WO1995034338A1

WO1995034338A1 - Medical guide wire and manufacture

Info

Publication number: WO1995034338A1
Application number: PCT/US1995/007456
Authority: WO
Inventors: Francis C. Peterson
Original assignee: Phillips Plastics Corporation
Priority date: 1994-06-13
Filing date: 1995-06-13
Publication date: 1995-12-21

Abstract

The guide wire has a helical mandrel cut from a unitary Nitinol wire. The pitch, cut depth and diameter of the helix all determine the flex characteristics of the completed guide wire. The guide wire is produced by a six-axis electrical discharge machining operation where the workpiece is gripped and advanced through a stationary guide located directly proximate the cutting wire.

Description

MEDICAL GUIDE WIRE AND MANUFACTURE

1. FIELD OF THE INVENTION The present invention is a guide wire of the type used in conjunction with medical procedures and the method for making the guide wire.

2. BACKGROUND OF THE INVENTION Medical guide wires are widely used during surgical procedures to help the physician to position catheters and other devices within the body. The use of guide wires reduces the trauma of many surgical procedures and there is a continuing effort to improve guide wires and to expand their use in interventional procedures. At present guide wires are widely used in cardiovascular surgical procedures as well as gastrointestinal tract and urinary tract procedures among others.

The typical medical guide wire used for cardiovascular procedures has an elongated body with a distal end and a proximal end. In use the distal end of the guide wire is introduced into the vascular system and manipulated from the proximal end by the physician. To navigate the vascular pathways the guide wire must be stiff enough to permit the physician to "push" the wire. However the guide wire must be flexible enough to not damage the patients vascular structures. For the guide wire to be effectively manoeuvered through the vasculature it must also smoothly transmit torque from the proximal end to the distal tip portion. It is also important that the distal tip itself be sufficiently flexible to not injure tissue and to bend smoothly when deflected.

It has also useful to have a distal tip which is readily deformable into a curved shape to aid in guiding the guide wire through the vascular system. Also many guide wires apply a radiopague indicator to the distal tip to assist in visualizing the location of the guide wire with X-rays. It is now common to meet these disparate requirements with a guide wire having a tapered inner mandrel within a distal coil. The coil can improve formability and radiopacity and it is mechanically attached to the mandrel. It is important to improve the physical integrity of the distal portion of the guide wire to ensure that the various components do not become detached. This problem is exacerbated when the guide wire diameter is reduced. There is a need for a guide wire construction which addresses these issues.

SUMMARY The guide wire of the present invention is formed from a unitary solid wire of metal machined to form a helical mandrel. The mandrel forms a portion of the flexible distal segment 14. The preferred metal material for the helical mandrel is Nitinol but other shape memory alloys and stainless steel alloys are contemplated as well. The guide wire is divided into an elongated body portion and a flexible distal portion. The elongate body portion is generally circular in cross section and it terminates in a proximal end while the flexible distal segment terminates in a distal tip. In all of the illustrative embodiments the flexible distal segment has a helical form cut from the elongate body portion forming a helical mandrel. In some embodiments the "pitch" of the helical mandrel varies along the length of the flexible^•distal segment. In some embodiments a coil is "screwed" onto the helical mandrel. In some embodiments the composite structure is encapsulated with a polymeric material. In some embodiments a safety fiber is located within the central space of the helical mandrel and attached to the elongate body portion. The distal tip is connected to a helical mandrel and the helical mandrel in turn is connected to the elongate body portion. In general, all of these elements are integral and formed by machining operations from a single monolithic piece of wire material.

The preferred method of making an illustrative guide wire involves electric discharge machining. It is preferred to "cut" the helical mandrel from wire stock. The method involves a multi-axis machine that rotates the wire stock adjacent a cutting wire. The wire stock is advanced toward the cutting wire while being rotated and advanced orthogonally from the cutting wire.

BRIEF DESCRIPTION OF THE DRAWING An illustrative and exemplary medical guide wire is shown in the drawings. The various embodiments of the present invention like reference numerals represent corresponding like structures throughout the several views:

FIG. 1 is a view of a medical guide wire of the present invention; FIG. 2 is a view of a portion of the guide wire of the present invention;

FIG. 3 is a view of a portion of the guide wire of the present invention;

FIG. 4 is a view of a portion of a completed guide wire;

FIG. 5 is a view of a portion of a completed guide wire;

FIG. 6 is a schematic diagram of a method of machining the mandrel; and, FIG. 7 is a schematic diagram of a method of machining the mandrel.

FIG. 8 is view of the support block; FIG. 9 is a view of the gear train for a multiple spindle machining center. DETAILED DESCRIPTION The Guide Wire Geometry

FIG. 1 shows a medical guide wire 10 that comprises an elongate body portion 12 having a generally circular cross section. The guide wire 10 may be divided for discussion into an elongate body portion 12 and a flexible distal segment 14. The body portion terminates in a proximal end 18 while the flexible distal segment 14 terminates in a distal end 16. In use the physician will introduce the flexible distal segment 14 into the patient and will advance and guide the medical guide wire 10 by manipulating the proximal end 18 and the body portion 12.

FIG. 2 shows a view of a portion of the flexible distal segment 14. In this drawing the distal end 16 has been machined to a substantially hemispheric shape having a maximum diameter substantially equal to the maximum diameter of the wire stock used to form the elongate body portion 12. In the particular example presented as FIG. 2 the pitch of the helical mandrel 20 is constant as indicated by the equality of angle 22 and angle 24. It should be recognized that the depth of the cut used to form the helical mandrel 20 is sufficient to generate a space wound coil form shape for the helical mandrel 20.

FIG. 3 shows a view of a portion of the flexible distal segment 14. Once again the distal end 16 has been machined into a hemispheric form. However in this embodiment the "pitch" of the helix 21 has been varied along the length of the flexible distal segment 14. In the drawing the angle 23 does not match the angle 33. Also, in this embodiment the depth of the "cut" has been varied along the length of the flexible distal segment 14. In general, when the cut depth is sufficient to from a helix rather than a screw-form the cross sectional shape 25 of the material is substantially triangular in form. It should also be noted that the helical mandrel 20 can be tapered as another independent variable to control the flexibility of the tip or end.

The effect of varying the depth of the cut results in loops having a "space wound" geometry near the distal end 16 as typified by loop 26 and loops having a solid center near the body portion 12 as typified by loop 29.

During the design process for a guide wire the desired flex characteristics will be defined and an appropriate pitch and cut depth will be defined for the mandrel. But it should be understood that the pitch and depth of cut are independent variables which can be used to generate a mandrel having arbitrarily defined flex characteristics. In general, the pitch is controlled by adjusting the rate at which the wire emerges from a machining fixture, while the depth of the cut is independently controlled by the movement of the cutting wire toward the mandrel. The design process should also accommodate the stiffness and flex characteristics of the coatings and other materials used to form the distal segment 14.

It is believed that shapes set forth in FIG. 2 and FIG. 3 are operable for many applications however certain additional structures may be added to helical mandrel 20 to enhance its functionality. FIG. 4 shows a space wound spring coil 30 which has been wound onto the helical mandrel 20. In many cardiovascular applications the guide wire 10 is observed under fluoroscopy and it may be desirable to add a radiopaque spring coil 30 or the like to the flexible distal segment to enhance visibility of the guide wire. Springs such as spring coil 30 can also alter the formability of the flexible distal segment 14 and may also be used to increase the diameter of the guide wire at the flexible distal segment 14. FIG. 5 shows a cross section of a guide wire having a helical mandrel 20. In this embodiment a spring coil 30 has been applied over the helical mandrel 20. Additionally a safety fiber 32 has been placed in the center of the helical mandrel 20 to permit a broken section to adhere to the proximal portion and therefore be removed from the body. In the figure the guide wire 10 is fitted with a radiopaque band 27 and is encapsulated with a polymeric material 34. Although any of several materials are acceptable it is believed that polyurethane will be preferred for cardiovascular applications. The polymeric sheath or coating may enhance the utility of the guide wire in some applications. It should also be noted that the process of filling the helix with a polymer also may severe a safety fiber function since the interior of the helix is open. The Method of Manufacture

The guide wire 10 is an exemplary element which can be formed by the process disclosed herein.. However it should be noted that the process can be used to from non-medical structures from a wide variety of materials. The process and structures are best suited to small parts formed from wire stock and made from demanding materials such as nitinol.

The preferred material for the elongate body portion 12 and integral or monolithic helical mandrel 20 is Nitinol which is an alloy of nickel and titanium. The preferred technique for machining is based on Electric Discharge Machining (EDM) . A brass cutting wire 28 is moved past the work piece 31 as indicated by path arrow 46. It has proved important to support the work piece close to the cutting wire 28 and it is preferred to use a support block 41 for this purpose. Generally it may prove useful to simply drill a plastic block to the nominal size of the work piece to provide this support. However it has been noted that the small diameter wire stock can move under the influence of the discharge process. Generally the work piece and cutting wire will be submerged in a dielectric fluid such as deionized water during the cutting operation. A high voltage source 68 is coupled across the workpeice and the cutting wire. Computer driven carriages advance the work piece out of the support block 41 as indicated by path arrow 40 in the figures. A computer driven chuck (not seen) grips the work piece 31 and rotates it about its about its axis as seen by path arrow 42. The support block 41 is mounted to a computer driven carriage and may advance the work piece 31 into the cutting wire 28 along a path indicated by path arrow 44. Independent control of these axes permits the manufacture of the helical mandrel in one pass. FIG. 8 shows a more preferred arrangement in which the support block is split along a vertical axis 48 and the wire reception apertures typified by aperture 50 are formed in part in each complimentary section of the support block 41. This form of support block allows very close tolerance over the multiple apertures typified by aperture 50. Suitable keyways can be provided to hold the support block portions together. This split form of support block is best made from metal to resist wear and to most effectively stabilize the wire work piece 31. However to prevent arcing between the cutting wire 28 and the metallic support block 41 it is desirable to incorporate a plastic or dielectric spacer 52 between the support block 41 and the cutting wire 28. This dielectric spacer 52 portion should be thin. It has been found that the wire work piece may be conveniently cut to the approximate desired length and then fixed in a rotating fixture. Multiple rotating fixtures may be slaved together by a gear train such as that set forth in FIG. 9. as gear train 56. The smallest gears typified by gear 58 have an aperture which can be used to mount a tube or the like. A single tube is depicted as tube 62, which contains a representative wire work piece 31. In the illustrative embodiment sixty four separate work pieces can be machined at a time with one moving cutting wire 28. Typically the gear train 56 of FIG. 9 and an appropriate motor are enclosed in a housing 64 and are translated in a direction toward the cutting wire 28 giving rise to the motion depicted by path arrow 40. Thus the cutting wire 28 is moved past a number of translating and rotating work pieces. The work piece emerges from a stationary support block 41 which is isolated from the cutting wire 28 by a dielectric insulator 52. This results in a six axis machine.

Claims

WHAT IS CLAIMED IS:

1. A guide wire (10) comprising: an elongated body portion (12) having a proximate end (18) ; a helical mandrel (20) monolithically formed with said elongated body portion (12) ; and said mandrel (20) forming a part of a flexible distal segment (14) .

2. The guide wire of claim 1 further comprising a spring coil (30) wound onto said helical mandrel (20) .

3. The guide wire of claim 2 wherein said spring coil (30) is formed of radiopaque material.

4. The guide wire of claim 1 further comprising a polymeric coating covering said elongate body portion

(12) .

5. The guide wire of claim 1 further comprising a polymeric coating (16) covering said flexible distal segment (14) .

6. The guide wire of claim 1 further including a safety fiber (32) located within said helical mandrel (20) and connected to said elongate body portion (12) .

7. The guide wire of claim 1, wherein the flexible distal segment (14) has a longitudinal length, and the helical mandrel (20) is formed by a helical cut extending along the longitudinal length of the flexible distal segment (14) , said helical cut produced by moving a cutting wire (28) past said distal segment while rotating said distal segment and providing a high voltage (68) across said distal segment and said cutting wire (28) .

8. The guide wire of claim 7, wherein the helical cut has a pitch which varies along the longitudinal length of the flexible distal segment (14) , by varying the speed that the distal segment is driven toward the cutting wire (28) .

9. The guide wire of claim 7, wherein the helical cut has a depth which varies along the longitudinal length of the flexible distal segment (14) .

10. The guide wire of claim 1, wherein the flexible distal segment (14) has a distal end (16) having a substantially hemispheric shape.