Single-walled carbon nanotube composite hydrogel and preparation, recovery method and application thereof

Abstract

This invention relates to an ion strength-responsive, self-dissolving single-walled carbon nanotube composite hydrogel, its preparation, recycling methods, and applications, belonging to the fields of biomedical polymer materials, photothermal therapy materials, flexible temperature sensing materials, and nanofiller recycling technology. The hydrogel comprises an anionic polysaccharide matrix, single-walled carbon nanotubes, and divalent zinc ions. The anionic polysaccharide matrix includes carboxymethyl cellulose and sodium alginate; the divalent zinc ions form dynamic coordination bonds with the carboxyl groups in the anionic polysaccharide matrix; the single-walled carbon nanotubes are dispersed in a three-dimensional hydrogel network. The hydrogel maintains its gel morphology in a physiologically isotonic medium and swells and self-dissolves in a low-ionic-strength aqueous medium, forming a mixture containing single-walled carbon nanotubes; further centrifugation, washing, and drying are used to obtain the recovered single-walled carbon nanotubes. This invention can balance structural stability, temperature feedback capability, trigger clearance, and the recycling of single-walled carbon nanotubes during the photothermal process.

Description

Technical Field

[0001] This invention belongs to the technical fields of biomedical polymer materials, photothermal therapy materials, flexible temperature sensing materials and nanofiller recycling technology, specifically involving an ion strength-responsive self-dissolving single-walled carbon nanotube composite hydrogel and its preparation, recycling method and application. Background Technology

[0002] Photothermal therapy (PTT), as a minimally invasive tumor treatment strategy, converts light energy into heat energy through photothermal agents to induce tumor cell apoptosis. However, existing PTT material systems face three major challenges in practical clinical translation: First, there is a contradiction between the "stability" and "degradability" of implantable materials.

[0003] Ideally, PTT materials should maintain structural integrity during treatment (usually 20-40 minutes) to ensure accurate photothermal agent positioning and good sensor contact. However, they should degrade rapidly after treatment to avoid long-term foreign body reactions or the need for secondary surgery for removal. Existing covalently cross-linked hydrogels (such as polyacrylamide and chemically cross-linked sodium alginate) have high mechanical strength and good stability, but they are difficult to degrade naturally in vivo, or the degradation cycle can be as long as several weeks to months, forcing patients to endure the pain and risks of secondary surgery for removal. Physically cross-linked hydrogels (such as simple freeze-thaw PVA and hydrogen-bonded cross-linked gels) are degradable, but they often have extremely poor stability in physiological fluids and may disintegrate before the treatment is completed, causing the photothermal agent to diffuse into healthy tissue and cause off-target toxicity, and they cannot maintain stable sensor contact. Enzymatic hydrogels rely on specific enzymes (such as hyaluronidase and alginate lyase) for degradation, but the enzyme concentration in vivo fluctuates greatly, the degradation time is uncontrollable, and exogenous enzymes are expensive and may trigger immune reactions. Existing technologies mostly focus on changes in the "swelling rate" of gels, and few materials can achieve "stability during treatment and complete molecular-level dissolution upon contact with water".

[0004] Second, there is the challenge of recycling expensive nanofillers.

[0005] Single-walled carbon nanotubes (SWCNTs) are widely used in PTT sensors due to their high photothermal conversion efficiency, good stability, and excellent conductivity, exhibiting significantly superior performance compared to metal oxides currently used in research. However, SWCNTs are costly to fabricate and are chemically locked or physically entangled within traditional hydrogel networks.

[0006] Currently, SWCNTs in medical waste are typically incinerated or landfilled, which is not only energy-intensive and produces toxic gases, but also severely damages the surface structure and photoelectric properties of SWCNTs, rendering them unusable in the biomedical field. While enzymatic hydrolysis is gentler, enzyme preparations are expensive, and the products after hydrolysis are complex, making it difficult to separate high-purity SWCNTs using simple methods.

[0007] Third, there is the issue of overheating safety.

[0008] Photothermal therapy has a narrow therapeutic window (typically 42-45°C), and temperatures exceeding 45°C can cause irreversible damage to normal tissue. Existing materials lack embedded real-time temperature measurement capabilities and generally rely on infrared temperature control cameras to monitor temperature changes. This results in slow temperature response, low accuracy, and an inability to provide feedback and cut off the heat source within milliseconds, posing serious safety hazards.

[0009] Fourth, the integration of functions is insufficient.

[0010] Most studies separate photothermal therapy and temperature monitoring. External infrared thermometry cannot penetrate deep tissues and is greatly affected by blood flow; invasive thermocouples, while accurate, are rigid, have poor biocompatibility, and are difficult to conformally fit into flexible tissues. There is a lack of an "integrated" material that can serve as both a highly efficient photothermal agent and a highly sensitive flexible temperature sensor, while also possessing intelligent degradation properties.

[0011] While some conductive hydrogels have been reported in existing technologies, they mostly focus on simple sensing or photothermal processes, lacking a systematic solution that organically combines "high-precision temperature safety feedback," "ion-responsive self-dissolution," and "green recycling of fillers." In particular, applications utilizing the material's own resistance abrupt changes as hardware-level safety trigger signals have not yet been reported. Therefore, developing a novel intelligent hydrogel system that can precisely balance "stability during treatment" and "self-dissolution during disposal," and achieve low-cost, pollution-free recycling of SWCNTs, is a key technical problem urgently needing to be solved in the field of biomaterials. Summary of the Invention

[0012] The purpose of this invention is to provide an ion-responsive, self-dissolving single-walled carbon nanotube composite hydrogel to solve the problems of existing photothermal hydrogels, such as difficulty in achieving structural stability during use and triggering clearance after use, insufficient temperature feedback capability, and difficulty in gently recycling single-walled carbon nanotubes.

[0013] Another object of the present invention is to provide a method for preparing the single-walled carbon nanotube composite hydrogel.

[0014] Another object of the present invention is to provide a method for recovering single-walled carbon nanotubes from the said single-walled carbon nanotube composite hydrogel.

[0015] Another object of the present invention is to provide the application of the single-walled carbon nanotube composite hydrogel in the preparation of photothermal treatment materials, photothermal therapy temperature feedback materials, or recyclable nanofiller composite materials.

[0016] To achieve the above objectives, the present invention provides an ion-responsive self-dissolving single-walled carbon nanotube composite hydrogel, comprising carboxymethyl cellulose, sodium alginate, single-walled carbon nanotubes, and zinc ions.

[0017] The zinc ions form dynamic coordination bonds with the carboxyl groups in the carboxymethyl cellulose and sodium alginate, constituting a three-dimensional hydrogel network. The single-walled carbon nanotubes are dispersed within the three-dimensional hydrogel network.

[0018] The hydrogel maintains a macroscopic gel structure in a physiologically saline environment and undergoes self-dissolution in an external aqueous medium with a lower total ion content compared to the physiologically saline environment. Specifically, when the external aqueous medium comes into contact with the hydrogel, a concentration gradient is formed that promotes the diffusion of zinc ions contained in the hydrogel into the external aqueous medium, thereby reducing the dynamic coordination bonds and causing the macroscopic gel structure to disappear.

[0019] The hydrogel maintains a workable macroscopic gel structure in a relatively dry environment where it does not form continuous contact with the external aqueous medium.

[0020] In this invention, the aqueous medium refers to a liquid medium with water as the continuous phase, including liquid systems containing inorganic salts, buffer salts, soluble polymers, proteins, or other water-soluble components.

[0021] In this invention, the physiological saline environment refers to an environment containing physiologically relevant electrolytes, ion composition, and osmotic environment similar to that of animal tissue fluid, extracellular fluid, or the physiological environment of the body surface. Preferably, the physiological saline environment includes a physiological saline environment, a phosphate buffer environment, a simulated body fluid environment, a simulated tissue fluid environment, a simulated plasma environment, a cell culture medium environment, or a moist saline environment on the body surface.

[0022] In some embodiments, the physiological saline environment includes an isotonic saline medium containing animal tissue fluid. The isotonic saline medium refers to a saline medium containing physiologically relevant electrolytes and having an osmotic environment similar to that of animal tissue fluid. Preferably, the osmolar concentration of the isotonic saline medium is between 280 mOsm / L and 320 mOsm / L. Preferably, when expressed as an equivalent sodium chloride concentration, the equivalent sodium chloride concentration of the isotonic saline medium is between 0.13 mol / L and 0.17 mol / L.

[0023] In this invention, the external aqueous medium refers to an aqueous medium with a lower total ion content relative to the physiological saline environment, capable of forming a concentration gradient with the hydrogel that promotes the diffusion of zinc ions contained in the hydrogel to the external aqueous medium. Preferably, the external aqueous medium is deionized water, purified water, water for injection, or a low-salt flushing solution. The low-salt flushing solution can be an aqueous flushing medium that has been verified to form a concentration gradient that promotes the outward diffusion of zinc ions and triggers the self-dissolution of the hydrogel.

[0024] In this invention, the relatively dry environment refers to an environment in which the hydrogel is exposed to air, adhered to a body surface, covered by a dressing, or similar operating conditions, and where a continuous external aqueous phase capable of continuously removing zinc ions contained in the hydrogel has not been formed. In this relatively dry environment, the hydrogel can maintain a workable macroscopic gel structure.

[0025] In this invention, self-dissolution refers to the disappearance of the macroscopic gel structure of the hydrogel, forming a mixture containing single-walled carbon nanotubes. Preferably, complete self-dissolution means that after treatment in an external aqueous medium, the mass residue of the hydrogel is less than 1%, and there are no visible gel clumps remaining. Preferably, when the hydrogel is prepared into a cylindrical sample with a diameter of 10 mm and a height of 5 mm, the mass residue rate is the ratio of the recyclable macroscopic gel residue mass after removal and absorption of surface liquid to the initial mass of the cylindrical sample.

[0026] Without being limited by specific theories, the ion-responsive self-dissolution behavior of the hydrogel of this invention is mainly related to the difference in ionic environments inside and outside the hydrogel and the migration of zinc ions. During the preparation process, the hydrogel adsorbs or binds zinc ions, which can dynamically coordinate with the carboxyl groups in carboxymethyl cellulose and sodium alginate, thereby crosslinking the polysaccharide chains into a three-dimensional hydrogel network. When the hydrogel is in a physiological saline environment, the external environment has an ionic composition and osmotic environment similar to animal tissue fluid or extracellular fluid, allowing the hydrogel to maintain a high effective crosslinking density and preserve its macroscopic gel structure. When the hydrogel forms continuous contact with an external aqueous medium that has a lower total ion content compared to the physiological saline environment, a concentration gradient is formed between the migratable zinc ions contained in the hydrogel and the external aqueous medium, causing zinc ions to diffuse from the hydrogel to the external aqueous medium. As zinc ions migrate out, the dynamic coordination bonds formed between zinc ions and carboxyl groups decrease, the crosslinking density of the hydrogel decreases, and the macroscopic gel structure disappears. This process does not rely on degradation by biological enzymes, strong acids, or strong bases.

[0027] When a hydrogel is in a relatively dry environment where it does not have continuous contact with an external aqueous medium, the lack of a continuous external aqueous phase that carries away the zinc ions contained in the hydrogel makes it difficult for the zinc ions in the hydrogel to continuously migrate to the external environment. Therefore, the hydrogel can maintain a workable macroscopic gel structure.

[0028] Regarding stability and solubility, preferably, in a physiologically saline environment, after being placed for 2 hours within a range of mammalian body temperature to 45°C, the residual mass is not less than 90%. Preferably, in an external aqueous medium, the complete self-dissolution time does not exceed 24 hours. Preferably, under the tested conditions, the complete self-dissolution time of the hydrogel in an external aqueous medium can be controlled by adjusting the zinc ion crosslinking conditions; in the tested formulation, as the concentration of the zinc ion crosslinking solution increases, the overall complete self-dissolution time is prolonged.

[0029] Regarding compatibility, the components used in this invention have a basis for use in biointerface materials. Carboxymethyl cellulose and sodium alginate are both natural polysaccharides or their derivatives, and can be used in fields such as drug delivery, tissue engineering, dressings, or biointerface materials. Zinc ions are both the dynamically crosslinking ions in this invention and one of the essential trace elements for the human body. Appropriate amounts of zinc ions participate in various biological processes. In this application, the main role of zinc ions is to form dynamic coordination bonds with carboxyl groups and construct a three-dimensional hydrogel network that can disintegrate in an ion-responsive manner.

[0030] Regarding single-walled carbon nanotubes (SUVs), the SUVs in this invention primarily serve as near-infrared photothermal conversion fillers and conductive fillers. The SUVs are dispersed within a three-dimensional hydrogel network, forming near-infrared photothermal conversion pathways and resistance-temperature response pathways. After the hydrogel undergoes self-dissolution, the SUVs enter a mixture containing polysaccharide components and zinc ions, and can be recovered through centrifugation, washing, and drying. When considering in vivo or surface applications, the amount of SUVs used, their dispersion state, exposure method, and subsequent treatment can be further evaluated based on specific application requirements. The core of this invention is to provide a material system capable of triggering self-dissolution through an external aqueous medium and achieving the recovery of SUVs.

[0031] Single-walled carbon nanotubes dispersed in the network have a dual function: first, as a near-infrared photothermal conversion agent, they convert absorbed near-infrared light energy into heat energy; second, they form conductive pathways, giving the hydrogel a negative temperature coefficient resistance response. Preferably, the hydrogel experiences a temperature rise under 808 nm near-infrared light irradiation. Preferably, the resistance response parameter of the hydrogel decreases with increasing temperature in the range of 25°C to 50°C. Preferably, under the tested sample and test conditions, a fitting relationship can be established between the resistance response parameter and temperature, providing a signal basis for temperature feedback in the photothermal process. In applications, the hydrogel can be used in conjunction with an external resistance acquisition device to output a temperature-dependent resistance signal.

[0032] In some embodiments, lithium chloride may be included in the hydrogel to further enhance temperature sensing sensitivity or regulate the internal ionic environment. Lithium chloride can be used as an optional ionic component to improve ionic conductivity or regulate the system's resistive response. The specific amount of lithium chloride added and its effect can be determined based on the target formulation and test results.

[0033] Regarding the composition and formulation, preferably, the mass ratio of carboxymethyl cellulose to sodium alginate is 1:4 to 1:1. Preferably, the total mass concentration of carboxymethyl cellulose and sodium alginate in the hydrogel precursor solution is 2.0 wt% to 10.0 wt%, more preferably 5.0 wt%. Preferably, the degree of substitution of the carboxymethyl cellulose is 0.7 to 1.2, and the viscosity is 300 mPa·s to 800 mPa·s. Preferably, the viscosity of the sodium alginate is 200 mPa·s to 500 mPa·s.

[0034] Preferably, the content of the single-walled carbon nanotubes is 0.1% to 5.0% of the total mass of the carboxymethyl cellulose and the sodium alginate. Preferably, the theoretical molar ratio of the zinc ions to the carboxyl groups in the carboxymethyl cellulose and sodium alginate is 1:5 to 1:20. This ratio range is beneficial for forming a stable hydrogel network and retaining the ability to trigger self-dissolution by the external aqueous medium.

[0035] The present invention also provides a method for preparing the hydrogel, the method employing an aqueous system and mild crosslinking conditions, comprising the following steps: S1, Dissolve carboxymethyl cellulose and sodium alginate in water to obtain a polysaccharide mixed solution; S2, add single-walled carbon nanotubes to the polysaccharide mixed solution, and after dispersion treatment, obtain a composite precursor solution containing single-walled carbon nanotubes; S3, the composite precursor solution is brought into contact with a crosslinking solution containing zinc ions, so that the zinc ions and carboxyl groups form dynamic coordination bonds to obtain the single-walled carbon nanotube composite hydrogel.

[0036] Preferably, in step S2, the dispersion treatment is ultrasonic dispersion. Preferably, the ultrasonic dispersion is carried out under ice bath conditions, with a power of 200 W and a time of 10 to 60 minutes, more preferably 30 minutes. Preferably, in step S3, the crosslinking solution containing zinc ions is an aqueous solution of zinc chloride with a concentration of 0.08 mol / L to 0.40 mol / L. The crosslinking method can be dropwise addition, immersion, or in-mold contact crosslinking, with a crosslinking time of 8 to 12 hours. After crosslinking is completed, residual ions on the surface can be quickly rinsed off with deionized water to obtain the finished product.

[0037] This invention also provides a method for recovering single-walled carbon nanotubes. This method can achieve single-walled carbon nanotube separation by triggering the self-dissolution of a hydrogel through an external aqueous medium and by centrifugation, without the use of biological enzymes, strong acids, or strong bases. Specific steps include: R1, the hydrogel is immersed in an external aqueous medium and left to stand until the hydrogel network undergoes self-dissolution to obtain a mixture containing single-walled carbon nanotubes; R2, the mixture is centrifuged to cause single-walled carbon nanotubes to precipitate; R3, collect the precipitate, wash and dry it to obtain the recovered single-walled carbon nanotube powder.

[0038] Preferably, the settling time in step R1 is 4 to 24 hours. Preferably, the centrifugation speed in step R2 is 5000 to 10000 rpm, and the centrifugation time is 20 to 40 minutes. Preferably, in step R3, the sample is washed 2 to 3 times with deionized water and 1 time with ethanol, and then vacuum dried at 60°C to 80°C.

[0039] Preferably, after multiple cycles of "preparation-self-dissolution-recycling-remanufacturing", the recycled single-walled carbon nanotubes can still maintain their photothermal conversion performance and Raman structural characteristics. In the tested embodiment, the photothermal conversion efficiency of the third-generation recycled single-walled carbon nanotubes decreased by 1.6 percentage points compared with the first generation, the photothermal conversion efficiency retention rate was approximately 96.3%, and the change in ID / IG for the third generation was +2.1%.

[0040] This invention also provides a remanufacturing method. The recycled single-walled carbon nanotube powder obtained according to the above method is redispersed in a polysaccharide mixed solution containing carboxymethyl cellulose and sodium alginate. The resulting composite precursor solution is then contacted with a crosslinking solution containing zinc ions to obtain a remanufactured single-walled carbon nanotube composite hydrogel. Preferably, the recycled single-walled carbon nanotubes can be subjected to performance testing before remanufacturing, such as Raman spectroscopy ID / IG ratio testing and photothermal conversion efficiency testing, to determine whether the recycled material is suitable for the next round of preparation.

[0041] This invention also provides the application of the single-walled carbon nanotube composite hydrogel in the preparation of photothermal treatment materials, photothermal therapy temperature feedback materials, resistance temperature response materials, or recyclable nanofiller composite materials. The hydrogel can utilize the near-infrared photothermal conversion properties of single-walled carbon nanotubes for photothermal treatment and can provide temperature feedback signals using its resistance temperature response characteristics. For applications on the body surface or superficial target areas, the hydrogel can maintain an operable macroscopic gel structure in a relatively dry adhesion environment; after use, it can be self-dissolved by contacting an external aqueous medium, and the single-walled carbon nanotubes can be further recovered.

[0042] In some applications, the hydrogel can be used in conjunction with a near-infrared light source, a resistance acquisition device, and a control device. The near-infrared light source irradiates the hydrogel to generate a photothermal effect; the resistance acquisition device acquires the resistance response signal of the hydrogel; and the control device adjusts the light source output based on a calibration relationship between the resistance response signal and temperature. These applications illustrate the applicability of the hydrogel as a photothermal temperature feedback material.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects: First, the present invention constructs a hydrogel network through the dynamic coordination between carboxymethyl cellulose, sodium alginate and zinc ions, so that the hydrogel maintains a macroscopic gel structure in a physiological saline environment and undergoes self-dissolution in an external aqueous medium with a lower total ion content than the physiological saline environment, thereby taking into account both stability during use and triggering disintegration after use.

[0044] Secondly, the hydrogel of the present invention can maintain a workable macroscopic gel structure in a relatively dry environment where it does not form continuous contact with the external aqueous medium, which is beneficial for material positioning in body surface adhesion, dressing coverage, short-term operation and photothermal treatment processes.

[0045] Third, this invention utilizes single-walled carbon nanotubes to simultaneously construct near-infrared photothermal conversion pathways and resistance-temperature response pathways, enabling the hydrogel to output temperature-related resistance response signals during photothermal processes, which is beneficial for achieving in-situ temperature feedback during photothermal processes.

[0046] Fourth, this invention utilizes an external aqueous medium to trigger the self-dissolution of the hydrogel network, releasing the single-walled carbon nanotubes from the hydrogel network. These nanotubes are then recovered through centrifugation, washing, and drying, which helps maintain the structural integrity and functional stability of the single-walled carbon nanotubes.

[0047] Fifth, this invention enables the preparation, self-dissolution, recycling, and remanufacturing of single-walled carbon nanotube composite hydrogels, which helps reduce the waste of high-value nanofillers and provides a material basis for the recycling of single-walled carbon nanotube composite hydrogels. Attached Figure Description

[0048] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0049] Figure 1 The graph shows the photothermal heating curve of the hydrogel in Example 4.

[0050] Figure 2 The graph shows the change in the mass residue of the hydrogel in PBS and deionized water in Example 4.

[0051] Figure 3 The graph shows the resistance response parameters of the hydrogel in Example 1 as a temperature-response curve.

[0052] Figure 4 A morphological comparison of original SWCNTs and third-generation recycled SWCNTs.

[0053] Figure 5 A comparison of the Raman spectra of original SWCNTs and third-generation recovered SWCNTs.

[0054] Figure 6 This is a picture of the hydrogel sample prepared in Example 1.

[0055] Figure 7 This is a diagram showing the self-dissolution process of the hydrogel sample prepared in Example 1 in deionized water. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0057] Experimental materials and instruments Sodium carboxymethyl cellulose (CMC, viscosity 300 mPa·s to 800 mPa·s), sodium alginate (SA, viscosity 200 mPa·s to 500 mPa·s), single-walled carbon nanotubes (SWCNTs, purity greater than 95%, diameter 1 nm to 2 nm), zinc chloride (ZnCl2), lithium chloride (LiCl), and other reagents were all of analytical grade.

[0058] Example 1

[0059] Sodium carboxymethyl cellulose and sodium alginate were dissolved in deionized water at a mass ratio of 1:1 and stirred overnight until completely dissolved to obtain a polysaccharide mixture with a total mass concentration of 5.0 wt%.

[0060] Weigh 0.1% of the polysaccharide mass of single-walled carbon nanotubes and add them to the polysaccharide mixture. Treat with an ultrasonic probe for 30 minutes at an ultrasonic power of 200 W. Use an ice bath during the treatment to obtain a uniform black composite precursor solution.

[0061] The composite precursor solution was poured into a mold and brought into contact with a 0.2 mol / L zinc chloride aqueous solution. The mixture was allowed to stand at room temperature for 8 hours to crosslink. The resulting hydrogel was then removed, and the surface was quickly rinsed with deionized water to remove any residual crosslinking solution, yielding the single-walled carbon nanotube composite hydrogel.

[0062] Example 2

[0063] Except for adjusting the zinc chloride concentration in the crosslinking solution to 0.4 mol / L, the other steps are the same as in Example 1.

[0064] Example 3

[0065] Except for adjusting the zinc chloride concentration in the crosslinking solution to 0.08 mol / L, the other steps are the same as in Example 1.

[0066] Example 4

[0067] Except for adjusting the amount of single-walled carbon nanotubes added to 5.0% of the polysaccharide mass, the remaining steps were the same as in Example 1. This example was used to test the effect of a higher single-walled carbon nanotube content on photothermal properties and resistance temperature response properties.

[0068] Example 5

[0069] Except for adjusting the mass ratio of sodium carboxymethyl cellulose to sodium alginate to 1:4, the other steps are the same as in Example 1.

[0070] Comparative Example 1 A composite hydrogel with a permanent covalent network was obtained by using acrylamide monomer and N,N'-methylenebisacrylamide crosslinking agent for free radical polymerization initiated by ammonium persulfate, and incorporating an equal amount of single-walled carbon nanotubes.

[0071] Comparative Example 2 The zinc ions in the formulation of Example 1 were replaced with calcium ions, and crosslinking was performed using calcium chloride solution. The remaining steps were the same as in Example 1.

[0072] Comparative Example 3 In Example 1, zinc ions were replaced with iron ions, and crosslinking was performed using a ferric chloride solution, with the remaining steps the same as in Example 1. The resulting hydrogel hardened, its flexibility decreased, and it did not readily swell or self-dissolve in deionized water.

[0073] Comparative Example 4 In Example 1, zinc ions were replaced with sodium ions, and the mixture was treated with sodium chloride solution, with the remaining steps the same as in Example 1. A stable hydrogel could not be formed after treatment.

[0074] Comparative Example 5 In Example 1, zinc ions were replaced with aluminum ions, and the mixture was treated with an aluminum chloride solution, with the remaining steps the same as in Example 1. After treatment, it became difficult to form the same flexible, self-dissolving hydrogel as in Example 1.

[0075] Comparative Example 6 The zinc chloride solution crosslinking step in Example 1 was omitted, and the composite precursor solution was placed directly in deionized water, with the remaining steps the same as in Example 1. The results showed that no stable gel was formed.

[0076] Comparative Example 7 A physically cross-linked hydrogel was prepared by mixing a polyvinyl alcohol solution with single-walled carbon nanotubes and then cyclically freezing the mixture at -20°C for 12 hours and thawing it at room temperature for 4 hours. The cycle was repeated 3 times and the hydrogel contained no zinc ions.

[0077] Comparative Example 8 The hydrogel prepared in Example 1 was not soaked in an external aqueous medium for self-dissolution in the recovery step. Instead, it was placed in a buffer solution containing alginate lyase and cellulase, treated at 37°C for 24 hours, and then centrifuged for recovery.

[0078] Comparative Example 9 Using the hydrogel prepared in Example 1, single-walled carbon nanotubes were recovered by centrifugation after acid digestion in the recovery step, in order to compare the effect of severe chemical treatment on recovery rate and photothermal properties.

[0079] Test Item 1: Ion Response Self-Dissolution Kinetics Hydrogels from each example and comparative example were prepared into cylindrical samples with a diameter of 10 mm and a height of 5 mm, and their weight was recorded as m0. These samples were then immersed in 50 mL of PBS and 50 mL of deionized water, respectively, at 37°C. The samples were removed at regular intervals, surface moisture was blotted off, and the weight was recorded as m. t Calculate the residual mass R using the following formula: R = m t / m0 × 100% When R is less than 1%, it is considered to be completely self-dissolving.

[0080] The test results are shown in Table 1.

[0081] Table 1. Comparison of solubility stability of hydrogels with different formulations

[0082] Table 1 shows that Examples 1 to 5 exhibit biphasic characteristics of stability in physiological saline environments and self-dissolution in external aqueous media. In PBS, the sample samples showed a high residual mass after 2 hours, indicating their ability to maintain a macroscopic gel structure in physiological saline media; in deionized water, the sample samples underwent self-dissolution. A comparison of Examples 1, 2, and 3 shows that under the tested conditions, the overall self-dissolution time of the hydrogel was prolonged as the concentration of the zinc chloride crosslinking solution increased. Comparative Example 1, due to its permanent covalent network, was difficult to self-dissolve in deionized water. The structure formed by calcium ion crosslinking in Comparative Example 2 only partially disintegrated in deionized water. Comparative Example 7 showed insufficient stability in PBS, indicating that a purely physical crosslinking network cannot simultaneously meet the requirements of stability in physiological saline environments and self-dissolution triggered by external aqueous media.

[0083] Test Item 2: Operability in a relatively dry environment The hydrogel samples prepared in Example 1 were placed in air exposure, body surface adhesion simulation, and dressing coverage simulation environments to observe their macroscopic morphology and manipulation. The results showed that the samples maintained their intact macroscopic gel structure in a relatively dry environment without continuous contact with deionized water, purified water, or low-salt rinsing solution, and could be grasped, moved, and adhered.

[0084] Subsequently, similar samples were placed in deionized water, and the samples gradually swelled, self-dissolved, and formed a black mixture. This result indicates that the self-dissolution of hydrogels requires continuous contact between the external aqueous medium and the hydrogel, and the formation of a concentration gradient between the zinc ions contained in the hydrogel and the external aqueous medium to promote the outward diffusion of zinc ions.

[0085] Test Item 3: Qualitative observation of zinc ion diffusion during hydrogel self-dissolution To verify the migration of zinc ions from the hydrogel to the external aqueous medium during the self-dissolution of the hydrogel, zinc ion test paper was used to qualitatively detect the external aqueous medium at different immersion time points.

[0086] The single-walled carbon nanotube composite hydrogel prepared in Example 1 was used to make a cylindrical sample with a diameter of 10 mm and a height of 5 mm.

[0087] The following experimental groups were set up: Group A: Place the hydrogel sample in 50 mL of deionized water; Group B: Place the hydrogel sample in 50 mL PBS; Group C: Only 50 mL of deionized water was used as a negative control, without the addition of hydrogel; Group D: An aqueous solution containing zinc ions was used as a positive control.

[0088] Under the same temperature conditions, external liquid samples were collected at different immersion time points. These time points included the initial time point, early immersion time point, mid-immersion time point, and the time point after the macroscopic gel structure disappeared. The zinc ion test strips were immersed in the external liquids collected at each time point, and color development was performed according to the color development time specified in the test strip instructions. The color changes of the test strips were recorded under the same light conditions.

[0089] The results showed that in group A, the color development of the zinc ion test strip gradually increased with prolonged soaking time; after the macroscopic gel structure disappeared, the external aqueous medium showed the most obvious color development of the test strip. In group B, the zinc ion test strip showed weak color development within the same observation time, and the hydrogel maintained its macroscopic gel structure. No obvious zinc ion color development was observed in group C. Obvious zinc ion color development was observed in group D.

[0090] The above results indicate that when the hydrogel comes into contact with an external aqueous medium having a lower total ion content compared to the physiological saline environment, the detection signal of zinc ions in the external aqueous medium increases with prolonged immersion time, suggesting that zinc ions contained in the hydrogel can migrate into the external aqueous medium. This result supports the following mechanism: when the external aqueous medium comes into contact with the hydrogel, a concentration gradient is formed that promotes the diffusion of zinc ions contained in the hydrogel into the external aqueous medium; as zinc ions migrate out, the dynamic coordination bonds formed between zinc ions and carboxyl groups decrease, the crosslinking density of the hydrogel decreases, and ultimately the macroscopic gel structure disappears.

[0091] Test Item 4: Self-dissolution behavior in external aqueous media with different ionic strengths Using the single-walled carbon nanotube composite hydrogel prepared in Example 1, cylindrical samples with a diameter of 10 mm and a height of 5 mm were prepared, with an initial mass denoted as m0. The samples were placed in sodium chloride aqueous solutions of different ionic strengths at a temperature of 37°C. The ionic strengths were 0 M, 0.005 M, 0.01 M, 0.02 M, and 0.05 M, respectively. The samples were removed at regular intervals, surface moisture was absorbed, and the weight was recorded as m. t Calculate the residual mass rate: Residual mass rate = m t / m0 × 100% When the residual mass is less than 1% and there is no visible gel residue, it is considered to be completely self-dissolving.

[0092] The test results are shown in Table 2.

[0093] Table 2. Self-dissolution behavior in external aqueous media with different ionic strengths

[0094] The results show that the self-dissolution behavior of the hydrogel of this invention is related to the ionic strength of the external aqueous medium. When the total ion content of the external aqueous medium is low, the hydrogel can undergo complete self-dissolution; when the ionic strength of the external aqueous medium increases, the self-dissolution of the hydrogel slows down significantly or only swells without complete dissolution. This result further illustrates that the difference in the ionic environment formed between the external aqueous medium and the hydrogel can affect the migration of zinc ions and the reduction of dynamic coordination bonds within the hydrogel.

[0095] Test item 5: Enzyme-free recovery efficiency and cycling performance of SWCNTs The mixture from Example 1 after complete autolysis was recovered by centrifugation. The recovery rate Y was calculated. Y = M_recycled / M_original × 100% Where M_recycled is the mass of the recycled single-walled carbon nanotubes, and M_original is the mass of the initially added single-walled carbon nanotubes.

[0096] The recycled powder was reconstituted into a hydrogel, and second- and third-generation cycle tests were conducted. The results are shown in Table 3.

[0097] Table 3 Comparison of SWCNTs recovery efficiency

[0098] As shown in Table 3, the recovery rate of SWCNTs using the method of this invention was 94.5% for the first generation, 93.3% for the second generation, and 91.4% for the third generation. Compared with enzymatic digestion, the water immersion + centrifugation method is simpler and does not use biological enzymes. Compared with acidic digestion, the method of this invention is more conducive to maintaining the structure and function of SWCNTs.

[0099] Test Item 6: Multi-generation Cyclic Performance of SWCNTs The photothermal conversion efficiency and Raman spectroscopy of the recovered SWCNTs were tested, and the results are shown in Table 4.

[0100] Table 4 Comparison of multi-generation cycle performance of SWCNTs

[0101] The results show that, using the water immersion + centrifugation recovery method of this invention, the photothermal conversion efficiency of the third-generation SWCNTs is 41.6%, a decrease of 1.6 percentage points compared to the first generation's 43.2%, with a photothermal conversion efficiency retention rate of approximately 96.3%. The ID / IG change of the third generation is +2.1%, indicating that the mild self-dissolution and centrifugation recovery process has little impact on the SWCNTs structure. In Comparative Example 9, acidic digestion treatment led to a decrease in photothermal conversion efficiency and a significant increase in the ID / IG change, indicating that vigorous chemical treatment is not conducive to maintaining the structure and function of SWCNTs.

[0102] Test Item 7: Photothermal Performance and Temperature Sensing Sensitivity A two-electrode system was constructed to test the resistance response changes of the hydrogel in the embodiment at different temperatures. The test temperature range was 25℃ to 50℃. Simultaneously, the temperature rise curve of the hydrogel under 808 nm laser irradiation was measured, and the photothermal conversion efficiency was calculated.

[0103] Example 4: Hydrogel at 1.0 W / cm 2Under irradiation with an 808 nm laser, the temperature can rise from 25°C to 55°C within 45 seconds, demonstrating excellent near-infrared photothermal conversion performance. The hydrogel in this example also exhibits a negative temperature coefficient of resistance response, meaning the resistance response parameter decreases with increasing temperature. Under the tested conditions, a goodness-of-fit relationship can be established between the hydrogel's resistance response parameter and temperature, with a goodness of fit R0. 2 The value was 0.999. Even within the first 4 hours of immersion in PBS, the sensing signal remained stable with a drift of less than 3%.

[0104] The results show that SWCNTs dispersed in a three-dimensional hydrogel network can simultaneously provide near-infrared photothermal conversion pathways and resistance temperature response pathways, making hydrogels a basis for photothermal treatment materials and resistance temperature feedback materials.

[0105] Test item 8: Remanufacturing hydrogels The single-walled carbon nanotube powder recovered in Example 1 was re-dispersed ultrasonically in a new mixed solution of sodium carboxymethyl cellulose and sodium alginate. The resulting composite precursor solution was then crosslinked with an aqueous solution of zinc chloride to obtain a remanufactured single-walled carbon nanotube composite hydrogel.

[0106] The remanufactured hydrogels can form macroscopic gel structures, remain structurally stable in PBS, and undergo self-dissolution in deionized water. These results demonstrate that recycled single-walled carbon nanotubes can be reused to prepare composite hydrogels, achieving the recycling of single-walled carbon nanotubes.

[0107] This invention constructs a three-dimensional hydrogel network through the dynamic coordination between carboxymethyl cellulose, sodium alginate and zinc ions, and disperses single-walled carbon nanotubes in the network. This enables the hydrogel to possess macroscopic structural stability in physiological saline environments, operability in relatively dry environments, self-dissolution triggered by external aqueous media, near-infrared photothermal conversion performance, resistance temperature response performance, and the ability to mildly recycle and remanufacture single-walled carbon nanotubes.

[0108] Those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An ion-responsive, self-dissolving single-walled carbon nanotube composite hydrogel, characterized in that, Including carboxymethyl cellulose, sodium alginate, single-walled carbon nanotubes, and zinc ions; The zinc ions form dynamic coordination bonds with the carboxyl groups in the carboxymethyl cellulose and sodium alginate, thus forming a three-dimensional hydrogel network. The single-walled carbon nanotubes are dispersed in the three-dimensional hydrogel network; The hydrogel maintains a macroscopic gel structure in a physiological saline environment and undergoes self-dissolution in an external aqueous medium with a lower total ion content relative to the physiological saline environment. When the external aqueous medium comes into contact with the hydrogel, a concentration gradient is formed that promotes the diffusion of zinc ions contained in the hydrogel into the external aqueous medium, thereby reducing the dynamic coordination bonds and causing the macroscopic gel structure to disappear. The hydrogel maintains a workable macroscopic gel structure in a relatively dry environment where it does not form continuous contact with the external aqueous medium.

2. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The physiological saline environment is a saline environment containing physiologically relevant electrolytes and with an osmotic environment similar to that of animal tissue fluid.

3. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The external aqueous medium is deionized water, purified water, water for injection, or a low-salt rinsing medium.

4. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The self-dissolution refers to the disappearance of the macroscopic gel structure and the residual mass of the recyclable macroscopic gel residue being less than 1%.

5. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The mass ratio of carboxymethyl cellulose to sodium alginate is 1:4 to 1:1, and the total mass concentration of carboxymethyl cellulose and sodium alginate in the precursor solution for preparing the hydrogel is 5.0 wt%.

6. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The mass of the single-walled carbon nanotubes is 0.1% to 5.0% of the total mass of the carboxymethyl cellulose and the sodium alginate.

7. The single-walled carbon nanotube composite hydrogel according to claim 1, characterized in that, The hydrogel exhibits a temperature rise under near-infrared light irradiation and has a negative temperature coefficient resistance response.

8. A method for recovering single-walled carbon nanotubes from the single-walled carbon nanotube composite hydrogel of claim 1, characterized in that, Includes the following steps: R1, the single-walled carbon nanotube composite hydrogel is placed in the external aqueous medium, causing the three-dimensional hydrogel network to self-dissolve, resulting in a mixture containing single-walled carbon nanotubes; R2, the mixture containing single-walled carbon nanotubes is centrifuged to cause the single-walled carbon nanotubes to precipitate. R3, collect the precipitate, and wash and dry the precipitate to obtain recovered single-walled carbon nanotubes.

9. A method for remanufacturing single-walled carbon nanotube composite hydrogels, characterized in that, The recycled single-walled carbon nanotubes obtained according to the method of claim 8 are dispersed in a polysaccharide mixed solution containing carboxymethyl cellulose and sodium alginate, and then the resulting composite precursor solution is contacted with a crosslinking solution containing zinc ions to obtain a remanufactured single-walled carbon nanotube composite hydrogel.

10. A method for preparing single-walled carbon nanotube composite hydrogels, characterized in that, Includes the following steps: S1, Dissolve carboxymethyl cellulose and sodium alginate in water to obtain a polysaccharide mixed solution; S2, add single-walled carbon nanotubes to the polysaccharide mixed solution and disperse them to obtain a composite precursor solution containing single-walled carbon nanotubes; S3, the composite precursor solution is brought into contact with a crosslinking solution containing zinc ions, so that the zinc ions and carboxyl groups form dynamic coordination bonds to obtain the single-walled carbon nanotube composite hydrogel.

Images