Chitosan-based hydrogel microspheres with high water-retaining property as well as preparation method and application of chitosan-based hydrogel microspheres

Abstract

The invention relates to the technical field of biomedical materials, and discloses chitosan-based hydrogel microspheres with high water-retaining property as well as a preparation method and application of the chitosan-based hydrogel microspheres. In order to solve the problems of poor water retention capacity and insufficient mechanical strength of the existing chitosan hydrogel, the invention constructs a hydrogel microsphere with three network cross-linked structures. The triple network cross-linked structure is jointly constructed by a dual cross-linked network consisting of glycidyl methacrylate modified chitosan and lipoic acid modified chitosan, and a nano reinforcing material uniformly dispersed in the dual cross-linked network. The preparation method comprises the following steps: firstly preparing two kinds of modified chitosan, namely glycidyl methacrylate and lipoic acid, then mixing the two kinds of modified chitosan with a nano reinforcing material and the like to obtain a precursor solution, and finally preparing the microspheres through a reverse emulsion method and a photocuring technology. By constructing a unique triple network, the water-retaining property and the mechanical strength of the hydrogel microspheres are remarkably improved.

Description

A highly water-retaining chitosan-based hydrogel microsphere, its preparation method and application Technical Field

[0001] This invention relates to the field of biomedical materials technology, and in particular to a highly water-retaining chitosan-based hydrogel microsphere, its preparation method, and its application. Background Technology

[0002] Hydrogel microspheres, due to their three-dimensional network structure, high water content, and good biocompatibility, have shown broad application prospects in biomedical fields such as tissue engineering, controlled drug release, and cell culture. In particular, chitosan-based hydrogel microspheres have attracted widespread attention because chitosan itself is biodegradable, biocompatible, and antibacterial.

[0003] To improve the properties of hydrogels, researchers have developed various modification methods. For example, Chinese invention patent CN113072716A discloses a method for preparing photocrosslinked chitosan hydrogels. This method involves mixing a chitosan ethanol solution with a lipoic acid-organic solvent solution. After homogeneous mixing, an amide reaction catalyst is added. After complete reaction, the mixture is dialyzed and dried to obtain water-soluble chitosan. The water-soluble chitosan is then dissolved in an aqueous solution, and the hydrogel is obtained under ultraviolet light. However, based on this existing technology, the product performance still has room for improvement and exhibits certain limitations, as follows:

[0004] (1) The hydrogel provided by this patent has poor water retention performance. The single cross-linked network of the hydrogel is easily destroyed, resulting in poor water storage and retention performance.

[0005] (2) The mechanical strength of the hydrogel provided by this patent needs to be further improved. Its hydrogel network is a single network composed of dynamic cross-linking of disulfide bonds. Compared with a dual network, the mechanical strength and long-term load stability of the single network are still insufficient. The hydrogel microspheres may collapse or degrade prematurely under the complex stress environment in vivo, resulting in the failure of their function and making it difficult to meet the requirements for long-term effectiveness. Summary of the Invention

[0006] To address the technical problem of poor water retention performance of the aforementioned hydrogels, this invention provides chitosan-based hydrogel microspheres with high water retention, their preparation method, and their applications.

[0007] The specific technical solution of this invention is as follows:

[0008] As a first aspect of the present invention, the present invention provides highly water-retaining chitosan-based hydrogel microspheres. The hydrogel microspheres comprise a dual crosslinked network composed of glycidyl methacrylate-modified chitosan and lipoic acid-modified chitosan, and nano-reinforcing materials uniformly dispersed within the dual crosslinked network, forming a triple-network crosslinked structure.

[0009] To address the poor water retention of existing chitosan hydrogels, this invention constructs a hydrogel microsphere with a triple-network cross-linking structure. This triple-network cross-linking structure comprises a dual cross-linking network of glycidyl methacrylate-modified chitosan and lipoic acid-modified chitosan, along with uniformly dispersed nano-reinforcing materials. By constructing this unique triple network, this invention significantly improves the water retention and mechanical strength of the hydrogel microspheres.

[0010] Excellent water retention ensures that the microspheres of this invention maintain their size and morphological stability over a long period during storage and use. This is crucial for providing a stable growth space for cells and maintaining the integrity of the drug-loaded structure during application. Furthermore, cell survival and proliferation require a humid environment, and the water retention of the hydrogel directly affects the quality of the microenvironment it provides to cells.

[0011] Preferably, the nano-reinforcing material is one or more of the following: cellulose nanocrystals, lactic acid-glycolic acid copolymer nanofibers, hydroxyapatite nanowires, or halloysite nanotubes.

[0012] Preferably, the mass fraction of the nano-reinforcing material in the hydrogel microspheres is 0.1% to 5%.

[0013] As a second aspect of the present invention, the present invention provides a method for preparing highly water-retaining chitosan-based hydrogel microspheres, comprising the following steps:

[0014] (1) Glycidyl methacrylate was grafted onto chitosan to obtain double-bonded chitosan;

[0015] (2) Grafting lipoic acid onto chitosan yields lipoic acid-modified chitosan;

[0016] (3) The double-bonded chitosan, the thioctic acid-modified chitosan and the nano-reinforcing material are mixed to obtain a composite hydrogel precursor solution;

[0017] (4) Composite hydrogel precursor liquid was prepared into composite hydrogel microspheres using reverse emulsion method and photocuring technology.

[0018] This invention significantly improves the water retention and mechanical strength of hydrogel microspheres by constructing a unique triple network structure. The first network layer is chemically cross-linked, generated by glycidyl methacrylate-modified chitosan cross-linking. The second network layer is composed of lipoic acid-modified chitosan cross-linking, achieved through dynamic disulfide bonds. These disulfide bonds can reversibly break and recombine under stress, endowing the hydrogel with self-healing ability and toughness, effectively dissipating energy and preventing crack propagation. After curing, the first and second network layers cross-link with each other, forming a double cross-linked network, while the third network layer is a physically reinforcing network, realizing the structural reinforcement and water-locking effect of the double cross-linked network. Specifically, the third network layer is formed by uniformly dispersing nano-reinforcing materials within the first and second network layers. The nano-reinforcing materials, through their large specific surface area, generate strong mechanical interlocking and hydrogen bonding with the polymer chains, forming physical cross-linking points. This greatly restricts the movement of the polymer chains in the first and second network layers, effectively improving the structural stability of the hydrogel under high water content and ensuring its excellent water retention performance.

[0019] As a preferred embodiment of the above preparation method, in step (2), the crosslinking monomer 1,3-phenylenediboric acid is also added during the synthesis of the thioctic acid modified chitosan.

[0020] Lipoic acid-modified chitosan provides a dynamic covalent cross-linked network based on disulfide bonds (-SS-), which endows the hydrogel with self-healing ability, but its long-term stability under physiological conditions may be insufficient. This invention introduces a specific amount of 1,3-phenylenediboronic acid, which reacts with the ortho-hydroxyl groups (-OH) on the chitosan molecular chain to form borate ester bonds, exhibiting better chemical stability under physiological pH conditions, thereby improving the water retention performance of the hydrogel.

[0021] As a preferred embodiment of the above preparation method, the amount of 1,3-phenylenediboronic acid added is 3 to 10% of the mass of chitosan.

[0022] As a preferred embodiment of the above preparation method, in step (3), the nano-reinforcing material is one or more of the following: nanocellulose crystals, lactic acid-glycolic acid copolymer nanofibers, hydroxyapatite nanowires, or halloysite nanotubes.

[0023] As a preferred embodiment of the above preparation method, in step (4), the oil phase used in the reverse emulsion method is epoxidized soybean oil, and the aqueous phase is the composite hydrogel precursor solution.

[0024] As a preferred embodiment of the above preparation method, in step (4), the photocuring technology is as follows: a photoinitiator is added to the composite hydrogel precursor liquid and mixed evenly to obtain a mixed liquid, and then the mixed liquid is irradiated with ultraviolet light.

[0025] Based on the above, as a third aspect of the present invention, the present invention provides a highly water-retaining chitosan-based hydrogel microsphere for the application of chitosan-based hydrogel microspheres in the preparation of antibacterial dressings.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] To address the problems of poor water retention and insufficient mechanical strength in existing chitosan hydrogels, this invention constructs a hydrogel microsphere with a triple-network cross-linking structure. The triple-network cross-linking structure is constructed from a dual cross-linking network consisting of glycidyl methacrylate-modified chitosan and lipoic acid-modified chitosan, along with uniformly dispersed nano-reinforcing materials. The preparation method includes: first preparing two types of modified chitosan, then mixing them with nano-reinforcing materials to obtain a precursor solution, and finally fabricating microspheres using a reverse emulsion method and photocuring technology. Preferably, 1,3-phenylenediboric acid can be introduced during the modification process to further enhance network stability. This invention significantly improves the water retention and mechanical strength of the hydrogel microspheres by constructing a unique triple network. Attached Figure Description

[0028] Figure 1 is a scanning electron microscope image of the cross-sectional microstructure of the hydrogel obtained in Example 1 of the present invention;

[0029] Figure 2 is a scanning electron microscope image of the microstructure of the hydrogel microspheres obtained in Example 1 of the present invention;

[0030] Figure 3 is a microscopic image of the cell fluorescence staining of the hydrogel obtained in Example 1 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0032] Example 1

[0033] A chitosan-based hydrogel microsphere with high water retention capacity is provided, and the preparation steps are as follows:

[0034] (1) Synthesis of lipoic acid modified chitosan (LA-CS): 1.2 g of chitosan was dispersed and dissolved in 1% (v / v) glacial acetic acid solution (60 mL). The solution was placed in a beaker and stirred to accelerate dissolution, resulting in a 2% (w / v) chitosan solution. After the chitosan powder was completely dissolved, an anhydrous ethanol solution (30 mL) containing lipoic acid (mass ratio of 1:1 to chitosan) and an anhydrous ethanol solution (10 mL) containing 1,3-phenylenediboric acid (mass ratio of 5:100 to chitosan) were added to the beaker. After reacting for a period of time, 0.6 g of EDC and 0.3 g of NHS were added sequentially. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain lipoic acid modified chitosan. According to the 1H NMR spectrum analysis, compared with pure chitosan, new and distinguishable characteristic peak groups appeared in the characteristic chemical shift range (δ4.0-4.5 ppm). These new signals are attributed to the proton resonance generated by the unique structure of the lipoic acid molecule (especially the protons near the disulfide bond and carboxyl group), indicating that lipoic acid has been successfully grafted onto chitosan, indicating that the modification was successful.

[0035] (2) Synthesis of methacrylic anhydride-grafted modified chitosan (GMA-CS): 1.2 g of chitosan (CS) powder was dissolved in 50 ml of 0.175 M glacial acetic acid solution. The solution was placed in a beaker and stirred to accelerate dissolution. After the chitosan powder was completely dissolved, 50 ml of methanol solution was added to the beaker and stirring was continued. After reacting for a period of time, 0.50 g of glycidyl methacrylate (GMA) was added. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain double-bonded chitosan. By 1H NMR spectroscopy analysis, compared with pure chitosan, a significant new peak was observed in the chemical shift range of 5.0-6.0 ppm. This region is the exclusive region of olefin hydrogen (=CH2). In the CS spectrum, this region only has a flat baseline, while the GMA-CS spectrum shows a clear peak signal in this region, indicating that the double bond grafting was successful.

[0036] (3) Preparation of hydrogel precursor fluid: LA-CS, nanocellulose crystals (NCC), photoinitiator 2959 and GMA-CS are mixed in a mass ratio of 70:1:1:30; and the hydrogel precursor fluid is obtained by irradiation with 365nm ultraviolet light for 90s.

[0037] (4) Preparation of hydrogel microspheres: The prepared hydrogel precursor fluid was used as the aqueous phase, and the epoxidized soybean oil mixed solution containing Span80 (the volume ratio of Span80 to epoxidized soybean oil was 1:10) was used as the oil phase. According to the volume ratio of aqueous phase to oil phase of 1:12, the reverse emulsion method was used to form an emulsion containing hydrogel microspheres under the irradiation of a 365 nm ultraviolet lamp by a magnetic stirrer (1200 rpm, 1 hour) and a cell disruptor (75 kW, 8 minutes).

[0038] After the emulsion containing microspheres was broken up, centrifuged and washed, it was placed on a silicon wafer and dried at 40°C for 5 minutes. The microstructure of the hydrogel microsphere sample prepared in this example was then observed. The sample was placed on a standard cross-sectional stage with conductive adhesive, and the surface was sputtered with gold using a conventional sputtering method. The scanning voltage was set to 15 kV, and the magnification was adjusted to 5000x to characterize the microstructure of the hydrogel microspheres. The obtained scanning electron microscope images are shown in Figures 1 and 2, which show the microstructure of the microspheres.

[0039] Example 2

[0040] A chitosan-based hydrogel microsphere with high water retention capacity is provided, and the preparation steps are as follows:

[0041] (1) Synthesis of lipoic acid modified chitosan (LA-CS): 1.2 g of chitosan was dispersed and dissolved in 1% (v / v) glacial acetic acid solution (60 mL). The solution was placed in a beaker and stirred to accelerate dissolution, resulting in a 2% (w / v) chitosan solution. After the chitosan powder was completely dissolved, an anhydrous ethanol solution (30 mL) containing lipoic acid (mass ratio to chitosan 1:2) and an anhydrous ethanol solution (10 mL) containing 1,3-phenylenediboric acid (mass ratio to chitosan 3:100) were added to the beaker. After reacting for a period of time, 0.6 g of EDC and 0.3 g of NHS were added sequentially. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain lipoic acid modified chitosan.

[0042] (2) Synthesis of methacrylic anhydride-grafted modified chitosan (GMA-CS): 1.2 g of chitosan (CS) powder was dissolved in 50 ml of 0.175 M glacial acetic acid solution. The solution was placed in a beaker and stirred to accelerate dissolution. After the chitosan powder was completely dissolved, 50 ml of methanol solution was added to the beaker and stirring was continued. After reacting for a period of time, 0.50 g of glycidyl methacrylate (GMA) was added. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain double-bonded chitosan. By 1H NMR spectroscopy analysis, compared with pure chitosan, a significant new peak was observed in the chemical shift range of 5.0-6.0 ppm. This region is the exclusive region of olefin hydrogen (=CH2). In the CS spectrum, this region only has a flat baseline, while the GMA-CS spectrum shows a clear peak signal in this region, indicating that the double bond grafting was successful.

[0043] (3) Preparation of hydrogel precursor fluid: LA-CS, lactic acid-glycolic acid copolymer nanofibers, photoinitiator 2959 and GMA-CS are mixed in a mass ratio of 70:5:1:30; and the hydrogel precursor fluid is obtained by irradiation with 365nm ultraviolet light for 90s.

[0044] (4) Preparation of hydrogel microspheres: The prepared hydrogel precursor fluid was used as the aqueous phase, and the epoxidized soybean oil mixed solution containing Span80 (the volume ratio of Span80 to epoxidized soybean oil was 1:20) was used as the oil phase. According to the volume ratio of aqueous phase to oil phase of 1:15, the reverse emulsion method was used to form an emulsion containing hydrogel microspheres under the irradiation of a 365 nm ultraviolet lamp by a magnetic stirrer (1200 rpm, 1 hour) and a cell disruptor (75 kW, 8 minutes).

[0045] Example 3

[0046] A chitosan-based hydrogel microsphere with high water retention capacity is provided, and the preparation steps are as follows:

[0047] (1) Synthesis of lipoic acid modified chitosan (LA-CS): 1.2 g of chitosan was dispersed and dissolved in 1% (v / v) glacial acetic acid solution (60 mL). The solution was placed in a beaker and stirred to accelerate dissolution, resulting in a 2% (w / v) chitosan solution. After the chitosan powder was completely dissolved, an anhydrous ethanol solution (30 mL) containing lipoic acid (mass ratio of 1:2 to chitosan) and an anhydrous ethanol solution (15 mL) containing 1,3-phenylenediboric acid (mass ratio of 1:10 to chitosan) were added to the beaker. After reacting for a period of time, 0.6 g of EDC and 0.3 g of NHS were added sequentially. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain lipoic acid modified chitosan.

[0048] (2) Synthesis of methacrylic anhydride-grafted modified chitosan (GMA-CS): 1.2 g of chitosan (CS) powder was dissolved in 50 ml of 0.175 M glacial acetic acid solution. The solution was placed in a beaker and stirred to accelerate dissolution. After the chitosan powder was completely dissolved, 50 ml of methanol solution was added to the beaker and stirring was continued. After reacting for a period of time, 0.50 g of glycidyl methacrylate (GMA) was added. The above mixed solution was neutralized and reacted overnight. The solution was then dialyzed in deionized water for 3 days to remove impurities and residual reagents. The dialyzed solution was lyophilized to obtain double-bonded chitosan. By 1H NMR spectroscopy analysis, compared with pure chitosan, a significant new peak was observed in the chemical shift range of 5.0-6.0 ppm. This region is the exclusive region of olefin hydrogen (=CH2). In the CS spectrum, this region only has a flat baseline, while the GMA-CS spectrum shows a clear peak signal in this region, indicating that the double bond grafting was successful.

[0049] (3) Preparation of hydrogel precursor fluid: LA-CS, nanocellulose crystals, photoinitiator 2959 and GMA-CS are mixed in a mass ratio of 70:1:1:30; 365nm ultraviolet light is irradiated for 90s to obtain hydrogel precursor fluid.

[0050] (4) Preparation of hydrogel microspheres: The prepared hydrogel precursor fluid was used as the aqueous phase, and the epoxidized soybean oil mixed solution containing Span80 (the volume ratio of Span80 to epoxidized soybean oil was 1:20) was used as the oil phase. According to the volume ratio of aqueous phase to oil phase of 1:15, the reverse emulsion method was used to form an emulsion containing hydrogel microspheres under the irradiation of a 365 nm ultraviolet lamp by a magnetic stirrer (1200 rpm, 1 hour) and a cell disruptor (75 kW, 8 minutes).

[0051] Example 4

[0052] A chitosan-based hydrogel microsphere with high water retention is provided. The preparation steps are the same as in Example 1, except that the nano-reinforcing material in step (3) is lactic acid-glycolic acid copolymer nanofiber. The other steps are the same as in Example 1.

[0053] Comparative Example 1

[0054] A chitosan-based hydrogel microsphere is provided. The preparation steps are the same as in Example 1, except that in step (3), no nano-reinforcing material is added; instead, nano-cellulose crystals are used. The other steps are the same as in Example 1.

[0055] Comparative Example 2

[0056] A chitosan-based hydrogel microsphere is provided. The preparation steps are the same as those in Example 1, except that the nanocellulose crystals added in step (3) account for 6% of the total mass of LA-CS and GMA-CS. The other steps are the same as those in Example 1.

[0057] Comparative Example 3

[0058] A chitosan-based hydrogel microsphere is provided. The preparation steps are the same as in Example 1, except that glycidyl methacrylate is replaced with methacrylic anhydride (MA) in step (2). The other steps are the same as in Example 1.

[0059] Performance Characterization

[0060] 1. Taking Example 1 as an example, the biocompatibility of the chitosan-based hydrogel microspheres provided by this invention is illustrated. The biocompatibility experiment method is as follows: HUVEC cells and NIH 3T3 cells in good growth condition were seeded into 24-well plates (cell seeding concentration: 2.5 × 10⁴ HUVEC cells per well, 1.5 × 10⁴ NIH 3T3 cells per well). 500 μL of serum-containing DMEM medium was added to each well. After overnight incubation to allow cell adhesion, the next day, the hydrogel extract (hydrogel:DMEM in DMEM medium, volume ratio 1:5) was co-cultured for 1 and 2 days, respectively. The cells were then stained with Calcein-AM / propidium iodide (PI) fluorescent staining agent. The medium was changed once a day. Finally, the stained cells were observed under an inverted fluorescence microscope (AxioObserver 3, Zeiss, Germany). Three samples were randomly selected from each group for imaging. The fluorescent staining image of the hydrogel microspheres (LAMC) prepared in Example 1 is shown in Figure 3 as LAMC-gel-7. As can be seen from the figure (the control group is DMEM medium containing only serum), HUVEC cells and NIH 3T3 cells grew well in the extract of the hydrogel and showed a tendency to proliferate, indicating that the hydrogel prepared in Example 1 has strong biocompatibility.

[0061] 2. The swelling rate of the hydrogels from Examples 1 to 4 and Comparative Examples 1 to 3 was tested to characterize their water retention performance. The results are shown in Table 1. The test method was as follows: Each hydrogel precursor solution was placed in a silicone mold and then cured under ultraviolet light to form a cylindrical sample with a diameter of approximately 18 mm and a height of approximately 4 mm. The initial weight was recorded as W0. The sample was immersed in deionized water at room temperature. After immersion for 1 h, 2 h, and 3 h, the swollen hydrogel was removed, excess water was absorbed, and the sample was placed on clean filter paper. The weight (Wt) of the swollen hydrogel after 3 hours of immersion was measured. The swelling rate of the hydrogel was calculated using the formula: .

[0062] Table 1

[0063] Swelling rate (%) Example 1: 315.3 Example 2: 289.6 Example 3: 276.8 Example 4: 296.7 Comparative Example 1: 124.8 Comparative Example 2: 238.6 Comparative Example 3: 244.7 surface

[0064] As can be seen from the characterization data:

[0065] This invention significantly improves the swelling rate of hydrogel microspheres by constructing a unique triple network structure. A higher swelling rate indicates that the hydrogel possesses good mechanical strength and water retention. The hydrogel of this invention is constructed by cross-linking glycidyl methacrylate-modified chitosan to create the first network layer, and by forming dynamic disulfide bonds through lipoic acid-modified chitosan. This dynamic disulfide bonding is used to construct the second network layer. The third network layer is formed by uniformly dispersing nano-reinforcing materials within the first and second networks. These nano-reinforcing materials, with their large specific surface area, generate strong mechanical interlocking and hydrogen bonding with the polymer chains, forming physical cross-linking points, thereby greatly restricting the movement of the polymer chains in the first and second networks. Through the mutual cross-linking of the first, second, and third networks, the structural stability and mechanical strength of the hydrogel at high water content are effectively improved, thus ensuring its excellent performance of high water retention and high swelling rate.

[0066] As can be seen from Example 1, the triple-network hydrogel prepared in Example 1 has the highest swelling ratio, at 315.3%. The significance of the third-layer reinforcing network in this invention is evident from Examples 1, 4, Comparative Example 1, and Comparative Example 2. In Example 4, after replacing the nano-reinforcing material with a different one, the swelling ratio decreased compared to Example 1. Comparative Example 1, without the addition of nano-reinforcing material, showed a significant decrease in swelling ratio. Comparative Example 2, with a larger amount of nano-reinforcing material added compared to Example 1, also showed a significant decrease in swelling ratio. Therefore, it is clear that only by adding an appropriate amount of nano-reinforcing material to the hydrogel network constructed in this invention can the improved water retention and mechanical strength, along with a high swelling ratio, be achieved.

[0067] As can be seen from the comparison between Comparative Example 3 and Example 1, glycidyl methacrylate is more effective as a double bond introducing factor.

[0068] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A chitosan-based hydrogel microsphere with high water retention capacity, characterized in that: The hydrogel microspheres comprise a dual crosslinked network composed of glycidyl methacrylate-modified chitosan and lipoic acid-modified chitosan, and nano-reinforcing materials uniformly dispersed in the dual crosslinked network, forming a triple network crosslinked structure.

2. The highly water-retaining chitosan-based hydrogel microspheres as described in claim 1, characterized in that: The nano-reinforcing material is one or more of the following: cellulose nanocrystals, lactic acid-glycolic acid copolymer nanofibers, hydroxyapatite nanowires, or halloysite nanotubes.

3. A highly water-retaining chitosan-based hydrogel microsphere as described in claim 1 or 2, characterized in that: The nano-reinforcing material has a mass fraction of 0.1% to 5% in the hydrogel microspheres.

4. A method for preparing highly water-retaining chitosan-based hydrogel microspheres, characterized in that: Includes the following steps: (1) Glycidyl methacrylate is grafted onto chitosan to obtain double-bonded chitosan; (2) Thioctic acid is grafted onto chitosan to obtain thioctic acid-modified chitosan; (3) The double-bonded chitosan, thioctic acid-modified chitosan and nano-reinforcing materials are mixed to obtain a composite hydrogel precursor liquid; (4) The composite hydrogel precursor liquid is made into composite hydrogel microspheres using reverse emulsion method and photocuring technology.

5. The preparation method according to claim 4, characterized in that: In step (2), the crosslinking monomer 1,3-phenylenediberic acid was also added during the synthesis of the thioctic acid modified chitosan.

6. The preparation method according to claim 4, characterized in that: The amount of 1,3-phenylenediboronic acid added is 3 to 10% of the mass of chitosan.

7. The preparation method according to claim 4, characterized in that: In step (3), the nano-reinforcing material is one or more of the following: nanocellulose crystals, lactic acid-glycolic acid copolymer nanofibers, hydroxyapatite nanowires, or halloysite nanotubes.

8. The preparation method according to claim 4, characterized in that: In step (4), the oil phase used in the reverse emulsion method is epoxidized soybean oil, and the aqueous phase is the composite hydrogel precursor solution.

9. The preparation method according to claim 4, characterized in that: In step (4), the photocuring technology is as follows: a photoinitiator is added to the composite hydrogel precursor liquid and mixed evenly to obtain a mixed liquid, and then the mixed liquid is irradiated with ultraviolet light.

10. The application of chitosan-based hydrogel microspheres as described in any one of claims 1 to 3 or chitosan-based hydrogel microspheres prepared by the preparation method described in any one of claims 4 to 9 in the preparation of antibacterial dressings.

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