Hyaluronic acid modified graphene nanosheet, conductive sponge and preparation method and application thereof

Abstract

The invention relates to a hyaluronic acid modified graphene nanosheet, a conductive sponge and a preparation method and application thereof. The modified graphene nanosheet comprises a graphene nanosheet and a hyaluronic acid-based azobenzene polymer, the hyaluronic acid-based azobenzene polymer comprises a hyaluronic acid main chain and a side group containing an azobenzene structure, and the hyaluronic acid-based azobenzene polymer is adsorbed on the surface of the graphene nanosheet. The conductive sponge comprises hyaluronic acid, polyurethane and the modified graphene nanosheet. The modified graphene nanosheet disclosed by the invention has excellent dispersity and biocompatibility, and can be used for conductive sponge. The conductive sponge disclosed by the invention has excellent biocompatibility, conductivity and sensitivity of resistance to pressure change.

Description

Technical Field

[0001] The present invention belongs to the technical fields of composite materials and signal sensing, and particularly relates to a hyaluronic acid-modified graphene nanosheet, a conductive sponge, and a preparation method and application thereof. Background Art

[0002] Wearable pressure sensing elements play a crucial role in fields such as human motion monitoring and health monitoring, and have thus received extensive attention. Its principle is to convert pressure signals applied by the human body, such as joint bending, heartbeat, breathing, etc., into changes in electrical signals such as resistance, thereby realizing the digital direct monitoring of these human signals. Wearable sensing pressure elements not only need to have sensitive signal sensing, but also need to have good biocompatibility due to possible direct contact with the human body. Common pressure sensing materials include conductive sponges, conductive gels, etc.

[0003] Polyurethane is a common polymer with high elasticity and has a wide range of applications in the preparation of high resilience materials. Polyurethane sponge is a common substrate for conductive sponges.

[0004] The large specific surface area and excellent electrical conductivity of graphene nanosheets make them have potential applications as conductive media in conductive sponges. However, due to their large specific surface area, it is difficult for them to be dispersed in aqueous solutions. When directly preparing conductive sponges, the conductivity is poor and the composite with the sponge is not firm. Usually, covalent / non-covalent modification is required to make them dispersible in solutions, and then the preparation of conductive sponges can be realized.

[0005] For example, Patent Document 1 discloses an rGO / PU conductive sponge and a preparation method thereof. By dispersing graphene oxide in water, fully mixing it with a PU sponge, adding a certain mass of ascorbic acid to form a mixed solution, and then heating and reacting the mixed solution, cooling, freezing, and then heating and reacting again, the rGO / PU conductive sponge is obtained.

[0006] Patent Document 2 discloses a chitosan-based three-dimensional porous conductive sponge and a preparation method and application thereof. By uniformly mixing conductive carbon black, conductive graphite, and chitosan in a solution, adding a pore-forming agent, freeze-drying, and washing to neutral, a chitosan-based three-dimensional porous conductive sponge is obtained.

[0007] Hyaluronic acid is a polysaccharide polymer with good biocompatibility and biodegradability in vivo. With the development of hyaluronic acid fermentation production technology, the price of hyaluronic acid has become increasingly low, and it has a wide range of applications in drug sustained-release materials, beauty and makeup materials, etc.

[0008] Cited Literature:

[0009] Patent Document 1: CN115010985A

[0010] Patent Document 2: CN114447346A Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In the conductive sponge of Patent Document 1, the composite firmness of graphene and the PU sponge is still insufficient, and there is still room for improvement in terms of biocompatibility, conductivity, and the sensitivity of resistance to pressure changes.

[0013] In Patent Document 2, an acid is required to dissolve chitosan, so subsequent washing is also needed. In addition, this method also requires a pore-forming agent, and the process is cumbersome.

[0014] An object of the present invention is to provide a modified graphene nanosheet, which has excellent dispersibility and biocompatibility and can be used as a conductive material for a conductive sponge.

[0015] Another object of the present invention is to provide a conductive sponge having excellent biocompatibility, conductivity, and sensitivity of resistance to pressure changes.

[0016] The object of the present invention is also to provide a preparation method and use of the above-mentioned modified graphene nanosheet and conductive sponge.

[0017] Solutions for Solving the Problems

[0018] In view of the above problems, the inventors of the present invention have conducted long-term and in-depth research and proposed: modifying graphene nanosheets with a hyaluronic acid-based azobenzene polymer to improve their dispersibility, biocompatibility, and composite firmness with the conductive sponge substrate, and introducing hyaluronic acid into the substrate of the conductive sponge to improve its biocompatibility, thereby completing the present invention.

[0019] Specifically, the present invention solves the problems of the present invention through the following solutions.

[0020] [1] A modified graphene nanosheet, which comprises graphene nanosheets and a hyaluronic acid-based azobenzene polymer, the hyaluronic acid-based azobenzene polymer comprises a hyaluronic acid main chain and a side group containing an azobenzene structure, and the hyaluronic acid-based azobenzene polymer is adsorbed on the surface of the graphene nanosheets.

[0021] [2] The modified graphene nanosheet according to [1], wherein the content of the graphene nanosheets is 30-70% by mass, and the content of the hyaluronic acid-based azobenzene polymer is 30-70% by mass.

[0022] [3]The modified graphene nanosheets according to [1] or [2], wherein in the hyaluronic acid-based azobenzene polymer, based on the total molar amount of the disaccharide units of the hyaluronic acid main chain, the amount of the disaccharide units having a side group containing an azobenzene structure is 10 to 90 mol%, preferably 20 to 80 mol%, more preferably 30 to 70 mol%; the weight-average molecular weight of the hyaluronic acid-based azobenzene polymer is 300,000 to 600,000;

[0023] The diameter of the graphene nanosheets is 1 to 10 μm, and the thickness is 1 to 10 nm.

[0024] [4]The method for preparing the modified graphene nanosheets according to any one of [1] to [3], which comprises the following steps:

[0025] Self-assembly: Mix the hyaluronic acid-based azobenzene polymer, graphene nanosheets and an organic solvent to obtain a mixed solution A, and then add water to the mixed solution A to obtain a self-assembly system;

[0026] Dialysis: Dialyze the self-assembly system to remove the organic solvent therein to obtain a dialysis system;

[0027] Freeze-drying: Perform freeze-drying on the dialysis system to obtain the modified graphene nanosheets.

[0028] [5]A conductive sponge, which comprises hyaluronic acid, polyurethane and the modified graphene nanosheets according to any one of [1] to [3].

[0029] [6]The conductive sponge according to [5], wherein, based on the total mass of the conductive sponge, the content of the hyaluronic acid is 20 to 60%, the content of the polyurethane is 20 to 60%, and the content of the modified graphene nanosheets is 10 to 40%;

[0030] Preferably, the weight-average molecular weight of the hyaluronic acid is 800,000 to 1,000,000;

[0031] Preferably, the polyurethane is a waterborne polyurethane.

[0032] [7]The method for preparing the conductive sponge according to [5] or [6], which comprises the following steps:

[0033] (1) Disperse the modified graphene nanosheets in water to obtain an aqueous dispersion of the modified graphene nanosheets;

[0034] (2) Mix the aqueous dispersion of the modified graphene nanosheets, hyaluronic acid and the aqueous dispersion of polyurethane to obtain a raw material solution;

[0035] (3) Perform freeze-drying on the raw material solution to obtain the conductive sponge.

[0036] [8] The conductive sponge according to [7], wherein, in the aqueous dispersion of the modified graphene nanosheets, the mass ratio of the modified graphene nanosheets to water is (3 to 15):1000; the solid content of the aqueous dispersion of the polyurethane is 40 to 80% by mass; the pressure of the freeze-drying is 1 to 100 Pa, the temperature is -10 to -20 °C, and the drying time is 60 to 150 hours.

[0037] [9] Use of the conductive sponge according to [5] or [6] for pressure sensing.

[0038]

[10] A wearable pressure sensing element, which comprises the conductive sponge according to [5] or [6].

[0039] Effects of the invention

[0040] The modified graphene nanosheets of the present invention have excellent dispersibility and biocompatibility and can be used for conductive sponges.

[0041] The conductive sponge of the present invention has excellent biocompatibility, conductivity, and sensitivity of resistance to pressure change.

[0042] The preparation method of the present invention has simple process, mild conditions, low cost, and is green and environmentally friendly. Description of the drawings

[0043] Figure 1 It is a synthetic route diagram of the hyaluronic acid-based carboxyazobenzene polymer used in the examples.

[0044] Figure 2 It is an ultraviolet-visible light absorption spectrogram of HA-Azo-COOH and graphene nanosheets before and after self-assembly in Example 1.

[0045] Figure 3 It is a thermogravimetric analysis result diagram of HA-Azo-COOH and graphene nanosheets as raw materials in Example 1 and the modified graphene nanosheets obtained in Example 1.

[0046] Figure 4 It is an SEM diagram of the cross section of the conductive sponge of Example 2.

[0047] Figure 5 It is an SEM diagram of the cross section of the conductive sponge of Example 3.

[0048] Figure 6 It is the test result of the resilience and the sensitivity of the resistance to pressure change of the conductive sponge of Example 2.

[0049] Figure 7 It is the test result of the resilience and the sensitivity of the resistance to pressure change of the conductive sponge of Example 3.

[0050] Figure 8 It is a photo of the pressure sensing test of the conductive sponge in Example 3.

[0051] Figure 9 It is the pressure sensing test result of the conductive sponge in Example 3. Detailed Implementation Modes

[0052] Hereinafter, the content of the present invention will be described in detail. The description of the technical features recorded below is based on representative implementation modes and specific examples of the present invention, but the present invention is not limited to these implementation modes and specific examples.

[0053] <Terms and Definitions>

[0054] In this specification, the term "alkyl" includes linear, branched or cyclic alkyl, unless otherwise explicitly stated.

[0055] In this specification, the numerical range expressed as "numerical value A to numerical value B" means a range including the endpoint numerical values A and B.

[0056] In this specification, the numerical range expressed as "above" or "below" means a numerical range including this number.

[0057] In this specification, the meaning expressed by "can" includes the meanings of both performing a certain process and not performing a certain process.

[0058] In this specification, the use of "optionally" or "optional" means that certain substances, components, execution steps, applied conditions and other factors are used or not used.

[0059] In this specification, the unit names used are all international standard unit names, and unless otherwise specified, the "%" used represents weight or mass percentage content.

[0060] In this specification, the "preferred implementation modes", "implementation modes" and the like mentioned refer to that the specific elements (for example, features, structures, properties and / or characteristics) related to the implementation mode are included in at least one of the implementation modes described herein, and may exist in other implementation modes or may not exist in other implementation modes. In addition, it should be understood that the elements can be combined in various implementation modes in any suitable manner.

[0061] 《Modified Graphene Nanosheets》

[0062] The object of the present invention is to provide a modified graphene nanosheet, which comprises graphene nanosheets and a hyaluronic acid-based azobenzene polymer, the hyaluronic acid-based azobenzene polymer comprises a hyaluronic acid main chain and side groups containing azobenzene structures, and the hyaluronic acid-based azobenzene polymer is adsorbed on the surface of the graphene nanosheets.

[0063] In the modified graphene nanosheets of the present invention, the azobenzene structure in the side chain of the hyaluronic acid-based azobenzene polymer has a large conjugated structure, which binds to the surface of the graphene nanosheets through π-π interactions, thereby endowing the modified graphene nanosheets of the present invention with excellent dispersibility and biocompatibility.

[0064] More specifically, the hyaluronic acid-based azobenzene polymer is physically adsorbed on the surface of the graphene nanosheets.

[0065] In some embodiments, in the modified graphene nanosheets of the present invention, the content of the graphene nanosheets is 30-70% by mass, preferably 40-60% by mass, more preferably 45-55% by mass.

[0066] In some embodiments, in the modified graphene nanosheets of the present invention, the content of the hyaluronic acid-based azobenzene polymer is 30-70% by mass, preferably 40-60% by mass, more preferably 45-55% by mass.

[0067] <Graphene nanosheets>

[0068] In the present invention, there is no particular limitation on the graphene nanosheets, and they can be graphene nanosheets known in the art. For example, in terms of the number of layers, they can be single-layer, few-layer, and multi-layer graphene nanosheets. In terms of the preparation method, they can be mechanically exfoliated graphene, chemical vapor deposition (CVD) graphene, liquid-phase exfoliated graphene, electrochemically exfoliated graphene, etc.

[0069] Preferably, the graphene nanosheets are graphene nanosheets that have not been chemically modified and / or functionalized, and they are composed essentially of only carbon elements.

[0070] Preferably, the graphene nanosheets are few-layer or multi-layer graphene nanosheets, and the number of layers is 2-30 layers, preferably 3-20 layers, more preferably 4-15 layers.

[0071] From the perspective of being used for a conductive sponge, the sheet diameter of the graphene nanosheets is preferably 1-10 μm, more preferably 1-5 μm; the thickness is preferably 1-10 nm, more preferably 1-7 nm.

[0072] <Hyaluronic acid-based azobenzene polymer>

[0073] In the present invention, the hyaluronic acid-based azobenzene polymer comprises a hyaluronic acid main chain and side chains containing azobenzene structures. Preferably, the side chains containing azobenzene structures are directly or via a linking group linked to residues derived from hydroxyl or carboxyl groups in the hyaluronic acid main chain.

[0074] For the linking group, there is no particular limitation in the present invention. From the perspective of easy synthesis, the linking group can be *-NR 0 R00 -#, where R 0 represents C 1-6 alkyl, and R 00 represents C 1-10 alkylene. The bond with * represents the bond connected to the benzene ring of azobenzene, and the bond with # represents the bond connected to the residue derived from hydroxyl or carboxyl in the hyaluronic acid main chain, preferably connected to the oxygen atom in the residue (-O-CO-) derived from carboxyl.

[0075] In some embodiments, the benzene ring of the azobenzene structure is optionally substituted with substituents selected from one or more of C 1-6 alkyl, carboxyl, nitro, and hydroxyl, preferably carboxyl.

[0076] Preferably, in the hyaluronic acid-based azobenzene polymer, based on the total number of moles of the disaccharide units in the hyaluronic acid main chain, the amount of the disaccharide units having side groups containing azobenzene structures is 10-90 mol%, preferably 20-80 mol%, more preferably 30-70 mol%.

[0077] In the present invention, the hyaluronic acid-based azobenzene polymer has the following structure:

[0078]

[0079] Among them, a% represents the mole percentage of the disaccharide units having side groups containing azobenzene structures in the parentheses, and (100 - a)% represents the mole percentage of the disaccharide units not having side groups containing azobenzene structures, based on 100% of the total number of moles of the disaccharide units in the hyaluronic acid main chain.

[0080] Preferably, the weight-average molecular weight of the hyaluronic acid-based azobenzene polymer is 300,000-600,000.

[0081] In the present invention, the hyaluronic acid-based azobenzene polymer can be prepared according to the methods described in the published literature or methods similar thereto. The published literature is, for example, Li H T, Qiao G, Zhang W L, et al. Hyaluronic AcidBased Azo Polymer: Synthesis, Characterization, and Photo-Responsiveness[J]. Macromol Chem Phys, 2023, 224(20): 2300194, etc.

[0082] Specifically, the preparation method of the hyaluronic acid-based azobenzene polymer includes the following steps:

[0083] (a) React hyaluronic acid with tetrabutylammonium hydroxide to obtain a hyaluronic acid-based tetrabutylammonium salt;

[0084] (b) Esterify N-alkyl-N-hydroxyalkyl aniline with p-toluenesulfonyl chloride to obtain N-alkyl-N-(alkyl p-toluenesulfonate) aniline;

[0085] (c) Perform a transesterification reaction between the hyaluronic acid-based tetrabutylammonium salt and N-alkyl-N-(alkyl p-toluenesulfonate) aniline to obtain hyaluronic acid modified with N-alkyl-N-hydroxyalkyl aniline;

[0086] (d) Diazotize the optionally substituted aniline, and then perform a diazo coupling reaction between the resulting diazonium salt and the hyaluronic acid modified with N-alkyl-N-hydroxyalkyl aniline to obtain a hyaluronic acid-based azobenzene polymer.

[0087] More specifically, in step (a), the reaction between hyaluronic acid and tetrabutylammonium hydroxide is carried out in water, for example, by mixing an aqueous solution of tetrabutylammonium hydroxide with an aqueous solution of hyaluronic acid. The reaction time of step (a) is preferably 12 to 36 hours, more preferably 18 to 30 hours. The reaction temperature of step (a) is preferably 10 to 40 °C, preferably 20 to 30 °C. In step (a), it is preferred to use an excess (e.g., 1 to 3 equivalents, preferably 2 equivalents) of tetrabutylammonium hydroxide, and after the reaction is completed, the excess tetrabutylammonium hydroxide is removed by dialysis, and then the product hyaluronic acid-based tetrabutylammonium salt (HA-TBA) is obtained by lyophilization.

[0088] More specifically, the esterification reaction in step (b) is preferably carried out in an organic solvent, such as one or more of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. The esterification reaction in step (b) is preferably carried out in the presence of a base catalyst, and the base catalyst can be, for example, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. The temperature of the esterification reaction is preferably -10 to 10 °C, preferably -5 to 5 °C, such as 0 to 3 °C. The reaction time of the esterification reaction is preferably 12 to 36 hours, more preferably 18 to 30 hours.

[0089] In step (b), it is preferred to obtain the product by cooling crystallization after the reaction is completed. The cooling crystallization can be carried out in petroleum ether, for example. Specifically, the reaction system can be added to petroleum ether for cooling crystallization, and the temperature of the cooling crystallization can be, for example, -10 to -30 °C (preferably -15 to -25 °C).

[0090] More specifically, the transesterification reaction in step (c) is preferably carried out in an organic solvent, such as one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide. The transesterification reaction in step (c) is preferably carried out in the presence of a catalyst, such as potassium carbonate, sodium carbonate, etc. The time of the transesterification reaction is preferably 40 to 100 hours, more preferably 60 to 80 hours. The temperature of the transesterification reaction is preferably 20°C to 40°C, preferably 25°C to 35°C.

[0091] In step (c), after the reaction is completed, it is preferred to pour the reaction solution into a mixed solvent of petroleum ether and ethyl acetate (volume ratio (0.8 to 1.2):1), then transfer the lower layer liquid to a dialysis bag for dialysis, and then lyophilize the liquid in the dialysis bag after dialysis to obtain the product.

[0092] More specifically, in step (d), the diazotization reaction is carried out by adding hydrochloric acid and sodium nitrite to an aqueous solution of optionally substituted aniline and sodium hydroxide to obtain an aqueous diazonium salt solution. The diazotization reaction is preferably carried out at a temperature of -10 to 10°C, preferably -5 to 5°C, such as 0 to 3°C. Preferably, the obtained aqueous diazonium salt solution is added to a solution of N-alkyl-N-hydroxyalkyl aniline-modified hyaluronic acid (such as a dimethyl sulfoxide solution) to carry out the diazo coupling reaction.

[0093] In step (d), after the diazo coupling reaction is completed, it is preferred to pour the reaction solution into a mixed solvent of petroleum ether and ethyl acetate (volume ratio (0.8 to 1.2):1), then transfer the lower layer liquid to a dialysis bag for dialysis, and then lyophilize the liquid in the dialysis bag after dialysis to obtain the product.

[0094] In a specific embodiment, the preparation method of the hyaluronic acid-based azobenzene polymer is as follows:

[0095] An aqueous solution of tetrabutylammonium hydroxide is dropped into an aqueous solution of hyaluronic acid. After reacting for 24 hours, the excess tetrabutylammonium hydroxide is removed by dialysis, and after lyophilization, hyaluronic acid-based tetrabutylammonium salt (HA-TBA) is obtained;

[0096] N-ethyl-N-hydroxyethyl aniline and p-toluenesulfonyl chloride are dissolved in tetrahydrofuran. Under an ice-water bath, the esterification reaction is catalyzed by potassium hydroxide. After reacting for 24 hours, N-ethyl-N-(4-methylbenzenesulfonic acid ethyl ester) aniline (NBNE) is obtained by cooling crystallization in petroleum ether;

[0097] Dissolve HA-TBA and NBNE in dimethyl sulfoxide solution. Catalyze the transesterification reaction with potassium carbonate. After reacting for 72 hours, pour the reaction solution into a mixed solution of petroleum ether and ethyl acetate. Transfer the lower layer liquid to a dialysis bag, and after dialysis, lyophilize to obtain hyaluronic acid modified with N-ethyl-N-hydroxyethylaniline (HA-NE).

[0098] Dissolve p-aminobenzoic acid and sodium hydroxide in an aqueous solution under an ice-water bath. Add hydrochloric acid and sodium nitrite to it successively to obtain an aqueous solution of diazonium salt. Drop the aqueous solution of diazonium salt into the dimethyl sulfoxide solution of HA-NE for diazo coupling reaction. Pour the reaction solution into a mixed solution of petroleum ether and ethyl acetate. Transfer the lower layer liquid to a dialysis bag, and after dialysis, lyophilize to obtain a hyaluronic acid-based azobenzene polymer (HA-Azo-COOH).

[0099] "Preparation Method of Modified Graphene Nanosheets"

[0100] The purpose of the present invention is to provide a preparation method of the modified graphene nanosheets of the present invention, which includes the following steps:

[0101] Self-assembly: Mix the hyaluronic acid-based azobenzene polymer, graphene nanosheets and an organic solvent to obtain a mixed solution A, and then add water to the mixed solution A to obtain a self-assembly system;

[0102] Dialysis: Dialyze the self-assembly system to remove the organic solvent therein to obtain a dialysis system;

[0103] Lyophilization: Freeze-dry the dialysis system to obtain the modified graphene nanosheets.

[0104] Self-assembly

[0105] In the present invention, by mixing the hyaluronic acid-based azobenzene polymer, graphene nanosheets and an organic solvent to obtain a mixed solution A, and then adding water to the mixed solution A, the hyaluronic acid-based azobenzene polymer and the graphene nanosheets are self-assembled through the π-π interaction and hydrophilic-hydrophobic interaction between the large conjugated structure of azobenzene on the hyaluronic acid-based azobenzene polymer and the large conjugated structure of graphene, so that the hyaluronic acid-based azobenzene polymer is adsorbed on the surface of the graphene nanosheets to form the modified graphene nanosheets of the present invention.

[0106] Preferably, the organic solvent is one or more selected from dimethyl sulfoxide, acetone, and N,N-dimethylformamide.

[0107] Preferably, the ratio of the mass (mg) of graphene nanosheets to the volume (mL) of the organic solvent is (1-3):1, preferably (1.5-2.5):1.

[0108] Preferably, the volume ratio of the organic solvent to water is 1:(1 - 3), preferably 1:(1.5 - 2.5).

[0109] For the smooth progress of self-assembly, it is preferred to add water continuously or batchwise to the mixture A within a water addition time of 0.5 - 3 hours.

[0110] Dialysis

[0111] In the present invention, the self-assembly system is dialyzed to remove the organic solvent therein.

[0112] Specifically, the self-assembly system is placed in a dialysis bag and then immersed in water for dialysis.

[0113] Preferably, the cut-off molecular weight of the dialysis bag is above 2000, preferably above 3000.

[0114] Preferably, the dialysis time is 1 - 5 days, preferably 2 - 4 days.

[0115] Preferably, within the dialysis time, water is changed every 6 - 18 hours, preferably every 10 - 14 hours.

[0116] Preferably, dialysis is carried out at room temperature, for example, at 20 - 30 °C.

[0117] Lyophilization

[0118] In the present invention, the dialysis system is freeze-dried to remove the water therein, obtaining the modified graphene nanosheets.

[0119] Preferably, the pressure of freeze-drying is 1 - 100 Pa, preferably 2 - 50 Pa, more preferably 3 - 20 Pa.

[0120] Preferably, the temperature of freeze-drying is -10 - -20 °C, preferably -12 - -18 °C.

[0121] Preferably, the drying time of freeze-drying is 60 - 150 hours, preferably 80 - 120 hours.

[0122] "Conductive Sponge"

[0123] An object of the present invention is to provide a conductive sponge, which comprises hyaluronic acid, polyurethane and the modified graphene nanosheets of the present invention.

[0124] In the conductive sponge of the present invention, the polyurethane structure and the hyaluronic acid / modified graphene nanosheets form an intertwined network-like three-dimensional structure. Specifically, the network structure of polyurethane presents a filamentous shape, while the network structure of hyaluronic acid / modified graphene nanosheets presents a porous and compact sponge-like shape, and the two cross through each other.

[0125] In the present invention, hyaluronic acid is introduced into the substrate of the conductive sponge, thereby endowing it with excellent biocompatibility. At the same time, hyaluronic acid and the modified graphene nanosheets interact through hydrogen bonds, so that the modified graphene nanosheets are firmly combined with the substrate of the conductive sponge.

[0126] In the present invention, polyurethane and hyaluronic acid are used together as the substrate of the conductive sponge to increase its resilience, which helps the sensitivity of the resistance of the conductive sponge to pressure changes.

[0127] Preferably, based on the total mass of the conductive sponge, the content of the hyaluronic acid is 20-50% by mass, preferably 22-40% by mass, more preferably 24-35% by mass.

[0128] Preferably, based on the total mass of the conductive sponge, the content of the polyurethane is 30-60%, preferably 32-55% by mass, more preferably 34-50% by mass.

[0129] Preferably, based on the total mass of the conductive sponge, the content of the modified graphene nanosheets is 10-45% by mass, preferably 15-40% by mass, more preferably 18-35% by mass.

[0130] The dosages of the above components can enable the conductive sponge to have good biocompatibility, resilience, conductivity and pressure sensitivity at the same time.

[0131] Preferably, the weight-average molecular weight of the hyaluronic acid is 800,000-1,000,000.

[0132] Preferably, the polyurethane is aqueous polyurethane, more preferably aliphatic polyurethane. More specifically, it is obtained by reacting an aliphatic diisocyanate, a polyol and an optional chain extender. The aliphatic diisocyanate is one or more selected from hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), hydrogenated phenylmethane diisocyanate (H12MDI). The polyol is one or more selected from polyether polyols, polyester polyols and polycarbonate polyols, preferably a diol. The polyether polyol is, for example, polyethylene glycol (PEG), polypropylene glycol (PPG), polytetrahydrofuran diol (PTMG), etc., the polyester polyol is, for example, polybutylene adipate (PBA), polylactic acid (PCL), etc., and the polycarbonate polyol is, for example, polycarbonate diol (PCDL). The chain extender is one or more selected from diamines, small molecule diols (molecular weight below 200), dihydroxycarboxylic acids, etc., and can be, for example, ethylene glycol, propylene glycol, butylene glycol, ethylenediamine (EDA), propylenediamine, dimethylolpropionic acid (DMPA), etc.

[0133] "Preparation Method of Conductive Sponge"

[0134] An object of the present invention is to provide a method for preparing the conductive sponge of the present invention, which comprises the following steps:

[0135] (1) Dispersing the modified graphene nanosheets in water to obtain an aqueous dispersion of the modified graphene nanosheets;

[0136] (2) Mixing the aqueous dispersion of the modified graphene nanosheets, hyaluronic acid, and the aqueous dispersion of polyurethane to obtain a raw material liquid;

[0137] (3) Subjecting the raw material liquid to freeze-drying to obtain the conductive sponge.

[0138] The present invention prepares the conductive sponge by the ice-templating method. This method directly uses water as the pore-forming agent and forms a three-dimensional network structure by freeze-drying.

[0139] The following separately describes in detail each step of the method for preparing the conductive sponge of the present invention.

[0140] Step (1)

[0141] In step (1), the modified graphene nanosheets are dispersed in water to obtain an aqueous dispersion of the modified graphene nanosheets.

[0142] Due to the excellent dispersibility of the modified graphene nanosheets of the present invention, they can be easily dispersed in water. In some embodiments, the modified graphene nanosheets are dispersed in water by applying ultrasonic waves. The present invention has no particular limitation on the ultrasonic time and intensity, as long as the modified graphene nanosheets can be uniformly dispersed.

[0143] Preferably, in the aqueous dispersion of the modified graphene nanosheets, the mass ratio of the modified graphene nanosheets to water is (3-15):1000, preferably (4-12):1000.

[0144] Step (2)

[0145] In step (2), the aqueous dispersion of the modified graphene nanosheets, hyaluronic acid, and the aqueous dispersion of polyurethane are mixed to obtain a raw material liquid.

[0146] Specifically, step (2) includes the following sub-steps:

[0147] (2-1) Mixing the aqueous dispersion of the modified graphene nanosheets with hyaluronic acid and dissolving the hyaluronic acid to obtain a mixed liquid B;

[0148] (2-2) Mixing the mixed liquid B with the aqueous dispersion of polyurethane to obtain a raw material liquid.

[0149] In some embodiments, in sub-step (2-1) and sub-step (2-2), the hyaluronic acid is dissolved by applying stirring.

[0150] In some embodiments, the solid content of the aqueous dispersion of polyurethane is 40 to 80% by mass, preferably 50 to 70% by mass.

[0151] Step (3)

[0152] In step (3), the raw material liquid is freeze-dried to obtain a conductive sponge.

[0153] Preferably, the pressure for freeze-drying is 1 to 100 Pa, preferably 2 to 50 Pa, more preferably 3 to 20 Pa.

[0154] Preferably, the temperature for freeze-drying is -10 to -20 °C, preferably -12 to -18 °C.

[0155] Preferably, the drying time for freeze-drying is 60 to 150 hours, preferably 80 to 120 hours.

[0156] The size of the pore diameter in the conductive sponge prepared by the ice-templating method mainly depends on the amount of water and the temperature during freezing. Generally, the lower the freezing temperature, the smaller the ice crystals formed, and thus the smaller the pore diameter of the obtained sponge.

[0157] Preferably, before the freeze-drying operation, the raw material liquid is pre-frozen in liquid nitrogen, and the temperature of the liquid nitrogen is between -196 °C and -210 °C. The extremely low temperature can promote the formation of small ice crystals, and a relatively uniform three-dimensional pore structure can be obtained in the freeze-dried conductive sponge.

[0158] The present invention also correspondingly relates to a conductive sponge prepared by the above method.

[0159] The present invention also relates to the use of the conductive sponge of the present invention for pressure sensing.

[0160] The present invention also relates to a wearable pressure sensing element comprising the conductive sponge of the present invention. Examples of wearable pressure sensing elements include pressure-mediated motion sensing elements, respiration sensing elements, etc.

[0161] Examples

[0162] Specific examples are listed below to further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content described in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present invention.

[0163] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0164] The materials, reagents, etc. used in the following examples can be obtained from commercial sources without special instructions.

[0165] The synthesis of the hyaluronic acid-based p-carboxyazobenzene polymer (HA-Azo-COOH) used in the following examples was carried out according to the method disclosed in the literature Li H T, Qiao G, Zhang W L, et al. Hyaluronic Acid Based Azo Polymer: Synthesis, Characterization, and Photo-Responsiveness [J]. Macromol Chem Phys, 2023, 224(20): 2300194. The reaction route diagram is as Figure 1 shown, and the specific method is as follows.

[0166] Synthesis of hyaluronic acid-based tetrabutylammonium salt (HA-TBA): Hyaluronic acid (relative molecular weight 400,000, 3.50 g) was completely dissolved in deionized water, and tetrabutylammonium hydroxide aqueous solution (22.00 g) was added thereto. After reacting for 24 hours, the reaction solution was transferred to a dialysis bag (3500), dialyzed for two days, and freeze-dried (vacuum degree 5 Pa, sample chamber -15 °C, cold trap -40 °C, freeze-drying time 100 hours) to obtain a white cotton-like solid hyaluronic acid-based tetrabutylammonium salt (HA-TBA, 4.47 g).

[0167] Synthesis of N-ethyl-N-(4-ethylbenzenesulfonate)aniline (NBNE): N-ethyl-N-hydroxyethylaniline (4.65 g) and p-toluenesulfonyl chloride (5.95 g) were fully dissolved in tetrahydrofuran (100 mL) in an ice-water bath, and potassium hydroxide solution (0.29 mg / mL, 10 mL) was added dropwise thereto. After reacting for 24 hours, the reaction solution was poured into petroleum ether (800 mL), the water in the mixed solution was extracted with saturated sodium chloride aqueous solution, and further dried with anhydrous magnesium sulfate. The dried solution was placed in a -30 °C refrigerator for cooling crystallization to obtain milky white needle-like crystals (NBNE, 7.03 g).

[0168] Synthesis of N-ethyl-N-hydroxyethylaniline modified hyaluronic acid (HA-NE): HA-TBA (2.40 g) was fully dissolved in dimethyl sulfoxide solution (110 mL). At room temperature, potassium carbonate powder (3.08 g) and NBNE (4.56 g) were added to the solution. After stirring the reaction system at room temperature for 48 hours, the mixed solution was poured into a mixed solution of petroleum ether and ethyl acetate (volume ratio 1:1) to extract dimethyl sulfoxide. The bottom layer solution was transferred to a dialysis bag (cut-off molecular weight 3500). After dialysis for 2 days, the reaction solution was freeze-dried (vacuum degree 5 Pa, sample chamber -15 °C, cold trap -40 °C, freeze-drying time 100 hours) to obtain a yellow cotton-like solid (HA-NE, 0.95 g).

[0169] Synthesis of hyaluronic acid-based p-carboxyazobenzene polymer (HA-Azo-COOH): p-Aminobenzoic acid (0.55 g) and sodium hydroxide (0.16 g) were fully dissolved in an aqueous solution (5 mL). Under an ice-water bath, concentrated hydrochloric acid (1.12 mL) was added to it. After the solution showed a white precipitate, an aqueous sodium nitrite solution (0.14 mg / mL, 2.4 mL) was added to obtain a pale yellow p-carboxy diazonium salt solution. The diazonium salt solution was dropped into a dimethyl sulfoxide solution of HA-NE (0.58 g). After reacting for 24 hours, the dark red reaction solution was poured into a mixed solution of petroleum ether and ethyl acetate (volume ratio 1:1) to extract the dimethyl sulfoxide solution and other impurities. The bottom layer solution was transferred to a dialysis bag (cut-off molecular weight 3500). After dialysis for two days, the solution in the dialysis bag was freeze-dried (vacuum degree 5 Pa, sample chamber -15 °C, cold trap -40 °C, freeze-drying time 100 hours) to obtain a red cotton-like solid (HA-Azo-COOH, 0.28 g).

[0170] Example 1

[0171] (1-1) HA-Azo-COOH (30 mg) and graphene nanosheets (sheet diameter 1 - 3 μm, thickness 1 - 5 nm, 30 mg) were ultrasonically mixed in dimethyl sulfoxide (15 mL) to obtain a mixed solution A.

[0172] (1-2) Deionized water (30 mL) was dropped into the mixed solution A at a rate of 20 mL / h, enabling HA-Azo-COOH and graphene nanosheets to self-assemble through π-π interaction and hydrophilic-hydrophobic interaction to obtain a self-assembly system.

[0173] (1-3) The mixed solution after adding water was transferred to a dialysis bag (cut-off molecular weight 3500) for dialysis treatment. The water was changed every 12 hours during dialysis for 3 days. The mixture in the dialysis bag was the dialysis system.

[0174] (1-4) The dialysis system was lyophilized (vacuum degree 5 Pa, sample chamber -15 °C, cold trap -40 °C, lyophilization time 100 hours) to obtain modified graphene nanosheets.

[0175] <Evaluation and Analysis>

[0176] The mixed solution A obtained in step (1-1) and the self-assembly system obtained after adding water in step (1-2) were filtered through a filter membrane made of polyethersulfone material with a pore size of 0.22 microns, and the ultraviolet-visible absorption spectrum of the filtrate was measured, as Figure 2 shown. It can be seen from Figure 2 that the hyaluronic acid-based azobenzene polymer has basically been completely adsorbed on the surface of the graphene nanosheets.

[0177] The HA-Azo-COOH used as a raw material in Example 1, the graphene nanosheets, and the modified graphene nanosheets obtained in Example 1 were subjected to thermogravimetric analysis, as Figure 3 shown. By calculating the thermogravimetric ratios of HA-Azo-COOH, graphene nanosheets, and modified graphene nanosheets during the heating process, the modification ratio of HA-Azo-COOH to graphene nanosheets was found to be 92%.

[0178] Example 2

[0179] (2-1) The modified graphene nanosheets (15 parts) obtained in Example 1 were ultrasonicated in water (3000 parts) for 1 hour to make them uniformly dispersed in the aqueous solution, obtaining an aqueous dispersion of modified graphene nanosheets.

[0180] (2-2) In the aqueous dispersion of modified graphene nanosheets, hyaluronic acid (20 parts) was added and dissolved thoroughly by stirring.

[0181] (2-3) To the mixed solution obtained in step (2-2), an aqueous dispersion of polyurethane (Shanghai Macklin Biochemical Co., Ltd., product number W909579-100g, solid content 60%, 50 parts) was added, and after thorough stirring, it was mixed evenly to obtain a raw material solution.

[0182] (2-4) The raw material solution obtained in step (2-3) was poured into a mold, frozen with liquid nitrogen, and lyophilized (vacuum degree 5 Pa, sample chamber -15 °C, cold trap -40 °C, lyophilization time 100 hours) to obtain a conductive sponge.

[0183] Example 3

[0184] Except for using 25 parts of the modified graphene nanosheets obtained in Example 1, a conductive sponge was obtained in the same manner as in Example 2.

[0185] <Evaluation and Analysis>

[0186] Observation of cross-sectional morphology

[0187] The conductive sponges of Example 2 and Example 3 were cut and adhered to conductive tapes. The cut surfaces were sputter-coated with gold for 60 s, and SEM images of the cross-sections of the conductive sponges of Example 2 and Example 3 were obtained using a Hitachi SU 8600 cold field emission scanning electron microscope (acceleration voltage 5 kV), as shown in Figure 4 and Figure 5 respectively. From Figure 4 and Figure 5 , it can be seen that the polyurethane structure and hyaluronic acid / modified graphene nanosheets form an intertwined network-like three-dimensional structure.

[0188] Test of resilience and sensitivity of resistance to pressure change

[0189] Test method: Weights of different masses (10 g, 20 g, 50 g, 100 g) were placed on the conductive sponge. Based on the weight of the weights and the force-bearing area of the conductive sponge (1.57 cm 2 ), the pressures applied to the conductive sponge (0.5 kPa, 1 kPa, 2.5 kPa, and 5 kPa) were calculated, and a resistivity meter (KEITHLEY DMM7510 7 1 / 2Digit Multimeter) was used to record the change in the resistance of the conductive sponge before and after the weights were placed.

[0190] The conductive sponges of Example 2 and Example 3 were tested according to the above method, and the results are shown in Figure 6 and Figure 7 respectively, where R0 is the original resistance of the conductive sponge and ΔR is the difference in resistance relative to the original resistance after the pressure is applied. From Figure 6 and Figure 7 , it can be seen that the resistance of the conductive sponges of Example 2 and Example 3 decreases as the pressure increases, and they have good resilience.

[0191] Pressure sensing test

[0192] As shown in Figure 8 , the two ends of the conductive sponge of Example 3 (length: 1.5 cm, width: 1.2 cm, height: 0.4 cm) were connected to wires, which were then connected to a resistivity meter, and it was adhered to the finger joint with tape. When the finger flexed and extended, the change in the resistance in the resistivity meter was recorded. As shown in Figure 9 , when the finger flexed and extended, the bending of the joint caused a change in the pressure on the conductive sponge, and the resistance of the conductive sponge changed significantly with high sensitivity. This indicates that the conductive sponge of the present invention can be used as a wearable pressure sensing element.

[0193] The above embodiments are the implementation schemes and applications with better experimental effects of the present invention. However, without departing from the concept of the present invention, obvious replacements are within the protection scope of the present invention.

[0194] Industrial applicability

[0195] The modified graphene nanosheets of the present invention can be widely used as conductive materials in conductive sponges, and the conductive sponges of the present invention have wide applications in wearable pressure sensing elements.

Claims

1. A modified graphene nanosheet, characterized in that, It contains graphene nanosheets and a hyaluronic acid-based azobenzene polymer. The hyaluronic acid-based azobenzene polymer contains a hyaluronic acid main chain and side groups containing azobenzene structures, and the hyaluronic acid-based azobenzene polymer is adsorbed on the surface of the graphene nanosheets.

2. The modified graphene nanosheet according to claim 1, wherein The content of the graphene nanosheets is 30 to 70% by mass, and the content of the hyaluronic acid-based azobenzene polymer is 30 to 70% by mass.

3. The modified graphene nanosheet according to claim 1 or 2, characterized in that, In the hyaluronic acid-based azobenzene polymer, based on the total molar number of disaccharide units of the hyaluronic acid main chain, the amount of disaccharide units having side groups containing azobenzene structures is 10 to 90 mol%, preferably 20 to 80 mol%, more preferably 30 to 70 mol%; the weight average molecular weight of the hyaluronic acid-based azobenzene polymer is 300,000 to 600,000; The sheet diameter of the graphene nanosheets is 1 to 10 μm, and the thickness is 1 to 10 nm.

4. The preparation method of the modified graphene nanosheets according to any one of claims 1 to 3, characterized in that, It includes the following steps: Self-assembly: Mix the hyaluronic acid-based azobenzene polymer, graphene nanosheets and an organic solvent to obtain a mixed solution A, and then add water to the mixed solution A to obtain a self-assembly system; Dialysis: Dialyze the self-assembly system to remove the organic solvent therein to obtain a dialysis system; Freeze-drying: Freeze-dry the dialysis system to obtain the modified graphene nanosheets.

5. A conductive sponge, characterized in that, It contains hyaluronic acid, polyurethane and the modified graphene nanosheets according to any one of claims 1 to 3.

6. The conductive sponge according to claim 5, wherein, Based on the total mass of the conductive sponge, the content of the hyaluronic acid is 20 to 60%, the content of the polyurethane is 20 to 60%, and the content of the modified graphene nanosheets is 10 to 40%; Preferably, the weight average molecular weight of the hyaluronic acid is 800,000 to 1,000,000; Preferably, the polyurethane is a waterborne polyurethane.

7. The preparation method of the conductive sponge according to claim 5 or 6, characterized in that, It includes the following steps: (1) Disperse the modified graphene nanosheets in water to obtain an aqueous dispersion of the modified graphene nanosheets; (2) Mix the aqueous dispersion of the modified graphene nanosheets, hyaluronic acid and an aqueous dispersion of polyurethane to obtain a raw material solution; (3) Freeze-dry the raw material solution to obtain the conductive sponge.

8. The electrically conductive sponge according to claim 7, characterized in that In the aqueous dispersion of the modified graphene nanosheets, the mass ratio of the modified graphene nanosheets to water is (3 to 15):1000; the solid content of the aqueous dispersion of the polyurethane is 40 to 80% by mass; the pressure for freeze-drying is 1 to 100 Pa, the temperature is -10 to -20 °C, and the drying time is 60 to 150 hours.

9. Use of the conductive sponge according to claim 5 or 6 for pressure sensing.

10. A wearable pressure sensing element, characterized in that, It contains the conductive sponge according to claim 5 or 6.

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