Gelatin / microfibrillated cellulose / graphene conductive hydrogel and its preparation method and application

Abstract

The present invention discloses a gelatin / microfibrillated cellulose / graphene conductive hydrogel, its preparation method and application. The preparation of the conductive hydrogel includes the following steps: graphene, microfibrillated cellulose, gelatin and water / organic binary solvent are made into a graphene / microfibrillated cellulose / gelatin dispersion liquid, which is frozen and thawed in sequence to obtain the gelatin / microfibrillated cellulose / graphene conductive hydrogel. The conductive hydrogel of the present invention has the advantages of high strength, good stretchability, good conductivity, good antifreeze property, good moisture retention property, good flexibility, good biocompatibility, good air permeability, etc. Among them, the tensile strength can reach 200 KPa - 329 KPa, and the elongation rate can reach 170% - 203%. It is a new type of flexible conductive material with excellent performance, and can be widely used in the preparation of flexible sensors, especially wearable flexible sensors, which is of great significance for improving the wide application of conductive hydrogels in flexible sensors.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite hydrogels, and relates to a gelatin / microfibrillated cellulose / graphene conductive hydrogel, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, flexible, stretchable, and user-friendly devices have attracted wide attention in multifunctional wearable electronic devices. As a basic component in soft electronics, stretchable strain sensors that can sense human movement have promoted the rapid development of personalized health detection, human motion monitoring, electronic skin, and robots. Hydrogels based on natural proteins, such as gelatin-based hydrogels and silk fibroin-based hydrogels, have shown great potential in medical devices and wearable devices due to their biocompatibility, degradability, non-toxicity, cell adhesion, and other properties. However, gelatin hydrogels have poor mechanical properties, such as poor strength and low elongation at break, which makes it difficult to use and limits its applications. Introducing various materials, such as carbon-based, cellulose, polymers, metal nanoparticles, etc., into hydrogels for compounding to prepare composite hydrogels can effectively improve the tensile strength and flexibility of hydrogels. However, the existing gelatin-based composite hydrogels still have the following defects: the preparation process is complex, the pH of the reaction system is limited, and toxic substances such as sodium periodate are required during the oxidation of MFC; at the same time, the existing gelatin-based conductive hydrogels still have the following defects: low tensile strength and poor stretchability, where the tensile stress is 120 - 180 KPa. Therefore, obtaining a conductive hydrogel with high strength, good stretchability, good conductivity, good antifreeze property, good moisture retention property, good flexibility, good biocompatibility, and good breathability, as well as a preparation method that is simple in process, convenient to operate, low in cost, green and environmentally friendly, and in line with the concept of sustainable development, is of great significance for improving the wide application of conductive hydrogels in flexible sensors. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a gelatin / microfibrillated cellulose / graphene conductive hydrogel with high strength and good stretchability, a preparation method thereof, and an application thereof.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions.

[0005] A preparation method of a gelatin / microfibrillated cellulose / graphene conductive hydrogel, comprising the following steps:

[0006] S1. Mix graphene, microfibrillated cellulose, gelatin with water / organic binary solvent to prepare a graphene / microfibrillated cellulose / gelatin dispersion; the water / organic binary solvent is obtained by mixing water and an organic solvent;

[0007] S2. Freeze and then thaw the graphene / microfibrillated cellulose / gelatin dispersion liquid in sequence to obtain a gelatin / microfibrillated cellulose / graphene conductive hydrogel.

[0008] In the above preparation method, further improved, in step S1, the mass ratio of water to organic solvent in the water / organic binary solvent is 5 - 9:2; the organic solvent is glycerol and / or ethylene glycol.

[0009] In the above preparation method, further improved, in step S1, the preparation process of the graphene / microfibrillated cellulose / gelatin dispersion liquid includes the following steps:

[0010] S1-1. Mix graphene with the water / organic binary solvent and perform ultrasonic dispersion to obtain a graphene dispersion liquid.

[0011] S1-2. Mix microfibrillated cellulose with the graphene dispersion liquid and perform ultrasonic dispersion to obtain a graphene / microfibrillated cellulose dispersion liquid.

[0012] S1-3. Mix gelatin with the graphene / microfibrillated cellulose dispersion liquid, stir, and perform ultrasonic treatment to obtain a graphene / microfibrillated cellulose / gelatin dispersion liquid.

[0013] In the above preparation method, further improved, in step S1-1, the mass concentration of graphene in the graphene dispersion liquid ≤ 0.8 wt%.

[0014] In the above preparation method, further improved, in step S1-3, the mass of microfibrillated cellulose in the graphene / microfibrillated cellulose / gelatin dispersion liquid is 1% - 5% of the total mass of microfibrillated cellulose and gelatin; the mass ratio of graphene to gelatin in the graphene / microfibrillated cellulose / gelatin dispersion liquid is 1 - 2:15 - 35.

[0015] In the above preparation method, further improved, in step S1-1, the mass concentration of graphene in the graphene dispersion liquid is 0.4 wt% - 0.8 wt%; the time of ultrasonic dispersion is 30 min - 60 min.

[0016] In the above preparation method, further improved, in step S1-2, the time of ultrasonic dispersion is 30 min - 60 min;

[0017] In the above preparation method, further improved, in step S1-3, the stirring is carried out at a temperature of 60°C - 70°C; the rotation speed of the stirring is 50 r / min - 120 r / min; the time of the stirring is 1.5 h - 2 h; the time of the ultrasonic treatment is 30 min - 60 min.

[0018] In the above preparation method, for further improvement, in step S2, the graphene / microfibrillated cellulose / gelatin dispersion is poured into a mold to prepare a conductive hydrogel with a target shape; the freezing is carried out at -20°C to 0°C; the freezing time is 8h to 16h; the thawing is carried out at 25°C; the thawing time is 2h to 5h.

[0019] As a technical concept in one aspect, the present invention also provides a gelatin / microfibrillated cellulose / graphene conductive hydrogel, including gelatin; the gelatin encapsulates microfibrillated cellulose and graphene; the mass ratio of gelatin, microfibrillated cellulose and graphene is 50 to 100∶1 to 5∶2 to 4.

[0020] For the above-mentioned gelatin / microfibrillated cellulose / graphene conductive hydrogel, for further improvement, the gelatin / microfibrillated cellulose / graphene conductive hydrogel is prepared by the above preparation method.

[0021] As a technical concept in one aspect, the present invention also provides an application of the above-mentioned gelatin / microfibrillated cellulose / graphene conductive hydrogel in the preparation of flexible sensors.

[0022] For the above application, for further improvement, the usage method of the flexible sensor includes the following steps:

[0023] (1) Fabricate the gelatin / microfibrillated cellulose / graphene conductive hydrogel into a flexible sensor;

[0024] (2) Fix the flexible sensor on the surface of the object to be detected;

[0025] (3) Connect the power supply and detect the change in surface resistance when the object is moving.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] (1)Aiming at the defects of the existing conductive hydrogels, such as complex preparation process, low tensile strength and low elongation rate, the present invention creatively proposes a preparation method of a gelatin / microfibrillated cellulose / graphene conductive hydrogel. First, graphene, microfibrillated cellulose, gelatin and a water / organic binary solvent are mixed to form a graphene / microfibrillated cellulose / gelatin dispersion, where the water / organic binary solvent is obtained by mixing water and an organic solvent; then the graphene / microfibrillated cellulose dispersion is frozen and thawed in sequence to obtain the gelatin / microfibrillated cellulose / graphene conductive hydrogel. In the present invention, graphene, microfibrillated cellulose and gelatin are added to the water / glycerol binary solvent in sequence, so that microfibrillated cellulose and graphene can be more evenly dispersed in gelatin. By improving their dispersion in gelatin, not only can the transfer stress be effectively reduced, the generation of microcracks be prevented, and the mechanical properties of the composite hydrogel be improved, but also the conductivity of the conductive hydrogel can be enhanced. At the same time, using the water / glycerol binary solvent as the solvent can enhance the moisture retention and antifreeze properties of the conductive hydrogel. On this basis, the graphene / microfibrillated cellulose / gelatin dispersion is frozen and thawed in sequence. Utilizing the unique sol-gel transition property of Gel, a physically cross-linked macromolecular three-dimensional network is formed through simple and efficient physical blending and hydrogen bonding. Without introducing any chemical cross-linking agent, a graphene / microfibrillated cellulose / gelatin (GR / MFC / Gel) conductive hydrogel with high tensile strength and stretchability can be prepared. Specifically, during the freezing process, gelatin cools and gels at low temperature, and at zero degree, water molecules are frozen to form ice cubes, whose volume expands, squeezing the gelatin molecular chains and microfibrillated cellulose molecular chains in the hydrogel, shortening the distance between chains, increasing the possibility of intermolecular hydrogen bonding, and increasing the physical cross-linking degree of the hydrogel network, thus being beneficial to strengthening the mechanical strength of the material. Then, during the thawing process, the ice cubes melt to form a gelatin / microfibrillated cellulose / graphene conductive hydrogel with high strength, good stretchability, good conductivity, good antifreeze property, good moisture retention property, good flexibility, good biocompatibility and good air permeability, where the tensile strength is 200 KPa - 329 KPa and the elongation rate is 170% - 203%. At the same time, the preparation method of the present invention also has the advantages of simple process, convenient operation, low cost, green environmental protection, conforming to the concept of sustainable development, etc., being suitable for large-scale preparation and facilitating industrial application.

[0028] (2) In the preparation method of the present invention, by optimizing the mass of microfibrillated cellulose in the graphene / microfibrillated cellulose / gelatin dispersion to be 1% - 5% of the total mass of microfibrillated cellulose and gelatin, and the mass ratio of graphene to gelatin to be 1 - 2:15 - 35, the supramolecular interaction between microfibrillated cellulose and graphene and the steric effect of microfibrillated cellulose itself can be better utilized to promote the dispersion of graphene. By optimizing the mass concentration of graphene in the graphene dispersion to be ≤ 0.8 wt%, especially 0.4 wt% - 0.8 wt%, the hydrogel has high electrical conductivity while ensuring good tensile properties. This is because although the addition of graphene is beneficial to improving the conductivity of the hydrogel, excessive graphene will lead to uneven dispersion in the composite material, resulting in a decrease in the tensile properties of the hydrogel. By optimizing the mass ratio of water to glycerol in the water / glycerol binary solvent to be 5 - 9:2, on the premise of ensuring good electrical conductivity and mechanical properties of the hydrogel, it is more conducive to improving the anti-freezing and moisturizing ability of the material. This is because glycerol is a non-conductive liquid, and the addition of glycerol will inevitably decrease the conductivity of the hydrogel. Small glycerol molecules can penetrate between the gelatin molecular chains, expanding the molecular chain spacing and thus affecting the tensile properties of the hydrogel. Therefore, by optimizing the mass ratio of water to glycerol, it is more conducive to preparing a composite material with excellent properties.

[0029] (3) In the preparation method of the present invention, gelatin is mixed with the graphene / microfibrillated cellulose dispersion and stirred at a temperature of 60°C - 70°C. During this process, gelatin can be better dissolved, so the unique sol-gel transition characteristics of gelatin can be utilized to make the dispersion of graphene and microfibrillated cellulose better, and at the same time, it is more conducive to forming a physically crosslinked macromolecular three-dimensional network. Without heating, gelatin cannot be dissolved, so it is difficult to achieve uniform dispersion of graphene and microfibrillated cellulose.

[0030] (4) The gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared by the preparation method of the present invention comprises gelatin, microfibrillated cellulose and graphene. Among them, gelatin (Gel) is used as the matrix, which has the advantages of flexibility, biocompatibility, air permeability, etc. Microfibrillated cellulose (MFC) is a reinforcing agent for the gelatin matrix, which can enhance the mechanical properties of the composite hydrogel. Graphene (GR) is a conductive filler with good electrical conductivity. The polar groups in the gelatin molecular chain and the polar groups in the microfibrillated cellulose molecular chain form hydrogen bonds, constituting the physical cross-linked network structure of the GR / MFC / Gel hydrogel. Therefore, without adding a cross-linking agent, microfibrillated cellulose and graphene can be wrapped in gelatin, which is beneficial to improving the mechanical properties, electrical conductivity and environmental stability of the conductive hydrogel, and can effectively avoid decomposition or shedding during use. More importantly, by optimizing the mass ratio of gelatin, microfibrillated cellulose and graphene to 50-100:1-5:2-4, the dispersibility of graphene and microfibrillated cellulose can be improved, which is beneficial to improving the mechanical properties and electrical conductivity of the hydrogel. The gelatin / microfibrillated cellulose / graphene conductive hydrogel of the present invention has the advantages of good mechanical properties, good electrical conductivity and good environmental stability. This is a novel flexible conductive material with excellent performance, which can be widely used in the preparation of flexible sensors, especially wearable flexible sensors, and is of great significance for improving the wide application of conductive hydrogels in flexible sensors.

[0031] (5) The present invention also provides an application of the gelatin / microfibrillated cellulose / graphene conductive hydrogel in the preparation of flexible sensors. The flexible sensor prepared therefrom can detect the resistance change conditions at different positions and different shapes, and thus can detect / monitor the activity status of objects (including the human body). Description of the Drawings

[0032] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0033] Figure 1 It is a scanning electron microscope image of the tensile cross-section of the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in the embodiment of the present invention.

[0034] Figure 2 It is a detection result diagram corresponding to the application of the wearable flexible sensor made of the gelatin / microfibrillated cellulose / graphene conductive hydrogel in the finger joint movement in Embodiment 4 of the present invention.

[0035] Figure 3 It is a detection result diagram corresponding to the application of the wearable flexible sensor made of the gelatin / microfibrillated cellulose / graphene conductive hydrogel in the wrist joint movement in Embodiment 4 of the present invention.

[0036] Figure 4 This is the detection result graph corresponding to the application of the wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel when smiling on the face in Embodiment 4 of the present invention.

[0037] Figure 5 This is the detection result graph corresponding to the application of the wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel during the mouth opening movement in Embodiment 4 of the present invention. Detailed implementation mode

[0038] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0039] The materials and instruments used in the following examples are all commercially available.

[0040] Embodiment 1

[0041] A preparation method of a gelatin / microfibrillated cellulose / graphene conductive hydrogel includes the following steps:

[0042] (1) Add 0.4 g of graphene (GR) powder to 99.6 g of a water / glycerol binary solvent, and ultrasonically disperse for 30 min to form a 0.4 w t% graphene dispersion; in this step, the water / glycerol binary solvent used is prepared by mixing water and glycerol, and the mass ratio of water to glycerol is 7:2.

[0043] (2) Take 0.15 g of dry microfibrillated cellulose (MFC, commercially purchased), add it to 100 g of the graphene dispersion prepared in step (1), and continue ultrasonic treatment for 30 min to form a uniformly dispersed graphene / microfibrillated cellulose dispersion.

[0044] (3) Add 10 g of gelatin (Gel) particles to 100.15 g of the graphene / microfibrillated cellulose dispersion prepared in step (2), heat and stir in a 70°C water bath for 1.5 h, with a rotation speed of 100 r / min during the stirring process, and then ultrasonically treat for 30 min to obtain a graphene / microfibrillated cellulose / gelatin dispersion.

[0045] (4) Pour the graphene / microfibrillated cellulose / gelatin dispersion prepared in step (2) into a polytetrafluoroethylene mold, freeze at 0°C for 12 h, and thaw at room temperature for 2 h to obtain a gelatin / microfibrillated cellulose / graphene conductive hydrogel.

[0046] The gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in this example includes gelatin, and microfibrillated cellulose and graphene are encapsulated in the gelatin. The mass ratio of gelatin, microfibrillated cellulose and graphene in the gelatin / microfibrillated cellulose / graphene conductive hydrogel is 200∶3∶8.

[0047] The gelatin / microfibrillated cellulose / graphene conductive hydrogel sample (gage length 25 mm, width 6 mm, thickness 2 mm) prepared in this example was subjected to a tensile test using a universal tensile testing machine at a tensile speed of 20 mm / min. The tensile stress (σ) was calculated by dividing the force (F) by the original cross-sectional area (A0) of the specimen, and the tensile strain (ε) was the ratio of the change in length to the original length (L0). It was calculated according to the following formula:

[0048] σ = F / A 0 ....................................(1)

[0049] ∈ = (L - L 0 ) / L 0 *100%.........................(2)

[0050] Each specimen was tested five times and the average value was taken.

[0051] After testing, the tensile strength of the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in Example 1 of the present invention was 222 KPa, and the elongation at break was 173%.

[0052] Example 2

[0053] A preparation method of a gelatin / microfibrillated cellulose / graphene conductive hydrogel includes the following steps:

[0054] (1) 0.4 g of graphene (GR) powder was added to 99.6 g of a water / glycerol binary solvent and ultrasonically dispersed for 30 min to form a 0.4 wt% graphene dispersion; in this step, the water / glycerol binary solvent used was prepared by mixing water and glycerol, and the mass ratio of water to glycerol was 7∶2.

[0055] (2) 0.30 g of dry microfibrillated cellulose (MFC) was taken and added to 100 g of the graphene dispersion prepared in step (1), and ultrasonic treatment was continued for 30 min to form a uniformly dispersed graphene / microfibrillated cellulose dispersion.

[0056] (3) Add 10 g of gelatin (Gel) particles to 100.15 g of the graphene / microfibrillated cellulose dispersion prepared in step (2), heat and stir in a water bath at 70 °C for 1.5 h, with the rotation speed during the stirring process being 100 r / min, and then perform ultrasonic treatment for 30 min to obtain a graphene / microfibrillated cellulose / gelatin dispersion.

[0057] (4) Pour the graphene / microfibrillated cellulose / gelatin dispersion prepared in step (2) into a polytetrafluoroethylene mold, freeze at 0 °C for 12 h, and thaw at room temperature for 2 h to obtain a gelatin / microfibrillated cellulose / graphene conductive hydrogel.

[0058] The gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in this example includes gelatin, and microfibrillated cellulose and graphene are wrapped in the gelatin. The mass ratio of gelatin, microfibrillated cellulose, and graphene in the gelatin / microfibrillated cellulose / graphene conductive hydrogel is 100∶3∶4.

[0059] After testing, the tensile strength of the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in Example 2 of the present invention is 292 KPa, and the elongation at break is 185%.

[0060] Example 3

[0061] A preparation method of a gelatin / microfibrillated cellulose / graphene conductive hydrogel includes the following steps:

[0062] (1) Add 0.4 g of graphene (GR) powder to 99.6 g of a water / glycerol binary solvent, and perform ultrasonic dispersion for 30 min to form a 0.4 wt% graphene dispersion; in this step, the water / glycerol binary solvent is prepared by mixing water and glycerol, and the mass ratio of water to glycerol is 7∶2.

[0063] (2) Take 0.45 g of dry microfibrillated cellulose (MFC), add it to 100 g of the graphene dispersion prepared in step (1), and continue ultrasonic treatment for 30 min to form a uniformly dispersed graphene / microfibrillated cellulose dispersion.

[0064] (3) Add 10 g of gelatin (Gel) particles to 100.15 g of the graphene / microfibrillated cellulose dispersion prepared in step (2), heat and stir in a water bath at 70 °C for 1.5 h, with the rotation speed during the stirring process being 1000 r / min, and then perform ultrasonic treatment for 30 min to obtain a graphene / microfibrillated cellulose / gelatin dispersion.

[0065] (4) Pour the graphene / microfibrillated cellulose / gelatin dispersion prepared in step (2) into a polytetrafluoroethylene mold, freeze at 0 °C for 12 h, and thaw at room temperature for 2 h to obtain a gelatin / microfibrillated cellulose / graphene conductive hydrogel.

[0066] In this embodiment, the prepared gelatin / microfibrillated cellulose / graphene conductive hydrogel includes gelatin, and microfibrillated cellulose and graphene are encapsulated in the gelatin. The mass ratio of gelatin, microfibrillated cellulose and graphene in the gelatin / microfibrillated cellulose / graphene conductive hydrogel is 200∶9∶8.

[0067] After testing, the tensile strength of the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in Example 3 of the present invention is 329 KPa, and the elongation at break is 203%.

[0068] Figure 1 This is a scanning electron microscope image of the tensile fracture surface of the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared in Example 3 of the present invention. Figure 1 In it, a is gelatin, and b is the gelatin / microfibrillated cellulose / graphene conductive hydrogel. It can be Figure 1 seen that the cross-section of the pure gelatin hydrogel is rough, with more and smaller holes, and the distribution is irregular. After adding MFC and GR, the structure of the hydrogel becomes denser. MFC and GR are tightly wrapped in the gelatin matrix, and can well disperse the external stress borne by the hydrogel, avoiding stress concentration, thereby endowing the hydrogel with stronger mechanical properties.

[0069] Example 4

[0070] An application of a gelatin / microfibrillated cellulose / graphene conductive hydrogel in the preparation of a flexible sensor, specifically: making the gelatin / microfibrillated cellulose / graphene conductive hydrogel into a wearable flexible sensor (GR / MFC / Gel hydrogel sensor).

[0071] In this embodiment, the usage method of the wearable flexible sensor includes the following steps:

[0072] (1) Using copper foil tape, make the gelatin / microfibrillated cellulose / graphene conductive hydrogel into a wearable flexible sensor.

[0073] (2) Fix the wearable flexible sensor on the surface of the object to be detected (such as the surface of a human finger, wrist and face).

[0074] (3) Connect the power supply (electrochemical workstation), detect the change of the surface resistance when the object moves, and monitor the surface activity status of the object (such as a human body) through the change of the resistance.

[0075] Such as Figure 2As shown, a wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel is used to detect the resistance change during finger joint movement. Specifically, the sensor is placed at the index finger joint, and the finger joint makes slow and fast 90° bends. According to the speed of resistance change, the movement of the finger joint of the hand can be accurately displayed. The results show that the faster the finger joint moves, the faster the resistance changes.

[0076] As Figure 3 shown, a wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel is used to detect the resistance change during wrist joint movement. Specifically, the sensor is placed at the wrist joint, and the wrist joint makes the maximum flexion movement. According to the resistance change value, the movement of the wrist joint can be accurately displayed. The results show that the GR / MFC / Gel hydrogel sensor can monitor the rotation of the wrist, can sense the movement of the human hand in real time, and has practical application value in the field of intelligent wearable devices.

[0077] As Figure 4 shown, a wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel is used to detect the resistance change during smiling at the corner of the mouth on the face. Specifically, the sensor is placed at the corner of the mouth on the face, and a smile is made. According to the resistance change value, the facial expression can be accurately displayed. The results show that the GR / MFC / Gel hydrogel sensor can accurately detect the smiling facial expression, which fully proves that the GR / MFC / Gel hydrogel sensor has excellent sensitivity and accuracy, and has great application potential in the fields of health monitoring, human motion detection, and sensory skin in intelligent wearable devices.

[0078] As Figure 5 shown, a wearable flexible sensor made of gelatin / microfibrillated cellulose / graphene conductive hydrogel is used to detect the resistance change during opening the mouth at the corner of the mouth on the face. Specifically, the sensor is placed at the corner of the mouth on the face, and the mouth is opened. According to the resistance change value, the facial expression can be accurately displayed. The results show that the GR / MFC / Gel hydrogel sensor can accurately detect the tiny movement of opening the mouth, which fully proves that the GR / MFC / Gel hydrogel sensor has excellent sensitivity and accuracy, and has great application potential in the fields of health monitoring, human motion detection, and sensory skin in intelligent wearable devices.

[0079] In summary, the gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared by the present invention has the advantages of high strength, good stretchability, good conductivity, good antifreeze property, good moisture retention property, good flexibility, good biocompatibility, good air permeability, etc. It is a novel flexible conductive material with excellent performance and can be widely used in the preparation of flexible sensors, especially wearable flexible sensors. The wearable flexible sensor can detect the resistance change of different positions and different shapes, and thus can detect / monitor the activity status of objects (including the human body).

[0080] The above description is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. Preparation method of gelatin / microfibrillated cellulose / graphene conductive hydrogel, characterized in that, it includes the following steps: S1. Mix graphene, microfibrillated cellulose, gelatin with water / organic binary solvent to make graphene / microfibrillated cellulose / gelatin dispersion; the water / organic binary solvent is obtained by mixing water and organic solvent; the preparation process of the graphene / microfibrillated cellulose / gelatin dispersion includes the following steps: S1-1. Mix graphene with water / organic binary solvent, and perform ultrasonic dispersion to obtain graphene dispersion; the mass concentration of graphene in the graphene dispersion is 0.4wt% - 0.8wt%; S1-2. Mix microfibrillated cellulose with graphene dispersion, and perform ultrasonic dispersion to obtain graphene / microfibrillated cellulose dispersion; S1-3. Mix gelatin with graphene / microfibrillated cellulose dispersion, stir, and perform ultrasonic treatment to obtain graphene / microfibrillated cellulose / gelatin dispersion; the mass of microfibrillated cellulose in the graphene / microfibrillated cellulose / gelatin dispersion is 1% - 5% of the total mass of microfibrillated cellulose and gelatin; the mass ratio of graphene to gelatin in the graphene / microfibrillated cellulose / gelatin dispersion is 1 - 2:15 - 35; S2. Freeze and then thaw the graphene / microfibrillated cellulose / gelatin dispersion in sequence to obtain gelatin / microfibrillated cellulose / graphene conductive hydrogel.

2. The preparation method according to claim 1, characterized in that, in step S1, the mass ratio of water to organic solvent in the water / organic binary solvent is 5 - 9:2; the organic solvent is glycerol and / or ethylene glycol.

3. The preparation method according to claim 1 or 2, characterized in that, in step S1-1, the time of ultrasonic dispersion is 30min - 60min; in step S1-2, the time of ultrasonic dispersion is 30min - 60min; in step S1-3, the stirring is carried out at a temperature of 60°C - 70°C; the rotation speed of the stirring is 50r / min - 120r / min; the time of the stirring is 1.5h - 2h; the time of the ultrasonic treatment is 30min - 60min.

4. The preparation method according to claim 1 or 2, characterized in that, in step S2, pour the graphene / microfibrillated cellulose / gelatin dispersion into a mold to prepare a conductive hydrogel with a target shape; the freezing is carried out at -20°C - 0°C; the time of the freezing is 8h - 16h; the thawing is carried out at 25°C; the time of the thawing is 2h - 5h.

5. A gelatin / microfibrillated cellulose / graphene conductive hydrogel prepared by the preparation method according to any one of claims 1 - 4, characterized in that, it includes gelatin; microfibrillated cellulose and graphene are wrapped in the gelatin; the mass ratio of gelatin, microfibrillated cellulose and graphene is 50 - 100:1 - 5:2 - 4.

6. Application of the gelatin / microfibrillated cellulose / graphene conductive hydrogel according to claim 5 in the preparation of flexible sensors.

7. The application according to claim 6, characterized in that, The method for using the flexible sensor includes the following steps: (1) Fabricate a flexible sensor from gelatin / microfibrillated cellulose / graphene conductive hydrogel; (2) Fix the flexible sensor on the surface of the object to be detected; (3) Connect a power supply and detect the change in surface resistance when the object is moving.

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