3D printing degradable interbody fusion cage

Abstract

The utility model discloses a 3D printing degradable interbody fusion cage which is made of polycaprolactone (PCL) and hydroxyapatite (HA) composite materials, is prepared through a melt differential 3D printing technology and has good degradability, mechanical supporting performance and biocompatibility. The cross section of the appearance is in a horseshoe shape, the interior is of a porous grid structure, the porosity is 48%, the aperture ranges from 450 micrometers to 490 micrometers, the compressive strength is 4.74 MPa, a natural bone microstructure is simulated, and stable support can be provided for the intervertebral space of the human body. The microscopic porous structure is beneficial to adhesion and proliferation of bone cells, and a suitable environment is provided for cell growth and bone tissue reconstruction. Two-dimensional regulation and control of the porous structure are achieved through two-parameter regulation of a printing process, the problems that an existing product does not have osteogenic activity, cannot be absorbed, is not matched in biomechanics and the like are solved, and important application value is achieved for solving spinal degenerative diseases. Theoretical and technical support is provided for research, development, design and clinical application of the novel spine interbody fusion cage.

Description

Technical Field

[0001] The utility model relates to the technical field of bone implant instruments, and in particular to a 3D printed degradable intervertebral fusion device and a preparation method thereof. Background Art

[0002] Spinal interbody fusion, the gold standard surgical procedure for treating lumbar and cervical spine disorders, focuses on restoring intervertebral disc height and physiological curvature, achieving stable fusion of the upper and lower vertebrae. However, conventional interbody fusion cages are often made of non-degradable materials, becoming permanent foreign bodies after implantation and posing the risk of long-term complications. Therefore, the development of a biodegradable and biocompatible interbody fusion cage is a pressing need in the orthopedics field.

[0003] In the field of materials science, polycaprolactone (PCL), a polymer material with excellent biocompatibility, degradation properties, and mechanical properties, has been widely used in bone tissue repair. However, single PCL materials have limitations in terms of mechanical strength and osteoinductivity. To overcome these shortcomings, researchers have attempted to fill PCL with bioactive particles such as β-calcium phosphate (β-TCP) and hydroxyapatite (HA) to enhance its bioactivity and mechanical properties.

[0004] In the field of medical engineering, 3D printing technology, with its digitalization, accuracy, and controllability, provides strong technical support for the manufacture of personalized implants. Through 3D printing, the pore size, shape, porosity, and interpore connectivity of intervertebral fusion cages can be precisely controlled, simulating the microstructure of natural bone and providing a suitable growth environment for cell growth and proliferation and bone tissue reconstruction. Furthermore, combined with individual 3D CT data, 3D printing technology can also enable personalized customization of intervertebral fusion cages, ensuring a precise match with the upper and lower endplates to meet personalized clinical needs.

[0005] While extensive research has been conducted on orthopedic implants and 3D printing technology, the availability of 3D-printed biodegradable intervertebral fusion devices remains insufficient. Therefore, this utility model utilizes melt differential 3D printing technology to fabricate a porous, biodegradable spinal intervertebral fusion device based on the biodegradable PCL material and the osteoinductive and mechanically enhanced HA filler. This device not only contributes to the development and design of novel spinal intervertebral fusion devices but also provides theoretical and technical support for their widespread clinical application. Utility Model Content

[0006] The purpose of the utility model is to overcome the problems of existing intervertebral fusion cages such as lack of osteogenic activity, non-absorbability, and biomechanical mismatch, and to provide a 3D printed degradable intervertebral fusion cage and a preparation method thereof.

[0007] For degradable intervertebral fusion devices that can be gradually absorbed and replaced in the body, the material formulation system is the decisive factor. The utility model uses PCL as the base material and fills HA to produce PCL / HA organic-inorganic composite material particles. The porous intervertebral fusion device made of this raw material has good mechanical support and biodegradability to meet the growth, proliferation and diffusion of bone cells. The bone tissue scaffold must have a high porosity, and the pores of the scaffold must be guaranteed to be interconnected to maintain its functionality. Therefore, the utility model uses the printing filament of the melt differential 3D printer to simulate bone trabeculae and control the filament spacing to form a pore structure. A filling rate of 40-60% is set to ensure the horizontal scale aperture of the fusion device, and the printing routing direction is 0° and 45°-90°. After printing 2-4 layers at the same filling angle, the wire bundle filling angle is changed once to ensure the vertical scale aperture, and finally realize the printing and forming of a porous intervertebral fusion device with internal penetration characteristics.

[0008] The porous grid structure inside the fusion device is composed of multiple layers of cross beams stacked crosswise with each other. It has a microscopic porous structure that can effectively solve the problem of bone tissue repair and promote spinal fusion.

[0009] In order to achieve the above-mentioned objectives, the present invention provides the following technical solutions: a 3D-printed degradable intervertebral fusion device, which has a horseshoe-shaped appearance, including an outer single-layer shell and an inner porous grid structure, wherein the outer single-layer shell has a dense and non-porous surface and surrounds the side of the fusion device; the upper and lower end plates of the fusion device have no shell and are in a porous mesh shape; the inner porous grid structure is composed of multiple layers of cross-beams stacked on each other, wherein the single-layer cross-beams are parallel to each other, and the upper and lower layers of cross-beams are staggered with each other, and the wire bundle staggering angle between the two layers of cross-beams is 45°-90°, and a single cross-beam is composed of multiple printing filaments stacked on the longitudinal scale; the outer single-layer shell and the inner porous grid structure are tightly connected and cannot be disassembled, and are printed and formed in one piece by melt differential 3D printing technology.

[0010] The utility model discloses a 3D printed biodegradable intervertebral fusion device, the cross-sectional profile of which is a horseshoe shape, the front edge of which is a circular arc with a radius of 12 mm, and the four corners of which are all circular arcs with a radius of 2 mm for rounded corner transition.

[0011] The utility model provides a 3D printed degradable intervertebral fusion device, wherein the hole shape of the internal porous grid structure is a rectangle or a parallelogram.

[0012] The utility model provides a 3D printed degradable intervertebral fusion device, wherein the porosity of the internal porous grid structure is 48.31%-60.01%, and the pore diameter is between 450-900 μm.

[0013] The utility model provides a 3D printed degradable intervertebral fusion device, wherein the crossbeam is formed by stacking 2-4 printing filaments.

[0014] The utility model provides a 3D printed degradable intervertebral fusion device, wherein the compressive strength of the intervertebral fusion device is 2.95-4.74 MPa, and the diameter of the printing filament is 0.49-0.53 mm.

[0015] The preparation method of the 3D printed degradable intervertebral fusion cage of the utility model is as follows:

[0016] Step 1: PCL particles and HA powder are premixed and granulated using a twin-screw extruder. After melt extrusion, cooling, and pelletization, 3mm PCL / HA composite material particles are produced for the preparation of biodegradable spinal intervertebral fusion devices.

[0017] Step 2: Construct the surface contours of the upper and lower end plates of the spinal cone with reference to the structure of the sixth vertebra in the cervical spine, design the cross-sectional profile of the intervertebral fusion cage, and use SolidWorks to build an intervertebral fusion cage model.

[0018] Step 3: Load the PCL / HA composite material particles prepared in step 1 into the melt differential 3D printer, and use Simplify 3D to plan the printing path and set the printing process according to the fusion device model in step 2. The lateral scale aperture size is controlled by changing the filling rate, and the longitudinal scale aperture size is controlled by changing the wire bundle staggered angle and the number of stacking layers. Then, the fusion device is printed and formed.

[0019] Step 4: Post-process the prepared fusion device, such as cleaning, drying and sterilization, to meet clinical application requirements.

[0020] The printing process is as follows: set the fill rate to 40-60%; the nozzle diameter is 0.5mm; the wire harness is staggered in the 0°, 45°-90° directions; the wire harness fill angle is changed every 2-4 layers; the printing temperature is 90℃, the printing layer height is 0.32mm, and the printing speed is 3.5mm / s.

[0021] The beneficial effects of the 3D-printed degradable intervertebral fusion device of the present invention are as follows: the porous degradable intervertebral fusion device is made of PCL / HA composite material, which can provide stable mechanical support to the intervertebral space of the human spine. In the 0-28 day artificial simulated body fluid (SBF) in vitro degradation experiment, the compressive strength of the intervertebral fusion device was maintained at 2.95-4.47MPa, which is higher than the minimum compressive strength requirement of human cancellous bone. During the degradation process, the fusion device can still maintain the integrity of its appearance structure, while obvious corrosion phenomena such as pits and gullies appear on the surface. This is because the degradation of PCL exposes the HA particles in the composite material, causing the surface of the fusion device to become rough, which is more conducive to cell adhesion and inducing osteogenesis.

[0022] This innovative 3D-printed biodegradable intervertebral fusion device boasts excellent biodegradability and biocompatibility, allowing it to be gradually absorbed and replaced after implantation, avoiding the long-term complications associated with traditional non-degradable materials. As the device degrades, new bone tissue gradually fills and replaces the original implant, achieving bone reconstruction and fusion.

[0023] The porous mesh structure within this 3D-printed biodegradable intervertebral fusion cage increases the cage's surface area, providing a larger contact surface for bone cell attachment and proliferation. During bone tissue reconstruction, adequate nutrient supply is crucial for cell growth and differentiation. The interconnected pores also facilitate the delivery of nutrients and the removal of metabolic waste, maintaining healthy bone tissue.

[0024] In summary, the 3D printed porous degradable intervertebral fusion device provided by the present invention has good degradability, biocompatibility and mechanical support. These advantages make the present invention an effective treatment option in spinal fusion surgery, promote the research and development and design of new spinal intervertebral fusion devices, and have important application value in solving spinal degenerative diseases.

[0025] The utility model realizes dual-dimensional control of the porous structure through dual-parameter adjustment of the printing process, overcoming the problems of existing products such as lack of osteogenic activity, non-absorbability, and biomechanical mismatch. It has important application value in solving spinal degenerative diseases and provides theoretical and technical support for the research and development, design and clinical application of new spinal intervertebral fusion devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of a 3D printed degradable intervertebral fusion device of the utility model;

[0027] Figure 2 This is a schematic diagram of the stacking of cross beams in a porous grid structure inside a 3D-printed biodegradable intervertebral fusion device of the present invention. DETAILED DESCRIPTION

[0028] The utility model provides a 3D printed degradable intervertebral fusion device and a preparation method thereof, such as Figure 1-2As shown, a 3D-printed biodegradable intervertebral fusion device has a horseshoe-shaped appearance and comprises an outer single-layer shell 1 and an inner porous mesh structure 2. The outer single-layer shell 1 has a dense, non-porous surface and surrounds the side of the device. The upper and lower endplates of the device are shell-free and have a porous mesh structure. The device is printed using HAwt% 25 / PCL composite particles loaded into a melt differential 3D printer. A fill rate of 60% is set to control the horizontal pore size. A 0.5mm nozzle is used, with staggered fill beams at 0° and 90°. The fill beam angle is changed every two layers to control the vertical pore size. The printing temperature is 90°C, the layer height is 0.32mm, and the printing speed is 3.5mm / s. After printing, the intervertebral fusion device is obtained.

[0029] The appearance structure and morphology of the printed intervertebral fusion device were analyzed. The results showed that the pore size of the fusion device in both horizontal and vertical dimensions was basically consistent, with a square hole of 450-490μm, which can ensure isotropy in the bone growth environment and is suitable for spinal fusion environment. The actual porosity was calculated to be 48.31%, which can not only ensure the mechanical properties and stability of the fusion device, but also take into account the cell permeability, which is conducive to cell colonization, growth and the formation of new tissue. In the 0-28 day in vitro degradation experiment, the fusion device was able to maintain the integrity of its appearance structure, and obvious corrosion phenomena such as pits and grooves appeared on the surface, which is conducive to cell adhesion and induction of osteogenesis. The quasi-static axial compression test of the printed samples showed that the compressive strength of the intervertebral fusion device was maintained at 2.95-4.47MPa, which is higher than the minimum compressive strength requirement of human cancellous bone, indicating that it can provide relatively stable support during spinal fusion.

Claims

1. A 3D printed biodegradable intervertebral fusion cage, characterized by: Its appearance is horseshoe-shaped, including an outer single-layer shell and an inner porous grid structure. The outer single-layer shell has a dense and non-porous surface and surrounds the side of the fusion device; the upper and lower end plates of the fusion device have no shell and are porous mesh; the inner porous grid structure is composed of multiple layers of crossbeams stacked on each other, wherein the single-layer beams are parallel to each other, and the upper and lower layers of beams are staggered with each other, and the wire bundle stagger angle between the two layers of beams is 45°-90°. A single beam is composed of multiple printing filaments stacked on the longitudinal scale; the outer single-layer shell and the inner porous grid structure are tightly connected and cannot be disassembled, and are printed in one piece using melt differential 3D printing technology.

2. The 3D printed biodegradable intervertebral fusion cage according to claim 1, characterized in that: The cross-sectional profile is horseshoe-shaped, the leading edge is an arc with a radius of 12 mm, and the four corners are all rounded with arcs with a radius of 2 mm.

3. The 3D printed biodegradable intervertebral fusion cage according to claim 1, characterized in that: The pore shape of the internal porous grid structure is rectangular or parallelogram, the porosity of the internal porous grid structure is 48.31%-60.01%, and the pore diameter is between 450-900 μm.

4. The 3D printed biodegradable intervertebral fusion cage according to claim 3, characterized in that: The crossbeam is formed by stacking 2-4 printing filaments.

5. The 3D printed biodegradable intervertebral fusion cage according to claim 1, characterized in that: The compressive strength is 2.95-4.74MPa, and the diameter of the printing filament is 0.49-0.53mm.

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