Patent Application
20220090268
The present invention relates to a method for fixing hydroxyapatite (Ca10 (PO4)6(OH)2) to a titanium-based metal substrate by a sintering method, and a hydroxyapatite-coated metal material. More specifically, it relates to a hydroxyapatite-coated metal material suitably used for medical materials such as artificial bones, artificial joints, implant, and the like, which becomes a foothold (scaffold) for osteo-blasts to proliferate. In the present specification, hydroxyapatite may be sometimes abbreviated to as “HAp”. Incidentally, the present application claims a priority of Japanese Patent Application No. 2019-074248 filed on Apr. 9, 2019, and the contents thereof are incorporated herein by reference.
For medical materials such as artificial bones, artificial joints, implant and the like, metals such as titanium, stainless steel, and the like, or ceramics are used. In particular, titanium has excellent corrosion resistance, high impact strength, is hard and tough, has good compatibility with living organisms and can be bonded to bone, and has elasticity close to that of bone. However, titanium cannot be utilized for artificial organs having a sliding part such as artificial joints since it is easily worn. Further, mold processing of titanium is more difficult than stainless steel. On the other hand, among ceramics, hydroxyapatite (HAp) has begun to be used for dental implant. This is because HAp is an inorganic component of bones and teeth and is an excellent biomaterial having extremely good affinity with bones. However, HAp sintered by hot pressing shows a compressive strength of 200 MPa or more, but bending strength and impact strength thereof are low, and it is easily broken so that it is difficultly utilized for uses that require strength.
In consideration of characteristics of HAp and characteristics of a metal substrate, it has been known a method in which hydroxyapatite is fixed on a metal substrate. Heretofore, as this kind of method, it has been disclosed a method for preparing a hydroxyapatite (HAp) coating on stainless steel (316L) by a wet method using a supersaturated simulated body fluid (simulated body fluid) (SBF) (for example, Patent Document 1 (see Claim 1, paragraph [0001] and paragraph [0025])).
This method comprises a) a step of roughening a surface of a metal substrate using acetone, ethanol and deionized water by a known method, and ultrasonically cleaning to obtain a clean metal substrate; b) a step of drying the clean metal substrate at a temperature in the range of 50 to 60° C. for about 1 to 2 hours, immersing the clean metal substrate in an aqueous solution of a protein with a concentration in the range of 4 to 10wt % at a temperature in the range of 40 to 50° C. and at a pH in the range of 6.5 to 7 for about 2 to 4 hours, and then, cleaning it with water 3 to 4 times repeatedly, and drying it at a temperature in the range of 20 to 30° C. for about 1 to 2 hours to obtain a dry surface-treated metal substrate; c) a step of immersing the dry surface-treated metal substrate in a simulated body fluid [SBF(N)] for 1 to 2 days at a temperature of 35 to 37° C. and at a pH in the range of 6.5 to 7 to obtain a nucleated hydroxyapatite-coated metal substrate, cleaning it with deionized water 3 to 4 times, and drying the clean hydroxyapatite nucleated metal at a temperature in the range of 20 to 30° C. for about 1 to 2 hours to obtain a dried hydroxyapatite nucleated metal substrate; and d) a step of immersing the dried hydroxyapatite nucleated metal substrate in another simulated body fluid [SBF(O)] for a time in the range of 2 to 4 days at a temperature of 35 to 37° C. and at a pH in the range of 6 to 6.5, cleaning it with deionized water 3 to 4 times, and drying it at a temperature in the range of 20 to 30° C. for about 1 to 2 hours to obtain a desired protein-mediated calcium hydroxyapatite (HAp) coating on the hydroxyapatite nucleated metal substrate.
Patent Document 1: JP 2009-67669A
In the method shown in Patent Document 1, an HAp coating having a thickness of 20 μm to 280 μm can be obtained on the surface of a metal substrate, but this method is a wet method, so that the number of the steps for producing the HAp coating is many, and the HAp coating cannot be produced on the surface of the metal substrate unless it takes long days of several days or more. In addition, there was a problem that the surface hardness of the resulting HAp coating was low.
An object of the present invention is to provide a method for fixing hydroxyapatite on a surface of a titanium-based metal substrate with a small number of steps and a relatively short time. In addition, another object of the present invention is to provide a hydroxyapatite-coated metal material on which a hydroxyapatite layer, which can be a scaffold for osteoblasts to proliferate, is coated with high hardness.
A first aspect of the present invention is a method for fixing hydroxyapatite to titanium-based metal substrate which comprises a step of a subjecting a surface of a titanium-based metal substrate comprising pure titanium or a titanium alloy to surface roughening treatment so that a surface roughness Ra becomes 1.6 μm or more and 4.0 μm or less, a step of adhering hydroxyapatite powder to entire surface or a part of the surface of the titanium-based metal substrate subjected to the surface roughening treatment at a ratio of 25 mg/cm2 or more and 70 mg/cm2 or less, and a step of retaining the titanium-based metal substrate, to which the hydroxyapatite powder has been adhered, at a sintering temperature of 800° C. or higher for 3 hours or longer and 11 hours or shorter when an atmosphere is atmospheric, argon gas or carbon dioxide gas gas, or retaining it at a sintering temperature of 1,050° C. or higher for 3 hours or longer and 11 hours or shorter when the atmosphere is nitrogen gas, or retaining it at a sintering temperature of 900° C. or higher for 3 hours or longer and 11 hours or shorter when the atmosphere is oxygen gas, to sinter the hydroxyapatite powder on the surface of the metal substrate.
A second aspect of the present invention is an invention based on the first aspect, and is characterized in that the titanium-based metal substrate is a metal injection molded substrate.
A third aspect of the present invention is a hydroxyapatite-coated metal material which comprises a hydroxyapatite layer having a thickness of 10 μm or more and 510 μm or less, which can be a scaffold for osteoblasts to proliferate, on a surface of a titanium-based metal substrate, a fixed amount of the hydroxyapatite of 5 mg/cm2 or more and 50 mg/cm2 or less, a hardness of a surface of the hydroxyapatite layer regulated by JIS-K5600-5-4 of 6H or more, and a Vickers hardness regulated by JIS-Z-2244 of 250 HV or more and 740 HV or less.
A fourth aspect of the present invention is an invention based on the third aspect, and is characterized in that the titanium-based metal substrate is a metal injection molded substrate.
In the method of the first aspect of the present invention, after the hydroxyapatite powder is adhered to the surface of a titanium-based metal substrate which has been subjected to a surface roughening treatment so that the surface roughness Ra becomes 1.6 μm or more and 4.0 μm or less with a prescribed ratio, the titanium-based metal substrate, to which the hydroxyapatite powder has been adhered is retained under an atmosphere of atmospheric, nitrogen gas, argon gas, oxygen gas or carbon dioxide gas gas at a prescribed temperature for 3 hours or longer and 11 hours or shorter, so that the hydroxyapatite powder is sintered and fixed on the surface of the titanium-based metal substrate. Therefore, hydroxyapatite can be fixed on the surface of the titanium-based metal substrate with a small number of steps and a relatively short time in this sintering method as compared with the wet method. At the fixed hydroxyapatite layer, it is possible to proliferate osteoblasts.
In the method of the second aspect of the present invention, the titanium-based metal substrate is a metal injection molded substrate, so that a hydroxyapatite-coated metal material having a complicated shape can be produced.
The hydroxyapatite-coated metal material of the third aspect of the present invention has characteristics that it has a hydroxyapatite layer, which can be a scaffold of osteoblasts to proliferate, on the surface of a titanium-based metal substrate with a prescribed thickness and a prescribed fixed amount per a unit area, and a surface of the hydroxyapatite layer has a high hardness of 6H or more in a hardness of a pencil hardness test, and 250 HV or more and 740 HV or less in a Vickers hardness regulated in JIS-Z-2244.
In the hydroxyapatite-coated metal material of the fourth aspect of the present invention, the titanium-based metal substrate is a metal injection molded substrate, so that it can be applied to a medical material having a complicated shape.
Next, an embodiment to carry out the present invention is explained with reference to the drawings.
The method for fixing hydroxyapatite to titanium-based metal substrate of the embodiment of the present invention comprises, Step A of subjecting a surface of a titanium-based metal substrate 11 to a surface roughening treatment so that a surface roughness Ra thereof becomes 1.6 μm or more and 4.0 μm or less as shown in
The metal substrate 11 used in the embodiment of the present invention is a pure titanium substrate or a titanium alloy substrate. As the pure titanium, titanium (for example, JIS type 2 titanium) regulated by JIS standard is mentioned, and as the titanium alloy, corrosion resistant titanium alloy (for example, JIS type 11, type 12 and type 13 titanium alloys), 64 titanium alloy (Ti6Al4V), etc., are mentioned. The shape of the metal substrate 11 can be determined from among plate-shaped, rod-shaped, columnar, tubular, etc., depending on the use such as artificial bones, artificial joints, implant, etc. When the metal substrate has a complicated shape, it is preferable to use a metal injection molded product. The surface roughening treatment of the surface of the titanium-based metal substrate is carried out by sandblasting treatment.
In the sandblasting treatment, alumina particles having an average particle diameter in the range of 30 lam to 300 lam are injected to the surface of the above-mentioned metal substrate at an injection pressure of, for example, 5.0 kg/cm2. Thereafter, this metal substrate is immersed in a 10% caustic soda aqueous solution at 50° C. for 2 minutes, further immersed in an 8% nitric acid aqueous solution at 20° C. for 2 minutes, and then, the metal substrate is washed with pure water or ultrasonically cleaned in pure water. Alternatively, it is ultrasonically cleaned in pure water immediately after injection. By this sandblasting treatment, the surface roughness Ra of the titanium-based metal substrate is adjusted to 1.6 μm or more and 4.0 μm or less, and preferably 1.6 μm or more and 1.8 μm or less.
If the surface roughness Ra obtained by the sandblasting treatment is less than 1.6 μm, when the hydroxyapatite powder is tried to be adhered as mentioned later, the degree of unevenness of the surface of the metal substrate is insufficient, and the powder difficultly adhered to the surface of the titanium-based metal substrate. Also, if it exceeds 4.0 μm, the surface uneven shape of the molded product is too large so that uniform teeth or bones are difficultly formed. The above-mentioned surface roughness Ra is measured using a surface roughness measurement device (Surfest SJ-400 manufactured by Mitutoyo Corporation).
The hydroxyapatite powder is spherical, and an average particle diameter thereof is preferably 20 μm or more and 40 μm or less. If it is less than 20 μm, adsorptivity to proteins and adhesive property to osteoblasts tend to be easily lowered, so that it is difficultly to form teeth or bones. If it exceeds 40 μm, the hydroxyapatite is difficultly fixed to the titanium-based metal substrate. The average particle diameter of the powder is measured by a laser diffraction method. As the hydroxyapatite powder, powders prepared by various synthetic methods can be used, and the crystallinity and the substitutability with various ions are not particularly limited. For example, hydroxyapatite in which the crystal structure site is partially replaced with a potassium ion, a sodium ion, a magnesium ion, a strontium ion, a fluoride ion, a carbonate ion, etc., may be used. As the commercially available hydroxyapatite powder, there may be mentioned a product number 289,396 available from Sigma-Aldrich Co.
The hydroxyapatite powder 13 is uniformly adhered to entire surface or a part of the surface of the titanium-based metal substrate 12, which has been subjected to surface roughening treatment. The hydroxyapatite powder is preferably adhered to the substrate 12 at a ratio of 25 mg/cm2 or more and 50 mg/cm2 or less. If it is less than 25 mg/cm2, there is a fear of difficultly forming a hydroxyapatite layer with a sufficient thickness as a foothold (scaffold) for osteoblasts to proliferate, while if it exceeds 50 mg/cm2, inconvenience of peeling is likely to occur. The adhered amount of the hydroxyapatite powder is further preferably 30 mg/cm2 or more and 40 mg/cm2 or less.
As a method of adhering the hydroxyapatite powder, there may be mentioned a method in which hydroxyapatite powder is applied by dropping from above the titanium-based metal substrate horizontally placed to coat thereon, then, the titanium-based metal substrate is turned over to remove excess powder by its own weight to form a hydroxyapatite powder layer having a uniform thickness on the titanium-based metal substrate, or a method in which the hydroxyapatite powder is stored in an opened container, and after contacting the titanium-based metal substrate with the hydroxyapatite powder in the container, the titanium-based metal substrate is pulled up to form a hydroxyapatite powder layer having a uniform thickness on the titanium-based metal substrate, and further a method in which the titanium-based metal substrate is buries in the hydroxyapatite powder in a container, then, the metal substrate is pulled up and the excessively adhered powder is removed to form a hydroxyapatite powder layer having a uniform thickness on the titanium-based metal substrate. According to these methods, the hydroxyapatite powder enters into the roughened recess portions of the titanium-based metal substrate and the hydroxyapatite powder adheres thereto.
The titanium-based metal substrate 14 to which the hydroxyapatite powder is adhered is heated by an electric furnace, a microwave furnace, a gas furnace, etc. Heating is carried out under a prescribed atmosphere at a sintering temperature of 800° C. or higher for 3 hours or longer and 11 hours or shorter. AS the atmosphere, there may be mentioned an atmosphere of atmospheric, nitrogen gas, argon gas, oxygen gas or carbon dioxide gas gas. Fixation of the hydroxyapatite to the titanium-based metal substrate differs depending on the kind of atmosphere. This is because decomposition of the hydroxyapatite differs depending on the kind of atmosphere. The atmosphere is most preferably carbon dioxide gas gas atmosphere since can easily decompose the hydroxyapatite, and an atmosphere containing carbon dioxide gas gas is more preferable. Sintering is carried out by retaining at a sintering temperature of 800° C. or higher, and preferably at a sintering temperature of 1,150° C. or lower for 3 hours or longer and 11 hours or shorter when the atmosphere is atmospheric, argon gas or carbon dioxide gas gas. Also, sintering is carried out by retaining at a sintering temperature of 1,050° C. or higher, and preferably at a sintering temperature of 1,150° C. or lower for 3 hours or longer and 11 hours or shorter when the atmosphere is nitrogen gas. Further, sintering is carried out by retaining at a sintering temperature of 900° C. or higher, and preferably at a sintering temperature of 1,150° C. or lower for 3 hours or longer and 11 hours or shorter when the atmosphere is oxygen gas. Also, the reason why the preferred upper limit of the sintering temperature is set to 1,150° C. is that unnecessary heat energy consumption is to be suppressed. The rate of temperature rising from room temperature is preferably 6° C./min or more and 30° C./min or less for forming CaTiO3 continuously from CaCO3. The sintering time is preferably 6 hours or longer. In the titanium-based metal substrate, TiO2 is formed on the surface of the substrate by oxygen in the atmosphere before sintering. After sintering, it is preferable to cool the furnace at a temperature lowering rate of 3° C./min or more and 10° C./min or less.
As shown in
As shown in
As shown in
Returning to
Hereinafter, Examples of the present invention will be explained in detail with Comparative Examples.
As shown in
After the titanium substrate 12 subjected to surface roughening treatment was arranged horizontally, as shown in
The material of the titanium substrate which is a starting material of this hydroxyapatite-coated titanium material, the surface roughness after surface roughening of the titanium substrate, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and its sintering conditions (atmosphere, sintering temperature and sintering time) are shown in the following Table 1.
With regard to the case where the atmosphere is atmospheric, the material of the titanium substrate which is a starting material, the surface roughness of the titanium substrate after surface roughening, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and the sintering conditions thereof (atmosphere, sintering temperature and sintering time) were each changed as shown in the above-mentioned Table 1, and hydroxyapatite-coated titanium materials of Examples 2 to 8 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1 except for the above.
With regard to the case where the atmosphere is nitrogen gas, the material of the titanium substrate which is a starting material, the surface roughness of the titanium substrate after surface roughening, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and the sintering conditions thereof (atmosphere, sintering temperature and sintering time) were each changed as shown in the following Table 2, and hydroxyapatite-coated titanium materials of Examples 9 and 10 and Comparative Example 7 were obtained in the same manner as in Example 1 except for the above.
With regard to the case where the atmosphere is argon gas, the material of the titanium substrate which is a starting material, the surface roughness of the titanium substrate after surface roughening, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and the sintering conditions thereof (atmosphere, sintering temperature and sintering time) were each changed as shown in the above-mentioned Table 2, and hydroxy-apatite-coated titanium materials of Examples 11 to 14 were obtained in the same manner as in Example 1 except for the above.
With regard to the case where the atmosphere is oxygen gas, the material of the titanium substrate which is a starting material, the surface roughness of the titanium substrate after surface roughening, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and the sintering conditions thereof (atmosphere, sintering temperature and sintering time) were each changed as shown in the above-mentioned Table 2, and hydroxy-apatite-coated titanium materials of Examples 15 to 17 and Comparative Example 8 were obtained in the same manner as in Example 1 except for the above.
With regard to the case where the atmosphere is carbon dioxide gas, the material of the titanium substrate which is a starting material, the surface roughness of the titanium substrate after surface roughening, the average particle diameter of the HAp powder, the adhered amount of the HAp powder on the titanium substrate, and the sintering conditions thereof (atmosphere, sintering temperature and sintering time) were each changed as shown in the above-mentioned Table 2, and hydroxyapatite-coated titanium materials of Examples 18 to 21 were obtained in the same manner as in Example 1 except for the above.
With regard to samples of 29 kinds of the hydroxyapatite-coated titanium materials obtained in Examples 1 to 21 and Comparative Examples 1 to 8, the surface properties were evaluated by the following items. The results of these evaluations are shown in the above-mentioned Table 1 and Table 2. In addition, with regard to the sample of the hydroxyapatite-coated titanium material of Example 20, the adhesion rate of osteoblasts was examined.
(1) Fixed Amount of HAp
The fixed amount of the hydroxyapatite is measured by placing a prescribed amount of hydroxyapatite on a titanium substrate whose mass has been measured before sintering, and after sintering, the hydroxyapatite that has not been fixed was removed from the substrate with a soft brush, and the mass thereof was measured and the mass of titanium before sintering was subtracted to make a fixed amount of the hydroxyapatite.
(2) Thickness of HAp Layer
The thicknesses of the substrate before sintering and after sintering were measured by a micrometer (straight-ahead type blade micrometer BLM-50MX manufactured by Mitutoyo Corporation) and obtained.
(3) Presence or Absence of Peaks of Ca and P by Fluorescent X-ray Analysis
Elements at the surface of each sample was analyzed using a fluorescent X-ray analyzer (X-ray Fluorescence: XRF) (Model Name: JSX-3222 manufactured by JEOL Ltd.). It was measured by making the radiation source element Rh, the tube voltage 30.0 kV, the tube current 0.150 mA, and the live time 1,200 seconds. When both peak waveforms corresponding to Ca and P, which are inorganic components of HAp, were observed in this XRF analysis, it was defined as “HAp component present”, and when both peak waveforms were not observed, it was defined as “no HAp component”.
(4) Presence or Absence of Peak of HAp Component by X-ray Diffraction
The substances at the surface of each sample were analyzed using an X-ray diffraction (X-ray diffraction: XRD) device (Model Name: RINT2000 manufactured by Rigaku Corporation). The measurement range was 5° to 60° , the scanning speed was 4 deg/min, the voltage was 40 kV, the current was 20 mA, the slit width was 1-1-0.15° , and a CuKα line (characteristic X-ray) and a monochromator were used. When both peak waveforms corresponding to P and Ca, which are inorganic components of HAp, were observed in this XRD measurement, it was defined as “HAp component present”, and when both peak waveforms were not observed, it was defined as “no HAp component”.
(5) Abrasion Strength (Pencil Hardness) of Fixed HAp Layer
A pencil hardness test was carried out to measure the wear strength of the fixed HAp layer. Specifically, a pencil hardness tester (Allgood 054 series) was used and a peeling test of each sample fixed on the surface of the titanium substrate was carried out. Only the wood portion of the Mitsubishi uni pencil for the pencil hardness test was scraped to expose only the core by 5 mm to 6 mm. This pencil was set to the tester, and retained in the state that a load of 750 g±10 g is applied to the tip of the lead of the pencil with an angle of 45°±1° and pushed with a speed of 0.5 mm/sec to 1 mm/sec at a distance of at least 7 mm. The powder of the lead of the pencil adhered to the surface of the sample was wiped off with a soft cloth, and scratches or indentations were confirmed. The pencil hardness softer just before the scratched pencil was made the pencil hardness of the HAp layer. This test corresponds to the JIS standard of JIS-K5600-5-4.
(6) Adhesion Strength (Vickers Hardness) of Fixed HAp Layer
A Vickers hardness test was carried out to measure the adhesion strength of the fixed HAp layer. The Vickers hardness is a Vickers hardness regulated by JIS Z2244, and, for example, pressure was applied to five different points on the surface of the sample, the average value of resistance to plastic deformation thereby was calculated, and this average value thereof was made the Vickers hardness.
(7) Adhesion Strength (Impact Strength) of Fixed HAp Layer
A free fall test was carried out by the following method to measure the adhesion strength of the fixed HAp layer. A drop height was made 80 cm (free fall energy: 5.3J), the hydroxyapatite-coated titanium material to which the hydroxyapatite layer has fixed was freely fallen five times on the surface of a smooth concrete floor material, and whether the hydroxyapatite layer on the surface of the sample is peeled off or not was evaluated. This impact test is an impact test in which, when the sample is made a glass plate, with such a degree that the glass plate is broken by free fall from a height of 20 cm.
(8) SEM Observation of fixed HAp Layer
The surface properties of the fixed HAp layer were observed using a scanning type electron microscope (Scanning Electron Microscope: SEM) (HITACHI S-4800). It was investigated whether or not there was a gap in the fixed HAp particles, and if it presents, whether or not osteoblasts could invade and fix to this gap and can be a foothold (scaffold) for proliferation.
(9) Adhesion Rate of Osteoblasts to fixed HAp Layer
Whether or not osteoblasts could proliferate on the fixed HAp layer was examined by the adhesion rate of osteoblasts to the HAp layer. This adhesion rate was obtained by the following method.
A titanium substrate or a titanium substrate fixed with a hydroxyapatite layer was fixed on the edge of a 35 mm culture dish with a transparent adhesive sheet. MC3T3-1 cells were seeded with 1.5×105 cells and cultured at 37° C. for 24 hours. After cultivation, the cells were observed using an optical microscope, and the adhesion rate of osteoblasts was calculated by the following equation using, as a control, the portion other than the titanium substrate was fixed or the titanium substrate, to which a hydroxyapatite layer had been fixed was fixed. The number of the samples was made 3 and the average value thereof was obtained. Osteoblasts adhesion rate (%)=number of cells on sample/number of cells on untreated substrate (control)
As clearly seen from Table 1, in the sample of Comparative Example 1 in which sintering was carried out in atmospheric, the surface roughness Ra of the titanium substrate, which has been subjected to surface roughening treatment, was 1.5 μm so that surface roughening was not sufficiently carried out, and the fixed amount of HAp on the titanium substrate was 1.6 mg/cm2, which was too small. Therefore, whereas both peak waveforms corresponding to Ca and P which were considered to be derived from HAp by fluorescent X-rays were observed, the thickness of HAp could not be measured, and the peak waveform of the HAp component by XRD was not observed. The evaluations of the pencil hardness test, Vickers hardness test and impact test (hereinafter referred to as pencil hardness test, etc.) were not carried out. As a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were impossible.
In the sample of Comparative Example 2 in which sintering was carried out in atmospheric, since the sintering temperature was 750° C., the fixed amount of HAp on the titanium substrate was 4.8 mg/cm2, which was too small. Therefore, neither the peak waveform corresponding to Ca and P, which is considered to be derived from HAp by fluorescent X-rays, was observed, and the thickness of HAp could not be measured, further the peak waveform of the HAp component by XRD was not observed. No evaluation such as pencil hardness test, etc., was carried out. As a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were impossible.
In the sample of Comparative Example 3 in which sintering was carried out in atmospheric, the adhered amount of the HAp powder on the titanium substrate was too much so that the fixed amount of HAp on the titanium substrate was 50.4 mg/cm2, which was too much, and the thickness of HAp was 770 μm, which was too thick. Therefore, the HAp layer was peeled off from the surface of the titanium substrate in the impact test. The pencil hardness was 6H or more and the Vickers hardness was 445 HV, and as a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were possible.
In the sample of Comparative Example 4 in which sintering was carried out in atmospheric, the adhered amount of the HAp powder was 75 mg/cm2, which was too much, so that the fixed amount of HAp on the titanium substrate was 54.4 mg/cm2, which was too much, and the thickness of HAp was 625 μm, which was too thick. The HAp layer was peeled off from the surface of the titanium substrate in the impact test. The pencil hardness was 6H or more and the Vickers hardness was 519 HV, and as a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were possible.
In the sample of Comparative Example 5 in which sintering was carried out in atmospheric, the sintering time was 2.0 hours, which was too short, the fixed amount of HAp on the titanium substrate was 27.5 mg/cm2 and the thickness of HAp was 239 μm, but the HAp layer was peeled off from the surface of the titanium substrate in the impact test. It is considered that this is because fixation of HAp on the titanium substrate could not be carried out. The pencil hardness was 6 H or more and the Vickers hardness was 567 HV, and as a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were possible.
In the sample of Comparative Example 6 in which sintering was carried out in atmospheric, the sintering time was 12.0 hours, which was too long, the fixed amount of HAp on the titanium substrate was 65.3 mg/cm2, which was too much and the thickness of HAp was 780 μm, which was too thick. Therefore, the HAp layer was peeled off from the surface of the titanium substrate in the impact test. The pencil hardness was 6 H or more and the Vickers hardness was 642 HV, and as a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were possible.
As clearly seen from Table 2, in the sample of Comparative Example 7 in which sintering was carried out in nitrogen gas atmosphere, the sintering temperature was 1,000° C. so that the fixed amount of HAp on the titanium substrate was 3.4 mg/cm2, which was too little. Therefore, neither the peak waveform corresponding to Ca and P, which is considered to be derived from HAp by fluorescent X-rays, was observed, and the thickness of HAp could not be measured, further the peak waveform of the HAp component by XRD was not observed. Evaluations such as the pencil hardness test, etc., were not carried out. As a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were impossible.
In the sample of Comparative Example 8 in which sintering was carried out in oxygen gas atmosphere, the sintering temperature was 850° C. so that the fixed amount of HAp on the titanium substrate was 4.7 mg/cm2, which was too little. Therefore, neither the peak waveform corresponding to Ca and P, which is considered to be derived from HAp by fluorescent X-rays, was observed, and the thickness of HAp could not be measured, further the peak waveform of the HAp component by XRD was not observed. Evaluations such as the pencil hardness test, etc., were not carried out. As a result of SEM observation of osteoblasts, invasion and fixation of osteoblasts were impossible.
To the contrary, in the samples of Examples 1 to 8 in which sintering was carried out in atmospheric, Examples 9 and 10 in which sintering was carried out in nitrogen gas atmosphere, 11 to 14 in which sintering was carried out in argon gas atmosphere, Examples 15 to 17 in which sintering was carried out in oxygen gas atmosphere, and Examples 18 to 21 in which sintering was carried out in carbon dioxide gas atmosphere, the peaks of Ca and P elements in the HAp composition were confirmed from fluorescent X-ray analysis in all the samples. Also, the peak of crystal structure of HAp was confirmed from the XRD (X-ray diffraction) analysis. Further, in the adhesion between the titanium substrate and HAp, it was confirmed that a part of the crystal structure of HAp was changed to tricalcium phosphate (β-TCP) and CaTiO3 with a perovskite structure was formed by the interaction of TiO2 and HAp formed on the surface of the titanium substrate from analyses of XRD peak analysis and XRF (fluorescent X-rays). According to this, it was inferred that the HAp layer was strongly bonded to the titanium substrate. That is, it was inferred that HAp was fixed to the surface of the titanium substrate.
In addition, in the samples of Examples 1 to 21, the HAp layer showed the hardness that these had a hardness of 6 H or more as a result of the pencil hardness test and the Vickers hardness was in the range of 250 HV or more and 740 HV or less. Moreover, in the impact strength by the free fall test, all of the HAp layers were not peeled off and had sufficient strength. In particular, it was confirmed that, in the carbon dioxide gas, the thickness could be increased while maintaining the adhesiveness of the hydroxyapatite layer to the substrate and hardness than the other gases.
Further, in the samples of Examples 1 to 21, a gap was confirmed between HAp particles constituting the fixed HAp layer from SEM observation, and a foothold (scaffold) in which osteoblasts proliferate is formed whereby invasion and fixation of osteoblasts were confirmed to be possible. In the sample of Example 20, osteoblasts adhered to the fixed HAp layer at a high rate of 84.3%.
The hydroxyapatite-coated metal material of the present invention serves as a foothold (scaffold) for osteoblasts to proliferate, and can be utilized for medical materials such as artificial bones, artificial joints, implant, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-074248 | Apr 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/015782 | 4/8/2020 | WO | 00 |
