U.S. patent application number 14/703391 was filed with the patent office on 2015-08-20 for guide wire core wire made from a substantially titanium-free alloy for enhanced guide wire steering response.
The applicant listed for this patent is Abbott Cardiovascular Systems, Inc.. Invention is credited to John A. Simpson.
Application Number | 20150231370 14/703391 |
Document ID | / |
Family ID | 47714577 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150231370 |
Kind Code |
A1 |
Simpson; John A. |
August 20, 2015 |
GUIDE WIRE CORE WIRE MADE FROM A SUBSTANTIALLY TITANIUM-FREE ALLOY
FOR ENHANCED GUIDE WIRE STEERING RESPONSE
Abstract
Guide wire devices and methods for their manufacture. Guide wire
devices include an elongate guide wire member that includes at
least one section fabricated from a substantially titanium-free
Co--Ni--Cr--Mo alloy. The substantially titanium-free
Co--Ni--Cr--Mo alloy exhibits superior stiffness (i.e., greater
Young's and shear moduli) as compared to stainless steel (e.g.,
304V stainless steel) and nickel-titanium (Ni--Ti) and a greater
yield strength as compared to stainless steel. Increasing the
Young's and shear moduli can significantly improve torque
transmission and steerability of the guide wire device and
increasing the yield strength can significantly improve the kink
resistance of the guide wire device.
Inventors: |
Simpson; John A.; (Carlsbad,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abbott Cardiovascular Systems, Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
47714577 |
Appl. No.: |
14/703391 |
Filed: |
May 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13364548 |
Feb 2, 2012 |
9061088 |
|
|
14703391 |
|
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Current U.S.
Class: |
72/41 ;
72/362 |
Current CPC
Class: |
C21D 7/00 20130101; C22C
19/055 20130101; C22F 1/10 20130101; A61L 31/14 20130101; A61L
29/02 20130101; A61F 2/95 20130101; C22C 19/056 20130101; A61M
25/09 20130101; A61M 2025/09108 20130101; C22C 30/00 20130101; B21F
45/008 20130101; Y10T 29/49826 20150115; A61M 2025/09175 20130101;
A61M 2025/09133 20130101; A61L 31/022 20130101; A61M 2025/09091
20130101; C22C 19/07 20130101 |
International
Class: |
A61M 25/09 20060101
A61M025/09; B21F 45/00 20060101 B21F045/00; C22C 19/07 20060101
C22C019/07; C22C 30/00 20060101 C22C030/00; C22C 19/05 20060101
C22C019/05 |
Claims
1. A method for fabricating a guide wire device, comprising:
fabricating an elongate guide wire member having a proximal section
and a distal section, wherein at least the distal section is
fabricated from a cobalt-nickel-chromium-molybdenum
(Co--Ni--Cr--Mo) alloy that comprises less than 0.05% of titanium
by weight; and imparting at least 50% to 95% cold work to at least
a portion of the Co--Ni--Cr--Mo alloy to yield a Co--Ni--Cr--Mo
alloy having a Young's modulus of at least about 230 GPa and a
yield strength of about 1 GPa to about 2 GPa.
2. The method of claim 1, wherein the method further comprises one
or more of: grinding the distal end section to a distally tapered
cross sectional dimension of about 0.1 mm to about 0.05 mm;
disposing a helical coil section about at least a distal end
portion of the distal section and joining the helical coil to the
elongate guide wire member at a proximal location; forming a
rounded cap section on a distal end of the elongate guide wire
member; or applying at least one lubricious outer coating layer
over at least a portion of the elongate guide wire member.
3. The method of claim 1, wherein the cold work includes one or
more of drawing, swaging, cold rolling, stamping, extrusion,
forging, or flattening.
4. The method of claim 1, further comprising: fabricating the
distal section of the elongate guide wire member from the
Co--Ni--Cr--Mo alloy; cold working at least a portion of the
Co--Ni--Cr--Mo alloy to yield a cold worked section that exhibits
at least about 50-95% cold work.
5. The method of claim 1, further comprising: fabricating the
proximal and distal sections of the elongate guide wire member from
the Co--Ni--Cr--Mo alloy; cold working at least a portion of the
Co--Ni--Cr--Mo alloy to yield a cold worked section that exhibits
at least about 50-95% cold work.
6. The method of claim 1, wherein the Co--Ni--Cr--Mo alloy
comprises: about 31.5 wt % to about 39 wt % cobalt; about 33 wt %
to about 37 wt % nickel; about 19 wt % to about 21 wt % chromium;
about 9 wt % to about 10.5 wt % molybdenum; and less than about
0.05 wt % titanium.
7. The method of claim 1, wherein the Co--Ni--Cr--Mo alloy exhibits
about 80% to about 95% cold work.
8. A method for fabricating a guide wire device, comprising:
fabricating an elongate guide wire member having a proximal section
and a distal section, wherein at least the distal section is
fabricated from a cobalt-nickel-chromium-molybdenum
(Co--Ni--Cr--Mo) alloy that comprises less than 0.05% of titanium
by weight; grinding the distal end section to a distally tapered
cross sectional dimension of about 0.1 mm to about 0.05 mm;
imparting at least 50% to 95% cold work to at least a portion of
the Co--Ni--Cr--Mo alloy to yield higher Young's and shear moduli
and greater yield strength, as compared to a non-cold worked
portion of the Co--Ni--Cr--Mo alloy; disposing a helical coil
section about at least a distal end portion of the distal section;
joining the helical coil to the elongate guide wire member at a
proximal location; forming a rounded cap section on a distal end of
the helical coil; and applying at least one lubricious outer
coating layer over at least a portion of the elongate guide wire
member to form the guide wire device.
9. The method of claim 8, wherein the cold work includes one or
more of drawing, swaging, cold rolling, stamping, extrusion,
forging, or flattening.
10. The method of claim 8, further comprising: fabricating the
distal section of the elongate guide wire member from the
Co--Ni--Cr--Mo alloy; cold working at least a portion of the
Co--Ni--Cr--Mo alloy to yield a cold worked section that exhibits
at least about 50-95% cold work.
11. The method of claim 8, further comprising: fabricating the
proximal and distal sections of the elongate guide wire member from
the Co--Ni--Cr--Mo alloy; cold working at least a portion of the
Co--Ni--Cr--Mo alloy to yield a cold worked section that exhibits
at least about 50-95% cold work.
12. The method of claim 8, wherein the cold worked Co--Ni--Cr--Mo
alloy has a Young's modulus of at least about 230 GPa and a yield
strength of about 1 GPa to about 2 GPa.
13. The method of claim 8, wherein the Co--Ni--Cr--Mo alloy
comprises: about 31.5 wt % to about 39 wt % cobalt; about 33 wt %
to about 37 wt % nickel; about 19 wt % to about 21 wt % chromium;
about 9 wt % to about 10.5 wt % molybdenum; and less than about
0.05 wt % titanium.
14. The method of claim 8, wherein the Co--Ni--Cr--Mo alloy
exhibits about 80% to about 95% cold work.
15. A method for fabricating a guide wire device, comprising:
fabricating an elongate guide wire member having a proximal section
joined to a distal section, wherein the distal section is
fabricated from a cobalt-nickel-chromium-molybdenum
(Co--Ni--Cr--Mo) alloy that comprises less than 0.05% of titanium
by weight and wherein the proximal section is fabricated from a
stainless steel alloy; imparting at least 50% to 95% cold work to
at least a portion of the Co--Ni--Cr--Mo alloy to yield higher
Young's and shear moduli and greater yield strength, as compared to
the proximal section.
16. The method of claim 1, wherein the method further comprises one
or more of: grinding the distal end section to a distally tapered
cross sectional dimension of about 0.1 mm to about 0.05 mm;
disposing a helical coil section about at least a distal end
portion of the distal section and joining the helical coil to the
elongate guide wire member at a proximal location; forming a
rounded cap section on a distal end of the elongate guide wire
member; or applying at least one lubricious outer coating layer
over at least a portion of the elongate guide wire member.
17. The method of claim 15, wherein the cold work includes one or
more of drawing, swaging, cold rolling, stamping, extrusion,
forging, or flattening.
18. The method of claim 15, wherein the cold worked Co--Ni--Cr--Mo
alloy has a Young's modulus of at least about 230 GPa and a yield
strength of about 1 GPa to about 2 GPa.
19. The method of claim 15, wherein the Co--Ni--Cr--Mo alloy
comprises: about 31.5 wt % to about 39 wt % cobalt; about 33 wt %
to about 37 wt % nickel; about 19 wt % to about 21 wt % chromium;
about 9 wt % to about 10.5 wt % molybdenum; and less than about
0.05 wt % titanium.
20. The method of claim 15, wherein the Co--Ni--Cr--Mo alloy
exhibits about 80% to about 95% cold work.
21. The method of claim 15, further comprising: forming the
proximal section to have a cross sectional diameter of 0.3 mm to
0.5 mm; and forming the distal section to have a ground surface
defining a second, smaller cross sectional dimension with a distal
taper section having a cross sectional diameter of 0.1 mm to 0.05
mm.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a Divisional and claims the benefit of
and priority to U.S. patent application Ser. No. 13/364,548, filed
2 Feb. 2012, the entirety of which is incorporated herein by
reference.
BACKGROUND
[0002] Guide wires are used to guide a catheter for treatment of
intravascular sites such as Percutaneous Transluminal Coronary
Angioplasty ("PTCA"), or in examination such as cardio-angiography.
For example, a guide wire used in the PTCA is inserted into the
vicinity of a target angiostenosis portion together with a balloon
catheter, and is operated to guide the distal end portion of the
balloon catheter to the target angiostenosis portion.
[0003] In order to facilitate guiding a guide wire through a
patient's vascular anatomy (e.g., from an exterior access point to
an intravascular treatment site), a guide wire needs to meet a
number of performance criteria. For example, a guide wire needs
appropriate flexibility, pushability and torque transmission
performance for transmitting an operational force from the proximal
end portion to the distal end, and kink resistance (resistance
against sharp bending).
BRIEF SUMMARY
[0004] The present disclosure describes guide wire devices and
methods for their manufacture. The guide wire devices described in
the present disclosure include an elongate guide wire member that
includes at least one section fabricated from a substantially
titanium-free Co--Ni--Cr--Mo alloy. The substantially titanium-free
Co--Ni--Cr--Mo alloy, which goes by the names MP35NLT.RTM. and 35N
LT.RTM., exhibits superior stiffness (i.e., greater Young's and
shear moduli) as compared to stainless steel (e.g., 304V stainless
steel) and nickel-titanium (Ni--Ti) and a greater yield strength as
compared to stainless steel. Increasing the Young's and shear
moduli can significantly improve torque transmission and
steerability of the guide wire device and increasing the yield
strength can significantly improve the kink resistance of the guide
wire device.
[0005] In one embodiment, a guide wire device is described. The
guide wire device includes an elongate guide wire member having a
proximal end section and a distal end section, wherein at least one
of the proximal end section or the distal end section of the
elongate guide wire member is fabricated from a
cobalt-nickel-chromium-molybdenum (Co--Ni--Cr--Mo) alloy that is
substantially free of titanium (e.g., less than about 0.05%
titanium by weight).
[0006] In another embodiment, a guide wire device includes an
elongate guide wire member having a proximal end section and a
distal end section, wherein at least one of the proximal end
section or the distal end section of the elongate guide wire member
is fabricated from a substantially titanium-free Co--Ni--Cr--Mo
alloy having a Young's modulus of at least about 230 GPa, a shear
modulus of at least about 80 GPa, and a yield strength of about 1
GPa to about 2 GPa. The Young's modulus and the shear modulus of
the Co--Ni--Cr--Mo alloy used to fabricate the guide wire device
are higher than stainless steel and significantly higher than
either austentic or martensitic Ni--Ti. The yield strength is
significantly higher that stainless steel. Wire diameter profile,
the Young's modulus, and shear modulus are reasonable predictors of
torque transmission and catheter support provided by a guide wire
device, whereas yield strength is a reasonable predictor of its
kink resistance.
[0007] In yet another embodiment, a method for fabricating a guide
wire device is disclosed. The method includes (1) fabricating an
elongate guide wire member having a proximal section and a distal
section, wherein at one of the proximal section or the distal
section is fabricated from a Co--Ni--Cr--Mo alloy that is
substantially free of titanium and (2) grinding the distal end
section to a distally tapered cross sectional diameter of about 0.3
mm to about 0.05 mm. The method further includes (3) disposing a
helical coil section about at least a distal end portion of the
distal section, (4) joining the helical coil to the elongate guide
wire member at a proximal location, (5) forming a rounded cap
section on a distal end of the helical coil, and (6) applying at
least one lubricious outer coating layer over at least a portion of
the elongate guide wire member to form the guide wire device.
[0008] In some embodiments of the guide wire device and methods
disclosed herein, the proximal end section is fabricated from a
stainless steel alloy (e.g., 304V or 316L stainless steel), the
distal end section is fabricated from the Co--Ni--Cr--Mo alloy, and
the proximal end section and the distal end section are joined to
one another by one or more of a welded joint, a brazed joint, or an
adhesive joint. In another aspect of the guide wire devices and
methods disclosed herein, the proximal end section and the distal
end section are fabricated from the Co--Ni--Cr--Mo alloy. In yet
another aspect, the proximal section is the Co--Ni--Cr--Mo alloy
and the distal section is superelastic or linear elastic
nitinol.
[0009] These and other objects and features of the present
disclosure will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the embodiments of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] To further clarify the above and other advantages and
features of the present disclosure, a more particular description
of the invention will be rendered by reference to specific
embodiments thereof which are illustrated in the appended drawings.
It is appreciated that these drawings depict only illustrated
embodiments of the invention and are therefore not to be considered
limiting of its scope. The present disclosure will be described and
explained with additional specificity and detail through the use of
the accompanying drawings in which:
[0011] FIG. 1 illustrates a partial cut-away view of a guide wire
device according to one embodiment of the present invention;
and
[0012] FIG. 2 is a side elevation view, in partial cross-section,
of a delivery catheter within a body lumen having a stent disposed
about the delivery catheter according to an embodiment of the
present disclosure.
DETAILED DESCRIPTION
I. Introduction
[0013] The present disclosure describes guide wire devices and
methods for their manufacture. The guide wire devices described in
the present disclosure include an elongate guide wire member that
includes at least one section fabricated from a substantially
titanium-free Co--Ni--Cr--Mo alloy. The substantially titanium-free
Co--Ni--Cr--Mo alloy, which goes by the names MP35NLT.RTM. or 35N
LT.RTM., exhibits superior stiffness (i.e., greater Young's and
shear moduli) as compared to stainless steel (e.g., 304V stainless
steel) and nickel-titanium and a greater yield strength as compared
to stainless steel. Increasing the Young's and shear moduli can
significantly improve torque transmission and steerability of the
guide wire device and increasing the yield strength can
significantly improve the kink resistance of the guide wire
device.
[0014] Because guide wire devices are designed to track through a
patient's vasculature, for example, guide wire devices may be quite
long (e.g., about 150 cm to about 300 cm in length) and thin. Guide
wire devices need to be long enough to travel from an access point
outside a patient's body to a treatment site and narrow enough to
pass freely through the patient's vasculature. For example, a
typical guide wire device has an overall diameter of about 0.2 mm
to about 0.5 mm for coronary use. Larger diameter guide wires may
be employed in peripheral arteries and other body lumens. The
diameter of the guide wire device affects its flexibility, support,
and torque. Thinner wires are more flexible and are able to access
narrower vessels while larger diameter wires offer greater support
and torque transmission.
[0015] Some typical examples of guide wire devices are constructed
with a superelastic Ni--Ti alloy core wire, a two part wire that
includes a binary Ni--Ti distal core section welded, brazed, or
otherwise joined to a stainless steel proximal core section, and
so-called all-stainless steel "core to tip" guide wire designs.
[0016] Superelastic Ni--Ti alloys are noted for their flexibility
and extreme kink resistance, but Ni--Ti core wires can be more
difficult to manipulate when a high level of torque transmission is
needed. Despite the advantages of a superelastic Ni--Ti guide wire
core (e.g., the ability to bend quite dramatically without causing
permanent deformation), typical Ni--Ti guide wires generally do not
transmit applied torque as effectively from the proximal shaft
because the shear modulus and the Young's modulus of Ni--Ti alloy
are substantially lower than those of stainless steel. As a result,
superelastic Ni--Ti tends to "wind up" or store twist as opposed to
transmitting torque directly from end-to-end. One way to increase
the bending and torsional stiffness of a guide wire core wire is to
increase its diameter. Nevertheless, the diameter of a core wire is
limited by the design specifications of the guide wire, which in
turn are limited by the lumen size of those catheters with which
the guide wire is intended to be used. While the distal grind
profiles of superelastic Ni--Ti core wires are typically larger
than those of stainless steel, there is an inherent limit to the
torque transmission that can be obtained with superelastic Ni--Ti
core wires without exceeding product dimensional requirements.
[0017] In contrast to Ni--Ti, stainless steel alloys are desired in
many applications because of their stiffness and torqueability.
Stainless steel guide wire cores are presently made from grades of
stainless steel such as 316L or 304V. Stainless steel is far
stiffer than Ni--Ti and it is thus easier to steer through a
patient's vasculature because torque is well transmitted from the
proximal end to the distal end of a wire. As a result, stainless
steel guide wire cores can generally be made thinner than
comparable Ni--Ti core wires. However, while stainless steel "core
to tip" guide wires can be made much thinner than Ni--Ti wires,
stainless steel is much more likely to kink when the wire is
prolapsed or when guiding through tortuous anatomy. If kinking
occurs, guide wire performance is often substantially reduced due
to "whipping," in which elastic windup builds within the section
proximal to the kink until sufficient torque causes the kinked
region to abruptly rotate one complete revolution. This behavior
makes delicate manipulation of the guide wire's distal end
difficult, if not impossible.
[0018] In contrast to either Ni--Ti or stainless steel, the present
disclosure relates to the use of a substantially titanium-free
cobalt-nickel-chromium-molybdenum (Co--Ni--Cr--Mo) alloy material
(known as MP35NLT or 35N LT.RTM.) that exhibits a superior
stiffness (i.e., greater Young's and shear moduli) as compared to
commonly used stainless steels and Ni--Ti and a greater yield
strength as compared to stainless steel. Such a material exhibits
many of the best properties of stainless steel and Ni--Ti, without
the drawbacks. For example, due to its higher Young's and shear
moduli, such a material would be expected to exhibit improved
steering response as compared to Ni--Ti and, to a lesser degree,
stainless steel because steering forces are more likely to be
transferred directly along the length of the guide wire. Likewise,
while MP35NLT can be torqued and steered even better than stainless
steel, it is expected to be less likely to kink due to its higher
yield strength.
[0019] Tables 1-3 illustrate some of the physical properties of
MP35NLT as compared to Ni--Ti alloy and stainless steel.
TABLE-US-00001 TABLE 1 Young's Modulus (GPa) MP35NLT ~232-235 304V
Stainless Steel ~193-200 Ni--Ti (austenite) 82 Ni--Ti (martensite)
30
TABLE-US-00002 TABLE 2 Shear Modulus (GPa) MP35NLT ~80-84 304V
Stainless Steel ~69-73 Ni--Ti (superelastic) ~24
[0020] To a first approximation, the Young's modulus and the shear
modulus (as reported in gigaPascals or "GPa") are measures of
tensile and torsional stiffness of a material, respectively. In
general, a material with higher Young's and shear moduli will be
easier to steer through a patient's anatomy because the material
will transfer torque applied at the proximal end to the distal end
as opposed to building significant elastic windup. As can be seen
from Tables 1 and 2, MP35NLT has Young's and shear moduli that are
comparable to but higher than 304V and considerably higher than
Ni--Ti. In general, a guide wire having a core wire made of MP35NLT
should be easier to steer through a patient's anatomy because the
material will transfer torque applied at the proximal end to the
distal more efficiently than either stainless steel or Ni--Ti.
[0021] Table 3 (below) illustrates the yield strength of MP35NLT as
compared to 304V stainless steel. The yield strength or yield point
of a material is defined as the stress (as reported in GPa) at
which a material begins to deform plastically. Prior to the yield
point the material will deform elastically in response to an
applied stress and, rather than permanently kinking, will return to
its original shape when the applied stress is removed. Once the
yield point is passed, however, some fraction of the deformation
will be permanent and non-reversible.
[0022] As can be seen from the data presented in Table 3, MP35NLT
has a higher yield strength than 304V stainless steel at all cold
work levels. As such, a guide wire core wire fabricated from
MP35NLT will be able to tolerate more severe bending stresses while
navigating tortuous anatomy without permanently deforming, as
compared to stainless steel. MP35NLT is not as kink resistant as
Ni--Ti, but MP35NLT has greater bending and torsional stiffness
that makes it more desirable than superelastic Ni--Ti in many
applications.
TABLE-US-00003 TABLE 3 YIELD STRENGTH (GPa) % Cold Work MP35NLT
304V Stainless Steel 0 0.90 0.35 20 1.31 0.48 37 1.66 0.62 50 1.86
0.97 60 2.00 1.10 68 2.07 1.24 75 2.10 1.38 80 2.17 1.48 84 2.24
1.59 90 2.30 1.69 93 2.33 1.72 95 2.34 1.93
[0023] The substantially titanium-free Co--Ni--Cr--Mo alloy
disclosed herein (i.e., MP35NLT) is a nickel-cobalt-based alloy
that has a face-centered cubic matrix of cobalt and nickel in which
chromium and molybdenum are soluble at elevated temperatures. The
face-centered cubic structure persists upon cooling to
room-temperature and below.
[0024] Conventionally prepared MP35N alloy includes up to about 1%
titanium as a deliberate additional alloying element. It is
believed that the addition of titanium may provide the alloy with
properties that are favored by manufacturers of some articles.
However, titanium has a strong tendency to form carbides and
nitrides as a result of exposure to carbon and nitrogen during
melting procedures. The resulting carbide and nitride inclusions
can reduce the fatigue life of the wires used for guide wire cores.
For example, the titanium carbide and nitride inclusions are
brittle and non-malleable, which is in contrast to the properties
of the bulk Co--Ni--Cr--Mo material, and, as such, they can act as
origins for crack formation of the fine wires used for guide wire
cores.
[0025] By reducing the titanium to an extremely low level (e.g.,
less than 0.05 wt %), the size and overall quantity of titanium
carbide and titanium nitride inclusions can be substantially
reduced (e.g., from about 550,000 inclusions per square inch for
conventional MP35N to about 35,000 inclusion per square inch for
MP35NLT). Such reductions on the numbers of inclusions can
significantly reduce the likelihood of breakage of a guide wire
core wire as a result of the torquing and bending forces
experienced by a guide wire while traversing a patient's
anatomy.
[0026] In one embodiment, the substantially titanium-free
Co--Ni--Cr--Mo alloy (i.e., MP35NLT) disclosed herein includes
about 31.5 wt % to about 39 wt % cobalt, about 33 wt % to about 37
wt % nickel, about 19 wt % to about 21 wt % chromium, about 9 wt %
to about 10.5 wt % molybdenum, and less than about 0.05 wt %
titanium. In another embodiment, the MP35NLT alloy disclosed herein
includes about 35 wt % cobalt, about 35 wt % nickel, about 20.5 wt
% chromium, about 9.5 wt % molybdenum, and less than about 0.05 wt
% titanium. Preferably, the MP35NLT contains less than about 0.01
wt % titanium, less than about 0.005 wt % titanium, or less than
about 0.001 wt % titanium.
[0027] To form a substantially titanium-free Co--Ni--Cr--Mo alloy,
each of the four principal elements (i.e., cobalt, nickel,
chromium, and molybdenum) can be refined to form a furnace charge
stock that is substantially free of titanium and other
contaminating elements. The refined principal elements are combined
in an alloy melt by vacuum induction melting. Homogenization and
final refining is performed in a vacuum arc remelt furnace. The
Co--Ni--Cr--Mo alloy material produced in this way typically
contains less than 0.05 wt % titanium, less than about 0.01 wt %
titanium, less than about 0.005 wt % titanium, or less than about
0.001 wt % titanium in comparison to conventionally processed
MP35N, which deliberately contains up to 1.0% titanium by
weight.
[0028] After vacuum arc refining and cooling, MP35NLT can be
processed into wire for forming a guide wire core by conventional
cold processing methods including one or more of drawing, swaging,
cold rolling, stamping, extrusion, forging, or other suitable cold
processing methods. Cold working the MP35NLT alloy using processes
such as those listed herein can yield significant increases in
strength (see, e.g., Table 3). In one embodiment, the MP35NLT alloy
has a yield strength of about 1 GPa to about 2.3 GPa imparted by at
least about 10% to about 95% cold work, about 10% to about 60% cold
work, or about 20% to about 50% cold work.
[0029] For further increases in yield strength, cold worked MP35N
or MP35NLT alloy can be age hardened by heat treating the alloy at
a temperature of at least about 430.degree. C. to about 650.degree.
C. for about 30 minutes to about 240 minutes. Such heat treatment
serves to strengthen the alloy by stabilizing the dislocation
structure produced during cold work. While age hardening thermal
treatments are used in a variety of alloy systems in order to cause
the formation of very fine precipitate particles that hinder
dislocation movement and thereby increase strength with only
moderate impact on ductility, the metallurgical reaction which
occurs in MP35N and MP35NLT involves another mechanism, the
organization and stabilization of stacking faults. At the high
levels of prior cold work needed to provide high yield strengths in
guide wire applications, deliberate age hardening of MP35N or
MP35NLT can lead to severe loss of ductility and is thus not
generally recommended.
II. Guide Wire Devices
[0030] As discussed in greater detail elsewhere herein, guide wire
devices are typically made from stainless steel, a conventionally
processed superelastic Ni--Ti alloy, or a combination of the two.
For a given wire diameter, stainless steel is quite a bit stiffer
than superelastic Ni--Ti and is generally better at transmitting
torque. Nevertheless, stainless steel is susceptible to kinking
while passing through tortuous anatomy. In contrast, superelastic
Ni--Ti is much less susceptible to kinking but it is not effective
for transmitting torque.
[0031] In ordinary applications, differences in flexibility between
two materials can be readily compensated for by dimensional
alterations. That is, for example, the tendency to wind up that is
typical of conventionally processed superelastic Ni--Ti can
ordinarily be compensated for by increasing the diameter of the
wire in order to attain equivalent deflection behavior when
compared to a stiffer wire material. However, guide wire devices
typically face inherent dimensional constraints that are imposed by
the overall product profile, by the allowable space within
overlying coils or polymeric jacketing, and/or the size of the
anatomy to be accessed. For this reason, use of substantially
titanium-free Co--Ni--Cr--Mo alloys exhibiting superior stiffness
(i.e., greater Young's and shear moduli) and a greater yield
strength significantly expand the maximum range of torsional or
bending stiffness that can be achieved in a guide wire of a given
profile.
[0032] In one embodiment, a guide wire device includes an elongate
guide wire member having a proximal section and a distal section.
At least a portion of the elongate guide wire member is fabricated
from a cobalt-nickel-chromium-molybdenum (Co--Ni--Cr--Mo) alloy
that is substantially free of titanium (e.g., less than about 0.05%
titanium by weight).
[0033] In another embodiment, a guide wire device includes an
elongate guide wire member having a proximal end section and a
distal end section, wherein at least one of the proximal end
section or the distal end section of the elongate guide wire member
is fabricated from a substantially titanium-free Co--Ni--Cr--Mo
alloy having a Young's modulus of at least about 230 GPa, a shear
modulus of at least about 80 GPa, and a yield strength of about 1
GPa to about 2 GPa. The Young's modulus and the shear modulus of
the Co--Ni--Cr--Mo alloy used to fabricate the guide wire device
are higher than stainless steel and significantly higher than
either austentic or martensitic Ni--Ti. The yield strength is
significantly higher than stainless steel. The Young's and shear
moduli are a reasonable predictor of navigability of a guide wire
device and yield strength is a reasonable predictor of kink
resistance of a guide wire device.
[0034] Referring now to FIG. 1, a partial cut-away view of an
example of a guide wire device 100 is illustrated. The guide wire
device 100 may be adapted to be inserted into a patient's body
lumen, such as an artery or another blood vessel. The guide wire
device 100 includes an elongated proximal portion 102 and a distal
portion 104. In one embodiment, both the elongated proximal portion
102 and the distal portion 104 may be formed from any of the
substantially titanium-free Co--Ni--Cr--Mo alloys disclosed herein.
In another embodiment, the elongated proximal portion 102 may be
formed from a first material such as stainless steel (e.g., 304V or
316L stainless steel) or a Ni--Ti alloy and the distal portion may
be formed from a second material such as any of the substantially
titanium-free Co--Ni--Cr--Mo alloys disclosed herein. In
embodiments where the elongated proximal portion 102 and the distal
portion 104 are formed from different materials, the elongated
proximal portion 102 and the distal portion 104 may joined to one
another via a welded, brazed, or adhesive joint 116 that joins the
proximal portion 102 and the distal portion 104 into a torque
transmitting relationship.
[0035] It is worth noting that MP35NLT is a very corrosion
resistant alloy and that, under certain conditions, joining MP35NLT
to a metal such as stainless steel could lead to galvanic corrosion
of the stainless steel. This should not be a problem with guide
wires, which are not designed to be implanted in the body for an
extended period of time. However, galvanic corrosion could possibly
be a problem only if the wire were left in the body for an extended
period of time (i.e., days or weeks or longer).
[0036] In one embodiment, selected portions of the guide wire
device 100 or the entire guide wire device 100 may be processed by
cold working one or more of the proximal and distal portions
followed by an optional aging step to yield a substantially
titanium-free Co--Ni--Cr--Mo alloy having a Young's modulus of at
least about 230 GPa, a shear modulus of at least about 80 GPa, and
a yield strength of about 1 GPa to about 2 GPa. As discussed
elsewhere herein, increasing levels of cold-work followed by aging
can affect the Young's and shear moduli to a limited degree and
could significantly raise the yield strength of the alloy, but this
would come at great expense in terms of ductility in guide wire
applications.
[0037] In one embodiment, selected portions of the guide wire
device 100 or the entire guide wire device 100 may be cold worked
to exhibit about 10% to about 95% cold work, about 10%, or about
60% cold work, or about 20% to about 50% cold work. Cold work can
be followed by aging at a temperature of at least about 430.degree.
C. to about 650.degree. C. for about 30 minutes to about 240
minutes.
[0038] Referring again to FIG. 1, the distal portion 104 has at
least one tapered section 106 that, in the illustrated embodiment,
becomes smaller in the distal direction. The length and diameter of
the tapered distal core section 106 can, for example, affect the
trackability of the guide wire device 100. Typically, gradual or
long tapers produce a guide wire device with less support but
greater trackability, while abrupt or short tapers produce a guide
wire device that provides greater support but also greater tendency
to prolapse (i.e., kink) when steering. The length of the distal
end section 106 can, for example, affect the steerability of the
guide-wire device 100. In one embodiment, the distal end section
106 is about 10 cm to about 40 cm in length.
[0039] The proximal end section 102 of the guide wire device has a
diameter of about 0.3 mm to about 1.0 mm. In one embodiment, the
tapered distal section can be formed by grinding the distal portion
104 to terminal diameter of diameter of about 0.1 mm to about 0.05
mm to form the very end 108 of the distal tapered end section 106.
That is, the tapered end section 106 gradually tapers from a
diameter of about 0.3 mm to about 0.5 mm to a terminal diameter of
about 0.1 mm to about 0.05 mm at the distal end (e.g., 108) of the
guide wire device 100.
[0040] In guide wires, which are typically single-use disposable
products that are not designed to be in place in the body or
implanted in the body for long periods of time, fatigue resistance
(i.e., long-term durability) is generally not a concern. However,
short-term measures of durability such as the consistency of
tensile break load and turns to failure (torsional ductility) are
very important. Because the distal tapered end section 106 section
is ground to such a small diameter, having sizeable inclusions in
this section could adversely impact either of these performance
attributes due to the fact that a guide wire's tensile break load
and turns to failure values depend primarily on the distal few
centimeters that have been ground to the smallest diameter.
[0041] In the illustrated embodiment, the tapered distal core
section 106 includes the shapeable very distal end section 108,
which is shapeable because MP35NLT's yield strength characteristics
are similar to stainless steel so it is possible for users to bend
the distal end section by hand. As such, shapeable end sections can
be integral to the guide wire device 100 as shown, or they can be a
separate piece (not shown) that is included as part of the distal
end of the guide wire device 100. Having a shapeable very distal
end section 108 can allow a practitioner to shape the distal and of
the guide wire device 100 to a desired shape (e.g., a J-bend) for
tracking through the patient's vasculature.
[0042] As illustrated in FIG. 1, the guide wire device 100 includes
a helical coil section 110. The helical coil section 110 affects
support, trackability, and visibility of the guide wire device and
provides tactile feedback. The most distal section of the helical
coil section 110 is made of radiopaque metal such as platinum or
platinum alloys such as platinum-nickel alloys to facilitate the
radiographic observation thereof while it is disposed within a
patient's body. As illustrated, the helical coil section 110 is
disposed about at least a portion of the distal portion 104 and has
a rounded, atraumatic cap section 120 on the distal end thereof.
The helical coil section 110 is secured to the distal portion 104
at proximal location 114 and at intermediate location 112 by a
suitable technique such as, but not limited to, soldering, brazing,
welding, or adhesive.
[0043] In one embodiment, portions of the guide wire device 100 are
coated with a coating 118 of lubricous material such as
polytetrafluoroethylene (PTFE) (sold under the trademark Teflon by
du Pont, de Nemours & Co.) or other suitable lubricous coatings
such as the polysiloxane coatings, polyvinylpyrrolidone (PVP), and
the like.
[0044] Referring now to FIG. 2, the guide wire device 100 is shown
configured to facilitate deploying a stent 210. FIG. 2 provides
more detail about the manner in which the guide wire device 100 may
be used to track through a patient's vasculature where it can be
used to facilitate deployment of a treatment device such as, but
not limited to the stent 210. FIG. 2 illustrates a side elevation
view, in partial cross-section, a delivery catheter 200 having a
stent 210 disposed thereabout according to an embodiment of the
present disclosure. The portion of the illustrated guide wire
device 100 that can be seen in FIG. 2 includes the distal portion
104, the helical coil section 110, and the atraumatic cap section
120. The delivery catheter 200 has an expandable member or balloon
202 for expanding the stent 210, on which the stent 210 is mounted,
within a body lumen 204 such as an artery.
[0045] The delivery catheter 200 may be a conventional balloon
dilatation catheter commonly used for angioplasty procedures. The
balloon 202 may be formed of, for example, polyethylene,
polyethylene terephthalate, polyvinylchloride, nylon, Pebax.TM. or
another suitable polymeric material. To facilitate the stent 210
remaining in place on the balloon 202 during delivery to the site
of the damage within the body lumen 204, the stent 210 may be
compressed onto the balloon 202. Other techniques for securing the
stent 210 onto the balloon 202 may also be used, such as providing
collars or ridges on edges of a working portion (i.e., a
cylindrical portion) of the balloon 202.
[0046] In use, the stent 210 may be mounted onto the inflatable
balloon 202 on the distal extremity of the delivery catheter 200.
The balloon 202 may be slightly inflated to secure the stent 210
onto an exterior of the balloon 202. The catheter/stent assembly
may be introduced within a living subject using a conventional
Seldinger technique through a guiding catheter 206. The guide wire
100 may be disposed across the damaged arterial section with the
detached or dissected lining 207 and then the catheter/stent
assembly may be advanced over the guide wire 208 within the body
lumen 204 until the stent 210 is positioned at the target location
207. The balloon 202 of the catheter 200 may be expanded, expanding
the stent 210 against the interior surface defining the body lumen
204 by, for example, permanent plastic deformation of the stent
210. When deployed, the stent 210 holds open the body lumen 204
after the catheter 200 and the balloon 202 are withdrawn.
III. Methods for Fabricating a Guide Wire Device
[0047] In another embodiment, a method for fabricating a guide wire
device is disclosed. The method includes (1) fabricating an
elongate guide wire member having a proximal section and a distal
section, wherein at least one of the proximal section or the distal
section is fabricated from any of the substantially titanium-free
Co--Ni--Cr--Mo alloys disclosed herein and (2) grinding the distal
end section to a distally tapered cross sectional diameter of about
0.1 mm to about 0.05 mm. The method further includes (3) disposing
a helical coil section about at least a distal end portion of the
distal section, (4) joining the helical coil to the elongate guide
wire member at a proximal location, (5) forming a rounded cap
section on a distal end of the helical coil, and (6) applying at
least one lubricious outer coating layer over at least a portion of
the elongate guide wire member to form the guide wire device.
[0048] To form the substantially titanium-free Co--Ni--Cr--Mo
alloy, each of the four principal elements (i.e., cobalt, nickel,
chromium, and molybdenum) can be refined to form a furnace charge
stock that is substantially free of titanium and other
contaminating elements. The refined principal elements are combined
in an alloy melt by vacuum induction melting. Homogenization and
final refining is performed in a vacuum arc refining furnace. The
Co--Ni--Cr--Mo alloy material produced in this way typically
contains less than 0.05 wt % titanium, less than about 0.01 wt %
titanium, less than about 0.005 wt % titanium, or less than about
0.001 wt % titanium in comparison to conventionally processed
MP35N, which contains up to 1.0% titanium by weight.
[0049] After vacuum arc refining and cooling, MP35NLT can be
processed into wire for forming a guide wire core by conventional
cold processing methods including one or more of drawing, swaging,
cold rolling, stamping, extrusion, forging, and other cold
processing methods known to persons having skill in the art. Cold
working the MP35NLT alloy using processes such as those listed
herein can yield significant increases in strength (see, e.g.,
Table 3). In one embodiment, the the MP35NLT alloy has a yield
strength of about 1 GPa to about 2.3 GPa imparted by at least about
10% to about 95% cold work. Preferably, the MP35NLT alloy includes
about 10% to about 60% cold work or about 20% to about 50% cold
work.
[0050] For further increases in yield strength, the cold worked
alloy can be precipitation hardened or "aged" by heat treating the
alloy at a temperature of at least about 430.degree. C. to about
650.degree. C. for about 30 minutes to about 240 minutes. However,
at the high levels of prior cold work needed to provide high yield
strengths in guide wire applications, deliberate age hardening of
MP35N or MP35NLT can lead to severe loss of ductility and is thus
not generally recommended.
[0051] In one embodiment, the methods disclosed herein further
include (a) fabricating the distal section of the elongate guide
wire member from the Co--Ni--Cr--Mo alloy, (b) cold working at
least a portion of the Co--Ni--Cr--Mo alloy to yield a cold worked
section that exhibits at least about 50% cold work.
[0052] In another embodiment, the methods disclosed herein include
(a) fabricating the proximal and distal sections of the elongate
guide wire member from any of the substantially titanium-free
Co--Ni--Cr--Mo alloys disclosed herein, (b) cold working at least a
portion of the Co--Ni--Cr--Mo alloy to yield a cold worked section
that exhibits at least about 80% cold work.
[0053] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *