U.S. patent application number 10/098785 was filed with the patent office on 2002-07-11 for stent design.
This patent application is currently assigned to Interventional Technologies, Inc.. Invention is credited to Trozera, Thomas.
Application Number | 20020091438 10/098785 |
Document ID | / |
Family ID | 25268358 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020091438 |
Kind Code |
A1 |
Trozera, Thomas |
July 11, 2002 |
Stent design
Abstract
The present invention is directed to an expandable stent which
is relatively flexible along its longitudinal axis to facilitate
delivery through tortuous body lumens, but which is stiff and
stable enough radially in an expanded condition to maintain the
patency of a body lumen such as an artery when implanted therein.
The struts of the present invention have a specific trapezoidal,
triangular or a reduced radii configuration projecting radially
outward that functions to reduce the forces necessary to penetrate
the vessel wall thereby minimizing trauma or damage imparted to the
wall during deployment. In addition, this design feature of the
present invention helps secure the expanded stent so that it does
not move once it is implanted and furthermore, minimizes
projections into the blood stream. The invention generally includes
a plurality of radially expandable loop elements which are
relatively independent in their ability to expand and to flex
relative to one another. The individual radially expandable
elements of the stent are dimensioned to minimize the strut from
twisting or rotating during expansion. Interconnecting elements or
a backbone extends between the adjacent loop elements to provide
increased stability and a preferable position for each loop to
prevent warping of the stent upon the expansion thereof. The
resulting stent structure is a series of radially expandable loop
elements which are spaced longitudinally close enough so that the
obstruction, vessel wall and any small dissections located at the
treatment site of a body lumen may be dilated or pressed back into
position against the lumenal wall. The manufacturing process of the
present invention utilizes optimized stress-strain curve
characteristics to achieve, unlike other non-wire stent designs,
improved mechanical properties throughout the stent. The optimized
stress-strain curve of the materail increases both the yield
strength and the ultimate tensile strength of the expanded stent,
increasing its resistance to structural failure (fracture) or stent
crushing.
Inventors: |
Trozera, Thomas; (Del Mar,
CA) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Assignee: |
Interventional Technologies,
Inc.
3574 Ruffin Road
San Diego
CA
|
Family ID: |
25268358 |
Appl. No.: |
10/098785 |
Filed: |
March 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10098785 |
Mar 13, 2002 |
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08956672 |
Oct 23, 1997 |
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08956672 |
Oct 23, 1997 |
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08835015 |
Apr 8, 1997 |
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5902475 |
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Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2230/0026 20130101;
A61F 2/915 20130101; G03B 27/04 20130101; A61F 2240/001 20130101;
A61F 2002/30158 20130101; A61F 2002/91575 20130101; G03F 7/00
20130101; A61F 2002/30156 20130101; A61F 2002/91533 20130101; A61F
2230/0023 20130101; A61F 2002/91516 20130101; G03F 7/18 20130101;
A61F 2002/3011 20130101; A61F 2/91 20130101; A61F 2230/0013
20130101; A61F 2230/0002 20130101 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Claims
I claim:
1. A low pressure stent for implanting in a vessel comprising; a
plurality of substantially cylindrical loop elements which are
independently expandable in the radial direction and which are
interconnected to generally align said cylindrical loop elements in
a common longitudinal axis; one or more connecting elements for
interconnecting said cylindrical loop elements; and an outer
surface on said cylindrical loop elements, said outer surface
comprising a converging configuration projecting radially from said
longitudinal axis prior to expansion of said stent, said converging
configuration maintaining its radial projection as said stent is
expanded radially outwardly from a first diameter to a second,
enlarged diameter.
2. A low pressure stent as recited in claim 1, wherein said
converging configuration of said outer surface of the loop element
comprises a trapezoidal configuration.
3. A low pressure stent as recited in claim 1, wherein said
converging configuration of said outer surface of the loop element
comprises a triangular configuration.
4. A low pressure stent as recited in claim 1, wherein said
converging configuration of said outer surface of the loop element
comprises a reduced radii configuration.
5. A low pressure stent as recited in claim 1, wherein said loop
elements include an undulating, alternating loop or serpentine
pattern.
6. A low pressure stent as recited in claim 1, wherein said outer
surface of said loop elements are embedded into the vascular wall
of the body lumen in order to more firmly attach said stent to the
vascular wall.
7. The low pressure stent as recited in claim 1, wherein said loop
elements are capable of maintaining their expanded condition upon
expansion thereof
8. The low pressure stent as recited in claim 1, wherein said stent
is formed of a material selected from the group of materials
consisting of stainless steel, platinum, gold alloy, or a
gold/platinum alloy.
9. The low pressure stent as recited in claim 1, wherein said stent
is formed from a single piece of tubing.
10. The low pressure stent as recited in claim 1, further
comprising coating said stent with a biocompatible coating.
11. The low pressure stent as recited in claim 1, wherein said loop
elements have a yield strength greater than 35,000 psi.
12. The low pressure stent as recited in claim 1, wherein said loop
elements have an ultimate tensile strength greater than 65,000
psi.
13. A low pressure stent for implanting in a vessel comprising; a
plurality of substantially cylindrical loop elements which are
independently expandable in the radial direction and which are
interconnected to concentrically align said cylindrical loop
elements in a common longitudinal axis; one or more connecting
elements for interconnecting said cylindrical loop elements, so
that said stent, when expanded radially outward, retains its
overall length without appreciable shortening; and an outer surface
on said loop elements, said outer surface comprising a converging
configuration projecting radially from said longitudinal axis prior
to expansion of said stent, said converging configuration
maintaining its radial projection as said stent is expanded
radially outwardly from a first diameter to a second, enlarged
diameter.
14. A low pressure stent as recited in claim 13, wherein said
converging configuration of said outer surface of the loop element
comprises a trapezoidal configuration.
15. A low pressure stent as recited in claim 13, wherein said
converging configuration of said outer surface of the loop element
comprises a triangular configuration.
16. A low pressure stent as recited in claim 13, wherein said
converging configuration of said outer surface of the loop element
comprises a reduced radii configuration.
17. A low pressure stent as recited in claim 13, wherein said loop
elements include an undulating, alternating loop or serpentine
pattern.
18. A low pressure stent as recited in claim 13, wherein said outer
surface of said loop elements are embedded into the vascular wall
of the body lumen in order to more firmly attach said stent to the
vascular wall.
19. The low pressure stent as recited in claim 13, wherein said
loop elements are capable of maintaining their expanded condition
upon expansion thereof.
20. The low pressure stent as recited in claim 13, wherein said
stent is formed of a material selected from the group of materials
consisting of stainless steel, stainless steel, platinum, gold
alloy, or a gold/platinum alloy.
21. The low pressure stent as recited in claim 13, wherein said
stent is formed from a single piece of tubing.
22. The low pressure stent as recited in claim 13, further
comprising coating said stent with a biocompatible coating.
23. The low pressure stent as recited in claim 13, wherein said
loop elements have a yield strength greater than 35,000 psi.
24. The low pressure stent as recited in claim 13, wherein said
loop elements have an ultimate tensile strength greater than 65,000
psi.
25. A low pressure stent for implanting in a vessel comprising; a
plurality of substantially cylindrical loop elements which are
independently expandable in the radial direction and which are
interconnected to concentrically align said loop elements in a
common longitudinal axis; one or more connecting elements for
interconnecting said cylindrical loop elements, so that said stent,
when expanded radially outward, retains its overall length without
appreciable shortening; and said loop elements having a yield
strength of at least 35,000 psi.
26. A low pressure stent for implanting in a vessel comprising; a
plurality of substantially cylindrical loop elements which are
independently expandable in the radial direction and which are
interconnected to concentrically align said cylindrical loop
elements in a common longitudinal axis; one or more connecting
elements for interconnecting said cylindrical loop elements, so
that said stent, when expanded radially outward, retains its
overall length without appreciable shortening; and said loop
elements having an ultimate tensile strength of at least 65,000
psi.
27. The method of deploying a stent having a plurality of
substantially cylindrical loop elements which are independently
expandable in the radial direction and which are interconnected and
generally aligned with said cylindrical loop elements in a common
longitudinal axis, one or more connecting elements for
interconnecting said loop elements, an outer surface on said loop
elements, said outer surface comprising a converging configuration
or reduce radius projecting radially from said longitudinal axis
prior to expansion of said stent, said converging configuration or
reduced radius maintaining its radial projection as said stent is
expanded radially outwardly from a first diameter to a second,
enlarged diameter; providing a catheter with an expandable member
on its distal end and positioning said stent coaxially on said
expandable member; positioning said expandable member with said
stent at a selected implantation site within a vessel of a patient;
expanding the expandable member radially to expand said stent
within a lumen of said vessel; contracting said expandable member;
and removing said catheter from said patient.
28. A method of deploying a stent as recited in claim 27, further
comprising the step of implanting said stent within a vessel wall
after the step of expanding said expandable member within said
lumen of said vessel.
Description
[0001] This is a continuation-in-part application of co-pending
U.S. patent application Ser. No. 08/835,015, filed on Apr. 8, 1997
and entitled "Method for Manufacturing a Stent." The contents of
the application identified in this paragraph, are incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] In general, the present invention relates to percutaneous
transluminal devices and methods which are used to treat obstructed
(sclerotic) vessel lumina in humans. In particular, the present
invention is an improved stent that requires low expansion pressure
for deployment and improved embedding of the struts within the
vessel wall.
BACKGROUND OF THE INVENTION
[0003] Cardiovascular disease is commonly accepted as being one of
the most serious health risks facing our society today. Diseased
and obstructed coronary arteries can restrict the flow of blood and
cause tissue ischemia and necrosis. While the exact etiology of
sclerotic cardiovascular disease is still in question, the
treatment of narrowed coronary arteries is more defined. Surgical
construction of coronary artery bypass grafts (CABG) is often the
method of choice when there are several diseased segments in one or
multiple arteries. Conventional open heart surgery is, of course,
very invasive and traumatic for patients undergoing such treatment.
In many cases, less traumatic, alternative methods are available
for treating cardiovascular disease percutaneously. These alternate
treatment methods generally employ various types of balloons
(angioplasty) or excising devices (atherectomy) to remodel or
debulk diseased vessel segments. A further alternative treatment
method involves percutaneous, intraluminal installation of one or
more expandable, tubular stents or prostheses in sclerotic lesions.
Intraluminal endovascular prosthetic grafting is an alternative to
conventional vascular surgery. Intraluminal endovascular grafting
involves the percutaneous insertion into a blood vessel of, a
tubular prosthetic graft and its delivery via a catheter to the
desired location within the vascular system. The alternative
approach to percutaneous revascularization is the surgical
placement of vein, artery, or other by-pass segments from the aorta
onto the coronary artery, requiring open heart surgery, and
significant morbidity and mortality. Advantages of the percutaneous
revascularization method over conventional vascular surgery include
obviating the need for surgically exposing, removing, replacing, or
by-passing the defective blood vessel, including heart-lung
by-pass, opening the chest, and general anesthesia.
[0004] Stents or prostheses are known in the art as implants which
function to maintain patency of a body lumen in humans and
especially to such implants for use in blood vessels. They are
typically formed from a cylindrical metal mesh which expand when
internal pressure is applied. Alternatively, they can be formed of
wire wrapped into a cylindrical shape. The present invention
relates to an improved stent design which by its specifically
configured struts can facilitate the deployment and embedment of
the stent within a vessel and is constructed from a manufacturing
process which provides a controlled and superior stress yield point
and ultimate tensile characteristics.
[0005] Stents or prostheses can be used in a variety of tubular
structures in the body including, but not limited to, arteries and
veins, ureters, common bile ducts, and the like. Stents are used to
expand a vascular lumen or to maintain its patency after
angioplasty or atherectomy procedures, overlie an aortic dissecting
aneurysm, tack dissections to the vessel wall, eliminate the risk
of occlusion caused by flaps resulting from the intimal tears
associated with primary interventional procedure, or prevent
elastic recoil of the vessel.
[0006] Stents may be utilized after atherectomy, which excises
plaque, cutting balloon angioplasty, which scores the arterial wall
prior to dilatation, or standard balloon angioplasty to maintain
acute and long-term patency of the vessel.
[0007] Stents may be utilized in by-pass grafts as well, to
maintain vessel patency. Stents can. also be used to reinforce
collapsing structures in the respiratory, biliary, urological, and
other tracts.
[0008] Further details of prior art stents can be found in U.S.
Pat. No. 3,868,956 (Alfidi et. al.); U.S. Pat. No. 4,739,762
(Palmaz); U.S. Pat. No. 4,512,338 (Balko et. al.); U.S. Pat. No.
4,553,545 (Maass et. al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S.
Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882
(Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No.
4,886,062 (Wiktor); U.S. Pat. No. 5,102,417 (Palmaz); U.S. Pat. No.
5,104,404 (Wolff); U.S. Pat. No. 5,192,307 (Wall); U.S. Pat. No.
5,195,984 (Schatz); U.S. Pat. No. 5,282,823 (Schwartz et. al.);
U.S. Pat. No. 5,354,308 (Simon et. al.); U.S. Pat. No. 5,395,390
(Simon et. al), U.S. Pat. No. 5,421,955 (Lau et. al.); U.S. Pat.
No. 5,443,496 (Schwartz et. al. ); U.S. Pat. No. 5,449,373
(Pinchasik et. al.); U.S. Pat. No. 5,102,417 (Palmaz); U.S. Pat.
No. 5,514,154 (Lau et. al); and U.S. Pat. No. 5,591,226 (Trerotola
et. al.).
[0009] In general, it is an object of the present invention to
provide a stent or prosthesis which can be readily expanded and
embedded into an obstruction or vessel wall with low dilatation
pressure thereby minimizing the trauma and damaged imparted to the
vessel wall during deployment of the stent.
[0010] It is also an object of the present invention to utilize a
specifically designed configuration of the outer strut surface to
facilitate embedment of the stent structure into the obstruction
and vessel wall with low dilatation pressure.
[0011] Another object of the present invention is to employ a
manufacturing process which optimizes the stress-strain curve
characteristics that achieves an increased yield strength and
ultimate tensile strength when compared to the other non-wire prior
art stents.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to an expandable stent
which is relatively flexible along its longitudinal axis to
facilitate delivery through tortuous body lumens, but which is
stiff and stable enough radially in an expanded condition to
maintain the patency of a body lumen such as an artery when
implanted therein. In addition, the struts of the present invention
have a specific trapezoidal, triangular or reduced radii
configuration projecting radially outward that functions to reduce
the forces necessary to penetrate the vessel wall with the stent
thereby minimizing trauma or damage imparted to the wall during
deployment.
[0013] The invention generally includes a plurality of radially
expandable loop elements which are relatively independent in their
ability to expand and to flex relative to one another. The
individual radially expandable elements of the stent (cross-section
of a strut) are dimensioned such that the aspect ratio of the
height to width minimizes twisting or rotation during expansion.
Interconnecting elements or a backbone extends between the adjacent
loop elements to provide increased stability and a preferable
position for each loop to prevent warping of the stent upon the
expansion thereof. The resulting stent structure is a series of
radially expandable loop elements which are spaced longitudinally
close enough so that the obstruction, vessel wall and any small
dissections located at the treatment site of a body lumen may be
dilated or pressed back into position against the lumenal wall. The
outward projecting strut surface converges towards the terminal end
and is configured in a trapezoidal, triangular or rounded shape to
facilitate embedment of the strut into the vessel wall utilizing
low dilatation pressure. The individual loop elements may bend
relative to adjacent loop elements without significant deformation,
cumulatively providing a stent which is flexible along its length
and about its longitudinal axis but is still very stiff in the
radial direction in order to resist collapse.
[0014] The presently preferred structure for the expandable loop
elements which form the stent of the present invention are
generally a circumferential undulating or alternating loop pattern
which comprises one of the radially expandable cylindrical
elements. The transverse cross-section of the undulating component
of the loop element preferably has an aspect ratio of about one to
one (base to height) thereby minimizing any tendency of the strut
to twist when expanded. The open reticulated structure of the stent
allows for a large portion of the vascular wall to be exposed to
blood which can improve the healing and repair of any damaged
vessel lining.
[0015] The radial expansion of the expandable cylinder deforms the
undulating or alternating loop pattern thereof similar to changes
in a waveform which result from decreasing the waveform's amplitude
and the frequency. Preferably, the undulating or alternation
patterns of the individual loop structures are in phase with each
other in order to yield uniform expansion and inhibit any crimping
along its length. The expandable cylindrical structures of the
stent are plastically deformed when expanded so that the stent will
remain in the expanded condition and therefore they must be
sufficiently rigid when expanded to prevent the compression of the
struts and therefore partial or total collapse of the stent after
deployment. The manufacturing process of the present stent
invention utilizes optimized stress-strain curve characteristics to
achieve, unlike other non-wire stent designs, improved mechanical
properties throughout the stent. The optimized stress-strain curve
increases both the yield strength and the ultimate tensile strength
of the expanded stent increasing its resistance to structural
failure (fracture) or stent crushing. During expansion of the
stent, the radially projecting trapezoidal, triangular or reduced
radii configuration of the struts outer surface will penetrate the
obstruction and vessel wall. Due to the reduced area of the outer
surface, the struts are able to pierce an obstruction or the vessel
wall with relative easy thereby resulting in minimal trauma or
damage to the vessel wall. In addition, this design feature of the
present invention helps secure the expanded stent so that it does
not move once it is implanted and furthermore, minimizes
projections into the blood stream.
[0016] The elongated elements which interconnects adjacent radially
expandable elements should have a transverse cross-section similar
to the transverse dimensions of the undulating or alternation loop
components of the radially expandable element. The interconnecting
elements preferably are not a unitary structure but rather
alternates sectionally along the length at various degrees around
the circumference of the stent. In an alternate embodiment, the
interconnecting element is a unitary structure which resembles a
backbone connecting the expandable loop elements.
[0017] In a presently preferred embodiment of the invention, the
stent is conveniently and easily formed by first heat-treating the
mechanically hardened tubular member to achieve optimum
stress-strain characteristics e.g. yield strength, elongation and
ultimate tensile strength. Then, the tubular member, comprising
stainless steel, platinum, gold alloy, or a gold/platinum alloy, is
electro-cleaned with an appropriate solution. Once the tubular
member is cleansed of contaminates, the outer surface is uniformly
coated with a photo-sensitive resist. Optionally, a coupling agent
may be used to facilitate the bonding of the photosensitive resist
to the tubular member. The coupling agent is not essential in that
some tubular member compositions bond directly to the
photo-sensitive resist solution without the need for a coupling
agent.
[0018] This coated tubular member is then placed in an apparatus
designed to rotate the tubular member while the coated tubular
member is exposed to a designated pattern of ultraviolet (UV)
light. The apparatus controls the exposure of the coated tubular
member by utilizing a photographic film with a specified computer
generated imprinted configuration, transferring the UV light in the
specified pattern to the coated tubular member. The UV light
activates the photosensitive resist causing the areas where UV
light is present to expose (cross-link) the photo-sensitive resist.
The photo-sensitive resist forms cross links where is it exposed to
the UV light thus forming a pattern of hardened and cured polymer
which mimics the particular stent design surrounded by uncured
polymer. The film is adaptable to virtually an unlimited number of
intricate stent designs. The process from the apparatus results in
the tubular member having a discrete pattern of exposed
photo-sensitive material with the remaining areas having unexposed
photo-sensitive resist.
[0019] The exposed tubular member is immersed in a negative resist
developer for a specified period of time. The developer removes the
relatively soft, uncured photo-sensitive resist polymer and leaves
behind the cured photo-sensitive resist which mimics the stent
pattern. Thereafter, excess developer is removed from the tubular
member by rinsing with an appropriate solvent. At this time, the
entire tubular member is incubated for a specified period of time,
allowing the remaining photo-sensitive resist polymer to fully cure
and bond to the surface of the processed tubular member.
[0020] The processed tubular member is then exposed to a
electrochemical etching process which removes uncovered metal from
the tubular member, resulting in the final tubular member or stent
configuration. Since the tubular member has not been subjected to
any process such as additional heat treatments, welding/brazing or
laser cutting, the finished stent will maintain the optimized
stress-strain characteristics obtained in the initial
heat-treatment process.
[0021] The stent embodying features of the invention can be readily
delivered to the desired lumenal location by mounting it on an
expandable member of a delivery catheter, for example, a balloon or
mechanical dilatation device, and passing the catheter/stent
assembly through the body lumen to the site of deployment.
[0022] Other features and advantages of the present invention will
become more apparent from the following detailed description of the
invention. When taken in conjunction with the accompanying
exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is an elevational view of a stent embodying features
of the invention which is mounted on a delivery catheter and
disposed within an arterial segment.
[0024] FIG. 2 is a plan view illustration of one frame of film with
a stent configuration of the present invention imprinted on the
film.
[0025] FIG. 3 is a plan view illustration of one frame of film with
a stent configuration of another embodiment of the present
invention imprinted on the film showing the single backbone
connecting element.
[0026] FIG. 4 is a perspective view of a entire stent embodying
features of the invention in an unexpanded state.
[0027] FIG. 5 is a perspective view of one stent configuration,
showing the position and relationship of the loop or struts with
the connecting elements. FIG. 6A is a cross-sectional view of one
configuration of the outer surface of a strut as seen along line
4-4 in FIG. 4 showing a trapezoidal protruding configuration that
is directed radially from the longitudinal axis of the stent.
[0028] FIG. 6B is a cross-sectional view of another configuration
of the outer surface of a strut as seen along line 4-4 in FIG. 4
showing a triangular protruding configuration that is directed
radially from the longitudinal axis of the stent.
[0029] FIG. 6C is a cross-sectional view of another configuration
of the outer surface of a strut as seen along line 4-4 in FIG. 4
showing a protrusio n with a reduced radius that is directed
radially from the longitudinal axis of the stent.
[0030] FIG. 7A is an enlarged partial view of one loop or strut of
the stent of FIG. 4 showing a trapezoidal protruding configuration
that is directed radially from the longitudinal axis of the
stent.
[0031] FIG. 7B is an enlarged partial view of one loop or strut of
the stent of FIG. 4 showing a triangular protruding configuration
that is directed radially from the longitudinal axis of the
stent.
[0032] FIG. 7C is an enlarged partial view of one loop or strut of
the stent of FIG. 4 showing a protrusion with a reduced radius that
is directed radially from the longitudinal axis of the stent.
[0033] FIG. 8A is a cross-sectional view showing the trapezoidal
configured strut scoring and penetrating an obstruction within in
an arterial wall.
[0034] FIG. 8B is a cross-sectional view showing the triangular
configured strut scoring and penetrating an obstruction within in
an arterial wall.
[0035] FIG. 8C is a cross-sectional view showing the reduced radius
configured strut scoring and penetrating an obstruction within in
an arterial wall.
[0036] FIG. 9A is an elevational view, partially in section,
similar to that shown in FIG. 1 wherein the stent is collapsed upon
the delivery catheter within the arterial segment, and just
proximal to a vascular obstruction.
[0037] FIG. 9B is an elevational view, partially in section,
similar to that shown in FIG. 1 wherein the stent, in its collapsed
configuration, is positioned within the vascular obstruction.
[0038] FIG. 9C is an elevational view, partially in section,
similar to that shown in FIG. 1 wherein the stent is expanded
within the vascular segment and embedding the specifically
configured struts of the stent against and into the arterial
wall.
[0039] FIG. 9D is an elevational view, partially in section,
similar to that shown in FIG. 1 wherein the delivery catheter has
been withdrawn and the stent is fully deployed within the vascular
segment.
[0040] FIG. 10 is an illustration of a single strut or loop in both
the unexpanded and expanded configurations demonstrating the amount
of optimized stress-strain characteristics obtained upon deployment
of prior art non-wire stents.
[0041] FIG. 11 is an illustration of a single strut or loop in both
the unexpanded and expanded configurations demonstrating the amount
of optimized stress-strain characteristics obtained upon deployment
of the present invention stent.
[0042] FIG. 12 is an representation of the stress-strain curve
showing the relative ultimate tensile of the prior art stents
versus the present invention stent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] FIG. 1 illustrates a stent 10 incorporating features of the
invention which is mounted onto a delivery catheter 11 threaded
over guidewire 20. The delivery catheter 11 has an expandable
portion or balloon 14 for expanding of the stent 10 within an
artery 21. The delivery catheter 11 onto which the stent 10 is
mounted, is essentially the same as a conventional balloon
dilatation catheter for angioplasty procedures or may consist of a
mechanical dilatation device. The balloon 14 may be formed of
suitable materials such as polyethylene, polyethylene terephthalate
(PET) or polyethylene napthalate (PEN). In order for the stent 10
to remain stationary on the balloon 14 during delivery to the site
of the obstruction within the artery 21, the stent 10 is generally
collapsed onto the balloon.
[0044] FIG. 2 shows a preferred stent configuration imprinted on a
transparent photographic film. The drawing of the pattern is
generated on a computer program, reduced and printed onto a
transparent film. For example, a mechanical drawing or stress
analysis program can be used to develop the computer generated
printouts. The printout is then sent to a film processing facility
which reduces the printout and generates a precisely dimensioned
negative. As discussed in more detail below, the dimensions of the
negative must be calibrated to render a specific stent design.
Because of regulations concerning patent drawings which prohibits
large blackened areas, an explanation of the drawings used to
represent the photographic film is necessary. In FIG. 2, the open
(transparent) spaces 38 which allow the UV light to pass through
the film are represented as solid black lines (with white cores)
which comprise a series of alternating loops 15. The alternating
loop of the film 32 create the struts 50 which circumferentially
comprise the expandable cylindrical elements 12 of stent 10 as
shown in FIG. 5. Similarly, the linear sections 36 connecting the
alternating or undulating patterns comprise the interconnecting
elements 32 of stent 10 (FIG. 5). The white areas 40 of the FIG. 2
represent the exposed (black) areas of the film which will block
the UV light from passing through the film and exposing the
underlying areas to UV. An example of a suitable film that can be
employed in the present invention is Kodak ALI-4 Accumax film made
by Kodak Industries. The length 30 of stent imprint is directly
equal (1 to 1) to the circumference of present stent invention. The
width 35 is equivalent to the working length of the processed
stent.
[0045] FIG. 3 illustrates another embodiment of the present stent
invention wherein linear section(s) 36 (which become the
interconnecting elements) are disposed between alternating loops 32
(which become the radially expandable cylindrical elements) in
different configurations. In FIG. 3, the resulting configuration of
the stent from the imprinted film will have a single connection
backbone 52. The single interconnecting element represents a
backbone 52 connecting the radially expandable cylindrical elements
12 of stent 10. Not shown but contemplated in the present
invention, the interconnecting elements 34 may be distributed 120
degrees around the circumference of the stent 10. Disposing three
or more interconnecting elements 34 between adjacent radially
expandable cylindrical elements 12 will generally give rise to the
same considerations discussed above for the one and two
interconnecting element designs.
[0046] FIG. 4 and 5 are representations of the preferred stent
design 10 that results from the photo and etch method and the
embodiment shown in FIG. 2. The stent generally comprises a
plurality of radially expandable cylindrical elements 12 disposed
generally coaxially and interconnected by elements 34 disposed
between adjacent expandable elements. The portion of the metal
covered by the photoresist that was exposed to UV illumination and
changed physical properties are retained during the electrochemical
process and remain intact as the struts or loops 50 of stent 10.
The portions of the photoresist that were not exposed to UV
illumination are removed during the development stage. The exposed
metal is then chemically dissolved by employing an electrochemical
process that results in the open spaces 39 in the stent 10. The
structure resulting from a pattern of loops or struts 50 and open
spaces 39 comprises the desired stent configuration. In keeping
with the invention, and with reference to FIGS. 4 and 5, radially
expandable cylindrical elements 12 are in the form of a number of
loop alterations or undulations 23 of the stent resembling a
serpentine pattern. FIG. 4 also illustrates the stent design in
which the radially expandable cylindrical elements 12 are in an
undulating pattern but out of phase with adjacent expandable
cylindrical elements.
[0047] FIG. 5 is an enlarged perspective view of the stent 10 shown
in FIG. 4 with one end of the stent shown in an exploded view to
illustrate in greater detail the placement of interconnecting
elements 34 between adjacent radially expandable elements 12. Each
pair of the interconnecting elements 34 on one side of an
expandable element 12 are preferably placed to achieve maximum
flexibility for a stent. In the embodiment shown in FIG. 5, stent
10 has two interconnecting elements 34 between adjacent radially
expandable cylindrical elements 12 which are approximately 180
degrees apart. The next pair of interconnecting elements 13 on one
side of a cylindrical element 12 are offset by ninety (90) degrees
from the adjacent pair. The alternation of the interconnecting
elements results in a stent which is longitudinally flexible in
essentially all directions. Various configurations for the
placement of interconnecting elements are possible and another
example is illustrated schematically in FIG. 3. However all of the
interconnecting elements of an individual stent should be secured
to either the peaks or valleys of the alternating loop elements in
order to prevent shortening of the stent during the expansion
thereof and all of the radially facing struts will have one of the
specifically designed configurations.
[0048] The pattern of FIGS. 4 and 5 can be formed of any size; a
preferable size of stent 10 is between 0.035 thousandths to 0.100
thousandths in diameter when formed and in the constrained
configuration. The expanded or deployed diameter of stent 10 ranges
from 2.0 mm to 8.0 mm with a preferred range for coronary
applications of 2.5 mm to 6.0 mm. The length of the stent 10 is
virtually constant from its initial formation length to its length
when expanded and ranges from 2 mm to 50 mm, with a preferred
length for coronary applications of 5 mm to 20 mm.
[0049] Each radially expandable cylindrical element 12 of the stent
10 may be independently expanded. Therefore, the balloon 14 may be
provided with an inflated shape other than cylindrical, e.g.
tapered, to facilitate implantation of the stent 10 in a variety of
body lumen shapes.
[0050] The particular pattern and how many undulations per unit of
length around the circumference of the radially expandable
cylindrical element 12, or the amplitude of the loops, are chosen
to fill particular mechanical requirements for the stent such as
expanded size and radial stiffness. The number of undulations may
also be varied to accommodate placement of interconnecting elements
34 at the peaks of the undulations or along the sides of the
undulations (not shown). As previously mentioned, each radially
expandable cylindrical element 12 is connected by interconnecting
elements 34. Undulating pattern 23 is made up of a plurality of U
shaped alternating loops. Alternately, the undulating pattern could
be made up of W-shaped members or Y-shaped members each having a
different radius so that expansion forces are more evenly
distributed over the various members.
[0051] The stent 10 serves to hold open the artery 21 after the
catheter 11 is withdrawn, as illustrated by FIG. 9D. The undulating
portion of the radially expandable sections 12 provide good tacking
characteristics to prevent stent movement within the artery.
Furthermore, the closely spaced radially expandable cylindrical
elements 12 at regular intervals provide uniform support for the
wall 22 of the artery 21, and consequently are well adapted to tack
up and hold in place small flaps or dissections in the wall 22 of
the artery 21.
[0052] The method of manufacturing the present invention results in
the preferred stent design having specifically configured struts
50. FIGS. 6A, 6B, and 6C illustrate, in cross-section, three
exemplary stent strut designs. As demonstrated in FIG. 6A, the
preferred stent design has the outer portion of the struts
protruding in a trapezoidal configuration 54 which is directed
radially from the longitudinal axis of the stent. The pattern of
the preferred stent employs cross-section FIG. 6A in a series of
U-shaped loops 50 and an alternating connecting elements 34 running
along the length of the stent, thereby forming the basic scaffold
of the stent design.
[0053] In an alternate embodiment the pattern of stent 10 is
similar to that of FIGS. 4, 5 and 6A but differs in the outer
portion of the strut comprising a triangular configuration (FIG.
6B) where the point of the triangle is directed radially from the
longitudinal axis of the stent. In an another alternate embodiment,
the pattern of stent 10 is similar to that of FIGS. 4, 5 and 6A,
but differs in the outer portion of the strut comprising an
extended base with a reduced radius 58 (FIG. 6C) that is directed
radially from the longitudinal axis of the stent.
[0054] A terminal section of the loop of stent 10 is shown in FIGS.
7A, 7B, and 7C. It can be seen in the cross-sectional illustration
that the strut has a trapezoidal configuration 53 in FIG. 7A, a
triangular configuration 55 in FIG. 7B, and an outer reduced radius
configuration 57 in FIG. 7C. Each strut configuration can be
associated with any combination of alternating loops or struts 50
and interconnecting elements 34. Furthermore, it can be seen that
the aspect radio of the height to width minimizes twisting or
rotation during expansion.
[0055] As shown in FIG. 8A, 8B and 8C, the specifically configured
radially facing strut surfaces are designed to facilitate the
embedment of the expanded stent into the arterial wall or
obstruction. By providing a trapezoidal 54 (FIGS. 8A), triangular
56 (FIGS. 8B) or reduced radius 58 (FIGS. 8C) configuration
embedment of the stent is relatively atraumatic because less strut
area is required to penetrate the vessel wall. Expansion and
eventual embedment of the present invention stent is accomplished
in such a way that vascular baropressure is overcome in a
controlled and relatively docile manner. Vessel trauma and damage
is thereby reduced resulting in less subsequent intimal or smooth
muscle proliferation. In contrast, the prior art non-wire stents
present a relatively flat surface to penetrate the vessel wall
therefore providing none of the advantages described above for the
present stent invention.
[0056] In a preferred embodiment, the delivery of the stent 10 is
accomplished in the following manner. The stent 10 is first mounted
onto an inflatable balloon 14 or mechanical delivery system (not
shown) on the distal extremity of the delivery catheter 11. The
stent 10 is crimped or collapsed to the exterior surface of balloon
14. The stent/catheter assembly is then introduced within the
patient's vasculature through a guiding catheter utilizing the
conventional Seldinger technique. A guidewire 20 is disposed across
the obstruction within the vascular section and the stent/catheter
assembly is advanced over a guidewire 20 to the obstruction (see
FIG. 9A) Then the stent/catheter assembly is advanced further until
the stent 10 is positioned and centered within the obstruction 25
(see FIG. 9B). The balloon 14 of the catheter is then inflated,
expanding the stent 10 against the obstruction 25 and possibly
arterial wall 22, as illustrated in FIG. 9C.
[0057] As shown in FIG. 9D, the artery 21 is preferably expanded
slightly by the expansion of stent 10 to provide volume for the
expanded lumen. As a result of this embedment, interference of
blood flow by the stent is minimized as well as to prevent further
movement. The radially expandable elements 12 (or struts 50) of
stent 10 which are pressed into the wall of the artery 21 will
eventually be covered with endothelial cell growth which further
minimizes blood flow interference.
[0058] FIG. 10 illustrates the limited amount hardening (increased
tensile loop or strength) that results when the prior art non-wire
stents are plastically deformed during deployment. When the prior
art non-wire strut 50 is expanded, a relatively small area 62
becomes hardened when deformed and therefore less resistance to
crushing or further deformation.
[0059] FIG. 11 illustrates a large amount of hardening (increased
tensile strength) that results when with the present invention is
plastically deformed during deployment. The amount of cross
sectional area having an increased tensile strength is achieved by
the present invention's representative manufacturing processes and
is substantially greater than for the non-wire prior art stents. As
depicted in the upper and lower comparisons, as the loop or strut
61 is expanded, the center of the loop becomes hardened. Once the
center becomes hardened, the adjacent areas on both sides of this
hardened center become hardened as the plastic deformation
continues. Due to the manufacturing process which optimizes the
stress strain characteristics, when the loop is expanded to its
fillest extent, the total area of hardening is significantly
greater in the present invention than the prior art non-wire
stents. The larger portion of hardening 66 equates to a stent
having increased resistance to crushing and further deformation.
Conversely, the prior art non-wire stents have a limited portion of
hardening and therefore significantly less resistance to crushing
or further deformation. This characteristic is clinically
important, for any tendency of a stent to become crushed during
deployment or worse yet, after deployed, could restrict blood flow
or increase the potential for restenosis.
[0060] FIG. 12 illustrates the a standard stress-strain chart
comparing the curves for the prior art non-wire stents with the
present stent invention. As the chart demonstrates, the prior art
non-wire stents have an approximate 30,000 psi yield strength at
which additional stain induces plastic deformation. The present
invention can produce a yield strength ranging from 35,000 to
70,000 psi. The manufacturing process can select a yield point
anywhere within this range to achieve the desired result. The
higher end of the range is significantly greater than the prior art
non-wire stents. These properties are responsible for the present
invention having increased resistance to crushing.
[0061] Furthermore, FIG. 12 also demonstrates that the prior art
non-wire stents have an ultimate tensile strength of approximately
60,000 psi. Any additional strain beyond this point results in
failure of the material. The present invention can produce an
ultimate tensile strength ranging from 65,000 to 120,000 psi. The
manufacturing process can select a ultimate tensile strength
anywhere within this range to achieve the desired result. The
higher end of this range is significantly stronger then the prior
art non-wire stents. These properties are responsible for the
present invention also having an increased resistance to
crushing.
[0062] While the invention has been illustrated and described
herein in terms of its use as an intravascular stent, it will be
apparent to those skilled in the art that the stent can be used in
other instances such as to expand prostate urethras in cases of
prostate hyperplasia. Other modifications and improvements may be
made without departing from the scope of the invention.
[0063] Other modifications and improvements can be made to the
invention without departing from the scope thereof:
* * * * *