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Endovascular graft coatingsRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Stent In Combination With GraftEndovascular graft coatings description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070173922, Endovascular graft coatings. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of co-pending U.S. Application Ser. No. 09/519,246 filed Mar. 6, 2000 and is herein incorporated by reference. TECHNICAL FIELD [0002] 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 [0003] 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. [0004] 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. [0005] 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. [0006] 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. [0007] 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. [0008] 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. [0009] 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 (Sept-Oct 1996) (abstract). [0010] 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. [0011] 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. [0012] 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 (Aug. 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) Oct;37(5):431-40 (1996)(abstract); and Ukpabi, et al. (abstract). "The Gelweave Polyester Arterial Prosthesis", Can. J Surg., 38(4):322-3 (Aug. 1995) (abstract). [0013] 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 (Aug. 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. [0014] 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 (Aug. 1999)(abstract), which reports an examination of explanted bifurcated endovascular aortic grafts for histologic evidence of early healing and incorporation. [0015] 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. [0016] 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. [0017] 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 [0018] 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. [0019] 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. [0020] 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. Continue reading about Endovascular graft coatings... Full patent description for Endovascular graft coatings Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Endovascular graft coatings patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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