A medical magnesium alloy surface biocompatibility self-healing coating and a preparation method thereof

Abstract

This invention addresses the problems of rapid degradation and severe wear of medical magnesium alloys during implantation by proposing a biocompatible self-healing coating for the surface of medical magnesium alloys and its preparation method. The magnesium alloy is a commercially available magnesium alloy; the coating is a composite coating, with an inner layer being a silicate-based micro-arc oxidation coating loaded with polyaspartic acid, and an outer layer being a chitosan polymer coating. The preparation method includes mechanical grinding, micro-arc oxidation, vacuum impregnation, and impregnation-lift.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology of metal materials, specifically relating to a biocompatible self-healing coating for medical magnesium alloy surfaces and its preparation method. Background Technology

[0002] Medical-grade magnesium alloys are a novel type of medical material. Compared to traditional medical metals (such as steel and titanium), medical-grade magnesium alloys possess superior comprehensive mechanical properties, good biocompatibility, and unique biodegradability. These advantages make magnesium alloys a promising biodegradable implant material for applications in orthopedics, cardiology, and dentistry. However, medical-grade magnesium alloys suffer from rapid degradation and severe wear within the body, leading to a decline in material performance and affecting their lifespan and therapeutic efficacy. Therefore, surface modification of medical-grade magnesium alloys is necessary.

[0003] Applying protective coatings is a common surface treatment method that can improve the corrosion resistance of medical-grade magnesium alloys. However, during the degradation process, these coatings inevitably develop defects such as cracks and pitting. Corrosive media can penetrate the coating through these defects and reach the substrate, causing the magnesium alloy to degrade rapidly through microgalvanic corrosion, resulting in irreversible damage to its performance. Therefore, self-healing coatings are needed to address this problem. Self-healing coatings are coatings with self-repairing capabilities that can effectively protect the magnesium alloy substrate and extend its service life. Generally, self-healing coatings consist of a self-healing agent and a physical barrier layer that acts as a carrier for the self-healing agent. When corrosion, wear, or other damage occurs on the coating surface, the self-healing agent in the carrier automatically flows to the damaged area to repair it, thereby restoring the damaged area. By rationally selecting self-healing materials and cleverly designing the coating structure, highly efficient protection for medical-grade magnesium alloys can be achieved. However, most self-healing agents currently used in the industrial field are toxic, such as cerium ions, benzotriazole, and 8-hydroxyquinoline, which are difficult to apply in the biomedical field. The key challenge in the development of self-healing coatings for medical magnesium alloys is balancing self-healing effectiveness with excellent biocompatibility.

[0004] Polyaspartic acid (PASP) is a natural amino acid polymer found in the shells of snails and mollusks. It is non-toxic, does not damage the ecological environment, and has biodegradable properties, making it a potential self-healing agent in the biomedical field. Qian B et al. used layer-by-layer deposition technology to alternately deposit chitosan (CS) and PASP on the surface of silica nanoparticles, obtaining a self-healing coating of nanocontainers loaded with PASP. Corrosion experiments proved its self-healing properties (Qian B, Song ZW, Hao L, et al. Enrapment of polyaspartic acid on silica nanoparticle for self-healing coatings. Materials and Corrosion, 2017, 68(7): 717-724). Among many surface modification technologies, micro-arc oxidation (MAO) technology is widely used in the biomedical field. Its coating has a porous structure. When the self-healing agent is loaded into these micropores, it can flow out from the micropores when it encounters external damage. After contacting the external environment, it undergoes a self-healing reaction, thereby repairing the damaged parts of the coating. Publicly available patent applications (CN114672864A, CN102534631A) further composite other coatings onto MAO coatings to improve the corrosion resistance of magnesium alloys, but these coatings lack self-healing capabilities. To improve overall surface performance, this invention proposes a biocompatible self-healing coating for medical magnesium alloys and its preparation method. A commercially available magnesium alloy is selected as the substrate. A porous ceramic coating is prepared using the MAO process as a carrier for the self-healing agent. PASP is loaded onto the MAO coating using a vacuum impregnation process. Finally, a CS polymer coating is prepared using an dip-coating process to seal the pores in the PASP-loaded MAO coating. Summary of the Invention

[0005] This invention addresses the problems of rapid degradation and severe wear of medical magnesium alloys during implantation by proposing a biocompatible self-healing coating for the surface of medical magnesium alloys and its preparation method. The magnesium alloy is a commercially available magnesium alloy; the coating is a composite coating, with an inner layer of silicate-based MAO coating loaded with PASP and an outer layer of CS polymer coating; the preparation method includes mechanical grinding, MAO, vacuum impregnation, and impregnation-lifting.

[0006] The functions of each part of the composite coating are as follows: For the inner MAO coating, the electrolyte includes Na2SiO3, NaOH, and KF silicate-based components. The electrolyte has good conductivity and an alkaline environment, which facilitates the control of the pore size and porosity of the MAO coating. The porous gradient structure of the MAO coating can support PASP self-healing agent. For the outer CS polymer coating, it is used to seal the pore structure of the inner MAO coating and further improve the corrosion resistance of the composite coating.

[0007] The functions of each process in the preparation method are as follows: mechanical grinding provides a uniform, flat, fresh and clean pre-treated surface for subsequent coating operations; MAO process can prepare a porous ceramic layer with high bonding strength and good corrosion resistance for loading PASP; vacuum impregnation process can load PASP into the pore structure of MAO coating, and the vacuum environment can improve the loading rate of PASP; impregnation pulling process is used to prepare a uniform and complete CS polymer coating and seal the pore structure of MAO coating.

[0008] The technical solution of this invention is as follows:

[0009] A biocompatible self-healing coating for a medical magnesium alloy surface, wherein the magnesium alloy is a commercially available magnesium alloy; the coating is a composite coating, the inner layer being a silicate-based MAO coating loaded with PASP, and the outer layer being a CS polymer coating.

[0010] A method for preparing a biocompatible self-healing coating on a medical magnesium alloy surface includes the following steps:

[0011] Step 1: Mechanical grinding to prepare the pretreated surface

[0012] For ease of testing, magnesium alloy blocks, plates, or rods were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire EDM machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and dried with cold air.

[0013] Step 2: Preparation of silicate-based coatings using MAO process

[0014] A silicate-based coating was prepared on the magnesium alloy pretreated surface obtained in the first step using the MAO process. The electrolyte consisted of NaOH, Na₂SiO₃, and KF, with Na₂SiO₃ concentrations of 20–28 g / L and KF concentrations of 5–15 g / L. The pH of the electrolyte was adjusted to 9–12 using NaOH, and the current density was 2 A / dm³. 2 It adopts a constant voltage mode with a voltage of 250-400V, a processing time of 5-15min, a pulse count of 30-80, a duty cycle of 30%-50%, and a frequency of 500Hz.

[0015] Preferably, the concentration of Na2SiO3 is 22-26 g / L, the concentration of KF is 8-10 g / L, the pH of the electrolyte is adjusted to 10-11 using NaOH, the voltage is 300-400 V, the treatment time is 8-12 min, the number of pulses is 40-60, and the duty cycle is 35%-45%.

[0016] Step 3: Vacuum impregnation process to load PASP

[0017] The magnesium alloy with MAO coating obtained in the second step was placed in a vacuum filtration apparatus, which consisted of a vacuum pump, a filtration flask, a vacuum tubing, a vacuum stopper, and a funnel. A buffer solution consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water was prepared. 100-500mg of PASP was dissolved in the buffer solution. The prepared solution was poured into the funnel, and then the apparatus was turned on to create a vacuum. After maintaining this state for a period of time, the valve was opened, and the solution was drawn into the filtration flask to submerge the sample. The sample was immersed for 5-12 minutes. After vacuum impregnation, the sample was removed.

[0018] Preferably, 200–400 mg of PASP is dissolved in a buffer solution, and the sample is soaked for 6–10 minutes.

[0019] Step 4: Preparation of CS polymer coating using dip-coating process

[0020] A CS polymer coating was prepared on the surface of the sample obtained in step 3 using an dip-coating machine. The CS purity was 99.1%–99.9%, and the average molecular weight was 10,000–150,000. The CS was dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10. The solution was stirred magnetically until the CS was completely dissolved. The sample was vertically immersed in the CS solution using a coating machine and allowed to stand for 10 minutes. The sample was then vertically removed at a speed of 10–40 cm / min. The number of dip-coating cycles was 2–10. After each dip-coating, the sample was dried in an oven at 60°C for 30 minutes to obtain the CS polymer coating.

[0021] Preferably, the purity of CS is 99.9%, the average molecular weight is 90,000 to 130,000, the lifting rate is 20 to 30 cm / min, and the number of lifting times is 4 to 8.

[0022] The biocompatible self-healing coating on the magnesium alloy surface prepared by the above method has a two-layer structure, consisting of a silicate-based MAO coating loaded with PASP and a CS polymer coating from the inside out. The composite coating is ingeniously designed: the MAO coating itself has good corrosion resistance, and as an intermediate layer, it can improve the interfacial bonding strength between the magnesium alloy substrate and the CS polymer coating. When the composite coating is damaged, the loaded PASP is released from the MAO coating, and a reaction occurs between the dissolved metal ions, adsorbed amino acid molecules, and ions from the corrosive medium on the sample surface. The amino acid molecules react with magnesium ions and phosphate ions to form magnesium phosphate precipitates that adhere to the damaged areas of the coating, thereby repairing the coating. The CS polymer coating can further improve the corrosion resistance of the MAO coating by sealing the pores within it. The preparation methods of the composite coating are closely linked: the mechanical grinding process can provide a uniform, flat, fresh and clean pre-treated surface for subsequent coating; the MAO process can prepare a porous ceramic layer with high bonding strength and good corrosion resistance for loading PASP; the vacuum impregnation process can load PASP into the pore structure of the MAO coating, and the vacuum environment can improve the loading rate of PASP; the dip-coating process is used to prepare a uniform and complete CS polymer coating and seal the pore structure of the MAO coating.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) The inventors comprehensively utilized mechanical grinding, MAO, vacuum impregnation, and impregnation-pulling processes, and through numerous experiments, prepared a biocompatible self-healing coating on the surface of magnesium alloys, summarizing the optimal range of process parameters: For the preparation of silicate-based MAO coatings, the concentration of Na2SiO3 was 22–26 g / L, the concentration of KF was 8–10 g / L, the pH of the electrolyte was adjusted to 10–11 using NaOH, the voltage was 300–400 V, the processing time was 8–12 min, the number of pulses was 40–60, and the duty cycle was 35%–45%. For loading PASP, 200–400 mg of PASP was dissolved in a buffer solution consisting of 8 g of tris(hydroxymethyl)aminomethane hydrochloride, 16 g of NaCl, and 500 mL of deionized water, and the sample soaking time was 6–10 min. For preparing CS polymer coatings, the CS purity is 99.9%, the average molecular weight is 90,000–130,000, the pulling rate is 20–30 cm / min, and the number of pulling cycles is 4–8. Using this combination of process parameters, a uniform, moderately thick, and highly adhesive biocompatible self-healing coating can be obtained on the magnesium alloy surface.

[0025] (2) The inventors prepared a biocompatible self-healing coating on the surface of a magnesium alloy. Performance analysis results showed that the coating exhibited self-healing behavior in a scratch test conducted in Hank's equilibrium salt (HBSS) solution. The coating thickness ranged from 10.0 to 21.5 μm, and the self-corrosion potential of the surface-modified magnesium alloy was 1.17–0.74 V / SCE, with a self-corrosion current density of (0.32–4.50) × 10⁻⁶. -6 A / cm 2 Compared with unmodified magnesium alloys, the self-corrosion potential increased by 22.4% to 51.0%, and the self-corrosion current density decreased by 189 to 1188 times, indicating that the composite coating significantly improved the corrosion resistance of magnesium alloys. Attached Figure Description

[0026] Figure 1 The image shows the microstructure of the MAO coating on the magnesium alloy surface in Example 1.

[0027] Figure 2 The image shows the microstructure of the MAO / CS composite coating on the magnesium alloy surface in Example 1.

[0028] Figure 3 This shows the healing of scratches on the MAO / CS composite coating on the magnesium alloy surface in HBSS solution in Example 1.

[0029] Figure 4 This is a schematic diagram of the self-healing mechanism of the MAO / CS composite coating on the magnesium alloy surface in Example 1.

[0030] Figure 5 This is a comparison of the corrosion resistance of the magnesium alloy before and after surface treatment in Example 1. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0032] The present invention discloses a biocompatible self-healing coating for medical magnesium alloy surfaces, wherein the magnesium alloy is a commercial magnesium alloy; the coating is a composite coating, the inner layer is a silicate-based MAO coating loaded with PASP, and the outer layer is a CS polymer coating.

[0033] The present invention discloses a method for preparing a biocompatible self-healing coating on a medical magnesium alloy surface, comprising the following steps:

[0034] Step 1: Mechanical grinding to prepare the pretreated surface

[0035] For ease of testing, magnesium alloy blocks, plates, or rods were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire EDM machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and dried with cold air.

[0036] Step 2: Preparation of silicate-based coatings using MAO process

[0037] A silicate-based coating is prepared on the magnesium alloy pretreated surface obtained in the first step using the MAO process. The electrolyte consists of NaOH, Na₂SiO₃, and KF. The concentration of Na₂SiO₃ is 20–28 g / L, preferably 22–26 g / L, and the concentration of KF is 5–15 g / L, preferably 8–10 g / L. The pH of the electrolyte is adjusted to 9–12, preferably 10–11, using NaOH. The current density is 2 A / dm³. 2 The system adopts a constant voltage mode with a voltage of 250-400V, preferably 300-400V, a processing time of 5-15min, preferably 8-12min, a pulse number of 30-80, preferably 40-60, a duty cycle of 30%-50%, preferably 35%-45%, and a frequency of 500Hz.

[0038] Step 3: Vacuum impregnation process to load PASP

[0039] The magnesium alloy with MAO coating obtained in the second step is placed in a vacuum filtration apparatus, which consists of a vacuum pump, a filtration flask, a vacuum tubing, a vacuum stopper, and a funnel. A buffer solution is prepared, consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water. 100-500mg of PASP is dissolved in the buffer solution, preferably 200-400mg of PASP. The prepared solution is poured into the funnel, and then the apparatus is turned on to create a vacuum. After maintaining this vacuum for a period of time, the valve is opened to draw the solution into the filtration flask to submerge the sample. The sample is immersed for 5-12 minutes, preferably 6-10 minutes. After vacuum impregnation, the sample is removed.

[0040] Step 4: Preparation of CS polymer coating using dip-coating process

[0041] A CS polymer coating is prepared on the surface of the sample obtained in the third step using an dip-coating machine. The CS purity is 99.1%–99.9%, preferably 99.9%, and the average molecular weight is 10,000–150,000, preferably 90,000–130,000. The CS is dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10. The solution is stirred magnetically until the CS is completely dissolved. The sample is vertically immersed in the CS solution using a coating machine and allowed to stand for 10 minutes. The sample is then vertically removed at a rate of 10–40 cm / min, preferably 20–30 cm / min, and the number of pull-ups is 2–10, preferably 4–8. After each pull-up, the sample is dried in an oven at 60°C for 30 minutes to obtain the CS polymer coating.

[0042] Microstructural analysis of the biocompatible self-healing coating on the magnesium alloy surface prepared by the method described in this invention revealed that the coating has a bilayer structure: an inner layer of PASP-loaded silicate-based MAO coating and an outer layer of CS polymer coating. No obvious defects were found in any of the coatings or their interfaces. Self-healing performance tests showed that the coating containing scratches underwent self-healing after being placed in an HBSS solution for a period of time.

[0043] The following detailed description is provided through specific embodiments.

[0044] Example 1:

[0045] Step 1: Mechanical grinding to prepare the pretreated surface

[0046] For ease of testing, WE43 magnesium alloy blocks, plates, or bars were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire EDM machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and dried with cold air.

[0047] Step 2: Preparation of silicate-based coatings using MAO process

[0048] A silicate-based coating was prepared on the magnesium alloy pretreated surface obtained in the first step using the MAO process. The electrolyte consisted of NaOH, Na₂SiO₃, and KF, with a Na₂SiO₃ concentration of 22 g / L and a KF concentration of 8 g / L. The pH of the electrolyte was adjusted to 10 using NaOH, and the current density was 2 A / dm³. 2 It adopts a constant voltage mode with a voltage of 300V, a processing time of 8min, a pulse count of 40, a duty cycle of 35%, and a frequency of 500Hz.

[0049] Step 3: Vacuum impregnation process to load PASP

[0050] The magnesium alloy with MAO coating obtained in the second step was placed in a vacuum filtration apparatus, which consisted of a vacuum pump, a filtration flask, a vacuum tubing, a vacuum stopper, and a funnel. A buffer solution consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water was prepared. 200mg of PASP was dissolved in the buffer solution. The prepared solution was poured into the funnel, and then the apparatus was turned on to create a vacuum. After maintaining this state for a period of time, the valve was opened, and the solution was drawn into the filtration flask to submerge the sample. The sample was immersed for 6 minutes. After vacuum impregnation was completed, the sample was removed.

[0051] Step 4: Preparation of CS polymer coating using dip-coating process

[0052] A CS polymer coating was prepared on the sample surface obtained in step 3 using an dip-coating machine. The CS had a purity of 99.9% and an average molecular weight of 90,000. It was dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10. The solution was stirred magnetically until the CS was completely dissolved. The sample was then vertically immersed in the CS solution using a coating machine and allowed to stand for 10 minutes. The coating was then lifted 4 times at a speed of 20 cm / min. After each lifting, the sample was dried in an oven at 60°C for 30 minutes to obtain the CS polymer coating.

[0053] The samples prepared in Example 1 were subjected to tissue structure analysis and performance characterization:

[0054] (A) Microstructure of MAO coating on WE43 magnesium alloy surface

[0055] Appendix Figure 1 The image shows the microstructure of the MAO coating on the surface of WE43 magnesium alloy. The coating has many large pores, which facilitates the loading of PASP.

[0056] (B) Microstructure of MAO / CS composite coating on WE43 magnesium alloy surface

[0057] Appendix Figure 2 The image shows the microstructure of the MAO / CS composite coating on the surface of WE43 magnesium alloy. The CS polymer coating can seal the pores of the MAO coating. The composite coating has a uniform microstructure and good sealing performance. The thickness of the composite coating is 10.0 μm.

[0058] (C) Healing of scratch-containing coatings on WE43 magnesium alloy surfaces in HBSS solution

[0059] Appendix Figure 3 The images show the healing of scratches on the MAO / CS composite coating of WE43 magnesium alloy in HBSS solution. Figures a, b, c, and d show the healing results after immersion for 5 min, 30 min, 1 h, and 3 h, respectively. A black precipitate was observed at the scratch site after 3 h, which is composed of PASP and Mg.2+ The precipitate formed by the reaction with the components of the HBSS solution completes the self-healing reaction. The reaction mechanism is as follows:

[0060] Mg 2+ +xC4H7NO 4+ H y PO4 (3-y)- →Mg(C4H7NO4) x H y PO4↓

[0061] (D) Self-healing mechanism of composite coating on WE43 magnesium alloy surface

[0062] Appendix Figure 4 This diagram illustrates the self-healing mechanism of the MAO / CS composite coating on the surface of WE43 magnesium alloy. The composite coating has a two-layer structure, consisting of a silicate-based MAO coating loaded with PASP and a CS polymer coating, from the inside out. When the coating cracks, reactions occur between dissolved metal ions, adsorbed amino acid molecules, and constituent ions of the corrosive medium on the sample surface. The amino acid molecules react with magnesium ions and phosphate ions to form magnesium phosphate precipitates that adhere to the damaged areas of the coating, thereby repairing it.

[0063] (E) Comparison of corrosion resistance of WE43 magnesium alloy before and after surface treatment

[0064] In HBSS solution, the potentiodynamic polarization curves of the samples were measured using an electrochemical workstation to evaluate their corrosion performance. (See attached...) Figure 5 As can be seen, after surface modification, the WE43 magnesium alloy in Example 1 has a self-corrosion potential of -1.17V / SCE and a self-corrosion current density of 4.50×10⁻⁶. -6 A / cm 2 Before surface modification, the self-corrosion potential and self-corrosion current density of WE43 magnesium alloy were -1.51V / SCE and 8.50×10⁻⁶, respectively. -4 A / cm 2 The composite coating increased the self-corrosion potential of WE43 magnesium alloy by 22.4% and reduced the self-corrosion current density by 189 times.

[0065] Example 2:

[0066] Step 1: Mechanical grinding to prepare the pretreated surface

[0067] For ease of testing, AZ31 magnesium alloy blocks, plates, or bars were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire EDM machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and dried with cold air.

[0068] Step 2: Preparation of silicate-based coatings using MAO process

[0069] A silicate-based coating was prepared on the magnesium alloy pretreated surface obtained in the first step using the MAO process. The electrolyte consisted of NaOH, Na₂SiO₃, and KF, with a Na₂SiO₃ concentration of 24 g / L and a KF concentration of 9 g / L. The pH of the electrolyte was adjusted to 10.5 using NaOH, and the current density was 2 A / dm³. 2 The system uses a constant voltage mode with a voltage of 350V, a processing time of 10 minutes, 50 pulses, a duty cycle of 40%, and a frequency of 500Hz.

[0070] Step 3: Vacuum impregnation process to load PASP

[0071] The magnesium alloy with MAO coating obtained in the second step was placed in a vacuum filtration apparatus, which consisted of a vacuum pump, a filtration flask, a vacuum tubing, a vacuum stopper, and a funnel. A buffer solution consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water was prepared. 300mg of PASP was dissolved in the buffer solution. The prepared solution was poured into the funnel, and then the apparatus was turned on to create a vacuum. After maintaining this state for a period of time, the valve was opened, and the solution was drawn into the filtration flask to submerge the sample. The sample was immersed for 8 minutes. After vacuum impregnation, the sample was removed.

[0072] Step 4: Preparation of CS polymer coating using dip-coating process

[0073] A CS polymer coating was prepared on the sample surface obtained in step 3 using an dip-coating machine. The CS had a purity of 99.9% and an average molecular weight of 110,000. It was dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10 and stirred magnetically until the CS was completely dissolved. The sample was then vertically immersed in the CS solution using a coating machine and allowed to stand for 10 minutes. The coating was then lifted 6 times at a speed of 25 cm / min. After each lifting, the sample was dried in an oven at 60°C for 30 minutes to obtain the CS polymer coating.

[0074] Microstructural analysis and performance testing revealed that the thickness of the composite coating on the AZ31 magnesium alloy surface in Example 2 was 15.5 μm. The self-corrosion potential and self-corrosion current density of the surface-modified sample were -0.96 V / SCE and 2.10 × 10⁻⁶ V / SCE, respectively. -6 A / cm 2 Before surface modification, the self-corrosion potential and self-corrosion current density of AZ31 magnesium alloy were -1.72V / SCE and 5.60×10⁻⁶, respectively. -4 A / cm 2 In contrast, the coating increased the self-corrosion potential of AZ31 magnesium alloy by 44.2% and decreased the self-corrosion current density by 267 times.

[0075] Example 3:

[0076] Step 1: Mechanical grinding to prepare the pretreated surface

[0077] For ease of testing, ZK60 magnesium alloy blocks, plates, or bars were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire EDM machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, and dried with cold air.

[0078] Step 2: Preparation of silicate-based coatings using MAO process

[0079] A silicate-based coating was prepared on the magnesium alloy pretreated surface obtained in the first step using the MAO process. The electrolyte consisted of NaOH, Na₂SiO₃, and KF, with a Na₂SiO₃ concentration of 26 g / L and a KF concentration of 10 g / L. The pH of the electrolyte was adjusted to 11 using NaOH, and the current density was 2 A / dm³. 2 The system uses a constant voltage mode with a voltage of 400V, a processing time of 12 minutes, 60 pulses, a duty cycle of 45%, and a frequency of 500Hz.

[0080] Step 3: Vacuum impregnation process to load PASP

[0081] The magnesium alloy with MAO coating obtained in the second step was placed in a vacuum filtration device, which consisted of a vacuum pump, a filtration flask, a vacuum tubing, a vacuum stopper, and a funnel. A buffer solution consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water was prepared. 400mg of PASP was dissolved in the buffer solution. The prepared solution was poured into the funnel, and then the device was turned on to create a vacuum. After maintaining this state for a period of time, the valve was opened, and the solution was drawn into the filtration flask to submerge the sample. The sample was immersed for 10 minutes. After vacuum impregnation, the sample was removed.

[0082] Step 4: Preparation of CS polymer coating using dip-coating process

[0083] A CS polymer coating was prepared on the sample surface obtained in step 3 using an dip-coating machine. The CS had a purity of 99.9% and an average molecular weight of 130,000. It was dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10. The solution was stirred magnetically until the CS was completely dissolved. The sample was then vertically immersed in the CS solution using a coating machine and allowed to stand for 10 minutes. The coating was then lifted 8 times at a speed of 30 cm / min. After each lifting, the sample was dried in an oven at 60°C for 30 minutes to obtain the CS polymer coating.

[0084] Microstructural analysis and performance testing revealed that the thickness of the composite coating on the ZK60 magnesium alloy surface in Example 3 was 21.5 μm. The self-corrosion potential and self-corrosion current density of the surface-modified sample were -0.74 V / SCE and 0.32 × 10⁻⁶, respectively. -6 A / cm 2 Before surface modification, the self-corrosion potential and self-corrosion current density of AZ31 magnesium alloy were -1.51V / SCE and 3.80×10⁻⁶, respectively. -4 A / cm 2 In contrast, the coating increased the self-corrosion potential of AZ31 magnesium alloy by 51.0% and decreased the self-corrosion current density by 1188 times.

[0085] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

[0086] Matters not covered in this invention are common knowledge.

Claims

1. A biocompatible self-healing coating for medical magnesium alloy surfaces, characterized in that, The magnesium alloy is a commercially available magnesium alloy; the coating is a composite coating, with an inner layer of silicate-based micro-arc oxidation coating loaded with polyaspartic acid and an outer layer of chitosan polymer coating; the thickness of the composite coating is 10.0–21.5 μm, and the self-corrosion potential of the surface-modified magnesium alloy is -1.17–-0.74 V / SCE, and the self-corrosion current density is (0.32–4.50) × 10⁻⁶. -6 A / cm 2 Compared with unmodified magnesium alloys, the self-corrosion potential increased by 22.4%–51.0%, and the self-corrosion current density decreased by 189–1188 times. In a scratch test conducted in Hank's equilibrium salt (HBSS) solution, the composite coating showed reactions between dissolved metal ions, adsorbed amino acid molecules, and constituent ions of the corrosive medium. The amino acid molecules reacted with magnesium ions and phosphate ions to form magnesium phosphate precipitates that adhered to the damaged areas of the coating, thereby repairing the coating and exhibiting self-healing properties. The preparation method of this composite coating is characterized by the following steps: Step 1: Mechanical grinding to prepare the pretreated surface For ease of testing, magnesium alloy blocks, plates or rods were cut into 120mm×120mm×3mm square pieces or Φ100×3mm round pieces using a wire cutting machine. The pieces were then mechanically ground with sandpaper to remove surface oxide scale and impurities. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes respectively and dried with cold air. Step 2: Preparation of silicate-based coatings using micro-arc oxidation process A silicate-based coating was prepared on the magnesium alloy pretreated surface obtained in the first step using a micro-arc oxidation process. The electrolyte consisted of NaOH, Na₂SiO₃, and KF, with Na₂SiO₃ concentrations of 20–28 g / L and KF concentrations of 5–15 g / L. The pH of the electrolyte was adjusted to 9–12 using NaOH, and the current density was 2 A / dm³. 2 It adopts a constant voltage mode with a voltage of 250-400V, a processing time of 5-15min, a pulse number of 30-80, a duty cycle of 30%-50%, and a frequency of 500Hz; Step 3: Vacuum impregnation process for loading polyaspartic acid The magnesium alloy with a micro-arc oxidation coating obtained in the second step was placed in a vacuum filtration device. The vacuum filtration device consisted of a vacuum pump, a filtration flask, a vacuum hose, a vacuum stopper, and a funnel. A buffer solution consisting of 8g of tris(hydroxymethyl)aminomethane hydrochloride, 16g of NaCl, and 500mL of deionized water was prepared. 100-500mg of polyaspartic acid was dissolved in the buffer solution. The prepared solution was poured into the funnel, and then the device was turned on to create a vacuum. After maintaining the vacuum for a period of time, the valve was opened to draw the solution into the filtration flask to submerge the sample. The sample was soaked for 5-12 minutes. After the vacuum impregnation was completed, the sample was removed. Step 4: Preparation of chitosan polymer coating using dip-coating process A chitosan polymer coating was prepared on the surface of the sample obtained in step three using an dip-coating machine. The chitosan had a purity of 99.1%–99.9% and an average molecular weight of 10,000–150,000. It was dissolved in a solution of acetic acid and deionized water with a volume ratio of 1:10 and stirred magnetically until the chitosan was completely dissolved. The sample was then vertically immersed in the chitosan solution using a coating machine and allowed to stand for 10 minutes. The sample was then vertically removed at a speed of 10–40 cm / min, and the number of pull-out cycles was 2–10. After each pull-out, the sample was dried in an oven at 60°C for 30 minutes to obtain the chitosan polymer coating.

2. The method for preparing a biocompatible self-healing coating on a medical magnesium alloy surface as described in claim 1, characterized in that, In the second step, the concentration of Na₂SiO₃ is 22–26 g / L, the concentration of KF is 8–10 g / L, the pH of the electrolyte is adjusted to 10–11 using NaOH, and the current density is 2 A / dm³. 2 It adopts a constant voltage mode with a voltage of 300-400V, a processing time of 8-12min, a pulse count of 40-60, a duty cycle of 35%-45%, and a frequency of 500Hz.

3. The method for preparing a biocompatible self-healing coating on a medical magnesium alloy surface as described in claim 1, characterized in that, In the third step, 200-400 mg of polyaspartic acid is dissolved in a buffer solution, and the sample is soaked for 6-10 minutes.

4. The method for preparing a biocompatible self-healing coating on a medical magnesium alloy surface as described in claim 1, characterized in that, In the fourth step, the chitosan purity is 99.9%, the average molecular weight is 90,000 to 130,000, the lifting rate is 20 to 30 cm / min, and the number of lifting times is 4 to 8.

5. The biocompatible self-healing coating for medical magnesium alloy surfaces as described in claim 1, characterized in that, It can be applied in the biomedical field.

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