Design method of bionic bone scaffold based on TPMS

Abstract

The invention discloses a design method of a bionic bone scaffold based on a TPMS (Tire Pressure Monitor System), and belongs to the technical field of bionic bone scaffolds. According to the method, on the basis of a G unit formula and a D unit formula, a bias function is adjusted to generate a G gradient unit CAD model and a D homogeneous unit CAD model; fusing the CAD model of the G gradient unit and the CAD model of the D homogeneous unit by using a fusion function to generate a GD radial fusion CAD model, and adjusting an offset function of the G gradient unit by adopting an interpolation method to enable the GD radial fusion CAD model to reach a target average porosity; reducing the wall thickness of the GD radial fusion CAD model to form a GD radial fusion CAD model with the wall thickness; then, a finite element simulation grid model is divided, and an inp-format simulation model file is output; importing the simulation model file in the inp format into HyperMesh software for repairing, and dividing grids to export the model in the inp file format. According to the porous scaffold designed by the invention, different functional grades of a natural bone structure are considered, and different unit cell polymorphic fusion is carried out, so that the porous scaffold better conforms to the mechanical properties of natural thighbones, and the specific surface area is increased by virtue of the lightweight design, so that more space is provided for bone cell adhesion and growth.

Description

Technical Field

[0001] The invention belongs to the technical field of bionic bone scaffolds, and in particular relates to a design method of a bionic bone scaffold based on TPMS. Background Art

[0002] At present, bone tissue damage is a common clinical disease, and bone tissue engineering is an emerging treatment method for bone tissue damage. It simulates the structure and physiological function of bones by building porous scaffolds to achieve the repair and reconstruction of damaged bone tissue. Its advantages include solving the problems of traditional treatment methods, such as limited autologous transplantation of bone tissue, high risk of allogeneic transplantation, and limited effect of drug treatment. In addition, bone tissue engineering can also accurately control the mechanical properties and bioactivity of the scaffold to meet the needs of different patients.

[0003] Commonly used methods for designing bionic bone scaffold structures include designing a unit cell to form a homogeneous porous structure, consisting of a single rod and node, or forming different unit cell structures by combining rods and nodes to form different porous structures. However, there are also obvious disadvantages, such as: not conforming to the natural femoral structure, prone to stress concentration in the connecting part, too low specific surface area, and not suitable for cell proliferation and differentiation and the transportation of nutrients.

[0004] However, the three-periodic minimal surface (TPMS) porous structure can effectively solve the above problems because of its controllable parameters and periodic smooth surface. The porous structure designed by the 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. Among the many TPMS structures, Gyroid (G) surface and Diamond (D) surface are two common TPMS surface types. In the TPMS porous structure made of G and D surfaces, by adjusting the parameters such as the geometry and porosity of the G surface, a porous structure with mechanical ability similar to that of cancellous bone can be obtained. The D type is more advantageous than the G type as an outer layer unit to simulate the load of cortical bone, because in terms of mechanical properties, the D type has a smoother wall surface that can effectively alleviate the stress concentration phenomenon. The G type porous structure has relatively small fluctuations on the stress-strain curve and a longer platform area, which is more stable and more suitable for energy absorption.

[0005] However, the radial gradient porous structure formed by only selecting one G unit in TPMS is still insufficient in simulating the characteristics of the real femoral structure. There is also a problem that the average porosity of the simulated outer cortical bone is low, which makes the porosity of the overall porous structure low. If the porosity is too high, the strength of the porous structure will be reduced and eventually it will fail. The transfer from cortical bone to cancellous bone should also be a smooth process. Summary of the invention

[0006] In view of the above shortcomings of the prior art, the present invention provides a design method of a bionic bone scaffold based on TPMS to solve the problems of stress concentration, cell proliferation and differentiation, and nutrient transport caused by the porous structure.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A design method of a bionic bone scaffold based on TPMS comprises the following steps:

[0009] (1) Based on the G unit formula and the D unit formula, the offset function is adjusted to generate the G gradient unit CAD model and the D homogeneous unit CAD model on the Ntopology software;

[0010] (2) using a fusion function to fuse the G gradient unit CAD model and the D homogeneous unit CAD model to generate a GD radial fusion CAD model;

[0011] (3) A CAD model A with a smaller size than the GD radial fusion CAD model but the same shape is established, and the GD radial fusion CAD model and the CAD model A are fused using a fusion function to generate a GD radial fusion CAD model with wall thickness. Then, the offset function of the G gradient unit CAD model is adjusted using an interpolation method to adjust the average porosity of the GD radial fusion CAD model with wall thickness to the target average porosity.

[0012] (4) reducing the wall thickness of the GD radial fusion CAD model with wall thickness of the target average porosity to form a GD radial fusion CAD model with wall thickness;

[0013] (5) Divide the CAD model of GD radial fusion with wall thickness into a finite element simulation mesh model in Ntopology software, and finally output the simulation model file in inp format;

[0014] (6) Import the simulation model file in inp format into HyperMesh software to repair and re-divide the mesh, use the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp file format model again;

[0015] (7) Import the inp format file model generated in step (6) into the display dynamics module of the Abaqus software to perform quasi-static compression finite element simulation

[0016] The present invention directly imports the inp file format model obtained by step (6) 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 cancellous bone and cortical bone, if within the range, then the model established is the target bionic bone scaffold. The target bionic bone scaffold model designed can be constructed by conventional means in the art, such as: the inp file format model obtained by step (6) is output as a model file in the form of STL using the Export command, then the computer is connected to a 3D printer, and the model file in the form of STL is imported into the 3D printer to print, and the target bionic bone scaffold is obtained.

[0017] As a preferred embodiment of the present invention, in step (1), the G unit formula is G (x,y,z)=cos(ωx)sin(ωy)+cos(ωy)sin(ωz)+cos(ωz)sin(ωx)-C1(x,y,z); D unit common

[0018] Ψ D (x,y,z)=sin(ωx)sin(ωy)sin(ωz)+cos(ωx)cos(ωy)sin(ωz)+

[0019] The formula is;

[0020] sin(ωx)cos(ωy)cos(ωz)+sin(ωx)sin(ωy)cos(ωz)-C2(x,y,z)

[0021] Where x, y, z represent the x, y and z directions in the rectangular space coordinate system; ω is a constant that determines the period of the surface, ω = 2Π / l, l is the unit cell size; C1(x, y, z) and C2(x, y, z) represent the offset functions that determine the surface; Ψ G (x,y,z) and Ψ D (x, y, z) represent the TPMS function formulas of G unit and D unit respectively.

[0022] As a preferred embodiment of the present invention, in step (1), according to the bias function C2 of the D homogeneous unit and the porosity P D The relationship formula of adjust the offset function to make the average porosity of the D homogeneous unit CAD model less than 50%; the offset function C2 of the D homogeneous unit and the average porosity P D The relationship formula is P D =(0.5002+0.4135C2)×100%; C2 is a fixed value.

[0023] As a preferred embodiment of the present invention, in step (1), the porosity and pore size of the G gradient unit CAD model increase in a gradient from the outside to the inside on the cross section, and there is a minimum porosity P at the edge of the G gradient unit CAD model. out , the center has the maximum porosity P in .

[0024] As a preferred embodiment of the present invention, in step (1), according to the bias function C1 of the G gradient unit and the porosity P G The relationship formula makes the average porosity of the G gradient unit CAD model 50-90%; the offset function C1 of the G gradient unit and the average porosity P G The relationship formula is P G =(0.4998+0.3246C1)×100%; where the offset function C1 is a function form related to the coordinates and is a variable; the expression of C1 is: C out = k(x 2 +y 2 )+C in , where C out is the offset function value of the outer edge of the G gradient unit CAD model, P out =(0.4998+0.3246C out )×100%; C in is the offset function value of the center of the G gradient unit CAD model, P in =(0.4998+0.3246C in )×100%; x, y are the coordinates x and y of the point where the xy plane intersects the edge of the G gradient unit CAD model, respectively. The present invention establishes an upper, lower, left, and right symmetrical CAD model with the origin (0,0,0) as the center in the three-dimensional Cartesian coordinate system, where each z value in the xy plane is zero.

[0025] The present invention G =(0.4998+0.3246C1)×100% and P D =(0.5002+0.4135C2)×100% is obtained by taking 7 bias function C values ​​of -0.8, -0.6, -0.4, -0.2, 0, 0.2, and 0.4 corresponding to 7 porosity P values ​​and taking linear fitting. The reliability (R) of both is 99.998%, which meets the requirement of more than 98%.

[0026] The present invention is based on the offset function C1 of the G gradient unit and the porosity P G The relationship formula and the offset function C2 of the D homogeneous unit and the porosity P DThe bias function is adjusted by the relationship formula to make the average porosity of the GD radial fusion CAD model 50-90%. In practical application, the GD radial fusion CAD model with the target average porosity can be selected according to actual needs, and the bias function of the G gradient unit CAD model can be adjusted by interpolation method to make the average porosity of the GD radial fusion CAD model the target average porosity.

[0027] The step (1) is specifically as follows: a cylindrical or cubic CAD model is established in the Create module of the Ntopology software, and then a G unit formula and a D unit formula are input in the Math module, the offset function is adjusted respectively, and a G gradient unit CAD model and a D homogeneous unit CAD model are generated respectively using a Boolean subtraction instruction.

[0028] More preferably, since the present invention is directed to a bionic bone scaffold that simulates the structure of a human femur (thigh bone), it is preferred to establish a cylindrical CAD model, and the ratio of the height to the diameter of the cylindrical CAD model is 1-2.

[0029] As a preferred embodiment of the present invention, the fusion function is tan(ax), wherein a is a constant representing the fusion period; and x is the x direction of the spatial coordinate system.

[0030] More preferably, the fusion function is tan(x / 2).

[0031] The step (2) is specifically as follows: firstly, a fusion function tan(ax) is created in the Math module of the Ntopology software, then a Ramp fusion instruction is called out, and finally a GD radial fusion CAD model is preliminarily generated using a Boolean intersection instruction.

[0032] As a preferred embodiment of the present invention, in the step (4), the wall thickness is reduced by reducing the Thickness parameter through the Shell command, so that the porosity of the CAD model of the GD radial fusion zone wall thickness is 50-90%.

[0033] As a preferred embodiment of the present invention, the wall thickness of the CAD model of the GD radial fusion zone wall thickness is smaller than that of the GD radial fusion CAD model. The target porosity can be obtained by changing the numerical value of the reduced wall thickness.

[0034] As a preferred embodiment of the present invention, the outer layer of the CAD model of the GD radial fusion zone wall thickness is a D homogeneous unit structure, and the inner layer is a G gradient unit structure. The porosity and pore size of the G gradient unit structure are both gradient changes that increase along the radial direction from the edge to the center.

[0035] The offset function C2 of the outer layer D homogeneous unit structure is set to a constant -0.4847. At this time, the porosity of the D unit porous structure CAD model formed is 30%. The G gradient unit porous structure is a function form related to the coordinates, which makes the G unit model gradually increase in porosity from the edge to the center along the radial direction, and the pore size formed also increases from the edge to the center along the radial direction. This has a gradient change. However, it is necessary to ensure that the porosity and pore size of the overall G gradient unit CAD model are within the range of 50% to 90% and 100μm-1200μm respectively. The proportion of G gradient units in the CAD model of GD radial fusion with wall thickness can be set by changing the InMax value in the fusion command Ramp as needed. When In Max is 0, the fusion model is all outer layer D homogeneous unit porous structure. As the value in In Max increases, the proportion of G gradient units gradually increases from the center to both sides.

[0036] As a preferred embodiment of the present invention, the unit cell size L1 of the D homogeneous unit structure is L1=2mm×2mm×2mm; the unit cell size L2 of the G gradient unit structure is L2=2mm×2mm×2mm.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention uses a new fusion method in structural design to fuse Gyroid surfaces and Domaind surfaces in multiple forms, and designs a new bionic bone scaffold by adjusting the offset function parameters and wall thickness. The surface of the scaffold is smooth and the pores are interconnected. The large specific surface area provides more space for bone cell adhesion and growth, and the scaffold conforms to the elastic modulus and yield strength of cancellous bone and cortical bone of the human body. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of forming gradient porous structure for G unit and generating uniform porous structure cylinder for D unit; (a) is the schematic diagram of generating Gyroid radial gradient porous structure CAD model for G unit; (b) is the schematic diagram of generating Domaind homogeneous porous structure CAD model for D unit.

[0039] Figure 2 is the G unit cell offset C1 and porosity P G The fitting relationship between the D unit cell offset C2 and the porosity P D The fitting relationship between the G unit cell offset C1 and the porosity P G (b) is the fitting relationship between the D unit cell offset C2 and the porosity P D The fitting relationship between them.

[0040] Figure 3Schematic diagram of the cross-section of the CAD model of the GD radial fusion zone wall thickness.

[0041] Figure 4 Schematic diagram of the model of the GD radial fusion CAD model of GD1, GD2 and GD3 generated in Example 1 and the GD radial fusion CAD model GD4 with wall thickness.

[0042] Figure 5 The upper surface strain distribution diagrams are produced for the elastic stage of the finite element models of GD1, GD2, GD3 and GD4 under different strains, where ε is the strain.

[0043] Figure 6 This is the yield strength and elastic modulus distribution diagram corresponding to the porous structure samples of GD1, GD2, GD3, and GD4 after the finite element simulation is completed. DETAILED DESCRIPTION

[0044] 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.

[0045] Example 1

[0046] A design method of a bionic bone scaffold based on TPMS comprises the following steps:

[0047] (1) First, in the Create module of the Ntopology software, a CAD model of a cylinder with a diameter and height of 8 mm × 12 mm is created. At this time, the internal coordinates (x, y, z) of the cylinder are in the range (-4 ≤ x ≤ 4, -4 ≤ y ≤ 4, -6 ≤ z ≤ 6). Then, in the Math module, enter the G unit formula Ψ shown in Table 1. G (x,y,z) and D unit formula Ψ D (x,y,z).

[0048] Table 1

[0049]

[0050] Where x, y, z represent the x, y and z directions in the rectangular space coordinate system; ω is a constant, i.e. ω = 2Π / l, which determines the period of the surface; in this embodiment, the unit cell size is 2mm×2mm×2mm, and l is 2mm; C1(x, y, z) and C2(x, y, z) represent the offset function that determines the surface, Ψ G (x,y,z) and Ψ D (x, y, z) represent the TPMS function formulas of G unit and D unit respectively.

[0051] (2) Figure 2 As shown, using P D=(0.5002+0.4135C2)×100% is set as C2(x, y, z) is a constant -0.4847, and a Domaind homogeneous porous structure CAD model with a porosity of 30% is formed using the Boolean subtraction command.

[0052] (3) Set C1(x, y, z) to a function related to the coordinates. This will make the G gradient unit CAD model have a minimum porosity P at the edge. out , the center will also have the maximum porosity P in ,The initial design scheme of the G gradient unit CAD model before fusion is shown in Table 2.

[0053] like Figure 2 As shown in Table 2, the specific calculation process of the initial design G gradient unit bias function is as follows: According to each selected group of P in Table 2 out and P in Using P G =(0.4998+0.3246C1)×100% linear relationship corresponds to a set of internal and external bias function values ​​C in and C out Then follow C out = k(x 2 +y 2 )+C in The form (k represents the urgency of the change from the central porosity to the edge porosity, the larger the k value, the faster the porosity changes with the coordinates, and the special point method is used to calculate each group of k values) is used to find the expression of the offset function of each group of G units. In this embodiment: P in =80% Substitute into P in =(0.4998+0.3246C in )×100% to get C in =0.9246; P out =20%Substitute into P out =(0.4998+0.3246C out )×100% to get C out = -0.9236, then take the coordinates of the special point (4, 0, 0) where the xy plane intersects the outermost edge of the cylinder with a diameter of 8 mm × height of 12 mm, so -0.9236 = k (4 2 +0 2 )+0.9246, k=-0.1155 is calculated. Similarly, the k values ​​of the first two groups are 0 and -0.0963 respectively. In summary, the initial design G unit bias function 0, -0.0963 (x 2 +y 2 )+0.771 and -0.1155(x 2 +y 2)+0.9246, and then the three initial design G unit offset functions (C1(x, y, z)) are obtained. Then the Boolean subtraction command is used to generate the Gyroid radial gradient porous structure CAD model.

[0054] Table 2

[0055]

[0056] (4) After the Gyroid radial gradient porous structure CAD model and the Domaind homogeneous porous structure CAD model are preliminarily generated through steps (1), (2), and (3), the tan(ax) formula is introduced as the fusion formula (where a is a constant, representing the fusion period; x is the x direction of the spatial coordinate system). In this embodiment, in order to better simulate the natural femoral structure, a is taken as a=1 / 2; then the Ramp fusion command is called out and the relevant parameters of the 8mm×12mm Domaind homogeneous porous structure CAD model and the Gyroid radial gradient porous structure CAD model generated by steps (2) and (3) are input, and then the Shell extraction command is called out and the Ramp is substituted into it (and the Thickness in the Shell is 1.5mm and remains unchanged), to obtain the 8mm×12mm GD radial fusion CAD model. In this embodiment, the GD radial fusion CAD model selects the initial wall thickness when the unit cell size is 2mm×2mm×2mm, and the initial wall thickness is 1.5mm. When the wall thickness is ≥1.5mm, the porosity of the GD fused CAD model remains unchanged. When the wall thickness value is between greater than 0mm and less than 1.5mm, the smaller the value, the greater the porosity. The initial wall thickness can be designed according to the needs of the research when the unit cells are of different sizes.

[0057] Then, a cylindrical CAD model with a diameter and height of 7mm×10mm was created in the Create module of the Ntopology software, and the Boolean Intersect command was used to intersect and fuse the 8mm×12mm GD radial fusion CAD model formed by the Shell extraction command with the 7mm×10mm cylindrical CAD model using the tan(ax) fusion formula to form a 7mm×10mm cylindrical GD radial fusion CAD model with a wall thickness. However, the overall average porosity of the 7mm×10mm cylindrical GD radial fusion CAD model with a wall thickness was not the target average porosity of 50%.

[0058] Finally, the initial wall thickness parameter of Thickness in the Shell extraction command remains unchanged at 1.5 mm. The interpolation method is used to fine-tune the parameters of the initial design G gradient unit offset function in Table 2. That is, the three G unit offset functions in the initial design are unchanged at 0, -0.0963 (x 2 +y 2)+0.751 parameter is changed to -0.1001(x 2 +y 2 )+0.771、-0.1155(x 2 +y 2 )+0.9246 parameter is changed to -0.1303(x 2 +y 2 )+0.907. (The interpolation method is to adjust the G gradient unit offset function while checking whether the porosity of the GD radial fusion CAD model with wall thickness is 50%. If it is not reached, continue to adjust the parameters). When the average porosity of the GD radial fusion CAD model with wall thickness is 50%, the actual scheme of the G gradient unit before fusion after fine-tuning is as shown in Table 3.

[0059] Table 3

[0060]

[0061] (5) As shown in Table 4, the overall average porosity of the GD radial fusion CAD models with wall thickness of GD1, GD2 and GD3 formed after parameter adjustment is 50%. The model schematic diagram is shown in Figure 4 As shown, GD1 serves as the control group, and the average homogeneous porosity of the G gradient unit structure and the D homogeneous unit structure is 50%. Figure 3 As shown, the outer layer of the GD radial fusion CAD model is a D homogeneous unit structure, and the inner layer is a G gradient unit structure; the homogeneous porosity of the D homogeneous unit structure is 30%, and the G gradient unit structure is a gradient porosity. The porosity and pore size of the G gradient unit CAD model both increase in the radial direction from the edge to the center in a gradient change manner.

[0062] (6) Select GD3 to reduce the wall thickness for lightweight design and generate GD4: In the Shell command, reduce the Thickness parameter of the GD radial fusion CAD model GD3 with wall thickness to reduce the wall thickness to form a 7mm×10mm GD radial fusion CAD model GD4 with wall thickness, and finally achieve the purpose of lightweight design. The model schematic diagram is shown in Figure 4 The specific model parameters are shown in Table 4.

[0063] Table 4

[0064]

[0065]

[0066] (7) The final 7mm×10mm GD radial fusion CAD model with wall thickness GD4, GD1, GD2 and GD3 GD radial fusion CAD model is preliminarily divided into finite element simulation mesh models 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 (Export FE Mesh).

[0067] (8) 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.

[0068] (9) The generated 4 inp format file models are imported into the display dynamics module of Abaqus software again for quasi-static compression finite element simulation. The elastic modulus of 110GPa and the Poisson's ratio of 0.3 are set as the properties of the Ti-6Al-4V material, and the grid unit is set to yield failure when the maximum deformation ratio reaches 1.5. At the same time, the boundary conditions of the porous structure compression are defined again, and a 60% displacement load is applied to the upper top surface. The lower bottom surface constrains the movement and rotational freedom of the porous structure in the X, Y, and Z coordinate directions. The upper top surface constrains the movement in the X, Y directions and the rotational freedom in the X, Y, and Z directions, and only allows movement in the Z direction. The upper top surface and the lower bottom surface are rigid surfaces, and the friction coefficient between the rigid surface and the pore structure is 0.1. The total simulation time is set to 0.006s.

[0069] like Figure 5 The deformation behavior and stress concentration distribution of the four model porous structures were simulated by finite element method. It can be seen from the strain cloud diagram that under the action of load, the deformation of the stent first develops at the edge of the surface and then gradually transfers to the center of the pillar. Increasing the volume fraction of the inner layer will lead to an increase in the equivalent stress of the porous structure, because the increased porosity exacerbates the volume fraction difference between the internal pillar and the surrounding connection part, thereby worsening the stress concentration. The stress of all pillars is mainly concentrated in the center of the oblique pillar and the fusion interface, which may cause the structure to be easily damaged, so strengthening the stress concentration area can improve the reliability of the structure.

[0070] Figure 6The result data of the above quasi-static compression finite element simulation of four different models are shown: 1. The yield strength of GD1, GD2 and GD3 is between 194.4Mpa and 253.4Mpa, which is slightly larger than the yield strength range of cortical bone (33-193MPa), and the yield strength of GD4 is 186.7Mpa, which is in line with the range of cortical bone. 2. The elastic modulus of the four models is between 4.2GPa and 6.6GPa, which is within the range of cortical bone elastic modulus, but only the elastic modulus of GD4, 4.2GPa, is within the range of cancellous bone. When the model meets the mechanical properties requirements of cortical bone, the stress shielding problem will be avoided. Therefore, in summary, only GD4 meets the mechanical properties requirements of the femur and can avoid stress shielding problems.

[0071] 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 design method for a bionic bone scaffold based on TPMS, characterized in that: The steps include: (1) Based on the G unit formula and the D unit formula, the offset function is adjusted to generate the G gradient unit CAD model and the D homogeneous unit CAD model on the Ntopology software; (2) using a fusion function to fuse the G gradient unit CAD model and the D homogeneous unit CAD model to generate a GD radial fusion CAD model; (3) A CAD model A with a smaller size than the GD radial fusion CAD model but the same shape is established, and the GD radial fusion CAD model and the CAD model A are fused using a fusion function to generate a GD radial fusion CAD model with wall thickness. Then, the offset function of the G gradient unit CAD model is adjusted using an interpolation method to adjust the average porosity of the GD radial fusion CAD model with wall thickness to the target average porosity. (4) reducing the wall thickness of the GD radial fusion CAD model with wall thickness of the target average porosity to form a GD radial fusion CAD model with wall thickness; (5) Divide the CAD model of GD radial fusion with wall thickness into a finite element simulation mesh model in Ntopology software, and finally output the simulation model file in inp format; (6) Import the simulation model file in inp format into the HyperMesh software to repair and re-divide the mesh, use the mesh type of C3D4 and the mesh unit size of 0.1 mm, and export and save the inp file format model again.

2. The design method of the TPMS-based bionic bone scaffold according to claim 1, characterized in that: In the step (1), the G unit formula is G (x,y,z)=cos(ωx)sin(ωy)+cos(ωy)sin(ωz)+cos(ωz)sin(ωx)-C1(x,y,z); the D unit formula is Where x, y, z represent the x, y and z directions in the rectangular space coordinate system; ω is a constant that determines the period of the surface, ω = 2Π / l, l is a constant that represents the side length of the unit cell; C1(x, y, z) and C2(x, y, z) represent the offset function that determines the surface; Ψ G (x,y,z) and Ψ D (x, y, z) represent the TPMS function formulas of G unit and D unit respectively.

3. The design method of the bionic bone scaffold based on TPMS as claimed in claim 1, characterized in that: In the step (1), according to the bias function C2 of the D homogeneous unit and the porosity P D The relationship formula is used to adjust the offset function so that the average porosity of the D homogeneous unit CAD model is less than 50%. The offset function C2 of the D homogeneous unit is related to the average porosity P D The relationship formula is P D =(0.5002+0.4135C2)×100%.

4. The design method of the bionic bone scaffold based on TPMS as claimed in claim 1, characterized in that: In the step (1), the porosity and pore size of the G gradient unit CAD model increase in a gradient from the outside to the inside on the cross section, and there is a minimum porosity P at the edge of the G gradient unit CAD model. out , the center has the maximum porosity P in .

5. The design method of the bionic bone scaffold based on TPMS as claimed in claim 4, characterized in that: In the step (1), according to the bias function C1 of the G gradient unit and the porosity P G The relationship formula makes the average porosity of the G gradient unit CAD model 50-90%; the offset function C1 of the G gradient unit and the average porosity P G The relationship formula is P G =(0.4998+0.3246C1)×100%; where the expression of the offset function C1 is: C out = k(x 2 +y 2 )+C in , where C 0ut is the offset function value of the outer edge of the G gradient unit CAD model, P out =(0.4998+0.3246C out )×100%; C in is the offset function value of the center of the G gradient unit CAD model, P in =(0.4998+0.3246C in )×100%.

6. The design method of the bionic bone scaffold based on TPMS as claimed in claim 1, characterized in that: The fusion function is tan(ax), where a is a constant representing the fusion period; and x is the x direction of the spatial coordinate system.

7. The design method of the bionic bone scaffold based on TPMS as claimed in claim 1, characterized in that: In the step (4), the wall thickness is reduced by reducing the Thickness parameter through the Shell command, so that the porosity of the CAD model of the GD radial fusion zone wall thickness is 50%-90%.

8. The design method of the bionic bone scaffold based on TPMS as claimed in claim 7, characterized in that: The wall thickness of the CAD model with the GD radial fusion zone wall thickness is less than the wall thickness of the GD radial fusion CAD model.

9. The design method of the bionic bone scaffold based on TPMS as claimed in claim 1, characterized in that: The outer layer of the CAD model of the GD radial fusion zone wall thickness is a D homogeneous unit structure, and the inner layer is a G gradient unit structure. The porosity and pore size of the G gradient unit structure are both gradient changes that increase along the radial direction from the edge to the center.

10. The design method of the bionic bone scaffold based on TPMS as claimed in claim 9, characterized in that: The unit cell size L1 of the D homogeneous unit structure is L1=2mm×2mm×2mm; the unit cell size L2 of the G gradient unit structure is L2=2mm×2mm×2mm.

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