KR20120105280A - A surface coating method of titanium by ha blasting, tio2 anodizing and gf magnetron sputtering - Google Patents

Abstract

PURPOSE: A titanium surface coating method by HA blasting, TiO2 anode oxidation, and RF magnetron sputtering is provided to improve hydrophilic property and reduce elastic modulus of titanium by HA blasting the titanium surface, forming a nanotube TiO2 coating layer on the blasted titanium surface, and then forming an RF magnetron sputtered HA coating layer. CONSTITUTION: A titanium surface coating method by HA blasting, TiO2 anode oxidation, and RF magnetron sputtering comprises the steps of: HA(hydroxyapatite) blasting the surface of titanium, washing, rinsing, and drying the titanium, forming a nanotube TiO2 coating layer on the titanium surface through anode oxidation, and forming an HA coating layer on the titanium surface with the nanotube TiO2 coating layer by RF magnetron sputtering.

Description

Titanium surface coating method by HA blasting, TiO₂ anodization and RF magnetron sputtering {A SURFACE COATING METHOD OF TITANIUM BY HA BLASTING, TIO2 ANODIZING AND GF MAGNETRON SPUTTERING}

The present invention relates to three methods of surface coating of titanium for use as dental and orthopedic implant materials.

Commercially pure titanium (cpTi) is widely used as a dental root implant material and orthopedic implant material in clinical dentistry due to its mechanical strength, stability and good compatibility with bone tissue. This high level of biocompatibility is a stable TiO ₂ naturally formed on the surface of cpTi that is believed to assist in the formation of osteogenic extracellular matrix at the implant-bone tissue interface. Due to layers.

However, this TiO ₂ layer is very stable and takes a long time for osseointegration. In addition, bone reactions to the implant surface influence the durability of the implant, depending on the chemical and physical properties of the Ti surface.

Therefore, studies on surface modification have been actively conducted to control titanium surface and increase biocompatibility according to specific needs of specific medical applications, but have not been able to obtain satisfactory results.

It is an object of the present invention to provide a nanotube TiO ₂ coating layer on a HA blasted titanium surface, and to provide a surface coating method of titanium as a dental and orthopedic implant material having an RF magnetron sputtered HA coating layer formed thereon. It is done.

Another object of the present invention is to provide a dental and orthopedic implant material titanium coated with HA blasting-nanotube TiO ₂ anodization layer-HA sputtering prepared according to the method of the present invention.

In order to achieve the above object, the present invention provides a titanium surface coating method comprising the following steps:

(1) blasting the surface of titanium with HA (hydroxyapatite);

(2) Nanotube TiO ₂ by anodization on HA blasted titanium surface Forming a coating layer; And

(3) forming a HA coating layer by RF magnetron sputtering on the titanium surface on which the nanotube TiO ₂ coating layer is formed.

The method may further include washing, rinsing and drying between steps (1) and (2).

The washing is preferably ultrasonic cleaning.

The washing is preferably carried out in the presence of acetone and ethanol.

The washing is preferably performed for 5 to 15 minutes.

The rinsing is preferably performed for 20 to 40 minutes using distilled water.

In the anodization of step (2), it is preferable to use HA blasted titanium as an anode and a platinum plate as a cathode.

The distance between the positive electrode and the negative electrode is preferably 10mm.

The anodization of step (2) is preferably carried out under a 1M H ₃ PO ₄ solution containing 1.5% by weight HF.

The anodization of step (2) is preferably carried out for 10 minutes at room temperature.

The anodization of step (2) is preferably carried out under a DC voltage of 20V.

The nanotubes of step (2) is preferably 100nm in diameter, 500nm in length.

The method of the present invention may further comprise a washing and drying step between the step (2) and step (3).

The washing is preferably using distilled water.

The washing is preferably performed for 10 to 30 minutes.

The drying is preferably carried out under the conditions of 100 ~ 200 ℃.

The target used for the RF magnetron sputtering of step (3) is preferably a copper disk with HA powder.

The RF magnetron sputtering of step (3) is preferably performed by including the following steps:

(1) evacuating the sputter chamber to fill with high purity argon until a 1 × 10 ⁻² Torr at a base pressure of less than 1 × 10 ⁻⁵ Torr;

(2) sputter cleaning the surface of the titanium substrate on which the nanotube TiO ₂ coating layer was formed;

(3) sputter cleaning a copper disk target with HA powder; And

(4) depositing at 200 W for 1-15 minutes.

The sputter cleaning of steps (2) and (3) is preferably performed for 30 minutes with a 1 kV DC voltage bias.

The deposition of step (4) is preferably carried out in the presence of 5 × 10 ⁻³ mbar of argon.

The deposition of step (4) is preferably deposited in situ at room temperature with a substrate-target distance of 100 mm.

The present invention also provides a HA blasted-nanotube TiO ₂ coating-HA sputtered titanium characterized in that it is produced by the process of the invention described above.

It is preferred that the surface is HA blasted-nanotube TiO ₂ coated-HA sputtered titanium for dental implants.

It is preferred that the surface is HA blasted-nanotube TiO ₂ coated-HA sputtered titanium for orthopedic implants.

Titanium coated by the foot has excellent hydrophilicity and reduced modulus of elasticity, which mitigates the mismatch between bone and implant devices, reducing bone resorption and reducing the time to osteointegration. have.

1 is a photograph showing a FE-SEM image (× 1,000) of the HA coating layer on the nanotube TiO ₂ surface, (a) is a Resorbable Blasted Media blasting (RBM) surface, (b) is an anodized RBM surface, ( c) to (f) represent HA coated surfaces for 1 minute, 5 minutes, 10 minutes and 15 minutes, respectively.
Figure 2 is a photograph showing the FE-SEM image (× 10,000) of the HA coating layer on the nanotube TiO ₂ surface, (a) is a RBM (Resorbable Blasted Media blasting) surface, (b) is an anodized RBM surface, ( c) to (f) represent HA coated surfaces for 1 minute, 5 minutes, 10 minutes and 15 minutes, respectively.
FIG. 3 is a photograph showing an FE-SEM image (× 100,000) of an HA coating layer on a nanotube TiO ₂ surface, wherein (a) is an anodized RBM surface and (b) to (e) are 1 minute and 5 minutes, respectively. HA coated surface for 10 minutes, 15 minutes.
4 shows EDX data of HA coating on nanotube TiO ₂ surface.
Figure 5 shows the X-ray analysis of the HA coating on the nanotube TiO ₂ surface, (a) before the HA coating, (b) after the HA coating.
6 shows the XPS spectrum of the HA coating on the nanotube TiO ₂ surface.
7 is a graph showing the Ca ^{2 +} ion concentration with the passage of time in the PBS solution.
Figure 8 is a graph showing the 15 days of the Ca ^{2 +} ion concentration in the PBS solution.

Hereinafter, the present invention will be described in detail.

The present invention seeks to combine the advantages of nano-scale HA coating and nanotube TiO ₂ layers by controlling the RF magnetron sputtered HA coating conditions on the HA-blasted nanotube TiO ₂ surface.

Accordingly, the present invention provides a titanium surface coating method comprising the following steps:

(1) blasting the surface of titanium with HA (hydroxyapatite);

(2) Nanotube TiO ₂ by anodization on HA blasted titanium surface Forming a coating layer; And

(3) forming a HA coating layer by RF magnetron sputtering on the titanium surface on which the nanotube TiO ₂ coating layer is formed.

The method may further include washing, rinsing and drying between steps (1) and (2).

The washing is preferably ultrasonically cleaned for 5-15 minutes, preferably 10 minutes in the presence of acetone and ethanol.

The rinsing is preferably performed for 20 to 40 minutes, preferably 30 minutes using distilled water.

In the anodization of step (2), it is preferable to use HA blasted titanium as an anode and a platinum plate as a cathode, and the distance between the anode and the cathode is preferably 10 mm.

As a preferred embodiment of the anodization of step (2), it is preferably carried out under a DC voltage of 20 V for 10 minutes at room temperature under a 1M H ₃ PO ₄ solution containing 1.5% by weight HF.

Preferably, the nanotubes of step (2) have a diameter of about 100 nm and a length of about 500 nm, and a nanotube layer containing nanotubes having a diameter of about 100 nm and a length of 500 nm is generated to significantly improve hydrophilicity. Reduced elastic modulus of the layers can alleviate severe elastic modulus mismatch between the bone and the implant device to reduce bone resorption.

The method of the present invention may further comprise a washing and drying step between the step (2) and step (3).

As a preferred embodiment, the washing is preferably performed for 10 to 30 minutes with distilled water, and the drying is preferably performed under the conditions of 100 ~ 200 ℃.

The target used for the RF magnetron sputtering of step (3) is preferably a copper disk with HA powder.

Preferred embodiments of the RF magnetron sputtering step can be carried out through the following steps:

(1) evacuating the sputter chamber to fill with high purity argon until a 1 × 10 ⁻² Torr at a base pressure of less than 1 × 10 ⁻⁵ Torr;

(2) sputter cleaning the surface of the titanium substrate on which the nanotube TiO ₂ coating layer was formed;

(3) sputter cleaning a copper disk target with HA powder; And

(4) depositing at 200 W for 1-15 minutes.

In one preferred embodiment, the sputter cleaning is preferably performed for 30 minutes with a 1kV DC voltage bias.

Further, preferred as a specific example, the deposition substrate of 100mm in the presence of 5 × 10 ^-3 mbar of argon-place at room temperature to the target distance (in situ ) is preferably deposited.

The present invention provides a HA blasting-nanotube TiO ₂ coating-HA sputtered titanium characterized by being produced by the process of the invention described above, which can be used for dental implants and orthopedic implants.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[ Example ]

One. Blasting , Anodization  And Sputtering  step

Commercial pure titanium (ASTM Grade II, Kobe Steel, Japan) discs of 15 mm diameter and 3 mm thickness were used. HA-blasting procedure was performed on one side of all disks. After ultrasonic cleaning for 10 minutes in acetone and ethanol, the disks were rinsed in distilled water for 30 minutes and dried.

Nanotube TiO ₂ surfaces were fabricated using anodization technology. The disks and the platinum plate were used as anodes and cathodes, respectively. The distance between the anode and the cathode was 10 mm. Anodization using 20 DC voltage (Fine Power F-3005, SG EMD, Korea) for 10 minutes at room temperature in 1M H ₃ PO ₄ solution containing 1.5 wt% HF based on optimized anodization parameters such as Cochran et al. The procedure was carried out. All solutions were prepared using reagent grade chemicals and distilled water. After anodization, the samples were washed in water for 20 minutes and dried in a 200 ° C. oven for 1 hour.

The HA coating procedure was performed using a commercially available RF magnetron sputter unit (hybrid coater system, A-Tech, Korea). The target material used in this deposition process was a copper disk with HA powder (Ca ₁₀ (PO _{4) 6 (OH) 2,} CERAC, Milwaukee, USA) was used to evacuate the sputtering chamber 1 × 10 ^{-. 5} Torr (Torr) to group the low pressure of less than, and a working pressure of 1 × 10 ^{- 2} Torr is achieved Backfilled with high purity (99.9995%) argon until 30. Prior to deposition, the substrate surface was first sputter cleaned with a 1 kV dc bias for 30 minutes to remove any surface contaminants and also to activate the target surface. Sputter rinse Deposition was carried out for 1, 5, 10 and 15 minutes at 200 W. In situ deposition was performed at room temperature with a substrate-target distance of 100 mm at 5 × 10 ⁻³ mbar (5 Pa) Ar. .

Surface topography and chemical properties of the implant devices are important for dental and orthopedic applications. Recent evidence has revealed improved cellular and tissue responses to nanoscale-implant surfaces. In another study, the inventors of the present invention demonstrated that nanotube structures can be fabricated on smooth titanium using anodization. Nanotube layers containing nanotube TiO ₂ structures of about 100 nm in diameter and 500 nm in length were fabricated and the hydrophilicity was significantly improved. The reduced elastic modulus of the nanotube layer is expected to mitigate severe elastic modulus mismatch between the bone and the implant device, possibly reducing bone absorption. The mechanism of formation of the nanotube layer on titanium is related to selective and orientationally localized dissolution and electric field assistance with the electrolyte.

In the present invention, a relatively uniform nanotube layer including a nanotube structure having a diameter of about 100 nm and 500 nm in length was fabricated at 20V regardless of rough RBM substrates in 1M H ₃ PO ₄ + 1.5 wt% HF electrolyte solution. The conditions used for the HA coating may vary depending on the RF magnetron sputtering conditions. Deposition was performed at 200 W for less than 20 minutes to not completely cover the nanotube TiO ₂ entrance.

2. Surface Characterization

The morphology of the surfaces was characterized by a field emission scanning electron microscope (FE-SEM, JSM-7500F, JEOL, Japan) with an energy dispersive spectrometer (EDS). The structure of the sample surfaces was determined using high resolution X-ray diffraction (HR-XRD, X'Pert PRO Multi Purpose X-Ray Diffractometer, PANalytical, Holland). A CuKα X-ray radiation (λ = 1.540 kV) source was used with a tube voltage of 40 kV and a tube current of 40 mA. Each diffraction scan was recorded between 20 ° and 50 ° 2θ with a scan dwell time for every 5 seconds increase with a step size of 0.02 °.

The composition of both the porous layer and the HA deposited surface was also examined by X-ray photoelectron emission spectroscopy (MultiLab 2000, Thermo electron corporation, England). Spectra were recorded using AlKα X-rays (hv = 14486.6 eV) generated with proper anode operation at 14.9 kV and 20 mA. During the analysis, hybrid lens modes (electrostatic and magnetic) were used with a take off angle of 90 ° for the analysis area and sample surface of about 300 μm × 700 μm. Wide energy survey scans were obtained over a binding energy range of 0-1300 eV at a pass energy of 160 eV. Narrow energy for Cls (278-295 eV), O1s (525-540 eV), Ca2p (340-362 eV), Ti2p (450-470 eV) and P2p (125-140 eV) at a pass energy of 20 eV Survey scandal was recorded. Sample charge effects on the measured BE positions were corrected by setting the lowest binding energy component of the C1s spectral envelope to 285.0 eV, i.e., to a generally acceptable value for adventitious carbon surface contamination. .

FE-SEM shows a representative surface morphology of the treated surface. At low magnification, the RBM surface was rough (Fig. 1 (a)). The sharp edges of the micro-roughened surface of the RBM were smoothed with anodization and HA coating, but the micro-roughness remained intact (FIG. 1 (b)). This suggests that the surface roughness of the titanium substrate does not affect the morphology and size of the nanotubes and HA coating layers produced by the anodization and HA coating. At higher magnifications, highly aligned nanotube tissues were observed on the coarse RBM (FIG. 2 (a)). The newly formed nanotube structures in all samples were similar in morphology and size. As the HA coating time increased, the nanotube TiO ₂ inlets were coated with HA. This pattern was particularly evident at the sharp edges (Fig. 2 (c, d, e, f)). At even higher magnification, highly aligned nanotube tissues were observed on rough RBM (FIG. 3 (a)). In all samples, the newly formed nanotube structures were similar in morphology and size. Formation of a nanotube TiO ₂ structure having a diameter of 100 nm was observed (FIG. 3 (b)). After coating, a 35-40 nm thick HA coating layer was observed to have similar morphology for the nanotube TiO ₂ structure. The morphology of the nanotube TiO ₂ inlet showed an increase in thickness with increasing coating time. As the coating time increased, the nanotube TiO ₂ inlet was coated with HA (Fig. 3 (c, d, e, f)). HA after coating it is over 15 minutes, due to the nanotube TiO ₂ HA-coated wall surrounding the entrance to the entrance nanotube TiO ₂ will disappear.

The chemical composition of the nanotube layer was characterized by EDS, which detected the presence of titanium and oxygen. The peak for iron is due to commercially available pure titanium specimens containing varying amounts of iron as impurities. Small amounts of calcium and phosphorus were detected (FIG. 4).

The three strongest peaks in all samples were observed at 35.1 °, 38.33 ° and 40.1 ° with the XRD pattern of each sample (FIG. 5), which was 25% in ICDD file # 00-044-1294 for titanium, Consistent with the results observed for 30% and 100% intensity peaks. This indicates that the TiO ₂ was amorphous at both the TiO ₂ surface and the HA coated nanotube TiO ₂ surface. In addition, the HA was amorphous in the HA coated samples.

XPS data for the titanium layer on the nanotube TiO ₂ surface showed the presence of oxygen and carbon in addition to titanium and fluorine (Table 1). The presence of this surface oxide layer was confirmed by the high resolution of the O1s spectral envelope, which clearly showed a strong effect from TiO ₂ at 530.9 eV. The high resolution Ti2p spectrum of the nanotube TiO ₂ surface showed the presence of TiO ₂ due to the peaks at 459.3eV (Ti2p3 / 2).

In addition, fluorine was detected on the nanotube TiO ₂ surface. As shown in Table 1, all HA coated discs after sputtering showed significant O1s and Ti2P peaks and Ca, P, O peaks but no fluorine. The corresponding O1s spectral envelope after HA coating confirmed the oxide properties of the surface due to the presence of a strong peak at 530.3 eV (TiO ₂ ) and a prominent shoulder in the high binding energy portion of the peak (˜532.1 eV). 6 (a), Table 1; As described above, this shoulder was normally associated with oxygen from PO4 ^3- and OH ⁻ . The binding energy of Ca2p (347.5 eV) and P2p (133.7 eV) is similar to the binding energy of HAp in the NIST database (Figure 6 (c, d), Table 1). XPS analysis showed that the chemical states of the components in the fabricated thin films were similar to those of amorphous HAp.

Sputtered HA films have low crystallinity, which accelerates the dissolution of the HA membrane in vivo. In addition, this high rate of dissolution causes membrane loss before bone tissue can bind to the membrane in the early stages after transplantation. This case is not a nano-scale HA membrane but a micro-size HA membrane.

If amorphous HA does not completely cover the substrate and only a small amount is present in the nanoscale, osteofusion will occur due to the properties of the original substrate on the uncoated surface. In addition, amorphous HA maintains stronger supersaturation at the membrane / SBF interface due to the higher dissolution rate of the amorphous sputtered membrane. This will lead to a condition where ion exchange and physiological rearrangement at the interface between physiological fluids and surface chemical species is accompanied by uptake of biological molecules or uptake of cell attachment. Cells attached to the surface of the biomass interact with some body fluid components and cause surface changes. Gradual changes to the ceramic surface support the synthesis of biologically equivalent hydroxyapatite.

In this case, small crystals integrate bioactive implants into developing bone tissue. The amorphous structure may be changed into a crystalline structure using heat treatment. The crystalline structure of the TiO ₂ layer affects the formation of apatite and its biocompatibility.

3. Dissolution Experiment and Statistical Analysis

After sputtering deposition, all samples were placed in separate vials (one sample per vial) containing phosphate buffer (PBS) (Sigma Aldrich (UK) -P. No. P4417, 0.0027M potassium chloride, 0.137M sodium chloride, 0.01M phosphate buffer). It was immersed in a thermostatic control environment to pH 7.4 and 37 ℃. The Ca ^{2 +} concentrations from SBF to ELISA (Versamax, Molecular Devices, USA ) 5, 10, 15 and 20 days in accordance with the manufacturer's recommendations was measured using a calcium reagent set (Pointe Scientific Inc., Michigan, USA ) . The data represents the mean ± a standard deviation (sd), were analyzed by one-way (One-Way) ANOVA using Tukey's HSD for all experiments. p-value <0.05 was considered significant.

Dissolution test results for each surface revealed the presence of calcium on all samples. Ca ^{2 +} ion concentration was as minus the HA for the structural rearrangement from the HA dissolved in PBS. For 15 days immersed in PBS concentration of Ca ^{2 +} ions is increased. However, after 15 days, the concentration of Ca ^{+ 2} ions has been reduced. This is a result of an increase in the re-arrangement in the speed of the increase in the reduction of the amorphous HA and for 15 days PBS Ca ^{+ 2} concentration on the surface. Thus, the maximum dissolution rate of the surface of each sample can occur on day 15. In addition, an increase in calcium concentration was observed with increasing coating time at each time point (FIG. 7).

Subjected to political analysis using the maximum value of Ca ^{2 +} concentrations of all samples in the second 15 days were evaluated for significance of HA dissolution amount in each sample. All coating groups showed a significant increase in calcium concentration. Only 15-minute HA coatings were significantly different from 1, 5 and 10-minute HA coatings compared to other coating groups (FIG. 8, Table 2).

Short dissolution of HA may complete the dissolution procedure before it affects the treatment phase of the implant. RF magnetron sputtering conditions must be adjusted for constant HA dissolution. The heat treatment or amount of HA coatings on the surface may be a controlling factor. As a result of the dissolution test, the amorphous HA coating by RF magnetron sputtering in all 1, 5, 10 and 15 minute CaP coating groups had a dissolution period longer than 15 days. In addition, the amount of dissolution showed a significant increase. This suggests that after a coating time of less than 20 minutes, the surface of the HA coating may exhibit HA dissolution for constant structural rearrangement of HA in PBS.

Although the present invention has been described with reference to the above-described embodiments and the accompanying drawings, other embodiments may be configured within the spirit and scope of the present invention. Therefore, the scope of the present invention is defined by the appended claims and equivalents thereof, and is not limited by the specific embodiments described herein.

Claims (24)

Titanium surface coating method comprising the following steps:
(1) blasting the surface of titanium with HA (hydroxyapatite);
(2) Nanotube TiO ₂ by anodization on HA blasted titanium surface Forming a coating layer; And
(3) forming a HA coating layer by RF magnetron sputtering on the titanium surface on which the nanotube TiO ₂ coating layer is formed.
The method of claim 1,
Titanium surface coating method further comprising the step of washing, rinsing and drying between the step (1) and step (2).
The method of claim 2,
The cleaning method of the titanium surface, characterized in that the ultrasonic cleaning.
The method of claim 2,
Wherein said washing is carried out in the presence of acetone and ethanol.
The method of claim 2,
Titanium surface coating method characterized in that the washing is performed for 5 to 15 minutes.
The method of claim 2,
The rinsing is titanium surface coating method, characterized in that performed for 20 to 40 minutes using distilled water.
The method of claim 1,
The anodization of the step (2) is a titanium surface coating method characterized in that using the HA blasted titanium as an anode and a platinum plate as a cathode.
8. The method of claim 7,
The distance between the anode and the cathode is titanium surface coating method, characterized in that 10mm.
The method of claim 1,
The anodization of step (2) is titanium surface coating method, characterized in that carried out under 1M H ₃ PO ₄ solution containing 1.5% by weight HF.
The method of claim 1,
Titanium surface coating method characterized in that the anodization of step (2) is carried out for 10 minutes at room temperature.
The method of claim 1,
Titanium surface coating method characterized in that the anodization of step (2) is carried out under a DC voltage of 20V.
The method of claim 1,
The nanotube of step (2) is a titanium surface coating method, characterized in that the diameter 100nm, 500nm long.
The method of claim 1,
Titanium surface coating method further comprising the step of washing and drying between the step (2) and step (3).
The method of claim 13,
The washing method of titanium surface coating, characterized in that using distilled water.
The method of claim 13,
Titanium surface coating method characterized in that the washing is performed for 10 to 30 minutes.
The method of claim 13,
The drying is titanium surface coating method, characterized in that carried out under the conditions of 100 ~ 200 ℃.
The method of claim 1,
The target used in the RF magnetron sputtering of step (3) is a titanium surface coating method, characterized in that the copper powder with HA powder.
The method of claim 1,
The RF magnetron sputtering of step (3) comprises the following steps:
(1) evacuating the sputter chamber to fill with high purity argon until a 1 × 10 ⁻² Torr at a base pressure of less than 1 × 10 ⁻⁵ Torr;
(2) sputter cleaning the surface of the titanium substrate on which the nanotube TiO ₂ coating layer was formed;
(3) sputter cleaning a copper disk target with HA powder; And
(4) depositing at 200 W for 1-15 minutes.
19. The method of claim 18,
The sputter cleaning of steps (2) and (3) is performed for 30 minutes with a 1 kV DC voltage bias.
19. The method of claim 18,
And the deposition of step (4) is carried out in the presence of 5 × 10 ⁻³ mbar of argon.
19. The method of claim 18,
And wherein the deposition of step (4) is deposited in situ at room temperature with a substrate-target distance of 100 mm.
22. A surface HA blasted-nanotube TiO ₂ coating-HA sputtered titanium, characterized in that it is produced by the method of any one of claims 1-21.
23. The method of claim 22,
Wherein the surface is HA blasted-nanotube TiO ₂ coated-HA sputtered titanium is for dental implants. The surface is HA blasted-nanotube TiO ₂ coated-HA sputtered titanium.
23. The method of claim 22,
Said surface is blasted HA-coated nanotube TiO ₂ -HA sputtering titanium is the HA blasted surface, it characterized in that the orthopedic implant Yongin-nanotube TiO ₂ coating -HA sputtered titanium.

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