Apatite carbonate-coated magnesium material, its manufacturing method, and medical devices and industrial components using the same; apatite carbonate-coated metal material, its manufacturing method, and medical devices and industrial components using the same.

Abstract

To provide a carbonate apatite coated magnesium material that exhibits interference colors, enabling both improved biocompatibility and device identification, and a method for producing the same. [Solution] An aqueous solution is prepared containing a calcium complex at a concentration higher than 0.2 mol / L and a phosphate solution in a concentration of 0.5 to 1.25 times that of the calcium complex (S100). A carbonate is dissolved in the aqueous solution containing the calcium complex and phosphate at the above concentrations to prepare a coating treatment solution (S102). The coating treatment solution is heated (S104). A magnesium material having a surface roughness Ra of 0.05 μm to 2.0 μm is immersed in the heated coating treatment solution (S106). The magnesium material is then coated with apatite mainly composed of carbonate apatite to a film thickness that exhibits the desired interference color (S108).

Description

[Technical Field]

[0001] This invention relates to a carbonate apatite-coated magnesium material having excellent design properties and corrosion resistance, a method for producing the same, and components for medical devices and industrial parts using the same. Furthermore, the present invention relates to apatite-coated metal materials (e.g., iron, zinc, aluminum, or titanium) other than magnesium materials, a method for manufacturing the same, and medical devices and industrial components using the same. [Background technology]

[0002] The inventors have previously developed hydroxyapatite coatings and carbonate apatite coatings for controlling the corrosion rate of magnesium and magnesium alloys for medical bioabsorbable materials (Patent Documents 1 and 2). These apatite coatings exhibited corrosion suppression effects and biocompatibility (cytocompatibility, osteoconductivity). However, hydroxyapatite coatings have a two-layer structure in which rod-shaped crystals grow from a dense inner layer to form an outer layer, and because the outer layer is porous, it scatters light and shows almost no interference colors. Conventional carbonate apatite coatings are formed by the aggregation of particles ranging from submicrometers to about 1 μm, resulting in a large surface roughness and scattering of light, which does not show much interference color or gloss.

[0003] In medical devices, for example, titanium devices have an anodic oxide coating that exhibits different interference colors on their surface, allowing for identification of the device type and size by color. Furthermore, in the casings of consumer electronics such as personal computers, cameras, and watches, coloring is sometimes achieved through the interference colors of oxide coatings on the surface of metal materials. In contrast, with hydroxyapatite and carbonate apatite coatings, the development of smooth coatings exhibiting interference colors has not been carried out, regardless of the type of metal material used as the substrate. For example, Non-Patent Literature 1 discloses the formation of Ca-depleted carbonate apatite coatings on pure Ti surfaces, but there are no reports of smooth, thin coatings exhibiting interference colors. As shown in Non-Patent Literature 4, carbonate apatite has received regulatory approval as an artificial bone material used in bone reconstruction surgery.

[0004] In developing transparent coatings that maintain the metallic luster of magnesium materials, Patent Document 3 describes a method for producing a transparent coating by anodic oxidation in an alkaline electrolyte and coloring by immersion in a dyeing solution. Patent Document 4 describes a method for making a plated precious metal exhibit surface gloss by polishing the surface to make it smooth after anodic oxidation or plasma electrolytic oxidation treatment. Patent Document 5 shows that an oxide film exhibiting interference colors can be formed on alloys containing rare earth elements, such as Mg-Sc alloys and Mg-Y alloys, by thermal oxidation even in the atmosphere.

[0005] Non-Patent Literature 2 describes an example of fabricating a carbonate apatite coating on a magnesium material surface, where the substrate is a magnesium alloy WE43 (Y4.0, RE3.4, Zr0.7) and conventional carbonate apatite coating is applied. Non-Patent Literature 3 examines in detail the carbonate content of conventional carbonate apatite coatings using pure Mg as the substrate. However, there is no disclosure regarding the fact that apatite carbonate coatings on the surface of metallic materials, including magnesium materials, exhibit interference colors. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5339347 [Patent Document 2] Patent No. 6783465 [Patent Document 3] Japanese Patent Publication No. 2004-18901 [Patent Document 4] Japanese Patent Publication No. 2009-185331 [Patent Document 5] WO2020 / 012890 issue [Non-patent literature]

[0007] [Non-Patent Document 1] Carbonate apatite coating on titanium induced rapidly by precalcification, Biomaterials, 23 (2002) 173-179. [Non-Patent Document 2] Osteoclast and osteoblast responsive carbonate apatite coatings for biodegradable magnesium alloys, STAM, 21(1) (2020) 346-358. [Non-Patent Document 3] Carbonate content control in carbonate apatite coatings of biodegradable magnesium, Ceramics International, 50 (2024) 6784-6792. [Non-Patent Document 4] Kunio Ishikawa, "The Amazing Artificial Bone Graft Material: Carbonate Apatite," Artificial Organs 47_189 (2018) [Overview of the project] [Problems that the invention aims to solve]

[0008] Applying a desired color to the surface of magnesium material enhances its aesthetic appeal. Furthermore, it facilitates the identification of magnesium device types and sizes. Magnesium materials require corrosion resistance regardless of their application, whether medical or industrial, and for medical applications, even greater biocompatibility is required. To date, oxide and / or hydroxide coatings such as anodic oxidation coatings, chemical conversion coatings, and apatite coatings, developed to improve the corrosion resistance of magnesium materials, have often been opaque due to rough or porous surfaces, rather than smooth, thin coatings that exhibit interference colors. For casings of electronic devices such as cameras, a metallic finish, exhibiting various colors and metallic luster, is sometimes required. While there are examples of dyeing magnesium materials after anodic oxidation coating formation, coatings characterized by the surface layer itself exhibiting interference colors have not been developed. This is likely because, in common surface modification processes such as anodic oxidation and chemical conversion, the magnesium material surface often corrodes and becomes rough during the treatment, resulting in the loss of the metallic luster of the magnesium material beneath the coating.

[0009] On the other hand, in conventional medical metal materials such as titanium and stainless steel, apatite coatings are used as surface coating materials to improve biocompatibility. However, apatite coatings produced by thermal spraying or cathode deposition are white and colorless, making it difficult to identify the size of devices.

[0010] The present invention solves the above problems and provides an apatite coating that exhibits interference colors by forming a carbonate apatite coating, a type of hydroxide coating, smoothly and with controlled thickness while maintaining the metallic luster of the base magnesium material, a method for manufacturing the same, and medical devices and industrial components using the same. [Means for solving the problem]

[0011] The inventors hypothesized that by forming a smooth, thickness-controlled coating on the magnesium material surface while maintaining its metallic luster, the dense, smooth coating of apatite, which is originally a transparent substance, could exhibit interference colors. Furthermore, they considered that the carbonate apatite coating, being a single layer rather than a two-layer hydroxyapatite coating, would be easier to smooth the surface of, leading to the invention. Specifically, to precipitate carbonate apatite while maintaining the metallic luster of the magnesium material in the coating solution, it is effective to increase the precipitation rate. Therefore, they decided to use a coating solution with higher concentrations of calcium and phosphate sources than conventional carbonate apatite coating solutions. To form a smooth carbonate apatite coating exhibiting interference colors on the surface of a magnesium material, the concentration of the carbonate apatite coating solution disclosed in Patent Document 2 was adjusted to 1.5 to 2 times or more. Then, by heating the solution to a predetermined temperature and immersing the magnesium substrate in the coating solution for a predetermined time, it was conceived that a carbonate apatite coating exhibiting the interference colors shown below could be applied to the surface of the magnesium material.

[0012] 〔1〕The magnesium material coated with calcium phosphate of the present invention, wherein the surface roughness Ra of the substrate satisfies the range of 0.05 μm or more and 2.0 μm or less, and the substrate is a calcium phosphate film having a surface roughness Ra of 65 nm or less, preferably a calcium phosphate film having a surface roughness Ra of 5 nm or more and 65 nm or less, more preferably a calcium phosphate film having a surface roughness Ra of 5 nm or more and 40 nm or less, and is a magnesium material having a calcium phosphate film with a film thickness of 10 nm or more and 600 nm or less, preferably a calcium phosphate film with a film thickness of 10 nm or more and 700 nm or less, more preferably a calcium phosphate film with a film thickness of 10 nm or more and 1000 nm or less. When the film thickness of the calcium phosphate film is less than 10 nm, it is considered that the anodic oxide film of Ti does not exhibit an interference color because the anodic oxide film of Ti starts to exhibit an interference color when it becomes thicker than 10 nm. When the film thickness of the calcium phosphate film exceeds 1000 nm, it is difficult to manufacture a calcium phosphate film that exhibits an interference color in the visible light region. In order for an interference color to appear in an oxide film or a hydroxide film, the thickness of the film needs to be about the same as or less than the wavelength range of visible light, which is about 380 nm to about 770 nm. Therefore, it is considered that when the film thickness of the calcium phosphate film exceeds 1000 nm, it does not exhibit an interference color. 〔2〕In the calcium phosphate-coated magnesium material〔1〕of the present invention, preferably, the film thickness of the calcium phosphate film is expressed by the following formula (3) as the film thickness t [nm] that generates reflected light of the visible light wavelength λ [nm] corresponding to the target interference color. t = (m + 1 / 2)·λ / (3.3cosθ) (3) Here, m is the order of interference, usually an integer of m = 1, 2, 3 or 4, and θ is the incident angle of the incident light with respect to the film. The wavelength λ of the visible light corresponding to the target interference color is purple (380 - 430 nm), blue (430 - 490 nm), green (490 - 550 nm), yellow (550 - 590 nm), orange (590 - 640 nm), red (640 - 770 nm). [3] In the magnesium material coated with calcium phosphate [1] of the present invention, preferably, the calcium phosphate coating constituting the film has a calcium carbonate content of 1 mass% or more and 20 mass% or less, and desirably, the magnesium material has a calcium phosphate coating of 2 mass% or more and 30 mass% or less. [4] In the magnesium material coated with calcium phosphate [1] of the present invention, preferably, the base material and the calcium phosphate coating are directly joined without an intervening magnesium hydroxide layer. [5] In the magnesium material coated with calcium phosphate [1] of the present invention, preferably, the calcium phosphate coating is joined to the base material through a mixed layer of MgO nanoparticles and magnesium-calcium phosphate nanocrystals.

[0013] [6] The method for producing the magnesium material coated with calcium phosphate of the present invention is, for example, as shown in FIG. 1, an aqueous solution in which a calcium complex having a concentration higher than 0.2 mol / L and a phosphate having a concentration of 0.5 times or more and 1.25 times or less the concentration of the calcium complex are dissolved is prepared (S100), a carbonate is dissolved in the aqueous solution in which the calcium complex and the phosphate of the above concentration are dissolved to prepare a coating treatment solution (S102), the coating treatment solution is heated (S104), and a magnesium material having a surface roughness Ra in the range of 0.05 μm or more and 2.0 μm or less is immersed in the heated coating treatment solution (S106), and the magnesium material is coated with an apatite mainly composed of calcium phosphate with a film thickness exhibiting a desired interference color (S108). Here, the main component of the film means a component occupying 50% or more of the volume or weight of the film. [7] In the method for producing the magnesium material coated with calcium phosphate [6] of the present invention, preferably, the calcium complex of the coating treatment solution is a calcium compound of a chelate selected from the group consisting of EDTA, NTA, HEDTE, aminopolycarboxylic acid, malic acid, citric acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, and sulfamic acid. [8] In the method for producing a carbonate apatite-coated magnesium material of the present invention [6] or [7], preferably the concentration of the calcium complex is 0.3 mol / L or more and 1 mol / L or less, more preferably 0.3 mol / L or more and 0.8 mol / L or less, and even more preferably 0.3 mol / L or more and 0.5 mol / L or less. [9] In the methods for producing a carbonate apatite-coated magnesium material of the present invention [6] to [8], preferably the phosphate in the coating solution is an inorganic phosphate selected from the group consisting of potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, calcium monohydrogen phosphate, tripotassium phosphate, and trisodium phosphate.

[10] In the methods for producing a carbonate apatite-coated magnesium material of the present invention [6] to [9], the concentration of the phosphate is preferably 0.3 mol / L or more and 2.4 mol / L or less, more preferably 0.3 mol / L or more and 1.0 mol / L or less, and even more preferably 0.3 mol / L or more and 0.5 mol / L or less. The saturated solubility of disodium hydrogen phosphate (KH2PO4) is 2.42 mol / L, and the solubility of Ca-EDTA is estimated to be about 1 mol / L by analogy with the solubility of 2Na (EDTA 2Na) which is 0.725 mol / L.

[11] In the methods for producing a carbonate apatite-coated magnesium material of the present invention [6] to

[10] , preferably the carbonate of the coating treatment solution is a carbonate selected from the group consisting of NaHCO3, Na2CO3, K2CO3, (NH4)2CO3, CaCO3, BaCO3, MgCO3, Li2CO3, and FeCO3.

[12] In the methods for producing a carbonate apatite-coated magnesium material of the present invention [6] to

[11] , preferably the concentration of the carbonate is greater than 0 mol / L and less than or equal to 2 mol / L, more preferably 0.02 mol / L or more and less than or equal to 2 mol / L, and even more preferably 0.1 mol / L or more and less than or equal to 2 mol / L.

[13] In the methods for producing a carbonate apatite coated magnesium material of the present invention [6] to

[12] , preferably the thickness of the carbonate apatite coating is expressed by the following formula (3) as the thickness t [nm] that generates reflected light of a visible light wavelength λ [nm] corresponding to the desired interference color. t = (m + 1 / 2)·λ / (3.3cosθ) (3) Here, m is the interference order, which is usually an integer such as m = 1, 2, 3, or 4, and θ is the angle of incidence of the incident light on the coating.

[0014]

[14] The carbonate apatite coated metal material of the present invention is a base material which is one of the metal materials from the group consisting of iron, zinc, aluminum, or titanium, the surface roughness Ra of the base material is in the range of 0.05 μm to 2.0 μm, and the surface of the base material has a carbonate apatite coating with a surface roughness Ra of 65 nm or less, and the thickness of the carbonate apatite coating is 10 nm to 1000 nm. In the carbonate apatite coated metal material

[14] of the present invention, preferably, in the method for producing a carbonate apatite coated magnesium material [6], the magnesium material is replaced with one of the metal materials from the group consisting of iron, zinc, aluminum, or titanium. In the carbonate apatite coated metal material

[14] of the present invention, preferably, the magnesium complex in the method for producing the carbonate apatite coated magnesium material [7] or [8] is replaced with one of the metal complexes from the group consisting of an iron complex, a zinc complex, an aluminum complex, or a titanium complex.

[15] The present invention provides a method for producing a carbonate apatite-coated metal material, which involves preparing an aqueous solution containing a calcium complex at a concentration higher than 0.2 mol / L and a phosphate at a concentration of 0.5 to 1.25 times the concentration of the calcium complex, dissolving a carbonate in the aqueous solution containing the calcium complex and phosphate at the aforementioned concentrations to prepare a coating solution, heating the coating solution, immersing a substrate which is one of the metal materials from the group consisting of iron, zinc, aluminum, or titanium, and whose surface roughness Ra is in the range of 0.05 μm to 2.0 μm, in the heated coating solution, and coating the substrate with apatite mainly composed of carbonate apatite to a film thickness that exhibits the desired interference color. In the method for producing a carbonate apatite-coated metal material of the present invention

[15] , it is preferable to replace the magnesium material in the method for producing a carbonate apatite-coated magnesium material [6] with any one of the metal materials from the group consisting of iron, zinc, aluminum, or titanium. In the method for producing a carbonate apatite-coated metal material of the present invention

[15] , it is preferable to replace the magnesium complex in the method for producing a carbonate apatite-coated magnesium material [7] or [8] with any one of the metal complexes from the group consisting of an iron complex, a zinc complex, an aluminum complex, or a titanium complex. A medical device using the apatite carbonate coated magnesium material described in

[16] [1] to [5] or the apatite carbonate coated metal material described in

[14] . Industrial components using the apatite carbonate coated magnesium material described in

[17] [1] to [5] or the apatite carbonate coated metal material described in

[14] .

[0015] By using a magnesium material coated with a smooth carbonate apatite film exhibiting interference colors according to the present invention, it becomes possible to identify the type and size of medical devices and industrial components made from this material by color. Furthermore, when used in the housings of electronic devices such as cameras, it is possible to obtain a magnesium material with excellent design. When used as a medical material, apatite is a substance with excellent biocompatibility, which can improve not only the corrosion resistance but also the biocompatibility of the magnesium base material. This makes it possible to provide a magnesium surface with a different texture and design from metal plating or anodized coatings, as well as a method for manufacturing the same. Furthermore, because it is a coating of apatite, which has excellent biocompatibility, it can improve the biocompatibility and corrosion resistance of magnesium materials. [Brief explanation of the drawing]

[0016] [Figure 1] This is a flowchart for the method of producing the apatite carbonate coated magnesium material of the present invention. [Figure 2] This is the minute-angle X-ray diffraction pattern of sample #1-09, which illustrates one embodiment of the present invention. [Figure 3] The Fourier transform infrared absorption spectrum of sample #1-09, which represents one embodiment of the present invention, is shown. [Figure 4] These are the appearance, surface electron microscope images, and surface topographic images of Comparative Example #1-04 and Samples #1-09 to #1-12 of the present invention. [Figure 5] The images show the appearance and estimated film thickness of samples #2-01 to #2-08, which were treated at a coating temperature of 60°C with varying processing times. [Figure 6] This figure shows the relationship between the coating treatment time and the estimated thickness of the smooth carbonate apatite coating. [Figure 7] These are photographs of the appearance and estimated film thickness of samples #3-01 to #3-03, each with a different carbonate concentration in the coating solution. [Figure 8] This figure shows the relationship between the carbonate concentration of the coating solution and the estimated film thickness. [Figure 9] These are photographs of the appearance and estimated film thickness of samples #3-04 to #3-15, each with varying concentrations of Ca-EDTA and KH2PO4 in the coating solution. [Figure 10] This figure shows the relationship between the concentrations of Ca-EDTA and KH2PO4 in the coating solution and the estimated film thickness. [Figure 11]This is a photograph of the appearance of a magnesium alloy AZ31 screw coated with a smooth carbonate apatite film. [Figure 12] These are photographs of the appearance of various metal materials coated with a smooth carbonate apatite film. [Figure 13] The polarization resistance Rp of samples #1-01 to #1-03 and samples #1-09 to #1-11 in Hanks' solution is shown. [Figure 14] This diagram illustrates the time evolution of the corrosion potential associated with indentation in Hanks solution for samples #1-01, #1-07, #1-09, and #1-09-b. [Figure 15] This figure shows cross-sectional transmission electron microscope (TEM) images of samples (1)#A-01, (2)#A-02, and (3)#A-03. [Figure 16] This figure shows the electron diffraction patterns of samples (1)#A-01, (2)#A-02, and (3)#A-03. The regions indicated by Point1 (surface side), Point2 (substrate side or center of the coating), and Point3 (substrate side) in the cross-sectional TEM observation image were measured. [Figure 17] This figure shows the energy-dispersive X-ray spectroscopy (EDS) elemental mapping image of sample #A-03. [Figure 18] This figure shows the XPS patterns of samples (1)#A-01, (2)#A-02, and (3)#A-03. [Figure 19] This figure shows the Mg2+ ion elution behavior in cell culture medium for samples #A-01 and #A-03, and for comparison, uncoated WE43 and uncoated pure Mg. [Figure 20] These are SEM images of indentation marks in Hanks' solution for samples (1)#A-04, (2)#A-01, and (3)#A-03, as well as comparative examples (4) uncoated WE43 and (5) uncoated pure Mg. [Figure 21] This figure shows Giemsa stained images of osteoblasts cultured on samples (1) #A-01, (2) uncoated WE43, (3) #A-03, and (4) uncoated pure Mg surface. [Figure 22]This figure shows the alkaline phosphatase (ALP) activity of osteoblasts cultured on (1) uncoated WE43 and (2) sample #A-01 surface. [Modes for carrying out the invention]

[0017] As a premise for this invention, a bone reconstruction procedure using carbonate apatite will be described. Bone reconstruction is a procedure to reconstruct bone function caused by malignant tumors, trauma, dental implants, etc., and the first choice is autogenous bone grafting. However, since autogenous bone grafting is a procedure in which the patient's own bone is transplanted to the bone defect site, the invasiveness to healthy tissue due to autogenous bone harvesting is a serious problem. Therefore, as a bone reconstruction method other than autologous bone grafting, hydroxyapatite [Ca 10 Bone reconstruction using [PO4]6(OH)2] artificial bone has also been established. However, a challenge has been that hydroxyapatite remains almost unchanged for many years and is not replaced by biological bone. Although hydroxyapatite has slightly lower osteoconductivity than carbonate apatite, it is recognized in the field of orthopedics that hydroxyapatite has superior osteoconductivity compared to β-tricalcium phosphate and metallic materials such as titanium alloys, which are used as soluble artificial bones. On the other hand, the skeletal composition of invertebrates is calcium carbonate, while the skeletal composition of vertebrates, including humans, is carbonate apatite [CO3Ap:Ca 10-a (PO4) 6-b (CO3) cIt is believed that during the evolution from invertebrates to vertebrates, it became necessary to store phosphate, which is essential for energy metabolism, within the body, and bone was selected as the storage organ. Furthermore, when a calcium carbonate block, which is a precursor, is immersed in an aqueous sodium phosphate solution, it has the property of being converted into carbonate apatite while maintaining its macroscopic state. Therefore, a method for preparing carbonate apatite blocks for artificial bone has been developed using this property. This prepared carbonate apatite block shows high biocompatibility with osteoclasts and osteoblasts, which play a role in bone formation in living organisms, and is replaced by new bone just like autologous bone, so it has received regulatory approval in the dental field as an artificial bone for bone composition (see Non-Patent Literature 4). Therefore, when magnesium material coated with carbonate apatite is used for artificial bone or bone screws, it is expected to be a material that shows high compatibility with surrounding tissues. Currently, magnesium materials are increasingly being applied to bone screws and nails for bone fixation, vascular dilation stents, and staples for soft tissue suturing. Applying magnesium materials coated with carbonate apatite to these medical devices is expected to result in devices with high compatibility with surrounding biological tissues.

[0018] In this specification, the arithmetic mean roughness (Ra) is defined using JIS B0601 (1994). The arithmetic mean roughness (Ra) is obtained by taking a reference length from the roughness curve in the direction of the mean line, plotting the X-axis in the direction of the mean line of this sampled portion and the Y-axis in the direction of the vertical scaling factor, and representing the roughness curve as y=f(χ), and expressing the value by the following formula in micrometers (μm).

number

[0019] Next, the method for producing the carbonate apatite-coated magnesium material of the present invention will be described. Figure 1 is a flowchart of the method for producing the carbonate apatite-coated magnesium material of the present invention. First, an aqueous solution containing a high concentration of calcium complex and phosphate is prepared (S100). Here, "high concentration" refers to a concentration close to or equal to the saturation solubility, but an aqueous solution of the calcium complex is prepared at a concentration that is supersaturated relative to the solubility of an aqueous solution of calcium chloride, which has the highest solubility among inorganic salts. For example, this does not preclude the addition of a chelating agent to an aqueous solution of calcium chloride, calcium acetate, or calcium nitrate to create a supersaturated state. By doing so, aqueous solutions with calcium concentrations of, for example, 2 to 100 times or 1.5 to 250 times the saturation solubility of calcium chloride can be prepared.

[0020] Next, a coating treatment solution is prepared by dissolving carbonate in an aqueous solution containing a high concentration of calcium complex and phosphate (S102). Then, the coating solution is heated (S104). Generally, increasing the processing temperature makes it easier for apatite crystals to form, so it is desirable to adjust the processing temperature of the solution to be in the range of 40 to 100°C, preferably 60 to 100°C, depending on the desired thickness of the coating and the size of the component (relative to the amount of solution used).

[0021] The magnesium material is immersed in a heated coating solution (S106). The magnesium material shall have a surface roughness Ra of 0.05 μm or more and 2.0 μm or less. The magnesium material is then coated with apatite mainly composed of carbonate apatite to a film thickness that exhibits the desired interference color (S108). Since increasing the immersion time increases the degree of crystallinity and the amount of precipitated apatite, it is desirable to adjust the immersion time to a range of 1 to 60 minutes, preferably 5 to 30 minutes, and more preferably 5 to 10 minutes, depending on the desired film thickness and the size of the component (relative to the amount of solution used).

[0022] The corrosion-resistant coating for bioabsorbable materials of the present invention is mainly composed of carbonate apatite, which has very low solubility in neutral salt solutions, and therefore exhibits higher corrosion resistance compared to the ordinary atmospheric oxidation coating on magnesium materials. The coating, which is mainly composed of carbonate apatite, is formed by the precipitation of carbonate apatite from the coating treatment solution. Furthermore, when a crystalline magnesium hydroxide layer is interposed as an interface with the substrate under certain processing conditions, its solubility is significantly lower than that of amorphous magnesium hydroxide normally formed in the atmosphere, thus enhancing the suppression of magnesium corrosion.

[0023] In order to ensure that the resulting coating does not contain elements or ions that are harmful to living organisms, the principle is that the solution used in the immersion treatment must not contain elements that are harmful to living organisms, such as Cr or Ni. However, this does not negate the possibility that even biotoxic elements may be present in amounts so small that their leaching would not substantially harm living organisms. To process magnesium substrates while suppressing thinning and surface roughening, it is desirable that the coating solution does not contain ions that cause localized corrosion of magnesium, such as chloride ions. Simulated Body Fluid (SBF) or Hanks' solution are usually used for the deposition of carbonate apatite from aqueous solutions on the surface of bio-metallic materials such as titanium, but these contain calcium chloride and are therefore undesirable as coating solutions for magnesium substrates.

[0024] The carbonate apatite phase is typically stable at a solution pH of 7 or higher. Furthermore, magnesium substrates exhibit higher corrosion resistance at higher solution pH levels. Conversely, the solubility of calcium salts such as calcium hydroxide and calcium chloride decreases with increasing pH. Therefore, it is desirable that the coating solution used to precipitate carbonate apatite on the magnesium substrate surface contains a certain concentration of calcium ions, even though its pH is alkaline rather than near neutral. In this invention, since the treatment is carried out in an environment where magnesium elements that inhibit apatite crystallization are present, it is desirable that the concentrations of calcium ions and phosphate ions in the coating treatment solution be higher than those in pseudo-body liquids such as SBF or Hanks' solution used for surface treatment of titanium alloys and the like. Typically, artificial body fluids are prepared by using calcium chloride, which has relatively high solubility, to dissolve calcium ions at a supersaturated concentration. In contrast, this invention uses a calcium chelate compound to stabilize the ionic state of calcium in aqueous solution, successfully obtaining an aqueous solution containing calcium ions at a concentration equal to or 800 times that of artificial body fluid. It is believed that the presence of high concentrations of calcium ions enables the deposition of carbonate apatite on the magnesium material surface, which releases magnesium elements that inhibit carbonate apatite formation.

[0025] Calcium compounds that can dissolve high concentrations of calcium ions over a wide pH range include EDTA (ethylenediaminetetraacetic acid), NTA (nitrilotriacetate), HEDTE ((Hydroxyethyl)ethylenediaminetriacetic acid), and calcium chelates of aminopolycarboxylic acids. Chelating agents for fruit acids include malic acid, citric acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, and sulfamic acid, some of which are biodegradable chelating agents. Furthermore, if the coating solution is near neutral to acidic, inorganic salts such as calcium hydroxide, calcium nitrate, calcium carbonate, calcium acetate, calcium dihydrogen phosphate, and calcium thiosulfate can also be used. At this time, by adding a chelating agent together with an inorganic salt, the calcium ion concentration can also be increased. In addition, due to the presence of the chelating agent, degreasing of the substrate surface and removal of smut proceed concurrently with film formation, so it can be expected that impurities in the formed film will be reduced. On the other hand, the chelating agent has an effect of corroding the magnesium surface. When the rate of overall surface corrosion by the chelating agent and the rate of apatite precipitation from the treatment solution are well balanced, an apatite film can be formed on the substrate surface while maintaining the metallic luster of the substrate surface. From such a situation, the chelating agent is 2.0×10 2 mM or more, preferably 2.5×10 2 mM or more, more preferably 3×10 2 mM or more. In addition, the calcium ion concentration in the solution is higher than 2.0×10 2 mM, preferably 2.5×10 2 mM or more, more preferably 3×10 2 mM or more. If it is less than this range, there will be a problem that apatite precipitation does not occur before corrosion occurs that roughens the surface of the magnesium material.

[0026] Examples of the inorganic phosphate constituting the coating treatment solution include various alkali salts such as potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, calcium hydrogen phosphate, tripotassium phosphate, trisodium phosphate, ammonium salts, and alkaline earth ortho dihydrogen salts. Since the Ca / P ratio in carbonated apatite is greater than 1.67, it is considered that carbonated apatite is difficult to form in an environment where phosphate ions are excessive with respect to calcium ions. Therefore, it is desirable not to exceed the calcium ion concentration. The Ca / P ratio is desirably 0.8 to 2.0, preferably 1.0 to 1.8. A Ca / P ratio of 0.8 to 2.0 corresponds to the dissolution of phosphates that are 0.5 times or more and 1.25 times or less the concentration of the calcium complex.

[0027] To adjust the pH of the coating solution prepared from the above calcium compounds and inorganic phosphates, an alkaline solution such as sodium hydroxide, potassium hydroxide, or ammonia is used. The pH range to be adjusted should preferably be pH 4 or higher, more preferably pH 5 or higher, and more preferably pH 6 or higher. This is because the magnesium substrate immersed in the coating solution dissolves, and the pH rise due to the dissolution reaction allows the pH near the surface of the magnesium substrate to reach a pH of 7 or higher, where the carbonate apatite phase is stable. Even in the pH range where magnesium materials become passive at pH 11 or higher, the carbonate apatite phase remains stable, allowing carbonate apatite to be deposited on the surface of the magnesium substrate. Furthermore, if the pH is too high, a problem arises in which carbonate apatite particles precipitate in the treatment solution rather than on the surface of the magnesium material. Therefore, it is desirable to set the pH to 13 or lower, preferably 12 or lower, and more preferably 11 or lower. Increasing the pH increases the stability of the carbonate apatite phase. This is one of the adjustment factors to consider when taking into account the desired corrosion resistance time of the coating.

[0028] Regarding immersion treatment conditions other than the coating treatment solution, the treatment temperature, treatment time, pH of the solution, concentration of calcium and phosphate in the solution, and Ca / P ratio can be changed according to the desired corrosion resistance and form of the coating. In summary, the pH of the solution, the processing temperature, the processing time, the concentrations of calcium and phosphate, and the Ca / P ratio are all modulating factors for coating formation. By appropriately adjusting these factors, it is possible to manufacture medical bioabsorbable materials with the desired corrosion resistance time and interference color of the coating.

[0029] The type of magnesium substrate used to form the carbonate apatite coating of the present invention is not particularly limited and may be pure magnesium or a magnesium alloy. The magnesium alloy may be solid solution strengthened alloys such as AZ31, AZ61, and Mg-1.0mass%Al alloy or Mg-0.8mass%Ca alloy, or precipitation strengthened alloys such as AZ91, or even bcc type alloys such as Mg-Sc alloy.

[0030] While pretreatment such as degreasing, smut removal, and activation of the substrate surface is desirable, it is not always necessary to perform these pretreatments to form a coating primarily composed of carbonate apatite. The pretreatment method should be selected according to the composition and structure of the magnesium alloy substrate, the application of the device, and the desired corrosion rate. Surface polishing is preferable for Mg alloys. Well-known methods such as manual polishing, mechanical polishing, chemical polishing, and electrolytic polishing can be employed. Ideally, the surface should be polished to a surface roughness Ra of 0.0001 μm to 2.0 μm. This results in a mirror or micro-mirror finish on the Mg alloy surface, providing excellent adhesion between the coating layer, primarily composed of carbonate apatite, and the substrate. For manual polishing, abrasive paper containing abrasives such as silicon carbide (SiC), zirconium corundum, or boron carbide is used. For mechanical polishing, wet polishing using abrasive powders such as diamond, cubic boron nitride, silicon carbide, or alumina can be employed. Chemical polishing can be exemplified by methods such as the phosphoric acid-nitric acid method using nitric acid, the Kaiser method, and the Alupol method using sulfuric acid. Electrolytic polishing can be exemplified by methods such as the Erfwerk method and the Aluflex method. A surface roughness Ra of 0.05 μm to 2.0 μm is preferable from the viewpoint of adhesion. Furthermore, by controlling the surface roughness, the aesthetic appearance of the Mg alloy surface can be freely altered. The smaller the surface roughness Ra, the higher the metallic luster of the Mg-based metal component, while the larger the surface roughness Ra, the more matte, frosted-glass-like the Mg-based metal component will have. For example, if the surface roughness Ra is controlled to be between 0.0001 μm and 0.2 μm, a Mg-based metal component with metallic luster will be produced, and if the surface roughness Ra is controlled to be between 0.2 μm and 1.6 μm, a Mg-based metal component with a matte surface will be produced. [Examples]

[0031] The substrates used were commercially available Mg-4Y-3RE (WE43), Mg-3Al-1Zn (AZ31), and pure Mg (>99.9%), in addition to Mg-1Sc alloy (MgSc) developed at NIMS. The substrate surface was finished with #1200 grit sandpaper. Table 1 shows the sample number, substrate, composition of the coating solution, treatment temperature, and treatment time for each sample. Samples #1-01 to #1-03 are uncoated materials with only polishing, while samples #1-04 to #1-08 are carbonate apatite coated materials and hydroxyapatite coated materials prepared by the methods described in Patent Documents 1 and 2, respectively, and used as comparative examples.

[0032] As the coating solution, an aqueous solution of ethylenediaminetetraacetate disodium (Ca-EDTA)-potassium dihydrogen phosphate (KH2PO4)-sodium bicarbonate (NaHCO3)-sodium hydroxide (NaOH) with the composition shown in Table 1 was prepared. The coating solution was heated to 90°C, the substrate was immersed in the solution, and the coating treatment was performed for 10 minutes to prepare each sample. Here, samples prepared by storing the coating solution for a certain period after preparation to allow impurities to settle before using it for coating treatment are denoted as #X-YY, and samples prepared by using the solution immediately after preparation for coating treatment are denoted as #X-YY-b.

[0033] [Table 1]

[0034] Figures 2 and 3 show the minute-angle X-ray diffraction pattern and Fourier transform infrared absorption spectrum of sample #1-09, a typical example of the present invention. Figure 2 shows diffraction peaks originating from the apatite structure in addition to diffraction peaks from the substrate WE43. Figure 3 shows that the apatite film contains carbonate groups and that absorption peaks from phosphate groups and hydration water in the apatite structure are present. Similar results were obtained for #1-09-b and #1-10 to #1-12. These results indicate that the films prepared under the conditions of #1-09 to #1-12 are mainly composed of carbonate apatite.

[0035] Figure 4 shows the external appearance (digital camera images), scanning electron microscope images, and surface topography images measured by atomic force microscope for samples #1-09 to #1-12 and #1-09-b, which are typical examples of the present invention. The results for sample #1-04 are shown as a comparative example. Here, the external appearance photographs were taken by irradiating the sample surface with white light, which was reflected by white paper with a color temperature of 5500K, at an angle that showed the strongest interference color. Sample #1-04 had a surface layer formed by the aggregation of submicrometer fine crystals, and due to the surface irregularities, it had almost no gloss. On the other hand, samples #1-09 to #1-12 of the present invention showed smooth surfaces even under electron microscopy observation, and the surface exhibited gloss and interference colors in the visual photographs. In sample #1-09-b, the adhesion of submicrometer fine crystals was observed on the outermost surface under electron microscopy, resulting in poor gloss, but interference colors were observed through the fine crystal layer. From these, it was found that a smooth surface is important for gloss and interference colors. On the other hand, it was shown that the coating process can be used to change the result to either obtain both gloss and interference colors, or obtain interference colors but have poor gloss.

[0036] The surface roughness Ra of the carbonate apatite coating was measured using an atomic force microscope. The gloss and surface microstructure (visual roughness) of the sample surface, as well as the interference colors exhibited by the coating, were confirmed by photographs of the surface. The thickness of the coating, estimated from the interference colors, was calculated using the following formula (1) and used as the estimated thickness. 2·n·t=(m+1 / 2)·λ (1) Here, n = refractive index of apatite = 1.65, t = thickness of the coating, m = interference order, and λ = wavelength of light. Since the film thickness of sample #1-06 was measured to be approximately 700 nm using a cross-sectional electron microscope, the film thickness t was calculated using an interference order m = 3, which gives a film thickness close to this value. However, the carbonate apatite coating of the present invention may have an interference order different from 3. In other words, the film thickness t that achieves the wavelength λ of the desired interference color is expressed by the following equation. t = (m + 1 / 2)·λ / 3.3 (2) When light is incident on a coating at an angle θ, the condition under which the incident and reflected light reinforce each other is given by t = (m + 1 / 2)·λ / (2ncosθ). Equations (1) and (2) are for when the incident angle is 0 degrees. Therefore, if the film thickness is calculated using the interference color obtained at a low line-of-sight incident angle, it will be thicker than it actually is. So, by correcting equations (1) and (2) with the incident angle θ of the light incident on the coating, the film thickness t that achieves the wavelength λ of the desired interference color is given by the following equation (3). t = (m + 1 / 2)·λ / (3.3cosθ) (3)

[0037] Furthermore, if the target interference color is visible light, the wavelength range that the human eye perceives as light can be defined as follows: The lower limit of the wavelength range is 360-400 nm, and the upper limit is 760-830 nm. Visible light gives different color perceptions depending on the wavelength and is perceived as violet (380-430 nm), blue (430-490 nm), green (490-550 nm), yellow (550-590 nm), orange (590-640 nm), and red (640-770 nm). Regarding the boundary values ​​and color classifications of this color perception, there are several theories other than this classification, and there are also classifications that further subdivide the color classifications as shown in Table 2. [Table 2]

[0038] Table 3 shows the results obtained regarding the surface roughness and interference color of the apatite coatings of Comparative Examples #1-04 to #1-06 and Samples #1-09 to #1-12 of the present invention. The surface roughness Ra of the smooth coatings of Samples #1-09, #1-10, and #1-11 of the present invention was less than 50 nm. On the other hand, the surface roughness Ra of the coatings of the non-smooth coatings of Samples #1-04 to #1-06 was greater than approximately 70 nm. Since calcium phosphate apatite is originally a colorless and transparent substance, it can exhibit interference colors if the surface is smooth. Therefore, it is thought that interference colors appear when the surface roughness Ra is less than 65 nm, and glossy interference colors appear when the surface roughness Ra is less than 50 nm. On the other hand, it is thought that if the surface roughness Ra is greater than 65 nm, light is diffusely reflected by the surface irregularities and interference colors do not appear. Furthermore, when smooth apatite coatings were prepared under the same conditions, the substrate was predominantly reddish-purple when using WE43, predominantly yellow when using AZ31, and predominantly yellowish-green when using pure Mg. This revealed that the color of the carbonate apatite coating changes depending on the composition of the substrate.

[0039] [Table 3] [Examples]

[0040] <Effects of coating temperature and time> The coating treatment was performed on substrates WE43, AZ31, and pure Mg at a processing temperature of 60°C, with processing times varied from 5 to 60 minutes. Table 4 summarizes the coating conditions at a processing temperature of 60°C with varying processing times. Figure 5 summarizes the appearance, estimated film thickness, and interference color of the samples at a processing temperature of 60°C with varying processing times. [Table 4]

[0041] From the appearance photos of the samples, even when the coating treatment temperature was lowered to 60 °C, a smooth apatite carbonate film showing a shiny interference color could be obtained. When the substrate was AZ31 and pure Mg and the coating treatment time was changed from 5 to 60 min, both gloss and interference color were observed when the coating treatment time was short. As the coating treatment time increased, the surface became rough and the gloss decreased, but the interference color was still observed. It was speculated that when the coating treatment time was increased, fine crystals adhered to the outermost surface as in Sample 1-09-b. When comparing the color of the film for each substrate with that in [Example 1] where the coating treatment temperature was 90 °C, for WE43 with a coating treatment temperature of 90 °C (#1-09), the main color was red-purple, while for 60 °C (#2-01), the main color was yellow. For AZ31 with a coating treatment temperature of 90 °C (#1-10), the main color was yellow, while for 60 °C (#2-03), the main color was green. This indicates that the interference color of the smooth apatite carbonate film can be changed by varying the coating treatment temperature.

[0042] Figure 6 shows the relationship between the coating treatment time and the estimated thickness of the smooth apatite carbonate film for samples #2-02 to #2-05 with a substrate of AZ31 and #2-06 to #2-08 with a substrate of pure Mg. For any substrate, the film thickness increased with an increase in the treatment time. It is known that the interference color of a thin film changes depending on the film thickness. This indicates that the interference color of the film can be controlled by the coating treatment time.

Examples

[0043] <Influence of the concentrations of NaHCO3 or Ca-EDTA and KH2PO4> The concentrations of sodium hydrogen carbonate (NaHCO3), calcium disodium ethylenediaminetetraacetate (Ca-EDTA), and potassium dihydrogen phosphate (KH2PO4) in the coating treatment solution were changed, and the coating treatments of substrates WE43, AZ31, and pure Mg were carried out. Table 5 summarizes the coating treatment conditions with different carbonate concentrations or different concentrations of Ca-EDTA and KH2PO4 in the coating treatment solution.

Table 5

[0044] Figure 7 summarizes the appearance, interference color, and estimated film thickness of the coating film when the carbonate concentration is varied using AZ31 as the substrate. It has been reported that increasing the carbonate concentration in the coating solution increases the carbon dioxide content incorporated into the carbonate apatite coating, and thus decreases the film thickness (Hiromoto et al., STAM, 21 (2020) 346-358, Midorikawa et al., Ceramics International., 50 (2024) 6784-6792). In Figure 7, as the carbonate concentration in the coating solution increases, the interference color of the coating film changes from predominantly yellow to predominantly blue-green, suggesting a decrease in film thickness. This indicates that the interference color of the coating film can be changed by the carbon dioxide content of the carbonate apatite coating film.

[0045] Figure 8 shows the relationship between the carbonate concentration in the coating solution and the estimated film thickness for samples #1-10 and #3-01 to #3-03, where the substrate is AZ31. The film thickness decreases as the carbonate concentration in the coating solution increases. This result is consistent with the results for conventional carbonate apatite coatings that do not exhibit interference color (Ceramics International, 50 (2024) 6784-6792). This indicates that the interference color of the coating can be controlled by the carbonate concentration in the coating solution.

[0046] Figure 9 summarizes the appearance of the coating, interference colors, and estimated coating thickness when the concentrations of Ca-EDTA and KH2PO4 (calcium complex and phosphate) in the coating solution are varied. In samples #3-04 to #3-09, which used WE43 as the substrate and were coated with Ca-EDTA and KH2PO4 concentrations lower than 0.4M in [Example 1], clear interference colors were not obtained, but interference colors as shown in Figure 9 were observed visually. From these results, it was found that concentrations of Ca-EDTA and KH2PO4 higher than 0.3M are desirable for the formation of a smooth carbonate apatite coating that exhibits glossy interference colors.

[0047] Using WE43, AZ31, and pure Mg as substrates, coating treatment was performed with a higher concentration of Ca-EDTA and KH2PO4 (0.5 M) than in [Example 1]. The appearance photographs of samples #3-10 to #3-15 in Figure 9 show that glossy interference color coatings can be obtained under many conditions. This result indicates that higher concentrations of Ca-EDTA and KH2PO4 in the coating solution result in glossy interference color coatings.

[0048] Figure 10 shows the relationship between the concentrations of Ca-EDTA and KH2PO4 in the coating solution and the estimated film thickness for samples #1-09, #3-04, #3-07, and #3-10, which use WE43 substrate. Here, cloudiness is observed on the surface of samples #3-04 and #3-07, which have low concentrations, suggesting a two-phase structure with fine crystals on top of a smooth layer. Since only the thickness of the lower layer can be estimated from the interference color, the thickness is considered to be relatively thin. On the other hand, it was found that increasing the concentration of Ca-EDTA and KH2PO4 above 0.3 mol / L increased the thickness of the smooth coating. This indicates that the interference color of the coating can be controlled by the concentration of Ca-EDTA and KH2PO4 in the coating solution. [Examples]

[0049] <Smooth carbonate apatite coating on screws> Table 6 shows the conditions for performing a smooth carbonate apatite coating treatment on commercially available AZ31 screws as a base material. Figure 11 shows an optical microscope image after coating. The coated AZ31 screws exhibit a glossy, light pink color, indicating that a transparent and smooth coating has been formed. This result demonstrates that the coating method of the present invention can be applied regardless of the shape of the base magnesium alloy. [Table 6] [Examples]

[0050] <Apatite coating on metal materials other than magnesium> Table 7 shows the conditions under which smooth carbonate apatite coating treatment was performed on substrates using zinc (Zn) and iron (Fe), which are attracting attention as biosoluble metal materials similar to magnesium, aluminum (Al), which is attracting attention as a lightweight material similar to magnesium, and titanium (Ti), a representative biometal material. All substrates were pure metals with a purity of >3N, and the surfaces were finished with #1200 abrasive paper. Figure 12 shows photographs of the appearance and color of the coatings of Zn, Fe, Al, and Ti coated with smooth carbonate apatite. Since the original substrate surfaces of Zn and Al had poor luster, they did not show a clear luster after the coating treatment. On the other hand, all metals showed interference colors, although not very clear. These results demonstrate that the smooth carbonate apatite coating of the present invention can be applied to various metal materials. [Table 7] [Examples]

[0051] <Corrosion resistance evaluation by electrochemical impedance testing> Figure 13 shows the corrosion resistance R obtained by performing an electrochemical impedance test in Hanks solution, a type of simulated body fluid, to evaluate the corrosion resistance of uncoated samples #1-01 (WE43), #1-02 (AZ31), and #1-03 (pure Mg) of the substrates WE43, AZ31, and pure Mg, and the smooth carbonate apatite coated samples #1-09 (WE43), #1-10 (AZ31), and #1-11 (pure Mg) of the present invention. p This demonstrates that WE43, AZ31, and pure Mg coated with a smooth carbonate apatite film have polarization resistance R equal to or greater than that of the uncoated sample. p These results demonstrate that the corrosion resistance of magnesium alloys can be improved by coating them with smooth carbonate apatite. [Examples]

[0052] <Electrochemical Indentation Test> Electrochemical indentation tests were conducted to evaluate the surface damage resistance of the coatings on uncoated sample #1-01 (WE43 substrate), conventional carbonate apatite coated sample #1-07, and the smooth carbonate apatite coated samples #1-09 and #1-09-b of the present invention. In this test, the corrosion potential of the sample was measured in an electrolyte solution, and the coating was damaged by indenting the surface with a sharpened rod for 1 second with a constant force. The extent of the potential drop due to the exposure of the newly formed metal surface and the time it took to recover to the original potential were used to evaluate the extent of the damage to the coating and the time required for repair. A larger drop in corrosion potential indicates a larger area of ​​newly exposed metal surface, suggesting greater damage to the surface layer such as the oxide film or coating.

[0053] Figure 14 shows the time evolution of the corrosion potential when an alumina rod with a tip diameter of approximately 500 micrometers was pressed with a constant force at five locations on the surface of various samples in Hanks' solution (a simulated body fluid) at regular time intervals. Indentation caused a decrease in corrosion potential of approximately 100 mV in the uncoated sample #1-01 and approximately 150 mV in the conventionally coated carbonate apatite sample, suggesting that the area of ​​newly exposed metal surface due to indentation is larger on the conventional carbonate apatite coated surface. On the other hand, in the smooth carbonate apatite coated samples #1-09 and #1-09-b, the potential decrease associated with indentation was very small, approximately 10 mV, regardless of the presence or absence of fine crystals on the outermost surface. Furthermore, the magnitude of the potential decrease associated with indentation did not depend on the presence or absence of fine crystals on the outermost surface of the smooth carbonate apatite coating. These results demonstrate that the smooth carbonate apatite coating of the present invention is more durable than conventional carbonate apatite coatings, i.e., it is more resistant to surface damage, regardless of the presence or absence of fine crystals on the outermost surface. [Examples]

[0054] <Characterization of the coating> Example 8 shows results that support the range of film thickness for the smooth carbonate apatite coating from 10 nm to 1000 nm. In addition, Example 8 also shows the results of electron diffraction (crystal structure), energy-dispersive X-ray spectroscopy (EDS) measurements, and X-ray photoelectron spectroscopy (XPS) measurements (elemental analysis). Commercially available Mg-4Y-3RE (WE43), Mg-3Al-1Zn (AZ31), and pure Mg (>99.9%) were used as substrates. The substrate surface was finished with #1200 grit sandpaper. Table 8 shows the sample number, substrate, composition of the coating solution, treatment temperature, and treatment time for each sample prepared. [Table 8]

[0055] From samples #A-01, #A-02, and #A-03, samples for transmission electron microscopy (TEM) observation were prepared by focused ion beam processing, and cross-sectional observation of the coating was performed. Figure 15 shows the cross-sectional TEM images of samples #A-01, #A-02, and #A-03. Figure 16 shows the electron diffraction (ED) patterns of the surface, center, and substrate side of the coating. Figure 17 shows the elemental mapping measured by EDS for sample #A-03. Note that the elemental mapping images measured by EDS for samples #A-01 and #A-02 are omitted. Based on the EDS results for each substrate, the composition and structure of the boundary between the carbonate apatite layer and the substrate differ depending on the composition of the substrate Mg alloy, as shown below. In the case of WE43 substrate (Sample #A-01), MgO nanoparticles are dispersed between the substrate and the carbonate apatite layer, but no layer is formed. It can be said that the carbonate apatite and the substrate are in direct contact. Intermetallic compounds of the substrate are incorporated into the carbonate apatite layer. When the substrate is AZ31 (Sample #A-02), the structure is very complex, with a layer between the substrate and the carbonate apatite layer containing a mixture of MgO nanoparticles and magnesium phosphate-calcium nanocrystals, as well as Al and Zn from the substrate. When the substrate is pure Mg (Sample #A-03), there is a layer between the substrate and the carbonate apatite layer in which MgO nanoparticles and magnesium phosphate-calcium nanocrystals are mixed. Regarding the thickness of the intermediate layer between the substrate and the carbonate apatite layer, the upper limit can be roughly determined from the part of the EDS map where the intermediate layer appears thickest, as follows: #A-01: 5min coated WE43: 45nm or less #A-02: 5min coating AZ31: 65nm or less #A-03:5min coated pure Mg: 50nm or less The lower limit of the intermediate layer thickness is 0 nm or more. In other words, in the case of WE43, there were areas where the intermediate layer appeared to be absent. Regarding the lower limit of the intermediate layer for AZ31 and pure Mg, since areas without an intermediate layer were observed in WE43, there is a possibility that there are areas in AZ31 and pure Mg where the substrate and the carbonate apatite layer are in direct contact.

[0056] Table 9 shows the film thickness determined from cross-sectional TEM images. It can be seen that a film thickness of approximately 125 nm was formed on the WE43 surface, approximately 165 nm on the AZ31 surface, and approximately 105 nm on the pure Mg surface. The film thickness of these 5-minute coated smooth carbonate apatite films was thinner than the 500 nm film thickness of the 10-minute coated smooth calcium carbonate film estimated with interference order m=3, as shown in Table 3 of Example 1. In Example 1, the film thickness was estimated using interference colors observed at a low line-of-sight incidence angle, which is thought to have resulted in an estimated value that was larger than the actual value. [Table 9]

[0057] TEM observation and EDS analysis revealed that all coatings were aggregates of calcium phosphate nanocrystals containing carbonic acid, with nanocrystals measuring several nanometers in size, and the ED patterns showed a halo pattern. A layer of magnesium phosphate nanocrystals or amorphous material containing calcium was present at the boundary between the substrate and the coating, with 10-20 nm MgO particles dispersed in places. The direct contact between the substrate and the calcium phosphate coating indicates that the coating of the present invention has high adhesion to the substrate.

[0058] Figure 18 shows the XPS measurement results for samples #A-01, #A-02, and #A-03. All of the sample coatings contained oxygen (O), calcium (Ca), carbon (C), phosphorus (P), magnesium (Mg), sodium (Na), and their respective alloying elements: neodymium (Nd), yttrium (Y), and aluminum (Al). It is thought that the Mg, Na, and Y in the coatings are incorporated into the Ca sites within the carbonate apatite crystal structure.

[0059] Therefore, quantitative analysis by XPS was performed to determine the (Ca+Mg+Na+Y) / (P+C) elemental ratio, which was found to be 1.48-1.73, as shown in Table 10. This value is close to the Ca / P ratio of Ca-deficient apatite. The results from TEM-ED-EDS and XPS suggest that the carbonate apatite contained in the coating of the present invention is Ca-deficient carbonate apatite, regardless of the base Mg alloy. Here, Ca-deficient carbonate apatite includes not only carbonate apatite in which the Ca site is vacant, but also carbonate apatite in which other cations such as Mg or Na are substituted on the Ca site. Since Ca-deficient carbonate apatite is a type of apatite, it can also be written as carbonate apatite. [Table 10] [Examples]

[0060] <Cell culture medium immersion test> Example 9 demonstrates that the smooth carbonate apatite coating of the present invention improves the corrosion resistance of the substrate Mg and Mg alloy. Samples #A-01 and #A-03, as well as uncoated WE43 and pure Mg as comparative materials, were subjected to a 42-day immersion test in cell culture medium. Figure 19 shows the relationship between the amount of Mg ions eluted per unit area of ​​the sample and the immersion time. With WE43 as the substrate, there was almost no change in the Mg ion elution behavior due to the smooth carbonate apatite coating. On the other hand, in the case of pure Mg, Mg ion elution was suppressed by the smooth carbonate apatite coating. From this, it was found that the smooth carbonate apatite coating of the present invention exhibits corrosion resistance superior to that of atmospheric oxide coatings of Mg and Mg alloys. [Examples]

[0061] <Indentation test in simulated bodily fluids> Example 10 demonstrates that the smooth carbonate apatite coating of the present invention reduces surface damage, and shows experimental results similar to those of Example 7. Samples #A-01 and #A-03 from Table 8, and #A-04 as a comparative material, uncoated WE43 and uncoated pure Mg were immersed in Hanks' solution for 3.6 ks, and an alumina rod with a tip diameter of approximately 400 μm was pressed against them at 15 N for approximately 1 second. Figure 20 shows SEM images of the formed indentation marks. Figure 20 shows SEM images of the indentation marks in Hanks' solution for samples (1) #A-04, (2) #A-01 and (3) #A-03, as well as comparative examples (4) uncoated WE43 and (5) uncoated pure Mg. Compared to the indentations of uncoated WE43 and pure Mg, the indentations of samples #A-01 and #A-03 of the present invention were smaller and shallower, respectively. Furthermore, while delamination of the coating was observed around the indentation of the conventional carbonate apatite coating #A-04, no delamination was observed in samples #A-01 and #A-03. These results demonstrate that the smooth carbonate apatite coating of the present invention is resistant to damage such as deformation of the substrate. [Examples]

[0062] <Cell Culture Test> Example 11 demonstrates that the smooth carbonate apatite coating of the present invention promotes biocompatibility and bone formation ability. Osteoblast cells MC3T3 were cultured for 48 hours on samples #A-01 and #A-03 in Table 8, and on uncoated WE43 and uncoated pure Mg surfaces as comparative materials. Figure 21 shows images taken with a light microscope after fixing cells to the sample surface with methanol, staining the cells with Giemsa stain. When the substrate was WE43, the effect of the smooth carbonate apatite coating on cell number and morphology was not significant. On the other hand, when the substrate was pure Mg, the surface coated with smooth carbonate apatite had a higher cell number than the uncoated surface. This indicates that the smooth carbonate apatite coating of the present invention can improve the biocompatibility of Mg and Mg alloy surfaces.

[0063] Figure 22 shows the results of measuring alkaline phosphatase (ALP) activity, a marker of osteogenicity, after culturing osteoblasts MC3T3 on the surface of sample #A-01 and the uncoated WE43 surface of the comparative material for 21 days. The WE43 coated with smooth carbonate apatite (#A-01) showed higher ALP activity than the uncoated WE43. This demonstrates that the smooth carbonate apatite coating of the present invention can improve the osteogenicity of Mg and Mg alloy surfaces.

[0064] Although the present invention has shown magnesium as the metallic material having a carbonate apatite coating, the present invention is not limited to magnesium and can be similarly applied to other metallic materials (for example, iron, zinc, aluminum, or titanium). Furthermore, it goes without saying that the present invention includes various embodiments and the like that are not described in this specification. At least one of the various omissions, substitutions, and modifications of the components can be made without departing from the spirit of the embodiments and modifications described above. Also, the effects described herein are merely illustrative and not limiting, and other effects may exist. [Industrial applicability]

[0065] The magnesium material having a carbonate apatite coating of the present invention uses a magnesium material coated with a smooth carbonate apatite coating that exhibits interference colors, making it possible to distinguish the type and size of medical devices and industrial components made from this material by color. Furthermore, when used in the housing of electronic devices such as cameras, a magnesium material with excellent design can be obtained. Industrial components include housings, rods, plates, and joining materials. According to the present invention's method for producing magnesium material having a carbonate apatite coating, a coating with a thickness that exhibits interference colors, i.e., a thickness approximately equal to the wavelength of visible light, can be easily obtained. Therefore, when used in medical devices or industrial components, their type and size can be identified by color, giving it great industrial potential.

[0066] Specific application examples of the magnesium material having a carbonate apatite coating of the present invention include its use in devices such as those listed below: fracture fixation materials such as bone plates, miniplates, intramedullary nails, bone screws, and bone nails; scaffolds (supporting materials) for regenerative medicine devices such as artificial bones and skull plates; soft tissue joining devices such as staples; cardiovascular treatment devices such as stents, aneurysm embolization coils, and atrial septal defect treatment devices; stents for blood vessels, digestive organs such as bile ducts and esophagi, and tubular organs such as tracheas; and drug-releasing medical devices that are implanted in tissues such as bones and blood vessels within the body. In these devices, the present invention can be implemented by molding a magnesium substrate into a predetermined shape and then applying the coating formation process shown in the above examples. Furthermore, the present invention has the same industrial applicability for metallic materials other than magnesium (for example, iron, zinc, aluminum, or titanium) as it does for magnesium.

[0067] Medical devices such as bone screws and plates are susceptible to surface damage during implantation surgery when gripped with surgical instruments, when deformed to conform to the affected area, and when screwed into the bone. Conventional apatite coatings have been developed with a focus on the corrosion resistance of the coating, and little attention has been paid to its resistance to surface damage. When a ceramic coating such as apatite is formed on the surface of a ductile metal material with a relatively low Young's modulus, such as magnesium, to a thickness of the micrometer order, the coating is easily damaged due to the difference in elastic modulus between the substrate and the coating. The smooth carbonate apatite coating of the present invention is thin, with a thickness of 1000 nm or less, so damage to the coating due to deformation of the substrate when gripped with surgical instruments can be minimized. Thus, due to its excellent resistance to surface damage, the coating of the present invention has potential for use in medical and industrial metal materials.

Claims

1. A substrate made of magnesium or a magnesium alloy, wherein the surface roughness Ra of the substrate is in the range of 0.05 μm or more and 2.0 μm or less. The substrate has a carbonate apatite coating with a surface roughness Ra of 65 nm or less, A magnesium carbonate coated material wherein the thickness of the carbonate apatite coating is 10 nm or more and 1000 nm or less.

2. The carbonate apatite coated magnesium material according to claim 1, wherein the thickness of the carbonate apatite coating is expressed by the following formula (3) as the thickness t [nm] that generates reflected light with a visible light wavelength λ [nm] corresponding to the desired interference color. t=(m+1 / 2)・λ / (3.3cosθ) (3) Here, m is the interference order, usually an integer of 1, 2, 3, or 4, and θ is the angle of incidence of the incident light on the coating. The wavelengths λ of visible light corresponding to the desired interference colors are violet (380-430 nm), blue (430-490 nm), green (490-550 nm), yellow (550-590 nm), orange (590-640 nm), and red (640-770 nm).

3. The carbonate apatite-coated magnesium material according to claim 1, having a carbonate apatite coating in which the carbonate content of the carbonate apatite constituting the coating is 1 mass% or more and 30 mass% or less.

4. The apatite carbonate coated magnesium material according to claim 1, wherein the substrate and the apatite carbonate coating are directly joined without a magnesium hydroxide layer in between.

5. The carbonate apatite coated magnesium material according to claim 1, wherein the carbonate apatite coating is bonded to the substrate via a mixed layer of MgO nanoparticles and magnesium phosphate-calcium nanocrystals.

6. Prepare an aqueous solution containing a calcium complex at a concentration higher than 0.2 mol / L and a phosphate solution at a concentration of 0.5 to 1.25 times that of the calcium complex. A coating treatment solution is prepared by dissolving a carbonate in an aqueous solution containing the calcium complex and phosphate at the aforementioned concentrations. The coating solution is heated, A magnesium material having a surface roughness Ra of 0.05 μm or more and 2.0 μm or less is immersed in the heated coating solution. The magnesium material is coated with apatite mainly composed of carbonate apatite to a film thickness that exhibits the desired interference color. A method for producing a carbonate apatite-coated magnesium material.

7. A method for producing a carbonate apatite-coated magnesium material according to claim 6, wherein the calcium complex in the coating treatment solution is a chelate calcium compound selected from the group consisting of EDTA, NTA, HEDTE, aminopolycarboxylic acid, malic acid, citric acid, gluconic acid, tartaric acid, maleic acid, itaconic acid, and sulfamic acid.

8. A method for producing a carbonate apatite-coated magnesium material according to claim 6 or 7, using a coating treatment solution in which the concentration of the calcium complex is 0.3 mol / L or more and 1 mol / L or less.

9. A method for producing a carbonate apatite-coated magnesium material according to claim 6, wherein the phosphate in the coating treatment solution is an inorganic phosphate selected from the group consisting of potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, calcium monohydrogen phosphate, tripotassium phosphate, and trisodium phosphate.

10. A method for producing a carbonate apatite-coated magnesium material according to claim 6, wherein the concentration of the phosphate is 0.3 mol / L or more and 1 mol / L or less.

11. The carbonate of the coating treatment solution is NaHCO ３ , Na ２ CO ３ , K ２ CO ３ , (NH ４ ) ２ CO ３ , CaCO ３ , BaCO ３ , MgCO ３ , Li ２ CO ３ , FeCO ３ The method for producing a magnesium material coated with carbonate apatite according to claim [6], which is a carbonate selected from the group consisting of.

12. A method for producing a carbonate apatite-coated magnesium material according to claim 6, wherein the concentration of the carbonate is greater than 0 mol / L and less than or equal to 2 mol / L.

13. A method for producing a carbonate apatite-coated magnesium material according to claim 6, wherein the film thickness exhibiting the desired interference color is expressed by the following formula (3) as the film thickness t [nm] that generates reflected light with a visible light wavelength λ [nm] corresponding to the desired interference color. t=(m+1 / 2)・λ / (3.3cosθ) (3) Here, m is the interference order, usually an integer of 1, 2, 3, or 4, and θ is the angle of incidence of the incident light on the coating. The wavelengths λ of visible light corresponding to the desired interference colors are violet (380-430 nm), blue (430-490 nm), green (490-550 nm), yellow (550-590 nm), orange (590-640 nm), and red (640-770 nm).

14. The base material is one of the following metallic materials: iron, zinc, aluminum, or titanium, and the surface roughness Ra of the base material is in the range of 0.05 μm to 2.0 μm. A carbonate apatite-coated metal material having a carbonate apatite film with a surface roughness Ra of 65 nm or less on the surface of the substrate, and the thickness of the carbonate apatite film being 10 nm or more and 1000 nm or less.

15. Prepare an aqueous solution containing a calcium complex at a concentration higher than 0.2 mol / L and a phosphate solution at a concentration of 0.5 to 1.25 times that of the calcium complex. A coating treatment solution is prepared by dissolving a carbonate in an aqueous solution containing the calcium complex and phosphate at the aforementioned concentrations. The coating solution is heated, A substrate which is one of the metal materials consisting of iron, zinc, aluminum, or titanium, wherein the surface roughness Ra of the substrate is in the range of 0.05 μm to 2.0 μm, is immersed in the heated coating treatment solution. The substrate is coated with apatite mainly composed of carbonate apatite to a film thickness that exhibits the desired interference color. A method for manufacturing apatite-coated metal material.

16. A medical device using a carbonate apatite-coated magnesium material according to any one of claims 1 to 5, or a carbonate apatite-coated metal material according to claim 14.

17. An industrial component using a carbonate apatite-coated magnesium material according to any one of claims 1 to 5, or a carbonate apatite-coated metal material according to claim 14.

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