U.S. patent application number 10/489181 was filed with the patent office on 2004-12-02 for expandable stent.
Invention is credited to Andersen, Erik, Wen, Ning.
Application Number | 20040243217 10/489181 |
Document ID | / |
Family ID | 26077612 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040243217 |
Kind Code |
A1 |
Andersen, Erik ; et
al. |
December 2, 2004 |
Expandable stent
Abstract
An expandable stent comprising a tubular body made up of a
plurality of separated tubular elements (1) arranged along a common
longitudinal axis. Each tubular element (1) comprises a plurality
of rhombic-shaped closed cell elements (2) joined by
circumferentially extending linking members (3). The closed cell
elements (2) are expandable to allow the tubular elements, and
hence the stent itself, to expand. In the direction of the
longitudinal axis of the stent, the extremities of each of the
closed cell elements has an enlarged loop (30) with waisted
portions (33) which allow the tubular elements to interlock to
create a stable structure, at least when in the unexpanded
condition.
Inventors: |
Andersen, Erik; (Roskilde,
DK) ; Wen, Ning; (Chantilly, FR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
26077612 |
Appl. No.: |
10/489181 |
Filed: |
March 10, 2004 |
PCT Filed: |
September 5, 2002 |
PCT NO: |
PCT/EP02/09931 |
Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2002/828 20130101;
A61F 2002/91591 20130101; A61F 2250/0063 20130101; A61F 2/915
20130101; A61F 2002/91533 20130101; A61F 2250/0068 20130101; A61F
2/852 20130101; A61F 2002/91525 20130101; A61F 2002/91575 20130101;
A61F 2230/0013 20130101; A61F 2002/826 20130101; A61F 2/91
20130101; A61F 2002/91508 20130101 |
Class at
Publication: |
623/001.15 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2001 |
GB |
0121980.7 |
Claims
1. A stent comprising a tubular body made up of a plurality of
separate, radially expandable, tubular elements aligned along a
common longitudinal axis, wherein at least some of the tubular
elements each comprise a plurality of closed cell elements, each
joined to the next by a circumferentially-extending linking
member.
2. A stent as claimed in claim 1 wherein the tubular elements are
also compressible.
3. A stent as claimed in claim 1 further including interlock means
for mechanically holding the tubular elements together, at least in
an unexpanded condition of the stent.
4. A stent as claimed in claim 3 in which said interlock means are
provided by inter-engaging elements provided on said tubular
elements.
5. A stent as claimed in claim 4 wherein each of said closed cell
elements is provided with a respective inter-engaging element which
engages a corresponding inter-engaging element on an adjacent
tubular element.
6. A stent as claimed in claim 1 wherein some, but not all, of said
closed cell elements are provided with a respective inter-engaging
element which engages a corresponding inter-engaging element on an
adjacent tubular element.
7. A stent as claimed in claim 1 wherein each closed cell element
is expandable in the circumferential direction of the tubular
element, thus allowing the tubular element to expand and
contract.
8. A stent as claimed in claim 7 wherein each closed cell element
is positioned symmetrically with respect to the circumferential
linking members.
9. A stent as claimed in claim 7 wherein each closed cell element
comprises two attachment points at each of which it joins to a
respective circumferential linking member, and wherein the closed
cell element is such as to be capable of expanding from a first
position in which the attachment points are relatively close
together, to a second position in which the attachment points are
relatively further apart.
10. A stent as claimed in claim 9 wherein, between said attachment
points, each closed cell element comprises proximal and distal
members, mutually spaced apart in the direction of the longitudinal
axis, said proximal and distal members being capable of bending to
accommodate the expansion from the first position to the second
position.
11. A stent as claimed in claim 10 wherein the proximal and distal
members of each closed cell element are joined together at each of
their circumferentially spaced ends by means of a respective hinge
member.
12. A stent as claimed in claim 11 wherein each hinge member is
attached at one end of a respective circumferentially-extending
linking members the other end of the linking member having attached
thereto the opposite hinge member of the next adjacent closed cell
element.
13. A stent as claimed in claim 10 wherein the proximal and distal
members each comprise a flexible member joining the attachment
points.
14. A stent as claimed in claim 10 wherein the proximal and distal
members each comprise two or more relatively rigid side members
joined by a hinge.
15. A stent as claimed in claim 14 wherein said four side members
together form the shape of a rhombus.
16. A stent as claimed in claim 14 wherein each of said side
members is of rectilinear shape.
17. A stent as claimed in claims 5 or 10 wherein said
inter-engaging elements are each formed by a respective loop formed
by each of said proximal and distal members.
18. A stent as claimed in claim 14 wherein the hinge joining each
of said two side members comprises a loop which forms one of said
inter-engaging elements, and wherein the loop joins the adjacent
side members by a waisted portion which, together with the
corresponding waisted portion from the next adjacent closed cell
element in the same tubular element, forms a cooperating
inter-engaging element.
19. A stent as claimed in claim 1 wherein all of the closed cell
elements making up each tubular element are of the same shape.
20. A stent as claimed in claim 1 wherein some of the closed cell
elements making up each tubular element are of a different shape to
the remainder.
21. A stent as claimed in claim 1 wherein the exterior surface of
the tubular body is equipped with wells which open onto its
exterior surface, said wells being suitable to contain one or more
therapeutic agents.
22. A stent as claimed in claim 21 in which the wells comprise
holes or grooves opening into the exterior surface of the
stent.
23. A stent as claimed in claim 22 wherein the holes or grooves are
blind, i.e. do not pass through the material of the stent.
24. A stent as claimed in claim 22 wherein the holes or grooves
pass through to the interior of the stent.
25. A stent as claimed in claim 24 in which the inner end of the
hole or groove, is plugged by a material which prevents or
considerably reduces the flow of therapeutic agent
therethrough.
26. A stent as claimed in claim 25 wherein said material is, or
contains, therapeutic agent.
27. A stent as claimed in claim 21 wherein the closed cell elements
are formed with blocks on each of which are formed one or more of
said wells.
28. A stent as claimed in claim 21 wherein at least some of said
wells contain multiple therapeutic agents arranged in layers so as
to release in sequence.
Description
[0001] This invention relates to an expandable tubular stent for
implantation in the lumen of a body duct in order to ensure a
passage therein.
[0002] Such stents are used mainly in the treatment of blood
vessels exhibiting stenoses, and more generally in the treatment of
diseases of various anatomical ducts of the human or animal body,
such as, for example, the urinary ducts, especially the urethra, or
the digestive ducts, especially the oesophagus.
[0003] The percutaneous implantation of an expandable tubular stent
in a stenotic blood vessel is generally recommended, for example
after a conventional angioplasty procedure, for preventing the
dilated vessel from closing up again spontaneously or for
preventing its occlusion by the formation of a new atheromatous
plaque and the possible recurrence of stenosis.
[0004] A known type of expandable tubular stent consists of an
assembly of radially expandable, tubular elements aligned along a
common longitudinal axis and successively joined together in pairs
by respective sets of linking members. Such a stent is disclosed,
for example, in international patent application WO 98/58600 in
which each of the tubular elements consists of a strip forming a
zigzag corrugation defining bent extreme portions which are
successively connected together in pairs in opposite directions by
rectilinear intermediate portions. By virtue of this zigzag
corrugation, the stent is expandable between a first, unexpanded
state, enabling it to be implanted percutaneously by means of an
insertion device of reduced diameter, and a second, expanded state,
in which the stent makes it possible to ensure a passage in the
lumen of the body duct. Stents of this type are also disclosed in
international patent applications WO 96/26689 and WO 98/20810.
[0005] To install the stent, it is placed in the unexpanded state
on an angioplasty balloon catheter. Once in place, the balloon is
inflated in order to cause the stent to expand. Alternatively, the
stent may be made from a material which has a recovery capacity, so
that the stent may automatically expand, once in place.
[0006] According to the invention there is provided a stent
comprising a tubular body made up of a plurality of separate,
radially expandable, tubular elements aligned along a common
longitudinal axis, wherein at least some of the tubular elements
each comprise a plurality of closed cell elements, each joined to
the next by a circumferentially-extending linking member.
[0007] It will thus be seen that each tubular element comprises a
closed loop consisting of a series of alternating closed cell
elements and circumferential linking members.
[0008] In most known stents, the tubular elements are physically
linked to one another by longitudinally extending linking members.
One or more of such longitudinally extending linking members may
link each pair of adjacent tubular elements. However, there are a
number of advantages to be obtained by not using
longitudinally-extending linking members, so that the stent
consists simply of a collection of separate tubular members whose
alignment along a common axis to form the stent is achieved by
other means. Preferably the tubular elements, as well as being
expandable, are also compressible.
[0009] By "separate" is meant that the tubular elements are not
directly connected together by longitudinally-extending linking
members. The word "separate" does not imply that the elements may
not touch and, as will be explained below, in certain conditions of
the stent, the linking members will touch and will indeed link
together. In the absence of longitudinally-extending linking
members, the structural integrity of the stent is realised by
alternative means, such as:
[0010] 1) A tubular member or framework which is not directly
joined to the adjacent tubular elements but over which or within
which the tubular elements are positioned in the desired alignment.
For example, the balloon which is used to expand the stent can be
used to maintain the position of the tubular members with respect
to one another.
[0011] 2) Interlock means which mechanically holds the tubular
members together even though they are not directly joined. An
example of this would be to provide co-operating interlock means on
the tubular elements themselves.
[0012] In an embodiment of the invention, both these techniques are
employed: the tubular elements are placed over the balloon and
interlocked together so that the stent remains structurally stable
during its often tortuous passage to the treatment site. Upon
expansion, the interlocking is released, and the balloon alone then
maintains the positional stability of the stent components. After
the balloon has been deflated, the expanded stent, which has
undergone plastic deformation, maintains its expanded shape and
thus keeps the vessel being treated at its desired diameter. The
expanded vessel applies a reaction force, due to its elastic
nature, against the stent and thus maintains the position of the
individual tubular elements making up the stent with respect to one
another.
[0013] In order to allow the stent to expand it is necessary that
the tubular elements be radially expandable. For this purpose, each
tubular element is constructed in such a way that it is expandable
in the circumferential direction. This may be achieved by the
closed cell construction of the invention in which the expansion
capabilities of the tubular elements are contained wholly or
primarily in the closed cell elements. To avoid out of balance
forces during expansion, it is preferred that the closed cell
elements be positioned symmetrically with respect to the
circumferential linking members, but asymmetric arrangements are
also possible.
[0014] The tubular elements making up the stent may be all
identical, or they may be different--for example, a stent could be
made up of a combination of tubular elements comprising closed cell
elements, and tubular elements constructed in some other way,
arranged to create particular desired properties of the stent as a
whole.
[0015] The circumferential linking members may simply consist of
rectilinear members extending in the circumferential direction.
Alternatively the circumferential linking members may be angled to
the circumferential direction, so long as they have a component in
the circumferential direction so that the adjacent closed cell
elements are spaced apart in the circumferential direction. In a
further alternative, the circumferential linking members are not
rectilinear, but are some other shape to create particular desired
characteristics--for example, the circumferential linking members
could be such as to provide a degree of flexibility in the
circumferential direction, although the expansion capabilities of
the tubular element will still be primarily due to the closed cell
elements. Preferably, all of the circumferential linking members
are the same length in the circumferential direction so that the
closed cell elements are evenly distributed about the circumference
of the tubular element.
[0016] The circumferential linking members attach to the closed
cell elements at respective spaced attachment points, and each
closed cell element is constructed in such a way that it is capable
of expanding from a first position in which the attachment points
are relatively close together to a second position in which the
attachment points are relatively further apart. In this way, the
circumferential length of the tubular element can be increased from
a relatively low value, corresponding to the unexpanded condition
of the stent, to a relatively higher value, corresponding to the
expanded condition of the stent. In one possible construction, each
closed cell element comprises two individual members extending
between said attachment points, said members being spaced apart in
the direction of the longitudinal axis of the stent. Thus, one of
said members may be said to be the proximal member, the other the
distal member. The proximal and distal members are preferably
symmetrically arranged about a straight line joining the two
attachment points, this line being coaxial around the circumference
with the general direction of the circumferential linking
members.
[0017] The proximal and distal members are capable of bending in
order to enable the expansion of the closed cell element from the
first position to the second position. This may be achieved in
various ways. For example, each of the proximal and distal members
may be fabricated from a flexible member which is thus able to bend
to accommodate the required movement. Alternatively, each of the
proximal and distal members is fabricated by a plurality of
relatively rigid side members joined by hinge members. In the
preferred embodiment, each of the proximal and distal members
comprises two such side members joined together by a hinge.
Preferably the two side members are of equal length, but they do
not need to be; however, for a symmetric construction the
corresponding side members in each of the proximal and distal
members should be of equal length.
[0018] In an embodiment, each closed cell element has a generally
rhombic or diamond shape, comprising four side members of
relatively stiff construction, joined by four hinge members
corresponding to the corners of the rhombus. The circumferential
linking members attach to the closed cell element at the location
of opposite hinge members. Thus, each circumferential linking
member has, at one end, one of the hinge members of one closed cell
element and, at the opposite end, the opposite hinge member of the
adjacent closed cell element.
[0019] It is not essential that all the closed cell elements in
each tubular element are the same shape. In an alternative
embodiment every other closed cell element is of rhombic shape, as
described above, whilst the closed cell elements in between
comprise "double rhombic" elements, each comprising two rhombic
shapes, as described above, aligned in the circumferential
direction, but joined by a narrow, but not closed, neck
portion.
[0020] Other arrangements of closed cell elements are possible,
according to the circumstances.
[0021] The aforesaid interlock means can conveniently be provided
by providing an enlarged portion at each of the hinge members to
which the link members are not attached. The narrowing side members
as they approach each hinge member, together with the respective
enlarged portion, form a narrow or waist portion which can overlap
with an enlarged portion from the next adjacent tubular element.
Two such waist portions acting together can thus retain an enlarged
portion from the next adjacent tubular element.
[0022] The interlock means do not have to be provided on every
closed cell element. It may be adequate to provide them on just a
few closed cell elements, but evenly spaced about the
circumference, so as to give a balanced attachment between adjacent
tubular elements. For this purpose some of the closed cell elements
may extend further in the axial direction of the stent than the
remaining closed cell elements, so that these extended portions may
interlink with the adjacent tubular element.
[0023] This enlarged portion can be formed as a flexible open cell
with a narrowed neck, or can be formed as a relatively rigid block,
from which, for example, the two side members may emerge via a
respective narrowed portion to act as a hinge--in this latter case,
the hinge member actually consists of two separate hinges.
[0024] In current medical practice, it is often the case that, in
addition to its role in providing ongoing support for the vessel
wall, the stent is required to act as a means whereby therapeutic
agents may conveniently be applied. Indeed the trauma caused during
the angioplasty procedure may call for localised drug treatment. In
addition, drugs may be used to counteract restenosis, and for other
purposes. Conventionally, such therapeutic agents are contained
within some form of coating which is applied to the stent so that
the drug will be released over a period of time. One problem with
such an arrangement, however, is that, whereas the drug needs
primarily to be applied through the wall of the vessel being
treated, in practice as much of the drug is released into the
fluid, e.g. blood, flowing within the vessel as passes through the
vessel wall. Not only is the drug which is washed away effectively
wasted, it can also do positive harm elsewhere if, for example, it
enters a sensitive organ such as the heart.
[0025] Thus, in an embodiment of the invention the stent is
equipped with wells opening into its exterior surface--that surface
which, when the stent is in place, will face the wall of the vessel
being treated--said wells being suitable to contain therapeutic
agent.
[0026] The wells may comprise holes or grooves opening into the
exterior surface of the stent, and may or may not pass right
through the material of the stent to the interior of the stent.
However, if the wells pass through to the interior of the stent
there is clearly a danger of at least some of the drug being
released into the fluid flowing within the vessel. Therefore it is
preferred that, in such a case, that end of the well which opens
into the interior of the stent is constructed, for example by being
made narrower, and/or being plugged by a material which prevents or
considerably reduces the tendency of the therapeutic agent to flow
therethrough.
[0027] Thus it is preferred that the well is wholly or primarily
open to the exterior surface of the stent so that the therapeutic
agent may act directly on the wall of the vessel and does not get
washed away by the fluid flowing along the vessel being
treated.
[0028] The wells may open onto any suitable exterior surface of the
stent. For example, the wells may conveniently be formed in the
blocks which form the enlarged portions of the closed cell
elements. For example, each block could be formed with a well in
the form of a hole, which may or may not be a through hole and
which opens into that surface of the block which forms part of the
exterior surface of the stent. Alternatively the wells may be
formed as grooves in the side members of the closed cell elements,
the grooves opening into that surface of the side members which
forms part of the exterior surface of the stent. It will be
understood, however, that the above positions are given just as
examples.
[0029] As mentioned above, the wells contain therapeutic agents
which are intended to be released at a controlled rate against the
wall of the vessel being treated. Not all of the wells necessarily
will contain the therapeutic agent, and not all wells need to
contain the same therapeutic agent. It is possible, for example,
that the wells of different tubular elements contain different
therapeutic agent, opening up the possibility of providing mixtures
of drugs by choosing particular tubular elements carrying
particular drugs to make up the stent. Clearly this is particularly
easy with a stent in which the tubular elements are separate from
one another. The therapeutic agents may also be provided in
separate layers within the well, with the drug needed first being
in the top layer, and the drugs needed later in lower layers, in
correct sequence.
[0030] In addition, it is possible to provide that some of the
wells contain therapeutic agents which have different rates of
release. For example the drug contained in the wells of those
tubular elements at or near the ends of the stent could be arranged
to have a more rapid or a slower release rate than the
remainder.
[0031] The therapeutic agents may be provided in any suitable form
for retention in the wells, and for sustained release, once
installed within the vessel. Examples are liquid, gel or powder
form.
[0032] In order that the invention may be better understood,
several embodiments thereof will now be described by way of example
only and with reference to the accompanying drawings in which:
[0033] FIG. 1 is a two-dimensional view of the evolute of the
surface of a stent according to a first aspect of the present
invention, in its "as cut" condition;
[0034] FIG. 2 is a view corresponding to FIG. 1, but showing just a
single tubular element;
[0035] FIG. 3 is an enlarged view of one of the closed cell
elements in the embodiment of FIG. 1;
[0036] FIGS. 4A and B are side and perspective views of the stent
of FIG. 1, but in which the number of elements is just three, in
its "as cut" condition;
[0037] FIG. 5 is a perspective view of a single tubular element
from the stent of FIG. 1;
[0038] FIGS. 6 and 7 are views similar to FIGS. 4A and 4B
respectively, but showing the stent in the crimped condition;
[0039] FIGS. 8 and 9 are views similar to FIGS. 4A and 4B
respectively, but showing the stent in the expanded condition;
[0040] FIGS. 10 and 11 are views similar to FIG. 4B, but showing
two further embodiments showing both the first and second aspect of
the invention;
[0041] FIG. 12 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
[0042] FIGS. 12A, B and C are views on the lines A-A, B-B and C-C
respectively of FIG. 12;
[0043] FIG. 13 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 12;
[0044] FIG. 14 is an enlarged view of part of FIG. 13;
[0045] FIG. 15 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
[0046] FIGS. 15A and B are views on the lines A-A and B-B
respectively of FIG. 15;
[0047] FIG. 16 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 15;
[0048] FIG. 17 is an enlarged view of part of FIG. 16;
[0049] FIG. 18 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
[0050] FIG. 18A is a view on the line A-A of FIG. 18;
[0051] FIG. 19 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 18;
[0052] FIG. 20 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
[0053] FIG. 21 is a view similar to FIG. 5, but showing the
embodiment of FIG. 20,
[0054] FIG. 22 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
[0055] FIG. 23 is a view similar to FIG. 5, but showing the
embodiment of FIG. 22; and
[0056] FIG. 24 is a view similar to FIG. 4b, but showing the
embodiment of FIG. 22.
[0057] Referring firstly to FIGS. 1 and 4, the stent comprises a
series of radially expandable tubular elements 1 aligned along a
common longitudinal axis. Both of these Figures show the stent in
its "as cut" condition by which is meant the condition in which it
comes out of the manufacturing process. FIG. 1 illustrates the
stent folded out in two dimensions, illustrated by the X-Y
coordinates printed to the side of the drawing. In practice the
stent is, of course, a three dimensional object, as illustrated in
elevation and in perspective in FIGS. 4A and 4B respectively; thus
it is assumed that the ends 12, 13 of each tubular element in FIG.
1 are in fact joined so that each element forms a closed loop of
generally tubular configuration. In this description the
longitudinal direction of the stent is parallel to the X-axis
illustrated in FIG. 1, while the circumferential direction of the
stent is parallel to the Y-axis in FIG. 1.
[0058] It will be noted that the tubular elements 1 are separate
from one another in the sense that there is no direct physical link
between them, keeping the tubular elements 1 in position. Instead
alternative means are used to maintain the structural integrity of
the stent. This will be explained in more detail below.
[0059] In the stent illustrated, all of the tubular elements are
identical in structure and size although, as mentioned above, this
need not necessarily be the case. A single tubular element 1 is
shown, in two dimensional form in FIG. 2, and in three dimensional
form in FIG. 5. Each tubular element comprises a plurality of
closed cell elements 2 equally spaced apart by circumferentially
extending linking members 3. In the embodiment illustrated each
tubular element 1 comprises six closed cell elements 2, spaced
apart circumferentially by 60.degree., but other numbers of closed
cell elements are possible, according to the circumstances.
[0060] A single closed cell element 2 is shown in enlarged detail
in FIG. 3. The closed cell element has a generally rhombic or
diamond shape defined by four side members 24 to 27 joined together
by respective hinge members 20 to 23. The circumferential linking
members 3 attached to respective opposite hinge members 21, 23.
[0061] The hinge members 21, 23 are formed by narrowed sections 28,
29 where the respective side members 24/27, 25/26 join the
respective linking member 3. The hinge members 20, 22 are formed as
a loop 30 having a narrowed opening 31 into the interior 32 of the
cell element. This narrowed opening 31 corresponds to a waisted
portion 33 which cooperates in the interlocking of individual
tubular elements 1, as will be explained below. Before the stent is
used, it will generally be crimped to the balloon which will carry
it to the treatment site and subsequently expand it. The crimping
process involves compressing the "as cut" stent onto the balloon so
that it is securely gripped. During compression the diameter of the
tubular elements, decreases and this is achieved by a deformation
of the closed cell elements 2 in such a way as to tend to close the
elements up--i.e. so that the hinge members 21 and 23 move towards
one another, thus reducing the circumferential length of the
tubular element 1. During this process the closed cell elements
bend at the hinge members 20 to 23 the crimped condition of the
stent is illustrated in FIGS. 6 and 7 and since, in effect, the
stent is expanded from this condition, the crimped condition can
also be regarded as the unexpanded condition of the stent.
[0062] It will be noted in FIGS. 6 and 7 that, in the crimped
condition of the stent, the hinge members 20, 22 belonging to
adjacent tubular elements are interlocked, thus maintaining the
structural integrity of the stent as a whole. This interlocking is
achieved by the cooperating interlocking shapes of the hinge
members 20, 22 in which each of the enlarged loops 30 lie between a
pair of waisted portions 33 belonging to circumferentially adjacent
closed cell elements 2 belonging to the same tubular element 1. By
careful design, the closed cell elements can be configured to grip
one another to maintain the shape of the stent so that it is not
dislodged or deformed during its often long and tortuous passage to
the treatment site. The longitudinal flexibility of the stent is
ensured in the crimped condition by the fact that each loop 30 is
allowed to move longitudinally a short but controlled distance
towards the adjacent linking member 3. Thus, as the stent is bent
longitudinally the loops 30 on one side move slightly, as
described, whilst those on the other side move in the opposite
direction. In an alternative embodiment (not shown) still greater
longitudinal flexibility can be achieved by arranging that the
elements are interlocked in such a way as to allow the loops to
move, in a controlled manner, in either longitudinal direction.
[0063] When the stent reaches the treatment site, and the physician
is satisfied as to its correct position, the balloon carrying the
stent is expanded, in the known manner, to expand the stent from
its condition shown in FIGS. 6 and 7 to its dilated condition shown
in FIGS. 8 and 9. During this expansion process, the closed cell
element 2 deform to a final shape clearly illustrated in FIG. 8. It
will be seen that the hinge members 21, 23 have moved apart in the
circumferential direction, thus increasing the circumferential
length of each tubular element 1. At the same time, the hinge
members 20, 22 of adjacent closed cell elements 2 move apart in the
circumferential direction thus releasing the grip which they had
previously exerted on the corresponding members of adjacent tubular
elements. The stent however by now is supported both from within
and without and so maintains its structural shape, even though the
interlocking is released. The support from within comes from the
balloon which is being internally pressurised to expand the stent;
the support from without comes from the wall of the vessel being
treated.
[0064] It will also be noted that, during expansion, the length, in
the longitudinal direction of the stent, of each of the closed cell
elements 2 reduces and this effect, in a stent with linking members
between adjacent tubular elements, causes the overall length of the
stent to reduce. This reduction in length is undesirable for
various reasons, and it will be seen that the use of independent
tubular elements 1 substantially eliminates this problem.
[0065] FIGS. 10 and 11 show modified versions of the stent of FIG.
1 in which the hinge members 20, 23 are modified from the open loop
form described previously.
[0066] The stents of FIGS. 10 and 11 differ from that of FIG. 1 in
that the hinge members 20, 22 comprise a block 34 of material from
which the side members 24/27 and 25/26 emerge, via a respective
narrowed portion to act as a hinge. Thus, in this case the hinge
members 20, 22 each comprise a pair of hinges by which the
respective side members 24/27 and 25/26 are attached to the blocks
34. Preferably these blocks 34 are formed integrally with the
remainder of the tubular element, and are of the same material.
[0067] The difference between the embodiments of FIGS. 10 and 11 is
in the shape of the blocks 34 which in the case of FIG. 10 is
substantially rectangular and in the case of FIG. 11 is
substantially circular. In both cases, each block 34 acts as an
enlarged end in a similar manner to loop 30 of the FIG. 1
embodiment, and defines a narrowed waist portion where it joins the
adjacent side members. The arrangement is thus able to interlock
the individual tubular elements 1 in the same way as described
above.
[0068] The advantages of a stent with independent tubular elements
over one in which the tubular elements are linked by linking
members can be summarised as follows:
[0069] 1) Manufacture is made easier because only a basic tubular
element has to be cut. Any stent length can readily be created by
adding the appropriate number of tubular elements at the
commencement of the assembly or crimping process.
[0070] 2) The crimped stent has a high degree of longitudinal
flexibility since it is not restrained by the inter-element linking
members of known stents.
[0071] 3) The crimped stent has a high degree of longitudinal
conformability due to its tubular elements being interlocked at
multiple cell locations.
[0072] 4) There is substantially no shortening of the stent during
expansion because the shortening of each tubular element does not
affect the stent as a whole.
[0073] 5) Once deployed, the stent has a high degree of
longitudinal flexibility and of longitudinal and radial
conformability due to the absence of the restraint imposed by
inter-element linking members.
[0074] 6) Once deployed the stent has a good vessel repartition and
vessel scaffolding, with homogeneous support for the vessel
wall--see particularly FIG. 8.
[0075] FIGS. 10 and 11 also illustrate the use of wells for
containing therapeutic agent. It will be seen that, in each of
FIGS. 10 and 1 the blocks 34 have formed on their exterior surface
a well 35 which is intended to act as a reservoir for a therapeutic
agent. Each well 35 takes the form of a shallow blind hole which
opens into the exterior surface which, when the stent is deployed
faces the wall of the vessel being treated.
[0076] Thus, any therapeutic agent contained within the wells 35
acts directly on the wall of the vessel, and is not substantially
affected by the flow of fluid within the vessel.
[0077] Although only a single well 35 is formed in each block 34,
it is possible for multiple smaller wells to be formed, perhaps
each containing different drugs. Different drugs can be supplied on
different tubular elements, making it easy to create a stent, as
needed, containing an appropriate recipe of drugs.
[0078] The holes making up the wells 35 can be formed as
through-holes, and plugged from the interior side to create a blind
hole. Alternatively, the through hole can be left, and a suitable
substance which will resist the washing away of the drug contained
within the well can be deposited at the inner end of the through
hole.
[0079] Although the wells 35 are shown as circular holes, it will
be understood that other shapes are possible, including
multi-sided, square or rectangular. Alternatively, the wells can be
formed as grooves or slots opening into the exterior surface of the
block 34.
[0080] The wells may additionally or instead of be provided at
other locations, such as on the side members 24 to 27 of the closed
cell elements 2. However, for this purpose, the side members would
have to be made less deformable than they might otherwise be since
any deformation of the reservoir during stent crimping or
deployment might result in delamination of the reservoir contents,
which would be undesirable. The blocks 34 are seen as attractive
since they suffer substantially less deformation than other parts
of the stent because their bulk, relative to the remaining
components of the stent, is such that they are relatively
stiff.
[0081] FIGS. 12 to 19 illustrate further embodiments similar to
that of FIGS. 10 and 11, showing alternative arrangements of
wells.
[0082] In the embodiment shown in FIGS. 12 to 14, two shapes of
wells are shown. Half of the wells 35 have the shape of a short
slot 36 which opens only into the exterior surface of the tubular
element; the other half of the wells 35 have the shape of a slot 37
which opens both into the exterior surface of the tubular element
1, but also info the edge of the tubular element 1. Various
combinations of these shaped wells can be used.
[0083] The enlarged view of FIG. 14 is of interest in that it
clearly shows the structure of the left-hand hinge member 20. This
can be seen to comprise two narrowed (i.e. less wide) portions
50,51 where the respective side members 24 and 27 join the block
34.
[0084] In the embodiment of FIGS. 15 to 17, there is again a
combination of different well shapes: a first type of well 35
formed of a short slot 38 extending in the circumferential
direction of the stent; a second type of well 35 formed of a slot
39 which extends right across the block 34 in the circumferential
direction of the stent, and is open at both ends.
[0085] FIGS. 18 and 19 show an embodiment in which again two
different styles of well 35 are shown. On the left hand side a
block 40 is formed within the loop 30 of a hinge member of the type
described above in relation to the embodiment of FIG. 1. The block
40 is formed with a well 35 formed as a blind hole, in a similar
manner to the wells 35 of the embodiment of FIG. 11.
[0086] On the right hand side a block 41 is formed outside of the
loop 30 and, once again, is equipped with a well 35 in the form of
a blind hole. Since there is room beyond the hinge members 20, 22,
the block 41 does not interfere with the interlocking of the
tubular element 1 together during crimping, as described above.
[0087] The advantages of stents incorporating wells, as described
above, can be summarised as follows:
[0088] 1) The well can hold drugs without the need for a polymer
matrix coating. The use of wells can eliminate coating delamination
during stent deployment, thus reducing the risk of thrombosis.
[0089] 2) The absence of a polymer matrix coating eliminates any
potential biocompatibility problems arising from their use.
[0090] 3) Once the stent is fully deployed, the outside surface of
the stent is pushed against the wall of the vessel being treated;
this means that the well is open only towards the vessel wall, to
enable diffusion of the drugs into the vessel wall. In addition,
the drug cannot be washed out by the flow of fluid in the vessel
and so cannot have undesired effects elsewhere.
[0091] 4) Compared to a thin (0.1-5 micron) drug layer coated on
the stent, the reservoir can be loaded with a high dose and long
life time.
[0092] 5) The reservoir dimensions (diameter, length, width, depth)
can be readily varied to the particular circumstances such as blood
flow direction and drug release kinetics.
[0093] 6) Each well can contain a single drug and therefore
different drugs can be individually held in different wells without
the danger of their reacting with each other.
[0094] FIGS. 20 to 24 show two further embodiments in which the
closed cell elements in each tubular element 1 are not all
identical, and in which the locating means are not provided on
every closed cell element.
[0095] Referring to FIGS. 20 and 21, there is shown an embodiment
in which each tubular element 1 is made up of two different shapes
of closed cell element which alternate around the tubular element.
The first shape of closed cell element, illustrated under reference
50 is similar to that of the closed cell elements described above
with reference to FIG. 3, except that the loops 30 on one side of
the rhombic shaped structure are positioned at the end of a pair of
extended arms 51,52. As a result these "extended" loops 30
protrude, in the axial direction of the stent, with respect to the
remaining parts of the tubular element 1, and are thus able to
interlock with the next adjacent tubular element.
[0096] FIGS. 22 to 24 illustrate an embodiment similar to that of
FIGS. 20 and 21 but in which the extended loops 30 are open at
their neck, as distinct from the arrangement in FIGS. 20 and 21,
where each extended loop 30 takes the form of a closed ring which
is attached at the ends of the arms 51,52.
[0097] In both embodiments, the closed cell elements between the
elements 50 are of different shape to the elements 50. These
elements, given the reference 53, each comprise two rhombic-shaped
sections 54,55 which are joined by a narrow open neck portion
57.
[0098] The joining of adjacent tubular elements is shown in FIG.
24. FIG. 24 actually shows the embodiment of FIGS. 22 and 23, but
it will be understood that the same interlocking technique can be
used for the embodiment of FIGS. 20 and 21. In relation to FIG. 24,
it should also be noted that the drawing shows the tubular elements
in their expanded state--i.e. in a state in which they would not
ordinarily be interlocked--see above.
[0099] The aperture 56 formed within the loop 30 in the embodiment
of FIGS. 20 and 21 could be used as a well for containing a
therapeutic agent, in the manner described above. For this purpose,
the aperture 56 may be a through aperture, plugged at its inner
end, or may be a blind bore, opening into the outer surface
only.
[0100] The stent which has been described is expandable between an
unexpanded state (in practice, probably the crimped condition
mentioned above), in which it is able to be guided inside the lumen
through a body duct, such as a blood vessel, for example, and an
expanded state, in which the stent, after a uniform expansion,
comes into contact with the inner wall of the body duct, defining a
passage of approximately constant diameter inside said duct.
[0101] The stent will generally be forcibly expanded mechanically
under the action of a force exerted radially outwards, for example
under the effect of the inflation of a balloon. However, the stent
may be of the "auto-expandable" type, i.e. capable of changing by
itself from a first, unexpanded condition under stress, enabling it
to be guided through the body duct, to a second, expanded, working
condition.
[0102] The stent may be made of any material compatible with the
body duct and the body fluids with which it may come into
contact.
[0103] In the case of an auto-expandable stent, it will be
preferable to use a material with a recovery capacity, for example,
stainless steel, Phynox.RTM. or nitinol.
[0104] In the case of a stent utilising a forced expansion, a
material with a low elastic recovery capacity may be used to
advantage. Examples are metallic materials such as tungsten,
platinum, tantalum, gold, or stainless steel.
[0105] The tubular elements 1 may be manufactured from a hollow
tube with an approximately constant thickness corresponding to the
desired thickness. The shape of the tubular elements may be formed
either by laser cutting followed by electrochemical polishing, or
by chemical or electrochemical treatment.
[0106] The tubular elements may alternatively be manufactured from
a sheet of approximately constant thickness corresponding to the
desired thickness of the stent. The geometric configuration of the
tubular elements can be obtained either by laser cutting followed
by electrochemical polishing, or by chemical or electrochemical
treatment. The sheet cut in this way is then rolled up to form a
cylinder and welded to give the desired final structure.
[0107] After assembly of the tubular elements 1 into a stent of the
desired length, the stent can be deployed in a manner known per se.
In the case of a stent utilising mechanically forced expansion, the
insertion system will preferably comprise a balloon catheter onto
which the stent will be crimped in the unexpanded state before
being introduced into an insertion tube for guiding it to the site
to be treated.
[0108] The stent of the invention can be intended for both
temporary or permanent placement in the duct or vessel to be
treated.
* * * * *