CA2181154A1 - Guidewire with superelastic distal portion - Google Patents

Abstract

An improved guidewire for advancing a catheter within a body lumen which has a high strength proximal portion, a distal portion formed of superelastic alloy and a connector formed of superelastic alloy to provide a torque transmitting coupling between the distal end of the proximal portion and the proximal end of the distal portion. The superelastic alloy elements are preferably cold worked and then heat treated at a temperature well above the austenite-to-martensite transformation temperature, while being subjected to longitudinal stresses equal to about 5 to about 50 % of the room temperature yield stress to impart to the metal a straight "memory". The guiding member using such improved material exhibits a stress induced austenite-to-martensite phase transformation at an exceptionally high constant yield strength of at least 70 ksi for solid members and at least 50 ksi for tubular members with a broad recoverable strain of at least about 4 % during the phase transformation.

Description

WO 9~i/19800 2 ~ 8 ~1~4 PCTNS94/00468 GUIDEVVIRE Wl'l'~l ~U~!;~;LAs~lc DBTAL PORTION
BAC~GROUND QF T~l~ VENTION
This invention relates to the field of medical devices, and more particularly to guiding means such as a guidewire for advancing a catheter within a body lumen in a lu~u~lu~e such as percutaneous transluminal coronary angioplasty (PTCA).

In a typical PTCA ,u~u~elul~ a guiding catheter having a prefor~ned distal tip is percutaneously intrûduced into the cardiovascular system of a patient in a conventional Seldinger technique and advanced therein until the distal l;ip of the guiding catheter is seated in the ostium of 10 a desired coronary artery. A guidewire is p-~it.ion~rl 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 , . _ _ _ _ _ _ . . .. .

2181~ ~

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 i~ vdu~ el guidewire until the balloon of the dilatation 5 catheter iB properly p-~itit~nPd across the lesion. Once in position across the lesion, the balloon is inflated to a pre~l~tPrminPd size with radiopaque liquid at relatively high pressures (e.g greater than 4 ~tm~cphPres) to compress the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then 10 deflated so that blood flow is resumed through the dilated artery and the di-latation catheter can be removed therefrom.

Conventional guidewires for angioplasty and other vascular IJ~V~.edUI~,3 usually comprise an elongated core member with one or more 15 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 20 plug at the distal end of the flexible body. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient's vascular system.

- 2 -WO 95/19800 2 18 1 1~ PCT/US94100468 Further details of ~ tsltit)n catheters, guidewires, and devices :l~Ro~i~tP~ therewith for angioplasty ~ ,6du~:B can be found in U.S. Patent 4,323,071 (Simpson-Robert); U.S. Patent 4,439,185 (Lundquist); U.S. Patent 4,516,972 (Samson); U.S. Patent 4,538,622 (Samson et aL); U.S. Patent 4,554,929 (Samson et a~); U.S. Patent 4,616,652 (.~imr~nn); and U.S. Patent 4,638,805 (Powell) which are hereby illcolluuldl~d herein in their entirety by reference thereto.

Steerable dilatation catheters with fixed, built-in guiding members, such as described in U.S. Patent 4,582,181 (now Re 33,166) are frequently used because they have lower deflated profiles than conventional over-the-wire ~ tsltitm catheters and a lower profile allows the catheter to cross tighter lesions and to be advanced much deeper into a patient's coronary anatomy.

A major requirement for guidewires and other guiding mem-bers, whether they be solid wire or tubular members, is that they have sufficient column strength to be pushed through a patient's vascular system 20 or other body lumen without kinking. However, they must also be flexible enough to avoid rl~m~EinE the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the

- 3 -WO 95/19800 2 1 8 ~ ~ S4 PCTIUS94100468 strength and flel~ibility of guidewires to make them more suitable for their intended uses, but these two properties a~ e for the most part diametrically opposed to one another in that an incrèase in one usually involves a decrease in the other.

The prior art makes reference to the use of alloys such as Nitinol (Ni-Ti alloy) which have shape memory andlor superelastic ~I~a~ Lics in medical devices which are designed to be inserted into a patient's body. The shape memory characteristics allow the devices to be 10 deformed to facilitate their insertion into a body lumen or cavity and then be heated within the body so that the device returns to~its original shape.
Superelastic characteristics on the other hand generally allow the metal to be deformed and restrained in the deformed condition to facilitate the insertion of the medical device rcmt.~inin~ the metal into a patient's body, 15 with such (lPfnrm~tion causing the phase ~Idll~rullllation. Once within the body lumen the restraint on the superelastic member can be removed, thereby reducing the stress therein so that the superelastic member can return to its original undeformed shape by the ~ r". "~,-t.ion back to the original phase.

Alloys having shape Illt llluly/~u,ut~l~lastic char~rtPri~ti~ c generally have at least two phases, a martensite phase, which has a

- 4 -WO gS/19800 2 ~ 811~ PCT/IJS941(1O468 ^, ; .
relatively low tensile strength and which is stable at relatively low tt:lllu~ldlul~s, and an austenite phase, which has a relatively high tensile strength and which is stable at tc~lllye~d~ulèS higher than the martensite phase.

Shape memory characteristics are imparted to the alloy by heating the metal at a t~.lp~dL-~ above which the ~li17~r~. ""1~ n from the martensite phase to the austenite phase is complete, i.e. a t~ d~u~è
above which the austenite phase is stable. The shape of the metal during 10 this heat treatment is the shape "remembered". The heat treated metal is cooled to a tt:lll,uc:ldLU~t: at which the martensite phase is stable, causing the austenite phase to l~dll~rullll to the llldlLt~ e phase. The metal in the martensite phase is then plastically deformed, e g to facilitate the entry thereof into a patient's body. Subsequent heating of the deformed 15 martensite phase to a temperature above the martensite to austenite -. ",,-l.ion tt:--lU~,ld~lllt~ causes the deformed martensite phase to transform to the austenite phase and during this phase transformation the metal reverts back to its original shape.

The prior methods of using the shape memory ch~ listics of these alloys in medical devices intended to be placed within a patient's body presented operational ~liffi~ lti~C For e~ample, with shape memory alloys

- 5 -WO95/19800 2~81154 PCT~Ss4mn4Cs --having a stable martensite LelllueldLu~e below body temperature, it was frequently diff1cult to maintain the temperature of the medical device rnnt.~inine such an alloy sllffiripnt~ly below body temperature to prevent the LL~rullllalion of the martensite phase to the austenite phase when the 5 device was being inserted into a patient's body. With intravascular devices formed of shape memory alloys having martensite-to-austenite tr~n~fnrTn~t.inn telllue~Lu~ek well above body telll~uelu-lule7 the devices could be introduced into a patient's body with little or no problem, but they had to be heated to the martensite-to-austenite transformation t~llluel~lLu~è
10 which was frequently high enough to cause tissue damage and very high levels of pain.

When stress is applied to a specimen of a metal such as Nltinol P~hihit.inF superelastic char~rtPri~tirq at a Leu~ Luue at or above which 15 the tr~n~fnrrnS~tinn of martensite phase to the austenite phase is complete, the specimen deforms elastically until it reaches a particular stress level where the alloy then ulldel~ues a stress-induced phase LLUII~r(II ",ul.inn from the austenite phase to the martensite phase. As the phase transformation proceeds, the alloy ul~d~J ~u~k ~iEnifirslnt. increases in strain but with little 20 or no ~ullr~lJ~ linE increases in stress. The strain increases while the stress remains essentially constant until the L~un~rul~ Lion of the austenite phase to the martensite phase is complete. Thereafter, further increase in

- 6 --WO 9S/19800 21 8 1 15 ~ PCT/US94/i`1!468 ,, ~
stress are neceæsary to cause further deformation. The ~ iLic metal first yields elastically upon the application of ~r~lit.ion~l stress and then plastically with permanent residual deforrnation.

If the load on the specimen is removed before any pPrm~n~nt ri~fnrms3tirm has occurred, the lll~l,~ll,i~ic 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 lll~rlr~ ilr phase transforms back into the austenite phase, the stress level in the specimen will remain essentially constant (but sllh~+S-nt.i:~lly less than the constant stress level at which the austenite Ll~ ,rJlllls to the ",aLl~ r-) until the transformation back to the austenite phase is complete, i.e. there is si~nifir7lnt recovery in strain with only n~ligih7f, ~ul~ ,..".lir.~ stress reduction. After the l~ "~ lion back to austenite 15 is complete, further stress reduction results in elastic strain reduction. This ability to incur ~i~nific~nt. strain at relatively constant stress upon the application of a load and to recover from thç deformation upon the removal of the load is commonly referred to as superelasticity or pse~ Q+irity.

.

The prior art makes reference to the use of metal alloys having superelastic characteristics in medical devices which are intended to be inserted or otherwise used within a patient's body. See for e~ample, U.S.

- 7 -WO 95/19800 2 1 8 1 t 5 ~ PCT/US94/00468 ;: .
Patent 4,665,905 (~ervis) and U.S. Patent 4,925,445 (Sakamoto et al.).

The Sakamoto et Ql. patent discloses the use of a nickel-titanium superelastic alloy in an illLr~v,~b1.11ar guidewire which could be 5 processed to develop relatively high yield strength levels. However, at the relatively high yield stress levels which cause the austenite-to-l.l~ L~l~iL~
phase transformation characteristic of the material, it did not have a very extensive stress-induced strain range in which the austenite Llall~rul~lls to martensite at relative constant stress. As a result, frequently as the 10 guidewire was being advanced through a patient's tortuous vascular system, it would be 6tressed beyond the superelastic region, i.e. develop a p~
set or even kink which can result in tissue damage. This p~rm~n~nt deformation would generally require the removal of the g udewire and the rerl~ ~m~nt thereof with another.

Products of the Jervis patent on the other hand had e~tensive strain ranges, i e. 2 to 8% strain, but the relatively constant stress level at which the austenite transformed to martensite was very low, e.g 50 ksi.

In copending application Serial No. 07/629,381, filed December 18, 1990 entitled Superelastic Guiding Member, guide wires or guiding members are described which have at least a solid or tubular portion

- 8 -WO 95/19800 2 ~ 8 i 154 PCTIUS94/00468 , 'l I .
thereof P~hihitin~ superelastic characteristics including an extended strain region over a very high, relatively constant high s.tress level which effects the austenite L~r<,lllla~ion to martensite. While the properties of the guidewire formed of the superelastic material were very advantageous, it 5 was found that the guidewires and g~uding members formed of materials having superelastic characteristics did not have optimum push and torque characteristics.

SUMMARY OF TT~F, INV~,l~TION

The present invention is directed to improve guidewires or guiding members, wherein the distal portion is provided with superelastic cl~ ics resulting from the stress-induced ~ r.,. "~;~til~n of auste~lite to .lldr~ e and wherein the proximal portion is provided with high strength elastic m~t.oriA 1~

The guidewire or guiding member of the invention has a high strength proximal section with a high strength distal section with superelastic properties and a connector element between the proximal and 20 distal sections which has superelastic properties to provide a smooth - transition between the proximal and the distal sections. In a presently preferred embodiment the guidewire or guiding member has a solid core , WO ssrlssoo 2 18 1 154 PCTIIL'S94/00468 , distal section formed of superelastic materials such as NiTi type alloys and the connector is a hollow tubular shaped member which has a inner passageway adapted to receive the proximal end of the solid core distal section.

The superelastic distal core member and the hollow connector of the invention exhibit stress-induced phase ~ ,ruLllld~ion at body ~:LILp~idLu~ (about 37 C) at a stress level well above about 50 ksi, preferably above 70 ksi and in many cases above about 90 ksi. The 10 complete stress-induced iLd~,rulllldLion of the austenite phase to the martensite phase causes a strain in the specimen of at least about 4%, preferably over 5%. The region of phase ~ r~,. ",~t.i~n resulting from stress preferably begins when the specimen has been strained about 2 to 3%
at the onset of the phase change from austenite to LLld~ ,L~e and extends 15 to about 7 to about 9% strain at the cnmrleti~7n of the phase change. The stress and strain referred to herein is measured by tensile testing. The stress-strain r~ t.i~,nchip determined by applying a bending moment to a cantilevered specimen is slightly different from the rPls7ti~7nchir7 .~ pd by tensile testing because the stresses which occur in the specimen during 20 bending are not as uniform as they are in tensile testing. There is considerably less change in stress during the phase Llr~ rlll "~ than either before or after the stress-induced Ll~ r.ll ,..~ ,n The stress level is WO 95/lg800 2 1 8 1 1 5 4 PCTIUS94/00468 relatively constant within the transformation period.
The portions of the guiding member having superelastic properties is preferably formed from an alloy rnnciF~in~ essentially of about 30 to about 52% titanium and the balance nickel and up to 10% of one or more ~ litionFI alloying elements. Such other alloying elements may be selected from the group cnnciQtine of up to 3 % each of iron, cobalt, platinum, palladium and ~ ullliulll and up to about 10% copper and vanadium. As used herein all references to percent composition are atomic percent unless otherwise noted.
To form the elongated superelastic portion of the g~uding member, elongated solid rod or tubular stock of the preferred alloy material is first cold worked, preferably by drawing, to effect a size reduction of about 30% to about 70% in the transverse cross section thereof. The cold worked material may then be given a memory imparting heat treatment at a t~ ueldLut~ of about 350 to about 600' C for about 0.5 to about 60 min-utes, while m~intF~inine a longitudinal stress on the elongated portion equal to about 5% to about 50%, preferably about 10% to about 30%, of the yield stress of the material (as measured at room tt~ ,U~.d~Ult). This t.h~rmnm~h~ni~ l processing imparts a straight "memory" to the superelastic portion and provides a relatively uniform residual stress in the WO 9S119800 21811~ PCT/US94/00468 material. Another method involves nnP~h~nir-~lly strsli~ht~nin~ the wire after the cold work and then heat treating the wire at t~ .d~UUti between about 300 and about 450 C., preferably about 330 to about 400' C. The latter treatment provides sl-hq~nL.i~lly higher tensile 5 properties. The cold worked and heat treated alloy material has an austenite finish L~ r.,. ,..~ I inn ~ Yla~u~t less than body temperature and generally about -10 C.to about 30 C. For more .~ Yllt final properties, it is preferred to fully anneal the solid rod or tubular stock prior to cold work so that the material will always have the same metallurgical structure at the start of the cold working and so that it will have adequate ductility for bul,~e-~uent cold working. It will be appreciated by those skilled in the art that means of cold working the metal other than drawing, such as rolling or swaging, can be employed. The constant yield stress levels for tubular products have been found to be slightly lower than the levels for solid products. For example, superelastic wire material of the invention will have a constant stress level usually above about 70 ksi, preferably above about 90 ksi, whereas, superelastic tubing material will have a constant stress level of above 50 ksi, preferable above about 70 ksi.
The ultimate tensile strength of both forms of the material is well above 200 ksi with an ultimate ~ n~ti~n at failure of about 15%.

The elongated superelastic members of the invention e~hibit WO 9S/19800 21 8 1 1~ ~ PCT/US94/00468 stress-induced austenite-to-martensite phase l~ rullllation over a broad region of strain at a very high, relatively constant stress levels. As a result a guiding member having a distal portion formed of this material is very flexible, it can be advanced through very tortuous passageways such as a patient's coronary vasculature with little risk that the superelastic portion of the guiding member will develop a permanent set and at the same time it will eLI~,l,iv~ly transmit the torque applied thereto without causing the guiding member to whip. The high strength proximal portion of the guidewire or guiding member provides excellent pushability and 10 torquability to the guidewire or guiding member.

These and other advantages of the invention will become more apparent from the following detailed ~ip~rrirlti()n thereof when taken in conjunction with the foilowing exemplary drawings.

l'~R~:~ DF`~t~RTPTION OF 1~, DRAWINGS

FIG. 1 is an elevational view of a guidewire which embodies features of the invention.

- FM. 2 is a srhP~n~t.ir, graphical illustration of the stress-strain rPl~tinn~hip of superelastic material.

WO 95J19800 PCT/US94/00468 ~1 2181~
DETATTlFT) DESCRIPTION OF THE INVENTION
.
FIG. 1 illustrates a guidewire 10 embodying features of the 6 invention that is adapted to be inserted into a patient's body lumen, such as an artery. The g~udewire 10 comprises an Plone~terll relatively high strength proximal portion 11, a relatively short distal portion 12 which is formed ællh~t~nti~lly of superelastic alloy material and a connector element 13 which is formed sl-het~nti~lly of superelastic alloy material and which 10 connects the proximal end of the distal portion 12 to the distal end of the proximal portion 11 into a torque L~ n~ rPl:~tionqhi~. The distal portion 12 has at least one tapered section 14 which becomes smaller in the distal direction. The connector element 13 is a hollow tubular shaped element having an inner lumen extending therein which is adapted to receive the proximal end 15 of the distal portion 12 and the distal end 16 of the proximal portion 11. The ends 15 and 16 may be press fit into the connector element or they may be secured therein by crimping or swaging the connector or by means such as a suitable adhesive or by welding, brazing or 5nl~Pring A helical coil 17 is disposed about the distal portion 12 and has a rounded plug 18 on the distal end thereof. The coil 17 is secured to the ~ woss/lssoo 218~15~ Pc~/uss4mo46s distal portion 12 at proximal location 20 and at intPI7nPtli~t~ location 21 by a suitable solder. A shaping ribbon 22 is secured by its proximal end to the distal portion 12 at the same location 21 by the solder and by the distal end thereof to the rounded plug 18 which is usually formed by soldering or welding the distal end of the coil 17 to the distal tip of the shaping ribbon 22. Preferably, the most distal section 24 of the helical coil 17 is made of radiopaque metal such as platinum or platinum-nickel alloys to facilitate the observation thereof while it is disposed within a patient's body. The most distal section 24 should be stretched about 10 to about 30%.
The most distal part 25 of the distal portion 12 is flattened into a rectangular section and preferably provided with a rounded tip 26, e.g.
solder to prevent the passage of the most distal part through the spacing between the stretched distal section 24 of the helical coil 17.
The exposed portion of the elongated proximal portion 11 should be provided with a coating 27 of lubricous material such as polytetrafluoroethylene (sold under the trademark Teflon by du Pont, de Nemours & Co.) or other suitable lubricous coatings such as the polysiloxane coatings disclosed in co-pending Prplit-~t;nn Serial No. 559,373, filed July 24, 1990 which is hereby in~,v, ~u~ ed by reference.

-218115~
WO 9!i/19800 PCTIUS94100468 .~
The elongated proximal portion 11 of the guidewire 10 is generally about 130 to about 140 cm in length with an outer diameter of about 0.006 to 0.018 inch for coronary use. Larger diameter g udewires may be employed in peripheral arteries and other body lumens. The 5 lengths of the smaller diameter and tapered sections can range from about 2 to about 20 cm, dPp~ndinE upon the stiffness or fle~ibility desired in the final product. The helical coil 17 is about 20 to about 45 cm in length, has an outer diameter about the same size as the diameter of the elongated pro~;imal portion 11, and is made from wire about 0.002 to 0.003 inch in 10 diameter. The shaping ribbon 22 and the flattened distal section 26 of distal portion 12 have rectangular ~ cross-sections which usually have dim~ncinnc of about 0.001 by 0.003 inch.

The superelastic members of the invention, i.e. the distal 15 portion 12 and the connector 13, is preferably made of an alloy material cnn~iPtin~ essentially of about 30 to abo~t 52 % titanium and the balance nickel and up to 10% of one or more other alloying elements. The other alloying elements may be selected from the group cnn~i~L;nE~ of iron, cobalt, vanadium, platinum, palladium and copper. The alloy can contain up to 20 about 10% copper and vanadium and up to 3% of the other alloying elements. The addition of nickei above the equiatomic amounts with titanimm and the other identified alloying elements increase the stress ¦~ WO 95/19800 21~ PCT/US94100468 levels at which the stress-induced austenite-to-"la~ ile transformation occurs and ensure that the t~ U~ldlU~ at which the Lu~ e phase l~îUlLUS to the austenite phase is well below human body t~ll,U~'d~Ult~ SO
that austenite is the only stable phase at body temperature. The excess 5 nickel and ~ it.ion~ll alloying elements also help to provide an expanded strain rarlge at very high stresses when the stress induced l~ r..,"~tinn of the austenite phase to the martensite phase occurs.

A presently preferred method for making the final 10 configuration of the superelastic portions of the guiding member is to cold work, preferably by drawing, a rod or tubular member having a cnmroqitinn according to the relative proportions described above and then heat treating the cold worked product while it is under stress to impart a shape memory thereto. Typical initial Lldn~ r~im~n~inn~ of the rod or the tubular member are about 0.045 inch and about 0.25 inch l~,uo~ ~iY~ly. If the final product is to be tubular, a small diameter ingot, e.g 0.25 to about 1.5 inch in diameter and 5 to about 30 inches in length, may be formed into a hollow tube by extruding or by m~rhinin~ a longitudinal center hole therethrough and grinding the outer surface thereof smooth. Before drawing the solid rod 20 or tubular member, it is preferably annealed at a t,~lllpt~ld~Ult: of about - 500 to about 75û C, typically about 650 C, for about 30 minutes in a u~u~ iv~ ,h~. ~ such as argon to relieve essentially all internal . . .

wo 95/19800 2 ~ 8 1 ~ ~4 PCTIIJS94/00468 Etresses. In this manner all of the .cperim~n~ start the subsequent t.h. . ,~ nirs~l processing in essentiaily the same metallurgical condition so that products with c.)~ . final properties are obtained.
Such treat~nent also provides the requisite ductility for effective cold 5 working.

The stressed relieved stock is cold worked by drawing to effect a reduction in the cross sectional area thereof of about 30 to about 70%.
The metal is drawn through one or more dieæ of appropriate inner diameter 10 with a reduction per pass of about 10 to 50%. Other forms of cold working can be employed such as swaging Following cold work, the drawn wire or hollow tubular product is heat treated at a t~Ut7ld~ between about 350' and about 600' C for 15 about 0.5 to about 60 minutes. Preferably, the drawn wire or hollow tubualr product is simultaneously subjected to a lnn~itll~;n~l stress between about 5% and about 50%, preferably about 10% to about 30% of the tensile strength of the material (as measured at room tt~ U~ dlUl~ ) in order to impart a straight "memory" to the metal and to ensure that any residual 20 stresses therein are uniform. This memory imparting heat treatment also fixes the austenite-martensite ~l~n~r ~ t.inn tt:~U~ld~Ult for the cold worked metal. By developing a straight "ll~ uly" and m~int.~inin~

- 1~3 -WO 95/19800 21~ 4 PCT/US94100468 uniform residual stresses in the superelastic material, there is little or no tendency for a guidewire made of this material to whip when it is torqued within a patient's blood vessel.
An alternate method for imparting a straight memory to the cold worked material includes m~rhs~lnir~lly str~i~ht~nin~ the wire or tube and then subjecting the strAiFht.rnrrl wire to a memory imparting heat treatment at a temperature of about 300' to about 450' C., preferably about 330' to about 400' C The latter treatment provides sllhE~ntisllly improved tensile properties, but it is not very effective on materials which have been cold worked above 55%, particularly above 60%. Materials produced in this manner e2hibit stress-induced austenite to ~ ~iL~
phase l~c~ru, I,-a~ion at very high levels of stress but the stress during the phase tr~n~fnrrn~t.ir,n is not nearly as constant as the previously discussed method Conventional mPrhzlnir~l str~ight~nin~ means can be used such as subjecting the material to sufficient l~n~it.lltlin~l stress to straighten it Fig. 2 illustrates an idealized stress-strain rrl~t.inn~hi~ of an alloy specimen having superelastic properties as would be exhibited upon tensile testing of the .cp~rimf~n The line from point A to point B thereon ,J~ i the elastic deformation of the s~im~n. After point B the strain or rl~fr,rm~t;~n is no longer proportional to the applied stress and it is in the WO 95~19800 2181 i~ 4 PCT/US94/00468 ~
region between point B and point C that ~he stress-induced L d~ rulllldLion of the austenite phase to the martensite ~hase begins to occur. There can be an intprmprlipte phase developed, snmetim~P called the rhnmbnhl~-lral phase"lepPnrlin{~ upon the rnmr~-citinn of the alloy. At point C the material enters a region of relatively constant stress with gi~nifi~Pnt.
nrm~tjnn or strain. It is in this region that the tr~npform7ltinn from austenite to martensite occurs. At point D the ~r~n~rulllldlion to the martensite phase due to the application of tenfiile stress to the specimen is ~ hP7~ntis~ly complete. Beyond point D the ~ld~Lt~ ,iL~ phase begins to 10 deform, elastically at first, but, beyond point E, the ~iPfnrmPt.inn is plastic or p~rm~nPnt.
When the stress applied to the superelastic metal is removed, the metal will recover to its original shape, provided that there was no 15 pPrmPnPnt deformation to the lld~L~ ,iLe phase. At point F in the recovery process, the metal begins to transform from the stress-induced, unstable martensite phase back to the more stable austenite phase. In the region from point G to point H, which is also an essentially constant stress region, the phase tr~n~fnrm~tinn from martensite back to austenite is essentially 20 complete. The line from point I to the starting point A ~ Lb the elastic recovery of the metal to its original shape.

1~ WO 95119800 2 i 8 1 1~ ~ PCTIUS94/00468 Because of the e~tended strain range under stress-induced phase l~ ",-"Atinn which is characteristic of the superelastic material described herein, a guidewire having a distal portion made at least in gllh~f~ntiAl part of such material can be readily advanced through tortuous 6 arterial passageways. When the distal end of the guidewire engages the wall of a body lumen such as a blood vessel, it will superelastically deform as the austenite L~l~rulllls to martensite. Upon the disengagement of the distal end of the guidewire from the vessel wall, the stress is reduced or Plimin~t~P~l from within the superelastic portion of the guidewire and it 10 recovers to its original shape, i.e. the shape "remembered" which is preferably straight. The straight "memory" in conjunction with little or no n"~ residual longitudinal stresses within the guidewire prevent whipping of the guidewire when it is torqued from the proximal end thereof.
Moreover, due to the very high level of stress needed t~ ru~ the 15 austenite phase to the martensite phase, there is little chance for per-manent deformation of the guidewire or the guiding member when it is advanced through a patient's artery.

The tubular connector formed of superelastic alloy material 20 provides a smooth transition between the high strength proximal portion and the relatively short distal section and retains a torque L~ g rPlAtinn~hi~ between these two portions.

WO 95119800 2 ~ 8 ~ PCTIUS94/00468 The present invention provides guidewires which have superelastic characteristics to facilitate the advancing thereof in a body lumen. The guiding members exhibit extensive, recoverable strain 5 resulting from stress induced phase tr~n.cfnrm~t.inn of austenite to martensite at l~repti(n~lly high stress levels which greatly minimi7~c the risk of damage to arteries during the advancement therein.

The Nitinol hypotubing from which the connector is formed generally may have an outer diameter from about 0.006 inch to about 0.02 inch with wall thi~knf~qc-~c of about 0.001 to about 0.004 inch. A presently preferred superelastic lly~u~ulJillg for the (~nnn.octin~ member has an outer diameter of about 0.014 inch and a wall thic_ness of about 0.002 inch.

Superelastic NiTi alloys, such as those described herein, are very difficult to solder due to the fnrm~tinn of a tenacious, naturally occurring oxide coating which prevents the molten solder from wetting the surface of the alloy in a manner necessary to develop a sound, essentially oxide free, sûldered joint. It has been found that by first treating the 20 surface of the ltr.~u,y superelastic alloy with molten al_ali metal hydroxide, e.g. sodium, potassium, lithium or mixtures thereof to form a nascent alloy surface and then pretinning with a suitable solder such as a - 2~ -~ wo 95/l9800 2 1 ~ 4 PCT/US94/00468 gold-tin solder witXout, nnt~rtin~ air, that the superelastic piece can be readily soldered in a conventional manner. A presently preferred alkali metal hydroxide is a mixture of about 59% K and about 41% Na. The solder may contain from about 60 to about 85% gold and the balance tin, 5 with the presently preferred solder cnntS~inin~ about 80% gold and about 20% tin In a presently preferred ~JlV~ a multilayered bath is provided with an upper layer of molten alkali metal hydroxide and a lower layer of molten gold-tin solder. The part of the superelastic distal portion, which is to be soldered, is thrust into the multilayered bath through the upper 10 surface of the molten alkali metal hydroxide which removes the oxide coating, leaving a nascent metal alloy surface, and then into the molten solder which wets the nascent metal surface. When the solder solidifies upon removal from the molten solder into a thin coating on the metal alloy surface, the underlying alloy surface is protected from an oxygen-cnnt~inin~
15 ~tnnn~phf~re. Any of the alkali metal hydroxide on the surface of the solder can be easily removed with water without detrimentally affecting either the pretinned layer or the underlying alloy surface. The superelastic member is then ready for conventional soldering. The ~u~ may be employed to prepare other metal alloys having ~i~nifil-~nt. titanium levels for soldering.

The high strength proximal portion of the guidewire generally WO 95/19800 2 1 8 ~ PCTIUS94/00468 is ~i~nifir~ntly stronger, i.e. higher ultimate tensile strength, than the superelastic distal portion. Suitable high strength materials include 304 stainless steel which is a conventional material in guidewire construction.
While the above description of the invention is directed to presently preferred embodiments, various rnotlifir~t.ion!~ and i~ v~lllents can be made to the invention without departing therefrom.

Claims (28)

WHAT IS CLAIMED:

1. An intravascular guidewire having proximal and distal ends, comprising:
a) an elongated high strength proximal portion having proximal and distal ends;
b) a distal portion having proximal and distal ends formed of a superelastic alloy in an austenite phase at body temperature which transforms to a martensite phase when subjected to stress; and c) connecting means to fix the distal end of the proximal portion to the proximal end of the distal portion, which is formed at least in part of a superelastic alloy in an austenite phase which transforms to a martensite phase when subjected to stress.

2. The guidewire of claim 1 wherein the connecting means for fixing the distal end of the proximal portion to the proximal end of the distal portionhas a tubular construction with an inner lumen extending therein, with a proximal end receiving the distal end of the proximal portion and a distal end receiving the proximal end of the distal portion.

3. The guidewire of claim 1 wherein a flexible coil is disposed about the distal portion and extends to a rounded plug in the distal end of the guidewire.

4. The guidewire of claim 1 wherein the distal portion temrinates short of the distal end of the guidewire and a non-superelastic shaping ribbon extends from the distal section to the rounded plug.

5. The guidewire of claim 1 wherein the superelastic distal portion has a straight memory

6. The guidewire of claim 1 wherein the strain of the distal portion during the transformation from the austenite phase to the martensite phase is within the range of about 2% to about 8%.

7. The guidewire of claim 6 wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 50 ksi.

8. The guidewire of claim 6 wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 70 ksi.

9. The guidewire of claim 6 wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 90 ksi.

10. The guidewire of claim 4 wherein the distal portion is formed of a superelastic alloy consisting essentially of about 40 to about 49%
titanium and the balance nickel and up to 10% of other alloying elements.

11. The guidewire of claim 10 wherein the other alloying elements are selected from the group consisting of iron, cobalt, vanadium and copper.

12. The guidewire of claim 11 wherein the alloy contains vanadium or copper in amounts up to about 10% and the other alloying elements up to about 3%.

13. The guidewire of claim 1 wherein the distal portion has a section which tapers in the distal direction.

14. The guidewire of claim 1 wherein a lubricous polymer coating covers at least part of the proximal portion.

15. The guidewire of claim 1 wherein the superelastic distal portion exhibits a strain of at least 5% during the stress induced transformation from the austenite phase to the martensite phase.

16. The guidewire of claim 2 wherein the connector means having a tubular construction has an outer diameter of about 0.006 to about 0.05 inch and a wall thickness of about 0.001 to about 0.004 inch.

17. An intravascular guidewire having proximal and distal ends, comprising:
a) an elongated high strength proximal portion having proximal and distal ends;
b) a distal portion having proximal and distal ends formed of a superelastic alloy in an austenite phase at body temperature.
which transforms to a martensite phase when subjected to stress; and c) a flexible tubular means for interconnecting the distal end of the proximal portion and the proximal end of the distal portion, has a tubular construction with an inner lumen extending therein, with a proximal end receiving the distal end of the proximal portion and a distal end receiving the proximal end of the distal portion.

18. The guidewire of claim 17 wherein a flexible coil is disposed about the distal portion and extends to a rounded plug in the distal end of the guidewire.

19. The guidewire of claim 17 wherein the superelastic distal portion has a straight memory.

20. The guidewire of claim 17 wherein the strain of the distal portion during the transformation from the austenite phase to the martensite phase is within the range of about 2% to about 8%.

21. The guidewire of claim 20 wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 50 ksi.

22. The guidewire of claim 20 wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 70 ksi.

23. The guidewire of claim 17 wherein the connector means having a tubular construction has an outer diameter of about 0.006 to about 0.05 inch and a wall thickness of about 0.001 to about 0.004 inch.

24. A method for forming a surface suitable for soldering on a metal alloy member containing substantial amounts of titanium comprising:
a) treating the metal alloy member with a molten alkali metal hydroxide;
b) contacting the thus treated metal alloy member with a compatible molten solder to form a thin coating of said solder; and c) solidifying the thin coating of molten solder.

25. The method of claim 24 wherein the metal alloy member comprises a nickel-titanium alloy.

26. The method of claim 24 wherein the solder is a gold-tin solder.

27. A sound soldered joint between a metal member containing substantially amounts of titanium and another metal element which includes essentially oxide free surface on the metal member containing titanium and a compatible solder bonding together the essentially oxide free surface and the metal element.

28. The soldered joint of claim 27 wherein the solder consists essentially of 60-85% by weight gold and the balance essentially tin.