A surface modification method for sequential repair of bone injuries based on hybrid processing

Abstract

The present invention provides a surface modification method for sequential repair of bone injuries based on hybrid processing, which relates to the technical field of fracture injury repair. This method first designs and manufactures a vibration texture surface; and based on the ultrasonic vibration-assisted machining trajectory and step-by-step simulation method, considering the tool morphology and interference conditions, establishes a prediction model for the vibration texture surface morphology; then conducts the processing quality detection and surface wettability detection of the ultrasonic vibration texture; then, according to the structural characteristics of the ultrasonic vibration texture, establishes an anisotropy-considering vibration texture friction coefficient model to determine the change in the friction characteristics of the implant surface caused by the introduction of the ultrasonic vibration texture; then manufactures a multi-level surface microstructure of the implant based on the femtosecond laser processing technology to complete the design of the sequential repair function of the new implant; finally, applies a plasma-sprayed TiN coating to the implant experimental sample to meet the long-term biocompatibility modification of the implant. This method realizes the repair and regulation of bone injuries through physical structure design.

Description

Technical Field

[0001] The present invention relates to the technical field of fracture injury repair, and particularly to a surface modification method for sequential repair of bone injuries based on hybrid processing. Background Art

[0002] The in-vivo transplantation of metal implants has gradually become a conventional means for fracture repair. It is used to fix or replace damaged bone tissue in the human body and restore the physiological behavior ability of patients. However, due to biocompatibility reasons, traditional implant prostheses are prone to phenomena such as osteogenic bonding failure, wound infection, and release of metal ions to damage surrounding tissues, resulting in the failure of implant treatment. Therefore, enhancing biocompatibility through implant modification is of great significance in orthopedic treatment. Research shows that the improvement of implant biocompatibility can be achieved from two aspects. On the one hand, it is the material selection of the implant itself. Common implants include austenitic stainless steel, titanium alloy, cobalt-chromium alloy, etc. Titanium alloy, as the focus of the present invention, is widely used in fracture repair as an excellent implant material. However, traditional titanium alloy implants may be invaded by bacteria attached to the implant and the immune response of the body to the implant triggers inflammation, resulting in tissue necrosis. In addition, the wear and tear of the titanium alloy oxide layer will also lead to the release of metal ions to poison surrounding tissues or the slow proliferation rate of osteoblasts, increasing the treatment duration, and even making it difficult to form a firm embedding with bone tissue, leading to the failure of implantation. On the other hand, it is the research on the modification of the contact surface between damaged tissues in the human body and the implant, which includes the change of surface topography, biocompatible coating technology, and the role of surfaces rich in biological components.

[0003] Current research on implant modification mainly focuses on the development of various biocompatible coatings. Surface coating with biocompatible coatings enhances the repair ability of implants to damaged tissues. He et al. from Sichuan University prepared a titanium dioxide-nano / HA composite coating to enhance biocompatibility and antibacterial properties. Wang Pu et al. from the University of Shanghai for Science and Technology used hydrothermal electrochemical deposition to generate an HA coating on the surface of titanium alloy, effectively improving the coating quality and biocompatibility of HA. These studies effectively generated coatings on the metal surface by directly applying coating methods to improve the repair behavior of implants. Titanium dioxide (TiO2), titanium nitride (TiN), and hydroxyapatite (HA) coatings are typical biocompatible coatings. After coating treatment, the biological properties of bio-implants will be significantly enhanced. Their coating mechanisms have been widely studied and used, and stable coatings can be obtained. However, this also greatly limits the research direction of implant modification. The implant interface is in direct contact with damaged bone tissue, and material and signal exchange occurs between the contact interfaces. The performance of the interface is affected by multiple factors, such as surface topography, molecular polarity, and biological factors. The increasingly developed surface microstructure manufacturing technologies, such as ultrasonic-assisted machining technology, laser ablation technology, acid etching technology, and 3D printing technology, can construct micro-nano scale structures on the surface of difficult-to-machine titanium alloys. This provides the possibility for designing functional surfaces to regulate cell behavior at the interface. Currently, some researchers improve the binding ability of coatings by manufacturing surface microstructures. Zhang et al. generated grooves and pit textures with different densities on the metal surface using ultraviolet nanosecond lasers. Then, diamond was coated using the hot wire chemical vapor deposition method. As the texture density increased, the adhesion of the coating increased significantly. Subsequently, using the EB-PVD technology, the surface adhesion strength of the coating increased with the decrease in surface roughness. Cai et al. proposed a method for preparing micro-textured coatings with antibacterial AgNPs by combining laser ablation and chemical deposition processes. The research shows that grain refinement brings excellent antibacterial properties and improved micro-texture strength. This indicates that the comprehensive modification of the contact interface between the implant and the human body can achieve the purpose of enhancing the bone injury repair ability of the implant and improving biocompatibility. These studies show that although surface microstructures have been emphasized by researchers, the research on modifying the local biological environment and biological capabilities of surface microstructures is still lacking.

[0004] Surface microstructures have become an important method for surface modification and obtaining excellent material properties. Inspired by bionic manufacturing concepts, various biological surface characteristics have been used to fabricate functional surfaces to improve material properties, such as the adhesion ability of gecko tentacles, the anti-fouling ability of shark skin, and the superhydrophobic surface of lotus leaves. In addition, some common surface microstructures (square, circular, groove, cross-shaped) also endow the surface with high performance, such as optical effects, the adhesion strength of coating systems, and controllable friction properties. Common machining methods for microstructures of difficult-to-machine metal materials include laser ablation machining, vibration machining, additive manufacturing, etc. Cai et al. prepared microporous structures by laser ablation to increase the bonding strength. Zhao et al. generated diamond-shaped structures on the surface by laser cladding technology and studied their wear resistance and antibacterial properties. Wang et al. created hierarchical microchannels generated by the superposition of low-frequency modulated motion and high-frequency elliptical vibration. Precise manufacturing of textures with arbitrary profiles and orientations. In addition, Wang et al. proposed a hybrid method combining surface engraving and elliptical vibration. The co-modulation of machining parameters was fully calculated to support sculptural contours and structural coloring. Berna et al. studied reproducible microtextures on tool steel by axial ultrasonic vibration-assisted milling. The simulated surface was generated using a discrete method and could well map the actual microtextures. The successful preparation of microstructured surfaces by various special machining methods makes it possible to construct composite functional surface microstructures. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a surface modification method for sequential repair of bone injuries based on hybrid machining, which realizes the biological modification of a new implant by designing the physical and chemical properties of the implant surface to improve biocompatibility in view of the above-mentioned prior art.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a surface modification method for sequential repair of bone injuries based on hybrid machining, comprising the following steps:

[0007] Step 1: Design and manufacture of a vibration texture surface; obtaining an ultrasonic vibration texture surface from the machining mechanism to the design goal;

[0008] Step 1.1: Generating a vibration texture surface by ultrasonic vibration-assisted machining;

[0009] Step 1.2: Based on the machining mechanism of axial ultrasonic vibration-assisted milling, establishing an ultrasonic dynamics motion model and determining the ultrasonic vibration time-displacement characteristics;

[0010] Through the analysis of the kinematics of ultrasonic vibration-assisted machining, the machining trajectory of ultrasonic vibration-assisted machining is determined as shown in the following formula:

[0011]

[0012] Among them, x, y, and z are the machining trajectory coordinates of ultrasonic vibration-assisted machining, R is the radius of the machining tool, n is the spindle speed of ultrasonic machining, A is the amplitude of ultrasonic vibration, f is the frequency of ultrasonic vibration, and t is the time of ultrasonic machining;

[0013] According to the principle of ultrasonic vibration-assisted machining, the surface topography of the vibration texture depends on the degree of vibration delay per revolution of the spindle rotation and can be characterized by the number of vibrations, as shown in the following formula:

[0014]

[0015] Among them, is the number of vibrations;

[0016] Step 1.3: Based on the machining parameters of ultrasonic vibration-assisted machining and considering the degree of vibration period delay caused by each parameter, establish a numerical model of the vibration texture size to achieve the controllable size design of the surface vibration texture; among them, the length of the vibration texture depends on the feed per tooth f of ultrasonic vibration-assisted machining t ; the width of the vibration texture is shown in the following formula:

[0017] w = πrn / 30f (3)

[0018] Among them, w is the width of the vibration texture;

[0019] Step 2: Based on the ultrasonic vibration-assisted machining trajectory and the step-by-step simulation method, considering the tool topography and interference conditions, establish a prediction model of the vibration texture surface topography;

[0020] Step 2.1: Input the machining parameters of ultrasonic vibration-assisted machining into the numerical simulation software;

[0021] Step 2.2: Discretize the spindle rotation angle of ultrasonic-assisted milling machining;

[0022] Step 2.3: Discretize the surface of the machined workpiece and assign an initial height value to the surface of the machined workpiece;

[0023] Initialize the virtual plane through the surface simulation matrix method to simulate the actual machined workpiece surface, which is used to accurately capture the change of the machining topography caused by the change of the tool trajectory;

[0024] Step 2.4: Discretize the time unit;

[0025] By dividing the time, the movement trajectory of the tool is changed into a discrete data set, so as to realize the calculation of each discrete point on the virtual plane;

[0026] Step 2.5: Discretize the tool unit; the tool unit includes a tooth number unit and a cutting edge unit;

[0027] Step 2.6: Generate a machining trajectory through machining parameters to form the motion set of the tool;

[0028] Based on Steps 2.1 - 2.5, generate a tool path set with ultrasonic-assisted milling motion information. This data set will provide all the information of the tool's path during this virtual simulation, and fully restore the actual motion trajectory of the tool;

[0029] Step 2.7: Compare the original coordinate Z - direction values at the tool's motion positions. When the height of the motion position is less than the initial height of the machined workpiece surface, use the height information of the motion position to replace the initial height of the machined workpiece surface to achieve simulation machining removal; otherwise, the height information of the machined workpiece surface remains unchanged;

[0030] Step 2.8: Complete all cycles in the order of discrete time units, tooth number units, and cutting edge units to achieve the simulation of the vibration texture surface topography. Finally, save the height information data of the machined workpiece surface at the end time, and draw and output the simulation machined workpiece surface topography based on the machining parameters;

[0031] Step 3: Conduct the machining quality inspection and surface wettability inspection of the ultrasonic vibration texture to ensure the realization of the design purpose and clarify the biocompatibility of the surface vibration texture;

[0032] Step 4: According to the structural characteristics of the ultrasonic vibration texture, establish a friction coefficient model of the vibration texture considering anisotropy to determine the change in the friction characteristics of the implant surface caused by the introduction of the ultrasonic vibration texture;

[0033] Based on the Bowden and Tabor theory, the inherent frictional force F of the object surface i is composed of the adhesion force F a and the deformation force F b The total friction coefficient μ i is composed of μ a the dynamic friction coefficient under the elastic deformation system and μ b the friction coefficient under the plastic deformation system, as shown in the following formula:

[0034]

[0035] The adhesion force F a is related to the actual contact area A r and the shear stress τ, and its expression is as follows;

[0036] F a = A r ·τ (5)

[0037] In addition, according to the friction law, the dynamic friction coefficient under the elastic deformation system is shown in the following formula:

[0038]

[0039] Among them, F is the total normal pressure received by the object surface, and P r is the normal pressure per unit area;

[0040] The deformation force F b is generated when the object undergoes elastoplastic deformation;

[0041] Due to the friction law, the friction coefficient under the plastic deformation system is expressed as:

[0042]

[0043] Among them, F f is the force along the direction of the vibrating texture surface, and F d is the force along the reverse direction of the depth of the vibrating texture surface. A TP is the load-bearing support projected area of the unilateral force of the trapped materials, and A SP is the projected area of the friction force;

[0044] Assume that the direction of the friction force on the vibrating texture surface is θ. Then, the friction coefficient model of the vibrating texture under any friction force direction is as follows:

[0045]

[0046] Among them, δ T (p), δ L (p) are the indentation depths in the transverse and longitudinal directions of the vibrating texture respectively, and p is the normal pressure on the vibrating texture surface;

[0047] Step 5: Manufacture the multi-level surface microstructures of the implant based on the femtosecond laser processing technology, and complete the timing repair function design of the new implant;

[0048] Step 5.1: Use femtosecond laser processing to generate a topological bionic honeycomb structure as the multi-level microstructures on the implant surface to meet the functional requirements of timing repair; Based on the functional design of the implant surface, perform precise 3D modeling on the multi-level microstructures of the implant surface through the solid modeling operation of 3D modeling software, and convert it into a CAD file for the laser processing equipment to automatically generate the processing path;

[0049] Step 5.2: Manufacture the multi-level surface microstructures of the implant to obtain an implant experimental sample with a vibrating texture surface; First, the sample needs to be ultrasonically cleaned, and a mixture of anhydrous ethanol and water is used as the cleaning solution to remove processing impurities. Subsequently, femtosecond laser processing is performed to generate micron-level multi-level microstructures;

[0050] Step 6: Perform plasma spraying of TiN coating on the implant experimental samples to meet the long-term biocompatibility modification of the implants.

[0051] The beneficial effects produced by adopting the above technical solutions are as follows: A surface modification method for sequential repair of bone injuries based on hybrid processing provided by the present invention. (1) In view of the prior art mainly achieving repair by adding drugs, there are certain limitations in both drug timeliness and systemic comprehensive metabolism. The method of the present invention mainly realizes the repair regulation of bone injuries through physical structure design, has higher biocompatibility compared with the addition of chemical substances, and reduces drug rejection. (2) In view of the lack of in-depth research on existing physical modification technologies, the sequential repair proposed by the present invention has specific repair functions in different bone injury repair periods. (3) In view of the limitations of existing manufacturing technologies, the implementation process of the present invention can be simply reproduced on alloy implants and the manufacturing process complies with green manufacturing. (4) The modification methods of the prior art generally have too strong limitations. The present invention takes into account the topological design of the physical structure, innovatively introduces a bionic structure, and has a deeper design concept in the surface microstructure modification of implants. (5) Compared with the randomness of the prior art, the design of the present invention can achieve precise manufacturing of the structure design, realize gradient region distribution repair at the implant interface, and has better flexibility. (6) There is little research on using hybrid processing to achieve surface modification of implants for bone injury repair. The invention has outstanding innovation in the field of medical-industrial integration. Description of the Drawings

[0052] Figure 1 It is a flowchart of a surface modification method for sequential repair of bone injuries based on hybrid processing provided by an embodiment of the present invention;

[0053] Figure 2 It is the processing trajectory simulation result and amplitude test result of ultrasonic vibration-assisted milling provided by an embodiment of the present invention. Among them, (a) is the longitudinal ultrasonic vibration trajectory, and (b) is the longitudinal ultrasonic vibration amplitude;

[0054] Figure 3 It is the simulation morphology result of the ultrasonic vibration textured surface under different spindle speeds and feed rates provided by an embodiment of the present invention. Among them, (a) is the spindle speed of 1200 rpm and the feed rate of 0.01 mm, (b) is the spindle speed of 1320 rpm and the feed rate of 0.01 mm, (c) is the spindle speed of 5000 rpm and the feed rate of 0.01 mm, (d) is the spindle speed of 5350 rpm and the feed rate of 0.01 mm, (e) is the spindle speed of 5000 rpm and the feed rate of 0.01 mm, (f) is the spindle speed of 5350 rpm and the feed rate of 0.02 mm; (g) is the spindle speed of 8400 rpm and the feed rate of 0.01 mm, (h) is the spindle speed of 8000 rpm and the feed rate of 0.01 mm;

[0055] Figure 4 This is the macro-morphology diagram of the time-sequential microstructure provided by the embodiment of the present invention. Among them, (a) is the experimental sample of the composite microstructure, (b) is the enlarged view of the experimental sample of the composite microstructure, (c) is the experimental sample of the TiN coating, and (d) is the

[0056] micro-morphology of the TiN coating;

[0057] Figure 5 This is the surface morphology diagram of the time-sequential microstructure observed under a laser confocal microscope provided by the embodiment of the present invention. Among them, (a) is the micro-morphology of the small-size vibration texture, and (b) is the micro-morphology of the large-size vibration texture;

[0058] Figure 6 This is the surface microstructure morphology diagram of the time-sequential microstructure provided by the embodiment of the present invention. Among them, (a) is the small-size composite micro-morphology x100, (b) is the small-size composite micro-morphology x180, (c) is the small-size composite micro-morphology x400, (d) is the large-size composite micro-morphology x100, (e) is the large-size composite micro-morphology x180, and (f) is the large-size composite micro-morphology x400;

[0059] Figure 7 This is the flow chart for manufacturing the time-sequential surface microstructure of the implant provided by the embodiment of the present invention;

[0060] Figure 8 This is the result of the cytotoxicity test provided by the embodiment of the present invention. Among them, (a) is the cell morphology, and (b) is the statistical result of the experiment. Detailed implementation manners

[0061] The following combines the drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0062] In this embodiment, a sample of titanium alloy Ti6Al4V is taken as an example, and the surface modification method for time-sequential repair of bone damage based on hybrid processing of the present invention is used to design an implant.

[0063] In this embodiment, a surface modification method for time-sequential repair of bone damage based on hybrid processing, as Figure 1 shown, includes the following steps:

[0064] Step 1: Design and manufacture of the vibration texture surface; Obtain the ultrasonic vibration texture surface from the processing mechanism to the design goal;

[0065] Step 1.1: Generate the vibration texture surface by ultrasonic vibration-assisted processing;

[0066] In the study of the adhesion ability of biological cells, it is clearly pointed out that a greater surface roughness will significantly enhance the cell adhesion ability. This is because a greater roughness provides more adhesion space for cell pseudopods. However, a surface accuracy that is too rough obviously cannot meet the requirements for implant use. Therefore, creating a surface structure with a small average roughness and a larger surface area has become the main design idea for enhancing the surface adhesion ability of implants. In this invention, the vibration texture surface is generated by ultrasonic vibration-assisted machining. Ultrasonic vibration machining technology is a special machining method that converts high-frequency alternating current signals into high-frequency mechanical vibrations through piezoelectric ceramics to achieve ultrasonic vibration-assisted machining. Different from other micro-structure machining forms, the continuous high-frequency vibration machining trajectory of ultrasonic-assisted machining makes the generation of vibration textures complex, and it is impossible to directly obtain the desired vibration textures. Therefore, this invention first analyzes the principle of ultrasonic vibration machining and the high-frequency motion trajectory to reveal the principle of generating surface vibration textures by ultrasonic vibration-assisted machining.

[0067] Step 1.2: Based on the mechanism of ultrasonic vibration-assisted milling machining, establish an ultrasonic dynamics motion model to determine the time-displacement characteristics of ultrasonic vibration.

[0068] Through the analysis of the kinematics of ultrasonic vibration-assisted machining, its motion mode is composed of the compound of high-frequency axial ultrasonic vibration and spindle rotation motion. The machining trajectory of ultrasonic vibration-assisted machining is determined as shown in the following formula:

[0069]

[0070] where x, y, and z are the machining trajectory coordinates of ultrasonic vibration-assisted machining, R is the radius of the machining tool, n is the spindle speed of ultrasonic machining, A is the amplitude of ultrasonic vibration, f is the frequency of ultrasonic vibration, and t is the time of ultrasonic machining.

[0071] In this embodiment, based on the Matlab software, the image visualization motion trajectory of ultrasonic vibration-assisted machining is as shown in Figure 2 (a). Due to the high-frequency contact separation characteristics of ultrasonic vibration-assisted machining, concave-convex vibration textures are formed on the surface, and there is continuity between the vibration textures, jointly forming the surface topography of the vibration texture.

[0072] Through the analysis of the principle of ultrasonic vibration-assisted machining, the surface topography of the vibration texture depends on the vibration delay degree per revolution of the spindle rotation and can be characterized by the vibration number, as shown in the following formula:

[0073]

[0074] where is the vibration number;

[0075] Step 1.3: According to the machining parameters of ultrasonic vibration-assisted machining and considering the degree of vibration period delay caused by each parameter, establish a numerical model of the vibration texture size to achieve the controllable size design of the surface vibration texture; among them, the length of the vibration texture depends on the feed per tooth f of ultrasonic vibration-assisted machining t ; the width of the vibration texture is shown in the following formula:

[0076] w = πrn / 30f (3)

[0077] where w is the width of the vibration texture;

[0078] Step 2: Based on the ultrasonic vibration-assisted machining trajectory and the step-by-step simulation method, considering the tool morphology and interference conditions, establish a prediction model of the vibration texture surface morphology; in this embodiment, the morphology simulation results under the corresponding machining plan are obtained through the iterative calculation of the simulation method, as Figure 3 shown, where (a, b, c, d, g, h) are the single-pass simulation surface morphologies under different parameters, and (e, f) are the interference simulation surface morphologies under the corresponding parameters. Visualize and guide the design and manufacture of ultrasonic vibration textures.

[0079] Step 2.1: Input the machining parameters of ultrasonic vibration-assisted machining into the numerical simulation software;

[0080] The surface simulation of ultrasonic vibration texture is determined by the machining parameters of ultrasonic vibration-assisted machining; for example, milling parameters (spindle speed, machining depth, feed rate), ultrasonic parameters (ultrasonic vibration frequency, ultrasonic vibration amplitude such as Figure 2 (b) shows the actual vibration amplitude obtained through testing), tool parameters (tip profile, number of teeth), so this numerical simulation model has the function of visually predicting the machining morphology for any machining parameter ratio. The surface simulation initially sets the specific machining parameters for this simulation;

[0081] Step 2.2: Discretize the spindle rotation angle of ultrasonic-assisted milling machining;

[0082] Ultrasonic-assisted milling machining is the combination of traditional machining and ultrasonic machining. Therefore, the motion trajectory of ultrasonic vibration-assisted machining is a composite trajectory of traditional machining and ultrasonic machining. Discretizing the spindle rotation angle facilitates the analysis of the tool position information of each rotation unit.

[0083] Step 2.3: Discretize the surface of the machined workpiece and assign an initial height value to the surface of the machined workpiece;

[0084] Initialize the virtual plane through the surface simulation matrix method to simulate the actual machined workpiece surface, which is used to accurately capture the change of the machining morphology caused by the change of the tool trajectory;

[0085] Step 2.4: Discretize the time unit;

[0086] By segmenting time, the tool's motion trajectory is transformed into a discrete data set, thereby enabling the calculation of each discrete point on the virtual plane. The discrete time accuracy is directly related to the surface topography accuracy, but a more precise discretization degree will lead to an increase in the calculation duration.

[0087] Step 2.5: Discretize the tool unit; the tool unit includes a tooth number unit and a cutting edge unit;

[0088] Milling cutters have diversity, and milling cutters produced by different manufacturers have different cutting edge profiles. For precision machining, their contour topography affects the surface topography after machining. By discretizing the tool contour into the smallest units, it is ensured that the tool topography is completely imprinted onto the simulated surface topography.

[0089] Step 2.6: Generate a machining trajectory through machining parameters to form the motion set of the tool;

[0090] Based on Steps 2.1 - 2.5, a tool path set with ultrasonic-assisted milling motion information is generated. This data set will provide all the information of the tool's passage during this virtual simulation, completely restoring the actual motion trajectory of the tool;

[0091] Step 2.7: Compare the original coordinate Z - direction value at the tool motion position. When the height of the motion position is less than the initial height of the machined workpiece surface, use the height information of the motion position to replace the initial height of the machined workpiece surface to achieve simulation machining removal; otherwise, the height information of the machined workpiece surface remains unchanged;

[0092] Step 2.8: Complete all cycles in the order of discrete time units, tooth number units, and cutting edge units to achieve the simulation of the vibration texture surface topography. Finally, save the height information data of the machined workpiece surface at the end moment, and use the Surf module in Matlab to plot and output the simulated machined workpiece surface topography based on the machining parameters, which includes the surface information of the machined workpiece formed under these machining parameters, for visual parameter design to guide the selection of machining parameters;

[0093] Step 3: Conduct the machining quality inspection and surface wettability inspection of the ultrasonic vibration texture to ensure the realization of the design objective and clarify the biocompatibility of the surface vibration texture;

[0094] To ensure the accuracy of the vibration texture design, the samples after ultrasonic vibration-assisted machining are observed for machining quality using a laser confocal microscope, such as Figure 5As shown, the texture morphology results with different designed texture sizes are presented, showing obvious texture differences, providing experimental conditions for the subsequent analysis of the cell adhesion degree of different vibration textures. In addition, surface wettability reflects the hydrophilicity and hydrophobicity of the material surface with water. Since the cells and ionic components in the repaired internal environment exist in the form of aqueous solutions, the biocompatibility of the implant is largely related to wettability. The wettability of the vibration texture is analyzed by a contact angle measuring instrument to clarify the biocompatibility of the vibration texture.

[0095] Step 4: According to the structural characteristics of the ultrasonic vibration texture, establish a friction coefficient model of the vibration texture considering anisotropy, and determine the change in the surface friction characteristics of the implant caused by the introduction of the ultrasonic vibration texture.

[0096] When a metal implant contacts bone tissue, although this movement is weak after mechanical fixation, during the long-term maintenance of human activities, the fretting wear between the elastic human bone and the harder metal implant under fretting conditions will cause bone damage. Human bone is a brittle material, but due to the loss of inorganic substances (Ca + ), the elasticity of the bone increases, and the implant pressure cannot cause brittle fracture of the bone. Therefore, an elastic friction specimen, ultra-high molecular weight polyethylene (UHMWP), is used to replace the bone tissue for friction system analysis.

[0097] Based on the Bowden and Tabor theory, the inherent frictional force F i of the object surface is composed of the adhesive force F a and the deformation force F b together. The total friction coefficient μ i is composed of the dynamic friction coefficient μ a in the elastic deformation system and the friction coefficient μ b in the plastic deformation system, as shown in the following formula:

[0098]

[0099] When two objects come into contact, the asperities on their surfaces are pressed against each other to form intermolecular forces, and an adhesive force is generated in the contact area when the static state is to be changed; the adhesive force F a is related to the actual contact area A r and the shear stress τ, and its expression is as follows:

[0100] F a = A r ·τ (5)

[0101] In addition, according to the friction law, the dynamic friction coefficient in the elastic deformation system is shown in the following formula:

[0102]

[0103] Among them, F is the total normal pressure received by the object surface, and P r is the normal pressure per unit area;

[0104] The deformation force F b is generated when the object undergoes elastoplastic deformation; the friction deformation process between the elastomer (polyethylene specimen) and the textured surface can be described in two periods. As the load increases, the elastic material is extruded by the harder metal, and elastic deformation occurs. The specimen is pressed into the surface microstructure to form mechanical interlocking. The elastic deformation is positively correlated with the load and satisfies Hooke's law.

[0105] Since the penetration depth of the elastomer is very small, assuming that the shape of the elastic material after being pressed into the texture is a rectangle-like shape, the maximum penetration depth is the same as the compression depth of the elastomer. At this time, when the force along the contact surface drives the slip between the interfaces, the texture boundary will extrude the material of the elastomer that has been embedded in the microstructure.

[0106] As the load is further increased, the elastic deformation will yield, and the elastomer material will undergo plastic deformation. The plastic deformation is affected by the yield stress, and the plastic deformation belongs to an energy dissipation system. Assuming that the yield stress of the material is isotropic, during the plastic deformation process, the trapped materials are stressed unidirectionally, and the load-bearing projection area is expressed as A TP , and the projection area of the frictional force is A SP . It should be noted that through the comparison of the actual machining results with the simulation surface, the actual machining effect cannot be ignored. Since the processed texture still retains some characteristics of ordinary milling, this makes the texture edge form higher convex bodies, turning the texture into a four-sided groove. Therefore, in the friction analysis, the boundaries of the texture are assumed to be of unequal height.

[0107] It is found that the directionality of the friction behavior of the implant in the body is variable, and at the same time, the structural characteristics of the textured surface indicate that the textured friction behavior is anisotropic. For the application of the implant, the anisotropic differential friction behavior of the textured surface has research significance.

[0108] In the analysis and research, the smallest texture unit is assumed to be a rectangular groove with different heights on both sides. Such an assumption is the result after considering the actual machining effect and conforms to the actual texture morphology.

[0109] Due to the friction law, the friction coefficient in the plastic deformation system is expressed as:

[0110]

[0111] Among them, Ff The force along the direction of the vibrating texture surface is F d The force along the reverse direction of the depth of the vibrating texture surface is A TP The load-bearing projection area of the trapped materials on one side is A SP The projected area of the frictional force

[0112] Set the direction of the frictional force on the vibrating texture surface as θ. Then, the friction coefficient model of the vibrating texture under any frictional force direction is as follows:

[0113]

[0114] where δ T (p), δ L (p) are the indentation depths in the transverse and longitudinal directions of the vibrating texture respectively, and p is the normal pressure on the vibrating texture surface;

[0115] Therefore, through the analysis of the entire vibrating texture friction system, an anisotropic tribological model of the vibrating texture is established to simulate the actual working conditions to the greatest extent. At the same time, in the tribological analysis of the vibrating texture on the implant surface, the vibrating texture area occupies the vast majority of the implant surface, so the adhesion force plays a very small role. And in the friction analysis of the elastomer, the deformation force plays a major role. Therefore, the influence of the adhesion force on the friction system can be ignored when necessary.

[0116] Step 5: Manufacture the multi-level surface microstructure of the implant based on the femtosecond laser processing technology to complete the timing repair function design of the new implant;

[0117] Step 5.1: In order to realize the design of the timing repair implant with specific recovery functions in specific periods during the full-time cycle of bone injury repair, the present invention proposes to use femtosecond laser processing to generate a topological bionic honeycomb structure as the multi-level microstructure on the implant surface to meet the functional requirements of timing repair; Based on the functional design of the implant surface, precise three-dimensional modeling of the multi-level microstructure on the implant surface is carried out through solid modeling operations such as extruding and cutting in three-dimensional modeling software, and it is converted into a CAD file for the laser processing equipment to automatically generate the processing path;

[0118] Step 5.2: Manufacture the multi-level surface microstructure of the implant to obtain the implant experimental sample with a vibrating texture surface as shown in Figure 4 (a)(b); First, the sample needs to be ultrasonically cleaned, and anhydrous ethanol and water are mixed as the cleaning solution to remove processing impurities, and then femtosecond laser processing is carried out to generate a micron-level multi-level microstructure;

[0119] Step 6: Coat the implant experimental sample with a TiN coating by plasma spraying to meet the long-term biocompatibility modification of the implant

[0120] In a corrosive human body environment, titanium alloy materials are prone to form titanium oxide on the surface, and the existence of a micron-scale multi-level structure will exacerbate the oxidation phenomenon, affecting the design and repair effect of implants. On the other hand, the titanium alloy (Ti4Al6V) material will slowly release metal V+ ions, which may cause toxic side effects and lead to immune rejection. Therefore, the present invention uses a plasma-sprayed biocompatible coating TiN to solve the above-mentioned practical problems.

[0121] The TiN coating has hydrophilicity, stable chemical properties, and does not react chemically with the in-vivo environment. The experimental sample is a titanium alloy plate with a multi-level surface microstructure, with dimensions of 20*20*3 mm 3 , and the surface with a vibration texture has a relatively high surface roughness, which ensures the adhesion strength of the coating. Therefore, the sandblasting treatment is avoided. The experimental sample is ultrasonically cleaned to remove machining residues and oil stains. The coating thickness is about 3 microns, evenly covering the overall structure, and a sequential orthopedic implant that meets the design requirements is manufactured. The effect of the TiN coating is as Figure 4 (c)(d) shown. In addition, the microscopic surface conforming to the microstructure is detected by SEM as Figure 6 shown. Although some unmolten particle residues are caused by the coating process, a honeycomb structure can still be shown, and a vibration texture is observed on the honeycomb coating. It is worth noting that the vibration texture is not obvious under SEM, but is very obvious under a laser confocal microscope. This is mainly due to different imaging principles.

[0122] The method of the present invention selects ultrasonic machining as the finishing method of the metal implant substrate. Ultrasonic machining is a special machining method suitable for difficult-to-machine materials and is currently widely used. The present invention utilizes the characteristics of the unique concave-convex vibration texture left on the surface of the substrate after ultrasonic machining to generate a concave-convex vibration substrate. Due to the greatly increased surface, it will be beneficial to the attachment of cell pseudopodia. The concave-convex vibration texture surface structure will guide the cells to spontaneously maintain a limited physical distance, which will be beneficial to the spreading and proliferation of cells in the early stage of repair and promote the process of bone damage repair. On the other hand, the surface morphology with vibration texture will cause changes in the surface friction properties. Due to the fixed relationship between the implant and the damaged bone tissue, the modification of friction properties will also improve the bone damage repair environment to a certain extent. In the later stage of repair, with the large amount of bone mineral deposition, the new bone will find a physical interlocking effect with the vibration texture, increase the bonding force between the two, and improve the secondary damage of bone wear caused by repeated friction during the repair process, resulting in a decline in the final repair quality or even failure. In addition, femtosecond laser processing technology is used to process the vibration texture into a multi-level microstructure. The bionic honeycomb structure boss is generated on the surface of the implant. In the early stage of bone damage repair, the physical distance of the honeycomb structure groove is the shortest of all structures, which promotes the circulation of nutrients required for bone repair and ensures the outflow of metabolic substances. In the later stage of repair, with the growth of new bone tissue, the new bone tissue will grow into a honeycomb structure in the form of an impression due to the existence of the bionic honeycomb structure, which will significantly improve the engineering stability of the bone tissue and increase the bonding strength between the implant and the bone tissue again through the multi-level microstructure. The overall design of the new implant ensures the efficient repair in the early stage of repair, and in the later stage, it spontaneously reinforces the repair, spontaneously completes the repair purpose of the composite repair period at different times, and spontaneously realizes the sequential repair of bone damage without external intervention. In addition, in order to avoid the release of metal ions from the implant material and the long-term corrosion of the metal implant in the human body environment, the biocompatible coating TIN is selected for overall spraying. In this embodiment, the process of manufacturing the sequential surface microstructure of the implant is as follows: Figure 7 shown.

[0123] An ideal bone implant should have excellent biocompatibility, good osteoinductivity, and structural plasticity. This embodiment provides a titanium alloy implant with a composite multi-level microstructure surface. After contacting the physiological environment in the body, the vibration texture surface improves the surface roughness, increases the surface area in contact with cells in the early stage of repair, and promotes adhesion with bone tissue cells; with the release of bone growth factors and nutritional factors, bone deposition, inducing bone tissue cells to ossify and form a more stable bone tissue with a topological honeycomb structure, thereby promoting bone repair and bone regeneration. This embodiment conducts molecular biological experimental detection to test the bone tissue repair effect of the timing implant. The test highlights include:

[0124] (1) Biocompatibility, no cytotoxicity

[0125] (2) Adhesion, the adhesion ability of cells on the surface of the microstructure;

[0126] (3) Changes in cell morphology (pseudopod adhesion, the number and direction polarity of pseudopods), physical distance, and biological phenotype;

[0127] (4) Cell growth ability and proliferation ability (survival and proliferation detection), phenotype, cell survival

[0128] (5) Detection of neonatal bone mineral molecule deposition, detection of bone mineral deposition of calcium salts; comparison of quantity, presence or absence, localization distribution, and osteogenic rate

[0129] (6) Ability to guide the structure of neonatal bone: induce osteogenesis of cells, guide the shape of osteogenesis and highly stable structures;

[0130] Step S1: Detection of adhesion, growth, and proliferation of bone tissue cells;

[0131] Step S1.1: Subculture of mouse embryonic osteoblast precursor cells (MC3T3-E1);

[0132] Cell resuscitation: Take out the cells from the liquid nitrogen tank and put them into a 37°C water bath, gently and quickly shake to melt the cell cryopreservation solution. After wiping and disinfecting with alcohol, put them into the laminar flow hood, transfer them to a sterile centrifuge tube with a pipette, and centrifuge at 800 rpm for 5 minutes. After centrifugation, remove the supernatant, add complete medium and gently pipette to mix evenly, inoculate the cells into a cell culture flask, and culture the cells in a 37°C carbon dioxide incubator. Change the medium the next day.

[0133] Cell passage: When the cells reach about 90% confluence, passage the cells. Digest the cells with 0.25% trypsin. When the cells detach from the wall and slide off, add complete medium to terminate the digestion. Transfer them to a sterile centrifuge tube with a pipette and centrifuge at 800 rpm for 5 minutes. After centrifugation, remove the supernatant, add complete medium and gently pipette to make a cell suspension. Inoculate the cells into a cell culture flask at a 1:2 ratio and continue to culture in a 37°C carbon dioxide incubator.

[0134] Step S1.2: Co-culture of MC3T3-E1 and the material;

[0135] The experimental samples are treated by conventional sterilization; after sterilization, bone marrow stromal stem cells (BMSCs) are inoculated on the surface of the samples at a certain density for co-culture.

[0136] Step S1.3: Observe the adhesion of BMSCs on the surface of the material by scanning electron microscopy

[0137] Inoculate MC3T3-E1 on the surface of the sterilized material, and incubate it in a complete medium in a 37°C carbon dioxide incubator for 48 - 72 h. Wash it 3 times with PBS for 5 min each time. Fix it with 2.5% glutaraldehyde, and dehydrate it with 30%, 50%, 70%, 90%, and 100% alcohol for 15 min. After drying, sputter gold on the surface, and observe the morphology of MC3T3-E1, the morphology of pseudopodia, and the cell adhesion on the material surface under a scanning electron microscope.

[0138] Step S1.4: Cytotoxicity experiment;

[0139] In this example, a CCK-8 kit was used to detect the toxic effect of the material on MC3T3-E1, and the experiment was carried out by extracting the material extract. Place the sterilized material in a complete medium and incubate it at 37°C for 48 h, and prepare an extract by adding 10% fetal bovine serum and antibiotics. Aspirate the original culture medium of the pre-inoculated MC3T3-E1, replace it with the extract, and continue to culture it in a 37°C carbon dioxide incubator for 24 h, 48 h, and 72 h. Aspirate the extract at each detection time point and wash it once with PBS. Prepare a CCK-8 working solution by mixing the complete medium and the CCK-8 reagent in proportion, add the CCK-8 working solution to each well of the cells, and incubate it at 37°C. After incubation, measure the absorbance value at 450 nm using an enzyme-linked immunosorbent assay (ELISA) reader. The experimental results are shown in Figure 8 , compared with the standard culture medium, the extract extracted from the titanium alloy implant experimental group did not show a toxic reaction to the cells, and its biocompatibility met the requirements.

[0140] Step S1.5: Cell proliferation experiment;

[0141] In this example, a CCK-8 kit was used to detect the proliferation of BMSCs after co-culture with the material. Inoculate BMSCs on the surface of the sterilized material and incubate it in a complete medium for 1 d, 3 d, and 7 d. Transfer the samples of each experimental group to a new cell culture plate, aspirate the original culture medium, add the CCK-8 working solution to each well of the cells, and incubate it at 37°C. After incubation, measure the absorbance value at 450 nm using an enzyme-linked immunosorbent assay (ELISA) reader.

[0142] Step S2: In vitro induction of osteogenic cells and detection

[0143] Inoculate MC3T3-E1 on the surface of the sterilized material and incubate it in a complete medium for 24 h. Transfer the samples of each group to a new cell culture plate, aspirate the original culture medium, add osteogenic induction medium (formula) to each well of the cells, and incubate it in a 37°C carbon dioxide incubator. Replace the fresh osteogenic induction medium every other day.

[0144] Step S2.1: Detection of osteogenic differentiation by alkaline phosphatase (ALP) staining

[0145] After osteogenic induction and differentiation for 3 days, 7 days, and 14 days, aspirate the culture medium and wash the cells 3 times with PBS. Take the cell lysate and use an ALP detection kit (Solarbio) for detection. Respectively set up a control group, a standard product group, and an experimental group, dilute them according to a certain ratio, mix them with ALP Assay buffer, and incubate them in a water bath at 37°C for 5 minutes; after mixing them with the ALP chromogenic solution preheated at 37°C, incubate them in a water bath at 37°C for 15 minutes; quickly add the chromogenic substrate solution and measure the absorbance value at 510 nm using an enzyme-linked immunosorbent assay (ELISA) reader.

[0146] Step S2.2: Detection of the expression levels of osteogenesis-related genes by real-time fluorescence quantitative PCR

[0147] After osteogenic induction and differentiation for 3 days, 7 days, and 14 days, extract the total RNA of BMSCs using Trizol, and synthesize the cDNA template by reverse transcription using a reverse transcription kit. Use a real-time fluorescence quantitative PCR kit and a real-time fluorescence quantitative PCR system (ABI) to perform PCR amplification reactions, use β-actin as an internal reference gene, and detect the relative expression levels of osteogenesis-related genes ALP, RUNX2, type I collagen, osteocalcin OCN, and osteopontin OPN. Perform semi-quantitative statistical analysis on the detection results by the 2 -△△Ct method.

[0148] Step S2.3: Detection of the spontaneous structure of newly formed bone

[0149] Test the structural information of newly formed bone by micro-CT X-ray tomography, reconstruct the structural characteristics of newly formed bone by CT, observe the ability of the honeycomb biomimetic structure to guide the growth of the newly formed bone structure, enhance the engineering stability, and verify the sequential repair of bone injury.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A surface modification method for sequential repair of bone injuries based on hybrid processing, characterized in that: It includes the following steps: Step 1: Design and manufacture of a vibrating texture surface; Obtain an ultrasonic vibrating texture surface from the processing mechanism to the design goal; Step 2: Based on the ultrasonic vibration-assisted machining trajectory and the step-by-step simulation method, considering the tool morphology and interference conditions, establish a prediction model for the vibrating texture surface morphology; Step 3: Conduct processing quality inspection and surface wettability inspection of the ultrasonic vibrating texture to ensure the realization of the design purpose and clarify the biocompatibility of the surface vibrating texture; Step 4: According to the structural characteristics of the ultrasonic vibrating texture, establish a friction coefficient model of the vibrating texture considering anisotropy, and determine the change in the friction characteristics of the implant surface caused by the introduction of the ultrasonic vibrating texture; Step 5: Manufacture a multi-level surface microstructure of the implant based on femtosecond laser processing technology, and complete the design of the timing repair function of the new implant; Step 6: Apply a TiN coating by plasma spraying to the implant experimental sample to meet the long-term biocompatibility modification of the implant.

2. The surface modification method for sequential repair of bone injury based on hybrid processing according to claim 1, wherein: The specific method of the said Step 1 is as follows: Step 1.1: Generate a vibrating texture surface through ultrasonic vibration-assisted machining; Step 1.2: Based on the machining mechanism of axial ultrasonic vibration-assisted milling, establish an ultrasonic dynamics motion model to determine the time-displacement characteristics of ultrasonic vibration; Step 1.3: According to the machining parameters of ultrasonic vibration-assisted machining and considering the degree of vibration period delay caused by each parameter, establish a numerical model of the vibrating texture size to realize the controllable size design of the surface vibrating texture.

3. A surface modification method for sequential repair of bone injuries based on hybrid processing according to claim 2, characterized in that: The specific method of the said Step 1.2 is as follows: Through the analysis of the kinematics of ultrasonic vibration-assisted machining, determine the machining trajectory of ultrasonic vibration-assisted machining as shown in the following formula: Where x, y, and z are the machining trajectory coordinates of ultrasonic vibration-assisted machining, R is the radius of the machining tool, n is the spindle speed of ultrasonic machining, A is the amplitude of ultrasonic vibration, f is the frequency of ultrasonic vibration, and t is the time of ultrasonic machining; According to the principle of ultrasonic vibration-assisted machining, the surface morphology of the vibrating texture depends on the degree of vibration delay per revolution of the spindle rotation and can be characterized by the number of vibrations, as shown in the following formula: wherein, is the vibration number.

4. A surface modification method for sequential repair of bone injuries based on hybrid processing according to claim 3, characterized in that: The length of the vibration texture designed in step 1.3 depends on the feed per tooth f of ultrasonic vibration assisted machining t ; The width of the vibration texture is shown in the following formula: w = πRn / 30f (3) Where w is the width of the vibrating texture.

5. A surface modification method for sequential repair of bone injuries based on hybrid processing according to claim 4, characterized in that: The specific method of the said Step 2 is as follows: Step 2.1: Input the machining parameters of ultrasonic vibration-assisted machining into the numerical simulation software; Step 2.2: Discretize the spindle rotation angle of ultrasonic-assisted milling; Step 2.3: Discretize the surface of the machined workpiece and assign an initial height value to the surface of the machined workpiece; Initialize the virtual plane in the form of a surface simulation matrix to simulate the actual machined workpiece surface, which is used to accurately capture the change in the machining morphology caused by the change in the tool trajectory; Step 2.4: Discretize the time unit; By dividing the time, the motion trajectory of the tool becomes a discrete data set, so as to realize the calculation of each discrete point on the virtual plane; Step 2.5: Discretize the tool unit; the tool unit includes a tooth number unit and a cutting edge unit; Step 2.6: Generate a machining trajectory through the machining parameters to form a motion set of the tool; Based on Steps 2.1 - 2.5, generate a tool trajectory set with ultrasonic-assisted milling motion information. This data set will provide all the information passed by the tool in this virtual simulation and fully restore the actual motion trajectory of the tool. Step 2.7: Compare the original coordinate value in the Z direction at the tool movement position. When the height of the movement position is less than the initial height of the machined workpiece surface, use the height information of the movement position to replace the initial height of the machined workpiece surface to achieve simulation machining removal; otherwise, the height information of the machined workpiece surface remains unchanged. Step 2.8: Complete all cycles in the order of discrete time units, tooth number units, and cutting edge units to achieve the simulation of the surface topography of the vibration texture. Finally, save the height information data of the machined workpiece surface at the end time, and draw and output the surface topography of the simulated machined workpiece based on the machining parameters.

6. A surface modification method for sequential repair of bone injuries based on hybrid processing according to claim 5, characterized in that: The specific method of the said Step 4 is as follows: Based on the Bowden and Tabor theory, the inherent frictional force F on the surface of an object i is composed of the adhesion force F a and the deformation force F b The total friction coefficient μ i is composed of μ a the dynamic friction coefficient under the elastic deformation system and the friction coefficient μ under the plastic deformation system b and is given by the following formula: Adhesion force F a is related to the actual contact area A r and the shear stress τ, and its expression is as follows; F a = A r ·τ (5) In addition, according to the friction law, the dynamic friction coefficient under the elastic deformation system is shown in the following formula: Among them, F is the total normal pressure received by the object surface, and P r is the normal pressure per unit area; Deformation force F b It is generated when an object undergoes elastoplastic deformation; Due to the friction law, the friction coefficient under the plastic deformation system is expressed as: Among them, F f is the force along the surface direction of the vibrating texture, and F d is the force along the depth direction of the vibrating texture surface. A TP is the load-bearing projection area of the unilateral force of the trapped materials, and A SP is the projection area of the frictional force; Assume that the direction of the frictional force on the vibration texture surface is θ, then the friction coefficient model of the vibration texture under any frictional force direction is as follows: where, δ T (p), δ L (p) are the indentation depths in the transverse and longitudinal directions of the vibration texture respectively, and p is the normal pressure on the surface of the vibration texture.

7. A surface modification method for sequential repair of bone injuries based on hybrid processing according to claim 6, characterized in that: The specific method of the said Step 5 is as follows: Step 5.1: Use femtosecond laser processing to generate a topological bionic honeycomb structure as the multi-level microstructure on the surface of the implant to meet the functional requirements of sequential repair; based on the functional design of the implant surface, perform precise three-dimensional modeling of the multi-level microstructure on the implant surface through solid modeling operations of three-dimensional modeling software, and convert it into a CAD file for the laser processing equipment to automatically generate the machining path. Step 5.2: Manufacture the multi-level surface microstructure of the implant to obtain an implant experimental sample with a vibration texture surface. First, the sample needs to be ultrasonically cleaned. Mix absolute ethanol and water as the cleaning solution to remove machining impurities, and then perform femtosecond laser processing to generate micron-level multi-level microstructures.

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