A magnesium alloy composite coating with corrosion resistance for promoting bone healing, its preparation method, and a medical magnesium alloy

Abstract

The present invention relates to a magnesium alloy composite coating with corrosion resistance for promoting bone healing, a preparation method thereof, and a medical magnesium alloy. The magnesium alloy composite coating includes a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward. The bottom coating includes microporous channels, and the components of the bottom coating include magnesium hydroxide and / or magnesium oxide. The surface coating includes a polymer material, and the polymer material includes polylactic acid or a mixture of polylactic acid and polycaprolactone. The surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating. The magnesium alloy composite coating provided by the present invention is connected in an interlaced and inserted manner by the bottom coating formed by a chemical conversion method and the surface coating formed by a polymer material, has good firmness, strength, and toughness, improves the corrosion resistance of the magnesium alloy, and meets the requirements for promoting bone healing.

Description

Technical Field

[0001] The present invention relates to the technical field of biomedical materials, and particularly relates to a magnesium alloy composite coating with corrosion resistance and promoting bone healing, a preparation method thereof, and a medical magnesium alloy. Background Art

[0002] Magnesium is one of the essential elements for the human body. Magnesium alloys have good biocompatibility and metabolic mechanisms, and have broad application prospects in the medical field. However, problems such as poor corrosion resistance and too fast degradation rate of magnesium alloys limit their expanded application.

[0003] In existing research, although the corrosion resistance of magnesium alloys has been continuously improved by means such as alloying, controlling impurity content, and improving processing technology, the improvement space is limited. In many application scenarios, magnesium alloys are still difficult to be directly put into use. Therefore, it is necessary to perform surface modification or surface decoration on magnesium alloys, which can greatly improve the corrosion resistance of magnesium alloys and is also the main research route in the application of magnesium alloys. There are many surface decoration methods for magnesium alloys, mainly considering several aspects such as biocompatibility, degradation ability, and effectiveness of inhibiting the degradation of magnesium alloys.

[0004] For example, CN118105548A discloses a medical degradable magnesium alloy coating and a preparation method thereof, including a magnesium hydroxide coating with a thickness of 15 - 20 μm or a magnesium hydroxide-calcium phosphate composite coating with a thickness of 50 - 150 μm; the magnesium hydroxide-calcium phosphate composite coating includes a magnesium hydroxide layer and a fish-scale-shaped calcium phosphate layer attached to the surface of the magnesium hydroxide layer. This method prepares a degradable magnesium alloy coating through a hydrothermal process. Although it can improve the corrosion rate to a certain extent, the strength and toughness of the coating are limited, and it is easy to be damaged and expose the substrate.

[0005] For magnesium alloys used for bone plates and bone nails, when the bone nail is twisted and screwed in, a large frictional force is formed. If the coating has insufficient bonding strength, microcracks are likely to occur, exposing the substrate magnesium alloy and accelerating local corrosion. Therefore, it is required that the magnesium alloy coating has good toughness and strength, and under the high shear force during the screwing of the bone nail, cracks or peeling of the coating are avoided, so that the magnesium alloy can maintain good corrosion resistance during service and meet the needs of bone healing.

[0006] Therefore, providing a magnesium alloy coating that can improve the bonding strength between the coating and the substrate, is corrosion-resistant and promotes bone healing, and a preparation method thereof, is a technical problem that needs to be solved in the current field. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a magnesium alloy composite coating with corrosion resistance and bone healing promotion, its preparation method and a medical magnesium alloy. Compared with the existing technology, the magnesium alloy composite coating provided by the present invention is connected in an interlaced and inserted manner between the bottom coating formed by chemical conversion and the surface coating formed by polymer materials, having good firmness, strength and toughness, improving the corrosion resistance of the magnesium alloy, and meeting the need for promoting bone healing.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] In the first aspect, the present invention provides a magnesium alloy composite coating with corrosion resistance and bone healing promotion, and the magnesium alloy composite coating includes a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outwards;

[0010] The bottom coating includes microporous channels, and the components of the bottom coating include magnesium hydroxide and / or magnesium oxide;

[0011] The surface coating includes a polymer material, and the polymer material includes polylactic acid or a mixture of polylactic acid and polycaprolactone. The surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating.

[0012] In the composite coating provided by the present invention, the bottom coating is prepared on the surface of the magnesium alloy through a hydrothermal reaction, with a dense structure and a relatively high bonding strength with the substrate. Its main components are magnesium hydroxide and / or magnesium oxide, without other components and impurities, and it is an intermediate product in the degradation process of the magnesium alloy, having excellent biocompatibility; the components of the surface coating are mainly polylactic acid or a mixture of polylactic acid and polycaprolactone. By using polycaprolactone and polylactic acid in combination, while ensuring the strength of polylactic acid, it can improve the problem of insufficient toughness of polylactic acid, effectively improve the toughness of the surface polymer coating, and when the product needs to be deformed, it will not break due to deformation. The coating takes into account both strength and toughness, and has good application prospects especially in the field of magnesium alloys for magnesium alloy bone plates and bone nails.

[0013] It should be noted that, on the one hand, the bottom coating has a greater surface roughness compared to the magnesium alloy surface, providing a better interface for the adhesion of the surface polymer coating, improving the bonding strength between the polymer coating and the product, and thus contributing to improving the corrosion resistance performance; on the other hand, the microporous channels on the bottom coating are conducive to forming an "interlaced and inserted" connection method between the surface coating and the bottom coating, improving the bonding force between the composite coating and the substrate, and thus still being able to maintain properties such as being not easily damaged and corrosion resistant under the action of external forces. In summary, the composite coating provided by the present invention has good biocompatibility, can be completely degraded, has good strength and toughness, can continuously and effectively inhibit the degradation of the magnesium alloy, improve the corrosion resistance of the magnesium alloy, and promote rapid bone healing.

[0014] Preferably, nano-hydroxyapatite is distributed in the polymer material; the particle size of the nano-hydroxyapatite is 20 - 60 nm, for example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm or 60 nm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] It should be noted that in the surface coating provided by the present invention, it is preferred to add nano-hydroxyapatite into the polymer material, which can be continuously released during the degradation of the coating, thereby improving the local microenvironment, promoting the adhesion, proliferation and differentiation of bone cells, accelerating bone tissue regeneration, and the alkalinity of nano-hydroxyapatite can neutralize the local acidic environment generated by the degradation of polylactic acid, reducing the inflammatory reaction. In the present invention, by preferably controlling the particle size of nano-hydroxyapatite within a specific range, it can be evenly distributed in the polylactic acid coating. When the particle size is too large, it is easy to precipitate in the solution and block the nozzle during the ultrasonic spraying process, resulting in too high a content per unit area of the polylactic acid coating, the coating cannot be completely coated, affecting the coating quality and the corrosion resistance decreases; when the particle size is too small, the specific surface area of the nanoparticles is large and the surface energy is high, making it easier to agglomerate crack sources, and it is more likely to be carried away by the air flow during the ultrasonic spraying process, resulting in mechanisms such as increased porosity and weak interface bonding deteriorating the uniformity and mechanical properties of the polylactic acid coating, reducing the coating quality and the corrosion resistance.

[0016] Preferably, the porosity of the bottom coating is 30 - 60%, for example, it can be 30%, 35%, 40%, 45%, 55% or 60%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the pore diameter of the microporous channels is 20 - 120 μm, for example, it can be 20 μm, 40 μm, 60 μm, 80 μm, 100 μm or 120 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0017] In the present invention, by making holes in the bottom coating, an interlocking mechanical structure can be formed on the basis of not completely damaging the magnesium alloy substrate, increasing the adhesion strength of the surface polymer coating. Under the action of external force, the coating is not easily damaged, improving the corrosion resistance, thereby forming a strong composite structure between the surface coating, the bottom coating and the substrate. In the present invention, by preferably controlling the porosity and pore diameter of the bottom coating within a specific range, the values are not too large. The main purpose is to match the molecular weight and structure of polylactic acid, so that under the ultrasonic spraying process, polylactic acid is more likely to form an interlocking structure with the micropores, thereby achieving the occlusion of the entire surface of the product, improving the adhesion strength, and avoiding local accumulation of polylactic acid.

[0018] Preferably, the thickness of the bottom coating is 8-12 μm, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm or 12 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0019] Preferably, the thickness of the surface coating is 15-30 μm, for example, it can be 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm or 30 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0020] In the present invention, by preferably controlling the thickness of the surface coating within a specific range, it is because the thickness of the coating mainly affects the degradation period and adhesion. When the thickness of the coating is too large, the corrosion resistance increases, and theoretically the degradation period will be extended. However, in fact, when the thickness of the coating exceeds the critical value, the internal stress of the coating increases and the adhesion decreases. When subjected to external forces, the coating is easily broken, resulting in a decrease in corrosion resistance and a shortening of the degradation period; when the coating thickness is too thin, the corrosion resistance decreases, the degradation period is shortened, and the protective effect on the magnesium alloy substrate is insufficient.

[0021] In a second aspect, the present invention provides a method for preparing a magnesium alloy composite coating with corrosion resistance promoting bone healing as described in the first aspect of the present invention, and the preparation method includes the following steps:

[0022] (1) Performing a hydrothermal reaction on the magnesium alloy substrate with water vapor to obtain a substrate with a bottom coating;

[0023] (2) Immersing the substrate with the bottom coating obtained in step (1) in a phosphate buffer solution for soaking to obtain a bottom coating with microporous channels;

[0024] (3) Spraying the bottom coating obtained in step (2) ultrasonically with a spraying solution containing a polymer material, and then drying to complete the preparation of the magnesium alloy composite coating.

[0025] In the present invention, using the magnesium alloy as the substrate, through chemical conversion by hydrothermal reaction, a dense and somewhat rough bottom coating is formed on the surface of the magnesium alloy. Then, microporous channels are formed by making holes in the bottom coating, and then through a specifically selected ultrasonic spraying process, the polymer material is sprayed on the surface of the bottom coating, so that the surface coating and the bottom coating form an interlaced and inserted structure, thereby obtaining a composite coating. This composite coating has good biocompatibility, can be completely degraded, has good strength and toughness, can continuously and effectively inhibit the degradation of the magnesium alloy, improve the corrosion resistance of the magnesium alloy, and promote rapid bone healing.

[0026] It should be noted that in the present invention, the process of specifically using ultrasonic spraying to prepare the surface coating can match the roughness and microporous channels on the surface of the bottom coating. Ultrasonic spraying can atomize through ultrasonic vibration (generally at 20 - 60 °C), enabling the polymer solution (or suspension) to be broken into droplets of 5 - 50 μm in the form of liquid or semi-solid and directly deposited in the bottom coating and its microporous channels, forming a smooth and dense coating, avoiding high-temperature damage, retaining the molecular structure and biocompatibility of the polymer, preventing the oxidation of magnesium alloy, and achieving mechanical interlocking to enhance the bonding between the substrate, bottom coating, and surface coating. In ultrasonic spraying, the thickness of the surface coating can be precisely controlled by adjusting the ultrasonic parameters to meet the mechanical requirements of different parts. Additionally, nano-hydroxyapatite or other functional components can be added to the spraying liquid used in ultrasonic spraying as needed for synchronous spraying, where the dispersion degree of nano-hydroxyapatite > 95%, thereby forming a uniform composite coating, avoiding problems such as the decomposition or agglomeration of nano-hydroxyapatite caused by other spraying methods in the prior art, such as plasma spraying, enabling the gradual release and efficacy of nano-hydroxyapatite, and promoting the effect of bone healing.

[0027] In the present invention, the method of using water vapor to perform hydrothermal reaction with the magnesium alloy substrate to prepare the magnesium hydroxide and / or magnesium oxide coating in step (1) is a conventional method in the art. For example, it can be: suspending the magnesium alloy substrate in a reaction vessel filled with purified water, sealing it and then performing hydrothermal reaction. The temperature of the hydrothermal reaction is 120 - 160 °C, such as 120 °C, 130 °C, 140 °C, 150 °C or 160 °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the pressure of the hydrothermal reaction is 1.0 - 2.0 MPa, such as 1.0 MPa, 1.5 MPa or 2.0 MPa, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the time of the hydrothermal reaction is 2 - 6 h, such as 2 h, 4 h or 6 h, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable. In the present invention, the magnesium alloy substrate is generally pretreated before the hydrothermal reaction. The pretreatment method is a conventional method in the art, generally including: sequentially performing physical grinding, cleaning and electrochemical polishing on the magnesium alloy substrate to remove surface stains, then placing it in a sealable reaction vessel, adding purified water at the bottom of the reaction vessel, and adjusting the distance between the magnesium alloy substrate and the purified water to generally be 30 - 50 mm, such as 30 mm, 40 mm or 50 mm, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable. Then seal the reaction vessel, and then place the reaction vessel in the equipment for preparing the bottom coating.

[0028] Preferably, the temperature of the soaking in step (2) is 60-80°C. For example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the soaking time is 5-15 min. For example, it can be 5 min, 8 min, 10 min, 12 min, 14 min or 15 min, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the concentration of the phosphate buffer solution is 8-15 mmol / L. For example, it can be 8 mmol / L, 10 mmol / L, 12 mmol / L, 14 mmol / L or 15 mmol / L, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0029] In the present invention, the phosphate buffer solution is a commonly used buffer solution in the art and can be prepared from commercially available phosphate buffer solution (PBS).

[0030] In the present invention, by preferably controlling parameters such as the concentration, time and temperature of the soaking solution in step (2), the porosity and pore size of the microporous channels are controlled, and the bottom coating has a certain roughness, so that the porosity and pore size match the molecular weight of the polylactic acid used, making it easier to bind with the polylactic acid, and then realizing the full-surface bite of the product, improving the bonding strength and avoiding local accumulation of the polylactic acid. In the present invention, after soaking, the substrate is generally taken out, washed with purified water, and then dried.

[0031] Preferably, the solvent of the spraying solution in step (3) includes dichloromethane.

[0032] In the present invention, the spraying solution generally uses dichloromethane as the solvent, and a polymer material is added to the solvent, as well as a functional component such as nano-hydroxyapatite. The preparation method of the spraying solution can adopt the conventional method in the art. Generally, polylactic acid and polycaprolactone are added to dichloromethane, and then magnetically stirred at room temperature (20-25°C) for 1-2 h to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then nano-hydroxyapatite is added, and magnetic stirring is continued for 15-30 min to uniformly disperse the nano-hydroxyapatite in the solution to obtain the spraying solution.

[0033] Preferably, the concentration of polylactic acid in the spraying liquid in step (3) is 0.005 - 0.020 g / mL. For example, it can be 0.005 g / mL, 0.006 g / mL, 0.008 g / mL, 0.010 g / mL, 0.012 g / mL, 0.014 g / mL, 0.016 g / mL, 0.018 g / mL or 0.020 g / mL. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the concentration of polycaprolactone in the spraying liquid is 0.25 - 1.50 mg / mL. For example, it can be 0.25 mg / mL, 0.30 mg / mL, 0.40 mg / mL, 0.50 mg / mL, 0.60 mg / mL, 0.70 mg / mL, 0.80 mg / mL, 0.90 mg / mL, 1.00 mg / mL, 1.10 mg / mL, 1.20 mg / mL, 1.30 mg / mL, 1.40 mg / mL or 1.50 mg / mL. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0034] Preferably, the concentration of nano-hydroxyapatite in the spraying liquid in step (3) is 0.05 - 0.50 mg / mL. For example, it can be 0.05 mg / mL, 0.10 mg / mL, 0.15 mg / mL, 0.20 mg / mL, 0.25 mg / mL, 0.30 mg / mL, 0.35 mg / mL, 0.40 mg / mL, 0.45 mg / mL or 0.50 mg / mL. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0035] In the present invention, by preferably controlling the concentration of nano-hydroxyapatite within a specific range, its dispersibility, interfacial bonding, mechanical properties and biological response can be further controlled, thereby jointly improving the overall quality of the polylactic acid coating. When the concentration of nano-hydroxyapatite is too high, it is easy to cause an increase in solution viscosity, the spraying process fails, the coating shrinks and cracks during the drying process, and at the same time, it will also increase the brittleness of the coating and reduce the fracture toughness, affecting the coating quality; when the concentration of nano-hydroxyapatite is too low, the activity of osteoblasts cannot be effectively regulated, resulting in a decrease in bone healing efficiency and affecting the functionality of the coating in bone healing.

[0036] Preferably, the weight-average molecular weight of the polylactic acid in step (3) is 100,000 - 200,000 Da. For example, it can be 100,000 Da, 120,000 Da, 140,000 Da, 160,000 Da, 180,000 Da or 200,000 Da. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the weight-average molecular weight of the polycaprolactone is 10,000 - 50,000 Da. For example, it can be 10,000 Da, 20,000 Da, 30,000 Da, 40,000 Da or 50,000 Da. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] In the present invention, by preferably controlling the molecular weights of polylactic acid and polycaprolactone within a specific range and controlling their concentrations, the coating quality can be further ensured and the corrosion resistance can be improved. When the molecular weight is too large, the viscosity of the solution is too high, resulting in difficulty in effectively breaking droplets by ultrasonic vibration, and thus the nozzle is prone to clogging and the equipment failure rate increases; in addition, too high a molecular weight will increase the glass transition temperature, and the segmental movement is restricted during solvent evaporation, the shrinkage stress accumulates, and reticular cracks appear after drying, making it easy to peel off. At the same time, too long molecular chains will also cause excessive chain entanglement, reducing the toughness of the coating, and thus the overall quality of the coating decreases, and the corrosion resistance will also decrease accordingly. When the molecular weight is too small, the droplet size in ultrasonic atomization is too small, and the drying speed of the droplets is too fast, easily forming a porous and loose structure. Due to too short molecular chains, the intermolecular force is relatively weak, making it difficult to form effective entanglements, resulting in poor abrasion resistance of the coating and easy scratching damage. In addition, the content of terminal carboxyl groups in low-molecular-weight polylactic acid is relatively high (more hydrolysis starting sites), and at the same time its crystallinity is relatively low, resulting in too fast a degradation rate and poor corrosion resistance.

[0038] Preferably, in the ultrasonic spraying in step (3), the height of the ultrasonic nozzle from the bottom coating is 10 - 25 cm, for example, it can be 10 cm, 12 cm, 14 cm, 16 cm, 18 cm, 20 cm, 22 cm, 24 cm or 25 cm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0039] In the present invention, by preferably controlling the height of the ultrasonic nozzle from the bottom coating in ultrasonic spraying, the adhesion of the coating and the thickness uniformity of the coating can be controlled, that is: when the height is too high, the kinetic energy of the droplets is insufficient, it is easy to disperse unevenly, resulting in a decrease in adhesion and uneven coating thickness; when the height is too low, it is easy to cause aggregation of polylactic acid and the spraying liquid is prone to splashing, resulting in uneven thickness or even damage to the coating, and the corrosion resistance becomes poor.

[0040] The spraying rate of the ultrasonic spraying is 0.08 - 0.15 mL / min, for example, it can be 0.08 mL / min, 0.10 mL / min, 0.12 mL / min, 0.14 mL / min or 0.15 mL / min, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0041] In the present invention, by preferably controlling the spraying rate of ultrasonic spraying, the atomization effect and the interlayer bonding strength can be controlled, that is: when the spraying rate is too high, the droplets are prone to agglomeration or incomplete atomization, and at the same time, the spraying liquid between layers fails to fully fuse, affecting the interlayer bonding strength; when the spraying rate is too low, the energy of ultrasonic waves causes uneven distribution of the droplets, the coating thickness is uneven, and even the coverage is incomplete. Under stress, delamination and peeling occur, and the adhesion decreases. Moreover, it is easy to cause uneven distribution of nano-hydroxyapatite in the spraying liquid, and local calcification is likely to occur during the degradation process, affecting the bone healing effect.

[0042] The gas pressure of the ultrasonic spraying is 0.01 - 0.05 MPa. For example, it can be 0.01 MPa, 0.02 MPa, 0.03 MPa, 0.04 MPa or 0.05 MPa, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0043] In the present invention, by preferably controlling the gas pressure of ultrasonic spraying, the deposition efficiency and the structure of the coating can be controlled, that is: when the pressure is too high, the droplets are blown away by the air pressure, evaporate rapidly and splash when hitting the substrate, resulting in orange peel phenomenon or increased porosity of the coating, affecting the quality of the coating; when the pressure is too low, the liquid mist is unevenly distributed, resulting in uneven coating thickness, and may also cause droplet accumulation, forming sag, and quality problems appear on the coating surface, the qualified rate and efficiency decrease, and the cost increases.

[0044] Preferably, the power of the ultrasonic spraying in step (3) is 0.5 - 1.5 W. For example, it can be 0.5 W, 0.6 W, 0.8 W, 1 W, 1.2 W, 1.4 W or 1.5 W, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0045] Preferably, the drying temperature in step (3) is 45 - 55 °C. For example, it can be 45 °C, 46 °C, 48 °C, 50 °C, 52 °C, 54 °C or 55 °C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0046] In the present invention, the main function of the drying is to volatilize the solvent used in the polymer coating to ensure that the solvent residue is within the safety limit. In the present invention, the drying temperature is preferably controlled. When the drying temperature is too high, approaching the glass transition temperature of the polymer material, the coating becomes soft and cures again at room temperature. This process will cause the adhesion of the coating to decrease; when the drying temperature is too low, the solvent is not easily volatilized, and the solvent residue causes the product to be unqualified.

[0047] Preferably, the drying time in step (3) is 48 - 72 h. For example, it can be 48 h, 50 h, 52 h, 54 h, 56 h, 58 h, 60 h, 62 h, 64 h, 66 h, 68 h or 70 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0048] In the present invention, it is preferred to control the drying time. If the drying time is too long, the cost is relatively high. If the drying time is too short, the solvent is not easily volatilized completely, and the solvent residue is unqualified.

[0049] In the present invention, the magnesium alloy matrix can be, for example, any one of AE series alloys, AS series alloys, WE series alloys, AZ series alloys, AM series alloys, ZK series alloys, ZM series alloys, Mg-Li series alloys, and Mg-Ca series alloys. Preferably, it is a series of magnesium alloys containing magnesium, zinc, and manganese.

[0050] As a preferred technical solution of the second aspect of the present invention, the preparation method includes the following steps: The preparation method includes the following steps:

[0051] (1) Suspend the magnesium alloy matrix in a reaction vessel filled with purified water. After sealing, carry out a hydrothermal reaction between the steam and the magnesium alloy matrix. The distance between the magnesium alloy matrix and the purified water is 30 - 50 mm. The temperature of the hydrothermal reaction is 120 - 160 °C, the pressure is 1.0 - 2.0 MPa, and the time is 2 - 6 h to obtain a matrix with a bottom coating.

[0052] (2) Immerse the matrix with the bottom coating obtained in step (1) in a phosphate buffer solution with a concentration of 8 - 15 mmol / L and soak it for 5 - 15 min at a temperature of 60 - 80 °C to obtain a bottom coating with microporous channels.

[0053] (3) Add polylactic acid (PLA, weight-average molecular weight of 100,000 - 200,000 Da) and polycaprolactone (PCL, weight-average molecular weight of 10,000 - 50,000 Da) to dichloromethane, and then magnetically stir at 25 °C for 1 - 2 h to fully dissolve the polylactic acid and polycaprolactone without suspended matter. Then add nano-hydroxyapatite and continue to magnetically stir for 15 - 30 min to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spraying solution. The concentration of polylactic acid in the spraying solution is 0.005 - 0.020 g / mL, the concentration of polycaprolactone is 0.25 - 1.50 mg / mL, and the concentration of nano-hydroxyapatite is 0.05 - 0.50 mg / mL.

[0054] The bottom coating obtained in step (2) is ultrasonically sprayed with a spraying liquid containing a polymer material. During the ultrasonic spraying, the height of the ultrasonic nozzle from the bottom coating is 10 - 25 cm, the spraying rate is 0.08 - 0.15 mL / min, and the gas pressure is 0.01 - 0.05 MPa. Then it is dried at 45 - 55 °C for 48 - 72 h to complete the preparation of the magnesium alloy composite coating.

[0055] Thirdly, the present invention provides a medical magnesium alloy with corrosion resistance promoting bone healing, and the surface of the medical magnesium alloy contains the magnesium alloy composite coating with corrosion resistance promoting bone healing as described in the first aspect of the present invention.

[0056] The medical magnesium alloy provided by the present invention adopts the composite coating, has good biocompatibility, corrosion resistance and mechanical properties, can promote bone healing, and is especially suitable for scenarios with high mechanical property requirements such as magnesium alloys for bone plates and bone nails.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The composite coating provided by the present invention is composed of a bottom coating made of magnesium hydroxide and / or magnesium oxide and a surface coating of a polymer material, has higher corrosion resistance, effectively reduces the degradation rate of the magnesium alloy, and expands the application scenarios of the magnesium alloy.

[0059] (2) In the composite coating provided by the present invention, the bottom coating and the surface coating are connected in an interlaced and inserted manner, achieving a high degree of firmness. Taking the surface of a magnesium alloy bone plate and bone nail as an example, even under the condition of large frictional force formed by twisting and screwing in the bone nail, it is still stably combined and not easy to break, and has the advantages of slow degradation rate, high strength and strong toughness.

[0060] (3) In the composite coating provided by the present invention and its preparation method, by preferably adding functional components such as nano-hydroxyapatite to the spraying liquid, the strength of the surface coating can be improved. In actual application, nano-hydroxyapatite is gradually released, promoting the adhesion, proliferation and differentiation of osteoblasts and accelerating bone tissue regeneration.

[0061] (4) Under relatively optimal conditions, the composite coating provided by the present invention can reduce the corrosion current to below 70.7 nA and the corrosion potential to above -1.52 V, and the coating has good integrity after being screwed in and out 3 times. Description of the Drawings

[0062] Figure 1 is the SEM image of the bottom coating containing microporous channels provided in Example 1 of the present invention;

[0063] Figure 2 is the SEM image of the composite coating after being screwed in and out 3 times provided in Example 1 of the present invention;

[0064] Figure 3 It is the SEM image of the composite coating provided in Embodiment 4 of the present invention after being screwed in and out three times;

[0065] Figure 4 It is the SEM image of the composite coating provided in Comparative Example 1 of the present invention after being screwed in and out three times;

[0066] Figure 5 It is the result comparison diagram of the corrosion resistance experiments of the composite coating provided in Embodiment 1 of the present invention, the coating provided in Comparative Example 3, and the magnesium alloy substrate provided in Comparative Example 4;

[0067] Figure 6 It is the bone healing effect diagram of the composite coating provided in Embodiment 1 of the present invention used in animal experiments;

[0068] Figure 7 It is the bone healing effect diagram of the composite coating provided in Embodiment 4 of the present invention used in animal experiments. Detailed implementation manners

[0069] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0070] Embodiment 1

[0071] This embodiment provides a magnesium alloy composite coating for promoting bone healing with corrosion resistance. The magnesium alloy composite coating includes a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

[0072] The bottom coating includes microporous channels. The components of the bottom coating include magnesium hydroxide and / or magnesium oxide. The porosity of the bottom coating is 50%, and the pore diameter of the microporous channels is 20 - 120 μm;

[0073] The surface coating includes a polymer material. The polymer material includes polylactic acid and polycaprolactone. The surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating. Nano-hydroxyapatite with an average particle size of 30 nm is distributed in the polymer material.

[0074] This embodiment provides a preparation method for the above-mentioned magnesium alloy composite coating. The preparation method includes the following steps:

[0075] (1) Suspend the magnesium alloy substrate (AE series alloy) in a reaction vessel filled with purified water. The amount of purified water added is 30% of the volume of the reaction vessel. After sealing, carry out a hydrothermal reaction between the steam and the magnesium alloy substrate. The distance between the magnesium alloy substrate and the purified water is 40 mm. The temperature of the hydrothermal reaction is 140 °C, the pressure is 1.5 MPa, and the time is 4 h. After the reaction, cool naturally, and then take out after cooling to obtain a substrate with a bottom coating.

[0076] (2) Immerse the substrate with the bottom coating obtained in step (1) in a phosphate buffer solution with a concentration of 12 mmol / L, and soak it at a temperature of 70 °C for 10 min. Take it out, rinse it with purified water, and dry it to obtain a bottom coating with microporous channels, as Figure 1 shown.

[0077] (3) Add polylactic acid (PLA, weight-average molecular weight of 180,000 Da) and polycaprolactone (PCL, weight-average molecular weight of 30,000 Da) to dichloromethane, and then stir magnetically at 25 °C for 1.5 h to fully dissolve the polylactic acid and polycaprolactone without suspended matter. Then add nano-hydroxyapatite and continue to stir magnetically for 20 min to evenly disperse the nano-hydroxyapatite in the solution to obtain a spraying solution. The concentration of polylactic acid in the spraying solution is 0.01 g / mL, the concentration of polycaprolactone is 0.5 mg / mL, and the concentration of nano-hydroxyapatite is 0.2 mg / mL.

[0078] Use the spraying solution containing the polymer material to ultrasonically spray the bottom coating obtained in step (2). During ultrasonic spraying, the height of the ultrasonic nozzle from the bottom coating is 15 cm, the spraying rate is 0.1 mL / min, the gas pressure is 0.02 MPa, the ultrasonic power is 1.2 W, and the coating thickness is 20 μm. Then dry it at 48 °C for 56 h to complete the preparation of the magnesium alloy composite coating.

[0079] This example provides a medical magnesium alloy with corrosion resistance promoting bone healing. The surface of the medical magnesium alloy contains the above-mentioned magnesium alloy composite coating with corrosion resistance promoting bone healing.

[0080] Example 2

[0081] This example provides a magnesium alloy composite coating with corrosion resistance promoting bone healing. The magnesium alloy composite coating includes a bottom coating and a surface coating arranged in sequence from the surface of the magnesium alloy outward.

[0082] The bottom coating includes microporous channels. The composition of the bottom coating includes magnesium hydroxide and / or magnesium oxide. The porosity of the bottom coating is 55%, and the pore diameter of the microporous channels is 20 - 120 μm.

[0083] The surface coating includes a polymer material, the polymer material includes polylactic acid and polycaprolactone, the surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating, and nano-hydroxyapatite with an average particle size of 30 nm is distributed in the polymer material.

[0084] This embodiment provides a method for preparing the above-mentioned magnesium alloy composite coating, and the preparation method includes the following steps:

[0085] (1) Suspend the magnesium alloy substrate (AE series alloy) in a reaction vessel filled with purified water. The addition amount of purified water is 30% of the volume of the reaction vessel. After sealing, carry out a hydrothermal reaction between the steam and the magnesium alloy substrate. The distance between the magnesium alloy substrate and the purified water is 40 mm. The temperature of the hydrothermal reaction is 140 °C, the pressure is 1.5 MPa, and the time is 4 h. After the reaction, cool naturally, take out after cooling to obtain a substrate with a bottom coating;

[0086] (2) Immerse the substrate with the bottom coating obtained in step (1) in a phosphate buffer solution with a concentration of 8 mmol / L, soak it at a temperature of 60 °C for 15 min, take it out, rinse it with purified water, and dry it to obtain a bottom coating with microporous channels;

[0087] (3) Add polylactic acid (PLA, weight average molecular weight of 180,000 Da) and polycaprolactone (PCL, weight average molecular weight of 30,000 Da) to dichloromethane, and then stir magnetically at 25 °C for 1.5 h to fully dissolve polylactic acid and polycaprolactone without suspended matter; then add nano-hydroxyapatite and continue to stir magnetically for 20 min to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spraying solution. The concentration of polylactic acid in the spraying solution is 0.005 g / mL, the concentration of polycaprolactone is 1.5 mg / mL, and the concentration of nano-hydroxyapatite is 0.5 mg / mL;

[0088] Use the spraying solution containing the polymer material to ultrasonically spray the bottom coating obtained in step (2). During ultrasonic spraying, the height of the ultrasonic nozzle from the bottom coating is 10 cm, the spraying rate is 0.15 mL / min, the gas pressure is 0.01 MPa, the ultrasonic power is 1.2 W, and the coating thickness is 20 μm. Then dry it at 55 °C for 48 h to complete the preparation of the magnesium alloy composite coating.

[0089] This embodiment provides a medical magnesium alloy with corrosion resistance and promoting bone healing, and the surface of the medical magnesium alloy contains the above-mentioned magnesium alloy composite coating with corrosion resistance and promoting bone healing.

[0090] Example 3

[0091] This embodiment provides a magnesium alloy composite coating that promotes bone healing with corrosion resistance. The magnesium alloy composite coating includes a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

[0092] The bottom coating includes microporous channels. The composition of the bottom coating includes magnesium hydroxide and / or magnesium oxide. The porosity of the bottom coating is 40%, and the pore diameter of the microporous channels is 20 - 120 μm;

[0093] The surface coating includes a polymer material. The polymer material includes polylactic acid and polycaprolactone. The surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating. Nano-hydroxyapatite with an average particle size of 30 nm is distributed in the polymer material.

[0094] This embodiment provides a preparation method of the above magnesium alloy composite coating. The preparation method includes the following steps:

[0095] (1) Hang the magnesium alloy substrate (AE series alloy) in a reaction vessel filled with purified water. The amount of purified water added is 30% of the volume of the reaction vessel. After sealing, carry out a hydrothermal reaction between the steam and the magnesium alloy substrate. The distance between the magnesium alloy substrate and the purified water is 40 mm. The temperature of the hydrothermal reaction is 140 °C, the pressure is 1.5 MPa, and the time is 4 h. After the reaction, cool naturally, and take it out after cooling to obtain a substrate with a bottom coating;

[0096] (2) Immerse the substrate with the bottom coating obtained in step (1) in a phosphate buffer solution with a concentration of 15 mmol / L, soak it at a temperature of 80 °C for 5 min, take it out, rinse it with purified water, and dry it to obtain a bottom coating with microporous channels;

[0097] (3) Add polylactic acid (PLA, weight average molecular weight of 180,000 Da) and polycaprolactone (PCL, weight average molecular weight of 30,000 Da) to dichloromethane, and then magnetically stir at 25 °C for 1.5 h to fully dissolve polylactic acid and polycaprolactone without suspended matter; then add nano-hydroxyapatite and continue to magnetically stir for 20 min to uniformly disperse nano-hydroxyapatite in the solution to obtain a spraying solution. The concentration of polylactic acid in the spraying solution is 0.02 g / mL, the concentration of polycaprolactone is 0.25 mg / mL, and the concentration of nano-hydroxyapatite is 0.05 mg / mL;

[0098] Use a spraying liquid containing a polymer material to ultrasonically spray the bottom coating obtained in step (2). During ultrasonic spraying, the height of the ultrasonic nozzle from the bottom coating is 25 cm, the spraying rate is 0.08 mL / min, the gas pressure is 0.05 MPa, the ultrasonic power is 1.2 W, and the coating thickness is 20 μm. Then dry it at 45 °C for 72 h to complete the preparation of the magnesium alloy composite coating.

[0099] This embodiment provides a medical magnesium alloy with corrosion resistance promoting bone healing, and the surface of the medical magnesium alloy contains the above-mentioned magnesium alloy composite coating with corrosion resistance promoting bone healing.

[0100] Example 4

[0101] This embodiment provides a magnesium alloy composite coating with corrosion resistance promoting bone healing. The difference compared with Example 1 is only that nano-hydroxyapatite is not added to the surface coating.

[0102] This embodiment also provides a preparation method of the above-mentioned magnesium alloy composite coating. The difference compared with Example 1 is only that nano-hydroxyapatite is not added to the spraying liquid in step (3).

[0103] Example 5

[0104] This embodiment provides a preparation method of a magnesium alloy composite coating with corrosion resistance promoting bone healing. The difference compared with Example 1 is only that the soaking temperature in step (2) is 55 °C.

[0105] Example 6

[0106] This embodiment provides a preparation method of a magnesium alloy composite coating with corrosion resistance promoting bone healing. The difference compared with Example 1 is only that the soaking temperature in step (2) is 85 °C.

[0107] Example 7

[0108] This embodiment provides a preparation method of a magnesium alloy composite coating with corrosion resistance promoting bone healing. The difference compared with Example 1 is only that the soaking time in step (2) is 2 min.

[0109] Example 8

[0110] This embodiment provides a preparation method of a magnesium alloy composite coating with corrosion resistance promoting bone healing. The difference compared with Example 1 is only that the soaking time in step (2) is 20 min.

[0111] Example 9

[0112] This embodiment provides a method for preparing a magnesium alloy composite coating with corrosion resistance and promoting bone healing. The difference compared with Embodiment 1 is only that the spraying rate in the ultrasonic spraying described in step (3) is 0.05 mL / min.

[0113] Embodiment 10

[0114] This embodiment provides a method for preparing a magnesium alloy composite coating with corrosion resistance and promoting bone healing. The difference compared with Embodiment 1 is only that the spraying rate in the ultrasonic spraying described in step (3) is 0.18 mL / min.

[0115] Embodiment 11

[0116] This embodiment provides a method for preparing a magnesium alloy composite coating with corrosion resistance and promoting bone healing. The difference compared with Embodiment 1 is only that the gas pressure in the ultrasonic spraying described in step (3) is 0.005 MPa.

[0117] Embodiment 12

[0118] This embodiment provides a method for preparing a magnesium alloy composite coating with corrosion resistance and promoting bone healing. The difference compared with Embodiment 1 is only that the gas pressure in the ultrasonic spraying described in step (3) is 0.08 MPa.

[0119] Comparative Example 1

[0120] This comparative example provides a method for preparing a magnesium alloy coating. The difference compared with Embodiment 1 is only that steps (1) and (2) are not carried out, and the method in step (3) is directly used to spray the surface of the magnesium alloy substrate.

[0121] Comparative Example 2

[0122] This comparative example provides a method for preparing a magnesium alloy composite coating. The difference compared with Embodiment 1 is only that step (2) is not carried out, and the method in step (3) is directly used to spray the substrate containing the bottom coating obtained in step (1).

[0123] Comparative Example 3

[0124] This comparative example provides a method for preparing a magnesium alloy coating. The difference compared with Embodiment 1 is only that steps (2) and (3) are not carried out, and the magnesium alloy coating is only the bottom coating.

[0125] Comparative Example 4

[0126] This comparative example provides a magnesium alloy substrate, which is the same as that in Embodiment 1.

[0127] Comparative Example 5

[0128] This comparative example provides a method for preparing a magnesium alloy composite coating, which is only different from Example 1 in that step (3) is replaced by: mixing equal amounts of polylactic acid, polycaprolactone, and nano-hydroxyapatite and molding them into a polymer thin sheet at 200 °C and 50 N; then placing the polymer thin sheet above the bottom coating with microporous channels and hot-pressing at 200 °C and 20 MPa to obtain a composite coating.

[0129] After the products obtained in the above examples and comparative examples were screwed in and out 3 times with a 40-grade polyurethane material (cortical bone hardness), the integrity of the coating was detected.

[0130] Taking Example 1, Example 4, and Comparative Example 1 as examples, the SEM images after being screwed in and out 3 times are respectively as Figure 2 , Figure 3 and Figure 4 shown. It can be seen from Figure 2 that the composite coating provided by Example 1 is intact on the surface, and granular nano-hydroxyapatite is distributed in the surface coating; it can be seen from Figure 3 that the composite coating in Example 4 still maintains good integrity, and the coating has good adhesion to the magnesium alloy matrix. After EDS detection, the main elements in the coating are composed of C and O, which are the main components of polylactic acid, indicating that the polymer coating effectively adheres to the surface. Using a film thickness measuring instrument to measure the coating thickness, the thickness of the surface coating is 16.5 μm; it can be seen from Figure 4 that after the coating provided by Comparative Example 1 was screwed in and out 3 times, the polymer coating cracked and the coating peeled off from the magnesium alloy matrix.

[0131] After the coating was screwed in and out 3 times, an electrochemical workstation was used to test the corrosion resistance during the service period. The reagent used in the electrochemical test was PBS solution with pH = 7.4; the initial voltage was -0.3 V, the termination voltage was 0.3 V, the time was 120 s, and the Scan Rate was 1 mV / s. The results are shown in Table 1.

[0132] Taking the comparison of the magnesium alloy with the composite coating provided by Example 1, the magnesium alloy with only the bottom coating provided by Comparative Example 3, and the pure magnesium alloy provided by Comparative Example 4 as an example, the comparison results of the corrosion resistance tested by an electrochemical workstation after the samples with the same shape were screwed in and out 3 times are as Figure 5 shown. It can be seen from Figure 5 that the composite coating has more excellent corrosion resistance and significantly improved corrosion resistance compared to the bottom coating and the magnesium alloy matrix.

[0133] Taking Example 1 and Example 4 as examples, the obtained magnesium alloy products were used in animal experiments. The experimental method was as follows: Separate the gingival tissue from the mandible of a dog, use tools to create a fracture model at an appropriate position. After repeatedly flushing the fracture site with normal saline to remove bone debris, select the medical magnesium alloy containing the composite coating in the above examples and make a bone plate and bone nail system for mandibular fracture repair and fixation implantation operation, and implant two sets of plate and nail systems unilaterally and in parallel. The bone healing effects of the obtained animal experiments are respectively as Figure 6 and Figure 7 shown. It can be seen from Figure 6 that the magnesium alloy product provided by Example 1 has a high bone healing efficiency, the fracture line can heal in time, and the bone plate and the fracture line heal to achieve good cycle matching; it can be seen from Figure 7 that for the magnesium alloy product provided by Example 4, the bone healing efficiency is low, the fracture line fails to heal in time, resulting in stress on the bone plate, stress corrosion, and the bone plate breaking.

[0134] Table 1

[0135]

[0136] In Table 1, "-" indicates no coating.

[0137] It can be seen from the data in Table 1 as follows:

[0138] (1) It can be seen from the data of Examples 1-4 that under relatively optimal conditions, using the composite coating provided by the present invention can reduce the corrosion current to below 70.7 nA, the corrosion potential reaches above -1.52 V, and the coating has good integrity after being screwed in and out 3 times.

[0139] (2) It can be seen from the data of Examples 1 and 5-8 that by preferably controlling the temperature and time of soaking in step (2), the present invention can control the structure of the microporous channels and the surface roughness of the bottom coating, thereby improving the bonding force of the coating and further improving the corrosion resistance and mechanical properties of the composite coating.

[0140] (3) It can be seen from the data of Examples 1 and 9-12 that by preferably controlling the parameters of ultrasonic spraying such as spraying rate, gas pressure, etc., the present invention can further improve the quality of the surface coating, thereby further improving the corrosion resistance and mechanical properties of the composite coating.

[0141] (4)It can be seen from the data of Example 1 and Comparative Examples 1-5 that compared with only magnesium alloy in Comparative Example 4, the composite coating in Example 1 can fully exert the corrosion resistance effect and inhibit the degradation of magnesium alloy; compared with only the surface coating in Comparative Example 1 and only the bottom coating in Comparative Example 3, the corrosion resistance in Example 1 is more excellent and the coating integrity is higher; compared with Comparative Example 2 where there are no microporous channels and thus no interdigitated connection can be formed, the coating in Example 1 has higher firmness, can maintain good integrity and has better corrosion resistance; compared with Comparative Example 5 where the bottom coating and the surface coating are combined by hot pressing, the corrosion resistance and mechanical properties in Example 1 are better, while the coating firmness in Comparative Example 5 is poor, and the high-temperature hot pressing has far exceeded the glass transition temperature of polylactic acid, resulting in the breakage of the polymer chain and the reduction of the molecular weight, ultimately leading to poor corrosion resistance.

[0142] In summary, the magnesium alloy composite coating provided by the present invention is connected in an interdigitated manner by the bottom coating formed by the chemical conversion method and the surface coating formed by the polymer material, has good firmness, strength and toughness, improves the corrosion resistance of the magnesium alloy, and meets the need for promoting bone healing.

[0143] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A corrosion-resistant magnesium alloy composite coating that promotes bone healing, characterized in that: The magnesium alloy composite coating comprises a bottom coating and a surface coating arranged in sequence from the surface of the magnesium alloy outward; The bottom coating comprises microporous channels, and the components of the bottom coating comprise magnesium hydroxide and / or magnesium oxide; the substrate comprising the bottom coating is immersed in a phosphate buffer solution to obtain a bottom coating comprising microporous channels, the immersion temperature is 60-80° C., the immersion time is 5-15 min, and the porosity of the bottom coating is 30-60%; The surface coating comprises a polymer material, which comprises polylactic acid or a mixture of polylactic acid and polycaprolactone. Nano-hydroxyapatite is distributed in the polymer material. The surface coating fills the microporous channels of the bottom coating and covers the surface of the bottom coating.

2. The magnesium alloy composite coating according to claim 1, characterized in that: The particle size of the nano-hydroxyapatite is 20-60nm.

3. The magnesium alloy composite coating according to claim 1, characterized in that: The pore size of the microporous channel is 20-120 μm.

4. A method for preparing the corrosion-resistant magnesium alloy composite coating for promoting bone healing as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) Using water vapor to hydrothermally react with a magnesium alloy substrate to obtain a substrate containing a bottom coating; (2) immersing the substrate containing the bottom coating obtained in step (1) in a phosphate buffer solution at a temperature of 60-80° C. for a time of 5-15 min to obtain a bottom coating containing microporous channels; (3) Ultrasonic spraying is performed on the bottom coating obtained in step (2) using a spraying liquid containing a polymer material, and then drying is performed to complete the preparation of the magnesium alloy composite coating.

5. The preparation method according to claim 4, characterized in that: The concentration of the phosphate buffer in step (2) is 8-15 mmol / L.

6. The preparation method according to claim 4, characterized in that: The concentration of polylactic acid in the spraying liquid in step (3) is 0.005-0.020 g / mL; The concentration of polycaprolactone in the spraying liquid is 0.25-1.50 mg / mL.

7. The preparation method according to claim 6, characterized in that: The concentration of nano-hydroxyapatite in the spraying liquid in step (3) is 0.05-0.50 mg / mL.

8. The preparation method according to claim 6, characterized in that: The weight average molecular weight of the polylactic acid in step (3) is 100,000-200,000 Da; The weight average molecular weight of the polycaprolactone is 10,000-50,000 Da.

9. The preparation method according to claim 4, characterized in that: In step (3), the height between the ultrasonic nozzle and the bottom coating layer is 10-25 cm; The spraying rate of the ultrasonic spraying is 0.08-0.15 mL / min; The gas pressure of the ultrasonic spraying is 0.01-0.05MPa.

10. A corrosion-resistant medical magnesium alloy that promotes bone healing, characterized in that: The surface of the medical magnesium alloy contains the corrosion-resistant magnesium alloy composite coating for promoting bone healing as described in any one of claims 1 to 3.

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