U.S. patent application number 10/759527 was filed with the patent office on 2005-03-17 for expandible stent.
Invention is credited to Crewe, Katherine H., Lee, J. Michael, Mastrangelo, Christine.
Application Number | 20050060024 10/759527 |
Document ID | / |
Family ID | 27267828 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050060024 |
Kind Code |
A1 |
Lee, J. Michael ; et
al. |
March 17, 2005 |
Expandible stent
Abstract
A stent has a tubular body with longitudinal struts
interconnected by multi-bar linkages. The struts inhibit
foreshortening of the body and relative rotation between the links
in the linkages permits radial expansion. The links are plastically
deformed as they are expanded to maintain the expanded
diameter.
Inventors: |
Lee, J. Michael; (Nova
Scotia, CA) ; Crewe, Katherine H.; (Etobicoke,
CA) ; Mastrangelo, Christine; (Etobicoke,
CA) |
Correspondence
Address: |
BLAKE, CASSELS & GRAYDON LLP
BOX 25, COMMERCE COURT WEST
199 BAY STREET, SUITE 2800
TORONTO
ON
M5L 1A9
CA
|
Family ID: |
27267828 |
Appl. No.: |
10/759527 |
Filed: |
January 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10759527 |
Jan 20, 2004 |
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09893253 |
Jun 27, 2001 |
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09893253 |
Jun 27, 2001 |
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09063496 |
Apr 20, 1998 |
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6261318 |
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09063496 |
Apr 20, 1998 |
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08687223 |
Jul 25, 1996 |
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5776181 |
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Current U.S.
Class: |
623/1.16 ;
623/1.17 |
Current CPC
Class: |
A61F 2230/0013 20130101;
A61F 2/915 20130101; A61F 2/91 20130101; A61F 2002/91575 20130101;
A61F 2002/91533 20130101; A61F 2002/9155 20130101 |
Class at
Publication: |
623/001.16 ;
623/001.17 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 1995 |
GB |
9515282.3 |
Mar 15, 1996 |
GB |
9605486.1 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A stent having a generally tubular body with a plurality of
circumferentially spaced longitudinal struts extending parallel to
a longitudinal axis of said body, circumferentially adjacent pairs
of said struts being interconnected solely b)(a set) of linkages
axially spaced from one another and defining a predetermined space
between adjacent pairs of said struts, each of said linkages having
a plurality of links angularly disposed relative to one another in
an unexpanded condition such that when a radial force is
exerted-on-said tubular body, relative rotation between adjacent
links and plastic deformation occurs, thereby increasing said space
between said adjacent pairs of said struts and permitting radial
expansion of said stent, said struts inhibiting relative axial
movement between said linkages and foreshortening of said body,
each of said linkages having hinge points spaced apart along said
linkage, said hinge points deforming upon radial expansion of said
stent to facilitate relative rotation of said links, wherein said
hinge points are provided by zones of relative weakness along said
links.
2. A stent according to claim 1 wherein said zones of relative
weakness are provided by a reduced cross-sectional area.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 09/893,253 filed on Jun. 27, 2001 which is a continuation of
U.S. application Ser. No. 09/063,496 filed on Apr. 20, 1998 which
is a continuation-in-part of U.S. Ser. No. 08/687,223 filed on Jul.
25, 1996, which claims priority from U.K. application no. 9605486.1
filed on Mar. 15, 1996 and U.K. application no. 9515282.3 filed on
Jul. 25, 1995 the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] Expandable stents are widely used to provide local
reinforcement in fluid-carrying vessels within the human body. The
stent is essentially a cylindrical member which may be expanded
radially to dilate the vessel and to provide support for the wall
of the vessel to maintain it in the dilated condition.
SUMMARY OF THE INVENTION
[0003] In order to insert the stent, it has previously been
proposed to place the stent into the vessel on an expandable or
balloon catheter. With the stent positioned at the appropriate
location, the catheter is inflated and the stent is caused to
expand radially against the wall of the vessel. Once the stent is
expanded to the required diameter, the catheter is deflated and may
be removed, leaving the stent in position.
[0004] The stent must of course remain expanded against the wall or
the vessel and should be capable of withstanding the forces imposed
by the wall of the vessel. Moreover, the stent should be able to
negotiate tight turns in the arterial system during placement while
minimizing damnage to the arterial wall.
[0005] A number of different mechanisms have been proposed to
permit the expansion of the stent, including devices which reorient
the components forming the stent so that they may adopt a greater
overall diameter.
[0006] In another class of stents, as typified by the stent shown
in U.S. Pat. No. 4,733,665 to Palmaz, the stent is configured to be
plastically deformable so that after expansion it retains the
increased diameter. In the Palmaz stent, the plastic deformation is
provided by means of an open-mesh diamond structure. As the
catheter is expanded, the intersecting members of the mesh deform
so that the stent adopts an increased diameter.
[0007] With the arrangements shown in the Palmaz stent and similar
configurations, a radial expansion of the stent is accompanied by
an axial foreshortening of the stent. The degree of foreshortening
is predictable but the ultimate location of the stent along the
vessel is not predictable. Thus, one end of the stent may remain
stationary relative to the blood vessel so that the opposite end is
subjected to the maximum axial displacement or there may be
progressive foreshortening from both ends with an intermediate
location remaining stationary. The foreshortening of the stent
leads to an unpredictable location for the stent in its expanded
condition and induces relative movement in an axial direction
between the vessel wall and the stent which is generally
undesirable.
[0008] It is therefore an object of the present invention to
provide a stent in which the above disadvantages are obviated or
mitigated.
[0009] In general terms, the present invention provides a stent in
which a plurality of circumferentially-spaced longitudinal struts
are interconnected by multibar linkages. Adjacent links of the
linkages are angularly disposed to one another such that a radial
force causes relative rotation between adjacent links to permit
radial enlargement of the stent. The longitudinal struts inhibit
foreshortening of the stent so that the final location of the stent
can be predicted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Embodiments of the invention will now be described by way of
example only with reference to the accompanying drawings, in
which
[0011] FIG. 1 is a side elevation of an assembled stent;
[0012] FIG. 2 is a view on the line 2-2 of FIG. 1;
[0013] FIG. 3 is a developed view of the stunt shown in FIG. 1;
[0014] FIG. 4 is a view on an enlarged scale of a portion of the
stent shown in FIGS. 1-3;
[0015] FIG. 5 is a view of the portion of the stent shown in FIG. 4
after radial expansion;
[0016] FIG. 6 is a view similar to FIG. 4 of an alternative
embodiment of stent;
[0017] FIG. 7 is a view of the embodiment of FIG. 6 after radial
expansion;
[0018] FIG. 8 is a further alternative of stent shown in FIG.
4;
[0019] FIG. 9 is a view of the embodiment of FIG. 8 after radial
expansion;
[0020] FIG. 10 is a comparative curve between the embodiments of
stent shown in FIGS. 4, 6 and 8;
[0021] FIG. 11 is a perspective view of a further embodiment of
stent;
[0022] FIG. 12 is a developed view of the embodiment of stent shown
in FIG. 11;
[0023] FIG. 13 is an enlarged view of a portion of the stent shown
in Figure .cndot.;
[0024] FIG. 14 is a view similar to FIG. 9 showing the stent after
radial expansion;
[0025] FIG. 15 is a sectional view of a stent support and
catheter;
[0026] FIG. 16 is a developed view, similar to FIG. 12, of a
further embodiment;
[0027] FIG. 17 is a developed view similar to FIG. 16 of a still
further embodiment;
[0028] FIG. 18 is an enlarged view of a portion of the embodiment
of FIG. 17; and
[0029] FIG. 19 is a developed view similar to FIG. 17 of a yet
further embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Referring therefore to FIG. 1, a stent 10 has a generally
tubular body 12 which is initially dimensioned to permit insertion
into a vessel such as an artery. The body 12 includes a plurality
of longitudinal struts 14 which are interconnected by multi-bar
linkages 16. The linkages 16 are regularly spaced along the axial
extent of the struts 14 and maintain struts 14 in circumferentially
spaced relationship.
[0031] As can best be seen in FIG. 4, each of the linkages 16
includes a pair of oppositely directed circumferential links 18
with axial links 20 connected to the circumferential links 18 and
extending parallel to the struts 14 but spaced therefrom. The axial
links 20 are connected to an L-shaped corner link 22 which has an
axial leg 24 and circumferential leg 26. The legs 26 of opposed
corner links 22 are interconnected by a circumferential connecting
link 28 to interconnect the adjacent struts 14. The links 18,20,22
and 28 of the linkage 16 are formed by removal of material from a
seamless tube of bio-compatible material so that the links are
integrally connected to one another. Typically such material would
be a metal such as both pure and alloyed titanium, platinum,
nitinol memory metals, gold or stainless steel, and the linkage may
suitably be machined through micro machining techniques. Other
materials could be used that are considered suitable for
implantation including plastics materials having the requisite
properties.
[0032] Each of the linkages 16 is similar and the relative
dimensions between the links in each linkage determine the change
in diameter for a given load. In a typical example, as shown in
FIG. 4, taking the length of the connecting link 28 to be of unit
length, then the relative dimensions of the other links as
indicated by the letters on FIG. 4 are as follows:
1 a b c d e f g h i J k 1 2 I 0.625 1.125 0.125 2.125 2.0 1.375
1.125 0.125
[0033] The stent 10 is typically inserted into the vessel by using
a balloon catheter 60. The stent 10 is mounted on the catheter 60
shown in FIG. 15. To assist in placement of the stent 10 on the
catheter 60, the stent is initially located on a support 62 that
has a bar-like head 64 and a tapered body 66. The stent 10 is
snugly received on the body 66 which has a concave recess 68 at one
end to locate the tip of catheter 60. A bore 70 extends through the
body 66 to accommodate a wire if the catheter is of the type that
employs such.
[0034] A protective sleeve 72 is located over the body 66 and is
retained on a boss 74 on the head 64. The sleeve 72 thus protects
the stent 10 from extraneous external forces with the body 66
providing support for the stent 10 in transit.
[0035] To transfer the stent to the catheter 60, the sleeve 72 is
removed and the body 66 is aligned with the catheter 60. The stent
may then be slid axially from the body 66 over the catheter 60 and
the support and sleeve discarded. In this way, the stent is guided
during transfer and the placement of the stent on the catheter
facilitated.
[0036] The recess 68 assists in locating and aligning the catheter
60 during transfer and of course the wire, if present, may be fed
through the bore 70.
[0037] The stent 10 is located on the body 66 such that the links
28 are closer to the boss 74 than the associated links 18. Transfer
of the stent 10 to the catheter thus ensures that the stent 10 is
oriented on the catheter 60 such that the connecting link 28 of the
linkage 16 is in advance of the circumferential links 18 during
insertion of the stent 10 into the vessel.
[0038] The catheter is inserted into the vessel in a conventional
manner until it is located at the stenosis.
[0039] After placement within the vessel, the catheter is then
inflated to apply a radially expanding force to the stent.
[0040] As shown in FIG. 5, the application of the radial force
causes the circumferential spacing of struts 14 to increase. The
circumferential links 18 are carried with the struts 14 and a
hinging action occurs at the connection of the axial link 20 to
both the circumferential link 18 and the corner link 22 by plastic
deformation of the links. Similarly, the connecting link 28 hinges
at its connection to the corner link 22 to provide a hinging action
between the links. The links 22 is thus bodily rotated as the
struts 14 are spread.
[0041] By virtue of the relatively narrow links 20,22, the hinging
at their junction to the larger links 18,22 exceeds the yield point
of the material and causes a permanent deformation and increase in
diameter. A pair of spaced hinge points is thus established and
thus the total rotation required between the axial links 20 and
circumferential link 28 is distributed between two locations.
[0042] The catheter is then deflated and removed, leaving the stent
10 in situ. It will be noted, however, that during inflation the
struts 14 maintain the axial spacing between the circumferential
links 18 so that the overall length of the stent remains the same
with no relative axial movement between the vessel and the
stent.
[0043] In tests with samples of the configuration of FIGS. 4 and 5,
an extension from the spacing of the struts 14 was increased from
an initial value of 6 units to 8.48 units upon application of loads
consistent with those used in the expansion of such stents.
[0044] An alternative embodiment of linkage 16 is shown in FIGS. 6
and 7, in which like components will be denoted with like reference
numerals with a suffix `a` added for clarity.
[0045] In the embodiment of FIG. 6, the circumferential link 18a is
formed as a pair of rectangular nodes 30,32 interconnected by a
narrow bar 34. The length of the axial link 20a is reduced to 0.5
of a unit value and a corresponding reduction in the length of the
connecting link 28 to 0.5 is made. As may be seen in FIG. 7, the
application of the radial load causes the connection at the bar 34
to plastically deform, allowing rotation of the rectangular bar 32.
The connecting link 28a is also subjected to bending load as well
as plastic deformation at the connection to the links 22a.
[0046] In tests conducted with samples of the arrangements shown in
FIGS. 6 and 7, the initial spacing of the struts 14 was increased
to 8.5 units after application of a radial force consistent with
that found in balloon catheters.
[0047] A further embodiment is seen in FIG. 8 where again like
reference numerals will be used to denote like components with a
suffix `b` added for clarity. In the embodiment of FIG. 8, the
connection between the connecting links 20b and the circumferential
links 18b progressively tapers to the dimension F. In a similar
manner, the junction between the connecting link 28b and the link
22b progressively tapers and in each case the overall length of the
links 20b,28b is reduced from 1 unit value to 0.5 unit value. A
tapering in the order of 45 is found to be appropriate.
[0048] The results of tests conducted on the embodiment shown in
FIGS. 4, 6 and 8 are represented on the curve of FIG. 9. This curve
represents the applied radial load and the deflection obtained and
it will be seen that in each embodiment there is an initial
proportional increase of load and deflection followed by a much
flatter curve indicating a plastic deformation. Thereafter, the
load progressively increases, indicating that the orientation of
the links is approaching a linear orientation. It will be seen that
the embodiment of FIG. 8 provides a lower load to achieve the
requisite deflections. With the provision of the relatively narrow
links, it is possible to control the radial force necessary to
expand the stent and the location at which the bending will occur.
The force necessary to achieve radial expansion must be compatible
with the forces available from a balloon catheter and the reduced
width of the links permits this. Moreover, the plastic deformation
of the narrow links maintains control of the orientation of the
wider links during expansion.
[0049] A further embodiment is shown in FIGS. 11-14 offering
enhanced flexibility for the stent during insertion, as may be
needed to negotiate tight turns in the arterial system during
placement, thereby minimizing damage to the arterial wall.
[0050] In the embodiment of FIGS. 11-14, each of the struts 14c is
segmented so as to be comprised of either a series of unitary
struts 40 or a series of linking struts 42.
[0051] The unitary struts 40 alternate with linking struts 42 about
the circumference of stent 10c and in the preferred embodiment an
even number of each is provided so that the linking struts 42 are
diametrically opposed. It is preferred that four linking struts 42
are provided and are circumferentially spaced at 90.degree.
intervals.
[0052] Each of the unitary struts 40 extend between two of the
linkages 16c so as to interconnect them. The unitary struts are
spaced apart from one another by a gap indicated at 44 so that each
linkage 16c is connected to only one of the adjacent linkages 16c.
By contrast, the linking struts 42 extend between four of the
linkages 16c and are then spaced from the next of the linking
struts 42 by a space indicated at 46.
[0053] The gaps 44 between the unitary struts are circumferentially
aligned to provide annular bands 48 whereas spaces 46 are staggered
between alternate linking struts 42. Each of the linking struts 42
has a waist 50 to provide a region of enhanced flexibility in a
plane tangential to the surface of the stent 10c The waist 50 is
aligned with one of the bands 48 and so provides the connection
across the band 48 between the linkages 16c.
[0054] As can be seen in FIG. 11, the waists 50 are located at
diametrically opposed locations in the respective bank 48 to define
a pair of pivot axes X-X. By virtue of the staggered relationship
between adjacent linking struts 42, the waists 50 are displaced by
90.degree. in adjacent bands 48 so that the pivot axes X-X are
disposed at 90.degree..
[0055] This arrangement provides flexibility about mutually
perpendicular axially spaced axes allowing relative pivotal
movement between sections of the stent to conform to the vessel
into which it is inserted.
[0056] The linkage 16c is shown in detail in FIG. 13 and includes
circumferential links 18c and axial links 20c connected by a node
32c.
[0057] The circumferential link 28c is connected to axial link 20c
by corner link 22c which is formed as a rectangular leg 24c.
[0058] It will be noted that the connection of each of the links
18c,20c,28c to the struts 134, nodes 32c and corner link 22c by
radiused fillets 52 that reduce local stress concentrations.
[0059] In one preferred example, the relative dimensions are as
follows:
2 a c e g i 1.20 0.75 1.40 1.40 2.00 0.90 0.25 6.9 5.30
[0060] The fillets 52 are each 0.125 and the thickness of the
material between 0.0625 and 0.125. With this configuration, the
application of a radial load results in the circumferential
expansion shown in FIG. 14 from which it can be seen that a uniform
bending of the links 18c is obtained and that the axial links 20
have assumed a circumferential orientation.
[0061] Upon circumferential expansion, the linking struts 42
inhibit foreshortening as each band 48 has two axial struts that
inhibit relative axial movement between adjacent linkages 16c. At
the same time the relatively flexible waists 50 disposed at
90.degree. to one another provides the requisite flexibility for
insertion of the stent 10c.
[0062] Although the embodiment of FIG. 11 shows axes of rotation at
90.degree. to one another, alternative arrangements may be used by
varying the relative orientation of the waisted links. For example,
by spacing the links at 60.degree. angles, three axes of rotation
are obtained at axially spaced locations.
[0063] The following relative dimensions of linkage 16 have also
been found to provide satisfactory performance:
EXAMPLE I
[0064]
3 a b c d e f g h i 10 7.5 11 17.8 38.6 12.3 3 46 74.2
EXAMPLE II
[0065]
4 a B c d e f g h i 10.3 7.7 12.2 17.8 38.6 12.3 3 48.2 74.2
EXAMPLE III
[0066]
5 a b c d e f g h i 10.0 7.5 11 14.3 20.4 9.2 3 46 49
[0067] In each of these examples, the units are 0.001 inches and
the thickness of the material used was 0.003 inches.
[0068] In Examples I and III, the width, ie. circumferential
dimension, of the struts 14 was 5 units and the axial spacing
between adjacent linkages 16 was 12 units.
[0069] In Example II the width of the struts 14 was 2.85 units and
the axial spacing between adjacent linkages was 3 units.
[0070] In each case, the linkages repeated 4 times about the
circumference. The diameter of the stent prior to expansion was 65
units and after expansion with a 45.degree. rotation of the links
20c an outside diameter of 197 units was obtained with Example II
and 152.3 units with Example III. The axial spacing between
linkages 16 was sufficient to permit the bodily rotation of the
corner links as the stent expands radially. The provision of the
strut 14 inhibits foreshortening and therefore ensures that the
linkages can rotate as required.
[0071] A further embodiment is shown in FIG. 16 in which like
components will be identified with like reference numerals with a
suffix `d` added for clarity, The embodiment of FIG. 16 is similar
to that shown in FIGS. 12 and 13. However, each of the struts 14d
is segmented into a series of unitary struts 40d that extend
between two adjacent linkages 16d. The struts 40d are staggered
circumferentially to alternate the direction of connection between
adjacent linkages. The unitary linkages 40d are thus aligned at
diametrically opposed locations and thus define a pair of
orthogonal axes at axially spaced locations to provide flexibility
during insertion. The stent will of course be dimensioned to fit
within the intended vessel and engage the wall when extended. A
typical stent for insertion in an artery will have a diameter of
between 1.5 mm and 3.5 mm when inserted and may have a diameter of
between 2 mm and 12 mm when expanded.
[0072] A further embodiment is shown in FIGS. 17 and 18 in which
like reference numerals identify like components with a suffix "e"
added for clarity. The embodiment of FIGS. 17 and 18 has unitary
struts 40e distributed at diametrically opposed locations as shown
in FIG. 16.
[0073] In the embodiment of FIG. 17 however the struts 40e are
increased in width to approximate the width of the nodes. And, as
can be seen in FIG. 18, the provided with radiused external corners
80 and radiused fillets 82 at the intersection with links 20e and
28e. Similarly, the nodes 32e are provided with radiused external
corners 84 and radiused fillets 86 at the connection to the links
34e and 20e.
[0074] The radiused external corners inhibit interference between
adjacent pairs of links 22e and nodes 3e as the stent 10c is
expanded to ensure a uniform expansion of the inflating balloon.
The fillets 82, 86 assist in stress distribution to effect the
proper hinging action of the links.
[0075] The relative dimensions of the links may be adjusted to suit
the requirements and in particular to suit the outside diameter of
the balloon. Using the same nomenclature as used in FIG. 13
suitable dimensions, in inches, for three stents with different
internal diameters, is as follows.
6 i.d. a b c d e F g h 1 0.0100 0.0060 0.0135 0.0180 0.0190 0.0110
0.0030 0.0515 2 0.0100 0.0060 0.0125 0.0180 0.0195 0.0110 0.0030
0.0505 3 0.0095 0.0060 0.0115 0.0180 0.0195 0.0110 0.0030
10.0485
[0076] It will be seen that by varying the spacing between links
20e (dimension `c`) or the length of link 34 (dimension `a`) the
spacing of the struts 40e and hence the circumference may be
varied. Appropriate adjustment can be made to the length of link
20e (dimension `e`) to maintain an expanded diameter of 4 mm. In
each of the above examples, the external corners and all fillets
except those at opposite ends of the links 20 have a radius of
0.002 inches. The fillets at opposite ends of links 20e have a
radius of 0.0015 inches.
[0077] A further embodiment is shown in FIG. 19 in which like
reference numerals will be used with like components with a suffix
"f" added for clarity.
[0078] In the embodiment of FIG. 19 each of the linkages 16f is
similar To that shown in FIG. 18. The unitary struts 40f
interconnect three linkages 18f except for the initial strut 40f
adjacent one end that interconnects two linkages 18f.
[0079] Circumferentially adjacent struts 40f are staggered relative
to one another so as to provide an axial overlap and a gap 46f.
Accordingly, diametrically opposed connections are established at
spaced axial locations to facilitate flexure of the stent 10f.
* * * * *