Preparation method and application of nano-particle micro-arc oxidation coating on surface of medical magnesium alloy

Abstract

The invention provides a preparation method and application of a nano-particle micro-arc oxidation coating on the surface of a medical magnesium alloy. The preparation method comprises the following steps: preparing an electrolyte, wherein the electrolyte comprises the following components: calcium glycerophosphate, sodium hexametaphosphate, potassium hydroxide, ammonium bifluoride, glycerol, hydrogen peroxide, Nano-SiO2 and nano-hydroxyapatite; sequentially adding the components into ultrapure water, and stirring to uniformly mix; a bipolar current mode power supply is used for MAO processing. The coating obtained based on the method has good biological activity and corrosion resistance at the same time, the coating has good stability in a body fluid environment, and the degradation time is prolonged so as to be matched with the bone healing rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical materials, and in particular relates to a preparation method of a nano-particle micro-arc oxidation coating on the surface of a medical magnesium alloy and an application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] In recent years, magnesium alloys have shown great application potential in the field of medical implant materials due to their unique biocompatibility, degradability, and mechanical properties similar to those of human bone tissue. After magnesium alloy implants degrade in the body, their degradation products can be naturally excreted through the kidneys, avoiding the disadvantage of traditional non-degradable materials such as stainless steel and titanium alloys requiring secondary surgery to remove. However, magnesium has active chemical properties and is prone to electrochemical corrosion in body fluid environments, leading to premature failure of the implant. Excessively rapid degradation rates not only reduce the mechanical strength of the implant, but may also cause local hydrogen bubble accumulation and inflammatory reactions, affecting the bone healing process. Therefore, how to effectively regulate the degradation rate of magnesium alloys while improving their corrosion resistance and bioactivity has become a key challenge in current research.

[0004] Micro-arc oxidation (MAO) is an advanced surface modification technology that electrochemically generates in situ ceramic coatings on valve metals (such as magnesium, aluminum, and titanium). MAO technology applies a high voltage to an electrolyte, causing micro-area discharges on the metal surface, forming a dense oxide coating. Electrolyte composition is a key factor influencing the performance of MAO coatings. Phosphate-based electrolytes have become a hot topic in research on MAO coatings for medical magnesium alloys due to their excellent biocompatibility and bone integration. Silicate- and aluminate-based electrolytes have also been extensively studied, but their low biocompatibility and corrosion resistance limit their application in the medical field.

[0005] In recent years, researchers have successfully optimized coating structure and expanded functionalities by incorporating nanoparticles into MAO electrolytes or coating systems, providing a new technological path for the development of medical implant materials. MAO coatings inevitably develop micropores and microcracks during the preparation process, resulting in a porous, non-dense morphology. Under long-term physiological conditions, physiological fluids enter the coating through the micropores, permeate the coating / substrate interface, and corrode the substrate. Consequently, micro-arc oxidation coatings cannot provide long-term corrosion protection for magnesium, compromising the coating's long-term corrosion resistance. The dispersion and stability of nanoparticles in MAO electrolytes directly impact the coating's uniformity and performance. Existing studies have primarily employed mechanical stirring or ultrasonic dispersion, but nanoparticles are still susceptible to agglomeration, resulting in localized inhomogeneous coating properties. Furthermore, existing research has primarily focused on the short-term performance of coatings (e.g., corrosion resistance and biocompatibility), but lacks systematic evaluation of their degradation behavior in long-term physiological environments and the biosafety of nanoparticle release. These issues have limited the widespread application of MAO coatings in medical implants.

[0006] Tian et al. prepared a high-crystallinity needle-shaped hydroxyapatite (HA) coating on the surface of micro-arc magnesium oxide by a hydrothermal method, completely covering the MAO coating. However, since the hydrothermal solution contains both Ca and P sources, in addition to the formation of HA on the surface of micro-arc magnesium oxide during the hydrothermal process, the Ca in the solution also forms a hydroxyapatite coating. 2+ and PO4 3- A reaction occurs, HA is precipitated in the solution, causing the chemical composition of the solution to change dynamically, resulting in uncontrollable HA structure formed on the surface of micro-arc magnesium oxide. Summary of the Invention

[0007] In order to overcome the shortcomings of the existing technology, the present invention provides a preparation method and application of nano-particle micro-arc oxidation coating on the surface of medical magnesium alloy; the present invention simultaneously introduces nano-SiO2 and nano-HA, utilizes the pore-filling effect of nano-SiO2 and the biological activity of nano-HA, and realizes the dual optimization of corrosion resistance and biological activity of the coating; the present invention proposes for the first time a synergistic modification strategy of nano-SiO2 and nano-HA, and optimizes the performance of MAO coating through the dual mechanisms of pore filling and biological activity enhancement.

[0008] As a first aspect of the present invention, a method for preparing a nanoparticle micro-arc oxidation coating on the surface of a medical magnesium alloy is provided, comprising the following steps: Step 1, preparing an electrolyte, the electrolyte composition including C3H7CaO6P 2-12.5 g / L, (NaPO3) 62-12.5 g / L, KOH 4.2-11.2 g / L, NH4HF 23.42-13.68 g / L, C3H6O 35-25 mL / L, H2O 25-25 mL / L, Nano-SiO2 1-7 g / L, and nano-HA 1-5 g / L; In step 2, a bipolar current mode power supply is used for MAO treatment. During the reaction, the electrolyte is continuously stirred and the temperature is controlled not to exceed 30° C. to prevent overheating.

[0009] In some embodiments of the present invention, in step 1, the ingredients are sequentially added to ultrapure water and stirred using a hot plate magnetic stirrer to ensure uniform mixing.

[0010] In some embodiments of the present invention, in step 2, the MAO treatment parameters are set as follows: positive voltage 350-500 V, negative voltage 10-40 V, positive duty cycle 10-40%, negative duty cycle 10-30%, frequency 400-800 Hz, and reaction time 5-30 min. During the reaction, the electrolyte is continuously stirred and the temperature is maintained at no more than 30°C using a cooling water circulator.

[0011] In some embodiments of the present invention, the particle size of Nano-SiO2 ranges from 30 to 500 nm.

[0012] In some embodiments of the present invention, the particle size of nano-HA ranges from 20 to 200 nm.

[0013] As a preferred embodiment of the present invention, the concentration of Nano-SiO2 is 3~5 g / L, and the concentration of nano-HA is 3~5 g / L.

[0014] More preferably, the concentration of Nano-SiO2 is 3 g / L and that of nano-HA is 5 g / L.

[0015] In terms of process optimization, this paper uses a bipolar current mode to improve the uniformity of nanoparticle dispersion in the coating. By optimizing the electrolyte composition and electrical parameters, nanoparticle agglomeration is reduced, ensuring the uniformity and consistency of the coating.

[0016] This study also systematically evaluated the coating's degradation behavior in simulated body fluids and the release kinetics of the nanoparticles through immersion experiments and cytotoxicity tests. The results showed that the synergistic effect of the dual nanoparticles (nano-SiO2 and nano-HA) significantly improved the coating's compactness and corrosion resistance. Furthermore, the coating's pore structure could be manipulated to achieve controlled drug adsorption and sustained release.

[0017] As a second aspect of the present application, there is provided a coating prepared by the method for preparing a nano-particle micro-arc oxidation coating on a surface of a medical magnesium alloy.

[0018] As a third aspect of the present application, there is further provided an application of the coating prepared by the method for preparing a nano-particle micro-arc oxidation coating on a surface of a medical magnesium alloy as a drug carrier.

[0019] The drug is selected from antibacterial drugs (such as gentamicin, silver ions) and bone repair drugs (such as BMPs, bisphosphonates), anti-inflammatory drugs such as ibuprofen, diclofenac and salts thereof.

[0020] Preferably, the drug is an anti-inflammatory drug, or a combination of the anti-inflammatory drug and a pH-sensitive material.

[0021] Compared with the prior art, the present application has the following beneficial effects: 1. The present application provides a method for preparing a nano-particle micro-arc oxidation coating on a surface of a medical magnesium alloy, which first proposes a synergistic modification strategy of nano-SiO2 and nano-HA, optimizes the performance of the coating through the dual mechanisms of pore filling and bioactivity enhancement, and overcomes the drawbacks of the prior art that the coating is difficult to simultaneously consider corrosion resistance and bioactivity by filling pores with a single nano-particle. The nano-SiO2 can effectively fill the micropores and microcracks in the coating due to its high specific surface area and chemical stability, thereby significantly improving the compactness and corrosion resistance of the coating; and the bone induction performance of the nano-HA enhances the bioactivity and bone integration ability of the coating by simulating the mineral composition of natural bone. This dual-nano-particle synergistic modification strategy not only solves the problem that a single nano-particle modification is difficult to simultaneously consider corrosion resistance and bioactivity, but also provides a new idea for the multifunctional design of the coating.

[0022] 2. The coating prepared by the method provided in the present application has good bioactivity and corrosion resistance, and the coating has good stability in a simulated body fluid environment, thereby prolonging the degradation time to match the bone healing rate.

[0023] 3. The use of a bipolar current mode improves the uniform distribution of nano-particles in the coating, and breaks through the limitations of traditional direct current power in the compactness control of the coating. The bipolar current mode can effectively reduce the agglomeration of nano-particles and ensure the uniform dispersion of the nano-particles in the coating, thereby improving the overall performance of the coating. In addition, the electrolyte composition and electrical parameters are optimized in the present application, which further improves the uniformity and consistency of the coating, and provides a new reference for the process optimization of the MAO technology.

[0024] 4. Although previous studies have achieved functionalization by incorporating antimicrobial agents or drug molecules into MAO coatings, these functions often rely on a single mechanism (such as sustained drug release or antibacterial properties) and lack multifunctional synergistic effects. This present invention addresses this gap by investigating and exploring the potential of coatings for drug loading, focusing on pharmaceutical needs. The porous structure of MAO coatings provides an ideal carrier for drug loading, enabling intelligent, responsive drug release through functional design. By loading antimicrobial agents, the coatings can impart long-lasting antimicrobial properties, effectively preventing implant-related infections. Further optimization of drug release kinetics and coating structural stability based on this invention could promote the clinical application of MAO coatings in drug delivery systems. By loading drug molecules (such as antibiotics, anti-inflammatory drugs, or growth factors) onto the coating surface or within its pores, controlled sustained drug release can be achieved. This functional design not only expands the application scenarios of MAO coatings but also provides new solutions for postoperative anti-inflammatory therapy and infection control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 Surface morphologies and EDS results of S0, S1, S3, S5, and S7. (a1) to (e1) are the surface morphologies of S0, S1, S3, S5, and S7, respectively; (a2) to (e2) are magnified images of the regions of (a1) to (e1), respectively; (a3) ​​is the EDS surface scan image of magnesium in S0; (b3) to (e3) are the EDS surface scan images of silicon in S1 to S7.

[0027] Figure 2 Electrochemical performance test in corrosion resistance evaluation test. (a) is the open circuit potential (OCP) of the substrate and sample, and (b) is the Tafel curve of the substrate and sample.

[0028] Figure 3 The electrochemical performance test results in the corrosion resistance evaluation test are shown in Figure 1. (a) is the Nyquist fitting plot, (b) is the matrix Bode fitting plot, (c) is the sample Bode fitting plot, and (d) is the matrix equivalent circuit, where Rs is the solution resistance between the working electrode and the reference electrode; Q is the solution resistance between the working electrode and the reference electrode; f (CPE f ):Oxide layer capacitance; R f : total resistance of matrix pores; Q dl (CPE dl ): double layer capacitance; R ct : Charge transfer resistance; R L: relaxation process of adsorbed species and related inductance resistance L: inductance related to the relaxation process of adsorbed species; (e) is the sample equivalent circuit diagram, where Rs: solution resistance between the working electrode and the reference electrode; Q out (CPE out ): capacitance of the outer interface of the oxide coating; R out : outer layer resistance; Q in (CPE in ): internal barrier layer capacitance; R in : internal barrier layer resistance; Q dl (CPE dl ): double layer capacitance; R ct : Charge transfer resistance.

[0029] Figure 4 Diagram of the corrosion resistance mechanism of MAO coating with added nano-SiO2.

[0030] Figure 5 Surface morphologies and EDS results of H0, H1, H3, and H5. (a1) to (d1) are the surface morphologies of H0, H1, H3, and H5, respectively; (a2) to (d2) are the magnified views of the regions of (a1) to (d1), respectively; (a3) ​​is the EDS surface scan image of magnesium element S0; (b3) to (e3) are the EDS surface scan images of silicon element S1 to S7; (a3) ​​to (d3) are the EDS results of H0, H1, H3, and H5, respectively.

[0031] Figure 6 Cross-sectional morphologies and EDS results of H0, H1, H3, and H5. (a1) to (d1) are the cross-sectional morphologies of H0, H1, H3, and H5, respectively; (a2) to (d2) are the EDS results of H0, H1, H3, and H5, respectively.

[0032] Figure 7 XRD patterns of samples H0, H1, H3, and H5 with different concentrations of nano-HA added.

[0033] Figure 8 Surface elemental composition and chemical state analysis of H5. (a) Wide scan XPS spectrum; (b) High resolution spectrum of Mg1s; (c) High resolution spectrum of Ca2p; (d) High resolution spectrum of P2p; (e) High resolution spectrum of O1s; (f) High resolution spectrum of Si2p.

[0034] Figure 9 Infrared spectra of the matrix and samples H0, H1, H3, and H5 with different concentrations of nano-HA added.

[0035] Figure 10The test results of the substrate and groups H0, H1, H3, and H5 during immersion in Hank's solution: (a) is the pH value, and (b) is the change in the weight loss rate of different samples.

[0036] Figure 11 The SEM surface morphology and EDS results after immersion in Hank's solution for 18 days; (a1)~(d1) are the surface morphologies of H0, H1, H3, and H5, respectively; (a2)~(d2) are the enlarged views of the areas of (a1)~(d1), respectively; (a3)~(d3) are the EDS surface scanning images of H0, H1, H3, and H5.

[0037] Figure 12 Fluorescence images of MC3T3-E1 cells on substrates and samples after 24 h of co-culture. The scale bar is 100 μm.

[0038] Figure 13 The proliferation activity of MC3T3-E1 osteoblasts cultured on the surface of each sample for 24, 72, and 168 hours. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0040] In this example, the experimental materials used included a matrix alloy composed of Mg-1.74Zn-0.55Ca (wt.%), melted from pure magnesium (99.99 wt.%), zinc (99.99 wt.%), and a 20% Mg-Ca alloy. The preparation method was based on the literature (Dou J, Yu H, Chen C. Preparation and characterization of composite coating on Mg-1.74Zn-0.55Ca alloy by micro-arc oxidation combined with sol-gel method [J]. Materials Letters, 2019, 255). The matrix measured 7.60 × 7.60 × 5.70 mm and was machined using a DK7735 wire-cut EDM machine (Shandong Guanke CNC Equipment Co., Ltd.). Each matrix was drilled with a 1.70 mm deep, 2.50 mm diameter hole for inserting a 2.40 mm diameter aluminum wire for subsequent MAO operations. After drilling, the substrate was polished with 800-grit coarse sandpaper and 2000-grit fine sandpaper in sequence to remove surface oil and oxidation layer, then cleaned three times with ethanol (analytical grade) and ultrapure water (UPY-Ⅲ-103 ultrapure water analyzer, Sichuan Youpu Ultrapure Technology Co., Ltd.), and finally dried with hot air.

[0041] The base electrolyte consists of calcium glycerophosphate, sodium hexametaphosphate, potassium hydroxide, ammonium bifluoride, glycerol, and hydrogen peroxide. To prepare the electrolyte, each component was added sequentially to 1 L of ultrapure water and stirred at 800 rpm using an HMS-203D magnetic stirrer to ensure uniform mixing. Analytical grade ethanol was used to clean the substrate and remove surface oil. Ultrapure water (UPY-Ⅲ-103 Ultrapure Water System, Sichuan Youpu Ultrapure Technology Co., Ltd.) was used for substrate cleaning and electrolyte preparation. Calcium glycerophosphate primarily provides film-forming elements (P and Ca), thereby regulating film composition and biocompatibility. Glycerol helps optimize the discharge process and coating uniformity. Ammonium bifluoride enhances the corrosion resistance and density of the coating through fluoride ions.

[0042] Hank's solution was used to simulate the body fluid environment. The composition of Hank's solution was NaCl 8.000 g / L, CaCl2 0.140 g / L, KCl 0.400 g / L, MgSO4∙7H2O 0.060 g / L, MgCl2∙6H2O 0.100 g / L, NaH2PO4∙2H2O 0.060 g / L, KH2PO4 0.060 g / L, C6H 12 O6(glycerol)1.000 g / L, NaHCO30.350 g / L.

[0043] The experimental equipment used in the present examples includes: During the MAO process, the electrolyte was prepared using an HMS-203D hot plate magnetic stirrer at 800 rpm to ensure uniform mixing of the electrolyte components. Because the MAO process generates significant heat, the electrolyte container was placed in an ice bath to prevent overheating.

[0044] The coatings were characterized using a variety of instruments: a Hitachi X-ray diffractometer (XRD) was used to analyze the composition and crystalline phase of the coatings, with a test range of 10°–90° and a scan rate of 10° / min; and a Bruker Fourier transform infrared spectrometer (FT-IR) was used to identify functional groups in the coatings, with a wavenumber range of 4000–400 cm -1 A Kratos Axis Supra+ X-ray photoelectron spectrometer (XPS) was used to investigate the elemental composition and chemical state of the coating. Furthermore, a Czech TESCAN MIRA LMS scanning electron microscope (SEM) was used to observe the surface and cross-sectional morphology of the coating, and an energy dispersive X-ray spectrometer (EDS) was used to analyze the elemental composition of the coating, specifically investigating the elemental composition and concentration of the coating surface through point scanning.

[0045] Electrochemical characterization experiments were performed using a CHI660E electrochemical workstation, including open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The samples were immersed in Hank's solution for 20 minutes to stabilize the open-circuit potential, followed by EIS and potential polarization measurements. ZsimpWin software was used to analyze and fit the impedance spectroscopy data.

[0046] In corrosion testing, samples were immersed in Hank's solution at 37 ± 0.5°C. The pH of the solution was regularly measured using a Sartorius PB-10 pH meter to assess the corrosion behavior of the samples. After immersion, the samples were cleaned, dried, and weighed. The weight change was recorded, and data analysis and graphing were performed using Origin 2018 Pro software.

[0047] In some embodiments of the present invention, a method for preparing a nanoparticle micro-arc oxidation coating on a surface of a medical magnesium alloy is provided, comprising the following steps: Step 1: Prepare the electrolyte. The electrolyte composition includes 2-12.5 g / L calcium glycerophosphate (C3H7CaO6P), 2-12.5 g / L sodium hexametaphosphate ((NaPO3)6), 4.2-11.2 g / L potassium hydroxide (KOH), 3.42-13.68 g / L ammonium bifluoride (NH4HF2), 5-25 mL / L glycerol (C3H6O3), 5-25 mL / L hydrogen peroxide (H2O2), 1-7 g / L nano-SiO2, and 1-5 g / L nano-hydroxyapatite (nano-HA). These ingredients were added sequentially to 1 L of ultrapure water and stirred at 800 rpm using an HMS-203D hot plate magnetic stirrer to ensure uniform mixing.

[0048] In step 2, MAO treatment was performed using a bipolar current-mode power supply with the following parameters: positive voltage 350-500 V, negative voltage 10-40 V, positive duty cycle 10-40%, negative duty cycle 10-30%, frequency 400-800 Hz, and reaction time 5-30 min. During the reaction, the electrolyte was continuously stirred and maintained at a temperature below 30°C using a cooling water circulator to prevent overheating.

[0049] After the completion of MAO, the coating was characterized by X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectrometer (XPS), scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS) to analyze its composition, structure, morphology and element distribution.

[0050] The electrochemical behavior of the coating was evaluated by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests using an electrochemical workstation. The corrosion resistance of the coating was also evaluated by periodically measuring pH and weight changes by immersing the sample in Hank's solution.

[0051] The electrochemical performance of the samples was tested using a CHI660E electrochemical workstation.

[0052] In some embodiments of the present invention, the average particle size of Nano-SiO2 is 30-500 nm and the purity is 99.5%, Macklin.

[0053] In some embodiments of the present invention, there is provided the use of the prepared nanoparticle micro-arc oxidation coating on the surface of medical magnesium alloy as a drug carrier.

[0054] The porous structure of the MAO coating provides an ideal carrier for drug loading. By loading drug molecules such as antibiotics, anti-inflammatory drugs, or growth factors onto the coating surface or into the pores, controlled release of the drugs can be achieved. For example, the controlled release of antibiotics can effectively prevent postoperative infections, while the release of growth factors can promote bone tissue regeneration. By adjusting the porosity, drug loading, and release kinetics of the coating, precise drug release can be achieved to meet the needs of different treatment stages. In addition, the surface modification capabilities of nano-SiO2 and nano-HA can be used to develop pH-responsive drug release systems. For example, by combining drug molecules with pH-sensitive materials such as chitosan, rapid release of drugs in an inflammatory environment (low pH) can be achieved, while maintaining stability in a normal physiological environment (neutral pH). This intelligent release system not only improves the utilization efficiency of drugs, but also reduces side effects, providing a new solution for postoperative anti-inflammatory treatment.

[0055] Example 1, Preparation method of nano-particle micro-arc oxidation coating on the surface of medical magnesium alloy Step 1, Prepare the electrolyte with the following components: 7.5 g / L of glycerol calcium phosphate (C3H7CaO6P), 7.5 g / L of sodium hexametaphosphate ((NaPO3)6), 5.0 g / L of potassium hydroxide (KOH), 7.0 g / L of ammonium hydrogen fluoride (NH4HF2), 10 mL / L of glycerol (C3H6O3), and 7.5 mL / L of hydrogen peroxide (H2O2), Nano-SiO21 ~7g / L, nano-hydroxyapatite (nano-HA) 1 ~5g / L. These components are added to 1 L of ultrapure water in sequence, and a HMS-203D hot plate magnetic stirrer is used to stir at a speed of 800 rpm to ensure uniform mixing.

[0056] Step 2, Use a bipolar current mode power supply for MAO treatment, with the following parameters: positive voltage 450 V, negative voltage 20 V, positive duty cycle 30%, negative duty cycle 20%, frequency 600 Hz, reaction time 10 min. During the reaction process, the electrolyte is continuously stirred, and an ice bath is used to control the temperature to prevent overheating.

[0057] Example 2, Preparation of nano-particle micro-arc oxidation coatings on the surfaces of different medical magnesium alloys In this example, nano-particle micro-arc oxidation coatings with different concentrations of nano-SiO2 and different concentrations of HA were prepared.

[0058] 1. Using a base electrolyte consisting of 7.5 g / L calcium glycerophosphate (C3H7CaO6P), 7.5 g / L sodium hexametaphosphate ((NaPO3)6), 5.0 g / L potassium hydroxide (KOH), 7.0 g / L ammonium bifluoride (NH4HF2), 10 mL / L glycerol (C3H6O3), and 7.5 mL / L hydrogen peroxide (H2O2), multiple experimental groups were set up. Nano-SiO2 (average particle size 500 nm, 99.5% purity, Macklin) was added to the electrolyte at concentrations of 1 g / L, 3 g / L, 5 g / L, and 7 g / L, forming different experimental groups, labeled S1, S3, S5, and S7, respectively. A control group without nano-SiO2 was also set up, labeled S0. MAO treatment was performed using the method described in Example 1.

[0059] 2. Based on the electrolyte consisting of a base electrolyte + 3 g / L Nano-SiO2, different concentrations of nano-HA were added to the electrolyte. The concentrations of Nano-HA were set to 1 g / L, 3 g / L, and 5 g / L, forming different experimental groups, labeled H1, H3, and H5. A control group without nano-HA was also set up, labeled H0. MAO treatment was performed using the method described in Example 1.

[0060] In order to comprehensively evaluate the morphology, structure and composition of the MAO coatings obtained in Examples 1 and 2, and to explore their application potential in drug carriers and sustained-release systems, this study used the above-mentioned multiple characterization techniques for detection.

[0061] Here are the results: 1 Effect of different nano-SiO2 concentrations: 1.1 Analysis of coating surface morphology and porosity Based on the surface topography image ( Figure 1 ). The MAO coating without nano-SiO2 (Group S0) exhibited numerous micropores and cracks on its surface, likely due to spark breakdown of the oxide layer during the MAO process. As the nano-SiO2 concentration in the electrolyte increased, the micropores and cracks on the coating surface gradually decreased, leading to a smoother and more uniform surface. The number of cracks decreased, and the micropore diameter decreased. Furthermore, dense particles appeared on the coating surface, with the number increasing with increasing nano-SiO2 concentration. These particles ranged in diameter from 2.4 to 10.4 μm.

[0062] The introduction of nano-SiO2 significantly improved the surface morphology of the coating. The reduction in micropores and cracks with increasing nano-SiO2 concentration (groups S1 to S7) suggests that the nanoparticles fill defects formed during the MAO process, thereby inhibiting the expansion of corrosion channels. The particle size (2.4 to 10.4 μm) is positively correlated with the nano-SiO2 concentration, suggesting that these particles may have formed by the melt agglomeration of nano-SiO2 under the high-temperature and high-pressure environment of MAO.

[0063] EDS surface scanning analysis results ( Figure 1 (a3)~(e3)) clearly reveal the distribution characteristics of the two elements in the coating. In the S0 sample without the addition of nano-SiO2, the distribution of Mg elements showed regional differences. The bright areas corresponded to Mg-rich areas, while the dark areas reflected Mg-poor areas or pore structures. This distribution feature was consistent with the porous morphology observed by SEM. With the increase of nano-SiO2 concentration in the electrolyte, the surface scanning image of Si elements showed a significant concentration gradient change. The distribution density of Si elements showed a positive correlation with the addition amount, and its dispersion uniformity gradually improved with the increase of concentration. In the high-concentration group samples, Si elements almost covered the entire scanning area.

[0064] By analyzing the mass fractions of elements on the surface of the five groups of coatings (Table 1), it was found that the mass fraction of silicon (Si) in each coating group was significantly linearly correlated with the concentration of nano-SiO2 added to the electrolyte. In addition, the contents of calcium (Ca) and phosphorus (P) in the coating remained relatively stable in all groups, indicating that the addition of nano-SiO2 did not significantly affect these elements that are essential for osteogenesis and bone regeneration. The magnesium (Mg) and oxygen (O) contents on the surface of the MAO coating also showed stability, where Mg originated from the matrix and O originated from the oxidation process. The presence of fluorine (F) was attributed to NH4HF2 in the electrolyte, which ionized in aqueous solution to form NH 4+ and HF 2- , HF 2- It is enriched in the anode area and remains in the coating. Carbon (C) may come from calcium glycerophosphate and glycerol in the electrolyte. The mass fraction of Si increased linearly from 0% in the S0 group to 7.72% in the S7 group (Table 1), confirming the successful incorporation of nano-SiO2. The stable contents of Ca (9.07% ~ 13.74%) and P (16.56% ~ 18.57%) indicate that the addition of nano-SiO2 did not interfere with the deposition behavior of calcium and phosphorus components in the electrolyte, which is crucial for the biological activity of the coating. The F content decreased with increasing nano-SiO2 concentration (16.54% in the S1 group to 6.05% in the S7 group), which may be related to the introduction of nanoparticles changing the HF content in the electrolyte. 2- migration and adsorption behavior.

[0065] Table 1 Element mass fraction in S0, S1, S3, S5, S7

[0066] S0 group has more surface micropores and cracks, indicating that it is more prone to localized corrosion in a corrosive environment. The increase in dense particles on the surface of high-concentration nano-SiO2 groups (such as S5 and S7) may delay the penetration of corrosive media through physical barrier action, but its effect on coating stability needs to be further verified in combination with immersion experiments.

[0067] The above analysis shows that the introduction of nano-SiO2 significantly changes the chemical composition of the coating. With the increase of nano-SiO2 concentration, the content of silicate phase (such as MgSiO3) and carbonate phase (such as MgCO3) in the coating increases significantly, and carbonyl compounds may be generated on the surface of the coating. These changes further confirm the successful incorporation of nano-SiO2 in the MAO coating and its optimization effect on the chemical composition of the coating. When the concentration of nano-SiO2 is about 5 g / L, the coating shows the best corrosion resistance and compactness.

[0068] However, since nano-SiO2 and nano-HA are both insoluble substances, the fixed nano-SiO2 test concentration is 3 g / L in the synthesis and characterization of the coating to reduce the phenomenon of coating surface peeling caused by too much insoluble substances in the electrolyte.

[0069] 2 Coating surface morphology and porosity analysis Figure 5 The surface morphology and corresponding element content of H0, H1, H3, and H5 MAO coatings are shown. As can be seen from the figure, all samples have particles of different sizes on the surface, mostly spherical or short rod-shaped, which are speculated to be agglomerates of added nanoparticles (nano-HA and nano-SiO2) formed during the MAO process. With the increase of HA addition amount, the uniformity of the coating surface micropores is significantly improved. The micropores in the H0 group are larger in size and unevenly distributed, while the micropores in the H5 group are smaller in size and evenly distributed, indicating that the introduction of nano-HA effectively improves the compactness of the coating.

[0070] EDS results revealed the presence of C, O, F, Mg, Si, P, and Ca on the coating surface. Mg originates from the matrix, while P and Ca originate from the nano-HA in the electrolyte. With increasing HA addition, the P and Ca contents increased significantly (H0: P ~6.68%, Ca ~3.18%; H5: P ~13.55%, Ca ~14.59%), demonstrating successful incorporation of nano-HA into the coating. Because human bone is rich in P and Ca, MAO coatings containing P and Ca exhibit excellent bioactivity, promoting the growth of bone cells.

[0071] The introduction of nano-HA significantly improved the uniformity of the micropores on the coating surface. The micropores in group H5 were smaller and more evenly distributed, indicating superior density compared to the other groups. EDS results showed that the contents of P and Ca elements increased significantly with increasing HA addition, indicating that nano-HA was successfully incorporated into the coating and enhanced its bioactivity.

[0072] 3 Effect of HA particle distribution on coating density Figure 6 The cross-sectional morphology and elemental distribution of four MAO coatings (H0, H1, H3, and H5) are presented. All cross-sections show a close bond between the substrate and the MAO coating, with no distinct demarcation line. The coatings, approximately 10 to 40 μm thick, completely cover the substrate surface, effectively protecting it from corrosion. Micropores of varying sizes are present in the coating cross-sections, but these do not penetrate deeply into the substrate, consistent with the surface morphology.

[0073] EDS results revealed the presence of elements such as C, O, F, Na, Mg, Si, P, K, and Ca in the coating cross-section. With increasing HA concentration, the P and Ca contents gradually increased (H0: P ~ 0.77%, Ca ~0.24%; H5: P ~ 11.77%, Ca ~ 4.47%), further confirming the successful incorporation of nano-HA. Furthermore, with increasing HA content, the F, Mg, and O contents also gradually increased, indicating that the increased phosphate groups in the electrolyte promoted the oxidation and fluorination of Mg in the matrix, thereby improving the coating's density.

[0074] Cross-sections of all samples showed a close bond between the substrate and the MAO coating, with coating thicknesses ranging from approximately 10 to 40 μm, effectively protecting the substrate from corrosion. With increasing HA concentration, the P and Ca content gradually increased, further confirming the successful incorporation of nano-HA. Increased F, Mg, and O content indicated that the introduction of nano-HA promoted the oxidation and fluorination of Mg in the substrate, thereby improving the coating's compactness.

[0075] 4 Phase composition and chemical bonding state in coatings 4.1 Phase formation in coatings XRD analysis was performed on four samples: H0, H1, H3, and H5. Figure 7 The results showed that the coating contained silicon dioxide (SiO2), magnesium (Mg), magnesium oxide (MgO), magnesium silicate (MgSiO3), calcium phosphate (Ca3(PO4)2) and hydroxyapatite (Ca 10 (PO4)6(OH)2).

[0076] The SiO2 peak intensity is highest in the H3 sample, indicating that the H3 sample contains the highest SiO2 content. This phenomenon may indicate that the maximum nano-SiO2 concentration that can be incorporated into the coating is reached when the nano-HA concentration is 3 g / L. Higher HA concentrations may cause agglomeration in the electrolyte, reducing the effective SiO2 incorporation amount.

[0077] The widespread presence of Mg in all samples suggests that some unreacted magnesium matrix may still be exposed on the coating surface. The highest magnesium oxide (MgO) content was found in sample H0, possibly indicating that the MAO sample without HA addition generated a higher amount of oxide during the MAO process. However, the increased MgO content did not significantly improve the corrosion resistance of the coatings; instead, this may indicate that sample H0 exhibited slightly weaker corrosion resistance than the other samples with HA addition.

[0078] Calcium phosphate (Ca3(PO4)2) was detected in all samples, and the content of calcium phosphate was the highest in sample H3. 10 The content of (PO4)6(OH)2) was also the highest, indicating that the maximum amount of HA was successfully incorporated into the H3 sample.

[0079] The contents of SiO2 and MgSiO3 in sample H3 were the highest, indicating that the synergistic effect of nano-SiO2 and HA significantly optimized the chemical composition of the coating. The introduction of HA not only increased the contents of calcium phosphate and hydroxyapatite in the coating, but also may have contributed to the improvement of the coating performance by providing Ca 2+ and PO4 3- source, enhancing the biological activity of the coating.

[0080] In order to study the effect of nano-HA incorporation on the phase composition of MAO coating, XPS was used to analyze the surface elemental composition and chemical state of H5 sample. XPS wide scan spectrum ( Figure 8 (a) shows that Mg, F, O, Ca, C, P and Si elements exist on the coating surface, which are derived from the magnesium alloy matrix, compounds in the electrolyte and the introduction of nano-HA.

[0081] Mg1s high-resolution spectrum ( Figure 8(b) Two characteristic peaks appear at 1304.9 eV and 1304.1 eV, respectively, attributable to elemental magnesium (Mg) and magnesium oxide (MgO). Compared with the coating without nano-HA addition, the intensity of the MgO peak increases significantly, indicating that the introduction of nano-HA promotes the formation of magnesium oxide, further enhancing the corrosion resistance of the coating.

[0082] Ca2p high-resolution spectrum ( Figure 8 (c) The characteristic double peaks of calcium carbonate (CaCO3) appeared at 347.2 eV and 350.9 eV, while the characteristic double peaks of calcium phosphate (Ca3(PO4)2) appeared at 348.2 eV and 352.2 eV. The formation of calcium phosphate directly confirmed the successful incorporation of nano-HA, while the formation of calcium carbonate may come from the reaction of CO2 in Hank's solution with Ca2+ on the coating surface. 2+ Compared with the coating without nano-HA addition, the intensity of the calcium phosphate peak increased significantly, indicating that the introduction of nano-HA significantly increased the content of phosphate phase in the coating.

[0083] P2p high-resolution spectrum ( Figure 8 (d) A characteristic peak appeared at 133.7 eV, which was attributed to phosphate (PO4 3- ), further confirming the presence of calcium phosphate (Ca3(PO4)2) on the coating surface. Compared with the coating without nano-HA addition, the intensity of the phosphate peak increased significantly, indicating that the introduction of nano-HA significantly increased the content of phosphate phase in the coating.

[0084] O1s high-resolution spectrum ( Figure 8 (e)) Three characteristic peaks appeared at 530.4 eV, 531.7 eV and 532.5 eV, respectively, which were attributed to hydroxyl groups (OH - ), silicon-oxygen bond (Si-O) and phosphate (PO4 3- ) and metal oxides (MO). The appearance of the hydroxyl peak indicates that there may be hydroxyapatite (Ca 10 (PO4)6(OH)2), while the peaks of silicon-oxygen bonds and phosphate groups further confirmed the presence of silicate and phosphate phases in the coating.

[0085] Si2p high-resolution spectrum ( Figure 8 (f) Two characteristic peaks appear at 101.6 eV and 102.9 eV, respectively, attributable to magnesium silicate (MgSiO3) and silicon dioxide (SiO2). The presence of these silicate phases indicates that the introduction of nano-SiO2 forms a stable silicate phase in the coating, further enhancing the corrosion resistance of the coating.

[0086] XPS analysis showed that the introduction of nano-HA significantly changed the phase composition of the MAO coating. Calcium phosphate (Ca3(PO4)2) and hydroxyapatite (Ca 10 Phosphate phases such as (PO₄)₆(OH)₂) are formed, along with compounds such as calcium carbonate (CaCO₃) and magnesium silicate (MgSiO₃). The formation of these compounds not only improves the coating's compactness and corrosion resistance but also potentially enhances its bioactivity. Compared to coatings without nano-HA, the introduction of nano-HA significantly increases the phosphate content in the coating, further optimizing its chemical composition and properties.

[0087] The H3 sample has the highest content of MgSiO3 and calcium phosphate, indicating that its corrosion resistance and bioactivity may be better than those of the other samples. The H0 sample has a higher content of magnesium oxide, but its corrosion resistance is poor, indicating that simply increasing the oxide content cannot significantly improve the corrosion resistance of the coating.

[0088] 4.2 Coating chemical state Figure 9 The infrared spectra of MAO coatings at different nano-HA concentrations are shown when the nano-SiO2 concentration is fixed at 3 g / L. S stands for Substrate, and this group serves as the control group. As can be seen from the figure, the infrared absorption peaks of the coatings change significantly with increasing nano-HA concentrations. 3718 ~ 2893 cm -1 The intensity of the broad and strong absorption peak in the range gradually increases with increasing nano-HA concentration. S has an absorption peak here, but it is significantly weaker than other groups. This peak is generally attributed to the stretching vibration of OH, indicating the presence of hydroxyl groups or adsorbed water molecules on the coating surface. The introduction of nano-HA significantly enhances the intensity of this peak, which may be due to the hydroxyl characteristics of HA or the increase in adsorbed water molecules on the coating surface. 1801 ~ 1525.5 cm -1 The absorption peak in the range gradually increases with the increase of nano-HA concentration, and S has an absorption peak here. This peak may come from C=O stretching vibration or HOH bending vibration. The weak peak of S indicates that there may be a small amount of water molecules in the matrix itself, and the introduction of nano-HA further enhances the intensity of this peak. 1402 and 1348.2 cm -1 The double absorption peak at the position gradually increases with the increase of nano-HA concentration. This peak may be attributed to CO3 2- The asymmetric stretching vibration of nano-HA indicates that the introduction of nano-HA promotes the formation of carbonate phase (such as MgCO3) on the coating surface. 1303.8 ~ 825 cm -1The broad and strong absorption peak in the range gradually increases with the increase of nano-HA concentration. S has an absorption peak here, but it is obviously narrow and sharp, and the intensity is significantly lower than that of other groups. This peak may include contributions from Si-O and PO stretching vibrations. The weak peak of S indicates that a small amount of phosphate phase may exist in the matrix itself, and the introduction of nano-HA significantly enhances the intensity of this peak, indicating that more silicate or phosphate phases are formed in the coating. 573.4 cm -1 The intensity of the absorption peak at shows no clear linear relationship with nano-HA concentration, although S exhibits a weak absorption peak there. This suggests that the peak is likely attributable to Si-O bending vibrations, indicating that the silicate phase content in the coating increases with the introduction of nano-HA. The S absorption peak at this location could be caused by the vibration of metal-metal bonds between certain metals in the matrix alloy, or by the influence of impurities in the alloy (such as oxides or hydrides in the oxide layer).

[0089] Infrared spectroscopy analysis revealed that the introduction of nano-HA significantly altered the chemical composition of the coating. With increasing nano-HA concentration, the content of phosphate phases (e.g., Ca3(PO4)2) and silicate phases (e.g., MgSiO3) in the coating increased significantly. Furthermore, the coating surface likely absorbed more water molecules or generated carbonyl compounds. These changes further confirmed the successful incorporation of nano-HA into the MAO coating and its effect on optimizing the coating's chemical composition.

[0090] 5 Corrosion resistance evaluation 5.1 Comparison of electrochemical performance Figure 2 (a) Shows the open-circuit potential (OCP) curves of coatings with varying nano-SiO2 concentrations. As the nano-SiO2 concentration in the electrolyte increases, the average open-circuit potential gradually increases, indicating enhanced thermodynamic stability of the coating and reduced corrosion tendency of the substrate in Hank's solution. This phenomenon directly confirms that the introduction of nano-SiO2 effectively inhibits the corrosion behavior of the substrate.

[0091] Figure 2 The Tafel curve (b) further reveals the corrosion kinetics of the coating. Combined with the electrochemical corrosion parameters in Table 2, it can be seen that the corrosion current density (Icorr) of the S0 group without nano-SiO2 is 1.50×10 -6 A / cm 2 , which is significantly lower than that of the matrix (4.02×10 -5 A / cm 2 ), indicating that the MAO coating itself has a certain protective effect. However, with the increase of nano-SiO2 concentration (groups S1 to S7), Icorr showed a trend of first increasing and then decreasing (S1: 3.04×10 -4A / cm 2 → S7: 1.93×10 -4 A / cm 2 This abnormal phenomenon may be related to the uneven distribution of low-concentration nano-SiO2 (such as S1 group) in the coating, which leads to increased local electrochemical activity.

[0092] Polarization resistance (Rp): from S0 group (5.08×10 4 Ω / cm 2 ) to S7 group (3.81×10 5 Ω / cm 2 ), the polarization resistance gradually increases, indicating that the introduction of nano-SiO2 significantly enhances the corrosion resistance of the coating. This trend is consistent with the increase in open circuit potential, further verifying the optimization effect of nano-SiO2.

[0093] Nano-SiO2 particles fill the micropores and cracks of the MAO coating, hindering the penetration of corrosive media. Nano-SiO2 reacts with corrosive ions (such as Cl⁻) in the electrolyte to form a silicate or silicon-based passivation layer, further inhibiting the corrosion reaction.

[0094] Table 2 Electrochemical corrosion parameters of substrate and sample in Hank's solution

[0095] Although the short-term corrosion current density of the low-concentration nano-SiO2 group (such as S1) is higher, the polarization resistance of the high-concentration groups (such as S5 and S7) is significantly improved, indicating that nano-SiO2 can maintain the stability of the coating during the immersion process.

[0096] The introduction of nano-SiO2 significantly improves the corrosion resistance of MAO coatings through the dual mechanisms of physical barrier and chemical passivation. Although low concentration of nano-SiO2 may lead to increased local electrochemical activity, the polarization resistance of the high concentration group (such as S7) reaches 3.81×10 5 Ω / cm 2 , which is nearly 700 times higher than that of the substrate, indicating its excellent application potential in highly corrosive environments. This discovery provides theoretical support for the design of long-lasting corrosion-resistant MAO coatings, which is particularly important in physiological environments rich in Cl⁻.

[0097] Figure 3(a) Shows the Nyquist curves of different samples. The Nyquist curve radius of the substrate is too small to be visible, indicating that its corrosion resistance is significantly lower than that of the MAO coating. As the nano-SiO2 concentration in the electrolyte increases, the arc diameter of the sample gradually increases, indicating that the introduction of nano-SiO2 effectively enhances the corrosion resistance of the coating in Hank's solution. Figure 3 (b) and (c) are the Bode plots and phase angle diagrams of the MAO coating samples, respectively. The corrosion tendency of samples S5 and S7 is significantly lower than that of the other samples. In particular, sample S7 exhibits a higher and wider phase angle peak, further confirming its excellent corrosion resistance.

[0098] Figure 3 (d) and (e) show the equivalent circuit models of the substrate and MAO sample, respectively. The equivalent circuit of the substrate consists of the solution resistance (Rs), the oxide film capacitance (Q f )、Oxide film resistance(R f ), double layer capacitance (Q dl ), charge transfer resistance (R ct ), the relaxation resistance of the adsorbed species (R L ) and inductance (L). The equivalent circuit of the MAO sample includes solution resistance (Rs), external layer capacitance (Q out ), outer layer resistance (R out ), inner layer capacitance (Q in )、Internal layer resistance(R in ), double layer capacitance (Q dl ) and the charge transfer resistance (R ct ).

[0099] Table 3 EIS curve fitting results of matrix and MAO samples

[0100] According to the EIS fitting parameters in Table 3, the following conclusions can be drawn: Charge transfer resistance (R ct ): The Rct of the matrix is ​​1.726×10 3 Ω•cm 2 , while the Rct of S0 sample increased significantly to 7.252×10 4 Ω•cm 2 , indicating that the MAO coating itself has a certain protective effect. With the increase of nano-SiO2 concentration, R ct Gradually increasing, the R ct Reaching 4.753×10 5 Ω•cm 2, which is 275 times higher than that of the substrate, indicating that the introduction of nano-SiO2 significantly inhibits the charge transfer process, thereby reducing the corrosion rate.

[0101] Outer and inner layer resistance (R out and R in ): R out and R in Represent the resistance of the outer and inner layers of the MAO coating, respectively. The higher the value, the greater the obstacle encountered by electron transport in the coating. out and R in They are 3.260×10 3 Ω•cm 2 and 1.454×10 4 Ω•cm 2 , which is significantly higher than that of other samples, indicating that the introduction of nano-SiO2 significantly enhances the barrier effect of the coating.

[0102] Capacitance parameters (Q out and Q in ):Q out and Q in Represent the capacitance of the outer and inner layers of the coating, respectively. The lower the value, the higher the density of the coating. out and Q in 2.068×10-7 Ω -1 •cm -2 •sn and 2.587×10 -8 Ω -1 •cm -2 •sn is significantly lower than that of other samples, indicating that the introduction of nano-SiO2 significantly improves the density of the coating.

[0103] In summary, the introduction of nano-SiO2 significantly improves the corrosion resistance of MAO coatings through the dual mechanisms of physical barrier and charge transfer inhibition. ct Reaching 4.753×10 5 Ω•cm 2 , which is 275 times higher than that of the substrate, indicating its excellent application potential in highly corrosive environments. This discovery provides theoretical support for the design of long-lasting corrosion-resistant MAO coatings, which is especially important in physiological environments rich in Cl⁻.

[0104] 6 Corrosion resistance test To evaluate the effect of different concentrations of nano-SiO2 and nano-HA on the corrosion resistance of MAO coating and explore its potential application in drug carriers and sustained-release systems, the corrosion resistance of the coating was tested by Hank's solution immersion experiment for 18 days. After 18 days of immersion, the surface morphology and elemental composition of the coating were analyzed using SEM and EDS. The experimental design aimed to simulate the degradation behavior of the coating in a physiological environment and evaluate its stability and controllable release performance in drug delivery systems.

[0105] The substrate (S group), control group containing only nano-SiO2 (H0), and experimental groups containing different concentrations of nano-HA (H1, H3, H5) were immersed in Hank's solution at 34°C. The pH value of the solution was measured regularly Figure 10 (a). The results showed that the pH value of the S group increased rapidly at the beginning of the immersion and then remained high, indicating that the magnesium alloy substrate underwent a severe corrosion reaction in the simulated body fluid environment, releasing a large amount of hydroxyl ions. In contrast, the pH value of the groups with added nanoparticles changed significantly slower, with the H0 group having a smaller pH increase, while the H3 and H5 groups had the smallest pH change (difference less than 0.5), indicating that the introduction of nano-HA further inhibited the corrosion reaction, which may be related to the reduction of magnesium ion release due to the formation of a dense coating by the nanoparticles.

[0106] The stability of the coating in the immersion was evaluated by weight loss rate Figure 10 (b). The weight loss rate = (m1-m2) / m1 x 100%, m1 is the weight before immersion (g), and m2 is the weight after immersion (g).

[0107] The weight loss rate of the S group gradually slowed down after 6 days of immersion, while the groups with added nanoparticles (H0, H1, H3, H5) had a more gradual change in weight loss rate over time, especially the H5 group, which had the lowest weight loss rate after 18 days of immersion, indicating that the synergistic effect of the double nanoparticles (nano-SiO2 and nano-HA) significantly improved the density and corrosion resistance of the coating. It is worth noting that the weight loss rate of the H5 group reached the lowest value at the beginning of the immersion, indicating that it can quickly form a protective layer and effectively delay the corrosion of the substrate.

[0108] The controllable degradation characteristics and stable weight loss rate of the coating indicate its potential as a drug carrier. The synergistic effect of nano-SiO2 and nano-HA not only enhances the corrosion resistance of the coating, but also may achieve controllable adsorption and release of drugs by regulating the pore structure of the coating. In addition, the stability of the pH value helps to reduce the risk of drug molecule degradation during the release process, further improving the reliability of the drug delivery system. The performance of the H5 group in the experiment is particularly outstanding, as its low weight loss rate and stable pH value change provide experimental evidence for the development of magnesium-based drug carriers with corrosion resistance and sustained-release functions.

[0109] The weight loss rates of some groups in the histogram show slight fluctuations over time, which may be related to minor differences in sample preparation or measurement, and require further verification in subsequent studies by adding parallel experimental groups. Overall, the experimental data clearly demonstrate the regulatory effect of nanoparticles on the corrosion resistance and degradation behavior of the coating.

[0110] 7 Analysis of immersion results Figure 11 The surface morphology and elemental content of four groups of samples (H0, H1, H3, and H5) after immersion in Hank's solution for 18 days are shown. Comparing the surface morphology with that before immersion, it can be observed that the MAO coating corrodes in Hank's solution, forming deposits on the sample surface.

[0111] After immersion, the H0 group exhibited noticeable cracks on its surface, attributed to the corrosive effects of Hank's solution on the oxides in the coating. The presence of these cracks indicates that the coating without HA addition exhibits poor corrosion resistance, allowing the corrosive medium to easily penetrate the substrate through the cracks. EDS results revealed that the surface elements of the H0 group were primarily C, O, F, and Mg, with low P and Ca contents (P ~10.92%, Ca ~8.65%), indicating that the primary corrosion products were Mg(OH)2 and MgCO3.

[0112] Although the surface of the H5 group had cracks after immersion, it was covered with a large amount of sediment. The enlarged image showed that the sediment was in the form of blocks or spheres of uneven sizes, which were presumably calcium phosphate (Ca3(PO4)2) and hydroxyapatite (Ca 10 EDS results showed that the surface P and Ca contents of group H5 were significantly higher than those of the other groups (P ~ 15.23%, Ca ~ 15.41%), indicating that nano-HA released P and Ca elements during the immersion process, forming a stable calcium-based deposition layer.

[0113] Groups H1 and H3, as samples with medium and low HA concentrations, exhibit surface morphologies intermediate between those of groups H0 and H5. The amount of deposits increases with increasing HA concentration, but the number of cracks is significantly reduced compared to group H0. EDS results show that the P and Ca content gradually increase with increasing HA concentration (H1: P ~ 13.11%, Ca ~ 9.85%; H3: P ~ 14.61%, Ca ~ 11.88%), indicating that the introduction of nano-HA effectively inhibits the penetration of corrosive media.

[0114] The H0 group without HA addition had more surface cracks, indicating poor corrosion resistance. With the increase of HA concentration, the number of surface deposits increased and the number of cracks decreased, indicating that the introduction of nano-HA effectively inhibited the penetration of corrosion medium. EDS results showed that the content of P and Ca elements increased significantly with the increase of HA concentration, indicating that nano-HA released P and Ca elements during the immersion process, forming a stable calcium-based deposition layer. The surface of the H5 group was covered with deposits, indicating better corrosion resistance than other groups. The introduction of nano-HA not only improved the corrosion resistance of the coating, but also enhanced the bioactivity of the coating by releasing P and Ca elements. The introduction of nano-HA significantly improved the corrosion resistance of the MAO coating in Hank's solution, inhibiting the penetration of corrosion medium and the expansion of cracks. The H5 group with high concentration of HA had the most surface deposits and the highest content of P and Ca elements, indicating better corrosion resistance and bioactivity than other groups.

[0115] Nano-SiO2 significantly blocked the corrosion channels of the MAO coating through the triple mechanisms of physical barrier, chemical passivation, and electrochemical inhibition, delaying the corrosion process of the magnesium alloy substrate. However, its protective effect tends to saturate when the concentration exceeds 5 g / L, and future research needs to further optimize the particle dispersion process or explore composite nanomaterials (such as SiO2 / HA co-doping) to break through the performance bottleneck.

[0116] Example 4, Biocompatibility Evaluation 1 Live / Dead cell staining to analyze cell survival status To evaluate the effect of different nano-SiO2 and nano-HA concentrations on the biocompatibility of MAO coating, this study analyzed the survival status of MC3T3-E1 cells on the coating surface through live / dead cell staining experiment. The experiment used live / dead cell staining reagent (Live / Dead reagent), and the survival of cells was observed by fluorescence microscope.

[0117] To quantitatively evaluate the effect of different coatings on cell proliferation behavior, this study used MTT method (tetramethylazoline salt method) to determine the metabolic activity of MC3T3-E1 cells.

[0118] According to the following formula, the relative growth rate (RGR) of cells was calculated to evaluate the cytotoxicity of materials:

[0119] As shown in Table 4, the toxicity grading standard of 0 level (RGR≥100%) and 1 level (75%≤RGR<100%) indicates that the material has no cytotoxicity, 2 level needs to be evaluated in combination with morphological analysis, and 3-5 level is determined as toxic material. This experiment systematically evaluates the long-term biocompatibility of the coating by analyzing the time-dependent change of RGR value.

[0120] Table 4 Cytotoxicity grading criteria

[0121] Fluorescence images show ( Figure 12 ), significant differences in cell activity were observed between the different groups. The matrix group had fewer live cells and more dead cells, indicating that the magnesium alloy matrix significantly inhibited cell growth. This may be due to the rapid release of magnesium ions in the simulated body fluid environment, which increases cytotoxicity and inhibits cell adhesion and proliferation.

[0122] Compared with the substrate group, the number of live cells in the S0 group increased significantly, while the number of dead cells decreased, indicating that the MAO coating effectively improved the biocompatibility of the substrate. The formation of the coating isolated the direct contact between the magnesium alloy substrate and the cells, reducing the release of magnesium ions and thus reducing cytotoxicity. The number of live cells in the S3 group increased further, while the number of dead cells continued to decrease, indicating that the introduction of nano-SiO2 further optimized the bioactivity of the coating. The addition of nano-SiO2 may promote cell adhesion and proliferation by regulating the surface morphology and chemical composition of the coating, while also enhancing the biocompatibility of the coating.

[0123] The H5 group had the highest number of live cells and the lowest number of dead cells, demonstrating the best cytocompatibility. This suggests that the synergistic effect of the two microparticles significantly improved the biological performance of the coating. The introduction of Nano-HA not only enhanced the bioactivity of the coating but also likely promoted cell growth and differentiation by releasing calcium and phosphate ions.

[0124] Fluorescence image analysis results indicate that the synergistic effect of nano-SiO2 and nano-HA significantly enhances the biocompatibility of the MAO coating. The H5 group exhibited the best cytocompatibility, confirming the significant effectiveness of the dual nanoparticles in optimizing the bioperformance of the coating. These results provide important insights for optimizing the biocompatibility of magnesium-based implants and lay the foundation for the development of drug-carrying coatings that combine corrosion resistance with bioactivity.

[0125] 2. MTT quantitative detection of cell proliferation activity The relative proliferation rate (RGR) determined by MTT assay showed that the proliferation behavior of MC3T3-E1 cells showed significant time-dependent differences among the materials in each group ( Figure 13 According to GB / T 16886.1-2001, all coating groups (S0, S3, and H5) showed no cytotoxicity (toxicity grade 0) during the culture period, meeting the biocompatibility requirements for medical materials.

[0126] At the initial stage of culture (D1), the H5 group exhibited a significant proliferative effect, with a significantly higher RGR than the matrix group (S group, 94.45±0.09%) and the pure MAO coating group (S0 group, 96.11±0.13%) (p<0.05). By day 3 (D3), the proliferative advantage of the H5 group further expanded (RGR=117.79±0.29%), a 17.8% increase compared to the TCP control group (100.00±0.29%), and a significant difference from the S3 group (112.63±0.27%) (p<0.01). By day 7 (D7), the RGRs of the H5 group (109.81±0.39%) and the S3 group (108.22±0.19%) remained significantly higher than those of the matrix group (93.06±0.21%), indicating the long-term effectiveness of the coating modification.

[0127] The excellent performance of the H5 group is attributed to the synergistic effect of nano-SiO2 and nano-HA: Nano-SiO2 promotes the extension of cell pseudopods and the expression of adhesion-related proteins (such as integrin β1) by optimizing the nanotopology of the coating surface (such as reducing the roughness to submicron level), thereby accelerating the early signal transduction of proliferation. 2+ With PO4 3- Directly participates in osteoblast metabolism, activates the PI3K / AKT pathway, and stimulates the expression of cyclin D1.

[0128] The peak RGR (112.63%) of the S3 group (containing only nano-SiO2) on day 3 indicated that nano-SiO2 delayed the release of magnesium ions through a physical barrier, thereby reducing ion toxicity. In the H5 group, the degradation products of nano-HA (Ca / P = 1.65) not only provided essential ions for osteogenesis but also inhibited the release of inflammatory factors (such as TNF-α) by forming a local weakly alkaline microenvironment (pH = 7.6-7.8), further promoting cell proliferation.

[0129] At day 7, there was no significant difference between the H5 and TCP groups (p>0.05), indicating that their bioactivity approached ideal tissue culture conditions. This characteristic is crucial for bone implant materials, supporting bone regeneration while avoiding the risk of ectopic osteogenesis caused by excessive proliferation. Compared with Ca-P coatings reported in the literature, the sustained proliferation-promoting effect of the H5 group (still reaching 109.81% at day 7) was superior to that of traditional hydroxyapatite coatings (approximately 105%), confirming the advantage of the synergistic modification of the dual nanoparticles.

[0130] Nano-SiO2 improved cell adhesion by optimizing the surface properties of the coating, while nano-HA promoted the proliferation process by ion release. The synergistic effect of the two made the H5 group maintain optimal bioactivity throughout the culture period. This result provides a theoretical basis for developing magnesium-based implants with both corrosion resistance and osteogenic activity.

[0131] 3 Bio-compatibility improvement mechanism EDS analysis found that the Ca / P ratio of the H5 group coating was close to the theoretical value of natural bone tissue (1.67) after immersion, indicating that the introduction of nano-HA significantly promoted the formation of calcium phosphate phase. This optimization of chemical composition not only simulates the composition of natural bone, but also provides a biomimetic microenvironment for cells, promoting cell adhesion, proliferation and mineralization. Combined with SEM observation, the H5 group coating surface showed a uniform porous structure, with a pore size distribution similar to that of natural bone trabecular structure. This porous morphology is not only beneficial to cell migration and nutrient transport, but also may serve as a reservoir for drug molecules, providing a structural basis for the design of subsequent drug delivery systems.

[0132] Nano-HA itself has excellent biocompatibility and osteoinductivity, and its chemical composition (Ca 10 (PO4)6(OH)2) is highly similar to human bone mineral. After introducing nano-HA into the coating, the released calcium and phosphorus ions can directly participate in the mineralization process of the extracellular matrix, accelerating bone tissue regeneration. At the same time, the surface active sites of nano-HA can bind to proteins or drug molecules through electrostatic interaction, further enhancing the functionality of the coating.

[0133] Combined with the characterization results of the immersion experiment, the introduction of nano-HA showed a significant synergistic effect on the corrosion resistance and bioactivity of the coating. After immersion in Hank's solution for 18 days, the H5 group had the lowest weight loss rate and the most stable pH change, indicating that the dense coating formed by nano-HA and nano-SiO2 effectively inhibited the corrosion degradation of the magnesium substrate and reduced the release of magnesium ions. This improvement in corrosion resistance not only prolongs the service life of the coating, but also reduces the toxicity of magnesium ions to cells, thereby indirectly enhancing the biocompatibility. In addition, nano-HA may promote the adsorption and slow release of drug molecules (such as antibiotics or growth factors) by regulating the chemical activity of the coating surface, providing a potential pathway for the application of the coating in drug delivery systems.

[0134] The introduction of nano-HA significantly enhances the coating's bioactivity and osseointegration capabilities by optimizing its chemical composition (Ca / P ratio) and porous morphology. Its synergistic effect with nano-SiO2 not only enhances corrosion resistance but also provides a physical and chemical foundation for the construction of sustained-release drug systems through the release of calcium and phosphate ions and the design of surface active sites. This mechanism provides theoretical support for the development of magnesium-based implant coatings that combine corrosion resistance, biocompatibility, and drug-carrying properties, and has important applications in pharmaceutical engineering.

[0135] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a nanoparticle micro-arc oxidation coating on the surface of a medical magnesium alloy, characterized in that: The steps include: Step 1, preparing an electrolyte, the electrolyte composition including C3H7CaO6P 2~12.5 g / L, (NaPO3)6 2~12.5 g / L, KOH 4.2~11.2 g / L, NH4HF2 3.42~13.68 g / L, C3H6O3 5~25 mL / L, H2O2 5~25 mL / L, Nano-SiO2 1~7 g / L, and nano-HA 1~5 g / L; Step 2: MAO treatment is performed using a bipolar current mode power supply. During the reaction, the electrolyte is continuously stirred and the temperature is controlled to be no higher than 30°C.

2. The preparation method according to claim 1, characterized in that In step 2, the MAO treatment parameters were set as follows: positive voltage 350-500 V, negative voltage 10-40 V, positive duty cycle 10-40%, negative duty cycle 10-30%, frequency 400-800 Hz, and reaction time 5-30 min.

3. The preparation method according to claim 1, characterized in that In step 1, the electrolyte composition is C3H7CaO6P 7.5 g / L, (NaPO3)6 7.5 g / L, KOH solution 5.0 g / L, NH4HF2 7.0 g / L, C3H6O3 10 mL / L, H2O2 7.5 mL / L, Nano-SiO2 1 ~7 g / L, nano-HA 1~5 g / L; in step 2, the positive voltage is 450 V, the negative voltage is 20 V, the positive duty cycle is 30%, the negative duty cycle is 20%, the frequency is 600 Hz, and the reaction time is 10 min.

4. The preparation method according to claim 1, characterized in that The particle size of Nano-SiO2 ranges from 30 to 500 nm.

5. The preparation method according to claim 1, characterized in that The particle size of nano-HA ranges from 20 to 200 nm.

6. The preparation method according to claim 1, characterized in that The concentration of Nano-SiO2 is 3~5 g / L, and the concentration of nano-HA is 3~5 g / L.

7. The preparation method according to claim 1, characterized in that The concentration of Nano-SiO2 is 3 g / L and that of nano-HA is 5 g / L.

8. A coating prepared by the method for preparing a nanoparticle micro-arc oxidation coating on the surface of a medical magnesium alloy according to any one of claims 1 to 7.

9. Use of the coating according to claim 8 as a drug carrier.

10. The use according to claim 9, characterized in that The drugs are selected from antibacterial, bone repair, and anti-inflammatory drugs; antibacterial drugs are selected from gentamicin or silver ions; bone repair drugs are selected from BMPs and bisphosphonates; and anti-inflammatory drugs are selected from ibuprofen, diclofenac, and salts thereof; Furthermore, the drug is an anti-inflammatory drug, or a combination thereof with a pH-sensitive material.

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