Preparation method of corrosion-resistant radial gradient porous bionic bone scaffold

Abstract

The present invention relates to a method for preparing a corrosion-resistant radial gradient porous bionic bone scaffold, and belongs to the field of medical machinery technology. The present invention first redesigns the offset C through the relationship between the Gyroid unit cell mathematical formula S (x, y, z) and the offset C, thereby improving the mathematical formula so that it is suitable for radial gradient porous scaffolds. Using the improved mathematical formula, a radial gradient porous rectangular parallelepiped model is generated using a Python script, and a cylindrical radial gradient porous model is obtained through a Boolean intersection operation. Subsequently, the model is smoothed and repaired, and a preliminary radial gradient porous scaffold is prepared by selective laser melting (SLM) forming technology. Finally, a finished radial gradient porous bionic bone scaffold is obtained by sandblasting. The present invention has stronger corrosion resistance, longer service life and larger specific surface area, is more conducive to the transmission, survival and attachment of bone cells, and has superior performance compared to traditional uniform porous scaffolds.

Description

Technical Field

[0001] The invention relates to a preparation method of a corrosion-resistant radial gradient porous bionic bone scaffold, belonging to the technical field of medical machinery. Background Art

[0002] Currently, bone tissue damage is a common clinical disease, and bone tissue engineering is an emerging treatment method for bone tissue damage. Ti6Al4V is an important lightweight structural material with advantages such as low density, high specific strength, and good heat resistance, and is widely used in the field of biomaterials. However, since the elastic modulus and density of solid Ti6Al4V do not match those of human bones, implantation into the human body will lead to a "stress shielding" effect, and the solid is not suitable for cell attachment and survival. Therefore, the three-dimensional network structure and high surface area provided by the porous Ti6Al4V biomaterial not only effectively reduce the stress shielding effect, but also support the survival, attachment, proliferation and differentiation of bone cells.

[0003] A common approach to designing biomimetic bone scaffold structures involves creating a uniform porous structure with single cells. However, this has significant drawbacks, such as stress concentration at the junctions and low surface area, which can be unsuitable for cell proliferation, differentiation, and nutrient transport. However, Gyroid-type porous structures based on triperiodic minimal surfaces (TPMS) offer a promising solution due to their controllable parameters and periodic, smooth surfaces. Porous structures designed using TPMS methods offer advantages such as smooth surface connections, large surface area, interconnected pores, and excellent mechanical properties, making them ideal for porous bone scaffold design. This structure is not without its drawbacks. Natural bone consists of cancellous bone, also known as trabecular bone, with a porosity of 50%-90%, primarily for nutrient transport. The outer layer of natural bone is dense cortical bone, with a porosity of no more than 10%, which plays a crucial role in maintaining mechanical strength. This uniform pore size structure is inconsistent with the natural structure of human bone and can also result in weak mechanical properties in the outer layer and limited mass transfer in the inner layer. And porous materials are more susceptible to corrosion than solid materials because they have a larger actual surface area exposed to the electrolyte, resulting in an increased corrosion rate.

[0004] During the 3D printing process, thermal adhesion and electrostatic adsorption of powder can cause unmelted powder particles to adhere to the surface of the printed part. Due to the unique structure of porous scaffolds, powder adhering to the pores cannot be removed through grinding or polishing. This results in a rough and uneven surface, which affects the cell delivery effect. Powder adhesion can also cause microscopic defects and cracks on the sample surface, thus reducing the service life of the porous scaffold in the human body.

[0005] In summary, it is crucial to study the corrosion resistance of porous titanium alloy bionic bone scaffolds. Improving the corrosion resistance, biocompatibility, and service life of porous scaffolds has very important application value and significance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a corrosion-resistant radial gradient porous bionic bone scaffold to solve the problems of poor corrosion resistance, short service life, limited cell proliferation and differentiation, and nutrient transport caused by the above-mentioned porous structure.

[0007] The technical solution of the present invention is: a method for preparing a radial gradient porous bionic bone scaffold structure based on TPMS, the method comprising the following steps:

[0008] S1 redesigned and calculated the bias C in the basic mathematical formula of the Gyroid unit cell to obtain an improved mathematical formula.

[0009] S2 imported the improved mathematical formula into the Python script to generate an STL file format model of a radial gradient porous rectangular block (7 mm × 7 mm × 10 mm).

[0010] S3 designed a cylindrical structure with a diameter of 7 mm and a height of 10 mm, and performed a Boolean intersection operation with the rectangular block to obtain a cylindrical radial gradient porous model.

[0011] Considering that the surface of the generated STL file was not smooth, S4 imported it into Geomagic Studio software and used the repair tool to repair and smooth the triangulated faces of the geometry to ensure that it met the design requirements.

[0012] S5: Transfer the data to the 3D printing device to prepare a preliminary radial gradient porous structure solid sample.

[0013] S6: sandblasting the surface and pore interior of the printed preliminary radial gradient porous sample to obtain a finished radial gradient porous bionic bone scaffold.

[0014] S7: The samples were subjected to electrochemical corrosion test in a SBF simulated body fluid environment at a constant temperature of 37°C.

[0015] Preferably, the basic mathematical model expression of the Gyroid cell in step S1 is:

[0016]

[0017] Where x, y, and z are spatial coordinates, w is the period, which can change the size of the aperture. In this invention, a unit cell with w = 2 mm is selected. C is the offset, which can adjust the shape of the surface to achieve the desired porosity.

[0018] Preferably, the bias C and porosity P in step S1 of the present invention are G Approximately satisfies the following relationship:

[0019] P G =(0.5000+0.3261C)×100%

[0020] Preferably, in order to achieve a continuous gradient distribution of porosity in step S1, the bias coefficient C is designed as a function of the x and y coordinates:

[0021]

[0022] Where a, n, and b are three parameters used to adjust the bias C and control the gradient distribution of porosity.

[0023] Preferably, the bone scaffold with an inner layer porosity of 50-90% of the natural bone in step S2 of the present invention is most conducive to bone cell growth, so a radial gradient porous rectangular block model with an average porosity of 50%, an inner layer porosity of 80%, and an outer layer porosity of 20% is designed.

[0024] Preferably, the ratio of the diameter to the height of the porous structure in step S3 is between 1 and 2. Therefore, a cylindrical structure with a diameter of 7 mm and a height of 10 mm was designed, and then a Boolean intersection operation was performed to obtain a model of a cylindrical radial gradient porous structure with a diameter of 7 mm and a height of 10 mm.

[0025] Preferably, in step S5, the porous model is sliced ​​using Magics software, and the data is then transferred to a German EOSM100 Selective Laser Melting (SLM) machine. Finally, Ti6Al4V powder is added to the powder bed chamber, the substrate is heated to 40°C, and printing is performed under the protection of an argon gas circulation system with an oxygen concentration below 0.1%. The sample is separated from the substrate using wire electrospark cutting and ultrasonically cleaned in alcohol for 30 minutes to remove any residual Ti6Al4V powder.

[0026] Preferably, in step S6, the radial gradient porous scaffold is surface treated by sandblasting technology. The air compressor power is 7.5kW, the pressure at the nozzle is 0.13Mpa, and the sandblasting material is corundum with an average particle size of 150 mesh.

[0027] Preferably, the instrument used in step S7 is a Swiss Metrohm AUTOLAB PGSTAT204 potentiostat. A classic three-electrode system is used, with the working electrode being a porous support, the auxiliary electrode being a platinum electrode, and a silver chloride electrode (Ag / AgCl / 3M KCl) as the reference electrode. The corrosive solution is SBF simulated body fluid at a constant temperature of 37°C. Electrochemical impedance spectroscopy (EIS) is performed in a frequency range of 10 -2HZ to 10 -5 The test was conducted at 100 Hz with an amplitude of 10 mV. The potentiodynamic polarization curves were tested in the potential range of ocp-0.3 V to ocp+2 V at a rate of 1 mV / s.

[0028] The beneficial effects of the present invention are:

[0029] The TPMS biomimetic bone scaffold structure was constructed using Gyroid surfaces, a type of minimal surface. This structure features a smooth surface and interconnected pores. By adjusting function parameters, the pore size and porosity can be flexibly adjusted to meet the needs of bone cell survival.

[0030] 2. Compared to traditional uniform porous scaffolds, this design better aligns with the structural characteristics of natural bone. Research has shown that natural bone has an uneven structure. The interior of natural bone is cancellous bone, also known as trabecular bone, with a porosity of 50%-90%, which is primarily used for the transport of nutrients. The outer layer of natural bone is dense cortical bone with a porosity of less than 10%, which plays an important role in maintaining the mechanical strength of the bone. Therefore, a radial gradient porous scaffold with an average porosity of 50% was designed. The porosity of the innermost layer was 80%, and the porosity gradually decreased from the innermost layer to the outermost layer, with a porosity of 20%. Therefore, this design better aligns with the structural characteristics of natural bone.

[0031] 3. Compared to traditional uniformly porous scaffolds, the radially gradient porous scaffold of the present invention offers enhanced corrosion resistance and a longer service life. Its innermost layer has a porosity of 80%, which decreases continuously from the innermost layer to the outermost layer. The smaller pore size of the outer layer slows the flow of electrolyte and charge exchange within the pores, making the outer supporting struts more corrosion-resistant and extending their service life.

[0032] 4. Compared with traditional 3D-printed porous scaffolds, the present invention reduces the roughness of the surface and the inside of the pores, reduces surface defects and cracks caused by powder adhesion, and thus improves the mechanical properties and service life of the scaffold.

[0033] 5. Compared with uniform porous scaffolds of the same volume, the surface area of ​​the radial gradient porous scaffold of the present invention is increased, which is more conducive to the survival, attachment, proliferation and differentiation of bone cells.

[0034] 6. Compared to traditional uniform porous scaffolds, this invention improves both cell delivery and mechanical properties. Because the porosity of the radially gradient porous scaffold increases radially from the edge to the center, the outer struts have larger diameters, providing better support. The inner pores are also larger, resulting in better cell and nutrient delivery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1It is the Boolean operation process of the porous structure of the present invention;

[0036] Figure 2 This is a model diagram of the radial gradient porous structure and uniform structure of the present invention;

[0037] Figure 3 This is the SEM image of the radial gradient porous scaffold and the uniform porous scaffold of the present invention;

[0038] Figure 4 is a macroscopic image of the radial gradient porous scaffold and the uniform porous scaffold of the present invention;

[0039] Figure 5 is a Nyquist plot of the electrochemical impedance spectroscopy test results of the radial gradient porous scaffold and the uniform porous scaffold of the present invention;

[0040] Figure 6 is a Bode diagram of the electrochemical impedance spectroscopy test results of the present invention;

[0041] Figure 7 is an equivalent circuit diagram of the electrochemical impedance spectroscopy fitting of the present invention;

[0042] Figure 8 It is a polarization curve diagram of the radial gradient porous scaffold and the uniform porous scaffold of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] Example 1: A method for preparing a radial gradient porous bionic bone scaffold structure based on TPMS, comprising the following steps:

[0045] S1: Construction of mathematical model;

[0046] The STL file format of the Gyroid radial gradient porous block structure is generated by importing the Gyroid unit cell mathematical formula into the Python script pymin. The basic mathematical formula of the Gyroid unit cell is shown in formula (1):

[0047]

[0048] Where x, y, and z are spatial coordinates, w is the period, which can change the size of the aperture. In this invention, a unit cell with w = 2 mm is selected. C is the offset, which can adjust the shape of the surface to achieve the desired porosity.

[0049] S2: Fit the bias C and unit porosity P G Linear relationship;

[0050] To achieve precise control of the porosity, it is necessary to model the Gyroid unit cell design and change the offset C in Equation (1) to determine the interface between the pore region and the solid region. It is defined that when S(x, y, z) > C, it is the solid part, and when S(x, y, z) < C, it is the pore part. By adjusting the value of C, we can offset the surface inward or outward, thereby changing the volumes of both the pore and solid regions simultaneously, that is, changing the porosity of the unit cell.

[0051] The unit cell porosity is calculated as:

[0052]

[0053] where P G is the unit cell porosity, V is the volume of the TPMS porous structure within a three-dimensional periodic unit cell, and V0 is the volume of this three-dimensional periodic cuboid.

[0054] By fitting different offset values C, different porous unit cell models are obtained. The unit cell model is imported into Magics to calculate its volume V, and then P G is calculated according to formula (2), and the approximate linear relationship between the offset C and the porosity P G approximately satisfies equation (3):

[0055] P G = (0.5 + 0.3261C) × 100% (3)

[0056] S3: Design the offset C;

[0057] To achieve a continuous gradient distribution of the porosity, the offset coefficient C is designed as a function of the x and y coordinates. From Equation (4), we get:

[0058]

[0059] where a, n, and b are three parameters used to adjust the offset coefficient C and are used to control the gradient distribution of the porosity.

[0060] Furthermore, given the radius R of the porous structure and the height H, r is the radius from the inner layer to the outer layer of the gradient porous structure (0 ≤ r ≤ R). In this structure, the porosity of the inner layer region (r = 0) is P in , and the porosity of the outer layer region (r = R) is P out . The corresponding offset values for the inner and outer layers are C in and C out . Given the premise of n = 2, the coefficients a and b can be obtained from Equation (5) and Equation (6) respectively:

[0061]

[0062] b = C in(6)

[0063] Inner layer porosity P in and outer layer porosity P out Satisfying the relationship in formula (7):

[0064] P in +P out =100% (7)

[0065] S4: Porosity P of the inner layer according to the radial gradient structure in , calculate the corresponding offset C and obtain the mathematical formula of the radial gradient porous structure model;

[0066] According to ISO 13314, the aspect ratio of the porous structure is set between 1 and 2. Therefore, this embodiment designs a cylindrical porous structure with a height of 10 mm and a diameter of 7 mm. This embodiment selects a structure with an average porosity of 50%.

[0067] Studies have shown that the porosity of natural femur is 50-90%. The porosity of bone scaffold at this time is most conducive to the growth of bone cells. Therefore, the inner layer porosity P is designed. in The 80% radial gradient porous scaffold and the 50% uniform porous scaffold were used as controls. For easy distinction, the uniform scaffold is represented by 0.5 and the radial gradient scaffold is represented by 0.8.

[0068] P in Assigned to 80%, P out Assign a value of 20%. Substituting into formula (3) we can calculate C in and C out , and then C in and C out Substituting (5) and (6) into equations can calculate a and b in the gradient structure, and then substituting a and b into equation (4) can obtain C(x, y).

[0069] Substituting w = 2 and C(x, y) into Equation (1) yields the complete mathematical formula for the radial gradient porous structure, as shown in Table 1. The C value for the uniform porous structure control group is 0. This expression is then imported into a Python script to generate an STL file for a gradient porous cuboid structure (7 mm × 7 mm × 10 mm).

[0070] Table 1: Mathematical formulas for radial gradient structure and uniform structure

[0071] sample Mathematical model Uniform 0.5 sin(πx)cos(πy)+sin(πy)cos(πz)+sin(πz)cos(πx)=0 Radial Gradient 0.8 <![CDATA[sin(πx)cos(πy)+sin(πy)cos(πz)+sin(πz)cos(πx)=-0.1502(x 2 +y 2 )+0.9199]]>

[0072] S5: The ratio of the diameter to the height of the porous structure is between 1 and 2. Therefore, a cylindrical structure with a diameter equal to its side length and a height equal to its side length is designed. Then, by performing a Boolean intersection operation, a cylindrical porous structure with a diameter of 7 mm and a height of 10 mm is obtained, as shown in Figure 1 shown.

[0073] S6: Considering that the surface of the generated STL file is not smooth, it is imported into Geomagic Studio software, and the repair tool is used to repair the triangulated faces and smooth the geometry to ensure that it meets the design requirements.

[0074] S7: Model of porous scaffolds such as Figure 2 As shown in Figure 2, the porosity of the radial gradient porous structure gradually decreases from the innermost layer to the outside, forming a porous structure with a continuous gradient distribution. The pore size range and surface area of ​​the radial gradient porous structure were measured by Magics, as shown in Table (2). According to Table (2), it can be seen that the surface area of ​​the radial gradient porous structure is significantly higher than that of the uniform structure, which is more suitable for the survival, attachment, proliferation, differentiation and transport of nutrients of bone cells.

[0075] Table 2: Porosity range and surface area for radial gradient structures and uniform structures

[0076] sample Pore ​​size range (μm) <![CDATA[Surface area (mm 2 )]]> Uniform 0.5 500.5 743.87 Radial Gradient 0.8 156.8～918.9 783.53

[0077] S8: Physical preparation of radial gradient porous samples;

[0078] The porous model was sliced ​​using Magics software, and the data was transferred to a German EOS M100 selective laser melting (SLM) machine. Finally, Ti6Al4V powder was added to the powder bed chamber, the substrate heated to 40°C, and printing was performed under an argon gas circulation system with an oxygen concentration below 0.1%. The printing laser power was 160W, the scan speed was 1100mm / s, the powder layer thickness was 0.02mm, the scan pitch was 0.1mm, and the scan width was 0.06mm. The sample was cut from the substrate using wire EDM and ultrasonically cleaned in alcohol for 30 minutes to remove any residual Ti6Al4V powder.

[0079] S9: The printed preliminary radial gradient porous scaffold was surface treated using sandblasting technology.

[0080] Since there are a lot of unmelted adhered powders on the surface and inside the pores of the 3D printed porous scaffolds, the roughness of the sample surface and the inside of the pores will be high, which is not conducive to cell transmission. Powder adhesion will also cause defects and cracks on the scaffold surface, thereby reducing the mechanical properties and service life of the scaffold. Therefore, the radial gradient porous scaffold is surface treated by sandblasting technology. The air compressor power is 7.5kW, the pressure at the nozzle is 0.13Mpa, the sandblasting material is corundum, and the average particle size is 150 mesh. The SEM pictures before and after sandblasting are as follows: Figure 3 The macroscopic images of the radial gradient porous scaffold and the uniform porous scaffold are shown in Figure 2. Figure 4 shown.

[0081] S10: The electrochemical corrosion experiment was carried out in a constant temperature environment (37°C) using a Swiss Metrohm AUTOLABPGSTAT204 potentiostat. A classic three-electrode system was used, with the porous support as the working electrode, the platinum electrode as the auxiliary electrode, and the silver chloride electrode (Ag / AgCl / 3M KCl) as the reference electrode. SBF was used as the corrosion solution to simulate body fluids. Before the electrochemical test, the sample was ultrasonically cleaned in SBF to ensure that the pores were filled with electrolytes. The sample was placed at -1.0V. Ag / AgCl The constant potential polarization was carried out for 180s at a potential to remove the oxide layer and impurities formed on the sample surface in the air. -2 HZ to 10 -5 Electrochemical impedance spectroscopy (EIS) was tested under the conditions of HZ and amplitude of 10mv. The Nyquist plot is shown in Figure 5 , Bode diagram as Figure 6 Then use Zview software to fit the data, the equivalent circuit diagram is as follows Figure 7 The fitting results are shown in Table 3.

[0082] Table 3: EIS fitting parameters of porous scaffolds in SBF solution at 37°C

[0083]

[0084] Table 3 summarizes the EIS fitting results of the porous scaffolds. R ct Is the charge transfer resistance. Generally speaking, the corrosion resistance of materials is mainly evaluated by R ct Value. ct The higher the value, the more difficult the reaction is and the better the corrosion resistance is. From Table 2, we can see that the R ct The value is significantly lower than that of radial gradient porous scaffolds. ct The value reached 22963Ωcm 2 , an improvement of nearly 50% compared to uniform brackets.

[0085] Then, the sample was subjected to potentiodynamic polarization curve test in SBF simulated body fluid at 37°C with a potential range of ocp-0.3V to ocp+2V and a speed of 1mV / s. The polarization curve is shown in the figure below. Figure 8 Then the corrosion potential (Ecorr) and corrosion current density (icorr) were calculated using the Tafel extrapolation method, and the corrosion parameters are shown in Table 4.

[0086] Table 4: Corrosion parameters of porous scaffolds in SBF solution at 37°C

[0087]

[0088] Table 4 summarizes the corrosion parameters of porous scaffolds. The corrosion current density (icorr) is a kinetic parameter and is usually used as an important parameter to evaluate the corrosion rate. corr The larger the value, the faster the corrosion rate, indicating that the corrosion resistance of the material is worse. From Table 4, we can find that the i of the uniform bracket corr The value is higher than that of radial gradient porous scaffolds. corr The value is only 1.5344×10 -7 A / cm 2 The corrosion resistance of the radial gradient porous scaffold is improved by nearly 50% compared with the uniform scaffold. This shows that the corrosion resistance of the radial gradient porous scaffold of the present invention is greatly improved compared with the ordinary uniform scaffold, which is consistent with the previous electrochemical impedance spectroscopy test results.

[0089] The electrochemical corrosion test results show that the corrosion resistance of the radial gradient porous scaffold of this design is significantly better than that of the ordinary uniform structure. The experimental results show that the corrosion resistance of the radial gradient porous scaffold of the present invention is nearly 50% higher than that of the uniform scaffold. The main reason is that the interconnected large pores can provide a large number of electrolyte capture points, which ultimately promote crevice corrosion. In the outer layer with low porosity of the present invention, the individual small pores can greatly limit the free flow of the electrolyte, slow down the charge transfer rate, and make it more resistant to crevice corrosion. The inner layer porosity of the radial gradient porous scaffold of the present invention is as high as 80%, which improves the cell transfer performance compared to the uniform scaffold. The outer layer porosity is only 20%, which greatly reduces the flow of electrolyte and charge exchange compared to the uniform scaffold, making the outer layer support pillars more corrosion-resistant and having a longer service life in the human body.

[0090] The above describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for preparing a corrosion-resistant radial gradient porous bionic bone scaffold, characterized in that: The method comprises: S1: Redesign and calculate the offset C in the basic mathematical formula of the Gyroid unit cell to obtain an improved mathematical formula; S2: Import the improved mathematical formula into the Python script to generate a radial gradient porous cuboid model; S3: Design a cylindrical structure with the same size as the inscribed cylinder of the rectangular parallelepiped model, and then perform a Boolean intersection operation with the rectangular parallelepiped model to generate a radial gradient porous cylindrical model; S4: Import the model into Geomagic Studio software and use the repair tool to perform triangulation repair and smoothing on the geometry; S5: Transfer the model data to the 3D printing device to print the radial gradient porous scaffold; S6: treating the surface and pore interior of the printed radial gradient porous scaffold using a sandblasting technique to obtain a finished radial gradient porous bionic bone scaffold; The basic mathematical model expression of the Gyroid cell in step S1 is: ； Where x, y, z are spatial coordinates, w is the period, and C is the offset; In step S1, the offset C and the porosity P G Approximately satisfies the following relationship: P G =(0.5000+0.3261C)×100%; The offset C is designed as a function of the x and y coordinates: ； Where a, n, and b are three parameters used to adjust the bias coefficient C, which is used to control the gradient distribution of porosity.

2. The method for preparing the corrosion-resistant radially gradient porous bionic bone scaffold according to claim 1, characterized in that: In step S2, the inner layer porosity of natural bone is 50-90%, the average porosity of the radial gradient scaffold is 50%, the inner layer porosity is 80%, and the outer layer porosity is 20%.

3. The method for preparing the corrosion-resistant radial gradient porous bionic bone scaffold according to claim 1, characterized in that: Step S3 is specifically as follows: A radial gradient porous scaffold with a diameter to height ratio of 1-2, a cylindrical structure with a circular diameter of 7 mm and a height of 10 mm was designed. The cylindrical structure was subjected to a Boolean intersection operation with a rectangular block to obtain a cylindrical radial gradient porous structure with a diameter of 7 mm and a height of 10 mm.

4. The method for preparing the corrosion-resistant radial gradient porous bionic bone scaffold according to claim 1, characterized in that: Step S5 is specifically as follows: The porous model was sliced ​​using Magics software, and the data was transferred to the laser melting equipment. The substrate was then heated to 40°C, and Ti6Al4V powder was added to the powder bed chamber. Printing was carried out under the protection of an argon circulation system with an oxygen concentration of less than 0.1%. The sample was cut from the substrate using wire electrospark cutting and ultrasonically cleaned in alcohol for 30 minutes to remove the residual Ti6Al4V powder on the sample.

5. The method for preparing the corrosion-resistant radially gradient porous bionic bone scaffold according to claim 1, characterized in that: When the surface of the radial gradient porous scaffold is sandblasted in step S6, the pressure at the nozzle is 0.13 MPa, and the sandblasting material is corundum with an average particle size of 280 mesh.

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