COMPOSITE WIRE WITH COATING
A composite wire suitable for use as a pacing or biostimulation lead has improved durability when compared to currently available materials. Specifically, a lead includes a superelastic wire including, e.g., nitinol. The wire is coated with polyimide and subsequently wound into a strand, cable, coil, or helically stranded tube. This wound structure is thermomechanically treated to shape-set the wire construct and retain a desired wound and shaped configuration, without adversely affecting the integrity of the polyimide coating.
1 . A coiled or wound composite wire comprising:
a shell made of a nickel-titanium alloy, and defining a hollow cavity having an inner diameter;
a core made of a conductive metal material, received within the hollow cavity, and defining an outer diameter equal to the inner diameter; and
a polyimide coating disposed over the outer diameter of the shell, the polyimide coating having a thermal degradation, as measured by thermogravimetric analysis, of less than 10% mass at 500° C. for 10 minutes or less in an inert environment,
wherein the composite wire exhibits a fatigue endurance surviving at least 10 8 cycles at 0.5% alternating strain.
2 . The composite wire of claim 1 , wherein the shell and the core are made of medical-grade materials.
3 . The composite wire of of claim 1 , wherein the core is centered in the hollow cavity.
4 . The composite wire of claim 1 , wherein the core consists of silver and incidental impurities.
5 . The composite wire of claim 1 , wherein the shell consists of about approximately 50 atomic % nickel, balance titanium and incidental impurities.
6 . The composite wire of claim 1 , wherein the composite wire exhibits at least twice the work energy to tensile fracture compared to the same wire configuration substituting CoNiCrMo for NiTi.
7 . The composite wire of claim 1 , wherein the core defines between 10% and 95% of an overall cross-sectional area of the shell and the core combined.
8 . The composite wire of claim 1 , wherein the composite wire is a drawn construct.
9 . The composite wire of claim 1 , wherein the composite wire is a shape set construct.
10 . A medical device comprising a composite wire in accordance with claim 1 .
11 . A multifilament cable construct comprising:
a plurality of wires, each of the wires comprising:
a shell made of nickel-titanium alloy and defining a hollow cavity having an inner diameter; and
a core made of a conductive metal material and received within the hollow cavity and defining an outer diameter equal to the inner diameter,
wherein the plurality of wires are configured into a helical shape which holds the helical shape without external forcing; and
a polyimide coating surrounding the plurality of wires, the polyimide coating having a thermal degradation, as measured by thermogravimetric analysis, of less than 10% mass at 500° C. for 10 minutes or less in an inert environment.
12 . The multifilament cable construct of claim 11 , wherein the multifilament cable construct exhibits a fatigue endurance surviving at least 10 7 cycles at 15% structural strain cycling.
13 . The multifilament cable construct of claim 11 , wherein the coiled or wound wire comprises a coiled monofilament wire exhibiting a fatigue endurance surviving at least 10 8 cycles at 0.5% alternating strain.
14 . The multifilament cable construct of claim 11 , wherein the core consists of silver and incidental impurities.
15 . The multifilament cable construct of claim 11 , wherein the shell consists of about approximately 50 atomic % nickel, balance titanium and incidental impurities.
16 . A method of making a wire comprising:
inserting a conductive core into a hollow cavity of a shell made of nickel-titanium alloy to create a composite wire in which the core defines an outer diameter equal to an inner diameter of the hollow cavity;
coating the composite wire with a polyimide coating, and
after the step of coating the composite wire, shape setting the composite wire.
17 . The method of claim 16 , wherein the step of shape setting comprises:
constraining the composite wire to a desired shape; and
thermally processing the composite wire to retain the desired shape.
18 . The method of claim 16 , wherein the step of thermally processing comprises heating the composite wire and the coating to at least 400° C.
19 . The method of claim 16 , wherein the step of thermally processing comprises heating the composite wire and the coating to at least 550° C.