PH-NIR dual-response degradable magnesium surface composite coating as well as preparation method and application thereof

Abstract

The invention discloses a pH-NIR dual-response degradable magnesium surface composite coating as well as a preparation method and application thereof, and belongs to the technical field of medical metal material surface modification. The pH-NIR dual-response magnesium alloy composite coating is of a double-layer structure, the inner layer is a conversion coating formed by complexing phytic acid and calcium ions, the outer layer is composed of metal-phenol network functionalized MXene nanosheets, and the polyphenol surface functionalized MXene nanosheets are Nb2C MXene wrapped on the surface of tannic acid. The coating can respond to an acid environment derived from infection, and magnesium is prevented from being degraded too fast in the acid environment while the antibacterial effect is achieved.

Description

Technical Field

[0001] This invention belongs to the field of medical metal material surface modification technology, and particularly relates to a pH-NIR dual-responsive biodegradable magnesium surface composite coating, its preparation method and application. Background Technology

[0002] In the field of clinical bone tissue repair, traditional metallic materials such as titanium alloys, stainless steel, and cobalt-chromium alloys are widely used. However, these materials have inherent drawbacks: First, they are not biodegradable and require a second surgery to remove them after implantation. Otherwise, long-term retention can easily lead to adverse reactions such as chronic inflammation and foreign body reactions. Second, their elastic modulus differs significantly from that of human bone, which can easily cause a stress shielding effect after implantation, resulting in weakened stimulation of bone formation and remodeling. This not only reduces the stability of the implant but may also induce secondary fractures.

[0003] To address these issues, biodegradable metals have become a research hotspot. Among them, magnesium and its alloys are considered revolutionary biomedical metal materials with great potential due to their excellent biodegradability, good biosafety, and mechanical properties that closely match bone tissue. However, magnesium and its alloys still face key bottlenecks in clinical applications: as bone repair materials, their degradation rate needs to be precisely matched with the bone tissue repair and reconstruction process to avoid implant breakage or functional failure due to excessively rapid degradation during their service life. Particularly noteworthy is that the degradation rate of magnesium and its alloys is further accelerated in the acidic microenvironment caused by bacterial infection, severely impacting their clinical efficacy. Therefore, constructing an anti-corrosion coating on the magnesium matrix surface through surface modification technology has become a crucial means to slow down its degradation rate and prevent premature failure.

[0004] Infected bone defects are often triggered by trauma or disease, causing severe loss and damage to bone tissue. In the infected microenvironment, the physiological balance between bone regeneration and resorption is completely disrupted: inflammatory cells infiltrate the defect site extensively, leading to a significant increase in pro-inflammatory factor levels, which in turn enhances osteoclast activity, inhibits osteoblast function, and ultimately hinders bone tissue regeneration and repair. Currently, the standard clinical treatment for infected bone defects involves debridement combined with systemic antibiotic therapy, followed by bone grafting. However, this approach has significant limitations: systemic medication is unlikely to achieve effective antibacterial concentrations in local tissues, and excessive antibiotic use can easily trigger systemic toxicity and exacerbate bacterial resistance.

[0005] In summary, developing functional bone repair materials that can precisely eliminate bacterial infection and efficiently promote bone growth, thereby achieving synergistic regulation of pathogen clearance and bone tissue regeneration, has significant clinical implications and application value for overcoming the challenges in treating infectious bone defects. Summary of the Invention

[0006] To address the problems of excessively rapid degradation rates and difficulty in synergistically exerting anti-infection and osteopromoting effects in vivo as bone repair materials, this invention proposes a pH-NIR dual-responsive biodegradable magnesium surface composite coating, its preparation method, and its application, to meet the clinical requirements for degradation rate, osteopromoting ability, and antibacterial properties of magnesium and its alloys in infectious bone defects.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One objective of this invention is to provide a pH-NIR dual-responsive biodegradable magnesium surface composite coating, which is formed on a biodegradable magnesium surface by an inner coating and an outer coating; wherein, the inner coating is a chemical conversion coating formed by phytic acid and calcium ions through layer-by-layer self-assembly; the outer coating is a metal-phenol network functionalized Nb2C MXene nanosheet coating; the metal-phenol network is formed by coordination of tannic acid and iron ions and has pH-NIR dual-responsiveness; the biodegradable magnesium surface is a micro-nano structure surface.

[0009] In this invention, the inner coating formed by phytic acid and calcium ions on the magnesium surface can tightly bind to the magnesium matrix. Calcium ions can enhance the intermolecular chelation of phytic acid, repair coating defects, and delay the corrosion of the magnesium matrix. The outer coating uses a metal-phenol network with both pH and near-infrared (NIR) responsive properties to functionalize niobium carbide (Nb2C). Under NIR irradiation, the metal-phenol network can kill bacteria through a photothermal effect; in the acidic environment derived from bacterial infection, it can accelerate lysis, releasing Nb2C MXene nanosheets with NIR responsive properties. This generates a photothermal antibacterial effect while simultaneously using its sharp edges to physically cut and destroy bacterial cell membranes and cell walls, leading to leakage of cell contents and cell death. Furthermore, Nb2C MXene has excellent reactive oxygen species (ROS) scavenging ability, interfering with ROS-related cellular signal transduction, thereby reducing the production of inflammatory cytokines and osteoclast formation, regulating the balance between bone regeneration and bone resorption, and improving bone loss caused by infectious bone defects.

[0010] The chemical conversion coating formed by phytic acid and calcium ions is obtained through a layer-by-layer self-assembly method. This layer-by-layer self-assembly technology allows phytic acid and calcium ions to form a dense protective coating through chemical chelation, filling the voids in the pure phytic acid coating, increasing the coating's density, and thus effectively slowing down its degradation rate.

[0011] The metal-phenol network is composed of tannic acid and iron ions. The tannic acid-iron ion coating has good pH and NIR responsiveness. Under NIR irradiation, it can exert antibacterial effect through photothermal effect and accelerate the release of Nb2C MXene in acidic environment to achieve synergistic antibacterial effect.

[0012] Furthermore, the biodegradable magnesium includes pure magnesium or magnesium alloys.

[0013] Furthermore, the surface of the micro-nano structure is obtained by polishing and ultrasonic cleaning to obtain a smooth and flat surface, and then prepared by alkaline heat treatment, fluorination treatment or micro-arc oxidation; the micro-nano structure includes micron or nano-sized particles, pores or sheet needle-like structures.

[0014] The second objective of this invention is to provide a method for preparing a pH-NIR dual-responsive biodegradable magnesium surface composite coating, comprising the following steps:

[0015] (1) Pre-treat biodegradable magnesium, and obtain a smooth and flat surface after grinding and ultrasonic cleaning. Then obtain micro-nano structures by alkaline heat treatment, fluorination treatment or micro-arc oxidation.

[0016] (2) The pretreated biodegradable magnesium was alternately immersed in phytic acid solution and calcium salt solution, and the operation was repeated after washing and drying. The inner coating was prepared by layer-by-layer self-assembly.

[0017] (3) The biodegradable magnesium with an inner coating is immersed in a dispersion solution of tannic acid-functionalized Nb2C MXene nanosheets, and an iron salt solution is added to react. After washing and drying, an outer coating is formed, resulting in a pH-NIR dual-response biodegradable magnesium surface composite coating, namely tannic acid-iron ion functionalized modified Nb2C MXene nanosheets.

[0018] In this invention, phytic acid and calcium ions form a stable structure through chelation, thereby obtaining a dense coating that effectively delays the corrosion of the magnesium substrate. The tannic acid molecules in the outer coating contain abundant pyrogallol groups, enabling them to achieve strong adhesion to various surfaces. They also form a metal-phenol network through chemical coordination with iron ions, ensuring a tight bond between the functionalized Nb2C MXene nanosheets and the inner coating. Simultaneously, the iron ions endow the metal-phenol network with excellent photothermal antibacterial properties and the ability to release Nb2C MXene nanosheets in response to acidic environments.

[0019] Furthermore, the biodegradable magnesium mentioned in step (1) includes pure magnesium or magnesium alloys.

[0020] Further, the concentration of the phytic acid solution in step (2) is 0.5-5 wt.%, preferably 1 wt.%; the pH value is 5-9, preferably 5.5.

[0021] Furthermore, the calcium salt mentioned in step (2) is derived from one or both of calcium nitrate and calcium sulfate.

[0022] Furthermore, the number of repetitions in step (2) is 1-20 times.

[0023] Further, the preparation process of the tannic acid-functionalized Nb2C MXene nanosheet dispersion in step (3) is as follows: Nb2AlC is slowly added to hydrofluoric acid solution and stirred at a constant temperature. After the first centrifugation, the precipitate is repeatedly washed with deionized water. The precipitate is dispersed in tetramethylammonium hydroxide aqueous solution, stirred at room temperature and centrifuged a second time to obtain multilayer Nb2C. After the second centrifugation, the multilayer Nb2C is repeatedly washed with deionized water to remove residual tetramethylammonium hydroxide. Then, ultrapure water is added to the multilayer Nb2C, and the mixture is shaken and stirred evenly. Nitrogen gas is bubbled into the solution, and sonicated under ice water protection. Then, a third centrifugation is performed to obtain a single-layer Nb2C MXene nanosheet dispersion. The single-layer Nb2C MXene nanosheet dispersion is ultrasonically dispersed and then tannic acid aqueous solution is added. The mixture is stirred in the dark to obtain the tannic acid-functionalized Nb2C MXene nanosheet dispersion.

[0024] The concentration of the hydrofluoric acid solution is 40 wt.%.

[0025] The constant temperature stirring temperature is 45℃, and the time is 48h;

[0026] The first and second centrifugations were both performed at 3000-5000 rpm for 5-10 minutes.

[0027] The concentration of the tetramethylammonium hydroxide aqueous solution is 25 wt.%.

[0028] The precipitate is repeatedly washed with deionized water 4-10 times.

[0029] The ultrasonic power under ice water protection is 100W, and the ultrasonic time is 30-60min;

[0030] The third centrifugation is performed at a speed of 3000-5000 rpm for 30-90 minutes.

[0031] The concentration of the monolayer Nb2C MXene nanosheet dispersion solution was 2 mg·mL. -1 ;

[0032] The concentration of the tannic acid aqueous solution is 2.5 mg·mL. -1 ;

[0033] The stirring time in the dark is 1-5 hours.

[0034] Furthermore, the iron salt mentioned in step (3) is selected from one or more of ferric nitrate, ferric sulfate and ferric chloride.

[0035] Furthermore, the cleaning described in step (3) is performed using deionized water, and the number of cleaning cycles is 2-5.

[0036] Furthermore, the reaction time in step (3) is 4-8 hours.

[0037] The third objective of this invention is to provide an application of a pH-NIR dual-responsive biodegradable magnesium surface composite coating in the preparation of bone tissue repair materials.

[0038] This invention presents a pH-NIR dual-responsive biodegradable magnesium surface composite coating prepared through surface modification, which offers significant advantages as a bone tissue repair material in the prevention and treatment of infected bone defects. Utilizing the coating's pH-NIR responsive characteristics, the coating enables the on-demand release of Nb₂C MXene nanosheets, which synergistically exert antibacterial effects with a metal-phenol network composed of tannic acid and iron ions. Furthermore, the excellent ROS scavenging properties of Nb₂C MXene promote a balance between bone resorption and bone regeneration, mitigating bone loss caused by infected bone defects while preventing excessive ROS generation that leads to rapid degradation of the magnesium matrix. This further ensures the early mechanical and structural integrity of magnesium and its alloys after implantation.

[0039] Compared with the prior art, the present invention has the following advantages and technical effects:

[0040] This invention utilizes a tannic acid-iron ion metal-phenol network with dual pH-NIR response to functionalize Nb2C MXene nanosheets, synergistically enhancing their antibacterial effect. Simultaneously, the chemical chelation between phytic acid and calcium ions is used to prepare an inner coating that effectively delays corrosion and slows the degradation rate of the magnesium matrix. The coating preparation method is simple, feasible, process-controllable, and low-cost. Immersion experiments show that the coating effectively inhibits the corrosion of the magnesium matrix; antibacterial experiments demonstrate its high efficiency in killing Staphylococcus aureus; and cell experiments show that the coating has excellent cell compatibility, effectively scavenging reactive oxygen species and promoting osteogenic differentiation. This provides a new method for constructing degradable magnesium-based bone tissue repair materials with both high bactericidal and osteointegration-promoting capabilities to treat infected bone defects, showing broad application prospects in the field of medical biotechnology. Attached Figure Description

[0041] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0042] Figure 1This diagram illustrates the preparation process of the pH-NIR dual-responsive biodegradable magnesium surface composite coating in this invention and the synergistic effect of the implant on antibacterial activity, inflammation regulation, and osteogenic promotion in an infectious bone defect model.

[0043] Figure 2 TEM image of the tannic acid-functionalized Nb2C MXene nanosheet dispersion prepared in Example 1;

[0044] Figure 3 Microscopic morphology of the magnesium alloy sample prepared in Example 2;

[0045] Figure 4 SEM images and elemental distribution of the pH-NIR dual-responsive biodegradable magnesium surface composite coating (PC-Nb2C-MPN) prepared in Example 3;

[0046] Figure 5 SEM image of the biodegradable magnesium surface composite coating (PC-Nb2C-TA) prepared in Comparative Example 1;

[0047] Figure 6 The concentration of Nb in the solution of the pH-NIR dual-responsive biodegradable magnesium surface composite coating (PC-Nb2C-MPN) obtained in Example 3 after soaking in PBS at different pH values ​​for 2 hours;

[0048] Figure 7 Infrared thermal images of the four groups of samples in Example 3: Uncoated, PC, PC-Nb2C-MPN, and PC-Nb2C-TA in Comparative Example 1;

[0049] Figure 8 Figure 1 shows the pH value change curves over time for four groups of samples (Uncoated, PC, PC-Nb2C-MPN) in Example 3 and PC-Nb2C-TA in Comparative Example 1, after immersion in SBF solution (a); Figure 2 is a magnified view of the pH value change over time for 0-8 hours in Figure 1.

[0050] Figure 9 DCFH-DA staining was used to detect the in vitro ROS scavenging performance of the four groups of samples in Example 3 (Uncoated, PC, PC-Nb2C-MPN) and Comparative Example 1 (PC-Nb2C-TA).

[0051] Figure 10 The in vitro antibacterial properties of the four groups of samples in Example 3 (Uncoated, PC, PC-Nb2C-MPN) and Comparative Example 1 (PC-Nb2C-TA) were tested.

[0052] Figure 11The results show the live / dead cell staining of the four groups of samples in Example 3: Uncoated, PC, PC-Nb2C-MPN, and PC-Nb2C-TA in Comparative Example 1. Detailed Implementation

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0055] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0056] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0057] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0058] This invention discloses a pH-NIR dual-response biodegradable magnesium surface composite coating, which consists of an inner chemical conversion coating formed by phytic acid and calcium ions and an outer coating formed by Nb2C MXene nanosheets functionalized with a metal-phenol network, forming a micro-nano structure on a magnesium surface.

[0059] In the following optional embodiments of the present invention, the magnesium with micro-nano structure is obtained by polishing and ultrasonic cleaning to obtain a smooth surface, and then by alkaline heat treatment, fluorination treatment or micro-arc oxidation.

[0060] In the following optional embodiments of the present invention, the chemical conversion coating formed by phytic acid and calcium ions is obtained by a layer-by-layer self-assembly method;

[0061] In the following optional embodiments of the present invention, the metal-phenol network is composed of tannic acid-iron ions.

[0062] This invention also provides a method for preparing a pH-NIR dual-responsive biodegradable magnesium surface composite coating, comprising the following steps:

[0063] (1) Pre-treat biodegradable magnesium, and obtain a smooth and flat surface after grinding and ultrasonic cleaning. Then obtain micro-nano structures by alkaline heat treatment, fluorination treatment or micro-arc oxidation.

[0064] (2) The pretreated biodegradable magnesium was alternately immersed in phytic acid solution and calcium salt solution, and the operation was repeated after washing and drying. The inner coating was prepared by layer-by-layer self-assembly.

[0065] (3) The biodegradable magnesium with an inner coating is immersed in a dispersion solution of tannic acid-functionalized Nb2C MXene nanosheets, and an iron salt solution is added to react. After washing and drying, an outer coating is formed, resulting in a pH-NIR dual-response biodegradable magnesium surface composite coating, namely tannic acid-iron ion functionalized modified Nb2C MXene nanosheets.

[0066] In the following optional embodiments of the present invention, the biodegradable magnesium in step (1) comprises pure magnesium or a magnesium alloy. Exemplarily, in the following preferred embodiments of the present invention, the biodegradable magnesium is selected as pure magnesium.

[0067] In the following optional embodiments of the present invention, the concentration of the phytic acid solution in step (2) is 0.5-5 wt.%, and the pH value is 5-9. Exemplarily, in the following preferred embodiments of the present invention, the concentration of the phytic acid solution is 1 wt.%, and the pH value is 5.5.

[0068] In the following optional embodiments of the present invention, the calcium salt in step (2) is derived from one or both of calcium nitrate and calcium sulfate. Exemplarily, in the following preferred embodiments of the present invention, the calcium salt is calcium nitrate.

[0069] In the following optional embodiments of the present invention, the number of repetitions in step (2) is 1-20 times. For example, in the following preferred embodiment of the present invention, the number of repetitions is 10 times.

[0070] In the following optional embodiments of the present invention, the preparation process of the tannic acid-functionalized Nb2C MXene nanosheet dispersion in step (3) is as follows: Nb2AlC is slowly added to hydrofluoric acid solution and stirred at a constant temperature. After the first centrifugation, the precipitate is repeatedly washed with deionized water. The precipitate is dispersed in tetramethylammonium hydroxide aqueous solution, stirred at room temperature and centrifuged a second time to obtain multilayer Nb2C. After the second centrifugation, the multilayer Nb2C is repeatedly washed with deionized water to remove residual tetramethylammonium hydroxide. Then, ultrapure water is added to the multilayer Nb2C, and the solution is shaken and stirred evenly. Nitrogen gas is bubbled into the solution, and sonicated under ice water protection. Then, a third centrifugation is performed to obtain a single-layer Nb2C MXene nanosheet dispersion. The single-layer Nb2C MXene nanosheet dispersion is ultrasonically dispersed and then added to tannic acid aqueous solution. The solution is stirred in the dark to obtain a tannic acid-functionalized Nb2C MXene nanosheet dispersion.

[0071] The concentration of the hydrofluoric acid solution is 40 wt.%.

[0072] The constant temperature stirring temperature is 45℃, and the time is 48h;

[0073] The first and second centrifugations are both performed at speeds of 3000-5000 rpm (for example, 3500 rpm) and for a time of 5-10 min (for example, 5 min).

[0074] The concentration of the tetramethylammonium hydroxide aqueous solution is 25 wt.%.

[0075] The number of times the precipitate is repeatedly washed with deionized water is 4-10 times (exemplary, such as 4 or 8 times);

[0076] The ultrasonic power under ice water protection is 100W, and the ultrasonic time is 30-60min (exemplary, such as 40min);

[0077] The third centrifugation is performed at a speed of 3000-5000 rpm (for example, 3500 rpm) for a time of 30-90 min (for example, 1 h).

[0078] The concentration of the monolayer Nb2C MXene nanosheet dispersion solution was 2 mg·mL. -1 ;

[0079] The concentration of the tannic acid aqueous solution is 2.5 mg·mL. -1 ;

[0080] The stirring time in the dark is 1-5 hours (for example, 2 hours).

[0081] In the following optional embodiments of the present invention, the iron salt in step (3) is selected from one or more of ferric nitrate, ferric sulfate, and ferric chloride. Exemplarily, in the following preferred embodiments of the present invention, the iron salt is ferric sulfate with a concentration of 7.5 mg·mL. -1 .

[0082] In the following optional embodiments of the present invention, the cleaning in step (3) is performed using deionized water, and the number of cleaning cycles is 2-5 times (e.g., 3 times).

[0083] In the following optional embodiments of the present invention, the reaction time in step (3) is 4-8 hours (exemplary, such as 6 hours).

[0084] This invention also provides the application of a pH-NIR dual-responsive biodegradable magnesium surface composite coating in the preparation of bone tissue repair materials. The bone tissue repair material exhibits both highly efficient bactericidal and osteopromoting effects, and degrades at an appropriate rate in vivo.

[0085] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0086] All raw materials used in this invention were purchased from the market.

[0087] The technical solution of the present invention will be further illustrated by the following embodiments.

[0088] Figure 1 This diagram illustrates the preparation process of the pH-NIR dual-responsive biodegradable magnesium surface composite coating in this invention and the synergistic effect of the implant in an infectious bone defect model, including antibacterial activity, inflammation regulation, and osteogenic promotion.

[0089] Example 1

[0090] The preparation steps of a tannic acid-functionalized Nb2C MXene nanosheet dispersion are as follows:

[0091] 1) Add 1g of Nb2AlC to a polytetrafluoroethylene reactor containing 8mL of 40wt.% hydrofluoric acid solution, stir at 45℃ for 48h, then centrifuge at 3500rpm for 5min, collect the precipitate and wash it repeatedly with deionized water 4 times.

[0092] 2) The precipitate obtained in step 1) was dispersed in a 25 wt.% tetramethylammonium hydroxide aqueous solution and stirred at room temperature for 96 h to obtain Nb2C multilayer nanosheets. The nanosheets were centrifuged at 3500 rpm for 5 min and washed 8 times with deionized water to remove residual tetramethylammonium hydroxide.

[0093] 3) Add ultrapure water to the precipitate obtained in step 2), shake and stir evenly, then bubble nitrogen gas into the solution, sonicate (100W) for 40 min under ice water protection, centrifuge at 3500 rpm for 1 h, collect the upper liquid to obtain a single-layer Nb2C nanosheet dispersion solution.

[0094] 4) Take 3 mL, 2 mg·mL -1 The Nb2C nanosheet dispersion obtained in step 3) was ultrasonically dispersed for 30 min, and then 0.12 mL and 2.5 mg·mL⁻¹ of sodium hydroxide solution were added. -1 A tannic acid solution was stirred in the dark for 2 hours to obtain a tannic acid-functionalized Nb2C MXene nanosheet dispersion.

[0095] Figure 2 The image shows a TEM image of the dispersion solution of tannic acid-functionalized Nb2CMXene nanosheets prepared in Example 1, which shows the morphology of the tannic acid-functionalized Nb2CMXene nanosheets.

[0096] Example 2

[0097] A pretreatment method for magnesium alloys, comprising the following steps:

[0098] Mg-Li-Zn alloy rods were cut into circular pieces with a thickness of 2 mm and a diameter of 10 mm. The pieces were polished with 800, 1200 and 2000 grit sandpaper in sequence, then ultrasonically cleaned with anhydrous ethanol and dried. The resulting samples were marked as Uncoated. The polished samples were then immersed in a 0.5 M potassium fluoride (KF) solution and fluorinated at room temperature for 96 h. After cleaning with deionized water and drying, the fluorinated magnesium alloy samples were obtained.

[0099] Figure 3 The image shows the microstructure of the magnesium alloy sample prepared in Example 2. Figure 3 As can be seen, after fluorination treatment, the film layer on the surface of the magnesium alloy is composed of a mixture of nano- and micro-scale grains, that is, a surface with micro- and nano-structures is formed.

[0100] Example 3

[0101] A method for preparing a pH-NIR dual-responsive biodegradable magnesium surface composite coating, comprising the following steps:

[0102] (1) Cut 4N pure magnesium (i.e., purity of 99.99%) rods into round pieces with a thickness of 2 mm and a diameter of 10 mm. Polish them with 800, 1200 and 2000 grit sandpaper in sequence, then ultrasonically clean them with anhydrous ethanol and dry them. The resulting samples are marked as Uncoated. The polished samples are immersed in a 13.8 wt.% sodium hydroxide solution, alkali heat treated at 80°C for 6 h, cleaned with deionized water and dried.

[0103] (2) The pure magnesium treated in step (1) was placed in a 1 wt.% phytic acid solution with pH = 5.5 and soaked at 40°C for 40 min. After washing with deionized water and drying, it was placed in a 0.5 M calcium nitrate solution and soaked at 40°C for 30 min. After washing with deionized water and drying, the above steps were repeated 10 times to prepare the inner coating. The resulting sample was labeled as PC.

[0104] (3) The pure magnesium with the inner coating from step (2) was immersed in the tannic acid-functionalized Nb2C nanosheet dispersion prepared in Example 1, and a concentration of 7.5 mg·mL was added. -1 The sample was soaked in ferric sulfate solution at room temperature for 6 hours, washed three times with deionized water, and dried. The resulting sample was labeled as PC-Nb2C-MPN.

[0105] Figure 4 SEM images and elemental distribution of the pH-NIR dual-responsive biodegradable magnesium surface composite coating (PC-Nb2C-MPN) prepared in Example 3; Figure 3 It can be seen that the elements are evenly distributed in the coating.

[0106] Comparative Example 1

[0107] Same as Example 3, except that ferric sulfate solution was not added in step (3), and the resulting sample was labeled as PC-Nb2C-TA.

[0108] Figure 5 SEM image of the biodegradable magnesium surface composite coating (PC-Nb2C-TA) prepared for Comparative Example 1.

[0109] Performance testing:

[0110] 1. Verification of pH response characteristics and NIR response characteristics

[0111] The pH response characteristics of the samples were verified using inductively coupled plasma atomic emission spectrometry (ICP-OES). The PC-Nb2C-MPN sample obtained in Example 3 was immersed in 1 mL of PBS solution (pH 5.5 and 7.4) at 37°C for 2 h. The concentration of Nb2C MXene released at different pH values ​​was measured using inductively coupled plasma atomic emission spectrometry (see [link to sample 1]). Figure 6 ).from Figure 6 As can be seen, the Nb content is significantly higher in an acidic environment of pH 5.5 compared to a neutral environment of pH 7.4, indicating that the biodegradable magnesium surface composite coating (PC-Nb2C-MPN) has pH-responsive characteristics, and the Nb2C MXene in the coating is released more rapidly in an acidic environment.

[0112] The NIR response characteristics of the samples were verified using an infrared thermal imager. Four groups of samples were used: uncoated pure magnesium obtained in step (1) of Example 3; phytic acid / calcium ion layer-by-layer self-assembled pure magnesium (PC) obtained in step (2) of Example 3; PC-Nb2C-TA obtained in Comparative Example 1; and PC-Nb2C-MPN obtained in Example 3. An 808nm laser was used to emit laser light, and the temperature change of the samples was measured by infrared thermal imaging. The results are as follows: Figure 7 As shown. From Figure 7 As can be seen, compared with uncoated pure magnesium and pure magnesium samples with phytic acid / calcium ion layer-by-layer self-assembly, PC-Nb2C-TA loaded with Nb2C MXene exhibits a significant photothermal effect. After modifying Nb2C MXene with tannic acid / iron ions, the photothermal effects of the two are superimposed, resulting in a more significant temperature rise in the PC-Nb2C-MPN sample compared with PC-Nb2C-TA.

[0113] 2. In vitro degradation experiment

[0114] Take three pieces each of the following samples: uncoated pure magnesium obtained in step (1) of Example 3, pure magnesium (PC) self-assembled from phytic acid / calcium ions obtained in step (2) of Example 3, PC-Nb2C-TA obtained in Comparative Example 1, and PC-Nb2C-MPN obtained in Example 3, and arrange them according to a solution volume to sample surface area ratio of 20 mL / cm². 2 Immersed in SBF simulated body fluid and placed in a 37°C constant temperature water bath, the pH value of the solution was tested periodically (results are shown in...). Figure 8 ).from Figure 8 As can be seen, after soaking for 216 hours, the pH value of the simulated body fluid in the uncoated pure magnesium group was the highest, indicating that its degradation was the most severe. The pure magnesium (PC) group with phytic acid / calcium ion layer-by-layer self-assembly was the second most severe. The degradation of the PC-Nb2C-TA group obtained in Comparative Example 1 was relatively slight, and the degradation rate of the PC-Nb2C-MPN group obtained in Example 3 was the lowest.

[0115] 3. ROS removal capability verification

[0116] Using cell culture medium as the extraction medium, four groups of samples were sterilized: uncoated pure magnesium obtained in step (1) of Example 3, pure magnesium (PC) obtained in step (2) of Example 3 with phytic acid / calcium ion layer-by-layer self-assembly, PC-Nb2C-TA obtained in Comparative Example 1, and PC-Nb2C-MPN obtained in Example 3. The samples were then sterilized at 1.25 cm⁻¹. 2The samples were immersed in culture medium at a ratio of / mL and incubated in a cell culture incubator for 24h. The extract was then aspirated, centrifuged, and the supernatant was retained. RAW264.7 cells were cultured in confocal culture dishes for 24h. The cell culture medium was then replaced with the material extract. After culturing the cells for 24h, they were exposed to 100mM H2O2 for 3h, incubated with 2,7-dichlorofluorescein diacetate (DCFH-DA) fluorescent probe for 30min to load the probe, washed with PBS, and fixed with cell fixation solution for 15min. The cells were washed again and 3mL of PBS solution was added. The results were observed using a confocal microscope (see results below). Figure 9 ).from Figure 9 As can be seen, the green fluorescence intensity of the PC-Nb2C-TA and PC-Nb2C-MPN samples loaded with Nb2CMXene is significantly lower than that of other groups, indicating that Nb2C MXene endows the coating with excellent ROS removal ability.

[0117] 4. Antibacterial test

[0118] Under anaerobic conditions, four groups of samples were incubated with 1 mL of Staphylococcus aureus suspension: uncoated pure magnesium obtained in step (1) of Example 3, pure magnesium (PC) with phytic acid / calcium ion layer-by-layer self-assembly obtained in step (2) of Example 3, PC-Nb2C-TA obtained in Comparative Example 1, and PC-Nb2C-MPN obtained in Example 3. For the PC-Nb2C-TA and PC-Nb2C-MPN groups, the samples were exposed to NIR (P = 2W, 808nm) for 5 minutes. Each group of samples was then transferred to centrifuge tubes, and sterile LB broth medium was added and sonicated for 5 minutes to resuspend the Staphylococcus aureus colonized on the sample surface in LB broth medium. Collect the above four groups of LB broth culture medium and dilute them 100-fold. Spread 100 μL of the diluted bacterial suspension evenly onto agar plates. Place the plates upright in a bacterial incubator (37℃) for 30 min, then invert them for 18 h. Photograph the four colonies. The results are as follows: Figure 10 As shown. From Figure 10 As can be seen, after surface modification of pure magnesium using Nb2C MXene functionalized with tannic acid / iron ions, the antibacterial ability of PC-Nb2C-MPN is significantly improved compared with the Uncoated and PC groups, and is superior to the PC-Nb2C-TA group. This is related to the strong photothermal antibacterial ability of tannic acid / iron ions and Nb2C MXene working synergistically.

[0119] 5. Cell compatibility test

[0120] Using cell culture medium as the extraction medium, four groups of samples were sterilized: uncoated pure magnesium obtained in step (1) of Example 3, pure magnesium (PC) obtained in step (2) of Example 3 with phytic acid / calcium ion layer-by-layer self-assembly, PC-Nb2C-TA obtained in Comparative Example 1, and PC-Nb2C-MPN obtained in Example 3. The samples were then sterilized at 1.25 cm⁻¹. 2 The samples were immersed in culture medium at a ratio of / mL and incubated in a cell culture incubator for 24h. The extract was then aspirated, centrifuged, and the supernatant was retained. Bone marrow mesenchymal stem cells were cultured in cell culture medium for 24h, then the cell culture medium was replaced with the material extract. After culturing for 24h, a live / dead cell staining working solution was prepared at a ratio of 2μM calcein AM: 8μM propidium iodide (PI). The extract was removed, and the live / dead cell working solution was added. The cells were incubated at room temperature for 20min and washed. After adding an anti-fluorescence quencher, the cells were photographed using an inverted fluorescence microscope to assess cell viability (results are shown in [link to results]). Figure 11 ).from Figure 11 As can be seen, the bone marrow mesenchymal stem cells cultured in the extracts of each group of samples were fully extended and in good growth condition, with no significant difference in cell proliferation among the groups.

[0121] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A pH-NIR dual-responsive biodegradable magnesium surface composite coating, characterized in that, It is formed on a biodegradable magnesium surface by an inner coating and an outer coating; The inner coating is a chemical conversion coating formed by the self-assembly of phytic acid and calcium ions layer by layer. The outer coating is a metal-phenol network functionalized Nb2C MXene nanosheet coating; The metal-phenol network is formed by coordination of tannic acid and iron ions and has dual pH-NIR responsiveness; The biodegradable magnesium surface is a micro / nano structure surface.

2. The pH-NIR dual-responsive biodegradable magnesium surface composite coating according to claim 1, characterized in that, The biodegradable magnesium includes pure magnesium or magnesium alloys.

3. The pH-NIR dual-responsive biodegradable magnesium surface composite coating according to claim 1, characterized in that, The surface of the micro-nano structure is obtained by polishing and ultrasonic cleaning to obtain a smooth and flat surface, and then prepared by alkaline heat treatment, fluorination treatment or micro-arc oxidation; the micro-nano structure includes micron or nano-sized particles, pores or sheet needle-like structures. The smooth surface is obtained by grinding and ultrasonic cleaning.

4. A method for preparing a pH-NIR dual-responsive biodegradable magnesium surface composite coating as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Pretreatment of biodegradable magnesium to obtain micro-nano structured surfaces; (2) The pretreated biodegradable magnesium was alternately immersed in phytic acid solution and calcium salt solution, and the operation was repeated after washing and drying. The inner coating was prepared by layer-by-layer self-assembly. (3) The biodegradable magnesium with an inner coating is immersed in a tannic acid-functionalized Nb2C MXene nanosheet dispersion solution, and an iron salt solution is added to react. After washing and drying, an outer coating is formed, resulting in a pH-NIR dual-response biodegradable magnesium surface composite coating.

5. The preparation method according to claim 4, characterized in that, The phytic acid solution has a concentration of 1 wt.% and a pH of 5.

5.

6. The preparation method according to claim 4, characterized in that, The calcium salt is derived from one or both of calcium nitrate and calcium sulfate.

7. The preparation method according to claim 4, characterized in that, The preparation process of the tannic acid-functionalized Nb2C MXene nanosheet dispersion solution is as follows: tannic acid is mixed with ultrasonically dispersed Nb2C MXene nanosheets and stirred in the dark; the stirring time in the dark is 2 hours.

8. The preparation method according to claim 4, characterized in that, The iron salt is selected from one or more of ferric nitrate, ferric sulfate, and ferric chloride.

9. The preparation method according to claim 4, characterized in that, The repeated operation in step (2) is performed 1-20 times; the cleaning in step (3) is performed using deionized water, and the cleaning is performed 2-5 times.

10. The application of a pH-NIR dual-responsive biodegradable magnesium surface composite coating as described in any one of claims 1-3 in the preparation of bone tissue repair materials.

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