Ag-au bimetallic titanium-based composite coating with antibacterial and osteogenic functions and preparation method thereof

Abstract

This invention discloses an Ag-Au bimetallic titanium-based composite coating with antibacterial and osteogenic functions, and its preparation method. The coating uses a medical-grade titanium alloy as a substrate and is constructed from the inside out as a nano-TiO2 transition layer, a dense Ag nano-intermediate layer, and an Au nano-current-transporting outer layer. The TiO2 transition layer is firmly bonded, and its nano-metasurface structure optimizes interfacial charge distribution and promotes electron transport. The Ag nanolayer continuously releases antibacterial Ag in physiological environments. + The Ag-Au nanolayer forms a bimetallic electric couple with the Au nanolayer, generating endogenous microcurrents that promote osteoblast proliferation. The Au nanolayer, as a good electron conductor, forms a bimetallic electric couple with the Ag layer, accelerating the oxidative dissolution of Ag by exporting electrons, significantly enhancing the overall microcurrent activity of the coating. This invention synergizes the Ag-Au bimetallic electric couple effect with the electron transport properties of the TiO2 metasurface, achieving a dual enhancement of antibacterial and electro-induced osteogenic functions, with broad application prospects in the field of surface modification for orthopedic and dental implants.

Description

Technical Field

[0001] This invention belongs to the field of biomedical materials technology, specifically relating to an Ag-Au bimetallic titanium-based composite coating with antibacterial and osteogenic functions and its preparation method, which can be used in the fields of medical implants and biosensors. Background Technology

[0002] Metallic materials are currently the most widely used category of materials in the field of orthopedic implants. Among them, titanium and titanium alloys have been widely promoted and applied in the biomedical field due to their core advantages, including high strength, lightweight, excellent corrosion resistance, high-temperature oxidation resistance, and excellent biocompatibility. These materials can be safely implanted into the human body and form a good interface with human tissue, and have been widely used in various orthopedic and dental medical devices such as artificial bones and dental prosthetics. However, postoperative infection related to orthopedic implants is a major cause of implant failure. Titanium and titanium alloy implants may still induce varying degrees of inflammatory reactions in the human body and are prone to bacterial and other microbial adhesion and colonization. To address the aforementioned issues, researchers have developed various improvement schemes (Surface modification techniques of titanium and titanium alloys for biomedical orthopaedics applications: A review. Colloids and Surfaces B: Biointerfaces, 2023, 227, 113339) to enhance the anti-infection properties of metallic implants. Among these, antibacterial coating technology has become the most widely used solution due to its high efficiency and cost-effectiveness. However, existing antibacterial coatings often contain high concentrations of bactericides or antibiotics, which pose potential threats to the environment and human health with long-term use. Furthermore, for orthopedic implants with bone defects, effectively enhancing the osteogenic capacity of the material remains a significant challenge in orthopedic clinical treatment. Therefore, developing novel orthopedic implant coating materials with both antibacterial and osteogenic functions has become an urgent need in this field.

[0003] Studies have shown that the unique piezoelectric properties of natural bone are a crucial foundation for maintaining its normal physiological functions (Micromotion-driven “mechanical-electrical-pharmaceutical coupling” bone-guiding membrane modulates stress-concentrating inflammation under diabetic fractures. Advanced Materials, 2025, 32, e70090). Natural bone tissue possesses an endogenous electroactive interface, which plays a key regulatory role in inducing directed differentiation of stem cells and resisting bacterial colonization and proliferation. Under physiological conditions, the physiological shear forces experienced by bone tissue can induce misalignment polarization of collagen fibers, thereby driving the bone tissue to autonomously generate endogenous micro-electric signals. This endogenous micro-electric field microenvironment is the core mechanism for regulating stem cell behavior and promoting bone tissue repair and regeneration.

[0004] Based on the electroactive properties of natural bone, researchers have demonstrated through simulations of its electrical stimulation that external electrical stimulation can effectively promote osteoblast attachment and proliferation while significantly inhibiting bacterial activity (Accelerated bone healing via electrical stimulation. Advanced Science, 2024, 2404190). However, currently used clinical exogenous electrical stimulation devices and implantable electronic devices mostly rely on battery power, which not only has a limited lifespan but also imposes a long-term economic burden and psychological stress on patients. Furthermore, traditional orthopedic implants struggle to effectively reconstruct the electrical stimulation microenvironment at the implantation site, and a comprehensive electroactive material system that can systematically meet the dual needs of antibacterial and osteopromoting processes during bone regeneration has not yet been developed. In conclusion, developing orthopedic implant coating materials with good biocompatibility and self-generating electrical stimulation activity has significant clinical value and research implications for alleviating postoperative infections and improving slow bone regeneration in orthopedic clinics. Summary of the Invention

[0005] The first objective of this invention is to provide an Ag-Au bimetallic titanium-based composite coating that can simulate the natural bone electroactive microenvironment, possesses excellent antibacterial and osteogenic functions, and exhibits good biocompatibility. The second objective of this invention is to provide a process-controllable and structurally stable method for preparing the aforementioned composite coating.

[0006] To achieve the above objectives, the present invention provides an Ag-Au bimetallic titanium-based composite coating with antibacterial and osteogenic functions. The coating uses titanium or titanium alloy as a substrate, and a nano-TiO2 transition layer, a dense Ag nano-intermediate layer, and an Au nano-current transport outer layer are sequentially constructed from the inside to the outside on the substrate surface.

[0007] Furthermore, the mechanism of the aforementioned technical solution is analyzed as follows:

[0008] This invention integrates a TiO2 nanosurface structure with an Ag-Au bimetallic electrode pair into a synergistic system through a sophisticated hierarchical design. In a physiological environment, the intrinsic potential difference between Au (high potential) and Ag (low potential) drives the formation of numerous micro-galvanic cells. Ag acts as the anode, continuously and controllably oxidizing and dissolving Ag with potent antibacterial activity. + And release electrons. Au, as the cathode, with its excellent conductivity, acts as an "electron highway" to promptly guide the electrons generated by the anode to the coating surface to participate in the electrochemical reduction process in the physiological environment, thereby greatly promoting the efficiency of the galvanic cell reaction and generating a continuous and enhanced microcurrent on the entire coating surface.

[0009] More importantly, the underlying TiO2 nanolayer is not an inert carrier. Its unique metasurface structure, composed of clusters of nanoneedle-like grains, optimizes the charge distribution at the coating's micro-interface, significantly accelerating carrier separation and transport, thereby more efficiently conducting the microcurrent generated by the Ag-Au electric couple to the surrounding biological tissue. Therefore, by adjusting the ratio of Ag to Au and the microstructure, Ag can be precisely controlled. + Release rate and microcurrent intensity are adjusted to meet the dual requirements of antibacterial properties and promoting a microenvironment conducive to osteoelectric activity.

[0010] This invention also provides a method for preparing the above-mentioned Ag-Au bimetallic titanium-based composite coating, comprising the following core steps:

[0011] (1) Pre-treat the titanium or titanium alloy substrate to obtain a clean surface;

[0012] (2) By combining alkaline heat treatment with acid washing and then high-temperature calcination, a TiO2 transition layer with a nano-rough structure is constructed in situ on the substrate;

[0013] (3) A dense Ag nano-intermediate layer was prepared on the TiO2 layer by sensitization-activation-chemical deposition method;

[0014] (4) Au nano-outer layer is deposited on Ag layer by magnetron sputtering to finally obtain the composite coating.

[0015] In the preferred embodiment, the control range of key process parameters is as follows:

[0016] In step (1), after the substrate is polished, it is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 10-30 minutes in sequence.

[0017] In step (2), the concentration of NaOH used in the hydrothermal reaction is 6-12M, and the reaction is carried out at 120-170℃ for 2-5 hours; the pH of the hydrochloric acid solution used for acid washing is 1.5-3, and the treatment is repeated 2-5 times; the calcination temperature is 400-900℃, and the time is 2-4 hours.

[0018] In step (3), the [Ag(NH3)2] used + The aqueous solution concentration is 5-20 mM; the reducing agent used is D-(+)-glucose, etc.

[0019] In step (4), the working gas pressure of magnetron sputtering is 0.5-1 Pa, the sputtering current is 200-350 mA, and the sputtering time is 10-40 min.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Achieving a highly efficient and safe balance between antibacterial and bone-promoting functions. This is achieved through physical microcurrent stimulation and chemical Ag... + The dual release mechanism achieves highly efficient antibacterial activity (killing rate of >97% for common pathogens) while avoiding toxicity to host cells and significantly promotes osteoblast proliferation (cell activity can reach 220%), solving the problem of poor biocompatibility of traditional antibacterial coatings.

[0022] (2) The coating has stable and long-lasting performance. The precise structure of the layered construction, especially the dense and uniform TiO2 and Ag intermediate layer, effectively avoids Ag corrosion. + The initial burst release achieved a stable and continuous release for up to 14 days, ensuring the safety and effectiveness of the implant for long-term use in the body.

[0023] (3) The process is controllable and adjustable, and has strong universality. By independently controlling the parameters of chemical deposition and physical sputtering, the Ag layer loading and Au layer thickness can be precisely tailored, thereby customizing the electroactivity and ion release behavior of the coating according to clinical needs. It has broad application prospects in the field of surface modification of implantable devices such as orthopedics and dentistry. Attached Figure Description

[0024] Figure 1 A photograph of the Ti-TiO2-AgAu composite coating prepared in Example 1.

[0025] Figure 2The images show scanning electron microscope (SEM) images of the coating prepared in Example 1 at different stages, where: (a) Ti-OH obtained after alkaline heat treatment, (b) Ti-TiO2 obtained after high-temperature calcination, (c) Ti-TiO2-Ag obtained after chemical deposition of Ag, and (d) the final Ti-TiO2-AgAu composite coating obtained after magnetron sputtering of Au.

[0026] Figure 3 The images show X-ray energy dispersive spectroscopy (EDS) patterns of the coatings prepared in Example 1 at different stages, where: (a) pure Ti alloy substrate, (b) Ti-TiO2 coating, (c) Ti-TiO2-Ag coating, and (d) final Ti-TiO2-AgAu composite coating.

[0027] Figure 4 Ag in samples from Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6 + Release kinetics curve.

[0028] Figure 5 The bar chart shows the relative cell viability of fibroblasts (L929) after co-culturing with samples from each example and comparative example.

[0029] Figure 6 The bar chart shows the relative cell viability of osteoblasts (MC3T3-E1) after co-culturing with samples from each example and comparative example. Detailed Implementation

[0030] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0031] Example 1:

[0032] This embodiment provides a method for preparing a Ti-TiO2-AgAu composite coating. The coating uses a titanium alloy (Ti-6Al-4V) as a substrate and comprises, from the inside out: a nano-TiO2 transition layer, a dense Ag nano-intermediate layer, and an Au nano-current transport layer. The specific preparation steps are as follows:

[0033] (1) Pretreatment of titanium alloy substrate: Select cylindrical titanium alloy (Ti-6Al-4V) sheets with a diameter of 10 mm and a thickness of 2 mm, and polish them thoroughly with 80-2000 grit sandpaper until the surface is smooth. Place the polished titanium alloy sheets in acetone, anhydrous ethanol, 75% ethanol and deionized water in sequence, and ultrasonically clean each for 20 min to remove surface impurities and grease. Dry the cleaned titanium alloy sheets in a 60℃ drying oven for 24 h for later use.

[0034] (2) Surface alkaline thermal activation treatment: The cleaned titanium alloy sheet was immersed in 25 ml of 10M NaOH solution and transferred to a reaction vessel with a polytetrafluoroethylene liner. The reaction was carried out hydrothermally at 150°C for 3 h. After naturally cooling to room temperature, the titanium alloy sheet was transferred to 500 ml of hydrochloric acid solution (pH=2) and reacted for 24 h under continuous stirring. This hydrochloric acid treatment process was repeated 3 times to remove residual Na. + The product was then washed with deionized water and freeze-dried to obtain a titanium-based material with a surface rich in hydroxyl groups, denoted as Ti-OH.

[0035] (3) Preparation of TiO2 layer by calcination: Ti-OH is placed in a muffle furnace and calcined at 450°C for 4 hours in air atmosphere. After cooling to room temperature with the furnace, a coating material with TiO2 nanostructure on the surface can be obtained, which is denoted as Ti-TiO2.

[0036] (4) Chemical deposition of Ag nanolayer: Ti-TiO2 was first sensitized by immersing it in 3 ml of an aqueous solution containing 0.3 mM SnCl2 and 0.1 μl HCl (32%) for 30 min; after thorough rinsing with ultrapure water, it was immediately immersed in 3 ml of 3 mM Pd(NO3)2 aqueous solution for 10 min to allow Pd to precipitate. 2+ Sn 2+ In-situ reduction to catalytic seed crystals. The treated sample was thoroughly rinsed with ultrapure water and then rapidly immersed in 3 ml of 10 mM [Ag(NH3)2]. + In an aqueous solution, immediately add 3 ml of 1 M D-(+)-glucose aqueous solution as a reducing agent. Let the reaction stand at room temperature for 5 minutes, then remove. [Ag(NH3)2] + The solution was prepared by adding 1 ml of concentrated ammonia (28%) dropwise to 10 ml of 1 M AgNO3 aqueous solution. The solution was observed to first turn brown and then become clear and transparent again. Finally, the product was rinsed with ultrapure water and dried with flowing nitrogen in a fume hood to obtain a coating material with a dense Ag nanolayer on the surface, denoted as Ti-TiO2-Ag.

[0037] (5) Magnetron sputtering of Au nano-outer layer: The Ti-TiO2-Ag composite coating was fixed on the sample stage of the magnetron sputtering instrument. A high-purity gold target (99.99%) was used as the sputtering source, and the base vacuum of the sputtering chamber was evacuated to ≤5×10⁻⁶. -4 Pa. High-purity argon gas (99.999%) was introduced, and the working pressure was adjusted to 0.8 Pa. The sputtering current was set to 320 mA, and the sputtering power to 70 W. The sample was sputtered at room temperature for 20 min. After sputtering, the sample was allowed to cool to room temperature in a vacuum before being removed, resulting in a Ti-TiO2-AgAu composite coating with a uniform Au nanolayer outer layer.

[0038] The macroscopic and microscopic morphology of the Ti-TiO2-AgAu composite coating prepared in Example 1 was characterized. See the photographs below. Figure 1 Scanning electron microscopy (SEM) results ( Figure 2 This revealed the microscopic morphological changes during the coating evolution process. After alkaline heat treatment, an irregular porous structure with a pore size of approximately 150 nm was formed on the Ti-OH surface. Figure 2 a). Subsequent high-temperature calcination treatment causes the porous structure to transform into spherical particles composed of numerous nano-needle-like crystal clusters, uniformly covering the surface, with a particle size of approximately 2 μm. Figure 2 b). This TiO2 nanostructure, with its ultra-high specific surface area and abundant interfaces, provides an ideal microscopic template for the subsequent uniform loading and charge transport of bimetals. Based on this, bimetals were successfully loaded via silver mirror reaction and ion sputtering, resulting in Ti-TiO2-Ag ( Figure 2 c) and Ti-TiO2-AgAu ( Figure 2 d) The composite coating has no significant change in microstructure compared to Ti-TiO2, indicating that the deposited Ag and AgAu bimetallic layers are thin, uniform and dense.

[0039] X-ray energy dispersive spectroscopy (EDS) analysis Figure 3 This confirmed the evolution of chemical composition at each step. Only characteristic peaks of Ti, Al, and V were detected in the pure titanium alloy matrix. Figure 3 a). Strong characteristic peaks of O element were newly formed in the spectrum of Ti-TiO2 ( Figure 3 (b) Qualitatively confirmed the formation of the TiO2 layer. Furthermore, characteristic peaks of Ag were observed in the Ti-TiO2-Ag spectrum ( Figure 3 c), while the spectrum of the Ti-TiO2-AgAu composite coating ( Figure 3 The presence of characteristic peaks for both Ag and Au in d) conclusively proves that the Ag-Au bimetallic component has been successfully loaded.

[0040] Example 2: Only the sputtering time of Au in step (5) of Example 1 is changed to 10 min.

[0041] Example 3: Only the sputtering time of Au in step (5) of Example 1 is changed to 30 min.

[0042] Example 4: Only change [Ag(NH3)2] in step (4) of Example 1. + The concentration of the aqueous solution is 5 mM.

[0043] Example 5: Only change [Ag(NH3)2] in step (4) of Example 1. + The concentration of the aqueous solution is 15 mM.

[0044] Comparative Example 1: Pure titanium alloy matrix, treated only by step (1) of Example 1.

[0045] Comparative Example 2: Ti-OH coating, treated only by steps (1) and (2) of Example 1.

[0046] Comparative Example 3: Ti-TiO2 coating, treated only by steps (1) to (3) of Example 1.

[0047] Comparative Example 4: Ti-TiO2-Ag coating, after being treated by steps (1) to (4) of Example 1, is the intermediate product without the deposited Au outer layer.

[0048] Comparative Example 5: Ti-AgAu coating, omitting the TiO2 transition layer, directly on the Ti-OH surface treated in steps (1) and (2), performing Ag deposition in step (4) and Au sputtering in step (5) in sequence.

[0049] Comparative Example 6: One-step Ti-TiO2-AgAu coating. On the Ti-TiO2 obtained after completing step (3) of Example 1, a dual-target magnetron sputtering system with independent high-purity gold (99.99%) and high-purity silver (99.99%) targets was used in the same vacuum chamber (base vacuum ≤ 5 × 10⁻⁶). -4 Ti-TiO2 was simultaneously sputtered with Ag (sputtering power 70W, 30min) and Au (sputtering power 70W, 20min) at a working pressure of 0.8Pa to obtain an Ag / Au disordered mixed coating.

[0050] To comprehensively evaluate the biological and electrochemical properties of the coatings, systematic tests were performed on all examples and comparative examples:

[0051] 1. Electrochemical performance and microcurrent generation mechanism:

[0052] A three-electrode system (working electrode: the prepared sample; reference electrode: Ag / AgCl; auxiliary electrode: Pt wire) was used with 1×PBS buffer (pH 7.4) as the electrolyte. The current-time curves of each sample were recorded using an electrochemical workstation. The steady-state microcurrent density data are summarized in Table 1.

[0053] As shown in Table 1, pure titanium and samples containing only TiO2 (Comparative Examples 1-3) showed almost no current output (~0.1µA / cm). 2 All coatings containing Ag / Au bimetals produced significant microcurrents (2.8~4.2µA / cm). 2 This directly proves that the electrical couple formed between Ag and Au is the core driving force for generating microcurrents. Specifically, Example 1 exhibits an excellent current density (4.0 µA / cm²). 2The comparative example 6, prepared by the one-step method, had the highest current density (4.2 µA / cm). 2 From the perspective of instantaneous power generation alone, the disordered Ag / Au layer appears to perform better. However, this indicator cannot reflect the coating's long-term ion release, cell compatibility, and long-term osteogenic repair capacity, and can only be used as a single reference.

[0054] Table 1. Current densities in PBS buffer for Examples 1-5 and Comparative Examples 1-6 of the present invention.

[0055]

[0056] 2. Cytotoxicity and Ag + Long-term effect assessment:

[0057] The obtained materials (Example 1, Comparative Example 4, Comparative Example 5, and Comparative Example 6) were placed in 10 ml of PBS buffer at 37°C. From day 1 to day 14, 3 ml of the release solution was taken every other day for Ag. + Concentration was determined, and 3 ml of fresh 1×PBS buffer (pH 7.4) was added to maintain a constant total volume. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to measure Ag at different time points. + Release amount. Figure 4 Ag in PBS buffer for the tested sample group + Release kinetics curve.

[0058] Compared with Example 1 and Comparative Example 5 (without TiO2 layer), the former showed a higher and more stable release, demonstrating that the TiO2 nanolayer not only acts as a carrier but also modulates Ag through its highly reactive interface. + The continuous and uniform dissolution. Crucially, the Ag in Comparative Example 6... + The release curve exhibited a harsh "burst-depletion" pattern: the release was extremely high from day 1 to 7, far exceeding other groups, which was the direct cause of its significant cytotoxicity; however, from day 9 onwards, the release decreased sharply, indicating that its long-lasting antibacterial and electrostimulatory capabilities would not be sustainable. This set of control experiments clearly shows that, although the initial microcurrent and Ag in control group 6... + It offers high release, but at the cost of long-term stability. In contrast, the finely layered structure of Example 1 achieves Ag... + Safe, stable, and long-term release.

[0059] 3. Cytotoxicity assay:

[0060] First, the toxicity of each sample to L929 fibroblasts was evaluated using the CCK-8 assay. Figure 5L929 fibroblasts were seeded into 24-well plates and cultured for 24 hours. Then, samples (Examples 1-5 and Comparative Examples 1-6) were added to the wells and incubated for another 24 hours. CCK-8 assay reagent was then added, and cell viability was detected using an ELISA reader.

[0061] The results showed that, compared with pure titanium (Comparative Example 1), the relative cell viability of Examples 1-4 and Comparative Examples 2-5 were all higher than 90%, demonstrating excellent biocompatibility. However, Comparative Example 6 had the lowest cell viability (~80%), exhibiting significant cytotoxicity.

[0062] 4. Microcurrent osteoblast proliferation activity:

[0063] To evaluate the effect of Ti-TiO2-AgAu coating electrostimulation on osteoblast proliferation, MC3T3-E1 cells were seeded at an appropriate density in 24-well plates. Cells were incubated at 37°C with 5% CO2 until adherence. Samples (Examples 1-5 and Comparative Examples 1-6) were then added to the wells. Cells were further incubated at 37°C with 5% CO2 for 48 h. Relative cell viability was determined using a CCK-8 cell viability assay kit. Figure 6 The bar chart shows the relative cell viability of osteoblasts after co-culturing with each sample (Examples 1-5 and Comparative Examples 1-6).

[0064] All Ag / Au bimetallic coatings exhibited significantly superior osteogenic activity compared to pure titanium (Comparative Example 1) and single TiO2 coatings (Comparative Examples 2 and 3), confirming the crucial role of microcurrent stimulation. Example 1 demonstrated the best osteogenic capacity, with cell activity reaching ~220%, significantly superior to Examples 2 (~180%) and 3 (~200%), determining the optimal Au sputtering time to be 20 min; it was also superior to Examples 4 (~150%) and 5 (~160%) with varying Ag concentrations, establishing the optimal Ag concentration. + The concentration was 10 mM. Although Comparative Example 6 had the highest initial current, its osteogenic activity (~180%) was significantly lower than that of Example 1 (~220%). This was in conjunction with L929 fibroblast toxicity and Ag... + Comprehensive analysis of the release curves suggests that this may be related to the early Ag release in Comparative Example 6. + The cytotoxicity caused by the burst release severely offset the positive stimulating effect of the high current and inhibited the proliferative potential of osteoblasts.

[0065] 5. Overall antibacterial properties:

[0066] Escherichia coli and Staphylococcus aureus were used as experimental strains for the antibacterial experiment. The revived bacteria were placed in liquid culture medium and incubated overnight at 37°C on a shaker. Samples from Examples 1-5 and Comparative Examples 1-6 were placed in 12-well plates, and 100 µl of bacterial suspension was added to the sample surface for each. After 4 hours of incubation, 1 ml of PBS solution was added to each sample, followed by sonication. 50 µl of bacterial suspension was then plated and incubated overnight at 37°C on a shaker. The number of bacterial colonies was then observed. The statistical data of plate colonies in the in vitro antibacterial experiment are shown in Table 2.

[0067] The results showed that all Ag-containing coatings exhibited effective short-term antibacterial activity, with antibacterial efficiency positively correlated with Ag content and microcurrent activity. Comparative Example 6 and Example 5 (high Ag concentration) showed the highest antibacterial rates (survival rate 1-3%); however, their antibacterial mechanisms were quite different, involving Ag... + The release kinetic curves indicate that the strong antibacterial activity of Comparative Example 6 may originate from the initial Ag. + "Burst release," this uncontrolled release of ions, leads to both cytotoxicity and functional decline, making it an undesirable sterilization mode. Example 1, however, cleverly combines continuous microcurrent physical sterilization with an appropriate amount of long-lasting Ag under optimized process parameters. + The synergistic effect of chemical sterilization achieves excellent antibacterial effect (survival rate ≤3%) while perfectly balancing cell compatibility and coating stability.

[0068] Table 2. Relative bacterial survival rates of Examples 1-5 and Comparative Examples 1-6 of the present invention.

[0069]

Claims

1. An Ag-Au bimetallic titanium-based composite coating with antibacterial and osteogenic functions, characterized in that: The composite coating uses titanium or titanium alloy as a substrate, and is constructed sequentially from the inside to the outside of the substrate surface as follows: The nano-TiO2 transition layer has a nano-rough structure composed of spherical particles formed by clusters of nano needle-like crystals. The Ag nano-intermediate layer is a dense coating formed by chemical deposition. The Au nano-outer layer is a current transport layer formed by physical sputtering.

2. The Ag-Au bimetallic titanium-based composite coating according to claim 1, characterized in that: The titanium alloy substrate is Ti-6Al-4V.

3. The Ag-Au bimetallic titanium-based composite coating according to claim 1, characterized in that: The nano-TiO2 transition layer is generated in situ from a titanium substrate after alkaline heat treatment, acid washing to remove residual alkali metal ions, and high-temperature calcination.

4. A method for preparing an Ag-Au bimetallic titanium-based composite coating as described in any one of claims 1-3, characterized in that: Includes the following steps: (1) The pretreated titanium or titanium alloy substrate is subjected to alkaline heat treatment, followed by pickling and drying to obtain a titanium-based material with hydroxyl-rich surface. (2) The material obtained in step (1) is calcined in air at high temperature and cooled to obtain a coating with TiO2 nanostructure on the surface; (3) On the surface of the coating obtained in step (2), a dense Ag nano-intermediate layer is chemically deposited by sensitization-activation treatment and then by using a silver mirror reaction with glucose as a reducing agent. (4) On the surface of the coating obtained in step (3), an Au nano-outer layer is physically deposited by magnetron sputtering to finally obtain the composite coating.

5. The preparation method according to claim 4, characterized in that: In step (1), the conditions for the alkaline heat treatment are: hydrothermal reaction at 150°C for 3 hours in a 10M NaOH solution.

6. The preparation method according to claim 4, characterized in that: In step (2), the conditions for high-temperature calcination are: calcination at 450°C for 4 hours in an air atmosphere in a muffle furnace.

7. The preparation method according to claim 4, characterized in that: In step (3), [Ag(NH3)2] is used for the silver mirror reaction. + The concentration of the aqueous solution is 10 mM.

8. The preparation method according to claim 4, characterized in that: In step (4), the time for depositing the Au nano-outer layer by magnetron sputtering is 20 min.

9. The use of the Ag-Au bimetallic titanium-based composite coating as described in any one of claims 1-3 in the preparation of antibacterial and / or bone-promoting medical implant materials.

10. The application according to claim 9, characterized in that, The medical implant material is an orthopedic or dental implant.

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