U.S. patent application number 13/173353 was filed with the patent office on 2013-01-03 for apparatus and method for formation of foil-shaped stent struts.
This patent application is currently assigned to ABBOTT CARDIOVASCULAR SYSTEMS INC.. Invention is credited to Kevin J. Ehrenreich, Randolf von Oepen.
Application Number | 20130005218 13/173353 |
Document ID | / |
Family ID | 47391113 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130005218 |
Kind Code |
A1 |
von Oepen; Randolf ; et
al. |
January 3, 2013 |
APPARATUS AND METHOD FOR FORMATION OF FOIL-SHAPED STENT STRUTS
Abstract
A device and method is disclosed for reducing turbulent blood
flow over stent struts of an intravascular stent implanted in, for
example, a coronary artery. An abrasive slurry is passed over the
struts of an intravascular stent in order to remove a portion of
the stent struts to form an airfoil shape. When the stent having
airfoil-shaped struts is implanted in an artery, the flow of blood
over the airfoil shape will reduce the likelihood of turbulent
blood flow and thereby will reduce the likelihood of turbulent
blood flow and thereby reduce the likelihood of a buildup in plaque
or injury to the vessel wall.
Inventors: |
von Oepen; Randolf; (Aptos,
CA) ; Ehrenreich; Kevin J.; (San Francisco,
CA) |
Assignee: |
ABBOTT CARDIOVASCULAR SYSTEMS
INC.
Santa Clara
CA
|
Family ID: |
47391113 |
Appl. No.: |
13/173353 |
Filed: |
June 30, 2011 |
Current U.S.
Class: |
451/36 |
Current CPC
Class: |
A61F 2002/068 20130101;
A61F 2/915 20130101; B24C 1/083 20130101; A61F 2002/91566 20130101;
A61F 2230/0004 20130101 |
Class at
Publication: |
451/36 |
International
Class: |
B24C 1/00 20060101
B24C001/00 |
Claims
1. A method for forming a stent, comprising: providing a metallic
stent having a cylindrical shape and a pattern of stent struts;
placing the stent in a chamber; injecting an abrasive slurry
through the chamber and through a lumen of the stent; removing
metal from an inner surface of at least one of the stent struts by
the abrasive slurry flowing over the inner surface of the
stent.
2. The method of claim 1, wherein as the abrasive slurry flows over
the inner surface of the at least one stent strut, a transverse
cross-section of the strut is transformed from a substantially
rectangular shape into the shape of an airfoil.
3. The method of claim 1, wherein the abrasive slurry has a low
viscosity so that it flows through the stent lumen without bending
the stent struts.
4. (canceled)
5. The method of claim 1, wherein the abrasive slurry has a
pressure range of 1500 psi to 3500 psi.
6. The method of claim 1, wherein the abrasive slurry contains
abrasive particles having an average particle in the range of 12.0
microns (0.0005 inch) to 6.5 microns (0.0003 inch).
7. The method of claim 1, wherein the abrasive slurry contains a
polymer.
8. The method of claim 1, wherein the airfoil-shaped cross-section
of the at least one stent strut has a first edge that is thinner
than a second edge.
9. The method of claim 7, wherein the at least one stent strut has
a curved inner surface that extends between the first edge and the
second edge.
10. The method of claim 7, wherein as the abrasive slurry flows
over the inner surface of the at least one stent strut, the slurry
flows in a direction from the first edge toward the second
edge.
11. The method of claim 9, wherein the abrasive slurry removes more
metal from the first edge than from the second edge.
12. The method of claim 2, wherein the transverse cross-sectional
shape of the at least one stent strut before flowing the abrasive
slurry over the inner surface is substantially rectangular with
radiused corners.
13. The method of claim 1, wherein the metal removed from the at
least one stent strut reduces the radial thickness of the first
edge from about 5% to about 20% and the second edge from about 3%
to about 15%.
14. The method of claim 1, wherein the stent has an outer surface
and a radial thickness defined by the outer surface and the inner
surface, the radial thickness being in a range of 0.002 inch to
0.060 inch.
Description
BACKGROUND
[0001] The invention relates generally to providing an apparatus
for using an abrasive slurry for the removal of metal on products
made from metals. More particularly, the invention relates to an
apparatus for and method of using an abrasive slurry on medical
devices made of titanium, stainless steel, tungsten,
nickel-titanium, tantalum, cobalt-chromium-tungsten,
cobalt-chromium, and the like to form a more hemodynamically
compatible device.
[0002] While a wide range of products or devices can be made from
the listed metal alloys for use with the present invention, medical
devices are particularly suitable due to the biocompatible
characteristics of these alloys. Thus, for example, implantable
medical devices or devices that are used within the human body are
particularly suitable and can be made from these alloys that have
been treated in accordance with the present invention. More
particularly, and as described in more detail herein, intravascular
stents can be made from the listed alloys that have been treated
according to the invention. Thus, while the description of prior
art devices and of the invention herein refers mainly to
intravascular stents, the invention is not so limited to medical
products or intravascular stents.
[0003] Stents are generally metallic tube shaped intravascular
devices which are placed within a blood vessel to structurally hold
open the vessel. The device can be used to maintain the patency of
a blood vessel immediately after intravascular treatments and can
be used to reduce the likelihood of development of restenosis.
Expandable stents are frequently used as they may travel in
compressed form to the stenotic site generally either crimped onto
an inflation balloon or compressed into a containment sheath in a
known manner.
[0004] Metal stents can be formed in a variety of expandable
configurations such as helically wound wire stents, wire mesh
stents, weaved wire stents, metallic serpentine stents, or in the
form of a chain of corrugated rings. Expandable stents, such as
wire mesh, serpentine, and corrugated ring designs, for example, do
not possess uniformly solid tubular walls. Although generally
cylindrical in overall shape, the walls of such stents are
perforated often in a framework design of wire-like elements or
struts connected together or in a weave design of cross threaded
wire.
[0005] Expandable stents formed from metal offer a number of
advantages and are widely used. Metallic serpentine stents, for
example, not only provide strength and rigidity once implanted they
also are designed sufficiently compressible and flexible for
traveling through the tortuous pathways of the vessel route prior
to arrival at the stenotic site. Additionally, metallic stents may
be radiopaque, thus easily visible by radiation illumination
techniques such as x-ray film.
[0006] It is highly desirable for the surface of the stent to be
extremely smooth so that it can be inserted easily and experience
low-friction travel through the tortuous vessel pathway prior to
implantation. A roughened outer surface may result in increased
frictional obstruction during insertion and excess drag during
travel to the stenotic site as well as damaging the endothelium
lining of the vessel wall. A rough surface may cause frictional
resistance to such an extent as to prevent travel to desired distal
locations. A rough finish may also cause damage to the underlying
inflation balloon. A less rough finish decreases thrombogenicity
and increases corrosion resistance.
[0007] Stents have been formed from various metals including
stainless steel, tantalum, titanium, tungsten, nickel-titanium
which is commonly called Nitinol, and alloys formed with cobalt and
chromium. Stainless steel has been extensively used to form stents
and has often been the material of choice for stent construction.
Stainless steel is corrosion resistant, strong, yet may be cut into
very thin-walled stent patterns.
[0008] Cobalt-chromium alloy is a metal that has proven advantages
when used in stent applications. Stents made from a cobalt-chromium
alloy may be thinner and lighter in weight than stents made from
other metallic materials, including stainless steel.
Cobalt-chromium alloy is also a denser metal than stainless steel.
Additionally, cobalt-chromium stents are nontranslucent to certain
electromagnetic radiation waves, such as X-rays, and, relative to
stainless steel stents, provide a higher degree of radiopacity,
thus being easier to identify in the body under fluoroscopy.
[0009] Metal stents, however, suffer from a number of
disadvantages. They often require processing to eliminate
undesirable burrs, nicks, or sharp ends. Expandable metal stents
are frequently formed by use of a laser to cut a framework design
from a tube of metal. The tubular stent wall is formed into a
lattice arrangement consisting of metal struts with gaps
therebetween. Laser cutting, however, typically is at high
temperature and often leaves debris and slag material attached to
the stent. Such material, if left on a stent, would render the
stent unacceptable for implantation. Treatment to remove the slag,
burrs, and nicks is therefore required to provide a device suitable
for use in a body lumen.
[0010] Descaling is a first treatment of the surface in preparation
for further surface treatment such as electropolishing. Descaling
may include, for example, scraping the stent with a diamond file,
followed by dipping the stent in a hydrochloric acid or an HCl
mixture, and thereafter cleaning the stent ultrasonically. A
successfully descaled metal stent should be substantially slag-free
in preparation for subsequent electropolishing.
[0011] Further finishing is often accomplished by the well known
technique of electropolishing. Grinding, vibration, and tumbling
techniques are often not suited to be employed on small detailed
parts such as stents.
[0012] Electropolishing is an electrochemical process by which
surface metal is dissolved. Sometimes referred to as "reverse
plating," the electropolishing process actually removes metal from
the surface desired to be smoothed. The metal stent is connected to
a power supply (the anode) and is immersed in a liquid electrolytic
solution along with a metal cathode connected to the negative
terminal of the power supply. Current is applied and flows from the
stent, causing it to become polarized. The applied current controls
the rate at which the metal ions of the anodic stent are generally
removed and diffused through the solution to the cathode.
[0013] The rate of the electrochemical reaction is proportional to
the current density. The positioning and thickness of the cathode
in relation to the stent is important to make available an even
distribution of current to the desired portion of the stent sought
to be smoothed. For example, some prior art devices have a cathode
in the form of a flat plate or a triangular or single wire loop
configuration, which may not yield a stent or other medical device
with a smooth surface on all exposed surfaces. For example, the
prior art devices do not always provide a stent having a smooth
surface on the inner tubular wall of the stent where blood flow
will pass.
[0014] Most prior art stents are laser cut from a thin-walled metal
tube leaving a mesh framework of stent struts. Typically, the stent
struts have a rectangular transverse cross-section. When implanted
in an artery, the rectangular-shaped cross-section of the stent
struts may produce blood flow turbulence in the artery resulting in
adverse vascular reactions such as the proliferation of
restenosis.
[0015] What is needed is an apparatus and a process for treating a
product or device made of a metal alloy to remove metal from the
device to thereby reduce the likelihood of turbulent blood flow
through the device. The present invention satisfies this need.
SUMMARY OF THE INVENTION
[0016] The invention is directed to an improved apparatus and
method for the treatment of an intravascular stent formed from a
metal alloy. The invention is directed to an apparatus and method
for passing an abrasive slurry over the struts of an intravascular
stent in order to remove a portion of the stent struts to form an
airfoil shape. More particularly, the transverse cross-section of
one more struts of the stent have a shape that resembles an airfoil
or a hydrofoil which will reduce turbulent blood flow in the
vasculature in which the stent is implanted, thereby improving
clinical outcome. In one embodiment, a chamber holds a stent
stationary while an abrasive slurry flows through the inner lumen
of the stent. As the abrasive slurry passes over the stent struts,
metal is removed from a first edge and, to a lesser degree, metal
is removed from a second edge of the strut. More metal is removed
from the first edge than from the second edge, resulting in a
cross-sectional shape resembling an airfoil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 an elevational view, partially in section, of a stent
of the present invention mounted on a rapid exchange delivery
catheter and positioned within an artery.
[0018] FIG. 2 is an elevational view, partially in section, similar
to that in FIG. 1, wherein the stent is expanded within the artery,
so that the stent embeds partially within the arterial wall.
[0019] FIG. 3 is an elevational view, partially in section, showing
the expanded stent implanted within the artery after withdrawal of
the rapid exchange delivery catheter.
[0020] FIG. 4 is a cross-sectional view of a prior art stent in
which the stent struts have a rectangular cross-section thereby
causing turbulent flow of blood through the artery.
[0021] FIG. 5 is a plan view of a flattened stent of one embodiment
of the invention which illustrates a pattern of rings and
links.
[0022] FIG. 6 is a partial plan view of the stent of FIG. 5 which
has been expanded to approximately 4.0 mm inside diameter.
[0023] FIG. 7 is a cross-sectional view taken along lines 7-7
depicting a rectangular cross-section of a stent strut of FIG.
6.
[0024] FIG. 8 is an elevational view, partially in section, of a
chamber assembly for pumping an abrasive slurry through the inner
diameter of the stent to remove metal from the stent struts.
[0025] FIG. 9 is a perspective view of the chamber assembly of FIG.
8.
[0026] FIG. 10 is a partial cross-sectional view of the chamber
assembly of FIG. 8 depicting the stent removably mounted in the
chamber.
[0027] FIGS. 11A-11D are a series of cross-sectional views of a
single strut of the stent of the invention as the abrasive slurry
passes over the stent and progressively removes metal from the
stent strut.
[0028] FIG. 12 is a transverse cross-sectional view airfoil-shaped
stent strut partially embedded in an artery wall.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The present invention stent improves on existing stents by
providing a longitudinally flexible stent having a uniquely
designed pattern and novel interconnecting members. In addition to
providing longitudinal flexibility, the stent of the present
invention also provides radial rigidity and a high degree of
scaffolding of a vessel wall, such as a coronary artery. The
present invention stent is processed so that it is more
hemodynamically compatible and causes less blood flow turbulence
when implanted in an artery.
[0030] Turning to the drawings, FIG. 1 depicts a prior art stent 10
mounted on a conventional catheter assembly 12 which is used to
deliver the stent and implant it in a body lumen, such as a
coronary artery, peripheral artery, or other vessel or lumen within
the body. The catheter assembly includes a catheter shaft 13 which
has a proximal end 14 and a distal end 16. The catheter assembly is
configured to advance through the patient's vascular system by
advancing over a guide wire by any of the well known methods of an
over the wire system (not shown) or a well known rapid exchange
catheter system, such as the one shown in FIG. 1.
[0031] Catheter assembly 12 as depicted in FIG. 1 is of the well
known rapid exchange type (RX) which includes an RX port 20 where
the guide wire 18 will exit the catheter. The distal end of the
guide wire 18 exits the catheter distal end 16 so that the catheter
advances along the guide wire on a section of the catheter between
the RX port 20 and the catheter distal end 16. As is known in the
art, the guide wire lumen which receives the guide wire is sized
for receiving various diameter guide wires to suit a particular
application. The stent is mounted on the expandable member 22
(balloon) and is crimped tightly thereon so that the stent and
expandable member present a low profile diameter for delivery
through the arteries.
[0032] As shown in FIG. 1, a partial cross-section of an artery 24
is shown with a small amount of plaque that has been previously
treated by an angioplasty or other repair procedure. Stent 10 is
used to repair a diseased or damaged arterial wall which may
include the plaque 26 as shown in FIG. 1, or a dissection, or a
flap which are sometimes found in the coronary arteries, peripheral
arteries and other vessels.
[0033] In a typical procedure to implant stent 10, the guide wire
18 is advanced through the patient's vascular system by well known
methods so that the distal end of the guide wire is advanced past
the plaque or diseased area 26. Prior to implanting the stent, the
cardiologist may wish to perform an angioplasty procedure or other
procedure (i.e., atherectomy) in order to open the vessel and
remodel the diseased area. Thereafter, the stent delivery catheter
assembly 12 is advanced over the guide wire so that the stent is
positioned in the target area. The expandable member or balloon 22
is inflated by well known means so that it expands radially
outwardly and in turn expands the stent radially outwardly until
the stent is apposed to the vessel wall. The expandable member is
then deflated and the catheter withdrawn from the patient's
vascular system. The guide wire typically is left in the lumen for
post-dilatation procedures, if any, and subsequently is withdrawn
from the patient's vascular system. As depicted in FIGS. 2 and 3,
the balloon is fully inflated with the stent expanded and pressed
against the vessel wall, and in FIG. 3, the implanted stent remains
in the vessel after the balloon has been deflated and the catheter
assembly and guide wire have been withdrawn from the patient.
[0034] The stent 10 serves to hold open the artery after the
catheter is withdrawn, as illustrated by FIG. 3. Due to the
formation of the stent from an elongated tubular member, the
undulating components of the stent are generally rectangular in
transverse cross-section. When the stent is expanded, it is pressed
into the wall of the artery, however, portions of the rectangular
cross-section may protrude into the artery lumen and may interfere
with the blood flow through the artery. The stent is pressed into
the wall of the artery and will eventually be covered with
endothelial cell growth which will minimize blood flow
interference. The undulating portion of the stent provides good
tacking characteristics to prevent stent movement within the
artery. Furthermore, the closely spaced cylindrical elements at
regular intervals provide uniform support for the wall of the
artery.
[0035] Referring to FIG. 4, a portion of an artery 24 is shown in
cross-section with a typical prior art stent at least partially
embedded in the artery wall. The stent is comprised of
rectangular-shaped stent struts 27 that have an inner surface 28
that faces the blood flow. In FIG. 4, the blood is flowing from
left to right in the artery. Because of the rectangular-shaped
stent struts 27 having a vertical surface impeding blood flow,
there is some turbulent blood flow in and around the stent struts
as shown by the diagrammatic arrows in FIG. 4. These localized
areas of turbulent blood flow produce adverse vascular reactions
such as the proliferation of restenosis and the formation of plaque
26. Typically, the rectangular-shaped stent struts 27 will have
rounded corners due to electropolishing, however, even though the
corners have been rounded there is still turbulent blood flow that
may produce the adverse vascular reactions.
[0036] Referring to FIG. 5, stent 30 is shown in a flattened
condition so that the pattern can be clearly viewed, even though
the stent is in a cylindrical form in use. The stent is typically
formed from a tubular member.
[0037] As shown in FIGS. 5-6, stent 30 is made up of a plurality of
cylindrical rings 40 which extend circumferentially around the
stent when it is in a tubular form (see FIG. 3). Each cylindrical
ring 40 has a cylindrical ring proximal end 46 and a cylindrical
ring distal end 48. Typically, since the stent is laser cut from a
tube there are no discreet parts such as the described cylindrical
rings and links. However, it is beneficial for identification and
reference to various parts to refer to the cylindrical rings and
links and other parts of the stent as follows.
[0038] Each cylindrical ring 40 defines a cylindrical plane 50
which is a plane defined by the proximal and distal ends 46,48 of
the ring and the circumferential extent as the cylindrical ring
travels around the cylinder. Each cylindrical ring includes
cylindrical outer wall surface 52 which defines the outermost
surface of the stent, and cylindrical inner wall surface 53 which
defines the innermost surface of the stent. Cylindrical plane 50
follows the cylindrical outer wall surface.
[0039] An undulating link 54 is positioned within cylindrical plane
50. The undulating links connect one cylindrical ring 40 to an
adjacent cylindrical ring 40 and contribute to the overall
longitudinal flexibility to the stent due to their unique
construction. The flexibility of the undulating links derives in
part from curved portion 56 connected to straight portions 58
wherein the straight portions are substantially perpendicular to
the longitudinal axis of the stent. Thus, as the stent is being
delivered through a tortuous vessel, such as a coronary artery, the
curved portions 56 and straight portions 58 of the undulating links
will permit the stent to flex in the longitudinal direction which
substantially enhances delivery of the stent to the target site.
The number of bends and straight portions in a link can be
increased or decreased from that shown, to achieve differing
flexibility constructions. With the straight portions being
substantially perpendicular to the stent longitudinal axis, the
undulating link acts much like a hinge at the curved portion to
provide flexibility. A straight link that is parallel to the stent
axis typically is not flexible and does not add to the flexibility
of the stent.
[0040] Referring to FIGS. 5-6, the stent 30 can be described more
particularly as having a plurality of first peaks 60, second peaks
61, and valleys 62. Although the stent is not divided into separate
elements, for ease of discussion references to peaks and valleys is
appropriate. The number of peaks and valleys can vary in number for
each ring depending upon the application. Thus, for example, if the
stent is to be implanted in a coronary artery, a lesser number of
peaks and valleys are required than if the stent is implanted in a
peripheral artery, which has a larger diameter than a coronary
artery. As can be seen for example in FIG. 6, peaks 60,61 are in
phase 63, meaning that the peaks 60,61 point in the same direction
and are substantially aligned along the longitudinal axis of the
stent. It may be desirable under certain circumstances to position
the peaks so that they are out of phase (not shown), that is, the
peaks of one ring would be circumferentially offset from the peaks
of an adjacent ring so that the apex of adjacent peaks pointed
toward each other. As shown in FIGS. 5-6, the peaks are
circumferentially offset 64 from the valleys and from the
undulating link 54. Positioning the peaks, valleys, and undulating
links in this manner, provides a stent having uniform expansion
capabilities, high radial strength, a high degree of flexibility,
and sufficient wall coverage to support the vessel.
[0041] As shown in FIG. 7, a rectangular-shaped stent strut 80 is
shown in a transverse cross-sectional configuration from one of the
peaks 69 from FIG. 6. More specifically, during a typical laser
cutting of a thin metallic tube, the resulting transverse
cross-sectional shape of all of the stent struts are generally a
rectangular-shaped stent strut 80 like that shown in FIG. 7.
Further processing including electropolishing will remove the sharp
corners so that the basic overall rectangular shape remains, only
with rounded corners so as to have a less invasive impact on the
arterial wall when the stent is delivered and implanted. As
previously described with respect to the rectangular-shaped stent
struts in FIGS. 4 and 7, such a cross-sectional shape likely will
result in turbulent blood flow and the adverse affects resulting
therefrom. While FIG. 7 illustrates a rectangular-shaped stent
strut, other cross-sectional configurations will benefit from the
present invention as well. Thus, for example, a square
cross-section, or any other cross-section having a leading edge
that will disrupt blood flow, will benefit from the present
invention.
[0042] As shown in FIGS. 8-11D, the stent of the present invention
is placed in a chamber in which an abrasive slurry flows through an
inner lumen of the stent in order to remove metal from the stent
struts and shape certain of the struts into an airfoil or hydrofoil
shape. More specifically, those stent struts that are substantially
perpendicular to the longitudinal axis of the stent and thereby the
flow of abrasive slurry, will be formed into a cross-sectional
shape of an airfoil or a hydrofoil, in which the leading edge of
the strut is thicker than the trailing end of the strut. When in
use, as blood flows along the strut surface, it will maintain a
laminar flow without disturbing the adjacent vasculature as much as
if the stent strut were rectangular shaped thereby causing
turbulent blood flow. While the stent struts of the present
invention may not be a perfect airfoil shape or hydrofoil shape
where the trailing edge would be relatively sharp, the trailing
edge thickness is reduced compared to the leading edge thickness,
but still has sufficient thickness to provide radial strength to
hold the stent open and to avoid mechanically scoring or otherwise
damaging the tissue of the vessel wall.
[0043] In keeping with the invention, as shown in FIGS. 8-10, a
chamber 82 has a longitudinal bore 84 extending therethrough and is
configured for receiving a stent 30. The diameter of the
longitudinal bore is configured to be slightly greater than the
outer diameter of the stent 30 so that the stent 30 can be placed
in the longitudinal bore without pushing on or having an
interference fit that may damage the stent struts. The chamber 82
has an end cap 86 that can be secured to the chamber by any
conventional means such as screw threads (not shown) or a
ratcheting lock, both of which are known in the art. A longitudinal
axis 88 extends through the longitudinal bore 84 of the chamber.
The chamber has a first end 90 and a second end 92 defining the
overall length of the chamber, which can vary depending upon the
length of the stent that is inserted therein.
[0044] As shown in FIG. 10, the stent 30 is mounted or inserted
into the longitudinal bore 84 and the outer diameter of the stent
is just slightly less than the diameter of the longitudinal bore
84. In this embodiment, the stent 30 is held in place in the
longitudinal bore by a flange 94 or ridge which will ensure that
the stent does not move longitudinally as the abrasive slurry flows
past the stent and removes metal. In this embodiment, a second
longitudinal bore 96 is formed near the second end 92 of the
chamber 82 wherein the second longitudinal bore has a diameter that
is less than the outer diameter of the stent and less than the
diameter of the longitudinal bore 84.
[0045] The longitudinal bore 84 has a diameter that is greater than
the outer diameter of the stent 30. It is intended that different
sized chamber 82 having different diameter longitudinal bores 84 be
used for stents having different outer diameters. For example, a
typical coronary artery stent in the manufactured configuration can
have an outer diameter from between 2 mm to 3.5 mm, and have a
length between 8 mm and 30 mm. More typically, a coronary stent has
an outer diameter of 3 mm and length of 20 mm. The longitudinal
bore 84 has a diameter that is greater than the outer diameter of
the stent so that the stent can be easily inserted into the chamber
82 and into longitudinal bore 84 without scraping or damaging the
stent struts. After the stent is inserted into the longitudinal
bore 84, the end cap 86 is secured to the chamber 82 so that the
end cap abuts one end of the stent 30 but does not force the stent
against the flange 94 or ridge which is at the opposite end of the
longitudinal bore from the end cap. Thus, after the end cap is
secured to the chamber, the stent should have substantially no
longitudinal movement within the longitudinal bore 84, and just
have a slight amount of clearance between the diameter of the
longitudinal bore and the outer diameter of the stent.
[0046] In further keeping with the invention, and referring to
FIGS. 11A-11D, an abrasive slurry 100 flows over the stent struts
102 of stent 30. The abrasive slurry 100 enters the chamber 82
through aperture 104 in the end cap 86 and flows through the
longitudinal bore 84 of the chamber. As can be seen in FIGS.
11A-11D, as the abrasive slurry flows over the stent struts 102,
which typically have a rectangular cross-section as shown in FIG.
7, the first edge 106 of the stent strut becomes rounded and metal
is removed from the first edge at a greater rate than at the second
edge 108. In other words, the first edge 106 of the stent strut 102
is directly in the flow of the abrasive slurry 100 and will wear
down by metal being removed from the first edge at a rate faster
than metal being removed from the second edge 108 on the downstream
side of the abrasive slurry. As the abrasive slurry 100 travels
over the stent strut 102, it removes less metal from second edge
108 since that edge is not directly in line with the flow of
slurry. Thus, the second edge 108 will have a thickness that is
greater than the thickness of first edge 106, and both the first
edge and the second edge will be curved, thereby taking the shape
of an airfoil or hydrofoil. It is noted that first edge 106 does
not have so much metal removed that it resembles a knife edge, like
a typical airfoil or hydrofoil, but that some metal is removed so
that the first edge 106 has less thickness than the second edge
108, yet the stent strut 102 still has enough cross-sectional area
so as to not compromise the structural integrity of the stent. In
other words, after processing with the abrasive slurry 100, the
stent 30 will still have the structural integrity to hold open a
vessel, such as a coronary artery, yet will have the benefit of the
stent struts having an airfoil shaped cross-section.
[0047] More specifically, the strut radial thickness of stent 30
for a coronary artery stent typically is about 0.0032 inch. It will
be appreciated, however, that the strut radial thickness can be
thicker or thinner, depending on the stent design and where it is
implanted. Thus, the strut radial thickness can be in the range
from 0.060 inch to 0.002 inch. The present invention reduction in
radial thickness of the struts can range from about 5% to about 20%
at the first edge 106 and from about 3% to about 15% at the second
edge 108. Preferably, the radial thickness of the first edge 106 is
reduced by 20% and radial thickness of the second edge is reduced
by 5%. As an example, for a stent strut that has a radial thickness
of 0.0032 inch, the first edge 106 will be 20% thinner, or about
0.0026 inch and the second edge 108 will be 5% thinner, or about
0.003 inch. Further, the strut surface extending between the first
edge 106 and second edge 108 may be straight or slightly curved and
essentially form a taper, gradually getting thicker going from the
first edge toward the second edge.
[0048] Referring to FIGS. 8-11D, it will be appreciated that those
stent struts 102 that will benefit the most from the use of the
abrasive slurry 100 in chamber 82 are those stent struts that are
perpendicular to the flow of the abrasive slurry. Thus, for
example, referring to FIG. 6, peak 69 and straight portions 58 are
stent struts that are substantially perpendicular to the
longitudinal axis of the stent and thus are perpendicular to the
flow of the abrasive slurry 100. It is expected that these stent
struts will have a cross-sectional shape that resembles an airfoil
or hydrofoil as previously discussed. Those stent struts that are
not substantially perpendicular to the direction of the flow of the
abrasive slurry 100, also benefit from the present invention in
that the transverse cross-section may not have a perfect
airfoil-shaped cross-section, however, the first edge 106 of such
stent struts will generally have more metal removed than the second
edge 108 of such stent struts.
[0049] The stent 30 of the present invention can be mounted on a
balloon catheter similar to that shown in FIG. 1. The stent is
tightly compressed or crimped onto the balloon portion of the
catheter and remains tightly crimped onto the balloon during
delivery through the patient's vascular system. When the balloon is
expanded, the stent expands radially outwardly into contact with
the body lumen, for example, a coronary artery. When the balloon
portion of the catheter is deflated, the catheter system is
withdrawn from the patient and the stent remains implanted in the
artery. Similarly, if the stent of the present invention is made
from a self-expanding metal alloy, such as nickel-titanium or the
like, the stent may be compressed or crimped onto a catheter and a
sheath (not shown) is placed over the stent to hold it in place
until the stent is ready to be implanted in the patient. Such
sheaths are well known in the art. Further, such a self-expanding
stent may be compressed or crimped to a delivery diameter and
placed within a catheter. Once the stent has been positioned within
the artery, it is pushed out of the catheter or the catheter is
withdrawn proximally and the stent held in place until it exits the
catheter and self-expands into contact with the wall of the artery.
Balloon catheters and catheters for delivering self-expanding
stents are well known in the art.
[0050] It is important to note that the airfoil shape of the stent
strut 102 as shown for example in FIG. 11D, has a second edge 108
that is thicker than a first edge 106. When the stent 30 is
implanted in a vessel, such as a coronary artery 24 shown in FIG.
12, it is more likely that blood in the artery will flow from the
second edge 108 toward the first edge 106 much like the airflow
over the airfoil of an airplane wing. In other words, the leading
edge (second edge 108) of the stent strut 102 is thicker than the
trailing edge (first edge 106), and as blood flows along the strut
surface as shown by Arrow A, it maintains a laminer flow without
disturbing the adjacent vasculature as much as if the stent strut
were more rectangular-shaped. Further, the present invention using
the slurry solution forming the stent strut, may also form a stent
strut that has a taper shape rather than an airfoil shape, and
still be beneficial in the reduction of blood flow turbulence.
[0051] While the invention has been illustrated and described
herein, in terms of its use as an intravascular stent, it will be
apparent to those skilled in the art that the stent can be used in
other body lumens. Other modifications and improvements may be made
without departing from the scope of the invention.
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