Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1999-06-15
2001-06-19
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S527000, C148S678000
Reexamination Certificate
active
06248190
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the manufacture of body implantable medical devices, and more particularly to making stents and other prostheses configured for high radio-opacity as well as favorable mechanical characteristics.
Several prostheses, typically of latticework or open frame construction, have been developed for a variety of medical applications, e.g. intravascular stents for treating stenosis, prostheses for maintaining openings in the urinary tracts, biliary prostheses, esophageal stents, renal stents, and vena cava filters to counter thrombosis. One particularly well accepted device is a self-expanding mesh stent disclosed in U.S. Pat. No. 4,655,771 (Wallsten). The stent is a flexible tubular braided structure formed of helically wound thread elements.
Alternatively, stents and other prostheses can be expandable by plastic deformation, usually by expanding a dilation balloon surrounded by the prosthesis. For example, U.S. Pat. No. 4,733,665 (Palmaz) discloses an intraluminal graft constructed of stainless steel strands, either woven or welded at their intersections with silver.
Regardless of whether the prosthesis is self-expanding or plastically expanded, accurate placement of the prosthesis is important to its effective performance. Accordingly, there is a need to visually perceive the prosthesis as it is being placed within a blood vessel or other body cavity. Further, it is advantageous to visually locate and inspect a previously deployed prosthesis.
Fluoroscopy is the prevailing technique for such visualization, and it requires radio-opacity of the materials to be imaged. The preferred structural materials for prosthesis construction, e.g. stainless steels and cobalt-based alloys, are not highly radiopaque in the thin-section sizes of stent wires. Consequently, endoluminal prostheses constructed of these materials do not lend themselves well to fluoroscopic imaging.
A particularly advantageous stent construction, in terms of providing radio-opacity and mechanical integrity, is disclosed in U.S. Pat. No. 5,630,840 (Mayer). The Mayer device discloses a stent formed of multiple filaments, preferably arranged in at least two sets of oppositely directed helical windings interwoven with one another in a braided configuration. Each filament is a composite including a core surrounded by a case. Preferably, the core provides the desired radio-opacity, while the case governs mechanical behavior. Suitable core materials include tantalum and a platinum nickel alloy. Suitable case materials include certain alloys composed primarily of cobalt and chromium, e.g. sold under the brand names Elgiloy and MP35N.
Although such composite filaments provide the desire d mechanic al characteristics and good fluoroscopic visibility, the primarily platinum core is expensive.
Accordingly, one object of the present invention is to provide a process for making composite filament for use in stents and other body insertable medical devices, that is less expensive than composite filaments with primarily platinum cores.
Tantalum cores are less expensive than platinum cores, but require special processing. During reduction of a tantalum billet or bar to a rod or wire for use as the core, the material is aninealed to enhance its formability. Annealing usually occurs in a hydrogen atmosphere to prevent oxidation of the tantalum. Hydrogen is absorbed by the tantalum during annealing, and must later be removed by a vacuum treatment to avoid hydrogen concent rations in the metal. During the age hardening stage of composite filament construction, any residual hydrogen in the tantalum core can lead to hydrogen outgassing, increasing the time needed to achieve satisfactory vacuum levels within the age hardening furnace for protecting the case material from oxidation.
Accordingly, another object of the present invention is to provide a process for making composite filaments in a manner that avoids hydrogen outgassing during the processing of filaments or stents and other devices composed of the composite filaments.
A further object of the invention is to provide a composite filament fabrication process incorporating cold-working stages and annealing stages performed under conditions more suitable for filaments having cores with melting temperatures lower than those of tantalum and platinum.
Another object is to provide a process for fabricating composite filaments for devices that, when inserted or implanted in the body, are less likely to interfere with magnetic resonance imaging of tissue adjacent and surrounding the devices.
Yet another object of the invention is to provide a process particularly well suited to fabricating a composite filament having a gold or gold alloy core.
SUMMARY OF THE INVENTION
To achieve these and other objects, there is provided a process for manufacturing a body insertable composite filament. The process includes the following steps:
a. providing (i) an elongate core substantially uniform in lateral cross-section and comprising a gold alloy containing from about 60 weight percent to about 99 weight percent gold, and having a melting temperature above 1600° F. (870° C.), and (ii) an elongate tubular case substantially uniform in lateral cross-section and formed of a metal;
b. inserting the core into the case to form an elongate composite filament in which the case surrounds the core;
c. cold working the composite filament to reduce its outside diameter;
d. annealing the composite filament after cold working, at an average annealing temperature of at most 2000 degrees F. (1093 degrees C) and at a maximum annealing temperature less than a melting point of the core, to substantially remove strain hardening induced by the cold working;
e. cold working the annealed composite filament in a final cold-working stage, and then forming the cold-worked composite filament into an intended shape; and
f. while maintaining the cold-worked composite filament in the intended shape, age hardening the case.
The cold-working step can include drawing the composite filament serially through several dies, with each die plastically deforming the composite filament to reduce the outside diameter. Whenever a stage including one or more cold working dies has reduced the cross-sectional area by at least 15 percent and the ductility of the composite filament is sufficiently low (i.e., less than about 10 percent tensile elongation) to raise a risk of fracture during further cold-working, an annealing step should be performed before any further cold-working. During each annealing step, the composite filament is heated to a temperature in the range of about 1400-2000 degrees F. (760 degrees C. to 1093 degrees C.) for a period depending on the filament diameter, typically in the range of several seconds to several minutes.
In an alternative version of the process, the initial outside diameter of the composite structure (billet) typically is at least fifty millimeters (about two inches) in diameter. Then, before cold-working, the composite filament is subjected to temperatures in the annealing range while the outside diameter is substantially reduced, either by swaging or by pulltrusion, in successive increments until the outside diameter is at most about 6 millimeters (0.25 inches). The resulting filament is processed as before, in alternative cold-working and annealing stages.
Further according to the process, the composite filament can be severed into a plurality of strands. Then, the strands are arranged in two oppositely directed sets of parallel helical windings about a cylindrical form, with the strands intertwined in a braided configuration to form multiple intersections. Then, while the strands are maintained in a predetermined uniform tension, they are heated to a temperature in the range of about 500-700° C. (930-1290° F.), more preferably about 550° C. (1020° F.), for a time sufficient to age harden the case material of the helical windings.
The process can be employed to form a body compatible device comprising an elongate filament substantially uniform in lateral
Larkin Hoffman Daly & Lindgren Ltd.
Niebuhr, Esq. Frederick W.
Sci-Med Life Systems, Inc.
Wyszomierski George
LandOfFree
Process of making composite stents with gold alloy cores does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process of making composite stents with gold alloy cores, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process of making composite stents with gold alloy cores will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2540324