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Medical devices for delivering a therapeutic agent and method of preparationRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Stent Combined With Surgical Delivery System (e.g., Surgical Tools, Delivery Sheath, Etc.)Medical devices for delivering a therapeutic agent and method of preparation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080051871, Medical devices for delivering a therapeutic agent and method of preparation. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application is a Continuation of U.S. application Ser. No. 11/292,171, filed Nov. 30, 2005, which is a Continuation of U.S. application Ser. No. 10/147,872, filed May 20, 2002, now U.S. Pat. No. 6,997,949, which is a Continuation of U.S. application Ser. No. 09/070,192, filed Apr. 30, 1998, now abandoned, which is a Continuation-in-Part of Ser. No. 08/728,541, filed Oct. 9, 1996, now U.S. Pat. No. 5,776,184, which is a Divisional of U.S. application Ser. No. 08/482,346, filed Jun. 7, 1995, now U.S. Pat. No. 5,679,400, which is a Continuation-in-Part of U.S. application Ser. No. 08/052,878, filed Apr. 26, 1993, now U.S. Pat. No. 5,464,650, the disclosures of which are all incorporated herein, in their entirety, by reference thereto. BACKGROUND OF THE INVENTION Field of the Invention [0002] This invention relates to a medical device employing a therapeutic agent as a component thereof. For example, in an arterial site treated with percutaneous transluminal coronary angioplasty therapy for obstructive coronary artery disease a therapeutic antithrombogenic substance such as heparin may be included with a device and delivered locally in the coronary artery. Also provided is a method for making a medical device capable of localized application of therapeutic agents. [0003] Medical devices which serve as substitute blood vessels, synthetic and intraocular lenses, electrodes, catheters, and the like, in and on the body, or as extracorporeal devices intended to be connected to the body to assist in surgery or dialysis are well known. For example, intravascular procedures can bring medical devices into contact with the patient's vasculature. In treating a narrowing or constriction of a duct or canal percutaneous transluminal coronary angioplasty (PTCA) is often used with the insertion and inflation of a balloon catheter into a stenotic vessel. Other intravascular invasive therapies include atherectomy (mechanical systems to remove plaque residing inside an artery), laser ablative therapy, and the like. However, this use of mechanical repairs can have adverse consequences for the patient. For example, restenosis at the site of a prior invasive coronary artery disease therapy can occur. Although angioplasty procedures have increased greatly in popularity for treatment of occluded arteries, the problem of restenosis following the angioplasty treatment remains a significant problem. Restenosis is the closure of a peripheral or coronary artery following trauma to the artery caused by efforts to open an occluded portion of the artery by angioplasty, such as, for example, by balloon dilation, atherectomy or laser ablation treatment of the artery. For these angioplasty procedures, restenosis occurs at a rate of about 30-60% depending upon the vessel location, lesion length and a number of other variables. Restenosis, defined angiographically, is the recurrence of a 50% or greater narrowing of a luminal diameter at the site of a prior coronary artery disease therapy, such as a balloon dilatation in the case of PTCA therapy. In particular, an intra-luminal component of restenosis develops near the end of the healing process initiated by vascular injury, which then contributes to the narrowing of the luminal diameter. This phenomenon is sometimes referred to as "intimal hyperplasia." It is believed that a variety of biologic factors are involved in restenosis, such as the extent of the injury, platelets, inflammatory cells, growth factors, cytokines, endothelial cells, smooth muscle cells, and extracellular matrix production, to name a few. [0004] Attempts to inhibit or diminish restenosis often include additional interventions such as the use of intravascular stents and the intravascular administration of pharmacological therapeutic agents. One aspect of restenosis may be simply mechanical; e.g. caused by the elastic rebound of the arterial wall and/or by dissections in the vessel wall caused by the angioplasty procedure. These mechanical problems have been successfully addressed by the use of stents to tack-up dissections and prevent elastic rebound of the vessel, thereby reducing the level of restenosis for many patients. The stent is typically inserted by catheter into a vascular lumen and expanded into contact with the diseased portion of the arterial wall, thereby providing internal support for the lumen. Examples of stents which have been successfully applied over a PTCA balloon and radially expanded at the same time as the balloon expansion of an affected artery include the stents disclosed in U.S. Pat. No. 4,733,665 (Palmaz), U.S. Pat. No. 4,800,882 (Gianturco), and U.S. Pat. No. 4,886,062 (Wiktor). [0005] Also, such stents employing therapeutic agents such as glucocorticoids (e.g. dexamethasone, beclamethasone), heparin, hirudin, tocopherol, angiopeptin, aspirin, ACE inhibitors, growth factors, oligonucleotides, and, more generally, antiplatelet agents, anticoagulant agents, antimitotic agents, antioxidants, antimetabolite agents, and anti-inflammatory agents have been considered for their potential to solve the problem of restenosis. Such substances have been incorporated into (or onto) stents by a variety of mechanisms. These mechanisms involve incorporating the therapeutic agents into polymeric coatings and films, including hydrogels, as well as covalently binding the therapeutic agents to the surface of the stent. [0006] For example, therapeutic agents have been dissolved or dispersed in a solution of polymer in an organic solvent. This is then sprayed onto the stent and allowed to dry. Alternatively, therapeutic agents have been incorporated into a solid composite with a polymer in an adherent layer on a stent body with fibrin in a separate adherent layer on the composite to form a two layer system. The fibrin is optionally incorporated into a porous polymer layer in this two layer system. The therapeutic agent, however, is incorporated into the underlying solid polymer. The overlying porous polymer layer provides a porous barrier through which the therapeutic agent is transferred. [0007] Conventional methods of loading the therapeutic agent into a polymer, such as spray coating, do not provide high concentrations of therapeutic agents. Typically, upon spray coating a therapeutic agent onto a stent body, only about 2 percent of the spray is captured by the stent. This can be prohibitively expensive for therapeutic agents that are extremely costly and scarce, such as peptidic drugs. [0008] Thus, what is needed is a medical device, preferably, a stent, having a porous polymeric material, typically a polymer layer in the form of a coating or film, with a therapeutic agent incorporated therein at sufficiently high concentrations that the therapeutic agent can be delivered over an extended period of time. Improved methods by which the therapeutic agent can be incorporated into the porous polymeric material with lower levels of waste are also needed. [0009] This invention also relates to intravascular stents for treatment of injuries to blood vessels and particularly to stents having a framework onto which a therapeutic substance or drug is applied. [0010] Metal stents such as those disclosed in U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco or U.S. Pat. No. 4,886,062 issued to Wiktor could be suitable for drug delivery in that they are capable of maintaining intimate contact between a substance applied to the outer surface of the stent and the tissues of the vessel to be treated. However, there are significant problems to be overcome in order to secure a therapeutically significant amount of a substance onto the metal of the stent; to keep it on the stent during expansion of the stent into contact with the blood vessel wall; and also controlling the rate of drug delivery from the drug on the stent to the vessel wall. [0011] It is therefore another object of the present invention to provide a stent having a therapeutically significant amount of a drug applied thereto. [0012] It is also an object of the present invention to provide a stent which may be delivered and expanded in a selected blood vessel without losing a therapeutically significant amount of a drug applied thereto. [0013] It is also an object of the present invention to provide a drug-containing stent which allows for a sustained release of the drug to vascular tissue. [0014] It is also an object of the present invention to provide a simple method for applying to a stent a coating of a therapeutic substance. SUMMARY OF THE INVENTION [0015] This invention relates to a medical device having a porous polymeric material with a therapeutic agent therein. Preferably, the device according to the invention is capable of applying a highly localized therapeutic agent into a body lumen to treat or prevent injury. The term "injury" means a trauma, that may be incidental to surgery or other treatment methods including deployment of a stent, or a biologic disease, such as an immune response or cell proliferation caused by the administration of growth factors. In addition, the methods of the invention may be performed in anticipation of "injury" as a prophylactic. A prophylactic treatment is one that is provided in advance of any symptom of injury in order to prevent injury, prevent progression of injury or attenuate any subsequent onset of a symptom of such injury. [0016] In accordance with the invention, a device for delivery of localized therapeutic agent includes a structure including a porous material and an elutable (i.e., capable of being dissolved under physiological conditions) therapeutic agent in the form of a solid, gel, or neat liquid, which is dispersed throughout at least a portion, and preferably a substantial portion, of the porous material. Preferably, the device is capable of being implanted in a body so that the localized therapeutic agent can be delivered in vivo, typically at a site of vascular injury or trauma. Preferably, the porous material is biocompatible, sufficiently tear-resistant, and nonthrombogenic. [0017] The porous material may be a layer (e.g., a film, i.e., a sheet material or a coating) on at least a portion of the structure. Alternatively, the porous material may be an integral portion of the structure. Preferably, the porous material is a polymeric material selected from the group of a natural hydrogel, a synthetic hydrogel, silicone, polyurethane, polysulfone, cellulose, polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, and a combination of two or more of these materials. Examples of natural hydrogels include fibrin, collagen, elastin, and the like. More preferably, the porous polymeric material is a nonswelling biostable polymer selected from the group of silicone, polyurethane, polysulfone, cellulose, polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, and a combination of two or more of these materials. [0018] The therapeutic agent can be one or more of a wide variety of therapeutic agents, including peptidic drugs. Preferably, the therapeutic agent includes an antithrombotic material. More preferably, the antithrombotic material is a heparin or heparin derivative or analog. Such therapeutic agents are soluble in water such that they elute from the porous polymeric material. [0019] The structure of the device can be adapted for its intended extracorporeal or intravascular purpose in an internal human body site, such as an artery, vein, urethra, other body lumens, cavities, and the like or in an extracorporeal blood pump, blood filter, blood oxygenator or tubing. In one aspect of the invention, the shape is preferably generally cylindrical, and more preferably, the shape is that of a catheter, a stent, or a guide wire. In particularly preferred embodiments, the medical device is an intralumenal stent. [0020] The invention also provides methods for making a medical device which includes therapeutic agents. In one embodiment, a method of the invention includes: providing a structure comprising a porous material; contacting the structure comprising a porous material with a concentrating agent to disperse the concentrating agent throughout at least a portion of the porous material; contacting the structure comprising a porous material and the concentrating agent with a solution of a therapeutic agent; and removing the therapeutic agent from solution within the porous material at the locations of the concentrating agent. Continue reading about Medical devices for delivering a therapeutic agent and method of preparation... 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