Note: Descriptions are shown in the official language in which they were submitted.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-1-
MECHANICALLY ACTUATED STENTS AND APPARATUS AND METHODS
FOR DELIVERING THEM
FIELD OF THE INVENTON
The present invention relates generally to endoluminal prostheses or "stents,"
and,
more particularly, to mechanically actuated flared stents, and to apparatus
and methods for
delivering such stents into an ostium of a blood vessel or other body lumen.
BACKGROUND
Tubular endoprosthesis or "stents" have been suggested for dilating or
otherwise
treating stenoses, occlusions, and/or other lesions within a patient's
vasculature or other
body lumens. For example, a self-expanding stent may be maintained on a
catheter in a
contracted condition, e.g., by an overlying sheath or other constraint, and
delivered into a
target, location, e.g., a stenosis within a blood vessel or other body lumen.
When the stent
is positioned at the target location, the constraint may be removed, whereupon
the stent
may automatically expand to dilate or otherwise line the vessel at the target
location.
Alternatively, a balloon-expandable stent may be carried on a catheter, e.g.,
crinlped or
otherwise secured over a balloon, in a contracted condition. When the stent is
positioned
at the target location, the balloon may be inflated to expand the stent and
dilate the vessel.
Sometimes, a stenosis or other lesion may occur at an ostium or bifurcation,
i.e.,
where a branch vessel extends from a main vessel or trunk. For example, suclz
a lesion
may form within a coronary artery immediately adjacent the aortic root. U.S.
Patent No.
5,749,890 to Shaknovich discloses a stent delivery assembly for placing a
stent in an ostial
lesion. U.S. Patent No. 5,632,762 to Myler discloses a tapered balloon on a
catheter for
positioning a stent within an ostium. U.S. Patent No. 5,607,444 to Lam
discloses an
expandable ostial stent including a tubular body and a deformable flaring
portion.
Published application US 2002/0077691 to Nachtigall discloses a delivery
system that
includes a sheath for holding a stent in a compressed state during delivery
and a retainer
that holds a deployable stop in an undeployed position while the delivery
system is '
advanced to a desired location.
Accordingly, stents and apparatus and methods for delivering stents within an
ostium would be useful.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-2-
SUMMARY OF THE INVENTION
The present invention is directed to endoluminal prostheses or "stents," and,
more
particularly, to mechanically actuated, flared stents, and to apparatus and
methods for
delivering such stents= into an ostium of a blood vessel or other body lumen.
In accordance with one embodiment, a stent is provided that includes a first
tubular
portion and a second flaring portion. The first portion may include a length,
and may be
expandable from a contracted condition to an expanded condition. The second
portion
may include a first annular band disposed adjacent the first tubular portion
and a second
annular band disposed adjacent the first tubular portion. The second tubular
portion may
be configured such that, upon application of an axial compressive force, the
first and
second annular bands buckle outwardly at a location between the first and
second annular
bands. In one embodiment, the second tubular portion may be further configured
such that
the second annular band expands into a ring upon application of a radially
outward
expansion force.
In accordance with another embodiment, a stent is provided that includes a
first
tubular portion including a length, the first tubular portion being expandable
from a
contracted condition to an expanded condition, and a second tubular portion.
The second
portion may include a first annular band disposed adjacent the first tubular
portion and a
second annular band disposed adjacent the first tubular portion. The second
annular band
may include a plurality of axial elements connected by alternating curved
elements, the
second tubular portion being configured such that, upon application of an
axial
compressive force, the first and second annular bands buckle outwardly at a
location
between the first and second annular bands. In one embodiment, the second
annular band
may be configured such that, upon application of a radially outward expansion
force, the
curved elements at least partially straighten such that the axial elements at
least partially
define a circle or ellipse.
In accordance with still another embodiment, an apparatus is provided for
treating
an ostium communicating between a main body lumen and a branch body lumen.
Generally, the apparatus includes an elongate member including proximal and
distal ends,
an expandable member on the distal end that is expandable from a collapsed
configuration
to an expanded configuration, a stent on the distal end, and an actuator
movable relative
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-3-
to the distal end for buckling a first flaring portion of the stent when the
actuator is
activated. In one embodiment, the first flaring portion may include first and
second
annular bands, the first flaring portion configured to buckle radially
outwardly between the
first and second annular bands when the actuator is activated.
Other aspects and features of the present invention will become apparent from
consideration of the following description taken in conjunction with the
accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate exemplary embodiments of the invention, in which:
FIG. 1 is a perspective view of an exemplary embodiment of a mechanically
actuated stent in an expanded, flared condition.
FIG. 2 is a top view of a portion of a cell pattern for a mechanically
actuated flared
stent that may be expanded into an enlarged, flared condition, such as that
shown in FIG.
1.
FIGS. 3A-3C are side views of an exemplary embodiment of a delivery catheter
carrying a stent, showing one end of the stent being buckled to expand from a
contracted
condition to an enlarged, flared condition.
FIGS. 3D-3H are perspective views of the stent of FIGS. 3A-3C being further
expanded within a body lumen communicating with an ostium.
FIGS. 4A-4C are schematic side views of another embodiment of a delivery
catheter carrying a stent, showing one end of the stent being buckled to
expand from a
contracted condition to an enlarged, flared condition.
FIG. 5 is a detail, showing a mechanism for mechanically actuated a stent to
cause
cells of the stent to expand and buckle.
FIGS. 6A and 6B are schematic side views of yet another embodiment of a
delivery catheter carrying a stent, showing one end of the stent being buckled
to expand
from a contracted condition to an enlarged, flared condition.
FIG. 7 is a detail, showing an alternative mechanism for mechanically
actuating a
stent.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-4-
FIGS. 8A and 8B are schematic side views of yet another embodiment of a
delivery catheter carrying a stent, showing one end of the stent being buckled
to expand
from a contracted condition to an enlarged, flared condition.
FIGS. 8C-8E are schematic side views of the delivery catheter of FIGS. 8A and
8B, showing the stent being radially expanded.
FIGS. 9A and 9B are schematic side views of still another embodiment of a
delivery catheter carrying a stent, showing the stent being buckled and
expanded from a
contracted condition to an enlarged, flared condition.
FIG. 10 is a detail of a mechanism that may be provided on a delivery catheter
for
capturing a portion of a stent to allow the stent to be mechanically actuated.
FIGS. 11A and 11B are details, showing the mechanism of FIG. 10 engaging
portions of a stent to allow the stent to be mechanically actuated.
FIG. 12 is a detail of another mechanism that may be provided on a delivery
catheter for capturing a portion of a stent to allow the stent to be
mechanically actuated.
FIG. 13 is a detail, showing the mechanism of FIG. 12 engaging a portion of a
stent to allow the stent to be mechanically actuated.
FIGS. 14A-14D are side views of a stent carried on a delivery catheter,
showing a
method for expanding the stent from a contracted condition to an expanded,
flared
condition.
FIG. 15 is a cross-sectional view of an ostium communicating between a main
vessel and a branch vessel.
FIG. 16 is a graph showing desired properties of a stent relative to the
ostium
shown in FIG. 15.
FIGS. 17-20 are top views of various cell patterns that may be provided for a
stent
including a flaring portion and having variable properties along its length.
FIGS. 20A-20C are details showing various connectors that may be provided on a
stent for comiecting adjacent bands of cells.
FIG. 21 is a top view of another cell pattern that may be provided for a stent
including a flaring portion and having variable properties along its length.
FIGS. 22A-22F are side views of a distal end of a delivery catheter, showing a
method for expanding a flaring stent.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-5-
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning to the drawings, FIG. 1 shows an exemplary embodiment of a stent
apparatus 40 that includes a generally cylindrical distal or first portion 42
and a flared
proximal or second portion 44. With additional reference to FIG. 2, the stent
40 may
include a plurality of annular bands 46-49 connected to adjacent bands between
first and
second ends 43, 45 of the stent. In addition or alternatively, the stent 40
may include a
plurality of cells that may be connected to one another around a circumference
and/or
along a length of the stent 40.
For example, as shown in FIG. 2, the first portion 42 of the stent 40 may
include a
plurality of annular bands (two exemplary bands 46 being shown) defined by
zigzag or
serpentine patterns of straight elements 46a whose ends are connected
alternately by
curved elements 46b extending about the circumference of the stent 40. The
zigzag
pattern of the bands 46 may include straight elements 46a having similar
lengths
(providing a predetermined amplitude or length for each band 46) and/or may
include
similar numbers of curved elements 46b around the circumference (providing a
predetermined period around the circumference). As shown, the first portion 42
of the
stent 40 has a substantially homogenous cell structure. Alternatively, other,
non-uniform
cell and/or band configurations may be provided, if desired. Any number of
annular bands
46 may be provided, e.g., to provide a first portion 42 having a desired
length, e.g.,
corresponding to a length of a lesion being dilated or otherwise treated using
the stent 40.
A band of transition elements 47 may connect the first and second portions 42,
44
of the stent 40. The transition elements 47 may include one or more sinusoidal
or other
curved segments that extend generally axially, as shown. Alternatively, the
transition
elements 47 may be substantially straight axial segments (not shown),
depending upon the
desired flexibility between the first and second portions 42, 44.
The second portion 44 of the stent 40 may include a first annular band 48
immediately adjacent the second end 45, including a zigzag or serpentine
pattern defined
by a plurality of straight elements 48a whose ends are connected alternately
by curved
elements 48b, 48d extending around the circumference of the stent 40. The
straight
elements 48a of the first annular band 48 may have longer lengths (amplitudes)
than the
straight elements 46a and/or the zigzag pattern may include fewer curved
elements 48b
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-6-
(i.e., may have a longer period) than the curved elements 46b included in the
annular
bands 46 of the first portion 42.
The second portion 44 may also include a second annular band 49 adjacent the
first
annular band 48, which may have similar amplitudes and/or periods than the
first annular
band 48, e.g., including similar straight elements 49a and/or alternating
curved elements
49b, 49d. As shown, the second annular band 49 is offset one hundred eighty
degrees
(180 ) from the first annular band 48 such that pairs of curved elements 48b,
49b are
disposed axially adjacent one another.
A link 48c may be provided that connects axially adjacent curved elements 48b,
49b of the first and second annular bands 48, 49. The link 48c may have a
width and/or
thickness that is smaller than the elements (e.g., the straight elements 48a,
49a and/or
curved elements 48b, 49b) of the first and second annular bands 48, 49. The
links 48c
may preferentially buckle when the first and second annular bands 48, 49 are
subjected to
an axially compressive force, as described further below.
The stent 40 may be formed from a variety of materials that may be plastically
defonned to allow expansion of the stent 40. For example, the stent 40 may be
formed
from metal, such as stainless steel, tantalum, MP35N, Niobium, Nitinol, and
L605, plastic,
or composite materials. In particular, the materials of the stent 40 may be
plastically
deformed under the pressures experienced when the stent 40 is expanded, e.g.,
such that
the first and/or second portions 42, 44 of the stent 40 are deformed beyond
their elastic
limit. Thus, when the stent 40 is deployed, the stent 40 may maintain its
expanded
configuration (e.g., that shown in FIG. 4C) with minimal recoil. Stated
differently, the
stent 40 material may resist collapsing back towards its reduced configuration
after
deployment, e.g., if the tissue surrounding the body lumen attempts to
constrict or
otherwise return to its occluded shape.
Alternatively, at least a portion of the stent 40 may be self-expanding. For
example, one or both of the first and second portions 42, 44 may be biased to
expand at
least partially outwardly yet may be constrained on a delivery device in a
contracted
condition to facilitate delivery. In this alternative, the stent 40 may be
formed from
Nitinol or other shape memory or superelastic materials.
Optionally, the resistance of the stent 40 to expansion may be varied along
its
length. This performance of the stent 40 may be based upon mechanical
properties of the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-7-
material, e.g., which may involve heat treating one or more portions of the
stent 40
differently than other portions. In addition or alternatively, the structure
of the stent 40
may be varied, e.g., by providing struts, fibers, or other components in
different portions
having different widths, thicknesses, geometry, and the like. In one
embodiment, the
material of the first portion 42 may require greater or less force to expand
than the second
portion 44.
Additional information on methods for making and/or using the stent 40, and/or
alternative configurations for the first portion 42 or other components of
the, stent 40 may
be found in co-pending applications Serial Nos. 60/710,521, filed August 22,
2005,
60/731,568, filed October 28, 2005, 60/757,600, filed January 9, 2006,
60/743,880, filed
March 28, 2006, and 60/745,177, filed April 19, 2006.
The stent 40 may be a generally tubular structure, e.g., including openings in
a
tubular wall that facilitate expansion of the stent 40 and/or allow tissue
ingrowth. For
example, the stent may be an elongate tube that has slots or other openings
formed in the
tube wall, e.g., by laser cutting, mechanical cutting, chemical etching,
machining, and the
like. Alternatively, the stent 40 may be a braided or other structure, e.g.,
formed from one
or wires or other filaments braided or otherwise wound in a desired manner.
Additional
possible stent structures may include helical coil wires or sheets.
If desired, one or more portions of the stent 40 may include a membrane, film,
or
coating (not shown), e.g., to create a nonporous, partially porous, or porous
surface
between cells of the stent 40. For example, as shown in FIG. 1 the second
portion 44 of
the stent 40 may include a substantially elastic membrane 41, e.g., PTFE,
ePTFE, silicone,
polyurethane, or polyethylene, that may be embedded into, coated onto,
sandwiched
around, or otherwise carried by the stent 40. The membrane 41 may be
substantially
elastic such that the membrane 41 may expand when the second portion 44 is
flared or
otherwise expanded. Alternatively, the membrane 41 may be folded or otherwise
compressed such that the membrane 41 may unfold or otherwise accommodate
expansion
as the stent 40 is expanded.
The meinbrane 41 may be provided on an outer and/or inner surface of the
second
portion 44. A membrane 41 on the inner surface may facilitate recrossing the
stent 40 at a
later time after implantation. For example, after the stent 40 is implanted
within a patient,
it may be desirable to advance a guidewire or other instrument (not shown)
through the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-8-
ostium into the branch vessel, e.g., to perform another procedure. This may
occur during
the same surgical procedure, or some time after the patient has recovered,
e.g., when the
branch vessel, lesion, or main vessel need subsequent treatment. The membrane
41 may
prevent the tip of a guidewire or other instrument from catching or tangling
in the struts,
cells, wires, or other structures of the stent 40. Instead, the membrane 41
may provide a
substantially smooth, possibly lubricious surface that may guide a guidewire
through the
stent 40 into the branch vessel.
In addition or alternatively, a membrane 41 on the stent 40 may carry
therapeutic
or other compounds or materials. For example, a membrane 41 on an outer
surface of the
stent 40 may be pressed into contact with the plaque, damaged tissue, or other
material of
the lesion, allowing the compound to act to enhance healing or otherwise treat
the lesion.
Optionally, the stent 40 may include one or more radiopaque or other markers
(not
shown), e.g., to facilitate monitoring the stent 40 during advancement,
positioning, and/or
expansion: For example, a band of radiopaque material, e.g., gold, platinunl,
iridium,
tungsten, or their alloys, may be provided on each end of the stent 40 and/or
adjacent the
location where the first and second portions 42, 44 meet. In addition or
alternatively,
wires, rods, disks, or other components (not shown) may be provided on
predetermined
locations on the stent 40 that are formed from radiopaque material to
facilitate monitoring
the stent 40 using fluoroscopy or other external imaging.
In addition or alternatively, the stent 40 may carry one or more therapeutic
or other
compounds (not shown) that may enhance or otherwise facilitate treatment of a
target
location within a patient's body. For example, the stent 40 may carry
compounds that
prevent restenosis at the target location.
Turning to FIGS. 4A and 4B, an exemplary embodiment of an apparatus 10 is
shown for delivering the stent 40 (which may be any of the embodiments
described
herein) to a desired location, e.g., within an ostium and/or branch vessel
(not shown).
Generally, the apparatus 10 includes a delivery catheter 12 and a pusher or
other actuator
50 for expanding or otherwise deploying the stent 40, as described further
below. The
delivery catheter 12 generally includes a proximal end 14, a distal end 16,
and one or more
lumens extending between the proximal and distal ends 14, 16, thereby defining
a
longitudinal axis 20 between the proximal and distal ends 14, 16. The delivery
catheter 12
includes one or more balloons or other expandable members 22 on the distal end
16 of the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-9-
delivery catheter 12 for expanding and/or deploying the stent 40, as described
fiirther
below. Optionally, the delivery catheter 12 may include a locator device (not
shown) on
the distal end 16, e.g., proximal or otherwise adjacent to the stent 40.
Exemplary locator
devices and methods for using them are disclosed in co-pending application
Serial No.
60/683,93 1, filed May 23, 2005.
The delivery catheter 12 may be formed from one or more tubular bodies, e.g.,
having variable flexibility along its length. For example, the distal end 16
may be
substantially flexible to facilitate insertion through tortuous anatomy, e.g.,
terminating in a
rounded, tapered, and/or other substantially atraumatic distal tip 17. The
distal end 16
may be sized and/or shaped for introduction into a body lumen, e.g., having a
diameter
between about one and seven millimeters (1-7 mm), or less than 1.5
millimeters. The
proximal end 14 may be substantially flexible or semi-rigid, e.g., having
sufficient column
strength to facilitate advancing the distal end 16 through a patient's
vasculature by pushing
on the proximal end 14. The delivery catheter 12 may be fomled from plastic,
metal, or
composite materials, e.g., a plastic material having a wire, braid, or coil
core, which may
preventing kinking or buckling of the catheter 12 during advancement.
The delivery catheter 12 may include a handle 30 on the proximal end 14, e.g.,
to
facilitate manipulating the delivery catheter 12. The handle 30 may include
one or more
side ports 32 communicating with respective lumens within the delivery
catheter 12, e.g., a
side port 32b communicating with a lumen (not shown) communicating with an
interior of
the balloon 22. The handle 30 may be molded, machined, or otherwise formed
from
plastic, metal, or composite material, e.g., providing an outer casing, which
may be
contoured or otherwise shaped to ease manipulation. The proximal end 14 of the
delivery
catheter 12 may be attached to the handle 30, e.g., by bonding, cooperating
connectors,
interference fit, and the like. Optionally, if the apparatus includes any
actuatable
components (not shown) on the distal end 16, the handle 30 may include one or
more
actuators (not shown), such as one or more slides, dials, buttons, and the
like, for actuating
or otherwise manipulating the components on the distal end 16 from the
proximal end 14,
as explained further below.
In the embodiment shown in FIGS. 4A-4C, the delivery catheter 12 includes at
least two lumens extending between the proximal ends 14, 16. For example, the
delivery
catheter 12 may include a guidewire or instrument lumen (not shown) that
extends from a
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-10-
side port 32a in the handle 30 to an opening 34 in the distal tip 17. The
instrument lumen
may have sufficient size to allow a guidewire or other rail or instrument (not
shown) to be
inserted therethrough, e.g., to facilitate advancing the delivery catheter 12
over the rail, as
explained further below. Optionally, the handle 30 may include one or more
seals (not
shown) within or adjacent the port 32a, e.g., a hemostatic seal that prevents
fluid, e.g.,
blood, from flowing proximally out of the port 32a, yet allows one or more
instruments to
be inserted therethrough and into the instrument lumen.
In addition, the delivery catheter 12 may include one or more inflation lumens
that
extend from respective side port(s) 32b in the handle 30 through the delivery
catheter 12 to
openings (not shown) that communicate with an interior of a respective balloon
22. The
side port(s) 32b on the handle 30 may include connectors, e.g., a luer lock
connector (not
shown), one or more seals (also not shown), and the like. A source of
inflation media
and/or vacuum, e.g., a syringe filled with saline (not shown), may be
connected to the side
port(s) 32b, e.g., via tubing (also not shown), for expanding and/or
collapsing the balloon
22.
As shown in FIGS. 4A-4C, the delivery catheter 12 includes one balloon 22 on
the
distal end 16. Alternatively, the delivery catheter 12 may include multiple
balloons (not
shown) on the distal end 16 over which the stent 40 may be placed. Additional
information on multiple balloon catheters and methods for using them are
disclosed in co-
pending application Serial No. 11/136,266, filed May 23, 2005.
The balloon (or balloons, not shown) 22 may be bonded or otherwise secured to
the distal end 16 of the delivery catheter 12. For example, ends of the
balloon 22 may be
attached to the distal end 16 using one or more of bonding with an adhesive,
sonic
welding, an annular collar or sleeve, and the like. The balloon 22 may be
expandable from
a contracted condition (not shown), which may facilitate advancement through a
patient's
vasculature to an enlarged condition for expanding or otherwise deploying the
stent 40.
The balloon(s) 22 may be formed from substantially inelastic material, e.g.,
PET,
nylon, or PEBAX, such that the balloon 22 expands to a predetermined size in
its enlarged
condition once sufficient fluid is introduced into the interior of the balloon
22.
Alternatively, the balloon 22 may be formed from substantially elastic
material, e.g.,
silicone, polyurethane, or polyethylene, such that the balloon 22 may be
expanded to a
variety of sizes depending upon the volume and/or pressure of fluid within the
interior.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-11-
With continued reference to FIGS. 4A-4C, the pusher 50 may include an elongate
member slidably coupled to the delivery catheter 12. For example, as shown,
the pusher
50 may include an elongate tubular member disposed around the delivery
catheter 12. The
pusher 50 may include a proximal end 52 disposed adjacent to and/or coupled to
the
handle 30 on the delivery catheter 12, and a distal end 54 disposed adjacent
to the balloon
22 and/or stent 40 on the distal end 16 of the delivery catheter 12.
From the proximal end 52, the pusher 50 may be directed distally relative to
the
delivery catheter 12, as shown in FIGS. 4B and 4C, such that the distal end 54
abuts
and/or otherwise engages the proximal portion 44 of the stent 40.
Alternatively, the
pusher 50 may be directed distally using a slider or other actuator (not
shown) on the
handle 30 that may be coupled to the pusher 50, e.g., by a wire, cable, or
other mechanism
(not shown).
One or more elements (not shown) may be provided on the distal end 16 of the
delivery catheter 12 for securing or otherwise preventing a portion of the
stent 40 from
moving distally on the distal end 16. For example, as explained further below,
stops,
detents, hooks, or other elements (not shown) may be provided that engage the
stent 40,
e.g., at the second annular band 49, transition band 47 (see FIG. 2), or
elsewhere on the
stent 40 to prevent the stent 40 from moving distally, e.g., off of the
balloon 22.
During use, as shown in FIGS. 4B and 4C the pusher 50 may be directed distally
against the stent 40, thereby subjecting the stent 40 to a compressive axial
force. This
force causes the proximal portion 44 of the stent to at least partially buckle
outwardly, as
explained further below. As shown, the distal end 54 of the pusher 50 includes
a collar or
sleeve that abuts the proximal end 45 of the stent 40 when the pusher 50 is
advanced.
Optionally, the pusher distal end 54 may include one or more features, e.g.,
clasps, detents,
hooks, and the like (not shown), that interlock or otherwise releasably
connect to the stent
40, e.g., to the proximal end 45 of the stent 40, similar to other embodiments
described
elsewhere herein. The features may disengage from the stent 40 simply by
pulling the
pusher 50 proximally, e.g., after expanding the proximal portion 44 of the
stent 40.
Alternatively, the features may be releasable upon activating an actuator on
the
proximal end 52 of the pusher 50 and/or on the handle 30, e.g., independent of
axial
movement of the pusher 50. This alternative may allow the proximal portion 44
of the
stent 40 to be collapsed back to the contracted condition, if desired, e.g.,
to remove and/or
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-12-
discontinue delivery of the stent 40. For example, if a user expands the
proximal portion
44 within a trunk, but then decides not to deliver the stent 40, the pusher
member 50 may
be pulled proximally, thereby collapsing the proximal portion 44 back to the
contracted
condition. The stent 40 may then be removed or directed to another location
for expansion
and delivery. In this alternative, the delivery catheter 12 may include one or
more
features, e.g., hooks, detents, stops, and the like (not shown), that prevent
proximal
movement of the distal end 43 of the stent 40 when the pusher 50 is pulled
proximally,
thereby subjecting the stent 40 to an axial tensile force that may allow
plastic deformation
of the proximal portion 44 of the stent 40 back to the contracted condition.
Turning to FIGS. 3A-3H, a method for delivering a stent 40, such as that shown
in
FIGS. 1 and 2, into an ostium 90 is now described. The ostium 90, a model of
which is
shown in FIGS. 3D-3H, may be an opening in a wall of a first or main body
lumen or
trunk (not shown) that communicates with a second body lumen or branch 94. In
an
exemplary embodiment, the trunk may be the aortic root and the branch 94 may
be a
coronary artery. In another embodiment, the trunk may be the distal aorta, and
the branch
94 may a renal artery or other abdominal branch. It will be appreciated that
the apparatus
and methods described herein may be applicable to a variety of bifurcations or
branches
that extend transversely, e.g., laterally (at relatively shallow angles) or
substantially
perpendicularly, from another body lumen or trunk, e.g., within a patient's
vasculature or
other systems.
An occlusion or other lesion (not shown) may exist at and/or adjacent to the
ostium
90, e.g., extending at least partially into the branch 94. The lesion may
include
atherosclerotic plaque or other material that partially or completely
obstructs blood or
other fluid flow between the trunk and the branch 94.
Initially, a guidewire or other rail (not shown) may be introduced from the
trunk
and through the ostium 90 into the branch 94 using conventional methods. For
example, a
percutaneous puncture or cut-down may be created at a peripheral location (not
shown),
such as a femoral artery, carotid artery, or other entry site, and the
guidewire may be
advanced through the patient's vasculature from the entry site, e.g., alone or
with the aid
of a guide catheter (not shown). Optionally, after the guidewire is directed
into the branch
94 beyond the lesion, it may be desirable to at least partially dilate or
otherwise treat the
lesion. For example, an angioplasty catheter (not shown) may be advanced
through the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-13-
guide catheter and/or over the guidewire into and through the lesion,
whereupon a balloon
or other element on the catheter may be expanded to at least partially dilate
the lesion. If
desired, other procedures may also be performed at the lesion, e.g., to
soften, remove, or
otherwise treat plaque or other material forming the lesion, before the stent
40 is
implanted. After completing any such procedures, instruments advanced over the
guidewire may be removed.
If a guide catheter is used, the distal end of the guide catheter may be
advanced
over the guidewire into the trunk, e.g., until the distal end is disposed
adjacent or proximal
to the ostium 90. A distal end 16 of the delivery catheter 12 may be advanced
over the
guidewire and/or through the guide catheter from the entry site into the
trunk. Optionally,
the guide catheter may be partially retracted to expose the balloon 22 and
stent 40, e.g., as
shown in FIG. 3A.
Turning to FIG. 3B, the actuator 50' may be activated from the proximal end
(not
shown) of the delivery catheter 12 to buckle and expand the proximal portion
44 of the
stent 40. In the embodiment shown, the actuator 50' includes a plurality of
arms 54' that
engage or otherwise contact the proximal end 55 of the stent 40. The arms 54'
may be
directed distally, while the stent 40 is maintained from moving distally, such
that the
proximal portion 44 buckles. For example, with additional reference to FIG. 2,
the first
and second annular bands 48, 49 may buckle outwardly causing links 48c to bend
as the
curved elements 48b, 49b move radially outwardly. Alternatively, other
actuators and/or
pusher members (not shown), such as those described elsewhere herein, may be
used
instead of the actuator 50.'
Turning to FIG. 3C, once the actuator 50' is fully activated, the proximal
portion
44 of the stent 40 may be flared outwardly, e.g., such that the second annular
band 49 is
flared or inclined, e.g., to define an obtuse angle with the longitudinal axis
of the delivery
catheter 12. The first annular band 48 may be oriented substantially
perpendicularly or
otherwise transversely relative to the longitudinal axis. In particular,
because the curved
elements 48d on the proximal end 45 of the stent 40 are engaged by the
actuator arms 54,'
the curved elements 48d may remain adjacent the surface of the delivery
catheter 12, while
the curved elements 48b coupled to the links 48c are disposed outwardly away
from the
surface of the delivery catheter 12.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-14-
Turning to' FIG. 3D, the distal end 16 of the delivery catheter 12 may then be
advanced into the ostium 90 and/or the branch 94 from the trunk. If desired, a
locator
device (not shown) may be used to facilitate positioning the stent 40, as
described in
application Serial No. 11/136,266. Alternatively, the flared condition of the
proximal
portion 44 shown in FIG. 3C may provide a locator for positioning the stent 40
relative to
the ostium 90. For example, the diameter of the proximal portion 44 in the
flared
condition may be selected to correspond to a size of the ostium 90, e.g., to
be larger than
the ostium 90, thereby allowing the stent 40 to be directed partially into the
ostium 90
without passing entirely into the branch 94.
Turning to FIGS. 3E and 3F, the stent 40 may be further expanded within the
ostium 90 and/or branch 94, e.g., to dilate or otherwise treat a lesion
therein. For example,
in the embodiment shown in FIG. 3E, the delivery catheter 12 includes a distal
balloon 22a
that may be inflated to expand the distal portion 42 of the stent 40. The
distal balloon 22a
may expand the distal portion 42 into a substantially uniform cylindrical
shape or into a
tapered shape, depending upon the shape of the distal balloon 22a selected and
the
anatomy encountered. As shown in FIG. 3F, a proximal balloon 22b may then be
inflated
to further expand the proximal portion 44 of the stent 40. In particular, this
action may
expand the first annular band 48 of the proximal portion 44, e.g., directing
the curved
elements 48d on the proximal end 45 of the stent 40 radially outwardly.
As best seen in FIG. 3H, this expansion may caused the curved elements 48d to
at
least partially straighten, e.g., as the straight elements 48a deform into a
circumferential
configuration, e.g., approximating a circle or ellipse extending around the
ostium 90.
Thereafter, as shown in FIG: 3G, the balloon(s) 22 may be deflated and the
distal end 16
of the delivery catheter 12 withdrawn from the branch 94 and ostium 90,
leaving the stent
90 in place. Optionally, the arms 54' of the actuator 50' may still engage the
now-
straightened curved elements 48d, thereby preventing the stent 40 from being
dislodged
while the delivery catheter 12 is withdrawn. The arms 54' may be disengaged by
directing
the actuator 50' proximally and/or by activating a release mechanism (not
shown) on the
handle 30 (also not shown) of the delivery catheter 12. As shown in FIG. 3H,
the delivery
catheter 12 and actuator 50' may be removed from the patient, leaving the
stent 40 within
the ostium 90 and/or branch 94.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-15-
The resulting deployed condition of the stent 40 shown in FIG. 3H may provide
a
structure that is substantially resistant to the heavy elastic recoil expected
when deploying
in a large artery, such as the aorta or other parent vessel. The strength of
the stent 40 is
enhanced by the uninterrupted circle of struts 48a obtained when the first row
of struts 48
are completely expanded during inflation of the proximal balloon 22b. Unlike
conventional stents where a significant angle is maintained between adjoining
struts to
allow the balloon inflation, this stent 40 leaves a row of struts 48a aligned
with each other
end-to-end. In addition, the resulting structure may facilitate re-crossing
the stent 40, e.g.,
should the patient ever need this ostium 90 to be accessed again by guidewire.
Conventional stents may have numerous struts and flexible connections
throughout their
construction, which may present obstacles to attempts made to re-access the
ostium 90
using a guidewire. In contrast, the stent 40 has relatively few struts 48a,
49a and flexible
connections in the proximal flared portion 44. The struts 49a defining the
flare are
oriented substantially in the longitudinal direction, to fiirther reduce their
impact on
attempts to re-cross the ostium 90 with a guidewire.
Turning to FIG. 5, another embodiment of an actuator 150 is shown that may be
used to flare and/or otherwise deploy the proximal portion 44 of sfent 40
(which may be
any of the embodiments described herein). Generally, the actuator 150 includes
a plurality
of arms 154 (one shown) including a slot 155, and a fiber 156. Similar to the
embodiment
described with reference to FIG. 2, the proximal portion 44 of the stent 40
includes a first
row of struts 48, which are attached to a second row of struts 49 via a
flexible connector
48c. The struts 48a in the first row 48 are connected at their proximal end to
another
portion of the stent 40 having one or more flexible connectors 48d, similar to
curved
elements described above (although shown here with a more complicated
geometry).
Unlike the previous embodiment, an eyelet 49e is provided adjacent each curved
loop 49d
in the second row of struts 49.
The curved element 48d of the first row of struts 48 may be received in the
slot 155
in the arm 154. The fiber 156, which may be composed of metal, plastic, or
other suitable
material, is threaded through a hollow bore or other passage of the arm 154,
over the
curved element 48 positioned in the slot 155, through the eyelet 49e, and back
into the
hollow bore of the arm 154.
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-16-
This embodiment of the actuator 150 may allow the proximal portion 44 of the
stent 40 to be compressed axially (in the longitudinal direction) by applying
a compressive
force to the arm 154, while simultaneously applying a tensile force to the
fiber 156. In
response to the applied stresses, the first and second rows 48, 49 of the
proximal portion
44 of the stent 40 may buckle radially outwardly, i.e., in the transverse
direction, by
bending the flexible connector 48c.
Turning to FIGS. 6A and 6B, another embodiment of an apparatus 210 is shown
that includes a delivery catheter 212 and a pusher or actuator 250, which may
be similar to
the embodiments described elsewhere herein. FIG. 6A shows the apparatus 210 in
a
condition suitable for tracking through a patient's body to a location in a
trunk or other
parent vessel. In this embodiment, a proximal balloon 222b is located under a
portion of
the stent 40 interfacing with the distal end 254 of the pusher 250. The
balloon 222b may
act as a catch mechanism, e.g., engaging the proximal end 45 of the stent 40,
e.g., based
upon frictional contact between the balloon 222b and the stent 40, using a low
tack
adhesive, and the like. Alternatively, the balloon 222b may be inflated or
otherwise
expanded to provide a stop before deploying the stent 40.
Turning to FIG. 6B, the proximal portion 44 of the stent 40 has been buckled
and
flared radially outwardly. This may be achieved by advancing pusher 250
distally relative
to the stent 40 and distal end 216 of the delivery catheter 212, similar to
the previous
embodiments described herein. In an alternate embodiment shown in FIG. 7, a
portion of
the stent 40 is located on the proximal balloon 222b,' but a reinforcement 256
has been
added to the proximal portion of the proximal balloon 222b.' This
reinforcement 256 may
act to add additional mechanical integrity to the balloon 222b' during the
linear actuation
of the flared portion 44 of the stent 40, e.g., to allow the balloon 222b' to
provide a stop
without having to inflate the balloon 222b.' The reinforcement 256 may simply
be a
thicker portion of the proximal balloon 222b' itself, an object embedded
inside a wall of
the proximal balloon 222b,' or an object placed inside or adjacent to the
proximal balloon
222b,' e.g., attached to the distal end 216 of the delivery catheter 210.
Thus, the balloon
222b' may provide a stop that compresses the proximal portion 44 of the stent
40, similar
to other embodiments described elsewhere herein.
Turning to FIGS. 8A and 8B, a schematic of yet another embodiment of an
apparatus 310 is shown including a delivery catheter 312 and a pusher or other
actuator
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-17-
350. The stent 40 shown may be similar to other embodiments described herein,
including
a distal portion 42 and a proximal portion 44 that includes first and second
bands of cells
48, 49 (connected by links or other connectors represented by dots). In this
alternative
embodiment, the pusher 350 includes a catch mechanism 354 and a proximal
balloon 322b
attached to and inflatable via the pusher 350. As shown in FIG. 8A, the catch
mechanism
354 engages or otherwise contacts a proximal end 45 of the stent 40, e.g.,
capturing the
proximal end 45 between the catch mechanism 354 and a wall of the delivery
catheter 312.
The stent 40 and balloons 322 are collapsed, allowing the distal end 316 of
the delivery
catheter 312 to be delivered into a main body lumen (not shown), similar to
other
embodiments described herein.
As shown in FIG. 8B, the flare on the proximal portion 44 of the stent 40 has
been
actuated by advancing the pusher 350 until a flared shape is achieved in the
proximal
portion of the stent (6). The stent 40 is maintained from slipping off of the
telescoped tube
by the catch mechanisni 354, which may resiliently or plastically bend
outwardly, as
shown, to accommodate flaring of the stent 40. As explained elsewhere herein,
the flare
of the proximal portion44 may be actuated in preparation for inserting the
stent 40 into an
ostium.
Turning to FIG. 8C, the distal balloon 322a may be inflated to expand the
distal
portion 42 of the stent 40 after proper location in the ostium is achieved
using the flared
proximal portion 44 of the stent 40.
Next, as shown in FIG. 8D, the distal balloon 322a has been deflated and the
pusher 350 has been advanced so that the proximal balloon 322b is disposed
under the first
row of struts 48 of the proximal portion 44 of the stent 40. The pusher 350
and/or delivery
catheter 312 may include tracks, guides, and the like (not shown), which may
limit distal
movement of the pusher 350, e.g., to place the balloon 322b under the proximal
end 45 of
the stent 40. When the pusher 350 is advanced, the first row of struts 48 of
the proximal
portion 44 of the stent 40 may be bent past an angle of ninety degrees (90 )
relative to the
longitudinal axis 320, which may release the distal end 45 of the stent 45
from the catch
mechanism 354. For example, as the first row of struts 48 is bent past ninety
degrees
(90 ), they are no longer under a compressive load, but are under a tensile
load.
Turning to FIG. 8E, the proximal balloon 322b may be inflated, causing the
proximal portion 44 of the stent 40 to obtain a final flared condition in the
ostium, with the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
- 18-
first row of struts 48 extending radially, similar to the embodiments
described above.
Optionally, the distal balloon 322a may remain inflated and/or may be inflated
in
conjunction with the proximal balloon 322b in order to achieve a desired fully
deployed
configuration for the stent 40.
Turning to FIGS. 9A and 9B, still another embodiment of an apparatus 410 is
shown that includes a delivery catheter 412 and an actuator 450, which may be
constructed
generally similar to other embodiments described herein. As shown in FIG. 9A,
the
delivery catheter 412 may include relatively small fingers, tabs, or catches
458, e.g.,
formed from metal or other strong material, attached to the distal end 416.
The fingers
458 may protrude through the stent 40 to form a mechanical attachment of the
stent 40 to
the distal end 416 of the delivery catheter 412. These fingers 458 may prevent
axial
movement of the stent 40 relative to the delivery catheter 412 in the
condition shown in
FIG. 9A, while allowing the stent 40 to be expanded radially outwardly. Once
the
balloon(s) 422 are inflated, e.g., as shown in FIG. 9B, the fingers 458 may
disengage from
the stent 40, releasing the stent 40 from the delivery catheter 412 to allow
implantation in
the patient.
Turning to FIG. 10, a flat-pattern is shown that may be used to cut the
fingers 458
from a tube. The diameter of the tube may be chosen to be slightly larger than
the distal
end 416 of the delivery catheter 412 to aid in crimping, bonding, welding, or
otherwise
attaching the fingers 458 to the delivery catheter 412. The fingers 458 may be
bent
radially outwardly from the tube surface to engage features, e.g., cells or
struts, of the stent
40 and act as an attachment mechanism. As shown, the tube includes a plurality
of
additional slits 459. The slits 459 may be useful to allow the tube to be
crimped,
expanded, or otherwise received over any features that exist on the distal end
416 of the
delivery catheter 412, thereby securing the fingers 458 on the distal end 416.
The slits 459
are not necessary for the use of the fingers 458.
Turning to FIGS. 11A and 11B, the interaction of the fingers 458 with the
geometry of a stent 40 is shown. The stent may have a strut 447 oriented in
the stent's
longitudinal axis that bifurcates into an arc 448. The strut 447 may be
inserted between
two fingers 458, effectively capturing the stent 40 and preventing axial
movement in
"Direction 1" shown in FIG. 11A. Upon inflation of the balloon(s) on the
delivery
catheter 412, the fingers 458 may bend out of the way, allowing the stent 40
to expand
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-19-
radially outward, and become free from the delivery catheter 412. In FIG. 11B,
in an
alternative embodiment, the finger 458 placed into an eyelet 446 formed into
the stent 40.
Again, the finger 458 may prevent axial migration of the stent 40, but bend
out of the way
and release the stent 40 upon balloon inflation.
Turning to FIGS. 12-14D, another embodiment of an apparatus 510 is shown that
includes a delivery catheter 512, a pusher or actuator 550, and a stent 40,
which may be
constructed similar to any of the embodiments described elsewhere herein. As
shown in
FIGS. 14A-14D, the delivery catheter 512 may include a distal end 516
including a
balloon 522 thereon and carrying the stent 40. The pusher 550 may include an
elongate
tubular member and the like (not shown) extending from a proximal end (not
shown) of
the delivery catheter 512 to the distal end 516, e.g., terminating adjacent
the proximal end
45 of the stent 40.
With particular reference to FIGS. 12 and 13, the pusher 550 may include a
plurality of connectors 558 on its distal end that may be interlocked or
otherwise
removably connected to the proximal end 45 of the stent 40. FIG. 12 shows a
flat pattern
that may be used to cut the distal end of the pusher 550 from a hollow tube of
material,
e.g., by laser cutting, die cutting, machining, chemical etching, and the
like. As shown,
the pattern includes a plurality of longitudinal fingers 552 including
proximal end 554,
which may be connected to the proximal portion (not shown) of the pusher 550,
and a
distal end 556. The distal ends 556 of the fingers 552 include the connectors
558, which
may be cut in a serpentine pattern that is loose relative to the fingers 552.
Optionally, the
fingers 552 may also contain second stabilizing connectors 560.
Turning to FIG. 13, during use, the stent 40 may be loaded onto the distal end
516
of the delivery catheter 512 (not shown, see FIGS. 14A-14D), and captured
using the
connectors 558. For example, as shown, curved elements 48d on the proximal end
45 of
the stent 40 may be captured under the connectors 558, while axial elements
48a may pass
over the connectors 558, thereby providing an interference fit. Thus, the
proximal portion
44 of the stent 40 may be limited in axial movement, similar to the previous
embodiments.
Turning to FIGS. 14A-14D, deployment of the stent 40 is shown, e.g., after
delivering the stent 40 into a trunk adjacent to an ostium, similar to the
previous
embodiments. As shown in FIG. 14A, the pusher 550 may be advanced to buckle
the
proximal portion 44 of the stent 40, with the connectors 558 maintaining
control of the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-20-
proximal end 45 of the stent 40 during the linear-actuation used to flare the
stent. Turning
to FIG. 14B, the proximal portion 44 of the stent 40 has been fully flared
condition due to
linear actuation, and the connector 558 of the pusher 550 still has control of
the proximal
end 45 of the stent 40. At this point, if desired, the pusher 550 could be
pushed
proximally, causing the stent 40 to retract back down to its shape before
linear actuation.
This may be useful, because, if necessary or desired, the stent 40 may be
removed without
substantial risk of harming the patient.
Turning to FIGS. 14C and 14D, a proximal balloon 522 on the delivery catheter
512 is shown being inflated, causing the fingers 552 of the pusher 550 to
flare out from
each other. This, in turn, pulls the connectors 558 out straight from its
original serpentine
configuration, thereby releasing the proximal end 45 of the stent 40 from the
connectors
558. Further, because the connectors 558 allow only limited expansion of the
fingers 552,
e.g., defined by the length of the serpentine configuration as it straightens,
this separates
the stent 40 and the pusher 550 as the balloon 522 inflates between them. The
flared
pusher 550 may also act to mechanically stabilize the balloon 522 in the
proximal
direction, e.g., when the apparatus 510 is being advanced into an ostium (not
shown)
and/or during proximal balloon inflation of the stent 40.
Turning to FIGS. 22A-22F, the various stages of expanding the stent 40 is
shown.
Although these drawings show the stent 40 being expanded using the delivery
catheter 512
and pusher of FIGS. 14A-14D, it will be appreciated that other embodiments
described
herein may expand the stent 40 using a similar sequence. Initially, in FIG.
22A, the stent
40 is shown in a contracted condition, e.g., for delivery through a patient's
vasculature.
Similar to the previous embodiments, the stent 40 generally includes a first
flaring portion
44 and a second main portion 42. In FIG. 22B, the pusher 550 is being directed
distally
relative to the delivery catheter 512 and/or the main portion 42, thereby
compressing the
flaring portion 44 axially. As shown in FIG. 22C, this causes the flaring
portion 44 to
buckle radially outwardly to an intermediate condition. Optionally, the pusher
550 may be
removed, as shown in FIG. 22D (or the pusher 550 is simply omitted for
clarity).
Turning to FIG. 22E, a first balloon 522a on the delivery catheter 512
(underlying
the main portion 42) may be expanded, thereby causing the main portion 42 to
expand
from the contracted condition to an enlarged condition. Then, as shown in FIG.
22F, a
second balloon 522a on the delivery catheter 512 may be expanded, thereby
causing the
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-21 -
flaring portion 44 to expand from the intermediate condition to an enlarged
condition.
Alternatively, the sequence of the expansion of the balloons 522 may be
reversed.
Alternatively, a single balloon may be provided, and the expansion of the main
portion 42
and the flaring portion to the enlarged condition may occur substantially
simultaneously.
Turning to FIGS. 15 and 16, in any of the embodiments described herein, it may
be
desirable to have variable properties along a length of the stent, e.g., to
accommodate
different needs for different portions of a diseased vessel.
For example, FIG. 15 shows a cross-section of a patient's body, including a
main
vessel, e.g., an aorta, and an ostium communicating with a branch vessel
extending from
the aorta. As described elsewhere herein, an aorto-ostial lesion may exist
within the
ostium and/or branch. As can be seen, a thickness of the wall of the vessels
may vary
from the portion defining the aorta to the portion defining the vessel. This
variation in
wall thickness provides a situation where a constant design along the stent
length is at a
disadvantage.
Turning to FIG. 16, expected mechanical properties of an aorto-ostial lesion
and
the desired mechanical properties of a stent used to treat such an aorto-
ostial lesion are
shown. The elastic recoil of the vessel (line "a") starts at a high value due
to the thick wall
thickness of the vessel riear the ostium, and decreases with distance distally
into the vessel.
To accommodate this high elastic recoil, the desired stent luminal support
(line "b") may
mimic the elastic recoil of the vessel. If a constant luminal support stent
design were
deployed, the designer would have to choose a luminal support that was either
too weak to
address the high elastic recoil of the vessel near the ostium, or too strong
(and potentially
damaging) to the distal portion of the vessel.
In addition, flexibility is also shown (line "c") in FIG. 16. In general,
flexibility is
always desired in a stent, but flexibility often comes by reducing the luminal
support of a
stent. For this reason, the desired flexibility is shown as an inverse
function of the luminal
support, having low flexibility near the ostium, and greater flexibility in
the distal portion
of the vessel.
Turning to FIG. 17, an exemplary embodiment of a cell pattern is shown that
may
be used to provide variable luminal support and flexibility, e.g., for the
reasons just
discussed. The exemplary cell pattern shown includes nine (9) columns of
cells. The cells
are defined as having a serpentine pattern along each of the cells' two sides,
and a
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
- 22 -
connector defining the top and bottom of each cell. The thicknesses of the
serpentine
patterns and connectors have been made such that Column 1 has the highest
thickness and
Column 9 has the lowest thickness. By varying the thickness of the straight
portions of the
serpentine pattern, the bent portions of the serpentine pattern, and the
connectors, the stent
may be made to have a greater luminal support in the columns of cells having
thicker cell
elements than those rows of cells having thinner cell elements.
Alternatively, as shown in FIG. 18, a cell pattern may be provided for a stent
that
includes variable cell width. Because the serpentine patterns provide the
majority of
luminal support, and the serpentine patterns are closer together in cells with
smaller widths
than larger widths, a gradient of luminal support may be achieved. In the case
of the
ostium shown, the area of the stent adjacent to the ostium would have small
cell widths,
and the cells would become wider distally along the length of the stent.
Turning to FIG. 19, yet another cell pattern is shown where the number of
connectors between cells has been varied along the length of the stent. By
varying the
number of connectors in each column of cells, the flexibility of the stent may
be modified.
For example, those rows with less connectors may be more flexible than those
columns
having more connectors. In addition, it is envisioned that luminal support may
be higher
in rows with more connectors because it is more constrained in how it may bend
under
elastic recoil loads. The number of connectors, therefore, may also enable
varying the
mechanical properties of the stent as needed for specific lesion types.
In another embodiment, shown in FIG. 20, a cell pattern may be provided where
the connector design varies from one side of the stent to the other. As shown,
the left
column has the bent portion of the serpentine pattern merged into the adjacent
serpentine
pattern. This may create a cell structure that has a high degree of luminal
support and low
flexibility due to the high degree of deformation that must occur in the small
area
contained in the junction between serpentine patterns. The adjacent cells show
a gradual
dissociation of serpentine patterns and the creation of a connector that
bridges the bent
portion of adjacent serpentine patterns. These cells may decrease in luminal
support and
increase in flexibility as the connector becomes more defined and longer.
The right-most cells show the creation and exaggeration of a bend in the
connector.
As the connector becomes bent to a greater degree from the longitudinal axis
of the stent,
it may become easier to bend under compressive, axial loads, and also may
become
CA 02609360 2007-11-22
WO 2006/127784 PCT/US2006/020041
-23-
capable of elongating in the axial direction under tensile, axial loads. In
general, bending
the flexible connector to a greater degree may make it more compliant. This
increase in
connector compliance may reduce the luminal support of the stent, and increase
its
flexibility. In addition to a single bend in the connector as shown in FIG.
20A, additional
bends can be designed into the connectors as shown in FIGS. 20B and 20C.
Finally, as shown in FIG. 21, it may be possible to vary the mechanical
properties
of a stent along its length by varying the number of serpentine convolutions
around its
circumference and/or varying the diameter of the radii of the bent portion of
the serpentine
convolutions. As shown, the first and second leftmost columns each have ten
(10) cycles
in their serpentine convolutions, while third column has eight (8) and the
fourth column
has six (6). This reduction in the number of serpentine convolutions alone, or
in
conjunction with the other methods described above may be used to vary the
mechanical
properties of the stent along its length.
In addition, the radius of the serpentine convolutions may be varied to change
the
mechanical properties of the stent along its length. For example, as shown,
the first and
second leftmost columns have a radius of that is smaller than the third
column, which has
a radius smaller than the fourth column. Generally, larger radii may allow
more uniform
stress distribution, and lower forces to deform the stent. This property,
however, may also
be combined with the other designs for varying the mechanical properties of a
stent along
its length. Thus, it will be appreciated that any of these combinations may be
utilized
alone or together to provide a stent having desired mechanical properties
along its length,
such as those shown in FIG. 15.
It will be appreciated that elements or components shown with any embodiment
herein are exemplary for the specific embodiment and may be used on or in
combination
with other embodiments disclosed herein.
While the invention is susceptible to various modifications, and alternative
forms,
specific examples thereof have been shown in the drawings and are herein
described in
detail. It should be understood, however, that the invention is not to be
limited to the
particular forms or methods disclosed, but to the contrary, the invention is
to cover all
modifications, equivalents and alternatives falling within the scope of the
appended
claims.
