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|United States Patent Application
;   et al.
December 2, 2004
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.
Andersen, Erik; (Roskilde, DK)
; Wen, Ning; (Chantilly, FR)
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
March 10, 2004|
September 5, 2002|
|Current U.S. Class:
|Class at Publication:
Foreign Application Data
|Sep 11, 2001||GB||0121980.7|
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
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
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
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
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
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,
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
 This invention relates to an expandable tubular stent for
implantation in the lumen of a body duct in order to ensure a passage
 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.
 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
 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.
 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.
 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
 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.
 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.
 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:
 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.
 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
 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
 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.
 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.
 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.
 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.
 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
 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.
 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
 Other arrangements of closed cell elements are possible, according
to the circumstances.
 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.
 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.
 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.
 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.
 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.
 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
 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.
 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.
 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.
 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.
 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.
 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:
 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
 FIG. 2 is a view corresponding to FIG. 1, but showing just a single
 FIG. 3 is an enlarged view of one of the closed cell elements in
the embodiment of FIG. 1;
 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"
 FIG. 5 is a perspective view of a single tubular element from the
stent of FIG. 1;
 FIGS. 6 and 7 are views similar to FIGS. 4A and 4B respectively,
but showing the stent in the crimped condition;
 FIGS. 8 and 9 are views similar to FIGS. 4A and 4B respectively,
but showing the stent in the expanded condition;
 FIGS. 10 and 11 are views similar to FIG. 4B, but showing two
further embodiments showing both the first and second aspect of the
 FIG. 12 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
 FIGS. 12A, B and C are views on the lines A-A, B-B and C-C
respectively of FIG. 12;
 FIG. 13 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 12;
 FIG. 14 is an enlarged view of part of FIG. 13;
 FIG. 15 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
 FIGS. 15A and B are views on the lines A-A and B-B respectively of
 FIG. 16 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 15;
 FIG. 17 is an enlarged view of part of FIG. 16;
 FIG. 18 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
 FIG. 18A is a view on the line A-A of FIG. 18;
 FIG. 19 is a view similar to that of FIG. 5, but showing the
embodiment of FIG. 18;
 FIG. 20 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
 FIG. 21 is a view similar to FIG. 5, but showing the embodiment of
 FIG. 22 is a view similar to FIG. 2 showing a still further
embodiment of the invention;
 FIG. 23 is a view similar to FIG. 5, but showing the embodiment of
FIG. 22; and
 FIG. 24 is a view similar to FIG. 4b, but showing the embodiment of
 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.
 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.
 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
 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.
 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.
 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.
 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.
 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.
 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
 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
 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
 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:
 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.
 2) The crimped stent has a high degree of longitudinal flexibility
since it is not restrained by the inter-element linking members of known
 3) The crimped stent has a high degree of longitudinal
conformability due to its tubular elements being interlocked at multiple
 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.
 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.
 6) Once deployed the stent has a good vessel repartition and vessel
scaffolding, with homogeneous support for the vessel wall--see
particularly FIG. 8.
 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
 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.
 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.
 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.
 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.
 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
 FIGS. 12 to 19 illustrate further embodiments similar to that of
FIGS. 10 and 11, showing alternative arrangements of wells.
 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
 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.
 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.
 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.
 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.
 The advantages of stents incorporating wells, as described above,
can be summarised as follows:
 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.
 2) The absence of a polymer matrix coating eliminates any potential
biocompatibility problems arising from their use.
 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
 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.
 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.
 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.
 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.
 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.
 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.
 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.
 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
 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.
 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.
 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.
 The stent may be made of any material compatible with the body duct
and the body fluids with which it may come into contact.
 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.
 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
 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
 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.
 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.
 The stent of the invention can be intended for both temporary or
permanent placement in the duct or vessel to be treated.
* * * * *