Fabrication method and system for LPBF magnesium-alloy tissue-engineering scaffold with smooth inner surface

Abstract

Provided in the present invention are a fabrication method and system for an LPBF magnesium-alloy tissue-engineering scaffold with a smooth inner surface. The method comprises: step S1, scanning a porous scaffold, and performing screening to obtain infill scanning parameters, which can achieve the greatest density, wherein the scanning comprises single-pass contour scanning and single infill scanning; step S2, on the basis of said infill scanning parameters, optimizing a contour scanning strategy; step S3, acquiring a corresponding molten-pool size, and using the optimized contour scanning strategy to adjust a spot compensation value; and step S4, on the basis of the contour scanning strategy and the adjusted spot compensation value, fabricating a magnesium-alloy tissue-engineering scaffold. In the present invention, the defects of powder adhesion and dross formation in a complex porous structure which seriously affect the inner surface roughness and the scaffold performance are eliminate in situ during fabrication, such that the fluidity, fatigue resistance and corrosion resistance of a porous scaffold are improved, cumbersome post-processing procedures are simplified, and the production cost is reduced, thereby achieving the concept of green production.

Description

Method and system for preparing LPBF magnesium alloy tissue engineering scaffold with smooth inner surface TECHNICAL FIELD

[0001] The present application relates to the technical field of biological medical material preparation, in particular to a method and system for preparing an LPBF magnesium alloy tissue engineering scaffold with smooth inner surface. BACKGROUND

[0002] 1. Large segmental bone defects caused by trauma, disease, developmental deformity, revision surgery, tumor resection or osteomyelitis, etc. with a length exceeding 2-2.5 times the diameter of the defect bone are one of the major challenges in orthopedic clinical treatment. An ideal bone scaffold must have sufficient mechanical strength, corrosion resistance and biocompatibility to meet its load-bearing function; at the same time, the scaffold should have a porous network connected to each other to deliver nutrients and allow cell migration. Among the many additive manufacturing technologies, laser powder bed fusion technology (LPBF) has the advantages of high degree of freedom in structure design, high preparation precision, short development cycle and avoidance of subsequent mechanical processing, etc., and is therefore widely used in the preparation of bone tissue engineering scaffolds. Compared with autologous or allogeneic bone graft scaffolds, LPBF magnesium alloy tissue engineering scaffolds have the advantages of being artificially manufactured, low cost and no immune rejection; compared with high polymer scaffolds, they have the advantages of good biocompatibility, osteogenesis promotion and high mechanical strength, and have received extensive attention in recent years. However, magnesium alloy has a low boiling point and a high vapor pressure, which can cause serious powder evaporation and spattering during 3D printing. In addition, due to the low melting point, high thermal conductivity and low surface tension of magnesium, a large molten pool and heat-affected zone are easily generated, and a large amount of un-melted powder is easily adhered to the surface and inside of the porous scaffold, forming a powder sticking defect; under the horizontal overhanging structure inside the scaffold, the powder is infiltrated downward by the melt under the action of gravity and capillary force after being melted by the laser, resulting in a large amount of powder adhering to the lower surface of the overhanging structure and forming a slag hanging defect. The formation process of the slag hanging defect is shown in FIG. 2.

[0003] 2. The powder sticking and slag hanging inside the scaffold can reduce the flowability, fatigue and corrosion performance of the porous scaffold. When the pore size of the scaffold is small, the powder sticking on the inner surface can hinder the entry of the external polishing medium, and the flowability inside the scaffold becomes worse and worse. The larger the size of the scaffold, the more difficult it is to polish the inner surface, and in severe cases, the detached powder particles and the originally adhered powder particles can be mechanically interlocked, resulting in complete blockage of the internal pores and loss of the three-dimensional connectivity of the scaffold. In addition, after the porous scaffold is implanted into the human body, it needs to bear periodic loads. The powder sticking can significantly increase the surface roughness of the scaffold, which on the one hand promotes the initiation of surface fatigue cracks, and on the other hand increases the contact area between the scaffold and the corrosion medium, which can greatly accelerate the corrosion of the scaffold, produce a large amount of hydrogen, and further form the emphysema phenomenon at the implantation site.

[0004] 3. In order to improve the surface smoothness, the porous scaffold is often subjected to post-processing such as chemical or electrochemical polishing. Because magnesium alloy will produce a large amount of hydrogen in the acid polishing solution, which seriously inhibits the flow of the polishing solution to the inside of the scaffold, resulting in the outer part of the scaffold being more easily polished to the target diameter, but the inside being difficult to polish to the target diameter, ultimately leading to the edge of the scaffold being thinner and the inside being thicker. The larger the size of the scaffold, the smaller the pore size, the worse the permeability of the structure (the difficulty of fluid flow in the porous medium), and the more obvious the difference in diameter between the inside and the outside. Therefore, for LPBF magnesium alloy porous scaffolds, there is an urgent need for a molding method that can effectively reduce the internal powder sticking and slag sticking defects and improve the corrosion resistance and corrosion fatigue performance of magnesium alloy porous scaffolds. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a method and system for preparing an LPBF magnesium alloy tissue engineering scaffold with smooth inner surface.

[0006] According to the method for preparing an LPBF magnesium alloy tissue engineering scaffold with smooth inner surface provided by the present application, the following steps are included:

[0007] Step S1: scanning the porous scaffold to select the most dense filling scanning parameters;

[0008] The scanning includes single-pass contour scanning and single filling scanning;

[0009] Step S2: optimizing the contour scanning strategy according to the most dense filling scanning parameters;

[0010] Step S3: obtaining the corresponding molten pool size, and adjusting the spot compensation value using the optimized contour scanning strategy;

[0011] Step S4: preparing a magnesium alloy tissue engineering scaffold based on the contour scanning strategy and the adjusted spot compensation value.

[0012] Preferably, the step S1 includes:

[0013] Single-pass contour scanning and single filling scanning are performed on the porous scaffold, the contour scanning parameters and the filling scanning parameters are consistent, after preparation, the sample is cut parallel to the preparation direction, the cross section is polished, the optical micrograph is obtained and the density is analyzed; in the parameter combination with a density greater than 99.5%, the parameters with 0.05≤P / V≤0.5 are selected and set as P 填 , V 填 ;

[0014] Wherein, P is the laser power, and V is the scanning speed.

[0015] Preferably, the step S2 includes:

[0016] The filling scanning parameters are selected as P填 、V 填 , let the profile scanning parameters be P 轮 、V 轮 , the profile scanning times be PT, and the profile parameters be calculated:

[0017] wherein the profile line energy density scaling coefficient Z = 5-30, the profile pre-scanning and the profile post-scanning can be scanned multiple times within the range of the profile compensation value, the scanning sequence includes from the inner circle profile scanning to the outer circle profile scanning, or from the outer circle profile scanning to the inner circle profile scanning; the profile pre-scanning and the profile post-scanning can select different laser power P, scanning speed V, profile scanning times PT, profile line energy density scaling coefficient Z and profile compensation value PC; the setting range of the filling compensation value FC is 0≤FC≤PC.

[0018] Preferably, the step S3 comprises:

[0019] acquiring the molten pool width under the structure and process parameters, and optimizing the spot compensation value;

[0020] let the wall thickness / rod diameter of the original design stent model be T0, and the wall thickness / rod diameter after the optimized profile scanning strategy be T1, then the spot compensation value is:

[0021] wherein SZ is the spot diameter, R 熔 is the molten pool width corresponding to P 填 / V 填 ; the size increase caused by multiple profile scanning is compensated by adjusting the spot compensation value.

[0022] Preferably, the step S1 further comprises multiple profile pre-scanning with a certain energy density before the filling scanning according to the specific stent structure and the length of the lower surface overhang area; and multiple profile post-scanning with a certain energy density after the filling scanning according to the surface powder adhesion of the specific stent.

[0023] According to the LPBF magnesium alloy tissue engineering stent preparation system with smooth inner surface provided by the application, the following steps are included:

[0024] Module M1: scanning the porous stent, and screening the most dense filling scanning parameters;

[0025] The scanning includes single-pass profile scanning and single filling scanning;

[0026] Module M2: optimizing the profile scanning strategy according to the most dense filling scanning parameters;

[0027] Module M3: acquiring the corresponding molten pool size, and adjusting the spot compensation value using the optimized profile scanning strategy;

[0028] Module M4: preparing magnesium alloy tissue engineering scaffold based on the contour scanning strategy and the adjusted spot compensation value.

[0029] Preferably, the module M1 comprises:

[0030] A single contour scanning and a single filling scanning are performed on the porous scaffold, the contour scanning parameters and the filling scanning parameters are consistent, after preparation, the sample is cut parallel to the preparation direction, the cross section is polished to obtain its optical micrograph and analyze its density; in the parameter combination with a density greater than 99.5%, the parameters of 0.05≤P / V≤0.5 are selected and set as P 填 , V 填 ;

[0031] Wherein, P is the laser power, and V is the scanning speed.

[0032] Preferably, the module M2 comprises:

[0033] The filling scanning parameters are selected as P 填 , V 填 , the contour scanning parameters are set as P 轮 , V 轮 , the contour scanning times are PT, and the contour parameters are calculated.

[0034] Wherein, the contour line energy density scaling factor Z=5-30, the contour scanning before and the contour scanning after can be scanned multiple times within the range of the contour compensation value, the scanning sequence includes from the inner circle contour scanning to the outer circle contour scanning, or from the outer circle contour scanning to the inner circle contour scanning; the contour scanning before and the contour scanning after can select different laser power P, scanning speed V, contour scanning times PT, contour line energy density scaling factor Z and contour compensation value PC; the setting range of the filling compensation value FC is 0≤FC≤PC.

[0035] Preferably, the module M3 comprises:

[0036] The melt pool width under the structure and process parameters is obtained, and the spot compensation value is optimized.

[0037] Let the wall thickness / diameter of the original design scaffold model be T0, and the wall thickness / diameter after the optimized contour scanning strategy be T1, then the spot compensation value is:

[0038] Wherein, SZ is the spot diameter, R 熔 is the melt pool width corresponding to P 填 / V 填 ; the size increase caused by multiple contour scanning is compensated by adjusting the spot compensation value.

[0039] Preferably, the module M1 further comprises a plurality of pre-scan profiles with a certain energy density before the filling scan according to the specific stent structure and the length of the under-surface overhang area; and a plurality of post-scan profiles with a certain energy density after the filling scan according to the specific stent surface powder adhesion.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] 1. The present application can eliminate the internal serious influence of the complex porous structure on the internal surface roughness and the stent performance in the preparation process, improve the flowability, fatigue and corrosion resistance of the porous stent, simplify the cumbersome post-processing process, reduce the production cost, and realize the concept of green production.

[0042] 2. The present application greatly widens the maximum printable size of the porous stent, reduces the printable minimum wall thickness / rod diameter, and improves the freedom of structural design, providing a new method for the preparation of magnesium alloy porous stents for large segment bone defects with small pore diameters; at the same time, by adopting a spot compensation strategy based on the size of the molten pool under a specific structure to regulate the wall thickness / rod diameter, the negative effects of multiple contour scans are eliminated, and the size deviation from the model is avoided.

[0043] Other beneficial effects of the present application will be described in the specific embodiments through the introduction of specific technical features and technical solutions, and those skilled in the art should be able to understand the beneficial technical effects brought by the technical features and technical solutions through the introduction of the technical features and technical solutions. BRIEF DESCRIPTION OF DRAWINGS

[0044] Other features, objects and advantages of the present application will become more apparent through reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0045] Fig. 1 is a flow chart of the method of the present application.

[0046] Fig. 2 is a schematic diagram of the relationship between spot compensation, contour compensation and filling compensation.

[0047] Fig. 3 is a schematic diagram of the step effect of the slice in the LPBF of the present application, and the slag generation in the overhang area.

[0048] Fig. 4 is an optical photograph of the top end of the stent before and after optimization of the present application.

[0049] Fig. 5 is the CT scan result of the stent overhang area section before and after optimization of the contour scan strategy of the present application. DETAILED DESCRIPTION

[0050] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0051] Referring to FIG. 1, a method for preparing an LPBF magnesium alloy tissue engineering scaffold with smooth inner surface, comprising:

[0052] Step 1: Single-pass contour scanning and filling scanning to obtain the most dense filling scanning parameters:

[0053] Single-pass contour scanning and single-pass filling scanning are performed on the porous scaffold. The contour scanning parameters and the filling scanning parameters are consistent. After preparation, the sample is cut parallel to the preparation direction, the cross section is polished, and the optical micrograph is obtained and analyzed for its density. In the parameter combination with a density greater than 99.5%, the parameters 0.05≤P / V≤0.5 are selected (P is the laser power, unit: W, V is the scanning speed, unit: mm / s, V is smaller to reduce powder splashing, and P is smaller to bring smaller molten pool size to improve precision), and set as P 填 , V 填 .

[0054] Step 2: Determine the contour scanning strategy with the least powder adhesion, determine the number of pre-contour scanning and post-contour scanning, contour shrinkage value and filling shrinkage value:

[0055] The filling scanning parameters are selected as P 填 , V 填 , and the contour scanning parameters are set as P 轮 , V 轮 . The number of contour scanning is PT (0≤PT≤15), and the contour scanning parameters are determined by the formula

[0056] The contour line energy density scaling factor Z=5-30, and the value of Z depends on factors such as the specific scaffold structure, powder state and filling scanning process. For example, when Z=10 and PT=2, P 轮 / V 轮 =0.8*P 填 / V 填 . The contour compensation value PC=(0-2)*S max , S maxFor the largest powder particle size, i.e. the outer ring profile scanning needs to be able to melt the adhered or agglomerated powder. Referring to Fig. 2, within the range of the profile compensation value, both the pre-profile scanning (edge scanning before the filling scanning) and the post-profile scanning (edge scanning after the filling scanning) can be scanned multiple times, and the scanning sequence gradually transitions from the inner ring profile scanning to the outer ring profile scanning, or gradually transitions from the outer ring profile scanning to the inner ring profile scanning. The pre-profile scanning and the post-profile scanning can select different P, V, PT, Z, PC. The setting range of the filling compensation value FC is 0≤FC≤PC, which depends on the rod diameter / thickness of the prepared stent, the profile scanning power and speed, and the profile scanning times PT.

[0057] Before the filling scanning, according to the specific stent structure and the length of the lower surface overhanging area, multiple pre-profile scanning with low energy density is set, which can effectively eliminate the slag hanging on the lower surface.

[0058] For the porous stent, the lower surface inevitably exists in the interior. Due to the "step effect" in the model slicing process, there is a certain length of overhanging area at the edge of the model slice, as shown in Fig. 3. When the critical forming angle (the angle at which support needs to be added, generally 45°) is reached under a certain layer thickness, the length of the overhanging area of the slice increases, resulting in an increase in the length of the laser spot acting on the overhanging area, and finally increasing the action area of the laser on the lower powder. Since the absorption rate of the powder to the laser is higher than that of the solidified entity structure, and the thermal conductivity of the powder is lower than that of the entity, the actual heat of the overhanging area is too high, resulting in an increase in the size of the molten pool, and since there is no support below, the shape of the solidified molten pool after flowing into the powder due to gravity, capillary action and low viscosity of liquid metal is very irregular, which is the slag hanging defect on the lower surface. The formation of slag is mainly caused by excessive local energy input. In order to avoid slag, for the overhanging structure part, the energy input of the pre-profile scanning needs to be reduced to reduce the volume of the molten pool, but too low energy input will bring unmelted defects, so the number of profile scanning needs to be increased to increase the actual energy input, and then the unmelted defects are eliminated. In the first profile scanning, the laser spot acts on the solidified entity, so the molten pool will not be too large, and finally the slag can be avoided. The specific profile compensation value PC 前 , the profile scanning times PT 前 depend on the overhanging angle of the lower surface area after model slicing and the overhanging length between layers of the slice. When the overhanging angle is smaller and the overhanging length is longer, the support of the solidified area of the previous layer on the model edge molten pool is smaller, and a larger profile compensation value PC is needed to make the first profile scanning act on the solidified entity of the previous layer, and a smaller P 轮 / V 轮 reduces the energy input and the size of the molten pool, and more profile scanning times PT make the edge area dense, and finally make the stent prepared without slag on the lower surface profile.

[0059] According to the surface powder adhesion of the specific support after the filling scan, the low-energy-density multiple contour post-scan is set to effectively eliminate the surface adhesion powder.

[0060] For the not fully melted powder particles adhered on the top and side of the strut after the filling scan, the re-melting can be performed through the contour post-scan expanded to the outer circle of the strut, so that the powder adhered on the surface of the strut is melted to part of the strut diameter, reducing the surface roughness of the strut, but at the same time, the wall thickness of the strut is also increased. Due to the unique denudation phenomenon of the LPBF process (denudation refers to the inward airflow caused by surface tension and molten pool evaporation to the powder particles around the scanning track to be absorbed into the molten pool), the powder around the strut is less after the filling scan, and the contour scan offset to the outside will not melt new powder. The specific contour compensation value PC 后 , the contour scanning times PT 后 depend on the particle size of the powder and the amount of adhered powder. When the particle size of the adhered powder is larger, a larger offset distance is required to make the spot better act on the powder; when the adhered powder is more, more scanning times are required to make the powder melt into part of the matrix. Therefore, through the low-energy-density contour post-scan strategy, the surface powder can be eliminated, and the surface roughness can be reduced.

[0061] Step 3, obtain the molten pool width under the structure and process parameters, and optimize the spot compensation value:

[0062] The wall thickness / diameter of the original design support model T0, the wall thickness / diameter after the optimized contour scanning strategy T1, and the spot compensation value

[0063] Wherein, SZ is the spot diameter, R 熔 is the molten pool width (obtained by observing the metallographic longitudinal section after cold inlaying) corresponding to P 填 / V 填 , the size increase caused by multiple contour scanning is compensated by adjusting the spot compensation value. For example, T0=750μm, T1=1000μm, then (T1-T0) / 2=125μm, when SZ=40μm, R 熔 =100μm, R 熔 / SZ=2.5, then

[0064] That is, when the spot compensation value SC=50μm, the target diameter / wall thickness can be obtained.

[0065] Referring to FIG. 4, a is the top end morphology of the scaffold before optimization by the method, and b is the top end morphology of the scaffold after optimization by the method. After optimization of the scanning strategy before the contour and the scanning strategy after the contour, the spot compensation value is adjusted according to the size of the molten pool in the filling scanning area under specific structure and process parameters, which can effectively reduce the difference between the scaffold wall thickness size and the design value.

[0066] Referring to FIG. 5, a is the CT section of the scaffold overhang area with slag before optimization by the method, and b is the CT section of the scaffold overhang area after optimization by the method. After the powder adhered to the edge of the scaffold is re-melted as part of the matrix, the wall thickness / rod diameter will increase to a certain extent. Therefore, the spot compensation value needs to be set when slicing to ensure that the wall thickness / rod diameter of the printed scaffold is close to the design value. The size of the molten pool has certain correlation with the structure, the thinner the wall thickness, the worse the vertical thermal conductivity, and the larger the size of the molten pool, so the spot compensation value needs to be adjusted according to the size of the molten pool of different structures. (T1-T0) is the wall thickness / rod diameter that needs to be reduced, and 2*(R 熔 / SZ) is the reduction of the wall thickness when the spot center moves a unit distance, and the division of the two is the spot compensation value.

[0067] Step 4, using the optimized contour scanning strategy and spot compensation value, a magnesium alloy tissue engineering scaffold with consistent wall thickness and design value, smooth inner surface and dense internal structure is prepared.

[0068] The above is the basic embodiment of the present application, and the technical solutions of the present application will be further described through three preferred embodiments.

[0069] Example 1

[0070] Preparation of minimal surface magnesium scaffold

[0071] This embodiment relates to a degradable magnesium alloy tissue engineering scaffold for bone defect repair. A minimal surface scaffold model with a unit type of G is designed by related modeling software, the scaffold diameter D is 5 mm, the height H is 7 mm, the unit size U is 2 mm, the model wall thickness T0 is 180 μm, and the porosity is about 75%.

[0072] This embodiment relates to the preparation method of the aforementioned high-precision magnesium alloy tissue engineering scaffold with smooth inner surface, and the method comprises the following steps:

[0073] Step 1, single-pass contour pre-scanning and filling scanning to obtain the most dense filling scanning parameters.

[0074] The stent three-dimensional structure model is imported into Materialise Mimics software for slicing, and the data after slicing is imported into a 3D printing device. The ProX DMP 320 metal 3D printer of the United States 3D SYSTEMS is used for layer-by-layer printing. The powder is a high-purity degradable medical magnesium powder with a purity of 99.99%, a smooth and regular spherical shape, a particle size of 50-90 μm, a normal distribution, and S 平均 = 70 μm. Before printing, the internal cabin of the 3D printer is repeatedly vacuumed and filled with inert gas three times until the oxygen content in the cabin is reduced to below 30 ppm. The spot diameter SZ = 80 μm is set, the layer thickness LT = 20 μm is set, the scanning interval HS = 80 μm is set, the adjacent layer is rotated by 67° scanning, the profile compensation value PC = 0 μm is set, the filling compensation value FC = 40 μm is set, the process window is tried at 100 mm / s and 10 W, the cross section of the obtained sample is mechanically polished to obtain its metallographic picture, and the density is counted (as shown in Table 1). The parameters with a density greater than 99.5% are selected, i.e. P 填 = 80 W, V 填 = 500 mm / s. The top of the stent under this parameter is shown in FIG. 4a.

[0075] Step 2, determine the profile scanning strategy with the least powder adhesion, determine the number of pre-scan and post-scan, profile shrinkage value and filling shrinkage value.

[0076] The profile scanning number PT = 6, wherein the pre-scan number PT 前 = 2, the post-scan number PT 后 = 4, Z = 20, P 轮 / V 轮 = (1-6 / 20)*P 填 / V 填 , V 填 = V 轮 = 500 mm / s, P 轮 = 0.7*P 填 = 56 W, the profile compensation value PC = 40 μm, the filling compensation FC = 40 μm, the pre-scan is twice inner circle profile scanning, and the post-scan sequence is twice inner circle profile scanning first, and then twice outer circle profile scanning.

[0077] Step 3, obtain the melt pool width under the structure and process parameters, and optimize the spot compensation value.

[0078] Under this profile parameter, the wall thickness T1 of the prepared stent is 260 μm. The melt pool width R 熔= 140 μm, then the spot compensation value SC = [(260-180)*80] / (2*140) = 22.86 μm.

[0079] Step 4, using the optimized contour scanning strategy and the spot compensation value, a magnesium alloy tissue engineering scaffold with consistent wall thickness, smooth surface and dense internal structure is prepared.

[0080] The optimized sample preparation parameters are: spot compensation value SC = 32 μm, contour compensation value PC = filling compensation FC = 40 μm, contour pre-scan number PT 前 = 2, contour post-scan number PT 后 = 4, P 轮 = 56 W, V 轮 = 500 mm / s, P 填 = 80 W, V 填 = 500 mm / s, and the printing is performed again. A minimum curved surface magnesium scaffold with a wall thickness of 180 μm and a smooth surface is prepared, and the optimized scaffold top end is shown in FIG. 4b. The obtained scaffold structure has good reproducibility, and the surface has a bright metallic luster.

[0081] Table 1 Relationship between different laser power and scanning speed and scaffold density

[0082] Example 2

[0083] Preparation of low porosity EK30 magnesium alloy tissue engineering scaffold

[0084] This example relates to a degradable gradient scaffold for repairing large bone defects. Through related modeling software, a minimum curved surface scaffold model with a unit type of G is designed, the scaffold diameter D = 5 mm, the height H = 3 mm, the unit size U = 2 mm, the model wall thickness T0= 450 μm, and the porosity is about 50%.

[0085] This example relates to a method for preparing the aforementioned high-precision magnesium alloy scaffold with a smooth inner surface, which comprises the following steps:

[0086] Step 1, filling scanning and single-pass contour post-scan to obtain the most dense filling scanning parameters.

[0087] The stent three-dimensional structure model is imported into Materialise Mimics software for slicing, and the data after slicing is imported into a 3D printing device. The ProX DMP 320 metal 3D printer of the United States 3D SYSTEMS is used for layer-by-layer printing. The powder is a medical degradable magnesium alloy Mg-3wt.%Nd-0.18wt.%Zn-0.45wt.%Zr, the shape is a smooth and regular sphere, the particle size is 20-50 μm, and the S average is 35 μm. Before printing, the internal cabin of the 3D printer is repeatedly vacuumed and inert gas filled three times until the oxygen content in the cabin is reduced to below 30 ppm. The spot diameter SZ is set to 60 μm, the layer thickness LT is set to 10 μm, the scanning interval HS is set to 100 μm, the adjacent layer is rotated by 67° for scanning, the profile compensation value PC is set to 0 μm, the filling compensation value FC is set to 40 μm, the process window is tried at 100 mm / s and 10 W, the cross section of the obtained sample is mechanically polished to obtain its metallographic picture, and the density is counted. The parameters with a density greater than 99.5% are selected, that is, P fill = 60 W and V fill = 600 mm / s.

[0088] Step 2, determine the profile scanning strategy with the least powder adhesion, determine the increase number of pre-scan and post-scan, profile shrinkage value and filling shrinkage value.

[0089] The profile scanning number PT is set to 8, wherein the pre-scan number PT 前 = 4, the post-scan number PT 后 = 4, Z = 24, P 轮 / V 轮 = (1-8 / 24)*P 填 / V 填 , V 填 = V 轮 = 600 mm / s, P 轮 = 2 / 3*P fill = 40 W, the profile compensation value PC is 20 μm, the filling compensation FC is 20 μm, the pre-scan is two outer circle profile scans and two inner circle profile scans, and the post-scan is two inner circle profile scans and two outer circle profile scans.

[0090] Step 3, obtain the molten pool width under the structure and process parameters, and optimize the spot compensation value.

[0091] Under the profile parameters, the wall thickness T1 of the prepared stent is 500 μm. The molten pool width R 熔 = 80 μm, and the spot compensation value SC is [(500-450)*60] / (2*80) = 18.75 μm.

[0092] Step 4, using the optimized contour scanning strategy and spot compensation value, a magnesium alloy tissue engineering scaffold with consistent wall thickness, smooth surface and dense internal structure was prepared.

[0093] The optimized sample preparation parameters are: spot compensation value SC = 18.75 μm, contour compensation value PC = filling compensation FC = 20 μm, contour pre-scan number PT 前 = 4, contour post-scan number PT 后 = 4, P 轮 = 40 W, Vwheel = 600 mm / s, P 填 = 60 W, V 填 = 600 mm / s, and then printing again, a small curved magnesium scaffold with a wall thickness of 450 μm and no slag in the overhanging area can be prepared. The cross-section of the scaffold overhanging area before and after optimization of the contour scanning strategy is shown in Figure 5.

[0094] Example 3

[0095] Preparation of WE43 magnesium alloy tissue engineering scaffold with diamond structure

[0096] This example relates to a degradable gradient scaffold for repairing large bone defects. Through related modeling software, a diamond structure scaffold model based on rods was designed, with a scaffold diameter D = 10 mm, a height H = 15 mm, a unit size U = 1.2 mm, a model rod diameter T0= 760 μm, and a porosity of about 60%.

[0097] This example relates to the preparation method of the aforementioned high-precision magnesium alloy tissue engineering scaffold with smooth inner surface, which comprises the following steps:

[0098] Step 1, single-pass contour pre-scan and filling scan to obtain the most dense filling scan parameters.

[0099] The stent three-dimensional structure model is imported into Materialise Mimics software for slicing, and the data after slicing is imported into a 3D printing device. A ProX DMP 320 metal 3D printer of 3D SYSTEMS, USA, is used for layer-by-layer printing. The powder is WE43 commercial magnesium alloy powder with a purity of 99.99%, a smooth and regular spherical shape, a particle size of 40-80 μm, and a normal distribution with S average = 60 μm. Before printing, the internal cabin of the 3D printer is repeatedly evacuated and filled with inert gas three times until the oxygen content in the cabin is reduced to below 30 ppm. The spot diameter SZ is set to 70 μm, the layer thickness LT is set to 30 μm, the scanning interval HS is set to 120 μm, the adjacent layer is rotated by 67° for scanning, the contour compensation value PC is set to 0 μm, the filling compensation value FC is set to 30 μm, and the process window is tried at 100 mm / s and 10 W. The cross section of the obtained sample is mechanically polished to obtain its metallographic picture, and the density is counted. The parameters with a density greater than 99.5% are selected, P fill = 90 W, and V fill = 500 mm / s.

[0100] Step 2, determine the least powder adhesion contour scanning strategy, determine the increase number of contour pre-scan and contour post-scan, contour shrinkage value and filling shrinkage value. Set the contour scanning number PT = 7, wherein the contour pre-scan number PT 前 = 1, the contour post-scan number PT 后 = 6, take Z = 21, then P 轮 / V 轮 = (1-7 / 21)*P 填 / V 填 , V 填 = V 轮 = 500 mm / s, then P 轮 = 2 / 3*P 填 = 60 W, take the contour compensation value PC = 30 μm, the filling compensation FC = 30 μm, the contour pre-scan is first 1 time of inner circle contour scanning, and the contour post-scan is first 3 times of outer circle contour scanning, and then 3 times of inner circle contour scanning.

[0101] Step 3, obtain the melt pool width under the structure and process parameters, and optimize the spot compensation value accordingly. Under the contour parameters, the prepared stent has a rod diameter T1 = 920 μm. The melt pool width R 熔 = 130 μm is obtained by grinding the sample, and the spot compensation value SC = [(920-760)*70] / (2*130) = 43.08 μm.

[0102] Step 4, using the optimized contour scanning strategy and spot compensation value, a magnesium alloy tissue engineering scaffold with consistent wall thickness, smooth surface and dense internal structure is prepared. The optimized sample preparation parameters are: spot compensation value SC=43.08 μm, contour compensation value PC=filling compensation FC=30 μm, contour pre-scan number PT 前 =1, contour post-scan number PT 后 =6, P 轮 =40 W, V 轮 =600 mm / s, P 填 =90 W, V 填 =500 mm / s, and then printing again, a diamond structure WE43 magnesium alloy tissue engineering scaffold with a rod diameter of 760 μm and no slag in the overhanging area can be prepared.

[0103] In summary, the advantages of the present application are that the powder sticking and slagging defects inside the complex porous structure which seriously affect the internal surface roughness and scaffold performance can be eliminated in situ during preparation, thereby improving the flowability, fatigue and corrosion resistance of the porous scaffold, simplifying the cumbersome post-processing process, reducing production costs, realizing the concept of green production, greatly widening the maximum printable size of the porous scaffold, reducing the printable minimum wall thickness / rod diameter, pore diameter, improving the degree of freedom of structure design, and providing a new method for the preparation of magnesium alloy porous scaffolds for large bone defects with small pore diameters. At the same time, by using the spot compensation strategy based on the size of the molten pool under a specific structure to regulate the wall thickness / rod diameter, the negative effects of multiple contour scans are eliminated, and the size deviation from the model is avoided.

[0104] The present application also provides a LPBF magnesium alloy tissue engineering scaffold preparation system with smooth internal surface, which can be realized by executing the process steps of the LPBF magnesium alloy tissue engineering scaffold preparation method with smooth internal surface, that is, the LPBF magnesium alloy tissue engineering scaffold preparation method with smooth internal surface can be understood by those skilled in the art as the preferred embodiment of the LPBF magnesium alloy tissue engineering scaffold preparation system with smooth internal surface.

[0105] Specifically, a LPBF magnesium alloy tissue engineering scaffold preparation system with smooth internal surface comprises:

[0106] Module M1: scanning the porous scaffold to select the most dense filling scanning parameters;

[0107] The scanning includes single-pass contour scanning and single filling scanning;

[0108] Module M2: optimizing the contour scanning strategy according to the most dense filling scanning parameters;

[0109] Module M3: Obtain the corresponding molten pool size, adjust the spot compensation value using the optimized contour scanning strategy;

[0110] Module M4: Prepare the magnesium alloy tissue engineering scaffold based on the contour scanning strategy and the adjusted spot compensation value.

[0111] The module M1 comprises:

[0112] A single contour scan and a single filling scan are performed on the porous scaffold, the contour scan parameters and the filling scan parameters are consistent, after preparation, the sample is cut parallel to the preparation direction, the cross section is polished to obtain its optical micrograph and analyze its density; in the parameter combination with a density greater than 99.5%, the parameters of 0.05≤P / V≤0.5 are selected and set as P 填 , V 填 ;

[0113] Wherein, P is the laser power, and V is the scanning speed.

[0114] The module M2 comprises:

[0115] The filling scan parameters are selected as P 填 , V 填 , the contour scan parameters are set as P 轮 , V 轮 , the contour scan times are PT, and the contour parameters are calculated:

[0116] Wherein, the contour line energy density scaling factor Z=5-30, the contour front scan and the contour rear scan can be scanned multiple times within the range of the contour compensation value, the scanning order includes from inner circle contour scanning to outer circle contour scanning, or from outer circle contour scanning to inner circle contour scanning; the contour front scan and the contour rear scan can select different laser power P, scanning speed V, contour scan times PT, contour line energy density scaling factor Z and contour compensation value PC; the setting range of the filling compensation value FC is 0≤FC≤PC.

[0117] The module M3 comprises:

[0118] Obtain the molten pool width under the structure and process parameters, and optimize the spot compensation value;

[0119] Let the wall thickness / rod diameter of the original design scaffold model be T0, and the wall thickness / rod diameter after using the optimized contour scanning strategy be T1, then the spot compensation value is:

[0120] Wherein, SZ is the spot diameter, R 熔 is the molten pool width under P 填 / V 填 , and the size increase caused by multiple contour scans is compensated by adjusting the spot compensation value.

[0121] The module M1 further comprises a plurality of pre-scan profiles with a certain energy density before the filling scan according to the specific stent structure and the length of the under-surface overhang; and a plurality of post-scan profiles with a certain energy density after the filling scan according to the specific stent surface powder adhesion.

[0122] Those skilled in the art understand that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures within the hardware component.

[0123] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0124] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict.

Claims

1. A method for preparing a LPBF magnesium alloy tissue engineering scaffold with smooth inner surface, characterized in that, The method comprises the following steps: Step S1: scanning the porous scaffold to screen the most dense filling scanning parameters; The scanning comprises single-pass contour scanning and single filling scanning; Step S2: optimizing the contour scanning strategy according to the most dense filling scanning parameters; Step S3: obtaining the corresponding molten pool size, and adjusting the spot compensation value by using the optimized contour scanning strategy; Step S4: preparing the magnesium alloy tissue engineering scaffold based on the contour scanning strategy and the adjusted spot compensation value.

2. The method for preparing an inner surface-smoothed LPBF magnesium alloy tissue engineering scaffold according to claim 1, characterized in that, The step S1 comprises: A single contour scan and a single fill scan are performed on the porous scaffold, the contour scan parameters and the fill scan parameters are consistent, after preparation, the sample is cut parallel to the preparation direction, the cross section is polished to obtain its optical micrograph and analyze its density; in the parameter combination with a density greater than 99.5%, parameters with 0.05≤P / V≤0.5 are selected, which are set as P 填 , V 填 ; Wherein, P is the laser power, and V is the scanning speed.

3. The method of claim 2, wherein the method further comprises the step of: The step S2 comprises: ​ Select the fill scan parameter as P 填 , V 填 , set the contour scan parameter as P 轮 , V 轮 , the contour scan times as PT, calculate the contour parameter: Wherein, the contour line energy density scaling factor Z is 5-30, the contour pre-scan and the contour post-scan can be scanned multiple times within the range of the contour compensation value, the scanning sequence comprises scanning from the inner circle contour to the outer circle contour or scanning from the outer circle contour to the inner circle contour; the contour pre-scan and the contour post-scan can select different laser power P, scanning speed V, contour scanning times PT, contour line energy density scaling factor Z and contour compensation value PC; the setting range of the filling compensation value FC is 0≤FC≤PC.

4. The method of claim 3, wherein the method further comprises the step of: The step S3 comprises: Obtaining the molten pool width under the structure and process parameters, and optimizing the spot compensation value; Let the wall thickness / rod diameter of the original design stent model be To, and the wall thickness / rod diameter after using the optimized profile scanning strategy be T1. Then the spot compensation value is: wherein SZ is the spot diameter, R 熔 is the molten pool width under the corresponding P 填 / V 填 Adjusting the spot compensation value to compensate for the size increase caused by multiple contour scans.

5. The method for preparing the inner surface-smooth LPBF magnesium alloy tissue engineering scaffold according to claim 2, characterized in that, The step S1 further comprises setting multiple contour pre-scans with a certain energy density before the filling scanning according to the specific scaffold structure and the length of the lower surface overhang area; and setting multiple contour post-scans with a certain energy density after the filling scanning according to the surface powder adhesion of the specific scaffold.

6. A method for preparing a smooth inner surface LPBF magnesium alloy tissue engineering scaffold, characterized in that, The method comprises the following steps: Module M1: scanning the porous scaffold to screen the most dense filling scanning parameters; The scanning comprises single-pass contour scanning and single filling scanning; Module M2: optimizing the contour scanning strategy according to the most dense filling scanning parameters; Module M3: obtaining the corresponding molten pool size, and adjusting the spot compensation value by using the optimized contour scanning strategy; Module M4: preparing the magnesium alloy tissue engineering scaffold based on the contour scanning strategy and the adjusted spot compensation value.

7. The method of claim 6, wherein the method further comprises the step of: The module M1 comprises: ​ A single contour scan and a single fill scan are performed on the porous scaffold, the contour scan parameters and the fill scan parameters are consistent, after preparation, the sample is cut parallel to the preparation direction, the cross section is polished to obtain its optical micrograph and analyze its density; in the parameter combination with a density greater than 99.5%, parameters with 0.05≤P / V≤0.5 are selected and set as P 填 , V 填 ; Wherein, P is the laser power, and V is the scanning speed.

8. The method of claim 7, wherein the method further comprises the step of: The module M2 comprises: ​ Select the fill scan parameter as P 填 , V 填 , and set the contour scan parameter as P 轮 , V 轮 , the contour scan times as PT, and calculate the contour parameter: Wherein, the contour line energy density scaling factor Z is 5-30, the contour pre-scan and the contour post-scan can be scanned multiple times within the range of the contour compensation value, the scanning sequence comprises scanning from the inner circle contour to the outer circle contour or scanning from the outer circle contour to the inner circle contour; the contour pre-scan and the contour post-scan can select different laser power P, scanning speed V, contour scanning times PT, contour line energy density scaling factor Z and contour compensation value PC; the setting range of the filling compensation value FC is 0≤FC≤PC.

9. The method of claim 8, wherein the method further comprises the step of: The module M3 comprises: ​ Obtaining the molten pool width under the structure and process parameters, and optimizing the spot compensation value; Let the wall thickness / rod diameter of the original design stent model be To, and the wall thickness / rod diameter after using the optimized profile scanning strategy be T1. Then the spot compensation value is: wherein SZ is the spot diameter, R 熔 is the molten pool width under the corresponding P 填 / V 填 adjusting the spot compensation value to compensate for the size increase caused by multiple contour scans.

10. The method for preparing an LPBF magnesium alloy tissue engineering scaffold with a smooth inner surface according to claim 7, characterized in that, The module M1 further comprises setting multiple contour pre-scans with a certain energy density before the filling scanning according to the specific scaffold structure and the length of the lower surface overhang area; and setting multiple contour post-scans with a certain energy density after the filling scanning according to the surface powder adhesion of the specific scaffold.

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