U.S. patent application number 11/771974 was filed with the patent office on 2008-01-17 for method and apparatus for attaching radiopaque markers to a stent.
Invention is credited to Patrick P. Wu.
Application Number | 20080015684 11/771974 |
Document ID | / |
Family ID | 38950256 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080015684 |
Kind Code |
A1 |
Wu; Patrick P. |
January 17, 2008 |
Method And Apparatus For Attaching Radiopaque Markers To A
Stent
Abstract
A mandrel for supporting a stent and rollers for pressing a
radiopaque marker into a stent are disclosed. The mandrel can have
a forward portion for carrying the stent and a rear portion for
urging the stent forward portion into a gap between the rollers.
The mandrel may be pushed or pulled into the gap, which is sized to
allow the rollers to press the marker into engagement with the
stent. Prior to moving the mandrel into the gap, the marker may be
placed on a surface of the stent or partially inside a recess in
the stent. Several markers can be efficiently and uniformly pressed
onto the stent by moving the mandrel into the gap in one continuous
movement in an axial or lateral direction. Markers can also be
pressed onto the stent by placing the stent in the gap and rotating
the stent about its central axis.
Inventors: |
Wu; Patrick P.; (Mountain
View, CA) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY LLP
1 MARITIME PLAZA
SUITE 300
SAN FRANCISCO
CA
94111
US
|
Family ID: |
38950256 |
Appl. No.: |
11/771974 |
Filed: |
June 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60830201 |
Jul 11, 2006 |
|
|
|
Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2002/91566
20130101; A61F 2250/0098 20130101; A61F 2/82 20130101; A61F
2002/91558 20130101; Y10T 29/49908 20150115; A61F 2/91 20130101;
Y10T 29/49927 20150115; Y10T 29/49945 20150115; Y10T 29/53
20150115; A61F 2240/00 20130101; Y10T 29/49826 20150115; A61F 2/915
20130101; A61M 25/0012 20130101; Y10T 29/53548 20150115; Y10T
29/49913 20150115 |
Class at
Publication: |
623/001.15 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. A method of attaching a radiopaque marker onto a stent, the
method comprising: conveying a stent positioned between two
rollers, wherein a radiopaque marker disposed at a surface of the
stent is pressed into a recess in the stent by one of the
rollers.
2. The method of claim 1, wherein conveying the stent includes
translating the stent along its central axis into a gap between the
rollers.
3. The method of claim 1, wherein conveying the stent includes
translating the stent into a gap between the rollers, wherein the
stent is translated along a direction perpendicular to a central
axis of the stent.
4. The method of claim 1, further comprising placing the radiopaque
marker on a surface of the stent prior to conveying the stent.
5. The method of claim 1, further comprising placing the radiopaque
marker partially in the recess in the stent prior to conveying the
stent.
6. The method of claim 1, wherein the radiopaque marker is deformed
when it is pressed into the recess to reduce or eliminate
protrusion of the marker from the stent surface.
7. The method of claim 1, wherein the stent is supported on a
mandrel and conveying the stent includes translating the
mandrel.
8. The method of claim 7, wherein the mandrel comprises a forward
portion for carrying the stent, the forward portion having a
diameter less than or equal to an inner diameter of the stent.
9. The method of claim 7, wherein the mandrel comprises a rear
portion having a diameter greater than or equal to an outer
diameter of the stent.
10. The method of claim 7, wherein the mandrel comprises a rear
portion having a diameter less than or equal to a gap between the
rollers.
11. The method of claim 1, wherein each of the rollers can rotate
about an axis that is substantially perpendicular to the central
axis of the stent.
12. The method of claim 1, wherein each of the rollers can rotate
about an axis that is substantially parallel to the central axis of
the stent.
13. A method of attaching a radiopaque marker onto a stent, the
method comprising: translating a stent mounted on a mandrel
relative to a roller, the stent including a radiopaque marker
positioned at a surface of the stent; and allowing the roller to
press the radiopaque marker in a manner that couples the radiopaque
marker to the stent.
14. The method of claim 13, wherein translating the stent relative
to the roller includes linearly translating the stent relative to
the roller in a direction parallel to a central axis of the
stent.
15. The method of claim 13, wherein translating the stent relative
to the roller includes linearly translating the stent relative to
the roller in a direction perpendicular to a central axis of the
stent.
16. The method of claim 13, wherein translating the stent relative
to the roller includes rotationally translating the stent relative
to the roller about a central axis of the stent.
17. The method of claim 13, wherein the stent is supported by the
mandrel while the radiopaque marker is pressed with the roller.
18. An apparatus for attaching a radiopaque marker onto a stent,
comprising: a cylindrical mandrel including a forward portion and a
rear portion, an outer diameter of the forward portion being less
than an outer diameter of the rear portion, the forward portion for
supporting a stent; and rollers spaced apart by a gap that is
greater than or equal to the outer diameter of the rear portion of
the mandrel; wherein the mandrel and rollers are movable in
relation to each other so that the mandrel passes through the
gap.
19. The apparatus of claim 18, wherein a stent is mounted over the
forward portion of the mandrel.
20. The apparatus of claim 18, wherein the rollers are oriented to
allow each of the rollers to rotate about a rotational axis that is
perpendicular to a longitudinal axis of the mandrel.
21. The apparatus of claim 18, wherein the rollers are oriented to
allow each of the rollers to rotate about a rotational axis that is
parallel to a longitudinal axis of the mandrel.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/830,201, filed Jul. 11, 2006, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to implantable medical
devices, such as stents, and, more particularly, to attaching
radiopaque markers to polymeric stents. Description of the State of
the Art Expandable endoprostheses are adapted to be implanted in a
bodily lumen. An "endoprosthesis" corresponds to an artificial
device that is placed inside the body. A "lumen" refers to a cavity
of a tubular organ such as a blood vessel. A stent is an example of
such an endoprosthesis. Stents are generally cylindrically shaped
devices, which function to hold open and sometimes expand a segment
of a blood vessel or other anatomical lumen such as urinary tracts
and bile ducts. Stents are often used in the treatment of
atherosclerotic stenosis in blood vessels. "Stenosis" refers to a
narrowing or constriction of the diameter of a bodily passage or
orifice. In such treatments, stents reinforce blood vessels and
prevent restenosis following angioplasty in the vascular system.
"Restenosis" refers to the reoccurrence of stenosis in a blood
vessel or heart valve after it has been treated (as by balloon
angioplasty, stenting, or valvuloplasty) with apparent success.
[0004] The structure of stents is typically composed of scaffolding
that includes a pattern or network of interconnecting structural
elements or struts. The scaffolding can be formed from wires,
tubes, or sheets of material rolled into a cylindrical shape. In
addition, a medicated stent may be fabricated by coating the
surface of either a metallic or polymeric scaffolding with a
polymeric carrier. The polymeric scaffolding may also serve as a
carrier of an active agent or drug.
[0005] The first step in treatment of a diseased site with a stent
is locating a region that may require treatment such as a suspected
lesion in a vessel, typically by obtaining an x-ray image of the
vessel. To obtain an image, a contrast agent, which contains a
radiopaque substance such as iodine is injected into a vessel.
"Radiopaque" refers to the ability of a substance to absorb x-rays.
The x-ray image depicts the lumen of the vessel from which a
physician can identify a potential treatment region. The treatment
then involves both delivery and deployment of the stent. "Delivery"
refers to introducing and transporting the stent through a bodily
lumen to a region in a vessel that requires treatment. "Deployment"
corresponds to the expanding of the stent within the lumen at the
treatment region. Delivery and deployment of a stent are
accomplished by positioning the stent about one end of a catheter,
inserting the end of the catheter through the skin into a bodily
lumen, advancing the catheter in the bodily lumen to a desired
treatment location, expanding the stent at the treatment location,
and removing the catheter from the lumen. In the case of a balloon
expandable stent, the stent is mounted about a balloon disposed on
the catheter. Mounting the stent typically involves compressing or
crimping the stent onto the balloon. The stent is then expanded by
inflating the balloon. The balloon may then be deflated and the
catheter withdrawn. In the case of a self-expanding stent, the
stent may be secured to the catheter via a retractable sheath or a
sock. When the stent is in a desired bodily location, the sheath
may be withdrawn allowing the stent to self-expand.
[0006] The stent must be able to simultaneously satisfy a number of
mechanical requirements. First, the stent must be capable of
withstanding the structural loads, namely radial compressive
forces, imposed on the stent as it supports the walls of a vessel
lumen. In addition to having adequate radial strength or more
accurately, hoop strength, the stent should be longitudinally
flexible to allow it to be maneuvered through a tortuous vascular
path and to enable it to conform to a deployment site that may not
be linear or may be subject to flexure. The material from which the
stent is constructed must allow the stent to undergo expansion,
which typically requires substantial deformation of localized
portions of the stent structure. Once expanded, the stent must
maintain its size and shape throughout its service life despite the
various forces that may come to bear thereon, including the cyclic
loading induced by the beating heart. Finally, the stent must be
biocompatible so as not to trigger any adverse vascular
responses.
[0007] In addition to meeting the mechanical requirements described
above, it is desirable for a stent to be radiopaque, or
fluoroscopically visible under x-rays. Accurate stent placement is
facilitated by real time visualization of the delivery of a stent.
A cardiologist or interventional radiologist can track the delivery
catheter through the patient's vasculature and precisely place the
stent at the site of a lesion. This is typically accomplished by
fluoroscopy or similar x-ray visualization procedures. For a stent
to be fluoroscopically visible it must be more absorptive of x-rays
than the surrounding tissue. Radiopaque materials in a stent may
allow for its direct visualization.
[0008] In many treatment applications, the presence of a stent in a
body may be necessary for a limited period of time until its
intended function of, for example, maintaining vascular patency
and/or drug delivery is accomplished. Therefore, stents fabricated
from biodegradable, bioabsorbable, and/or bioerodable materials may
be configured to meet this additional clinical requirement since
they may be designed to completely erode after the clinical need
for them has ended. Stents fabricated from biodegradable polymers
are particularly promising, in part because they may be designed to
completely erode within a desired time frame.
[0009] However, a significant shortcoming of biodegradable polymers
(and polymers generally composed of carbon, hydrogen, oxygen, and
nitrogen) is that they are radiolucent with no radiopacity.
Biodegradable polymers tend to have x-ray absorption similar to
body tissue.
[0010] One way of addressing this problem is to attach radiopaque
markers to structural elements of the stent. A radiopaque marker
can be disposed within a structural element in such a way that the
marker is secured to the structural element. However, the use of
stent markers on polymeric stents entails a number of challenges.
One challenge relates to the difficulty of insertion of
markers.
[0011] Another challenge pertains to the fact that some regions of
polymeric struts tend to undergo significant deformation or strain
during crimping and expansion. In particular, such changes are due
to plastic deformation of polymers. Thus, during stent deployment,
the portion of a stent containing an element may crack or stretch
as stress is being applied to the expanding stent. As a result, the
marker may become dislodged.
[0012] Attachment of radiopaque markers to stents usually requires
a significant amount of time to perform with reliability and
uniformity. The amount of time required is increased when several
markers must be attached at different locations on the stent. Also,
conventionally-placed markers may project inward from the luminal
surface of the stent to such a degree that blood flow is disrupted,
or project outward from the abluminal surface of the stent to such
a degree that the walls of the blood vessel are traumatized.
[0013] Accordingly there is a need to for an apparatus and method
of easily attaching radiopaque markers on stents. There is also a
need for an apparatus and method of attaching radiopaque markers on
stents such that the marker is retained in the stent during
deformation of the stents during subsequent stent crimping and
expansion. There is a further need for an apparatus and method of
attaching a plurality of radiopaque markers to a stent with greater
efficiency and uniformity. Also, there is a need to attach
radiopaque markers such that the radiopaque markers do not overly
protrude from the stent. The present invention satisfies these and
other needs.
SUMMARY OF THE INVENTION
[0014] Briefly and in general terms, the present invention is
directed to a method and apparatus of attaching a radiopaque marker
onto a stent. Such a method can comprise conveying a stent
positioned between two rollers, wherein a radiopaque marker
disposed at a surface of the stent is pressed into a recess in the
stent by one of the rollers
[0015] In detailed aspects of the present invention, conveying the
stent includes translating the stent along its central axis into a
gap between the rollers. In other detailed aspects, conveying the
stent includes translating the stent into a gap between the
rollers, wherein the stent is translated along a direction
perpendicular to a central axis of the stent.
[0016] In further aspects of the invention, the method comprises
placing the radiopaque marker on a surface of the stent prior to
conveying the stent between the two rollers. In yet other aspects,
the method comprises placing the radiopaque marker partially in the
recess in the stent prior to conveying the stent between the two
rollers.
[0017] In other detailed aspects, each of the rollers can rotate
about an axis that is substantially perpendicular to the central
axis of the stent. Each of the rollers, in other detailed aspects,
can rotate about an axis that is substantially parallel to the
central axis of the stent.
[0018] A method of attaching a radiopaque marker onto a stent can
comprise translating a stent mounted on a mandrel relative to a
roller, the stent including a radiopaque marker positioned at a
surface of the stent, and allowing the roller to press the
radiopaque marker in a manner that couples the radiopaque marker to
the stent.
[0019] In detailed aspects of the invention, translating the stent
relative to the roller includes translating the stent relative to
the roller in a direction parallel to a central axis of the stent.
In other detailed aspects, translating the stent relative to the
roller includes linearly translating the stent relative to the
roller in a direction perpendicular to a central axis of the stent.
Translating the stent relative to the roller, in yet other detailed
aspects, includes rotationally translating the stent relative to
the roller about a central axis of the stent.
[0020] An apparatus for attaching a radiopaque marker onto a stent
comprises a cylindrical mandrel including a forward portion and a
rear portion, an outer diameter of the forward portion being less
than an outer diameter of the rear portion, the forward portion for
supporting a stent, and rollers spaced apart by a gap that is
greater than or equal to the outer diameter of the rear portion of
the mandrel, wherein the mandrel and rollers are movable in
relation to each other so that the mandrel passes through the
gap.
[0021] In other aspects, the rollers are oriented to allow each of
the rollers to rotate about a rotational axis that is perpendicular
to a longitudinal axis of the mandrel. In yet other aspects, the
rollers are oriented to allow each of the rollers to rotate about a
rotational axis that is parallel to a longitudinal axis of the
mandrel.
[0022] The features and advantages of the invention will be more
readily understood from the following detailed description which
should be read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective view showing a cylindrically-shaped
stent.
[0024] FIG. 2 is a plan view showing a flattened stent pattern with
depots for receiving radiopaque markers.
[0025] FIG. 3 is a perspective view of a portion of a stent,
showing a depot for receiving a radiopaque marker.
[0026] FIG. 4 is a perspective view of the stent of FIG. 3, showing
a spherical radiopaque marker disposed over the depot.
[0027] FIG. 5 is a side view showing a stent with two radiopaque
markers disposed over openings in the stent.
[0028] FIG. 6 is an end view showing the stent and one of the
markers of FIG. 5.
[0029] FIG. 7 is a side view showing a mandrel for carrying a
stent, the mandrel having a forward portion and a rear portion.
[0030] FIG. 8 is a side view of an apparatus for attaching
radiopaque markers onto a stent, showing the mandrel of FIG. 7
carrying the stent of FIG. 5, and showing rollers having a
rotational axis substantially perpendicular to the central axis of
the stent, and the forward portion of the mandrel placed in a gap
between the rollers.
[0031] FIG. 9 is a side view of the apparatus of FIG. 8 showing the
mandrel and stent having been moved axially through the gap between
the rollers and showing the markers pressed into engagement with
the stent.
[0032] FIG. 10 is a perspective view of a portion of the stent of
FIG. 5, showing one of the radiopaque markers pressed into
engagement with the stent after having passed through the gap
between the rollers.
[0033] FIG. 11 is a side view of a marker attachment apparatus,
showing a stent mounted on a mandrel and rollers adjacent the stent
and mandrel, the rollers having a rotational axis substantially
parallel to the central axis of the stent such that a marker and
the stent are pressed into engagement with each other when the
stent is moved laterally through a gap between the rollers.
[0034] FIG. 12 is a side view of a marker attachment apparatus,
showing a stent mounted on a mandrel and rollers adjacent the stent
and mandrel, the rollers having a rotational axis substantially
parallel to the central axis of the stent such that a marker and
the stent are pressed into engagement with each other when the
stent is placed between a gap between the rollers and rotated about
its central axis.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The present invention may be applied to stents and, more
generally, implantable medical devices such as, but is not limited
to, self-expandable stents, balloon-expandable stents,
stent-grafts, vascular grafts, cerebrospinal fluid shunts,
pacemaker leads, closure devices for patent foramen ovale, and
synthetic heart valves.
[0036] A stent can have virtually any structural pattern that is
compatible with a bodily lumen in which it is implanted. Typically,
a stent is composed of a pattern or network of circumferential and
longitudinally extending interconnecting structural elements or
struts. In general, the struts are arranged in patterns, which are
designed to contact the lumen walls of a vessel and to maintain
vascular patency. A myriad of strut patterns are known in the art
for achieving particular design goals. A few of the more important
design characteristics of stents are radial or hoop strength,
expansion ratio or coverage area, and longitudinal flexibility. The
present invention is applicable to virtually any stent design and
is, therefore, not limited to any particular stent design or
pattern. One embodiment of a stent pattern may include cylindrical
rings composed of struts. The cylindrical rings may be connected by
connecting struts.
[0037] A stent may be formed from a tube by laser cutting the
pattern of struts in the tube. The stent may also be formed by
laser cutting a polymeric sheet, rolling the pattern into the shape
of the cylindrical stent, and providing a longitudinal weld to form
the stent. Other methods of forming stents are well known and
include chemically etching a polymeric sheet and rolling and then
welding it to form the stent. A polymeric wire may also be coiled
to form the stent. The stent may be formed by injection molding of
a thermoplastic or reaction injection molding of a thermoset
polymeric material. Filaments of the compounded polymer may be
extruded or melt spun. These filaments can then be cut, formed into
ring elements, welded closed, corrugated to form crowns, and then
the crowns welded together by heat or solvent to form the stent.
Lastly, hoops or rings may be cut from tubing stock, the tube
elements stamped to form crowns, and the crowns connected by
welding or laser fusion to form the stent.
[0038] Referring now in more detail to the exemplary drawings for
purposes of illustrating embodiments of the invention, wherein like
reference numerals designate corresponding or like elements among
the several views, there is shown in FIG. 1 a cylindrically-shaped
stent 10 with struts 4 that form cylindrical rings 12 which are
connected by linking struts 8. The cross-section of the struts in
stent 10 is rectangular-shaped. The struts have abluminal faces 20,
luminal faces 22, and sidewall faces 26. The cross-section of
struts is not limited to what has been illustrated, and therefore,
other cross-sectional shapes are applicable with embodiments of the
present invention. The pattern should not be limited to what has
been illustrated as other stent patterns are easily applicable with
embodiments of the present invention.
[0039] A stent can be made of a biostable and/or biodegradable
polymer. As indicated above, a stent made from a biodegradable
polymer is intended to remain in the body for a duration of time
until its intended function of, for example, maintaining vascular
patency and/or drug delivery is accomplished. After the process of
degradation, erosion, absorption, and/or resorption has been
completed, no portion of the biodegradable stent, or a
biodegradable portion of the stent will remain.
[0040] It is generally desirable to minimize the interference of a
stent or marker with the structure of a lumen and/or with flow of
bodily fluid through the lumen. Sharp edges, protrusions, etc. in
the path of blood flow can result in formation of turbulent and
stagnant zones which can act as a nidus for thrombosis. A smaller
and/or smoother profile of a body portion may be more
hemocompatible. Additionally, a smaller and smoother profile
presented by a marker has much less likelihood of catching on other
parts of the delivery system such as the guidewire or guiding
catheter. The embodiments discussed herein involve markers, which
after having been pressed into engagement onto a stent, do not
contribute significantly to the form factor, or profile, of the
stent in such a way that interferes with the structure of a lumen
and/or with flow of bodily fluid through the lumen.
[0041] As indicated above, it is desirable to have the capability
of obtaining images of polymeric stents with x-ray fluoroscopy
during and after implantation. Various embodiments of the present
invention involve stents with markers disposed within depots or
holes in a stent. A depot may be formed in a structural element by
laser machining. The depot may extend partially or completely
through the portion of the stent. For example, an opening of a
depot may be on an abluminal or luminal surface and extend
partially through the stent or completely through to an opposing
surface. The markers may be sufficiently radiopaque for imaging the
stent.
[0042] FIG. 2 shows a stent pattern 40 with depots 44 for receiving
a marker. In FIG. 2, the stent pattern 40 is shown in a flattened
condition showing an abluminal or luminal surface so that the
pattern can be clearly viewed. When the flattened portion of the
stent pattern 40 is in a cylindrical condition, it forms a radially
expandable stent. The stent pattern 40 includes cylindrically
aligned structural elements 46 and linking structural elements
48.
[0043] FIG. 3 shows a portion of a stent 60 with a depot 62 for
retaining a radiopaque marker. The stent 60 includes cylindrically
aligned structural elements 64 and linking structural elements 66.
The depot 62 is located in a portion 68 which is a region of
intersection of four structural elements. As depicted in FIG. 3,
the depot 62 has a cylindrical shape and extends completely through
the radial thickness of the structural elements 64.
[0044] Certain embodiments of the present invention involve a
deformed radiopaque marker disposed in a depot in a portion of the
stent. The marker may be coupled to the portion at least partially
by an interference or press fit between an expanded section of the
marker and an internal surface of the portion of the stent within
the depot. In some embodiments, a marker in an undeformed state may
be disposed in a depot and compressed to couple the marker within
the depot. Compressing the marker may expand a portion of the
marker within the depot to create the interference fit.
Alternatively, the stent material may deform to achieve the
interference fit with little or no deformation of the marker.
[0045] FIG. 4 shows a marker 70 disposed over the depot 62
extending through an abluminal surface 72 of the stent 60. In
practice, the marker 70 may be positioned using a syringe so that
the marker rests on top of the abluminal surface 72, partially
inside the depot 62, or both. The marker 70 may be held at the end
of the syringe by a vacuum or surface tension of a viscous
fluid.
[0046] The present invention encompasses markers fabricated by
methods including, but not limited to, molding, machining,
assembly, or a combination thereof. All or part of a metallic or
polymeric marker may be fabricated in a mold or machined by a
method such as laser machining. Markers can have any shape or size.
Preferably, though not necessarily, the markers are spherical in
shape. Compared to markers of a cylindrical or other shape having a
longitudinal axis, spherical markers are easier to align for
placement on top of or into an opening formed in the stent.
[0047] Markers may be biodegradable. It may be desirable for the
markers to degrade at the same or substantially the same rate as
the stent. For instance, the markers may be configured to
completely or almost completely erode at the same time or
approximately the same time as the stent. Alternatively, the
markers may degrade at a faster rate than the stent. In this case,
the markers may completely or almost completely erode before the
body of the stent is completely eroded.
[0048] Also, a biocompatible biodegradable metal may be used for
the markers. A biocompatible biodegradable metal forms erosion
products that do not negatively impact bodily functions. The
markers may be composed of a pure or substantially pure
biodegradable metal. Representative examples of biodegradable
metals for use in a marker may include, but are not limited to,
magnesium, zinc, and iron. Representative mixtures or alloys may
include magnesium/zinc, magnesium/iron, zinc/iron, and
magnesium/zinc/iron. Radiopaque compounds such as iodine salts,
bismuth salts, or barium salts may be compounded into the metallic
biodegradable marker to further enhance the radiopacity. Other
representative examples of biostable metals include platinum and
gold.
[0049] Further, the markers may be a mixture of a biodegradable
polymer and a radiopaque material. The radiopaque material may be
biodegradable and/or bioabsorbable. Representative radiopaque
materials may include, but are not limited to, biodegradable
metallic particles and particles of biodegradable metallic
compounds such as biodegradable metallic oxides, biocompatible
metallic salts, gadolinium salts, and iodinated contrast
agents.
[0050] Certain embodiments of the present invention include
disposing, coupling, or pressing radiopaque markers within a recess
or depot in a stent structure. Such embodiments are described below
in connection with FIGS. 7-12.
[0051] FIGS. 5 and 6 show a stent 100 with markers 102 protruding
radially from the stent 100. The markers 100 have been placed
partially inside recesses formed in the stent. The recesses are not
shown for clarity and ease of illustration. The recesses can be
depots that extend completely through a stent structure, from an
abluminal surface 104 to a luminal surface 106. Alternatively, the
recesses can be cavities that extend partially into the stent
structure. The terms "recess" and "opening" are used
interchangeably herein. The stent has a central axis 108 extending
along the entire length of the stent 100.
[0052] FIG. 7 shows a step mandrel 110 having a forward portion 1
12 and a rear portion 114. The forward portion 112 has a diameter
116 that is less than the diameter 118 of the rear portion 114. The
forward portion is adapted to carry the stent 100. The mandrel 110
has a longitudinal axis 119 extending along the entire length of
the mandrel. The mandrel 110 can be made of a relatively rigid
material, in comparison to a stent, selected to provide firm
support for the stent. Examples of suitable materials includes
plastics, such as Delrin, PVC, nylon, and others; metals such as
steel, stainless steel, aluminum, titanium, and others; and glass.
The mandrel 110 can also include a relatively resilient and
compliant material that is selected to provide sufficient support
to the stent and to cushion the stent from excessive pressure from
rollers described below.
[0053] In FIG. 8, the stent 100 has been mounted onto the forward
portion 112 of the mandrel 1 10, which has been moved between two
rollers 120 that may rotate about a retaining pin 122 in the
direction of rotational arrows 124. The forward portion 112
supports the stent 100 at its luminal surface when the markers 102
are later pressed onto the stent. The rollers 120 have a circular
cross-section. The retaining pin 122 is substantially perpendicular
to the central axis of the stent, which allows each roller 120 to
rotate about an axis that is substantially perpendicular to the
longitudinal axis 119 of the stent 100. Further movement of the
mandrel 110 and the stent 100 in the direction of axial arrow 126
will cause the markers 102 to be pressed into the surface of the
stent 100 without damaging stent 100.
[0054] The rollers 120 can be made of a relatively rigid material,
in comparison to the stent 100 and markers 102, to facilitate
pressing the markers into engagement with stent. Examples of
suitable materials includes plastics, such as Delrin, PVC, nylon,
and others; metals such as steel, stainless steel, aluminum,
titanium, and others; and glass. The rollers 120 can also include a
relatively resilient and compliant material that is selected to
avoid damaging the stent 100 or markers 102 yet provide sufficient
pressure to press the markers into engagement with the stent.
[0055] In some embodiments, the rollers 120 are positioned over the
mandrel 110 such that the top roller 120 does not contact stent 100
and contacts only the markers 102. In this way, stress on the stent
100 is minimized. The bottom roller 120 contacts the stent to
support the stent when the top roller 120 presses the markers 120.
The markers 102 are compacted tightly against the opening of stent
100 and the markers 102 are retained in the stent during stent
crimping, delivery, and deployment in a bodily lumen.
[0056] FIG. 9 shows the stent 100 and mandrel 110 after having been
moved axially in the direction of axial arrow 126 from their
positions in FIG. 8. As a result, the markers 102 have been pressed
into the openings of stent 100 to fabricate a stent with markers
that partially protrude from the stent 100. In one embodiment, the
rollers 120 cause the markers 102 to deform to reduce or eliminate
protrusion of the markers 102 from the stent 100. Thus, the
invention provides a method and apparatus for pressing markers into
the stent such that the marker is tightly fit into the stent,
thereby improving marker retention onto the stent as well as
reducing or eliminating protrusion of the marker from the
stent.
[0057] Both markers 102 have been pressed into engagement with the
stent 100 with one continuous axial movement of the mandrel 110
carrying the stent 100. FIG. 10 shows one of the markers 102 after
having been pressed into one of the openings 127 of the stent 100.
Although only two markers 102 are illustrated in FIGS. 8 and 9, it
will be appreciated that any number of markers may be positioned on
the stent and pressed into engagement with efficiency by one
continuous axial movement of the mandrel 110. Use of the same set
of rollers 120 on all the markers allows for uniformity in pressing
the markers into engagement with the stent 100.
[0058] In other embodiments, the stent 100 may be passed through
the gap 128 between the rollers 120 in a plurality of discrete
movements. In yet other embodiments, the stent 100 may be passed
through the gap 128 more than one time in order to press markers
located at other portions of the stent. Also, the stent 100 may be
passed through the gap 128 more than one time to press the markers
into engagement with the stent 100 in a progressive fashion. For
example, the gap 128 may be decreased after each time the stent 100
passes through the gap.
[0059] Referring again to FIG. 8, the gap 128 between the two
rollers may be equal to or slightly larger than the outer diameter
130 of stent 100, thereby avoiding damage to the stent. The outer
diameter 118 of the rear portion 114 of the mandrel 110 may be made
equal to or substantially equal to the stent outer diameter 130.
The outer diameter 118 may be greater than or equal to the stent
outer diameter 130. Also, the outer diameter 116 of the mandrel
forward portion 112 may be equal to or smaller than the inner
diameter of the stent 100. In this way, the stent 100 can have a
slip or interference fit with the mandrel forward portion 112.
[0060] The markers 102 are deformed by pushing the stent 100
through the rollers 120. When the stent 100, having luminal
surfaces supported by the forward portion 112 of the mandrel 110,
is pushed through the rollers 120, the markers 102 are pressed
inward and against the stent by the rollers 120.
[0061] In practice, the free end 140 of the mandrel forward portion
112 may be pulled axially in the direction of axial arrow 126 until
the markers 102 are pressed by the rollers 120. In this manner, the
mandrel rear portion 114 engages a rear end 142 of the stent 100 so
as to push the stent 100 into the gap 128 between the rollers.
[0062] In some embodiments, the free end 144 of the mandrel rear
portion 114 may be pushed axially in the direction of axial arrow
126 until the markers 102 are pressed by the rollers 120.
[0063] FIGS. 8 and 9 show how the stent 100 can be linearly
translated relative to the rollers 120. Linear translation of the
stent 100 relative to the rollers 120 can be achieved in other
ways. For example, in other embodiments, the stent 100 and the
mandrel 110 are held fixed in position while the rollers 120 are
moved axially over the stent and mandrel until the markers 102 are
pressed into engagement with the stent. In yet other embodiments,
the mandrel 110 and rollers 120 are both moved relative to each
other to facilitate pressing the markers 102 onto the stent
100.
[0064] It will be appreciated that any number of rollers may be
used. For example, the mandrel 110 may be supported at one or both
its ends such that the bottom roller 102 in FIGS. 8 and 9 can be
eliminated, and only the top roller 120 in FIGS. 8 and 9 is needed
to press the markers 102 into engagement with the stent 100. More
than two rollers, on the same or different sides of the stent 100,
may be used to provide greater support of the stent 100 or to guide
the mandrel 110 into the gap between the rollers. Also, more than
two rollers may be used to press markers in a progressive fashion.
For example, a first set of rollers may be used to press the
markers onto the stent, and a second set of rollers that are spaced
closer together may be used to press the markers further onto the
stent. Progressive sets of rollers can have gaps between them that
become smaller with each succeeding set of rollers.
[0065] FIG. 11 shows an apparatus and method in accordance with
another embodiment of the present invention. A stent 150 is mounted
over a mandrel 152. A radiopaque marker 154 has been placed on the
stent 150. Two rollers 156, adjacent the stent 150, are vertically
aligned and are oriented such that a retaining pin 158 at the
center of each roller is substantially parallel to the central axis
of the stent 150. In this way, each of the rollers 156 may rotate
along the direction of rotational arrows 160 about a rotational
axis that is substantially parallel to the central axis of the
stent.
[0066] Instead of being moved axially as in FIG. 9, the stent 150
and the mandrel 152 of FIG. 11 are moved laterally along the
direction of lateral arrow 162 into a gap 164 between the rollers
156. The stent 150 is oriented such that the marker 154 is pressed
into engagement against the stent as the stent passes through the
gap 164. The lateral direction of movement of the stent 150 is
substantially perpendicular to the central axis of the stent 150.
In other embodiments, the lateral direction is at an angle between
zero and ninety degrees from the central axis of the stent 150.
[0067] Preferably, the stent 150 is prevented from rotating about
its central axis 168 while the stent passes through the gap 164.
For example, the stent 150 may be held on the mandrel 152 with a
slight interference fit, and the ends of the mandrel 152 may be
secured against rotation. Also, the top roller 156 preferably
rotates along the direction of arrow 160 while the marker 154
passes beneath it to ensure that the marker is pressed downward
onto the stent 150 and to avoid pushing the marker sideways.
[0068] Referring again to FIG. 11, the gap 164 is carefully
selected to allow the stent 150 to pass through the gap 164 without
being damaged. Preferably, the vertical size of the gap 164 is
greater than or equal to the outer diameter 166 of the stent 150.
The vertical size of the gap 164 is selected such that the rollers
provide sufficient pressure to deform the marker 154 into
engagement with an opening in the stent 154 and to reduce the
amount with which the marker 154 protrudes radially from the stent
154.
[0069] FIG. 12 shows an apparatus and method in accordance with yet
another embodiment of the present invention. A stent 170 is mounted
over a mandrel 172. Three radiopaque makers 174 have been placed on
the stent 170. Two rollers 176, adjacent the stent 170, are each
held by a retaining pin 178. The rollers 176 are vertically aligned
and are oriented such that their rotational axes 177 are
substantially parallel to the central axis 179 of the stent 170. In
this way, the rollers 176 may rotate along the direction of
rotational arrows 180. The stent 170 is placed between in the gap
between the two rollers 176. The stent 170 is oriented such that
the markers 174 avoid contact with the rollers when first placed in
the gap. Then, the stent 170 is rotated about its central axis
along rotational arrow 182, thereby bringing the markers 174 into
contact with the rollers. As the stent 170 continues to rotate, the
rollers 176 press the markers 174 into engagement with the
stent.
[0070] FIG. 12 shows how the stent 170 can be rotationally
translated relative to the rollers 176. Rotational translation of
the stent 170 relative to the rollers 176 can be achieved in other
ways. For example, in other embodiments, the rollers 176 may rotate
about the central axis 179 of the stent 170. After the stent 170 is
placed between in the gap between the two rollers 176, the rollers
176 are rotated about the central axis 179 of the stent 170 while
the stent 170 is prevented from rotating about its central axis
179, thereby bringing the rollers 176 into contact with the markers
174. As the rollers 176 continue to rotate, the rollers 176 press
the markers 174 into engagement with the stent 170. Further, in
other embodiments, both the stent 170 and the rollers 176 are
rotated about the central axis 179 of the stent 170.
[0071] Although three markers 174 are illustrated in FIG. 12, it
will be appreciated that any number of markers may be positioned on
the stent and pressed into engagement with efficiency by one
continuous rotational movement of the stent 170. It will also be
appreciated that additional rollers may be used. Additional rollers
may be used to provide greater support to the stent 170 or help
keep the stent aligned within the gap between the rollers.
[0072] In FIGS. 8-12, the retaining pins at the center of the
rollers are fixed in position relative to each other. In other
embodiments, retaining pins are movable relative to each other. For
example, movable retaining pins may be held by a spring or device
the biases the rollers to achieve a nominal gap between the
rollers. The nominal gap may be less than, equal to, or greater
than the outer diameter of the stent. When the stent is passed
through the gap, the spring or other biasing device allows the
rollers to move apart so as to maintain a selected level of
pressure on the stent and marker. In this manner, the risk of
damage to the stent and marker is reduced.
[0073] While several particular forms of the invention have been
illustrated and described, it will also be apparent that various
modifications can be made without departing from the scope of the
invention. It is also contemplated that various combinations or
subcombinations of the specific features and aspects of the
disclosed embodiments can be combined with or substituted for one
another in order to form varying modes of the invention.
Accordingly, it is not intended that the invention be limited,
except as by the appended claims.
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