U.S. patent application number 13/686448 was filed with the patent office on 2013-06-06 for stent and stent retrieval system and a method of pulling a stent into a tubular member.
This patent application is currently assigned to STENZ CORPORATION. The applicant listed for this patent is Stenz Corporation. Invention is credited to Zaza Alexandrovich Kavteladze.
Application Number | 20130144371 13/686448 |
Document ID | / |
Family ID | 34931939 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130144371 |
Kind Code |
A1 |
Kavteladze; Zaza
Alexandrovich |
June 6, 2013 |
Stent and Stent Retrieval System and a Method of Pulling a Stent
into a Tubular Member
Abstract
A stent has an engagement member (9). A stent retrieval system
has a tubular member (13) and a retrieval member (14) with an
engagement means (15). The engagement member is attached to an end
row of cells of the tubular stent body (1). The cells in one
annular row of cells are interconnected with the subsequent row of
similarly oriented cells (2a) at areas of interconnection (7) which
in the subsequent annular row of cells are circumferentially offset
with respect to the connections (8) between the cells in said
subsequent annular row of cells.
Inventors: |
Kavteladze; Zaza Alexandrovich;
(Potomac, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Stenz Corporation; |
The Hague |
|
NL |
|
|
Assignee: |
STENZ CORPORATION
The Hague
NL
|
Family ID: |
34931939 |
Appl. No.: |
13/686448 |
Filed: |
November 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11597759 |
Jul 1, 2008 |
8343210 |
|
|
13686448 |
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Current U.S.
Class: |
623/1.11 |
Current CPC
Class: |
A61F 2/95 20130101; A61F
2250/0067 20130101; A61F 2002/9511 20130101; A61F 2002/9528
20130101; A61F 2/90 20130101 |
Class at
Publication: |
623/1.11 |
International
Class: |
A61F 2/95 20060101
A61F002/95 |
Claims
1. A stent and stent retrieval system, said stent retrieval system
comprising a tubular member with a lumen terminating in a distal
end opening, and a retrieval member having an engagement mechanism,
the tubular member and the retrieval member being mutually axially
displaceable while the retrieval member extends in said lumen of
the tubular member, said stent comprising an engagement member
engagable with the engagement mechanism, and a tubular body having
a plurality of annular rows of cells, with the annular rows being
arranged axially one after the other, adjacent annular rows being
joined together at interconnections, and adjacent cells within an
annular row of cells being joined together at connections, the
interconnections being circumferentially offset from the
connections within a common annular row of cells, an end annular
row of cells having first cell sides together forming a
circumferentially closed loop with an attachment point that is
circumferentially offset from the connections in the end annular
row of cells, the engagement member being secured to the attachment
point.
2. A stent and stent retrieval system as in claim 1, including at
least three attachment points circumferentially spaced about said
loop.
3. A stent and stent retrieval system as in claim 2 wherein said
engagement member includes tie members extending from a junction to
respective ones of said attachment points.
4. A stent and stent retrieval system as in claim 3 wherein said
junction is located in a longitudinal central axis of the stent.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. Nonprovisional
patent application Ser. No. 11/597,759 titled "STENT AND STENT
RETRIEVAL SYSTEM AND A METHOD OF PULLING A STENT INTO A TUBULAR
MEMBER" and filed Jul. 1, 2008, the content of which being
incorporated herein in its entirety.
SUMMARY OF THE INVENTION
[0002] The present invention relates in a first aspect to a stent
and a stent retrieval system, said retrieval system comprising a
tubular member with a lumen terminating in a distal end opening,
and a retrieval member with at least one engagement means, the
tubular member and the retrieval member being mutually axially
displaceable while the retrieval member extends in said lumen of
the tubular member, said stent comprising at least one engagement
member to which said at least one engagement means can engage and a
tubular body of a plurality of annular rows of cells that are
interconnected and located one after the other in the axial
direction of the tubular body, the cells in one annular row of
cells being interconnected with the subsequent row of similarly
oriented cells at areas of interconnection which in said subsequent
annular row of cells are circumferentially offset with respect to
the connections between the cells in said subsequent annular row of
cells.
[0003] Such a stent and a stent retrieval system is known from WO
2004/008991 disclosing a stent having in one end larger cells that
are not arranged in annular rows but instead in rows extending over
only one side of the stent. The cells in this end structure have
been given a more coarse structure, and in the end row there is
only a single cell into which an engagement member can engage.
[0004] U.S. Pat. No. 5,643,309 describes a stent provided with a
number of inward projecting hooks at a distance from each end of
the stent. The stent retrieval system comprises an outer sheath and
a tubular member with an engagement ring fixed to carrier legs on
the outside of the tubular member, and an inner retrieval member
provided displaceably in the tubular member. The retrieval member
is also provided with an engagement ring fixed to carrier legs on
the outside of the member. When the stent is to be removed from a
vascular site, the sheath is introduced into the stent and the
tubular member and the retrieval member are both advanced out of
the sheath and tubular member, respectively, so that both
engagement rings are allowed to expand within the stent. The two
engagement rings are brought into engagement with the two sets of
hooks on the stent, and then the tubular member and the retrieval
member are moved in opposite directions so that the stent is pulled
out to a longer length by the action of the rings on the hooks. Due
to the elongation of the stent its diameter is reduced to such an
extent that the stent is released from the vascular wall, and then
the stent is pulled out. The system is complicated and difficult to
use.
[0005] EP 0 829 242 A1 and US 2002 0120277 A1 both describe a stent
retrieval system comprising a tubular member with a lumen
terminating in a distal end opening, and a retrieval member with a
plurality of engagement means shaped as tines with outward open
hooks that after introduction to a position inside the stent can be
moved radially outwards into the wire mesh of the stent. When the
retrieval member is withdrawn the hooks engage in the wire mesh and
pulls the stent out to a longer length. As the stent is pulled
longer its diameter is reduced. The combined pulling action and
diameter reduction acts to tear the stent loose from the vascular
wall.
[0006] In U.S. Pat. No. 5,910,144 a plurality of gripper elements
can be moved to the position of a stent and be allowed to radially
spread out to a larger diameter than the stent diameter so that the
gripper elements can be pushed in on the outside of the stent. Then
the grippers are moved radially together so that the stent is
compressed to a smaller diameter and can be pulled out.
[0007] It is in the first aspect of the present invention an object
of the invention to obtain a stent and a stent retrieval system
providing a more secure retrieval of the stent.
[0008] To meet this object the stent and stent retrieval system is
characterized in that the end row of cells is an annular row of
cells comprising first cell sides forming at least one
circumferentially closed loop in which the individual cell has an
attachment point, that said at least one engagement member
comprises at least three tie members that are mutually connected at
a junction and extend individually from the junction to the
attachment point of an associated cell, and that the attachment
points in the annular end row of cells are circumferentially offset
with respect to the connections or areas of interconnection at the
end of the tubular body between the cells in said end row.
[0009] The at least three tie members in the engagement member
provide a firm and suitably distributed grip in the first row of
cells at the end of the tubular body so that the cells are folded
in a symmetrical manner. By attaching the engagement member to the
annular end row of cells at points that are circumferentially
offset with respect to the connections between the cells in the
row, a pulling act on in the engagement member will cause
deformation of the cell sides extending between the individual
attachment point and the adjacent connections between cells. The
initial pull draws the engagement member towards the tubular member
and into abutment with the distal end opening thereof, and during
further pulling the engagement member is pulled into the lumen of
the tubular member and the end row of cells is brought to abutment
with the rim of the opening. As the engagement member is pulled
into the lumen it acts on the end row of cells and cause some
deformation thereof. As these deformations act locally and only to
the end side of the annular row of cells, that row of cells will
radially collapse to a smaller diameter at the end side, but remain
at almost the initial diameter at the opposite side of the annular
row. It is an advantage that the tie members extend individually to
the attachment points because this on the one hand minimizes any
obstructing effect from the tie members on the flow in the vascular
vessel as any filtering effect or the like on the flow in the
vessel is highly undesired, which could easily have occurred had
the tie members been interconnected in between the junction and the
attachment points, and on the other hand any pull at the junction
is automatically evenly balanced between the tie members when they
extend individually to the attachment points.
[0010] The collapsed end side can be drawn radially down towards
and into the distal end opening by pulling in the engagement
member. As this is done, the cell sides in the end row of cells are
turned and/or bend inwards in an angle that increases as the end
side is pulled down to a smaller diameter. This pattern of movement
of cell sides is very advantageous, especially when the stent is to
be removed from a vascular site where it has been temporarily
positioned for a desired period of time, because only minimum
damage is done to the vascular wall.
[0011] When a stent is placed in a vessel, e.g. a blood vessel,
tissue will within few days be formed around the stent material.
Such ingrowth of tissue makes the stent become an integral part of
the vascular wall. The ingrowth results in a layer of tissue,
called intima, on the inside of the stent. If a stent is removed by
using the prior art techniques of stent removal where the diameter
of the stent is reduced by pulling the whole stent out to a longer
length the tearing loose from the intima acts along a large area of
the vascular wall, and the risks of damaging the vascular wall are
high. If the vessel is weak, which is often the case in places
where a stent is utilized, there is even a quite high risk of
tearing the vessel apart when the stent is removed. With the
present invention it has been recognized that the tearing apart can
be caused by an axially directed pull in the stent in conjunction
with a radial contraction that acts along a substantial length of
the stent.
[0012] The stent according to the present invention is not
subjected to any substantial axial pull during removal. The pulling
in the engagement member only needs to be sufficient to pull down
one side of one annular row of cells. When this pulling is effected
the vascular wall remains supported by all remaining cells in the
annular rows that have not yet been moved into the tubular member.
The stent is thus kept axially stationary with respect to the parts
of the vascular wall being in contact with the stent. The annular
row of cells which is in the process of being pulled radially down
into the tubular member is released in a gentle manner from the
vascular wall. This is so, because only one side of the row is
initially moved free of the vascular wall, and then the cell
material is gradually moved free in direction of the other side of
the row due to the cell material turning or bending inwards in the
vessel. When one side of the annular row has been moved into the
distal end opening, the tubular member is pushed forwards in
direction of the other side of the annular row located at the
subsequent annular row of cells.
[0013] During this pushing of the tubular member the cell material
enters the distal end opening and then the other side of the
annular row is pulled down to a smaller diameter and in doing so
the cell material is moved radially inwards and out of the vascular
wall. Then the process is repeated with the subsequent annular rows
of cells. The areas of interconnection between one row and the
subsequent row are offset in the circumferential direction with
respect to the connections between the cells in the subsequent row.
A pulling action in interconnections will cause deformation of the
cell sides extending between the individual attachment point and
the adjacent connections between cells. As these deformations act
locally and only to the end side of the annular row of cells that
row of cells will radially collapse to a smaller diameter at the
end side, but remain at almost the initial diameter at the opposite
side of the annular row. Then the tubular member can be pushed
forward to the next annular row. The procedure is repeated until
the stent has been placed completely within the tubular member, and
then the retrieval system is withdrawn from the vascular
system.
[0014] From the above explanation it follows that the cell material
of the stent is released from the vascular wall by effecting
radially acting local pulls in the cell material anchored in the
vascular wall so that the cell sides are moved towards the centre
line of the tubular body during the release from the vascular wall,
and the radially directed pulling forces act symmetrically on the
tubular body in the circumferential direction. The pulling forces
furthermore only act on the annular row of cells that are in the
process of collapse. The cells in the tubular body located more
than one annular row of cells away from the collapsing cells are
consequently unaffected by the forces used to collapse cells.
[0015] Also the annular end row of cells is released from the
vascular wall my mainly radially acting forces caused by the
engagement member being drawn in through the distal end opening of
the tubular member. The tie members collectively and simultaneously
act on the attachment points in all cells in the end row when the
engagement member is moved into the lumen of the tubular member.
The tie members extend directly from the common junction to their
individual attachment point on the cell to which the individual tie
member is connected.
[0016] The stent retrieval system can also be utilized to position
a stent in the tubular member from an unloaded stent condition
before the stent is introduced into a patient. The retrieval system
can in other words be used as a system for loading a stent into a
tubular member, e.g. an introducer system.
[0017] In an embodiment the individual attachment point is
circumferentially located approximately at the middle between the
two adjacent connections. With such a location the cells in the end
row will collapse evenly about the attachment points. It is of
course also possible, but not preferred, to position the attachment
points in an asymmetric manner with respect to the adjacent
connections.
[0018] In another embodiment the individual area of interconnection
to a subsequent annular row is circumferentially located
approximately at the middle between the two adjacent connections.
With this location the cells in the subsequent row will collapse
evenly about the areas of interconnection. It is of course also
possible, but not preferred, to position the areas of
interconnection in an asymmetric manner with respect to the
adjacent connections.
[0019] In a preferred embodiment the first cell sides extending
from the individual attachment point form mutually on the side of
the attachment point an angle (.delta..sub.1) of less than
176.degree.. As a consequence of this design the first cell sides
have to be raised through the angle of 180.degree. before end cells
in the end row begin to collapse. During this movement the diameter
of the end of the tubular body is slightly increased and this
causes some resistance which allow the engagement member to be
drawn partly into the distal end opening and said end opening to be
pushed closer towards the end row so that the tie members are
oriented more radially, or in mainly radial directions, in areas
adjacent the attachment points before the cells in the end row are
brought to collapse. This design enhances the effect of causing
radial directed pulls in the cell sides during release of the cell
sides from the vascular wall.
[0020] In an embodiment the same principle is utilized in the
internal rows of cells in the tubular body, in that the individual
annular rows of cells located within the tubular body the first
cell sides form at least one circumferentially closed loop in which
the first cell sides extending from the individual area of
interconnection form mutually on the side facing the end row with
the attachment points an angle (.delta..sub.2) of less than
176.degree.. This embodiment can be used either in conjunction with
the just mentioned design of the annular end row or on its own if
the increased resistance against pulling down the annular end row
is considered undesirable. In any case, in this embodiment the
second cell sides will during their being pulled into the tubular
member act as described above in connection with the tie members so
that they will be oriented more radially, or in mainly radial
directions, in vicinity of the areas interconnection just before
the cells in the subsequent row are brought to collapse.
[0021] In a preferred embodiment the first cell sides in the
individual annular row of cells form at least one circumferentially
closed loop in which said first cell sides constituting the loop
extend in directions forming angles in the range from 60.degree. to
120.degree. with the axial direction of the tubular body, when the
tubular body is in an unloaded state. The closed loop provides the
stent with high stiffness against radial compression and thus good
properties for keeping a vessel patent, even at locations where the
vessel exhibits a bend, but more importantly the closed loop has a
high ability of maintaining its initial diameter when a local pull
is performed in adjacent cell material. If the angle deviates well
above 30.degree. from 90.degree. the tendency of maintaining the
initial diameter can become feeble. It is preferred that the
angular range is in the range from 70.degree. to 110.degree.,
because the annular row of cell will then only to a small extent
obtain a larger diameter when the first cell sides are pulled in
direction of the distal opening. If the angular range is limited to
the range from 75.degree. to 105.degree. the pull in the engagement
member can be kept more constant.
[0022] In an embodiment second cell sides in the individual annular
row of cells interconnect the circumferentially closed loops and
extend at least along part of their length in directions forming
angles in the range from 20.degree. to 70.degree. with the axial
direction of the tubular body, when the tubular body is in an
unloaded state. The flexibility of the second cell sides and the
width of the individual annular row are comparatively well balanced
when the angles are within the stated range. The range is
preferably from 30.degree. to 60.degree..
[0023] Preferably, said first cell sides extend substantially in a
radial plane at the distal end opening of the tubular member, when
said second cell sides in the adjacent annular row of cells have
been pulled in through the distal end opening to extend from said
distal end opening and into the tubular member. When the first cell
sides can turn or flex to extend in or approximately in a radial
plane when the second cell sides have been pulled through the
distal end opening then the tubular body can maintain its initial
diameter for as long time as possible.
[0024] It is preferred that the outer diameter of the subsequent
loop outside the tubular member remains mainly unaffected while a
loop is pulled into the distal end opening. As the subsequent loop
is not affected the vascular wall at the subsequent loop is neither
affected.
[0025] The junction of the engagement member is preferably located
at the longitudinal central axis of the tubular body. By locating
the junction at the central axis establishment of the engagement
between the engagement means and the engagement member is more
easily accomplished. The pull in the engagement member is also more
evenly distributed to the attachment points when the junction is
located at the central axis where the junction is symmetrically
positioned with respect to the end row of cells.
[0026] In a most preferred embodiment the tie members a length so
that the junction is located at least 0.5.times.W away from the
annular end row of cells at the end of the tubular body, W being
the width in the axial direction of the annular row of cells. By
positioning the junction at such a distance from the end loop, this
loop is more easily subjected to mainly radially acting forces when
the junction is pulled in through the distal end opening because
the length of the tie members assists to the bending of the tie
members in the area in front of the distal end opening before the
tie members are pulled completely into the lumen. The bent tie
members will gradually pull the attachment points radially inwards
as the tubular member is pushed in direction of the end loop, until
the attachment points are located at the distal end opening with a
mutual radial separation corresponding to the inner diameter of the
lumen in the tubular member. This embodiment can be utilized on its
own or in con junction with the above mentioned embodiment where
the first cell sides form an angle of less than 180.degree. on the
side facing the attachment point to which the first cell sides are
connected.
[0027] In an embodiment the at least one engagement member
comprises magnetic material. The engagement member can e.g. be of a
ferromagnetic material which can attract a magnet, or it can be a
magnet with a certain direction, such as in the axial direction or
the radial direction of the tubular body. In case the magnetic
material has a polarity, this polarity can be opposite to the
polarity of a magnetic material located on the engagement means so
that the engagement means is attracted to the engagement member.
Such an attraction effect can also be obtained with a magnet on one
of the engagement member and the engagement means, when the other
of the two parts is of a ferromagnetic material. The purpose of the
magnetic materials is to facilitate the establishment of the
engagement grip in the engagement member when this is located
inside a vessel.
[0028] The inner lumen of the tubular member can have a diameter in
the range from 20% to 80%, preferably from 30% to 60%, of the outer
diameter of the tubular body in the unloaded state of the tubular
body. Although it is possible to use a tubular member with a lumen
of less than 20% of the outer diameter of the tubular body, there
is not obtained any advantage by this, but to the contrary the
lumen gets so diminutive that is may be more difficult to receive
the tubular body in the lumen. The upper limit of 80% is sufficient
to obtain full release of the stent from the tubular wall. The
preferred range from 30% to 60% entails the advantages of providing
more space in the lumen and a comparatively small outer diameter of
the tubular member, thus facilitating the introduction of the stent
retrieval system through the vascular system to the stent
position.
[0029] In an embodiment the tubular body is provided with at least
one additional means selected from the group consisting of a
medically active substance, a bioactive factor inhibiting
proliferation of a tumor cell, a bioactive substance, a bioactive
agent, a drug, and a coating layer for controlled release of one or
more of a bioactive material, a medically active substance or a
bioactive factor. The bioactive substance or agent can e.g. be of a
kind that reduces negative influences from the stent on the
vascular wall or of a kind that enhances the effects of placing a
stent in the vascular system. Alternatively the stent can be
utilized as a carrier for introducing the said substance, agent,
factor, or drug into a vascular site where localized release of
said substance, agent, factor or drug is desired. The stent is kept
in place in the vascular system in the period required for
obtaining the desired release of the substance, agent, factor or
drug at the vascular site, and then the stent is removed by using
the stent retrieval system. The stent retrieval system is in
particular advantageous for such use, because of the very gentle
removal procedure where the stent material is released from the
vascular wall without or almost without subjecting the vascular
wall to substantial forces directed in the axial direction of the
tubular body. The annular rows of cells are individually released
from the vascular wall by the mainly radial collapse of the rows.
The vascular wall is quite often very weak at the locations where
local release of drugs etc. is required. The weakening can e.g. be
caused by the presence of tumor cells in vicinity of the vascular
wall. Because of the gentle removal of the stent the risks of
damaging the vascular wall by the removal are reduced to a minimum.
It is consequently possible to treat even quite weak vascular sites
with a temporary stent, which has hitherto not been possible.
[0030] In an embodiment said additional means has a predetermined
active period in the range from three days to one month, preferably
from 5 to 14 days. Ingrowth of an intima layer on the inside of the
stent will increase with the duration of the placement. Due to the
gentle removal of the stent it becomes possible to treat the
vascular site for a longer period, such as up to one month, and yet
remove the stent without inflicting intolerable damage to the
vascular site.
[0031] It is possible to provide the tubular body with a tubular
covering, such as a weave of graft material. The covering can serve
to provide the stent with a large surface area, which cam be an
advantage, interalia in cases where large amounts of a drug or a
bioactive substance or agent needs to be introduced to the vascular
site. The covering can also be required in order to obtain
temporarily closure of a branch vessel, an aneurysm or another
vascular malformation.
[0032] In another aspect the present invention relates to a method
of pulling a stent into a tubular member, the stent comprising at
least one engagement member and a tubular body having a plurality
of annular rows of cells that are interconnected and located one
after the other in the axial direction of the tubular body, where
at least one engagement means grips the at least one engagement
member and pulls it through a distal end opening of the tubular
member and into an inner lumen of said tubular member, said annular
rows of cells having an initial diameter which is larger than the
diameter of said inner lumen. Such a method is known from the
abovementioned U.S. Pat. No. 5,643,309.
[0033] In relation to this second aspect the object of the
invention is to load a stent into a tubular member in a simple
manner and without use of complicated additional equipment.
[0034] With a view to this the method is characterized by pulling
said at least one engagement member into and along the lumen of the
tubular member and pushing the tubular member towards the tubular
body, whereby the annular rows of cells are brought towards the end
opening and are collapsed one-by-one at the end opening to a state
with a radially reduced diameter, while the annular rows of cells
maintain their initial diameter at least until they are within one
row from said end opening.
[0035] The forces required to move the stent into the tubular
member are quite low because the forces act mainly on the annular
row of cells positioned immediately in front of the tubular
opening. When cell sides in the annular row are pulled against the
rim of the opening these cell sides deflect under the action of the
rim to be oriented towards the inner lumen in the tubular member.
During the continued pull in the engagement member the cell sides
reorient themselves at the radially reduced diameter corresponding
to the inner lumen in the tubular member. Then the tubular member
can be pushed towards the stent so that the rim of the end opening
is moved towards the other side of the annular row of cells. During
this movement the inner cell sides in the annular row are brought
into the lumen, and because of the smaller diameter of the lumen
these inner cell sides effect an increasingly strong radially
directed pull in the cell sides at the opposite side of the annular
row of cells so that these cell sides come to extend from the next
annular row of cells at the initial diameter of the stent and
inwards to radially more closely spaced locations at the end of the
inner lumen of the tubular member. Then the procedure can be
repeated with the next annular row of cells.
[0036] As there is no need for using complicated equipment in order
to load the stent into the tubular member by the method of the
present invention the loading can be performed shortly before the
stent is to be used. This provides the substantial advantage of
allowing a preparation of the stent with a coating having active
properties of time-limited effect. If the active property of the
coating only lasts for e.g. 7 or 14 days then the effects are lost
during shelving of manufactured stents. By applying the coating to
the stent shortly before the stent is to be used, and by loading
the coated stent into the tubular member in the above-mentioned
manner, the stent is ready for use without any decay of the active
property.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The invention will be explained in detail in the following
by means of examples of embodiments with reference to the schematic
drawing, in which
[0038] FIG. 1 is a plane view to illustrate the cell structure used
in an embodiment of a tubular body of a stent according to the
invention,
[0039] FIG. 2 depicts a side view of the stent having a cell
structure as illustrated in FIG. 1,
[0040] FIGS. 3a to 3e show side views of sequential steps of the
stent of FIG. 2 being pulled into a tubular member by use of a
retrieval system,
[0041] FIG. 4 shows a cross section along the line IV-IV of FIG. 3e
viewed from the left side of FIG. 3e, and
[0042] FIG. 5 shows a plane view corresponding to the view of FIG.
1 of another embodiment of a stent according to the invention made
by laser cutting or etching in a tubular member.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIGS. 1 and 2 illustrate the structure of a stent according
to the invention, the stent being in an unloaded state. The stent
is made up of wires that are bent or wound in a pattern to form a
tubular body 1, see FIG. 2. For the sake of ease the cell pattern
is illustrated in FIG. 1 in a cut up, unfolded state of the stent.
The pattern is formed by annular rows of arrow-head-shaped or
heart-shaped cells 2a, the rows being interconnected and arranged
one after the other in the axial direction A of the tubular body 1.
The annular rows of cells 2a have the same orientation in the
tubular body. In between these rows of cells there are cells 2b
having the opposite orientation in the axial direction, viz. the
arrow-head or heart point in the opposite direction.
[0044] The tubular body is cylindrical in the unloaded state, and
consequently all the annular rows, including the annular end row of
cells are capable of expanding into contact with the vascular wall,
and preferably the annular end row has the same diameter as the
subsequent rows when the tubular body is in the unloaded state, but
it can alternatively also have a larger diameter than the
subsequent annular row.
[0045] Each cell 2a has two first cell sides 3 converging towards
one another to become mutually connected in an area of
interconnection 8 between the cells 2a in one row and the cells 2a
in the subsequent annular row. The first cell sides 3 form at
either end side of the annular row of cells a circumferentially
closed loop 20 in which the first cell sides extend at an angle
.alpha. of approx. 107.degree. with respect to the axial direction
A. On the side facing the area of interconnection the two first
cell sides 3 extending from the area of interconnection 8
consequently form an angle
.delta.=360.degree.-2.times..alpha.=146.degree.. Each cell 2a also
has two mutually converging second cell sides 4 converging towards
one another to become mutually connected in connections 7 between
the cells 2a in the annular row. The second cell sides 4
interconnect the loops 20 at either side at the annular row of
cells 2a. The second cell sides 4 extend in directions forming an
angle .beta. of approx. 38.degree. with respect to the axial
direction A. In other embodiments the mentioned angles can take
other values. The angle .alpha. can e.g. be in the range from
60.degree. to 120.degree., and the angle .beta. can e.g. be in the
range from 20.degree. to 70.degree.. Preferably the angle
.delta..sub.1 or .delta..sub.2 is less than 180.degree., and
suitably less than 176.degree..
[0046] The cell sides 3 are positioned opposite to cell sides 4 of
the same cell, and the cells 2a of each cell row are connected by
means of connections 7 forming loop-shaped nodes. The areas of
interconnection 8 interconnecting one annular row of cells with the
next row of cells form a node made up by wires wound once around
each other. In the embodiment shown, the connections 7 and areas of
interconnection 8 are mutually circumferentially offset with a
distance corresponding substantially to the circumferential extent
of one of the cell sides 3.
[0047] FIG. 2 depicts the tubular body 1 of the stent. An
engagement member 9 is attached to an end row 12 of cells located
at the left end of tubular body 1. The engagement member 9 is
formed by four tie members in the form of wire sections, which are
connected to each other at a junction 10 located at the
longitudinal central axis of the tubular body 1. The individual tie
member is connected to the tubular body 1 at an attachment point
11, the attachment points 11 being circumferentially offset with
respect to the connections 7 at the end of the tubular body 1 with
a distance corresponding substantially to the circumferential
extent of one of the first cell sides 3. This locates each
individual attachment point 11 at the middle of the cells 2a
between the two adjacent connections 7 in the annular row 12 of
cells at the end of the tubular member 1. The tie members have a
length so that the junction 10 is located approximately 1.0.times.W
away from the loop of the end row 12 of cells at the end of the
tubular body 1, W being the width of one row of cells in the axial
direction of the tubular body. There is preferably one tie member
extending from each attachment point to the central junction 10,
and preferably each cell in the annular end row of cells has one
attachment point.
[0048] FIGS. 3a to 3d show sequential steps of the stent of FIG. 2
being pulled into a tubular member 13 of a retrieval system
according to the invention. A retrieval member 14 is located
displaceable within the lumen of the tubular member 13 and has a
longer length than the tubular member so that it can extend out of
both the distal end and also out of the proximal end wherefrom it
can be manipulated. The retrieval member is provided with an
engagement means in the form of a hook 15 at its distal end. The
retrieval member is e.g. made of steel or another material of
sufficient strength.
[0049] The tubular member 13 terminates at its distal end in a
distal end opening surrounded by an annular end surface 16 on the
tubular member. In the illustrated embodiment the diameter of the
tubular member 16 corresponds to approximately 55% of the initial
diameter of the tubular body 1 when the latter is in the unloaded
(relaxed) state.
[0050] In FIG. 3a the retrieval member 14 of the retrieval system
has engaged the tie members of the engagement member 9 at the
junction 10 by means of the hook 15 being hooked around tie
members. In the illustration the engagement member has been pulled
towards the tubular member to the position in which the tie members
abut the annular end surface 16 of the tubular member 13. The
tubular body 1 is seen to still remain in its unloaded state.
[0051] FIGS. 3b to 3e show how the third row of cells is pulled
into the tubular member 13. In FIG. 3b the hook 15 has pulled the
engagement member 9 and two rows of cells into the tubular member
13 of the retrieval system, and the loop 20 at the proximal side of
the third annular row of cells is located at the annular opening.
The areas of interconnection 8 interconnecting the second and third
rows of cells have been pulled inwards toward the central axis of
the tubular body 1 and have just passed by the annular end surface
16 and entered the end opening of the tubular member 13. It is the
second cell sides 4 of the second row of cells that have pulled the
areas of interconnection of the second row of cells inwards towards
the central axis of the tubular body 1, bending the first cell
sides 3 of the third row of cells inwards.
[0052] As can be seen from the illustration in FIG. 3b, the second
cell sides 4 of the third row of cells are slightly deformed. Thus,
further pulling in the retrieval member 14 causes the first cell
sides 3 and the connections 7 of the third row of cells to be
radially drawn down to and pass in through the end opening of the
tubular member 13, see FIGS. 3c and 3d. It should be noted that in
FIGS. 3b to 3d the fourth row of cells remains unaffected of the
collapse of the third row of cells and thus has not begun to
collapse.
[0053] Once the connections 7 in the loop 20 at the proximal side
of the third annular row have been drawn into the distal end
opening of the tubular member, tubular body 13 can be displaced to
the right hand side of the figure, viz. in direction of the tubular
body. During this displacement of the tubular member the second
cell sides 4 in the third annular row are moved into the lumen of
the tubular member under concurrent diminishing of the diameter of
the cells to correspond to the lumen.
[0054] In FIG. 3e the tubular member has been advanced to be
positioned with the distal end opening located near the proximal
end loop 20 of the fourth annular row of cells, the first cell
sides 3 of the fourth row of cells are bending inwards and are
starting to pull the fourth row of cells into the tubular member
13. The process illustrated in FIGS. 3b to 3e with respect to the
third row of cells is then repeated for the fourth row of cells,
and similarly so forth for the subsequent rows of cells until the
entire stent is located inside the tubular member.
[0055] In FIG. 4 the initial collapse of the fourth row of cells is
elaborated, the illustration showing a cross section along the line
IV-IV of FIG. 3e viewed from the left of FIG. 3e. In FIG. 4 the
first cell sides 3 of the proximal loop in the fourth row of cells
are partially collapsed and extend from the areas of
interconnection 8 inside the tubular member 13 and outwards to the
connections 7. The first cell sides 3 of the fourth row of cells
have been bend to form curved shapes forming a flower-like shape
with four leaves. The fifth row of cells is still in its initial
state, and the first cell sides 3 of the fifth row of cells extend
along the contours of the larger outer circle of the
illustration.
[0056] The engagement member on the stent can take other forms than
the one illustrated in the above. It can e.g. be embodied in the
form of several wires crossing each other, so that the junction 10
is formed of the wires intercrossing one another, but the tie
members are preferably joined at the junction, in particular if
they are of a flexible material. The tie members can be embodied as
flexible threads or they can be embodied as loops or eyes or legs
extending from the circumference of the end annular row of cells
and radially or obliquely inwards towards the centre line of the
tubular body. Preferably, only one tie member extends from the
junction to the individual attachment point, but one or more of the
attachment points can be connected to more than one tie member. The
engagement member can comprise a magnet or magnetic material. The
engagement means on the retrieval member can also be shaped with
several hooks or it can include a gripper means, a tongue, an eye
or a string to be fixed to the one or several engagement members on
the tubular body. What matters is that the engagement means can be
brought into a condition where the retrieval member can act with a
pulling force distributed to the engagement points on the
individual cells in the annular end row of the tubular body.
[0057] The length of the tie members can depart from the above
mentioned length causing the junction 10 to be located
approximately 1.0.times.W away from the loop of the end row 12. In
one embodiment the length of the tie members correspond to half the
diameter of the tubular body which causes the tie members to be
radially directed towards the junction, but preferably the tie
members are substantially longer. The tie members can also be
preshaped to locate the junction asymmetrically with respect to the
longitudinal central axis of the tubular body when there is no pull
in the junction and of sufficient flexible construction to allow
the junction to be centered once the engagement means establishes
the pull in the engagement means. This embodiment can be
advantageous when it is important to maintain the largest possible
unobstructed flow area through the tubular body during the
temporary placement thereof in the vascular vessel. In an
embodiment where the tie members are of flexible thread of having
an individual thread length of more than 1.0.times.W the tie
members can be folded and temporarily mounted in a storage position
on the end of the tubular body so that approximately the full lumen
of the tubular body is unobstructed during the placement in the
vascular vessel. When the stent is to be retrieved it is then
required to loosen the folded up tie members so that they are only
attached to the tubular body at the attachment points, before the
engagement means can be brought in proper engagement with the
engagement member.
[0058] FIG. 5 illustrates another embodiment of a stent according
to the invention made by laser cut-ting or etching of a tubular
member, the stent being in an unfolded state corresponding to FIG.
1 for the sake of illustration. In FIG. 5, parts similar to the
previous illustrations have been given similar numerals. The
operation of the embodiment of FIG. 5 corresponds substantially to
the previously described embodiment. Thus, in the embodiment of
FIG. 5 the connections 7 between the cells 2a, 2b and the points 8
of interconnection interconnecting subsequent rows of cells are
formed as S-shaped joints. This makes said connections 7 and said
interconnections 8 behave substantially similarly to the previously
described embodiment. The cells in the tubular body can be of
others cell patterns than the ones described. The cell sides can
e.g. have an undulating run and they can have unequal widths or a
width varying along the length of the cell side.
[0059] The number of cells in the individual annular rows of cells
can vary depending on the actual cell shape and the diameter of the
tubular body in its unloaded state. To give an example there can be
four cells of even orientation in the annular row, but there can
also be three cells or more than four, such as five, six or seven
cells of the same orientation. Preferably the number of attachment
points corresponds to the number of cells, and more preferably the
number of tie members corresponds to the number of attachment
points. However, if e.g. one or more of the cells are of weak or
more open construction in comparison to the other cells it is
possible to omit the attachment point on the weak cell.
[0060] The diameter of the tubular body in the unloaded state vary
with the application of the stent. For use in arteries the stent
can e.g. have a diameter in the range of 0.5 mm to 3 mm when it is
to be placed in diminutive arteries or veins, such as in the brain,
it can have a diameter in the range of 2 mm to 4 mm for coronary
use or pancreatic uses, it can have a diameter in the range from 6
mm to 12 mm for iliac, femoral, renal and carotid uses etc.
[0061] The stent can also be provided with a covering on a part of
or on the complete peripheral surface of the tubular body. The
stent can be made of nitinol thread, such as a round or flat
thread, or it can be of stainless steel, titanium, tantalum,
platinum, composite materials or of synthetic materials.
[0062] In an embodiment the stent is provided with a bioactive
material, such as heparin or another thrombin inhibitor,
anti-inflammatory steroids including but not limited to
dexamethasone and its derivatives, and mixtures of heparin and such
steroids. The bioactive material or agent can also be an
anti-proliferative agent such as methotrexate. The stent can e.g.
be placed in the arterial supply of the tumor to provide a means of
delivering a relatively high dose of the antiproliferative agent
directly to the tumor. The bioactive material can furthermore be a
vasodilator such as a calcium channel blocker or a nitrate. The
stent can also be provided with a drug, such as an anti-cancer
chemotherapeutic agent for delivery to a localized tumor, e.g.
tamoxifen citrate, Taxol or derivatives thereof. Proscar.RTM.,
Hytrin.RTM., or Eulexin.RTM.. Dopamine or a dopamine agonist such
as bromocriptine mesylate or pergolide mesylate can be mentioned as
examples of drugs for other purposes. The stent can also be
provided with a factor that exhibit anti-proliferative activity
against cells. Such factors or compositions can e.g. be a
cytotoxic/cytostatic, anti-proliferative factor. A pharmaceutically
acceptable form of an anti-proliferative factor or a functional
analog thereof can typically be used.
[0063] Details of the above mentioned embodiments can be combined
into other embodiments within the scope of the appended claims. The
cell shapes need not be of the particular type illustrated on the
drawing, as the scope of the claims comprises other cell shapes,
such as approximately rectangular cells, cells where the
connections between the cells in the individual row of cells extend
mainly or completely in the axial direction of the tubular body and
the cell sides (the abovementioned first cell sides) forming
circumferentially closed loops extend in directions forming angles
of at least 92.degree. or less that 88.degree. with the axial
direction of the tubular body. The cells can also be polygonal,
such as hexagonal, or the first cell sides in the circumferentially
closed loops can have a wavy shape or form a meander shape.
[0064] The invention has been described herein in considerable
detail in order to comply with the patent statutes, and to provide
those skilled in the art with the information needed to apply the
novel principles and to construct and use embodiments of the
invention as required. However, it is to be understood that the
invention can be carried out by specifically different devices and
that various modifications can be accomplished without departing
from the scope of the invention itself.
* * * * *