A method of designing and manufacturing a custom artificial intervertebral disc prosthesis

Abstract

This invention discloses a method for designing and fabricating a personalized artificial intervertebral disc prosthesis, belonging to the field of artificial intervertebral disc prosthesis technology. The invention aims to solve the problems of poor mechanical adaptability, lack of biomimetic structure, and design-manufacturing disconnect in existing prostheses. The steps include: S1, collecting kinematic and dynamic data of the lumbar spine under healthy conditions to obtain the torque-rotation curve of the target vertebral segment; S2, establishing and validating a finite element model based on MRI / CT, ​​with motion deviation within 5%; S3, constructing a biomimetic intervertebral disc including a biomimetic nucleus pulposus, transition zone, annulus fibrosus, and endplate, wherein the number, diameter, stiffness gradient, and arrangement of biomimetic fibers are adjustable; S4, establishing a quadratic regression equation with the target curve as the optimization target to obtain optimal parameters with a matching degree ≥90%; S5, using multi-material additive manufacturing for integrated molding. This invention achieves individualized stiffness matching and biomimetic structure reproduction, improves fatigue and shear resistance, and is suitable for personalized customization of the lumbar spine.

Description

Technical Field

[0001] This invention belongs to the field of artificial intervertebral disc prosthesis technology, specifically relating to a method for designing and preparing a personalized artificial intervertebral disc prosthesis. Background Technology

[0002] Chronic low back pain is one of the most disabling musculoskeletal diseases worldwide, with lumbar disc degeneration being the primary cause, particularly prevalent in the L4-L5 segment. For advanced disc degeneration unresponsive to conservative treatment, the mainstream surgical procedures include lumbar fusion and total disc replacement. However, fusion sacrifices range of motion in the operated segment, easily leading to compensatory increases in adjacent segments and accelerated degeneration. While existing artificial disc prostheses preserve some degree of mobility, they have long faced core bottlenecks such as insufficient biomechanical adaptation.

[0003] Existing commercially available artificial intervertebral discs (such as mechanical arthroscopic prostheses like Charité, ProDisc-L, and Activ-L, as well as hydrogel-based viscoelastic integrated prostheses) share the following common design problems: First, there is a lack of personalized stiffness matching based on the physiological kinematic data of the target individual. Current prostheses adopt a "homogeneous" design, and their range of motion and stiffness curves are set based on the statistical mean of the population, which cannot reflect the three-dimensional anisotropic motion characteristics of a specific patient in a healthy state (such as different torque-rotation responses under flexion / extension, lateral bending, and axial rotation). Clinical studies have shown that the intervertebral disc stiffness difference between individuals can be more than 30%. After implantation of universal prostheses, excessive restriction or abnormal increase in range of motion often occurs, leading to abnormal facet joint stress, prosthesis subsidence, or even revision surgery.

[0004] Second, the simplification of the structure makes it difficult to replicate the gradient stiffness and fiber arrangement of the natural intervertebral disc. The natural human lumbar intervertebral disc consists of the nucleus pulposus (viscoelastic core), transition zone, annulus fibrosus (containing 10-20 layers of matrix layer containing collagen fibers, with the fibers arranged in an X-shape and the stiffness decreasing from the inside to the outside), and endplate. Existing prostheses either use a single metal / polyethylene sliding surface (ignoring the constraint mechanism of the annulus fibrosus) or a homogeneous hydrogel (lacking a layered anisotropic structure), neither of which can simulate the nonlinear mechanical response of the annulus fibrosus under combined compression-shear loads. In particular, they lack the ability to independently control key parameters such as fiber quantity, fiber diameter, stiffness gradient, and X-shaped / woven spatial arrangement, causing the biomechanical behavior of the prosthesis under axial rotation and lateral bending conditions to deviate significantly from that of the natural intervertebral disc.

[0005] Third, the design, verification, and manufacturing processes are disconnected, lacking a closed-loop optimization process; the development of existing prostheses often relies on trial and error based on experience, failing to establish a complete chain methodology encompassing "target individual kinematic data—finite element model verification—bionic parametric design—multivariate regression optimization—additive manufacturing"; specifically manifested in: 1) Few studies have used inverse multibody dynamics to obtain the load-displacement / torque-rotation curves of the target vertebral segment under multiple working conditions such as flexion, extension, lateral bending, and rotation as the gold standard for prosthesis design.

[0006] 2) The construction of finite element models often ignores the nonlinear tensile properties of ligaments and the fine layered structure of the annulus fibrosus, and lacks a model calibration process based on individual medical images and measured kinematic data.

[0007] 3) There is a lack of experimental establishment of regression equations between design variables such as biomimetic fiber arrangement, hardness gradient, and fiber diameter and six-degree-of-freedom motion angles, thus making it impossible to achieve a personalized optimal parameter combination with a high degree of motion matching.

[0008] 4) The manufacturing process mostly uses traditional machining or single-material casting, which cannot achieve spatial differentiation of multiple materials and stiffnesses, thus failing to meet the requirements of biomimetic design.

[0009] In summary, current technologies have not yet disclosed a systematic approach that starts with multi-source physiological kinematics and dynamics data collected from a healthy target individual, extracts anisotropic target motion curves through inverse multibody dynamics, constructs a refined finite element model using individual medical images and validated by kinematics, then introduces a biomimetic intervertebral disc structure including a biomimetic nucleus pulposus, transition zone, multi-layer matrix layers, and adjustable parameters (fiber quantity, diameter, stiffness gradient, X-type / woven arrangement), obtains the optimal combination of matching parameters through multivariate orthogonal experiments and regression equations, and finally uses multi-material additive manufacturing for integrated molding. Therefore, there is an urgent need for a method for designing and fabricating artificial intervertebral disc prostheses that can achieve personalization, high biomimicry, verifiability, and optimization, to solve the technical problems of poor mechanical adaptability, lack of biomimetic structure, and disconnect between design and manufacturing in existing prostheses. Summary of the Invention

[0010] The purpose of this invention is to provide a method for designing and fabricating a personalized artificial intervertebral disc prosthesis, aiming to overcome the shortcomings of existing total disc replacement prostheses in terms of mechanical adaptability, structural biomimicry, and long-term dynamic stability. The artificial intervertebral disc prosthesis prepared using this invention possesses excellent cushioning and shock absorption properties and dynamic fatigue resistance, can highly match the anisotropic range of motion of the target individual's diseased spinal segment under physiological movement states such as flexion, extension, lateral bending, and axial rotation, and has excellent compressive and shear mechanical properties.

[0011] A method for designing and fabricating a personalized artificial intervertebral disc prosthesis includes the following steps: Step S1: Acquisition of multi-source physiological data and acquisition of target three-dimensional motion characteristics: The kinematic and dynamic data of the lumbar spine of the target object are obtained. This data can be collected when the target object is healthy or when there is a slight intervertebral disc lesion, ensuring the health status and accuracy of the collected data. Based on the data, combined with the inverse multibody dynamics method, the load-displacement curve or torque-rotation curve of the target vertebral segment (such as the L4-L5 segment in the human lumbar spine, which is most prone to lesions) under physiological motion states such as flexion, extension, lateral bending and axial rotation is obtained. This is used as the target three-dimensional motion data for the design and preparation of personalized artificial intervertebral disc prostheses.

[0012] Step S2: Reverse engineering design and finite element model establishment and verification: Collect MRI or CT medical image information of the target object in step S1, obtain a three-dimensional model of the target vertebral segment (such as the L4-L5 segment including L4 vertebra, L5 vertebra, L4-L5 intervertebral disc) through reverse engineering technology, and establish the finite element model of the target vertebral segment through finite element analysis software (such as Hypermesh and Abaqus). The finite element model includes vertebrae, intervertebral discs, anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, supraspinous ligament, interspinous ligament, ligamentum flavum, and joint capsule ligaments. The intervertebral disc comprises the annulus fibrosus, nucleus pulposus, transition zone, and endplate. The annulus fibrosus contains a matrix layer and collagen fibers, with at least four matrix layers. Preprocessing was performed using software such as Hypermesh. The completed lumbar spine model components were imported into Abaqus simulation software in *inp format, and the material properties and interactions of each component were set. Considering the biomechanical properties of ligaments, the materials of the seven ligament tissues were... The properties are set to withstand only tensile force, and finally the finite element models of the target lumbar vertebral segments are integrated together. The torque of the target vertebral segment load obtained in step S1 is applied to the established finite element model of the target lumbar vertebral segment to obtain the corresponding motion angle. At the same time, the torque-rotation curve of the target vertebral segment obtained in step S1 is compared to verify the effectiveness of the finite element model. The motion angle deviation is controlled within 5%. If the required deviation is not achieved, the corresponding material properties in the finite element model can be adjusted to meet the standard. Since each material property has a certain range and varies from person to person, there will be deviations in the material properties.

[0013] Step S3: Parametric design of biomimetic structures and integration of finite element models: Geometric features of the target intervertebral disc (such as the L4-L5 segment of the lumbar spine, which is most prone to protrusion or disease) are extracted from MRI or CT medical images of the target object; a bionic intervertebral disc is constructed, including a bionic nucleus pulposus, a bionic transition zone, a bionic annulus fibrosus, and a bionic endplate; the overall contour features of the bionic nucleus pulposus conform to the overall shape of the lumbar intervertebral disc, the bionic transition zone is tightly attached to the bionic nucleus pulposus and the bionic annulus fibrosus in a ring, and the bionic annulus fibrosus includes a bionic matrix layer and bionic fibers, and the bionic fibers have all of the following characteristics: The biomimetic fibers exhibit a gradient of stiffness, mimicking the decreasing stiffness of a natural intervertebral disc from the outside in. The fibers are arranged in an X-shape or woven pattern in space. The diameter of the biomimetic fibers is adjustable between 0.1 mm and 2 mm. The number of biomimetic fibers is adjustable between 10 and 200. Different biomimetic matrix layers use the same soft matrix material, such as Agilus30 FLX935. The biomimetic fibers and the biomimetic matrix layer form a biomimetic ring layer. Because the biomimetic fibers have a stiffness gradient from hard to soft from the outside in, the biomimetic ring layer also has a stiffness gradient from hard to soft from the outside in, conforming to the biological structural characteristics of a natural intervertebral disc. The biomimetic endplate fits tightly against the contact surfaces of the upper and lower vertebrae. The constructed biomimetic artificial intervertebral disc model is integrated into the vertebral segment finite element model established and verified in step S2, and the original intervertebral disc model is removed.

[0014] Step S4: Personalized Matching and Optimization Using the three-dimensional anisotropic stiffness characteristics represented by the target moment-rotation curve obtained in step S1 as the optimization objective, and the biomimetic fiber arrangement, stiffness gradient, and fiber diameter in step S3 as experimental factors, a quadratic multiple regression equation for flexion, extension, left-side bending, right-side bending, left-axis rotation, and right-axis rotation is established through a multivariate orthogonal experiment. The confidence level of the regression equation is 99%, and the relative root mean square error is used as the matching degree calculation method. The formula is as follows: ; Among them, X i Y represents the angle values ​​of the biomimetic intervertebral disc model under different loads. i The angle values ​​corresponding to the target torque-rotation curves under different loads are given, where N is the number of angle values. The optimal combination of parameters that achieves the best matching degree for flexion, extension, lateral bending, and rotational motion is obtained with a matching degree of over 90% as the convergence condition.

[0015] Step S5: Preparation and Verification Based on the personalized optimal combination parameters determined in step S4, a bionic intervertebral disc prosthesis is fabricated in an integrated manner using a multi-material additive manufacturing method. By adjusting the combination of printing materials in different regions, the stiffness of the bionic intervertebral disc prosthesis is differentiated at different spatial locations.

[0016] In step S1: the kinematic data is acquired using the Vicon optical 3D motion capture system, which consists of 6 high-precision infrared capture cameras with a sampling frequency of 100Hz, and can accurately record the three-dimensional spatial motion trajectory of the subject during routine physiological activities; the dynamic data is acquired using the Kistler 3D force measurement system, the experimental platform consists of three force plates with a specification of 200mm×400mm, and each force plate has a high-precision piezoelectric sensor array integrated at its four corners, which can simultaneously acquire the three-component data (Fx, Fy, Fz) of the plantar contact force in a spatial rectangular coordinate system and the data information of the stress torque; during the experiment, while acquiring the subject's kinematic parameters, plantar dynamic data is acquired simultaneously; the load-displacement curve or torque-rotation curve is calculated using Opensim software, and musculoskeletal system mechanical simulation analysis is carried out for specific subjects. Considering the differences between the individual anatomical characteristics of the subjects and the standard whole-body lumbar spine model, a multi-level optimization strategy is used to personalize the model. First, the model mass parameters were adjusted according to the actual weight of the subjects. Then, based on the marker point data collected by the motion capture system, the spatial point group matching method was used to optimize the model's posture. To ensure the three-dimensional spatial correction effect, the optimized point groups of each anatomical segment were designed with non-coplanar distribution.

[0017] In step S2: the finite element simulation model is constructed based on medical images of the L4-L5 segment using reverse engineering technology and Abaqus software; the CT scanner scanning parameters for acquiring medical images are set as follows: tube voltage 120kV, tube current 300mA, scanning slice thickness 0.75mm, and image matrix 512×512; during the scanning process, the subject remains supine to ensure that the L4-L5 lumbar vertebrae are completely contained within the scanning field of view.

[0018] The quadratic multiple regression equation in step S4 is: y = a + bz1 + cz2 + dz1 2 +ez2 2 +fz1z2+⋯ Where y is the motion angle of flexion, extension, left bend, right bend, left axial rotation or right axial rotation, and z1, z2, ... are biomimetic fiber variable parameters. Each coefficient is obtained by fitting through multivariate orthogonal experiments. It can effectively adjust the stiffness matching degree of flexion, extension, left and right lateral bending and left and right axial rotation by changing parameters such as fiber hardness gradient, diameter and arrangement.

[0019] The multi-material additive manufacturing method in step S5 is as follows: using a variety of 3D printing methods, such as the J850 3D printer based on ultraviolet curing technology, which is widely used in the medical and other fields. Its outstanding material combination capability enables it to print multiple resin materials at the same time, so that the prepared physical sample can simulate the material characteristics of the soft and hard combination of the human lumbar intervertebral disc. By adjusting the printing material combination in different areas, the stiffness of the bionic intervertebral disc prosthesis can be differentiated in different spatial positions.

[0020] The beneficial effects of this invention are as follows: Compared with existing total disc replacement prostheses and their design and fabrication methods, the present invention has the following advantages: 1. Achieving precise matching of anisotropic stiffness based on individual physiological kinematic data, significantly improving postoperative motor function recovery; This invention collects lumbar spine kinematic and dynamic data of the target subject in a healthy state, and combines it with inverse multibody dynamics to obtain load-displacement curves or torque-rotation curves of the target vertebral segment under multiple conditions such as flexion-extension, lateral bending, and axial rotation. This personalized curve is used as the gold standard for the design of artificial intervertebral disc prostheses. Further verification using finite element models controls the deviation between the simulated motion angle and the target curve to within 5%, ensuring that the constructed bionic intervertebral disc is highly matched to the patient's own three-dimensional anisotropic motion characteristics before implantation. Compared with existing general prostheses based on population mean, this invention can avoid abnormal facet joint stress, prosthesis instability, or limited movement caused by excessive or insufficient postoperative mobility, thereby restoring more natural spinal segmental motor function.

[0021] 2. Constructing a highly biomimetic, multi-parameter adjustable intervertebral disc structure to realistically replicate the gradient stiffness and anisotropic constraint mechanism of the natural annulus fibrosus. Existing prostheses mostly use simplified sliding surfaces or homogeneous materials, which cannot simulate the complex mechanical behavior of the natural annulus fibrosus. This invention constructs a complete biomimetic intervertebral disc comprising a biomimetic nucleus pulposus, a biomimetic transition zone, a biomimetic annulus fibrosus (multi-layer matrix layer + biomimetic fibers), and a biomimetic endplate. The biomimetic fibers have characteristics such as hardness gradient, adjustable diameter (0.1-2mm), adjustable number (10-200 fibers), and adjustable arrangement (X-type or woven type). This multi-parameter adjustable structure can independently control the nonlinear response of the prosthesis under different loads such as compression, shear, and torsion, effectively simulating the decrease in stiffness from the outer periphery to the inner side of the natural annulus fibrosus and the limiting effect of cross fibers on axial rotation. This solves the problems of insufficient mechanical strength and easy fatigue fracture of existing viscoelastic integrated prostheses, while overcoming the lack of cushioning and shock absorption of mechanical joint prostheses.

[0022] 3. A closed-loop system of "design-verification-optimization-manufacturing" is established, and the matching quantification is achieved through multivariate orthogonal experiments and regression equations. This invention uses the obtained target anisotropic stiffness characteristics as the optimization objective, and biomimetic fiber arrangement, stiffness gradient, and fiber diameter as experimental factors. Through multivariate orthogonal experiments, quadratic multivariate regression equations are established for six motion directions: flexion, extension, left lateral bending, right lateral bending, left axial rotation, and right axial rotation, with a confidence level of 99%. Using relative root mean square error as the matching degree calculation method, the stiffness characteristics of the prepared biomimetic intervertebral disc prosthesis match the target curve by more than 90% in the six motion directions. This quantitative standard far exceeds the empirical verification of existing technologies, providing an objective and reproducible basis for preclinical evaluation of the prosthesis, and significantly reducing the risk of revision surgery due to insufficient matching degree.

[0023] 4. Employing multi-material additive manufacturing for integrated molding enables spatially differentiated stiffness distribution, enhancing fatigue and shear resistance. The integrated molding process eliminates weak areas at the interface, strengthening the prosthesis's fatigue and fracture resistance under long-term compression-shear combined loads and extending its lifespan. Refined finite element modeling and verification based on individual medical images improves design reliability and provides a reliable virtual testing platform for subsequent bionic intervertebral disc design and optimization, significantly reducing the number of physical prototype trials and shortening the development cycle.

[0024] 5. It fully covers the entire chain of "data acquisition - model verification - biomimetic design - parameter optimization - additive manufacturing", forming an industrializable technical solution. Starting from the acquisition of multi-source physiological data, through reverse engineering design and finite element verification, biomimetic structural parameterization integration, personalized matching and optimization, to multi-material additive manufacturing, it forms a systematic, standardized, and reproducible personalized customization process. This method is not only applicable to the L4-L5 segment, but can also be extended to other segments of the lumbar spine and even the customization of artificial intervertebral discs for the cervical and thoracic spine, with broad prospects for clinical translation.

[0025] In summary, this invention solves the technical challenges of existing full-disc prostheses in terms of personalized mechanical adaptation, precise biomimetic structure reproduction, quantitative design optimization, and integrated manufacturing by organically combining the above-mentioned technical features. It has produced significant beneficial effects such as improving matching accuracy, enhancing fatigue and shear resistance, reducing revision rate, and achieving personalized intelligent customization. Attached Figure Description

[0026] Figure 1 A flowchart illustrating the steps involved in the design and fabrication of personalized artificial intervertebral disc prostheses. Figure 2 A schematic diagram of the load-displacement curve or moment-rotation curve for the target vertebral segment; Figure 3A schematic diagram of a three-dimensional model of the target vertebral segment; Figure 4 This is a schematic diagram of the structure of the L4-L5 intervertebral disc; Figure 5 This is a schematic diagram of the structure of a biomimetic intervertebral disc; Figure 6 This is a schematic diagram of a force measuring plate.

[0027] Wherein: 1—L4 vertebra; 2—L4-L5 intervertebral disc; 3—L5 vertebra; 4—annulus fibrosus; 5—transition zone; 6—nucleus pulposus; 7—endplate; 8—bionic nucleus pulposus; 9—bionic transition zone; 10—bionic annulus fibrosus; 11—bionic endplate; 12—bionic matrix layer; 13—bionic fiber. Detailed Implementation

[0028] like Figure 1 As shown, a method for designing and fabricating a personalized artificial intervertebral disc prosthesis includes the following steps: Step S1: Acquisition of multi-source physiological data and acquisition of target three-dimensional motion characteristics: Acquire lumbar spine kinematic and dynamic data of the target subject. This data can be collected in a healthy state or with mild intervertebral disc lesions to ensure the health and accuracy of the collected data. Based on this data, combine inverse multibody dynamics methods, such as... Figure 2 As shown, load-displacement curves or torque-rotation curves of the target vertebral L4-L5 segment under physiological motion states such as flexion, extension, lateral bending and axial rotation are obtained, which are used as the target three-dimensional motion data for the design and preparation of personalized artificial intervertebral disc prostheses. Step S2: Reverse engineering design and finite element model establishment and verification: Acquire MRI or CT medical image information of the target object in step S1, such as Figure 3 As shown, a three-dimensional model of the target vertebral segment L4-L5 (including L4 vertebra 1, L5 vertebra 3, and L4-L5 intervertebral disc 2) was obtained through reverse engineering. A finite element model of the L4-L5 segment was then established using finite element analysis software (such as Hypermesh and Abaqus). The finite element model includes the L4 vertebra, L5 vertebra, L4-L5 intervertebral disc, anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, supraspinous ligament, interspinous ligament, ligamentum flavum, and joint capsule ligaments. Figure 4As shown, the L4-L5 intervertebral disc comprises annulus fibrosus 4, nucleus pulposus 6, transition zone 5, and endplate 7; the annulus fibrosus 4 comprises a matrix layer and collagen fibers; the number of matrix layers is greater than or equal to 4; preprocessing is performed using software such as Hypermesh, and the completed lumbar spine model components are imported into Abaqus simulation software in *inp format, and the material properties and interactions of each component are set. Considering the biomechanical characteristics of ligaments, the material properties of the seven groups of ligament tissues are set to withstand only tensile forces. Finally, the finite element models of the L4-L5 lumbar spine segments are integrated together, and the torque of the target vertebral segment load obtained in step S1 is applied to the established finite element model of the L4-L5 lumbar spine segments to obtain the corresponding motion angle; at the same time, it is compared with the values ​​obtained in step S1 as shown in the figure. Figure 2 The torque-rotation curves of the target vertebral segment are compared to verify the effectiveness of the finite element model. The deviation of the motion angle is controlled within 5%. If the required deviation is not achieved, the corresponding material properties in the finite element model can be adjusted to meet the standard. Since each material property has a certain range and varies from person to person, there will be deviations in the material properties.

[0029] Step S3: Parametric design of biomimetic structures and integration of finite element models: Extracting geometric features of the target L4-L5 intervertebral disc from MRI or CT medical images of the target object; such as Figure 5 As shown, a bionic intervertebral disc is constructed comprising a bionic nucleus pulposus 8, a bionic transition zone 9, a bionic annulus fibrosus 10, and a bionic endplate 11. The overall contour of the bionic nucleus pulposus 8 conforms to the overall shape of the lumbar intervertebral disc. The bionic transition zone 9 is tightly attached to the bionic nucleus pulposus 8 and the bionic annulus fibrosus 10 in a ring. The bionic annulus fibrosus 10 comprises a bionic matrix layer 12 and bionic fibers 13, and the bionic fibers 13 have all of the following characteristics: The biomimetic fiber 13 exhibits a gradient of stiffness, mimicking the decrease in stiffness of a natural intervertebral disc from the outside to the inside. The biomimetic fiber 13 is arranged in an X-shape or woven pattern in space; The diameter of the biomimetic fiber 13 is adjustable between 0.1 mm and 2 mm; the number of biomimetic fibers 13 is adjustable between 10 and 200. Different biomimetic matrix layers 12 use the same soft matrix material, such as Agilus30 FLX935 material; biomimetic fibers 13 and biomimetic matrix layers 12 form a biomimetic ring layer. Since the hardness gradient of biomimetic fibers 13 changes from hard to soft from the outside to the inside, the hardness gradient of the biomimetic ring layer changes from hard to soft from the outside to the inside, which conforms to the biological structural characteristics of natural intervertebral discs; biomimetic endplates 11 are in close contact with the upper and lower vertebral bone contact surfaces; the constructed biomimetic artificial intervertebral disc model is integrated into the vertebral segment finite element model established and verified in step S2, and the original intervertebral disc model is removed.

[0030] Step S4: Personalized Matching and Optimization Using the three-dimensional anisotropic stiffness characteristics represented by the target moment-rotation curve obtained in step S1 as the optimization objective, and the arrangement of biomimetic fiber 13, stiffness gradient, and fiber diameter in step S3 as experimental factors, a quadratic multiple regression equation for flexion, extension, left-side bending, right-side bending, left-axis rotation, and right-axis rotation was established through a multivariate orthogonal experiment. The confidence level of the regression equation was 99%. The relative root mean square error was used as the matching degree calculation method, and the formula is as follows:

[0031] Among them, X i Y represents the angle values ​​of the biomimetic intervertebral disc model under different loads. i The angle values ​​corresponding to the target torque-rotation curves under different loads are given, where N is the number of angle values. With a matching degree of over 90% as the convergence condition, the personalized optimal combination parameters that achieve the best matching degree for flexion-extension, lateral bending, and rotational movements are obtained. A matching degree of over 90% makes the stress distribution of the artificial intervertebral disc more uniform, thereby significantly improving its fatigue life.

[0032] Step S5: Preparation and Verification Based on the personalized optimal combination parameters determined in step S4, a bionic intervertebral disc prosthesis is fabricated in an integrated manner using a multi-material additive manufacturing method. By adjusting the combination of printing materials in different regions, the stiffness of the bionic intervertebral disc prosthesis is differentiated at different spatial locations.

[0033] In step S1: the kinematic data is acquired using the Vicon optical 3D motion capture system, which consists of 6 high-precision infrared capture cameras with a sampling frequency set to 100Hz, and can accurately record the three-dimensional spatial motion trajectory of the subject during routine physiological activities; for example... Figure 6 As shown, the dynamic data was acquired using a Kistler 3D force measurement system. The experimental platform consisted of three 200mm × 400mm force plates, each with a high-precision piezoelectric sensor array integrated at each of its four corners. This allowed for the simultaneous acquisition of the three components (Fx, Fy, Fz) of the plantar contact force in a Cartesian coordinate system, as well as data on the stress torque. During the experiment, plantar dynamic data was acquired simultaneously with the acquisition of the subject's kinematic parameters. The load-displacement curve or torque-rotation curve was calculated using Opensim software, and mechanical simulation analysis of the musculoskeletal system was performed for specific subjects. Considering the differences between the individual anatomical characteristics of the subjects and the standard whole-body lumbar spine model, a multi-level optimization strategy was adopted to personalize the model. First, the model's mass parameters were adjusted according to the subject's actual weight. Then, based on the marker point data acquired by the motion capture system, a spatial point group matching method was used to optimize the model's posture. To ensure the effectiveness of the 3D spatial correction, the optimization point groups for each anatomical segment were designed with a non-coplanar distribution.

[0034] In step S2: the finite element simulation model is constructed based on medical images of the L4-L5 segment using reverse engineering technology and Abaqus software; the CT scanner scanning parameters for acquiring medical images are set as follows: tube voltage 120kV, tube current 300mA, scanning slice thickness 0.75mm, and image matrix 512×512; during the scanning process, the subject remains supine to ensure that the L4-L5 lumbar vertebrae are completely contained within the scanning field of view.

[0035] The quadratic multiple regression equation in step S4 is: y = a + bz1 + cz2 + dz1 2 +ez2 2 +fz1z2+⋯ Where y is the motion angle of flexion, extension, left bend, right bend, left axial rotation or right axial rotation, and z1, z2, ... are biomimetic fiber variable parameters. The coefficients are obtained by fitting through multivariate orthogonal experiments. It can effectively adjust the stiffness matching degree of flexion, extension, left and right lateral bending and left and right axial rotation by changing parameters such as fiber hardness gradient, diameter and arrangement.

[0036] The multi-material additive manufacturing method in step S5 is as follows: using a multi-material 3D printing method, such as the J850 3D printer based on ultraviolet curing technology, which is widely used in the medical and other fields; its outstanding material combination capability enables it to print multiple resin materials at the same time, so that the prepared physical sample can simulate the material characteristics of the soft and hard combination of the human lumbar intervertebral disc; by adjusting the printing material combination in different regions, the stiffness of the bionic intervertebral disc prosthesis is differentiated in different spatial positions.

Claims

1. A method for designing and fabricating a personalized artificial intervertebral disc prosthesis, characterized in that, Includes the following steps: Step S1: Acquisition of multi-source physiological data and acquisition of target three-dimensional motion characteristics: The kinematic and dynamic data of the lumbar spine of the target object are obtained. The data is collected when the target object is healthy or when there is a slight intervertebral disc lesion. Based on the data, combined with the inverse multibody dynamics method, the torque-rotation curve of the target vertebral segment under the physiological motion states of flexion, extension, lateral bending and axial rotation is obtained. This is used as the target three-dimensional motion data of the personalized artificial intervertebral disc prosthesis. Step S2: Reverse engineering design and finite element model establishment and verification: In step S1, MRI or CT medical image information of the target object is acquired, and a three-dimensional model of the target vertebral segment is obtained through reverse engineering. A finite element model of the target vertebral segment is established using finite element analysis software. The finite element model includes vertebrae, intervertebral discs, anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, supraspinous ligament, interspinous ligament, ligamentum flavum, and joint capsule ligaments. The intervertebral disc includes the annulus fibrosus, nucleus pulposus, transition zone, and endplate. The annulus fibrosus includes a matrix layer and collagen fibers, and the number of matrix layers is greater than or equal to 4. After processing the model components using preprocessing software, the model is imported into the finite element simulation software. The material properties and interactions of each component are set, and the material properties of the ligament tissue are set to withstand only tensile forces. Based on the torque of the target vertebral segment obtained in step S1, the load is applied to the established finite element model to obtain the corresponding motion angle. The motion angle is then compared with the target torque-rotation curve obtained in step S1 to verify the effectiveness of the finite element model. The motion angle deviation is controlled within 5%. Step S3: Parametric design of biomimetic structures and integration of finite element models: Geometric features of the target intervertebral disc are extracted from MRI or CT medical images of the target object; a bionic intervertebral disc is constructed, including a bionic nucleus pulposus, a bionic transition zone, a bionic annulus fibrosus, and a bionic endplate; the overall contour features of the bionic nucleus pulposus conform to the overall shape of the lumbar intervertebral disc; the bionic transition zone is tightly attached to the bionic nucleus pulposus and the bionic annulus fibrosus; the bionic annulus fibrosus includes a bionic matrix layer and bionic fibers, and the bionic fibers have all of the following characteristics: the bionic fibers exhibit a gradient of stiffness, simulating the decrease in stiffness from the outside to the inside of the natural intervertebral disc; the bionic fibers are arranged in an X-shape or woven pattern in space; the diameter of the bionic fibers is adjustable between 0.1 mm and 2 mm; the number of bionic fibers is adjustable between 10 and 200; the bionic endplate is tightly attached to the contact surfaces of the upper and lower vertebrae; the constructed bionic artificial intervertebral disc model is integrated into the vertebral segment finite element model established and verified in step S2, and the original intervertebral disc model is removed; Step S4: Personalized Matching and Optimization Using the three-dimensional anisotropic stiffness characteristics represented by the target moment-rotation curve obtained in step S1 as the optimization target, and the biomimetic fiber arrangement, stiffness gradient, and fiber diameter in step S3 as experimental factors, a quadratic multiple regression equation for flexion, extension, left-side bending, right-side bending, left-axis rotation, and right-axis rotation is established through a multivariate orthogonal experiment. The confidence level of the regression equation is 99%. The relative root mean square error is used as the matching degree calculation method, and the formula is: ； Among them, X i Y represents the angle values ​​of the biomimetic intervertebral disc model under different loads. i The angle values ​​corresponding to the target torque-rotation curves under different loads are given, where N is the number of angle values. The optimal combination of parameters that achieves the best matching degree for flexion, extension, lateral bending, and rotational motion is obtained with a matching degree of over 90% as the convergence condition. Step S5: Preparation and Verification Based on the personalized optimal combination parameters determined in step S4, a bionic intervertebral disc prosthesis is fabricated in an integrated manner using a multi-material additive manufacturing method. By adjusting the combination of printing materials in different regions, the stiffness of the bionic intervertebral disc prosthesis is differentiated at different spatial locations.

2. The method for designing and fabricating a personalized artificial intervertebral disc prosthesis according to claim 1, characterized in that: In step S1: the kinematic data is acquired using the Vicon optical 3D motion capture system; the dynamic data is acquired using the Kistler 3D force measurement system; and the torque-rotation curve is calculated using Opensim software.

3. The method for designing and fabricating a personalized artificial intervertebral disc prosthesis according to claim 1, characterized in that: In step S2: the finite element model is constructed based on medical images of the L4-L5 segment using reverse engineering methods and Hypermesh or Abaqus software.

4. The method for designing and fabricating a personalized artificial intervertebral disc prosthesis according to claim 1, characterized in that, The quadratic multiple regression equation in step S4 is: y=a+bz1+cz2+dz1 2 +ez2 2 +fz1z2+⋯ Where y is the motion angle of flexion, extension, left bend, right bend, left-axis rotation or right-axis rotation, and z1, z2, ... are biomimetic fiber variable parameters, and each coefficient is obtained by fitting through multivariate orthogonal experiments.

5. The method for designing and fabricating a personalized artificial intervertebral disc prosthesis according to claim 1, characterized in that: The multi-material additive manufacturing method in step S5 uses a UV curing 3D printer to print multiple resin materials simultaneously, and achieves a differentiated stiffness distribution by adjusting the material combination in different regions.

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