Corrosion-resistant magnesium alloy composite coating capable of promoting bone healing, preparation method of corrosion-resistant magnesium alloy composite coating and medical magnesium alloy

Abstract

The invention relates to a corrosion-resistant magnesium alloy composite coating capable of promoting bone healing, a preparation method of the corrosion-resistant magnesium alloy composite coating and a medical magnesium alloy. The magnesium alloy composite coating comprises a bottom coating and a surface coating which are sequentially arranged from the surface of the magnesium alloy to the outside. The bottom coating comprises micropore channels, and components of the bottom coating comprise magnesium hydroxide and / or magnesium oxide; the surface coating comprises a high polymer material, the high polymer material comprises polylactic acid or a mixture of polylactic acid and polycaprolactone, and the surface coating fills the micropore channels of the bottom coating and covers the surface of the bottom coating. According to the magnesium alloy composite coating provided by the invention, the bottom coating formed by a chemical conversion method is connected with the surface coating formed by a high polymer material in a staggered and inserted manner, so that the magnesium alloy composite coating has good firmness, strength and toughness, the corrosion resistance of magnesium alloy is improved, and the requirement of promoting bone healing is met.

Description

Technical Field

[0001] The invention relates to the technical field of biomedical materials, and in particular to a corrosion-resistant magnesium alloy composite coating for 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 mechanism and have broad application prospects in the medical field. However, problems such as poor corrosion resistance and rapid 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 alloying, controlling impurity content, and improving processing technology, the room for improvement is limited. In many application scenarios, magnesium alloys are still difficult to put into use directly. Therefore, surface modification or surface modification of magnesium alloys is necessary, which can greatly improve the corrosion resistance of magnesium alloys and is also the main research approach in the application of magnesium alloys. There are many methods for surface modification of 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-phosphorus composite coating with a thickness of 50-150 μm; the magnesium hydroxide-calcium-phosphorus composite coating includes a magnesium hydroxide layer and a fish-scale-like calcium-phosphorus layer attached to the surface of the magnesium hydroxide layer. The method prepares a degradable magnesium alloy coating by 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 alloy bone plates and bone screws, the large friction force generated when the bone screw is twisted and screwed in, if the coating has insufficient bonding strength, it is easy to produce micro cracks, expose the base magnesium alloy, and accelerate local corrosion. Therefore, the magnesium alloy coating is required to have good toughness and strength, and avoid cracks or peeling of the coating under the high shear force when the bone screw is screwed in, 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] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a corrosion-resistant magnesium alloy composite coating that promotes bone healing, a preparation method thereof, and a medical magnesium alloy. Compared with the prior art, the magnesium alloy composite coating provided by the present invention is connected in an interlaced manner by a bottom coating formed by a chemical conversion method and a surface coating formed by a polymer material, and has good firmness, strength and toughness, thereby improving the corrosion resistance of the magnesium alloy and meeting the need to promote bone healing.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a magnesium alloy composite coating that is corrosion-resistant and promotes bone healing, the magnesium alloy composite coating comprising a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

[0010] The bottom coating comprises microporous channels, and the composition of the bottom coating comprises magnesium hydroxide and / or magnesium oxide;

[0011] The surface coating comprises a polymer material, wherein the polymer material comprises 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 by a hydrothermal reaction, has a dense structure and a high bonding strength with the substrate, and its main components are magnesium hydroxide and / or magnesium oxide, and it does not contain other components and impurities, is an intermediate product of the magnesium alloy degradation process, and has excellent biocompatibility; the components of the surface coating are mainly polylactic acid or a mixture of polylactic acid and polycaprolactone, and the combination of polycaprolactone and polylactic acid is used. While ensuring the strength of polylactic acid, the problem of insufficient toughness of polylactic acid can be improved, and the toughness of the surface polymer coating can be effectively improved. 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 than the magnesium alloy, which provides a better interface for the attachment of the polymer coating on the surface, improves the bonding strength between the polymer coating and the product, and thus helps to improve the corrosion resistance; on the other hand, the microporous channels on the bottom coating are conducive to the formation of a "staggered plug-in" connection between the surface coating and the bottom coating, which improves the bonding force between the composite coating and the substrate, and then under the action of external forces, it can still maintain properties such as not easily damaged and corrosion-resistant. 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 magnesium alloys, improve the corrosion resistance of magnesium alloys, and promote rapid bone healing.

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

[0015] It should be noted that in the surface coating provided by the present invention, nano-hydroxyapatite is preferably added to 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 produced by the degradation of polylactic acid, reducing inflammatory reactions. In the present invention, by preferably controlling the particle size of nano-hydroxyapatite in 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, blocking the nozzle during ultrasonic spraying, resulting in too high a content per unit area of ​​the polylactic acid coating, and the coating cannot be completely coated, affecting the coating quality, and reducing corrosion resistance; when the particle size is too small, the nanoparticles have a large specific surface area and high surface energy, and are more likely to agglomerate crack sources, and are more likely to be carried and lost by airflow during ultrasonic spraying, resulting in increased porosity, weak interface bonding, and other mechanisms that degrade the uniformity and mechanical properties of the polylactic acid coating, reduce the coating quality, and reduce 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 values ​​not listed within the numerical range are also applicable; the pore size of the microporous channel is 20-120μm, for example, it can be 20μm, 40μm, 60μm, 80μm, 100μm or 120μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0018] Preferably, the thickness of the bottom coating is 8-12 μm, for example, 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 also applicable.

[0019] Preferably, the thickness of the surface coating is 15-30 μm, for example, 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 also applicable.

[0020] In the present invention, the thickness of the surface coating is preferably controlled within a specific range because the thickness of the coating mainly affects the degradation cycle and adhesion. If the thickness of the coating is too large, the corrosion resistance increases, and theoretically the degradation cycle is prolonged. However, in practice, when the thickness of the coating exceeds a critical value, the internal stress of the coating increases, the adhesion decreases, and when subjected to external forces, the coating is easily broken, resulting in reduced corrosion resistance and shortened degradation cycle. If the thickness of the coating is too thin, the corrosion resistance decreases, the degradation cycle 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 the corrosion-resistant magnesium alloy composite coating for promoting bone healing as described in the first aspect of the present invention, the preparation method comprising the following steps:

[0022] (1) Using water vapor to hydrothermally react with a magnesium alloy substrate to obtain a substrate containing a bottom coating;

[0023] (2) immersing the substrate containing the bottom coating obtained in step (1) in a phosphate buffer solution to obtain a bottom coating containing microporous channels;

[0024] (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.

[0025] In the present invention, magnesium alloy is used as a matrix, chemical conversion is carried out through hydrothermal reaction, and a dense bottom coating with a certain degree of roughness is formed on the surface of the magnesium alloy. Then, microporous channels are formed by making holes on the bottom coating, and then a polymer material is sprayed on the surface of the bottom coating through a specific ultrasonic spraying process, so that the surface coating and the bottom coating form an interlaced structure, thereby obtaining a composite coating. The composite coating has good biocompatibility, can be completely degraded, has good strength and toughness, can sustainably and effectively inhibit the degradation of magnesium alloy, improve the corrosion resistance of magnesium alloy, and promote rapid bone healing.

[0026] It should be noted that the process of preparing the surface coating by ultrasonic spraying specifically adopted in the present invention can match the roughness and microporous channels of the bottom coating surface. Ultrasonic spraying can be atomized by ultrasonic vibration (generally at 20-60°C), so that the polymer solution (or suspension) can be broken into 5-50μm droplets in liquid or semi-solid form 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, avoiding oxidation of magnesium alloy, and achieving mechanical interlocking to enhance the bonding between the substrate, the bottom coating and the surface coating. In ultrasonic spraying, the thickness of the surface coating can be accurately controlled by adjusting the parameters of ultrasound to meet the mechanical requirements of different parts. In addition, nano-hydroxyapatite or other functional components can be added to the spray liquid used for ultrasonic spraying as needed for simultaneous spraying, wherein the dispersion of nano-hydroxyapatite is greater than 95%, thereby forming a uniform composite coating, avoiding problems such as decomposition or agglomeration of nano-hydroxyapatite caused by other spraying methods in the prior art such as plasma spraying, so that nano-hydroxyapatite is gradually released and exerts its efficacy, thereby promoting the effect of bone healing.

[0027] In the present invention, the method of preparing magnesium hydroxide and / or magnesium oxide coating by hydrothermal reaction of water vapor with magnesium alloy substrate in step (1) is a conventional method in the art, for example, the method may be: suspending the magnesium alloy substrate in a reaction vessel filled with purified water, sealing and then conducting hydrothermal reaction, the temperature of the hydrothermal reaction is 120-160°C, for example, 120°C, 130°C, 140°C, 150°C or 160°C, but not limited to the listed values, other values ​​not listed in the numerical range are also applicable; the pressure of the hydrothermal reaction is 1.0-2.0MPa, for example, 1.0MPa, 1.5MPa or 2.0MPa, but not limited to the listed values, other values ​​not listed in the numerical range are also applicable; the time of the hydrothermal reaction is 2-6h, for example, 2h, 4h or 6h, but not limited to the listed values, other values ​​not listed in the numerical range are also 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: physically grinding, cleaning and electrochemically polishing the magnesium alloy substrate in sequence to remove surface stains, and then placing it in a sealable reaction container, adding purified water to the bottom of the reaction container, and adjusting the distance between the magnesium alloy substrate and the purified water to generally 30-50 mm, for example, it can be 30 mm, 40 mm or 50 mm, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, and then the reaction container is sealed, and then the reaction container is placed in the equipment to prepare the bottom coating.

[0028] Preferably, the soaking temperature 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 values ​​not listed in the numerical range are also applicable; the soaking time is 5-15min, for example, it can be 5min, 8min, 10min, 12min, 14min or 15min, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the concentration of the phosphate buffer is 8-15mmol / L, for example, it can be 8mmol / L, 10mmol / L, 12mmol / L, 14mmol / L or 15mmol / L, but is not limited to the listed values, and other values ​​not listed in the numerical range are also 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, the porosity and pore size of the microporous channel are controlled by preferably controlling the concentration, time and temperature of the soaking solution in step (2), and the bottom coating has a certain degree of roughness, so that the porosity and pore size match the molecular weight of the polylactic acid used, making it easier to combine with the polylactic acid, thereby achieving full surface bite of the product, improving the bonding strength, and avoiding local accumulation of polylactic acid. In the present invention, after the soaking, the substrate is generally taken out and washed with purified water, and then dried.

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

[0032] In the present invention, the spraying liquid generally uses dichloromethane as a solvent, and polymer materials and functional components such as nano-hydroxyapatite are added to the solvent. The preparation method of the spraying liquid can adopt the conventional method in the art, generally: adding polylactic acid and polycaprolactone to dichloromethane, and then magnetically stirring for 1-2 hours at room temperature (20-25°C) to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then adding nano-hydroxyapatite, and continuing magnetic stirring for 15-30 minutes to evenly disperse the nano-hydroxyapatite in the solution to obtain the spraying liquid.

[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, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the concentration of polycaprolactone in the spraying liquid is 0.25-1 .50mg / mL, for example, it can be 0.25mg / mL, 0.30mg / mL, 0.40mg / mL, 0.50mg / mL, 0.60mg / mL, 0.70mg / mL, 0.80mg / mL, 0.90mg / mL, 1.00mg / mL, 1.10mg / mL, 1.20mg / mL, 1.30mg / mL, 1.40mg / mL or 1.50mg / mL, but 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] In the present invention, by preferably controlling the concentration of nano-hydroxyapatite within a specific range, its dispersibility, interface 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 the solution viscosity to increase, the spraying process to fail, and the coating to shrink and crack during the drying process. At the same time, it will also increase the brittleness of the coating, reduce the fracture toughness, and affect the quality of the coating; when the concentration of nano-hydroxyapatite is too low, it is impossible to effectively regulate the activity of osteoblasts, so that the bone healing efficiency is reduced, 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, 100,000 Da, 120,000 Da, 140,000 Da, 160,000 Da, 180,000 Da or 200,000 Da, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the weight average molecular weight of the polycaprolactone is 10,000-50,000 Da, for example, 10,000 Da, 20,000 Da, 30,000 Da, 40,000 Da or 50,000 Da, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0037] In the present invention, by preferably controlling the molecular weight of polylactic acid and polycaprolactone within a specific range, and controlling their concentration, 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, which makes it difficult for ultrasonic vibration to effectively break the droplets, and then the nozzle is easily blocked, and the equipment failure rate increases; in addition, too high a molecular weight will increase the glass transition temperature, the movement of the chain segments is limited when the solvent evaporates, the shrinkage stress accumulates, and a network of cracks appears after drying, which is easy to peel off. At the same time, too long a molecular chain will also cause excessive chain entanglement, which will reduce the toughness of the coating, and then cause the overall quality of the coating to decrease, and the corrosion resistance will also decrease accordingly. When the molecular weight is too small, the droplet size of the ultrasonic atomization is too small, and the drying speed of the droplets is too fast, which is easy to form a porous and loose structure. Because the molecular chain is too short, the intermolecular force is relatively weak, and it is difficult to form an effective entanglement, which makes the coating poor in wear resistance and easy to be scratched and damaged. In addition, low molecular weight polylactic acid has a higher terminal carboxyl content (more starting sites for hydrolysis) and a lower degree of crystallinity, which results in a faster degradation rate and poor corrosion resistance.

[0038] Preferably, in the ultrasonic spraying of step (3), the height between the ultrasonic nozzle and the bottom coating is 10-25 cm, for example, 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 values ​​not listed within the numerical range are also applicable.

[0039] In the present invention, by preferably controlling the height of the ultrasonic nozzle from the bottom coating during ultrasonic spraying, the adhesion of the coating and the uniformity of the thickness of the coating can be controlled, that is: when the height is too high, the kinetic energy of the droplets is insufficient, and uneven dispersion is easy to occur, resulting in decreased adhesion and uneven coating thickness; when the height is too low, polylactic acid is easily aggregated, and the spray liquid is easy to splash, resulting in uneven thickness and even damage to the coating, and poor corrosion resistance.

[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 values ​​not listed within the numerical range are also 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 the spraying liquid between the layers fails to fully fuse, affecting the interlayer bonding strength; when the spraying rate is too low, the droplets are unevenly distributed due to the energy of the ultrasonic wave, the coating thickness is uneven, and even the coverage is incomplete. Under the condition of force, stratification and peeling occur, the adhesion decreases, and 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 effect of bone healing.

[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, and other values ​​not listed within the numerical range are also 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 gas pressure, evaporate quickly and splash when hitting the substrate, resulting in an 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 thickness of the coating, and may also cause droplet accumulation, forming sagging, quality problems on the coating surface, reduced pass rate and efficiency, and increased costs.

[0044] Preferably, the power of the ultrasonic spraying in step (3) is 0.5-1.5 W, for example, 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, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the drying temperature in step (3) is 45-55°C, for example, 45°C, 46°C, 48°C, 50°C, 52°C, 54°C or 55°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] In the present invention, the drying function is mainly to volatilize the solvent used in the polymer coating and ensure that the solvent residue is within a safe limit. In the present invention, it is preferred to control the drying temperature. When the drying temperature is too high, it is close to the glass transition temperature of the polymer material, the coating becomes soft, and solidifies 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 easy to volatilize, and the solvent residue causes the product to be unqualified.

[0047] Preferably, the drying time in step (3) is 48-72 h, for example, 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, and other values ​​not listed within the numerical range are also applicable.

[0048] In the present invention, it is preferred to control the drying time. If the drying time is too long, the cost is high. If the drying time is too short, the solvent is not easy to evaporate 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 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 comprises the following steps:

[0051] (1) The magnesium alloy substrate is suspended in a reaction vessel containing purified water, and after sealing, water vapor is used to perform a hydrothermal reaction on the magnesium alloy substrate. The distance between the magnesium alloy substrate 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 substrate containing a bottom coating;

[0052] (2) immersing the substrate containing the bottom coating obtained in step (1) in a phosphate buffer solution having a concentration of 8-15 mmol / L at a temperature of 60-80° C. for 5-15 min to obtain a bottom coating containing microporous channels;

[0053] (3) Adding 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 stirring at 25°C for 1-2 hours to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then adding nano-hydroxyapatite, and continuing magnetic stirring for 15-30 minutes to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spray liquid, wherein the concentration of polylactic acid in the spray liquid 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, the gas pressure is 0.01-0.05 MPa, and then dried at 45-55° C. for 48-72 hours to complete the preparation of the magnesium alloy composite coating.

[0055] In a third aspect, the present invention provides a medical magnesium alloy that is corrosion-resistant and promotes bone healing, wherein the surface of the medical magnesium alloy contains the corrosion-resistant magnesium alloy composite coating that promotes 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 particularly suitable for scenes with high requirements for mechanical properties, such as magnesium alloys for magnesium alloy 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 has higher corrosion resistance by combining a bottom coating composed of magnesium hydroxide and / or magnesium oxide with a surface coating of a polymer material, effectively reducing the degradation rate of magnesium alloys and expanding the application scenarios of magnesium alloys.

[0059] (2) In the composite coating provided by the present invention, the bottom coating and the surface coating are connected in an interlaced manner to achieve a high degree of firmness. For example, when used on the surface of a magnesium alloy bone plate and bone screw, even when the bone screw is twisted and screwed in to form a large friction force, the combination is still stable and not easy to break. It has the advantages of slow degradation rate, high strength, and strong toughness.

[0060] (3) In the composite coating and its preparation method provided by the present invention, 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, the nano-hydroxyapatite is gradually released to promote the adhesion, proliferation and differentiation of osteoblasts and accelerate the regeneration of bone tissue.

[0061] (4) Under optimal conditions, 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 rotated in and out three times. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0065] Figure 4 This is a 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 a comparison chart of the results of corrosion resistance tests on the composite coating provided by Example 1 of the present invention, the coating provided by Comparative Example 3, and the magnesium alloy substrate provided by Comparative Example 4;

[0067] Figure 6 This is a diagram showing the bone healing effect of the composite coating provided in Example 1 of the present invention in an animal experiment;

[0068] Figure 7 This is a diagram showing the bone healing effect of the composite coating provided in Example 4 of the present invention used in animal experiments. DETAILED DESCRIPTION

[0069] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0070] Example 1

[0071] This embodiment provides a magnesium alloy composite coating that is corrosion-resistant and promotes bone healing, wherein the magnesium alloy composite coating comprises a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

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

[0073] The surface coating comprises a polymer material, which comprises 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 method for preparing the above-mentioned magnesium alloy composite coating, and the preparation method comprises the following steps:

[0075] (1) A magnesium alloy substrate (AE series alloy) is suspended in a reaction vessel containing purified water, wherein the amount of purified water added is 30% of the volume of the reaction vessel. After sealing, water vapor is used to perform a hydrothermal reaction with 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, the substrate is naturally cooled and taken out after cooling to obtain a substrate containing a bottom coating.

[0076] (2) The substrate containing the bottom coating obtained in step (1) is immersed in a phosphate buffer solution with a concentration of 12 mmol / L at a temperature of 70° C. for 10 min, and then taken out, rinsed with purified water, and dried to obtain a bottom coating containing microporous channels, such as Figure 1 As shown;

[0077] (3) Adding 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 stirring at 25°C for 1.5 hours to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then adding nano-hydroxyapatite, and continuing magnetic stirring for 20 minutes to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spray liquid, wherein the concentration of polylactic acid in the spray liquid 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] The bottom coating obtained in step (2) is ultrasonically sprayed with a spray liquid containing a polymer material. During the 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, the coating thickness is 20 μm, and then dried at 48° C. for 56 hours to complete the preparation of the magnesium alloy composite coating.

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

[0080] Example 2

[0081] This embodiment provides a magnesium alloy composite coating that is corrosion-resistant and promotes bone healing, wherein the magnesium alloy composite coating comprises a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

[0082] The bottom coating comprises microporous channels, the bottom coating comprises magnesium hydroxide and / or magnesium oxide, the bottom coating has a porosity of 55%, and the microporous channels have a pore size of 20-120 μm;

[0083] The surface coating comprises a polymer material, which comprises 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.

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

[0085] (1) A magnesium alloy substrate (AE series alloy) is suspended in a reaction vessel containing purified water, wherein the amount of purified water added is 30% of the volume of the reaction vessel. After sealing, water vapor is used to perform a hydrothermal reaction with 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, the substrate is naturally cooled and taken out after cooling to obtain a substrate containing a bottom coating.

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

[0087] (3) Adding 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 stirring at 25°C for 1.5 hours to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then adding nano-hydroxyapatite, and continuing to magnetically stir for 20 minutes to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spray liquid, wherein the concentration of polylactic acid in the spray liquid 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] 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 cm, the spraying rate is 0.15 mL / min, the gas pressure is 0.01 MPa, the ultrasonic power is 1.2 W, the coating thickness is 20 μm, and then dried at 55° C. for 48 hours 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. 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 is corrosion-resistant and promotes bone healing, wherein the magnesium alloy composite coating comprises a bottom coating and a surface coating sequentially arranged from the surface of the magnesium alloy outward;

[0092] The bottom coating comprises microporous channels, the components of the bottom coating comprise magnesium hydroxide and / or magnesium oxide, the porosity of the bottom coating is 40%, and the pore size of the microporous channels is 20-120 μm;

[0093] The surface coating comprises a polymer material, which comprises 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 method for preparing the above-mentioned magnesium alloy composite coating, and the preparation method comprises the following steps:

[0095] (1) A magnesium alloy substrate (AE series alloy) is suspended in a reaction vessel containing purified water, wherein the amount of purified water added is 30% of the volume of the reaction vessel. After sealing, water vapor is used to perform a hydrothermal reaction with 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, the substrate is naturally cooled and taken out after cooling to obtain a substrate containing a bottom coating.

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

[0097] (3) Adding 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 stirring at 25°C for 1.5 hours to fully dissolve the polylactic acid and polycaprolactone without suspended matter; then adding nano-hydroxyapatite, and continuing to magnetically stir for 20 minutes to uniformly disperse the nano-hydroxyapatite in the solution to obtain a spray liquid, wherein the concentration of polylactic acid in the spray liquid 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] The bottom coating obtained in step (2) is ultrasonically sprayed with a spray liquid containing a polymer material. During the 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, the coating thickness is 20 μm, and then dried 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 and promoting bone healing. The surface of the medical magnesium alloy contains the above-mentioned magnesium alloy composite coating with corrosion resistance and promoting bone healing.

[0100] Example 4

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

[0102] This embodiment also provides a method for preparing the above-mentioned magnesium alloy composite coating, which is different from that of Embodiment 1 only in that nano-hydroxyapatite is not added to the spraying liquid in step (3).

[0103] Example 5

[0104] This embodiment provides a method for preparing a corrosion-resistant magnesium alloy composite coating that promotes bone healing. The only difference from Embodiment 1 is that the immersion temperature in step (2) is 55°C.

[0105] Example 6

[0106] This embodiment provides a method for preparing a corrosion-resistant magnesium alloy composite coating that promotes bone healing. The only difference from Embodiment 1 is that the immersion temperature in step (2) is 85°C.

[0107] Example 7

[0108] This embodiment provides a method for preparing a corrosion-resistant magnesium alloy composite coating that promotes bone healing. The only difference from Embodiment 1 is that the immersion time in step (2) is 2 minutes.

[0109] Example 8

[0110] This embodiment provides a method for preparing a corrosion-resistant magnesium alloy composite coating that promotes bone healing. The only difference from Embodiment 1 is that the immersion time in step (2) is 20 minutes.

[0111] Example 9

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

[0113] Example 10

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

[0115] Embodiment 11

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

[0117] Example 12

[0118] This embodiment provides a method for preparing a corrosion-resistant magnesium alloy composite coating that promotes bone healing. The only difference compared with Embodiment 1 is that the gas pressure in the ultrasonic spraying 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 only difference from Example 1 is that step (1) and step (2) are not performed, and the method in step (3) is used to directly 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 only difference compared with Example 1 is that step (2) is not performed, and the method in step (3) is used to directly 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 only difference compared with Example 1 is that step (2) and step (3) are not performed, and the magnesium alloy coating is only a bottom coating.

[0125] Comparative Example 4

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

[0127] Comparative Example 5

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

[0129] The products obtained in the above-mentioned examples and comparative examples were screwed in and out of a 40-grade polyurethane material (cortical bone hardness) for three times, and then the integrity of the coating was tested.

[0130] Taking Example 1, Example 4 and Comparative Example 1 as examples, the SEM images after three times of screwing in and out are as follows: Figure 2 , Figure 3 and Figure 4 As shown, from Figure 2 It can be seen that the surface of the composite coating provided in Example 1 is intact, and granular nano-hydroxyapatite is distributed in the surface coating; Figure 3 It can be seen that the composite coating in Example 4 still maintains good integrity, and the coating has good bonding with the magnesium alloy substrate. 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 is effectively attached to the surface. The coating thickness is tested by a thin film measuring instrument, and the thickness of the surface coating is 16.5 μm; Figure 4 It can be seen that after the coating provided in Comparative Example 1 was screwed in and out three times, the polymer coating was cracked and the coating was peeled off from the magnesium alloy substrate.

[0131] After the coating was rotated in and out three times, the corrosion resistance during the service period was tested using an electrochemical workstation. The reagent used in the electrochemical test was a PBS solution with a pH of 7.4; the initial voltage was -0.3 V, the end 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 composite coating provided in Example 1, the magnesium alloy with only bottom coating provided in Comparative Example 3, and the pure magnesium alloy provided in Comparative Example 4 as an example, the corrosion resistance of the samples of the same shape after being screwed in and out three times and tested by the electrochemical workstation is compared as follows: Figure 5 As shown, from Figure 5 It can be seen that the composite coating has better corrosion resistance than the bottom coating and the magnesium alloy substrate, and the corrosion resistance is significantly improved.

[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: the gum tissue was separated from the mandibular bone of dogs, and fracture models were made at appropriate locations using tools. After repeated rinsing with saline to remove bone debris at the fracture location, the medical magnesium alloy containing the composite coating in the above embodiment was selected and made into a bone plate and bone nail system for mandibular fracture repair and fixation implantation. Two sets of plate and nail systems were implanted in parallel on one side. The bone healing effects of the obtained animal experiments were as follows: Figure 6 and Figure 7 As shown, from Figure 6 It can be seen that the magnesium alloy product provided by Example 1 has a higher bone healing efficiency, the fracture line can be healed in time, and the healing of the bone plate and the fracture line achieves good cycle matching; Figure 7 It can be seen that the magnesium alloy product provided in Example 4 has a low bone healing efficiency, and the fracture line fails to heal in time, resulting in stress on the bone plate, stress corrosion, and fracture of the bone plate.

[0134] Table 1

[0135]

[0136] In Table 1, “-” means no coating.

[0137] From the data in Table 1, we can see the following points:

[0138] (1) From the data of Examples 1-4, it can be seen that under optimal conditions, 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 three times.

[0139] (2) It can be seen from the data of Example 1 and Examples 5-8 that the present invention can control the structure of the microporous channels and the surface roughness of the bottom coating by preferably controlling the temperature and time of immersion in step (2), thereby improving the bonding strength 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 Examples 9-12 that the present invention can further improve the quality of the surface coating by optimally controlling the parameters of ultrasonic spraying such as spraying rate, gas pressure, etc., thereby further improving the corrosion resistance and mechanical properties of the composite coating.

[0141] (4) From the data of Example 1 and Comparative Examples 1-5, it can be seen 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 the absence of microporous channels in Comparative Example 2, which cannot form an interlaced connection, the coating in Example 1 has higher firmness, can maintain good integrity, and has better corrosion resistance; compared with Comparative Example 5, which combines the bottom coating with the surface coating by hot pressing, the corrosion resistance and mechanical properties in Example 1 are better, while the coating firmness in Comparative Example 5 is not good, and the high temperature hot pressing has far exceeded the glass transition temperature of polylactic acid, the polymer chain breaks, the molecular weight decreases, and ultimately leads to poor corrosion resistance.

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

[0143] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and 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 composition of the bottom coating comprises magnesium hydroxide and / or magnesium oxide; The surface coating comprises a polymer material, wherein the polymer material comprises 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.

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

3. The magnesium alloy composite coating according to claim 1, characterized in that: The porosity of the bottom coating is 30-60%; 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 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 soaking temperature in step (2) is 60-80°C; The soaking time is 5-15min; The concentration of the phosphate buffer 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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