Preparation method of porous silicon nitride interbody fusion cage based on photocuring 3D printing

Abstract

The invention relates to a preparation method of a porous silicon nitride interbody fusion cage based on photocuring 3D printing, 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 preparation method of a porous silicon nitride intervertebral fusion cage based on photocuring 3D printing. Background Art

[0002] Intervertebral fusion cages can significantly improve the defects of traditional bone graft fusion surgery and enhance the fusion effect by wrapping the graft bone. Titanium alloy is widely used as the material of 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 number CN 115568986A, titled "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 ingredients in the embedded tube are gradually released to promote the regeneration of bone structure, aiming 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 ingredients. 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 ingredients 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 number CN115089353A, titled "A Bio-Mimetic Intervertebral Fusion Cage", places alloy components inside the mold cavity for injection molding. The molten PEEK material enters the injection cavity through the injection port and fills the reserved injection space. After injection molding, the alloy components and the PEEK injection components 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 injected material and the outer shell. Moreover, 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 into the alloy porous structure, and its mechanical properties are difficult to guarantee.

[0004] Silicon nitride ceramics are widely used in the field of medical devices. The technology of photocuring 3D printing silicon nitride ceramics has the advantages of high precision, smooth surface of printed products, and fast forming speed. However, silicon nitride has light absorption properties, resulting in a small curing depth. The forming process requires a high exposure power and a long exposure time. In addition, the microscopic pores of silicon nitride are not easy to control, resulting in difficulty in improving the strength of the finished product, which limits its wide use. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a preparation method of a porous silicon nitride intervertebral fusion cage based on stereolithography 3D printing, which solves the technical problems of unstable connection structure and easy displacement of the existing intervertebral fusion cages, and aims to improve the mechanical properties on the premise of ensuring biocompatibility.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A preparation method of a porous silicon nitride intervertebral fusion cage based on stereolithography 3D printing, the 3D printed intervertebral fusion cage includes a support body and a filling body, the support body is used to provide support, a hollowed-out area is provided on a part of the surface of the support body, and a receiving space is formed inside the support body, and the filling body is placed in the receiving space;

[0008] The support body is silicon nitride ceramic, and is formed by stereolithography 3D printing;

[0009] The filling body is biphasic calcium phosphate ceramic, and is formed by stereolithography 3D printing;

[0010] The filling body is a porous structure, and the porous structure includes a number of through holes or channels that connect the surface and the interior;

[0011] The preparation method includes preparing the support body, which includes:

[0012] Silicon nitride pretreatment: spreading silicon nitride powder into a thin layer, oxidizing the thin layer in high-temperature pure oxygen to form silicon dioxide on the outer surface, and obtaining silicon nitride powder with surface oxidation;

[0013] Taking the surface-oxidized silicon nitride powder, the first photocurable resin and the photoinitiator in proportion, and homogenously mixing them to obtain a silicon nitride photocurable material;

[0014] Using a three-roll mill to successively perform rough rolling and fine rolling on the silicon nitride photocurable material;

[0015] Performing vacuum degassing treatment on the roll-pressed material to obtain a silicon nitride photocurable printing material with uniform dispersion and stable state;

[0016] Using the silicon nitride photocurable printing material for stereolithography forming, and after cleaning, obtaining a green body;

[0017] Debinding the green body in a vacuum or nitrogen atmosphere at 800 °C;

[0018] After debinding, performing impregnation treatment with a nitrate solution, adjusting the pH of the solution with ammonia water to perform in-situ precipitation, and then sintering the precipitate to obtain a porous silicon nitride support body; the sintering conditions are: nitrogen atmosphere, pressure 0.1 - 0.3 Mpa, temperature 1700 °C.

[0019] A further technical solution is as follows:

[0020] The thickness of the thin layer formed by spreading silicon nitride powder is less than 2 mm; the oxidation temperature of the thin layer in high-purity oxygen at high temperature is 800°C - 1000°C.

[0021] The solid content of the silicon nitride photocurable material is 40 vol% - 58 vol%.

[0022] The concentration of the nitrate solution is 10% - 50%; the nitrate is aluminum nitrate or / and yttrium nitrate.

[0023] The temperature control process during the debinding process is as follows: Under normal pressure, the temperature of the debinding device is raised from room temperature to 200°C at a heating rate of 2°C / min; then from 200°C to 400°C at a heating rate of 1°C / min; then from 400°C to 800°C at a heating rate of 2°C / min, and held at 800°C for 1 h.

[0024] The active groups of the first photocurable resin include monofunctional groups, bifunctional groups and trifunctional groups.

[0025] Using the silicon nitride photocurable printing material for photocuring forming includes:

[0026] 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 spacing 0.02 mm, printing layer thickness 25 μm.

[0027] The preparation method further includes preparing the filler, which includes:

[0028] Weigh the second 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;

[0029] Add the second photocurable resin, photoinitiator and hydroxyapatite into a ball mill for ball milling and dispersion, then transfer to a homogenizer and add the β-tricalcium phosphate for homogenizing and mixing, then add PMMA balls with a particle size of 50 μm and continue to homogenize and mix, and finally further evenly distribute through a three-roll mill, evacuate to remove 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;

[0030] The green body is obtained by photocuring 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.

[0031] The green body is degreased in a nitrogen environment at a degreasing temperature of 800 °C.

[0032] After degreasing, when the temperature drops to room temperature, decarburization is carried out: air containing 5 vol% - 10 vol% oxygen is introduced into the degreasing device and heated to 500 °C; then air containing 20 vol% oxygen is introduced and the temperature is further raised to 800 °C.

[0033] 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.

[0034] The proportion of the PMMA microspheres in the material in the homogenizer is 5 wt% - 20 wt%.

[0035] The active groups of the second photocuring resin include monofunctional groups, bifunctional groups and trifunctional groups, and the monofunctional groups include hydroxyl groups.

[0036] The beneficial effects of the present invention are as follows:

[0037] The present invention prepares a porous biphasic calcium phosphate ceramic filler and a silicon nitride support by photopolymerization curing forming additive manufacturing technology. The two can be directly combined and each play its role, and the forming accuracy of the 3D printing technology is utilized to ensure the reliability and high accuracy of the connection. The support can provide a supporting effect 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.

[0038] The present invention uses a treatment method of pre-treatment oxidation + degreasing + impregnation + sintering to replace the traditional pore-forming agent, obtaining a microscopically porous structure of the support body, which is beneficial for bone cells to grow therein. Among them, the silicon nitride powder is pre-treated by high-temperature oxidation, and a thin layer of silicon dioxide is formed on the surface of the silicon nitride, reducing the refractive index, decreasing the refractive index difference between the ceramic and the resin, increasing the curing depth, and being beneficial for the photo-curing forming of silicon nitride. After photo-curing forming, degreasing is carried out in vacuum or nitrogen to leave some carbon residues; sintering is carried out in a nitrogen atmosphere to convert the silicon carbide generated during the degreasing process and the silicon dioxide formed by surface oxidation during the pre-treatment into silicon nitride, and at the same time, more rod-shaped grains can be generated. The rod-shaped grains are connected to each other through an interlocking structure, thereby improving the strength of the porous structure. The precipitate obtained by nitrate impregnation treatment and pH adjustment for in-situ precipitation reacts under high-temperature calcination to form liquid ultrafine nano-oxides, which is beneficial for sintering.

[0039] The preparation of the support body of the present invention does not require a low solid content (less than 40% by volume) to prepare pores, avoiding defects such as cracks caused by the violent escape of gas after resin cracking during the degreasing process due to too low solid content. Similarly, it also avoids large shrinkage and high internal stress during sintering, resulting in cracks.

[0040] The composition of the filling body of the present invention is hydroxyapatite (HAP) and β-tricalcium phosphate (β-TCP), and the two are mixed in a ratio of 1:1 to form a biphasic calcium phosphate ceramic (BCP), which has good biocompatibility. It can achieve chemical bonding with the body tissue at the interface, has a certain solubility in the body, can release calcium and phosphorus 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. At the same time, the filling body of the present invention uses 50-micron PMMA spheres as the pore-forming agent, and the PMMA spheres are consistent with the printing layer thickness, making the size of the fracture source larger 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, and through the setting of printing parameters, the filling body forms a macroscopically porous structure, which can fully meet the needs of bone growth.

[0041] Other features and advantages of the present invention will be described in the subsequent specification, and some of them will be obvious from the specification or understood by implementing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic structural diagram of the support body in an embodiment of the present invention.

[0043] Figure 2 It is a schematic structural diagram of the filling body in an embodiment of the present invention.

[0044] Figure 3 This is a schematic structural diagram of the intervertebral fusion device according to an embodiment of the present invention.

[0045] Figure 4 This is a schematic process diagram of the preparation of the support system according to an embodiment of the present invention.

[0046] Figure 5 This is a schematic microstructural diagram of the support body prepared according to an embodiment of the present invention.

[0047] Figure 6 This is a schematic process diagram of the preparation of the filling body according to an embodiment of the present invention. <*

[0048] Figure 7 This is a schematic microstructural diagram of the filling body prepared according to an embodiment of the present invention.

[0049] In the figure: 1. Support body; 2. Filling body; 10. Opening; 11. Hollowed-out area; 21. Hole or channel. Specific embodiments

[0050] The following describes the specific embodiments of the present invention with reference to the accompanying drawings.

[0051] A preparation method of a porous silicon nitride intervertebral fusion device based on photocuring 3D printing according to this embodiment is shown in Figures 1 to 3 , the 3D printed intervertebral fusion device includes a support body 1 and a filling body 2. The support body 1 is used to provide support. An opening 10 for inserting the filling body 2 is provided at one end of the support body 1. A hollowed-out 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 filling body 2 is placed in the receiving space;

[0052] The support body 1 is silicon nitride ceramic and is formed by photocuring 3D printing;

[0053] The filling body 2 is biphasic calcium phosphate ceramic and is formed by photocuring 3D printing;

[0054] As shown in Figure 2 , the filling body 2 is macroscopically a porous structure. The porous structure includes a number of holes or channels 21 that connect the surface and the inside, which can fully meet the needs of bone growth.

[0055] Through the setting of printing parameters, the size and shape of the macroscopically porous structure of the filling body can be adjusted.

[0056] Figure 3 As shown in Figure 3As shown, when the intervertebral fusion cage is assembled, the filler 2 is directly pressed into the support 1, and a tight fit is formed between the two to form an assembly. After the support 1 is implanted into the body, it can provide a supporting effect. 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, and can promote the repair of defective tissues, showing biological activity. During the dissolution and metabolism process of the internal filler 2, sufficient strength can be provided by the external silicon nitride support 1. Silicon nitride is very stable as the support 1, will not decompose, and its mechanical properties meet the support requirements for the filler 2.

[0057] The preparation method includes

[0058] S1. Preparing the support by photocuring 3D printing.

[0059] S2. Preparing the filler by photocuring 3D printing.

[0060] S3. Inserting the prepared filler into the support to form Figure 3 the assembly shown.

[0061] See Figure 4 , step S1 of preparing the support by photocuring 3D printing includes:

[0062] S11. Pretreatment of silicon nitride: Spreading the silicon nitride powder into a thin layer with a thickness less than 2 mm, oxidizing the thin layer in high-purity oxygen at a high temperature of 800°C - 1000°C to form silicon dioxide on the outer surface, and obtaining the silicon nitride powder with a surface oxidation.

[0063] S12. Taking the surface-oxidized silicon nitride powder, the first photocurable resin and the photoinitiator in proportion, and homogenously mixing them to obtain the silicon nitride photocurable material.

[0064] Among them, the solid content of the silicon nitride photocurable material is 40 vol% - 58 vol%.

[0065] Among them, the active groups of the first photocurable resin include monofunctional groups, bifunctional groups and trifunctional groups.

[0066] Specifically, the first photocurable resin may be 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 hydroxyethyl methacrylate, lauryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and methyl methacrylate laurate; the difunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate; the trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate.

[0067] Among them, for homogeneous mixing, a homogenizer is used and homogenized for 30 s at a rotation speed of 1200 rpm.

[0068] Among them, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0069] S13. Use a three-roll mill to perform rough rolling and fine rolling on the silicon nitride photocurable material successively.

[0070] S14. Perform vacuum degassing treatment on the roll-pressed material to obtain a silicon nitride photocurable printing material with uniform dispersion and stable state.

[0071] S15. Use the silicon nitride photocurable printing material for photocuring forming. After cleaning, a green body is obtained.

[0072] Among them, the photocuring forming process includes:

[0073] Use computer graphics software to design the size and geometric shape of the sample to be printed and generate an STL file. Subsequently, 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 spacing 0.02 mm, and printing layer thickness 25 μm.

[0074] S16. Debind the green body in a vacuum or nitrogen atmosphere at 800 °C.

[0075] During the debinding process, the temperature control process is as follows: under normal pressure, raise the temperature of the debinding device from room temperature to 200 °C at a heating rate of 2 °C / min; then raise the temperature from 200 °C to 400 °C at a heating rate of 1 °C / min; then raise the temperature from 400 °C to 800 °C at a heating rate of 2 °C / min, and hold at 800 °C for 1 h.

[0076] S17. After debinding, perform impregnation treatment with a nitrate solution, adjust the pH of the solution with ammonia water to cause in-situ precipitation, and then sinter the precipitate to obtain a porous silicon nitride support.

[0077] Among them, the concentration of the nitrate solution is 10%-50%; the nitrate is aluminum nitrate or / and yttrium nitrate. The sintering conditions are: nitrogen atmosphere, pressure 0.1-0.3 Mpa, temperature 1700 °C.

[0078] This embodiment is based on pre-treatment oxidation + degreasing + impregnation + sintering to obtain the micro-porous structure of the support, see Figure 5 . The micro-porous structure includes a large number of structural units, and the micro-pores are formed between adjacent structural units. The structural units are one or more of rhombic dodecahedron, tetrahedron, diamond type, and triply periodic minimal surface structure (TPMS). Such micro-pores can allow bone cells to grow in them and have good mechanical properties at the same time. The overall elastic modulus of the silicon nitride support is relatively close to that of bone, and stress shielding will not occur.

[0079] Among them, high-temperature oxidation in the pre-treatment of silicon nitride generates a thin layer of silicon dioxide on the surface of silicon nitride. Since the refractive index of silicon dioxide is 1.4-1.5 and the refractive index of silicon nitride is 2.0-2.1, the refractive index of the silicon nitride surface is changed, and at the same time, the refractive index difference between the photosensitive resin (refractive index of the photosensitive resin is 1.4-1.5) and the ceramic powder is reduced, which is beneficial to photocuring forming, improves the curing depth, and is beneficial to the photocuring forming of silicon nitride. And the effect of forming silicon dioxide through pre-treatment oxidation is completely different from directly adding silicon dioxide. The silicon dioxide formed by oxidation is only a thin layer, about a few nanometers in magnitude, while the ceramic powder directly added with silicon dioxide is at the level of several hundred nanometers or a few micrometers.

[0080] The degreasing after photocuring forming is carried out in vacuum or nitrogen to leave some carbon residues. The sintering after photocuring forming is carried out in a nitrogen atmosphere to convert the silicon carbide generated during the degreasing process into silicon nitride, and at the same time, more rod-shaped grains can be generated. The rod-shaped grains are connected to each other through an interlocking structure, thereby improving the strength of the multi-porous structure. The relevant chemical reaction formulas are as follows:

[0081] 3C(s)+SiO2→SiC(s)+2CO(g)

[0082] 3C(s)+Si3N4→3SiC(s)+2N2(g)

[0083] C(s)+SiO2(s)+N2(g)→Si3N4(s)+2CO(g)

[0084] See Figure 6 , the filling body is prepared by photocuring 3D printing, including:

[0085] S21. Weigh the second photocurable resin, photoinitiator, hydroxyapatite, and β-tricalcium phosphate proportionally; the particle sizes of the hydroxyapatite and β-tricalcium phosphate are 15 microns and 7 microns respectively, and the mass ratio is 1:1.

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

[0087] The second photocurable resin can specifically adopt a monofunctional photosensitive resin monomer, a bifunctional 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 bifunctional photosensitive resin monomer includes one or more of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate; the trifunctional photosensitive resin monomer includes propoxylated glycerol triacrylate or ethoxylated trimethylolpropane triacrylate.

[0088] S22. Add the second photocurable resin, photoinitiator, and hydroxyapatite to a ball mill for ball milling and dispersion, then transfer to a homogenizer and add the β-tricalcium phosphate for homogenization and mixing, then add PMMA balls with a particle size of 50 μm and continue to homogenize and mix, and finally further evenly distribute through a three-roll mill, evacuate to remove bubbles, and obtain a biphasic calcium phosphate photocurable material with a solid content of 65 vol% - 68 vol%; the roll spacing of the three-roll mill is 60 μm.

[0089] The specific type of photoinitiator can refer to the type used in step S12.

[0090] Among them, the proportion of the PMMA balls in the material in the homogenizer is 5 wt% - 20 wt%.

[0091] Due to the addition of PMMA, there is a large amount of carbon residue during the nitrogen degreasing process, so by controlling the oxygen content in the atmosphere, the intensity of the oxidation reaction is controlled, thereby avoiding cracks caused by a large amount of gas generated due to too violent a reaction.

[0092] 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.

[0093] S24. Degrease the green body in a nitrogen environment at a degreasing temperature of 800 °C.

[0094] S25. 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 the temperature is raised to 500 °C; then air with an oxygen content of 20 vol% is introduced, and the temperature is continuously raised to 800 °C.

[0095] S26. 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 to obtain the filler body.

[0096] Among them, a microwave sintering furnace is specifically used during sintering. In order to ensure the uniformity of the temperature field during the microwave sintering process, a plate made of high-purity alumina (4N grade) with a thickness of 5 mm is used to surround the sintering reaction zone on all sides.

[0097] See Figure 7 , the filler body prepared in this embodiment has good mechanical properties. In the preparation of the filler body of this embodiment, 50-micron PMMA microspheres are used as the pore-forming agent, and the PMMA microspheres are consistent with the printing layer thickness, so that the size of the fracture source is 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.

[0098] When preparing the filler body of the embodiment, degreasing is carried out in nitrogen, and only pyrolysis 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 problem of carbon residue in the subsequent high-temperature sintering process is solved through decarburization, preventing the carbon residue from affecting the performance of silicon nitride.

[0099] 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 recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a photocuring 3D printing porous silicon nitride intervertebral fusion device, characterized in that The 3D printed intervertebral fusion cage includes a support body and a filling body. The support body is used to provide support. A hollowed-out area is provided on a part of the surface of the support body, and an accommodation space is formed inside the support body. The filling body is placed in the accommodation space; The support body is silicon nitride ceramic 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 through holes or channels that communicate the surface and the interior; The preparation method includes preparing the support body, which includes: Silicon nitride pretreatment: Spread the silicon nitride powder into a thin layer, oxidize the thin layer in high-temperature pure oxygen to form silicon dioxide on the outer surface, and obtain silicon nitride powder with a surface oxidation; Take the surface-oxidized silicon nitride powder, the first photocuring resin and the photoinitiator in proportion, and mix them homogeneously to obtain the silicon nitride photocuring material; 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; Use the silicon nitride photocuring printing material for photocuring forming, and after cleaning, obtain a green body; Debind the green body in a vacuum or nitrogen atmosphere at 800 °C; After debinding, perform impregnation treatment with a nitrate solution, adjust the pH of the solution with ammonia water to cause in-situ precipitation, and then sinter the precipitate to obtain a porous silicon nitride support body; The sintering conditions are: nitrogen atmosphere, pressure 0.1-0.3 Mpa, temperature 1700 °C.

2. The preparation method according to claim 1, characterized in that, The thickness of the thin layer formed by spreading the silicon nitride powder is less than 2 mm; the temperature for oxidizing the thin layer in high-temperature pure oxygen is 800 °C - 1000 °C.

3. The preparation method according to claim 1, characterized in that, The solid content of the silicon nitride photocuring material is 40 vol% - 58 vol%.

4. The preparation method according to claim 1, wherein The concentration of the nitrate solution is 10% - 50%; the nitrate is aluminum nitrate or / and yttrium nitrate.

5. The preparation method according to claim 1, characterized in that, The temperature control process during the debinding process is: Under normal pressure, raise the temperature of the debinding device from room temperature to 200 °C at a heating rate of 2 °C / min; then raise the temperature from 200 °C to 400 °C at a heating rate of 1 °C / min; then raise the temperature from 400 °C to 800 °C at a heating rate of 2 °C / min, and keep the temperature at 800 °C for 1 h.

6. The preparation method according to claim 1, characterized in that, The active groups of the first photocuring resin include monofunctional groups, bifunctional groups and trifunctional groups.

7. The preparation method according to claim 1, characterized in that, Using the silicon nitride photocuring printing material for photocuring forming includes: Use computer graphics software to design the size and geometry 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.

8. The preparation method according to claim 1, characterized in that, The preparation method also includes preparing the filling body, which includes: Weigh the second photocuring 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; Add the second photocurable resin, photoinitiator, and hydroxyapatite to a ball mill for ball milling and dispersion, then transfer to a homogenizer and add the β-tricalcium phosphate for homogenizing and mixing. Then add PMMA microspheres with a particle size of 50 μm and continue to homogenize and mix. Finally, further evenly distribute 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; 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; Debind the green body in a nitrogen environment at a debinding temperature of 800 °C; After debinding, wait for the temperature to drop to room temperature and carry out decarburization: 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; After decarburization, 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 at 1100 - 1200 °C for 10 - 50 minutes, and then cool with the furnace.

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

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

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