Note: Descriptions are shown in the official language in which they were submitted.
WO 9~i/19800 2 ~ 8 ~1~4 PCTNS94/00468
- 1 -
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
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, . _ _ _ _ _ _ . . .. .
2181~ ~
WO 95/19800 PCTNS94/00468
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.
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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
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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 -
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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
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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
- 11 -
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
- 12 -
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.
- 13 -
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
- 14 -
~ 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.
- 15 -
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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
- 16 -
¦~ 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
- 17 -
. . .
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
- 19 -
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.
- 20 -
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.
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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
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~ 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
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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.
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