A method for constructing a hard and soft bimodal coating on the surface of a magnesium implant

Abstract

The present invention discloses a method for constructing a hard and soft dual-state coating on the surface of a magnesium implant. By subjecting the surface of the magnesium implant to alkalization treatment with an alkaline solution to construct a hard coating, and machining a layer of hydrogel soft coating on the surface of the hard coating, finally a dense hard and soft dual-state coating with a micron-level thickness is formed, which can significantly improve the anti-wear ability and anti-corrosion ability of the surface of the magnesium implant.

Description

Technical Field

[0001] The present invention relates to the field of biomedical technologies, and particularly relates to a method for constructing a hard-soft dual-state coating on the surface of a magnesium implant. Background Art

[0002] In recent years, degradable metal materials have received extensive attention due to their degradability and mechanical properties superior to those of degradable polymers. Among them, magnesium and its alloys are regarded as revolutionary metal biomaterials and have been widely studied and clinically explored. The advantages of magnesium and magnesium alloys, such as good biocompatibility, mechanical compatibility, biodegradability, density and elastic modulus similar to those of human cortical bone, and certain antibacterial properties, have been gradually confirmed by researchers one by one. The main degradation product, magnesium ions, is also an essential trace element in the human body, participates in human life activities, and the excess magnesium ions can be excreted from the body through the body's autonomous excretion process without causing additional effects on the human body.

[0003] Magnesium alloys have the following advantages: First, their mechanical properties are similar to those of natural bone, so the stress shielding effect caused by the mismatch of elastic modulus can be avoided; second, magnesium is the fourth most abundant metal element in the human body. There is about 30 g of magnesium in the human body, about 60% of which is stored in human bones and 30% in soft tissues such as muscles. It is crucial for metabolism and is also an activator of various enzymes in the human body, participating in muscle contraction; it affects the transmission of neuromuscular excitability and inhibits the abnormal excitation conduction; the recommended daily intake of magnesium element for adults is 310 mg - 420 mg, which is excreted from the body through the intestines and kidneys.

[0004] The main problems faced by magnesium and its alloys in the field of bone implant materials are: the problems such as the too-fast degradation rate of magnesium and its alloys in the body and the too-fast attenuation of mechanical strength, which lead to the mismatch between the effective mechanical support time of the magnesium implant and the repair time of damaged tissues. The damaged tissues have not been completely repaired, and the implant has already lost its mechanical support. This is the most important problem in current clinical applications and restricts the popularization and application of magnesium alloys in the orthopedic and other medical fields.

[0005] Modifying magnesium and its alloys through surface treatment or surface coating is one of the main ways to improve the properties of magnesium and its alloys. The coating on the surface of biomedical magnesium alloys not only needs to have a protective effect on the substrate, but also needs to have good biocompatibility, bioactivity or drug release performance, etc. The coating also needs to degrade within a certain period of time. Degradable organic polymer coatings have become a method for surface modification of magnesium and its alloys. Currently, commonly used biodegradable polymers mainly include PLA, PLGA, PCL, and chitosan, etc. These materials themselves have excellent biocompatibility and can also endow the magnesium alloy substrate with special functionality.

[0006] CN114404652A discloses a method for preparing a chitosan intermediate layer on the surface of a medical magnesium alloy. The pretreated magnesium alloy substrate is placed in a chitosan acetic acid solution; a chitosan coating is prepared by the dip-coating method. First, the magnesium alloy substrate is immersed in the chitosan acetic acid solution and left standing for 4 - 30 s in the chitosan acetic acid solution, and then the magnesium alloy is pulled out of the chitosan acetic acid solution at a rate of 0.3 - 2 mm / s and left standing at room temperature for drying for 5 - 20 min; this is repeated 1 - 6 times; then the magnesium alloy with the chitosan coating is hermetically left standing in an oven at 50 - 90 °C for drying for 30 - 60 min to obtain the chitosan intermediate layer. However, in the acetic acid solution of chitosan, a violent hydrogen evolution reaction will occur on the magnesium alloy, severely corroding the magnesium alloy and making it difficult to form a dense and uniform chitosan thin film. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for constructing a hard and soft dual-state coating on the surface of a magnesium implant, which can significantly improve the anti-wear and anti-corrosion capabilities of the surface of the magnesium implant.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0009] A method for constructing a hard and soft dual-state coating on the surface of a magnesium implant, comprising the following steps:

[0010] (1) Pretreatment: The magnesium implant is polished, cleaned, and dried. The purpose of this step is to improve the surface flatness of the magnesium implant, reduce the roughness, prevent uneven corrosion, and facilitate the subsequent alkali treatment.

[0011] (2) Constructing the hard coating: Then the magnesium implant is placed in an alkaline solution for alkalization treatment to form a hard coating, and after the treatment is completed, it is taken out and dried. The purpose of the alkalization treatment is to form a uniform and dense hard coating on the surface of the magnesium implant, slow down its corrosion in the hydrogel solution, prevent hydrogen gas generated by the corrosion of magnesium from aggregating on the surface of the magnesium implant to form bubbles that block the hydrogel liquid film, and facilitate the formation of the hydrogel coating.

[0012] (3) Constructing the soft coating: The magnesium implant treated in step (2) is immersed in a hydrogel solution, and bubbles are removed by ultrasonic treatment or vacuum pumping, and then taken out and placed in a low-temperature environment for low-temperature curing to form a soft coating;

[0013] (4) Post-treatment: The magnesium implant treated in step (3) is freeze-dried at -50 °C to -60 °C and then dried at a high temperature, thereby forming a dense hard and soft dual-state coating on the surface of the magnesium implant. Freeze-drying can make the hydrogel form a three-dimensional porous structure with interconnected pores, which is beneficial for adsorbing magnesium ions generated after the degradation of the magnesium implant and the attachment and migration of cells. High-temperature drying can temporarily shrink the porous structure to form a high-strength dense coating, improve the mechanical strength of the coating, and significantly improve the wear resistance and anti-corrosion ability of the magnesium implant during the implantation process.

[0014] Preferably, in step (2), the alkaline substance of the alkaline solution is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and sodium phosphate.

[0015] Preferably, in step (2), the concentration of the alkaline solution is 0.5 - 5 M.

[0016] Furthermore, in step (2), the concentration of the alkaline solution is 1 M, 2 M, or 3 M.

[0017] Preferably, in step (2), the number of alkalization treatments is 1 - 10 times, the temperature of the alkalization treatment is -20 - 120°C, and the specific operation of the alkalization treatment is as follows: first, perform low-temperature alkalization treatment at -20 - 10°C for 6 - 24 hours, and then perform high-temperature alkalization treatment at 60 - 120°C for 6 - 24 hours. This step of operation is to adjust the uniformity and thickness of the hard coating.

[0018] Preferably, in step (3), the gel component of the hydrogel solution is selected from one or more of polyvinyl alcohol, polyethylene glycol, chitosan, chitosan derivatives, sodium hyaluronate, and polyvinylpyrrolidone. The chitosan derivatives are preferably water-soluble chitosan derivatives such as quaternary ammonium salt chitosan and carboxymethyl chitosan.

[0019] Preferably, in step (3), the total mass concentration of the hydrogel solution is 1 - 20%. In this mass concentration range, the solution has an appropriate viscosity, which is beneficial to the spreading and adhesion of the solution on the surface of the magnesium implant.

[0020] Preferably, in step (3), the number of low-temperature curing times is 1 - 10 times, and the temperature of the low-temperature curing is -80 - 0°C. Multiple curing is beneficial to the tight combination of the hydrogel coating and the hard coating, improving the bonding strength, and at the same time, it is beneficial to make the hydrogel coating more flat.

[0021] Furthermore, the specific operation of the low-temperature curing is as follows: first, perform low-temperature curing at -20°C for 2 - 6 hours, and then perform low-temperature curing at -80°C for 6 - 22 hours. The total curing time is 8 - 24 hours. Low-temperature curing can retain the intrinsic properties of the hydrogel material and retain the functional groups and chain structures beneficial to cells and tissues.

[0022] Preferably, in step (4), the temperature of the high-temperature drying is 60 - 100°C, and the number of high-temperature drying times is 1 - 5 times; the specific operation of the high-temperature drying is as follows: first, dry at 60 - 75°C for 2 - 6 hours, and then dry at 80 - 100°C for 4 - 12 hours. The total drying time is 8 - 18 hours. Multiple drying can improve the bonding strength between the hard and soft coatings and at the same time reduce the aging effect of long-term high temperature on the hydrogel soft coating.

[0023] The hard-soft dual-state coating, due to its excellent lubrication performance, biocompatibility and flexibility, has opened up a new path for improving the lubricity, biocompatibility and flexibility of solid surfaces. After the surface of the magnesium implant is pretreated with an alkaline solution, a hydrogel solution is evenly formed into a liquid film on the surface of the magnesium implant, and then through low-temperature curing and freeze-drying methods, the curing of the hydrogel solution and the volatilization of the solvent are promoted respectively. Finally, a dense hard-soft dual-state coating with a micron-level thickness is formed, which can significantly improve the anti-wear and anti-corrosion capabilities of the magnesium implant surface.

[0024] In the present invention, the surface of the magnesium implant is alkalized by an alkaline solution. After the treatment, the surface defects of the magnesium implant are reduced, and at the same time, a uniform and dense hard coating is formed, which slows down the corrosion effect of the hydrogel solution on the magnesium implant. The magnesium implant with the hard coating formed is immersed in the hydrogel solution to remove air bubbles, and then taken out and placed at low temperature to promote the curing of the hydrogel. After curing, a hydrogel soft coating is formed on the surface of the hard coating. To improve the bonding force between the hydrogel soft coating and the hard coating, the hard-soft coating is freeze-dried and then dried at high temperature. After the surface of the magnesium implant forms a hard coating through alkaline solution pretreatment in the present invention, a uniform hydrogel solution is dip-coated on its surface, and a dense polymer soft coating is formed through freeze-drying and high-temperature drying. The soft coating has the characteristics of toughness and low friction coefficient, and can significantly improve the anti-wear and anti-corrosion capabilities of the magnesium implant surface. Controlling the concentration of the hydrogel solution and the number of dip-coating times can regulate the thickness of the hard-soft dual-state coating, and further regulate the anti-wear and anti-corrosion capabilities of the magnesium implant. The hard-soft dual-state coating systematically prepared by alkaline treatment - low-temperature gelation - freeze-drying - high-temperature drying in the present invention has excellent properties such as good anti-wear, water barrier, acid and alkali resistance, and high biocompatibility. The hard-soft dual-state coating is beneficial to cell and tissue adhesion due to its water absorption and swelling in the later stage.

[0025] The hard-soft dual-state coating constructed on the surface of the magnesium implant can regulate the corrosion rate and degradation rate after the magnesium implant is implanted, and further improve the biocompatibility of the biomaterial.

[0026] The beneficial effects of the present invention are:

[0027] Alkalization treatment forms a dense waterproof coating on the surface of the magnesium implant without corroding the magnesium, overcomes the problem of too fast reaction between the magnesium implant and water, can ensure the original size, quality and shape of the magnesium implant to the greatest extent, and is beneficial to the further preparation of the soft coating on its surface.

[0028] After the surface of the magnesium implant is pretreated with an alkaline solution, a hydrogel solution is formed into a uniform liquid film on the surface of the magnesium implant, and then through freeze-drying and high-temperature drying methods, the curing of the hydrogel solution and the volatilization of the solvent are promoted. Finally, a dense hard-soft dual-state coating with a micron-level thickness is formed, which can significantly improve the anti-wear and anti-corrosion capabilities of the magnesium implant surface. Description of the Drawings

[0029] Figure 1 It is the characterization of the surface morphology, roughness, and contact angle of the pure magnesium implant after alkalization treatment in Example 1;

[0030] Figure 2 It is the characterization of the surface morphology, roughness, and contact angle of the pure magnesium implant after alkalization treatment and then preparation of a hydrogel coating in Example 2;

[0031] Figure 3 It is the characterization of the surface morphology, roughness, and contact angle of the magnesium implant in Example 1 after being stationary in simulated body fluid SBF for 7 days;

[0032] Figure 4 It is the characterization of the surface morphology, roughness, and contact angle of the magnesium implant in Example 2 after being stationary in simulated body fluid SBF for 7 days;

[0033] Figure 5 It is the characterization of the surface morphology, roughness, and contact angle of the pure magnesium implant in Comparative Example 1 after direct high-temperature treatment;

[0034] Figure 6 It is the characterization of the surface morphology, roughness, and contact angle of the magnesium implant in Comparative Example 2 after being stationary in simulated body fluid SBF for 7 days;

[0035] Figure 7 It is the characterization of the surface morphology, roughness, and contact angle of the pure magnesium implant in Comparative Example 3;

[0036] Figure 8 It is the characterization of the surface morphology, roughness, and contact angle of the magnesium implant in Comparative Example 4 after being stationary in simulated body fluid SBF for 7 days;

[0037] Figure 9 It is the pure magnesium implant, high-temperature alkali treatment, low-temperature alkali treatment followed by high-temperature alkali treatment, and low-temperature alkali treatment followed by high-temperature alkali treatment + hydrogel coating, testing their pull-out force in the bone of a pig's leg bone through a mechanical testing machine;

[0038] Figure 10 It is the thermal conductivity of pure magnesium implant 1, high-temperature alkali treatment 2, low-temperature alkali treatment followed by high-temperature alkali treatment 3, and low-temperature alkali treatment followed by high-temperature alkali treatment + hydrogel coating 4;

[0039] Figure 11 It is the change in the pH of the solution when pure magnesium implant 1, high-temperature alkali treatment 2, low-temperature alkali treatment followed by high-temperature alkali treatment 3, and low-temperature alkali treatment followed by high-temperature alkali treatment + hydrogel coating 4 corrode in SBF for different days; 5 in the figure is the SBF control of the standard solution;

[0040] Figure 12Degradation of pure magnesium implants 1, high-temperature alkali treatment 2, high-temperature alkali treatment after low-temperature alkali treatment 3, and high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating 4 after being implanted in SD rats for two weeks. Detailed implementation manners

[0041] The following are specific examples to further illustrate the technical solutions of the present invention.

[0042] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art unless otherwise specified.

[0043] Example 1

[0044] Construct a hard coating on the surface of the magnesium implant:

[0045] The magnesium implant was polished successively with sandpapers of 500 mesh, 1000 mesh, 2000 mesh, and 5000 mesh. After polishing, it was ultrasonically cleaned in an acetone solution for 30 minutes, then rinsed 2 - 3 times with deionized water at 0 - 10 °C and quickly dried. After drying, it was placed in a sodium hydroxide solution with a mass concentration of 5M, and then alkalized at -20 °C for 12 hours. Then it was placed in an environment at 100 °C and alkalized for 12 hours. After the alkalization treatment, it was taken out and quickly dried, and a uniform and dense hard coating was formed on the surface of the magnesium implant.

[0046] The surface morphology and structure of the magnesium implant were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) ( Figure 1 )). It can be seen from Figure 1 the SEM and AFM images in a that the surface of the magnesium implant after low-temperature and then high-temperature alkali treatment is very smooth, without cracks, and has a small surface roughness. Figure 1 The contact angle image in b shows that the surface of the magnesium implant after low-temperature and then high-temperature alkali treatment is hydrophilic.

[0047] Example 2

[0048] The magnesium implant with a hard coating constructed on its surface in Example 1 was immersed in a composite solution of polyvinyl alcohol, polyethylene glycol, and carboxymethyl chitosan, with mass concentrations of 10%, 5%, and 1% respectively. Then, the hydrogel solution was ultrasonically treated or evacuated to remove bubbles. After the bubbles were removed completely, the magnesium implant was taken out and placed in a low-temperature environment at -20 °C to promote the curing of the hydrogel solution. The curing time was 6 hours, and then it was cured at -80 °C for 12 hours. After curing, it was taken out, freeze-dried at -50 °C for 12 hours, baked at 65 °C for 4 hours, and baked at 90 °C for 10 hours. Finally, a polymer soft coating was formed on the surface of the hard coating of the magnesium implant ( Figure 2 ). It can be seen from Figure 2SEM and AFM images of a show that a hydrogel soft coating is prepared on the hard coating, with a very smooth surface, no cracks, and a small surface roughness. Figure 2 The contact angle image of b shows that a hydrogel soft coating is prepared on the hard coating. Compared with the hard coating in Example 1, the water contact angle slightly increases, but it is still hydrophilic.

[0049] Example 3

[0050] The magnesium implant in Example 1 was placed in 10 ml of simulated body fluid SBF, left standing at room temperature of 25 °C for 7 days, taken out, the surface was washed 3 times with 50 ml of deionized water, then the surface was washed 3 times with 20 ml of absolute ethanol, and after natural drying, the surface morphology and structure after corrosion were observed by SEM and AFM, and the elemental species on the surface after corrosion were characterized by combining EDS ( Figure 3 )). From Figure 3 the SEM and AFM images of a, it can be seen that after static immersion in the SBF solution for 7 days, micron wrinkles are generated on the surface of the magnesium implant, the surface roughness increases, the contact angle further decreases, and the hydrophilicity increases ( Figure 3 b). Through Figure 3 c, it can be seen that after static immersion in the SBF solution for 7 days, some elements in the SBF can be seen deposited on the surface of the magnesium implant, indicating that weak corrosion has occurred on the surface of the magnesium implant in the SBF solution.

[0051] Example 4

[0052] The magnesium implant in Example 2 was placed in 10 ml of simulated body fluid SBF, left standing at room temperature of 25 °C for 7 days, taken out, the surface was washed 3 times with 50 ml of deionized water, then the surface was washed 3 times with 20 ml of absolute ethanol, and after natural drying, the surface morphology and structure after corrosion were observed by SEM and AFM, and the elemental species on the surface after corrosion were characterized by combining EDS ( Figure 4 )). From Figure 4 the SEM and AFM images of a, it can be seen that after static immersion in the SBF solution for 7 days, some small air sacs or small bubbles are generated on the surface of the magnesium implant, the surface roughness increases, the contact angle further decreases, and the hydrophilicity increases ( Figure 4 b). Through Figure 4 c, it can be seen that after static immersion in the SBF solution for 7 days, some elements in the SBF can be seen deposited on the surface of the magnesium implant, indicating that weak corrosion has occurred on the surface of the magnesium implant in the SBF solution, and the corrosion degree is smaller than that in Example 3, indicating that the hard and soft dual coatings have special functions respectively, and at the same time have the ability to synergistically delay corrosion ( Figure 12 ).

[0053] Comparative Example 1

[0054] Construct a hard coating on the surface of the magnesium implant:

[0055] The magnesium implant was polished successively with sandpapers of 500 mesh, 1000 mesh, 2000 mesh and 5000 mesh. After polishing, it was ultrasonically cleaned in acetone solution for 30 minutes, then rinsed 2 - 3 times with deionized water at 0 - 10 °C and quickly dried. After drying, it was put into a sodium hydroxide solution with a mass concentration of 5M, and then placed in an environment of 100 °C for 12 hours of alkalization treatment. After the alkalization treatment, it was taken out and quickly dried, and a cracked hard coating was formed on the surface of the magnesium implant ( Figure 5 )). As can be seen from Figure 5 a, there are obvious cracks on the surface of the magnesium implant after direct high-temperature alkali solution treatment, and the surface roughness is very large. The existence of cracks is not conducive to the formation of the subsequent hydrogel soft coating. Figure 5 The contact angle image in

[0056] Comparative Example 2

[0057] The magnesium implant in Comparative Example 1 was placed in 10 ml of simulated body fluid SBF and left standing at room temperature of 25 °C for 7 days. After taking it out, it was washed 3 times with 50 ml of deionized water on the surface, and then washed 3 times with 20 ml of absolute ethanol on the surface. After natural drying, the surface morphology and structure after corrosion were observed by SEM and AFM, and the elemental types on the surface after corrosion were characterized by EDS ( Figure 6 )). As can be seen from Figure 6 the SEM and AFM images in Figure 6 a, after static immersion in the SBF solution for 7 days, the cracks on the surface of the magnesium implant were significantly enlarged and deepened, the surface roughness increased, the contact angle further decreased, and the hydrophilicity increased ( Figure 6 b). As can be seen from

[0058] Comparative Example 3

[0059] On the surface of the pure magnesium implant:

[0060] The magnesium implant was polished successively with sandpapers of 500 mesh, 1000 mesh, 2000 mesh and 5000 mesh. After polishing, it was ultrasonically cleaned in acetone solution for 30 minutes, then rinsed 2 - 3 times with deionized water at 0 - 10 °C and quickly dried ( Figure 7 ). As can be seen from Figure 7 a, there are obvious processing scratches on the surface of the pure magnesium implant, and the surface roughness is very large. The existence of scratches is not conducive to the formation of the subsequent hydrogel soft coating. Figure 7 The contact angle image in

[0061] Comparative Example 4

[0062] The magnesium implant in Comparative Example 3 was placed in 10 ml of simulated body fluid SBF, left standing at room temperature of 25 °C for 7 days, taken out, the surface was washed 3 times with 50 ml of deionized water, then the surface was washed 3 times with 20 ml of absolute ethanol, and after natural drying, the surface morphology and structure after corrosion were observed by SEM and AFM ( Figure 8 ). As can be seen from Figure 8 the SEM and AFM images in Figure 8 a, after static immersion in the SBF solution for 7 days, the scratches on the surface of the pure magnesium implant became cracks, and significantly expanded and deepened, the surface roughness increased, the contact angle further decreased, and the hydrophilicity increased (

[0063] Test Example 1

[0064] The pure magnesium implant (Comparative Example 3), high-temperature alkali treatment (Comparative Example 1), high-temperature alkali treatment after low-temperature alkali treatment (Example 1), and high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating (Example 2) were tested for their pull-out force on the bone of a pig's leg bone by a mechanical testing machine, and the results are shown in Figure 9 , Figure 9 as shown.

[0065] Test Example 2

[0066] The thermal conductivities of the pure magnesium implant (Comparative Example 3), high-temperature alkali treatment (Comparative Example 1), high-temperature alkali treatment after low-temperature alkali treatment (Example 1), and high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating (Example 2) were tested, and the results are shown in Figure 10 , Figure 10 as shown.

[0067] Test Example 3

[0068] The changes in the pH of the solution during different days of corrosion of the pure magnesium implant (Comparative Example 3), high-temperature alkali treatment (Comparative Example 1), high-temperature alkali treatment after low-temperature alkali treatment (Example 1), and high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating (Example 2) in SBF were tested; the results are shown in Figure 11 . Through the continuous change of pH, it is shown that the pure magnesium implant corrodes the fastest in the SBF solution, the pH increases the fastest, and the magnesium implant with hard and soft coatings corrodes the slowest, and the pH increases the slowest.

[0069] Test Example 4

[0070] The degradation of pure magnesium implants (Comparative Example 3), high-temperature alkali treatment (Comparative Example 1), high-temperature alkali treatment after low-temperature alkali treatment (Example 1), and high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating (Example 2) after being implanted in SD rats for two weeks was tested. The results showed that the degradation rate of pure magnesium implants was much higher than that of implants with surface coatings and the cavity volume generated was the largest. With the optimization and improvement of the coating process, the degradation rate decreased and the cavity volume decreased. In particular, the degradation rate of high-temperature alkali treatment after low-temperature alkali treatment + hydrogel coating was the slowest and the cavity volume generated was the smallest ( Figure 12 ).

[0071] The above-described embodiments are only a preferred solution of the present invention and do not impose any form of limitation on the present invention. There are other variations and modifications without exceeding the technical solutions described in the claims.

Claims

1. A method for constructing a hard and soft dual-state coating on the surface of a magnesium implant, characterized in that, it includes the following steps: (1) Pretreatment: Polish, clean, and dry the magnesium implant; (2) Constructing the hard coating: Then place the magnesium implant in an alkaline solution for alkalization treatment to form a hard coating, and take it out and dry it after the treatment is completed; (3) Constructing the soft coating: Immerse the magnesium implant treated in step (2) in a hydrogel solution, remove air bubbles by ultrasonic or vacuum pumping, take it out and place it in a low-temperature environment for low-temperature curing to form a soft coating; (4) Post-treatment: Freeze-dry the magnesium implant treated in step (3) at -50°C to -60°C and then dry it at a high temperature, so as to form a dense hard and soft dual-state coating on the surface of the magnesium implant; In step (2), the alkaline substance in the alkaline solution is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, and sodium phosphate; In step (2), the number of alkalization treatments is 1 to 10 times. The specific operation of the alkalization treatment is: first perform low-temperature alkalization treatment at -20 to 10°C for 6 to 24 hours, and then perform high-temperature alkalization treatment at 60 to 120°C for 6 to 24 hours; In step (3), the total mass concentration of the hydrogel solution is 1 to 20%; In step (3), the number of low-temperature curing times is 1 to 10 times. The specific operation of low-temperature curing is: first perform low-temperature curing at -20°C for 2 to 6 hours, and then perform low-temperature curing at -80°C for 6 to 22 hours, and the total curing time is 8 to 24 hours; In step (4), the number of high-temperature drying times is 1 to 5 times; the specific operation of high-temperature drying is: first dry at 60 to 75°C for 2 to 6 hours, and then dry at 80 to 100°C for 4 to 12 hours, and the total drying time is 8 to 18 hours.

2. The method according to claim 1, characterized in that, in step (2), the concentration of the alkaline solution is 0.5 to 5 M.

3. The method according to claim 2, characterized in that, in step (2), the concentration of the alkaline solution is 1 M, 2 M or 3 M.

4. The method according to claim 1, characterized in that, in step (3), the gel component of the hydrogel solution is one or more of polyvinyl alcohol, polyethylene glycol, chitosan derivative, sodium hyaluronate, and polyvinylpyrrolidone.

Images