Sea cucumber-inspired ion-derived dual-dynamic topological hydrogel, its preparation method, and applications.

Abstract

This application relates to the field of stimulus-responsive hydrogel preparation technology, specifically to a dual-dynamic topological hydrogel mimicking sea cucumber ionic skin, its preparation method, and applications. A thermosensitive poly(N-isopropylacrylamide) hydrogel serves as a continuous matrix to simulate the dynamic adaptability of sea cucumber skin; an ionically conductive microgel serves as a rigid dispersed phase to simulate the collagen fiber network of the sea cucumber connective tissue layer. The microgel is dispersed within the poly(N-isopropylacrylamide) hydrogel and physically entangled with it, forming cross-linking points to construct a dynamic network of "rigid nodes-flexible matrix." This dynamic network structure endows the dual-dynamic topological hydrogel with both mechanical and thermal toughening and ultra-low mechanical hysteresis, giving it excellent elasticity, fatigue resistance, low hysteresis, and strain rate insensitivity, thus demonstrating broad application prospects in the fields of flexible sensing and wearable devices.

Description

Technical Field

[0001] This invention relates to the field of stimulus-responsive hydrogel preparation technology, specifically to a dual-dynamic topological hydrogel that mimics sea cucumber ion skin, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible electronics technology, wearable devices are gradually penetrating core fields such as health monitoring, human-computer interaction, and smart healthcare, placing higher demands on the mechanical adaptability, environmental stability, and functional integration of materials. Traditional rigid electronic devices, lacking ductility and biocompatibility, struggle to conform to the complex curves of the human body or withstand dynamic deformation, severely limiting their application in long-term wear scenarios. Hydrogels, as highly hydrated and tunable three-dimensional network materials, have become ideal carriers for constructing flexible sensors and actuators due to their bio-tissue-like softness and ion / electron conductivity. However, the static network structure of conventional hydrogels results in weak mechanical properties and environmental sensitivity, making it difficult to meet durability and reliability requirements.

[0003] Conductive hydrogels combine the hydrophilicity of hydrogels with the functionality of conductive materials. With their unique electromechanical properties and biocompatibility, they hold great promise in fields such as biomedicine and smart wearables, and a series of breakthroughs have already been achieved. However, the research and application of conductive hydrogels still face a core challenge: achieving synergistic optimization of their three key mechanical properties—toughness, resilience, and stiffness. Specifically, in existing technological explorations, some studies have attempted to enhance the toughness of conductive hydrogels by introducing sacrificial bond structures, but this strategy leads to a significant reduction in the material's resilience. Meanwhile, entropy-elastic hydrogel systems, which aim to improve resilience, generally suffer from insufficient crack resistance. Although some studies have used single dynamic topologies, such as sliding ring structures and strain-induced crystallization, to improve the mechanical properties of hydrogels, they still cannot simultaneously meet the requirements of resilience, high toughness, and adjustable stiffness under complex environments. Therefore, the difficulty in achieving a balance between the mechanical properties of hydrogels has become a critical issue that urgently needs to be addressed in current research. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-dynamic topological hydrogel that mimics sea cucumber ion skin, its preparation method, and its application, in order to solve the problem that the mechanical properties of hydrogels in the prior art are difficult to balance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a dual dynamic topological hydrogel that mimics the ionic skin of sea cucumbers, comprising: a thermosensitive poly(N-isopropylacrylamide) hydrogel as a continuous matrix for simulating the dynamic adaptability of sea cucumber skin;

[0006] Ion-conductive microgels, as rigid dispersion phases, are used to simulate the collagen fiber network of the connective tissue layer of sea cucumbers. The ion-conductive microgels are dispersed in the poly(N-isopropylacrylamide) hydrogel and are physically entangled with the poly(N-isopropylacrylamide) hydrogel to form cross-linking points, so as to construct a dynamic network of "rigid nodes-flexible matrix".

[0007] In the dual dynamic topological hydrogel, the content of the ion-conductive microgel is any value between 0.08wt% and 1.2wt%.

[0008] Furthermore, the particle size of the ion-conductive microgel is limited to the range of 10 μm to 550 μm.

[0009] Furthermore, the crosslinking density of the ion-conductive microgel is limited to the range of 1 mol% to 8 mol%.

[0010] This application also provides a method for preparing the above-mentioned dual-dynamic topological hydrogel, comprising the following steps:

[0011] S1. Mix the obtained N-isopropylacrylamide monomer, the first crosslinking agent and the photoinitiator evenly to form a mixture;

[0012] S2. The obtained microgel monomer, second crosslinking agent and initiator are added to deionized water and mixed evenly to form an aqueous phase. An emulsifying agent is added to the aqueous phase, and pre-emulsification and emulsification are performed. After that, the mixture is filtered to obtain ion-conductive microgel.

[0013] S3. Add the ion-conductive microgel to the mixture and stir until homogeneous to obtain a hydrogel precursor solution.

[0014] S4. The hydrogel precursor solution is placed at a temperature of -5℃ to 5℃ and subjected to polymerization under ultraviolet light to obtain a dual dynamic topological hydrogel.

[0015] Further, in step S1, the molar content of the N-isopropylacrylamide monomer in the mixture is 1.5 mol / L to 3 mol / L, the molar content of the first crosslinking agent is 0.05% to 0.2% of the molar content of the N-isopropylacrylamide monomer, and the molar content of the photoinitiator is 0.005% to 0.05% of the molar content of the N-isopropylacrylamide monomer.

[0016] Further, in step S2, before adding the emulsifying agent to the aqueous phase, nitrogen gas is first introduced into the aqueous phase to remove oxygen from the aqueous phase; the emulsifying agent is cyclohexane containing Span 80.

[0017] Furthermore, in step S2, during the pre-emulsification process, the stirring speed is any value between 100 rpm and 1500 rpm, and the processing temperature of the emulsification process is any value between 20°C and 80°C.

[0018] Further, in step S2, the ion-conducting microgel is any one of sodium polyacrylate microgel, sodium polystyrene sulfonate microgel, and sodium polyvinyl sulfonate microgel, and the ion-conducting microgel monomer is the corresponding sodium acrylate, sodium styrene sulfonate, or sodium vinyl sulfonate.

[0019] Further, in step S2, the ion-conductive microgel is sodium polyacrylate microgel; in the aqueous phase, the molar content of the second crosslinking agent is 1% to 8% of the molar content of the sodium acrylate, and the molar content of the initiator is 0.05% to 0.2% of the molar content of the sodium acrylate.

[0020] This application also provides applications of the aforementioned dual-dynamic topological hydrogel, including its application in multimodal smart wearable sensors.

[0021] The beneficial effects of this invention are as follows: The sea cucumber-like ionic skin dual-dynamic topological hydrogel provided in this application is composed of a microgel with ionic conductivity and a PNIPAm hydrogel with temperature responsiveness. Sodium polyacrylate microgel and poly(N-isopropylacrylamide) form cross-linking points through physical entanglement, thereby constructing a hybrid network structure resembling sea cucumber skin, i.e., a dynamic network structure of "rigid nodes-flexible matrix". This dynamic network structure endows the dual-dynamic topological hydrogel with both mechanical and thermal toughening and ultra-low mechanical hysteresis, giving it excellent elasticity, fatigue resistance, low hysteresis, and strain rate insensitivity. The strong hydrophilicity of the PANa microgel locks in the water released by PNIPAm during heating, preventing the dynamic network structure from shrinking and collapsing, maintaining an isovolute thermal response, and ensuring the reversibility of thermal toughening. The PANa microgel provides stable ion channels, enabling the dual-dynamic topological hydrogel to also possess conductive properties, and ion transport is unaffected by mechanical deformation, providing a prerequisite for its use as a highly stable wearable sensor material.

[0022] By adjusting parameters such as the particle size, crosslinking density, and content of the microgels in this dual-dynamic topological hydrogel, its mechanical properties can be optimized, resulting in excellent crack resistance and a unique longitudinal crack propagation mechanism. This demonstrates the broad application prospects of this dual-dynamic topological hydrogel in flexible sensing and wearable devices. As a multimodal sensor material, this dual-dynamic topological hydrogel exhibits excellent force-electric coupling characteristics. In human motion monitoring experiments, this dual-dynamic topological hydrogel successfully captured motion signals from various parts of the human body and maintained high reliability even under extreme conditions, such as after being cut, subjected to 1000 torsions, or thermal shocks, its sensing performance did not degrade.

[0023] The method for preparing dual-dynamic topological hydrogels provided in this application uses reverse emulsion polymerization to prepare PANa microgels. The crosslinking density of the microgels can be controlled by adjusting the amount of the second crosslinking agent added. Microgels with different particle sizes can be obtained by adjusting the stirring speed of the pre-emulsification process, thereby obtaining dual-dynamic topological hydrogels with different mechanical properties to meet practical application requirements.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the PNIPAm / PANa hydrogel network prepared in Example 2 of the present invention, as well as its hardening behavior under tension and its puncture resistance under thermal toughening.

[0026] Figure 2 The image shows a comparison of SEM images of the PNIPAm hydrogel prepared in Example 1 and the PNIPAm / PANa hydrogel prepared in Example 2 of this invention.

[0027] Figure 3 The stress relaxation curves of the PNIPAm hydrogel prepared in Example 1 and the PNIPAm / PANa hydrogel prepared in Example 2 under 100% strain are shown.

[0028] Figure 4 The stress-strain curves are shown for the PNIPAm hydrogel prepared in Example 1 and the PNIPAm / PANa hydrogel prepared in Example 2 of this invention.

[0029] Figure 5 The stress-strain curve of the PNIPAm / PANa hydrogel prepared in Example 2 of the present invention after 1000 loading-unloading cycles at 100% strain;

[0030] Figure 6 The stress-strain curves of the PNIPAm / PANa hydrogel prepared in Example 2 of this invention at different temperatures are shown.

[0031] Figure 7 Comparison of fracture energy and fatigue threshold of PNIPAm / PANa hydrogel prepared in Example 2 of the present invention at different temperatures;

[0032] Figure 8 This is a comparison image of the PNIPAm / PANa hydrogel prepared in Example 2 of the present invention before and after 3000 single-notch cycles at 40°C;

[0033] Figure 9 The resistance change and response characteristics of the PNIPAm / PANa hydrogel prepared in Example 2 of this invention under 100% static strain are shown.

[0034] Figure 10 This is a real-time monitoring of the oscillation decay process of the PNIPAm / PANa hydrogel prepared in Example 2 of the present invention;

[0035] Figure 11 This document presents the results of 1000 torsional sensing stability verification and signal sensing stability test after thermal stress mechanical damage of the PNIPAm / PANa hydrogel prepared in Example 2 of this invention.

[0036] Figure 12 The actual stress-strain curves of the PNIPAm / PANa hydrogels prepared in Examples 2-5 of this invention are shown (the vertical axis represents the actual stress, i.e., σ). ture The horizontal axis represents the stretching ratio, i.e., λ(L / L0).

[0037] Figure 13 The actual stress-strain curves of the PNIPAm / PANa hydrogels obtained in Examples 2 and 6-8 of this invention are shown.

[0038] Figure 14 These are micrographs of microgels obtained at different stirring speeds during the pre-emulsification process in Examples 2 and 9-11 of the present invention.

[0039] Figure 15 The actual stress-strain curves of the PNIPAm / PANa hydrogels obtained in Examples 2 and 9-11 of this invention are shown.

[0040] Figure 16 This is a comparison chart of the elastic modulus, toughness, and maximum differential modulus performance parameters of the PNIPAm / PANa hydrogels prepared in Examples 2-11 of this invention. Detailed Implementation

[0041] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] Please see Figure 1 This application discloses a preferred embodiment of a dual-dynamic topological hydrogel mimicking sea cucumber ionic skin, comprising a thermosensitive poly(N-isopropylacrylamide) hydrogel and an ionically conductive microgel. The thermosensitive poly(N-isopropylacrylamide) hydrogel serves as a responsive unit, utilizing the hydrophilic-hydrophobic transition (thermosensitivity) and orientation reconfiguration (mechanical sensitivity) of its molecular chains to simulate the dynamic hardening mechanism of sea cucumber skin. Specifically, the physical state of the poly(N-isopropylacrylamide) hydrogel changes accordingly under different temperature environments, endowing the hydrogel with dynamic characteristics similar to the response of sea cucumber skin to environmental temperature. The ionically conductive microgel, utilizing its hydrophilicity and high swelling capacity, can lock in the water expelled by PNIPAM when heated, maintaining a substantially unchanged network volume and ensuring that the ion conductivity is unaffected by mechanical deformation or thermal stimulation. This ionically conductive microgel is dispersed within the poly(N-isopropylacrylamide) hydrogel and physically entangled with it, forming cross-linking points. In this way, a dynamic network structure of "rigid nodes-flexible matrix" is constructed. In dual-dynamic topological hydrogels, the content of ionically conductive microgels is controlled within the range of 0.08 wt% to 1.2 wt%. Within this range, the hydrogel can be ensured to possess both good electrical conductivity and suitable mechanical properties.

[0043] In one embodiment, the particle size of the ion-conductive microgel is limited to the range of 10 μm to 550 μm. A suitable particle size has a significant impact on the microstructure and properties of the dual-dynamic topological hydrogel. Within this range, the ion-conductive microgel can better interact with the hydrogel matrix to form a uniform and stable structure, thereby ensuring the consistent performance of the hydrogel in various application scenarios.

[0044] In one embodiment, the crosslinking density of the ion-conductive microgel is limited to the range of 1 mol% to 8 mol%. The crosslinking density of the ion-conductive microgel directly affects its mechanical and electrical properties. By controlling it within this range, the flexibility and conductivity of the microgel can be balanced, enabling it to work synergistically better when constructing dual-dynamic topological hydrogels, thereby optimizing the overall performance of the dual-dynamic topological hydrogel.

[0045] This application also provides a method for preparing the above-mentioned dual-dynamic topological hydrogel, which includes the following steps:

[0046] S1. Mix the obtained N-isopropylacrylamide (NIPAm) monomer, the first crosslinking agent and the photoinitiator evenly to form a mixture;

[0047] S2. Add the obtained microgel monomer, second crosslinking agent and initiator to deionized water, mix evenly to form an aqueous phase, add emulsifying agent to the aqueous phase, and perform pre-emulsification and emulsification treatment. After filtration, ion-conductive microgel is obtained.

[0048] S3. Add the ion-conductive microgel to the mixture and stir until homogeneous to obtain the hydrogel precursor solution.

[0049] S4. The hydrogel precursor solution was placed at a temperature of -5℃ to 5℃ and subjected to a polymerization reaction under ultraviolet light to obtain a dual dynamic topological hydrogel, namely the PNIPAm / PANa hydrogel that mimics sea cucumber ionic skin.

[0050] In step S1, the uniform mixing of the components promotes the smooth progress of the subsequent polymerization reaction between N-isopropylacrylamide monomers and also helps to ensure the uniformity of the properties of the dual dynamic topological hydrogel. In this embodiment and other embodiments, the first crosslinking agent can be any one of N,N-dipropylacrylamide (MBAA), ethylene dimethacrylate, glutaraldehyde, etc., and the photoinitiator can be any one of benzophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, α-ketoglutaric acid, etc.

[0051] In step S2, the microgel monomer is first prepared into an ion-conductive microgel, which is then mixed with the mixture from step S1 and proceeded to subsequent steps. Specifically, compared to directly polymerizing PANa and NIPAm into a composite hydrogel, this sea cucumber-inspired ion-skin dual-dynamic topological hydrogel prepares sodium acrylate monomers into microgels before polymerizing them with NIPAm. The structural design of the microgels addresses the performance defects of conventional copolymerization, achieving a dual mechanical-thermal response. If this step is omitted, i.e., the sodium acrylate monomers are directly mixed with the mixture from step S1, the PANa chains will randomly crosslink during the subsequent polymerization reaction, failing to form effective physical entanglement points. The resulting hydrogel will lack strain hardening and thermo-toughening properties. Furthermore, the strong hydrophilicity of PANa during polymerization leads to localized water accumulation or expulsion, preventing the formation of a uniform network. The uneven ion-conductive pathways within the hydrogel prevent temperature sensing and thermal stimulation self-protection. In the microgel preparation process, thorough stirring ensures the ionically conductive microgel monomers, the second crosslinking agent, and the initiator are completely dissolved in deionized water, forming a stable aqueous phase to guarantee a uniform and stable emulsion in subsequent operations. During the pre-emulsification process, key parameters such as the stirring speed can be precisely controlled to ensure the uniformity and stability of the emulsion. In this embodiment and other embodiments, the second crosslinking agent can be any one of N,N-dipropylacrylamide (MBAA), ethylenedimethacrylate, glutaraldehyde, etc., and can be the same as or different from the first crosslinking agent. The initiator can be any one of peroxides such as ammonium persulfate, potassium sulfate, benzoyl peroxide, etc., or one of azo compounds such as azobisisobutyronitrile. The emulsifying agent can be cyclohexane containing Span 80, fatty alcohol ether sulfate salts, or other emulsifiers. In cyclohexane containing Span 80, Span 80 exists as an emulsifier or stabilizer to improve the dispersibility of cyclohexane or its compatibility with other substances. Span 80 is sorbitan monooleate, a nonionic surfactant.

[0052] In step S3, the ion-conductive microgel is mixed evenly with the mixture to ensure that the microgel is uniformly dispersed in the mixture, providing a basis for the subsequent formation of a uniform dual dynamic topology.

[0053] In step S4, the hydrogel precursor solution is placed at a temperature of -5℃ to 5℃ and subjected to a polymerization reaction under ultraviolet light irradiation. During the polymerization reaction, the crosslinking agent and initiator promote free radical polymerization to generate PNIPAM long chains. The number of long chain entanglements in the polymer network is much greater than the number of covalent crosslinking points. Entanglement forms between PNIPAM long chains and between PNIPAM long chains and the ionically conductive microgel network. At this point, the ionically conductive microgel acts as a connecting point, linking the polymer long chains formed by polymerization to the ionically conductive microgel, thereby constructing a hybrid network structure resembling sea cucumber skin. By precisely controlling the temperature of the polymerization reaction, the formation process of the dual-dynamic topological hydrogel can be precisely controlled, thus ensuring the stability and reliability of the dual-dynamic topological hydrogel structure.

[0054] In one embodiment, step S1 precisely defines the concentration of each component in the mixture. Specifically, the molar content of N-isopropylacrylamide monomer in the mixture is controlled within the range of 1.5 mol / L to 3 mol / L. Experimental verification has shown that this concentration range ensures that the poly(N-isopropylacrylamide) hydrogel matrix exhibits good gelling properties and suitable mechanical strength. The molar content of the first crosslinking agent is 0.05% to 0.2% of the molar content of N-isopropylacrylamide monomer, and the molar content of the photoinitiator is 0.005% to 0.05% of the molar content of N-isopropylacrylamide monomer. By precisely controlling the proportions of these components, the polymerization rate and crosslinking degree of the poly(N-isopropylacrylamide) hydrogel can be effectively adjusted, thereby achieving precise control over the properties of the dual-dynamic topological hydrogel.

[0055] In one embodiment, in step S2, the ionically conductive microgel is any one of sodium polyacrylate microgel, sodium polystyrene sulfonate microgel, or sodium polyvinyl sulfonate microgel. Different types of microgels have their own unique chemical and physical properties. For example, sodium polyacrylate microgel has good water absorption and ion conductivity. Appropriate microgel types can be selected according to different application requirements to meet diverse usage scenarios. The microgel monomer is the corresponding sodium acrylate, sodium styrene sulfonate, or sodium vinyl sulfonate. For example, when sodium polyacrylate microgel is selected, its corresponding microgel monomer is sodium acrylate.

[0056] In one embodiment, in step S2, since the presence of oxygen can combine with free radicals, consuming the active free radicals generated by the initiator, and thus inhibiting the polymerization reaction, affecting the yield and performance of the microgel, nitrogen gas is first introduced into the aqueous phase to remove oxygen before adding the emulsifying agent. Meanwhile, the emulsifying agent is preferably cyclohexane containing Span 80. Span 80 has excellent emulsifying properties, effectively dispersing the aqueous phase in the oil phase to form a stable emulsion, providing a favorable reaction environment for the formation of ionically conductive microgels.

[0057] In one embodiment, step S2 specifies the proportions of each component in the aqueous phase. The molar content of the second crosslinking agent is 1% to 8% of the molar content of sodium acrylate, and the molar content of the initiator is 0.05% to 0.2% of the molar content of sodium acrylate. This strict control of proportions helps ensure that the crosslinking structure and molecular weight distribution of the microgel meet the design requirements, thereby guaranteeing its good ionic conductivity and mechanical properties.

[0058] In one embodiment, during step S2, the stirring speed is controlled within the range of 100 rpm to 1500 rpm during the pre-emulsification process. During the emulsification process, the processing temperature is controlled within the range of 20°C to 80°C. The processing temperature and stirring speed have a significant impact on the quality, particle size, and properties of the resulting ion-conductive microgels. Different temperatures affect the stability of the emulsion and the formation rate of the microgels. A suitable stirring speed ensures thorough mixing of the aqueous and oil phases, forming emulsion particles with uniform particle size, thereby affecting the particle size distribution and properties of the microgels.

[0059] This application also provides applications of the aforementioned dual-dynamic topological hydrogel, which has broad application prospects, especially in the field of multimodal smart wearable sensors. Its unique "rigid node-flexible matrix" dynamic network structure and excellent ionic conductivity enable it to sensitively sense various physical and chemical signals, such as pressure, temperature, and strain, and accurately convert these signals into electrical signals for transmission and processing. In smart wearable devices, this hydrogel can achieve real-time monitoring and feedback of human physiological signals, providing a novel, efficient, and comfortable solution for health monitoring, motion analysis, and other fields. Simultaneously, its good flexibility and biocompatibility allow it to adhere closely to human skin without causing irritation or damage, demonstrating extremely high application value and development potential.

[0060] Example 1

[0061] S1. Dissolve 2.26 g of N-isopropylacrylamide monomer and 0.0030 g of N,N-dipropylacrylamide in 10 ml of deionized water and stir at 1000 rpm for 30 min to obtain a monomer solution. Dissolve 0.0060 g of α-ketoglutaric acid in 500 μL of deionized water and stir until completely dissolved to obtain an α-ketoglutaric acid solution, which will serve as the photoinitiator solution. Add 25 μL of the photoinitiator solution to the monomer solution and stir at 1000 rpm for 15 min to obtain a mixed solution.

[0062] S2. The mixed solution is placed at a temperature of 5°C and subjected to a polymerization reaction under ultraviolet light to obtain poly(N-isopropylacrylamide) hydrogel, namely PNIPAm hydrogel.

[0063] Example 2

[0064] S1. Weigh 2.26 g of N-isopropylacrylamide monomer and 0.0030 g of N,N-dipropylacrylamide, and dissolve them in 10 mL of deionized water. Stir at 1000 rpm for 30 min to obtain a monomer solution. Weigh 0.0060 g of α-ketoglutaric acid and dissolve it in 500 μL of deionized water. Stir until completely dissolved to obtain an α-ketoglutaric acid solution, which will be used as the photoinitiator solution. Add 25 μL of the photoinitiator solution to the monomer solution and stir at 1000 rpm for 15 min to obtain a mixed solution.

[0065] S2. Weigh 6.345 g of sodium acrylate monomer, 0.2 g of N,N-dipropylacrylamide, and 0.015 g of ammonium persulfate, and add them to 30 mL of deionized water. Stir at 500 rpm for 30 min to obtain an aqueous phase. The molar content of N,N-dipropylacrylamide in this aqueous phase is 2% of the molar content of sodium acrylate. Weigh 3.6 g of Span80 and add it to 60 mL of cyclohexane, mixing thoroughly to obtain the oil phase. Continuously purge the aqueous phase with nitrogen to remove oxygen. After purging with nitrogen for 15 min, slowly pour the aqueous phase into the oil phase and stir continuously at 1500 rpm for pre-emulsification. After stirring for 2 hours, an emulsion is formed. Pour the emulsion into a three-necked flask filled with nitrogen and stir at 200 rpm in a 60°C water bath for 4 hours to carry out the emulsification reaction. After the reaction was complete, the product was poured into methanol for demulsification, slowly while stirring. The resulting precipitate was then filtered off, washed three times repeatedly with ethanol, and dried in a vacuum oven to obtain sodium polyacrylate microgel, or PANa microgel. The particle size distribution of this PANa microgel was 10–40 μm, with an average particle size of approximately 20 μm.

[0066] S3. Take 0.15g of the PANa microgel obtained in step S2 and add it to the mixed solution obtained in step S1. Stir at 1000rpm for 30min to obtain the hydrogel precursor solution. At this time, the mass of PANa microgel accounts for 0.8% of the total mass of the hydrogel precursor solution.

[0067] S4. Pour the hydrogel precursor solution into a mold and irradiate it with a 30W UV lamp at 5°C for 3 hours to induce polymerization reactions between N-isopropylacrylamide monomers and between N-isopropylacrylamide monomers and PANA microgels in the hydrogel precursor solution. After polymerization is complete, remove the solidified gel from the mold to obtain the PNIPAm / PANa hydrogel that mimics sea cucumber ionic skin.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 2 is that, in step S2, 0.1 g of NN dipropylacrylamide is weighed. At this point, the molar content of the crosslinking agent is 1% of the molar content of sodium acrylate.

[0070] Example 4

[0071] The difference between this embodiment and Embodiment 2 is that, in step S2, 0.4 g of NN dipropylacrylamide is weighed. At this point, the molar content of the crosslinking agent is 4% of the molar content of sodium acrylate.

[0072] Example 5

[0073] The difference between this embodiment and Embodiment 2 is that, in step S2, 0.8 g of NN dipropylacrylamide is weighed. At this point, the molar content of the crosslinking agent is 8% of the molar content of sodium acrylate.

[0074] Example 6

[0075] The difference between this embodiment and embodiment 2 is that in step S3, 0.015g of the PANa microgel obtained in step S2 is taken, so that the mass of the microgel accounts for 0.08% of the total mass of the hydrogel precursor solution.

[0076] Example 7

[0077] The difference between this embodiment and embodiment 2 is that in step S3, 0.075g of the PANa microgel obtained in step S2 is taken, so that the mass of the microgel accounts for 0.4% of the total mass of the hydrogel precursor solution.

[0078] Example 8

[0079] The difference between this embodiment and embodiment 2 is that in step S3, 0.225g of the PANa microgel obtained in step S2 is taken, so that the mass of the microgel accounts for 1.2% of the total mass of the hydrogel precursor solution.

[0080] Example 9

[0081] The difference between this comparative example and Example 2 is that in step S2, during the pre-emulsification process, the mixture is stirred at a speed of 500 rpm, so that the resulting microgel particles are distributed in the range of 350 μm to 550 μm, with an average particle size of 456 μm.

[0082] Example 10

[0083] The difference between this comparative example and Example 2 is that in step S2, during the pre-emulsification process, the mixture is stirred at a speed of 750 rpm, so that the resulting microgel particles are distributed in the range of 240 μm to 340 μm, with an average particle size of about 286 μm.

[0084] Example 11

[0085] The difference between this comparative example and Example 2 is that in step S2, during the pre-emulsification process, the mixture is stirred at a speed of 1100 rpm so that the resulting microgel particles are distributed in the range of 40 μm to 120 μm, with an average particle size of about 79 μm.

[0086] The internal structures of the PNIPAm hydrogel obtained in Example 1 and the PNIPAm / PANa hydrogel obtained in Example 2 were examined and compared. The results are shown in [the table below]. Figure 2 .

[0087] like Figure 2 As shown in (c) and (d), the PNIPAm hydrogel obtained in Example 1 exhibits a significant reduction in network gaps after thermal stimulation. This is because PNIPAm undergoes a phase transition upon temperature increase, resulting in enhanced hydrophobicity, water molecule expulsion, and gel volume shrinkage. In contrast, the PNIPAm / PANa hydrogel mimicking sea cucumber ionic skin obtained in Example 2... Figure 2 As shown in (a) and (b), due to the presence of both PNIPAm and PANa microgels, the network structure becomes denser after thermal stimulation, but the gaps only slightly decrease, allowing for effective water retention. This difference is mainly due to the hydrophilicity of PANa microgels, which enables the PNIPAm / PANA hydrogel to maintain hydration at 40℃, thus inhibiting excessive water loss. Therefore, the single PNIPAm hydrogel exhibits significant volume shrinkage after thermal stimulation, displaying typical thermosensitive shrinkage behavior; while the PNIPAm / PANA hydrogel network exhibits rapid and reversible isovolemic response, meaning its volume remains almost constant with temperature changes, responding to external stimuli only through internal structural adjustments. This characteristic is key to its highly reversible thermal toughening properties.

[0088] Stress relaxation tests were performed on the PNIPAm hydrogel obtained in Example 1 and the PNIPAm / PANa hydrogel obtained in Example 2, and their mechanical behavior under stress conditions was detected respectively. The test results are as follows: Figure 3 , Figure 4 As shown.

[0089] Depend on Figure 3 It can be seen that, under 100% constant strain conditions, the PNIPAm / PANa hydrogel with sea cucumber-like ion skin obtained in Example 2 exhibits a mechanical relaxation of less than 5% within 5 minutes. This value is significantly lower than the mechanical relaxation of the PNIPAm hydrogel obtained in Example 1. This indicates that the PNIPAm / PANa hydrogel shows a smaller degree of stress decay over time during continuous stress application, demonstrating superior mechanical properties. Figure 4As can be seen, the PNIPAm hydrogel obtained in Example 1 exhibits extremely low mechanical strength, while the PNIPAm / PANa hydrogel obtained in Example 2 exhibits typical strain hardening characteristics. The improved mechanical strength of the PNIPAm / PANa hydrogel mainly stems from the synergistic effect of the PANa microgel and PNIPAm, with the PANa microgel and PNIPAm chains forming dense physical entanglements. In the initial stage of stretching, these entanglements disperse stress through reversible slip, allowing the PNIPAm / PANa hydrogel to maintain a low stress level under low strain conditions. When the strain exceeds a critical value of 300%, the PNIPAm chains straighten along the stretching direction, initiating significant strain hardening, and the slope of the stress-strain curve increases sharply. This stress-strain curve clearly demonstrates the enhancement mechanism of the PANa microgel on the PNIPAm hydrogel, fully proving that the dual dynamic topology network design can effectively regulate the mechanical response behavior of the hydrogel, laying a mechanical foundation for its application in wearable sensing, flexible actuation, and other fields.

[0090] Under 100% strain, the sea cucumber-inspired ionic skin PNIPAm / PANa hydrogel obtained in Example 2 was subjected to 1000 load-unload cycles of stress-strain testing. The test results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the mechanical properties of the PNIPAm / PANa hydrogel remained stable throughout the repeated cycles, which demonstrates that the PNIPAm / PANa hydrogel, which mimics sea cucumber ion skin, can still exhibit excellent stability and durability under the harsh conditions of repeated cyclic loading, providing a reliable guarantee for its long-term and stable application in the field of smart wearable sensors.

[0091] To further investigate the influence of temperature on material properties, the stress-strain behavior, fracture energy, and fatigue threshold of the PNIPAm / PANa hydrogel obtained in Example 2 were tested at different temperatures. Furthermore, the PNIPAm / PANa hydrogel obtained in Example 2 underwent 3000 single-notch cycle tests at 40°C. The test results are as follows: Figure 6 , Figure 7 , Figure 8 As shown.

[0092] Depend on Figure 6It is evident that the mechanical properties of the thermally stimulated PNIPAm / PANa hydrogel are significantly improved compared to the hydrogel at room temperature. This is mainly attributed to the temperature responsiveness of the PNIPAm polymer within the PNIPAm / PANa hydrogel, a characteristic that endows it with unique thermodynamic mechanical properties. Specifically, at an ambient temperature of 20℃, the PNIPAm / PANa hydrogel exhibits typical strain hardening characteristics, meaning that as strain increases, stress shows a nonlinear growth trend, and the PNIPAm / PANa hydrogel demonstrates strong resistance to deformation. However, when the temperature rises to 40℃, its mechanical properties change significantly, reflecting the adjustment of the internal structure and alteration of intermolecular interactions at different temperatures. Figure 7 It can be seen that the tear resistance of the PNIPAm / PANa hydrogel varies significantly at different temperatures. At 40℃, both the fatigue threshold and fracture energy of the PNIPAm / PANa hydrogel are significantly increased, with the fracture energy increasing by approximately 26 times and the fatigue threshold by approximately 23 times. Figure 8 As shown in (a) and (b), no crack propagation was observed in the pre-notched sample at 40°C after 3000 cycles at 90% strain.

[0093] The PNIPAm / PANa hydrogel of the sea cucumber-inspired ionic skin obtained in Example 2 was used to fabricate a dual-dynamic topological hydrogel sensor for sea cucumber-inspired ionic skin. Under 100% static strain, the resistance change of the sensor over 1.5 hours and its response characteristics under static-dynamic combined loading were measured. The results are as follows: Figure 9 As shown.

[0094] Depend on Figure 9 It can be seen that under 100% static strain conditions, the sensor's resistance decreased from 224% to 218% within 1.5 hours, and quickly recovered to its initial resistance after strain release. This demonstrates the sensor's ability to stably monitor large strains over a long period without performance degradation. Furthermore, under 48% static strain loading and a 5% strain cycle at a frequency of 1Hz, the sensor did not exhibit signal distortion, indicating that even under high strain conditions, the sensor can still stably monitor dynamic small strains of 5%.

[0095] To evaluate the monitoring effect of the PNIPAm / PANa hydrogel prepared in Example 2 on random vibration stretching, its oscillation decay process under the action of gravity was monitored in real time. Figure 10As shown, during the free oscillation and decaying motion under the influence of gravity, the tensile force signal and resistance signal of the PNIPAm / PANa hydrogel exhibit a highly consistent correspondence. Specifically, throughout the oscillation process, their trends over time are almost synchronous, indicating that the resistance signal of the PNIPAm / PANa hydrogel can accurately map the dynamic changes in tensile force. Especially in the later stages of oscillation, when the amplitude gradually decays to a weak state, the resistance sensing signal can still accurately reflect the minute changes in tensile force, thus demonstrating the hydrogel's excellent signal response performance. Even in the face of weak mechanical stimuli, its resistance signal maintains high sensitivity and accuracy. The minimum detectable tensile force of the hydrogel is approximately 0.003 N, which also confirms the high sensitivity of the PNIPAm / PANa hydrogel under weak mechanical stimuli. Therefore, the sea cucumber-inspired ion-skin dual-dynamic topological hydrogel provided in this application has excellent monitoring capabilities for irregular unidirectional tensile deformation, demonstrating good application potential in the field of mechanical sensing.

[0096] To comprehensively evaluate the sensing stability of the PNIPAm / PANa hydrogel obtained in Example 2, the PNIPAm / PANa hydrogel was subjected to 1000 cycles of torsional sensing stability verification and signal sensing stability tests after thermal stress mechanical damage. The test results are as follows: Figure 11 As shown. The PNIPAm / PANa hydrogel was subjected to 1000 cycles of cyclic torsion stimulation to evaluate its sensing performance stability under the extreme mechanical condition of repeated torsion. Specifically, 25% strain was selected as the key test parameter, and sensing tests were conducted before and after cyclic torsion. The purpose of the signal sensing stability test after thermal stress and mechanical damage was to further explore the sensing performance of the PNIPAm / PANa hydrogel in complex and extreme environments. A puncture experiment was conducted on the PNIPAm / PANa hydrogel under thermal stress conditions to simulate extreme mechanical damage conditions such as impacts from sharp objects that might be encountered in real-world applications.

[0097] Depend on Figure 11 As shown in (a), under a 25% strain condition, the resistance change of the PNIPAm / PANa hydrogel remained almost constant throughout the test, without significant fluctuations or deviations. This demonstrates the extremely high stability of the strain-sensing resistance signal of the PNIPAm / PANa hydrogel before and after cyclic torsion. After 1000 cycles of torsion, its internal microstructure and sensing mechanism were not significantly affected, and it could still stably and reliably sense strain changes and accurately convert these changes into resistance signals. Figure 11As shown in (b), the sensing signal of the PNIPAm / PANa hydrogel exhibits high consistency and stability, indicating that even under the dual extreme conditions of thermal stimulation and puncture damage, the sensing function of the PNIPAm / PANa hydrogel can still function normally. Its internal mechanisms for sensing and transmitting signals are not substantially damaged, and it can continuously and accurately reflect external mechanical stimulation information, demonstrating excellent puncture resistance. Therefore, the PNIPAm / PANa hydrogel not only possesses self-protection capabilities against a series of extreme external mechanical stimuli, maintaining the relative integrity of its structure under extreme conditions such as thermal stimulation, repeated torsion, and puncture, but also maintains high stability of its sensing function, ensuring reliable sensing and transmission of mechanical signals in various complex environments. This characteristic makes the PNIPAm / PANa hydrogel have broad application prospects and enormous development potential in many fields such as intelligent sensing, biomedicine, and soft robotics.

[0098] To investigate the effects of crosslinking density, particle size, and content of microgels on the mechanical properties of PNIPAm / PANa hydrogels that mimic sea cucumber ionic skin, the actual stress-strain conditions of the PNIPAm / PANa hydrogels obtained in Examples 2-11 were tested and compared.

[0099] like Figure 12 As shown, comparing the actual stress-strain curves of the PNIPAm / PANa hydrogels obtained in Examples 2-5 reveals that, with the increase of microgel crosslinking density, the overall strain hardening capacity of the PNIPAm / PANa hydrogel exhibits a trend of first significantly increasing and then decreasing. Its strain hardening capacity gradually increases from an initial 14 times to 58 times, and then decreases to 10 times. This phenomenon is mainly due to the microgels acting as physical crosslinking points in the PNIPAm / PANa hydrogel system. When the crosslinking density of the microgels increases, their rigidity also increases. Higher rigidity reduces the deformation capacity that the microgels can withstand. Under external force, this hinders the slippage and orientation process of the molecular chains within the PNIPAm / PANa hydrogel, ultimately leading to a significant decrease in the strain hardening performance of the PNIPAm / PANa hydrogel.

[0100] like Figure 13As shown, comparing the actual stress-strain curves of the PNIPAm / PANa hydrogels prepared in Examples 2 and 6-8 reveals that, with the gradual increase of microgel content, the overall strain hardening capacity of the PNIPAm / PANa hydrogel also exhibits a trend of first increasing and then slightly decreasing. Specifically, the strain hardening capacity gradually increases from an initial 7 times to 58 times, and then slightly decreases to 53 times. This phenomenon is mainly because when the microgel content increases, the number of stress concentration points inside the PNIPAm / PANa hydrogel increases accordingly. These stress concentration points can enhance the strain hardening performance of the PNIPAm / PANa hydrogel to a certain extent, enabling it to better resist deformation under external forces. However, when the microgel content is too high, excessive microgels will occupy a large amount of space inside the PNIPAm / PANa hydrogel, thereby hindering the full extension of the molecular chains and limiting further improvement in its strain hardening performance.

[0101] like Figure 14 As shown, in Examples 2 and 9-11, the microgel particle size can be effectively controlled by adjusting the stirring speed during the pre-emulsification process in step S2. Furthermore, as the stirring speed increases during the pre-emulsification process, the microgel particle size becomes smaller, and the particle size distribution becomes narrower. Figure 15 As shown, a comparison of the actual stress-strain curves of the PNIPAm / PANa hydrogels prepared in Examples 2 and 9-11 reveals that the mechanical properties of the PNIPAm / PANa hydrogel significantly improve with the gradual reduction of the microgel particle size. When the microgel particle size is large, its interaction with the surrounding PNIPAm molecular chains is weak, resulting in poor overall mechanical properties of the PNIPAm / PANa hydrogel. However, as the microgel particle size gradually decreases, its distribution in the PNIPAm / PANa hydrogel becomes more uniform and dense, and the interaction with the molecular chains is significantly enhanced. Smaller microgel particle sizes can better embed into the molecular chain network, forming more physical cross-linking points, effectively limiting the slippage and orientation of the molecular chains, thereby improving the PNIPAm / PANa hydrogel's resistance to external deformation. Simultaneously, this close interaction also facilitates the uniform transmission of stress within the PNIPAm / PANa hydrogel, enabling it to more effectively disperse stress under load, avoiding damage caused by localized stress concentration, and thus significantly improving the overall mechanical properties of the PNIPAm / PANa hydrogel.

[0102] Therefore, the crosslinking density, particle size, and content of the microgels all significantly affect the strain hardening properties of the PNIPAm / PANa hydrogel, which mimics sea cucumber ionic skin. In practical preparation and application, it is necessary to precisely control the crosslinking density, particle size, and content of the microgels to optimize the strain hardening properties of the hydrogels and enable them to better meet the mechanical performance requirements of different application scenarios.

[0103] The elastic modulus, toughness, and maximum differential modulus of the PNIPAm / PANa hydrogels prepared in Examples 2-11 were tested and compared to verify their resistance to deformation, energy absorption capacity, and sensitivity of their internal structure to external forces under different stress conditions. Figure 16 As shown, the PNIPAm / PANa hydrogel prepared in Example 2 achieves optimal strain hardening performance, making it more widely applicable and more reliable in practical applications. In the PNIPAm / PANa hydrogel prepared in Example 2, the average particle size of the microgels is 20 μm, enabling the microgels to form a tighter and more effective interaction with the surrounding molecular chains. The crosslinking density of the microgels is 2 mol%, ensuring the rigidity and stability of the microgels themselves without limiting their movement and deformation coordination ability in the hydrogel system due to excessive crosslinking. The microgel content is 0.8 wt%, allowing the microgels to fully exert their reinforcing effect in the hydrogel system without adversely affecting the overall performance of the hydrogel due to excessively high or low content.

[0104] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0105] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A dual-dynamic topological hydrogel mimicking sea cucumber ion skin, characterized in that, include: Thermosensitive poly(N-isopropylacrylamide) hydrogel, as a continuous matrix, is used to mimic the dynamic adaptability of sea cucumber skin; Ionically conductive microgels, as rigid dispersed phases, are used to simulate the collagen fiber network of the connective tissue layer of sea cucumbers. The ionically conductive microgels are dispersed within the poly(N-isopropylacrylamide) hydrogel and are physically entangled with the hydrogel, forming cross-linking points to construct a dynamic network of "rigid nodes-flexible matrix." The ionically conductive microgels are any one of sodium polyacrylate microgels, sodium polystyrene sulfonate microgels, and sodium polyvinyl sulfonate microgels. In the dual-dynamic topological hydrogel, the content of the ion-conducting microgel is any value between 0.08wt% and 1.2wt%. The preparation method of the dual-dynamic topological hydrogel includes the following steps: S1. Mix the obtained N-isopropylacrylamide monomer, the first crosslinking agent and the photoinitiator evenly to form a mixture; S2. The obtained microgel monomer, second crosslinking agent and initiator are added to deionized water and mixed evenly to form an aqueous phase. An emulsifying agent is added to the aqueous phase, and pre-emulsification and emulsification are performed. After that, the mixture is filtered to obtain ion-conductive microgel. S3. Add the ion-conductive microgel to the mixture and stir until homogeneous to obtain a hydrogel precursor solution. S4. The hydrogel precursor solution is placed at a temperature of -5℃ to 5℃ and subjected to polymerization under ultraviolet light to obtain a dual dynamic topological hydrogel.

2. The dual dynamic topological hydrogel as described in claim 1, characterized in that, The particle size of the ion-conductive microgel is limited to the range of 10 μm to 550 μm.

3. The dual dynamic topological hydrogel as described in claim 1, characterized in that, The crosslinking density of the ion-conductive microgel is limited to the range of 1 mol% to 8 mol%.

4. The dual dynamic topological hydrogel as described in claim 1, characterized in that, In step S1, the molar content of the N-isopropylacrylamide monomer in the mixture is 1.5 mol / L to 3 mol / L, the molar content of the first crosslinking agent is 0.05% to 0.2% of the molar content of the N-isopropylacrylamide monomer, and the molar content of the photoinitiator is 0.005% to 0.05% of the molar content of the N-isopropylacrylamide monomer.

5. The dual dynamic topological hydrogel as described in claim 1, characterized in that, In step S2, before adding the emulsifying agent to the aqueous phase, nitrogen gas is first introduced into the aqueous phase to remove oxygen from the aqueous phase; the emulsifying agent is cyclohexane containing Span 80.

6. The dual dynamic topological hydrogel as described in claim 1, characterized in that, In step S2, during the pre-emulsification process, the stirring speed is any value between 100 rpm and 1500 rpm, and the emulsification temperature is any value between 20°C and 80°C.

7. The dual dynamic topological hydrogel as described in claim 1, characterized in that, In step S2, the ion-conductive microgel monomer is the corresponding sodium acrylate, sodium styrene sulfonate, or sodium vinyl sulfonate.

8. The dual dynamic topological hydrogel as described in claim 7, characterized in that, In step S2, the ion-conductive microgel is sodium polyacrylate microgel; in the aqueous phase, the molar content of the second crosslinking agent is 1% to 8% of the molar content of sodium acrylate, and the molar content of the initiator is 0.05% to 0.2% of the molar content of sodium acrylate.

9. The application of the dual-dynamic topological hydrogel according to any one of claims 1 to 8, characterized in that, This includes applications in multimodal smart wearable sensors.

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