U.S. patent application number 09/837872 was filed with the patent office on 2002-07-18 for hollow medical wires and methods of constructing same.
Invention is credited to Bagaoisan, Celso J., Muni, Ketan P., Zadno-Azizi, Gholam-Reza.
Application Number | 20020095137 09/837872 |
Document ID | / |
Family ID | 25210854 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020095137 |
Kind Code |
A1 |
Zadno-Azizi, Gholam-Reza ;
et al. |
July 18, 2002 |
Hollow medical wires and methods of constructing same
Abstract
The present invention provides an apparatus for performing
angioplasty or vascular intervention procedures. The apparatus of
the present invention comprises a catheter apparatus comprised of a
superelastic hollow guidewire, a balloon member and a flexible tip.
The superelastic hollow guidewire of the invention is preferably a
hypotube of nitinol alloy. The use of nitinol alloy as hollow
guidewire provides a catheter apparatus having high flexibility and
torqueability as well as small cross sectional diameter.
Inventors: |
Zadno-Azizi, Gholam-Reza;
(Newark, CA) ; Muni, Ketan P.; (San Jose, CA)
; Bagaoisan, Celso J.; (Union City, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
25210854 |
Appl. No.: |
09/837872 |
Filed: |
April 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09837872 |
Apr 17, 2001 |
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09415607 |
Oct 8, 1999 |
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09415607 |
Oct 8, 1999 |
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08812876 |
Mar 6, 1997 |
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Current U.S.
Class: |
604/530 ;
604/96.01; 606/194 |
Current CPC
Class: |
A61M 25/09 20130101;
A61M 25/10 20130101; A61M 2025/09141 20130101; A61M 2025/09175
20130101; A61M 2025/09183 20130101; A61M 2025/09008 20130101; A61M
2025/1052 20130101 |
Class at
Publication: |
604/530 ;
604/96.01; 606/194 |
International
Class: |
A61M 025/00 |
Claims
What is claimed is:
1. A medical guidewire adapted to have a medical device ride over
it to a location within a patient, said guidewire comprising: an
elongate body having distal and proximal sections, said body being
at least partially constructed using a transformational,
non-linear, superelastic nickel titanium alloy material, at least
said distal section of said body receiving heat treatments in the
range of 300.degree. C.-600.degree. C. for about 10 seconds to 60
minutes such that said alloy material has recoverable strains in
the range of about 1% to about 8%; said distal section being
constructed from a first nickel titanium alloy section having
sufficient flexibility to navigate the guidewire through the
patient; said proximal section being constructed from a second
nickel titanium alloy section having sufficient stiffness to
provide the guidewire with pushability and trackability for
advancing the guidewire through the patient and for riding a
medical device over the guidewire; and an occlusion device mounted
on said distal section of said body.
2. The medical guidewire of claim 1, further comprising a lumen in
said body for communicating fluids from said proximal section of
said body to said distal section of said body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/415,607, filed Oct. 8, 1999, which is a
continuation of U.S. patent application Ser. No. 08/812,876, filed
Mar. 6, 1997, now U.S. Pat. No. 6,068,623.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to surgical device
design and fabrication and, more particularly, to hollow medical
wires used as guidewires, catheters, and the like, and methods of
constructing same.
[0004] 2. Description of the Related Art
[0005] In the medical community, the continuing trend of
less-invasive and noninvasive surgical techniques is driving the
medical industry to explore new materials and processes for
fabricating surgical instruments and devices having smaller size
and better material properties. Examples of such instruments
include angioplasty catheters incorporating balloons to dilate an
occluded blood vessel. Other catheters are used to deploy stents or
other types of therapeutic devices.
[0006] Because of the success and acceptance of procedures which
utilize such catheters, new procedures are being developed which
require variations and adaptations of previous catheter technology.
For example, in the U.S., one of the more common applications for
medical catheter technology is the "over-the-wire" balloon
angioplasty catheter. In this application, the catheter is
comprised of an elongate hollow body which has mounted on its
distal end an inflatable therapy balloon. The catheter body in this
case is typically constructed from a plastic material and is hollow
(e.g., sometimes referred to as "microtubing"), both to supply
inflation fluids to the balloon and to allow the catheter device to
ride over a thin wire to the site to be treated. Thus, this medical
device is referred to as an "over-the-wire" therapy catheter.
[0007] The thin wire over which the catheter rides is commonly
referred to as a "guidewire," obviously, because it guides the
therapy balloon to the treatment location. Such medical guidewires
are typically made from a solid construction, i.e., they are not
normally hollow since they do not need to carry fluids to the
therapy site. Such medical wires can be adapted to guide other
types of therapy devices well, such as stents, atherectomy devices,
laser devices, ultrasound devices, drug delivery devices, and the
like.
[0008] Another type of balloon angioplasty device is referred to as
a "single operator" balloon catheter. More common in Europe, this
type of device rides along a guidewire with only a short section of
the device (i.e., the "single operator") actually riding completely
over with the guidewire.
[0009] Another type of therapy balloon device which does not
require a guidewire is referred to as a "balloon-on-a-wire" or a
"fixed-wire balloon" catheter. The body of the catheter in this
case is typically a hollow metallic wire (e.g., a "hypotube") or
plastic wire, providing inflation fluid to the balloon mounted on
the distal end. This type of therapy balloon device is less common
in the U.S., being used in about less than 5% of the angioplasty
procedures which are performed, compared with both over-the-wire
and single operator type therapy balloon catheters which are used
about 70% and 25% of the time, respectively.
[0010] In order to successfully perform the desired therapy using
present catheter technology, there are a number of functional
requirements which guidewires must exhibit. These are, not in any
particular order of importance, as follows: pushability;
trackability; torqueability; flexibility; and handleability. To the
extent that a medical guidewire (or a guiding catheter or another
similar guiding devices) exhibits one or more of these functional
characteristics, it is more likely to be successful, both medically
and commercially.
[0011] Pushability refers to the ability of a medical guidewire to
be efficiently and easily pushed through the vasculature of the
patient without damage thereto, but also without getting hung up,
blocked, kinked, etc. Excessive force should not be necessary. The
relative stiffness or rigidity of the material from which the wire
is made is a key mechanical feature of the wire, at least with
respect to its pushability. That is, the wire must be stiff enough
to be successfully and efficiently pushed through the vessels to
the treatment site, but not too stiff to cause damage. Likewise, a
guidewire that is not sufficiently stiff or rigid will suffer
"prolapse." This condition occurs when the wire bends over on
itself or strays down a branching vessel without progressing to its
intended site. Thus, a wire that is too limp lacks sufficient
strength to have good pushability characteristics, which are
important in virtually all guidewire applications.
[0012] Trackability, in the case of guidewires, refers to the
ability of the wire to have another device, such as a therapy
catheter, efficiently pushed over it to a particular location.
Thus, this is also an important feature of catheters which must
also "track" efficiently over a guidewire. Time is usually of the
essence with respect to many noninvasive therapy procedures since
the blood flow of the patient may be interrupted partially or
wholly, during such therapy. In addition, there are often a number
of "exchanges" during such procedures in which one over the wire
device is removed and replaced with another--both riding on the
same guidewire. Thus, the ability of the guidewire to provide good
tracking characteristics is important to the success of the wire.
Again, the stiffness of the wire plays an important role in its
trackability characteristics. Also, the lubricity of the material
from which the wire is made will enhance its trackability by
reducing frictional forces.
[0013] Torqueability refers to the ability of a medical wire to be
accurately turned or rotated. It is often important, in traversing
bends or turns, that the wire be rotated into a certain position.
Ideally, a guidewire should exhibit 1:1 torqueability
characteristics; for example, a one-quarter turn by the physician
at the proximal end should result in precisely a one-quarter turn
in the wire at the distal end. As one may expect, such ideal
torqueability is very difficult to achieve in present medical wire
technology.
[0014] Flexibility is another important characteristic of medical
wires. It relates to the ability of the wire to follow a tortuous
path, i.e., winding and bending its way through the tight turns of
a patient's vasculature. Small radius turns are found especially in
the coronary arteries. Furthermore, diseased blood vessels become
even more tortuous. For example, if plastic deformation in the wire
results from traversing smaller, tight radius turns, the rigidity
of the wire will be reduced. In addition, due to the permanent
deformation, the straightness of the material is lost. It is
therefore more likely to kink or possibly even break. Moreover, if
the distal tip is bent, upon rotation, an injurious effect known as
"whipping" occurs as the distal tip of the wire beats against the
inner wall of the vessel. Thus, the ability of a guidewire to
traverse such tortuous paths without kinking, deformation, or
damage to the vessel walls, is very important.
[0015] The handleability of medical wire relates to its feel during
use. Especially important are reduced functional characteristics,
such that the physician can actually "feel" the tip as it is
manipulated (including both torquing and pushing) from the proximal
end. The therapeutic procedures using such wires require precise
accuracy; thus, the movements of the wire must be smooth,
controllable, and consistent. This is especially difficult to
achieve in consideration of the long lengths of the wires
(approximately 100 cm or more), and the fact that large sections
remain outside the body while other sections are in the body and
more or less hidden from view. Thus, it is important for the wire
to be readily handled by the physician without kinking or requiring
excessive forces or awkward movements.
[0016] It will also be noted that present guidewire technology also
faces the challenge of extremely small dimensions. For example,
guidewires used in therapeutic procedures performed in peripheral
vessels often have an outer diameter of about 0.035 inches to
around 0.038 inches. Wires used in connection with the coronary
arteries are even smaller, ranging from 0.014 inches to 0.018
inches OD. Some devices even utilize guidewires with outer
diameters of 0.009 inches. With these extremely small dimensions,
it is very difficult to maintain the functional requirements for
medical guidewires as outlined above.
[0017] Moreover, medical guidewires should also meet a number of
structural requirements. The straightness of the wire is very
important. If it is not as straight as possible, many functional
features are lost, including most significantly the risk of damage
to the vessel. Moreover, the roundness of the wire contributes to
its accurate torqueability. Consistent wall thickness, lubricity,
and many other structural and dimensional characteristics also play
an important role.
[0018] In order to achieve these functional and structural
characteristics, various materials have been proposed for the
construction of the medical guidewires of the prior art. For the
most part, elastic materials such as stainless steel have
heretofore been used. Other so-called "superelastic materials" have
also been utilized. Elasticity in a material is its ability to
recover strain after deformation. High elasticity (or "super
elasticity") therefore refers to the ability of the material to
undergo deformation and to return to its original configuration
without being permanently or "plastically" deformed. When such
permanent or plastic deformation occurs, the structural integrity
of the material is diminished (e.g., it loses, to some degree, its
rigidity, and/or torqueability), and it assumes a new configuration
(sometimes referred to as the "permanent set") from which
subsequent loading begins. Moreover, the plastic deformation of a
superelastic material may be accelerated through a number of
cyclical deformations, sometimes referred to as fatigue. Such
cyclical deformations can occur if the wire experiences a number of
tight turns, such as is possible in the coronary arteries. Such
superelastic materials include a variety of nickel titanium (NiTi)
alloys, commonly referred to as "nitinol," and other alloys
exhibiting similar properties such as Cu-Zn-Mn and Fe-Mn-Si ternary
alloys.
[0019] In medical guidewire applications, probably the most common
of elastic materials is stainless steel. It provides good stiffness
characteristics to supply desired pushability and torqueability.
However, superelastic materials, including nitinol have also been
suggested for medical wire applications. Although such elastic and
superelastic materials provide acceptable results for typical
applications, there is a need for more versatile and functional
guidewires, especially as new therapeutic procedures are developed.
In particular, there is a need for hollow medical guidewires which
provide a lumen for inflation fluids, drug-delivery, device
deployment and the like. As compared to the standard solid
construction, such a hollow guidewire would provide much greater
functionality or performance.
[0020] However, the challenges facing catheter designers today are
greatly magnified in the case of a hypotube (even those made from a
superelastic material) used to construct hollow guidewires.
Furthermore, the adverse conditions experienced in actual practice
may have a deleterious effect on the functional characteristics of
the hollow wires, particularly those having extremely small
diameters and thin wall thicknesses. For medical wire applications,
such adverse conditions would include primarily the need to
cyclically traverse a number of highly tortuous turns. This bending
and twisting may result in plastic deformation which tests the true
superelasticity of the material from which the wires are
constructed. As a result, patients may suffer certain injuries, the
full effects of which may not be known for years.
SUMMARY OF THE INVENTION
[0021] The aforementioned needs are satisfied by the medical wire
device of the present invention which provides a highly versatile,
efficient apparatus for performing angioplasty and other
therapeutic procedures. In one embodiment, the present invention
comprises a catheter having an elongate hollow body and a distally
mounted occlusion device, preferably an occlusion balloon. The
catheter body, which serves as a guidewire, comprises a hypotube
constructed from a specially selected superelastic nitinol
material. The nitinol material exhibits unique non-linear
characteristics which provide unexpectedly high guidewire
performance features. Moreover, because it is a hollow guidewire,
the present catheter can deliver deployment media to the distal
occlusion device, or assist in many other functions such as
irrigation, drug delivery, and the like.
[0022] Thus, it will understood that the terms "catheter" and
"guidewire," as used herein with reference to the medical device of
the present invention are not to be limiting in any respect to
their construction, materials, or functions, since the principals
of the present invention are applicable to a wide variety of
medical devices. The distal end of the catheters also provide it
with a soft tip in order to avoid injury to the patient. Moreover,
the body of the catheter, just proximal the occlusion balloon, is
provided with a series of spaced radial radiopaque markers in order
to provide visible reference points for the physician within the
working space.
[0023] In another embodiment, the present invention comprises a
catheter of similar construction in which the superelastic nitinol
body does not necessarily serve as a guidewire. In yet another
embodiment, the present invention comprises a composite medical
wire device in which the wire is only partially constructed from
the preferred non-linear superelastic nitinol material. In this
embodiment, in order to achieve certain advantageous performance
characteristics, the material may be joined with other materials
(such as stainless steel, polymers or plastics, etc.) so as to be
utilized for a given application. In a preferred embodiment, the
distal section is constructed from the special nitinol material in
order to achieve superior performance in softness and elasticity,
but other sections may be formed from this material as well. In
addition to such composite devices, the elongate body of the
catheter can be internally constructed from the preferred nitinol
material and then covered with a bilayer of stainless steel to form
a concentric construction. Likewise, special heat treatments can be
applied to the distal section to provide it with superior softness
and flexibility. Also, such flexibility can be achieved through
tapering to very small wall thicknesses. Thus, it will be
understood that the principals of the present invention can be
applied to medical wires of all types, partially or wholly
metallic, hollow or nonhollow, etc., which may be used alone or in
combination with other devices including therapeutic devices.
[0024] The preferred superelastic medical wire comprises a Ni-Ti
(nitinol) binary alloy having a nickel content between 50.0% and
51.5% by atomic weight, and preferably about 50.8%. The wire
material can also be selected from a group of nitinol family
ternary alloys comprising of Ni-Ti-V, Ni-Ti-Co, Ni-Ti-Cu, Ni-Ti-Cr,
Ni-Ti-Nb, Ni-Ti-Pd or from a group of non-nitinol ternary alloys
comprising Fe-Mn-Si. A catheter or guidewire of the present
invention constructed from the selected nitinol material exhibits
outstanding performance characteristics. However, in addition, due
to the special character of this material, the present invention
wire devices also exhibit important characteristics of high
recoverable strain and low modulus. Thus, recoverable strains in
the range of about 1% to about 8% are feasible. This allows the
present medical wire device to undergo high deformation without
plastically deforming, a characteristic which is especially
important in the case of thin-walled hollow hypotubes.
[0025] At the same time, due to the low modulus characteristics of
the material, low stresses are induced as the device traverses the
tortuous paths of the vasculature of the patient. Because of the
low stress forces, reduced frictional forces are experienced; thus,
the medical wire device of the present invention provides excellent
handleability and "feel" for the physician. In addition, there is
reduced risk of injury. Moreover, in one embodiment, the nitinol
material undergoes special heat treatment in order to achieve
transformational effects. In this case, substantially constant
stresses are maintained over a wide range of recoverable strains,
improving even further the performance of the device.
[0026] Thus, in one embodiment, the present invention comprises a
medical guidewire having an elongate body with distal and proximal
sections. The body is constructed at least partially from a
non-linear, superelastic nickel titanium alloy material having a
nickel content in the range of about 50% to 51.5% atomic weight.
The distal section of the body receives heat treatments in the
range of 300.degree. C.-600.degree. C. for about 10 seconds to 60
minutes such that the material has recoverable strains in the range
of about 1% to about 8%. The device also is provided with an
occlusion device mounted on its distal section, and a lumen formed
in the elongate body for communicating fluids from the proximal
section to the distal section of the body. A passageway is formed
through the distal section to communicate said fluids to the
occlusion device.
[0027] In another embodiment, the present invention comprises a
medical catheter having an elongate body and having distal and
proximal sections. The body is constructed from a nickel titanium
alloy material having a nickel content in the range of 50.0%-51.5%
by atomic weight. At least the distal section of the body is
constructed from a transformational nickel titanium alloy material
exhibiting substantially constant stress over a range of
recoverable strain from about 1% to about 8%. The device is also
provided with a balloon mounted on its distal section and a lumen
formed in the elongate body for communicating fluids from the
proximal section to the distal section of the body. A passageway is
formed through the distal section to communicate fluids to the
balloon.
[0028] In yet another embodiment, present invention comprises a
medical wire having an elongate body with distal and proximal
sections. At least the distal section is partially constructed from
a nickel titanium alloy material having substantially constant
stress values over a range of recoverable strains from about 1% to
about 8%. The proximal section is constructed from a second
material having a modulus which is different for a given strain
than the alloy material.
[0029] In yet another embodiment, the present invention comprises a
medical wire having an elongate body comprising a hollow non-linear
superelastic nickel titanium alloy material having recoverable
strain in the range of 1% to at least 8%.
[0030] These and other advantages of the present invention will
become more fully apparent from the following description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic view of the medical catheter of the
present invention;
[0032] FIG. 2 is a schematic cross-sectional view of a distal
portion of the catheter apparatus shown in FIG. 1;
[0033] FIG. 3 is a schematic view of a hollow guide wire comprising
a series of radiopaque markers;
[0034] FIG. 4A is a graph comparing the stress-strain
characteristics of non-transformational and transformational
superelasticity;
[0035] FIG. 4B is a graph comparing the stored deformation energies
of non-transformational and transformational superelasticity;
[0036] FIG. 5A is a schematic cutaway view of a vessel and a
medical wire positioned within the vessel;
[0037] FIG. 5B is a schematic view of a medical wire positioned
within the coronary arteries;
[0038] FIG. 6 is a Ni-Ti phase diagram;
[0039] FIG. 7A is a schematic view of an embodiment to straighten
the hypotube by rolling;
[0040] FIG. 7B is a schematic view of an alternative embodiment to
straighten the hypotube by twisting;
[0041] FIG. 8A is a schematic cross-sectional view of an embodiment
of a composite hollow guidewire;
[0042] FIG. 8B is a schematic cross-sectional view of a joint in
the composite hollow guidewire; and
[0043] FIG. 8C is a schematic cross sectional view of another
embodiment of the composite hollow guidewire.
[0044] FIGS. 9A-9C are schematic cross-sectional views of
alternative embodiments of a hollow catheter having holes, valves,
and the like, to permit the escape of irrigation or other
fluids.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0045] As will be described hereinbelow the apparatus of one
embodiment of the present invention is a catheter apparatus for
treatment of stenosis in a lumen in a blood carrying vessel.
Although the catheter includes a hollow medical guidewire as
illustrated and described, it will be understood that the
principles of the present invention apply equally to other types of
medical wires and catheters.
[0046] Hollow Medical Guidewires
[0047] As shown in FIGS. 1-2, the catheter apparatus 10 is
generally comprised of four communicating members including an
elongated body or tubular member 14, a balloon member 16 and a
core-wire member 20 and a coil member 22. The catheter apparatus 10
is preferably provided with an outer coating of a lubricous
material, such as Teflon. The body member 14 of the catheter
apparatus 10 is in the form of hypotubing and is provided with
proximal and distal ends 14A and 14B and as well as an inner lumen
15 extending along the tubular member 14. The balloon member 16 is
coaxially mounted on the distal end 14B of the tubular member 14 by
suitable adhesives 19 and 21 at a proximal end 16A and a distal end
16B of the balloon member 16 as in the manner shown in FIG. 2. A
passageway 23 is formed through the tubular member to communicate
fluids to the balloon 16. The core-wire member 20 of the catheter
10 may be comprised of a flexible wire 20. The flexible wire 20 is
joined by soldering, brazing or using adhesives at a proximal end
20A of the flexible wire 20 to the distal end 14B of the tubular
member 14 as in the manner show in FIG. 2.
[0048] Preferably, the proximal end 20A of the flexible wire 20 has
a transverse cross sectional area substantially less than the
smallest transverse cross-sectional area of the inner lumen 15 of
the tubular member 14. In the preferred embodiment, the flexible
wire 20 tapers in the distal end 20B to smaller diameters to
provide greater flexibility to the flexible wire 20. However, the
flexible wire may be in the form of a solid rod or a helical coil
or wire ribbon or combinations thereof.
[0049] As shown in FIG. 2, the distal end 20B of the flexible wire
20 is secured to a rounded plug 18 of solder or braze at a distal
end of the coil member 22. The coil member 22 of the catheter 10
may be comprised of a helical coil. The coil member 22 is coaxially
disposed about the flexible wire 20, and is secured to the flexible
wire 20 by soldering, brazing or using adhesives at about the
proximal end 20A of the flexible wire 20 as in the manner shown in
FIG. 2. The balloon member 16 is preferably a compliant balloon
formed of a suitable elastic material such as C-Flex.TM., a latex
or the like. Other occlusive or therapy devices could also be used.
The flexible coil 22 is preferably formed of a wire of platinum
based alloy so as to be visible during fluoroscopy. The flexible
core-wire 20 may preferably be formed of a superelastic
nickel-titanium alloy or stainless steel. However, the tubular
member 14 is preferably formed of a superelastic nickel-titanium
alloy described below in more detail. Further details regarding the
catheter and its construction are found in co-pending applications
all filed on Mar. 6, 1997 and assigned Ser. No. 08/813,024, now
abandoned, entitled Catheter Balloon Core Wire, Ser. No.
08/812,140, now U.S. Pat. No. 5,868,705, entitled Pre-Stretched
Catheter Balloon, and Ser. No. 08/812,139, now abandoned, entitled
Low Profile Catheter Value, all of which are hereby incorporated by
reference in their entirety.
[0050] FIG. 3 illustrates another aspect of the catheter of the
present invention. There is illustrated a guide wire 12 with an
inflated occlusion balloon 25 extending from the distal end of a
guiding catheter 11, also having an occlusion balloon 24 mounted
thereon. As is typical with such guide catheters 11, a radiopaque
marker ring 11A is indicated near the distal tip of the catheter
11. This allows the physician to detect the location of the
catheter under fluoroscopy or other visualization. It is also
typical in the construction of therapy catheters 13 (dashed lines)
to provide a similar radiopaque marker 17 near the distal tip. For
simplicity, FIG. 3 illustrates a hypothetical location of this
therapy catheter marker 17, but illustrates the therapy catheter 13
itself in dashed lines. Again, the position of the therapy marker
17 is gauged by visualization means such as fluoroscopy.
[0051] With occlusion guidewires 12 of the type shown, however, the
exact location of the occlusion balloon 25 is not always known.
Moreover, the occlusion balloon 25 is typically relatively short so
as to avoid interfering with the therapy in the treatment location.
Thus, the guidewire 12 in which the occlusion balloon 25 is mounted
may shift slightly during the procedure, and may interfere
therewith or become damaged itself from the action of the therapy
catheter 13.
[0052] In order to provide the physician with an ability to detect
and rectify such movement, a series of radiopaque markers are
formed on the body of the guidewire 12 as indicated in FIG. 3.
These markers 22 are uniformly spaced apart by a given dimension
such as 1 mm in order to also provide the physician with a
reference system within the working area. In using these markers,
once the relative positions of the guide catheter ring 11A and the
therapy marker 17 are determined, the number of guidewire markers
22 in between these two reference points can be used to reposition
the guidewire if necessary. Thus, any relative movement of any of
these devices, i.e., the guide catheter 11, the therapy catheter
13, or the guidewire 12, can be detected and steered into the
desired location in the patient's body as well as measured for easy
correction.
[0053] Such markers 22 can be of a typical type and manufactured
from radiopaque materials such as platinum, gold, etc. They can be
embodied in the wall of the guidewire 12 or applied as plating to a
reduced diameter portion thereof in order to maintain its smooth
outer profile. Moreover, it should be noted that this feature of
the invention can also be applied to other types of medical wires,
with or without occlusion balloons, and in conjunction with other
types of guiding or therapy catheters.
[0054] Non-linear Superelastic Nitinol
[0055] In accordance with the principles of the present invention,
the elongated body member 14 of the catheter 10 described above is
advantageously constructed from a superelastic material which has
been carefully selected and treated to provide unexpectedly
excellent performance characteristics. In the preferred embodiment,
the body 14 is constructed from a superelastic nitinol and, more
particularly, a superelastic nitinol which exhibits non-linear
behavior characteristics with respect to its stress-strain
relationship (FIG. 4A). As a result, in addition to the catheter
described above, many types of medical wires can be constructed to
take advantage of these performance characteristics.
[0056] Although there are literally thousands of superelastic
nitinol and stainless steel materials, their elasticity alone does
not provide ideal performance in a medical wire. For example, there
are many superelastic nitinol and stainless steel materials which,
if formed into a medical wire, are too rigid or too limp to provide
good performance characteristics, i.e., their modulus of elasticity
is either too high or too low, respectively. Thus, it has been
discovered that there is a category of nitinol materials having
structural and mechanical characteristics, besides superelasticity,
which make them particularly suitable for medical wire
applications. However, in order to fully appreciate these
characteristics, a basic understanding of nickel titanium alloys
and their construction is helpful.
[0057] Ni-Ti alloys or nitinol alloys are the most important of the
shape memory alloys (SMA). Such materials can adjust their
properties and shape according to changes in their environment,
specifically changes in applied stress and temperature. In this
respect, nitinol alloys can change their shape by strains greater
than 8% and adjust constraining forces by a factor of 5 times. The
scientific foundations of the shape memory effect is well known in
the art.
[0058] Superelasticity refers to the ability of a material to
reversibly transform its crystal structure and shape in order to
relieve applied stresses so that the material can undergo large
elastic deformations without the onset of plastic deformation. This
superelasticity, often referred to as transformational
superelasticity, exhibits itself as the parent crystal structure of
the material as it transforms into a different crystal structure.
In superelastic materials the parent crystal structure or the phase
is known as the austenitic phase and the product crystal structure
is known as the martensitic phase. Such formed martensite is termed
stress induced martensite.
[0059] As will be explained more fully hereinbelow, superelastic
characteristics of the nitinol alloys can be best viewed by the
stress strain diagrams obtained from various mechanical testing
methods such as tensile tests, torsion tests, bending tests or
compression tests. Among these methods, the tensile test emerges as
the most common mechanical testing method. In particular, tensile
tests provide very useful information about both the type of
deformation and the amount of deformation that a test sample
undergoes under an applied stress. In this respect, FIGS. 4A and 4B
provide very valuable information about the deformation
characteristics of the superelastic nitinol alloys under tensile
test conditions. For the nitinol alloys, these tensile stress
strain diagrams are equivalent to stress strain diagrams provided
with torsion, bending and compression tests.
[0060] As shown in FIG. 4A, in a tensile stress-strain
(deformation) diagram of austenitic superelastic alloys,
superelastic materials in general exhibit two different types of
non-linear elastic deformation characteristic. The first
deformation characteristic, which is referred to as
transformational non-linear superelastic deformation, can be
depicted by a first hysteresis 31 defined by a loading curve 30 and
an unloading curve 40. As is understood, the loading curve 30 and
unloading curve 40 are non-linear curves thereby representing a
non-linear superelastic deformation behavior. Similarly, FIG. 4A
illustrates a second deformation characteristic referred to as
non-transformational. Although sometimes referred to as "linear"
superelastic deformation, non-transformational superelastic
deformation is also non-linear due to a second hysteresis 51
defined by a loading curve 50 and an unloading curve 52. However,
as will be explained more fully hereinbelow, the non-linearity in
this case is a less emphasized non-linearity so that the curves 50
and 52 follow a rather smooth change. It is well-known in the art
that the first and second hysteresis 31 and 51 occur due to
internal friction and plastic deformation.
[0061] During transformational superelastic behavior, under the
applied stress the curve 30 first follows a linear path 33 where
the austenitic phase elastically deforms. The austenitic phase
elastically deforms with increasing stress up to a critical
yielding stress value 35 where martensitic transformation begins.
After this critical stress point 35, the material continues to
transform into martensite. Throughout the transformation, despite a
constant increase in deformation rate of the material, the applied
stress remains about the same critical stress value 35 thereby
revealing the superelastic property of the material.
[0062] This is very important in the field of angioplasty since one
can engineer a catheter apparatus to deliver a physiologically
ideal stress and rely on the fact that this stress will be held
constant throughout the angioplasty application. This superelastic
behavior forms a loading plateau 32 on the curve 30 until the
entire austenite phase transforms into the martensitic phase.
[0063] Still referring to FIG. 4A, at the end of the
transformation, the curve 30 no longer follows a straight path but
a linearly increasing path 39 where the martensitic material
elastically deforms up to a point 37 where unloading begins. During
the unloading, the martensite structure transforms into austenite
structure. Due to internal friction, there is not an overlap of
loading and unloading curves 30 and 40, and the unloading curve 40
moves down to lower stress values.
[0064] During the course of unloading, the martensitic phase is
first unloaded along the linear portion 49 of the curve 40. At a
critical stress value 47, martensite to austenite transformation
begins and continues along the unloading plateau 42. Upon
completion of austenitic transformation, the elastic deformation on
austenitic material is unloaded along the linear portion 43.
However, as is seen in FIG. 4A, the unloading does not totally
reverse the superelastic deformation. In fact a permanent
deformation or "set" 48 remains after the completion of
unloading.
[0065] As also shown in FIG. 4A, in hysteresis 51,
non-transformational superelastic deformation does not produce a
plateau of constant stress. Due to little or no martensitic
transformation, the loading and unloading curves 50 and 52
demonstrate a less non-linear increase and decrease respectively.
In other words, changes in superelastic deformation behavior are
not as drastic as in the case of transformational superelasticity.
In fact, as is seen in FIG. 4A, curves 50 and 52 adopt a rather
smooth change in non-linearity. In such materials, a high level of
elastic deformation can only be possible with the application of
high levels of stress. However, it is understood that the modulus
of elasticity for such non-transformational nitinol alloys is still
significantly lower than the modulus of elasticity for stainless
steels.
[0066] The difference in elastic deformation behavior for the
transformational and non-transformational cases can be clearly seen
in FIG. 4B by means of stored elastic energies for each deformation
case. The stored elastic deformation energy can be defined with
areas 55 and 56 under the respective unloading curves 40 and 52. It
would be understood that, at a random deformation value
.epsilon..sub.x, the non-transformational superelastic deformation
stores more elastic deformation energy which is equivalent to
spring back energy of the superelastic material. The spring back
energy in transformational case can be increased by increasing the
deformation range beyond .epsilon..sub.x. However, an increase more
than 6% deformation reduces the stiffness of the material and hence
reduces the spring back force and the unloading stress.
[0067] Medical Wires
[0068] The medical wires of the present invention take advantage of
particular non-linear superelastic nitinol characteristics to
achieve better functional performance, especially in terms of
flexibility and handleability. In addition, because of their
ability to withstand permanent deformation, the present medical
wires also demonstrate, in practice and under adverse conditions,
improved characteristics of pushability, trackability, and
torqueability, especially in comparison to previous superelastic
and elastic wires. Thus, in addition to its superelasticity, the
present medical wire also exhibits the following excellent
characteristics: very high recoverable strain with virtually no
permanent set; a relatively low modulus compared to other elastic
materials; and some hysteresis in its unloading curve.
[0069] As noted above, superelasticity refers to the ability of a
material to recover strain after deformation. However, under
adverse medical conditions, such recovery is not only inhibited,
but is very important in order to avoid injurious effects on the
patient. The medical wire of the present invention advantageously
recovers strain over a wide range of deformations, typically 1-8%
and even 9-10% in some cases where there has been careful attention
to the heat treatment of the wire material. This high recoverable
strain characteristic in the present wire allows the wire to
traverse a wide range of tortuous turns without plastic
deformation, which of course would inhibit or destroy the
performance of a wire.
[0070] This characteristic can be illustrated schematically with
reference to FIG. 5A. This figure is a cutaway view of a vessel 26
exhibiting a sharp turn. The medical wire is shown traversing the
turn; although, it will be noted that no guide catheter within the
vessel 26 is illustrated for simplicity, and that the medical wire
14 of the present invention may be used with or without a guide
catheter. With the medical wire 14 of the present invention, it has
unexpectedly been discovered that turns of even very small radii
can be traversed with confidence without plastic deformation. The
following calculations adequately illustrate this point. That is,
for a hollow tube, the strain experienced in bending is given as
follows 1 = t 2 r m
[0071] where:
[0072] .epsilon.=recoverable strain (%)
[0073] t=diameter of the hypotube
[0074] R.sub.m=mean radius of the bend in the tube
[0075] In this case, the radius of the bend is that which is
illustrated in FIG. 5A and is the degree of bending that the tube
can suffer without plastic deformation. Since the maximum
recoverable strain is usually known, the equation can be easily
solved for the mean radius (r.sub.m) of the smallest bend possible
without plastic deformation, which is as follows: 2 r m = t 2
[0076] For an elastic material, such as stainless steel, a typical
recoverable strain for a hollow medical wire can be as high as
0.4%. If the medical tube has a diameter of 0.014" (average), then
the radius is 1.75". This means that an elastic stainless steel
wire having this maximum strain cannot bend around a turn having a
radius smaller than 1.75" without suffering plastic deformation.
However, for the medical wire 14 of the present invention, having
similar dimensions, maximum recoverable strain can easily be about
6%. Thus, solving the above equation for the radius yields a result
of only 0.117". For maximum recoverable strains of 8%, which are
within the range of the present invention, even tighter turns can
be traversed.
[0077] Thus, it should be observed that the medical wire 14 of the
present invention can successfully avoid permanent deformation over
a wide variety of adverse conditions, thus providing excellent
tortuosity characteristics. Furthermore, because plastic
deformation is avoided, the pushability and torqueability
characteristics of the present wire 14 are maintained. This is
compared with previous medical wires which begin with as good or
even better characteristics of pushability and torqueability, but
because they experience plastic deformation traversing a certain
number of tortuous turns or pushing against obstructions, their
performance characteristics in actuality are greatly
diminished.
[0078] This point can be illustrated in greater detail with the
following discussion. Nitinol, in general, is used in certain
medical wire applications because of its enhanced flexibility and
corresponding kink resistance in comparison with stainless steel.
Kinking greatly reduces the ability to push or steer a wire into
the desired location, and also obviously reduces the ability to
slide a catheter over the wire. Thus, the flexibility of nitinol,
which derives generally from its low modulus, is an advantage in
certain applications. Stainless steel, however, according to
conventional thought, is more often selected for medical wire and
catheter applications due to its enhanced torqueability and
pushability characteristics. These characteristics are derived from
the greater rigidity of stainless as compared to nitinol. From this
perspective, therefore, the flexibility of nitinol can be
considered a disadvantage, and indeed, many nitinol alloys are too
flexible to perform well in connection with torqueability and
pushability.
[0079] It can be demonstrated, on the other hand, that nitinol
alloys which are carefully selected in accordance with the
principles of the present invention can out perform stainless steel
not only in terms of flexibility, but of torqueability and
pushability as well. This is true for a wide range of recoverable
strains, including, but not limited to those within the elastic
limit of stainless steel (being about 0.4 to 0.6% in tension). It
is especially true for strains beyond the elastic limit of
stainless steel. It will be noted that, in bending, the elastic
limit of a solid stainless steel wire may be slightly higher than
the range quoted above (such as about 0.8%); although, in a tubular
construction (e.g., a hypotube), the elastic limit of stainless may
vary. Nevertheless, it has been demonstrated that the hollow
medical wires and catheters of the present invention, constructed
in accordance with the material selection criteria prescribed
herein, provide excellent torqueability and pushability
characteristics, as well as flexibility and kink resistance.
Moreover, as an important aspect of the present invention, because
the forces necessary to torque and to push the present nitinol
wires and catheters are greatly reduced as compared to stainless
steel, the present invention also demonstrates enhanced
characteristics of handleability.
[0080] Thus, it has been demonstrated in torqueability tests that,
under bending strain and in conditions of low wall friction,
nitinol wires within the scope of the present invention come much
closer to the ideal 1:1 than stainless steel wires of similar
diameter. The wall friction, illustrated in FIGS. 5A and 5B,
relates to the containment of the wire as it undergoes bending.
Under conditions of higher wall friction, the nitinol wire again
out- performed the stainless steel wire, even below the elastic
limit of the stainless steel. This is probably due to the higher
coefficient of friction and higher modulus of the stainless, which
causes it to form local indentations in the wall of the tubing
(which may take the form of a guide catheter or the wall of a blood
vessel). Thus, the stainless steel wire tends to lock in place
where it pushes against the containment wall, resulting in greater
resistance to torquing. Under actual conditions, this can result in
damage to a guide catheter or, more seriously, the wall of a blood
vessel. Thus, nitinol wires within the scope of the present
invention not only provide enhanced torqueability, but also help to
avoid damage to sensitive tissue.
[0081] Likewise, it has been demonstrated that the forces to
achieve torque in a nitinol wire are approximately five times less
than those of stainless steel wires, both within and beyond the
bending elastic limit of the stainless. This low force requirement
makes the nitinol wire much easier to manipulate and provides
greater handleability and "feel" for the physician.
[0082] With respect to pushability, likewise the forces for nitinol
wires as compared to stainless are several times less, particularly
beyond the elastic limit of the stainless undergoing bending
strain. Overall, as noted above, the nitinol wires and catheters of
the present invention provide enhanced characteristics over similar
sized stainless wires and catheters not only in terms of
flexibility, but also torqueability, pushability, and
handleability.
[0083] In addition to the advantages of unexpectedly high
recoverable strain, the medical wire of the present invention is
also able to achieve other advantages by exhibiting a relatively
low modulus. That is, for a given strain, the stress exhibited by
the present medical wire 14 is relatively lower than with previous
superelastic medical wires. This characteristic advantageously
exhibits itself in the functionality of the present wire 14. For
example, in the context of a tortuous path, as the wire 14 turns
the corner of a tight radius turn, it becomes "loaded" in the sense
that the bending it experiences causes a certain amount of
deformation or strain. According to this stress-strain
relationship, there is induced a corresponding stress force in the
wire 14, which manifests itself in the tendency of the material to
want to straighten out to its original straight configuration. In
the medical procedures of the type in which the present wire is
utilized, this can be a dangerous situation. As illustrated in FIG.
5A, the bent portion of the wire pushes against the wall of the
vessel 26 with a particular force F.sub.s (or in the case of a
guide catheter, the wire pushes against the guide catheter which in
turn contacts the wall of the vessel 26). With higher modulus
materials, this force may be great enough to cause damage to the
vessel 26. However, with the present wire 14, even over a wide
range of recoverable strains, this force is minimal.
[0084] Perhaps an even more important advantage of these low
modulus characteristics is the reduced frictional forces
experienced by the wire as it courses through the vasculature of
the patient. Because the frictional force is proportional to force
and the area of contact against the wall of the vessel or guide
catheter, such frictional forces are proportionally reduced as the
force is reduced. Thus, the pushability and handleability of the
present wire 14 are excellent. These characteristics can be best
demonstrated by the example illustration in FIG. 5B. FIG. 5B shows
the guide wire 14 of the present invention within a coronary artery
29 in the heart 34. Smooth and consistent pushing forces provide a
better feel of the wire for the physician, and can be utilized to
precisely traverse the vasculature of the patient and position the
wire at the precise location for successful treatment.
[0085] Although stress values can be advantageously adjusted
according to heat treatment or other post-construction condition,
stress values in the range of 20-100 (Klbs. per square inch) (ksi)
(150 MPa-750 MPa) have been found to be suitable for the present
medical wire, at least at strains in the range of 2-6% or more.
[0086] Another advantageous characteristic of the present medical
wire is its ability to generate an even lower stress upon
unloading. That is, in contrast to the above discussion directed to
low stress values upon loading (i.e., as the wire traverses a tight
turn), the present wire exhibits even lower stress values as the
wire completes the turn (i.e., during unloading). As soon as a
length of the wire is sufficiently beyond a turn to allow it to
straighten itself, it may be considered unloaded. Thus, the
unloading portion of the stress strain curve in the present wire
gives, for a given strain, the stress value induced in the material
as it recovers its strain. As noted above, because of the
hysteresis or the non-linearity of the present superelastic
nitinol, unloading stress will be even less than that of the
loading stress. Thus, the area under the unloading curve is
sometimes referred to as the elastic or springback energy because
it characterizes the forces experienced by the material as it
returns to its original configuration. However, a high springback
energy causes a whipping effect at the distal end. Thus, these
lower unloading stresses contribute to the smooth handleability of
the present wire.
[0087] These advantages of the present medical wire, which derive
from the non-linear superelastic behavior of the particular nitinol
alloys used therein, may be achieved through heat treating
(annealing). However, although other condition methods can be
utilized to achieve the present advantages, where careful attention
is paid to the heat treatment of the wire, it can reach a unique
stage of non-linear superelastic nitinol referred to as
"transformational." This is because the material actually undergoes
a phase transformation during loading and unloading, as explained
above. Such transformational superelastic nitinol provide
additional advantages in connection with the medical wire of the
present invention. For example, they exhibit a substantially higher
recoverable strain in the range of 8-9%, as compared to 4-5%
maximum recoverable strains with non-transformational nitinols. As
explained in detail above, these higher recoverable strains
achievable from the transformational material provides many
functional advantages.
[0088] In addition, the corresponding stress levels of such
transformational nitinols are in the range of 200-500 MPa. Under
loaded conditions, the plateau stresses are preferably in the range
of 300-500 MPa, while upon unloading the stresses are less, e.g.
80-400 MPa. Furthermore, the hysteresis of the unloading curve
increases with greater deformation; thus, at about 7% strain, an
unloading stress of about 200 MPa is preferred.
[0089] Moreover, an even lower modulus is achievable with such
transformational nitinols. In fact, as noted above and illustrated
in FIGS. 4A and 4B, one of the distinguishable characteristics of
such materials is a relatively constant loading stress which is
typically referred to as a "loading plateau." That is, over a wide
range of recoverable strains, the material exhibits a substantially
constant stress value. As explained above, this allows the material
to exhibit excellent performance characteristics, in terms of low
friction and handleability. In use, doctors are able to apply
smooth, constant pushing forces without a concern for excessive
forces needed to traverse tight turns.
[0090] Thus, an important aspect of the present invention is the
selection of the proper non-linear superelastic nitinol sufficient
to achieve the desired functional characteristics which are desired
for a particular application. It should be noted that the selection
of the appropriate non-linear material may vary depending on such
desired characteristics and the various design tradeoffs which must
be made. Thus, in a given application, a transformational
non-linear nitinol may be selected versus a non-transformational
type. That is, in an application where cyclical deformations are
experienced, the resistance to fatigue-induced plastic deformations
is an important functional characteristic. Thus, one may select a
non-transformational type non-linear nitinol because of its
narrower hysteresis and higher strength. On the other hand, where
the material must undergo many cycles (about more than 100 cycles)
better fatigue-resistant characteristics can be achieved with the
transformational nitinols.
[0091] Likewise, as discussed below in more detail, a given medical
wire may also be constructed so as to have characteristics of both
transformational and non-transformational materials. For example,
the proximal end of the medical wire may be constructed from a
non-transformational nitinol to provide enhanced pushability and
trackability characteristics, while the distal end of the same wire
(say, in the range of the distal 2 to 15 cm) undergoes special
conditioning in order to achieve a transformational state. Thus,
the distal end will be softer and will exhibit the constant,
reduced stress forces at even very high recoverable strains which
are characteristic of non-transformational nitinols. Other
advantages can be achieved with composite wires constructed from
non-linear nitinols and stainless steel or other materials.
[0092] In the case of hollow medical hypotubes, special problems
must be overcome. First, the trackability of the wire will be a
challenge due to the reduced body mass. Thus, it is preferable to
select materials with a higher loading plateau stress than solid
wire. Secondly, the frictional characteristics of tubing will have
to be addressed by applying friction reducing treatments. Third,
the ductility of hypotubes must be addressed. Because of the
reduced wall thickness, failure of the material is a risk. Greater
resistance to failure can be achieved by heat treating at higher
temperatures and less cold work. Finally, surface defects must be
avoided because stress tends to localize at such nicks or
indentations (it being recognized that such defects represent a
large percentage of the surface wall thickness). Thus, careful
inspection and selection of materials must be exercised such that
the hypotube has defects of 15 microns or less.
[0093] As merely one example of a suitable non-linear superelastic
nitinol, the catheter illustrated in FIGS. 1-2 can be constructed,
at least in part, from a transformational non-linear nitinol having
a recoverable strain of about 8%. However, maximal elongation and
failure is at least about 14%, providing strong safety
characteristics. Because of the material's transformation, it
exhibits a loaded plateau stress at room temperature of about 75
ksi (500 MPa) and an unloading plateau stress of about 25 ksi (170
MPa).
[0094] In regard to material selection, it will be noted that the
process of alloying, nickel and titanium is a well-established art
for the production of nitinol; however, as noted above, there are
many nitinol materials which may not supply the desired performance
characteristics. Nevertheless, various types of nitinol materials
which may be successfully used in the construction of the medical
wires of the present invention are commercially available from
companies such as Memry Corp. which provides one suitable nitinol
material known as Tinel.RTM. Alloy BB.
[0095] Superelasticity in Ni-Ti alloys also depends on temperature.
Martensitic or austenitic transformations start and finish at
certain temperature ranges. Thermal or mechanical treatments in the
history of the material may change these temperature ranges. In
this respect Ms-temperature refers to temperature that martensitic
transformation from austenite begins. At the Mf-temperature
martensitic transformation finishes. Further, temperatures As and
Af indicate the respective beginning and the end of austenitic
reversion. However, as indicated before, the applied stress shifts
these temperature ranges. In case of stress induced martensitic
transformation, Md temperature is defined as the temperature above
which stress-induced martensitic transformation cannot occur. It is
understood by those skilled in the art, that superelastic
properties can be observed at temperatures above Af and below Md.
In fact fully superelastic effects are found over an even narrower
range, typically only 10-40.degree. C. in width.
[0096] Thus, for a given superelastic nitinol at room temperature,
it will be noted that, at body temperature, the stress roughly
increases according to the equation:
.DELTA..delta.=6.times..DELTA.T
[0097] where .DELTA.T is the temperature difference between the
body and the room temperatures. .DELTA..delta. is the amount of
added stress due to the increase in temperature. For purposes of
the present discussion, the superelasticity of nitinol is
considered to be its state during use more or less at body
temperature.
[0098] The alloy composition range 60 of the superelastic Ni-Ti
alloy of the present invention is shown graphically in the Ni-Ti
binary phase diagram in FIG. 6. Binary phase diagrams are
composition-temperature diagrams which provide valuable information
for specific alloy compositions, such as the formation of various
equilibrium phases of these alloy compositions and their respective
temperature ranges. In the preferred embodiment, Ni-Ti alloy
composition is preferably selected from a Nickel rich composition
ranging from 50.0 atomic % Ni to 51.5 atomic % Ni, preferably from
50.6 atomic % Ni to 50.9 atomic % Ni. However, in accordance with
the principles of the present invention, the superelastic alloy of
the present invention may be selected from the group of nitinol
family ternary alloys including Ni-Ti-V, Ni-Ti-Fe, Ni-Ti-Cu,
Ni-Ti-Co, Ni-Ti-Cr, Ni-Ti-Nb, Ni-Ti-Pd or non-nitinol Fe-Mn-Si
ternary alloys. For the nitinol family ternary alloys, a preferred
composition range basically determined by the formula:
Ni(Atomic %)+Ti(Atomic %)+3.sup.rd Element(Atomic %)=100
[0099] where, 3.sup.rd Element(Atomic %) is less than 14% atomic
weight. The 3.sup.rd Element defines V, Fe, Cu, Co, Cr, Pd and Nb
elements of the ternary compositions, such as Ni-Ti-V, etc.
[0100] Distal Section
[0101] The distal section 14B (FIG. 1) of the nitinol hypotube 14
must be very flexible to facilitate the entry of the distal section
14B into a desired blood vessel during angioplasty procedures. This
is especially true of the distal most 30 cm or so of the medical
wire which, in the case of a coronary guidewire, must enter the
vessel without the protection of a guide catheter. Therefore, this
section must exhibit a high degree of softness and a very low
modulus. In accordance with the principles of present invention,
this flexibility can be provided in various ways such as reducing
the thickness at distal-end 14B or applying appropriate
heat-treatments to the distal-end 14B, or both. Within the scope of
this invention, it will be understood that the term heat treatment
refers to any thermal treatment that has been applied to the
material before or after inserting into patient's body.
[0102] In one embodiment, the wall thickness of the distal portion
14B of the hypotube 14 can be reduced to accommodate the need for
flexibility at the distal end 14B. Thus, for example, the wall
thickness can be reduced to about 0.001 to about 0.0015". Thickness
reduction at the distal-end 14B can be done by either tapering the
distal-end or performing a uniform thickness reduction along the
distal-end 14B. Preferably, the distal-end 14B of the hypotube 14
can be tapered to a lower diameter to provide distal flexibility
and proximal stiffness.
[0103] In another embodiment, the distal-end may be heat treated
for a period of time to provide flexibility and softness. The
heat-treatment reduces the force required to reach the elastic
plateau 32 (FIG. 4A) so that the heat treated distal-end 14B is
more flexible than the proximal-end. The heat treatment can be done
in salt baths such as the salt baths containing potassium nitrates,
and preferably at a temperature range between 300 and 600.degree.
C., and for a preferred time range of 10 to 60 minutes. It should
also be noted that other sections of the medical wire, besides the
distal section, could also receive special heat treatments in order
to vary their characteristics for a particular purpose.
[0104] Manufacturing Process
[0105] In the manufacturing of the preferred embodiment, the alloy
of the present invention can be made superelastic by facilitating
various thermal and/or mechanical treatments. The alloy can
typically be shaped into the hypotube 14 or core wire 20 by cold
working the material and/or heat treating the alloy. In the case of
the hypotubing 14, the cold work can be performed by reducing the
tube wall diameter or the outer diameter of the tube. Various
facilitating instruments such as swager, metal extrusion and
drawing equipment can be utilized to provide cold work. In the
preferred embodiment, the hypotube 14 is shaped by cold working the
material at a preferred cold work range of 20-40%. In the general
manufacturing process, Ni-Ti tubes are typically manufactured by
inserting a core element in a cylindrical Ni-Ti bar and drawing
this bar into smaller diameters through the use of series of dies
and intermediate heat treatments above 600.degree. C.
[0106] Following the cold work, the hypotube is preferably heat
treated at a temperature range between 500 and 600.degree. C. This
heat treatment can preferably be done in a salt bath, such as
potassium nitrate, or in a protective atmosphere, such as Argon
gas, for 10 seconds to 60 minutes. In this embodiment, the heat
treated hypotube 14 may not be quenched but preferably cooled down
to room temperature in a protective atmosphere. In the preferred
embodiment, the resulting superelastic hypotube has a martensitic
transformation temperature (Ms) of -30.degree. C., and an
austenitic transformation temperature (As) of 11.degree. C. The
stress level at loading plateau 32 (FIG. 4A) or loading plateau
stress is 450 MPa, and the stress at unloading plateau 42 is 150
MPa. Under these conditions the material presents more than 6%
superelasticity.
[0107] In another embodiment, the heat treatment can be performed
at less than 500.degree. C. This material can also have more than
6% superelasticity. However, the heat treatment temperature causes
a significant shift in stress and transformation temperatures, Ms
and As respectively. Particularly, lower heat treatment temperature
increases the plateau stress. In this embodiment, the resulting
material has a loading plateau stress of 550 MPa and an unloading
plateau stress of 320 MPa. In this respect, Ms temperature is
-75.degree. C. and As temperature is -3.degree. C.
[0108] During the manufacturing of hypotube 14, the roundness and
the straightness of the hypotube present an important problem. It
is well-known that many cardiovascular applications require the use
of straight and round tubing. This can be done through a series of
thermo-mechanical treatments following the production of hypotube
by the method given above. Thermo-mechanical treatments include
twisting, pulling and bendings combined with heat treatments above
300.degree. C. Various facilitating instruments can be used to
provide roundness. As illustrated in FIG. 7A, the hypotube 14 of
the present invention can be drawn (in the direction of arrow 65)
among a series of rotating rollers 64 to provide required
roundness. Similarly, as illustrated in FIG. 7B, the body of the
hypotube 14 can be twisted about the longitudinal axis of the
hypotube to provide further roundness. Twisting can be performed
continuously or in discrete process steps. Twisting may be
performed by securing the one end of the hypotube 14 using suitable
means 66, and rotating the other end in the direction of the arrow
67 as in the manner shown in FIG. 7B. During the twisting,
variations in tube wall thickness are uniformly distributed along
the length of the tube. However, it will be appreciated that
twisting methods are well-known in the art and may be performed in
a variety of ways.
[0109] In another embodiment, following the cold work, a solution
treatment above 500.degree. C. and an aging process at relatively
low temperatures, preferably 400.degree. C., may be applied to the
cold worked hypotube. In such solution treated and aged structure,
the resulting material has a loading plateau stress of 300 MPa,
unloading plateau stress of 100 MPa. This process also presents
more than 6% recoverable strain.
[0110] In another embodiment, the material may only be cold worked
and the cold working process is not followed by an annealing step.
In this embodiment, the material superelasticity follows the
hysteresis 51 as shown in FIG. 4A. There are no plateau stresses or
definite transformation temperatures. This material exhibits about
4% superelasticity.
[0111] The hypotube 14 is preferably coated with an outer lubricous
material coating, such as Teflon, to increase the lubricity of the
hypotube 14. The process of Teflon coating requires temperatures
above 200.degree. C. However, such high temperatures may interfere
with the previous heat treatments and cause unwanted property
changes, such as over softening of the material. In order to
prevent such drawbacks, it is preferred that the Teflon coating be
performed during some of the final heat treatments of the hypotube
14 so that the properties of the hypotube remains unchanged.
[0112] Composite Wires and Methods of Construction
[0113] In manufacturing of the catheter apparatus 10, it may be
constructed using a single nitinol hypotubing or a composite
structure comprising various tubing materials such as stainless
steel, tantalum, titanium or nitinol alloys with varying Ni
contents or even plastics.
[0114] As illustrated in FIG. 8A, an exemplary composite structure
can be formed by attaching a stainless steel hypotube 70 to a Ni-Ti
hypotube 75 by using suitable adhesives, soldering, brazing, or
press fitting, as in the manner shown in FIG. 8A. In this
embodiment, Ni-Ti hypotube 75 may form the distal portion of the
catheter apparatus 10 and have a length of about 20 cm. However, it
will be noted that the composite wires of the present invention may
also include other sections, beside the distal section, comprised
of non-linear nitinol. Thus, in this regard, the present composite
medical wire will have two or more effective moduli in order to
provide greater versatility in performance.
[0115] Another method of joinder is illustrated in FIG. 8B. A
portion 78 of the proximal end of the nitinol hypotube 75 is fitted
into the distal end of the stainless steel tube 70 and a joint 74
can be formed as in the manner shown in FIG. 8B. The joint
material, such as solder or adhesives, can be applied through one
or more holes 72 that are previously formed at the distal end of
the stainless steel tubing 70. Additionally, in order to provide a
better adhesion between the joint material and the nitinol
hypotube, the outer surface of the fitting end 78 of the hypotube
may be modified as shown, or in other ways. Alternatively, crimping
or press fitting may be also applied to join materials.
[0116] As illustrated in FIG. 8C, in an alternate embodiment, the
stainless steel hypotube 75 may be disposed concentrically about
the Ni-Ti hypotube 70. In this embodiment, the stainless steel
hypotube is sealingly secured about the periphery of the Ni-Ti
hypotube 75 by using suitable adhesives.
[0117] In some cases, the component sections of the composite wire
may have equal or approximately equal diameters. In other cases,
one section may have a diameter greater than the other. For
example, in order to avoid a problem known as "scooping", a
composite guidewire may be constructed so as to have a proximal
section OD of 0.035" or 0.018" (to allow certain therapy devices to
ride thereover more efficiently) and a distal section of 0.014" (to
provide a narrow profile to cross the lesion).
[0118] Irrigation Catheters
[0119] The hollow guidewire of the present invention can be
advantageously used to deliver fluids for specific medical
applications including coronary and neurological applications.
During the course of such applications, it is often essential to
deliver fluids to specific locations within the body. This fluid
delivery is carried out using irrigation catheters. Particularly,
irrigation catheters serve as passage ways for delivery of fluids
comprising either a contrast media to permit X-ray detection or
other media to achieve localized drug therapy. However, if there is
a balloon incorporated at the distal end this fluid may also
comprise a fluid, such as saline, to inflate the balloon.
[0120] In prior applications, typical fluid delivery procedure
incorporates the use of a guidewire in combination with the use of
an irrigation catheter. In this type of combination system, the
irrigation catheter simply rides over the guidewire to reach the
desired body location. The diameter of this combination system is
significantly larger than the external diameter of the guidewire
itself. Therefore, such systems are bulky and have limited
applications for especially narrow and tortuous vessels such as
vessels within the brain.
[0121] As illustrated in FIGS. 9A-9C, irrigation catheters
constructed from the present invention overcome these limitations
by providing a nitinol hollow guide wire having the capability to
pass fluid therethrough. FIG. 9A illustrates a preferred embodiment
of an irrigation catheter 80A constructed from superelastic nitinol
hollow wire of the present invention. In this embodiment, the
irrigation catheter 80A is comprised of an hypotube 81 and a coil
member 82. The hypotube 81 is provided with proximal and distal
ends 81A and 81B and as well as a lumen 84 extending along the
hypotube 81 and thereby providing a fluid passage way. The coil
member 82 of the catheter 80A is joined to the distal end 81B of
the hypotube 81 as in the manner shown in FIG. 9A. The distal end
81B of the hypotube 81 may also include one or more perforations 85
thereof so that fluids can be delivered into or received from the
desired body locations. In addition to distal perforations 85, gaps
between the coil turns 86 also provide an effective passage way to
deliver or receive fluids through coil member 82. Therefore, in
this embodiment, perforations 85 at the distal end 81B of the
hypotube 81 are optional so that the fluid may exit or enter the
catheter 80A from the coil member 82. Although the catheter 80A of
the present invention can be used for delivering drugs to the
distal body locations, the catheter 80A can also be used in those
applications where irrigation and aspiration are necessary for
emboli removal. For the most available cardiovascular catheters,
the outer diameter of this irrigation catheter must be 0.38" or
smaller.
[0122] FIG. 9B shows a second embodiment of the present invention
which comprises a multilumen irrigation catheter 80B. In this
embodiment, a portion of the catheter 80B comprising the hypotube
81 and the coil member 82 is configured similar to that of first
embodiment. As a departure from the previous embodiment, however,
the present embodiment also comprises a balloon member 88 and a
conduit 90. The conduit 90 is preferably disposed along the inner
lumen 84 of the hypotube 81. The balloon member 88 is coaxially
mounted on the distal end 81B of the hypotube 81 as in the manner
shown in FIG. 9B. The conduit 90 is provided with distal and
proximal ends 90A and 90B as well as an inner lumen 91.
[0123] In this embodiment, the proximal end 90A of the conduit is
preferably connected to a gas source (not shown), while the distal
end 90B is connected to the balloon member 88 through an inlet port
92 in the distal end 81B of the hypotube 80. The distal end 90B of
the conduit 90 and the inlet port 92 are sealably connected to each
other by suitable means such as adhesive to avoid any gas leak. In
this arrangement, the inner lumen 91 of the conduit 90 connects the
gas source to the balloon member 88 so that the gas from the gas
source can inflate the balloon member 88.
[0124] The conduit 90 is preferably made of a flexible material
such as polymide, polyamide, or the like alloy and is in the form
of hypotubing. Preferably, the outer diameter of the conduit 90 is
significantly smaller than the inner diameter of the lumen 84 of
the hypotube 81 so that fluid in the lumen 84 can flow without any
restriction. In this embodiment, carbon dioxide (CO.sub.2) gas is
preferably employed to inflate balloon member 88. In fact,
(CO.sub.2) gas easily dissolves in blood and does not cause any
harm in the patient's body, if an accidental leak occurs. If
desired, however, the balloon member may be inflated using any of a
number of harmless gases or fluids, or possible combinations
thereof In applications, the irrigation catheter 80B may function
as the catheter 80A in the first embodiment. However, with the
inflatable balloon member 88, the catheter 80B can be
advantageously used for occlusion and irrigation therapies.
[0125] FIG. 9C shows a third embodiment of the present invention
which comprises another single lumen catheter 80C as in the case of
first embodiment. In this embodiment, a portion of the catheter 80C
comprising the hypotube 81 and the coil member 82 is also
configured similar to that of first embodiment. The present
embodiment also comprises a balloon member 88. The balloon member
88 is coaxially mounted on the distal end 81B of the hypotube 81 as
in the manner shown in FIG. 9B. Fill holes 93 are provided in the
wall of the distal end 81B of the hypotube 81 along the section of
hypotube enclosed within the balloon member 88. During the
application, these fill holes 93 allow the passage of irrigation
fluid into the balloon member 88. As the fluid pressure reaches up
to inflation pressure of the balloon member 88, the balloon member
is inflated. An exemplary inflation pressure range for the
occlusion balloons can be given as 40 psi. However, for the
therapeutic balloons, such pressure range can be as high as 200
psi.
[0126] As shown in FIG. 9C, a number of valve members are also
provided over the inner wall of the distal end 81B of the hypotube
81. The valve members are attached over the perforations 85 as in
the manner shown in FIG. 9C. Preferably, the valve members 94 are
comprised of elastomeric membranes. These membranes 94 can be
configured and dimensioned to withstand some threshold fluid
pressure, such as the inflation pressure of the balloon member
88.
[0127] In applications, any pressure over this threshold pressure
breaks open these membranes 94, i.e., activates valves 94, and
delivers the irrigation fluid, through perforations 85, into the
body locations. The fluid delivery can be also provided through
leakages from both optional the slits (not shown) in the balloon
member 88 and the gaps between the coil turns 86. As in the
previous embodiment, the catheter 80C can be advantageously used
for occlusion and irrigation therapies.
[0128] Hence, although the foregoing description of the preferred
embodiment of the present invention has shown, described and
pointed out the fundamental novel features of the invention, it
will be understood that various omissions, substitutions, and
changes in the form of the detail of the apparatus and method as
illustrated as well as the uses thereof, may be made by those
skilled in the art, without departing from the spirit of the
present invention. Consequently, the scope of the present invention
should not be limited to the foregoing discussions, but should be
defined by the appended claims.
* * * * *