U.S. patent application number 11/728373 was filed with the patent office on 2007-08-16 for endovascular graft coatings.
Invention is credited to David L. Clapper, Stuart K. Williams.
Application Number | 20070191936 11/728373 |
Document ID | / |
Family ID | 24067474 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070191936 |
Kind Code |
A1 |
Williams; Stuart K. ; et
al. |
August 16, 2007 |
Endovascular graft coatings
Abstract
An endovascular graft, e.g., having both an expandable stent
portion and a stent cover portion positioned within and/or
surrounding the expandable portion, the graft itself and/or a stent
cover portion being coated with a bioactive agent adapted to
promote initial thrombus formation, preferably followed by long
term fibrous tissue ingrowth. The endovascular graft addresses
concerns regarding endoleaking by permitting the graft to be
deployed and used in a manner that promotes a short term hemostatic
effect in the perigraft region. This short term effect can, in
turn, be used to promote or permit long term fibrous tissue
ingrowth. Particularly where the stent cover portion is prepared
from a porous material selected from PET and ePTFE, the bioactive
agent can include a thrombogenic agent such as collagen covalently
attached in the form of a thin, conformal coating on at least the
outer surface of the stent cover. An optimal coating of this type
is formed by the activation of photoreactive groups provided by
either the cover material itself, by the bioactive agent itself,
and/or by a linking agent.
Inventors: |
Williams; Stuart K.;
(Tucson, AZ) ; Clapper; David L.; (Shorewood,
MN) |
Correspondence
Address: |
SURMODICS, INC.
9924 WEST 74TH STREET
EDEN PRAIRIE
MN
55344
US
|
Family ID: |
24067474 |
Appl. No.: |
11/728373 |
Filed: |
March 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09519246 |
Mar 6, 2000 |
7220276 |
|
|
11728373 |
Mar 26, 2007 |
|
|
|
Current U.S.
Class: |
424/422 ;
427/2.25; 427/2.27; 623/1.46 |
Current CPC
Class: |
A61L 31/048 20130101;
C08L 27/18 20130101; C08L 27/18 20130101; A61L 27/16 20130101; A61L
31/048 20130101; A61L 27/56 20130101; A61L 27/16 20130101; A61L
2430/36 20130101 |
Class at
Publication: |
623/001.42 ;
427/002.25; 623/001.46 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. An endovascular graft comprising an expandable stent portion and
a stent cover portion, wherein the stent cover portion comprises a
porous, fibrous material having both an outer perigraft surface and
an inner luminal surface, and is coated on at least the outer
surface with a hemostatic bioactive agent covalently attached by
the activation of photoreactive groups provided by the stent cover
portion, by the bioactive agent itself, and/or by a linking agent,
wherein the coating comprises the bioactive agent attached to the
fibers of the material without occluding its pores.
2-5. (canceled)
6. A graft according to claim 1 wherein the agent is selected from
the group consisting of proteins having a specific hemostatic
effect, and positively charged compounds having a nonspecific
effect.
7. (canceled)
8. A graft according to claim 6 wherein the agent is (a) a
positively charged polymeric molecule selected from the group
consisting of chitosan, polylysine, poly(ethyleneimine) and acrylic
polymers incorporating positively-charged groups in the form of
primary, secondary, or tertiary amines or quaternary salts, or (b)
a positively charged non-polymeric molecule selected from the group
consisting of alkyldimethylbenzylammonium chloride and
tridodecylmethylammonium chloride.
9-10. (canceled)
11. A method of preparing an endovascular graft comprising an
expandable stent portion and a stent cover portion, comprising the
step of coating at least the outer surface of the stent cover
portion with a hemostatic bioactive agent that is covalently
attached by the activation of photoreactive groups provided by the
stent cover portion, by the bioactive agent, and/or by a linking
agent.
12-15. (canceled)
16. A method according to claim 11 wherein the agent is selected
from the group consisting of proteins having specific hemostatic
effect, and positively charged compounds having a nonspecific
hemostatic effect.
17. (canceled)
18. A method according to claim 16 wherein the agent is (a) a
positively charged polymeric molecule selected from the group
consisting of chitosan, polylysine, poly(ethyleneimine) and acrylic
polymers incorporating positively-charged groups in the form of
primary, secondary, or tertiary amines or quaternary salts, or (b)
a positively charged non-polymeric molecule selected from the group
consisting of alkyldimethylbenzylammonium chloride and
tridodecylmethylammonium chloride
19-20. (canceled)
21. A method of preventing endoleaking in the course of deploying
and using an endovascular graft that comprises an expandable stent
portion and a stent cover, the method comprising the step of first
coating the stent cover by a method that comprises the step of
coating at least the outer surface of the stent cover portion with
a hemostatic bioactive agent that is covalently attached by the
activation of photoreactive groups provided by the stent cover
portion, by the bioactive agent, and/or by a linking agent.
22. A method according to claim 21 wherein the stent cover portion
is prepared from a porous material selected from PET and ePTFE.
23. A method according to claim 21 wherein the agent is selected
from the group consisting of proteins having a specific hemostatic
effect, and positively charged compounds having a nonspecific
hemostatic effect.
24-25. (canceled)
26. A method according to claim 21 wherein the coating is provided
on the perigraft, as opposed to luminal, surface of the stent
cover.
27. A method according to claim 21 wherein the coating adds about
5%, or less, to the original thickness of the material used as the
stent cover portion.
28. A method according to claim 21 wherein the bioactive agent used
to coat the surface is itself photoderivatized.
29-30. (canceled)
31. A method of preventing endoleaking in the course of deploying
and using an endovascular graft, the method comprising the steps
of: a) providing an endovascular graft comprising an expandable
stent portion and a stent cover portion, wherein the stent cover
portion comprises a porous, fibrous material having both an outer
perigraft surface and an inner luminal surface, the cover portion
having a hemostatic bioactive agent on at least the outer surface
in the form of a coating covalently attached to the fibers of the
material without occluding its pores, by the activation of
photoreactive groups provided by the stent cover portion, by the
bioactive agent, and/or by a linking agent, and b) implanting the
stent in the vessel in a manner that avoids endoleaking.
32. A method according to claim 31 wherein the stent cover portion
is prepared from a porous material selected from PET and ePTFE.
33. A method according to claim 31 wherein the agent is selected
from the group consisting of proteins having a specific hemostatic
effect, and positively charged compounds having a nonspecific
hemostatic effect.
34-35. (canceled)
36. A method according to claim 31 wherein the coating is provided
on the perigraft, as opposed to luminal, surface of the stent
cover.
37. A method according to claim 31 wherein the coating adds about
5%, or less, to the original thickness of the material used as the
stent cover portion.
38. A method according to claim 31 wherein the bioactive agent used
to coat the surface is itself photoderivatized.
39-40. (canceled)
41. A method according to claim 31 wherein the agent is immobilized
in an amount between about 0.05 .mu.g/cm.sup.2 to about 10
.mu.g/cm.sup.2.
42. A method according to claim 31 wherein the endovascular graft
is provided in the form of a collapsed small diameter tube of on
the order of two mm or less overall diameter, and can be expanded
to form a larger diameter tube in situ of between about six mm and
about thirty mm.
43. A method according to claim 39 wherein the bioactive agent used
to coat the surface is itself photoderivatized, and is immobilized
in an amount between about 0.05 .mu.g/cm.sup.2 to about 10
.mu.g/cm.sup.2, and wherein the endovascular graft is provided in
the form of a collapsed small diameter tube of on the order of two
mm or less overall diameter, and can be expanded to form a larger
diameter tube in situ of between about six mm and about thirty
mm.
44. A graft according to claim 1 wherein the bioactive agent is
attached to the surface in the form of a thin, conformal
coating.
45. A graft according to claim 1 wherein the coating adds no more
than 25% to the original thickness of the material used as the
stent cover portion.
46. A graft according to claim 1 wherein the stent cover portion is
prepared from a porous material selected from PET and ePFTE.
47. A graft according to claim 1 wherein the bioactive agent is
immobilized in a range of about 0.01 .mu.g/cm.sup.2 to about 50
.mu.g/cm.sup.2.
48. A graft according to claim 1 wherein the photoreactive group is
provided on the bioactive agent itself.
49. A graft according to claim 1 wherein the photoreactive group is
provided on at least the outer surface of the stent cover
portion.
50. A graft according to claim 1 wherein the coating is provided in
a manner sufficient to prevent endoleaking.
Description
TECHNICAL FIELD
[0001] The present invention relates to endovascular grafts,
particularly including endovascular grafts that include both a
rigid and expandable stent portion and a stent cover portion. In
another aspect, the invention relates to the manufacture and use of
such devices.
BACKGROUND OF THE INVENTION
[0002] Endovascular grafts (also known by such terms as endoluminal
grafts, endografts, endovascular stent grafts, expandable
transluminal grafts, vascular endoprostheses, and intravascular
stent grafts) can be broadly defined as vascular grafts that are
positioned within existing veins and arteries. As such, they can be
contrasted with non-endovascular grafts, more commonly known as
vascular grafts, which can be provided in the form of either bypass
grafts or interpositional grafts. As compared to endovascular
grafts, vascular grafts are instead positioned in a manner that
replaces a portion (interpositional), or provides a shunt (bypass)
between one or more portions, of veins or arteries, or between an
artery and a vein. Endovascular grafts have been gaining increased
attention in recent years, particularly for use in treating
aneurysms such as aortic aneurysms. An aneurysm is generally
defined as a sac formed by the pathologic dilation of an artery or
vein beyond its normal physiological diameter.
[0003] Abdominal aortic aneurysms (AAA), which are aneurysms of the
aorta in the abdominal cavity, are of particular interest, as are
thoracic aneurysms. See, for example, "Endovascular Graft Treatment
of Aortic Aneurysms: Future Perspectives", Kondo, et al., Nippon
Geka Gakkai Zasshi 100(8):506-12, (1999) (abstract), which
describes the manner in which the use of endovascular grafts to
treat aortic aneurysms, first clinically applied by Parodi et al.,
has gained popularity. Although the use of endovascular grafts were
initially limited to high-risk patients, their indications have
been gradually expanded.
[0004] A typical approach involves the initial placement of an
endovascular graft in the aneurysm, in order to exclude the
aneurysmal sac while maintaining the arterial blood flow, thus
preventing further dilatation and possible rupture of the vessel.
Over recent years, however, Kondo et al. and others have described
various instances in which aneurysms, excluded completely during
surgery, can became patent due to "endoleaking", a phenomenon that
can occur immediately or even years after the procedure.
Considering these and other features, some practitioners hold that
endovascular grafting should continue to be limited to high-risk
patients. In most cases, however, and particularly with thoracic
aortic aneurysms, endovascular treatment is considered a useful
alternative for those with localized aneurysms because of the high
perioperative morbidity accompanying conventional open repair.
[0005] With regard to the continuing concern about endoleaking,
however, see also Wain, et al., "Endoleaks after Endovascular Graft
Treatment of Aortic Aneurysms: Classification, Risk Factors, and
Outcome", J Vasc. Surg. 27(1):69-78 (1998) (abstract), which also
describes the manner in which incomplete endovascular graft
exclusion of an abdominal aortic aneurysm can result in
endoleaking.
[0006] Finally, see Jacobowitz et al., "The Significance and
Management of the Leaking Endograft", Semin. Vasc. Surg.
12(3):199-206 (1999) (abstract), which defines endoleaking as the
persistence of blood flow outside the lumen of an endograft, but
within an aneurysm sac or adjacent vessel being treated by the
graft. Diagnosis may be difficult, and treatment remains somewhat
controversial. The article discusses the clinical significance and
appropriate management of endoleaks within the context of current
understanding of this phenomenon.
[0007] On another subject, the literature provides several examples
of the use of hemostatic agents in the course of surgery.
Generally, "hemostasis" can be defined as the interruption of blood
flow to any anatomical area. Hemostasis is typically caused by
biological processes (such as clot formation) or surgical
procedures (including manual compression). The word "thrombosis",
in turn, is generally used to refer to hemostasis produced by clot
formation. A variety of commercial hemostatic products exist that
promote localized clot formation, and which generally incorporate
one or more thrombogenic proteins. Such proteins include thrombin
and certain collagens, which are known to activate platelets and/or
fibrin formation (Colman, R. W., "Mechanisms of Thrombus Formation
and Dissolution", Cardiovascular Pathol. 2:23S-31S (1993). The
primary use, currently, for such hemostatic products is to halt
diffuse bleeding from wound sites, vascular punctures, or other
surgical procedures. Examples of such products include FluoSeal
Matrix.RTM. (Fusion Medical Technologies, MountainView, Calif.) and
CoStasis.RTM. (Cohesion Corporation, Palo Alto, Calif.), each of
which is composed of thrombin mixed with bovine collagen.
Angio-Seal.RTM. (Kensey Nash Corporation, Exton, Pa.) is a
three-component preparation, one of which is bovine skin collagen.
Each of the above hemostatic products consists of two or more
components, which are mixed immediately before use.
[0008] There is a dichotomy in the medical device industry with
regard to the use of thrombogenic coatings on grafts, depending in
large part on the diameter of the graft involved. Small diameter
grafts (e.g., less than about 6 mm in diameter) are typically not
provided with thrombogenic lumenal surfaces, since to do so would
tend to promote the rapid accumulation of thrombi on the surface,
and/or to speed the invasion and proliferation of myofibroblasts
(leading to intimal hyperplasia), either or both of which processes
can tend to occlude the graft itself. Typically, therefore,
nonthromogenic coatings and materials are commonly preferred for
usein preparing small diameter bypass grafts (e.g., peripheral and
coronary artery grafts). See, for instance, Ozaki, et al., "New
Stent Technologies", Prog. Cardiovasc. Dis., 39(2):129-40
(September-October 1996) (abstract).
[0009] Large diameter vascular grafts, and particularly those
intended for use as aortic vascular grafts, are typically not prone
to being occluded in a similar fashion. To the contrary, these
grafts have a different inherent problem, namely, the tendency of
blood to seep through what are typically porous materials used to
form the graft itself. Hence these grafts can be, and often are,
coated with a hemostatic agent that acts as a barrier to blood flow
by physically occluding the pores. The pores of materials such as
polyethylene terephthalate (PET), for instance, can be plugged by a
variety of methods, including, 1) by preclotting the graft (e.g.,
dipping the grafts in the patients own blood, to permit clots to
form in the pores), or 2) by filling the pores with materials such
as crosslinked gelatins.
[0010] Hemostatic barrier agents are therefore occasionally used in
connection with conventional large diameter vascular (though
non-endovascular) grafts. Guidoin, et al., for instance, evaluated
three clinically-used PET grafts (available under the tradenames
Gelseal.TM., Hemashield.TM., and Tascon.TM.) whose pores were
filled with gelatin or collagen ("Collagen Coated Polyester
Arterial Prostheses: An Evaluation", Transplantation/Implantation
Today, pp. 21-25, February 1988). With these grafts, the applied
gelatin or collagen was crosslinked with either formaldehyde or
glutaraldehyde. When evaluated in vitro, the collagen or gelatin
"coatings" decreased water flow through the graft walls by more
than 99%, therefore confirming that each provided an immediate
physical barrier to blood flow. Additional barrier coatings that
are reported to block blood flow through the walls of polyester
grafts include albumin and alginate.
[0011] Simlarly, a variety of other coatings have been described
for use on large diameter arterial (though again, typically
non-endovascular) grafts. See for instance, Marios, et al. "In Vivo
Biocompatibility and Degradation Studies of Polyhydroxyoctanoate in
the Rat: A New Sealant for the Polyester Arterial Prosthesis",
Tissue Eng., 5(4):369-386 (1999) (abstract); Ben Slimane, et al.,
"Albumin-coated Polyester Arterial Prostheses: Is Xenogenic Albumin
Safe?", Biomater. Artif. Cells Artif. Organs. 15(2):453-81 (1987)
(abstract): Lee, et al., "Development and Characterization of an
Alginate-impregnated Polyester Vascular Graft.", J. Biomed. Mater.
Res., 36(2):200-8 (August 1997) (abstract); Chafke, et al.,
"Albumin as a Sealant for a Polyester Vascular Prosthesis: Its
Impact on the Healing Sequence in Humans.", J. Cardiovasc. Surg.,
(Torino) October;37(5):431-40 (1996) (abstract); and Ukpabi, et al.
(abstract). "The Gelweave Polyester Arterial Prosthesis", Can. J.
Surg., 38(4):322-3 (August 1995) (abstract).
[0012] For reasons that include those above, therefore, it appears
that thrombogenic agents have rarely, if ever, been used in any
connection with endovascular grafts, and then typically for reasons
quite unrelated to either coating the article itself, or in turn,
for preventing endoleaking. See, for instance, Henry, et al., "A
New Access Site Management Tool: the Angio-Seal Hemostatic Puncture
Closure Device.", J. Endovasc. Surg., 2(3):289-96 (August 1995)
(abstract) suggests that with the increasing number of
percutaneously applied endovascular therapies, the incidence of
access-related vascular complications can be expected to rise,
particularly in association with those techniques requiring large
sheaths or anticoagulation. Recognizing the need for a safe, easy
to use, and effective hemostatic technique to replace the
labor-intensive method of manual compression, the authors describe
a bioabsorbable, sheath-delivered vascular device (Angio-Seal) that
deposits a small collagen plug within the arterial wall to
mechanically seal the puncture defect.
[0013] On a separate subject, long-term responses of the body to
various materials, including those used to fabricate endovascular
grafts, have been studied as well. See, for instance Shin, et al.,
"Histology and Electron Microscopy of Explanted Bifurcated
Endovascular Aortic Grafts: Evidence of Early Incorporation and
Healing.", J. Endovasc. Surg., 6(3):246-50 (August 1999)
(abstract), which reports an examination of explanted bifurcated
endovascular aortic grafts for histologic evidence of early healing
and incorporation.
[0014] However, there are many references in the art that describe
the undesirable role of "intimal hyperplasia" in promoting
occlusions. See, for instance, Gates and Kent, 1994 in "Alternative
Bypass Conduits and Methods for Surgical Coronary
Revascularization". Few references, if any, however, describe this
or any other process of long term fibrous tissue ingrowth as being
a positive event to be encouraged with a bypass graft, let alone
with an endovascular graft.
[0015] Finally, and on yet another subject, the assignee of the
present invention has previously described a variety of
applications for the use of photochemistry, and in particular,
photoreactive groups, e.g., for attaching polymers and other
molecules to support surfaces. See, for instance, U.S. Pat. Nos.
4,722,906, 4,979,959, 5,217,492, 5,512,329, 5,563,056, 5,637,460,
5,714,360, and 5,744,515.
[0016] In spite of these various advances, however, to date there
appears to have been little if any progress made with respect to
the solving the problem of endoleaking, per se. This in spite of
the fact that the widespread acceptance and true value of
endovascular grafts are likely to remain hampered until this
problem is resolved.
SUMMARY OF THE INVENTION
[0017] The present invention comprises an endovascular graft, e.g.,
in the form of an expandable stent portion and a stent cover
portion positioned either within and/or surrounding the expandable
portion, the graft (e.g., stent cover portion) being coated with a
bioactive agent adapted to promote initial thrombus formation when
the graft is positioned within a blood vessel. Optionally, and
preferably, the coated stent and/or cover of the present invention
also provides improved fibrous tissue ingrowth over time. The term
"fibrous tissue ingrowth", as used herein, refers to the repair
process that occurs as a response to injury (in this case, the
placement of an endovascular graft), by which the body provides new
tissue containing a high density of collagen fibers.
[0018] In a preferred embodiment, the stent cover portion is
prepared from a porous material selected from PET or expanded
polytetrafluoroethylene (ePTFE), and the bioactive agent comprises
a thrombogenic agent such as collagen. In one preferred embodiment,
for instance, the bioactive agent is covalently attached in the
form of a thin (e.g., one to three monolayers), and conformal
coating on at least the outer surface of a stent cover, most
preferably by the activation of photoreactive groups provided by
either the cover material itself, by the bioactive agent itself,
and/or by a linking agent. In another aspect, the invention relates
to a method of preparing an endovascular graft that includes
coating the graft with a bioactive agent in the manner described
herein, as well as a method of using such an endovascular graft to
avoid endoleaking upon placement of the graft in vivo. With the
endovascular graft in place, and continuity of the vascular lumen
reestablished, the coating is preferably adapted to then permit, if
not encourage, long term fibrous ingrowth to occur into the stent
and/or stent cover. Hence the invention further provides a graft as
described herein, positioned within a vein or artery, and
preferably, including new fibrous tissue grown into the pores of
the graft.
[0019] A "conformal" coating, as used herein, refers to one in
which the bioactive agent has been carefully attached (e.g., to the
individual fibers making up the material, without plugging the
pores therein) in a manner that provides an optimal combination of
low bulk and effective thrombogenic effect in vivo. By contrast,
non-conformal coatings of bioactive agents on a material may
provide a thrombogenic effect, but tend to be too bulky to deliver
in the manner required. In turn, a conformal coating that provides
an inadequate amount of agent, or that provides the agent in a form
not suitably tenacious for its intended use, may permit the graft
to be delivered in a minimally invasive fashion, but will not tend
to provide bioactivity in the desired region, or in an effective
amount and duration. Hence the present invention provides an
optimal balance between such parameters as bulk, coating density
and tenacity, and ultimately, bioactivity in vivo.
DETAILED DESCRIPTION
[0020] The method of the present invention can be used in
connection with any suitable endovascular graft. Such grafts are
typically inserted into the lumen of a blood vessel to form a
barrier between the aneurysm and circulating blood, for instance,
to treat abdominal aortic aneurysms. The word "perigraft", as used
in this context, will refer to the position situated or occurring
around an endovascular graft, such that "endoleaking" (also known
as perigraft leaking), can be defined as blood flowing around the
endovascular graft and into the aneurysm itself. Such blood flow,
therefore, is generally within the perigraft space between the
ablumenal surface of the endovascular graft and the surrounding
blood vessel. The method and apparatus of this invention can be
used to provide acute perigraft hemostasis, that is, hemostasis in
the perigraft space, within on the order of an hour or less, and
more preferably within several minutes or less, of endovascular
graft placement.
[0021] Given the present description, those skilled in the art will
be able to identify and incorporate a variety of bioactive agents
for use as coatings of the present invention. Preferred bioactive
agents, for instance, can be selected from those materials
presently used as sealants or hemostatic agents in the course of
surgery, and preferably those having thrombogenic qualities. The
word "thrombosis", and inflections thereof, will be used herein to
refer to hemostasis produced by clot formation, and "thrombogenic
agents", for instance, to proteins and other agents (e.g.,
positively charged agents such as chitosan) that actively promote
clot formation.
[0022] In a preferred embodiment a "bioactive agent" of the present
invention will be thrombogenic under the conditions of use. Those
skilled in the art will appreciate the manner in which such agents
can be identified, coated and used. Preferably, for instance, both
the selection of an appropriate bioactive agent and the
effectiveness of a coating of the agent upon a stent cover can be
evaluated using a "Test Assay" as described herein.
[0023] Bioactive agents suitable for use in the present invention
include those having a specific action within the body, as well as
those having nonspecific actions. Specific action agents are
typically proteinaceous, e.g., including thrombogenic types and/or
forms of collagen, thrombin and fibrinogen (each of which tend to
provide an optimal combination of activity and cost), as well as
elastin and von Willebrand factor (which tend to be less active
and/or more expensive agents), and active portions and domains of
each of these agents. Thrombogenic proteins typically act by means
of a specific interaction with either platelets or enzymes that
participate in a cascade of events leading eventually to clot
formation.
[0024] Agents having a nonspecific thrombogenic action are
generally positively charged molecules, e.g., polymeric molecules
such as chitosan, polylysine, poly(ethylenimine) or acrylics
polymerized from acrylamide or methacrylamide which incorporate
positively-charged groups in the form of primary, secondary, or
tertiary amines or quaternary salts, or non-polymeric agents such
as benzalkonium chloride (alkyldimethylbenzylammonium chloride) and
TDMAC (tridodecylmethylammonium chloride). Positively charged
hemostatic agents promote clot formation by a non-specific
mechanism, which includes the physical adsorption of platelets via
ionic interactions between the negative charges on the surfaces of
the platelets and the positive charges of the agents
themselves.
[0025] The word "collagen", as used herein, will refer both to
native collagen, in which the molecules substantially retain their
native triple helix structure, as well as "gelatin", in which the
structure has been denatured, resulting in the partial or complete
dissociation of the triple helix strands. Native collagens include
one or more members of a class of at least 14 proteins, each of
which includes a distinctive triple helix as a part of its
structure. Type I collagen is the most abundant animal protein, is
readily isolated, and has useful physical and biological
properties. Bovine tendon and skin are two common sources of this
collagen, with nearly pure type I collagen being obtained from
tendons and skin yielding a mixture of 5% type III and 95% type I
collagen. For the above reasons, type I (.+-.5% type III) is the
collagen most commonly used to formulate medical materials
(Pachence, J. M., "Collagen-Based Devices for Soft Tissue Repair",
J. Biomed. Mater. Res. 33:35-40, 1996). Type I (native) collagen
promotes soft tissue repair when incorporated into several types of
wound dressings. Collagen type I is also capable of promoting the
attachment of fibroblasts and the production of new collagen by
such attached fibroblasts.
[0026] Another commonly available hemostatic protein is von
Willebrand factor, which is reported to mediate the adhesion of
platelets to collagen types 1, III and VI (Cruz et al.,
"Interaction of the von Willebrand Factor (vWF) with Collagen.
Localization of the Primary Collagen-Binding Site by Analysis of
Recombinant vWF A Domain Polypeptides", J. Biol. Chem.,
270:10822-10827, 1995).
[0027] Elastin and fibrinogen are two additional proteins that are
abundant in the body, hemostatic, and able to mediate wound
healing. Fibrinogen directly promotes platelet aggregation and its
product (fibrin) serves as a scaffold for wound healing (Colman,
above). The activities of elastin are indirect and are due to its
ability to bind types I and III collagens (Dutoya et al.,
"Unexpected Original Property of Elastin Derived Proteins:
Spontaneous Tight Coupling with Natural and Synthetic Polymers"
Biomaterials 19,147-155 (1998), which in turn are hemostatic and
mediate wound healing.
[0028] A hemostatic agent will typically be immobilized in an
amount between about 0.01 .mu.g/cm.sup.2 to about 50 .mu.g/cm.sup.2
of graft cover material, preferably between about 0.05
.mu.g/cm.sup.2 to about 10 .mu.g/cm.sup.2, and most preferably
between about 0.1 .mu.g/cm.sup.2 to about 5 .mu.g/cm.sup.2. Native
thrombogenic proteins will typically be active at about the middle
of the preferred range (e.g., between about 1 .mu.g/cm.sup.2 and
about 10 .mu.g/cm.sup.2), while active peptide segments are likely
to be active at about 10-fold lower concentration. Positively
charged reagents may require levels toward the upper ends of these
concentration ranges, since they tend to act in a non-specific
manner.
[0029] The endovascular grafts addressed by the application of this
invention will typically include both a stent portion adapted to be
delivered in a condensed form, and expanded in situ, as well as a
cover portion adapted to substantially prevent the flow of blood
from the lumen of the vessel itself through the walls and toward
the ablumenal surface of the endovascular graft. The cover, in
turn, can be of any suitable style or dimensions, e.g., it can
cover the internal and/or external portions or surfaces, of some or
substantially the entire length, of the expandable stent portion.
Optionally, a reagent of this invention can also be used to coat an
expandable metallic or polymeric stent with a thrombogenic layer,
i.e., without employing or coating a stent cover. Several such
stents can be deployed, for instance, in an overlapping or
superimposed manner, such that they effectively provide a
substantially impermeable barrier to the flow of blood components.
In such an embodiment, one or all of the overlapping stents can be
provided with a thrombogenic surface in the manner described
herein.
[0030] Endovascular grafts in conventional use today typically
include an expandable mesh tube covered with a fabric-like cover.
The expandable portions are generally formed of a "shape memory"
alloy such as nickel titanium alloys (referred to commonly as
"nitinol"). Endovascular grafts formed of such materials (including
both the stent and cover portions) can be collapsed to form a small
diameter tube (e.g., on the order of two mm or less overall
diameter), which can be expanded using force and/or by
self-expansion, to form a larger diameter tube in situ (e.g.,
between about six mm and about thirty mm).
[0031] The method of the present invention can be adapted for use
with a variety of available endovascular grafts and endovascular
graft designs, and in particular with "endovascular grafts" that
include an expandable (e.g., self-expanding or pressure-expandable)
stent portion which is affixed to or formed within a pliable
tubular graft. Because of their radial
compressibility/expandability, these grafts are particularly useful
in applications wherein it is desired to insert the graft into an
anatomical passageway (e.g., blood vessel) while the graft is in a
radially compact state, and to subsequently expand and anchor the
graft to the surrounding wall of the anatomical passageway.
[0032] Typically, the stent portions of such endovascular grafts
are provided in the form of metallic mesh tubes, e.g., formed in
various styles and patterns of intersecting metallic wires, strands
or bars, into a structure that permits the endovascular graft to be
collapsed or condensed for purposes of its delivery, and once in
place, expanded towards its fullest desired diameter (e.g., using a
balloon positioned within the device). Once expanded, the resultant
endovascular grafts provide a lumen sufficient to restore function
to the vessel, and provide an external (ablumenal) surface that
abuts the internal surface of the original vessel itself. Materials
commonly used or suggested for use as endovascular graft covers
include polytetrafluroethylene, expanded polytetrafluroethylene,
polyethylene terephthalate, polycarbonate, polyethyelene,
polyurethane, as well as biodegradable materials such as elastin,
polyglycolic acid, and polylactic acid.
[0033] Recent methods have been developed for introducing and
implanting tubular prosthetic vascular grafts within the lumen of a
blood vessel, by percutaneous or minimal incision means. Such
endovascular implantation initially involves translumenal delivery
of the graft, in a compacted state, by way of a catheter or other
transluminally advancable delivery apparatus. Thereafter, the graft
is radially expanded and anchored to the surrounding blood vessel
wall, thereby holding the graft at its intended site of
implantation within the host blood vessel. An affixation method,
such as proximal and distal uncovered stent portions sized to
over-expand and push into the native vessel wall, can be used to
anchor at least the opposite ends of the generally tubular graft to
the surrounding blood vessel wall.
[0034] One particular application for endovascular grafts of this
type is in the treatment of vascular aneurysms, without the need
for open surgical access and resection of the aneurysmic blood
vessel. Also, such endovascular grafts can also be used to treat
occlusive vascular disease--especially, in cases where the graft is
constructed in such a manner that the tubular graft material forms
a complete barrier between the endovascular graft and the blood
flowing through the blood vessel. In this manner the tubular graft
material can serve as a smooth, biologically compatible, inner
"covering" for the endovascular graft, thereby serving to: a)
prevent turbulent blood-flow as the blood flows over the wire
members or other structural material of which the endovascular
graft is formed; b) prevent immunologic reaction to the metal or
other material of which the endovascular graft is formed; and c)
provide a barrier to separate a diseased or damaged segment of
blood vessel from the blood-flow passing therethrough. The
prevention of turbulent blood-flow and/or immunologic reaction to
the endovascular graft material are particularly desirable since
both phenomena are thought to be associated with thrombus formation
and/or restenosis of the blood vessel.
[0035] Coated endovascular grafts of the present invention are
particularly useful, for instance, in repair of the aorta, vena
cava, femoral artery and vein, iliac artery and vein, subclavian
artery and vein, tibial artery, peroneal artery, saphenous vein,
pulmonary artery and vein, coronary arteries, carotid artery,
jugular vein, radial artery, subclavian artery.
[0036] In the method of this invention, a bioactive agent is coated
on an endovascular graft cover in order to provide the desired
level of thrombogenicity (acute hemostasis) under the conditions of
deployment and use in vivo. In a preferred embodiment, the coating
provides an optimal combination of such properties as low bulk,
coating density, coating tenacity, and bioactivity in vivo. Given
these functional requirements, and depending on such variables as
the type of endovascular graft cover, the method of endovascular
graft deployment, and the bioactivity of the agent itself, those
skilled in the art will be able to determine an optimal manner of
coating a endovascular graft cover for any particular combination
of bioactive agent, endovascular graft cover material, and
endovascular graft design.
[0037] The coating agent of this invention can be coated on the
endovascular graft cover in any suitable manner (e.g., by dipping,
spraying or brushing) within the skill of those in the relevant
art. In a preferred embodiment, a bioactive agent is first
derivatized with photogroups, and then brought into contact (i.e.,
sufficient proximity to permit binding) with a previously formed
graft cover. The photoreactive groups are then energized via an
external stimulation (e.g., exposure to a suitable light source) to
form via free active specie generation, a covalent bond between the
agent and either another reagent molecule, the cover surface, or
chemical moieties present in the coating solution itself and/or
upon the surface. This coating method can be referred to as a "one
step" method, since photoreactive coupling chemistry attaches the
bioactive agent to the cover surface, and no subsequent steps
(other than perhaps washing steps) are required. The external
stimulation that is used is preferably in the form of
electromagnetic radiation, and preferably is radiation in the
ultraviolet, visible or infrared regions of the electromagnetic
spectrum.
[0038] The coating can be applied at the time of manufacture of the
material itself, in the course of its fabrication into a
endovascular graft cover, and/or at the time of use. Suitable
non-photoreactive methods for coating such materials (in either a
covalent or noncovalent fashion) are described in Hoffman, A. S.,
"Immobilization of Biomolecules and Cells on and within Polymeric
Biomaterials", Clin. Mat. 11:61-66 (1992), the disclosure of which
is incorporated herein by reference.
[0039] One suitable method for covalent coupling to the surface
involves an initial step of adding a reactive group to the surface
(e.g., amine, carboxyl, etc.), for instance, by the application of
ionizing radiation, plasma gas discharge, chemical derivatization,
etc. This can be followed by the use of thermochemical crosslinking
reagents to couple the hemostatic agent to the surface bound
reactive group. Yet other methods can be used to form films around
fibers, for instance, using thermochemical crosslinking reagents to
crosslink thin films of the hemostatic agent around individual
fibers. Other methods, though generally less preferred, can be used
to enhance the adsorption of coating agent to the material, e.g.,
denucleation in ethanol followed by adsorption from phosphate
buffered saline (PBS) (see, e.g., Poole-Warren et. al., J. Biomed.
Mater. Res., 30:221-229 (1996) used this method to adsorb
fibronectin onto ePTFE). In yet another approach, hydrophobic
"anchor" groups are added to the hemostatic agent to increase
adsorption to implant device polymers. Haverstick, et .al., Trans.
Soc. Biomat., 22:287 (1999) have used this method to immobilize ECM
peptides onto hydrophobic substrates.
[0040] In one preferred embodiment, for instance, a thin, conformal
coating of this invention is provided on the perigraft surface
(i.e., the external, vessel-contacting surface of the graft itself)
and optionally within the pores of the material itself. The coating
agent is preferably not coated on the interior (luminal) surface of
the graft, since its presence there is likely to be inconsequential
at best, and detrimental at worst. The coating agent can be coated,
for instance, as a thin conforming layer on and/or around
individual fibers of the graft.
[0041] A coating of the present invention will typically not add
significantly to the bulk of the graft, or interfere with its
delivery via a catheter. Nor, in turn, will it interfere with (and
preferably will enhance) long term ingrowth by fibrous tissue.
Surprisingly, it has been found that bioactive agents can be coated
in a manner that provides suitable physical qualities (e.g., bulk,
tenacity), chemical qualities (e.g., biocompatibility), and
biological qualitites (e.g., hemostatic activity) sufficient to
lessen or avoid endoleaking yet permit the graft to be delivered
and positioned in a minimally invasive fashion (typically, through
a catheter). In a preferred embodiment, an effective coating of
this invention adds about 25%, or less, preferably about 10%, or
less, and most preferably about 5%, or less, to the original
thickness of the material used as the stent cover portion. In this
manner the resultant endovascular graft can be packaged and
delivered in substantially the manner originally intended by the
manufacturer.
[0042] Typically, it is not desirable to have the coating fill the
pores within the graft. The coating agent can be attached to the
surface in any suitable manner, e.g., it can be passively adsorbed,
entrapped, or covalently bound to the surface itself, or to a
coating that is itself positioned within or upon the surface, so
long as the coating is sufficiently tenacious and effective for its
intended use (e.g., is not removed by flowing blood or by the
abrasion associated with delivery via catheter). As such, the
coating can be in any suitable form, e.g., impregnated within the
pores of the cover itself, as a discrete layer thereon, or as a
coating (e.g., film) around the individual fibers of a fabric.
[0043] Preferably, the coating agent is covalently atached by
photochemical means, e.g., in the manner described in the
approaches described in U.S. Pat. Nos. 4,722,906, 4,979,959,
5,217,492, 5,512,329, 5,563,056, 5,637,460, 5,714,360, and
5,744,515. In a particularly preferred embodiment, for instance,
various types of collagen can be photoderivatized (e.g., with
BBA-EAC-NOS) and radiolabeled using protocols for derivatizing
proteins as described in U.S. Pat. No. 5,744,515; columns 13 and 14
(Method and Implantable Article for Promoting
Endothelialization).
[0044] A preferred composition of this invention includes one or
more pendent latent reactive (preferably photoreactive) groups
covalently attached, directly or indirectly, to either the surface
of the endovascular graft cover, to the bioactive agent itself, or
to a linking moeity for use in attaching an agent to a surface.
Photoreactive groups are defmed herein, and preferred groups are
sufficiently stable to be stored under conditions in which they
retain such properties. See, e.g., U.S. Pat. No. 5,002,582, the
disclosure of which is incorporated herein by reference. Latent
reactive groups can be chosen that are responsive to various
portions of the electromagnetic spectrum, with those responsive to
ultraviolet and visible portions of the spectrum (referred to
herein as "photoreactive") being particularly preferred.
[0045] Photoreactive groups respond to specific applied external
stimuli to undergo active specie generation with resultant covalent
bonding to an adjacent chemical structure, e.g., as provided by the
same or a different molecule. Photoreactive groups are those groups
of atoms in a molecule that retain their covalent bonds unchanged
under conditions of storage but that, upon activation by an
external energy source, form covalent bonds with other
molecules.
[0046] The photoreactive groups generate active species such as
free radicals and particularly nitrenes, carbenes, and excited
states of ketones upon absorption of electromagnetic energy.
Photoreactive groups may be chosen to be responsive to various
portions of the electromagnetic spectrum, and photoreactive groups
that are responsive to e.g., ultraviolet and visible portions of
the spectrum are preferred and may be referred to herein
occasionally as "photochemical group" or "photogroup".
[0047] Photoreactive aryl ketones are preferred, such as
acetophenone, benzophenone, anthraquinone, anthrone, and
anthrone-like heterocycles (i.e., heterocyclic analogs of anthrone
such as those having N, O, or S in the 10-position), or their
substituted (e.g., ring substituted) derivatives. Examples of
preferred aryl ketones include heterocyclic derivatives of
anthrone, including acridone, xanthone, and thioxanthone, and their
ring substituted derivatives. Particularly preferred are
thioxanthone, and its derivatives, having excitation energies
greater than about 360 nm.
[0048] The functional groups of such ketones are preferred since
they are readily capable of undergoing the
activation/inactivation/reactivation cycle described herein.
Benzophenone is a particularly preferred photoreactive moiety,
since it is capable of photochemical excitation with the initial
formation of an excited singlet state that undergoes intersystem
crossing to the triplet state. The excited triplet state can insert
into carbon-hydrogen bonds by abstraction of a hydrogen atom (from
a support surface, for example), thus creating a radical pair.
Subsequent collapse of the radical pair leads to formation of a new
carbon-carbon bond. If a reactive bond (e.g., carbon-hydrogen) is
not available for bonding, the ultraviolet light-induced excitation
of the benzophenone group is reversible and the molecule returns to
ground state energy level upon removal of the energy source.
Photoactivatible aryl ketones such as benzophenone and acetophenone
are of particular importance inasmuch as these groups are subject
to multiple reactivation in water and hence provide increased
coating efficiency.
[0049] The azides constitute a preferred class of photoreactive
groups and include arylazides (C.sub.6R.sub.5N.sub.3) such as
phenyl azide and particularly 4-fluoro-3-nitrophenyl azide, acyl
azides (--CO--N.sub.3) such as benzoyl azide and p-methylbenzoyl
azide, azido formates (--O--CO--N.sub.3) such as ethyl
azidoformate, phenyl azidoformate, sulfonyl azides
(--SO.sub.2--N.sub.3) such as benzenesulfonyl azide, and phosphoryl
azides (RO).sub.2PON.sub.3 such as diphenyl phosphoryl azide and
diethyl phosphoryl azide. Diazo compounds constitute another class
of photoreactive groups and include diazoalkanes (--CHN.sub.2) such
as diazomethane and diphenyldiazomethane, diazoketones
(--CO--CHN.sub.2) such as diazoacetophenone and
1-trifluoromethyl-1-diazo-2-pentanone, diazoacetates
(--O--CO--CHN.sub.2) such as t-butyl diazoacetate and phenyl
diazoacetate, and beta-keto-alpha-diazoacetates
(--CO--CN.sub.2--CO--O--) such as t-butyl alpha diazoacetoacetate.
Other photoreactive groups include the diazirines (--CHN.sub.2)
such as 3-trifluoromethyl-3-phenyldiazirine, and ketenes
(--CH.dbd.C.dbd.O) such as ketene and diphenylketene.
[0050] Upon activation of the photoreactive groups, the reagent
molecules are covalently bound to each other and/or to the material
surface by covalent bonds through residues of the photoreactive
groups. Exemplary photoreactive groups, and their residues upon
activation, are shown as follows (where R and R' are independently
non-interfering organic radicals): TABLE-US-00001 Residue
Photoreactive Group Functionality aryl azides amine R--NH--R' acyl
azides amide R--CO--NH--R' azidoformates carbamate R--O--CO--NH--R'
sulfonyl azides sulfonamide R--SO.sub.2--NH--R' phosphoryl azides
phosphoramide (RO).sub.2PO--NH--R' diazoalkanes new C--C bond
diazoketones new C--C bond and ketone diazoacetates new C--C bond
and ester beta-keto-alpha- new C--C bond diazoacetates and
beta-ketoester aliphatic azo new C--C bond diazirines new C--C bond
ketenes new C--C bond photoactivated new C--C bond ketones and
alcohol
Test Assay
[0051] An assay can be performed in the following manner in order
to evaluate the usefulness of a particular bioactive agent and
manner of coating. The assay, based on a canine model, is used to
evaluate and predict the manner and/or extent to which an
endovascular graft (the cover portion of which has been treated
with a bioactive agent) can prevent endoleaking when positioned in
vivo. The canine model has been extensively used to evaluate the in
vivo performance of vascular grafts, and Applicants have determined
the manner in which the intercostal arteries in the dog provide a
unique ability to evaluate endoleaking.
[0052] A standard endovascular graft is provided, e.g., in the form
of a hook-less, nitinol spring graft system covered with a
polymeric (e.g., PET) material. The device cover is coated with the
bioactive agent to be evaluated for use in preventing endoleaking.
At the end of the implant phase (12 weeks) the animals are
anesthetized and the grafts removed. Upon recovery, the grafts are
processed for light microscopy.
[0053] The grafts are inserted through the femoral artery and
placed in the aorta of a dog, just distal to the renal artery.
After insertion, an angiogram (at about 30 minutes) is performed to
evaluate perigraft blood flow, which is visualized as blood flowing
through adjacent intercostal arteries (and particularly those in
the region of the aorta that are covered by the endovascular
graft). Grafts with an effective coating will substantially prevent
both acute and long-term blood flow through adjacent intercostal
arteries. Uncoated grafts (or unsuitably coated grafts), by
comparison, will not prevent acute perigraft blood flow; however
some such grafts may prevent blood flow at 12 weeks.
[0054] In addition, the grafts and adjacent aorta are removed at 12
weeks, fixed and evaluated histologically for tissue ingrowth.
Grafts with an effective coating will preferably also have the
perigraft region largely filled with stable tissue (smooth muscle
cells and/or myofibroblasts). Uncoated grafts may have channels
through which blood flows from the lumen of the aorta into the
perigraft space and out through the intercostal arteries. If the
dog model reproduced results observed in human patients, about
20-25% of the uncoated grafts at 12 weeks would show perigraft
blood flow during angiography and corresponding perigraft blood
channels upon histological evaluation.
[0055] In evaluating and comparing uncoated (or unsuitably) coated
grafts with those coated in the manner presently described, it can
be seen that detectable endoleaking will occur in substantially
none (<5%) of coated grafts when evaluated one-half hour after
placement (the initial angiogram). By comparison, substantially all
(>95%) of the uncoated (or unsuitably) coated grafts will show
detectable endoleaking. At 12 weeks, it can be seen that the coated
grafts of this invention will continue to prevent detectable
endoleaking in substantially all cases (i.e., detectable
endoleaking in less than 5% of the cases), as compared to the
uncoated grafts, in which detectable endoleaking is likely to
continue in up to 20% of the cases.
Protocol
[0056] 12 Canine animals are used (conditioned mongrels, approx.
27-45 kg, may include both sexes). A pretrial screen is performed
to ensure the good general health status of the animals. On the day
of surgery, the animals are premedicated with a mixture of
intramuscular ketamine, acepromazine and atropine. General
anesthesia is induced using intravenous pentothal and the airway
maintained with orotracheal intubation. Anesthesia is maintained
with a mixture of inhaled halothane and oxygen. The inner thigh is
shaved and prepared with betadine. Intravenous cephalexin 500 mg is
given prior to the initial incision.
[0057] For deploying the graft the inner thigh is prepared for a
cut-down to the femoral artery. Heparin is administered, 3,000
units IV, prior to catheter insertion. The femoral artery is
isolated and an arteriotomy performed on the artery. A 7 to 9 FR
introducer sheath is inserted in the artery. An angiographic
catheter is introduced and an angiogram is performed. All
angiographic and fluoroscopic procedures are recorded on VCR. The
aortic-iliac vasculature is mapped with the diameter of the aorta
measured and location of the renal arteries determined. A guide
wire is inserted and the catheter removed. The endovascular graft
is then inserted over the guide wire and advanced to the proximal
position below the renal arteries. Once the device is in the proper
position, the central balloon catheter is withdrawn and inflated
along the entire length of the device as per the manufacturer's
procedures. The delivery catheter is removed and the sheath and
angiographic catheter replaced in the vessel. An angiogram is
performed and any abnormalities are observed. If abnormalities are
observed, the balloon catheter may be reintroduced to correct the
situation. The catheter, guide wire and sheath are removed and the
arteriotomy repaired. The incision is closed and the dog
recovered.
[0058] An additional angiogram is performed 30 minutes after
implantation to evaluate perigraft blood flow, as indicated by flow
through intercostal arteries in the region of the aorta that is
covered by the endovascular graft. At 12 weeks, the dogs are
re-anesthetized and another angiogram is performed to evaluate
perigraft blood flow. Then the grafts are surgically recovered. The
graft is exposed under aseptic sterile conditions through an
abdominal midline laparotomy. Heparin is administered IV five
minutes prior to clamping of the aorta proximal and distal to the
endovascular graft. Photographs are taken of the graft in situ. The
graft is excised with at least 2 cm of the aorta at both
anastomoses. The excised graft is placed in sterile buffer
(Dulbecco's CF PBS; pH 7.4 with 1% bovine serum albumin). Animals
are euthanized after graft harvest using intravenous
B-euthanasia-D.RTM. solution. The graft is cut into sections,
placed in labeled containers with Histochoice.TM. fixative for
light microscopy.
[0059] Each graft is stained with hematoxylin/eosin (H&E) and
Masson trichrome. The samples are also immunostained for von
Willebrand factor (vWF), .alpha. smooth muscle cell actin
(.alpha.SMC actin) and proliferating cell nuclear antigen (PCNA).
The slides are examined and photomicrographs taken. In addition,
the slides are analyzed for neointimal thickness. Cells both within
the graft and in the tissue associated with the graft are
characterized.
Data Analysis
[0060] Angiographic evaluation of grafts with an effective coating
of this invention will show unimpeded blood flow through the lumen
of the graft but no blood flow through adjacent intercostal
artieries when evaluated at either the initial angiogram after
implantation or at 12 weeks. In addition, histological evaluation
of such grafts at 12 weeks preferably shows the perigraft space to
be filled with a high density of cells that stain positive with
.alpha.SMC actin (smooth muscle cells and/or myofibroblasts). The
perigraft space around such grafts lacks channels that would allow
blood to flow from the aorta to the intercostal arteries. The lumen
of such grafts does not contain sufficient thrombus or layers of
cells to significantly reduce blood flow through the aorta.
Uncoated grafts or grafts with unsuitable coatings produce two
types of detrimental features, namely either: 1) blood flow from
the aorta through channels in the perigraft space and into
intercostal arteries, and/or 2) the formation of thrombus or
excessive layers of cells on the luminal surface, which
significantly decreased blood flow through the aorta.
[0061] The invention will be further described with reference to
the following non-limiting Example. It will be apparent to those
skilled in the art that many changes can be made in the embodiments
described without departing from the scope of the present
invention. Thus the scope of the present invention should not be
limited to the embodiments described in this application, but only
by embodiments described by the language of the claims and the
equivalents of those embodiments. Unless otherwise indicated, all
percentages are by weight.
EXAMPLE
[0062] Four dogs were studied in the manner described above, with
two dogs receiving uncoated grafts and two receiving grafts coated
with collagen.
[0063] Bovine skin collagen (Semed S Powder) was purchased from
Kensey Nash Corporation (Exton, Pa.). This collagen has the
proportions of type 1 collagen (95%) and type III collagen (5%)
that are usual for skin-derived collagens. Such collagen is
abbreviated below as Col I-S. Col I-S was photoderivatized by the
addition of (benzoylbenzoic acid)--(epsilon aminocaproic
acid)--(N-oxysuccinimide) (BBA-EAC-NOS) and radiolabeled using
protocols described in U.S. Pat. No. 5,744,515 (columns 13 and 14).
Photoderivatized Col I-S is abbreviated below as photo-Col I-S.
[0064] The coating procedure consisted of immersing endovascular
grafts in a solution of photo-Col I-S, removing the grafts, and
illuminating for 2.5 minutes at 320 to 340 nm to activate the BBA
moieties and produce covalent coupling. The above coating steps
were repeated to generate 2 coats of photo-Col I-S. The coated
grafts were then washed in sterile phosphate buffered saline (PBS)
to remove loosely adherent photo-Col I-S, sterilized by soaking for
30 minutes in 70% ethanol, and washed in sterile PBS to remove
ethanol. Coated grafts were stored prior to implantation at
4.degree. C. in PBS plus antibiotics (10 units penicillin G, 10
.mu.g steptromycin, 0.025 .mu.g amphotericin B per ml.).
[0065] The amount of immobilized photo-Col I-S was quantitated by
applying tritium-labeled photo-Col I-S as described above and
measuring retained counts via standard liquid scintillation
spectrometry methods. The amount of immobilized photo-Col I-S was
found to be 1.8 .mu.g of photo-Col I-S per square cm of
endovascular graft material. The coating process can be shown to
immobilize photo-Col-I-S in a conformal manner, in that the coating
is substantially uniform in coverage, but does not significantly
fill the pores between adjacent polymer fibers (less than 10% of
the pore volume is filled by the coating material). Coating
conformity can be evalutated by staining coated grafts with FITC
(fluorescein-5-isothiocyanate) and viewing the stained grafts via
fluorescence microscopy. When stained and viewed in this manner the
individual polymer fibers of the coated endovascular grafts appear
uniformly green in color, with the spaces between such fibers
appearing black (i.e., unfilled).
[0066] During the implant procedures all devices deployed easily.
The use of a balloon catheter following initial deployment
completed the expansion of the devices. Angiograms performed
following device deployment revealed unimpeded flow through the
lumen of each of the devices. Endoleaking was not detected in
either of the coated grafts, but was detected in both of the
uncoated grafts, as evidenced by contrast agent present in branch
vessels off the aorta. Comparison of device position, both before
and after re-establishment of blood flow, indicated that all
devices remained in their initial position with no evidence of
device movement within the aorta. At the time of device
explantation (12 weeks), a repeat angiogram was performed. Neither
coated nor uncoated grafts showed blood flow through intercostal
arteries, evidence of gross lumenal thickening, or loss of lumenal
patency.
[0067] All explant samples were subjected to histologic evaluation
which included hematoxylin and eosin (H&E) staining, and
immunocytochemical evaluation of von Willebrand factor positive
cells (endothelium), alpha smooth muscle cell actin positive cells
(smooth muscle/myofibroblasts), and proliferating cell nuclear
antigen positive cells (cell proliferation/hyperplasia).
[0068] Microscopic evaluation of H&E stained sections revealed
no significant difference between coated and uncoated grafts. A
cellular lining (defined as a neointima) was evident on all
samples; however the thickness of the neointima was not sufficient
to significantly decrease the lumenal diameter. No thrombus
formation was observed.
[0069] Immunocytochemistry confirmed the presence of endothelial
cells on the lumenal surface (positive staining with vWF
antibodies). The cell layers under the endothelium (in the
neointima, within the fibers of the graft, and in the perivascular
space) were composed predominantly of cells that stained positive
with antibodies to .alpha.SMC actin, suggesting the predominance of
smooth muscle cells or myofibroblasts.
* * * * *