Metal implant preparation method based on gradually-changed pores and atmosphere regulation and control of modulus of elasticity and yield strength of middle section of similar femur

Abstract

The invention relates to a preparation method of a metal implant based on gradient pores and atmosphere regulation and control of modulus of elasticity and yield strength of a similar femoral middle section, and belongs to the technical field of bottom design of pore structures and preparation of pore materials. The method comprises the following steps: designing a CAD model of a homogeneous pore structure; preparing a homogeneous pore structure sample according to the CAD model by using a selective laser melting method, and carrying out a uniaxial compression experiment on the sample to obtain a relation model between the elastic modulus of the homogeneous pore structure and the structural parameters of the homogeneous pore structure; according to the relation model, based on programming, constructing a gradient pore structure which is similar to a human skeleton and has the same elasticity modulus as the human skeleton; specific reaction gas is added in the additive manufacturing process to improve the yield strength of the additive part; and finally obtaining the gradually-changed pore structure which is similar to the human skeleton and has the same elastic modulus and yield strength as the human skeleton. The method is suitable for manufacturing artificial bones, repairing bones, tissue engineering scaffolds, drug release systems, cell culture substrates and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of bottom layer design of pore structure and preparation of pore material, and specifically relates to a method for preparing a metal implant based on gradual pore and atmosphere regulation of elastic modulus and yield strength of the middle segment of femur. Background Art

[0002] Porous structure is a bionic structure with natural advantages. It contains a large number of pore structures and has the advantages of low relative density, high specific surface area, good permeability, and light weight. It is widely used in engineering fields such as aerospace, automobile manufacturing, material chemistry, and medicine. Among them, the pores of the open-cell porous structure are connected, and the application range is wider. Common porous structures include lattice structures, honeycomb structures, and minimal surfaces. Among them, the three-periodic minimal surfaces, also known as TPMS (Triply Periodic Minimal Surfaces) structures, have attracted more and more attention from scholars and universities in recent years. The three-periodic minimal surfaces have the advantages of diverse geometric shapes, high specific surface area, fully connected pores, controllable parameters, and quasi-self-support. Therefore, they are widely used in energy-absorbing structures, skeleton modeling, etc.

[0003] Additive Manufacturing (AM), or 3D printing, is a special processing technology that uses metal or non-metal materials to construct parts by printing layer by layer based on a three-dimensional digital model. As a fast and accurate parts processing method, it is used in aerospace, automobile, medical, mold, construction and other fields.

[0004] TPMS structures prepared based on AM are widely used for filling human bone implants, but it should be noted that the elastic modulus of the prepared TPMS porous structure must be the same as the elastic modulus of the human bone where it is implanted, in order to overcome the "stress shielding" phenomenon (the difference between the stiffness of the implant and the stiffness of the surrounding bones leads to a reduction in the stress on the bones, causing bone loss). Since the mechanical properties of certain bones in different positions of the human body are different, such as bones, the modulus of the outer dense bone is higher than that of the inner loose bone, so gradient porous structures are widely used. The current problems are that the construction of the gradient TPMS structure is too difficult and complicated. The second is the lack of a systematic method to directly obtain the gradient TPMS point structure with the expected elastic modulus and yield strength. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the background technology and to provide a method for preparing a metal implant based on gradual porosity and atmosphere regulation of the elastic modulus and yield strength of the mid-femoral segment.

[0006] To achieve the above object, the technical solution of the present invention is: a method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femoral midsection, comprising:

[0007] Constructing a uniform pore structure CAD model controlled by implicit function based on programming:

[0008] The CAD model is prepared by additive manufacturing, and a compression test is performed to obtain a relationship model between pore structure parameters and mechanical properties;

[0009] Based on the relational model, a gradient pore structure similar to the human bone structure and with the same elastic modulus is constructed based on programming;

[0010] During the additive manufacturing process, a predetermined proportion of reactive gas is introduced to increase the yield strength of the additively manufactured parts;

[0011] The obtained structure is similar to that of human bone, and the elastic modulus and yield strength are the same as those of human bone.

[0012] Preferably, the modeling method used is to perform underlying design modeling using programming based on implicit functions of the pore structure surface.

[0013] Preferably, the modeling step used is to directly construct the entire model without constructing unit cells and then arranging and connecting them.

[0014] Optionally, during the additive manufacturing process, the powder used is selected to include one of biocompatible metal powders such as titanium and titanium alloys, tantalum, cobalt-chromium-molybdenum, stainless steel, nickel-titanium, etc.

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

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

[0017] Optionally, the similarity to the human skeletal structure is specifically manifested in that the overall structural shape is the same as that of the bone, including cylindrical, spherical, plate-shaped, etc.

[0018] Optionally, the gradient pore structure changes continuously, including one-dimensional gradient, two-dimensional gradient, and three-dimensional gradient pore structures, and its mechanical properties also change continuously, which is specifically manifested in the elastic modulus of the structure.

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

[0020] Optionally, it is characterized in that a gradient pore structure similar to that of human bones, having a preset elastic modulus and a required yield strength can be obtained.

[0021] Preferably, an implicit surface of the pore structure is constructed based on a programming language and one side of it is closed to obtain an end face. The surface and the end face 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, and a CAD model in STL format is written according to the vertex coordinates and the normal vectors.

[0022] Preferably, when writing the code, the entire area of ​​the model is represented by spatial coordinates and written into the definition domain of the implicit function to obtain the entire pore structure model.

[0023] Preferably, the method for calculating the cross-sectional area of ​​the part is to calculate the sum of the areas of all triangular facets on the cross section, and the strain of the structural specimen is accurately measured using a video extensometer during the compression process.

[0024] Optionally, the modulus space position function refers to the selective definition of the elastic modulus value at a specific position of a certain overall structure, such as a human bone having different elastic moduli at different positions.

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

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

[0027] Preferably, the structure prepared by the method is suitable for bones in any part of the human body, ensuring that it has the same elastic modulus as the human bone to overcome stress shielding while also ensuring that the structure has a corresponding yield strength to have the ability to resist external damage. In addition, its bone-like structure facilitates the transportation of nutrients and the growth of tissues.

[0028] Compared with the prior art, the present invention has the following beneficial effects: the present invention directly models by controlling implicit functions based on programming, then obtains a physical object based on AM additive manufacturing and performs compression experiments, constructs a modulus field based on experimental data analysis, obtains a gradient pore structure with the required elastic modulus based on modulus field control, and then increases the yield strength of the additive parts by introducing a certain amount of reaction gas during the additive manufacturing process, and finally obtains a gradient pore structure with the required structural type and mechanical properties. It not only solves the problem of modeling difficulties, but also provides a method for designing a gradient pore structure with the required elastic modulus. In addition, the invention adopts a method of combining computer modeling with additive manufacturing and compression experiments to prepare a spatial gradient pore structure, so that it has the required elastic modulus, yield strength, porosity and pore structure. This technology is suitable for a variety of applications such as manufacturing artificial bones, repairing bones, tissue engineering scaffolds, drug release systems, and cell culture matrices. This technology has the characteristics of high preparation efficiency, high precision, large production volume, and low cost, and the process flow is simple and can produce complex porous structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flow chart of the preparation of a metal implant with elastic modulus and yield strength similar to the mid-end of the femur based on gradual porosity and atmosphere regulation in an embodiment of the present invention.

[0030] Figure 2 This is a CAD model of a uniform Gyroid porous structure controlled by implicit functions based on programming in an embodiment of the present invention. (a) is a Gyroid structure closed by implicit surfaces and end faces, and (b) is a CAD model in STL format written based on programming.

[0031] Figure 3 The SEM microstructure and particle size distribution diagram of the TA1 powder used in the examples of the present invention.

[0032] Figure 4 This is a schematic diagram of a cross-sectional area obtained by calculating the sum of the areas of all triangular facets on a cross section in an embodiment of the present invention.

[0033] Figure 5 3 and 4. The figures are the morphology comparison diagrams and stress-strain diagrams of the uniform structure before and after compression in the embodiments of the present invention, wherein (a), (b), (c), (d), and (e) are the morphology comparison diagrams of the uniform Gyroid structure before and after compression with offset values ​​of t=-0.9, t=-0.6, t=-0.3, t=0, and t=0.3, respectively, and (f) shows the stress-strain curves of the five groups of structures during the compression process.

[0034] Figure 6 These are the three-dimensional gradient Gyroid structures obtained in the embodiments of the present invention, (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 The two-dimensional gradient Gyroid structure obtained in the embodiment of the present invention can be used to replace human bones, (a) schematic diagram of the two-dimensional gradient Gyroid structure, (b) stress-strain curve of the two-dimensional gradient Gyroid structure subjected to a compression test under pure argon conditions, (c) stress-strain curve of the two-dimensional gradient Gyroid structure subjected to a compression test under argon-nitrogen mixed gas conditions. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is specifically described below in conjunction with the accompanying drawings. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0038] The present invention provides a method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femoral midsection, comprising:

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

[0040] The CAD model is prepared by additive manufacturing, and a compression test is performed to obtain a relationship model between pore structure parameters and mechanical properties;

[0041] According to the relational model, a gradient pore structure similar to the human bone structure and with the same elastic modulus is constructed based on programming;

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

[0043] The obtained structure is similar to that of human bone, and the elastic modulus and yield strength are the same as those of human bone.

[0044] The following is a specific implementation process of the present invention.

[0045] like Figure 1 As shown, the present invention is a method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femoral midsection, the steps comprising:

[0046] S1. Constructing a uniform pore structure CAD model controlled by implicit function based on programming:

[0047] S2. Prepare the above CAD model by additive manufacturing, and conduct compression test to obtain the relationship model between pore structure parameters and mechanical properties;

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

[0049] S4. Introducing a certain proportion of reactive gas into the additive manufacturing process to improve the yield strength of the additively manufactured parts;

[0050] S5. A gradient pore structure is obtained that is similar to human bones and has the same elastic modulus and yield strength as human bones.

[0051] Embodiment: The structure is similar to that of human femur, and the longitudinal gradient pore structure with the same elastic modulus and yield strength as human bone is used for femoral replacement surgery in the medical field. Its similar structure facilitates the transportation of nutrients and tissue growth in the patient's body. The same elastic modulus as that of femur can overcome the bone necrosis caused by stress shielding. Sufficient yield strength enables the plant to have a certain ability to resist external damage.

[0052] Take the structure Gyroid as an example, which is one of the 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, let L = π / ω, which is the side 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 underlying design modeling is performed using programming, and it is written into a CAD model in STL format for direct printing, such as Figure 2 In (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] Using pure titanium TA1 as raw material, the powder microstructure is as follows Figure 3 As shown, the selective photo-melting technique was used for preparation under pure argon conditions.

[0056] Uniaxial compression tests were performed on five groups of CAD models with different porosities. The cross-sectional area of ​​the structure was measured before the compression test. The cross-sectional area of ​​the structure was obtained by calculating the sum of the areas of all triangular facets on the cross section, such as Figure 4 The compressive stress-strain curves of the five groups of specimens are shown in Figure 5 , and record the structural offset value and elastic modulus as shown in Table 1.

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

[0058]

[0059] From Table 1, we can get

[0060] According to the 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 Indicates the yield strength of the solid material. C1, C2, n1, n2 are constants related to the structure.

[0064] The data in Table 1 are imported into Origin for fitting to obtain the TPMS structure. The relationship between the structural parameters and the elastic modulus and yield strength is as follows:

[0065]

[0066]

[0067] in, represents the volume ratio of the structure. Substituting it and equation (2) into equations (5) and (6), we obtain:

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

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

[0070] From the above formula, we get t=f(E). We can construct the required continuously changing modulus field E=g(x, y, z) in space based on programming as needed. Finally, we can substitute t=f(E)=f(g(x, y, z)) into f G(x,y,z) In this way, the required Gyroid porous structure with gradient changes in elastic modulus in different dimensions can be obtained, such as Figure 6 As shown, Figure 6 (a) is a one-dimensional gradient structure. Figure 6 (b) is a two-dimensional gradient structure. Figure 6 (c) is a three-dimensional gradient structure. Based on the structural shape of the femur, the above prediction company is used to construct Figure 7 The radial gradient TPMS cylindrical structure with an overall porosity of 0.24 shown in (a) has an elastic modulus of 25.22 GPa, which is within the elastic modulus range of 25.0±4.3 GPa 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 human femoral cortical bone yield strength. Figure 7 (b).

[0071] Application Examples

[0072] According to the research of Zysset et al., the elastic modulus of human femur is 25.0±4.3GPa, and the femur is divided into internal loose bone and external compact bone, that is, the elastic modulus of the internal bone is lower than that of the external femur, and the yield strength of human cortical bone is 205±17.3MPa. Therefore, based on the modulus relationship model constructed by the present invention, a cylindrical structure with a radial gradient change of 25.62GPa, a yield strength of 106.67MPa and a structure similar to the femur is directly constructed. Figure 7 As shown in a, the stress-strain curve is obtained by compressing it. Figure 7 As shown in Figure b, the actual modulus is 25.22GPa, which is only 1.6% different from the predicted value, and 11.44% different from the actual yield strength of 120.41MPa. Its elastic modulus meets the elastic modulus requirements of human bones, but its yield strength is lower than the requirement. Therefore, 5% nitrogen is added during the additive manufacturing process, and the radial gradient Gyroid porous structure is finally obtained. It is very suitable for the replacement of human femurs and can overcome stress shielding. The pores in the structure are also suitable for the growth of bone tissue, and it has sufficient strength to resist external damage.

[0073] In summary, the present invention is based on programming to directly model by controlling implicit functions, and then obtains the physical object based on AM additive manufacturing and performs compression experiments. The modulus field is constructed according to the experimental data, and finally the gradient TPMS porous structure with the required elastic modulus is obtained. In addition, by introducing nitrogen during the additive manufacturing process, the yield strength of the material is improved. It not only solves the problem of modeling difficulties, but also provides a method for designing a gradient TPMS porous structure with the required structure, elastic modulus and yield strength. In addition, the present invention adopts a method of combining computer modeling with additive manufacturing and compression experiments to prepare a TPMS porous structure with spatial gradient changes, so that it has the required elastic modulus, yield strength, porosity and pore structure. This technology is suitable for a variety of applications such as manufacturing artificial bones, repairing bones, tissue engineering scaffolds, drug release systems, and cell culture matrices. This technology has the characteristics of high preparation efficiency, high precision, large production volume, and low cost, and the process flow is simple and can produce complex porous structures.

[0074] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. A method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femoral midsection, characterized in that: include: Constructing a uniform pore structure CAD model controlled by implicit function based on programming: The CAD model is prepared by additive manufacturing, and a compression test is performed to obtain a relationship model between pore structure parameters and mechanical properties; According to the relational model, a gradient pore structure similar to the human bone structure and with the same elastic modulus is constructed based on programming; During the additive manufacturing process, a predetermined proportion of reactive gas is introduced to increase the yield strength of the additively manufactured parts; The obtained structure is similar to that of human bone, and the elastic modulus and yield strength are the same as those of human bone.

2. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 1, characterized in that: The CAD model uses a modeling method that uses programming based on implicit functions of the pore structure surface to perform underlying design modeling; the modeling steps used are to directly construct the entire model without constructing unit cells and then arraying and connecting them.

3. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 1, characterized in that: In the additive manufacturing process, the powder used is selected from one of the biocompatible metal powders including titanium and titanium alloy, tantalum, cobalt-chromium-molybdenum, stainless steel, and nickel-titanium.

4. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femur midsection according to claim 1, characterized in that: Using the CAD model prepared by additive manufacturing, the elastic modulus and yield strength were obtained by uniaxial compression test, and the Gibson-Ashby relationship model between the pore structure parameters and the elastic modulus and yield strength was constructed. The spatial position function of the modulus was written according to the required modulus distribution, and then the modulus spatial position function was written into the implicit function of the pore structure surface based on programming through the Gibson-Ashby relationship bridge.

5. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 1, characterized in that: The gradient pore structure changes continuously, including a one-dimensional gradient pore structure, a two-dimensional gradient pore structure, and a three-dimensional gradient pore structure. Its mechanical properties also change continuously, which is specifically manifested in the elastic modulus of the structure and the structural thickness parameter t=f(x), that is, the structural thickness is gradient in the X direction, that is, a one-dimensional gradient structure. Similarly, t=f(x, y) and t=f(x, y, z) respectively indicate that the structural thickness is a two-dimensional gradient structure and a three-dimensional gradient structure.

6. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femur midsection according to claim 1, characterized in that: The predetermined proportion of reaction gas refers to a non-toxic gas that can react with the metal powder used in the additive manufacturing process or can be dissolved and distributed in the metal deposition layer to cause precipitation strengthening and solid solution strengthening.

7. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 2, characterized in that: The underlying design modeling is performed using programming based on the implicit function of the pore structure surface. That is, the pore structure surface is constructed based on the programming language and one side of it is closed to obtain the end face. The surface and the end face are divided into triangular patches and the coordinates of the three vertices of the triangular patches and the normal vectors of the patches are recorded. A CAD model in STL format is written according to the vertex coordinates and normal vectors.

8. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 2, characterized in that: When writing the code, the entire area of ​​the CAD model is represented by spatial coordinates and written into the definition domain of the implicit function to obtain the entire pore structure CAD model.

9. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the mid-femoral segment according to claim 4, characterized in that: In the uniaxial compression test, the strain of the structural sample is accurately measured by a video extensometer during the compression process; the modulus space position function refers to the selective definition of the elastic modulus value of a specific position of a certain overall structure.

10. The method for preparing a metal implant based on gradual porosity and atmosphere regulation of elastic modulus and yield strength of the femoral midsection according to claim 1, characterized in that: The structure prepared by the method is suitable for bones in any part of the human body, ensuring that it has the same elastic modulus as human bones to overcome stress shielding while also ensuring that the structure has a corresponding yield strength to have the ability to resist external damage. In addition, its structure similar to bones facilitates the transportation of nutrients and the growth of tissues.

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