U.S. patent application number 13/963333 was filed with the patent office on 2013-12-05 for stent delivery catheter with improved stent retention and method of making same.
This patent application is currently assigned to Advanced Cardiovascular Systems, Inc.. The applicant listed for this patent is Advanced Cardiovascular Systems, Inc.. Invention is credited to Tim A. Limon, Stephen D. Pacetti, Wouter Roorda.
Application Number | 20130325100 13/963333 |
Document ID | / |
Family ID | 48952111 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130325100 |
Kind Code |
A1 |
Roorda; Wouter ; et
al. |
December 5, 2013 |
STENT DELIVERY CATHETER WITH IMPROVED STENT RETENTION AND METHOD OF
MAKING SAME
Abstract
A stent delivery catheter system having a catheter with stent
releasably mounted on a stent retention portion of the catheter for
delivery and deployment within a patient's body lumen, and a method
of mounting the stent on the stent retention portion of the
catheter. The method generally includes exposing the stent
retention portion and/or the stent to a solvent, the solvent being
in the vapor phase. The vapor phase solvent typically softens the
stent retention portion of the catheter, and/or, in one embodiment
in which the stent has a coating on the stent body, the vapor phase
solvent softens the stent coating. In a presently preferred
embodiment, the stent polymeric coating has a therapeutic agent,
and the method of the invention prevents or inhibits
disadvantageously affecting the therapeutic agent coating during
mounting of the stent on the catheter.
Inventors: |
Roorda; Wouter; (Palo Alto,
CA) ; Limon; Tim A.; (Cupertino, CA) ;
Pacetti; Stephen D.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Cardiovascular Systems, Inc. |
Santa Clara |
CA |
US |
|
|
Assignee: |
Advanced Cardiovascular Systems,
Inc.
Santa Clara
CA
|
Family ID: |
48952111 |
Appl. No.: |
13/963333 |
Filed: |
August 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10877873 |
Jun 24, 2004 |
8512388 |
|
|
13963333 |
|
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Current U.S.
Class: |
623/1.11 |
Current CPC
Class: |
A61F 2/9522 20200501;
A61L 2300/00 20130101; A61F 2002/9583 20130101; A61F 2/915
20130101; A61L 31/16 20130101; A61L 31/10 20130101; A61F 2/958
20130101; A61F 2002/91558 20130101; A61F 2230/0054 20130101 |
Class at
Publication: |
623/1.11 |
International
Class: |
A61F 2/958 20060101
A61F002/958 |
Claims
1-25. (canceled)
26. A stent delivery balloon catheter system, comprising: a balloon
catheter having an elongated shaft with an inflation lumen and a
balloon sealingly secured to the shaft with an interior in fluid
communication with the inflation lumen, the balloon having a
noninflated condition which inflates to an inflated condition; and
a stent releasably mounted on the noninflated balloon for delivery
and deployment within a patient's body lumen, the stent comprising
a body and a polymeric coating on the body, and the noninflated
balloon having an outer surface releasably adhered directly to an
inner surface of the stent.
27. The stent delivery catheter system of claim 26 wherein the
stent polymeric coating has a therapeutic agent, and the
therapeutic agent polymeric coating defines the inner surface of
the stent releasably adhered to the outer surface of the
balloon.
28. The stent delivery catheter system of claim 27 wherein the
therapeutic agent polymeric coating of the stent releasably adhered
to the balloon has a therapeutic agent release rate which is the
same or substantially the same as a therapeutic agent release rate
of the coated stent prior to mounting and adhering to the
balloon.
29. The stent delivery catheter system of claim 27 wherein the
therapeutic agent polymeric coating of the stent releasably adhered
to the balloon has a therapeutic agent concentration which is the
same or substantially the same as a therapeutic agent concentration
of the coated stent prior to mounting and adhering to the
balloon.
30. The stent delivery catheter system of claim 27 wherein the
therapeutic agent polymeric coating of the stent releasably adhered
to the balloon has a therapeutic agent distribution which is the
same or substantially the same as a therapeutic agent distribution
of the coated stent prior to mounting on the balloon.
31. The stent delivery catheter system of claim 26 wherein the
balloon in the inflated condition is not adhered to the stent, the
inflated condition being at a pressure within a working pressure
range of the balloon.
32. The stent delivery catheter system of claim 26 wherein the
stent mounted on the noninflated balloon comprises interconnected
spaced-apart struts, and portions of the noninflated balloon
protrude in the spaces between adjacent struts of the mounted
stent.
33. The stent delivery catheter system of claim 26 wherein the
stent mounted on the noninflated balloon comprises interconnected
spaced-apart struts, and spaces between adjacent struts are free or
substantially free of the noninflated balloon.
Description
BACKGROUND OF THE INVENTION
[0001] This invention generally relates to catheters, and
particularly intravascular catheters for use in percutaneous
transluminal coronary angioplasty (PTCA) or for the delivery of
stents.
[0002] 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 over expand the artery wall. After
the balloon is finally deflated, blood resumes through the dilated
artery and the dilatation catheter and the guidewire can be removed
therefrom.
[0003] 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.
[0004] One difficulty has been securely mounting the stent on the
balloon catheter such that the stent remains in place on the
balloon (generally referred to as "stent retention") during
positioning within a patient's body lumen, without inhibiting
release of the stent at the desired location in the body lumen.
Additionally, mounting the stent on the balloon is more difficult
if the stent or balloon has a coating, such as a drug delivery
coating, which must be protected from damage during the mounting
processes. Accordingly, it would be a significant advance to
provide a stent delivery system with improved stent retention,
without disadvantageously effecting stent release or a coating on
the stent.
INVENTION SUMMARY
[0005] The invention is directed to a stent delivery catheter
system having a catheter with a stent releasably mounted on a stent
retention portion of the catheter for delivery and deployment
within a patient's body lumen, and a method of mounting the stent
on the stent retention portion of the catheter. The method
generally includes exposing the stent retention portion and/or the
stent to a solvent, the solvent being in the vapor phase. The vapor
phase solvent typically softens the stent retention portion of the
catheter, and/or, in one embodiment in which the stent has a
coating on the stent body, the vapor phase solvent softens the
stent coating. Softening the stent retention portion and/or stent
coating facilitates releasably mounting the stent on the stent
retention portion. Preferably, the softening effect of the vapor
allows the balloon to be deformed during mounting of the stent on
the balloon under conditions of lower pressure and/or temperature
compared to the process without the solvent vapor. The method of
the invention provides a stent delivery catheter with improved
stent retention during advancement of the stent in the patient's
body lumen, preferably without inhibiting stent release after
expansion of the stent in the patient's body lumen. In a presently
preferred embodiment, the stent polymeric coating has a therapeutic
agent, and the method of the invention prevents or inhibits
disadvantageously affecting the therapeutic agent coating during
mounting of the stent on the catheter.
[0006] In one embodiment, the stent is a balloon expandable stent
mounted on the balloon (i.e., stent retention portion) of a balloon
catheter. In an alternative embodiment, the stent is a
self-expanding stent mounted on a self-expanding stent delivery
catheter. Although discussed below primarily in terms of the
embodiment in which the catheter system is a balloon expandable
stent mounted on a balloon catheter, it should be understood that
the catheter system can be a self expanding stent system. Details
regarding self-expanding stent delivery systems can be found in
U.S. Pat. Nos. 6,676,693 and 6,576,006, incorporated herein by
reference in their entirety.
[0007] The stent delivery balloon catheter of the invention
typically comprises an elongated shaft having a proximal end, a
distal end, an inflation lumen, and a guidewire lumen configured to
slidably receive a guidewire therein. A balloon is secured to the
shaft so that an inflatable interior of the balloon is in fluid
communication with the inflation lumen.
[0008] Mounting the stent on the balloon typically comprises
positioning the stent on the balloon, and forcing the balloon and
stent together. Forcing the balloon and stent together can be
achieved using a variety of suitable methods and should be
understood to include methods in which only one of the balloon or
stent are forced toward the other component. For example, mounting
the stent on the balloon typically involves crimping the stent to a
radially collapsed diameter on the balloon. One or more additional
steps may be used to mount the stent on the balloon, typically
involving pressurizing the balloon. For example, in one embodiment,
mounting the stent on the balloon includes pressurizing the balloon
with the stent radially constrained by a mold or sheath
therearound, which forces the balloon into the spaces between
adjacent struts of the stent. Similarly, there are optional steps,
such as one in which the balloon is pressurized and is radially
constrained by a sheath, and heat is applied to all or part of the
balloon during mounting of the stent on the balloon. The softening
effect of the solvent vapor may be used in any one or more of the
steps used to mount the stent on the balloon. Thus, in one
embodiment in which the stent is mounted on the balloon by being
positioned on the balloon, then crimped on the balloon, and then
pressurized to force the balloon into spaces in the stent wall, the
balloon and/or stent may be exposed to the solvent vapor before,
during, or after any one or more of the mounting steps. In one
embodiment, the stent is positioned on the balloon, and the balloon
and stent thereon are exposed to the solvent vapor prior to the
stent being fully crimped onto the balloon, which preferably
facilitates softening the entire surface of the balloon and/or
stent coating. However, in an alternative embodiment, the balloon
and/or stent are exposed to the solvent vapor during or after the
stent is fully crimped onto the balloon. In one presently preferred
embodiment, after the stent is crimped on the balloon, the balloon
and stent are exposed to the solvent vapor during pressurization of
the balloon to force the balloon into the spaces between adjacent
stent struts.
[0009] Use of the softening effect of the solvent vapor in
accordance with the invention preferably results in an interference
fit and/or adhesion between the balloon and mounted stent. For
example, in one embodiment, forcing the balloon and stent together
during mounting of the stent causes portions of the softened
balloon to protrude a sufficient amount into the spaces between
adjacent struts of the stent to inhibit longitudinal movement of
the stent mounted on the balloon. However, in an alternative
embodiment, the balloon does not protrude in the mounted stent
spaces, so that the stent spaces are free or substantially free of
the balloon. Although discussed below primarily in terms of a
system having a coated stent, it should be understood that in one
embodiment the stent is not coated (e.g., a bare metal stent), and
stent retention is enhanced primarily due to the portions of the
balloon which are caused to protrude into the stent spaces
according to a method of the invention.
[0010] The solvent vapor softens the polymeric material of the
balloon and/or stent coating typically by being a temporary
plasticizer of the polymer, or by temporarily swelling the polymer,
depending on the nature of the solvent and the polymer. A variety
of suitable solvents can be used including an organic solvent
(e.g., an alcohol, acetone) or an inorganic solvent (e.g., water).
For example, in one embodiment, the balloon comprises a polyamide
such as nylon or a copolyamide such as PEBAX (polyether block
amide) and the solvent is selected from the group consisting of
water vapor, hydroxylated organic solvents (e.g., alcohols such as
isopropyl alcohol), and dipolar aprotic solvents (e.g., DMSO, DMF,
DMAC). In another embodiment, the balloon comprises a polyurethane
and the solvent is selected from the group consisting of the
hydroxylated organic solvents, the dipolar aprotic solvents, and
polar organic solvents (e.g., ketones, ethers, esters, and
chlorinated solvents). In another embodiment, the balloon comprises
an acrylate or methacrylate and the solvent is selected from the
group consisting of the dipolar aprotic solvents and the polar
organic solvents. In another embodiment, the balloon comprises
latex and the solvent is the dipolar aprotic solvent. In another
embodiment, the balloon comprises polyethylene terephthalate (PET)
and the solvent is selected from the group consisting of the
hydroxylated organic solvents and the dipolar aprotic solvents. In
another embodiment, the balloon comprises polyethylene and the
solvent is selected from the group consisting of the polar organic
solvents, and non-polar solvents (e.g., hydrocarbons,
fluorocarbons, and aromatics). In another embodiment, the balloon
comprises a fluoropolymer such as expanded polytetrafluoroethylene
(ePTFE) and the solvent is the non-polar solvent.
[0011] In a presently preferred embodiment, the solvent is a liquid
phase solvent at room temperature and pressure, although in
alternative embodiments, the solvent is a solid or gas phase
solvent at room temperature and pressure. In one embodiment, the
method includes generating the solvent vapor, to provide a
sufficiently high concentration of solvent vapor at the surface of
the balloon and/or stent to soften the balloon and/or a coating on
the stent.
[0012] In a presently preferred embodiment, the stent comprise a
body and a polymeric coating on the body. The stent body is
typically metallic although it can alternatively be non-metallic
(e.g., a plastic or a bioabsorbable compound). Details regarding
stents can be found for example in, U.S. Pat. No. 5,507,768 (Lau,
et al.), incorporated herein by reference in its entirety. A
variety of suitable coatings can be used on the stent including
therapeutic, diagnostic, or lubricious coatings.
[0013] In one embodiment, the stent polymeric coating has a
therapeutic agent, such as an antirestenosis agent or an
antithrombosis agent. The solvent vapor softens the stent polymeric
coating and/or the balloon without disadvantageously affecting the
therapeutic agent polymeric coating. For example, the softening
effect of the solvent vapor avoids the need for exposing the
therapeutic agent coating to relatively high temperatures and
pressures to soften and force the balloon and stent together during
mounting of the stent on the balloon. In conventional methods of
mounting a stent on a catheter balloon, the stent is mounted on the
balloon with the balloon at elevated temperature and/or pressure.
However, because the balloon and/or stent coating are softened by
the solvent vapor in the method of the invention, the method
securely mounts the stent onto the balloon while avoiding the use
of high temperatures and pressures during stent mounting. Thus, in
a method of the invention, the stent is mounted onto the balloon
with the balloon and stent at room temperature, or at an elevated
temperature lower than the elevated temperatures normally used
during conventional stent mounting methods. In one embodiment in
which the stent is coated with an anti-restenosis drug, the stent
coating is at room temperature, or at an elevated temperature of
less than about 70.degree. C. to about 80.degree. C., as the stent
is mounted on the balloon. Similarly, in one embodiment, lower
pressures are used to pressurize the balloon and radially collapse
the stent onto the balloon during stent mounting in a method of the
invention. Moreover, if no higher temperature or pressure can be
used during stent mounting, better stent retention can be obtained
at a given temperature and pressure with the solvent vapor than
without the solvent vapor (including the temperatures and pressures
normally used in conventional stent mounting methods) due to the
softening provided by the solvent vapor.
[0014] Unlike a liquid solvent, the solvent vapor avoids the
potential leaching of the therapeutic agent from the polymeric
coating. Consequently, the therapeutic agent polymeric coating of
the stent has a therapeutic agent concentration which is the same
or substantially the same as (i.e., not more than about 0 to about
10% less than) a therapeutic agent concentration of the coated
stent prior to mounting on the stent receiving portion. Similarly,
in one embodiment, exposing the coating to the vapor phase solvent
does not cause the therapeutic agent to migrate in the coating, so
that the therapeutic agent polymeric coating of the stent mounted
on the balloon has a therapeutic agent distribution which is the
same or substantially the same as a therapeutic agent distribution
of the coated stent prior to mounting on the balloon. Moreover, the
solvent vapor preferably does not change the therapeutic agent or
polymer morphology (e.g., crystalline structure) of the therapeutic
agent polymeric coating, and thus avoids affecting the therapeutic
agent release rate from the polymeric coating, so that the
therapeutic agent polymeric coating of the stent has a therapeutic
agent release rate which is the same or substantially the same as
(i.e., not more than about 0 to about 25% different than) a
therapeutic agent release rate of the coated stent prior to
mounting on the stent receiving portion. Moreover, unlike a liquid
solvent which may over-wet the balloon and/or stent, the solvent
vapor facilitates exposing the balloon and/or stent to small
amounts of solvent over a short duration, which prevents or
inhibits the solvent vapor from weakening bonded regions of the
stent delivery catheter (e.g., the bonds between the balloon and
the catheter shaft). Additionally, the solvent vapor easily
evaporates from the balloon and/or stent, so that residual solvent
does not remain behind. Thus, the method of the invention
preferably avoid the potential of a liquid solvent to pool within
folds and spaces of the stent delivery system. These and other
advantages of the invention will become more apparent from the
following detailed description and exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an elevational view, partially in section, of a
stent delivery balloon catheter which embodies features of the
invention having a stent mounted on the balloon.
[0016] FIG. 2 illustrates a method of mounting the stent on the
balloon, with the distal end of the catheter inside a chamber for
exposing the balloon and stent thereon to a solvent vapor.
[0017] FIG. 3 illustrates the distal end of the catheter after the
stent is fully crimped onto the balloon.
[0018] FIG. 3A is a transverse cross sectional view of the catheter
shown in FIG. 3, taken along line 3A-3A.
[0019] FIG. 4 illustrates an enlarged view of the balloon and stent
of FIG. 3A within circle 4.
[0020] FIG. 5 illustrates an alternative embodiment of the catheter
of FIG. 3A, having portions of the balloon wall protruding into
spaces between adjacent struts of the stent.
[0021] FIG. 6 illustrates the balloon catheter of FIG. 1, with the
balloon inflated in a patient's body lumen to implant the stent
therein.
[0022] FIG. 7 illustrates a self-expanding stent delivery system
embodying features of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] FIG. 1 illustrates a stent delivery balloon catheter 10
embodying features of the invention, generally comprising a shaft
11 with an inflation lumen 12, and a guidewire lumen 13 configured
to slidingly receive a guidewire 15, and a balloon 14 on a distal
shaft section. An adapter 16 at the proximal end of catheter shaft
11 is configured to direct inflation fluid into inflation lumen 12
to thereby inflate the balloon 14, and provide access to guidewire
lumen 13. FIG. 1 illustrates the balloon 14 in a low profile
configuration prior to inflation, with a radially expandable stent
30 mounted on the balloon, for introduction and advancement within
the patient's body lumen. In use, the distal end of catheter 10 is
advanced to a desired region of the patient's body lumen in a
conventional manner either over previously positioned guidewire 15,
or with guidewire 15 already in the catheter 10. The balloon 14 is
inflated to expand stent 30, and the balloon deflated for removal
of the catheter 10 from the body lumen, leaving the stent 30
implanted in the body lumen.
[0024] In the embodiment of FIG. 1, the shaft 11 comprises an outer
tubular member 17 defining the inflation lumen 12, and an inner
tubular member 18 defining the guidewire lumen 13 extending from a
guidewire distal port in a distal end portion of the catheter shaft
to a guidewire proximal port at the proximal end of the inner
tubular member 18. Inflatable balloon 14 has a proximal skirt
section 19 sealingly secured to the distal end of outer tubular
member 17, a distal skirt section 20 sealingly secured to the inner
tubular member 18, and an inflatable cylindrical working length
section therebetween, so that its interior is in fluid
communication with inflation lumen 12.
[0025] The stent 30 is mounted onto the balloon according to a
method which embodies features of the invention in which the
balloon and/or a coating on the body of the stent are softened by
being exposed to a solvent vapor. The balloon 14 and/or stent 30
may be exposed to the solvent vapor during, before, or after any of
the steps used to mount the stent onto the balloon. In a presently
preferred embodiment, the balloon and/or stent coating are in the
softened condition during pressurization of the balloon to force
the balloon into spaces in the wall of the stent. Specifically,
during mounting of the stent on the balloon, the subassembly of the
stent on the balloon typically has a restraining member such as a
mold or sheath therearound, and the balloon is pressurized which
forces the balloon and stent together. The balloon is pressurized
by directing an inflation medium into the interior of the balloon,
and the pressure within the balloon typically reaches pressures
within or above the working pressure range of the balloon, such as
about 14 atm, due to the restraining member therearound.
[0026] The balloon and/or stent coating may additionally or
alternatively be in the softened condition during crimping of the
stent on the balloon. FIG. 2 illustrates the distal end of the
balloon catheter 10 with the stent 30 positioned on the balloon 14,
within a chamber 40 for exposure to solvent vapor in the chamber
40. The stent 30 is typically radially collapsed to a pre-crimped
intermediate diameter to position it securely on the balloon 14. In
one embodiment, following exposure to the solvent vapor, the
pre-crimped stent is then further radially collapsed to a crimped
diameter. A variety of suitable devices can be used as the chamber
40, including the crimping equipment used to crimp the stent 30 on
the balloon 14, or other pieces of equipment normally used during
catheter assembly. Alternatively, the chamber 40 can be a separate
container not normally used during catheter assembly. Thus, in one
embodiment, after exposure to the solvent vapor in the chamber 40,
the catheter 10 and stent 30 positioned thereon are moved from the
chamber 40 to the crimping equipment to fully crimp the stent 30
onto the balloon 14.
[0027] Generally, a sufficient amount of solvent vapor to soften
the balloon and/or stent coating is typically at least about 1% of
atmospheric pressure, corresponding to a solvent vapor pressure of
at least about 7.6 Torr. In one embodiment, the liquid solvent, has
a sufficiently high vapor pressure at ambient temperature and
pressure to provide a sufficient amount of solvent vapor to soften
the balloon and/or stent coating. For example, fluorocarbons and
low-boiling polar organic solvents typically provide sufficient
solvent vapor without being heated. However, higher boiling
solvents would required heating to generate sufficient vapor. Thus,
in one embodiment, the method of the invention involves heating a
liquid or solid solvent to provide a sufficient amount of solvent
vapor to soften the balloon, or at least to increase the solvent
vapor pressure. For example, in one embodiment in which the solvent
is water, the solvent is vaporized, so that the solvent vapor is
steam. In one embodiment in which the chamber 40 is also the
crimping equipment used to crimp the stent onto the balloon, a
reservoir of the solvent is provided in the chamber 40, and the
solvent in the reservoir is heated to an elevated temperature at
which sufficient vapor is generated locally within the chamber 40.
Another suitable method that is less dependent on temperature would
be to pass an inert gas, such as nitrogen or argon, through a
reservoir of the solvent, and then pass this saturated vapor stream
past the balloon and/or stent coating.
[0028] Following exposure to the solvent vapor, the solvent is
allowed to evaporate from the exposed balloon and stent thereon.
The balloon with the stent thereon can be dried to quicken
evaporation of the solvent. However, depending on the conditions of
operation and the solvent used, the solvent may flash off quickly
from the exposed balloon and stent without heating or otherwise
drying the balloon and stent.
[0029] FIG. 3 illustrates the distal end of the catheter 10 of FIG.
2 after the stent 30 is mounted onto balloon 14 for delivery and
deployment within a patient's body lumen. FIG. 3A illustrates a
transverse cross sectional view of the stent delivery system of
FIG. 3 taken along line 3A-3A. FIG. 4 illustrates an enlarged view
of the balloon 14 and stent 30 of FIG. 3A taken within circle 4. In
one embodiment, the stent 30 comprises a body 32 and a polymeric
coating 34 on the body. The stent body 32 is typically metallic,
and typically comprises a radially expandable tubular structure of
interconnected spaced-apart struts, as is conventionally known in
the design of stents. In accordance with one embodiment of the
invention, with the stent mounted on the uninflated balloon 14, the
balloon 14 and stent coating 34 are releasably adhered together.
Specifically, at least one of the balloon 14 and stent coating 34
are temporarily softened by the solvent vapor so that they
releasably adhere together when in contact as the solvent
evaporates therefrom. As illustrated in FIG. 4, an inner surface of
the fully crimped stent 30 is in contact with an outer surface of
the balloon 14. The outer surface of the balloon 14 is releasably
adhered directly to the inner surface of the stent 30 (i.e., a
separate adhesive is not provided between the stent and balloon
surface). In one embodiment, in order to prevent or inhibit
damaging the adhesion between the balloon and stent during the
crimping process, the stent is fully crimped onto the balloon in
the temporarily softened condition before the surfaces become
releasably adhered together. In a presently preferred embodiment,
the section of the balloon under the stent mounted thereon does not
have a lubricious coating. Thus, the polymeric material forming the
inflatable wall of the balloon defines the outer surface of the
balloon. However, in an alternative embodiment, the section of the
balloon under the stent does have a lubricious coating, and
exposing the balloon to the vapor phase solvent softens the
material forming the lubricious coating of the balloon and/or the
polymeric material forming the inflatable wall of the balloon.
[0030] In one embodiment, the stent coating has a therapeutic agent
and the therapeutic agent polymeric coating 34 defines the stent
inner surface releasably adhered to the balloon outer surface.
Alternatively, in one embodiment, a release rate limiting top coat
(not shown) is on the outer surface of the therapeutic agent
polymeric coating 34. The therapeutic agent polymeric coating 34
typically has the therapeutic agent dispersed throughout the
coating 34 although it can alternatively be on a surface of the
coating 34 or otherwise limited to a portion of the coating 34. A
variety of suitable polymers can be used for polymeric coating 34,
including acrylates, methacrylates, poly(vinylidene fluoride),
poly(vinylidene fluoride-co-hexafluoropropene), fluorocarbons,
vinyl-based polymers, silicone-urethanes, polyurethanes, ethylene
vinyl acetate, poly(ethylene-co-vinyl alcohol),
styrene-isobutylene-styrene triblock copolymers,
styrene-ethylene/butane-styrene triblock copolymers, silicones,
polymers functionalized with active groups like heparin or with
biomimetic compounds, poly-esters, bioerodible as well as biostable
compounds, and any other polymers, copolymers or polymer
combinations with acceptable vascular biocompatibility. The
polymeric coating 34 can be applied to the stent body by a variety
of suitable means including, dipping, spraying, wiping, and
depositing.
[0031] In the embodiment of FIG. 4, the uninflated balloon wall has
a flat outer surface which does not protrude into the spaces
between adjacent stent body struts 32. In an alternative embodiment
illustrated in FIG. 5, portions of the wall of the uninflated
balloon 14 protrude in the spaces between adjacent struts of the
mounted stent. In the embodiment illustrated in FIG. 5, the
protrusions extend into the spaces such that less than half of the
width of the wall of the stent is occupied by the protrusions.
However, it should be understood that in alternative embodiments
(not shown) the protrusions extend into the spaces in the stent
wall an amount which is greater or lesser than the amount
illustrated in FIG. 5. Temporarily softening the balloon 14 by
exposure to the solvent vapor facilitates forcing portions of the
balloon into the spaces between the stent body struts 32. Thus, the
otherwise smooth surface of the balloon 14 (i.e., it is not
preformed with protrusions prior to the mounting of the stent
thereon), forms protrusions extending in the wall of the mounted
stent which enhance stent retention by providing resistance to
longitudinal displacement of the stent mounted on the balloon.
Additionally, in one embodiment, the balloon protruding into the
stent spaces is releasably adhered to the stent coating 34, as
discussed above in relation to the embodiment of FIG. 4. Although
FIG. 5 illustrates the stent 30 with a coating 34 on the stent body
32, it should be understood that a non-coated stent 30 can
alternatively be used, with the enhanced stent retention being
provided by the interference caused by the balloon wall protruding
into the stent wall.
[0032] FIG. 6 illustrates the balloon catheter 10 of FIG. 1 with
the balloon 14 fully inflated in a patient's body lumen 27. The
balloon 14 is inflated to an inflated condition at a pressure
within a working pressure range of the balloon, typically about 5
to about 20 atm, so that the balloon cylindrical working section
expands the stent 30 to an expanded diameter. In the embodiment in
which the balloon and stent coating are adhered together, the
adhesion between the balloon and stent coating preferably fails as
the balloon inflates to the inflated condition within the working
pressure range, so that the balloon in the inflated condition is
not adhered to the expanded stent. Similarly, in the embodiment in
which the balloon protrudes into the spaces in the stent wall, the
protrusions are typically not a permanent feature of the balloon,
so that the expanded balloon typically does not protrude into the
spaces in the stent wall. Thus, the balloon can be deflated to
retract radially away from the expanded stent, leaving the expanded
stent 30 implanted in the body lumen.
[0033] FIG. 7 illustrates a self-expanding stent delivery system 50
embodying features of the invention. The catheter 50 comprises an
outer tubular member 51 having a lumen 52 therein, and an inner
tubular member 53 having a stent receiving portion 54 with an
unexpanded self-expanding stent 55 mounted thereon. The inner
tubular member 53 and outer tubular member 51 typically extend from
the proximal to the distal end of the catheter, allowing the distal
end of the inner tubular member 53 to be displaced distally out the
distal end of the outer tubular member 51 when the stent receiving
portion 54 is in the desired position within the patient's body
lumen. The stent expands as the outer and inner tubular members 51,
53 are moved relative to one another to advance the inner tubular
member 53 out the distal end of the outer tubular member 51 and
thereby remove a radially restraining force from around the stent
55. The stent receiving portion 54 and/or stent are exposed to
solvent vapor in accordance with the invention during mounting of
the stent 55 on the stent receiving portion 54.
[0034] To the extent not previously discussed herein, the various
catheter 10, 50 components may be formed and joined by conventional
materials and methods. The inner and outer tubular members can be
formed by conventional techniques, such as by extruding and necking
materials found useful in intravascular catheters such as
polyethylene, polyvinyl chloride, polyesters, polyamide,
polyimides, polyurethanes, and composite materials. The balloon can
be formed by a variety of conventional methods including blow
molding or otherwise forming an inflatable tubular member from
conventional balloon materials such as polyamide (nylon), PEBAX,
and polyurethane.
[0035] The length of the balloon catheter 10, 50 is generally about
137 to about 145 centimeters, and typically about 140 centimeters
for PTCA. The outer tubular member has an OD of about 0.017 to
about 0.034 inch (0.43-0.87 mm), and an inner diameter (ID) of
about 0.017 to about 0.026 inch (0.43-0.66 mm). The inner tubular
member has an OD of about 0.015 to about 0.022 inch (0.38-0.56 mm),
and an ID of about 0.012 to about 0.018 inch (0.30-0.46 mm)
depending on the diameter of the guidewire to be used with the
catheter. The balloon 14 is typically about 8 to about 38 mm in
length, with an inflated working diameter of about 1.5 to about 5
mm.
[0036] While the present invention has been described herein in
terms of certain preferred embodiments, those skilled in the art
will recognize that modifications and improvements may be made
without departing from the scope of the invention. For example,
although the catheter illustrated in FIG. 1 is an over-the-wire
type balloon catheter, a variety of suitable catheter designs can
be used including rapid exchange type catheters. Rapid exchange
type catheters generally comprise a distal guidewire port in a
distal end of the catheter, a proximal guidewire port in a distal
shaft section and typically spaced a substantial distance from the
proximal end of the catheter, and a relatively short guidewire
lumen extending between the proximal and distal guidewire ports.
Moreover, while individual features of one embodiment of the
invention may be discussed 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.
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