A pickling film coating method for preparing a fishnet-shaped magnesium alloy stent by selective laser melting forming

Abstract

This invention discloses an acid pickling and coating method for selective laser melting (SLM) forming of a fishing net-shaped magnesium alloy scaffold, belonging to the field of scaffold manufacturing technology. The method includes the following steps: S1: Generating a printing model of the magnesium alloy scaffold using modeling software and printing it to obtain a first scaffold prototype; S2: Preparing an acid pickling solution, wiping the first scaffold prototype, placing it in an ultrasonic cleaning tank containing the acid pickling solution, performing ultrasonic acid pickling, followed by deacidification cleaning and drying to obtain a second scaffold prototype; S3: Preparing a coating solution, using a lifting device to fix the second scaffold prototype above a container containing the coating solution and uniformly raising and lowering it, obtaining a third scaffold prototype after multiple raising and lowering operations; S4: Vacuum drying the coated third scaffold prototype to form the final magnesium alloy scaffold. This method solves the problems of unreasonable surface impurity removal and poor coating uniformity in magnesium alloy scaffolds prepared by SLM.

Description

Technical Field

[0001] This invention relates to the field of stent manufacturing technology, specifically to an acid pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy stent. Background Technology

[0002] With the rapid development of medical materials and molding technologies, metal stents are increasingly used in minimally invasive treatments. Commercially available AZ31 magnesium alloy, due to its excellent biocompatibility, controllable degradation rate, and mechanical properties that match human tissue, has become one of the core stent materials for biodegradable medical stents. Selective laser melting (SLM) technology, as the mainstream process for metal 3D printing, effectively solves the industry pain points of "cumbersome steps, low precision, and poor consistency" in the traditional processing of complex stent structures, significantly simplifying the manufacturing process and improving production efficiency.

[0003] However, the surface of the magnesium alloy support after SLM forming has inherent defects: unmelted AZ31 magnesium alloy powder particles during the forming process adhere firmly to the wire surface and nodes. Simultaneously, high-temperature forming results in a dense oxide layer on the surface. The presence of these impurities directly affects the bonding effect between the subsequent coating and the support. Currently, the commonly used surface cleaning method in the industry is anhydrous ethanol ultrasonic cleaning, but its limitations are significant: even with extended ultrasonic time, only surface dust and a small amount of loosely attached particles can be removed; the firmly attached unmelted particles and oxide layer cannot be peeled off. Residual impurities become "obstacles" in the coating process, preventing the PLA / PLGA coating from spreading evenly.

[0004] To address the issue of surface impurities, pickling processes have been gradually adopted. However, existing technologies have significant shortcomings: First, there is a lack of suitable pickling processes for complex scaffolds formed by integrated SLM molding, leading to haphazard parameter selection. Second, the positive impact of residual particles on the coating effect has not been considered, and the effect of pickling on coating has not been systematically analyzed, resulting in a lack of basis for process optimization. Furthermore, research on the compatibility of existing coating processes with the scaffold surface condition is insufficient: PLA and PLGA, as biocompatible coating materials, exhibit bonding strength with magnesium alloy scaffolds that depends not only on surface cleanliness but also on surface microstructure. Surfaces that are too smooth or contain excessive impurities cannot achieve uniform coating and tight bonding, thus affecting the scaffold's performance and lifespan. Therefore, it is urgent to establish an optimized preparation-pickling-coating method based on "SLM molding-surface cleaning-lift coating" to fully leverage the advantages of SLM technology and solve core problems such as the difficulty in preparing complex structures, inadequate surface impurity removal, and poor coating uniformity. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the issue of unreasonable removal of surface impurities and poor coating uniformity in magnesium alloy scaffolds prepared by SLM.

[0006] A pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy scaffold includes the following steps: S1: Use modeling software to generate a printing model of the magnesium alloy bracket, and use a selective laser melting and forming equipment to perform laser printing according to the printing model to obtain a first bracket prototype with a cylindrical fishing net shape; S2: Prepare the pickling solution. After wiping the first stent body, place it in an ultrasonic cleaning tank containing the pickling solution for ultrasonic pickling treatment. Then, perform deacidification cleaning and drying to obtain the second stent body. After ultrasonic pickling treatment, deacidification cleaning and drying, a small number of tiny particles remain on the surface of the second stent body. The pickling solution includes N parts of 650ml phosphoric acid, N parts of 350ml glycerol and N parts of 0.6g citric acid powder. The pickling treatment time is 25min-30min and the pickling solution is kept at a constant temperature of 40-50℃. Wherein, N>0. S3: Prepare the coating solution. Use a lifting device to fix the second support body above the container containing the coating solution and move the second support body up and down at a uniform speed. The central axis of the second support body, which has a cylindrical structure, is perpendicular to the surface of the coating solution. During coating, each lifting and lowering will cause the second support body to be completely immersed in the coating solution for a period of time before being removed from the coating solution, so that the coating solution can adhere to the microparticles. After 5-10 lifting and lowering cycles, a third support body is obtained. The period of time is 5-10 seconds. The interval between two adjacent lifting and lowering cycles is 120-180 seconds. After each lifting and lowering cycle, the third support body is dried without wind during the interval. The coating solution needs to be in M ​​parts. Each part of the coating solution includes 1g PLA or 1g PLGA and 20ml dichloromethane solvent, where M>0. S4: Vacuum drying is performed on the third scaffold prototype after the coating is completed to form the final magnesium alloy scaffold.

[0007] As a preferred embodiment of the present invention, the magnesium alloy support includes S first magnesium alloy wires and L second magnesium alloy wires. The S first magnesium alloy wires are uniformly arranged in a clockwise rotation around the z-axis of a spatial rectangular coordinate system, and the L second magnesium alloy wires are uniformly arranged in a counterclockwise rotation around the same axis. Each first magnesium alloy wire is cross-connected with each second magnesium alloy wire to form a cylindrical fishing net-shaped support with a diameter of 10mm-20mm and a height of 20mm-40mm, wherein the sum of S and L is in the range of 20-24.

[0008] As a preferred embodiment of the present invention, the first magnesium alloy wire and the second magnesium alloy wire are made of the same material and are both commercial AZ31 magnesium alloy. The cross-section of the first magnesium alloy wire and the second magnesium alloy wire are both circular and the diameter is 0.2-0.4 mm.

[0009] As a preferred embodiment of the present invention, the preparation of the pickling solution in S2 specifically includes: N parts of 650 ml of the phosphoric acid and N parts of 350 ml of glycerol are poured into a corrosion-resistant container to form a mixture. The mixture is stirred at 25-30°C at a stirring speed of 300-500 r / min for 5-10 min. Then, N parts of 0.6 g of citric acid powder are added to the mixture and stirring is continued for 10-15 min to form the pickling solution.

[0010] As a preferred embodiment of the present invention, the ultrasonic cleaning tank in the ultrasonic acid pickling process has an ultrasonic power of 300-400W and an ultrasonic frequency of 40-60kHz.

[0011] As a preferred embodiment of the present invention, the step of further deacidification, cleaning, and drying in S2 to obtain the second scaffold body specifically includes: The first stent, after undergoing ultrasonic acid pickling, is placed in an ultrasonic cleaning tank containing anhydrous ethanol for ultrasonic cleaning. After ultrasonic cleaning for 2-4 minutes, it is removed and dried to obtain the second stent.

[0012] As a preferred embodiment of the present invention, the preparation of the coating liquid in step S3 specifically includes: Prepare M portions of the coating solution. For each portion of the coating solution, pour 20 ml of the dichloromethane solvent into a light-proof and corrosion-resistant container, then add 1 g PLA or 1 g PLGA and mix and stir in a light-proof environment. The stirring speed during the light-proof mixing and stirring is 200 r / min. After mixing and stirring in a light-proof environment for 30 min to 60 min, the coating solution is obtained.

[0013] As a preferred embodiment of the present invention, the lifting rate during the lifting process is 5-8 mm / s.

[0014] As a preferred embodiment of the present invention, the interval between two adjacent lifting and lowering operations in S3 is 120s-180s, specifically including: The interval between two consecutive lifting and lowering operations is 120s-180s, and the coating liquid is stirred during the interval for 1-2 minutes.

[0015] As a preferred embodiment of the present invention, step S4, which involves vacuum drying of the third scaffold substrate after coating to form the final magnesium alloy scaffold, specifically includes: The third scaffold, after being coated, is placed in a vacuum drying oven and dried at 40°C under a vacuum of less than 10 Pa for 2-4 hours.

[0016] The beneficial effects of this invention are reflected in: Optimize surface cleaning and coating adaptation process: Overcome the limitation of existing ethanol ultrasonic cleaning which can only remove dust. Based on the magnesium alloy scaffold prepared by SLM, the optimal pickling time for the pickling solution corresponding to the magnesium alloy scaffold adapted to PLA / PLGA coating is obtained through the process of "wiping followed by ultrasonic pickling-deacid cleaning-drying" and experimental comparison results. This allows the magnesium alloy scaffold to remove most of the harmful impurities (large particles, oxide layer) while retaining an appropriate amount of small particles as anchor points for coating.

[0017] The coating-assisted mechanism of residual particles was revealed: it was found that a small number of tiny residual particles can slow down the flow of solution through the "anchoring effect" and promote uniform coating adhesion. The coating is highly repeatable, and the prepared coated magnesium alloy scaffold has a coating coverage of ≥95% with no obvious defects, which can meet the needs of high-precision medical and industrial applications. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a stereomicroscopic image of the surface of the magnesium alloy support without acid washing (only ultrasonic cleaning with ethanol) before the coating of the present invention; Figure 3 This is a stereomicroscopic image of the magnesium alloy support surface after 20 minutes of acid pickling without coating according to the present invention; Figure 4 This is a stereomicroscopic image of the magnesium alloy support surface after 30 minutes of acid pickling without coating according to the present invention; Figure 5 This is a stereomicroscopic image of the magnesium alloy support surface after 40 minutes of acid pickling without coating according to the present invention; Figure 6 This is a stereomicroscope photograph of the un-acid-washed support after direct coating according to the present invention; Figure 7 This is a stereomicroscope image of the support after acid washing for 20 minutes and subsequent coating according to the present invention; Figure 8 This is a stereomicroscope image of the support after acid washing for 30 minutes and subsequent coating according to the present invention; Figure 9 This is a stereomicroscope image of the support after acid washing for 40 minutes and subsequent coating. Detailed Implementation

[0019] The invention will now be described in further detail with reference to the accompanying drawings.

[0020] Combined with appendix Figure 1 As shown, an acid pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support includes the following steps: S1: A printing model of the magnesium alloy support is generated using modeling software, and a selective laser melting forming device is used to perform laser printing based on the printing model to obtain a first support prototype with a radial array of straight wires in a cylindrical fishing net shape. The magnesium alloy support includes S first magnesium alloy wires and L second magnesium alloy wires. The S first magnesium alloy wires are uniformly arranged in a clockwise rotation around the z-axis of a spatial rectangular coordinate system, and the L second magnesium alloy wires are uniformly arranged in a counterclockwise rotation around the same axis. Each first magnesium alloy wire is cross-connected with each second magnesium alloy wire to form a cylindrical fishing net-shaped support with a diameter of 10mm-20mm and a height of 20mm-40mm. The sum of S and L is in the range of 20-24, where S=L, and both S and L are integers. Furthermore, all the wires are evenly and equidistantly distributed radially around the central axis of the cylindrical support. Each wire extends spirally along the axial direction of the cylinder (parallel to the z-axis of the spatial rectangular coordinate system), and its two ends are integrally fused with the annular base at the top and bottom of the support to form a complete cylindrical support body. Preferably, the total number of the first and second magnesium alloy wires is 22, i.e., S=L=11. The diameter of the cylinder is 10-20mm and the height is 20-40mm. Preferably, the diameter is 15mm and the height is 30mm. On the same radial cross section, the shortest distance between two adjacent wires is 1.5mm-2.0mm. The angle between the magnesium alloy wire and the horizontal plane is 60°. The first and second magnesium alloy wires are made of the same material and are both commercial AZ31 magnesium alloy. They are integrally formed without splicing nodes. The cross section of the first and second magnesium alloy wires is circular and the diameter is 0.2-0.4mm. Preferably, the diameter of the magnesium alloy wire is 0.3mm. Specifically: S1.1: Using modeling software, a printed model of the magnesium alloy stent is generated based on the structural model determined by the stent. SolidWorks software is selected, and a three-dimensional model of the magnesium alloy stent is established according to the actual application requirements of medical stents. The magnesium alloy stent is a cylindrical, net-shaped stent with the following core parameters: cylinder diameter 10-20mm, height 20-40mm, preferably 15mm in diameter and 30mm in height. There are 22 magnesium alloy wires, evenly distributed around the central axis of the cylinder, with a projection distance of 1.5-2.0mm between adjacent wires on the cross-section of the cylinder. The cross-section of the cylinder is a circular cross-section perpendicular to the central axis of the magnesium alloy stent (i.e., the diameter of the stent). The projection spacing of the cross section is 1.5-2.0mm. Specifically, since the magnesium alloy wires are distributed in an inclined manner with the central axis of the cylinder as the center (with an angle of 60° with the forming substrate, that is, the angle between all wires and the forming substrate is 60°), each wire (space curve) is vertically projected onto the above circular cross section. Its projection shape is "radial line segment extending from the center of the cross section to the circumference". The shortest straight line distance between the above projection line segments of two adjacent first magnesium alloy wires or second magnesium alloy wires on the circular cross section is 1.5-2.0mm. The wire cross connection node adopts an integrated welding design, and the overall dimensional tolerance is controlled within ±0.1mm. A standard model file in STL format is generated. S1.2: Use slicing software to slice the printing model and generate a printing file; S1.3: Select commercial AZ31 magnesium alloy powder with a particle size of <53μm, uniformly fill it into the material cylinder of the selective laser melting and forming equipment, and simultaneously import the printing file to complete the pre-adjustment and calibration of core parameters such as laser power and scanning rate to ensure stable operation of the equipment; S1.4: Start the selected area laser melting and forming equipment, and introduce argon gas with a purity of ≥99.99% into the forming chamber as a protective gas. Continue to introduce argon gas until the oxygen content in the chamber is lower than 300ppm. Set the core forming parameters according to the printing file, including laser power of 85-95W, scanning rate of 1000-1100mm / s, and spot diameter of 130-140μm. Melt the magnesium alloy powder point by point with the laser and stack it layer by layer according to the slicing path. After every 10 layers of printing, observe the forming quality. If defects such as wire deviation or porosity are found, adjust the powder spreading rate or laser power in time to correct them. After forming is completed, keep the protective gas in the state. After the first support body cools naturally in the chamber, remove it. S2: Prepare the pickling solution. After wiping the first stent body, place it in an ultrasonic cleaning tank containing the pickling solution for ultrasonic pickling treatment. Then, perform deacidification cleaning and drying to obtain the second stent body. After ultrasonic pickling treatment, deacidification cleaning and drying, a small number of tiny particles remain on the surface of the second stent body. The pickling solution includes N parts of 650ml phosphoric acid, N parts of 350ml glycerol and N parts of 0.6g citric acid powder. The pickling treatment time is 25min-30min and the pickling solution is kept at a constant temperature of 40-50℃. Wherein, N>0. Specifically: S2.1: Prepare the pickling solution by pouring N parts of 650ml of the phosphoric acid and N parts of 350ml of glycerol into a corrosion-resistant container to form a mixture. Stir the mixture at 25-30°C to ensure thorough mixing. The stirring speed is 300-500r / min and the stirring time is 5min-10min, preferably 10min. Then, add N parts of 0.6g of citric acid powder to the mixture and continue stirring for 10min-15min to form the pickling solution. Preferably, the stirring time is 15min. The citric acid powder is added slowly, and stirring for 15min ensures complete dissolution of the citric acid, thereby forming a homogeneous, stable, and precipitate-free pickling solution. Wherein, N>0. S2.2: Pour the pickling solution into an ultrasonic cleaning tank and heat the pickling solution to 50°C using a constant temperature water bath to ensure a constant temperature during the pickling process; S2.3: The first stent body is wiped with a lint-free cloth soaked in anhydrous ethanol to remove surface dust and loose attachments. After wiping, the first stent body is placed in an ultrasonic cleaning tank containing pickling solution for pickling. In the ultrasonic pickling process, the ultrasonic cleaning tank has an ultrasonic power of 300-400W and an ultrasonic frequency of 40-60kHz, preferably 40kHz. The pickling time is 30min. During the pickling process, the first stent body is ensured to be completely immersed in the pickling solution. The phosphoric acid, glycerol, and citric acid are selected to dissolve the oxide layer and particles, glycerol adjusts the corrosion rate, and citric acid optimizes the surface smoothness. S2.4: The first stent body after ultrasonic acid washing is placed in an ultrasonic cleaning tank containing anhydrous ethanol for ultrasonic cleaning. After ultrasonic cleaning for 2-4 minutes, it is taken out and dried to obtain the second stent body. Preferably, after ultrasonic cleaning for 3 minutes, it is taken out and dried to obtain the second stent body. The transfer of the first stent body needs to be done quickly. Through ultrasonic cleaning, the residual acid washing solution and reaction products on the surface are thoroughly removed. After ultrasonic cleaning is completed, the second stent body with a clean surface and a small number of tiny particles is obtained by drying. S3: Prepare the coating solution. Use a lifting device to fix the second support body above the container containing the coating solution and move the second support body up and down at a uniform speed. The central axis of the second support body, which has a cylindrical structure, is perpendicular to the surface of the coating solution. During coating, each lifting and lowering will cause the second support body to be completely immersed in the coating solution for a period of time before being removed from the coating solution, so that the coating solution can adhere to the microparticles. After 5-10 lifting and lowering cycles, a third support body is obtained. The period of time is 5-10 seconds. The interval between two adjacent lifting and lowering cycles is 120-180 seconds. After each lifting and lowering cycle, the third support body is dried without wind during the interval. The coating solution needs to be in M ​​parts. Each part of the coating solution includes 1g PLA or 1g PLGA and 20ml dichloromethane solvent, where M>0. Specifically: S3.1: Prepare M portions of the coating solution. For each portion of the coating solution, pour 20 ml of the dichloromethane solvent into a light-proof and corrosion-resistant container, then add 1 g PLA or 1 g PLGA and mix and stir in a light-proof environment. The stirring speed during the light-proof mixing and stirring is 200 r / min. After 30 min to 60 min of light-proof mixing and stirring, the coating solution is obtained. Preferably, the coating solution is obtained after 40 min of light-proof mixing and stirring. The light-proof mixing and stirring is carried out at room temperature. Through light-proof mixing and stirring, complete dissolution is ensured, air bubbles are removed, and a uniform, transparent, and particle-free coating solution is obtained. Then, it can be sealed and stored in a light-proof environment for later use. Wherein, M > 0, and the specific selection of M can be made according to the subsequent coating requirements. S3.2: The second support body is fixed above the container containing the coating liquid using a lifting and pulling device, and the central axis of the second support body with a cylindrical structure is kept perpendicular to the liquid surface of the coating liquid. The lifting and pulling device includes a support, a base, a lifting drive mechanism, and a clamp. The support is set on the side of the base, the container containing the coating liquid is located on the base, the lifting drive mechanism is set on the support and the drive end is connected to the clamp to drive the clamp to perform vertical lifting and lowering movements. The clamp is used to clamp the second support body. The lifting drive mechanism is a lifting cylinder, or it can be a structure combining a linear drive motor and a vertically extending guide rail. By keeping the central axis of the second support body perpendicular to the liquid surface of the coating liquid, it is ensured that the second support body is not tilted or has no air bubbles adhering when fully immersed in the solution. S3.3: The lifting and pulling device drives the second support body to rise and fall. The lifting and falling rate is 5-8 mm / s, preferably 5 mm / s. During the coating process, each lifting and falling will cause the second support body to be completely immersed in the coating liquid for a period of time before being removed from the coating liquid, so that the coating liquid can adhere to the microparticles. After 10 lifting and falling cycles, the third support body is obtained. The period of time is 10 seconds. The interval between two adjacent lifting and falling cycles is 120 seconds to 180 seconds. During the interval, the coating liquid is stirred for 1-2 minutes, preferably 1 minute, to prevent PLA or PLGA from settling and to ensure uniform coating liquid concentration. After each lifting and falling cycle, the third support body is dried without wind during the interval. The windless drying is at room temperature. By repeating the coating process of complete immersion 10 times, the anchoring effect of the residual particles is used to stack the film layers to the target thickness. S4: Vacuum drying is performed on the third scaffold prototype after the coating is completed to form the final magnesium alloy scaffold; Specifically: The third scaffold, after being coated, is placed in a vacuum drying oven and dried at 40°C under a vacuum of less than 10 Pa for 2-4 hours, preferably 2 hours, to completely remove residual dichloromethane solvent from the coating. After drying, the appearance is inspected using a stereomicroscope to ensure that the coating is free of defects such as cracks, peeling, and pinholes, thus obtaining the final magnesium alloy scaffold after coating.

[0021] Combined with appendix Figure 2-9 As shown, the scaffold was tested using a stereomicroscope to determine the impact of different surface treatments on the scaffold surface condition and coating effect, as detailed below: To systematically verify the effects of no pickling and different pickling times on the surface condition of the stent and the coating effect, this invention selected four sets of comparative experiments as examples for supporting evidence: Four sets of primary scaffolds prepared with identical parameters (number of wires, diameter, angle, molding parameters, etc.) were selected. Surface treatment methods were applied at four different pickling times: "no pickling," "pickling for 20 minutes," "pickling for 30 minutes," and "pickling for 40 minutes." For the pickling group, the pickling solution ratio, ultrasonic power, and pickling temperature were kept consistent. The "no pickling" group underwent only anhydrous ethanol ultrasonic cleaning. Subsequently, all four scaffolds were coated using the same pull-up coating method. The surface condition and coating effect of the scaffolds were examined using a stereomicroscope. The results are as follows: Un-acid-washed group (ethanol ultrasonic cleaning only): Surface condition: The surface of the support still has a large number of unmelted particles attached, which are densely and unevenly distributed; Coating effect: PLA / PLGA solution will form localized adhesion at some particle accumulation sites. Due to the disordered particle distribution, the coating layer exhibits uneven accumulation. The adhered film is prone to cracking and peeling, failing to meet the usage requirements. A stereomicroscopic image of the surface before coating is shown below. Figure 2 As shown, the stereomicroscopic image of the surface after coating is as follows: Figure 6 As shown.

[0022] Pickling for 20 minutes: Surface condition: Most of the unmelted particles and oxide layer on the surface of the support have been removed, but a large number of particles still remain. Coating effect: Although residual particles can provide some anchoring effect, the excessive number and uneven particle size of the particles result in poor membrane uniformity, and there are exposed particles. A stereomicroscopic image of the surface before coating is shown below. Figure 3 As shown, the stereomicroscopic image of the surface after coating is as follows: Figure 7 As shown.

[0023] Pickling for 30 minutes: Surface condition: Most of the unmelted particles on the surface of the support have been removed, with only tiny particles remaining at a few wire nodes. The remaining particles are evenly dispersed and low in height, and do not affect the overall surface flatness. Coating effect: Residual microparticles form evenly distributed "anchoring points," effectively slowing down the flow rate of the solution on the support surface, allowing the solution to spread and adhere evenly. The coating layer completely covers the surface of the filaments and the inner walls of the pores, without accumulation, exposure, or cracking defects. The coating coverage is ≥95%, and the thickness is uniform. This group has the best coating effect among the four groups. The surface stereomicroscopic photograph before coating is as follows: Figure 4 As shown, the surface stereomicroscopic image after coating is as follows: Figure 8 As shown.

[0024] Pickling for 40 minutes: Surface condition: Unmelted particles and oxide layer on the surface of the support have been completely removed, the surface is smooth and free of impurities, there is no excessive corrosion, and there are no obvious protrusions or depressions. Coating effect: Due to the lack of anchoring effect from residual particles on the surface, the solution flows significantly faster on the smooth surface, making it difficult for the solution to form a stable adhesion layer. Only localized coatings can be formed in areas with slower flow rates, such as filament nodes, resulting in large exposed areas and extremely poor overall coating uniformity. However, the solution encapsulation effect is relatively good. A stereomicroscopic photograph of the surface before coating is shown below. Figure 5 As shown, the surface stereomicroscopic image after coating is as follows: Figure 9 As shown.

[0025] The above comparative examples clearly demonstrate that: Residual particles have a significant auxiliary effect on coating, as they can slow down solution flow and promote coating adhesion through the "anchoring effect". A specific pickling time can remove most of the large particles and oxide layer that affect the uniformity of the coating, while retaining an appropriate amount of small particles as anchoring points, thus achieving a balance between cleanliness and coating compatibility. Specifically, with a pickling time of 30 minutes, PLA or PLGA coating is the best for the size of the magnesium alloy stent. That is, for the use requirements of medical magnesium alloy stents, PLA or PLGA coating can be used to ensure the use requirements. For magnesium alloy stents of this size, a 30-minute pickling with the pickling solution can obtain the magnesium alloy stent with the best performance that meets the use requirements. Direct coating without pickling results in uneven coating due to excessive impurities, while excessive pickling time makes coating difficult due to lack of particle anchoring, neither of which can achieve the desired effect. Meanwhile, complex structure scaffolds prepared by SLM technology retain their structural advantages and can achieve uniform coating after undergoing a suitable pickling process, further demonstrating the unique value of this technology in the preparation of complex structure scaffolds.

[0026] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support, characterized in that: Includes the following steps: S1: Use modeling software to generate a printing model of the magnesium alloy bracket, and use a selective laser melting and forming equipment to perform laser printing according to the printing model to obtain a first bracket prototype with a cylindrical fishing net shape; S2: Prepare the pickling solution. After wiping the first stent body, place it in an ultrasonic cleaning tank containing the pickling solution for ultrasonic pickling treatment. Then, perform deacidification cleaning and drying to obtain the second stent body. After ultrasonic pickling treatment, deacidification cleaning and drying, a small number of tiny particles remain on the surface of the second stent body. The pickling solution includes N parts of 650ml phosphoric acid, N parts of 350ml glycerol and N parts of 0.6g citric acid powder. The pickling treatment time is 25min-30min and the pickling solution is kept at a constant temperature of 40-50℃. Wherein, N>0. S3: Prepare the coating solution. Use a lifting device to fix the second support body above the container containing the coating solution and move the second support body up and down at a uniform speed. The central axis of the second support body, which has a cylindrical structure, is perpendicular to the surface of the coating solution. During coating, each lifting and lowering will cause the second support body to be completely immersed in the coating solution for a period of time before being removed from the coating solution, so that the coating solution can adhere to the microparticles. After 5-10 lifting and lowering cycles, a third support body is obtained. The period of time is 5-10 seconds. The interval between two adjacent lifting and lowering cycles is 120-180 seconds. After each lifting and lowering cycle, the third support body is dried without wind during the interval. The coating solution needs to be in M ​​parts. Each part of the coating solution includes 1g PLA or 1g PLGA and 20ml dichloromethane solvent, where M>0. S4: Vacuum drying is performed on the third scaffold prototype after the coating is completed to form the final magnesium alloy scaffold.

2. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 1, characterized in that: The magnesium alloy support includes S first magnesium alloy wires and L second magnesium alloy wires. The S first magnesium alloy wires are evenly arranged in a clockwise rotation around the z-axis of a spatial rectangular coordinate system, and the L second magnesium alloy wires are evenly arranged in a counterclockwise rotation around the same axis. Each first magnesium alloy wire is cross-connected with each second magnesium alloy wire to form a cylindrical fishing net-shaped support with a diameter of 10mm-20mm and a height of 20mm-40mm, wherein the sum of S and L is in the range of 20-24.

3. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 2, characterized in that: The first magnesium alloy wire and the second magnesium alloy wire are made of the same material and are both commercial AZ31 magnesium alloy. The cross-section of the first magnesium alloy wire and the second magnesium alloy wire are both circular and the diameter is 0.2-0.4 mm.

4. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 1, characterized in that: The pickling solution prepared in S2 specifically includes: N parts of 650 ml of the phosphoric acid and N parts of 350 ml of glycerol are poured into a corrosion-resistant container to form a mixture. The mixture is stirred at 25-30°C at a stirring speed of 300-500 r / min for 5-10 min. Then, N parts of 0.6 g of citric acid powder are added to the mixture and stirring is continued for 10-15 min to form the pickling solution.

5. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 4, characterized in that: The ultrasonic acid pickling process uses an ultrasonic cleaning tank with an ultrasonic power of 300-400W and an ultrasonic frequency of 40-60kHz.

6. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 5, characterized in that: The process of further deacidification, cleaning, and drying in step S2 to obtain the second scaffold precursor specifically includes: The first stent, after undergoing ultrasonic acid pickling, is placed in an ultrasonic cleaning tank containing anhydrous ethanol for ultrasonic cleaning. After ultrasonic cleaning for 2-4 minutes, it is removed and dried to obtain the second stent.

7. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 6, characterized in that: The coating liquid preparation in S3 specifically includes: Prepare M portions of the coating solution. For each portion of the coating solution, pour 20 ml of the dichloromethane solvent into a light-proof and corrosion-resistant container, then add 1 g PLA or 1 g PLGA and mix and stir in a light-proof environment. The stirring speed during the light-proof mixing and stirring is 200 r / min. After mixing and stirring in a light-proof environment for 30 min to 60 min, the coating solution is obtained.

8. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 7, characterized in that: The lifting rate during the lifting process is 5-8 mm / s.

9. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 8, characterized in that: The interval between two consecutive rises and falls in S3 is 120s-180s, specifically including: The interval between two consecutive lifting and lowering operations is 120s-180s, and the coating liquid is stirred during the interval for 1-2 minutes.

10. The pickling and coating method for selective laser melting forming of a fishing net-shaped magnesium alloy support according to claim 1, characterized in that: The process of vacuum drying the third scaffold substrate after coating in step S4 to form the final magnesium alloy scaffold specifically includes: The third scaffold, after being coated, is placed in a vacuum drying oven and dried at 40°C under a vacuum of less than 10 Pa for 2-4 hours.

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