U.S. patent application number 10/299524 was filed with the patent office on 2003-04-10 for superelastic guiding member.
Invention is credited to Abrams, Robert M., Fariabi, Sepehr.
Application Number | 20030069492 10/299524 |
Document ID | / |
Family ID | 27395736 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030069492 |
Kind Code |
A1 |
Abrams, Robert M. ; et
al. |
April 10, 2003 |
Superelastic guiding member
Abstract
An improved guiding member for use within a body lumen having a
unique combination of superelastic characteristics. The
superelastic alloy material has a composition consisting of about
30% to about 52% (atomic) titanium, and about 38% to 52% nickel and
may have one or more elements selected from the group consisting of
iron, cobalt, platinum, palladium, vanadium, copper, zirconium,
hafnium and niobium. The alloy material is subjected to
thermomechanical processing which includes a final cold working of
about 10 to about 75% and then a heat treatment at a temperature
between about 450.degree. and about 600.degree. C. and preferably
about 475.degree. to about 550.degree. C. Before the heat treatment
the cold worked alloy material is preferably subjected to
mechanical straightening. The alloy material is preferably
subjected to stresses equal to about 5 to about 50% of the room
temperature ultimate yield stress of the material during the
thermal treatment. The guiding member using such improved material
exhibits a stress-induced austenite-to-martensite phase
transformation at an exceptionally high constant yield strength of
over 90 ksi for solid members and over 70 ksi for tubular members
with a broad recoverable strain of at least about 4% during the
phase transformation. An essentially whip free product is
obtained.
Inventors: |
Abrams, Robert M.;
(Carlsbad, CA) ; Fariabi, Sepehr; (Fremont,
CA) |
Correspondence
Address: |
FULWIDER PATTON LEE & UTECHT, LLP
HOWARD HUGHES CENTER
6060 CENTER DRIVE
TENTH FLOOR
LOS ANGELES
CA
90045
US
|
Family ID: |
27395736 |
Appl. No.: |
10/299524 |
Filed: |
November 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10299524 |
Nov 19, 2002 |
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09884432 |
Jun 18, 2001 |
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09884432 |
Jun 18, 2001 |
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09498695 |
Feb 7, 2000 |
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6280539 |
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09498695 |
Feb 7, 2000 |
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08484218 |
Jun 7, 1995 |
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6165292 |
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08484218 |
Jun 7, 1995 |
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08212431 |
Mar 11, 1994 |
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08212431 |
Mar 11, 1994 |
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07994679 |
Dec 22, 1992 |
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5341818 |
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07994679 |
Dec 22, 1992 |
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07629381 |
Dec 18, 1990 |
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Current U.S.
Class: |
600/407 |
Current CPC
Class: |
A61M 2025/09008
20130101; A61M 25/09 20130101; C22C 30/00 20130101; A61M 2025/09141
20130101; A61M 2025/09175 20130101; C22C 14/00 20130101; A61L
31/022 20130101; A61M 2205/0266 20130101; A61L 2400/16 20130101;
A61M 2025/09083 20130101; A61L 31/14 20130101; C22F 1/006
20130101 |
Class at
Publication: |
600/407 |
International
Class: |
A61B 005/05 |
Claims
What is claimed is:
1. An intravascular guidewire comprising a) an elongated member
having a proximal portion and a distal portion and being formed at
least in part of a superelastic alloy consisting essentially of
about 30 to about 52% titanium, about 38 to about 52% nickel and up
to 20% additional alloying elements selected from the group
consisting of iron, cobalt, platinum, palladium, copper and
vanadium, said alloy part having an austenite phase which has a
final transformation temperature below about 45.degree. C., which
transforms to a martensite phase upon the application of stress and
which has been thermomechanically formed in a procedure which
includes a final cold working followed by a heat treatment at a
temperature between about 450.degree. to about 600.degree. C. while
applying tension to the cold worked elongated member; and b)
torquing means on the proximal end of the elongated member.
2. The guidewire of claim 1 wherein the alloy contains one or more
additional alloying elements selected from the group consisting of
iron, cobalt, platinum and palladium in amounts of up to about
3%.
3. The guidewire of claim 1 wherein the alloy contains one or more
additional alloying elements selected from the group consisting of
copper in amounts of up to 12% and vanadium in amounts of up to
about 10%.
4. The guidewire of claim 1 wherein the temperature of the heat
treatment is between about 475.degree. and about 550.degree. C.
5. The guidewire of claim 1 wherein the superelastic portion has a
straight memory at a temperature less than about 450.degree. C.
6. The guidewire of claim 1 wherein the final cold worked alloy
part is mechanically straightened before the heat treatment.
7. A superelastic alloy body having an austenite phase which is
stable at a desired operating temperature and which will transform
to martensite phase upon the application thereto of stress,
exhibiting a recoverable strain of at least about 4% upon the
stress induced transformation of the austenite phase to martensite
phase and having been formed by thermomechanical processing which
includes a final cold working about 10 to about 75% and a memory
imparting heat treatment at a temperature between about 475.degree.
and about 600.degree. C.
8. The body of claim 7 wherein the strain of the body during the
stress induced transformation of the austenite phase to the
martensite phase is within the range of about 2% to about 8%.
9. The body of claim 7 wherein the austenite-to-martensite
transformation occurs at a relatively constant stress above about
50 ksi.
10. The body of claim 7 wherein the austenite-to-martensite
transformation occurs at a relatively constant stress above about
70 ksi.
11. The body of claim 7 wherein a distal portion thereof has a
plurality of sections which have progressively smaller
cross-sections in the distal direction.
12. The body of claim 7 further comprising a flexible member
disposed about the superelastic distal portion thereof.
13. The body of claim 12 wherein the flexible member is a helical
coil with a rounded plug on the distal end thereof.
14. The body of claim 6 wherein tension is applied to the elongated
body while being subjected to the memory imparting heat
treatment.
15. The body of claim 6 wherein the body is subjected to mechanical
straightening between the cold working and heat treating steps.
16. A fixed-wire balloon angioplasty catheter comprising: a) an
elongated catheter body with an inner lumen extending therein; b)
an inflatable balloon on the distal extremity of the catheter body
and having an interior in fluid communication with the inner lumen
of the catheter body; and c) a guiding member which is disposed at
least in part within the interior of the inflatable balloon and
which is formed at least in part of a superelastic alloy body
having an austenite phase which is stable at a desired operating
temperature and which will transform to martensite phase upon the
application thereto of stress, exhibiting a recoverable strain of
at least about 4% upon the stress induced transformation of the
austenite phase to martensite phase and having been formed by a
thermomechanical processing which includes a final cold working of
about 10 to about 75% and then a memory imparting heat treatment at
a temperature between about 450.degree. and about 600.degree. C.
while tension is applied thereto.
17. The fixed wire balloon angioplasty catheter of claim 17 wherein
the thermomechanical processing includes a mechanical straightening
between the cold working and heat treating.
18. A method of forming a superelastic elongated member being in an
austenite phase which is stable at temperatures less than about
45.degree. C.: providing an elongated member formed of an alloy
consisting essentially of about 30 to about 52% titanium, about 38
to about 52% nickel and up to a total of about 20% of one or more
additional alloying elements selected from the group consisting of
iron, cobalt, chromium, platinum, palladium, copper, vanadium,
zirconium, hafnium and niobium; subjecting the elongated member to
thermomechanical processing which includes a final cold working of
about 10 to about 75% and a heat treatment at a temperature between
about 450.degree. and about 600.degree. C. while subjecting the
elongated member to a tension of up to about 50% of the room
temperature tensile strength.
19. The method of claim 18 wherein the elongated member is
subjected to mechanical straightening after the final cold working
but before the heat treatment.
20. The method of claim 18 wherein the heat treating temperature is
between about 475.degree. and about 550.degree. C.
21. The method of claim 18 wherein the final cold-worked number is
heat treated for about 0.5 to about 60 minutes.
22. An elongated tubular body suitable for use within a human body
which has a cylindrical wall defining an inner lumen therein, which
is formed of a superelastic alloy consisting essentially of about
30 to about 52% titanium, about 38 to 52% nickel, and to about 20%
of one or more elements selected from the group consisting of iron,
cobalt, chromium, platinum, palladium, copper, vanadium, zirconium,
hafnium and niobium in a stable austenite phase which will
transform to martensite phase upon the application of stress, which
will exhibit a recoverable strain of at least about 4% from the
application of stress which transforms the austenite phase to the
martensite phase and which has been fabricated by a
thermomechanical processing which includes a final cold working of
about 10 to about 75% and then a memory imparting heat treatment at
a temperature of about 450.degree. to about 600.degree. C.
23. The tubular body of claim 22 wherein the stress level at which
the austenite phase transforms to the martensite phase is above 50
ksi.
24. The tubular body of claim 22 wherein the
austenite-to-martensite transformation occurs at a relatively
constant yield stress above about 70 ksi.
25. The tubular body of claim 22 wherein the alloy contains at
least one element selected from the group consisting of up to about
20% copper and up to about 10% vanadium.
26. The tubular body of claim 22 wherein the alloy contains at
least one element selected from the group consisting of iron,
cobalt, palladium and platinum in amounts up to about 3%.
27. The tubular body of claim 24 having an outer diameter of about
0.006 to about 0.05 inch and a wall thickness of about 0.001 to
about 0.004 inch.
28. A method of forming a superelastic elongated member having a
straight memory comprising subjecting an elongated member having a
composition consisting of a predominant amount of NiTi
intermetallic constituent to thermomechanical processing which
includes a final cold working of about 10 to about 75% and a heat
treatment at a temperature between about 450.degree. and about
600.degree. C. while subjecting the cold worked elongated member to
sufficient tension to ensure a straight memory.
29. The method of claim 28 wherein the elongated member is formed
of an alloy consisting essentially of about 30 to about 52%
titanium, abut 38 to about 52% nickel and up to a total of about
10% of one or more additional alloying elements selected from the
group consisting of iron, cobalt, chromium, platinum, palladium,
coppers vanadium, zirconium, hafnium and niobium.
30. The method of claim 29 wherein the elongated member is in the
austenite phase.
31. The method of claim 29 wherein the heat treatment is at a
temperature between about 475.degree. to about 550.degree. C.
32. The method of claim 29 wherein the elongated member is
mechanically straightened after the final cold working and before
the heat treating.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part application to
application Ser. No. 07/629,381, filed Dec. 18, 1990, entitled
SUPERELASTIC GUIDING MEMBER.
BACKGROUND OF THE INVENTION
[0002] This invention relates to the field of medical devices, and
more particularly to guiding means such as guidewires for advancing
catheters within body lumens in procedures such as percutaneous
transluminal coronary angioplasty (PTCA).
[0003] In typical PTCA procedures a guiding catheter having a
preformed distal tip is percutaneously introduced into the
cardiovascular system of a patient in a conventional Seldiger
technique and advanced therein until the distal tip of the guiding
catheter is seated in the ostium of a desired coronary artery. A
guidewire is positioned within an inner lumen of a dilatation
catheter and then both are advanced through the guiding catheter to
the distal end thereof. The guidewire is first advanced out of the
distal end of the guiding catheter into the patient's coronary
vasculature until the distal end of the guidewire crosses a lesion
to be dilated, then the dilatation catheter having an inflatable
balloon on the distal portion thereof is advanced into the
patient's coronary anatomy over the previously introduced guidewire
until the balloon of the dilatation catheter is properly positioned
across the lesion. Once in position across the lesion, the balloon
is inflated to a predetermined size with radiopaque liquid at
relatively high pressures (e.g. greater than 4 atmospheres) to
compress the arteriosclerotic plaque of the lesion against the
inside of the artery wall and to otherwise expand the inner lumen
of the artery. The balloon is then deflated so that blood flow is
resumed through the dilated artery and the dilatation catheter can
be removed therefrom.
[0004] Conventional guidewires for angioplasty and other vascular
procedures usually comprise an elongated core member with one or
more tapered sections near the distal end thereof and a flexible
body such as a helical coil disposed about the distal portion of
the core member. A shapable member, which may be the distal
extremity of the core member or a separate shaping ribbon which is
secured to the distal extremity of the core member extends through
the flexible body and is secured to a rounded plug at the distal
end of the flexible body. Torquing means are provided on the
proximal end of the core member to rotate, and thereby steer, the
guidewire while it is being advanced through a patient's vascular
system.
[0005] Further details of dilatation catheters, guidewires, and
devices associated therewith for angioplasty procedures can be
found in U.S. Pat. No. 4,323,071 (Simpson et al.); U.S. Pat. No.
4,439,185 (Lundquist); U.S. Pat. No. 4,516,972 (Samson); U.S. Pat.
No. 4,538,622 (Samson et al.); U.S. Pat. No. 4,554,929 (Samson et
al.); U.S. Pat. No. 4,616,652 (Simpson); and U.S. Pat. No.
4,638,805 (Powell).
[0006] Steerable dilatation catheters with fixed, built-in guiding
members, such as described in U.S. Pat. No. 4,582,181 (now Re
33,166) are frequently used because they have lower deflated
profiles than conventional over-the-wire dilatation catheters and a
lower profile allows the catheter to cross tighter lesions and to
be advanced much deeper into a patient's coronary anatomy.
[0007] A major requirement for guidewires and other guiding
members, whether they be solid wire or tubular members, is that
they have sufficient columnar strength to be pushed through a
patient's vascular system or other body lumen without kinking.
However, they must also be flexible enough to avoid damaging the
blood vessel or other body lumen through which they are advanced.
Efforts have been made to improve both the strength and flexibility
of guidewires to make them more suitable for their intended uses,
but these two properties are for the most part diametrically
opposed to one another in that an increase in one usually involves
a decrease in the other.
[0008] The prior art makes reference to the use of alloys such as
NITINOL, which is an acronym for Ni-Ti Naval Ordnance Laboratory.
These alloys have shape memory and/or superelastic characteristics
and may be used in medical devices which are designed to be
inserted into a patient's body. The 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 on the other hand 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
undeformed shape by the transformation back to the original
phase.
[0009] Alloys having shape memory/superelastic characteristics
generally have at least two phases. These phases are a martensite
phase, which has a relatively low tensile strength and which is
stable at relatively low temperatures, and an austenite phase,
which has a relatively high tensile strength and which is stable at
temperatures higher than the martensite phase.
[0010] Shape memory characteristics are imparted to the alloy by
heating the metal at a temperature above which the transformation
from the martensite phase to the austenite phase is complete, i.e.
a temperature above which the austenite phase is stable. The shape
of the metal during this heat treatment is the shape "remembered".
The heat treated metal is cooled to a temperature at which the
martensite phase is stable, causing the austenite phase to
transform to the martensite phase. The metal in the martensite
phase is then plastically deformed, e.g. to facilitate the entry
thereof into a patient's body. Subsequent heating of the deformed
martensite phase to a temperature above the martensite to austenite
transformation temperature causes the deformed martensite phase to
transform to the austenite phase and during this phase
transformation the metal reverts back to its original shape.
[0011] The prior methods of using the shape memory characteristics
of these alloys in medical devices intended to be placed within a
patient's body presented operational difficulties. For example,
with shape memory alloys having a stable martensite temperature
below body temperature, it was frequently difficult to maintain the
temperature of the medical device containing such an alloy
sufficiently below body temperature to prevent the transformation
of the martensite phase to the austenite phase when the device was
being inserted into a patient's body. With intravascular devices
formed of shape memory alloys having martensite-to-austenite
transformation temperatures well above body temperature, the
devices could be introduced into a patient's body with little or no
problem, but they had to be heated to the martensite-to-austenite
transformation temperature which was frequently high enough to
cause tissue damage and very high levels of pain.
[0012] When stress is applied to a specimen of a metal such as
NITINOL exhibiting superelastic characteristics at a temperature
above which the austenite is stable (i.e. the temperature at which
the transformation of martensite phase to the austenite phase is
complete), the specimen deforms elastically until it reaches a
particular stress level where the alloy then undergoes a
stress-induced phase transformation from the austenite phase to the
martensite phase. As the phase transformation proceeds, the alloy
undergoes significant increases in strain but with little or no
corresponding increases in stress. The strain increases while the
stress remains essentially constant until the transformation of the
austenite phase to the martensite phase is complete. Thereafter,
further increase in stress are necessary to cause further
deformation. The martensitic metal first yields elastically upon
the application of additional stress and then plastically with
permanent residual deformation.
[0013] If the load on the specimen is removed before any permanent
deformation has occurred, the martensitic specimen will elastically
recover and transform back to the austenite phase. The reduction in
stress first causes a decrease in strain. As stress reduction
reaches the level at which the martensite phase transforms back
into the austenite phase, the stress level in the specimen will
remain essentially constant (but substantially less than the
constant stress level at which the austenite transforms to the
martensite) until the transformation back to the austenite phase is
complete, i.e. there is significant recovery in strain with only
negligible corresponding stress reduction. After the transformation
back to austenite is complete, further stress reduction results in
elastic strain reduction. This ability to incur significant strain
at relatively constant stress upon the application of a load and to
recover from the deformation upon the removal of the load is
commonly referred to as superelasticity or pseudoelasticity.
[0014] The prior art makes reference to the use of metal alloys
having superelastic characteristics in medical devices which are
intended to be inserted or otherwise used within a patient's body.
See for example, U.S. Pat. No. 4,665,905 (Jervis) and U.S. Pat. No.
4,925,445 (Sakamoto et al.).
[0015] The Sakamoto et al. patent discloses the use of a
nickel-titanium superelastic alloy in an intravascular guidewire
which could be processed to develop relatively high yield strength
levels. However, at the relatively high yield stress levels which
cause the austenite-to-martensite phase transformation
characteristic of the material, it did not have a very extensive
stress-induced strain range in which the austenite transforms to
martensite at relative constant stress. As a result, frequently as
the guidewire was being advanced through a patient's tortuous
vascular system, it would be stressed beyond the superelastic
region, i.e. develop a permanent set or even kink which can result
in tissue damage. This permanent deformation would generally
require the removal of the guidewire and the replacement thereof
with another.
[0016] Products of the Jervis patent on the other hand had
extensive strain ranges, i.e. 2 to 8% strain, but the relatively
constant stress level at which the austenite transformed to
martensite was very low, e.g. 50 ksi.
[0017] What has been needed and heretofore unavailable is an
elongated solid or tubular body for intravascular devices, such as
guide wires or guiding members, which have at least a portion
thereof exhibiting superelastic characteristics including an
extended strain region over a relatively constant high stress level
which effects the austenite transformation to martensite and still
provide a one-to-one torque response. The present invention
satisfies these and other needs.
SUMMARY OF THE INVENTION
[0018] The present invention is directed to an improved
superelastic body which is suitable for intraluminal devices, such
as guidewires or guiding members, wherein superelastic
characteristics result from the stress-induced transformation of
austenite to martensite.
[0019] The superelastic alloy body of the invention has a stable
austenite phase which will transform to martensite phase upon the
application of stress and will exhibit a recoverable strain of at
least about 4% upon the stress induced transformation of the
austenite phase to the martensite phase. The formation of the alloy
body includes a final cold working about 10 to about 75% and then a
final memory imparting heat treatment at a temperature of about
450.degree. to about 600.degree. C., preferably 475.degree. to
about 550.degree. C. The cold worked, heat treated product exhibits
a stress-induced phase transformation at temperatures below about
450.degree. C. at a relatively high stress level, e.g. above about
70 ksi, (483 Mpa) preferably above about 90 ksi (620 Mpa) for solid
products and about 40 ksi (276 Mpa) for hollow tubular products.
The superelastic product exhibits at recoverable strain of at least
4% upon completion of the stress-induced transformation of the
austenite phase to the martensite phase. The onset of the stress
induced phase change from austenite to martensite, preferably
begins when the specimen has been strained about 2% and extends to
a strain level of about 8% at the completion of the phase change.
The stress and strain referred to herein is measured by tensile
testing. The stress-strain relationship determined by applying a
bending moment to a cantilevered specimen is slightly different
from the relationship determined by tensile testing because the
stresses which occur in the specimen during bending are not as
uniform as they are in tensile testing. The stress change during
the phase transformation is much less than the stress either before
or after the stress-induced transformation. In some instances the
stress level during the phase change is almost constant.
[0020] The elongated portion of the guiding member having
superelastic properties is preferably formed from an alloy
consisting essentially of about 30 to about 52% titanium, about 38%
to about 52% nickel and additional alloying elements in amount up
to 20% for copper and up to about 10% in the case of other alloying
elements. The additional alloying elements may be selected from the
group consisting of up to 3% each of iron, cobalt, chromium,
platinum, palladium, zirconium, hafnium and niobium and up to about
10% vanadium. At nickel levels above 52% the alloy becomes too
brittle to fabricate by cold working. Metallurgically the alloy
consist essentially of a predominant quantity of a NiTi
intermetallic compound and small quantities of other constituents.
Additionally, when nickel is in excess Ni.sub.3Ti is formed,
whereas when titanium is in excess Ti.sub.2Ni is formed. As used
herein, all references to percent alloy compositions are atomic
percent unless otherwise noted.
[0021] To form the elongated superelastic portion of the guiding
member, elongated solid rod or tubular stock of the preferred alloy
material is first thermomechanically processed through a series of
cold working, e.g. drawing and inter-annealing at temperatures
between about 600.degree. to about 800.degree. C. for about 5 to
about 30 minutes and is then given a final cold working, e.g.
drawing, to effect a final size reduction of about 10% up to about
75% in the transverse cross section thereof. For solid products the
final cold work is preferably about 30 to about 70% and for hollow
tubular products the final cold work is preferably about 10% to
about 40%. As used herein % cold work is the size reduction of the
transverse dimension of the work piece effected by the cold
working. After the final cold working, the material is given a heat
treatment at a temperature of about 450.degree. to about
600.degree. C., preferably about 475.degree. to about 550.degree.
C., for about 0.5 to about 60 minutes to generate the superelastic
properties. To impart a straight memory, the cold worked material
may be subjected to a longitudinal stress equal to about 5% to
about 50%, preferably about 10% to about 30%, of the yield stress
of the material (as measured at room temperature) during a heat
treatment of about 450.degree. to about 600.degree. C. This
thermomechanical processing imparts a straight "memory" to the
superelastic portion and provides a relatively uniform residual
stress in the material. Preferably, the final cold worked product
is subjected to mechanically straightening between the final cold
working and heat treating steps to provide the wire or tubular
product with substantially improved, one-to-one torque response,
i.e. it is substantially whip free. The alloy composition and
thermal treatment are selected to provide an austenite finish
transformation temperature generally about -20.degree. to about
400.degree. C. and usually less than body temperature (approx.
37.degree. C.). To obtain more consistent final properties, it is
preferred to fully anneal the solid rod or tubular stock prior to
cold working so that the material will always have the same
metallurgical structure at the start of the cold working. The
pre-annealing also ensures adequate ductility for cold working. It
will be appreciated by those skilled in the art that the alloy can
be cold worked in a variety of ways other than drawing, such as
rolling or swaging. The constant stress levels for tubular products
have been found to be slightly lower than the constant stress
levels for solid products due to the inability to cold work the
tubular products to the extent the solid products can be cold
worked. For example, solid superelastic wire material of the
invention can have a relatively constant stress level above about
70 ksi, usually above about 90 ksi, whereas, hollow superelastic
tubing material of the invention can have a relatively constant
stress level above about 50 ksi (345 Mpa) usually above about 60
ksi (414 Mpa). The ultimate tensile strength of both forms of the
material is well above 200 ksi (1380 Mpa) with an ultimate
elongation at failure of about 15%.
[0022] The elongated body of the invention exhibits a
stress-induced austenite-to-martensite phase transformation over a
broad region of strain at very high, relatively constant stress
levels. As a result a guiding member formed of this material is
very flexible, it can be advanced through very tortuous passageways
such as a patient's coronary vasculature with little risk that the
superelastic portion of the guiding member will develop a permanent
set and at the same time it will effectively transmit the torque
applied thereto without causing the guiding member to whip.
[0023] These and other advantages of the invention will become more
apparent from the following detailed description thereof when taken
in conjunction with the following exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates a guidewire which embodies features of
the invention.
[0025] FIG. 2 illustrates another embodiment of a guidewire of the
invention.
[0026] FIG. 3 is a partial side elevational view, partially in
section, of a guiding member embodying features of the invention
which is incorporated into a fixed-wire dilatation catheter adapted
for balloon angioplasty procedures.
[0027] FIG. 4 is a schematic, graphical illustration of the
stress-strain relationship of superelastic material.
[0028] FIG. 5 illustrates another embodiment of a guidewire
embodying features of the invention.
[0029] FIG. 6 illustrates the effects of the temperature during
heat treatment after final cold working on the final austenite
transformation temperature (Af).
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIG. 1 illustrates a guidewire 10 embodying features of the
invention that is adapted to be inserted into a body lumen such as
an artery. The guidewire 10 comprises an elongated body or core
member 11 having an elongated proximal portion 12 and a distal
portion 13, at least part of which, preferably the distal portion,
is formed of superelastic material of the invention. The distal
portion 13 has a plurality of sections 14, 15 and 16 having
sequentially smaller diameters with tapered sections 17, 18 and 19
connecting the smaller diameter sections with adjacent sections.
The elongated proximal portion 12 is provided with a female distal
end 20 which receives the male end 21 of the distal portion 13. The
ends 20 and 21 may be press fit together or may be secured together
by means such as a suitable adhesive or by welding, brazing or
soldering.
[0031] A helical coil 22 is disposed about the distal portion 13
and has a rounded plug 23 on the distal end thereof where the
distal end of the helical coil is welded to the distal end of a
shaping ribbon 24 which is secured by its proximal end to the
distal portion 13 by suitable means (e.g. brazing) at location 25.
The coil 22 is also secured to the distal portion 13 of the
elongated body 11 at location 25 and to the tapered section 17 at
location 26. Preferably, the most distal section 27 of the helical
coil 22 is made of radiopaque metal such as platinum or alloys
thereof to facilitate the fluoroscopic observation of the distal
portion of the guidewire while it is disposed within a patient's
body.
[0032] The exposed portion of the elongated body 11 should be
provided with a coating 28 of lubricous material such as
polytetrafluoroethylene (sold under the trademark Teflon by du
Pont) or other suitable lubricous coatings such as the polysiloxane
coatings disclosed in copending application Ser. No. 559,373, filed
Jul. 24, 1990 which is hereby incorporated by reference.
[0033] FIG. 2 illustrates another embodiment of a guidewire which
incorporates features of the invention. This embodiment is very
similar to the embodiment shown in FIG. 1 except that the entire
elongated body 11 is formed of material having superelastic
characteristics and the distal portion 13 of the core member 11
extends all the way to the plug 23 and is preferably flattened at
its most distal extremity 29 as ribbon 24 in the embodiment shown
in FIG. 1. All of the parts of the guidewire shown in FIG. 2 which
correspond to the parts shown in FIG. 1 are numbered the same as in
FIG. 1.
[0034] FIG. 3 illustrates a fixed wire, steerable dilatation
catheter 40 which has incorporated therein a guiding member 41 in
accordance with the invention. In this embodiment, the catheter 40
includes an elongated tubular member 42 having an inner lumen 43
extending therein and an inflatable, relatively inelastic
dilatation balloon 44 on the distal extremity of the tubular
member. Guiding member 41 which includes an elongated body 45, a
helical coil 46 disposed about and secured to the distal end of the
elongated body 45 and a shaping ribbon 50 extending from the distal
end of the elongated body to rounded plug 51 at the distal end of
the coil 46. The proximal portion 52 of the elongated body 45 is
disposed within the inner lumen 43 of the tubular member 42 and the
distal portion 53 of the elongated body 45 extends through the
interior of the dilatation balloon 44 and out the distal end
thereof. The distal end of the balloon 44 is twisted and sealed
about the distal portion 53 of the elongated body 45 extending
therethrough in a manner which is described in more detail in
copending application Ser. No. 521,103, filed May 9, 1990, which is
hereby incorporated by reference. The helical coil 46 is secured to
the distal portion 53 of the elongated body 45 by suitable means
such as brazing at location 54 which is the same location at which
the shaping ribbon 50 is secured to the distal portion of the
elongated body. Preferably, the distal portion 53 is free to rotate
within the twisted seal of the distal end of the balloon 44 and
means are provided to seal the distal portion 53 therein to allow
air to be vented therethrough but not inflation fluid such as shown
in U.S. Pat. No. 4,793,350 (Mar et al.). The proximal end of the
catheter 40 is provided with a multiple arm adapter 55 which has
one arm 56 for directing inflation fluid through the inner lumen 43
and the interior of the balloon 44. The proximal end of the
elongated body 45 extends through the adapter 55 and is secured to
the torquing handle 57 which rotates the guiding member 41 within
the catheter 40 as the catheter is advanced through a patient's
vascular system. The tubular member 42 may be formed of suitable
plastic material such as polyethylene or polyamide or metals such
as stainless steel or NITINOL. All or at least the distal portion
of the tubular member 42 may be formed of the superelastic NiTi
type alloy material of the invention. In an alternative
construction, the elongated body 45 has a flattened distal portion
which is secured to the rounded plug 51.
[0035] The elongated body 11 of the guidewire 10 and elongated body
45 of the fixed-wire catheter 40 are generally about 150 to about
200 cm (typically about 175 cm) in length with an outer diameter of
about 0.01 to 0.018 inch (0.25-0.46 mm) for coronary use. Larger
diameter guidewire and guiding members may be employed in
peripheral arteries. The lengths of the smaller diameter sections
14, 15 and 16 can range from about 5 to about 30 cm. The tapered
sections 17, 18 and 19 generally are about 3 cm in length, but
these too can have various lengths depending upon the stiffness or
flexibility desired in the final product. The helical coils 22 and
46 are about 20 to about 40 cm in length, have an outer diameter
about the same size as the diameter of the elongated bodies 11 and
45, and are made from wire about 0.002 to 0.003 inch (0.051-0.076
mm) in diameter. The last or most distal 1.5 to about 4 cm of the
coil is longitudinally expanded and preferably made of platinum or
other radiopaque material to facilitate the fluoroscopic
observation thereof when the guidewire or fixed wire catheter is
inserted into a patient. The remaining portion of the coils 22 and
45 may be stainless steel. The transverse cross-section of the
elongated bodies 11 and 45 is generally circular. However, the
shaping ribbons 24 and 50 and the flattened distal section 29 have
rectangular transverse cross-sections which usually have dimensions
of about 0.001 by 0.003 inch (0.025-0.076 mm).
[0036] The superelastic guiding member of the invention, whether it
is the entire elongated body 11 or 45 or just a portion thereof, is
preferably made of an alloy material consisting essentially of
about 30 to about 52% titanium, about 38 to 50% nickel and the
balance one or more additional alloying elements in amounts of up
to about 20%, preferably up to about 12% in the case of copper and
up to 10% for other additional alloying elements. The other
additional alloying elements may be selected from the group
consisting of iron, cobalt, platinum, palladium, zirconium, hafnium
and niobium in amounts up to 3% each and vanadium in an amount of
up to 10%. The addition of nickel above equiatomic amounts with
titanium and the other identified alloying elements increases the
stress levels at which the stress-induced austenite-to-martensite
transformation occurs and ensures that the temperature at which the
martensite phase transforms to the austenite phase is well below
human body temperature so that austenite is the only stable phase
at body temperature. The excess nickel and additional alloying
elements also help to provide an expanded strain range at very high
stresses when the stress induced transformation of the austenite
phase to the martensite phase occurs.
[0037] A presently preferred method for making the final
configuration of the superelastic portion of the guiding member is
to cold work, preferably by drawing, a rod or tubular member having
a composition according to the relative proportions described above
to effect a final size reduction of about 10 to about 75% and then
providing a memory imparting heat treatment to the cold worked
product at a temperature of about 450.degree. to about 600.degree.
C. preferably about 475.degree. to about 550.degree. C., for about
0.5 to about 60 minutes. In one preferred embodiment the cold
worked product is subjected to tensile stress to hold the product
straight during the heat treatment to impart a straight memory
thereto. In the embodiment with a solid wire product, the final
cold work preferably ranges from about 30 to about 70% and the heat
treatment temperature ranges from about 450.degree. to about
600.degree. C., preferably about 475.degree. to about 550.degree.
C. In another presently preferred embodiment with tubular products,
the final cold work ranges from about 10 to about 40% and the final
memory imparting heat treatment temperature ranges are the same as
mentioned above. Typical initial transverse dimensions of the rod
or the tubular member prior to cold working are about 0.045 inch
(1.14 mm) and about 0.25 inch (6.35 mm) respectively. If the final
product is to be a tubular product, a small diameter ingot, e.g.
0.20 to about 1.5 inch (5.1-38.1 mm) in diameter and 5 to about 48
inches (12.7-122 cm) in length, may be formed into a hollow tube by
extruding or by machining a longitudinal center hole through a
solid rod and grinding the outer surface thereof smooth.
[0038] After each drawing step, except the last, the solid rod or
tubular member is preferably annealed at a temperature of about
600.degree. to about 800.degree. C., typically about 675.degree.
C., for about 15 minutes in air or a protective atmosphere such as
argon to relieve essentially all internal stresses. In this manner
all of the specimens start the subsequent thermomechanical
processing in essentially the same metallurgical condition so that
consistent final properties are obtained. Such treatment also
provides the requisite ductility for effective subsequent cold
working. The stress relieved stock is preferably drawn through one
or more dies of appropriate inner diameter with a reduction per
pass of about 10 to 70%. The final heat treatment fixes the
austenite-martensite transformation temperature. Mechanical
straightening prior to the final heat treatment, particularly when
tension is applied during the last heat treatment ensures a uniform
level of residual stresses throughout the length of the
superelastic material which minimizes or eliminates guidewire
whipping when made of this material when torqued within a patient's
blood vessel.
[0039] In a typical procedure, starting with solid rod stock 0.100
inch (2.54 mm) in diameter, the cold working/heat treatment
schedule would be performed as follows:
[0040] 1. Cold work 60% from 0.100 inch to 0.0632 inch (1.61 mm)
and anneal at 675.degree. C. for 15 minutes.
[0041] 2. Cold work 60% form 0.0632 inch to 0.0399 inch (1.02 mm)
and anneal at 675.degree. C. for 15 minutes.
[0042] 3. Cold work 60% by drawing through 2-3 dies from 0.0399
inch to 0.0252 inch (0.64 mm) and anneal at 675.degree. C. for 15
minutes.
[0043] 5. Cold work 69% by drawing through 2-3 dies from 0.0252
inch to 0.014 inch (0.36 mm).
[0044] 6. Mechanically straighten and then continuously heat treat
at 510.degree. C. at 1 ft/min (0.0305 m/min) under sufficient
tension to impart a straight memory.
[0045] When the cold worked material is subjected to the slightly
lower thermal treatments, it has substantially higher tensile
properties and it exhibits stress-induced austenite to martensite
phase transformation at very high levels of stress but the stress
during the phase transformation is not very constant. The addition
of mechanical straightening prior to the final memory imparting
heat treatment under tension will substantially improve the
whipping characteristics of the final product.
[0046] FIG. 4 illustrates an idealized stress-strain relationship
of an alloy specimen having superelastic properties as would be
exhibited upon tensile testing of the specimen. The line from point
A to point B thereon represents the elastic deformation of the
specimen. After point B the strain or deformation is no longer
proportional to the applied stress and it is in the region between
point, B and point C that the stress-induced transformation of the
austenite phase to the martensite phase begins to occur. There can
be an intermediate phase developed, sometimes called the
rhombohedral phase, depending upon the composition of the alloy. At
point C the material enters a region of relatively constant stress
with significant deformation or strain. It is in the region of
point C to point D that the transformation from austenite to
martensite occurs. At point D the stress induced transformation to
the martensite phase is substantially complete. Beyond point D the
stress-induced martensite phase begins to deform, elastically at
first, but, beyond point E, the deformation is plastic or
permanent. If plastic deformation occurs, the strain will not
return to zero upon the removal of the stress.
[0047] When the stress applied to the superelastic metal is
removed, the metal will recover to its original shape, provided
that there was no permanent deformation to the martensite phase. At
point F in the recovery process, the metal begins to transform from
the stress-induced, unstable martensite phase back to the more
stable austenite phase. In the region from point G to point H,
which is also an essentially constant stress region, the phase
transformation from martensite back to austenite is essentially
complete. The line from point I to the starting point A represents
the elastic recovery of the metal to its original shape.
[0048] FIG. 5 illustrates a guidewire 60 embodying features of the
invention which comprises an elongated, relatively high strength
proximal portion 61, a relatively short distal portion 62 which is
formed substantially of superelastic alloy material and a tubular
connector element 63 which is formed substantially of superelastic
alloy material and which connects the proximal end of the distal
portion 62 to the distal end of the proximal portion 61 into a
torque transmitting relationship. The distal portion 62 has at
least one tapered section 64 which becomes smaller in the distal
direction. The connector element 63 is a hollow tubular shaped
element having an inner lumen extending therein which is adapted to
receive the proximal end 65 of the distal portion 62 and the distal
end 66 of the proximal portion 61. The ends 65 and 66 may be press
fit into the connector element 63 or they may be secured therein by
crimping or swaging the connector element or by means such as a
suitable adhesive or by welding, brazing or soldering.
[0049] A helical coil 67 is disposed about the distal portion 62
and has a rounded plug 68 on the distal end thereof. The coil 67 is
secured to the distal portion 62 at proximal location 70 and at
intermediate location 71 by a suitable solder. A shaping ribbon 72
is secured by its proximal end to the distal portion 62 at the same
location 71 by the solder and by the distal end thereof to the
rounded plug 68 which is usually formed by soldering or welding the
distal end of the coil 67 to the distal tip of the shaping ribbon
72. Preferably, the distal section 74 of the helical coil 67 is
made of radiopaque metal such as platinum or platinum-nickel alloys
to facilitate the observation thereof while it is disposed within a
patient's body. The distal section 74 should be stretched about 10
to about 30%.
[0050] The most distal part 75 of the distal portion 62 is
flattened into a rectangular section and preferably provided with a
rounded tip 76, e.g. solder, to prevent the passage of the most
distal part through the spacing between the stretched distal
section 74 of the helical coil 67.
[0051] The exposed portion of the elongated proximal portion 61
should be provided with a coating 77 of lubricous material such as
polytetrafluoroethylene (sold under the trademark Teflon by du
Pont, de Nemours & Co.) or other suitable lubricous coatings
such as the polysiloxane coatings disclosed in co-pending
application Ser. No. 559,373, filed Jul. 24, 1990 which is hereby
incorporated by reference.
[0052] The elongated proximal portions of the guidewires of the
invention for coronary use are generally about 130 to about 140 cm
in length with outer diameters of about 0.006 to 0.018 inch
(0.152-0.457 mm). Larger diameter guidewires may be employed in
peripheral arteries and other body lumens. The lengths of the
smaller diameter and tapered sections can range from about 2 to
about 20 cm, depending upon the stiffness or flexibility desired in
the final product. The helical coils are about 20 to about 45 cm in
length, have an outer diameter about the same size as the diameter
of the elongated proximal portions, and are made from wire about
0.002 to 0.003 inch in diameter. The shaping ribbons and the
flattened distal sections of the distal portions have rectangular
transverse cross-sections which usually have dimensions of about
0.001 by 0.003 inch.
[0053] An important feature of the present invention is the
capability of maintaining the level of the yield stress which
effects the stress induced austenite-to-martensite transformation
as high as possible, e.g. above 70 ksi, preferably above 90 ksi for
solid products (lower with tubular products), with an extensive
region of recoverable strain, e.g. a strain range of at least 4%,
preferably at least 5%, which occurs during the phase
transformation particularly at relatively constant stress.
[0054] FIG. 6 graphically illustrates the relationship of the final
austenite transformation temperature (Af) of a binary NiTi alloy of
the invention with the temperature to which the alloy is subjected
during the heat treatment. The amount of cold work and composition
will shift the curve to the other valves but will not change the
general shape of the curve.
[0055] Because of the extended strain range under stress-induced
phase transformation which is characteristic of the superelastic
material described herein, a guidewire made at least in part of
such material can be readily advanced through tortuous arterial
passageways. When the guidewire or guiding member of the invention
engages the wall of a body lumen such as a blood vessel, it will
deform and in doing so will transform the austenite of the
superelastic portion to martensite. Upon the disengagement of the
guidewire or guiding member, the stress is reduced or eliminated
from within the superelastic portion of the guidewire or guiding
member and it recovers to its original shape, i.e. the shape
"remembered" which is preferably straight. The straight "memory" in
conjunction with little or no nonuniform residual stresses within
the guidewire or guiding member prevent whipping of the guidewire
when it is torqued from the proximal end thereof. Moreover, due to
the very high level of stress needed to transform the austenite
phase to the martensite phase, there is little chance for permanent
deformation of the guidewire or the guiding member when it is
advanced through a patient's artery.
[0056] The present invention provides guiding members for
guidewires and fixed wire catheters which have superelastic
characteristics to facilitate the advancing thereof in a body
lumen. The guiding members exhibit extensive, recoverable strain
resulting from stress induced phase transformation of austenite to
martensite at exceptionally high stress levels which greatly
minimizes the risk of damage to arteries during the advancement
therein.
[0057] The superelastic tubular members of the present invention
are particularly attractive for use in a wide variety of
intravascular catheters, such as fixed-wire catheters wherein the
Nitinol hypotubing having superelastic properties may be employed
to direct inflation fluid to the interior of the dilatation
balloon. In this case a guiding member may be secured to the distal
end of the superelastic Nitinol tubing and extend through the
interior of the inflatable balloon and out the distal end thereof.
The guiding member may also be made of the superelastic Nitinol of
the invention.
[0058] Superelastic hypotubing generally has been found to have a
slightly lower stress level compared to wire when the austenite is
transformed to martensite. However, this stress level is above 40
ksi and is usually above 70 ksi. The hypotubing of the invention
generally may have an outer diameter from about 0.05 inch down to
about 0.006 inch (1.27-0.152 mm) with wall thicknesses of about
0.001 to about 0.004 inch. (0.0254-0.102 mm) A presently preferred
superelastic hypotubing has an outer diameter of about 0.012 inch
(0.31 mm) and a wall thickness of about 0.002 inch (0.051 mm).
[0059] While the above description of the invention is directed to
presently preferred embodiments, various modifications and
improvements can be made to the invention without departing
therefrom.
* * * * *