A multilayer assembled piezoresistive hydrogel sensor and a preparation method thereof

Abstract

This invention discloses a multilayer assembled piezoresistive hydrogel sensor and its fabrication method. The sensor uses hydrogel as the matrix material and is obtained by assembling layers of hydrogels with different conductivity. The sensitivity of the multilayer assembled piezoresistive hydrogel sensor can be adjusted by modifying the type of matrix material, the thickness of each hydrogel layer, the concentration of conductive filler in the matrix material, the number of assembled layers, and / or the overall thickness of the piezoresistive sensor.

Description

Technical Field

[0001] This invention relates to a piezoresistive hydrogel sensor, specifically to a highly sensitive piezoresistive hydrogel sensor fabricated using a multilayer assembly method. Background Technology

[0002] Traditional piezoresistive sensors suffer from low sensitivity, poor mechanical properties, and poor repeatability. Traditional sensors made from metal or semiconductor materials cannot withstand large mechanical deformations due to their inherent rigidity. The sensitivity of commonly used one-step fabrication methods for piezoresistive hydrogel sensors can only be adjusted by the concentration of the conductive filler, and the adjustable range is relatively small. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention provides a multilayer assembled piezoresistive hydrogel sensor with high sensitivity, good mechanical properties, good repeatability, and controllable sensitivity.

[0004] To achieve the objective, the technical solution adopted by this invention is as follows:

[0005] A multilayer assembled piezoresistive hydrogel sensor is characterized in that: the piezoresistive hydrogel sensor uses hydrogel as the matrix material and is assembled by assembling hydrogel layers with different conductivity to obtain the final sensor.

[0006] Furthermore, the thickness of each hydrogel layer ranges from 0.5 to 1 mm, the number of assembled layers ranges from 10 to 20, and the total thickness of the sensor is no more than 2 cm.

[0007] Further: the hydrogel is a single-network hydrogel or a double-network hydrogel; the single-network hydrogel is obtained by chemical crosslinking or physical crosslinking; the first network of the double-network hydrogel is obtained by physical crosslinking and the second network is obtained by chemical crosslinking; the physical crosslinking monomer in the hydrogel is one of sodium alginate, chitosan, gelatin, carrageenan and cardlan gum, and the chemical crosslinking monomer is one of acrylamide, acrylic acid, isopropyl acrylamide and acrylamide methylpropanesulfonic acid.

[0008] Furthermore, the hydrogel contains a conductive filler, which is at least one of carbon nanotubes, graphene, and MXenes.

[0009] Furthermore, the carbon nanotubes are short-walled carbon nanotubes, and their surfaces contain both hydroxyl and carboxyl hydrophilic groups. The carboxyl content in these short-walled carbon nanotubes is 0.71–5.58 wt%, the hydroxyl content is 0.49–3.86 wt%, and the aspect ratio ranges from 80 to 500. The graphene is oxidized graphene oxide with fewer than 3 layers, a purity greater than 98 wt%, a carbon content of 50–65 wt%, and an oxygen content of 30–50 wt%. The MXenes are obtained by etching away the metallic phase with Ti3AlC2, resulting in a porous structure into which hydrogel macromolecules can be intercalated.

[0010] Furthermore, the sensitivity of the multilayer assembled piezoresistive hydrogel sensor can be adjusted by regulating the type of matrix material, the thickness of the single-layer hydrogel, the concentration of conductive filler in the matrix material, the number of assembled layers, and / or the overall thickness of the piezoresistive sensor.

[0011] The preparation method of the multilayer assembled piezoresistive hydrogel sensor of the present invention is as follows: First, prepare the hydrogel prepreg required for each layer of hydrogel, then pour each layer of hydrogel prepreg into the mold and solidify it in sequence, and finally encapsulate it on the top layer of hydrogel with a flexible protective layer to obtain the multilayer assembled piezoresistive hydrogel sensor.

[0012] Furthermore, the material of the flexible protective layer is one of Ecoflex00-10, Ecoflex00-20, Ecoflex00-30, Ecoflex00-35, and Ecoflex00-50.

[0013] Furthermore, in the dual-network hydrogel, carbon nanotubes, graphene, and MXenes conductive fillers are dispersed in a physically cross-linked phase.

[0014] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0015] Compared to traditional one-step sensor fabrication methods where sensitivity can only be adjusted by the concentration of conductive filler, the sensor fabricated using a multi-layer assembly method in this invention allows for sensitivity adjustment not only by the concentration of conductive filler but also by the thickness of each layer, the total number of layers, the total thickness, the concentration of conductive filler in each layer of hydrogel, and the concentration difference of conductive filler between adjacent layers, thus expanding the sensitivity adjustment range. This invention uses hydrogel as the matrix material and overcomes the limitations of traditional rigid sensors in handling large mechanical deformations. The sensor of this invention is encapsulated with a flexible protective layer, effectively preventing water loss from the hydrogel, further expanding its application range and conditions, and extending its service life. The conductive fillers used in this invention are short-walled carbon nanotubes, graphene oxide, and MXenes. These three conductive fillers have high conductivity and abundant functional groups on their surfaces, allowing them to be firmly locked onto the hydrogel framework. This reduces the amount of filler used while maintaining or even increasing conductivity. Attached Figure Description

[0016] Figure 1 The resistivity of the multilayer assembled piezoresistive hydrogel sensor prepared in Example 1 changes with compressive strain.

[0017] Figure 2 The image shows a scanning electron microscope (SEM) image of the multilayer assembled piezoresistive hydrogel sensor prepared in Example 2.

[0018] Figure 3 The EIT imaging test images obtained by pressing the multilayer assembled piezoresistive hydrogel sensor prepared in this embodiment with different pressing pressures are shown in (a), (b), and (c). The pressing pressure at the dark spot in the upper right is 5N, and the pressing pressure at the dark spot in the lower left is 1N, 2N, and 3N, respectively. Detailed Implementation

[0019] To further illustrate the features and advantages of the present invention, the embodiments of the present invention are described in detail below. The following embodiments are only a part of the present invention, and the scope of protection of the present invention is not limited to the following embodiments.

[0020] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0021] The carbon nanotubes used in the following examples are short-walled carbon nanotubes with a carboxyl content of 0.71–5.58 wt%, a hydroxyl content of 0.49–3.86 wt%, and an aspect ratio of 80–500.

[0022] The graphene used in the following examples is oxidized graphene oxide with fewer than 3 layers, a purity greater than 98 wt%, a carbon content of 50-65 wt%, and an oxygen content of 30-50 wt%.

[0023] Example 1

[0024] This embodiment prepares a multilayer assembled piezoresistive hydrogel sensor according to the following steps:

[0025] (1) Prepare four hydrogel prepregs: A, B, C, and D, using an aqueous solution of 15 wt% cardlan gum as prepreg; a mixed solution of 15 wt% acrylamide and 0.1 wt% MXenes as prepreg; a mixed solution of 10 wt% cardlan gum and 0.05 wt% MXenes as prepreg; and a 20 wt% acrylamide solution as prepreg.

[0026] (2) Pour the hydrogel prepreg A into a pre-prepared circular mold with a diameter of 25 mm and a thickness of 0.5 mm, place it in an oven at 60°C, and take it out after 10 minutes to obtain hydrogel 1.

[0027] (3) Pour the hydrogel prepreg B into the mold and spread it evenly on the surface of hydrogel 1 with a thickness of 0.7 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain hydrogel 2.

[0028] (4) Pour the hydrogel prepreg A into the mold and spread it evenly on the surface of hydrogel 2 with a thickness of 0.6 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain hydrogel 3.

[0029] (5) Pour the hydrogel prepreg C into the mold and spread it evenly on the surface of the hydrogel 3 with a thickness of 0.8 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 4.

[0030] (6) Pour the hydrogel prepreg D into the mold and spread it evenly on the surface of the hydrogel 4 with a thickness of 0.5 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 5.

[0031] (7) Repeat steps (1) to (6) twice to obtain a hydrogel sensor with a thickness of 9.3 mm and an assembly structure of ABACDABACDABACD.

[0032] (8) Use Ecoflex00-30 to encapsulate the final hydrogel sensor. The thickness of the encapsulation layer is 0.5mm, and a multilayer assembled piezoresistive hydrogel sensor can be obtained.

[0033] Figure 1 The resistivity of the multilayer assembled piezoresistive hydrogel sensor prepared in this embodiment changes with compressive strain. As can be seen from the figure, its conductivity decreases significantly with increasing compressive strain, indicating that it is sensitive to compressive strain.

[0034] Figure 2 The image shows a scanning electron microscope (SEM) image of the multilayer assembled piezoresistive hydrogel sensor prepared in this embodiment. As can be seen from the image, its internal structure is uniform.

[0035] Figure 3 The images show EIT imaging test results obtained by pressing the multilayer assembled piezoresistive hydrogel sensor prepared in this embodiment with different pressing pressures. In (a), (b), and (c), the pressing pressure at the dark dot in the upper right is 5N, and the pressing pressure at the dark dot in the lower left is 1N, 2N, and 3N, respectively. It can be seen from the figures that the greater the pressing pressure, the stronger the signal.

[0036] Example 2

[0037] This embodiment prepares a multilayer assembled piezoresistive hydrogel sensor according to the following steps:

[0038] (1) Prepare four hydrogel prepregs: A, B, C, and D, using a mixed solution of 20 wt% cardlan gum and 0.1 wt% graphene oxide as hydrogel prepreg, B, C, D, using a mixed solution of 10 wt% acrylamide and 0.02 wt% short-walled carbon nanotubes as hydrogel prepreg, C, D, using a mixed solution of 10 wt% acrylamide and 0.05 wt% MXenes as hydrogel prepreg, and D, using a 15 wt% acrylamide solution as hydrogel prepreg.

[0039] (2) Pour the hydrogel prepreg A into a pre-prepared circular mold with a diameter of 25 mm and a thickness of 0.8 mm, place it in an oven at 60°C, and take it out after 10 minutes to obtain hydrogel 1.

[0040] (3) Pour the hydrogel prepreg D into the mold and spread it evenly on the surface of hydrogel 1 with a thickness of 0.7 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain hydrogel 2.

[0041] (4) Pour the hydrogel prepreg B into the mold and spread it evenly on the surface of hydrogel 2 with a thickness of 0.5 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain hydrogel 3.

[0042] (5) Pour the hydrogel prepreg C into the mold and spread it evenly on the surface of the hydrogel 3 with a thickness of 0.6 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 4.

[0043] (6) Pour the hydrogel prepreg D into the mold and spread it evenly on the surface of the hydrogel 4 with a thickness of 0.5 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 5.

[0044] (7) Repeat steps (1) to (6) three times to obtain a hydrogel sensor with a thickness of 12.4 mm and an assembly structure of ADBCDADBCDADBCDADBCD;

[0045] (8) Use Ecoflex00-30 to encapsulate the final hydrogel sensor. The thickness of the encapsulation layer is 0.5mm, and a multilayer assembled piezoresistive hydrogel sensor can be obtained.

[0046] Example 3

[0047] This embodiment prepares a multilayer assembled piezoresistive hydrogel sensor according to the following steps:

[0048] (1) Prepare four hydrogel prepregs: A with 15 wt% acrylamide solution, B with a mixed solution of 10 wt% acrylamide, 15 wt% gelatin, and 0.05 wt% graphene oxide, C with a mixed solution of 10 wt% acrylamide, 15 wt% gelatin, and 0.05 wt% MXenes, and D with 15 wt% sodium alginate solution.

[0049] (2) Pour the hydrogel prepreg B into a pre-prepared circular mold with a diameter of 25 mm and a thickness of 0.7 mm, place it in an oven at 60°C, and take it out after 10 minutes to obtain hydrogel 1.

[0050] (3) Pour the hydrogel prepreg D into the mold and spread it evenly on the surface of hydrogel 1 with a thickness of 0.8 mm. Place it in an oven at 60°C and take it out after 10 min to obtain hydrogel 2.

[0051] (4) Pour the hydrogel prepreg A into the mold and spread it evenly on the surface of hydrogel 2 with a thickness of 0.6 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain hydrogel 3.

[0052] (5) Pour the hydrogel prepreg C into the mold and spread it evenly on the surface of the hydrogel 3 with a thickness of 0.5 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 4.

[0053] (6) Pour the hydrogel prepreg D into the mold and spread it evenly on the surface of the hydrogel 4 with a thickness of 0.7 mm. Place it in an oven at 60°C and take it out after 10 minutes to obtain the hydrogel 5.

[0054] (7) Repeat steps (1) to (6) three times to obtain a hydrogel sensor with a thickness of 13.2 mm and an assembly structure of BDACDBDACDBDACDBDACD;

[0055] (8) Use Ecoflex00-20 to encapsulate the final hydrogel sensor. The thickness of the encapsulation layer is 0.5mm, and a multilayer assembled piezoresistive hydrogel sensor can be obtained.

[0056] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multilayer assembled piezoresistive hydrogel sensor, characterized in that: The piezoresistive hydrogel sensor uses hydrogel as the matrix material and is assembled by layering hydrogels with different conductivity to obtain the final sensor. The thickness of each hydrogel layer ranges from 0.5 to 1 mm, the number of assembled layers ranges from 10 to 20, and the total thickness of the sensor is no more than 2 cm. The hydrogel is a single-network hydrogel or a double-network hydrogel; the single-network hydrogel is obtained by chemical crosslinking or physical crosslinking; the first network of the double-network hydrogel is obtained by physical crosslinking and the second network is obtained by chemical crosslinking; the physical crosslinking monomer in the hydrogel is one of sodium alginate, chitosan, gelatin, carrageenan and cardlan gum, and the chemical crosslinking monomer is one of acrylamide, acrylic acid, isopropyl acrylamide and acrylamide methylpropanesulfonic acid; The hydrogel contains a conductive filler, which is at least one of carbon nanotubes, graphene, and MXenes. The sensitivity of the multilayer assembled piezoresistive hydrogel sensor is adjusted by regulating the type of matrix material, the thickness of the single-layer hydrogel, the concentration of conductive filler in the matrix material, the number of assembled layers, and / or the overall thickness of the piezoresistive sensor.

2. The multilayer assembled piezoresistive hydrogel sensor according to claim 1, characterized in that: The carbon nanotubes are short-walled carbon nanotubes, and the surface of the short-walled carbon nanotubes contains two hydrophilic groups: hydroxyl and carboxyl groups. The carboxyl content in the short-walled carbon nanotubes is 0.71–5.58 wt%, the hydroxyl content is 0.49–3.86 wt%, and the aspect ratio is 80–500.

3. The multilayer assembled piezoresistive hydrogel sensor according to claim 1, characterized in that: The graphene is oxidized graphene oxide, which has fewer than 3 layers, a purity greater than 98 wt%, a carbon content of 50-65 wt%, and an oxygen content of 30-50 wt%.

4. The multilayer assembled piezoresistive hydrogel sensor according to claim 1, characterized in that: The MXenes are obtained by etching away the metal phase with Ti3AlC2 and have a fluffy structure into which hydrogel macromolecules can be intercalated.

5. A method for preparing a multilayer assembled piezoresistive hydrogel sensor according to any one of claims 1 to 4, characterized in that: First, prepare the hydrogel prepreg required for each layer of hydrogel. Then, pour each layer of hydrogel prepreg into the mold and solidify it. Finally, encapsulate the top layer of hydrogel with a flexible protective layer to obtain a multilayer assembled piezoresistive hydrogel sensor.

6. The preparation method according to claim 5, characterized in that: The flexible protective layer is made of one of Ecoflex 00-10, Ecoflex 00-20, Ecoflex 00-30, Ecoflex 00-35, and Ecoflex 00-50.

Images