Method of making a guidewire core

This is a divisional application of application Ser. No. 09/224,453 filed on Dec. 31, 1998, now U.S. Pat. No. 6,142,975, all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to the field of guidewires for advancing intraluminal devices such as stent delivery catheters, balloon dilatation catheters, atherectomy catheters and the like within body lumens.

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.

In a typical coronary procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into a patient's peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger 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 procedure is performed.

A requirement for guidewires is that they have sufficient column 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.

Further details of guidewires, and devices associated therewith for various interventional procedures can be found in U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.); U.S. Pat. No. 5,135,503 (Abrams); U.S. Patent 5,341,818 (Abrams et al.); and U.S. Pat. No. 6,345,945 (Hodgson et al.) which are hereby incorporated herein in their entirety by reference thereto.

Pseudoelastic alloys can be used to achieve both flexibility and strength. When stress is applied to NiTi alloy exhibiting pseudoelastic characteristics at a temperature at or above 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.

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 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 pseudoelasticity. These properties to a large degree allow a guidewire core of a psuedoelastic material to have both flexibility and strength. However, psuedoelastic alloy components are typically difficult to join or secure to other components. This is due primarily to a tenacious oxide layer that develops on the surface of some such alloys, particularly those containing titanium.

Prior methods of pre-treatment for securing subassemblies to a distal core made of pseudoelastic alloys such as NiTi include molten or fusion salt etching and then pre-tinning the core to facilitate forming a strong bond, as seen in U.S. Pat. No. 6,695,111 to Nanis et al. which is hereby incorporated in its entirety by reference. While this method represents a significant advance, what has been needed is a method for manufacturing a guidewire with a superelastic or psuedoelastic component which will allow the component to accept a weld, solder or adhesive joint with ease of manufacture and low cost. It is also desirable to have a manufacturing process in which the mechanical properties of psuedoelastic and high strength alloys can be combined.

SUMMARY OF THE INVENTION

The present invention is directed to an intracorporeal device, preferably a guidewire, and method for making the device. The guidewire has an elongate core member with a proximal section and a distal section. The elongate core has an inner core element of a desired metal and an outer layer of material disposed about the inner core element. The outer layer of material is typically applied to the inner core element as a braid which is then cold drawn through a die which conforms and secures the outer layer to the inner core element. The outer layer of material may be cold drawn to a smooth continuous layer, or may be cold drawn to a lesser extent where the outer layer maintains a braided flattened configuration.

In an alternative embodiment of the invention, an elongate core member has a second outer layer of material applied to an inner core element and a first outer layer of material which may be drawn filled tubing. The drawn filled metallic tubing preferably consists of an inner core element of stainless steel and a first outer layer of psuedoelastic alloy, normally consisting of NiTi alloy disposed about the inner core element. The second outer layer of braided stainless steel is applied and cold drawn through a die so as to create an elongate core member having a layer of NiTi alloy sandwiched between an inner core element and an outer layer of stainless steel. When the distal section of this elongate core member is tapered to a distally smaller cross section, the various layers of the elongate core member are exposed.

Typically, a flexible body is disposed over and secured to at least a portion of the distal section of the elongate core member. The flexible body can be a helical spring but can also be a polymer jacket of material that can be thin or sufficiently thick to provide a diameter similar to that of the proximal section.

The distal end of the helical coil, or other flexible body, is preferably secured to a distal end of the elongated core member, by soldering, brazing, welding, bonded polymeric materials or other suitable means.

The inner core element, which is preferably stainless steel or other suitable high strength bondable or solderable material, is exposed at the distal end of the elongate core member as a result of the tapering of the distal section. Exposure of the inner core element allows the distal end of the flexible body to ha bonded or soldered to the distal end of the bondable or solderable material of the inner core element. A proximal end of the flexible body is preferably bonded or soldered to a distal section of the second outer layer of material. Preferably, the second outer layer of material is comprised of stainless steel or some other suitable bondable or solderable material. In this way, the flexible body will have its distal and proximal ends secured to bondable or solderable materials. If the first outer layer of material is made of a pseudoelastic alloy, a desired amount of the distal section can exhibit mechanical properties of the pseudoelastic alloy which comprises the majority of the distal section material. This results in high strength bonding or soldering between the guidewire components, smooth flexibility transitions in the elongate core member and the desired pseudoelastic mechanical characteristics in the distal section of the elongate core member. In addition to solderablity and bondability, the outer layers of material may be selected for desired mechanical strength properties. For example, a second outer layer of material may be made from a precipitation hardenable alloy such as MP35N in order to give the proximal section of the elongate core member a desired amount of strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

depicts a longitudinal cross sectional view of a guidewire having features of the invention.

FIG. 2

is a transverse cross sectional view of the guidewire of

FIG. 1

taken at lines

2

—

2

in FIG.

1

.

FIG. 3

is a transverse cross sectional view of the guidewire of

FIG. 1

taken at lines

3

—

3

in FIG.

1

.

FIG. 4

is a schematic view of an outer layer of material being braided onto an inner core element and cold drawn.

FIG. 5

is a transverse cross sectional view of the outer layer of material and inner core element of

FIG. 4

taken at lines

5

—

5

in FIG.

4

.

FIG. 6

is a transverse cross sectional view of a stranded outer layer of material over an inner core element.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1

is a longitudinal cross sectional view of a guidewire

10

having features of the invention. An elongate core member

11

has an inner core element

12

, a first outer layer of material

13

disposed on an outer surface

14

of the inner core element, and a second outer layer of material

15

disposed on an outer surface

16

of the first outer layer of material. The first outer layer of material

13

and second outer layer of material

15

are shown as smooth continuous layers. The inner core element

12

has a proximal section

17

, a distal section

18

and a distal end

21

. The second outer layer

15

has a proximal section

22

and a distal section

23

. A distal section

24

of the elongate core member

11

has a distally tapered segment

25

which can be adjusted in length, taper angle and cross sectional shape to achieve the desired flexibility and performance characteristics for the guidewire

10

. The distally tapered segment

25

also serves to expose the distal end

21

of the inner core element

12

to which a distal end

26

of a flexible body

27

is secured. The distal end

26

of the flexible body

27

is secured to the distal end

21

of the inner core element

12

by a first body of solder

28

. A proximal end

31

of the flexible body

27

is secured to the distal section

23

of the second outer layer of material

15

with a second body of solder

32

. Although a single distally tapered segment

25

is shown, the distal section

24

of the elongate core member

11

may have two or more such tapered segments which may or may not be separated by segments of substantially constant diameter.

A flexible body

27

, such as a helical coil, polymer jacket, or the like, surrounds and covers at least a portion of the distal section

24

of the elongate core member

11

. Polymers suitable for forming a flexible body

27

can include polyimide, polyethylene, polyurethane, TFE, PTFE, ePTFE and other similar materials. A flexible body

27

in the form of a helical coil may be formed of a suitable radiopaque material such as tantalum, gold, iridium, platinum or alloys thereof or formed of other material such as stainless steel and coated with a radiopaque material such as gold. The wire from which the coil is made generally has a transverse diameter of about 0.001 to about 0.004 inch, preferably about 0.002 to about 0.003 inch (0.05 mm). Multiple turns of a distal portion of coil

27

may be expanded to provide additional flexibility. The helical coil

27

may have transverse dimensions about the same as a proximal core section

35

. The coil

27

may have a length of about 2 to about 40 cm or more, but typically will have a length of about 2 to about 10 cm in length.

The inner core element

12

and second outer layer of material

16

are made of stainless steel but can also be made of any other suitable solderable or bondable high strength materials. The first outer layer of material

13

disposed between the inner core element

12

and the second outer layer of material

15

is a pseudoelastic alloy, more specifically, NiTi alloy, which is chosen for its mechanical properties and performance. The first outer layer of material may also be made of any suitable metal or alloy having desired properties. The inner core element

12

, first outer layer of material

13

, and second outer layer of material

15

may be formed of stainless steel, NiTi alloys, MP35N, L605 or combinations thereof such as described in U.S. Pat. No. 5,341,818 (Abrams at al) which is incorporated herein in its entirety. Other materials such as the high strength alloys as described in U.S. Pat. No. 5,636,641 (Fariabi), entitled HIGH STRENGTH MEMBER FOR INTRACORPOREAL USE, which is incorporated herein by reference, may also be used.

As is known in the art, many materials used for guidewire construction have desirable mechanical properties, but are difficult to assemble to other guidewire components using conventional technology such as soldering or use of polymer adhesives due to inherent surface properties such as tenacious oxide layers. The construction shown in

FIG. 1

allows the use of materials which have poor bondability or solderability, such as NiTi alloy in a guidewire core without concern for the bondability or solderability of the material.

FIG. 2

shows a transverse cross sectional view of the guidewire

10

of

FIG. 1

taken at lines

2

—

2

in FIG.

1

. The inner core element

12

is surrounded by a substantially coaxial or concentric first outer layer of material

13

. The first outer layer of material

13

is surrounded by a second outer layer of material

15

. The inner core element has a nominal transverse dimension of up to 0.02 inches, preferably about 0.005 to about 0.01 inches more preferably about 0.006 to about 0.008 inches. The first outer layer of material

13

and second outer layer of material

15

have a nominal wall thickness of up to about 0.015 inches, preferably about 0.0005 to about 0.01 inches, and more preferably about 0.001 to about 0.003 inches. Although the inner core element

12

is shown as solid, the inner core element may also be hollow with a lumen extending longitudinally therethrough. A lumen extending longitudinally through the inner core element

12

could be used for delivery of diagnostic or therapeutic agents, such as radioactive therapy agents or growth factors or the like. The lumen may also be used for advancement of elongated medical devices into a patient's vasculature.

FIG. 3

shows a transverse cross sectional view of the guidewire

10

of

FIG. 1

taken at lines

3

—

3

in FIG.

1

. The flexible body

27

is disposed partially about a distal segment

33

of the elongate core member

11

. Referring back to

FIG. 1

, distal segment

33

is configured to provide a highly flexible segment at a distal end

34

of the guidewire

10

in order to facilitate advancement through a patient's vasculature without causing injury thereto. The distal segment

33

is shown as a flattened portion of the exposed inner core element

12

which facilitates shapeability of the distal segment, however, the flexible segment can have a round cross section, or any other suitable configuration.

FIG. 4

illustrates a portion of a method having features of the invention used to produce an elongate core member

40

. An outer layer of material

41

is being braided onto an outer surface

42

of an inner core element

43

. The inner core element

43

and outer layer of braided material

41

are drawn through a die

44

so as to compress the outer layer of braided material onto the outer surface

42

of the inner core element and produce a smooth coaxial layer of material thereon. The outer layer

41

may be cold drawn or co-drawn down to a smooth continuous layer, or may be partially cold drawn or co-drawn to a lesser extent where the outer layer retains a braided or stranded character that has been flattened against the outer surface

42

of the inner core member

43

. It is desirable for the cold drawing or co-drawing process to create a bond between the inner core member

43

and the outer layer of material

41

. The bond between the inner core member

43

and the outer layer of material

41

. The bond between the inner core member

43

and the outer layer of material

41

can be partially or wholly mechanical. As used herein, the term braid or braided is intended to refer to the process or object resulting from the process of interweaving filaments

45

of material such that the individual filaments overlap each other at regular intervals or pick points

46

. Such a braid can be produced in a cylindrical configuration by itself, or it can be formed over a mandrel such as the inner core element

43

. A braid can be defined by the number of filaments

45

, the transverse dimension of the filaments, the transverse dimension of the mandrel over which the braid is formed and the picks

46

per unit length as the braid is laid down. The term strand or stranded is intended to refer to the process or object resulting from the process of laying filaments of material in a single layer without overlap of the filaments. The filaments

45

of an outer layer of material

41

may all be of the same material or may be from a variety of different materials. For example, filaments

45

may all be stainless steel, or some may be stainless steel and others MP35N or NiTi alloy. Filaments of radiopaque materials such as gold, platinum, tantalum and the like may also be used.

FIG. 5

shows a transverse cross sectional view of the inner core element

43

and outer layer of material

41

after passing through the die

44

. The inner core element

43

is shown as solid and non-layered, however, the inner core element may have multiple layers prior to the application of the outer layer of braided material

41

. The multiple layering of the inner core element

43

may be achieved by the braiding and drawing through a die as discussed above, or the layers may be achieved by conventional drawn filled tubing techniques which are known in the art. In addition, the method depicted in

FIG. 5

which shows an outer layer of material

41

applied as braid may also be achieved by applying the layer of material as a strand or other suitable configuration. An elongate core member

40

having four, five, six or more layers can be achieved by using the above described methods.

FIG. 6

shows a transverse cross section of an elongate core member

50

having an inner core element

51

and an outer layer of material

52

. The outer layer of material

52

has been applied as a strand and partially cold drawn or co-drawn and retains a stranded character. The outer layer of material

52

has been flattened against an outer surface

53

of the inner core element

51

and is at least partially mechanically secured thereto. Individual filaments

64

can be seen in the outer layer of material

52

.

While particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.