U.S. patent application number 11/657858 was filed with the patent office on 2007-05-31 for braided stent.
This patent application is currently assigned to Schneider (Europe) GmbH. Invention is credited to Marc Gianotti.
Application Number | 20070123969 11/657858 |
Document ID | / |
Family ID | 8228539 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070123969 |
Kind Code |
A1 |
Gianotti; Marc |
May 31, 2007 |
Braided stent
Abstract
A stent for use in a body passageway includes a plurality of
wires braided to form a self-expanding braided tubular structure.
The braided wires form braiding angles along a length of the
tubular structure. A portion of the wires are plastically deformed
to reduce foreshortening of the braided structure.
Inventors: |
Gianotti; Marc;
(Wiesendangen, CH) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
Schneider (Europe) GmbH
|
Family ID: |
8228539 |
Appl. No.: |
11/657858 |
Filed: |
January 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10674729 |
Sep 30, 2003 |
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11657858 |
Jan 25, 2007 |
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09874609 |
Jun 5, 2001 |
6652577 |
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10674729 |
Sep 30, 2003 |
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09431988 |
Nov 2, 1999 |
6240978 |
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09874609 |
Jun 5, 2001 |
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08993033 |
Dec 18, 1997 |
5993483 |
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09431988 |
Nov 2, 1999 |
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Current U.S.
Class: |
623/1.2 ;
623/23.7 |
Current CPC
Class: |
A61F 2230/0002 20130101;
D04C 1/06 20130101; D04C 3/48 20130101; A61F 2/90 20130101; D10B
2403/0241 20130101; D10B 2509/06 20130101; Y10T 29/49874 20150115;
A61F 2/88 20130101; A61F 2002/3011 20130101 |
Class at
Publication: |
623/001.2 ;
623/023.7 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 1997 |
EP |
97202152.1 |
Claims
1-76. (canceled)
77. A stent for use in a body passageway, comprising: a plurality
of wires braided to form a self-expanding braided tubular
structure, the braided wires forming braiding angles along a length
of the tubular structure; wherein a portion of the wires are
plastically deformed to reduce foreshortening of the braided
structure.
78. The stent of claim 77, wherein the braiding angles are obtuse
angles.
79. The stent of claim 78, therein the obtuse angles from about
110.degree. to about 120.degree..
80. The stent of claim 77, wherein the wires comprise metallic
material.
81. The stent of claim 77, wherein the plastically deformed portion
is a bend.
82. The stent of claim 77, wherein the plastically deformed portion
is an arched portion.
83. The stent of claim 77, wherein the plastically deformed portion
is a smooth curved portion.
84. The stent of claim 77, wherein braided tubular structure has a
substantially uniform diameter.
85. The stent of claim 77, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
86. The stent of claim 85, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
87. The stent of claim 81, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
88. The stent of claim 87, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
89. A stent for use in a body passageway, comprising: a plurality
of wires braided to form a self-expanding braided tubular
structure, the braided wires forming braiding angles along a length
of the tubular structure; wherein a portion of the wires are
plastically deformed to reduce flattening of the braided structure
under radial deformation.
90. The stent of claim 89, wherein the braiding angles are obtuse
angles.
91. The stent of claim 90, therein the obtuse angles from about
110.degree. to about 120.degree..
92. The stent of claim 89, wherein the wires comprise metallic
material.
93. The stent of claim 89, wherein the plastically deformed portion
is a bend.
94. The stent of claim 89, wherein the plastically deformed portion
is an arched portion.
95. The stent of claim 89, wherein the plastically deformed portion
is a smooth curved portion.
96. The stent of claim 89, wherein braided tubular structure has a
substantially uniform diameter.
97. The stent of claim 89, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
98. The stent of claim 97, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
99. The stent of claim 93, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
100. The stent of claim 99, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
101. A stent for use in a body passageway, comprising: a plurality
of wires braided to form a self-expanding braided tubular
structure, the braided wires forming braiding angles along a length
of the tubular structure; wherein a portion of the wires are
plastically deformed to restrict their movement within the braided
tubular structure.
102. The stent of claim 101, wherein the braiding angles are obtuse
angles.
103. The stent of claim 102, wherein the obtuse angles from about
110.degree. to about 120.degree..
104. The stent of claim 101, wherein the wires comprise metallic
material.
105. The stent of claim 101, wherein the plastically deformed
portion is a bend.
106. The stent of claim 101, wherein the plastically deformed
portion is an arched portion.
107. The stent of claim 101, wherein the plastically deformed
portion is a smooth curved portion.
108. The stent of claim 101, wherein braided tubular structure has
a substantially uniform diameter.
109. The stent of claim 101, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
110. The stent of claim 101, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
111. The stent of claim 105, wherein the braided structure further
comprises a proximal end and a distal end; and a plurality of
plastically deformed portions, wherein the plastically deformed
portions are disposed at at least one of the proximal end or the
distal end.
112. The stent of claim 111, wherein the plastically deformed
portions are disposed at both the proximal end and the distal
end.
113. A stent for use in a body passageway, comprising: a plurality
of wires braided to form a self-expanding braided tubular
structure, the braided wires forming braiding angles along a length
of the tubular structure; wherein portions of the wires are
plastically deformed to provide smooth curved, arched portions.
114. The stent of claim 113, wherein the braiding angles are obtuse
angles.
115. The stent of claim 114, therein the obtuse angles from about
110.degree. to about 120.degree..
116. The stent of claim 113, wherein the wires comprise metallic
material.
117. The stent of claim 113, wherein the smooth curved, arched
portions are bends.
118. The stent of claim 113, wherein the smooth curved, arched
portions equidistant from one and another.
119. The stent of claim 113, wherein braided tubular structure has
a substantially uniform diameter.
120. The stent of claim 113, wherein the braided structure further
comprises a proximal end and a distal end; and wherein the arched
portions are disposed at at least one of the proximal end or the
distal end.
121. The stent of claim 120, wherein the arched portions are
disposed at both the proximal end and the distal end.
122. The stent of claim 117, wherein the braided structure further
comprises a proximal end and a distal end; and wherein the arched
portions are disposed at at least one of the proximal end or the
distal end.
123. The stent of claim 117, wherein the arched portions are
disposed at both the proximal end and the distal end.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
10/674,729, filed Sep. 30, 2003, which is a divisional of
application Ser. No. 09/874,609, filed Jun. 5, 2001, now U.S. Pat.
No. 6,652,577, which is a divisional of application Ser. No.
09/431,988, filed Nov. 2, 1999, now U.S. Pat. No. 6,240,978, which
is a divisional of application Ser. No. 08/993,033, filed Dec. 18,
1997, now U.S. Pat. No. 5,993,483, which claims the benefit of
European Patent Application No. 97202152.1, filed in the European
Patent Office on Jul. 17, 1997, the contents of all of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a stent for use in a body
passageway, comprising a flexible self-expanding braided tubular
wall being composed of helically wound wires and having proximal
and distal ends. The invention also relates to a method for
manufacturing such a stent.
[0003] A stent of the type as mentioned in the introduction is
described for example in U.S. Pat. No. 4,655,771. The tubular wall
is composed of several flexible thread elements each of which
extends along a helix with the center line of the tubular wall as a
common axis. The thread elements are arranged in two groups of
opposite directions of winding crossing each other in a way to form
a braided configuration. This is to impart to the tubular body the
necessary stability for supporting a vessel. The diameter of the
tubular wall can be changed by axial movement of the ends relative
to each other. The stent is transluminally inserted into position
in its radially compressed state and then subjected to expansion
staying in place by a permanent pressure against the inner wall of
the body passageway. The stability of the tubular body depends in
general from the number of the thread elements, their diameter and
material and from the braiding angle of the thread elements at
their crossings. It is preferred to have the axially directed
braiding angle being obtuse, i.e. larger than 90.degree., in order
to obtain a large force in radial directions. But the braiding
angle also influences the shortening of the stent, which is the
reduction of the scent length upon conversion from its compressed
to its expanded state. At a given diameter expansion the stent
shortens less at braiding angles smaller than around 120.degree.
than at larger angles.
[0004] In the following stents with a braiding angle larger than
about 120.degree. are referred to as "normal-shortening" whereas
stents having a braiding angle of less than about 120.degree. are
referred to as "less-shortening." It is an advantage of
less-shortening stents that they can be placed more accurately
because the practitioner can better estimate the final positions of
the stent ends after expansion. The less-shortening feature comes
also to fruition when the stent is implanted in a moving hollow
organ in which the stent is repeatedly radially compressed, such as
in the esophagus, in the trachea or in a pulsating blood vessel. In
those cases the reduced shortening of the stent is less traumatic
for the inner wall of the hollow organ since the stent ends perform
smaller axial movements than normal-shortening stents do. For the
aforesaid reasons less-shortening stents are preferably implanted
in ostium regions, for example in the aorta next to the entries
into the renal arteries or in side branches. Exact placement
capability and less axial movement of the stent ends reduce the
risk of unwanted perturbation or obstruction of the blood flow by
stent ends projecting into the ostium.
[0005] However, stents of the less-shortening type comprise smaller
hoop strength compared to normal-shortening prostheses due to their
smaller braiding angle. A consequence of the lower radial force is
a reduction of the self fixation characteristics with the risk of a
local axial displacement of the stent within the body passageway.
Moreover, the stent is not stable enough to resist flattening if it
is implanted in arched vessels. This means that a more or less
strong deformation of the stent cross-section deviating from its
original circular shape can partially close the stent.
[0006] In EP-A-O 775 471 an improved stent is disclosed comprising
a flexible self expanding braided tubular wall having a proximal
segment of smaller diameter and a distal segment of larger diameter
and in-between an intermediate segment forming a truncated cone. A
covering layer is arranged within the tubular wall. Although the
document does not disclose any specific braiding angles the
proximal segment will have a similar braiding angle as the above
described less-shortening stent and the distal segment will have a
larger braiding angle. The different geometry can be derived from
the manufacturing methods as described in the document. The
large-diameter segment serves as a migration anchor while the
less-shortening segment with smaller diameter makes an easier and
safer way through curves or at the end of for example a food pipe.
But the less-shortening stent segment still has not sufficient
shape stability for use in curved areas of body vessels. The
cross-section of this segment may be deformed elliptically if
bended in curved body vessels as it will occur generally for
less-shortening stents. Moreover, because of the conical shape such
a stent can be used only at particular areas, such as in food
pipes. In addition, it is to be said that the used manufacturing
methods are quite expensive.
[0007] All documents cited herein, including the foregoing, are
incorporated herein by reference in their entireties for all
purposes.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of the present invention to
improve a less-shortening stent such that it can be used
universally, and more specifically in moving and/or in curved body
passageways avoiding migration and flattening deformation thereof.
A further object of the invention is to provide a stent which can
be manufactured easier.
[0009] The term "elevation" has the meaning of an impression or
bulge of the stent wall as well in the negative as in the positive
sense, i.e. extending inwardly or outwardly of the tubular stent
wall. Accordingly, the tubular wall has at least a local inwardly
and/or outwardly formed elevation, whereby the wires are
plastically deformed in a way that the number of degrees of freedom
for their movement within the braiding is reduced. This means that
the mesh cells defined by the braided wires are "frozen" by a
reduced capability of the wires to rotate and shift relative to
each other at their crossing points. The braided tubular wall
retains its less-shortening feature and becomes more stable against
radial deformation. A further advantage of the formed elevations is
the possibility to make a short stent of the type mentioned in the
introduction. Such stents are usually cut from the braiding blank
and comprise an unwanted conical shape due to a memory effect from
the braiding process. This shape can be converted into a
cylindrical tube and conserved by forming elevations on the stent
wall.
[0010] Where the elevations are distributed regularly over the
tubular wall, the stent will be anchored firmly with the tissue of
the body vessel without damaging. The homogeneity of the elevation
distribution is for example preferred if the stent is to be
implanted in a curved area of a body passageway.
[0011] More dense distribution of the elevations at the proximal
and distal ends of the stent will provide higher stability at these
areas for better anchoring thereof with the tissue of the body
vessel. This embodiment is preferred if the stent is to be
implanted in ostium positions for a safe fixation of the stent ends
in order to prevent migration of the stent and disturbing for
example the blood flow into a side branch through this ostium.
Another preferred application of such a stent is the support of a
vessel having a hard plaque stenosis whereby the stent comprises a
higher density of elevations in the stenotic region.
[0012] In a preferred embodiment of the invention the elevations
are formed outwardly so that they can serve as an anchor against
stent migration by engaging into the inner vessel wall to be
supported. Moreover, the deployment of such a stent with delivery
devices as known in the art is enhanced since the retraction of the
outer sheath is easier. This results from a reduced friction
between the inside of the delivery sheath and the radially
outwardly pressing stent touching the sheath only at the
elevations.
[0013] In another preferred embodiment of the present invention the
local elevations have an elongate shape which makes the
manufacturing of such stents very easy by using wires to emboss the
tubular wall. The elevations may have an arched cross-sectional
shape. Preferably the height of the elevations are approximately
one to two times the wire diameter of the braid.
[0014] These embossments or elevations can be formed in patterns
helically on the tubular wall, where in a preferred embodiment the
helical elevation pattern has a different pitch than the wires of
the braid in order to deform as many wires as possible. The
elevations may also be formed annularly or in an axial direction on
the tubular wall depending on the desired effect. Where the
elevations are placed annularly the stent wall comprises an
improved radial stability, whereas elevations in axial directions
impart to the stent a higher longitudinal stability which is
especially useful for implantation in the airways.
[0015] The manufacturing method according to the present invention
is determined by the steps of forming an elongate mandrel having at
least one local outwardly bound elevation, forming an elongated
tubular braid of spring steel having proximal and distal ends and
an inner diameter commensurate with the diameter of the mandrel,
engaging said tubular braid over said mandrel, heating the tubular
braid on the mandrel, cooling the tubular braid and disengaging the
braid from the mandrel. Preferably previous to the disengaging step
the braid will be compressed in the axial direction.
[0016] In sum the present invention relates to a stent for use in a
body passageway. A flexible self expanding braided tubular wall is
composed of helically wound wires and has proximal and distal ends,
wherein the tubular wall has at least a local inwardly and/or
outwardly formed elevation. The local elevations may be distributed
regularly over the tubular wall and distributed more densely at the
proximal and distal ends. The local elevations of the stent may be
formed outwardly and may have an elongated shape. The stent
elevations may have an arched cross-sectional shape and/or a height
of approximately one to two times of the diameter of the wires. The
elevations may be formed helically on the tubular wall. The helical
elevation may have a different pitch than the wires of the braid.
The elevation may be formed annularly on the tubular wall or formed
in an axial direction on the tubular wall.
[0017] The invention further relates to a method for manufacturing
a stent by forming or providing an elongated mandrel having at
least one local outwardly bound elevation; forming or providing an
elongated tubular braid of spring steel having proximal and distal
ends and an inner diameter commensurate with the diameter of the
mandrel; engaging the tubular braid over the mandrel; heating the
tubular braid over the mandrel; cooling the tubular braid; and
disengaging the braid from the mandrel. Prior to disengaging the
braid from the mandrel, the braid may be compressed in an axial
direction. The steps of heating the tubular braid over the mandrel
and cooling the tubular braid may be performed under vacuum
condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other objects, features and advantages of the
present invention will become readily apparent from the subsequent
description, wherein the invention will be explained in further
details with reference to the accompanying drawings which show,
diagrammatically and by way of example only, preferred but still
illustrative embodiments of the invention.
[0019] FIG. 1 shows a stent with a helical elevation in side
view,
[0020] FIG. 2 shows a cross-sectional view according to line A-A in
FIG. 1,
[0021] FIG. 3 shows a stent with a plurality of radial elevations
in side view,
[0022] FIG. 4 shows a stent with a plurality of axial elevations in
side view,
[0023] FIG. 5 shows the stent of FIG. 4 in front view according to
arrow B,
[0024] FIG. 6 shows a stent similar to that in FIG. 1, but with
increased densities of elevations at its ends, and
[0025] FIG. 7 shows a stent similar to that in FIG. 3, but with
increased densities of elevations at its ends.
[0026] In the following description of the drawings the same
reference numbers have been used for all figures if not mentioned
otherwise.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The stent depicted in FIG. 1 comprises a flexible self
expanding braided tubular wall 1 which is composed of a first
plurality of parallel spring stainless steel wires 2 helically
wound in a first direction crossing a second plurality of parallel
spring stainless steel wires 3 helically wound in a second
direction opposite to the first one. The braided structure assures
contraction of the stent in the radial direction when the proximal
and distal ends 4 and 5 of the stent are pulled away from one
another as exemplified by arrows 6, and self expansion of the stent
in the radial direction when the pull according to arrows 6 is
released. This configuration is well known in the art and needs no
further explanation. Of course, other known braidings or patterns
providing the same effect may be used.
[0028] The tubular wall 1 of the stent having a helical pattern of
elevations 7 which is outwardly formed and has an angle of gradient
or pitch slightly smaller than the angle of gradient or pitch of
the steel wires 2 shown in the same winding direction. The
elevations 7 have an elongate and arched cross-sectional shape. The
height of the elevations 7 over the tubular wall 1 is about once or
twice the diameter of the wires 2 or 3 of the braided
configuration. The wires 2 and 3 may be made of a metallic
material, e.g. stainless steel, which may be filled with a
radiopaque core, or made of a thermoplastic polymer, such as
polyesters, polyurethanes, polycarbonates, polysulphides,
polypropylene, polyethylene or polysulphonates. Normally the
diameter of the wires 2 and 3 lie within the range 0.01 to 0.5 mms.
The helical elevation 7 provides a greater stability of the meshes
of the braided tubular wall 1, i.e. the parallel wires 2 and the
parallel wires 3 will be prevented from moving apart at the
crossing points 8. Especially in the cross-sectional view of FIG. 2
it can be seen that wires 2 and 3 have been deformed locally in a
tubular shape. The elevation pattern is normally distributed in a
regular manner over the tubular wall 1. Therefore a specific wire 2
or 3 will have several elevation areas over its whole length within
the tubular wall 1 and a much greater stability of the wires 2 and
3 within the braid will be obtained. The elevation is further
smooth curved, i.e. having a continuous smoothly inclining and
declining curvature with the effect that the spring activity of the
wires 2 and 3 will be reduced in the areas of the elevations. On
the other hand the braiding angle between the wires 2 and 3 will be
enlarged locally in the area of the elevations which will
additionally enhance the mechanical stability of the tubular wall
1. In fact, the meshes are immobilized or "frozen" at the crossing
points of the wires 2 and 3 in the area of the elevation. By the
frozen meshes the tubular wall 1 will obtain an enlarged shape
stability which will resist the deforming forces of the body
vessel. The elevation 7 will also reduce the tendency of the wires
2 and 3 to debraid at the proximal and distal ends 4 and 5 of the
tubular wall 1. Thus the aforementioned stent will have a greater
form or shape stability if the tubular wall 1 will be bent in blood
vessels with a strong curvature, i.e. the circular cross-section of
the tubular wall 1 will be retained and not deformed to an
elliptical one as can be observed with less-shortening stents.
[0029] Another possibility of providing elevations for stents
according to the present invention is shown in FIG. 3, where the
stent having annular pattern of outwardly formed elevations 12
which, are equidistant and parallel to each other. Here also the
stability of the stent has been improved over the well-known
stents. If an annular pattern of elevations 12 will be provided
near the proximal and distal ends 4 and 5 the tendency of
debraiding of the wires 2 and 3 can be reduced further.
[0030] In FIG. 4 another example of a stent according to the
invention is shown, wherein outwardly formed elevations 13 are
provided in an axial direction on the tubular wall-1, which
elevations 13 are also equidistant and parallel to each other. The
front view of FIG. 5 shows that these elevations are also smoothly
curved as in the previous examples. Since the wires 2 and 3 are
intertwined with a relatively dense mesh the four patterns of
elevations 13 as depicted in this example are sufficient to prevent
debraiding at the proximal and distal ends 4 and 5 of the
stent.
[0031] Although the elevations 7, 12 and 13 in the examples of
FIGS. 1, 3 and 4 are formed outwardly on the tubular wall 1, they
may also be formed inwardly on the tubular wall 1 or possibly
provided in combination of outwardly and inwardly formed
elevations.
[0032] As mentioned previously, more dense distributions of
elevations at the proximal and distal ends of the stent will
provide higher stability at these areas for better anchoring of the
stent with the tissue of the body vessel. Also, in connection with
FIG. 3 it is noted above that an annular elevation pattern 12 near
the proximal and distal ends 4 and 5 can reduce the debraiding
tendency. FIG. 6 shows a stent of the type shown in FIG. 1, but
with increased densities of elevations at the proximal and distal
ends. FIG. 7 shows a stent of the type shown in FIG. 3, but with
annular elevation patterns near the proximal and distal ends 4 and
5.
[0033] The manufacturing of the aforementioned stents is as
follows:
[0034] Firstly the stent will be produced in the known manner, i.e.
the wires 2 and 3 will be intertwined with a predetermined braiding
angle and with a predetermined mesh size dependent from the wire
cross-section. The braiding angle of the so formed stent will
normally be between 100.degree.and 120.degree.. Thereafter the
stent will be pushed over a cylindrical mandrel with a regular
pattern of outwardly formed elevations like the helical shape of
wires provided on the surface of the mandrel as will be used to
form a stent according to FIG. 1. The mandrel with the stent will
then be heated up to process temperature, kept under process
temperature for a certain period of time, and cooled down
afterwards. The heating and cooling procedure is carried out under
vacuum condition. In the case of stainless steel wires the thermal
treatment may take up to sixteen hours, whereby the process
temperature of 550.degree. C. is maintained for about two hours.
Then the stent will be pulled from the mandrel. In cases where the
patterns of elevations are not axially directed as for the stent
depicted in FIG. 4, the tubular wall 1 may be compressed in order
to enlarge the diameter thereof for an easier disengagement. In
case of the helical pattern of the elevations the stent may also be
unscrewed from the mandrel.
[0035] Although other patterns of elevations may also be used for
the stents according to the invention the shown patterns are
preferred since they guarantee a smooth outer surface of the
tubular wall 1 which is especially important for stents to be used
at delicate areas such as blood vessels in order not to damage the
tissue. The helical shape and the annular shape of the pattern of
elevations are preferred for stents used at the junction between
the esophagus and the stomach as these will prevent much better the
migration of the stent as in case of the axial pattern of
elevations. In particular the elevations may also be formed
inwardly instead of outwardly as shown and described above, i.e.
the tubular stent wall having depressions. This may be advantageous
if the body vessel to be repaired needs more support and a larger
contact area with the stent.
[0036] Stents according to the present invention have a further
advantage in that they can be handled easier in the flexible shaft
of the positioning instrument since the friction between the stent
and the inner wall thereof will be reduced. This applies more for
the outwardly formed elevations as for the ones inwardly formed.
But in both cases the friction will be reduced in comparison to
conventional stents. Thus repositioning of stents with elevations
as shown before has been improved also.
[0037] The above-described embodiments of the invention are merely
descriptive of its principles and are not to be considered
limiting. Further modifications of the invention herein disclosed
will occur to those skilled in the respective arts and all such
modifications are deemed to be within the scope of the invention as
defined by the following claims.
* * * * *