Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-11-30
2004-08-17
Mayes, Melvin C. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C428S701000, C623S023560, C623S901000
Reexamination Certificate
active
06776860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic composite and a manufacturing method thereof, and more particularly to a method for manufacturing a ceramic composite suitable for medical applications, and to a ceramic composite manufactured by this method.
2. Description of the Related Art
Hydroxyapatite, which is a calcium phosphate-based ceramic, has the same structure as inorganic bone components. For this reason, hydroxyapatite has excellent biocompatibility and thus is used for various biocompatible materials such as artificial dental implants, bone replacement materials, dental cements, and the like.
In clinical practice, hydroxyapatite is used by being formed into dense articles, granular articles, porous articles having arbitrary porosity, or the like.
Dense hydroxyapatite articles have sufficient strength required for implant materials. However, because of its dense structure, these articles involve problems in that they impede circulation of body fluids such as blood and they have a poor bonding ability to the surrounding bone tissue when implanted in the living body.
In contrast with this, porous hydroxyapatite articles allow blood and other fluids to pass through the pores. Such porous hydroxyapatite articles are advantageous in that they are quickly surrounded by newly formed bone cells, and thus have a good bonding ability to bone tissue. On the other hand, however, such porous hydroxyapatite articles involve a problem in that it is difficult to maintain sufficient strength required for implant materials.
In view of the above-described problems, attempts have been made to provide a hydroxyapatite ceramic composite composed of hydroxyapatite ceramic bodies having different porosities.
As a method for producing such a ceramic composite, it has been proposed to produce a dense ceramic body and a porous ceramic body, and then to bond these bodies using a shrinkage fitting method in which the bodies are fitted together by utilizing a difference in the coefficients of thermal shrinkage therebetween. This method was disclosed by Japanese Patent No. 1677470.
However, when the ceramic bodies to be bonded together possess similar coefficients of thermal shrinkage, it is difficult to bond these bodies with the above-mentioned method. Further, in the case where the ceramic bodies are bonded together with this method, the shapes of the fitted sections of respective ceramic bodies have to be in advance determined taking heat-induced dimensional changes and the like which will occur into consideration. However, it is difficult to pre-adjust the densities, dimensions, and other characteristics of ceramic bodies to be bonded together by taking the heat-induced dimensional changes into consideration. Furthermore, the ceramic bodies to be bonded have limitations in their shapes, since these ceramic bodies have to be formed into fittable shapes.
Another method has also been proposed to bond ceramic bodies together, in which the ceramic bodies are bonded together by interposing an intermediate layer such as a resin-containing adhesive and the like therebetween.
This method imposes no limitations on the materials, shapes, or other characteristics of the ceramic bodies to be bonded, because there is no need to take heat-induced dimensional changes or the like into consideration. However, when an adhesive or the like is used to bond ceramic bodies together, it is difficult to obtain a ceramic composite having adequate bonding strength. Further, even if such a ceramic composite could be obtained, it is difficult to maintain the bonding strength for a long time. Furthermore, when ceramic composites containing adhesives or the like are applied to the living body, there is a danger that the resins and other components contained in the adhesive will elute into the living body.
Therefore, the method using the adhesive described above involves problems in terms of biosafety and bioaffinity.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of manufacturing ceramic composite that can manufacture, with a simple technique, a ceramic composite having required strength and excellent bioaffinity and biosafety.
Further, another object of the present invention is to provide a ceramic composite which has required strength and excellent bioaffinity and biosafety and which can be obtained with a simple manufacturing method.
In view of these objects, the present invention is directed to a method of manufacturing a ceramic composite. The method comprising the steps of: preparing at least two ceramics bodies to be bonded together, each of the at least two ceramics bodies having a bonding surface; preparing a slurry in which primary particles of a bonding ceramic are dispersed; applying the slurry to the bonding surface of at least one of the ceramic bodies to be bonded; and sintering the ceramic bodies between which the slurry has been interposed to bond them.
According to the method of manufacturing the ceramic composite of the present invention, it is possible to bond a plurality of ceramic bodies with a simple technique. Further, the slurry in which primary particles of a bonding ceramic are dispersed is applied to the bonding surface of one of the ceramic bodies to be bonded, it becomes possible to obtain the ceramic composite having an excellent bonding strength by sintering such ceramic bodies. Further, it becomes possible to completely integrate the ceramic bodies with each other, thereby preventing the strength at the bonding area between the sintered ceramic bodies from being deteriorated. Further, according to the present invention, it is possible to easily manufacture ceramic composites having complex shapes.
In the present invention, it is preferred that the at least two ceramics bodies have different porosities. Bonding the ceramic bodies having such different porosities together makes it possible to obtain a ceramic composite in which different sections exhibit different functions. Therefore, it becomes possible to manufacture, with a simple technique, a ceramic composite (e.g., biocompatible materials such as artificial dental implants, bone replacement materials, dental cements and the like) having the required strength and excellent bioaffinity and biosafety. In this case, it is preferable that the at least one of the ceramic bodies has a porosity of 15 to 70%.
Further, in the present invention, it is also preferred that the at least two ceramics bodies have the identical compositions. Preferably, the at least one of the ceramic bodies is composed of calcium phosphate-based compounds. More preferably, the at least one of the ceramic bodies is composed of calcium phosphate-based compounds with a Ca/P ratio of 1.0 to 2.0. In this case, it is preferable that the calcium phosphate-based compounds is hydroxyapatite.
Further, in the present invention, it is also preferred the bonding ceramic in the slurry is constituted from the same material as that of at least one of the ceramic bodies to be bonded, and that the slurry does not contain any resin components therein. This means that the slurry that is applied to the ceramic bodies to be bonded does not contain any water-soluble polymers such as binders, that is the ceramic composite does not contain any organic components. Accordingly, the ceramic composite of the present invention eliminates the danger that these organic components will elute into the living body when this ceramic composite is used as a biocompatible material. In this case, it is preferred that the content of the bonding ceramic in the slurry is 0.1 to 20 vol %.
Furthermore, in the present invention, it is also preferred that the particles of the bonding ceramic have an average grain size of 0.05 to 0.5 &mgr;m. Further, it is preferred that the bonding ceramic is composed of calcium phosphate-based compounds, and that the particles of the bonding ceramic have an average grain size of 0.05 to 0.5 &mgr;m.
Moreover, it is also preferred that the bonding ceramic is composed of calcium pho
Arai Kaoru
Kohketsu Masahiro
Matsushima Asako
Nakasu Masanori
Greenblum & Bernstein P.L.C.
Mayes Melvin C.
PENTAX Corporation
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