A 4D printed flexible sensor and its preparation method and application

Abstract

The present invention provides a 4D printed flexible sensor, the 4D printed flexible sensor includes a base layer, a sensing layer and an electrode layer, the base layer includes gelatin, N-isopropyl acrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone and cellulose nanofibers, and the sensing layer includes gelatin, N-isopropyl acrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, cellulose nanofibers and reduced graphite oxide. The 4D printed flexible sensor prepared by the present invention has good shape-fitting ability, controllable deformation characteristics and mechanical properties, and can change shape with changes in ambient temperature; it can sense a wide range of pressure signals, and has high sensitivity, and can realize monitoring of various human physiological activities and health status, insect crawling activities, robot labor production status, stylus, etc.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a 4D printed flexible sensor and a preparation method and application thereof. Background Art

[0002] With the rapid development of information technology, various technological innovations continue to emerge in the fields of artificial intelligence, smart devices, and the Internet of Things. Flexible sensors that are dedicated to simulating or even surpassing the functions of human skin are also one of them. Flexible sensors refer to sensors made of flexible materials. They have good flexibility and ductility, and can even be bent and folded freely. They have flexible and diverse structural forms and can be arranged arbitrarily according to the requirements of measurement conditions. They can very conveniently detect complex measurements. At the same time, by giving flexible sensors comprehensive characteristics such as wearability, comfort, remote operability, and timely feedback, their application in medical electronics, environmental monitoring, health monitoring, human-computer interaction and other fields has been promoted.

[0003] The application of 3D printing technology has promoted the technological innovation of micro-nano structures of flexible sensors, but the materials of 3D printing are only static structures and will not change with changes in the environment, time, etc. For example, when used as a wearable device, it will not produce corresponding deformation with changes in skin temperature and humidity, so it cannot fit the skin better and there are comfort issues; when used as an in vivo sensor, such as drug delivery, after the device reaches the target position in the body, the sensor needs to deform to achieve specific functions, and it also needs to have a time effect. Considering the time dimension on the basis of 3D printing, that is, 4D printing technology, can achieve structural control of materials, thereby giving the materials more varied functional properties.

[0004] There are two main strategies for achieving flexibility in electronic devices. One is to use inorganic semiconductor materials and metal materials to achieve flexibility through special structural design, and the other is to directly use organic semiconductors, polymer materials and nanomaterials to achieve flexibility. Although there are many types of flexible electronic devices, their structures are basically similar, that is, they are mainly composed of substrate materials, electrodes, functional components, packaging materials, etc. Commonly used carrier materials include flexible polymers with good curling properties such as polydimethylsiloxane (PDMS), polyethylene terephthalate, polyimide, polyurethane, polyethylene, etc., but most of them are not breathable or water-permeable. When used as wearable devices, they are not only uncomfortable, but can even cause skin inflammation. Hydrogels have become a carrier material that has attracted much attention due to their biocompatibility, controllable softness, and environmental friendliness.

[0005] Therefore, the existing technology still needs to be improved and developed. How to provide a flexible sensor that has little stimulation to the human body, good shape-fitting ability, controllable deformation characteristics and mechanical properties has become an urgent problem that researchers need to solve. Summary of the invention

[0006] In order to solve the above-mentioned technical problems in the prior art, the present invention provides a 4D printed flexible sensor and a preparation method and application thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A first aspect of the present invention provides a 4D printed flexible sensor, comprising a base layer, a sensing layer and an electrode layer, wherein the base layer comprises gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone and cellulose nanofibers, and the sensing layer comprises gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, cellulose nanofibers and reduced graphene oxide.

[0009] The second aspect of the present invention provides a method for preparing a 4D printed flexible sensor sensing layer, comprising the following steps:

[0010] Step 1: Printing the printing ink of the base layer using 4D printing technology to generate the base layer;

[0011] Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer;

[0012] Step three, forming an electrode layer on the surface of the sensing layer, and then curing it to obtain a 4D printed flexible sensor.

[0013] Furthermore, the specific steps of printing the base layer are:

[0014] Step 1: Dissolve gelatin and N-isopropylacrylamide separately and mix them, then add 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, heat and stir to form a uniform solution;

[0015] Step 2, then adding the pre-dispersed cellulose nanofibers, stirring evenly and then ultrasonicating in an ice bath to obtain the printing ink for the base layer;

[0016] Step three: print out the model shape through a printer, and then use ultraviolet light curing to obtain a 4D printed flexible base layer.

[0017] Furthermore, the specific steps of printing the sensing layer are:

[0018] Step 1: Dissolve gelatin and N-isopropylacrylamide separately and mix them, then add 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, heat and stir to form a uniform solution;

[0019] Step 2, then adding the pre-dispersed cellulose nanofibers and reduced graphene oxide, stirring evenly and then ultrasonicating in an ice bath to obtain the printing ink for the sensing layer;

[0020] Step three: print out the model shape through a printer, and then use ultraviolet light curing to obtain a 4D printed flexible sensing layer with controllable deformation characteristics.

[0021] Furthermore, in the step 1, the mass ratio of N-isopropylacrylamide, gelatin and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone is 3:2:(0.125-0.5).

[0022] Furthermore, in the step 1, gelatin is dissolved in water at 40-45°C; and the heating temperature is 50-60°C.

[0023] Furthermore, in the step 2, the ultrasonic time is 30-60 min.

[0024] Furthermore, in step 2, the amount of cellulose nanofiber added is 0.1-1.5wt% of the total mass of the printing ink, and the amount of reduced graphene oxide added is 1.5-2.5wt% of the total mass of the printing ink.

[0025] Furthermore, in step three, the printing speed and air pressure are 600-2000 mm / min and 15-45 kPa respectively; the ultraviolet light wavelength is 365 nm, the intensity is 800 mW, the light source distance is 8-12 cm, and the cross-linking time is 150-180 s.

[0026] The third aspect of the present invention is to provide a 4D printed flexible sensor for use in detecting various physiological activities and health conditions, insect crawling activities, robot labor production status, and a stylus pen.

[0027] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0028] 1. It has unique directional deformation characteristics; by combining reduced graphene oxide with thermosensitive hydrogel, the sensing layer is given temperature-controlled deformation characteristics; by introducing cellulose nanofibers into the hydrogel and controlling the distance of UV cross-linking, the sensing layer and the substrate layer are given a gradient structure, which can achieve the function of directional bending when the temperature changes.

[0029] 2. It has the characteristic of controllable deformation temperature; the introduction of gelatin into the system improves the hydrophilicity of the system, thereby increasing the lower critical phase transition temperature of the poly (N-isopropylacrylamide) hydrogel, thereby regulating the deformation temperature of the system to better meet the needs of the application.

[0030] 3. The base layer and the sensing layer have the same deformation characteristics, which are highly compatible and stable. Since the base layer and the sensing layer are prepared in the same process, they both show similar controllable deformation characteristics with temperature changes.

[0031] 4. It has good mechanical strength and is consistent with the elasticity of the skin. The introduction of reduced graphene oxide and cellulose nanofibers enhances the mechanical properties of the system.

[0032] 5. The preparation method of the present invention is simple and convenient to operate and easy to industrialize. The prepared 4D printed flexible sensor has excellent comprehensive performance.

[0033] 6. The 4D printed flexible sensor prepared by the present invention has good shape-fitting ability, controllable deformation characteristics and mechanical properties, and can change its shape with changes in ambient temperature; it can sense a wide range of pressure signals and has high sensitivity, and can realize the monitoring of various human physiological activities and health conditions, insect crawling activities, robot labor production status, stylus, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the tensile stress-strain curve of the sensing layer in Examples 1-4 of the present invention;

[0035] Figure 2 is a resistance change curve diagram of the flexible sensor of Example 3 of the present invention;

[0036] Figure 3 4 is a curve diagram showing the change in resistance of the flexible sensor according to Example 3 of the present invention as a function of the bending angle. DETAILED DESCRIPTION

[0037] The following specific embodiments further illustrate the present invention, but are not intended to limit the present invention. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0038] Example 1

[0039] A first aspect of the present embodiment is to provide a 4D printed flexible sensor, comprising a base layer, a sensing layer and an electrode layer, wherein the base layer comprises gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone and cellulose nanofibers, and the sensing layer comprises gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, cellulose nanofibers and reduced graphene oxide.

[0040] A second aspect of the present embodiment provides a method for preparing a 4D printed flexible sensor, which is characterized by comprising the following steps:

[0041] Step 1: Printing the printing ink of the base layer using 4D printing technology to generate the base layer;

[0042] Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer;

[0043] Step 3: forming an electrode layer on the surface of the sensing layer, and then curing the electrode layer to obtain a 4D printed flexible sensor. The specific steps of printing the sensing layer are:

[0044] Step 1: first, add 1.2g of N-isopropylacrylamide to 3ml of water and stir to dissolve at room temperature; dissolve 0.8g of gelatin in 5ml of water at 45°C, then mix the dissolved N-isopropylacrylamide and gelatin, add 0.05g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone while stirring, heat to 60°C and stir until a uniform solution is formed.

[0045] Step 2: 0.1 wt% of cellulose nanofibers and 2.5 wt% of reduced graphene oxide are added to the above solution in sequence while stirring, and then ultrasonicated in an ice bath for 30 minutes after stirring evenly to obtain a hydrogel ink for printing.

[0046] Step three: print the designed model shape at a speed of 2000 mm / min and an air pressure of 15 kPa, under ultraviolet light with a wavelength of 365 nm and an intensity of 800 mW, at a distance of 12 cm, and cross-link for 180 s to obtain the sensing layer of the flexible sensor.

[0047] The same method was used to prepare the base layer of the flexible sensor without adding reduced graphene oxide.

[0048] Example 2

[0049] This embodiment provides a method for preparing a 4D printed flexible sensor, which is characterized by comprising the following steps:

[0050] Step 1: Printing the printing ink of the base layer using 4D printing technology to generate the base layer;

[0051] Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer;

[0052] Step 3: forming an electrode layer on the surface of the sensing layer, and then curing the electrode layer to obtain a 4D printed flexible sensor. The specific steps of printing the sensing layer are:

[0053] Step 1: first, add 1.2g of N-isopropylacrylamide to 3ml of water and stir to dissolve at room temperature; dissolve 0.8g of gelatin in 5ml of water at 45°C, then mix the dissolved N-isopropylacrylamide and gelatin, add 0.05g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone while stirring, heat to 60°C and stir until a uniform solution is formed.

[0054] Step 2: Add 0.5 wt% of cellulose nanofibers and 2.0 wt% of reduced graphene oxide to the above solution in sequence while stirring, stir evenly, and then ultrasonicate in an ice bath for 30 minutes to obtain a hydrogel ink for printing.

[0055] Step three, printing out the designed model shape at a speed of 2000 mm / min and an air pressure of 15 kPa, under ultraviolet light with a wavelength of 365 nm and an intensity of 800 mW, at a distance of 10 cm, and cross-linking for 180 s, to obtain the sensing layer of the flexible sensor of Example 1.

[0056] The same method was used to prepare the base layer of the flexible sensor without adding reduced graphene oxide.

[0057] Example 3

[0058] This embodiment provides a method for preparing a 4D printed flexible sensor, which is characterized by comprising the following steps:

[0059] Step 1: Printing the printing ink of the base layer using 4D printing technology to generate the base layer;

[0060] Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer;

[0061] Step 3: forming an electrode layer on the surface of the sensing layer, and then curing the electrode layer to obtain a 4D printed flexible sensor. The specific steps of the sensing layer are:

[0062] Step 1: first, add 1.2g of N-isopropylacrylamide to 3ml of water and stir to dissolve at room temperature; dissolve 0.8g of gelatin in 5ml of water at 45°C, then mix the dissolved N-isopropylacrylamide and gelatin, add 0.05g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone while stirring, heat to 60°C and stir until a uniform solution is formed.

[0063] Step 2: 1.0 wt% of cellulose nanofibers and 2.0 wt% of reduced graphene oxide are added to the above solution in sequence while stirring, and then ultrasonicated in an ice bath for 30 minutes after stirring evenly to obtain a hydrogel ink for printing.

[0064] Step three, printing out the designed model shape at a speed of 2000 mm / min and an air pressure of 15 kPa, under ultraviolet light with a wavelength of 365 nm and an intensity of 800 mW, at a distance of 10 cm, and cross-linking for 180 s, to obtain the sensing layer of the flexible sensor of Example 1.

[0065] The same method was used to prepare the base layer of the flexible sensor without adding reduced graphene oxide.

[0066] The resistance curve of the 4D printed flexible sensor prepared in this embodiment is as follows: Figure 2 As shown, it can be seen that when the pressure increases from 4kPa to 600kPa, the resistance drops sharply at first and then tends to be stable, indicating that the sensor has a sensitive response to the effect of pressure within a certain pressure range.

[0067] The resistance of the 4D printed flexible sensor prepared in this embodiment changes with the bending angle as shown in Figure 3 As shown, it can be seen that when the bending angle of the sensor increases from 0 to 65 degrees, the resistance of the sensor gradually increases with the increase of the bending angle, and it has good bending response characteristics.

[0068] Example 4

[0069] This embodiment provides a method for preparing a 4D printed flexible sensor, which is characterized by comprising the following steps:

[0070] Step 1: Printing the printing ink of the base layer using 4D printing technology to generate the base layer;

[0071] Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer;

[0072] Step 3: forming an electrode layer on the surface of the sensing layer, and then curing the electrode layer to obtain a 4D printed flexible sensor. The specific steps of printing the sensing layer are:

[0073] Step 1: first, add 1.2g of N-isopropylacrylamide to 3ml of water and stir to dissolve at room temperature; dissolve 0.8g of gelatin in 5ml of water at 45°C, then mix the dissolved N-isopropylacrylamide and gelatin, add 0.05g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone while stirring, heat to 60°C and stir until a uniform solution is formed.

[0074] Step 2: 1.5 wt% of cellulose nanofibers and 1.5 wt% of reduced graphene oxide are added to the above solution in sequence while stirring, and after stirring evenly, ultrasonic treatment is performed in an ice bath for 30 minutes to obtain a hydrogel ink for printing.

[0075] Step three, printing out the designed model shape at a speed of 2000 mm / min and an air pressure of 15 kPa, under ultraviolet light with a wavelength of 365 nm and an intensity of 800 mW, at a distance of 8 cm, and cross-linking for 180 s, to obtain the sensing layer of the flexible sensor of Example 1.

[0076] The substrate layer of the flexible sensor of Example 1 was prepared in the same manner without adding reduced graphene oxide.

[0077] The tensile stress-strain curves of the sensing layers of the 4D printed flexible sensors prepared in Examples 1-4 are shown in Figure 1 As shown, it can be seen that the prepared sensor has good comprehensive mechanical properties, and the modulus is similar to that of human skin (0.13-0.66 MPa), and has good shape-fitting ability.

[0078] The deformation performance testing method is as follows: the materials of Examples 1 to 4 are prepared into discs with a diameter of 10 mm and a thickness of 0.15 mm, and then placed in a water bath at 37°C for heating for a period of time, and the change in the diameter of the material before and after is recorded. The shrinkage rate SR=(D0-D) / D0 is calculated, wherein D0 is the diameter before shrinkage and D is the diameter after shrinkage. The test results are shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] The results are shown in Table 1. Due to the differences in cellulose nanofibers, reduced graphene oxide and ultraviolet light distances, the shrinkage rates of the materials obtained in different embodiments are different. The deformation characteristics of the material can be regulated by adjusting the composition and cross-linking distance.

[0083] Example 5

[0084] This embodiment provides an application of a 4D printed flexible sensor in detecting various physiological activities and health conditions, insect crawling activities, robot labor production status, and a stylus pen.

[0085] The specific embodiments of the present invention are described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modification and substitution of the practical is also within the scope of the present invention. Therefore, the equalization transformation and modification made without departing from the spirit and scope of the present invention should be included in the scope of the present invention.

Claims

1. A 4D printed flexible sensor, characterized in that: The 4D printed flexible sensor includes a base layer, a sensing layer and an electrode layer. The base layer includes gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone and cellulose nanofibers. The sensing layer includes gelatin, N-isopropylacrylamide, 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, cellulose nanofibers and reduced graphene oxide.

2. A method for preparing a 4D printed flexible sensor as claimed in claim 1, characterized in that: The steps include: Step 1, using 4D printing technology to print the printing ink of the base layer to generate the base layer; Step 2: Printing the printing ink of the sensing layer on the base layer using 4D printing technology to generate the sensing layer; Step three, forming an electrode layer on the surface of the sensing layer, and then curing it to obtain a 4D printed flexible sensor.

3. The method for preparing a 4D printed flexible sensor according to claim 2, characterized in that: The specific steps of printing the base layer are: Step 1: Dissolve gelatin and N-isopropylacrylamide separately and mix them, then add 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, heat and stir to form a uniform solution; Step 2, then adding the pre-dispersed cellulose nanofibers, stirring evenly and then ultrasonicating in an ice bath to obtain the printing ink for the base layer; Step three: print out the model shape through a printer, and then use ultraviolet light curing to obtain a 4D printed flexible base layer.

4. The method for preparing a 4D printed flexible sensor according to claim 2, characterized in that: The specific steps of printing the sensing layer are: Step 1: Dissolve gelatin and N-isopropylacrylamide separately and mix them, then add 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, heat and stir to form a uniform solution; Step 2, then adding the pre-dispersed cellulose nanofibers and reduced graphene oxide, stirring evenly and then ultrasonicating in an ice bath to obtain the printing ink for the sensing layer; Step three: print out the model shape through a printer, and then use ultraviolet light curing to obtain a 4D printed flexible sensing layer with controllable deformation characteristics.

5. The method for preparing a 4D printed flexible sensor according to claim 3 or 4, characterized in that: In the step 1, the mass ratio of N-isopropylacrylamide, gelatin and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone is 3:2:(0.125-0.5).

6. The method for preparing a 4D printed flexible sensor according to claim 3 or 4, characterized in that: In the step 1, gelatin is dissolved in water at 40-45°C; the heating temperature is 50-60°C.

7. The method for preparing a 4D printed flexible sensor according to claim 3 or 4, characterized in that: In the step 2, the ultrasonic time is 30-60 min.

8. The method for preparing a 4D printed flexible sensor according to claim 4, characterized in that: In the step 2, the amount of cellulose nanofibers added is 0.1-1.5 wt% of the total mass of the printing ink, and the amount of reduced graphene oxide added is 1.5-2.5 wt% of the total mass of the printing ink.

9. The method for preparing a 4D printed flexible sensor according to claim 3 or 4, characterized in that: In the step three, the printing speed and air pressure are 600-2000 mm / min and 15-45 kPa respectively; the ultraviolet light wavelength is 365 nm, the intensity is 800 mW, the light source distance is 8-12 cm, and the cross-linking time is 150-180 s.

10. An application of the 4D printed flexible sensor as claimed in claim 1 in detecting insect crawling activities, robot labor production status, and stylus.

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