Structure and method for manufacturing same

Abstract

A structure (1) includes a plurality of crystal grains (2) containing a calcium phosphate compound, and a bonding portion (3) that bonds each of the crystal grains (2) and contains a calcium phosphate compound. The average grain diameter of the crystal grains (2) is 60 nm or less. The relative density of the structure (1) is 80% or more. When the thickness of the structure (1) is 1 mm, the total light transmittance of light having a wavelength of 589 nm is 45% or more. The Vickers hardness of the structure (1) is 1 GPa or more.

Description

Technical Field

[0001] The present invention relates to a structure and a method for manufacturing the same. Background Art

[0002] As a method for manufacturing inorganic components composed of ceramics, a sintering method is known. The sintering method is a method of obtaining a sintered body by heating an aggregate of solid powders composed of inorganic substances at a temperature lower than the melting point. However, the sintering method requires heating the solid powders at high temperatures, which results in high energy consumption and high costs during manufacturing. Therefore, methods for combining solid powders composed of inorganic substances at low temperatures have been developed.

[0003] Patent Document 1 discloses a transparent calcium phosphate obtained by allowing a dispersion containing calcium phosphate dispersed in a solvent to dry at a temperature within the range of higher than the freezing point of the solvent and 100°C higher than the boiling point of the solvent. The transparent calcium phosphate, when formed into a film having a thickness of 500 μm, has a visible light transmittance within the range of 30% to 100%.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-246299 Summary of the Invention

[0007] However, the transparent calcium phosphate body described in Patent Document 1 may not have sufficient mechanical strength.

[0008] The present invention has been made in view of the problems of the prior art. Another object of the present invention is to provide a structure having excellent mechanical strength and light transmittance, and a method for producing the structure that can be produced under low temperature conditions.

[0009] To address the above-mentioned issues, a first embodiment of the present invention relates to a structure comprising: a plurality of crystal grains containing a calcium phosphate compound; and a bonding portion connecting the crystal grains and containing the calcium phosphate compound. The average grain size of the crystal grains is 60 nm or less. The relative density of the structure is 80% or greater. When the structure has a thickness of 1 mm, the total light transmittance at a wavelength of 589 nm is 45% or greater. The Vickers hardness of the structure is 1 GPa or greater.

[0010] The method for manufacturing a structure according to a second aspect of the present invention comprises the following steps: pressurizing and heating a mixture comprising raw material particles having an average particle size of 60 nm or less and containing crystals of a calcium phosphate compound, and an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or greater, under conditions of a pressure of 3000 MPa or less and a temperature of 300° C. or less for 20 minutes or more and 12 hours or less. The mixture comprises: raw material particles having an average particle size of 60 nm or less and containing crystals of a calcium phosphate compound; and an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or greater. The relative density of the structure is 80% or greater. When the structure has a thickness of 1 mm, the total light transmittance of light having a wavelength of 589 nm is 45% or greater, and the Vickers hardness of the structure is 1 GPa or greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] [ Figure 1 ] Figure 1 This is a cross-sectional view schematically showing an example of a structure according to this embodiment.

[0012] [ Figure 2 ] Figure 2 This is a schematic diagram showing a state in which an aqueous solution exists between adjacent crystal grains during the manufacturing process of a structure.

[0013] [ Figure 3 ] Figure 3 It is a schematic diagram showing a state where a bonding portion is formed between adjacent crystal grains.

[0014] [ Figure 4 ] Figure 4 This is a graph showing the relationship between the heating time of raw material particles and the relative density of the structure.

[0015] [ Figure 5 ] Figure 5 This is a graph showing the relationship between the wavelength and the total light transmittance of the structure of the Example.

[0016] [ Figure 6 ] Figure 6 This is a graph showing the relationship between the heating time of raw material particles and the Vickers hardness and fracture toughness of the structure.

[0017] [ Figure 7 ] Figure 7 This is a graph showing the relationship between the heating time of raw material particles and the biaxial bending strength and Young's modulus of the structure.

[0018] [ Figure 8 ] Figure 8 This is an SEM image of the raw material particles used in Examples observed at a magnification of 200,000 times.

[0019] [ Figure 9 ] Figure 9 This is an SEM image of a cross section of the structure of Example 1 observed at a magnification of 30,000 times.

[0020] [ Figure 10 ] Figure 10 This is a SEM image of a cross section of the structure of Example 1 observed at a magnification of 70,000 times.

[0021] [ Figure 11 ] Figure 11 This is an SEM image of a cross section of the structure of Example 2 observed at a magnification of 30,000 times.

[0022] [ Figure 12 ] Figure 12 This is a SEM image of a cross section of the structure of Example 2 observed at a magnification of 70,000 times.

[0023] [ Figure 13 ] Figure 13 This is an SEM image of a cross section of the structure of Example 3 observed at a magnification of 30,000 times.

[0024] [ Figure 14 ] Figure 14 This is an SEM image of a cross section of the structure of Example 3 observed at a magnification of 70,000 times.

[0025] [ Figure 15 ] Figure 15 This is an SEM image of the cross section of the structure according to Example 4 observed at a magnification of 30,000 times.

[0026] [ Figure 16 ] Figure 16 This is a SEM image of the cross section of the structure according to Example 4 observed at a magnification of 70,000 times.

[0027] [ Figure 17 ] Figure 17 This is a TEM image of raw material particles used in examples.

[0028] [ Figure 18 ] Figure 18 This is a TEM image of a cross section of the structure of Example 1.

[0029] [ Figure 19 ] Figure 19 This is a TEM image of a cross section of the structure of Example 4.

[0030] [ Figure 20 ] Figure 20 This is a TEM image of a cross section of the structure of Example 4 that was further magnified and observed.

[0031] [ Figure 21 ] Figure 21 This is a SEM image of the cross section of the structure according to Example 1 observed at a magnification of 30,000 times.

[0032] [ Figure 22 ] Figure 22 This is a SEM image of the cross section of the structure according to Example 1 observed at a magnification of 100,000 times.

[0033] [ Figure 23 ] Figure 23 This is an SEM image of a cross section of a structure of a comparative example observed at a magnification of 30,000 times.

[0034] [ Figure 24 ] Figure 24 This is an SEM image of a cross section of a structure of a comparative example observed at a magnification of 100,000 times.

[0035] [ Figure 25 ] Figure 25 This is a graph showing the relationship between the heating time of raw material particles and the aspect ratio of the raw material particles.

[0036] [ Figure 26 ] Figure 26 It is a figure which shows the X-ray diffraction pattern of the structure body concerning Example 1 - Example 4.

[0037] [ Figure 27 ] Figure 27 Graphs showing X-ray diffraction patterns of raw material particles used in Examples and an X-ray diffraction pattern of the structure of Example 4. DETAILED DESCRIPTION

[0038] Hereinafter, the structure and the manufacturing method of the present embodiment will be described in detail using the drawings. Dimension ratios in the drawings are exaggerated for ease of description and may differ from actual ratios.

[0039] [Structure]

[0040] like Figure 1 As shown, the structure 1 of this embodiment includes a plurality of crystal grains 2 and a bonding portion 3 that bonds the crystal grains 2. Adjacent crystal grains 2 are bonded to form a structure 1 in which the crystal grains 2 are connected. The crystal grains 2 may be in point contact or in surface contact, where the grain surfaces of the crystal grains 2 are in contact with each other.

[0041] The crystal grains 2 contain a calcium phosphate compound. A calcium phosphate compound is a compound containing phosphorus and calcium. Specifically, a calcium phosphate compound is a calcium ion (Ca 2+ ) and phosphate ions (PO4 3- ), phosphite ion (HPO3 2- ), diphosphate ion (P2O7 4- ) or metaphosphoric acid (PO3 -) is a general term for salts of phosphate. Calcium phosphate compounds can include apatite, calcium monohydrogen phosphate CaH(PO4), calcium dihydrogen phosphate (Ca(H2PO4)2), tricalcium phosphate (Ca3(PO4)2), Ca 10 (PO4)6F2、Ca 10 (PO4)6Cl2, dicalcium diphosphate (Ca2P2O7), calcium metaphosphate (Ca(PO3)2), or a combination thereof.

[0042] Apatite may include at least one selected from the group consisting of fluorapatite, chlorapatite and hydroxyapatite (hydroxyapatite). Specifically, hydroxyapatite, for example, has a composition formula: Ca 10 (PO4)6(OH)2 represents. Regarding apatite, in Ca 10 In the composition formula (PO4)6(OH)2, a portion of Ca can be replaced by at least one of alkaline earth metals other than Ca and lead. 10 A portion of P in the composition formula represented by (PO4)6(OH)2 can be replaced by at least one selected from the group consisting of As, V and S. 10 In the composition formula represented by (PO4)6(OH)2, OH may be replaced by at least one selected from the group consisting of F, Cl, Br, O and CO3.

[0043] The grains 2 preferably contain Ca 10-x (HPO4) x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by (0≤x<1). Thus, structure 1 becomes structurally and chemically stable. Therefore, structure 1 can be suitably used as, for example, a biological material or an optical material. Furthermore, as described above, fluorine plasma can be introduced into such hydroxyapatite. Therefore, a variety of structures 1 can be obtained.

[0044] The crystal grains 2 preferably contain apatite crystals. Apatite crystals have a higher mechanical strength than amorphous ones. When the crystal grains 2 contain apatite crystals, the strength of the crystal grains 2 is improved. Therefore, the mechanical strength of the structure 1 can be further improved.

[0045] The crystal grains 2 contain a calcium phosphate compound as a main component. Here, the crystal grains 2 containing a calcium phosphate compound as a main component means that the crystal grains 2 contain 50% by mass or more of the calcium phosphate compound. The crystal grains 2 may contain 60% by mass or more of the calcium phosphate compound, or 70% by mass or more, or 80% by mass or more, or 90% by mass or more, or 95% by mass or more, or 99% by mass or more.

[0046] The average particle size of the crystal grains 2 is 60 nm or less. By making the average particle size 60 nm or less, the deviation of the internal structure of the structure 1 becomes smaller and becomes denser, so the mechanical strength and light transmittance of the structure 1 become higher. The average particle size is preferably 50 nm or less, more preferably 40 nm or less. There is no special limit on the lower limit of the average particle size of the crystal grains 2, and the average particle size can be 1 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more. It should be noted that in this specification, unless otherwise specified, the "average particle size" is the average value of the diameter converted into a circle by converting particles observed in several to dozens of fields of view using a microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0047] The shape of the crystal grains 2 is not particularly limited, and may be, for example, spherical particles or ellipsoidal particles. Alternatively, the crystal grains 2 may be polyhedral particles including cubes and rectangular parallelepipeds, whisker-like (needle-like) particles, or scaly particles.

[0048] The aspect ratio of the crystal grains 2 may be 2 or less. If the aspect ratio is below the above value, the anisotropy of the crystal grains 2 in the structure 1 becomes smaller, and sometimes the light transmittance is improved. In addition, if the aspect ratio is below the above value, the structure in the structure 1 becomes denser, and sometimes the mechanical strength is improved. The aspect ratio of the crystal grains 2 may be less than 1.8, less than 1.5, less than 1.3, or less than 1.2. In addition, the aspect ratio of the crystal grains 2 is the ratio of the length of the major axis direction of each crystal grain 2 to the length of the minor axis direction. The lengths of the minor axis direction and the major axis direction of the crystal grains 2 can be measured by observation with a microscope such as a transmission microscope.

[0049] The bonding portion 3 contains a calcium phosphate compound. The phosphate compound contained in the bonding portion 3 can be the calcium phosphate compound contained in the crystal grains 2 as described above.

[0050] The binding portion 3 preferably contains Ca 10-x (HPO4) x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by (0≤x<1). Thus, the structure 1 becomes structurally and chemically stable. Therefore, for example, the structure 1 of this embodiment can be suitably used as a biological material, an optical material, a structural material, etc. Furthermore, as described above, fluorine ions can be introduced into such hydroxyapatite. Therefore, a variety of structures 1 can be obtained.

[0051] The binding portion 3 contains a calcium phosphate compound as a main component. Here, the binding portion 3 containing a calcium phosphate compound as a main component means that the binding portion 3 contains 50% by mass or more of the calcium phosphate compound. The binding portion 3 may contain 60% by mass or more of the calcium phosphate compound, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more.

[0052] The calcium phosphate compound contained in the binding portion 3 may be the same as or different from the calcium phosphate compound contained in the crystal grains 2. It should be noted that when the calcium phosphate compound contained in the binding portion 3 is the same as the calcium phosphate compound contained in the crystal grains 2, light is not easily refracted at the interface between the crystal grains 2 and the binding portion 3, and the total light transmittance of the structure 1 can be improved, which is therefore preferred.

[0053] The refractive index difference between the crystal grain 2 and the bonding portion 3 is preferably 0.05 or less, more preferably 0.03 or less, and further preferably 0.01 or less. By making the refractive index difference below the above value, the refraction of light at the interface between the crystal grain 2 and the bonding portion 3 can be suppressed, thereby improving the total light transmittance of the structure 1. It should be noted that the lower limit of the refractive index difference is not particularly limited, and the refractive index difference is greater than 0. In addition, the refractive index can be the value of the NaD line (589 nm) measured using an Abbe refractometer.

[0054] The bonding portion 3 may be amorphous, crystalline, or a mixture thereof. Regardless of its state, the bonding portion 3 preferably comprises apatite crystals. Apatite crystals have a higher mechanical strength than amorphous ones. When the bonding portion 3 comprises apatite crystals, the strength of the bonding portion 3 is improved. Therefore, the mechanical strength of the structure 1 can be further improved. From the perspective of reducing the refractive index difference between the crystal grains 2 and the bonding portion 3, the compound constituting the crystals of the bonding portion 3 is preferably the same as the compound constituting the crystal grains 2.

[0055] The content of the crystal grains 2 in the structure 1 may be 50% by volume or more, 60% by volume or more, 70% by volume or more, or 80% by volume or more. Furthermore, the total content of the crystal grains 2 and the bonding portion 3 in the structure 1 may be 50% by volume or more, 70% by volume or more, 90% by volume or more, or 99% by volume or more.

[0056] The relative density of the structure 1 is 80% or greater. This makes the internal structure of the structure 1 denser, thereby improving the mechanical strength of the structure 1. The relative density is preferably 90% or greater. It should be noted that the relative density may be greater than 90%, greater than 93%, greater than 94%, greater than 95%, or greater than 97%. It should be noted that there is no particular upper limit to the relative density, and the relative density may be 100% or less. The relative density can be measured by the method described in the Examples section below.

[0057] When the thickness of the structure 1 is 1 mm, the total light transmittance for light of a wavelength of 589 nm is 45% or greater. By increasing the total light transmittance to a value greater than this, the light transmittance of the structure 1 can be improved. The total light transmittance can be greater than 60%, greater than 70%, greater than 71%, greater than 74%, or greater than 80%. It should be noted that there is no particular upper limit to the total light transmittance, and the total light transmittance can be 100% or less. The total light transmittance can be measured by the method described in the Examples section below.

[0058] The Vickers hardness of the structure 1 is 1 GPa or more. By having a Vickers hardness of at least the above value, the mechanical strength of the structure 1 can be improved. The Vickers hardness may be greater than 2 GPa, greater than 2.3 GPa, greater than 3 GPa, or greater than 3.5 GPa. It should be noted that the upper limit of the Vickers hardness is not particularly limited, and for example, may be 10 GPa or less. The Vickers hardness can be measured by the method described in the Examples section below.

[0059] The fracture toughness of the structure 1 is preferably 0.3 MPa·m 1 / 2 When the fracture toughness is greater than the above value, the mechanical strength of the structure 1 can be improved. The fracture toughness can exceed 0.4 MPa·m 1 / 2 , more than 0.43MPa·m 1 / 2 , more than 0.47MPa·m 1 / 2 , more than 0.56MPa·m 1 / 2 The upper limit of fracture toughness is not particularly limited, and may be, for example, 1 MPa·m 1 / 2 The fracture toughness can be measured by the method described in the Examples section below.

[0060] The biaxial flexural strength of the structure 1 is preferably 20 MPa or greater. By having a biaxial flexural strength above this value, the mechanical strength of the structure 1 can be improved. The biaxial flexural strength may exceed 25 MPa, or may exceed 31 MPa, 35 MPa, or 38 MPa. The upper limit of the biaxial flexural strength is not particularly limited, and for example, may be 100 MPa or less. The biaxial flexural strength can be measured by the method described in the Examples section below.

[0061] The Young's modulus of the structure 1 is preferably 40 MPa or greater. A Young's modulus of at least this value can improve the mechanical strength of the structure 1. The Young's modulus may be greater than 50 MPa, greater than 60 MPa, greater than 62 MPa, greater than 65 MPa, or greater than 75 MPa. The Young's modulus can be measured by the method described in the Examples section below.

[0062] The structure 1 may have pores between adjacent crystal grains 2. The porosity in the cross section of the structure 1 is preferably 15% or less. That is, when observing the cross section of the structure 1, the average value of the ratio of pores per unit area is preferably 15% or less. When the porosity is 15% or less, the ratio of the crystal grains 2 bonding to each other increases, so the structure 1 becomes dense and the mechanical strength can be improved. In addition, when the porosity is 15% or less, the structure 1 can be suppressed from cracking starting from the pores, so the bending strength of the structure 1 can be improved. It should be noted that the porosity in the cross section of the structure 1 is more preferably 10% or less, and further preferably 5% or less. The smaller the porosity in the cross section of the structure 1, the more cracks starting from the pores are suppressed, so the strength of the structure 1 can be improved.

[0063] In this specification, the porosity can be calculated as follows. First, observe the cross section of the structure 1 to distinguish the grains 2 and the pores. Then, measure the unit area and the area of ​​the pores in the unit area to calculate the ratio of the pores per unit area. After calculating the ratio of such pores per unit area at multiple locations, the average value of the ratio of the pores per unit area is taken as the porosity. It should be noted that when observing the cross section of the structure 1, an optical microscope, a scanning electron microscope (SEM) or a transmission electron microscope (TEM) can be used. In addition, the unit area and the area of ​​the pores in the unit area can also be measured by binarizing the image observed with a microscope.

[0064] The size of the pores present in the structure 1 is not particularly limited, but is preferably as small as possible. Small pore size can suppress cracks originating from the pores, thereby improving the mechanical strength of the structure 1. It should be noted that the size of the pores in the structure 1 is preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 100 nm or less. The size of the pores present in the structure 1 can be determined by observing a cross section of the structure 1 under a microscope, similar to the porosity described above.

[0065] When structure 1 comprises apatite crystals, the peak intensity from the (300) plane in the XRD pattern of structure 1 using CuKα radiation as the X-ray source may be higher than the peak intensity from the (002) plane. This reduces the anisotropy of crystal grains 2. Consequently, the light transmittance of structure 1 may be increased.

[0066] The shape of the structure 1 is not particularly limited, and the shape of the structure 1 can be, for example, a plate, a film, a rectangle, a block, a rod or a sphere. In addition, when the structure 1 is plate-shaped or film-shaped, its thickness t is not particularly limited, and for example, it can be 50 μm or more. As described later, the structure 1 of this embodiment is formed by a pressurized heating method. Therefore, a structure 1 with a large thickness can be easily obtained. It should be noted that the thickness t of the structure 1 can be 1 mm or more, or 1 cm or more. The upper limit of the thickness t of the structure 1 is not particularly limited, and for example, it can be 50 cm.

[0067] Thus, the structure 1 of this embodiment includes: a plurality of crystal grains 2 containing a calcium phosphate compound, and a bonding portion 3 that bonds the crystal grains 2 and contains the calcium phosphate compound. The average particle size of the crystal grains 2 is 60 nm or less. The relative density of the structure 1 is 80% or greater. When the thickness of the structure 1 is 1 mm, the total light transmittance of light with a wavelength of 589 nm is 45% or greater. The Vickers hardness of the structure 1 is 1 GPa or greater. As a result, the internal structure of the structure 1 becomes dense, and the light transmittance ratio increases. Therefore, the structure 1 has excellent mechanical strength and light transmittance. In addition, as described later, the structure 1 can be manufactured under low temperature conditions. Therefore, compared to structures manufactured under high temperature conditions such as high temperature sintering, a structure 1 with lower crystallinity can be obtained, and thus a structure 1 with higher reactivity, such as biological activity, can be obtained. In addition, the crystal grains 2 of the structure 1 of this embodiment are small and have a large surface area. Compared to structures manufactured under high temperature conditions such as high temperature sintering, a larger amount of hydroxyl groups with infrared absorption ability remain in the structure 1. Therefore, it is also possible to provide the structure 1 having infrared shielding capability.

[0068] [Method for manufacturing structure]

[0069] Next, the method for producing the structure 1 of this embodiment is described. The method for producing the structure 1 includes the steps of mixing raw material particles containing crystals of a calcium phosphate compound with an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or higher to prepare a mixture; and heating and pressurizing the mixture.

[0070] The method for producing the structure 1 according to this embodiment utilizes a biomineralization reaction, in which organisms produce minerals (inorganic compounds) within their own bodies. The method for producing the structure 1 involves heating raw material particles and the aqueous solution while applying pressure to cause the raw material particles and the aqueous solution to react, thereby forming a bond 3 on the surface of a crystal grain 2 derived from the raw material particles.

[0071] The method for preparing the raw material particles is not particularly limited and can be prepared, for example, by a sol-gel method. The raw material particles can be formed, for example, from a calcium salt such as calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and a hydrogen phosphate such as diammonium hydrogen phosphate ((NH4)2HPO4).

[0072] The raw material particles contain a calcium phosphate compound. The raw material particles may contain the same calcium phosphate compound as the above-mentioned crystal grains 2. The composition of the raw material particles is the same as that of the above-mentioned crystal grains 2, so the description thereof is omitted.

[0073] The average particle size of the raw material particles is not particularly limited and is 60 nm or less. By making the average particle size of the raw material particles within this range, the reactivity with the aqueous solution can be improved, and the bonding portion 3 can be easily formed. The average particle size is preferably 50 nm or less, more preferably 40 nm or less. The lower limit of the average particle size is not particularly limited, and the average particle size can be 1 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more. It should be noted that in this specification, unless otherwise specified, the "average particle size" is the average value of the diameters converted into circles by converting particles observed in several to dozens of fields of view using a microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0074] The shape of the raw material particles is not particularly limited, and may be, for example, spherical particles or ellipsoidal particles. In addition, the raw material particles may be polyhedral particles including cubes and rectangular parallelepipeds, whisker-like (needle-like) particles, or scaly particles.

[0075] The aspect ratio of the raw material particles can be greater than 1 and less than 10. The aspect ratio of the raw material particles can be greater than 1.5, greater than 1.8, or greater than 2. Alternatively, the aspect ratio of the raw material particles can be less than 8, less than 5, less than 3, or less than 2.5. The aspect ratio of the raw material particles is the ratio of the length of the major axis to the length of the minor axis of each raw material particle. The lengths of the minor and major axes of the raw material particles can be measured by observation using a microscope such as a transmission microscope.

[0076] The aqueous solution may contain less than 360 mM sodium ions (Na + ). Such an aqueous solution is close to the composition of commonly used simulated body fluids. The above aqueous solution may contain less than 290mM, less than 220mM or less than 180mM sodium ions (Na + In addition, the aqueous solution may contain more than 40mM, more than 80mM or more than 120mM sodium ions (Na + ).

[0077] The aqueous solution may contain less than 13 mM potassium ions (K +Such an aqueous solution is close to the composition of commonly used simulated body fluids. The aqueous solution may contain less than 10 mM, less than 8 mM or less than 6 mM potassium ions (K + In addition, the aqueous solution may contain more than 2 mM or more than 4 mM potassium ions (K + ).

[0078] The aqueous solution may contain less than 3.8 mM magnesium ions (Mg 2+ ). Such an aqueous solution is close to the composition of commonly used simulated body fluids. The above aqueous solution may contain less than 3.1mM, less than 2.3mM or less than 1.6mM magnesium ions (Mg 2+ In addition, the aqueous solution may contain more than 0.5 mM or more than 1.0 mM magnesium ions (Mg 2+ ).

[0079] The aqueous solution may contain more than 0.5 mM and less than 12.5 mM calcium ions (Ca 2+ Such an aqueous solution can easily form a calcium phosphate compound. The aqueous solution may contain more than 1.0 mM, more than 1.5 mM or more than 2.0 mM calcium ions (Ca 2+ In addition, the aqueous solution may contain less than 10 mM, less than 7.5 mM, less than 5.0 mM or less than 3.0 mM calcium ions (Ca 2+ ).

[0080] The aqueous solution may contain less than 380 mM chloride ions (Cl - ). Such an aqueous solution is close to the composition of commonly used simulated body fluids. The above aqueous solution may contain less than 300mM, less than 240mM or less than 180mM chloride ions (Cl - In addition, the aqueous solution may contain more than 40 mM, more than 80 mM or more than 120 mM chloride ions (Cl - ).

[0081] The aqueous solution may contain less than 10.5 mM bicarbonate ions (HCO 3- ). Such an aqueous solution is close to the composition of commonly used simulated body fluids. The above aqueous solution may contain less than 10mM, less than 8mM, or less than 6mM bicarbonate ions (HCO 3- In addition, the aqueous solution may contain more than 2 mM or more than 4 mM bicarbonate ions (HCO 3- ).

[0082] The aqueous solution may contain more than 0.1 mM and less than 5.0 mM hydrogen phosphate ions (HPO4 2-). Such an aqueous solution can easily form a calcium phosphate compound. The aqueous solution may contain more than 0.3 mM, more than 0.6 mM or more than 0.9 mM hydrogen phosphate ions (HPO4 2- In addition, the aqueous solution may contain less than 4 mM, less than 3 mM, less than 2 mM, or less than 1.5 mM hydrogen phosphate ions (HPO4 2- ).

[0083] The aqueous solution may contain less than 1.25 mM sulfate ions (SO4 2- ). Such an aqueous solution is close to the composition of commonly used simulated body fluids. The above aqueous solution may contain less than 1mM, less than 0.8mM or less than 0.6mM sulfate ions (SO4 2- In addition, the aqueous solution may contain more than 0.2 mM or more than 0.4 mM sulfate ions (SO4 2- ).

[0084] The pH of the aqueous solution is 4.0 or higher. By setting the pH to 4.0 or higher, the reaction by pressurization and heating can be promoted. The pH of the aqueous solution may be 5 or higher, or 6 or higher. Furthermore, the pH of the aqueous solution may be less than 10, less than 9, or less than 8.

[0085] An aqueous solution containing calcium and phosphorus and having a pH of 4.0 or higher can be, for example, a simulated body fluid (SBF). SBF is an aqueous solution in which the concentration of inorganic ions is roughly equal to that of human extracellular fluid. By using this solution, the reaction of the surface of the material in the body can be easily predicted even outside the body. Moreover, by reacting the raw material particles with SBF, a calcium phosphate compound can be easily generated on the surface of the raw material particles. Therefore, a binding portion 3 containing a calcium phosphate compound such as hydroxyapatite can be easily formed. As a simulated body fluid, an aqueous solution in the concentration range described above can be used.

[0086] The amount of the aqueous solution added to the raw material particles is preferably an amount sufficient for the reaction to proceed. The amount of the aqueous solution added is preferably 1 to 200% by mass, more preferably 7 to 100% by mass, relative to the raw material particles.

[0087] Next, the mixture formed by mixing the raw material particles with the aqueous solution is filled into the interior of the mold. After the mixture is filled into the mold, the mold can be heated as needed. Then, by applying pressure to the mixture inside the mold, the interior of the mold becomes a high-pressure state. At this time, the raw material particles are highly filled, and the particles of the raw material particles are mutually bonded to each other, thereby achieving high density. That is, it is believed that when the mixture formed by mixing the raw material particles and the aqueous solution is heated and pressurized, a reaction such as biomineralization will be carried out.

[0088] In detail, Figure 2 As shown in FIG, when the raw material particles come into contact with the aqueous solution, calcium ions and phosphate ions form a calcium phosphate compound on the surface of the raw material particles. Figure 3 As shown, a bond 3 containing a calcium phosphate compound is formed between adjacent raw material particles. Here, by extending the heating and pressurizing time of the mixture formed by mixing the raw material particles with the aqueous solution, the calcium phosphate compound is generated, and the proportion of the calcium phosphate compound is increased. Therefore, by heating and pressurizing the mixture for a predetermined time, a bond 3 containing a calcium phosphate compound can be formed.

[0089] It should be noted that the heating and pressurizing conditions for the mixture formed by mixing the raw material particles with the aqueous solution are not particularly limited as long as they are conditions under which the raw material particles react with the aqueous solution. For example, the mixture formed by mixing the raw material particles with the aqueous solution is preferably heated to a temperature of 40°C or higher and 300°C or lower, and pressurized at a pressure of 3000 MPa or lower. Furthermore, the time for heating and pressurizing the mixture is preferably 20 minutes or higher and 12 hours or lower. Under such conditions, a bonding portion 3 containing a crystalline calcium phosphate compound can be easily formed. It should be noted that the pressure when pressurizing the mixture can be 1 MPa or higher, or 10 MPa or higher. In addition, the pressure when pressurizing the mixture can be 2000 MPa or lower, or 1000 MPa or lower. The temperature when heating the mixture can be 80°C or higher, or 100°C or higher. In addition, the temperature when heating the mixture can be 250°C or lower, or 200°C or lower.

[0090] Finally, by removing the formed body from the interior of the mold, a structure 1 can be obtained in which a plurality of crystal grains 2 are bonded to each other via the bonding portion 3. It should be noted that in this embodiment, an example is described in which a mixture of raw material particles and an aqueous solution is filled into the interior of a mold and then heated and pressurized. However, the present invention is not limited to an example in which such a mold is used. For example, the mixture may be heated and pressurized while being sandwiched between two plates.

[0091] Thus, the method for manufacturing the structure 1 of this embodiment includes the steps of pressurizing and heating a mixture containing raw material particles having an average particle size of 60 nm or less and containing crystals of a calcium phosphate compound, and an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or greater. In the pressurizing and heating steps, pressurization and heating are performed at a pressure of 3000 MPa or less and a temperature of 300°C or less for 20 minutes or more and 12 hours or less. In this method, the structure 1 can be formed under low-temperature conditions. Therefore, compared to structures manufactured under high-temperature conditions such as high-temperature sintering, a structure 1 with low crystallinity can be obtained, thereby achieving a structure 1 with high reactivity, such as biological activity. In addition, the crystal grains 2 of the structure 1 of this embodiment are small and have a large surface area. Compared to structures manufactured under high-temperature conditions such as high-temperature sintering, a large amount of hydroxyl groups with infrared absorption ability remain in the structure 1. Therefore, a structure 1 with infrared shielding ability can also be provided.

[0092] [Components with a structure]

[0093] Next, the components of the structure 1 of the present embodiment are described. As described above, the structure 1 of the present embodiment can be made into a plate-like shape with a large thickness. In addition, the mechanical strength of the structure 1 is high, and it can be cut in the same way as a general ceramic component, and surface processing can also be performed. Therefore, the structure 1 can be suitable for use as a building component, a dental material, a medical material, or a basic research material for biochemistry such as a cell culture container. As a building component, there is no particular limitation, and for example, outer wall materials (wall panels), roofing materials, road materials, outer tank materials, etc. can be cited. In addition, the light transmittance of the structure 1 of the present embodiment is excellent. Therefore, the structure 1 can also be suitable for use as an optical component such as an infrared cutoff filter, a biological lens, a transmission observation window, etc.

[0094] Furthermore, the structure 1 of this embodiment has a composition similar to that of bones or teeth in a living body and has excellent transparency, so cells can be cultured on the surface of the structure 1. Therefore, the structure 1 can also be suitably used as a cell culture material that can directly evaluate cell activity.

[0095] Furthermore, the structure 1 of this embodiment has excellent bioadhesiveness and transparency. Therefore, by connecting or applying the structure 1 to a transcutaneous device such as a central venous catheter for nutritional supplementation, a medical material can be provided that can measure transmitted light in vivo while preventing bacterial infection.

[0096] The structure 1 of this embodiment may contain various functional materials, and the functional materials may be used in combination with the crystal grains 2 or the bonding portion 3. Furthermore, since the structure 1 of this embodiment is produced at a low temperature, the functional material may be an organic substance such as a polymer.

[0097] For example, when a luminescent material such as a phosphor or fluorescent pigment is incorporated into the structure, the light emitted by the luminescent material can be efficiently extracted due to its high light transmittance. Furthermore, when the excitation source is light, the luminescent material can efficiently absorb the excitation light. The structure 1 incorporating a luminescent material can be used in lighting, display devices, and the like.

[0098] Furthermore, by compounding a colorant containing a pigment such as a biological pigment, pigment, or dye, a colored structure can be obtained that displays its color with good reproducibility, or a translucent structure with controlled transmission wavelength. The translucency of the structure 1 can be controlled by parameters such as the particle size, refractive index, and amount of the pigment. These structures 1 can be used in decorative parts or optical filters for sensor devices.

[0099] Furthermore, the structure 1 can be suitably used as a cell culture material by combining functional materials useful for cell culture and activity, such as growth factor amino acids, peptides, proteins, enzymes, serum, and plasma components useful for physiological activity.

[0100] It should be noted that the above-mentioned functional material is an example, and it is obvious to those skilled in the art that various other functional materials can be compounded to produce a structure 1 having functions derived from the functional materials.

[0101] Example

[0102] Hereinafter, the structure of this embodiment will be described in more detail with reference to examples, but this embodiment is not limited thereto.

[0103] (Synthesis of Hydroxyapatite Raw Material Particles)

[0104] Hydroxyapatite nanoparticles were synthesized via the sol-gel method, as described in the literature (F. Bakan et al., A novel low-temperature sol-gel synthesis process for thermally stable nanocrystalline hydroxyapatite, Powder Technol., 233 (2013) 295-302). Specifically, 100 mL of a 5 M (mol / L) calcium aqueous solution was synthesized using Ca(NO3)2·4H2O (Fujifilm Wako Pure Chemical Industries, Ltd.), and a 3 M (mol / L) hydrogen phosphate aqueous solution was synthesized using (NH4)2HPO4 (Fujifilm Wako Pure Chemical Industries, Ltd.). Subsequently, the pH of each aqueous solution was adjusted to 10.5 using ammonia (Fujifilm Wako Pure Chemical Industries, Ltd.). The hydrogen phosphate aqueous solution was then added dropwise to the calcium aqueous solution while stirring at 300 rpm to form a mixed solution. Ammonia was added to maintain the pH of the mixed solution at 10.5. The mixed solution was stirred for 1 hour and aged for 12 hours, and the resulting gel was washed with ultrapure water. The washed product was heat-treated at 110° C. for 24 hours to obtain hydroxyapatite nanoparticles (raw material particles) having an average particle size of 30 nm.

[0105] (Preparation of Simulated Body Fluid (SBF))

[0106] SBF was prepared using a known method (T. Kokubo et al., Solutions able to reproduce in vivo surface-structure changes in bioactive glass-ceramic AW, J. Biomed. Mater. Res., 24 (1990) 721-734). The pH of SBF was 7.4. The composition of SBF is shown in Table 1, along with that of human plasma.

[0107] Table 1

[0108]

[0109] (Structure Production)

[0110] (Example 1)

[0111] 0.4 g of the raw material particles and 0.08 mL of SBF were mixed in a mortar to achieve an SBF content of 20% by mass. The mixture was then placed in a 12 mm diameter superhard mold and heated at 180°C and 800 MPa for 30 minutes while applying pressure. The sample was removed from the mold and dried in an oven at 110°C for 24 hours to evaporate any residual moisture. This produced the structure of this example.

[0112] (Example 2)

[0113] A structure was produced in the same manner as in Example 1 except that the pressurizing and heating time was changed from 30 minutes to 1 hour.

[0114] (Example 3)

[0115] A structure was produced in the same manner as in Example 1 except that the pressurizing and heating time was changed from 30 minutes to 2 hours.

[0116] (Example 4)

[0117] A structure was produced in the same manner as in Example 1 except that the pressurizing and heating time was changed from 30 minutes to 6 hours.

[0118] (Comparative Example)

[0119] A structure was produced in the same manner as in Example 1 except that SBF was replaced with ultrapure water.

[0120] [evaluate]

[0121] (Relative density determination)

[0122] The relative density of the structure was calculated by the Archimedean method using ethanol (EtOH, 99.5%, Fujifilm Wako Pure Chemical Industries, Ltd.) as a solvent. The results are shown in Tables 2 and Figure 4 .

[0123] (Total light transmittance)

[0124] The structure was mirror-polished to a thickness of 1 mm, and the total light transmittance in the wavelength range of 300 to 800 nm was measured using an ultraviolet-visible spectrophotometer UV-2600 manufactured by Shimadzu Corporation using an integrating sphere unit. The results are shown in FIG. Figure 5 In addition, Table 2 shows the total light transmittance at a wavelength of 589 nm.

[0125] (Vickers hardness test)

[0126] Regarding Vickers hardness, the structure was tested 6 times under the conditions of a load (test force) of 19.8 N and a holding time of 15 seconds, and the average value was used as the Vickers hardness of each structure. The Vickers hardness was measured using a Vickers hardness tester FV-310e manufactured by Fuchs Tech Co., Ltd. The results are shown in Tables 2 and Figure 6 .

[0127] (Fracture toughness)

[0128] The fracture toughness was tested under the same conditions as the Vickers hardness test and calculated based on the results by the indentation method (IF method). The results are shown in Tables 2 and Figure 6 .

[0129] (Biaxial bending strength)

[0130] The biaxial bending strength was measured using an Autograph AGX-V series universal testing machine (Shimadzu Corporation) capable of measuring a load of 50N. Specifically, a circular test piece with a diameter of 11mm was supported by three spherical balls (4.5mm in diameter) arranged at 120° intervals, and a loading piston with a diameter of 1.4mm and a flat end face was used to apply a load to the center of the test piece. At this time, 5 tests were performed at a constant crosshead displacement speed (0.5mm / s), and the average value of the measurement results was calculated. The results are shown in Tables 2 and Figure 7 .

[0131] (Young's modulus)

[0132] The Young's modulus was calculated based on ultrasonic velocity data obtained using a digital storage oscilloscope (DSOX3052T, Keysight) and an ultrasonic pulser / receiver (Model 5072, PANAMETRICS). The results are shown in Tables 2 and Figure 7 .

[0133] Table 2

[0134]

[0135] As shown in Table 2 and Figures 4 to 7 As shown, it can be seen that the relative density, transmittance, and mechanical properties of the structure increase as the heating time of the mixture increases. It is speculated that as the heating time of the mixture increases, the structure becomes denser, and the mechanical strength and light transmittance increase.

[0136] (Scanning electron microscope observation)

[0137] The fracture surface of the transparent structure was observed using a scanning electron microscope (FE-SEM, SU9000, Hitachi High-Technologies Corporation) at an accelerating voltage of 15 kV or 30 kV.

[0138] (Transmission electron microscope (TEM) observation)

[0139] The shape of the crystal grains of the structure was observed using a transmission electron microscope (JEM-ARM200F, JEOL Ltd.).

[0140] Figure 8 This is an SEM image of raw material particles. Figure 9 and Figure 10 These are SEM images of the cross section of the structure of Example 1 observed at magnifications of 30,000 times and 70,000 times. Figure 11 and Figure 12 These are SEM images of the cross section of the structure of Example 2 observed at magnifications of 30,000 times and 70,000 times. Figure 13 and Figure 14 These are SEM images of the cross section of the structure of Example 3 observed at magnifications of 30,000 times and 70,000 times. Figure 15 and Figure 16 The cross-section of the structure of Example 4 was observed at 30,000 times and 70,000 times the SEM image. Figures 8 to 16 It is found that as the heating time of the raw material particles increases, the structure becomes denser and the proportion of pores decreases.

[0141] Figure 17 This is a TEM image of raw material particles. Figure 18 This is a TEM image showing the shape of the crystal grains of the structure of Example 1. Figure 19 This is a TEM image showing the shape of crystal grains of the structure according to Example 4. Figure 20 This is a TEM image of a further magnified cross section of the structure of Example 4. Figures 17 to 20 It is known that as the heating time of the raw material particles becomes longer, the bonding of the hydroxyapatite particles is promoted, and the ellipsoidal raw material particles become spherical. Figure 20 It was confirmed that re-precipitated hydroxyapatite was generated as a bonding portion between the raw material particles.

[0142] Next, SEM images of the structure of Example 1 and the structure of the comparative example were observed. Figure 21 and Figure 22 These are SEM images of the cross section of the structure of Example 1 observed at magnifications of 30,000 times and 100,000 times. Figure 23 and Figure 24The cross-section of the structure of the comparative example is observed at 30,000 times and 100,000 times the SEM image. Figures 21 to 24 It was confirmed that the structure of Example 1 was a dense structure, but the structure of the structure of the comparative example was not as dense as that of Example 1.

[0143] Next, the relative density and transmittance of the structure of the comparative example were measured. The evaluation results of the comparative example are shown in Table 3 along with the evaluation results of Example 1. As shown in Table 3, the relative density of Comparative Example 1 was measured to be 87.2%, and the total light transmittance at a wavelength of 589 nm was measured to be 43.7%. These results show that when an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or higher is used as the liquid mixed with the raw material particles, the relative density and transmittance of the structure are increased compared to when ultrapure water is used, thereby improving the mechanical strength and light transmittance of the structure.

[0144] Table 3

[0145] Relative density (%) Transmittance (%) Example 1 93.3 70.2 Comparative Example 87.2 43.7

[0146] Next, the aspect ratios of the raw material particles and the structures of Examples 1 to 4 were measured. The results are shown in Tables 4 and Figure 25 As shown in Table 4 and Figure 25 As shown in FIG. 1 , it was confirmed that as the heating time of the raw material particles increased, the aspect ratio of the hydroxyapatite particles decreased and approached 1, and the particles that were elongated gradually became closer to a true spherical shape.

[0147] Table 4

[0148] Heating time (h) Aspect ratio Raw material particles 0 2.21±0.88 Example 1 0.5 1.65±0.47 Example 2 1.0 1.36±0.25 Example 3 2.0 1.20±0.17 Example 4 6.0 1.18±0.18

[0149] (X-ray diffraction measurement)

[0150] Next, the X-ray diffraction pattern of the structure was measured using an X-ray diffractometer. A Bruker AXS D8 ADVANCE X-ray diffractometer was used. CuKα radiation was used as the X-ray source. The X-ray diffraction pattern was measured under the conditions of a tube voltage of 40 kV, a tube current of 40 mA, a diffraction angle 2θ of 10° to 70°, and a step size of 0.02°. Figure 26 The X-ray diffraction patterns of Examples 1 to 4 are shown in FIG. Figure 27 ] The X-ray diffraction patterns of the raw material particles and Example 4 are shown in FIG.

[0151] like Figure 26 As shown in FIG. 1 , in the structures of Examples 1 to 4, diffraction peaks of hydroxyapatite derived from pure water were confirmed, but no significant differences were found in the XRD spectra. Figure 27It can be seen that by heating the raw material particles, the peak intensity of the crystal plane (002) and the crystal plane (004) related to the c-axis decreases, and the peak intensity of the crystal plane (300) and the crystal plane (310) related to the a-axis increases. This result is different from the previous Cold Sintering Process (Hassan et.al., J.Hazard.Mater., vol.374, 2019, 228-237) and Hotisotactic pressing (Uematsu et.al., J.Am.Ceram.Soc., vol.72, 1989, 1476-1478). Figure 27 It can be seen that the length of the raw material particles in the major axis direction becomes shorter and the length in the minor axis direction becomes longer as the heating time of the raw material particles increases.

[0152] Based on the above results, it is believed that when the raw material particles are heated and pressurized, the raw material particles are bonded to each other via the bonding parts. As the heating time increases, the raw material particles become shorter in the major axis direction and longer in the minor axis direction, thereby promoting the densification of the structure.

[0153] (Note)

[0154] The following techniques are disclosed through the description of the above embodiments.

[0155] (Technique 1) A structure comprising: a plurality of crystal grains containing a calcium phosphate compound; and a bonding portion that bonds the crystal grains together and contains the calcium phosphate compound, wherein the average particle size of the crystal grains is 60 nm or less, the relative density of the structure is 80% or more, the total light transmittance of light with a wavelength of 589 nm is 45% or more when the thickness of the structure is 1 mm, and the Vickers hardness of the structure is 1 GPa or more.

[0156] This configuration makes the internal structure of the structure denser and increases the light transmittance ratio, thereby providing a structure having excellent mechanical strength and light transmittance.

[0157] (Technique 2) The structure according to Technique 1, wherein the crystal grains comprise apatite crystals. This configuration improves the strength of the crystal grains, thereby further enhancing the mechanical strength of the structure.

[0158] (Technique 3) The structure according to Technique 1 or 2, wherein the bonding portion comprises apatite crystals. This configuration improves the strength of the bonding portion, thereby further enhancing the mechanical strength of the structure.

[0159] (Technique 4) The structure according to any one of Techniques 1 to 3, wherein the crystal grains contain Ca 10-x (HPO4)x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by (0≤x<1). This structure makes the structure structurally and chemically stable. Therefore, for example, the structure can be suitably used as a biological material, an optical material, etc.

[0160] (Technique 5) The structure according to any one of Techniques 1 to 4, wherein the binding portion comprises Ca 10-x (HPO4) x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by (0≤x<1). This structure makes the structure structurally and chemically stable. Therefore, for example, the structure can be suitably used as a biological material, an optical material, etc.

[0161] (Technique 6) The structure according to any one of Techniques 2 to 5, wherein, in an XRD pattern using CuKα radiation as an X-ray source, the peak intensity originating from the (300) plane is higher than the peak intensity originating from the (002) plane. This configuration reduces the anisotropy of the crystal grains. Consequently, the light transmittance of the structure may be increased.

[0162] (Technique 7) The structure according to any one of Techniques 1 to 6, wherein the relative density is 90% or more.

[0163] This configuration makes the internal structure of the structure 1 denser, thereby further improving the mechanical strength of the structure 1.

[0164] (Technique 8) A method for manufacturing a structure, comprising pressurizing and heating a mixture under conditions of a pressure of 3000 MPa or less and a temperature of 300°C or less for 20 minutes or more and 12 hours or less, the mixture comprising raw material particles having an average particle size of 60 nm or less and containing crystals of a calcium phosphate compound, and an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or more, wherein the relative density of the structure is 80% or more, the total light transmittance of light of a wavelength of 589 nm is 45% or more when the thickness of the structure is 1 mm, and the Vickers hardness of the structure is 1 GPa or more. According to this configuration, the structure can be formed under low temperature conditions. Therefore, a structure with high reactivity such as biological activity, a structure with high biocompatibility, a structure with visible light transmittance, or a structure with infrared shielding ability can be obtained.

[0165] (Technique 9) The method for producing a structure according to Technique 8, wherein the aqueous solution is a simulated body fluid. This configuration allows for the easy generation of a calcium phosphate compound on the surface of the raw material particles. Thus, a bond containing the calcium phosphate compound can be easily formed.

[0166] The entire contents of Tokugan Application No. 2023-027739 (filing date: February 24, 2023) are incorporated herein by reference.

[0167] As mentioned above, the content of this embodiment was described based on the examples, but this embodiment is not limited to these descriptions, and various modifications and improvements are possible, which will be apparent to those skilled in the art.

[0168] Industrial Applicability

[0169] According to the present disclosure, it is possible to provide a structure having excellent mechanical strength and light transmittance and a method for producing the structure that can be produced under low temperature conditions.

[0170] Reference numerals

[0171] 1 Structure

[0172] 2 grains

[0173] 3 Joint

[0174] 3a Aqueous solution

Claims

1. A structure comprising: containing a plurality of crystallites of a calcium phosphate compound, and The bonding portion of each of the crystal grains is bonded together and contains a calcium phosphate compound, The average particle size of the crystal grains is less than 60 nm, The relative density of the structure is above 80%, When the thickness of the structure is 1 mm, the total light transmittance of light with a wavelength of 589 nm is 45% or more. The structure has a Vickers hardness of 1 GPa or greater.

2. The structure according to claim 1, wherein The grains have crystals of apatite.

3. The structure according to claim 1 or 2, wherein The bonding portion has apatite crystals.

4. The structure according to any one of claims 1 to 3, wherein The grains contain Ca 10-x (HPO4) x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by , wherein 0≤x<1.

5. The structure according to any one of claims 1 to 4, wherein The binding portion comprises Ca 10-x (HPO4) x (PO4) 6-x (OH) 2-x Hydroxyapatite represented by , wherein 0≤x<1.

6. The structure according to any one of claims 2 to 5, wherein In the XRD pattern when CuKα rays are used as the X-ray source, the peak intensity from the (300) plane is higher than the peak intensity from the (002) plane.

7. The structure according to any one of claims 1 to 6, wherein The relative density of the structure is greater than 90%.

8. A method for producing a structure, comprising pressurizing and heating a mixture containing raw material particles having an average particle size of 60 nm or less and containing crystals of a calcium phosphate compound, and an aqueous solution containing calcium and phosphorus and having a pH of 4.0 or higher, under conditions of a pressure of 3000 MPa or less and a temperature of 300° C. or less for 20 minutes or more and 12 hours or less. The relative density of the structure is above 80%, When the thickness of the structure is 1 mm, the total light transmittance of light with a wavelength of 589 nm is 45% or more. The structure has a Vickers hardness of 1 GPa or greater.

9. The method for manufacturing a structure according to claim 8, wherein: The aqueous solution is a simulated body fluid.

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