Deep eutectic solvent regulated and controlled sericin modified carbon nanotube-acrylamide composite conductive hydrogel as well as preparation method and application thereof

Abstract

The invention discloses a deep eutectic solvent regulated and controlled sericin modified carbon nanotube-acrylamide composite conductive hydrogel as well as a preparation method and application thereof, and relates to the field of flexible electronic devices and biosensing. The preparation method comprises the following steps: firstly, mixing sericin and carbon nanotubes under a water phase condition, carrying out ultrasonic treatment, and constructing an SS-coated CNT composite solution through a non-covalent coating effect; then, a choline chloride-urea deep eutectic solvent is introduced, and a composite interface is reconstructed and stabilized through interaction of multiple hydrogen bonds; and finally, adding an acrylamide monomer, a cross-linking agent and an initiator, and carrying out thermal initiation polymerization to form the three-dimensional network conductive hydrogel. The deep eutectic solvent is used as an interface regulation factor to promote the formation of a continuous conductive network, and the piezoresistive sensitivity and the linear response interval of the hydrogel can be synergistically regulated by adjusting the dosage of the deep eutectic solvent; the process of firstly constructing SS (at) CNT in a water phase and then introducing the deep eutectic solvent can effectively inhibit carbon nanotube agglomeration and sericin chain collapse, and the structural stability, the electrical continuity and the cycle durability of a conductive network are remarkably improved.

Description

Technical Field

[0001] This invention relates to the fields of flexible electronic devices and biosensing technology, specifically to a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent regulation, its preparation method, and its application. Background Technology

[0002] With the development of flexible electronics, wearable devices, and human-computer interaction technologies, flexible mechanical sensors that can closely adhere to the human body surface and sense deformation, pressure, and vibration signals in real time have attracted widespread attention. Conductive hydrogels, due to their excellent flexibility, deformability, and conductive response characteristics, have become important sensitive materials for flexible mechanical sensors. Conductive hydrogels typically use synthetic polymers (such as polyacrylamide and polyvinyl alcohol) or natural polymers (such as gelatin and silk fibroin) as a matrix, forming a three-dimensional network structure through chemical or physical cross-linking. Conductive fillers such as carbon nanotubes, graphene, and conductive polymers are introduced, or conductive pathways are constructed through electrolyte ions. Under external mechanical forces such as stretching, compression, or bending, the internal conductive pathways of the conductive hydrogel change, leading to changes in resistance or conductivity, thus enabling the detection of mechanical signals. These hydrogel sensors are often prepared into thin films or patches using processes such as free radical polymerization and ionic cross-linking, and are applied to the monitoring of large-scale deformations such as human joint movements.

[0003] However, existing conductive hydrogel sensors have some significant drawbacks in practical applications. First, under repeated stretching, compression, and minute deformation, their internal conductive network structure is prone to irreversible damage or fatigue, leading to reduced continuity of the conductive pathway. This results in increased baseline drift, exacerbated response fluctuations, and decreased cyclic stability, making it difficult to maintain long-term monitoring reliability. Second, their response accuracy to minute force changes is insufficient, easily leading to signal drift, inconsistent responses, or decreased sensitivity over time, hindering accurate monitoring. Furthermore, current research often focuses on optimizing single response indicators, lacking the ability to extract multidimensional features from different types of mechanical / physiological signals, making it difficult to achieve comprehensive perception and effective differentiation of various human behaviors and physiological signals. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a sericin-modified carbon nanotube-acrylamide composite conductive hydrogel with eutectic solvent regulation, its preparation method, and its applications. The method first constructs a sericin-modified carbon nanotube composite dispersion system in an aqueous phase, then introduces a eutectic solvent and performs subsequent polymerization to obtain a composite three-dimensional network with continuous conductive pathways. By adjusting the amount of eutectic solvent introduced, the piezoresistive sensitivity, linear response range, and cyclic stability are synergistically regulated, thereby meeting the requirements for small signal recognition and stable output over a wide strain range in flexible strain sensing.

[0005] To achieve the above objectives, the specific solution adopted in this invention is as follows: a method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel controlled by a deep eutectic solvent, comprising the following steps: (1) under stirring conditions, adding carbon nanotube dispersion to a sericin aqueous solution, stirring and reacting at 55-65℃ and undergoing ultrasonic treatment to obtain a sericin-modified carbon nanotube composite solution; (2) mixing choline chloride and urea at a molar ratio of 1:2, heating and stirring at 75-85℃ to obtain a deep eutectic solvent; (3) adding the deep eutectic solvent, acrylamide monomer, crosslinking agent and initiator obtained in step (1) sequentially to the sericin-modified carbon nanotube composite solution obtained in step (2), stirring and mixing, and then carrying out a thermally initiated polymerization reaction at 55-65℃ to obtain a composite conductive hydrogel.

[0006] As an optimized method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with a deep eutectic solvent controlled by the above-mentioned method, the mass fraction of sericin in the sericin aqueous solution is 1%-5%.

[0007] As another optimized method for preparing the above-mentioned deep eutectic solvent-controlled silk fibroin modified carbon nanotube / acrylamide composite conductive hydrogel, the mass fraction of carbon nanotubes in the carbon nanotube dispersion is 10%-20%.

[0008] As another optimized method for preparing the above-mentioned deep eutectic solvent-controlled sericin-modified carbon nanotube / acrylamide composite conductive hydrogel, the volume ratio of the sericin aqueous solution to the carbon nanotube dispersion in the composite solution is 3:1-5:1.

[0009] As another optimized method for preparing the above-mentioned deep eutectic solvent-controlled sericin-modified carbon nanotube / acrylamide composite conductive hydrogel, the mass-volume ratio of the acrylamide monomer to the sericin-modified carbon nanotube composite solution is 2-4 g: 10 mL.

[0010] As an optimized method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel regulated by a deep eutectic solvent, the mass-volume ratio of the crosslinking agent to the sericin-modified carbon nanotube composite solution is 3-8 mg:10 mL; the mass-volume ratio of the initiator to the sericin-modified carbon nanotube composite solution is 20-40 mg:10 mL.

[0011] As an alternative optimization of the above-mentioned method for preparing sericin-modified carbon nanotube / acrylamide composite conductive hydrogels regulated by a deep eutectic solvent, the initiator is ammonium persulfate and the crosslinking agent is N,N′-methylenebisacrylamide.

[0012] The present invention also provides a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent regulation, which is prepared by the above preparation method; the composite conductive hydrogel exhibits a uniform three-dimensional porous network structure, and the carbon nanotubes are uniformly dispersed in the polyacrylamide matrix to form a continuous conductive pathway.

[0013] The present invention also provides a flexible strain sensor, comprising a sensitive unit formed of the above-mentioned composite conductive hydrogel, wherein the sensitive unit is a strip-shaped or sheet-shaped structure and flexible electrodes are provided at both ends; the flexible electrodes are any one of conductive copper foil tape, conductive silver paste or flexible conductive fabric.

[0014] The present invention also provides the application of the above-mentioned composite conductive hydrogel in the detection and recognition of weak physiological movements, wherein the weak physiological movements include one or more of the following: facial expression changes, vocalization, swallowing movements, and electrocardiogram signals.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel regulated by a deep eutectic solvent. The deep eutectic solvent is introduced as an interface structure regulating component to improve the dispersion and interfacial stability of sericin-modified carbon nanotubes in the polymerization system, which is beneficial for the construction of a continuous conductive network. This invention specifies the process sequence: first, an SS@CNT composite solution is prepared under aqueous conditions, then the deep eutectic solvent is introduced and subsequent polymerization is carried out. This sequence control reduces the probability of re-aggregation of carbon nanotubes in a strong hydrogen-bonded environment and minimizes the impact of sericin chain conformational changes on the uniformity of the network structure. The resulting composite conductive hydrogel exhibits lower baseline drift and higher signal retention in cyclic deformation testing, and maintains a stable and repeatable piezoresistive response over a wide strain range.

[0016] 2. In this invention, the composite conductive hydrogel has good flexibility and skin-fitting conformity, and can stably adhere to complex curved areas such as the face and throat, so as to achieve stable perception of different types of human movements and physiological electrical signals.

[0017] 3. The preparation method of the present invention has a simple process, low requirements for equipment conditions, wide availability of raw materials, and controllable cost. It is suitable for large-scale preparation and integrated application. While ensuring performance, it has high economic efficiency and practical value, which is conducive to the promotion and application of flexible multifunctional sensors in the fields of daily health monitoring and human-computer interaction.

[0018] 4. By adjusting the amount of eutectic solvent introduced, this invention can achieve synergistic control of the piezoresistive response sensitivity and linear response range of the composite conductive hydrogel, so that the resulting hydrogel maintains stable and repeatable electrical response behavior over a wide strain range (sensitivity of about 2.3 in the low strain region, about 5.3 in the medium strain region, and about 7.3 in the high strain region), with a response time of about 64ms, and still maintains good signal stability after 5000 cycles of testing. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the cross-section of a flexible strain sensor.

[0020] Figure 2 These are the electrical response curves of flexible strain sensors with different eutectic solvent contents.

[0021] Figure 3 This is the electrical response characteristic curve of the flexible strain sensor.

[0022] Figure 4 These are test graphs showing the electrical response stability of a flexible strain sensor under different loading speeds.

[0023] Figure 5 This is a test diagram of the long-term cyclic stability of a flexible strain sensor under the same loading speed conditions.

[0024] Figure 6 This is a schematic diagram of the electrical signal response of a flexible strain sensor under facial smiling deformation.

[0025] Figure 7 This is a schematic diagram of the electrical signal response of a flexible strain sensor caused by changes in facial surface condition.

[0026] Figure 8 This is a schematic diagram illustrating the application of flexible strain sensors in electrocardiogram (ECG) signal monitoring. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments of the present invention should be understood as prior art known or should be known by those skilled in the art.

[0028] A method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent regulation includes the following steps: (1) Under stirring conditions, carbon nanotube dispersion is added to the sericin aqueous solution, and the mixture is reacted and sonicated at 55-65℃ to obtain a sericin-modified carbon nanotube composite solution (i.e., SS@CNT composite solution). Specifically, sericin is dissolved in deionized water to form a homogeneous aqueous solution, i.e., the sericin aqueous solution of the present invention, wherein the mass fraction of sericin in the sericin aqueous solution is 1%-5%; under continuous stirring conditions, carbon nanotube dispersion is added dropwise to the sericin aqueous solution at a rate of 1-2 drops / s, and the mixed solution is heated to 55-65℃ for sonication; the mass fraction of carbon nanotubes in the carbon nanotube dispersion is 10%-20%; the volume ratio of sericin aqueous solution to carbon nanotube dispersion in the SS@CNT composite solution is 3:1-5:1. This method enables sericin molecules to coat and stabilize the surface of carbon nanotubes through non-covalent interactions, thereby constructing a protein-modified sericin-modified carbon nanotube composite solution with a stable interface structure. This achieves uniform dispersion of carbon nanotubes at the molecular scale and provides an interface basis for the stable construction of subsequent conductive networks.

[0029] (2) Choline chloride and urea are mixed in a 1:2 molar ratio and stirred at 75-85℃ until a transparent and uniform liquid is formed, thus obtaining a transparent and uniform eutectic solvent.

[0030] (3) Add the eutectic solvent, acrylamide monomer, crosslinking agent, and initiator obtained in step (2) to the SS@CNT composite solution obtained in step (1) in sequence. After stirring and mixing, carry out a thermally initiated polymerization reaction at 55-65℃ to form a composite conductive hydrogel. Specifically, add the eutectic solvent and acrylamide monomer to the obtained composite solution and stir at room temperature to obtain a mixed solution. The ratio of acrylamide monomer to composite solution in the mixed solution is 2-4 g:10 mL, and the volume ratio of eutectic solvent to composite solution is 1:10. The conductive filler-polymer interface structure is reconstructed and stabilized through the intermolecular interaction of the eutectic solvent, thereby promoting the formation of continuous conductive pathways. Then, add the crosslinking agent and initiator to the above mixed solution, stir, and react at 55-65℃ to obtain a composite conductive hydrogel. The ratio of crosslinking agent to composite solution is 3-8 mg:10 mL, and the ratio of initiator to composite solution is 20-40 mg:10 mL. Acrylamide was subjected to a free radical polymerization reaction under thermal initiation conditions to form a three-dimensional network conductive hydrogel with polyacrylamide as the backbone, a deep eutectic solvent and a sericin-modified carbon nanotube composite structure (SS@CNT).

[0031] This invention significantly improves the water retention and low-temperature adaptability of the composite conductive hydrogel by introducing a deep eutectic solvent and forming multiple hydrogen bond interactions with the polymer network. It also reduces the degradation of mechanical and conductive properties caused by water loss or temperature changes, thereby enhancing the stability and durability of the composite conductive hydrogel during long-term wear and repeated use.

[0032] 0.2 g of sericin was added to 8 mL of deionized water and mixed under magnetic stirring until completely dissolved to form a homogeneous and transparent solution – a sericin aqueous solution. 2 mL of a 14 wt% carbon nanotube dispersion was added dropwise to the obtained sericin aqueous solution at a rate of 1 drop / s. The mixture was stirred at 60 °C and 500 rpm for 2 h, and then sonicated for 1 h to obtain a homogeneous and stable SS@CNT composite solution.

[0033] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 80°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0034] Add 1 mL of eutectic solvent and 3 g of acrylamide to the obtained SS@CNT composite solution, and stir at room temperature and 500 rpm for 2 h. Then, add 5 mg of N,N′-methylenebisacrylamide and 30 mg of ammonium persulfate to the mixed solution, and stir for 20 min to obtain the precursor solution. Inject the obtained precursor solution into a mold and react at 60 °C for 6 h to obtain the composite conductive hydrogel.

[0035] Example 2 0.2g of sericin was added to 8mL of deionized water and mixed under magnetic stirring until it was completely dissolved to form a uniform and transparent solution - sericin aqueous solution. 2mL of carbon nanotube dispersion with a mass fraction of 14wt% was slowly added to the obtained sericin aqueous solution and stirred at 60℃ and 500rpm for 2h. The obtained solution was then sonicated for 1h to obtain a uniform and stable SS@CNT composite solution.

[0036] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 80°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0037] Add 0.5 mL of eutectic solvent and 3 g of acrylamide to the obtained SS@CNT composite solution, and stir at room temperature and 500 rpm for 2 h. Then, add 5 mg of N,N′-methylenebisacrylamide and 30 mg of ammonium persulfate to the mixed solution, and stir for 20 min to obtain the precursor solution. Inject the obtained precursor solution into a mold and react at 60 °C for 6 h to obtain the composite conductive hydrogel.

[0038] Compared with Example 1, this example has a lower eutectic solvent content, resulting in a relatively weaker continuity of the conductive network in the obtained composite conductive hydrogel, and exhibits a lower piezoresistive response sensitivity in the low strain range.

[0039] Example 3 0.2g of sericin was added to 8mL of deionized water and mixed under magnetic stirring until it was completely dissolved to form a uniform and transparent solution - sericin aqueous solution. 2mL of carbon nanotube dispersion with a mass fraction of 14wt% was slowly added to the obtained sericin aqueous solution and stirred at 60℃ and 500rpm for 2h. The obtained solution was then sonicated for 1h to obtain a uniform and stable SS@CNT composite solution.

[0040] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 80°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0041] Add 2 mL of eutectic solvent and 3 g of acrylamide to the obtained SS@CNT composite solution, and stir at room temperature and 500 rpm for 2 h. Then, add 5 mg of N,N′-methylenebisacrylamide and 30 mg of ammonium persulfate to the mixed solution, and stir for 20 min to obtain the precursor solution. Inject the obtained precursor solution into a mold and react at 60 °C for 6 h to obtain the composite conductive hydrogel.

[0042] Compared with Example 1, this example has a higher content of eutectic solvent, and the resulting composite conductive hydrogel has better water retention and low temperature adaptability. However, the structural stability of the conductive network is slightly reduced, and the linearity of the response is reduced in the high strain range.

[0043] Example 4 0.1 g of sericin was added to 10 mL of deionized water and mixed under magnetic stirring until completely dissolved to form a homogeneous and transparent solution – a sericin aqueous solution. 2 mL of a 10 wt% carbon nanotube dispersion was added dropwise to the obtained sericin aqueous solution at a rate of 1 drop / s. The mixture was stirred at 55 °C and 500 rpm for 2 h, and then sonicated for 1 h to obtain a homogeneous and stable SS@CNT composite solution.

[0044] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 75°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0045] 1.2 mL of eutectic solvent and 2.4 g of acrylamide were added to the obtained SS@CNT composite solution, and the mixture was stirred at room temperature and 500 rpm for 2 h. Then, 3.6 mg of N,N′-methylenebisacrylamide and 24 mg of ammonium persulfate were added to the mixed solution, and the mixture was stirred for 20 min to obtain the precursor solution. The precursor solution was injected into a mold and reacted at 55 °C for 6 h to obtain the composite conductive hydrogel.

[0046] Compared with Example 1, this example has a lower concentration of sericin (1wt%), a lower concentration of carbon nanotube dispersion (10wt%), a lower reaction temperature (55℃), and the amounts of acrylamide monomer, crosslinking agent, and initiator are all taken at the lower limit. As a result, the conductive filler content of the composite conductive hydrogel is lower, the crosslinking density is smaller, the mechanical strength and conductivity are relatively weaker, but the flexibility is better.

[0047] Example 5 0.5 g of sericin was added to 10 mL of deionized water and mixed under magnetic stirring until completely dissolved to form a homogeneous and transparent solution – a sericin aqueous solution. 2 mL of a 20 wt% carbon nanotube dispersion was added dropwise to the obtained sericin aqueous solution at a rate of 2 drops / s. The mixture was stirred at 65 °C and 500 rpm for 2 h, and then sonicated for 1 h to obtain a homogeneous and stable SS@CNT composite solution.

[0048] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 85°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0049] 1.2 mL of eutectic solvent and 4.8 g of acrylamide were added to the obtained SS@CNT composite solution, and the mixture was stirred at room temperature and 500 rpm for 2 h. Then, 9.6 mg of N,N′-methylenebisacrylamide and 48 mg of ammonium persulfate were added to the mixed solution, and the mixture was stirred for 20 min to obtain the precursor solution. The precursor solution was injected into a mold and reacted at 65 °C for 6 h to obtain the composite conductive hydrogel.

[0050] Compared with Example 1, this example has a higher concentration of sericin (5wt%), a higher concentration of carbon nanotube dispersion (20wt%), a higher reaction temperature (65℃), and the upper limits of the dosage of acrylamide monomer, crosslinking agent, and initiator are all used. The resulting composite conductive hydrogel has a higher content of conductive filler, a higher crosslinking density, and improved mechanical strength and conductivity. However, the flexibility and tensile properties of the gel are reduced.

[0051] Example 6 0.3 g of sericin was added to 10 mL of deionized water and mixed under magnetic stirring until completely dissolved to form a homogeneous and transparent solution – a sericin aqueous solution. 2.5 mL of a 15 wt% carbon nanotube dispersion was added dropwise to the obtained sericin aqueous solution at a rate of 1 drop / s. The mixture was stirred at 60 °C and 500 rpm for 2 h, and then sonicated for 1 h to obtain a homogeneous and stable SS@CNT composite solution.

[0052] Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 80°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0053] 1.25 mL of eutectic solvent and 3.75 g of acrylamide were added to the obtained SS@CNT composite solution, and the mixture was stirred at room temperature and 500 rpm for 2 h. Then, 6.9 mg of N,N′-methylenebisacrylamide and 37.5 mg of ammonium persulfate were added to the mixed solution, and the mixture was stirred for 20 min to obtain the precursor solution. The precursor solution was injected into a mold and reacted at 60 °C for 6 h to obtain the composite conductive hydrogel.

[0054] Compared with Example 1, all parameters in this example are taken as the midpoint of the range. The concentration of sericin is 3wt%, the concentration of carbon nanotube dispersion is 15wt%, and the dosage of acrylamide monomer, crosslinking agent, and initiator are all taken as the midpoint. The resulting composite conductive hydrogel achieves a good balance between mechanical properties, conductivity, and flexibility, and its overall performance is comparable to that of Example 1.

[0055] Comparative Example 1 Choline chloride and urea were mixed in a molar ratio of 1:2, heated and stirred at 80°C until a transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent.

[0056] Dissolve 0.2g of sericin in 8mL of deionized water, then add 1mL of the above eutectic solvent mixture and mix under magnetic stirring until completely dissolved; then slowly add 2mL of 14wt% carbon nanotube dispersion to the above solution, stir at 60℃ and 500rpm for 2h, and sonicate the resulting solution for 1h.

[0057] The results showed that in the presence of a eutectic solvent with strong hydrogen bonds, carbon nanotubes underwent significant secondary aggregation, resulting in a black precipitate and stratification of the solution, failing to form a homogeneous and stable composite solution. Further polymerization with the addition of acrylamide monomer, crosslinking agent, and initiator resulted in a hydrogel with extremely uneven carbon nanotube distribution, obvious aggregates, poor and unstable electrical conductivity.

[0058] This comparative example demonstrates that the process sequence specified in this invention, namely "first preparing a sericin-modified carbon nanotube composite solution under aqueous conditions, and then introducing a deep eutectic solvent," is crucial for obtaining a uniform and stable composite conductive hydrogel.

[0059] Comparative Example 2 Add 0.2g of sericin to 8mL of deionized water and mix under magnetic stirring until completely dissolved to form a uniform and transparent solution. Slowly add 2mL of carbon nanotube dispersion with a mass fraction of 14wt% to the obtained sericin aqueous solution, stir at 60℃ and 500rpm for 2h, and sonicate the obtained solution for 1h to obtain SS@CNT composite solution.

[0060] 3g of acrylamide (without adding a deep eutectic solvent) was added directly to the obtained SS@CNT composite solution, and stirred at room temperature and 500rpm for 2h. Then, 5mg of N,N′-methylenebisacrylamide and 30mg of ammonium persulfate were added, and stirred for 20min to obtain a precursor solution. The precursor solution was injected into a mold and reacted at 60℃ for 6h to obtain a hydrogel.

[0061] The obtained hydrogel was used to prepare a flexible strain sensor and its performance was tested. The results showed that: (1) poor cyclic stability: after 1000 cycles of loading and unloading, the sensor sensitivity decreased by about 35% and the signal baseline drifted significantly; (2) low sensitivity: under the same strain conditions, the relative resistance change was only about 60% of that in Example 1; (3) poor water retention: after being placed at room temperature for 7 days, the hydrogel lost about 25% of its mass and its mechanical and electrical properties both showed significant degradation.

[0062] This comparative example demonstrates that the introduction of a deep eutectic solvent plays a crucial role in improving the conductive network stability, piezoresistive response sensitivity, and long-term performance of the composite conductive hydrogel.

[0063] Comparative Example 3 The composite conductive hydrogel was prepared according to the method of Example 1, but the amount of eutectic solvent added was increased from 1 mL to 4 mL (the volume ratio of eutectic solvent to composite solution was 4:10).

[0064] The results showed that the polymerization reaction of acrylamide monomer was inhibited due to the excessively high content of eutectic solvent, and the polymerization time needed to be extended to more than 12 hours. The mechanical strength of the resulting hydrogel was significantly reduced, and it was too soft to be cut and processed. At the same time, the hydrogel was prone to plastic deformation in the tensile test, and the reversibility and repeatability of the electrical response were poor.

[0065] The comparative example shows that the amount of eutectic solvent introduced needs to be controlled within a suitable range (0.5:10-2:10). Excessive eutectic solvent content will have an adverse effect on the mechanical properties and electrical response stability of the hydrogel.

[0066] Example 7 A flexible strain sensor includes a sensitive unit obtained by cutting the composite conductive hydrogel described in Example 1. The sensitive unit has a strip-shaped or sheet-shaped structure, and flexible electrodes are provided at both ends of the sensitive unit. The flexible electrodes are conductive copper foil tapes. Figure 1 This is a scanning electron microscope image of the cross-section of the flexible strain sensor, created by... Figure 1 It is evident that the composite conductive hydrogel exhibits a relatively uniform porous structure with clear pore morphology, a relatively concentrated pore size distribution, and continuous and intact pore walls, without any obvious collapse. A stable three-dimensional network framework is formed within the hydrogel, providing continuous support for the dispersion and connection of carbon nanotubes in the matrix. Simultaneously, the presence of the eutectic solvent helps to construct an ion transport environment, providing structural support for the material's conductivity and overall structural stability.

[0067] Example 8 An application of the above-mentioned composite conductive hydrogel in detecting and identifying weak physiological movements is first described by preparing a flexible strain sensor from the composite conductive hydrogel.

[0068] The aforementioned flexible strain sensor is attached to the facial expression muscles of the human face, ensuring close contact with the skin surface. When a person makes facial expressions such as smiling, frowning, or pursing their lips, the facial muscles undergo minute deformations, which are transmitted to the flexible strain sensor. This causes reversible changes in the sensor's internal conductive network structure, resulting in changes in the resistance signal. The electrical signals corresponding to different facial expressions exhibit distinguishable characteristics in amplitude and rate of change, enabling the recognition and monitoring of facial expression changes.

[0069] The aforementioned flexible strain sensor is attached to the skin surface of the human throat and secured with medical adhesive material, covering the area near the Adam's apple. When a person performs different vocalizations, coughs, or swallows, the local muscles and soft tissues of the throat produce different patterns of minute displacements and vibrations. The flexible strain sensor detects these corresponding mechanical changes and converts them into resistance signals. The signals corresponding to different laryngeal behaviors exhibit significant differences in waveform morphology, amplitude, and frequency characteristics, thus allowing for the differentiation of different vocalization states and actions such as coughing and swallowing.

[0070] The aforementioned flexible strain sensor is attached to the heart region of the human chest and connected to a signal acquisition circuit. In a resting state, the weak electrical signals generated by the heartbeat are conducted and collected through hydrogel electrodes, forming periodic electrocardiogram-related signals. Therefore, the sensor maintains good skin compliance and electrical contact stability during wear, making it suitable for continuous sensing of electrocardiogram signals.

[0071] Electrical Response of Flexible Strain Sensors Based on Conductive Hydrogels with Different Eutectic Solvent Contents Four composite conductive hydrogels were prepared using the method of Example 1, and flexible strain sensors were fabricated using these four composite conductive hydrogels. The eutectic solvent contents in the four flexible strain sensors were 0.5 mL, 1 mL, 1.5 mL, and 2 mL, respectively, with the same contents of other components. The electrical response curves of the four flexible strain sensors were obtained, as shown below. Figure 2 As shown, by Figure 2 It is evident that variations in the eutectic solvent content significantly impact the electrical response behavior of the flexible strain sensor. Compared to flexible strain sensors with excessively low or high eutectic solvent content, those with moderate content exhibit a larger relative resistance variation and better response continuity across a wider strain range. This suggests that appropriately controlling the eutectic solvent content helps construct a more stable and continuous conductive path, thereby effectively improving the electrical performance of the composite conductive hydrogel. With increasing applied strain, the relative resistance of the flexible strain sensor shows a continuous upward trend, exhibiting segmented response characteristics across different strain ranges: a sensitivity of 2.3 in the low strain range, increasing to 5.3 in the medium strain range, and further improving to 7.3 in the high strain range. Even under large strain conditions, the flexible strain sensor maintains a stable and continuous resistance response, demonstrating its good applicability in large deformation monitoring.

[0072] <Fast Response Feature> A composite conductive hydrogel was prepared using the method of Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. This flexible strain sensor exhibits a short electrical response time under external stimuli, such as... Figure 3 As shown, the response time is approximately 64 ms, and the response and recovery processes are clearly discernible. The signal changes rapidly follow the application and removal of external stimuli, with no significant signal delay observed. This rapid electrical response characteristic makes it suitable for real-time monitoring of transient or high-frequency mechanical signals.

[0073] <Electrical Response Stability Test> A composite conductive hydrogel was prepared using the method of Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. The electrical response stability of the flexible strain sensor under different loading speeds was tested, such as... Figure 4 As shown. By Figure 4 It can be seen that the relative resistance change of the flexible strain sensor exhibits a stable and repeatable periodic response characteristic over time. When the loading speed is 1 mm / s, 2 mm / s and 4 mm / s, the flexible strain sensor can maintain a clear response peak and a stable signal amplitude in each speed range, without obvious signal attenuation or drift, indicating that the flexible strain sensor has good electrical response stability and structural reliability under different loading rates.

[0074] Long-term cycling stability testing A composite conductive hydrogel was prepared using the method of Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. The long-term cyclic stability of the flexible strain sensor under the same loading conditions was tested, such as... Figure 5 As shown. By Figure 5 It can be seen that after 5000 consecutive cyclic loading and unloading tests on the flexible strain sensor, its relative resistance change remained stable over time, with no significant signal attenuation or baseline drift. Figure 5 The insets show magnified views of the initial and final stages of the cyclic test, respectively. It can be seen that the electrical response curves of the two stages are basically consistent in terms of amplitude, waveform, and periodicity, indicating that the flexible strain sensor still has good electrical response stability and structural durability under long-term and multiple cycles.

[0075] <Flexible strain sensor detects facial smile> A composite conductive hydrogel was prepared using the method of Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. The flexible strain sensor was then attached to the surface of a human cheek, such as... Figure 6 As shown, when the face is in a natural state, the flexible strain sensor attached to the cheek does not undergo significant morphological changes, corresponding to a stable initial resistance value. When the face is smiling, the flexible strain sensor attached to the cheek deforms under the stretching of the skin, causing its internal conductive network to reconstruct and resulting in a change in resistance.

[0076] <Flexible strain sensor for detecting facial expressions> A composite conductive hydrogel was prepared using the method of Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. The flexible strain sensor was then attached to the cheek or glabella of a human body, such as... Figure 7As shown, when a person makes different facial expressions, the flexible strain sensor can generate electrical signal responses with distinguishable characteristics: During a smile, the skin in the cheek area stretches, and the sensor outputs a relatively large positive resistance change signal; during a frown, the skin between the eyebrows compresses, and the sensor outputs resistance change signals with different waveform characteristics; during a pursed-lip movement, the muscle movement in the perioral area causes the sensor to generate a corresponding resistance response. The electrical signals corresponding to these different facial expressions show significant differences in amplitude, rate of change, and waveform characteristics, indicating that the flexible strain sensor can effectively identify and distinguish various facial expression changes.

[0077] <Flexible strain sensor for monitoring electrocardiogram signals> A composite conductive hydrogel was prepared using the method described in Example 1, and a flexible strain sensor was fabricated using this composite conductive hydrogel. The flexible strain sensor was attached to the surface of human skin and electrically connected to an electrocardiogram (ECG) signal acquisition device, enabling the acquisition of cardiac electrical activity signals without affecting normal human activities. Due to the good flexibility, adhesion, and interfacial adaptability of the hydrogel, it can form a stable and continuous contact interface with the skin surface, thereby effectively reducing contact impedance and its fluctuations, ensuring that the acquired ECG signal waveform is clear, continuous, and complete, with good signal-to-noise ratio and repeatability.

[0078] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent regulation, characterized in that, Includes the following steps: (1) Under stirring conditions, carbon nanotube dispersion is added to the sericin aqueous solution, stirred and reacted at 55-65℃ and subjected to ultrasonic treatment to obtain sericin modified carbon nanotube composite solution; (2) Choline chloride and urea are mixed at a molar ratio of 1:2 and heated and stirred at 75-85℃ to obtain eutectic solvent; (3) Eutectic solvent, acrylamide monomer, crosslinking agent and initiator are added sequentially to the sericin modified carbon nanotube composite solution obtained in step (1), stirred and mixed, and then subjected to thermally initiated polymerization reaction at 55-65℃ to obtain composite conductive hydrogel.

2. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, characterized in that: The mass fraction of sericin in the aqueous solution is 1%-5%.

3. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, characterized in that: The mass fraction of carbon nanotubes in the carbon nanotube dispersion is 10%-20%.

4. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, characterized in that: The volume ratio of the sericin aqueous solution to the carbon nanotube dispersion in the composite solution is 3:1-5:

1.

5. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, characterized in that: The mass-to-volume ratio of the acrylamide monomer to the sericin-modified carbon nanotube composite solution is 2-4 g: 10 mL.

6. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, wherein the mass-to-volume ratio of the crosslinking agent to the sericin-modified carbon nanotube composite solution is 3-8 mg:10 mL; and the mass-to-volume ratio of the initiator to the sericin-modified carbon nanotube composite solution is 20-40 mg:10 mL.

7. The method for preparing a sericin-modified carbon nanotube / acrylamide composite conductive hydrogel with eutectic solvent control as described in claim 1, characterized in that: The initiator is ammonium persulfate, and the crosslinking agent is N,N′-methylenebisacrylamide.

8. A deep eutectic solvent-controlled sericin-modified carbon nanotube / acrylamide composite conductive hydrogel, characterized in that: The composite conductive hydrogel is prepared by any one of the preparation methods described in claims 1-7; the interior of the composite conductive hydrogel exhibits a uniform porous three-dimensional network structure, and the carbon nanotubes are uniformly dispersed in the polyacrylamide matrix to form a continuous conductive pathway.

9. A flexible strain sensor, characterized in that: It includes a sensitive unit cut from the composite conductive hydrogel of claim 8, wherein the sensitive unit is provided with flexible electrodes at both ends, and the flexible electrodes are any one of conductive copper foil tape, conductive silver paste or flexible conductive fabric.

10. An application of the composite conductive hydrogel as described in claim 9 in detecting and identifying subtle physiological movements, wherein the subtle physiological movements include one or more of facial expression changes, vocalizations and swallowing movements, and electrocardiogram signals.

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