Photocuring-based 3D printed silicon nitride interbody fusion cage and preparation method thereof

Abstract

The invention relates to a silicon nitride interbody fusion cage based on photocuring 3D printing and a preparation method, the interbody fusion cage comprises a support body and a filling body, the support body is used for providing support, a part of the surface of the support body is provided with a hollow area, an accommodating space is formed in the support body, and the filling body is arranged in the accommodating space; the support body is made of a silicon nitride material and is formed through photocuring 3D printing; the filling body is made of biphase calcium phosphate ceramic and is formed through photocuring 3D printing; the filling body is of a porous structure. The support body and the filling body can be directly matched and play roles respectively, so that the connection reliability and higher precision are ensured, and the external silicon nitride bracket can provide enough strength in the dissolution and metabolism process of the filling body. The technical problems that an existing interbody fusion cage is unstable in connecting structure, prone to displacement and poor in mechanical property are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of intervertebral fusion cages, and in particular to a light-curing 3D printed silicon nitride intervertebral fusion cage and a preparation method thereof. Background Art

[0002] Intervertebral fusion cages can significantly improve the defects of traditional bone grafting fusion surgery and enhance the fusion effect by wrapping the graft bone. Titanium alloy is widely used as the material for intervertebral fusion cages due to its good corrosion resistance, low dissolution rate, and nearly chemically inert titanium dissolution products. However, the elastic modulus of titanium alloy is 70-100 GPa, while the elastic modulus of cortical bone is generally 18.6 GPa. Obviously, there is a large gap with bone tissue, and stress shielding is likely to occur.

[0003] In the prior art, the patent with the patent number CN 115568986A and the name of a 3D printed intervertebral fusion cage uses a porous titanium alloy fusion cage and is fixed by welding an embedded tube to the porous structure. The active components in the embedded tube are gradually released to promote the regeneration of bone structure, which is used to solve the problem of poor bone ingrowth effect inside the fusion cage. At the same time, the degradation rate is relatively slow, avoiding the premature release of active components. The problems of this solution include: the welding fixation method is complex in operation, and it is difficult to ensure the connection accuracy and reliability. And after the active components are gradually degraded and released through the embedded tube, displacement may occur with the porous structure, resulting in settlement. At the same time, titanium alloy will release metal ions such as titanium, aluminum, and vanadium in the body for a long time, which will cause local tissue inflammation in the body. The patent with the patent number CN115089353A and the name of a bio-mimetic intervertebral fusion cage places the alloy component inside the mold cavity for injection molding. The molten PEEK material enters the injection cavity through the injection port to fill the reserved injection space. After injection molding, the alloy component and the PEEK injection molded component are tightly connected to complete the manufacture of the bio-mimetic intervertebral fusion cage. The problems of this solution include: it is difficult to ensure the tight connection between the injection molded material and the outer shell. And the PEEK material is a completely inert material and does not dissolve, and cannot promote the differentiation of bone cells. During injection molding, the PEEK material will cross the boundary and enter the alloy porous structure, and its mechanical properties are difficult to guarantee. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a light-curing 3D printed silicon nitride intervertebral fusion cage and a preparation method thereof, which solves the technical problems of unstable connection structure and easy displacement of existing intervertebral fusion cages, and aims to improve the mechanical properties on the premise of ensuring biocompatibility.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The present invention provides a silicon nitride intervertebral fusion cage based on photocuring 3D printing, which includes a support body and a filling body. One end of the support body is provided with an opening for inserting the filling body. A hollowed-out area is provided on a part of the surface of the support body. A containing space is formed inside the support body, and the filling body is placed in the containing space.

[0007] The support body is made of silicon nitride material and is formed by photocuring 3D printing.

[0008] The filling body is biphasic calcium phosphate ceramic and is formed by photocuring 3D printing.

[0009] The filling body has a porous structure, and the porous structure includes a number of holes or channels that connect the surface and the interior.

[0010] The present invention also provides a preparation method of the above-mentioned silicon nitride intervertebral fusion cage based on photocuring 3D printing. The preparation method includes preparing the support body, which includes:

[0011] Mix 1,6-hexanediol diacrylate and trimethylolpropane triacrylate in proportion, add a photoinitiator, and then add silicon nitride ceramic powder and a sintering aid in multiple times. After adding the silicon nitride ceramic powder and the sintering aid each time, add a dispersant and carry out homogenization. Finally, a silicon nitride photocuring material with a solid content of 40 vol% to 58 vol% is obtained.

[0012] Use a three-roll mill to roll the silicon nitride photocuring material through a coarse roll and a fine roll successively.

[0013] Perform vacuum degassing treatment on the roll-pressed material to obtain a silicon nitride photocuring printing material with uniform dispersion and stable state without sedimentation.

[0014] Use the silicon nitride photocuring printing material for photocuring forming to obtain a green body.

[0015] Debind the green body in a nitrogen environment: Introduce nitrogen into an integrated device, raise the temperature in the device from room temperature to 200 °C at normal pressure with a heating rate of 2 °C / min; then raise the temperature from 200 °C to 400 °C with a heating rate of 1 °C / min; then raise the temperature from 400 °C to 800 °C with a heating rate of 2 °C / min, and keep the temperature at 800 °C for 1 h, and then cool down to 750 °C at a rate of 120 °C / h.

[0016] After debinding, perform carbon removal: Stop introducing nitrogen into the integrated device and introduce air, and keep the temperature at 750 °C for 5 hours.

[0017] After decarbonization, sintering is carried out: nitrogen is introduced into the integrated device, and the air pressure is controlled at 0.1 MPa. The temperature is first raised from 750 °C to 1400 °C at a heating rate of 2 °C / min and kept at 1400 °C for 1 h; then it is raised from 1400 °C to 1750 °C at a heating rate of 1 °C / min and kept at 1750 °C for 4 h.

[0018] A further technical solution is:

[0019] The mass ratio of the 1,6 - hexanediol diacrylate and trimethylolpropane triacrylate is 1:1.

[0020] The sintering aid adopts a mixture of alumina powder and yttrium oxide powder, and the addition amounts of the alumina powder and yttrium oxide powder are respectively 5% of the addition amount of the silicon nitride ceramic powder; the particle sizes of the alumina and yttrium oxide are 50 - 100 nanometers.

[0021] After adding the dispersant each time, use a homogenizer to homogenize for 30 s at a rotation speed of 1200 rpm.

[0022] The photoinitiator adopts 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide; the dispersant includes a polyphosphate solution.

[0023] The photocuring forming includes:

[0024] Use computer graphics software to design the size and geometric shape of the sample to be printed and generate an STL file, and then transfer it to a 3D printer to slice the STL file and set the parameters: light intensity 230 - 260 mw, laser scanning speed 1000 - 2000 mm / s, scanning pitch 0.02 mm, printing layer thickness 25 μm.

[0025] The preparation method also includes the preparation of the filler, which includes:

[0026] Weigh the photocurable resin, photoinitiator, hydroxyapatite and β - tricalcium phosphate in proportion; the particle sizes of the hydroxyapatite and β - tricalcium phosphate are 15 microns and 7 microns respectively, and the mass ratio is 1:1;

[0027] Add the photocurable resin, photoinitiator and hydroxyapatite to a ball mill for ball - milling dispersion, then transfer to a homogenizer, add the β - tricalcium phosphate and homogenize and mix well, then add PMMA balls with a particle size of 50 μm and continue to homogenize and mix well, and finally further evenly distribute through a three - roll mill, evacuate to remove air bubbles to obtain a biphasic calcium phosphate photocurable material with a solid content of 65 vol% - 68%; the roll spacing of the three - roll mill is 60 μm;

[0028] The green body is obtained by photocuring and forming using the biphasic calcium phosphate photocuring material. During the forming process, the printing layer thickness is 50 μm, the light intensity is 50-100 mw, the laser scanning speed is 10,000-20,000 mm / s, and the scanning pitch is 0.02 mm.

[0029] The green body is degreased in a nitrogen environment at a degreasing temperature of 800 °C.

[0030] After degreasing and waiting for the temperature to drop to room temperature, decarburization is carried out: Air with an oxygen content of 5 vol% - 10 vol% is introduced into the degreasing device and heated to 500 °C; then air with an oxygen content of 20 vol% is introduced and the temperature is further raised to 800 °C.

[0031] After decarburization, sintering is carried out: The temperature in the microwave sintering furnace is raised from room temperature to 1100-1200 °C at a heating rate of 20-60 °C per minute, held at 1100-1200 °C for 10-50 minutes, and then cooled with the furnace.

[0032] The proportion of the PMMA microspheres in the material in the homogenizer is 5 wt% - 20 wt%.

[0033] The active groups of the photocuring resin include monofunctional groups, bifunctional groups, and trifunctional groups, and the monofunctional groups include hydroxyl groups.

[0034] The beneficial effects of the present invention are as follows:

[0035] The present invention prepares a porous structure biphasic calcium phosphate ceramic filler and a silicon nitride support by photocuring and forming additive manufacturing technology. The two can be directly combined and each play its role, and can ensure the reliability and high precision of the connection based on the forming precision of 3D printing technology. The support can provide a support function after being implanted into the body, and the filler can achieve chemical bonding with the body tissue at the interface. It has a certain solubility in the body, can release ions harmless to the body, can participate in the body metabolism, has a stimulating or inducing effect on bone hyperplasia, and can promote the repair of defective tissues, showing biological activity. During the dissolution and metabolism process of the internal filler, sufficient strength can be provided by the external silicon nitride support. Silicon nitride is very stable as a support, will not decompose, and has mechanical properties.

[0036] The components of the filling body of the present invention are hydroxyapatite (HAP) and β-tricalcium phosphate (β-TCP). The two are mixed in a ratio of 1:1 to form biphasic calcium phosphate ceramics (BCP), which have good biocompatibility. It can achieve chemical bonding with the body tissue at the interface. It has a certain solubility in the body, can release calcium and phosphorus ions that are harmless to the body, can participate in the body's metabolism, has a stimulating or inducing effect on bone hyperplasia, can promote the repair of damaged tissues, and shows biological activity. At the same time, the filling body of the present invention uses 50-micron PMMA microspheres as pore-forming agents. The PMMA microspheres are consistent with the printing layer thickness, making the size of the fracture source greater than 50 microns, thereby avoiding the influence of layer lines, enabling the XY direction and the Z direction to have the same mechanical properties, achieving isotropy, and solving the anisotropy problem existing in additive manufacturing. Therefore, the mechanical properties of the filling body of the present invention fully meet the requirements of the filler. Through the setting of printing parameters, the filling body forms a macroscopically porous structure, which can fully meet the needs of bone growth.

[0037] The support body of the present invention uses silicon nitride material, which has a microscopic pore structure and can enable bone cells to grow in it. The overall elastic modulus of the porous silicon nitride support is adjusted to be relatively close to the bone elastic modulus, and stress shielding will not occur. When preparing the support, degreasing is carried out in nitrogen, and only thermal cracking reactions occur, which can avoid violent oxidation-reduction reactions and the generation of a large amount of gas in a short time, resulting in crack formation. And the carbon residue problem during the subsequent high-temperature sintering process is solved by carbon removal, preventing the carbon residue from affecting the performance of silicon nitride, and realizing the integration of degreasing and sintering through the oxygen partial pressure.

[0038] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. Brief Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of the support body in the embodiment of the present invention.

[0040] Figure 2 It is a schematic structural diagram of the filling body in the embodiment of the present invention.

[0041] Figure 3 It is a schematic structural diagram of the intervertebral fusion device in the embodiment of the present invention.

[0042] Figure 4 It is a schematic flow diagram of the preparation of the support body in Example 2 of the present invention.

[0043] Figure 5 It is a schematic microscopic structure diagram of the support body in the embodiment of the present invention.

[0044] Figure 6 It is a schematic flow diagram of the preparation of the filling body in Example 2 of the present invention.

[0045] Figure 7 Schematic diagram of the microstructure of the filler prepared in the embodiment of the present invention.

[0046] In the figure: 1, support body; 2, filler; 10, opening; 11, hollow area; 21, hole or channel. Detailed implementation manners

[0047] The following describes the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0048] Embodiment 1

[0049] Referring to Figures 1 to 3 , a light-curing 3D printed silicon nitride intervertebral fusion device in this embodiment includes a support body 1 and a filler 2. The support body 1 is used to provide support. An opening 10 for inserting the filler 2 is provided at one end of the support body 1. A hollow area 11 is provided on a part of the surface of the support body 1. A receiving space is formed inside the support body 1, and the filler 2 is placed in the receiving space;

[0050] The support body 1 is silicon nitride ceramic and is formed by light-curing 3D printing;

[0051] The filler 2 is biphasic calcium phosphate ceramic and is formed by light-curing 3D printing;

[0052] As Figure 2 shown, the filler 2 is a porous structure macroscopically. The porous structure includes a number of holes or channels 21 that connect the surface and the interior, which can fully meet the needs of bone growth.

[0053] Through setting the printing parameters, the size and shape of the porous structure formed by the filler 2 can be adjusted macroscopically.

[0054] For the 3D printed intervertebral fusion device in this embodiment, the filler 2 is directly pressed into the support body 1, and the two are tightly fitted as Figure 3 shown. The support body 1 can provide a support function after being implanted into the body. The filler 2 can achieve chemical bonding with the body tissue at the interface. It has a certain solubility in the body, can release ions harmless to the body, can participate in the body metabolism, has a stimulating or inducing effect on bone hyperplasia, can promote the repair of defective tissues, and shows biological activity. During the dissolution and metabolism process of the internal filler 2, the external silicon nitride support body 1 can provide sufficient strength. Silicon nitride is very stable as the support body 1 and will not decompose, and its mechanical properties meet the support requirements for the filler 2.

[0055] Embodiment 2

[0056] This embodiment provides a preparation method for the light-curing 3D printed silicon nitride intervertebral fusion device described in Embodiment 1, including:

[0057] S1. Prepare the support body.

[0058] S2. Prepare the filler body.

[0059] S3. Insert the prepared filler body into the support body to form Figure 3 the assembled body as shown.

[0060] See Figure 4 , step S1 for preparing the support body includes:

[0061] S11. Mix 1,6 - hexanediol diacrylate and trimethylolpropane triacrylate in proportion, add a photoinitiator, then add silicon nitride ceramic powder and sintering aids in multiple times. After adding the silicon nitride ceramic powder and sintering aids each time, add a dispersant and perform homogenization. Finally, obtain a silicon nitride photocuring material with a solid content of 40 vol% - 58 vol%;

[0062] S12. Use a three - roll mill to successively perform rough rolling and fine rolling on the prepared silicon nitride photocuring material;

[0063] S13. Perform vacuum degassing treatment on the ground material to obtain a silicon nitride photocuring printing material with uniform dispersion and stable state;

[0064] S14. Use the silicon nitride photocuring printing material for photocuring forming to obtain a green body;

[0065] S15. Debind the green body in a nitrogen environment: Pass nitrogen into the integrated device, raise the temperature in the device from room temperature to 200 °C at normal pressure with a heating rate of 2 °C / min; then raise the temperature from 200 °C to 400 °C with a heating rate of 1 °C / min; then raise the temperature from 400 °C to 800 °C with a heating rate of 2 °C / min, and hold at 800 °C for 1 h, and then cool down to 750 °C at a rate of 120 °C / h;

[0066] S16. After debinding, perform decarburization: Stop passing nitrogen into the integrated device and pass in air, and hold at 750 °C for 5 hours;

[0067] S17. After decarburization, perform sintering: Pass nitrogen into the integrated device, and control the air pressure at 0.1 MPa. First, raise the temperature from 750 °C to 1400 °C with a heating rate of 2 °C / min, and hold at 1400 °C for 1 h; then raise the temperature from 1400 °C to 1750 °C with a heating rate of 1 °C / min, and hold at 1750 °C for 4 h.

[0068] Among them, the microstructure of silicon nitride after sintering at 1750 °C under normal pressure is as Figure 5As shown. It can be seen from the figure that the prepared and formed support body in this embodiment has a micro-porous structure. Microscopically, it includes a large number of structural units, and micro-pores are formed between adjacent structural units. The structural unit is one of a rhombic dodecahedron, a tetrahedron, a diamond type, and a triply periodic minimal surface structure (TPMS). Such micro-pores can enable bone cells to grow therein. The overall elastic modulus of the silicon nitride support is relatively close to that of bone, and stress shielding will not occur. Moreover, when preparing the support in this embodiment, degreasing is carried out in nitrogen, and only cracking reactions occur, which can avoid violent redox reactions and the generation of a large amount of gas in a short time leading to crack formation. And the problem of carbon residue during the subsequent high-temperature sintering process is solved by carbon removal to prevent the carbon residue from affecting the performance of silicon nitride.

[0069] Among them, the integrated device is an integrated device for degreasing, carbon removal, and sintering, and the integration of degreasing and sintering is achieved by controlling the oxygen partial pressure.

[0070] Among them, the mass ratio of the 1,6-hexanediol diacrylate and the trimethylolpropane triacrylate is 1:1.

[0071] Among them, the sintering aid adopts a mixture of alumina powder and yttrium oxide powder, and the addition amounts of the alumina powder and the yttrium oxide powder are respectively 5% of the addition amount of the silicon nitride ceramic powder; the particle sizes of the alumina and the yttrium oxide are 50-100 nanometers.

[0072] Among them, after each addition of the dispersant, a homogenizer is used to homogenize for 30 s at a rotation speed of 1200 rpm.

[0073] Among them, the photoinitiator adopts 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the main component of the dispersant is a polyphosphate solution.

[0074] Among them, the photocuring forming includes:

[0075] Using computer graphics software to design the size and geometric shape of the sample to be printed and generate an STL file, and then transfer it to a 3D printer to slice the STL file and set the parameters: light intensity 230-260 mw, laser scanning speed 1000-2000 mm / s, scanning pitch 0.02 mm, printing layer thickness 25 μm.

[0076] See Figure 6 , step S2 for preparing the filler includes:

[0077] S21. Weigh the photocurable resin, photoinitiator, hydroxyapatite, and β-tricalcium phosphate in proportion; the particle sizes of the hydroxyapatite and the β-tricalcium phosphate are 15 microns and 7 microns respectively, and the mass ratio is 1:1;

[0078] S22. Add the photocurable resin, photoinitiator, and hydroxyapatite into a ball mill for ball milling and dispersion, then transfer them to a homogenizer and add the β-tricalcium phosphate for homogenization and mixing. Then add PMMA microspheres with a particle size of 50 μm and continue to homogenize and mix. Finally, further uniformly distribute them through a three-roll mill, evacuate to remove air bubbles, and obtain a biphasic calcium phosphate photocurable material with a solid content of 65 vol% to 68 vol%. The roll spacing of the three-roll mill is 60 μm.

[0079] S23. Use the biphasic calcium phosphate photocurable material for photocuring forming to obtain a green body. During the forming process, the printing layer thickness is 50 μm, the light intensity is 50 - 100 mw, the laser scanning speed is 10000 - 20000 mm / s, and the scanning pitch is 0.02 mm.

[0080] S24. Debind the green body in a nitrogen environment at a debinding temperature of 800 °C.

[0081] S25. After debinding and waiting for the temperature to drop to room temperature, carry out decarbonization: Introduce air with an oxygen content of 5 vol% - 10 vol% into the debinding device and heat up to 500 °C; then introduce air with an oxygen content of 20 vol% and continue to heat up to 800 °C.

[0082] S26. After decarbonization, carry out sintering: The temperature in the microwave sintering furnace rises from room temperature to 1100 - 1200 °C at a heating rate of 20 - 60 °C per minute, hold for 10 - 50 minutes at 1100 - 1200 °C, and then cool with the furnace.

[0083] Among them, the proportion of the PMMA microspheres in the material in the homogenizer is 5 wt% - 20 wt%.

[0084] Due to the addition of PMMA, there are a large number of carbon residues during the nitrogen debinding process. Therefore, by controlling the oxygen content in the atmosphere, the intensity of the oxidation reaction is controlled, so as to avoid cracks caused by a large amount of gas generated due to too violent reaction.

[0085] Among them, a microwave sintering furnace is specifically used for sintering. In order to ensure the uniformity of the temperature field during the microwave sintering process, the sintering reaction zone is surrounded by a plate made of high-purity alumina (4N grade) with a thickness of 5 mm.

[0086] Among them, the active groups of the photocurable resin include monofunctional groups, bifunctional groups, and trifunctional groups. The monofunctional groups include hydroxyl groups. Since the surfaces of HAP and β-TCP are both hydroxyl groups, the solid content can be increased, and finally it can reach more than 65 vol.%.

[0087] Specifically, the photocurable resin may adopt a monofunctional photosensitive resin monomer, a difunctional photosensitive resin monomer, and a trifunctional photosensitive resin monomer with a mass ratio of 1:1:1 to 1:2:3. The monofunctional photosensitive resin monomer includes one or more of 2-hydroxyethyl methacrylate, lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and lauryl methacrylate; the difunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, dipropylene glycol triacrylate, and dipropylene glycol diacrylate; the trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate.

[0088] Among them, the photoinitiator may adopt 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0089] The mechanical properties of the filler prepared in this embodiment can meet the application requirements. For the microscopic structure of the filler, see Figure 7 . In the preparation of the filler in this embodiment, 50-μm PMMA spheres are used as the pore-forming agent. The PMMA spheres are kept consistent with the printing layer thickness, so that the size of the fracture source is greater than 50 μm, thereby avoiding the influence of layer lines, enabling the XY direction and the Z direction to have the same mechanical properties, achieving isotropy, and solving the anisotropy problem existing in additive manufacturing.

[0090] When preparing the filler in this embodiment, degreasing is carried out in nitrogen, and only cracking reactions occur, which can avoid violent oxidation-reduction reactions and the generation of a large amount of gas in a short time, resulting in crack formation. And carbon removal is carried out to solve the problem of carbon residue in the subsequent high-temperature sintering process and prevent the carbon residue from affecting the performance of silicon nitride.

[0091] Those of ordinary skill in the art can understand that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A light-curing 3D printing silicon nitride intervertebral fusion device, characterized in that, It includes a support body and a filling body. One end of the support body is provided with an opening for inserting the filling body. A hollowed-out area is provided on a part of the surface of the support body. A receiving space is formed inside the support body, and the filling body is placed in the receiving space; The support body is made of silicon nitride material and is formed by photocuring 3D printing; The filling body is biphasic calcium phosphate ceramic and is formed by photocuring 3D printing; The filling body has a porous structure, and the porous structure includes a number of pores or channels that connect the surface and the interior.

2. The preparation method of the silicon nitride intervertebral fusion device based on photocuring 3D printing according to claim 1, characterized in that The preparation method includes preparing the support body, which includes: Mix 1,6 - hexanediol diacrylate and trimethylolpropane triacrylate in proportion, add a photoinitiator, then add silicon nitride ceramic powder and sintering aids in multiple times. After adding the silicon nitride ceramic powder and sintering aids each time, add a dispersant and perform homogenization. Finally, obtain a silicon nitride photocuring material with a solid content of 40vol% - 58vol%; Use a three - roll mill to perform rough rolling and fine rolling on the silicon nitride photocuring material successively; Perform vacuum degassing treatment on the roll - pressed material to obtain a silicon nitride photocuring printing material with uniform dispersion and stable state without sedimentation; Use the silicon nitride photocuring printing material for photocuring forming to obtain a green body; Debind the green body in a nitrogen environment: Introduce nitrogen into the integrated device, raise the temperature in the device from room temperature to 200°C at normal pressure with a heating rate of 2°C / min; then raise the temperature from 200°C to 400°C with a heating rate of 1°C / min; then raise the temperature from 400°C to 800°C with a heating rate of 2°C / min, and hold at 800°C for 1h, and then cool down to 750°C at a rate of 120°C / h; After debinding, perform carbon removal: Stop introducing nitrogen into the integrated device and introduce air, and hold at 750°C for 5 hours; After carbon removal, perform sintering: Introduce nitrogen into the integrated device, and control the air pressure at 0.1MPa. First, raise the temperature from 750°C to 1400°C with a heating rate of 2°C / min, and hold at 1400°C for 1h; then raise the temperature from 1400°C to 1750°C with a heating rate of 1°C / min, and hold at 1750°C for 4h.

3. The preparation method according to claim 2, characterized in that, The mass ratio of 1,6 - hexanediol diacrylate and trimethylolpropane triacrylate is 1:

1.

4. The preparation method according to claim 2, characterized in that, The sintering aids adopt a mixture of alumina powder and yttrium oxide powder, and the addition amounts of the alumina powder and yttrium oxide powder are 5% of the addition amount of the silicon nitride ceramic powder respectively; the particle sizes of alumina and yttrium oxide are 50 - 100 nanometers.

5. The preparation method according to claim 2, wherein After adding the dispersant each time, use a homogenizer to homogenize for 30s at a rotation speed of 1200rpm.

6. The preparation method according to claim 3, characterized in that, The photoinitiator adopts 2,4,6 - trimethylbenzoyl - diphenylphosphine oxide; the dispersant includes a polyphosphate solution.

7. The preparation method according to claim 2, wherein, The photocuring forming includes: Use computer graphics software to design the size and geometric shape of the sample to be printed and generate an STL file, then transfer it to a 3D printer to slice the STL file, and set the parameters: light intensity 230 - 260mw, laser scanning speed 1000 - 2000mm / s, scanning pitch 0.02mm, printing layer thickness 25μm.

8. The preparation method according to claim 2, wherein, The preparation method further includes preparing the filler, which includes: Weighing photocurable resin, photoinitiator, hydroxyapatite and β-tricalcium phosphate in proportion; the particle sizes of the hydroxyapatite and β-tricalcium phosphate are 15 microns and 7 microns respectively, and the mass ratio is 1:1; Adding the photocurable resin, photoinitiator and hydroxyapatite into a ball mill for ball milling and dispersion, then transferring to a homogenizer and adding the β-tricalcium phosphate for homogenizing and mixing, then adding PMMA balls with a particle size of 50μm and continuing to homogenize and mix, and finally further evenly distributing through a three-roll mill, evacuating to remove air bubbles, to obtain a biphasic calcium phosphate photocurable material with a solid content of 65vol% - 68vol%; the roll spacing of the three-roll mill is 60μm; Using the biphasic calcium phosphate photocurable material for photocuring forming to obtain a green body; during the forming process, the printing layer thickness is 50μm, the light intensity is 50 - 100mw, the laser scanning speed is 10000 - 20000mm / s, and the scanning spacing is 0.02mm; Debinding the green body in a nitrogen environment at a debinding temperature of 800°C; After debinding, waiting for the temperature to drop to room temperature and then performing decarburization: introducing air with an oxygen content of 5vol% - 10vol% into the debinding device and heating to 500°C; then introducing air with an oxygen content of 20vol% and continuing to heat to 800°C; After decarburization, sintering is carried out: the temperature in the microwave sintering furnace rises from room temperature to 1100 - 1200°C, the heating rate is 20 - 60°C / minute, holding for 10 - 50 minutes at 1100 - 1200°C, and then cooling with the furnace.

9. The preparation method according to claim 8, characterized in that, The proportion of the PMMA balls in the material in the homogenizer is 5wt% - 20wt%.

10. The preparation method according to claim 8, characterized in that, The active groups of the photocurable resin include monofunctional groups, bifunctional groups and trifunctional groups, and the monofunctional groups include hydroxyl groups.

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