JP2021110006A - Production method of nickel-titanium alloy having titanium dioxide film - Google Patents

Abstract

To provide a production method of NiTi alloy having a TiO2 film, in which elution of a Ni ion can be fully suppressed.SOLUTION: A production method of NiTi alloy having a TiO2 film includes: an immersion step in which an NiTi alloy is immersed in an electrolyte that can elute Ni from the surface of the NiTi alloy; and an anodization step in which an anodization processing is performed for forming the TiO2 film on the surface of the NiTi alloy by applying a pulse voltage intermittently to the NiTi alloy immersed in the electrolyte in the immersion step.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing a NiTi alloy having a titanium dioxide film.

NiTi (nickel-titanium) alloy is known as a kind of shape memory alloy, and is used as a material for medical devices such as vascular stents, orthodontic wires, and guide wires. The NiTi alloy is excellent in strength, corrosion resistance, etc., but Ni ions may elute from the surface. Since Ni ions may exhibit cytotoxicity or induce allergies in vivo, attempts have been made to reduce the Ni content in the surface layer of the NiTi alloy and suppress the elution of Ni ions. For example, Patent Document 1 discloses a surface treatment method for forming a _{TiO 2} (titanium dioxide) film on the surface of a NiTi alloy in order to reduce the Ni content in the surface layer of the NiTi alloy.

Japanese Unexamined Patent Publication No. 2017-133101

_{In the method of Patent Document 1, a TiO 2} film is formed on the surface of the NiTi alloy by performing anodizing treatment on the NiTi alloy in an aqueous solution containing nitric acid or nitrate. Since the TiO ₂ film has biocompatibility, the _{NiTi alloy having the TiO 2} film is suitable as a material for medical devices. Further, since this method does not require heat treatment, the structure and structure of the NiTi alloy do not change, and important properties such as superelasticity and shape memory are not impaired. However, in the method of Patent Document 1, a _{very small amount of Ni ions may be eluted from the fine pores formed in the TiO 2} film, and there is room for further improvement in suppressing the elution of Ni ions.

The present invention has been made based on such a background, and an object of the present invention is to provide a method for producing a NiTi alloy having _{a TiO 2 film capable of sufficiently suppressing elution of Ni ions.}

In order to achieve the above object, the method for producing a NiTi alloy having a _{TiO 2 film according to the present invention is:}
A dipping step of immersing the NiTi alloy in an electrolytic solution capable of eluting Ni from the surface of the NiTi alloy, and
Anodizing step of performing anodizing treatment to form a _{TiO 2} film on the surface of NiTi alloy by intermittently applying a pulse voltage to the NiTi alloy immersed in the electrolytic solution in the dipping step.
including.

The pulse voltage in the anodizing step has a rectangular waveform, and the pulse width may be in the range of 100 ms to 1 s.

In the anodizing step, a pulse voltage is periodically applied to the NiTi alloy.
The duty ratio, which is the ratio of the pulse width to the period of the pulse voltage, may be in the range of 25% to 75%.

The maximum voltage of the pulse voltage in the anodizing step may be in the range of 10V to 100V.

The electrolytic solution in the dipping step may be an aqueous solution containing nitric acid or nitrate, or an aqueous solution containing phosphoric acid or phosphate.

According to the present invention, it is possible to provide a method for producing a NiTi alloy having _{a TiO 2 film capable of sufficiently suppressing the elution of Ni ions.}

It is sectional drawing which shows the structure of the surface treatment apparatus of NiTi alloy which concerns on embodiment of this invention. It is a graph which shows an example of the waveform of the pulse voltage applied to the NiTi alloy which concerns on embodiment of this invention. (A) to (d) are FE-SEM (field emission scanning electron microscope) images obtained by photographing the NiTi alloy subjected to the anodizing treatment in Example 1. (A) is a graph showing the average value of the amount of Ni ions eluted from the NiTi alloy subjected to the anodizing treatment in Example 2, and (b) is the graph showing the average value of the amount of Ni ions eluted from the NiTi alloy subjected to the anodizing treatment in Example 2. It is a figure which shows the measured value of the Ni ion elution amount from an alloy. (A) to (f) are images of the NiTi alloy subjected to the anodizing treatment in Example 3. It is a graph which shows the absorbance of Ni ion when the NiTi alloy which was anodized at the maximum voltage 5V in Example 3 was immersed in an electrolytic solution. It is a graph which shows the amount of Ni ion elution from the NiTi alloy in Example 4. It is a graph which shows the amount of Ni ions elution from the NiTi alloy immersed in the electrolytic solution of Example 5 for 3 days. 6 is a graph showing the number of specific cells on the surface of NiTi alloy in which osteoblast-like cells in Example 5 were cultured for 7 days.

Hereinafter, embodiments of a method for producing a NiTi alloy having a _{TiO 2} film according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing the configuration of the surface treatment apparatus 1 according to the embodiment. The surface treatment apparatus 1 is an apparatus for producing a NiTi alloy having a _{TiO 2} film on the surface by performing anodizing treatment in an electrolytic solution 2 capable of eluting Ni ions contained in the NiTi alloy. The surface treatment device 1 includes a container 11, an anode 12, a cathode 13, and a pulse power supply 14. Each part is electrically connected via an electric wire 15 or the like.

The container 11 is a container in which the NiTi alloy is immersed in the electrolytic solution 2 that elutes the Ni ions contained in the NiTi alloy having a predetermined concentration. The electrolytic solution 2 that elutes Ni ions contained in the NiTi alloy is, for example, an aqueous solution containing nitric acid or nitrate, an aqueous solution containing phosphoric acid or phosphate, or the like, and is preferably an aqueous solution containing nitric acid or nitrate. Since nitric acid ion and phosphate ion have strong oxidizing power, Ni ion is eluted from the surface of NiTi alloy in an aqueous solution containing nitric acid or nitrate, phosphoric acid or phosphate.

The nitrate is, for example, a salt of an alkali metal such as ammonium nitrate, calcium nitrate, Na, or K and nitric acid. The phosphate is, for example, a salt of an alkali metal such as ammonium phosphate, calcium phosphate, Na, or K and phosphoric acid.

The concentration and temperature of the aqueous solution containing nitric acid or nitrate, phosphoric acid or phosphate are set in consideration of the dissolution rate of Ni in the surface layer of the NiTi alloy. The concentration of the aqueous solution containing nitric acid or nitrate, phosphoric acid or phosphate is, for example, in the range of 0.03M to 0.3M, preferably in the range of 0.05M to 0.2M, and more preferably in the range of 0.05M to 0.2M. It is 0.1M. The temperature of the aqueous solution containing nitric acid or nitrate, phosphoric acid or phosphate is, for example, in the range of 10 ° C. to 30 ° C., preferably in the range of 20 ° C. to 30 ° C., and more preferably 25 ° C. ..

The anode 12 is, NiTi alloy as an object to form a TiO ₂ film plays the role, attached to the wire 15 before the formation of the TiO ₂ film is removed from the wire 15 after the formation of the TiO ₂ film. The _{NiTi alloy forming the TiO 2} film may have any shape, for example, a plate shape, a columnar shape, a wire shape, a spherical shape, a mesh shape, or the like. The NiTi alloy may contain metal elements other than Ni and Ti as long as the characteristics such as superelasticity and shape memory are not impaired.

The anode 12 is detachably connected to the electric wire 15. For example, a clip capable of energizing may be provided at the end of the electric wire 15 on the anode 12 side, and the anode 12 and the electric wire 15 may be electrically connected by sandwiching the anode 12 with the clips.

The cathode 13 is made of a chemically stable metal material, such as platinum. The cathode 13 may have any shape as long as it can supply electrons to the electrolytic solution 2. The cathode 13 may be connected to the end of the electric wire 15 by, for example, soldering.

The pulse power supply 14 is connected between the anode 12 and the cathode 13 via an electric wire 15, and periodically energizes a pulse voltage having a waveform having the same shape, for example, a rectangular waveform. The pulse power supply 14 has an operation unit for adjusting a parameter of the pulse voltage, and when the operation unit accepts a user's operation, the pulse width, duty ratio, maximum voltage, and the like of the pulse voltage can be individually adjusted.

FIG. 2 is a graph showing an example of the waveform of the pulse voltage applied to the NiTi alloy according to the embodiment. Since the pulse voltage has a rectangular waveform applied in a predetermined period T, the characteristics can be specified by each parameter of _{the pulse width tp, the duty ratio, and the maximum voltage Vo'p.} The duty ratio can be expressed by the ratio tp / T of the pulse width tp to the period T. These parameters are set so that the TiO ₂ film formed on the surface of the NiTi alloy does not have fine pores that can cause the elution of Ni ions from the NiTi alloy. Since a pulse voltage is applied to the NiTi alloy, the current applied to the NiTi alloy is a pulse current.

The pulse width tp of the pulse voltage is, for example, in the range of 100 ms to 1 s, preferably in the range of 100 ms to 0.5 s, and more preferably in the range of 100 ms to 250 ms.

The duty ratio tp / T of the pulse voltage is, for example, in the range of 25% to 75%, preferably in the range of 25% to 50%, and more preferably in the range of 25% when expressed as a percentage.

The maximum voltage _{V O'p} pulse voltage is, for example, in the range of 10V～100V, preferably in the range of 10V～50V, more preferably within the range of 10V to 20V, more preferably 10V be.

The time required for the anodizing treatment (treatment time) is set in consideration of the film thickness of the _{TiO 2 film and the like.} The treatment time is, for example, in the range of 30 minutes to 20 hours, preferably in the range of 30 minutes to 1 hour.

When the NiTi alloy is anodized using continuous energization, the electrochemical action of binding Ti and O by energization becomes predominant as compared with the chemical action of elution of Ni ions by the electrolytic solution. _{Therefore, it is presumed that a TiO 2} film is formed on the surface in a state where Ni ions are not sufficiently eluted from the NiTi alloy, and as a result, a large number of fine pores are formed in the _{TiO 2 film.}

On the other hand, since the surface treatment apparatus 1 according to the embodiment has the above configuration, a pulse voltage is intermittently applied to the NiTi alloy. During the ON time when the maximum voltage is applied, anodizing strongly acts on the NiTi alloy, and Ti and O of the NiTi alloy are bonded to promote the formation of _{the TiO 2 film.} Further, in the OFF time when the pulse voltage is zero, the voltage does not act on the NiTi alloy, so that the elution of Ni from the NiTi alloy is promoted. By performing anodizing treatment on the NiTi alloy in which Ni is eluted from the surface in the OFF time in the ON time, _{the formation of fine pores derived from Ni in the TiO 2} film can be suppressed, and as a result, the TiO ₂ film is fine. It is possible to prevent the elution of Ni ions from the pores.

Next, the flow of the surface treatment method for the NiTi alloy executed by using the surface treatment device 1 according to the embodiment will be described. Hereinafter, it is assumed that the cathode 13 is connected to the electric wire 15 in advance.

First, an electrolytic solution 2 capable of eluting Ni ions, for example, an aqueous solution containing nitric acid or nitrate having a predetermined concentration is put into the container 11.

Next, the NiTi alloy, which is the object to be anodized, is connected to the electric wire 15 as the anode 12, and is completely immersed in the aqueous solution containing nitric acid or nitrate stored in the container 11 (immersion step).

Next, the pulse power supply 14 is started, and a pulse voltage is periodically applied between the anode 12 and the cathode 13 to perform anodizing treatment on the NiTi alloy (anodizing step). The pulse power supply 14 is set to supply a predetermined pulse width, duty ratio, and maximum voltage.

After a predetermined processing time has elapsed from the start of the anodizing treatment, the operation of the pulse power supply 14 is stopped, and the anode 12 is removed from the electric wire. Then, the removed anode 12 is washed with water, ethanol, or the like to complete the treatment. _{By the above treatment, a smooth TIO 2} film having no fine pores that promotes elution of Ni ions is formed on the surface portion of the NiTi alloy that was in contact with the electrolytic solution 2.
The above is the flow of the surface treatment method for a NiTi alloy having _{a TiO 2 film.}

As described above, in the method for producing a NiTi alloy according to the embodiment, the NiTi alloy is immersed in an electrolytic solution 2 capable of eluting Ni from the surface of the NiTi alloy, for example, an aqueous solution containing nitric acid or nitric acid. It includes a dipping step and an anodizing step of performing anodizing treatment by periodically applying a pulse voltage to the NiTi alloy immersed in the electrolytic solution 2 in the dipping step. Therefore, a large number of fine pores that promote the elution of Ni ions are not _{formed in the TiO 2} film formed on the surface of the NiTi alloy, and the elution of Ni ions from the _{TiO 2 film can be suppressed.}

The present invention is not limited to the above-described embodiment, and the modifications described below are also possible.

(Modification example)
In the above embodiment, the electrolytic solution 2 capable of eluting Ni ions is charged into the container 11, and then _{the NiTi alloy, which is the object for forming the TiO 2} film, is connected to the electric wire 15 as the anode 12. The present invention is not limited to this. For example, _{a NiTi alloy, which is an object for forming a TiO 2} film, is connected to an electric wire 15 as an anode 12, placed in a container 11, and then an electrolytic solution 2 capable of eluting Ni ions is charged into the container 11. May be good.

In the above embodiment, the waveform of the pulse voltage applied to the NiTi alloy is rectangular, but the present invention is not limited to this. The waveform of the pulse voltage may have any shape as long as the pulse voltage can be intermittently applied to the NiTi alloy, and may be, for example, a triangular wave pulse or a sine wave pulse.

In the above embodiment, the pulse voltage applied to the NiTi alloy is a repetition of waveforms having the same shape, but the present invention is not limited to this. _{In order to prevent the formation of a large number of fine pores in the TiO 2} film on the surface of the NiTi alloy, it is only necessary that the pulse voltage can be applied intermittently to the NiTi alloy, for example, the period of the pulse voltage waveform. The pulse width, maximum voltage, etc. may be changed over time.

The above-described embodiment is an example, and the present invention is not limited thereto, and various embodiments are possible without departing from the spirit of the invention described in the claims. The components described in each embodiment and modification can be freely combined. The present invention also includes inventions equivalent to those described in the claims.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
In Example 1, an experiment in which a NiTi alloy is anodized by changing the pulse width of a pulse voltage and the result thereof are shown. The pulse width of the pulse voltage used in the anodizing treatment is 10 ms and 100 ms. Since the duty ratio is 50%, the pulse voltage periods are 20 ms and 200 ms, respectively. The maximum pulse voltage is 10 V and the processing time is 120 minutes. The electrolytic solution is a 0.1 M _{aqueous solution of HNO 3} (nitric acid), and its temperature is 25 ° C.

First, a NiTi alloy anodized with a pulse width of 10 ms and a pulse voltage of 100 ms was photographed with an FE-SEM, and the surface state was observed. For comparison, the NiTi alloy that had been anodized by continuous energization and the untreated NiTi alloy were also photographed by FE-SEM, and the surface condition was observed.

3 (a) to 3 (d) are FE-SEM images obtained by photographing the NiTi alloy under the conditions of continuous energization, pulse width 10 ms, pulse width 100 ms, and non-energization. When the NiTi alloy was continuously energized, a large number of fine pores were formed on the surface of the _{TiO 2 film.} On the other hand, when a pulse voltage having a pulse width of 10 ms and 100 ms was applied, a TiO ₂ film having a smooth surface was formed.

(Example 2)
In Example 2, a NiTi alloy anodized with a pulse voltage of 10 ms and 100 ms was immersed in an electrolytic solution for 24 hours, and the amount of Ni ions eluted from the surface of the NiTi alloy was measured. Other conditions are the same as in the case of Example 1. For comparison, the NiTi alloy that has been anodized using continuous energization (duty ratio 100%) and the untreated NiTi alloy are also immersed in the electrolytic solution in the same manner to determine the amount of Ni ions eluted from the NiTi alloy surface. It was measured. The number of samples n under each condition is 3 (n = 3).

FIG. 4A is a graph showing the average value of the amount of Ni ions eluted from the NiTi alloy surface under each energization condition, and FIG. 4B is a graph showing the amount of Ni ions elution from the NiTi alloy surface under each energization condition. It is a figure which shows. In the case of continuous energization, the Ni ion elution amount was measured after diluting the concentration of the electrolytic solution 5 times for convenience of measuring the Ni ion elution amount. The Ni ion elution amount of the continuous energization in FIG. 4 (a) is a value obtained by multiplying the Ni ion elution amount of the continuous energization in FIG. 4 (b) by five.

In the case of continuous energization (ON time 100%), the average value of the amount of Ni ions eluted was 264 μg / L. This is because, as shown in FIG. 3A, a _{large number of fine pores were formed in the TiO 2} film, and Ni ions were eluted from these pores. On the other hand, when the pulse widths are 10 ms and 100 ms, the average value of the Ni ion elution amount is 13.1 μg / L and 2.4 μg / L, respectively, which means that the Ni ion elution amount is higher than that of the NiTi alloy subjected to continuous energization. It is greatly suppressed. _{This is because a smooth TiO 2} film was formed on the surface of the NiTi alloy as shown in FIGS. 3 (b) and 3 (c). Since the average value of the amount of Ni ions eluted in the case of the untreated NiTi alloy is 5.1 μg / L, the NiTi alloy anodized with a pulse voltage of 100 ms in pulse width is more than the untreated NiTi alloy. It can be understood that the amount of Ni ions eluted can be suppressed.

(Example 3)
In Example 3, an experiment in which a NiTi alloy is anodized with a maximum pulse voltage of 5 V and the result thereof are shown. Other conditions are the same as in the experiment of Example 1.

5 (a) to 5 (f) are images of NiTi alloy subjected to anodizing treatment with pulse widths of pulse voltage of 1 ms, 10 ms, 100 ms, 250 ms, 0.5 s, and 1 s, respectively. As can be seen from FIGS. 5 (a) to 5 (f), when the maximum voltage was lowered to 5 V, the TiO ₂ film could not be formed on the surface of the NiTi alloy regardless of the pulse width. Since a calibration curve could not be created from the absorbance of Ni ions in the electrolytic solution, the absorbance of Ni ions in the electrolytic solution is shown below.

FIG. 6 is a graph showing the absorbance of Ni ions in the electrolytic solution when the maximum voltage is 5 V. _{Absorbance is expressed by -log (I / I 0} ), where I irradiates a substance with incident light of _{intensity I 0} and the intensity of the transmitted light is I. Since the absorbance is proportional to the abundance of the substance that absorbs light, it is estimated that the larger the absorbance, the larger the amount of Ni ions eluted. In the NiTi alloy subjected to the anodizing treatment at the maximum voltage of 5 V, the amount of Ni elution increased as compared with the untreated NiTi alloy regardless of the pulse width. _{From the above, in the anodizing treatment using a pulse voltage with a maximum voltage of 5 V, the TiO 2} film cannot be formed on the surface of the NiTi alloy depending on the conditions such as the distance between the anode and the cathode, the period, and the duty ratio, and NiTi It can be understood that the elution of Ni ions from the alloy may not be suppressed.

(Example 4)
In Example 4, an experiment in which a NiTi alloy is anodized by changing the duty ratio of the pulse voltage and the result thereof are shown. The duty ratios are 0%, 25%, 50%, 75% and 100%. A duty ratio of 0% indicates that it is not energized, and a duty ratio of 100% indicates that it is continuously energized. The pulse width is 100 ms under all conditions. Other conditions are the same as in the case of the first embodiment.

FIG. 7 is a graph showing the elution amount of Ni ions when the duty ratio of the pulse voltage is changed. When the duty ratio was 100%, the Ni ion elution amount was measured after diluting the concentration of the electrolytic solution 5 times for convenience of measuring the Ni ion elution amount. When the duty ratio was 100%, the Ni ion elution amount was about 60 μg / L at 5-fold dilution, but the Ni ion elution amount decreased as the duty ratio decreased to 75%, 50%, 25%, and 0%. ..

(Example 5)
In Example 5, an experiment for measuring the amount of Ni ions eluted when immersed in an electrolytic solution for 3 days and the result thereof are shown. First, based on the experimental results of Examples 1 to 4, a NiTi alloy having _{a TiO 2} film was produced by performing anodizing under the conditions of a pulse width of 100 ms, a duty ratio of 50%, a maximum voltage of 10 V, and a processing time of 120 minutes. did. In the anodizing treatment, the electrolytic solution was a 0.1 M _{aqueous solution of HNO 3} , and the temperature was 25 ° C. The surface of the NiTi alloy on which the _{TiO 2} film was formed by the anodizing treatment was _{polished with a # 800 file and immersed in a 0.1 M HNO 3} aqueous solution for 3 days, and the amount of Ni ions eluted was measured. For comparison, the amount of Ni ions eluted from the untreated NiTi alloy was measured by the same method.

FIG. 8 is a graph showing the amount of Ni ions eluted from the NiTi alloy immersed for 3 days. The amount of Ni ions eluted from the untreated NiTi alloy was 5.6 μg / L. On the other hand, the amount of Ni ions eluted with the anodizing treatment was suppressed to 3.7 μg / L. From the above, it can be understood that by optimizing the conditions of the pulse voltage used in the anodizing treatment for the NiTi alloy, a TiO _{2 film capable of suppressing the elution of Ni ions can be formed as compared with the untreated NiTi alloy.}

In Example 5, osteoblast-like cells (MC3T3-E1) were seeded on the surface of the NiTi alloy, then cultured for 7 days, and the number of specific cells at the 7th day was measured. For comparison, the number of specific cells was measured in the same manner for the untreated NiTi alloy. The specific number of viable cells is the ratio of the number of viable cells to the number of seeded cells, and the higher the value, the larger the number of viable cells, and it can be judged that the biosafety is high.

FIG. 9 is a graph showing the number of generative cells on the surface of the NiTi alloy in which osteoblast-like cells were cultured for 7 days. The untreated NiTi alloy had a specific number of cells of 15 or less, whereas the anodized NiTi alloy had a specific number of cells of 25 or more. From the above, it can be understood that the NiTi alloy subjected to the anodizing treatment by the method of the present embodiment has higher biosafety than the untreated NiTi alloy.

1 Surface treatment device 2 Electrolyte 11 Container 12 Anode 13 Cathode 14 Pulse power supply 15 Electric wire

Claims (5)

A dipping step of immersing the NiTi alloy in an electrolytic solution capable of eluting Ni from the surface of the NiTi alloy, and
Anodizing step of performing anodizing treatment to form a _{TiO 2} film on the surface of NiTi alloy by intermittently applying a pulse voltage to the NiTi alloy immersed in the electrolytic solution in the dipping step.
A method for producing a NiTi alloy including. The pulse voltage in the anodizing step has a rectangular waveform, and the pulse width thereof is in the range of 100 ms to 1 s.
The method for producing a NiTi alloy according to claim 1. In the anodizing step, a pulse voltage is periodically applied to the NiTi alloy.
The duty ratio, which is the ratio of the pulse width to the period of the pulse voltage, is in the range of 25% to 75%.
The method for producing a NiTi alloy according to claim 1 or 2. The maximum pulse voltage in the anodizing step is in the range of 10V to 100V.
The method for producing a NiTi alloy according to any one of claims 1 to 3. The electrolytic solution in the dipping step is an aqueous solution containing nitric acid or nitrate, or an aqueous solution containing phosphoric acid or phosphate.
The method for producing a NiTi alloy according to any one of claims 1 to 4.

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