U.S. patent application number 11/784912 was filed with the patent office on 2007-08-16 for angioplasty stents.
This patent application is currently assigned to Sorin Biomedica Cardio S.p.A.. Invention is credited to Osvaldo Cerise, Paolo Gaschino, Giovanni Rolando, Franco Vallana.
Application Number | 20070191928 11/784912 |
Document ID | / |
Family ID | 25508195 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070191928 |
Kind Code |
A1 |
Rolando; Giovanni ; et
al. |
August 16, 2007 |
Angioplasty stents
Abstract
An angioplasty stent comprises a body comprising a plurality of
successive segments connected in pairs by bridge means so that the
successive segments can be oriented relative to one another for the
purposes of bending of the body in any direction defined by a
linear combination of respective orientation axes defined by the
bridge connection means. During the radial expansion of the stent,
the axial contraction of the segments resulting from the
opening-out of the respective loops is compensated by axial
projection of the bridge elements from the respective concave
portions. The wall of the body comprises arms for supporting a
lumen as well as regions which are selectively deformable during
the expansion of the stent, the arms and the selectively deformable
regions having different cross-sections and/or cross-sectional
areas. At least one portion of the body may have a substantially
reticular structure, the branches of which define geometrical
figures identifiable as fractals.
Inventors: |
Rolando; Giovanni; (Chivasso
(Torino), IT) ; Gaschino; Paolo; (Chivasso (Torino),
IT) ; Vallana; Franco; (Torino (Torino), IT) ;
Cerise; Osvaldo; (Aosta, IT) |
Correspondence
Address: |
POPOVICH, WILES & O'CONNELL, PA;650 THIRD AVENUE SOUTH
SUITE 600
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Sorin Biomedica Cardio
S.p.A.
|
Family ID: |
25508195 |
Appl. No.: |
11/784912 |
Filed: |
April 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11136002 |
May 24, 2005 |
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11784912 |
Apr 10, 2007 |
|
|
|
10626292 |
Jul 24, 2003 |
6896698 |
|
|
11136002 |
May 24, 2005 |
|
|
|
10002783 |
Oct 30, 2001 |
6616690 |
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10626292 |
Jul 24, 2003 |
|
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|
08964158 |
Nov 4, 1997 |
6309414 |
|
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10002783 |
Oct 30, 2001 |
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Current U.S.
Class: |
623/1.15 ;
623/901 |
Current CPC
Class: |
A61F 2/91 20130101; A61F
2002/91516 20130101; A61F 2/915 20130101; A61F 2002/91566 20130101;
A61F 2002/91508 20130101; A61F 2002/9155 20130101; A61F 2002/91533
20130101 |
Class at
Publication: |
623/001.15 ;
623/901 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. A stent for supporting the wall of a vessel, the stent having a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
stent comprising: at least two annular segments including a first
annular segment and a second annular segment, the first and second
annular segments each having a wave shape, at least one annular
segment being configured such that a first portion of the at least
one annular segment has a first outer wall surface width at an
intersection of a first plane with the first portion and a second
portion of the at least one annular segment has a second outer wall
surface width at an intersection of a second plane with the second
portion, the first plane being perpendicular to the wave shape at
the first portion, the second plane being perpendicular to the wave
shape at the second portion, the first outer wall surface width
being greater than the second outer wall surface width; and at
least two bridge connectors including first and second bridge
connectors connected between the first and second annular segments,
the at least two bridge connectors each having a shape defining a
sinusoidal path of greater than 360 degrees between the first and
second annular segments.
2. The stent of claim 1, wherein the wave shape of the first and
second annular segments comprises a plurality of peaks connected by
a plurality of arm sections and wherein the first bridge connector
is connected between a first peak of the first annular segment and
a first peak of the second annular segment and the second bridge
connector is connected between a second peak of the first annular
segment and a second peak of the second annular segment.
3. The stent of claim 1 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving, or
machining.
4. The stent of claim 1 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, or machining.
5. The stent of claim 1 wherein the tubular body is formed from a
metal wire.
6. The stent of claim 1 wherein the shape of the at least two
bridge connectors defines a plurality of alternating peaks oriented
in opposing directions.
7. A stent for supporting the wall of a vessel comprising a tubular
body having a wall including an inner wall surface and an outer
wall surface, the tubular body capable of being expanded from a
radially contracted position to a radially expanded position, the
tubular body including a plurality of annular segments, each
annular segment connected to at least one other annular segment by
at least two bridge connectors, a first portion of at least one
annular segment having a first cross-sectional shape at an
intersection of a first plane with the first portion, a second
portion of the at least one annular segment having a second
cross-sectional shape at an intersection of a second plane with the
second portion, the first plane being perpendicular to the annular
segment at the first portion, the second plane being perpendicular
to the annular segment at the second portion, the first
cross-sectional shape being different from the second
cross-sectional shape, the plurality of annular segments including
first and second annular segments having a wave shape, the first
and second annular segments being connected by first and second
bridge connectors, the first and second bridge connectors having a
shape defining a sinusoidal path of greater than 360 degrees from
the first annular segment to the second annular segment.
8. The stent of claim 7 wherein the wave shape of the first and
second annular segments comprises a plurality of peaks connected by
a plurality of arm sections and wherein the first bridge connector
is connected between a first peak of the first annular segment and
a first peak of the second annular segment and the second bridge
connector is connected between a second peak of the first annular
segment and a second peak of the second annular segment.
9. The stent of claim 7 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
10. The stent of claim 7 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
11. The stent of claim 7 wherein the tubular body is formed from a
metal wire.
12. The stent of claim 7 wherein the shape of the first and second
bridge connectors defines a plurality of alternating peaks oriented
in opposing directions.
13. A method of making a stent for supporting a vessel wall
comprising: providing a tubular body having a wall including an
inner wall surface and an outer wall surface; and forming a
plurality of openings in the wall of the tubular body, the openings
defining a plurality of annular segments, at least one annular
segment being configured such that a first portion of the at least
one annular segment has a first outer wall surface width at an
intersection of a first plane with the first portion, and a second
portion of the at least one annular segment has a second outer wall
surface width at an intersection of a second plane with the second
portion, the first plane being perpendicular to the at least one
annular segment at the first portion, the second plane being
perpendicular to the at least one annular segment at the second
portion, the first outer wall surface width being greater than the
second outer wall surface width, each annular segment connected to
at least one other annular segment by at least two bridge
connectors, the tubular body being expandable from a radially
contracted position to a radially expanded position, the plurality
of annular segments including a first annular segment and a second
annular segment, the first and second annular segments each having
a wave shape, the first annular segment being connected to the
second annular segment by at least first and second bridge
connectors, the first and second bridge connectors each having a
shape defining a sinusoidal wave of greater than 360 degrees
between the first and second annular segments.
14. The method of claim 13 wherein, in the forming step, the wave
shape of the first and second annular segments comprises a
plurality of peaks connected by a plurality of arm sections and
wherein the first bridge connector is connected between a first
peak of the first annular segment and a first peak of the second
annular segment and the second bridge connector is connected
between a second peak of the first annular segment and a second
peak of the second annular segment.
15. The method of claim 13 wherein, in the forming step, the
tubular body is formed from a tubular blank and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
16. The method of claim 13 wherein, in the forming step, the
tubular body is formed from a strip-like element closed to form a
tube and further wherein the plurality of openings is formed from
one of laser cutting, photo-engraving, electron-discharge, or
machining.
17. The method of claim 13 wherein, in the forming step, the
tubular body is formed from a metal wire.
18. The method of claim 13 wherein the shape of the first and
second bridge connectors defines a plurality of alternating peaks
oriented in opposing directions.
19. A stent for supporting the wall of a vessel comprising a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
tubular body including a plurality of annular segments, at least
one annular segment being configured such that a first portion of
the at least one annular segment has a first outer wall surface
width at an intersection of a first plane with the first portion
and a second portion of the at least one annular segment has a
second outer wall surface width at an intersection of a second
plane with the second portion, the first plane being perpendicular
to the at least one annular segment at the first portion, the
second plane being perpendicular to the at least one annular
segment at the second portion, the first outer wall surface width
being greater than the second outer wall surface width, each
annular segment connected to at least one other annular segment by
at least two bridge connectors, the plurality of annular segments
including first and second annular segments having a shape defining
a sinusoidal path which includes a plurality of alternating peaks
connected by a plurality of arm sections, the first and second
annular segments being connected by first and second bridge
connectors, the first and second bridge connectors defining a
sinusoidal path of approximately 720 degrees from the first annular
segment to the second annular segment, the first bridge connector
being connected between a first peak of the first annular segment
and a first peak of the second annular segment and the second
bridge connector being connected between a second peak of the first
annular segment and a second peak of the second annular
segment.
20. The stent of claim 19 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
21. The stent of claim 19 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
22. The stent of claim 19 wherein the tubular body is formed from a
metal wire.
23. The stent of claim 19 wherein the plurality of alternating
peaks are oriented in opposing directions.
24. A stent for supporting the wall of a vessel, the stent having a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
stent comprising: at least two annular segments including a first
annular segment and a second annular segment, the first and second
annular segments each having a wave shape, a first portion of at
least one annular segment having a first cross-sectional shape at
an intersection of a first plane with the first portion, a second
portion of the at least one annular segment having a second
cross-sectional shape at an intersection of a second plane with the
second portion, the first plane being perpendicular to the at least
one annular segment at the first portion, the second plane being
perpendicular to the at least one annular segment at the second
portion, the first cross-sectional shape being different from the
second cross-sectional shape; and at least two bridge connectors
including first and second bridge connectors connected between the
first and second annular segments, the at least two bridge
connectors each having a wave shape defining a repeating pattern,
the pattern of the at least two bridge connectors repeating
approximately twice between the first and second annular
segments.
25. The stent of claim 24 wherein the wave shape of the first and
second annular segments comprises a plurality of peaks connected by
a plurality of arm sections and wherein the first bridge connector
is connected between a first peak of the first annular segment and
a first peak of the second annular segment and the second bridge
connector is connected between a second peak of the first annular
segment and a second peak of the second annular segment.
26. The stent of claim 24 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
27. The stent of claim 24 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
28. The stent of claim 24 wherein the tubular body is formed from a
metal wire.
29. The stent of claim 24 wherein the shape of the at least two
bridge connectors defines a plurality of alternating peaks oriented
in opposing directions.
30. A stent for supporting the wall of a vessel comprising a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
tubular body including a plurality of annular segments, at least
one annular segment being configured such that a first portion of
the at least one annular segment has a first outer wall surface
width at an intersection of a first plane with the first portion
and a second portion of the at least one annular segment has a
second outer wall surface width at an intersection of a second
plane with the second portion, the first plane being perpendicular
to the at least one annular segment at the first portion, the
second plane being perpendicular to the at least one annular
segment at the second portion, the first outer wall surface width
being greater than the second outer wall surface width, each
annular segment connected to at least one other annular segment by
at least two bridge connectors, the plurality of annular segments
including first and second annular segments having a shape defining
a sinusoidal path which includes a plurality of alternating peaks
connected by a plurality of arm sections, the first and second
annular segments being connected by first and second bridge
connectors, the first and second bridge connectors defining a
repeating pattern, the pattern of the first and second bridge
connectors repeating approximately twice from the first annular
segment to the second annular segment, the first bridge connector
being connected between a first peak of the first annular segment
and a first peak of the second annular segment and the second
bridge connector being connected between a second peak of the first
annular segment and a second peak of the second annular
segment.
31. The stent of claim 30 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
32. The stent of claim 30 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
33. The stent of claim 30 wherein the tubular body is formed from a
metal wire.
34. The stent of claim 30 wherein the plurality of alternating
peaks are oriented in opposing directions.
35. A stent for supporting the wall of a vessel, the stent having a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
stent comprising: at least two annular segments including a first
annular segment and a second annular segment, a first portion of at
least one annular segment having a first cross-sectional shape at
an intersection of a first plane with the first portion, a second
portion of the at least one annular segment having a second
cross-sectional shape at an intersection of a second plane with the
second portion, the first plane being perpendicular to the at least
one annular segment at the first portion, the second plane being
perpendicular to the at least one annular segment at the second
portion, the first cross-sectional shape being different from the
second cross-sectional shape; and at least two bridge connectors
including first and second bridge connectors connected between the
first and second annular segments, the at least two bridge
connectors each having a shape defining a sinusoidal path of
between 360 degrees and 720 degrees from the first annular segment
to the second annular segment.
36. The stent of claim 35 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
37. The stent of claim 35 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
38. The stent of claim 35 wherein the tubular body is formed from a
metal wire.
39. The stent of claim 35 wherein the shape of the at least two
bridge connectors defines a plurality of alternating peaks oriented
in opposing directions.
40. A stent for supporting the wall of a vessel, the stent having a
tubular body having a wall including an inner wall surface and an
outer wall surface, the tubular body capable of being expanded from
a radially contracted position to a radially expanded position, the
stent comprising: at least two annular segments including a first
annular segment and a second annular segment, at least one annular
segment being configured such that a first portion of the at least
one annular segment has a first outer wall surface width at an
intersection of a first plane with the first portion and a second
portion of the at least one annular segment has a second outer wall
surface width at an intersection of a second plane with the second
portion, the first plane being perpendicular to the at least one
annular segment at the first portion, the second plane being
perpendicular to the at least one annular segment at the second
portion, the first outer wall surface width being greater than the
second outer wall surface width; and at least two bridge connectors
including first and second bridge connectors connected between the
first and second annular segments, the at least two bridge
connectors each having a wave shape defining a repeating pattern,
the pattern being repeated more than once but less than twice
between the first and second annular segments.
41. The stent of claim 40 wherein the tubular body is formed from a
tubular blank and further wherein the plurality of openings is
formed from one of laser cutting, photo-engraving,
electron-discharge, or machining.
42. The stent of claim 40 wherein the tubular body is formed from a
strip-like element closed to form a tube and further wherein the
plurality of openings is formed from one of laser cutting,
photo-engraving, electron-discharge, or machining.
43. The stent of claim 40 wherein the tubular body is formed from a
metal wire.
44. The stent of claim 40 wherein the shape of the at least two
bridge connectors defines a plurality of alternating peaks oriented
in opposing directions.
Description
[0001] This application is a continuation of application Ser. No.
11/136,002, filed May 24, 2005, which is a continuation of
application Ser. No. 10/626,292, filed Jul. 24, 2003, now U.S. Pat.
No. 6,896,698 B2, issued May 24, 2005, which is a continuation of
application Ser. No. 10/002,783, filed Oct. 30, 2001, now U.S. Pat.
No. 6,616,690 B2, issued Sep. 9, 2003, which is a continuation of
application Ser. No. 08/964,158, filed Nov. 4, 1997, now U.S. Pat.
No. 6,309,414, issued Oct. 30, 2001, the contents of each of which
are hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates in general to so-called stents
for angioplasty.
BACKGROUND OF THE INVENTION
[0003] The term "stent" is intended to indicate in general a device
to be fitted in a lumen (for example, inside a blood vessel),
usually by catheterization, and subsequently spread out in situ in
order to support the lumen locally. This has the main purpose of
preventing the re-establishment of a stenotic site in the location
treated. It should, however, be pointed out that it has already
been proposed in the art to use substantially similar structures
for spreading-out and anchoring vascular grafts in situ; naturally
this possible extension of the field of application is also
intended to be included in the scope of the invention.
[0004] For a general teaching with regard to vascular stents,
reference may usefully be made to the work "Textbook of
Interventional Cardiology" by Eric J. Topol, W.B. Saunders Company,
1994 and, in particular, to Section IV of Vol. II, entitled
"Coronary stenting".
[0005] A large number of patent documents are also dedicated to the
subject as is shown, for example, by U.S. Pat. No. 4,776,337, U.S.
Pat. No. 4,800,882, U.S. Pat. No. 4,907,336, U.S. Pat. No.
4,886,062, U.S. Pat. No. 4,830,003, U.S. Pat. No. 4,856,516, U.S.
Pat. No. 4,768,507, and U.S. Pat. No. 4,503,569.
[0006] In spite of extensive research and experimentation as
documented at the patent level, only a very small number of
operative solutions has up to now been used in practice.
[0007] This fact can be attributed to various factors, amongst
which the following problems or requirements may be mentioned:
[0008] to ensure that, during its advance towards the site to be
treated, the stent can adapt in a sufficiently flexible manner to
the path along which it is travelling even with regard to portions
having small radii of curvature such as those which may be
encountered, for example, in some peripheral vessels; this must be
achieved without adversely affecting the ability of the stent to
perform an effective supporting action once positioned and spread
out, [0009] to prevent, or at least limit the effect of
longitudinal shortening which occurs in many stents when they are
spread out, [0010] to offer as broad as possible a bearing surface
to the wall of the lumen to be supported, [0011] to avoid giving
rise to complex geometry and/or to possible stagnation sites which,
particularly in applications in blood vessels, may give rise to
adverse phenomena such as coagulation, clotting, etc., and [0012]
to reconcile the requirements set out above with simple and
reliable production methods and criteria, within the scope of
currently available technology.
SUMMARY OF THE INVENTION
[0013] The object of the present invention, which has the specific
characteristics claimed in the following claims, is to solve at
least some of the problems outlined above.
[0014] In one aspect, this invention is an angioplasty stent
comprising a body which has a generally tubular envelope and can be
expanded in use from a radially contracted condition towards a
radially expanded condition, said body comprising a plurality of
successive segments connected in pairs by bridge means, each of the
bridge means defining a connecting relationship between two of the
segments with a capability for relative orientation identified by
at least one respective orientation axis, so that the successive
segments can be oriented relative to one another for the purposes
of bending of the body in any direction defined by a linear
combination of respective orientation axes defined by the bridge
connection means.
[0015] In another aspect, this invention is an angioplasty stent
comprising a body which has a generally tubular envelope and can be
expanded in use from a radially contracted condition towards a
radially expanded condition, wherein: [0016] the body comprises a
plurality of generally annular segments, the wall of each segment
being defined by a plurality of loops, and [0017] at least some of
the segments are interconnected by bridge elements extending in the
general direction of the longitudinal axis of the stent and having
at least one end connected to the concave or inside portion of a
respective loop so that, during the radial expansion of the stent,
the axial contraction of the segments resulting from the
opening-out of the respective loops is compensated by axial
projection of the bridge elements from the respective concave
portions.
[0018] In another aspect, this invention is an angioplasty stent
comprising a body which has a generally tubular envelope and can be
expanded in use from a radially contracted position towards a
radially expanded condition in which the stent supports the wall of
a lumen, wherein the wall of the body comprises arms for supporting
the lumen, as well as regions which are selectively deformable
during the expansion of the stent, and in that the arms and the
selectively deformable regions have different cross-sections and/or
cross-sectional areas.
[0019] In yet another aspect, this invention is an angioplasty
stent comprising a body which has a generally tubular envelope and
can be expanded in use from a radially contracted condition towards
a radially expanded condition, wherein: [0020] the body comprises a
plurality of successive radially expandable segments interconnected
by bridge elements extending substantially in the direction of the
longitudinal axis of the stent so that the bridge elements are
substantially unaffected by the radial expansion of the segments
and the bridge elements are generally deformable in the direction
of the longitudinal axis so that the length of the stent along the
axis can change substantially independently of the radial
expansion.
[0021] And in yet another aspect, this invention is an angioplasty
stent comprising a body which has a generally tubular envelope and
can be expanded in use from a radially contracted condition towards
a radially expanded condition, wherein at least one portion of the
body has a substantially reticular structure, the branches of which
define geometrical figures identifiable as fractals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention will now be described, purely by way of
non-limiting example, with reference to the appended drawings, in
which:
[0023] FIG. 1 is a general perspective view of a first angioplasty
stent formed in accordance with the invention,
[0024] FIG. 2 is a side view of the stent of FIG. 1, on a slightly
enlarged scale,
[0025] FIG. 3 shows the geometrical characteristics of the wall of
the stent of FIGS. 1 and 2 in an imaginary development in a
plane,
[0026] FIG. 4, which is generally comparable to FIG. 3, shows a
first variant of the stent generally similar to that shown in FIGS.
1 and 2,
[0027] FIGS. 5 and 6 are two sections taken on the lines V-V and
VI-VI of FIG. 4, respectively,
[0028] FIG. 7 is a perspective view of another angioplasty
stent,
[0029] FIG. 8 is a side view of the stent of FIG. 7,
[0030] FIG. 9 shows essentially in the same manner as FIG. 3, an
imaginary development in a plane of the wall of the stent of FIGS.
7 and 8, and
[0031] FIGS. 10 and 11 show further possible developments of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Although several variants are referred to, the reference
numeral 1 is used for generally indicating a so-called angioplasty
stent FIGS. 1, 2, 7 and 8.
[0033] For a general identification of the method of use and the
structural characteristics of an implant of this type, reference
should be made to the documentation cited in the introductory part
of the description.
[0034] In summary, it will be remembered that the stent 1 is
usually produced in the form of a body with a tubular envelope
having an overall length of between a few millimetres and a few
tenths of a millimetre, a wall thickness (the wall usually having a
mesh or loop structure with openings, as will be explained further
below) of the order, for example, of a few hundredths of a
millimetre, in view of its possible insertion in a lumen (such as a
blood vessel) in a site in which a stenosis is to be remedied. The
stent is normally put in position by catheterization, after which
radial expansion from an insertion diameter of the order, for
example of 1.5-1.8 mm to an expanded diameter, for example, of the
order of 3-4 mm takes place in a manner such that, in the expanded
condition, the stent supports the lumen, preventing the recurrence
of a stenosis. In general, the outside diameter in the radially
contracted condition is selected so as to allow the stent to be
introduced into the lumen being treated, whereas the expanded
diameter corresponds in general to the diameter to be maintained
and established in the lumen once the stenosis has been eliminated.
It should again be pointed out that, although the main application
of the stents described relates to the treatment of blood vessels,
its use as an element for supporting any lumen in a human or animal
body can certainly be envisaged (and is therefore included within
the scope of the invention).
[0035] With regard to the methods and criteria which enable the
stent to be spread out (that is, expanded in situ), the solution
which is currently most widespread is that of the use of a
so-called balloon catheter, the stent being disposed around the
balloon of the catheter in the contracted condition and the balloon
then being expanded once the stent has been brought to the site in
which it is to be positioned. However, other solutions are
possible, for example, the use of superelastic materials which
cause the stent to expand once the restraining elements, which are
intended to keep the stent in the contracted condition until the
implant site has been reached, are removed. In addition or
alternatively, the use of materials having so-called "shape memory"
to form the stent so as to achieve the radial expansion in the
implant position has also been proposed.
[0036] Usually (for more precise indications, reference should be
made to the bibliographical and patent documentation cited in the
introduction to the description) the stent is made of metal which
can reconcile two basic requirements for the application, that is,
plastic deformability during the expansion stage and the ability to
withstand any stresses which would tend to cause the stent to close
up, preserving the expanded shape. The material known by the trade
name of "Nitinol" is well known and also has super-elasticity and
shape-memory properties which may be required in the expansion
stage.
[0037] In any case, these technological aspects will not be dealt
with in detail in the present description since they are not
relevant per se for the purposes of understanding and implementing
the invention. This also applies essentially to the technology for
the production of the stents according to the invention. As already
stated, in general terms, these adopt the appearance of bodies with
tubular envelopes having walls with openings. With regard to the
production methods, according to the prior art, at least three
basic solutions may be used, that is: [0038] forming the stent from
a continuous tubular blank to be cut up into individual stents, the
walls with openings being formed by techniques such as laser
cutting, photo-engraving, electron-discharge, machining, etc;
[0039] producing the stent from a strip-like body in which the
regions with openings are formed, for example, by the techniques
mentioned above, with a view to the subsequent closure of the
strip-like element to form a tube, and [0040] producing the stent
from a metal wire shaped by the successive connection of loops of
wire, for example, by means of micro-welding, brazing, gluing,
crimping operations, etc.
[0041] The first solution described is that which is currently
preferred by the Applicant for producing stents according to the
embodiments described below, with the exception of the solution to
which FIG. 4 relates which intrinsically involves the use of a
metal wire. In particular, laser-beam cutting has been found the
most flexible solution with regard to the ability to modify the
characteristics of the stents quickly during production according
to specific requirements of use.
[0042] In any case, it is stressed, that this production aspect is
of only marginal importance for the purposes of the implementation
of the invention in the terms which will be recited further below,
particularly with reference to FIG. 4. This also applies with
regard to the selection of the individual techniques and of the
order in which the various steps described (the production of the
walls with openings, parting, any bending of the strip-like
element, etc.) are carried out.
[0043] In all of the embodiments described herein, the body of the
stent 1 extends in a longitudinal direction generally identified by
an axis z. For clarity, it should however be pointed out that the
stent is intended to be bent, possibly significantly, during use,
easy flexibility actually being one of the characteristics
sought.
[0044] In all of the embodiments described herein, the body of the
stent 1 comprises a series of successive, generally annular
segments, indicated as 2 in the drawings. As can easily be seen,
the stent 1 of FIGS. 1 and 2 comprises seven of these segments,
whereas the stent of FIGS. 7 and 8 comprises six.
[0045] By way of indication, although this should not be
interpreted as limiting of the scope of the invention, the length
of the segments 2 measured longitudinally of the stent 1, and hence
along the axis z, is of the order of about 2 mm. In other words,
for reasons which will become clearer from the following, the
segments 2 are quite "short" lengthwise.
[0046] As can be appreciated best in the side view of FIG. 2, the
various segments of the stent 1 shown therein are connected to one
another by pairs of bridges 3, 4 (actually constituting integral
parts of the stent wall, as will be explained further below, for
example, with reference to FIG. 3) the essential characteristic of
which (this applies both to the stent of FIGS. 1 and 2 and to the
stent of FIGS. 7 and 8) is to articulate the segments 2 connected
respectively thereby in an alternating sequence about mutually
perpendicular flexing or bending axes.
[0047] This type of solution achieves two advantages.
[0048] In the first place, the longitudinal flexibility of the
stent 1 which is necessary to facilitate its location at the
implantation site, is demanded essentially of the bridges 3, 4,
whereas the structural strength and hence the support for the lumen
is demanded of the actual structures of the segments 2; all of this
is achieved with a capability to optimize the desired
characteristics by precise adaptation of the sections of the
various component elements.
[0049] In the second place, the arrangement of the bridges in a
sequence (usually, but not necessarily, alternating), in
combination with the fact that, as stated, the segments 2 are quite
short, enables a bend to be formed easily, in practice, at any
point along the length of the stent 1 in any direction in space,
and with very small radii of curvature.
[0050] This concept can be understood more easily with reference to
the solution of FIGS. 1 and 2 (as will be explained, the same also
applies to the solution according to FIGS. 7 and 8) if it is noted
that, by virtue of their arrangement at 180.degree. in diametrally
opposed positions on the wall of the stent 1, the bridges 3 allow
the stent 1 to bend locally about a respective axis x generally
transverse the axis z.
[0051] The bridges 4, which are also arranged at 180.degree. to one
another in a plane perpendicular to that of the bridges 3, allow
the stent 1 to bend locally about a second axis y transverse the
longitudinal axis z and, in the embodiment shown, perpendicular to
the above-mentioned axis x.
[0052] Since, as already stated, the segments 2 are quite short,
the aforesaid axes x and y are arranged in close proximity to one
another in alternating sequence along the length of the stent 1,
however many segments 2 there may be.
[0053] As a result, the stent can easily be bent, in practically
any longitudinal position of the stent 1, about a generic axis d
which can be defined on the basis of an equation such as {right
arrow over (d)}={right arrow over (ax)}+{right arrow over (by)} (1)
that is, as a linear combination of the bending movements about the
axes identified by the vectors
[0054] {right arrow over (x)} and {right arrow over (y)}.
[0055] With reference to the general theory of vectorial spaces, it
can also easily be understood that the availability of respective
capabilities for bending along two perpendicular axes in sequence,
preferably in alternating sequence, constitutes the simplest
solution for achieving the desired object. Solutions in which
successive segments 2 of the stent 1 are connected by bridges such
as the bridges 3 and 4 (or by elements which provide for similar
bending capabilities, as will be explained further below with
reference to FIGS. 7 and 8) in the region of axes which are not
mutually perpendicular would however, at least in principle, be
possible. A solution in which, for example, pairs of
diametrally-opposed bridges arranged in sequence and spaced apart
angularly by 60.degree. may be mentioned by way of example.
[0056] Moreover, the alternating sequence described above, that is:
axis x, axis y, axis x, axis y may, at least in principle, be
replaced by a different sequence, for example, axis x, axis x, axis
y, axis y, axis x, axis x, etc. Provision for a capability to bend
about the axis x in two adjacent segments 2 followed by a
capability to bend about the axis y repeated for two adjacent
segments 2, as in the latter example mentioned may, in fact, be
advantageous in applications in which an ability to achieve very
small radii of curvature is to be given preference.
[0057] In the solution of FIGS. 7 and 8, the same conceptual
solution is achieved in a slightly different manner.
[0058] In the solution shown in FIGS. 7 and 8, the various segments
2 are in fact connected to one another by means of bridges forming
respective portions of two "spines" of the stent constituted by
integral parts of the stent 1 which extend along a generally
winding path along two generatrices of the imaginary cylindrical
surface of the stent in diametrally opposed positions. The
respective structural details will become clearer from the
description given below.
[0059] From an observation, in particular, of FIG. 8 and with the
use of the same conventions as were used with reference to FIG. 2,
it can be seen that the flexibility in the region of respective
loops extending between successive segments 2 provided for by the
spines 30 achieves the local flexibility about the axis y relative
to the general direction defined by the axis z.
[0060] The local extensibility of the aforementioned bridges and,
in particular, the ability of one of the bridges to extend while
the diametrally-opposed bridge retains approximately corresponding
longitudinal dimensions, or extends to a more limited extent, or
possibly contracts slightly longitudinally, enables the bending
movement about the axis x to be achieved, as indicated
schematically by a broken line for the segment 2 which is farthest
to the left in FIG. 8.
[0061] In this embodiment, the stent 2 can thus also be bent in the
location of each connection between adjacent segments 2 about a
generic axis d defined by an equation such as equation (1)
introduced above.
[0062] As will be appreciated once again, all of this is achieved
while the structure of the individual segments 2 remains
substantially unchanged and thus in a manner such that the
longitudinal bending of the stent 1 can be attributed essentially
to the bending and/or, in general, to the local deformation, solely
of the bridges connecting adjacent segments 2.
[0063] With reference to FIG. 3, it can be seen that, as already
indicated above, this constitutes an imaginary development in a
plane, reproduced on an enlarged scale, of the wall of the stent of
FIGS. 1 and 2.
[0064] In fact, the seven segments 2 connected in alternating
sequence by the pairs of bridges 3 and 4 arranged in pairs of
diametrally-opposed elements disposed at 90.degree. in alternating
sequence can be seen in FIG. 3. As already stated, this is an
imaginary development in a plane which may correspond to the
development of a strip-like blank from which the stent 1 is then
produced by bending of the blank to form a tube.
[0065] It can also be noted from an observation of FIG. 3 that the
generally annular body of each segment 2 comprises in the
embodiments shown, a set of approximately sinusoidal loops of
substantially uniform size (measured circumferentially relative to
the element 2) which is doubled in the region of the loops from
which the bridges 3, 4 extend, in the manner explained further
below.
[0066] It is possible to recognise, within each segment 2, a
respective imaginary median plane X2 which, in the embodiments
illustrated, is generally perpendicular to the longitudinal axis z.
Two of these planes, indicated X2 are shown in FIG. 3 (and in FIG.
9); naturally, since these are developments in a plane, the median
planes in question are represented in the drawings by straight
lines.
[0067] It can thus be noted that each segment 2 comprises a
sequence of loops, each loop (approximately comparable to half of a
sinusoidal wave) defining a respective concave portion 5, the
concave side of which faces towards the median plane X2, and which
is connected to two approximately straight arms 6.
[0068] By way of indication, only two of these loops interconnected
by a bridge 3 have been marked specifically in FIG. 3. In
particular, these are the two loops of which the concave portions
are indicated 5 and the lateral arms are indicated 6.
[0069] It can easily be understood that the radial expansion of the
stent 1 takes place substantially as a result of an opening-out of
the aforementioned loops; by way of indication, with reference to
the development in a plane of FIG. 3, the radial expansion of the
stent corresponds to a stretching of the development in a plane
shown in FIG. 3 in the sense of an increase in height and hence a
vertical expansion of FIG. 3.
[0070] In practice, this radial expansion corresponds to an
opening-out of the concave portions 5, whereas the lateral arms 6
of each loop remain substantially straight.
[0071] The localization of the plastic deformation of the stent 2
in the concave portions of the loops 5 may be favored (as will be
explained further below with reference to FIG. 4) by means of the
cross-sections and/or the cross-sectional areas of the portions of
each loop.
[0072] In any case, the radial expansion (vertical stretching of
the development in a plane of FIG. 3) affects essentially the
concave portions 5 of the loops of the elements 2 and in no way
affects the bridges 3, 4 which extend longitudinally (axis z).
[0073] It will be appreciated that the same also applies to the
solution shown in FIG. 4 (which will be referred to further below)
in which one of the median planes X2 has been shown, only one of
the loops being indicated and its concave portion 5 and its lateral
arms 6 being identified specifically. The same criterion also
applies to the solution of FIGS. 7 and 8; in this connection,
reference should be made to the development in a plane of FIG. 9.
In this drawing, as in FIG. 3, two median planes X2 of two segments
2 have been indicated, and the concave portion 5 and the lateral
arms 6 of two opposed loops, between which a portion of one of the
sinusoidal spines 30 extends like a bridge, are also shown.
[0074] As can be seen best from a comparison of FIGS. 3, 4 and 9, a
feature common to all of the solutions described is that the radial
expansion of the segments 2 corresponds, within each segment 2, to
an imaginary movement of the concave portion 5 of each loop towards
the median plane X2 of the segment 2 of which this loop forms
part.
[0075] Anyone reading this description can easily perceive this,
for example, by thinking of the segment 2 corresponding to the
plane X2 farthest to the right in FIG. 3 as extending vertically.
As a result of this stretching, carried out precisely along the
line X2 which identifies the aforesaid plane, the concave portion 5
of the loop indicated in fact moves towards the line X2, the same
behaviour being followed, in opposite directions, according to
their different locations relative to the line X2, by the concave
portions of all of the other loops.
[0076] If, with reference to the bridges 3 (and the same also
applies to the bridges 4 as well as to the individual portions of
the spines 30 which define the parts equivalent to the bridges 3
and 4 in FIG. 9), it is considered that the connection to the
relative segments 2 is formed in the region of the concave (or
inside) portion of a respective loop, it can easily be appreciated
that the radial expansion of the segments 2 is accompanied, so to
speak, by a thrust exerted on the bridges 3, 4 (and on the
respective spine portions 30). This thrust corresponds, so to
speak, to an expulsion of the bridges or of the spine portions in
question from the corresponding segment 2.
[0077] To concentrate attention once again on the segment 2 the
median plane X2 of which is farthest to the right in FIG. 3, if the
segment 2 in question is thought of as being stretched vertically,
it will be seen that, as a result of the movement of the concave
portions (such as, for example, the concave portion indicated 5 in
the segment 2 in question) towards the plane X2, the respective
bridges 3 tend to move towards the left relative to the median
plane X2 of the corresponding segment 2.
[0078] This expulsion effect on the bridges 3 is beneficial for
eliminating the tendency demonstrated by many stents of the prior
art to contract longitudinally during radial expansion.
[0079] By the adoption of a geometry such as that shown in FIGS. 3
and 4, for example, the axial contraction of the segments 2
resulting from their radial expansion is in fact compensated (and
possibly even overcome) by the above-described "expulsion" of the
bridges 3 and 4. Tests carried out by the Applicant show, in this
connection, that, a geometry, for example, such as that illustrated
in FIGS. 3 and 4 causes the stent 1 not only not to shorten but, on
the contrary, to lengthen slightly during the radial expansion.
[0080] The explanation of this mechanism is quite simple. In this
connection, it suffices to consider, again with reference to FIG.
3, what would happen if, theoretically, instead of being located
where they are shown (and thus connecting respective concave loop
portions of adjacent segments 2), the bridges 4 of two aligned
loops of two adjacent segments 2 were arranged as indicated by
broken lines and indicated 4' and hence not connecting concave
(inside) loop portions but connecting convex (or outside) loop
portions.
[0081] The bridges 4' indicated above are extremely short (it will
be remembered, by way of reference, that the axial length of the
segments 2 may be of the order of 2 mm). Even during radial
expansion, the concave portions (and consequently the convex
portions) of all of the loops of each segment in any case retain
their alignment with a plane parallel to the median plane X2 at
each end of each segment 2. This alignment is thus also retained by
the concave or convex portions connected between two adjacent
segments 2 by the same bridge 3, the length of which is not changed
during the radial expansion.
[0082] Consequently, the length of a stent in which the bridges 3
were arranged as shown in FIG. 3 and the bridges 4 as schematically
indicated 4', again in FIG. 3, (naturally with reference to all of
the pairs of bridges 4 present in the stent) would remain
practically unchanged during radial expansion.
[0083] On the other hand, as already stated, with the use of the
geometry shown in FIG. 3, owing to the superimposition of the
various deformation movements, the axial length of the stent 1 is
not merely kept constant but even increases slightly. It will also
be understood from the explanation given above that, even though
the location of the bridges indicated 4' is mentioned theoretically
for explanation, it could actually be used, according to specific
requirements. Moreover, it can easily be understood from the
foregoing explanation that the conservation of the axial length
during the radial expansion does not necessarily require all of the
bridge elements (which are not affected by the deformation
resulting from the radial expansion) to be connected to concave or
inside portions of respective loops of the segments 2. In fact it
suffices, for this purpose, for one such connection to be provided
for each longitudinal section which is intended to contract
longitudinally as a result of the radial expansion of the stent
1.
[0084] For example, in the embodiment shown by solid lines in FIG.
3, (the same also applies to the embodiment of FIGS. 4 and 9) each
of the segments 2 comprises a section which is intended to contract
longitudinally as a result of the radial expansion. A corresponding
connection of bridges 3, 4 is therefore provided in each of these
segments according to the criteria described above.
[0085] With reference, on the other hand, to the connection
arrangement of the bridges 4' indicated primarily for didactic
purposes in FIG. 3, it can be noted that each set of two segments 2
interconnected by respective bridges 3 constitutes, precisely for
the reasons described above, a section of stent which does not
contract substantially longitudinally during radial expansion. For
this reason, the connection between these sections can take place
by means of bridges such as those which are indicated 4' and shown
in broken outline in the drawing and which are not connected to a
concave (or inside) loop portion.
[0086] It can be noted from an examination of the diagram of FIG.
9, that all of the segments 2 illustrated therein can contract
axially as a result of radial expansion. For this reason, the
bridges defined by the sinusoidal spines 30 and connecting adjacent
segments 2 satisfy precisely the condition described above, that
is, connection to the concave portion of a respective loop.
[0087] With regard to the general geometry, the variant of FIG. 4
again proposes the connection arrangement described above with
reference to FIG. 3.
[0088] FIG. 4 shows how a stent wall structure having the geometry
described with reference to FIG. 3 can also be formed from one or
more pieces of wire bent so as to form a set of loops which is
substantially similar to that shown in FIG. 3, and in which the
bridges 3 and 4 comprise wire portions which are coupled (that is,
placed side by side parallel to one another) and connected, for
example, by welding or other joining methods (for example, brazing,
gluing, crimping, etc.).
[0089] The use of a wire enables different cross-sections and/or
cross-sectional areas to be attributed (for example, by a
mechanical operation to shape the wire) to the concave portions 5
of the loops and to the straight arms 6 which extend therefrom. For
example, it can readily be appreciated that the cross-section of
FIG. 5 is in fact the cross section of a concave portion taken in
its tip portion, whereas the cross-section of FIG. 6 corresponds to
the connection region of two straight arms extending generally
longitudinally relative to the stent (axis z).
[0090] In particular, in the concave portions of the loops, the
wire constituting the stent wall may retain a round cross-section,
but in the straight portions 6 may adopt a cross-section which is
generally flattened in the plane of the wall (and hence along the
imaginary cylindrical envelope) of the stent 1.
[0091] This different shaping enables various results to be
achieved.
[0092] The straight portions 6 are intrinsically more resistant to
bending in the plane in which they are generally flattened so that
the force opening out the two arms 6 connected to a common concave
portion 5 brings about a deformation of the loop in the concave
portion 5. Although the arms 6 are opened out, they retain a
generally straight shape; in this connection, it will be noted that
the arms which are coupled to form the bridges 3 and 4 nevertheless
retain a straight orientation along the longitudinal axis z of the
stent 1.
[0093] By virtue of their flattened shape the arms 6 expose a wider
surface to the wall of the lumen supported by the stent in its
radially expanded condition. The wall of the lumen is therefore
subjected to a distributed load preventing the formation of
concentrated stress regions.
[0094] The dimensions of the wire can be optimized in the concave
portions 5 in order to achieve optimal characteristics of plastic
deformability when the stent is expanded radially and, at the same
time, resistance to subsequent stresses which may tend to close up
the stent 1.
[0095] It should in any case be pointed out, for clarity, that the
solution of making the cross-sections and/or the cross-sectional
areas of the various parts of the stent wall different in the terms
illustrated by way of example with reference to FIG. 4 is also
practicable in the solutions described with reference to FIGS. 3
and 9, (although with technological solutions other than the
mechanical squashing of the wire mentioned with reference to FIG.
4).
[0096] To examine this latter solution, and with further reference
to the perspective and elevational views of FIGS. 7 and 8, it can
be noted that, as a general rule, the structure and shape of the
loops constituting the various segments 2 is generally similar to
that described above with reference to FIGS. 3 and 4. In
particular, as indicated in the segment 2 situated farthest to the
left, it is also possible generally to distinguish in the loops
shown in FIG. 9 a concave (or inside) portion 5, extending from
which are two straight arms 6 which are intended to be opened out
when the stent 1 is expanded radially.
[0097] The wall structure of FIG. 9 differs from that shown in
FIGS. 3 and 4 essentially in that the bridges which interconnect
the various segments 2 comprise the two spines 30 extending with a
generally sinusoidal shape along two diametrally opposed
generatrices of the structure of the stent 1.
[0098] Naturally, the presence of two of these spines does not
constitute an essential choice. For example, instead of having two
spines 30 which are diametrally opposed (and hence spaced apart
angularly by 180.degree.) it is possible to use a single spine of
this type or three spines spaced angularly by 120.degree. etc.
[0099] In any case a structure with spines of the type described
can also implement an equation such as equation (1) given above,
for the purposes of the longitudinal bending of the stent 1. The
difference in comparison with the embodiment shown in FIGS. 1 to 4
lies in the fact that, in this first solution, the axes x and y in
fact correspond to the axes about which the bending of the pairs of
bridges 3, 4 can take place. In the embodiment of FIGS. 7 to 9, on
the other hand, (in this connection see also the elevational view
of FIG. 8), each section of the spine 30 extending to connect two
adjacent segments 2 can express two possibilities for relative
orientation between the two segments 2 connected, that is: [0100]
twisting or, more correctly, bending in the general plane of the
spine 30, and [0101] extension, or in general, variation in length
in this plane.
[0102] This concept may become clearer to experts in mechanics if
it is noted that, in practice, both the solution illustrated in
FIGS. 1 to 4 and the solution illustrated in FIGS. 7 to 9 form
structures generally comparable to that of a universal joint.
[0103] The generally sinusoidal shape of the two spines 30 enables
the longitudinal extensibility of the spines to be utilised for
bending purposes without giving rise to stresses which are oriented
tangentially relative to the wall of the stent and hence risk
giving rise to undesired twisting. It will, in any case, be
appreciated that the length of the stent of FIGS. 7 to 9 (that is,
its extent along the axis z) can change entirely independently of
the radial expansion of the segments 2. This can easily be seen if
it is noted that the overall shape of the spines 30 is sinusoidal
and, even where they are connected to concave portions of
respective loops (see in particular the portion of the spine 30
which is shown in the lower portion of FIG. 9 connecting the two
elements 2 of which the median planes X2 are indicated) the
connection with these concave portions 5 does not change the
general sinusoidal shape of the spine in question. In other words,
the spine 30 is connected to the outer edge of the outside of the
concave portion 5 on one side or wall thereof and continues from
the inside of the concave portion, from the opposite side or
wall.
[0104] The solution described provides for the entire body 1 of the
stent, or at least part of it, to comprise a substantially
reticular structure, the branches of which (in the embodiment
shown, the annular walls of the segments 2 and the two spines 30)
define geometrical figures which can be identified as fractals.
[0105] The term "fractal", coined by the mathematician B.
Mandelbrot in 1975, indicates in general a geometrical figure which
has internal symmetries to whatever scale it is enlarged, and which
is produced as a limit configuration of a succession of fragmentary
curves from each of which the next is obtained on the basis of an
assigned rule, for example, by replacing each side with a
predetermined fragmentary, so-called generative or generator
line.
[0106] Solutions such as those shown by way of example in FIGS. 2,
7 and 9 can be developed with the use of higher-order fractals, as
shown schematically in FIGS. 10 and 11.
[0107] In particular, FIG. 10 shows, by way of example, the use of
higher-order fractals to produce segments 2, and Figure 11 shows,
by way of example, the use of higher-order fractals to produce the
spine or spines 30. Clearly the solutions shown by way of example
may be combined, in the sense that the higher-order fractals may be
used both for the segments 2 and for the spines 30.
[0108] In any case, the use of fractal geometry has been found
advantageous since it enables the performance and/or the mechanical
characteristics of the various portions of the wall of the stent 1
to be optimized with regard to the specific stresses to which it
has to respond in use.
* * * * *