Note: Descriptions are shown in the official language in which they were submitted.
CA 02502504 1995-05-18
-I-
i~'RO''PED TISSUE SUPIfORTISIG DEVICES
This invention relates to tissue supporting devices in general and most
5 particularly to vascular sterns for placement in blood vessels. A primary
featuK of
the devices of this invention is that they are expandable within the body.
In the past, such devices have been provided for implantation within
body passageways. These devices have been characterized by the ability to be
enlarged radially, often having been i~roducec! into the desired position in
the body
i0 as by percutaneous techniques or surgical techniques.
These devices are either expanded mechanically, such as by expansion
of a balloon positioned inside the device, or are capable of releasing sfloral
energy m
sdf-expand themselves within. the body.
References designated as defining the general state of the art but not
15 considered to be of par;icular relevance to the invention disclosed and
claimed harem
are as follows. French Patent 2,617,721 appears to disclose a catheter used
for
permanently dilating a stenosis in a tubular organ or blood vessel.
'W09d1031~7
appears do disclose a prosthetic device for sustaiain,g a blood vessel or
hollow organ
lumen comprising a tubular wire frame. European Patent Application 364,787 and
20 fiuropean Pateut Apglication 335,341 appear to disclose expandable
intraluminal
vasrcular grafts. W092II9310 appears to disclose a tissue supporting device of
a
shape memory alloy. U. S. Patent 5,147, 370 appears to disclose a nitinol stmt
for
hollow body conduits. UK Patent 2,I75,824A appears to disclose a method of
producing a composite metal materiel and a bil'kt for jet engine carbine
blades,
25 armor, helicopter rotor blades, car suspension stress parts or sword blades
made of
said composite material.
The materials which have bean used to make up these devices have
itxluded ordinary metals, shape metnory alloys, various plastics, both
biodegradable
and not, and the Iike.
30 . This invention is concerned with the use of these materials in a now
multiple componenx arrdagrment which allows for initial self expansion and
subsequent deformation to a fuial enlarged diameter in the body.
1
CA 02502504 1995-05-18
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Balloon expandable std do not always expand uniformly around
their circumference. As a result, healing may not take place in a consistent
manner.
If the scent is coated or covered, non-uniform expansion may tear the covering
or
coating. Additionally, long starts of this type may require long balloons
which can
5 be difficult to handle, difficult to size, and may not offer Ideal
performance in
tortuous passages in blood vessels and the like.
Thus, when addressing such isseus, self-cacgandabl~ stenta hava been
thought to be generally more desirable. Unfortunately, one cannot control the
degree of expansion and hence the degree of embedment in the vessel wall. It
has
IO been determined that a stmt must be embedded to some degree to be
clinically
satisfactory.
The stenfs of the present invention provide the best features of both of
these types of scents without their drawbacks.
CA 02502504 1995-05-18
_J_
The tissue supporting devices of this invemion are generally
cylindrical or tubular in overall shape and of such a configuration as to
allow radial
expansion for enlargement. They are often referred to herein in the general
sense as
5 "slants" . Furthermore, the devices are comprised of at least one component,
element, constituent or portion which exhibits a tendency to self-expand the
device
to an expanded size and at least one other component, element, constituent or
portion which is deformabk so as to allow an external force, such as a balloon
positioned within the body of the device, to further expand it to a final,
larger
10 desned expanded size. Tile terms "compotrent", "ektnent", "constituent" and
"portion" are often refa~ed to herein collectively as "portion" .
Preferably, the devices of the invention are made of metal and most
preferably of shape memory alloys.
In one embodiment, a first portion is a resilient spring-Like metal for
15 self expansion and a second portion is a defortaabk metal for final sizing.
In a
~re p~gory ~bodiment, a first portion is a self-expanding
austenitic one and a second is a martensidc o~ eapabk of deformation. In the
case
of shape manory embodiments the "portions" may be discrete or merely different
phases of an alloy.
20 The most preferred embodiment of tha invention is a stunt, preferably
of shape memory alloy. The most preferred shape memory alloy is Ni-'Fi,
although
any of tl~ other known shape memory alloys may be used as well. Such other
alloys include: Au-Cd, Cu-Zn, In-Ti, Cu-Zn Al, Ti-Nb, Au-Cu-Za, Cu-ZtrSn, Cu-
Zn-Si, Cu-Al-Ni, Ag-Cd, Cu-Sn, Cu-Zn-Ga, Ni-Al, Fe-Pt, U-Nb, Ti-Pd-Ni, Fo-Mn-
3.S Si, and the Iike. These alloys may also be doped with small amounts of
other
elements for various pmperty modifications as may be desired and as is known
in
the art.
The invention will be specifically described hereiabelow with
reference to stems, a prefcrned embodiment of the invention although it is
broadly
30 applicable to tissue support devices in general.
CA 02502504 1995-05-18
-4-
~3~~~c~'g~an of the Fisures
Figure 1 is a braided stcnt according to one embodiment of this
invention.
Figure 2 is a graph showing the tnartensitic/austenitic temperature
5 transformation curve and the superelasdc area of a shape memory alloy.
Figures 3 is an end view of a layered slant having two discrete
components according w one aspect of this invention.
Figures 4a and 4b are graphs showing the martensiticlaustenitic
temperature transformation curves of the layers in the slant of Figure 3.
10 ~ Figure Sa and Sb are views of another embodiment of the invemion
comprisod of alternating rings of shape memory alloy.
Figure 6 is a showing of a stem fragment of a braided version of a
shape memory slant of this invention.
Figure 7 is a graph showing a temperature window for a shape
15 . memory alloy to be used in yet another scent version of this invention.
Figurc 7a is a graph showing expansion of a scent with temperature.
Figure 7b is a graph of the same type, the scent having been cold
wotiCed.
Figure ~c is a gisph of the same type, the stem having had
20 pseuctoelastic prestraining.
Figure 7d is a graph of the same type, the stmt having amnesia
inducement.
Figures 8-11 show various expandabk configurations (closed and
open) illustrated in fragment which may be used in the stems of this
invention.
25 Figures 9a acrd 9b show a preferred embodiment of an articulated scent.
Figurc I2 shows another version of an expandable slant of the
invcntioa.
Figure I3 shows yet another version of a scent which may be used
with the invention.
34 Figure I4 is a schematic showing of a braided stunt made up of a
plurality of strands.
Figure 15 is a detail of a single strand fmm the stmt of Figure 14
showing that the strand is made up of a plurality of wires of two different
types.
CA 02502504 1995-05-18
Figure 16 is a cross-sectional view taken along line 15-16 of Figurc
15 showing the two different types of wire.
5 Preferred embodiments of this invention are described below with
particular reference to the accompanying drawing Figures.
Referring first to the embodiment shown in Figure 1, a stmt I0 is
shown comprised of braided or interwoven metal strands I2 and 14. Strands 12
are
of a resilient spring-like metal such as spring steel, Elgiloym for example.
I0 Pttferably, strands I2 are spirally extending in the same direction,
spiraling to the
right as seen in Figure I. Strands 14 are of a deformable or anncaial metal
such as
stainless steel and are preferably spiralai in the opposite direction as
strands 12, as
shown in Figure 1.
Given such a scent construction of two components 1. e. , strands I2
15 and 14, it can be seen that stmt I0 may be readily loaded on a catheter as
by
placing it over an uninflat&d balloon on a balloon catheter and compressing it
tightly
amend the balloon and then glaring a sheath over the stoat to hold it in piece
during
the translumvinal placement procure. Otux in place, the sheath is removed, for
example slid back, to expose the scent, allowing it to self-expand by force of
the
20 resilient strands 12 to substantially assume a self-expanded shape/siu.
Some self
expansion may be restrained if held back by strands 14. Ta finally adjust the
size of
the scent, the balloon may be expanded by inflation fmm within the scent to
exert an
outward radial force on the stmt and fir enlsxge it by stretching and
deforming
the deformable metal of strands I4. This may be aided by building into strands
14,
25 a series of readily defotmable structures or means such as bends or kinks
l6 as
shown in Figure I. It can be sera that a pet3nanent adjustable size beyond the
self
expanded size may be obtained with this embodiment. It is to be noted that
many
configurations other. than braided may be readily devised to take advantage of
this
two component cotxept, including various of the subsequent configurations
descn'bed
30 hereiabelow. Also, it should be notrod that, although not preferred, the
runt may be
initially deployed without a balloon; the balloon following on a sepatnte
catheter.
R,efeiring now to subsequent faatut~es, other preferred embodiments of
the invention will be described which make use of shape memory alloys and some
of
CA 02502504 1995-05-18
-6-
P~~ Pr~Y ~ sP~ h'P~ of deformation i.e., shape
memory deformation in marteasite and/or superelastic deformation in austcnite.
The term "superelasticity" is used to describe the property of certain
shape memory alloys to return to their original shape upon unloading after a
S substantial deformation while in their austenitic state. SupereIastic alloys
can be
strained while in their austenitic state more than ordinary spring materials
without
being plastically defornud. This unusually large elasticity in the austenitic
state is
also called "pseudoelasticity", because the mechanisms is nonconventioual in
nature,
or is also sometimes referred to as "transformational superelasticity"
t~ecausc it is
IO caused by a stress induced phase transformation. Alloys that show
superelasticity
also undergo a thermoelastic martensitic transformation which is also the
prerequisite
for the shape memory effect. Superelasticity and shape memory effects are
therefore
closely related. Superelasticity can even be considered part of the shape
memory
effect.
I5 The shape meamory and supezelastlcity effects are particularly
pronouncxd in Ni-Ti alloys. This application will therefore focus on these
alloys as
the preferred shape memory alloys. The shape memory effect in Ni-Ti alloys has
been described many times and is well known.
In near-equiatomic Ni-Ti alloys, martensite forms on cooling from the
20 body centered cubic high temperature phase, teamed ae~stenite, by a shear
type of
process. This martensitic phase is heavily twinned. In the absence of any
externally
applied force transformation takes place with almost no external macr~copic
shape
change. Tf~ martensite can be easily defornaed by a "flipping over" type of
shear
until a single orien~t~on is achieved. This pmcess is also celled.
"detwinning".
25 . . If a deformed martensite is now IKated, it reverts to austJenite. The
crystallographic restrictions are such that it transfouns back to the initial
orientation
tt~roby rGStaring the original shape, Thus, if a straight piece of wire in the
austenide condition is cooled to form maricasite it remains straight. If it is
now
deformed by bending, the twitmed mar~nsite is converted to deforaned
marbensite.
30 On lxating, the transformation back to austenite occurs and the bent wire
becomes
straight again. This process illustrates the shape memory deformation referred
to
above.
CA 02502504 1995-05-18
_7_
The transformation from austenite to martensite and the reverse
transformation from mattansite to austenite do not take place at the same
temperature. A plot of the volume fraction of austenite as a function of
temperature
pxovides a curve of the type shown schematically in Fig. 2. The complete
5 transformation cycle is characterized by the following temperatures:
austenite start
teznperaaue (A,), austenite finfsh temperature (A~), both of which are
involved in the
fn~t part {1) of an increasing temperature cycle and martensite start
temperature
(M,) and martensite finish temperature (Mf), both of which are involved in the
second part (2) of a decreasing temperature cycle.
10 Figure 2 represents the transformation cycle without applied stress.
However, if a stt~ess is applied in the temperature range betwxn A, and Ma,
marGensite can be stress-induced. Stress induced martensite is deformed by
detwinning as described above. Ixss energy is needed to stress induce and
deform
marocnsitc than to deform the austerute by conventional mechanisms. Up to
about
15 896 strain can be accommodated by this process (single crystals of specific
alloys
can show as much as about 2S °~ pseudoelastic strain in certain
directions). As
austenite is the thermodynamically stable phase at tanpeTatures between A, and
Md
under no-load conditions, the matcrlai springs back into its original shape
when the
stress is no longer applied.
20 It becomes incrsasingiy diffcult to stt~,ss-induce martensite at
increasing rremperauires above Af. Eventually, it is easier to deform the
material by
cotnrentional mechanisms (movement of the dislocation, slip) than by inducing
and
~iefvrmitng martensite. The ttmptrature at which martensite can no longer be
stress-
inducod is called Md. Above Md, Ni Ti alloys are deformed like ordinary
materials
25 by slipping.
Additional information regarding shape memory alloys is found in the
following references, all of which are incorporated fully herein by reference;
"Super ;Elastic Nickel Titanium lyres" by Dieter Stsckel and
Weikang Yu of Raychaar Corporation, Menlo Park, California, copy
30 receivod November 1992;
~gj,~~, Tenth Edition, Vol. 2, Propaxies and
"Shape
Memory Alloys" by Hodgson, Wu and 8iertnarui, pp. 897 - 902; and,
CA 02502504 1995-05-18
_g_
In Press, T ~taryiicrn~~, ASM (1994), Section entitled
"Stmerure and Properties of ?i-N Alloys by T.W. Duerig and A.R.
Pelton.
Since the most preferred shape memory alloy is Ni-Ti, the martensitic
5 state of this alloy may be used to advantage in the two component concept of
this
invention.
For example, with reference to Figure 3, a layered construction may
be provided in a stoat 30 (shown in end view) which is generally a hollow
cylindrical or tubular body in shape but which may be formed in a wide variety
of
10 specific configurations or patterns to foster radial expansion of the body
as
exemplified in Figures 1, 5, 6 and in subsequent Figures 8-11.
Stent 30 is comprised of at least two layers 32 and 34, one of which
32 is a Ni-Ti alloy (50.8 atonaitc wt. % Ni, Ti, transition temperature of
Af=0° C) and normally in the austenitic state, the other of which 34 is
a Ni-Ti
15 (49.4 atomic wt. 96 Ni, b~anoe Ti, transition t~par~utro A~ = 60° C)
and
normally in the martensitic state. Preferably, the inner layer is 32 and the
outer
layer is 34. However, this may be reversed and also a plurality of layers,
alternating or othe~vvise, may be utilized in this particular embodiment.
Stem 30 is made to a fabricated size and shape (parent shape) which
20 provides austenitic layer 32 its parent shape and size i. e. , its
supereiastic high
t~nperature shape and size. Obviously, is its as fabricated condition, the Ni-
Ti
alloy of austenidc layer 32 is selected so as to have a transition temperature
range
between its austenitic and tnartensitic states which is lower than body
temperature as
to ensure that in the body and at body temperawr~s the austtrritic state will
always
.25 prevail.
4n the other band, marrensitic layer 34 is of a Ni-Ti alloy having a
transition te~etature range significarnly greater than body temperature so as
to
ensure that under body conditions the martensitic state will always prevail
and the
alloy will never transform to aust~enite in stem use. This is shown in the
graphs of
30 Figure 4a atxi 4b which demonstrate tIx relative transition temperatures of
layers 32
and 34, respectively far purposes of this invention. It can be seen from these
graphs
that the normal cotxlition of layer 32 (Figure 4a) at body temperatures and
higher is
CA 02502504 1995-05-18
-9-
the austcnitic state while the normal condition of layer 34 (Figure 4b) at
body
temperatuu~es is martn~sitic.
To manufacture the layered construction, one may make the austenitic
portion with arty standard metallurgical technique and vapor deposit the
martensitic
portion on its surface. Other tpanufacairiag techniques such as diffusion
bonding,
welding, ion beam deposition, and various others will be apparent to those
familiar
with this art.
Such a stmt may be compressed or constrained (deformed to a small
diameter) onto a balloon catheter as d~xibed for tlx previous embodiment and
30 captured within a sheath. During the constraintnent, austenitic layer 32
may stress
induce to a marcensitic state. Tn the alternative, the scent may be cooled
below the
transition temperature of Layer 32 to facilitate its deformation and
constrainment.
Martensitic layer 34 t~rely undergoes deformation. Thus tie scent may be
"loaded"
onto a balloon catheter. However, with temperature changes occutiirtg up to
body
15 temperature, layer 32 will remain marrensite until the constraint is
removed. When
released in place in the body, slant 30 will expand to a p~e~ge of its self
expanded size and shape due to the transformation of layer 32 from martensite
to
austenite at which point the balloon may be used tv radially expand the stem
to a
greater permanent diameter by deforming ntartensitic layer 34. On the other
hand,
~20 initial deployment can take plane without a balloon which may be
separately inserted
after deployment.
The two component concept of the invention in the layered
embodiment of Figure 3 requires both the maroensitic and austenitic phase
characteristic of shape memory alioy(s) in the two discrete components 32 and
34.
25 Preferably, the steal is fabricated in such a way that the austenitic
layer 32 tends to self-expand slant 30 to a predetermined fabricated diameter
(parent
shape). The martensitic layer 34 feuds to hold back this self-expansion,
preventing
full expansion. For example, the stmt may only be able to self-expand to 759b
of
its ful! possible diameter (as detetmitxd by the austenitic layer). Therefore,
30 expansion beyond 75 ~b is accomglislted by an applied external force, as by
the
balloon inside the scent. It is suggested that the scent not be expanded
beyond its
normal fabricated diameter for the auste~tic layer 32 will have the tendency
of
making the stmt diameter smaller as it tries to recover its fabricated
diameter
CA 02502504 1995-05-18
(parent shape). If the stem is subjected to a temperature above body
temperature
and above the transition temperature of the marr~ensitic layer (which is
clinically
unlikely), the stmt will self-expand to the fabricated diameter only.
Depending on
design size there are thus provided permanent stems capable of fulfiFling any
needed
S range of sizes with an adjustable sizing capability.
As is lrnown in the art, the desired properties of the shape memory
alloys requitfed for use in this invention may be obtained by alloy
composition and
working and heat treatment of the alloys, in various combinations or singly.
Manufacatring techniques influence the phase characteristics of the
10 material. Alloy composition, work history, and lust ueaament all influence
the final
chararxeristics. At a specific operating temperature, say body temperature,
the
austenite phase material will have a transition temperature below body
temperature
{i.e., A~=0°C). Tlie material is capable of taking high strains and
recovering after
the load is released. The martensite phase material will have a higher
transition
15 temperature than body temperature {i.e., A~=60°C), and is
characteristically soft
and pliable and retains the deformed shape after load removal. 'This
tnartensite
deformation is caused by detwinning, not the typical plastic deformation, or
yielding, of crystal slip.
'With reference to Figttrts 5 and 6, other stmt constructions are shown
20 which are similar to the layered version of Figure 3 in so far as
utilization of the
two component concept of this invention is concerned.
Figure Sa and 5b shows a slant 50 made up of alternating expandable
rings 52 and 54 of austenitic ara3 tnaroettsitic alloys, respectively,
anaiogaus to layers
32 and 34 of the Figure 3 embodiment. Ringsv 52 and 54 for example are
25 interconnected by stmt members 56 which tray be of any material capable of
rigidly
holding the rings togettur. Other int~erc:otu~ctor nmay be used. As can be
seen in Figufe'Sb, the pia~ment of strut members 56 does not require them w
take
part in the radial expansion of the stem and tl~y can therefore be of a
relatively
ordinary material such as stainless steel.
30 Referring now to Figure 6, a braided or interwoven cot>~uction is
shown similar in construction to that of the embodimem of Figure 1. In this
anbodiment, strat~s 62 extending to the right in Figure 6 are an alloy in the
CA 02502504 1995-05-18
-11-
austenitic state whereas strands 64 extending to the left in Figure 6 are an
a~'oy in
the marrensitic state. _
Referring now to the graph of Figure 7, it is demonstrated that the
two componetu concept of the invention may be embodied in two phases, i.e.,
components of a single shape memory alloy and need not be in the form of two
discrete components such as layers, members, wir~;s, etc. Ia the graph of
Figure 7,
it can be seen that an alloy composition can be selected such that it has a
phase
transition temperature window that bounds the proposed operating temperatures
of
the stem, such as the normal 'body temperature range. Within this transitional
window or zone, the material undergoes the phase transition and is effectively
compositionally comprisai of a ratio of austenitic to n>aMCasitic phase
depending on
the tcrnperature of the stem. This ratio should be selected so as to provide
sufficient
radial force fmm the austenite phase while still allowing for further
expansion of the
martensite phase with a mechanical expansion means such as a balloon.
Selecting
body temgeraaue as the operating temperature, a Ni-Ti alloy of about 50150
atmnic
wt. 9b composition (range about 4915196) will provide an acceptable "window"
for
this embodiment, the two components are the austeniu and martensite phases of
the
nititml.
The method of malting a scent may be descn'bed as follows. Age the
shape memory material (hli Ti) until body tanperature falls somewhere within
the
transformation window. Therefore the stern will not fully recover to its high
temperature shape at body temperature. An example of this technique is
described
below.
A stem of tubular 50.89b N balance Ti was prepared having a 1.5
mm diameter. It was suhstantlally alI austenite at room temperature, the Af
being
about 15-20°C and therefore being supereIastic at roam temperature. The
stmt was
cooled to below room temperature to form substantially alI marteasite and
mechxnir~cally exto 4.7 mm in diameter. It was maintainal at the 4.7 mm in
diameter and heat treated at S00°C for 30 minutes and water quenched.
Finally, it
was again cooled to below room temperature to form substantially all
tnarcensite and
compressed to a diameter of 1, 5 mm. After deployment and at body temperature
the
scent has a diameter of 3.5 mm. At about 70~ of full expansion, i.e., about
40°C it
had a diameter of 4.5 tnm and at 42°C it had a fully exdiameter of 4.7
mm.
CA 02502504 1995-05-18
-12-
This method works fairly wolf, but due to the slope of the temperature
versus diameter Blot being extremely vertical at body temperature, a small
change in
body temperature, or nianufacruring control, can have a large impact on the
actual
self expansion diameter. As can be seen fmm Figure ?, the sloge of the line
5 between At and A, is rather steep with small changes in temperature Leading
to large
changes in percent austenite and consequently Iarge changes in diameter of a
steal
made of such an alloy. Figure 7a shows a temperature versus diameter plot.
Three
methods of modifying the slope of the line on the ttamra versus diameter graph
are cold work, pseudaelastic presuaining, and aaxnesia itxluccment,
illustrated in
10 Figures 7b, 7c and 7d, respectively.
Residual cold work in nitinoi draws out or masks the point of Ar on
the diameter versus the temperature curve. This is sees by the sluggish
increase in
diametiGr as temperature increases in the last 20-30~ of recover. By utilizing
the
15 effects of cold work, the effects of temperature change on diatiuxer can be
reduced
in the last 20 to 30°.6 of street expansion. Shown in Figure 7b is an
example of a
temperature versus diameter plot for a cold worked part. Figure 7a above shows
an
example of a part without cold work.
20 Utilizing the effects of gsrudoclastic prestraiuing (S . Euckcn and
T.W. Duerig, AGTA Metal, Vol. 37, No. 8, pp 2245-2232, 1989) one can create
two distinct plateaus in the stress-strain behavior. This difference in stress
strain
behaviors can be directly linked to two distinct At temperatures for the two
plateaus.
By placing the transition between the two plateaus at the transition from self
25 expanding to balloon expanding, i.e., 7096, one can control the
characteristics of the
stunt at body temperature. The goal would be to place the A,~ temperature for
the
first plateau (from maximum compression to 7096 expansion) below body
temperature such that the stmt has self expanding charad~tristics. The .A f
temperature for the second plateau would be above body temperature such that
there
30 is no additional self expansion in this region (70 to 100% expansion) a
mechanical
device, like a balloon, ran then be used to custom size the steel between 70~
and
10096 of the high temperature shape. Results of such a technique is shown in
Figure 7c.
CA 02502504 1995-05-18
-13-
AMNESIA INDUCF.11~.NT
One of the characteristics of nitinol is cycle amnesia. This was also
discussed about in the article referral to ittunodiately above. As nitinol is
cycled
from its heat set shape as shown in Figure Td, there is an increase in the
amount of
amnesia to recover to the heat set shape with each cycle. As long as this
amnesia is
not caused by permanent plastic deformation, the amnesia can be removed by
heating the part above lvi~. This shows there is martensite left in the part
after
cycling which is preventing full recovery in the austenitc phase (gust above
Af).
This grescace of nun recoverable tnarrensite (below M~ is what may be used for
the
I0 balloon expansion region of the stunt.
Figures 8-11 represent examples of various expandable configurations
(a ~ closed, b = expanded) which may be incorporated inm the devices of this
invention. The version shown in Figures l0a and lOb may be modified as shown
in
Figures lOc and IOd (closed and open, respectively) by omitting portions
(indicated
at 100 in Figures IOc and lOd) as to render the stmt flexible for
articulation. This
may be done to other of the structures as well to improve flexibility.
Yet another version of a device incorporating the two component
concept of the invention is shown in Figure 12. In this embodiment, a fragment
of a
scent 110 is shown. The stmt includes a self-extending compornent 112 and a
deformable, external force expandable component 114. Self expanding component
112 may be resilient spring like metal such a stainless steel or it may
preferably be a
shape memory alloy in the austenitic state. Component 114 may be any
deformable
metal or the like such as annealed stainless steel or preferably a shape
memory alloy
in the martensitic state. The two components may simply be mechanically,
welded
or bonded together, Functions and operations are as described hereinabove.
Referring to Figure 13 a version analogous to the embodimesu of
Pigure 12 is shown in which the two component concept is again embodied as
different zones or portions of a single metal material.
As slmwn in Figure 13, a stem 120 (fragment showing) is of a self
expanding component 122 and a defotmable component 124, both of which may be a
single metal as spring steel or austenitic Ni-Ti which has been appropriately
treated
with r~ect to component 124 as by localized heat treatment or the like to
alter the
characteristics of the material of the 122 component so as to render it
deformable or
CA 02502504 1995-05-18
-14-
martensitic, depending on whether it is merely resiliern or is austenitic.
Again,
function and operation are the same as with other embodiments.
Referring now to Figures 14-16, a mufti-strand braided stem is shown
in Figure 15. Each strand I50 in the stmt is a micro-cable. That is, each
strand is
5 made up of a plurality of wires 152 and I54 as is seen in Figures i5 and 16.
Each
of the wires 152 and I54 consists of two different nitiuol alloys as seen best
in
Figwre 1b, or one nitinol and one ordinary metal such as stainless steel,
platinum or
tantalum. The latter two would provide enhanced radiogacity. One nitinol alloy
v~rire 154 has an austenitic finish (A,) temperature less than body
temperature. The
10 other wire 152 could be nitinol having an A, (austenitic start) greater
than body
temperature. Also, it could be an ordinary rn~l. Additionally, one or more of
the
strands may be of a biodegradable material such as a plastic or may be of a
material
including an absorbable drug.
Since the two alloys are into micro-cable one does not have
15 to caga$e in selective, discrete heat treating methods to produce both
shape memory
and martettsitic effects.
lZadiapaque portivas or coatings may be included on any parts of
these sterns as is known in the prior art.
While this invention may be embodied in many different forms, there
20 are described in detail herein specific preferred embodimants of the
invention. This
description is an exemplification of the principles of the invention and is
not
intended to Iimit the invention to the particular embodiments illustrated.
The above Examples and disclosure are intended to be illustrative and
not exhaustive. These examples and description will suggest many variations
and
25 alternatives to one of ordinary skill in this art. All tt~sc alternatives
and variations
are intended to be included within the scope of the attached claims. Those
familiar
with the art may reeogniu other eduivalents to the specific embodiments
described
herein which equivalents are also intended to be e~ompassed by the claims
attached
hereto.
