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EP1657318A1 - Quaternäre Kobalt-Nickel-Chrom-Molybän ermüdungsbeständige Legierung für medizinische intravaskuläre Einrichtungen - Google Patents

Quaternäre Kobalt-Nickel-Chrom-Molybän ermüdungsbeständige Legierung für medizinische intravaskuläre Einrichtungen Download PDF

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Publication number
EP1657318A1
EP1657318A1 EP05256860A EP05256860A EP1657318A1 EP 1657318 A1 EP1657318 A1 EP 1657318A1 EP 05256860 A EP05256860 A EP 05256860A EP 05256860 A EP05256860 A EP 05256860A EP 1657318 A1 EP1657318 A1 EP 1657318A1
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Prior art keywords
weight percent
range
biocompatible
load
structure according
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EP05256860A
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English (en)
French (fr)
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Robert Burgermeister
Randy-David Burce Grishaber
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Cordis Corp
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Cordis Corp
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt

Definitions

  • the present invention relates to alloys for use in manufacturing or fabricating implantable medical devices, and more particularly, to implantable medical devices manufactured or fabricated from alloys that are highly fatigue resistant.
  • Percutaneous transluminal angioplasty is a therapeutic medical procedure used to increase blood flow through an artery.
  • the angioplasty balloon is inflated within the stenosed vessel, or body passageway, in order to shear and disrupt the wall components of the vessel to obtain an enlarged lumen.
  • the relatively incompressible plaque remains unaltered, while the more elastic medial and adventitial layers of the body passageway stretch around the plaque. This process produces dissection, or a splitting and tearing, of the body passageway wall layers, wherein the intima, or internal surface of the artery or body passageway, suffers fissuring.
  • This dissection forms a "flap" of underlying tissue, which may reduce the blood flow through the lumen, or completely block the lumen.
  • the distending intraluminal pressure within the body passageway can hold the disrupted layer, or flap, in place. If the intimal flap created by the balloon dilation procedure is not maintained in place against the expanded intima, the intimal flap can fold down into the lumen and close off the lumen, or may even become detached and enter the body passageway. When the intimal flap closes off the body passageway, immediate surgery is necessary to correct the problem.
  • transluminal prostheses have been widely used in the medical arts for implantation in blood vessels, biliary ducts, ureters, or other similar organs of the living body. These prostheses are commonly referred to as stents and are used to maintain, open, or dilate tubular structures.
  • An example of a commonly used stent is given in US-4733665 to Palmaz.
  • Such stents are often referred to as balloon expandable stents.
  • the stent is made from a solid tube of stainless steel. Thereafter, a series of cuts are made in the wall of the stent.
  • the stent has a first smaller diameter, which permits the stent to be delivered through the human vasculature by being crimped onto a balloon catheter.
  • the stent also has a second, expanded diameter, upon application of a radially, outwardly directed force, by the balloon catheter, from the interior of the tubular shaped member.
  • stents are often impractical for use in some vessels such as the carotid artery.
  • the carotid artery is easily accessible from the exterior of the human body, and is close to the surface of the skin.
  • a patient having a balloon expandable stent made from stainless steel or the like, placed in their carotid artery might be susceptible to severe injury through day-to-day activity. A sufficient force placed on the patient's neck could cause the stent to collapse, resulting in injury to the patient.
  • self-expanding stents have been proposed for use in such vessels. Self-expanding stents act like springs and will recover to their expanded or implanted configuration after being crushed.
  • Nitinol Ni-Ti alloy
  • shape memory characteristics allow the devices to be deformed to facilitate their insertion into a body lumen or cavity and then be heated within the body so that the device returns to its original shape.
  • superelastic characteristics generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device containing the metal into a patient's body, with such deformation causing the phase transformation. Once within the body lumen, the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original un-deformed shape by the transformation back to the original phase.
  • markers made from highly radiopaque materials
  • Those materials typically include gold, platinum, or tantalum.
  • the prior art makes reference to these markers or processes in US-5632771 to Boatman et al., US-6022374 to Imran, US-5741327 to Frantzen, US-5725572 to Lam et al., and US-5800526 to Anderson et al.
  • the size of the markers and the relative position of the materials forming the markers in the galvanic series versus the position of the base metal of the stent in the galvanic series, there is a certain challenge to overcome; namely, that of galvanic corrosion.
  • the size of the markers increases the overall profile of the stent.
  • typical markers are not integral to the stent and thus may interfere with the overall performance of the stent as well as become dislodged from the stent.
  • a concern with both balloon expandable and self-expandable stents is magnetic resonance imaging compatibility.
  • Currently available metallic stents are known to cause artifacts in magnetic resonance generated images.
  • metals having a high magnetic permeability cause artifacts, while metals having a low magnetic permeability cause less or substantially no artifacts.
  • the stent or other medical device is fabricated from a metal or metals having a low magnetic permeability, then less artifacts are created during magnetic resonance imaging which in turn allows more tissue in proximity to the stent or other medical device to be imaged.
  • Artifacts created under magnetic resonance imaging are promoted by local magnetic field inhomogeneities and eddy currents induced by the magnetic field generated by the magnetic resonance imaging machine.
  • the strength of the magnetic field disruption is proportional to the magnetic permeability of the metallic stent or other medical device.
  • signal attenuation within the stent is caused by radio frequency shielding of the metallic stent or other medical device material.
  • the radio frequency signals generated by the magnetic resonance imaging machine may become trapped within the cage like structure of the stent or other medical device. Induced eddy currents in the stent may also lead to a lower nominal radio frequency excitation angle inside the stent. This has been shown to attenuate the signal acquired by the receiver coil of the magnetic resonance imaging device.
  • Artifact related signal changes may include signal voids or local signal enhancements which in turn degrades the diagnostic value of the tool.
  • any intravascular device should preferably exhibit certain characteristics, including maintaining vessel patency through a chronic outward force that will help to remodel the vessel to its intended luminal diameter, preventing excessive radial recoil upon deployment, exhibiting sufficient fatigue resistance and exhibiting sufficient ductility so as to provide adequate coverage over the full range of intended expansion diameters.
  • the present invention overcomes the limitations of applying conventionally available materials to specific intravascular therapeutic applications as briefly described above.
  • the present invention is directed to a biocompatible, load-carrying metallic structure.
  • the metallic structure being formed from a solid-solution alloy comprising nickel in the range from about 33 weight percent to about 37 weight percent, chromium in the range from about 19 weight percent to about 21 weight percent, molybdenum in the range from about 9 weight percent to about 11 weight percent, iron in the range from about 0 weight percent to about 1 weight percent, manganese in the range from about 0 weight percent to about 0.15 weight percent, silicon in the range from about 0 weight percent to about 0.15 weight percent, carbon in the range from about 0 to about 0.025 weight percent, phosphorous in the range from about 0 to about 0.015 weight percent, boron in the range from about 0 to about 0.015 weight percent, sulfur in the range from about 0 to about 0.010 weight percent, titanium in an amount not to exceed 0.015 weight percent and the remainder cobalt.
  • the biocompatible, solid-solution alloy for implantable medical devices of the present invention offers a number of advantages over currently utilized alloys.
  • the biocompatible alloy of the present invention has improved magnetic resonance imaging compatibility than currently utilized ferrous materials, is less brittle than other alloys, has enhanced ductility and toughness, and has increased fatigue durability.
  • the biocompatible alloy also maintains the desired or beneficial characteristics of currently available alloys including strength and flexibility.
  • the biocompatible, solid-solution alloy for implantable medical devices of the present invention may be utilized for any number of medical applications, including vessel patency devices such as vascular stents, biliary stents, ureter stents, vessel occlusion devices such as atrial septal and ventricular septal occluders, patent foramen ovale occluders and orthopedic devices such as fixation devices.
  • vessel patency devices such as vascular stents, biliary stents, ureter stents
  • vessel occlusion devices such as atrial septal and ventricular septal occluders
  • patent foramen ovale occluders such as fixation devices.
  • the biocompatible, solid-solution alloy of the present invention is simple and inexpensive to manufacture.
  • the biocompatible alloy may be formed into any number of structures or devices.
  • the biocompatible, solid-solution alloy may be thermomechanically processed, including cold-working and heat treating, to achieve varying degrees of strength and ductility.
  • the biocompatible alloy of the present invention may be age hardened to precipitate one or more secondary phases.
  • Biocompatible, solid-solution strengthened alloys such as iron-based alloys, cobalt-based alloys and titanium-based alloys as well as refractory metals and refractory-based alloys may be utilized in the manufacture of any number of implantable medical devices.
  • the biocompatible, solid-solution alloy for implantable medical devices in accordance with the present invention offers a number of advantages over currently utilized medical grade alloys. The advantages include the ability to engineer the underlying microstructure in order to sufficiently perform as intended by the designer without the limitations of currently utilized materials and manufacturing methodologies.
  • a traditional Cobalt-based alloy such as MP35N (i.e. UNS R30035) which is also broadly utilized as an implantable, biocompatible device material may comprise a solid-solution alloy comprising nickel in the range from about 33 weight percent to about 37 weight percent, chromium in the range from about 19 weight percent to about 21 weight percent, molybdenum in the range from about 9 weight percent to about 11 weight percent, iron in the range from about 0 weight percent to about 1 weight percent, titanium in the range from about 0 weight percent to about 1 weight percent, manganese in the range from about 0 weight percent to about 0.15 weight percent, silicon in the range from about 0 weight percent to about 0.15 weight percent, carbon in the range from about 0 to about 0.025 weight percent, phosphorous in the range from about 0 to about 0.01 5 weight percent, boron in the range from about 0 to about 0.015 weight percent, sulfur in the range from about 0 to about 0.010 weight percent, and the remainder cobalt.
  • nickel in the range from about 33 weight
  • elemental additions such as chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si) and molybdenum (Mo) were added to iron- and/or cobalt-based alloys, where appropriate, to increase or enable desirable performance attributes, including strength, machinability and corrosion resistance within clinically relevant usage conditions.
  • an implantable medical device may be formed from a solid-solution alloy comprising nickel in the range from about 33 weight percent to about 37 weight percent, chromium in the range from about 19 weight percent to about 21 weight percent, molybdenum in the range from about 9 weight percent to about 11 weight percent, iron in the range from about 0 weight percent to about 1 weight percent, manganese in the range from about 0 weight percent to about 0.15 weight percent, silicon in the range from about 0 weight percent to about 0.15 weight percent, carbon in the range from about 0 to about 0.025 weight percent, phosphorous in the range from about 0 to about 0.015 weight percent, boron in the range from about 0 to about 0.015 weight percent, sulfur in the range from about 0 to about 0.010 weight percent, titanium in an amount not to exceed 0.015 weight percent and the remainder cobalt.
  • the intended composition does not include any elemental titanium (Ti) above conventional accepted trace impurity levels. Accordingly, this exemplary embodiment will exhibit a marked improvement in fatigue durability (i.e. cyclic endurance limit strength) due to the minimization of secondary phase precipitates in the form of titanium-carbides.
  • the preferred embodiment may be processed from the requisite elementary raw materials, as set-forth above, by first mechanical homogenization (i.e. mixing) and then compaction into a green state (i.e. precursory) form.
  • appropriate manufacturing aids such as hydrocarbon based lubricants and/or solvents (e.g. mineral oil, machine oils, kerosene, isopropanol and related alcohols) may be used to ensure complete mechanical homogenization.
  • other processing steps such as ultrasonic agitation of the mixture followed by cold compaction to remove any unnecessary manufacturing aides and to reduce void space within the green state may be utilized. It is preferable to ensure that any impurities within or upon the processing equipment from prior processing and/or system construction (e.g.
  • mixing vessel material, transfer containers, etc. be sufficiently reduced in order to ensure that the green state form is not unnecessarily contaminated. This may be accomplished by adequate cleaning of the mixing vessel before adding the constituent elements by use of surfactant based cleaners to remove any loosely adherent contaminants.
  • Initial melting of the green state form into a ingot of desired composition is achieved by vacuum induction melting (VIM) where the initial form is inductively heated to above the melting point of the primary constituent elements within a refractory crucible and then poured into a secondary mold within a vacuum environment (e.g. typically less than or equal to 10 -4 mmHg).
  • VIM vacuum induction melting
  • the vacuum process ensures that atmospheric contamination is significantly minimized.
  • the ingot bar is substantially single phase (i.e. compositionally homogenous) with a definable threshold of secondary phase impurities that are typically ceramic (e.g. carbide, oxide or nitride) in nature. These impurities are typically inherited from the precursor elemental raw materials.
  • VAR vacuum arc reduction
  • Other methods may be enabled by those skilled in the art of ingot formulation that substantially embodies this practice of ensuring that atmospheric contamination is minimized.
  • the initial VAR step may be followed by repetitive VAR processing to further homogenize the solid-solution alloy in the ingot form.
  • the homogenized alloy will be further reduced in product size and form by various industrially accepted methods such as, but not limited too, ingot peeling, grinding, cutting, forging, forming, hot rolling and/or cold finishing processing steps so as to produce bar stock that may be further reduced into a desired raw material form.
  • the initial raw material product form that is required to initiate the thermomechanical processing that will ultimately yield a desired small diameter, thin-walled tube, appropriate for interventional devices is a modestly sized round bar (e.g. 25.4 mm (one inch) diameter round bar stock) of predetermined length.
  • a modestly sized round bar e.g. 25.4 mm (one inch) diameter round bar stock
  • an initial clearance hole must be placed into the bar stock that runs the length of the product.
  • These tube hollows i.e. heavy walled tubes
  • 'gun-drilling' i.e. high depth to diameter ratio drilling
  • Other industrially relevant methods of creating the tube hollows from round bar stock may be utilized by those skilled-in-the-art of tube making.
  • Consecutive mechanical cold-finishing operations such as drawing through a compressive outer-diameter (OD), precision shaped (i.e. cut), circumferentially complete, diamond die using any of the following internally supported (i.e. inner diameter, ID) methods, but not necessarily limited to these conventional forming methods, such as hard mandrel (i.e. relatively long travelling ID mandrel also referred to as rod draw), floating-plug (i.e. relatively short ID mandrel that 'floats' within the region of the OD compressive die and fixed-plug (i.e. the ID mandrel is ⁇ fixed' to the drawing apparatus where relatively short workpieces are processed) drawing.
  • hard mandrel i.e. relatively long travelling ID mandrel also referred to as rod draw
  • floating-plug i.e. relatively short ID mandrel that 'floats' within the region of the OD compressive die
  • fixed-plug i.e. the ID mandrel is ⁇ fixed'
  • tube sinking i.e. OD reduction of the workpiece without inducing substantial tube wall reduction
  • tube sinking is typically utilized as a final or near-final mechanical processing step to achieve the desired dimensional attributed of the finished product.
  • all metallic alloys in accordance with the present invention will require incremental dimensional reductions from the initial raw material configuration to reach the desired dimensions of the finished product.
  • This processing constraint is due to the material's ability to support a finite degree of induced mechanical damage per processing step without structural failure (e.g. strain-induced fracture, fissures, extensive void formation, etc.).
  • thermal heat-treatments are utilized to stress-relieve (i.e. minimization of deleterious internal residual stresses that are the result of processes such as cold-working) thereby increasing the workability (i.e. ability to support additional mechanical damage without measurable failure) the workpiece prior to subsequent reductions.
  • stress-relieve i.e. minimization of deleterious internal residual stresses that are the result of processes such as cold-working
  • workability i.e. ability to support additional mechanical damage without measurable failure
  • thermal treatments are typically, but not necessarily limited to, conducted within a relatively inert environment such as an inert gas furnace (e.g. nitrogen, argon, etc.), a oxygen rarified hydrogen furnace, a conventional vacuum furnace and under less common process conditions, atmospheric air.
  • an inert gas furnace e.g. nitrogen, argon, etc.
  • oxygen rarified hydrogen furnace e.g. nitrogen, argon, etc.
  • subatmospheric pressure typically measured in units of mmHg or torr (where 1 mmHg is equal to 1 unit torr), shall be sufficient to ensure that excessive and deteriorative high temperature oxidative processes are not functionally operative during heat treatment. This process may usually be achieved under vacuum conditions of 10 -4 mmHg (0.0001 torr) or less (i.e. lower magnitude).
  • the stress relieving heat treatment temperature is typically held constant between 82 to 86% of the conventional melting point (i.e. industrially accepted liquidus temperature, 0.82 to 0.86 homologous temperatures) within an adequately sized isothermal region of the heat-treating apparatus.
  • the workpiece undergoing thermal treatment is held within the isothermal processing region for a finite period of time that is adequate to ensure that the workpiece has reached a state of thermal equilibrium and for that sufficient time is elapsed to ensure that the reaction kinetics (i.e. time dependent material processes) of stress-relieving and/or process annealing, as appropriate, is adequately completed.
  • the finite amount of time that the workpiece is held within the processing is dependent upon the method of bringing the workpiece into the process chamber and then removing the working upon completion of heat treatment.
  • this process is accomplished by, but not limited to, use of a conventional conveyor-belt apparatus or other relevant mechanical assist devices.
  • the conveyor belt speed and appropriate finite dwell-time, as necessary, within the isothermal region is controlled to ensure that sufficient time at temperature is utilized so as to ensure that the process is completed as intended.
  • heat-treatment temperatures and corresponding finite processing times may be intentionally utilized that are not within the typical range of 0.82 to 0.86 homologous temperatures.
  • Various age hardening i.e. a process that induces a change in properties at moderately elevated temperatures, relative to the conventional melting point, that does not induce a change in overall chemical composition change in the metallic alloy being processed
  • processing steps may be carried out, as necessary, in a manner consistent with those previously described at temperatures substantially below 0.82 to 0.86 homologous temperature.
  • these processing temperatures may be varied between and inclusive of approximately 0.29 homologous temperature and the aforementioned stress relieving temperature range.
  • the workpiece undergoing thermal treatment is held within the isothermal processing region for a finite period of time that is adequate to ensure that the workpiece has reached a state of thermal equilibrium and for that sufficient time is elapsed to ensure that the reaction kinetics (i.e. time dependent material processes) of age hardening, as appropriate, is adequately completed prior to removal from the processing equipment.
  • secondary-phase ceramic compounds such as carbide, nitride and/or oxides will be induced or promoted by age hardening heat treating.
  • These secondary-phase compounds are typically, but not limited to, for Co-based alloys in accordance with the present invention, carbides which precipitate along thermodynamically favorable regions of the structural crystallographic planes that comprise each grain (i.e. crystallographic entity) that make-up the entire polycrystalline alloy.
  • These secondary-phase carbides can exist along the intergranular boundaries as well as within each granular structure (i.e. intragranular).
  • the principal secondary phase carbides that are stoichiometrically expected to be present are M 6 C where M typically is cobalt (Co).
  • M 6 C typically is cobalt
  • the intermetallic M 6 C phase is typically expected to reside intragranularly along thermodynamically favorable regions of the structural crystallographic planes that comprise each grain within the polycrystalline alloy in accordance with the present invention.
  • the equivalent material phenomena can exist for a single crystal (i.e. monogranular) alloy.
  • Another prominent secondary phase carbide can also be induced or promoted as a result of age hardening heat treatments.
  • This phase when present, is stoichiometrically expected to be M 23 C 6 where M typically is chromium (Cr) but is also commonly observed to be cobalt (Co) especially in Co-based alloys.
  • M typically is chromium (Cr) but is also commonly observed to be cobalt (Co) especially in Co-based alloys.
  • the intermetallic M 23 C 6 phase is typically expected to reside along the intergranular boundaries (i.e. grain boundaries) within a polycrystalline alloy in accordance with the present invention.
  • the equivalent presence of the intermetallic M 23 C 6 phase can exist for a single crystal (i.e. monogranular) alloy, albeit not practically common.
  • this secondary phase is conventionally considered most important, when formed in a manner that is structurally and compositionally compatible with the alloy matrix, to strengthening the grain boundaries to such a degree that intrinsic strength of the grain boundaries and the matrix are adequately balanced.
  • solutionizing i.e. sufficiently high temperature and longer processing time to thermodynamically force one of more alloy constituents to enter into solid solution - ⁇ singular phase', also referred to as full annealing
  • the typical solutionizing temperature can be varied between and inclusive of approximately 0.88 to 0.90 homologous temperatures.
  • the workpiece undergoing thermal treatment is held within the isothermal processing region for a finite period of time that is adequate to ensure that the workpiece has reached a state of thermal equilibrium and for that sufficient time is elapsed to ensure that the reaction kinetics (i.e. time dependent material processes) of solutionizing, as appropriate, is adequately completed prior to removal from the processing equipment.
  • thermomechanical processing steps that may comprise but not necessarily include mechanical cold-finishing operations, stress relieving, age hardening and solutionizing can induce and enable a broad range of measurable mechanical properties as a result of distinct and determinable microstructural attributes.
  • This material phenomena is represented by the curves illustrated in Figure 1.
  • Figure 1 illustrates a relationship of change in measurable mechanical properties such as yield strength and ductility (presented in units of percent elongation) as a function of thermomechanical processing (TMP), for example, cold working and in-process heat-treatments.
  • TMP thermomechanical processing
  • thermomechanical (TMP) groups one (1) through five (5) were subjected to varying combinations of cold-finishing, stress relieving and age hardening and not necessarily in the presented sequential order.
  • the principal isothermal age hardening heat treatment applied to each TMP group varied between about 0.74 to 0.78 homologous temperatures for group (1), about 0.76 to 0.80 homologous temperatures for group (2), about 0.78 to 0.82 homologous temperatures for group (3), about 0.80 to 0.84 homologous temperatures for group (4) and about 0.82 to 0.84 homologous temperatures for group (5).
  • Each workpiece undergoing thermal treatment was held within the isothermal processing region for a finite period of time that was adequate to ensure that the workpiece reached a state of thermal equilibrium and to ensure that sufficient time was elapsed to ensure that the reaction kinetics of age hardening was adequately completed.
  • thermomechanical TMP
  • TMP group (2) from this figure as utilized in this specific example shows a marked increase in the fatigue strength (i.e. endurance limit, the maximum stress below which a material can presumably endure an infinite number of stress cycles) over and above the TMP group (4) process.
  • the above-described alloy may be utilized in any number of implantable medical devices.
  • the alloy is particularly advantageous in situations where magnetic resonance imaging is a useful diagnostic tool such as determining in-stent restenosis. Accordingly, although the alloy may be utilized for any implantable medical device, an exemplary stent constructed from the alloy is described below.
  • FIG 3 is a flat layout of an exemplary embodiment of a stent that may be constructed utilizing the alloy of the present invention.
  • the stent 10 comprises end sets of strut members 12 located at each end of the stent 10 and central sets of strut members 14 connected each to the other by sets of flexile "M" links 16.
  • Each end set of strut members 12 comprises alternating curved sections 18 and diagonal sections 20 connected together to form a closed circumferential structure.
  • the central sets of strut members 14 located longitudinally between the end sets of strut members 14 comprise curved sections 22 and diagonal sections 24 connected together to form a closed circumferential ring-like structure.
  • each "M” link 16 has a circumferential extent, i.e. length, L' above and L" below line 11.
  • the line 11 is drawn between the attachment points 13 where the "M” link 16 attaches to adjacent cured sections 18 or 22.
  • Such a balanced design preferably diminishes any likelihood of the flexible connecting link 16 from expanding into the lumen of artery or other vessel.
  • the diagonal sections 20 of the end sets of strut members 12 are shorter in length than the diagonal sections 24 of the central sets of strut members 14.
  • the shorter diagonal sections 20 will preferably reduce the longitudinal length of metal at the end of the stent 10 to improve deliverability into a vessel of the human body.
  • the widths of the diagonal sections 20 and 24 are different from one another.
  • FIG. 5 there is illustrated an expanded view of a stent section comprising an end set of strut members 12 and a central set of strut members 14.
  • the diagonal sections 24 of the central sets of strut members 14 have a width at the center thereof, T c , and a width at the end thereof, T e , wherein T c is greater than T e .
  • This configuration allows for increased radiopacity without affecting the design of curved sections 22 that are the primary stent elements involved for stent expansion.
  • the curved sections 22 and 18 may be tapered and may have uniform widths with respect to one another as is explained in detail subsequently.
  • the diagonal sections 20 of the end sets of strut members 12 also have a tapered shape.
  • the diagonal sections 20 have a width in the center, T c -end, and a width at the end, T e -end, wherein T c -end is greater than T e -end. Because it is preferable for the end sets of strut members 12 to be the most radiopaque part of the stent 10, the diagonal section 20 center width T c -end of the end sets of strut members 12 is wider than the width T c of the diagonal section 24. Generally, a wider piece of metal will be more radiopaque.
  • the stent 10 has curved sections with a single bend connecting the diagonal sections of its sets of strut members, and flexible connecting links connecting the curved sections of its circumferential sets of strut members.
  • the width of the curved sections 22 and 18 taper down as one moves away from the center of the curve until a predetermined minimum width substantially equal to that of their respective diagonal sections 24 and 20.
  • the inside arc of the curved sections 22 and 18 have a center that is longitudinally displaced from the center of the outside arc.
  • This tapered shape for the curved sections 22 and 18 provides a significant reduction in metal strain with little effect on the radial strength of the expanded stent as compared to a stent having sets of strut members with a uniform strut width.
  • This reduced strain design has several advantages. First, it can allow the exemplary design to have a much greater usable range of radial expansion as compared to a stent with a uniform strut width. Second, it can allow the width at the center of the curve to be increased which increases radial strength without greatly increasing the metal strain (i.e. one can make a stronger stent). Finally, the taper reduces the amount of metal in the stent and that should improve the stent thrombogenicity.
  • the curved sections 18 of the end sets of strut members 12 and the curved sections 22 of the central sets of strut members 14 have the same widths.
  • the end sets of strut members 12, which have shorter diagonal sections 20, will reach the maximum allowable diameter at a level of strain that is greater than the level of strain experienced by the central sets of strut members 14.
  • the alloy may be utilized for any number of implantable medical devices.

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EP05256860A 2004-11-09 2005-11-05 Quaternäre Kobalt-Nickel-Chrom-Molybän ermüdungsbeständige Legierung für medizinische intravaskuläre Einrichtungen Ceased EP1657318A1 (de)

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US10/984,062 US20060096672A1 (en) 2004-11-09 2004-11-09 Quaternary cobalt-nickel-chromium-molybdenum fatigue resistant alloy for intravascular medical devices

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EP3202427A1 (de) * 2016-02-03 2017-08-09 Deutsche Edelstahlwerke GmbH Verwendung einer ausscheidungshärtenden oder durch mischkristallbildung verfestigenden, biokompatiblen kobalt-basislegierung und verfahren zur herstellung von implantaten oder prothesen durch materialabhebende bearbeitung
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US20060096672A1 (en) 2006-05-11
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