A method for preparing a high-mechanical matching degree restoration body based on topology optimization

Abstract

The application discloses a preparation method of a high-mechanical-matching-degree prosthesis based on topological optimization, which comprises the following steps: reconstructing a bone defect model by scanning CT data of a target region, and performing smoothing treatment on the model; constructing a prosthesis contour; determining a prosthesis porosity distribution through topological optimization, and obtaining regions with different density ranges of the prosthesis; replacing the regions with different density ranges in step 3 with random microporous structures with different pore diameters and porosities according to required biological properties and mechanical properties, so as to obtain a prosthesis model matched with a mechanical environment of a defect; and printing a prosthesis embryo, and performing a defatting and sintering process to obtain the prosthesis. The application realizes the best distribution of micropores in the prosthesis through topological optimization, and designs the random microporous structures with natural transition according to the topological optimization result, so that the stress distribution of the prosthesis is more uniform, and the mechanical and biological requirements of the prosthesis in bone repair are met.

Description

Technical Field

[0001] This invention relates to a method for preparing a high mechanical compatibility prosthesis based on topology optimization, belonging to the field of biomedical engineering technology. Background Technology

[0002] Bioactive prostheses such as calcium phosphate ceramics and magnesium phosphate possess excellent biocompatibility and osteoinductive properties, while their porous structure endows them with good osteoconductive properties. Therefore, porous bioactive prostheses are widely used in clinical bone defect repair. However, the micropore distribution of traditional porous bioactive prostheses is difficult to control or is often unreasonable, resulting in generally poor mechanical properties and a high risk of fracture. Consequently, they cannot adequately meet the mechanical and aesthetic requirements of bone repair, limiting their clinical application.

[0003] Porous structures play a crucial role in the performance of bioactive materials, significantly influencing their mechanical properties. Current design methods often uniformly distribute micropores throughout the restoration. However, this distribution is not entirely optimal. After implantation, the restoration is not uniformly stressed; some areas bear a greater load than others. A uniform micropore distribution leads to higher stress in these areas and minimal stress in other areas, failing to utilize their load-bearing capacity. Reducing micropores in areas of higher stress concentration and increasing them in areas of lower stress can achieve a more uniform stress distribution without changing the overall porosity. Topology optimization is a method that optimizes material distribution given load conditions, boundary conditions, and target parameters. It can achieve various objectives by changing the relative density of different regions of the material. Since the trends of material mechanical properties with porosity and relative density are somewhat similar, porosity can be considered as a substitute for relative density.

[0004] However, assigning different porosities to different regions also brings new challenges, namely, how to connect and transition between these regions. Directly connecting regions with different porosities may lead to cracking of the restoration due to differences in shrinkage rates. Therefore, designing a microporous structure with a natural transition has become an urgent problem to be solved.

[0005] How to fabricate the designed porous restorations is also a problem that needs to be solved. Traditional fabrication methods, such as foaming, are difficult to precisely control the porous structure during the fabrication process, thus limiting its accuracy and performance. 3D printing technology, also known as additive manufacturing technology, has been widely used in the fabrication of various personalized materials in recent years. It has a strong ability to control the geometry of materials, which can meet the fabrication needs of complex structural restorations, and has a significant advantage in the fabrication of porous bioactive restorations.

[0006] Therefore, this invention, based on topology optimization, achieves the optimal distribution of micropores within the prosthesis. By combining computer programming and using porosity instead of relative density, a non-uniformly distributed random pore structure with mechanical compatibility is constructed. This results in a highly osteoinductive prosthesis with excellent biological and mechanical properties. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention aims to provide a method for preparing a high mechanical compatibility prosthesis based on topology optimization. This invention achieves the optimal distribution of micropores inside the prosthesis through topology optimization. Based on the topology optimization results, a random micropore structure with natural transitions is designed in the prosthesis to make the stress distribution of the prosthesis more uniform, so as to meet the mechanical and biological requirements of multiple prostheses in bone repair.

[0008] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for preparing a high mechanical matching degree restoration based on topology optimization, comprising:

[0009] Step 1: Reconstruct the bone defect model using CT scan data of the target area, and smooth the model.

[0010] Step 2: Construct the outline of the restoration using the mirror method;

[0011] Step 3: Determine the micropore distribution inside the restoration through topology optimization to obtain regions of the restoration with different density ranges;

[0012] Step 4: According to the required biological and mechanical properties, replace the regions with different density ranges in Step 3 with fully connected random microporous structures with different pore sizes and porosities to obtain a prosthesis model that matches the mechanical environment of the defect.

[0013] Step 5: Print the preform of the restoration and perform degreasing and sintering processes to obtain the restoration.

[0014] Preferably, the specific process of step 2 is as follows: import the bone defect model into the 3D modeling software, then select a mirror plane, which should be as close as possible to the midsagittal plane; create a mirror image of the defective skull based on the mirror plane, adjust the relative position of the mirror image and the original model to make them coincide, and then use Boolean difference set to obtain the prosthesis model. Trim the edges of the prosthesis to remove burrs in order to facilitate subsequent porosification.

[0015] Preferably, the specific process of step 3 is as follows: import the prosthesis model and the bone defect model into the finite element analysis software;

[0016] Add loads and fixed ends to the model according to the common load conditions of the damaged area and surrounding area;

[0017] The model is assigned numerical values ​​for each attribute based on the material properties of the bone in the defect area and the material properties of the prosthesis.

[0018] After completing the above preparations, the restoration area is set as a density model, and the initial value of the relative density of the area and the upper and lower limits during the optimization process are adjusted; the interpolation type is selected as SIMP, RAMP, or Darcy method, and the filter is Helmholtz filter; the optimization objective is set as achieving the minimum elastic strain energy within the density range to obtain the maximum stiffness and thus enhance the mechanical properties of the restoration scaffold.

[0019] By setting relative tolerance and maximum number of iterations, topology optimization is performed to obtain the optimal material distribution under simulation conditions.

[0020] The restoration is divided into regions with different density ranges by setting density thresholds according to requirements.

[0021] Preferably, the microporous structure in step 4 is a fully connected random pore structure with adjustable pore size and porosity, or a hexagonal close-packed structure or a diamond structure.

[0022] Preferably, the detailed steps of step 4 are as follows:

[0023] Create a uniformly distributed array of cubes in 3D modeling software such as Magics and Solidworks, where the spacing between the cubes is equal to the side length of the cubes.

[0024] Perform a Boolean intersection operation between the cube array and the regions with different density ranges obtained in step 3 to obtain a cube array with the shape of the repair body;

[0025] All cube arrays were imported into software such as Rhino and CloudCompare and converted into point cloud format. The point cloud files were then imported into programming programs such as Matlab and PyCharm. A program was written to read the file information and remove points that were not square vertices. Based on the remaining points, spherical holes were randomly generated according to the given parameters of their density regions. The given parameters were the spherical hole diameter, the minimum spacing between spherical holes, and the distribution density of spherical holes. During the generation process, the spherical holes were checked for intersection to ensure that they would not intersect.

[0026] Create a through hole connecting to a spherical hole according to the given parameters; the given parameters are the diameter of the through hole and the number of other spherical holes connected to the spherical hole, and the connection principle is to connect the nearest one;

[0027] Import the generated data for spherical holes and through holes into COMSOL Multiphysics 6.1 with MATLAB, and create spherical holes and random holes in COMSOL according to the data;

[0028] By performing Boolean difference operations on the original dense restoration and the spherical and through holes, a restoration model with high mechanical matching degree is obtained. The circular holes in different regions of this model are connected by connecting holes, so there is no need to design an additional transition structure between regions with different porosity. The hole distribution conforms to the load distribution. The circular holes in regions with higher mechanical matching degree are connected by connecting holes, so there is no need to design an additional transition structure between regions with different porosity.

[0029] Preferably, in step 4, the pore size of the microporous structure can vary from 200 μm to 1000 μm, its porosity can vary from 20% to 80%, the number of single-pore connections can vary from 2 to 6, and the pore size of the connecting pores can vary from 200 μm to 400 μm.

[0030] Preferably, the printing method in step 5 is any one or more of selective laser sintering, stereolithography, and digital light processing 3D printing technologies.

[0031] Preferably, in step 5, the restoration model from step 4 is imported into the slicing software to obtain a printing file; the printing file is then imported into the printer for printing to obtain the restoration embryo; after printing, the restoration embryo is subjected to processes such as degreasing and sintering according to different printing methods to obtain the restoration.

[0032] Preferably, the specific process of step 5 is as follows:

[0033] Import the above print file into the UV printer, select the light source wavelength according to the properties of the paste used, and adjust the curing power and curing time according to the curing thickness to ensure that the curing thickness is greater than the slice thickness;

[0034] Then adjust the scraper position and the thickness of the material to ensure that the thickness of the material is greater than the thickness of the slice. After adjustment, print. After printing, remove the model blank from the forming table and place it in an ultrasonic cleaner and add cleaning agent to clean until the solvent is clear.

[0035] Place the cleaned embryos into an oven and dry them until their surface is no longer damp. The drying temperature should be less than 80℃.

[0036] The dried green body is placed in a muffle furnace for sintering, and the sintering process is adjusted according to the slurry used.

[0037] Preferably, the repair is composed of one or more of the following: calcium phosphate, calcium silicate, magnesium, and zinc.

[0038] This invention offers the following advantages: Its design and principles are scientifically sound, and its preparation process is simple. By reconstructing CT data of the patient's defect area, a prosthesis with a contour consistent with the defect is obtained, resulting in higher fit and reducing stress concentration. By designing a random pore structure with adjustable pore size and porosity, the prosthesis has better nutrient and metabolic waste exchange capabilities, making it more suitable for cell retention and thus inducing osteogenic formation. Topology optimization determines the optimal density distribution of the prosthesis, and porosity is used instead of relative density to achieve a reasonable distribution of the micropore structure, resulting in a more uniform stress distribution within the prosthesis.

[0039] In conclusion, this invention is of great significance for the clinical treatment of bone defects and may generate significant economic value. Attached Figure Description

[0040] Figure 1 This is a diagram showing the topology optimization process of the repair body described in this invention, as well as the curves showing the changes in average and maximum stress during the process;

[0041] Figure 2 A comparison diagram showing the stress distribution of the prosthesis described in this invention in the cranial biomechanical environment with the stress distribution of a prosthesis designed using conventional methods;

[0042] Figure 3 These are macroscopic images of the restoration used in Example 2 before and after sintering, as well as microscopic images after sintering. Detailed Implementation

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The present invention provides a method for preparing a high mechanical compatibility restoration based on topology optimization, comprising the following steps:

[0045] Step 1: Reconstruct the bone defect model using CT scan data of the target area, and smooth the model to facilitate subsequent processing.

[0046] Step 2: Construct the outline of the restoration using the mirror method;

[0047] Take a skull defect as an example. Import the skull defect model into 3D modeling software, then select a mirror plane, which should be as close as possible to the midsagittal plane; create a mirror image of the defective skull based on the mirror plane, adjust the relative position of the mirror image and the original model so that they coincide, and then use Boolean difference to obtain the prosthesis model;

[0048] The model contour is constructed using a mirror method, resulting in a high degree of visual matching between the restoration and the defect. The curvature of the restoration closely matches that of the defect, ensuring the aesthetic appeal of the restoration. Preferably, the shape of the restoration perfectly matches the contour of the defect.

[0049] Step 3: Topology optimization to determine the porosity distribution of the restoration;

[0050] In the finite element analysis software, import the prosthesis model and the bone defect model; add loads and fixation ends to the model according to the common load conditions of the defect and surrounding area; assign attribute values ​​to the model according to the material properties of the bone in the defect area and the material properties of the prosthesis; after completing the above preparations, set the prosthesis area as a density model and perform topology optimization to obtain the optimal material distribution under simulation conditions; set density thresholds according to requirements to divide the prosthesis into regions with different density ranges.

[0051] In some embodiments of the present invention, the repair body has regions with different porosities, and these regions have different mechanical properties and bioactivity, which can meet the requirements of different defect areas.

[0052] Step 4: Microporous structure design;

[0053] A program for generating controllable random pores was developed using programming software such as Matlab and Python. Based on the required biological and mechanical properties, regions with different densities in step 3 were replaced with random pores of varying diameters and porosities to obtain a restoration model that matches the mechanical environment of the defect, thereby reducing stress on the restoration and improving its safety.

[0054] The micropore distribution of the prosthesis in this invention is derived from topology optimization, resulting in a uniform stress distribution that can withstand greater loads and ensure patient safety.

[0055] The microporous structure connects different circular holes via a variable number of connecting holes, which are programmed to connect to the nearest other circular holes. Connecting circular holes in different regions eliminates the need for additional transition structures between regions with different porosities, achieving a natural transition between them.

[0056] Its optimal microporous structure is a random pore structure of bone-like trabeculae with adjustable pore size and porosity. Alternatively, hexagonal close-packed structures, diamond structures, and other structures can be used to ensure permeability and retention of body fluids in the repair body, thereby promoting the bone regeneration process.

[0057] The pore size of the microporous structure can vary from 200 μm to 1000 μm, the porosity from 20% to 80%, the number of single-pore connections from 2 to 6, and the diameter of the connecting pores from 200 μm to 400 μm to meet the needs of different defect conditions. Preferably, the micropore size is 600 μm, the porosity is 50%, the number of single-pore connections is 3, and the diameter of the connecting pores is 300 μm.

[0058] Step 5: Printing and post-processing of the restoration;

[0059] Import the restoration model from step 4 into the slicing software to obtain a print file; import the print file into the printer to print and obtain the restoration embryo; after printing, perform degreasing, sintering and other processes on the restoration embryo according to different printing methods to obtain the restoration.

[0060] The printing method described in this invention includes any one or more of selective laser sintering, stereolithography, and digital light processing 3D printing technologies to achieve high-precision forming of microporous structures. Preferably, digital light processing 3D printing is selected.

[0061] The repair material described in this invention is composed of one or more of the following components: calcium phosphate, calcium silicate, magnesium, zinc, etc., to achieve multiple functions. Preferably, calcium phosphate is selected as the raw material for the repair material.

[0062] Example 1

[0063] In this embodiment, a calcium phosphate prosthesis for repairing skull defects in beagle dogs was designed. The calcium phosphate powder used was biphasic calcium phosphate (HA:β-TCP = 3:7), and ceramic forming was achieved using DLP printing technology. Its overall width is 30 mm, and its overall thickness is 3 mm. The corresponding load condition is a 100 N pressure on the forehead of the beagle dog. Based on the topology optimization results under this load condition, the prosthesis was divided into two parts with porosities of 30% and 65%, respectively, for a total overall porosity of 50%. The 30% porosity region is mainly used to bear the load. The microporous structure used in this model has a 600 μm diameter for circular pores, a 300 μm diameter for through pores, and a connection number of 3.

[0064] Import the above print file into the UV-curable printer, and set the light source wavelength to 405nm and the light source power to 6.2mJ / cm². 2The exposure time was 2 seconds, and then printing began using the prepared ceramic slurry. After printing, the model blank was removed from the forming table. The resulting printed blank was placed in a beaker containing anhydrous ethanol and then ultrasonically cleaned for 15 minutes. After ultrasonication three times, the blank was removed and dried in a 60℃ oven for 8 hours. The dried blank was placed in a muffle furnace, and under air atmosphere, the furnace was heated from room temperature to 300℃ at a heating rate of 2.5℃ / min and held for 2 hours; then heated to 550℃ at a heating rate of 1℃ / min and held for 2 hours; then heated to 1000℃ at a heating rate of 5℃ / min and held for 2 hours. Finally, the furnace was cooled to obtain the calcium phosphate ceramic restoration.

[0065] Example 2

[0066] In this embodiment, a calcium phosphate prosthesis for femoral implantation in New Zealand white rabbits was designed. The calcium phosphate powder used was biphasic calcium phosphate (HA:β-TCP = 3:7), and ceramic forming was achieved using DLP printing technology. It is a cylinder with a diameter of 6 mm and an overall height of 10 mm, corresponding to a load of 100 N on the femur when the rabbit is standing. Based on the topology optimization results under this load condition, the prosthesis was divided into two parts with porosities of 30% and 70%, respectively, for a total overall porosity of 52%. The 30% porosity region primarily bears the load. The microporous structure used in this model has a 600 μm diameter for circular pores, a 300 μm diameter for through pores, and a connection count of 3.

[0067] Import the above print file into the photopolymer printer, set the light source wavelength to 405nm, the light source power to 6.2mJ / cm2, and the exposure time to 2s. Then, use the prepared ceramic slurry to start printing. After printing, remove the model blank from the forming stage. Place the obtained printed blank in a beaker containing anhydrous ethanol, and then place it in an ultrasonic cleaner for 15 minutes. After ultrasonication 3 times, remove the blank and dry it in a 60℃ oven for 8 hours. Place the dried blank in a muffle furnace, and under air atmosphere, raise the furnace temperature from room temperature to 300℃ at a rate of 2.5℃ / min and hold for 2 hours; then raise the temperature to 550℃ at a rate of 1℃ / min and hold for 2 hours; then raise the temperature to 1000℃ at a rate of 5℃ / min and hold for 2 hours. Finally, cool the furnace to obtain the calcium phosphate ceramic restoration.

[0068] Example 3

[0069] Compared with Example 1, this embodiment uses a circular through-hole structure, with a pore diameter of 1.3 mm in the high-porosity region and 0.92 mm in the low-porosity region, resulting in an overall porosity of 50%. A skull prosthesis is thus obtained.

[0070] Example 4

[0071] Compared to Example 1, this embodiment involves simultaneously subjecting the forehead, the side opposite the defect, and the occipital region to a load of 50N. All other preparation conditions remain the same, resulting in a skull prosthesis.

[0072] Example 5

[0073] Compared to Example 2, in this embodiment, the prosthesis was divided into three regions with porosities of 30%, 50%, and 70%, respectively, with an overall porosity of 55%. The aim was to minimize the difference in porosity between different regions and reduce stress concentration problems that might result from sudden changes in porosity. All other preparation conditions remained the same, resulting in a femoral prosthesis.

[0074] Example 6

[0075] Compared with Example 1, this embodiment uses a porous structure with a pore diameter of 800 μm for the round pores, a pore diameter of 400 μm for the connecting pores, and 6 connecting round pores. All other preparation conditions are the same, resulting in a calcium phosphate repair.

[0076] Example 7

[0077] Compared with Example 1, this embodiment uses a porous structure with a pore diameter of 400 μm for the circular pores, a pore diameter of 200 μm for the connecting pores, and a number of circular pore connections of 2. All other preparation conditions are the same, resulting in a calcium phosphate repair.

[0078] Example 8

[0079] Compared with Example 1, the sintering temperature in this embodiment is 1200℃, the sintering time is 4h, and all other preparation conditions are the same, thus obtaining a cranial repair body.

[0080] Comparative Example

[0081] Compared with Example 1, the microporous structure in this embodiment is a uniform through-hole. All other preparation conditions are the same. Finite element analysis was performed on the model described in Example 3 and the model in this embodiment, and the stress distribution of the two was compared under the loading conditions of the forehead, the side opposite the defect, and the occipital region of the skull.

[0082] Table 1 Maximum stress values ​​of different prostheses under different skull loading conditions.

[0083]

[0084] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high mechanical compatibility restoration based on topology optimization, characterized in that, include: Step 1: Reconstruct the bone defect model using CT scan data of the target area, and smooth the model. Step 2: Construct the outline of the restoration using the mirror method; Step 3: Determine the material distribution inside the restoration through topology optimization to obtain regions of the restoration with different density ranges; Step 4: According to the required biological and mechanical properties, replace the regions with different density ranges in Step 3 with fully connected random microporous structures with different pore sizes and porosities to obtain a prosthesis model that matches the mechanical environment of the defect. Create a uniformly distributed array of cubes in 3D modeling software, where the spacing between the cubes is equal to the side length of the cubes; Perform a Boolean intersection operation between the cube array and the regions with different density ranges obtained in step 3 to obtain a cube array with the shape of the repair body; Import all cube arrays into the software and convert them into point cloud format; import the point cloud file into the programming program and write a program to read the file information and remove points that are not square vertices from the file; then, based on the remaining points, randomly generate spherical holes according to the given parameters of their respective density regions; the given parameters are the spherical hole diameter, the minimum spacing between spherical holes, and the distribution density of spherical holes; during the generation process, the spherical holes are subjected to intersection detection to ensure that the spherical holes do not intersect. Create a through-hole connection to a spherical hole according to the given parameters; The given parameters are the diameter of the through hole and the number of other spherical holes connected to the spherical hole, with the connection principle being to connect the nearest one; Import the generated data of spherical holes and through holes into COMSOL Multiphysics 6.1 with MATLAB, and create spherical holes and random holes in COMSOL according to the data; By performing Boolean difference operations on the original dense restoration and the spherical and through holes, a restoration model with high mechanical matching degree is obtained. The circular holes in different regions of this model are connected by connecting holes, so there is no need to design an additional transition structure between regions with different porosity. The hole distribution conforms to the load distribution. The circular holes in regions with higher mechanical matching degree are connected by connecting holes, so there is no need to design an additional transition structure between regions with different porosity. Step 5: Print the preform of the restoration and perform degreasing and sintering processes to obtain the restoration.

2. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, The specific process of step 2 is as follows: import the bone defect model into the 3D modeling software, and then select a mirror plane. The mirror plane should be as close as possible to the midsagittal plane. A mirror image of the defective skull is created based on a mirror plane. The relative positions of the mirror image and the original model are adjusted to make them coincide. Then, Boolean difference is used to obtain the prosthesis model. The edges of the prosthesis are trimmed to remove burrs in order to facilitate subsequent porosification.

3. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, The specific process of step 3 is as follows: import the prosthesis model and the bone defect model into the finite element analysis software; Add loads and fixed ends to the model according to the common load conditions of the damaged area and surrounding area; The model is assigned numerical values ​​for each attribute based on the material properties of the bone in the defect area and the material properties of the prosthesis. After completing the above preparations, the restoration area is set as a density model, and the initial value of the relative density of the area and the upper and lower limits during the optimization process are adjusted; the interpolation type is selected as SIMP, RAMP, or Darcy method, and the filter is Helmholtz filter; the optimization objective is set as achieving the minimum elastic strain energy within the density range to obtain the maximum stiffness and thus enhance the mechanical properties of the restoration scaffold. By setting relative tolerance and maximum number of iterations, topology optimization is performed to obtain the optimal material distribution under simulation conditions. The restoration is divided into regions with different density ranges by setting density thresholds according to requirements.

4. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, In step 4, the microporous structure is a fully connected random pore structure with adjustable pore size and porosity.

5. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, In step 4, the pore size of the microporous structure varies from 200μm to 1000μm, its porosity varies from 20% to 80%, the number of single-pore connections varies from 2 to 6, and the pore size of the connecting pores varies from 200μm to 400μm.

6. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, In step 5, the printing method can be any one or more of selective laser sintering, stereolithography, and digital light processing 3D printing technologies.

7. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, In step 5, the restoration model from step 4 is imported into the slicing software to obtain a print file; Import the print file into the printer and print it to obtain the restoration embryo. After printing, the restoration embryo is degreased and sintered according to the different printing methods to obtain the restoration.

8. The method for preparing a high mechanical compatibility restoration based on topology optimization according to claim 1, characterized in that, The repair is composed of one or more of the following: calcium phosphate, calcium silicate, magnesium, and zinc.

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