Bionic bone implant for 4D printed porous NiTi alloy spine

Abstract

The invention discloses a bionic bone implant for a 4D printed porous NiTi alloy spine, and relates to the technical field of bionic bone implants.The bionic bone implant comprises an implant body, and the implant body is integrally formed by porous NiTi alloy containing microelements through the 4D printing technology; after the implant main body is implanted into a human body, the shape or porosity of the implant main body can be controllably changed under the stimulation of the body temperature of 35-42 DEG C, the shape recovery rate is larger than or equal to 90%, and the porosity adjusting range is + / -5%-10%. According to the bionic bone implant for the 4D printed porous NiTi alloy spine, the porosity and the aperture are regulated and controlled, and a gradient porous structure is designed in the mechanical conduction direction of the spine, so that the elastic modulus is reduced, the elastic modulus is highly matched with the mechanical property of cancellous bones of the spine of a human body, the stress shielding effect is effectively eliminated, and the risk of surrounding bone atrophy is reduced; meanwhile, the shape memory effect of the NiTi alloy can realize controllable adjustment of shape / porosity under the stimulation of body temperature, the shape memory effect is adaptive to the physiological curvature change of the post-operation spine, and the long-term stability of the implant is improved.

Description

Technical Field

[0001] This invention relates to the field of biomimetic bone implant technology, specifically a 4D-printed porous NiTi alloy biomimetic bone implant for the spine. Background Technology

[0002] In the clinical treatment of spinal degenerative diseases (such as herniated discs and spinal stenosis) and spinal trauma, bone implants are the core devices for achieving spinal stability reconstruction and functional recovery. Currently, commonly used spinal implants are mainly divided into two categories: one is traditional metal implants (such as titanium alloys and cobalt-chromium alloys), and the other is bioceramic or polymer-based composite implants. However, both types of products have significant technical defects and cannot meet the comprehensive clinical needs of "mechanical adaptation, osseointegration, and long-term stability".

[0003] While traditional metal implants possess high mechanical strength, they present two key problems: First, their elastic modulus is much higher than that of the cancellous bone of the human spine, which can easily lead to a "stress shielding effect" after surgery, causing disuse atrophy of the bone tissue around the implant and increasing the risk of implant loosening and displacement; second, their surface bioactivity is poor, resulting in low bone ingrowth efficiency, requiring long-term fixation with internal fixation devices after surgery, thus prolonging the patient's recovery period.

[0004] Meanwhile, most existing spinal implants are designed for "static fixation," which cannot adapt to the dynamic adjustment of the physiological curvature of the spine after surgery. Although some products attempt to improve bone integration capacity through porous structure optimization, the porosity and pore size design lack biomimetic adaptability and do not combine synergistic technologies such as trace element regulation and surface coating modification, resulting in slow bone ingrowth and lack of antibacterial properties. The postoperative infection rate remains at 3%-5%, which seriously affects the treatment effect.

[0005] To address these issues, the present invention provides a 4D-printed porous NiTi alloy biomimetic bone implant for the spine. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a 4D-printed porous NiTi alloy biomimetic bone implant for the spine, solving the problems mentioned in the background section.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a 4D-printed porous NiTi alloy biomimetic bone implant for the spine, comprising an implant body, wherein the implant body is integrally formed using a porous NiTi alloy containing trace elements through 4D printing technology;

[0008] After being implanted into the human body, the implant body can undergo controllable changes in shape or porosity under body temperature stimulation of 35-42℃, with a shape recovery rate of ≥90% and a porosity adjustment range of ±5%-10%, in order to adapt to the physiological curvature and mechanical environment of the spine.

[0009] The implant body has a biomimetic porous structure, and after being implanted into the human body, the implant body can undergo controllable changes in shape or porosity under external stimuli to adapt to the physiological curvature and mechanical environment of the spine.

[0010] The porous NiTi alloy contains the following trace elements: Mg 0.2%-0.5%, Sr 0.1%-0.3%, Zn 0.3%-0.6%, with the remainder being Ni and Ti, and the atomic ratio of Ni to Ti is 1-1.1.

[0011] The implant body has a bioactive coating on its surface that promotes bone ingrowth. The bioactive coating includes a base layer and a functional layer. The base layer is a dense hydroxyapatite layer formed by plasma spraying, and the functional layer is a porous hydroxyapatite layer prepared by the sol-gel method.

[0012] Preferably, the thickness of the substrate is 80-100μm, the plasma arc voltage is 60-80V, the current is 500-600A, the spraying distance is 120-150mm, and the powder feeding rate is 5-8g / min.

[0013] Preferably, the method for preparing the functional layer is as follows:

[0014] (1) Dissolve calcium nitrate, ammonium dihydrogen phosphate and antibacterial salt in a water-ethanol mixed solvent, then add citric acid and polyethylene glycol, heat to 50-60℃, and stir at a rate of 400-500r / min for 2-2.5h to form a uniform sol;

[0015] (2) The sol is coated onto the bottom surface using the dip-coating method. The coating speed is 1-1.5 mm / s, and the coating is applied 2-3 times. After each coating, the surface is dried in a forced-air drying oven at 60°C for 20-30 min.

[0016] (3) Sintering is carried out by step heating. The heating program is as follows: heating from room temperature to 200-220℃ at a rate of 5-6℃ / min, then heating to 520-550℃ at a rate of 2-3℃ / min, and holding at this temperature for 2-2.5h. After cooling to room temperature in the furnace, the functional layer is obtained.

[0017] Preferably, the functional layer has a thickness of 30-50 μm, a porosity of 15-20%, and a pore size of 2-5 μm.

[0018] Preferably, the antibacterial salt is selected from either silver nitrate or zinc nitrate, and the metal ions in the antibacterial salt react with the Ca in calcium nitrate. 2+ The molar ratio is 0.5%-5%.

[0019] Preferably, in the water-ethanol mixed solvent, the volume ratio of water to ethanol is 1:1.6-2; the polyethylene glycol is PEG-2000, and its addition amount is 4%-6% of the mass of the water-ethanol mixed solvent.

[0020] Preferably, the implant body consists of an endplate contact area, a central load-bearing area, a lateral connection area, and a bone ingrowth induction area.

[0021] Preferably, the implant body is composed of an endplate contact area, a central load-bearing area, a lateral connection area, and a bone ingrowth induction area.

[0022] Preferably, the 4D printed porous NiTi alloy has a porosity of 50%-80%, a pore size of 200-300μm, and the pores are interconnected; the phase transformation temperature range of the 4D printed porous NiTi alloy is 36-40℃.

[0023] Preferably, the porous structure of the implant body exhibits a gradient distribution along the direction of spinal mechanical conduction, with a porosity of 55%-65% near the endplate region and 65%-75% in the middle load-bearing region.

[0024] Beneficial effects

[0025] This invention provides a 4D-printed porous NiTi alloy biomimetic bone implant for the spine. Compared with existing technologies, it has the following advantages:

[0026] (1) The 4D printed porous NiTi alloy biomimetic bone implant for the spine, by controlling the porosity and pore size and designing a gradient porous structure along the direction of spinal mechanical transmission, reduces the elastic modulus and highly matches the mechanical properties of human spinal cancellous bone, effectively eliminating stress shielding effect and reducing the risk of surrounding bone atrophy; at the same time, the shape memory effect of NiTi alloy can achieve controllable adjustment of shape / porosity under body temperature stimulation, adapting to postoperative changes in the physiological curvature of the spine and improving the long-term stability of the implant.

[0027] (2) The 4D printed porous NiTi alloy biomimetic bone implant for the spine, through the addition of trace elements, Mg can activate osteoblast proliferation-related pathways and promote new bone formation; Sr can inhibit osteoclast activity, reduce bone resorption, and increase bone density around the implant; Zn can optimize the passivation film structure on the alloy surface, increase the self-corrosion potential, and significantly enhance corrosion resistance; all three can form solid solutions with Ni and Ti, without destroying the alloy crystal structure, thus taking into account both function and mechanical stability.

[0028] (3) The 4D printed porous NiTi alloy biomimetic bone implant for the spine uses plasma spraying to coat dense hydroxyapatite at the bottom layer. By precisely controlling the spraying parameters, the bonding strength between the coating and the substrate is ensured, effectively blocking the erosion of the alloy by body fluids. The functional layer is porous hydroxyapatite containing antibacterial agents, in which the antibacterial agents can be slowly released, with an antibacterial rate of ≥95% against Escherichia coli and Staphylococcus aureus, reducing the risk of postoperative infection. At the same time, the porous structure provides channels for bone cell migration and nutrient transport, accelerating the fusion of the bone-implant interface. Attached Figure Description

[0029] Figure 1 The antibacterial performance test diagram provided by the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] NiTi alloy powder: Ni powder and Ti powder with a purity of ≥99.9% are selected and mixed in an atomic ratio of 1:1. Mg powder (99.5% purity), Sr powder (99.5% purity), and Zn powder (99.9% purity) are added at the same time to make the final content of trace elements 0.2% Mg, 0.1% Sr, and 0.3% Zn. After mixing, the mixture is ball-milled to make uniform alloy powder with the powder particle size controlled at 20μm.

[0033] Preparation of the base layer (dense hydroxyapatite layer): Hydroxyapatite powder (particle size 5μm) was fed into the spray gun using an atmospheric plasma spraying equipment. The spraying parameters were set as follows: plasma arc voltage 60V, current 500A, spraying distance 120mm, powder feed rate 5g / min, and spraying gas (argon + hydrogen) flow ratio of 5:1. The implant body was fixed on a rotating worktable (speed 5r / min) for spraying. The coating thickness was controlled at 80μm. After spraying, the material was allowed to cool naturally to room temperature.

[0034] Preparation of functional layer (porous antibacterial hydroxyapatite layer):

[0035] (1) Sol preparation: Weigh calcium nitrate and ammonium dihydrogen phosphate (Ca / P=1.67) according to the stoichiometric ratio, add water-ethanol mixed solvent (water to ethanol volume ratio of 1:1.6), and then add silver nitrate (Ag) + With Ca 2+Add 0.5% molar ratio of citric acid (1:1 molar ratio with metal ions) and PEG-2000 (4% by mass of mixed solvent), heat the system to 50°C, and stir at 400 r / min for 2 h to form a uniform and transparent sol.

[0036] (2) Coating and drying: The sol was coated onto the bottom surface using the dip-lift method at a lifting speed of 1 mm / s, and the coating was applied twice. After each coating, the implant was placed in a 60℃ forced-air drying oven for 20 min to remove the solvent.

[0037] (3) Step sintering: The dried implant is placed in a muffle furnace and sintered according to the following procedure: The heating procedure is as follows: the temperature is increased from room temperature to 200℃ at a rate of 5℃ / min, and then increased to 520℃ at a rate of 2℃ / min. The temperature is held at this temperature for 2 hours and then cooled to room temperature in the furnace to obtain a functional layer with a thickness of 30μm, a porosity of 15%, and a pore size of 2μm.

[0038] Example 2

[0039] NiTi alloy powder: Ni powder and Ti powder with a purity ≥99.9% are selected and mixed at an atomic ratio of 1:1.05. Mg powder (purity 99.5%), Sr powder (purity 99.5%) and Zn powder (purity 99.9%) are added at the same time to make the final content of trace elements Mg 1.5%, Sr 0.2% and Zn 0.5%. After mixing, the powder is ball-milled to make uniform alloy powder with the particle size controlled at 35μm.

[0040] Preparation of the base layer (dense hydroxyapatite layer): Hydroxyapatite powder (particle size 10μm) was fed into the spray gun using an atmospheric plasma spraying equipment. The spraying parameters were set as follows: plasma arc voltage 70V, current 550A, spraying distance 135mm, powder feeding rate 7g / min, and spraying gas (argon + hydrogen) flow ratio of 5:1. The implant body was fixed on a rotating worktable (speed 5r / min) for spraying. The coating thickness was controlled at 90μm. After spraying, the material was allowed to cool naturally to room temperature.

[0041] Preparation of functional layer (porous antibacterial hydroxyapatite layer):

[0042] (1) Sol preparation: Weigh calcium nitrate and ammonium dihydrogen phosphate (Ca / P=1.67) according to the stoichiometric ratio, add water-ethanol mixed solvent (water to ethanol volume ratio of 1:1.8), and then add silver nitrate (Ag) + With Ca 2+Add 2.5% molar ratio of citric acid (1:1 molar ratio with metal ions) and PEG-2000 (5% of the mixed solvent mass), heat the system to 55°C, and stir at 450 r / min for 2.2 h to form a uniform and transparent sol.

[0043] (2) Coating and drying: The sol was coated onto the bottom surface using the dip-coating method at a lifting speed of 1.2 mm / s, and a total of 3 coatings were applied. After each coating, the implant was placed in a 60℃ forced-air drying oven for 25 min to remove the solvent.

[0044] (3) Step sintering: The dried implant is placed in a muffle furnace and sintered according to the following procedure: The heating procedure is as follows: the temperature is increased from room temperature to 210℃ at a rate of 5.5℃ / min, and then increased to 530℃ at a rate of 2.5℃ / min. The temperature is held at this temperature for 2.2h, and then cooled to room temperature in the furnace to obtain a functional layer with a thickness of 40μm, a porosity of 18%, and a pore size of 3μm.

[0045] Example 3

[0046] NiTi alloy powder: Ni powder and Ti powder with a purity of ≥99.9% are selected and mixed at an atomic ratio of 1:1.1. At the same time, Mg powder (purity 99.5%), Sr powder (purity 99.5%) and Zn powder (purity 99.9%) are added to make the final content of trace elements 0.5% Mg, 0.3% Sr and 0.6% Zn. After mixing, the powder is ball-milled to make uniform alloy powder with the particle size controlled at 50μm.

[0047] Preparation of the base layer (dense hydroxyapatite layer): Hydroxyapatite powder (particle size 20μm) was fed into the spray gun using an atmospheric plasma spraying equipment. The spraying parameters were set as follows: plasma arc voltage 80V, current 600A, spraying distance 150mm, powder feed rate 8g / min, and spraying gas (argon + hydrogen) flow ratio of 5:1. The implant body was fixed on a rotating worktable (speed 5r / min) for spraying. The coating thickness was controlled at 100μm. After spraying, the material was allowed to cool naturally to room temperature.

[0048] Preparation of functional layer (porous antibacterial hydroxyapatite layer):

[0049] (1) Sol preparation: Weigh calcium nitrate and ammonium dihydrogen phosphate (Ca / P=1.67) according to the stoichiometric ratio, add water-ethanol mixed solvent (volume ratio of water to ethanol is 1:2), and then add zinc nitrate (Zn 2+ With Ca 2+Add 5% molar ratio of PEG-2000 (6% by mass of mixed solvent) and stir until completely dissolved; then add citric acid (1:1 molar ratio with metal ions) and PEG-2000 (6% by mass of mixed solvent), heat the system to 60°C, and stir at 500 r / min for 2.5 h to form a uniform and transparent sol.

[0050] (2) Coating and drying: The sol was coated onto the bottom surface using the dip-lift method at a lifting speed of 1.5 mm / s, and a total of 3 coatings were applied. After each coating, the implant was placed in a 60℃ forced-air drying oven for 20-30 min to remove the solvent.

[0051] (3) Step sintering: The dried implant is placed in a muffle furnace and sintered according to the following procedure: The heating procedure is as follows: the temperature is increased from room temperature to 220℃ at a rate of 6℃ / min, and then increased to 550℃ at a rate of 3℃ / min. The temperature is held at this temperature for 2.5h, and then cooled to room temperature in the furnace to obtain a functional layer with a thickness of 50μm, a porosity of 20%, and a pore size of 5μm.

[0052] The implant body is 4D printed:

[0053] Selective Laser Melting (SLM) 4D printer was used, with the following printing parameters: laser power 250W, scanning speed 1000mm / s, layer thickness 30μm, scanning spacing 0.15mm, and inert gas (argon) purity in the forming chamber ≥99.99%.

[0054] Based on the patient's spinal CT data, an implant model was designed using 3D modeling software. The model included the endplate contact area (porosity 55-65%, pore size 200-300μm), the central load-bearing area (porosity 65-75%, pore size 300-400μm), the lateral connection area (local densification, porosity 50%), and the bone ingrowth induction area (pore size 200μm). The model was imported into a printer, alloy powder was added, and printing was performed according to the set parameters. After molding, the model was cooled to room temperature in the furnace, and the supporting structure was removed to obtain the main body blank of the implant.

[0055] In Example 1, the porosity of the contact area of ​​the end plate is 55% and the pore size is 200 μm, while the porosity of the central load-bearing area is 65% and the pore size is 300 μm; in Example 2, the porosity of the contact area of ​​the end plate is 60% and the pore size is 250 μm, while the porosity of the central load-bearing area is 70% and the pore size is 350 μm; in Example 3, the porosity of the contact area of ​​the end plate is 65% and the pore size is 300 μm, while the porosity of the central load-bearing area is 75% and the pore size is 400 μm.

[0056] Subsequent processing: The blank is placed in a vacuum heat treatment furnace and kept at 600℃ for 1.5h to eliminate the internal stress of printing. Then, the surface of the contact area of ​​the end plate is finely polished (roughness Ra≤0.8μm) to ensure the fit with the cone end plate.

[0057] like Figure 1 As shown, a small number of bacteria adhered to the sample surface, but it can be observed that the bacterial structure has shrunk and deformed. The remaining bacteria have been severely shrunk and deformed, and their cell wall structure has been destroyed. Many cytoplasm particles were observed around the bacteria, indicating that the bacterial cell membrane has been severely ruptured and dissolved.

[0058] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A 4D-printed porous NiTi alloy biomimetic bone implant for the spine, characterized in that: Includes the implant body, which is integrally formed using a porous NiTi alloy containing trace elements through 4D printing technology; After being implanted into the human body, the implant body can undergo controllable changes in shape or porosity under body temperature stimulation of 35-42℃, with a shape recovery rate of ≥90% and a porosity adjustment range of ±5%-10%, in order to adapt to the physiological curvature and mechanical environment of the spine. The implant body has a biomimetic porous structure, and after being implanted into the human body, the implant body can undergo controllable changes in shape or porosity under external stimuli to adapt to the physiological curvature and mechanical environment of the spine. The porous NiTi alloy contains the following trace elements: Mg 0.2%-0.5%, Sr 0.1%-0.3%, Zn 0.3%-0.6%, with the remainder being Ni and Ti, and the atomic ratio of Ni to Ti is 1-1.

1. The implant body has a bioactive coating on its surface that promotes bone ingrowth. The bioactive coating includes a base layer and a functional layer. The base layer is a dense hydroxyapatite layer formed by plasma spraying, and the functional layer is a porous hydroxyapatite layer prepared by the sol-gel method.

2. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 1, characterized in that: The thickness of the substrate is 80-100μm, the plasma arc voltage is 60-80V, the current is 500-600A, the spraying distance is 120-150mm, and the powder feeding rate is 5-8g / min.

3. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 1, characterized in that: The method for preparing the functional layer is as follows: (1) Dissolve calcium nitrate, ammonium dihydrogen phosphate and antibacterial salt in a water-ethanol mixed solvent, then add citric acid and polyethylene glycol, heat to 50-60℃, and stir at a rate of 400-500r / min for 2-2.5h to form a uniform sol; (2) The sol is coated onto the bottom surface using the dip-coating method. The coating speed is 1-1.5 mm / s, and the coating is applied 2-3 times. After each coating, the surface is dried in a forced-air drying oven at 60°C for 20-30 min. (3) Sintering is carried out by step heating. The heating program is as follows: heating from room temperature to 200-220℃ at a rate of 5-6℃ / min, then heating to 520-550℃ at a rate of 2-3℃ / min, and holding at this temperature for 2-2.5h. After cooling to room temperature in the furnace, the functional layer is obtained.

4. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 1, characterized in that: The functional layer has a thickness of 30-50 μm, a porosity of 15-20%, and a pore size of 2-5 μm.

5. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 3, characterized in that: The antibacterial salt is selected from either silver nitrate or zinc nitrate, and the metal ions in the antibacterial salt react with the Ca in calcium nitrate. 2+ The molar ratio is 0.5%-5%.

6. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 3, characterized in that: In the water-ethanol mixed solvent, the volume ratio of water to ethanol is 1:1.6-2; the polyethylene glycol is PEG-2000, and its addition amount is 4%-6% of the mass of the water-ethanol mixed solvent.

7. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 1, characterized in that: The implant consists of an endplate contact area, a central weight-bearing area, a lateral connection area, and a bone ingrowth induction area.

8. The 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 1, characterized in that: The 4D printed porous NiTi alloy has a porosity of 50%-80%, a pore size of 200-300μm, and the pores are interconnected; the phase transformation temperature range of the 4D printed porous NiTi alloy is 36-40℃.

9. A 4D-printed porous NiTi alloy biomimetic bone implant for the spine according to claim 8, characterized in that: The porous structure of the implant body exhibits a gradient distribution along the direction of spinal mechanical conduction, with a porosity of 55%-65% near the endplate and 65%-75% in the middle load-bearing area.

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