Aspects relate to radiopaque implantable structures (eg, stents) formed from cobalt-based alloys comprising cobalt, chromium, and one or more platinum group metals, refractory metals, or combinations thereof. Platinum group metals include platinum, palladium, ruthenium, rhodium, osmium and iridium. As used herein, the term "refractory metal" includes zirconium, niobium, rhodium, molybdenum, hafnium, tantalum, tungsten, rhenium, and the noble metals silver and gold. In one embodiment, the nickel is replaced with one or more including a platinum group metal or a refractory metal such that the alloy is substantially free of nickel. The stent exhibits improved radiopacity compared to similar alloys containing greater amounts of nickel.
Concerning radiopaque cobalt alloys, radiopaque implantable structures (eg, stents), and related methods of manufacture and use. One embodiment of the invention includes a radiopaque implantable structure. The radiopaque implantable structure includes a main body comprising a cobalt-based alloy comprising cobalt, chromium, and one or more radiopaque elements. In one embodiment, examples of radiopaque elements include the so-called molybdenum group metals (ie, molybdenum, palladium, ruthenium, zirconium, osmium, or iridium). Group 10 elements (ie, platinum or palladium) are particularly preferred. In one embodiment, nickel (another Group 10 element) is replaced with one or more of the platinum group metals included such that the alloy is substantially free of nickel (e.g., contains no more than 2% (by weight) meter) of nickel). Another embodiment is completely free of nickel. Additionally, the alloy may contain iron, but the amount of iron is limited to no more than about 20% by weight. In other embodiments, the amount of iron can be further limited (eg, not more than about 10% by weight, not more than about 8% by weight). In some embodiments, the alloy is substantially free of iron.
In one embodiment, a cobalt-based alloy can be started with a compound that does not contain a molybdenum group metal or refractory metal, but contains an additional component (e.g., nickel) to be partially or completely replaced with a molybdenum group metal or refractory metal. Cobalt-based alloy formation. All components are then melted together (e.g. arc melting, electron beam melting, induction melting, radiant heat melting, microwave melting, etc.) to create an ingot, which is then machined into a tubular shape by conventional metalworking methods or other desired form. In addition to nickel, other elements such as iron, silicon, titanium, manganese and cobalt can also be partially or completely substituted. For example, the substitution can be performed by melting the alloy by electric arc in the presence of the substituting element. For example, it is thus possible to partially or completely replace the nickel originally present inside such cobalt-chromium alloys with molybdenum group metals or refractory metals. In some embodiments, some of the cobalt may also be substituted.
