Application of conductive hydrogel with anisotropic characteristic in hydrogel strain sensor and biological electrode

Abstract

The invention relates to application of conductive hydrogel with anisotropic characteristics in a hydrogel strain sensor and a biological electrode, and in the aspect of strain sensing, the hydrogel can show high-precision monitoring capability on large-range movement of human joints and facial micro-expressions; in the aspect of biological electrodes, better performance can be shown in ECG, EMG and EEG signal acquisition, and the signal-to-noise ratio (SNR = 24.67) during detection is remarkably higher than that of a commercial Ag / AgCl electrode (SNR = 20.64).

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, relates to conductive hydrogels, and particularly relates to the application of conductive hydrogels with anisotropic characteristics in hydrogel strain sensors and bioelectrodes. Background Art

[0002] The development of flexible electronics is driving the evolution of human-computer interaction from "mechanical adaptation" to "bio-integration." In this process, conductive hydrogels, due to their unique "soft matter" properties, are becoming a core material system for building biomimetic sensor devices. However, while traditional homogeneous hydrogel networks can achieve basic deformation responses, their disordered, tangled molecular chains result in a significant lack of directional dependence in the sensing signal, severely hindering the accurate interpretation of complex motion trajectories.

[0003] Unlike traditional isotropic materials, structurally guided anisotropic hydrogels, through precise control of microscopic order, have demonstrated tremendous potential in strain sensing and bioelectrical signal capture, offering new insights into the intrinsic mismatch between rigid electronic devices and dynamic biological tissues. Based on biomimetic concepts, the construction of directional conduction pathways within the material allows the sensor to possess spatial resolution capabilities. This heterogeneous design, aligned with biomechanical properties, not only significantly improves the accuracy of multi-directional joint motion detection but, more importantly, enables cross-scale monitoring of both minute muscle tremors and large limb movements.

[0004] In the field of bioelectrodes, the advantages brought by structural orientation are even more significant. Conventional hydrogel electrodes are limited by disordered ion migration paths, which easily lead to interfacial charge accumulation, resulting in baseline drift during electrophysiological signal acquisition. The conductive network with an oriented structure can effectively reduce interfacial impedance fluctuations by establishing a fast ion transmission channel. This feature plays a decisive role in capturing microvolt-level EEG signals. It is worth noting that the oriented structure gives the material dynamic adaptive mechanical properties, enabling it to adapt to changes in the topology of the skin surface, maintain a stable electrode-tissue interface during continuous motion, and suppress the generation of motion artifacts. More importantly, structural orientation provides a physical basis for multimodal signal decoupling. By designing a conductive network with a specific orientation, spatially selective acquisition of signals such as electrocardiogram and electromyography can be achieved. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the existing technology by providing an anisotropic conductive hydrogel for use in hydrogel strain sensors and bioelectrodes. The study demonstrates that the mechanical and electrical properties of hydrogels with oriented structures are significantly improved parallel to the orientation direction, demonstrating their potential for application in flexible electronics. Using anisotropic PVA-P:P hydrogel as the base material, the strain sensing properties of the hydrogel were investigated. Based on this, strain sensors and bioelectrodes were fabricated, and their practical applications in related fields were systematically studied.

[0006] The present invention solves the technical problem by the following technical solutions:

[0007] A conductive hydrogel with anisotropic characteristics is used in a hydrogel strain sensor. The conductive hydrogel is cut into samples with a length of 50 mm, a width of 5 mm, and a thickness of 2 mm. Copper electrodes connected to wires are fixed to both ends of the sample with copper tape. The sample is then wrapped and clamped with two strips of VHB tape to produce a hydrogel strain sensor. The hydrogel strain sensor is connected to an electrochemical workstation and fixed to the finger, wrist, elbow, and knee joints to test its ability to recognize and transmit human motion signals.

[0008] Moreover, the hydrogel strain sensor is attached to the skin surface of the human face and throat to study the tiny facial expressions and tiny vibrations generated by the throat when speaking.

[0009] Moreover, the strain sensing sensitivity value of the hydrogel strain sensor parallel to the orientation direction within a strain range of more than 140% is 19.67.

[0010] Moreover, the conductive hydrogel uses polyvinyl alcohol (PVA) as a flexible matrix and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a conductive component. The flexible matrix and the conductive component form a physical cross-linked network through freeze-thaw cycles, and utilize the Hofmeister effect of sodium citrate solution to densify the polymer chains and fix the orientation structure, thereby obtaining a conductive hydrogel with anisotropic characteristics.

[0011] A conductive hydrogel with anisotropic characteristics is used in a hydrogel bioelectrode. The conductive hydrogel is cut into square patches with a length of 10 mm to obtain a hydrogel bioelectrode. The hydrogel bioelectrode is attached to human skin and connected to an electrophysiological recorder to monitor electrophysiological signals, including electrocardiogram, electromyography, and electroencephalogram signals.

[0012] Moreover, the electrocardiogram monitoring signal-to-noise ratio of the hydrogel bioelectrode is 24.67.

[0013] The advantages and beneficial effects of the present invention are:

[0014] 1. The anisotropic PVA-P:P conductive hydrogel strain sensor of the present invention has excellent strain sensing properties. The strain sensing sensitivity (GF value) in the direction parallel to the orientation direction is significantly higher than that in the perpendicular direction and isotropic hydrogels, especially in a large strain range of more than 140% (GF reaches 19.67), showing high-precision monitoring capabilities for large-scale human joint movements and facial micro-expressions.

[0015] 2. The hydrogel bioelectrode of the present invention, the anisotropic PVA-P:P hydrogel, exhibits superior performance in ECG (electrocardiogram), EMG (electromyogram) and EEG (electroencephalogram) signal acquisition. The signal-to-noise ratio (SNR=24.67) during ECG detection is significantly higher than that of commercial Ag / AgCl electrodes (SNR=20.64).

[0016] 3. The conductive hydrogel of the present invention maintains a stable response (with minimal fluctuation in ΔR / R0) after 300 cycles of testing at 20% strain and has a fast response / recovery time (0.5s), verifying its reliability in long-term wearable real-time monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a diagram showing the monitoring of large-scale motion of human joints by the anisotropic hydrogel strain sensor of the present invention;

[0018] Figure 2 This is a diagram showing the monitoring of human facial micro-expressions by the anisotropic hydrogel strain sensor of the present invention;

[0019] Figure 3 This is a comparison chart of the anisotropic hydrogel bioelectrode of the present invention and commercial electrodes monitoring human electrocardiogram signals;

[0020] Figure 4 This is a comparison chart of the anisotropic hydrogel bioelectrode of the present invention and commercial electrodes monitoring human electromyographic signals;

[0021] Figure 5 This is a comparison chart of the monitoring of human EEG signals by the anisotropic hydrogel bioelectrode of the present invention and commercial electrodes. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0023] Example 1: Anisotropic Conductive Hydrogel Strain Sensor

[0024] Anisotropic PVA-P:P hydrogel samples were cut into 50 mm long, 5 mm wide, and 2 mm thick samples. Copper electrodes connected to wires were affixed to both ends of the hydrogel sample with copper tape (detecting parallel and perpendicular to the orientation direction, respectively). The hydrogel was then wrapped and clamped with two strips of VHB tape to create an anisotropic PVA-P:P hydrogel strain sensor. This anisotropic PVA-P:P hydrogel sensor was connected to an electrochemical workstation and affixed to joints such as the finger, wrist, elbow, and knee to test its ability to recognize and transmit human motion signals.

[0025] Example 2: Anisotropic PVA-P:P hydrogel was cut into samples with a length of 50 mm, a width of 5 mm, and a thickness of 2 mm. Copper electrodes connected to wires were affixed to both ends of the hydrogel sample with copper tape (to detect parallel and perpendicular to the orientation direction, respectively). The hydrogel was then wrapped and clamped with two strips of VHB tape to produce an anisotropic PVA-P:P hydrogel strain sensor. This anisotropic PVA-P:P hydrogel sensor was connected to an electrochemical workstation and affixed to the skin surfaces of the face and throat to study subtle facial expressions and the minute vibrations produced by the throat during vocalization.

[0026] like Figure 1 As shown, anisotropic PVA-P:P hydrogel was applied to the skin on the back of the wrist joint. When the wrist was bent at 30°, 60°, and 90°, the conducted electrical signal values ​​varied accordingly, reaching 3.8%, 10.5%, and 20.3%. During tests of finger, elbow, and knee flexion, clear and relatively stable electrical signal output was achieved. Over a certain period of time, the signal output remained stable and repeatable.

[0027] like Figure 2 As shown, when a PVA-P:P hydrogel strain sensor with an oriented structure is placed on the skin surface of the cheek or above the eyebrow, it can detect changes caused by subtle changes in facial expressions such as smiling and frowning, and the sensor can be seen to output a stable electrical signal. The ability of the anisotropic PVA-P:P hydrogel strain sensor to recognize even smaller signals was explored. When the sensor was installed on the skin on the surface of the throat and vocalized, different electrical response signals were output when we read "apple" and "hello". Therefore, the above test results all prove that the anisotropic PVA-P:P hydrogel strain sensor has high electrochemical sensitivity and can be used for the recognition and output of small signals.

[0028] Example 3: Anisotropic Conductive Hydrogel Bioelectrode

[0029] Anisotropic PVA-P:P hydrogel was cut into square patches with a length and width of 10 mm, which were used to replace the commercial Ag / AgCl hydrogel in human electrode patches to prepare PVA-P:P hydrogel electrode patches. These patches were attached to the corresponding positions of human skin and connected to an electrophysiological recorder to monitor electrophysiological signals and corresponding data output.

[0030] like Figures 3-5 As shown in the figure, the anisotropic PVA-P:P hydrogel can achieve complete, continuous and stable signal output for both ECG and EMG signals. Compared with commercial Ag / AgCl electrodes, it can output clearer waveform signals and a higher signal-to-noise ratio. For EEG signals, it can be seen that the time domain signals and frequency domain signals received when monitoring volunteers listening to "Moonlight" and watching horror videos are clearer and the output is more stable.

[0031] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. Application of an anisotropic conductive hydrogel in a hydrogel strain sensor, characterized in that: The conductive hydrogel was cut into samples with a length of 50 mm, a width of 5 mm, and a thickness of 2 mm. Copper electrodes with wires were fixed to both ends of the sample with copper tape. The sample was then wrapped and clamped with two strips of VHB tape to produce a hydrogel strain sensor. The hydrogel strain sensor was connected to an electrochemical workstation and fixed to the finger, wrist, elbow, and knee joints to test its ability to recognize and transmit human motion signals.

2. The use according to claim 1, characterized in that: The hydrogel strain sensor is attached to the skin surface of the human face and throat to study the tiny facial expressions and tiny vibrations generated by the throat when speaking.

3. The use according to claim 1, characterized in that: The strain sensing sensitivity value of the hydrogel strain sensor parallel to the orientation direction within a strain range of more than 140% is 19.

67.

4. The use according to claim 1, characterized in that: The conductive hydrogel uses polyvinyl alcohol (PVA) as a flexible matrix and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a conductive component. The flexible matrix and the conductive component form a physical cross-linked network through freeze-thaw cycles, and the Hofmeister effect of sodium citrate solution is used to densify the polymer chains and fix the orientation structure, thereby obtaining a conductive hydrogel with anisotropic characteristics.

5. Application of an anisotropic conductive hydrogel in a hydrogel bioelectrode, characterized in that: The conductive hydrogel was cut into square patches with a length of 10 mm to obtain a hydrogel bioelectrode; the hydrogel bioelectrode was attached to human skin and connected to an electrophysiological recorder to monitor electrophysiological signals, including electrocardiogram, electromyography and electroencephalogram signals.

6. The use according to claim 5, characterized in that: The hydrogel bioelectrode has an electrocardiogram monitoring signal-to-noise ratio of 24.

67.

7. The use according to claim 5, characterized in that: The conductive hydrogel uses polyvinyl alcohol (PVA) as a flexible matrix and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a conductive component. The flexible matrix and the conductive component form a physical cross-linked network through freeze-thaw cycles, and the Hofmeister effect of sodium citrate solution is used to densify the polymer chains and fix the orientation structure, thereby obtaining a conductive hydrogel with anisotropic characteristics.

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