A pH-responsive injectable hydrogel and preparation method and application thereof

Abstract

The application belongs to the technical field of biomedical materials, and discloses a pH-responsive injectable hydrogel as well as a preparation method and application thereof.The pH-responsive injectable hydrogel is prepared by the following steps: (1) dissolving sodium alginate in water to form a uniform solution; (2) adding a fat-soluble small-molecule drug and Fe3O4 nanoparticles to the solution, shearing and dispersing at a high speed under an ice-water bath condition to form a drug / nano composite system, and standing; and (3) sequentially adding a calcium carbonate suspension and gluconolactone to the drug / nano composite system, stirring uniformly, and incubating until complete solidification, so as to obtain the pH-responsive injectable hydrogel.The obtained hydrogel not only has excellent injectability and pH-responsive release performance, but also can significantly improve the loading efficiency of a fat-soluble drug, thereby providing a new technical approach for realizing local anti-tumor treatment.

Description

Technical Field

[0001] This invention relates to the field of biomedical materials technology, and more specifically to a pH-responsive injectable hydrogel based on sodium alginate, its preparation method, and its application. Background Technology

[0002] The incidence and mortality rates of malignant tumors such as gastric cancer continue to rise globally, especially in high-incidence regions like China. Cancer treatment still faces the dual challenges of limited efficacy and high recurrence rates. Traditional chemotherapy drugs are mostly administered systemically, which, while inhibiting tumor cell growth, often lead to systemic toxicity and low targeting efficiency due to their widespread distribution and strong non-specificity, severely impacting patients' quality of life. Therefore, developing safe, precise, and locally controlled drug delivery systems has become an important direction in cancer treatment research in recent years.

[0003] Among numerous drug delivery platforms, injectable hydrogels have attracted significant attention due to their excellent biocompatibility, plasticity, and in-situ gelation properties. Hydrogels are three-dimensional cross-linked hydrophilic polymer networks that can absorb water and swell in bodily fluids while maintaining structural stability. Compared to solid implant materials, injectable hydrogels can be injected into tumors or lesions via minimally invasive procedures, forming a flexible scaffold in situ within the body. This allows for local retention and sustained release of drugs, avoiding secondary surgeries and systemic side effects.

[0004] However, most injectable hydrogels still have significant shortcomings in their preparation and application: (1) the preparation process is complex and the reaction conditions are harsh, which limits large-scale application; (2) the drug loading capacity is limited, especially for lipid-soluble or poorly soluble drugs; (3) they lack intelligent response characteristics, making it difficult to achieve precise release regulation targeting the tumor microenvironment (such as weak acidity). In addition, some chemical cross-linking systems may introduce organic solvents or reaction byproducts, reducing biosafety.

[0005] In recent years, researchers have proposed ion-crosslinked injectable hydrogel systems based on natural polysaccharides such as sodium alginate (SA). These materials exhibit good biocompatibility and biodegradability, and can be degraded by Ca2+. 2+ Ion-induced molecular chain crosslinking achieves mild gelation.

[0006] However, many existing pH-responsive hydrogel systems rely on introducing ionized groups such as phenylboronic acid, imidazole, or pyrrolidone onto the polymer chain to achieve environmental responsiveness. These chemical grafting or copolymerization processes typically require organic solvents, catalysts, or multi-step reactions, resulting in high preparation costs, complex processes, and potential chemical residues that affect biocompatibility. Therefore, there is an urgent need for a pH-responsive hydrogel system that does not require chemical grafting, is easy to operate, and is inexpensive.

[0007] Furthermore, poorly soluble drugs such as lipid small molecule inhibitors (e.g., 2-bromopalmitate, 2-BP) exhibit poor stability and are prone to precipitation and aggregation in conventional aqueous systems, severely limiting their application in hydrogel drug delivery systems. Meanwhile, the weakly acidic nature of the tumor microenvironment provides a natural triggering condition for smart responsive materials. Utilizing pH changes to regulate the release rates of drugs and metal ions could facilitate local synergistic therapy.

[0008] Based on this, the present invention provides a pH-responsive injectable hydrogel and its preparation method. Summary of the Invention

[0009] To address the problems of complex preparation, demanding reaction conditions, high cost, and low loading efficiency for lipid-soluble drugs in existing pH-responsive hydrogel systems, this invention provides a pH-responsive injectable hydrogel, its preparation method, and its applications. This hydrogel can achieve efficient loading and controlled release of poorly soluble lipid drugs, making it suitable for applications such as local tumor drug delivery and microenvironment regulation.

[0010] This invention employs a physical composite strategy without chemical grafting, utilizing a simple high-speed stirring process to achieve the synergistic composite of the lipid-soluble drug 2-bromopalmitic acid (2-BP) and Fe3O4 nanoparticles. A "lactone-calcium ion sustained-release crosslinking mechanism" is formed through a CaCO3 / GDL system, resulting in in-situ gelation under mild and non-toxic conditions. The resulting hydrogel possesses high drug loading capacity, excellent pH responsiveness, and injectability, enabling the synergistic release of drugs and iron ions in the microacidic environment of tumors, providing a new technical pathway for precise local anti-tumor therapy.

[0011] To achieve the above objectives, the present invention provides a method for preparing a pH-responsive injectable hydrogel, comprising the following steps:

[0012] (1) Dissolve sodium alginate in deionized water, stir until completely dissolved, and let stand overnight at 4°C to remove bubbles, and obtain a transparent sodium alginate solution.

[0013] (2) Add lipid-soluble small molecule drugs and Fe3O4 nanoparticles to the solution, disperse them under high-speed shear to form a drug / nanocomposite system, and let it stand to eliminate pH fluctuations caused by high-speed shear and ensure that the drug is fully dispersed;

[0014] (3) Add sustained-release crosslinking agent calcium carbonate suspension to the drug / nanocomposite system and stir evenly. Add acid source gluconolactone (GDL) and stir evenly. Initially gel at room temperature and incubate until fully cured to obtain pH-responsive injectable hydrogel.

[0015] The preparation process of this invention is carried out entirely in an aqueous system, without the need for organic solvents, chemical grafting or catalytic steps. It is simple to operate, green and safe, and suitable for large-scale production and in vivo application.

[0016] Preferably, in step (1), the mass fraction of sodium alginate in the solution is 1-3% w / v, preferably 2% w / v.

[0017] Preferably, the lipid-soluble small molecule drug is selected from 2-bromopalmitic acid, erlastine, imidazolidone erlastine (IKE), RSL3 compound, FIN56 compound, FINO2 compound, sorafenib, vitriol A, α-oleic acid, docosahexaenoic acid (DHA), ferromagnesia and its derivatives, camptothecin, or natural lipid-soluble quinone compounds.

[0018] Preferably, the lipid-soluble small molecule drug is 2-bromopalmitic acid (2-BP), and the dosage of 2-bromopalmitic acid is 37.5-225 mg / mL.

[0019] The hydrogel uses sodium alginate as a three-dimensional network matrix, uniformly disperses Fe3O4 nanoparticles and 2-bromopalmitic acid, and has good injectability, pH responsiveness and sustained-release properties.

[0020] Preferably, the Fe3O4 nanoparticles are fed at an amount of 75-150 mg / mL and have a particle size of 10-50 nm.

[0021] The average particle size of the Fe3O4 nanoparticles in this invention can be 10-50 nm, with particles of approximately 20 nm exhibiting good dispersibility and stability in this system, which is beneficial for Fe... 2+ Controlled release and uniform distribution in the injection system are achieved. Smaller particle sizes (e.g., 10-20 nm) facilitate metabolism and clearance in vivo, while larger particle sizes, although also used to construct hydrogels, may increase the risk of aggregation, thereby affecting cross-linking uniformity and drug loading stability. Therefore, the particle size of the nanoparticles in this invention can be adjusted as needed and is not limited to a single fixed value.

[0022] Preferably, the mass ratio of 2-bromopalmitic acid to Fe3O4 nanoparticles is 1:0.25-1:1, and more preferably 1:0.5.

[0023] A mass ratio of 1:0.25 to 1:1 between the two yields excellent gelling properties, drug loading stability, and responsive release under acidic conditions. The ratio described in this invention can be adjusted according to the target drug dosage, release requirements, and mechanical performance requirements, and is not limited to a single ratio.

[0024] Preferably, the high-speed shearing speed is 15000-30000 rpm and the time is 3 minutes.

[0025] Further preferably, the high-speed shearing process is carried out under ice-water bath conditions to prevent local overheating from causing 2-BP degradation or Fe3O4 agglomeration.

[0026] Preferably, the settling operation is performed by settling for 12-36 hours, preferably 24 hours, to allow the pH of the drug / nanocomposite system to recover to 6.8-7.4.

[0027] Furthermore, the hydrogel exhibits significantly accelerated release of 2-BP and Fe at pH 6.5. 2+ However, it releases slowly at pH 7.4, exhibiting a clear pH response.

[0028] Preferably, the concentration of the calcium carbonate suspension is 5-10% w / v, the dosage is 0.1 mL per 1 mL of drug / nanocomposite system, and the final concentration in the hydrogel is maintained at 0.5%-1% w / v. Calcium carbonate is not added to the system before high-speed shearing to prevent premature cross-linking and ensure uniform dispersion of the drug and nanoparticles. The amount of gluconolactone added is 0.3-1% w / v of the drug / nanocomposite system, preferably 0.5% w / v.

[0029] All ratios within this range can achieve gradual acid release and drive Ca2+ release. 2+ Slow release results in a uniformly structured SA crosslinked network. The CaCO3 / GDL system described in this invention exhibits good parameter compatibility and can be flexibly adjusted according to gelation rate, injectability, and local release requirements.

[0030] Preferably, the incubation is carried out at 37°C for 30 minutes.

[0031] Further preferred, the resulting hydrogel can be smoothly injected through a 23-25G needle, exhibiting good shear-thinning behavior and in-situ gelation ability.

[0032] The pH-responsive injectable hydrogel of this invention can be widely used in the fields of local drug sustained release, tissue repair, and tumor microenvironment response therapy.

[0033] In addition, this hydrogel system can also serve as a general platform for the local delivery of other hydrophobic small molecules.

[0034] Especially suitable for drug delivery systems of lipid-soluble small molecule drugs (such as 2-bromopalmitic acid), enabling drug delivery to react with Fe in the weakly acidic environment of tumors. 2+ The synergistic release of these substances induces ferroptosis and inhibits tumor cell proliferation.

[0035] This system employs a simple high-speed stirring method to achieve efficient synergistic loading of 2-BP and Fe3O4 nanoparticles, and achieves in-situ gelation under mild conditions through a CaCO3 / GDL lactone-calcium ion sustained-release crosslinking mechanism. The resulting hydrogel not only possesses excellent injectability and pH-responsive release properties, but also significantly improves the loading efficiency of lipid-soluble drugs, providing a new technical approach for local antitumor therapy.

[0036] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0037] (1) No chemical grafting required and simple preparation process: It does not rely on chemical modification groups such as phenylboronic acid and imidazole. pH response can be achieved through the CaCO3 / GDL system, avoiding complex organic reactions and high-cost synthesis.

[0038] (2) High lipid-soluble drug loading efficiency: The drug is uniformly dispersed and physically embedded through high-speed shearing, exhibiting high loading rate and good stability for poorly soluble lipid drugs (such as 2-BP);

[0039] (3) Excellent pH responsiveness and controlled release performance: It achieves rapid release in the microacidic environment of tumors, while maintaining sustained release in neutral conditions to achieve targeted control effect;

[0040] (4) Good injectability and biocompatibility: The material is mild in gel formation and can be injected in situ through fine needles to form gels. There is no organic solvent residue and excellent biocompatibility.

[0041] (5) Synergistic anti-tumor potential: Simultaneous release of palmitoylation inhibitor (2-BP) and Fe 2+ Ions, to achieve synergistic therapy of "palmitoylation inhibition + ferroptosis activation";

[0042] (6) Low cost and easy to industrialize: The selected components are widely available and inexpensive, the process conditions are mild and easy to scale up, and they have good transformation prospects. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0044] Figure 1 This is a schematic diagram illustrating the preparation process and gelation of the pH-responsive injectable hydrogel of the present invention.

[0045] Figure 2This is a structural and morphological characterization diagram of the pH-responsive injectable hydrogel of the present invention;

[0046] (a–b) TEM image of Fe3O4 and F@2-BP complex; (c) Zeta potential of the complex system; (d) XRD pattern of the complex system; (e–s) SEM image of the hydrogel; (g–h) EDS elemental distribution of Br and Fe in the hydrogel.

[0047] Figure 3 The figures show (a) drug release curves and (b) iron ion release curves of the hydrogel of the present invention under different pH conditions.

[0048] Figure 4 The figure shows the rheological properties and injectability test results of the pH-responsive injectable hydrogel of the present invention;

[0049] (a) Storage modulus (G′) vs. loss modulus (G″) curves, (b) Compression recovery test diagram, and (c) Injection gelation process diagram using needles of different specifications.

[0050] Figure 5 The figure shows the in vitro biocompatibility test results of the hydrogel of this invention;

[0051] (a) EDU staining images of the Control group and Blank-Gel group at different culture times (1, 3, 5 days); (b) Statistical graph of the proportion of EDU-positive cells at different time points; (c) CCK-8 cell viability detection results at 24, 72 and 120 h time points.

[0052] Figure 6 The following figures illustrate the in vivo performance verification of the pH-responsive hydrogel of this invention in animal models: (a) Statistical graph of tumor weight in different treatment groups; (b) Statistical graph of the proportion of surviving tumor tissue in each group; (c) HE staining image of tumor tissue corresponding to each treatment group.

[0053] Figure 7 This invention compares the killing power of the pH-responsive hydrogel against tumor cells after changes in the ratio of 2-BP and Fe3O4. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Example 1: A method for preparing a pH-responsive injectable hydrogel

[0056] 2-BP is 75 mg / mL, Fe3O4 is 75 mg / mL

[0057] This embodiment uses the preferred drug formulation of the present invention to prepare a pH-responsive injectable hydrogel. 2 g of sodium alginate (SA) was dissolved in 100 mL of deionized water to prepare a 2% (w / v) SA solution. 150 mg of 2-BP and 150 mg of 20 nm Fe3O4 were weighed and added to 2 mL of the SA solution. The mixture was homogenized at 28,000 rpm for 3 min in an ice-water bath to ensure complete dispersion. After standing for 24 h, 200 μL of 5% CaCO3 suspension was added and mixed thoroughly. Then, 10 mg of GDL (approximately 0.5% of the system mass) was added to trigger sustained-release crosslinking. The system began to gel at room temperature and a stable hydrogel with good flowability and injectability was obtained after incubation at 37°C for approximately 30 min.

[0058] The hydrogel exhibits a continuous porous structure with uniform distribution of Br and Fe elements, indicating successful co-encapsulation of 2-BP and Fe3O4. The material possesses a storage modulus greater than its loss modulus, exhibits elastic-dominant properties, and maintains structural stability after repeated compression. The release of 2-BP and Fe is accelerated under pH 6.5 conditions. 2+ It exhibits typical acidic microenvironment response behavior. Overall, this formulation demonstrates optimal gelling properties, mechanical properties, and pH-responsive release, making it the preferred embodiment of this invention.

[0059]

Characteristics and Results

[0060] like Figure 1-2 As shown, the hydrogel obtained in this embodiment can rapidly gel under mild conditions in the CaCO3 / GDL system. Fe3O4 and 2-BP are uniformly dispersed and stably embedded in the gel network, and the whole structure is a continuous porous structure.

[0061] Figure 3 The gel showed good adhesion to 2-BP and Fe at pH 6.5. 2+ All showed significantly accelerated release, while the release rate decreased significantly at pH 7.4, demonstrating typical acid response characteristics and verifying its excellent pH-responsive release performance. Figure 4 This indicates that the material has good mechanical stability and injectability, and that the hydrogel has good mechanical stability and injectability.

[0062] Figure 5 and Figure 6 In vitro and in vivo evaluation results showed that the gel has good biocompatibility, can form a stable gel locally and does not induce a significant inflammatory response; Figure 5 This indicates that the hydrogel has no significant adverse effects on cell proliferation and activity, and has good biocompatibility and tissue adaptability; Figure 6 This study demonstrates the in-situ gelation and sustained-release properties of hydrogel after local injection into tissues. HE staining and Ki67 immunoassay showed that the material was evenly distributed in the tissue and accompanied by a decrease in cell proliferation level, indicating that the system has a stable structure in vivo and potential anti-tumor application prospects.

[0063] Figure 7 Cell experiments further demonstrated that the 2-BP / Fe3O4 ratio (1:0.5) used in this embodiment has a better cell inhibition effect.

[0064] In summary, this embodiment demonstrates outstanding performance in terms of gelation properties, structural stability, pH-responsive release, and biosafety, and can be considered a preferred embodiment of the present invention.

[0065] Example 2: A method for preparing a pH-responsive injectable hydrogel

[0066] 2-BP was 37.5 mg / mL, while Fe3O4 remained fixed at 75 mg / mL.

[0067] To verify the feasibility of this invention under the lower limit of the 2-BP usage range, this embodiment prepares a hydrogel with a reduced amount of 2-BP. 2 g of SA was dissolved in 100 mL of deionized water to prepare a 2% (w / v) solution. 75 mg of 2-BP and 150 mg of Fe3O4 were weighed and added to 2 mL of SA, and homogenized at 28,000 rpm for 3 min to obtain a homogeneous mixture. After standing for 24 h, 200 μL of 5% CaCO3 suspension and 10 mg of GDL were added sequentially, allowing the system to gradually crosslink at room temperature and completely solidify at 37°C.

[0068] The hydrogel obtained in this embodiment can still form a stable gel, maintain a uniform structure, and has good injectability, indicating that the material system of the present invention can still be prepared normally and has application feasibility within the minimum effective concentration range of 2-BP.

[0069] Example 3: A method for preparing a pH-responsive injectable hydrogel

[0070] 2-BP is 225 mg / mL (upper limit), and Fe3O4 remains fixed at 75 mg / mL.

[0071] To verify the operability of this invention under high-concentration conditions of 2-BP, this embodiment further increases the amount of 2-BP used. 2 g of SA was prepared into a 2% (w / v) solution. 450 mg of 2-BP and 150 mg of Fe3O4 were weighed and added to 2 mL of SA, and homogenized at 28000 rpm for 3 min to ensure thorough mixing. After standing for 24 h, 200 μL of 5% CaCO3 suspension was added and mixed thoroughly. Then, 10 mg of GDL was added to achieve cross-linking. Finally, a stable hydrogel was formed at 37 °C for approximately 30 min.

[0072] Despite the increased 2-BP concentration, the system can still successfully gel and form a complete gel network, proving that the present invention is still feasible under the upper limit concentration of 2-BP, and supports the parameter range of the claims of the present invention.

[0073] Example 4: A method for preparing a pH-responsive injectable hydrogel

[0074] 2-BP was fixed at 75 mg / mL; Fe3O4 = 150 mg / mL

[0075] To verify the feasibility of using high-concentration Fe3O4, 2 g of SA was dissolved in 100 mL of deionized water to prepare a 2% (w / v) SA solution. 150 mg of 2-BP and 300 mg of Fe3O4 were weighed and added to 2 mL of the SA solution. The mixture was homogenized at 28,000 rpm for 3 min in an ice-water bath. After standing for 24 h, 200 μL of 5% CaCO3 suspension was added and thoroughly stirred. 10 mg of GDL was then added to trigger sustained-release crosslinking. The system formed a structurally complete hydrogel after incubation at 37 °C for 30 min.

[0076] Despite the increase in Fe3O4 concentration, the resulting hydrogel can still form a stable gel and maintain a certain mechanical strength and good injectability, indicating that the present invention is still feasible at the upper limit of Fe3O4 concentration.

[0077] Example 5: A method for preparing a pH-responsive injectable hydrogel

[0078] 2-BP was fixed at 75 mg / mL; Fe3O4 = 112.5 mg / mL

[0079] 2 g of SA was dissolved in 100 mL of deionized water to prepare a 2% (w / v) solution. 150 mg of 2-BP and 225 mg of Fe3O4 were weighed and added to 2 mL of SA, and homogenized at 28,000 rpm for 3 min to obtain a homogeneous mixture. After standing for 24 h, 200 μL of 5% CaCO3 suspension and 10 mg of GDL were added, and the mixture was passed through Ca... 2+Slow-release crosslinking is achieved. The system gels within approximately 30 minutes at 37°C.

[0080] The hydrogel exhibits structural stability, gelation rate, and pH-responsive release behavior that fall between those of Example 1 and Example 3, and can serve as a supplementary example to further support the scope of the claims.

[0081] Comparative Example 1: Without 2-BP

[0082] When 2-BP is not added to the system at all, while the amount of Fe3O4 added remains the same as in Example 1 of this invention, the resulting hydrogel can still be successfully gelled in the CaCO3 / GDL system and maintain a certain amount of Fe under pH 6.5 / 7.4 conditions. 2+ Release capacity. However, due to the lack of synergistic effect of 2-BP, the inhibitory effect of this system on tumor cells in vitro was significantly reduced, and the cell activity and proliferation level were close to those of the blank control group, failing to achieve the "dual regulation" therapeutic effect described in this invention, indicating that the addition of 2-BP is a key condition for obtaining significant tumor-killing activity.

[0083] Comparative Example 2: Without Fe3O4

[0084] In this comparative system, Fe3O4 was not added; 2-BP was supported on sodium alginate and cross-linked via CaCO3 / GDL. While the resulting hydrogel formed a stable three-dimensional network structure, the dispersion and dissolution behavior of 2-BP within the gel were primarily limited by the physical embedding and diffusion processes of the SA matrix due to the lack of Fe3O4. This resulted in low drug release efficiency, with no significant difference in release under acidic and neutral conditions. In contrast, the introduction of Fe3O4 improved the dispersion of 2-BP in the system and promoted its transformation from a crystalline to an amorphous state, thereby enhancing drug dissolution and release efficiency. Furthermore, the surface properties of Fe3O4 in a weakly acidic environment could provide some auxiliary regulation of release behavior. Since this comparative system did not contain Fe3O4, the above effects could not be achieved, and no source of iron ions could be provided to trigger subsequent ferroptosis-related reactions, significantly weakening the overall synergistic effect.

[0085] Summary and Explanation

[0086] The pH-responsive injectable hydrogel preparation method provided in this embodiment is simple and can achieve high loading and acidic environment-responsive release of lipid-soluble drugs. The prepared hydrogel has good mechanical properties, injectability, and biocompatibility, providing a new approach and technical basis for local drug sustained release and anti-tumor materials.

[0087] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a pH-responsive injectable hydrogel, characterized by, The method comprises the following steps: (1) dissolving sodium alginate in water to form a uniform solution; (2) adding a fat-soluble small-molecule drug and Fe3O4 nanoparticles to the solution, and dispersing the mixture under high-speed shearing in an ice-water bath to form a drug / nano composite system, and then standing; (3) sequentially adding a calcium carbonate suspension and gluconolactone to the drug / nano composite system, stirring uniformly, and incubating until complete solidification to obtain a pH-responsive injectable hydrogel; The concentration of the calcium carbonate suspension is 5-10% w / v, the volume ratio of the calcium carbonate suspension to the drug / nano composite system is 0.1 mL:1 mL, and the addition amount of the gluconolactone is 0.3-1% w / v of the drug / nano composite system; The fat-soluble small-molecule drug is 2-bromopalmitic acid, and the addition amount of the 2-bromopalmitic acid is 37.5-225 mg / mL; The addition amount of the Fe3O4 nanoparticles is 75-150 mg / mL, and the particle size is 10-50 nm.

2. The method of claim 1, wherein the pH-responsive injectable hydrogel is prepared by the steps of: In step (1), the mass fraction of sodium alginate in the solution is 1-3% w / v.

3. The method of claim 1, wherein the pH-responsive injectable hydrogel is prepared by the steps of: In step (2), the high-speed shearing speed is 15000-30000 rpm, and the time is 3 min; The standing operation is standing for 12-36 h to restore the pH of the drug / nano composite system to 6.8-7.

4.

4. The method of claim 1, wherein the pH-responsive injectable hydrogel is prepared by the steps of: The incubation is incubation at 37°C for 30 min.

5. The pH-responsive injectable hydrogel obtained by the preparation method according to any one of claims 1-4.

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