JP2006095018A - Biological member and joint prosthesis using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological member with high strength, high toughness, and a high degree of hardness, a joint prosthesis using the same, and the biological member and the joint prosthesis showing high abrasion resistance in an in vivo environment. <P>SOLUTION: The biological member comprises ceramics which includes ZrO<SB>2</SB>and shows a Charpy impact value of at least 45 kJ/m<SP>2</SP>in a Charpy impact test. The ceramics shows a decreasing rate equal to or less than 10% of the Charpy impact value in the Charpy impact test before and after an accelerated aging test performed under the condition of saturated water vapor at 121°C for 152 hours. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a living body member made of a high-strength ceramic containing ZrO ₂ and an artificial joint using the living body member.

  Alumina ceramics and zirconia ceramics are biologically inert materials, and are excellent in mechanical strength and wear resistance, and thus are being applied as medical materials such as artificial joints and artificial tooth roots. For example, in artificial hip joints, the combination of alumina or zirconia ceramics / ultra high molecular weight polyethylene is less likely to wear and defects than metal. Polyethylene has been employed (see Patent Document 1).

  Furthermore, an artificial hip joint having a sliding portion between alumina ceramics has been developed (see Patent Document 2).

In recent years, alumina and zirconia-based oxide ceramics have been widely used as structural members that require high strength, wear resistance, and corrosion resistance. In particular, when alumina and zirconia are compounded at a certain ratio, it has been noticed that a higher strength than each simple substance can be obtained due to the effect of crystal grain refinement (see Non-Patent Document 1).
Japanese Patent Publication No. 06-22572 JP 2000-16836 A Ryoichi Shikata et al., “Powder and Powder Metallurgy”, Powder Powder Metallurgy Association, April 10, 1991, Volume 38, No. 3 p. 57-61

The alumina ceramic is a very excellent biomaterial, but it is far from zirconia ceramic in terms of strength and toughness. For example, in the above-mentioned artificial hip joint having a sliding portion between alumina ceramics, the strength and toughness of alumina ceramics are insufficient, and unfortunately, a case of destruction has been reported. The cause of the destruction was found to be the contact between the head and acetabular cup when the head enters the acetabular cup from the subluxation state of the acetabular cup and head, which is called micro-separation. ing. It is a well-known fact that fracture due to impact is improved by the toughness of the material (for example, Patent Document 4).
On the other hand, zirconia ceramics have higher strength and higher toughness than alumina ceramics, but far from the toughness of metals. However, as described above, the combination of metal and ultrahigh molecular weight polyethylene tends to wear more easily than the combination of ceramics and ultra high molecular weight polyethylene. Therefore, a biomaterial having higher strength and toughness has been desired for higher safety.

In addition, when Y ₂ O ₃ is used as a stabilizer, zirconia ceramics are likely to undergo phase transformation in an environment where water is present, and the strength and surface roughness may deteriorate. When the surface roughness is deteriorated, wear powder is generated with wear at the sliding portion, and when this wear powder is accumulated in the tissue near the artificial hip joint, bone resorption is caused. This bone resorption causes loosening of the artificial hip joint and bone. The generation of such wear powder is particularly noticeable at the sliding portion between the zirconia ceramics. In addition, when CeO ₂ is used as a stabilizer for this measure, phase transformation due to water is eliminated, but since crystallization grows compared to Y ₂ O ₃ , the zirconia ceramics have good sliding characteristics and strength. Is not obtained.

  About the above-mentioned composite material, while the fracture toughness improves by generation | occurrence | production of a shape anisotropic particle, it is known that intensity | strength and hardness will fall. In order to further increase the fracture toughness, it is necessary to grow the shape anisotropic particles longer and longer, but the strength and the hardness decrease as the particles become larger. In Patent Document 1, although an effect of improving toughness is observed due to the anisotropic growth of alumina, the bending strength is 1050 MPa or less, and the strength is reduced due to the formation of shape anisotropic particles. Therefore, in order to obtain a high strength and high toughness material, it is necessary to study a method for improving toughness while suppressing grain growth.

  The presence of zirconia dispersed as tetragonal crystals, which are metastable phases in alumina ceramics, and the transformation of external stress, cause phase transformation to stable monoclinic crystals (stress-induced transformation). The volume expansion due to this phase transformation hinders the progress of cracks and improves toughness. However, zirconia is originally monoclinic at normal temperature, and in order to disperse as metastable tetragonal crystals, it is difficult to stably disperse tetragonal crystals without adding a small amount of stabilizer. It is said that when the ionic radius at the time of 8-coordination of alkaline earth and rare earth elements is 140% or less of the ionic radius of zirconium, it dissolves and becomes a stabilizer. Sr, Ba, etc. are known as substances that do not become stabilizers, such as Mg, Ca, Y.

  This invention is made | formed in view of the subject of such a prior art, and it aims at providing the biological member which has very high intensity | strength and toughness. Another object of the present invention is to provide an artificial joint having wear resistance in an in vivo environment.

A biological member made of ceramics containing ZrO _{2 and} having a Charpy impact value of 45 kJ / m ² or more in the Charpy impact test is not only tough, but is less likely to cause strength deterioration even in a moisture-rich environment such as in vivo. The present inventors have found that the wear resistance is not easily deteriorated, and have reached the present invention.

In addition, the present inventors added SrO to alumina-based Al ₂ O ₃ —ZrO ₂ ceramics and fired at a low temperature to suppress the formation of shape anisotropic particles, and at the same time, grain growth of dispersed zirconia. It was discovered that Sr, which is said not to be solid solution, can be dissolved in a small amount in ZrO ₂ because strain remains in the zirconia particles. As a result, SrO exhibits an effect as a stabilizer, realizes metastabilization of tetragonal ZrO ₂ , can improve strength and fracture toughness by stress-induced phase transition to monoclinic crystal, and further, sintering aid It was found that by adding TiO ₂ , MgO and SiO ₂ , solid solution of Sr in ZrO ₂ is promoted, and the effect of strengthening the stress-induced phase transition can be increased.

That is, the present invention contains 65% by mass or more of Al ₂ O ₃ , 4 to 34% by mass of ZrO ₂ , and 0.1 to 4% by mass of SrO, and Sr is fixed in a part of the ZrO ₂ particles. The present invention relates to a living body member made of ceramics characterized by melting and an artificial joint using the same.

In the present invention,
(1) containing TiO ₂ , MgO and SiO ₂ as sintering aids,
(2) wherein (1) the SiO ₂ 0.20 wt% or more at the TiO ₂ 0.22% by mass or more, MgO and containing more than 0.12 wt%, and a total of _SiO 2, TiO ₂ and MgO It is desirable to contain 0.6-4.5 mass%.

The ceramic constituting the living body member of the present invention is a composite ceramic obtained by converting a main raw material containing Al, Zr, and Sr as a metal or a metal compound thereof into a metal oxide. _Al 2 _{O 3} 65 wt% or more in the medium, the ZrO ₂ 4 to 34 wt%, and mixing SrO with to contain 0.1 to 4 wt%, was molded into a predetermined shape, 1300 ° C. to 1500 It can be produced by firing at a temperature range of ° C. and further subjecting to a hot isostatic pressure at a temperature lower by 30 ° C. or more than the firing temperature.

In this case, the main raw material containing Al, Zr and Sr as a metal or these as a metal compound, further sintering aid containing Ti, Mg and Si as a metal, or these as a metal compound, these metals. Alternatively, when the metal compound is converted into a metal oxide, in the composite ceramic, SiO ₂ is 0.20% by mass or more, TiO ₂ is 0.22% by mass or more, MgO is 0.12% by mass or more, and SiO ₂ , it is desirable to TiO ₂ and MgO are mixed so as to contain 0.6 to 4.5 mass% in total.

The ceramic constituting the living body member of the present invention contains 65% by mass or more of Al ₂ O ₃ , 4 to 34% by mass of ZrO ₂ , and 0.1 to 4% by mass of SrO, and further includes one of the ZrO ₂ particles. SrO is dissolved in the part.

When the ceramic is in the above composition range and SrO is dissolved in a part of the ZrO ₂ particles, the effect of stabilizing the tetragonal ZrO ₂ by SrO is expressed, and the strength and toughness are improved. In addition, a decrease in strength and hardness due to an increase in zirconia content and generation of shape anisotropic particles is small, and a product that can withstand practical use can be obtained.

  In the method for producing a biological member of the present invention, first, raw materials are mixed at a predetermined ratio and formed into a predetermined shape. As the raw material here, it is possible to use metals, metal oxides, metal hydroxides, salts such as metal carbonates and the like as powders or aqueous solutions. When used as the powder, the average particle size is preferably 1.0 μm or less.

  For the molding, a molding method such as press molding, casting, cold isostatic pressing, or cold isostatic pressing can be used.

  Next, according to the present invention, firing is performed in a temperature range of 1300 to 1500 ° C., and hot isostatic treatment is performed at a temperature lower by 30 ° C. or more than the firing temperature. As a result, it is possible to produce a dense body in which alumina and zirconia are fine particles and the anisotropic grain growth of alumina is suppressed.

According to the present invention, the effect of stress-induced phase transition is large in ZrO ₂ in which Sr is dissolved, and the effect becomes even more remarkable by adding SiO ₂ , TiO ₂ and MgO as sintering aids. Moreover, the addition of SiO ₂ , TiO _2, and MgO lowers the firing temperature, resulting in higher densification and finer structure, thereby providing a biological member made of a composite ceramic with high strength, high toughness, and high hardness.

According to the present invention, a biological member made of ceramics containing ZrO _{2 and} having a Charpy impact value of 45 kJ / m ² or more in the Charpy impact test is used, so that not only toughness but also moisture as in the living body is high. Less susceptible to strength degradation even in the environment.

In the sliding of the composite ceramics, the specific wear amount by the pin-on-disk test method after the accelerated deterioration test performed under the condition of saturated steam at 121 ° C. for 152 hours is 0.3 × 10 ⁻¹⁰ mm ² / N. It can be: Therefore, high strength, high toughness, and high wear resistance can be realized in the artificial joint by configuring the sliding portion of the artificial joint that slides with the composite ceramic.

Moreover, in ZrO ₂ in which Sr is dissolved, tetragonal crystals are metastable, and a high-strength and high-toughness material is obtained due to the effect of stress-induced phase transition. Furthermore, the effect becomes more remarkable by simultaneously adding SiO ₂ , TiO ₂ and MgO as sintering aids, and the addition of these sintering aids lowers the firing temperature and produces shape anisotropic particles. Without high densification and fine structure. As a result, it is possible to obtain a living body member made of a composite ceramic having high strength, high toughness, and high hardness and an artificial joint using the living body member.

  The present invention is described in detail below.

  1 to 2 illustrate an embodiment of the biological member of the present invention. According to FIG. 1, the ceramic is used for the sliding part of the artificial joint. Specifically, an artificial hip joint is constituted by a metal stem, a ceramic head ball and a acetabular socket. The present invention is not limited to a case where an artificial joint such as an artificial hip joint has a pair of sliding parts made of the ceramics, and a pair of biological members including these sliding parts constitutes an artificial joint. Including the case where only the ceramics is used.

  Moreover, the living body member of the present invention includes those that do not have a sliding portion. For example, an artificial bone that does not include a joint portion may be used.

Usually, ZrO ₂ can improve mechanical properties by dissolving a stabilizer such as Y ₂ O ₃ in an appropriate amount of ZrO ₂ . However, if the amount of Y ₂ O ₃ is too large in the Al ₂ O ₃ —ZrO ₂ ceramics, cubic crystals increase and the contribution to the fracture toughness of the phase transformation becomes small. On the other hand, if the blending amount of Y ₂ O ₃ is too small, monoclinic ZrO ₂ increases, and both strength and toughness decrease. Further, the increase in Al ₂ O ₃ content increases the hardness but decreases the strength and toughness.

  In order to compensate for this, SrO is added to improve fracture toughness by forming anisotropically shaped particles. However, high temperature firing is required, and strength and hardness are greatly reduced due to grain growth and densification inhibition.

In the material developed in the present invention, tetragonal ZrO ₂ is stabilized by solid solution of Sr. However, since the amount of solid solution in ZrO ₂ is small in Sr, it is difficult to form a cubic crystal. As a result, the stress-induced phase transition effect is large, the fracture toughness can be improved regardless of the formation of shape anisotropic particles, and the strength and hardness are also increased.

The composite ceramic forming the living body member of the present invention is a composite ceramic containing at least Al ₂ O ₃ , ZrO ₂ and SrO, wherein Al ₂ O ₃ is 65% by mass or more, ZrO ₂ is 4 to 34% by mass, And SrO is contained in an amount of 0.1 to 4% by mass, and Sr is dissolved in a part of the ZrO ₂ particles. The content of Al ₂ O ₃ is preferably 65% by mass or more, preferably Is 67 to 90% by mass, particularly preferably 76 to 84% by mass, and the content of ZrO ₂ is 4 to 34% by mass, preferably 10 to 34% by mass, and particularly preferably 11 to 20% by mass.

By containing 65% by mass or more of Al ₂ O ₃ , the effect of high strength and high hardness can be obtained. When the content of ZrO ₂ is less than 4% by mass, the strength is lowered and the toughness is reduced, whereas 34% by mass. If it exceeds 50%, the hardness decreases due to a decrease in Young's modulus.

  Moreover, the addition amount of SrO is 0.1-4 mass% in composite ceramics, Preferably it is 0.5-3 mass%, Most preferably, it is 0.7-1.5 mass%.

  It is important that the amount of SrO added is 0.1 to 4 mass%.

When the amount of SrO added is less than 0.1% by mass, the monoclinic system of ZrO ₂ increases and the strength decreases. On the other hand, when the amount of SrO added exceeds 4% by mass, the firing temperature becomes high, densification is inhibited due to formation of shape anisotropic particles, and strength or hardness is reduced due to zirconia grain growth.

By further adding a certain proportion of SiO ₂ , TiO ₂ and MgO to the above composition range, the sintered body can be densified under low temperature conditions while suppressing the growth of crystal grains of Al ₂ O ₃ and ZrO ₂ . High strength can be realized by forming a high-density structure.

That is, 65% by mass or more of Al ₂ O ₃ , 4 to 34% by mass of ZrO ₂ , 0.1 to 4% by mass of SrO, 0.20% by mass or more of SiO ₂ , and 0.1% of TiO ₂ . High strength, high toughness, and high hardness in a composition containing 22% by mass or more, 0.12% by mass or more of MgO, and 0.6 to 4.5% by mass of SiO ₂ , TiO ₂ and MgO in total amount Realized.

Here, the content of SiO ₂ is 0.20 wt% or more, preferably from 0.4 to 1.5 wt%, the content of TiO ₂ is 0.22 wt% or more, preferably 0.3 The content of MgO is 0.12% by mass or more, preferably 0.2-1.4% by mass.

When the content of SiO ₂ is less than 0.20% by mass, the content of TiO ₂ is less than 0.22% by mass, or the content of MgO is less than 0.12% by mass, the liquid phase is insufficient, and Al ₂ O ₃ causes the inconvenience that it is difficult to densify.

By adding SiO ₂ , TiO ₂ , and MgO in the above proportions as sintering aids, solid solution of SrO in ZrO ₂ is promoted, strength and toughness are improved, and the eutectic point is 1300 ° C. or lower. A liquid phase is generated during the sintering, and the sintering of the material is greatly promoted. For this reason, a highly dense sintered body can be obtained even at a lower temperature. Further, by sintering at a relatively low temperature, anisotropic grain growth is suppressed, and a fine structure is obtained and strength and hardness are not reduced.

Next, in order to obtain material properties of high strength, high toughness, and high hardness, it is important to suppress grain growth of Al ₂ O ₃ and ZrO ₂ by low-temperature firing at 1500 ° C. or less, particularly 1490 ° C. or less. Is desirable. When firing at a high temperature with SrO added, Al ₂ O ₃ grows anisotropically and the strength, toughness, and hardness decrease. This is because the monoclinic ZrO ₂ amount by grain growth of ZrO ₂ is increased, the strength and hardness is lowered.

  As understood from the above description, the ceramics having the above composition effectively avoids densification inhibition due to shape anisotropic particles and a decrease in strength or hardness due to zirconia grain growth.

, For example, _Al 2 _{O 3} particles in said ceramic particles of _Al 2 _{O 3} in the composite ceramic, with exhibits an elongated shape in SEM images, the longest direction long axis of each _Al 2 _{O 3} particles, the When the length is the major axis diameter, the direction perpendicular to the major axis is the minor axis, and the length is the minor axis diameter, the average of the major axis diameter (major axis average diameter) is 1.5 μm or less. And the average of the aspect ratio, which is the ratio of the major axis diameter to the minor axis diameter, is 2.5 or less, and the intermediate value between the average minor axis diameter and the average major axis diameter (average particle diameter) is It is preferable that it is 1 micrometer or less. That is, when the average aspect ratio of Al ₂ O ₃ particles exceeds 2.5, or when the average major axis diameter is larger than 1.5 μm, densification is inhibited by shape anisotropic particles, resulting in a decrease in strength. End. Also, if the mean value of the minor axis diameter and the average major axis diameter of ZrO2 particles is larger than 1.0 μm, the stability of tetragonal crystal is lowered, cracks are generated due to phase transformation, and the strength and toughness are increased. Will result in a decrease in.

For example, the Al ₂ O ₃ particles in the ceramic have an average aspect ratio of 2.5 or less and a major axis average particle size of 1.5 μm or less, particularly 1 μm or less. The average particle size of ZrO ₂ particles Is preferably 0.7 μm or less, particularly preferably 0.5 μm or less. That is, when the average aspect ratio of Al ₂ O ₃ particles exceeds 2.5, or when the major axis average particle size is larger than 1.5 μm, densification is inhibited by shape anisotropic particles, resulting in a decrease in strength. End. On the other hand, if the average particle size of the ZrO ₂ particles is larger than 0.7 μm, the stability of the tetragonal crystal is lowered, microcracks are generated due to phase transformation, and the strength and toughness are lowered.

Therefore, it is important to sinter at 1500 ° C. or less and densify by hot isostatic pressing while suppressing the grain growth of Al ₂ O ₃ and ZrO ₂ . As this hot isostatic firing condition, a temperature lower by 30 ° C. or more than the main firing temperature, particularly a temperature lower by 50 ° C. or more, more preferably a temperature lower by 100 ° C. or more is preferable.

An Al ₂ O ₃ powder having a purity of 99.95% by mass and an average particle size of 0.22 μm, a ZrO ₂ powder having a purity of 99.95% by mass and an average particle size of 0.4 μm, Mg having an average particle size of 0.6 μm ( OH) ₂ , SiO ₂ powder having an average particle diameter of 0.5 μm, and SrO powder having an average particle diameter of 0.2 μm were weighed and mixed to have a composition as shown in Table 1 to obtain a mixed powder. Then, this mixed powder is molded with a pressure of 1 t / cm ² and further subjected to hydrostatic pressure treatment with a pressure of 3 t / cm ² to produce a molded body. Hydrostatic baking (indicated as HIP in the table) was performed.

For each of the obtained sintered bodies, the bending strength at room temperature according to JIS-R1601, the fracture toughness value according to the SEPB method according to JIS-R1607, and the Vickers hardness according to JIS-R1610 were measured. The Charpy impact test was performed in accordance with an impact test defined in JIS K 7111 using a test piece processed to 3 mm × 3 mm × 14 mm and having a 0.5 mm notch in the center. In addition, the crystal grain size is measured by mirror-polishing the test piece and then performing thermal etching at a temperature lower by about 50 ° C. than the firing temperature, and the photograph on the polished surface by SEM shows Al ₂ O ₃ particles and ZrO ₂ particles respectively. Take 100 or more images and extract the Al ₂ O ₃ particle crystal having the complete particle shape from the photograph. The longest part of the shape is the long axis and the longest part in the direction perpendicular to it is the short axis. As a direct measurement, the aspect ratio was calculated. Further, after an accelerated deterioration test performed in saturated steam at 121 ° C. for 152 hours, the wear resistance was evaluated using a pin-on-disk test method (JIS-T0303, where the material of the test piece was a composite ceramic). did. The obtained results are shown in Table 2. Further, it was confirmed by X-ray diffraction (XRD) that tetragonal ZrO ₂ by SrO was stabilized, and solid solution of Sr in ZrO ₂ was confirmed by an electron beam probe microanalyzer (EPMA).

As shown in Table 2, the material containing SrO and no other sintering aid (sample No. 8) had higher strength and fracture toughness than the material not containing SrO (sample No. 12). However, materials containing SrO and sintering aids SiO ₂ , TiO ₂ , MgO and sintered at a lower temperature (sample Nos. 1, 2, 6, and 14) have a strength of 1410 to 1540 MPa and a fracture toughness of 5.1. The characteristics of ˜5.4 MPa√m and hardness of 1740 to 1790 Hv were exhibited, and the characteristics were improved as compared with the material of Sample No. 8.

In the material of sample No. 4, the firing temperature was high, and slightly anisotropically shaped particles were formed, so the strength and hardness were slightly reduced, but the fracture toughness was higher than that of the material of sample No. 8. In the material containing ZrO _{2 in} which Y ₂ O ₃ is dissolved (sample No. 12), the content of cubic ZrO ₂ is increased, and the effect of stabilizing the tetragonal ZrO ₂ by SrO is reduced. Therefore, SrO and SiO ₂ Despite containing TiO ₂ and MgO, the strength and toughness were small.

Moreover, by comparing the X-ray diffraction (XRD) measurement results of the materials of sample No. 1 and 11, it was confirmed that tetragonal ZrO ₂ was stabilized by adding SrO in the material of sample No. 1. It was confirmed that Sr was dissolved in ZrO ₂ by analyzing the composition of the material of sample No. 1.

    From sample No. 8, when the Charpy impact test was 45 MPa√m or less, the fracture toughness was 4.5 MPa√m lower than No. 15.

Sample No. In Nos. 21 to 23, any of the sintering aids TiO ₂ , MgO, and SiO ₂ is small or large, but if any of them is small, the sintering temperature increases and the crystal grain size increases. As a result, the bending strength was low. When the amount of either of them was high, the liquid phase component was high although the sintering temperature was low, and the bending strength was low.

It is a schematic diagram of an artificial hip joint. It is a schematic diagram of an artificial knee joint.

Explanation of symbols

    Unsigned

Claims (12)

A biological member comprising ZrO ₂ and made of ceramics having a Charpy impact value of 45 kJ / m ² or more in a Charpy impact test.   2. The biomaterial according to claim 1, wherein the ceramic has a Charpy impact value reduction rate of 10% or less in a Charpy impact test before and after an accelerated deterioration test conducted in saturated steam at 121 ° C. for 152 hours. . The ceramic contains 65% by mass or more of Al ₂ O ₃ , 4 to 34% by mass of ZrO ₂ , and 0.1 to 4% by mass of SrO, and Sr is dissolved in a part of the ZrO ₂ particles. The living body member according to claim 1, wherein the living body member is a living body member. Biological component according to claim 1, characterized in that it comprises _TiO 2, MgO and SiO ₂ as a sintering aid to the ceramics. The SiO ₂ 0.20 wt% or more in said ceramic, the TiO ₂ 0.22 wt% or more of MgO containing more than 0.12 wt%, and the _SiO 2, TiO ₂ and MgO in total 0.6 It contains 4.5 mass%, The biological member of Claim 4 characterized by the above-mentioned. The Al ₂ O ₃ particles in the ceramic exhibit an elongated shape in the SEM image, and the longest direction of each of the Al ₂ O ₃ particles is the long axis and the length is the long axis diameter, and the long axis is When the minor axis is the minor axis and the length is the minor axis diameter, the average major axis diameter is 1.5 μm or less, and the average aspect ratio is the ratio of the major axis diameter to the minor axis diameter. 6. The biological member according to at least one of claims 1 to 5, wherein an intermediate value between the average of the short axis diameter and the average of the long axis diameter is 1 μm or less. The ceramic has a specific wear amount of 0.3 × 10 ⁻¹⁰ mm ² / N or less by a pin-on-disk test method after an accelerated deterioration test performed in saturated steam at 121 ° C. for 152 hours. The biological member according to any one of claims 1 to 6.   The living body member according to at least one of claims 1 to 7, wherein a sliding portion of the artificial joint is configured by the ceramics.  The living body member according to claim 1, wherein the artificial joint is an artificial hip joint.   The living body member according to claim 9, wherein the sliding portion of the artificial joint is a bone head of an artificial hip joint.   The living body member according to claim 9, wherein the sliding portion of the artificial joint is a acetabular socket sliding portion of an artificial hip joint.   An artificial joint comprising the pair of biological members according to claim 8, wherein the sliding portions slide relative to each other.

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