U.S. patent application number 11/928188 was filed with the patent office on 2008-10-23 for multilayer stent.
Invention is credited to Marc M. Jalisi.
Application Number | 20080262600 11/928188 |
Document ID | / |
Family ID | 23031203 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080262600 |
Kind Code |
A1 |
Jalisi; Marc M. |
October 23, 2008 |
MULTILAYER STENT
Abstract
A composite stent having a substrate tube made of stainless
steel, a nickel-cobalt-chromium-molybdenum alloy, or chonichrome
with at least one metal cladding tube is disclosed. Specifically,
the substrate tube is placed within a metal cladding tube made of
platinum, gold, tantalum, tungsten, platinum-iridium, palladium, or
nickel-titanium, preferably with an interference fit therebetween.
The composite, laminate tube then undergoes a series of rolling or
cold drawing processes interspersed with heat treating to release
built up stresses. When the final diameter of the laminate tube is
reached, the cladding has been laminated to the exterior of the
substrate tube by a bond generated from the rolling and/or cold
drawing operations. The finished laminate tube is then cut by laser
cutting or chemical etching to form a suitable stent pattern.
Inventors: |
Jalisi; Marc M.; (Temecula,
CA) |
Correspondence
Address: |
ABBOTT CARDIOVASCULAR SYSTEMS INC./;FINNEGAN HENDERSON L.L.P.
901 NEW YORK AVENUE , N.W.
WASHINGTON
DC
20001
US
|
Family ID: |
23031203 |
Appl. No.: |
11/928188 |
Filed: |
October 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10618149 |
Jul 10, 2003 |
7335227 |
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11928188 |
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09270403 |
Mar 16, 1999 |
6620192 |
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10618149 |
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Current U.S.
Class: |
623/1.16 ;
623/1.34 |
Current CPC
Class: |
A61F 2002/91533
20130101; A61F 2/91 20130101; A61F 2230/0013 20130101; A61F
2210/0076 20130101; A61F 2/915 20130101 |
Class at
Publication: |
623/1.16 ;
623/1.34 |
International
Class: |
A61F 2/82 20060101
A61F002/82 |
Claims
1-38. (canceled)
39. A laminate stent for implantation within a body lumen,
comprising: a substrate tube formed from a superelastic alloy and
having an exterior surface; a first cladding layer formed from a
metallic radiopaque material and bonded to the exterior surface of
the substrate tube; a second metallic cladding layer comprising a
NiTi alloy bonded to the first layer thereby forming a laminate
tube; and a stent pattern formed in the laminate tube such that the
resultant laminate stent includes a plurality of radially
expandable cylindrical elements disposed generally coaxially and
interconnected by elements disposed between adjacent cylindrical
elements, the cylindrical elements and the interconnecting elements
being entirely formed of the substrate tube, the first radiopaque
cladding layer, and the second metallic cladding layer.
40. The laminate stent of claim 39, wherein the superelastic alloy
of the substrate tube comprises NiTi.
41. The laminate stent of claim 39, wherein the wall thickness of
the second metallic cladding layer is less than the wall thickness
of the metallic substrate tube.
42. The laminate stent of claim 39, wherein the substrate tube has
a coefficient of thermal expansion that is less than a coefficient
of thermal expansion of the first radiopaque cladding layer.
43. The laminate stent of claim 39, wherein the radiopaque material
in the first cladding layer is a metal selected from the group
consisting of platinum, gold, tantalum, tungsten, a
platinum-iridium alloy, and palladium.
44. The laminate stent of claim 43, wherein the radiopaque material
in the first cladding layer is a platinum-10% iridium alloy.
45. The laminate stent of claim 39, wherein the radiopaque material
in the first cladding layer is selected from the group consisting
of platinum, gold, tantalum, tungsten, a platinum-iridium alloy,
and palladium.
46. The laminate stent of claim 39, wherein the laminate stent has
an unexpanded diameter of up to about 0.1 inches.
47. The laminate stent of claim 46, wherein the laminate stent has
an unexpanded diameter ranging from about 0.05 inches to about 0.07
inches.
48. The laminate stent of claim 39, wherein the laminate stent has
an expanded diameter ranging from about 0.06 inches to about 0.3
inches.
49. The laminate stent of claim 48, wherein the laminate stent has
an expanded diameter ranging from about 0.1 inches to about 0.2
inches.
50. The laminate stent of claim 39, wherein the laminate stent has
a length ranging from about 10 to 50 mm.
51. The laminate stent of claim 50, wherein the laminate stent has
a length ranging from about 15 to 25 mm.
52. The laminate stent of claim 39, wherein each of the plurality
of radially expandable cylindrical elements is independently
expandable.
53. The laminate stent of claim 39, wherein the substrate tube, the
first cladding layer, and the second cladding layer are bonded by
rolling and cold drawing.
54. The laminate stent of claim 39, wherein the substrate tube, the
first cladding layer, and the second cladding layer have been heat
treated.
55. The laminate stent of claim 39, wherein the stent pattern is
formed by a process selected from the group consisting of chemical
etching and laser cutting.
Description
RELATED APPLICATIONS
[0001] This is a divisional application of co-pending parent
application having U.S. Ser. No. 09/270,403, filed Mar. 16, 1999,
the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to expandable intraluminal
vascular devices, generally referred to as stents. More precisely,
the present invention is directed to stents that have a metallic
cladding for improved expansion characteristics and
radiopacity.
[0003] Stents are used to maintain patency of vessels in the body,
such as a patient's arteries. A variety of delivery systems have
been devised that facilitate the placement and deployment of
stents. The stent is initially manipulated while in its contracted
or unexpanded state, wherein its reduced diameter more readily
allows it to be introduced into the body lumen, such as a coronary
artery, and maneuvered into the target site where a lesion has been
dilated. Once at the target site, the stent is expanded into the
vessel wall to allow fluid to flow through the stent, thus
performing a scaffolding function. Stents are usually mounted on
balloon catheters and advanced to a lesion site by advancing the
catheter. At the site, the stent is expanded by inflating the
balloon on which the stent is mounted. Deflation of the balloon and
removal of the catheter leave the stent implanted in the vessel in
an expanded state. It is also possible to dilate a vascular lesion
and deploy a stent at the same time using the same expandable
member or inflatable balloon. This variation of the procedure
described above obviates the need for a separate balloon dilation
catheter and stent deployment catheter.
[0004] Stents are typically formed from biocompatible metals such
as stainless steel, nickel-titanium, tantalum, and the like, to
provide sufficient hoop strength to perform the scaffolding
function of holding the patient's vessel open. Also, stents have
minimal wall thickness in order to minimize blood flow blockage.
But stents can sometimes cause complications including thrombosis,
and neointimal hyperplasia by inducement of smooth muscle cell
proliferation at the site of implantation of the stent. Such stents
typically also do not provide for delivery of localized therapeutic
pharmacological treatment of a blood vessel at the location being
treated with the stent, which can be useful for overcoming such
problems.
[0005] In the evolution of stents, there have been developments in
the field of stents coated with a layer of polymers. The polymeric
materials are typically capable of absorbing and releasing
therapeutic drugs. Examples of such stents are disclosed in U.S.
Pat. No. 5,443,358 to Eury; U.S. Pat. No. 5,632,840 to Campbell;
U.S. Ser. No. 08/842,660, filed Apr. 15, 1997, by J. Yan; and U.S.
Ser. No. 08/837,993, filed Apr. 15, 1997, by J. Yan.
[0006] Aside from coated stents, there have been developments in
the field of multilayer grafts. An example of a multilayer graft is
disclosed in U.S. Pat. No. 4,743,252 to Martin, Jr. et al. Martin
et al. shows a composite graft having a porous wall structure to
permit ingrowth, which graft includes a generally nonporous,
polymeric membrane in the wall to prevent substantial fluid passage
therethrough so as to provide an implantable porous graft that does
not require preclotting prior to implantation. Grafts are known
which have multiple layers for strength reinforcement. For example,
U.S. Pat. No. 5,282,860 to Matsuno et al. discloses a stent tube
comprising an inner tube and an outer polyethylene tube with a
reinforcing braided member fitted between the inner tube and the
outer tube. The inner tube is made of a fluorine-based resin.
[0007] U.S. Pat. No. 5,084,065 to Weldon et al. discloses a
reinforced graft assembly made from a vascular graft component and
a reinforcing sleeve component. The reinforcing sleeve component
may include one or more layers. The second component of the two
component system includes the reinforcing sleeve component. Like
the graft component, the reinforcing component includes a porous
surface and a porous subsurface. Specifically, the reinforcing
sleeve component includes multiple layers formed from synthetic,
biologic, or biosynthetic and generally biocompatible materials.
These materials are typically biocompatible polyurethane or similar
polymers.
[0008] Despite progress in the art, there is presently no stent
available that has a metallic cladding for improved strength
reinforcement, expansion characteristics and radiopacity.
Therefore, there is a need for such a multilayer metallic clad or
laminate stent.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to a multilayer
intracorporeal device, specifically a multilayer or laminate stent
that has a metallic substrate and at least one layer of metallic
cladding. The cladding is generally joined to the substrate under
high pressure resulting in a structure that resists separation or
delamination under normal stress. The cladding metal and the base
or substrate material form a bond between them during a deep
drawing, cold drawing, or co-drawing on a mandrel process. The
method of combining two or more layers of different materials
allows for the combination of desirable properties of those
materials. Typical material properties to be considered for stent
design and performance include strength, ductility, and
radiopacity. For example, a substrate layer material may be chosen
for its strength, a first cladding material chosen for its
ductility, and a second cladding material chosen for its
radiopacity.
[0010] The present invention provides a method of fabricating a
stent for implantation within a body lumen, comprising the steps of
providing a substrate tube having an outside surface and an inside
surface; disposing a first cladding tube about the substrate tube,
wherein the first cladding tube includes a metal; joining the first
cladding tube to the outside surface of the substrate tube to form
a laminate tube; and forming a stent pattern in the laminate tube
to provide for expansion of the stent. In a preferred embodiment,
the substrate tube includes a metal selected from the group
consisting of stainless steel, a nickel-cobaltchromium-molybdenum
alloy, or chonichrome; and the first cladding tube includes a
radiopaque metal, preferably selected from the group consisting of
platinum, gold, tantalum, tungsten, platinum-10% iridium, or
palladium. It may also be desirable to have a substrate tube of a
psuedoelastic alloy such as NiTi. A substrate tube from such an
alloy can provide mechanical characteristics which facilitate
expansion of a stent within a patient's vessels and minimize trauma
to the vessels, particularly in indications such as carotid artery
treatment.
[0011] Joining the first cladding tube to the outside surface of
the substrate tube can include rolling and drawing the laminate
tube to bond or secure the first cladding tube to the substrate
tube. This process is known in the art as deep drawing, cold
drawing, or co-drawing on a mandrel. Concurrent or in series with
the cold drawing process, the laminate tube can be heat treated or
annealed to release stress build-up from the cold working. The bond
between the substrate tube and the first cladding tube can be
mechanical in whole or in part.
[0012] In an alternative method, the present invention further
includes disposing a second cladding tube about the first cladding
tube; and joining the second cladding tube to the first cladding
tube. As a result, the finished stent has two cladding layers
laminated on the tubular substrate. Typically, the second cladding
layer will be made of a radiopaque metal, preferably including a
metal selected from the group consisting of platinum, gold,
tantalum, tungsten, platinum-iridium, or palladium. A preferred
platinum-iridium alloy is a platinum-10% iridium alloy.
[0013] The present invention further contemplates a device which is
preferably produced by the above methods, i.e. a stent for
implantation within a body lumen having a substrate tube with an
exterior surface; a metallic cladding bonded under pressure about
the exterior surface of the substrate tube; and a stent pattern
formed in the substrate tube and the metallic cladding. In a
preferred embodiment, the cladding includes a radiopaque metal,
preferably selected from the group consisting of platinum, gold,
tantalum, tungsten, platinum-iridium, or palladium. Furthermore,
the substrate tube generally includes a metal selected from the
group consisting of stainless steel, a
nickel-cobalt-chromium-molybdenum alloy, or chonichrome. The
substrate tube can also include a superelastic or superelastic
alloy such as NiTi.
[0014] In particular, it has been found that for the substrate
tube, materials such as 316L stainless steel,
nickel-cobalt-chromium-molybdenum alloys such as MP35N, or
cobalt-chromium-tungsten-nickel-iron alloys such as L605,
(chonichrome) are preferable. For the cladding tube, it has been
found that platinum, gold, tantalum, tungsten, platinum-10%
iridium, or palladium are preferred. Each of the cladding material
adds to the performance of the finished laminate tube which would
otherwise not be possible with a pure 316L stainless steel, MP35N,
or chonichrome tube alone. Another benefit of the present invention
is that the metal cladded stent can have a desired amount of
radiopacity. Indeed, using cladding tubes made of radiopaque alloys
or metals such as platinum, gold, tantalum, or platinum-iridium
increases the radiopacity of the stent to assist the cardiologist
in tracking the stent during implantation.
[0015] The present invention can additionally benefit from use of a
substrate or cladding tube made from nickel-titanium, which is a
shape memory alloy which can exhibit superelastic properties. With
a higher deformation rate due to a nickel-titanium cladding tube,
the laminate stent eliminates the need for higher pressure balloons
and as a result, the risk of injury to the vessel walls is reduced.
The nickel-titanium eases the expansion of the stent in normal
temperatures and contraction in relatively elevated temperatures.
Where a superelastic alloy such as NiTi is used as a cladding layer
in combination with a non-radiopaque high strength alloy substrate
such as stainless steel, MP35N or L605, it is generally preferred
to include a second cladding layer or tube of a radiopaque metal
such as those described above. In this way, the desired mechanical
characteristics of the stent can be achieved with the appropriate
combination of substrate and first cladding materials, and
radiopacity is added to the stent by the second cladding layer or
tube.
[0016] These and other advantages of the present invention will
become apparent from the following detailed description thereof
when taken in conjunction with the accompanying exemplary
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of a preferred embodiment stent
with a tubular cladding mounted on a mandrel, and undergoing
compression applied by an external roller.
[0018] FIG. 2 is a perspective view of a deep drawing operation
showing the present invention stent prior to passing through a
die.
[0019] FIG. 3 is a perspective view of a preferred embodiment
metallic clad stent having struts formed therein.
[0020] FIG. 4 is a perspective view of an alternative embodiment
stent having multiple cladding layers with the stent struts formed
therein.
[0021] FIG. 5 is an elevational view in partial section of a
delivery catheter within an artery with a laminate stent having
features of the invention disposed about the delivery catheter.
[0022] FIG. 6 is a perspective view of a laminate stent having
features of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] FIG. 1 is a perspective view of a preferred embodiment of a
laminate tube having features of the present invention. As seen in
this simplified view, the present invention contemplates creation
of laminate tube 10 by joining metal cladding tube 12 to an
exterior surface of substrate tube 14. Fundamental to this joining
process is first defining the initial diameters of metal cladding
tube 12, which should already be in a tubular configuration as seen
in FIG. 1, and of substrate tube 14. Tubes 12, 14 can be made by
conventional fabrication processes, such as drawing, rolling sheet
stock and welding the seam, etc. During these preliminary steps,
the diameters and wall thickness of tubes 12 and 14 are selected
and set.
[0024] In the preferred embodiment of the present invention, there
should be an interference fit between the outside diameter of
substrate tube 14 and the inside diameter of metal cladding tube
12. The interference fit prevents unwanted, relative shifting
between substrate tube 14 and the concentrically disposed cladding
tube 12. It is further preferable that the wall thickness of
substrate tube 14 be greater than the wall thickness of metal
cladding tube 12. The initial wall thicknesses can be important,
because the present invention processes encompass a co-drawing or
cold drawing operation that reduces the diameter and wall thickness
of each tube while increasing its length. To maintain continuous
contact at the interface between the interior of metal cladding
tube 12 and the exterior of substrate tube 14, it is preferable
that the initial wall thicknesses of the respective parts be as
described above.
[0025] The volumes of metal cladding tube 12 and substrate tube 14
are conserved throughout the various cold drawing stages of
diameter reduction. Because the outer tube has a larger surface
area than the inner tube, its initial wall thickness must be
thinner than the initial wall thickness of the inner tube in order
to obtain a decrease in diameter proportionate to the inner tube.
In this way, the respective diameters of tubes 12, 14 and their
wall thicknesses are reduced proportionately and their lengths
increased identically thus minimizing the chance of
delamination.
[0026] In the preferred embodiment of FIG. 1, metal cladding tube
12 is made from a radiopaque material such as platinum, gold,
tantalum, tungsten, platinum-iridium alloy, or palladium. Substrate
tube 14 is preferably made from a material such as stainless steel
including 316L, a nickel-cobalt-chromium-molybdenum alloy such as
MP35N, or from a chonichrome such as L605. MP35N is a trade name
for a metal alloy comprising 35% nickel, 33.2% cobalt, 20%
chromium, 9.53% molybdenum, and trace amounts of other elements.
L605 is a trade name for a metal alloy comprising 50.5% cobalt, 20%
chromium, 15.28% tungsten, 9.8% nickel, and trace amounts of iron
and other elements. The aforementioned materials facilitate
consistent tube diameter and wall thickness reduction while
minimizing the chance of delamination of the concentric tubes. Of
course reversing the material selection for the substrate tube and
the cladding tube in specific applications is also contemplated. In
addition, a substrate tube containing a superelastic alloy such as
NiTi can also be used.
[0027] Laminate tube 10 comprising of metal cladding tube 12 over
substrate tube 14 is optionally mounted on mandrel 16 and rolled by
application of external pinching pressure through roller 18. This
is represented in the perspective view of FIG. 1. Along with the
rolling operation depicted in FIG. 1, the present invention
contemplates a co-drawing or cold drawing operation shown in the
perspective view of FIG. 2. Here, laminate tube 10 with metal
cladding tube 12 surrounding substrate tube 14 is shown prior to
passing through opening 20 of die 22. By passing through a series
of dies 22 with sequentially decreasing opening diameters, it is
possible to deep draw laminate tube 10 to the final desired
diameter. As the name suggests, this cold drawing process is
preferably carried out at room temperature, below the
recrystallization temperatures of the tube materials. By repeating
the operations shown in FIGS. 1 and 2, it is possible to reduce
laminate tube 10 from a starting outside diameter of, for example,
about 0.5 inch down to about 0.06 inch. The starting wall thickness
for the laminate tube 10 is about 0.03 to about 0.065 inches and is
reduced down to about 0.003 inch.
[0028] In a preferred embodiment process, the rolling and cold
drawing operations are repeated to achieve a maximum of 25 percent
in reduction of surface area, to be followed by a heat treating
step to release built up internal stresses. Without the heat
treating step, there is a possibility that the deformations are
sufficient to exceed the ultimate yield strength of the materials
thereby causing ruptures or cracks. Each sequence of operations
slowly reduces the diameter of composite stent while
proportionately increasing its length.
[0029] Although the rolling and cold drawing processes of the
present invention 20 are conducted at room temperature, the
pressures involved may cause the temperature between metal cladding
tube 12 and substrate tube 14 to elevate sufficiently to facilitate
a mechanical bond which is typically created between the two
adjacent layers. In this manner, metal cladding tube 12 is
permanently attached to substrate tube 14 and delamination of the
two materials is minimized under normal operating conditions for
the stent. It is desirable to eliminate delamination between the
two or more layers entirely. Preferably, the material used as
substrate tube 14 has a smaller coefficient of thermal expansion
than the material used for the cladding tube 12. This facilitates
maintaining contact between the two tubes 12 and 14 during the
rolling and cold drawing processes and prevents delamination of the
tubes subsequent thereto.
[0030] In a preferred method, laminate tube 10 undergoes about a
twenty-five percent (25%) diameter reduction from the rolling or
cold drawing operations. This is accomplished by passing laminate
tube 10 through a series of dies 22 with each die reducing the
diameter by preferably one percent (1%). With a series of
twenty-five dies 22, it is possible to achieve the twenty-five
percent (25%) diameter reduction.
[0031] Laminate tube 10 then undergoes a heat treat process to
release stress and to eliminate restrained dislocations. Next,
laminate tube 10 undergoes another twenty-five percent (25%)
diameter reduction by cold drawing or rolling, followed by another
heat treating process. This cycle is repeated until the desired
diameter of laminate tube 10 is reached. Throughout the present
invention process, laminate tube 10 may optionally undergo anneal
cycles in order to impart desired material properties such as
ductility, strength, etc. Through the present invention process, it
has been observed that the finished laminate tube 10 has a
straightness of 0.02 inch per inch for a six to twelve inch length
tube. When the final diameter is reached, the laminate tube is cut
to length.
[0032] Laminate tube 10 is further processed to form a stent
pattern therein such as illustrated by stent 40 in FIGS. 5 and 6
discussed below. One method for forming such a stent pattern is by
chemical etching. Such a process is disclosed in, for example, U.S.
Pat. No. 5,735,893 to Lau et al., entitled "Expandable Stents and
Method for Making Same," the contents of which is hereby
incorporated by reference. Alternatively, a stent pattern may be
formed by a laser cutting process. Such a process is shown and
disclosed in, for example, U.S. Pat. No. 5,759,192 to Saunders,
entitled "Method and Apparatus for Direct Laser Cutting of Metal
Stents," the contents of which is hereby incorporated by
reference.
[0033] FIG. 3 is a perspective view of a finished laminate tube 24
having metal cladding tube 12 laminated to substrate tube 14. The
thickness of a single wall of the metal cladding tube 12 is about
0.0001 to about 0.010 inches, preferably about 0.0005 to about
0.004 inches. The thickness of a single wall of the substrate tube
14 is about 0.0001 to about 0.010 inches, preferably about 0.001 to
about 0.004 inches. The material of the substrate tube 14 is
preferably 316L stainless steel, but can also be other types of
stainless steel, MP35N, L605 or superelastic alloys such as NiTi.
The material of the metal cladding tube 12 is preferably
platinum-10% iridium, but can also be gold, tantalum, platinum,
palladium, tungsten or the like.
[0034] FIG. 4 provides a perspective view of an alternative
embodiment of a laminate tube 28 having substrate tube 30 that is
laminated with first metallic cladding tube 32. Second metallic
cladding tube 34 is laminated to the outer surface of first
metallic cladding tube 32. The thickness of a single wall of the
substrate tube 30 is about 0.0001 to about 0.010 inches, preferably
about 0.001 to about 0.004 inches. The thickness of a single wall
of the first metallic cladding tube 32 is about 0.0001 to about
0.002 inches, preferably about 0.0005 to about 0.001 inches. The
thickness of a single wall of the second metallic cladding tube 34
is about 0.0001 to about 0.002 inches, preferably about 0.0005 to
about 0.001 inches. The material of the substrate tube 30 is
preferably 316L stainless steel, but can also be other types of
stainless steel, MP35N, L605, NiTi or the like or any suitable
radiopaque metal such as those discussed above. The material of the
first cladding tube 32 is preferably NiTi, but can also be
stainless steel, MP35N, L605 or the like, or any suitable
radiopaque metal such as those discussed above. The material of the
second metallic cladding tube 34 is preferably platinum-10%
iridium, but can also be any other suitable radiopaque metal such
as those discussed above, or a superelastic alloy such as NiTi, or
a high strength metal or alloy such as stainless steel, MP35N, L605
or the like.
[0035] The multiple layers of cladding of laminate tube 28 are
created as previously described in connection with FIGS. 1 and 2,
except that second metallic cladding tube 34 is added to the
outside surface of first metallic cladding tube 32. The three tubes
30, 32, 34 then undergo the rolling or cold drawing, and heat
treating operations as described previously. When the final
diameter is reached, laminate tube 28 is cut to the desired length
and processed to form a stent pattern.
[0036] As previously discussed, one typical metallic cladding or
substrate material is superelastic or pseudoelastic nickel-titanium
(NiTi) alloy. Because nickel-titanium is a superelastic or shape
memory alloy, it is possible to create a stent that reverts to
various formations based on the ambient temperature and applied
stress. In one example, a NiTi-clad stent is formed full size but
deformed (i.e., compressed) into a smaller diameter onto the
balloon of a delivery catheter to facilitate transfer to the
intended intraluminal site. The stress induced by the deformation
transforms the stent from an austenitic phase to a martensitic
phase. Upon release of the restraining force, when the stent
reaches the desired site, the stent self-expands isothermally by
transformation back to the austenitic phase. Similarly, for shape
memory NiTi alloys, the metal transforms from the martensitic to
the austenitic phase upon application of heat, such as exposure to
body temperature, resulting in self-expansion of the cladding
material. The behavior of such superelastic alloys and their
processing are well known in the art. Certainly a benefit is that
the nickel-titanium eases the expansion of the stent in normal body
temperatures. In a preferred embodiment, if the cladding includes a
radiopaque metal such as gold, platinum, tantalum, platinum-iridium
alloy, the radiopacity of the stent is improved. Accordingly, the
present invention can have enhanced performance or expansion
characteristics as well as improved visibility for the
cardiologist.
[0037] In FIG. 5 a laminate stent 40 incorporating features of the
invention is illustrated mounted on a delivery catheter 41. The
laminate stent 40 generally has a plurality of radially expandable
cylindrical elements 42 disposed generally coaxially and
interconnected by elements 43 disposed between adjacent cylindrical
elements. The delivery catheter 41 has an expandable member or
balloon 44 for expanding the laminate stent 40 within an artery 45.
The artery 45, as shown in FIG. 5, has a dissected lining 46 which
has occluded a portion of the arterial passageway.
[0038] A laminate stent 40 can have an outside diameter of up to
about 0.1 inch in the unexpanded condition, preferably, about 0.05
to about 0.07 inches. The laminate stent 40 can be expanded to an
outside diameter of about 0.06 to about 0.3 inches or more,
preferably about 0.1 to about 0.2 inches, when deployed in a body
lumen. The length of the laminate stent 40 prior to expansion is
about 10 to about 50 mm, preferably about 15 to about 25 mm. In
addition, multiple laminate stents 40 can be connected in order to
create a stent with an effective length of any multiple of the
previously discussed lengths. Thus, 2, 3, 4, 5 or more laminate
stents 10 can be connected in order to create a stent with a longer
effective length.
[0039] The delivery catheter 41, onto which the stent 40 is
mounted, can be essentially the same as a conventional balloon
dilatation catheter used for angioplasty procedures. The balloon 44
may be formed of suitable materials such as polyethylene,
polyethylene terephthalate, polyvinylchloride, nylon and ionomers
such as Surlyn.TM. manufactured by the polymer products division of
the DuPont Company. Other polymers may also be used. In order for
the laminate stent 40 to remain in place on the balloon 44 during
delivery to the site of the damage within the artery 45, the
laminate stent 40 is compressed onto the balloon. A retractable
protective delivery sleeve 50 as described in co-pending
application Ser. No. 07/647,464 filed on Apr. 25, 1990 and entitled
STENT DELIVERY SYSTEM may be provided to further ensure that the
stent stays in place on the expandable portion of the delivery
catheter 41 and prevent abrasion of the body lumen by the open
surface of the stent 40 during delivery to the desired arterial
location. Other means for securing the laminate stent 40 onto the
balloon 44 may also be used, such as providing collars or ridges on
the edges of the working portion, i.e., the cylindrical portion, of
the balloon.
[0040] Each radially expandable cylindrical element 42 of the
laminate stent 40 may be independently expanded. Therefore, the
balloon 44 may be provided within an inflated shape other than
cylindrical, e.g., tapered, to facilitate implantation of the
laminate stent 40 in a variety of body lumen shapes.
[0041] In a preferred embodiment, the delivery of the laminate
stent 40 is accomplished in the following manner. The laminate
stent 40 is first mounted onto the inflatable balloon 44 on the
distal extremity of the delivery catheter 41. The balloon 44 is
slightly inflated to secure the laminate stent 40 onto the exterior
of the balloon. The catheter/stent assembly is introduced within
the patient's vasculature in a conventional Seldinger technique
through a guiding catheter 47. A guide wire 48 is disposed across
the damaged arterial section with the detached or dissected lining
46 and then the catheter/stent assembly is advanced over a guide
wire 48 within the artery 45 until the laminate stent 40 is
directly under the detached lining 46. The balloon 44 of the
catheter is expanded, expanding the laminate stent 40 against the
artery 45.
[0042] The laminate stent 40 serves to hold open the artery 45
after the catheter 41 is withdrawn. Due to the formation of the
laminate stent 40 from an elongated laminate tube, the undulating
component of the cylindrical elements of the laminate stent 10 is
relatively flat in transverse cross-section, so that when the stent
is expanded, the cylindrical elements are pressed into the wall of
the artery 45 and as a result do not interfere with the bloodflow
through the artery 45. The cylindrical elements 42 of the laminate
stent 40 which are pressed into the wall of the artery 45 will
eventually be covered with endothelial cell growth which further
minimizes bloodflow interference. The undulating portion of the
cylindrical sections 42 provide good tracking characteristics to
prevent stent movement within the artery. Furthermore, the closely
spaced cylindrical elements 42 at regular intervals provide uniform
support for the wall of the artery 45, and consequently are well
adopted to tack up and hold in place small flaps or dissections in
the wall of the artery 45.
[0043] FIG. 6 is an enlarged perspective view of the laminate stent
40 shown in FIG. 5 with one end of the stent shown in an exploded
view to illustrate in greater detail the placement of
interconnecting elements 43 between adjacent radially expandable
cylindrical elements 42. Each pair of interconnecting elements 43
on one side of cylindrical elements 42 are preferably placed to
achieve maximum flexibility for a stent. In the embodiment shown in
FIG. 6, the laminate stent 40 has three interconnecting elements 43
between adjacent radially expandable cylindrical elements 42 which
are 120.degree. apart. Each pair of interconnecting elements 43 of
one side of a cylindrical elements 42 are offset radially
60.degree. from the pair on the other side of the cylindrical
element. The alternation of the interconnecting elements result in
a stent which is longitudinally flexible in essentially all
directions. Various configurations for the placement of
interconnecting elements 43 are possible. In addition, while the
expandable cylindrical elements 42 and interconnecting elements 43
have been shown in the stent pattern depicted in FIGS. 5 and 6, any
suitable stent pattern that allows for a desired amount of
expansion and radial strength for a given application is also
contemplated. For example, the laminate tubes 10, 24 and 28 could
have any of a number of mesh-like or spiral stent patterns formed
thereon.
[0044] While particular embodiments of the present invention have
been illustrated and described, it is apparent to those skilled in
the art that various modifications can be made without departing
from the spirit and scope of the invention. Any of a variety of
stent designs and applications can benefit from the present
invention. Accordingly, it is not intended that the present
invention be limited except by the appended claims.
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