CA2126314C

CA2126314C - Super elastic alloy guidewire

Info

Publication number: CA2126314C
Application number: CA002126314A
Authority: CA
Inventors: Thomas J. Palermo
Original assignee: Target Therapeutics Inc
Current assignee: Target Therapeutics Inc
Priority date: 1993-05-11
Filing date: 1994-05-11
Publication date: 1999-01-26
Anticipated expiration: 2014-05-11
Also published as: IL109621A0; ES2159559T3; EP0681492B1; CA2126314A1; DE69427465T2; JP2799248B2; EP0681492A4; US5636642A; ATE201998T1; EP0681492A1; AU6946794A; DE69427465D1; TW280775B; WO1994026337A1; US5409015A; JPH07505561A; AU670204B2

Abstract

This invention is a surgical device. It is a guidewire for use in a catheter and is used for accessing a targeted site in a lumen system of a patient's body. The guidewire may be of a high elasticity metal alloy, preferably a Ni-Ti alloy, having specified physical parameters, and is especially useful for accessing peripheral or soft tissue targets. A special variation of the inventive guidewire includes the concept of coating the wire with a one or more lubricious polymers to enhance its suitability for use within catheters and with the interior of vascular lumen. The "necked" guidewire tip also forms a specific variant of the invention.

Description

~ ~ ~ 6 ~ ~ 4 S SUPER ELASTIC ALLOY GUID

FIELD OF T~ lNv~JTIQN
~ hi~ invention is a surgical device. It is a guidewire for use in a catheter and i~ used for accessing a targeted site in a lumen system of a patient's body. The guidewire may be of a high elasticity metal alloy, preferably a Ni-Ti alloy, having specified physical parameters, and is especiAIly useful for accessing peripheral or soft tissue targets. A special variation o~ the inventive guidewire includes the coating of the wire with a one or more lubricious polymers to e~ ce its suitability for use within catheters and with the interior of v~-c~ r lumen. The "~cke~ guidewire tip also forms a specific variant of the invention.
BACKGROUND OF TH~ lNv~NllON
Catheters are used increasingly as a means for delivering diagnostic and therapeutic agents to internal sites within the human body that can be accesoe~ through the various of the body's lumen systems, particularly through the v~ Ature. A
catheter guidewire is u~ed for guiding the catheter through the bends, loops, and br~n~s forming the blood ves-~l R within the body. One method of using a guidewire to direct the catheter through the tor~l UUS

-2- ~26~ ~4 ~ . . .
paths of these systems of lumen involves the use of a torqueable guidewire which is directed as a unit from a body access point such as the femoral artery to the tissue region containing the target site. The guidewire is typically bent at its distal end, and may be guided by alternately rotating and advancing the guidewire along the small vessel pathway to the desired target. Typically the guidewire and the catheter are advanced by alternately moving the guidewire along a distance in the vessel pathway, holding the guidewire in place, and then advancing the catheter along the axis of the guidewire until it reaches the portion of the guidewire already advanced farther into the human body.
The difficulty in Acce-~ing remote body regions, the body's periphery or the soft tissues within the body such as the brain and the liver, are apparent. The catheter and its attenAAnt guidewire must be both flexible, to allow the combination to follow the complicated path through the tissue, and yet stiff enough to allow the distal end of the catheter to be manipulated by the physician from the external Acce~ site. It is common that the catheter is as long as a meter or more.
The catheter guidewires used in guiding a catheter through the human vA~clllAture have a number of variable flexibility constructions. For instance, U.S. Patent Nos. 3,789,841; 4,545,390; and 4,619,274 show guidewires in which the distal end section of the wire is tapered along its length to allow great flexibility in that remote region of the guidewire.
This is so, since the distal region is where the sharpest turns are encountered. The tapered section of the wire is often enclosed in a wire coil, typically a platinum coil, to increase the column strength of the tapered wire section without significant loss of flexibility in that region and ..,~

-3- ~ ~6 ~ ~ 4 also to increase the radial capacity of the guidewire to allow fine manipulation of the guidewire through the vasculature.
Another effective guidewire design is found in U.S. Patent No. 5,095,915 which shows a guidewire having at least two sections. The distal portion i8 encased in an elongated polymer sleeve having axially spaced grooves to allow increased hen~ing flexibility of the sleeve.
Others have suggested the USQ of guidewires made of various super-elastic alloys in an attempt to achieve some of the noted functional desires.
U.S. Patent 4,925,445, to Sakamoto et al., suggests the USQ of a two-portion guidewire having a body portion relatively high in rigidity and a distal end portion which is comparatively flexible. At least one portion of the body and thQ distal end portion~ is formed of super-elastic metallic materials. Although a number of materials are suggested, including Ni-Ti alloys of 49 to 58% (atm) nickel, the patent expresses a strong preference for Ni-Ti alloys in which the - transformation between austentite and martensite is complete at a temperature of 10~C or below. The reason given is that ~for the guidewire to be useable in the human body, it must bQ in the range of 10~ to 20~C due to anesthesia at a low body temperature. n The temperature of the human body is typically about 37~C.
Another document disclosing a guidewire using a metal alloy having the same composition as a Ni-Ti super-elastic alloy is WO91/15152 (to Sahat~ian et al. and owned by Boston Scientific Corp.). That disclosure suggests a guidewire made of the precursor to the Ni-Ti elastic alloy. Super-elastic alloys of this type are typically made by drawing an ingot of the precursor alloy while simultaneously heating it.
In the unstressed state at room temperature, such 6 3 ~ 4 ~_ 4 super-elastic materials occur in the austenite crystalline phase and, upon application of stress, exhibit stress-induced austenite-martensite (SIM) crystalline transformations which produce nonlinear elastic behavior. The guidewires described in that published application, on the other hand, are said not to undergo heating during the drawing process. The wires are cold-drawn and great pain is taken to assure that the alloy is maint~ne~ well below 300~F during each of the stages of its manufacture. This temperature control is maint~in~ during the step of grinding the guidewire to form various of its tapered sections.
U.S. Patent 4,665,906 su~e_Ls the use of stress-induced marten~ite (SIM) alloys a~ constituQnts in a variety of different medical devices. Such devices are said to include catheter~ and cannulas.
U.S. Patent 4,969,890 to Sugita et al., suggests the production of a catheter having a main body fitted with a shape memory alloy member, and having a liquid in~ection mean~ to supply a warming liquid to allow th~ shape memory alloy member to recover its original shape upon being warmed by the fluid.
U.S. Patent 4,984,581, to Stic~, suggests a guidewire having a core of a shapQ memory alloy, the guidewire using the two-way memory properties of the alloy to provide both tip-deflecting and rotational movement to thQ guidewire in response to a controlled thermal stimulus. The controlled thermal stimulu~ in this instance is provided through application o~ an RF
alternating current. The alloy selected is one that has a transition temperature between 36~C and 45~C.
The temperature 36~C is chc-en because of the temperature of the human body; 45~C i8 chos~n because operating at higher temperatures could be destructive to body tissue, particularly some body proteins.

_ 2~63~14 U.S. Patent 4,991,602 to Amplatz et al., suggests a flexible guidewire made up of a shape memory alloy such as the nickel-titanium alloy known as nitinol. The guidewire i8 one having a single diameter throughout its midcourse, is tapered toward each end, and has a bead or ball at each of those ends. The bead or ball is selected to allow ease of movement through the catheter into the vA~ ture.
The guidewire is symmetrical 80 that a physician lo cannot make a wrong choice in determining which end of the guidewire to insert into the catheter. The patent suggests tha~ wound wire coils at the guidewire tip are undesirable. The patent further ~ ge_~s the use of a polymeric coating (PTFE) and an anticoagulant.
lS The patent does not suggest that any particular type of shape memory alloy or particular chemical or physical variations of these alloys are in any manner advantageous.
Another catheter guidewire using Ni-Ti alloys is described in U.S. Patent No. 5,069,226, to Yamauchi, et al. Yamauchi et al. describes a catheter guidewire using a Ni-Ti alloy which additionally contains some iron, but iB typically heat-treated at a temperature of about 400~ to 500~C so as to provide an end section which exhibits pr~~Ao-elasticity at a temperature of about 37~C and plasticity at a temperature below about 80~C. A variation is that only the end portion is plastic at the temperatures below 80~C.
U.S. Patent No. 5,171,383, to Sagae, et al., shows a guidewire pro~l~s~ from a au~a alastic alloy which is then subjected to a heat treatment such that the flexibility is sequentially increased from its proximal portion to its distal end portions. A
thermoplastic coating or coil spring may be placed on the distal portion of the wire material. Generally speaking, the proximal end portion of the guidewire ~.r - 213~63 ~4 maintains a comparatively h~gh r$gidity and the most distal end portion i8 very flexible. The proximal end section is said in the claims to have a yield stress of approximately five to seven kg/mm2 and an intermediate portion of the guidewire is shown in the claims to have a yield stress of approximately 11 to 12 kg/mm2.
Published Eu~o~ean Patent Application 0,515,201-Al also discloses a guidewire produced at least in part of a superelastic alloy. The publication describes a guidewire in which the most distal portion can be bent or ~.ved into a desired shape by a physician immediately prior to USQ in a surgical procedure. Proximal of the guide tip, the guidewire is of a superelastic alloy. Although nickel-titanium alloys are said to be most desirable of the class shown in that disclosure, no particular physical description of those alloys is disclosed to be any more desirable than another.
Published EulG~ean Patent Application 0,519,604-A2 similarly disclose~ a guidewire which may be produced from a superelastic material such as nitinol. The guidewire core is coated with a plastic jacket, a portion of which may be hyd-v~llilic and a portion of which is not.
Examples of Ni-Ti alloys are disclosed in U.S. Patent Nos. 3,174,851; 3,351,463; and 3,753,700.

None of these disclGa~e3 suggest the guidewire composition or configuration described below.

SUMMARY OF THE lNv~NllON
This invention is a guidewire, preferably a guidewire suitable for i..~.od~ction into the ~asculature of the brain, and a method for its use.
At least a distal portion of the guidewire may be of a ~ ~ ~ 6 ~ ~ 4 super-elastic alloy which preferably is a Ni-Ti alloy having specific physical characteristics, e.~., a stress-strain plateau at about 75 + 10 ksi and another at 25 ~ 7.5 ksi (each measured at 3% strain) when the s stress-strain relationship is measured to a strain of 6%.
A highly desirable variation of the inventive guidewire comprises a long wire having a proximal section, an intermediate section, and a lo distal section. The guidewire further may have an eccentricity ratio of 1 + 104. The distal end section is typically the most flexible of the sections and is at least about three centimeters long. Desirably, the flexible distal end section i8 partially tapered and is covered by a coil assembly which is co~scted to the distal end of the guidewire at its distal tip.
The coil assembly may be attached to the distal tip by soldering, perhaps after plating or coating the distal end section with a malleable or solderable metal, such as gold. The guidewire assembly may be coated with a polymer or other material to e~hAncs its ability to traverse the lumen of the catheter. A lubriciou~
polymer may be placed directly upon the core wire or upon a "tie" layer. The tie layer may be a shrink-wrap tubing or a plasma deposition or may be a dip orspray coating of an appropriate material. The tie layer may also be radio opaque.
The guidewire of this invention may be of a compositQ in which a distal portion of the core is a super-elastic alloy of the type described below and the more proximal section or sections are of another material or configuration, e.g., stainless steel wire or rod, stainless steel hypotube, super-elastic alloy tubing, carbon fiber tubing, etc.
Ideally there will be one or more radiopaque markers placed upon the guidewire, e.g., at its distal tip and potentially along the length of the ._ : " '~

-8- ~fi3 ~4 intermediate section. These markers may be used both to enhance the guidewire's radiopacity and its ability to transmit torque from the proximal end to the distal end while maintAining a desired flexibility.
A specific variation of the inventive guidewire includes a distal guidewire section having a "neck" or portion of smaller diameter surrounded by areas of larger diameter thereby allowing secure soldering of a ribbon or wire within a coil assembly which extends beyond the guidewire core distal end.
The enclosed ribbon or wire may be bent or shaped prior to insertion of the guidewire into the catheter to facilitate movement of the guidewire through turn~
in the v~cl~lAture.
Another physical variation o~ this invention involves the use of yL oo~e~ in the guidewire to e~hAnc~ flexibility in those sections without' sacrificing the guidewire's columnar strength.
This invention also includes a catheter apparatus made up of the guidewire core and a thin-walled catheter designed to be advanced along the guidewire through the vasc~llAture for positioning at a desired site.

BRI~F DESC~TPTTON OF T~ DRAWT~GS
Figure 1 shows a schematic side view (not to scale) of the major components of the inventive guidewire.
Figure 2 is a partial cutaway, side view of composite guidewire according to this invention having a distal portion of a highly elastic alloy.
Figure 3 is a partial cutaway sidQ view of one embodiment of the distal tip of the Figure 1 device.
Figure 4 is a partial cutaway side view of a second embodiment of the distal tip of the Figure 1 device.

~ff 2 ~ Z6 3 14 g Figure 5A is a partial cutaway side view of a third embodiment of the distal tip of the Figure 1 device.
Figure 5B is a partial cutaway ~op view of s the embodiment shown in ~igure 5A.
Figure 6 is a partial side view of a midsection joint in the inventive guidewire.
Figure 7 shows a typical stress-strain diagram for a Ni-Ti alloy displaying objective criteria for selection of alloys for the inventive guidewire.

DESCRIPTION OF TH~ lNv~lrON
Figure 1 shows an enlarged side view of a guidewire made according to a very desirable variation of the inventive guidewire (100). The guidewire (100) is made up of the wire core formed of a flexiblQ
torqueable wire filament material, of the alloys described below, and has a total length typically between about 50 and 300 centimeters. The proximal section (102) preferably has a uniform diameter (along its length) of about 0.010 to 0.025 ~nchr~, preferably 0.010 to 0.018 ~n~e~. The relatively more flexible distal section (104) extends for 3 to 30 centimeters or more of the distal end of the guidewire (100).
There may be a middle section (106) having a diameter intermediate between the diameter of the two portions of the wire ad;oining the middle section. The middle section (106) may be continuously tapered, may have a number of tapered sections or sectionQ of differing diameters, or may be of a uniform diameter along its length. If middle section (106) is of a generally uniform diameter, the guidewire core will neck down as is seen at (108). The distal section (104) of the guidewire (100? typically has an end cap (110), a fine wire coil (112), and a solder joint (114). The fine wire coil (112) may be radiopaque and made from a 9 2~ 3 ~ 4 materials including but not limited to platinum and its alloys. Specific inventive variations of the distal section (104) are described below. The end cap (110) may be radiopaque to allow knowledge of the position of the coil (112) during the process of inserting the catheter and traversal of the guidewire through the vasculature. All or part of the guidewire proximal section (102) and middle section (106) and distal section (104) may be coated with a thin layer (116) of polymeric material to improve it~ lubricity without adversely affecting the flexibility or shapeability of the guidewire.
Figure 2 shows a variation of the inventive guidewire which is a composite, e.g., a distal portion of the guidewire core is pro~l~ce~ of the specified alloy and the composite is of another material or configuration. In particular, the composite guidewire (140) is made up of a proximal section (142) that i~ a section of small diameter tubing of, e.g., an appropriate stainless steel or high elasticity alloy such as those ~arl~C~~~ elsewhere herein. The ~l~hlll~r proximal section (142) is att~çhD~ by soldering or by gluing or by other ~oining method suitablQ for the materials involved at the ~oint (144) to a distal section (146) that extends to the distal end of the composite guidewire assembly (140). The distal tip (148) of the catheter assembly (140) may be of the same configuration as those otherwise described herein. The catheter assembly may be coated (150) with polymeric material, as desired.
Figure 3 shows a partial cutaway of one embodiment of the distal section (104) and the distal end of the intermediate section (106). The metallic guidewire core is shown partially coated with polymer (116) and a malleable metal coating (118) on the tapered portion of the distal tip. The malleable metal may be selected from suitable radiopaque 26 3 ~ 4 materials such as gold or other easily solderable materials such as silver, platinum, palladium, rhodium, and alloys of the above. The tip also includes a radiopaque coil (112) which i5 bounded on its proximal end by a solder joint (114) and i8 joined with the end of the guidewire at (110). The radiopaque coil (112) may be made of known suitable materiala such as platinum, p~llA~ium, rhodium, silver, gold, and their alloys. Preferred is an alloy cont~in~ng platinum and a small amount of tungsten.
The proximal and distal ends of coil (112) may be secured to the core wirQ by soldering.
Figure 4 shows a partial cutaway of another embodiment of the distal section (104) of the inventive guidewire. In this emhoA~ment, the metal guidewire core has a proximal tapered portion (120), a distal tapered section (122) with a solder ~oint (114) separating the two sections, and a constant diameter tip (124). The distal tip (124) may have constant diameter typically between about 0.002 and 0.005 inches, preferably about 0.003 ~n~h~. The distal tip (124) is preferably between about 1 and 5 cm in length, preferably about 2 cm but the portion of constant diameter extends for at least about 2S% of the distancQ between the solder ~oint (128) and the solder ~oint (114). This constant diameter section marginally stiffens the distal tip assembly for ~n~nceA control. The entire distal section (104) desirably is between about 20 and 50 cm, preferably about 25 cm in length. ThQ maximum diameter of the proximal tapered portion (120) of thQ guidewire core typically is between about 0.005 and 0.020 ;n~h~, preferably about 0.010 inches. The distal tapered portion (122) and distal tip (124) are again shown with a malleable metal coating (118) such that the distal tapered portion (122) and distal tip (124) stay bent upon forming by the physician. In this 3 ~ 4 -12- Ip~ ?4 "..
embodiment, the fine wire coil (llZ) is bounded on its proximal end by a solder joint (114) and on its distal end by an end cap (110). The end cap (110) is connected to the guidewire by means of a metallic ribbon (126). The ribbon (126) may be made of stainless steel, platinum, palladium, rhodium, silver, gold, tungsten, and their alloys or other materials which are plastic and that are easily soldered. The ribbon (126) is soldered to the fine wire coil (112) and to the distal tip (124) of the distal section (104) of the guidewire at a solder joint (128) such that the end cap (110) is secured against the fine wire coil (112).
Figures 5A and 5B show yet another inventive embodiment of the distal section (104) of the guidewire (100). Figure 5A shows a side view, partial cutaway of the inventive guidewire. The fine wire coil (112) may be bounded by a polymer adhesive (136) that joins the coil (112) to the core wire and an end cap (110) and further secured to the guidewire core by a solder joint (128). In this embodiment, the distal section (104) of the guidewire again comprises a tapered portion (120) that is proximal to the polymer adhesive (136) and a tapered portion (122) that is distal to the polymer adhesive (136). The distal section (104) also comprises a smaller diameter portion (130) or "neck" that may be surrounded by optional inner coil (132). As may be seen from Figure 5A, just distal of the neck (130) is a section which is larger in side view than is the neck. The inner coil (132) may be made of a suitable metallic material preferably that is easy to solder and preferably radiopaque. It is preferably platinum or stainless steel. One way to produce neck (130) is to flatten the distal portion of the guidewire (134) distal to the neck so that the resulting spade (134) is no longer of circular cross-section but rather is of ; .:

P~ / 0 5 2 1 9 IPEA/~ '-. t~

rectangular shape. This may be more easily visualized in Figure 5B since that Figure shows a cutaway top view of the guidewire shown 3 ~ 4 in Figure 5A. As in above-described embodiments, the end cap (110) is secured to the guidewire by a metallic ribbon (126). The solder joint (128) secures the guidewire core to the inner helical coil (132) S which secures the end cap (110) via the ribbon (126) and further secures the outer fine wire coil (112).
This configuration is especially valuable for use with guidewire materials which are not easily solderable. -The solder joint need not adhere to th~ guidewire and yet the inner coil (132), ribbon (126), and outer fine wire coil (112) all are maint~ne~ as a single integral unit and have no r-h~cQ of slipping proximally or distally on the guidewire assembly.
Although the embodiment described with reference to Figures 5A and SB speaks generally of a guidewire made of a high elasticity alloy, materials for the guidewire and the ribbon such as stainless steel, platinum, p~llA~um, rhodium and the like are suitable with that embodiment.
Figure 6 is a partial side view of a midsection joint in the inventive guidewire. On many variations o~ the inventive guidewire, various sections of the core are ~oined by tapered sections such as seen at (160). This means that the guidewire core is significantly stiffer at the proximal end of the tapered ~oint (160). We have found that it is sometimes desirable to place yLoo~e-L (162) in that proximal end to lower the overall stiffness of the guidewire at that junction and yet retain the columnar strength.

G~Dg~TP~ r~ R
This guidewire is typically used in a catheter which is made up of an elongate tl~h~ r member having proximal and distal ends. The cathete~
is (again) about S0 to 300 centimeters in length, typically between about 100 and 200 centimeters in length. Often, the catheter tubular member has a relatively stiff proximal section which extends along a major portion of the catheter length and one or more relatively flexible distal sections which provide greater ability of the catheter to track the guidewire through sharp bends and turns encountered as the catheter is advanced through the to~ us paths found -~in the vasculature. The construction o~ a suitable catheter assembly having differential flexibility along its length i5 described in U.S. Patent No.
4,739,768.
We have found that certain alloys, particularly Ni-Ti alloys, retain their super-elastic properties during traversal through the v~C~ ture and yet are sufficiently pliable that they provide the physician using the guidewire with e~h~nce~ ~feel" or feedback and yet do not "whip~ during USQ . That i~ to say, as a guidewire is turned it stores energy during as a twist and releases it precipitously as it "whips"
to quickly recover the stored stress. The preferred alloys do not incur significant unrecovered strain during use. We have also found that if the eccentricity of the wire, i.e., th~ deviation of the cross-section of the guidewirQ from n ~ o~ es~
(particularly in the middle section) is main~ne~ at a very low value, the guidewire i8 much ea~ier to steer or direct through the va~ ture.
The material used in the guidewires of this invention are of shape memory alloy~ which exhibit super-elastic/pseudo-elastic shape recovery characteristics. These alloys are known. See, for instance, U.S. Patent Nos. 3,174,851 and 3,351,463 as well as 3,753,700; however, the ~700 patent describes a less desirable material becausQ of the higher modulus of the material due to an increased iron content. These metals are characterized by their ability to be transformed from an austenitic crystal ~1~6 3 ~ 4 structure to a stress-induced martensitic (SIM) structure at certain temperatures, and ~e~
elastically to the austenitic structure when the stress is removed. These alternating crystalline structures provide the alloy with its super-elastic properties. One such well-known alloy, nitinol, is a nickel-titanium alloy. It i8 readily commercially available and undergoes the austenite-SIM-austenite transformation at a variety of temperature ranges between -20~C and 30~C.
These alloys are especially suitable because of their capacity to elastically ~e~ov~r almost completely to the initial configuration once the stres~ is removed. Typically there i8 little plastic deformation, even at relativQly high strains. Thi~
allows the guidewirQ to undertake substantial bend~ as it p~sQe~ through the body'~ vA~c~lAturQ, and yet return to its original shap~ once the bend has been traversed without retA~ng any hint of a kink or a bend. However, the tips shown are often sufficiently plastic that the initial tip formation i8 re~A i n~~ .
Nevertheless, compared to similar stainless steel guidewire~, less force need b~ exertQd against the interior walls of the v~ to deform the guidewire of the invention along the desired path through the blood vessel thereby decreasing trauma to the interior of th~ blood vessel and reducing friction against the coaY~AI catheter.
A guidewire, during it~ passagQ through the vasculature to its target site, may undertake numerous bends and loops. The desirably of ~n~ncing thQ easQ
with which a guidewire may be twisted to allow the bent distal tip to enter a desired branch of the vasculature cannot be overstated. WQ have found that 3S a major factor in ~h~cing such ease of use, that is, in enhancing the controllability of the guidewires is by controlling the eccentricity of the cross-section re, ~' 6 ~ ~ ~
.,.

of the middle portion of the guidewire. We have found that by maintaining the middle portion of the guidewire (106 in Figure 1) to an eccentricity ratio of 1 i 104, the guidewire is significantly more controllable than those which fall outside this ratio.
By "eccentricity", we mean that at any point along the guidewire the ratio of the largest diameter at that cross-section to the smallest diameter of the wire at that cross-section.
To achieve these results of high strength - and e~h~nce~ control even while allowing feedback to the atten~n~ physician during use, WQ have found that the following physical paramQters o~ the alloy are important. In a stress-strain test as shown on a stress-strain diagram such as that found in Figure 7, the stress found at the midpoint of the upper plateau (UP) (measured, e.g. at about 3% strain when the test end point is about 6% strain) should be in the range of 75 ksi (thousand pounds per square inch) ~ 10 ksi and, preferably, in the range of 75 ksi + 5 ksi.
Additionally, this material should exhibit a lower plateau (LP) of 25 + 7.5 ksi, preferably 20 ~ 2.5 ksi, measured at the midpoint of the lower plateau. The material preferably has no more than about 0.25%
residual strain (RS) (when stressed to 6% strain and allowed to return) and preferably no more than about 0.15% residual strain.
The preferred material is nominally 50.6%
0.2% Ni and the remainder Ti. The alloy should contain no more than about 500 parts per million of any of 0, C, or N. Typically such commercially available materials will be sequentially mixed, cast, formed, and separately co-worked to 30-40%, ~nne~led and stretched.
By way of further explanation, Figure 7 shows a stylized stress-strain diagram showing the various parameters noted above and their measurement , ., ~.~

3 ~ ~
._ on that diagram. As stress i8 initially applied to a sample of the material, the strain is at first proportional (a) until the phase ch~ng~ from austentite to martensite begins at (b). At the upper plateau (UP), the energy i~ Gl~lceA with the applied stress is stored during the formation of the quasi-stable martensite phase or s~e6s-inAll~e~-martensite (SIM). Upon substantial completion of the phase change, the stress-strained relatio~ p again lo approaches a proportional relatio~ at (c). The stress is no longer applied when the strain reaches 6%. The measured value (UP) is found at the midpoint between zero and 6% strain, i.e., at 3% strain. If another terminal condition of strain is r-hosen, e.g., 7%, the measured valued of (UP) and (LP) would be found at 3.5%.
Materials having high UP values produce guidewires which are quite strong and allow exceptional torque transmission but cause a compromise in the resulting "straightness" of the guidewire. We have found that guidewire~ having high UP valuQs in conjunction with high LP valuQs arQ not straight.
These guidQwires are difficult to UgQ bsc~ q of their tenAency to "whip" as they arQ ~u~ -~. Again, that is to say, as a guidewirQ is turned it storQs enQrgy during as a twist and releases it quickly. The difficulty of using such a whipping guidewire should be apparent. Materials having UP values as noted above are suitable as guidewires.
Furthermore, materials having values of LP
which are high, again, are not straight. Low~ring the value of LP compromises the ability of the guidewire to transmit torque but improves the ease with which a straight guidewire may be proAl~ceA. Lowering the LP
value too far, however, results in a guidewire which, although round, has poor tactilQ response. It feels somewhat "vagueN and "soupy" during its use. The LP

-18- ~2~3 ~
values provided for above allow excellent torque transmission, straightness, and the valuable tactile response.
The values of residual strain discussed S above define a materials which do not kink or otherwise retain a "set" or configuration after stress during USQ as a guidewire.
EXAMpT.P!
In each instance, the following procedure was used in producing the data displayed in the table which follows: commercial Ni-Ti alloy wires having a nominal composition o~ 50.6% Ni and the rem~ r Ti, and diameter~ of 0.13n, 0.16n, or 0.18" were stressed at room temperature. In each instanc~, values for transition temperature, PS, UP, and LP wQrQ measured.
Additionally, several of the noted wires were introduced into a U-s~pe~ Tygon tube and spun to allow qualitative evaluation of th~ ro~ es~ and tactile response of the wires. Comments on that response are. also found in the following table.

~ -~
~=

~ w ~ ~ ~ l~
~n o u- o In o u Table Comparative Qualitative /Invention_ UP LP PS A* Spin Test ~ (C/I) !ksi)_ (ksi) (%~
1l I 74.48 31.45 0.06 -11Smooth rotation, good feel 22 I 76.94 18.90 0.121 -8Smooth rotation, good feel 33 I 71.92 ¦ 24.06 0.10 13.5 Smooth 44 l C 78.24 ¦ 58.82 0.20 -9Very rough turning, whipped 55 l C 63.80 ¦ 13.25 ¦ 0.2 12.5Smooth turninq, mushy feel I ¦ 58.30 ¦ 13.31 ¦ 0.0 ¦ -12¦Turned roughly, mu~hy feel . _ ___ _ ~ C ~ ~ ~ _ Difflcult to turn 1 Commercially available from U.S. Nitinol, Inc.
2 Commercially available from Special Hetals, Inc. ~9 3 Commercially available from Shape Netal Alloys, Inc.
4 Commerci~lly available a~ a pla~tic coated 0.13~ guidewire from Fu~i Terumo, Inc.
Commercially available from ITI.
6 Co~mercially available from Netal Tek 7 Stainles~ Steel * Measured at room temperature with no applied ~tress.

,~ a ~ ~ 3 ~ ~

These data describe both guidewires made according to the invention and comparative guidewires.
Additionally, they show that guidewire made from a typical stainless steel alloy is very difficult to turn using the qualitative test described above.

GUIDE~IRE C~R~ COATIN~8 As mentioned above, all or part of the guidewire core may be covered or coated with one or morQ layers of a polymeric material. The coating is applied typically to ~hAns~~ the lubricity of the guidewire c,ore during its traversal of the catheter lumen or the vascular walls.

Coating Materials As noted above, at least a portion of the guidewire core may simply be coated by dipping or spraying or by similar procQss with such materials as polysulfones, polyfluorocarbons (such as TEFLON), polyolefins such as polyethylene, polypropylene, polyesters (including polyamidQs such as the NYLON's), and polyurQ~h~nes; thQir blends and copolymQrs such as polyethQr block amides (e.g., PEBAX).
It i8 often desirablQ to utilize a coating such as ~r~~ ust abovQ on the proximal portion of the guidewirQ and a coating such as discussed below on thQ more distal sections. Any mixture of coatings placed variously on the guidewir~ is acceptablQ as chosen for the task at hand.
The guidewire core may also be at least partially covered with other hydlo~l.ilic polymQrs including those made from monomer~ such as ethylenQ
oxide and its higher homologs; 2-vinyl pyridine; N-vinylpyrrolidone; polyethylene glycol acrylates such as mono-alkoxy polyethylene glycol mono(meth) acrylates, including mono-methoxy triethylene glycol mono (meth) acrylate, mono-methoxy tetraethylene * tradc ~ rk ~,j, 6 ~ ~ 4 glycol mono (meth) acry-late, polyethylene glycol mono (meth) acrylate; other hydrophilic acrylates such as 2-hydroxyethylmethacrylate, glycerylmethacrylate;
-acrylic acid and its salts; acrylamide and acrylonitrile; acrylamidomethylpropane sulfonic acid and its salts cellulose, cellulose derivatives such as methyl cellulose ethyl cellulose, carboxymethyl cellulose, cyanoethyl cellulosQ, cellulosQ acetate, polysaccharides such as amylose, pectin, amylopectin, alginic acid, and cross-lin~e~ heparin; maleic anhydride; aldehydes. ThesQ monomers may be formed into homopolymers or block or random copolymers. The use of oligomers of these monomers in coating the guidewire for further polymerization i8 al~o an alternative. Preferred ~e~sors includ~ ethylene oxide; 2-vinyl pyridine; N-vinylpyrrolidone and acrylic acid and its salts; acrylamide and acrylonitrile polymerized (with or without substantial crosslin~ing) into homopolymers, or into random or block copolymers.
Additionally, hy~l~yhobic monomers may be included in the coating polymeric material in an amount up to about 30% by weight Or the resulting copolymer so long as the hydrophilic nature of the resulting copolymer is not substantially compromised.
Suitable monomers include ethylene, propylene, styrene, styrene derivatives, alkylmethacrylates, vinylchloride, vinyli~n~chloridQ, methacrylonitrile, and vinyl acetate. Pre~erred are ethylene, propylene, styrene, and styrene derivatives.
The polymeric coating may be cross-linked using various terh~iques~ e.g., by light such as ultraviolet light, heat, or ionizing radiation, or by peroxides or azo compounds such as acetyl peroxide, cumyl peroxide, propionyl peroxide, benzoyl peroxide, or the like. A polyfunctional monomer such as divinylbenzene, ethylene glycol dimethacrylate, f '~
~.L.: ~

trimethylolpropane, pentaerythritol di- (or tri- or tetra-) methacrylate, diethylene glycol, or polyethylene glycol dimethacrylate, and similar multifunctional monomer~ capable of linking the monomers and polymers ~cll~re~ above.
Polymers or oligomers applied using the proceAllre described below are activated or functionalized with photoactive or radiation-active y ou~s to permit reaction of the polymer~ or oligomers lo with the underlying polymeric surface. Suitable activation groups include benzophenone, thioxanthone, and the like, acetophenone and its derivatives specified as:
Ph C-O
R' where R' iS H, R2 ig OH, R3 ig Ph; or R' is H, R' ig an alkoxy group including -O CH3, -O C2H3, R3 i8 Ph; or 2 0 R' -- R'-- an alkoxy group, ~ is Ph; or R' = R' -- an alkoxy group, R3 i~2 H; or R' = R' = C 1, R3 ig H or Cl.
Other known activators are suitable.
The polymeric coating may then be linked 2 5 with the substrate using known and appropriate t~c~niques selected on the basis of the chosen activators, e.g., by ultraviolet light, heat, or ionizing radiation. Crossl~nk~ng with the listed polymer~ or oligomer~ may be accomplished by use of peroxide~ or azo compounds such as acetyl peroxide, cumyl peroxide, propionyl peroxide, benzoyl peroxide, or the like. A polyfunctional monomer such a~
divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane, pentaerythritol di- (or tri- or tetra-) methacrylate, diethylene glycol, or polyethylene glycol dimethacrylate, and similar multifunctional monomers capable of linking the ),~,j ~ 9 ~ 4 . .

polymers and oligomers discussed above is also appropriate for this invention.
The polymeric coating may be applied to the guidewire by any of a variety of methods, e.g., by spraying a solution or suspension of the polymers or of oligomers of the monomers onto the guidewire core or by dipping it into the solution or 3-~r~ion.
Initiators may be included in the solution or applied in a separate. step. The guidewire may be sequentially or simultaneously dried to remove solvent after application of the polymer or oligomer to the guidewire and~crossl~nke~.
The solution or ~U~p~ncion ~hould be very dilute since only a very thin layer of polymer is to be applied. We have found that an amount of oligomer or polymer in a solvent of between 0.25% and 5.0%
(wt), preferred i~ 0.5 to 2.0% (wt), i~ excellent for thin and complete coverage of the resulting polymer.
Preferred solvents for this ~oce~ e when using the preferred polymers and pro~ e are water, low mol~c~l Ar weight alcohols, and ethers, especially methanol, propanol, isopropanol, ethanol, and their mix~uLe_. Other water miscible solvents, e.g., tetrahydrofuran, methylene dichloride, 2s methylethyl~etone, dimethylacetate, ethyl acetate, etc., are suitable for the listed polymers and must be r~o~~n according to the characteristics of the polymer; they should be polar because of the hyd~ophilic nature of the polymers and oligomers but, because of the reactivity of the terminal ~L OU~ - of those materials, known q~ ng effects caused by oxygen, hydroxyl ~ou~s and the like must be r~co~nized by the user of this process when choosing polymers and solvent systems.
Particularly preferred as a coating for the guidewire cores discllcse~ herein are physical mixtures of homo-oligomers of at least one of polyethylene ~F

~1~6 ~ ~ 4 oxide; poly 2-vinyl pyridine; polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, and polyacrylonitrile. The catheter bodies or substrates are preferably sprayed or dipped, d~ied, and irradiated to produce a polymerized and crosslinked polymeric skin of the noted oligomers.
The lubricious hy~.G~hilic coating is preferably produced using generally simultaneous solvent removal and crossli nk~ ng operations. The coating is applied at a rate allowing "sheeting" of the solution, e.g., formation of a visibly smooth layer without nruns~. In a dipping operation for use with most polymeric substrates including those noted below, the optimum co~ting rate~ are found at a linear removal rate between 0.25 and 2.0 in~h~/seC~
preferably 0.5 and 1.0 ~n~h~s/sec.
The solvent evaporation operations may be conducted using a heating chamber suitable for main~ining the surface at a temperature between 25~C
and the glass transition temperature (T~) of the underlying substrate. Preferred temperatures are 500C
to 125~C. Most preferred for th~ noted and preferred solvent systems is the range of 75~ to 110~C.
Ultraviolet light sou~ may be used to crosslink the polymer ~.e~ ors onto the substrate.
Movement through an irradiation chamber having an ultraviolet light source at 90-375nm (preferably 300-350nm) having an irradiation density of 50-300 mW/cm2 (preferably 150-250 mW/cm2) for a period of three to seven ~ecQn~ is desired. Passage of a guidewire core through the chamber at a rate of 0.25 to 2.0 inches/seco~ (0.5 to 1.0 ;n~hea/~o~) in a chamber having three to nine inches length is suitable. When using ionizing radiation, a radiation density of 1 to 100 kRads/cm2 (preferably 20 to 50 kRads/cm2) may be applied to the solution or suspension on the polymeric substrate.

'"~

~63 ~4 Exceptional durability of the resulting coating is produced by repetition of the dipping/solvent removal/irradiation steps up to five times. Preferred are two to four repetitions.

Tie LaYers We have found that it is often desirable to incorporate a "tie" layer a~ a coating between the outer polymeric surface and the guidewire core to enhance the overall adhesion of the outer polymeric surface to thQ core. Of course, these materials must be able to t~lerate thQ various other solvents, cleaners, sterilization procedures, etc. to which the guidewire and its comron~ts are placed during other production steps.
Choice of materials for such tie layers is determined through their functionality. Specifically, the materials ar~ cho~~n for thQir affinity or tenacity to the outer polymeric lubricious or hyd-G~llilic coating. Clearly, the tie layer material must be flexible and 4~GI~. The material must be extrudablQ and prefQrably easily made into shrinkablQ
tubing for mounting onto the guidewire through heating. We have found that variou~ NYLON's, polyethylenQ, poly4 ~yL ene, polyurQthane, and preferably polyethylenQ terephthalatQ (PET) make excellent tie layers. ThesQ tubing materials may be also formulated to include radio opaque materials such as barium sulfate, bismuth trioxidQ, bismuth carbonate, L~i~s~en, tantalum or thQ like.
As noted above, one readily achievablQ
manner of applying a tie layer is by hQat-shr1n~n~
the tubing onto the guidewirQ. The guidewirQ core i8 simply inserted into a tubing of suitable size --often with a small amount of a "calllk~n~" at eitherend to seal the tubing from incursion of fluids or unsterile materials from beneath the tubing. The tubing is cut to length and heated until it is sufficiently small in size. The resulting tubing tie layer desirably is between about 0.0025 and 0.015 inches in thickness. The thinner layers are typically produced from polyurethane or PET. The layer of lubricious polymer is then placed on the outer surface of the shrunk tubing.
Another proce~llrQ for preparing or pretreating guidewires prior to receiving a mlhAs~uent coating of a polymer, preferably a polymer which is lubricious, biocompatible, and hydkophilic, i8 via the use of a plasma stream to deposit a ~d~ocarbon or fluorocarbon residue. The PL Gre-l~lrQ is described as follows: the guidewire core i8 placed in a plasma chamber and cleaned with an oxygen plasma etch. The guidewire core is then ~YpO-~ to a h~d.o arbon plasma to deposit a plasma-polymerized tie layer on the guidewire core to complete the pretreatment. The hydrocarbon plasma may comprise a lower mole~llAr weight (or gaseous) AlkAn~ such as methane, ethane, propane, isobutanQ, butane or the like; lower moleclllAr weight ~lk~n~- such a~ ethene, propene, isobutene, butene or the like or; g~r~
fluorocarbons such a~ tetrafluoromethane, trichlorofluoromethane, dichlorodifluoromethane, trifluorochloromethane, tetrafluoroethylene, trichlorofluoroethylene, dichlorodifluoroethylene, trifluorochloroethylene and other such materials.
Mixture~ of these materials are also acceptable. The tie layer apparently provides C-C bond~ for 3-lh~e~uent covalent bonding to the outer hyd~o~hilic polymer coating. Preferred flow rates for the l.ydkG~arbon into the plasma chamber are in the range of 500 c.c./min. to 2000 c.c./min. and the residence time of the guidewire in the chamber is in the range of 1-20 minutes, dPpDn~ing on the cho~en hy~G arbon and the plasma chamber operating parameters. Power settings "~ 2 ~ 4 for the plasma chamber are preferably in the range of 200W to 1500W.
A tie layer of plasma-produced hydrocarbon residue having a thickness on the order of loA thick is dispo~ed between core and coating. This procesa typically produces layers of hydrocarbon residue lesa than about loOOA in thickness, and more typically less than about loOA. Tie layer effectively bonds the outer layer to the guidewire core while adding very little additional bulk to the guidewire. Guidewires made according to this invention therefore avoid the size and maneuverability problems of prior art guidewires.
The pretreated guidewire may be coated by a polymer u~ing a proced~Q such as de~cribed above. For example, the pretreated guidewire may be dipped in a solution of a photoactive hy~G~hilic polymer system, i.e., a latently photoreactive binder group covalently bonded to a hydrophilic polymer. After drying, the coated guidewire i~ cured by exposing it to W light.
The W light activates the latently reactive group in the photoactive polymer system to form covalent bond~
with crosslinked C-C bonds in the hyd~o~arbon re~idue tie layer. The dipping and curing steps are preferably repeated often enough, typically twice, to achievQ th~ appropriate thi~knec~ of the hydrophilic coating layer.
One highly preferred variation of the invention involves a guidewire with metal core, preferably 0.010 to 0.025" thick stainless steel or nitinol. The exterior surface of guidewire is a biocompatible coating of a polyacrylamide/polyvinylpyrrolidone mixture bonded to a photoactive binding agent. The preferred coating is made from a mixture of Bio-Metric Sy~tems PA03 and PV05 (or PV01) binding systems according to the Examples below.

* trade-mark -28- 2~ ~6 ~ ~ 4 The photoactive hydrophilic polymer system of this preferred embodiment is a mixture of Bio-Metric Systems PA03 polyacrylamide/binder system and Bio-Metric Systems PV05 polyvinylpyrrolidone system.
The polyacrylamide system provides lubricity, and the polyvinylpyrrolidone system provides both lubricity and bin~g for durability. The exact proportions of the two systems may be varied to suit the application.
As an alternative, however, the hyd~o~llilic biocompatible coating may be polyacrylamide alone, polyvinylpyrrolidone alone, polyethylene oxide, or any suitable coating known in the art. In addition, a coating of heparin, albumin or other proteins may deposited over the hydrophilic coating in a manner known in the art to provide additional biocompatibility features.
The guidewire or other devicQ may be cleaned by using an argon plasma etch in place of the oxygen plasma etch. The thic~ of the plasma-polymerized tie layer may also vary without departing from tho scope of this invention.
The following examplQs are further illustrative of the articlQs and mQthods of thi~
invention. The invention is not limited to these examples.

Example A 0.016" diameter nitinol guidewire was placed in a Plasma Etch MK II plasma chamber and cleaned with an oxygen plasma for 10 minutes. Methane flowing at a rate of 2000 c.c./min. was admitted into the chamber, and the chamber operated at a power setting of 400W for 2 minutes to deposit a hydrocarbonaceous residue onto the surface of the wire. All but approximately six inches of the wire was dipped in a polyvinylpyrrolidone/polyacrylamide * trade-mark "r ~ -29- ~ ~ ~ 63~4 (PVP/PA) photocrosslinkable solution of a mixture of 67% BSI PV01 and 33% BSI PA03. The coated guidewire was then dried and exposed to an ultraviolet light (325 nm.) for 8 seconds. The dipping, drying, and exposing steps were repeated tWiCQ. When wetted, the resulting wire felt lubricious and required less force to pull through an 0.018" ID catheter than an uncoated wire.

Example A 0.016" diameter nitinol guidewire was placed in a Plasma Etch NK II plasma chamber and cleaned with an oxygen plasma for 10 minutes. Methane flowing at a rate of 1500 c.c./min. was admitted into the chamber, and the chamber was operated at a power setting of 600W for 5 minutes to plasma-treat the methane into a hydrocarbon~cqs~ residue on the surface of the wire. All but approx~mately six inches of the wire was dipped in a polyvinyl-pyrrolidone/polyacrylamide (PVP/PA) photocrosslinkablesolution consi~ting essentially a mixture of 50% BSI
PV01 and 50% BSI PA03. The coated guidewire was then dried and ex~o--cd to an ultraviolet light (325 nm.) for 8 seconds. The dipping, drying, and exposing steps were repeated. When wetted, the resulting wire felt lubricious and required less force to pull through an 0.018" ID catheter than an uncoated wire.

Example A 0.016" diameter nitinol guidewire was placed in a Plasma Etch MR II plasma chamber and - cleaned with an oxygen plasma for 10 minutes. Ethane flowing at a rate of 900 c.c./min. was admitted into the chamber, and the chamber was operated at a power 35 setting of 600W for 10 minutes to deposit a hydrocarbon residue onto the surface of the wire. All but approximately six inche~ of the wire was dipped in .~ .

- 2 7 ~
.~_ a polyvinylpyrrolidone/polyacrylamide (PVP/PA) photocrosslinkable solution of a mixture of 33% BSI
PV01 and 67% BSI PA03. The coated guidewire was then dried and exposed to an ultraviolet light (325 nm.) for 8 seconds. The dipping, drying, and exposing steps were repeated twice. When wetted, the resulting wire felt lubricious and required less force to pull through an 0.018" ID catheter than an uncoated wire.

Although preferred embodiments of the present invention have been described, it should be understood that various c~n~, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the claims which follow.

. .,, ~
,~,~ ,.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERT
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A guidewire suitable for guiding a catheter within a body lumen, comprising an elongated, flexible metal wire core of a super-elastic alloy characterized by a stress-strain curve having an upper plateau of 75 ksi + 10 ksi, a lower plateau of 25 ksi +
7.5 ksi measured at 3% strain and a residual strain of less than 0.25% where measured in a stress-strain test to 6% strain.

2. The guidewire of claim 1 where the guidewire has a eccentricity ratio of 1+10.

3. The guidewire of claim 1 having a distal section, a middle section, and a proximal section.

4. The guidewire of claim 1 in which the super-elastic alloy is Ni-Ti.

5 . The guidewire of claim 3 in which the distal section is tapered to a point.

6. The guidewire of claim 5 in which the distal section is coated with a malleable metal.

7 . The guidewire of claim 6 in which the malleable metal is selected from the group consisting of gold, nickel, silver, platinum, palladium and alloys thereof.

8. The guidewire of claim 6 in which at least a portion of the malleable metal coating on the distal portion is covered by an outer coil comprising platinum, tungsten, or an alloy thereof.

9. The guidewire of claim 4 in which the distal section comprises a proximal tapered portion and a constant diameter distal portion.

10. The guidewire of claim 9 in which the distal section is coated with a malleable metal.

11. The guidewire of claim 10 in which the malleable metal is selected from the group consisting of gold, silver, platinum, palladium and alloys thereof.

12. The guidewire of claim 11 in which at least a portion of the malleable metal coating on the distal portion is covered by an outer coil comprising platinum, tungsten, or an alloy thereof.

13. The guidewire of claim 11 wherein an inner coil surrounds the constant diameter distal portion.

14. The guidewire of claim 13 wherein the inner coil comprises a radiopaque metal selected from the group consisting of platinum, tungsten, and an alloy of platinum and tungsten.

15. The guidewire of claim 14 wherein a metallic ribbon secures the wire core to the inner coil and further to the outer coil.

16. The guidewire of claim 4 in which the distal section comprises a necked down portion of smaller diameter than its surrounding distal section.

17. The guidewire of claim 16 in which at least a portion of the necked down section of the distal portion is covered by an outer coil.

18. The guidewire of claim 17 in which the outer coil is connected at its distal end by a ribbon joined to the necked down section of the distal portion.

19. The guidewire of claim 18 in which an inner coil is secured between the ribbon and the necked down section all within the outer coil.

20. The guidewire of claim 1 in which at least a portion of the guidewire is coated with a polymeric material.

21. The guidewire of claim 20 where the polymeric material comprises polymers produced from monomers selected from the group consisting of ethylene oxide; 2-vinyl pyridine; N-vinylpyrrolidone;
polyethylene glycol acrylates mono-methoxy triethylene glycol mono (meth) acrylate, mono-methoxy tetraethylene glycol mono (meth) acrylate, and polyethylene glycol mono (meth), acrylate; other hydrophilic acrylates 2-hydroxyethylmethacrylate and glycerylmethacrylate;
acrylic acid and its salts; acrylamide and acrylonitrile; acrylamidomethylpropane sulfonic acid and its salts; cellulose; cellulose derivatives; methyl cellulose ethyl cellulose, carboxymethyl cellulose, cyanoethyl cellulose, cellulose acetate; and polysaccharides amylose, pectin, amylopectin, alginic acid, and cross-linked heparin.

22. The guidewire of claim 21 additionally comprising a tie layer disposed between the polymeric layer and the guidewire core.

23. The guidewire of claim 22 where the tie layer disposed between the polymeric layer and the guidewire core is a heat shrunk tubing.

24. The guidewire of claim 23 where the tie layer disposed between the polymeric layer and the guidewire core is a heat shrunk tubing comprising a material selected from the group consisting of polyethylene terephthalate and polyurethane.

25. The guidewire of claim 23 where the tie layer disposed between the polymeric layer and the guidewire core is a heat shrunk tubing and further comprises a radiopaque material.

26. The guidewire of claim 22 where the tie layer disposed between the polymeric layer and the guidewire core is deposited by plasma.

27. The guidewire of claim 1 additionally comprising a catheter sheath.

28. A guidewire suitable, for guiding a catheter within a blood vessel, comprising an elongated flexible metal wire core having a distal section, wherein the distal section comprises a necked down portion of smaller diameter than its surrounding distal section and wherein an outer coil surrounds at least a portion of the distal section and wherein an outer coil surrounds at least a portion of the distal section comprising at least the smaller diameter portion and wherein a metallic ribbon secures the outer coil to the smaller diameter portion of the distal section.

29. The guidewire of claim 28 wherein an inner coil is located within the smaller diameter portion of the distal section.

30. The guidewire of claim 28 wherein the wire core comprises a material selected from the group consisting of super-elastic alloys, stainless steel, platinum, palladium, rhodium and alloys thereof.

31. The guidewire of claim 30 where the material is a Ni-Ti alloy.

32. The guidewire of claim 28 wherein the outer coil comprises a radiopaque material selected from the group consisting of platinum, tungsten, and an alloy of platinum and tungsten.

33. The guidewire of claim 29 wherein the inner coil comprises a radiopaque material selected from the group consisting of platinum, tungsten and an alloy of platinum and tungsten.

34. A guidewire suitable for guiding a catheter within a blood vessel, comprising an elongated flexible metal wire core of a super-elastic alloy having a tie layer disposed about at least a portion of the core, where said tie layer has been shrunk onto the wire core.

35. The guidewire of claim 34 where the super-elastic alloy material is a Ni-Ti alloy.

36. The guidewire of claim 34 where the tie layer comprises at least one of NYLON, polyethylene, polystyrene, polyurethane, and polyethylene terephthalate.

37. The guidewire of claim 34 where the tie layer comprises polyethylene terephthalate or polyurethane.

38. The guidewire of claim 36 where the tie layer further comprises one or more radio opaque materials selected from the group consisting of barium sulfate, bismuth trioxide, bismuth carbonate, tungsten, and tantalum.

39. The guidewire of claim 34 additionally comprising a layer disposed about the tie layer comprising polymers produced from monomers selected from the group consisting of ethylene oxide; 2-vinyl pyridine; N-vinylpyrrolidone; polyethylene glycol acrylates; other hydrophilic acrylates acrylic acid and its salts; acrylamide and acrylonitrile;
acrylamidomethylpropane sulfonic acid and its salts;
cellulose; cellulose derivatives; and polysaccharides.

40. The guidewire of claim 21 or 39, wherein the polyethylene glycol acrylate is a mono-alkoxy polyethylene glycol mono(meth) acrylate selected from the group consisting of mono-methoxy triethylene glycol mono (meth) acrylate, mono-methoxy tetraethylene glycol mono (meth) acrylate, and polyethylene glycol mono (meth) acrylate; other hydrophilic acrylates.

41. The guidewire of claim 21 or 39, wherein the polyethylene glycol acrylate is a hydrophilic acrylate selected from the group consisting of 2-hydroxyethylmethacrylate and glycerylmethacrylate.

42. The guidewire of claim 21 or 39, wherein the polyethylene glycol acrylate is a cellulose derivatives selected from the group consisting of methyl cellulose ethyl cellulose, carboxymethyl cellulose, cyanoethyl cellulose, cellulose acetate.

43. The guidewire of claim 21 or 39, wherein the polyethylene glycol acrylate is a polysaccharides selected from the group consisting of amylose, pectin, amylopectin, alginic acid, and cross-linked heparin.