A polysaccharide-based highly permeable carbon dot hydrogel and its preparation method

Abstract

This invention discloses a polysaccharide-based highly permeable carbon dot hydrogel and its preparation method, belonging to the field of hydrogels. This invention introduces specific carbon dots (chitosan carbon dots) as nanofillers, which are then linked to a polyvinyl alcohol hydrogel network via hydrogen bonds, promoting effective cross-linking and polymerization. Simultaneously, a sand core filtration device is used to vacuum filter the hydrogel at 0.1 MPa for 24 hours, thereby constructing the porous structure of the hydrogel. This not only enhances the mechanical properties of the hydrogel but also significantly improves its electrical conductivity and permeability. Furthermore, the preparation process is simple and the performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, and particularly relates to a polysaccharide-based highly permeable carbon dot hydrogel and its preparation method. Background Technology

[0002] Conductive hydrogels, as a novel flexible electronic material, have broad application prospects in wearable electronic devices due to their tunable mechanical flexibility. Polysaccharides, proteins, polyethylene glycol (PEG), and polyvinyl alcohol (PVA) are widely used to construct hydrogels due to their multifunctionality and biocompatibility. Among them, polysaccharides have many advantages such as low cost, non-toxicity, and biodegradability. Furthermore, polysaccharides possess abundant functional groups and high gel strength. PVA hydrogels can be easily obtained through methods such as cyclic freeze-thaw cycles due to the large number of hydroxyl groups on their molecular chains. However, traditional physically cross-linked hydrogels have insufficient mechanical properties, failing to withstand the human body and support daily activities, resulting in problems such as narrow detection range and poor durability in hydrogel-based sensors. In addition, most current hydrogel sensors have poor environmental stability, easily losing water at high or even room temperatures and freezing at low temperatures, severely affecting their practical applications. Therefore, the fabrication of hydrogel sensors with excellent mechanical properties and environmental stability is of great significance to the development of flexible electronics. Summary of the Invention

[0003] In view of this, in order to solve the above-mentioned technical problems, the present invention proposes a polysaccharide-based highly permeable carbon dot hydrogel and its preparation method.

[0004] It should be noted that carbon dots are composed of ultrafine, dispersed, nearly spherical carbon nanoparticles, typically with a diameter of less than 10 nm. In recent years, carbon nanoparticles (CDs) have attracted widespread attention due to their high specific surface area, low cost, good water solubility, easy surface modification, and low biotoxicity. Traditional hydrogels have poor mechanical strength. Besides strengthening strategies such as constructing dual networks, topological structures, and supramolecular polymerization, the composite of nano-inorganic particles can also significantly improve the mechanical properties of hydrogels. As zero-dimensional carbon nanomaterials, the incorporation of CDs can significantly improve the mechanical strength of materials, playing a role in strengthening and toughening. When CDs are embedded as nanofillers in hydrogels, they can form physical or chemical cross-linking nodes with polymer chains through various interactions, increasing the cross-linking density within the hydrogel and forming a denser hydrogel network structure, thereby enhancing the mechanical properties of the hydrogel.

[0005] This invention utilizes chitosan to sinter carbon dots to prepare polysaccharide-based, highly breathable carbon dot hydrogels. The introduction of carbon dots endows the hydrogel with sensing properties. Furthermore, the innovative method of vacuum filtration self-assembly employed in the construction of the carbon dot hydrogel effectively constructs a uniform three-dimensional porous structure. This structure effectively improves the hydrogel's breathability. When applied to the skin, this breathable hydrogel not only effectively avoids skin discomfort and sweat accumulation caused by prolonged wear, but also further reduces the risk of skin allergies or inflammation, making it particularly suitable for medical and personal care applications. Simultaneously, the introduction of carbon dots (CDs) lowers the hydrogel's freezing point and reduces its swelling resistance, broadening the application range of hydrogel electronic skin.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] One of the technical solutions of the present invention:

[0008] A method for preparing a polysaccharide-based highly permeable carbon dot hydrogel involves using chitosan carbon dot solution and polyvinyl alcohol (PVA) as reactants, followed by high-temperature reaction, filtration, and freeze-thaw cycles to obtain the polysaccharide-based highly permeable carbon dot hydrogel.

[0009] Preferably, the preparation method of the polysaccharide-based high-permeability carbon dot hydrogel further includes: vacuum filtration of the carbon dot-polyvinyl alcohol hydrogel prepared by high-temperature reaction using a sand core filtration device and a microporous aqueous filter membrane with a pore size of 0.22 μm; vacuum filtration for 24 h under 0.1 MPa conditions, thereby constructing the pore structure of the hydrogel.

[0010] Preferably, the chitosan carbon dot solution is prepared by using chitosan as raw material, water as solvent, ethanol as auxiliary dissolution, and undergoing hydrothermal reaction and cooling to obtain the chitosan carbon dot solution.

[0011] Furthermore, in the above method for preparing chitosan carbon dot solution, the hydrothermal reaction temperature is 160°C and the time is 2 hours; the concentration of chitosan carbon dot solution is (0.5-4) wt%, preferably 1 wt%.

[0012] Preferably, the mass ratio of the chitosan carbon dot solution to polyvinyl alcohol is (16-19):(1-4), more preferably 18:2.

[0013] Preferably, the high-temperature reaction is carried out at a temperature of 95°C for 3 hours.

[0014] Preferably, the freeze-thaw cycle involves freezing at -20°C for 8 hours and then thawing at 20°C for 3 hours, with the freeze-thaw cycle repeated at least once.

[0015] To improve the mechanical properties of hydrogels, this invention designs specific carbon dots (chitosan carbon dots) as nanofillers, which are linked to polyvinyl alcohol networks via hydrogen bonds. These specific carbon dots possess attractive SP... 2 Crystal nuclei can impart excellent interfacial interactions to materials (e.g., π-π stacking, CH-π, etc.), and carbonization can effectively retain the functional groups of the carbonized precursor, resulting in good dispersibility. Furthermore, the mechanical properties of the hydrogel are enhanced through non-covalent bonds between specific carbon points and polyvinyl alcohol, including π-π, CH-π, van der Waals forces, and ionic bonds.

[0016] The second technical solution of the present invention:

[0017] The present invention also provides a polysaccharide-based highly permeable carbon dot hydrogel prepared according to the above preparation method, which has good conductivity and permeability.

[0018] It should be noted that the polysaccharide-based highly permeable carbon dot hydrogel prepared in this invention exhibits a tensile strength of up to 6.12 MPa and a toughness of up to 23.39 MJ / m. -3 Its conductivity can reach 1.44 S m -1 The sweat-wicking effect can reach 120g m -2 d -1 .

[0019] In summary, this invention prepares a hydrogel with high strength, high toughness, good electrical conductivity, and good air permeability.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) The polysaccharide-based high-permeability carbon dot hydrogel prepared in this invention uses chitosan carbon dots as nanofillers and forms a cross-linked network with polyvinyl alcohol. By utilizing the intermolecular interactions between polyvinyl alcohol hydrogels and employing a sand core filtration device, vacuum filtration is carried out for 24 hours under 0.1 MPa conditions, thereby constructing the pore structure of the hydrogel and building a hydrogel with excellent mechanical properties, good electrical conductivity and air permeability.

[0022] 2) The specific carbon dots (chitosan carbon dots) used in this invention not only possess attractive sp... 2 Crystal nuclei can impart excellent interfacial interactions to materials (such as π-π stacking, CH-π, etc.). Moreover, carbonized chitosan can retain the functional groups of the carbonized precursor well, has good dispersibility, and introduces a large number of physical crosslinking reaction sites to polyvinyl alcohol hydrogel, which endows the hydrogel with excellent fracture strength and toughness.

[0023] 3) The hydrogel preparation process disclosed in this invention is simple and has excellent performance. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 The stress-strain curves of the hydrogels prepared in Examples 1 to 4 are shown.

[0026] Figure 2 The stress-strain curves of the hydrogels prepared in Examples 1, 5, and 6 are shown.

[0027] Figure 3 The stress-strain curves of the hydrogels prepared in Example 1 and Comparative Examples 1 and 2 are shown.

[0028] Figure 4 FT-IR images of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0029] Figure 5 Nyquist plots of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0030] Figure 6 Scanning electron microscope (SEM) images of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0031] Figure 7 The image shows the sweat dissipation of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as any smaller range between any other stated value or intermediate value within said range, are also included in this invention, and the upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0038] All raw materials and reagents used in the embodiments of this invention are commercially available products.

[0039] Example 1

[0040] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with a chitosan carbon dot solution concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0041] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1wt%.

[0042] S2. The above chitosan carbon dot solution (18g) and polyvinyl alcohol (2g) are mixed and reacted at 95°C for 3h. After the mixed solution is cooled to room temperature, it is vacuum filtered at 0.1MPa for 24h. Then the obtained reaction product is subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles). The resulting chitosan carbon dot / polyvinyl alcohol hydrogel is a polysaccharide-based high-permeability carbon dot hydrogel.

[0043] Example 2

[0044] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with carbon dot concentration of 0.5 wt% and polyvinyl alcohol (PVA) concentration of 10 wt%:

[0045] S1. Add 0.5g of chitosan to 100mL of deionized water, add 1mL of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 0.5wt%.

[0046] S2. The above chitosan carbon dot solution (18g) and polyvinyl alcohol (2g) were mixed and reacted at 95°C for 3h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1MPa for 24h. Then the reaction product was subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain chitosan carbon dot / polyvinyl alcohol hydrogel.

[0047] Example 3

[0048] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with carbon dot concentration of 2 wt% and polyvinyl alcohol (PVA) concentration of 10 wt%:

[0049] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1wt%.

[0050] S2. The above chitosan carbon dot solution (36g) was rotary evaporated to 18g, and then mixed with polyvinyl alcohol (2g). The mixture was reacted at 95°C for 3h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1MPa for 24h. The reaction product was then subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h, and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain chitosan carbon dots / polyvinyl alcohol hydrogel.

[0051] Example 4

[0052] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with carbon dot concentration of 4 wt% and polyvinyl alcohol (PVA) concentration of 10 wt%:

[0053] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1wt%.

[0054] S2. The above chitosan carbon dot solution (72g) was rotary evaporated to 18g, and then mixed with polyvinyl alcohol (2g). The mixture was reacted at 95°C for 3h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1MPa for 24h. The resulting reaction product was then subjected to freeze-thaw cycles (freeze-thaw cycle is freezing at -20°C for 8h, then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain chitosan carbon dots / polyvinyl alcohol hydrogel.

[0055] Example 5

[0056] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with a carbon dot concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 5 wt%:

[0057] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1wt%.

[0058] S2. The above chitosan carbon dot solution (19g) was mixed with polyvinyl alcohol (1g) and reacted at 95°C for 3h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1MPa for 24h. Then the obtained reaction product was subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain chitosan carbon dot / polyvinyl alcohol hydrogel.

[0059] Example 6

[0060] Preparation steps of polysaccharide-based highly permeable carbon dot hydrogel with a carbon dot concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 15 wt%:

[0061] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, place in a pressure-resistant reaction flask and heat to 160℃ for 2h. Let the reaction container cool naturally to room temperature to obtain a chitosan carbon dot solution with a concentration of 1wt%.

[0062] S2. The above chitosan carbon dot solution (17g) and polyvinyl alcohol (3g) were mixed and reacted at 95°C for 3h. After the mixed solution was cooled to room temperature, it was vacuum filtered at 0.1MPa for 24h. Then the reaction product was subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain chitosan carbon dot / polyvinyl alcohol hydrogel.

[0063] Comparative Example 1

[0064] Preparation steps of chitosan-based high-permeability hydrogel with a concentration of 1 wt% and a polyvinyl alcohol (PVA) concentration of 10 wt%:

[0065] S1. Add 1g of chitosan to 100mL of deionized water, add 2ml of glacial acetic acid, and stir at room temperature to obtain a chitosan aqueous solution.

[0066] S2. The above chitosan aqueous solution (18g) and polyvinyl alcohol (2g) are mixed and reacted at 95°C for 3h. After the mixed solution is cooled to room temperature, it is vacuum filtered at 0.1MPa for 24h. Then the reaction product is subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles). The resulting chitosan / polyvinyl alcohol hydrogel is chitosan / polyvinyl alcohol hydrogel.

[0067] Comparative Example 2

[0068] The preparation steps for a 10 wt% polyvinyl alcohol (PVA) hydrogel are as follows:

[0069] Polyvinyl alcohol (2g) was mixed with deionized water (18g) and reacted at 95°C for 3h. After the reaction product was cooled to room temperature, it was subjected to freeze-thaw cycle treatment (freeze-thaw cycle is freezing at -20°C for 8h and then thawing at 20°C for 3h, for a total of 3 freeze-thaw cycles) to obtain polyvinyl alcohol hydrogel, denoted as PVA.

[0070] The mechanical properties and toughness calculations of the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2 were performed as follows:

[0071] The hydrogels prepared in Examples 1-6 and Comparative Examples 1-2 were cut into samples measuring 15 mm × 5 mm × 1.5 mm and subjected to tensile property testing at room temperature. Uniaxial tensile measurements were performed using an electronic universal testing machine (Shenzhen Suntech Power Technology Co., Ltd., China) at an elongation speed of 40 mm / min.

[0072] Toughness is calculated based on the area under the stress-strain curve using the formula shown below:

[0073] ΔU=∫σdε

[0074] In the formula, σ and ε are the stress (MPa) and strain (%) of the hydrogel, respectively.

[0075] The conductivity of the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2 was tested and calculated using the following methods:

[0076] The electrochemical performance of the hydrogel was evaluated using an electrochemical workstation (model). Hydrogel samples were cut into strips measuring 7 mm (length) × 8 mm (width) × 2 mm (thickness). Electrochemical impedance spectroscopy (EIS) was performed at a voltage of 0.1 V and a frequency range of 10⁵–0.1 Hz. The conductivity was calculated using the following formula:

[0077]

[0078] In the formula, L represents the distance between adjacent electrodes (cm), R represents the resistance of the hydrogel (Ω), and S represents the contact area between the hydrogel and the electrode (cm²). 2 ).

[0079] The tensile strength, elongation at break, and toughness of the hydrogels prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0080] Table 1

[0081] Specimen Tensile strength (MPa) Elongation at break (%) <![CDATA[Toughness (MJ / m 3 )]]> Example 1 6.12 672 23.39 Example 2 1.03 292 1.57 Example 3 1.99 290 3.58 Example 4 2.04 227 2.91 Example 5 0.68 50 0.21 Example 6 0.65 135 0.69 Comparative Example 1 2.8 440 6.68 Comparative Example 2 0.22 6.68 0.078

[0082] As can be seen from the data in Table 1, the hydrogel prepared in Example 1 exhibits the highest fracture strength and toughness, reaching 6.12 MPa and 23.39 MJ / m, respectively. 3 Furthermore, the data changes from Examples 2-6 and Comparative Examples 1-2 show that the mechanical properties of chitosan carbon dots / polyvinyl alcohol hydrogels are affected by different carbon dot concentrations and different polyvinyl alcohol concentrations. This indicates that the hydrogels prepared by using chitosan carbon dots as nanofillers in polyvinyl alcohol hydrogels and at 1 wt% carbon dot concentration and 10 wt% polyvinyl alcohol concentration have good mechanical properties.

[0083] Figure 1 The stress-strain curves of the hydrogels prepared in Examples 1-4 show that as the carbon dot content increases from 0.5 wt% to 1 wt%, 2 wt%, and 4 wt%, the mechanical properties of the hydrogels exhibit a trend of first increasing and then decreasing. The hydrogel prepared in Example 1 with a carbon dot content of 1 wt% shows better tensile strength, elongation at break, and toughness. The mechanical properties of the hydrogel improve with increasing carbon dot content because an appropriate concentration of carbon dots not only acts as a filler, effectively restricting the movement of polymer chains and increasing crosslinking density, thus enhancing the mechanical strength of the hydrogel, but also acts as stress concentration points, improving the toughness of the hydrogel. However, when the carbon dot concentration is too high, it can lead to local entanglement of polymer chains, forming a dense network structure, resulting in excessive crosslinking. It can also increase defects within the polymer network, reducing the uniformity of the hydrogel network structure and thus causing a decrease in mechanical properties.

[0084] Figure 2The stress-strain curves of the hydrogels prepared in Examples 1, 5, and 6 show that the mechanical strength of the hydrogels is significantly improved with the increase of polyvinyl alcohol (PVA) content. This is because a higher PVA concentration means that more polymer chains participate in the cross-linking process, thus forming a denser and stronger network structure. However, when the PVA concentration is too high, the crystallinity of the hydrogel is too high, and the degree of cross-linking is too tight, reducing the material's ability to absorb impact and weakening its ability to cope with deformation, thereby reducing its mechanical properties.

[0085] Figure 3 The stress-strain curves of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 show that the tensile strength, elongation at break, and toughness of the hydrogels significantly increase with the introduction of chitosan and chitosan carbon dots. The hydrogel prepared in Example 1 exhibits higher mechanical strength and tensile strain, with a stress of 6.12 MPa and an elongation at break of 672%. Compared to the hydrogel in Comparative Example 2, the hydrogel prepared in Example 1 has higher mechanical properties. This is because the introduction of carbon dots enhances the degree of cross-linking of the hydrogel. While the high water content of the polyvinyl alcohol hydrogel provides good flexibility and water absorption, it also leads to a decrease in the mechanical strength of the material. The presence of water weakens the mechanical strength of the PVA chains, making the hydrogel prone to deformation and breakage under tension or pressure.

[0086] Figure 4 The FT-IR images of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2 show that at 3340 cm⁻¹... -1 The characteristic absorption band at 1639 cm⁻¹ is related to the stretching vibration of OH, while at 1639 cm⁻¹... -1 The characteristic absorption bands at these locations are related to hydrogen bond vibrations. Furthermore, the peaks in the infrared spectra of the three hydrogel samples—the polyvinyl alcohol hydrogel of Comparative Example 2, the chitosan / polyvinyl alcohol hydrogel of Comparative Example 1, and the chitosan carbon dot / polyvinyl alcohol hydrogel of Example 1—showed a trend towards higher wavenumbers. This indicates an increased degree of crosslinking in the hydrogels. A higher degree of crosslinking may lead to a decrease in the distance between polymer chains, thereby affecting the vibrational modes of specific functional groups and causing a shift in the positions of certain absorption peaks. In other words, the crosslinked structure becomes more compact, leading to an increase in vibrational frequency and a shift of peaks towards higher wavenumbers.

[0087] Figure 5The Nyquist plots of the hydrogels prepared in Examples 1, 1, and 2 show that the chitosan carbon dot / polyvinyl alcohol hydrogel exhibits high conductivity. The Nyquist plots demonstrate the stable electrical properties of the hydrogel, with a conductivity of 1.44 S / m, contrasting with the 0.33 S / m of the chitosan / polyvinyl alcohol (uncarbonized, Comparative Example 2) hydrogel and the 0.08 S / m of the polyvinyl alcohol (Comparative Example 3) hydrogel. This is because the surface of the chitosan carbon dots retains abundant -OH functional groups, exhibiting high electron mobility and good electron transport properties. Therefore, when chitosan carbon dots are dispersed in the polyvinyl alcohol hydrogel network, they can form conductive pathways, increasing the electron migration rate. Furthermore, the carbon dots are typically nanoscale in size, exhibiting quantum size effects, which can adjust their band structure and electronic properties, thereby further optimizing conductivity. The carbon dots in the hydrogel can form a three-dimensional conductive network, which helps improve charge transport efficiency and enhances the overall conductivity of the hydrogel. Meanwhile, the porous structure created by filtration provides channels for the directional movement of electrons, further improving the conductivity of the hydrogel prepared in Example 1. Polyvinyl alcohol (PVA) is a non-conductive polymer, lacking freely moving charge carriers. Its carbon and oxygen atoms are primarily covalently bonded, resulting in a stable molecular structure that hinders charge transfer and leads to low conductivity. The three-dimensional network structure of the PVA hydrogel, composed of cross-linked PVA molecular chains, restricts charge carrier migration, thereby reducing conductivity.

[0088] Figure 6 The images show scanning electron microscope (SEM) images of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. The first row shows SEM images of the surface morphology of the three hydrogel samples, and the second row shows SEM images of the cross-sectional morphology of the three hydrogel samples after liquid nitrogen embrittlement. The three hydrogel samples demonstrate that vacuum filtration using a sand core filter can effectively construct the porous structure of the hydrogel. These micropores ensure the breathability of the hydrogel when used in close contact with the skin, effectively improving the comfort and skin compatibility of the wearable sensor.

[0089] Figure 7 The figures show the sweat diffusion of the hydrogels prepared in Example 1, Comparative Example 1, and Comparative Example 2. It can be seen that the hydrogel samples prepared in Example 1 and Comparative Example 1 have similar air permeability. This is because the chitosan carbon dots produced by high-temperature calcination are small in size and have a low degree of carbonization, resulting in a large amount of chitosan coexisting within the carbon dots. In contrast, the hydrogels prepared in Example 1 and Comparative Example 1 utilize an innovative filtration method to construct a porous structure. These micropores ensure free water vapor exchange between the human skin and the external environment, thereby guaranteeing the hydrogel's air permeability.

[0090] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a polysaccharide-based highly permeable carbon dot hydrogel, characterized in that, Using chitosan carbon dot solution and polyvinyl alcohol as reactants, the polysaccharide-based high-permeability carbon dot hydrogel was obtained through high-temperature reaction and freeze-thaw cycle. It also includes: vacuum filtration of carbon dot-polyvinyl alcohol hydrogel prepared by high-temperature reaction using a sand core filtration device and a microporous aqueous filter membrane; vacuum filtration for 24 h at 0.1 MPa.

2. The method for preparing polysaccharide-based highly permeable carbon dot hydrogel according to claim 1, characterized in that, The chitosan carbon dot solution is prepared as follows: Chitosan was used as the raw material, water as the solvent, and acetic acid as the auxiliary dissolution agent. After hydrothermal reaction and cooling, the chitosan carbon dot solution was obtained.

3. The method for preparing polysaccharide-based highly permeable carbon dot hydrogel according to claim 2, characterized in that, The hydrothermal reaction was carried out at a temperature of 160 °C for 2 h.

4. The method for preparing polysaccharide-based highly permeable carbon dot hydrogel according to claim 2, characterized in that, The concentration of the chitosan carbon dot solution is (0.5~4) wt%.

5. The method for preparing polysaccharide-based highly permeable carbon dot hydrogel according to claim 1, characterized in that, The mass ratio of the chitosan carbon dot solution to polyvinyl alcohol is (16~19):(1~4).

6. The method for preparing the polysaccharide-based highly permeable carbon dot hydrogel according to claim 1 or 5, characterized in that, The high-temperature reaction was carried out at a temperature of 95 °C for 3 hours.

7. The method for preparing polysaccharide-based highly permeable carbon dot hydrogel according to claim 1, characterized in that, The freeze-thaw cycle operation is as follows: Freeze at -20°C for 8 hours, then thaw at 20°C for 3 hours. Repeat the freeze-thaw cycle at least once.

8. A polysaccharide-based highly permeable carbon dot hydrogel prepared by the method according to any one of claims 1 to 7.

Images