Design method of 3D printed porous interbody fusion cage

Abstract

The invention discloses a design method of a 3D printed porous interbody fusion cage, and relates to the field of medical instruments. According to the anatomical form of the human body and the operation approach mode, the three-dimensional model appearance design of the interbody fusion cage is completed; performing static analysis on the three-dimensional model in an in-vivo physiological state; performing multi-target topological optimization on the three-dimensional model based on the static analysis result of the three-dimensional model; carrying out entity framework modeling on the interbody fusion cage based on a topological optimization result; obtaining a porous structure of the interbody fusion cage based on the three-dimensional model and the entity framework, and performing Boolean merge operation on the porous structure and the entity framework to obtain a porous interbody fusion cage design scheme; and carrying out comprehensive mechanical property evaluation on the designed and prepared porous interbody fusion cage product. A physiological stress induction topological structure optimization mode is adopted, the research and development difficulty is reduced, the research and development period is shortened, and the product performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to a design method for a 3D-printed porous intervertebral fusion device. Background Art

[0002] Spinal intervertebral fusion surgery is a type of spinal surgery that is often used to treat spinal degenerative diseases, fix fractures, reshape the spine, or increase spinal stability. In this type of surgery, doctors usually first remove all intervertebral discs according to the specific needs of the disease treatment, and then implant intervertebral fusion devices between the intervertebral spaces to maintain the height of the intervertebral space; on this basis, the spinal internal fixation system is used to effectively fix and reconstruct the spinal surgical segment.

[0003] Among them, whether the intervertebral fusion device can provide effective fixation and support will determine whether the operation is successful, and the realization of bone graft fusion between vertebrae will determine the final expected therapeutic effect of the operation. In order to ensure the effectiveness of the intervertebral fusion device product, in the design process of the intervertebral fusion device, the appearance and structure design of the intervertebral fusion device product should match the patient's spinal characteristics as much as possible. The overall strength of the intervertebral fusion device product must meet the mechanical performance requirements of the intervertebral support. At the same time, materials with good modulus matching and biocompatibility should be used to promote the growth and fusion of bone tissue. 3D printing technology can be used to prepare metal porous scaffolds that are conducive to bone growth, and its external morphology and internal structure can be adjusted more finely, which makes 3D printed porous intervertebral fusion devices a future development trend in this direction.

[0004] However, in the current industry, there are very few scientific and systematic design methods for 3D printed intervertebral fusion devices. Most R&D personnel conduct mechanical structural design based on intervertebral fusion devices made by traditional processes through personal experience and habits, and then conduct structural design, optimization and performance confirmation through product mechanical testing. The above method is overly dependent on previous bone implant design experience, lacks scientific theoretical basis, requires high experience from technical R&D personnel, has high R&D uncertainty, long cycle and high cost, and the designed intervertebral fusion devices still have problems such as insufficient mechanical properties or excessive mechanical properties.

[0005] Therefore, the scientific and reasonable design method of 3D printed porous intervertebral fusion cage has become the focus of researchers. At present, there is an urgent need to provide a new design method to design an intervertebral fusion cage with excellent mechanical properties and good biological properties, and to reduce the difficulty of intervertebral fusion research and development and improve research and development efficiency. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a design method for a 3D-printed porous intervertebral fusion device, which makes the product structure design more scientific and reasonable, reduces the difficulty of developing porous intervertebral fusion devices, shortens the development cycle of intervertebral fusion devices, improves the dynamic and static mechanical properties and biological properties of the products, and makes the products more adaptable to various needs of the human body.

[0007] The embodiment of the present invention provides a design method of a 3D printed porous intervertebral fusion cage, which comprises the following steps: Complete the appearance design of the three-dimensional model of the intervertebral fusion cage according to the human anatomy and surgical approach; Performing static analysis on the three-dimensional model under a physiological state of the body; Performing multi-objective topology optimization on the three-dimensional model based on the static analysis results of the three-dimensional model; Modeling of the solid frame of the intervertebral fusion cage based on the results of topology optimization; Obtaining a porous structure of an intervertebral fusion cage based on the three-dimensional model and the solid frame, and performing a Boolean merge operation on the porous structure and the solid frame to obtain a design scheme of a porous intervertebral fusion cage; A comprehensive mechanical properties evaluation was conducted on the designed and manufactured porous intervertebral fusion device product.

[0008] The design method of a 3D-printed porous intervertebral fusion device according to an embodiment of the present invention has at least the following beneficial effects: according to the human anatomical morphology and the surgical approach, the three-dimensional model of the intervertebral fusion device is modeled and designed for its external structure, so that the designed intervertebral fusion device can be adapted to actual clinical use scenarios; based on the three-dimensional model of the intervertebral fusion device, according to the physiological state of the intervertebral fusion device when applied to the patient's body, a static analysis is performed on the three-dimensional model of the intervertebral fusion device, and based on the obtained static analysis results, a multi-objective topological optimization is performed on the three-dimensional model, so that the physical material of the intervertebral fusion device is distributed more reasonably, the structural stress concentration and the stress shielding effect are reduced, and bone growth and bone fusion are better stimulated.

[0009] Since the three-dimensional model of the intervertebral fusion device after multi-objective topology optimization is rough and difficult to manufacture using existing manufacturing processes, it is necessary to remodel the three-dimensional model of the intervertebral fusion device based on the results of the multi-objective topology optimization to obtain a solid frame of the intervertebral fusion device, and reduce the roughness through secondary design to meet manufacturability. Since the porous intervertebral fusion device consists of a solid frame and a porous structure, the porous structure of the intervertebral fusion device can be obtained based on the solid frame and the original three-dimensional model. Finally, a Boolean merge operation is performed on the obtained solid frame and the porous structure to obtain a design scheme for the porous intervertebral fusion device. After the porous intervertebral fusion device product is designed after multi-objective topology optimization, a comprehensive mechanical performance evaluation is performed on it.

[0010] Through the above-mentioned method, a porous intervertebral fusion device product with sufficient mechanical properties, reasonable stress distribution and sufficient overall structural stiffness can be scientifically and rationally designed, which well replaces the empirical design method of previous researchers, effectively reduces the difficulty of research and development, and improves the efficiency of research and development.

[0011] In some embodiments of the present invention, after the appearance design of the three-dimensional model of the intervertebral fusion cage is completed according to the human anatomical morphology and the surgical approach, the following steps are also included: Designing the edge portion of the three-dimensional model into a protective structure with a set thickness; A portion of the three-dimensional model containing the protective structure is set as an exclusion region, and a portion of the three-dimensional model excluding the protective structure is set as an optimization region.

[0012] In some embodiments of the present invention, the performing of static analysis on the three-dimensional model under a physiological state of the body comprises the following steps: A plurality of motion conditions are set, wherein the plurality of motion conditions include a forward bending condition, a backward extension condition, a left bending condition, a right bending condition, a left twisting condition, and a right twisting condition; Setting a load, wherein the load includes gravity and moment; According to each of the motion conditions and the corresponding loads, a static analysis is performed on the three-dimensional model to obtain a stress distribution cloud diagram.

[0013] In some embodiments of the present invention, setting the load comprises the following steps: Under each of the motion conditions, applying a simulated gravity in a vertically downward direction to the upper surface of the three-dimensional model; In each of the motion conditions, a torque having a direction consistent with the direction of the corresponding motion condition is applied to the upper surface of the three-dimensional model.

[0014] In some embodiments of the present invention, performing multi-objective topology optimization on the three-dimensional model based on the static analysis result of the three-dimensional model comprises the following steps: For each of the motion conditions, the optimization objective function is set to maximize flexibility, and the weight ratios of all the motion conditions are set to the same set value; On the premise of satisfying the mechanical and biological properties of orthopedic implants, a set volume fraction is used as a volume constraint, and based on the static analysis results corresponding to all the motion conditions, multi-objective topological optimization is performed on the optimization area.

[0015] In some embodiments of the present invention, after performing multi-objective topological optimization on the three-dimensional model based on the static analysis results of the three-dimensional model, the following step is also included: by adjusting the topological density threshold, material structure distribution screening of the intervertebral fusion device is performed to obtain a final topologically optimized three-dimensional model.

[0016] In some embodiments of the present invention, after adjusting the topological density threshold to screen the material structure distribution of the intervertebral fusion device to obtain the final topologically optimized three-dimensional model, the following step is also included: exporting the final topologically optimized three-dimensional model in STL format.

[0017] In some embodiments of the present invention, obtaining the porous structure of the intervertebral fusion cage based on the three-dimensional model and the solid frame comprises the following steps: performing a Boolean subtraction operation on the three-dimensional model and the solid frame to obtain a porous region of the intervertebral fusion cage; The porous region is filled with a porous unit structure to obtain a porous structure.

[0018] In some embodiments of the present invention, the comprehensive mechanical performance evaluation of the designed and manufactured porous intervertebral fusion cage product comprises the following steps: Conducting finite element analysis of static compression test, shear test and torsion test on the porous intervertebral fusion device product, applying compression, shear and torsion loads to the upper surface of the porous intervertebral fusion device product respectively to obtain stress distribution data; The uniformity of stress distribution of the porous intervertebral fusion device product is evaluated based on the stress distribution data.

[0019] In some embodiments of the present invention, the comprehensive mechanical performance evaluation of the designed and manufactured porous intervertebral fusion cage product further includes the following steps: Conducting actual mechanical performance tests of static compression, shear and torsion as well as fatigue tests of dynamic compression, shear and torsion on the porous intervertebral fusion cage product to obtain mechanical test results; By comparing the mechanical test results with the standard values, the dynamic and static mechanical properties of the porous intervertebral fusion device product are evaluated.

[0020] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of a design method of a 3D printed porous intervertebral fusion cage according to an embodiment of the present invention; Figure 2 is a specific flow chart of step S10 in the method for designing a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention; Figure 3 is a schematic diagram of a specific flow chart of step S20 in the method for designing a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention; Figure 4 is a specific flow chart of step S22 in the method for designing a 3D-printed porous intervertebral fusion cage provided in an embodiment of the present invention; Figure 5 is a schematic diagram of a specific flow chart of step S30 in the method for designing a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention; Figure 6 is a flow chart after step S32 in the design method of a 3D printed porous intervertebral fusion cage provided in an embodiment of the present invention; Figure 7 is a schematic diagram of a specific flow chart of step S50 in the method for designing a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention; Figure 8 is a specific flow chart of step S60 in the method for designing a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention; Fig. 9 is a schematic diagram of a specific flow chart after step S62 in the method for designing a 3D-printed porous intervertebral fusion cage provided in an embodiment of the present invention; Fig.10 is the appearance structure of the three-dimensional model of the intervertebral fusion cage obtained after executing step S10; Fig.11 is a stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under six motion conditions obtained after executing step S20; Fig.12 is a schematic diagram of the multi-objective topology optimization process when executing step S30; Fig.13 is a schematic structural diagram of a physical frame of the intervertebral fusion cage obtained after executing step S30; Fig.14 is a schematic structural diagram of a physical frame of the intervertebral fusion cage obtained after executing step S40; Fig.15 is a schematic structural diagram of a porous intervertebral fusion cage product obtained after executing step S50; Fig.16 It is a stress distribution cloud diagram of the porous intervertebral fusion device product under three test conditions obtained after executing step S60. DETAILED DESCRIPTION

[0022] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0023] In the description of the present invention, it is to be understood that if a feature is defined as "first" or "second", it may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0024] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Reference below Figures 1 to 16 A design method for a 3D-printed porous intervertebral fusion cage according to an embodiment of the present invention is described.

[0026] like Figures 1 to 16 As shown, according to the design method of the 3D printed porous intervertebral fusion device in the embodiment of the present invention, a porous intervertebral fusion device with sufficient product mechanical properties, reasonable stress distribution and appropriate overall structural stiffness can be designed. The porous intervertebral fusion device is a type of orthopedic implant medical device and can be used in spinal intervertebral fusion surgery for the treatment of spinal degenerative diseases to achieve postoperative bone grafting and fusion.

[0027] like Figure 1As shown, the design method of the 3D printed porous intervertebral fusion cage includes the following steps: Step S10: completing the appearance design of the three-dimensional model of the intervertebral fusion cage according to the human anatomical morphology and surgical approach.

[0028] Step S20: Perform static analysis on the three-dimensional model under the physiological state of the body.

[0029] Step S30: performing multi-objective topology optimization on the three-dimensional model based on the static analysis results of the three-dimensional model.

[0030] Step S40: Modeling the solid frame of the intervertebral fusion cage based on the result of topology optimization.

[0031] Step S50: obtaining a porous structure of the intervertebral fusion cage based on the three-dimensional model and the solid frame, and performing a Boolean merge operation on the porous structure and the solid frame to obtain a design scheme of the porous intervertebral fusion cage; Step S60: Conduct a comprehensive mechanical performance evaluation on the porous intervertebral fusion device product that has been designed and manufactured.

[0032] In step S10, since the overall appearance design of the current intervertebral fusion device product mainly depends on the patient's anatomical morphology and surgical approach, the appearance structure of the intervertebral fusion device product must be designed based on these two factors.

[0033] It is understandable that, with the rapid development of spinal surgery technology, the appearance design of existing intervertebral fusion device products has become mature, and the corresponding surgical technology has also been widely recognized. In order to improve the adaptability of intervertebral fusion device products to temporary actual use scenarios, the appearance design of the three-dimensional model of the intervertebral fusion device can follow the existing design scheme. In this embodiment, the appearance structure of the three-dimensional model of the intervertebral fusion device adopts the product specifications and models that are more commonly used in actual clinical practice, such as Fig.10 As shown, the size of the intervertebral fusion cage is 14×16×6 mm. The three-dimensional model of the intervertebral fusion cage can be established using existing three-dimensional modeling software. At this time, the three-dimensional model of the intervertebral fusion cage does not have a solid frame and a porous structure.

[0034] In some embodiments, Figure 2 As shown, after step S10, that is, completing the shape design of the three-dimensional model of the intervertebral fusion cage according to the human anatomical morphology and the surgical approach, the following steps are also included: Step S11: Designing the edge portion of the three-dimensional model into a protective structure with a set thickness.

[0035] Step S12: The portion of the protection structure of the three-dimensional model is set as an exclusion area, and the portion of the three-dimensional model other than the protection structure is set as an optimization area.

[0036] It can be understood that in step S11, if Fig.10 As shown, the performance of the edge portion of the three-dimensional model of the intervertebral fusion device is enhanced, mainly by designing a protective structure with a certain thickness at its edge portion, which is equivalent to thickening the edge portion. The set thickness can be but is not limited to 1mm, so as to ensure that during the process of implanting the intervertebral fusion device product into the patient's body, there will be no structural damage when the edge of the intervertebral fusion device product contacts the human tissue.

[0037] In step S12, Fig.10 As shown, after the design of the protection structure is completed, the protection structure of the three-dimensional model of the intervertebral fusion cage is set as the exclusion area, and the part of the three-dimensional model of the intervertebral fusion cage after removing the protection structure is set as the optimization area, so that in the subsequent multi-objective topology optimization process, only the optimization area is optimized and the exclusion area is avoided. In addition, the middle position of the three-dimensional model of the intervertebral fusion cage has a bone grafting area to establish a bone grafting bin.

[0038] like Figure 3 As shown, step S20, i.e., the step of performing static analysis on the three-dimensional model under the physiological state of the body, specifically includes the following steps: Step S21: setting a plurality of motion conditions, wherein the plurality of motion conditions include a flexion condition, an extension condition, a left-side bending condition, a right-side bending condition, a left-twisting condition and a right-twisting condition.

[0039] Step S22: setting the load, wherein the load includes gravity and torque.

[0040] Among them, Figure 4 As shown, step S22, i.e. the step of setting the load, specifically includes the following steps: Step S221: Under each motion condition, a simulated gravity in a vertically downward direction is applied to the upper surface of the three-dimensional model.

[0041] Step S222: Under each motion condition, a torque having a direction consistent with the direction of the corresponding motion condition is applied to the upper surface of the three-dimensional model.

[0042] Step S23: According to each motion condition and the corresponding load, a static analysis is performed on the three-dimensional model to obtain a stress distribution cloud diagram.

[0043] It is understandable that, considering that the actual stress to which the intervertebral fusion device product is subjected during use mainly depends on the gravity of the human tissue structure and the load on the spinal vertebrae during daily movement, in order to obtain the approximate stress distribution cloud map of the intervertebral fusion device product after implantation in the human body, it is necessary to perform a static analysis of the confirmed three-dimensional model of the intervertebral fusion device under the physiological state of the body. Before starting the static analysis, it is necessary to set the motion conditions and loads. The motion conditions and load sizes can be formulated with reference to the currently widely recognized academic research papers. In this embodiment, the simulated gravity is set to 73.6N and the torque is set to 1.8N·m.

[0044] Among them, multiple motion conditions include flexion, extension, left bending, right bending, left torsion and right torsion. For each motion condition, a static analysis is performed on the three-dimensional model of the intervertebral fusion device. In each motion condition, the load includes gravity and torque. The load loading method is as follows: first, a constant simulated gravity is applied to the upper surface of the three-dimensional model of the intervertebral fusion device, and the direction of the simulated gravity is set vertically downward. According to the type of motion condition, a constant torque is applied to the upper surface of the three-dimensional model of the intervertebral fusion device, and the direction of the torque is consistent with the direction of the motion condition. The values ​​of simulated gravity and torque can be selected according to actual needs.

[0045] In this embodiment, the sources of the force value and the torque value refer to the physiological stress borne by the local bone tissue mentioned in the existing public literature. Gravity is equal in each motion condition, and the magnitude of the torque is equal in each motion condition, but the direction of the torque needs to be set according to the type of motion condition.

[0046] After setting the motion conditions and loads, the three-dimensional model of the intervertebral fusion cage can be subjected to static analysis to obtain the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under various motion conditions, such as Fig.11 As shown. Among them, Fig.11 (a) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under the forward flexion condition. Fig.11 (b) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under the extension condition. Fig.11 (c) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under the left bending condition. Fig.11 (d) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under the right bending condition. Fig.11 (e) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under left torsion condition. Fig.11 (f) shows the stress distribution cloud diagram of the three-dimensional model of the intervertebral fusion cage under right torsion condition.

[0047] like Figure 5As shown, step S30, i.e., the step of performing multi-objective topology optimization on the three-dimensional model based on the static analysis result of the three-dimensional model, specifically includes the following steps: Step S31: For each motion condition, the optimization objective function is set to maximize flexibility, and the weight ratios of all motion conditions are set to the same set value.

[0048] Step S32: On the premise of satisfying the mechanical properties and biological properties of the orthopedic implant, taking the set volume fraction as the volume constraint, and based on the static analysis results corresponding to all the motion conditions, multi-objective topology optimization is performed on the optimization area.

[0049] It is understandable that after completing the static analysis of the three-dimensional model of the intervertebral fusion device under the above six motion conditions, the topological optimization of the overall structure of the three-dimensional model of the intervertebral fusion device can be performed. In the topological optimization process, the functional part of the intervertebral fusion device product (i.e., the supporting function) is used as the exclusion area, and the other parts are used as the optimization area, such as Fig.10 shown.

[0050] In the multi-objective topology optimization process, the optimization objective is to minimize the stiffness (i.e., maximize the flexibility) of the intervertebral fusion cage, and the volume fraction of the intervertebral fusion cage is used as the volume constraint. The specific optimization method refers to the following two multi-objective topology optimization functions, which are Formula 1 and Formula 2, respectively. In Formula 1 and Formula 2, ω is the weight ratio coefficient, n is the number of motion conditions, and ω is j is the weight ratio coefficient of the jth motion condition, C j is the total structural stiffness of the jth motion condition; Formula 1: ;Formula 2: ; By setting the optimization objective function to maximize flexibility, that is, minimize stiffness, the stress shielding effect of the intervertebral fusion device is reduced. In this embodiment, the set volume fraction is set to 15%, which is based on the result of repeated optimization of the cervical intervertebral fusion device product. For intervertebral fusion devices used in other parts, the set volume fraction is not necessarily 15%. The set volume fraction can be set according to actual conditions. Under the premise of satisfying sufficient mechanical and biological properties of orthopedic implants, using a lower volume fraction as a volume constraint can ensure that the structure of the intervertebral fusion device has sufficient structural morphology and achieves good mechanical properties. At the same time, it provides enough porous areas to facilitate the proliferation and adhesion of bone cells.

[0051] After completing step S20, i.e., performing a static analysis on the three-dimensional model under the physiological state of the body, a multi-objective topological optimization is performed on the three-dimensional model of the intervertebral fusion cage based on the static analysis results under six motion conditions of flexion, extension, left bending, right bending, left torsion and right torsion. Fig.12 As shown, the weight ratio coefficient ω has the same value in each motion condition.

[0052] It can be understood that topology optimization is a method of structural optimization based on stress demand relationship. It mainly uses a mathematical method that can optimize the material distribution in a specified area according to given load conditions, constraints and performance indicators, so as to maximize the utilization of materials. Specifically, it means that by discretizing the area into enough sub-areas, using finite element analysis technology to perform strength analysis or modal analysis on the structure, a certain number of units are deleted from these sub-areas according to the specified optimization strategy and criteria, and the retained units are used to describe the optimal topology of the structure.

[0053] The use of topological optimization methods for the structural design of intervertebral fusion device products can not only distribute materials more reasonably and reduce the structural stress concentration of intervertebral fusion device products, but also reduce the stress shielding effect of intervertebral fusion device products, thereby better stimulating bone growth and promoting bone fusion.

[0054] like Figure 6 As shown, after step S30, that is, the step of performing multi-objective topology optimization on the three-dimensional model based on the static analysis result of the three-dimensional model, the following steps are also included: Step S33: By adjusting the topological density threshold, the material structure distribution of the intervertebral fusion cage is screened to obtain a final topologically optimized three-dimensional model.

[0055] Step S34: Export the final topology optimized three-dimensional model in STL format.

[0056] It is understandable that after the topology optimization process is completed, the topology density threshold can be adjusted to select the material of the intervertebral fusion cage. Among them, the material closer to 1 has a greater contribution to the mechanical properties of the structure, and the material closer to 0 has almost no role in bearing the load. In this embodiment, the topology density threshold is set to 0.6. After the topology optimization is completed, a relatively rough solid frame of the intervertebral fusion cage will be obtained, such as Fig.13 and export it in STL format.

[0057] The topological density threshold is the density value used to determine whether a unit is retained during the structural topology optimization process. During the topology optimization process, units with a unit density lower than a certain topological density threshold will be considered invalid and are usually ignored or deleted during the topology optimization process, while units with a density higher than the topological density threshold will be retained. The main function of the topological density threshold is to control the manufacturability and structural performance of the optimization results. By setting a reasonable topological density threshold, it can be ensured that the optimized structure has good manufacturability while meeting the design requirements.

[0058] In step S40, i.e., the step of modeling the solid frame of the intervertebral fusion device based on the results of topology optimization, since the derived model of the solid frame of the intervertebral fusion device is relatively rough and has problems that are difficult to manufacture, such as holes and overlapping triangular faces, it is necessary to remodel it according to the results of multi-objective topology optimization to obtain a solid frame of the intervertebral fusion device with low roughness, such as Fig.14 shown.

[0059] In the process of modeling, the model logic of the multi-objective topology optimization results must be strictly followed. The location of the main load structure cannot be changed, that is, the starting point and end point of the structural stress remain unchanged, while the size and shape can be appropriately changed within a reasonable range. After remodeling, the solid frame of the intervertebral fusion cage becomes fine and smooth, with good manufacturability.

[0060] like Figure 7 As shown, step S50, i.e., the step of obtaining the porous structure of the intervertebral fusion cage based on the three-dimensional model and the solid frame, specifically includes the following steps: Step S51: performing a Boolean subtraction operation on the three-dimensional model and the solid frame to obtain the porous area of ​​the intervertebral fusion cage.

[0061] Step S52: filling the porous area with porous unit structures to obtain a porous structure.

[0062] It can be understood that in step S50, i.e., obtaining the porous structure of the intervertebral fusion device based on the three-dimensional model and the solid frame, and performing a Boolean merge operation on the porous structure and the solid frame to obtain the design scheme of the porous intervertebral fusion device, since the structure of the porous intervertebral fusion device is mainly composed of two parts, the solid frame and the porous structure, the solid frame is the main stress structure of the porous intervertebral fusion device, which is responsible for bearing most of the load after implantation in the body, and the porous structure provides sufficient space for bone cells to proliferate, adhere and differentiate.

[0063] The solid frame is obtained by multi-objective topological optimization of the three-dimensional model of the intervertebral fusion device, and the porous region is obtained by subtracting the three-dimensional model of the intervertebral fusion device from the solid frame. After obtaining the porous region, the porous unit structure with good spatial morphology, mechanical properties and biological functions is filled into the porous region obtained after subtraction, thereby obtaining a model of the porous structure of the porous intervertebral fusion device. It is understandable that the porous unit structure belongs to the prior art and is well known to those skilled in the art, and will not be described in detail here.

[0064] Then, the obtained solid frame and porous structure are processed by Boolean merging, and finally the porous intervertebral fusion cage product after multi-objective topology optimization is designed, such as Fig.15 The model of the porous intervertebral fusion cage product can be exported, for example, in STL format or other formats, and manufactured by existing 3D printing technology.

[0065] like Figure 8 As shown, step S60, i.e., the step of conducting a comprehensive mechanical performance evaluation on the porous intervertebral fusion cage product that has been designed and manufactured, specifically includes the following steps: Step S61: performing finite element analysis of static compression test, shear test and torsion test on the porous intervertebral fusion cage product, applying compression, shear and torsion loads to the upper surface of the porous intervertebral fusion cage product respectively to obtain stress distribution data.

[0066] Step S62: Evaluate the uniformity of stress distribution of the porous intervertebral fusion device product according to the stress distribution data.

[0067] It is understandable that after completing the structural design of the porous intervertebral fusion device product, it is necessary to evaluate its actual mechanical properties. Specifically, the obtained porous intervertebral fusion device product is subjected to static compression, shear and torsion finite element analysis, and the corresponding stress distribution data, such as stress distribution cloud map, are obtained under the three loads of compression, shear and torsion. The goal of the finite element analysis is to determine that the peak surface stress of the porous intervertebral fusion device after multi-objective topology optimization processing decreases, and the stress distribution is more uniform.

[0068] like Fig.16 As shown in the figure, by comparing the finite element simulation results before and after the multi-objective topology optimization, it is found that the porous intervertebral fusion cage processed by the multi-objective topology optimization has the following advantages: the stress peak on the surface is reduced and the stress distribution is more uniform.

[0069] Further, such as Fig. 9 As shown, step S60, i.e., the step of conducting a comprehensive mechanical performance evaluation on the porous intervertebral fusion cage product that has been designed and manufactured, further includes the following steps: Step S63: Performing actual mechanical property tests of static compression, shear and torsion and fatigue tests of dynamic compression, shear and torsion on the porous intervertebral fusion cage product to obtain mechanical test results.

[0070] Step S64: Evaluate the dynamic and static mechanical properties of the porous intervertebral fusion device product by comparing the mechanical test results with the standard values.

[0071] After completing step S61 and step S62, the actual mechanical properties test of the porous intervertebral fusion device product can be carried out. The standard value can be set according to the acceptable standard of mechanical properties of intervertebral fusion devices in ISO23089, and is not specifically limited here. According to the requirements of the mechanical test plan for intervertebral fusion devices specified in YY / T0959-2014 Test Method for Mechanical Properties of Spinal Implant Intervertebral Fusion Devices, the porous intervertebral fusion device products after multi-objective topology optimization are subjected to static compression, shear and torsion performance tests as well as dynamic compression, shear and torsion fatigue tests. After the above-mentioned test inspections, it was found that the obtained mechanical test results reached three times the acceptable standard of mechanical properties of intervertebral fusion devices in ISO23089, confirming that the porous intervertebral fusion device product has excellent mechanical properties and can meet the needs of implantation.

[0072] The design method of the 3D printed porous intervertebral fusion device provided by the embodiment of the present invention takes the topological optimization technology under physiological stress induction as the core design concept to design the structural scheme of the 3D printed porous intervertebral fusion device. Specifically, the embodiment of the present invention takes the external morphology of the commonly used intervertebral fusion device as the basis, takes the stress environment of the intervertebral fusion device in the human body as the core, and takes finite element statics analysis and topological optimization design as the approach to develop a set of overall structural design methods for porous intervertebral fusion device products suitable for 3D printing.

[0073] Among them, the specific method is to conduct multi-objective topological optimization design on the 3D printed porous intervertebral fusion device with volume fraction as constraints, physiological motion conditions as loads, and minimum stiffness (maximum flexibility) of the sample as the optimization goal, so as to design the overall structure of the porous intervertebral fusion device product with sufficient product mechanical properties, reasonable stress distribution, and appropriate overall structural stiffness.

[0074] Moreover, the above-mentioned design method based on physiological stress analysis as the principle and topological structure optimization as the method to complete the structural design of the 3D printed porous intervertebral fusion device can replace the empirical design method of previous researchers, effectively avoid the structural design failure of the porous intervertebral fusion device product caused by the lack of experience of the R&D personnel, and make the design method of the porous intervertebral fusion device more scientific, effective and reasonable. In addition, it can reduce the difficulty of R&D of the porous intervertebral fusion device product, shorten the R&D cycle of the porous intervertebral fusion device product, improve R&D efficiency, reduce R&D costs, and at the same time, improve the dynamic and static mechanical properties and biological properties of the product, so that the product is more suitable for various needs of the human body.

[0075] It is understandable that in the process of topological structure optimization, physiological stress is used as the load condition, and multi-objective topological optimization under full motion conditions is used as the method to fully consider the comprehensive stress requirements of the porous intervertebral fusion device product after implantation, and in the final performance evaluation of the porous intervertebral fusion device product, compression, shear and torsion performance tests are combined to prove that the porous intervertebral fusion device product has good dynamic and static mechanical properties, and achieves the balance of mechanical properties of the porous intervertebral fusion device product, thereby ensuring that the porous intervertebral fusion device product has high safety under fatigue stress conditions after implantation.

[0076] In addition, in the process of topological structure optimization, physiological stress is used as the load condition and minimum stiffness is used as the optimization goal, which can fully meet the mechanical stress requirements of the porous intervertebral fusion device product and reduce the overall stiffness of the porous intervertebral fusion device product as much as possible, reduce the stress shielding of the porous intervertebral fusion device product after implantation, make the internal stress distribution of the porous intervertebral fusion device product more uniform, promote the growth of internal and external bone tissue of the porous intervertebral fusion device product, and thus ensure that the vertebrae have good bone grafting and fusion effects in the mid- and long-term after surgery.

[0077] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0078] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A design method for a 3D printed porous intervertebral fusion cage, characterized in that: The steps include: Complete the appearance design of the three-dimensional model of the intervertebral fusion cage according to the human anatomy and surgical approach; Performing static analysis on the three-dimensional model under a physiological state of the body; Performing multi-objective topology optimization on the three-dimensional model based on the static analysis results of the three-dimensional model; Modeling of the solid frame of the intervertebral fusion cage based on the results of topology optimization; Obtaining a porous structure of an intervertebral fusion cage based on the three-dimensional model and the solid frame, and performing a Boolean merge operation on the porous structure and the solid frame to obtain a design scheme of a porous intervertebral fusion cage; A comprehensive mechanical properties evaluation was conducted on the designed and manufactured porous intervertebral fusion device product.

2. The design method of the 3D printed porous intervertebral fusion cage according to claim 1, characterized in that: After the appearance design of the three-dimensional model of the intervertebral fusion cage is completed according to the human anatomical morphology and the surgical approach, the following steps are also included: Designing the edge portion of the three-dimensional model into a protective structure with a set thickness; A portion of the three-dimensional model containing the protective structure is set as an exclusion region, and a portion of the three-dimensional model excluding the protective structure is set as an optimization region.

3. The design method of a 3D printed porous intervertebral fusion cage according to claim 2, characterized in that: The static analysis of the three-dimensional model under the physiological state of the body comprises the following steps: A plurality of motion conditions are set, wherein the plurality of motion conditions include a forward bending condition, a backward extension condition, a left bending condition, a right bending condition, a left twisting condition, and a right twisting condition; Setting a load, wherein the load includes gravity and moment; According to each of the motion conditions and the corresponding loads, a static analysis is performed on the three-dimensional model to obtain a stress distribution cloud diagram.

4. The design method of the 3D printed porous intervertebral fusion cage according to claim 3, characterized in that: The load setting includes the following steps: Under each of the motion conditions, applying a simulated gravity in a vertically downward direction to the upper surface of the three-dimensional model; In each of the motion conditions, a torque having a direction consistent with the direction of the corresponding motion condition is applied to the upper surface of the three-dimensional model.

5. The method for designing a 3D printed porous intervertebral fusion cage according to claim 3 or 4, characterized in that: The performing multi-objective topology optimization on the three-dimensional model based on the static analysis result of the three-dimensional model comprises the following steps: For each of the motion conditions, the optimization objective function is set to maximize flexibility, and the weight ratios of all the motion conditions are set to the same set value; On the premise of satisfying the mechanical and biological properties of orthopedic implants, a set volume fraction is used as a volume constraint, and based on the static analysis results corresponding to all the motion conditions, multi-objective topological optimization is performed on the optimization area.

6. The design method of the 3D printed porous intervertebral fusion cage according to claim 5, characterized in that: After the three-dimensional model is subjected to multi-objective topological optimization based on the static analysis result of the three-dimensional model, the following step is also included: by adjusting the topological density threshold, the material structure distribution of the intervertebral fusion cage is screened to obtain a final topologically optimized three-dimensional model.

7. The design method of a 3D printed porous intervertebral fusion cage according to claim 6, characterized in that: After the material structure distribution screening of the intervertebral fusion cage is performed by adjusting the topological density threshold to obtain the final topologically optimized three-dimensional model, the following step is also included: exporting the final topologically optimized three-dimensional model in STL format.

8. The design method of a 3D printed porous intervertebral fusion cage according to claim 1, characterized in that: The method of obtaining the porous structure of the intervertebral fusion cage based on the three-dimensional model and the solid frame comprises the following steps: performing a Boolean subtraction operation on the three-dimensional model and the solid frame to obtain a porous region of the intervertebral fusion cage; The porous region is filled with a porous unit structure to obtain a porous structure.

9. The method for designing a 3D printed porous intervertebral fusion cage according to claim 1, characterized in that: The comprehensive mechanical performance evaluation of the designed and manufactured porous intervertebral fusion device product includes the following steps: Conducting finite element analysis of static compression test, shear test and torsion test on the porous intervertebral fusion device product, applying compression, shear and torsion loads to the upper surface of the porous intervertebral fusion device product respectively to obtain stress distribution data; The uniformity of stress distribution of the porous intervertebral fusion device product is evaluated based on the stress distribution data.

10. The design method of the 3D printed porous intervertebral fusion cage according to claim 9, characterized in that: The comprehensive mechanical performance evaluation of the designed and manufactured porous intervertebral fusion device product also includes the following steps: Conducting actual mechanical performance tests of static compression, shear and torsion as well as fatigue tests of dynamic compression, shear and torsion on the porous intervertebral fusion cage product to obtain mechanical test results; By comparing the mechanical test results with the standard values, the dynamic and static mechanical properties of the porous intervertebral fusion device product are evaluated.

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