3D Printed Degradable Magnesium Mesh for Personalized Reconstruction of Alveolar Bone Defects

Abstract

The present invention discloses a degradable magnesium mesh for personalized reconstruction of alveolar bone defects in 3D printing; the magnesium mesh designs a personalized model structure based on CT data, and uses 3D printing technology to achieve high-precision preparation of the magnesium mesh, so that the magnesium mesh closely fits the anatomical shape of the alveolar bone; it overcomes the disadvantages of traditional titanium meshes that need to be bent during surgery and have a high exposure rate after surgery, reduces the surgical difficulty and time, and improves the surgical success rate. The surface of the magnesium mesh is a completely open regular hexagonal structure, and this mesh hole structure has the advantages of self-supporting, easy forming, high printing accuracy, and good mechanical properties. At the same time, combining the degradability of magnesium materials and the osteogenic advantages of magnesium ion bone induction, it solves problems such as stress shielding of titanium meshes, non-degradability, and the need for secondary surgery to remove them during dental implantation. The preparation process of the present invention is simple, the preparation cycle is short, the loss of raw materials is small, the repeatability is high, there is no pollution, and the obtained magnesium mesh has the characteristics of controllable shape and high precision, and can be used as a new generation of repair scaffolds for large-area bone defects in oral alveolar bone.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of biomedical materials, and relates to a degradable magnesium mesh for personalized alveolar bone defect reconstruction by applying 3D printing; in particular, it relates to a degradable magnesium mesh for personalized alveolar bone defect reconstruction prepared by applying 3D printing technology, which has the advantages of self-supporting, easy to form, high printing accuracy and good mechanical properties. Background Art

[0002] For oral clinical practice, the treatment of large-area jaw defects has always been a difficult problem for oral implant doctors. The insufficient bone mass at the implant implantation site affects the indications of implant treatment, the quality of implants, functional load, implant aesthetics and the effective survival time of implants in the oral cavity. Therefore, it is very necessary to increase the bone height and bone width of the bone defect part by means of bone regeneration. Commonly used bone augmentation techniques include autologous bone grafting, distraction osteogenesis and guided bone regeneration. Among them, the guided bone regeneration (GBR) technique that promotes bone growth by isolating the bone defect site from soft tissues with a biological membrane layer has remarkable effects and has been widely used in clinical practice. However, due to the low mechanical strength of the biological membrane layer, it cannot maintain a stable three-dimensional space at the defect site for larger bone defects. Therefore, the effect of bone augmentation by simply applying the GBR technique is not ideal. At present, the use of the excellent mechanical properties of titanium mesh to provide a stable three-dimensional space at the defect is increasingly accepted. However, the traditional formed titanium mesh commonly used clinically has the disadvantages of not fitting the alveolar bone anatomical shape, being time-consuming and laborious to bend during the operation, and having a high exposure rate of the titanium mesh after the operation.

[0003] With the continuous development of additive manufacturing technology, personalized titanium mesh prepared by combining digital modeling technology with 3D printing additive manufacturing process has become the best choice at present. The personalized titanium mesh can be designed in situ according to the defect site of the reconstructed jaw model, can closely fit the alveolar bone anatomical shape, provide sufficient osteogenesis space to guide and control the contour shape of the regenerated bone, and can be applied to horizontal bone defects, vertical bone defects, horizontal-vertical combined bone defects, especially suitable for the repair of large-area bone defects. At the same time, using the personalized titanium mesh can also formulate the surgical plan in advance, eliminating the need for manual shaping during the operation, greatly shortening the operation time, and having the characteristics of good appearance, high accuracy, simplicity and convenience; such as CN108992211A and CN109662807A.

[0004] However, since the titanium mesh cannot be degraded, a second operation is required to remove it during later dental implant procedures, increasing the patient's pain and economic burden. Therefore, it is necessary to optimize and improve the material. As a new generation of degradable medical metal material, magnesium alloy materials have attracted much attention. They also have excellent mechanical properties, can provide a stable osteogenic space for the defect site, and at the same time, personalized structures can be precisely prepared using 3D printing and can fit well with the contour of the defect site. In particular, due to its good biocompatibility, mechanical properties, and degradable characteristics, it has been widely used in the field of bone defects. The mechanical properties of magnesium materials are similar to those of human bones, which can avoid the "stress shielding" effect caused by too large a difference in the elastic modulus between the implant and the bone. Due to the degradability of magnesium alloys, they can gradually degrade in the body until they finally disappear, eliminating the need for a second operation. At the same time, magnesium alloys also have excellent biocompatibility. The magnesium ions released during their degradation can also promote the adhesion, proliferation of osteoblasts, and the growth of osteoid, thereby promoting the regeneration of bone tissue and having an obvious osteogenic induction effect. Therefore, combining 3D printing technology may obtain a new degradable structure for alveolar bone defect, which can optimize the commonly used titanium mesh in current clinical practice.

[0005] However, due to the flammable and easily oxidizable characteristics of magnesium alloys, there are significant safety risks during the 3D printing of magnesium alloys. At the same time, magnesium alloys also have the characteristics of low boiling point and high vapor pressure, resulting in serious powder splashing during the 3D printing process. Coupled with the preparation precision limitations of 3D printing, the mesh holes on the surface of the prepared magnesium mesh often become distorted or blocked. These defects seriously damage the mechanical properties of the magnesium mesh and are prone to cause local corrosion, thereby affecting the degradation performance of the magnesium mesh. Therefore, the application of 3D printed magnesium mesh in the reconstruction of alveolar bone defects has been severely restricted. Summary of the Invention

[0006] The technical problem solved by the present invention is to overcome the defects of the prior art and provide a 3D printed personalized degradable magnesium mesh for alveolar bone defect reconstruction.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] In the first aspect, the present invention relates to a personalized degradable magnesium mesh for alveolar bone defect reconstruction prepared by applying 3D printing technology. The magnesium mesh generates a three-dimensional structural model that completely covers the alveolar bone defect in situ based on the scanned and reconstructed alveolar bone model, and this three-dimensional structural model fits tightly with the alveolar bone defect site. The magnesium mesh is a completely open-pored structure, with mesh holes on its surface, and the mesh holes are evenly distributed as a whole. Multiple fixing holes are provided at the edge of the magnesium mesh, and the magnesium mesh is fixed to the alveolar bone defect site through the fixing holes and fixing nails on its surface.

[0009] Preferably, the cross-sectional shape of the magnesium mesh is U-shaped, with smooth transitions at the edges. The height of the magnesium mesh reaches the height of the cementoenamel junction of the adjacent tooth or the height of the alveolar crest of the adjacent tooth, and the mesiodistal width is 2-3 mm from the top boundary of the magnesium mesh to the boundary of the adjacent tooth.

[0010] Preferably, the overall dimensions of the magnesium mesh are 10-100 mm in length, 5-15 mm in height, and 0.1-0.5 mm in thickness.

[0011] Preferably, the surface mesh holes are regular hexagons, and the hole diameter (diameter of the circumscribed circle of the hexagon) is 100-2000 μm.

[0012] In the system of the present invention, the regular hexagonal mesh holes have excellent self-supporting effects, and the mesh holes will not collapse during the printing process; the included angles of the connecting rods of the mesh holes are obtuse angles (120°), which is beneficial to 3D printing forming and the mesh holes will not be blocked; the rod-shaped structure is easy to form and the printing error is small. At the same time, under the premise of the same mesh hole size and thickness, the regular hexagonal mesh holes have the best mechanical support performance. By adopting the regular hexagonal mesh holes, a magnesium mesh for alveolar bone reconstruction more suitable for clinical needs can be prepared.

[0013] Preferably, there are fixing holes on both sides of the magnesium mesh; the fixing holes are located at the bottom edge position of the magnesium mesh, and there are at least two fixing holes on each side, and the distance between adjacent fixing holes is equal. Further preferably, the shape of the fixing holes is circular, and the hole diameter is 1-3 mm.

[0014] Preferably, the materials of the magnesium mesh and the fixing nails are any one of pure magnesium or magnesium alloy materials; the pure magnesium is high-purity magnesium with a purity of ≥99.99%; the magnesium alloy is JDBM: magnesium 95.2-97.5 wt.%, neodymium 2-4 wt.%, zinc 0.2-0.3 wt.%, zirconium 0.3-0.5 wt.%.

[0015] The high-purity magnesium has few impurities, and the microstructure is a uniform single-phase structure, with good corrosion resistance. The corrosion rate is lower than that of magnesium alloys (such as AZ31, WE43, etc.), and the degradation mode is uniform degradation; in the Mg-Nd-Zn-Zr alloy of the present invention, by adding a small amount of light rare earth element Nd with slight cytotoxicity (clinically acceptable) as a low-alloying element, the addition of Nd can ensure that the magnesium alloy has good age hardening and solid solution strengthening effects, and can greatly increase the electrode potential of the magnesium alloy matrix, reduce the galvanic corrosion potential difference between the matrix and the second phase, thereby improving the uniform corrosion resistance of the magnesium alloy. The corrosion rate in simulated body fluid is similar to that of high-purity magnesium and lower than that of common magnesium alloy materials such as AZ31 and WE43. At the same time, the Mg-Nd-Zn-Zr alloy can also achieve uniform degradation and will not show the local corrosion phenomenon exhibited by the above alloys. Only by using the magnesium material in the present invention can a magnesium mesh with uniform degradation be printed to obtain the clinical required effect.

[0016] The surface of the magnesium mesh also has a biocompatible coating; the thickness of the coating is 5-100 μm.

[0017] Preferably, the coating is at least one of a degradable calcium phosphate coating, a degradable polymer coating, and a micro-arc oxidation coating. Specifically, the main component of the degradable calcium phosphate coating is brushite or hydroxyapatite; the main component of the degradable polymer coating is polylactic acid; the main component of the micro-arc oxidation coating is magnesium oxide.

[0018] In a second aspect, the present invention also relates to a method for preparing the aforementioned degradable magnesium mesh for personalized alveolar bone defect reconstruction, the method comprising the following steps:

[0019] Step 1, perform a CT scan on the oral cavity to obtain tooth and jaw data, and import the obtained data into software to reconstruct a three-dimensional model of the alveolar bone;

[0020] Step 2, based on the reconstructed three-dimensional model of the alveolar bone, determine the bone defect site, simulate the implantation site and virtual bone augmentation in the software, and generate a three-dimensional structure model of the magnesium mesh that can cover the bone defect site; based on the generated three-dimensional structure model of the magnesium mesh, determine the position and size of the fixing screw holes, and generate corresponding fixing holes;

[0021] Step 3, import the three-dimensional structure model of the magnesium mesh into a 3D printing device, place the magnesium mesh at an angle of 30°-60°, determine the support structure according to the placement position of the magnesium mesh, and use the laser powder bed melting technology to layer by layer print on the powder bed to generate a personalized magnesium mesh;

[0022] Step 4, after the magnesium mesh is cooled to room temperature, take it out of the device, remove the support, perform surface treatment on the magnesium mesh, and remove the unmelted particles adhering to the surface to obtain the magnesium mesh.

[0023] Preferably, in step 1, the three-dimensional CT scan method is cone beam CT (CBCT) scan. The CBCT scan uses a cone-shaped X-ray and can rotate around the scan position for one week. Compared with the traditional CT scan technology, it can obtain more comprehensive image information. At the same time, the CBCT scan also has the characteristics of low radiation dose and high spatial resolution.

[0024] Preferably, in step 2, the magnesium mesh is generated in situ in the software, which can ensure that the magnesium mesh fully covers the defect site; the fixing holes are specially made according to the implantation site and the structure of the magnesium mesh, which can ensure that the magnesium mesh closely fits the defect, reducing the surgical operation difficulty and time.

[0025] Preferably, in step 3, the magnesium mesh is placed at an angle of 30°-60° during printing. If the inclination angle is less than 30°, it will be difficult for the magnesium mesh to be formed; if the inclination angle is greater than 60°, it will be difficult to add support to the magnesium mesh and raw material waste will occur.

[0026] Preferably, the magnesium powder needs to be preheated before printing, and the preheating temperature is 150 °C. If the powder bed is not preheated, due to the poor thermal conductivity of the powder bed, there will be a large temperature gradient in the powder bed during the printing process. Coupled with the high thermal cracking tendency of the magnesium material, it is easy to cause thermal cracks in the magnesium mesh.

[0027] Preferably, the shape of the magnesium powder is regular spherical, and the particle size is 20 - 80 μm; the 3D printing preparation parameters are laser power of 50 - 100 w, scanning speed of 300 - 600 mm / s, scanning line width of 60 - 100 μm, scanning layer thickness of 20 - 50 μm, and adjacent layers are scanned with a 73° rotation. If the roundness of the magnesium powder is low, the fluidity of the magnesium powder becomes poor during powder spreading, and the uniformity of powder spreading cannot be guaranteed, resulting in defects easily occurring during the printing process; at the same time, if the magnesium powder size is less than 20 μm, the preparation cost will increase, and splashing is likely to occur during the printing process. If the magnesium powder size is greater than 80 μm, the powder is not easily melted, and the gap between adjacent powders is large, and pores are easily generated after melting. In addition, when the laser power is less than 50 w or the scanning speed is greater than 600 mm / s or the scanning line width is greater than 100 μm or the scanning layer thickness is greater than 50 μm, the magnesium powder cannot be completely melted, resulting in an increase in unfused defects; when the laser power is greater than 100 w or the scanning speed is less than 300 mm / s or the scanning line width is less than 60 μm or the scanning layer thickness is less than 20 μm, the magnesium alloy melt pool overheats, resulting in the easy formation of thermal cracks, and at the same time, the temperature gradient increases, resulting in coarse microstructure; when printing, adjacent layers are scanned with a 73° rotation, which can avoid the cumulative effect formed by multi-layer stacking and reduce the influence of residual stress.

[0028] Preferably, in step 4, the magnesium mesh obtained by 3D printing also needs to be surface-treated, specifically including shot peening and chemical polishing. This is because surface treatment can remove the unmelted powder adhered to the surface of the magnesium mesh, significantly improve the surface flatness, and well achieve the structural integrity similar to the model. At the same time, the smooth surface is conducive to subsequent coating.

[0029] Preferably, after the magnesium mesh is polished, it also includes the step of surface coating with at least one of a degradable calcium phosphate coating, a degradable polymer coating, and a micro-arc oxidation coating. If the surface of the magnesium mesh is not coated with a coating, due to the relatively fast degradation rate of the magnesium alloy material in the physiological environment, the formation of hydrogen bubbles will occur, and the accumulation around the implantation site will cause inflammation.

[0030] In the present invention, the preparation method of the degradable calcium phosphate coating is any one of chemical conversion method and hydrothermal conversion method;

[0031] The chemical conversion method refers to first immersing the magnesium mesh in hydrofluoric acid for 8 - 24 h, generating a MgF2 coating on the sample surface through a chemical reaction, and the obtained coating thickness is 1 - 2 μm; then placing the magnesium mesh coated with the MgF2 coating in a supersaturated calcium phosphate treatment solution and standing for different times to form a uniform brushite coating on the sample surface. The calcium phosphate treatment solution is a mixed solution of Ca(H2PO4)2·H2O, NaNO3, and 30% H2O2, and the standing time is 12 - 72 h; the obtained coating thickness is 5 - 20 μm;

[0032] The hydrothermal conversion method refers to placing the magnesium mesh with the previously prepared brushite coating in a solution containing a certain concentration of calcium ions and hydrogen phosphate ions, adjusting the pH value and reaction temperature of the solution, and standing for different times to convert the brushite coating on the sample into a hydroxyapatite coating. The pH value of the solution is 7 - 10, the chemical reaction temperature is 60 - 100 °C, the standing time is 6 - 24 h, and the obtained coating thickness is 5 - 20 μm;

[0033] The preparation method of the polylactic acid coating in the degradable polymer coating is the dip - coating method; the dip - coating method refers to dissolving polylactic acid in ethyl acetate to obtain a polylactic acid solution, and then using a dip - coating instrument to prepare a polylactic acid coating on the surface of the magnesium mesh; the obtained coating thickness is 5 - 10 μm;

[0034] The preparation method of the micro - arc oxidation coating refers to immersing the magnesium mesh in an electrolyte with a basic component of silicate or phosphate, adopting a current control mode, and the selected current is direct current or alternating current or pulsed current, with a frequency range of 100 - 500 Hz. After processing for 5 - 30 min, post - treatment for sealing pores is carried out, and the selected pore - sealing method is silicate pore - sealing or phosphate pore - sealing or sol - gel pore - sealing; the obtained coating thickness is 5 - 75 μm.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention determines the model structure of the support mesh for personalized alveolar bone reconstruction based on CT data, which can achieve controllable dimensions and at the same time achieve the optimal positioning of the fixing nails. Using 3D printing technology to prepare the support mesh with high precision can make the support mesh closely fit the alveolar bone anatomical shape of different patients, provide sufficient mechanical support for the three - dimensional space of the defect site, and protect the shape of the bone filler; it overcomes the disadvantages of traditional titanium meshes that require intraoperative bending and have a high postoperative exposure rate, reduces the surgical difficulty and time, and improves the surgical success rate;

[0037] (2) The present invention uses 3D printing technology to prepare the magnesium mesh, which can directly form implants with complex structures, has a short preparation cycle, small raw material loss, high repeatability, and no pollution to the magnesium mesh during the preparation process;

[0038] (3) The present invention uses a magnesium mesh with regular hexagonal mesh holes. This mesh hole structure has excellent self-supporting effect and will not collapse during the printing process; the included angle between the connecting rods of each mesh hole is an obtuse angle (120°), which is beneficial to 3D printing and forming and will not cause mesh blockage; the rod-shaped structure is easy to form and has small printing errors. At the same time, under the premise of the same mesh size and thickness, the regular hexagonal mesh hole has the best mechanical support performance;

[0039] (4) The present invention makes full use of the mechanical properties, full degradation and osteoinductive osteogenesis advantages of magnesium alloy materials similar to human bones to solve problems such as stress shielding, non-degradability, small bone increment of traditional titanium meshes for alveolar bone, and the need for secondary surgery to remove the titanium mesh during dental implantation;

[0040] (5) Compared with the currently commonly used magnesium alloy materials such as AZ31 and WE43, both have too fast degradation rate and severe local corrosion (pitting) as the corrosion mode, which will cause the problem of premature loss of mechanical support due to too fast degradation in the early stage. The present invention provides high-purity magnesium (purity ≥ 99.99%) and magnesium alloys: magnesium 95 - 97.8 wt.%, neodymium 2 - 4 wt.%, zinc 0.2 - 0.3 wt.%, zirconium 0.3 - 0.5 wt.%, and thus can print a magnesium mesh with uniform degradation performance to obtain the effects required clinically;

[0041] (6) The present invention coats a biocompatible coating on the smooth surface of the polished magnesium mesh, which can ensure that the coating can evenly and flatly cover the sample. The coating can not only effectively regulate the corrosion and degradation behavior of the magnesium mesh, but also promote the adhesion and proliferation of bone cells, further promoting bone healing. Description of the Drawings

[0042] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objectives and advantages of the present invention will become more obvious:

[0043] Figure 1 It is the three-dimensional model and corresponding printed physical diagram of the magnesium mesh sample: (a) magnesium mesh with triangular mesh holes, (b) magnesium mesh with quadrilateral mesh holes, (c) magnesium mesh with hexagonal mesh holes, (d) magnesium mesh with circular mesh holes, (e) magnesium mesh with honeycomb circular mesh holes;

[0044] Figure 2 It is the overall structure and hole structure schematic diagram of the present invention: (a) overall structure schematic diagram, where 1 is alveolar bone, 2 is magnesium mesh, 3 is surface mesh hole, 4 is fixing hole, 5 is fixing screw; (b) regular hexagonal mesh hole structure schematic diagram;

[0045] Figure 3 It is the three-dimensional structure model schematic diagram of the magnesium mesh and the physical diagram after the magnesium mesh is polished; among them, (a) is the three-dimensional structure model schematic diagram of the magnesium mesh; (b) is the physical diagram after the magnesium mesh is polished;

[0046] Figure 4 Schematic diagram of the physical object and microstructure morphology of the magnesium mesh coated with brushite coating; among them, (a) is the physical object diagram of the magnesium mesh coated with brushite coating; (b) is the microstructure morphology diagram of the magnesium mesh coated with brushite coating. Specific implementation mode

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention.

[0048] During the research and development process of the present invention, it was found that serious powder splashing would occur during the 3D printing process of magnesium alloys. Coupled with the preparation accuracy limitation of 3D printing, the mesh holes on the surface of the prepared magnesium mesh often became distorted or blocked. Further, the above defects were overcome by optimizing the design of the mesh hole structure of the magnesium mesh. At the same time, the mechanical strength of the degradable magnesium mesh for alveolar bone defect reconstruction is closely related to the mesh hole structure, and the mesh hole structure is also crucial for preventing the exposure of the magnesium mesh and the growth of soft tissues. The present invention finally realized the preparation of a 3D printed personalized degradable magnesium mesh for alveolar bone defect reconstruction. See the following embodiments for details:

[0049] Example 1: Design and Preparation of Magnesium Meshes with Different Mesh Structures

[0050] Five support meshes with different hole structures were designed using 3-matic 12.0 software (Materialise, Belgium). The mesh hole structures were triangular, quadrilateral, hexagonal, circular, and honeycomb circle respectively, and the maximum mesh hole size was 2 mm. Since the personalized magnesium mesh has a specific structure and it is not easy to measure its mechanical properties subsequently, a flat mesh plate was used for equivalent substitution here. According to the provisions of the national standard GB / T 232-2010 Metallic materials - Bend test method, the length and width of the standard specimen of the flat mesh plate were designed to be 40 mm and 20 mm respectively, and the thickness was designed to be 0.4 mm. Laser powder bed melting technology was used for preparation, and the material used was Mg-3wt.%Nd-0.2wt.%Zn-0.5wt.%Zr magnesium alloy material.

[0051] The three-dimensional model and the corresponding printed physical object diagram of the flat mesh plate specimen are as Figure 1 shown: (a) Magnesium mesh with triangular mesh holes, (b) Magnesium mesh with quadrilateral mesh holes, (c) Magnesium mesh with hexagonal mesh holes, (d) Magnesium mesh with circular mesh holes, (e) Magnesium mesh with honeycomb circle mesh holes. From Figure 1As can be seen from the printed physical diagrams, the sides of the triangular and quadrilateral magnesium mesh specimens are discontinuous, and there are many protrusions on the sides, partially blocking the edge mesh holes. This is because there are many acute angles in the triangular and quadrilateral mesh holes. Due to the limitation of 3D printing accuracy during preparation, the sharp parts of the acute angles cannot be formed. The small holes in the circular and honeycomb circular magnesium mesh specimens are completely blocked by the magnesium alloy powder adhered to the surface, and obvious accuracy deviations and unconnected defects appear in some circular mesh holes, indicating that there are large printing errors between the printed physical objects and the design models of these two types of hole-structured magnesium meshes. This is because the self-supporting performance of the circular mesh holes is poor, and collapse will occur during printing, resulting in incomplete formation of the circular holes; at the same time, due to the limitation of printing accuracy, the roundness in the design model cannot be completely replicated, resulting in the prepared circular holes being distorted into ellipses. However, the forming accuracy of the hexagonal mesh holes is good, and there are no phenomena such as mesh hole discontinuity or blockage, and the repeatability with the design model is very high.

[0052] Example 2: Mechanical Property Testing of Magnesium Meshes with Different Mesh Structures

[0053] The flat magnesium meshes with different hole structures prepared in Example 1 were subjected to a mechanical bending test using a universal testing machine according to the bending standard of GB / T 232-2010. The load was applied perpendicular to the plane mesh plate at a rate of 1 mm / min until the magnesium mesh specimen was damaged.

[0054] Record the load (N) and real-time crossbeam displacement (mm) of the magnesium mesh specimen, obtain the load-displacement curve, and calculate the flexural strength and flexural stiffness of the magnesium mesh specimen using the formula. The data results are shown in Table 1. It can be seen that the magnesium meshes with hexagonal and circular mesh holes have the maximum flexural strength and flexural stiffness; while the magnesium meshes with triangular and honeycomb circular mesh holes have the worst bending mechanical properties. Considering the printing errors and mechanical properties of the magnesium meshes with different hole structures comprehensively, the hexagonal mesh hole structure is the optimal configuration.

[0055] Table 1

[0056]

[0057] Example 3: Design and Preparation of Pure Magnesium Meshes with Regular Hexagon Mesh Holes

[0058] This example relates to a degradable magnesium mesh for alveolar bone defect reconstruction. Figure 2 (a) is a schematic diagram of the overall structure of this example, including an alveolar bone 1 and a magnesium mesh 2. There is a bone defect site on the surface of the alveolar bone 1. The magnesium mesh 2 completely covers the bone defect site. Uniformly distributed mesh holes 3 are opened on the surface of the magnesium mesh 2. The magnesium mesh 2 is connected and fixed to the alveolar bone 1 through fixing holes 4 opened at the bottom and fixing screws 5. Figure 2 (b) is a schematic diagram of the structure of the magnesium mesh holes.

[0059] The length of the magnesium mesh is 100 mm, the height is 15 mm, and the thickness is 0.5 mm. The mesh holes are regular hexagons with a pore diameter of 1000 μm. The fixing holes are circular with a pore diameter of 3 mm. The magnesium mesh and the fixing screws are made of high-purity magnesium (purity ≥ 99.99%).

[0060] This embodiment relates to the aforementioned method for preparing a degradable magnesium mesh for alveolar bone defect reconstruction, and the method includes the following steps:

[0061] Step 1: Perform a cone beam CT (CBCT) scan on the patient's oral cavity, import the obtained DICOMS format data into Mimics 19.0 software for three-dimensional reconstruction of the skull, and obtain the three-dimensional model STL file of the jawbone through threshold adjustment;

[0062] Step 2: Import the jawbone STL file into the reverse engineering Geomagic Studio software for fine processing of the model; import the refined data into 3-matic Research 10.0 to determine the bone defect site, simulate the implantation site, and then use the Geomagic Studio software for virtual bone augmentation to generate a three-dimensional structure model of the magnesium mesh that can cover the bone defect site. Based on the generated three-dimensional structure model of the magnesium mesh, determine that the screw hole position is at the end of the bottom edge of the magnesium mesh, and generate circular fixing holes with a diameter of 3 mm.

[0063] Step 3: Import the three-dimensional structure model of the magnesium mesh into a 3D printing device, place the magnesium mesh model at a 45° inclination with the substrate to generate a rod-shaped support structure. The support structure is in point contact with the magnesium mesh for easy removal. Use the EP-M250 metal 3D printer of Beijing Yijia 3D Technology Co., Ltd. for layer-by-layer printing. The powder is high-purity magnesium powder with a medical degradable purity of 99.99%, in the shape of regular spheres, and the magnesium powder particle size is 50 - 80 μm. Before printing starts, fill the 3D printer cabin with inert gas until the oxygen content in the cabin drops below 100 ppm. The 3D printing preparation parameters are a laser power of 90 w, a scanning speed of 500 mm / s, a scanning line width of 90 μm. When each layer of scanning is completed, the substrate descends by a layer thickness of 30 μm and repeats the manufacturing process of the previous layer until printing is completed. During preparation, the laser scanning direction of adjacent layers rotates 73° in sequence for scanning.

[0064] Step 4: After printing is completed, wait for the temperature of the 3D printer cabin to drop to room temperature, then take out the sample, remove the rod-shaped support, and separate the magnesium mesh from the substrate; perform surface treatment on the magnesium mesh after removing the support, specifically including shot peening and chemical polishing, to remove the unmelted powder adhered to the surface of the magnesium mesh and improve its surface flatness. After polishing, ultrasonically clean in an anhydrous ethanol solution for 10 min, and then dry to obtain the degradable magnesium mesh. The obtained magnesium mesh has a complete structure, the surface mesh holes are of the same size and evenly distributed, and no phenomena such as mesh hole blockage or distortion occur.

[0065] Example 4: Design and Preparation of Magnesium Alloy Meshes with Regular Hexagon Mesh Holes

[0066] This embodiment relates to a degradable magnesium mesh for alveolar bone 1 defect reconstruction. The overall structural schematic diagram is as shown in Figure 2 shown. The magnesium mesh 2 and the fixing screws 5 are made of Mg-3wt.%Nd-0.2wt.%Zn-0.5wt.%Zr magnesium alloy material. The length of the magnesium mesh 2 is 20 mm, the height is 10 mm, and the thickness is 0.3 mm. The shape of the surface mesh holes 3 is a regular hexagon, and the hole diameter is 500 μm. Three fixing holes 4 are provided at the bottom outside the magnesium mesh 2, and the distance between adjacent fixing holes 4 is equal. Two fixing holes 4 are provided at the bottom inside, and the shape of the fixing holes 4 is a circle, and the hole diameter is 2 mm. Figure 3 (a) is a schematic diagram of the three-dimensional structure model of the magnesium mesh, which accurately reflects the structural features described in the present invention. For example, the hexagonal hole shape and their distribution characteristics, the number of fixing holes and their arrangement methods, etc.

[0067] This embodiment relates to the preparation method of the aforementioned degradable magnesium mesh for alveolar bone defect reconstruction. The method includes the following steps:

[0068] Step 1: Perform cone beam CT (CBCT) scanning on the patient's oral cavity, import the obtained DICOMS format data into Mimics19.0 software for three-dimensional reconstruction of the skull, and obtain the three-dimensional model STL file of the jawbone through threshold regulation;

[0069] Step 2: Import the jawbone STL file into the reverse engineering Geomagic Studio software for fine processing of the model; import the refined data into 3-matic Research 10.0 to determine the bone defect site, simulate the implantation site, and then use the Geomagic Studio software for virtual bone augmentation to generate a three-dimensional structure model of the magnesium mesh that can cover the bone defect site. Based on the generated three-dimensional structure model of the magnesium mesh, determine that the positions of the two screw holes are located at the ends of the bottom edge of the magnesium mesh, and generate circular fixing holes with a diameter of 2 mm.

[0070] Step 3: Import the three-dimensional structure model of the magnesium mesh into the 3D printing device. Place the magnesium mesh model at an angle of 30° to the substrate to generate a rod-shaped support structure. The support structure is in point contact with the magnesium mesh, facilitating removal. Use the EP-M250 metal 3D printer of Beijing Yijia 3D Technology Co., Ltd. for layer-by-layer printing. The powder is a medical degradable magnesium alloy Mg-3wt.%Nd-0.2wt.%Zn-0.5wt.%Zr, in the shape of regular spheres, and the particle size of the magnesium alloy powder is 20 - 50μm. Before printing starts, fill the 3D printer chamber with inert gas until the oxygen content in the chamber drops below 100ppm. The 3D printing preparation parameters are: laser power 80w, scanning speed 400mm / s, scanning line width 80μm. When each layer of scanning is completed, the substrate descends by a layer thickness of 30μm and repeats the manufacturing process of the previous layer until printing is completed. During preparation, the laser scanning direction of adjacent layers rotates 73° in sequence for scanning.

[0071] Step 4: After printing, wait for the temperature of the 3D printer chamber to drop to room temperature, then take out the sample, remove the rod-shaped support, and separate the magnesium mesh from the substrate; perform surface treatment on the magnesium mesh after removing the support, specifically including shot peening and chemical polishing, to remove the unmelted powder adhered to the surface of the magnesium mesh, improve its surface flatness. After polishing, ultrasonically clean in an absolute ethanol solution for 10 minutes, and then dry it to obtain the degradable magnesium mesh.

[0072] Figure 3 (b) The figure shows the physical picture of the polished magnesium mesh. It can be seen from the physical picture that the surface of the magnesium mesh presents a metallic luster, the surface mesh holes are of the same size and evenly distributed, and there are no phenomena such as mesh hole blockage or collapse. The overall structure is Figure 3 consistent with the design model in (a), indicating the feasibility of 3D printing technology for preparing personalized magnesium mesh structures, showing that regular hexagonal mesh holes are suitable for the forming of magnesium meshes, and at the same time indicating that surface treatment can effectively remove the adhered powder on the surface and can achieve high-precision preparation of magnesium meshes.

[0073] Example 5: Coating of Calcium Phosphate Coating on the Surface of Magnesium Meshes

[0074] First, prepare the magnesium mesh according to the method in Example 3 of the present invention. Immerse the magnesium mesh in 40% hydrofluoric acid for 12h, and use a shaker to oscillate the hydrofluoric acid to form a uniform MgF2 coating on the surface of the sample. Then ultrasonically clean with deionized water and absolute ethanol for 5 minutes respectively, and dry. Place the fluorinated magnesium mesh in a supersaturated calcium phosphate treatment solution. The calcium phosphate treatment solution is 5g / L Ca(H2PO4)2·H2O, 60g / L NaNO3, and 20ml 30% H2O2. Let it stand for 12h, then ultrasonically clean with deionized water and absolute ethanol for 5 minutes respectively, and dry. A uniform brushite coating can be formed on the surface of the sample, and the morphology of the coating is observed using an electron microscope.

[0075] Figure 4 (a) is a physical picture of a magnesium mesh coated with a brushite coating. It can be seen that the brushite coating is evenly distributed on the surface of the magnesium mesh, and the structure of the magnesium mesh is consistent with that of Figure 3 the magnesium mesh without surface coating treatment in (b), and the coating shows a dark gray color; Figure 4 (b) is an electron micrograph of the brushite coating on the surface of the magnesium mesh. It can be seen that the microstructure morphology of the coating is petal-shaped, and the coating components are three elements of O, Ca, and P. It shows that the brushite coating can be evenly formed on the surface of the magnesium alloy, completely cover the magnesium alloy matrix, and play a protective role.

[0076] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A personalized degradable magnesium mesh for alveolar bone defect reconstruction prepared by 3D printing technology, characterized in that, The magnesium mesh generates a three-dimensional structural model that completely covers the alveolar bone defect in situ based on the scanned and reconstructed alveolar bone model, and this three-dimensional structural model fits tightly to the alveolar bone defect site; the magnesium mesh is a completely open-pored structure, with mesh holes on its surface, and the mesh holes are evenly distributed as a whole, without any discontinuity or blockage of the mesh holes; multiple fixing holes are opened at the edge of the magnesium mesh, and the magnesium mesh is fixed to the alveolar bone defect site through the fixing holes and fixing nails on its surface; the surface mesh holes are regular hexagons with a pore diameter of 100 - 2000 μm; the materials of the magnesium mesh and the fixing nails are any one of pure magnesium or magnesium alloy materials; the pure magnesium is high-purity magnesium with a purity ≥ 99.99%; the magnesium alloy is: magnesium 95.2 - 97.5 wt.%, neodymium 2 - 4 wt.%, zinc 0.2 - 0.3 wt.%, zirconium 0.3 - 0.5 wt.%. The magnesium mesh is prepared by a method including the following steps: Step 1, perform a CT scan on the oral cavity to obtain tooth and jaw data, and import the obtained data into software to reconstruct an alveolar bone three-dimensional model; Step 2, based on the reconstructed alveolar bone three-dimensional model, determine the bone defect site, simulate the implantation site and virtual bone augmentation in the software, and generate a three-dimensional structural model of the magnesium mesh that can cover the bone defect site; based on the generated three-dimensional structural model of the magnesium mesh, determine the position and size of the fixing nail holes, and generate corresponding fixing holes; Step 3, import the three-dimensional structural model of the magnesium mesh into a 3D printing device, place the magnesium mesh at an inclination of 30° - 45°, determine the support structure according to the placement position of the magnesium mesh, and use the laser powder bed melting technology to layer by layer print a personalized magnesium mesh on the powder bed; Step 4, after the magnesium mesh cools to room temperature, take it out of the device, remove the support, perform surface treatment on the magnesium mesh, and remove the unmelted particles adhered to the surface, thus obtaining the magnesium mesh; Among them, in Step 3, the magnesium powder needs to be preheated before printing, and the preheating temperature is 150°C; the shape of the magnesium powder is a regular sphere, and the particle size is 20 - 80 μm; the 3D printing preparation parameters are a laser power of 50 - 100 w, a scanning speed of 300 - 600 mm / s, a scanning line width of 60 - 100 μm, a scanning layer thickness of 20 - 50 μm, and adjacent layers are scanned with a rotation of 73°.

2. The magnesium mesh according to claim 1, characterized in that, The cross-sectional shape of the magnesium mesh is U-shaped, with a smooth transition at the edge; the overall dimensions of the magnesium mesh are a length of 10 - 100 mm, a height of 5 - 15 mm, and a thickness of 0.1 - 0.5 mm.

3. The magnesium mesh according to claim 1, characterized in that, There are fixing holes on both sides of the magnesium mesh; the fixing holes are located at the bottom edge position of the magnesium mesh, and there are at least two fixing holes on each side, and the distance between adjacent fixing holes is equal; the shape of the fixing holes is circular, and the pore diameter is 1 - 3 mm.

4. The magnesium mesh according to any one of claims 1 to 3, characterized in that, The surface of the magnesium mesh also has a biocompatible coating; the thickness of the coating is 5 - 100 μm; the coating is at least one of a degradable calcium phosphate coating, a degradable polymer coating, and a micro-arc oxidation coating.

5. The magnesium mesh according to claim 1, characterized in that, In Step 4, the surface treatment of the magnesium mesh includes shot peening and chemical polishing, and after polishing, it is ultrasonically cleaned in an absolute ethanol solution for 5 - 30 min.

6. The magnesium mesh according to claim 5, characterized in that, After the magnesium mesh is polished, it also includes the step of surface coating with at least one of a degradable calcium phosphate coating, a degradable polymer coating, and a micro-arc oxidation coating.

Images