U.S. patent application number 12/837809 was filed with the patent office on 2010-11-04 for method for retaining a vascular stent on a catheter.
This patent application is currently assigned to ABBOTT CARDIOVASCULAR SYSTEMS INC.. Invention is credited to Boyd V. Knott, Sean McNiven, Jeremy Stigall.
Application Number | 20100278956 12/837809 |
Document ID | / |
Family ID | 38634056 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100278956 |
Kind Code |
A1 |
Knott; Boyd V. ; et
al. |
November 4, 2010 |
METHOD FOR RETAINING A VASCULAR STENT ON A CATHETER
Abstract
A method of securely mounting a stent on a balloon of a balloon
catheter. The method generally includes crimping a stent on a
balloon of a balloon catheter, and positioning the balloon with the
drug delivery stent thereon within a polished bore of a mold formed
at least in part of a metallic material. The balloon is pressurized
and heated within the mold as the mold radially restrains the stent
from expanding. The stent is recrimped on the balloon after removal
from the mold to increase retention of the stent on the
balloon.
Inventors: |
Knott; Boyd V.; (Menifee,
CA) ; McNiven; Sean; (Del Mar, CA) ; Stigall;
Jeremy; (Murrieta, CA) |
Correspondence
Address: |
FULWIDER PATTON, LLP (ABBOTT)
6060 CENTER DRIVE, 10TH FLOOR
LOS ANGELES
CA
90045
US
|
Assignee: |
ABBOTT CARDIOVASCULAR SYSTEMS
INC.
Santa Clara
CA
|
Family ID: |
38634056 |
Appl. No.: |
12/837809 |
Filed: |
July 16, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11453747 |
Jun 15, 2006 |
7763198 |
|
|
12837809 |
|
|
|
|
11105085 |
Apr 12, 2005 |
7563400 |
|
|
11453747 |
|
|
|
|
Current U.S.
Class: |
425/395 |
Current CPC
Class: |
A61F 2250/0067 20130101;
Y10T 29/49913 20150115; A61F 2/9522 20200501; A61F 2/958
20130101 |
Class at
Publication: |
425/395 |
International
Class: |
B28B 21/50 20060101
B28B021/50 |
Claims
1. A method of mounting a stent on a balloon catheter, comprising:
positioning the stent on a balloon of the balloon catheter;
applying a first radially compressive force on an outer surface of
the stent, thereby decreasing the outer diameter of the stent on
the balloon catheter; pressurizing and heating the balloon while
restricting radial expansion of the outer surface of the stent; and
applying a second radially compressive force on the outer surface
of the stent.
2. The method of claim 1, wherein the pressurizing and heating of
the balloon is performed in a mold configured to restrict the
radial expansion of the outer surface of the stent.
3. The method of claim 2, wherein the stent is a drug delivery
stent and mounting the stent on the balloon without damaging the
drug delivery layer of the stent, includes heating the balloon by
heating the mold by contacting a surface of the mold with a
conductive heating element member which heats the mold purely by
conduction and which provides temperature control to the mold with
a tolerance of about .+-.1 degree to about .+-.2 degrees F.
4. The method of claim 2, wherein heating the mold includes
submerging the mold in a liquid bath.
5. The method of claim 2, wherein heating the mold includes
contacting a surface of the mold with a conductive heating element
member.
6. The method of claim 2, wherein the mold is a split mold, and
further including removing the balloon catheter with the stent
mounted thereon from the split mold by opening of the split
mold.
7. The method of claim 1, wherein at least one of the radially
compressive forces is applied by a crimping apparatus.
8. The method of claim 1, wherein at least one of the radially
compressive forces is applied by a hand tool.
9. The method of claim 1, wherein at least one of the radially
compressive forces is applied by hand.
10. A method of mounting a stent on a balloon catheter, comprising:
positioning a stent on a balloon catheter, the balloon catheter
having an elongated shaft with an inflation lumen and a guidewire
lumen and an inflatable balloon on a distal shaft section with an
interior in fluid communication with the inflation lumen, and the
stent having an open-walled body of stent struts with gaps between
adjacent stent struts; applying a first radially compressive force
on an outer surface of the stent and thereby decreasing the outer
diameter of the stent on the balloon catheter; heating the balloon
and introducing inflation media into the interior of the balloon to
radially expand the balloon with the stent restrained from radially
expanding, wherein the balloon expands into the stent gaps to embed
the stent in an outer surface of the balloon; removing the
inflation media from the balloon interior; and applying a second
radially compressive force on an outer surface of the stent,
thereby decreasing the outer diameter of the stent on the balloon
catheter.
11. The method of claim 10, further including sterilizing the stent
mounted on the balloon catheter.
12. The method of claim 10, wherein at least one of the radially
compressive forces is applied by a crimping apparatus.
13. The method of claim 10, wherein at least one of the radially
compressive forces is applied by a hand tool.
14. The method of claim 10, wherein at least one of the radially
compressive forces is applied by hand.
15. The method of claim 10, wherein the stent is restrained from
radially expanding by a mold.
16. The method of claim 15, wherein the mold is a split mold and
the balloon catheter with the stent mounted thereon is removed from
the split mold by opening of the split mold.
17. The method of claim 10, further including sterilization of the
balloon catheter and stent with ethylene oxide.
18. A method of increasing retention of an intravascular device on
a balloon catheter, comprising: a first stage of crimping the
intravascular device onto a balloon of the balloon catheter; a
second stage of heating and pressurizing the balloon; and a third
stage of re-crimping the intravascular device onto the balloon of
the balloon catheter.
19. The method of claim 18, further including heating the
intravascular device and the balloon catheter during the third
stage.
20. The method of claim 18, further including pressurizing the
balloon catheter during the third stage.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to and is a
continuation-in-part of U.S. Ser. No. 11/105,085 filed Apr. 12,
2005 and entitled "METHOD OF STENT MOUNTING TO FORM A BALLOON
CATHETER HAVING IMPROVED RETENTION OF A DRUG DELIVERY STENT," the
entirety of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to catheters and stents,
and particularly to methods for retention of stents on
intravascular stent delivery catheters.
[0003] In percutaneous transluminal coronary angioplasty (PTCA)
procedures a guiding catheter is advanced in the patient's
vasculature until the distal tip of the guiding catheter is seated
in the ostium of a desired coronary artery. A guidewire is first
advanced out of the distal end of the guiding catheter into the
patient's coronary artery until the distal end of the guidewire
crosses a lesion to be dilated. A dilatation catheter, having an
inflatable balloon on the distal portion thereof, is advanced into
the patient's coronary anatomy over the previously introduced
guidewire until the balloon of the dilatation catheter is properly
positioned across the lesion. Once properly positioned, the
dilatation balloon is inflated with inflation fluid one or more
times to a predetermined size at relatively high pressures so that
the stenosis is compressed against the arterial wall and the wall
expanded to open up the vascular passageway. Generally, the
inflated diameter of the balloon is approximately the same diameter
as the native diameter of the body lumen being dilated so as to
complete the dilatation but not overexpand the artery wall. After
the balloon is finally deflated, blood flow resumes through the
dilated artery and the dilatation catheter and the guidewire can be
removed therefrom.
[0004] In such angioplasty procedures, there may be restenosis of
the artery, i.e. reformation of the arterial blockage, which
necessitates either another angioplasty procedure, or some other
method of repairing or strengthening the dilated area. To reduce
the restenosis rate of angioplasty alone and to strengthen the
dilated area, physicians now normally implant an intravascular
prosthesis, generally called a stent, inside the artery at the site
of the lesion. Stents may also be used to repair vessels having an
intimal flap or dissection or to generally strengthen a weakened
section of a vessel or to maintain its patency. Stents are usually
delivered to a desired location within a coronary artery in a
contracted condition on a balloon of a catheter which is similar in
many respects to a balloon angioplasty catheter, and expanded
within the patient's artery to a larger diameter by expansion of
the balloon. The balloon is deflated to remove the catheter and the
stent left in place within the artery at the site of the dilated
lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and
U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated
herein by reference.
[0005] The stent must be securely yet releasably mounted on the
catheter balloon for delivery and deployment at the desired
location in a patient's body lumen. If the stent becomes dislodged
from or moved relative to the balloon during delivery, the system
will not correctly implant the stent in the body lumen. However,
the stent can't be so strongly fixed to the balloon that it
inhibits expansion of the balloon and/or release of the stent once
the balloon is positioned at the desired location. One difficulty
has been retention of stents, including stents having a drug
delivery layer. The mounting process used to secure the drug
delivery stent to the balloon must not damage the stent.
Furthermore, the stent retention process must not damage a stent
including a drug or the matrix material containing the drug. It
would be a significant advance to provide a catheter balloon having
improved retention of a stent, for example, a drug delivery stent,
and without inhibiting balloon or stent function. The present
invention satisfies these and other needs.
SUMMARY OF THE INVENTION
[0006] One aspect of the present invention is directed to a method
of mounting a stent on a stent delivery balloon catheter. Yet
another aspect of the invention is a method of mounting a drug
delivery stent on a balloon, and a stent delivery balloon catheter
produced therefrom. Still another aspect of the invention is a
method that securely mounts a drug delivery stent on a balloon
catheter without damaging the drug delivery layer of the stent.
[0007] In one aspect of the invention, the method generally
comprises positioning a stent, for example, a drug delivery stent,
on a balloon of a balloon catheter, and positioning the balloon
with the stent thereon within a polished bore of a mold formed at
least in part of a metallic material. In yet a further aspect of
the invention, the stent is a drug delivery stent, and the balloon
is pressurized and heated within the mold to mount the stent on the
balloon, without damaging the drug delivery layer of the stent. The
mold radially restrains the stent from expanding when the balloon
is pressurized therein, so that the balloon can be forced into the
gaps in the stent wall using inflation pressures higher than those
which normally cause radial expansion of the stent. The bore of the
mold is defined by a polished inner surface with a polished finish
which is sufficiently smooth so that contact and relative movement
between the stent and polished inner surface of the mold does not
roughen or otherwise damage or create a texture on the drug
delivery layer of the stent. As a result, the release rate of the
drug from the drug delivery layer is substantially equal to the
release rate prior to stent mounting. In another aspect of the
invention, the smooth surface of the drug delivery layer, which is
free of roughness and irregularities caused by the stent mounting,
provides the drug delivery layer with a uniform thickness which is
within the normal variance produced by the method used to form the
drug delivery layer. Additionally, the inner surface of the mold
does not cause the drug delivery layer to transfer drug to the
inner surface of the mold during the stent mounting, so that the
amount of drug present in the drug delivery layer is substantially
equal to the amount prior to stent mounting.
[0008] In yet another aspect of the invention, the drug delivery
layer of the stent is a coating applied to a surface of the
radially expandable tubular body of the stent. However, a variety
of suitable configurations may be used as are well known in the
art, including embodiments in which the tubular body of the stent
is itself formed of a drug delivery matrix, or the drug delivery
layer is a tubular sleeve on a surface of the body of the stent.
Additionally, the drug delivery layer should be understood to
broadly refer to configurations which deliver or present one or
more drugs by any of a variety of suitable mechanisms including
eluting the drug from the layer, bioab sorption of a drug delivery
matrix, and the like. The stent may be biostable and/or
bioabsorable. The terminology "drug" as used herein should be
understood to refer to a variety of therapeutic and diagnostic
agents. In a further aspect of the invention, the drug is intended
to prevent or inhibit restenosis.
[0009] The balloon is heated by heating the mold using a heat
transfer medium which provides temperature control to the mold with
a tolerance of about .+-.1 degree to about .+-.2 degrees Fahrenheit
(F)). In still another aspect of the invention, heating the mold
comprises submerging the mold in a liquid bath, or contacting the
surface of the mold with a conductive heating element. As a result,
the heat transfer medium heats the mold primarily by conduction,
and provides for finer temperature control and quicker heating than
is provided by heating methods which heat primarily by convection
(e.g., heating with hot air). In contrast, heating with hot air
provides a heating tolerance of about .+-.10 degrees. In a
presently preferred embodiment, the heat transfer medium is a
conductive heating element such as a platen (e.g., a heated flat
metal plate) configured to provide uniform heating of the balloon
within the mold when the platen is in contact with the mold. Thus,
the temperature is uniform (i.e., within about .+-.2 degrees F.)
along the length of the section of the mold exposed to the heating
medium, and the temperature at any given point of the heated length
remains constant (i.e., within .+-.2 degrees F.) during the
heating. With the metal platen pressed against an outer surface of
the mold, the platen heats purely by conduction (unlike a hot
circulating heating medium which heats by both conduction and
convention), and provides for finer temperature control at the
surface of the mold than a hot liquid bath or hot air. The
temperature control provided by the heat transfer medium prevents
the drug from being exposed to an elevated temperature which is
above the thermal limit of the drug, while allowing the balloon to
be quickly heated to a sufficiently high temperature to soften the
balloon material during stent mounting.
[0010] In still another aspect of the invention, in which the heat
transfer medium is a hot liquid bath, the mold is configured to
seal the bore of the mold with the catheter therein, so that the
mold is submerged without liquid or humidity from the liquid bath
contacting the drug delivery stent in the mold. As a result, the
drug delivery layer is not dissolved or otherwise damaged by
exposure when the mold is submerged in the liquid bath.
[0011] The metallic material of the mold allows the mold to be
machined with tight dimensional tolerances, to provide an accurate
and uniform bore diameter. Additionally, the metallic material of
the mold provides sufficient strength, even at elevated
temperature, so that the mold radially restrains the stent during
the stent mounting procedure without the diameter of the mold bore
increasing. Thus, unlike a radial restraining member which expands
somewhat during pressurization of the balloon therein, the mold of
the invention controls the outer diameter of the mounted stent, so
that the profile of the mounted stent is not disadvantageously
increased during the stent mounting. The profile of the mounted
stent can impact the ability of the stent delivery balloon catheter
to advance and cross tight lesions in the patient's
vasculature.
[0012] The mold is a split-mold having hinged halves. The mold
halves swing open and close at the hinge so that the balloon with
the stent thereon can be introduced or removed from the mold
without damaging the drug delivery layer of the stent. The mold
therefore prevents or inhibits the damage to the drug delivery
layer which can otherwise occur with tubular radial restraining
members which don't open up for introduction of the balloon
catheter and which must be cut off the balloon catheter after the
stent mounting. Additionally, the mold of the invention is
reusable, and provides for accurate, uniform heating which does not
vary with each subsequent use.
[0013] In another aspect of the invention, the mold body defining
the entire length of the bore and outer surface of the mold is
formed of metal. As a result, the metal mold substantially
uniformly heats the entire length of the balloon within the bore of
the mold. However, in yet another aspect of the invention, the mold
has a body with a heat conducting metallic section and an
insulating non-metal section, so that heating the mold selectively
heats sections of the balloon within the bore of the mold. The
insulating section of the mold insulates the drug-delivery stent
during the stent mounting procedure, so that the drug delivery
stent is heated to a lower temperature than the inflatable sections
of the balloon at either end of the stent. As a result, the balloon
is sufficiently heated for the stent mounting procedure without
exposing the drug-delivery stent to a disadvantageously high
temperature (e.g., a temperature above the thermal limit of the
drug).
[0014] A stent delivery balloon catheter of the invention generally
comprises an elongated shaft having an inflation lumen and a
guidewire lumen, a balloon on a distal shaft section having an
interior in fluid communication with the inflation lumen, and a
stent releasably mounted on the balloon for delivery and deployment
within a patient's body lumen. The stent typically comprises an
open-walled body of stent struts with gaps between adjacent struts.
The balloon typically has a folded noninflated configuration with
wings wrapped around the circumference of the balloon. In
alternative embodiments, the balloon is a wingless balloon which
expands by stretching from a wingless noninflated
configuration.
[0015] Yet another aspect of the invention is directed to a mold
having a stepped inner diameter comprising enlarged inner diameter
sections on either end of a middle section. During stent mounting,
the stepped inner diameter forms one or more external shoulders in
the balloon. The balloon shoulders are located adjacent the end(s)
of the stent, to prevent or inhibit the stent from moving
longitudinally relative the balloon during delivery and deployment
of the stent. The balloon external shoulders have an outer diameter
larger than the outer diameter of the unexpanded stent, and thus
provide a barrier that the stent would have to overcome in order to
move longitudinally relative to the balloon. The external shoulders
are thus molded into the balloon material during stent mounting and
are not the result of material added to the shaft or balloon. As a
result, the shoulders are formed without affecting the stiffness
transitions of the catheter.
[0016] Another aspect of the invention is directed to a method of
mounting a stent on a stent delivery balloon catheter using the
mold having a stepped inner diameter. The method generally
comprises introducing inflation media into the interior of the
balloon, and heating the balloon, to radially expand the balloon
with the stent restrained from radially expanding by a mold around
an outer surface of the stent, so that the balloon expands into the
stent gaps to embed the stent in an outer surface of the balloon,
to thereby mount the stent on the balloon, wherein the mold has a
stepped inner diameter so that expanding the balloon forms at least
one shoulder in the balloon adjacent an end of the stent with an
outer diameter greater than an outer diameter of the mounted stent
in an unexpanded configuration.
[0017] In one aspect, the invention provides a method of mounting a
drug delivery stent on a catheter balloon which provides a low
profile mounted stent, and which securely and consistently mounts
the stent on the balloon for delivery and deployment within a
patient's body lumen without damaging the drug delivery layer of
the stent. The metallic mold, heated primarily by conduction during
stent mounting, allows temperature control to the mold sufficient
to prevent heat damage of the drug delivery layer. The mold is
heated with a method configured to avoid the nonuniformity and
irreproducibility of convective heat transfer. Additionally, the
mold is configured to prevent or reduce roughening or otherwise
mechanically damaging the drug delivery layer, so that the drug
delivery layer release rate and drug amount are not
disadvantageously effected by the stent mounting procedure of the
invention. In still another aspect of the invention, the mold has
heat conducting portions and insulating portions, and heating the
mold selectively heats sections of the balloon and stent within the
bore of the mold. In yet another aspect of the invention directed
to a mold with a stepped inner diameter, the mold produces one or
more shoulders in the balloon which enhance stent retention on the
balloon.
[0018] In yet one further aspect of the present invention, the
method may further including re-crimping the catheter assembly
after removal from the split mold. Recrimping may be done by hand,
hand tool, or using a crimping tool or machine. In one aspect of
the invention, the re-crimping is performed using an MSI crimper
available from Machine Solutions Incorporated, Flagstaff Ariz. In
yet another aspect of the invention, the re-crimping may be
performed using a stent press machine available from Advanced
Cardiovascular Systems, Inc., Santa Clara, Calif.
[0019] In still another aspect of the invention, during the
re-crimping process, the balloons may be pressurized and heated to
increase the protrusion of balloon material into the openings in
the stent pattern, thereby further increasing stent retention on
the balloons. In one aspect of the invention, the balloon may be
pressurized in the range of 10 to 300 pounds per square inch (psi)
(7 to 207 newtons per square centimeter). In one aspect of the
invention, the balloon and the mounted stent are heated to the
range of about 100 degrees to 250 degrees Fahrenheit (38 to 121
degrees Celsius) during re-crimping. In yet another aspect of the
invention, the mounted stent is heated to about 130 degrees
Fahrenheit (54 degrees Celsius) during re-crimping. In another
aspect of the invention, the balloon may be pressurized to about 70
psi (48 newtons per sq. centimeter). In yet a further aspect of the
invention, the balloon may be pressurized to more or less
pressure.
[0020] Re-crimping may increase the retention of the stent to the
balloon, particularly if the catheter assembly is to be gas
sterilized with ethylene oxide (EtO). In one aspect of the
invention, the method includes a first stage of crimping the stent
on the balloon catheter assembly before sterilization. The crimping
before sterilization may be performed using any presently available
crimping machine or crimping assembly. A crimping assembly may also
be referred to sometimes as a crimping press. In yet a further
aspect of the invention, after the first stage of crimping, the
balloon is pressurized and heated within the mold to further mount
the stent on the balloon. In still another aspect of the invention,
a second crimping of the stent on the balloon catheter assembly is
performed after removal from the mold, hereinafter also referred to
as re-crimping.
[0021] In one aspect of the present invention, the method includes
re-crimping the catheter assembly after removal from a split mold
process. During the split mold process, pressure is applied to the
balloon, and heat is applied to the balloon-stent assembly. It is
after the split mold process that the balloon is likely to pull
away from the stent, especially after EtO sterilization.
Re-crimping is advantageous in securing the stent onto the balloon
after the split mold process and when sterilization is accomplished
by EtO sterilization. Re-crimping may also be advantageous in
securing the stent onto the balloon after the split mold process
when other sterilization methods are used.
[0022] In accordance with certain aspects of the present invention
there may be provided a stent crimping assembly as disclosed in
U.S. Pat. No. 6,840,081 filed Nov. 18, 2002 and entitled "ASSEMBLY
FOR CRIMPING AN INTRALUMINAL DEVICE OR MEASURING THE RADIAL
STRENGTH OF THE INTRALUMINAL DEVICE AND METHOD OF USE" which issued
Jan. 11, 2005, the entire contents of which are incorporated herein
by reference.
[0023] In further accordance with the present invention, there may
be provided a stent crimping assembly as disclosed in U.S. Ser. No.
10/330,016 filed Dec. 26, 2002 and entitled "ASSEMBLY FOR CRIMPING
AN INTRALUMINAL DEVICE AND METHOD OF USE" the entire contents of
which are incorporated herein by reference.
[0024] One aspect of the present invention is a method of mounting
a stent on a balloon catheter, including positioning the stent on a
balloon of the balloon catheter and applying a first radially
compressive force on an outer surface of the stent, thereby
decreasing the outer diameter of the stent on the balloon catheter.
The method also includes pressurizing and heating the balloon while
restricting radial expansion of the outer surface of the stent. Yet
a further aspect of the invention includes applying a second
radially compressive force on the outer surface of the stent.
[0025] At least one aspect of the invention is a method of mounting
a stent on a balloon catheter. The method includes positioning a
stent on a balloon catheter, the balloon catheter having an
elongated shaft with an inflation lumen and a guidewire lumen and
an inflatable balloon on a distal shaft section with an interior in
fluid communication with the inflation lumen. The stent has an
open-walled body of stent struts with gaps between adjacent stent
struts. The method further includes applying a first radially
compressive force on an outer surface of the stent and thereby
decreasing the outer diameter of the stent on the balloon catheter.
In yet another aspect, the invention includes heating the balloon
and introducing inflation media into the interior of the balloon to
radially expand the balloon with the stent restrained from radially
expanding, so that the balloon expands into the stent gaps to embed
the stent in an outer surface of the balloon, and thereby mount the
stent on the balloon. In at least one aspect of the invention, the
stent is restrained from radially expanding by a mold. In yet one
other aspect of the invention, the method includes removing the
inflation media from the balloon interior and applying a second
radially compressive force on an outer surface of the stent. In at
least another aspect of the invention, one factor in increased
retention of the stent on the balloon is that the second radially
compressive force decreases the outer diameter of the stent on the
balloon catheter.
[0026] Still another aspect of the invention is a method of
increasing retention of an intravascular device on a balloon
catheter, including a first stage of crimping the intravascular
device onto a balloon of the balloon catheter, a second stage of
heating and pressurizing the balloon, and a third stage of
re-crimping the intravascular device onto the balloon of the
balloon catheter.
[0027] Other features and advantages of the invention will become
more apparent from the following detailed description of preferred
embodiments of the invention, when taken in conjunction with the
accompanying exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is an isometric view of a mold useful in a method
which embodies features of the invention, in which a drug delivery
stent is mounted onto a balloon catheter.
[0029] FIG. 2 is an isometric view of the mold of FIG. 1 in a
closed configuration, illustrating a distal section of a balloon
catheter within the mold.
[0030] FIG. 3 is a longitudinal cross sectional view illustrating
the mold of FIG. 2 with heating platens on an outer surface of the
mold during a method of mounting a drug delivery stent on the
balloon of the balloon catheter.
[0031] FIG. 4 is a diagrammatic transverse cross section of the
assembly of FIG. 3, taken along line 4-4.
[0032] FIG. 5 is a perspective view of the mold of FIG. 3 in an
open configuration allowing for removal from the mold of the stent
delivery balloon catheter having the drug delivery stent mounted on
the balloon.
[0033] FIG. 6 is an elevational view of the stent delivery balloon
catheter of FIG. 5 after being removed from the mold.
[0034] FIG. 7 is a transverse cross sectional view of the stent
delivery balloon catheter of FIG. 6, taken along line 7-7.
[0035] FIG. 8 illustrates a stent delivery balloon catheter
embodying features of the invention, in which the balloon forms
shoulders adjacent the ends of the stent.
[0036] FIG. 9 illustrates a mold useful in a method of mounting a
stent on a balloon catheter, having a stepped inner diameter, to
form the shoulders in the balloon.
[0037] FIG. 10 illustrates a longitudinal cross sectional view of
an alternative embodiment of a stepped inner diameter mold useful
in a method of mounting a stent on a balloon catheter, in which end
portions of the middle section of the mold have a smaller inner
diameter than the portion of middle section therebetween.
[0038] FIG. 11 is an isometric view of an alternative mold useful
in a method embodying features of the invention, having an
insulating non-metal body portion and a metal body portion.
[0039] FIG. 12 illustrates a longitudinal cross sectional view of
the mold bottom half of FIG. 11, taken along line 12-12.
[0040] FIG. 13 is an isometric view of an alternative partially
insulating mold useful in a method embodying features of the
invention, having a metallic body with insulating non-metal
inserts.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] FIG. 1 illustrates a metal mold 10 useful in a method of
mounting a drug delivery stent on a balloon catheter, embodying
features of the invention. Mold 10 generally comprises a split
metal body 11 with a bottom half, a top half, and a polished bore
12 configured to receive a balloon catheter therein. In the
embodiment illustrated in FIG. 1, the top and bottom halves of the
mold are joined by a hinge, and the mold is illustrated in an open
configuration. FIG. 2 illustrates the mold in a closed
configuration with a distal section of a balloon catheter 20 in
position within the mold.
[0042] FIG. 3 illustrates the mold 10 with the distal section of
the balloon catheter 20 therein, partially in longitudinal cross
section, during a method of mounting a drug delivery stent on the
balloon catheter 20. The balloon catheter 20 has an elongated shaft
21 with a balloon 22 on a distal section thereof and a drug
delivery stent 23 on the balloon. The balloon 22, with the drug
delivery stent 23 thereon, are completely contained within the
polished bore 12 of the mold 10. FIG. 4 illustrates a diagrammatic
transverse cross sectional view of FIG. 3, taken along line
4-4.
[0043] A method of releasably mounting the drug delivery stent 23
on the balloon 22 generally comprises positioning the drug delivery
stent 23 on the uninflated balloon 22 of the balloon catheter 20.
The stent is typically mechanically crimped (i.e., radially
collapsed) down onto the balloon 22. A distal end section of the
catheter 20 is placed within the mold, to position the balloon with
the crimped stent 23 thereon within the polished bore 12 of the
mold 10. The hinged halves of the mold are closed together, and the
balloon 22 is pressurized by introducing inflation fluid into the
interior of the balloon 22 and heated to an elevated temperature.
In a presently preferred embodiment, the balloon is pressurized and
then heated in the pressurized condition. In an alternative
embodiment, the balloon is simultaneously pressurized and heated.
The balloon material at the elevated temperature and pressure is
forced into the gaps in the wall of the stent 23, to embed the
stent within the outer surface of the balloon. FIG. 3 illustrates
the balloon in the pressurized and heated state, with the stent
contacting the polished inner surface of the bore of the mold to
radially restrain the stent from radially expanding. In one
embodiment, the balloon is pressurized to a relatively high
pressure of about 15 to about 23 atm, more specifically about 19 to
about 21 atm. The balloon is then cooled in the mold prior to
depressurization of the balloon, and the cooled balloon
depressurized, and the balloon catheter removed from the mold with
the stent mounted on the balloon. FIG. 5 illustrates the mold 10 in
an open configuration facilitating removal of the balloon catheter
20 therefrom after the stent 23 is mounted onto the balloon 22.
[0044] The mold bore 12 is defined by a polished inner surface of
the top and bottom halves of the mold. In a presently preferred
embodiment, the polished inner surface has a polish finish of about
0.4 microns or less. The bore is polished by techniques known in
the art, such as honing The polished inner surface contacts the
stent, and provides a smooth surface which prevents or inhibits
roughening the surface of the drug delivery stent 23 during the
stent mounting procedure.
[0045] In the embodiment illustrated in FIGS. 1-5, the diameter of
the bore 12 is the same along the entire length of the mold 10. The
bore 12 is preferably formed by machining so that the diameter of
the bore is highly accurate and uniform (i.e., the diameter varies
by no more than .+-.0.025 mm along the length of the mold, and
multiple molds can be made having the same dimensions). The bore 12
is preferably machined within the block which forms the body of the
mold 10, with the two halves of the mold 10 in place together
during the machining. As a result, the top and bottom sections of
the bore 12 perfectly and repeatably mate together when the two
halves of the mold 10 are closed together. In a presently preferred
embodiment, the diameter of the mold bore 12 is slightly larger
than the outer diameter of the crimped stent 23 on the balloon 22.
As a result, the diameter of the mold bore 12 is large enough to
avoid scuffing/damaging the drug delivery layer of the stent 23
when the balloon 22 and stent 23 crimped thereon are placed within
the bore 12. In an alternative embodiment, the diameter of the mold
bore 12 is equal to the diameter of the crimped stent 23 on the
balloon 22, so that the stent does not radially expand during the
stent mounting. Each half of the mold 10 preferably has relatively
thin walls, e.g., with a wall thickness of not greater than about
0.25 to about 0.5 mm, at its thinnest along a midline of the bore
12 of the mold (i.e., the wall thickness from the outer surface of
the mold half to the bore), to provide fast heating and cooling
within the bore 12 of the mold 10.
[0046] In accordance with the invention, the balloon 22 is heated
by heating the mold 10 with a heat transfer medium which provides
very accurate temperature control to the mold 10. In the embodiment
illustrated in FIG. 3, the heat transfer medium is a conductive
heating element member in the form of metal platens 30. The metal
platens 30 have a heating element (not shown) such as a resistive
heater which heats the metal of the platens, and an inner surface
typically configured to correspond to the outer surface of the mold
10. In the illustrated embodiment, the inner surface of the platens
30 and the outer surface of the mold 10 are flat, although, in
alternative embodiments (not shown), the surfaces have irregular
mating surfaces designed to increase the surface area thereof The
temperature at the surface of the platens 30 is very accurately
controllable, so that, with the surface of the metal platens 30
pressed against the outer surface of the mold 10, the temperature
of the mold can be very accurately controlled (i.e., with a
tolerance which is not larger than about .+-.2 degrees F., more
preferably with a tolerance of about .+-.1 degree F.).
[0047] With the balloon catheter 20 in position within the bore 12
of the mold 10, the mold 10 is slid into the space between the
metal platens 30, and the metal platens 30 brought into contact
with the outer surface of the top and bottom halves of the mold, to
thereby heat the mold 10. The mold 10 is heated to an elevated
temperature sufficient to soften the balloon 22 but lower than the
thermal limit of the drug of the drug delivery stent 23. In a
presently preferred embodiment, the temperature within the mold 10
is below a temperature which would cause the drug delivery layer of
the stent 23 to flow. However, in an alternative embodiment in
which the drug delivery layer of stent 23 is heated and flows
somewhat at the elevated temperature, the smooth inner surface of
the polished bore 12 causes the drug delivery layer to remain
uniform in thickness without a roughened or irregular exterior. In
one embodiment, the mold 10 is heated to a temperature of about
160.degree. F. to about 190.degree. F., with the balloon catheter
20 therein during the stent mounting procedure, to soften a balloon
formed of polymeric material.
[0048] The metal platens 30 have a relatively high thermal
conductivity, higher than that of air at least in the temperature
range of interest, providing a relatively fast rate of heating. In
one embodiment, the mold 10 is in contact with the heating platens
30 for not greater than about 120 seconds, and more specifically
for about 60 to about 120 seconds during the stent mounting
procedure. In contrast, hot air would take significantly longer,
and for example not less than about 120 seconds (e.g., on the order
of about 120 to about 240 seconds), to heat the mold to the desired
temperature. The platens 30 and mold 10 are configured to provide a
fast heating rate in combination with fine control of the elevated
temperature, for improved mounting of the drug delivery stent 23
without damage to the drug delivery layer.
[0049] The platens 30 have a length which, in one embodiment, is at
least as long as the stent 23, and the platens are brought into
contact with a length of the mold 10 corresponding to the location
of the drug delivery stent 23 therein. In the embodiment
illustrated in FIG. 3, the platens are longer than the stent but
shorter than the balloon, although a variety of suitable
configurations can be used including platens having a length which
is shorter than the stent, or platens having a length equal to the
length of the mold 10. In a presently preferred embodiment, the
platens have a length which is at least as long as, or
substantially equal to, the length of the inflatable section of the
balloon (i.e., the working length and tapered sections). Although
discussed primarily in terms of the embodiment in which the mold is
heated with platens 30, alternative heating mediums that heat
primarily by conduction can be used including a hot liquid bath. In
the embodiment using a hot liquid bath (not shown), the mold 10 has
seals (not shown) at either end of the mold which seal around the
balloon catheter 20 to prevent the liquid or humidity of the hot
liquid bath from contacting the drug delivery stent 23 within the
mold 10 when the mold is submerged within the bath.
[0050] FIG. 6 illustrates the stent delivery balloon catheter 20
embodying features of the invention, after removal from the mold 10
with the drug delivery stent 23 mounted on the balloon 22. In the
illustrated embodiment, the catheter shaft 21 comprises an outer
tubular member 24 defining an inflation lumen 25 therein, and an
inner tubular member 26 defining a guidewire lumen 27 therein
configured to slidingly receive a guidewire 28. Specifically, in
the illustrated embodiment, the coaxial relationship between outer
tubular member 24 and inner tubular member 26 defines annular
inflation lumen 25. In the embodiment illustrated in FIG. 6, the
guidewire lumen 27 extends to the proximal end of the catheter.
Inflatable balloon 22 has a proximal skirt section sealingly
secured to the distal end of outer tubular member 24 and a distal
skirt section sealingly secured to the distal end of inner tubular
member 26, so that the balloon interior is in fluid communication
with inflation lumen 25. An adapter 29 at the proximal end of
catheter shaft 21 is configured to provide access to guidewire
lumen 27, and to direct inflation fluid through the arm into
inflation lumen 25. As best shown in FIG. 7 illustrating a
transverse cross section of the balloon catheter of FIG. 6, taken
along line 7-7, the stent gaps are partially filled by the balloon
material so that the balloon material contacts and partially
encapsulates the side surfaces of the stent struts, to securely
mount the stent on the balloon. In an alternative embodiment (not
shown), the balloon material completely fills the stent gaps to
fully encapsulate the side surfaces of the stent struts. In the
embodiment illustrated in FIGS. 6 and 7 the portions of the balloon
which protrude between the stent struts have an outer surface flush
with the outer surface of the stent.
[0051] FIG. 6 illustrates the balloon 22, in a folded configuration
with wings wrapped around the circumference of the balloon prior to
complete inflation of the balloon. The balloon 22 typically has two
or more, and most preferably three wings in the noninflated
configuration, which unwrap during inflation of the balloon 22. For
ease of illustration, a substantial gap is illustrated between the
inner surface of the inflatable balloon interior and the shaft
inner tubular member 26 in FIGS. 6 and 7, although it should be
understood that the noninflated balloon is typically collapsed down
around to inner tubular member in the noninflated configuration.
The balloon expands to a generally cylindrical inflated
configuration with a central working length inflated section, a
proximal inflated conical tapered section proximal to the stent
(and distal to the proximal skirt section), and a distal inflated
conical tapered section distal to the stent (and proximal to the
distal skirt section). FIG. 6 illustrates the stent 23 mounted on
the central, working length section of the balloon 22, prior to
complete expansion. The distal end of catheter 20 may be advanced
to a desired region of the patient's body lumen in a conventional
manner with the balloon in the noninflated configuration, and the
balloon 22 inflated by directing inflation fluid into the balloon
interior to expand the stent 23. The balloon is then deflated,
leaving the drug delivery stent 23 implanted in the body lumen.
[0052] The stent 23 generally comprises an open-walled tubular body
of interconnected, spaced-apart stent struts 31 with gaps 32
between adjacent stent struts. In the illustrated embodiment, the
stent struts 31 form rings which have a serpentine wave pattern of
opposed turns and which are longitudinally spaced apart and
connected by links 33. However, the stent 23 can have a variety of
suitable configurations as are conventionally known. The tubular
body of the stent 23 is typically a biostable material such as a
metal, although it can alternatively be formed of a bioabsorable
material. In a presently preferred embodiment, the drug delivery
layer is a coating (not shown) applied to the surface of the
tubular body of the stent 23.
[0053] Although the embodiment illustrated in FIG. 6 is directed to
embedding the drug delivery stent 23 in the outer surface of the
layer of a single-layered balloon, it should be understood that the
balloon can alternatively be formed of multiple layers or with an
outer sleeve member, so that embedding the stent into the balloon
embeds the stent in the outer surface of the outer most layer or
outer sleeve of the balloon.
[0054] FIG. 8 illustrates an alternative embodiment of a stent
delivery balloon catheter 40 embodying features of the invention,
having an elongated shaft 41 and a balloon 42 on a distal shaft
section with a proximal external shoulder 44 adjacent a proximal
end of the stent 43 with an outer diameter larger than the outer
diameter of the nonexpanded stent mounted on the balloon, and a
distal external shoulder 45 adjacent a distal end of the stent 43
with an outer diameter larger than the outer diameter of the
nonexpanded stent mounted on the balloon. Alternatively, the
balloon can have only one of the proximal 44 or distal 45 external
shoulders. For example, in one embodiment (not shown), the balloon
has the distal external shoulder 45, and not the proximal external
shoulder 44. The external shoulders 44, 45 are located along the
proximal and distal inflatable sections of the balloon (e.g., along
the sections of the balloon which inflate to form the proximal and
distal conical tapered sections in the inflated configuration, at
the junction between the inflatable conical tapered section of the
balloon and the end of the working length section). The stent 43 is
similar to drug delivery stent 23 discussed above in relation to
the embodiment of FIG. 1.
[0055] In the illustrated embodiment, the balloon 42 comprises an
inner layer 46 and an outer sleeve member 47 which defines the
outer surface of the external shoulders 44, 45. The outer sleeve 47
is typically formed of a relatively low melting point elastomeric
polymer. In the embodiment illustrated in FIG. 8, molding the
external shoulders 44, 45 in the outer sleeve 47 of the balloon
also forms shoulders in the balloon inner layer 46.
[0056] The balloon 42 is illustrated in a partially inflated
configuration in FIG. 8 for ease of illustration, but it should be
understood that the working length of the balloon is typically
collapsed down to the shaft inner tubular member in the noninflated
configuration for advancement within the patient's body lumen. In
one embodiment, the balloon inflates to a cylindrical, fully
inflated configuration (i.e., with no shoulders 44, 45 in the outer
surface of the expanded balloon). The shoulders 44, 45 thus
substantially disappear as the balloon expands, with the working
length of the balloon expanding to define the maximum inflated
diameter of the balloon, and the conical sections on either end of
the working length section tapering away from the working length
section to a smaller outer diameter in the inflated
configuration.
[0057] In a method of mounting the stent 43 on the balloon catheter
40 to form the stent delivery system of FIG. 8, the radial
restraining mold 50 has a stepped inner diameter which forms the
external shoulders 44, 45 in the balloon during the stent gripping.
FIG. 9 illustrates balloon catheter 40 within a radial restraining
mold 50 having an inner chamber 51 configured for receiving the
balloon portion of the balloon catheter 40. The radial restraining
mold 50, similar to the embodiment of FIG. 1, typically has a
bottom half attached by hinges to a top half, which facilitates
positioning the balloon portion of the catheter in the inner
chamber 51 of the mold. The inner chamber 51 has enlarged inner
diameter sections 52 and 53 on either end of a middle section 54.
The balloon is illustrated with the outer sleeve 47 and stent 43
thereon, during pressurization of the balloon to mount the stent on
the balloon. As set forth above, the mold 50 radially restrains the
stent 43 as inflation media is introduced into the interior of the
balloon and the mold is heated to heat the balloon, so that the
balloon expands into the stent gaps and the external shoulders 44,
45 are formed in the balloon by the enlarged inner diameter
sections 52, 53 of the mold 50. In the embodiment illustrated in
FIG. 8, the inner surface of the balloon also has a stepped
configuration at the shoulders. As a result, a gap exists between
the inner surface of the balloon at the shoulders 44, 45 and the
outer surface of the shaft (or the outer surface of a radiopaque
marker (not shown) on the shaft if the radiopaque marker is located
beyond the end of the stent) in the noninflated configuration.
Although the embodiment illustrated in FIGS. 8 and 9 has the outer
sleeve 47 on the balloon inner layer 46, it should be understood
that in an alternative embodiment (not shown) the outer sleeve 47
is omitted. The method fully or partially embeds the stent 43 in
the balloon 42 depending on the balloon material and stent mounting
method conditions.
[0058] FIG. 10 illustrates a longitudinal cross sectional view of
an alternative radial restraining mold 60 with a stepped inner
diameter, in which end portions 65, 66 of the middle section 64 of
the mold have a smaller inner diameter than the portion of middle
section 64 therebetween. The reduced inner diameter end portions
65, 66, cause the ends of the stent 30 to further embed down into
the balloon during the stent mounting. Embedding the ends of the
stent to a greater degree than a central section of the stent
improves stent retention and advanceability of the system.
[0059] In a presently preferred embodiment, the mold 10/50/60 is
formed of metal, so that the metallic body of the mold defines the
entire length of the bore that receives the balloon, and defines an
outer surface of the mold. The metallic body substantially
uniformly heats the entire length of the balloon within the mold.
In an alternative embodiment, the mold selectively heats sections
of the balloon within the bore of the mold (i.e., the mold has
sections which differentially conduct heat). For example, FIG. 11
illustrates an isometric view of an alternative radial restraining
mold 70, having a body 71 formed of an insulating material such as
a plastic with metal portions 72, which allows for selective
heating of the balloon portion of a catheter. The metal portions 72
are heat conducting, and the insulating (e.g., plastic) body 71 is
not heat conducting, or at least is substantially less heat
conducting than the metal portions. For example, when a metal
portion was heated to 163.degree. F. (73.degree. C.), the maximum
temperature measured in the adjacent insulating plastic portion was
109.degree. F. (43.degree. C.). As a result, the balloon portion
proximal and distal to the stent can be placed at the metal
portions 72, with the balloon central working length section
(having the stent thereon) located between the metal portions 72,
so that the plastic of the mold body insulates the working length
section of the balloon portion from the elevated temperatures used
during the stent mounting.
[0060] Insulating at least the central working length section of
the balloon portion from heat protects the drug delivery coating of
the stent from damage during the stent mounting procedure.
Depending on the length of the metal portions 72, the plastic body
71 typically also insulates the balloon skirt sections (secured to
the shaft) from heat of the heat transfer medium during the stent
mounting procedure.
[0061] In a presently preferred embodiment, the insulating material
forming the mold body 71 is a plastic such as polyetheretherketone
(PEEK), or a machinable polyimide such as Vespel, although
non-plastic insulating materials can alternatively be used such as
ceramics including Macor (a machinable glass ceramic).
[0062] FIG. 12 illustrates a longitudinal cross sectional view of
the bottom half of the mold 70 of FIG. 11, taken along line 12-12.
In a presently preferred embodiment, the metal portions 72 have,
along at least a section thereof, a larger wall thickness (from the
inner to the outer surface) than the adjacent sections of the
plastic body 71 so that the metal portions 72 have at least a
section which protrudes from the outer surface of the plastic body
71. The heating platens (discussed above in relation to the
embodiment of FIG. 3) will therefore contact the protruding outer
surface of the metal portions 72 without contacting the plastic
body 71 during the stent mounting procedure. The air gap between
the heating platens and the plastic body 71 sections will further
reduce heat transfer to the drug delivery layer of a stent within
the mold 70. In the illustrated embodiment, the plastic body 71,
which together with the metal portions 72 defines the length of the
bore receiving the balloon, is within an outer housing, typically
formed of a metal, which surrounds the outer surfaces of the
plastic body. The illustrated metal portions 72 have a section with
a sufficiently large wall thickness such that the metal portions 72
protrude from the outer surface of the outer housing.
[0063] FIG. 13 illustrates an isometric view of an alternative
embodiment of a selective heating mold 80 which embodies features
of the invention, having a metallic body 81 with insulating plastic
inserts 82. In the illustrated embodiment, three plastic inserts 82
are present, positioned at sections of the mold configured to
receive the central working length section of balloon, and the
skirt sections of the balloon secured to the shaft. The sections of
the metallic body 81 of the mold located between the adjacent
plastic inserts 82 are configured to receive the inflatable conical
sections of the balloon (i.e., the balloon sections which extend
between the central working length and the skirt sections of the
balloon). The plastic inserts 82 preferably have a wall thickness
which is less than the wall thickness of the metallic body 81. As a
result, the metallic body 81 preferably defines the outer surface
of the mold along the entire length thereof, and the metallic body
81 together with the plastic inserts 82 define sections of the bore
of the mold. Alternatively, the wall thickness of the plastic
inserts is equal to the wall thickness of the metallic body, so
that the metallic body together with the plastic inserts define
sections of the outer surface of the mold 80.
[0064] The dimensions of the stent delivery balloon catheter 20, 40
are determined largely by the size of the balloon and guidewire to
be employed, the catheter type, and the size of the artery or other
body lumen through which the catheter must pass or the size of the
stent being delivered. Typically, the outer tubular member 24 has
an outer diameter of about 0.025 to about 0.04 inch (0.064 to 0.10
cm), usually about 0.037 inch (0.094 cm), and the wall thickness of
the outer tubular member 24 can vary from about 0.002 to about
0.008 inch (0.0051 to 0.02 cm), typically about 0.003 to 0.005 inch
(0.0076 to 0.013 cm). The inner tubular member 26 typically has an
inner diameter of about 0.01 to about 0.018 inch (0.025 to 0.046
cm), usually about 0.016 inch (0.04 cm), and a wall thickness of
about 0.004 to about 0.008 inch (0.01 to 0.02 cm). The overall
length of the catheter 20, 40 may range from about 100 to about 150
cm, and is typically about 143 cm. Preferably, balloon 22, 42 has a
length of about 0.8 cm to about 6 cm, and an inflated working
diameter of about 2 mm to about 10 mm.
[0065] Inner tubular member 26 and outer tubular member 24 can be
formed by conventional techniques, for example by extruding and
necking materials already found useful in intravascular catheters
such a polyethylene, polyvinyl chloride, polyesters, polyamides,
polyimides, polyurethanes, and composite materials. The various
components may be joined using conventional bonding methods such as
by fusion bonding or use of adhesives. Although the shaft is
illustrated as having an inner and outer tubular member, a variety
of suitable shaft configurations may be used including a dual lumen
extruded shaft having a side-by-side lumens extruded therein.
Similarly, although the embodiment illustrated in FIG. 6 is an
over-the-wire type balloon catheter, the catheter of this invention
may comprise a variety of intravascular catheters, such as rapid
exchange type balloon catheters. Rapid exchange catheters generally
comprise a shaft having a relatively short guidewire lumen
extending from a guidewire distal port at the catheter distal end
to a guidewire proximal port spaced a relatively short distance
from the distal end of the catheter and a relatively large distance
from the proximal end of the catheter.
[0066] The terms crimping and compressing as used herein are meant
to be interchangeable and mean that the diameter of the stent is
reduced to some degree. Typically, balloon-expandable stents 23 are
known by persons having ordinary skill in the art to be "crimped"
onto the balloon 22 portion of a catheter 20 while self-expanding
stents are compressed onto a mandrel or sheath and then inserted
into a catheter. The term re-crimping as used herein refers to a
second radially compressive force on an outer surface of the stent
following a first radially compressive force on an outer surface of
the stent. The re-crimping may use the same crimping apparatus
and/or method as the first crimping, or a different crimping
apparatus and/or method. Both crimping and re-crimping include
applying a radially compressive force on an outer surface of the
stent and thereby decreasing the outer diameter of the stent on the
balloon catheter. Re-crimping as used herein also refers to
applying a radially compressive force on an outer surface of the
stent after removal from the mold 10. The term pre-mounting as used
herein refers to the stent being placed onto the catheter assembly
and compressed before the stent mounted catheter is inserted into
the crimping assembly for the first crimping process. In one
embodiment, pre-mounting the stent onto the balloon of the catheter
assembly includes compressing the stent onto the catheter with
finger pressure before the stent mounted catheter is inserted into
the crimping assembly.
[0067] Further, while reference is made herein to crimping or
compressing "stents," the invention can be used with any
intraluminal device to reduce the diameter or measure radial
strength. Thus, the invention is particularly useful with stents,
grafts, tubular prostheses, embolic devices, embolic filters, and
embolic retrieval devices.
[0068] The crimping processes referred to herein may be performed
using the crimping assembly or apparatus referred to above or any
other acceptable stent crimping assembly, apparatus, or method
known in the art. A crimping assembly or apparatus may also be
referred to sometimes as a crimping press. In one embodiment of the
invention, a stent crimping assembly is used to crimp an expandable
stent 23 onto the balloon 22 portion of a balloon catheter 20,
however, the invention can be used with self-expanding stents as
well. Examples of stent assemblies that may be used to crimp an
expandable stent onto a balloon catheter include a stent crimping
assembly as disclosed in U.S. Pat. No. 6,840,081 filed Nov. 18,
2002 and entitled "ASSEMBLY FOR CRIMPING AN INTRALUMINAL DEVICE OR
MEASURING THE RADIAL STRENGTH OF THE INTRALUMINAL DEVICE AND METHOD
OF USE" which issued Jan. 11, 2005, the entire contents of which
are incorporated herein by reference and/or a stent crimping
assembly as disclosed in U.S. Ser. No. 10/330,016 filed Dec. 26,
2002 and entitled "ASSEMBLY FOR CRIMPING AN INTRALUMINAL DEVICE AND
METHOD OF USE" the entire contents of which are incorporated herein
by reference.
[0069] In at least one embodiment, the invention includes a method
of mounting a stent 23 on a balloon catheter 20. The stent is
positioned on the balloon catheter by hand or apparatus. In at
least one embodiment, the stent is pre-mounted onto the balloon 22
of the balloon catheter by a slight compressive pressure, for
example, hand pressure. After positioning of the stent on the
balloon, a first radially compressive force is applied on an outer
surface of the stent, thereby decreasing the outer diameter of the
stent on the balloon catheter. After applying of the first radially
compressive force, the balloon is pressurized and heated while
restricting radial expansion of the outer surface of the stent. In
one embodiment, the pressurizing and heating of the balloon is done
in a mold, for example, a split mold, configured to restrict the
radial expansion of the outer surface of the stent. During the
pressurizing and heating, outpouchings of the balloon may extend
between undulations of the stent, further securing the stent on the
balloon. However, the balloon may pull away from the stent somewhat
as the balloon cools. The pulling away of the balloon from the
stent may be exaggerated during EtO sterilization. Therefore, at
least one embodiment includes applying a second radially
compressive force on the outer surface of the stent. The second
radially compressive force may decrease the outer diameter of the
stent on the balloon catheter, wherein the stent is more securely
mounted on the balloon. The first and/or second radially
compressive forces may be applied by hand, by hand tool, or by
machine, for example, a crimping maching In at least one further
embodiment, the assembly including the stent and balloon catheter
may then be sterilized, for example, by EtO sterilization.
[0070] In at least one embodiment, the invention includes a method
of increasing stent 23 retention on a balloon catheter 20. In one
embodiment, the method includes a first stage of crimping the stent
onto the balloon catheter before placing the balloon catheter with
the stent mounted thereon in the mold 10, and a second stage of
crimping of the stent onto the balloon catheter after the split
mold process, described elsewhere herein, and before sterilization
of the stent and balloon catheter assembly.
[0071] In a further embodiment, the invention is a method of
increasing retention of an intravascular device on a balloon
catheter, including a first stage of crimping the intravascular
device onto a balloon of the balloon catheter, a second stage of
heating and pressurizing the balloon, and a third stage of
re-crimping the intravascular device onto the balloon of the
balloon catheter.
[0072] In another embodiment, after the first stage of crimping,
the stent 23 crimped on the balloon 22 is submitted to the split
mold process described in greater detail above. After the first
stage of crimping and the split mold process, the undulating rings
of the stent indent into the balloon 22 resulting in out pouching
or pillowing of the balloon into the openings between the
undulations of the stent. In yet another embodiment, heating of the
balloon and introducing inflation media into the interior of the
balloon radially expands the balloon. The stent is restrained from
radially expanding, for example, by the mold around an outer
surface of the stent. As the balloon radially expands under heat,
the balloon expands into the stent gaps to embed the stent in an
outer surface of the balloon, thereby mounting the stent on the
balloon.
[0073] However, a loss of stent retention may occur if
sterilization of the balloon catheter 20 with the stent mounted
thereon is performed directly after the split mold process. The
loss of stent retention typically occurs with EtO (ethylene oxide)
sterilization. One factor in the loss of stent retention may be
that the balloon shrinks and pulls away from the stent during the
sterilization process. Yet another factor in the loss of stent
retention may be that the balloon shrinks and pulls away from the
stent as it cools after the split mold process.
[0074] In one embodiment of the invention, the method may include
applying at least one radially compressive force on the outer
surface of the stent 23 that has been mounted on the balloon
catheter 20 after removal from the mold 10. The mold may be a split
mold. In one embodiment, the stent is pre-mounted on the balloon
and positioned in the mold. After removal from the mold, a radially
compressive force is applied on the outer surface of the stent
before sterilization of the stent-balloon catheter assembly.
[0075] During the split mold process, pressure is applied to the
balloon 22, and heat is applied to the balloon-stent assembly. It
is after the split mold process that the balloon may pull away from
the stent 23. Re-crimping is advantageous in securing the stent
onto the balloon after removal from the mold 10. The advantage of
re-crimping the stent onto the balloon catheter 20 is that the
re-crimping may increase the retention of the stent to the balloon,
particularly if the catheter assembly is to be gas sterilized with
ethylene oxide (EtO). In at least one embodiment, the re-crimping
is performed after the split mold process without another stage of
crimping having been performed before the split mold process.
[0076] Re-crimping may be done by hand, using a crimping tool, a
crimping machine, a crimping press, and/or a crimping assembly. In
one preferred embodiment, the re-crimping is performed using an MSI
crimper available from Machine Solutions Incorporated, Flagstaff
Ariz. In one embodiment, the re-crimping may be performed using a
stent press machine available from Advanced Cardiovascular Systems,
Inc., Santa Clara, Calif.
[0077] In one embodiment, during the crimping and/or re-crimping
process the balloon 22 may be pressurized and heated to increase
the protrusion of balloon material into the openings in the stent
23 pattern, thereby further increasing stent retention on the
balloon. In yet another embodiment of the invention, the balloon
may be pressurized in the range of 10 to 300 pounds per square inch
(psi) (7 to 207 newtons per square centimeter).
[0078] In at least one embodiment of the invention, the balloon 22
having the stent 23 mounted thereon is heated to the range of about
70 degrees to 250 degrees Fahrenheit (21 to 121 degrees Celsius)
during re-crimping. In one embodiment the mounted stent is heated
to about 130 degrees Fahrenheit (54 degrees Celsius) during
re-crimping. In one embodiment, the balloon may be pressurized to
about 70 psi (48 newtons per sq. centimeter). In other embodiments,
the balloon may be pressurized to more or less pressure. In one
embodiment, processing time during the re-crimping is in the range
of one second to five minutes. In at least one embodiment, the
processing time is approximately 10 seconds.
[0079] While the present invention is described herein in terms of
certain preferred embodiments, those skilled in the art will
recognize that various modifications and improvements may be made
to the invention without departing from the scope thereof. For
example, while discussed primarily in terms of a stent or a drug
delivery stent, aspects of the invention may be useful with an
alternative prosthesis or stent (e.g., a bare metal stent).
Moreover, although individual features of one embodiment of the
invention may be discussed herein or shown in the drawings of the
one embodiment and not in other embodiments, it should be apparent
that individual features of one embodiment may be combined with one
or more features of another embodiment or features from a plurality
of embodiments.
* * * * *