CN108690967B

CN108690967B - Nickel-titanium alloy medical instrument with surface coating and coating preparation method

Info

Publication number: CN108690967B
Application number: CN201810419376.4A
Authority: CN
Inventors: 童丽萍; 王怀雨; 傅劲裕; 朱剑豪; 罗哲民
Original assignee: China Morefound Technology Ltd Shenzhen
Current assignee: China Morefound Technology Ltd Shenzhen
Priority date: 2018-05-04
Filing date: 2018-05-04
Publication date: 2020-07-28
Anticipated expiration: 2038-05-04
Also published as: CN108690967A

Abstract

The invention discloses a method for preparing a surface coating of a nickel-titanium alloy medical instrument, which comprises the following steps: (1) carrying out ion implantation of titanium by loading pulse type negative bias to form a titanium transition layer; and (2) under the condition of keeping the pulse type negative bias and titanium injection, introducing nitrogen at the flow rate which is increased in a gradient manner from 0 to 20sccm to form a titanium-titanium nitride gradient transition layer, and finally forming a pure titanium nitride layer. The invention also discloses a nickel-titanium alloy medical instrument with the surface coating, wherein the surface coating comprises a titanium transition layer, a titanium-titanium nitride gradient transition layer and a pure titanium nitride layer from inside to outside; and in the titanium-titanium nitride gradient transition layer, the content of titanium nitride is increased in a gradient manner.

Description

Nickel-titanium alloy medical instrument with surface coating and coating preparation method

Technical Field

The invention belongs to the technical field of biomedical materials, and particularly relates to a method for preparing a surface coating of a nickel-titanium alloy medical instrument and the nickel-titanium alloy medical instrument with the surface coating.

Background

Malocclusion is an oral disease with a high incidence in all countries of the world. The developmental deformity is the deformity of dentition, jaw bone and craniofacial bone caused by congenital genetic factors or acquired environmental factors, such as diseases, bad habits of oral cavity, dysdontia, etc., during the growth and development of children. It not only affects the beauty of the face, but also the jaw function. In recent years, with the improvement of living standard of people, not only children but also more and more adults are undergoing orthodontic treatment.

In orthodontic treatment, orthodontic wires are a class of metal arch wires clinically used for manufacturing orthodontic appliances, and are key components for generating force in the appliances. The main function of the orthodontic wire is an auxiliary tool commonly used for oral cavity correction of a patient, and the orthodontic wire plays a decisive role in achieving the best possible dentition relationship, keeping the post-healing stability and increasing the facial attractiveness. The common orthodontic wire in the market is mainly made of stainless steel and nickel titanium memory alloy.

Stainless steel orthodontic wires have been used clinically for a long time, but they have a high degree of stiffness and a large degree of force variation when moving teeth. In addition, the degree of coincidence of the steel wire and the bracket groove is poor, which shows that the control capability to the tooth position is poor, and the correcting effect is not ideal enough. CN 90219653 proposes that the orthodontic treatment is realized by using a titanium steel combined arch wire, wherein a titanium wire is used at the orthodontic position of the malformed teeth, and a steel wire is used at the fixed position, so as to improve the arrival rate and anchorage force of the malposed teeth. However, the titanium-steel material is still a steel material, the yield strength is high, and the residual stress in the bent material is high, so that the elastic property of the bent material is influenced; moreover, different materials are likely to form a potential therebetween, and thus corrosion is likely to occur in the oral cavity.

Nickel titanium (NiTi) alloy is a shape memory alloy that can automatically restore its plastic deformation to its original shape at a certain temperature, and has good plasticity. Besides the unique shape memory function, the nickel-titanium alloy also has the excellent characteristics of wear resistance, corrosion resistance, high damping, superelasticity and the like. Moreover, the corrosion resistance of the nickel-titanium alloy is superior to that of the best medical stainless steel at present, so that the nickel-titanium alloy can meet the application requirements of various medicines and is a very excellent functional material.

Andreasen et al used Nitinol wire for use in orthodontics in 1971 for the first time (Andreasen G F, Hilleman T B. An evaluation of 55cobalt substistuted nitinol wire for use in orthodontics [ J ]. J.Am.Dent Ashoc., 1971,82(6):1373 + 1375; Andreasen G F, Brady PR. Ause hydrothesis for 55nitinol wire for orthodontics [ J ]. Angle Orthod.,1972,42(2):172 + 177). To date, nitinol orthodontic products have played an important role in orthodontic treatment.

For example, CN 92221550.2 discloses "shape memory nickel titanium alloy: the correcting spring is made of nickel-titanium alloy with shape memory and super elasticity, so that the correcting spring can automatically and slowly exert force during the use process. CN 91224652.9 discloses a "orthodontic tension spring", wherein the tension spring is composed of a spring body and a suspension loop, and the tension spring is made by winding a nickel-titanium alloy wire. CN 201410821176.3 discloses "an orthodontic tooth arch wire with gradually changed orthodontic force value and its forming process and device". None of these nitinol surfaces were coated. CN 200810155809.6 discloses a method for making invisible brackets and invisible dental archwires, which discloses that the surface of a metal dental archwire can be coated with organic materials by electrophoresis, dip coating and spray coating, but does not disclose the specific structure of the organic material coating.

At present, the domestic optimization of the nickel-titanium orthodontic wire mostly focuses on the aspects of orthodontic wire function and mechanical property. For example, CN 201410013363.9, applied by shanghai emmondi materials science and technology gmbh, proposes a process for producing a novel copper-nickel-titanium dental arch wire. The process uses Ni (50.14%) Ti (43.54%) copper (Cu, 6.26%) to make vacuum consumable arc melting into new alloy, then makes it into orthodontic wire. The manufactured orthodontic wire has unique mechanical property and characteristic, and can overcome the defects of the traditional stainless steel dental arch wire and the nickel-titanium alloy dental arch wire. Also, CN 201410821176.3 applied by emmondi adopts a graded heat treatment process to gradually heat different positions of the nitinol arch wire, and the orthodontic wire gradually changes the orthodontic force value and the elastic modulus at different positions by regulating and controlling the aging temperature and the heat preservation time, so as to meet the requirements of different patients.

In addition, the industry prepares colored coatings on the outer surface of the metal orthodontic wire to play a role in beauty. For example, CN201110296307.7 prepares such a color coating on the outer surface of the metal orthodontic wire by a painting-high temperature curing method. The invisible orthodontic wire is a novel coated orthodontic wire which is concerned in the industry at present, a coating layer close to teeth is prepared on the surface of the orthodontic wire by a physical or chemical method, the embarrassment that a patient smiles metal in the using process is avoided, and the attractive effect is achieved. CN201510386774.7 proposes to prepare a porous titanium oxide layer on the surface of nitinol by anodic oxidation, then soaking in epoxy/teflon varnish to obtain a transparent coating. CN 200710021147.9 is to coat a layer of aluminum or aluminum alloy on the surface of the dental arch wire and then coat the outer layer of aluminum with polymer material.

However, nickel-titanium (NiTi) alloys used in clinical practice are nickel-rich nickel-titanium alloys in which the percentage of the mass fraction of the nickel (Ni) element exceeds 50%, since the reactivity of Ti in the composition is much higher than Ni, the main components in the surface layer of NiTi alloys are thin Ti oxides (TiO2, TiO, etc.), Ni simple substance and very small amount of Ni oxide, and there is a Ni-rich layer under the surface oxide layer, the naturally formed titanium oxide layer is very thin and not dense enough to prevent the release of Ni ions in the base material, and the corrosion resistance of NiTi materials is still insufficient, although Ni is one of the essential trace elements for the human body, the excessive intake of Ni ions may cause respiratory dysfunction, allergic reaction, and even may inhibit the proliferation of cells (Regina L W, Sanford B, L inda C L. Effects of metallic tissue on physiological tissue pathology [ J ]. Biomaterials,1999,20: 1657, 1657.5.7.7.5. purity, 16435.

The prior art focuses on aesthetic and mechanical property control, and ignores the potential long-term hazard that nickel ions may generate after being released and ingested during the use of the nickel-titanium orthodontic wire. In order to reduce Ni release in NiTi alloy medical devices and to reduce the coefficient of friction/friction, other types of coatings have also been attempted on the NiTi alloy device surfaces.

CN 200910243794.3 discloses a method for preparing a biological coating from a titanium-niobium-aluminum based titanium alloy as a base material, and at least one of Ti, niobium (Nb), and tin, aluminum, silicon, zirconium, tantalum, hafnium, palladium, gallium, germanium, nickel, and oxygen, and coating the biological coating on the surface of an orthodontic wire by using ion plating technology and Dual Ion Beam Sputter Deposition (DIBSD) thin film technology. The prepared orthodontic wire has the composite characteristics of biocompatibility, corrosion resistance, superelasticity, shape memory effect, fatigue performance and the like which are greatly improved.

CN 200680039938.8 discloses a method for manufacturing a coated endovascular device by means of magnetron sputter deposition to produce a coating on the surface of an endovascular device made of an inert and biocompatible metal alloy, such as nitinol. The method specifically comprises the following steps: depositing a first titanium layer; subjecting the first titanium layer to a first nitrogen treatment by transmitting a high ionic current over the substrate to convert at least a portion of the first titanium layer to a titanium nitride ceramic coating; depositing a second titanium layer; the second titanium layer is subjected to a second nitrogen treatment by transmitting a high ion current over the substrate to convert at least a portion of the second titanium layer into a titanium nitride ceramic coating. By such a method, a mixed coating of titanium and titanium nitride is finally obtained. But the method is by way of sputter deposition, which readily bombards ions into the substrate. Moreover, the nitrogen ions left in the previous nitrogen treatment affect the quality of the titanium implanted layer. In addition, during the process, the gas path is frequently switched to apply different layers, which makes the preparation efficiency low.

CN 200680054491.1 discloses a method for preparing a surface coating of a nickel-titanium alloy medical instrument, which uses a dc power supply to load negative bias, and firstly performs alternate pure titanium and titanium-titanium nitride mixed coating on the nickel-titanium alloy, and finally plates a pure titanium nitride layer. During the whole coating process, negative bias exists all the time, which leads to continuous ion acceleration, and the temperature of the substrate material (namely the nickel-titanium orthodontic wire) is rapidly increased, which may cause the phase transition temperature of the nickel-titanium alloy to change, and lead to the reduction of the mechanical property and the loss of the super-elastic property of the orthodontic wire. Therefore, in order to control the temperature of the substrate material, in the method disclosed in CN 200680054491.1, the duration of each plating is short (generally 20 to 120s), and the ion source is turned off immediately after the plating, and the next coating is plated after the ion source is kept for more than 20s, which makes the method less efficient.

How to efficiently complete the coating preparation and simultaneously balance the substrate temperature and the coating bonding force in the coating treatment process is a technical problem to be solved. Therefore, in order to overcome the problems in the prior art, the invention aims to continuously and efficiently prepare a low-friction-coefficient and biosafety coating on the surface of the NiTi alloy medical instrument by loading pulse type negative bias in a multi-component ion implantation deposition mode so as to increase the wear resistance of the NiTi alloy medical instrument and prevent the release of Ni ions of a base material, thereby further improving the effectiveness and safety of the medical instrument. More particularly, the invention aims at solving the problem of safety, and prepares a biosafety titanium nitride coating on the surface of the nickel-titanium orthodontic wire by an ion implantation deposition technology, thereby increasing the wear resistance of the orthodontic wire, preventing the nickel ions of a substrate material from being separated out, reducing the friction coefficient of the surface of the orthodontic wire and achieving safer and more effective orthodontic effect.

Disclosure of Invention

The invention aims to provide a method for efficiently preparing a surface coating of a low-friction-coefficient and biosafety nickel-titanium alloy medical instrument.

It is another object of the present invention to provide a low coefficient of friction and biosafety nitinol medical device with a surface coating.

In order to achieve the above object, the present invention provides a method for preparing a surface coating of a nickel titanium alloy medical device, the method comprising the steps of:

(1) carrying out ion implantation of titanium by loading pulse type negative bias to form a titanium transition layer; and

(2) under the condition of keeping pulse type negative bias and titanium injection, nitrogen is introduced at the flow rate which is increased in a gradient manner from 0sccm to 20sccm to form a titanium-titanium nitride gradient transition layer, and a pure titanium nitride layer is formed outside the titanium-titanium nitride gradient transition layer.

In the above method of the present invention, before step (1), step (0') may be further included: putting the nickel-titanium alloy medical instrument into a vacuum chamber, introducing inert gas and loading pulse type negative bias to perform plasma surface cleaning on the nickel-titanium alloy medical instrument.

In the above method of the present invention, the pulsed negative bias voltage applied in the step (0'), the step (1) or the step (2) may be-50 to-250V, preferably-100 to-200V, respectively. For example, the pulsed negative bias voltage loaded can be-50, -60, -70, -80, -90, -100, -110, -120, -130, -140, -150, -160, -170, -180, -190, -200, -210, -220, -230, -240, -250V, respectively.

In the above method of the present invention, the frequency of the pulsed negative bias in step (0'), step (1) or step (2) may be 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000Hz, preferably 400 to 1500Hz, and more preferably 500 to 1000Hz, respectively. The duty cycle of the pulsed negative bias voltage may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, preferably 10% to 20%, respectively.

In the above method of the present invention, the step (0'), the step (1) or the step (2) may be continued for 10 to 20 minutes each.

Further, the thickness of the titanium transition layer prepared by the step (1) can be 100 to 500nm, preferably 100 to 300nm, and more preferably 100 to 200 nm. Through the step (3), the thickness of the prepared titanium-titanium nitride gradient transition layer and the pure titanium nitride layer can be 100-500 nm, preferably 100-300 nm, and more preferably 200-300 nm.

Further, after the step (0'), the inert gas may be turned off.

Optionally, the inert gas may not be turned off after said step (0'). That is, the inert gas is kept continuously fed throughout the treatment, in which case in step (2) the ratio of the amount of nitrogen fed to the inert gas is finally 9:1 to 1:1, for example 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1 or 1:1, preferably 1: 1. The continuous introduction of the inert gas can better help nitrogen ionization and promote the injection deposition of the titanium nitride.

Further, in the step (2), the flow rate of the inert gas can be uniformly increased by a range of 1 to 5sccm/min, preferably 1 to 4sccm/min, more preferably 1 to 3sccm/min, and even more preferably 2sccm/min, so that the amount of the titanium nitride in the titanium-titanium nitride gradient transition layer is uniformly and gradiently increased. On the other hand, the titanium-titanium nitride gradient transition layer also shows corresponding gradient change in structure.

Further, in the above method, the inert gas is preferably argon gas.

In the method of the present invention, prior to step (0'), the nitinol medical device may be chemically polished to remove the surface oxide layer. In this context, "chemical polishing" is a method of removing wear marks and leveling etching by selective dissolution of the surface irregularities of a sample by chemical etching with a chemical agent. For example, a strong acid reagent may be used as the chemical polishing liquid.

Further, the temperature of the nitinol medical device may be controlled to not exceed 300 ℃, preferably not exceed 290 ℃, 280 ℃, 270 ℃, 260 ℃ or 250 ℃ throughout the treatment. More preferably, the present invention can monitor the reaction temperature on the target table in real time by adding a temperature sensor to control the temperature.

Further, a filter device may be provided at the exit position of the ion beam to prevent large particles from entering the vacuum chamber, depositing on the substrate and causing non-uniformity of the coating. The filter device is preferably a filter screen.

Further, the nickel titanium alloy medical device may be a nickel titanium orthodontic wire.

By the method, other ceramic coatings such as TiN, CrN, CrAlN and the like can be coated in a pulse ion implantation mode.

In another aspect, the present invention provides a nickel titanium alloy medical device having a surface coating, wherein the surface coating is prepared by the above-described method for preparing a surface coating of a nickel titanium alloy medical device of the present invention.

Further, the surface coating may include a titanium transition layer, a titanium-titanium nitride gradient transition layer, and a pure titanium nitride layer from the inside to the outside.

Further, in the titanium-titanium nitride gradient transition layer, the content of titanium nitride is increased in a gradient manner.

The method for preparing the surface coating of the nickel-titanium alloy medical instrument uses pulse type negative bias voltage to replace direct current power supply bias voltage, can reduce bombardment energy and total action time of particles on the base material in the coating preparation process, and provides heat dissipation time for the base material, thereby effectively controlling the temperature rise of the base material in the treatment process and preventing the martensite phase transition temperature rise and the loss of mechanical properties of the base material. Furthermore, by using the pulse power supply, the gas circuit is prevented from being switched in the processing process, so that the preparation efficiency is improved.

The nickel-titanium alloy medical instrument prepared by the method has a biosafety and wear-resistant surface coating, and the surface coating covers the surface of the nickel-titanium alloy medical instrument (such as an orthodontic wire), so that the corrosion resistance of the nickel-titanium alloy medical instrument is improved, the release of nickel ions in the medical instrument in a complex body (such as an oral cavity) environment is reduced, the aim of reducing the intake of the nickel ions is fulfilled, and the health risk possibly brought by the nickel is reduced. In addition, the surface coating uses titanium and a titanium-titanium nitride gradient transition layer as transition, so that the stress difference between the titanium nitride coating and the NiTi substrate can be reduced, and the binding force between the coating and the substrate is improved.

On the other hand, the surface coating prepared by the method of the invention can reduce the friction coefficient of the surface of the nickel-titanium medical instrument. For the orthodontic wire, the reduced surface friction coefficient can reduce the friction between the surface of the orthodontic wire and the bracket, which has important significance on the rearrangement of teeth in early stage of orthodontics.

Drawings

Fig. 1 shows a formed nickel titanium (NiTi) orthodontic wire. Fig. 1a is an appearance of a formed NiTi orthodontic wire; fig. 1b is a cross-sectional view of an oval orthodontic wire; fig. 1c is a cross-sectional view of a square orthodontic wire.

Fig. 2 shows a flow chart of an ion implantation deposition process for a NiTi orthodontic wire according to the method of the invention.

Fig. 3 shows the appearance (a) and the micro-morphology (b) of a biosafety NiTi orthodontic wire prepared according to the method of the invention.

Fig. 4 shows an apparatus for determining the coefficient of static friction of the surface of an orthodontic wire.

Fig. 5 shows the cell activity of NCTC clone 929 and He L a cells cultured using the coated NiTi orthodontic wire soaked cell culture media prepared according to the method of the present invention, indicating p < 0.05 compared to uncoated NiTi orthodontic wires.

Fig. 6 shows corrosion resistance tests of uncoated NiTi orthodontic wires and coated NiTi orthodontic wires prepared according to the method of the invention in a physiological saline environment.

Detailed Description

The present invention is explained in detail by the following embodiments. It should be understood that the following embodiments are only preferred embodiments of the present invention, and that several improvements or modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention, and these improvements and modifications are also considered to be within the scope of the present invention.

As described above, Nitinol has been widely popular in the oral field because of its heat-activated effect and superelastic properties, which produces a sustained and gentle mechanical spring force that is important for initial alignment treatment of orthodontics-the selection of orthodontic wire and bracket determines the rate of tooth alignment and the comfort of the patient during treatment-compared to conventional stainless steel wires, patients using Nitinol wire tend to have shorter alignment and correction times and less pain for the patient (West AE, joints M L, New com RG. multiflex cover subelementation: a randomised clinical trial of the dental alignment [ J ]. am. J. original. 471. Dentacial Ortho., 1995; 108: 464-).

However, since the titanium oxide layer naturally formed on the surface of nickel titanium (NiTi) alloy is thin and not dense enough, it is impossible to prevent the release of Ni ions in the base material. On the other hand, the oral environment of human body is very complicated, and factors such as acid, alkali, salt, temperature and the like in food are changed violently. The corrosion resistance and safety of the NiTi orthodontic wire which is used for a long time in the environment are important problems which are ignored all the time. Therefore, in order to reduce the release of Ni in the NiTi orthodontic wire during the correction process and reduce the friction coefficient/friction force, it is necessary to prepare a coating on the surface of the NiTi orthodontic wire.

The ion implantation deposition technology adopted in the prior art isAnd coating the NiTi orthodontic wire. The ion implantation deposition technique is to use plasma ionization technique under vacuum condition to ionize the target atom into ions partially and generate many high-energy neutral atoms. By applying negative bias to the substrate to be coated, ions are implanted and deposited on the surface of the substrate to form a coating under the action of an external electric field. However, the ion implantation deposition technique has a certain limitation in the application of the NiTi alloy orthodontic wire. In the coating preparation process, if a direct-current power supply is adopted to load bias voltage to the target platform, the plasma can continuously move to the substrate at high speed under the action of an electric field to generate a large amount of heat for bombarding the surface of the substrate, so that the temperature of the fine NiTi alloy orthodontic wire is rapidly increased; while the martensite final temperature A of the NiTi alloy_fThe NiTi alloy is particularly sensitive to the external heating environment and can be increased along with the increase of the temperature of the base material, so that the shape memory function of the NiTi alloy is influenced. However, if the bias voltage is not applied, the coating obtained by the slow deposition of the plasma is poor in the binding force with the substrate, and the coating is easy to peel off in use, so that the ideal effect is not achieved.

Therefore, the inventor develops a method for efficiently preparing the surface coating of the low-friction-coefficient and biosafety nickel-titanium alloy medical instrument by recording the pulse type negative bias voltage, and a low-friction-coefficient and biosafety nickel-titanium orthodontic wire with the surface coating.

The present invention is described in detail by the following examples, but the present invention is not limited thereto.

Example 1 treatment of NiTi orthodontic wires before coating preparation

The appearance of the formed NiTi orthodontic wire is shown in figure 1, the formed NiTi orthodontic wire is a clinical commonly used untreated NiTi orthodontic wire, the diameter of the formed NiTi orthodontic wire can be from 0.3mm to 0.51mm, the length L of the square wire can be from 0.4mm to 0.65mm, and the width W can be from 0.4mm to 0.55mm, before treatment, the NiTi orthodontic wire can be subjected to treatment such as surface oxide layer removal, ultrasonic cleaning, blow drying and the like, and the specific process is as follows:

strong acid is used as surface polishing liquid, and the solution comprises HF and HNO₃:H₂O1: 10:20, acid wash to material and liquid surfaceNo bubble escaping, or using solution with HF and HNO as the components and the proportion₃:H₂Pickling with strong acid (1.5-2.5): 8-15): 10-20) as surface polishing liquid for 5-10 min;

taking out the NiTi orthodontic wire, and rinsing the NiTi orthodontic wire by using deionized water;

ultrasonic cleaning with acetone, anhydrous ethanol and deionized water for 10 min;

blow-drying with nitrogen for standby.

Example 2 ion implantation deposition treatment of NiTi orthodontic wire

As shown in fig. 2, the NiTi orthodontic wire is subjected to an ion implantation deposition process.

2-1, the plasma injection deposition equipment used in the embodiment evaporates the target material by arc discharge to generate ions, and the ions are loaded to the target platform by pulse type negative bias voltage to realize intermittent ion injection deposition. The specific operation is as follows:

and placing the blow-dried NiTi orthodontic wire in plasma treatment equipment. The direct current filters the arc source to evaporate the titanium target, the current of the arc source is 60A, the negative bias voltage loaded on the target table is-200V, the frequency is 1000Hz, and the duty ratio is set to 20%. And introducing argon gas for surface sputtering cleaning, wherein the introducing flow of the argon gas is 30sccm, and the cleaning time is 5-8 minutes. After the cleaning is finished, the flow of argon is adjusted to be 20sccm, the target platform bias voltage is reduced to-100V, the frequency is reduced to 500Hz, the duty ratio is set to be 10%, the intermittent ion implantation deposition of the titanium transition layer is carried out, and the processing time is 10 minutes. And then, gradually introducing nitrogen, wherein the flow rate of the nitrogen is increased in a gradient manner from 0-20 sccm, and finally the flow rate of the nitrogen and argon reach 1:1, wherein the treatment time of the step lasts for 15 minutes. The continuous introduction of argon can better help the ionization of nitrogen and promote the injection and deposition of titanium nitride. And after all treatments are finished, closing the arc source, the air valve and the vacuum pump, and opening the vacuum chamber for sampling after the air pressure in the vacuum chamber is recovered to the atmospheric pressure.

2-2. in this example, the same plasma implantation deposition apparatus as in example 2-1 was used to perform the ion implantation deposition treatment. The specific operation is as follows:

and placing the blow-dried NiTi orthodontic wire in plasma treatment equipment. And (3) carrying out direct-current filtering, arc source evaporation and titanium target, wherein the arc source current is 80A, the negative bias voltage loaded on the target table is minus 100V, the frequency is 500Hz, the duty ratio is set to be 10%, argon is introduced for carrying out surface sputtering cleaning, the flow of the argon is 20sccm, and the cleaning time is 15 minutes. And (4) closing the argon after the cleaning is finished, keeping other parameters unchanged, and performing injection deposition treatment on the titanium transition layer, wherein the treatment time of the step is 15 minutes. Then, nitrogen is introduced, the flow rate of the nitrogen is increased from 0-20 sccm in a gradient manner, and the treatment time lasts for 15 minutes. And after all treatments are finished, closing the arc source, the air valve and the vacuum pump, and starting the vacuum chamber for sampling when the air pressure in the vacuum chamber is restored to the atmospheric pressure.

2-3. in this example, the same plasma implantation deposition apparatus as in example 2-1 was used to perform the ion implantation deposition treatment. The specific operation is as follows:

and placing the blow-dried NiTi orthodontic wire in plasma treatment equipment. The direct current filtering arc source evaporates the titanium target, and the magnitude of the arc source current is 80A. The filter screen is arranged at the outlet of the arc source, so that larger particles can be filtered, the large particles are prevented from being gathered when the particles are injected into a substrate and deposited, and the surface flatness and uniformity are reduced. Loading negative bias voltage of-200V on the target platform, setting the frequency to be 1000Hz and the duty ratio to be 20%, and introducing argon gas to perform surface sputtering cleaning, wherein the introduction flow of the argon gas is 20sccm, and the cleaning time is 10 minutes. After cleaning, reducing the bias voltage of the target platform to-100V, the frequency to 500Hz, setting the duty ratio to be 10 percent, keeping other parameters unchanged, and carrying out intermittent ion implantation deposition on the titanium transition layer for 15 minutes. And then, gradually introducing nitrogen, wherein the flow rate of the nitrogen is increased in a gradient manner from 0-20 sccm, and finally the flow rate of the nitrogen and argon reach 1:1, wherein the treatment time of the step lasts for 15 minutes. And after all treatments are finished, closing the arc source, the air valve and the vacuum pump, and starting the vacuum chamber for sampling when the air pressure in the vacuum chamber is restored to the atmospheric pressure.

2-4. in this example, the same plasma implantation deposition apparatus as in example 2-1 was used to perform the ion implantation deposition treatment. The specific operation is as follows:

and placing the blow-dried NiTi orthodontic wire in plasma treatment equipment. The direct current filtering arc source evaporates the titanium target, and the magnitude of the arc source current is 80A. The filter screen is arranged at the outlet of the arc source, so that larger particles can be filtered, the large particles are prevented from being gathered when the particles are injected into a substrate and deposited, and the surface flatness and uniformity are reduced. Loading negative bias voltage of-100V on the target platform, setting the frequency to be 1000Hz and the duty ratio to be 20%, introducing argon gas for surface sputtering cleaning, wherein the introduction flow of the argon gas is 30sccm, and the cleaning time is 15 minutes. After cleaning, reducing the bias voltage of the target platform to-100V, the frequency to 500Hz, setting the duty ratio to be 10 percent, keeping other parameters unchanged, and carrying out intermittent ion implantation deposition on the titanium transition layer for 20 minutes. And then, gradually introducing nitrogen, wherein the flow rate of the nitrogen is increased in a gradient manner from 0-20 sccm, and finally the flow rate of the nitrogen and argon reach 1:1, wherein the treatment time of the step lasts for 15 minutes. And closing the argon and nitrogen valves, reducing the current of the arc source to 60A, continuously working for 3 minutes, finally closing the arc source and the vacuum pump, and opening the vacuum chamber for sampling when the air pressure in the vacuum chamber is restored to the atmospheric pressure. The last step of arc source continues to work for a little time to effectively seal the columnar crystal possibly formed in the titanium nitride coating, which is beneficial to improving the corrosion resistance and the safety.

Through the preparation steps, a gradient coating which is gradually transited from a titanium-titanium nitride gradient transition layer to pure titanium nitride can be formed on the surface of the nickel-titanium orthodontic wire without frequently switching the gas circuit, so that the friction force of the orthodontic wire in the using process can be reduced by the coating, and early tooth rearrangement is better facilitated; meanwhile, the existence of the coating can also reduce the precipitation of free nickel ions in the base material and improve the safety of the base material.

EXAMPLE 3 appearance of NiTi orthodontic wire after coating application

As shown in fig. 3(a), the NiTi orthodontic wire after the coating treatment has a light gold color, and the NiTi orthodontic wire without the treatment has a metallic primary color. The color difference indicates the success of the Ti-TiN coating. Fig. 3(b) shows the microstructure of the NiTi orthodontic wire prepared in example 2-2 under an optical microscope, indicating that the surface of the NiTi orthodontic wire prepared by the method of the present invention is tightly and uniformly wrapped with a coating layer consisting of a titanium transition layer, a titanium-titanium nitride gradient transition layer, and a pure titanium nitride layer.

EXAMPLE 4 testing of the martensitic transformation temperature of NiTi orthodontic wires after coating application

The NiTi substrate is extremely sensitive to the temperature change in the external environment, and ensures that the martensite phase transformation end point temperature A of the NiTi substrate material is not obviously improved in the surface coating treatment process_fAnd martensite start formation temperature M_sIs particularly important. If A_fThe point temperature exceeds 37 ℃, the orthodontic wire basically cannot normally function in the orthodontic process. To this end, this example tested the martensitic transformation temperature A of NiTi orthodontic wires before and after the coatings prepared by examples 2-3_fAnd M_s。

The phase transition temperatures of the material of the NiTi orthodontic wire before and after the preparation of the coating are detected by using Differential Scanning Calorimetry (DSC), and the results are shown in Table 1, wherein the phase transition temperatures of the NiTi orthodontic wire before and after the treatment are basically unchanged.

Table 1. phase transition temperatures of untreated NiTi orthodontic wires and coated NiTi orthodontic wires prepared by the method of the invention.

	NiTi orthodontic wire	NiTi orthodontic wire with coating
			A_f	21.5±1.25	22.45±0.82
M_s	18.19±0.67	18.82±1.15

EXAMPLE 5 measurement of the coefficient of friction of the surface of NiTi orthodontic wire after coating application

In this example, the coefficient of friction of the surface of the coated NiTi orthodontic wire prepared by examples 2-4 was measured.

The measurement was carried out by means of a Micro-force material Tester (Instron 5848Micro Tester). The method comprises the following specific steps: the orthodontic bracket made of stainless steel materials is fixed on a smooth stainless steel substrate sheet by using the 3M adhesive, and the orthodontic bracket can be used after the adhesive is dried and solidified. As shown in figure 4, the stainless steel lining plate and the bracket are both fixed vertical to the table top, after a NiTi orthodontic wire with the length of 12cm is cut out and penetrates through the bracket, the opening of the bracket is tied by using artificial rubber. The lower end of the orthodontic wire is hung with a 500g weight, the upper end of the orthodontic wire is fixed by a testing machine clamp, and the device is used for simulating the real friction environment between the orthodontic wire and the bracket when the orthodontic wire works in the oral cavity. The initial loading force is 1N, and the loading force value F is gradually increased until the orthodontic wire is pulled, the marked loading force is Fm, and the loading force is determined by the static friction force and the gravity of the weight. The magnitude of the friction coefficient can be judged by reading the magnitude of the upper end loading force Fm.

As can be seen from table 2, the Fm value of the pulled coated NiTi orthodontic wire is smaller than that of the untreated NiTi orthodontic wire, which demonstrates that the coating of the present invention consisting of the titanium transition layer, the titanium-titanium nitride gradient transition layer and the pure titanium nitride layer can reduce the static friction force of the surface of the NiTi orthodontic wire.

TABLE 2 micro-force test System for comparing the static friction of different orthodontic wires of NiTi

Example 6 Biosafety verification of NiTi orthodontic wire after coating application

This example tested the biological safety of the NiTi orthodontic wires with a coating consisting of a titanium transition layer, a titanium-titanium nitride gradient transition layer and a pure titanium nitride layer prepared by examples 2-4.

According to the standard GB/T16886.5-2003, the cell culture is carried out on a cell culture medium in which orthodontic wires are soaked, and the biological safety of the orthodontic wires is characterized through a cytotoxicity experiment.

TABLE 3 cytotoxicity evaluation for different NiTi orthodontic wires (note: set the DMSO cell culture medium group containing 5% volume fraction as positive control).

The "grade" in table 3 means "cytotoxicity grade", which was classified as shown in table 4 below.

Table 4. international standard for cytotoxicity rating.

Grade of cytotoxicity	Relative proliferation rate%
		0	≥100
1	80～99
		2	50～79
3	30～49
		4	0～29

From the results in table 3, it can be seen that the cells of the positive control (using 5% volume fraction DMSO) did not proliferate, whereas the cells cultured in the medium soaked with the coated NiTi orthodontic wire prepared by the method of the present invention had a relative proliferation rate of NCTC clone 929 and He L a cells of 102% ± 4.3% or 105% ± 3.9%, respectively, which is significantly higher than the relative proliferation rate of 84% ± 2.1% or 91% ± 2.7% of the uncoated NiTi orthodontic wire, which demonstrates that the coating application prepared by the method of the present invention significantly reduced the acute toxicity of NiTi orthodontic wire to the cells, and accordingly the safety of the coated NiTi orthodontic wire composed of the titanium transition layer, the titanium-titanium nitride gradient transition layer and the pure titanium nitride layer prepared by the present invention was significantly improved.

Example 7 Corrosion resistance testing of coated NiTi orthodontic wires

Another important criterion that determines the safety of metallic materials is corrosion resistance. The oral environment is complex, and the change of sugar, salt, acid, temperature and the like is various, which puts higher requirements on the corrosion resistance of metal materials. This example therefore examined the electrochemical corrosion behavior of NiTi orthodontic wires in a saline solution environment at 37 ℃ before and after the coating was applied by example 2-2.

The detection is carried out by using a double constant potential rectifier CHI760E Chenghua, the test conditions of the OCPT curve include that the voltage range is-3V, the test time is at least 2h, the actual test time is 8000s, and the test conditions of the curve L SV include that the voltage range is-3V, the sensitivity is 10^-2The scanning speed was 1 mV/s.

Results as shown in fig. 6, the results of OCPT curve and L SV curve both indicate that the corrosion resistance of the biosafety orthodontic wire in physiological saline environment is better than that of the NiTi orthodontic wire.

Example 8 abrasion resistance test on NiTi orthodontic wire after coating application

This example examined the wear resistance of NiTi orthodontic wires after application of the coating by examples 2-2. With stainless steel as a counter-grinding surface, the NiTi orthodontic wire with the coating prepared by the method of the invention has the advantages that after the NiTi orthodontic wire is rubbed for 400 times, the surface coating is still intact, and the NiTi orthodontic wire does not fall off or remarkably abrade.

Claims

1. A method of making a surface coating for a nickel titanium alloy medical device, the method comprising the steps of:

(2) under the condition of keeping pulse type negative bias and titanium ion implantation, introducing nitrogen at a flow rate which is increased in a gradient manner from 0 to 20sccm to form a titanium-titanium nitride gradient transition layer, and forming a pure titanium nitride layer outside the titanium-titanium nitride gradient transition layer;

in the step (1) or the step (2), the loaded pulse type negative bias is-50 to-250V; the frequency is 300-2000 Hz; the duty ratio is 5% -25%.

2. The method according to claim 1, characterized in that, prior to said step (1), the method further comprises a step (0'): putting the nickel-titanium alloy medical instrument into a vacuum chamber, introducing inert gas and loading pulse type negative bias to perform plasma surface cleaning on the nickel-titanium alloy medical instrument.

3. The method of claim 1 or 2, wherein the temperature of the nitinol medical device is controlled to not exceed 300 ℃ throughout the treatment.

4. The method of claim 1 or 2, wherein the temperature of the nitinol medical device is controlled to not exceed 250 ℃ throughout the treatment.

5. The method according to claim 1 or 2, characterized in that in step (1) or step (2), the pulsed negative bias voltage loaded is-100 to-200V; the frequency is 400-1500 Hz; the duty ratio is 10% -20%.

6. The method according to claim 5, wherein in step (1) or step (2), the frequency of the applied pulses is 500 to 1000 Hz.

7. The method according to claim 1 or 2, wherein step (1) and step (2) each last 10 to 20 minutes.

8. The method of claim 2, wherein after step (0'), the inert gas is turned off.

9. The method according to claim 2, wherein the inert gas is kept being fed during the treatment, and the ratio of the amount of nitrogen fed to the amount of the inert gas in step (2) is finally 9:1 to 1: 1.

10. The method according to claim 2, wherein the inert gas is kept being fed during the treatment, and the ratio of the amount of nitrogen fed to the amount of the inert gas in step (2) finally reaches 1: 1.

11. A nickel titanium alloy medical device having a surface coating, wherein the surface coating is prepared by the method of any one of claims 1 to 10; the surface coating comprises a titanium transition layer, a titanium-titanium nitride gradient transition layer and a pure titanium nitride layer from inside to outside; and in the titanium-titanium nitride gradient transition layer, the content of titanium nitride is increased in a gradient manner.

12. The nickel titanium alloy medical device of claim 11, wherein the medical device is an orthodontic wire.