U.S. patent application number 09/852094 was filed with the patent office on 2001-09-27 for method for making a multi-laminate stent having superelastic articulated sections.
Invention is credited to Tomonto, Charles V..
Application Number | 20010025130 09/852094 |
Document ID | / |
Family ID | 23101203 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010025130 |
Kind Code |
A1 |
Tomonto, Charles V. |
September 27, 2001 |
Method for making a multi-laminate stent having superelastic
articulated sections
Abstract
In accordance with the present invention, there is provided a
stent for implantation into a vessel of a patient. The stent has at
least two plastically deformable and expandable tubular graft
members for expansion within a vessel. Each of the graft member has
a first end, a second end, a wall section disposed therebetween and
a lumen extending therethrough. The stent further includes at least
one articulation connecting the first end of one of the graft
members with the second end of the other graft member. Wherein the
articulation is made from a superelastic material.
Inventors: |
Tomonto, Charles V.; (Miami,
FL) |
Correspondence
Address: |
AUDLEY A. CIAMPORCERO JR.
JOHNSON & JOHNSON
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
08933-7003
US
|
Family ID: |
23101203 |
Appl. No.: |
09/852094 |
Filed: |
May 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09852094 |
May 9, 2001 |
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09287036 |
Apr 6, 1999 |
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6264687 |
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Current U.S.
Class: |
600/36 ;
623/1.16 |
Current CPC
Class: |
A61F 2210/0076 20130101;
A61F 2230/0013 20130101; A61F 2250/0018 20130101; A61F 2/91
20130101; A61F 2002/91541 20130101; A61F 2002/91558 20130101; Y10T
29/49908 20150115; A61F 2250/0029 20130101 |
Class at
Publication: |
600/36 ;
623/1.16 |
International
Class: |
A61F 002/06; A61F
002/04 |
Claims
That which is claimed is:
1. A method for making a stent for expansion within a human vessel,
said method comprising: a) forming a tubular member having an inner
layer comprising a superelastic material and an outer layer
comprising a plastically deformable material; b) removing portions
of said inner and outer layers of said tube so as to form at least
two plastically deformable and expandable tubular graft members
connected together by at least one strut; and c) removing said
outer plastically deformable layer from said at least one
articulation.
2. The method according to claim 1 wherein said step of removing
portions of said inner and outer layers of said tube so as to form
at least two plastically deformable and expandable tubular graft
members, comprises removing portions of said inner and outer layers
and forming a plurality of circumferential loops and struts on each
said graft, wherein adjacent loops are connected together by at
least one strut.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 09/287,036 filed on Apr. 6, 1999.
FIELD OF THE INVENTION
[0002] The present invention relates to an expandable intraluminal
graft for use within a body passageway or duct and, more
particularly, expandable intraluminal vascular grafts which are
particularly useful for repairing blood vessels narrowed or
occluded by diseased luminal grafts.
BACKGROUND OF THE INVENTION
[0003] Intraluminal endovascular grafting or stenting has been
demonstrated to be an effective alternative to conventional
vascular surgery. Intraluminal endovascular grafting involves the
percutaneous insertion into a blood vessel of a tubular prosthetic
graft or stent and its delivery via a catheter to the desired
location within the vascular system. Advantages of this method over
conventional vascular surgery include obviating the need for
surgically exposing, incising, removing, replacing, or bypassing
the defective blood vessel.
[0004] Structures which have previously been used as intraluminal
vascular grafts have included various types of stents which are
expanded within a vessel by a balloon catheter such as the one
described in U.S. Pat. No. 5,304,197 issued to Pinchuk et al. on
Apr. 19, 1994, which is hereby incorporated herein by reference.
Examples of different types of stents include helical wound wires
such as those described in U.S. Pat. No. 5,019,090 issued to
Pinchuk on May 28, 1991, which is hereby incorporated herein by
reference, and stents formed by cutting slots into a metal tube,
such as the one described in U.S. Pat. No. 4,733,665 issued to
Palmaz on Mar. 29, 1988, which is hereby incorporated herein by
reference.
[0005] Other types of stents include self expanding stents,
typically made from a superelastic material, such as a nickel
titanium alloy (Nitinol). The prior art makes reference to the use
of Nitinol, which has shape memory and/or superelastic
characteristics, in medical devices which are designed to be
inserted into a patient's body. The shape memory characteristics
allow the devices to be 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 containing the metal into a
patient's body, with such deformation causing the phase
transformation. 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
un-deformed shape by the transformation back to the original
phase.
[0006] Alloys having shape memory/superelastic characteristics
generally have at least two phases. These phases are a martensite
phase, which has a relatively low tensile strength and which is
stable at relatively low temperatures, and an austenite phase,
which has a relatively high tensile strength and which is stable at
temperatures higher than the martensite phase.
[0007] Shape memory characteristics are imparted to the alloy by
heating the metal at a temperature above which the transformation
from the martensite phase to the austenite phase is complete, i.e.
a temperature above which the austenite phase is stable (the Af
temperature). The shape of the metal during this heat treatment is
the shape "remembered." The heat treated metal is cooled to a
temperature at which the martensite phase is stable, causing the
austenite phase to transform to the martensite 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 martensite phase to a temperature above the
martensite to austenite transformation temperature causes the
deformed martensite phase to transform to the austenite phase and
during this phase transformation the metal reverts back to its
original shape if unrestrained. If restrained, the metal will
remain martensitic until the restraint is removed.
[0008] Methods of using the shape memory characteristics of these
alloys in medical devices intended to be placed within a patient's
body present operational difficulties. For example, with shape
memory alloys having a stable martensite temperature below body
temperature, it is frequently difficult to maintain the temperature
of the medical device containing such an alloy sufficiently below
body temperature to prevent the transformation of the martensite
phase to the austenite phase when the device was being inserted
into a patient's body. With intravascular devices formed of shape
memory alloys having martensite-to-austenite transformation
temperatures well above body temperature, the devices can be
introduced into a patient's body with little or no problem, but
they must be heated to the martensite-to-austenite transformation
temperature which is frequently high enough to cause tissue damage
and very high levels of pain.
[0009] When stress is applied to a specimen of a metal such as
Nitinol exhibiting superelastic characteristics at a temperature
above which the austenite is stable (i.e. the temperature at which
the transformation of martensite phase to the austenite phase is
complete), the specimen deforms elastically until it reaches a
particular stress level where the alloy then undergoes a
stress-induced phase transformation from the austenite phase to the
martensite phase. As the phase transformation proceeds, the alloy
undergoes significant increases in strain but with little or no
corresponding increases in stress. The strain increases while the
stress remains essentially constant until the transformation of the
austenite phase to the martensite phase is complete. Thereafter,
further increases in stress are necessary to cause further
deformation. The martensitic metal first deforms elastically upon
the application of additional stress and then plastically with
permanent residual deformation.
[0010] If the load on the specimen is removed before any permanent
deformation has occurred, the martensitic 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 martensite phase transforms back
into the austenite phase, the stress level in the specimen will
remain essentially constant (but substantially less than the
constant stress level at which the austenite transforms to the
martensite) until the transformation back to the austenite phase is
complete, i.e. there is significant recovery in strain with only
negligible corresponding stress reduction. After the transformation
back to austenite is complete, further stress reduction results in
elastic strain reduction. This ability to incur significant strain
at relatively constant stress upon the application of a load and to
recover from the deformation upon the removal of the load is
commonly referred to as superelasticity or pseudoelasticity. It is
this property of the material which makes it useful in
manufacturing tube cut self-expanding stents. 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
example, U.S. Pat. No. 4,665,905 (Jervis) and U.S. Pat. No.
4,925,445 (Sakamoto et al.).
[0011] However, in general, the foregoing structures, both balloon
expandable and self-expanding, have one major disadvantage in
common. Insofar as these structures must be delivered to the
desired location within a given body passageway in a collapsed
state, in order to pass through the body passageway. While it is
necessary for the expanded stent to have enough rigidity to
maintain the integrity of the vessel it is implanted into, it also
needs to have sufficient flexibility so that it can be navigated
through tortuous vessels. For repairing blood vessels narrowed or
occluded by disease, or repairing other body passageways, the
length of the body passageway which requires repair, as by the
insertion of a stent, may present problems if the length of the
required graft cannot negotiate the curves or bends of the body
passageway through which the graft is passed by the catheter. In
other words, in many instances, it is necessary to support a length
of tissue within a body passageway by a graft, wherein the length
of the required graft exceeds the length of a graft which can be
readily delivered via a catheter to the desired location within the
vascular system. Some grafts do not have the requisite ability to
bend so as to negotiate the curves and bends present within the
vascular system, particularly prostheses or grafts which are
relatively rigid and resist bending with respect to their
longitudinal axes.
[0012] Accordingly, one solution to this problem has been the
development of an articulated stent. An example of an articulated
stent is given in U.S. Pat. No. 5,195,984 issued to Schatz on Mar.
23, 1993, which is hereby incorporated herein by reference. Such a
stent is particularly useful for critical body passageways, such as
the left main coronary artery of a patient's heart. Schatz
discloses a stent having a plurality of expandable and deformable
individual intraluminal vascular grafts or stents wherein and
adjacent grafts are flexibly connected by a single connector
members.
[0013] Recently, however, there has been a need to improve upon the
stent disclosed in the Schatz reference. Specifically, it has been
a desire to the technical community to make such a stent which is
even more flexible, so that the stent can navigate tortuous vessels
better than before. The present invention provides such a
stent.
SUMMARY OF THE INVENTION
[0014] In accordance with the present invention, there is provided
a stent for implantation into a vessel of a patient. The stent has
at least two plastically deformable and expandable tubular graft
members for expansion within a vessel. Each of the graft member has
a first end, a second end, a wall section disposed therebetween and
a lumen extending therethrough. the stent further includes at least
one articulation connecting the first end of one of the graft
members with the second end of the other graft member. Wherein the
articulation is made from a superelastic material.
BRIEF DESCRIPTION OF DRAWINGS
[0015] The foregoing and other aspects of the present invention
will best be appreciated with reference to the detailed description
of the invention in conjunction with the accompanying drawings,
wherein:
[0016] FIG. 1 is a partial perspective view of a stent made in
accordance with the present invention.
[0017] FIG. 2 is a side view of a stent made in accordance with the
present invention.
[0018] FIG. 3 is a partial cross sectional view of the stent shown
in FIG. 2 taken along line 3-3.
[0019] FIG. 4 is a view similar to that of FIG. 2 but showing the
stent as it would appear when navigating a body vessel.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring now to the drawings in detail wherein like
numerals indicate the same element throughout the views, there is
shown in FIGS. 1 and 2 a stent 10 made in accordance with the
present invention. Stent 10 is shown in its collapsed condition
ready to be disposed on a balloon catheter for delivery and
subsequent deployment into a vessel of a patient. Stent 10 includes
at least two expandable grafts. Stent 10 is shown as having three
expandable grafts 20, 30 and 40 each having a first end, 22, 32 and
42, and a second end, 24, 34 and 44, and a wall surface, 26, 36 and
46, disposed therebetween. The wall surface has a plurality of
slots, for example 28, 38 and 48, formed therein. The grafts are
formed from a metal tube and the slots are cut therein, typically
by laser cutting or photochemical processing. After the slots are
cut therein, each graft comprises a plurality of loops 50, 60 and
70, wherein adjacent loops are connected by at least one strut 52,
62 and 72.
[0021] Grafts 20 and 30 and 40 are connected together by at least
one articulation 80, and grafts 30 and 40 are connected together by
at least one articulation 90. As seen from the figures, the
articulations connect a loop from one graft to a loop from another
graft. However, it is preferable that the articulation does not
connect one loop of one stent to a loop of another stent directly
across it. In stead it connects the loops along a curved path which
is angled with respect to the longitudinal axis of the stent
running through the lumen.
[0022] The particular design of the present stent and its
advantages are best understood by describing the materials the
stent is made from and how the slots and articulations are cut
therefrom. By referring to FIG. 3, stent 10 is made from a multi
laminate hollow tube, or hypotube as it is often referred to by
those skilled in the art, having at least two layers, wherein one
layer is made from a plastically deformable material, such as
stainless steel or titanium, and the inner layer is made from a
superelastic material such as Nitinol. Stent 10 preferably has a
stainless steel outer layer 100 and a superelastic Nitinol layer
110. The stent could have more than two layers and still possess
all the advantages of the present invention. For example, the stent
could be made of a superelastic material, such as Nitinol,
sandwiched between two layers of a plastically deformable, such as
stainless steel. The inner layer of stainless is preferably
relatively thin so that the articulated sections remain
elastic.
[0023] The laminate hypotube may be manufactured by any number of
processes known to those skilled in the art, as evidenced in U.S.
Pat. No. 5,858,566 issued on Jan. 12, 1999. In the first process
the hypotube may be produced by hot rolling a series of layers of
material into laminate sheets. The hot rolling process may be
optimized to ensure mechanical bonding between the layers and that
the composite material has the necessary tensile strength. The
laminate sheets may then be rolled up around a mandrel and seam
welded to form a tube. The seam welded tube can then be drawn to
final size.
[0024] The second process for making the hypotube is to place
multiple layers of tubes within each other around a core mandrel.
The composite structure may then be drawn and heat treated using
conventional wire drawing practices until the finished tube
diameter meets the physical properties and dimensions required. A
sacrificial ductile core mandrel is placed within the hypotube
prior to the wire drawing process. The composite system is then
drawn to finish dimensions and the core mandrel is removed. Removal
of the mandrel is achieved by reducing the cross section of the
mandrel. By solely pulling the mandrel, the diameter of the mandrel
can be reduced sufficiently to be easily removed.
[0025] Once a composite hypotube is obtained, the structure may be
loaded onto a lathe type tool and the slots and articulations may
be cut from this tube using, for example, a laser etching cutting
tool, a water saw, or an electron discharge machine. Other ways of
cutting the slots, such as by photochemically etching, are well
known by those of ordinary skill the art.
[0026] The present invention has an advantage in that after the
stent design is cut from the tube, the articulations can then be
processed so that the outer layer of stainless steel is removed
from the articulations. Therefore, the articulations are now only
made from the superelastic Nitinol material. This additional
process is done by selective etching or laser scribing. After all
etching and selective etching is complete, the tube may then be
deburred by a procedure such as shot peening, abrasive tumbling,
honing, electropolishing and electroetching.
[0027] By making the stent from a multi-laminate tube, wherein one
layer is plastically deformable and the inner layer is
superelastic, a stent having relatively rigid grafts connected by
very flexible and shape recoverable articulations can be formed.
This allows for a stent which is flexible enough to navigate
through tortuous paths, but which is long enough to cover a
relatively large target site within a vessel. As seen from FIG. 4,
the stent 10 often has to pass through tight curves. FIG. 4 shows
the stent 10 loaded onto a balloon catheter 120 and being navigated
through a vessel 130. Because articulations 80 and 90 are made from
a superelastic material, they make the stent more flexible so that
it can better pass through tight curves such as the one shown here.
The stent need not have the particular design shown in the figures.
It could simply be a stent having a plastically deformable layer
and an elastic layer, wherein the stent has elastic zones along its
body where the plastically deformable layer has been removed. That
is the stent could simply be a graft member having at least two
layers wherein one of the layers comprises an elastic layer of
material extending from end to end, and said other layer comprises
a plastically deformable material covering only a predetermined
portion of the elastic layer.
[0028] The multilaminate stent described herein can also be used to
make a crush recoverable balloon expandable stent of the type
described in U.S. patent application Ser. No. 08/735,128, filed on
Oct. 22, 1996, which is hereby incorporated herein by reference. By
controlling the wall thickness of the plastically deformable layer
relative to the superelastic section, the performance of the device
can be adjusted. For this characteristic, the wall thickness of the
plastically deformable layer is targeted to plastically deform
during deployment. At the same load condition, the superelastic
layer is targeted to accept a load greater than the lower plateau
of the stress versus strain curve for the superelastic layer and
less than the upper plateau of the stress versus strain curve for
the superelastic layer. In this loading condition, the radial
outward force is controlled by the plastically deformable member
(yield point on the stress versus strain curve) and the crush
resistance is controlled by the superelastic member (upper plateau
on the stress versus strain curve). This combination will develop a
stent which is balloon catheter deliverable to a known stent
diameter, crush resistant, and exhibits no chronic outward
force.
[0029] Although particular embodiments of the present invention
have been shown and described, modification may be made to the
device and/or method without departing from the spirit and scope of
the present invention. The terms used in describing the invention
are used in their descriptive sense and not as terms of
limitations.
* * * * *