CN109172860B

CN109172860B - Degradable iron-based implant and preparation method thereof

Info

Publication number: CN109172860B
Application number: CN201810906076.9A
Authority: CN
Inventors: 高成德; 帅词俊
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2018-08-10
Filing date: 2018-08-10
Publication date: 2021-04-23
Anticipated expiration: 2038-08-10
Also published as: CN109172860A

Abstract

A degradable iron-based implant and a preparation method thereof, the implant is composed of an iron matrix and carbon nano tubes uniformly distributed in the iron matrix, and the preparation steps are as follows: the degradable iron-based implant is prepared by taking carbon nanotubes and iron powder, mechanically stirring, mixing and ball-milling under the protection of argon, and then adopting a selective laser melting process under the protection of argon. The preparation method has the advantages that the carbon nano tube is used as a cathode of galvanic corrosion, the characteristics of high standard potential, good conductivity and large specific surface area of the carbon nano tube are utilized, the degradation rate of the iron-based implant is greatly improved, the problem that the conventional iron-based implant is degraded too slowly is solved, meanwhile, the prepared iron-based implant can provide enough mechanical support, and the preparation method can realize the uniform dispersion of the carbon nano tube in an iron matrix and maintain the structural integrity, so that the improvement effect of the carbon nano tube on the degradation behavior of the iron-based implant is fully exerted.

Description

Degradable iron-based implant and preparation method thereof

Technical Field

The invention belongs to the technical field of biomedical implants, and particularly relates to a degradable iron-based implant and a preparation method thereof.

Background

In recent years, degradable medical metals represented by iron-based alloys have become an important direction for the development of orthopedic implants. The medical metal skillfully utilizes the characteristic that the medical metal can be corroded in the human body environment, can achieve the aim that the implant is gradually degraded while repairing the defective tissue, and changes the common practice that people use non-degradable metals such as stainless steel, cobalt-nickel alloy, titanium alloy and the like as the implant. Meanwhile, iron is one of the essential trace nutrient elements of human body, can participate in the processes of metabolism, DNA and RNA synthesis and the like, and plays an important role in playing various physiological functions in human body. Therefore, the iron-based alloy has potential application prospect in the aspect of repairing bone defects as a degradable implant.

However, due to the slow degradation rate of iron, part of the iron-based implant remains in the body after the bone tissue has healed, which greatly limits its application. It is known that the degradation of iron-based alloys is mainly galvanic corrosion in electrochemical reactions, wherein the iron matrix serves as an anode of galvanic corrosion and the other phases serve as a cathode of galvanic corrosion, and therefore the rate of galvanic corrosion determines the rate of degradation of the iron-based alloy. Factors influencing the degradation rate of the galvanic couples mainly comprise potential difference, conductivity, the number of the galvanic couples and the like, and currently, a learner increases the degradation rate of the galvanic couples by adding high-potential noble metal elements, namely Au (+1.83V), Ag (+0.7996V), Pt (+1.2V) and the like, and forming a large potential difference with iron (-0.44V), so that the degradation of the iron is accelerated, but the noble metal elements are expensive, have limited improvement effect and have high biological toxicity; the scholars also utilize elements such as Co, Al, W, B, C, S and the like to form a new compound with the iron matrix, and galvanic corrosion is formed between the new compound and the iron matrix to accelerate the degradation of iron, but the degradation rate of iron is not obviously improved, and the prepared iron-based implant has a larger gap with the clinical use requirement.

Therefore, how to effectively accelerate galvanic corrosion of the iron-based alloy to match the degradation rate with the tissue repair rate becomes a key to promote application thereof in the field of degradable implants.

Disclosure of Invention

In order to overcome the defects of slow degradation and the like of the iron-based alloy in the prior art, the invention aims to provide the degradable iron-based implant and the preparation method thereof.

In order to achieve the purpose, the invention adopts the technical scheme that:

a degradable iron-based implant is composed of an iron matrix and carbon nanotubes uniformly distributed in the iron matrix, wherein preferably, the content of the carbon nanotubes is 0.3-0.9%, and the content of iron is 99.1-99.7%. More preferably, the content of the carbon nanotube is 0.6-0.9%, and the content of iron is 99.1-99.4%. Further preferably, the content of the carbon nanotube is 0.9%, and the content of iron is 99.1%.

Preferably, the diameter of the carbon nano tube is 3-20nm, the length is 1-10 μm, the resistivity is 0.1-12 μ Ω/m, the particle size of the iron powder is controlled to be 30-50 μm, and the shape of the iron powder is spherical to ensure that the iron powder has better fluidity.

The invention also provides a preparation method of the degradable iron-based implant, which comprises the following steps:

step one

Under the protection of argon, mechanically stirring and mixing iron powder and carbon nano tube powder;

step two

Placing the powder after mechanical stirring and mixing in a ball mill for dispersing to obtain uniformly dispersed mixed powder;

step three

And (3) taking the uniformly dispersed mixed powder as a raw material, taking selective laser melting as a process, and obtaining the iron-based/carbon nano tube implant after melting and solidifying under the protection of argon.

Preferably, in the first step, the mixture is mechanically stirred for 20 to 40 minutes.

Preferably, in the second step, the mass ratio of the ball material is 20:1, the ball milling rotation speed is 100-.

Preferably, in the third step, the laser power is 100-120W, the laser spot diameter is 0.1-0.3mm, and the powder spreading thickness is 100-150 μm.

The invention not only utilizes the high potential difference between the carbon nano tube and iron to form strong galvanic corrosion to promote the degradation of an iron matrix, but also utilizes the good conductivity of the carbon nano tube, and the extremely high conductivity of the carbon nano tube reduces the electron transfer impedance in the galvanic corrosion, thereby increasing the corrosion current density; in addition, the huge specific surface area of the carbon nano tube can be fully contacted with the iron matrix, a plurality of galvanic corrosion contact points are formed, the number of microscopic galvanic corrosion units of the iron-carbon nano tube is increased, and the degradation of the iron matrix is further accelerated.

The dosage of the carbon nano tube must be strictly controlled, because the carbon nano tube is a one-dimensional nano material, has the characteristics of large specific surface area, high surface energy and strong intermolecular force, and is easy to agglomerate in a matrix when the content is too high, the forming performance of the iron-based implant is reduced, even serious pitting corrosion is caused, and the implant fails in the service period; on the other hand, if the amount is too small, the improvement of the galvanic corrosion effect is limited, or the use requirement cannot be satisfied. Therefore, when the content of the carbon nano tubes is increased, the control of the ball milling dispersion process parameters is a key ring for solving the problem of carbon nano tube agglomeration. In the ball milling process, the main parameters are the rotating speed of the ball mill and the ball milling time: the effect of uniform dispersion cannot be achieved when the ball milling rotating speed is low, and the carbon nano tubes are easily bonded on the inner wall of the ball milling tank and have poor dispersion effect when the ball milling rotating speed is high; if the ball milling time is short, the effect of uniform dispersion cannot be achieved, and if the ball milling time is too long, the structure of the carbon nanotube is damaged.

Meanwhile, the diameter of the carbon nanotube needs to be strictly controlled, the conductivity of the carbon nanotube is closely related to the diameter of the carbon nanotube, and generally, the smaller the diameter of the carbon nanotube is, the better the conductivity is, and the lower the electron transfer resistance is. In the invention, if the diameter of the carbon nano tube is too small, the technical requirement and the cost are too high; if the diameter is too large, the conductivity is reduced. In addition, the energy density in the selective laser melting and forming process is controlled, if the energy density is too low, the energy obtained by the powder is too low, the forming quality is poor, and even the forming effect cannot be achieved; if the energy density is too high, the temperature during the forming process is too high, which may cause structural damage of the carbon nanotubes.

Compared with the prior art, the invention has the following advantages:

(1) in the invention, the carbon nano tube with good conductivity is dispersed in the iron matrix to form microscopic galvanic corrosion, and the low electron transfer impedance of the carbon nano tube can increase the current density of the galvanic corrosion and accelerate the corrosion of the iron matrix, thereby improving the degradation rate of the degradable iron-based implant.

(2) In the invention, the carbon nanotubes with large specific surface area are dispersed in the iron matrix and can fully contact with the iron matrix to form a plurality of galvanic corrosion contact points, and compared with other methods, the number of galvanic corrosion units is increased.

(3) According to the invention, the degradable iron-based implant can be naturally corroded and decomposed in vivo, disappears after reaching a treatment effect, and avoids the defect that the traditional implants such as stainless steel, titanium alloy and the like need to be taken out after the tissues are healed through a secondary operation.

(4) In the invention, the degradation product of the degradable iron-based implant has no toxicity to human body, for example, the degraded ferrous ions can be combined with hemoglobin to participate in oxygen transportation; the carbon nano tube is usually used as a carrier for targeted drug delivery, can be dissolved by phagocytes in a human body after being degraded, and is discharged out of the body along with metabolism of the human body.

(5) In the invention, the carbon nano tube has a large length-diameter ratio (1000-6000), can be inserted into an iron matrix, and enhances the mechanical function of the iron matrix through the function of a needle-threading lead, thereby providing sufficient mechanical support for the implant.

(6) The preparation method of the degradable iron-based implant is simple and reliable, and can realize personalized implant customization, so that the requirements of different patients are met.

Drawings

FIG. 1 surface topography before and after removal of corrosion products in example 1.

Figure 2 calculated degradation rate after 25 days soaking in simulated body fluid.

Fig. 3 is an agglomeration of carbon nanotubes in comparative example 1.

Fig. 4 pitting occurred after 25 days of immersion in comparative example 1.

Fig. 5 is an agglomeration of carbon nanotubes in comparative example 2.

Fig. 6 pitting occurred after 25 days of immersion in comparative example 2.

Figure 7 cracks appear in the indentation test in comparative example 4.

Detailed Description

The embodiments of the present invention will be described in detail below with reference to the drawings and examples.

Example 1

Carbon nano tubes and iron powder are used as raw materials, the diameter of the carbon nano tubes is 3-10nm, the length of the carbon nano tubes is 1-5 mu m, the particle size of the round iron powder is controlled to be 30-40 mu m, and the ratio of the round iron powder to the round iron powder is controlled according to the following weight percentage of 0.9: weighing 0.45g of carbon nano tube and 49.55g of iron powder according to the mass ratio of 99.1, and mechanically stirring and mixing the iron powder and the carbon nano tube powder for 30 minutes under the protection of argon; placing the powder after mechanical stirring and mixing in a ball mill for dispersion, wherein the mass ratio of ball materials is 20:1, the ball milling rotating speed is 120r/min, the ball milling time is 50 minutes, and stopping the ball mill for 2 minutes after the ball mill runs for 20 minutes in the ball milling process to obtain uniformly dispersed mixed powder; the uniformly dispersed mixed powder is used as a raw material, selective laser melting is used as a process, the laser power is 100W, the diameter of a laser spot is 0.1mm, the powder spreading thickness is 100 mu m, and the iron/carbon nanotube-based implant is obtained after melting and solidification under the protection of argon.

The implementation effect is as follows: the prepared iron-based implant is tested, and the carbon nano tubes are uniformly dispersed in an iron matrix, and after the iron-based implant is soaked in a human body simulation body liquid for 25 days, the degradation rate is calculated to be 0.15mm/y, and the surface of the implant is uniformly corroded and is relatively flat, as shown in figure 1.

Example 2

Carbon nano tubes and iron powder are used as raw materials, the diameter of the carbon nano tubes is 3-10nm, the length of the carbon nano tubes is 1-5 mu m, the particle size of the round iron powder is controlled to be 30-40 mu m, and the ratio of the round iron powder to the round iron powder is controlled according to the following weight percentage of 0.3: weighing 0.15g of carbon nano tube and 49.85g of iron powder according to the mass ratio of 99.7, and mechanically stirring and mixing the iron powder and the carbon nano tube powder for 30 minutes under the protection of argon; placing the powder after mechanical stirring and mixing in a ball mill for dispersion, wherein the mass ratio of ball materials is 20:1, the ball milling rotating speed is 120r/min, the ball milling time is 50 minutes, and stopping the ball mill for 2 minutes after the ball mill runs for 20 minutes in the ball milling process to obtain uniformly dispersed mixed powder; the uniformly dispersed mixed powder is used as a raw material, selective laser melting is used as a process, the laser power is 100W, the diameter of a laser spot is 0.1mm, the powder spreading thickness is 100 mu m, and the iron/carbon nanotube-based implant is obtained after melting and solidification under the protection of argon.

The implementation effect is as follows: the prepared iron-based implant is tested, and the calculated degradation rate is 0.10mm/y after the carbon nano tubes are uniformly dispersed in the iron matrix and soaked in the human body simulation body liquid for 25 days, as shown in figure 2.

Example 3

The method adopts carbon nano tubes and iron powder as raw materials, the diameter of the carbon nano tubes is 11-20nm, the length of the carbon nano tubes is 1-5 mu m, the particle size of the round iron powder is controlled to be 30-40 mu m, and the ratio of the round iron powder to the round iron powder is controlled according to the following weight percentage of 0.9: weighing 0.45g of carbon nano tube and 49.55g of iron powder according to the mass ratio of 99.1, and mechanically stirring and mixing the iron powder and the carbon nano tube powder for 30 minutes under the protection of argon; placing the powder after mechanical stirring and mixing in a ball mill for dispersion, wherein the mass ratio of ball materials is 20:1, the ball milling rotating speed is 120r/min, the ball milling time is 50 minutes, and stopping the ball mill for 2 minutes after the ball mill runs for 20 minutes in the ball milling process to obtain uniformly dispersed mixed powder; the uniformly dispersed mixed powder is used as a raw material, selective laser melting is used as a process, the laser power is 100W, the diameter of a laser spot is 0.1mm, the powder spreading thickness is 100 mu m, and the iron/carbon nanotube-based implant is obtained after melting and solidification under the protection of argon.

The implementation effect is as follows: the prepared iron-based implant is tested, and the carbon nano tubes are uniformly dispersed in the iron matrix, and the calculated degradation rate of the iron-based implant prepared by the method is 0.13mm/y after the iron-based implant is soaked in human body simulation body liquid for 25 days, as shown in figure 2.

In the process of developing the technology of the invention, the following schemes (such as comparative example 1, comparative example 2, comparative example 3 and comparative example 4) are also tried, but the performance of the obtained product is far worse than that of the examples.

Comparative example 1

The other conditions were the same as in example 1 except that: according to the following steps of 6: weighing 3g of carbon nanotubes and 47g of iron powder according to a mass ratio of 94 to obtain a degradable iron-based implant, detecting that the carbon nanotubes are seriously agglomerated, as shown in figure 3, in the process of selective laser melting, the carbon nanotubes block the bonding of liquid-phase iron, the obtained iron-based implant has poor forming performance, after being soaked in a human body simulation body liquid for 25 days, the calculated degradation rate is 0.22mm/y, as shown in figure 2, but the corrosion surface is uneven, a serious pitting pit appears, as shown in figure 4, and with the development of the pitting pit, serious local corrosion appears, and after further observation, the occurrence of crevice corrosion appears.

Comparative example 2

The other conditions were the same as in example 1 except that: placing the powder after mechanical stirring and mixing in a ball mill for dispersion, wherein the mass ratio of ball materials is 5:1, the ball milling speed is 50r/min, obtaining a degradable iron-based implant, detecting and finding that the carbon nano tube is agglomerated in an iron matrix, as shown in figure 5, after soaking in human body simulated body fluid for 25 days, the calculated degradation rate is 0.15mm/y, and the corrosion morphology is observed to be uneven, wherein pitting pits are distributed in a part of the area, as shown in figure 6.

Comparative example 3

The other conditions were the same as in example 1 except that: the diameter of the carbon nano tube is 90-100nm, a degradable iron-based implant is obtained, and meanwhile, after the iron-based implant is soaked in a human body simulation body liquid for 25 days, the calculated degradation rate is 0.072mm/y, because the conductivity of the carbon nano tube is related to the parameters of the carbon nano tube and is influenced by the diameter and the length, the smaller the conductivity, the larger the impedance is, the transfer of electrons in galvanic corrosion is hindered, and the degradation rate is reduced.

Comparative example 4

The other conditions were the same as in example 1 except that: the laser power was 40W and it was found that there were unmelted areas during the forming process and the iron powder particles could not be completely melt bonded to each other. The calculated degradation rate of the iron-based implant after soaking in the simulated body fluid of the human body for 25 days was 0.27mm/y as shown in fig. 2, but the microhardness test found that the obtained iron-based implant exhibited indentation cracks after being subjected to a small load (0.49N) as shown in fig. 7, which indicates that the mechanical properties of the iron-based implant were deteriorated.

As can be seen from example 1 and comparative examples 1, 2, 3 and 4, the components and preparation process of the present invention are an organic whole, and the effect is significantly reduced when any one or more of the key parameters is out of the scope of the present invention. The inherent comparison of example 1 and examples 2 and 3 of the present invention shows that the preferred embodiment of the present invention has unexpected advantages.

In conclusion, the carbon nano tube is used as a cathode of galvanic corrosion, the characteristics of high standard potential, good conductivity and large specific surface area of the carbon nano tube are utilized, the degradation rate of the iron-based implant is greatly improved, the problem that the conventional iron-based implant is degraded too slowly is solved, meanwhile, the prepared iron-based implant can provide enough mechanical support, and the preparation method can realize the uniform dispersion of the carbon nano tube in an iron matrix and maintain the structural integrity, so that the improvement effect of the carbon nano tube on the degradation behavior of the iron-based implant is fully exerted.

Claims

1. A method for preparing a degradable iron-based implant for repairing bone defects, the degradable iron-based implant consisting of an iron matrix and carbon nanotubes uniformly distributed therein, the method comprising the steps of:

step one

step two

Placing the powder after mechanical stirring and mixing in a ball mill for dispersion to obtain uniformly dispersed mixed powder, wherein the mass ratio of ball materials is 20:1, the ball milling rotation speed is 100-;

step three

The uniformly dispersed mixed powder is used as a raw material, selective laser melting is used as a process, and the iron-based/carbon nano tube implant is obtained after melting and solidifying under the protection of argon, wherein the laser power is 100-120W, the diameter of a laser spot is 0.1-0.3mm, the powder paving thickness is 100-150 mu m, the content of the carbon nano tube is 0.3-0.9%, the content of iron is 99.1-99.7%, the diameter of the carbon nano tube is 3-20nm, the length of the carbon nano tube is 1-10 mu m, the resistivity of the carbon nano tube is 0.1-12 mu omega/m, the particle size of the iron powder is controlled to be 30-50 mu m, and the shape of the iron powder is spherical.

2. The method for preparing a degradable iron-based implant for repairing a bone defect of claim 1, wherein in the first step, the mixture is mechanically stirred for 20-40 minutes.

3. The method of claim 1, wherein the carbon nanotubes are contained in an amount of 0.6 to 0.9% and the iron is contained in an amount of 99.1 to 99.4%.

4. The method of claim 1, wherein the carbon nanotubes are 0.9% and the iron is 99.1%.