A thermoreversible hydrogel for collecting human physiological electrical signals and a preparation method thereof

Abstract

The present invention relates to a thermoreversible hydrogel for collecting physiological electrical signals from the human body and a preparation method thereof. Compared with previous physiological electrical signal collection electrode materials, the hydrogel of the present invention is composed of biocompatible materials such as natural gelatin and a low eutectic solvent. The hydrogel has excellent conductivity, adhesion, mechanical properties and biocompatibility, which significantly improves the quality of the collected signals. At the same time, since it does not require an additional conductive coating, it can provide users with a more comfortable use experience, making it an ideal choice for electrode materials that are worn for a long time. The invention is expected to provide hardware support for the collection of EEG and other physiological electrical signals, and has broad application prospects in fields such as biomedicine.

Description

Technical Field

[0001] The invention relates to the field of thermoreversible hydrogels, in particular to a thermoreversible hydrogel for collecting physiological electrical signals of a human body and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of the Internet of Things (IoT) and artificial intelligence (AI) technologies, the demand for low-cost, fast, and easy-to-use wearable sensors in fields such as health monitoring and smart healthcare has continued to grow. In particular, biosensors based on the acquisition of physiological electrical signals have been widely researched because they can reflect human health and disease progression. These sensors can continuously monitor physiological parameters such as electroencephalogram (EEG), electrocardiogram (ECG), and electromyography (EMG) in real time, providing a new solution for the biomedical field. Traditional signal acquisition typically relies on metal electrodes attached to the skin, requiring the use of conductive adhesive to ensure good electrical signal sensing. However, due to inherent material limitations, most wearable sensors suffer from issues such as comfort, breathability, and biocompatibility in practical applications, resulting in a poor user experience and poor signal quality. To achieve long-term, high-quality electrophysiological recordings, bioelectrodes connected to soft skin tissue must meet stringent requirements, such as good adaptability, stable mechanical interaction, and long-term reliability.

[0003] In this context, several innovative electrode designs have been proposed to improve the performance of wearable sensors. In 2019, Liu et al. proposed a contactless electrode made of a multilayer flexible printed circuit. This electrode can measure physiological signals without direct contact with the skin or conductive gel and can be bent freely according to local shape to achieve optimal capacitive coupling with the skin surface. In 2020, Li et al. developed a novel printable flexible Ag / AgCl dry electrode array for forehead electroencephalogram (EEG) acquisition. The array consists primarily of a screen-printed Ag / AgCl coating and a conductive sweat-absorbing sponge. Experimental results demonstrated that the flexible dry electrode array exhibited reproducible electrode potentials, low electrode-skin impedance, and good stability. However, while these sensors achieve high-quality signal acquisition, their morphology hinders effective contact with the skin, requiring additional mechanical fixation (such as pressure intervention) to ensure reliable contact and prevent electrode detachment. This suggests that, in addition to improving signal acquisition performance, effective contact with the skin is also a key consideration when designing new sensors.

[0004] As a hydrophilic, three-dimensional network gel, hydrogels are formed by chemically or physically crosslinking water molecules and polymers. They can absorb and retain large amounts of water, forming a gel state. They possess excellent mechanical properties and biocompatibility, making them suitable for wearable sensor interface materials and proven to be a reliable and effective electrode interface. In recent years, researchers have proposed various hydrogel preparation methods and functional improvements to expand their applications. In 2023, Duan invented a hydrogel preparation method using cellulose derivatives as raw materials, eliminating the need for external crosslinking agents, but this method did not achieve conductivity. Zeng et al. invented a viscous conductive hydrogel. By adding a nano-titanium carbide solution to the hydrogel, combined with hydroxymethoxybenzenesulfonic acid, the hydrogel's conductivity and mechanical properties were enhanced, increasing its viscosity without compromising its mechanical properties. Zhang et al. invented a multifunctional conductive hydrogel that can be used in flexible sensors, catheters, cardiovascular devices, or diabetic wound dressings. It can accelerate skin wound healing under external electrical stimulation. While these inventions primarily focus on stress testing and skin wound healing, they do not explicitly address the acquisition of physiological electrical signals. In addition, the hydrogel has stable thermoreversibility and exhibits reversible volume changes and phase transitions during heating or cooling.

[0005] In summary, bioelectrical signal research based on thermoreversible hydrogel sensors has enormous potential, providing new technical references for a deeper understanding of brain function, diagnosis and treatment of physical diseases, and brain-computer interface applications. Continuous innovation in this field will drive neuroscience research forward, help improve quality of life, and bring innovation and development to new medical and engineering applications.

[0006] Currently, physiological electrical signal acquisition systems on the market are primarily categorized into two types: implantable and non-implantable. Implantable electrodes measure local potential differences or electrical activity by placing electrodes directly in contact with tissues or organs within the body. These electrodes are implanted in locations such as the brain, heart, and muscles to record bioelectrical signals from the corresponding area. Non-implantable electrodes, however, do not require surgical implantation. Instead, electrodes are placed on or near the surface of the body, acquiring electrical signals directly using non-invasive devices such as EEG caps. These systems are suitable for clinical, research, and monitoring settings and are generally non-invasive. Therefore, non-implantable systems are often easier to implement, avoiding the complexity and potential risks of surgery. However, their signal resolution is relatively low and they are susceptible to surface properties. Therefore, the electrode material is crucial, directly impacting the quality of signal acquisition. Commonly used electrode types include dry electrodes, wet electrodes, and some specialized electrodes. Dry electrodes are placed directly on the skin, eliminating the need for conductive paste or liquid media, making them easy to prepare. However, they offer lower signal quality, sensitivity, and stability. Wet electrodes require application of a liquid medium such as conductive paste or saline to improve conductivity between the electrode and the skin. Its signal quality is usually better because the liquid medium can better adapt to the characteristics of the skin surface. However, its preparation process is relatively cumbersome, and its comfort and stability are poor. At the same time, the conductive paste or liquid medium needs to be replaced regularly. As a special electrode, hydrogel has mechanical and chemical properties similar to those of biological tissues, and exhibits excellent biocompatibility and mechanical adaptability. It can reduce some discomfort reactions, provide better skin contact, reduce impedance, and avoid the use of conductive paste or liquid medium. Therefore, hydrogel has become a highly sought-after electrode material with excellent conductivity, high stretchability, comfort and biocompatibility, providing an ideal solution for the long-term acquisition of EEG and other physiological signals. How to develop an electrode material with excellent conductivity, high stretchability, comfort and good biocompatibility to maintain high-quality and continuous acquisition of bioelectric signals is an urgent problem that researchers need to solve. Summary of the Invention

[0007] In view of the defects in the prior art, the object of the present invention is to provide a thermoreversible hydrogel for collecting physiological electrical signals of the human body.

[0008] Compared to previous physiological electrical signal acquisition electrode materials, the hydrogel of the present invention uses biocompatible materials such as natural gelatin as a matrix, and adds a functional solvent component with ion conductivity. The hydrogel has excellent conductivity, adhesion, mechanical properties and biocompatibility, significantly improving the quality of the collected signal. At the same time, because it does not require an additional conductive coating, it can provide users with a more comfortable use experience, making it an ideal choice for electrode materials that are worn for a long time. This invention is expected to provide hardware support for the acquisition of EEG and other physiological electrical signals, and has broad application prospects in fields such as biomedicine.

[0009] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0010] A thermoreversible hydrogel for collecting physiological electrical signals from the human body.

[0011] The hydrogel is characterized in that the hydrogel is composed of a deep eutectic solvent and a gelatin aqueous solution, and the mass ratio of the gelatin aqueous solution to the deep eutectic solvent is 0.25-8:1;

[0012] The deep eutectic solvent comprises choline chloride and glycerol, and the molar ratio of choline chloride to glycerol is 0.25-4:1.

[0013] On the basis of the above scheme,

[0014] The mass ratio of the gelatin aqueous solution to the deep eutectic solvent is 0.7-2:1.

[0015] On the basis of the above scheme,

[0016] The molar ratio of the choline chloride to the glycerol is 0.5-2:1.

[0017] On the basis of the above scheme,

[0018] The mass ratio of the gelatin aqueous solution to the deep eutectic solvent is 1-2:1.

[0019] On the basis of the above scheme,

[0020] The molar ratio of the choline chloride to the glycerol is 0.5-1:1.

[0021] Another object of the present invention is to provide a method for preparing a thermoreversible hydrogel for collecting physiological electrical signals of the human body.

[0022] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0023] A method for preparing a thermoreversible hydrogel for collecting physiological electrical signals of the human body, characterized by comprising the following steps:

[0024] Step 1, mixing choline chloride and glycerol in a molar ratio of 0.25-4:1, and then heating and stirring at 60-100° C. to obtain a deep eutectic solvent;

[0025] Step 2: Dissolve 2 parts of gelatin in 3-6 parts of water, then add 1-24 parts of the low eutectic solvent obtained in step 1, and stir evenly to obtain a thermoreversible hydrogel.

[0026] On the basis of the above scheme,

[0027] In the step 1, the molar ratio of the choline chloride to glycerol mixture is 0.5-2:1.

[0028] On the basis of the above scheme,

[0029] In the step 2, 2 parts of gelatin are dissolved in 3-4 parts of deionized water, and then 5-10 parts of the low eutectic solvent obtained in step 1 are added and stirred evenly to obtain a thermoreversible hydrosol.

[0030] Another object of the present invention is to provide an application of a thermoreversible hydrogel in the field of human physiological electrical signal acquisition.

[0031] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0032] The invention discloses an application of a thermoreversible hydrogel in the field of collecting physiological electrical signals of the human body.

[0033] Based on the above scheme, a thermoreversible hydrogel is used in the field of human EEG acquisition.

[0034] The thermoreversible hydrogel for collecting human physiological electrical signals and the preparation method thereof described in the present invention have the following beneficial effects:

[0035] (1) As a special electrode, the hydrogel is very similar to biological tissue in mechanical and chemical properties, with excellent biocompatibility and mechanical adaptability, which can reduce some discomfort reactions and provide better skin contact. At the same time, the addition of a low eutectic solvent can reduce impedance and improve conductivity.

[0036] (2) Compared with dry electrodes, this hydrogel improves signal quality and reduces the need for electrode gel or liquid media compared with wet electrodes. It can be widely used in the collection of physiological electrical signals. Its advantages lie in solving the problems of existing electrode materials such as insufficient conductivity, poor adhesion, limited stretchability, low comfort, and existing biotoxicity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention has the following accompanying drawings:

[0038] Figure 1 This is a state diagram of the hydrogel at room temperature according to the present invention;

[0039] Figure 2 Raw materials for preparing the hydrogel of the present invention: (a) the morphology and chemical expression of gelatin; (b) the chemical expression of the deep eutectic solvent used for ion conduction;

[0040] Figure 3 Schematic diagram of the adhesion of the hydrogel of the present invention;

[0041] Figure 4 Schematic diagram of the stretchability of the hydrogel of the present invention;

[0042] Figure 5 The stress-strain characteristics of the hydrogel of the present invention are: (a) compression curve; (b) tensile curve;

[0043] Figure 6 is the impedance characteristic curve of the hydrogel of the present invention;

[0044] Figure 7 The electroencephalogram (EEG) signal recorded by the hydrogel electrode of the present invention in the eyes-open / eyes-closed mode;

[0045] Figure 8 The power spectral density analysis of the EEG signal in the first (a) eyes closed and (b) eyes open state;

[0046] Figure 9 Power spectral density analysis of the EEG signal in the second (a) eyes closed and (b) eyes open condition. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below with reference to the accompanying drawings.

[0048] like Figure 2 As shown, the thermoreversible hydrogel of the present invention uses biocompatible materials such as natural gelatin as a matrix, combined with ion-conductive deep thermal ionic liquids (DESs) and other ingredients. It has softness, conductivity and biocompatibility, can effectively reduce the user's discomfort, and provide a comfortable signal acquisition experience.

[0049] The detailed preparation process is as follows:

[0050] Example 1:

[0051] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed at a molar ratio of 0.25:1, and then heated and stirred at 60°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0052] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 6 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 1 part of deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0053] Example 2:

[0054] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed at a molar ratio of 0.6:1, and then heated and stirred at 90°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0055] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 3 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 8 parts of deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times) to obtain a light yellow, transparent, and clear hydrogel.

[0056] Example 3:

[0057] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 1:2, and then heated and stirred at 90°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0058] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 4 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 5 parts of a deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0059] Example 4:

[0060] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 4:1, and then heated and stirred at 100°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0061] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 5 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 10 parts of a deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0062] Example 5:

[0063] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 1:1, and then heated and stirred at 100°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0064] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 6 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 8 parts of deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0065] Example 6:

[0066] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 2:1, and then heated and stirred at 100°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0067] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 4 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 7 parts of deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0068] Example 7:

[0069] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 1:1, and then heated and stirred at 100°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0070] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 4 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 24 parts of a deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0071] Example 8:

[0072] (1) Preparation of deep eutectic solvents (DESs): Choline chloride (ChCl) and glycerol were first mixed in a molar ratio of 3:1, and then heated and stirred at 100°C until the choline chloride was completely dissolved to obtain a uniform and transparent deep eutectic solvent.

[0073] (2) Preparation of hydrogel: Weigh 2 parts of gelatin and dissolve it in 4 parts of deionized water, stir thoroughly, and heat until completely dissolved. Add 3 parts of a deep eutectic solvent, stir thoroughly, and heat until completely dissolved (repeat the heating and dissolution process 3 times). Finally, a light yellow, transparent, and clear hydrogel is obtained.

[0074] The hydrogel obtained in Example 3 was selected for characterization analysis and application research:

[0075] Room temperature hydrogels such as Figure 1 As shown. When heated to a higher temperature, the hydrogel transforms into a liquid state. This thermoreversible process provides potential application possibilities for hydrogels in physiological electrical signal sensing, making the hydrogel a very promising material designed to provide both biocompatibility and electrical conductivity: gelatin as the main matrix has excellent biocompatibility and is suitable for contact with biological tissues, while the doped low eutectic solvent performs well in terms of electrical conductivity, which helps to effectively conduct physiological electrical signals. Therefore, the hydrogel has excellent skin adaptability, effectively reducing the interference of movement on signal quality, and improving the signal quality and spatiotemporal resolution. At the same time, there is no need for additional conductive media, and the biocompatibility is excellent, which can provide a more comfortable use experience, making it an electrode material suitable for long-term wear, providing a potential platform for the collection of EEG and other physiological signals.

[0076] like Figure 3 As shown, the hydrogel exhibits extremely high transparency and can be applied to the skin surface or used to fix sensing electrodes on the skin without any additional physical fixation. In the event of pulling, the hydrogel and electrodes can still be tightly attached to the skin surface, while in contrast, electrodes made of commercial EEG glue and adhesive gel easily fall off. Figure 4 The hydrogel's mechanical properties are demonstrated, allowing it to stretch to several times its length, which facilitates dynamic adaptability to the skin and scalp. This superior mechanical interaction is highly beneficial for recording bioelectrical signals through the skin. Consequently, the hydrogel possesses exceptional mechanical robustness, excellent stretchability, and excellent stretch-cyclability, making it ideal for practical applications incorporating conformable structures onto soft and curved skin surfaces.

[0077] like Figure 5 As shown, the hydrogel exhibits good stress-strain properties, and its elastic behavior enables it to effectively withstand pressure without losing stability when subjected to external forces. Figure 5 (a) shows the compression and recovery curves of the hydrogel. Figure 5 (b) shows the tensile curves of the hydrogels with different amounts of DESs added to the solvent. Notably, the tensile strength and stretching range vary linearly. These properties are crucial for many applications, particularly where the material must be able to adapt to different shapes and external forces. These superior properties of hydrogels offer broad application prospects in medicine, biosensing, and engineering, as they can adapt to complex environments and various strain requirements, delivering exceptional performance.

[0078] At the same time, the hydrogel showed consistency in impedance curve compared with commercial hydrogels ( Figure 6 This means that both homemade and commercially available hydrogels exhibit similar electrical properties, providing reliable resistance change responses. Furthermore, the hydrogel's resistance is an order of magnitude lower than that of commercial hydrogels, further demonstrating its superior signal acquisition performance. This ensures comparable and stable data acquisition, making hydrogels a reliable material choice for a variety of applications requiring high electrical performance, stability, and consistency.

[0079] High-quality EEG recordings are crucial for clinical and neurological applications such as disease diagnosis and fatigue monitoring. While EEG recordings use a noninvasive method to monitor brain electrical activity, efficient recording of EEG signals is more challenging than for electrocardiographic and myoelectric signals due to weak signals (microvolt amplitude) and obstruction by the skull and hair. Specific brain activity is correlated with the frequency of the EEG signal. The normal waveform for an adult in a quiet, closed-eyes state is an alpha EEG wave, ranging from 8-12 Hz. In this state, the brain is alert and relaxed, easily focused and less easily distracted by external factors, and less prone to fatigue. Figure 7 The hydrogel electrode prepared by the present invention is used to record the occipital position of the electroencephalogram (EEG) alpha wave. It can be clearly seen that the recorded eyes-closed and eyes-open signals have significant differences in the time domain. In the eyes-closed mode, the signal amplitude is low and relatively stable overall, while in the eyes-open mode, the signal fluctuates more due to eye movement. In addition, we performed power spectral density (PSD) analysis on the EEG signals recorded twice in eyes-open and eyes-closed modes. Figure 8 and Figure 9 As shown, a clear alpha rhythm is observed with eyes closed ((a) in both figures), whereas no alpha rhythm is observed with eyes open ((b) in both figures). The hydrogel, with its advantages of conformability to the hairy scalp and long-term electrical stability, has been shown to possess excellent capabilities for long-term, high-quality EEG recordings. Throughout the signal recording, the hydrogel exhibited stable rhythmic and periodic patterns, facilitating reliable, long-term EEG recordings.

[0080] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. Application of a thermoreversible hydrogel in the field of human electroencephalogram acquisition, characterized in that: The thermoreversible hydrogel is used as an electrode for collecting human electroencephalograms; the hydrogel is composed of a deep eutectic solvent and a gelatin aqueous solution, the mass ratio of the gelatin aqueous solution to the deep eutectic solvent is 0.7-2:1, wherein the gelatin aqueous solution is prepared by dissolving 2 parts of gelatin in 3-6 parts of water; The deep eutectic solvent comprises choline chloride and glycerol, and the molar ratio of choline chloride to glycerol is 0.5-2:

1.

2. The use according to claim 1, characterized in that: The mass ratio of the gelatin aqueous solution to the deep eutectic solvent is 1-2:

1.

3. The use according to claim 2, characterized in that: The molar ratio of the choline chloride to the glycerol is 0.5-1:

1.

4. The use according to claim 1, wherein The preparation method of the thermoreversible hydrogel comprises the following steps: Step 1, mixing choline chloride and glycerol in a molar ratio of 0.5-2:1, and then heating and stirring at 60-100° C. to obtain a deep eutectic solvent; Step 2: Dissolve 2 parts of gelatin in 3-6 parts of water, then add 3-10 parts of the low eutectic solvent obtained in step 1, and stir evenly to obtain a thermoreversible hydrogel.

5. The use according to claim 4, characterized in that: In the step 2, 2 parts of gelatin are dissolved in 3-4 parts of deionized water, and then 5-10 parts of the low eutectic solvent obtained in step 1 are added and stirred evenly to obtain a thermoreversible hydrogel.

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