A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting

Abstract

The present invention is applicable to the field of additive manufacturing technology, and provides a method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting, comprising the following steps: weighing raw materials according to the following mass percentages: Sr 1-3%, Zr 0.5-1.5%, Bi 0.2-1%, Si 0.5-2%, Ti 0.1-0.5%, and the balance being Mg, melting to form a uniform liquid alloy, and then spraying the liquid alloy with high-pressure argon gas to cool it to form powder particles, and screening to obtain magnesium alloy powder; designing the wall thickness and pore structure of the stent according to the size and blood flow characteristics of the blood vessel; laying the magnesium alloy powder on a substrate, designing a laser scanning path according to the structure of the stent, and adopting interlayer scanning to prepare a magnesium alloy stent; polishing the magnesium alloy stent, washing and drying it, then fluorinating the stent, and then washing and drying it by blowing. Without affecting the biocompatibility and mechanical strength of the magnesium alloy material, the present invention successfully prepares a vascular stent with good biodegradable characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and particularly relates to a method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting. Background Art

[0002] For cardiovascular diseases such as coronary heart disease and hypertension, vascular stents are used as an effective treatment means. The main materials of traditional vascular stents are metal materials such as stainless steel and cobalt alloy. These materials have high mechanical strength, but long-term presence in the body may cause complications such as thrombosis, in-stent restenosis, and chronic inflammatory reactions inside and outside the stent. To reduce these problems, in recent years, degradable metal materials, especially magnesium alloys, have gradually become the focus of research on vascular stent materials. Magnesium alloy materials have excellent biocompatibility, degradability, and good mechanical properties. Especially in the interaction with human tissues, the degradation process of magnesium can effectively reduce the adverse reactions that may be brought about by the long-term presence of metal stents in the body. However, the degradation rate of magnesium alloy materials in the body is relatively fast, which limits their application in vascular stents. To balance the degradation rate and mechanical properties, researchers have conducted extensive explorations in the composition, microstructure, and surface treatment of magnesium alloys and proposed various methods, but these methods still have many deficiencies in practical applications.

[0003] Laser powder bed melting (LPBF) technology, as an additive manufacturing process, has shown broad application prospects in the medical field. By precisely controlling the thermal energy input of the laser beam, this technology can layer by layer melt metal powder on the metal powder bed and finally obtain a three-dimensional structure with complex geometric shapes. Compared with traditional processing methods, LPBF has the following significant advantages: high-precision manufacturing: LPBF technology can achieve micron-level processing accuracy, can precisely control the microstructure and porosity of the stent, and meet the strict requirements of vascular stents for dimensional accuracy and mechanical properties; high material utilization rate: Since powder materials are used, the unmelted powder can be recycled and reused, with less material waste and relatively low cost; capable of manufacturing complex structures: LPBF technology can manufacture complex geometric structures such as porous, gradually changing porosity, and internal channels, and these structures are of great significance in improving the biocompatibility of vascular stents, promoting the growth of vascular endothelial cells, and reducing complications. Therefore, laser powder bed melting technology has great application potential in the preparation of magnesium alloy vascular stents and can effectively solve the problems of complex structures and performance optimization that are difficult to achieve by traditional manufacturing methods.

[0004] In the early stage, due to its high degradation rate and low mechanical strength, magnesium alloy materials were not widely used in the field of vascular stents. In the prior art, by adjusting the composition, microstructure and surface treatment methods of magnesium alloys, their mechanical properties and biocompatibility have been gradually improved. For example, adding zinc, calcium, rare earth elements, etc. can improve the mechanical properties and corrosion behavior of magnesium alloys; through surface coatings (such as polymer coatings, phosphating coatings, etc.), the degradation rate can be effectively controlled and the stability of vascular stents can be improved, such as patent applications CN108014379A, CN104189963A, CN114904052A, CN116370709A, CN103418035A, international patent WO2023151343(A1), WO2015172664(A1) and European Union patent EP3144018(A4), etc. At present, the main method for manufacturing magnesium alloy vascular stents is to first prepare magnesium alloy microtubes, and then perform laser cutting and laser engraving on the microtubes. Using the high energy density of the laser to cut and engrave the magnesium alloy material, and finally obtain a reticulated thin tube, such as patent applications CN109433841A, CN105964716A and CN101249286A, etc. However, the vascular stents obtained by this method have areas of oxide layer and thermal damage, which may make the surface quality uneven, and local overheating or ablation is likely to occur, resulting in unsatisfactory surface quality and low yield; in contrast, additive manufacturing technology provides higher flexibility and manufacturing precision, such as patent applications CN 101856723A and CN106620837A, etc., which disclose the forming methods for preparing magnesium alloy vascular stents using additive manufacturing technology. Nevertheless, there is still a lack of reliable data support for the mechanical properties, degradation rate and biocompatibility of the degradable magnesium alloy vascular stents prepared by the existing additive manufacturing technology; currently, the magnesium alloy stents prepared by laser powder bed melting still face the problem of too fast degradation rate, which may lead to premature failure of the stent and inability to effectively support blood vessels; at the same time, there is also the problem of insufficient mechanical strength, which cannot meet the high strength requirements of vascular stents. Summary of the Invention

[0005] An object of an embodiment of the present invention is to provide a method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting, aiming to solve the problems proposed in the above background technology.

[0006] The embodiment of the present invention is implemented as follows. A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting includes the following steps:

[0007] Preparation of magnesium alloy powder: Weigh the raw materials according to the following mass percentages: Sr 1-3%, Zr 0.5-1.5%, Bi 0.2-1%, Si 0.5-2%, Ti 0.1-0.5%, and the balance is Mg. Melt to form a uniform liquid alloy, and then use high-pressure argon gas to spray the liquid alloy to cool it to form powder particles, and screen to obtain magnesium alloy powder;

[0008] Stent structure design: Design the wall thickness and pore structure of the stent according to the size and blood flow characteristics of the blood vessel;

[0009] Laser powder bed melting: Lay the magnesium alloy powder on the substrate, design the laser scanning path according to the stent structure, and use interlayer scanning to prepare the magnesium alloy stent;

[0010] Surface treatment: Polish the magnesium alloy stent, wash and dry it, then fluorinate the stent, and then wash and blow dry.

[0011] Preferably, in the step of preparing the magnesium alloy powder, the melting temperature is 700-750 °C, and the particle size of the magnesium alloy powder obtained by screening is 30-60 μm.

[0012] Preferably, in the step of stent structure design, the porosity of the stent is 80-90%, and the wall thickness of the stent is 0.3-0.5 mm.

[0013] Preferably, in the step of laser powder bed melting, the magnesium alloy powder is laid on the substrate with a thickness of 30-50μm.

[0014] Preferably, in the step of laser powder bed melting, the interlayer scanning is specifically in the way of rotating 67° for each printed layer, and the layer thickness is 20-30 μm.

[0015] Preferably, in the step of laser powder bed melting, the heating temperature of the substrate is 400-450 °C.

[0016] Preferably, the parameters of the laser powder bed melting are: laser power 50-100 w, scanning speed 200-600mm / s, scanning spacing 80-100 μm;

[0017] The parameters of the outer contour are: laser power 40-50 w, scanning speed 400-600 mm / s.

[0018] Preferably, in the step of surface treatment, the polishing treatment is specifically to polish the magnesium alloy stent with a phosphoric acid solution for 300-350 s.

[0019] Preferably, in the surface treatment step, the fluorination treatment is specifically as follows: the magnesium alloy stent is immersed in hydrofluoric acid for 12 - 24 h, and a shaker is used to shake it to make the fluorination uniform, forming a layer of MgF2 film on the surface of the magnesium alloy stent. Then, it is placed in a supersaturated hydroxyapatite solution and treated with a shaker for 24 - 48 h.

[0020] Another object of the embodiment of the present invention is to provide a degradable magnesium alloy vascular stent prepared by the above method.

[0021] A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting provided by the embodiment of the present invention obtains excellent mechanical properties and an ideal controllable degradation rate by reasonably designing the alloy composition, controlling the process parameters during laser printing, and optimizing the surface treatment technology. This method can successfully prepare a vascular stent with good biodegradation characteristics without affecting the biocompatibility and mechanical strength of the magnesium alloy material. By precisely controlling the porosity and structural morphology of the stent through the laser powder bed melting process, the compressive strength, degradability, and biocompatibility of the stent are further improved. Compared with the traditional stent preparation method, the stent prepared by the embodiment of the present invention can be stably degraded in vivo, while causing little irritation to the vascular inner wall, reducing the risk of inflammatory reaction and foreign body rejection, thereby enhancing the clinical application effect after implantation. Description of the Drawings

[0022] Figure 1 It is the design drawing of the magnesium alloy vascular stent provided by Embodiment 1 of the present invention;

[0023] Figure 2 It is the morphology diagram of the degradable magnesium alloy vascular stent prepared in Embodiment 1 of the present invention;

[0024] Figure 3 It is the mechanical property result of the degradable magnesium alloy vascular stent prepared in Embodiment 3 of the present invention;

[0025] Figure 4 It is the corrosion resistance result of the degradable magnesium alloy vascular stent prepared in Embodiment 3 of the present invention.

[0026] Figure 5 It is the cell survival rate result of the degradable magnesium alloy vascular stent prepared in Embodiment 3 of the present invention;

[0027] Figure 6 It is the hemolysis rate result of the degradable magnesium alloy vascular stent prepared in Embodiment 3 of the present invention. Detailed Embodiments

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting, comprising the following steps:

[0030] First step, preparing magnesium alloy powder: The magnesium alloy is composed of magnesium, strontium, zirconium, bismuth, silicon, and titanium elements, and its composition is calculated by mass percentage (Wt / %): strontium (Sr) 1-3, zirconium (Zr) 0.5-1.5, bismuth (Bi) 0.2-1, silicon (Si) 0.5-2, titanium (Ti) 0.1-0.5, and the balance is made up of magnesium (Mg). The purity of the used metallic magnesium, strontium, zirconium, bismuth, silicon, and titanium is greater than 99.99%; put it into an electric furnace for melting, and the melting temperature is generally controlled at 700-750 °C. At this temperature, the alloy components will be fully dissolved to form a uniform liquid alloy. During the melting process, an appropriate amount of degassing agent is added to remove gas impurities in the solution, and the alloy is protected by furnace gas to avoid reaction with oxygen in the air; then, high-pressure argon gas is used to spray the liquid alloy, and it is rapidly cooled to form fine powder particles, and magnesium alloy powder with a particle size range of 30-60 μm is screened out;

[0031] Second step, stent structure design: The design of the stent should conform to the anatomical characteristics of the human blood vessel to ensure its correct positioning in the blood vessel and sufficient mechanical support. According to the size and blood flow characteristics of the blood vessel, the wall thickness and pore structure of the stent are designed. The wall thickness is 0.3-0.5 mm, and the porosity should be between 80-90% to promote blood circulation and provide sufficient biodegradation space. The included angle between the support unit and the axis should not be greater than 45°;

[0032] Third step, laser powder bed melting: The prepared magnesium alloy powder is evenly laid on the substrate to ensure the uniformity of the magnesium alloy layer, and the thickness is controlled at 30-50 μm. According to the stent structure design, the laser scanning path is determined, and a strategy of rotating 67° for each printed layer is adopted for interlayer scanning, and the layer thickness is 20-30 μm to ensure the uniform melting and densification of the material. During the laser powder bed melting process, ultra-high purity argon gas is used for protection, and the substrate heating temperature is maintained at 400-450 °C; the laser powder bed melting process parameters are: laser power 50-100 w, scanning speed 200-600 mm / s, scanning spacing 80-100 μm; in addition, the outer contour is scanned once with a laser power of 40-50 w and a scanning speed of 400-600 mm / s to further improve the printing quality and accuracy;

[0033] Step 4, Surface treatment: The magnesium alloy stent is polished using a 5% phosphoric acid solution for 300 s. Subsequently, the polished stent is thoroughly rinsed by shaking in absolute ethanol and then fully dried in a drying oven. Then, the magnesium alloy stent is immersed in 35% hydrofluoric acid for 12 - 24 h and shaken on a shaker to ensure uniform fluorination, forming a MgF2 film layer on the stent surface. Next, the stent is placed in a supersaturated hydroxyapatite solution and shaken on a shaker for 24 - 48 h, rinsed with deionized water and absolute ethanol, and dried. Through surface treatment, the corrosion resistance and biocompatibility of the stent are enhanced, and the degradation rate of the magnesium alloy is retarded to ensure the quality and function of the final stent.

[0034] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0035] Example 1, A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting, comprising the following steps:

[0036] Step 1, Preparation of magnesium alloy powder: The composition of the magnesium alloy is by mass percentage (Wt / %): strontium (Sr) 1, zirconium (Zr) 0.5, bismuth (Bi) 1, silicon (Si) 0.5, titanium (Ti) 0.5, and the balance is made up of magnesium (Mg). It is put into an electric furnace for melting, and the melting temperature is controlled at 700 - 750 °C. Then, high-pressure argon gas is used to spray the liquid alloy, and it is rapidly cooled to form fine powder particles. Magnesium alloy powder with a particle size range of 30 - 60 μm is screened out.

[0037] Step 2, Stent structure design: The wall thickness of the stent is 0.5 mm, the porosity is 85%, and the angle between the support unit and the axis is not greater than 45°. Specifically, as shown in Figure 1 shown;

[0038] Step 3, Laser powder bed melting: The prepared magnesium alloy powder is evenly spread on the substrate with a thickness controlled at 30 - 50 μm. According to the stent structure design, the laser scanning path is determined, and a strategy of rotating 67° for each printed layer is adopted for interlayer scanning. The layer thickness is 30 μm, and ultra-high purity argon gas is used for protection during the laser powder bed melting process. The heating temperature of the substrate is maintained at 420 °C. The process parameters of the laser powder bed melting are: laser power 60 w, scanning speed 200 mm / s, and scanning spacing 80 μm. In addition, the outer contour is scanned once using a process with a laser power of 40 w and a scanning speed of 400 mm / s.

[0039] Step 4. Surface treatment: The magnesium alloy stent is polished with a 5% phosphoric acid solution for 300 s. Subsequently, the polished stent is thoroughly washed by shaking in absolute ethanol and then fully dried in a drying oven. Then, the magnesium alloy stent is immersed in 35% hydrofluoric acid for 15 h and shaken on a shaker to make the fluorination uniform, so that a MgF2 film layer is formed on the surface of the stent. Then, the stent is placed in a supersaturated hydroxyapatite solution and shaken on a shaker for 48 h, washed with deionized water and absolute ethanol, and dried to obtain a degradable magnesium alloy vascular stent, whose morphology is as Figure 2 shown.

[0040] Example 2: Compared with Example 1, the difference is only that the magnesium alloy composition by mass percentage (Wt / %) is strontium (Sr) 2, zirconium (Zr) 0.5, bismuth (Bi) 1, silicon (Si) 1, titanium (Ti) 0.25, and the balance is made up with magnesium (Mg). Other steps and parameters are the same as those in Example 1.

[0041] Example 3: Compared with Example 1, the difference is only that the magnesium alloy composition by mass percentage (Wt / %) is strontium (Sr) 3, zirconium (Zr) 1, bismuth (Bi) 0.5, silicon (Si) 2, titanium (Ti) 0.1, and the balance is made up with magnesium (Mg). Other steps and parameters are the same as those in Example 1.

[0042] Example 4: Compared with Example 1, the difference is only that the magnesium alloy composition by mass percentage (Wt / %) is strontium (Sr) 1, zirconium (Zr) 1, bismuth (Bi) 0.5, silicon (Si) 0.5, titanium (Ti) 0.5, and the balance is made up with magnesium (Mg). Other steps and parameters are the same as those in Example 1.

[0043] Example 5: Compared with Example 1, the difference is only that the magnesium alloy composition by mass percentage (Wt / %) is strontium (Sr) 2, zirconium (Zr) 1.5, bismuth (Bi) 0.2, silicon (Si) 1, titanium (Ti) 0.25, and the balance is made up with magnesium (Mg). Other steps and parameters are the same as those in Example 1.

[0044] Example 6: Compared with Example 1, the difference is only that the magnesium alloy composition by mass percentage (Wt / %) is strontium (Sr) 3, zirconium (Zr) 1.5, bismuth (Bi) 0.2, silicon (Si) 2, titanium (Ti) 0.1, and the balance is made up with magnesium (Mg). Other steps and parameters are the same as those in Example 1.

[0045] Performance test:

[0046] The samples prepared in Example 3 are tested for mechanical properties, corrosion resistance and biocompatibility. The results of tensile strength and elongation are as Figure 3 shown, and the degradation rate in a simulated blood environment is as Figure 4As shown, the cytotoxicity test results of Example 3 are compared with those of the untreated vascular stent on the surface Figure 5 As shown, the hemolysis test results are compared as Figure 6 As shown;

[0047] The samples prepared from other examples were tested respectively, and the results are summarized in Table 1 as follows:

[0048] Table 1

[0049] ;

[0050] It can be seen from Table 1 that the samples prepared in the embodiments of the present invention have a tensile strength of 300-322 MPa, an elongation rate of 17-22.4%, good mechanical properties, a degradation rate of 0.4-0.5 mm / y in a simulated blood environment, good corrosion resistance, can be slowly degraded in vivo, the cell survival rate after soaking for 7 days is 96-99%, and the hemolysis rate after incubation in blood at 37°C for 1 hour is 2.8-3.2%, having excellent biocompatibility.

[0051] In summary, the method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting provided in the embodiments of the present invention obtains a vascular stent with excellent mechanical properties, a controllable degradation rate and good biocompatibility through the composition design of the magnesium alloy material, controlling the process parameters during laser printing and surface treatment, and solves the following problems:

[0052] The problem of insufficient mechanical properties of the magnesium alloy vascular stent. Traditional magnesium alloy vascular stents may have problems with insufficient mechanical properties and cannot provide sufficient support force, resulting in possible rupture or excessive deformation of the vascular stent after implantation. Through the laser powder bed melting technology provided in the embodiments of the present invention, the alloy composition and microstructure of the magnesium alloy can be precisely controlled to optimize its mechanical properties and ensure the stability and effectiveness of the stent after implantation;

[0053] The problem of too fast or too slow degradation rate of the magnesium alloy vascular stent. Too fast degradation will cause the stent to fail before vascular repair, and too slow degradation may cause foreign body reactions or thrombosis in the blood vessel. In the embodiments of the present invention, the microstructure of the magnesium alloy is precisely regulated by laser powder bed melting technology, and the degradation rate is optimized through surface treatment to synchronize it with the vascular repair process, thereby avoiding the problems of too fast or too slow degradation;

[0054] The surface of the magnesium alloy stent may have problems of uneven roughness and corrosiveness, which affect the bonding between the stent and the blood vessel wall, resulting in poor biocompatibility and even triggering immune reactions or inflammation. In the embodiments of the present invention, by optimizing the surface roughness of the stent and adopting an appropriate post-treatment process, the vascular stent helps the attachment and growth of vascular endothelium, improves the bonding between the stent and the blood vessel wall, thereby enhancing its biocompatibility, reducing immune reactions and inflammatory reactions, and reducing the risk of secondary surgery.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting, characterized in that: The following steps are involved: Preparation of magnesium alloy powder: weighing raw materials according to the following mass percentages: Sr 1-3%, Zr 0.5-1.5%, Bi 0.2-1%, Si 0.5-2%, Ti 0.1-0.5%, and the balance Mg, smelting to form a uniform liquid alloy, then spraying the liquid alloy with high-pressure argon gas, cooling it to form powder particles, and screening to obtain magnesium alloy powder; Stent structure design: Design the stent wall thickness and pore structure according to the size of the blood vessel and blood flow characteristics; Laser powder bed melting: magnesium alloy powder is laid on a substrate, the laser scanning path is designed according to the structure of the bracket, and interlayer scanning is used to prepare the magnesium alloy bracket; Surface treatment: The magnesium alloy stent is polished, cleaned and dried, then fluorinated, cleaned and dried; In the step of designing the support structure, the porosity of the support is 80-90%, and the wall thickness of the support is 0.3-0.5 mm; The parameters of the laser powder bed melting are: laser power 50-100 W, scanning speed 200-600 mm / s, scanning spacing 80-100 μm; The parameters of the outer contour are: laser power 40-50 W, scanning speed 400-600 mm / s.

2. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the step of preparing the magnesium alloy powder, the smelting temperature is 700-750° C., and the particle size of the magnesium alloy powder obtained by screening is 30-60 μm.

3. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the step of laser powder bed melting, the magnesium alloy powder is laid on a substrate with a thickness of 30-50 μm.

4. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the step of laser powder bed melting, the interlayer scanning is specifically a method of rotating 67° for each printed layer, and the layer thickness is 20-30 μm.

5. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the step of laser powder bed melting, the heating temperature of the substrate is 400-450°C.

6. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the step of surface treatment, the polishing treatment is specifically to polish the magnesium alloy stent with a phosphoric acid solution for 300-350 seconds.

7. The method for preparing a degradable magnesium alloy vascular stent by laser powder bed melting according to claim 1, characterized in that: In the surface treatment step, the fluorination treatment is specifically as follows: the magnesium alloy stent is immersed in hydrofluoric acid for 12-24 hours, and shaken with a shaker to make the fluorination uniform, forming a layer of MgF2 film on the surface of the magnesium alloy stent, and then placed in a supersaturated hydroxyapatite solution, and shaken with a shaker for 24-48 hours.

8. A degradable magnesium alloy vascular stent, characterized in that: It is prepared by the method described in any one of claims 1 to 7.

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