JPH06197947A - Composite organic implant and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a composite organic implant which is high both in organic affinity and mechanical strength by covering the surface of a metal substrate by a crystallized glass method with a cover layer containing non-calcium phosphate based ceramics mainly composed of diopside. CONSTITUTION:A composite organic implant has a ceramic cover layer of crystallized glass formed on the surface of a metal substrate. The ceramic cover layer is made of a non-calcium phosphate based composition containing silicon oxide, calcium oxide and magnesium oxide and 50% by volume of the total crystalline region is diopside crystal. A diffusion layer containing oxygen and silicon is formed at a surface layer part of the metal substrate baked and enables the upgrading of adhesion strength between the ceramic cover layer and the metal substrate.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an artificial tooth root, an artificial tooth crown,
TECHNICAL FIELD The present invention relates to a bioactive implant such as an artificial bone or an artificial joint and a method for manufacturing the same.

[0002]

2. Description of the Related Art Bioimplants are used as biosubstitutes or replenishers for implanting in artificial tissues such as artificial tooth roots, artificial dental crowns, artificial bones, artificial joints, bone filling materials, artificial blood vessels, etc. It is used.

In order to achieve both mechanical strength and biocompatibility of a bioimplant, a composite implant in which the surface of a metal substrate is coated with biocompatible ceramics has been proposed. For example, various proposals as described below have been proposed. Has been done.

1) Plasma sprayed hydroxyapatite on a metal (Japanese Patent Publication No. 58-39533). However, in this method, since the temperature becomes high during thermal spraying, hydroxyapatite is changed to another substance, and the desired biocompatibility cannot be obtained.

2) Metals coated with hydroxyapatite by a baking method (Japanese Patent Publication No. 61-40623). However, since the temperature at which hydroxyapatite seizes is high, when Ti is used as the metal substrate, the mechanical strength of Ti deteriorates significantly.

3) A material in which hydroxyapatite powder mixed with a low-melting glass frit is coated on a metal by a baking method (Japanese Patent Publication No. 61-40623). However, in this method, the bioactivity is decreased by mixing the glass.

4) β-TCP was converted into T by the crystallized glass method.
i coating (Journal of the Ceramic Society of Japan, 1991 1
February issue). However, in this method, the pore diameter of β-TCP is as small as about 1 μm, and biocompatibility is insufficient. Further, in order to crystallize, additives or mixtures such as TiO ₂ and Na ₂ O must be added, which lowers the bioactivity and poses a problem of harm to the living body.

5) A metal is coated with hydroxyapatite by sputtering (Japanese Patent Publication No. 2-23179). However, in this method, the adhesion between the hydroxyapatite and the metal is insufficient.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite bioimplant having both high biocompatibility and high mechanical strength.

[0010]

The above objects are achieved by the present invention described in (1) to (17) below. (1) A ceramic coating layer is formed on the surface of a metal substrate, and the ceramic coating layer is a non-calcium phosphate-based composition containing silicon oxide, calcium oxide and magnesium oxide, and comprises 50% by volume or more of the entire crystalline material. Diopside crystals occupy the surface of the metal substrate,
A composite bioimplant having a diffusion layer containing oxygen and silicon. (2) The composite bioimplant according to (1), wherein the ceramic coating layer has a structure in which a crystalline material is dispersed in a glass material, and the crystalline material accounts for 30% by volume or more. (3) The composite biological implant according to (1) or (2) above, wherein the metal substrate is composed of a metal that exhibits a ductility of 50% or more at a temperature of 70% or less of the melting point. (4) Any one of the above (1) to (3), wherein an embedded layer in which ceramic particles are embedded is formed on the surface layer of the metal substrate, and the ceramic coating layer is formed on the embedded layer. The composite living body implant. (5) The composite bioimplant according to any one of (1) to (4), wherein the ceramic coating layer includes a porous body having pores. (6) The composite biological implant according to (5), wherein the ceramic coating layer has regions having different average pore diameters. (7) The composite bioimplant according to the above (5) or (6), wherein regions having different compositions are present in the ceramic coating layer. (8) The ceramic coating layer has an average diameter of 5 to 100 μm.
The composite biological implant according to any one of (5) to (7) above, which comprises a porous body having m 2 pores. (9) The composite bioimplant according to (8) above, wherein the ceramic coating layer includes a porous body having pores having an average diameter of less than 5 μm. (10) The ceramic coating layer is TiO ₂ , Zn
The composite biological implant according to any one of (1) to (9) above, which contains at least one of O, B ₂ O ₃ , FeO, ZrO ₂ and Ag ₂ O. (11) The composite biological implant according to any one of (1) to (10) above, which is an artificial tooth root. (12) A method for producing the composite living body implant according to any one of (1) to (11) above, which comprises a step of producing a glass powder by melting a ceramic powder, cooling it, and then pulverizing it to obtain a glass powder, and the glass. A method for producing a composite biological implant, comprising: an applying step of applying the powder to the surface of the metal base; and a baking step of baking the applied glass powder onto the surface of the metal base to form a ceramic coating layer. (13) The baking temperature in the baking step is 700 to
The method for producing a composite biological implant according to the above (12), which is 1000 ° C. (14) The melting temperature of the ceramic powder is 140
The method for producing the composite living body implant according to (12) or (13), which is 0 ° C. or higher. (15) The method for producing a composite biological implant according to any one of (12) to (14), wherein the glass powder has an average particle size of 1 to 500 μm. (16) The method for producing a composite biological implant according to any one of (12) to (15), wherein in the applying step, at least two kinds of slurries containing glass powders having different average particle diameters are applied to the surface of the metal substrate. (17) The method for producing a composite biological implant according to any one of (12) to (16), wherein in the applying step, at least two kinds of slurries containing glass powders having different compositions are applied to the surface of the metal substrate.

[0011]

In the present invention, the surface of the metal substrate is coated with the coating layer containing non-calcium phosphate-based ceramics mainly composed of diopside by the crystallized glass method.

In the crystallized glass method, ceramic powder is once melted, cooled to vitrify, and then crushed into glass powder. This glass powder is baked on the surface of a metal substrate, and at least a part of the vitreous material is obtained. Is crystallized to form a ceramic coating layer. The temperature during this baking is 800 ℃
Since it can be as low as before and after, the oxidation of the metal base such as Ti is little, and the deterioration of the mechanical strength of the metal base can be avoided. Moreover, since a diffusion layer in which oxygen and silicon in the ceramic coating layer are diffused is formed on the surface layer of the metal substrate, the adhesive strength of the ceramic coating layer is improved. Since the ceramic coating layer has good biocompatibility, a composite bioimplant with high biocompatibility and mechanical strength is realized.

Furthermore, a highly plastic metal having high strength and high ductility is used as a substrate, and ceramic particles are embedded on the surface by a metal plastic working process to form an embedded layer, and a ceramic coating layer is formed on the embedded layer. The formed mode is also included in the present invention. Since the metal base and the ceramic particles are joined by mechanical meshing, extremely high joining strength can be obtained. Further, since the implant surface is roughened by the formation of the embedding layer, the initial fixing strength is improved by the anchor effect at the time of transplantation into the hard tissue of the living body, and the generation of new bone is promoted. Further, by making the ceramic particles and the material of the ceramic coating layer substantially the same, the ceramic coating layer is integrated with the ceramic particles mechanically bonded to the metal substrate, and the bonding strength of the ceramic coating layer is extremely high. can do.

The non-phosphoric acid ceramic coating layer is
When the film is formed by a normal baking method without using the crystallized glass method, the baking temperature becomes as high as about 1200 ° C., so that the metal substrate is deteriorated and the mechanical strength is remarkably lowered. Further, in this case, an oxide layer may be formed on the surface of the metal substrate, and the ceramic coating layer may peel off together with the oxide layer. Even when the non-phosphoric acid ceramic coating layer is formed by using the crystallized glass method, the composition mainly composed of wollastonite at the time of crystallization causes the crystallization temperature to be too high. The effect of is not realized. For example,
_{JP-A-4-36107,} a main component SiO 2, CaO and MgO, wollastonite (CaO ·
SiO ₂ ) crystal and diopside (CaO ・ MgO
A crystallized glass having a structure in which 2SiO ₂ ) crystals are dispersed in glass is disclosed, and as an example thereof, a sample containing 60% wollastonite and 40% diopside is described. The publication does not describe that the metallized substrate is coated with this crystallized glass. However, even if it is coated, if such a large amount of wollastonite crystals are contained, it is disclosed in the publication. 1050
The effect of the present invention cannot be realized because heating up to ℃ is required. Further, in this case, when the heat treatment is performed at a low temperature of about 800 ° C., which does not adversely affect the metal substrate, the crystallization becomes insufficient, and the vitreous remains much, so that the mechanical strength of the ceramic coating layer itself is increased. Will be insufficient.

The oxygen content of the oxide layer is remarkably higher than that of the diffusion layer, and the oxygen diffusion distance from the surface of the metal substrate is significantly large, so that the diffusion layer and the oxide layer can be easily distinguished.

[0016]

Specific Structure The specific structure of the present invention will be described in detail below.

The composite biological implant of the present invention has a structure in which a ceramic coating layer of crystallized glass is formed on the surface of a metal substrate.

[Metal Substrate] The metal used for the metal substrate can be selected without particular limitation as long as it is a metal which is harmless to the living body, but preferably has a strength of a certain level or higher, for example, 5 or less.
Having a high plasticity, having a pressure of 00 MPa or more, that is,
It is preferable that the material exhibits large plasticity at a temperature at which strength is significantly deteriorated, for example, 70% or less of the melting point. In particular, when the ceramic particles are embedded in the surface layer of the metal substrate as described later, ductility is maintained at a temperature of 70% or less of the melting point and a pressure of 50 MPa in order to facilitate the bonding between the metal and the ceramic particles. It is preferable to use a highly plastic metal material of 50% or more, more preferably a superplastic metal material of 200% or more.

As such a superplastic metal material, T
i, Ti-6Al-4V (numbers are weight%), Ti-Al
-Sn, Ti-Pd, Ti-Mo, Ti-Zr, Ti-
Fe, Ti-Al-V-Mo-Fe, Ti-Fe-N-
A, such as O, Ti-Cr-Si, Ti-Pd-Cr
l, V, Fe, Mo, Cr, Zr, Pd, N, Si,
Ti containing one or more of N, O, etc. in a total amount of 20% by weight or less
System alloy, Zn-22Al, Zn-21.5Al-0.0
Al-based alloys such as 1Mg alloy (SPZ), stainless steel, Ni-based alloys and the like are preferable. However, in terms of biocompatibility, pure Ti (ductility of about 200%) and Ti-based alloys are preferable. These Ti or Ti-based alloys are generally 8 ×
It has a thermal expansion coefficient α ₁ of about 10 ⁻⁶ to 10 × 10 ⁻⁶ ° C. ⁻¹ .

When embedding ceramic particles,
The surface of the metal substrate may be flat because it is deformed by the embedding process described later, but the surface may be roughened in advance. For example, the surface roughness specified in JIS B0601 may be in the range of the measurement lower limit to 300 μm.

[Ceramics Coating Layer] The ceramics coating layer formed on the surface of the metal substrate is a non-calcium phosphate type composition containing silicon oxide, calcium oxide and magnesium oxide, and contains diopside crystals.

In the biosubstitute or the supplement of the implant, it is preferable that the generated new bone is directly bonded to the implant surface material. That is, it is preferable that the implant surface has so-called bioactivity, but the ceramic coating layer having a high diopside content is
It has bioactivity, high strength, and when it is placed in a tissue, bone can be formed on its surface, and bonds are formed from both the material side and the bone side. And this material is
When brought into contact with an aqueous solution containing phosphorus (for example, body fluid or simulated body fluid), a calcium phosphate-based compound such as hydroxyapatite (HAP) is produced at the contact surface.

The composition of Diopside contained in the ceramic coating layer is (Ca, Mg) O-MgO.
-2SiO _2, preferably 2SiO ₂ -CaO-MgO
Is. In the present invention, in the ceramic coating layer,
It is desirable that diopside occupy 50% by volume or more, preferably 70% by volume or more, more preferably 90% by volume or more, and further preferably 100% by volume of the entire crystalline material. If the ratio of diopside is too low, the mechanical strength of the ceramic coating layer will be insufficient.

The crystalline substances other than diopside include wollastonite {Wollastonite: β- (Ca, Mg) O-SiO ₂ particularly CaO-SiO ₂ }, a as shown in the three-component composition diagram of FIG. Light (alite: 3CaO-S
iO), belite (belite: 2CaO-SiO ₂ ), akermanite (Akermanite: 2CaO-MgO-2S)
iO _2), Monch Celite (Monti-cellite: CaO-M
gO-SiO ₂ ), forsterite {Forsterite: 2
(Mg, Ca) O-SiO 2}, proto enstatite (Protoenstatite {(Mg, Ca) O-SiO 2}, tridymite (Tridymite: sometimes SiO _2), etc. appear.

The ceramic coating layer usually has a structure in which a crystalline material mainly composed of diopside is dispersed in a glassy matrix. The crystalline ratio in the coating layer is preferably 30% by volume or more, more preferably 50% by volume or more, still more preferably 90% by volume or more. If the crystal ratio is too small, the mechanical strength of the ceramic coating layer will be insufficient.

The crystalline ratio in the ceramic coating layer and the diopside crystal ratio in the crystalline can be determined by the peak separation method using an X-ray diffraction chart. In the X-ray diffraction chart of crystallized glass in which the crystalline substance is dispersed in the vitreous substance, there are halos indicating the presence of the vitreous substance and peculiar peaks depending on the type of the crystalline substance. In the peak separation method, an integrated intensity obtained by summing only peak areas and an overall integrated intensity obtained by combining halos and peaks are obtained, and the former is divided by the latter to obtain a crystallization rate.

The ratio of diopside in the crystal is calculated by obtaining the integrated intensity of the diopside peak and dividing this by the integrated intensity of all the peaks.

In the ceramics used in the present invention, in addition to the above-mentioned components, if necessary, optional components such as TiO ₂ , ZnO, etc. are added in an amount that does not impair desired physical properties, usually within a range of 5% by weight or less. B ₂ O ₃ , FeO, ZrO ₂ , Ag
_At least one type such as ₂ O can be blended. In particular, by including an oxide of a metal base material such as TiO ₂ in the ceramic, it is possible to improve the bonding strength with the metal base. Moreover, since Ag ₂ O promotes crystallization, a homogeneous and high-strength crystallized glass can be obtained. In addition,
The inclusion of Al ₂ O ₃ is not preferable because it tends to reduce bioactivity.

{Ceramic coating layer forming method} (Ceramic material synthesizing method) The ceramic material powder used for forming the coating layer can be synthesized by various dry synthesizing methods or wet synthesizing methods, but is fine and uniform. In order to produce such a powder, it is preferable to use a spray pyrolysis method, a liquid phase synthesis method such as a coprecipitation method or a precipitation method, an alkoxide method, a sol-gel method or the like.

In the spray pyrolysis method, an aqueous solution containing ceramic component ions adjusted to a desired composition is atomized by a gas or an ultrasonic vibrator, and this is heated for synthesis to obtain spherical or hollow fine particles. be able to. Also,
It is also preferable to further pulverize the obtained hollow particles to increase the BET value.

The coprecipitation method is to uniformly mix the respective ceramic component ions in an aqueous solution state, and then chemically deposit the mixed components simultaneously as a solid phase by utilizing the difference in solubility. Fine particles of ² / g or more can be obtained.

The alkoxide method includes Ca alkoxide and S
The i alkoxide and the like are mixed, an alkoxide solution containing each ceramic component is prepared, and this is hydrolyzed and synthesized, and fine particles having a high purity and a large BET value can be obtained.

The sol-gel method is a method in which desired components are mixed with an aqueous solution to give a sol state, which is dehydrated to gel and calcined to give an oxide.

In the present invention, the raw material composition may be selected so that the ceramic coating layer having the above-mentioned structure is formed, but preferably the composition of the diopside region shown in the three-component composition diagram of FIG. Use raw materials.

(Glass Powder Manufacturing Step) In this step, the ceramic material is melted, cooled, and then ground to obtain glass powder.

The temperature for melting the ceramic material may be appropriately determined according to the composition, but is usually 1400 ° C. or higher. The ceramic material does not have to have a crystal structure such as diopside in advance, and the oxide of each component of the intended composition or a substance capable of forming these oxides when melted, for example, a carbonate , A mixture of bicarbonate, hydroxide and the like may be used. In such a case, a composite oxide is formed by the reaction between the raw materials during heating. The melting is usually performed in air.

The method for cooling the molten ceramic material is
There is no particular limitation as long as it is a method capable of forming an amorphous glass after cooling. For example, the melt may be put into water to be cooled, the melt may be brought into contact with a cooling substrate such as a metal to be cooled, or may be left to cool in air.

The amorphous glass obtained by cooling is pulverized into glass powder. The size of the glass powder is not particularly limited, and may be appropriately determined according to the thickness of the target ceramic coating layer and the size of the pores in the coating layer.
The average particle size is preferably 1 to 500 μm, more preferably 1 to 50 μm. In particular, in order to provide the pores described below with a preferable size and distribution in the ceramic coating layer, it is preferable that the average particle diameter of the glass powder be 2 to 30 μm.

(Coating Step) In the coating step, the glass powder obtained in the glass powder manufacturing step is mixed with a binder component such as an organic resin or a solvent component such as alcohol to prepare a slurry, and the slurry is applied onto a metal substrate. Apply.

The concentration of glass powder in the slurry is usually
It is preferably 30 to 80% by weight. If the concentration is less than the above range, cracks are likely to occur in the ceramic coating layer during firing, and if it exceeds the above range, coating is difficult.

The method of applying the slurry is not particularly limited, and any method such as dipping or brush coating may be used. Examples of preferred coating methods are shown in FIGS.

The method shown in FIG. 5 is an ordinary dipping method, in which a metal substrate 2 (a metal substrate for artificial tooth root in the illustrated example) is dipped in a slurry 101 in a container and pulled up to form a coating film of the slurry on the surface of the metal substrate. To form. In this way,
The preferable range of the rate of pulling up the metal substrate 2 from the slurry 101 is usually 0.1 to 10 mm / s, although it varies depending on the concentration of the slurry and the target coating film thickness. If the pulling rate is too slow, the coating film tends to be too thick, and if too fast, the coating film tends to be too thin.

The method shown in FIG. 6 is a modified example of the dipping method, and is a method of simultaneously performing coating film formation and coating film thickness adjustment. The container 102 containing the slurry 101 includes
Holes are provided on two opposite side surfaces. The metal base 2 is
It is inserted into the container through one hole and taken out of the container through the other hole. In order to allow the metal base 2 to pass through and to prevent the slurry from flowing out, each hole is provided with a lid 103 that opens when pushed by the metal base. The structure of the lid 103 is not particularly limited, but for example, a rubber film having radial cuts as shown in the drawing is preferable. When the metal substrate 2 passes through the hole and goes out of the container, the slurry adhered to the surface of the metal substrate 2 is wicked off by the opened rubber film to regulate the thickness. By appropriately setting the thickness of the rubber film, the size of the holes, etc., a coating film having a desired thickness can be obtained. In this method, from the slurry 101 to the metal substrate 2
The preferable range of the speed for taking out is, although it varies depending on the concentration of the slurry and the like, it is usually 1 to 10 mm / s. If this speed is too slow or too fast, the thickness of the coating film tends to be non-uniform. In addition to the illustrated example, only one hole may be provided on the side surface of the container so that it serves as both the insertion port and the ejection port of the metal base.

Also in the method shown in FIG. 7, the coating film formation and the coating film thickness adjustment are performed at the same time. This method allows more precise control of the coating thickness than the method shown in FIG. In this method, while rotating the metal substrate 2 around the axis,
The slurry is discharged from the nozzle 105 between the peripheral side surface of the metal base 2 and the peripheral side surface of the rotating body 104. A part of the discharged slurry forms a coating film on the peripheral side surface of the metal substrate 2, and unnecessary convex portions on the coating film surface are scraped off by the peripheral side surface of the rotating body 104. The peripheral side surface of the rotating body 104 has a shape capable of forming a predetermined gap with the peripheral side surface of the metal base 2. This gap will determine the thickness of the slurry coating. It should be noted that the size of this gap does not have to be the same in all the regions on both side surfaces facing each other. For example, in order to form a coating film having a partially different thickness, the size of the gap is partially changed. In this method, the rotating body 104 is also preferably rotated about the axis. In the illustrated example, the metal base 2 and the rotating body 104 rotate in opposite directions,
It may be configured to rotate in the same direction. In this method, the preferable range of the rotation speed of the metal substrate 2 and the rotating body 104 is usually about 6 to 60 rpm, though it varies depending on various conditions such as the slurry concentration, the diameter of the metal substrate, and the diameter of the rotating body. If the rotation speed is too slow, the thickness of the coating tends to become non-uniform due to drying, and if it is too fast, it becomes difficult to control the thickness of the coating due to vibration. Although the material of the rotating body 104 is not particularly limited, it is usually preferable to be composed of rubber or the like.

After forming the coating film by dipping or the like, the coating film thickness can be adjusted by using the rotating body 104 shown in FIG.

When it is desired to form the coating film only on a part of the surface of the metal substrate, the region where the coating film is not formed may be covered with a mask material and dipping may be performed. The mask material is not particularly limited, but it can be easily removed by using a material such as wax that burns in the baking step described later.
Note that the mask material may be removed by wiping or the above-mentioned scraping.

A method of partially forming a coating film by coating with a mask material is a method of containing different glass powders.
It can also be applied when different types of slurries are applied. In case of separately coating, first, after masking, the first slurry is applied to form a first coating film. Next, the mask material is removed by heat treatment, wiping, scraping, or the like. Next, the second slurry is applied to the area where the first coating film was not formed to form the second coating film. In addition to this method, the second coating film is formed not only on the uncoated area but also on the first coating film, and the second coating film on the first coating film is wiped or scraped off. You may use the method of removing by. In this case, if the formation of the second coating film is performed after the drying of the first coating film, the selective removal of the second coating film can be easily performed. The same applies to the case of coating three or more slurries separately.

(Baking Step) In the baking step, the glass powder applied to the surface of the metal substrate is baked to crystallize the glass to form a ceramic coating layer.

The firing conditions may be appropriately determined so that the glass powder can be crystallized, and further, the deterioration of the metal substrate and the formation of an easily peelable oxide layer on the surface of the metal substrate do not occur.
The firing temperature is preferably 700 to 900 ° C, particularly preferably 750 to 850 ° C. If the firing temperature is less than the above range, crystallization of the glass powder is not sufficiently carried out, and if it exceeds the above range, an easily peelable oxide layer tends to be formed on the surface of the metal substrate, and the metal substrate is deteriorated. Occurs and the strength tends to decrease. The temperature holding time is preferably 0.5 to 2 hours, particularly preferably 0.5 to 1 hour. If the firing time is less than the above range, the crystallization of the glass powder tends to be insufficient, and if it exceeds the above range, an easily peelable oxide layer tends to be formed on the surface of the metal substrate.

In order to provide pores, which will be described later, in the ceramic coating layer with a preferable size and distribution, it is preferable to set the rate of temperature rise to 2 to 30 ° C./minute.

The atmosphere during firing is usually preferably in the air or an oxygen partial pressure atmosphere similar thereto. When firing in a non-oxidizing atmosphere such as a vacuum, the formation of a diffusion layer described below becomes insufficient and the adhesive strength of the ceramic coating layer becomes insufficient. However, an atmosphere in which the oxygen partial pressure is controlled may be used if necessary. For example, when an atmosphere having an oxygen partial pressure lower than that of air is used instead of vacuum, a good diffusion layer can be formed even if the firing temperature is raised above the range. However, when the temperature exceeds 1000 ° C., the strength of the metal substrate is remarkably reduced, so the firing temperature is preferably 1000 ° C. or lower.

In the ceramic coating layer thus formed, the average crystal grain size is usually 0.001 to 100 μm.
m 2 is preferably 1 μm or less, more preferably 0.1 μm or less. It is difficult to make the crystal grain size smaller than the above range. On the other hand, if the crystal grain size is too large, the strength decreases. The crystal grain size can be measured by determining the average diameter of the crystal grain area, which is assumed to be a circle, from the crystal grain area measured by a scanning electron microscope (SEM).

It is preferable that a part or the whole of the ceramic coating layer is a porous body having independent pores or continuous pores as long as the strength is not impaired. The continuous pores are pores in which two or more pores communicate with each other inside the ceramic coating layer and have two or more openings on the surface of the ceramic coating layer. In addition, you may form a porous layer on the dense ceramics layer baked beforehand. By providing pores in the ceramic coating layer, the retention of osteoblasts and the distribution of osteoblasts, blood, etc. are promoted, and the formation of new bone,
Binding can be facilitated.

The average diameter of the pores for obtaining such an effect is preferably 5 to 100 μm, more preferably 10 to
It is 80 μm. The porosity is preferably 10 to 70%, more preferably 20 to 60%. If the average diameter is too small, cells cannot enter the pores, and the healing cannot be accelerated. If it is too large, the strength will be reduced, and in addition, the voids will become too large for cells, and the effect will be reduced.
Further, if the porosity is too small, the biocompatibility cannot be sufficiently improved, and if it is too large, the strength is lowered. The pore diameter and the porosity are calculated by observing with an optical microscope or a scanning electron microscope.

As a method of forming pores in the ceramic coating layer, various conventionally known methods can be used. For example, glass powder is mixed with pyrolyzed substances such as cellulose particles and resin particles corresponding to the desired pore size and porosity, and then a solvent and resin binder are mixed to prepare a slurry, which is applied to the implant. , There is a method of firing. During firing of the slurry, the particles of the thermally decomposable substance decompose and disappear, and pores corresponding to the particles are formed. The structure of the pores formed here can be various depending on the kind of the pyrolysis material to be mixed. For example, in the case of resin particles, it is possible to form a relatively large pore portion in the shape of the particle and a pore passage formed by the decomposition gas generated when the decomposition gas disappears. Further, when crystalline cellulose or the like is used, it is possible to form an amorphous pore passage that communicates with the whole. The particles of the thermally decomposable substance used here have an average particle size of usually 10 to 100 μm, preferably 20 to 80 μm.
The mixing amount is 10 to 70% by weight, preferably 30 to 60% by weight in the slurry.

However, since it is difficult to evenly distribute pores of uniform diameter in the method using a pyrolyzed substance, a method of controlling the particle diameter of glass powder, the temperature rising rate during firing, etc., is used as described above. It is preferable to use.

The pore diameter and porosity do not have to be uniform over the entire ceramic coating layer. For example, if the pore size is large, the biocompatibility is good, but the mechanical strength of the ceramic coating layer is low. Moreover, when the pore size is large, the surface property of the ceramic coating layer is lowered. Therefore, it is preferable to reduce the pore diameter only in the region where strength and smoothness are required. In addition, when the pore diameter is increased, the porosity is generally increased. The target of application of the present invention is, for example, the artificial tooth root shown in FIG. 8, the artificial joint shown in FIG. 9, the artificial vertebral body shown in FIG. 10, the artificial intervertebral disc shown in FIG. 11, the artificial intestinal tract shown in FIG. 12, and the artificial intestine shown in FIG. There are artificial bone screws and the like, but of these, for example, in artificial tooth roots,
It is preferable to provide regions having different average pore diameters.
The artificial root typically has an upper root 201, as shown.
It is composed of a tooth root taper portion 202 and a tooth root lower portion 203.
In the vicinity of the upper part 201 of the tooth root, foreign matter such as food waste may be attached to reduce the affinity of the ceramic coating layer for bone. Therefore, in the ceramic coating layer near the tooth root upper portion 201, in order to smooth the surface and prevent foreign matter from adhering,
It is preferable to reduce the pore diameter or not provide the pores. The average diameter of the pores in such a region is 5
It is preferably less than μm.

The method for forming the regions having different average pore diameters in the ceramic coating layer is not particularly limited,
A method of using two or more kinds of slurries containing glass powders having different average particle diameters and / or compositions is preferable. If these slurries are applied separately on the surface of the metal substrate and then fired, pores having a diameter corresponding to the average particle diameter and composition of each glass powder can be formed, so that the average diameter of the pores can be set to a desired value in any region. can do.

The thickness of the ceramic coating layer is usually 1 to
The thickness is 5000 μm, preferably 10 to 2000 μm, more preferably 50 to 1000 μm. If the ceramic coating layer is too thin, the formation of new bone tends to be insufficient, and if it is too thick, the peel strength tends to decrease. In addition, this thickness is
It is measured as the thickness from the envelope of the surface convex portion of the metal substrate to the surface envelope of the ceramic coating layer.

(Diffusion Layer) In the present invention, a diffusion layer containing oxygen and silicon is formed on the surface layer portion of the metal substrate after firing. This diffusion layer improves the adhesive strength between the ceramic coating layer and the metal substrate.

The concentrations of oxygen and silicon in the metal substrate are
Although it decreases from the surface of the metal substrate toward the center, the difference between the diffusion layer and the above-mentioned easy-to-peel oxide layer can be confirmed by examining the elemental strength distribution of oxygen. The element strength corresponds to the diffusion amount of the element and is obtained from the EPMA count amount and the like. When only the diffusion layer is formed, the elemental strength of oxygen sharply decreases almost in proportion to the increase in the distance from the surface of the metal substrate. On the other hand, TiO ₂
When an oxide layer such as oxide is formed, the elemental strength of oxygen is almost constant from the surface of the metal substrate to a position of several tens of μm, and this region corresponds to the oxide layer that is easily peeled off. To do. Then, the elemental strength of oxygen sharply decreases as it goes further from the oxide layer toward the center side of the metal substrate.
That is, in this case, an oxide layer is present on the surface of the metal substrate,
There will be a diffusion layer inside it.

Assuming that the oxygen diffusion distance is the distance from the surface of the metal substrate where oxygen is not substantially detected by EPMA or the like, in the present invention, the diffusion distance is preferably 2 to 20 μm, particularly 3 to 10 μm. . If the diffusion distance is less than the above range, the adhesive strength of the ceramic coating layer becomes insufficient, and if it exceeds the above range, an oxide layer may be formed.

The presence of the region containing oxygen can be detected from the secondary electron image of the cross section of the metal substrate.

[Embedding Processing] The present invention also includes a mode in which ceramic particles are embedded in the surface layer of a metal substrate to form an embedded layer, and the ceramic coating layer is formed on the embedded layer. To form the embedding layer, a “metal plastic working process” can be used, in which the metal base and the ceramic particles are heated and pressed in contact with each other, and the metal is plastically deformed to be embedded and joined. It is preferred to use a (superplastic) working process.

This metal plastic working process can be carried out by an ordinary hot press (HP), hot isostatic press (HIP), warm isostatic press (WIP) or the like. If the implant has a simple shape, HP
Is preferably used, and HIP or WIP is used for a complicated shape.

The pressing temperature is usually in the range of 200 to 1200 ° C. and is not higher than the melting point of the metal material forming the metal substrate. The pressing is preferably performed in a non-oxidizing atmosphere such as a vacuum in order to prevent the metal substrate from being oxidized. The pressing pressure is usually 1 to 500 MPa, more preferably 5 to 30 MPa.
The pressure is 0 MPa, and more preferably 5 to 100 MPa. The treatment time is usually preferably 1 to 600 minutes. The amount of deformation depends on the size of the particles to be embedded, but generally the true strain of the entire metal substrate is 0.1 or more, preferably 1
It is about 3.

For example, grease or the like may be applied to a metal substrate processed into a predetermined shape, the ceramic particles may be densely adhered to necessary portions of the metal substrate, and the above-described processing may be performed.

[Ceramic Particles] The ceramic particles used here usually have an average particle size of 1 to 5000 μm,
Preferably 10 to 2000 μm, more preferably 3
The one having a range of 0 to 300 μm is used. Within this range, plastic embedding becomes easy. If the particle size is too large, plastic embedding tends to be difficult, the gaps between the particles become large, and the particles themselves are large, so that the implant itself also becomes large. If the particle size is too small, embedding becomes difficult. Then, by using the ceramic particles in the above particle size range, an implant having a preferable surface roughness described later can be produced.

The particle size distribution of the ceramic particles is preferably as uniform as possible. When the particle size of ceramic particles is uniform, the embedding depth of each particle (embedding ratio)
This is because the uniformity of the bonding strength is achieved and the bonding strength is uniform. However, when relatively large particles are used, it is also possible to simultaneously use small particles and use particles having two or more particle size distributions. In this case, small particles enter the gaps between the large particles and are embedded, so that the uniformity of the embedded layer in the plane direction is achieved.

The shape of the ceramic particles is
Those having an average shape factor of 2 or less, preferably 1.5 or less are preferable. The larger the shape factor, the more irregular the shape, and the more likely the ceramic particles are unevenly distributed on the metal substrate,
A gap is likely to occur. Therefore, the shape factor is preferably close to 1. The shape factor is a value obtained by dividing the longest diameter by the shortest diameter of the particles. Average shape factor is 1 randomly selected
It may be calculated from about 00 particles.

Further, it is preferable that the ceramic particles have a spherical shape, because the particles slip with each other at the time of pressing, there is no unevenness, and it becomes easy to form a uniform embedded layer in the surface direction. Further, even after the implantation of the implant into the living tissue, an extremely acute angle portion is not formed in the ceramic coating layer, so that unnecessary stimulation is not given to the living body and bone resorption hardly occurs. On the contrary, in the case of enhancing the anchoring effect of the implant to the hard tissue such as bone and further immobilizing it, it is preferable to use particles having an acute angle portion as the ceramic particles.

Furthermore, the coefficient of thermal expansion α of the ceramic particles is
₁ is preferably 0.5 to 1.5 times the thermal expansion coefficient α ₁ of the metal substrate. This prevents the ceramic particles from being damaged or falling off during the embedding process.

As for the composition of the ceramic particles, it is preferable to use a ceramic material of substantially the same kind as the ceramic coating layer (ceramic material having the same main components) in order to increase the bonding strength by combining with the ceramic coating layer. , And more preferably, materials having the same composition are used. In this case, the main components being the same means 30% by weight or more,
In particular, it contains a component contained in an amount of 20% by weight or more, and further 10% by weight or more, and the amount ratio of the components is 1/3 to 3, particularly about 1/2 to 2.

It is considered that the ceramic particles are firmly bonded to the metal substrate by the mechanical caulking structure and solid-phase bonding is also generated at the interface.

Ceramic particles are obtained by pulverizing a sintered body, spray pyrolysis method, tumbling granulation method, granulation in a fluidized bed and then sintering, or liquid phase synthesis method such as solution. It may be manufactured by sintering, spray roasting sintering, rolling bed or fluidized bed sintering.

[Embedding Layer] The embedding depth of ceramic particles, that is, the embedding rate is 10 to 100% of the particle diameter.
Is preferable, and more preferably 40 to 70%. Since implants such as artificial tooth roots are continuously stressed after transplantation, if the implanting rate is small, particles may be missing, and if the implanting rate is too large, the anchor effect of the implant is reduced. The embedding rate is
It may be calculated from the ratio of the embedding length of, for example, 100 randomly embedded particles to the particle length in the normal direction to the metal substrate, by observing the cross section under the microscope field.

The ratio of the area covered with the ceramic particles (coverage of the ceramic particles) on the surface of the metal substrate contacting the hard tissue of the living body through the ceramic coating layer is preferably 20% or more, more preferably. Is 40%
As described above, it is more preferably 70% to 100%.

The ceramic particles are not substantially deformed by the embedding process, and the metal substrate is deformed. The amount of deformation in the surface layer of the metal substrate corresponds to the above-mentioned embedding rate, and is about 10% or more of the grain size. The ceramic particles are
Since the embedding process does not substantially deform, the embedding layer is usually formed from one layer of embedded particles.

The thickness of the ceramic particle embedding layer is usually 1 to 500 μm, preferably 5 to 120 μm.
The range is. The thickness of the layer formed by the embedded ceramic particles (embedded layer) can be calculated from the difference between the envelope curve of the convex part of the metal substrate with the uneven surface layer and the envelope curve of the upper part of the embedded particles from the micrograph. Good. If the burying layer is too thin, the anchoring effect becomes small, and the peel strength of the ceramic coating layer decreases. Also, if it is too thick, it becomes easy to peel off.

Surface Roughness of Buried Layer (JIS B 06
Ra of 01 is preferably 1 to 2000 μm, particularly 10
˜300 μm is preferred. If it is too smooth, the surface will be slippery and the anchor effect will be difficult to obtain. If it is too rough, the contact surface with the bone will be small and the bonding speed will be slow.

When the burying layer is provided, it is preferable to adjust the thickness of the ceramic coating layer to leave the surface properties of the irregularities formed by the ceramic particle burying layer. The concavo-convex surface of the ceramic coating layer exhibits an anchoring effect on the living body hard tissue when transplanted to the living body hard tissue, and enables firm initial fixation. In addition, this uneven shape made of a biocompatible ceramic material promotes the induction of new bones, and the new bones intervene between the unevenness and integrate, thereby achieving a strong final fixation. The average surface roughness Ra (JIS B 060) of the surface of the ceramic coating layer in this case
1) is preferably in the range of 1 to 2000 μm, particularly 5 to 100 μm.

[0082]

EXAMPLES Examples of the present invention will be described below.

Example 1 <Artificial Root with Ceramics Coating Layer> As a superplastic metal material, pure metal Ti having a ductility of 200% or more at a temperature of 70% of the melting point (1000 ° C.) was used and artificially molded. It was used as a root base. The dimension of the artificial tooth root base has a length of 13.
5 mm, root diameter (lower diameter) 2.7 mm, tooth neck diameter (upper diameter) 3.7 mm, and the surface of the substrate was roughened by blasting (Ra 35 μm).

SiO ₂ , CaCO ₃ and MgO were mixed in a ball mill for 1 hour and then put in a platinum alloy crucible for 14 hours.
It was melted by heating at 00 ° C for 1 hour. The melt was dropped into water and rapidly cooled to obtain an amorphous glass frit. This glass frit was ground for 2 hours with a vibration mill and a sand mill to obtain glass powder having an average particle size of 5 μm. This glass powder and 3
A weight% metrolose aqueous solution was mixed at a weight ratio of 1: 1 to form a slurry. This slurry was applied to the surface of the artificial dental root substrate by the method shown in FIG. Then, calcined in air at the temperature and time shown in Table 1 below,
An artificial dental root sample was obtained by forming a ceramic coating layer having a thickness of about 5 μm. The heating rate was 10 ° C./minute. The thickness of the ceramic coating layer was determined from the micrograph of the cross section. Table 1 below shows the composition of the ceramic coating layer, the crystallization rate, and the type of precipitated crystals. The crystallization rate was determined by the peak separation method described above.

For comparison, H was added to the surface of the Ti substrate.
An artificial tooth root sample having a coating layer of AP, alumina, β-TCP, and zirconia was prepared.

With respect to the obtained artificial tooth root sample, the diffusion distance of oxygen from the surface of the substrate, the presence or absence of an oxide layer, the adhesive strength of the ceramic coating layer, the average diameter of the pores in the ceramic coating layer, and the bioactivity were measured. The average diameter of the pores was measured by a scanning electron microscope. A scanning electron micrograph of the surface of the ceramic coating layer of Sample No. 1 is shown in FIG.

The oxygen diffusion distance and the presence / absence of an oxide layer are determined by E
It judged by the method mentioned above using PMA. In the samples of the present invention (Nos. 1 to 6), only the diffusion layer in which the element strength sharply decreased was formed, but the comparative samples (Nos. 7, 8 and
In 10), an oxide layer having a substantially constant elemental strength was formed, and the elemental strength drastically decreased from there to the central portion.

The adhesive strength was measured by the following method. First,
Prepare two Ti plates (diameter 30 mm, thickness 5 mm) of the same material as that used for the substrate, and apply the slurry used for forming the ceramic coating layer to the main surface of one Ti plate, dry it, and apply it. A film was formed. The other Ti plate was overlaid on this coating film and fired at the same temperature and time as in the preparation of the artificial tooth root sample to give a coating film as a ceramic film. Next, fix both Ti plates with a jig, pull the Ti plates in a direction perpendicular to the main surface,
The force when the ceramic film started to peel from the Ti plate was measured, and this was taken as the adhesive strength.

The bioactivity test was carried out by the following method. A bone defect was made in the lower edge of the mandible of a rabbit, and an artificial root sample was embedded in this defect. And after 24 weeks and 48
After a week, the sample was cut out, and new bone covering the sample was observed and evaluated according to the following criteria.

◯: New bone was completely matured after 24 weeks Δ: New bone was not matured after 24 weeks, but 4
It was completely mature after 8 weeks. ×: New bone was not matured even after 48 weeks.

The Young's modulus of the ceramic test pieces prepared under the same conditions as the ceramic coating layer of each sample was measured. When the Young's modulus is high, the ceramic coating layer is easily peeled off.

Further, after preparing a test piece (JIS Z 2201 No. 2 test piece) made of Ti of the same material as that used for the substrate, after performing heat treatment under the same firing conditions as those of the above samples, respectively. A tensile strength test was conducted according to JIS Z 2241.

The results are shown in Table 1.

[0094]

[Table 1]

In Sample Nos. 7, 8 and 10, the ceramic film was peeled off from the Ti plate after firing, and the adhesive strength could not be measured.

<Artificial Dental Root Having Embedding Layer and Ceramics Coating Layer> Ceramic particles were embedded on the surface of an artificial dental root substrate to form an embedding layer, and then a ceramics coating layer was formed thereon. The ceramic particles were obtained as follows. CaCO ₃ , SiO ₂ and MgO,
After mixing by a conventional method and calcining at 1000 ° C, crushing,
Molded and then fired at 1280 ° C. This product was crushed in an alumina mortar and classified by a sieve to obtain an average particle size of 250.
Precise diopside of ~ 300μm (CaO ・ 2Si
O ₂ .MgO) particles were obtained. The compressive strength of the diopside particles obtained here was 200 MPa, and the coefficient of thermal expansion was 10 × 10 ⁻⁶ ° C. ⁻¹ . The coefficient of thermal expansion of the Ti substrate is 9.
Since it is 7 × 10 ^-6 ° C ^-1, it is 1.0 times that.

Next, as shown in FIG. 2, high vacuum grease was applied to the surface of the metal base 2 made of Ti, whereby the ceramic particles 30 were adhered tightly to the entire side surface and bottom surface, and the ceramic particles 30 were placed in vacuum. Then, hot pressing was performed in a uniaxial direction using a mold made of alumina, and the metal base was radially expanded to perform plastic working. The mold is as shown in FIG. 2 and FIG.
As shown in FIG. 2, the upper punch 61 and the lower punch 65 are arranged above and below the split mold 4 arranged in the tubular body 5, and the pressing means 67 presses the upper punch 61 and the lower punch 65. In the press, the sample 10 was first fixed in a mold and heated at 950 ° C. for 1 hour, and then, while being heated, it was pressed at 15 MPa for 30 minutes. As a result, the ceramic particles were embedded in the surface layer of the metal substrate, and the embedded layer was formed.

On the buried layer, sample No. 1 in Table 1 was obtained.
A ceramic coating layer was formed in the same manner as in 1 to obtain an artificial tooth root sample.

In this case, the same measurement as above was carried out, and it was found that the adhesive strength was 18.5 kg of Sample No. 1.
It was improved from f / cm ² to 20.5 kgf / cm ² .

Example 2 A slurry containing the glass powder shown in Table 2 was prepared in the same manner as in Example 1. The composition of the glass powder was the same as that of sample Nos. 1 to 6 of Example 1, and 2-3 kinds of glass powders having different average particle diameters were prepared for each composition. After coating two kinds of slurries containing glass powders having the same composition but different average particle diameters or glass powders having the same average particle diameter but different compositions, respectively on the surface of the substrate, sample Nos. 1 to 6 were used.
It was fired under the same conditions as above to form a ceramic coating layer.
An artificial dental root substrate having the structure shown in FIG. 8 was used as the substrate. The slurry was applied by the method shown in FIG. The coating of the slurries was performed by first immersing the lower root 203 and the tapered root portion 202 in the slurry to form a coating film, drying the coating, and then immersing the upper root 201 in the slurry. The concentration of the slurry was selected from the range of 30 to 80% by weight according to the average particle diameter of the glass powder so that the thickness of the ceramic coating layer was 20 μm. Specifically, the glass powder having a large average particle diameter has a low slurry concentration, and the glass powder having a small average particle diameter has a high slurry concentration.

The pore diameter of the ceramic coating layer was measured, and the average of the respective coating areas of each slurry was obtained.
Table 2 shows the relationship between the composition and average particle diameter of the glass powder and the average diameter of the pores of the ceramic coating layer.

[0102]

[Table 2]

It can be seen from Table 2 that the pore diameter can be greatly changed by changing the composition and average particle diameter of the glass powder.

In each of the above examples, the ceramic coating layer was formed with TiO ₂ , ZnO, B ₂ O ₃ , FeO, Z.
Even when one or more kinds of rO ₂ and Ag ₂ O were contained in a total amount of 5% by weight or less, the characteristics equal to or more than the above were obtained.

The effects of the present invention are clear from the results of the above examples.

[Brief description of drawings]

FIG. 1 is a SiO ₂ —CaO—MgO 3 component composition diagram for explaining a preferable composition of a ceramic material.

FIG. 2 is an exploded perspective view for explaining the method for manufacturing the composite biological implant of the present invention.

FIG. 3 is a partially cutaway front view for explaining the method for manufacturing the composite biological implant of the present invention.

FIG. 4 is a drawing-substitute photograph showing a crystal structure, which is a scanning electron microscope photograph of a ceramic coating layer.

FIG. 5 is a cross-sectional view showing an example of a glass powder slurry coating method.

FIG. 6 is a perspective view showing an example of a method for applying a glass powder slurry.

FIG. 7 is a side view showing an example of a method for applying a glass powder slurry.

FIG. 8 is a perspective view showing an example of an artificial tooth root.

FIG. 9 is a perspective view showing an example of an artificial joint.

FIG. 10 is a perspective view showing an example of an artificial vertebral body.

FIG. 11 is a perspective view showing an example of an artificial intervertebral disc.

FIG. 12 is a perspective view showing an example of an artificial intestinal tract.

FIG. 13 is a side view showing an example of an artificial bone screw.

[Explanation of symbols]

 2 Metal Substrate 40 Split Type 5 Cylindrical Body 10 Sample 30 Ceramic Particle 61 Upper Punch 65 Lower Punch 67 Pressing Means 101 Slurry 102 Container 103 Lid 104 Rotating Body 105 Nozzle 201 Top Root 202 Top Root Taper 203 Bottom Root

Claims (17)

[Claims] 1. A ceramic coating layer is formed on the surface of a metal substrate, and the ceramic coating layer is a non-calcium phosphate-based composition containing silicon oxide, calcium oxide and magnesium oxide, and 50% by volume of the entire crystalline material. A diopside crystal occupies the above, and a composite bioimplant having a diffusion layer containing oxygen and silicon on the surface layer of the metal substrate. 2. The ceramic coating layer has a structure in which a crystalline material is dispersed in a glass material, and the crystalline material is 30% by volume.
The composite bioimplant according to claim 1, occupying the above. 3. The composite bioimplant according to claim 1, wherein the metal substrate is composed of a metal exhibiting a ductility of 50% or more at a temperature of 70% or less of a melting point. 4. An embedded layer in which ceramic particles are embedded is formed on the surface layer of the metal substrate,
The composite biological implant according to claim 1, wherein the ceramic coating layer is formed on the embedded layer. 5. The composite bioimplant according to claim 1, wherein the ceramic coating layer includes a porous body having pores. 6. The composite bioimplant according to claim 5, wherein the ceramic coating layer has regions having different average pore diameters. 7. The composite bioimplant according to claim 5, wherein the ceramic coating layer has regions having different compositions. 8. The ceramic coating layer has an average diameter of 5 to 5.
7. A porous body having pores of 100 .mu.m.
A composite bioimplant of any of. 9. The ceramic coating layer has an average diameter of 5 μm.
9. The composite bioimplant of claim 8, comprising a porous body having pores less than m 2. 10. The ceramic coating layer is TiO 2.
₂ , ZnO, B ₂ O ₃ , FeO, ZrO ₂ and Ag ₂
The composite bioimplant according to any one of claims 1 to 9, containing at least one of O. 11. The composite bioimplant according to claim 1, which is an artificial tooth root. 12. A method for producing a composite living body implant according to claim 1, wherein a glass powder producing step of melting and cooling a ceramic powder and then pulverizing it to obtain a glass powder, and the glass powder. And a baking step of baking the applied glass powder on the surface of the metal substrate to form a ceramic coating layer. 13. The method for producing a composite biological implant according to claim 12, wherein the firing temperature in the baking step is 700 to 1000 ° C. 14. The method for producing a composite biological implant according to claim 12, wherein the temperature at which the ceramic powder is melted is 1400 ° C. or higher. 15. The average particle diameter of the glass powder is 1 to 50.
The method for producing a composite living body implant according to any one of claims 12 to 14, which has a diameter of 0 µm. 16. The method for producing a composite biological implant according to claim 12, wherein in the applying step, at least two kinds of slurries containing glass powders having different average particle diameters are applied to the surface of the metal substrate. 17. The method for producing a composite biological implant according to claim 12, wherein in the applying step, at least two kinds of slurries containing glass powders having different compositions are applied to the surface of the metal substrate.