A gradient artificial vertebra and its design method

Abstract

This invention claims protection for a novel gradient artificial vertebra and its design method, belonging to the technical field of medical devices. It mainly includes a biomimetic porous structure design method, an axial gradient design method, and a radial gradient design method. First, simulating the in vivo loading conditions of a spinal vertebra, a density gradient design is performed along the axial direction. This reduces the relative density of the bone contact surfaces at both ends to lower the elastic modulus, weaken the stress shielding effect, and promote bone ingrowth. Simultaneously, the relative density of the middle portion is increased to reduce stress concentration and improve specific strength. Then, a radial gradient design is performed, increasing the relative density on the inner side to enhance central mechanical properties. Finally, the gradient designs in both directions are integrated into the final artificial vertebra, resulting in an artificial vertebra with reduced stress concentration, increased specific strength, reduced stress shielding at the bone contact surfaces, promoted bone ingrowth, and enhanced fatigue performance. This method is applicable to most devices requiring reduced stress concentration and enhanced fatigue performance.

Description

Technical Field

[0001] This invention relates to orthopedic medical devices, computer-aided design, biomechanics, and additive manufacturing technology, and particularly to gradient porous structure design for enhancing biomechanical properties. Background Technology

[0002] In the field of medical devices, the purpose of designing functional vertebral body implants is to replace diseased vertebrae and reconstruct the support and movement functions of natural vertebrae. During the design process, two major standards for vertebral body implants must be met to ensure safety and stability. The first is the strength standard: based on the maximum distortion energy criterion, the maximum stress of each component of the spinal reconstruction system under various load conditions must be lower than the yield strength of the corresponding material. The safety factor, defined by the ratio of the yield strength to the maximum stress of each component, can be used to assess the safety of the spinal reconstruction system. The second is the bone reconstruction standard: although the initial stability of the spinal reconstruction system can be achieved through the posterior fixation system, long-term stability depends on good bone ingrowth at the interface between the vertebral endplate and the prosthesis. Therefore, it is necessary to design a reasonable porous structure at the prosthesis endface to effectively promote bone ingrowth.

[0003] Current implant materials have a higher stiffness than bone, preventing the necessary stress from being transferred to adjacent bone and affecting bone resorption around the implant, thus leading to implant loosening. This biomechanical incompatibility that causes bone cell death is known as the "stress shielding effect." In artificial vertebral body implants, the main causes of failure are: firstly, point / line contact between the vertebral body implant and the adjacent vertebral endplate interface leads to stress concentration and eventual subsidence; secondly, the stress shielding effect caused by the high stiffness mismatch between bone and metal implants. These problems can be improved by considering more personalized morphological features and parameters, such as implant gradient design, endface morphology, and physiological curvature. In artificial vertebral body design, the lumbar shape is designed by controlling the transverse and sagittal diameters of the midsection, where the transverse and sagittal diameters are the average of the corresponding diameters in the upper and lower endfaces. If a patient's spine collapses, appropriate correction with an artificial vertebral body implant is required under the guidance of a clinician. The gap height and physiological curvature of the defect area are measured based on the corrected state to complete the design of the artificial vertebral body implant's dimensions and curvature.

[0004] The perfect fit between the natural vertebra and the implant interface facilitates uniform stress transfer under different load conditions. Gradient design of the implant is an effective way to achieve biomimetic performance. TriplyPeriodic Minimal Surface (TPMS) provides a reference for vertebral gradient design. It is a design method based on implicit functions, characterized by simple expressions and high design efficiency. The resulting porous structure has the advantages of continuous structure, smooth surface, and low stress concentration. By changing the parameters in the function, the pore size and relative density can be easily varied. Current TPMS lattice structures have implemented some gradient design methods, but most designs cannot be directly and reasonably applied to the design of devices. This invention will simultaneously design the axial and radial gradients of the artificial vertebra and apply them reasonably to the design of the artificial vertebra to optimize stress concentration during implantation, stress shielding at the bone contact surface, bone ingrowth promotion, and fatigue performance of traditional artificial vertebrae.

[0005] CN110929379B discloses a topology-optimized artificial vertebral body and its design method. The artificial vertebral body includes a perforated topological thin-walled structure and a porous structure placed within the perforated topological thin-walled structure. The topological thin-walled structure is designed for lightweight prosthesis based on topology optimization methods under various gait biomechanical environments. While meeting the strength requirements of the prosthesis under different movement states, the porous structure is added to meet bone ingrowth requirements, thereby achieving bio-fixation of the prosthesis in the later stages and ensuring good stability. The topology-optimized artificial vertebral body described in this invention, through the organic combination of the perforated topological thin-walled structure and the porous structure, can simultaneously ensure the immediate and mid-to-long-term stability of the artificial vertebral body after implantation, which is beneficial to the recovery of spinal function and the improvement of quality of life for patients.

[0006] Difference: In patent CN110929379B, topology optimization design is performed on the thin-walled structure to enhance the mechanical strength performance of the external thin-walled structure, thereby enhancing the overall mechanical performance of the artificial vertebra.

[0007] This invention focuses on the gradient biomimetic design of the porous filling portion of the artificial vertebral body. This design not only enhances the mechanical properties of the artificial vertebral body, but also allows the gradient design of the porous structure to better adapt to bone ingrowth, thereby enhancing the long-term stability of the artificial vertebral body implant. Furthermore, this patent employs a radial gradient design to enhance the fatigue performance of the vertebral body under load.

[0008] Limitations: In patent CN110929379B, the mechanical properties are enhanced through an external thin-walled structure. Although topology optimization further improves biomechanical performance, the external thin-walled structure also obstructs direct contact between surrounding tissues and the porous structure, affecting the fusion of tissues and the artificial vertebral body. At the bone contact surfaces at the upper and lower ends, because the porous structure is only a uniform array design, the pore size and porosity at the bone contact surface remain consistent with the interior. However, the artificial vertebral body is not a uniform cylindrical model, and the uniform array design of the porous structure has room for optimization in terms of mechanical properties and promoting bone ingrowth.

[0009] This patent, while ensuring that the interconnected pores of the porous structure promote bone ingrowth, further optimizes the porous structure through a gradient-based biomimetic design. Through axial gradient design, the relative density in the middle of the device is increased to avoid or reduce stress concentration and improve specific strength, while the relative density at both ends of the bone contact surface is reduced to lower the elastic modulus, alleviate stress shielding at the bone contact surface, and promote bone ingrowth. Through radial gradient design, the relative density on the inner side is increased, enhancing the mechanical properties of the center and improving the load-bearing capacity of the artificial vertebral body model, thus achieving enhanced fatigue performance. Finally, by integrating the gradient designs in both directions, the advantages of both directions are combined to obtain an artificial vertebral body that reduces stress concentration, improves specific strength, reduces stress shielding at the bone contact surface, promotes bone ingrowth, and enhances fatigue performance. Summary of the Invention

[0010] This invention aims to solve the problems of the prior art mentioned above. It proposes a gradient artificial vertebral body and its design method. The technical solution of this invention is as follows:

[0011] A method for designing a gradient artificial vertebral body, comprising:

[0012] A biomimetic porous cone model design method; an axial gradient design method to reduce stress shielding; a radial gradient design method to improve the fatigue performance of the cone; and a method for integrated manufacturing using metal additive manufacturing.

[0013] The axial gradient design method for the artificial vertebral body specifically includes:

[0014] To ensure an overall relative density of approximately 20%, the surface area of ​​the artificial vertebral body in the (x,y) plane along the Z-axis is used. relative density and the average area of ​​the (x,y) plane , Lianlide ,get We design a density gradient along the Z-axis, and fit the density along the Z-axis using a quadratic function to obtain the function:

[0015]

[0016] The relationship between the Z-axis position and the relative density can be obtained through formulas (2) and (3).

[0017]

[0018] In formula (4) Substituting into (1) will give the required Z-axis gradient;

[0019] The radial gradient design method for the artificial vertebral body specifically includes:

[0020] Based on the biomimetic design, a radial gradient is designed to enhance the fatigue performance of the structure. There are two approaches to the design of the radial gradient: one is to control the number of radial elements, and the other is to control the radial density. The design of the number of radial elements can be directly controlled by the value of n in the formula, and then the Sigmoid activation function is used to realize the transition of the model. The design of the radial density gradient adopts the fitting of the Boltzmann function to realize the biomimetic design according to the needs of the patient.

[0021] The Boltzmann function is used for fitting, and the formula is as follows:

[0022]

[0023] , , , These are all constants in the Boltzmann fitting function. This represents the radius in the cone model;

[0024] The Sigmoid activation function is used to achieve the transition between models. The formula for the Sigmoid activation function is as follows:

[0025]

[0026] and The axes represent the functions of Gyroid porous structure unit cells with relative densities of 20% and 50% on the coordinate axis. and These represent the starting points of the two structures that are smoothly connected using the Sigmoid activation function.

[0027] Furthermore, the design method for the biomimetic porous structure specifically includes:

[0028] Based on real-world applications of artificial vertebral bodies, an artificial vertebral body model was designed, and a Gyroid structure from a three-period minimal surface TPMS lattice structure was selected to establish an artificial vertebral body with a relative density of 20%.

[0029] Functions are created using a programming language to design porous structures; the modeling process of porous structures involves converting from rectangular coordinates to polar coordinates to achieve the filling of porous structures in cylindrical components.

[0030] Furthermore, in the design of the Gyroid lattice structure, an algorithm is used to control the relative density and the number of radial elements in the porous structure, the expression of which is:

[0031]

[0032] It is used to control relative density The parameters, and The functional relationship is:

[0033]

[0034] These represent the angle, radius, and height in the artificial vertebral model, respectively. It is the number of porous structural units in the model. The function representing the Gyroid porous structure in polar coordinates.

[0035] Relative density By mapping values, the density gradient of the porous structure can be established, as shown in the formula. The number of units in the radial direction of the structure can be controlled.

[0036] A novel gradient artificial vertebral body is provided, which employs any of the design methods described above and uses a selective laser melting process to integrally form the artificial vertebral body.

[0037] The advantages and beneficial effects of this invention are as follows:

[0038] 1. This invention proposes a reasonable Z-axis gradient design, which increases the relative density of the middle part to reduce or avoid stress concentration and improve specific strength. At the same time, it reduces the relative density of the bone contact surfaces at both ends to reduce the elastic modulus, thereby reducing the impact of stress shielding and promoting bone ingrowth.

[0039] 2. A continuous radial gradient design was implemented using the Boltzmann function, simulating the biomimetic design of natural bones, which helps improve the fatigue performance of artificial vertebrae. Furthermore, a design for controlling the number of radial elements to achieve the radial gradient was proposed.

[0040] 3. The radial direction is divided into several parts using the Boltzmann fitting function. Within each part, the Z-axis gradient is designed by controlling the relative density using the fitting function. An activation function is then used to achieve a smooth transition between the two parts. The resulting artificial vertebral body possesses both Z-axis and radial gradients, and exhibits the ability to reduce or avoid stress concentration, improve specific strength, reduce stress shielding at the bone contact surface, promote bone ingrowth, and enhance fatigue performance.

[0041] In this invention, the axial gradient design, the radial gradient design, and the fusion design of gradients in both directions are all innovative designs. The ingenuity of each design method is described below.

[0042] Axial gradient design: This increases the relative density in the middle of the device, improving its mechanical strength and preventing premature collapse during compression of the artificial vertebral body with a uniform Gyroid lattice structure, thus increasing the model's specific strength. Simultaneously, it reduces the relative density of the bone contact surfaces at both ends, lowering the elastic modulus and mitigating stress shielding at the bone contact surfaces. Furthermore, the reduced relative density also increases the porosity in the porous vertebral model, providing favorable conditions for bone ingrowth.

[0043] Radial gradient design: This increases the relative density on the inner side of the device, enhances the mechanical properties at the center, and improves the load-bearing capacity of the artificial vertebral model. Under the same load conditions, the model's resistance to failure is improved, achieving the goal of enhancing the fatigue performance of the vertebral body.

[0044] Fusion design of gradients in two directions: Combining the advantages of gradient design in two directions, an artificial vertebra is obtained that reduces stress concentration, increases specific strength, reduces stress shielding at the bone contact surface, promotes bone ingrowth, and enhances fatigue performance. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of an artificial vertebra with a relative density of 20% provided by a preferred embodiment of the present invention;

[0046] Figure 2 This is a flowchart of the design method for an axial and radial dual-gradient artificial vertebral body according to a preferred embodiment of the present invention;

[0047] Figure 3 This is a comparison diagram of compression simulation experiments of a uniform Gyroid lattice structure and a gradient-designed Gyroid lattice structure artificial vertebra.

[0048] Figure 4 This is a schematic diagram of converting the rectangular coordinates of a porous structure to polar coordinates;

[0049] Figure 5 This is a schematic diagram of an artificial vertebra designed by fitting a quadratic function curve of the z-axis density gradient and the axial gradient.

[0050] Figure 6 This is a comparative schematic diagram of the radial design of an artificial vertebral body that maintains a relative density of approximately 20%.

[0051] Figure 7 This is a schematic diagram of the radial density gradient design controlled by the Boltzmann fitting function;

[0052] Figure 8 This is a schematic diagram illustrating the transition between TPMS lattice structures using the Sigmoid activation function.

[0053] Figure 9 This is a schematic diagram of a dual-gradient artificial vertebral body model with Z-axis gradient and radial gradient;

[0054] Figure 10 This is a schematic diagram of the gradient design of an artificial vertebral body model. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention.

[0056] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0057] Preferably, the working principle and process of the present invention are as follows: Figure 1-10 As shown:

[0058] This invention addresses the problems of stress shielding, adjacent vertebral bone collapse, and insufficient long-term implantation stability that often occur after implantation of artificial vertebrae. It proposes a porous structure design method with dual axial and radial gradients. By designing interconnected pores, it promotes bone ingrowth, reduces the elastic modulus of the bone interface to avoid stress shielding, enhances the central mechanical properties, and improves fatigue strength, thus resolving the contradiction between low elastic modulus and insufficient mechanical fatigue performance.

[0059] 1. Artificial Vertebral Body Design Model and Method

[0060] Based on real-world examples of artificial vertebral bodies, a reasonably sized artificial vertebral body model was designed. A Gyroid structure from a TPMS lattice structure was selected (refer to patent CN201911407257.8, which will not be elaborated here), and an artificial vertebral body with a relative density of 20% was constructed. Figure 1 .

[0061] Preferably, the design concept of the present invention has the following characteristics:

[0062] 1. Bionics. Structural bionics, biomechanical bionics.

[0063] 2. Better adapted to human biomechanics and biomechanics.

[0064] 3. Connected porous structure: promotes bone ingrowth;

[0065] 4. Suitable biomechanics: Avoids stress shielding and prevents bone degeneration of adjacent bones;

[0066] 5. Improve the long-term stability of the vertebral body within the body.

[0067] The implementation method of this invention is as follows:

[0068] 1. Porous design of three-period minimal surface: interconnected pores and better mechanical properties.

[0069] 2. Gradient design: Reduce the elastic modulus in the area of ​​contact with bone. Axial gradient.

[0070] 3. Gradient design: Radial gradient. Fatigue performance.

[0071] First, a traditional uniform lattice artificial cone with a relative density of 20% was constructed. Stress distribution and failure were analyzed through simulation experiments. The gradient design of the cone model was then driven by the stress distribution and failure modes of the traditional uniform lattice artificial cone. Figure 2 The design method of the axial and radial dual-gradient artificial vertebral body is shown, and Figure 3 (a) Compression simulation experiment of artificial vertebrae with uniform Gyroid lattice structure (b) Compression simulation experiment of artificial vertebrae with gradient design Gyroid lattice structure to achieve optimization of artificial vertebrae.

[0072] 2. Design method of radial porous structure

[0073] Functions are created using programming languages ​​(such as MATLAB, C++, etc.) to design porous structures. The modeling process for porous structures involves transforming from Cartesian coordinates to circular coordinates to achieve porous structure filling of cylindrical components, such as... Figure 4 The rectangular coordinates of the porous structure shown are converted to polar coordinates. The resulting porous structure has the advantages of structural continuity and radial isotropy.

[0074] In the design of the Gyroid lattice structure, an algorithm is used to control the relative density and the number of radial elements of the porous structure. The expression for this is:

[0075]

[0076] It is used to control relative density The parameters, and The functional relationship is:

[0077]

[0078] Relative density By mapping values, the density gradient of the porous structure can be established, as shown in the formula. The number of units in the radial direction of the structure can be controlled.

[0079] 3. Axial gradient design method for artificial vertebral bodies

[0080] Based on the stress analysis and stress distribution results of the uniform lattice, the artificial vertebrae with a uniform Gyroid lattice structure exhibit significant stress concentration. By using an axial gradient design, the relative density in the middle of the device is increased to avoid or reduce stress concentration and improve specific strength. Simultaneously, the relative density at both ends of the bone contact surface is reduced to decrease the elastic modulus, alleviate stress shielding at the bone contact surface, and promote bone ingrowth.

[0081] The specific design method for the axial gradient is as follows: To ensure an overall relative density of approximately 20%, the surface area of ​​the artificial vertebral body in the (x,y) plane at the Z-axis is used as a reference. relative density and the average area of ​​the (x,y) plane , Lianlide ,get Perform density gradient design along the Z-axis. For example... Figure 5 The artificial vertebrae designed with the quadratic function curve of the density gradient along the z-axis and the axial gradient are shown. The density along the z-axis is fitted using a quadratic function, yielding the function:

[0082]

[0083] The relationship between the Z-axis position and the relative density can be obtained through formulas (2) and (3).

[0084]

[0085] In formula (4) Substituting into (1) will give you the required Z-axis gradient.

[0086] In the axial gradient design of the artificial vertebral body, the relative density in the middle of the device was increased, improving its mechanical strength and preventing premature collapse during compression of the uniform Gyroid lattice structure artificial vertebral body, thus increasing the model's specific strength. Simultaneously, the relative density at both ends of the bone contact surface was reduced, lowering the elastic modulus and alleviating stress shielding at the bone contact surface. Furthermore, the reduced relative density also increases the porosity in the porous vertebral body model, providing favorable conditions for bone ingrowth.

[0087] 4. Radial gradient design method for artificial vertebral bodies

[0088] Based on biomimetic design principles, radial gradients are designed to enhance the fatigue performance of structures. There are two main approaches to radial gradient design: Figure 6 The design involves two aspects: controlling the number of radial units and controlling their density. The number of radial units can be directly controlled by the value of 'n' in the formula, and the Sigmoid activation function is used to achieve a smooth transition in the model. The density gradient of the radial units can be designed by fitting a Boltzmann function, achieving a biomimetic design tailored to the patient's needs.

[0089] Among them, Figure 6 The radial design diagrams of artificial vertebrae with a relative density of approximately 20% are as follows: (a) uniform array Gyroid lattice structure; (b) radially designed Gyroid lattice structure; (c) Gyroid lattice structure with varying radial element count; (d) radial density gradient designed Gyroid lattice structure.

[0090] Relative density Value mapping enables the establishment of gradients in porous structures. In artificial vertebral body design, increasing the relative density on the inner side enhances the central mechanical properties, thereby improving the fatigue performance of the vertebral body. Taking this invention as an example (the model was enlarged during design),... Establish a radially distributed density gradient function: the cone is designed with a radius of... For a cylinder, the relative density is greatest at the inside and gradually decreases from the center outwards. For example... Figure 7 A schematic diagram of the radial density gradient design controlled by the Boltzmann fitting function is shown. From arrive When it changes, the corresponding relative density is from arrive change.

[0091] The Boltzmann function is used for fitting, as shown in the following formula:

[0092]

[0093] Based on the Boltzmann fitting function and the above conditions, the parameters are obtained as follows: .

[0094] In the radial gradient design of the artificial vertebral body, the relative density of the inner surface of the device is increased, enhancing the mechanical properties of the center and improving the load-bearing capacity of the artificial vertebral body model. Under the same load conditions, the model's resistance to failure is improved, achieving the goal of enhancing the fatigue performance of the vertebral body.

[0095] 5. A biomimetic porous structure design method combining axial and radial gradients

[0096] To obtain an artificial vertebra that simultaneously satisfies the requirements of stress concentration reduction or avoidance, high specific strength, stress shielding at the bone contact surface, promotion of bone ingrowth, and enhanced fatigue performance, the design incorporates a combination of axial and radial gradients.

[0097] The radial density gradient was designed using the Boltzmann function to maintain a relative density of approximately 20%. Six points with significant changes in relative density within the Boltzmann function were selected, dividing the designed cone into five parts. These five parts were then connected using an activation function. For the Z-axis gradient of each part, a quadratic function was fitted based on the previous Z-axis gradient design method, following the inverse relationship between area and gradient. - :

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] Will - Substituting into (1) yields the relative density functions at the six points of the Boltzmann function. The Sigmoid activation function is used to achieve seamless transitions between models, such as... Figure 8 .

[0105] The formula for the Sigmoid activation function is as follows:

[0106]

[0107]

[0108] Finally, the gradient designs in both directions were integrated into the artificial vertebral body, resulting in a dual-gradient artificial vertebral body model with Z-axis and radial gradients. Combining the advantages of both gradient designs, this yields an artificial vertebral body that exhibits reduced stress concentration, increased specific strength, reduced stress shielding at the bone contact surface, and promoted bone ingrowth in the Z-axis gradient, while also demonstrating enhanced fatigue performance in the radial gradient. Figure 9 .

[0109] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0110] The above embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A method of designing a gradient artificial vertebral body, comprising: determining a desired gradient of the artificial vertebral body; and designing the artificial vertebral body to have a gradient that matches the desired gradient. include: A design method for a biomimetic porous cone model; A design method for reducing stress shielding along the axial gradient; A radial gradient design method to improve the fatigue performance of the vertebral body; A method for integrated manufacturing using metal additive manufacturing; The design method for the biomimetic porous structure specifically includes: Based on real-world applications of artificial vertebral bodies, an artificial vertebral body model was designed, and a Gyroid structure from a three-period minimal surface TPMS lattice structure was selected to establish an artificial vertebral body with a relative density of 20%. Functions are created using a programming language to design porous structures; the modeling process for porous structures involves converting from Cartesian coordinates to polar coordinates to achieve porous structure filling of cylindrical components. In the design of Gyroid lattice structures, algorithms are used to control the relative density and the number of radial elements in the porous structure. The expression for this is: ； It is used to control relative density The parameters, and The functional relationship is: ； These represent the angle, radius, and height in the artificial vertebral model, respectively. It is the number of porous structural units in the model. The function representing the porous structure of Gyroid in polar coordinates; Relative density By mapping values, the density gradient of the porous structure can be established, as shown in the formula. The number of units in the radial direction of the structure can be controlled; The axial gradient design method for the artificial vertebral body specifically includes: To ensure an overall relative density of approximately 20%, the surface area of ​​the artificial vertebral body in the (x,y) plane along the Z-axis is used. relative density and the average area of ​​the (x,y) plane , Lianlide ,get We design a density gradient along the Z-axis, and fit the density along the Z-axis using a quadratic function to obtain the function: ； The relationship between the Z-axis position and the relative density can be obtained through formulas (2) and (3). ； In formula (4) Substituting into (1) will give the required Z-axis gradient; The radial gradient design method for the artificial vertebral body specifically includes: Based on the biomimetic design, a radial gradient is designed to enhance the fatigue performance of the structure. There are two approaches to the design of the radial gradient: one is to control the number of radial elements, and the other is to control the radial density. The design of the number of radial elements can be directly controlled by the value of n in the formula, and then the Sigmoid activation function is used to realize the transition of the model. The design of the radial density gradient adopts the fitting of the Boltzmann function to realize the biomimetic design according to the needs of the patient. The Boltzmann function is used for fitting, and the formula is as follows: ； , , , These are all constants in the Boltzmann fitting function. This represents the radius in the cone model; The Sigmoid activation function is used to achieve the transition between models. The formula for the Sigmoid activation function in Cartesian coordinates is as follows: ； and The axes represent the functions of Gyroid porous structure unit cells with relative densities of 20% and 50% on the coordinate axis. and These represent the starting points of the two structures that are smoothly connected using the Sigmoid activation function; The activation function under multi-segment radial gradient, i.e., in cylindrical coordinates, is: 。 2. A gradient artificial vertebral body, characterized in that, Using the design method described in claim 1, an artificial vertebral body is integrally formed using a selective laser melting process.

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