A medical zinc-based nano-composite bone implant and its preparation method

Abstract

The present invention relates to a medical zinc-based nano-composite bone implant and a preparation method thereof, belonging to the field of degradable biomedical metals. The medical zinc-based nano-composite bone implant is composed of a zinc-iron (1.4 wt.%) matrix and nano-tungsten carbide, wherein the mass percentage of nano-tungsten carbide is 1.0 - 5.0 wt.%. After the zinc powder, iron powder and nano-tungsten carbide powder are mechanically mixed and ball-milled and dispersed, spark plasma sintering is used for forming. The beneficial effect of the present invention is that a high-toughness and high-strength medical zinc-based nano-composite bone implant can be rapidly formed at a temperature lower than the melting point of the material.

Description

Technical Field

[0001] The present invention relates to a zinc-based bone implant for biomedical use, belonging to the field of degradable biomedical metals. Background Art

[0002] Compared with other biomedical materials such as permanent metals, degradable biomedical metals have attracted wide attention due to their excellent biocompatibility and biodegradability. In the past few years, significant progress has been made in the development of biodegradable metal materials for medical applications, especially in the field of bone implants. Degradable biomedical metals can corrode in the physiological environment of the human body, achieving gradual degradation while repairing bone tissue. The released corrosion products may trigger an appropriate host response, but these corrosion products can be metabolized by cells and tissues, or assimilated by cells and tissues, and then completely dissolved after completing their tasks to help bone tissue heal without implant residues. This avoids the psychological and economic burdens on patients and their relatives caused by secondary surgery after complete recovery of bone tissue. In addition, degradable biomedical metals overcome the disadvantages of permanent metal implants, such as physical implant irritation, chronic inflammatory reactions, revision surgeries, and stress shielding. They are a type of orthopedic implant with great clinical application prospects and are known as "revolutionary metal biomaterials".

[0003] Research shows that degradable biomedical metals mainly include magnesium, iron, and zinc. The biodegradation rate of magnesium is too fast, and accompanied by a hydrogen evolution reaction, generating bubbles around bone tissue, which affects the healing of bone tissue. On the contrary, the biodegradation rate of iron is too low, and it usually remains almost intact after tissue repair. In addition, the degradation products of iron are difficult to metabolize and may cause an inflammatory reaction in the surrounding bone tissue. The standard potential of zinc (-0.763V) is between that of magnesium (-2.37V) and iron (-0.440V). Therefore, theoretically, its degradation rate is milder than those of iron and magnesium. In addition, zinc is one of the essential trace elements in the human body, is a cofactor of many enzymes, and plays an important role in regulating the formation of proteins and nucleic acids.

[0004] Appropriate mechanical properties are also one of the important factors to be considered for degradable biomedical metals. Degradable biomedical metals need to have mechanical properties similar to those of bone tissue. However, the low elongation rate and strength of as-cast pure zinc limit its application in bone repair. Research has found that alloying is an effective way to improve the mechanical properties of zinc metal. In zinc metal, the addition of iron refines the zinc grains, achieving the effects of fine grain strengthening and dispersion strengthening, but brittle zinc-iron compounds (FeZn 13 ) are easily generated. Therefore, it is urgent to regulate the mechanical properties of zinc-iron alloys to accelerate their biomedical applications. Summary of the Invention

[0005] In view of the problem that brittle zinc-iron compounds are likely to be produced in biomedical zinc-iron alloys in the prior art, making it difficult to meet the mechanical properties required for bone implant-related applications, the present invention proposes adding nano-tungsten carbide to the zinc-iron alloy to make a high-toughness zinc-based composite bone implant. The high melting point and thermal conductivity of nano-tungsten carbide change the morphology of brittle zinc-iron compounds from faceted to non-faceted. At the same time, its uniform distribution can inhibit the growth of brittle zinc-iron compounds. In addition, tungsten carbide has the characteristic of high hardness, which also enhances the hardness of the zinc-based composite bone implant to a certain extent. Nano-tungsten carbide is chemically stable, usually inert and non-reactive in the human body, without tungsten ion leaching, and has no acute toxicity to mammalian cell lines, so introducing it into bone implants has certain biological safety.

[0006] In order to achieve the purpose of improving the brittleness of zinc-iron compounds, the present invention provides the following technical solutions:

[0007] A medical zinc-based nano-composite bone implant is composed of a zinc-iron (1.4 wt.%) matrix and nano-tungsten carbide, where the mass percentage of nano-tungsten carbide is 1.0 - 5.0 wt.%.

[0008] Further, in the medical zinc-based nano-composite bone implant, the mass percentage of the nano-tungsten carbide is 1.3 - 3.5 wt.%.

[0009] Further, in the medical zinc-based nano-composite bone implant, the mass percentage of the nano-tungsten carbide is 2.3 wt.%.

[0010] Further, the size of the zinc powder is 25 - 30 microns, the size of the iron powder is 10 - 20 microns, and the size of the nano-tungsten carbide is 100 - 200 nanometers.

[0011] In the medical zinc-based nano-composite bone implant, the introduction of iron restricts the growth of zinc grains. The finer the grains, the more plastic deformation can be dispersed into more grains when subjected to external forces, the smaller the stress concentration, the more uniform the deformation, and at the same time the grain boundaries become more tortuous, making it difficult for cracks to propagate, and the greater the resistance to dislocation movement. However, the generation of brittle zinc-iron compounds reduces the toughness of the zinc-iron alloy to a certain extent. The addition of nano-tungsten carbide with a high melting point and thermal conductivity accelerates the solidification of the melt around the unmelted tungsten carbide. Heat flows to the remaining tungsten carbide nanoparticles in the molten metal at a low temperature, forming micro-zone directional growth, making the surrounding tissue grow perpendicular to its boundary, changing the morphology of brittle zinc-iron compounds from faceted to non-faceted, and inhibiting crack propagation; when the nano-tungsten carbide around the brittle zinc-iron compounds acts simultaneously, the zinc-iron compounds form a certain boundary for directional growth from the outside to the inside. Therefore, the distribution of nano-tungsten carbide restricts the size of brittle zinc-iron compounds, refines the size of brittle zinc-iron compounds, and improves the mechanical properties of the zinc-iron matrix.

[0012] Furthermore, the elongation at break of the medical zinc-based nano-composite bone implant is 10 - 16%.

[0013] Furthermore, the elongation at break of the medical zinc-based nano-composite bone implant is 12 - 15%.

[0014] The medical zinc-based nano-composite bone implant described in the present invention is prepared through the following technical steps:

[0015] Step 1: Mechanical mixing:

[0016] After drying the iron powder and nano-tungsten carbide at a constant temperature respectively, weigh a certain mass and introduce them into the zinc powder in 2 - 5 equal portions and stir for 10 - 20 minutes. During the stirring process, turn it over up and down to evenly disperse the iron powder and nano-tungsten carbide.

[0017] Step 2: Ball milling and dispersion:

[0018] After mechanical mixing, the mixed powder of zinc powder, iron powder and nano-tungsten carbide is loaded into a ball mill for ball milling and dispersion. The ball-to-powder ratio is 8:1, and the rotation speed of the ball mill is 150 - 220 r / min. During the ball milling and dispersion process, the ball mill stops for 5 - 10 minutes every 30 - 45 minutes of operation to avoid excessive heat generation due to friction in the ball mill tank. The ball milling time is 80 - 100 minutes.

[0019] Step 3: Spark plasma sintering:

[0020] The zinc powder, iron powder and nano-carbide powder after ball milling and dispersion are solidified and formed by spark plasma sintering process. The sintering temperature is 350 - 440 °C, the sintering pressure is 3.9 - 5.2 kN, and the heat preservation time is 10 - 15 minutes.

[0021] Furthermore, in the medical zinc-based nano-composite bone implant, the rotation speed of the ball mill is 220 r / min.

[0022] Furthermore, in the medical zinc-based nano-composite bone implant, the spark plasma sintering temperature is 350 - 400 °C.

[0023] Furthermore, in the medical zinc-based nano-composite bone implant, the spark plasma sintering pressure is 3.9 - 4.4 kN.

[0024] In the present invention, the boiling point of zinc (907 °C) is lower than 950 °C, while the melting temperatures of iron and nano-tungsten carbide are higher than 950 °C. Therefore, zinc will volatilize before iron is fully melted. In order to retain the complete zinc, fully melt the iron, and at the same time eliminate the possibility of decomposition of nano-tungsten carbide particles due to thermal damage, the present invention uses the spark plasma sintering process. This process can sinter and form at a temperature lower than the melting point of iron, ensuring the chemical structure and physical properties of nano-tungsten carbide while fully melting the iron, so as to fully exert the purpose of enhancing the mechanical properties of the zinc-iron matrix by nano-tungsten carbide.

[0025] The spark plasma sintering process can rapidly form a medical zinc-based nano-composite bone implant. The rapid heating rate limits grain growth and achieves the effect of fine grain strengthening. During the melting and solidification of the medical zinc-based nano-composite bone implant, it is subjected to a certain degree of extrusion, avoiding structural defects such as micropores and cracks in the conventional powder forming process, improving the structural integrity, and ensuring the mechanical properties of the medical zinc-based nano-composite bone implant.

[0026] The spark plasma sintering can rapidly form a medical zinc-based nano-composite bone implant, and can directly form large-sized massive dense specimens in one step. The size and shape of the specimens can be formed according to the mold, which is convenient for subsequent processing and meets the requirements of large-sized and complex-structured bone implants.

[0027] In the present invention, after adding iron, the zinc grains are refined, which plays the role of fine grain strengthening, but brittle zinc-iron compounds are generated, reducing the toughness. The addition of nano-tungsten carbide with a high melting point, thermal conductivity and hardness improves the toughness and strength of the zinc-iron matrix by changing the morphology of the brittle zinc-iron compounds, reducing the size of the brittle zinc-iron compounds, and at the same time the nano-tungsten carbide particles also increase the dislocation resistance between grains.

[0028] In the present invention, the content of nano-tungsten carbide needs to be strictly controlled. Adding too much nano-tungsten carbide will cause uneven mixing in the zinc-iron (1.4 wt.%) matrix, and the dense distribution of nano-tungsten carbide particles makes it difficult to form a good transition with the zinc-iron-based metal flux. On the other hand, too many nano-tungsten carbide particles will increase the difference in the average thermal expansion coefficient between the zinc-based alloy and the nano-tungsten carbide particles. Therefore, during the rapid solidification process, excessive thermal stress will generate cracks. Thus, the mechanical mixing and ball milling dispersion process steps of zinc powder, iron powder and nano-carbon powder are particularly important, including stirring time, ball milling time, ball-to-powder ratio, etc.; if the addition amount of nano-tungsten carbide is too small, the improvement effect of the mechanical properties of the zinc matrix is limited and it is difficult to play a strengthening role. Therefore, it is necessary to reasonably select the powder ratio.

[0029] The electrospark sintering process has a great influence on the forming performance of medical zinc-based nanocomposite bone implants. If the electrospark sintering temperature is low, it is difficult for the mixed powder to completely melt, and the formed sample contains powder particles and is soft, and the mechanical integrity of the formed sample is poor. If the electrospark sintering pressure is small, the densification degree is greatly affected and the densification performance is low.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) In the present invention, the medical zinc-based nanocomposite bone implant can gradually degrade as the bone tissue repairs. During the bone tissue repair process, the medical zinc-based nanocomposite bone implant can provide good mechanical properties, overcoming the disadvantage of insufficient mechanical properties of zinc.

[0032] (2) In the present invention, the chemically stable tungsten carbide nanoparticles are usually inert and non-reactive in the human body, and there is no leaching of tungsten ions. In addition, tungsten carbide nanoparticles have no acute toxicity to mammalian cell lines and have biological safety.

[0033] (3) In the present invention, the preparation method of the medical zinc-based nanocomposite bone implant is simple and reliable. Electrospark sintering can quickly solidify the zinc powder, iron powder and tungsten carbide nanopowder, can shorten the preparation time and improve the properties of the sintered body.

[0034] (4) In the present invention, zinc, as an essential trace element for the human body, has important application values in many aspects such as medicine and biology. Zinc plays an important physiological role in the human body, and a certain amount of zinc needs to be supplemented every day in the human body to maintain normal physiological functions.

[0035] (5) In the present invention, the electrospark sintering rapid prototyping medical zinc-based nanocomposite bone implant can simply form large-size massive dense specimens, and the specimen forming performance is good.

[0036] (6) In the present invention, the electrospark sintering medical zinc-based nanocomposite bone implant has high toughness, can be processed into the required structure, and has good mechanical properties. Detailed implementation manners

[0037] Example 1

[0038] Weigh 2.3 wt.% of tungsten carbide nanoparticles and dry them at a constant temperature. The average particle size of the tungsten carbide nanoparticles is 150 nm. Introduce them into the mixed powder of zinc powder with an average particle size of 27 μm and iron powder (1.4 wt.%) with an average particle size of 15 μm in 4 equal amounts and stir for 5 minutes. During the stirring process, turn it over up and down to evenly disperse the tungsten carbide nanopowder; after mechanical mixing, load the zinc powder, iron powder and tungsten carbide nanopowder into a ball mill for ball milling and dispersion. The ball-to-material ratio is 8:1, and the rotation speed of the ball mill is 200 r / min. During the ball milling and dispersion process, the ball mill stops for 10 minutes every 40 minutes of operation, and the ball milling time is 95 minutes; the zinc powder, iron powder and tungsten carbide nanopowder after ball milling and dispersion are solidified and formed by an electric spark sintering process. The sintering temperature is 350 °C, the sintering pressure is 3.9 kN, and the heat preservation time is 10 minutes;

[0039] Implementation effect:

[0040] The fracture elongation of the medical zinc-based nano-composite bone implant prepared by this method is 16% after cleaning in distilled water. In the compression experiment, there are no obvious brittle cracks, and the compression yield strength is 140 MPa.

[0041] Example 2

[0042] Weigh 4.1 wt.% of tungsten carbide nanoparticles and dry them at a constant temperature. The average particle size of the tungsten carbide nanoparticles is 150 nm. Introduce them into the mixed powder of zinc powder with an average particle size of 27 μm and iron powder (1.4 wt.%) with an average particle size of 15 μm in 5 equal amounts and stir for 5 minutes. During the stirring process, turn it over up and down to evenly disperse the tungsten carbide nanopowder; after mechanical mixing, load the zinc powder, iron powder and tungsten carbide nanopowder into a ball mill for ball milling and dispersion. The ball-to-material ratio is 8:1, and the rotation speed of the ball mill is 220 r / min. During the ball milling and dispersion process, the ball mill stops for 10 minutes every 40 minutes of operation, and the ball milling time is 100 minutes; the zinc powder, iron powder and tungsten carbide nanopowder after ball milling and dispersion are solidified and formed by an electric spark sintering process. The sintering temperature is 400 °C, the sintering pressure is 4.3 kN, and the heat preservation time is 10 minutes;

[0043] Implementation effect: The fracture elongation of the medical zinc-based nano-composite bone implant prepared by this method is 10% after cleaning in distilled water. In the compression experiment, there are no obvious brittle cracks, and the compression yield strength is 130 MPa.

[0044] Example 3

[0045] After weighing 1.3 wt.% of tungsten carbide nanoparticles and drying them at a constant temperature, the average particle size of the tungsten carbide nanoparticles is 150 nm. The tungsten carbide nanoparticles are introduced into a mixed powder of zinc powder with an average particle size of 27 μm and iron powder (1.4 wt.%) with an average particle size of 15 μm in three equal portions and stirred for 5 minutes. During the stirring process, the mixture is turned over up and down to evenly disperse the tungsten carbide nanopowder. After mechanical mixing, the zinc powder, iron powder, and tungsten carbide nanopowder are loaded into a ball mill for ball milling and dispersion. The ball-to-material ratio is 8:1, and the rotational speed of the ball mill is 160 r / min. During the ball milling and dispersion process, the ball mill stops for 10 minutes every 40 minutes of operation, and the ball milling time is 85 minutes. After ball milling and dispersion, the zinc powder, iron powder, and tungsten carbide nanopowder are solidified and formed by an electric spark sintering process. The sintering temperature is 380 °C, the sintering pressure is 4.1 kN, and the heat preservation time is 10 minutes.

[0046] Implementation effect: The fracture elongation rate of the medical zinc-based nano-composite bone implant prepared by this method is 14% after being washed in distilled water. In the compression experiment, there are no obvious brittle cracks, and the compression yield strength is 134 MPa.

[0047] Example 4

[0048] After weighing 1.9 wt.% of tungsten carbide nanoparticles and drying them at a constant temperature, the average particle size of the tungsten carbide nanoparticles is 150 nm. The tungsten carbide nanoparticles are introduced into a mixed powder of zinc powder with an average particle size of 27 μm and iron powder (1.4 wt.%) with an average particle size of 15 μm in three equal portions and stirred for 5 minutes. During the stirring process, the mixture is turned over up and down to evenly disperse the tungsten carbide nanopowder. After mechanical mixing, the zinc powder, iron powder, and tungsten carbide nanopowder are loaded into a ball mill for ball milling and dispersion. The ball-to-material ratio is 8:1, and the rotational speed of the ball mill is 170 r / min. During the ball milling and dispersion process, the ball mill stops for 10 minutes every 40 minutes of operation, and the ball milling time is 90 minutes. After ball milling and dispersion, the zinc powder, iron powder, and tungsten carbide nanopowder are solidified and formed by an electric spark sintering process. The sintering temperature is 400 °C, the sintering pressure is 4.3 kN, and the heat preservation time is 10 minutes.

[0049] Implementation effect: The fracture elongation rate of the medical zinc-based nano-composite bone implant prepared by this method is 15% after being washed in distilled water. In the compression experiment, there are no obvious brittle cracks, and the compression yield strength is 138 MPa.

[0050] Comparative Example 1

[0051] All other conditions were the same as in Example 1, except that tungsten carbide nanoparticles, zinc powder, and iron powder (1.4 wt.%) were stirred and mixed at a mass ratio of 20:80 to obtain a medical zinc-based nanocomposite bone implant. After washing with distilled water, it was found that the elongation at break was low, the microscopic pore distribution was uneven, and brittle cracks appeared in the specimen during compression after the block was compressed.

[0052] Comparative Example 2

[0053] All other conditions were the same as in Example 1, except that tungsten carbide nanopowder, zinc powder, and iron powder (1.4 wt.%) were stirred and mixed at a mass ratio of 0.2:99.8 to obtain a medical zinc-based nanocomposite bone implant. After testing, it was found that the elongation at break was not significantly improved compared with that of the zinc-iron alloy.

[0054] Comparative Example 3

[0055] All other conditions were the same as in Example 2, except that the spark plasma sintering temperature was 250 °C to obtain a medical zinc-based nanocomposite bone implant. It was found that the mechanical properties of the overall formed specimen were poor and there was no good mechanical integrity.

[0056] Comparative Example 4

[0057] All other conditions were the same as in Example 1, except that the ball-to-material ratio was 3:1, the rotation speed of the ball mill was 50 r / min, and the ball milling time was 20 minutes to obtain a medical zinc-based nanocomposite bone implant. It was found that the distribution of tungsten carbide nanoparticles was severely dense and local brittleness appeared in the specimen in the microscopic structure.

[0058] It can be seen from Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4 that the components and preparation process of the present invention are an organic whole. When any one or several of the key parameters are not within the protection scope of the present invention, the effect is significantly reduced. Through the internal comparison of Example 1, Example 2, Example 3, and Example 4 of the present invention, it is found that the preferred scheme of the present invention has achieved unexpected effects.

Claims

1. A preparation method of a medical zinc-based nano-composite bone implant, characterized in that: the mass percentage of nano tungsten carbide is 1.0 - 5.0 wt.%, and it includes the following preparation steps: Step 1: Mechanical mixing: After the iron powder and nano tungsten carbide powder are dried at a constant temperature of 40 - 60 degrees, a certain mass is weighed and introduced into the zinc powder in 2 - 5 equal amounts and stirred for 10 - 20 minutes. During the stirring process, it is turned over up and down to make the three evenly mixed; Step 2: Ball milling and dispersion: The zinc powder, iron powder and nano tungsten carbide powder are loaded into a ball mill for ball milling and dispersion. The ball-to-material ratio is 8:1, and the rotation speed of the ball mill is 150 - 220 r / min. During the ball milling and dispersion process, the ball mill stops for 5 - 10 minutes every 30 - 45 minutes of operation to avoid excessive heat generation due to friction in the ball mill tank. The ball milling time is 80 - 100 minutes; Step 3: Spark plasma sintering: The zinc powder, iron powder and nano tungsten carbide powder after ball milling and dispersion are solidified and formed by spark plasma sintering process. The sintering temperature is 350 - 440 degrees, the sintering pressure is 3.9 - 5.2 kN, and the heat preservation time is 10 - 15 minutes.

2. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the medical zinc-based nano-composite bone implant is composed of a zinc-iron matrix and nano tungsten carbide, wherein the mass percentage of nano tungsten carbide is 1.0 - 5.0 wt.%.

3. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the mass percentage of the nano tungsten carbide is 1.3 - 3.5 wt.%.

4. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the mass percentage of the nano tungsten carbide is 2.3 wt.%.

5. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the size of the zinc powder is 25 - 30 microns, the size of the iron powder is 10 - 20 microns, and the size of the nano tungsten carbide is 100 - 200 nanometers.

6. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the elongation at break of the medical zinc-based nano-composite bone implant is 10 - 16%.

7. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the elongation at break of the medical zinc-based nano-composite bone implant is 12 - 15%.

8. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the rotation speed of the ball mill is 220 r / min.

9. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the spark plasma sintering temperature is 350 - 400 degrees.

10. The preparation method of a medical zinc-based nano-composite bone implant according to claim 1, characterized in that: the spark plasma sintering pressure is 3.9 - 4.4 kN.