A method for preparing a metal implant based on gradual porosity and atmosphere control to modulate the elastic modulus and yield strength of the femoral midshaft

Abstract

The present application relates to a kind of based on gradual change pore and atmosphere control femoral midshaft elastic modulus and yield strength metal implant preparation method, belong to pore structure bottom design and pore material preparation technical field.The method includes: design the CAD model of homogeneous pore structure;Using selective laser melting method, according to CAD model preparation homogeneous pore structure sample, the uniaxial compression experiment of sample is carried out and the relationship model of homogeneous pore structure elastic modulus and its structure parameter is obtained;According to relationship model, based on programming, the gradual change pore structure similar to human bone in structure and elastic modulus is constructed;Add specific reaction gas in additive manufacturing process to improve the yield strength of additive parts;Finally, the gradual change pore structure similar to human bone in structure, elastic modulus and yield strength is obtained.The present application is suitable for manufacturing artificial bone, repairing bone, tissue engineering scaffold, drug release system and cell culture medium and other various applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bottom design of pore structure and preparation of porous materials, and particularly relates to a preparation method of a metal implant for regulating elastic modulus and yield strength of a femoral midshaft based on a gradually changing pore and atmosphere control. BACKGROUND

[0002] Porous structure is a kind of biomimetic structure with natural advantages, which contains a large number of pore structures, has the advantages of low relative density, high specific surface area, good permeability, lightweight, etc., and is widely used in engineering fields such as aerospace, automobile manufacturing, material chemistry, medical treatment, etc. Among them, the pores of the open porous structure are connected, and the application range is more extensive. Common porous structures include lattice structure, honeycomb structure, minimal surface, etc. Among them, triply periodic minimal surface (TPMS) structure has attracted more and more attention from scholars and colleges in recent years. Triply periodic minimal surface has the advantages of various geometric shapes, high specific surface area, full connectivity of pores, controllable parameters, quasi-self-supporting, etc., and is widely used in energy absorption structures, bone scaffold modeling, etc.

[0003] Additive manufacturing (AM), also known as 3D printing, is a special processing technology that uses metal or non-metal materials to construct parts layer by layer based on a three-dimensional digital model. As a fast and accurate part processing method, it is applied in the fields of aerospace, automobile, medical treatment, mold, building, etc.

[0004] TPMS structures prepared based on AM are widely used in filling of human bone implants, but it needs to be noted that the elastic modulus of the prepared TPMS porous structure should be the same as that of the human bone to be implanted, so as to overcome the "stress shielding" phenomenon (the difference in stiffness between the implant and the surrounding bone leads to a reduction in the stress borne by the bone, causing bone loss). Since the mechanical properties of some bones in the human body are different at different positions, such as the modulus of the outer compact bone being higher than that of the inner cancellous bone, therefore, gradient porous structures are widely used. The existing problems are as follows: one is that the construction of gradient TPMS structure is too difficult and complex; the other is the lack of a systematic method to directly obtain a gradient TPMS point structure with expected elastic modulus and yield strength. SUMMARY

[0005] The purpose of the present application is to solve the problems in the background art and provide a preparation method of a metal implant for regulating elastic modulus and yield strength of a femoral midshaft based on a gradually changing pore and atmosphere control.

[0006] In order to achieve the above object, the technical scheme of the present application is: a preparation method of a metal implant for regulating the elastic modulus and yield strength of a femoral midshaft based on a gradual pore and atmosphere control, comprising:

[0007] Constructing a CAD model of a uniform pore structure based on programming control of an implicit function:

[0008] Preparation of the CAD model by additive manufacturing, compression test to obtain a relationship model between the pore structure parameters and the mechanical properties;

[0009] According to the relationship model, a gradual pore structure similar to the human bone structure and having the same elastic modulus is constructed based on programming;

[0010] During the additive manufacturing process, a predetermined proportion of reaction gas is introduced to improve the yield strength of the additive manufactured part;

[0011] A gradual pore structure similar to the human bone structure, having the same elastic modulus and yield strength as the human bone is obtained.

[0012] Preferably, the modeling method used is an implicit function based on the pore structure surface, which is designed and modeled by programming.

[0013] Preferably, the modeling step is to directly construct the entire model without constructing a unit cell and then arraying and connecting.

[0014] Optionally, during the additive manufacturing process, the powder used is selected from one of titanium and titanium alloy, tantalum, cobalt-chromium-molybdenum, stainless steel, nickel-titanium and other biocompatible metal powders.

[0015] Preferably, the prepared model is subjected to uniaxial compression test to obtain its elastic modulus and yield strength, and a Gibson-Ashby relationship model of the pore structure parameters and the elastic modulus and yield strength is constructed.

[0016] Preferably, according to the required modulus distribution, a modulus spatial position function is written, and then the Gibson-Ashby relationship bridge is used to write the modulus spatial position function into the pore structure surface implicit function based on programming.

[0017] Optionally, the human bone structure similar to the human bone structure is specifically manifested as the same overall structure shape as the bone, including cylindrical, spherical, plate-shaped and the like.

[0018] Optionally, the gradual pore structure is continuously variable, including one-dimensional gradient, two-dimensional gradient and three-dimensional gradient pore structures, and the mechanical properties are also continuously variable, specifically manifested as the elastic modulus of the structure.

[0019] Optionally, the specific reaction gas refers to a non-toxic gas such as nitrogen gas, which can react with the metal powder used in the slm process to form precipitates or can be free in the metal deposition layer.

[0020] Optionally, the gradual porosity structure with a similar structure to human bone, a preset elastic modulus and a required yield strength can be obtained.

[0021] Preferably, the implicit surface of the porosity structure is constructed based on a programming language, and one side of the surface is closed to obtain an end surface. The surface and the end surface are divided into triangular facets, and the coordinates of the three vertices of the triangular facets and the normal vectors of the facets are recorded. The coordinates of the vertices and the normal vectors are written into a CAD model in STL format.

[0022] Preferably, the entire region of the model is represented by spatial coordinates when writing the code, and the entire porosity structure model can be obtained by writing the spatial coordinates into the definition domain of the implicit function.

[0023] Preferably, the cross-sectional area of the part is calculated by calculating the sum of the areas of all the triangular facets in the cross-section, and the strain of the structure sample is accurately measured by a video extensometer during the compression process.

[0024] Optionally, the modulus space position function refers to the size of the elastic modulus value of a specific position of a certain overall structure, such as a piece of human bone with different elastic modulus values at different positions.

[0025] Optionally, the gradient in any direction depends on the position function of the structure parameter, for example, the structure thickness parameter t=f(x), that is, the structure thickness is gradually changed in the X direction, that is, a one-dimensional gradual change structure. Similarly, t=f(x,y) and t=f(x,y,z) represent two-dimensional and three-dimensional gradual change structures, respectively, such as a planar radial gradual change structure and a spatial gradual change structure.

[0026] Optionally, the content of the specific gas used needs to be strictly controlled, and it is used by mixing with an inert protective gas such as argon gas in a certain proportion.

[0027] Preferably, the structure prepared by the method is suitable for the bone of any part of the human body, ensures the same elastic modulus as the human bone to overcome stress shielding, and also ensures that the structure has a corresponding yield strength to resist external damage. In addition, the structure similar to the bone is convenient for nutrient transportation and tissue growth.

[0028] Compared with the prior art, the present application has the following beneficial effects: the present application is based on programming to control implicit functions for direct modeling, and then based on AM additive manufacturing to obtain a physical object and perform compression experiments, analyze and construct a modulus field according to experimental data, control a gradient pore structure with a required elastic modulus based on the modulus field, then pass a certain amount of reaction gas in the additive manufacturing process to improve the yield strength of the additive part, and finally obtain a gradient pore structure with a required structure type and mechanical property. Not only does the present application solve the problem of difficult modeling, but also provides a method for designing a gradient pore structure with a required elastic modulus. In addition, the present application adopts a method of computer modeling combined with additive manufacturing and compression experiments to prepare a spatial gradient pore structure with a required elastic modulus, yield strength, porosity and pore structure. The present application is suitable for manufacturing artificial bone, repairing bone, tissue engineering scaffolds, drug release systems and cell culture substrates and the like. The present application has the characteristics of high preparation efficiency, high accuracy, large production capacity and low cost, and the process flow is simple, and a complex porous structure can be produced. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A flow chart for preparing a metal implant body with a gradient pore and atmosphere-controlled elastic modulus and yield strength similar to the middle end of a femur in an embodiment of the present application.

[0030] Figure 2 A CAD model of a uniform Gyroid porous structure controlled by programming to construct an implicit function in an embodiment of the present application, (a) is a Gyroid structure enclosed by an implicit surface and an end surface, and (b) is a CAD model in STL format based on programming.

[0031] Figure 3 An SEM microstructure diagram and a particle size distribution diagram of TA1 powder used in an embodiment of the present application.

[0032] Figure 4 A schematic diagram of summing up the areas of all triangular facets on the cross section as the cross-sectional area in an embodiment of the present application.

[0033] Figure 5 A comparison diagram of morphologies before and after compression of a uniform structure and a stress-strain diagram in an embodiment of the present application, wherein (a), (b), (c), (d) and (e) are comparison diagrams of morphologies before and after compression of uniform Gyroid structures with offset values t = -0.9, t = -0.6, t = -0.3, t = 0 and t = 0.3, respectively, and (f) represents stress-strain curves of the compression processes of the five groups of structures.

[0034] Figure 6 Three-dimensional gradient Gyroid structures obtained in an embodiment of the present application, (a) is a one-dimensional gradient structure, (b) is a two-dimensional gradient structure, and (c) is a three-dimensional gradient structure.

[0035] Figure 7 Fig. 8 is a schematic diagram of a two-dimensional gradient gyroid structure, (b) a stress-strain curve diagram of a compression experiment of the two-dimensional gradient gyroid structure under pure argon gas condition, (c) a stress-strain curve diagram of a compression experiment of the two-dimensional gradient gyroid structure under argon-nitrogen mixed gas condition. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described in detail below with reference to the drawings. In order to make the purpose, technical solutions and effects of the present application clearer and more explicit, the present application will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the specification of the present application herein is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0038] The present application provides a metal implant preparation method based on gradual porosity and atmosphere regulation to control the elastic modulus and yield strength of the femoral midshaft, comprising:

[0039] Constructing a CAD model of a uniform porosity structure controlled by an implicit function based on programming:

[0040] Preparation of the CAD model by additive manufacturing, compression test to obtain a relationship model between porosity structure parameters and mechanical properties;

[0041] According to the relationship model, a gradual porosity structure similar to the structure of human bone and having the same elastic modulus is constructed based on programming;

[0042] During the additive manufacturing process, a predetermined proportion of reaction gas is introduced to improve the yield strength of the additive manufactured parts;

[0043] A gradual porosity structure is obtained, which has a structure similar to human bone, and the same elastic modulus and yield strength as human bone.

[0044] The following is the specific implementation process of the present application,

[0045] As Figure 1 shown, the present application is a metal implant preparation method based on gradual porosity and atmosphere regulation to control the elastic modulus and yield strength of the femoral midshaft, comprising the following steps:

[0046] S1, constructing a CAD model of a uniform porosity structure controlled by an implicit function based on programming:

[0047] S2, using additive manufacturing to prepare the above-mentioned CAD model, and performing compression test to obtain a relationship model between pore structure parameters and mechanical properties;

[0048] S3, constructing a gradually changing pore structure similar to human bone structure and having the same elastic modulus based on programming according to the model;

[0049] S4, introducing a certain proportion of reaction gas during the additive manufacturing process to improve the yield strength of the additive manufacturing part;

[0050] S5, obtaining a gradually changing pore structure similar to human bone structure and having the same elastic modulus and yield strength as human bone.

[0051] Embodiment: Construct a longitudinally gradually changing pore structure similar to human femur structure and having the same elastic modulus and yield strength as human bone for medical field patient femur replacement surgery. The similar structure facilitates the transportation of nutrients in the patient's body, the growth of tissues, and the same elastic modulus as the femur to overcome the bone necrosis caused by stress shielding, and sufficient yield strength to make the plant have a certain resistance to external damage.

[0052] Take the structure Gyroid as an example, which is a kind of TPMS, and its implicit function is:

[0053] f G(x,y,z) = sin(ωx)cos(ωy)+sin(ωy)cos(ωz)+sin(ωz)cos(ωx)-t (1)

[0054] where ω is the frequency, and let L=π / ω, which is the edge length of the G-type TPMS structure unit cell. t is the offset value of the surface. Based on the implicit function of the TPMS surface, the bottom design modeling is carried out by programming, and the CAD model in STL format is written to facilitate direct printing, such as Figure 2 (a) The gray part is the implicit surface of Gyroid, and the black part is the end face, Figure 2 (b) is the CAD model in STL format.

[0055] Take pure titanium TA1 as the raw material, and its powder micro-morphology is shown in Figure 3 , and the selective light melting technology is used to prepare it under pure argon gas condition.

[0056] The five groups of CAD models with different uniform porosities prepared are subjected to uniaxial compression test. The cross-sectional area of the structure is measured before the compression test, and the total area of all triangular facets on the cross-section is calculated to obtain the cross-sectional area of the structure, as shown in Figure 4 . The compression stress-strain curves of the five groups of samples are shown in Figure 5 , and the structure offset value and the elastic modulus are recorded in Table 1.

[0057] Table 1 Relationship between Gyroid structure parameters and its elastic modulus.

[0058]

[0059] From Table 1, we get

[0060] According to Gibson-Ashby model:

[0061]

[0062]

[0063] where E * represents the equivalent elastic modulus of the lattice structure, E S the elastic modulus of the solid material, is the porosity of the lattice structure, σ 0.2 is the yield strength of the lattice structure, σ S represents the yield strength of the solid material. C1, C2, n1, n2 are constants related to the structure.

[0064] The data in Table 1 is imported into origin for fitting, and the relationship between the structure parameters of TPMS structure and its elastic modulus and yield strength is obtained as:

[0065]

[0066]

[0067] where, represents the volume fraction of the structure, which is brought into (5) and (6) formula with (2) formula, we get:

[0068] E * = 108.574 x (0.43t + 0.5) 1.012 (7)

[0069] σ 0.2 = 397.081 x (0.43t + 0.5) 0.921 (8)

[0070] From the above formula, we get t = f(E), according to the needs of programming in space to build the required continuous change modulus field E = g(x, y, z), finally t = f(E) = f(g(x, y, z)), into f G(x,y,z) , we can get the required elastic modulus of different dimensions gradient change of Gyroid porous structure, as Figure 6 shown, Figure 6 one-dimensional gradient structure in (a),Figure 6 (b) is a two-dimensional gradient structure, Figure 6 (c) is a three-dimensional gradient structure. According to the structural shape of the femur, the above-mentioned prediction company is used to construct a radial gradient TPMS cylindrical structure with an overall porosity of 0.24 as shown in Figure 7 (a) The radial gradient TPMS cylindrical structure has an overall porosity of 0.24, an elastic modulus of 25.22 GPa, which is within the range of 25.0±4.3 GPa of the elastic modulus of human femoral cortical bone studied by Zysset et al. Its yield strength is 120 MPa, which is less than the range of 205±17.3 MPa of the yield strength of human femoral cortical bone, as shown in Figure 7 (b).

[0071] Application example

[0072] According to the research of Zysset et al. on the elastic modulus of human femur, the elastic modulus of human femur is 25.0±4.3 GPa, and the femur is divided into internal loose bone and external dense bone, i.e. the elastic modulus of internal bone is lower than that of external femur, and the yield strength of human cortical bone is 205±17.3 MPa. Therefore, based on the modulus relationship model constructed according to the present application, a cylindrical structure with an elastic design modulus of 25.62 GPa, a yield strength of 106.67 MPa and a radial gradient change similar to the femur is directly constructed as shown in Figure 7 a, and the stress-strain curve obtained by compressing it is shown in Figure 7 b, the actual modulus is measured to be 25.22 GPa, and the predicted value only differs by 1.6%, and the actual yield strength is 120.41 MPa, which differs by 11.44%. The elastic modulus meets the requirements of the elastic modulus of human bone, but the yield strength is lower than the requirements, so 5% nitrogen is added during the additive manufacturing process, and finally a radial gradient Gyroid porous structure is obtained, which is very suitable for replacing the human femur, can overcome stress shielding, and the structure of the pores is also suitable for the growth of bone tissue, has enough strength to resist external damage.

[0073] In summary, the present application is based on programming to control implicit function for direct modeling, then based on AM additive manufacturing to obtain the real object and carry out compression experiment, according to the experimental data to analyze and construct modulus field, finally obtain the gradient TPMS porous structure of the required elastic modulus, in addition, by passing nitrogen in the additive manufacturing process, the yield strength of the material is improved. Not only solves the problem of modeling difficulty, but also provides a method for designing the gradient TPMS porous structure of the required structure, elastic modulus and yield strength. In addition, the present application adopts the method of computer modeling combined with additive manufacturing and compression experiment to prepare the TPMS porous structure with spatial gradient change, so that it has the required elastic modulus, yield strength, porosity and pore structure. The present application is suitable for manufacturing artificial bone, repairing bone, tissue engineering scaffold, drug release system and cell culture medium and other applications. The present application has the characteristics of high preparation efficiency, high accuracy, large production capacity and low cost, and the process flow is simple, and complex porous structure can be produced.

[0074] The above is the preferred embodiment of the present application, any change made according to the technical scheme of the present application, as long as the function generated does not exceed the scope of the technical scheme of the present application, belongs to the protection scope of the present application.

Claims

1. A method for producing a metal implant for regulating the elastic modulus and the yield strength in the femoral condyles based on a gradual porosity and atmosphere, characterized in that, The application relates to a CAD model of a uniform pore structure controlled by an implicit function, a method for preparing the CAD model by additive manufacturing, and a method for obtaining a relationship model between pore structure parameters and mechanical properties by compression test. The CAD model is prepared by additive manufacturing, and a relationship model between pore structure parameters and mechanical properties is obtained by compression test; in the additive manufacturing process, the metal powder used is selected from one of biocompatible metal powders such as titanium and titanium alloy, tantalum, cobalt-chromium-molybdenum, stainless steel and nickel-titanium; the CAD model prepared by additive manufacturing is subjected to uniaxial compression test to obtain the elastic modulus and yield strength, and a Gibson-Ashby relationship model of pore structure parameters and the elastic modulus and yield strength is constructed; a modulus spatial position function is written according to the required modulus distribution, and the modulus spatial position function is written into the implicit function of the pore structure surface based on programming according to the Gibson-Ashby relationship bridge; In the additive manufacturing process, a predetermined proportion of reaction gas is introduced to improve the yield strength of the part prepared by additive manufacturing; the predetermined proportion of reaction gas refers to a non-toxic gas which can react with the metal powder used or can be dissolved in the metal deposition layer to cause precipitation strengthening and solid solution strengthening during the additive manufacturing process; According to the relationship model, a gradually changing pore structure similar to the human bone structure and having the same elastic modulus is constructed based on programming; the gradually changing pore structure is continuously changed, including a one-dimensional gradually changing pore structure, a two-dimensional gradually changing pore structure, and a three-dimensional gradually changing pore structure, and the mechanical properties thereof are also continuously changed, specifically in the form of the elastic modulus of the structure and the thickness parameter of the structure , that is, the structure thickness is gradually changed in the X direction, that is, a one-dimensional gradually changing structure, and similarly , , respectively, represent a two-dimensional gradually changing structure and a three-dimensional gradually changing structure, respectively. A gradual pore structure similar to human bone is obtained, and the elastic modulus and yield strength of the gradual pore structure are the same as those of human bone. The implicit function of the pore structure surface is programmed to be used for bottom design modeling, that is, the pore structure surface is constructed based on a programming language, one side of the pore structure surface is closed to obtain an end face, the pore structure surface and the end face are divided into triangular facets, and the triangular facet three vertex coordinates and the facet normal vector are recorded, and a CAD model in STL format is written according to the vertex coordinates and the normal vector.

2. The method of claim 1, wherein the metal implant is a femoral condyle implant. The entire region of the CAD model is expressed by spatial coordinates and written into the definition domain of the implicit function to obtain the entire pore structure CAD model.

3. The method of claim 1, wherein the metal implant is a femoral condyle implant. In the uniaxial compression test, the strain of the structure sample is accurately measured by a video extensometer during the compression process; the modulus spatial position function refers to the size of the elastic modulus value of a specific position of a certain overall structure which is selectively defined.

4. The method of claim 1, wherein the metal implant is a femoral condyle implant. The structure prepared by the method is suitable for the bone of any part of the human body, ensures the same elastic modulus as the human bone to overcome stress shielding, and also ensures the corresponding yield strength of the structure to have the ability to resist external damage, in addition, the structure similar to the bone is convenient for nutrient transportation and tissue growth.

5. The method of claim 1, wherein the metal implant is a femoral condyle implant. ​

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