Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-08-31
2001-08-21
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S126100, C174S128100
Reexamination Certificate
active
06278057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates broadly to medical devices incorporating elements having a low modulus of elasticity. More particularly, this invention relates to medical devices incorporating one or more cable elements made from a plurality of twisted and drawn wires, at least one of the wires comprising a nickel-titanium alloy.
2. State of the Art
Wires are utilized throughout the medical arts. In many medical devices a particularly desirable feature for the wires is high elasticity. For example, in baskets and snares high elasticity may be the most important property of the wires used. The elasticity of the wires comprising snares and baskets is a factor in the extent to which each may be compressed for insertion to the surgical site and yet still be able to expand upon use. In addition, higher elasticity permits the baskets and snares to be contracted about smaller radii.
The need for highly flexible self-expanding stents is also well-known. Flexibility not only permits proper stent deployment, but also enables the stent to better conform to the vascular walls.
In endoscopic instruments, a control wire is often coupled between a proximal handle and a distal end effector. The control wire is used to translate movement of the handle into operation of the end effector. The wire must be able to easily bend through the tortuous paths through which endoscopic instruments are guided.
Wire flexibility is also important in numerous other medical devices. For that reason, the medical arts have recently had much interest in nickel-titanium alloy (Nitinol) wires which exhibit superelastic characteristics. For the same reasons which have made Nitinol so popular, an even more elastic wire than a nickel-titanium wire is desirable for many medical device applications.
In addition, with respect to many medical devices, the art has gone to great lengths and expense to provide radiopaque materials to the distal end of Nitinol elements (see, e.g., U.S. Pat. No. 5,520,194 to Miyata et al.). This is particularly required in devices using very fine (i.e., small diameter) Nitinol wires which cannot easily be seen during fluoroscopy. However, radiopaque materials are difficult to attach to the Nitinol components owing, in part, to their dissimilarity with the Nitinol material. Moreover, it is preferable in certain applications to have a highly elastic component which conducts electricity sufficiently to permit cautery functions or to permit the component to function as an electrical lead. However, nickel-titanium alloys are not particularly good conductors.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a variety of medical devices which utilize one or more nickel-titanium alloy cables that exhibit improved flexibility characteristics over nickel-titanium alloy wires of the art.
It is another object of the invention to provide medical devices with a radiopaque highly elastic element.
It is also object of the invention to provide medical devices which include a conductive highly elastic element.
It is a further object of the invention to provide medical devices which include a radiopaque, conductive, and highly elastic element.
In accord with these objects, which will be discussed in detail below, medical devices are provided which utilize a highly flexible cable of two and preferably three or more strands of wire, at least one of which is a nickel-titanium alloy strand, which are twined to form a wire rope which is drawn through successive dies to reduce its diameter until the outer surface of the cable is substantially smooth. A cable of all nickel-titanium alloy strands has been found to have an improved elasticity over a nickel-titanium wire of the same diameter. The cable is used in medical devices in which increased elasticity of a wire-like element is desired. Twisted and drawn cables incorporating one or more nickel-titanium strands and at least one strand of a radiopaque metal or alloy may be used in devices in which radiopacity of an elastic portion of the device is desired. Twisted and drawn cables incorporating one or more nickel-titanium alloys strands and at least one strand of a highly electrically conductive metal or alloy may be used in devices in which electrical conductivity of an elastic portion of the device is desired. Twisted and drawn cables incorporating at least one strand of nickel-titanium alloy with at least one strand of a radiopaque metal or alloy with at least one strand of a highly electrically conductive alloy may be used in devices in which radiopacity of an electrically conductive elastic portion of a device is desired.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described by first introducing the concept of cables formed from multistrand twisted and drawn wires. Then, with respect to multistrand twisted and drawn cables formed from nickel-titanium (Nitinol) wire, the benefit of such cables over nickel-titanium wires of the same diameter will be discussed. Finally, examples will be provided illustrating how such cables can be substituted for conventional wires, and particularly nickel-titanium alloy wires, in medical devices to achieve the beneficial results of the invention.
The invention is the improvement of a variety of medical devices by utilizing therein a cable of two and preferably three or more strands of wire, at least one of which is a nickel-titanium wire, which are twined to form a wire rope. The wire rope is drawn through successive dies to reduce its diameter until the outer surface of the cable is substantially smooth, the cross section of the cable is substantially circular, and the overall diameter of the wire rope is reduced by 20-50%. The cable is then annealed to remove the effects of cold working.
When the cable is constructed from only nickel-titanium alloy wires, the resulting cable has been found to have an improved flexibility (i.e., a lower modulus of elasticity) relative to a single nickel-titanium wire of the same diameter as the cable. In order to exemplify the benefit of a twisted and drawn cable comprised of nickel-titanium strands, three strands of 0.010 inch diameter Nitinol wire were helically twisted at a lay length of approximately 0.080 inches to form a wire rope of approximately 0.021″ diameter, and fed through successive dies of 0.019″, 0.018″, 0.016″, 0.014″, and 0.013″ diameters to form a Nitinol cable. After each die, it was noticed that the Nitinol cable rebounded to a slightly larger diameter than the diameter of the die. Thus, after the last die, the Nitinol cable was found to have a diameter of 0.014″ rather than 0.013″. The so-formed Nitinol cable was then annealed for approximately one minute at a temperature of approximately 500° C. to remove the effects of cold-working from the cable. Pieces of the resulting twisted and drawn Nitinol cable were then subjected to bend radius testing by wrapping pieces of the cables around pins of different diameters and by clamping the cable back on itself with a pair of pliers to simulate a zero-diameter bend. Comparison tests were conducted on 0.014″ diameter Nitinol wires (single strands). The results of the bend radius testing are set forth in Table 1, with percent recovery calculated according to (180°−x°)/180°, where x° is the angle of set taken by the wire or cable from longitudinal axis of the wire before the bend:
TABLE 1
Pin Diameter (inch)
% Recovery NiTi cable
% Recovery NiTi Wire
.201
100
100
.169
100
98.3
.155
100
98.0
.139
100
94.4
.121
99.1
93.8
.093
98.8
92.7
.078
98.0
91.6
.039
96.1
63.8
.034
91.6
55.5
.027
95.8
53.6
0 diameter bend
38.8
6.6
From the results of the tests set forth in Table 1, it will be appreciated that the Nitinol cable of the invention exhibited significantly increased flexibility relative to the same diameter Nitinol wire. For example, the
Gallagher Thomas A
General Science and Technology Corp.
Gordon David P
Jacobson David S
Mayo III William H.
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