Calcium phosphate-carbon atom-zirconium oxide composite, restorative material, medical device, and method for producing calcium phosphate-carbon atom-zirconium oxide composite

Abstract

To provide an apatite-zirconium oxide composite having high mechanical strength and low elastic modulus, a restorative material, a medical device, and a method for producing a calcium phosphate-carbon atom-zirconium oxide composite.SOLUTION: A calcium phosphate-carbon atom-zirconium oxide composite comprises tricalcium phosphate, apatite represented by formula (1): Cas(PO4)t(X)u, and carbon atoms, and further comprises zirconium oxide, wherein in formula (1), X represents at least one selected from the group consisting of OH and CO3, s represents a number of 8 to 10, t represents a number of 4 to 6, and u represents a number of 1 to 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to calcium phosphate-carbon atom-zirconium oxide composites, restorative materials, medical devices, and methods for making calcium phosphate-carbon atom-zirconium oxide composites. [Background technology]

[0002] Calcium phosphates such as hydroxyapatite (HAp) have a similar composition to the inorganic main component of bone and have therefore been widely studied as medical materials, for example, materials for artificial bones. Non-Patent Document 1 discloses a composite containing tricalcium phosphate, apatite represented by a specific chemical formula, and carbon atoms. Non-Patent Document 1 discloses that the composite can be produced by firing octacalcium phosphate represented by a specific chemical formula and having divalent carboxylate ions. The composite disclosed in Non-Patent Document 1 exhibits a layered structure consisting of a layer of the tricalcium phosphate, apatite represented by a specific chemical formula, and a layer of the carbon atoms, which makes it less likely to crack.

[0003] On the other hand, zirconium oxide, also known as zirconia, has a high melting point of 2715°C at atmospheric pressure and is therefore used as a material for heat-resistant ceramics. Zirconium oxide is characterized by a change in volume that occurs with a phase transition in its crystal structure. Furthermore, when zirconium oxide is dissolved in an oxide such as yttrium oxide, the cubic and tetragonal crystals become stable or metastable at room temperature. Thus, zirconium oxide stabilized by an oxide is used as a good conductor due to its electrical properties. Furthermore, zirconium oxide stabilized by an oxide is also used in the medical field, such as in artificial dental roots, due to its excellent mechanical properties. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Karen Kuroyama,et al.(2023),Science and Technology of Advanced Materials,24:1,2261836 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, calcium phosphate and zirconium oxide have been used as materials for forming artificial bones, artificial dental roots, and medical devices used in conjunction with these. These materials are required to have strength and elastic modulus equivalent to those of endogenous bones in living bodies. Conventionally known calcium phosphates and calcium phosphate composites have had the problem of not satisfying both sufficiently high strength and sufficiently low elastic modulus compared to endogenous bones in living bodies. Therefore, an object of the present disclosure is to provide a calcium phosphate-carbon atom-zirconium oxide composite, a restorative material, a medical device, and a method for producing a calcium phosphate-carbon atom-zirconium oxide composite that has higher strength and a lower elastic modulus than conventionally known calcium phosphates and calcium phosphate composites. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that a composite of zirconium oxide and a raw material composite containing tricalcium phosphate, apatite having a specific structure, and carbon atoms has high strength and a low elastic modulus, and have thus completed the present disclosure.

[0007] The present disclosure encompasses the following: <1> A calcium phosphate-carbon atom-zirconium oxide composite comprising: a raw composite containing tricalcium phosphate, an apatite represented by formula (1), and carbon atoms; and zirconium oxide. Formula (1): Ca s (PO4) t (X) u (In formula (1), X represents at least one selected from the group consisting of OH and CO3; s represents the numbers 8 to 10, t represents the numbers 4 to 6, u represents the numbers 1 and 2.) <2> The raw material composite is contained in an amount of 5% by mass to 50% by mass relative to the total amount of the raw material composite and the zirconium oxide. <1> The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <3> The zirconium oxide is stabilized zirconia in which an oxide is dissolved. <1> or <2> The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <4> The oxide is at least one selected from the group consisting of yttrium oxide, cesium oxide, calcium oxide, and magnesium oxide. <3> The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <5> The zirconium oxide is predominantly tetragonal. <1> ~ <4> 1. A calcium phosphate-carbon atom-zirconium oxide composite according to any one of the preceding claims. <6> the zirconium oxide is island-shaped in a cross section of the composite, and the raw material composite is arranged so as to surround at least a portion of the periphery of the zirconium oxide in the cross section. <1> ~ <5> 1. A calcium phosphate-carbon atom-zirconium oxide composite according to any one of the preceding claims. <7> the raw material composite has a laminated structure of a layer containing the tricalcium phosphate and the apatite and a layer containing the carbon atom; <1> ~ <6> 1. A calcium phosphate-carbon atom-zirconium oxide composite according to any one of the preceding claims. <8> The maximum bending strength is 320 MPa or more. <1> ~ <7> 1. A calcium phosphate-carbon atom-zirconium oxide composite according to any one of the preceding claims. <9> Young's modulus is 170 GPa or less, <1> ~ <8> 1. A calcium phosphate-carbon atom-zirconium oxide composite according to any one of the preceding claims. <10> <1> ~ <9> A restorative material comprising the calcium phosphate-carbon atom-zirconium oxide composite according to any one of the above. <11> Used in bone or dental treatment, <10> The restorative material according to claim 1. <12> <10> or <11> 2. A medical device comprising the repair material described in claim 1. <13> a step of forming a raw material composite containing tricalcium phosphate, an apatite represented by formula (1), and carbon atoms, and zirconium oxide to obtain a formed body; sintering the compact; A method for producing a calcium phosphate-carbon atom-zirconium oxide composite having the formula: Formula (1): Ca s (PO4) t (X) u (In formula (1), X represents at least one selected from the group consisting of OH and CO3; s represents the numbers 8 to 10, t represents the numbers 4 to 6, u represents the numbers 1 and 2.) <14> The step of obtaining the molded body and the step of firing are carried out simultaneously by a spark plasma sintering method. <13> 1. A method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <15> The amount of the raw material composite is 5% by mass to 50% by mass with respect to the total amount of the raw material composite and the zirconium oxide. <13> or <14> 1. A method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <16> The zirconium oxide is stabilized zirconia in which an oxide is dissolved. <13> 1. A method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <17> The oxide is at least one selected from the group consisting of yttrium oxide, cesium oxide, calcium oxide, and magnesium oxide. <16> 1. A method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 1. <18> The zirconium oxide is mainly tetragonal. <13> ~ <17> 1. A method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to any one of the above. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a calcium phosphate-carbon atom-zirconium oxide composite having high strength and low elastic modulus, a restorative material, a medical device, and a method for producing the calcium phosphate-carbon atom-zirconium oxide composite. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a calcium phosphate-carbon atom-zirconium oxide composite according to the present disclosure. [Figure 2A] 1 is a scanning electron microscope photograph of a sample of Example 1. [Figure 2B] 1 is a scanning electron microscope photograph of a sample of Comparative Example 1. [Figure 2C] 1 is a scanning electron microscope photograph of a sample of Comparative Example 2. [Figure 2D] 1 is a scanning electron microscope photograph of a sample of Comparative Example 3. [Figure 3A] 1 is an enlarged scanning electron microscope photograph of the sample of Example 1. [Figure 3B] This is a further enlarged photograph of the photograph in FIG. 3A. [Figure 4A] 1 shows a scanning electron microscope photograph of a sample prepared in Example 1, a photograph showing the distribution of Ca in the same sample, and a photograph showing the distribution of Zr in the same sample. [Figure 4B] 1 shows a scanning electron microscope photograph of a sample prepared in Comparative Example 3, a photograph showing the distribution of Ca in the same sample, and a photograph showing the distribution of Zr in the same sample. [Figure 5] FIG. 1 is a characteristic diagram showing the results of a cell proliferation test for the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2. [Figure 6] 1 is a characteristic diagram showing the results of X-ray diffraction analysis of the samples prepared in Test Examples 1 to 4. FIG. [Figure 7] 1 shows photographs showing the results of a bone-bonding ability test using simulated body fluid for the samples prepared in Test Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. For example, the present disclosure allows addition, omission, substitution, modification, etc. of the number, amount, position, ratio, material, configuration, type, order, etc., within the scope of the spirit of the present disclosure.

[0011] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple types of corresponding substances. When multiple types of substances corresponding to each component are present in a composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.

[0012] <Calcium phosphate-carbon dioxide-zirconium oxide composite> A calcium phosphate-carbon atom-zirconium oxide composite shown as one embodiment of the present disclosure contains tricalcium phosphate, a raw material composite containing apatite represented by formula (1) and carbon atoms, and zirconium oxide. Formula (1): Ca s (PO4)t (X) u (In formula (1), X represents at least one selected from the group consisting of OH and CO3, s represents a number from 8 to 10, t represents a number from 4 to 6, and u represents a number from 1 to 2.)

[0013] The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure is composed of a region containing zirconium oxide and a region containing a raw material composite disposed between the regions. The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure has the ability to bind to bones present in living bodies, high strength, and a low elastic modulus. In particular, in the region containing zirconium oxide in the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, cracks (also referred to as "cracks") cause a stress-induced phase transition in the zirconium oxide, thereby suppressing the progression of the cracks. Furthermore, in the region containing the raw material composite, cleavage can deflect the progression of cracks that have occurred in the region containing zirconium oxide. The stress-induced phase transition in the region containing zirconium oxide and the effect of deflecting the progression of cracks in the region containing the raw material composite provide the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure with high toughness.

[0014] In the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, the raw composite is preferably contained in an amount of 5% by mass to 50% by mass relative to the total amount of the raw composite and the zirconium oxide. Furthermore, in the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, the content of the raw composite is more preferably 5% by mass to 40% by mass, even more preferably 5% by mass to 30% by mass, even more preferably 5% by mass to 20% by mass, and even more preferably 8% by mass to 12% by mass. By setting the content of the raw composite within the above range, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can achieve higher strength and a lower elastic modulus.

[0015] <Raw material complex> The raw material composite according to the present disclosure is a raw material composite that allows for crack deflection because it contains tricalcium phosphate, apatite represented by the above formula (1), and carbon atoms. The reason for this is presumably as follows: The calcium phosphate layer (tricalcium phosphate and apatite represented by formula (1)) and the carbon atom layer form a layered structure, and the bonding strength between these layers is weak, so cracks do not destroy the calcium phosphate layer but rather propagate by peeling the calcium phosphate layer from the carbon atom layer. Therefore, it is presumed that the raw material composite according to the present disclosure, due to the above configuration, imparts a crack propagation suppression effect to the calcium phosphate-carbon atom-zirconium oxide composite.

[0016] (apatite) The raw material composite contains tricalcium phosphate and an apatite represented by formula (1) (hereinafter, the apatite represented by formula (1) will also be referred to as "specific apatite"). Formula (1): Ca s (PO4) t (X) u In formula (1), X represents at least one selected from the group consisting of OH and CO3; s represents the numbers 8 to 10, t represents the numbers 4 to 6, u represents the numbers 1 and 2.

[0017] From the viewpoint of obtaining a raw material composite that exhibits the above-mentioned effect of inhibiting crack propagation, the specific apatite is preferably an apatite represented by formula (1-A). Formula (1-A): Ca 10 (PO4)6(X)2 In formula (1-A), X represents at least one selected from the group consisting of OH and CO3.

[0018] The specific apatite is specifically Ca 10 (PO4)6(OH)2, Ca 10 (PO4)6(CO3)2, and Ca 10 It is preferably at least one selected from the group consisting of (PO4)6(OH)(CO3).

[0019] The crystal system of tricalcium phosphate is not particularly limited, and may be any of α-tricalcium phosphate, α'-tricalcium phosphate, and β-tricalcium phosphate.

[0020] The total content of the specific apatite and tricalcium phosphate is preferably 90% by mass or more based on the total mass of the composite.

[0021] The composite may contain an apatite represented by the following formula (2). Formula (2):A 10 (B)6C2 In formula (2), A is Sr, Ba, Zn, Mg, Mn, Fe, Ra, Na, K, Al, Y, Ce, Nd, La, or C; B is HPO4, PO4, CO3, CrO4, VO4, UO4, SO4, SiO4, GeO4, or C; and C is OH, OD, F, Cl, Br, BO, CO3, or O.

[0022] (carbon atoms) The raw material composite contains carbon atoms. Here, the carbon atoms refer to carbon atoms other than those contained in the specific apatite and the apatite represented by formula (2) (hereinafter also referred to as "specific carbon atoms").

[0023] The specific carbon atoms are generated by thermal decomposition of the carboxylic acid introduced into the octacalcium phosphate, and preferably exist in the form of a compound consisting of carbon atoms, with the specific carbon atoms forming bonds with each other. Examples of the compound consisting of carbon atoms include amorphous carbon and graphite.

[0024] The content of the specific carbon atoms is preferably 1% by mass or more and 10% by mass or less with respect to the entire raw material composite.

[0025] (Structure of raw material composite) The raw material composite according to the present disclosure preferably has a layer (calcium phosphate layer) containing tricalcium phosphate and a specific apatite (i.e., an apatite represented by formula (1)) and a layer containing a specific carbon atom laminated together. The raw material composite according to the present disclosure has the above-described layered structure, which results in a raw material composite with a higher crack propagation suppression effect in the layered structure. The reason for this is presumed to be as follows. Even if a force is applied to the raw material composite and a crack occurs in the calcium phosphate layer, the presence of the layer containing the specific carbon atoms makes it difficult for the crack to propagate throughout the raw material composite. Furthermore, the stacking of these layers makes it even more difficult for the crack to propagate.

[0026] (Method of manufacturing raw material composite) The method for producing a raw material composite according to the present disclosure includes a step (firing step) of firing powdered octacalcium phosphate (hereinafter also referred to as "specific octacalcium phosphate") containing a compound represented by the following formula (3):

[0027] (Specific octacalcium phosphate) The specific octacalcium phosphate is an octacalcium phosphate containing a compound represented by formula (3). Formula (3): Ca8(HPO4) 2-a (Y) a (PO4)4 nH2O In formula (3), Y represents a divalent carboxylate ion, a is 0 to 1, and n is a number greater than 0.

[0028] Here, the divalent carboxylate ion is a carboxylate anion (-COO - ) is a divalent anion. In other words, it is a divalent anion obtained by dissociating the proton of the carboxyl group contained in a dicarboxylic acid.

[0029] Examples of divalent carboxylate ions include divalent anions obtained by dissociation of a proton from a carboxy group contained in a divalent carboxylic acid, which will be described later.

[0030] Examples of divalent carboxylate ions include isophthalate ion, phthalate ion, 2,2'-bipyridine-5,5'-dicarboxylate ion, malonate ion, succinate ion, glutarate ion, adipate ion, pimelate ion, suberate ion, azelaate ion, sebacate ion, maleate ion, fumarate ion, malate ion, mercaptosuccinate ion, methylsuccinate ion, aspartate ion, and glutamate ion.

[0031] From the viewpoint of obtaining a raw material composite having a high crack propagation suppression effect, the divalent carboxylate ion is preferably an isophthalate ion, a succinate ion, or a suberate ion.

[0032] Specific examples of specific octacalcium phosphate include Ca8(HPO4)2(C6H4(COO)2)1(PO4)4·nH2O, Ca8(HPO4)2(C2H4(COO)2)1(PO4)4·nH2O, and Ca8(HPO4)2(C6H 12 (COO)2)1(PO4)4·nH2O, etc. In the formula showing the specific example of the specific octacalcium phosphate, n has the same meaning as n in formula (3).

[0033] (preparation process) The method for producing a raw material composite according to the present disclosure may include preparing a powder of specific octacalcium phosphate by reacting a dicarboxylic acid, a calcium salt, and phosphoric acid.

[0034] Divalent carboxylic acids include divalent aliphatic carboxylic acids and divalent aromatic carboxylic acids. Divalent aliphatic carboxylic acids are compounds in which two carboxy groups are bonded to a saturated aliphatic hydrocarbon group (an alkyl group) or an unsaturated aliphatic hydrocarbon group (an alkenyl group or an alkynyl group). Divalent aromatic carboxylic acids are compounds in which two carboxy groups are bonded to an aromatic hydrocarbon.

[0035] The number of carbon atoms in the hydrocarbon group (i.e., saturated aliphatic hydrocarbon group or unsaturated aliphatic hydrocarbon group) contained in the divalent aliphatic carboxylic acid is preferably from 1 to 20, more preferably from 2 to 10, and even more preferably from 2 to 6. Examples of aromatic hydrocarbons contained in the divalent aromatic carboxylic acid include benzene, naphthalene, and phenanthrene, with benzene being preferred.

[0036] Specific examples of divalent aliphatic carboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. The divalent aliphatic carboxylic acids may have a substituent on the side chain. Examples of the substituent include a methyl group, a mercapto group, a hydroxy group, and an amino group. Specific examples of divalent aromatic carboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid. From the viewpoint of obtaining a raw material composite with a high crack propagation suppression effect, isophthalic acid, succinic acid, or suberic acid is preferred as the divalent carboxylic acid.

[0037] Examples of calcium salts include calcium carbonate, calcium phosphate, calcium acetate, and calcium chloride.

[0038] The ratio of the amounts of dicarboxylic acid, calcium salt, and phosphoric acid added (dicarboxylic acid:calcium salt:phosphoric acid) is preferably 1 or more:8:5 in molar ratio.

[0039] A method for reacting a dicarboxylic acid, a calcium salt, and phosphoric acid includes adding the dicarboxylic acid to water, adjusting the pH of the solution containing the dicarboxylic acid to 5 to 7 with aqueous ammonia, and then adding the calcium salt and phosphoric acid and stirring the mixture. After reacting the dicarboxylic acid, calcium salt, and phosphoric acid by the above method, the pH of the reaction solution is adjusted to 4 to 6 with hydrochloric acid or the like as necessary to remove excess calcium salts, etc., and the precipitate contained in the solution is preferably filtered and dried to obtain powdered specific octacalcium phosphate.

[0040] (Firing process) The firing step is a step of firing the powdered specific octacalcium phosphate. In the firing step, the powdered specific octacalcium phosphate is preferably fired at a temperature of 500° C. to 1000° C. for 1 hour to 48 hours.

[0041] The firing step is preferably carried out while flowing in an inert gas such as nitrogen. The flow rate of the inert gas such as nitrogen is preferably adjusted appropriately depending on the size of the heating device used in the firing step. When a tubular furnace with an inner diameter of 30 mm and a length of 500 mm is used as the heating device, the flow rate of nitrogen is preferably 10 mL / min or more and 20 mL / min or less.

[0042] The heating device is not particularly limited as long as it is capable of heating the molded body in an inert gas atmosphere at the above-mentioned temperature, and examples thereof include batch furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces; and continuous furnaces such as screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces.

[0043] <Zirconium oxide> The zirconium oxide contained in the calcium phosphate-carbon dioxide-zirconium oxide composite of the present disclosure is represented by ZrO2 and is also called zirconia. The zirconium oxide is not particularly limited, but it is preferable to use stabilized zirconia, which is a solid solution of an oxide. Examples of oxides include yttrium oxide (YO3), cesium oxide (Cs2O), calcium oxide (CaO), and magnesium oxide (MgO). Zirconium oxide undergoes a phase transition from monoclinic to tetragonal to cubic as the temperature rises from room temperature. Stabilized zirconia refers to zirconium oxide that is cubic or tetragonal at room temperature. Note that stabilized zirconia is not limited to zirconia that is entirely cubic or tetragonal, but also includes partially stabilized zirconia, in which the crystal phase is partially cubic or tetragonal and the remainder is monoclinic.

[0044] Among these, it is preferable to use stabilized zirconia, which is mainly tetragonal and is prepared by dissolving yttrium oxide (YO) as a stabilizer, as the zirconium oxide. The mainly tetragonal stabilized zirconia is not particularly limited, but can be obtained by dissolving yttrium oxide in a range of 1 mol% to 10 mol%, preferably 1 mol / % to 8 mol / %, more preferably 1 mol / % to 6 mol / %, even more preferably 1 mol / % to 4 mol / %, and most preferably 1 mol / % to 3 mol / %, for example, about 3 mol / % relative to the total of zirconium oxide and yttrium oxide.

[0045] The crystalline phase of zirconium oxide can be analyzed by X-ray diffraction, the intensities of the peaks based on monoclinic crystals, tetragonal crystals, and cubic crystals can be measured, and the proportion of crystalline phases contained in the analyzed zirconium oxide can be calculated. In the present disclosure, zirconium oxide being primarily tetragonal means that the proportion of crystalline phases calculated as above is 90% or more, particularly 93% or more, 95% or more, 97% or more, or 99% or more.

[0046] The zirconium oxide may be a commercially available zirconium oxide product or may be produced according to a standard method. Commercially available zirconium oxide products and zirconium oxide produced according to a standard method contain components derived from trace elements contained in the raw materials. Examples of trace elements contained in the raw materials include hafnium, vanadium, chromium, manganese, iron, cobalt, nickel, and niobium. Therefore, the raw materials containing zirconium oxide used to produce the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure may contain components derived from these trace elements.

[0047] <Method of manufacturing calcium phosphate-carbon atom-zirconium oxide composite> The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be produced by a step of molding a raw material composite containing tricalcium phosphate, an apatite represented by formula (1), and carbon atoms, and zirconium oxide to obtain a molded body, and a step of firing the molded body. This manufacturing method makes it possible to produce a calcium phosphate-carbon atom-zirconium oxide composite that has high strength and a low elastic modulus comparable to that of bone.

[0048] In the method for producing a calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, the amount of the raw composite is preferably 5% by mass to 50% by mass relative to the total amount of the raw composite and the zirconium oxide. Furthermore, in the method for producing a calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, the content of the raw composite is more preferably 5% by mass to 40% by mass, even more preferably 5% by mass to 30% by mass, even more preferably 5% by mass to 20% by mass, and even more preferably 8% by mass to 12% by mass. In the method for producing a calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, by setting the content of the raw composite within the above range, a calcium phosphate-carbon atom-zirconium oxide composite having higher strength and a lower elastic modulus can be produced.

[0049] In the method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to the present disclosure, in the step of molding the raw material composite and zirconium oxide to obtain a molded body, the powdered raw material composite and powdered zirconium oxide are mixed together. At this time, a mixer generally used for mixing powders or a mill device capable of mixing powders while performing pulverization processing can be used.

[0050] In the method for producing a calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure, the step of forming the raw material composite and zirconium oxide to obtain a molded body and the step of firing the molded body can be performed simultaneously by spark plasma sintering. Spark plasma sintering (SPS) is a processing method for sintering, joining, and synthesizing workpieces by mechanical pressure and pulse current heating. Note that the method for producing a calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure may also be a method in which the molded body is produced and then fired, without using the SPS method.

[0051] <Structure of calcium phosphate-carbon atom-zirconium oxide composite> The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure configured as described above includes a region containing zirconium oxide and a region containing a raw material composite disposed between the regions, as described above. To facilitate understanding of the structure, Fig. 1 shows a schematic cross-sectional view of the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure. Note that Fig. 1 is a schematic cross-sectional view of the composite, and does not in any way limit the technical scope of the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure.

[0052] As shown in FIG. 1 , in the cross section of the composite, region R1, which is a region containing zirconium oxide, is island-shaped, and region R2, which is a region containing the raw composite, is disposed so as to surround at least a portion of region R1 in the cross section. When a crack occurs in region R1 in the calcium phosphate-carbon dioxide-zirconium oxide composite of the present disclosure, the progression of the crack is suppressed by a stress-induced phase transition of zirconium oxide. That is, as shown schematically in FIG. 1 , although crack C propagates in the direction of arrow A, crack C imposes stress on zirconium oxide, causing a phase transition from tetragonal to monoclinic crystals near crack C. This phase transition increases the volume by approximately 4%, so that pressure is applied in the direction of arrow B in FIG. 1 , suppressing the progression of crack C. Furthermore, even if crack C reaches region R2, the progressing crack C can be deflected by cleavage in region R2 (arrow D in FIG. 1 ). This is because in region R2, the raw material composite has a laminated structure of calcium phosphate layers and layers containing carbon atoms, and cracks C are more likely to cleave between the layers than to propagate in the stacking direction. Thus, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be provided with high toughness due to the stress-induced phase transition in region R1 and the effect of deflecting the propagation direction of cracks C in region R2.

[0053] <Physical properties of calcium phosphate-carbon atom-zirconium oxide composite> The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure contains calcium phosphate in the raw material composite, and therefore has the ability to bind to bones in vivo. Furthermore, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure is characterized by exhibiting high strength and a low elastic modulus similar to those of bones in vivo, compared to other calcium phosphates and calcium phosphate composites. The strength of the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be evaluated, for example, by comparing its maximum bending stress with that of other materials. The elastic modulus of the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be evaluated, for example, by comparing its Young's modulus with that of other materials.

[0054] The procedure for measuring the maximum bending stress of the calcium phosphate-carbon dioxide-zirconium oxide composite of the present disclosure is as follows. First, the prepared sintered body was processed to prepare test pieces with dimensions of 15 mm length × 4 mm width × 1.2 mm thickness. Each prepared test piece was subjected to a three-point bending test using a bending strength tester (INSTRON5585, INSTRON, Massachusetts, USA) with a support distance of 10 mm, and the load displacement was measured (partially in accordance with JIS R1601 2008). Additionally, a three-point bending test is performed using a cemented carbide round bar with a support distance of 10 mm to obtain the load displacement of the bending jig. A numerical process is performed to subtract the load displacement of the bending jig from the load displacement of the test piece to obtain the measurement data. The range before the load is applied to the test piece is removed from the measurement data, and the load displacement curve is then approximated using a sixth-order polynomial to calculate the approximate equation. A coefficient is then subtracted from the approximate equation. A stress-strain curve is then created from the load displacement curve approximated by the sixth-order polynomial using the following equation: Bending strain = 6hw / L 2 Bending stress = 3PL / 2bh 2 where the variables in the above formula are as follows: Bending load: P, distance between supports: L, width of test piece: b, thickness of test piece: h, bending displacement: w The maximum values ​​of this stress-strain curve are defined as the maximum bending strain and maximum bending stress, respectively.

[0055] The procedure for measuring Young's modulus for the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure is as follows: A stress-strain curve obtained in the same manner as in the procedure for measuring maximum bending strain and maximum bending stress is linearly approximated in the range with good linearity (i.e., the elastic range), and the Young's modulus is calculated from the slope.

[0056] The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure has a maximum bending stress of preferably 320 MPa or more, more preferably 330 MPa or more, even more preferably 340 MPa or more, and even more preferably 350 MPa or more. The calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure has a Young's modulus of preferably 170 GPa or less, and even more preferably 160 GPa or less.

[0057] Furthermore, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure has excellent physical properties, such as a high maximum bending strain and a low Vickers hardness. Vickers hardness is measured in accordance with JIS R 1610:2003. That is, Vickers hardness is measured by pressing an indenter into the calcium phosphate-carbon atom-zirconium oxide composite using a micro Vickers hardness tester (product name: HM-114, manufactured by Mitutoyo Corporation) or a Vickers hardness tester (product name: HMV G20, manufactured by Shimadzu Corporation). The measurement is performed under the following measurement conditions: an indentation load of 0.05 kgf and an indentation time of 15 seconds. Furthermore, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure exhibits an excellent fracture toughness value Kc calculated by the indentation fracture method (IF method). In the IF method, a Vickers hardness tester is used in accordance with JIS R1607 to press a Vickers indenter into the test surface, the lengths of the resulting indentation and crack are measured, and the fracture toughness value Kc is calculated from the indentation load, the diagonal length of the indentation, the crack length, and the elastic modulus.

[0058] <Application example 1 of calcium phosphate-carbon atom-zirconium oxide composite> As described above, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure has both high strength and a low elastic modulus, and compared to conventionally known calcium phosphates, calcium phosphate composites, etc., it can be said to be a material that has the ability to bind to bone in a living body and has physical properties closer to those of bone. Therefore, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be used as a bone and tooth repair material. The term "repair material" refers to a material that fills in a defect (including a defect caused by artificial resection) in bone or tooth treatment, and includes artificial bones, artificial joints, artificial teeth, etc.

[0059] (bone repair material) One embodiment of the repair material of the present disclosure is a bone repair material containing the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure. The shape of the bone repair material of the present disclosure is not particularly limited, and it is preferably a shape that fits the damaged part of the bone. When the bone repair material is used to repair a damaged bone, it is preferably a shape that fits the shape of the damaged part of the bone.

[0060] (Method for repairing bone damage using bone repair materials) The bone repair material of the present disclosure can be applied to a damaged bone site to repair the damaged bone site. Methods for applying the bone repair material to a damaged bone site include, for example, embedding the bone repair material in the damaged bone site, and fixing the bone repair material to the damaged bone site using a fixing device such as a screw.

[0061] Specific methods for implanting bone repair material into the damaged bone site include implanting a bone repair material having a shape that fits the shape of the damaged bone site into the damaged bone site, or shaping the bone repair material to fit the shape of the damaged bone site and then implanting the bone repair material into the damaged bone site.

[0062] Methods for fixing a bone repair material to a damaged bone site using a fixing device such as a screw include, for example, a method using a bone repair material with a hole for inserting the screw, inserting the screw into the hole in the bone repair material, and fixing the screw into the damaged bone site (living bone). Another method includes a method for fixing a bone repair material to a damaged bone site using a screw and a bridging member.

[0063] <Application example 2 of calcium phosphate-carbon atom-zirconium oxide composite> As described above, the apatite-zirconium oxide composite of the present disclosure combines high strength with a low elastic modulus. Compared with conventionally known calcium phosphates and calcium phosphate composites, the apatite-zirconium oxide composite possesses in vivo bone-binding properties and is closer to the physical properties of bone. Therefore, the calcium phosphate-carbon atom-zirconium oxide composite of the present disclosure can be used not only as the above-mentioned restorative material, but also as medical devices such as screws and bridging members for fixing restorative materials such as artificial bones, artificial joints, and artificial teeth. The term "medical device" refers to a mechanical device or instrument intended to be used in the diagnosis, treatment, or prevention of human or animal diseases or to affect the structure or function of the human or animal body, excluding restorative materials such as artificial bones, artificial joints, and artificial teeth. In particular, the medical device of the present disclosure is preferably a mechanical device or instrument attached to the bones or teeth of a human or animal. Examples of such medical devices include, but are not limited to, screws, bridging members, and bone plates for fixing artificial bones, artificial joints, artificial teeth, and the like to damaged sites. [Example]

[0064] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0065] [Example 1] (Raw material complex) In this example, a raw material composite containing 98 mass % calcium phosphate and 2 mass % carbon atoms was prepared as the raw material composite. The raw material composite was prepared as follows. 25.0 mmol of isophthalic acid as a divalent aromatic carboxylic acid was added to 100 mL of ultrapure water at 60°C and stirred. Ammonia water was added to the solution to adjust the pH of the solution to 5.5. Next, 8.0 mmol of calcium carbonate and 5.0 mmol of phosphoric acid were added as calcium salts to the solution, and the solution was stirred at 60°C for 6 hours, and it was confirmed that a precipitate had formed in the solution. Thereafter, the pH of the solution was adjusted to 5.0 (60°C) using hydrochloric acid, and the solution was stirred at 60°C for 30 minutes. The precipitate contained in the solution was filtered and dried in a thermostatic chamber at 40°C to obtain powdered specific octacalcium phosphate (Ca8(HPO4)2(C6H4(COO)2)). 0.94 (PO4)4·nH2O (n has the same meaning as n in equation (3)) was obtained.

[0066] (Firing process) Powdered specific octacalcium phosphate was placed in a tubular furnace (inner dimensions: diameter 30 mm, length 500 mm; hereinafter the same). The temperature inside the furnace was raised at a rate of 5°C / min until it reached 1000°C. The powdered specific octacalcium phosphate was then fired at 1000°C for 24 hours and allowed to cool to obtain a composite. During the firing process, the flow rate of nitrogen flowing inside the furnace was 15 mL / min.

[0067] (zirconium oxide) In this example, zirconium oxide powder containing 3 mol % of yttrium oxide was used, and the zirconium oxide powder used was trade name TZ-3Y-E (Tosoh Corporation).

[0068] (Pressure molding, firing process) In this example, the zirconium oxide powder and the raw material composite powder were weighed out to a weight ratio of 90:10 and thoroughly mixed. Then, in this example, a LABOX325R manufactured by Sinterland Co., Ltd. was used as a spark plasma sintering apparatus, and pressure molding and sintering processes were simultaneously carried out under vacuum conditions of 1250°C, 3 minutes, and 100 MPa to produce a cylindrical sample.

[0069] [Comparative Example 1] A cylindrical sample was prepared in the same manner as in Example 1, except that only apatite was used. The apatite used was HAP-200 (Taihei Chemical Industry Co., Ltd.).

[0070] Comparative Example 2 A cylindrical sample was prepared in the same manner as in Example 1, except that the zirconium oxide used in Example 1 was used and no raw material composite was used.

[0071] Comparative Example 3 A cylindrical sample was prepared in the same manner as in Example 1, except that the weight ratio of the zirconium oxide used in Example 1 to the apatite used in Comparative Example 1 was 90:10.

[0072] Comparative Example 4 The powdered specific octacalcium phosphate prepared in Example 1 was molded using a press (RIKEN SEIKI, product name P-168) to obtain a disk-shaped molded body (diameter 20 mm, thickness 2 mm). The molded body was then placed in a tubular furnace (interior dimensions: diameter 30 mm, length 500 mm; the same applies hereinafter). The temperature inside the furnace was increased at a heating rate of 5°C / min to 1000°C. The molded body was then fired at 1000°C for 24 hours and allowed to cool to obtain a composite. Note that during the firing process, the flow rate of nitrogen flowing into the furnace was 15 mL / min. The cylindrical sample prepared as described above was designated Comparative Example 4.

[0073] <Physical property evaluation> The samples prepared in Example 1 and Comparative Examples 1 to 4 were measured for maximum bending stress, maximum bending strain, Young's modulus, Vickers hardness, and fracture toughness according to the procedures described above. The results are shown in Table 1. The three-point bending test was performed using an Instron universal testing machine, Model 5582, with test specimens measuring 15 mm length x 4 mm width x 1.2 mm thickness. The Vickers hardness test for Example 1 and Comparative Examples 1 to 3 was performed using a micro Vickers hardness tester HM-114 (Mitutoyo Corporation). The Vickers hardness test for Comparative Example 4 was performed using a Vickers hardness tester (product name: HMV G20, manufactured by Shimadzu Corporation).

[0074] [Table 1]

[0075] In Table 1, the fracture toughness value of Example 1 is a reference value calculated assuming a crack length of 1 μm. Furthermore, for cortical bone, the maximum bending stress is set to 50 MPa to 150 MPa, and the Young's modulus is set to 7 GPa to 30 GPa.

[0076] <Microstructure observation> The surface microstructures of the samples prepared in Example 1 and Comparative Examples 1 to 3 were observed using a scanning electron microscope (SEM). SEM photographs of the sample of Example 1 are shown in Fig. 2(A), the sample of Comparative Example 1 in Fig. 2(B), the sample of Comparative Example 2 in Fig. 2(C), and the sample of Comparative Example 3 in Fig. 2(D). In addition, Fig. 3(A) shows an enlarged SEM photograph taken of the sample of Example 1, and Fig. 3(B) shows a further enlarged version of the SEM photograph shown in Fig. 3(A).

[0077] <Element distribution evaluation> The Ca distribution and Zr distribution were evaluated for the sample prepared in Example 1 and the sample prepared in Comparative Example 3. The Ca distribution was measured as follows: That is, while observing the sample with a scanning electron microscope (SEM), the measurement was performed using energy dispersive X-ray spectroscopy attached to the SEM. The method for analyzing the Zr distribution was the same as the method for analyzing the Ca distribution. FIG. 4(A) shows a photograph of the measurement results for the sample of Example 1, and FIG. 4(B) shows a photograph of the measurement results for the sample of Comparative Example 3.

[0078] <Cell proliferation test> The influence on cell proliferation of the samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 was evaluated by a cell proliferation test. The cell proliferation test was carried out according to the following procedure. Osteoblast cell lines, culture and seeding protocols Mouse osteoblastic cells (MC3T3-E1) (RIKEN Cell Bank; Tokyo, Japan; Sudo, H et al. 1983, J. Cell Biol. 96(1):191-198) were maintained in Dulbecco's modified Eagle's medium (DMEM, supplied by SIGMA-ALDRICH) supplemented with 10% fetal bovine serum (Gibco), 100 μg / ml penicillin, and 100 μg / ml streptomycin (Fujifilm Wako Pure Chemical Industries, Ltd.) in a humidified atmosphere of 95% air and 5% CO2 and passaged every 4 days using standard techniques. Before seeding, each sample was sterilized by dry heat at 160°C for 120 minutes, rinsed twice with sterile water, and dried in a sterile hood. MC3T3-E1 cells were trypsinized, collected, and plated on the sample-containing dishes at 1000 cells / cm2 for cell growth determination. 2 , for determination of cell area 6000 cells / cm 2 All were seeded in the same medium as above at a density of 1000 x g. <Evaluation Protocol> Cell proliferation was assessed by measuring intracellular dehydrogenase activity by absorbance using the Cell Counting Kit-8 (CCK-8, Dojindo Laboratories). Osteoblastic cells (MC3T3-E1) were cultured as described above. Cell proliferation on each sample was assessed 3 and 7 days after seeding by washing the cell-containing sample with PBS. Cells on the sample were then added to a medium containing 1-(2-Methoxy-4-nitrophenyl)-3-(2,4-disulfophenyl)-5-(4-nitrophenyl)formazan, disodium salt hydrate (WST-8) and incubated for 3 hours in a 5% CO2 incubator at 37°C. After the color reaction, the reacted medium was transferred to a 96-well plate and the absorbance was measured using a microplate reader (GloMAX Discover System GM3000, Promega, Tokyo). A calibration curve was prepared using cells cultured in a 60-mm culture dish. The results of the cell proliferation test are shown in FIG.

[0079] <Evaluation> As shown in Table 1, the sample of Example 1 was found to have physical properties that combine high strength and low Young's modulus, and are closer to the physical properties of living bone, compared to the samples of Comparative Examples 1 to 4. Further, as shown in FIGS. 2 to 4, in the sample of Example 1, the region containing zirconium oxide was in an island shape, and the region containing the raw material composite was arranged between these island-shaped regions. Also, the region containing the raw material composite in the sample of Example 1 showed a structure in which layers of apatite and layers of carbon atoms were laminated, suggesting a structure that can deflect the progress of cracks by cleavage. Furthermore, as shown in FIG. 5, it was revealed that the sample of Example 1 has an influence on cell growth comparable to that of the sample of Comparative Example 1 and is superior to the sample of Comparative Example 2.

[0080] [Test Examples 1 to 4] In Test Examples 1 to 4, zirconium oxide without yttrium oxide (product name 264-01482, FUJIFILM Wako Pure Chemical Corporation) was used, and molded bodies were prepared with weight ratios of zirconium oxide to the octacalcium phosphate containing isophthalic acid prepared in Example 1 of 100:0, 90:10, 80:20, and 50:50, respectively. A firing process was performed under conditions of 1000 °C for 24 hours and normal pressure to prepare samples.

[0081] <X-ray Diffraction Analysis> For the samples prepared in Test Examples 1 to 4, the crystal phase was evaluated using an X-ray diffractometer MiniFlex (Rigaku Corporation). The results of the X-ray diffraction analysis are summarized in FIG. 6.

[0082] <Evaluation of Osteoconductivity> The bone-bonding ability of the samples prepared in Test Examples 1 to 4 was evaluated using simulated body fluid (SBF). SBF is an aqueous solution with a composition nearly equivalent to the inorganic ion concentration of human plasma, and is a solution that is supersaturated with respect to apatite. Therefore, if apatite is formed when a sample is immersed in SBF, it is expected that the sample will also form apatite on the material surface in vivo and bond to bone. The evaluation of bone-bonding ability using SBF complies with ISO 23317:2014.

[0083] Photographs of the samples prepared in Test Examples 1 to 4 taken before and after immersion in SBF are shown in FIG.

[0084] <Result> As shown in FIG. 6, it was confirmed that the samples prepared in Test Examples 2 to 4 formed a composite of zirconium oxide and calcium phosphate. Furthermore, as shown in FIG. 7, it was confirmed that the samples prepared in Test Examples 2 to 4 underwent vigorous apatite formation when immersed in SBF. It was shown that a composite with bone-bonding ability could be formed when the amount of isophthalic acid-containing calcium phosphate added to zirconium oxide was in the range of 10% by mass to 50% by mass. Furthermore, in Test Example 2, where the weight ratio of zirconium oxide to calcium phosphate was 90:10, the extremely vigorous apatite formation strongly suggested that a composite with bone-bonding ability could be formed even when the weight ratio of zirconium oxide to calcium phosphate was 95:5.

[0085] These results strongly suggest that in Example 1, even for samples prepared with a raw material composite in an amount of 5% by mass to 50% by mass relative to the total amount of raw material composite and zirconium oxide, it is possible to prepare composites that have bone bonding ability and combine high strength with a low Young's modulus.

Claims

1. A calcium phosphate-carbon atom-zirconium oxide composite comprising: a raw composite containing tricalcium phosphate, an apatite represented by formula (1), and carbon atoms; and zirconium oxide. Formula (1): Ca ｓ (PO ４ ) ｔ (X) ｕ (In formula (1), X is OH and CO ３ represents at least one selected from the group consisting of s represents a number from 8 to 10, t represents a number from 4 to 6, u represents the number 1 or 2.)

2. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, wherein the raw composite is contained in an amount of 5% by mass to 50% by mass with respect to the total amount of the raw composite and the zirconium oxide.

3. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, wherein the zirconium oxide is stabilized zirconia in which an oxide is dissolved in a solid solution.

4. 4. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 3, wherein the oxide is at least one selected from the group consisting of yttrium oxide, cesium oxide, calcium oxide, and magnesium oxide.

5. 2. The calcium phosphate-carbon atom-zirconium oxide composite of claim 1, wherein the zirconium oxide is predominantly tetragonal.

6. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, wherein the zirconium oxide is island-shaped in a cross section of the composite, and the raw material composite is arranged so as to surround at least a part of the periphery of the zirconium oxide in the cross section.

7. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, wherein the raw material composite has a layered structure of a layer containing the tricalcium phosphate and the apatite and a layer containing the carbon atom.

8. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, which has a maximum bending strength of 320 MPa or more.

9. 2. The calcium phosphate-carbon atom-zirconium oxide composite according to claim 1, having a Young's modulus of 170 GPa or less.

10. A restorative material comprising the calcium phosphate-carbon atom-zirconium oxide composite according to any one of claims 1 to 9.

11. 11. The restorative material of claim 10 for use in bone or tooth treatment.

12. A medical device comprising the repair material of claim 10 or claim 11.

13. a step of molding a raw material composite containing tricalcium phosphate, an apatite represented by formula (1), and carbon atoms, and zirconium oxide to obtain a molded body; sintering the compact; A method for producing a calcium phosphate-carbon atom-zirconium oxide composite having the formula: Formula (1): Ca ｓ (PO ４ ) ｔ (X) ｕ (In formula (1), X is OH and CO ３ represents at least one selected from the group consisting of s represents a number from 8 to 10, t represents a number from 4 to 6, u represents the number 1 or 2.)

14. The method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 13, wherein the step of obtaining the compact and the step of firing are carried out simultaneously by a spark plasma sintering method.

15. 14. The method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 13, wherein the amount of the raw composite is 5% by mass to 50% by mass with respect to the total amount of the raw composite and the zirconium oxide.

16. The method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 13, wherein the zirconium oxide is stabilized zirconia in which an oxide is dissolved in a solid solution.

17. 17. The method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 16, wherein the oxide is at least one selected from the group consisting of yttrium oxide, cesium oxide, calcium oxide, and magnesium oxide.

18. The method for producing a calcium phosphate-carbon atom-zirconium oxide composite according to claim 13, wherein the zirconium oxide is mainly tetragonal.

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