U.S. patent application number 12/483953 was filed with the patent office on 2009-10-15 for method of stent mounting to form a balloon catheter having improved retention of a drug delivery stent.
This patent application is currently assigned to ADVANCED CARDIOVASCULAR SYSTEMS, INC.. Invention is credited to Christopher C. Andrews, Daniel G. Brown, Darrin J. Kent, Shahin Sarkissian, Jeremy L. Stigall, Plaridel Kimpo Villareal, Kenneth l. Wantink, Bruce Wilson.
Application Number | 20090259289 12/483953 |
Document ID | / |
Family ID | 36951014 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090259289 |
Kind Code |
A1 |
Wilson; Bruce ; et
al. |
October 15, 2009 |
METHOD OF STENT MOUNTING TO FORM A BALLOON CATHETER HAVING IMPROVED
RETENTION OF A DRUG DELIVERY STENT
Abstract
A method of mounting a drug delivery stent on a balloon of a
balloon catheter. The method securely mounts the drug delivery
stent on the balloon without damaging the drug delivery layer of
the stent. In one embodiment, the method generally comprises
positioning a drug delivery 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,
to mount the stent on the balloon without damaging the drug
delivery layer of the stent.
Inventors: |
Wilson; Bruce; (Temecula,
CA) ; Andrews; Christopher C.; (Lake Elsinore,
CA) ; Wantink; Kenneth l.; (Temecula, CA) ;
Brown; Daniel G.; (Temecula, CA) ; Kent; Darrin
J.; (Murrieta, CA) ; Stigall; Jeremy L.;
(Murrieta, CA) ; Villareal; Plaridel Kimpo; (San
Jose, CA) ; Sarkissian; Shahin; (San Jose,
CA) |
Correspondence
Address: |
FULWIDER PATTON, LLP (ABBOTT)
6060 CENTER DRIVE, 10TH FLOOR
LOS ANGELES
CA
90045
US
|
Assignee: |
ADVANCED CARDIOVASCULAR SYSTEMS,
INC.
Santa Clara
CA
|
Family ID: |
36951014 |
Appl. No.: |
12/483953 |
Filed: |
June 12, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11105085 |
Apr 12, 2005 |
7563400 |
|
|
12483953 |
|
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Current U.S.
Class: |
623/1.11 ;
425/500; 623/1.42 |
Current CPC
Class: |
A61F 2/9522 20200501;
A61F 2/958 20130101; B29C 2049/2017 20130101; B29C 49/20 20130101;
B29C 49/24 20130101; B29C 33/3828 20130101; B29K 2105/258 20130101;
B29C 2049/0089 20130101; B29L 2031/7542 20130101; A61F 2250/0067
20130101; B29C 33/3807 20130101; B29C 2049/2412 20130101 |
Class at
Publication: |
623/1.11 ;
623/1.42; 425/500 |
International
Class: |
A61F 2/84 20060101
A61F002/84; B28B 23/08 20060101 B28B023/08 |
Claims
1-18. (canceled)
19. An assembly for mounting a drug-delivery stent on a balloon of
a balloon catheter, comprising: a) a mold having a body formed at
least in part of a metallic material and defining a polished bore
configured to receive a balloon of a balloon catheter having a
drug-delivery stent on the balloon; and b) a heat transfer medium
which is configured to contact the mold and thereby heat the mold
and the balloon within the mold, and which provides temperature
control to the mold with a tolerance of about .+-.1 degree to about
.+-.2 degrees F.
20. The assembly of claim 19 wherein the heat transfer medium has a
relatively high thermal conductivity higher than that of air, and
is a metal platen with a surface configured to press against an
outer surface of the mold to thereby heat the mold.
21. The assembly of claim 19 wherein the heat transfer medium has a
relatively high thermal conductivity higher than that of air, and
is a hot liquid bath, and the mold includes sealing members which
seal around the balloon catheter within the mold to thereby prevent
the liquid bath from contacting the balloon within the mold.
22. The assembly of claim 19 wherein the bore is defined by a
polished inner surface having a polish finish equal to or smaller
than about 0.4 microns.
23. The assembly of claim 19 wherein the mold is split-mold with
hinged halves.
24. The assembly of claim 19 wherein the mold bore has a stepped
inner diameter comprising enlarged inner diameter sections on
either end of a middle section, configured to form shoulders in the
balloon adjacent ends of the stent with an outer diameter greater
than an outer diameter of the unexpanded stent mounted on the
balloon.
25. The assembly of claim 19 wherein the mold has a metallic body
defining the bore and an outer surface of the mold, so that heating
the mold substantially uniformly heats the entire length of the
balloon within the bore of the mold.
26. The assembly of claim 19 wherein the mold has a body with a
heat conducting metallic section, and an insulating non-metal
section defining a region of the bore configured to receive the
drug delivery stent, so that heating the mold selectively heats
sections of the balloon within the bore of the mold.
27. A balloon catheter having a drug delivery stent releasably
mounted thereon, comprising: a) an elongated shaft having a
proximal end, a distal end, and an inflation lumen; b) a balloon
sealingly secured to a distal shaft section with an interior in
fluid communication with the inflation lumen, which inflates from a
noninflated configuration to an inflated configuration; and c) a
drug-delivery stent having a drug delivery layer and an open-walled
body of stent struts with gaps between adjacent stent struts,
mounted on the noninflated balloon so that the stent is embedded in
an outer surface of the noninflated balloon with the drug delivery
layer having a uniform thickness and defining an outer surface of
the embedded stent.
28. The stent delivery balloon catheter of claim 27 wherein the
balloon has a shoulder adjacent an end of the mounted stent with an
outer diameter greater than an outer diameter of the mounted stent
in an unexpanded configuration.
29-30. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to catheters, and
particularly intravascular stent delivery catheters.
[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 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.
[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. 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.
[0004] 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 a stent having a drug delivery layer. The
mounting process used to secure the drug delivery stent to the
balloon must not damage the drug or the matrix material containing
the drug. It would be a significant advance to provide a catheter
balloon having improved retention of a drug delivery stent, and
without inhibiting balloon or stent function. The present invention
satisfies these and other needs
SUMMARY OF THE INVENTION
[0005] The invention is directed to a method of mounting a drug
delivery stent on a balloon, and a stent delivery balloon catheter
produced therefrom. The method securely mounts the drug delivery
stent on the balloon without damaging the drug delivery layer of
the stent.
[0006] In one embodiment, the method generally comprises
positioning a drug delivery stent on a balloon of a balloon
catheter, the stent having a drug delivery layer, 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 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
one embodiment, 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.
[0007] In a presently preferred embodiment, 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, bioabsorption 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 presently preferred embodiment, the drug is intended
to prevent or inhibit restenosis.
[0008] 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 one embodiment, 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.
[0009] In the embodiment 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.
[0010] 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.
[0011] 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.
[0012] In a presently preferred embodiment, 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 alternative embodiments, 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).
[0013] 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.
[0014] One embodiment 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.
[0015] 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.
[0016] 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 an embodiment of the
invention in which the mold has heat conducting portions and
insulating portions, heating the mold selectively heats sections of
the balloon and stent within the bore of the mold. In another
embodiment 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. These and other
advantages of the invention will become more apparent from the
following detailed description and exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] 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.
[0018] 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.
[0019] 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.
[0020] FIG. 4 is a diagrammatic transverse cross section of the
assembly of FIG. 3, taken along line 4-4.
[0021] 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.
[0022] FIG. 6 is an elevational view of the stent delivery balloon
catheter of FIG. 5 after being removed from the mold.
[0023] FIG. 7 is a transverse cross sectional view of the stent
delivery balloon catheter of FIG. 6, taken along line 7-7.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] FIG. 12 illustrates a longitudinal cross sectional view of
the mold bottom half of FIG. 11, taken along line 12-12.
[0029] 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
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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, while being sufficiently small so that expansion of
the crimped stent 23 during the stent mounting is minimized. 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.
[0035] 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.).
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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).
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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 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.
* * * * *