Composite hydrogel as well as preparation method and application thereof

Abstract

The invention discloses composite hydrogel as well as a preparation method and application thereof, and relates to the technical field of hydrogel. The composite hydrogel is prepared from oxidized sodium alginate, carboxymethyl chitosan and agar. The composite hydrogel provided by the invention has excellent biocompatibility, time-controllable injectable molding performance, self-healing performance and good mechanical properties, and has great application prospects in the field of biological medicines.

Description

Technical Field

[0001] The present application relates to the technical field of hydrogels, and in particular to a composite hydrogel and a preparation method and application thereof. Background Art

[0002] Hydrogels have attracted widespread attention in the field of biomedical materials research due to their structure similar to the human extracellular matrix and excellent water-holding properties. Traditional hydrogels are usually formed by cross-linking synthetic polymers. However, due to the biocompatibility issues of synthetic polymers, these hydrogels are subject to certain limitations when used as biomedical materials. Sodium alginate, as a natural polysaccharide compound, has been widely recognized for its excellent biocompatibility. The molecular structure of sodium alginate contains a large number of hydroxyl and carboxyl groups. These groups can form a three-dimensional network structure through chemical modification and cross-linking reactions, thereby constructing a natural biopolysaccharide hydrogel.

[0003] In related technologies, the preparation of hydrogels based on sodium alginate introduces some synthetic polymers, which may weaken their originally good biocompatibility and degradability. In addition, biopolysaccharide-based hydrogels with a single network structure generally exhibit poor mechanical properties, and their strength and functionality are often mismatched, which seriously limits the potential of biopolysaccharide-based hydrogels in practical applications. Summary of the Invention

[0004] In view of this, the present application provides a composite hydrogel and a preparation method and application thereof.

[0005] The embodiment of the present application is implemented as follows: in a first aspect, the embodiment of the present application provides a composite hydrogel comprising oxidized sodium alginate, carboxymethyl chitosan and agar; wherein,

[0006] The polymerization unit of the oxidized sodium alginate is:

[0007] The polymerization unit of the carboxymethyl chitosan is:

[0008] Optionally, in some embodiments of the present application, in the composite hydrogel, the mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is (1-3): (1-3): (1-3);

[0009] The composite hydrogel has a double network structure.

[0010] In a second aspect, the present invention also provides a method for preparing a composite hydrogel, comprising the following steps:

[0011] Provided are oxidized sodium alginate, carboxymethyl chitosan, and agar; wherein the polymerization unit of the oxidized sodium alginate is: The polymerization unit of the carboxymethyl chitosan is:

[0012]

[0013] The oxidized sodium alginate, the carboxymethyl chitosan and the agar are mixed and reacted to obtain a composite hydrogel.

[0014] Optionally, in some embodiments of the present application, the method for preparing oxidized sodium alginate comprises:

[0015] Providing a sodium alginate dispersion, wherein the sodium alginate dispersion comprises sodium alginate and a first solvent;

[0016] Sodium periodate and ethylene glycol are added to the sodium alginate dispersion to react and obtain oxidized sodium alginate.

[0017] Optionally, in some embodiments of the present application, the first solvent is selected from water; and / or,

[0018] In the sodium alginate dispersion, the mass concentration of the sodium alginate is 2% w / v to 8% w / v; and / or,

[0019] The molar ratio of the polymerized units of sodium alginate to the sodium periodate is 1:(0.2-2); and / or,

[0020] The mass ratio of the sodium alginate to the ethylene glycol is (2-8):2.

[0021] Optionally, in some embodiments of the present application, the reaction of the sodium alginate, the sodium periodate and the ethylene glycol comprises: adding the sodium periodate to perform a first reaction; adding the ethylene glycol to perform a second reaction; wherein,

[0022] The first reaction time is 20h to 28h; and / or,

[0023] The first reaction is carried out in the dark; and / or,

[0024] The second reaction time is 0.5h to 2h; and / or,

[0025] After the sodium alginate, the sodium periodate and the ethylene glycol react, the method further comprises: performing a first dialysis; the first dialysis lasts for 2 to 4 days, and the water change time for the first dialysis is 5 to 10 hours per time.

[0026] Optionally, in some embodiments of the present application, the method for preparing the carboxymethyl chitosan comprises:

[0027] providing a sodium hydroxide solution and chitosan, mixing them, and freezing them to obtain an intermediate product;

[0028] The intermediate product and the second solvent are mixed, chloroacetic acid is added, and the mixture is reacted to obtain carboxymethyl chitosan.

[0029] Optionally, in some embodiments of the present application, the mass fraction of the sodium hydroxide solution is 20% to 80%; and / or,

[0030] The mass volume ratio of the chitosan and the sodium hydroxide solution is (2-5) g:20 mL; and / or,

[0031] The mixing of the sodium hydroxide solution and the chitosan is carried out in an ice-water bath; and / or,

[0032] The freezing time is 20h to 28h; and / or,

[0033] The second solvent is selected from one or more of isopropanol, ethanol, and butanol; and / or,

[0034] The mass volume ratio of the chitosan and the second solvent is (2-5) g:100 mL; and / or,

[0035] The mass ratio of the chitosan to the chloroacetic acid is (2-5):10; and / or,

[0036] The reaction of the intermediate product and the chloroacetic acid is carried out in an oil bath; and / or,

[0037] The reaction temperature of the intermediate product and the chloroacetic acid is 50° C. to 100° C.; the reaction time of the intermediate product and the chloroacetic acid is 5 h to 10 h; and / or,

[0038] After the intermediate product reacts with the chloroacetic acid, the method further comprises: performing a second dialysis; the second dialysis lasts for 3 to 8 days, and the water change time for the second dialysis is 5 to 10 hours per time.

[0039] Optionally, in some embodiments of the present application, the mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is (1-3): (1-3): (1-3); and / or,

[0040] The reaction temperature of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is 50° C. to 60° C.

[0041] In a third aspect, embodiments of the present application further provide the above-mentioned composite hydrogel, or the use of the composite hydrogel prepared by the above-mentioned preparation method in biomedical materials.

[0042] The composite hydrogel provided in the embodiments of the present application includes oxidized sodium alginate, carboxymethyl chitosan and agar. The oxidized sodium alginate has a more active aldehyde group. Carboxymethyl chitosan can improve its water solubility by carboxymethylating chitosan. The large number of amino functional groups in the carboxymethyl chitosan can react with the aldehyde groups of the oxidized sodium alginate through a Schiff base reaction under mild conditions without adding any initiator or cross-linking agent to construct a cross-linked network to form a hydrogel with a full biological matrix. In addition, in order to achieve high reinforcement of the full biological polysaccharide matrix hydrogel and maintain its good biocompatibility, agar is further introduced to construct a double network. Through the structural synergy and complementary enhancement of different polysaccharide molecules, the composite hydrogel has excellent biocompatibility, time-controllable injection moldability, self-healing properties and good mechanical properties, and has great application prospects in the field of biomedicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 This is a flow chart of a method for preparing a composite hydrogel provided in an embodiment of the present application;

[0045] Figure 2 This is a schematic diagram of the preparation process of a composite hydrogel provided in an embodiment of the present application;

[0046] Figure 3 This is a schematic diagram of the preparation process of a composite hydrogel provided in Comparative Example 1;

[0047] Figure 4 is an infrared spectrum of sodium alginate and oxidized sodium alginate in Example 3 of the present application;

[0048] Figure 5 is an infrared spectrum of chitosan and carboxymethyl chitosan in Example 3 of the present application;

[0049] Figure 6 3 is an infrared spectrum of the oxidized sodium alginate, carboxymethyl chitosan in Example 3 of the present application and the composite hydrogel in Comparative Example 1;

[0050] Figure 7 This is a self-healing performance test diagram of the composite hydrogel provided in Example 4 of the present application. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0052] In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of a device in actual use or operation, specifically in the drawing directions of the accompanying drawings; whereas "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "including" means "including but not limited to." Terms such as first, second, and third are used merely as designations and do not impose numerical requirements or establish a sequential order.

[0053] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0054] In this application, "at least one" means one or more, and "plurality" means two or more. "One or several", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0055] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0056] The structural formulas and molecular weights of some chemical reagents used in this application are described below:

[0057] Sodium alginate (SA): The molecular weight of the structural unit is 216.2, the viscosity is 500-1000 mPa.s, the reagent is pure, and it was purchased from Aladdin Reagent Co., Ltd.

[0058] Sodium periodate (NaIO4): reagent grade, molecular weight = 213.89, purchased from Aladdin Reagent Co., Ltd.

[0059] Chitosan (CS): Weight average molecular weight = 100,000, pharmaceutical grade, purchased from Aladdin.

[0060] Ethylene glycol: Molecular weight = 62.07, reagent pure, purchased from Aladdin Purchased from Aladdin Reagent Co., Ltd.;

[0061] Chloroacetic acid: Molecular weight = 94.5, reagent pure, purchased from Aladdin Purchased from Aladdin Reagent Co., Ltd.;

[0062] Agar (Agr): Number average molecular weight = 1200, pharmaceutical grade, purchased from Aladdin.

[0063] The technical solution of this application is as follows:

[0064] In a first aspect, the present invention provides a composite hydrogel comprising oxidized sodium alginate (ODSA), carboxymethyl chitosan (CMCS) and agar (Agr); wherein,

[0065] The polymerization unit of the oxidized sodium alginate is:

[0066] The polymerization unit of the carboxymethyl chitosan is:

[0067] The composite hydrogel provided in the embodiments of the present application includes oxidized sodium alginate, carboxymethyl chitosan and agar. The oxidized sodium alginate has a more active aldehyde group. Carboxymethyl chitosan can improve its water solubility by carboxymethylating chitosan. The large number of amino functional groups in the carboxymethyl chitosan can react with the aldehyde groups of the oxidized sodium alginate through a Schiff base reaction under mild conditions without adding any initiator or cross-linking agent to construct a cross-linked network to form a hydrogel with a full biological matrix. In addition, in order to achieve high reinforcement of the full biological polysaccharide matrix hydrogel and maintain its good biocompatibility, agar is further introduced to construct a double network. Through the structural synergy and complementary enhancement of different polysaccharide molecules, the composite hydrogel has excellent biocompatibility, time-controllable injection moldability, self-healing properties and good mechanical properties, and has great application prospects in the field of biomedicine.

[0068] In some embodiments, in the composite hydrogel, the mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan, and the agar is (1-3):(1-3):(1-3), for example, 1:1:1, 2:1:1, 3:1:1, 1:2:1, 1:3:1, 1:1:2, 1:1:3, or a range between any two of the foregoing values. Within this mass ratio range, the oxidized sodium alginate, the carboxymethyl chitosan, and the agar complement each other, resulting in the composite hydrogel having excellent properties.

[0069] In some embodiments, the composite hydrogel has a double network structure. It is understood that the oxidized sodium alginate, the carboxymethyl chitosan, and the agar are all polysaccharides, and their structures can synergistically complement each other to form a fully biological matrix composite hydrogel with a double network structure.

[0070] Second, see Figure 1 and Figure 2 The present invention also provides a method for preparing a composite hydrogel, comprising the following steps:

[0071] Step S11: providing oxidized sodium alginate, carboxymethyl chitosan, and agar; wherein the polymerization unit of the oxidized sodium alginate is: The polymerization unit of the carboxymethyl chitosan is:

[0072]

[0073] Step S12: mixing the oxidized sodium alginate, the carboxymethyl chitosan and the agar, and reacting them to obtain a composite hydrogel.

[0074] In the step S11:

[0075] In some embodiments, the method for preparing oxidized sodium alginate comprises:

[0076] Step S111: providing a sodium alginate dispersion, wherein the sodium alginate dispersion comprises sodium alginate and a first solvent;

[0077] Step S112: adding sodium periodate and ethylene glycol to the sodium alginate dispersion to react and obtain oxidized sodium alginate.

[0078] In some embodiments, the first solvent is selected from water.

[0079] In some embodiments, the mass concentration of sodium alginate in the sodium alginate dispersion is 2% w / v to 8% w / v, for example, 2% w / v, 3% w / v, 4% w / v, 5% w / v, 6% w / v, 7% w / v, 8% w / v, or a range between any two of the foregoing values. Within this mass concentration range, the sodium alginate is facilitated to be uniformly dissolved and dispersed.

[0080] In some embodiments, the reaction of the sodium alginate, the sodium periodate and the ethylene glycol comprises:

[0081] The sodium periodate is added to carry out a first reaction; and the ethylene glycol is added to carry out a second reaction.

[0082] In some embodiments, the polymerized units of sodium alginate The molar ratio of sodium periodate to sodium alginate is 1:(0.2-2), for example, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, or a range between any two of the above values. Within the molar ratio range, the reaction yield of sodium periodate and sodium alginate is improved.

[0083] In some embodiments, the first reaction time is 20 hours to 28 hours, for example, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, or a range between any two of the above values. Within the first reaction time range, the sodium periodate and the sodium alginate are conducive to efficient reaction.

[0084] In some embodiments, the first reaction is performed in the absence of light.

[0085] In some embodiments, the mass ratio of the sodium alginate to the ethylene glycol is (2-8):2, for example, 1:1, 3:2, 4:2, 5:2, 6:2, 7:2, 8:2, or a range between any two of the above values. Within this mass ratio range, the yield of the oxidized sodium alginate is improved.

[0086] In some embodiments, the second reaction time is 0.5 h to 2 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, or a range between any two of the above values. Within the second reaction time range, the ethylene glycol is facilitated to efficiently participate in the reaction.

[0087] In some embodiments, after the sodium alginate, the sodium periodate, and the ethylene glycol react, the method further comprises: performing a first dialysis.

[0088] Furthermore, the duration of the first dialysis is 2 to 4 days, and the water change time of the first dialysis is 5 to 10 hours per time.

[0089] It is understood that after the first dialysis, oxidized sodium alginate can be obtained by freeze-drying, and the oxidized sodium alginate can be in the form of a white sponge.

[0090] The synthesis route of the sodium alginate to form the oxidized sodium alginate is shown in the following formula:

[0091]

[0092] In some embodiments, the method for preparing the carboxymethyl chitosan comprises:

[0093] Step S113: providing a sodium hydroxide solution and chitosan, mixing, and freezing to obtain an intermediate product;

[0094] Step S114: mixing the intermediate product and the second solvent, adding chloroacetic acid, and reacting to obtain carboxymethyl chitosan.

[0095] In some embodiments, the mass fraction of the sodium hydroxide solution is 20% to 80%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or a range between any two of the above values. Within the mass concentration range, uniform dissolution and dispersion of sodium hydroxide is facilitated.

[0096] In some embodiments, the mass-to-volume ratio of the chitosan to the sodium hydroxide solution is (2-5) g:20 mL, for example, 2 g:20 mL, 3 g:20 mL, 4 g:20 mL, 5 g:20 mL, or a range between any two of the above values. Within the mass-to-volume ratio range, the chitosan and the sodium hydroxide solution are facilitated to be fully mixed.

[0097] In some embodiments, the mixing of the sodium hydroxide solution and the chitosan is performed in an ice-water bath.

[0098] In some embodiments, the freezing time is 20 hours to 28 hours, for example, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, or a range between any two of the above values. Within the freezing time range, the chitosan is facilitated to be fully frozen.

[0099] In some embodiments, the second solvent is selected from one or more of isopropanol, ethanol, and butanol.

[0100] In some embodiments, the mass-to-volume ratio of the chitosan to the second solvent is (2-5) g:100 mL, for example, 2 g:100 mL, 3 g:100 mL, 4 g:100 mL, 5 g:100 mL, or a range between any two of the above values. Within the mass-to-volume ratio range, the chitosan is facilitated to be fully dissolved and dispersed.

[0101] It should be noted that the frozen chitosan is dissolved in the second solvent after thawing.

[0102] In some embodiments, the mass ratio of the chitosan to the chloroacetic acid is (2-5):10, for example, 2:10, 3:10, 4:10, 5:10, or a range between any two of the above values. Within the mass ratio range, the yield of the carboxymethyl chitosan is improved.

[0103] In some embodiments, the reaction of the intermediate product and the chloroacetic acid is carried out in an oil bath.

[0104] In some embodiments, the reaction temperature of the intermediate product and the chloroacetic acid is 50° C. to 100° C., for example, 50° C., 60° C., 70° C., 80° C., 90° C., 100° C., or a range between any two of the foregoing values; the reaction time of the intermediate product and the chloroacetic acid is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a range between any two of the foregoing values. Thus, under the reaction conditions, the intermediate product and the chloroacetic acid are conducive to efficient reaction.

[0105] In some embodiments, after the intermediate product and the chloroacetic acid react, the method further comprises: performing a second dialysis.

[0106] Furthermore, the duration of the second dialysis is 3 to 8 days, and the water change time of the second dialysis is 5 to 10 hours per time.

[0107] It is understood that after the second dialysis, carboxymethyl chitosan can be obtained by freeze drying, and the carboxymethyl chitosan can be in the form of a white sponge.

[0108] The synthesis route of the chitosan to carboxymethyl chitosan is shown in the following formula:

[0109]

[0110] In the step S12:

[0111] In some embodiments, the mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan, and the agar is (1-3):(1-3):(1-3), for example, 1:1:1, 2:1:1, 3:1:1, 1:2:1, 1:3:1, 1:1:2, 1:1:3, or a range between any two of the foregoing values. Within this mass ratio range, the oxidized sodium alginate, the carboxymethyl chitosan, and the agar react efficiently, thereby increasing yield.

[0112] It should be noted that the oxidized sodium alginate, the carboxymethyl chitosan and the agar are mixed by dissolving each substance in a solvent to form a solution and then mixing the solutions.

[0113] In some embodiments, the reaction temperature of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is 50°C to 60°C, for example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C or a range between any two of the above values.

[0114] It can be understood that under the above reaction temperature conditions, a gel can be formed by shaking and evenly standing, and a composite hydrogel with a double network structure can be formed by cooling.

[0115] The preparation method of the composite hydrogel provided in the present application is as follows: in order to improve the reaction activity of sodium alginate, sodium alginate is oxidized and ring-opened to prepare oxidized sodium alginate, thereby generating new aldehyde groups with higher activity; carboxymethyl chitosan is selected (chitosan is the only alkaline natural polysaccharide compound in nature, its raw materials are naturally easy to obtain, and carboxymethylation can improve its water solubility), and its large number of amino functional groups are utilized to construct a cross-linked network with the aldehyde groups of oxidized sodium alginate through Schiff base reaction under mild conditions without adding any initiator or cross-linking agent, thereby forming a hydrogel with a full biological matrix; in order to achieve high reinforcement of the full biological polysaccharide matrix hydrogel and maintain its good biocompatibility, another natural organism (polysaccharide agar) is introduced into the oxidized sodium alginate / carboxymethyl cellulose biomass hydrogel to construct a double network. Through the structural synergy and complementary enhancement of different polysaccharide molecules, the prepared full biological polysaccharide composite hydrogel has excellent biocompatibility, time-controllable injection molding performance, self-healing performance and good mechanical properties.

[0116] In a third aspect, embodiments of the present application further provide applications of the composite hydrogel or the composite hydrogel prepared by the above-mentioned preparation method.

[0117] Specifically, the composite hydrogel can be applied to biomedical materials.

[0118] The present application will be described in detail below through specific examples. The following examples are only some examples of the present application and are not limitations of the present application.

[0119] Example 1

[0120] This embodiment provides a composite hydrogel, the preparation method of which includes the following steps:

[0121] Step 1: Add 5.0 g of sodium alginate (SA) to a 250 mL three-necked flask, then add 100 mL of deionized water and mechanically stir until completely dissolved to obtain a 5% (w / v) sodium alginate solution; after uniform stirring, add sodium periodate (molar ratio of sodium periodate to sodium alginate polymerization units = 0.4:1) under light-proof conditions, and react at room temperature in the dark for 24 hours. After 24 hours of reaction, add 2 g of ethylene glycol and continue the reaction for 1 hour to terminate the reaction; the resulting reaction solution is placed in a dialysis bag (Viskase, USA) (MD44-7000Da) and dialyzed for three days, changing the water every 8 hours; after dialysis, freeze-dry for three days to obtain a white sponge-like product, namely oxidized sodium alginate (ODSA);

[0122] Step 2: First, prepare 40mL of 50% sodium hydroxide solution by mass, cool it in an ice-water bath, add 8g of chitosan powder (CS), and mechanically stir until the chitosan becomes fluffy, then put it in the refrigerator and freeze it for 24h; take out the frozen chitosan and thaw it, then transfer it to a three-necked flask, add 200mL of isopropanol as a dispersion medium, and stir at room temperature for 6h to allow the chitosan to form a good dispersion state; then place the three-necked flask in an oil bath, heat it to 70°C, add 20g of chloroacetic acid, and continue mechanical stirring for 6h; after the reaction is completed, wash the product with anhydrous ethanol 3-5 times, then put it in a dialysis bag and dialyze it for 5 days, changing the water every 8 hours. After the dialysis is completed, the mixed solution is freeze-dried to obtain a white sponge-like carboxymethyl chitosan product (CMCS);

[0123] Step 3: Prepare a 4% (w / v) agar solution by heating to 85°C and dissolving it, then place it in a 55°C oven until ready for use. Add 0.2g of the oxidized alginate from Step 1 to 5ml of the 4% (w / v) agar solution and shake to dissolve. Once dissolved, add 5ml of the 4% (w / v) carboxymethyl chitosan solution from Step 2, shake rapidly and evenly, and allow to stand to form a gel. The entire process is performed in a 55°C oven. Once the gel is formed, cool the mold at room temperature for 24 hours to obtain a composite hydrogel.

[0124] Example 2

[0125] This embodiment is substantially the same as embodiment 1, except that in step 1, the molar ratio of the polymerization units of sodium periodate to sodium alginate is 0.6:1.

[0126] Example 3

[0127] This embodiment is substantially the same as embodiment 1, except that in step 1, the molar ratio of the polymerization units of sodium periodate to sodium alginate is 0.8:1.

[0128] Example 4

[0129] This embodiment is substantially the same as embodiment 1, except that in step 1, the molar ratio of the polymerization units of sodium periodate to sodium alginate is 1:1.

[0130] Example 5

[0131] This embodiment is substantially the same as embodiment 1, except that in step 1, the molar ratio of the polymerization units of sodium periodate to sodium alginate is 1.2:1.

[0132] Example 6

[0133] This embodiment is substantially the same as embodiment 1, except that in step 1, the molar ratio of the polymerization units of sodium periodate to sodium alginate is 1.5:1.

[0134] Comparative Example 1

[0135] This comparative example is basically the same as Example 3, except that agar solution is not added in step 3. For a schematic diagram of its preparation process, please refer to Figure 3 .

[0136] Comparative Example 2

[0137] This comparative example is substantially the same as Example 4, except that no agar solution is added in step 3.

[0138] Comparative Example 3

[0139] This comparative example is substantially the same as Example 5, except that no agar solution is added in step 3.

[0140] The sodium alginate and oxidized sodium alginate in Example 3 were tested by infrared spectroscopy. Figure 4 .

[0141] Depend on Figure 4 It can be seen that there are a large number of highly polar hydroxyl groups in sodium alginate, which easily form hydrogen bonds with groups containing lone pairs of electrons (such as -NH2 and -OH). As the number of hydrogen bonds increases, the stretching vibration frequency of the hydroxyl group will be greatly attenuated. Figure 5 Appears at 3400cm -1The strong and broad absorption peak at the center is the stretching vibration of -OH in sodium alginate. In oxidized alginate, the hydroxyl groups are partially oxidized to aldehyde or ketone structures, which weakens the degree of hydroxyl association. Therefore, the stretching vibration frequency of -OH increases, and the wave number rises to 3427cm -1 At the same time, we can see that 1298cm-1 corresponds to the stretching vibration peaks of -OCH and -CCH in the sodium alginate structure, and 1082cm -1 The peak at 1024 cm-1 is attributed to the -CO- stretching vibration in the sodium alginate structure. -1 Attributed to the stretching vibration peaks of -CC- and -CO-pyran rings in the sodium alginate structure; 1406 cm -1 , 1590cm -1 The peak at 1722 cm is attributed to the symmetric and asymmetric stretching vibration peaks of -CC=O in sodium alginate. Compared with the infrared spectrum of pure sodium alginate, the infrared spectrum of oxidized sodium alginate can be observed at 1722 cm -1 A new peak appears at 2721 cm, which is attributed to the stretching vibration peak of C=O in the -CHO aldehyde group of sodium alginate obtained by oxidation. -1 An absorption peak also appeared at , although it was not particularly strong. This was mainly because the characteristic functional groups of the polymer modification were greatly affected by other groups and the peaks were generally weak. Through the analysis of the above characteristic peak positions, it can be confirmed that the preparation of oxidized sodium alginate was successful.

[0142] Chitosan and carboxymethyl chitosan in Example 3 were tested by infrared spectroscopy. Figure 5 .

[0143] Depend on Figure 5 It can be seen that 3375cm -1 The left and right sides are the stretching vibration absorption peaks of chitosan amino and hydroxyl groups, 2880 cm -1 The C—H stretching vibration peak is 1656 cm -1 、1598cm -1 The characteristic absorption peaks of amide I and II are shown in Figure 2. Compared with the infrared spectrum of chitosan raw materials, the absorption peak of carboxymethyl chitosan at 1074 cm -1 The characteristic absorption peak of CO stretching appeared at 1604 cm -1 The peak that appears is attributed to the carbonyl characteristic absorption peak, which is a new absorption peak generated by merging with the amide bond and amino absorption bands in the chitosan structure, 1606 cm -1 、1411cm -1 is the asymmetric and symmetric stretching vibration of the carboxyl group in carboxymethyl chitosan. The original chitosan has a wavelength of 1384 cm -1 The stretching vibration peak shifted to 1325 cm -1It was about 2.5, indicating that more C-N bonds were formed. The results showed that the carboxyl groups were successfully grafted into the chitosan skeleton.

[0144] The oxidized sodium alginate, carboxymethyl chitosan and the composite hydrogel of comparative example 1 were tested by infrared spectroscopy. Figure 6 .

[0145] Depend on Figure 6 It can be seen that 3420cm -1 The broad and strong absorption peak is the stretching vibration absorption peak of OH, at 2920cm -1 , 1580cm -1 , 1406cm -1 , and 1024cm -1 The absorption peak at 1590 cm is the characteristic absorption peak of polysaccharide derivatives, and sodium alginate and carboxymethyl chitosan are both polysaccharide macromolecules, so the infrared spectra of several substances show that they all contain these absorption peaks. These absorption peaks correspond to CH stretching vibration, C=O stretching vibration (carboxyl group), CH bending vibration and CN stretching vibration (two vibrations act together), as well as CO stretching vibration. The aldehyde group of oxidized sodium alginate and the amino group of carboxymethyl chitosan undergo Schiff base cross-linking reaction to generate -C=N- bond, and due to the peak at 1590 cm -1 The strong absorption peak of C=O stretching vibration at 1633 cm is close to that of C=N stretching vibration, so the strong absorption peak of C=O stretching vibration will affect the formation absorption peak of C=N bond, but it can still be seen at 1633 cm -1 The absorption peak of -C=N- bond can be seen. And by comparing the curves of ODSA and ODSA-CMCS, it can be found that 1722cm -1 The characteristic peak of the aldehyde group disappeared, which indicated that the aldehyde group reacted with the amino group to form a -C=N- bond.

[0146] It should be noted that the infrared spectrum test method is as follows: After the washed sample is freeze-dried, the sample is cut into small pieces and tested by KBr pelleting. The scanning range is 4000-450cm -1 , the number of scans per second is 64 times, and the step length is 4 cm -1 .

[0147] The oxidation degrees of the oxidized sodium alginate of Examples 1 to 6 were tested. The test results are shown in Table 1.

[0148] Among them, the hydroxylamine hydrochloride titration method is used to determine the aldehyde content of ODSA. The principle of this method is: the aldehyde group can react with the amino group in hydroxylamine hydrochloride to produce oxime and HCl; the HCl produced by the reaction is titrated with a certain concentration of NaOH solution, and the aldehyde content in OSA can be calculated. The specific operation process is as follows: 0.1g of freeze-dried ODSA is dissolved in 25mL of 0.25mol / L hydroxylamine hydrochloride solution containing 0.001wt% of methyl orange reagent (pH maintained at 4.5), and stirred at room temperature for 12h. Then, the hydrochloric acid released by the reaction of aldehyde group and hydroxylamine hydrochloride is titrated with sodium hydroxide solution (0.1mol / L) until the solution changes from red to yellow, and the effect of the amount of sodium hydroxide solution added on the pH value is recorded. The corresponding chemical reaction and calculation formula are as follows: SA-(CHO) n +nH2N-OH·HCl=SA-(CH=N-OH) n +nH2O+nHCl(1), HCl+NaOH=NaCl+H2O(2), [CHO]=ΔV×c×10 -3 / w(3), OD=198ΔV×c×10 -3 / 2w(4). Wherein, [CHO] is the aldehyde content, in mmol / g; OD is the degree of oxidation of SA-CHO; ΔV is the volume of NaOH solution consumed, in mL; c is the concentration of NaOH solution, in mol / L; w is the mass of SA-CHO, in g; 198 is the molecular weight of the sodium alginate repeating unit, in g / mol.

[0149] Table 1

[0150]

[0151] As shown in Table 1, as the molar ratio of sodium periodate to sodium alginate increases, the degree of oxidation rises from 20.12% to 72.65%. However, as the molar ratio continues to rise to 1.5, the degree of oxidation actually decreases. This indicates that within a certain molar ratio range, the degree of oxidation increases with increasing sodium periodate levels, but decreases after reaching the maximum reaction limit. This may be because the number of alcoholic hydroxyl groups in sodium alginate is limited; after a certain reaction period, no new aldehyde groups are formed. Further increases in the amount of sodium periodate would oxidize existing aldehyde groups to carboxyl groups, thereby reducing the number of aldehyde groups.

[0152] It can also be seen from Table 1 that the maximum value of the oxidation degree does not reach 100%. This may be because sodium periodate not only oxidizes and breaks the carbon-carbon bonds connecting the glycol bonds of sodium alginate during the reaction, but also partially oxidizes and breaks the glycosidic bonds between the polysaccharide molecular chains. Therefore, part of the sodium periodate oxidizes the glycosidic bonds and is consumed.

[0153] The gelation time of the composite hydrogels of Examples 1 to 6 and Comparative Examples 1 to 3 was tested under neutral conditions (pH=7). See Table 2 for the test results.

[0154] The gelation time plays a crucial role in the practical application of injectable hydrogels. If the precursor solution gelation time is too short, the hydrogel forms too quickly, making it difficult to inject into the desired area. If the time is too long, the precursor solution may partially lose its gelation, resulting in suboptimal results. Therefore, an appropriate gelation time is crucial. It ensures that the precursor solution gels quickly and effectively in vivo, facilitating the application of injectable hydrogels.

[0155] The test method involves mixing oxidized sodium alginate, carboxymethyl chitosan, and agar solution, immediately shaking and evenly adding the mixture to the rheometer's heating plate (no agar solution was used in the comparative example). A thin layer of silicone oil was pipetted around the mixture to prevent excessive evaporation. The gel point was then measured using a plate-type time-scan method. The time-scan mode was used, with the frequency set at 1 Hz, the strain at 1%, and the temperature set at 25°C.

[0156] Table 2

[0157]

[0158]

[0159] As shown in Table 2, the gel point time of composite hydrogels prepared using oxidized sodium alginate with different oxidation degrees is closely related to the oxidation degree. The table shows that when the molar ratio of sodium periodate to sodium alginate monomer is 0.40, the gel time is the longest, reaching 16.7 minutes. As the oxidation degree of the oxidized sodium alginate increases, the gel time shortens, reaching a minimum of 5.7 minutes when the molar ratio of NaIO4:SA is 1.0. This is mainly because as the oxidation degree increases, the concentration of aldehyde groups increases, and the number of reactive sites in the system increases, shortening the gel time. However, further increasing the oxidation degree of the sodium alginate does not significantly shorten the gel time. In fact, when the molar ratio reaches 1.50, the gel time increases slightly. This may be because excessive sodium periodate, the oxidant, oxidizes the aldehyde groups in the oxidized sodium alginate into carboxyl groups, reducing the aldehyde concentration in the overall system, resulting in a slight increase in the gel time. Comparing the gelation time of Examples 3 to 5 with that of Comparative Examples 1 to 3, it can be seen that the introduction of the double network slightly reduces the gelation time. This is because the introduction of the agar network hinders the movement of the oxidized sodium alginate and carboxymethyl chitosan molecular chains.

[0160] The gelation time of the composite hydrogel of Example 4 was further tested under different acid-base conditions (pH=2-11). The test results are shown in Table 3.

[0161] The test method is as follows: oxidized sodium alginate and carboxymethyl chitosan from Example 4 are prepared with PBS solutions or buffer solutions at pH values ​​of 2, 4, 7, 9, or 11 to form a 4% agar / oxidized sodium alginate solution and a 4% carboxymethyl chitosan solution. 1 mL of the agar / oxidized sodium alginate solution and 1 mL of the CMCS solution are mixed and immediately shaken to uniformly distribute the mixture onto the heating plate of the rheometer. A thin layer of silicone oil is pipetted around the mixture to prevent excessive evaporation of the solution. The gel point is then measured using a plate-type time-scan method. The time-scan mode is used: the frequency is set to 1 Hz, the strain is 1%, and the temperature is set to 25°C.

[0162] Table 3

[0163]

[0164]

[0165] As shown in Table 3, the gelation time is significantly shortened in an acidic environment, especially at pH = 2, where gelation occurs almost instantly. At pH = 4, the gelation time is significantly shorter than the 5.7 min in a neutral pH environment. This suggests that the acidic environment accelerates the formation of the Schiff base. Furthermore, it can be seen that while the reaction time in an alkaline environment is longer than that in an acidic environment, it is still shorter than that in a neutral environment, indicating that alkaline conditions also favor rapid reaction. This shortening of the reaction time may be attributed to the presence of a large number of aldehyde groups and entanglements of molecular chains in ODSA, which favors the reaction between aldehyde groups and amino groups in acidic and alkaline environments, thereby accelerating the gelation of the entire system. It is worth noting that although hydrogels can form under acidic conditions, the resulting hydrogels lack long-term stability and degrade very rapidly, with the gel network collapsing within a short period of time to form a mixed solution.

[0166] The gel mechanical properties of the composite hydrogels of Examples 1 to 6 and Comparative Examples 1 to 3 were tested. The test results are shown in Table 4.

[0167] The test method is as follows: the composite hydrogel is molded into a cylindrical gel with a diameter of 25 mm and a height of 20 mm in a vial. The mechanical properties of the hydrogel are tested using a compression method. The test is conducted at room temperature (25°C) and the compression speed is fixed at 2 mm / min. Before the test, a thin layer of silicone oil is applied to the surface of the hydrogel to prevent excessive evaporation of water inside the hydrogel during the test. The compressive stress and compressive strain are calculated using formulas (5) and (6).

[0168] The compressive stress is defined as the compressive load divided by the original cross-sectional area of ​​the specimen and is calculated using formula (5).

[0169]

[0170] In formula (5), P is the compressive stress, in Pa; F is the force applied to produce the compressive strain, in N; S is the initial cross-sectional area of ​​the sample, in m 2 .

[0171] The compressive strain is defined as the ratio of the change in the sample's compressed length to the sample's initial length. The gel strain is calculated using formula (6).

[0172]

[0173] In formula (6), ε is the compressive strain, in %, ΔL is the change in the compressed length of the sample, in m, and L0 is the initial length of the sample, in m.

[0174] Table 4

[0175]

[0176] As shown in Table 4, the introduction of an agar network significantly improves the compressive strength of the composite hydrogel. Comparing the compression performance data of Example 4 with that of Comparative Example 2, the dual-network gel formed by introducing 2% agar into a 2% ODSA-2% CMCS network achieves a maximum compressive stress of 210 kPa, a fourfold increase in strength compared to the ODSA-CMCS network gel, while maintaining a maximum strain of 62%. Analysis suggests that the agar network in the dual-network gel provides more strength, while the ODSA-CMCS network provides more strain. This coordinated effect of the dual networks results in the dual-network composite hydrogel exhibiting both high compressive strength and high compressive strain.

[0177] The self-healing performance of the composite hydrogel of Example 4 was tested. The test results are shown in Figure 7 .

[0178] The test method is as follows: the composite hydrogel provided in Example 4 is cut into two halves, one half is dyed purple, and the cut ends are placed together naturally. After 24 hours, one half of the gel is lifted to observe whether it has healed.

[0179] Depend on Figure 7 It can be seen that the composite hydrogel undergoes self-healing, which is mainly due to the dynamic effect of Schiff base. Schiff base can react spontaneously, so the self-healing phenomenon occurs. If it is under acidic conditions or some acidic aqueous solution is sprayed on the incision, the healing will be faster and better.

[0180] The above is a detailed introduction to the technical solutions provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A composite hydrogel, characterized in that It includes oxidized sodium alginate, carboxymethyl chitosan and agar; among which, The polymerization unit of the oxidized sodium alginate is: The polymerization unit of the carboxymethyl chitosan is:

2. The composite hydrogel according to claim 1, characterized in that In the composite hydrogel, the mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is (1-3): (1-3): (1-3); The composite hydrogel has a double network structure.

3. A method for preparing a composite hydrogel, characterized in that: The steps include: Provided are oxidized sodium alginate, carboxymethyl chitosan, and agar; wherein the polymerization unit of the oxidized sodium alginate is: The polymerization unit of the carboxymethyl chitosan is: The oxidized sodium alginate, the carboxymethyl chitosan and the agar are mixed and reacted to obtain a composite hydrogel.

4. The preparation method according to claim 3, characterized in that The preparation method of the oxidized sodium alginate comprises: Providing a sodium alginate dispersion, wherein the sodium alginate dispersion comprises sodium alginate and a first solvent; Sodium periodate and ethylene glycol are added to the sodium alginate dispersion to react and obtain oxidized sodium alginate.

5. The preparation method according to claim 4, characterized in that The first solvent is selected from water; and / or, In the sodium alginate dispersion, the mass concentration of the sodium alginate is 2% w / v to 8% w / v; and / or, The molar ratio of the polymerized units of sodium alginate to the sodium periodate is 1:(0.2-2); and / or, The mass ratio of the sodium alginate to the ethylene glycol is (2-8):

2.

6. The preparation method according to claim 4, characterized in that The reaction of sodium alginate, sodium periodate and ethylene glycol includes: adding sodium periodate to carry out a first reaction; adding ethylene glycol to carry out a second reaction; wherein, The first reaction time is 20h to 28h; and / or, The first reaction is carried out in the dark; and / or, The second reaction time is 0.5h to 2h; and / or, After the sodium alginate, the sodium periodate and the ethylene glycol react, the method further comprises: performing a first dialysis; the first dialysis lasts for 2 to 4 days, and the water change time for the first dialysis is 5 to 10 hours per time.

7. The preparation method according to claim 3, characterized in that The preparation method of the carboxymethyl chitosan comprises: providing a sodium hydroxide solution and chitosan, mixing them, and freezing them to obtain an intermediate product; The intermediate product and the second solvent are mixed, chloroacetic acid is added, and the mixture is reacted to obtain carboxymethyl chitosan.

8. The preparation method according to claim 7, characterized in that The mass fraction of the sodium hydroxide solution is 20% to 80%; and / or, The mass volume ratio of the chitosan and the sodium hydroxide solution is (2-5) g:20 mL; and / or, The mixing of the sodium hydroxide solution and the chitosan is carried out in an ice-water bath; and / or, The freezing time is 20h to 28h; and / or, The second solvent is selected from one or more of isopropanol, ethanol, and butanol; and / or, The mass volume ratio of the chitosan and the second solvent is (2-5) g:100 mL; and / or, The mass ratio of the chitosan to the chloroacetic acid is (2-5):10; and / or, The reaction of the intermediate product and the chloroacetic acid is carried out in an oil bath; and / or, The reaction temperature of the intermediate product and the chloroacetic acid is 50° C. to 100° C.; the reaction time of the intermediate product and the chloroacetic acid is 5 h to 10 h; and / or, After the intermediate product reacts with the chloroacetic acid, the method further comprises: performing a second dialysis; the second dialysis lasts for 3 to 8 days, and the water change time for the second dialysis is 5 to 10 hours per time.

9. The preparation method according to claim 3, characterized in that The mass ratio of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is (1-3): (1-3): (1-3); and / or, The reaction temperature of the oxidized sodium alginate, the carboxymethyl chitosan and the agar is 50° C. to 60° C.

10. Use of the composite hydrogel according to any one of claims 1 to 2, or the composite hydrogel prepared by the preparation method according to any one of claims 3 to 9 in biomedical materials.

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