Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-10-04
2003-05-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S469000, C428S697000, C428S698000, C428S699000, C428S701000, C623S016110, C623S023560, C623S023570, C623S023580, C623S023600, C427S002260, C427S372200
Reexamination Certificate
active
06569547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hard tissue repairing materials and, particularly, to a bone repairing material that is used to repair when articular function and/or bone function of hands and feet are lost. Furthermore, the invention relates to an implant that can be used as an artificial tooth, for rebuilding the teeth and tusks when the teeth had been lost because of senility or illness.
2. Description of the Prior Art
In the case of damage in a hard tissue repairing material, e.g., a bone and a tooth, any artificial hard tissue repairing materials may be inserted in living body for treatment. The hard tissue repairing material has to be bonded to the living hard tissue in living body after having been inserted. In order to bond the hard tissue repairing material to a living hard tissue, the hard tissue repairing material should have any functional group capable of inducing the nucleation of hydroxyapatite so that hard tissue repairing material should have a “bone-like apatite” on its surface. The bone-like apatite is the hydroxyapatite which has carbonate ion (CO
3
2−
) and low Ca ion concentration (Ca deficiting) regarding with stoichiometric composition (Ca
10
(PO
4
)
6
(OH)
2
). The bone-like apatite also has a Ca/P ratio that is lower than 1.67 of the stoichiometric hydroxyapatite. The bone-like apatite has a plurality of lattice defect and is constructed by fine particles. Therefore, the bone-like apatite is nearly equal to the bone apatite of living bone.
It is known that a hard tissue repairing material including a base material, e.g., metal or ceramics, and a zirconia gel layer made by a sol-gel process. The zirconia gel layer has a Zr—OH group that may induce a nucleation of apatite. (See, Bioceramics volume 11 Ed. by R. Z. LeGros and J. P. LeGros, World Scientific, (1998) pp77-80).
By the way, several prior art methods of giving the bioactive function at the surface of a base material are disclosed in some literature. For example, the Japanese Laid-open Patent Publication No. 6-23030 discloses a method of forming a coating layer of silica gel or titania gel on the surface of a base material. The Japanese Laid-open Patent Publication No. 10-179718 discloses a method of improving the surface of a base material of titanium metal and titanium alloys to bioactive by soaking in an alkaline fluid.
The layer having the hydroxyl group formed by the method of the Japanese Laid-open Patent Publication No. 6-23030 is a silica gel layer or a titania gel layer on the surface of the base materials. Similarly, the bioactive layer formed by the method of the Japanese Laid-open Patent Publication No. 10-179718 is titania phase, titania gel phase, alkaline-titanate phase, and alkaline-titanate gel phase
However, the prior art hard tissue repairing material has a low level ability of inducing the nucleation of hydroxyapatite and, accordingly, the prior art hard tissue repairing material can not be bonded greatly to a living hard tissue in living body.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a hard tissue repairing material having a high bioactivity.
In accordance with one aspect of the present invention, there is provided a hard tissue repairing material including a base material and a surface layer having a crystalline zirconia covering the base material, which the surface layer includes a Zr—OH group.
The hard tissue repairing material includes a surface layer having a Zr—OH group to induce a nucleation of apatite. Additionally, the hard tissue repairing material of this invention can form large amount of apatite, so that the hard tissue repairing material may have a good bioactivity. We consider that the hard tissue repairing material includes a surface layer having the crystalline zirconia so that the apatite can grow as maintaining the coordination between the crystalline direction of the Zr—OH group and the crystalline direction of the OH group of apatite. The surface layer having the crystalline zirconia may have a thickness ranging from 0.5 to 50 &mgr;m, preferably thickness ranging from 1 to 10 &mgr;m, more preferably thickness ranging from 1 to 5 &mgr;m.
Preferably, a middle layer between the base material and the surface layer, which includes at least one element of the base material and at least one element of the surface layer having a crystalline zirconia, may be formed. With the middle layer, the contact between the base material and the surface layer having the crystalline zirconia can have a good contact strength. The middle layer may include an amorphous phase or crystal phase. Additionally, the middle layer may include a composite, e.g., double salt, or solid solution including at least two elements.
The surface layer may have a tetragonal zirconia, a monoclinic zirconia, or the both. Preferably, the surface layer may contain at least an ionic component that is selected from the group consisting of calcium ion, sodium ion, potassium ion, and phosphate ions. Consequently, the ionic component within the surface layer can promote a bone-like apatite. More preferably, the hard tissue repairing material may further include a second layer containing an apatite layer as a main component formed on the surface layer having the crystalline zirconia. The apatite layer in the second layer can promote the apatite spontaneously in the living body.
The base material may be a ceramic material including an oxide group, a carbide group, a nitride group, or a boride group. Additionally, e.g., silica-glass, preferably zirconia, zirconia-alumina composite may be used. The base material may be a metal material, e.g., titanium, Co—Cr—Mo alloy, and may be a polymer material.
A process for producing a hard tissue repairing material includes preparing a base material, coating the base material with a zirconia sol, and crystallizing the zirconia sol.
The zirconia sol solution may include zirconium alkoxide, alcohol, distilled water, acid catalyst. Preferably, a solution including Zr(OC
3
H
7
)
4
, C
2
H
5
OH, H
2
O and HNO
3
may be used as zirconium sol solution. Soaking the base material in the zirconia sol solution may result in coating of the base material with the zirconia sol. Additionally, crystallizing the zirconia sol may be effected by heating. It is noted that coating the zirconia sol and heating the base material having the zirconia sol on the surface may be repeated. According to desired repeats of coating and heating, the surface layer having the crystalline zirconia may have a thickness ranging from 0.5 &mgr;m to 50 &mgr;m, preferably from 1 &mgr;m to 10 &mgr;m, and more preferably from 1 &mgr;m to 5 &mgr;m.
The heating temperature is not limited, provided that the crystalline zirconia can be formed by heating. The temperature will be dependent on any conditions, e.g., the composition of the zirconia sol solution and/or the atmosphere. In the case that the zirconia sol solution including Zr(OC
3
H
7
)
4
, C
2
H
5
OH, H
2
O and HNO
3
is used, the base material having the zirconia sol on the surface may be heated at not lower than 500° C. in air. More preferably, the base material may be heated at not higher than 800° C. If the base material is heated under other condition, e.g., in a hydrothermal bath, the base material may be heated at much lower than 500° C.
A process for producing a hard tissue repairing material includes preparing a base material, coating the base material with a zirconia sol, heating the base material having the zirconia sol on the surface. Then, the diffusing layer having at least an element of the base material and at least an element of the zirconia sol is formed on the base material. Subsequently, coating the diffusing layer with a zirconia sol, and crystallizing the zirconia sol on the diffusing layer. Therefore, the surface layer having a crystalline zirconia is formed, and a middle layer between the base material and the surface layer is formed by the diffusion layer.
The heating condition to form the middle layer is not limited, provided
Kokubo Tadashi
Nawa Masahiro
Uchida Masaki
Jones Deborah
Matsushita Electric & Works Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sperty Arden B.
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