U.S. patent application number 13/295488 was filed with the patent office on 2012-03-08 for endoprosthesis for controlled contraction and expansion.
Invention is credited to Anton G. Clifford, Brett Cryer, Jeff Pappas.
Application Number | 20120059453 13/295488 |
Document ID | / |
Family ID | 29408067 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120059453 |
Kind Code |
A1 |
Pappas; Jeff ; et
al. |
March 8, 2012 |
ENDOPROSTHESIS FOR CONTROLLED CONTRACTION AND EXPANSION
Abstract
Endoprosthesis including a plurality of annular elements, each
annular element connected to an adjacent annular element at least
one connection location, is provided. Each annular element includes
an interconnected series of strut members, at least one strut
member connected to a first circumferentially adjacent strut member
at a first longitudinal apex and to a second circumferentially
adjacent strut member at a second longitudinal apex. The at least
one strut member includes a first end portion at a first end of the
strut member, the first end extending to the first apex, an
intermediate portion hingedly connected to the first end portion,
and a second end portion hingedly connected to the intermediate
portion and extending to the second apex. The endoprosthesis has a
delivery diameter when in a delivery condition and a deployed
diameter when in a deployed condition.
Inventors: |
Pappas; Jeff; (Santa Clara,
CA) ; Clifford; Anton G.; (Mountain View, CA)
; Cryer; Brett; (Sunnyvale, CA) |
Family ID: |
29408067 |
Appl. No.: |
13/295488 |
Filed: |
November 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12618325 |
Nov 13, 2009 |
8075610 |
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13295488 |
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10430636 |
May 6, 2003 |
7637935 |
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12618325 |
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60378278 |
May 6, 2002 |
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60378279 |
May 6, 2002 |
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60378345 |
May 8, 2002 |
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60379310 |
May 8, 2002 |
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Current U.S.
Class: |
623/1.16 |
Current CPC
Class: |
A61F 2002/91558
20130101; A61F 2002/9155 20130101; A61F 2220/0075 20130101; A61F
2002/91508 20130101; A61F 2002/91533 20130101; A61F 2/91 20130101;
A61F 2/915 20130101; A61F 2002/91566 20130101; A61F 2210/0076
20130101 |
Class at
Publication: |
623/1.16 |
International
Class: |
A61F 2/82 20060101
A61F002/82 |
Claims
1. An endoprosthesis, comprising: a plurality of annular elements,
each annular element connected to an adjacent annular element at
least one connection location; each annular element including an
interconnected series of strut members, at least one strut member
connected to a first circumferentially adjacent strut member at a
first longitudinal apex and to a second circumferentially adjacent
strut member at a second longitudinal apex, the first apex and the
second apex being on longitudinally opposite sides of the annular
element; the at least one strut member including: a first end
portion at a first end of the strut member, the first end extending
to the first apex, an intermediate portion hingedly connected to
the first end portion, and a second end portion hingedly connected
to the intermediate portion and extending to the second apex; and
wherein the endoprosthesis has a delivery diameter when in a
delivery condition and a deployed diameter when in a deployed
condition.
2. The endoprosthesis of claim 1, wherein the first apex includes a
first circumferential member extending between the first end of the
at least one strut member and the first circumferentially adjacent
strut member.
3. The endoprosthesis of claim 2, wherein the second apex includes
a second circumferential member extending between the second end of
the at least one strut member and the second circumferentially
adjacent strut member.
4. The endoprosthesis of claim 1, wherein the first and second end
portions of at least one strut member extend in a first
circumferential direction, and the intermediate portion thereof
extends in an opposite circumferential direction to define a
lightning bolt shape.
5. The endoprosthesis of claim 1, wherein the first end portion,
the intermediate portion, and the second end portion of the strut
member are hingedly connected to each other at elbows.
6. The endoprosthesis of claim 1, wherein each of the first end
portion, the intermediate portion, and the second end portion of
the strut member is a substantially straight member.
7. An endoprosthesis, comprising: a plurality of strut members
interconnected to form a repeating pattern of interconnected cells,
each cell including at least two arrowhead portions extending
longitudinally and directed in opposite directions, each arrowhead
portion connected with an arrowhead portion of an adjacent cell,
wherein each arrowhead portion includes two strut members, each
strut member having a first end portion, a second end portion, and
an intermediate portion hingedly connected to each of the first end
portion and the second end portion, wherein the cells are connected
in a generally tubular shape having a delivery condition for
facilitating delivery of the endoprosthesis to a deployment site
and a deployed condition for deployment in a vessel at the
deployment site.
8. The endoprosthesis of claim 7, wherein the at least one
arrowhead portion includes a circumferential member extending
between the first end portion of the two strut members.
9. The endoprosthesis of claim 7, wherein the first end portion,
the intermediate portion, and the second end portion of at least
one of the two strut members define a lightning bolt shape.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/618,325, filed Nov. 13, 2009, which is a continuation of
U.S. application no. 10/430,636, filed May 6, 2003 and issued as
U.S. Pat. No. 7,637,935, which claims the benefit of U.S.
provisional patent application No. 60/378,278, filed May 6, 2002;
No. 60/378,279, filed May 6, 2002; No. 60/378,345, filed May 8,
2002; No. 60/379,310, filed May 8, 2002; the contents of each of
these prior filed applications are incorporated herein by reference
thereto.
FIELD OF THE INVENTION
[0002] The present invention relates to an endoprosthesis having
delivery and deployed configurations for implantation into a
vessel. More particularly, the invention relates to a stent with
improved contraction and expansion characteristics.
BACKGROUND OF THE INVENTION
[0003] Stents, grafts and a variety of other endoprosthesis are
well known and used in interventional procedures, such as for
treating aneurysms, for lining or repairing vessel walls, for
filtering or controlling fluid flow, and for expanding or
scaffolding occluded or collapsed vessels. Such endoprosthesis can
be delivered and used in virtually any accessible body lumen of a
human or animal, and can be deployed by any of a variety of
recognized means. One recognized indication of endoprosthesis, such
as stents, is for the treatment of atherosclerotic stenosis in
blood vessels. For example, after a patient undergoes a
percutaneous transluminal coronary angioplasty or similar
interventional procedure, an endoprosthesis, such as a stent, is
often deployed at the treatment site to improve the results of the
medical procedure and to reduce the likelihood of restenosis. The
endoprosthesis is configured to scaffold or support the treated
blood vessel; if desired, the endoprosthesis can also be loaded
with a beneficial drug so as to act as a drug delivery platform to
reduce restenosis or the like.
[0004] The endoprosthesis is typically delivered by a catheter
delivery system to a desired location or deployment site inside a
body lumen of a vessel or other tubular organ. To facilitate such
delivery, the endoprosthesis must capable of having a particularly
small cross profile to access deployment sites within small
diameter vessels. Additionally, the intended deployment site is
often difficult to access by a physician and involves traversing
the delivery system through the tortuous pathway of the anatomy. It
therefore is desirable to provide the endoprosthesis with a
sufficient degree of longitudinal flexibility during delivery to
allow advancement through the anatomy to the deployed site.
[0005] Once deployed, the endoprosthesis should be capable of
satisfying a variety of performance characteristics. The
endoprosthesis should have sufficient rigidity or outer bias when
deployed to perform its intended function, such as opening a lumen
or supporting a vessel wall. Similarly, the endoprosthesis should
have suitable flexibility along its length when deployed so as not
to kink or straighten when deployed in a curved vessel. It also may
be desirable to vary the rigidity or flexibility of the
endoprosthesis along its length, depending upon the intended use.
Additionally, it may be desirable for the endoprosthesis to provide
substantially uniform or otherwise controlled coverage, e.g., as
determined by the ratio of the outer surface of the endoprosthesis
to the total surface of the vessel wall along a given length. For
example, increased coverage may be desired for increased
scaffolding, whereas decreased coverage may be desired for side
access to branch vessels. Control of the cross profile and length
of the endoprosthesis upon deployment also is desirable, at least
for certain indications.
[0006] Particularly, tradeoffs are traditionally required between
device performance during the interventional procedure, in which an
endoprosthesis is placed in a vessel, and long term device
performance. Excellent placement performance (deliverability, ease
of access; stent retention, etc.) favors a stent design that is
highly flexible and that has a low profile. Long-term device
performance (e.g., coverage, scaffolding, low restenosis) often
requires a stent with significant rigidity or outer bias to support
the vessel. High scaffolding stents employ a relatively large
amount of metal, and this metal can restrict how tightly the stent
can be crimped, thus limiting its profile, retention on an
expansion balloon, and deliverability performance. The following
formula illustrates the relationship between inner diameter (ID)
and strut width and number (i.e., scaffolding) in a particular
cross-section of a traditional crimped stent, where n is the number
of struts and w is the width of each strut:
ID = circumference .pi. = nw .pi. ##EQU00001##
[0007] The deliverability of a stent device can be also limited by
the amount of material at the distal end of the delivery catheter.
The force exerted by stent geometry generally corresponds to the
amount of strain in the material, which increases as the stent
geometry is deformed from the set state. A traditional stent that
is set, such as by heat, in the expanded state exerts the greatest
force when it is the most crimped, and a typical stent that is heat
set in the crimped state exerts the greatest force when it is the
most expanded. The material of typical stents either keeps the
stent crimped on the delivery system during delivery or expands the
stent at the site of treatment. Traditional stents can only
accomplish one of these two tasks and require significant
additional material on the delivery system to accomplish the other.
Balloon expandable stents, typically made of stainless steel, have
mechanical properties allowing them to be easily and securely
crimped on a delivery catheter. However, they require a relatively
bulky balloon to expand them into the vessel wall. On the other
hand, self-expanding stents made of NiTi alloy or other
super-elastic materials readily deploy themselves at the site of
treatment but use a relatively bulky sheath to keep them
constrained on the delivery system during delivery. Both
traditional catheter balloons and stent sheaths tend to add
significant profile and stiffness to the distal end of the
implantation device.
[0008] Significant research effort has been devoted to the task of
developing higher performance balloons (lower profile, more
flexible) to minimize their impact on the delivery of the system.
Similarly much work has focused on minimizing the impact of a
constraining sheath for self-expanding stents. The use of such low
profile, highly flexible delivery system could be furthered by the
development of a stent or similar endoprosthesis that requires less
force to maintain mounted on and deployed from the delivery
system.
[0009] Numerous designs and constructions of various endoprosthesis
embodiments have been developed to address one or more of the
performance characteristics summarized above. For example, a
variety of stent designs are disclosed in the following patents:
U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 5,102,417 to
Palmaz; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 5,133,732
to Wiktor; U.S. Pat. No. 5,292,331 to Boneau; U.S. Pat. No.
5,514,154 to Lau et al.; U.S. Pat. No. 5,569,295 to Lam; U.S. Pat.
No. 5,707,386 to Schnepp-Pesch et al.; U.S. Pat. No. 5,733,303 to
Israel et al.; U.S. Pat. No. 5,755,771 to Penn et al.; U.S. Pat.
No. 5,776,161 to Globerman; U.S. Pat. No. 5,895,406 to Gray et al.;
U.S. Pat. No. 6,033,434 to Borghi; U.S. Pat. No. 6,099,561 to Alt;
U.S. Pat. No. 6,106,548 to Roubin et al.; U.S. Pat. No. 6,113,627
to Jung; U.S. Pat. No. 6,132,460 to Thompson; and U.S. Pat. No.
6,331,189 to Wolinsky; each of which is incorporated herein by
reference.
[0010] Although the various designs for endoprosthesis that have
been developed to date may address one or more of the desired
performance characteristics, there remains need for a more
versatile design for an endoprosthesis that allows improvement of
one or more performance characteristics without sacrificing the
remaining characteristics.
SUMMARY OF THE INVENTION
[0011] The present invention provides an endoprosthesis with
improved control over its contraction and expansion. A preferred
embodiment of the endoprosthesis has a plurality of annular
elements, each of which is connected to an adjacent annular element
at least one connection location. Each annular element includes an
interconnected series of strut members. Selected strut members are
each connected to an adjacent strut member at a longitudinal apex
and extend to a strut end portion located on a longitudinally
opposite side of the annular element from the apex. At least one of
the strut members includes a first end portion and a first end of
the strut member located at the strut end portion. At least this
strut member also has an intermediate portion hingedly connected to
the first end portion, and a second end portion hingedly connected
to an intermediate portion and extending to the apex. The
endoprosthesis preferably has a delivery diameter when in a
delivery condition and a deployed diameter when in a deployed
condition.
[0012] A circumferential member is preferably connected between
corresponding ends of at least one pair of adjacent strut members
to form a contoured arrowhead shape. This shape can be defined at a
selected apex. At least one pair of adjacent strut members are
preferably hingedly connected together to form the arrowhead shape,
which can define a five-point hinge configuration. This adjacent
pair of strut members of the arrowhead shape can extend
substantially equally in opposite circumferential directions when
the endoprosthesis is in the deployed condition. Also, the
connection location at which the annular elements are connected can
be the arrowhead of at least one of the adjacent annular
elements.
[0013] The intermediate portion of the strut members in the
preferred embodiment is disposed at an angle of less than about
90.degree. to the first end portion, and preferably also to the
second end portion. One or more of the arrowheads preferably
defines a tip at the apex, with the intermediate portion disposed
at an angle of about 90.degree. or less to the longitudinal axis of
the endoprosthesis in the deployed condition.
[0014] In the preferred embodiment, the first and second end
portions of at least one strut member extend in a circumferential
direction, and the intermediate portion thereof extends in an
opposite circumferential direction to the final lightning bolt
shape. The portions of the strut can thus be hingedly connected to
each other at elbows. Also, each portion of the strut can be a
substantially straight member, and in the delivery condition, the
strut members can be substantially aligned within the longitudinal
axis of the endoprosthesis.
[0015] A preferred endoprosthesis has strut members interconnected
to form a repeated pattern of interconnected cells. Each cell has
at least two arrowhead portions extending longitudinally and
directed in opposite directions. Each arrowhead portion is
connected with an arrowhead portion of an adjacent cell, and the
cells are connected in a generally tubular shape, which can be in
the delivery condition for facilitating delivery of the
endoprosthesis to the deployment site, or the deployed condition
for deployment in a vessel at the deployment site. Preferably, the
arrowhead portions are configured to compensate for foreshortening
of the endoprosthesis during expansion from the delivery to the
deployed condition.
[0016] In one embodiment of the invention, the endoprosthesis could
have a cell-defining structure that is radially expandable from a
first diameter to a second diameter. The cell-defining structure
defines at least one cell and includes a first set of strut members
defining a base cell section and a second set of strut members
defining an upper cell section that has a generally trapezoidal
shape when the cell-defining structure is in the second diameter.
The upper cell section preferably has generally parallel opposing
sides, one of which is generally aligned with a first side of the
base cell section. The base cell section can have a quadrilateral
shape when the second cell-defining structure is in the second
diameter, and this quadrilateral shape is preferably a
parallelogram. Additionally, the base cell section can have a major
and a minor axis, the major axis being oriented generally
longitudinally with respect to the cell-defining structure.
[0017] The cell-defining structure can further include a third set
of strut portions defining a lower cell section that has a
generally trapezoidal shape when the cell-defining structure has
the second diameter. The lower cell section preferably has
generally parallel opposing sides, one of which is generally
aligned with the second set of the base cell section that is
opposite the first side thereof.
[0018] The cell-defining structure preferably defines a plurality
of cells, with each cell having a base cell section, an upper cell
section, and a lower cell section. Each of the upper and lower
sections are preferably disposed at opposite sides of their
respective base cell sections, and each cell from the plurality of
cells can be connected to a circumferentially adjacent cell by a
strut member that extends between adjacent upper and lower cell
sections. The strut members can be common strut members of two
longitudinally adjacent base cell sections.
[0019] A plurality of circumferentially adjacent cells can be
arranged to provide at least two adjacent annular elements. These
adjacent annular elements can have common strut portions defining
adjacent upper and lower cell sections. When the cell-defining
structure has a first diameter, one of the strut members of the
second set of strut members is preferably folded towards one of the
strut members of the first set of strut members, and one of the
strut members of the third set of strut members can be folded
towards one of the strut members of the first set of strut
members.
[0020] An embodiment of the endoprosthesis has a series of
interconnected strut members with a repeating group of a first
generally longitudinal strut member, a first angled strut member
contoured to have a nesting feature, and a second longitudinal
strut member. The nesting feature is preferably configured for
nestingly receiving at least one longitudinal strut member therein
when the endoprosthesis body has the first diameter. The first and
second ones of the annular elements preferably share a common
second angled strut member. Also, the first and second annular
elements can be connected by a connector member. The strut member
that is nestingly received in the nesting feature can be a strut
member of the first or second sets. In one embodiment of the
endoprosthesis, a generally tubular scaffolding body thereof has an
outer component that includes a first set of interconnected strut
members and an inner component that includes a second set of
interconnected strut members. The first set of interconnected strut
members overlaps the second set of interconnected strut members,
such as in a radial direction, to define a cooperating cell
pattern. The inner and outer components preferably comprise inner
and outer tubes, which can be substantially coaxial. The first and
second sets of interconnected strut members can be abutting when
the tubular scaffolding body is in the expanded, or delivery,
state. Also, each of the inner and outer components can
independently comprise an integral tubular structure.
[0021] The tubular scaffolding body of an endoprosthesis according
to the invention can be configured with a first bias when in a
first range of diameter between compressed and expanded diameters,
and a second bias when in a second range of diameter between the
first range and the expanded diameter. The second bias is expansive
and has a greater expansive magnitude than the first bias. In one
embodiment, the body naturally tends to contract when the body is
smaller than a predetermined diameter and then naturally expand
when the body is larger than a predetermined diameter.
[0022] Preferably, the body includes a contractile portion that is
biased to contract the body, and also an expansive portion that is
biased to expand the body. The contractile portion is preferably
disposed within the expansive portion. Also, the contractile and
expansive portions can be disposed in longitudinally adjacent
annular elements of the body. With this layout, a plurality of
longitudinal spines can couple the plurality of adjacent rings, and
at least one of the longitudinal spines can extend across at least
three adjacent annular rings, preferably providing either
contractive or expansive forces at the ends thereof, with opposite
forces in the middle thereof.
[0023] One of the contractile and expansive portions can comprise
an outer tubular structure with the other comprising an inner
tubular structure received coaxially within the outer tubular
structure. Preferably the contractile portion comprises the outer
tubular structure, and the expansive portion comprises the inner
tubular structure.
[0024] Additionally, the contractile portion can have a geometry
for decreasing the leverage of its bias when the body is expanded,
and the expansive portion can have a geometry for increasing the
leverage of its bias when the body is expanded. One embodiment of
the endoprosthesis has a generally tubular scaffolding body that
includes a first portion tending to contract and a second portion
tending to expand when the body is at a predetermined diameter.
[0025] Another endoprosthesis embodiment has a tubular scaffolding
body that is biased for expanding towards an expanded diameter from
a contracted diameter. The body is configured such that the bias
increases as the diameter approaches the expanded diameter from the
contracted diameter. The bias can increase at any selected part of
the expansion, either as it begins to expand from the contracted
diameter, as it finalizes its expansion to the expanded diameter,
or somewhere in between. This is preferably achieved by providing a
contractile portion with a first geometry for decreasing the
leverage of the bias thereof when the body is expanded and an
expansive portion with a geometry for increasing the leverage
thereof when the body is expanded.
[0026] A preferred method of manufacturing the endoprosthesis
comprises setting a contractile portion of the endoprosthesis body
to bias the body to contract the diameter and setting an expansive
portion of the endoprosthesis body to bias the body to expand the
diameter that is larger than the contracted diameter. Preferably,
each of the contractile and expansive portions are formed as a
tubular structure, one of which is placed within and coupled with
the other.
[0027] In a preferred method of expanding an endoprosthesis, the
endoprosthesis has both a contractile portion and an expansive
portion positioned on a balloon of an endoprosthesis delivery
catheter. The balloon is inflated to an intermediate endoprosthesis
diameter that is less than the fully expanded diameter thereof. In
this manner, the balloon causes the endoprosthesis to expand only
to the intermediate endoprosthesis diameter, and the expansive
section of the endoprosthesis expands the endoprosthesis to its
fully expanded diameter. Preferably, the balloon has a maximum
inflated diameter that is at most equal to the intermediate
endoprosthesis diameter. The balloon is preferably inflated to a
pressure that will selectively cause it to only inflate to the
intermediate endoprosthesis diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a planar view of an embodiment of a stent
cell-pattern constructed according to the invention in a deployed
configuration;
[0029] FIG. 2 is a side view of a stent having the cell-pattern of
FIG. 1 in the deployed configuration;
[0030] FIG. 3 is a planar view of another embodiment of a stent
pattern similar to FIG. 1, but for a coiled-sheet stent;
[0031] FIG. 4 is a planar side view of another embodiment of a
stent cell-pattern in a delivery configuration in accordance with
another aspect of the invention;
[0032] FIG. 5 is a planar side view thereof in a deployed
configuration;
[0033] FIG. 6 is a planar view of an annular element thereof;
[0034] FIG. 7 is an enlarged, partial side view of the embodiment
of FIG. 5, showing longitudinally adjacent cells;
[0035] FIG. 8 is a partial perspective view of the embodiment of
FIG. 5;
FIG. 9 is an end view of a modified embodiment of FIG. 5;
[0036] FIGS. 10-12 are cross-sectional views of different
embodiments of single layer stents in a contracted position
according to the invention;
[0037] FIGS. 13 and 14 are cross-sectional views of an embodiment
of a multilayer stent in accordance with another aspect of the
invention in contracted and expanded states, respectively;
[0038] FIGS. 15 and 16 are planar views of portions of inner and
outer stent components, respectively, of a multilayer stent
embodiment according to the invention in an expanded state;
[0039] FIG. 17 is a planar view of a portion of the multilayer
stent with the inner and outer components of FIGS. 15 and 16
combined in the expanded state;
[0040] FIG. 18 is a planar view of the inner component of FIG. 15
in a contracted state;
[0041] FIG. 19 is a planar view of the combined portion of FIG. 17
in a contracted state;
[0042] FIGS. 20-23 show simplified portions of typical stent
scaffolding patterns in planar view;
[0043] FIGS. 24-27 show planar views of simplified portions of
other embodiments of stent scaffolding patterns that can be
combined according with the invention;
[0044] FIGS. 28-31 embodiments show portions of stent scaffolding
patterns in planar view having expansive both and contractile
sections;
[0045] FIG. 32 is a planar view of a portion of a stent scaffolding
structure having alternating rings of expansive and contractile
patterns; and
[0046] FIG. 33 is an axial diagrammatic view of a stent having both
coaxial expansive and contractile layers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] In accordance with the present invention, an endoprosthesis
is provided for delivery within a body lumen of a human or animal.
The endoprosthesis can include, but is not limited to, stents,
stent grafts, valves, occlusive devices and aneurysm treatment
devices or the like. The endoprosthesis of the present invention
can be configured for a variety of intraluminal applications,
including vascular, coronary, biliary, esophageal,
gastrointestinal, urological or the like. The present invention
provides improved control to the contraction, expansion, and the
contracted and expanded states of the endoprosthesis.
[0048] Generally, the endoprosthesis of the present invention
includes a first set of interconnected strut members defining a
first annular element, and a second set of interconnected strut
members defining a second annular element. The endoprosthesis can
include only one annular element if suitable, or additional annular
elements defined by interconnected strut members as desired or
needed. Each annular element defines a structure extending
circumferentially about a longitudinal axis. The cross profile of
each annular element preferably is at least arcuate, and more
preferably either circular or spiral, although alternative cross
profiles, such as rectilinear or the like, can be used if
desired.
[0049] The first annular element is aligned longitudinally adjacent
to the second annular element along the longitudinal axis, and
connected to each other at least one connection location.
Preferably, the first and second annular elements generally define
a tubular structure. For example, each annular element can define a
continuous closed ring such that the longitudinally-aligned annular
elements form a closed tubular structure having a central
longitudinal axis. Alternatively, each annular element can define
an open ring such that a rolled sheet or open tubular type
structure is defined by the annular elements.
[0050] Each strut member of the annular elements includes a first
end and a second end. The strut members of each annular element are
disposed circumferentially adjacent to each other, and
interconnected so as to define an expandable structure. For
example, and with reference to the closed tubular structure above,
circumferentially-adjacent strut members of each annular element
can be interconnected, either directly or indirectly, in an
end-to-end format to define a continuous ring having a generally
circular cross profile. By altering the angle or distance defined
between circumferentially-adjacent strut members, as well as by
opening or unfolding the portions of each stent as described
further below, the tubular structure can be radially expanded
between a delivery configuration and a deployed configuration. As
discussed in detail below, the expandable structure can be expanded
by the application of an external force, such as by a balloon, or
by a change in delivery conditions, such as an increase in
temperature or the removal of a restraint, so as to allow the
structure to self expand.
[0051] In accordance with one aspect of the invention, an
endoprosthesis is provided having a plurality of annular elements
that are connected to adjacent annular elements at least one
connection location. Each annular element includes an
interconnected series of strut members, each connected to an
adjacent strut member at a longitudinal apex and extending to a
strut end portion at a location on the longitudinally opposite side
of the annular element from the apex. At least one of the strut
members includes a first end portion, an intermediate portion, and
a second end portion. The first end portion is located at the strut
end portion. The intermediate portion is hingedly connected to the
first end portion. The second end portion is hingedly connected to
the intermediate portion and extends to the apex. The
endoprosthesis has a delivery diameter when in a delivery condition
and a deployed diameter when in a deployed condition.
[0052] With reference to FIG. 1, for purpose of illustration and
not limitation, a representative embodiment of an endoprosthesis,
which in this embodiment is a stent 10 of the present invention, is
depicted in a planar format for clarity. As shown in FIG. 1, the
stent 10 includes a plurality of annular elements 12 arranged
generally circumferentially and disposed and preferably aligned
adjacent to each other along a longitudinal axis 36. Although only
one annular element need be provided, it is preferable that the
stent 10 include a plurality of annular elements 12, defined herein
at least by first and second annular elements 12. The annular
elements 12 are preferably longitudinally displaced from or
adjacent to each other and are connected to an adjacent annular
element 12 at least one connection location 16.
[0053] The annular elements 12 include an interconnected series of
strut members 20. Each strut member 20 of the embodiment shown in
FIG. 1 has an end portion 18 at a first end of the strut member 20,
an intermediate portion 22 hingedly connected to the first end
portion, and a second portion 24 hingedly connected to intermediate
portion 22.
[0054] Preferably, at least one pair of adjacent strut members 20
are hingedly connected together to form an arrowhead shape 26,
defined by the first end portion 18, intermediate portion 22, and
second end portion 24. This configuration generally can be
construed as a five point hinge, with hinge points 28 between the
portions.
[0055] The arrowhead portions 26 preferably include two
circumferential sides 30 that are preferably mirror images of each
other, but in other embodiments may differ from each other. Each
circumferential side 30 comprises a first end portion 18, an
intermediate portion 22, and a second end portion 24. Preferably
attached end to end, these portions 18, 22, 24 extend along a
lightning-bolt shaped path that doubles back upon itself, with
hinges or elbows that generally reverse the direction of the path
between portions 18, 22, 24, so as to collapse in a folding or
accordion manner. All of the portions 18, 22, 28 are preferably
oriented at an angle to both the longitudinal and circumferential
axes 36, 14 when deployed. In this embodiment, the portions of the
strut members 20 are substantially straight, but can be curved in
other embodiments. For example, the first and/or second end
portions can be contoured to allow the intermediate portion to nest
therein when in the delivery state. Also, the hinges between the
arrowhead portions are preferably sharp angles, although can be
rounded to remove stress concentration if desired. Each side 30 of
the arrowhead shape 26 preferably extends substantially equally in
opposite circumferential directions, but in alternative
embodiments, may extend to each side by a different amount.
[0056] As shown in FIG. 1, selected ends can be connected directly
together to define an apex 29 at the tip of the arrowhead shape 26.
In the embodiment of FIG. 1, each sharp apex 29 is connected to an
apex 29 of an opposing arrowhead shape 26 at a connection location
16. In an alternative embodiment, however, the arrowhead shapes 26
may protrude into each other, or a separate longitudinal connector
can be provided therebetween.
[0057] As further embodied herein, some of the arrowhead shapes 32
are longitudinally free from connection to adjacent annular
elements 12. These longitudinally free arrowhead shapes 32
preferably have a shorter longitudinal extent than the sharp
arrowheads that are connected to adjacent annular members 12. The
opposing second end members 24 on each side of the free arrowheads
32 are connected by a circumferential member 34, which is disposed
in substantial alignment with the circumferential direction 14 to
form a blunt arrowhead shape as embodied herein. Alternatively, a
V-shaped or otherwise contoured member can be provided. The blunt
or flat arrowhead shapes can provide a height or circumferential
direction of the flat apex at the end of a longitudinally free
arrowhead that is equivalent or slightly less than the height of
the remaining folding members of the annular elements, including
the struts and strut portions, in the delivery condition. This aids
in maximizing packing density.
[0058] In alternative embodiments, some or all connection locations
can be disposed on the circumferential members 34. For example, a
straight or curved connector can extend longitudinally between the
circumferential members 34 to connect adjacent annular elements. In
these embodiments, a large range of phase differences can be
selected between adjacent annular elements 12, as the
circumferential elements 34 provide a wide base for the connection
locations 16, providing versatility in the design of the
pattern.
[0059] The annular elements 12 are preferably similar to each other
in a particular stent pattern. In other embodiments, the layout and
configuration of the annular elements 12 can be varied for desired
characteristics such as varied rigidity or flexibility.
Additionally, the pattern formed by the strut members 20 of annular
elements 20 can be in or out of phase with those of adjacent
annular elements 12. In FIG. 1, the patterns of adjacent annular
members 12 are 180.degree. out of phase, which can be seen as the
apices 29 and circumferential members 34 of adjacent annular
elements 12 are directly opposed and substantially in alignment
with and facing towards and away from each other. Embodiments with
annular members 12 that are in phase have circumferentially aligned
arrowheads all facing in the same longitudinal direction. The
adjacent annular elements 12 that are connected with adjacent
annular elements 12 are preferably positioned sufficiently out of
phase so that the connection locations 16 are disposed at the
arrowheads 26 of the adjacent annular elements 12, so that the
arrowheads themselves are directly connected.
[0060] In the preferred embodiment, each annular member 12 defines
a series of arrowheads 26 alternating in opposite longitudinal
directions 36. Preferably, one or more free arrowheads 32 are
disposed circumferentially adjacent to connected arrowheads 38 on
adjacent annular elements or a selected side of each annular member
12 so that connected arrowheads 38 are not immediately
circumferentially adjacent to each other in the preferred
embodiment. The number of free arrowheads between connection
locations can be varied in other embodiments.
[0061] In the preferred arrowhead shapes 26, the intermediate
portions 22 are disposed at an angle of about 90.degree. or less to
the first end portion 18 and to the second end 24 portion when
deployed. Also, the intermediate portions 22 are disposed at an
angle of about 90.degree. or less to the longitudinal axis when
deployed, as measured on a longitudinal side of the intermediate
portion 22 opposite from the tip of the arrowhead 26, Preferably,
the circumferential width of the base of the arrowheads 26, at the
end of the first end portions 18, opposite from the tip of the
arrowheads 26, is wider than the midsection of the arrowheads 26,
at the circumferentially widest portion of the intermediate
portions 22.
[0062] The pattern 10 of the preferred embodiment is configured
such that each portion of the strut members 20 is substantially
aligned with the longitudinal axis of the stent when in the
delivery configuration. In addition, the plurality of strut members
20 are interconnected to form a cell pattern that includes the
arrowhead portions 26. Along the circumferential length of the
annular elements 12 that define the cell patterns 40 are arrowheads
26 that point in opposite longitudinal directions and which
preferably share common strut members 20. For instance, as shown in
FIG. 1, first end portion 42 of arrowhead 44 is the second end
portion of arrowhead 46. Similarly, the arrowheads 26 of the cells
share the same boundaries and strut members 20 with adjacent cells
in the preferred embodiment, such as cells 48 and 50. As shown in
FIG. 2, the cells are connected in a generally cylindrical shape to
define the cylindrical stent.
[0063] The preferred stent is substantially cylindrical, and the
circumferential edges of the stent 10 are preferably continuous
with each other. In an alternative embodiment, the stent is made of
a coiled sheet, in which the lateral edges of the pattern are not
affixed to each other and in which the annular elements 12 are
open. The coiled sheet can be delivered in a small diameter, coiled
state to the deployment site, with the opposing edges of the sheet
preferably configured for engaging each other when the stent is
expanded to the deployed position, to prevent collapse of the
stent. For example, uneven lateral edges can be used on the
opposite circumferential edges 56 to hook with each other to
prevent collapse. FIG. 3 shows a coiled sheet embodiment 54, with
saw tooth circumferential edges 56 to catch in interlocking
engagement with opposing saw tooth circumferential edges 56 to
prevent collapse of the sheet from the deployed position. In this
manner, the coil sheet will both unravel and expand
circumferentially when deployed.
[0064] The connection locations 16 and, if present, any connectors
extending between connection locations 16 on longitudinally
adjacent annular elements 12, are preferably circumferentially
displaced with respect to each other to improve flexibility of the
stent. Another embodiment has all of the connection locations 16
aligned if desired.
[0065] The arrowhead portions 26 are preferably configured and
dimensioned relative to the strut members and the remainder of the
stent pattern to compensate for longitudinal foreshortening upon
stent expansion. This is preferably achieved by the position and
angle of the intermediate portions 22 with respect to the
longitudinal axis and other strut portions. The intermediate
portions 22 open in an elongating direction relative to the
foreshortening which occurs as each pair of adjacent strut members
open relative to each other. The geometry of the arrowhead portion
can be selected otherwise to provide a desired amount of
lengthening or shortening upon expansion, depending on the stent
application and is preferably selected to provide an even
distribution of strain in expanding areas of the stent. The
arrowhead portions also are provided to improve and control the
flexibility of the stent, preferably without substantially
degrading the coverage thereof or the scaffolding the stent
provides. In some embodiments, the arrowhead portions are
configured to produce a torque on the longitudinally free
protrusions of the pattern to bias these longitudinally free
portions back inward towards the general cylindrical shape of the
stent when the stent is flexed along its longitudinal axis. This
feature can be increased or decreased if desired to embed portions
of the stent into an arterial wall or other tissue.
[0066] To achieve these characteristics, several aspects of the
geometry can be varied. These aspects include the strut member
length, width, thickness and cross section; the shape and amount of
hinge points within the arrowhead portions; the phase difference
between adjacent annular elements; the number of connection
locations and the length of any connectors; the number of apices or
free arrowheads between connections; and the shape of strut members
and any connectors.
[0067] In accordance with another aspect of the invention, an
endoprosthesis is provided having a cell-defining structure that is
radially expandable from a first diameter to a second diameter. The
structure has at least one cell, which includes a first and a
second set of stent members. The first set defines a base cell
section. The second set defines an upper cell section that has a
generally trapezoidal shape when the cell-defining structure is in
the second diameter, and preferably generally parallel opposing
sides. One of the opposing sides is preferably generally aligned
with a first side of the base cell section.
[0068] Referring to FIGS. 4 and 5, in one embodiment, a stent 100
includes a generally tubular stent body 110, which is radially
expandable between a delivery configuration as shown in FIG. 4 and
a deployed configuration as shown in FIG. 5. As shown in FIG. 4,
the contracted configuration may be referred to as the "delivery"
configuration or "crimped" configuration. The expanded
configuration may be referred to as the "deployed" diameter.
[0069] Referring to FIGS. 5 and 7, the stent body 110 includes a
cell-defining structure 120 defining at least one cell 130. The
cell-defining structure 120 includes a first set of strut portions
140 defining a base cell section 142, and a second set of strut
portions 150 defining an upper cell section 152. The upper cell
section has a generally trapezoidal shape when the stent body has
the expanded diameter, as shown in FIG. 5. The upper cell section
152 has generally parallel opposing sides 155, 154. The side 155
disposed longitudinally farthest from the base cell section
includes a strut portion that forms a generally flat apex. The
other of the generally parallel opposing sides 154 of the upper
cell section is generally aligned with and defined by an opening
145 in a first side 144 of the base cell section 142. In the
embodiment shown, the trapezoidal-shaped upper cell section 152 has
an open side that corresponds to the opening 145 in the first side
144 of the base cell section 142. The opening 145 provides
increased longitudinal flexibility to the stent.
[0070] The base cell section 142 has a generally quadrilateral
shape when the stent body 110 has the expanded diameter. The
quadrilateral shape is preferably a parallelogram having sides 111.
The base cell section 142 may be considered to have a major axis
and a minor axis. In the embodiment shown, the major axis is
oriented generally longitudinally with respect to the stent
body.
[0071] The cell-defining structure 120 may further include a third
set of strut portions 160 defining a lower cell section 162 having
a generally trapezoidal shape when the stent body has the expanded
diameter. The lower cell section may have generally parallel
opposing sides 164, similar to the upper cell section described
above. One of the opposing sides 164 of the lower cell section 162
is preferably generally aligned with a second side 146 of the base
cell section 142 that is opposite the first side 144 of the base
cell section.
[0072] In the embodiment of FIG. 5, the cell-defining structure
defines a plurality of cells 130, each cell having a base cell
section, an upper cell section, and a lower cell section. Each of
the upper and lower cell sections are oriented at circumferentially
opposite sides of a respective base cell section, and each cell of
the plurality of cells is connected to a circumferentially adjacent
cell by a strut 170 extending between adjacent upper and lower cell
sections. As shown, the strut 170 may be a common strut portion of
two longitudinally adjacent base cell sections 142.
[0073] When a plurality of adjacent cells is provided to form a
plurality of adjacent annular members, the cell-defining structure
may define a plurality of cells arranged to defame a uniform
pattern throughout the stent body. The uniformity of the cell
pattern may be provided in selected sections of the stent body,
e.g. longitudinal sections may have differing uniform patterns, to
provide selected characteristics of the stent, such as variable
flexibility or scaffolding throughout the stent. Alternatively, the
cell pattern can be configured such that a non-uniform pattern is
provided.
[0074] The mechanism by which the stent body 110 is moved between
the delivery configuration and the deployed configuration includes
folding and nesting of the various strut portions making up the
sections of the cells. For instance, as can be seen when comparing
FIG. 4 and FIG. 5, one strut portion of the second set of strut
portions is folded toward one strut portion of the first set of
strut portions when the stent body has the delivery configuration.
Also, when the stent body has the delivery configuration, one strut
portion of the third set of strut portions is folded toward one
strut portion of the first set of strut portions.
[0075] Another feature of the strut portions of the cell defining
structure is that at least one strut portion of the first, second,
or third sets of strut portions may be contoured to nest with an
adjacent strut portion when the stent body has the contracted
diameter so as to provide a nesting feature. For example, FIG. 5
shows a contour or detent in member 15 to receive member 120 when
contracted to the delivery configuration as shown in FIG. 4.
Similar contours are depicted in the angled side members of the
upper and lower cell sections 152, 162.
[0076] The stent 100 preferably includes a plurality of
circumferentially adjacent cells 130 that are arranged to provide
at least two adjacent annular elements. A plurality of
circumferentially adjacent cells 130 can be arranged to provide two
or more longitudinally adjacent annular elements as identified in
FIG. 5 for illustrative purposes. For example, a first annular
element 180 is generally positioned between reference lines 132 and
134 and a second annular element 180 is positioned between
reference lines 134 and 136. The lines 132, 134, 136 in FIG. 5 that
indicate the adjacent annular elements 180 are shown extending
along longitudinal edges of respective annular elements. The
adjacent annular elements have common strut portions defining
adjacent upper and lower cell sections as depicted more clearly in
FIG. 6. The struts 170 extending between adjacent upper and lower
cell sections 152 and 162 of the central annular element 134
include common strut portions of two longitudinally adjacent base
sections 142 of the adjacent annular elements.
[0077] FIG. 6 shows a portion of the stent body that may be
considered an annular element 180. The annular element 180 includes
a first series of interconnected strut members 181. The first
series of interconnected strut members includes a repeating group
186 of a first longitudinal strut 182, a first angled strut 183
having a nesting feature 187, a second longitudinal strut 184, and
a second angled strut 185. Stents with this pattern are shown for
the purpose of illustration in a closed-ring embodiment in FIG. 8,
and in a coiled, open-tube embodiment in FIG. 9.
[0078] The stent body will further include a second annular element
including a second series of interconnected strut members. The
second series of interconnected strut members also will include a
repeating group of a first longitudinal strut, a first angled strut
having a nesting feature, a second longitudinal strut, and a second
angled strut. In one embodiment, the first and second annular
elements share at least one common second angled strut. In another
embodiment, the first and second annular elements are connected by
a separate connector member, such as between longitudinal struts to
define another nesting feature as shown in FIG. 5. In yet another
embodiment, a connector member extends between respective second
angled struts of each of the first and second annular elements.
[0079] The nesting feature 187 is contoured for nestingly receiving
one or more adjacent strut portions of the first or second sets in
nested association therein when the stent is in the delivery
configuration, as shown in FIG. 4. Some nesting features 187
nestingly receive a longitudinal strut 184 on opposite sides
thereof generally parallel to the angled strut 183 in the
contracted state, while other nesting features 187 nestingly
receive the longitudinal struts 182 on opposite sides thereof at an
angle to the angled strut 183 in the contracted state.
[0080] Referring to FIGS. 10-12, which are greatly simplified for
purposes of illustration, various single-layer endoprosthesis
having different numbers of strut members in an annular element are
shown in cross-section in the delivery or compressed configuration.
These figures are representative of certain stent embodiments known
in the art, as well as embodiments in accordance with one aspect of
the present invention, as described above. Stent 210 has eighteen
struts in the cross-section shown, stent 211 has ten struts, and
stent 212 has sixteen struts in an annular element. It is
recognized that in stent patterns, the adjacent struts generally do
not touch because the amount of movement (or how tightly the stent
can be crimped or compressed) is limited by the strain in the metal
or other material from which the stent is made. Generally, however,
the inner diameter 200 of the contracted stent 210-212 is a
function of the number of struts in the annular element and the
widths of the strut members.
[0081] In accordance with another aspect of the invention, a
multilayer endoprosthesis has a scaffolding body with inner and
outer components that each include a set of interconnected strut
members. The strut members of each set overlap the strut members of
the other set to define a cooperating cell pattern. For example,
and as shown in the embodiment of FIGS. 13 and 14, stent 214
includes multiple layers of struts 216, in which the struts 216
overlap each other as the stent is crimped or compressed to the
delivery configuration. By providing multiple layers, the struts
216 can nest more tightly during crimping to enable the stent to
crimp or compress to a smaller diameter while maintaining
scaffolding characteristics similar to that of a single layer stent
with an equal number of stents. That is, this embodiment provides a
reduced profile stent without compromising the ability of the stent
to support the vessel. A total of seventeen struts 216 are depicted
in the embodiment shown of stent 216, although more or fewer can be
provided.
[0082] The stent 216 preferably includes inner and outer components
218,220, each including a set of interconnected struts, preferably
with about an equal number of struts. Preferably, struts of each
set are interconnected to define corresponding annular elements
capable of being moved between a delivery configuration and an
expanded configuration, such as disclosed in the embodiments
herein, or may be varied as desired for the particular application.
The inner and outer components 218,220 are preferably separately
manufactured as independent tubular members, each with about half
(or other fraction depending on the embodiment) of the struts
contemplated for the complete stent 216. The inner component 218 is
preferably placed within the outer component 220 and attached
thereto, such as at some or all of the points where the struts of
the inner and outer components overlap in the expanded
configuration. Preferably, the components 218,220 are attached
directly to each other, without another material layer in between.
In stents with more than two layers, preferably at least two of the
layers that provide scaffolding or other supportive, expansive, or
contractive structure are placed directly adjacent each other,
without an intervening layer, and attached directly to each other
as well.
[0083] Although a variety of stent patterns can be constructed with
inner and outer components or layers, FIGS. 15-19 depict a
representative embodiment of a stent having an arrowhead pattern
defined by inner and outer components in accordance with the
invention for purpose of illustration and not limitation. The
annular element or set of strut members of inner stent component
222 shown in FIG. 15 includes a plurality of strut members
interconnected in a zigzag manner to form an annular element. Each
strut 226 has several strut portions 228 hingedly connected in a
manner similar to that of the stent of FIGS. 1-3 above, but
preferably extending in a double lightning-bolt pattern, as shown.
Adjacent struts 226 are connected to form inner arrowheads 224. The
apices 230 of these arrowheads 224 can be connected directly to
longitudinally adjacent arrowheads 232 directly, as shown in dotted
lines, or via connectors. Selected apices of the arrowheads can
remain unconnected as desired. The annular element or set of strut
members of the outer stent component 234 shown in FIG. 16 is
embodied herein of substantially the same pattern as the strut
members of the inner stent component 222, so as to form arrowheads
236.
[0084] The inner component is then positioned within the outer
component and, preferably, affixed together. As shown in FIG. 17,
the inner and outer stent components 222, 234 are attached and
preferably fixed together, with the strut members of each component
180.degree. out of phase circumferentially, at points of overlap
between the struts of each component, preferably forming hinges
238. The strut members of the attached stent components define
double-sided arrowhead 240, each circumferential side of which
belongs to a different one of the inner and outer stent components
222, 234.
[0085] As shown in FIG. 18, when the complete multilayer stent 242
is crimped or contracted, the struts of each component 222, 234
nests preferably only with other struts of the same component or
layer, so as to be contracted to a diameter less than that of a
single layer stent having the same number of struts as the two
components combined. Referring to FIG. 19, portions of the inner
and outer components 222, 234 overlap radially when the stent 242
is contracted, permitting a reduced contracted diameter which can
be easily delivered to a desired site and then expanded to a
deployed configuration. As will be understood, other types of
patterns can be made with inner and outer components or layers,
including but not limited to arrowheads or quadrilateral areas as
disclosed in the previous embodiments herein.
[0086] The multilayer embodiments of the invention can be
constructed by making the components or layers separately and then
assembling the components together. Local welds, clips, crimps,
sutures or other techniques can be used to attach the layers
together. The different layers of the endoprosthesis can be made
with substantially different patterns to maximize or control stent
performance. For example, one layer or component can be a coil-type
structure to provide suitable strength without compromising
flexibility, while the other layer or component can be a thin
slotted tube for optimum scaffolding. Additionally, the different
layers or components can be made of different materials chosen to
optimize the performance of each layer. For example, the outer
layer can be made of a NiTi alloy designed and set to provide a
slight contractile force, such as just enough to engage the
underlying layer. In this embodiment, the stent components need not
be fixed, but may naturally press against each other to stabilize
the multiple layers of the stent or the like.
[0087] In accordance with yet another aspect of the invention, an
endoprosthesis can be provided, which generally can both
self-contract and self-expand. Embodiments that can both constrain
themselves on the delivery system and deploy themselves at the site
of treatment can make it possible to reduce or eliminate a
significant amount of material on the catheter or delivery system,
thus allowing such a system to be used in more tortuous or smaller
sized vessels. In the preferred examples of these embodiments,
diameter-dependent competing mechanical forces within the
endoprosthesis, such as a stent, are provided to cause the stent
either to expand or to contract, depending on its diameter. Some
parts of the stent are configured to exert contractive forces that
tend to crimp or compress the stent, while other parts of the stent
are configured to exert expansive forces that tend to deploy the
stent. Both forces are generated through the particular patterns
designed into each part of the stent.
[0088] For example, and in one embodiment, the geometry of the
patterns is such that when the stent is at a low,
contractive-dominant profile, such as in the delivery
configuration, the contracting forces are dominant and the stent
stays compressed, while when the stent is at least partially
expanded to an expansive-dominant profile, the expansive forces
become dominant and the stent expands, such as in the deployed
configuration. In this manner, the delivery system need only
require a thin balloon of minimum mass to deploy the stent from the
contractive-dominant profile to the expansive-dominant profile, at
which point the stent continues to expand on its own to its fully
deployed diameter.
[0089] Alternatively, the stent can be designed such that the
expansive forces are always dominant, but at the delivery
configuration, the expansive forces are marginal, such that only a
very thin sheath or other mechanism of minimal mass and volume need
be used to constrain the stent. The expansive forces thus increase
as the stent approaches the deployed configuration. In either case
the assistive material, or stent deployment material of the
delivery system, can be significantly thinner and less bulky than
the traditional balloon expandable or self-expanding stent delivery
systems.
[0090] In accordance with one aspect of this invention, the stent
is preferably made from a super elastic material, such as Nitinol
or Elgiloy, to accommodate the changes in geometry employed for
expansion without plastically deforming the material. In one
embodiment, a stent with both contractile and expansive properties
has two different competing geometries within the stent, one for
each type of force. As used here, "geometry" is defined as being a
cellular or sub-cellular pattern designed to provide a specific
force-deformation characteristic. The stent as a whole may include
both contractile and expansive sections, wherein each section
includes one or more repeats of a particular geometry. The
different super elastic sections are preferably heat set in the
appropriate states: the contractile sections corresponding to the
stent crimped or compressed in the delivery configuration, and the
expansive sections corresponding to the stent expanded in a
deployed configuration. The separately set sections can then be
combined to form a stent in accordance with the invention.
[0091] The preferred self-crimping and expanding stent can employ
different geometries for each section. To achieve the
self-crimping-at-low-profile and self-expanding-at-high-profile
function of the preferred embodiment described herein, the stent
comprises regions of different strut geometries. Preferably, at
least one of the geometries is configured such that its leverage or
corresponding force is reduced as it is deformed from its set
state, with an effect that counteracts and exceeds the increases in
force caused by stress of the deformation from the set state.
[0092] For example, the stent pattern subcomponent geometries shown
in FIGS. 20 and 21 are made up of strut portions 301 and have a
series of undulating bends 300 that unfold as the stent expands.
The stent pattern subcomponents of FIGS. 22 and 23 have closed
cells 302 that can contract or expand circumferentially. Pattern
subcomponents of these types may be used for either the expansive
or the contractile sections when made of super-elastic material and
set separately as described above.
[0093] A preferred embodiment, however, incorporates the use of
decreasing leverage patterns to enhance contractile forces.
Examples of "decreasing leverage" pattern subcomponent 304, 304
geometries are shown in FIGS. 24-27. As the stent expands, the
lever arm 308 of the geometry increases with respect to the
direction of force 310 applied circumferentially as shown in FIGS.
24 and 25 for one exemplary embodiment, and in FIGS. 26 and 27 for
another exemplary embodiment. As the force 310 causes the bends of
the geometry to open from a subcomponent contracted state to a
subcomponent expanded state, the perpendicular distance from the
direction of force to the bending point increases, thus increasing
the lever arm 308. As the lever arm 308 increases, there is a point
at which the expansion force 310 overcomes the opposing contraction
force of the bends in the geometry. Conversely, in the portions of
the geometry that make up contractile sections of the stent, as
discussed below, the contraction force will overcome the force in
the geometry that tends to expand the stent. Such decreasing
leverage patterns can be made of super elastic material or
deformable material.
[0094] The annular element 312 shown in FIGS. 28 and 29 for purpose
of illustration and not limitation has cells 314 that include
expansive sections 316 fixed to contractile sections 318,
preferably at hinge points 320. FIGS. 30 and 31 show another stent
embodiment 322 with cells 324 that incorporate both expansive
sections 326 and contractile sections 328 that are naturally biased
opposite each other. In both of these embodiments, the expansive
sections 316,326 preferably each have an elongated shape generally
aligned in a longitudinal direction 330, and contractile sections
318,328 each have an S-shape or folded shape that extends generally
in a circumferential direction 332. When moved from the contracted
state to the expanded state, the expansive sections preferably
expand circumferentially, and the contractile sections preferably
expand circumferentially as well as longitudinally, with the
S-shape uncoiling.
[0095] In the embodiment of FIGS. 30 and 31, the contractile
sections 328 are contained within a closed cell defined between two
expansive sections 326 that are oriented in opposite longitudinal
directions. The contractile section 326 and both expansive sections
328 of each cell 334 are preferably connected at circumferentially
opposite hinges 336, each of which hinge 336 connects to both
struts from the expansive sections 326 and the strut from the
contractile section. Connector struts 338 connect hinges 336 of
circumferentially adjacent cells 334. Selected expansive sections
326 are connected to connector struts 338 extending longitudinally
to longitudinally adjacent annular elements 340, such as by
attaching to circumferential connectors 338.
[0096] Referring to FIG. 32, stent 342 has expansive annular
elements 344 and contractile annular elements 346, which are
preferably disposed in alternating order along the longitudinal
axis 346 of the stent 342, although other arrangements are
possible. Preferably, a plurality of expansive or contractile
annular elements are positioned circumferentially adjacent each
other in the series to define annular elements of interconnecting
struts as previously described. The expansive and contractile
annular elements 344,346 are preferably coupled by longitudinal
connectors 348 that preferably extend across several or all of the
annular elements to provide a backbone linking the expansive and
contractile forces. The backbone connectors 348 are preferably
configured to maintain a generally even diameter of the stent in
the expanded position, and preferably also in the contracted
position. Other longitudinal connectors 350 can also or
alternatively be used as desired for the performance of the
particular stent. Connectors 350 preferably extend longitudinally
along less than all of the annular elements and can connect to
directly adjacent annular elements, while leaving the next
longitudinally adjacent annular elements unconnected thereby.
[0097] The various subcomponents with the different geometries
including those of FIGS. 1-3 and FIGS. 4-9 can be integrated to
form a complete stent in several ways. The contractile or expansive
properties can be alternated within a single piece of cut or etched
material, making up the stent. This would result in a simple step
of cutting and polishing, while the contractile and expansive
sections of the stent would be set separately so that the
contractile sections tend to contract the stent, and the expansive
sections tend to expand the stent. The stent can also be built up
from subassemblies of each section. As shown in FIG. 33, a
multilayer stent 356 can be made up of two thin layers or stent
components, with the outer layer 352 having the contractile pattern
and the inner layer 354 having the expansive pattern. The inner and
outer stent components can be attached or connected as described
above in relation to and further in accordance with the
multi-layered stent embodiments.
[0098] As noted above, the various aspects of the present invention
allow for a variety of different endoprosthesis embodiments, based
upon selective combinations of the features previously described
and shown. Similarly, the endoprosthesis of the present invention
can be made using any of a number of known manufacturing techniques
and materials.
[0099] The material of construction is preferably selected
according to the performance and biological characteristics
desired. For example, the endoprosthesis of the invention can be
made to be expanded by the change of a delivery condition, such as
by the removal of a restraint or exposure to the environment within
the body lumen, so as to be self expanding, or by the application
of an external force or energy, such as by a balloon or by a radio
frequency. For purpose of illustration and not limitation,
embodiments of "self-expanding" and "balloon expandable"
endoprosthesis of the present invention are provided
[0100] Self-expanding embodiments, or those that must be set, can
be made from any of a variety of known suitable materials including
super elastic or shape memory materials, such as nickel-titanium
(NiTi) alloys, chromium alloys such as Elgiloy, or any equivalents
thereof. An endoprosthesis made of a suitable super elastic
material can be compressed or restrained in its delivery
configuration on a delivery device using a sheath or similar
restraint, and then deployed to its deployed configuration at a
desired location by removal of the restraint as is known in the
art. An endoprosthesis made of shape memory material generally can
be delivered in a like manner, and if thermally sensitive, can be
deployed by exposure of the endoprosthesis to a sufficient
temperature to facilitate expansion as is known in the art. It also
is possible to make the self-expanding embodiment of a
biocompatible material capable of expansion upon exposure to the
environment within the body lumen, such as a suitable hydrogel or
hydrophilic polymer, including biodegradable or bioabsorbable
polymers. For example, if made of an expandable hydrophilic
material, the endoprosthesis can be delivered to the desired
location in an isolated state, and then exposed to the aqueous
environment of the body lumen to facilitate expansion. Alternative
known delivery devices and techniques for a self-expanding
endoprosthesis likewise can be used.
[0101] Balloon expandable embodiments or the like can be made of
any of a variety of known suitable deformable materials, including
stainless steel, silver, platinum, cobalt chromium alloys such as
L605, MP35N or MP20N, or any equivalents thereof. "L605" is
understood to be a trade name for an alloy available from UTI
Corporation of Collegeville, Pa. including about 53% cobalt, 20%
chromium and 10% nickel. "MP35N" and "MP20N" are understood to be
trade names for alloys of cobalt, nickel, chromium and molybdenum
available from Standard Press Steel Co., Jenkintown, Pa. MP35N
generally includes about 35% cobalt, 35% nickel, 20% chromium, and
10% molybdenum. MP20N generally includes about 50% cobalt, 20%
nickel, 20% chromium and 10% molybdenum. For delivery, the
endoprosthesis of a suitable material is mounted in the delivery
configuration on a balloon or similar expandable member of a
delivery device. Once properly positioned within the body lumen at
a desired location, the expandable member is expanded to expand the
endoprosthesis to its deployed configuration as is known in the
art. Additionally, or alternatively, balloon expandable embodiments
can be made of suitable biocompatible polymers, including
biodegradable or bioabsorbable materials, which are either
plastically deformable or capable of being set in the deployed
configuration. If plastically deformable, the material is selected
to allow the endoprosthesis to be expanded in a similar manner
using an expandable member so as to have sufficient radial strength
and scaffolding and also to minimize recoil once expanded. If the
polymer is to be set in the deployed configuration, the expandable
member can be provided with a heat source or infusion ports to
provide the catalyst to set or cure the polymer. Alternative known
delivery devices and techniques for a self-expanding endoprosthesis
likewise can be used.
[0102] Additional materials or compounds also can be incorporated
into or on the endoprosthesis if desired. For example, the
endoprosthesis can be provided with one or more coatings of
biocompatible material to enhance the biocompatibility of the
device. Such coatings can include hydrogels, hydrophilic and/or
hydrophobic compounds, and polypeptides, proteins or amino acids or
the like, such as PVP, PVA, parylene, and heparin. A preferred
coating material includes phosphorylcholine, as disclosed in U.S.
Pat. Nos. 5,705,583 and 6,090,901 to Bowers et al. and U.S. Pat.
No. 6,083,257 to Taylor et al., each of which is incorporated by
reference herein. Such coatings can also be provided on the
endoprosthesis to facilitate the loading or delivery of beneficial
agents or drugs, such as therapeutic agents, pharmaceuticals and
radiation therapies. Alternatively, the surface of the
endoprosthesis can be porous or include one or more reservoirs or
cavities formed therein to retain beneficial agent or drug therein
as is known in the art. For purposes of illustration and not
limitation, the drug or beneficial agent can include
antithrombotics, anticoagulants, antiplatelet agents,
thrombolytics, antiproliferatives, anti-inflammatories, agents that
inhibit hyperplasia, inhibitors of smooth muscle proliferation,
antibiotics, growth factor inhibitors, or cell adhesion inhibitors,
as well as antineoplastics, antimitotics, antifibrins,
antioxidants, agents that promote endothelial cell recovery,
antiallergic substances, radiopaque agents, viral vectors,
antisense compounds, oligionucleotides, cell permeation enhancers,
and combinations thereof.
[0103] The endoprosthesis can also be provided with coverings, such
as PTFE, ePTFE, Dacron, woven materials, cut filaments, porous
membranes, or others materials to form a stent graft prosthesis.
Similarly, a medical device, such as a valve, a flow regulator or
monitor device, can be attached to the endoprosthesis, such that
the endoprosthesis functions as an anchor for the medical device
within the body lumen.
[0104] Additionally, an imaging compound or radiopaque material can
be incorporated with the endoprosthesis. For example, one or more
of the annular elements of the endoprosthesis can be made of a
suitable radiopaque material, such as gold, tantalum or a similar
material. Alternatively, the radiopaque material can be applied on
selected surfaces of one or more of the annular elements using any
of a variety of known techniques, including cladding, bonding,
adhesion, fusion, deposition or the like. In a preferred
embodiment, the material used for fabrication of at least a portion
of the endoprosthesis includes a composite structure having
multi-layers of different materials or compositions. Generally, at
least one layer is a base material such as stainless steel,
nickel-titanium alloy or cobalt chromium alloy to impart the
intended structural characteristic of the endoprosthesis, and at
least another layer is a radiopaque material such as gold or
tantalum for imaging purposes. For example, a tri-layer structure
of 316L-Ta-316L is preferred for a balloon expandable stent and a
tri-layer structure of NiTi-Ta-NiTi is preferred for a
self-expanding stent. Suitable multi-layered composite structures
are available in sheet or tube form from UTI Corporation of
Collegeville, Pa., and are disclosed in U.S. Pat. No. 5,858,556,
which is incorporated herein by reference. In yet another
embodiment, one or more marker elements of radiopaque material can
be attached to the endoprosthesis. For example, eyelets or tabs can
be provided, preferably at least a distal or proximal longitudinal
end of the endoprosthesis. A rivet or bead of radiopaque material
can then be attached to the eyelet or tab in a manner as known in
the art. Alternatively, the separate marker can be attached
directly to annular element. For example, and in accordance with a
preferred embodiment of the invention, a wire or strip of
radiopaque material can be wrapped around and secured to one or
more nondeforming portions at one or both longitudinal ends of the
endoprosthesis.
[0105] A variety of manufacturing techniques are well known and may
be used for fabrication of the endoprosthesis of the present
invention. For example, and in a preferred embodiment, the
endoprosthesis can be formed from a hollow tube of suitable
material using a known technique, such as by laser cutting, milling
or chemical etching. The structure is then electropolished or
otherwise finished to remove burrs and eliminate sharp edges and
contaminates. Alternatively, the endoprosthesis can be fabricated
from a sheet of suitable material using a similar cutting, milling
or etching technique, and then rolled or bent about a longitudinal
axis into the desired shape. If desired, the lateral edges of the
structure can be joined together, such as by welding or bonding, to
form a closed tubular structure, or the lateral edges can remain
unattached to form an coiled, rolled sheet or open tubular
structure. Conversely, a suitable material of construction can be
applied selectively to a substrate to define the desired pattern of
the endoprosthesis structure, and then the substrate can be
removed. Other methods of manufacture also can be used for the
endoprosthesis of the present invention, such as by bending
toroidal rings or elongate lengths of wire into appropriately
shaped members, such as that corresponding to each annular element,
and then joining the appropriately shaped members together by a
welding or bonding technique or the like. If a shape memory
material is used, such as a nickel titanium alloy, the fabricated
structure can be heat treated on a mandrel or the like using known
techniques to establish the desired endoprosthesis shape and
dimensions at a predetermined temperature, e.g. when above
austenitic transition temperature.
[0106] As originally cut or fabricated, the endoprosthesis can
correspond to its delivery configuration or a deployed
configuration or a configuration therebetween. Preferably, however,
the endoprosthesis is fabricated with a configuration at least
slightly larger than the delivery configuration. In this manner,
the endoprosthesis can be crimped or otherwise compressed into its
delivery configuration on a corresponding delivery device. In
another preferred embodiment, the endoprosthesis is originally
fabricated from a tube having a diameter corresponding to the
deployed configuration. In this manner, the longitudinally-free
portions of the annular elements (e.g., apices not at a connection
location) and circumferentially-free portions (e.g., the lateral
sides of the arrowheads that are free) can be maintained within the
general cylindrical shape (e.g., diameter) of the endoprosthesis
when deployed, so as to avoid such portions from extending radially
inwardly when in the deployed configuration. The endoprosthesis is
therefore designed to match the target vessel in which the
endoprosthesis is to be deployed. For example a stent will
typically be provided with an outer diameter in the deployed
configuration ranging from about 2 mm for neurological vessels to
about 25 mm for the aorta. Similarly, a stent will typically be
provided with a length ranging from 5 mm to 100 mm. Variations of
these dimensions will be understood in the art based upon the
intended application for the endoprosthesis.
[0107] As previously noted, the geometry of each part of the
endoprosthesis, such as the width, thickness, length and shape of
the strut members and other featured, as well as of the connectors
if provided, is preferably selected to obtain predetermined
expansion, flexibility, foreshortening, coverage scaffolding, and
cross profile characteristics. For example, longer strut members
can promote greater radial expansion or scaffolding coverage. The
phase difference or circumferential alignment between adjacent
annular elements likewise can be altered to control coverage and
flexibility as well as facilitate more uniform drug delivery.
Similarly, the number and placement of connection locations and, if
present, the connectors, between longitudinally adjacent annular
elements are preferably selected to obtained the desired
flexibility of the endoprosthesis. The number of apices and other
features can be varied to achieve desired performance
characteristics.
[0108] While illustrative embodiments of the invention are
disclosed herein, it will be appreciated that numerous
modifications and other embodiments may be devised by those skilled
in the art. For example, the various features of each embodiment
may be altered or combined to obtain the desired stent
characteristics. Therefore, it will be understood that the appended
claims are intended to cover all such modifications and embodiments
that come within the spirit and scope of the present invention.
* * * * *