Method for designing bionic bone scaffold based on TPMS unit and lattice unit multi-plane fusion

Abstract

The invention discloses a method for designing a bionic bone scaffold based on TPMS unit and lattice unit multi-plane fusion, and belongs to the technical field of bionic bone scaffolds. The porosity is adjusted by adjusting the wall thickness, so that an S and SC homogeneous unit porous structure with the target porosity is formed, and then a Schwarz unit cell and a simple cubic unit cell are subjected to plane smooth transition fusion in a fusion region or fusion function tan (x / w) mode; and respectively importing the established fusion model into mechanical simulation software to carry out quasi-static compression finite element simulation so as to obtain the elastic modulus and the yield strength which accord with the thighbone. According to the design, different types of TPMS units and traditional lattice units are subjected to heterogeneous unit fusion, the fused novel porous structure model has different function grading expressions, and a new thought is provided for design of the porous structure as a bionic bone scaffold.

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 multi-plane fusion of a TPMS unit and a lattice unit. Background Art

[0002] Bone tissue damage is a common clinical problem, and bone tissue engineering can repair and reconstruct damaged bones by designing porous scaffolds to simulate the structure and function of natural bone tissue. Compared with traditional treatment methods, this method can precisely regulate the mechanical properties and bioactivity of the scaffold to meet the personalized needs of different patients, and optimize the scaffold design to promote tissue regeneration and functional recovery. Therefore, it has great potential and application prospects in the field of bone damage repair.

[0003] The simple cubic (SC) structure has significant advantages in bionic femoral scaffolds, which can provide sufficient mechanical strength and stiffness, ensure long-term stability, reduce rejection and inflammation, and promote the integration of scaffolds with tissues. In addition, the SC structure helps bone cell growth and angiogenesis, optimizes nutrient exchange, and reduces stress shielding effects by adjusting mechanical properties. Its surface properties also support bone cell attachment and growth, ensuring the stability and functionality of the scaffold. However, the simple cubic structure has the problems of single design and low specific surface area, which limits cell proliferation and nutrient transport. However, lattice units such as SC structures also have certain limitations, such as single design methods and low specific surface area, which are not conducive to cell proliferation and differentiation and the transport of nutrients.

[0004] Triperiodic minimal surfaces (TPMS) such as Schwarz (S) are very suitable for bone scaffold design due to their flexible parameter adjustment, smooth and periodic surface, large specific surface area and interconnected pores. However, the existing TPMS porous structure design is mostly focused on homogeneous structure, while the natural bone structure is heterogeneous and anisotropic. This homogeneous design can easily lead to failure of a single pillar during compression, which in turn causes the collapse of the entire structure. Therefore, research is more inclined to design porous structures with functional gradient changes. However, the existing functional gradient TPMS scaffold design is mostly focused on the porosity gradient in a single direction, and the use of a single TPMS unit type may result in too low porosity in the outer cortical bone part, low overall porosity, or too high porosity leading to reduced structural strength. Therefore, it is necessary to further optimize the design strategy to overcome these limitations. Summary of the invention

[0005] 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 multi-plane fusion of TPMS units and lattice units.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units includes:

[0008] (1) Use Ntopology software to create a simple cubic homogeneous unit porous structure CAD model in the form of a cylinder and a Schwarz homogeneous unit porous structure CAD model;

[0009] (2) The simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model are fused to obtain a fusion model;

[0010] (3) The fusion 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] (4) 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 0.2 mm, and export and save the inp format file model again;

[0012] In step (2), the fusion method is selected from:

[0013] A: Set the fusion start plane and fusion end plane to build the fusion area for fusion;

[0014] B: Set the fusion function tan(x / w) for fusion, where w is a constant representing the fusion period, and its value is 0<w<6; x represents the x direction in the three-dimensional Cartesian space coordinate system.

[0015] The present invention directly imports the inp file format model obtained by step (4) 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. 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 (4) is outputted in the form of an STL model file using the Export command, then the computer is connected to a 3D printer, and the model file in the form of an STL model file is imported into the 3D printer to print, and the target bionic bone scaffold is obtained.

[0016] As a preferred embodiment of the present invention, the fusion start plane and the fusion end plane are parallel. The fusion start plane and the fusion end plane are not the same plane.

[0017] More preferably, the fusion start plane is z=a, and the fusion end plane is z=b, wherein a and b are constants, z is the z direction in the rectangular space coordinate system, -Mmm<a<b<Mmm and ba<the distance between the adjacent simple cubic homogeneous unit and the Schwarz homogeneous unit at the fusion interface mm, M=(1 / 2)cylinder height-unit cell size; or the fusion start plane is x=c, and the fusion end plane is x=d, wherein c and d are constants, x represents the x direction in the rectangular space coordinate system, -Nmm<c<d<Nmm and dc<the distance between the adjacent simple cubic homogeneous unit at the fusion interface and the distance between the Schwarz homogeneous unit in mm, N = cylinder radius - unit cell size; or the fusion start plane is y = m, and the fusion end plane is y = n, where m and n are constants, y represents the y direction in the rectangular space coordinate system, -Nmm<m<n<Nmm and mn<the distance between the adjacent simple cubic homogeneous unit and the Schwarz homogeneous unit at the fusion interface in mm; the lengths L of the above three fusion areas are L1 = ba, L2 = dc and L3 = nm respectively, and 0<L<the distance between the adjacent simple cubic homogeneous unit and the Schwarz homogeneous unit at the fusion interface in mm.

[0018] The simple cubic and Schwarz unit cells of the present invention have the same size, both of which are equilateral in three directions w×w×w. The distance between adjacent simple cubic homogeneous units and Schwarz homogeneous units at the fusion interface is measured using a measuring device provided in the Ntopology software interface.

[0019] As a preferred embodiment of the present invention, the porosity of the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model is 50-90%.

[0020] As a preferred embodiment of the present invention, a Schwarz homogeneous unit porous structure CAD model of target porosity is constructed according to the relationship between the Midsurface Offset parameter and the porosity; the relationship between the Midsurface Offset parameter M and the porosity P1 is: P1 = (0.50166-2.0494M) × 100%.

[0021] As a preferred embodiment of the present invention, in step (1), a simple cubic homogeneous unit porous structure CAD model of target porosity is constructed based on the relationship between wall thickness T and porosity P2; the relationship between wall thickness parameter and porosity is: P2 = (1.15998-0.7501T) × 100%.

[0022] As a preferred embodiment of the present invention, the wall thickness is: 0<T<2.16mm; the Midsurface Offset parameter is: -0.374<M<0.374.

[0023] The height-to-diameter ratio of the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model in the cylindrical form of the present invention is 1-2.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention fuses different types of TPMS units and traditional lattice units (beam units) by regional fusion or fusion function tan(x / w), and the fused new porous structure model has stability and compression resistance, stress buffering and balance, and torsion resistance. It can also regularly guide the growth of bone tissue and promote cell attachment and proliferation; the connectivity of the porous structure promotes the diffusion of nutrients, and the curved surface design of the Schwarz unit increases the fluidity of nutrients in the scaffold. By combining the characteristics of the simple cube and the Schwarz unit, the present invention achieves comprehensive optimization of the bone scaffold in terms of mechanical stability, stress dispersion, cell growth and nutrient transport, providing an innovative idea for the design of bionic bone scaffolds. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagrams of simple cubic homogeneous unit porous structure model and Schwarz homogeneous unit porous structure model; (a) is the Schwarz homogeneous unit porous structure model, and (b) is the simple cubic homogeneous unit porous structure model.

[0026] Figure 2 These are the fitting curves of porosity and M value or T in the Schwarz homogeneous unit porous structure model and the simple cubic homogeneous unit porous structure model; (a) is the fitting curve of porosity and M value in the Schwarz homogeneous unit porous structure model, and (b) is the fitting curve of porosity and wall thickness T in the simple cubic homogeneous unit porous structure model.

[0027] Figure 3 Schematic diagram of the fusion connection of the simple cubic homogeneous unit porous structure model and the Schwarz homogeneous unit porous structure model in Example 1 and Comparative Example 1; (a) is a schematic diagram of the fusion of the simple cubic homogeneous unit porous structure model and the Schwarz homogeneous unit porous structure model in Comparative Example 1 through the fusion surface; (b) is a schematic diagram of the simple cubic homogeneous unit porous structure model and the Schwarz homogeneous unit porous structure model in the embodiment through the fusion area.

[0028] Figure 4Schematic diagram of the fusion models SSC1, SSC2, SSC3 and SSC4, which are the simple cubic homogeneous unit porous structure model and the Schwarz homogeneous unit porous structure model.

[0029] Figure 5 Schematic diagram of the specific distribution of simple cubic homogeneous units and Schwarz homogeneous units in the four fusion models SSC1, SSC2, SSC3 and SSC4.

[0030] Figure 6 Schematic diagram of the deformation behavior and stress concentration distribution of the axial center section during quasi-static compression simulation of the fusion model finite element model; (a) SSC1 fusion model; (b) SSC2 fusion model; (c) SSC3 fusion model; (b) SSC4 fusion model. DETAILED DESCRIPTION

[0031] 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.

[0032] Example 1

[0033] The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units includes:

[0034] (1) First, a cylindrical CAD model with a diameter and height of 10 mm × 14 mm was created in the Create module of the Ntopology software. The model structure was a vertically and horizontally symmetrical CAD model established with the origin (0, 0, 0) as the center point in the three-dimensional Cartesian coordinate system. Then, the S (Schwarz) unit cell was selected using the TPMS Unite cell with Offset command. Five M values ​​were taken within the range of the MidsurfaceOffset parameter M: -0.374<M<0.374. The porosity of the generated S homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 were fitted to obtain the relationship between the Midsurface Offset parameter M and the porosity P1: P1=(0.50166-2.0494M)×100% and the fitting reliability was R=99.516% (as shown in Table 1). Figure 2 (a)), and then set the Midsurface Offset parameter to -0.0434 through the Rectangular Volume Lattice command to generate a cylindrical S homogeneous unit porous structure CAD model with a diameter and height of 10mm×14mm (such as Figure 1(a)) The porosity is 60% (the Midsurface Offset parameter indicates that the wall thickness can be increased or decreased). Similarly, the Graph Unite Cell command is used to select the SC (simple cubic) unit cell, and 5 T values ​​are taken in the range of wall thickness: 0<T<2.16mm. The porosity of the generated SC homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 are fitted to obtain the relationship between the wall thickness parameter and the porosity: P2=(1.15998-0.7501T)×100% and the fitting reliability R=99.147%(as shown in Table 1). Figure 2 (b)), and then set the wall thickness parameter (Thickness) to 0.7489mm through the Rectangular Volume Lattice command to generate a cylindrical SC homogeneous unit porous structure CAD model with a diameter and height of 10mm×14mm (such as Figure 1 (b) The porosity is also 60%. In the other parameters of the Rectangular Volume Lattice command used by both, the unit cell size is designed to be 1.5mm×1.5mm×1.5mm, because the pore size between 100μm and 1200μm can meet the pore size requirements for bone cell proliferation and differentiation, and the default settings of the Frame and Trim commands can be used.

[0035] Table 1

[0036] M(mm) -0.2 -0.1 0 0.1 0.2 <![CDATA[P1(%)]]> 89.78 72.99 50.07 27.11 10.25 T(mm) 0.3 0.5 0.6 0.7 0.9 <![CDATA[P2(%)]]> 91.95 79.65 72.14 64.09 47.13

[0037] (2) The fusion interface is not designed to be directly fused only on one plane, but is set as a plane fusion area on the basis of the plane, so that the simple cubic homogeneous unit porous structure model and the Schwarz homogeneous unit porous structure model are smoothly connected. Figure 3(b) is shown. The specific method is to call out the Plane from Normal command and input the parameters of the starting fusion plane and the ending fusion plane, call out the Ramp command and adjust the In Max parameter (In Max parameter is the length L of the fusion area) to set the starting fusion plane and the ending fusion plane as a fusion command of a fusion area, call out the Mix command, and substitute the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model and the Ramp fusion command into Mix to generate a smoothly connected fusion model. In this embodiment, the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model both take a unit cell size of 1.5mm×1.5mm×1.5mm, therefore, the fusion start plane is z=a, and the fusion end plane is z=b, wherein a and b are constants, -5.5mm<a<b<5.5mm and ba<2.5mm; or the fusion start plane is x=c, and the fusion end plane is x=d, wherein c and d are constants, -3.5mm<c<d<3.5mm and dc<2.5mm; or the fusion start plane is y=m, and the fusion end plane is y=n, wherein m and n are constants, -3.5mm<m<n<3.5mm and mn<2.5mm, and the length L of the fusion area is L1=ba, L2=dc and L3=nm, respectively, and 0<L<2.5mm.

[0038] In this embodiment, two schemes are set. The fusion areas of the two schemes are respectively: Scheme 1: z = -1 is the starting fusion plane to z = 1 fusion plane cutoff, and the Ramp instruction sets the relevant parameters: In Min: 0, In Max: 2, Out Min: 0, Out Max: 1; Scheme 2: x = -1 is the starting fusion plane to x = 1 fusion plane cutoff, and the Ramp instruction sets the relevant parameters: InMin: 0, In Max: 2, Out Min: 0, Out Max: 1. The plane numerical algorithm is -1 + 2 = 1. The fusion models designed by the above two schemes are named SSC1 and SSC2, respectively. Figure 4 , 5 As shown. The In Max parameter of the fusion area can be adjusted as needed. In this embodiment, the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model both take a unit cell size of 1.5mm×1.5mm×1.5mm. At this time, the distance between the adjacent S unit and SC unit at the fusion interface is a fixed value of 2.5mm, so the In Max parameter of this fusion area is selected to be 0<L<2.5mm.

[0039] (3) The SSC1 and SSC2 models with a cylindrical shape of 10 mm × 14 mm in diameter and height were divided into finite element simulation mesh models using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model files in inp format were output using the output command (Export FE Mesh).

[0040] (4) Import the simulation model file in inp format into the HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.2 mm, and export and save the inp format file model again.

[0041] (5) The two generated inp format file models were imported into the display dynamics module of Abaqus software for quasi-static compression finite element simulation. The elastic modulus of 110 GPa, Poisson's ratio of 0.3 and 4.51 g / cm 3 The density is set as the property of Ti-6Al-4V material, and the mesh 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, and a 60% displacement load is applied to the top surface (the height of the model is 14mm this time, that is, the compression stops when the pressure is 8.4mm). The bottom surface constrains the movement and rotational freedom of the porous structure in the X, Y, and Z coordinate directions, and the 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 top surface and the bottom surface are rigid surfaces, and the friction coefficient between the rigid surface and the porous structure is 0.2. The total simulation time is set to 0.1 seconds and the analysis step is 5e-6 seconds.

[0042] Example 2

[0043] The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units includes:

[0044] (1) First, a cylindrical CAD model with a diameter and height of 10 mm × 14 mm was created in the Create module of the Ntopology software. The model structure was a vertically and horizontally symmetrical CAD model established with the origin (0, 0, 0) as the center point in the three-dimensional Cartesian coordinate system. Then, the S (Schwarz) unit cell was selected using the TPMS Unite cell with Offset command. Five M values ​​were taken within the range of the MidsurfaceOffset parameter M of -0.374 < M < 0.374. The porosity of the generated S homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 were fitted to obtain the relationship between the Midsurface Offset parameter M and the porosity P1: P1 = (0.50166-2.0494M) × 100% and the fitting reliability was R = 99.516%. Then, the Midsurface was set using the RectangularVolume Lattice command. The Offset parameter is -0.0434, which generates a CAD model of a homogeneous unit porous structure in the form of a cylinder with a diameter and height of 10mm×14mm (such as Figure 1 (a)) The porosity is 60% (the Midsurface Offset parameter indicates that the wall thickness can be increased or decreased). Similarly, the Graph Unite Cell command is used to select the SC (simple cubic) unit cell, and 5 T values ​​are taken within the range of wall thickness: 0<T<2.16mm. The porosity of the generated SC homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 are fitted to obtain the relationship between the wall thickness parameter and the porosity: P2=(1.15998-0.7501T)×100% and the fitting reliability R=99.147%. Then, the wall thickness parameter (Thickness) is set to 0.7489mm through the RectangularVolume Lattice command to generate a cylindrical SC homogeneous unit porous structure CAD model with a diameter and height of 10mm×14mm (as shown in Figure 1 (b) The porosity is also 60%. In the other parameters of the Rectangular Volume Lattice command used by both, the unit cell size is designed to be 1.5mm×1.5mm×1.5mm, because the pore size between 100μm and 1200μm can meet the pore size requirements for bone cell proliferation and differentiation, and the default settings of the Frame and Trim commands can be used.

[0045] (2) The simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model are introduced into the fusion function tan(x / w), where w is a constant representing the fusion period, and then the fusion command Ramp instruction is called to generate a multi-plane region fusion model. In this embodiment, w=2 or w=1 is taken, and the fusion models created are SSC3 and SSC4 respectively, as shown in FIG. Figure 4 , 5 As shown in the figure. The larger w is, the greater the proportion of the intermediate S unit model is. When w is greater than 6, the fused CAD model is all S units. When w is greater than 0, the smaller w is, the more fusion interfaces there are, that is, the more dense the plane fusion of S units and SC units that penetrate each other (such as Figure 6 Schematic diagram of the SSC4 model).

[0046] (3) The SSC3 and SSC4 models with a cylindrical shape of 10 mm × 14 mm in diameter and height were divided into finite element simulation mesh models using the Mesh From Implicit Body command in the Ntopology software, and finally the simulation model files in inp format were output using the output command (Export FE Mesh).

[0047] (4) Import the simulation model file in inp format into the HyperMesh software to repair and re-divide the mesh, using tetrahedral meshing, with the mesh type of C3D4 and the mesh unit size of 0.2 mm, and export and save the inp format file model again.

[0048] (5) The two generated inp format file models were imported into the display dynamics module of Abaqus software for quasi-static compression finite element simulation. The elastic modulus of 110 GPa, Poisson's ratio of 0.3 and 4.51 g / cm 3 The density is set as the property of Ti-6Al-4V material, and the mesh 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, and a 60% displacement load is applied to the top surface (the height of the model is 14mm this time, that is, the compression stops when the pressure is 8.4mm). The bottom surface constrains the movement and rotational freedom of the porous structure in the X, Y, and Z coordinate directions, and the 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 top surface and the bottom surface are rigid surfaces, and the friction coefficient between the rigid surface and the porous structure is 0.2. The total simulation time is set to 0.1 seconds and the analysis step is 5e-6 seconds.

[0049] like Figure 5As shown: the upper part of the SSC1 model is S unit and the lower part is SC unit, the right part of SSC2 is S unit and the left part is SC unit, the middle part of SSC3 is S unit and the two sides are SC unit, and the SSC4 model is S unit and SC unit relative distribution, which is more uniform than the first three. In each model, the solid line box is S unit and the dotted line box is SC unit structure.

[0050] like Figure 6 (a), (b), (c) and (b) represent the deformation behavior and stress concentration distribution of the axial center section of the SSC1, SSC2, SSC3 and SSC4 finite element models during quasi-static compression simulation, respectively. The four models are selected with the elastic stage strain ε of 5%, the yield stage strain ε of 25% and 50%, and the densification stage strain ε of 75% and 100% (corresponding to compression to 8.4mm at this time) as representatives to show the changes in the model's full-stage compression simulation process. The compression simulation of the four models at different stages shows their own deformation behavior and stress distribution characteristics. For the SSC1 model ( Figure 6 (a) Elastic stage: The Schwarz unit acts as a stress-bearing surface, dispersing stress through the concave surface, and the SC unit below maintains elastic deformation. Yield stage: The internal lattice of the surface structure changes, transmitting pressure to the SC unit, affecting the internal fluid transport, and the SC unit provides stable support to maintain the basic shape. Densification stage: The surface structure partially collapses, the SC unit lattice yields, and eventually leads to overall collapse. For the SSC2 model ( Figure 6 (b) Elastic stage: The right side of the Schwarz unit first undergoes elastic deformation, and the stress is transferred from right to left. The left connection area of ​​the SC unit is under pressure. Yield stage: The internal lattice deformation of the Schwarz unit transfers more pressure to the SC unit, and the stress concentration in the connection area is improved. Densification stage: The Schwarz unit is partially destroyed, the SC unit yields, and finally the entire unit part fails. For the SSC3 model ( Figure 6 (c) Elastic stage: stress is mainly concentrated at the pillar nodes of SC unit and Schwarz unit, and the stress concentration of fusion interface is not obvious. Yield stage: SC unit pillars bend, stress transfers to nodes and fusion interface, the internal pores of Schwarz unit shrink, and the stress concentration of fusion interface increases. Densification stage: SCC pillars yield, Schwarz unit surface structure collapses, fusion interface debonds or cracks propagate, leading to overall destruction. For SSC4 model ( Figure 6(d) Elastic stage: The outer pillars of the SC unit structure are first subjected to pressure, the center and the two sides of the Schwarz unit elastically deform, and the stress concentration of the fusion interface is relatively uniform. Yield stage: The SC unit pillars bend, the stress is transmitted to the nodes and multiple fusion interfaces, and the stress concentration of the fusion interface gradually increases. In the densification stage, the SC unit structure is locally destroyed, the stress concentration of the Schwarz unit fusion interface leads to local deformation, and multiple fusion interfaces accumulate damage and eventually lose their bearing capacity. In summary, each model shows unique deformation and stress distribution characteristics at different compression stages. By combining the performance of the simple-centered cubic and Schwarz units, the mechanical stability and stress dispersion ability of the bone scaffold are optimized.

[0051] The yield strength simulation results of SSC1, SSC2, SSC3 and SSC4 models are shown in Table 2 below, all of which are within the range of cortical bone yield strength (33-193MPa) in the femur, and their elastic moduli after simulation are also within the range of cortical bone elastic modulus (3-20GPa). Therefore, the four porous structures are suitable for implantation as bionic femoral scaffolds in the body and can avoid stress shielding problems.

[0052] Table 2

[0053] type SSC1 SSC2 SSC3 SSC4 Yield strength (MPa) 174.84 183.07 180.14 180.48 Elastic modulus(GPa) 13.08 13.69 14.88 14.92

[0054] Comparative Example 1

[0055] The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units includes:

[0056] (1) First, a cylindrical CAD model with a diameter and height of 10 mm × 14 mm was created in the Create module of the Ntopology software. The model structure was a vertically and horizontally symmetrical CAD model established with the origin (0, 0, 0) as the center point in the three-dimensional Cartesian coordinate system. Then, the S (Schwarz) unit cell was selected using the TPMS Unite cell with Offset command. Five M values ​​were taken within the range of the MidsurfaceOffset parameter M of -0.374 < M < 0.374. The porosity of the generated S homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 were fitted to obtain the relationship between the Midsurface Offset parameter M and the porosity P1: P1 = (0.50166-2.0494M) × 100% and the fitting reliability was R = 99.516%. Then, the Midsurface was set using the RectangularVolume Lattice command. The Offset parameter is -0.0434, which generates a CAD model of a homogeneous unit porous structure in the form of a cylinder with a diameter and height of 10mm×14mm (such as Figure 1(a)) The porosity is 60% (the Midsurface Offset parameter indicates that the wall thickness can be increased or decreased). Similarly, the Graph Unite Cell command is used to select the SC (simple cubic) unit cell, and 5 T values ​​are taken within the range of wall thickness: 0<T<2.16mm. The porosity of the generated SC homogeneous unit porous structure CAD model is shown in Table 1. The data in Table 1 are fitted to obtain the relationship between the wall thickness parameter and the porosity: P2=(1.15998-0.7501T)×100% and the fitting reliability R=99.147%. Then, the wall thickness parameter (Thickness) is set to 0.7489mm through the RectangularVolume Lattice command to generate a cylindrical SC homogeneous unit porous structure CAD model with a diameter and height of 10mm×14mm (as shown in Figure 1 (b) The porosity is also 60%. In the other parameters of the Rectangular Volume Lattice command used by both, the unit cell size is designed to be 1.5mm×1.5mm×1.5mm, because the pore size between 100μm and 1200μm can meet the pore size requirements for bone cell proliferation and differentiation, and the default settings of the Frame and Trim commands can be used.

[0057] (2) In the Ntopology software, the Plane from Normal command is called to realize arbitrary surface fusion in the plane Ax+By+Cz+D=0, where A, B, C and D are all constants and A, B, C are not 0 at the same time. When D is 0, it means that the fusion plane passes through the origin. x, y, z are the coordinate values ​​of any point in the three-dimensional Cartesian coordinate system). Specifically, the Origin and Normal parameters are set in the Plane from Normal command. The three parameters of Normal and Origin are set to (0, 0, 1) and (0, 0, -1) as a group (in this case, z=-1 is the fusion plane) and (1, 0, 0) and (-1, 0, 0) as a group (in this case, x=-1 is the fusion plane). At this time, it is found that the S and SC homogeneous unit porous structures are directly fused in a plane, and the connection at the fusion interface is not smooth and has edge corners (such as Figure 3 (a) shows that this connection method shows that a large stress concentration is generated at the fusion interface during compression simulation, which will cause the fusion interface to break first, thereby reducing the service life of the porous structure as a bionic bone scaffold.

[0058] 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 multi-plane fusion of TPMS units and lattice units, characterized in that: include: (1) Use Ntopology software to create a simple cubic homogeneous unit porous structure CAD model of a cylinder and a Schwarz homogeneous unit porous structure CAD model; (2) The simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model are fused to obtain a fusion model; (3) The fusion model is 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; (4) 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 0.2 mm, and export and save the inp format file model again; In step (2), the fusion method is selected from: A: Set the fusion start plane and fusion end plane to form a fusion area for fusion; B: Set the fusion function tan(x / w) for fusion; w is a constant representing the fusion period, and its value is 0<w<6; x represents the x direction in the rectangular space coordinate system.

2. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: In the step (1), the height-to-diameter ratio of the simple cubic homogeneous unit porous structure CAD model of the cylinder and the Schwarz homogeneous unit porous structure CAD model is 1-2.

3. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 2, characterized in that: The fusion start plane and the fusion end plane are parallel.

4. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 3, characterized in that: The fusion start plane is z=a, and the fusion end plane is z=b, wherein a and b are constants, z is the z direction in the rectangular space coordinate system, -M<a<b<M and ba<the distance between the adjacent simple cubic homogeneous unit and the Schwarz homogeneous unit at the fusion interface, M=(1 / 2)cylinder height-unit cell size; or the fusion start plane is x=c, and the fusion end plane is x=d, wherein c and d are constants, x represents the x direction in the rectangular space coordinate system, -N<c<d<N and dc<the distance between the adjacent simple cubic homogeneous unit and the Schwarz homogeneous unit at the fusion interface hwarz homogeneous unit, N = cylinder radius - unit cell size; or the fusion start plane is y = m, the fusion end plane is y = n, where m and n are constants, y represents the y direction in the rectangular space coordinate system, -N<m<n<N and mn<the distance between the adjacent simple cubic homogeneous unit and Schwarz homogeneous unit at the fusion interface; the lengths L of the above three fusion regions are L1 = ba, L2 = dc and L3 = nm respectively, and 0<L<the distance between the adjacent simple cubic homogeneous unit and Schwarz homogeneous unit at the fusion interface.

5. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: w is 1 or 2.

6. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: The porosity of the simple cubic homogeneous unit porous structure CAD model and the Schwarz homogeneous unit porous structure CAD model is 50-90%.

7. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: In the step (1), a Schwarz homogeneous unit porous structure CAD model of target porosity is constructed according to the relationship between the Midsurface Offset parameter M and the porosity P1; the relationship between the Midsurface Offset parameter M and the porosity P1 is: P1 = (0.50166-2.0494M) × 100%.

8. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: In the step (1), a simple cubic homogeneous unit porous structure CAD model of target porosity is constructed according to the relationship between the wall thickness T and the porosity P2; the relationship between the wall thickness T and the porosity P2 is: P2 = (1.15998-0.7501T) × 100%.

9. The method for designing a bionic bone scaffold based on multi-plane fusion of TPMS units and lattice units as claimed in claim 1, characterized in that: The wall thickness is: 0<T<2.16mm; the Midsurface Offset parameter is: -0.374<M<0.374.

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