U.S. patent application number 12/717024 was filed with the patent office on 2010-06-24 for system for coating a tubular implantable medical device.
Invention is credited to Hung Manh Le, Stephen D. Pacetti.
Application Number | 20100154705 12/717024 |
Document ID | / |
Family ID | 34394443 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154705 |
Kind Code |
A1 |
Pacetti; Stephen D. ; et
al. |
June 24, 2010 |
System for Coating a Tubular Implantable Medical Device
Abstract
A system for coating a tubular implantable medical device, such
as a stent, can include a rotatable applicator and a rotatable
support for the medical device. The axes of rotation of applicator
and the support can be substantially non-parallel.
Inventors: |
Pacetti; Stephen D.; (San
Jose, CA) ; Le; Hung Manh; (San Jose, CA) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY LLP
1 MARITIME PLAZA, SUITE 300
SAN FRANCISCO
CA
94111
US
|
Family ID: |
34394443 |
Appl. No.: |
12/717024 |
Filed: |
March 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10680905 |
Oct 7, 2003 |
7704544 |
|
|
12717024 |
|
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Current U.S.
Class: |
118/232 ;
118/200; 118/258 |
Current CPC
Class: |
A61F 2/91 20130101; B05C
1/08 20130101; A61F 2250/0067 20130101; B05D 1/28 20130101; B05C
1/022 20130101; B05C 11/04 20130101; B05D 1/002 20130101; B05C
11/06 20130101 |
Class at
Publication: |
118/232 ;
118/200; 118/258 |
International
Class: |
B05C 1/08 20060101
B05C001/08; B05C 1/00 20060101 B05C001/00 |
Claims
1. A system for coating a tubular implantable medical device with a
coating composition, the system comprising: an applicator substrate
including a surface configured to receive a composition and to
transfer the composition to a tubular implantable medical device;
and a mandrel configured to support the tubular implantable medical
device in close proximity to or in contact with the applicator
substrate.
2. The system of claim 1, wherein the applicator substrate is
configured to rotate about a first rotational axis, and the mandrel
is configured to rotate about a second rotational axis that is not
parallel to the first rotational axis.
3. The system of claim 2, wherein the applicator substrate is
configured to move over the mandrel in a linear direction that is
substantially parallel to the second rotational axis.
4. The system of claim 1, wherein the applicator substrate is
configured to move over the mandrel in a linear direction, and the
mandrel is configured to rotate about a rotational axis that is
substantially parallel to the linear direction.
5. The system of claim 1, further comprising an apparatus to rotate
the mandrel.
6. The system of claim 1, wherein the medical device comprises a
hollow, longitudinal bore and wherein the applicator substrate is
further configured to fit into the hollow, longitudinal bore of the
medical device.
7. The system of claim 1, wherein an outer surface of the mandrel
comprises a non-stick material.
8. The system of claim 1, further comprising a leveling apparatus
configured to be positioned along the surface of the applicator
substrate for reducing variation of composition thickness.
9. A system for coating a tubular implantable medical device with a
coating composition, the system comprising: a reservoir holding a
coating composition; an application roller configured to receive
the coating composition from the reservoir; and a support element
to support a tubular implantable medical device in close proximity
to or in contact with the application roller.
10. The system of claim 9, wherein the application roller is
configured to rotate about a first rotational axis, and the support
element is configured to rotate about a second rotational axis that
is not parallel to the first rotational axis.
11. The system of claim 10, wherein the application roller is
configured to move over the support element in a linear direction
that is substantially parallel to the second rotational axis.
12. The system of claim 9, wherein the application roller is
configured to move over the support element in a linear direction,
and the support element is configured to rotate about a rotational
axis that is substantially parallel to the linear direction.
13. The system of claim 9, further comprising a metering roller in
communication with the application roller.
14. The system of claim 13, further comprising a barrier positioned
adjacent to the metering roller for removing excess composition
from the metering roller.
15. The system of claim 9, wherein an outer surface of the
application roller has grooves.
16. The system of claim 9, wherein the reservoir is housed within
the application roller, and the application roller comprises pores
in an outer surface of the application roller and in communication
with the reservoir such that the coating composition can flow from
the reservoir and out of the pores to be disposed on the outer
surface of the application roller.
17. The system of claim 9, further comprising a leveling member to
provide a uniform thickness of the coating composition on the
surface of the application roller.
18. The system of claim 9, further comprising a temperature
controller in communication with the reservoir for heating or
cooling the coating composition.
19. The system of claim 9, wherein the support element is a
cylindrical body configured to be inserted into a longitudinal bore
of the tubular implantable medical device.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
10/680,905, filed Oct. 7, 2003, which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to a system for coating a tubular
implantable medical device, such as a stent.
BACKGROUND
[0003] Blood vessel occlusions are commonly treated by mechanically
enhancing blood flow in the affected vessels, such as by employing
a tubular implantable medical device known as a stent. Stents act
as scaffoldings, functioning to physically hold open and, if
desired, to expand the wall of the passageway. Stents are capable
of being compressed, so that they can be inserted through small
lumens via catheters, and then expanded to a larger diameter once
they are at the desired location.
[0004] FIG. 1 illustrates a conventional stent 10 formed from a
plurality of structural elements including struts 12 and connecting
elements 14. The plurality of struts 12 are radially expandable and
interconnected by connecting elements 14 that are disposed between
adjacent struts 12, leaving lateral openings or gaps 16 between
adjacent struts 12. Struts 12 and connecting elements 14 define a
tubular stent body having an outer, tissue-contacting surface and
an inner surface.
[0005] Stents are used not only for mechanical intervention but
also as vehicles for providing biological therapy. Biological
therapy can be achieved by medicating the stents. Medicated stents
provide for the local administration of a therapeutic substance at
the diseased site. Local delivery of a therapeutic substance is a
preferred method of treatment because the substance is concentrated
at a specific site and thus smaller total levels of medication can
be administered in comparison to systemic dosages that can produce
adverse or even toxic side effects for the patient.
[0006] One method of medicating a stent involves the use of a
polymeric carrier coated onto the surface of the stent. A
composition including a solvent, a polymer dissolved in the
solvent, and a therapeutic substance dispersed in the blend is
applied to the stent by immersing the stent in the composition or
by spraying the composition onto the stent. The solvent is allowed
to evaporate, leaving on the stent surfaces a coating of the
polymer and the therapeutic substance impregnated in the
polymer.
[0007] As noted above, one of the methods of applying a drug
composition to a stent involves spraying the composition onto the
stent. The composition can be atomized to produce small droplets.
Atomization is used because the droplet size can be made smaller
than the size of the stent's structural elements, thus enabling a
substantially conformal coating. However, there are potential
shortcomings associated with a spray coating process. For instance,
many of the drugs and polymers that are applied to stents are toxic
when inhaled by humans. As the polymeric drug solutions are
atomized, therefore, great care must be taken to avoid occupational
exposure to the personnel conducting the process. Hoods, glove
boxes, enclosures, and shrouds can be used to prevent toxic aerosol
inhalation, but at a cost of decreased efficiency and increased
expenditures on equipment. In light of these safety and
manufacturing concerns, a stent coating method that avoids
atomization of the coating can be advantageous.
[0008] Another disadvantage of a spray coating process is that the
transfer efficiency can be comparatively low. Only droplets which
fall onto the stent's structural elements are incorporated into the
coating. If the spray pattern is larger than the stent, much of the
spray can be wasted. Moreover, the stent's body can have a number
of open spaces or gaps between the structural elements that allow
the spray to pass through, and therefore be unused. The components
of the coating compositions can be very expensive. For instance,
many of the drugs applied to stents are small molecule agents or
biologically derived substances such as peptides and gene therapy
agents that are very costly. A stent coating method which transfers
the coating solution in a more direct manner to the stent structure
would therefore have a manufacturing cost advantage.
[0009] Yet another shortcoming of a spray coating process is that
it can be difficult to direct the coating composition to a selected
stent surface such as only onto the outer surface of the stent. The
outer or tissue-contacting surface of the stent is the surface that
is pressed against the vessel wall. Drug released from the outer
surface of the stent is mostly diffused into the tissue, thereby
maximizing the local delivery of the drug. Drug present on the
inner or lumen contacting surface of the stent, on the other hand,
can diffuse into the blood stream where it is transported by the
blood flow to an area away from the site of stent implantation. For
particular drugs, it may be advantageous to have a stent where the
coating is only present on the outer surface of the stent. For
example, certain drugs can produce adverse or even toxic side
effects for the patient when they are released into the blood
stream and carried into the vascular system. By having a drug
coating limited to the outer surface of the stent, one can minimize
the amount of these types of drugs that are delivered outside of
the treatment area.
[0010] There are other reasons to produce a stent that only has the
drug coating on the outer surface of the stent. In manufacturing
drug eluting stents, one of the goals of the manufacturing process
is to minimize the contribution of the coating to the stent
dimensions (i.e., to minimize the thickness of the coating). By
minimizing the thickness, or profile, of the stent's structural
members, one can achieve better maneuverability as the stent is
delivered to the site of implantation. Furthermore, because foreign
materials in the body can elicit a chronic foreign body response,
it is desirable to minimize the amount of polymer applied to the
stent body. By applying the polymeric drug coating to only the
outer surface of the stent, the amount of polymer exposed to the
body of the patient can be reduced.
[0011] Spray or dip coating processes coat both the inner and outer
surfaces of the stent. Masking techniques can be used to limit the
coating application to the inner or outer surface. For example, a
mandrel can be inserted through the longitudinal bore of the stent
to mask the inner surface such that the coating is deposited only
on the outer surface. It may be, however, desirable to coat the
inner surface of the stent with a first type of drug, such as an
angiogenic drug, and the outer surface with a second type of a drug
such as one used for the treatment of restenosis. If the inner
surface of the stent is first masked for the deposition of a
coating on the outer surface of the strut, masking the coated outer
surface of the stent to form a coating on the inner surface of the
stent may cause damage to the coating on the outer surface.
Accordingly, a shortcoming of the conventional coating techniques
is the inability of manufacturers to coat the inner and outer
surfaces of the stent with different pharmaceutical agents.
[0012] Another shortcoming of the above-described method of
medicating a stent is the potential for coating defects. While some
coating defects can be minimized by adjusting the coating
parameters, other defects occur due to the nature of the
application process. For example, during a spray coating process, a
stent is commonly supported by a mandrel. Because the spray
applicator sprays the entire surface of a stent as the composition
is applied, and because there is a high degree of surface contact
between the stent and the mandrel, there can be stent regions in
which the liquid composition can flow, wick, and collect. Upon the
removal of the coated stent from the mandrel, the excess coating
may stick to the mandrel, thereby removing some of the coating from
the stent in the form of peels as shown in FIG. 2, or leaving bare
areas as shown in FIG. 3. Alternatively, as illustrated in FIG. 4,
the excess coating may stick to the stent, thereby leaving excess
coating as clumps or pools on the struts or webbing between the
struts. These types of defects can cause adverse biological
responses after the coated stent is implanted into a biological
lumen. For instance, the tissue surrounding the biological lumen
adjacent to the ends of stent 10 can adversely react to the coating
defects (known as the "edge effect.")
[0013] Accordingly, the present invention provides a system and
method for coating a tubular implantable medical device that
addresses these needs.
SUMMARY OF THE INVENTION
[0014] In aspects of the present invention, a system for coating a
tubular implantable medical device with a coating composition
comprises an applicator substrate and a mandrel. The applicator
substrate has a surface configured to receive a composition and to
transfer the composition to a tubular implantable medical device.
The mandrel is configured to support the tubular implantable
medical device in close proximity to or in contact with the
applicator substrate. In further aspects, the system further
includes an apparatus to rotate the mandrel. In other aspects, the
device includes a hollow, longitudinal bore, and the applicator
substrate is further configured to fit into the hollow,
longitudinal bore of the medical device.
[0015] In aspects of the present invention, a system for coating a
tubular implantable medical device with a coating composition
comprises a reservoir, an application roller, and a support
element. The reservoir holds a coating composition. The application
roller is configured to receive the coating composition from the
reservoir. The support element is configured to support a tubular
implantable medical device in close proximity to or in contact with
the application roller. In further aspects, the system further
comprises a metering roller in communication with the application
roller. In other aspects the surface of the application roller has
grooves.
[0016] The features and advantages of the inventions will be more
readily understood from the following detailed description which
should be read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 illustrates a conventional stent;
[0018] FIGS. 2-4 are scanning electron microscope images of stent
coatings with coating defects;
[0019] FIG. 5 illustrates a coating system for coating a stent in
accordance with one embodiment of the present invention;
[0020] FIGS. 6A-6D are top views of applicator substrates in
accordance with various embodiments;
[0021] FIG. 7 illustrates a system for leveling a coating
composition in accordance with one embodiment of the present
invention;
[0022] FIG. 8 is a perspective view of a support assembly for a
stent to be used during a coating process;
[0023] FIGS. 9-13 illustrate coating systems for coating a stent in
accordance with various other embodiments of the present
invention;
[0024] FIGS. 14A and 14B illustrate a coating system for coating an
inner surface of a stent in accordance with an embodiment of the
present invention; and
[0025] FIG. 15 is a scanning electron microscope image of a stent
coating in accordance with the Example.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Tubular Implantable Medical Device
[0026] Herein is disclosed a method and system for coating a
tubular implantable medical device, such as a stent. In the
interests of brevity, a method and system for coating a tubular
stent including a polymeric coating are described herein. However,
one of ordinary skill in the art will understand that other tubular
medical devices having therapeutic capabilities can be coated using
the system and method of the present invention. For example, the
medical device can be a polymeric covering device such as a
sheath.
[0027] Examples of tubular implantable medical devices for the
present invention include self-expandable stents,
balloon-expandable stents, stent-grafts, sheaths and grafts (e.g.,
aortic grafts). The underlying structure of the device can be of
virtually any design. The device can be made of a metallic material
or an alloy such as, but not limited to, cobalt chromium alloy,
stainless steel (316L), high nitrogen stainless steel, e.g., BIODUR
108, cobalt chrome alloy L-605, "MP35N," "MP20N," ELASTINITE
(Nitinol), tantalum, nickel-titanium alloy, platinum-iridium alloy,
gold, magnesium, or combinations thereof "MP35N" and "MP20N" are
trade names for alloys of cobalt, nickel, chromium and molybdenum
available from Standard Press Steel Co., Jenkintown, Pa. "MP35N"
consists of 35% cobalt, 35% nickel, 20% chromium, and 10%
molybdenum. "MP20N" consists of 50% cobalt, 20% nickel, 20%
chromium, and 10% molybdenum. The device can also be made partially
or completely from bioabsorbable or biostable polymers.
System and Method for Coating a Tubular Implantable Medical
Device
[0028] As disclosed herein, a coating system can be used to coat a
tubular stent by transferring a portion of a coating composition
from the surface of an applicator onto a stent. The coating
composition can be applied directly to the surface of the stent, or
to a previously applied layer of a coating material. In one
embodiment, referring to FIG. 5, a coating system 20 for coating a
tubular stent 22 is illustrated to include a composition feeder 24
and an applicator 26 having an applicator substrate 28. Feeder 24
can be used to apply a coating composition 30 onto applicator
substrate 28. Coating composition 30 can include a solvent and a
polymer dissolved in the solvent. Coating composition 30 can also
include an active agent.
[0029] Feeder 24 can be any suitable apparatus configured to
deposit coating composition 30 onto applicator substrate 28.
Representative examples of feeder 24 include a spray apparatus, a
twin screw gravimetric feeder or a belt resin feeder. To realize
greater process efficiency, coating composition 30 can be
introduced into the process by means of individually metered,
continuous mass flow streams through feeder 24. The flow rate of
coating composition 30 from feeder 24 can be from about 0.02
mg/second to about 20 mg/second, for example about 1 mg/second.
[0030] As coating composition 30 is applied to stent 22, coating
composition 30 should be in a substantially free-flowing or liquid
form. The viscosity of coating composition 30 when applied onto
stent 22 can be at the maximum of about 10 centipoises at ambient
temperature and pressure to about 1000 centipoises at ambient
temperature and pressure. The consistency of the coating
composition can affect how the composition is received by stent
22.
[0031] Applicator substrate 28 can be capable of moving in a linear
direction towards stent 22 as indicated by arrow 32 to deposit
coating composition 30 on stent 22. Applicator 26, for instance,
can be integrated with a plurality of conveyer rollers 34 that move
applicator substrate 28 towards stent 22. In other words, to
provide movement, applicator substrate 28 can be incorporated into
a conveyer belt system that is a component of applicator 26.
Applicator substrate 28 can be moved at about 1 mm/second to about
12 mm/second, for example about 6 mm/second.
[0032] Stent 22 can be supported by a mandrel during the coating
process. The mandrel can be used to position stent 22 in close
proximity to or in contact with applicator substrate 28. The
mandrel is configured to allow stent 22 to be rotated about a
central longitudinal axis of stent 22 during the coating process.
The mandrel can also be configured so that stent 22 can be rolled
towards feeder 24 (i.e., moved in a linear direction as shown by
arrow 36). As shown in FIG. 5, the rotational motion of stent 22 is
depicted by arrow 38. Stent 22 can be rotated so that at least some
of a layer 40 of coating composition 30 is transferred to outer
surface 42 of stent 22. Rotational speed of stent 22 depends on the
speed of applicator substrate 28, and can be, for example, from
about 1 rpm to about 250 rpm, more narrowly from about 10 rpm to
about 120 rpm. In one embodiment, the mandrel is connected to a
motor that provides rotational motion to stent 22 during the
coating process. In this embodiment, the rotation of stent 22 can
drive applicator substrate 28.
[0033] Applicator substrate 28 has a surface capable of receiving a
layer of the coating composition as deposited from feeder 24. In
one embodiment, the surface of applicator substrate 28 includes
grooves 44 to receive the coating composition. The surface of
applicator substrate 28 can include grooves 44 having any suitable
pattern. Referring to FIGS. 6A-6D, the surface of applicator
substrate 28 can have vertical grooves 44 (FIG. 6A), horizontal
grooves 44 (FIG. 6B), grooves 44 with a zigzag (FIG. 6C) and/or a
discontinuous (FIG. 6D) pattern.
[0034] In one embodiment, applicator substrate 28 is substantially
flat, and without any curvatures along the length of applicator
substrate 28 wherein stent 22 is coated. By providing a
substantially flat surface for applicator substrate 28, the
thickness of coating 46 applied to stent 22 can be substantially
uniform. Applicator substrate 28 can be made of a material that is
flexible so that applicator substrate 28 can be a component of the
conveyer belt system as illustrated in FIG. 5. In one embodiment,
applicator substrate 28 can be made of a material that is
"non-stick," having a low friction coefficient. The material should
be resistant to solvents and heat, which may be directed onto
applicator substrate 28 during the coating process.
[0035] Representative examples of materials that can be used for
applicator substrate 28 include polyurethanes,
polyetheretherketone, polytetrafluoroethylene (Teflon.TM.),
Delrin.TM., Rulon.TM. Pebax.TM., Kynar.TM., Solef.TM., fluorinated
ethylene-propylene copolymer, poly(vinylidene
fluoride-co-chlorotrifluoroethylene), poly(vinyl fluoride),
poly(ethylene terephthalate) (MYLAR), polyesters, or any suitable
nylon.
[0036] Coating system 20 can include a leveling bar 48 to produce a
substantially uniform thickness for layer 40. Leveling bar 48 can
be supported by any suitable structure and positioned at a set
distance from applicator substrate 28 to define an opening through
which coating composition 30 is passed. The size of the opening is
generally comparable with the thickness of layer 40 on the stent
side of leveling bar 48. Representative examples of the thickness
of layer 40 include about 2.5 microns to about 1000 microns. In one
embodiment, the thickness is about 25 microns to about 100
microns.
[0037] Referring to FIG. 7, a leveling system 50 that includes an
air gun 52 can be used to level coating composition 30. Air gun 52
can be capable of producing and directing an air flow to
composition 30 applied to applicator substrate 28. The air flow can
be of sufficient force to reduce the profile of the composition
mass that has been applied to applicator substrate 28, and
therefore level the composition to provide a substantially uniform
thickness. Air gun 52 can have a nozzle 54 with a relatively narrow
slit to help provide the sufficient force. Use of air gun 52 can be
especially appropriate if coating composition 30 does not contain a
highly volatile solvent, and has a low viscosity. By way of
example, the air flow velocity from air gun 52 can be from about 10
meters/second to about 400 meters/second, more narrowly about 20
meters/second to about 200 meters/second.
[0038] The mandrel can have any design that is suitable to support
stent 22 during the coating process. Referring to FIG. 8, stent 22
can be integrated with a mandrel 56 that includes a plug 58
positioned at a distal end of a stem 60. Plug 58 can be circular in
cross-section making contact with the inner surface of the stent.
Plug 58 can have an almost equivalent diameter to the inner
diameter of stent 22 as positioned on mandrel 56 so as to allow a
friction fit between plug 58 and stent 22. By way of example, the
outer diameter of the plug 58 can be from about 1 mm to about 8 mm.
Plug 58 can also have other cross-sectional shapes.
[0039] Plug 58 can be made of materials that are rigid or
semi-pliable. The material can be a "non-stick" material having a
low friction coefficient and should be resistant to solvents and
heat, which may be directed onto plug 58 during the coating
process. Representative examples of materials that can be used for
plug 58 include the same materials listed above for applicator
substrate 28 as well as rigid materials such as stainless steel,
titanium alloys, cobalt-chromium alloys, ceramics, metallic
carbides, inorganic carbides, and nitrides.
[0040] In addition to a single plug 58, stent 22 can also be held
by other support designs. For example, stent 22 can be supported by
two plugs, one at each end of stent 22. The two plugs in this type
of support apparatus could be connected by an internal mandrel.
Alternatively, the two plugs could be unconnected having their
relative orientation maintained by an external fixture. The two end
plugs can be conical in shape, and therefore, contact stent 22 at
contact points at the end struts.
[0041] As coating composition 30 is applied using coating system
20, the temperature of coating composition 30 can be controlled
during the coating process. In one embodiment, coating system 20
includes a temperature controller for heating or cooling coating
composition 30. The temperature controller can be used to heat or
cool coating composition 30 in order to produce and maintain a
coating consistency that is suitable for coating composition 30.
Additionally, the temperature controller can be used to cool
coating composition 30 especially if a volatile solvent is one of
the components of coating composition 30. The temperature
controller can include any suitable apparatus for heating or
cooling the coating composition, and can be in communication with
any suitable component of coating system 20. In one embodiment,
applicator substrate 28 is in communication with the temperature
controller so that the temperature controller can modify the
temperature of coating composition 30 during the coating process,
for example as coating composition is deposited from feeder 24. In
another embodiment, mandrel 56 is in communication with the
temperature controller so that the temperature controller can
modify the temperature of stent 22 during the coating process.
[0042] In another embodiment of the present invention, referring to
FIG. 9, a coating system 61 including an application roller 62 can
be used to apply a layer of composition to the outer surface of
stent 22. Stent 22 can be supported by a mandrel so that stent 22
is in close proximity to or in contact with application roller 62.
Referring to FIG. 9, application roller 62 is partially submerged
in a coating composition disposed in a reservoir 64. The viscosity
of the coating composition in reservoir 64 can be at the maximum,
about 10 centipoises to about 10,000 centipoises at ambient
temperature and pressure. As application roller 62 rotates, the
coating composition is transferred from application roller 62 to
stent 22.
[0043] Application roller 62 can be capable of rotating as
indicated by arrow 66, while stent 22 can be rotated as indicated
by arrow 68. As application roller 62 is rotated, a layer of
coating composition is deposited onto the outer surface of
application roller 62. In one embodiment, application roller 62 can
include grooves or pores 70 that facilitate the transfer of the
composition from reservoir 64 to the outer surface of application
roller 62. In another embodiment, application roller 62 is
completely smooth or only slightly textured. In yet another
embodiment, application roller 62 is surfaced with bristles,
fibers, brushes, or other absorbent materials, including sponge or
sponge-like material.
[0044] In one embodiment, application roller 62 is cylindrical in
shape. Application roller 62 can have an outer circumference with a
radius of curvature about equal to the radius of curvature of the
outer circumference of stent 22. Also, the outer diameter of
application roller 62 can be larger than the outer diameter of
stent 22. By way of example, the outer diameter of application
roller 62 can be from about 3 mm to about 50 mm for a stent having
an outer diameter of about 1 mm to about 8 mm. Since stent 22 is
radially expandable, when referring to the diameter stent 22, the
measurement is the diameter of stent 22 as positioned on a fixture
during the coating process.
[0045] Rotation of application roller 62 and stent 22 are arranged
so that the tangential velocities at the stent and roller surfaces
are similar. The rotational speeds can therefore differ according
the difference between the radius of application roller 62 and the
radius of stent 22. Rotation of stent 22 can be from about 1 rpm to
about 200 rpm, more narrowly from about 2 rpm to about 30 rpm.
Since application roller 62 can have a larger diameter than stent
22, rotation of application roller 62 can be from about 0.02 rpm to
about 500 rpm, more narrowly from about 0.04 rpm to about 80
rpm.
[0046] Coating system 61 can also include a leveling blade 72 to
produce a substantially uniform thickness on the outer surface of
application roller 62. Leveling blade 72 can be supported by any
suitable structure and can be positioned at a set distance from
application roller 62 to produce a selected thickness for the
composition applied to the surface of application roller 62.
Coating system 61 can include a temperature controller. Any
suitable component of coating system 61 can be in communication
with the temperature controller, such as the mandrel supporting
stent 22, application roller 62 and/or reservoir 64. A motor can be
used to drive application roller 62 or stent 22.
[0047] In another embodiment, referring to FIG. 10, a coating
system 74 can have a metering roller 76 positioned in close
proximity to an application roller 78. In one embodiment,
application roller 78 and/or metering roller 76 are cylindrical in
shape. Application roller 78 can have an outer surface configured
to receive a composition from feeder 24. Application roller 78 can
be capable of rotating as illustrated by arrow 80. Metering roller
76, in turn, can be capable of rotating as shown by arrow 82. The
rotational direction of metering roller 76 can be opposite from the
direction of application roller 78 to provide a controlled
deposition of coating composition 30 onto the surface of
application roller 78. Coating system 74 can further include a
barrier 84 positioned in close proximity to the outer surface of
metering roller 76. Barrier 84 can be supported by any suitable
structure and can be used to prevent excess composition from being
carried away by metering roller 76 as metering roller 76 is
rotated.
[0048] Feeder 24 can be any suitable apparatus configured to
deposit coating composition 30 onto application roller 78. As an
alternative or in addition to feeder 24, application roller 78 can
be configured to have an internal deposition system capable of
depositing the coating composition onto the outer surface of
application roller 78. For example, application roller 78 can
include an open pore network in communication with a composition
reservoir disposed in the interior of application roller 78. A
pressure applied to the reservoir within application roller 78 can
force the composition from the reservoir to outer surface 86.
[0049] Coating system 74 can include a temperature controller. Any
suitable component of coating system 74 can be in communication
with the temperature controller, such as the mandrel supporting
stent 22, feeder 24, application roller 78, and/or metering roller
76. As noted above, the temperature controller can be used to heat
or cool coating composition 30 as appropriate.
[0050] In another embodiment of the present invention, referring to
FIG. 11, a coating system 88 can have an application roller 90 that
is used to apply a coating composition along the length of stent
22. The coating composition can be applied to the surface of
application roller 90 by the methods as described herein. The
composition can also be applied by dipping application roller 90
into a coating composition prior to the coating of stent 22.
Application roller 90 can then be rolled along the length of stent
22 to apply a stripe of coating composition. Stent 22 can be
mounted on a mandrel that is capable of maintaining a fixed
position for stent 22 as application roller 90 is applying the
composition. Once application roller 90 has completed one pass
along the length of stent 22, stent 22 can be rotated, and then
application roller 90 can apply another stripe of coating
composition to stent 22. Coating system 88 can include a
temperature controller. Any suitable component of coating system 88
can be in communication with the temperature controller, such as
the mandrel supporting stent 22, or application roller 90.
[0051] In a further embodiment, referring to FIG. 12, a coating
system 91 including an application roller 92 and a support roller
94 can be used to apply a layer of composition to the outer surface
of stent 22. Application roller 92 is partially submerged in
reservoir 64. As application roller 92 and stent 22 are rotated,
application roller 92 receives coating composition 30 from
reservoir 64, and transfers coating composition 30 to stent 22.
Coating system 91 can also have an optional leveling bar positioned
in close proximity to the surface of application roller 92. For
example, the leveling bar can be located at a position where the
coated surface of application roller 92 emerges from reservoir 64.
In this embodiment, instead of being supported by a mandrel, stent
22 can be supported by application roller 92 and support roller 94
during the coating process. Additionally, support roller 94 can be
rotated to provide rotational motion to stent 22 during the coating
process. Coating system 91 can also include a temperature
controller.
[0052] Referring to FIG. 13, in another embodiment, a coating
system 96 can be used to coat stent 22. Coating system 96 includes
reservoir 64 and a support assembly 98 that is connected to a
rotating apparatus. Support assembly 98 includes a mandrel 100 and
stems 102. For the coating process using coating system 96, stent
22 is partially submerged into coating composition 30 along the
longitudinal length of stent 22. Stent 22 is then rotated while in
a substantially horizontal position to coat stent 30 with coating
composition 30.
[0053] As illustrated by FIG. 13, by using support assembly 98,
stent 22 can be positioned so that only the outer surface of stent
22 is in contact with the surface of coating composition 30 as
disposed in reservoir 64. The coating process can include rotating
stent 22 while the outer surface of stent 22 barely touches coating
composition 30. By precisely positioning stent 22, the outer
surface of stent 22 can be coated without coating the inner surface
of stent 22.
[0054] The method of using coating system 96 can include selecting
process parameters that account for the viscosity and surface
tension of coating composition 30. Coating composition 30 that is
applied using coating system 96 has a viscosity range that is lower
than the viscosity range of coating composition 30 as applied using
the other embodiments described herein. The viscosity is lower so
that coating composition 30 can coat in a conformal manner onto
stent 22 as stent 22 is rotated. The viscosity for coating
composition 30 for this embodiment can be about 2 centipoises at
ambient temperature and pressure to about 500 centipoises at
ambient temperature and pressure. The viscosity of coating
composition 30 in reservoir 64 can be adjusted by selecting solutes
(e.g., polymers) having a lower molecular weight, increasing the
ratio of solvent to solute of coating composition 30, selecting a
solvent that more effectively dissolves the solute, and/or
adjusting the temperature via a temperature controller in
communication with reservoir 64. For instance, the temperature
controller can heat coating composition 30 in reservoir 64 in order
to decrease the viscosity of coating composition 30. Additionally,
the surface tension can be lowered by using additives in coating
composition 30 such as surfactants, selecting an appropriate
solvent and/or adjusting the temperature of reservoir 64. For
instance, raising the temperature of coating composition 30 to near
the solvent boiling point will lower the surface tension, allowing
the coating to be more conformal and reduce the webbing produced by
the process.
[0055] In another embodiment, a system is provided for coating an
inner surface of stent 22. Coating just the inner surface can be
advantageous for the delivery of therapeutic agents to the blood
system to prevent thrombosis or promote rapid reendothelialization.
For instance, certain drugs may effectively treat cardiovascular
injuries when carried away by the blood flow to an area adjacent to
the site of stent implantation. These drugs, for example, may be
used to treat "edge restenosis." Referring to FIGS. 14A and 14B, a
coating system 104 includes a stent 22 and an application roller
106. The outer surface of application roller 106 can be coated with
a wet coating by dipping, or other coating methods as described
herein, before contacting the inner surface of stent 22.
Application roller 106 can then be inserted into the longitudinal
bore of stent 22 and rolled around the inner circumference of stent
22. As with the above described embodiments, coating system 104 can
include a temperature controller for heating or cooling coating
composition 30 during the coating process.
[0056] Application roller 106 can have a smooth surface, or be
coated with an absorbent material to facilitate loading the outer
surface of applicator roller 106 with the coating composition.
Application roller 106 can be supported by a stem 110. Stent 22, in
turn, can be supported in a tube 108. Tube 108 can have an inner
diameter that is slightly larger than the outer diameter of stent
22 and masks an outer surface 112 of stent 22. Application roller
106 can be sized to provide an effective circumference to deliver a
coating composition to the inner surface of stent 22. By way of
example, the outer diameter of application roller 106 can be from
about 0.5 mm to about 5 mm for a stent having an inner diameter of
about 0.9 mm to about 9.9 mm. In one embodiment, application roller
106 and/or tube 108 are in communication with a temperature
controller.
[0057] Multiple repetitions for applying the coating composition
can be performed using the system and method of the present
invention. The amount of composition applied by each repetition can
be about 1 microgram/cm.sup.2 (of stent surface) to about 100
micrograms/cm.sup.2, for example less than about 10
micrograms/cm.sup.2 per application. Each repetition can be
followed by removal of a significant amount of the solvent(s).
Depending on the volatility of the particular solvent employed, the
solvent can evaporate essentially upon contact with the stent.
Alternatively, removal of the solvent can be induced by baking the
stent in an oven at a mild temperature (e.g., 60.degree. C.) for a
suitable duration of time (e.g., 2-4 hours) or by the application
of warm air. The application of warm air between each repetition
prevents coating defects and minimizes interaction between the
active agent and the solvent. The temperature of the warm air can
be from about 30.degree. C. to about 60.degree. C., more narrowly
from about 40.degree. C. to about 50.degree. C. The flow rate of
the warm air can be from about 20 cubic feet/minute (CFM) (0.57
cubic meters/minute (CMM)) to about 80 CFM (2.27 CMM), more
narrowly about 30 CFM (0.85 CMM) to about 40 CFM (1.13 CMM). The
warm air can be applied for about 3 seconds to about 60 seconds,
more narrowly for about 10 seconds to about 20 seconds. By way of
example, warm air applications can be performed at a temperature of
about 50.degree. C., at a flow rate of about 40 CFM, and for about
10 seconds.
[0058] Any suitable number of repetitions of applying the
composition followed by removing the solvent(s) can be performed to
form a coating of a desired thickness or weight. The coating
process as described herein can be used to form a coating on the
stent having a thickness of about 0.5 microns to about 100 microns,
more narrowly, about 1 micron to about 20 microns.
[0059] Operations such as wiping, centrifugation, or other web
clearing acts can also be performed to achieve a more uniform
coating. Briefly, wiping refers to the physical removal of excess
coating from the surface of the stent; and centrifugation refers to
rapid rotation of the stent about an axis of rotation. The excess
coating can also be vacuumed off of the surface of the stent.
[0060] The stent can be at least partially preexpanded prior to the
application of the composition. For example, the stent can be
radially expanded about 20% to about 60%, more narrowly about 27%
to about 55%--the measurement being taken from the stent's inner
diameter at an expanded position as compared to the inner diameter
at the unexpanded position. The expansion of the stent, for
increasing the interspace between the stent struts during the
application of the composition, can further prevent "cob web"
formation between the stent struts.
Coating Composition
[0061] As noted above, the coating composition can include a
solvent and a polymer dissolved in the solvent, and optionally an
active agent. Representative examples of polymers that can be used
to coat a medical device in accordance with the present invention
include ethylene vinyl alcohol copolymer (commonly known by the
generic name EVOH or by the trade name EVAL);
poly(hydroxyvalerate); poly(L-lactic acid); polycaprolactone;
poly(lactide-co-glycolide); poly(hydroxybutyrate);
poly(hydroxybutyrate-co-valerate); polydioxanone; polyorthoester;
polyanhydride; poly(glycolic acid); poly(D,L-lactic acid);
poly(glycolic acid-co-trimethylene carbonate); polyphosphoester;
polyphosphoester urethane; poly(amino acids); cyanoacrylates;
poly(trimethylene carbonate); poly(iminocarbonate);
copoly(ether-esters) (e.g. PEO/PLA); polyalkylene oxalates;
polyphosphazenes; biomolecules, such as fibrin, fibrinogen,
cellulose, starch, collagen and hyaluronic acid; polyurethanes;
silicones; polyesters; polyolefins; polyisobutylene and
ethylene-alphaolefin copolymers; acrylic polymers and copolymers;
vinyl halide polymers and copolymers, such as polyvinyl chloride;
polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidene
halides, such as polyvinylidene fluoride, polyvinylidene chloride
poly(vinylidene fluoride-co-hexafluoropropene), and poly(vinylidene
fluoride-co-chlorotrifluoroethylene); polyacrylonitrile; polyvinyl
ketones; polyvinyl aromatics, such as polystyrene; polyvinyl
esters, such as polyvinyl acetate; copolymers of vinyl monomers
with each other and olefins, such as ethylene-methyl methacrylate
copolymers, acrylonitrile-styrene copolymers, ABS resins, and
ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 and
polycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes;
polyimides; polyethers; epoxy resins; polyurethanes; rayon;
rayon-triacetate; cellulose; cellulose acetate; cellulose butyrate;
cellulose acetate butyrate; cellophane; cellulose nitrate;
cellulose propionate; cellulose ethers; and carboxymethyl
cellulose.
[0062] "Solvent" is defined as a liquid substance or composition
that is compatible with the polymer and is capable of dissolving
the polymer at the concentration desired in the composition.
Examples of solvents include, but are not limited to,
dimethylsulfoxide, chloroform, acetone, water (buffered saline),
xylene, methanol, ethanol, 1-propanol, tetrahydrofuran, 1-butanone,
dimethylformamide, dimethylacetamide, cyclohexanone, ethyl acetate,
methylethylketone, propylene glycol monomethylether, isopropanol,
isopropanol admixed with water, N-methyl pyrrolidinone, toluene,
and combinations thereof.
[0063] The active agent can be for inhibiting the activity of
vascular smooth muscle cells. More specifically, the active agent
can be aimed at inhibiting abnormal or inappropriate migration
and/or proliferation of smooth muscle cells for the inhibition of
restenosis. The active agent can also include any substance capable
of exerting a therapeutic or prophylactic effect in the practice of
the present invention. For example, the agent can be for enhancing
wound healing in a vascular site or improving the structural and
elastic properties of the vascular site.
[0064] By using the system and method of the present invention, the
same active agent can be applied to the inner and outer surfaces of
stent 22. Alternatively, different active agents can be applied to
the two surfaces. For example, the outer surface of stent 22 can be
coated with a drug that is capable of treating restenosis. The
inner surface of stent 22, on the other hand, can be coated with an
angiogenic drug.
[0065] Examples of agents include antiproliferative substances such
as actinomycin D, or derivatives and analogs thereof (manufactured
by Sigma-Aldrich 1001 West Saint Paul Avenue, Milwaukee, Wis.
53233; or COSMEGEN available from Merck). Synonyms of actinomycin D
include dactinomycin, actinomycin IV, actinomycin I.sub.1,
actinomycin X.sub.1, and actinomycin C.sub.1. The active agent can
also fall under the genus of antineoplastic, anti-inflammatory,
antiplatelet, anticoagulant, antifibrin, antithrombin, antimitotic,
antibiotic, antiallergic and antioxidant substances. Examples of
such antineoplastics and/or antimitotics include paclitaxel (e.g.,
TAXOL.RTM. by Bristol-Myers Squibb Co., Stamford, Conn.), docetaxel
(e.g., Taxotere, from Aventis S. A., Frankfurt, Germany),
methotrexate, azathioprine, vincristine, vinblastine, fluorouracil,
doxorubicin hydrochloride (e.g., Adriamycin.RTM. from Pharmacia
& Upjohn, Peapack N.J.), and mitomycin (e.g., Mutamycin.RTM.
from Bristol-Myers Squibb Co., Stamford, Conn.). Examples of such
antiplatelets, anticoagulants, antifibrin, and antithrombins
include sodium heparin, low molecular weight heparins, heparinoids,
hirudin, argatroban, forskolin, vapiprost, prostacyclin and
prostacyclin analogues, dextran, D-phe-pro-arg-chloromethylketone
(synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa
platelet membrane receptor antagonist antibody, recombinant
hirudin, and thrombin inhibitors such as Angiomax a (Biogen, Inc.,
Cambridge, Mass.). Examples of such cytostatic or antiproliferative
agents include angiopeptin, angiotensin converting enzyme
inhibitors such as captopril (e.g., Capoten.RTM. and Capozide.RTM.
from Bristol-Myers Squibb Co., Stamford, Conn.), cilazapril or
lisinopril (e.g., Prinivil.RTM. and Prinzide.degree. from Merck
& Co., Inc., Whitehouse Station, N.J.), calcium channel
blockers (such as nifedipine), colchicine, fibroblast growth factor
(FGF) antagonists, fish oil (omega 3-fatty acid), histamine
antagonists, lovastatin (an inhibitor of HMG-CoA reductase, a
cholesterol lowering drug, brand name Mevacor.RTM. from Merck &
Co., Inc., Whitehouse Station, N.J.), monoclonal antibodies (such
as those specific for Platelet-Derived Growth Factor (PDGF)
receptors), nitroprusside, phosphodiesterase inhibitors,
prostaglandin inhibitors, suramin, serotonin blockers, steroids,
thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist),
and nitric oxide. An example of an antiallergic agent is pemirolast
potassium. Other therapeutic substances or agents which may be
appropriate include alpha-interferon, genetically engineered
epithelial cells, dexamethasone and rapamycin and structural
derivatives or functional analogs thereof, such as
40-O-(2-hydroxy)ethyl-rapamycin (known by the trade name of
EVEROLIMUS available from Novartis),
40-O-(3-hydroxy)propyl-rapamycin,
40-0-[2-(2-hydroxy)ethoxy]ethyl-rapamycin, and
40-O-tetrazole-rapamycin.
EXAMPLE
[0066] Some embodiments of the present invention are illustrated by
the following Example. The Example is being given by way of
illustration only and not by way of limitation. The parameters and
data are not be construed to unduly limit the scope of the
embodiments of the invention.
[0067] A 20% EVAL solution in N,N-dimethlyacetamide (DMAC) (w/w)
was prepared. A bead of the solution was applied to the surface of
a stainless steel (316L) coupon. The bead was formed into a thin
film by dragging a glass slide, held lengthwise, down the length of
the coupon. A 12 mm VISION stent (Guidant Corporation) was expanded
to 0.069 inches (1.75 mm) (inner diameter), mounted onto a section
of a thin walled stainless steel tubing with an outer diameter of
0.07 inches (1.78 mm). The stent was then carefully laid down at
one end of the thin film of polymer solution. The stent was rolled
along the wet polymer film to coat the entire circumference of the
outer surface of the stent. The stent was baked at 80.degree. C.
for one hour. After baking, the stent was removed from the
tube.
[0068] The stent was weighed and it was determined that the process
applied a polymeric coating of 70 .mu.g. The coating was then
studied using a Scanning Electron Microscope (SEM) to view the
distribution of the coating and to determine if there were visible
coating defects as a result of the coating process. As illustrated
in FIG. 15, the coating was limited to the outer surface of the
stent and there were substantially no visible coating defects.
[0069] While particular embodiments of the present invention have
been shown and described, it will be obvious to those skilled in
the art that changes and modifications can be made without
departing from this invention in its broader aspects. Therefore,
the appended claims are to encompass within their scope all such
changes and modifications as fall within the true spirit and scope
of this invention. It is not intended that the invention be
limited, except by the appended claims.
* * * * *