Micro-scale bone tissue damage simulation and verification method

Abstract

The present application belongs to the cross field of bone tissue mechanical property testing and numerical simulation, and discloses a mesoscale bone tissue damage simulation simulation and verification method. By obtaining the required bone material elastic modulus and critical fracture energy parameters, the original multi-stage axial compression CT test obtains the scanning data of the structural change of the bone material at different stages and carries out reverse three-dimensional reconstruction, and based on the initial data three-dimensional reconstruction data without loading force, finite element simulation simulation is carried out, and the original CT compression mode loading multi-stage axial force is simulated. The difference between the finite element simulation results and the axial cross-section pore proportion and crack propagation volume of the real original CT compression test sample is compared, and the experimental dynamic observation and numerical simulation precise coupling verification of the mesoscale structure damage process of bone tissue are realized. The method realizes the experimental dynamic observation and numerical simulation precise coupling verification of the mesoscale structure (micron level) damage process of bone tissue, and provides technical support for bone disease mechanism analysis and bone repair material research and development.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of bone tissue mechanical property testing and numerical simulation, specifically involving a method for simulating and verifying microscale bone tissue damage based on in-situ CT compression testing. Background Technology

[0002] Bone tissue is a typical multi-scale biological composite material, and its microscale (micrometer-level) structural damage (such as porosity evolution and crack initiation / propagation) directly determines its macroscopic mechanical properties and failure modes. In-depth analysis of microscale damage mechanisms is of core significance for the diagnosis of bone metabolic diseases (such as osteoporosis) and the design of bone implant materials. However, current technologies have significant shortcomings in the experimental observation, simulation modeling, and coupled verification of microscale damage. 1. Limitations of experimental observation Current bone injury experiments mostly employ a "macro-loading + post-operative CT scan" approach, which has two major drawbacks: The dynamic process is missing: it is impossible to capture the real-time damage of the microstructure during loading (such as pore expansion and crack initiation during the loading stage), and only the static results after loading can be observed, resulting in the loss of the temporal-spatial continuity of damage evolution. Insufficient precision in detail: Even with in situ CT loading, it is often difficult to quantitatively record the damage evolution pattern at the micrometer scale due to "single-stage loading design" (failure to simulate the multi-stage characteristics of physiological load) and "coarse image segmentation" (failure to accurately distinguish bone tissue / pores).

[0003] 2. Limitations of numerical simulation Finite element simulation relies on mesoscopic geometric models and accurate material parameters, but existing methods have key shortcomings: Coarse material parameter assignment: Traditional methods obtain elastic modulus and fracture energy through macroscopic mechanical tests (such as tensile and compression tests), ignoring the mechanical heterogeneity of the microscopic regions of bone tissue (such as the degree of mineralization and differences in fiber arrangement); although nanoindentation technology can measure microscopic mechanical parameters, it has not been effectively integrated into the damage simulation model (such as the assignment of fracture parameters of Cohesive units), resulting in a significant deviation between the constitutive relation and the real bone tissue. Geometric model distortion: The simulation model often uses simplified geometry (such as regular pores and homogeneous bone matrix) and does not reverse reconstruct based on the real microstructure of in situ CT (such as irregular pores and bone trabecular morphology), which further amplifies the difference between simulation and reality.

[0004] 3. Missing dimension in simulation-experimental verification Existing verification focuses only on "macroscopic mechanical indicators" (such as load-displacement curves and stress distribution), but: the essence of bone tissue damage is the deterioration of microstructure (such as increased porosity and crack volume propagation), and macroscopic indicators cannot reflect the true nature of microscopic damage mechanisms; The lack of direct comparison of microscale damage characteristics (such as the proportion of axial and transverse pores and crack propagation volume) makes it impossible to effectively verify the microscale damage prediction capability of the simulation model.

[0005] In summary, current technologies have not yet established a complete technical chain encompassing "acquisition of microscopic parameters → in-situ dynamic damage observation → simulation of realistic microscopic models → verification of microscopic damage indicators," which limits the accuracy of research on the microscopic damage mechanism of bone tissue. Therefore, there is an urgent need to invent a method that integrates nanoindentation testing, in-situ multi-stage CT loading, microscopic three-dimensional reconstruction, finite element simulation, and microscopic indicator verification to achieve precise coupling between experiment and simulation of the microscopic damage process of bone tissue. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one deficiency of the prior art and to provide a method for simulating and verifying microscale bone tissue damage based on in-situ CT compression testing.

[0007] The technical solution adopted in this invention is: A method for simulating or verifying microscale bone tissue damage based on in-situ CT compression testing includes the following steps: Obtain bone materials of the required size and shape for the experiment as needed; Obtain the required elastic modulus and critical fracture energy parameters of the bone material; In situ multi-stage axial compression CT test: The bone material is fixed in the X-ray in situ CT tester. The target compressive load is applied to the bone material using a multi-stage axial loading method. After each loading, the load is maintained and the CT scan of that stage is completed. The DICOM format data of each scan from no loading force to the last compressive load is exported. Reverse 3D reconstruction based on scanning data from each stage; Finite element simulation was performed on the three-dimensional reconstructed data based on the initial data without loading force to simulate multi-stage axial force loading in in-situ CT compression mode. By comparing the axial cross-sectional pore ratio and crack propagation volume of the finite element simulation results with those of the real in-situ CT compression test samples, the experimental dynamic observation and numerical simulation of the bone tissue microstructural damage process are accurately coupled and verified.

[0008] In some instances, reverse 3D reconstruction specifically involves importing scanned data into Avizo visualization data analysis software, using software segmentation algorithms to segment bone tissue and bone pore images, and then performing reverse 3D reconstruction.

[0009] In some instances, a nanoindentation tester was used to test bone materials. At least five representative areas were selected on the surface of the bone sample to obtain the required material elastic modulus and critical fracture energy parameters.

[0010] In some instances, the fracture energy and the critical normal and tangential fracture energy parameters can be calculated by using the integral method based on the microscale load-displacement curves of different sites in bone materials obtained from nanoindentation testing.

[0011] In some instances, the elastic modulus is obtained by using the Oliver-Pharr method, fitting the indentation load-displacement curve, calculating the elastic modulus of each region, and statistically analyzing the mesoscopic mean and dispersion.

[0012] In some instances, the critical fracture energy was determined by monitoring the initiation of microcracks around the indentation using a continuous stiffness mode, and by deriving the mesoscale fracture energy threshold using the energy balance equation.

[0013] In some instances, the bone material includes cartilage, cancellous bone, and compact bone. This allows for a more comprehensive understanding. In some instances, Abagus software is used for finite element simulation to construct cohesive damage elements and assign fracture parameters based on the critical fracture energy parameters obtained.

[0014] In some instances, the bone material required for the experiment was 100–1000 μm in size.

[0015] In some instances, the bone material required for the experiment was polished to a surface roughness of ≤1μm.

[0016] In some instances, during in-situ multi-stage axial compression CT testing, a "graded loading → load holding → CT scan" mode was adopted, with a load holding period of ≥30s after each loading stage to eliminate the effects of viscoelastic relaxation.

[0017] The beneficial effects of this invention are: The method of this invention can achieve precise coupling and verification of experimental dynamic observation and numerical simulation of bone tissue microstructural (micrometer level) damage process, providing technical support for the analysis of bone disease mechanisms and the development of bone repair materials. Attached Figure Description

[0018] Figure 1 This is an analysis flowchart of some examples of the present invention.

[0019] Figure 2 This is a schematic diagram of femoral head bone material extraction.

[0020] Figure 3 These are photographs of bone material samples used in experiments.

[0021] Figure 4 It is a nanoindentation measurement.

[0022] Figure 5 These are load-displacement curves at different microscale sites in bone materials, based on nanoindentation testing.

[0023] Figure 6 It is the in-situ compression stage and the CT scan imaging process.

[0024] Figure 7 It is a simulation and in-situ observation of bone material tissue damage and destruction at a fine scale.

[0025] Figure 8 It is an axial (Z-axis) comparison showing the ratio of the cross-sectional pores of bone material between the simulation model and the in-situ CT-compressed bone material. Detailed Implementation

[0026] The technical solution of the present invention will be further illustrated below with examples.

[0027] The main process of the method of the present invention is as follows: Figure 1 As shown. The specific operation of the microscale bone tissue damage simulation or verification method based on in-situ CT compression testing is as follows: 1. Preparation of micron-sized bone materials To ensure sample compatibility with the in-situ CT testing platform, target bone tissue (cortical bone / cancellous bone / cartilage) was selected and precision-machined into elongated cylindrical specimens measuring 1.5cm x 1.6cm x 1cm using diamond precision cutting. After machining, the specimen surface was treated with a grinding and polishing process (roughness ≤ 1μm) to eliminate interference from initial defects on damage observation.

[0028] 2. Obtaining micromechanical parameters through nanoindentation testing Using a nanoindentation tester (Bruker Hysitron PI 89), ≥5 representative areas (covering heterogeneous areas such as bone matrix and mineralization interface) were selected on the surface of the bone sample, and key parameters were obtained through the following tests: Elastic modulus: The Oliver-Pharr method was used to fit the indentation load-displacement curve, calculate the elastic modulus of each region, and statistically analyze the mesoscopic mean and dispersion. Critical fracture energy: The initiation of microcracks around the indentation is monitored by continuous stiffness (CSM) mode, and the fracture energy threshold at the mesoscale is derived by combining the energy balance equation (for assigning parameters to the finite element Cohesive element).

[0029] 3. In-situ multi-stage axial compression CT test Sample clamping: Fix the bone sample on the mechanical loading fixture of the X-ray in situ CT testing instrument (ZEISS Xradia 610) to ensure axial alignment accuracy ≤0.05mm and avoid off-center loading; Loading and scanning strategy: Adopting a "tiered loading → load preservation → CT scan" mode. Loading gradient: 4 levels, 0-3 levels (0→50→100→400N, covering physiological load to injury stage), simulating the dynamic injury process of bone tissue; Hold time: Hold for ≥30s after each loading stage to eliminate the effect of viscoelastic relaxation; CT scan: After each load level, a high-resolution scan (resolution 1-10 micrometers) is performed to cover the entire cross section of the sample, and DICOM format tomographic images are exported to record the temporal characteristics of damage (pore expansion, crack initiation location).

[0030] 4. Reverse 3D Reconstruction of Microstructure Import multi-stage CT data into Avizo software and execute: Image segmentation: Adaptive threshold segmentation combined with manual correction is used to distinguish between bone tissue (high-density area) and bone pores (low-density area), and scanning noise is eliminated through Gaussian filtering and morphological opening operation; 3D Reconstruction: Voxel-level 3D reconstruction is performed on the segmented tomographic images to generate a multi-stage (corresponding to each loading level) dynamic model of bone tissue and pores, preserving the true morphology of the microstructure (such as irregular pores and trabecular topology).

[0031] 5. Finite element simulation modeling of microscopic damage Model import and mesh generation: Import the initial state (unloaded) 3D reconstruction model into Abaqus and construct a mesoscopic finite element mesh (element size ≤ 5μm, matching CT resolution). Damage element and parameter assignment: Cohesive damage elements are pre-set at the bone-pore interface and within the bone matrix (to simulate crack initiation / propagation); The elastic properties of the cohesive unit (based on nanoindentation elastic modulus) and the fracture parameters (based on critical fracture energy, with damage evolution defined by energy release rate) are directly related to experimental data. Loading simulation: Reproduce the multi-stage axial loading path of in-situ CT (with load and holding time perfectly matched experiment), simulate the microscopic damage process, and output numerical results of pore evolution and crack propagation.

[0032] 6. Verification of the coupling of microscopic damage indicators At the same loading stage and cross-sectional location, the microscopic damage characteristics of the simulation results were compared with those of the in-situ CT experimental data: Axial transverse porosity ratio: In statistical simulation and experiment, the area / volume ratio of bone pores in the axial transverse section is used to quantify the deviation of pore expansion. Crack propagation volume: The volume and spatial distribution differences between simulated cracks and experimentally observed cracks are compared using the Avizo crack tracking module.

[0033] If the deviation exceeds the threshold (e.g., porosity deviation > 5%, crack volume deviation > 10%), the simulation parameters (e.g., Cohesive fracture energy) are inverted and corrected until the two reach a consensus on the microscopic damage characteristics, thus forming an experimental-simulation closed-loop verification.

[0034] Taking the femoral head as an example, samples are extracted from bone material specimens of the femoral head, and bone materials from different regions and structures are selected as samples to achieve a more comprehensive analysis, such as... Figure 2 As shown, the femoral head is longitudinally sectioned. Figure 2 The areas marked 2-5 are the bone tissue sampling areas. Bone material samples for experiments are taken from these areas. Figure 3 As shown.

[0035] A nanoindentation tester was used to test bone materials to obtain the required elastic modulus and critical fracture energy parameters. For example... Figure 4 As shown, bone samples were fixed on the testing platform, and the trabecular bone region was located under a microscope (microscopic view) for testing. The microscopic load-displacement curves of the bone material at different sites are shown below. Figure 5 As shown, the fracture energy can be derived and the critical fracture energy parameters in the normal and tangential directions can be calculated using the integral method.

[0036] Bone material is fixed to an in-situ X-ray CT scanner. A multi-stage axial loading method is used to apply the target compressive load to the bone material. After each loading, the load is maintained, and a CT scan for that stage is completed. DICOM format data for each scan from no loading force to the final compressive load is exported. Exemplary stages include... Figure 6 As shown.

[0037] Based on initial unloaded data and 3D reconstructed data, finite element simulation was performed using Abagus software. Cohesive damage elements were constructed, and fracture parameters were assigned using critical fracture energy parameters obtained from the baseline. The simulation simulated multi-stage axial force loading under in-situ CT compression. The micro-scale simulation and in-situ observation of bone tissue damage were also performed. Figure 7 As shown in the figure. a, b, and c represent the three stages of damage and failure; Figure A shows the simulated process of bone material damage and failure based on finite element analysis; Figure B shows the actual process of bone material damage and failure observed by in-situ CT reconstruction. Axial (Z-axis) comparison shows the cross-sectional area ratio of the simulated model and the bone material compressed by in-situ CT. Figure 8 As shown in the figure, the solid colored line represents the actual damage result from in-situ CT, the solid black line represents the simulation result, and the dashed line represents the bone material result in the initial stage (without load).

[0038] The experimental results show that the method of the present invention can achieve precise coupling and verification of experimental dynamic observation and numerical simulation of bone tissue microstructural (micrometer level) damage process, providing technical support for the analysis of bone disease mechanisms and the development of bone repair materials.

[0039] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for simulating or verifying microscale bone tissue damage based on in-situ CT compression testing, characterized in that, Includes the following steps: Obtain bone materials of the required size and shape for the experiment as needed; Obtain the required elastic modulus and critical fracture energy parameters of the bone material; In situ multi-stage axial compression CT test: The bone material is fixed in the X-ray in situ CT tester. The target compressive load is applied to the bone material using a multi-stage axial loading method. After each loading, the load is maintained and the CT scan of that stage is completed. The DICOM format data of each scan from no loading force to the last compressive load is exported. Reverse 3D reconstruction based on scanning data from each stage; Finite element simulation was performed on the three-dimensional reconstructed data based on the initial data without loading force to simulate multi-stage axial force loading in in-situ CT compression mode. By comparing the axial cross-sectional pore ratio and crack propagation volume of the finite element simulation results with those of the real in-situ CT compression test samples, the experimental dynamic observation and numerical simulation of the bone tissue microstructural damage process are accurately coupled and verified.

2. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, Reverse 3D reconstruction specifically involves importing scanned data into Avizo visualization data analysis software, using software segmentation algorithms to segment bone tissue and bone pore images, and then performing reverse 3D reconstruction.

3. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, The bone material was tested using a nanoindentation tester. At least 5 representative areas were selected on the surface of the bone sample to obtain the required elastic modulus and critical fracture energy parameters.

4. The mesoscale bone tissue injury simulation or validation method of claim 3, wherein, Based on the load-displacement curves at different microscale sites of bone material obtained by nanoindentation testing, the fracture energy can be derived using the integral method, and the critical fracture energy parameters in the normal and tangential directions can be calculated.

5. The mesoscale bone tissue injury simulation or validation method of claim 3, wherein, The elastic modulus was obtained by fitting the indentation load-displacement curve using the Oliver-Pharr method, calculating the elastic modulus of each region, and statistically analyzing the mesoscopic mean and dispersion. The critical fracture energy is obtained by monitoring the initiation of microcracks around the indentation using a continuous stiffness mode, and by deriving the mesoscale fracture energy threshold using the energy balance equation.

6. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, The bone material includes cartilage, cancellous bone, and compact bone.

7. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, Finite element simulation was performed using Abagus software to construct Cohesive damage elements and assign fracture parameters based on the critical fracture energy parameters obtained.

8. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, The bone material required for the experiment was 100–1000 μm in size.

9. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, The bone material required for the experiment was polished to a surface roughness of ≤1μm.

10. The mesoscale bone tissue injury simulation or validation method of claim 1, wherein, During in-situ multi-stage axial compression CT testing, a "graded loading → load holding → CT scan" mode was adopted, with a load holding period of ≥30s after each loading stage to eliminate the effects of viscoelastic relaxation.

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