A degradable ZnMgCa medium-entropy alloy for intervertebral fusion cage and a preparation method thereof

Abstract

The application relates to a degradable ZnMgCa medium-entropy alloy for an intervertebral fusion cage and a preparation method, the degradable ZnMgCa medium-entropy alloy comprises: 84at.%<=Zn<=91at.%, 4at.%<=Mg<=11at.%, Ca5at.%, and the preparation method of the ZnMgCa medium-entropy alloy comprises the following steps: vacuum smelting and rotary injection refining of raw materials; then, ultrasonic treatment is conducted on the melt; then, the melt is injected into a mold with a shape-following cooling water channel to be precisely die-cast into a shape; finally, the die-cast piece is solid-solution quenched and aged, and an intervertebral fusion cage is obtained. Through the melt ultrasonic treatment, the combination of the precise die-casting and the heat treatment, the melt and the organization are effectively refined, the material uniformity and the brittleness are improved, the hardness of the obtained product reaches 250-350HV, and the product has excellent mechanical properties, a controllable degradation rate and good bone integration potential.

Description

Technical Field

[0001] This invention relates to the field of medical materials technology, and in particular to a biodegradable ZnMgCa medium-entropy alloy with a specific composition range, a near-net-shape die casting and heat treatment method including melt ultrasonic external field treatment, and an interbody fusion implant made therefrom. Background Technology

[0002] Biodegradable metal implants for medical use represent a significant development direction in the field of orthopedic materials. Zinc is considered a highly promising matrix material. In recent years, the concept of multi-principal alloy design, particularly medium-entropy alloys, has provided new avenues for improving material performance. Medium-entropy alloys typically consist of 2 to 4 elements, possessing high mixed configuration entropy, which promotes the formation of simple solid solution phases and generates a slow diffusion effect, potentially leading to more uniform and stable microstructures and better overall performance. Based on this, the ZnMgCa medium-entropy alloy system, constructed by adding essential nutrients such as magnesium and calcium to the zinc matrix, theoretically possesses excellent degradation characteristics, mechanical properties, and bioactivity potential, making it particularly suitable for load-bearing bone repair applications such as interbody fusion devices.

[0003] However, translating this forward-looking material design into a reliable product for clinical application still faces significant challenges in preparation and forming processes. First, existing preparation methods cannot fully leverage the theoretical advantages of medium-entropy alloys. For systems containing reactive elements such as magnesium and calcium, traditional casting methods are prone to problems such as element burn-off, oxidation inclusions, and coarse as-cast structures, which impair the purity and uniformity of the material. While powder metallurgy can achieve alloying to some extent, its process is complex, costly, and difficult to directly manufacture devices with complex three-dimensional structures.

[0004] On the other hand, bottlenecks exist in precision forming and microstructure control. Even if alloy blanks are obtained through the aforementioned methods, to fabricate intervertebral fusion devices with complex cavities, porous structures, and fine surfaces, traditional machining methods will cut off metal flow lines and introduce damage. Conventional die casting processes, on the other hand, lack sufficient control over melt purity and uniformity, making it difficult to eliminate micron-level inclusions and compositional segregation. These microscopic defects originating from the preparation process will become fatal weaknesses affecting the fatigue strength, corrosion resistance uniformity, and long-term service reliability of implants, severely restricting the realization of high-performance medium-entropy alloy implants. Summary of the Invention

[0005] The technical problem to be solved by this invention is: in order to overcome the shortcomings of the prior art, this invention provides a biodegradable ZnMgCa medium-entropy alloy for interbody fusion devices and a preparation method thereof, in order to ensure the purity and uniformity of the material from the source and realize the direct precision manufacturing of complex structures, thereby transforming the excellent theoretical performance potential of medium-entropy alloys into practical and reliable performance advantages of implants.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a biodegradable ZnMgCa medium-entropy alloy for intervertebral fusion devices, wherein the biodegradable ZnMgCa medium-entropy alloy comprises: 84at.%≤Zn≤91at.%, 4at.%≤Mg≤11at.%, and Ca5at.%.

[0007] A method for preparing a biodegradable ZnMgCa medium-entropy alloy for interbody fusion devices, comprising the following steps: (1) Vacuum melting and refining: The raw materials are melted under a protective atmosphere and then refined by rotary jetting. (2) Ultrasonic treatment of melt: Apply ultrasonic treatment to the refined melt; (3) Precision die casting: The ultrasonically treated melt is transferred to a die casting machine and injected into a preheated mold cavity to form a fusion die casting. Under the set die casting pressure and holding time, the fusion die casting is obtained. (4) Multi-stage heat treatment: The die castings are subjected to solution treatment and aging treatment in sequence.

[0008] Preferably, the melting in step (1) is carried out under an argon protective atmosphere, the melting temperature is 600-650°C, and the refining is carried out by spraying the melt with high-purity argon through a rotating nozzle for 5-15 minutes, followed by standing for 3-10 minutes.

[0009] Preferably, in step (2), the parameters of the ultrasonic treatment are: ultrasonic power density of 100-500 W / cm², frequency of 15-25 kHz, and treatment time of 30-180 seconds.

[0010] Furthermore, the ultrasonic probe is inserted into the melt to a depth of 1 / 3 to 1 / 2 of the melt depth.

[0011] Preferably, in step (3), the preheating temperature of the mold cavity is 200-300°C, and the mold is provided with conformal cooling water channels manufactured by 3D printing; the die casting pressure is 60-110 MPa, and the holding time is 10-20 seconds.

[0012] Preferably, in step (4), the solution treatment is performed by water quenching after holding at 320-380°C for 2-6 hours; the aging treatment is performed by holding at 120-180°C for 8-24 hours.

[0013] This invention provides an application of the biodegradable ZnMgCa medium-entropy alloy prepared according to the above-described method for preparing ZnMgCa medium-entropy alloy, which is used in the fabrication of an intervertebral fusion device.

[0014] The beneficial effects of this invention are: (1) The biodegradable ZnMgCa medium entropy alloy provided by the present invention contains alloying elements Mg and Ca. Mg can produce significant solid solution strengthening and grain refinement effects, thereby improving the strength, hardness and creep resistance of the alloy. The Ca content is 5 at.%, which plays a role in refining the structure and inhibiting excessive grain growth. The two work together to significantly improve the comprehensive mechanical properties of the alloy matrix.

[0015] (2) The biodegradable ZnMgCa medium-entropy alloy provided by this invention improves upon the shortcomings of traditional biodegradable zinc alloys, such as insufficient strength, poor wear resistance, and poor corrosion resistance. Its Vickers hardness can reach 250-350 HV, which is a significant improvement. At the same time, it also has excellent wear resistance and significantly improved corrosion resistance. The prepared ZnMgCa medium-entropy alloy intervertebral fusion device has excellent performance and meets the key requirements of high mechanical strength, long-term wear resistance, and uniform degradation for implants in load-bearing areas.

[0016] (3) The method for preparing biodegradable ZnMgCa medium-entropy alloy for use in intervertebral fusion devices provided by the present invention integrates vacuum melting and rotary blowing refining, especially the innovative introduction of ultrasonic external field treatment of melt, precision die casting based on conformal cooling mold and multi-stage aging heat treatment process, so that the alloy composition is uniform and pure, the as-cast structure is dense and refined, and the material hardness, wear resistance and corrosion resistance are successfully controlled to the optimal matching state. Moreover, the process flow of this method is coherent and suitable for industrial production.

[0017] (4) More importantly, the above-mentioned ultrasonic treatment of the melt can effectively break up the primary grains in the melt, homogenize the alloy composition, and promote the flotation of impurities through cavitation and acoustic flow effects, thereby achieving the purification, refinement, and homogenization of the melt. This key innovation provides a fundamental guarantee for obtaining a highly dense and uniform microstructure from the source, which is not available in traditional die casting or existing powder metallurgy processes, thus significantly improving the mechanical reliability and degradation uniformity of the final product. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a morphology diagram of the ZnMgCa medium-entropy alloy prepared in Example 1 of the present invention.

[0020] Figure 2 The image shows the morphology of the ZnMgCa medium-entropy alloy prepared in Example 2 of this invention.

[0021] Figure 3 This is a morphology diagram of the ZnMgCa medium-entropy alloy prepared in Example 3 of the present invention.

[0022] Figure 4This is a comparison chart of the average Vickers hardness values ​​of the ZnMgCa medium-entropy alloys prepared in Examples 1, 2, and 3 of this invention.

[0023] Figure 5 The graph shows a comparison of the friction coefficient-time curves of the ZnMgCa medium-entropy alloys prepared in Examples 1, 2, and 3 of this invention.

[0024] Figure 6 The image shows a comparison of the electrochemical polarization curves of the ZnMgCa medium-entropy alloys prepared in Examples 1, 2, and 3 of this invention.

[0025] Figure 7 The above are comparative electrochemical impedance spectra of the ZnMgCa medium-entropy alloys prepared in Examples 1, 2, and 3 of this invention. Detailed Implementation

[0026] The invention will now be described in further detail with reference to the accompanying drawings.

[0027] A biodegradable ZnMgCa medium-entropy alloy for use in interbody fusion devices, the biodegradable ZnMgCa medium-entropy alloy comprising 84 at.% ≤ Zn ≤ 91 at.%, 4 at.% ≤ Mg ≤ 11 at.%, and 5 at.% Ca.

[0028] A method for preparing a biodegradable ZnMgCa medium-entropy alloy for interbody fusion devices includes the following steps: (1) Vacuum melting and refining: The raw materials are melted under a protective atmosphere and the melt is refined by a high-purity argon rotary blowing process. The melting temperature is preferably 600-650℃. The refining process involves blowing the melt with high-purity argon through a rotary nozzle for 5-15 minutes and then letting it stand for 3-10 minutes after blowing.

[0029] (2) Ultrasonic treatment of melt: Ultrasonic treatment is applied to the refined melt; the preferred parameters for ultrasonic treatment are: ultrasonic power density of 100-500 W / cm², ultrasonic frequency of 15-25 kHz, and ultrasonic treatment time of 30-180 seconds; the ultrasonic treatment is carried out under argon protection, and the depth of the ultrasonic probe inserted into the melt is 1 / 3 to 1 / 2 of the depth of the melt.

[0030] (3) Precision die casting: The ultrasonically treated melt is transferred to a die casting machine and injected into a preheated mold cavity to form a fusion die casting part under the set die casting pressure and holding time; wherein the preheating temperature of the mold cavity is 200-300℃, and the mold is equipped with conformal cooling water channels manufactured by 3D printing; the die casting pressure is 60-110MPa, and the holding time is 10-20 seconds.

[0031] (4) Multi-stage heat treatment: The die castings are subjected to solution treatment and aging treatment in sequence. The solution treatment is: water quenching after holding at 320-380℃ for 2-6 hours; the aging treatment is: holding at 120-180℃ for 8-24 hours to improve the microstructure of the die castings and enhance their comprehensive mechanical properties.

[0032] The technical effects achievable by the present invention will be further illustrated below with reference to specific embodiments. However, the selected embodiments are for illustrative purposes only and do not limit the scope of the invention.

[0033] Unless otherwise specified, all percentage contents used in the following examples are atomic percentage contents. The raw materials used are pure zinc (99.99 wt.%), pure magnesium (99.99 wt.%), and pure calcium (99.99 wt.%). Example

[0034] A type of Zn 84 Mg 11 The preparation method of Ca5 medium entropy alloy specifically includes the following steps: Weigh the high-purity raw materials according to the atomic ratio Zn:Mg:Ca = 84:11:5, place the raw materials in a vacuum induction melting furnace, and evacuate to 5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced to a positive pressure of 0.05 MPa, and the mixture is heated to 600℃ to completely melt the raw material and held at that temperature for 10 minutes. Subsequently, a rotary jetting device is used to refine the melt by introducing high-purity argon gas at a flow rate of 0.8 L / min, with a nozzle speed of 400 rpm for 12 minutes. After refining, the melt is allowed to stand for 8 minutes, and surface scum is skimmed off. Next, the refined melt undergoes ultrasonic treatment: an ultrasonic probe (frequency 20 kHz) is inserted into the melt to half its depth under argon protection, and the ultrasonic probe is applied at a power density of 350 W / cm². The ultrasonically treated melt was then rapidly transferred to a die-casting machine barrel preheated to 220°C. Using a mold with an integrated selective laser melting technology-based conformal cooling water channel, the melt was held at 70 MPa for 12 seconds to obtain the intervertebral fusion device die-casting part. The die-cast part was then placed in an argon protective atmosphere and solution-treated at 340°C for 5 hours, followed by water quenching, and then aging at 130°C for 10 hours. After air cooling, the heat-treated sample was used to prepare a metallographic specimen, the microstructure of which is shown below. Figure 1 As shown. Example

[0035] A type of Zn 87 The preparation method of Mg8Ca5 medium entropy alloy specifically includes the following steps: The raw materials were weighed according to the atomic ratio Zn:Mg:Ca = 87:8:5. The smelting and refining steps were the same as in Example 1, except that the smelting temperature was adjusted to 620℃, the argon rotary jet refining time was adjusted to 10 minutes, and the settling time was adjusted to 5 minutes; the ultrasonic treatment parameters were adjusted to: power density 300W / cm², treatment time 75 seconds; in the precision die casting step, the mold preheating temperature was adjusted to 240℃, the die casting pressure was adjusted to 85MPa, and the holding time was adjusted to 15 seconds. The heat treatment step was adjusted to: solution treatment at 330℃ for 4 hours followed by water quenching, then aging treatment at 150℃ for 24 hours followed by air cooling. The microstructure morphology is as follows. Figure 2 As shown, the tissue is dense and uniform. Example

[0036] A type of Zn 91 The preparation method of Mg4Ca5 medium entropy alloy specifically includes the following steps: The raw materials were weighed according to the atomic ratio Zn:Mg:Ca = 91:4:5. The smelting and refining steps were the same as in Example 1, except that the smelting temperature was adjusted to 640℃, the argon rotary spray refining time was adjusted to 8 minutes, and the settling time was adjusted to 5 minutes. The ultrasonic treatment parameters were adjusted to: power density 250W / cm², treatment time 60 seconds. In the precision die casting step, the mold preheating temperature was adjusted to 260℃, the die casting pressure was adjusted to 100MPa, and the holding time was adjusted to 20 seconds. The heat treatment step was adjusted to: solution treatment at 350℃ for 3 hours followed by water quenching, then aging treatment at 170℃ for 16 hours followed by air cooling. Its microstructure is as follows. Figure 3 As shown.

[0037] To comprehensively evaluate the mechanical properties of the ZnMgCa medium-entropy alloy intervertebral fusion device, hardness and tribological wear tests were conducted on the alloy samples prepared in Examples 1, 2, and 3. The test surfaces of the samples were prepared to a mirror finish using standard metallographic methods (polishing with 400# to 2000# sandpaper and 0.5μm diamond polishing paste).

[0038] (1) Hardness test A Vickers hardness tester was used with a square pyramidal diamond indenter. At least 10 different locations were randomly selected on the surface of each sample under a test load of 0.1 kgf for 10 seconds. After unloading, the diagonal length of each indentation was precisely measured using the equipment's optical system, and the Vickers hardness value (HV) was automatically calculated. The final hardness value was the arithmetic mean of the multi-point measurements for each sample. The test results are as follows: Figure 4 As shown.

[0039] (2) Friction and wear test Friction and wear tests were conducted using a ball-and-disc friction and wear testing machine. The polished alloy sample was fixed as the disk, and Al2O3 ceramic balls with a diameter of 6 mm were selected as the grinding balls. The tests were performed in a dry environment at room temperature, with an applied load of 3 N, a reciprocating friction stroke of 5 mm, and a total test duration of 20 minutes. The equipment recorded the friction coefficient in real time. A comparison of the friction coefficient-time curves for the three sample examples is provided. Figure 5 As shown.

[0040] according to Figure 4 and Figure 5 The mechanical property test results show that the ZnMgCa medium-entropy alloy of the present invention exhibits excellent comprehensive mechanical properties.

[0041] like Figure 4 As shown, the Vickers hardness of all three alloys was significantly improved, remaining within the range of 250–350 HV. This hardness value is much higher than that of pure zinc and most traditional biodegradable zinc-based alloys, indicating that the material achieved effective solid solution and precipitation strengthening through the synergistic effect of composition design and die-casting heat treatment. More importantly, within the specific composition range of this invention, the hardness of the alloy showed a continuous increasing trend with the increase of Mg content, which directly confirms the decisive role of Mg as the main strengthening component in improving the material's resistance to plastic deformation. For intervertebral fusion cages, this significantly improved hardness and strength are crucial. It can effectively resist the micromotion, creep, or early plastic deformation of the implant under complex loads in the human body, thereby providing a stable mechanical support environment for the bone. This is the mechanical basis for preventing fusion cage subsidence, maintaining intervertebral height, and ultimately achieving successful bone fusion.

[0042] In terms of tribological properties, such as Figure 5 The friction coefficient-time curves show that the wear resistance varies among alloys with different compositions. Among them, Zn... 91 Mg4Ca5 exhibits the lowest and most stable coefficient of friction, indicating its optimal wear resistance. Excellent wear resistance is crucial for interbody fusion devices, as it significantly reduces wear debris generated during implant service due to micro-movements at the bone interface or within the implant itself, thereby lowering the risk of inflammatory reactions and osteolysis caused by wear debris. Simultaneously, a smooth and stable friction surface helps maintain the initial mechanical stability of the implant-bone interface, creating favorable conditions for subsequent biological osseointegration.

[0043] In summary, the ZnMgCa medium-entropy alloy prepared by this invention achieves synergistic optimization of hardness and wear resistance by controlling the Mg content. Higher hardness ensures the structural integrity and long-term support capacity of the implant, while good wear resistance guarantees its interfacial biocompatibility and long-term safety. This organic combination of mechanical properties makes this alloy system particularly suitable for manufacturing interbody fusion devices with extremely high requirements for mechanical performance and service reliability.

[0044] To characterize the corrosion resistance of the ZnMgCa medium-entropy alloy in a physiological environment, electrochemical tests were performed using an electrochemical workstation (Gamry Reference 3000) in a three-electrode system. The experimental setup consisted of ZnMgCa medium-entropy alloy working electrodes (exposed area 1 cm²) prepared in Examples 1, 2, and 3. 2 It consists of a platinum auxiliary electrode and a saturated calomel reference electrode (SCE). The electrolyte is SBF, which simulates body fluid. Before the test, it is placed in a constant temperature water bath at 37±0.5℃ for 30 minutes to achieve a stable open circuit potential.

[0045] The test parameters were set as follows: a sinusoidal perturbation signal with an amplitude of 10mV was applied at an open-circuit potential, with a frequency scan range of 100kHz to 0.1Hz (logarithmic scan, acquiring 10 data points every ten octaves). Open-circuit potential monitoring was performed for 30 minutes before testing, and formal measurements began after confirming that the potential fluctuation was less than ±2mV. All tests were conducted in a Faraday shielded box to reduce electromagnetic interference, and each sample group was tested three times to ensure data reproducibility. The test results are as follows: Figure 6 and Figure 7 As shown.

[0046] according to Figure 6 and Figure 7 Electrochemical testing results showed a significant correlation between the corrosion resistance of the ZnMgCa medium-entropy alloy and the magnesium content. This phenomenon is mainly attributed to the fact that the addition of Mg promotes the formation of a second phase, which forms a micro-electrical couple with the zinc matrix, accelerating the electrochemical corrosion process. Simultaneously, a higher Mg content tends to lead to coarsening and uneven distribution of the second phase grains, further deteriorating the material's degradation uniformity. Among the three compositions, Zn... 87 Mg8Ca5 exhibits the best corrosion resistance, with a relatively high corrosion potential and the lowest corrosion current density. This indicates that within this composition range, the distribution and size of the second phase and the electrochemical matching between it and the matrix have reached a relatively optimized balance.

[0047] This controllable and improved corrosion resistance has multiple key impacts on the clinical application of interbody fusion devices. An appropriate corrosion rate ensures that the implant maintains sufficient mechanical support strength during the critical period of bone healing (typically 3-6 months), providing a stable mechanical environment for bony fusion between vertebrae—the mechanical basis for successful fusion. Simultaneously, uniform degradation effectively avoids excessive metal ions and corrosion debris generated by rapid localized corrosion, which is crucial for ensuring the biosafety of the implant, as it significantly reduces the risk of localized inflammatory reactions or adverse tissue reactions. Furthermore, a uniform and predictable corrosion pattern helps the implant maintain structural integrity during long-term service, effectively avoiding stress concentration and premature failure caused by localized corrosion problems such as pitting, ensuring the safety and reliability of the entire degradation process.

[0048] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A biodegradable ZnMgCa medium-entropy alloy for use in interbody fusion devices, characterized in that: The biodegradable ZnMgCa medium entropy alloy comprises: 84 at.% ≤ Zn ≤ 91 at.%, 4 at.% ≤ Mg ≤ 11 at.%, and 5 at.% Ca.

2. A method for preparing a biodegradable ZnMgCa medium-entropy alloy for interbody fusion devices, characterized by comprising the following steps: (1) Vacuum melting and refining: The raw materials are melted under a protective atmosphere and then refined by rotary jetting. (2) Ultrasonic treatment of melt: Apply ultrasonic treatment to the refined melt; (3) Precision die casting: The ultrasonically treated melt is transferred to a die casting machine and injected into a preheated mold cavity to form a fusion die casting. Under the set die casting pressure and holding time, the fusion die casting is obtained. (4) Multi-stage heat treatment: The die castings are subjected to solution treatment and aging treatment in sequence.

3. The method for preparing ZnMgCa medium-entropy alloy as described in claim 2, characterized in that: The melting in step (1) is carried out under an argon protective atmosphere. The melting temperature is 600-650℃. The refining is carried out by spraying the melt with high-purity argon through a rotating nozzle for 5-15 minutes. After spraying, the melt is left to stand for 3-10 minutes.

4. The method for preparing ZnMgCa medium-entropy alloy as described in claim 2, characterized in that: In step (2), the parameters of the ultrasonic treatment are: ultrasonic power density of 100-500 W / cm², frequency of 15-25 kHz, and treatment time of 30-180 seconds.

5. The method for preparing ZnMgCa medium-entropy alloy as described in claim 4, characterized in that: The ultrasonic probe is inserted into the melt to a depth of 1 / 3 to 1 / 2 of the melt depth.

6. The method for preparing ZnMgCa medium-entropy alloy as described in claim 2, characterized in that: In step (3), the preheating temperature of the mold cavity is 200-300℃, and the mold is equipped with a conformal cooling water channel manufactured by 3D printing; the die casting pressure is 60-110MPa, and the holding time is 10-20 seconds.

7. The method for preparing ZnMgCa medium-entropy alloy as described in claim 2, characterized in that: In step (4), the solution treatment is performed by water quenching after holding at 320-380℃ for 2-6 hours; the aging treatment is performed by holding at 120-180℃ for 8-24 hours.

8. An application of a biodegradable ZnMgCa medium-entropy alloy prepared by the method according to any one of claims 2 to 7, characterized in that: The application of the biodegradable ZnMgCa medium-entropy alloy in the fabrication of intervertebral fusion devices.

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