves as a physical reinforcing filler, embedded within the hydrogel backbone to provide a "skeletal support." After amino acid modification, the particle surface contains a variety of hydrophilic groups (-NH2, -COOH, and -OH), which can form stable hydrogen-bonding networks with the functional groups of PVA and AAm. Certain amino acids possess pH-sensitive side chains, such as the imidazole group of histidine, which can variably adjust the hydrogel's swelling and release properties under varying acidic and alkaline conditions. The carbon structure of the microspheres imparts a degree of electrical conductivity to the hydrogel, enabling applications in smart sensing. While conventional hydrogel conductivity enhancement often relies on materials such as carbon nanotubes and graphene, modified porous carbon microspheres utilize a tunable structure combined with biofunctional groups to create functional microspheres, resulting in greater biocompatibility and system stability. Their low cost and green nature make them suitable for large-scale production and applications in emerging fields such as environmental monitoring and flexible sensing.

[0040] The hyperbranched synergistic network is a hyperbranched polyamide-polyester synergistic network, which uses pentaerythritol as the core initiator and is prepared by a gradual polycondensation reaction with adipoyl chloride and lactic acid under solvent method conditions. The molecular structure contains a large number of terminal carboxyl groups -COOH, amino groups -NH2 and ester bond bridging units, presenting a highly branched molecular network.

[0041] The multi-branched structure provides dozens of potential hydrogen bonding and transesterification sites, forming a "star-shaped" secondary crosslinked network. Its high swelling adaptability and dispersibility enable stress buffering during freeze-thaw cycles. After freeze-thaw damage, the multifunctional groups can re-engage in dynamic crosslinking, improving the fatigue life and recovery properties of the hydrogel. Furthermore, HPAE-PE interacts with backbone polymers such as PVA, significantly enhancing modulus and tensile properties. Compared to conventional linear polyesters (such as PEG) or polyamides (such as nylon-6), HPAE-PE has a spherical hyperbranched structure with high reactivity and low aggregation. The synergistic polyester and polyamide dual structure combines rigidity and flexibility, meeting the requirements for multi-performance coexistence in extreme environments (freeze-thaw and high humidity).

[0042] The preparation method of the hydrogel material comprises the following specific steps: S1. Preparation of main chain monomer and comonomer compound system.

[0043] The main chain monomer and comonomer were weighed, added to deionized water, and stirred in a 90°C water bath for 2 hours until the main chain monomer was fully dissolved to form a transparent solution; the solution was then cooled to 50°C, and the comonomer was slowly added while stirring, and stirring was continued for 30 minutes to obtain a uniform polymerization precursor solution.

[0044] This step aims to build the hydrogel's basic network skeleton. The main-chain monomers provide the physical crosslinking sites necessary for hydrogel formation, while the comonomers impart good polymerization activity and flexibility to the network. Their synergistic combination forms the key matrix for subsequent freeze-thaw-induced crosslinking.

[0045] S2, cross-linking agent and moisturizing enhancer are added in combination.

[0046] The crosslinker and the moisturizing enhancer are sequentially added to the mixed system obtained in step S1, and mixed for 40 minutes under stirring conditions to ensure that the crosslinker is evenly dispersed and a partial reaction begins. At the same time, the moisturizing enhancer is evenly distributed within the system, thereby increasing the solution viscosity and the initial synergistic effect of the network formation.

[0047] A cross-linking agent is introduced to enhance the chemical cross-linking density between the main chain and the copolymer system, and a moisturizing enhancer is added to improve the low-temperature flexibility of the hydrogel, retain moisture, and enhance the structural stability under freeze-thaw cycles.

[0048] S3. Synchronous pretreatment activation of pH regulator and initiator.

[0049] Slowly add a pH adjuster to adjust the system pH to 6.5-7.0, then add the initiator at 40–50°C. Maintain constant temperature and magnetic stirring for 30 minutes to complete the initiator pre-decomposition and uniform distribution. This step ensures a free radical-generating environment for subsequent network formation.

[0050] By introducing a pH regulator to adjust the pH of the system to the optimal pH range required for free radical polymerization, the stability of the initiation system is enhanced, and the initiator is activated under appropriate temperature control to form free radical seeds, thereby promoting the polymerization reaction of the main chain monomer and comonomer.

[0051] S4. Multi-stage coordinated dispersion of additives.

[0052] In the step S3 reaction system, the following reinforcing components are added in sequence in parts by mass: phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres, and hyperbranched synergistic networks. After each additive is added, ultrasonic dispersion is performed for 10 minutes, and high shear homogenization and stirring operations are performed alternately. The total dispersion time is not less than 90 minutes to ensure that various additives form a stable composite cross-linking potential structure in the system.

[0053] Additives are introduced to form a molecular-nano-micrometer multi-scale synergistic cross-linking structure, which effectively improves the mechanical properties, antifreeze properties and functional responsiveness of the hydrogel.

[0054] S5, mold forming and freeze-thaw cycle induced cross-linking structure construction.

[0055] The homogeneous solution obtained in step S4 is injected into a mold and allowed to stand for degassing before undergoing freeze-thaw treatment. A freeze-thaw cycle is set to alternate between 12 hours of freezing at –20°C and 12 hours of thawing at room temperature, for a total of 3-5 cycles. During the freezing phase, the main chain monomers crystallize and aggregate, forming strong physical crosslinks. During the thawing phase, the comonomers and functional enhancement units interact synergistically, establishing a highly resilient composite network.

[0056] Through freeze-thaw cycle treatment, the main chain monomers are guided to form physical crystallization cross-linking points, and the copolymer monomers and various reinforcing units work together to construct a molecular-level network, realizing the integration of high-strength structural configuration and freeze resistance of the hydrogel.

[0057] S6. Drying and stabilization treatment.

[0058] After the freeze-thaw treatment, the gel was demolded and dried in a vacuum environment at 60°C for 8 hours to remove free water and small molecules. It was then equilibrated in a constant humidity of 60% and a temperature of 25°C for 48 hours to stabilize the internal structure and ultimately lock in the mechanical and functional properties, resulting in the target freeze-thaw cyclic cross-linked network hydrogel material.

[0059] Through the post-processing process, unreacted small molecules and free water are removed, the internal molecular structure is stabilized, and the network morphology is solidified to ensure that the hydrogel has long-term service capability and performance stability in environmental temperature changes.

[0060] Example 2: This embodiment provides applications of a cross-linked network hydrogel material under freeze-thaw cycles, based on the hydrogel material described in Example 1, including the following specific application scenarios: Scenario A: This hydrogel material, formed through freeze-thaw-induced crystalline-chemical dual-network structure, exhibits excellent low-temperature flexibility and shape recovery. Its high water content, combined with the synergistic effect of a moisturizing enhancer, allows it to remain soft in extreme environments as low as -20°C without structural fracture or shrinkage, making it suitable for use as a soft support or cushioning material in outdoor equipment, cryogenic transportation systems, and cold-weather engineering projects.

[0061] The prepared hydrogel material is cut into suitable sizes and implanted into the desired contact interface or embedded into a supporting framework. By adjusting the proportion of phosphorylated lignin nanoparticles as needed, a cushioning response with varying elastic moduli at low temperatures is achieved. No additional heating equipment is required to maintain its performance during use, and the material provides flexible support and protection through environmental adaptation.

[0062] Scenario B: Due to the material's dense internal cross-linked network structure and good hydration permeability, especially the multi-channel network structure formed by the introduction of modified porous carbon microspheres and hyperbranched synergistic networks, it has excellent molecular screening and diffusion control capabilities. It can be used as a sustained-release or intelligent release platform for drugs, small molecule nutritional factors, plant growth regulators, etc.

[0063] Before the preparation step S4, the target release substance is uniformly premixed with a solution and loaded into the system. As the polymerization and freeze-thaw formation process progresses, the target molecule is physically embedded or chemically adsorbed into the internal network nodes. When the material is exposed to external physiological fluids or water environments, it is slowly released in an orderly manner according to the osmotic gradient or pH value (controlled by a pH regulator), and the release rate is controlled by adjusting the cross-linker content.

[0064] Scenario C: This material is highly flexible, stretchable, and exhibits excellent structural resilience, making it particularly suitable for constructing biomimetic electronic interfaces. The introduced benzothiazole chitosan derivative exhibits a certain charge transfer capability, enabling changes in ionic conduction pathways under mechanical strain. Combined with the stress amplification mechanism of the network structure, it can be used as a flexible strain-sensing device.

[0065] The prepared hydrogel material is thinned and integrated as a sensing membrane onto a flexible printed circuit board. The peripheral electrode structure is formed using screen printing or conductive ink. The material's instantaneous response to stretching, compression, or bending creates a stable impedance output, enabling precise detection of human motion, contact force, or external deformation. This technology has wide applications in wearable electronics, physiological monitoring, and human-machine interface systems.

[0066] Scenario D: Leveraging the synergistic water-locking mechanism of the moisturizing enhancer and hyperbranched synergistic network in the material, the hydrogel maintains high water content while exhibiting excellent adhesion and moisture permeability. During the freeze-thaw process, it can guide the formation of continuous hydrophilic channels, facilitating exudate absorption, while also providing a good cooling effect and wound cooling.

[0067] After refrigeration, the prepared hydrogel material is applied directly to the skin or wound surface. It absorbs exudate and slowly releases a cooling sensation, effectively alleviating local swelling and micro-inflammatory reactions. The material is soft and highly malleable, adapting to various shapes and areas. It persists after application and does not cause secondary trauma upon removal. It is highly practical for acute sports injuries, postoperative cold compresses, and chronic wound protection.

[0068] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. Preparation of cross-linked network hydrogel material under freeze-thaw cycle, characterized in that: The hydrogel material includes the following specific components: Main chain monomers, comonomers, cross-linking agents, initiators, moisturizing enhancers and pH adjusters; The hydrogel material further comprises additives, which specifically include: Phosphorylated lignin nanoparticles, benzothiazole chitin derivatives, modified porous carbon microspheres, and hyperbranched synergistic networks.

2. The preparation of a cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The mass fractions of the specific components are as follows: The main chain monomer is 40-60 parts; The comonomer is 10-20 parts; The cross-linking agent is 0.05-0.5 parts; The initiator is 0.1-0.5 parts; Moisturizing enhancer is 5-20 parts; The pH adjuster is 1-5 parts.

3. The preparation of cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The mass fractions of the additives are as follows: 3-10 parts of phosphorylated lignin nanoparticles; 2-8 parts of benzothiazole chitosan derivative; Modified porous carbon microspheres are 1-5 parts; The hyperbranched cooperative network is 0.5-2 copies.

4. The preparation of a cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: Among the specific components: The main chain monomer is polyvinyl alcohol (PVA), which is a linear polymer with a repeating structural unit of [-CH2CH(OH)-]. The comonomer is acrylamide AAm, which is a small molecule monomer containing polymerizable double bonds and amide groups; The cross-linking agent is N,N'-methylenebisacrylamide MBAA, which has two double bonds in its molecular structure; The initiators are ammonium persulfate APS and N,N,N',N'-tetramethylethylenediamine TEMED. APS is a thermal initiator and TEMED is an accelerator, which form free radicals at room temperature. The moisturizing enhancer is glycerin, which, as a triol, contains three hydroxyl groups in its molecule; The pH regulator is triethanolamine TEA, which is an organic alkaline compound used to adjust the pH value of the hydrogel material.

5. The preparation of cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The phosphorylated lignin nanoparticles are made from natural plant-derived lignin, which is subjected to a phosphating reaction under alkaline conditions using a phosphating agent, thereby introducing phosphate functional groups into the lignin molecular chain. Subsequently, the modified lignin is treated with high-energy ultrasound and high-shear homogenization to control the particle size within the range of 30-100 nm, thereby obtaining nanoparticles with uniform particle size distribution.

6. The preparation of a cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The benzothiazole chitosan derivative is synthesized by amidation reaction of high-purity chitosan with a deacetylation degree of ≥80% and 2-aminobenzothiazole under the action of a carbodiimide condensation agent; This reaction covalently grafts the benzothiazole ring onto the chitin backbone through an amide bond. The resulting product retains the multi-hydroxyl / amino active sites of chitin and introduces a new thiazole electron conjugation system.

7. The preparation of a cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The modified porous carbon microspheres are prepared by hydrothermal carbonization of a glucose solution at 180-200° C. for 6-8 hours to form primary carbon spheres; Then, thermal activation was performed under nitrogen protection to obtain a porous structure with a specific surface area greater than 300 m² / g and a pore size concentrated in the range of 20-50 nm; Subsequently, biological amino acids such as L-lysine or L-histidine are used to undergo covalent or ion adsorption with the active sites on the microsphere surface to achieve amino acid functionalization coating.

8. The preparation of cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The hyperbranched synergistic network is a hyperbranched polyamide-polyester synergistic network, which uses pentaerythritol as the core initiator and is prepared by a gradual polycondensation reaction with adipoyl chloride and lactic acid under solvent method conditions. The molecular structure contains a large number of terminal carboxyl groups -COOH, amino groups -NH2 and ester bond bridging units, presenting a highly branched molecular network.

9. The preparation of a cross-linked network hydrogel material under freeze-thaw cycle according to claim 1, characterized in that: The preparation method of the hydrogel material comprises the following specific steps: S1. Preparation of main chain monomer and comonomer compound system; S2, cross-linking agent and moisturizing enhancer compound addition; S3, simultaneous pretreatment activation of pH regulator and initiator; S4, multi-stage synergistic dispersion of additives; S5, mold forming and freeze-thaw cycle induced cross-linking structure construction; S6. Drying and stabilization treatment.

10. Application of a cross-linked network hydrogel material under freeze-thaw cycles, based on the hydrogel material according to any one of claims 1 to 9, characterized in that: Including the following specific application scenarios: Scenario A: The prepared hydrogel material is cut into an appropriate size and shape and implanted into the desired contact interface or embedded into a supporting frame structure. The proportion of phosphorylated lignin nanoparticles is adjusted as needed to achieve a buffering response with different elastic modulus ranges at low temperatures. Scenario B: Before the preparation step S4, the target release substance is uniformly premixed with a solution and loaded into the system. During the polymerization and freeze-thaw formation process, the target molecule is physically embedded or chemically adsorbed into the internal network nodes. When the material is exposed to external physiological fluids or water environment, it is slowly released in an orderly manner according to the osmotic gradient or pH value. The release rate is controlled by adjusting the cross-linker content. Scenario C: The prepared hydrogel material is thinned and integrated as a sensing membrane onto a flexible circuit board, with the peripheral electrode structure formed by screen printing or conductive ink. Scenario D: The prepared hydrogel material is refrigerated and then applied directly to the skin or wound surface. The material absorbs exudate and slowly releases a cooling sensation, effectively alleviating local swelling and micro-inflammatory reactions.

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