U.S. patent application number 10/695255 was filed with the patent office on 2004-05-06 for radially expansible vessel scaffold having modified radiopacity.
This patent application is currently assigned to AVANTEC VASCULAR CORPORATION. Invention is credited to Klein, Enrique J..
Application Number | 20040088043 10/695255 |
Document ID | / |
Family ID | 26740524 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040088043 |
Kind Code |
A1 |
Klein, Enrique J. |
May 6, 2004 |
Radially expansible vessel scaffold having modified radiopacity
Abstract
The present invention provides improved prostheses and methods
for their endolumenal placement within body lumens, particularly
blood vessels. In one embodiment, the prosthesis of the present
invention comprises a plurality of radially expansible rings
having, a plurality of beams connecting axially remote points on
adjacent rings, and a plurality of expansion joints connecting
axially proximate points on adjacent rings. The beams maintain the
remote points at a fixed distance when the prosthesis is radially
expanded and the expansion joints allow for relative movement of
the proximate points during delivery of the prosthesis. The
combination of the beams and expansion joints minimizes the risk of
injury to the body lumen during delivery of the prosthesis to a
target site and provides improved tracking capabilities.
Inventors: |
Klein, Enrique J.; (Los
Altos, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
AVANTEC VASCULAR
CORPORATION
Sunnyvale
CA
94089
|
Family ID: |
26740524 |
Appl. No.: |
10/695255 |
Filed: |
October 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10695255 |
Oct 27, 2003 |
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09687606 |
Oct 11, 2000 |
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09687606 |
Oct 11, 2000 |
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08968319 |
Nov 12, 1997 |
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6602281 |
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60060938 |
Oct 3, 1997 |
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Current U.S.
Class: |
623/1.16 ;
623/1.15 |
Current CPC
Class: |
A61F 2/88 20130101; A61F
2002/91508 20130101; A61F 2250/0039 20130101; A61F 2/958 20130101;
A61F 2002/91525 20130101; A61F 2/915 20130101; A61F 2002/825
20130101; A61F 2002/91566 20130101; A61F 2002/8486 20130101; A61F
2002/9155 20130101; A61F 2002/91541 20130101; A61F 2/0095 20130101;
A61F 2250/0018 20130101; A61F 2002/91558 20130101; A61F 2250/0098
20130101; A61F 2/91 20130101; A61F 2/86 20130101; A61F 2002/91516
20130101 |
Class at
Publication: |
623/001.16 ;
623/001.15 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. An expandable tubular stent comprising: an expandable tubular
body having a first end, a second end, a plurality of
interconnected cylindrical wall sections including a first
cylindrical wall section at the first end of the tubular body, a
second cylindrical wall section at the second end of the tubular
body, and at least one intermediate cylindrical wall section
between the first and second cylindrical wall sections, and a
plurality of S-shaped connectors which extend between and are
secured to a cylindrical wall section and a longitudinally adjacent
cylindrical wall section and configured to provide both expansion
and contraction between adjacent cylindrical wall sections.
2. The expandable tubular stent of claim 1, wherein the S-shaped
connectors comprise a double curvature shape.
3. The expandable tubular stent of claim 1, wherein the connecting
members are secured to proximate points of adjacent cylindrical
wall sections.
4. The expandable tubular stent of claim 2, wherein the connecting
members are secured to proximate points of adjacent cylindrical
wall sections.
5. The expandable tubular stent of any of claims 1 to 4, wherein
the S-shaped connectors, connect at least some of the
longitudinally adjacent cylindrical wall sections extending along
an intermediate section of the stent which is disposed between ends
of the stent.
6. An expandable tubular stent comprising: an expandable tubular
body having a first end, a second end, a plurality of
interconnected cylindrical wall sections including a first
cylindrical wall section at the first end of the tubular body, a
second cylindrical wall section at the second end of the tubular
body, and at least one intermediate cylindrical wall section
between the first and second cylindrical wall sections, having an
unexpanded and expanded configuration; and a plurality of S-shaped
connectors which extend between and are secured to a cylindrical
wall section and a longitudinally adjacent cylindrical wall section
and configured to provide a flexibility in both the expanded and
unexpanded configurations.
7. An expandable tubular stent comprising: an expandable tubular
body having a first end, a second end, a plurality of
interconnected cylindrical wall segments including a first
cylindrical wall segment at the first end of the tubular body, a
second cylindrical wall segment at the second end of the tubular
body, and at least one intermediate cylindrical wall segment
between the first and second cylindrical wall segments, and at
least one extendable connector which has a first end secured to a
cylindrical wall segment at a first location and a second end
secured to a longitudinally adjacent cylindrical wall segment at a
second location circumferentially off set from the first
location.
8. The expandable tubular stent of claim 7, wherein the at least
one extendable connector has an S-shape.
9. The expandable tubular stent of claim 7, wherein the at least
one extendable connector has a double curvature.
10. The expandable tubular stent of claim 7, wherein the at least
one extendable connector is configured to provide both expansion
and contraction between adjacent cylindrical wall segments.
11. The expandable tubular stent of claim 7, wherein a plurality of
cylindrical wall segments have at least one extendable connector
which has a first end secured to a cylindrical wall segment at a
first location and a second end secured to a longitudinally
adjacent cylindrical wall segment at a second location
circumferentially off set from the first location.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present invention is a continuation of U.S. patent
application Ser. No. 09/687,606 (Attorney Docket No. 20460-000710),
filed Oct. 11, 2000, which was a continuation of U.S. patent
application Ser. No. 08/968,319 (Attorney Docket No. 20460-000700),
filed on Nov. 12, 1997, which claimed the benefit of provisional
U.S. Patent Application Serial No. 60/060,938, filed on Oct. 23,
1997 (Attorney Docket No. 15509-5000). The full disclosures of each
of these patents and patent applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the structure of
radially expansible lumenal prostheses, including stents and
grafts. More particularly, the present invention relates to the
provision of articulation structures for the construction of
flexible and pseudo-flexible prostheses and the provision of end
structures for the construction of atraumatically deliverable
prostheses.
[0004] Lumenal prostheses are provided for a variety of medical
purposes. For example, lumenal stents can be placed in various body
lumens, such as blood vessels, the ureter, the urethra, biliary
tract, and gastrointestinal tract, for maintaining patency. Lumenal
stents are particularly useful for placement in pre-dilated
atherosclerotic sites in blood vessels. Lumenal grafts can be
placed in blood vessels to provide support in diseased regions,
such as aortic abdominal, and other aneurysms.
[0005] Both stent and graft prostheses must meet certain mechanical
criteria to function successfully. In particular, such prostheses
should be at least partly flexible or articulated (such as rigid
sections that articulate relative to one another) over their
lengths so that they may be advanced through tortuous body lumens,
such as those of the coronary vasculature. In addition, the
prostheses should preferably maintain their original length or
foreshorten minimally when the prostheses assume an expanded
configuration. Further such prostheses must have sufficient
mechanical strength, particularly hoop strength, in order to
mechanically augment the lumenal wall strength and thus assure
lumen patency. The ability to meet these requirements is severely
limited in the case of cylindrical endolumenal prostheses which are
delivered in a radially constrained or collapsed configuration.
Such prostheses must radially expand at a target site within the
body lumen, so any adaptations which are intended to enhance
flexibility will not interfere with the ability to radially expand
or to maintain strength once expanded.
[0006] Prior lumenal prostheses often have structures which present
a risk of injury as they are endolumenally delivered (i.e. tracked)
to and/or released at a target site within a patient's body lumen.
In particular, many vascular stents comprise a plurality of
circumferentially connected and spaced-apart longitudinal elements
which deform circumferentially as the stent is radially expanded.
The Palmaz stent described in U.S. Pat. Nos. 5,102,417 and
4,776,337, is typical of such stents. When these prostheses are
flexed or articulated during delivery or tracking, these
longitudinal elements of conventional prosthesis tend to create a
phenomenon known as "fishscaling" which occurs when these elements
distributed along the length of the prosthesis protrude outward
from the surface of the prosthesis. Such stents exhibit poor
"tracking" characteristics, where "tracking" is defined as the
ability to pass smoothly through tortuous pathways. These
protruding elements along the length of the prosthesis increase the
likelihood that the prosthesis will dig into or otherwise engage
the wall of the body lumen during delivery and even arrest the
progress of the prosthesis and its delivery system to the diseased
region (or target site). Additionally, a lesser-known phenomenon
called "flaring" occurs when the longitudinal elements of the
distal or proximal end of the prosthesis are bent outward to assume
a crown-like configuration due to bending forces placed on these
elements as the prosthesis passes through tortuous body
passageways. Flaring can create the same deleterious effects as the
previously described fishscaling phenomenon, injuring or
traumatizing the blood vessel wall as the prosthesis is delivered
or tracked within the blood vessel.
[0007] A separate problem in stent construction and deployment
relates to the ability to detect the stent fluoroscopically during
the deployment procedure. Stainless steel, the most common stent
material, is generally radiolucent, i.e. it is minimally visible
under x-rays and permits fluoroscopic examination therethrough.
Advantageously, such stents do not interfere with subsequent
fluoroscopic examination of the treated region of the body lumen,
such as six-month-followup examinations. They are, however, much
more difficult to accurately position within the lumen due to their
radiolucency. To increase radiopacity, these prostheses may be
manufactured from radiopaque materials such as tantalum, platinum,
or nickel titanium (NiTi). Alternatively, the entire prosthesis may
be plated or coated with a uniform layer of radiopaque material to
improve prosthesis visualization as disclosed in commonly assigned,
co-pending U.S. patent application Ser. No. 08/691,661, filed Aug.
2, 1996 (Attorney Docket No. 15509-003900), the complete disclosure
of which is incorporated herein by reference. Although these
methods address the issue of radiopacity, uniform layers of such
materials or prostheses made entirely of such materials typically
improve radiopacity at the cost of reduced visibility of tissue
inside the prosthesis.
[0008] For these reasons, it would be desirable to provide improved
stents and other lumenal prostheses. In particular, it would be
desirable to provide improved lumenal prostheses and methods for
their endolumenal placement, where the prostheses can be delivered
or tracked to a target site within a body lumen without
traumatically engaging the walls of the body lumen. Preferably, the
prostheses will have elements which minimize "fishscaling" with its
concomitant risk of injury or even retention within the body lumen.
Such prostheses may also be provided with minimally traumatic end
rings in order to reduce the risk of lumenal injury as the
prostheses is both delivered and radially expanded within the body
lumen. Optionally, the ends of the prostheses may incorporate
stiffening elements which reduce the occurrence of prosthesis
flaring or trumpeting during tracking through tortuous body lumens.
Additionally, the prostheses will be radially expansible at the
target location, and will preferably retain both their cylindrical
configuration and flexibility or ability to articulate after
expansion. Such prostheses should further have sufficient hoop
strength and other mechanical characteristics so that they may
effectively function as stents in maintaining lumenal patency
and/or grafts in enhancing lumenal wall strength. To more precisely
direct scaffolding force at a diseased site, the prosthesis may
have specific expanded configurations. Furthermore, it would be
desirable to provide improved prostheses having radiopacity
characteristics which permit visualization of the prosthesis both
during tracking and deployment as well as visualization of tissue
within the lumen during subsequent angiographic followup after
deployment. The present invention will provide at least some of the
desired improvements.
[0009] 2. Description of the Background Art
[0010] Vascular stents comprising multiple segments joined by axial
hinge structures are described in U.S. Pat. Nos. 5,195,984;
5,104,404; and 5,102,417 and European Patent Publication EP 540
290. Other stent structures are described in U.S. Pat. No.
5,282,824, European Patent Publication EP 481 365; and Canadian
Patent Publication 2,079,944. U.S. Pat. No. 4,776,337 describes the
Palmaz stent which consists of multiple longitudinal box elements
joined to each other by short circumferentially oriented tabs and
usually having at least two such sections joined longitudinally by
a single short beam as shown in U.S. Pat. No. 5,195,984.
SUMMARY OF THE INVENTION
[0011] The present invention provides improved prostheses and
methods for their endolumenal placement within body lumens,
particularly blood vessels. The prostheses may be in the form of
stents, intended for maintaining lumenal patency, or may be in the
form of grafts, intended for protecting or enhancing the strength
of the lumenal wall. The prostheses of the present invention will
be radially expansible, either by the application of an internal
force to expand a minimally resilient (usually malleable)
prosthesis structure or by release of radial constraint from a
resilient prosthesis structure (self-expanding).
[0012] In a first aspect of the present invention, the prosthesis
comprises a plurality of radially expansible unit segments, such as
rings, having a plurality of beams connecting axially remote points
on adjacent unit segments, and a plurality of compliant elements
referred to hereinafter as expansion joints connecting axially
proximate points on adjacent unit segments. The beams are usually
aligned axially and maintain the remote points at a fixed distance
at all times including when the prosthesis is radially expanded.
The expansion joints, in contrast, allow for relative movement of
the proximate points during bending, expansion, or any other
deformation of the prosthesis. The expansion joint may have any
convenient geometry, such as an "S" shape, a "Z" shape, a
serpentine pattern, a zig-zag pattern, or the like. Thus, the
expansion joints will provide a compliant, flexible connection of
the proximate points on the unit segments to reduce or prevent
protrusion or "fishscaling" of these points as the prosthesis is
delivered through a tortuous path or deployed (expanded) at a
curved target site.
[0013] To create the tracking and expansion characteristics desired
in the prosthesis, the beams and expansion joints may be positioned
in particular patterns between each unit segment. For example,
although adjacent unit segments of the prosthesis may be coupled by
both expansion joints and beams, they are preferably joined by only
one beam and some number of expansion joints. Having only one beam
balances the benefits of length compensation and prosthesis
flexibility. Beams of the prosthesis are preferably positioned in a
"laddered" configuration where the sequence of longitudinal beams
is circumferentially and longitudinally staggered, typically with a
predetermined amount of longitudinal overlap between the beams when
in the unexpanded configuration. The amount of overlap may be about
one-third the length of each beam or more preferably one-half the
length of each beam. In certain embodiments, beams may also have a
weakened midportion of lesser width or lesser thickness than the
remainder of the beam to increase transverse flexibility of the
prosthesis. The expansion joints may also be weakened to maximize
flexibility and minimize interference with the ability of the
prosthesis to track. Typically, weakened expansion joints have
smaller width or smaller thickness than the longitudinal struts in
the unit segments.
[0014] In a second aspect of the present invention, the prosthesis
may include elements to increase radial stiffness both when
unexpanded and when expanded, such as an end segment requiring a
greater radial expansion force than another segment in the middle
of the prosthesis. In one embodiment, the end segment is a
serpentine ring having longitudinal struts of shorter length than
the longitudinal struts of segments in the middle of the
cylindrical frame. Alternatively, the end rings could have
increased stiffness by using hinges of increased width or thickness
between each longitudinal portion or strut, as disclosed in
commonly assigned, co-pending U.S. patent application Ser. No.
08/691,661, filed Aug. 2, 1996 (Attorney Docket No. 15509-003900),
the complete disclosure of which has been previously incorporated
herein. Increased radial stiffness at the ends of the prosthesis,
such as through struts of shorter lengths or box structures with
unequal strut lengths, tends to reduce flaring or trumpeting of
these ends which may occur during tracking through tortuous
passageways. A still further improvement for reducing prosthesis
flaring or trumpeting involves using a radially stiffened end
segment that is hinged by a long beam to an adjacent segment. The
single beam provides articulation between the segments and thus
reduces the load placed on the struts in the end segments.
Additionally, a prosthesis can be mounted on an inflation member
such as a balloon which can shape the expanded prosthesis into a
noncylindrical shape. For example, the prosthesis may be expanded
into a tapered configuration to provide improved fit and
scaffolding in body lumens which have conical configurations. The
ability of the inflation member, such as a noncylindrical balloon,
to expand a prosthesis into a shape that better conforms to the
lumenal geometry may also be enhanced by having unit segments of
various radial stiffnesses, such as having a stiffness gradient
from one segment to the next, or other nonuniform stiffnesses along
the length of the prosthesis.
[0015] In a third aspect, a system according to the present
invention includes a cylindrical frame forming a prosthesis having
a plurality of radially expansible unit segments, a longitudinal
length, a distal end and a proximal end. The frame is preferably
mounted over an expansible cylindrical section of an inflation
member such as a balloon. In this third aspect, the expansible
cylindrical section has the same length as the length of the
cylindrical frame. Advantageously, this minimizes expansion of the
balloon beyond the ends of the prosthesis which may do
dissectogenic damage, particularly to the distal the body lumen in
which the system is delivered. The inflation section of the balloon
is preferably no more than about 1 mm longer from each end of the
typically cylindrical frame, more preferably about the same length
as the cylindrical frame. The present invention also provides a kit
with instructions for use describing a method for mounting a
prosthesis over such a matching length balloon together with a
mounting tool.
[0016] In a fourth aspect, a prosthesis according to the present
invention may have a coating of radiopaque material such as gold
covering at least the entire outer surface of the prosthesis. The
coating will preferably have areas of a first desired thickness and
other areas of a second desired thickness. In one embodiment, the
ends of the prosthesis have a coating of 0.0006 inches of gold
while the remainder of the prosthesis, typically the middle area,
has a coating of 0.0003 inches. In another embodiment, a prosthesis
may be created using the method of the present invention to create
ends having a coating of 0.0006 inches of gold while the middle
area has no coating at all. Advantageously, a prosthesis having
different thicknesses of radiopaque material added to a radiolucent
prosthesis will facilitate the accurate positioning of the
prosthesis in the lumen while also allowing for tissue examination
following the expansion of the prosthesis and during angiographic
followup.
[0017] In a further aspect, the present invention provides a method
for reinforcing the wall of a body lumen by introducing a
prosthesis, having the proximal points of the unit segments
constrained by expansion joints and the remote points of adjacent
units segments joined preferably by a single beam, to a target site
within the body lumen and radially expanding the prosthesis once
the target site is reached. The prosthesis may be expanded by
applying an expansive force, such as that supplied by a balloon
catheter, or alternatively, the prosthesis may be released from a
radial constraint at the target site. Alternatively, the method of
the present invention may comprise delivering and then expanding a
prosthesis having radially constrained or limited ends to reduce
the likelihood of prosthesis flaring or trumpeting during delivery
or tracking through tortuous body passageways.
[0018] A further understanding of the nature and advantages of the
invention may be realized by reference to the remaining portions of
the specification and the drawings.
[0019] BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a longitudinal side view of a prosthesis
according to the present invention.
[0021] FIG. 2 is a "rolled out" view of a first exemplary
embodiment of a prosthesis of the present invention.
[0022] FIG. 3A shows a longitudinal side view of portions of a
prosthesis using box structures.
[0023] FIG. 3B shows a longitudinal side view of portions of a
prosthesis using zig-zag structures.
[0024] FIG. 3C shows a prior art prosthesis in a curved
configuration exhibiting "fishscaling."
[0025] FIG. 3D shows the prosthesis of FIG. 1 in a curved
configuration.
[0026] FIGS. 4A-4C show a side view of a expansion joint according
to the present invention.
[0027] FIGS. 5-7 illustrate aside view of alternative embodiments
of a expansion joint of the present invention.
[0028] FIGS. 8A-8D show length compensation effects for beams and
box structures used in the present invention.
[0029] FIG. 9 is a perspective view of a portion of a serpentine
ring.
[0030] FIG. 10A depicts a prior art stent displaying flared ends
due to tracking.
[0031] FIG. 10B shows a prosthesis of the present invention having
radially stiffer end rings.
[0032] FIG. 11 is a "rolled out" view of a second exemplary
embodiment of a prosthesis of the present invention.
[0033] FIG. 12 shows an alternate embodiment of a device for
minimizing flaring in a prosthesis.
[0034] FIG. 13 shows a prosthesis of the present invention mounted
on a balloon of a catheter.
[0035] FIG. 14 shows a catheter/prosthesis assembly of FIG. 6 being
endovascularly delivered or tracked to a target site in a body
lumen.
[0036] FIGS. 15A-15D shows the catheter/prosthesis system of FIGS.
13 and 14 being delivered, expanded, and secured in a body
lumen.
[0037] FIGS. 16A-16C are cross-sectional views of the expansion of
a balloon and prosthesis resulting in dissectogenic bulbous
ends.
[0038] FIGS. 17A-17C are cross-sectional views of the expansion of
a length matched balloon and prosthesis of FIGS. 13 and 14.
[0039] FIGS. 18A-18C illustrate a method for mounting a prosthesis
onto an expansible inflation member.
[0040] FIG. 19 shows a kit according to the present invention.
[0041] FIGS. 20A-20F show prostheses with various unit segment
configurations.
[0042] FIGS. 21A-21E depict cross-sectional views of a prosthesis
being covered with a layer of radiopaque material having selective
thicknesses according to the present invention.
[0043] FIGS. 22A-22C show cross-sectional views of a prosthesis
being covered by a method for depositing a layer of radiopaque
material having selective thicknesses according to the present
invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0044] I. Introduction The present invention provides devices and
methods for the endolumenal placement of prostheses, particularly
within the vascular system for the treatment of cardiovascular
disease, such as vascular stenoses, dissections, aneurysms, and the
like. The apparatus and methods, however, are also useful for
placement in other body lumens, such as the ureter, urethra,
biliary tract, gastrointestinal tract and the like, for the
treatment of other conditions which may benefit from the
introduction of a reinforcing or protective structure within the
body lumen. The prostheses will be placed endolumenally. As used
herein, "endolumenally" will mean placement through a body opening
or by percutaneous or cutdown procedures, wherein the prosthesis is
translumenally advanced through the body lumen from a remote
location to a target site in the lumen. In vascular procedures, the
prostheses will typically be introduced "endovascularly" using a
catheter over a guidewire under fluoroscopic guidance. The
catheters and guidewires may be introduced through conventional
access sites to the vascular system, such as through the femoral
artery, or brachial, subclavian or radial arteries, for access to
the coronary arteries.
[0045] A lumenal prosthesis according to the present invention will
comprise usually at least two radially expansible, usually
cylindrical, body or unit segments. By "radially expansible," it is
meant that the segment can be converted from a small diameter
configuration (used for endolumenal placement) to a radially
expanded, usually cylindrical, configuration which is achieved when
the prosthesis is implanted at the desired target site. The
prosthesis may be minimally resilient, e.g., malleable, thus
requiring the application of an internal force to expand and set it
at the target site. Typically, the expansive force can be provided
by a balloon, such as the balloon of an angioplasty catheter for
vascular procedures. As will be described below, the present
invention provides atraumatic connections between successive unit
segments which are particularly useful to prevent "fishscaling" in
prosthesis which are not protected by sheaths during delivery.
Alternatively, the prosthesis can be self-expanding. Such
self-expanding structures are provided by utilizing a resilient
material, such as a tempered stainless steel or a superelastic
alloy such as an NiTi alloy, and forming the body segment so that
it possesses its desired, radially-expanded diameter when it is
unconstrained, i.e. released from he radially constraining forces
of a sheath. In order to remain anchored in the body lumen, the
prosthesis will remain partially constrained by the lumen. The
self-expanding prosthesis can be tracked and delivered in its
radially constrained configuration, e.g. by placing the prosthesis
within a delivery sheath or tube and removing the sheath at the
target site.
[0046] The dimensions of the lumenal prosthesis will depend on its
intended use. Typically, the prosthesis will have a length in the
range from about 5 mm to 100 mm, usually being from about 8 mm to
50 mm, for vascular applications. The small (radially collapsed)
diameter of cylindrical prostheses will usually be in the range
from about 1 mm to 10 mm, more usually being in the range from 1.5
mm to 6 mm for vascular applications. The expanded diameter will
usually be in the range from about 2 mm to 50 mm, preferably being
in the range from about 2.5 mm to 30 mm for vascular
applications.
[0047] The body or unit segments may be formed from conventional
materials used for body lumen stents and grafts, typically being
formed from malleable metals, such as 300 series stainless steel,
or from resilient metals, such as shape memory alloys, e.g. NiTi
alloys, spring steel, and the like. It is possible that the body
segments could be formed from combinations of these metals, or
combinations of these types of metals and other non-metallic
materials. Additional structures for the body or unit segments of
the present invention are illustrated in U.S. Pat. Nos. 5,195,417;
5,102,417; and 4,776,337, the full disclosures of which are
incorporated herein by reference.
[0048] The present invention provides improvements over
conventional stents by including both beams and compliant members,
preferably nonradially protruding expansion joints, in the design
of the prosthesis to minimize longitudinal foreshortening during
radial expansion and to maintain a generally smooth outer surface
on the prosthesis during delivery. The beams and expansion joints
connect together a plurality of unit segments, such as rings with
serpentine and/or box structures, and hold the segments at a
substantially fixed distance apart from one another. The expansion
joints are preferably connected between protruding elements of the
unit segments and prevent these protrusions from engaging the wall
of the body lumen as the prosthesis is traversed through in the
body lumen. The expansion joint is designed to accommodate the
flexing of the prosthesis that occurs when tracking the device
through tortuous passageways in the body.
[0049] The present invention may further include unit segments such
as radial rings having increased radial stiffness on the distal and
proximal ends of the prosthesis. Radial expansion as well as
compression stiffness may be increased by shortening the length of
longitudinal struts in the ring. These longitudinally shorter unit
segments, which may take the form of rings with box structures or
serpentine structures, are more resistant to radial expansion than
rings having longer struts. Alternatively, segments may be made
stiffer by adjusting the hinges connecting the struts together.
Whether these stiffer segments are directly connected to the
adjacent unit segments or connected by long single beams, these
structures minimize flaring or trumpeting of the ends of the
prosthesis. Flaring or trumpeting of the prosthesis occurs due to
its transverse stiffness which resists the bending and curving of
the prosthesis mounted on its delivery catheter during tracking
through tortuous pathways. The flaring or trumpeting is undesirable
as it will likely cause the prosthesis to engage the body lumen
wall and either create trauma to the wall or arrest the delivery of
the prosthesis to a target site. Additionally, the prosthesis may
be mounted on an expansible inflation member, such as a balloon,
having a typically cylindrical inflation section of about the same
length as the catheter to reduce especially distal dissectogenic
expansion of the balloon. The prosthesis may also be mounted on
expansible inflation members with shaped expanded configurations,
such a single or multiple taper, to match the prosthesis to the
contour of the body lumen or to direct dilatation force of the
prosthesis at a target site, such as the ostium of a body
lumen.
[0050] Still further, the present invention may improve over
conventional prostheses by having a coating of radiopaque material
having selective thicknesses covering at least parts of the surface
of the prosthesis. Advantageously, this allows the radiopacity of
the prosthesis to be customized to create, for example, more
radiolucent midsections for increased visualization of treated
tissue inside the prosthesis while having more radiopaque end
sections for facilitating positioning one and
juxtaposing/overlapping more than one of the prostheses in a body
lumen. These coatings of radiopaque materials may be applied by
using selective electroplating or other processes such as dipping
or sputtering.
[0051] While the prostheses of the present invention will
preferably include beams/expansion joints, radially stiffer
segments, and selective radiopaque marking schemes as described, it
will be appreciated that each of these aspects of the present
invention may be employed by itself or in other combinations to
provide an improved prosthesis.
[0052] II. Embodiments of the Prosthesis Referring now to FIG. 1, a
radially expansible lumenal prosthesis 10 generally comprises a
frame 20 formed from a plurality of radially expansible unit
segments 22. Although the final shape of the prosthesis 10 will
generally be cylindrical, it should be appreciated that the
prosthesis may also be conformable to non-cylindrical
cross-sectional lumens and may also be conformable to transversely
curved lumens. In a first exemplary embodiment of FIG. 2, the frame
20 is formed from a plurality of longitudinally adjacent unit
segments 22 connected to one another by a plurality of beams 24 and
expansion joints 26. The frame 20 is typically defined as having a
midsection 27 which comprises those segments 22 which are not on
the longitudinal ends of the frame.
[0053] A. Unit Segments The radially expansible unit segment 22 is
the building block from which the frame 20 is formed. Unit segment
22 is preferably formed in the shape of a single, elongate element
patterned in a serpentine or "undulating" configuration. It should
be noted, however, that a variety of structures incorporating
members such as box 30 or zig-zag shapes 32 shown in FIGS. 2, 3A,
and 3B may be used so long as the resulting unit segments 22 are
capable of producing the desired radial expansion of lumenal
prosthesis 10. Box 30 typically has sets of longitudinal struts 31
and 33 of unequal lengths. The unit segments 22 typically retain a
"zig-zag", diamond, or other pattern even after radial expansion to
provide adequate support or scaffolding for the vessel wall between
consecutive segments and to inhibit localized hyperplasia.
Conveniently, the entire prosthesis 10, including the unit
segments, beams, and expansion joints can be formed by laser
cutting, electric discharge machining, or photochemical etching of
thin-wall tubular (i.e. cylindrical) materials. Such techniques are
well described in the technical and patent literature.
[0054] Radially expansible unit segment 22 is typically
characterized as having a plurality of proximate points 34 and
remote points 36. The proximate points 34 are defined herein as
those locations on the cut surface of the unit segment 22 axially
closest to another longitudinally adjacent unit segment 22. These
proximate points 34 are typically those locations most likely to
engage the wall of a body lumen during tracking or delivery of the
prosthesis. The remote points 36 are defined herein, in the
broadest definition, as any point spaced apart from a proximate
point 34 on the same element of unit segment 22. Remote points 36
on longitudinally adjacent unit segment 22 are generally locations
opposed and furthest from each other. The proximate points 34 and
remote points 36 are illustrated in FIGS. 2-3B for a variety of
segment 22 configurations such as serpentine, zig-zag, and box.
[0055] B. Beams and Expansion Joints Referring now to FIGS. 1-2,
the beams 24 and expansion joints 26 used to couple the unit
segments 22 together will now be described. As shown in FIG. 1, the
beams 24 are usually straight elongate members in axial alignment
with the longitudinal axis of the prosthesis 10. The beams 24 may
have a variety of profiles or contours so long as they do not
interfere with the function of the prosthesis 10. For example,
beams 24 as depicted in FIGS. 1 and 4 have narrowed midportions 25
(narrowing is exaggerated for illustrative purposes) to allow the
beams to bend around their midpoints. This enhances longitudinal
flexibility and prevents interference between the beam 24 and
adjacent struts of segment 22 while the prosthesis flexes during
delivery or tracking to the luminal target site. The beams 24 are
usually axially aligned, connected to the remote points 36 between
unit segments 22, and maintain the remote points 36 at a fixed
distance at all times including when the prosthesis 10 is radially
expanded.
[0056] Expansion joints 26, which interconnect proximate points 34
between unit segments 22, are used to prevent fishscaling by
maintaining a substantially smooth outer surface on the cylindrical
frame 20 when the prosthesis 10 assumes a curved configuration.
Fishscaling is prominently exhibited by a prior art prosthesis
shown in FIG. 3C where the protruding elements of the prior art
prosthesis (available as the Freedom.quadrature. stent from Global
Therapeutics Inc. of Broomfield, Colo.) can impede the progress or
damage the body lumen if the prosthesis is ever retracted or
advanced as indicated by arrow 27. The expansion joints 26 of the
present invention minimize any detrimental effects from such
protrusions. As shown in FIG. 3D, the expansion joints 26 are
designed to connect proximate points 34 to maintain a smooth outer
surface for the prosthesis 10, while minimally interfering with the
relative axial positioning of the unit segments 22. Preferably, the
flexibility of prosthesis 10 allows it to remain in this curved
configuration without a tendency to straighten, which will unduly
strain a curved body lumen and unnecessarily traumatize the lumen
at the ends of the prosthesis.
[0057] Referring to FIGS. 1-4, the expansion joint 26 may be formed
as an "S" shaped member. The "S" configuration allows for axial
linear expansion and compression as shown in FIGS. 4A-4C. During
this linear expansion and compression, as shown in FIG. 3D, the
outer surface remains substantially smooth while the expansion
joint 26 is expanded or compressed. When the prosthesis 10 assumes
a curved configuration, some of the expansion joints 26 are in
compression while others are in expansion, maintaining a smooth
outer surface on the frame 20 both on the expanded and the
compressed sides of the prosthesis. As shown in FIGS. 1 and 2, not
every proximate point 36 is necessarily connected by a expansion
joint 26.
[0058] Referring again to FIGS. 4A-4C, the expansion joints are
generally made weaker than their adjacent struts to facilitate
their plastic deformation. In the example shown, the expansion
joints are weakened by having reduced widths. The joints 26 may
also be weakened by increasing the length of the joint (when fully
extended) or by decreasing the thickness of the joint. As shown in
FIGS. 5-7, the expansion joint 26 may assume a variety of other
configurations, such as "U"-shaped, "O"-shaped, or zig-zag shaped
joints, with the understanding that the joints maintain a
substantially smooth outer surface on the prosthesis 10 during
delivery. The expansion joint 26 is preferably adapted for axial
compression/expansion and transverse flexing, so as to provide the
desired linear and flexural degrees of freedom as noted by arrows
42, 44, and 46. The joints 26 are preferably compliant, malleable
structures. Though not restricted in this manner, it is desired
that the beams are the dominant longitudinal structures and are at
most, only minimally inhibited by the joints 26.
[0059] C. Pattern Aside from the flexural characteristics inherent
to the beams and joints, the tracking and expansion characteristics
of the prosthesis 10 are typically determined by the positions of
the beams 24 and expansion joints 26 between the unit segments 22
(FIGS. 1 and 2). For example, a prosthesis 10 using expansion
joints 26 will typically have improved tracking capability since
the proximal ends are constrained and there is a reduced risk of
fishscaling. Likewise, a prosthesis 10 using beams 24 will also
have enhanced tracking characteristics by joining adjacent unit
segments 22 with a single, long and flexible (malleable) beam
providing substantially enhanced articulation between segments
during tracking. An important additional advantage of beams 24
relates to improved radial expansion characteristics since
prosthesis foreshortening will be substantially compensated by the
geometric arrangement of beams and segments. However, having too
many beams 24 and joints 26 or too few joints may create other
undesirable qualities such as reduced transverse flexibility
characteristics of the prosthesis. Hence, there are performance
tradeoffs which must be accounted for in the number of and
positioning of beams 24 and joints 26 used in the prosthesis
10.
[0060] Referring to FIGS. 1 and 2, it should be understood that the
beams 24 and expansion joints 26 may be placed in a variety of
patterns between the unit segments 22 to balance prosthesis
flexibility with competing performance characteristics. In one
embodiment shown in FIG. 1, the beams 24 and expansion joints 26
may be linearly aligned in an alternating manner to connect a
plurality of adjacent unit segments 22. Adjacent unit segments are
connected to one another using only a single beam 24 and one or
more expansion joints 26.
[0061] FIG. 2 shows a first exemplary embodiment of the prosthesis
10 in a "rolled out" configuration. As shown, adjacent unit
segments 22 in FIG. 2 are connected together using both beams 24
and expansion joints 26. As shown in FIG. 2, these beams 24 and
expansion joints 26 are not necessarily aligned longitudinally. In
this embodiment, only one beam 24 is used per connection between
adjacent unit segments 22. This maximizes longitudinal flexibility
while providing compensation for longitudinal foreshortening.
Further, the beams 24 are in a "laddered" configuration where
adjacent beams are laterally (representing the circumferential
direction) and longitudinally staggered, with a predetermined
amount of longitudinal overlap as shown in FIG. 2 and in a second
exemplary embodiment in FIG. 11. The overlap is preferably at least
one-third, more preferably about one-half of the length of the
beams 24 when the prosthesis 10 is in a collapsed configuration.
Advantageously, positioning beams 24 in a laddered configuration
results in a spiralling connecting pattern when the prosthesis is
seen in its typical cylindrical configuration. This connecting
pattern enhances the transverse flexibility of the prosthesis by
distributing the single beams around the circumference of the
device.
[0062] Axial length compensation for the prosthesis, as it is
expanded radially from a collapsed to an expanded or deployed
configuration, is conveniently achieved by the previously described
interconnecting pattern between beams 24 and unit segments 22. The
geometrical relationship is best appreciated in FIGS. 8A and 8B
which depict three adjacent unit segments 22 both in their
collapsed and radially expanded configurations. The axial strut
lengths M2 in the expanded configuration are smaller than the axial
strut lengths M1 in the collapsed configuration, which is a serious
concern in many of the prior art designs. In the present pattern,
however, the overall length of the prosthesis, actually grows
because the longitudinal distance L2 from the base of a first beam
24a to the base of the next beam 24b is longer than the distance L1
in the collapsed configuration. Furthermore, when the end segments
22 are of the box type as shown in FIGS. 1 and 2, there will be a
shortening of the longitudinal length of each box section relative
to the base of a first beam 24 as shown in FIGS. 8C and 8D by the
difference in the lengths N1 and N2. The lengthening and shortening
of the prosthesis described in relation to FIGS. 8A/8B and FIGS.
8C/8D, respectively, can be used advantageously in attaining
optimal length compensation when the prosthesis is expanded or
deployed.
[0063] III. Axially Selective Radial Stiffness Referring now to
FIGS. 9 and 10, a prostheses having axially selective radial
stiffnesses can be adapted to control geometrical characteristics
resulting in undesired tracking performance. One factor in
determining radial stiffness is the type of material used to
fabricate the prosthesis. The material is preferably a material
such as 316L stainless steel which in its annealed condition is
strong yet malleable and will therefore remain in an expanded
configuration with a minimum of recoil. Of course, the stronger the
material, the harder the prosthesis will be to expand. Another
factor in radial stiffness is the length of the struts 102 used in
the unit segments 22. The shorter the struts 102, the less leverage
or mechanical advantage it will have to deform the hinge element.
Therefore shorter struts will require greater forces than longer
struts to expand the hinge element between two struts. A further
factor involves the design of the hinges 104 connecting adjacent
struts 102. The longer, narrower, and thinner the hinge 104 is, as
indicated by arrows 106, 107, and 108 respectively, the weaker the
hinge will be. The shorter, wider, and thicker the hinge 104 is,
the stiffer the hinge 104 will be.
[0064] Referring to FIGS. 10A and 10B, a prosthesis 10 having
axially selective radial expansion stiffnesses will be described.
As shown in FIG. 10A, conventional lumenal prostheses have a
tendency to flare near the distal end 110 and proximal end 112,
especially during tracking through tortuous anatomy, but also when
radially expanded by a balloon. This produces an hourglass or
double trumpet configuration which may cause trauma to the body
lumen wall and even inhibit the progress of the catheter mounted
prosthesis during tracking of the prosthesis to the target site. It
may also cause excessive end deformation when being expanded, thus
potentially being the focus of a stronger restenotic effect.
Flaring or trumpeting occurs because the prosthesis resists
excessive bending while tracking through tortuous pathways and the
struts on the ends of the prosthesis will preferably deform (as
illustrated in FIG. 10A), causing the prosthesis to assume a double
trumpet shape rather than remaining in the desired cylindrical
configuration along its entire length. This occurs particularly in
the prior art because the unit segments in the middle of the
prosthesis 10 are connected to or constrained by adjacent unit
segments and provide transverse rigidity to the prosthesis while
those segments on the ends are cantilevered, with only one side
constrained. Hence they are more susceptible to deformation during
tracking. Because these prosthesis are typically made from
malleable materials, they remain deformed even though the delivery
catheter may have returned to a straight configuration.
[0065] In a preferred embodiment of the prosthesis 10, unit
segments near the vicinity of the distal end 111 and proximal end
113 have a higher radial stiffness than the unit segments near the
center or in the midsection 27 of the prosthesis 10. Although the
prosthesis is not limited in this manner, the additional radial
stiffness minimizes the observed flaring. Radial stiffness may be
increased in a variety of ways, such as using longitudinally
shorter unit segments or by altering the geometry, i.e. widths,
lengths, and thicknesses, of the outermost components of the unit
segments. The amount of force required to expand the prosthesis may
therefore vary over the length of the prosthesis.
[0066] In one embodiment as shown in FIG. 10B, end rings 120 and
121 which form the distal end and the proximal end of the
prosthesis 10 incorporate a plurality of substantially longitudinal
portions or struts 122 which are shorter in length than the
longitudinal portions 130 characteristic of the unit segments 22
near the middle of the prosthesis. Although the portions 122 may
assume a variety of lengths, the portions are typically half as
long as those portions 130 in unit segments 22. These end rings 120
and 121 with the shorter and therefore stronger longitudinal
portions will preferably become only minimally flared during the
tracking and the expansion of the prosthesis. The end rings 120 and
121 having higher radial stiffness are preferably included in
embodiments of the prosthesis 10, as shown in FIGS. 1 and 2. The
end rings 120 and 121 may have a serpentine, zig-zag, or other
similar configuration.
[0067] In the embodiment of FIG. 11, it is shown that rings 120 and
121 having shorter struts 122 may be coupled to adjacent unit
segments by a combination of a single beam 24 and expansion joints
26. One ring 120 or 121 may be directly connected to a unit segment
22, thus forming an articulated structure with the unit segment.
Rings 120 or 121 may also be coupled to unit segment 22 by
expansion joints 26 to prevent fishscaling without inhibiting
transverse flexibility.
[0068] In an alternative embodiment, the serpentine ring may
incorporate other elements to increase radial stiffness. For
example, in FIG. 13, the distal end and proximal end of the
prosthesis 10 may be covered by annular sheaths 130 and 131 made of
expansible material that radially constrains the ends to minimize
flaring and will typically become implanted in body lumen together
with the prosthesis. Other suitable devices and methods for
constraining the expansion of unit segments 120, 121, and 22, such
as expansion limiting hinges, may be found in commonly assigned,
co-pending U.S. patent application Ser. No. 08/691,661, filed Aug.
2, 1996 (Attorney Docket No. 15509-003900), the complete disclosure
of which was previously incorporated herein.
[0069] IV. Endolumenal Delivery and Expansion As shown in FIG. 13,
in a preferred embodiment, the prosthesis 10 is preferably crimped
onto a collapsed expansible inflation member 80 having a typically
cylindrical inflation section 82 which is typically located at the
distal end of a catheter 100 (FIG. 14). It should be understood,
however, that the prosthesis 10 may be coupled to inflation member
80 by other methods known in the art, such as stent delivery
sleeves as described in commonly assigned U.S. Pat. No. 5,599,306
or commonly assigned, copending U.S. patent application Ser. No.
08/704,801, filed Aug. 26, 1996 (Attorney Docket No. 15509-002810),
the complete disclosures of which are incorporated herein by
reference. In a preferred embodiment, the prosthesis 10 as mounted
over an expansible inflation member 80, such as a non-compliant
elastomeric balloon, is designed to track through curved and
tortuous body lumens as shown in FIG. 14 to reach a target site T.
As shown, the expansion joints 26 prevent the prosthesis 10 from
engaging the lumen wall when the prosthesis 10 is in a curved
configuration. Additionally, the prosthesis 10 preferably includes
stiffened radial ends to reduce prosthesis trumpeting. These
features improve tracking of the prosthesis 10 through the lumen.
When the prosthesis and balloon reach the desired target site T,
the expansible member 80 will be expanded to deploy the prosthesis
10 as shown in FIGS. 15A-15D. After the prosthesis 10 has been
deployed, the balloon or expansible member 80 will be deflated and
removed along with the catheter from the body lumen. The prosthesis
10 will remain in the body lumen to maintain the lumen patency.
[0070] In preferred embodiments of the present invention, the
prosthesis 10 is mounted on a inflation member 80 of "matching"
length to minimize dissectogenic balloon expansion that is
characteristic of known catheter/stent assemblies. "Matching" is
defined as having an expansible member 80 with an inflation section
82 (cylindrical, tapered, or other shape) of substantially the same
length as the length of the prosthesis 10. As can be observed in
FIGS. 16A-16C, even when the end sections of the prosthesis are
strengthened, the diameter of the outer ends of a conventional
balloon 86 exceeds the outer diameter of the prosthesis as the
balloon attempts to expand the prosthesis and even following full
expansion. The balloon's excessive radial expansion results from
inflating portions of the balloon unconstrained by the prosthesis.
High pressure inflation (in the range of 10-20 atmospheres) to
fully expand the prosthesis into the body lumen may cause these
unconstrained portions or bulbs 84 to reach a size sufficient to
damage or dissect the body lumen, particularly at the distal end.
To eliminate these bulbs 84, a system 200, shown in FIGS. 15A-15D
and 17A-17C, according to the present invention preferably uses an
expansible inflation member 80 having a cylindrical or other shaped
inflation section 82 with approximately the same longitudinal
length as that of the prosthesis 10. The "inflation section" may be
defined as those areas of the inflation member 80 which can extend
beyond the outer diameter of the prosthesis 10 under typical high
pressure inflation if unconstrained. Although not limited in this
manner, the distal and proximal ends or tips of the member 80 are
typically molded and will not expand beyond the diameter of the
member. The cylindrical inflation section 82 is no more than about
1.0 mm longer than the prosthesis on each end, preferably no more
than about 0.5 mm longer, and most preferably the same length as
the prosthesis. As shown in FIGS. 17A-17C, matching the length of
the expanding balloon portion with the length of the prosthesis
significantly reduces undesired balloon configurations 84 as the
prosthesis 10 is fully expanded in place. It should be understood
that the inflation section 82 may assume a variety of
configurations once expanded.
[0071] In a preferred embodiment, a system 200 with a prosthesis 10
and expansible member 80 of similar lengths comes with the
prosthesis 10 coupled to the expansible member 80. Alternatively,
the prosthesis 10 may come as a separate entity that is
subsequently mounted onto a suitable expansible inflation member
80. Referring to FIGS. 18A-18C, a method for mounting a prosthesis
10 onto a suitable inflation member 80 includes selecting an
expansible inflation member having an inflation section 82 of about
the same longitudinal length as the length of a prosthesis 10 (as
discussed above). The expansible inflation member 80 is positioned
in a longitudinal lumen of said prosthesis 10 prior to the clinical
intervention. The position of the longitudinal length of the
prosthesis 10 is aligned with the length of the inflation section
82 of the inflation member 80. The prosthesis 10 is then mounted
onto the inflation member 80 either by hand crimping or preferably
with a crimping tool (not shown). As shown, the inflation member 80
preferably comes with a catheter 100. It is understood, however,
that the prosthesis may be premounted at the factory on a delivery
device such as a balloon or a sleeve catheter.
[0072] Referring to FIG. 19, a prosthesis 10 according to the
present invention may be packaged together with instructions for
use (IFU) in a kit as shown in FIG. 12. A conventional package,
which may be a pouch 202 or any other suitable package, such as a
tray, box, tube, or the like, may be used to contain the prosthesis
10 and IFU 204, where the IFU may be printed on a separate sheet
and/or may be printed on the packaging itself. The kit may also
include a mounting tool 206 such as a crimping device and/or an
expansible inflation member 80 which may be permanently or
releasably coupled to the prosthesis 10. Typically, the expansible
member 80 is attached to catheter 100. The instructions will set
forth any of the aspects of the method of the present invention
described above, including the method for mounting a prosthesis
10.
[0073] Further embodiments of the prosthesis 10 of the present
invention may have expanded configurations designed to address
specific interventional needs. For example, expanded prostheses
configurations may be designed to match the shape of the lumens for
which they are targeted. Many body lumens have irregular
configurations, and it has been suggested that over 40% of all
blood vessels in the body are tapered. To match these body lumen
shapes, a prosthesis according to the present invention are
preferably be mounted on an expandable balloon 90 which will shape
the expanded configuration of the prosthesis as shown in FIGS.
20A-20D respectively. These balloons 90 such as the
Banka.quadrature. tapered balloon from C. R. Bard, Inc. of
Billerica, Mass. or the CAT.quadrature. balloon from CardioVascular
Dynamics, Inc. of Irvine, Calif. may expand into tapered or other
desired configurations. A prosthesis of the present invention
mounted on such a balloon 90 will have a matching expanded
configuration.
[0074] Advantageously, matching the prosthesis 10 to the body lumen
reduces stress concentrations which may occur when the body lumen
is excessively distended by nonconforming (typically cylindrically)
expanded prosthesis. A shaped prosthesis further allows for
effective scaffolding of lesions having tapered configurations,
grant more effective support of lesions at anastomosis sites, and
more accurate sizing and scaffolding of ostial lesions. In contrast
to conventionally delivered prosthesis, a prosthesis shaped through
specific delivery means can concentrate the majority of the
supporting force more directly at a lesion site, sparing the
surrounding lumenal wall from potentially damaging dilation forces.
It should be understood that an unlimited number of results and
configurations can be created by varying the radial stiffnesses
along the length of the prosthesis and the shape of the delivery
system.
[0075] Additionally, as can be seen in FIGS. 20A-20F, the strut
lengths can be varied to optimize the dilatation and support forces
of the shaped prosthesis. Varying the strut lengths can create a
radial stiffness gradient between the unit segments to further
enhance lumenal scaffolding. The various prostheses may have struts
212 and 214 with shorter and longer lengths in a tapered expanded
configuration (FIG. 20A). Other tapered expanded configurations may
have short struts S with long struts L (FIG. 20B), all long struts
L (FIG. 20C), or short struts with gradually longer struts L/L+/L++
(FIG. 20D). In cylindrical configurations, the prosthesis 10 may
have short struts S and long struts L (FIG. 20E) or short struts S,
long struts L, and medium struts M (FIG. 20F). As shown, any
combination of strut lengths may be used to optimize desired
prosthesis characteristics.
[0076] V. Radiopaque Marking Schemes Proper positioning of a
prosthesis in a body lumen can be critical to attain the optimal
therapeutic effect from the device. For example, it is sometimes
necessary to juxtapose several prostheses in the same body lumen to
treat a long lesion. This may require abutting the end of one
prosthesis against the end of another prosthesis or slightly
overlapping their ends. To visualize the position of these
prosthesis as they are delivered into the body lumen, physicians
use fluoroscopy or angiography to illuminate the devices in the
body lumen. The prostheses preferably have some radiopaque marking
features or may be made from radiopaque materials to be detectable
by a fluoroscope or similar visualization devices.
[0077] Referring to FIGS. 22A-22E, a method for plating a typical
prosthesis made from stainless steel with radiopaque material, such
as gold, platinum, platinum/iridium, tungsten, tantalum, or the
like, will now be described. The method of the present invention
creates a prosthesis with a coating of radiopaque material having
an axially selective thickness. It should be understood, however,
that the method is not limited to thickness variations in the axial
direction and may be used to create an unlimited number of
thickness configurations. Preferably, the prosthesis is entirely
covered with a layer of radiopaque material while having thicker
deposits of the same or other materials near its ends and having
thinner deposits over the remainder, typically midsection, of the
device. When the coating material is gold, the thickness near the
ends 111 and 113 is preferably between 0.0003 and 0.0009 inches,
more preferably between 0.0004 and 0.0007 inches. Thicknesses over
the remainder of the prosthesis may be in the range of 0.0002 to
0.0004 inches. The thicker deposits near the ends of the prosthesis
make the ends more radiopaque and thus create a stronger image,
facilitating the positioning of the prosthesis in its desired
location. The middle area 304 is also preferably coated so as to be
more radiopaque than the uncoated material under the fluoroscope,
but permitting sufficient radiolucency so that the lumen inside the
prosthesis may still be inspected fluoroscopically. Alternatively,
the middle area 304 may be left uncoated while only the ends of the
prosthesis remain coated to achieve an optimal axial radiopacity
distribution. Visualization through this middle area 304 may be
crucial for observing future restenosis or hyperplasia within the
prosthesis. Coating the entire prosthesis at a uniform thickness
using the optimal thickness applied to the ends would likely
obscure such visualization. Having an axially selective coating
customizes the prosthesis to the desired task. It should be
understood that the present method may be used to add materials of
a variety of thicknesses to a prosthesis.
[0078] One embodiment of the present method uses electroplating
steps to add radiopaque material to the prosthesis. It should be
understood, however, that other processes known in the art may also
be adapted according to the present invention. The method comprises
immersing the completed prosthesis (i.e. cut and polished) in an
electrolyte and electroplating the entire prosthesis with a layer
300 of radiopaque material such as gold at a preferred thickness of
0.0003 inches (FIG. 21A). The prosthesis is shown in cross-section,
and the plating is shown disproportionately thick for better
clarity. The portions of the prosthesis 10 desired to have greater
thickness (in this example the two ends) are then covered with a
resist material 302 to protect the covered materials from plating
removal or plating addition (FIG. 21B). Such resist material 302
may be for example Microposit.RTM. FSC.RTM. Surface Coating
manufactured by the Shipley Company in Marlbourough, Mass. The
electroplating process is then reversed to remove radiopaque
material not covered with the resist material. In this example of
FIG. 21C, it is shown completely removed. The resist material is
then removed, leaving behind a prosthesis 10 with select areas
covered with a layer 300 of radiopaque material while other areas
304 remain bare (FIG. 21D). The entire prosthesis 10 is then
covered with another layer 306 of radiopaque material, such as gold
at 0.0003 inches thickness (FIG. 21E). The resulting embodiment of
the prosthesis will thus have ends coated with 0.0006 inches of
gold, while the remainder of the prosthesis is covered with 0.0003
inches of gold. If a radiopaque coating is desired only at the ends
of the prosthesis, the initial coating as shown in FIG. 21A may be
made thicker, such as 0.0006 inches of gold, and the final coating
step in FIG. 21E may be omitted. This will resulting in a
prosthesis having a coating of 0.0006 inches of gold at its ends,
and not coating the middle area.
[0079] Alternatively, another method for creating selective
coatings of radiopaque material may use a combination of
electrolytic deposition, electroless dipping, and sputter processes
(FIGS. 22A-22C). For example, both ends of the prosthesis are
sequentially dipped in radiopaque material, resulting in a
prosthesis with a bare middle area 310 and two covered ends 312.
This prosthesis can then be entirely recoated using a sputtering
process in a vacuum chamber 314 (FIG. 22B). This results in a
prosthesis entirely covered with radiopaque material, but having
thicker, more opaque ends (FIG. 22C). Although the process using
electroplating and the resist material is more flexible as to the
shape and location of the areas with thicker coatings, the dipping
and/or sputtering processes may also be used to create a prosthesis
entirely covered with radiopaque material but having thicker
coatings on the ends. It should be understood these method steps
may be performed in a variety of different sequences, such as
coating the entire prosthesis first and then coating the ends, to
create the desired radiopaque coating distribution. Similar
thicknesses to gold may be used with other commonly used radiopaque
materials such as platinum or platinum/iridium alloys.
[0080] Although the foregoing invention has been described in some
detail by way of illustration and example, for purposes of clarity
of understanding, it will be obvious that certain changes and
modifications may be practiced within the scope of the appended
claims. For example, the prostheses may be sized as appropriate for
use in a variety of body lumens such as the aorta or other
vasculature in the body.
* * * * *