A high-sensitivity conductive hydrogel low-temperature 3D printing device and preparation method

Abstract

The present invention discloses a high-sensitivity conductive hydrogel low-temperature 3D printing device, which consists of four parts: a parallel shaft transmission mechanism, a hydraulic extrusion mechanism, a low-temperature control device and an electronic control device. The parallel shaft transmission mechanism realizes the precise movement of the nozzle of the low-temperature 3D printing device, the hydraulic extrusion mechanism realizes the controllable extrusion of the conductive hydrogel reaction liquid, the low-temperature control device realizes the low-temperature 3D printing environment of 0°C to ‑20°C, and the electronic control device realizes the coordinated operation of the various components of the low-temperature 3D printing device. The four parts cooperate with each other to construct various types of three-dimensional structures using the low-temperature rheological properties of the material to be 3D printed. The present invention also discloses a low-temperature 3D printing preparation method for a high-sensitivity conductive hydrogel. Under the premise of not changing the original material ratio of the conductive hydrogel matrix, the conductive hydrogel is realized through a self-designed 3D printing path. High-strength, diversified and complex structures and a high-sensitivity electrical sensing functional structural foundation are established.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive hydrogel-based flexible sensing materials, and in particular to a high-sensitivity conductive hydrogel low-temperature 3D printing device and a preparation method thereof. Technical Background

[0002] Conductive hydrogel-based flexible sensing materials have good electrochemical properties, flexibility and biocompatibility, and are important ideal materials in the fields of smart wearable devices, flexible sensors, tissue engineering, etc. As a typical conductive hydrogel matrix material, non-toxic, high-strength polyvinyl alcohol-based hydrogels are often used as "green" flexible sensing materials. With the widespread application of polyvinyl alcohol-based conductive hydrogels in many high-tech fields, their diverse structural forms, good mechanical properties, stable material properties, high-sensitivity electrical sensing performance and simple and efficient preparation processes have become technical bottlenecks that need to be urgently solved in this field.

[0003] In view of the technical bottlenecks in the structure, strength, materials and functions of polyvinyl alcohol-based conductive hydrogels, domestic and foreign scholars have mainly carried out research and application around (1) developing new preparation methods such as 3D printing; (2) adding reinforcing phases to improve mechanical strength; (3) adding various types of conductive fillers to achieve conductive functions; (4) adding rheological modifiers to achieve 3D printing. While the relevant technical solutions have achieved beneficial effects, there are still many technical deficiencies, which are mainly reflected in the following aspects: (1) Although a series of 3D printing technologies have been developed to enrich the structural forms of polyvinyl alcohol-based conductive hydrogels, due to the limitations of material rheological properties and synthesis methods, the structural forms of 3D-printed conductive hydrogels are mainly simple long strips and circles. In addition, due to the limitations of the 3D printing process, the mechanical strength is much lower than that of traditional mold forming technology. (2) Although the mechanical strength is improved by adding materials such as nanoparticles and nanofibers, the addition of reinforcing phases weakens the 3D printability, flexibility and conductive functional properties of polyvinyl alcohol-based hydrogels to a certain extent. (3) Although the resistance of polyvinyl alcohol-based conductive hydrogels was reduced by adding materials such as graphene oxide, carbon nanotubes, and metal nanoparticles, the degree of improvement in conductivity was limited, and no substantial changes were made to electrical sensing properties such as sensitivity. (4) Although the mechanical properties, conductive properties, and rheological properties were improved by the comprehensive use of additives, the improvement effects on viscosity, storage modulus, and loss modulus were limited, and it was not possible to effectively construct a diverse and complex structure by changing the rheological properties.

[0004] In summary, the existing polyvinyl alcohol-based conductive hydrogel 3D printing device has a relatively complex structure and weak integration, and the realized structure type is single, and it is impossible to prepare complex structures such as hollow structures with high precision. The existing polyvinyl alcohol-based conductive hydrogel 3D printing preparation method cannot take into account the rheological characteristics, mechanical properties, and high sensitivity characteristics. How to achieve the complex three-dimensional structure and high-sensitivity electrical sensing function of polyvinyl alcohol-based conductive hydrogel based on the new 3D printing device without changing the material ratio and maintaining the original material properties is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention proposes a high-sensitivity conductive hydrogel low-temperature 3D printing device and preparation method. The first purpose of the present invention is to propose an efficient high-sensitivity conductive hydrogel low-temperature 3D printing preparation method, which utilizes the low-temperature rheological properties of polyvinyl alcohol-based hydrogels, which increase viscosity under low-temperature conditions and significantly increase 3D printability, without changing the polyvinyl alcohol-based material ratio, maintaining the original in-situ reduced silver nanoparticle properties, and innovatively constructing a variety of complex three-dimensional structures through a low-temperature 3D printing method, and realizing its high-sensitivity electrical sensing function; another purpose of the present invention is to design and build a corresponding low-temperature 3D printing device for polyvinyl alcohol-based hydrogels with unique low-temperature rheological properties, and establish an equipment foundation for an efficient high-sensitivity conductive hydrogel low-temperature 3D printing preparation method proposed by the present invention; combined with the 3D printing G code written by the present invention, the high mechanical strength characteristics of complex structures are realized.

[0006] Technical solution of the present invention

[0007] To achieve the above purpose, the technical solution of the present invention is as follows:

[0008] The present invention provides a high-sensitivity conductive hydrogel low-temperature 3D printing device, which consists of four parts: a parallel shaft transmission mechanism, a hydraulic extrusion mechanism, a low-temperature control device and an electric control device. The hydraulic extrusion mechanism, the low-temperature control device and the electric control device are all fixed on the parallel shaft transmission mechanism.

[0009] The parallel shaft transmission mechanism comprises a stainless steel optical axis, a pulley, a stepper motor, a fisheye rod, a fisheye rod end joint bearing, a fisheye effector hanging platform, a synchronous pulley, a synchronous belt, and an aluminum alloy profile; the parallel shaft transmission mechanism is an overall triangular prism structure, three independent pulleys are installed on the vertical stainless steel optical axis and connected to the fisheye rod, the fisheye rod is connected to the fisheye effector hanging platform via a joint bearing; the pulley is connected to the stepper motor via a synchronous belt; the fisheye effector hanging platform is used to place the storage tube;

[0010] The hydraulic extrusion mechanism includes a stepper motor, a synchronous wheel, a Luer connector, a silicone tube, a syringe, a nozzle, a screw, a screw seat, a screw support, a stainless steel optical axis, a stainless steel optical axis seat, a stainless steel optical axis guide rail, a slider, a flange bearing, and a polylactic acid resin push plate, a bottom plate, a side plate, and a top plate; the push plate is connected to the screw via a flange bearing, and the two sliders are connected to the push plate via the stainless steel optical axis; the screw is connected to the stepper motor via a 1:3 reduction transmission synchronous wheel-synchronous belt system; the piston core rod of the water-containing syringe contacts the push plate, and the syringe barrel of the water-containing syringe is connected to the syringe barrel of another empty syringe via a Luer connector and a silicone tube, and the piston core rod of the empty syringe is placed in the material storage tube;

[0011] The low temperature control device comprises a circulating water system, a main control board of the low temperature system, a temperature sensor, a cooling plate, a cooling fan, an aluminum plate, and a support plate; the semiconductor cooling plate is placed under the aluminum plate and connected to the circulating water system, and a low temperature environment of 0°C to -20°C is achieved under the control of the temperature sensor and the main control board of the low temperature system, and the cooling fan achieves uniform environmental temperature;

[0012] The electronic control device mainly includes a 3D printer main control board and a limit switch, and mainly realizes the coordinated operation between the parallel shaft transmission mechanism and the hydraulic extrusion mechanism to realize the three-dimensional structure of the hydrogel reaction liquid to be printed.

[0013] The invention discloses a method for preparing a high-sensitivity conductive hydrogel by low-temperature 3D printing, which uses the low-temperature 3D printing device of the invention, and the preparation method includes the following four stages in sequence: the first stage is "preparation of hydrogel reaction solution", the second stage is "low-temperature 3D printer debugging", the third stage is "low-temperature 3D printing of conductive hydrogel matrix", and the fourth stage is "conductivity of low-temperature 3D printed hydrogel matrix".

[0014] The "hydrogel reaction solution preparation" stage is to prepare a variety of polyvinyl alcohol-based hydrogel reaction solutions for low-temperature 3D printing operations by determining the material type, ratio, and synthesis method;

[0015] The "low temperature 3D printer debugging" stage is to adjust the height between the nozzle and the aluminum plate, import the G code and run the low temperature 3D printing device empty to test the operation stability of the whole machine;

[0016] The "low-temperature 3D printing of conductive hydrogel matrix" stage is to install the material storage tube on the low-temperature 3D printer, complete the low-temperature 3D printing of polyvinyl alcohol-based conductive hydrogel, and obtain the conductive hydrogel matrix through freeze-thaw cycles and solvent replacement;

[0017] The "low-temperature 3D printed hydrogel matrix conductive" stage is to use the low-temperature 3D printed polyvinyl alcohol-based hydrogel through an in-situ silver reduction process to prepare a continuous and dense silver elemental nanoparticle layer on the surface of the matrix, obtain the low-temperature 3D printed conductive hydrogel, and establish the foundation for its high-sensitivity electrical sensing function.

[0018] The present invention discloses a method for preparing a high-sensitivity conductive hydrogel by low-temperature 3D printing, wherein the materials used are: polyvinyl alcohol (PVA), sodium lignin sulfonate (LS), sodium carboxymethyl cellulose (CMC), dimethyl sulfoxide (DMSO), silver nitrate (AgNO 3 ), K30 polyvinyl pyrrolidone (PVP), ascorbic acid (VC), deionized water (DI). Among them, polyvinyl alcohol is used as the matrix, sodium lignin sulfonate and sodium carboxymethyl cellulose are used as the reinforcing phase, dimethyl sulfoxide is used as the dispersant of sodium lignin sulfonate and sodium carboxymethyl cellulose, silver nitrate is used as the reducing agent, K30 polyvinyl pyrrolidone is used as the solution dispersant, ascorbic acid is used as the reducing agent, and deionized water is used as the solvent.

[0019] The present invention discloses a method for preparing a highly sensitive conductive hydrogel by low-temperature 3D printing, and the specific preparation steps are as follows:

[0020] Step 1, preparation of polyvinyl alcohol-based hydrogel reaction solution:

[0021] 1. By volume ratio V DMSO :V DI =4:1, prepare a 45mL mixed solution of dimethyl sulfoxide and deionized water;

[0022] 2. Add 0.15 g of sodium lignin sulfonate to a mixture of dimethyl sulfoxide and deionized water and stir magnetically until it is completely dissolved; then, ultrasonically disperse the mixed solution containing sodium lignin sulfonate for 20 min-30 min, add 4.85 g of polyvinyl alcohol, and mechanically stir at a constant temperature of 140°C-150°C and 400 r / min-450 r / min for 2 h-2.5 h to obtain a PVA-LS reaction solution;

[0023] 3. Cool the PVA-LS reaction solution to 80℃-85℃, then pour it into the storage tube for low-temperature 3D printing;

[0024] 4. Place 0.15g of sodium carboxymethyl cellulose at the bottom of the beaker, soak it completely with ethanol for 2 minutes, then pour in 45mL of deionized water and stir magnetically for 20 minutes; add 4.85g of polyvinyl alcohol to the sodium carboxymethyl cellulose solution and stir mechanically at 90℃-100℃, 800r / min-850r / min for 2h-2.5h to obtain a PVA-CMC reaction solution;

[0025] 5. Cool the PVA-CMC reaction solution to 60℃-65℃, then pour it into the storage tube for low-temperature 3D printing;

[0026] Step 2: Low-temperature 3D printing of polyvinyl alcohol-based hydrogel reaction solution:

[0027] 1. Import the designed G code into the low-temperature 3D printer;

[0028] 2. Connect the storage tube containing the polyvinyl alcohol-based hydrogel reaction solution to the piston core rod of the empty syringe and fix it on the fisheye effector hanging platform to exhaust the air in the storage tube;

[0029] 3. Turn on the low temperature control device, lower the 3D printing environment temperature to -20℃, pre-tighten the hydraulic extrusion mechanism push plate and extrude a proper amount of reaction liquid before running the low temperature 3D printing program;

[0030] 4. After low-temperature 3D printing is completed, place the sample in a refrigerator at -18℃-20℃ for 12h-13h, thaw it at room temperature for 2h-2.5h to obtain a solidified polyvinyl alcohol-based hydrogel and place it in a beaker filled with deionized water. Replace the deionized water every 6h-6.5h during the day and every other day at night to replace the dimethyl sulfoxide inside the gel with deionized water. At this time, the low-temperature 3D printing preparation of the conductive hydrogel matrix is ​​completed.

[0031] Step 3, preparing a silver nanoparticle layer on the surface of a polyvinyl alcohol-based hydrogel by low-temperature 3D printing;

[0032] 1. Add 1.0 M AgNO 3 The solution, 0.08M VC solution and 10wt.% PVP solution were mixed in equal volumes to prepare AgNO 3 -PVP and VC-PVP solutions;

[0033] 2. Soak the low-temperature 3D printed polyvinyl alcohol-based hydrogel in AgNO 3 -PVP mixed solution for 8 hours, and then soaked in VC-PVP mixed solution for 48 hours to complete the preparation of the silver layer on the surface of polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel. At this point, the low-temperature 3D printing preparation of conductive hydrogel is completed.

[0034] Beneficial effects of the present invention

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) Low-temperature 3D printing technology is reliable

[0037] The prior art only changes the rheological parameters (such as viscosity, storage modulus, and loss modulus) of the polyvinyl alcohol-based hydrogel reaction solution by adding organic or inorganic fillers to achieve direct ink writing 3D printing. The three-dimensional structure achieved is single in form, has low mechanical strength, and weak electrical sensing function. Inspired by the phenomenon that the viscosity of polyvinyl alcohol-based hydrogels gradually increases during freeze-thaw cycles, the present invention innovatively integrates a low-temperature control device into a direct ink writing 3D printer, and relies on the low-temperature rheological characteristics of the polyvinyl alcohol-based hydrogel reaction solution under low-temperature conditions to achieve 3D printing of its complex structure. Low-temperature 3D printing technology does not add any form of filler, but simply relies on the low-temperature environment to change the rheological parameters of the polyvinyl alcohol-based hydrogel reaction solution. While achieving a complex structure, it retains the properties of the polyvinyl alcohol-based hydrogel in-situ reduction of silver nanoparticles, effectively taking into account the structure, strength, and high sensitivity functions.

[0038] (2) High technological openness

[0039] The existing technology is limited by the limitations of the old 3D printing technology and cannot achieve the high stacking capacity of the polyvinyl alcohol-based hydrogel reaction liquid. Even with the support of the support, it does not have the technical basis for building complex three-dimensional structures. At the same time, the limitations of the existing 3D printing technology make it impossible to improve the mechanical strength of the polyvinyl alcohol-based conductive hydrogel from the perspective of structural design through self-compiled G code. The present invention benefits from the high stacking capacity of the polyvinyl alcohol-based hydrogel reaction liquid under low temperature conditions. Through self-compiled G code and auxiliary support, a diversified structure is achieved in an optimal path. Based on the adsorption characteristics of the polyvinyl alcohol hydrogel microphase separation structure for silver ions, a dense silver nanoparticle layer can be formed on the outer surface of the hydrogel through a reduction reaction to achieve a high conductivity function. The technical method described in the present invention has the openness of structural design and material function, effectively establishes the foundation of high-sensitivity electrical sensing function and takes into account high structural strength.

[0040] (3) Stable technology and wide application range

[0041] The prior art often adopts the method of adding conductive fillers to realize the electrical sensing function by internal conduction, but the resistance value is still large and the sensitivity is still low. The method of changing the type or content of conductive fillers has low technical stability and large limitations on the scope of application. However, the present invention does not change the material properties of the polyvinyl alcohol-based hydrogel during the entire preparation process. It can still generate silver nanoparticles on the surface by reducing the function of silver nanoparticles, and realize the high conductivity function by external conduction. No matter what complex structure is constructed by the low-temperature 3D printing technology of the present invention, silver nanoparticles can be generated on the surface of the structure to realize the high conductivity function, which has high technical stability and wide application. At the same time, in addition to polyvinyl alcohol-based hydrogels, polymer materials with low-temperature rheological properties can be effectively 3D printed by the device described in the present invention, and the material has a wide range of adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the general assembly drawing of the low-temperature 3D printing device.

[0043] Figure 2 This is the assembly diagram of the hydraulic extrusion mechanism of the low-temperature 3D printing device.

[0044] Figure 3 This is the assembly diagram of the low-temperature control device of the low-temperature 3D printing device.

[0045] Figure 4 This is a picture of the physical prototype of the low-temperature 3D printing device.

[0046] Figure 5 This is a physical prototype picture of the hydraulic extrusion mechanism of the low-temperature 3D printing device.

[0047] Figure 6 This is a picture of the actual prototype of the low-temperature control device of the low-temperature 3D printing device.

[0048] Figure 7 It is a flow chart of the method for preparing polyvinyl alcohol-based conductive hydrogel by low-temperature 3D printing.

[0049] Figure 8 This is the room temperature viscosity diagram of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0050] Fig. 9 This is the low temperature viscosity diagram of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0051] Fig.10 This is a graph of the low-temperature storage modulus and loss modulus of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0052] Fig.11 This is a physical comparison chart of the room temperature and low temperature rheological properties of polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0053] Fig.12 This is a diagram of the low-temperature 3D printing cube process based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0054] Fig.13 This is a diagram of the low-temperature 3D printing process of grooved cuboids based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0055] Fig.14 This is a diagram of the low-temperature 3D printing process of hollow cuboids based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution.

[0056] Fig.15 This is a diagram of the process of low-temperature 3D printing layered spiral structures based on self-compiled G code.

[0057] Fig.16 It is the stress-strain diagram of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose hydrogel with different helical angles.

[0058] Fig.17 This is a stress-strain comparison chart of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate hydrogel with and without helical angle.

[0059] Fig.18 This is a picture of the actual samples of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate and polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel.

[0060] Fig.19 It is the microscopic morphology and energy spectrum analysis diagram of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel.

[0061] Fig. 20 The conductivity of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel and ΔR / R under 5% strain and 100 cycles 0 picture.

[0062] Fig.21 The ΔR / R of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under 7 cycles of different strains 0 picture.

[0063] Fig. 22 ΔR / R of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under 25% strain and 150 cycles 0 picture.

[0064] Fig.23 This is the linearity and sensitivity diagram of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under continuous strain conditions.

[0065] Note:

[0066] In the figure, 1 is a silicone tube, 2 is an aluminum alloy profile, 3 is a stainless steel optical axis, 4 is a pulley, 5 is a fisheye rod, 6 is an empty syringe, 7 is a fisheye effector hanging platform, 8 is a water-containing syringe, 9 is a limit switch, 10 is a synchronous belt, 11 is a material storage tube fixing device, 12 is a nozzle, 13 is a stepping motor, 14 is a push plate, 15 is a stainless steel optical axis, 16 is a lead screw, 17 is a slider, 18 is a stainless steel optical axis seat, 19 is a top plate, 20 is a synchronous wheel, 21 is a synchronous belt, 22 is a bottom plate, 23 is a stepping motor, 24 is a side plate, 25 is a cooling fan, 26 is a cooling fan support frame, 27 is a cooling plate, 28 is a heat preservation sleeve, 29 is an aluminum plate, 30 is a support plate, 31 is a low-temperature cooling device power supply, 32 is a circulating water storage barrel, 33 is a circulating water pipe, 34 is a material storage tube piston, and 35 is a material storage tube. DETAILED DESCRIPTION

[0067] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] It should be noted that in the description of the present invention, certain words indicating mechanisms, devices, temperatures, positions, orientations, and connections are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices, mechanisms, components, temperatures, etc. referred to must have specific technical requirements, and therefore cannot be understood as limitations on the present invention. In the description of the present invention, it should be noted that "low temperature" should be understood in a broad sense, referring to 0°C to -20°C. At the same time, "connection" should also be understood in a broad sense, and can be a fixed connection, a detachable connection, or an integral connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0069] like Figure 1 As shown, the low-temperature 3D printing device has a triangular prism structure as a whole, and has high structural stability. From top to bottom, there are hydraulic extrusion mechanism, parallel shaft transmission mechanism, low-temperature control mechanism and electronic control device. The nozzle 12 is connected to the material storage tube, and is fixed on the fisheye effector hanging platform 7 by the material storage tube fixing device 11. The two fisheye rods 5 are respectively connected to the pulley 4 and the fisheye effector hanging platform 7 to form a set of parallel shafts. The stainless steel optical axis 3 limits the moving direction of the pulley. The limit switch 9 is fixed on the aluminum alloy profile 2 frame to limit the moving distance of the pulley 4. The three-dimensional positioning of the nozzle is coordinated by three independent pulleys 4. The power is provided by the stepping motor 13, and the movement of the nozzle 12 on the X-axis, Y-axis and Z-axis is realized through the synchronous wheel and the synchronous belt 10, which has the advantages of accurate positioning and high moving speed. In order to effectively avoid the influence of excessive inertia on the 3D printing accuracy during the movement of the nozzle 12, the low-temperature 3D printing device adopts a remote extrusion method. With water as the hydraulic medium, water flows through the hydraulic extrusion mechanism water-containing syringe 8, through the silicone tube 1, into the empty syringe 6 connected to the storage tube, so that the hydrogel reaction liquid in the storage tube is squeezed out.

[0070] like Figure 2As shown, the polylactic acid resin bottom plate 22, side plate 24, top plate 19, and push plate 14 prepared by fused deposition 3D printing constitute the main structure of the hydraulic extrusion mechanism, and the stepping motor 23 drives the synchronous wheel 20 and the synchronous belt 21 to achieve a 1:3 reduction drive. The power is transmitted to the push plate 14 connected to it through the screw 16. The push plate 14 moves forward to compress the water-containing syringe 8, and pushes the water into the empty syringe 6 through the silicone tube 1 to achieve the transmission of the extrusion force. Two stainless steel optical axes 15 are connected to the push plate 14 through the slider 17, and are fixed on the aluminum alloy profile frame through the stainless steel optical axis seat 18, which limits the moving direction of the push plate and ensures the direction of the push plate force.

[0071] like Figure 3 As shown, the low temperature area is confined within the insulation sleeve 28, and the low temperature is achieved by the cooling plate 27 through which the circulating water flows. The cooling plate 27 is located under the aluminum plate 29, and the aluminum plate 29 is used to receive the hydrogel reaction liquid printed by 3D. The cooling fan 25 is installed on the cooling fan support frame 26 and fixed together on the aluminum alloy profile frame. The support plate 30 is connected to the aluminum alloy profile at the bottom of the low temperature 3D printing device to support the cooling plate. The control circuit board of the electronic control device is located under the support plate.

[0072] like Figure 4 , Figure 5 , Figure 6 As shown, the low temperature control device is controlled by a separate power supply 31, and the circulating water is stored in a circulating water storage barrel 32. When the low temperature 3D printing device is running, the circulating water enters the cooling plate 27 through the circulating water pipe 33 to achieve cooling and stabilize the temperature range of 0°C to -20°C. The hydraulic extrusion mechanism transmits the hydraulic thrust to the storage pipe piston 34, and squeezes out the hydrogel reaction liquid in the storage pipe 35 through the nozzle 12. The parallel axis traditional mechanism realizes the three-dimensional movement of the nozzle. The operation of the low temperature 3D printing device is coordinated and controlled by the electronic control device.

[0073] Figure 7The present invention provides a flow chart of a method for preparing a high-sensitivity conductive hydrogel by low-temperature 3D printing. The process includes four stages, namely: the first stage "preparation of hydrogel reaction solution", the second stage "debugging of low-temperature 3D printer", the third stage "low-temperature 3D printing of conductive hydrogel matrix", and the fourth stage "conductivity of low-temperature 3D printed hydrogel matrix". In the first stage, the specific type, ratio, and preparation conditions of polyvinyl alcohol-based hydrogel materials are selected according to different technical requirements. The polyvinyl alcohol-based hydrogel reaction solution for application and low-temperature 3D printing is prepared by a synthetic process. In the second stage, the height between the nozzle and the aluminum plate is adjusted to avoid damage to the 3D printing path structure and ensure the accuracy of the path structure. At the same time, the designed path structure can be edited into a G code and imported into the low-temperature 3D printing device, and the validity of the compiled G code is verified by dry running. In the third stage, the polyvinyl alcohol-based hydrogel reaction solution prepared in the first stage is poured into the storage tube 35 and sealed with the storage tube piston 34, the nozzle 12 is installed, and the storage tube piston is manually pushed to discharge the air in the storage tube. Connect the storage tube 35 and the empty syringe 6 with the storage tube fixing device 11 and fix them on the fisheye effector hanging platform 7. Turn on the power supply 31 of the low-temperature cooling device and wait for the temperature in the insulation sleeve 28 to drop to -18°C to -20°C. Pre-tighten the hydraulic extrusion device to ensure that the hydraulic thrust is continuous during the 3D printing process. Then run the 3D printing program to complete the pre-designed path structure. The low-temperature 3D printed polyvinyl alcohol-based hydrogel obtained by freeze-thaw cycle and solvent replacement will be used as the matrix of the conductive hydrogel. In the fourth stage, the low-temperature 3D printed polyvinyl alcohol-based hydrogel is subjected to the in-situ silver reduction process described in the present invention to obtain a dense and firm silver nanoparticle layer on its surface, thereby establishing a high-sensitivity electrical sensing function foundation.

[0074] The entire processing method of the present invention is further introduced below through examples.

[0075] Embodiment 1:

[0076] The feasibility of low-temperature 3D printing technology was verified by analyzing the rheological properties (including viscosity, storage modulus, and loss modulus) of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solutions at room temperature and low temperature environments.

[0077] See also Figure 8 Room temperature viscosity diagram of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution, Fig. 9 Low temperature viscosity diagram of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution, Fig.10 Low temperature storage modulus and loss modulus of polyvinyl alcohol and polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution. Fig.11 Actual comparison of the rheological properties of polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution at room temperature and low temperature.

[0078] Based on the preparation method described in the claims, the present invention successfully prepared a polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution and a polyvinyl alcohol liquid. Figure 8 As shown in the figure, under room temperature, the viscosity of the polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction liquid and the polyvinyl alcohol liquid both decreases with the increase of shear rate, and has shear thinning characteristics. When the temperature gradually decreases from room temperature to -20°C, the viscosity of the polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction liquid and the polyvinyl alcohol liquid both gradually increases, such as Fig. 9 As shown. In this process, the storage modulus and loss modulus of both change with temperature, and there is a sol-gel transition point in a low temperature environment, such as Fig.10 As shown. The low-temperature rheological results show that the polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution and the polyvinyl alcohol liquid are 3D printable under low-temperature conditions. The addition of sodium lignin sulfonate does not change the inherent low-temperature rheological properties of the polyvinyl alcohol material, and further reduces the low-temperature 3D printing temperature range, improving the convenience of subsequent operations. Fig.11 The actual comparison results of the room temperature and low temperature rheological properties of the polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution shown in the figure show that the hydrogel reaction solution 3D printed under room temperature conditions cannot maintain its shape and is completely flattened and mixed into one. The hydrogel reaction solution 3D printed under low temperature conditions has a very high solid effect, and the 3D printing path on the upper surface is clearly visible, and there is no phenomenon of structural collapse and flattening. The comparison of 3D printing under room temperature and low temperature conditions effectively verifies the correctness and feasibility of the low temperature 3D printing technology principle involved in the present invention.

[0079] Embodiment 2:

[0080] The effectiveness of the low-temperature 3D printing device was verified by analyzing the process of constructing a cubic structure, a groove structure, and a hollow cubic structure under support-assisted conditions using a low-temperature 3D printing device using a polyvinyl alcohol-based hydrogel reaction solution (including a polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution and a polyvinyl alcohol-sodium carboxymethylcellulose hydrogel reaction solution). The effect of the self-woven layered spiral structure on the mechanical strength of the low-temperature 3D printed polyvinyl alcohol-based hydrogel was analyzed to verify the effectiveness of the present invention in improving the mechanical strength of the low-temperature 3D printed polyvinyl alcohol-based hydrogel from the perspective of structural design.

[0081] See also Fig.12 Low-temperature 3D printing cube process diagram based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution, Fig.13 The process diagram of low-temperature 3D printing of grooved cuboids based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction liquid. Fig.14 The process diagram of low-temperature 3D printing of hollow cuboids based on polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction solution. Fig.15Low temperature 3D printing process diagram of layered spiral structure based on self-compiled G code, Fig.16 Stress-strain diagram of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose hydrogel with different helical angles. Fig.17 Comparison of stress and strain of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate hydrogel with and without helical angle.

[0082] Based on the preparation method described in the claims of the present invention, a cubic structure of 30mm×30mm×3mm (length×width×height) was prepared by a low-temperature 3D printing device. Fig.12 As shown, after the polyvinyl alcohol-sodium lignin sulfonate hydrogel reaction liquid is extruded by the low-temperature 3D printing device, it completely maintains the shape at the time of extrusion under low-temperature conditions. At the same time, the previous layer printed by low-temperature 3D printing is effectively solidified in a low-temperature environment, providing a solid foundation for the next layer to be stacked on it. After freeze-thaw cycles and solvent replacement, the structural dimensions of the polymerized polyvinyl alcohol-sodium lignin sulfonate hydrogel are consistent with the designed values, which effectively proves the effectiveness of the preparation device and method involved in the present invention. The groove structure dimensions are shown in Figure 1. Fig.13 As shown, the two thin long sides are small in size. The low-temperature 3D printing device can effectively realize the groove structure, indicating that the preparation device of the present invention has the characteristics of high precision. The effectiveness and high precision of the low-temperature 3D printing device lay the foundation for realizing complex structures through support assistance. Fig.14 The complex hollow structure shown in the figure uses a glass slide with a size of 24mm×20mm×1mm (length×width×height) as a support aid. In order to reserve enough time for the installation of the support aid, two auxiliary paths are designed in the hollow cube structure. When the low-temperature 3D printing device runs to the auxiliary path, the support aid is installed. The results of low-temperature 3D printing of hollow cubes verify the feasibility of the device and preparation method involved in the present invention to construct complex structures. In order to verify the flexibility and wide application of the low-temperature 3D printing device and preparation method, the present invention designs a series of layered spiral structures with different angle ranges (0°, 15°, 30°, 45°, 60°, 75°, 90°). The structural size parameters are 40mm×5mm×3mm (length×width×height), with a total of 7 layers. The angle refers to the first layer path along the long side direction of the structure, and the second layer and the first layer path angle increase the designed angle in the counterclockwise direction, and the path angles of the remaining layers are analogous. Based on different forms of layered spiral structures, the corresponding G code is edited and imported into the low-temperature 3D printing device to realize the preparation of polyvinyl alcohol-sodium carboxymethyl cellulose hydrogel with layered spiral structure characteristics. Low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose hydrogels with different layered spiral structures have different stress-strain values, such as Fig.16As shown. When the interlayer angle of the layered spiral structure is 30 degrees, the stress value of the low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose hydrogel is the largest. The stress values ​​of the samples with interlayer angle values ​​are all greater than those of the samples without interlayer angles. After the hydrogel reaction liquid is replaced with polyvinyl alcohol-sodium lignin sulfonate, the effect of the layered spiral structure still exists, as shown in Fig.17 The mechanical properties of low-temperature 3D printed polyvinyl alcohol-based hydrogels show that the device and preparation method of the present invention can not only improve the application flexibility by designing the path structure by itself, but also take into account the mechanical strength while realizing various types of complex structures through structural design.

[0083] Embodiment 3:

[0084] The practicability of the device and preparation method involved in the present invention is verified by analyzing the microscopic morphology, energy spectrum, resistance, sensitivity gauge factor, etc. of the conductive hydrogel obtained by low-temperature 3D printing of polyvinyl alcohol-based hydrogels (including polyvinyl alcohol-sodium lignin sulfonate hydrogels and polyvinyl alcohol-sodium carboxymethyl cellulose hydrogels) after in-situ silver reduction process.

[0085] See also Fig.18 Low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate and polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel samples. Fig.19 Microstructure and energy spectrum analysis of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel. Fig. 20 Conductive effect of low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel and ΔR / R under 5% strain and 100 cycles 0 picture, Fig.21 ΔR / R of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under 7 cycles of different strains 0 picture, Fig. 22 ΔR / R of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under 25% strain and 150 cycles 0 picture, Fig.23 Linearity and sensitivity diagram of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel under continuous strain conditions.

[0086] Based on the preparation method described in the claims of the present invention, the low-temperature 3D printed polyvinyl alcohol-based hydrogel (including polyvinyl alcohol-sodium lignin sulfonate hydrogel and polyvinyl alcohol-sodium carboxymethyl cellulose hydrogel) with a layered spiral structure is subjected to an in-situ reduction silver process to obtain a low-temperature 3D printed polyvinyl alcohol-based conductive hydrogel such as Fig.18 The sample surface presents a uniform light grey silver layer, and its microscopic morphology characterizes its nanoparticle form, such as Fig.19As shown. The energy spectrum analysis results verified that the outer surface of the conductive hydrogel is silver. The low-temperature 3D printed polyvinyl alcohol-sodium lignin sulfonate conductive hydrogel can light up the circuit board at a voltage of 3V, reflecting that the conductive hydrogel prepared by the present invention has high conductivity characteristics. The resistance change (ΔR / R 0 , ΔR is the resistance under different strains relative to the initial resistance R 0 The characteristic of the change in the strain (the amount of change) shows its strain sensitivity. It outputs a stable signal with small fluctuations under 100 cycles of 5% fixed strain. The low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel was tested for 7 consecutive cycles at 5%, 10%, 15%, 20%, and 25% strain, and the results show that it also has a stable strain signal detection function. Fig.21 The results of the 25% strain and 150 cycles of low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel strain signal indicate that the device and preparation method of the present invention establish a good durability foundation under large strain and multi-frequency conditions by giving the polyvinyl alcohol-based hydrogel high mechanical strength. Fig. 22 As shown. Within the strain range of 0%-30%, the sensitivity gauge factor of the low-temperature 3D printed polyvinyl alcohol-sodium carboxymethyl cellulose conductive hydrogel is 62.5. This sensitivity value is at a relatively high level in the field of conductive hydrogels, reflecting the high sensitivity characteristics of the device and preparation method involved in the present invention. Combined with the electrical sensing results, it can be seen that the high-sensitivity conductive hydrogel low-temperature 3D printing device and preparation method involved in the present invention retain the original properties of polyvinyl alcohol-based hydrogels, while taking into account the high strength, high sensitivity and structural diversity of conductive hydrogels from the perspective of structural design. Combined with high-tech openness, the device and preparation method involved in the present invention effectively solve the relevant technical bottlenecks in structure, strength, materials and functions of polyvinyl alcohol-based conductive hydrogels.

Claims

1. A method for preparing a highly sensitive conductive hydrogel by low-temperature 3D printing, characterized in that: The printing device used is composed of four parts: a parallel shaft transmission mechanism, a hydraulic extrusion mechanism, a low temperature control device and an electric control device. The hydraulic extrusion mechanism, the low temperature control device and the electric control device are all fixed on the parallel shaft transmission mechanism. The parallel shaft transmission mechanism comprises a stainless steel optical axis, a pulley, a stepper motor, a fisheye rod, a fisheye rod end joint bearing, a fisheye effector hanging platform, a synchronous pulley, a synchronous belt, and an aluminum alloy profile; the parallel shaft transmission mechanism is an overall triangular prism structure, three independent pulleys are installed on the vertical stainless steel optical axis and connected to the fisheye rod, the fisheye rod is connected to the fisheye effector hanging platform via a joint bearing; the pulley is connected to the stepper motor via a synchronous belt; the fisheye effector hanging platform is used to place the storage tube; The hydraulic extrusion mechanism includes a stepper motor, a synchronous wheel, a Luer connector, a silicone tube, a syringe, a nozzle, a screw, a screw seat, a screw support, a stainless steel optical axis, a stainless steel optical axis seat, a stainless steel optical axis guide rail, a slider, a flange bearing, and a polylactic acid resin push plate, a bottom plate, a side plate, and a top plate; the push plate is connected to the screw via a flange bearing, and the two sliders are connected to the push plate via the stainless steel optical axis; the screw is connected to the stepper motor via a 1:3 reduction transmission synchronous wheel-synchronous belt system; the piston core rod of the water-containing syringe contacts the push plate, and the syringe barrel of the water-containing syringe is connected to the syringe barrel of another empty syringe via a Luer connector and a silicone tube, and the piston core rod of the empty syringe is placed in the material storage tube; The low temperature control device comprises a circulating water system, a main control board of the low temperature system, a temperature sensor, a cooling plate, a cooling fan, an aluminum plate, and a support plate; the semiconductor cooling plate is placed under the aluminum plate and connected to the circulating water system, and a low temperature environment of 0°C to -20°C is achieved under the control of the temperature sensor and the main control board of the low temperature system, and the cooling fan achieves uniform environmental temperature; The electronic control device mainly includes a 3D printer main control board and a limit switch, and mainly realizes the coordinated operation between the parallel shaft transmission mechanism and the hydraulic extrusion mechanism to realize the three-dimensional structure of the hydrogel reaction liquid to be printed; The preparation method includes the following four stages in sequence: the first stage is "preparation of hydrogel reaction solution", the second stage is "low-temperature 3D printer debugging", the third stage is "low-temperature 3D printing of conductive hydrogel matrix", and the fourth stage is "conductivity of low-temperature 3D printed hydrogel matrix"; The "hydrogel reaction solution preparation" stage is to prepare a variety of polyvinyl alcohol-based hydrogel reaction solutions for low-temperature 3D printing operations by determining the material type, ratio, and synthesis method; The "low temperature 3D printer debugging" stage is to adjust the height between the nozzle and the aluminum plate, import the G code and run the low temperature 3D printing device in vain to test the operation stability of the whole machine; The "low-temperature 3D printing of conductive hydrogel matrix" stage is to install the material storage tube on the low-temperature 3D printer, complete the low-temperature 3D printing of polyvinyl alcohol-based conductive hydrogel, and obtain the conductive hydrogel matrix through freeze-thaw cycles and solvent replacement; The "low-temperature 3D printed hydrogel matrix conductivity" stage is to prepare a continuous and dense silver single-substance nanoparticle layer on the surface of the matrix by an in-situ silver reduction process on the low-temperature 3D printed polyvinyl alcohol-based hydrogel to obtain the low-temperature 3D printed conductive hydrogel and establish its high-sensitivity electrical sensing function foundation; The materials used in this scheme are: polyvinyl alcohol PVA, sodium lignin sulfonate LS, sodium carboxymethyl cellulose CMC, dimethyl sulfoxide DMSO, silver nitrate AgNO3, K30 polyvinyl pyrrolidone PVP, ascorbic acid VC, and deionized water DI, among which polyvinyl alcohol is used as a matrix, sodium lignin sulfonate and sodium carboxymethyl cellulose are used as reinforcing phases, dimethyl sulfoxide is used as a dispersant for sodium lignin sulfonate and sodium carboxymethyl cellulose, silver nitrate is used as a reducing agent, K30 polyvinyl pyrrolidone is used as a solution dispersant, ascorbic acid is used as a reducing agent, and deionized water is used as a solvent.

2. A method for preparing a highly sensitive conductive hydrogel by low-temperature 3D printing according to claim 1, characterized in that: The three sets of parallel axes are all moved in the vertical direction on the vertical side of the triangular prism by the pulley, driving the fisheye effector hanging platform and realizing the three-dimensional movement of the X-axis, Y-axis and Z-axis of the nozzle; the screw is driven by the transmission system to rotate, causing the push plate to move forward to squeeze the piston core rod of the water-containing syringe, and the water enters the empty syringe through the silicone tube. The piston core rod of the empty syringe is squeezed out and pushes the hydrogel reaction liquid to be 3D printed in the storage tube to be controllably extruded through the nozzle; the polylactic acid resin push plate, bottom plate, side plate, top plate, etc. used are directly printed by a fused deposition 3D printer.

3. A method for preparing a highly sensitive conductive hydrogel by low-temperature 3D printing according to claim 2, characterized in that: The hydraulic extrusion mechanism is located above the parallel shaft transmission mechanism, and the low-temperature control device and the electronic control device are located below the parallel shaft transmission mechanism. The overall structure is compact. The hydraulic extrusion mechanism adopts a remote extrusion method to reduce the adverse effect of the moving inertia of the fisheye effector crane on the 3D printing accuracy. Combined with the self-3D printed polylactic acid resin structural parts, the cost of the whole machine is reduced on the basis of ensuring the structural strength, achieving high precision, high stability and low cost.

4. A method for preparing a highly sensitive conductive hydrogel by low-temperature 3D printing according to claim 1, characterized in that: A high-sensitivity conductive hydrogel low-temperature 3D printing preparation step is as follows: Step 1, preparation of polyvinyl alcohol-based hydrogel reaction solution:

1. According to volume ratio V DMSO :V DI =4:1, prepare a 45mL mixed solution of dimethyl sulfoxide and deionized water; 2. Add 0.15 g of sodium lignin sulfonate to a mixture of dimethyl sulfoxide and deionized water and stir magnetically until it is completely dissolved; then, ultrasonically disperse the mixed solution containing sodium lignin sulfonate for 20 min-30 min, add 4.85 g of polyvinyl alcohol, and mechanically stir at a constant temperature of 140°C-150°C and 400 r / min-450 r / min for 2 h-2.5 h to obtain a PVA-LS reaction solution; 3. Cool the PVA-LS reaction solution to 80℃-85℃, then pour it into the storage tube for low-temperature 3D printing; 4. Place 0.15g of sodium carboxymethyl cellulose at the bottom of a beaker, soak it in ethanol for 2 minutes, then pour in 45mL of deionized water and stir it magnetically for 20 minutes; add 4.85g of polyvinyl alcohol into the sodium carboxymethyl cellulose solution and stir it mechanically at 90℃-100℃, 800r / min-850r / min for 2h-2.5h to obtain a PVA-CMC reaction solution; 5. Cool the PVA-CMC reaction solution to 60℃-65℃, then pour it into the material storage tube for low-temperature 3D printing; Step 2: Low-temperature 3D printing of polyvinyl alcohol-based hydrogel reaction solution:

1. Import the designed G code into the low-temperature 3D printer; 2. Connect the storage tube containing the polyvinyl alcohol-based hydrogel reaction solution to the piston core rod of the empty syringe and fix it on the fisheye effector hanging platform to exhaust the air in the storage tube; 3. Turn on the low temperature control device, lower the 3D printing environment temperature to -20℃, pre-tighten the hydraulic extrusion mechanism push plate and extrude a proper amount of reaction liquid before running the low temperature 3D printing program; 4. After low-temperature 3D printing is completed, place the sample in a refrigerator at -18℃-20℃ for 12h-13h, thaw it at room temperature for 2h-2.5h to obtain a solidified polyvinyl alcohol-based hydrogel and place it in a beaker filled with deionized water. Replace the deionized water every 6h-6.5h during the day and every other day at night to replace the dimethyl sulfoxide in the gel with deionized water. At this time, the low-temperature 3D printing preparation of the conductive hydrogel matrix is ​​completed; Step 3, preparing a silver nanoparticle layer on the surface of a polyvinyl alcohol-based hydrogel by low-temperature 3D printing; 1. Mix 1.0M AgNO3 solution, 0.08M VC solution and 10wt.% PVP solution in equal volumes to prepare AgNO3-PVP and VC-PVP solutions; 2. Soak the polyvinyl alcohol-based hydrogel printed at low temperature 3D in the AgNO3-PVP mixed solution for 8 hours, and then soak it in the VC-PVP mixed solution for 48 hours to complete the preparation of the silver layer on the surface of the polyvinyl alcohol-based conductive hydrogel. At this point, the low-temperature 3D printing preparation of the conductive hydrogel is completed.

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