JPH10102288A - Coating method with calcium phosphate compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrodeposit a calcium phosphate compd. on the surface of a metallic material to be coated by supplying electric current to the material as the cathode in an aq. soln. contg. Ca ions, phosphate ions, a complex forming agent, etc. SOLUTION: A metallic material to be coated such as an artificial bone made of Ti or stainless steel is put in an aq. soln. of >=pH 4.0 contg. 0.1mol (expressed in terms of Ca ions) Ca(NO3 )2 , 0.01mol (expressed in terms of phosphate ions) (NH4 )3 PO4 and 0.1mol EDTA as a complex forming agent and electric current is supplied to the material as the cathode to electrodeposit a calcium phosphate compd. such as hydroxyapatite on the surface of the material. When CaHP4 .2H2 O is electrodeposited, it is converted into the calcium phosphate compd. such as hydroxyapatite by further treatment with a coating soln. adjusted to >=pH 4.0 with ammonia, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for coating a calcium phosphate compound on a metal material for medical implants such as artificial joints, artificial bones, artificial dental roots and the like.

[0002]

2. Description of the Related Art Conventionally, titanium, a titanium alloy, a cobalt-chromium alloy, stainless steel, and the like have been used as an implant material for replacing a living hard tissue having a defect due to a disease or accident. However, since these metal materials do not directly bond to a living tissue, there is a problem that initial fixing strength is low and loosening occurs over a long period of time.

[0003] As a method for improving the initial fixing strength of an implant material, polymethyl methacrylate (PMM) is used.
A method has been developed in which bone cement containing A) or the like is injected into an affected area and solidified. However, this method has a problem that reaction heat generated during coagulation affects surrounding tissues.

[0004] In order to solve these problems, there has been proposed a method using an implant material such as a metal coated with a calcium phosphate compound such as hydroxyapatite on the surface thereof. In this method, the initial fixation strength, long-term stability, and the like can be improved by directly bonding the implant material to hard tissue such as bone via a bioactive coating layer.

[0005] As a method for forming such a coating layer, a plasma spray method, a sputtering method, a dipping method, a sol-gel method and the like have been conventionally used. Among them, the plasma spray method is a relatively practical technique,
There is a problem that a soluble by-product or an amorphous component is generated, and the coating layer is dissolved after living body transplantation, and separation occurs in a gap between the base material and the coating layer. Also, other methods of forming a coating layer than the plasma spray method have problems such as insufficient adhesion strength of the coating and non-uniformity, and are not sufficiently practical.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to easily form a coating layer having high adhesion strength, which is composed of fine and uniform particles of a calcium phosphate compound, on a metal object to be coated. An object of the present invention is to provide a method for coating a calcium phosphate compound.

[0007]

According to the present invention, in an aqueous solution containing calcium ions, phosphate ions and a complexing agent, a metal object to be coated is used as an electrode, and a calcium phosphate compound salt is applied to the object to be coated. There is provided a method for coating a calcium phosphate compound, comprising a step of electrodeposition.

According to the present invention, there is provided the coating method, wherein the calcium phosphate compound is hydroxyapatite, and the pH of the aqueous solution is adjusted to 4.0 or more during the electrodeposition.

Further, according to the present invention, the calcium phosphate compound salt is other than hydroxyapatite, and after completion of the electrodeposition, the coated object on which the calcium phosphate compound salt has been deposited is adjusted to pH 4.0. The method further comprises a step of immersing the calcium phosphate compound salt in the aqueous solution, whereby the calcium phosphate compound salt is converted into hydroxyapatite.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the coating method of the present invention,
In an aqueous solution containing calcium ions, phosphate ions and a complexing agent, a metal object to be coated is used as an electrode, and a calcium phosphate compound salt is electrodeposited on the object to be coated.

The object to be coated is not particularly limited as long as the effect of the present invention is not impaired as long as it is made of metal, but titanium, which has excellent corrosion resistance and does not show toxicity in vivo.
Metals such as a titanium alloy, stainless steel, and a cobalt-chrome alloy can be used.

As the shape of the object to be coated, any shape including a plate, a sphere, a column, a prism, a cone, a pyramid, and other irregular shapes simulating teeth and bones can be used. It is.

The aqueous solution containing calcium ions, phosphate ions and complexing agent can be prepared by dissolving a compound containing calcium ions, a compound containing phosphate ions, and a complexing agent in water.

The compounds containing calcium ions include, for example, Ca (OH) ₂ , Ca (NO ₃ ) ₂ , CaCl ₂ , Ca (CH ₃ COO) ₂ ,
Examples thereof include calcium citrate and calcium lactate. Examples of the compound containing a phosphate ion include H ₃ PO ₄ , Na ₃ PO ₄ , (NH ₄ ) ₃ PO ₄ , K ₃ PO ₄ , or a salt obtained by partially hydrogen-substituting a cation in these salts. (For example,
(NH ₄ ) ₂ HPO ₄ ). Instead of using both the compound containing calcium ions and the compound containing phosphate ions, phosphate ions such as hydroxyapatite, tricalcium phosphate, tetracalcium phosphate, and calcium hydrogen phosphate are used together with calcium ions. Can also be used.

The concentration of the calcium ion and the phosphate ion in the aqueous solution is [Ca ²⁺ ] = 0.0
1 to 2.0 mol / l, and [PO ₄ ^3-] = 0.0
It is preferably from 0.5 to 2.0 mol / l. Further, the molar ratio of the calcium ion and the phosphate ion in the aqueous solution is such that the value of Ca / P is 1.0 to 3.0 in molar ratio.
It is preferred that By appropriately adjusting these ion concentrations, the thickness of the formed coating layer can be controlled.

Further, as the complexing agent, citric acid,
Examples include ethylenediaminetetraacetic acid (EDTA), lactic acid, and nitrilotriacetic acid (NTA). The concentration of the complexing agent in the aqueous solution is preferably from 0.01 to 1.0 mol / l.

In the coating method of the present invention, the metal object to be coated is used as an electrode, and a calcium phosphate compound salt is electrodeposited on the object to be coated. At this time, the counter electrode is not particularly limited as long as the effect of the present invention is not impaired, and the same metal as the object to be coated can be used, and a conductive plastic or the like can be used. The distance between the electrodes in the aqueous solution is 1 to 50 m.
m is preferable.

The voltage for performing the electrodeposition is 1 to 100 V
/ Cm ² . By appropriately adjusting the voltage, the layering speed and structure of the formed coating layer can be controlled.

The time for the electrodeposition is preferably 3 to 120 minutes. By appropriately adjusting the electrodeposition time, the thickness of the formed coating layer can be controlled.

In performing the electrodeposition, it is preferable to maintain the temperature of the aqueous solution at a constant temperature in the range of 15 to 100 ° C. When the aqueous solution is kept at a high temperature, the electrodeposition time can be reduced. When the temperature of the aqueous solution is kept high, a coating layer having a large particle diameter is obtained, and when the temperature is kept low, a coating layer having a small particle diameter is obtained.

At the time of the electrodeposition, the pH of the aqueous solution is adjusted to 4.0 or more, preferably 4.0 to 12.0, so that hydroxyapatite can be electrodeposited as a coating layer.

As a method of adjusting the pH of the aqueous solution to 4.0 or more, a method of adding a pH adjuster to the aqueous solution can be mentioned. It is not always necessary to dissolve all the pH adjusters before the start of electrodeposition, but may be gradually added after the start of electrodeposition. That is, if the pH of the aqueous solution is 4.0 or more at the time of dissolving the calcium ion, the phosphate ion, and the complexing agent, it is not necessary to add the pH adjuster before starting the electrodeposition. Hydroxyapatite can be electrodeposited by gradually adding it after starting the current so as to prevent the pH from falling below 4.0 during the precipitation.

As the pH adjuster, ammonia, sodium hydroxide, potassium hydroxide and the like can be used, but from the viewpoint of preventing unnecessary metal ions from being mixed.
It is particularly preferred to use ammonia. When the pH adjuster is gradually added during electrodeposition, the pH adjuster is preferably dissolved in water to form an alkaline solution. The concentration of the alkaline solution is preferably, for example, 0.03 to 0.5 mol / L when using ammonia, and 0.01 to 0.1 mol / L when using sodium hydroxide.

The calcium phosphate compound of the coating layer obtained by the coating method of the present invention includes calcium hydrogen phosphate dihydrate (CaHPO ₄ .2H ₂ O), monetite
(CaHPO ₄ ), tricalcium phosphate (Ca ₃ (PO ₄ ) ₂ ), and the aforementioned hydroxyapatite.

When a layer of a calcium phosphate compound salt other than hydroxyapatite is obtained by the electrodeposition, after the completion of the electrodeposition, the coated object on which the calcium phosphate compound salt has been deposited has a pH of 4.0 or more, preferably Is 4.0
By further performing a step of immersion in an aqueous solution of １12.0, the layer of the calcium phosphate compound salt other than the hydroxyapatite obtained by the electrodeposition can be changed to a more stable hydroxyapatite. This step is not particularly limited, but a method of adjusting the pH to a desired value by, for example, adding an alkali while immersing the object to be coated in the aqueous solution used during the electrodeposition, or after the electrodeposition, The method can be carried out by, for example, a method of immersing the object to be coated in another aqueous solution in which the pH is adjusted to a desired value by dissolving an alkali or the like. The immersion time is preferably 10 to 50 hours. Further, as the alkali, ammonia, sodium hydroxide, potassium hydroxide, or the like can be used, but ammonia is particularly preferable from the viewpoint of preventing unnecessary metal ions from being mixed.

The coating strength of the calcium phosphate compound obtained by the method of the present invention can be increased by further heat treatment. The heat treatment can improve the adhesion strength of the coating layer even at a relatively low temperature that does not affect the object to be coated, for example, about 750 ° C. in the case of titanium. At such a relatively low temperature, the adhesion strength of the coating layer can be improved because the aqueous solution as a coating bath is accompanied by an electrophoretic effect, and the coating target of the electrode is formed of finer particles than before. This is probably because the coating layer was formed.

[0027]

According to the coating method of the present invention, since a coating layer of a calcium phosphate compound is formed by electrodeposition, even a surface of a metal material having a complicated shape is coated with a calcium phosphate compound composed of fine and uniform particles. This is useful as a method for improving the biocompatibility of the implant material.

[0028]

The present invention will be described in more detail with reference to the following examples.
The present invention is not limited to these. In the following examples, all reagents were manufactured by BDH.

[0029]

Example 1 0.1 mol of calcium hydroxide and 0.06
One mole of orthophosphoric acid and 0.2 mole of citric acid were dissolved in one liter of distilled water. The aqueous solution was placed in containers in three water baths and controlled at temperatures of 20 ° C., 60 ° C., and 90 ° C., respectively. Two pure titanium plates (50 × 20 × 1 mm) were inserted into each container at an interval of 10 mm, and electrodeposition was performed at 20 VDC for 30 minutes. As a result, a porous coating layer of calcium hydrogen phosphate dihydrate (CaHPO ₄ .2H ₂ O) having a thickness of 5 μm, 10 μm and 20 μm was obtained on the surface of the cathode plate.

[0030]

Example 2 0.1 mol of calcium nitrate, 0.06 mol of ammonium phosphate and 0.1 mol of EDTA were mixed with 1 mol.
Dissolved in 1 liter of distilled water. This aqueous solution was put in a container in a water bath and controlled at 95 ° C. Pure platinum plate (anode,
50 × 20 × 0.1mm) and stainless steel SUS31
6 L (cathode, 50 × 20 × 1 mm) was inserted at an interval of 10 mm, and electrodeposition was performed at a direct current of 10 volts for 30 minutes. As a result, a coating layer of monetite (CaHPO ₄ ) having a thickness of 10 μm was obtained on the surface of the cathode plate.

[0031]

Example 3 0.2 mol of calcium hydroxide and 0.12
One mole of orthophosphoric acid and 0.5 mole of lactic acid were dissolved in one liter of distilled water. The aqueous solution was placed in containers in three water baths and controlled at temperatures of 20 ° C., 60 ° C., and 90 ° C., respectively. In each container, a plate (50 × 20) of an alloy (hereinafter abbreviated as Ti-6Al-4V alloy) containing 6% by weight of aluminum and 4% by weight of vanadium in titanium was used.
× 1 mm) were inserted at 10 mm intervals, and electrodeposition was performed at 10 VDC for 20 minutes. As a result, a dense monetite coating layer having a thickness of 10 μm, 15 μm and 30 μm was obtained on the surface of the cathode plate.

[0032]

Example 4 0.1 mol of calcium hydroxide and 0.06
One mole of orthophosphoric acid and 0.3 mole of lactic acid were dissolved in one liter of distilled water. This aqueous solution was placed in a container in a water bath and controlled at 20 ° C. Next, two pure titanium plates (5
0 × 20 × 1 mm) at an interval of 10 mm, and electrodeposited at 5 VDC for 10 minutes. As a result, a dense coating layer of calcium hydrogen phosphate dihydrate having a thickness of 30 μm was obtained on the surface of the cathode plate.

After completion of the electrodeposition, ammonia was further added to the aqueous solution to adjust the pH to 5.0, and the cathode was placed in the aqueous solution.
After soaking for a time, the calcium hydrogen phosphate dihydrate coating changed to a uniform hydroxyapatite coating.

[0034]

Example 5 The coating material prepared in Example 3 (30
μm) is heat-treated at 750 ° C. for 60 minutes, and the adhesive strength before and after the heat treatment is measured according to JIS H8666.
The comparison was made by measuring according to the “Ceramic thermal spray test method”. As a result, the adhesion strength is reduced from 13 MPa to 2 without deteriorating the alloy plate to be coated.
Improved to 2MPa.

[0035]

COMPARATIVE EXAMPLE 1 On a Ti-6Al-4V alloy plate similar to that in Example 3, a plasma spray gun (METCO 9) manufactured by Metco Corporation was used.
Using MB), monetite was sprayed to a thickness of 30 μm. Spraying conditions were as follows: Ar: H ₂ = 100: 3 mixed gas, 500 A, 40 V, spray distance 50 m
m. The film adhesion strength in this case was measured by the same method as in Example 5, and was 5 MPa.

[0036]

Example 6 0.1 mol of calcium hydroxide and 0.06
One mole of orthophosphoric acid and 0.2 mole of lactic acid were dissolved in one liter of distilled water. The aqueous solution was placed in containers in three water baths and controlled at temperatures of 20 ° C., 60 ° C., and 90 ° C., respectively. Each container contains two pure titanium plates (50
× 20 × 1 mm) were inserted at 10 mm intervals, and an aqueous 0.1 mol / liter ammonia solution was dropped until the pH reached 4.5. Next, while monitoring the pH, the above-mentioned aqueous ammonia solution was gradually dropped using a low-speed motor while maintaining the pH at 4.5. As a result, a thickness of 5
Dense hydroxyapatite coating layers of μm, 20 μm and 30 μm were obtained. In addition, p
H was maintained at 4.5 ± 0.2.

[0037]

EXAMPLE 7 0.1 mol of calcium nitrate, 0.06 mol of ammonium phosphate and 0.2 mol of citric acid were mixed with 1 mol.
Dissolved in 1 liter of distilled water. This aqueous solution was placed in containers in two water baths and controlled at 60 ° C. and 90 ° C., respectively. Two Ti-6Al-4V alloy plates (50 × 20 × 1 mm) are inserted into each container at an interval of 10 mm, and 0.05 mol / L of sodium hydroxide is added to each container at a pH of 0.05%.
It was dropped until it reached 5.0. Next, while monitoring the pH, the sodium hydroxide was gradually added dropwise using a low-speed motor while maintaining the pH at 5.0.
Electrodeposition was performed with a volt for 20 minutes. As a result, a 10 μm and 25 μm-thick hydroxyapatite coating layer was obtained on the cathode plate surface. In addition, throughout the reaction,
The pH was maintained at 5.0 ± 0.2.

[0038]

Example 8 The coating material prepared in Example 7 (25
) was heat-treated at 750 ° C for 60 minutes, and the adhesive strength before and after the heat treatment was measured in the same manner as in Example 5 for comparison. As a result, the adhesion strength was improved from 15 MPa to 25 MPa without deteriorating the alloy plate as the object to be coated.

[0039]

Comparative Example 2 On the same Ti-6Al-4V alloy plate as in Example 7, a plasma spray gun (METCO 9) manufactured by Metco Corporation was used.
Hydroxyapatite was sprayed to a thickness of 25 μm using MB). The thermal spraying conditions were Ar: H ₂ = 100: 3.
Using a mixed gas of 500A, 40V, spray distance 5
The measurement was performed at 0 mm. In this case, the film adhesion strength was measured in Example 5.
It was 6 MPa when measured by the same method as in the above.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Serena Michelle Best Bedfordshire Emckey 43.0 TS, Ridgemond, High Street 17, The Old Month (72) Invention Nobuyuki Asaoka 1-297 Kitabukuro-cho, Omiya City, Saitama Prefecture Inside Mitsubishi Materials Corporation

Claims (3)

[Claims] 1. A method for coating a calcium phosphate compound in a solution containing calcium ions, phosphate ions and a complexing agent, the method comprising: using a metal object to be coated as an electrode; and depositing a calcium phosphate compound salt on the object to be coated. Method. 2. The coating method according to claim 1, wherein the calcium phosphate compound is hydroxyapatite, and the pH of the aqueous solution is adjusted to 4.0 or more during the electrodeposition. 3. The method according to claim 1, wherein the calcium phosphate compound salt is other than hydroxyapatite, and after completion of the electrodeposition, the step of immersing the coated object on which the calcium phosphate compound salt is electrodeposited in an aqueous solution having a pH of 4.0 or more. The coating method according to claim 1, further comprising changing the calcium phosphate compound salt to hydroxyapatite.