U.S. patent application number 10/123883 was filed with the patent office on 2002-10-31 for intravascular stent.
Invention is credited to Jang, G. David.
Application Number | 20020161429 10/123883 |
Document ID | / |
Family ID | 26689933 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020161429 |
Kind Code |
A1 |
Jang, G. David |
October 31, 2002 |
Intravascular stent
Abstract
A stent in a non-expanded state has a first column expansion
strut pair. A plurality of the first column expansion strut pair
form a first expansion column. A plurality of second column
expansion strut pair form a second expansion column. A plurality of
first serial connecting struts form a first connecting strut column
that couples the first expansion column to the second expansion
column. The first expansion column, the second expansion column,
and the first connecting strut column form a plurality of geometric
cells. At least a portion of the plurality are asymmetrical
geometric cells.
Inventors: |
Jang, G. David; (Redlands,
CA) |
Correspondence
Address: |
HELLER EHRMAN WHITE & MCAULIFFE LLP
275 MIDDLEFIELD ROAD
MENLO PARK
CA
94025-3506
US
|
Family ID: |
26689933 |
Appl. No.: |
10/123883 |
Filed: |
April 15, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10123883 |
Apr 15, 2002 |
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09839442 |
Apr 20, 2001 |
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6409761 |
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09839442 |
Apr 20, 2001 |
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08824142 |
Mar 25, 1997 |
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6241760 |
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10123883 |
Apr 15, 2002 |
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09839287 |
Apr 20, 2001 |
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09839287 |
Apr 20, 2001 |
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09237537 |
Jan 26, 1999 |
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6235053 |
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60017484 |
Apr 26, 1996 |
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60073412 |
Feb 2, 1998 |
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Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2/915 20130101;
A61F 2002/91525 20130101; A61F 2002/91558 20130101; A61F 2/91
20130101; A61F 2/958 20130101; A61F 2250/0018 20130101; A61F
2230/0013 20130101; A61F 2002/91533 20130101; A61F 2/89 20130101;
A61F 2230/0054 20130101 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A tubular stent with a plurality of expansion columns and
connector columns arranged along a longitudinal axis in a
horizontal plane, comprising: a plurality of expansion columns
having expansion strut pairs, the plurality of expansion columns
including an unbroken first expansion column made of a plurality of
first expansion strut pairs each having a first expansion strut and
an adjacent second expansion strut, and a second unbroken expansion
column made of a plurality of second expansion strut pairs each
having a first expansion strut and an adjacent second expansion
strut, wherein expansion strut pairs of each expansion column of
the plurality of expansion columns have geometric configurations
similar to the first expansion column or the second expansion
column; and a plurality of connector columns that couple adjacent
expansion columns, the plurality of connector columns including a
first connector column that couples the first and second expansion
columns, each connector column of the plurality of connector
columns having at least one or more connector struts selectively
skipped and leaving a bank connector strut space between adjacent
expansion columns.
2. The stent of claim 1, wherein the skipped connector struts
increase a flexibility of the connector columns.
3. The stent of claim 1, wherein the skipped connector struts
enlarge a size of a related stent cell.
4. The stent of claim 1, wherein a first connector column having at
least one connector strut skipped, leaving a blank connector space
in a first connector column and one link missing between first and
second expansion columns.
5. The stent of claim 1, wherein each of plurality of connector
columns having at least one connector strut skipped, leaving at
least one connector space blank in each of plurality of connector
columns and at least one link missing between each adjacent
expansion columns of plurality of expansion columns.
6. The stent of claim 1, wherein some of plurality of connector
columns having at least one connector strut skipped, leaving at
least one connector space blank in some of plurality of connector
columns and at least one link missing between some of adjacent
expansion columns of plurality of expansion columns.
7. The stent of claim 1, wherein a first connector column having
more than one connector strut skipped, leaving more than one
connector space blank in a first connector column and more than one
link missing between first and second expansion columns.
8. The stent of claim 1, wherein each of plurality of connector
columns having more than one connector strut skipped, leaving more
than one connector space blank in each of plurality of connector
columns and more than one link missing between each adjacent
expansion columns of plurality of expansion columns.
9. The stent of claim 1, wherein some of plurality of connector
columns having more than one connector strut skipped, leaving more
than one connector space blank in some of plurality of connector
columns and more than one link missing between some of adjacent
expansion columns of plurality of expansion columns.
10. The stent of claim 1, wherein a first connector column having
every connector strut except one connector strut skipped, leaving
every connector space blank except one connector strut space in a
first connector column and every link, except one link, missing
between a first and a second expansion columns.
11. The stent of claim 1, wherein each of plurality of connector
columns having every connector strut except one connector strut
skipped, leaving every connector space blank except one connector
strut space in each of plurality of connector columns and every
link, except one link, missing between each adjacent expansion
columns of plurality of expansion columns.
12. The stent of claim 1, wherein some of plurality of connector
columns having every connector strut except one connector strut
skipped, leaving every connector space blank except one connector
strut space in some of plurality of connector columns and every
link, except one link, missing between some of adjacent expansion
columns of plurality of expansion columns.
13. The stent of claim 1, wherein a first connector column having
every connector strut except two connector struts skipped, leaving
every connector strut space blank except two connector struts in a
first connector column and every link, except two links, missing
between a first and a second expansion columns.
14. The stent of claim 1, wherein each of plurality of connector
columns having every connector strut except two connector struts
skipped, leaving every connector strut space blank except two
connector struts in each of plurality of connector columns and
every link, except two links, missing between each adjacent
expansion columns of plurality of expansion columns.
15. The stent of claim 1, wherein some of plurality of connector
columns having every connector strut except two connector struts
skipped, leaving every connector strut space blank except two
connector struts in some of plurality of connector columns and
every link, except two links, missing between some of adjacent
expansion columns of plurality of expansion columns.
16. The stent of claim 1, wherein a first connector column having
every connector strut, except three connector struts, skipped,
leaving every connector strut space blank except three connector
struts in a first connector column and every link, except three
links, missing between a first and a second expansion columns.
17. The stent of claim 1, wherein each of plurality of connector
column having every connector strut, except three connector struts
skipped leaving every connector strut space blank except three
connector struts in each of plurality of connector column and every
link, except three links, missing between each adjacent expansion
columns of plurality of expansion columns.
18. The stent of claim 1, wherein some of plurality of connector
column having every connector strut, except three connector struts
skipped leaving every connector strut space blank except three
connector struts in some of plurality of connector columns and
every link, except three links missing in some of adjacent
expansion columns of plurality of expansion columns.
19. The stent of claim 1, wherein a first connector column having
every other connector struts skipped leaving every other connector
strut space blank in a first connector column and every other link
missing between first and second expansion columns.
20. The stent of claim 1, wherein each of plurality of connector
columns having every other connector struts skipped leaving every
other connector strut space blank in each of plurality of connector
columns and every other link missing between each adjacent
expansion columns of plurality of expansion columns.
21. The stent of claim 1, wherein some of plurality of connector
columns having every other connector struts skipped leaving every
other connector strut space blank in some of plurality of connector
columns and every other link missing in some of adjacent expansion
columns of plurality of expansion column.
22. The stent of claim 1, wherein said stent is a balloon
expandable stent.
23. The stent of claim 1, wherein said stent is self-expanding
stent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
09/839,442 filed Apr. 20, 2001 which is a continuation of U.S. Pat.
No. 6,241,760 which claims the benefit of U.S. Ser. No. 60/017,484
filed Apr. 26, 1996. This application is also a continuation of
U.S. Ser. No. 09/839,287 filed Apr. 20, 2001 which is a
continuation of U.S. Ser. No. 09/237,537 filed Jan. 26, 1999 which
claims the benefit of U.S. Ser. No. 60/073,412 filed Feb. 2, 1998,
all of which applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to intravascular stents, and more
particularly to an intravascular stent which provides easy
introduction through tortious sections of vessels.
[0004] 2. Description of the Related Art
[0005] Angioplasty, either coronary or general vascular, has
advanced to become the most effective means for revascularization
of stenosed vessels. In the early 1980's, angioplasty first became
available for clinical practice in the coronary artery, and has
since proven an effective alterative to conventional bypass graft
surgery. Balloon catheter dependent angioplasty has consistently
proven to be the most reliable and practical interventional
procedure. Other ancillary technologies such as laser based
treatment, or directional or rotational arthrectomy, have proven to
be either of limited effectiveness or dependent on balloon
angioplasty for completion of the intended procedure. Restenosis
following balloon-based angioplasty is the most serious drawback
and is especially prevalent in the coronary artery system.
[0006] Many regimens have been designed to combat restenosis, with
limited success, including laser based treatment and directional or
rotational arthrectomy. Intravascular stenting, however, noticeably
reduces the restenosis rate following angioplasty procedures. The
procedure for intravascular stent placement typically involves
pre-dilation of the target vessel using balloon angioplasty,
followed by deployment of the stent, and expansion of the stent
such that the dilated vessel walls are supported from the
inside.
[0007] The intravascular stent functions as scaffolding for the
lumen of a vessel. The scaffolding of the vessel walls by the stent
serve to: (a) prevent elastic recoil of the dilated vessel wall,
(b) eliminate residual stenosis of the vessel; a common occurrence
in balloon angioplasty procedures, (C) maintain the diameter of the
stented vessel segment slightly larger than the native unobstructed
vessel segments proximal and distal the stented segment and (d) as
indicated by the latest clinical data, lower the restenosis rate.
Following an angioplasty procedure, the restenosis rate of stented
vessels has proven significantly lower than for unstented or
otherwise treated vessels; treatments include drug therapy and
other methods mentioned previously.
[0008] Another benefit of vessel stenting is the potential
reduction of emergency bypass surgery arising from angioplasty
procedures. Stenting has proven to be effective in some cases for
treating impending closure of a vessel during angioplasty. Stenting
can also control and stabilize an unstable local intimal tear of a
vessel caused by normal conduct during an angioplasty procedure. In
some cases, an incomplete or less than optimal dilatation of a
vessel lesion with balloon angioplasty can successfully be opened
up with a stent implant.
[0009] Early in its development, the practice of stenting,
especially in coronary arteries, had serious anticoagulation
problems. However, anticoagulation techniques have since been
developed and are becoming simpler and more effective. Better and
easier to use regimens are continuously being introduced, including
simple outpatient anticoagulation treatments, resulting in reduced
hospital stays for stent patients.
[0010] An example of a conventional stent patent is U.S. Pat. No.
5,102,417 (hereafter the Palmaz Patent). The stent described in the
Palmaz Patent consists of a series of elongated tubular members
having a plurality of slots disposed substantially parallel to the
longitudinal axis of the tubular members. The tubular members are
connected by at least one flexible connector member.
[0011] The unexpanded tubular members of the Palmaz Patent are
overly rigid so that practical application is limited to short
lengths. Even with implementation of the multilink design with
flexible connector members connecting a series of tubular members,
longer stents can not navigate tortuous blood vessels. Furthermore,
the rigidity of the unexpanded stent increases the risk of damaging
vessels during insertion. Foreshortening of the stent during
insertion complicates accurate placement of the stent and reduces
the area that can be covered by the expanded stent. There is,
further, no method of programming the stent diameter along its
longitudinal axis to achieve a tapered expanded stent, and no
method of reinforcement of stent ends or other regions is provided
for.
[0012] Another example of a conventional stent patent is WO
96/03092, the Brun patent. The stent described in the Brun patent
is formed of a tube having a patterned shape, which has first and
second meander patterns. The even and odd first meander patterns
are 180 degrees out of phase, with the odd patterns occurring
between every two even patterns. The second meander patterns run
perpendicular to the first meander patterns, along the axis of the
tube.
[0013] Adjacent first meander patterns are connected by second
meander patterns to form a generally uniform distributed pattern.
The symmetrical arrangement with first and second meander patterns
having sharp right angled bends allows for catching and snagging on
the vessel wall during delivery. Furthermore, the large
convolutions in the second meander pattern are not fully
straightened out during expansion reducing rigidity and structural
strength of the expanded stent. There is, further, no method of
programming the stent diameter along its longitudinal axis to
achieve a tapering stent design, and no method of reinforcement of
stent ends or other regions is provided for.
[0014] These and other conventional stent designs suffer in varying
degrees from a variety of drawbacks including: (a) inability to
negotiate bends in vessels due to columnar rigidity of the
unexpanded stent; (b) lack of structural strength, radial and axial
lateral, of the unexpanded stent; (c) significant foreshortening of
the stent during expansion; (d) limited stent length; (e) constant
expanded stent diameter; (f) poor crimping characteristics; and (g)
rough surface modulation of the unexpanded stent.
[0015] There is a need for a stent with sufficient longitudinal
flexibility in the unexpanded state to allow for navigation through
tortuous vessels. There is a further need for a stent that is
structurally strong in the unexpanded state such that risk of
damage or distortion during delivery is minimal. A further need
exists for a stent that maintains substantially the same
longitudinal length during expansion to allow greater coverage at
the target site and simplify proper placement of the stent. Yet a
further need exists for a stent design with sufficient longitudinal
flexibility that long stents of up to 100 mm can be safely
delivered through tortuous vessels. There is a need for a stent
that is configured to expand to variable diameters along its
length, such that a taper can be achieved in the expanded stent to
match the natural taper of the target vessel. A need exists for a
stent which, (i) can be crimped tightly on the expansion balloon
while maintaining a low profile and flexibility, (ii) has a smooth
surface modulation when crimped over a delivery balloon, to prevent
catching and snagging of the stent on the vessel wall during
delivery or (iii) with reinforcement rings on the ends or middle or
both to keep the ends of the stent securely positioned against the
vessel walls of the target blood vessel.
SUMMARY OF THE INVENTION
[0016] Accordingly an object of the present invention is to provide
a scaffold for an interior lumen of a vessel.
[0017] Another object of the invention is to provide a stent which
prevents recoil of the vessel following angioplasty.
[0018] A further object of the invention is to provide a stent that
maintains a larger vessel lumen compared to the results obtained
only with balloon angioplasty.
[0019] Yet another object of the invention is to provide a stent
that reduces foreshortening of a stent length when expanded.
[0020] Another object of the invention is to provide a stent with
increased flexibility when delivered to a selected site in a
vessel.
[0021] A further object of the invention is to provide a stent with
a low profile when crimped over a delivery balloon of a stent
assembly.
[0022] Yet a further object of the invention is to provide a stent
with reduced tupeling of the vessel wall.
[0023] Another object of the invention is to provide a chain mesh
stent that reduces vessel "hang up" in a tortious vessel or a
vessel with curvature.
[0024] These and other objects of the invention are achieved in a
stent in a nonexpanded state with a first column expansion strut
pair. A plurality of the first column expansion strut pair form a
first expansion column. A plurality of second column expansion
strut pair form a second expansion column. A plurality of first
serial connecting struts form a first connecting strut column that
couples the first expansion column to the second expansion column.
The first expansion column, the second expansion column, and the
first connecting strut column form a plurality of geometric cells.
At least a portion of the plurality are asymmetrical geometric
cells.
[0025] In another embodiment, at least a portion of the first
connecting struts include a proximal section, a distal section a
first linear section and a first slant angle.
[0026] It yet another embodiment, a first expansion strut in the
first expansion column is circumferentially offset from a
corresponding second expansion strut of the second expansion
column.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1A is a side elevation view of the pre-expansion mode
of an embodiment of the stent of the present invention;
[0028] FIG. 1B is a cross sectional view of an embodiment of the
stent of the present invention;
[0029] FIG. 1C is a longitudinal cross sectional view of an
embodiment of the stent of the present invention;
[0030] FIG. 2A is a scale drawing of the strut pattern of an
embodiment of the stent of the present invention.
[0031] FIG. 2B is an expanded view of a section of the pattern of
FIG. 2A.
[0032] FIG. 3A is a schematic illustration of a the pre-expansion
mode of an embodiment of the stent of the present invention.
[0033] FIG. 3B is a schematic illustration of the post-expansion
mode of an embodiment of the stent of the present invention.
[0034] FIG. 4A is a scale drawing including dimensions of an
embodiment of the stent of the present invention.
[0035] FIG. 4B is an enlarged section of the scale drawing of FIG.
4A.
[0036] FIG. 5 is a scale drawing of an embodiment of the stent of
the present invention with a tapered diameter in its post-expansion
mode.
[0037] FIG. 6A is a scale drawing of an embodiment of the stent of
the present invention with reinforcement expansion columns.
[0038] FIG. 6B is a perspective view of the embodiment of FIG.
6A.
[0039] FIG. 7A is a scale drawing of an embodiment of the stent of
the present invention including relief notches at strut joints to
increase flexibility of the joints.
[0040] FIG. 7B is an enlarged region of the embodiment of FIG.
7A.
[0041] FIG. 7C is an enlarged view of a single connecting strut
joining two expansion strut pairs in accordance with the embodiment
of FIG. 7A.
[0042] FIG. 8A is a drawing of an alternate geometry of connecting
struts and joining struts in accord with the present invention.
[0043] FIG. 8B is a drawing of an alternate geometry of connecting
struts and joining struts in accord with the present invention.
[0044] FIG. 8C is a drawing of an alternate geometry of connecting
struts and joining struts in accord with the present invention.
[0045] FIG. 8D is a drawing of an alternate geometry of connecting
struts and joining struts in accord with the present invention.
[0046] FIG. 8E is a drawing of an alternate geometry of connecting
struts and joining struts in accord with the present invention.
[0047] FIG. 9 is a delivery balloon catheter, illustrating a method
of deliver of a stent in accord with the present invention.
DETAILED DESCRIPTION
[0048] A first embodiment of the present invention is shown in
FIGS. 1A, 1B, 1C, 2A and 2B. Referring to FIG. 1A, an elongate
hollow tubular stent 10 in an unexpanded state is shown. A proximal
end 12 and a distal end 14 define a longitudinal length 16 of stent
10. The longitudinal length 16 of the stent 10 can be as long as
100 mm. or longer. A proximal opening 18 and a distal opening 20
connect to an inner lumen 22 of stent 10. Stent 10 can be a single
piece, without any seams or welding joints or may include multiple
pieces.
[0049] Stent 10 is constructed of two to fifty or more expansion
columns or rings 24 connected together by interspersed connecting
strut columns 26. The first column on the proximal end 12 and the
last column on the distal. end 14 of stent 10 are expansion columns
24.
[0050] Expansion columns 24 are formed from a series of expansion
struts 28, and joining struts 30. Expansion struts 28 are thin
elongate members arranged so that they extend at least in part in
the direction of the longitudinal axis of stent 10. When an outward
external force is applied to stent 10 from the inside by an
expansion balloon or other means, expansion struts 28 are
reoriented such that they extend in a more circumferential
direction, Le along the surface of cylindrical stent 10 and
perpendicular to its longitudinal axis. Reorientation of expansion
struts 28 causes stent 10 to have an expanded circumference and
diameter. In FIG. 1A, expansion struts 28 of unexpanded stent 10
are seen to extend substantially parallel to the longitudinal axis
of stent 10.
[0051] Expansion struts 28 are joined together by joining struts 30
to form a plurality of expansion strut pairs 32. Expansion strut
pairs have a closed end 34 and an open end 36. Additional joining
struts 30 join together expansion struts 28 of adjacent expansion
strut pairs 32, such that expansion struts 28 are joined
alternately at their proximal and distal ends to adjacent expansion
struts 28 to form expansion columns 24. Each expansion column 24
contains a plurality, typically eight to twenty, twenty to sixty,
or larger of expansion struts 28.
[0052] Connecting struts 38 connect adjacent expansion columns 24
forming a series of interspersed connecting strut columns 26 each
extending around the circumference of stent 10. Each connecting
strut 38 joins a pair of expansion struts 28 in an expansion column
24 to an adjacent pair of expansion struts 28 in an adjacent
expansion column 24. For stent 10 of FIG. 1A, the ratio of
expansion struts 28 in an expansion column 24 to connecting struts
38 in a connecting strut column 26 is two to one; however, this
ratio in general can be x to 1 where x is greater or less than two.
Furthermore, since the stent 10 of FIG. 1A begins with an expansion
column 24 on the proximal end 12 and ends with an expansion column
24 on the distal end 14, if there are n expansion columns 24 with m
expansion struts 28 per column, there will be m-1 connecting strut
columns 26, and n(m1)/2 connecting struts 38.
[0053] The reduced number of connecting struts 38 in each
connecting strut column 26, as compared to expansion struts 28 in
each expansion column 24, allows stent 10 to be longitudinally
flexibility. Longitudinal flexibility can be further increased by
using a narrow width connecting strut, providing additional
flexibility and suppleness to the stent as it is navigated around
turns in a natural blood vessel.
[0054] At least a portion of the open spaces between struts in
stent 10 form asymmetrical cell spaces 40. A cell space is an empty
region on the surface of stent 10, completed surrounded by one or a
combination of stent struts, including expansion struts 28,
connecting struts 38, or joining struts 30. Asymmetrical cell
spaces 40 are cell spaces which have no geometrical symmetry i.e.
no rotation, reflection, combination rotation and reflection or
other symmetry.
[0055] Asymmetrical cell spaces 40 in FIG. 1A are surrounded by a
first expansion strut pair 32 in a first expansion column 24, a
first connecting strut 38, a second expansion strut pair 32 in an
adjacent expansion column 24, a first joining strut 30, a second
connecting strut 38, and a second joining strut 30. Furthermore,
expansion strut pairs 32 of asymmetrical cell space 40 may be
circumferentially offset i.e. have longitudinal axes that are not
collinear and have their open ends 36 facing each other. The space
between two expansion struts of an expansion strut pair 32 is known
as a loop slot 42.
[0056] FIG. 1B shows inner lumen 22, radius 44 and stent wall 46 of
stent 10. Stent wall 46 consists of stent struts including
expansion struts 28, connecting struts 38 and joining struts
30.
[0057] FIG. 1C shows, proximal end 12, distal end 14, longitudinal
length 16, inner lumen 22, and stent wall 46 of stent 10. Inner
lumen 22 is surrounded by stent wall 46 which forms the cylindrical
surface of stent 10.
[0058] Referring now to FIGS. 2A and 2B, joining struts 30 of stent
10 are seen to extend at an angle to the expansion struts 28,
forming a narrow angle 48 with one expansion strut 28 in an
expansion strut pair 32 and a wide angle 50 with the other
expansion strut 28 of an expansion strut pair 32. Narrow angle 48
is less than ninety degrees, while wide angle 50 is greater than
ninety degrees. Joining struts 30 extend both longitudinally along
the longitudinal axis of stent 10 and circumferentially, along the
surface of the stent 10 perpendicular its longitudinal axis.
[0059] Expansion strut spacing 52 between adjacent expansion struts
28 in a given expansion column 24 are uniform in stent 10 of FIGS.
2A and 2B; however, non-uniform spacings can also be used.
Expansion strut spacings 52 can be varied, for example, spacings 52
between adjacent expansion struts 28 in an expansion column 24 can
alternate between a narrow and a wide spacing. Additionally,
spacings 52 in a single expansion column 24 can differ from other
spacings 52 in other columns 24.
[0060] It is noted that varying expansion strut spacings 52 which
form the loop slots 42 results in variable loop slot widths.
Furthermore, the longitudinal axis of the loop slots 42 need not be
collinear or even parallel with the longitudinal axis of loop slots
42 of an adjacent expansion column 24. FIGS. 2A and 2B show an
arrangement of expansion struts 28 such that collinear, parallel
adjacent loop slots 42 are formed, but non-collinear and
non-parallel loop slots 42 can also be used.
[0061] Additionally the shape of loop slots 42 need not be the same
among loop slots of a single or multiple expansion columns 24. The
shape a loop slots 42 can be altered by changing the orientation or
physical dimensions of the expansion struts 28 and/or joining
struts 30 which connect expansion struts 28 of expansion strut
pairs 32 defining the boundaries of loop slots 42.
[0062] Connecting struts 38 couple adjacent expansion columns 24,
by connecting the distal. end of an expansion strut pair in one
expansion column 24 to the proximal end of an adjacent expansion
strut pair 32 in a second expansion column 24. Connecting struts 38
of FIGS. 2A and 2B are formed from two linear sections, a first
linear section 54 being joined at its distal end to a second linear
section 56 at its proximal end to form a first slant angle 58.
[0063] The first linear section 54 of a connecting strut 38 is
joined to expansion strut 28 at the point where joining strut 30
makes narrow angle 48 with expansion strut 28. First linear section
54 extends substantially collinear to joining strut 30 continuing
the line of joining strut 30 into the space between expansion
columns 24. The distal end of the first linear section 54 is joined
to the proximal end of the second linear section 56 forming slant
angle 58. Second linear section 56 extends substantially parallel
to expansion struts 28 connecting at its distal. end to joining
strut 30 in an adjacent expansion column 24. The distal end of
second linear section 56 attaches to expansion strut 28 at the
point where joining strut 30 makes narrow angle 48 with expansion
strut 28. Further, joining strut 30 can have a second slant angle
with a width that can be the same or different from the width of
the first slant angle.
[0064] FIGS. 2A and 2B show connecting struts 38 and joining struts
30 slanted relative to the longitudinal axis of stent 10, with the
circumferential direction of the slanted struts alternating from
column to adjacent column. Circumferential direction refers to the
handedness with which the slanted struts wind about the surface of
the stent 10. The circumferential direction of the slant of
connecting strut first linear sections 54 in a connecting strut
column 26 is opposite the circumferential direction of the slant of
connecting strut first linear sections 54 in an adjacent connecting
strut column 26. Similarly, the circumferential direction of the
slant of joining struts 30 in an expansion column 24 is opposite
the circumferential direction of the slant of joining struts 30 in
an adjacent expansion column 24. Alternating circumferential slant
directions of connecting struts 38 and joining struts 30 prevents
axial warping of stent 10 during deliver and expansion. Other
non-alternating slant direction patterns can also be used for
connecting struts 38 or joining struts 30 or both.
[0065] FIG. 3A and 3B show a schematic illustration of a stent
design according to the present invention in an unexpanded and
expanded state respectively. The design is depicted as a flat
projection, as if stent 10 were cut lengthwise parallel to its
longitudinal axis and flattened out. The connecting struts 38
consist of first and second linear sections 54 and 56 forming slant
angle 58 at pivot point 60. An asymmetrical cell space 40 is formed
by expansion strut pairs 32, connecting struts 38 and joining;
struts 30. Multiple interlocking asymmetrical cell spaces 40 make
up the design pattern.
[0066] As the stent is expanded, see FIG. 3B, the expansion strut
pairs 32 spread apart at their open ends 36, shortening the length
of expansion struts 28 along the longitudinal axis of the
cylindrical stent. The longitudinal shortening of expansion struts
28 during expansion is countered by the longitudinal lengthening of
connecting struts 38. The widening of slant angle 58 during
expansion straightens connecting struts 38 and lengthens the
distance between the coupled expansion strut pairs 32. The
lengthening of the distance between coupled expansion strut pairs
32 substantially compensates for the longitudinal shortening of
expansion struts 28. Thus, the stent has substantially constant
unexpanded and expanded longitudinal lengths.
[0067] When the stent is expanded, each expansion column 24 becomes
circumferentially stretched, enlarging the space between struts.
The interlinking of expansion columns 24 by connecting struts 38
that have been straightened through the expansion process gives the
stent 10 a high radial support strength. The entire stent 10 when
expanded is unitized into a continuous chain mesh of stretched
expansion columns 24 and connecting strut columns 26 forming an
asymmetrical interlocking cell geometry which resists collapse both
axially and radially. When the stent is expanded it has increased
rigidity and fatigue tolerance.
[0068] In addition, efficient bending and straightening of
connecting struts 38 at pivot points 60 allows increased
longitudinal flexibility of the stent. For the stent to bend
longitudinally, at least some of connecting struts 38 are forced to
bend in their tangent plane. The tangent plane of a specific
connecting strut 38 refers to the plane substantially tangent to
the cylindrical surface of the stent at that connecting strut 38.
The width of connecting struts 38 is typically two to four, or more
times the thickness, which makes connecting struts 38 relatively
inflexible when bending in their tangent plane. However, pivot
points 60 in connecting struts 38 provide connecting struts 38 a
flexible joint about which to more easily bend increasing
longitudinal flexibility of the stent.
[0069] Referring to FIGS. 4A and 4B, a variation of the first
embodiment of stent 10 of the present invention is shown. In this
variation, stent 10 has a length 16 of 33.25 mm and an uncrimped
and unexpanded circumference 88 of 5.26 mm. Fifteen expansion
columns 24 are interspersed with connecting strut columns 26. Each
expansion column 24 consists of twelve expansion struts 28 joined
alternately at their proximal and distal ends by joining struts 30
forming six expansion strut pairs 32. Expansion struts 28 are
aligned parallel to the longitudinal axis of cylindrical stent 10.
Joining struts 30 form a narrow angle 48 and a wide angle 50 with
the respective expansion struts 28 of expansion strut pairs 32.
Adjacent expansion columns 24 employ alternating circumferential
slant directions of joining struts 30.
[0070] In this variation of the first embodiment, expansion strut
width 62 is 0.20 mm, expansion strut length 64 is 1.51 mm, and
connecting strut width 66 is 0.13 mm. Distance 68 from the outer
edge of a first expansion strut 28 to the outer edge of a second
adjacent expansion strut 28 in the same expansion column 24 is 0.64
mm, leaving a loop slot width 70 of 0.24 mm.
[0071] In this variation of the first embodiment, connecting struts
38 consist of a slanted first linear section 54 joined to a second
linear section 56 at a slant angle 58. First linear section 54 is
slightly longer than second linear section 56 and is attached at
its proximal end to an expansion strut 28 in an expansion column
24. The attachment of the proximal end of first linear section 54
to expansion strut 28 is at the point where joining strut 30 makes
narrow angle 48 with expansion strut 28. First linear section 54
extends substantially collinear to joining strut 30 attaching at
its distal end to the proximal end of second linear section 56 to
form slant angle 58. Second linear section 56 extends substantially
collinear to expansion struts 28, attaching at its distal end to an
expansion strut 28 in an adjacent expansion column 24. The
attachment occurs at the point where expansion strut 28 forms
narrow angle 48 with joining strut 30. Joining struts 30 and
connecting strut first linear sections 54 slant in alternating
circumferential directions from column to adjacent column.
[0072] The joining of connecting struts 38 and expansion struts 28
at the point where narrow angle 48 is formed aids smooth delivery
of stent 10 by streamlining the surface of the unexpanded stent and
minimizing possible catching points. Bare delivery of stent 10 to
the target lesion in a vessel will thus result in minimal snagging
or catching as it is navigated through turns and curvatures in the
vessel. Stent 10 behaves like a flexible, tubular sled as it is
moved forward or backward in the vessel on the delivery catheter,
sliding through tortuous vessels and over irregular bumps caused by
atherosclerotic plaques inside the vessel lumen.
[0073] When fully expanded Stent 10 of FIGS. 4A and 4B has an
internal diameter of up to 5.0 mm, while maintaining an acceptable
radial strength and fatigue tolerance. The crimped stent outer
diameter can be as small as 1.0 mm or less depending on the
condition of the underlying delivery balloon profile; A small
crimped outer diameter is especially important if stent delivery is
to be attempted without predilation of the target site. When the
stent is optimally crimped over the delivery balloon, the surface
of the crimped stent is smooth allowing for no snagging of the
stent struts during either forward or backward movement through a
vessel.
[0074] FIG. 5 shows a second embodiment of the present invention in
which the stent 10 in its expanded form has a gradual taper from
proximal end 12 to distal end 14. The shaded segments 72, 74, 76,
78, 80, 82 and 84 of expansion struts 28 represent regions of
expansion struts 28 to be removed. Removal of the shaded segments
72, 74, 76, 78, 80, 82 and 84 provides stent 10 with a gradual
taper when expanded with distal end 14 having a smaller expanded
diameter than proximal end 12. The degree of shortening of the
expanded diameter of the stent 10 at a given expansion column 24
will be proportional to the length of the removed segment 72, 74,
76, 78, 80, 82, or 84 at that expansion column 24. In the expanded
stent 10 the shortened expansion struts 28 will have a shortened
component along the circumference of the stent resulting in a
shortened circumference and diameter. The tapered diameter portion
can be positioned anywhere along the length of stent 10, and the
tapering can be made more or less gradual by removing appropriately
larger or smaller portions of the expansion struts 28 in a given
expansion column 24. Tapering is especially important in long
stents, longer than 12 mm, since tapering of blood vessels is more
pronounced over longer lengths. A long stent with a uniform stent
diameter can only be matched to the target vessel diameter over a
short region. If the proximal vessel size is matched with the stent
diameter, the expanded distal end of the stent will be too large
for the natural vessel and may cause an intimal dissection of the
distal. vessel by stent expansion. On the other hand, if the distal
vessel size is matched with the stent diameter, the proximal end of
the expanded stent will be too small to set inside the vessel
lumen. It is therefore desirable to have a stent with a tapered
expanded diameter.
[0075] Another way achieve a tapered expanded stent is to change
the stiffness of the stent struts, expansion struts, connecting
struts or joining struts such that the stiffness of the struts
varies along the length of the stent. The stiffness of the struts
can be changed by altering length, width or thickness, adding
additional stiffening material, using a chemical or mechanical
means to alter the physical properties of the stent material, or
applying one or a series of elastic elements about the stent.
[0076] Along with the use of a tapered diameter stent, a matching
tapered balloon catheter would ideally be made for delivery and
deployment of the tapered diameter stent. The method of using a
tapered matching balloon catheter with a tapered diameter stent is
within the scope of the present invention.
[0077] Using a tapered balloon to expand a non-tapered stent will
also achieve a tapered expanded stent; however, since no metal is
removed from the stent, the stent is tapered as a result of
incomplete expansion. The stent will therefore have increased metal
fraction at the tapered end resulting in increased risk of acute
thrombosis. Metal fraction is the proportion of the surface of the
expanded stent covered by the stent strut material. Shortening the
expansion struts as shown in FIG. 5 allows for a tapered expanded
stent with substantially constant metal fraction along its
length.
[0078] A third embodiment of the present invention shown in FIGS.
6A and 6B has multiple reinforcement expansion columns 86 placed
along the length of the stent 10. The reinforcement columns 86 are
placed along the stent length to provide additional localized
radial strength and rigidity to stent 10. Additional strength and
rigidity are especially important at the ends of the stent to
prevent deformation of the stent both during delivery and after
placement. During delivery the stent ends can catch on the vessel
wall possibly deforming the unexpanded stent and altering its
expansion characteristics. After the stent has been placed it is
important that the stent ends are rigid so that they set firmly
against the vessel wall, otherwise, during a subsequent catheter
procedure, the catheter or guidewire can catch on the stent ends
pulling the stent away from the vessel wall and possibly damaging
and/or blocking the vessel.
[0079] The specific variation of the third embodiment of stent 10
depicted in FIGS. 6A and 6B has a length 16 of 20.70 mm and an
uncrimped and unexpanded circumference 88 of 5.26 mm. The stent 10
consists of six expansion columns 24 and three reinforcement
expansion columns 86, each consisting respectively of twelve
expansion struts 28 or reenforcement expansion struts 90. The
reenforcement expansion columns 86 are positioned one at either
end, and one along the length of the stent 10.
[0080] The expansion strut width 62 is 0.15 mm, reenforcement
expansion strut width 92 is 0.20 mm, and the connecting strut width
66 is 0.10 mm. The narrow angle 48 formed by joining strut 30 and
expansion strut 28 is 75 degrees, and the narrow angle 94 formed by
reenforcement joining strut 96 and reenforcement expansion strut 90
is 60 degrees.
[0081] Other arrangements of reenforcement expansion columns 86,
such as providing reenforcement expansion columns 86 only on the
ends of the stent, only on one end, or at multiple locations
throughout the length of the stent can also be used and fall within
the scope of the present invention. A taper can also be programmed
into the reenforced stent 10 by shortening expansion struts 28 and
reenforcement expansion struts 90 in appropriate expansion columns
24 and 86.
[0082] A fourth embodiment of the present invention, shown in the
FIGS. 7A, 7B and 7C, is similar to the third embodiment but has the
added feature of relief notches 98 and 100. A relief notch is a
notch where metal has been removed from a strut, usually at a joint
where multiple struts are connected. Relief notches increase
flexibility of a strut or joint by creating a thinned, narrow
region along the strut or joint. Relief notch 98 is formed at the
joint formed between first linear section 54 of connecting strut 38
and expansion strut 28. Relief notch 100 is formed at the joint
between second linear section 56 of connecting strut 38 and
expansion strut 28. The positioning of the relief notches gives
added flexibility to the unexpanded stent. Relief notches can be
placed at other joints and can be included in any of the previously
mentioned embodiments.
[0083] FIGS. 8A, 8B, 8C, 8D and 8E illustrates some examples of
alternate connecting strut designs which can be used in any of the
previously discussed embodiments. FIG. 8A shows a rounded loop
connecting strut 38 which joins two circumferentially offset
expansion strut pairs 32 in adjacent expansion columns. Expansion
struts 28 in each expansion strut pair 32 are joined by a joining
strut 30. Joining struts 30 are slanted such as to form a narrow
angle 48 and a wide angle 50 with the expansion struts 28 they
connect. The rounded loop connecting strut 38 connects expansion
struts 28 at the point where narrow angle is formed between
expansion strut 28 and joining strut 30. The slopes of the rounded
connecting strut 38 at its proximal end 102 and distal end 104
substantially match the slopes of the joining struts 30 connecting
the pairs of expansion struts 28. The rounded loop connecting strut
38 thus blends smoothly into the joining struts 30. Additionally
the rounded loop connecting strut 38 has a first radius of
curvature 106 and a second radius of curvature 108.
[0084] In the design of FIG. 8B a rounded loop connecting strut 38
joins two circumferentially offset expansion strut pairs 32 in
adjacent expansion columns. Expansion struts 28 in each expansion
strut pair 32 are joined by a joining strut 30. Joining struts 30
are at right angles to the expansion struts 28 they connect. The
rounded loop connecting strut 38 connects to expansion struts 28 at
the same point as joining struts 30. The rounded connecting strut
38 has a first radius of curvature 106 and a second radius of
curvature 108 such that it connects circumferentially offset
expansion strut pairs 32.
[0085] In the design of FIG. 8C connecting strut 38 joins two
circumferentially offset expansion strut pairs 32 in adjacent
expansion columns. Expansion struts 28 in each expansion strut pair
32 are joined by a joining strut 30. Joining struts 30 are slanted
such as to form a narrow angle 48 and a wide angle 50 with the
expansion struts 28 they connect. The connecting strut 38 connects
expansion struts 28 at the point where narrow angle 48 is formed
between expansion strut 28 and joining strut 30.
[0086] The connecting strut 38 is made up of three linear sections
110, 112, and 114 forming two slant angles 116 and 118. The
proximal end of section 110 is attached to expansion strut 28 at
the point where joining strut 30 forms narrow angle 48 with
expansion strut 28. Section 110 extends substantially collinear to
joining strut 30 and is attached at its distal end to section 112
forming slant angle 116. Section 112 extends at an angle to section
110 such that section 112 is substantially parallel to expansion
struts 28 and is connected at its distal end to the proximal end of
section 114 forming slant angle 118. Section 114 extends at an
angle such that it is substantially collinear to joining strut 30
of the adjacent expansion strut pair 32. Section 114 attaches at
its distal end to expansion strut 28 of the adjacent expansion
strut pair 32, at the point where joining strut 30 forms narrow
angle 48 with expansion strut 28.
[0087] In the design of FIGS. 8D and 8E a connecting strut 38 joins
two circumferentially offset expansion strut pairs 32 in adjacent
expansion columns. Expansion struts 28 in each expansion strut pair
32 are joined by a joining strut 30. Joining struts 30 are at right
angles to the expansion struts 28 they connect. The connecting
strut 38 connects to expansion struts 28 at the same point as
joining struts 30.
[0088] The connecting struts 38 of FIGS. 8D and 8E are made up of
multiple connecting strut sections connected end to end to form a
jagged connecting strut 38 with multiple slant angles, coupling
expansion strut pair 32 to adjacent expansion strut pair 32. The
connecting strut of FIG. 8D is made up of three connecting strut
sections 120, 122, and 124 with two slant angles 126 and 128, while
the connecting strut of FIG. 8E consists of four connecting strut
sections 130, 132, 134, and 136 with three slant angles 138, 140
and 142. In addition, the connecting strut section 134 can be
modified by replacing connecting strut section 136 by the dotted
connecting strut section 144 to give another possible geometry of
connecting struts 38.
[0089] One skilled in the art will recognize that there are many
possible arrangements of connecting struts and joining struts
consistent with the present invention; the above examples are not
intended to be an exhaustive list.
[0090] The stent of the present invention is ideally suited for
application in coronary vessels although versatility in the stent
design allows for applications in non-coronary vessels, the aorta,
and nonvascular tubular body organs.
[0091] Typical coronary vascular stents have expanded diameters
that range from 2.5 to 5.0 mm. However, a stent with high radial
strength and fatigue tolerance that expands to a 5.0 mm diameter
may have unacceptably high stent metal fraction when used in
smaller diameter vessels. If the stent metal fraction is high, the
chances of acute thrombosis and restenosis potential will increase.
Even with the same metal fraction a smaller caliber vessel is more
likely than a larger one to have a high rate of thrombosis. It is,
therefore, preferred to have at least two different categories of
stents for coronary application, for example, small vessels stents
for use in vessels with diameters from 2.5 mm, to 3.0 mm, and large
vessel stents for use in vessels with diameters from 3.0 mm. to 5.0
mm. Thus, both small vessels and large vessels when treated with
the appropriate sized stent will contain stents of similar
idealized metal fraction.
[0092] The stent of the present invention can be made using a
CAM-driven laser cutting system to cut the stent pattern from a
stainless steel tube. The rough-cut stent is preferably
electro-polished to remove surface imperfections and sharp edges.
Other methods of fabricating the stent can also be used such as
EDM, photo-electric etching technology, or other methods. Any
suitable material can be used for the stent including other metals
and polymers so long as they provide the essential structural
strength, flexibility, biocompatibility and expandability.
[0093] The stent is typically at least partially plated with a
radiopaque metal, such as gold, platinum, tantalum or other
suitable metal. It is preferred to plate only both ends of the
stent by localized plating; however, the entire stent or other
regions can also be plated. When plating both ends, one to three or
more expansion columns on each end of the stent are plated to mark
the ends of the stent so they can be identified under fluoroscopy
during the stenting procedure. By plating the stent only at the
ends, interference of the radiopaque plating material with
performance characteristics or surface modulation of the stent
frame is minimized. Additionally the amount of plating material
required is reduced, lowering the material cost of the stent.
[0094] After plating, the stent is cleaned, typically with
detergent, saline and ultrasonic means that are well-known in the
art. The stents are then inspected for quality control, assembled
with the delivery balloon catheter, and properly packaged, labeled,
and sterilized.
[0095] The stent can be marketed as stand alone or as a pre-mounted
delivery balloon catheter assembly as shown in FIG. 9. Referring to
FIG. 9, the stent 10 is crimped over a folded balloon 146 at the
distal end 148 of a delivery balloon catheter assembly 150. The
assembly 150 includes a proximal end adapter 152, a catheter shaft
154, a balloon channel 156, a guidewire channel 158, a balloon 146,
and a guidewire 160. Balloon 146 can be tapered in an expanded
state, be curved from a proximal end to a distal end in the
expanded state. Additionally stent 10 can be non-tapered or tapered
in the expanded state.
[0096] Typically the guidewire 160 is inserted into the vein or
artery and advanced to the target site. The catheter shaft 154 is
then forwarded over the guidewire 160 to position the stent 10 and
balloon 146 into position at the target site. Once in position the
balloon 146 is inflated through the balloon channel 156 to expand
the stent 10 from a crimped to an expanded state. In the expanded
state, the stent 10 provides the desired scaffolding support to the
vessel. Once the stent 10 has been expanded, the balloon 146 is
deflated and the catheter shaft 154, balloon 146, and guidewire 160
are withdrawn from the patient.
[0097] The stent of the present invention can be made as short as
less than 10 mm in length or as long as 100 mm or more. If long
stents are to be used, however, matching length delivery catheter
balloons will typically be needed to expand the stents into their
deployed positions. Long stents, depending on the target vessel,
may require curved long balloons for deployment. Curved balloons
which match the natural curve of a blood vessel reduce stress on
the blood vessel during stent deployment. This is especially
important in many coronary applications which involve stenting in
curved coronary vessels. The use of such curved balloons is within
the scope of the present invention.
[0098] The foregoing description of a preferred embodiment of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obviously, many
modifications and variations will be apparent to practitioners
skilled in this art. It is intended that the scope of the invention
be defined by the following claims and their equivalents.
* * * * *