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Degradable implantable medical devicesRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Arterial Prosthesis (i.e., Blood Vessel), Absorbable In Natural TissueDegradable implantable medical devices description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060229711, Degradable implantable medical devices. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application No. 60/668,707 (Attorney Docket No. 022265-000200US), filed on Apr. 5, 2005, incorporated herein by reference for all purposes. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to medical devices and methods. More particularly, the present invention relates to implantable luminal prostheses and other medical devices which degrade in a body environment. [0004] 2. Description of the Background Art [0005] Coronary artery disease is the leading cause of death in the industrialized countries around the world. It begins as the accumulation of atherosclerotic deposits in the walls of the major arteries which supply blood to the heart. As the deposits accumulate, normal blood flow to the heart is restricted. The heart has several compensatory mechanisms, which, to a point, can offset such diminished blood flow. Beyond these compensatory mechanisms, a number of well established pharmaceutical treatments have been shown to improve both symptoms and mortality in patients with mild to moderate coronary artery disease. However, as the disease progresses, its symptoms become more apparent, despite drug therapy. When the heart does not get enough blood, particularly during exercise or stress, advanced coronary artery disease is manifested as debilitating chest pain or angina. At this point, mechanical intervention is required to increase the amount of blood flowing to the heart. [0006] Angioplasty is one of the most common interventional treatments for advanced coronary artery disease. Andreas Gruntzig performed the first percutaneous transluminal coronary angioplasty (PTCA) procedure. He advanced a catheter with a small balloon through the aorta and into a coronary artery with a partial occlusion. He then inflated the balloon, compressing the plaque against the arterial wall, and restoring blood flow to the heart. [0007] PTCA has grown rapidly, and angioplasty catheters have become smaller and more maneuverable, allowing interventional cardiologists to access more difficult coronary blockages. However, restenosis, or reocclusion of the treated lesion, has plagued PTCA. Typically 30-40% of all patients have restenosis following PTCA. [0008] Coronary stents were introduced in the mid 1990's to prevent restenosis. A stent is a small metal coil, slotted tube, mesh or scaffold structure that is placed in a coronary artery. It is a permanent implant that remains in the coronary artery following PTCA. The stent helps hold the artery open, improves the flow of blood, and relieves symptoms of coronary artery disease. Coronary stents were the first devices proven to reduce restenosis, dropping the rate of restenosis to 15-20%. Stents have since been used in the majority of PTCA procedures. [0009] Conventional stents have taken two forms, balloon expandable stents and self-expanding stents. Both are typically made of metallic materials and may include a biocompatible coating. Such stents are permanently implanted into the human body by deploying them on or through a catheter. Such permanent implantation may increase the amount of intimal hyperplasia, thrombosis or other adverse medical effects. Coronary stents accomplish a lower restenosis rate of 15-20% post angioplasty compared to PTCA alone as a result of maintaining a higher acute gain post procedure. [0010] Drug eluting stents, which elute drugs such as rapamycin and paclitaxel, were designed to further reduce intimal hyperplasia rates with stents. Such drug eluting stents incorporate metal or metal alloys with degradable or non degradable polymers which control release of the drug. The use of such drugs has further reduced the rates of restenosis as compared to stents alone. [0011] The metals or metal alloys used for both conventional and drug eluting stents are intended to be biologically stable and remain in the body for the patient's life unless surgically removed at a later date along with surrounding tissue. Thus, these stents do not permit temporary placement within the body unless patient and surgeon are prepared to undertake a second procedure to remove the stent, which is difficult or impossible in most cases. [0012] Although one of the primary functions of stenting is to provide mechanical support to the blood vessel wall and to preserve the lumen for blood flow, once the vessel wall heals the stent serves little or no continuing purpose. Further, the presence of a stent which remains mechanically rigid could potentially cause complications to the patient. It has therefore been desired to provide a stent which dissolves or degrades during or shortly after healing of the vessel or thereafter [0013] There have been several attempts to make stents from biodegradable polymer materials such as poly-lactic acids (PLA). Such polymer stents, however, tend to provide less mechanical support for the vessel wall and therefore have to be substantially thicker than a comparable metallic stent. The thickness can reduce the available blood flow lumen and can cause undesirable biologic responses. [0014] Recent attempts have been made to make metal stents which decompose in the body, as described for example in U.S. Pat. No. 6,287,332 B1 and U.S. Pat. No. 6,854,172 B2. See also US2004/009808 and WO 02/053202. Such degradable metal stents, however, often compromise strength, profile, and other desirable characteristics which are found in conventional metal stents. [0015] For these reasons, it would be desirable to provide degradable devices that have improved physical and mechanical characteristics. In particular, it would be desirable to provide a stent or other luminal prosthesis which is degradable during and/or upon healing of the vessel or thereafter and which has features to reduce the risk of injury to the vessel or restenosis. It would also be desirable to provide localized and controlled release of a pharmacological agent from the stent or other device for the treatment of blood vessels and other body structures at the location being treated with the stent. Such pharmacological agents could minimize both restenosis and any inflammatory response towards the stent or other device and degradation products thereof. At least some of these objectives will be met by the aspects of the present invention. BRIEF SUMMARY OF THE INVENTION [0016] Medical devices and methods utilize an implantable structure comprising a body which is degradable over a clinically relevant period of time. The body may have a variety of forms and may be used in a variety of medical treatments. In preferred embodiments, the body has the form of a stent, particularly a vascular stent of the type used in the treatment of coronary artery disease. The body comprises or is formed or constructed from a material which provides desired physical and mechanical attributes for the device. In preferred embodiments, the body comprises a metal (pure or with impurities), a metal alloy or a combination thereof. The term "metal" as used hereinafter will include such pure and impure metals as well as metal alloys and other combinations of two or more metals and metal alloys. The implantable bodies are at least partially degradable in a physiologic environment. Preferably, the materials of implantable structures are fully degradable so that no structure remains after a clinically relevant time period, as discussed below, and produce degradation byproducts which are physiologically benign, preferably being of a type which is naturally occurring in the body environment. More preferably, the bodies of the implantable structures produce degradation byproducts in amounts lower than what is typically present in the physiologic environment. The degradation rate of the implantable structure may be controlled in a variety of aspects individually or in combination thereof. Exemplary physiologic environments include vascular and other body lumens including the ureter and the urethra, solid tissues, cerebral tissue, and the like. [0017] In a first aspect of the present invention, the degradation rate of the body of the implantable structure is controlled by selection of the composition of the implant material. The implant material is selected from a metal or metal alloys or combination thereof which can degrade in a clinically relevant time period ranging from approximately one month to 5 years, usually from 4 months to 2 years, and often from 6 months to one year. Thus, the weight or volume of the implantable structure will typically diminish each day by a percentage in the range from about 0.05% to 3%, usually from 0.1% to 0.75% per day, and more usually from 0.25% to 0.5% per day. [0018] The metal, alloy, or combination material of the implantable structure will usually have a corrosion current (Icorr) in the range from 0.0001 amps/cm.sup.2 to 0.1 amps/cm.sup.2, usually from typically 0.001 amps/cm.sup.2 to 0.01 amps/cm.sup.2, and usually from 0.0025 amps/cm.sup.2 to 0.008 amps/cm.sup.2. The corrosion current is proportional to the corrosion rate, so materials with higher Icorr values will corrode more rapidly in the vascular or other physiologic environment. Icorr varies with the material property, geometry, and surface characteristics of the implant, and also physiologic environment among other factors. The Icorr value will typically represent an average value for the body as a whole or for any portion of the body. [0019] In a second aspect, the degradation rate of the implantable structure is controlled at least in part by modifying its geometry. Such geometry modifications may include surface area to volume ratio. For example, attributes such as holes, reservoirs, trenches or others can be incorporated into the body to increase the surface area without significantly increasing the volume which can be used to control the degradation rate of the structure. When the implantable body comprises a stent having a strut, the geometry to be modified may include the strut width to strut thickness ratios. [0020] In a third aspect of the present invention, the degradation rate of the implantable structure is controlled at least in part by the addition of corrosion inducing features. For example, in some embodiments, the implantable structure comprises an implantable body having at least one surface and at least one corrosion inducing feature on the at least one surface which causes at least a portion of the structure to degrade at a controlled degradation rate. In preferred embodiments, the implantable body comprises a metal, a metal alloy or a combination thereof. In some embodiments, the corrosion inducing feature comprises a pit, pore, partial hole, void or combination of these. In other embodiments, the corrosion inducing feature comprises a surface irregularity, scratch, streak, ridge, bump, texture, sintered porous metal or alloy, roughened surface or combination of these. In still other embodiments, the corrosion inducing feature comprises a hole, either partial or complete sintered pores, or combination of these. Further, in some embodiments, the implantable body has a first surface with a first associated portion of the body and a second surface with a second associated portion of the body, wherein the first surface has corrosion inducing features present in a density and/or configuration which causes the first associated portion to degrade at a rate which differs from the second associated portion. [0021] Exemplary metals include iron, cobalt, tungsten, molybdenum, silver, and the like. These metals may be substantially pure, typically having purities about 90% by weight, often above 95% by weight, and frequently above 99.5% by weight. Alternatively, these metals may be combined as alloys with other metals or materials. Exemplary alloys include iron-containing alloys, such as AISI series 1000 carbon steels, AISI series 1300 manganese steels, AISI series 4000 molybdenum steels, AISI series 4100 chromium-molybdenum steels, AISI series 4300 and AISI series 8600 nickel-chromium-molybdenum steels, AISI series 4600 nickel-molybdenum steels, AISI series 5100 chromium steels, AISI series 6100 chromium-vanadium steels, AISI series 9200 silicon steels, and the like. Other iron-containing alloys will have at least 25% iron, preferably 50% iron, more preferably 75% iron, and often 90% iron, 95% iron, or 99% iron, or greater by weight. Iron alloys may contain carbon ranging from 0.05% to 3% by weight, preferably 0.05% to 1.0% by weight, more preferably 0.1% to 0.6% by weight. Alloys of silver, tin, cobalt, tungsten, molybdenum, and the like, will usually have at least 25% by weight of the pure metal, usually at least 50% by weight, often at least 75% by weight, and sometimes 90% by weight, 95% by weight, or 98% by weight, or greater. Continue reading about Degradable implantable medical devices... Full patent description for Degradable implantable medical devices Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Degradable implantable medical devices 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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