U.S. patent application number 11/803651 was filed with the patent office on 2008-11-20 for implantable medical devices with a topcoat layer of phosphoryl choline acrylate polymer for reduced thrombosis, and improved mechanical properties.
Invention is credited to Stephen D. Pacetti.
Application Number | 20080286332 11/803651 |
Document ID | / |
Family ID | 39531419 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080286332 |
Kind Code |
A1 |
Pacetti; Stephen D. |
November 20, 2008 |
Implantable medical devices with a topcoat layer of phosphoryl
choline acrylate polymer for reduced thrombosis, and improved
mechanical properties
Abstract
The present invention relates to implantable medical devices
coated with phosphoryl choline acrylate polymer topcoat layer, an
acrylate copolymer layer containing a therapeutic agent, and their
use in the treatment of vascular diseases.
Inventors: |
Pacetti; Stephen D.; (San
Jose, CA) |
Correspondence
Address: |
SQUIRE, SANDERS & DEMPSEY LLP
1 MARITIME PLAZA, SUITE 300
SAN FRANCISCO
CA
94111
US
|
Family ID: |
39531419 |
Appl. No.: |
11/803651 |
Filed: |
May 14, 2007 |
Current U.S.
Class: |
424/424 ;
623/1.42 |
Current CPC
Class: |
A61L 2300/606 20130101;
A61L 27/54 20130101; A61L 31/16 20130101; A61L 2420/08 20130101;
A61L 2300/42 20130101; A61L 2300/416 20130101; A61L 27/34 20130101;
A61L 2300/41 20130101; A61P 9/00 20180101; A61P 9/10 20180101; A61L
31/10 20130101 |
Class at
Publication: |
424/424 ;
623/1.42 |
International
Class: |
A61F 2/06 20060101
A61F002/06; A61K 9/00 20060101 A61K009/00; A61P 9/00 20060101
A61P009/00; A61P 9/10 20060101 A61P009/10 |
Claims
1. An implantable medical device, comprising: a device body; an
optional primer layer disposed over the device body; a drug
reservoir layer disposed over the device body or the primer layer,
if opted, wherein the drug reservoir layer comprises one or more
therapeutic agents; and a topcoat layer disposed as an outermost
layer over the drug reservoir layer, wherein the topcoat layer
comprises a phosphoryl choline acrylate polymer.
2. The implantable medical device of claim 1, wherein the device is
a stent.
3. The implantable medical device of claim 1, wherein the
phosphoryl choline acrylate polymer comprises
poly(2-(methacryloyloxyethyl)-2-(trimethylammoniumethyl)-phosphate,
inner
salt)-co-(n-dodecylmethacrylate)-co-(hydroxypropylmethacrylate)-co-(3-tri-
methoxysilyl)propylmethacrylate).
4. The implantable medical device of claim 1, wherein the
(trimethylammoniumethyl)-phosphate, inner
salt)/(n-dodecylmethacrylate)/(hydroxypropylmethacrylate)/(3-trimethoxysi-
lyl)propylmethacrylate) constitutional unit wt/wt ratio is from
about 28.8:50.7:15.3:5.3.
5. The implantable medical device of claim 1, wherein the
phosphoryl choline acrylate polymer is substantially amorphous.
6. The implantable medical device of claim 1, wherein the drug
reservoir layer comprises acrylate or methacrylate polymer.
7. The implantable medical device of claim 6, wherein the acrylate
or methacrylate polymer has an average molecular weight of about
20,000 to about 600,000 Daltons.
8. The implantable medical device of claim 6, wherein the acrylate
or methacrylate polymer comprises poly(butyl methacrylate).
9. The implantable medical device of claim 6, wherein the drug
reservoir layer comprises poly(acrylate) or poly(methacrylate)
having the formula: ##STR00009## wherein: m=0.005 to 0.90 n=0.10 to
0.995 m+n=1 x=65 to 6960 R.sub.1 and R.sub.2 are independently
selected from the group consisting of hydrogen and methyl; and,
Hydrocarbon Group is selected from the group consisting of an
unsaturated or saturated, branched or straight chain C.sub.1 to
C.sub.16 aliphatic, a cycloaliphatic or an aromatic moiety.
10. The implantable medical device of claim 9, wherein the Polar
Group is selected from the group consisting of an alkyl ether and
an amide.
11. The implantable medical device of claim 10, wherein the alkyl
ether is selected from the group consisting of: ##STR00010##
12. The implantable medical device of claim 10, wherein the amide
is selected from the group consisting of: ##STR00011##
13. A method of treating a vascular disease, comprising: deploying
in the vasculature of a patient in need thereof an implantable
medical device, wherein the device comprises: a device body; an
optional primer layer disposed over the device body; a drug
reservoir layer disposed over the device body or the primer layer,
if opted, wherein the drug reservoir layer comprises one or more
therapeutic agents; and a topcoat layer disposed as an outermost
layer over the drug reservoir layer, wherein the topcoat layer
comprises a phosphoryl choline acrylate polymer.
14. The method of claim 13, wherein the device is a stent.
15. The method of claim 13, wherein the phosphoryl choline acrylate
polymer comprises
poly(2-(methacryloyloxyethyl)-2-(trimethylammoniumethyl)-phosphate,
inner
salt)-co-(n-dodecylmethacrylate)-co-(hydroxypropylmethacrylate)-co-(3-tri-
methoxysilyl)propylmethacrylate).
16. The method of claim 13, wherein the
(trimethylammoniumethyl)-phosphate, inner
salt)/(n-dodecylmethacrylate)/(hydroxypropylmethacrylate)/(3-trimethoxysi-
lyl)-propylmethacrylate) constitutional unit wt/wt ratio is from
about 28.8:50.7:15.3:5.3.
17. The method of claim 13, wherein the phosphoryl choline acrylate
polymer is substantially amorphous.
18. The method of claim 13, wherein the drug reservoir layer
comprises acrylate or methacrylate polymer.
19. The method of claim 18, wherein the acrylate or methacrylate
polymer has an average molecular weight of about 20,000 to about
600,000 Daltons.
20. The method of claim 18, wherein the acrylate or methacrylate
polymer comprises poly(butyl methacrylate).
21. The method of claim 18, wherein the drug reservoir layer
comprises poly(acrylate) or poly(methacrylate) having the formula:
##STR00012## Wherein: m=0.005 to 0.90 n=0.10 to 0.995 m+n=1 x=65 to
6960 R.sub.1 and R.sub.2 are independently selected from the group
consisting of hydrogen and methyl; and, Hydrocarbon Group is
selected from the group consisting of an unsaturated or saturated,
branched or straight chain C.sub.1 to C.sub.16 aliphatic, a
cycloaliphatic or an aromatic moiety.
22. The implantable medical device of claim 21, wherein the Polar
Group is selected from the group consisting of an alkyl ether and
an amide.
23. The implantable medical device of claim 22, wherein the alkyl
ether is selected from the group consisting of: ##STR00013##
24. The implantable medical device of claim 22, wherein the amide
is selected from the group consisting of: ##STR00014##
25. The method of claim 13, wherein the vascular disease is
atherosclerosis.
26. The method of claim 13, wherein the vascular disease is
restenosis.
27. The method of claim 13, wherein the vascular disease is
vulnerable plaque.
28. The method of claim 13, wherein the vascular disease is
peripheral vascular disease.
29. The method of claim 13, wherein the vascular disease is late
stent thrombosis.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the fields of organic chemistry,
polymer science, material science and medical devices. In
particular, it relates to a medical device having a phosphoryl
choline acrylate polymer topcoat layer for treating vascular
diseases.
BACKGROUND OF THE INVENTION
[0002] Percutaneous transluminal coronary angioplasty (PTCA) is a
common procedure for treating heart disease. A problem associated
with the PTCA includes the formation of intimal flaps or torn
arterial linings which can collapse and occlude the conduit after
the balloon is deflated. Moreover, thrombosis and restenosis of the
artery may develop over several months after the procedure, which
may require another angioplasty procedure or a surgical by-pass
operation. To reduce the partial or total occlusion of the artery
by the collapse of arterial lining, and to reduce the chance of the
development of thrombosis and restenosis, a stent is implanted in
the lumen to maintain the vascular patency.
[0003] Stents are used not only as a mechanical intervention but
also as a vehicle for providing biological therapy. As a mechanical
intervention, stents act as scaffoldings, functioning to physically
hold open and, if desired, to expand the wall of the passageway.
Biological therapy can be achieved by medicating the stents.
Medicated stents provide for the local administration of a
therapeutic substance at the desired site. Local delivery produces
fewer side effects and achieves more favorable results.
[0004] However, the use of drug eluting stents (DESs) has resulted
in a new problem, late stent thrombosis, the forming of blood clots
long after the stent is in place. It was deduced that the formation
of blood clots was most likely due to delayed healing which was
postulated to be a side-effect of the use of cytostatic drugs.
[0005] To address the above situation, stents can be fabricated
from materials that are biocompatible, biodegradable and, if
desired, bio-absorbable. The goal is for the stent to have a
biocompatible coating which demonstrates great safety with regard
to stent thrombosis. Ideally, the stent coatings should preferably
lower acute and sub-acute thrombosis rates. The coating material
selected must not only have sufficient mechanical properties but
also show excellent coating integrity. The preceding problem has
been at least partially ameliorated by the use of increasingly
biocompatible materials and/or biocompatible coating.
[0006] What is needed is an implantable medical device that
includes a polymer coating which reduces stent thrombosis. While
this would be particularly useful with regard to coronary stents,
it would also provide substantial benefit to any manner of
implantable medical devices. Such implantable medical devices for
use as drug delivery systems should also demonstrate excellent
mechanical properties when implanted in a patient. The present
invention provides such implantable medical devices.
SUMMARY OF THE INVENTION
[0007] Thus, in one aspect, the current invention relates to an
implantable medical device, comprising: [0008] a device body;
[0009] an optional primer layer disposed over the device body;
[0010] a drug reservoir layer disposed over the device body or the
primer layer, if opted, wherein the drug reservoir layer comprises
one or more therapeutic agents; and [0011] a topcoat layer disposed
as an outermost layer over the drug reservoir layer, wherein the
topcoat layer comprises a phosphoryl choline acrylate polymer.
[0012] In an aspect of this invention, the implantable medical
device is a stent.
[0013] In an aspect of this invention, the phosphoryl choline
acrylate polymer comprises
poly(2-(methacryloyloxyethyl)-2-(trimethylammoniumethyl)-phosphate,
inner
salt)-co-(n-dodcylmethacrylate)-co-(hydroxypropylmethacrylate)-co-(3-trim-
ethoxysilyl)-propylmethacrylate).
[0014] In an aspect of this invention, the
(trimethylammoniumethyl)-phosphate, inner
salt)/(n-dodecylmethacrylate)/(hydroxypropylmethacrylate)/(3-trimethoxysi-
lyl)-propylmethacrylate) constituent wt/wt ratio is from about
28.8:50.7:15.3:5.3.
[0015] In an aspect of this invention, the phosphoryl choline
acrylate polymer is substantially amorphous.
[0016] In an aspect of this invention, the drug reservoir layer
comprises acrylate or methacrylate polymer.
[0017] In an aspect of this invention, the acrylate or methacrylate
polymer has an average molecular weight of about 20,000 to about
600,000 Daltons.
[0018] In an aspect of this invention, the acrylate or methacrylate
polymer comprises poly(butyl methacrylate).
[0019] In an aspect of this invention, the drug reservoir layer
comprises poly(acrylate) or poly(methacrylate) having the
formula:
##STR00001##
wherein: [0020] m 0.005 to 0.90 [0021] n=0.10 to 0.995 [0022] m+n=1
[0023] x=65 to 6960 [0024] R.sub.1 and R.sub.2 are independently
selected from the group consisting of hydrogen and methyl; and,
[0025] Hydrocarbon Group is selected from the group consisting of
an unsaturated or saturated, branched or straight chain C.sub.1 to
C.sub.16 aliphatic, a cycloaliphatic or an aromatic moiety.
[0026] In an aspect of this invention, the Polar Group is selected
from the group consisting of an alkyl ether and an amide.
[0027] In an aspect of this invention, the alkyl ether is selected
from the group consisting of:
##STR00002##
[0028] In an aspect of this invention, the amide is selected from
the group consisting of:
##STR00003##
[0029] An aspect of this invention is a method of treating a
vascular disease, comprising: [0030] deploying in the vasculature
of a patient in need thereof an implantable medical device, wherein
the device comprises: [0031] a device body; [0032] an optional
primer layer disposed over the device body; [0033] a drug reservoir
layer disposed over the device body or the primer layer, if opted,
wherein the drug reservoir layer comprises one or more therapeutic
agents; and [0034] a topcoat layer disposed as an outermost layer
over the drug reservoir layer, wherein the topcoat layer comprises
a phosphoryl choline acrylate polymer.
[0035] In an aspect of this invention, the implantable medical
device is a stent.
[0036] In an aspect of this invention, the phosphoryl choline
acrylate polymer comprises
poly(2-(methacryloyloxyethyl)-2-(trimethylammoniumethyl)-phosphate,
inner
salt)-co-(n-dodecylmethacrylate)-co-(hydroxypropylmethacrylate)-co-(3-tri-
methoxysilyl)-propylmethacrylate).
[0037] In an aspect of this invention, the
(trimethylammoniumethyl)-phosphate, inner
salt)/(n-dodecylmethacrylate)/(hydroxypropyl
methacrylate)/(3-trimethoxysilyl)-propylmethacrylate) constituent
wt/wt ratio is from about 28.8:50.7:15.3:5.3.
[0038] In an aspect of this invention, the phosphoryl choline
acrylate polymer is substantially amorphous.
[0039] In an aspect of this invention, the drug reservoir layer
comprises acrylate or methacrylate polymer.
[0040] In an aspect of this invention, the acrylate or methacrylate
polymer has an average molecular weight of about 20,000 to about
600,000 Daltons.
[0041] In an aspect of this invention, the acrylate or methacrylate
polymer comprises poly(butyl methacrylate).
[0042] In an aspect of this invention, the drug reservoir layer
comprises poly(acrylate) or poly(methacrylate) having the
formula:
##STR00004##
Wherein:
[0043] m=0.005 to 0.90 [0044] n=0.10 to 0.995 [0045] m+n=1 [0046]
x=65 to 6960 [0047] R.sub.1 and R.sub.2 are independently selected
from the group consisting of hydrogen and methyl; and, [0048]
Hydrocarbon Group is selected from the group consisting of an
unsaturated or saturated, branched or straight chain C.sub.1 to
C.sub.16 aliphatic, a cycloaliphatic or an aromatic moiety.
[0049] In aspect of this invention, in the formula immediately
above, the Polar Group is selected from the group consisting of an
alkyl ether and an amide.
[0050] In an aspect of this invention, the alkyl ether is selected
from the group consisting of:
##STR00005##
[0051] In an aspect of this invention, the amide is selected from
the group consisting of:
##STR00006##
[0052] In an aspect of this invention, the drug reservoir layer
further comprising one or more therapeutic agents.
[0053] In an aspect of this invention, the vascular disease is
atherosclerosis.
[0054] In an aspect of this invention, the vascular disease is
restenosis.
[0055] In an aspect of this invention, the vascular disease is
vulnerable plaque.
[0056] In an aspect of this invention, the vascular disease is
peripheral vascular disease.
[0057] In an aspect of this invention, the vascular disease is late
stent thrombosis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] The figures are provided as examples of certain embodiments
of this invention to aid in its understanding and are not intended
nor are they to be construed as limiting the scope of the invention
in any manner whatsoever.
[0059] FIG. 1 depicts an embodiment of this invention showing a
portion of a stent strut in cross section. The stent coating
structure includes a stent body, optional primer layer, drug
reservoir layer and the topcoat layer.
[0060] FIG. 2 depicts an embodiment of this invention showing the
chemical structure of an exemplary phosphoryl choline acrylate
polymer that may comprise a topcoat layer.
DETAILED DESCRIPTION OF THE INVENTION
[0061] Use of the singular herein includes the plural and visa
versa unless expressly stated to be otherwise. That is, "a" and
"the" refer to one or more of whatever the word modifies. For
example, "a therapeutic agent" includes one such agent, two such
agents, etc. Likewise, "the layer" may refer to one, two or more
layers and "the polymer" may mean one polymer or a plurality of
polymers. By the same token, words such as, without limitation,
"layers" and "polymers" would refer to one layer or polymer as well
as to a plurality of layers or polymers unless, again, it is
expressly stated or obvious from the context that such is not
intended.
[0062] As used herein, "hydrocarbon" refers to a chemical entity
made up entirely of carbon and hydrogen atoms. Hydrocarbons useful
for the purposes of this invention include, but are not limited to,
saturated or unsaturated, branched or straight-chain aliphatic
moieties, saturated or unsaturated cycloaliphatic moieties and
aromatic moieties. An aliphatic moiety of this invention may have
from 1 to 16 total carbon atoms in the straight or branched chain,
designated herein as C.sub.1 to C.sub.16. A saturated aliphatic
chain contains only single covalent bonds between carbon atoms
while an unsaturated aliphatic chain contains one or more double
and/or triple covalent bonds between carbon atoms. Examples of
alkyl groups include, without limitation, methyl, ethyl, n-propyl,
isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, amyl,
tert-amyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl.
Cycloaliphatic moieties are saturated or unsaturated aliphatic
moieties in which all or a portion of the carbon chain constitutes
one or more rings, each having from 3 to 8 carbon atoms. Examples
of cycloaliphatic groups include, without limitation, cyclopropyl,
cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl. As used
herein, "aryl" refers to a carbocyclic (all carbon) ring or two or
more fused rings (rings that share two adjacent carbon atoms) that
have a fully delocalized pi-electron system and from 6 to 14 carbon
atoms in the ring(s). Examples of aryl groups include, but are not
limited to, benzene, naphthalene and azulene.
[0063] As used herein, the following graphic representation of a
polymer:
[[--Y-].sub.n/[-Z-}.sub.m].sub.x
refers to a regular alternating, a random or a block, preferably at
present random, copolymer. As use herein, the letters "n" and "m"
connote mole fractions of the constitutional units Y and Z and
n+m=1. The letter "x" connotes sequence multiplicity, that is, the
number of repeats of the entity within the outside brackets in the
polymer.
[0064] As used herein, an "implantable medical device" refers to
any type of appliance that is totally or partly introduced,
surgically or medically, into a patient's body or by medical
intervention into a natural orifice, and which is intended to
remain there after the procedure. The duration of implantation may
be essentially permanent, i.e., intended to remain in place for the
remaining lifespan of the patient; until the device biodegrades; or
until it is physically removed. Examples of implantable medical
devices include, without limitation, implantable cardiac pacemakers
and defibrillators; leads and electrodes for the preceding;
implantable organ stimulators such as nerve, bladder, sphincter and
diaphragm stimulators, cochlear implants; prostheses, vascular
grafts, self-expandable stents, balloon-expandable stents,
stent-grafts, grafts, artificial heart valves and cerebrospinal
fluid shunts.
[0065] An implantable medical device specifically designed and
intended solely for the localized delivery of a therapeutic agent
is within the scope of this invention.
[0066] As used herein, "device body" refers to a fully formed
implantable medical with an outer surface to which no coating or
layer of material different from that of which the device itself is
manufactured has been applied. By "outer surface" is meant any
surface however spatially oriented that is in contact with bodily
tissue or fluids. A common example of a "device body" is a BMS,
i.e., a bare metal stent, which, as the name implies, is a
fully-formed usable stent that has not been coated with a layer of
any material different from the metal of which it is made on any
surface that is in contact with bodily tissue or fluids. Of course,
device body refers not only to BMSs but to any uncoated device
regardless of what it is made of.
[0067] Implantable medical devices made of virtually any material,
i.e., materials presently known to be useful for the manufacture of
implantable medical devices and materials that may be found to be
so in the future, may be used with a coating of this invention. For
example, without limitation, an implantable medical device useful
with this invention may be made of one or more biocompatible metals
or alloys thereof including, but not limited to, cobalt-chromium
alloy (ELGILOY, L-605), cobalt-nickel alloy (MP-35N), 316L
stainless steel, high nitrogen stainless steel, e.g., BIODUR 108,
nickel-titanium alloy (NITINOL), tantalum, platinum,
platinum-iridium alloy, gold and combinations thereof.
[0068] Implantable medical devices may also be made of polymers
that are biocompatible and biostable or biodegradable, the latter
term including bioabsorbable and/or bioerodable.
[0069] As used herein, "biocompatible" refers to a polymer that
both in its intact, as synthesized state and in its decomposed
state, i.e., its degradation products, is not, or at least is
minimally, toxic to living tissue; does not, or at least minimally
and reparably, injure(s) living tissue; and/or does not, or at
least minimally and/or controllably, cause(s) an immunological
reaction in living tissue.
[0070] Among useful biocompatible, relatively biostable polymers
are, without limitation, polyacrylates, polymethacryates,
polyureas, polyurethanes, polyolefins, polyvinylhalides,
polyvinylidenehalides, polyvinylethers, polyvinylaromatics,
polyvinylesters, polyacrylonitriles, alkyd resins, polysiloxanes
and epoxy resins.
[0071] Biocompatible, biodegradable polymers include
naturally-occurring polymers such as, without limitation, collagen,
chitosan, alginate, fibrin, fibrinogen, cellulosics, starches,
dextran, dextrin, hyaluronic acid, heparin, glycosaminoglycans,
polysaccharides and elastin.
[0072] One or more synthetic or semi-synthetic biocompatible,
biodegradable polymers may also be used to fabricate an implantable
medical device useful with this invention. As used herein, a
synthetic polymer refers to one that is created wholly in the
laboratory while a semi-synthetic polymer refers to a
naturally-occurring polymer than has been chemically modified in
the laboratory. Examples of synthetic polymers include, without
limitation, polyphosphazines, polyphosphoesters, polyphosphoester
urethane, polyhydroxyacids, polyhydroxyalkanoates, polyanhydrides,
polyesters, polyorthoesters, polyamino acids, polyoxymethylenes,
poly(ester-amides) and polyimides.
[0073] Blends and copolymers of the above polymers may also be used
and are within the scope of this invention. Based on the
disclosures herein, those skilled in the art will recognize those
implantable medical devices and those materials from which they may
be fabricated that will be useful with the coatings of this
invention.
[0074] At present, preferred implantable medical devices for use
with the coatings of this invention are stents.
[0075] A stent refers generally to any device used to hold tissue
in place in a patient's body. Particularly useful stents, however,
are those used for the maintenance of the patency of a vessel in a
patient's body when the vessel is narrowed or closed due to
diseases or disorders including, without limitation, tumors (in,
for example, bile ducts, the esophagus, the trachea/bronchi, etc.),
benign pancreatic disease, coronary artery disease, carotid artery
disease and peripheral arterial disease such as atherosclerosis,
restenosis and vulnerable plaque. Vulnerable plaque (VP) refers to
a fatty build-up in an arterial wall thought to be caused by
inflammation. The VP is covered by a thin fibrous cap that can
rupture leading to blood clot formation. A stent can be used to
strengthen the wall of the vessel in the vicinity of the VP and act
as a shield against such rupture. A stent can be used in, without
limitation, neuro, carotid, coronary, pulmonary, aorta, renal,
biliary, iliac, femoral and popliteal as well as other peripheral
vasculatures. A stent can be used in the treatment or prevention of
disorders such as, without limitation, thrombosis, restenosis,
hemorrhage, vascular dissection or perforation, vascular aneurysm,
chronic total occlusion, claudication, anastomotic proliferation,
bile duct obstruction and ureter obstruction.
[0076] In addition to the above uses, stents may also be employed
for the localized delivery of therapeutic agents to specific
treatment sites in a patient's body. In fact, therapeutic agent
delivery may be the sole purpose of the stent or the stent may be
primarily intended for another use such as those discussed above
with drug delivery providing an ancillary benefit.
[0077] A stent used for patency maintenance is usually delivered to
the target site in a compressed state and then expanded to fit the
vessel into which it has been inserted. Once at a target location,
a stent may be self-expandable or balloon expandable. In any event,
due to the expansion of the stent, any coating thereon must be
flexible and capable of elongation.
[0078] FIG. 1 depicts an embodiment of this invention showing stent
coating structure which includes stent body, optional primer layer,
drug reservoir layer and the topcoat layer.
[0079] As used herein, "optional" means that the element modified
by the term may or may not be present. For example, without
limitation, a device body (db) that has coated on it an "optional"
primer layer (pl), a drug reservoir layer (dr), and a top-coat
layer (tc) (which it should be noted is not optional herein)
refers, without limitation, to any of the following devices:
db+pl+dr+tc and db+dr+tc.
[0080] As used herein, a "primer layer" refers to a coating
consisting of a polymer or blend of polymers that exhibit good
adhesion characteristics with regard to the material of which the
device body is manufactured and good adhesion characteristic with
regard to whatever material is to be coated on the device body.
Thus, a primer layer serves as an intermediary layer between a
device body and materials to be affixed to the device body and is,
therefore, applied directly to the device body. Examples without
limitation, of primers include acrylate and methacrylate polymers
with poly(n-butyl methacrylate) being a presently preferred primer.
Some additional examples of primers include, but are not limited
to, poly(ethylene-co-vinyl alcohol), poly(vinyl acetate-co-vinyl
alcohol), poly(methacrylates), poly(acrylates), polyethyleneamine,
polyallylamine, chitosan, poly(ethylene-co-vinyl acetate), and
parylene-C.
[0081] As use herein, a material that is described as a layer
"disposed over" an indicated substrate, e.g., without limitation, a
device body or another layer, refers to a relatively thin coating
of the material applied, preferably at present, directly to
essentially the entire exposed surface of the indicated substrate.
By "exposed surface" is meant that surface of the substrate that,
in use, would be in contact with bodily tissues or fluids.
"Disposed over" may, however, also refer to the application of the
thin layer of material to an intervening layer that has been
applied to the substrate, wherein the material is applied in such a
manner that, were the intervening layer not present, the material
would cover substantially the entire exposed surface of the
substrate.
[0082] As used herein, "drug reservoir layer" refers either to a
layer of one or more therapeutic agents applied neat or to a layer
of polymer or blend of polymers that has dispersed within its
three-dimensional structure one or more therapeutic agents. A
polymeric drug reservoir layer is designed such that, by one
mechanism or another, e.g., without limitation, by elution or as
the result of biodegradation of the polymer, the therapeutic
substance is released from the layer into the surrounding
environment. For the purpose of this invention, the drug reservoir
layer also acts as rate-controlling layer. As used herein,
"rate-controlling layer" refers to a polymer layer that controls
the release of therapeutic agents or drugs into the environment.
While any thermoplastic acrylate or methacrylate polymer may be
used to construct a drug reservoir layer of this invention,
particularly useful polymers include, but not limited to,
poly(n-butyl methacrylate) (PBMA). However, a limitation of PBMA is
that it can have to low a drug permeability. Drug permeability may
be increased by the introduction of polar groups.
[0083] As used herein, a "polar group" refers to a group in which
the center of negative charge does not coincide with the center of
positive charge due to differing electronegativities of the atoms
comprising the group. For the purposes of this invention, a polar
group is intended to increase the overall polarity of the polymer
which will increase the equilibrium water absorption, and thus,
increase the drug permeability.
[0084] While any polar moiety that does not adversely affect the
physical or chemical characteristics required of a polymer used as
a coating on an implantable medical device may be used to construct
a drug reservoir layer of this invention, a presently preferred
polar group is alkyl ether. As use herein, "alkyl ether" refers to
an unsaturated or saturated, branched- or straight-chain aliphatic
group in which one or more of the carbon atoms in the chain are
replaced by oxygen atoms. Examples of alkyl ethers useful for the
purposes of this invention include, without limitation:
##STR00007##
[0085] Poly(2-methoxyethylacrylate) is known, and is used in blood
oxygenators as a non-fouling polymer. The polar group
1-methyl-2-methoxyethyloxy- when placed on an acrylate results in a
monomer that if hydrolysis occurs to the acrylate ester in vivo
releases a very benign compound, 1-methoxy-2-propanol. These
polyacrylates with alkyl ethers are quite polar, but have a Tg near
room temperature so they will not be brittle.
[0086] Another presently preferred polar group is the amide moiety.
Amide groups will not elevate the dry Tg (embrittling the polymer)
as much as a polar moiety containing a hydroxyl group. They can
also mimic the R-groups of the amino acids glutamine and asparagine
which contain an amide group. Thus, they may be considered
peptido-mimetic. Two of these compounds are lactamide and
glycinamide, which are biocompatible. Examples of amides useful for
the purposes of this invention include, without limitation:
##STR00008##
[0087] Acrylate/methacrylate copolymer of the drug reservoir layer
can be formed by selecting a polar group which enhances adhesion of
the layer to the phosphoryl choline acrylate polymer of the topcoat
layer, and which also effectively controls the drug release rate.
The ratio of monomers is selected to give a Tg when dry in the
range of 0.degree. C. to 70.degree. C. When hydrated, the Tg should
be in the range of -30.degree. C. to 37.degree. C. Some
representative examples of non-polar monomers to copolymerize with
the polar acrylate include, but are not limited to, methyl
methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl
methacrylate, n-butyl methacrylate, isobutyl methacrylate,
sec-butyl methacrylate, 2-ethyl-hexyl methacrylate, n-hexyl
methacrylate, cyclohexyl methacrylate, n-hexyl methacrylate,
isobornyl methacrylate, trimethylcyclohexyl methacrylate, methyl
acrylate, ethyl arylate, n-propyl acrylate, isopropyl acrylate,
n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, pentyl
acrylate, n-hexyl acrylate, cyclohexyl acrylate, and combinations
thereof.
[0088] As used herein, "therapeutic agent" refers to any substance
that, when administered in a therapeutically effective amount to a
patient suffering from a disease, has a therapeutic beneficial
effect on the health and well-being of the patient. A therapeutic
beneficial effect on the health and well-being of a patient
includes, but it not limited to: (1) curing the disease; (2)
slowing the progress of the disease; (3) causing the disease to
retrogress; or, (4) alleviating one or more symptoms of the
disease. As used herein, a therapeutic agent also includes any
substance that when administered to a patient, known or suspected
of being particularly susceptible to a disease, in a
prophylactically effective amount, has a prophylactic beneficial
effect on the health and well-being of the patient. A prophylactic
beneficial effect on the health and well-being of a patient
includes, but is not limited to: (1) preventing or delaying on-set
of the disease in the first place; (2) maintaining a disease at a
retrogressed level once such level has been achieved by a
therapeutically effective amount of a substance, which may be the
same as or different from the substance used in a prophylactically
effective amount; or, (3) preventing or delaying recurrence of the
disease after a course of treatment with a therapeutically
effective amount of a substance, which may be the same as or
different from the substance used in a prophylactically effective
amount, has concluded.
[0089] As used herein, the terms "drug" and "therapeutic agent" are
used interchangeably.
[0090] As used herein, "treating" refers to the administration of a
therapeutically effective amount of a therapeutic agent to a
patient known or suspected to be suffering from a vascular disease.
A "therapeutically effective amount" refers to that amount of a
therapeutic agent that will have a beneficial affect, which may be
curative or palliative, on the health and well-being of the patient
with regard to the vascular disease with which the patient is known
or suspected to be afflicted. A therapeutically effective amount
may be administered as a single bolus, as intermittent bolus
charges, as short, medium or long term sustained release
formulations or as any combination of these. As used herein,
short-term sustained release refers to the administration of a
therapeutically effective amount of a therapeutic agent over a
period from about several hours to about 3 days. Medium-term
sustained release refers to administration of a therapeutically
effective amount of a therapeutic agent over a period from about 3
day to about 14 days and long-term refers to the delivery of a
therapeutically effective amount over any period in excess of about
14 days.
[0091] As used herein, a "vascular disease" refers to a disease of
the vessels, primarily arteries and veins, which transport blood to
and from the heart, brain and peripheral organs such as, without
limitation, the arms, legs, kidneys and liver. In particular
"vascular disease" refers to the coronary arterial system, the
carotid arterial system and the peripheral arterial system. The
disease that may be treated is any that is amenable to treatment
with a therapeutic agent, either as the sole treatment protocol or
as an adjunct to other procedures such as surgical intervention.
The disease may be, without limitation, atherosclerosis, vulnerable
plaque, restenosis or peripheral arterial disease.
[0092] "Atherosclerosis" refers to the depositing of fatty
substances, cholesterol, cellular waste products, calcium and
fibrin on the inner lining or intima of an artery. Smooth muscle
cell proliferation and lipid accumulation accompany the deposition
process. In addition, inflammatory substances that tend to migrate
to atherosclerotic regions of an artery are thought to exacerbate
the condition. The result of the accumulation of substances on the
intima is the formation of fibrous (atheromatous) plaques that
occlude the lumen of the artery, a process called stenosis. When
the stenosis becomes severe enough, the blood supply to the organ
supplied by the particular artery is depleted resulting is strokes,
if the afflicted artery is a carotid artery, heart attack if the
artery is a coronary artery, or loss of organ function if the
artery is peripheral.
[0093] "Restenosis" refers to the re-narrowing or blockage of an
artery at or near the site where angioplasty or another surgical
procedure was previously performed to remove a stenosis. It is
generally due to smooth muscle cell proliferation and, at times, is
accompanied by thrombosis. Prior to the advent of implantable
stents to maintain the patency of vessels opened by angioplasty,
restenosis occurred in 40-50% of patients within 3 to 6 months of
undergoing the procedure. Post-angioplasty restenosis before stents
was due primarily to smooth muscle cell proliferation. There were
also issues of acute reclosure due to vasospasm, dissection, and
thrombosis at the site of the procedure. Stents eliminated acute
closure from vasospasm and greatly reduced complications from
dissections. While the use of IIb-IIIa anti-platelet drugs such as
abciximab and epifabatide, which are anti-thrombotic, reduced the
occurrence of post-procedure clotting (although stent placement
itself can initiate thrombosis). Stent placement sites are also
susceptible to restenosis due to abnormal tissue growth at the site
of implantation. This form of restenosis tends also to occur at 3
to 6 months after stent placement but it is not affected by the use
of anti-clotting drugs. Thus, alternative therapies are
continuously being sought to mitigate, preferably eliminate, this
type of restenosis. Drug eluting stents (DES) which release a
variety of therapeutic agents at the site of stent placement have
been in use for some time. To date these stents comprised delivery
interfaces (lengths) that are less than 40 mm in length and, in any
event, have delivery interfaces that are not intended, and most
often do not, contact the luminal surface of the vessel at the
non-afflicted region at the periphery of the afflicted region.
[0094] "Vulnerable plaque" refers to an atheromatous plaque that
has the potential of causing a thrombotic event and is usually
characterized by a very thin wall separating it from the lumen of
an artery. The thinness of the wall renders the plaque susceptible
to rupture. When the plaque ruptures, the inner core of usually
lipid-rich plaque is exposed to blood, with the potential of
causing a potentially fatal thrombotic event through adhesion and
activation of platelets and plasma proteins to components of the
exposed plaque.
[0095] The phenomenon of "vulnerable plaque" has created new
challenges in recent years for the treatment of heart disease.
Unlike occlusive plaques that impede blood flow, vulnerable plaque
develops within the arterial walls, but it often does so without
the characteristic substantial narrowing of the arterial lumen
which produces symptoms. As such, conventional methods for
detecting heart disease, such as an angiogram, may not detect
vulnerable plaque growth into the arterial wall.
[0096] The intrinsic histological features that may characterize a
vulnerable plaque include increased lipid content, increased
macrophage, foam cell and T lymphocyte content, and reduced
collagen and smooth muscle cell (SMC) content. This fibroatheroma
type of vulnerable plaque is often referred to as "soft," having a
large lipid pool of lipoproteins surrounded by a fibrous cap. The
fibrous cap contains mostly collagen, whose reduced concentration
combined with macrophage-derived enzyme degradation can cause the
fibrous cap of these lesions to rupture under unpredictable
circumstances. When ruptured, the lipid core contents, thought to
include tissue factor, contact the arterial bloodstream, causing a
blood clot to form that can completely block the artery resulting
in an acute coronary syndrome (ACS) event. This type of
atherosclerosis is coined "vulnerable" because of unpredictable
tendency of the plaque to rupture. It is thought that hemodynamic
and cardiac forces, which yield circumferential stress, shear
stress, and flexion stress, may cause disruption of a fibroatheroma
type of vulnerable plaque. These forces may rise as the result of
simple movements, such as getting out of bed in the morning, in
addition to in vivo forces related to blood flow and the beating of
the heart. It is thought that plaque vulnerability in fibroatheroma
types is determined primarily by factors which include: (1) size
and consistency of the lipid core; (2) thickness of the fibrous cap
covering the lipid core; and (3) inflammation and repair within the
fibrous cap.
[0097] "Thrombosis" refers to the formation or presence of a blood
clot (thrombus) inside a blood vessel or chamber of the heart. A
blood clot that breaks off and travels to another part of the body
is called an embolus. If a clot blocks a blood vessel that feeds
the heart, it causes a heart attack. If a clot blocks a blood
vessel that feeds to brain, it causes a stroke.
[0098] Peripheral vascular diseases are generally caused by
structural changes in blood vessels caused by such conditions as
inflammation and tissue damage. A subset of peripheral vascular
disease is peripheral artery disease (PAD). PAD is a condition that
is similar to carotid and coronary artery disease in that it is
caused by the buildup of fatty deposits on the lining or intima of
the artery walls. Just as blockage of the carotid artery restricts
blood flow to the brain and blockage of the coronary artery
restricts blood flow to the heart, blockage of the peripheral
arteries can lead to restricted blood flow to the kidneys, stomach,
arms, legs and feet.
[0099] Suitable therapeutic agents include, without limitation,
antiproliferative agents, anti-inflammatory agents, antineoplastics
and/or antimitotics, antiplatelet, anticoagulant, antifibrin, and
antithrombin drugs, cytostatic or antiproliferative agents,
antibiotics, antiallergic agents, antioxidants and other bioactive
agents known to those skilled in the art.
[0100] Suitable antiproliferative agents include, without
limitation, actinomycin D, or derivatives or analogs thereof, i.e.,
actinomycin D is also known as dactinomycin, actinomycin IV,
actinomycin I.sub.1, actinomycin X.sub.1, and actinomycin C.sub.1.
Antiproliferative agents can be natural proteineous agents such as
a cytotoxin or a synthetic molecule, all taxoids such as taxols,
docetaxel, and paclitaxel, paclitaxel derivatives, all olimus drugs
such as macrolide antibiotics, rapamycin, everolimus, structural
derivatives and functional analogues of rapamycin, structural
derivatives and functional analogues of everolimus, FKBP-12
mediated mTOR inhibitors, biolimus, perfenidone, prodrugs thereof,
co-drugs thereof, and combinations thereof. Representative
rapamycin derivatives and analogs include
40-O-(2-hydroxyethyl)rapamycin (EVEROLIMUS.RTM.),
40-O-(3-hydroxypropyl)rapamycin,
40-O-[2-(2-hydroxy)ethoxy]ethyl-rapamycin,
40-O-tetrazolylrapamycin, or 40-epi-(N1-tetrazolyl)-rapamycin,
prodrugs thereof, co-drugs thereof, and combinations thereof.
[0101] Suitable anti-inflammatory agents include, without
limitation, steroidal anti-inflammatory agents, a nonsteroidal
anti-inflammatory agent, or a combination thereof. In some
embodiments, anti-inflammatory agents include clobetasol,
alclofenac, alclometasone dipropionate, algestone acetonide, alpha
amylase, amcinafal, amcinafide, amfenac sodium, amiprilose
hydrochloride, anakinra, anirolac, anitrazafen, apazone,
balsalazide disodium, bendazac, benoxaprofen, benzydamine
hydrochloride, bromelains, broperamole, budesonide, carprofen,
cicloprofen, cintazone, cliprofen, clobetasol propionate,
clobetasone butyrate, clopirac, cloticasone propionate,
cormethasone acetate, cortodoxone, deflazacort, desonide,
desoximetasone, dexamethasone dipropionate, diclofenac potassium,
diclofenac sodium, diflorasone diacetate, diflumidone sodium,
diflunisal, difluprednate, diftalone, dimethyl sulfoxide,
drocinonide, endrysone, enlimomab, enolicam sodium, epirizole,
etodolac, etofenamate, felbinac, fenamole, fenbufen, fenclofenac,
fenclorac, fendosal, fenpipalone, fentiazac, flazalone, fluazacort,
flufenamic acid, flumizole, flunisolide acetate, flunixin, flunixin
meglumine, fluocortin butyl, fluorometholone acetate, fluquazone,
flurbiprofen, fluretofen, fluticasone propionate, furaprofen,
furobufen, halcinonide, halobetasol propionate, halopredone
acetate, ibufenac, ibuprofen, ibuprofen aluminum, ibuprofen
piconol, ilonidap, indomethacin, indomethacin sodium, indoprofen,
indoxole, intrazole, isoflupredone acetate, isoxepac, isoxicam,
ketoprofen, lofemizole hydrochloride, lomoxicam, loteprednol
etabonate, meclofenamate sodium, meclofenamic acid, meclorisone
dibutyrate, mefenamic acid, mesalamine, meseclazone,
methylprednisolone suleptanate, momiflumate, nabumetone, naproxen,
naproxen sodium, naproxol, nimazone, olsalazine sodium, orgotein,
orpanoxin, oxaprozin, oxyphenbutazone, paranyline hydrochloride,
pentosan polysulfate sodium, phenbutazone sodium glycerate,
pirfenidone, piroxicam, piroxicam cinnamate, piroxicam olamine,
pirprofen, prednazate, prifelone, prodolic acid, proquazone,
proxazole, proxazole citrate, rimexolone, romazarit, salcolex,
salnacedin, salsalate, sanguinarium chloride, seclazone,
sermetacin, sudoxicam, sulindac, suprofen, talmetacin,
talniflumate, talosalate, tebufelone, tenidap, tenidap sodium,
tenoxicam, tesicam, tesimide, tetrydamine, tiopinac, tixocortol
pivalate, tolmetin, tolmetin sodium, triclonide, triflumidate,
zidometacin, zomepirac sodium, aspirin (acetylsalicylic acid),
salicylic acid, corticosteroids, glucocorticoids, tacrolimus,
pimecorlimus, prodrugs thereof, co-drugs thereof, and combinations
thereof. The anti-inflammatory agent may also be a biological
inhibitor of proinflammatory signaling molecules including
antibodies to such biological inflammatory signaling molecules.
[0102] Suitable antineoplastics and/or antimitotics include,
without limitation, paclitaxel, docetaxel, methotrexate,
azathioprine, vincristine, vinblastine, fluorouracil, doxorubicin
hydrochloride, and mitomycin.
[0103] Suitable antiplatelet, anticoagulant, antifibrin, and
antithrombin drugs include, without limitation, sodium heparin, low
molecular weight heparins, heparinoids, hirudin, argatroban,
forskolin, vapiprost, prostacyclin, prostacyclin dextran,
D-phe-pro-arg-chloromethylketone, dipyridamole, glycoprotein
IIb/IIIa platelet membrane receptor antagonist antibody,
recombinant hirudin and thrombin, thrombin inhibitors such as
Angiomax a (Biogen, Inc., Cambridge, Mass.), calcium channel
blockers (such as nifedipine), colchicine, 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), nitric oxide or nitric oxide donors, super oxide
dismutases, super oxide dismutase mimetic,
4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO),
estradiol, anticancer agents, dietary supplements such as various
vitamins, and a combination thereof. Examples of such cytostatic
substance 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.RTM. from Merck &
Co., Inc., Whitehouse Station, N.J.). An example of an antiallergic
agent is permirolast potassium. Other bioactive substances or
agents that may be appropriate include alpha-interferon, and
genetically engineered epithelial cells.
[0104] Suitable cytostatic or antiproliferative agents include,
without limitation, angiopeptin, angiotensin converting enzyme
inhibitors such as captopril, cilazapril or lisinopril, calcium
channel blockers such as nifedipine; colchicine, fibroblast growth
factor (FGF) antagonists; fish oil (.omega.-3-fatty acid);
histamine antagonists; lovastatin, monoclonal antibodies such as,
without limitation, 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.
[0105] Suitable antiallergic agents include, without limitation,
permirolast potassium. Other suitable bioactive agents include,
without limitation, alpha-interferon, genetically engineered
epithelial cells, dexamethasone and its derivatives, rapamycin
derivatives and analogs such as 40-O-(2-hydroxyethyl)rapamycin
(EVEROLIMUS.RTM.), 40-O-(3-hydroxypropyl)rapamycin,
40-O-[2-(2-hydroxyethoxy)]ethyl-rapamycin, and
40-O-tetrazolylrapamycin, synthetic inorganic and organic
compounds, proteins and peptides, polysaccharides and other sugars,
lipids, and DNA and RNA nucleic acid sequences having therapeutic,
prophylactic or diagnostic activities, nucleic acid sequences
include genes, antisense molecules which bind to complementary DNA
to inhibit transcription, and ribozymes. Some other examples of
suitable bioactive agents include antibodies, receptor ligands,
enzymes, adhesion peptides, blood clotting factors, inhibitors or
clot dissolving agents such as streptokinase and tissue plasminogen
activator, antigens for immunization, hormones and growth factors,
oligonucleotides such as antisense oligonucleotides and ribozymes
and retroviral vectors for use in gene therapy; antiviral agents;
analgesics and analgesic combinations; anorexics; antihelmintics;
antiarthritics, antiasthmatic agents; anticonvulsants;
antidepressants; antidiuretic agents; antidiarrheals;
antihistamines; antimigrain preparations; antinauseants;
antiparkinsonism drugs; antipruritics; antipsychotics;
antipyretics; antispasmodics; anticholinergics; sympathomimetics;
xanthine derivatives; cardiovascular preparations including calcium
channel blockers and beta-blockers such as pindolol and
antiarrhythmics; antihypertensives; diuretics; vasodilators
including general coronary; peripheral and cerebral; central
nervous system stimulants; cough and cold preparations, including
decongestants; hypnotics; immunosuppressives; muscle relaxants;
parasympatholytics; psychostimulants; sedatives; tranquilizers;
naturally derived or genetically engineered lipoproteins; and
restenoic reducing agents.
[0106] Preferred therapeutic agents include corticosteroids,
everolimus, zotarolimus, sirolimus, sirolimus derivatives,
paclitaxel, bisphosphonates, ApoA1, mutated ApoA1, ApoA1 milano,
ApoA1 mimetic peptides, ABC A1 agonists, anti-inflammatory agents,
anti-proliferative agents, anti-angiogenic agents, matrix
metalloproteinase inhibitors and tissue inhibitors of
metalloproteinases.
[0107] As used herein, a "topcoat layer" refers to an outermost
layer, that is, a layer that is in contact with the external
environment and that is coated over all other layers. The topcoat
layer may be applied to provide better hydrophilicity to the
device, to better lubricate the device or merely as a physical
protectant of the underlying layers. The topcoat layer comprises a
phosphoryl choline acrylate polymer. The phosphoryl choline
acrylate polymer moiety of the topcoat layer more specifically
comprises
poly(2-(methacryloyloxyethyl)-2-(trimethylammoniumethyl)-phosphate,
inner
salt)-co-(n-dodcylmethacrylate)-co-(hydroxypropylmethacrylate)-co-(3-trim-
ethoxysilyl)-propylmethacrylate), (PC1036.RTM. made by
Biocompatibles UK Ltd.).
[0108] As used herein, "constitutional unit" refers to monomer
component unit of the polymer moiety. The phosphoryl choline
acrylate polymer has particularly designed to have 28.8 weight
percentage of phosphoryl choline containing monomer which may have
further crosslinking for strength. The
(trimethylammoniumethyl)-phosphate, inner
salt)/(n-dodcylmethacrylate)/(hydroxypropylmethacrylate)/(3-trimethoxysil-
yl)-propylmethacrylate) constitutional unit wt/wt ratio is from
about 28.8:50.7:15.3:5.3.
[0109] As used herein, "substantial" or "substantially" refers to a
condition that when modified by the word "substantially" is
understood to not be necessarily absolute or perfect but would be
considered close enough to those of ordinary skill in the art to
warrant designating the condition as being present. Thus, for the
purpose of this invention, a construct that exhibits at least 80%
of a particular characteristic, preferably at least 90%, more
preferably at least 95% and most preferably at present at least 99%
of the full characteristic, the construct "substantially" exhibits
the characteristic. Thus, the phosphoryl choline acrylate polymer
of topcoat layer is substantially amorphous, if it is at least 80%
amorphous.
[0110] FIG. 2 depicts an embodiment of this invention showing
chemical structure of phosphoryl choline acrylate polymer topcoat
layer. The phosphoryl choline acrylate polymer topcoat has unique
structure which includes phosphoryl choline, lauryl, isopropyl and
silane moieties. The major advantage of the biocompatible
phosphoryl choline acrylate polymer topcoat is its surface
chemistry. Phosphoryl choline (PC) has a zwitterionic functionality
that mimics the outer blood-contacting surface of the lipid bilayer
structure in blood corpuscles. PC possesses numerous beneficial
properties such as hemocompatibility, non-thrombogenicity, arterial
tissue acceptance and long-term in vivo stability. PC has been used
to increase biocompatibility of polymers, especially that of
acrylic copolymers. The lauryl group improves the adhesion of
topcoat layer with drug reservoir layer and fine tunes the amount
of hydrophobicity on the polymer. The hydroxypropyl group improves
coating integrity and mechanical properties. The silane moiety acts
as a cross-linker.
[0111] Throughout the development of drug eluting stents, careful
attention has been paid to their safety compared to bare metal
stents. In all randomized clinical trials, the rates of stent
thrombosis out to one year have been equivalent to those of bare
metal stent controls. However, recent analysis has shown a trend
for more late thrombosis at time frames beyond one year.
Consequently, more attention is being placed on the issue of late,
or very late, thrombosis. The phosphoryl choline acrylate polymer
of the topcoat layer has all-acrylate backbone, synthetic polymer,
which crosslinks to form a contiguous coating. PC has long been
proposed to be a biocompatible polymer due to the biomimicry of the
phosphoryl choline headgroup with the phospholipids found in cell
membranes of erythrocytes and endothelial cells. An unexpected
difference in the subacute thrombosis rates between two different
types of stents was observed, namely, the stent which has a topcoat
layer of phosphoryl choline acrylate polymer and the stent which
does not have a topcoat layer. The adjudicated stent thrombosis
rate at 2 years is statistically lower for stent which has a
topcoat layer of PC containing polymer compared to the stent which
does not have a topcoat layer. As both systems are based on the
same stent, and were part of a randomized trial, it can be
concluded that this unexpected result is due to either the presence
of a drug, or the phosphoryl choline acrylate polymer in the
topcoat layer, or both. It is known that the drug ABT-578 does not
reduce the subacute stent thrombosis rate, which indicates that the
phosphoryl choline acrylate polymer of the topcoat layer coating is
a promising candidate for the lowering stent thrombosis rates.
Nonetheless, the stent with topcoat layer of phosphoryl choline
acrylate polymer demonstrates greater safety with regards to stent
thrombosis.
* * * * *