Metal Alloy For Medical Devices

Abstract

A method and process for at least partially forming a medical device.

Claims

1-20. (canceled)

21. A medical device in the form of an orthopedic device or an orthodontics device that is formed of a metal alloy that includes 40 wt. % to 99.9 wt. % molybdenum and one or more other material, said metal alloy having an average density of up to about 14 gm/cc, said metal alloy of said medical device has an average grain size of 4-14 ASTM, said other materials selected from the group consisting of the group consisting of calcium, carbon, cerium oxide, chromium, cobalt, copper, gold, hafnium, iron, lanthanum oxide, lead, magnesium, nickel, niobium, osmium, platinum, rare earth metals, rhenium, silver, tantalum, technetium, titanium, tungsten, vanadium, yttrium, yttrium oxide, zinc, zirconium, zirconium oxide.

22. The medical device as defined in claim 21, wherein said metal alloy is selected from the group consisting of MoTiZr, MoHfC, MoY.sub.2O.sub.3, MoCe.sub.2O, MoW, MoTa, MoZrO.sub.2, MoLa.sub.2O.sub.3, and MoY.sub.2O.sub.3Ce.sub.2O.

23. The medical device as defined in claim 21, wherein said metal alloy is MoTiZr, a weight percent of titanium in said MoTiZr is less than 1 weight percent, a carbon content in said MoTiZr is no more than 150 ppm, and a weight percent of zirconium in said MoTiZr is less than 1 weight percent and said MoTiZr has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

24. The medical device as defined in claim 21, wherein said metal alloy is MoHfC, a weight percent of said hafnium in said MoHfC is about 0.8-1.4 weight percent and a weight percent of said carbon in said MoHfC is about 0.05-0.15, and said MoHfC has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

25. The medical device as defined in claim 21, wherein said metal alloy is MoY.sub.2O.sub.3, a weight percent of Y.sub.2O.sub.3 in said MoY.sub.2O.sub.3 is about 0.3-0.5, a carbon content in said MoY.sub.2O.sub.3 is no more than 150 ppm, and said MoY.sub.2O.sub.3 has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

26. The medical device as defined in claim 21, wherein said metal alloy is MoCe.sub.2O, a weight percent of Ce.sub.2O in said MoCe.sub.2O is about 0.04-0.1, a carbon content in said MoCe.sub.2O is no more than 150 ppm, and said MoCe.sub.2O has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

27. The medical device as defined in claim 21, wherein said metal alloy is MoW, a weight percent of tungsten in said MoW is about 20-50 weight percent, a carbon content in said MoW is no more than 150 ppm, and said MoW has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

28. The medical device as defined in claim 21, wherein said metal alloy is MoTa, a weight percent of Ta in said MoTa is about 10-50 weight percent, a carbon content in said MoTa is no more than 150 ppm, and said MoTa has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

29. The medical device as defined in claim 21, wherein said metal alloy is MoZrO.sub.2, a weight percent of ZrO.sub.2 in said MoZrO.sub.2 is about 1.2-1.8, a carbon content in said MoZrO.sub.2 is no more than 150 ppm, and said MoZrO.sub.2 has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 Gpa.

30. The medical device as defined in claim 21, wherein said metal alloy is MoLa.sub.2O.sub.3, a weight percent of La.sub.2O.sub.3 in said MoLa.sub.2O.sub.3 is about 0.3-0.7, and a carbon content in said MoLa.sub.2O.sub.3 is no more than 150 ppm, and said MoLa.sub.2O.sub.3 has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

31. The medical device as defined in claim 21, wherein said metal alloy is MoY.sub.2O.sub.3Ce.sub.2O, a weight percent of Ce.sub.2O in said MoY.sub.2O.sub.3Ce.sub.2O is about 0.04-0.1, a carbon content in said MoY.sub.2O.sub.3Ce.sub.2O is no more than 150 ppm, and a weight percent of Y.sub.2O.sub.3 in said MoY.sub.2O.sub.3Ce.sub.2O is about 0.3-0.5 weight percent, and said MoY.sub.2O.sub.3Ce.sub.2O has an elongation of greater than 10%, a UTS of 60-320 ksi, and a modulus of elasticity of >300 GPa.

32. The medical device as defined in claim 21, wherein said metal alloy includes a nitride layer on an outer surface of said metal alloy.

33. The medical device as defined in claim 21, wherein said metal alloy formed of isostatically pressed together metal powder that has been sintered.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0113] Reference may now be made to the drawings, which illustrate various embodiments that the invention may take in physical form and in certain parts and arrangements of parts wherein:

[0114] FIG. 1 is a perspective view of a section of a non-limiting medical device in the form of an unexpanded stent which permits delivery of the stent into a body passageway; and,

[0115] FIG. 2 is one non-limiting process in accordance with the invention for manufacturing a medical device from a molybdenum and rhenium alloy, cobalt chromium, tungsten and tantalum alloy, or other type of metal alloy.

DETAILED DESCRIPTION OF THE INVENTION

[0116] Referring now to the drawings wherein the showing is for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting the same, FIG. 1 discloses a medical device in the form of a stent for use in a body passageway. The stent is particularly useful in the cardiovascular field; however, the stent can be used in other medical fields such as, but not limited to, orthopedics, cardiology, pulmonology, urology, nephrology, gastrointerology, gynecology, otolaryngology or surgical fields. Additionally or alternatively, the medical device is not limited to a stent, thus can be in the form of many other medical devices (e.g., orthopedic implant, orthopedic device, PFO (patent foramen ovale) device, valve, spinal implant, vascular implant, graft, guide wire, sheath, stent catheter, electrophysiology catheter, hypotube, catheter, staple, cutting device, any type of implant, pacemaker, dental implant, bone implant, prosthetic implant or device to repair, replace and/or support a bone and/or cartilage, nail, rod, screw, post, cage, plate, pedicle screw, spinal rod, cap, hinge, joint system, wire, anchor, spacer, shaft, anchor, disk, ball, tension band, locking connector, or other structural assembly that is used in a body to support a structure, mount a structure and/or repair a structure in a body, dental restorations, crowns, bridges, braces, dentures, retainers, tubes, pins, palatal expander, orthodontic headgear, orthodontic archwire, teeth aligners, quadhelix, etc.).

[0117] The stent, when used for vascular applications, can be used to addresses various medical problems such as, but not limited to, restenosis, atherosclerosis, atherogenesis, angina, ischemic disease, congestive heart failure or pulmonary edema associated with acute myocardial infarction, atherosclerosis, thrombosis, controlling blood pressure in hypertension, platelet adhesion, platelet aggregation, smooth muscle cell proliferation, vascular complications, wounds, myocardial infarction, pulmonary thromboembolism, cerebral thromboembolism, thrombophlebitis, thrombocytopenia or bleeding disorders.

[0118] As illustrated in FIG. 1, stent 20 is in the form of an expandable stent that includes at least one tubular shaped body member 30 having a first end 32, a second end 34, and member structures 36 disposed between the first and second ends. As can be appreciated, the stent can be formed of a plurality of body members connected together. Body member 30 has a first outer cross-sectional area or diameter which permits delivery of the body member into a body passageway. The first outer cross-sectional area or diameter of the body member is illustrated as substantially constant along the longitudinal length of the body member. As can be appreciated, the body member can have a varying first outer cross-sectional area or diameter along at least a portion of the longitudinal length of the body member. The body member also has a second expanded outer cross-sectional area or diameter, not shown. The second outer cross-sectional area or diameter typically can vary in size; however, the second outer cross-sectional area or diameter can be non-variable in size. The stent can be expanded in a variety of ways such as by a balloon. A balloon expandable stent is typically pre-mounted or crimped onto an angioplasty balloon catheter. A balloon catheter is then positioned into the patient via a guide wire. Once the stent is properly positioned, the balloon catheter is inflated to the appropriate pressure for stent expansion. After the stent has been expanded, the balloon catheter is deflated and withdrawn, leaving the stent deployed at the treatment area.

[0119] One or more surfaces of the stent can be treated so as to have generally smooth surfaces; however, this is not required. Generally, one or more ends of the stent are treated by filing, buffing, polishing, grinding, coating, and/or the like to remove or reduce the number of rough and/or sharp surfaces; however, this is not required. The smooth surfaces of the ends reduce potential damage to surrounding tissue as the stent is positioned in and/or expanded in a body passageway.

[0120] The stent can be at least partially coated with one or more therapeutic agents (not shown). One or more polymers (not shown) can be used in conjunction with the one or more therapeutic agents to 1) facilitate in the bonding of the one or more therapeutic agents to the stent, and/or 2) at least partially control the release of one or more therapeutic agents from the stent.

[0121] Referring now to FIG. 2, there is illustrated one non-limiting process for forming the stent as illustrated in FIG. 1 or some other type of medical device. The medical device can be formed of different types of metal alloys. The present invention is particularly directed to forming all or a portion of a medical device such as a stent from metal alloys that are difficult to work with such as alloys of molybdenum, titanium, yttrium, zirconium, rhenium, tantalum, cobalt, chromium and/or tungsten.

[0122] When the medical device is formed of 1) molybdenum and rhenium alloy, 2) molybdenum and rhenium alloy with small additions of other metals (e.g., titanium, yttrium, and/or zirconium), 3) tungsten and tantalum, 4) tungsten and tantalum and small additions of other metals, 5) cobalt and chromium, or some other metal alloy, medical device that is formed from such metal alloys can be form in a variety of ways in accordance with the present invention. Process step 100 illustrates that metal powders of the alloy are selected to form a tube, rod or some other structure of the medical device. The powders of metal alloys generally constitute a majority weight percent of the medical device; however, this is not required. The purity of the metal powders is selected to minimize the carbon, oxygen and nitrogen content in the metal powder; however, this is not required.

[0123] After the metal powders have been selected, the metal powders are substantially homogeneously mixed together as illustrated in process step 110. After the metal powders are mixed together, the metal powders are isostatically consolidated to form in a tube, rod or some other form for the medical device. In some situations, the metal powders can be formed into the final or near final form of the medical device (e.g., screw, etc.). One non-limiting isostatic consolidation process is a cold isostatic pressing (CIP) process. The isostatic consolidation process typically occurs in a vacuum environment (e.g., less than about 1-10.sup.5 Torr, etc.), an oxygen reducing environment, or in an inert atmosphere; however, this is not required. The average density of the metal tube obtained by the isostatic consolidation process is about 80-90% of the final average density of the final medical device that includes the metal alloy.

[0124] One non-limiting composition of the metal alloy is a solid solution of about 44-48 wt % rhenium and about 52-56 wt % molybdenum. One non-limiting metal alloy can include about 44.5-47.5 wt % Re and 52.5-55.5 wt % Mo, a weight percent of Re plus Mo of at least about 99.9%, and no more than about 0.2 weight impurities. Another non-limiting composition of the tube is a solid solution of about 44-48 wt % rhenium, about 52-56 wt % molybdenum, up to about 0.5 wt % Ti, Y and/or Zr, and no more than about 0.2 weight impurities. One non-limiting metal alloy can include a majority weight percent of Mo and Re and an additional metal selected from Ti, Y and/or Zr. One non-limiting metal alloy composition includes about 44-48 wt % Re, about 52-56 wt % Mo, and up to about 0.5 wt % Ti, Y and/or Zr. Another non-limiting metal alloy composition includes about 44.5-47.5 wt % Re, 52.5-55.5 wt % Mo, a weight percent of Mo plus Re plus Ti, Y and/or Zr that is at least about 99.9%, 0.3-0.4 wt % Ti, 0.06-0.1 wt % Zr, 0-0.05 wt % Y, a weight ratio of Ti:Zr of 1-3:1, and no more than about 0.2 weight impurities.

[0125] After the metal powder has been selected and pressed together, the metal powder is sintered to fuse the metal powders together and to form the tube, rod or some other form for the medical device. The sinter of the metal powders occurs at an appropriate temperature for the particular metal alloy. For a MoRe alloy, a sintering temperature of about 2000-2500 C. for about 5-120 minutes can be used; however, other temperatures and/or sintering time can be used. The sintering of the metal powder typically takes place in an oxygen reducing environment to inhibit or prevent impurities from becoming embedded in the metal alloy and/or to further reduce the amount of carbon and/or oxygen in the metal alloy; however, this is not required. After the sintering process, the solid solution of the metal alloy generally has an as-sintered average density of about 90-99% the minimum theoretical density of the metal alloy. Typically, for a MoRe sintered metal alloy, the final average density is about 13-14 gm/cc. Higher sintering temperatures will generally be required (e.g., 2000-3000 C.) and greater average densities will be obtained (e.g., greater than 14 gm/cc) when forming tungsten and tantalum alloys. For other types of alloys, the sinter temperature and time and the final average density of the metal alloy may be different.

[0126] When the metal powders are formed into a rod or tube, the length of the formed rod or tube is typically about 48 inches or less; however, longer lengths can be formed. Generally, when the final medical device is to be a stent or a rod, a tube is first formed. For other types of medical devices, a tube may not be formed. In one non-limiting arrangement, the length of the rod or tube is about 8-20 inches. The average concentricity deviation of the rod or tube is typically about 1-18% for use in forming a stent. In one non-limiting tube configuration, the tube has an inner diameter of about 0.31 inch (i.e., 0.0755 sq. in. cross-sectional area) plus or minus about 0.002 inch and an outer diameter of about 0.5 inch (i.e., 0.1963 sq. in. cross-sectional area) plus or minus about 0.002 inch. The wall thickness of the tube is about 0.095 inch plus or minus about 0.002 inch. As can be appreciated, this is just one example of many different sized tubes that can be formed.

[0127] In another alternative tube forming process, a rod of metal alloy is first formed from one or more ingots of metal alloy. These ingots can be formed by an arc melting process; however, other or additional process can be used to form the metal ingots. The ingots can be formed into a rod by extruding the ingots through a die to form a rod of a desired outer cross-sectional area or diameter. The length of the formed rod is typically about 48 inches or less; however, longer lengths can be formed. In one non-limiting arrangement, the length of the rod or tube is about 8-20 inches. After the rod is formed, the rod is hollowed by EDM to form a tube. The inner cross-sectional area or diameter of the hollowed tube is carved to the exact inner cross-sectional area or diameter by a wire EDM process. As can be appreciated, the rod can be drawn down to an intermediate size, and then hollowed by EDM to a tube, and then further drawn down to a desired size. In one non-limiting tube configuration, the tube has an inner diameter of about 0.2-0.4 inch plus or minus about 0.005 inch and an outer diameter of about 0.4-0.6 inch plus or minus about 0.005 inch. The wall thickness of the tube is about 0.001-0.15 inch, and generally about 0.001-0.1 inch, and typically about 0.04-0.1 inch plus or minus about 0.005 inch. As can be appreciated, this is just one example of many different sized tubes that can be formed.

[0128] After the tube is formed, the tube can be drawn down to a desired OD and/or wall thickness. When the tube is drawn down, the annealing temperature and time is generally adjusted based on the wall thickness of the tube. For example, the annealing temperature for a molybdenum and rhenium alloy should be about 1500 C. for 30 minutes for drawn tubes with wall thickness from 0.050-0.015, 1475 C. for 30 minutes for drawn tubes with wall thickness from 0.015-0.080, and about 1425 C. for 30 minutes for drawn tubes with wall thickness from 0.005-0.002. Slight differences in temperature and/or annealing times may be used for tungsten and tantalum alloys or other types of metal alloys. The annealing temperature is generally reduced for thinner walls in order to obtain a smaller grain structure for the tubing. For MoRe alloys, the annealing process can optionally take place in a hydrogen atmosphere or in a vacuum. For MoRe alloys, after each annealing process, the grain size of the tubing should be no greater than about an ASTM grain number 6, and typically no greater than an ASTM grain number of 8. A final grain size of the tube of MoRe alloy can be up to an ASTM grain number of 14. For other metal alloys, the grain size can be different. The grain size in the final tube should be generally uniform. For a MoRe alloy, the final tube generally has a minimum amount of sigma phase, which sigma phase has a generally spherical, elliptical or tetragonal shape. When the tubing is formed primarily of molybdenum and rhenium, the sigma phase is generally made up of both rhenium and molybdenum, with a heavier concentration of rhenium. When a shape other than a rod or tube is formed, the formed metal allot can also be subjected to one or more annealing steps to achieve the desired properties of the metal alloy.

[0129] The formed tube, rod or other metal alloy structure can be cleaned and/or polished after being formed; however, this is not required. The cleaning and/or polishing of the tube, rod or other metal alloy structure is used to remove impurities and/or contaminants from the surfaces of the tube, rod or other metal alloy structure and/or to remove rough areas from the surface of the tube, rod or other metal alloy structure. Impurities and contaminants (e.g., carbon, oxygen, lubricants, etc.) can become incorporated into the metal alloy during the processing of the tube, rod or other metal alloy structure. The inclusion of impurities and contaminants in the metal alloy can result in premature micro-cracking of the metal alloy and/or the adverse effect on one or more physical properties of the metal alloy. The cleaning of the tube, rod or other metal alloy structure can be accomplished by a variety of techniques such as, but not limited to, 1) using a solvent (e.g., acetone, methyl alcohol, etc.) and wiping the metal alloy with a Kimwipe or other appropriate towel, and/or 2) by at least partially dipping or immersing the metal alloy in a solvent and then ultrasonically cleaning the metal alloy. As can be appreciated, the tube, rod or other metal alloy structure can be cleaned in other or additional ways. The tube, rod or other metal alloy structure, when polished, is generally polished by use of a polishing solution that typically includes an acid solution; however, this is not required. In one non-limiting example, the polishing solution includes sulfuric acid; however, other or additional acids can be used. In one non-limiting polishing solution, the polishing solution can include by volume 60-95% sulfuric acid and 5-40% de-ionized water (DI water). The polishing solution can be increased in temperature during the making of the solution and/or during the polishing procedure. One non-limiting polishing technique that can be used is an electro-polishing technique. The time used to polish the metal alloy is dependent on both the size of the tube, rod or other metal alloy structure and the amount of material that needs to be removed from the tube, rod or other metal alloy structure. The tube, rod or other metal alloy structure can be processed by use of a two-step polishing process wherein the metal alloy piece is at least partially immersed in the polishing solution for a given period (e.g., 0.1-15 minutes, etc.), rinsed (e.g., DI water, etc.) for a short period of time (e.g., 0.02-1 minute, etc.), and then flipped over and at least partially immersed in the solution again for the same or similar duration as the first time; however, this is not required. The tube, rod or other metal alloy structure can be rinsed (e.g., DI water, etc.) for a period of time (e.g., 0.01-5 minutes, etc.) before rinsing with a solvent (e.g., acetone, methyl alcohol, etc.); however, this is not required. The tube, rod or other metal alloy structure can be dried (e.g., exposure to the atmosphere, maintained in an inert gas environment, etc.) on a clean surface. These polishing procedures can be repeated until the desired amount of polishing of the tube, rod or other metal alloy structure is achieved. Typically, after the tube, rod or other metal alloy structure has been first formed and/or hollowed out, the inner surface (i.e., the inner passageway of the tube) and the outer surface of the tube, rod or other metal alloy structure are polished. The polishing techniques for the inner and outer surfaces of the tube, rod or other metal alloy structure can be the same or different. The inner surface and/or outer surface of the tube, rod or other metal alloy structure is also typically polished at least after one drawing process. As can be appreciated, the inner and/or outer surface of the tube, rod or other metal alloy structure can be polished after each drawing process, and/or prior to each annealing process. A slurry honing polishing process can be used to polishing the inner and/or outer surface of the tube, rod or other metal alloy structure; however, other or additional processes can be used.

[0130] After the tube has been formed (e.g., sintering process, extrusion process, etc.), and optionally cleaned, the tube is then drawn through a die one or more times to reduce the inner and outer cross-sectional area or diameter of the tube and the wall thickness of the tube to the desired size. As illustrated in process step 130, the tube can be optionally reduced in size by the use of a drawing process such as, but not limited to, a plug drawing process. During the drawing process, the tube is heated. During the drawing process, the tube can be protected in a reduced oxygen environment such as, but not limited to, an oxygen reducing environment or inert environment. One non-limiting oxygen reducing environment includes argon and about 1-10 volume percent hydrogen. When the temperature of the drawing process is less than about 400-450 C., the need to protect the tube from oxygen is significantly diminished. As such, a drawing process that occurs at a temperature below about 400-450 C. can optionally occur in air. At higher temperatures, the tube is generally drawn in an oxygen reducing environment or an environment. Typically, the drawing temperature for a MoRe alloy does not exceed about 500-550 C. A mandrel removal process can be used during the drawing process for the tube to improve the shape and/or uniformity of the drawn tube; however, this is not required. The amount of outer cross-sectional area or diameter draw down of the tube each time the tube is plug drawn is typically no more than about 10-20%. Controlling the degree of draw down facilitates in preventing the formation of micro-cracks during the drawing process. After each drawing process, the tube can be cleaned; however, this is not required. During the drawing process, the inner surface of the tube can be at least partially filled with a close-fitting rod. When a close-fitting rod is used, the metal rod is inserted into the tube prior to the tube being drawn through a die. The close-fitting rod is generally facilitates in maintaining a uniform shape and size of the tube during a drawing process. The close-fitting rod is generally an unalloyed metal rod; however, this is not required. Non-limiting examples of metals that can be used to form the close-fitting rod are tantalum and niobium. When a close-fitting rod is used, the close-fitting rod can be used for each drawing process or for selected drawing processes. Prior to the high temperature annealing of the tube, the close-fitting rod, when used, it removed from the tube. The tube can be heated to facilitate in the removal of the close-fitting rod from the tube; however, this is not required. When the tube is heated to remove the close-fitting rod, a MoRe alloy tube is generally not heated above about 1000 C., and typically about 600-800 C.; however, other temperatures can be used. When the tube is heated above about 400-450 C., a vacuum, an oxygen reducing environment or an inert environment is generally used to shield the tube from the atmosphere. As can also be appreciated, a close-fitting tube can also or alternatively be used during the formation of the tube during an extrusion process. Generally, after the close-fitting rod is removed from the tube, the inner and/or outer surface of the tube is polished; however, this is not required.

[0131] The tube is typically exposed to a nitriding step prior to drawing down the tube; however, this is not required. The layer of nitride compound that forms on the surface of the tube after a nitriding process has been found to function as a lubricating layer for the tube as the tube is drawn down to a smaller cross-sectional area or diameter. The nitriding process occurs in a nitrogen containing atmosphere at temperatures exceeding 400 C. Typically the nitriding process is about 5-15 minutes at a temperature of about 450-600 C. The nitrogen atmosphere can be an essentially pure nitrogen atmosphere, a nitrogen-hydrogen mixture, etc.

[0132] Prior to the tube being drawn down more than about 35-45% from its original outer cross-sectional area or diameter after the sintering process, the tube is optionally annealed as illustrated in process step 150. If the tube is to be further drawn down after being initially annealed, a subsequent annealing process generally is completed prior to the outer cross-sectional area or diameter of the tube being drawn down more than about 35-45% since a previous annealing process. As such, the tube generally is annealed at least once prior to the tube outer cross-sectional area or diameter being drawn down more than about 35-45% since being originally sintered or being previously annealed. This controlled annealing facilitates in preventing the formation of micro-cracks during the drawing process. The annealing process of for a MoRe tube typically takes place in a vacuum environment, an inert atmosphere, or an oxygen reducing environment (e.g., hydrogen, argon, argon and 1-10% hydrogen, etc.) at a temperature of about 1400-1600C for a period of about 5-60 minutes; however, other temperatures and/or times can be used. The use of an oxygen reducing environment during the annealing process can be used to reduce the amount of oxygen in the tube. The chamber in which the tube is annealed should be substantially free of impurities such as, but not limited to, carbon, oxygen, and/or nitrogen. The annealing chamber typically is formed of a material that will not impart impurities to the tube as the tube is being annealed. One non-limiting material that can be used to form the annealing chamber is a molybdenum TZM alloy. The parameters for annealing the tube as the cross-sectional area or diameter and thickness of the tube is changed during the drawing process can remain constant or be varied. It has been found that good grain size characteristics of the tube can be achieved when the annealing parameters are varied during the drawing process. In one non-limiting processing arrangement, the annealing temperature of a MoRe tube having a wall thickness of about 0.015-0.05 inch is generally about 1480-1520 C. for a time period of about 5-40 minutes. In another non-limiting processing arrangement, the annealing temperature of a MoRe tube having a wall thickness of about 0.008-0.015 inch is generally about 1450-1480 C. for a time period of about 5-60 minutes. In another non-limiting processing arrangement, the annealing temperature of a MoRe tube having a wall thickness of about 0.002-0.008 inch is generally about 1400-1450 C. for a time period of about 15-75 minutes. As such, as the wall thickness is reduced, the annealing temperature is correspondingly reduced; however, the times for annealing can be increased. As can be appreciated, the annealing temperatures of the tube can be decreased as the wall thickness decreases, but the annealing times can remain the same or also be reduced as the wall thickness reduces. After each annealing process, the grain size of the metal in the tube should be no greater than 4 ASTM, typically no greater than 6 ASTM, more typically no greater than 7 ASTM, and even more typically no greater than about 7.5 ASTM. Grain sizes of 7-14 ASTM can be achieved by the annealing process of the present invention. It is believed that as the annealing temperature is reduced as the wall thickness reduces, small grain sizes can be obtained. The grain size of the metal in the tube should be as uniform as possible. In addition, the sigma phase of the metal in the tube should be as reduced as much as possible. The sigma phase is a spherical, elliptical or tetragonal crystalline shape in a MoRe metal alloy. The sigma phase is commonly formed of both rhenium and molybdenum, typically with a larger concentration of rhenium. After the final drawing of the tube, a final annealing of the tube can be done for final strengthening of the tube; however, this is not required. This final annealing process for a MoRe alloy, when used, generally occurs at a temperature of about 1425-1500 C. for about 20-40 minutes; however, other temperatures and/or time periods can be used. The grain structure can be altered using the final anneal process.

[0133] After each annealing process, the tube, rod or other structure can optionally be cooled at a fairly quick rate so as to inhibit or prevent sigma phase formations in the metal alloy; however, this is not required. Typically, a MoRe alloy tube is cooled at a rate of about 100-400 C. per minute, and more typically about 200-300 C. per minute. The tube is can be cooled in a variety of ways (e.g., subjecting the annealed tube to a cooling gas and/or cooling liquid, placing the annealed tube in a refrigerated environment, etc.).

[0134] Prior to each annealing process, the tube, rod or other structure is optionally cleaned and/or pickled to remove oxides and/or other impurities from the surface of the tube as illustrated in process step 140. Typically, the tube, rod or other structure is cleaned by first using a solvent (e.g., acetone, methyl alcohol, etc.) and wiping the metal alloy with a Kimwipe or other appropriate towel, and/or by at least partially dipping or immersing the tube in a solvent and then ultrasonically cleaning the metal alloy. As can be appreciated, the tube, rod or other structure can be cleaned other and/or additional ways. After the tube, rod or other structure has been cleaned by use of a solvent, the tube, rod or other structure is optionally further cleaned by use of a pickling process. The pickling process includes the use of one or more acids to remove impurities from the surface of the tube, rod or other structure. Non-limiting examples of acids that can be used as the pickling solution include, but are not limited to, nitric acid, acetic acid, sulfuric acid, hydrochloric acid, and/or hydrofluoric acid. The acid solution and acid concentration and time of pickling are selected to remove oxides and other impurities on the tube surface without damaging or over etching the surface of the tube, rod or other structure. During the pickling process, the tube, rod or other structure is fully or partially immersed in the pickling solution for a sufficient amount of time to remove the impurities from the surface of the tube, rod or other structure. After the tube, rod or other structure has been pickled, the tube, rod or other structure is typically rinsed with a solvent (e.g., acetone, methyl alcohol, etc.) to remove any pickling solution from the tube, rod or other structure and then the tube, rod or other structure is allowed to dry. The cleaning of the tube, rod or other structure prior to the tube being annealed removes impurities and/or other materials from the surfaces of the tube, rod or other structure that could become permanently embedded into the tube, rod or other structure during the annealing processes. These imbedded impurities could adversely affect the physical properties of the metal alloy as the tube, rod or other structure is formed into a medical device, and/or can adversely affect the operation and/or life of the medical device. As can be appreciated, the tube, rod or other structure can be again clean and/or pickled after being annealed and prior to be drawn down in the plug drawing process; however, this is not required.

[0135] Process steps 130-150 can be repeated as necessary until the rod or tube is drawn down to the desired size. In one non-limiting process, a tube that is originally formed after being sintered has an inner diameter of about 0.31 inch plus or minus about 0.002 inch, an outer diameter of about 0.5 inch plus or minus about 0.002 inch, and a wall thickness of about 0.095 inch plus or minus about 0.002 inch. After the tube has been fully drawn down, the tube has an outer diameter of about 0.070 inch, a wall thickness of about 0.0021-0.00362 inch, and the average concentricity deviation of less than about 10%. Such small sizes for stents which can be successfully used in a vascular system have heretofore not been possible when formed by other types of metal alloys. Typically, the wall thickness of stent had to be at least about 0.0027-0.003 inch, or the stent would not have sufficient radial force to maintain the stent in an expanded state after being expanded. The metal alloy of the present invention is believed to be able to have a wall thickness of as small as about 0.0015 inch and still have sufficient radial force to maintain a stent in an expanded state after being expanded. As such, when a tube is formed into a stent, the wall thickness of the tube can be drawn down to less than about 0.0027 inch to form a stent. As can be appreciated, this is just one example of many different sized tubes that can be formed by the process of the present invention.

[0136] Once the rod or tube has been drawn down to its final size, the rod or tube is typically cleaned (Process Step 140), annealed (Process Step 150) and then again cleaned (Process Step 160). The cleaning step of process step 160 can include merely solvent cleaning, or can also include pickling.

[0137] After the tube, rod or other structure has been cleaned in process step 160, the tube, rod or other structure can be optionally cut into the form of the desired medical device (e.g., a stent as illustrated in FIG. 1). The cutting of the tube, rod or other structure can be accomplished by use of a laser; however, this is not required. When a laser is used, the laser that is used to cut the tube, rod or other structure is selected so that it has a desired beam strength. When cutting MoRe alloys, the desired beam strength of the laser should be sufficient to obtain a cutting temperature of at least about 2350 C. Non-limiting examples of lasers that can be used include a pulsed Nd:YAG neodymium-doped yttrium aluminum garnet (Nd:Y.sub.3Al.sub.5O.sub.12) or CO.sub.2 laser. The cutting of tube, rod or other structure by the laser can occurs in an oxygen reducing environment such as an argon and 1-10 percent by volume hydrogen environment; however, a vacuum environment, an inert environment, or another type of oxygen reducing environment can be used. During the cutting of tube, rod or other structure, tube, rod or other structure is typically stabilized so as to inhibit or prevent vibration of tube, rod or other structure during the cutting process, which vibrations can result in the formation of micro-cracks in the tube as tube, rod or other structure. The tube, rod or other structure can be stabilized by an apparatus that will not introduce contaminates to the tube, rod or other structure during the cutting process; however, this is not required. The average amplitude of vibration during the cutting of the tube, rod or other structure is typically no more than about 50% the wall thickness of the tube, rod or other structure. As such, for a tube having a wall thickness of about 0.0024 inch, the average amplitude of vibration of the tube during the cutting process is no more than about 0.0012 inch.

[0138] After the medical device has been cut, the medical device can be further processed; however, this is not required. The one or more processes can include, but are not limited to, 1) electro-polishing the medical device, 2) treating one or more surfaces of the medical device to create generally smooth surfaces and/or other types of surfaces (e.g., filing, buffing, polishing, grinding, coating, nitriding, etc.), 3) at least partially coating the medical device with one or more therapeutic agents, 4) at least partially coating the medical device with one or more polymers, 5) forming one or more surface structures and/or micro-structures on one or more portions of the medical device, 6) inserting one or more markers on one or more portions of the medical device, and/or 7) straightening process for the medical device.

[0139] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.