Method for designing bionic bone scaffold based on wall thickness mixed gradient change

Abstract

The invention discloses a method for designing a bionic bone scaffold based on wall thickness mixed gradient change, and belongs to the technical field of bionic bone scaffolds. By designing the wall thickness mixed gradient function, the lattice unit can have wall thickness gradient change in the radial direction and the axial direction at the same time, so that the porosity also has gradient change in three directions at the same time, and the defect that a bone scaffold is designed by using a lattice material (beam unit) unit and a TPMS unit in the prior art can be well overcome; and the stent better conforms to the natural bone structure and mechanical property requirements. The designed bionic bone scaffold is excellent in mechanical property, high in compression resistance and deformation resistance and capable of promoting cell growth and tissue regeneration.

Description

Technical Field

[0001] The invention belongs to the technical field of bionic bone scaffolds, and in particular relates to a method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness. Background Art

[0002] The existing use of lattice units to construct bionic bone scaffolds mostly focuses on homogeneous porous structures or single axial and lateral gradient changes. Among the many lattice material unit structures, the Fluorite unit belongs to the cubic crystal system and has a face-centered cubic structure. Its good biocompatibility can reduce the rejection reaction between implant materials and human tissues. In addition, Fluorite has moderate hardness and can provide sufficient mechanical support without causing damage to surrounding tissues. By adjusting the geometry and porosity, mechanical properties close to those of the femur can be achieved.

[0003] The porous structure of tri-periodic minimal surface (TPMS) has controllable parameters and periodic smooth surfaces. The porous structure designed by TPMS method can achieve smooth surface connection, large specific surface area, and interconnected pores, which is very suitable for the structural design of porous bone scaffolds. However, the G unit in TPMS is the representative, and its design methods are mostly focused on homogeneous or single gradient changes to form porous structures, and most of them focus on research and innovation of offset, while there is little involvement in the design of new porous scaffolds by directly changing the wall thickness. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness, comprising:

[0007] (1) Use Ntopology software to create a CAD model of a cylindrical Fluorite unit homogeneous porous structure;

[0008] (2) Fitting the relationship between the wall thickness T1 and porosity P1 of the homogeneous porous structure of Fluorite unit by changing the wall thickness;

[0009] (3) According to the relationship between the structural wall thickness T1 and the porosity P1 obtained in step (2), a Fluorite unit mixed gradient porous structure function is established, thereby obtaining a Fluorite unit mixed gradient porous structure CAD model;

[0010] (4) The Fluorite unit mixed gradient porous structure CAD model is preliminarily divided into a finite element simulation mesh model using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model file in inp format is output using the output command;

[0011] (5) Import the simulation model file in inp format into HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp format file model again.

[0012] A method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness, comprising:

[0013] (1) Use Ntopology software to create cylindrical Gyroid unit homogeneous porous structure CAD models;

[0014] (2) Fitting the relationship between the wall thickness T2 and porosity P2 of the homogeneous porous structure of the Gyroid unit by changing the wall thickness;

[0015] (3) according to the relationship between the structure wall thickness T2 and the porosity P2 obtained in step (2), a Gyroid unit mixed gradient porous structure function is obtained, and then a Gyroid unit mixed gradient porous structure CAD model is established;

[0016] (4) The Gyroid unit mixed gradient porous structure CAD model is preliminarily divided into a finite element simulation mesh model using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model file in inp format is output using the output command;

[0017] (5) Import the simulation model file in inp format into HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp format file model again.

[0018] The present invention directly imports the inp file format model obtained by step (5) into the abaqus dynamics simulation module to simulate the quasi-static compression simulation, obtains the result data after the quasi-static compression finite element simulation, evaluates whether the yield strength and elastic modulus of the model are respectively within the yield strength and elastic modulus range of the cortical bone, if within the range, then the model established is the target bionic bone scaffold. Then the target bionic bone scaffold model of the design is constructed by conventional means in the art, such as: the inp file format model obtained by step (5) is outputted in the form of a model file of STL, then the computer is connected to a 3D printer, and the model file of STL form is imported into the 3D printer to print, and the target bionic bone scaffold is obtained.

[0019] As a preferred embodiment of the present invention, the relationship between the wall thickness T1 and the porosity P1 of the Fluorite unit homogeneous porous structure is P1=(1.10465-0.52955T1)×100%.

[0020] As a preferred embodiment of the present invention, the relationship between the wall thickness T2 and the porosity P2 of the Gyroid unit homogeneous porous structure is P2=(1.00186-0.4886T2)×100%.

[0021] As a preferred embodiment of the present invention, the gradient variation of the axial wall thickness of the Fluorite unit mixed gradient porous structure CAD model is as follows: 中心轴F +a F ×(H F / 2) 2 =T 上F and T 中心轴F +a F ×(H F / 2) 2 =T 下F Regular changes, the gradient of radial wall thickness changes according to T 中心轴F +b F ×R F 2 =T 边缘F Regular changes; among them, T 中心轴F is the wall thickness at the center of the Fluorite unit mixed gradient porous structure CAD model; T 上F and T 下F Respectively represent the wall thickness of the upper top surface and lower bottom surface of the Fluorite unit mixed gradient porous structure CAD model; T 边缘F is the wall thickness at the radial edge; H F and R F are the height and radius of the CAD model of the Fluorite unit mixed gradient porous structure; a F , bF is a constant, which is obtained by setting the target center porosity, upper top or lower bottom surface porosity, and edge porosity according to the relationship between the wall thickness T1 and the porosity P1 of the Fluorite unit homogeneous porous structure.

[0022] As a preferred embodiment of the present invention, the axial porosity and wall thickness of the Fluorite unit mixed gradient porous structure CAD model or the Gyroid unit mixed gradient porous structure CAD model change gradiently from the center to the upper top surface or the lower bottom surface, and the difference between the porosity at the center and the porosity at the upper top surface or the lower bottom surface is within 45%; the radial porosity and wall thickness change gradiently from the center to the edge, and the difference between the porosity at the center and the porosity at the edge is within 45%.

[0023] The porosity of the center, upper top surface or lower bottom surface of the Fluorite unit mixed gradient porous structure CAD model or the Gyroid unit mixed gradient porous structure CAD model is 50% to 95%. The porosity of the center, upper top surface or lower bottom surface can be adjusted according to actual needs to adjust the difference between the porosity at the center and the porosity at the edge or the difference between the porosity at the center and the porosity at the upper top surface or lower bottom surface to achieve the target porosity and wall thickness gradient change.

[0024] As a preferred embodiment of the present invention, the gradient change of the axial wall thickness of the Gyroid unit mixed gradient porous structure CAD model is as follows: 中心轴G +a G ×(H G / 2) 2 =T 上G and T 中心轴G +a G ×(H G / 2) 2 =T 下G Regular changes, the gradient of radial wall thickness changes according to T 中心轴G +b G ×R G 2 =T 边缘G Regular changes; among them, T 中心轴G is the wall thickness at the center of the CAD model of the Gyroid unit mixed gradient porous structure; T 上G and T 下G Respectively represent the wall thickness of the upper top surface and lower bottom surface of the Gyroid unit mixed gradient porous structure CAD model; T 边缘G is the wall thickness at the radial edge; H G and R G are the height and radius of the CAD model of the Fluorite unit mixed gradient porous structure; a G , b Gis a constant, which is obtained based on the relationship between the wall thickness T1 and the porosity P1 of the Gyroid unit homogeneous porous structure.

[0025] As a preferred embodiment of the present invention, the Fluorite unit mixed gradient porous structure function is specifically: T F =(T 中心轴F +b F (x 2 +y 2 ))+(T 中心轴F +a F z 2 ), where T F is the wall thickness of the Fluorite unit mixed gradient porous structure, x, y, z are the coordinate values ​​of the x, y, z directions of the three-dimensional Cartesian space coordinate system, a F and b F are all constants.

[0026] As a preferred embodiment of the present invention, the Gyroid unit mixed gradient porous structure function is specifically: T F =(T 中心轴G +b G (x 2 +y 2 ))+(T 中心轴G +a G z 2 ), where T G is the wall thickness of the Gyroid unit mixed gradient porous structure, x, y, and z are the coordinate values ​​of the x, y, and z directions of the three-dimensional Cartesian space coordinate system, respectively, and a F and b F are all constants.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention realizes that the lattice unit can have a wall thickness gradient change in the radial and axial directions, that is, in the three directions of x, y, and z in the spatial coordinate system by designing a wall thickness mixed gradient function, thereby causing the porosity to have a gradient change in the three directions at the same time, and the porosity gradient change in different parts enables the bracket to distribute stress more reasonably when subjected to external force. The higher porosity at the center of the axial direction can relieve pressure to a certain extent, while the lower porosity of the upper and lower bottom surfaces ensures the stability and support of the structure. On the radial plane, the design of low porosity at the edge and high porosity at the center enables the edge to provide better support and constraint, and the central part can absorb energy to a certain extent to reduce stress concentration. The overall cylindrical shape combined with the gradient porosity makes the mechanical properties of the bracket more balanced in all directions, and improves the overall anti-compression and anti-deformation ability. In addition, different porosities provide a diverse growth environment for cells. The low porosity area at the edge can guide the directional growth of cells and provide certain support; the high porosity area in the center is conducive to the exchange of nutrients and the discharge of metabolic waste of cells, and promotes cell proliferation and differentiation. This gradient pore structure is closer to the microstructure of natural tissue, providing a suitable biomechanical microenvironment for tissue regeneration and helping to accelerate tissue repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagrams of the Fluorite unit porous structure CAD model and the Gyroid unit porous structure CAD model, where (a) is the Fluorite unit porous structure CAD model and (b) is the Gyroid unit porous structure CAD model.

[0029] Figure 2 These are the fitting relationship diagrams of the wall thickness T1 and porosity P1 of the Fluorite unit homogeneous porous structure and the fitting relationship diagram of the wall thickness T2 and porosity P2 of the Gyroid unit homogeneous porous structure.

[0030] Figure 3 Schematic diagrams of the structures of the Fluorite unit mixed gradient porous structure CAD model and the Gyroid unit mixed gradient porous structure CAD model established in Example 1 and Example 2, respectively.

[0031] Figure 4 Strain distribution diagrams of the finite element models of the A1 and A2 porous structures established in Example 1 and Example 2 respectively under different strains in the elastic stage. DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] A method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness, comprising:

[0035] (1) Create a Fluorite (F) unit porous structure CAD model with homogeneous wall thickness, i.e., homogeneous porosity: In the Create module of the Ntopology software, create a cylindrical CAD model with a diameter and height of 14 mm × 20 mm. The model structure is a CAD model that is vertically and horizontally symmetrical with the origin (0, 0, 0) as the center point in the three-dimensional Cartesian coordinate system. Then, use the Graph Unite Cell command to select the Fluorite unit cell, and then use the Rectangular Volume Lattice command to set the initial wall thickness parameter (Thickness, T) to 0.5 mm to generate the following: Figure 1 The F unit homogeneous porous structure CAD model is shown. When the pore size is between 100μm and 1200μm, the porous scaffold can provide a good living space for bone cells, so the unit cell size is designed to be 4mm×4mm×4mm, and the default settings of Trim and Frame commands are sufficient.

[0036] (2) By changing the wall thickness of the Fluorite (F) unit porous structure CAD model of homogeneous porosity established in step (1), the relationship between the wall thickness T1 and the porosity P1 of the Fluorite unit homogeneous porous structure is fitted. The specific corresponding values ​​are shown in Table 1 below:

[0037] Table 1

[0038] <![CDATA[T1(mm)]]> 0.2 0.4 0.6 0.8 1 <![CDATA[F unit P1(%)]]> 97.53 90.77 80.83 68.74 55.59

[0039] According to the above parameters, the linear fitting results are as follows: Figure 2 As shown, P1 = (1.10465-0.52955T1) × 100%, and its linear fitting reliability is 98.561%, which meets the requirement of reliability of more than 98%.

[0040] (3) Determine the Fluorite unit mixed gradient porous structure scheme: There is a 15% porosity gradient change in the axial direction (Z direction of the three-dimensional Cartesian space coordinate system), that is, the porosity at the axial center axis is 95%, and the porosity of the upper top surface and the lower bottom surface is 80%. In the radial direction (x and y directions of the three-dimensional Cartesian space coordinate system), there is a 20% porosity gradient change, that is, the radial center porosity is 95%, and the edge porosity is 75%. At this time, the porosity gradually increases from the edge to the center along the radial direction. Substituting the specific porosities of 95%, 80%, and 75% into P1=(1.10465-0.52955T1)×100%, the corresponding wall thickness values ​​can be obtained as shown in Table 3 below.

[0041] Table 3

[0042] <![CDATA[Porosity P1%]]> 95 80 75 <![CDATA[T1 (mm) of Unit F]]> 0.2882 0.6148 0.7000

[0043] (4) Fluorite unit mixed gradient porous structure change function formula T F :Axial wall thickness according to T 中心轴F +a F ×(H F / 2) 2 =T 上F and T 中心轴F +a F ×(H F / 2) 2 =T 下F The radial wall thickness changes according to the rule of T 中心轴F +b F ×R F 2 =T 边缘F The regular changes (where H F and R F are the height and radius of the cylindrical F unit homogeneous porous structure CAD model, respectively. F 20mm, R F 7mm; T 中心轴F , T 上F and T 下F Respectively represent the wall thickness at the axial center axis, the upper top surface, and the lower bottom surface; T 边缘F represents the wall thickness of the radial edge) and thus the mixed gradient function of the wall thickness of the F unit is obtained as follows: T F =(T 中心轴F +b F ×(x 2 +y 2 ))+(T 中心轴F +a F × 2 ).

[0044] In this embodiment, the axial gradient function: According to Table 1, the central axis porosity of the Fluorite unit mixed gradient porous structure is 95% corresponding to the wall thickness T 中心轴F 0.2882mm, the porosity of the top and bottom surfaces is 80% corresponding to the wall thickness T 上F and T 下F is 0.6148 mm, therefore, the axial gradient function is 0.2882+a F ×(20 / 2) 2 =0.6148, we get a F =0.003266. Radial gradient function: According to Table 1, the central porosity of the Fluorite unit mixed gradient porous structure is 95% corresponding to the wall thickness T 中心轴F0.2882mm, edge porosity 75% corresponds to wall thickness T 边缘F is 0.7 mm, then 0.2882+b F ×7 2 = 0.7, so b F =0.0084, so the Fluorite unit mixed gradient porous structure change function formula T F =(0.2882+0.0084(x 2 +y 2 ))+(0.2882+0.003266z 2 ).

[0045] Complete T F After designing, create T in the Math module of Ntopology software F Formula, finally T F Substitute the formula into the Thickness in the Rectangular Volume Lattice command to complete the transformation from the homogeneous wall thickness value to the wall thickness following the coordinate position change. At this time, the regenerated CAD model is the Fluorite unit mixed gradient porous structure CAD model and is named A1. Figure 3 As shown, the overall average porosity is 62.51%, which meets the requirement that the porosity of cancellous bone should be between 50% and 90%.

[0046] (5) The Mesh form Implict Body command in the Ntopology software was used to preliminarily divide the mesh of the Fluorite unit mixed gradient porous structure CAD model file. Then, the Export FE Mesh command was used to generate an inp form CAD model file and imported into the HyperMesh software. The tetrahedral unit meshing method was used to re-divide the model, and the mesh unit type was set to C3D4 and the size was set to 0.1 mm. Finally, the Export command in the HyperMesh software was used to export the model again as an inp form CAD model file. The inp form CAD model file was then imported into the dynamics module of the Abaqus software for quasi-static compression finite element simulation and the elastic modulus of 110 GPa, the Poisson's ratio of 0.3, and the density of 4.51 g / cm 3 Set the material properties of Ti-6AL-4V, and set the mesh unit to yield failure when the maximum deformation ratio reaches 1.5. Set the compression boundary conditions: apply a 60% displacement load to the top surface, and only the Z direction is free to move in the X, Y, and Z directions, and other movements and rotations are completely restricted. Set the top and bottom surfaces as rigid surfaces, with a friction coefficient of 0.2 and a total simulation time of 0.006 seconds.

[0047] Example 2

[0048] A method for designing a bionic bone scaffold based on mixed gradient changes in wall thickness, comprising:

[0049] (1) Create a sheet-like (Sheet) Gyroid (G) unit porous structure CAD model with homogeneous wall thickness, i.e., homogeneous porosity: Step 1. In the Create module of the Ntopology software, create a cylindrical CAD model with a diameter and height of 14 mm × 20 mm. The model structure is a vertically and horizontally symmetrical CAD model with the origin (0, 0, 0) as the center point in the three-dimensional Cartesian coordinate system. Then, use the Walled TPMS Unite cell command to select the Gyroid unit cell. Then, use the RectangularVolume Lattice command to set the initial wall thickness parameter (Thickness, T) to 0.5 mm to generate the following: Figure 1 The CAD model of the homogeneous porous structure of unit G is shown. When the pore size is between 100μm and 1200μm, the porous scaffold can provide a good living space for bone cells, so the unit cell size is designed to be 4mm×4mm×4mm, and the default settings of Trim and Frame commands are sufficient.

[0050] (2) The relationship between the wall thickness T2 and the porosity P2 of the Gyroid unit homogeneous porous structure is fitted by changing the wall thickness. The specific corresponding values ​​are shown in Table 2 below:

[0051] Table 2

[0052] <![CDATA[T2(mm)]]> 0.2 0.4 0.6 0.8 1 <![CDATA[G unit P2 (%)]]> 90.35 80.65 70.95 61.17 51.23

[0053] According to the above parameters, the linear fitting results are as follows: Figure 2 As shown, P2=(1.00186-0.4886T2)×100%, and its linear fitting reliability is 99.997%, which meets the requirement of reliability of more than 98%.

[0054] (3) Determine the mixed gradient porous structure scheme of the G unit: there is a 25% porosity gradient change in the axial direction (Z direction of the three-dimensional Cartesian space coordinate system), that is, the porosity at the axial center axis is 90%, and the porosity of the upper top surface and the lower bottom surface is 65%. In the radial direction (x and y directions of the three-dimensional Cartesian space coordinate system), there is a 20% porosity gradient change, that is, the radial center porosity is 90%, and the edge porosity is 70%. At this time, the porosity gradually increases from the edge to the center along the radial direction. Substituting the specific porosities of 90%, 70%, and 65% into P1=(1.10465-0.52955T1)×100%, the corresponding wall thickness values ​​can be obtained as shown in Table 4 below.

[0055] Table 4

[0056] Porosity % 90 70 65 <![CDATA[G cell T2 (mm)]]> 0.2075 0.6202 0.7222

[0057] (4) Gyroid unit mixed gradient porous structure change function formula T G :Axial wall thickness according to T 中心轴G +a G ×(H G / 2) 2 =T 上G and T 中心轴G +a G ×(H G / 2) 2 =T 下G The radial wall thickness changes according to the rule of T 中心轴G +b G ×R G 2 =T 边缘G The regular changes (where H G and R G The height and radius of the cylindrical G unit homogeneous porous structure CAD model are respectively G 20mm, R G 7mm; T 中心轴G , T 上G and T 下G Respectively represent the wall thickness at the axial center axis, the upper top surface, and the lower bottom surface; T 边缘G Represents the wall thickness of the radial edge) From this, the mixed gradient function of the G unit wall thickness is obtained as follows: T G =(T 中心轴G +b G ×(x 2 +y 2 ))+(T 中心轴G +a G × 2 ).

[0058] In this embodiment, the axial gradient function: According to Table 1, the central axis porosity of the Gyroid unit mixed gradient porous structure is 90% corresponding to the wall thickness T 中心轴G 0.2075mm, the porosity of the top and bottom surfaces is 65% corresponding to the wall thickness T 上G and T 下G is 0.7222mm, so the axial gradient function is 0.2075+a G ×(20 / 2) 2 =0.7222, we get a G =0.005147. Radial gradient function: According to Table 1, the central porosity of the Gyroid unit mixed gradient porous structure is 90% corresponding to the wall thickness T 中心轴G 0.2075mm, edge porosity 70% corresponds to wall thickness T 边缘Gis 0.6202mm, then 0.2075+b G ×7 2 =0.6202 to get b G =0.00842, so the Gyroid unit mixed gradient porous structure change function formula T G =(0.2075+0.00842(x 2 +y 2 ))+(0.2075+0.005147z 2 ).

[0059] Complete T G After designing, create T in the Math module of Ntopology software G Formula, finally T G Substitute the formula into the Thickness in the Rectangular Volume Lattice command to complete the transformation from homogeneous wall thickness value to wall thickness following the change of coordinate position. At this time, the regenerated CAD model is the Gyroid unit mixed gradient porous structure CAD model and is named A2. Figure 3 As shown, the overall average porosity is 61.47%, which meets the requirement that the porosity of cancellous bone should be between 50% and 90%.

[0060] (5) The Mesh form Implict Body command in the Ntopology software was used to preliminarily divide the Gyroid unit mixed gradient porous structure CAD model file into a mesh. Then, the Export FE Mesh command was used to generate an inp CAD model file and imported into the HyperMesh software. The model was re-divided using the tetrahedral unit meshing method, and the mesh unit type was set to C3D4 and the size was set to 0.1 mm. Finally, the Export command in the HyperMesh software was used to export the model again as an inp CAD model file. The inp CAD model file was then imported into the dynamics module of the Abaqus software for quasi-static compression finite element simulation and the elastic modulus of 110 GPa, the Poisson's ratio of 0.3, and the density of 4.51 g / cm were set. 3 Set the material properties of Ti-6AL-4V, and set the mesh unit to yield failure when the maximum deformation ratio reaches 1.5. Set the compression boundary conditions: apply a 60% displacement load to the top surface, and only the Z direction is free to move in the X, Y, and Z directions, and other movements and rotations are completely restricted. Set the top and bottom surfaces as rigid surfaces, with a friction coefficient of 0.2 and a total simulation time of 0.006 seconds.

[0061] like Figure 4The deformation behavior of the A1 and A2 hybrid gradient porous structures was analyzed by finite element simulation. The results show that under load, the low-porosity area at the axial edge of the two hybrid gradient porous structures first bears pressure as the compression progresses. Because the material is dense, the deformation is small. The low-porosity parts of the upper and lower bottom surfaces provide support to limit the vertical deformation. The high-porosity area in the radial center gradually deforms, the pores shrink, and absorbs energy. At the axial center: the deformation of the high-porosity part increases, and the low-porosity area continues to support to prevent excessive deformation. In the final densification stage of this simulation: the overall structure deforms greatly under a large compressive force. The materials in the radial edge and the low-porosity areas on the upper and lower sides of the axial are dense, providing higher resistance to deformation. The pores in the central part are almost completely closed, but they gradually adapt to the pressure and maintain a certain structural integrity. In summary, the progressive compression and fracture behavior of the G unit helps to buffer the compression force, while the anisotropic mechanical properties and non-uniform deformation of the F unit help to adapt to different biomechanical environments.

[0062] Table 5 shows the yield strength and elastic modulus of the A1 and A2 mixed gradient porous structures after the above-mentioned quasi-static compression finite element simulation. From the data, it can be seen that the yield strength and elastic modulus of A1 and A2 are within the elastic modulus (3-20GPa) and yield strength (33-193MPa) of cortical bone, which can avoid stress shielding problems.

[0063] Table 5

[0064] type A1 A2 Yield strength (MPa) 79.66 150.06 Elastic model (GPa) 4.02 8.72

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness, characterized in that: include: (1) Use Ntopology software to create a CAD model of a cylindrical Fluorite unit homogeneous porous structure; (2) Fitting the relationship between the wall thickness T1 and porosity P1 of the homogeneous porous structure of Fluorite unit by changing the wall thickness; (3) Based on the relationship between the structural wall thickness T1 and the porosity P1 obtained in step (2), a Fluorite unit mixed gradient porous structure function with axial wall thickness and radial wall thickness gradient changes is established, thereby obtaining a Fluorite unit mixed gradient porous structure CAD model; (4) The Fluorite unit mixed gradient porous structure CAD model is preliminarily divided into a finite element simulation mesh model using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model file in inp format is output using the output command; (5) Import the simulation model file in inp format into HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp format file model again.

2. A method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness, characterized in that: include: (1) Use Ntopology software to create cylindrical Gyroid unit homogeneous porous structure CAD models; (2) Fitting the relationship between the wall thickness T2 and porosity P2 of the homogeneous porous structure of the Gyroid unit by changing the wall thickness; (3) Based on the relationship between the structural wall thickness T2 and the porosity P2 obtained in step (2), a Gyroid unit mixed gradient porous structure function with axial wall thickness and radial wall thickness gradient changes is obtained, and then a Gyroid unit mixed gradient porous structure CAD model is established; (4) The Gyroid unit mixed gradient porous structure CAD model is preliminarily divided into a finite element simulation mesh model using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model file in inp format is output using the output command; (5) Import the simulation model file in inp format into HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp format file model again.

3. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 1, characterized in that: The relationship between the wall thickness T1 and the porosity P1 of the Fluorite unit homogeneous porous structure is P1=(1.10465-0.52955T1)×100%.

4. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 2, characterized in that: The relationship between the wall thickness T2 and the porosity P2 of the Gyroid unit homogeneous porous structure is P2=(1.00186-0.4886T2)×100%.

5. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 3 or 4, characterized in that: The axial porosity and wall thickness of the Fluorite unit mixed gradient porous structure CAD model or the Gyroid unit mixed gradient porous structure CAD model change gradiently from the center to the upper top surface or the lower bottom surface, and the difference between the porosity at the center and the porosity at the upper top surface or the lower bottom surface is within 45%; the radial porosity and wall thickness change gradiently from the center to the edge, and the difference between the porosity at the center and the porosity at the edge is within 45%.

6. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 5, characterized in that: The gradient variation of the axial wall thickness of the Fluorite unit hybrid gradient porous structure CAD model is shown in Figure 2. 中心轴F +a F ×(H F / 2) 2 =T 上F and T 中心轴F +a F ×(H F / 2) 2 =T 下F Regular changes, the gradient of radial wall thickness changes according to T 中心轴F +b F ×R F 2 =T 边缘F Regular changes; among them, T 中心轴F is the wall thickness at the center of the Fluorite unit mixed gradient porous structure CAD model; T 上F and T 下F Respectively represent the wall thickness of the upper top surface and lower bottom surface of the Fluorite unit mixed gradient porous structure CAD model; T 边缘F is the wall thickness at the radial edge; H F and R F are the height and radius of the CAD model of the Fluorite unit mixed gradient porous structure; a F 、b F is a constant, which is obtained based on the relationship between the wall thickness T1 and the porosity P1 of the Fluorite unit homogeneous porous structure.

7. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 5, characterized in that: The gradient variation of the axial wall thickness of the Gyroid unit hybrid gradient porous structure CAD model is shown in Figure 2. 中心轴G +a G ×(H G / 2) 2 =T 上G and T 中心轴G +a G ×(H G / 2) 2 =T 下G Regular changes, the gradient of radial wall thickness changes according to T 中心轴G +b G ×R G 2 =T 边缘G Regular changes; among them, T 中心轴G is the wall thickness at the center of the CAD model of the Gyroid unit mixed gradient porous structure; T 上G and T 下G Respectively represent the wall thickness of the upper top surface and lower bottom surface of the Gyroid unit mixed gradient porous structure CAD model; T 边缘G is the wall thickness at the radial edge; H G and R G are the height and radius of the CAD model of the Fluorite unit mixed gradient porous structure; a G 、b G is a constant, which is obtained based on the relationship between the wall thickness T1 and the porosity P1 of the Gyroid unit homogeneous porous structure.

8. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 6, characterized in that: The Fluorite unit mixed gradient porous structure function is specifically: T F =(T 中心轴F +b F (x 2 +y 2 ))+(T 中心轴F +a F z 2 ), where T F is the wall thickness of the Fluorite unit mixed gradient porous structure, x, y, z are the coordinate values ​​of the x, y, z directions of the three-dimensional Cartesian space coordinate system, a F and b F are all constants.

9. The method for designing a bionic bone scaffold based on mixed gradient variation of wall thickness as claimed in claim 7, characterized in that: The Gyroid unit mixed gradient porous structure function is specifically: T F =(T 中心轴G +b G (x 2 +y 2 ))+(T 中心轴G +a G z 2 ), where T G is the wall thickness of the Gyroid unit mixed gradient porous structure, x, y, and z are the coordinate values ​​of the x, y, and z directions of the three-dimensional Cartesian space coordinate system, respectively, and a G and b G are all constants.

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