U.S. patent application number 15/137465 was filed with the patent office on 2016-08-18 for flexible stent with torque-absorbing connectors.
The applicant listed for this patent is Abbott Laboratories Vascular Enterprises Limited. Invention is credited to Brendan J. Casey.
Application Number | 20160235562 15/137465 |
Document ID | / |
Family ID | 40243943 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160235562 |
Kind Code |
A1 |
Casey; Brendan J. |
August 18, 2016 |
FLEXIBLE STENT WITH TORQUE-ABSORBING CONNECTORS
Abstract
The present invention concerns an endoprosthesis with a highly
flexible structure that is configured to provide an elevated degree
of vessel scaffolding and to absorb torque applied on the
endoprosthesis. In one embodiment, a method of deploying the
endoprosthesis in a body lumen includes locating an endoprosthesis
in a contracted delivery configuration in the body lumen, disposing
the endoprosthesis in a location of the body lumen to receive the
endoprosthesis in an expanded deployed configuration, and deploying
the endoprosthesis to transition the endoprosthesis from the
contracted delivery configuration to the expanded deployed
configuration. The endoprosthesis includes a plurality of
longitudinally adjacent web rings including a plurality of adjoined
web elements and a plurality of junction bends adjoining pairs of
the plurality of adjoined web elements, and S-shaped connectors for
connecting the web rings.
Inventors: |
Casey; Brendan J.; (Galway,
IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abbott Laboratories Vascular Enterprises Limited |
Dublin |
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IE |
|
|
Family ID: |
40243943 |
Appl. No.: |
15/137465 |
Filed: |
April 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13411135 |
Mar 2, 2012 |
9320627 |
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15137465 |
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11973707 |
Oct 9, 2007 |
8128679 |
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13411135 |
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11805584 |
May 23, 2007 |
8016874 |
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11973707 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2250/0031 20130101;
A61F 2/89 20130101; A61F 2230/0069 20130101; A61F 2/86 20130101;
A61F 2002/91541 20130101; A61F 2002/91558 20130101; A61F 2/915
20130101 |
International
Class: |
A61F 2/89 20060101
A61F002/89; A61F 2/86 20060101 A61F002/86 |
Claims
1. A method of deploying an endoprosthesis in a body lumen, the
method comprising: positioning an endoprosthesis in a contracted
delivery configuration in the body lumen, the endoprosthesis
comprising: a plurality of web rings, each web ring including a
plurality of web elements and a plurality of junction bends
disposed between adjacent web elements of the plurality of web
elements; and a plurality of S-shaped connectors extending from the
plurality of junction bends and between longitudinally spaced apart
web rings of the plurality of web rings, at least three junction
bends separating the junction bends from which adjacent S-shaped
connectors extend; and deploying the endoprosthesis to transition
the endoprosthesis from the contracted delivery configuration to an
expanded deployed configuration.
2. The method of claim 1, wherein the S-shaped connector comprises
a first segment, a second segment, and a central segment disposed
between the first segment and the second segment, a junction
between the first segment and the central segment being
non-parallel to a junction between the second segment and the
central segment.
3. The method of claim 2, wherein the junction between the first
segment and the central segment and the junction between the second
segment and the central segment are transverse to a longitudinal
axis of the web rings.
4. The method of claim 2, wherein the junction between the first
segment and the central segment is tilted in a direction opposite
the junction between the second segment and the central segment
when in the expanded deployed configuration.
5. The method of claim 2, wherein an angle between the first
segment and the central segment, and the central segment and the
second segment, is between about 45 and 135 degrees or about 100
and 170 degrees.
6. The method of claim 1, wherein deploying the endoprosthesis
comprises twisting the S-shaped connector as the endoprosthesis
transitions from the contracted delivery configuration to the
expanded deployed configuration.
7. A method of deploying an endoprosthesis in a body lumen, the
method comprising: locating an endoprosthesis in a contracted
delivery configuration in the body lumen, the endoprosthesis
comprises a plurality of longitudinally adjacent web rings defining
an essentially tubular web structure, each web ring including a
plurality of adjoined web elements and a plurality of junction
bends adjoining pairs of the plurality of adjoined web elements, a
junction bend in a first web ring of the plurality of
longitudinally adjacent web rings is connected to a second junction
bend in a neighboring web ring of the plurality of longitudinally
adjacent web rings by an S-shaped connector, the second junction
bend being longitudinally offset from the first junction bend and
being circumferentially offset from the first junction bend by a
plurality of other junction bends of a plurality of junction bends
of the neighboring web ring, the S-shaped connector having a
plurality of segments disposed one in relation to the other in
step-wise configuration; disposing the endoprosthesis in a location
of the body lumen to receive the endoprosthesis in an expanded
deployed configuration; and deploying the endoprosthesis to
transition the endoprosthesis from the contracted delivery
configuration to the expanded deployed configuration.
8. The method of claim 7, wherein the S-shaped connector comprises
three segments, two segments of the three segments being
essentially parallel, wherein deploying the endoprosthesis
comprises translating one of the two essentially parallel segments
relative to the other essentially parallel segments by application
of a bending force on the essentially tubular web structure.
9. The method of claim 7, wherein deploying the endoprosthesis
further comprises applying pressure to an interior surface of the
essentially tubular web structure.
10. The method of claim 7, wherein disposing the endoprosthesis
comprises advancing the endoprosthesis through the body lumen.
11. A method of deploying an endoprosthesis in a body lumen, the
method comprising: positioning an endoprosthesis in a contracted
delivery configuration in the body lumen, the endoprosthesis
comprising: a plurality of longitudinally adjacent web rings, each
web ring including a plurality of adjoined web elements and a
plurality of junction bends adjoining pairs of the plurality of
adjoined web elements, wherein, a junction bend in a first web ring
of the plurality of longitudinally adjacent web rings is connected
to a second junction bend in a neighboring web ring of the
plurality of longitudinally adjacent web rings by an S-shaped
connector, the first junction bend being separated from a third
junction bend, from which another S-shaped connector extends, by at
least three junction bends without an associated S-shaped
connector; and deploying the endoprosthesis to transition the
endoprosthesis from the contracted delivery configuration to an
expanded deployed configuration.
12. The method of claim 11, wherein the S-shaped connector
comprises three segments, two segments of the three segments being
essentially parallel, wherein the web rings are essentially
tubular, wherein deploying the endoprosthesis comprises translating
one of the two essentially parallel segments relative to the other
essentially parallel segments by application of a bending force on
the essentially tubular web rings.
13. The method of claim 11, wherein deploying the endoprosthesis
further comprises applying pressure to an interior surface of the
essentially tubular web rings.
14. The method of claim 11, wherein positioning the endoprosthesis
comprises advancing the endoprosthesis through the body lumen.
15. The method of claim 11, wherein the S-shaped connect comprises
a plurality of segments disposed one in relation to the other in a
step-wise configuration.
16. The method of claim 15, wherein a central segment of the
plurality of segments within the connector is disposed in a
direction essentially parallel to a longitudinal axis of the
endoprosthesis.
17. The method of claim 11, wherein each of the web elements
comprises a central member having a first and a second ends,
wherein the central member is disposed essentially parallel to a
longitudinal axis in the contracted delivery configuration, wherein
the central member is connected at the first end to a first end
member at a first obtuse angle, and wherein the central member is
connected at the second end to a second end member at a second
obtuse angle.
18. The method of claim 17, wherein the first and the second obtuse
angles are essentially equal.
19. The method of claim 17, wherein the web elements of each web
ring are nested one into the other in the contracted delivery
configuration, and wherein the junction bends have an arcuate
shape.
20. The method of claim 11, wherein the web elements in the first
web ring are oriented at approximately 180 degrees in relation to
the web elements in the neighboring web ring.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 13/411,135 filed Mar. 2, 2012, which is
a continuation application of U.S. patent application Ser. No.
11/973,707, filed on Oct. 9, 2007, now U.S. Pat. No. 8,128,679,
which is a Continuation-in-Part application of U.S. patent
application Ser. No. 11/805,584 filed on May 23, 2007, now U.S.
Pat. No. 8,016,874, the entireties of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates to a medical device. More
particularly, the present invention relates to a flexible stent
that provides elevated torque-absorbing properties.
[0004] 2. The Relevant Technology
[0005] Atherosclerosis, sometimes called the hardening or clogging
of the arteries, is an accumulation of cholesterol and fatty
deposits, called plaque, on the inner walls of the arteries.
Atherosclerosis causes a partial or total blockage of the arteries
and, consequently, a reduced blood flow to the heart, legs,
kidneys, or brain.
[0006] Traditionally, clogged arteries have been treated with
surgical procedures that involve the removal of the diseased
arterial tract. Angioplasty procedures, during which a stent is
inserted in the diseased portion of the artery, have gained
increased acceptance during the last two decades because of the
reduced complexity of this procedure in comparison with other
surgical procedures and because of the consequent reduction in risk
and discomfort to the patient.
[0007] Referring first to FIG. 1, a stent 20 is a small tubular
element that typically has a cylindrical structure 22 and that,
once placed within a blocked vessel, acts as a scaffold that keeps
the vessel open. Stent 20 may be implanted in a bodily vessel by
disposing the stent over a balloon tipped catheter, by driving the
stent to a target location in a vessel, and by subsequently
inflating the balloon at the target location.
[0008] Alternatively, stent 20 may be caused to self-expand without
the use of a balloon by manufacturing stent 20 from a shape memory
material and by disposing stent 20 over a catheter in a contracted
delivery configuration. Stent 20 is successively driven to a target
location in a vessel, where a sheath covering stent 20 is withdrawn
and stent 20 is allowed to self-expand. One type of self-expanding
stent is produced from a superelastic material and is compressed
inside the sheath into a contracted delivery configuration. When
the stent is released from the sheath, the flexible material causes
the stent to spring back to its original shape and size before
compression. Another type of self-expanding stent is produced from
a thermo-elastic shape-memory material that is formed into a
desired size and shape and is then annealed at a temperature higher
than a transition temperature. After cooling the stent to a
temperature below the transition temperature, the stent becomes
soft and can be reduced to a smaller size by crimping, so that it
can be delivered to the target location, where the stent is warmed
to a temperature above the transition temperature and returns to
the preprogrammed size and shape. The present invention relates to
both to balloon expandable stents and to self-expanding stents, as
explained in greater detail in the following sections.
[0009] The stents in the prior art are formed as a metal mesh or,
in general, as a web structure that provides some degree of
flexibility. Certain types of anatomies require that stents with
elevated degrees of flexibility be employed, for example, stents to
be implanted in the carotid artery, because the bifurcated anatomy
of the carotid artery and frequent movements of that part of the
body require a stent that can adapt to such anatomy. The stent
designs in the prior art typically increase flexibility by
increasing cells size in the mesh or in the web structure.
Therefore, whenever stent flexibility is increased in the stents in
the prior art, scaffolding support is affected negatively due to
the related reduction in web density.
[0010] A prior art stent is disclosed in U.S. Pat. No. 5,104,404,
which teaches an articulated stent in which stent segments, formed
by diamond-shaped cells disposed in ring form, are connected one to
the other at some but not all of the tips of the diamond-shaped
cells. This arrangement provides for a stent with a high degree of
longitudinal flexibility, but also for limited support to the
arterial walls at the junctions areas between the different stent
segments.
[0011] With reference now to FIG. 2, other designs in the prior art
have attempted to increase stent flexibility by forming the stent
as a plurality of web rings 24 that are disposed longitudinally
along tubular body 22 and that are coupled one to the other by
flexible connectors 26. Designs of this type are disclosed in U.S.
patent application Ser. No. 10/743,857, U.S. Pat. Nos. 6,682,554
and 6,602,285, International Application PCT/EP99/06456, and German
Patent Application Serial No. 19840645.2, the entireties of which
are incorporated herein by reference. The function of flexible
connectors 26 is to facilitate the bending of stent 20 by creating
longitudinal segments softer than web rings 24. At the same time,
flexible connectors 26 transmit torque from one web ring 24 to
adjacent web rings 24 when a bending force is applied to tubular
body 22 or when a radial force is applied to tubular body 22, for
example, during deployment of stent 22 from the contracted delivery
configuration to the expanded delivery configuration. Such a
transmission of torque may cause different web rings 24 to rotate
differentially upon application of a bending force or upon
deployment of stent 20.
[0012] One example of stent construction based on longitudinally
alternating of web rings coupled by flexible connectors can be
found in U.S. Pat. No. 6,190,403, which discloses a stent having a
plurality of web rings disposed in longitudinal order. Each of the
web rings is formed by longitudinally-oriented cells disposed
circumferentially and is joined to a neighboring web ring by
sinusoidal connectors that couple cell tips that are longitudinally
aligned one with the other. The stent of the '403 patent provides
an elevated degree of scaffolding to the arterial walls, though its
structure provides only for a limited degree of longitudinal
flexibility due to the limited extent of longitudinal translation
that is possible between web rings when a compressive force is
applied.
[0013] Another example of stent construction based on
longitudinally alternating web rings coupled by flexible connectors
can be found in U.S. Pat. No. 6,451,049, which discloses a stent
having a plurality of waveform rings coupled by longitudinal
connectors that include a "U" bend. This construction also provides
for an elevated degree of scaffolding of the vessel walls, but its
flexibility is constrained by the limited ability to compress of
the flexible segments.
[0014] In order to increase stent flexibility, stent designs have
been introduced in which the flexible connectors between web rings
do not have a longitudinal orientation but instead have a
transverse orientation. Examples of such stent designs can be found
in U.S. Pat. Nos. 5,980,552; 6,059,811; 6,508,834; and 6,589,276.
The transverse orientation of the flexible connectors induce the
web rings to rotate one in relation to the other upon the
application of a bending or radial force to the stent, and in order
to reduce torsional stress in the stent during bending and during
expansion, the flexible connectors may have alternating directions.
For example, the flexible connectors connecting two neighboring
rings may be oriented in a direction opposite to the direction of
the next set of flexible connectors. If the web rings are prevented
from rotating, the torsional stress in the stent becomes absorbed
by the flexible connectors and by the web rings, possibly causing
the connectors to warp along their entire length. Additionally,
this type of construction causes a foreshortening of the stent
during expansion.
[0015] This problem is illustrated in greater detail in FIGS.
3A-3B. A typical connector 28 couples first web ring 30 to second
web ring 32 by connecting junction bend 34 on first ring 30 to
junction bend 36 on second ring 32. In order for stent 38 to
provide an elevated degree of scaffolding to the vessel within
which stent 38 is implanted, each junction bend 34 on web ring 30
is coupled to a junction bend 36 in web ring 32, increasing stent
density. The higher the density of stent 38, however, the lower the
flexibility, which may be increased by increasing the length of
connector 28.
[0016] When the length of connector 28 is increased, the bending
capability and the flexibility of stent 38 is increased
correspondingly because the moment applied by connector 28 to web
rings 30 and 32 upon the application of a bending force on stent 34
is increased correspondingly. Unfortunately, long connectors
disposed transversally on stent 38 can extend along a significant
amount of the outer circumference of stent 38. For example, if
stent 38 has a diameter of 1.6 mm and if connector 28 is one mm
long, connector 28 extends for approximately 72 degrees along the
circumference of stent 38. In turn, long connectors 28 will exert a
significant amount of torque on junction bends 34 and 36, and,
consequently, on web rings 30 and 32, and may warp along their
entire length. In addition, long connectors 28 cause the size of
stent cells to increase during expansion, therefore, long
connectors cause a reduction in the scaffolding properties of stent
20, or a reduction in the ability of stent 20 to effectively
support the vessel, into which stent 20 is implanted.
[0017] By having long connectors 28 disposed in a direction
essentially perpendicular to the longitudinal axis of stent 20,
connector 28 also tend to retain the bend radius of stent 20 during
expansion and to cause a distortion of stent 20 in the expanded
configuration.
[0018] Attempts have been made in the prior art to provide long
connectors that extend along relatively limited portions of the
circumference of stent 38 and that increase vessel support. For
example, U.S. Pat. Nos. 5,449,373; 6,203,569; 6,740,114; 6,790,227;
6,942,689; 6,955,686; 6,998,060; 6,679,911; and 6,875,228 disclose
stent constructions, in which the connectors have a variety of
shapes in the form of the letters "M", "N", "W" or similar shapes,
but which all include a plurality of segments oriented at certain
angles with respect to the longitudinal axis of the stent. In
particular, each of the prior art designs contains one or more
central segments that are oriented at an angle with respect to the
longitudinal axis of the stent, causing rotations in different
degrees upon the application of a torsional force on the connector,
for example due to a bending of the stent or during expansion.
[0019] Therefore, it would be desirable to provide a stent that
generates an elevated degree of scaffolding to a bodily vessel
while remaining highly flexible.
[0020] It would also be desirable to provide a stent, in which long
connectors can be employed to increase stent flexibility and that
can absorb torsional forces applied to the stent without warping
along their entire lengths.
BRIEF SUMMARY OF THE INVENTION
[0021] A stent according to the present invention exhibits a highly
flexible structure and elevated scaffolding properties, and at the
same time is configured to absorb torque applied on the stent by
bending or radial forces.
[0022] The stent according to the present invention is expandable
from a contracted delivery configuration to an expanded deployed
configuration and includes an essentially tubular body formed by a
plurality of web rings disposed longitudinally. Each of the web
rings is defined by a plurality of web elements that are disposed
circumferentially and that, in the contracted delivery
configuration, are substantially parallel to the longitudinal axis
of the tubular body. Pairs of the web elements are sequentially
adjoined at junction bends, and a junction bend in a first web ring
is coupled to a junction bend in a neighboring web ring by one of
the connectors.
[0023] Each of the connectors is formed by a plurality of segments
disposed in a step-wise configuration. At least one of the
connector segments is situated in a central position within the
connector and is disposed with an orientation essentially parallel
to the longitudinal axis of the stent. These connectors couple
junction bends that are laterally offset one in relation to the
other, making the connectors span diagonally along the profile of
the tubular body.
[0024] The second segment may be rectilinear in shape and become
twisted to acquire a helical curvature when a bending or expansion
stress is applied to the stent. In one embodiment, the central
element may be pre-deformed with a helical curvature in the
contracted delivery configuration that becomes more accentuated
during a bending or expansion of the stent. The central element may
also be manufactured to have a cross-sectional area that is
different from the cross-sectional areas of the end segments.
[0025] In one embodiment, each of the junction bends in the first
web ring is connected to one junction bend in one neighboring web
ring by one connector, so that each junction bend in one web ring
is coupled to another junction bend in an adjacent web ring.
[0026] The stent of the present invention may be manufactured from
a variety of materials, including metallic materials and plastic
materials. When the stent is to be self-expanding, Nitinol or
another shape memory material may be employed, while a
balloon-expandable stent may be manufactured from stainless steel
or other biocompatible metallic or plastic material. All or part of
the stent (for example, the connector) may also be manufactured
from a biodegradable material, for example, from a plastic
absorbing material. In addition, the stent of the present invention
may include a number of ancillary features known in the art, for
example, may be coated with a bioactive agent or contain
radio-opaque markers.
[0027] Methods of use of the stent according to the present
invention are also provided.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0028] The drawings constitute a part of this specification and
include exemplary embodiments of the invention, which may be
embodied in various forms. It is to be understood that in some
instances various aspects of the invention may be shown exaggerated
or enlarged to facilitate an understanding of the invention.
[0029] FIG. 1 is a perspective view of an essentially tubular body
of a stent.
[0030] FIG. 2 is a front view of a stent connector according to the
prior art.
[0031] FIG. 3A illustrates a configuration of stent connector
according to the prior art, and
[0032] FIG. 3B is a schematic top view of the essentially tubular
body of a stent highlighting the span of the connector of FIG. 3B
when disposed within the tubular body.
[0033] FIG. 4 is a perspective view of one embodiment of the
present invention, showing the stent pattern in a detail view.
[0034] FIG. 5 is a detail view, illustrated as a flattened surface,
of the web structure of a stent according to one embodiment of the
present invention.
[0035] FIG. 5A is a detail view, illustrated as a flattened
surface, of the web structure of a stent according to an embodiment
of the present invention.
[0036] FIG. 6 is a detail view of the web structure of FIG. 5.
[0037] FIG. 7 is a schematic plan view of a connector connecting
two neighboring junction bends according to one embodiment of the
present invention.
[0038] FIG. 8 is a perspective view of the connector of FIG. 7.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0039] The present invention relates to stent designs that can
absorb an elevated degree of torque during expansion and after
implantation in a patient while at the same time providing a highly
flexible stent structure. One application of the present invention
relates to closed cell stents, in particular, carotid stents, for
which an elevated degree of lesion scaffolding and the capability
of conforming to tortuous anatomies are key design features.
[0040] Detailed descriptions of embodiments of the invention are
provided herein. It is to be understood, however, that the present
invention may be embodied in various forms. Therefore, the specific
details disclosed herein are not to be interpreted as limiting, but
rather as a representative basis for teaching one skilled in the
art how to employ the present invention in virtually any detailed
system, structure, or manner.
[0041] Referring to FIG. 4, a stent 40 constructed according to the
principles of the present invention includes an essentially tubular
body 42 expandable from a contracted delivery configuration to an
expanded deployed configuration. While body 42 is depicted in FIG.
4 as essentially cylindrical in shape, body 42 may be provided with
other shapes, for example, with a frustoconical shape or with the
shape of a hyperboloid.
[0042] Body 42 is defined by a web structure 44, shown in FIG. 4
only in a detail view that relates to the contracted delivery
configuration. Web structure 44 includes a plurality of web
elements 46, each formed by a plurality of crowns 48.
[0043] Referring now to FIG. 5, each crown 48 includes a central
member 50 having a first end member 52 and a second end member 54
extending respectively from the opposite ends of central member 50.
Central member 50, first end member 52 and second end member 54 are
each essentially linear in shape, and, in the contracted delivery
configuration of stent 40, central member 50 is disposed
essentially parallel to the longitudinal axis of body 42 (see also
FIG. 4), while first and second members 52 and 54 extend from
central member 50 at obtuse angles. Preferably, first and second
members 52 and 54 extend from central member 50 at the same angle,
but in other embodiments, first and second members 52 and 54 may
extend from central member 50 at different angles. In still other
embodiments, one or more of central member 50 and first and second
members 52 and 54 may be non-rectilinear and have a curved
shape.
[0044] Crowns 48 are nested one into the other in the contracted
delivery configuration and are sequentially adjoined at one end by
a junction bend 56 that exhibits an essentially arcuate shape. A
series of crowns 48 is disposed circumferentially about the
longitudinal axis of body 42 to form web rings 46, which are joined
one to the other by connectors 58. As shown in FIG. 5, the crowns
in one web ring may be disposed with an orientation that is
opposite to the orientation of the crowns in a neighboring web
ring. In the illustrated embodiment, two adjacent web rings are
disposed with an orientation of crowns 48 that is 180 degrees
different one from the other.
[0045] Stent 40 may be manufactured from a variety of biocompatible
materials, including metal and plastic materials. For example but
not by way of limitation, stent 40 may be manufactured from Nitinol
or other shape memory material if a self-expanding configuration of
stent 40 is desired, or from stainless steel if balloon expansion
is foreseen. Alternatively, stent 40 may be manufactured from a
plastic material that enables either a permanent stent placement or
a temporary stent placement, for example, from a plastic absorbing
material.
[0046] In some embodiments, crowns 48 and connectors 58 may be
manufactured from a biodegradable material when it is expected that
only temporary vessel support is required. In another embodiment,
only connectors 58 may be manufactured from a biodegradable
material, so that the scaffolding provided by stent 40 may change
over time and connectors 58 will gradually dissolve in the fluid
carried by the vessel (for example, blood), leaving web rings 46
intact and allowing web rings 46 to be disposed at specific angles
in relation to each other, as required by the patient's anatomy or
by the movements of the patient's body.
[0047] While FIG. 5 illustrates that each junction bend 56 in one
web ring is adjoined by connector 58 to a junction bend 60 in the
adjacent web ring, only one out of a plurality of junction bends in
one web ring (for example, one every three) may be adjoined to a
junction bend in an adjacent web ring, providing stent 40 with
larger open spaces between adjacent web rings 46. An example of
which is shown in FIG. 5A. For example, the web ring 45a shown on
the left is only connected to the web ring 45b in the middle by a
single connector 58 (e.g. shown in black), such that the connector
58 is separated by at least seven junction bends 60. In another
example, the web ring 45c on the right is connected to the web ring
45b in the middle by two connectors 58, such that the two
connectors 58 are separated by three unadjoined junction bends 60.
Thus, FIG. 5A illustrates an embodiment of an endoprosthesis
configured to transition from a contracted delivery configuration
to an expanded deployed configuration. The endoprosthesis includes
a plurality of longitudinally adjacent web rings 45a-c defining an
essentially tubular web structure, each web ring 45a-c including a
plurality of adjoined web elements 46, 48. The endoprosthesis
includes a plurality of junction bends 56, 60 adjoining pairs of
the plurality of adjoined web elements 46, 48, a first junction
bend 56 in a first web ring 45b of the plurality of longitudinally
adjacent web rings 45a-c is connected to a second junction bend 60
in an adjacent neighboring web ring 46c of the plurality of
longitudinally adjacent web rings 45a-c by a first S-shaped
connector 58a, the second junction bend 60 being longitudinally
offset from the first junction bend 56 and being circumferentially
separated from the first junction bend 56, a third junction bend 57
in the first web ring 45b of the plurality of longitudinally
adjacent web rings 45a-c is connected to a fourth junction bend 61
in the adjacent neighboring web ring 45c of the plurality of
longitudinally adjacent web rings 45a-c by a second S-shaped
connector 58b, the fourth junction bend 61 being longitudinally
offset from the third junction bend 57 and being circumferentially
separated from the third junction bend 57, the first junction bend
56 being circumferentially separated from the third junction bend
57 by at least three unadjoined junction bends 59, the first and
second S-shaped connectors 58a, 58b having a plurality of segments
disposed one in relation to the other in step-wise configuration,
the plurality of segments being interconnected by connectors. While
this more open design increases stent flexibility, the scaffolding
properties of the stent are correspondingly decreased because of
decreased stent density.
[0048] One aspect of the present invention is to provide an
elevated degree of flexibility while retaining a closed cell
structure, in which each junction bend 56 in one web ring 46 is
coupled to a junction bend 60 in a neighboring web ring 46.
Therefore, stent 40 is well suited for delivery and implantation at
sites that require elevated flexibility and elevated scaffolding,
for example, in carotid arteries. At the same time, the step-wise
configuration of connectors 58 enables the use of connectors 58
which are relatively long, increasing flexibility to suit tortuous
anatomies and various body movements, but through which the torsion
of one web ring 46 in relation to the other is decreased or
eliminated, as explained in greater detail below.
[0049] It should be observed that each of connectors 58 does not
adjoin two junction bends that are longitudinally aligned, but
instead adjoin two junction bends 56 and 60 that are laterally
offset one in relation to the other. This offset configuration is
more advantageous than a configuration linking adjacent junction
bends. More specifically, a configuration with connectors 58
linking junction bends 56 and 60 that are offset one from the other
provides an elevated degree of flexibility to stent 40, because in
this configuration neighboring web rings have a greater ability to
rotate one in relation to the other when stent 40 is deployed or
becomes subjected to a bending stress.
[0050] Connectors 58 may join adjacent junction bends 56 and 60 at
different points within the junction bends. For example, in the
embodiment shown in FIG. 5 and, in greater detail, in FIG. 6,
connector 58 adjoins essentially the middle points of junction
bends 56 and 60 by extending from essentially the middle point of
junction bend 56 to essentially the middle point of junction bend
60. In other embodiments, connector 58 may adjoin the lowest point
in junction bend 56 with the highest point of junction bend 60, or
the highest point of junction bend 56 with the lowest point of
junction bend 60. It should be understood that in still other
embodiments, connectors 58 may join junction bends 56 and 60 at a
plurality of different points of the junction bends, and that some
of the crowns 46 and connectors 58 are shown in FIGS. 5 and 6 in
darkened color only for illustrative purposes and not for
indicating any particular structural or design differences from the
neighboring crowns and connectors.
[0051] The structure and mode of operation of connector 58 is
illustrated in greater detail in FIGS. 6 and 7. More particularly,
connector 58 includes a first segment 62, a second (middle) segment
64 and a third segment 66, disposed one in relation to the other in
a step-wise configuration. Within the structure of connector 58,
first segment 62 couples connector 58 with junction bend 56, third
connector 66 couples connector 58 with junction bend 60, while
second segment 64 couples first segment 62 with third segment 66.
Second segment 64 is arranged in a direction essentially parallel
to the longitudinal axis of body 42, while first segment 62 and
third segment 66 are arranged at an angle A with respect to second
segment 64, for example, 110 degrees as shown in FIG. 7. In
different embodiments, connector 58 may be composed of different
numbers of segments, which may further be arranged at angles of
varying amplitudes, for example, between 100 and 170 degrees.
[0052] Referring now to FIGS. 7 and 8, the configuration of
connector 58 is such to absorb a torsional stress applied to body
42, particularly during expansion of the stent from the contracted
delivery configuration to the expanded deployed configuration. Such
an ability to absorb torque is provided not only by the relative
movements of first segment 62 and third segment 66, by which the
widths of angle A between second segment 64 and first segment 62,
and of angle B between second segment 64 and third segment 66, may
change as a consequence of torsional stress, but also by the
twisting motion of second segment 64 to assume an essentially
helical shape. By the twisting motion of second segment 64, the
torsional stress from, for example, first segment 62 is not
entirely transmitted to third segment 66, but is absorbed (entirely
or partially) by the twisting motion of second segment 64.
[0053] By disposing second segment 64 in a direction essentially
parallel to the longitudinal axis of tubular body 42, torque
developing, for example, during deployment of the stent is absorbed
at a much greater rate than in stent configurations having second
segment 64 disposed at an angle in relation to the longitudinal
axis of tubular body 42. Therefore, the connector design of the
present invention absorbs torque at a greater rate than, for
example, designs where the connectors between the web rings have
shapes reminiscent of the letters "N" or "W", because the structure
of connector 58 according to the present invention minimizes or
eliminates the relative rotations of one web ring 46 in relation of
a neighboring web ring 46. At the same time, second segment 64
provides for a greater scaffolding of the vessel walls than
connector designs in which no step-like pattern is present, in
particular, than designs having no longitudinally disposed
segments. By having second segment 64 disposed essentially parallel
to the longitudinal axis of tubular body 42, second segment 64 can
become twisted, minimizing or eliminating the distortion problems
in stents of the prior art that have long connectors, and improving
surface contact of stent 40 with the vessel, within which stent 40
is disposed.
[0054] FIG. 8 illustrates in greater detail that second segment 64
has become deflected after the application of torsional stress on
web structure 44, for example, when web structure 44 is expanded
during the deployment of stent 40 and the web rings on which
junction bends 56 and 60 are situated tend to rotate one with
respect to the other. During such absorption of torque, connecting
area 68 between first segment 62 and second segment 64 may become
tilted in a direction opposite to that of connecting area 70
between second segment 64 and third segment 66 when second segment
64 assumes a helical disposition. This phenomenon is particularly
relevant when stent 40 is manufactured by producing its shape from
a tube, for example through a laser cutting process, so that
connectors 58 exhibit edges that are substantially square. In one
embodiment of the invention, the twisting motion of second segment
64 towards a helical disposition may be facilitated by
manufacturing connector 58 with connecting areas 68 and 70 disposed
not one parallel to each other, but instead at an angle one with
respect to the other.
[0055] Stent 40 may be disposed into a target vessel location, for
example, in a location within a carotid artery, by inserting a
guide wire into the artery, and by successively translating a
catheter along the guide wire that carries the stent in a
contracted condition. When the stent has reached the target
location, as may be determined by tracking radio-opaque markers
embedded in the stent, a balloon disposed on the catheter and
within the stent is inflated, causing the stent to expand from the
contracted condition to the deployed condition until contact with
the vessel walls is achieved. Alternatively, if the stent is
manufactured from a self-expanding material, after the target
location has been reached, a sheath covering the stent is
withdrawn, enabling the stent to self-expand until contact with the
vessel walls is made and a support structure is created.
[0056] By providing a stent having a structure formed by web
elements that are disposed in web rings and that are coupled by
connectors in the manner described herein, so to form a closed cell
structure, an improved support is provided to the vessel walls in
comparison with open cell stents, and a highly flexible structure
is achieved that provides an elevated degree of scaffolding support
to the vessel walls even when the vessel is bent.
[0057] Stent 40 may include different features known in the art to
provide certain beneficial properties. For example but not by way
of limitation, stent 40 may be coated with a therapeutic coating
that includes a bioactive agent, or may contain radiopaque markers,
or may be coupled to a fabric that prevents the passage of emboli
from the vessel wall into the blood stream.
[0058] It should be noted that, while the invention has been
described in connection with the above described embodiments, it is
not intended to limit the scope of the invention to the particular
forms set forth, but on the contrary, it is intended to cover such
alternatives, modifications, and equivalents as may be included
within the scope of the invention. Accordingly, the scope of the
present invention fully encompasses other embodiments that may
become obvious to those skilled in the art and the scope of the
present invention is limited only by the appended claims.
* * * * *