Metal treatment – Stock – Titanium – zirconium – or hafnium base
Reexamination Certificate
2000-04-17
2004-07-27
Oltmans, Andrew (Department: 1742)
Metal treatment
Stock
Titanium, zirconium, or hafnium base
C420S417000, C420S422000, C623S023700, C623S023710, C623S900000
Reexamination Certificate
active
06767418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a Ti—Zr type alloy which possesses exceptionally high strength and yet manifests low Young's modulus, exhibits sufficient malleability required for the use in structural members, and further excels in plastic workability.
This invention also relates to a medical appliance including a guide wire, a stent, a ventricular assisting device and a catheter which is formed of a Ti—Zr type alloy and used for therapeutic acts under X-ray fluoroscopy represented by a percutaneous transluminal angioplasty (PTA), for example, prevailing in such a medical field as radiology, cardiovascular internal medicine and surgical medicine. More particularly, this invention relates to a medical appliance which is formed of a Ti—Zr type alloy combining sufficient in vivo corrosion resistance, strength and workability necessary for the use in a structural material, biocompatibility, proper contrast and opaqueness, and applicability to MRI.
The Ti—Zr type alloy of this invention comprises Ti, Zr, Nb, and Ta and, optionally such a biocompatible element as Sn, Pd, Pt, and Au, and contains no metallic elements tending to arouse anxiety about toxicity. Thus, the present invention relates to a group of Ti type alloys which is essentially possessed of safety necessary for the use in a grafting material.
These medical appliances will be explained below with reference to a stent, a guide wire, and a ventricular assisting device which are cited as examples of particularly preferable uses found therefor. The alloys mentioned above, in view of their physicochemical properties, should be understood as manifesting additional availability in medical applications and popular applications as well. The alloys ought not to be limited to those uses that are cited by way of illustration in the present specification.
2. Description of the Related Art
A Ti-based alloy excels in corrosion resistance by forming a dense oxide coating of titanium dioxide (TiO
2
) on the surface thereof in the open air. Owing to its various excellent properties including light weight, great strength, and high specific strength (which is the quotient resulting from the division of the tensile strength by the specific gravity), Ti-based alloys find extensive use as materials for aerospace industry, materials for chemical devices, corrosion-resistant materials for industry utilizing seawater, and materials for consumer products such as camera shutter parts, communication equipment, optical instruments, eyeglass frames, heads, faces, and shafts in wood clubs and iron clubs used in golf. Since the Ti-based alloys mentioned above are in &agr;-phase which exhibits a rigid metallic texture at room temperature, however, they admit of no easy mechanical working such as rolling, forging, or cutting, and are mechanically worked solely in their &bgr;-phase region which is separated in a high temperature range and is capable of being machined under the existing circumstances. Moreover, in terms of material, they have the problem of manifesting unusually inferior workability in spite of their fine qualities as in corrosion resistance and strength as compared with other metals. This defect has inhibited conventional Ti-based alloys from finding expansion of their use in general industries.
It has been ascertained as a result of the study pursued to date that titanium (Ti), as well as zirconium (Zr), niobium (Nb), tantalum (Ta), platinum (Pt), and inorganic tin (inorganic Sn) are elements excelling in biocompatibility. They have begun to attract attention as materials for medical appliances. When they are to be used as a materials for medical appliances, however, this use requires them to manifest exacting corrosion resistance as compared with other general industrial uses. Specifically, in the use for medical appliances, since a component separated, even if in a minute amount, by elution from a given material brings adverse effects on a human body to an extent hardly deserving disregard, a material for a medical appliance is required to manifest quality of avoiding elution of a maternal component thereof via an oxide coat manifesting a passive state, even upon contacting with humor or blood. Besides the quality just mentioned above, such a fact as that a material for a medical appliance excels in affinity for the surrounding tissue and approximates closely to a Young's modulus of a living bone constitutes itself a very important element.
For the purpose of attaining the various properties mentioned above, various Ti-based alloys have been reported to date. As typical examples of the Ti-based alloy, an alloy for the used in a dental device which comprises titanium, about 10 to 20% by weight or about 35 to 50% by weight, as the sum of a metal selected from the group consisting of niobium and tantalum, and sufficient zirconium to act as a beta stabilizer and to reduce the rate of transformation of beta structure in the alloy (WO 95/34251); and a titanium alloy containing a first metal, titanium, a second metal selected from the group consisting of zirconium and hafnium, and mixtures thereof, and a third metal selected from the group consisting of niobium, tantalum, vanadium, and mixtures thereof in a prescribed composition (WO 95/25183) may be cited. As regards the former alloy, the weight ratio of zirconium to titanium and the weight ratio of tantalum to niobium has not been referred to anywhere in the relevant official gazette. Specifically, zirconium has been described to account for a proportion of not more than 18% by weight most preferably, tantalum is referred to as accounting for a total proportion in conjunction with niobium and allowing a part of niobium to be substituted with tantalum, and the proportion of tantalum for the most preferable alloy has been stated to be zero. The alloy of this composition is deficient in malleability and proof stress, as well as in corrosion resistance which is expected to be exceptionally strong.
The latter alloy, either in the form of an oxide or on being oxidized, is allowed to form a cermet or ceramic body and is enabled to acquire an expected working efficiency by heating the alloy in a certain temperature range and oxidizing the heated alloy with an oxidant gas thereby altering the quality thereof. The alloy disclosed in WO 95/25183, however, has the problem of failing to manifest a fine beta phase at the time of forming the alloy, revealing deficiency in plasticity and workability at normal temperature, and offering inferior corrosion resistance.
Thus, the development of a Ti-based alloy which has high strength, outstanding corrosion resistance and acid resistance, easy workability, and a low Young's modulus, particularly a Young's modulus close to that of a living bone has been earnestly yearned for. None of the alloys perfected to date, however, satisfies all these properties.
Incidentally, medical appliances using various metals led by the Ti-based alloys have been now in use. A stent, for example, is a hollow cylindrical article which is applied to interiors of a urinary tract, a bile duct, an esophagus, and a nephric tubule as well as a blood vessel with an object of dilating a narrow intracorporeal vessel. As the materials for the stent retaining intracorporeally for a long time, stainless steel (JIS SUS316L), Ta as a pure metal, and Ni—Ti type superelasticity alloys have been already reduced to practice.
Meanwhile, various implant grade Ti-based alloys for the use mainly in artificial joints have been studied from numerous angles. Typically, pure Ti and Ti-6Al-4V alloy (hereinafter all the compositions will be expressed in “weight percent”, with the balance assumed to comprise Ti and inevitable impurities, also expressed in “weight percent”, unless otherwise specified, in accordance with the general notation of alloy) may be cited. Various Ti-based alloys centering around the &bgr;-Ti-based alloys which have been developed to date, however, have not perfectly overcome the problems of corrosion resistance and inc
Kaneko Takashi
Kasori Yuu
Kurosaka Kei
Ogata Yuzi
Sato Kazuya
Burns Doane , Swecker, Mathis LLP
Oltmans Andrew
Terumo Kabushiki Kaisha
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