Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-02-28
2002-08-13
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023510, C623S023540
Reexamination Certificate
active
06432142
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for producing implants having high biological affinity by means of molding an artificial bone, such as an artificial hip joint stem, made of titanium or titanium alloy, through plastic working by using a split die in a high-temperature inert atmosphere, while simultaneously implanting granules of a bioactive ceramic, such as hydroxyapatite, into the surfaces thereof. More particularly, the invention relates to a mold for working a titanium or titanium alloy substrate into a desired product shape, and to artificial bone, such as an artificial hip joint stem, molded by hot pressing employing the mold.
2. Description of the Related Art
Medical implants, such as artificial tooth roots, artificial joints, and artificial bone, of various kinds made from titanium or titanium alloys exhibit both exceptional biocompatibility (i.e., the property to give rise to tissue no lesions, etc. in vivo) and mechanical properties, and are thus used increasingly. Recently, it has been attempted to produce an even better implant by imparting biological affinity (the ability to positively bond with bone in vivo) by implanting granules of a ceramic similar to a component of bone, such as hydroxyapatite, into the surface thereof (Japanese Laid-Open patent publication No. 5-57013/1993, “COMPOUND IMPLANT OF TITANIUM OR TITANIUM ALLOY AND MANUFACTURE THEREOF”) using a casting method.
The cited invention is proposed as a substitute for surface coating formation by a conventional thermal spraying method. Specifically, surface coatings produced by the conventional thermal spraying method do not exhibit adequate bonding strength with metal, resulting in problems such as exfoliation of the coatings with extended use; therefore, granules of a bioactive ceramic are implanted into the surface of the implant, rather than forming a coating thereon. However, as titanium is highly reactive at high temperatures, when casting processes are employed, there forms a surface reaction layer that must be removed through grinding, etc. Accordingly, the bioactive ceramic granules employed in the cited invention have particle size of 1 mm or larger, which does not represent an appropriate particle size in terms of improving biological affinity thereof. Further, the problem of changes in product dimensions and shape due to grinding processes, etc., conducted after casting remains unsolved. With the foregoing in view, there has been developed a newer technique employing a superplastic forming process that is associated with minimal surface reaction layer formation, and that involves implanting granules of a bioactive ceramic, such as hydroxyapatite, into the surface of titanium or a titanium alloy (“Hydroxyapatite Granule Implantation into Superplastic Titanium Alloy”, Tooru NONAMI, Katsuyoshi NAGANUMA, Akira KAMIYA, and Tetsuya KAMEYAMA, Journal of the Ceramic Society of Japan, Vol. 105, August ed., p. 710-712 (1997) and Japanese Patent Application No. 11-170436/1999, “IMPLANTS HAVING HIGH BIOLOGICAL AFFINITY AND A PRODUCTION PROCESS THEREFOR”)
However, processes for implanting bioactive ceramic granules such as hydroxyapatite are either adapted for simple smooth surfaces, such as plate surfaces, or adapted primarily to small implants such as artificial tooth roots. Further technical efforts are needed to adapt such processes for use with other types of artificial bone, particularly artificial hip joint stems, etc., for which significantly increased demand is anticipated. Specifically, conventional techniques are not readily adapted to stems, etc. having long narrow forms that include various curves, and having larger dimensions than artificial tooth roots, etc.
Thus, in the technical field to which the invention pertains, there has been a need for development of a technique whereby granules of bioactive ceramic such as hydroxyapatite ranging from the micron order to the millimeter order can be uniformly implanted into the surface of artificial bone, such as an artificial hip joint stem.
SUMMARY OF THE INVENTION
The present invention provides a mold for pressing a substrate, as well as a titanium or titanium alloy artificial bone having biological affinity imparted to its surface, for use as an artificial hip joint stem, etc.
The invention relates to a mold comprising a split die to be arranged in opposition about a substrate, and an outer frame situated about the perimeter of the split die, wherein the outer frame and the split die function as a wedge and move slidably so as to convert the load produced by a vertical uniaxial press into load applied from two opposing directions across the horizontal, the split die move in such a way as to compress the titanium or titanium alloy substrate and uniformly press the side faces thereof so as to impart the required shape to the substrate; and to artificial bone having high biological affinity produced by imparting to a substrate the required shape through hot pressing using this mold, while simultaneously implanting granules of a bioactive ceramic, such as hydroxyapatite, into the surfaces thereof.
The invention is intended to solve the problems described previously, and has as an object to provide a mold for uniformly pressing the side faces of a substrate, which utilizes plastic deformation of titanium or titanium alloys at high temperature, making it possible to impart the required product shape thereto, while at the same time uniformly implanting granules of a bioactive ceramic, such as hydroxyapatite, into the surfaces thereof; and to provide titanium or titanium alloy artificial bone having high biological affinity obtained thereby.
To solve the problems described previously, the present invention comprises the following constitutions.
(1) A mold comprising split dies to be arranged in opposition about a substrate, and an outer frame situated about the perimeter thereof,
wherein the outer frame and split dies function as a wedge and move slidably so as to convert the load produced by a vertical uniaxial press into load applied from two opposing directions across the horizontal,
the split dies move in such a way as to compress the substrate and uniformly press the side faces thereof so as to impart the required configuration to the substrate.
(2) Titanium or titanium alloy artificial bone, which is produced by setting a titanium or titanium alloy substrate in the split dies of the mold as defined in (1) above, and then molding it through hot pressing.
(3) The artificial bone according to (2) above, having granules of a bioactive ceramic implanted in the surfaces of the substrate, which is produced by steps of spreading the granules of the bioactive ceramic over split die surfaces and/or substrate surfaces, and then implanting the granules of the bioactive ceramic present on the surfaces thereinto, while molding the substrate through hot pressing.
(4) The artificial bone according to (3) above, wherein the granules of the bioactive ceramic have particle size of from 30 to 100 &mgr;m.
Specifically, in a temperature region of from 700° C. to 900° C. in an atmosphere that is non-reactive with titanium, such as a vacuum or argon atmosphere, a pair of split dies of the desired product shape are arranged in opposition about a titanium or titanium alloy substrate, the split dies function as a wedge and move slidably within an outer frame so as to convert the load produced by a vertical uniaxial press into load applied from two opposing directions across the horizontal, thereby moving in such a way that the split dies compress the substrate during molding. In this case, since granules of a bioactive ceramic such as hydroxyapatite are spread over the split die surface and/or substrate surface, these granules are simultaneously implanted into the surface of the implant. That is, according to the present invention, molding of the material to its final product shape and imparting biological affinity thereto by implanting granules of a bioactive ceramic such as hydroxyapatite into the surfaces t
Kamiya Akira
Naganuma Katsuyoshi
Watazu Akira
Zhu Jun
Japan as represented by Secretary of Agency of Industrial Scienc
McDermott Corrine
Phan Hieu
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