U.S. patent application number 11/995685 was filed with the patent office on 2009-03-05 for stent with polymer coating containing amorphous rapamycin.
This patent application is currently assigned to Micell Technologies, Inc.. Invention is credited to James Deyoung, Jim McCain, Doug Taylor.
Application Number | 20090062909 11/995685 |
Document ID | / |
Family ID | 37669386 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090062909 |
Kind Code |
A1 |
Taylor; Doug ; et
al. |
March 5, 2009 |
STENT WITH POLYMER COATING CONTAINING AMORPHOUS RAPAMYCIN
Abstract
A coated coronary stent, comprising: a stainless steel sent
framework coated with a primer layer of Parylene C; and a
rapamycin-polymer coating having substantially uniform thickness
disposed on the stent framework, wherein the rapamycin-polymer
coating comprises polybutyl methacrylate (PBMA),
polyethylene-co-vinyl acetate (PEVA) and rapamycin, wherein
substantially all of the rapamycin in the coating is in amorphous
form and substantially uniformly dispersed within the
rapamycin-polymer coating.
Inventors: |
Taylor; Doug; (Franklinton,
NC) ; Deyoung; James; (Durham, NC) ; McCain;
Jim; (Raleigh, NC) |
Correspondence
Address: |
WILSON SONSINI GOODRICH & ROSATI
650 PAGE MILL ROAD
PALO ALTO
CA
94304-1050
US
|
Assignee: |
Micell Technologies, Inc.
Raleigh
NC
|
Family ID: |
37669386 |
Appl. No.: |
11/995685 |
Filed: |
July 14, 2006 |
PCT Filed: |
July 14, 2006 |
PCT NO: |
PCT/US06/27322 |
371 Date: |
April 16, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60699650 |
Jul 15, 2005 |
|
|
|
60765339 |
Feb 3, 2006 |
|
|
|
Current U.S.
Class: |
623/1.42 |
Current CPC
Class: |
A61F 2240/002 20130101;
A61F 2/86 20130101; A61F 2/07 20130101; A61L 31/10 20130101; A61L
31/16 20130101; A61L 2300/606 20130101; A61L 31/022 20130101; A61F
2250/0067 20130101; A61L 2420/08 20130101; A61L 2300/216 20130101;
A61F 2002/821 20130101 |
Class at
Publication: |
623/1.42 |
International
Class: |
A61F 2/82 20060101
A61F002/82 |
Claims
1. A coated coronary stent, comprising: a stainless steel sent
framework coated with a primer layer of Parylene C; and a
rapamycin-polymer coating having substantially uniform thickness
disposed on the stent framework, wherein the rapamycin-polymer
coating comprises polybutyl methacrylate (PBMA),
polyethylene-co-vinyl acetate (PEVA) and rapamycin, wherein
substantially all of the rapamycin in the coating is in amorphous
form and substantially uniformly dispersed within the
rapamycin-polymer coating.
2. The stent of claim 1, wherein PBMA, PEVA and rapamycin are
present in a ratio of about 1:1:1.
3. The stent of claim 1, wherein rapamycin is in the form of
particles having an average diameter from 2 nm to 500 nm.
4. The stent of claim 1, wherein said coating has a thickness of
about 1 to about 30 microns.
5. The stent of claim 1, wherein said coating is substantially free
of solvent residue.
6. The stent of claim 1, wherein the rapamycin-polymer coating is
sintered in dense carbon dioxide at a temperature of about 50 C to
about 60 C and a pressure below 1000 psig, whereby bulk properties
and adhesion of the coating to said stent are improved without
altering the quality of the rapamycin, PBMA or PEVA.
7. The stent of claim 1, wherein said rapamycin-polymer coating
covers substantially the entire surface of said stent
framework.
8. The stent of claim 1, wherein said rapamycin-polymer coating is
substantially free of aggregated particles.
9. A stent coated with a polymer and rapamycin, comprising: a
stainless steel stent framework coated with a primer layer of
Parylene C; and a rapamycin-polymer coating disposed on the stent
framework, wherein the rapamycin-polymer coating comprises PBMA,
PEVA; and rapamycin substantially uniformly dispersed within the
rapamycin-polymer coating, wherein substantially all of rapamycin
in the coating is in amorphous form, wherein disposing said coating
is carried out by a spray coating process whereby rapamycin spray
particles are formed by rapid expansion of a supercritical or near
critical fluid mixture, and said rapamycin spray particles and said
stent framework are oppositely charged so that said spray particles
are electrostatically attracted to said stent framework.
10. The stent of claim 9, wherein said spray coating process is
carried out under RESS conditions.
11. The stent of claim 10, wherein said supercritical or near
critical fluid mixture comprises PBMA, PEVA and rapamycin dissolved
in dimethylether, chlorofluorocarbon, hydrofluorocarbon, carbon
dioxide or mixtures thereof.
12. The stent of claim 10, wherein PBMA, PEVA and rapamycin are
co-deposited from a single mixture.
13. The stent of claim 10, wherein PBMA, PEVA and rapamycin are
separately deposited on the stent.
Description
BACKGROUND OF THE INVENTION
[0001] It is often beneficial to provide coatings onto substrates,
such that the surfaces of such substrates have desired properties
or effects. It is useful to coat biomedical implants to provide for
the localized delivery of pharmaceutical or biological agents to
target specific locations within the body, for therapeutic or
prophylactic benefit. One area of particular interest is drug
eluting stents (DES) that has recently been reviewed by Ong and
Sermuys in Nat. Clin. Pract. Cardiovasc. Med., (December 2005), Vol
2, No 12, 647. Typically such pharmaceutical or biological agents
are co-deposited with a polymer. Such localized delivery of these
agents avoids the problems of systemic administration, which may be
accompanied by unwanted effects on other parts of the body, or
because administration to the afflicted body part requires a high
concentration of pharmaceutical or biological agent that may not be
achievable by systemic administration. The coating may provide for
controlled release, including long-term or sustained release, of a
pharmaceutical or biological agent. Additionally, biomedical
implants may be coated with materials to provide beneficial surface
properties, such as enhanced biocompatibility or
lubriciousness.
[0002] Conventional solvent-based spray coating processes are
generally hampered by inefficiencies related to collection of the
coating constituents onto the substrate and the consistency of the
final coating. As the size of the substrate decreases, and as the
mechanical complexity increases, it grows increasingly difficult to
uniformly coat all surfaces of a substrate.
[0003] What is needed is a cost-effective method for depositing
inert polymers and pharmaceutical or biological agents, such as
rapamycin onto a substrate, where the collection process is
efficient, the coating produced is conformal, substantially
defect-free and uniform, and the composition of the coating can be
regulated.
SUMMARY OF THE INVENTION
[0004] The present invention provides a coated coronary stent
comprising: a stainless steel sent framework coated with a primer
layer of Parylene C; and a rapamycin-polymer coating having
substantially uniform thickness disposed on the stent framework,
wherein the rapamycin-polymer coating comprises polybutyl
methacrylate (PBMA), polyethylene-co-vinyl acetate (PEVA) and
rapamycin, wherein substantially all of the rapamycin in the
coating is in amorphous form and substantially uniformly dispersed
within the rapamycin-polymer coating. In one embodiment, the PBMA,
PEVA and rapamycin are present in a ratio of about 1:1:1.
[0005] In one aspect, the invention provides coated stents, wherein
rapamycin is in the form of particles having an average diameter
from 2 nm to 500 nm.
[0006] In another aspect, the invention provides coated stents,
wherein the rapamycin-polymer coating has a thickness of about 1 to
about 30 microns. The coating is preferably substantially free of
solvent residue.
[0007] In yet another aspect, the invention provides a coated
stent, wherein the rapamycin-polymer coating is sintered in dense
carbon dioxide at a temperature of about 40 C to about 60 C,
whereby bulk properties and adhesion of the coating to the stent
are improved without altering the quality of the rapamycin, PBMA or
PEVA. Preferably, the rapamycin-polymer coating covers
substantially the entire surface of the stent framework and/or the
rapamycin-polymer coating is substantially free of aggregated
particles.
[0008] In another aspect, the invention provides a stent coated
with a polymer and rapamycin comprising: a stainless steel stent
framework coated with a primer layer of Parylene C; and a
rapamycin-polymer coating disposed on the stent framework, wherein
the rapamycin-polymer coating comprises PBMA, PEVA; and rapamycin
substantially uniformly dispersed within the rapamycin-polymer
coating, wherein substantially all of rapamycin in the coating is
in amorphous form, wherein disposing the coating is carried out by
a spray coating process whereby rapamycin spray particles are
formed by rapid expansion of a supercritical or near critical fluid
mixture, and the rapamycin spray particles and the stent framework
are oppositely charged so that the spray particles are
electrostatically attracted to the stent framework. Preferably, the
spray coating process is carried out under RESS condition. The
supercritical or near critical fluid mixture preferably comprises
PBMA, PEVA and rapamycin dissolved in dimethylether,
chlorofluorocarbon, hydrofluorocarbon, carbon dioxide or mixtures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings of which:
[0010] FIG. 1. Rapid Expansion of Supercritical Solutions (RESS)
process equipment see C. Domingo et al, Journal of Supercritical
Fluids 10, 39-55 (1997)
[0011] FIG. 2. Infrared spectra of each component and the spray
coating mixture. Individual peaks for each component are
labeled.
[0012] FIG. 3. Stents coated (top panel) and sintered under
different conditions (lower two panels) with rapamycin, PEVA and
PBMA. All stent surfaces are coated
[0013] FIG. 4. Infrared spectra with all components coated, before
and after sintering. The spectra indicate that no damage is done to
the coating during the sintering process.
[0014] FIG. 5. XRD for RESS sprayed and as received rapamycin. The
RESS sprayed rapamycin does not show any diffraction peaks
indicating the RESS sprayed material is in amorphous form
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention is explained in greater detail below.
This description is not intended to be a detailed catalog of all
the different ways in which the invention may be implemented, or
all the features that may be added to the instant invention. For
example, features illustrated with respect to one embodiment may be
incorporated into other embodiments, and features illustrated with
respect to a particular embodiment may be deleted from that
embodiment. In addition, numerous variations and additions to the
various embodiments suggested herein will be apparent to those
skilled in the art in light of the instant disclosure, which do not
depart from the instant invention. Hence, the following
specification is intended to illustrate some particular embodiments
of the invention, and not to exhaustively specify all permutations,
combinations and variations thereof.
DEFINITIONS
[0016] As used in the present specification, the following words
and phrases are generally intended to have the meanings as set
forth below, except to the extent that the context in which they
are used indicates otherwise.
[0017] "Compressed fluid" as used herein refers to a fluid of
appreciable density (e.g., >0.2 g/cc) that is a gas at standard
temperature and pressure. "Supercritical fluid", "near-critical
fluid", "near-supercritical fluid", "critical fluid", "densified
fluid" or "densified gas" as used herein refers to a compressed
fluid under conditions wherein the temperature is at least 80% of
the critical temperature of the fluid and the pressure is at least
50% of the critical pressure of the fluid. Examples of substances
that demonstrate supercritical or near critical behavior suitable
for the present invention include, but are not limited to carbon
dioxide, isobutylene, ammonia, water, methanol, ethanol, ethane,
propane, butane, pentane, dimethyl ether, xenon, sulfur
hexafluoride, halogenated and partially halogenated materials such
as chlorofluorocarbons, hydrochlorofluoro carbons,
hydrofluorocarbons, perfluorocarbons (such as perfluoromethane and
perfluoropropane, chloroform, trichloro-fluoromethane,
dichloro-difluoromethane, dichloro-tetrafluoroethane) and mixtures
thereof.
[0018] "Sintering" as used herein refers to the process by which
the polymer or polymers form continuous coating by treatment of the
coated substrate with a densified gas, compressed fluid, compressed
gas, near critical fluid or supercritical fluid that is a
non-solvent for both the polymer and the pharmaceutical agent and
biological agents, but an agent that induces formation of
continuous domains of polymer. Through the sintering process, the
adhesion properties of the coating are improved to reduce flaking
of detachment of the coating from the substrate during
manipulation.
[0019] "Rapid Expansion of Supercritical Solutions" or "RESS" as
used herein involves the dissolution of a polymer into a compressed
fluid, typically a supercritical fluid, followed by rapid expansion
into a chamber at lower pressure, typically near atmospheric
conditions. The rapid expansion of the supercritical fluid solution
through a small opening, with its accompanying decrease in density,
reduces the dissolution capacity of the fluid and results in the
nucleation and growth of polymer particles. The atmosphere of the
chamber is maintained in an electrically neutral state by
maintaining an isolating "cloud" of gas in the chamber. Carbon
dioxide or other appropriate gas is employed to prevent electrical
charge is transferred from the substrate to the surrounding
environment.
[0020] "Electrostatically charged" or "electrical potential" or
"electrostatic capture" as used herein refers to the collection of
the spray-produced particles upon a substrate that has a different
electrostatic potential than the sprayed particles. Thus, the
substrate is at an attractive electronic potential with respect to
the particles exiting, which results in the capture of the
particles upon the substrate. i.e. the substrate and particles are
oppositely charged, and the particles transport through the fluid
medium of the capture vessel onto the surface of the substrate is
enhanced via electrostatic attraction. This may be achieved by
charging the particles and grounding the substrate or conversely
charging the substrate and grounding the particles, or by some
other process, which would be easily envisaged by one of skill in
the art of electrostatic capture.
[0021] "Open vessel" as used herein refers to a vessel open to the
outside atmosphere, and thus at substantially the same temperature
and pressure as the outside atmosphere.
[0022] "Closed vessel" as used herein refers to a vessel sealed
from the outside atmosphere, and thus may be at significantly
different temperatures and pressures to the outside atmosphere.
Rapamycin is an immunosuppressive lactam macrolide that is produced
by Streptomyces hygroscopicus, and having the structure depicted in
Formula:
##STR00001##
[0023] See, e.g., McAlpine, J. B., et al., J. Antibiotics (1991)
44: 688; Schreiber, S. L., et al., J. Am. Chem. Soc. (1991) 113:
7433; U.S. Pat. No. 3,929,992.
[0024] The present invention provides a coated coronary stent
comprising: a stainless steel sent framework coated with a primer
layer of Parylene C; and a rapamycin-polymer coating having
substantially uniform thickness disposed on the stent framework,
wherein the rapamycin-polymer coating comprises polybutyl
methacrylate (PBMA), polyethylene-co-vinyl acetate (PEVA) and
rapamycin, wherein substantially all of the rapamycin in the
coating is in amorphous form and substantially uniformly dispersed
within the rapamycin-polymer coating.
[0025] In one embodiment, the PBMA, PEVA and rapamycin are present
in a ratio of about 1:1:1.
[0026] In another embodiment, the invention provides coated stents,
wherein rapamycin is in the form of particles having an average
diameter from 2 nm to 500 nm.
[0027] In another embodiment, the invention provides coated stents,
wherein the rapamycin-polymer coating has a thickness of about 1 to
about 30 microns. The coating is preferably substantially free of
solvent residue.
[0028] In yet another embodiment, the invention provides a coated
stent, wherein the rapamycin-polymer coating is sintered in dense
carbon dioxide at a temperature of about 40 C to about 60 C,
whereby bulk properties and adhesion of the coating to the stent
are improved without altering the quality of the rapamycin, PBMA or
PEVA. Preferably, the rapamycin-polymer coating covers
substantially the entire surface of the stent framework.
[0029] The invention encompasses embodiments wherein the
rapamycin-polymer coating is substantially free of aggregated
particles.
[0030] The invention also provides a stent coated with a polymer
and rapamycin comprising: a stainless steel stent framework coated
with a primer layer of Parylene C; and a rapamycin-polymer polymer
coating disposed on the stent framework, wherein the
rapamycin-polymer coating comprises PBMA, PEVA; and rapamycin
substantially uniformly dispersed within the rapamycin-polymer
coating, wherein substantially all of rapamycin in the coating is
in amorphous form, wherein disposing the coating is carried out by
a spray coating process whereby rapamycin spray particles are
formed by rapid expansion of a supercritical or near critical fluid
mixture, and the rapamycin spray particles and the stent framework
are oppositely charged so that the spray particles are
electrostatically attracted to the stent framework. Preferably, the
spray coating process is carried out under RESS condition. The
supercritical or near critical fluid mixture preferably comprises
PBMA, PEVA and rapamycin dissolved in dimethylether,
chlorofluorocarbon, hydrofluorocarbon, carbon dioxide or mixtures
thereof.
EXAMPLES
[0031] The following examples are given to enable those skilled in
the art to more clearly understand and to practice the present
invention. They should not be considered as limiting the scope of
the invention, but merely as being illustrative and representative
thereof.
Example 1
[0032] The RESS process equipment used in the present studies is
depicted in FIG. 1. This is a common design for a RESS apparatus
see C. Domingo et al, Journal of Supercritical Fluids 10, 39-55
(1997).
[0033] A solution containing rapamycin that is saturated in a
solvent or supersaturated in a solvent is sprayed at a flow rate
sufficient to achieve flow into a chamber of known volume
pressurized above ambient pressure and containing a coronary stent.
The system temperature is held constant or allowed to vary so that
any number of points in the phase diagrams of the solution or
mixture or any of its individual components can be mapped in
pressure-temperature, volume-pressure or pressure-volume space
constituting liquid, gas or supercritical CO.sub.2 conditions.
CO.sub.2 in any single phase or combination of phases flows through
the chamber at a mass flow rate of 5 gm/min to some multiple of
this flow rate. After a period of time ranging from seconds to
minutes or hours have elapsed, the solute and solvent flow that is
a solution of the therapeutic compound and suitable solvent for the
chosen solute or solutes cease but CO.sub.2 flow continues for an
additional period of time maintaining constant pressure during this
period. After this time period, the pressure is dropped to
atmospheric pressure. During the spray coating process the
particles are attracted to the stent by charging the substrate
oppositely to that of the sprayed particle charge by applying a
voltage that is greater than 5000 V but less than the ionization
potential of the most easily ionized component of the mixture. The
particles may also traverse an electromagnetic field such that the
field is used to guide the particle to a target.
Example 2
[0034] The ability to uniformly coat arterial stents with rapamycin
with controlled composition and thickness using electrostatic
capture in a rapid expansion of supercritical solution (RESS)
experimental series has been demonstrated. This technique involves
spraying an equal part mixture of the therapeutic compound such as
rapamycin and polymers such as PBMA and PEVA using a spray coating
and collection technique described herein. To determine coating
composition, infrared spectroscopy was used to collect the spectrum
of a silicon wafer chip coated simultaneously with an arterial
stent (FIG. 2). Unique absorption bands were identified for each
mixture component and band area was used as a metric to determine
incorporation of each compound in the coating.
[0035] The individual bands used for compositional analysis were
determined by spray coating Si wafer chips with each component
separately. The coating thickness was determined gravimetrically
and calculated from the density of the materials. It was assumed
that the layer is fully dense. The thickness can be controlled by
varying the spray time.
[0036] In the as sprayed state, the coating lacks strong adhesion
to the substrate. Sintering the coated substrate (see FIG. 3)
dramatically improves coating adhesion while leaving the components
unaltered as the infrared spectra shown in FIG. 4 confirm. The
coating is sintered in a supercritical carbon dioxide environment
allowing mild sintering conditions to be used with temperature
below 80 C.
[0037] FIG. 4 shows Infrared spectra with all components coated,
before and after sintering. The spectra indicate that no damage is
done to the coating during the sintering process. The spectra
demonstrate that the sintering process does not adversely impact
the coating since no new stretches appear in the after sintering
spectrum.
[0038] FIG. 5 shows XRD data taken for an authentic rapamycin
sample (as received rapamycin) and RESS sprayed rapamycin. The RESS
sprayed rapamycin does not show any diffraction peaks indicating
the RESS sprayed material is in amorphous form. In other words, the
RESS sprayed rapamycin lacks any crystallinity as indicated by the
absence of diffraction peaks in the XRD.
[0039] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
* * * * *