Multifunctional coating with compact-porous double-layer structure on surface of magnesium alloy and preparation method

Abstract

The invention discloses a multifunctional coating with a compact-porous double-layer structure on the surface of magnesium alloy and a preparation method, and belongs to the technical field of biological materials. According to the multifunctional coating, magnesium alloy serves as a substrate, a compact layer and a porous layer are sequentially stacked from the substrate to the outside, and the compact layer is composed of two-dimensional transition metal carbide / nitride, calcium silicate nanowires and a positively charged polymer. The porous layer is composed of copper-containing complex / biopolymer composite fibers, mineralized silk fibers loaded with bioactive metal ions and astragalus polysaccharide on the surface, and natural polymers. According to the multifunctional coating with the compact-porous double-layer structure prepared on the surface of the magnesium alloy, the porous layer on the surface layer has a unique porous structure, growth and proliferation of osteoblasts can be well promoted, meanwhile, the multifunctional coating has the characteristics of pressure resistance, bacteria resistance and oxidation resistance, the compact layer on the bottom layer can improve the corrosion resistance of the magnesium alloy, and the service life of the magnesium alloy is prolonged. The coating is particularly suitable for surface coating of magnesium alloy implant materials and can be used in the field of medical instruments.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomaterials, and particularly relates to a multifunctional coating with a dense-porous double-layer structure on the surface of a magnesium alloy and a preparation method thereof. Background Art

[0002] The treatment of bone defects has always been an important topic in clinical research. Magnesium alloys have broad application prospects in the field of bone repair due to their good biocompatibility, degradability, and mechanical properties suitable for bone tissues. However, after magnesium alloys are implanted into the body, their degradation rate is too fast and they are extremely prone to corrosion. This situation will gradually erode the implant, causing its overall structure to be severely damaged, and finally making the implant completely lose its mechanical support function. In addition, the antibacterial properties and osteogenesis-promoting properties of magnesium alloys are not yet ideal, which not only increases the risk of postoperative infection but may also have an adverse impact on the repair effect of bone defects. There are many methods for surface modification of magnesium alloys, such as alloying surface modification, chemical coatings, and chemical conversion films. Among them, the coating modification technology forms an anti-corrosion layer on the surface of magnesium implants through physical coating or chemical deposition, significantly reducing the corrosion rate of implants in the body fluid environment, effectively delaying the attenuation of the mechanical properties of magnesium metal, making its corrosion rate match the fracture healing rate, and winning valuable time for the damaged bone tissue to recover mechanical strength. Bone tissue repair is divided into an inflammatory period of 3 - 7 days and a healing period of 3 - 4 months. For different stages of bone tissue repair, the implant needs to have different functions, that is, in the inflammatory period, the implant needs to have antibacterial properties to prevent the aggravation of inflammation; in the healing period, it needs to promote osteogenesis and calcium phosphate deposition, and at the same time have a moderate degradation rate to avoid losing the bearing capacity prematurely.

[0003] The following problems exist in the existing technical solutions for osteogenic coatings on the surface of magnesium alloys:

[0004] 1. Currently constructed coatings mostly start from the composition perspective, such as selecting mineralized bone analogs to deposit on the surface of magnesium alloys, but lack the bionic construction of polymer porous coatings from the perspective of bone tissue structure to guide the growth of osteoblasts.

[0005] 2. Although porous coatings are beneficial to promoting the nutrient diffusion rate and uniform cell distribution, they also make corrosive ions, bacteria, or microorganisms easy to enter, resulting in problems of matrix surface corrosion and infection. In addition, for polymer porous coatings, under the action of environmental external forces, they are easy to deform, causing the original pore structure to deform.

[0006] In summary, in order to provide a relatively pure and stable microenvironment for the formation of bone tissue, from the perspective of the integration of structure and function, how to develop a porous structure coating with excellent mechanical properties, antibacterial, anti-inflammatory, and osteogenesis-promoting properties while reducing the degradation rate of magnesium alloys is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] Object of the Invention: The first object of the present invention is to provide a multifunctional coating with a dense-porous double-layer structure on the surface of a magnesium alloy, which has excellent mechanical properties, antibacterial, anti-inflammatory and osteogenic properties. The second object of the present invention is to provide a preparation method for the multifunctional coating with a dense-porous double-layer structure on the surface of the above-mentioned magnesium alloy.

[0008] Technical Solution: The multifunctional coating with a dense-porous double-layer structure on the surface of the magnesium alloy provided by the present invention uses the magnesium alloy as a substrate, and a dense layer and a porous layer are sequentially stacked outward from the substrate. The dense layer is composed of two-dimensional transition metal carbides / nitrides with a two-dimensional layered structure, calcium silicate nanowires and positively charged polymers. The porous layer is composed of copper-containing complex / bio-polymer composite fibers, mineralized silk fibers with bioactive metal ions and astragalus polysaccharide loaded on the surface, and natural polymers.

[0009] Further, the thickness ratio of the dense layer to the porous layer is (1-30):1, preferably (1-20):1.

[0010] Further, the mass ratio of the two-dimensional transition metal carbides / nitrides with a two-dimensional layered structure to the calcium silicate nanowires is 1:1-5; the mass ratio of the copper-containing complex / bio-polymer composite fibers, the mineralized silk fibers with bioactive metal ions and astragalus polysaccharide loaded on the surface to the natural polymers is 1-4:1-2:4-10.

[0011] The preparation method for the multifunctional coating with a dense-porous double-layer structure on the surface of the above-mentioned magnesium alloy includes the following steps:

[0012] (1) Mix two-dimensional transition metal carbides / nitrides with a two-dimensional layered structure and calcium silicate nanowires in a solvent, carry out a hydrothermal reaction, and after completion, dry. Mix the obtained two-dimensional transition metal carbides / nitrides loaded with calcium silicate nanowires with an aqueous solution of a positively charged polymer to prepare a precursor solution for the dense layer;

[0013] (2) Through coaxial electrospinning technology, prepare a copper-containing complex / bio-polymer composite fiber felt with a copper-containing complex as the skin layer and a bio-polymer as the core layer, cut it into pieces and set aside;

[0014] (3) Immerse the degummed silk fibers alternately in a silk mineralization treatment solution and a mixed solution containing bioactive metal ions, a phosphorus source and astragalus lipid polysaccharide. After the immersion is completed, filter and dry to obtain mineralized silk fibers with bioactive metal ions and astragalus lipid polysaccharide loaded on the surface;

[0015] (4) The shredded copper-containing complex / bio-polymer composite fiber felt prepared in step (2) and the mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on its surface prepared in step (3) are jointly added to a natural polymer solution, and stirred to obtain a porous layer precursor solution;

[0016] (5) The dense layer precursor solution prepared in step (1) is sprayed on the surface of the magnesium alloy after alkali heat treatment, dried to form a dense layer, and then the porous layer precursor solution prepared in step (4) is spin-coated on the dense layer. After that, it is quickly immersed in liquid nitrogen for freezing, and then immersed in a low-temperature NaOH ethanol solution. After that, it is rinsed and freeze-dried to obtain a porous layer;

[0017] (6) The material prepared in step (5) is subjected to activation treatment, and then dried to obtain a multi-functional coating with a dense-porous double-layer structure on the surface of the magnesium alloy.

[0018] Furthermore, in step (1), the two-dimensional transition metal carbide / nitride is monolayer MXene; the diameter of the calcium silicate nanowires is 50 - 100 nm; the conditions of the hydrothermal treatment are: reacting at 60 - 120 °C for 0.5 - 2 h; the positively charged polymer includes one or more of carboxymethyl chitosan, quaternary ammonium salt chitosan, or polyethyleneimine, and the concentration of the aqueous solution of the positively charged polymer is 2.0 - 10.0 wt.%; the mass ratio of the positively charged polymer to the two-dimensional transition metal carbide / nitride loaded with calcium silicate nanowires is 100 - 10:1.

[0019] Furthermore, in step (2), the preparation method of the copper-containing complex is: a complexing reaction is carried out between the complexing ligand and the copper salt in a solvent, and after completion, it is centrifuged and washed with water to obtain; wherein, the mass ratio of the complexing ligand to the copper salt is 1:1 - 5; the complexing ligand is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, and the copper salt is copper chloride; the conditions of the complexing reaction are: reacting at 100 - 160 °C for 0.5 - 3 h; the bio-polymer includes one or more of regenerated silk fibroin, chitosan, gelatin, polylactic acid, and polyvinyl alcohol.

[0020] Furthermore, in step (3), the length of the degummed silk fiber is 20 - 300 μm; the silk mineralization treatment solution includes a calcium-containing compound solution and a phosphorus-containing compound solution. The calcium-containing compound solution is a calcium chloride solution with a concentration of 0.5 - 0.8 mol / l, and the phosphorus-containing compound solution is a sodium hydrogen phosphate solution with a concentration of 0.2 - 0.4 mol / l; the bioactive metal ions include one or more of strontium, cerium, magnesium, calcium, or gallium; the molar ratio of the bioactive metal ions, the phosphorus source, and astragalus lipid polysaccharide is 1 - 5:1 - 5:2 - 10; the number of cycles of alternating impregnation is 2 - 8 rounds, the impregnation temperature is 30 - 40 °C, and the impregnation time for each solution is 5 - 30 min.

[0021] Further, in step (4), the length of the shredded copper-containing complex / biopolymer composite fiber felt is 0.01-1 mm; the natural polymer includes one or more of chitosan, hyaluronic acid, pectin, collagen, gelatin, sodium alginate, and agarose, and the concentration of the natural polymer solution is 2.0-5.0 wt.%.

[0022] Further, in step (5), the conditions for alkali heat treatment are: treating in a sodium hydroxide solution with a temperature of 60-80°C and a concentration of 1-10 mol / l for 6-24 hours; the temperature of the low-temperature NaOH ethanol solution is -20 to -15°C, and the concentration is 0.3-1 mol / L.

[0023] Further, in step (6), the parameters for activation treatment are: treating in a mixed solution containing 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide at 4-6°C for 6-24 h; the concentration of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride in the mixed solution is 50-100 mmol / l, and the concentration of N-hydroxysuccinimide in the mixed solution is 25-50 mmol / L.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The present invention sequentially prepares a dense layer and a porous layer on the surface of a magnesium alloy, solving the problems of poor barrier property, insufficient osteoinductive activity, and no antibacterial property of the existing magnesium alloy respectively. The dense layer, as the bottom layer, improves the bonding force between the porous layer and the magnesium alloy and can further play a role in protecting the magnesium alloy. The dense layer is a "brick and tile" structure composed of a transition metal carbide / nitride / calcium silicate nanowire composite with a two-dimensional layered structure and a positively charged polymer. The transition metal carbide / nitride / calcium silicate nanowire composite is formed by compounding two-dimensional layered MXene with one-dimensional calcium silicate nanowires, having a complex three-dimensional structure, so that the dense layer has better barrier property and mechanical properties. At the same time, calcium silicate nanowires have natural osteoinductive properties, which is beneficial to further improving the osteo-integration ability of the implant. The porous layer, as the surface layer of the composite coating, mimics the natural bone tissue in structure and has a good guiding effect on cell growth, adhesion, and spreading. However, traditional porous polymer coatings have problems of insufficient mechanical properties and easy collapse, resulting in deformation of the pore structure. In the present invention, a copper-containing complex / bio-polymer composite fiber and a mineralized silk fiber surface-loaded with bioactive metal ions and astragalus polysaccharide are added simultaneously. The two are distributed and interpenetrated in the porous coating. On the one hand, under the synergistic action of the two, the compressive strength of the porous layer can be effectively improved to prevent it from collapsing. On the other hand, the two fibers can be intertwined with each other in the coating, which can not only change the pore size on a three-dimensional scale but also increase the penetration path of corrosive ions to the inside, delaying the diffusion of the corrosive medium and increasing the barrier property. In the initial stage of stent implantation, macrophages and bacteria will aggregate and enter the porous layer, causing inflammation and infection. The astragalus polysaccharide on the surface of the mineralized silk fiber and the copper-containing complex in the composite fiber cortex can play a good role in reducing inflammation and antibacterial. In addition, the apatite with bioactive ions (such as strontium, cerium, magnesium, calcium, or gallium) on the surface of the mineralized silk fiber has a significant induction effect on osteoblasts. Furthermore, the coating matrix material used is a natural polymer material and a positively charged polymer. The two can improve the bonding force between the porous layer and the dense layer by virtue of positive and negative electrostatic attraction and non-covalent interaction. In summary, the unique structure and multifunctional coating proposed by the present invention not only provide a relatively pure and stable microenvironment for the formation of bone tissue to promote the repair and regeneration of bone defects but also can play a good role in protecting the magnesium alloy matrix. Description of the Drawings

[0025] Figure 1 Schematic diagram of the structure of the multifunctional coating with a dense-porous double-layer structure on the surface of the magnesium alloy in Example 1;

[0026] Figure 2 Morphology diagram of the dense layer in the multifunctional coating prepared in Example 2;

[0027] Figure 3 Morphology diagram of the porous layer in the multifunctional coating prepared in Example 2;

[0028] Figure 4 Morphology diagram of the porous layer in the multifunctional coating prepared in Example 3;

[0029] Figure 5 Polarization curves of pure magnesium alloy, samples of Example 2 - Example 3, Comparative Example 1 and Comparative Example 3;

[0030] Figure 6 CCK-8 result diagrams of osteoblasts growing on pure magnesium alloy, Comparative Example 1 and Comparative Example 3, and samples of Example 1 - Example 3 for 1 day and 2 days;

[0031] Figure 7 Diagrams of the scavenging ability of samples of Comparative Example 5 - Comparative Example 6 and Example 1 - Example 3 against DPPH radicals. Detailed implementation manners

[0032] Next, the present invention will be further described in conjunction with specific embodiments and the accompanying drawings.

[0033] Example 1: As Figure 1 shown, in this example, a dense layer and a porous layer are successively constructed on the surface of a magnesium alloy. Among them, the dense layer is composed of a transition metal carbide / nitride / calcium silicate nanowire composite and carboxymethyl chitosan, and the porous layer is composed of a copper-containing complex / regenerated silk fibroin composite fiber, a mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on the surface, and chitosan. The thickness ratio of the dense layer to the porous layer is 1:1, and the thickness of the dense layer is about 180 ± 15 μm.

[0034] The preparation process includes the following steps:

[0035] (1) Select monolayer carbonitride metal oxide (MXene) and calcium silicate nanowires with a diameter of about 50 nm, mix the two according to a mass ratio of 1:1, heat-treat at 80 °C for 2 h to synthesize carbonitride metal oxide loaded with calcium silicate nanowires on the surface, dissolve carboxymethyl chitosan with a carboxylation degree of 80% in water to obtain a solution with a concentration of 2.0 wt.%. Mix the carbonitride metal oxide loaded with calcium silicate nanowires on the surface and the carboxymethyl chitosan solution according to a mass ratio of 100:1 to prepare a dense layer precursor solution.

[0036] (2) 1,4,7,10 - tetraazacyclododecane - 1,4,7,10 - tetraacetic acid reacts with copper chloride at a mass ratio of 1:1, a temperature of 100 °C, and a time of 0.5 h. After centrifugation and washing with water, a copper - containing complex is obtained. Using the copper - containing complex solution as the shell solution and the regenerated silk fibroin aqueous solution as the core spinning solution, a composite fiber mat is obtained through coaxial electrospinning technology. The parameters of coaxial electrospinning are as follows: the flow rate of the cortical solution is 1.5 ml / h, the flow rate of the core layer is 1.0 ml / h, and the voltage is 20 kV. After post - treatment, the fiber mat is cut into pieces with a size of 0.05 - 0.1 mm.

[0037] (3) By mechanical shearing, the degummed silk fibers are cut to a length of about 50 - 100 μm. The degummed silk fibers are alternately immersed in a 0.5 mol / l calcium chloride solution, a 0.2 mol / l sodium hydrogen phosphate solution, and a mixed solution of astragalus polysaccharide. The mixed solution of astragalus polysaccharide is a solution composed of astragalus polysaccharide, cerium nitrate, strontium nitrate, calcium nitrate, and diammonium hydrogen phosphate, and the molar ratio of the five is 1:1:1:1:1. The above solutions are alternately immersed for 3 rounds at 37 °C, and the immersion time for each solution is 10 minutes. After immersion, filtration and drying are carried out to obtain mineralized fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface.

[0038] (4) Chitosan with a degree of deacetylation ≥ 95% and a viscosity of 100 - 200 mPa·s is selected to prepare a solution with a concentration of 2 wt.%. The composite fiber mat and the mineralized silk fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface prepared in steps (2) and (3) are added to the chitosan solution. The mass ratio of the composite fiber mat, the mineralized silk fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface to chitosan is 1:1:4. After mixing, a porous layer precursor solution is prepared by magnetic stirring.

[0039] (5) The magnesium alloy is immersed in an 8 mol / l sodium hydroxide solution at a temperature of 60 °C for 6 hours. The dense layer precursor solution is coated on the alkali - heat - treated magnesium alloy substrate by spraying, dried to obtain a dense layer. Then, the porous layer precursor solution is sprayed onto the surface of the dense layer by spin - coating, and the sample is quickly immersed in liquid nitrogen, and then quickly immersed in a 0.3 mol / l cold NaOH ethanol solution (about - 20 °C). After rinsing with deionized water multiple times and freeze - drying, a porous layer is obtained.

[0040] (6) The material obtained in step (5) is immersed in a mixed solution of 50 mmol / L 1 - ethyl - (3 - dimethylaminopropyl) carbodiimide hydrochloride and 25 mmol / L N - hydroxysuccinimide at 4 °C for 8 h, then taken out and dried to obtain the product.

[0041] Example 2: In this example, a dense layer and a porous layer are sequentially constructed on the surface of a magnesium alloy. The dense layer is composed of a transition metal carbide / nitride / calcium silicate nanowire composite and carboxymethyl chitosan, and the porous layer is composed of a copper-containing complex / regenerated silk fibroin-gelatin composite fiber, a mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on the surface, and chitosan. The thickness ratio of the dense layer to the porous layer is 10:1.

[0042] The preparation process includes the following steps:

[0043] (1) Select a single-layer carbonitride metal oxide (MXene) and calcium silicate nanowires with a diameter of about 80 nm. Mix the two in a mass ratio of 1:3, perform hydrothermal treatment at a temperature of 100 °C for 1 h to synthesize carbonitride metal oxide loaded with calcium silicate nanowires on the surface. Dissolve carboxymethyl chitosan with a carboxylation degree of 85% in water to obtain a solution with a concentration of 4.0 wt.%. Mix the carbonitride metal oxide loaded with calcium silicate nanowires on the surface and the carboxymethyl chitosan solution in a mass ratio of 50:1 to prepare a precursor solution for the dense layer.

[0044] (2) React 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid with copper chloride, with a mass ratio of 1:3, at a temperature of 130 °C for 2 h, and perform centrifugation and washing with water to obtain a copper-containing complex. Use the copper-containing complex solution as the shell solution and an aqueous solution of regenerated silk fibroin and gelatin (with a mass ratio of 7:3) as the core spinning solution, and obtain a composite fiber felt through coaxial electrospinning technology. The parameters of coaxial electrospinning are: the flow rate of the cortical solution is 1.2 ml / h, the core flow rate is 0.8 ml / h, and the voltage is 18 kV; after post-treatment, cut the fiber felt into pieces with a size of 0.1 - 0.5 mm.

[0045] (3) Cut degummed silk fibers to a length of about 100 - 200 μm by mechanical shearing. Immerse the degummed silk fibers alternately in a mixed solution of 0.5 mol / l calcium chloride solution, 0.2 mol / l sodium hydrogen phosphate solution, and astragalus polysaccharide. The astragalus polysaccharide mixed solution is a solution composed of astragalus polysaccharide, cerium nitrate, strontium nitrate, calcium nitrate, and diammonium hydrogen phosphate, and the molar ratio of the five is 1.5:1.5:1.5:3:3. Immerse the above solution in cycles for 5 rounds at 37 °C, and the impregnation time for each solution is 20 minutes. After the impregnation is completed, perform filtration and drying to obtain mineralized fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface.

[0046] (4) Select chitosan with a degree of deacetylation ≥ 95% and a viscosity of 100 - 200 mPa·s, and prepare a solution with a concentration of 3 wt.%. Add the composite fiber mat prepared in steps (2) and (3) and the mineralized silk fiber surface-loaded with astragalus polysaccharide, strontium, and cerium ions into the chitosan solution. Among them, the mass ratio of the composite fiber mat, the mineralized silk fiber surface-loaded with astragalus polysaccharide, strontium, and cerium ions to chitosan is 1:2:4. After mixing, magnetically stir to obtain a porous layer precursor solution.

[0047] (5) Immerse the magnesium alloy in a 5 mol / l sodium hydroxide solution at 70 °C for 12 hours. Coat the alkali-heat-treated magnesium alloy substrate with the dense layer precursor solution by spraying method, and dry to obtain the dense layer. Then, spray the porous layer precursor solution onto the surface of the dense layer by spin coating method, and quickly immerse the sample in liquid nitrogen. Immediately immerse the obtained sample in a cold NaOH ethanol solution with a concentration of 0.5 mol / l (about -18 °C). After rinsing with deionized water multiple times, freeze-dry to obtain the porous layer.

[0048] (6) Immerse the material obtained in step (5) into a mixed solution of 75 mmol / L 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 35 mmol / L N-hydroxysuccinimide, and treat at 4 °C for 16 h, then take it out and dry.

[0049] Example 3: In this example, a dense layer and a porous layer are successively constructed on the surface of the magnesium alloy. Among them, the dense layer is composed of a transition metal carbide / nitride / calcium silicate nanowire composite and carboxymethyl chitosan, and the porous layer is composed of a copper-containing complex / regenerated silk fibroin-polyvinyl alcohol composite fiber, a mineralized silk fiber surface-loaded with bioactive metal ions and astragalus polysaccharide, and chitosan. The thickness ratio of the dense layer to the porous layer is 20:1.

[0050] The preparation process includes the following steps:

[0051] (1) Select single-layer carbonitride metal oxide (MXene) and calcium silicate nanowires with a diameter of about 100 nm, mix the two according to a mass ratio of 1:5, heat-treat at 120 °C for 2 h to synthesize carbonitride metal oxide surface-loaded with calcium silicate nanowires. Dissolve carboxymethyl chitosan with a carboxylation degree of 95% in water to obtain a solution with a concentration of 8.0 wt.%. Mix the carbonitride metal oxide surface-loaded with calcium silicate nanowires and the carboxymethyl chitosan solution according to a mass ratio of 10:1 to prepare a dense layer precursor solution.

[0052] (2) React 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid with copper chloride, with a mass ratio of the two of 1:5, at a temperature of 150 °C for 3 h, and obtain a copper-containing complex through centrifugation and washing with water. Use the copper-containing complex solution as the shell solution, and use regenerated silk fibroin and an aqueous solution of polyvinyl alcohol (with a mass ratio of the two of 7:3) as the core spinning solution. Through coaxial electrospinning technology, obtain a composite fiber mat. The parameters of coaxial electrospinning are: the flow rate of the cortical solution is 1.0 ml / h, the flow rate of the core layer is 0.7 ml / h, and the voltage is 16 kV; after post-treatment, cut the fiber mat into pieces with a size of 0.5 - 1.0 mm.

[0053] (3) By mechanical shearing, cut the degummed silk fibers to a length of about 200 - 300 μm. Immerse the degummed silk fibers alternately in a 0.5 mol / l calcium chloride solution, a 0.2 mol / l sodium hydrogen phosphate solution, and a mixed solution of astragalus polysaccharide. Among them, the mixed solution of astragalus polysaccharide is a solution composed of astragalus polysaccharide, cerium nitrate, strontium nitrate, calcium nitrate, and diammonium hydrogen phosphate, and the molar ratio of the five is 2:2:2:5:5. Immerse in the above solutions alternately for 5 rounds at 37 °C, and the immersion time for each solution is 30 minutes. After the immersion is completed, filter and dry to obtain mineralized fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface.

[0054] (4) Select chitosan with a deacetylation degree ≥ 95% and a viscosity of 100 - 200 mPa·s, and prepare a solution with a concentration of 5 wt.%. Add the composite fiber mat and the mineralized silk fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface prepared in steps (2) and (3) into the chitosan solution. Among them, the mass ratio of the composite fiber mat, the mineralized silk fibers with astragalus polysaccharide, strontium, and cerium ions loaded on the surface, and chitosan is 4:2:4. After mixing, stir magnetically to obtain a porous layer precursor solution.

[0055] (5) Immerse the magnesium alloy in a 3 mol / l sodium hydroxide solution at a temperature of 75 °C for 24 h. Use the spraying method to coat the dense layer precursor solution on the magnesium alloy substrate after alkali heat treatment, and dry to obtain a dense layer. Then use the spin-coating method to spray the porous layer precursor solution onto the surface of the dense layer, and quickly immerse the sample in liquid nitrogen. Then quickly immerse the obtained sample in a cold NaOH ethanol solution with a concentration of 1.0 mol / l (about -15 °C), rinse with deionized water multiple times, and freeze-dry to obtain a porous layer.

[0056] (6) Immerse the material obtained in step (5) in a mixed solution of 100 mmol / L 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 50 mmol / L N-hydroxysuccinimide, and treat at 4 °C for 24 h, then take out and dry.

[0057] Comparative Example 1: Only a dense layer was constructed on the magnesium alloy surface, and the remaining steps were the same as those in Example 2.

[0058] Comparative Example 2: Only a dense layer was constructed on the magnesium alloy surface. Among them, transition metal carbides / nitrides / calcium silicate nanowire composites were not added to the dense layer, and the remaining steps were the same as those in Example 2.

[0059] Comparative Example 3: Only a porous layer was constructed on the magnesium alloy surface, and the remaining steps were the same as those in Example 2.

[0060] Comparative Example 4: Only a porous layer was constructed on the magnesium alloy surface, and mineralized silk fibers loaded with astragalus polysaccharide, strontium, and cerium ions on the surface and electrospun fibers with a copper-containing complex in the cortex were not added. The remaining steps were the same as those in Example 2.

[0061] Comparative Example 5: A dense layer and a porous layer were constructed on the magnesium alloy surface. Among them, in the porous layer, only mineralized silk fibers loaded with astragalus polysaccharide, strontium, and cerium ions on the surface were added, and the remaining steps were the same as those in Example 2.

[0062] Comparative Example 6: A dense layer and a porous layer were constructed on the magnesium alloy surface. Among them, in the porous layer, only silk fibers (without load on the surface) were added, and the remaining steps were the same as those in Example 2.

[0063] Comparative Example 7: A dense layer and a porous layer were constructed on the magnesium alloy surface. Among them, in the porous layer, only electrospun fibers were added, and the remaining steps were the same as those in Example 2.

[0064] Comparative Example 8: A dense layer and a porous layer were constructed on the magnesium alloy surface. Among them, in the porous layer, only electrospun fibers were added, and at this time, the fiber cortex had no copper-containing complex. The remaining steps were the same as those in Example 2.

[0065] For the above-mentioned examples, Figure 2 and Figure 3 are the surface morphologies of the dense layer and the porous layer in the multifunctional coating prepared in Example 2, respectively. The results show that the surface of the dense layer presents a granular shape, and in the porous layer, electrospun fibers and degummed silk fibers penetrate the pore structure. Figure 4 is the surface morphology of the porous layer in the multifunctional coating prepared in Example 3. By comparing Figure 3 and Figure 4 , it can be clearly seen that by changing the content of composite fibers and mineralized silk fibers loaded with metal ions such as astragalus polysaccharide, strontium, and cerium on the surface, the pore size can be effectively regulated.

[0066] Figure 5Polarization curves of the samples of pure magnesium alloy, Examples 2 - 3, Comparative Example 1, and Comparative Example 3. It can be seen that covering the magnesium alloy surface with a dense layer alone (Comparative Example 1) and a porous layer alone (Comparative Example 3) can both increase the corrosion potential of the magnesium alloy, but the effect is limited. While covering both the dense layer and the porous layer simultaneously, the corrosion resistance of the magnesium alloy is improved, and with the increase in the total content of composite fibers and mineralized silk fibers surface - loaded with astragalus polysaccharide, strontium, and cerium ions, the corrosion resistance is enhanced.

[0067] Figure 6 CCK - 8 value diagrams of the samples of pure magnesium alloy, Comparative Example 1, Comparative Example 3, and Examples 1 - 3. It can be found that compared with pure magnesium alloy, a single dense layer, and a single porous layer, the samples with a composite double - layer are more conducive to the growth and proliferation of osteoblasts. In addition, from Examples 1 - 3, it shows that increasing the astragalus polysaccharide, cerium, strontium, and calcium ions loaded on the fiber surface helps to promote the proliferation of osteoblasts.

[0068] Figure 7 Diagrams of the DPPH free - radical scavenging ability of the samples of Comparative Example 5 - Material 6 and Examples 1 - 3. It can be seen that from Comparative Example 5 and Comparative Example 6, the antioxidant performance of the coating can be improved by loading astragalus polysaccharide on the silk fiber surface. From Examples 1 - 3, it can be known that with the increase in the content of silk fibers surface - loaded with astragalus polysaccharide, strontium, and cerium ions, the antioxidant performance of the composite coating gradually increases.

[0069] Tables 1 and 2 are respectively the test results of the antibacterial rates of the samples of Examples 1 - 3 and Comparative Examples 1 - 8. It can be found from the tables that in the dense layer, adding the MXene / calcium silicate nanowire composite can, to a certain extent, help improve the antibacterial property. In the porous layer, adding both mineralized silk fibers surface - loaded with astragalus polysaccharide, strontium, and cerium ions and electrospun fibers with a copper - containing complex in the cortex can help improve the antibacterial property of the samples, and among them, the antibacterial effect of the latter is more excellent. In the porous layer, with the increase in the content of both, the antibacterial property is continuously improved.

[0070] Table 1. Antibacterial test results of the samples obtained from Examples 1 - 3

[0071]

[0072] Table 2. Antibacterial test results of the samples obtained from Comparative Examples 1 - 8

[0073]

[0074] Table 3. Compressive strength and coating bonding strength results of the samples obtained from Examples 1 - 3

[0075] Example 1 Example 2 Example 3 Compressive strength (Mpa) 2.1 3.5 5.2 Bonding strength (Mpa) 1.3 1.5 1.8

[0076] Table 4. Compressive strength and coating bonding strength results of the samples obtained from Comparative Example 1 - Comparative Example 8

[0077]

[0078] Table 3 shows the compressive strength and coating bonding strength of the samples of Examples 1 - 3. It can be seen that as the content of mineralized silk fibers loaded with astragalus polysaccharide, strontium and cerium ions on the surface and the composite fibers with a copper complex-containing cortex increases, the compressive strength of the composite coating gradually increases. In addition, as the ratio of the thickness of the dense layer to the porous layer increases, the bonding strength between the coating and the substrate gradually increases.

[0079] Table 4 shows the compressive strength and coating bonding strength of the samples of Comparative Example 1 - Comparative Example 8. It can be seen that compared with the silk fibers without surface loading, the mineralized silk fibers loaded with astragalus polysaccharide, strontium and cerium ions on the surface are more helpful in improving the compressive strength of the scaffold. For the composite fibers, whether the cortex is a copper complex does not affect the compressive strength of the scaffold. In addition, the bonding strength between the single porous layer and the magnesium alloy substrate is small. In the absence of the dense layer, the greater the compressive strength of the porous layer, the smaller the bonding strength between the coating and the substrate.

Claims

1. A multifunctional coating with a dense-porous double-layer structure on the surface of a magnesium alloy, characterized in that, The multifunctional coating uses a magnesium alloy as the substrate, and a dense layer and a porous layer are sequentially stacked outward from the substrate. The dense layer is composed of a two-dimensional transition metal carbide / nitride with a two-dimensional layered structure, calcium silicate nanowires, and a positively charged polymer. The porous layer is composed of a copper-containing complex / bio-polymer composite fiber, a mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on the surface, and a natural polymer.

2. The multi-functional coating according to claim 1, wherein, The thickness ratio of the dense layer to the porous layer is (1 - 30):

1.

3. The multi-functional coating according to claim 1, wherein The mass ratio of the two-dimensional transition metal carbide / nitride to the calcium silicate nanowires is 1:1 - 5; the mass ratio of the copper-containing complex / bio-polymer composite fiber, the mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on the surface to the natural polymer is 1 - 4:1 - 2:4 - 10.

4. A method for preparing a multifunctional coating with a dense-porous double-layer structure on the surface of a magnesium alloy according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Mix a two-dimensional transition metal carbide / nitride with a two-dimensional layered structure and calcium silicate nanowires in a solvent, carry out a hydrothermal reaction, and after completion, dry it. Mix the obtained two-dimensional transition metal carbide / nitride loaded with calcium silicate nanowires with an aqueous solution of a positively charged polymer to prepare a dense layer precursor solution; (2) Through the coaxial electrospinning technique, prepare a copper-containing complex / bio-polymer composite fiber felt with a copper-containing complex as the skin layer and a bio-polymer as the core layer, cut it into pieces and set aside; (3) Immerse the degummed silk fibers alternately in a silk mineralization treatment solution and a mixed solution containing bioactive metal ions, a phosphorus source, and astragalus lipid polysaccharide. After the immersion is completed, filter and dry to obtain a mineralized silk fiber with bioactive metal ions and astragalus lipid polysaccharide loaded on the surface; (4) Add the cut copper-containing complex / bio-polymer composite fiber felt prepared in step (2) and the mineralized silk fiber with bioactive metal ions and astragalus polysaccharide loaded on the surface prepared in step (3) to a natural polymer solution, and stir to prepare a porous layer precursor solution; (5) Spray the dense layer precursor solution prepared in step (1) on the surface of the magnesium alloy after alkali heat treatment, dry to form a dense layer, then spin-coat the porous layer precursor solution prepared in step (4) on the dense layer. After completion, quickly immerse it in liquid nitrogen for freezing, and then immerse it in a low-temperature NaOH ethanol solution. After completion, remove, rinse, and freeze-dry to obtain a porous layer; (6) Activate the material prepared in step (5), and dry it to obtain a multifunctional coating with a dense-porous double-layer structure on the surface of the magnesium alloy.

5. The preparation method according to claim 4, characterized in that, In step (1), the two-dimensional transition metal carbide / nitride is a single layer; the diameter of the calcium silicate nanowires is 50 - 100 nm; the conditions for the hydrothermal treatment are: react at 60 - 120 °C for 0.5 - 2 h; the positively charged polymer includes one or more of carboxymethyl chitosan, quaternary ammonium salt chitosan, or polyethyleneimine, and the concentration of the aqueous solution of the positively charged polymer is 2.0 - 10.0 wt.%; the mass ratio of the positively charged polymer to the two-dimensional transition metal carbide / nitride loaded with calcium silicate nanowires is 100 - 10:

1.

6. The preparation method according to claim 4, wherein In step (2), the method for preparing the copper-containing complex is as follows: a complexing ligand and a copper salt are subjected to a complexation reaction in a solvent, and after completion, centrifugation and water washing are carried out to obtain the product; wherein, the mass ratio of the complexing ligand to the copper salt is 1:1-5; the complexing ligand is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, and the copper salt is copper chloride; the conditions for the complexation reaction are: reacting at 100-160 °C for 0.5-3 h; the biological macromolecule includes one or more of regenerated silk fibroin, chitosan, gelatin, polylactic acid, and polyvinyl alcohol.

7. The preparation method according to claim 4, characterized in that In step (3), the length of the degummed silk fiber is 20-300 μm; the silk mineralization treatment solution includes a calcium compound solution and a phosphorus compound solution; the bioactive metal ions include one or more of strontium, cerium, magnesium, calcium, or gallium; the molar ratio of the bioactive metal ions, the phosphorus source, and astragalus polysaccharide is 1-5:1-5:2-10; the number of cycles of alternate impregnation is 2-8 rounds, the impregnation temperature is 30-40 °C, and the impregnation time for each solution is 5-30 min.

8. The preparation method according to claim 4, characterized in that, In step (4), the length of the cut copper-containing complex / biological macromolecule composite fiber felt is 0.01-1 mm; the natural macromolecule includes one or more of chitosan, hyaluronic acid, pectin, collagen, gelatin, sodium alginate, and agarose, and the concentration of the natural macromolecule solution is 2.0-5.0 wt.%.

9. The preparation method according to claim 4, characterized in that, In step (5), the conditions for alkali heat treatment are: treating in a sodium hydroxide solution with a temperature of 60-80 °C and a concentration of 1-10 mol / l for 6-24 hours; the temperature of the low-temperature NaOH ethanol solution is -20 to -15 °C, and the concentration is 0.3-1 mol / L.

10. The preparation method according to claim 4, characterized in that, In step (6), the parameters for activation treatment are: treating in a mixed solution containing 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide at 4-6 °C for 6-24 h; the concentration of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride in the mixed solution is 50-100 mmol / l, and the concentration of N-hydroxysuccinimide in the mixed solution is 25-50 mmol / L.

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