U.S. patent application number 10/390100 was filed with the patent office on 2003-08-07 for expandable intraluminal endoprosthesis.
Invention is credited to Becker, Gary J..
Application Number | 20030149474 10/390100 |
Document ID | / |
Family ID | 26146599 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030149474 |
Kind Code |
A1 |
Becker, Gary J. |
August 7, 2003 |
Expandable intraluminal endoprosthesis
Abstract
An expandable intraluminal endoprosthesis including a tubular
member (1) a first diameter which permits intraluminal delivery of
the member into a lumen of a body passageway, particularly a blood
vessel. The tubular member (1) is capable of acquiring a second,
expanded and deformed diameter upon the application from the
interior of the tubular member of a radially outwardly extending
force, which second diameter is variable and dependent on the
amount of the force applied to the tubular member. Such a tubular
member may-be expanded and deformed to expand the lumen of the body
passageway. The wall of the tubular member includes a substantially
continuous structure (2) of mutually staggered undulations. This
structure has been separated from a tube wall and exhibits at lest
one pattern which advances substantially helically along a
longitudinal axis of the tubular member. Connection elements within
the structure connect adjacent undulations to each other. These
connection elements are an integral extension of the undulations
thereby interconnected.
Inventors: |
Becker, Gary J.; (Miami,
FL) |
Correspondence
Address: |
NEIFELD IP LAW, PC
2001 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
26146599 |
Appl. No.: |
10/390100 |
Filed: |
March 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10390100 |
Mar 17, 2003 |
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09511481 |
Feb 23, 2000 |
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09511481 |
Feb 23, 2000 |
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09094402 |
Jun 10, 1998 |
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6117165 |
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Current U.S.
Class: |
623/1.15 ;
623/1.22 |
Current CPC
Class: |
A61F 2/915 20130101;
A61F 2002/91516 20130101; A61F 2002/91541 20130101; A61F 2/91
20130101; A61F 2002/91525 20130101; A61F 2002/91558 20130101; A61F
2/88 20130101; A61F 2230/0013 20130101; A61F 2002/91508 20130101;
A61F 2002/91533 20130101; A61F 2002/91583 20130101; A61F 2002/9155
20130101 |
Class at
Publication: |
623/1.15 ;
623/1.22 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 1997 |
EP |
97201799.0 |
May 6, 1998 |
EP |
98201446.6 |
Claims
What is claimed is:
1. An expandable intraluminal endoprosthesis comprising a tubular
member having a first and second end and a wall surface disposed
between said first and second end, the wall having a substantially
uniform thickness and having a first diameter in a first,
unexpanded state which permits intraluminal delivery of the member
into a lumen of a body passageway, particularly a blood vessel,
which member is capable of acquiring a second diameter in an
expanded and deformed state upon the application from the interior
of the tubular member of a radially outwardly extending force,
which second diameter is variable and dependent on the amount of
said force applied to the tubular member, whereby the tubular
member may be expanded and deformed to expand the lumen of the body
passageway, wherein at least in said first unexpanded state at
least a part of said wall of said tubular member comprises a
substantially continuous structure of mutually staggered
undulations which has been separated from a tube wall, wherein said
substantially continuous structure comprises at least one pattern
which advances substantially helically along a longitudinal axis of
said tubular member and in that said structure comprises connection
elements connecting adjacent undulations, which connection elements
are an integral extension of the undulations which they
connected.
2. Endoprosthesis according to claim 1, wherein said structure
comprises a continuous filament which is separated from a tube
wall, said adjacent undulations are staggered in a substantially
helical configuration advancing along the longitudinal axis of the
tubular member to form one of said at least one substantially
helical pattern within said structure, and a first helical turn of
said filament around said longitudinal axis of said tubular member
is connected to an adjacent second such turn of said filament by
means of at least one of said connection elements, being an
integral extension of said filament.
3. Endoprosthesis according to claim 2, wherein adjacent turns of
said filament are connected to one another by means of a number of
connection elements less than the number of undulations in said
turns.
4. Endoprosthesis according to claim 2, wherein said structure
comprises a number of turns of said filament whereby the connection
elements to subsequent turns are radially shifted to form at least
one further substantially helical pattern of said at least one
substantial helical pattern within said structure.
5. Endoprosthesis according to claim 4, wherein the connection
elements to subsequent turns are radially shifted by approximately
half undulation pitch distance.
6. Endoprosthesis according to claim 4, wherein at least a portion
of the structure comprises a number of connection elements which
are substantially equally divided in each turn of said filament and
in that connection elements in successive turns are helically
shifted by approximately one undulation pitch distance.
7. Endoprosthesis according to claim 4, wherein said one and
further substantially helical patterns run in substantially
different helical directions along the longitudinal axis.
8. Endoprosthesis according to claim 2, wherein the undulations in
said filament have a first mutual pitch in a first of said turns of
said filament and a second mutual pitch in a second of said turns,
the first and second pitch being different from each other.
9. Endoprosthesis according to claim 1, wherein at least a part of
at least one undulation in at least one turn of said at least one
substantially helical pattern has an increased amplitude, while at
least the adjoining part of an adjoining undulation in an adjacent
turn has a correspondingly decreased amplitude.
10. Endoprosthesis according to claim 1, wherein a first pair of
adjacent undulations of said structure is connected by means of a
first connection element, in that a second pair of adjacent
undulation of said structure is connected by means of a second
connection element, in that in between said first and second pair
of connection elements at least one undulation of an intermediate
pair of undulations has an increased amplitude, to bridge at least
part of the length of said first and second connection element.
11. Endoprosthesis according to claim 1, wherein said structure
comprises at least one series of connection elements which are
substantially regularly distributed over at least part of the
length of said tubular member and in that successive connection
elements within said at least one series are radially shifted to
form one substantially helical pattern of said at least one
substantially helical pattern within said structure.
12. Endoprosthesis according to claim 11, wherein said successive
connection elements are mutually connected by an elongated member
which has a greater length than the linear distance between said
connection elements in said first unexpanded state of the
structure, in order to impart radially expandability to the
structure.
13. Endoprosthesis according to claim 12, wherein said elongated
member comprises a substantially S-curved bent.
14. Endoprosthesis according to claim 13, wherein said
substantially S-curved bent is orientated substantially parallel to
the center axis of the longitudinal axis of the tubular member.
15. Endoprosthesis according to claim 1, wherein at least some of
the connection elements comprise a strut diagonally interconnecting
a first side of a first adjoining undulation to an opposite side of
a second adjoining undulation, the strut being entirely integral
with said adjoining undulations and having a direction different to
the helical direction of said one substantially helical pattern
within said structure.
16. Endoprosthesis according to claim 15, wherein the first side of
said first undulation, said opposite side of said second undulation
and said strut, have a first filament width and in that the
opposite side of said first undulation and the first side of the
second undulation have a second filament width, the first filament
width being larger than the second filament width.
17. Endoprosthesis according to claim 15, wherein said strut
connecting opposite sides of adjoining undulations has a
substantially S-shaped structure.
18. Endoprosthesis according to claim 1, wherein the connection
elements each comprise two intersecting struts which are entirely
integral with each other and with the adjoining undulations which
they connect.
19. Endoprosthesis according to claim 18, wherein a first of said
intersecting struts extends substantially in the helical direction
of said at least one substantially helical pattern and has a strut
width which is larger than a strut width of the other of said
intersecting struts.
20. Endoprosthesis according to claim 1, wherein the tubular body
comprises a central portion, two outer portions at opposite ends of
said tubular member and at least one intermediate portion in
between the central portion and each of said end portions, the
different portions being designed according to their specific
function in the device.
Description
[0001] The present invention relates to an expandable intraluminal
endoprosthesis comprising a tubular member having a first and
second end and a wall surface disposed between said first and
second end, the wall having a substantially uniform thickness and
having a first diameter in a first, unexpanded state which permits
intraluminal delivery of the member into a lumen of a body
passageway, particularly a blood vessel, which member is capable of
acquiring a second diameter in an expanded and deformed state upon
the application from the interior of the tubular member of a
radially outwardly extending force, which second diameter is
variable and dependent on the amount of said force applied to the
tubular member, whereby the tubular member may be expanded and
deformed to expand the lumen of the body passageway. More
particularly the invention relates to an expandable intraluminal
vascular endoprosthesis which is especially useful for repairing or
reconstructing blood vessels narrowed or occluded by a disease.
Commonly this kind of medical device is referred to as vascular
stent or graft.
[0002] Stents are prosthetic devices which are implanted inside a
lumen in order to provide support for its wall and to assure an
undisturbed flow through the lumen. This is particularly important
in the field of angioplasty which is concerned with the repair and
reconstruction of blood vessels. In that particular field stents
are implanted within the vascular system to reinforce collapsing,
partially occluded, weakened, or abnormally dilated sections of
blood vessels. More generally, however, stents can be used inside
the lumen of any physiological conduit or duct including the
arteries, veins, bile ducts, the urinary tract, alimentary tracts,
the tracheobronchial tree, a cerebral aqueduct and the
genitourinary system. Moreover stents can be used inside lumina of
animals besides humans.
[0003] Generally two types of stents may be distinguished. First
there are self-expandable stents which automatically expand once
they are released to assume a permanent deployed, expanded state.
These stents expand to a defined diameter and are unable to remodel
the true vascular anatomy over lengths greater than 2 cm. Their
drawback is that the physician needs to place the right device and
thereby has to rely on information derived from fluoro and
angiographic equipment. A second type of stents concerns the
so-called balloon expandable stents which generally involve a
tubular member capable of receiving a balloon of a balloon-tipped
catheter by means of which it may be deployed. The present
invention particularly pertains to this second kind of stents.
[0004] A common procedure for implanting a balloon-expandable stent
in a blood vessel involves mounting the stent in its unexpanded,
crimped state on a balloon-tip catheter of a suitable delivery
system. The catheter is then slipped through an incision in the
vessel wall and down the length of the vessel until it is
positioned to bridge the diseased or narrowed portion of the
vessel. The stent is then expanded with the aid of the
balloon-catheter against the internal wall of the vessel. This may
be done after the vessel has been predialated and it has been
determined that a stent is necessary. Alternatively the vessel
could be dilated by the stent itself while the latter is expanded
by means of the balloon. It both cases the stent will maintain its
deployed, expanded form once the balloon is evacuated and the
catheter retracted again in order to provide a permanent support
for the blood vessel concerned.
[0005] A wide overview of vascular stents which are nowadays
available is given in the Handbook of Coronary Stents by Patrick W.
Serruys et al. of the Rotterdam Thoraxcentre Interventional
Cardiology Group. This overview describes at page 21 ff. the so
called Palmaz-Schatz.TM. stent as the gold standard in the field of
stents. This stent concerns a number of consecutive slotted tubes
of stainless steel which are mutually connected by means of one or
more bridges. Although this stent is most widely used and tested in
practice, it has been implanted in over 600000 patients all over
the world, it still suffers from a number of drawbacks. The main
drawbacks have to do with the stent-to-vessel-ratio uniformity and
crimped as well as deployed flexibility. The stent-to-vessel-ratio
involves the degree to which the vessel is supported by the stent
in its expanded state and should not only be high, but preferably
also uniform throughout the length of the stent. However, due to
the inevitable bridges between adjacent tubes of the
Palmaz-Schatz.TM. stent, there will be a bare area between adjacent
segments of the stent once it has been deployed giving rise to a
decreased and even poor stent-to-vessel-ratio at these locations.
The other drawback concerns the rather high rigidness of the stent
segments in their crimped and deployed state. As a consequence the
stent has only a limited flexibility which hinders the delivery of
the stent to its intended position inside the body. The poor
deployed flexibility of this stent gives rise to a straightening of
the vessel over segments longer than typically 2 cm which appears
to be a primary cause for late term restenosis of the stented area.
Typically this occurs after about 6 months after surgical post
procedural.
[0006] A balloon expandable stent with a highly uniform
stent-to-vessel ratio as well as an excellent flexibility in its
crimped state is described at page 63 ff. of the same reference and
concerns the Cordis Coronary Stent. This device is composed of a
single piece of tantalum (Ta) wire. The wire is wrapped to form a
continuous sine wave and helically wound along a longitudinal axis.
Both ends of the wire are weld terminated. A similar device was
presented at the annual symposium of the Radiological Society of
North America (RSNA) 11/95. This peripheral stent embodiment
incorporates intermediate welds, patterned through the length of
the stent. This device contains adjacent helical turns of the wire
which are welded together at adjoining locations and exhibits a
highly regular distribution of the wire along the length of the
device. Its properties, such as crimped profile and stent-to-vessel
ratio, are uniform over its length both in the crimped and deployed
states. However, because of its constitution this device offers
only a poor design freedom when it comes to tailoring the design to
add specific functionality and remove certain drawbacks. Also the
internal stress in the device once it has been wound hinders the
provision of reliable welds between adjacent turns. These welds as
well as those to the ends of the wire moreover remain a weak point
especially during expansion of the device.
[0007] It is an aim of the present invention to provide a balloon
expandable stent which combines a high degree of uniformity and
flexibility with excellent design capabilities.
[0008] To this end an expandable intraluminal endoprosthesis of the
kind described in the opening paragraph according to the invention
is characterized in that at least in said first unexpanded state at
least a part of said wall of said tubular member comprises a
substantially continuous structure of mutually staggered
undulations which has been separated from a tube wall, in that said
substantially continuous structure comprises at least one pattern
which advances substantially helically along a longitudinal axis of
said tubular body and in that said structure comprises connection
elements connecting adjacent undulations, which connection elements
are an integral extension of the undulations which they
connected.
[0009] The structure making up the wall of the tubular member may
be separated from a hollow tube by means of for instance laser
cutting or a similar technique available to a skilled person. In
this manner a substantially stress-free structure may be created
incorporating a substantially helically advancing pattern which can
be highly uniform and flexible throughout the length of the device
but still facilitates unimpaired design freedom to tailor the
pattern to meet additional functionality and to remove specific
drawbacks. Moreover as the connecting elements are likewise
separated from the tube as the rest of the structure and
consequently are entirely integral with said structure the
drawbacks associated with the welds in the prior art device may be
avoided. The substantial helical pattern within the structure may
be designed to form, upon deployment, a substantially continuously
advancing spine as a kind of backbone of the device.
[0010] A specific embodiment of the endoprosthesis according to the
invention is characterized in that said structure comprises a
continuous filament which is separated from a tube wall, in that
said adjacent undulations are staggered in a substantially helical
configuration advancing along a longitudinal axis of the tubular
body to form one of said at least one substantially helical pattern
within said structure, and in that a first helical turn of said
filament around said longitudinal axis of said tubular member is
connected to an adjacent second such turn of said filament by means
of at least one of said connection elements, being an integral
extension of said filament. This embodiment to large extend
compares to the Cordis Coronary Stent referred to above, without
however sharing the above described drawbacks of that device.
[0011] In order to improve on flexibility in a compressed as well
as in a deployed state of the device a further specific embodiment
of the endoprosthesis is according to the invention characterized
in that adjacent turns of said filament are connected to one
another by means of a number of connection elements less than the
number of undulations in said turns. Due to the fairly unlimited
design freedom in the device of the invention, the number of
interconnections between adjacent turns may be adapted freely to
suit the flexibility of the device. The less connection between
adjacent turns, the more flexible the device will be. Said design
freedom moreover allows a variation of the number of
interconnections between adjacent turns within the same device to
suit an optimal behaviour.
[0012] In a preferred embodiment an endoprosthesis is according to
the invention characterized in that said structure comprises a
number of turns of said filament whereby the connection elements to
subsequent turns are radially shifted to form at least one further
substantially helical pattern of said at least one substantial
helical pattern within said structure. In this manner a kind of
primary framework structure may be obtained which supports the
vessel wall while maintaining deployed flexibility. More
specifically a preferred embodiment of the endoprosthesis according
to the invention is chracterized in that at least a portion of the
structure comprises a number of connection elements which are
substantially equally divided in each turn of said filament and in
that connection elements in successive turns are helically shifted
by approximately one undulation pitch distance. By shifting the
connection elements substantially a full pitch distance a structure
is realized in which successive connection elements are linked to
each other by substantially a full undulation of said first
pattern. This undulation introduces significant slack and
expandable diameter within the helical spine created by the
interlinked connection elements which allows a very gradual
expansion of the device tranverse to its longitudinal direction.
This reduces so called foreshortening which is a longitudinal
shrinking of the device as it is expanded and would otherwise limit
the effective range of the device.
[0013] A further specific embodiment of the device according to the
invention is characterized in that at least some of the connection
elements comprise a strut diagonally interconnecting a first side
of a first adjoining undulation to an opposite side of a second
adjoining undulation, the strut being entirely integral with said
adjoining undulations and having a direction different to the
helical direction of said one substantial helical pattern within
said structure. Upon deployment, this structure will create a kind
of spine which runs over a series of connection elements in a
different, or even contra-, helical direction compared to that of
said one substantially helical pattern. Such multiple-helix
structure is capable of withstanding a significant hoop strength
whilst still being flexible and conformal to the natural vessel
wall.
[0014] In a still further embodiment an endoprosthesis is according
to the invention characterized in that the connection elements to
subsequent turns are radially shifted by approximately one
undulation pitch distance. Due to this regular pattern of
connection elements one or more continuous, helically turning
spines will be obtained in the deployed state of the device, formed
by subsequent struts and the respective sides of the undulations
they interconnect. These spines may form a scaffolding lattice
which uniformly supports the vessel wall while maintaining deployed
flexibility in order to be as conformal as possible with the
natural form of the vessel concerned. It has been found that
especially lack of the latter, resulting in a unnatural
straightening of the vessel over a certain length, is a primary
cause for late term restenosis of the stented segment. Due to the
deployed flexibility and its highly conformal deployed shape this
still further embodiment of the invention aims to avoid this
problem.
[0015] To further improve on flexibility while maintaining hoop
strength, i.e. the ability to withstand inwardly directed radial
forces, a further specific embodiment of the endoprosthesis
according to the invention is characterized in that the first side
of said first undulation, said opposite side of said second
undulation and said strut have a first filament width and in that
the opposite side of said first undulation and the first side of
the second undulation have a second filament width, the first
filament width being larger than the second filament width. The
inventor has recognized that said second filament width may be made
smaller than said first filament width, thus gaining flexibility,
without deteriorating the strength of the device and particularly
its radial hoop strength.
[0016] In a further specific embodiment the endoprosthesis
according to the invention is characterized in that said strut
connecting opposite sides of adjoining undulations of subsequent
turns have a substantially S-shaped structure. Such a double curved
structure of the connection elements creates more slack between
mutually interconnected undulations allowing more expansion as well
as an improved stent to vessel ratio at said area once the
prosthesis has been deployed.
[0017] A still further preferred embodiment of the endoprosthesis
according to the invention is characterized in that the connection
elements each comprise two intersecting struts which are entirely
integral with each other and with the adjoining undulations which
they connect. The inventor has recognized that on deployment of the
device such an interconnection element will first rotate around its
central axis before the entire force applied pulls axially on the
point of intersection. As a consequence a certain stress relief is
incorporated in the device which allows for a smaller filament
width. This does not only add to the flexibility of the device but
also leads to a more favourable radio-opacity. Moreover, the
intersecting struts leave a substantially unchanged scaffolding
area or footprint upon deployment of the structure thereby
improving on the eventual stent-to-vessel ratio of the device
compared to a connection element which will almost entirely stretch
upon deployment.
[0018] The design freedom gained by the endoprosthesis according to
the invention appears fairly unlimited and can be applied to
precisely tailor the properties of the device to specific
requirements. Not only the form, number and the location of
connection elements but also the filament width and form of
particular parts may be adapted in this sense. As an example, a
further specific embodiment of the invention is characterized in
that the undulations in said filament have a first mutual pitch in
a first of said turns of said filament and a second mutual pitch in
a second of said turns, the first and second pitch being different
from each other. Varying the mutual pitch of the undulations will
generally give rise to more or less flexibility in combination with
less or more vessel support at the zones concerned.
[0019] A still further embodiment of the endoprosthesis according
to the invention is characterized in that at least a part of at
least one undulation in at least one turn of said at least one
substantially helical pattern has an increased amplitude, while at
least the adjoining part of an adjoining undulation in an adjacent
turn has a correspondingly decreased amplitude. In this case the
mechanical properties of the device and especially the manner of
deployment as well as the stent-to-vessel ratio may be tailored by
offsetting the point where adjacent undulations meet.
[0020] More specifically a further embodiment of the endoprosthesis
according to the invention is characterized in that a first pair of
adjacent undulations of said structure is connected by means of a
first connection element, in that a second pair of adjacent
undulation of said structure is connected by means of a second
connection element, in that in between said first and second pair
of connection elements at least one undulation of an intermediate
pair of undulations has an increased amplitude, to bridge at least
part of the length of said first and second connection element. In
this case the inevitable length of the connection elements between
adjacent turns of the device is at least partly compensated by the
increased amplitude of said at least one undulation, leading to a
more uniform deployed stent-to-vessel ratio.
[0021] Besides or even instead of being formed by a series of
substantially helically staggered undulations, a substantially
helically advancing pattern within the structure may also be
created by the connection elements in themselves. I this respect, a
specific embodiment of the endoprosthesis according to the
invention is characterized in that said structure comprises at
least one series of connection elements wich are substantially
regularly distributed over at least part of the length of said
tubular body and in that successive connection elements within said
at least one series are radially shifted to form one substantially
helical pattern of said at least one substantially helical pattern
within said structure. More specifically, a preferred embodiments
of the endoprosthesis according to the invention is characterized
said successive connection elements are mutually connected by an
elongated member which has a greater length than the linear
distance between said connection elements in said first unexpanded
state of the structure, in order to impart radial expandability to
the structure.
[0022] In this manner a helically advancing spine is realised
throughout at least a part of the device which adds to the
scaffolding lattice of the structure, especially in the deployed
state of the device. One or even more of such spines may give the
device a considerable hoop-strength and supporting capability,
without depriving the structure of its crimped as well as deployed
flexibility. The greater length of the elongated member adds
expandable diameter to the individually connected connection
elements, imparting additional slack within the structure, an
improved expandability and less fore-shortening on the device. This
additional circumference allows for side branch access greater than
the maximum expanded diameter of the stent along the longitudinal
axis. In this respect, a specific embodiment of the endoprosthesis
according to the invention is characterized in that said elongated
member comprises a substantially S-curved bent. The S-curved
members are situated along the spiral helix equidistantly spaced,
along the longitudinal axis of the tubular body, and primarily
allow the device to uniformly expand out radially enabling the
structure to orient itself into a helical structure upon
deployment. In a more particular embodiment the S-curved bent is
orientated substantially parallel to the longitudinal axis of the
tubular body, which allows the member to uniformly expand
perpendicular to said axis. This prevents the device from twisting
and rotating on the balloon-catheter, or the like, as the device
undergoes expansion.
[0023] The endoprosthesis according to the invention may have a
uniform structure throughout the device. A preferred embodiment of
the device is however characterized in that the tubular body
comprises a central portion, two outer portions at opposite ends of
said tubular body and at least one intermediate portion in between
the central portion and each of said end portions, the different
portions being designed according to their specific function in the
device. This embodiment is based on the recognition that different
requirements may have to be imposed on different parts of the
endoprosthesis to precisely meet the specific function or desired
behaviour of the part concerned while the device is either
unexpanded, expanded or in a transition between the unexpanded and
expanded state. The present invention provides for a device in
which this kind of tailoring may be implemented.
[0024] More particularly a further embodiment of the endoprosthesis
according to the invention is characterized in that at least in one
of the two outer portions of the tubular body the undulations in
said structure have a gradually decreasing amplitude whether or not
in combination with a changing pitch or filament width in order to
render a free end of said portion substantially transverse to the
longitudinal axis of said body, at least in said first unexpanded
state of said structure. Such a square-like tubular end of the
endoprosthesis prevents an undesired cantilever protrusion of the
last turn which otherwise could harm the wall of the lumen while
the device is being navigated to its intended position. Moreover
this structure improves the mechanical bond between the
endoprosthesis and the balloon of the catheter used to manipulate
the device within the body. The square end is created by gradually
decreasing the amplitude and changing the pitch of the last few
undulations until there is a final smooth transition forming the
desired square end. Modifications of the filament width at this
area may further improve this part's behaviour.
[0025] A still further embodiment of the endoprosthesis according
to the invention is characterized in that said central portion of
the tubular body comprises a first number of connection elements
per full helical turn of said at least one substantially helical
pattern within said structure, in that at least one of said
intermediate portions comprises a second number of connection
elements of the structure per full helical turn of said at least
one substantially helical pattern within said structure, and in
that the first number of connection elements is smaller than said
second number of connection elements imparting a difference in
flexibility between both portions of the tubular body. More
precisely, the central portion will exhibit more flexibility than
the intermediate portions due to the lower number of
interconnections between adjacent turns. To accommodate this
difference within the structure, a specific embodiment of the
endoprosthesis according to the invention is characterized in that
the central portion and anyone of said intermediate portions are
separated from each other by a transitional portion in order to
smoothly change the number of interconnections between adjacent
turns from the first number to the second number of connection
elements per full helical turn of said pattern.
[0026] In a more specific embodiment the endoprosthesis according
to the invention is characterized in that adjacent turns in said
central portion comprise a number of connection elements which are
equally divided and in that connection elements in subsequent turns
are helically shifted by approximately one undulation pitch
distance. For example six adjoining helical segments with three
equally spaced connection elements, situated approximately
120.degree. with respect to one another or six opposing helical
segments with two equally spaced connection elements situated
approximately 180.degree. with respect to one another. This
specific design yields the most flexible structure in the central
region, both crimped and deployed. Once deployed, the structure
will orient itself in line with the helical lattice structure which
it forms, exhibiting three intertwining continuous lattice legs
within the intermediate region and only two of those legs in the
central region. The intermediate region will posses more stiffness
in order to counteract the balloon expansion, known as the "dog
bone effect", which causes the ends of the device to flare
prematurely prior to the deployment of the central section and
which results in an undo amount of foreshortening upon expansion.
Moreover the intermediate regions serve as a relief between the end
portions and the central region of the device.
[0027] The present invention will now be further described in more
detail with reference to the following figures in which like
elements are provided with the same reference numerals.
[0028] FIG. 1 shows an isometric view of an embodiment of an
expandable intraluminal endoprosthesis in accordance with the
present invention;
[0029] FIG. 2 is a plan view of the endoprosthesis of FIG. 1;
[0030] FIG. 3 shows alternative embodiments of interconnection
elements to be in a device according to the invention;
[0031] FIG. 4 is an enlarged view of an end portion of the
endoprosthesis of FIG. 1;
[0032] FIG. 5 shows an isometric view of a second embodiment of an
expandable intraluminal endoprosthesis in accordance with the
present invention;
[0033] FIG. 6 shows a plan view of the device of FIG. 5 in a
unexpanded state; and
[0034] FIG. 7 is a plan view of the device of FIG. 5 in a expanded,
deployed state.
[0035] The figures are drawn merely schematically and not to scale.
More particularly some dimensions may be exaggerated to more
clearly point out one or more aspects of the present invention.
Like parts the drawings are indicated as much as possible by like
reference signs.
[0036] FIG. 1 gives an isometric view of an expandable intraluminal
endoprosthesis according to a specific embodiment of the present
invention. The endoprosthesis, hereinafter briefly referred to as
stent, comprises a tubular member 1 which has been separated out of
a tubular body of a suitable bio-compatible material. As such for
instance high grade stainless steel (SST), a nickel-titanium based
alloy referred to as Nitinol (NiTi), several cobalt based alloys
and a Niobium-Titanium (NbTi) based alloy qualify. In this case the
latter material may be chosen because of its excellent mechanical
strength, corrosion resistance and radiopaque fluoroscopic
signature. In the first, unexpanded state shown, the tubular member
1 is drawn with a first diameter d which permits delivery of the
member into a lumen of a body passageway, particularly a blood
vessel. The member 1 is capable of acquiring a second, expanded and
deformed diameter upon the application of a radially outwardly
extending force from its interior, usually by means of a
balloon-catheter. This second diameter is variable and dependent on
the amount of force applied. Inevitably the member will show a
certain amount of recoil which means that the device will retract
more or less after the balloon has been evacuated. Accordingly the
second diameter will be slightly smaller than the diameter to which
the stent has been expanded. Nevertheless the tubular member may be
expanded and deformed to expand the lumen of the body passageway to
again assure an undisturbed flow through the lumen, like a blood
vessel.
[0037] The wall of the stent comprises a substantially continuous
structure which in this example consists of a continuous filament
which has been cut out from the tube wall in a substantially
helical fashion with a width between about 0.10 and 0.17 mm. This
may be done by means of laser cutting, electrochemical etching,
electromechanical discharge or any other suitable technique
preferably followed by a suitable surface treatment, like etching
to deburr and or round off possible sharp edges. In this example a
tubular body with an internal diameter of about 3.0 mm, a wall
thickness of about 1.0 mm and a length of about 30 mm has been
chosen as a starting material. However other dimensions are
likewise feasible within the scope of the present invention.
Particularly the length may be adapted to the diseased part of the
lumen to be stented in order to avoid the necessity of separate
stents to cover the total area. The filament-structure comprises a
number of undulations 2 which are mutually staggered in helical
pattern advancing around a central longitudinal axis I-I of the
device. In order to retain a coherent body subsequent turns A-H of
the filament are interconnected by means of one or more connection
elements 31,32 which are entirely integral with the undulations
thereby connected as they are cut altogether from one and the same
tubular body. To retain flexibility, both unexpanded as well as
deployed, the number of connection elements per helical turn is
less than the number of undulations in said turn. This is further
elucidated in FIG. 2 which gives plan view of the device as if it
were cut open. As emerges quit clearly from this figure, the
connection elements 31 to subsequent turns are radially shifted by
about half undulation pitch distance 1/2L to form a helical pattern
X-X, Y-Y. Once deployed, these patterns will expand to a helically
turning spines which form a primary framework or scaffolding
lattice of the deployed stent. This framework supports the vessel
wall highly uniformly throughout the device and moreover is capable
of withstanding substantial inwardly directed radial forces, which
is referred to as its hoop strength.
[0038] The lower drawing part of FIG. 2 shows a part of a central
modular portion of the device in which successive turns of the
filament are interconnected by means of only two connection
elements 31, which are shifted about 180.degree. with respect to
one another, while the upper part shows an end portion of the
device together with an intermediate portion in which three equally
spaced connection elements 31,32 interconnect adjacent undulations
from successive turns of the filament with each other. As a result
the parent scaffolding lattice of the deployed device will be
composed of only one helically advancing spline within the central
region and will comprise two helically revolving spines within the
other regions. Although the latter provides less flexibility, it
leads to an improved adhesion to the balloon-catheter by which the
device is guided through the lumen and moreover counteracts a so
called dog bone effect, which is a premature expansion at the tail
ends of the device. The central portion of the device, i.e. the
lower drawing part, on the other hand retains maximum flexibility
and conformability due to the smaller number of interconnections
between adjacent undulations within this segment.
[0039] In this example two kinds of connection element are used,
denoted 31 and 32 respectively. Both types of connection elements
feature a strut 3 which is S-shaped and diagonally interconnects
opposite sides of adjacent undulation from successive turns of the
filament in a helical direction different to that of the staggered
undulations themselves, see also FIG. 3E. These struts will be
referred to as major struts as they are part of the lattice spines
described hereinbefore. The second type of interconnection element
32 moreover features a second, S-shaped diagonal 4 strut
intersecting the first one, see also FIG. 3D. Due to this shape an
interconnection element of the second kind 32 will first start to
rotate around its central axis once the stent is being deployed
with only a limited force being exerted axially in the diagonal 3
of the connection element. Only after the first diagonal 3 has
become fully in line with the sides of the undulations it
interconnects, it has to withstand the entire force axially. This
incorporated slack and stress relief allows thinner strut width and
filament width over the lattice legs which can be useful for
decreasing the radio-opacity at this area as well as improves its
unexpanded, crimped as well as deployed, expanded flexibility.
Moreover the support area covered by a connection elements of this
second kind will not decrease much upon deployment of the device.
As a result a larger "scaffolding footprint" will remain after
deployment compared to any of the other types of connection
elements shown which all will stretch substantially upon deployment
leaving only the thin major strut 3 as "scaffolding footprint".
[0040] Besides the types connection elements depicted in the
drawing also other shapes are feasible, as the invention imposes
hardly no limitation of the design of any part of the device
including the shape of the interconnections used. Examples of other
shapes which could advantageously be used in a device according to
the invention are shown in FIGS. 3A-3G. The connection elements of
FIGS. 3A-3C merely comprise a straight strut 3 connection adjacent
undulations, whereas the main strut 3 of the connection elements
shown in FIGS. 3D-3F have a clearly S-curved shape. This shape
introduces more slack and expandability in the structure. The
longer this segment, the more slack and expandability there is in
the structure and especially in the spinal ladder created by these
connection elements in the eventual deployed device. A simple
formula can be derived from the expanded state, defining the
relative increase of the strut length and the effect it has on the
expansion range of the device.
[0041] The major strut 3, i.e. the strut eventually forming part of
the parent scaffold or framework of the device once it is deployed,
is indicated in FIG. 3 by a dotted hatch. In a special embodiment
this strut as well as the undulation sides which it interconnects
are given a first filament width w.sub.1 sufficiently large to
withstand the axial forces imposed thereon during expansion of the
device, whilst the other undulation sides and if applicable the
other strut of the connection element are given a second filament
width w.sub.2, at least locally, to gain flexibility and decrease
radio-opacity. Specifically the filament width is modified in the
central portion of the device to improve its overall flexibility
such that a first filament width w.sub.1 of approximately 0.14 mm
is taken whereas the second filament width w.sub.2 is reduced to
about 0.11 mm.
[0042] In order to avoid a substantial disruption of the stent to
vessel support by pairs of undulations from successive turns of the
filament which are not mutually interconnected by a connection
element, the amplitudes of the undulations within such pair may be
adapted to fill the gap which would otherwise remain due to the
inevitable length of a connection element elsewhere in the
structure. This is for instance apparent from FIG. 2 where all
adjacent peaks and valleys of pairs of undulations out of
successive turns which are not interconnected nevertheless adjoin
one another. This is a result of the adapting the amplitude of at
least one of the undulations within such pair of undulations. This
can imply that both, the peak and the valley have an increased
amplitude, that only one of those parts is enlarged, the other part
remaining unchanged, or even that either the peak or the valley has
a increased amplitude while the other part has a decreased
amplitude. Also in this respect, the designer has full freedom to
tailor the stent design to allow optimal behaviour of the stent in
its unexpanded state, expanded and/or transitional state.
[0043] The end portion of the device ends substantially transverse
to the central axis of the device in order to avoid a cantilever
usually associated with a helix shape which could otherwise harm
the wall of the lumen through which the stent is navigated. This
end portion is shown in more detail in FIG. 4. Its particular shape
is obtained by gradually decreasing the amplitude in the last few
undulations and adapting their mutual pitch. Due to the invention
this may be done without introducing any stress in the device as
the filament is simply cut in the desired pattern. The deviating
amplitudes and mutual pitch are best recognized from the plan view
of FIG. 2. The end modules exhibit a greater stent-to-vessel ratio
than the central and intermediate portions due to the increased
metal-to-surface-area in the expanded configuration. The more
complex structure of the end portions moreover give rise to a
greater amount of foreshortening upon expansion, thus producing a
more dense pattern yielding additional stent-to-vessel ratio.
[0044] A second embodiment of the device according to the invention
is depicted in FIGS. 5-7. This device comprises a tubular body 1
and has been manufactured using similar techniques as the first
embodiment, although in this case a more complicated structure has
been created consisting of more than just a single, wrapped
filament. However, like in the first embodiment, the structure of
the device is composed of a substantially helical pattern of
mutually staggered undulations 2, with connection elements 33
interconnection some undulations from successive turns of said
pattern. The connection elements within this structure primarily
comprise two intersecting struts like the type reflected in FIG.
3D.
[0045] Different to the structure of the first embodiment,
connection elements 33 to subsequent turns of said pattern are
shifted by about a full pitch distance. As a result a full
undulation 25 will link said connection elements 33 to one another
and as such creates an elongated member 25 in between the
connection elements 33. Said elongated member formed by an
intermediate undulation comprises a S-curved bent and is longer
than the linear distance between the interconnection elements
thereby linked to each other, at least in the crimped state shown
in FIGS. 5 and 6. This imparts additional slack and considerable
expandability to the spinal ladders which are formed by such a
series of linked connection elements in the deployed state shown in
FIG. 7. Moreover the orientation of the S-curved bents in said
elongated members 25, which is substantially parallel to the
longitudinal axis of the body at least in the crimped state shown
in FIGS. 5 and 6, allows the member 25 to uniformly expand in a
direction which is substantially perpendicular to said axis. This
prevents the device from twisting and turning on the
balloon-catheter once it is being expanded.
[0046] Like in the first embodiment, also in this case said series
of interlinked connection elements mutually shifted by a pitch
distance, form further substantially helically advancing patterns
within the structure. Like the staggered undulations themselves,
these further helically revolving patterns will mature to helical
spines running through the structure once it is being expanded, see
FIG. 7. These additional spines however run in a different
direction than the spines created by the undulations, indicated by
the straight lines in FIG. 7, which results in an eventual
structure with a considerable hoop strength in combination with an
excellent unexpanded and deployed flexibility. As the device of the
invention allows for a very large design freedom, these aspects may
be once more tailored throughout the device to fit the best overall
characteristics in each portion of the device.
[0047] Although the invention has been described hereinbefore with
reference to merely a few embodiments, it will be appreciated that
the invention is far more wide spread applicable. Within the scope
of the invention many other embodiments and variations are feasible
for a skilled practitioner. As such he may vary for instance the
mutual pitch of a few or more subsequent undulation with or without
a variation of the amplitude in order to tailor the stent-to-vessel
ratio and flexibility at the area concerned. Also, additional
modular portions individually recognizable in the stent could be
implemented in the stent in order to add specific functionality. As
such, a transitional portion might be interposed between the
relatively flexible central portion and the more stiff intermediate
and end portion in order to alleviate the structural transition
between those parts of the stent. Also the number of connection
elements within a full turn of the helical pattern may be raised to
introduce additional lattice spines to the deployed device,
resulting in even a larger hoop strength and supporting capability
of the device.
[0048] Likewise, the filament width as well as undulation shapes
may be varied and adapted to suit specific required characteristics
besides the flexibility and stent-to-vessel ratio. For instance,
the foreshortening of the device, i.e. the amount of length
reduction upon expansion from the crimped to the deployed state of
the device, its degree of recoil, its hoop strength as well as its
radio-opacity. In any event the present invention provides the
designer with the greatest amount of freedom conceivable.
[0049] Also the elongated members interlinking a series of
connections elemnets like in the second embodiment need not
coincide with undulations of the pattern and can be introduced in
the structure as separate elements. These members moreover need not
neccssarrily comprise a full S-curved bent or even no S-curved bent
at all and may on the other hand consist of more than just one such
bent. Also in this respect the designer has total freedom to tailor
the device to his demands.
* * * * *