Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-03-13
2001-02-13
Milano, Michael J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S018110, C623S023360, C623S023480, C623S023610
Reexamination Certificate
active
06187046
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prosthetic bone material, i.e., a prosthetic material to be embedded in a lacking portion of the bone, and its production process. More particularly, the present invention relates to a calcium phosphate-based prosthetic bone material having a block-like shape as an original state and capable of changing its shape into granules when the prosthetic bone material is embedded into a lacking portion of the bone during a surgical operation, thereby ensuring the ease of shaping the material. The present invention also relates to a process for the production of such prosthetic bone material.
2. Description of the Related Art
Hitherto, granular calcium phosphate-based prosthetic bone materials have been developed and are commercially available. However, since the prosthetic bone materials are in the form of granules, when they are actually embedded into a lacking portion of the bone during a surgical operation, a problem arises with the granules scattering around unnecessary portions of the bone.
Furthermore, the use of block-shaped prosthetic bone materials makes the shaping of the block in conformity with the configuration of the lacking portion of the bone troublesome upon surgery.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the above-described related art problems by providing a calcium phosphate-based prosthetic bone material having bonded granules of calcium phosphate compound, the material having a shape that is retained until the material is separated under pressure.
Another object of the present invention is to provide a production process suitable for the production of the prosthetic bone material according to the present invention.
The present invention is based on the findings that the above objects can be accomplished if the granules of calcium phosphate compound are bonded and sintered to each other to make a block-shaped product, while retaining their shape as granules, so that the resulting product may be easily handled and can be easily disintegrated and separated via the application of hand-pressure or the like (1-50 kg/cm
2
) into granules, when the product is embedded in a lacking portion of the bone at the scene of surgical operation. The granules after disintegration have or substantially have the same size and shape as the granules in the block-shaped object. Preferably, the size and shape of the granules do not change during disintegration and separation.
That is, in one aspect of the present invention, there is provided a prosthetic bone material comprising a bonded and sintered product of granules of calcium phosphate compound having a particle size of at least about 100 &mgr;m, each of the granules being bonded with particulates of calcium phosphate compound having a particle size of about 1 to 40 &mgr;m, in which the granules are bonded to each other while retaining their original shape, and the granules have a bonding strength that is at a level sufficient to maintain or substantially maintain the size and shape of the granules when the bonded and sintered product is disintegrated.
In another aspect of the present invention, there is provided a process for the production of a prosthetic bone material which includes: mixing granules of calcium phosphate compound having a particle size of at least about 100 &mgr;m with particulates of calcium phosphate compound having a particle size of about 1 to 40 &mgr;m, and firing the mixture at a temperature of about 800 to 1,200° C.
In yet another aspect of the present invention, there is provided a process for the production of a prosthetic bone material which includes: mixing granules of calcium phosphate compound having a particle size of at least about 100 &mgr;m with particulates of calcium phosphate compound having a particle size of about 1 to 40 &mgr;m, adding to the mixture an aqueous solution of dispersing agent and/or binding agent capable of being dissipated during firing, and, after molding and drying, firing the molded and dried product at a temperature of about 800 to 1,200° C.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 09-60567 (filed on Mar. 14, 1997) and No. 09-278757 (filed on Oct. 13, 1997) which are expressly incorporated herein by reference in their entireties.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As described above, the prosthetic bone material according to the present invention is basically composed of a bonded product of granular calcium phosphate compound having a particle size of at least about 100 &mgr;m, and in this bonded product, the granules are bonded to each other under the condition of retaining their original shape and at a bonding strength which is sufficient to be easily disintegrated with the pushing pressure of a human finger or the like (1-50 kg/cm
2
) and, after disintegration, is able to maintain or substantially maintain the shape of granules. The bonding of the granules to each other relies upon the aid of the particulates of calcium phosphate compound having a particle size of about 1 to 40 &mgr;m.
The calcium phosphate compound used herein can comprise a single calcium phosphate compound or a mixture of calcium phosphate compounds. For example, the calcium phosphate compound can have a molar Ca/P ratio of 1.0 to 2.0, and can comprise, for example, hydroxyapatite, fluoroapatite, calcium hydrogenphosphate, tricalcium phosphate, tetracalcium phosphate and other calcium phosphates. The most preferred calcium phosphate compound includes hydroxyapatite as a principal component thereof.
The particle size of the granules of calcium phosphate compound is not specifically restricted as long as it is included in the scope of the definition “granular prosthetic bone material” and is generally about 100 &mgr;m or more, and an upper limit of about 5000 &mgr;m.
Further, the granules of calcium phosphate compound may be either dense (having a porosity of 0%) or porous (having a porosity of up to 60%), and they may be produced in any manner, such as by using any conventional production methods. Moreover, the granules of calcium phosphate compound can have any shape. Preferably, the granular calcium phosphate compound has a spherical shape.
From only granules of calcium phosphate compound having a particle size of at least about 100 &mgr;m, it is difficult to produce, upon sintering the granules, a bonded product in which the granules simply contact each other. Contrary to this, according to the present invention, to aid the bonding of the granules, particulates of calcium phosphate compound are added to the granules of calcium phosphate compound. Because they can be easily sintered in comparison with the granular calcium phosphate compound, in the sintering process, the particulates of calcium phosphate compound can significantly contribute to an improved bonding of the granules as a function of the sintering of the particulates themselves. The particulates of calcium phosphate compound that enables the aiding of bonding of the granules of calcium phosphate compound can be of any size smaller than that of the granules of calcium phosphate compound. Preferably, the particulates of calcium phosphate compound have a particle size in the range of about 1 to 40 &mgr;m. Particle sizes above or below the above range will not ensure the function of the particulates as a bonding aid, that is, it will only show an insufficient binding effect.
As in the production of the granules of calcium phosphate compound, the particulates of calcium phosphate compound may be produced in any manner, such as by using any conventional production methods.
In addition, it is preferred in the prosthetic bone material of the present invention that the granules of calcium phosphate compound having a particle size of at least about 100 &mgr;m and the particulates of calcium phosphate compound having a particle size of about 1 to 40 &mgr;m are contained in a ratio by weight of about 1:0.1 to 1:1. If the particulates are used in a lesser am
Nakasu Masanori
Tominaga Yoshie
Yamamoto Akira
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Milano Michael J.
Phan Hieu
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