A method and apparatus for preparing a lumbar cage based on melt extrusion

Abstract

This invention proposes a method and apparatus for preparing lumbar fusion devices based on melt extrusion. Using single-component or multi-component metal powder and low-melting-point single-component or multi-component polymer powder as raw materials, a uniformly mixed composite metal powder material is prepared using a high-speed mixer. Materials with different compositions can be prepared according to different production needs. The printhead is simply heated above the melting point of the polymer powder, and then 3D printed using melt extrusion. The resulting metal preform is then degreased and sintered to obtain the final lumbar fusion device. This method significantly reduces the manufacturing cost of lumbar fusion devices, results in low residual stress in the metal preform, and the surface texture of the lumbar fusion device is conducive to cell adhesion and growth.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing of metal materials, and mainly relates to a method and apparatus for preparing lumbar fusion devices based on melt extrusion. Background Technology

[0002] Compared to traditional processing methods, 3D printing technology has advantages such as fast forming speed, low processing cost (no mold required), and material saving. For highly complex parts that are difficult to complete using traditional processing methods, the advantages of 3D printing technology are particularly obvious. In theory, 3D printing technology can manufacture workpieces of any shape. It can automatically, quickly, directly, and relatively accurately convert three-dimensional designs in the computer into solid models, and even directly manufacture parts or molds, thereby effectively shortening the product development cycle. It is a truly digital and intelligent forming method.

[0003] Selective laser melting (SLM) is a common method in metal 3D printing. This technology uses a laser as a heat source and metal powder as the material. It scans the metal powder layer by layer according to the path planned in the 3D CAD slicing model. The metal powder melts and solidifies to achieve a metallurgical bonding effect, and finally obtains the metal part designed by the model. However, this technology has high environmental requirements, high manufacturing and maintenance costs, and large residual stress in the formed parts. At present, it is only widely used in the aerospace field and is difficult to promote in civilian manufacturing.

[0004] Unlike ordinary orthopedic implants, which have a uniform shape and cannot be changed, 3D printed orthopedic implants can bring patients personalized products: (1) They can simulate the trabecular structure of human bones and have better biological fixation; they can achieve product customization and are more in line with the patient's anatomical structure. (2) The 3D printing manufacturing process is short and fully automated, and can be manufactured on-site, so the manufacturing is faster and more efficient, which can reduce surgical risks and medical costs and reduce the burden on patients. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention proposes a method and apparatus for preparing lumbar fusion devices based on melt extrusion. Using single-component or multi-component metal powder and low-melting-point single-component or multi-component polymer powder as raw materials, a uniformly mixed composite metal powder material is prepared using a mixing mixer. Materials with different compositions can be prepared according to different production needs. The print head is simply heated above the melting point of the polymer powder, and then 3D printed using melt extrusion. The resulting metal blank is then degreased and sintered to finally obtain the lumbar fusion device. This method significantly reduces the manufacturing cost of lumbar fusion devices, results in low residual stress in the metal blank, and the surface texture of the lumbar fusion device is conducive to cell adhesion and growth.

[0006] The specific steps to implement the above technical solution are as follows:

[0007] S1 sets the grayscale threshold between 100 and 3500, obtains 100 to 350 CT tomographic images of the L3 to L5 lumbar vertebrae with an interslice spacing of 0.3 to 1.0 mm, imports the CT data into Mimics medical image processing software, determines the correct orientation of the images (anterior-posterior, left-right, and vertical), sets the grayscale threshold of the corresponding bone tissue to 150 to 3200, and obtains a dataset of CT tomographic images of the bone region filled with color. Using the Edit Masks tool in Mimics software, selects the Circle mode, sets its Width and Height to 1 to 5 pixels, divides the lumbar intervertebral space along the middle, and assigns half of the space to the superior and inferior articular processes of the adjacent vertebrae. Uses the Calculate 3D command to perform three-dimensional reconstruction of the lumbar CT tomographic image data to obtain a three-dimensional model of the lumbar spine. Imports the lumbar spine model into the modeling software and extracts the model of the lumbar fusion device using Boolean operation commands. Saves the lumbar fusion device model as an STL file.

[0008] S2 uses single-component or multi-component metal powder and low-melting-point single-component or multi-component polymer powder as raw materials. A uniformly mixed polymer / metal powder composite material is prepared by mixing and stirring. The polymer powder content is 10-30 wt%, and the metal powder content is 70-90 wt%. The composite material powder is poured into the material tank of the 3D printing device.

[0009] S3 imports the STL format file into the FDM 3D printer and replaces the print head of the FDM 3D printer with this 3D device. The spring heating coil is heated to above the melting point of the polymer. Then the extrusion motor and cooling fan are turned on. The molten polymer material, wrapped with metal material, is extruded through the nozzle. The 3D printing device moves along the planned path and stacks layers to form the green part of the lumbar fusion device.

[0010] S4 Place the green blank of the lumbar fusion device into the vacuum atmosphere furnace, close the furnace cover, and use a vacuum pump to extract the air from the vacuum atmosphere furnace to ensure that the gas pressure in the furnace chamber is ≤-0.05MPa. Fill with protective gas, and close the gas inlet valve when the gas pressure in the furnace reaches -0.01MPa~0MPa to prevent oxidation of the parts during the heat treatment process. Set the heating temperature of the heat treatment to 500℃~1500℃, the heating rate to 3℃ / min~10℃ / min, and the holding time to 60min~3000min. After the holding time is completed, open the furnace cover and take out the lumbar fusion device.

[0011] To implement the above method, the device includes: the extrusion motor 1 is connected to the extrusion screw 3 via a coupling 2; the extrusion motor 1 is fixed to the adapter plate 12 via a connecting rod 11 and a threaded connection; the adapter plate 12 is fixed to the effector platform 4 via a nut; a material trough 13 is installed on the adapter plate 12; an air jet pipe 10 is installed at the end of the effector platform 4; a heat dissipation bracket 5 and a material cylinder 6 are installed on the effector platform 4; a cooling fan 9 is installed on the heat dissipation bracket 5; the material cylinder 6 is installed on the effector platform 4 via the heat dissipation bracket 5; the upper part of the material cylinder 6 is provided with heat dissipation fins; the lower part is fitted with a spring heating coil 8 via clearance fit; and the bottom is fitted with a nozzle 7 via a threaded connection.

[0012] Furthermore, the distance from the three ends of the effector platform 4 to the center of the effector platform is the same, and the three ends are symmetrically distributed at 120° in pairs.

[0013] Furthermore, the cooling fan 9 blows air toward the heat sink of the material cylinder 6 to prevent the composite metal powder in the material tank 13 from melting due to the heat from the spring heating coil 8 being conducted to the upper part of the material cylinder 6.

[0014] Furthermore, one end of the jet pipe 10 is connected to compressed air, and the blown air cools and solidifies the molten material.

[0015] The polymer powder is selected from at least one of polyamide (PA), polylactic acid (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), polyurethane (TPU), and polycarbonate (PC), with an average particle size of 10 μm to 100 μm; the metal powder is selected from at least one of 316 / 316L stainless steel, cobalt-chromium alloy, and Ti6Al4V, with an average particle size of 10 μm to 100 μm.

[0016] The modeling software used is at least one of SolidWorks, Creo, Mathematics, Rhino, Materialise3-matic, and Magics, and the simulation analysis software used is at least one of ANSYS, COMSOL, ABAQUS, and Hypermesh.

[0017] The present invention has the following advantages:

[0018] (1) This invention provides an indirect metal 3D printing method and apparatus based on melt extrusion, which has less residual stress in the printed metal blank compared with SLM forming process; (3) Single or multi-component metal powder and low-melting-point single or multi-component polymer powder are used as raw materials, and there are many types of metal powder and polymer powder that can be selected; (3) The screw extrusion method provides the power for melt extrusion of composite powder materials, avoiding gear jamming in traditional extrusion methods; (4) The rough surface of the lumbar fusion device prepared by melt extrusion is conducive to the attachment and growth of bone cells. Attached Figure Description

[0019] Figure 1 This is an indirect metal 3D printing device based on melt extrusion.

[0020] 1: Extrusion motor, 2: Coupling, 3: Extrusion screw, 4: Effector platform, 5: Heat dissipation bracket, 6: Barrel, 7: Nozzle, 8: Spring heating coil, 9: Cooling fan, 10: Jet pipe, 11: Connecting rod, 12: Adapter plate, 13: Material trough. Detailed Implementation

[0021] The design schemes in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific design schemes. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Example 1

[0023] The specific steps to implement the above technical solution are as follows:

[0024] S1 sets the grayscale threshold to a lower limit of 200 and an upper limit of 3000, obtaining 300 CT tomographic images of the L3-L5 lumbar spine segments with an interslice spacing of 0.5mm. The CT data is imported into Mimics medical image processing software to determine the correct orientation of the images in terms of front-back, left-right, and up-down directions. The grayscale threshold is set to a lower limit of 300 and an upper limit of 2700, resulting in a dataset of color-filled CT tomographic images of the bone region. Using the Edit Masks tool in Mimics software, the Circle method is selected, and its Width and Height are both set to 1 pixel. The intervertebral spaces are divided along the middle, with each half of the space belonging to the superior and inferior articular processes of the adjacent vertebrae. The Calculate 3D command is used to perform three-dimensional reconstruction of the lumbar spine CT tomographic image data to obtain a three-dimensional model of the lumbar spine. The lumbar spine model is imported into the modeling software, and the lumbar fusion device model is extracted using Boolean operations. The lumbar fusion device model is saved as an STL file.

[0025] S2 prepares a uniform mixture of PA2200 powder material with a melting point of 176℃ and Ti6Al4V metal powder material using a mixer. The powder is then poured into the material tank of the 3D printing device. The content of PA2200 powder is 15wt%, the content of Ti6Al4V powder is 85wt%, the average particle size of PA2200 powder material is 48μm, and the average particle size of Ti6Al4V powder material is 30μm.

[0026] The S3 imports the STL format file into the 3D printer and replaces the print head of the FDM 3D printer with this 3D device. The heating coil is heated to 180°C, and then the extrusion motor and cooling fan are turned on. Molten PA2200 material, which encapsulates 304 stainless steel powder material, is extruded through the nozzle. The 3D printing device moves along the planned path and stacks layers to form a 304 stainless steel green part.

[0027] S4 places the Ti6Al4V lumbar fusion device blank into a vacuum atmosphere furnace, closes the furnace lid, and uses a vacuum pump to extract the air from the vacuum atmosphere furnace to ensure that the gas pressure inside the furnace is ≤-0.05MPa. Protective gas is then introduced, and the inlet valve is closed when the gas pressure inside the furnace reaches -0.01MPa to prevent oxidation of the parts during the heat treatment process. The heating temperature for heat treatment is set to 1400℃, the heating rate is 5℃ / min, and the holding time is 1200min. After the holding time is completed, the furnace lid is opened and the Ti6Al4V lumbar fusion device is removed.

[0028] The present invention has the following advantages:

[0029] (1) This invention provides an indirect metal 3D printing method and apparatus based on melt extrusion. Compared with the SLM forming process, the residual stress of the printed metal blank is small; (3) Single or multi-component metal powder and low-melting-point single or multi-component polymer powder are used as raw materials, and there are many types of metal powder and polymer powder that can be selected; (3) The screw extrusion method provides the power for melt extrusion of composite powder materials, avoiding gear jamming in the traditional extrusion method; (4) The texture structure on the surface of the lumbar fusion device prepared by melt extrusion is conducive to the attachment and growth of bone cells.

[0030] Please note to all technical personnel: Although the present invention has been described according to the specific embodiments above, the inventive concept of the present invention is not limited thereto. Any modifications that utilize the inventive concept will be included within the scope of protection of this invention.

Claims

1. A method of making a lumbar interbody fusion cage based on melt extrusion, characterized in that, Includes the following steps: S1 imports the patient's CT scan data into Mimics to model the lumbar spine data, imports the lumbar spine model into the modeling software to design the lumbar fusion device model, and then uses finite element simulation analysis software to perform biomechanical simulation on the lumbar fusion device to verify the reliability of the model. Finally, the lumbar fusion device model is saved as an STL format. S2 uses single-component or multi-component metal powder or single-component or multi-component polymer powder as raw materials, with the polymer powder content being 10~30wt% and the metal powder content being 70~90wt%, to prepare a uniformly mixed polymer / metal powder composite material, and then pours the composite material powder into the material tank of the 3D printing device. S3 imports the STL format file into the 3D printer and replaces the print head of the FDM 3D printer with this 3D printing device. The spring heating coil is heated to above the melting point of the polymer. Then the extrusion motor and cooling fan are turned on. The molten polymer material encapsulates the metal material and is extruded through the nozzle. The 3D printing device moves along the planned path and stacks layers to form the green part of the lumbar fusion device. S4 Place the green blank of the lumbar fusion device into the vacuum atmosphere furnace, close the furnace cover, use a vacuum pump to extract the air from the vacuum atmosphere furnace to ensure that the gas pressure in the furnace chamber is ≤-0.05MPa, fill with protective gas, and close the gas inlet valve when the gas pressure in the furnace reaches -0.01MPa~0MPa to prevent the parts from oxidizing during the heat treatment process. Set the heating temperature of the heat treatment to 500℃~1500℃, the heating rate to 3℃ / min~10℃ / min, and the holding time to 60min~3000min. After the holding time is completed, open the furnace cover and take out the lumbar fusion device. The apparatus used in this method comprises: an extrusion motor connected to an extrusion screw via a coupling to provide power, feeding uniformly mixed metal powder and polymer powder from a feed trough into a feed cylinder; the upper part of the feed cylinder is equipped with heat sinks, and the lower part is fixed with a spring heating coil; the feed cylinder is mounted on an effector lifting platform via a heat dissipation bracket; the spring heating coil heats and melts the plastic powder in the mixed powder in the feed cylinder, and the molten material is extruded through a nozzle; the extrusion motor is connected to an adapter plate via a connecting rod; the adapter plate is fixed to the effector lifting platform; an air jet pipe is also installed at the end of the effector lifting platform; the air blown out by the air jet pipe cools and solidifies the molten material; a cooling fan is installed on the heat dissipation bracket to blow air towards the heat sinks of the feed cylinder, preventing the heat from the spring heating coil from being conducted to the upper part of the feed cylinder, which would cause the composite metal powder in the feed trough to melt; The polymer powder is selected from at least one of polyamide (PA), polylactic acid (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), polyurethane (TPU), and polycarbonate (PC), with an average particle size of 10 μm to 100 μm; the metal powder is selected from at least one of stainless steel, aluminum alloy, copper alloy, and titanium alloy, with an average particle size of 10 μm to 100 μm.

2. A method of making a lumbar interbody fusion cage based on melt extrusion as claimed in claim 1, wherein: The modeling software used is at least one of SolidWorks, Creo, Mathematics, Rhino, Materialise 3-matic, Magics, and the simulation analysis software used is at least one of ANSYS, COMSOL, ABAQUS, Hypermesh.

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