Abstract:
Medical devices, such as stents, and methods of the devices are described. In some embodiments, the invention features a method of making a medical device including providing a body having an electrically insulating first member defining an elongated lumen, and an electrically conducting second member on a first surface of the first member, removing a portion of the second member, and forming the body into the medical device, e.g., a stent.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to medical devices, such as, for example, stents and stent-grafts, and methods of making the devices. 
       BACKGROUND 
       [0002]    The body includes various passageways such as arteries, other blood vessels, and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprostheses include stents and covered stents, sometimes called “stent-grafts”. 
         [0003]    An endoprosthesis can be delivered inside the body by a catheter that supports the endoprosthesis in a compacted or reduced-size form as the endoprosthesis is transported to a desired site. Upon reaching the site, the endoprosthesis is expanded, for example, so that it can contact the walls of the lumen. 
         [0004]    When the endoprosthesis is advanced through the body, its progress can be monitored, e.g., tracked, so that the endoprosthesis can be delivered properly to a target site. After the endoprosthesis is delivered to the target site, the endoprosthesis can be monitored to determine whether it has been placed properly and/or is functioning properly. 
         [0005]    One method of monitoring a medical device is magnetic resonance imaging (MRI). MRI is a non-invasive technique that uses a magnetic field and radio waves to image the body. In some MRI procedures, the patient is exposed to a magnetic field, which interacts with certain atoms, e.g., hydrogen atoms, in the patient&#39;s body. Incident radio waves are then directed at the patient. The incident radio waves interact with atoms in the patient&#39;s body, and produce characteristic return radio waves. The return radio waves are detected by a scanner and processed by a computer to generate an image of the body. 
       SUMMARY 
       [0006]    In one aspect, the invention features a method of making a medical device, such as a stent. In some embodiments, the stent includes one or more electrically conductive layers that are unable to carry an electrical current in a closed loop. As explained below, this lack of electrical continuity can enhance the visibility of material present in the lumen of the stent during MRI. At the same time, the stent can be made relatively strong, e.g., the stent is capable of supporting a body lumen. 
         [0007]    In another aspect, the invention features a method of making a medical device, such as a stent, including providing a body having an electrically insulating first member defining an elongated lumen, and an electrically conducting second member on a first surface of the first member, removing a portion of the second member and forming the body into the device, e.g., stent. The medical device can be, for example, a catheter, a marker band, a hypotube, or a guidewire. 
         [0008]    Embodiments of aspects of the invention may include one or more of the following features. The method includes removing the portion of the second member to expose a portion of the first member. The portion of the second member is removed by electropolishing. The second member defines a non-centric lumen. The first member includes a polymer, a cement, or a ceramic. A thinnest portion of the second member is removed. The method further includes providing an electrically conducting third member on a second surface of the first member. The third member defines a non-centric lumen. The second member defines a non-centric lumen, and the lumens of the second and third members are spaced relative to each other about a perimeter of the body. The second member defines a non-centric lumen, and the lumens of the second and third members are spaced about 180° relative to each other about a perimeter of the body. The second member defines a lumen having a non-circular cross section. The lumen of the second member has an oval cross section or a polygonal cross section. The second member defines a lumen having a circular cross section. 
         [0009]    In another aspect, the invention features a method of making a stent, including providing an electrically insulating first tubular member, providing an electrically conducting second tubular member on a surface of the first tubular member, the second tubular member defining a non-centric lumen, removing a portion of the second tubular member to expose a portion of the first tubular member, and forming the first and second tubular members into the stent. 
         [0010]    The method can further include providing an electrically conducting third tubular member on a second surface of the first tubular member, and removing a portion of the third tubular member to expose a portion of the first tubular member. 
         [0011]    In another aspect, the invention features a medical device, such as a stent, including a body defining a lumen (e.g., a tubular body) including an electrically insulating first member defining a lumen, and an electrically conducting second member on a first surface of the first member, the second member defining a lumen and having multiple thicknesses. The medical device can be, for example, a catheter, a marker band, a hypotube, or a guidewire. 
         [0012]    Embodiments of aspects of the invention may include one or more of the following features. The second member defines a non-centric lumen. The second member defines a circular lumen. The second member defines a non-circular lumen. The first member includes a cement, a polymer, and/or a ceramic. The second member includes a non-ferrous material. The stent further includes an electrically conducting third member on a second surface of the first member, the third member defining a lumen. The lumens of the second and third members are displaced relative to each other about a circumference of the body. The third member has multiple thicknesses. The stent further includes a strut having only a portion of the insulating first member and a portion of the conducting third member. The stent further includes a strut having only a portion of the insulating first member and a portion of the conducting second member. 
         [0013]    In another aspect, the invention features a method of making a device, such as a stent, including forming a member having an electrically insulating coating into a first structure defining a lumen, the first structure having edges spaced from each other, contacting the edges together, and forming the first structure into the device, e.g., stent. 
         [0014]    Embodiments of aspects of the invention may include one or more of the following features. The edges are contacted together by drawing the first structure. The method further includes providing a second structure on a first surface of the first structure, the second structure defining a lumen and having an electrically insulating coating, the second structure further including edges spaced from each other. The edges of the first and second structures are spaced relative to each other about a perimeter. 
         [0015]    In another aspect, the invention features a method of making a device, e.g., stent, including forming an electrically conducting first tubular body, removing a first portion of the first tubular body, depositing an electrically insulating material in the first portion, and forming the first tubular body into the device, e.g., stent. 
         [0016]    Embodiments of aspects of the invention may include one or more of the following features. The first portion is a seam portion of the first tubular body. The method further includes forming an electrically insulating layer on the first tubular body. The method further includes drawing the first tubular body. The method further includes providing a second tubular body on a surface of the first tubular body. The first and second tubular bodies include seams spaced relative to each other about a perimeter. The seams are spaced about 180° relative to each other. 
         [0017]    Embodiments may have one or more of the following advantages. The methods described below can be used to make other medical devices, such as those that include tubes or other enclosing structures, to enhance visibility of material in the devices. The medical devices can be, for example, catheters, marker bands, or hypotubes. 
         [0018]    Other aspects, features and advantages of the invention will be apparent from the description of the preferred embodiments and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  illustrates a method of making a stent. 
           [0020]      FIG. 2  is a detailed illustration of a portion of the stent of  FIG. 1 . 
           [0021]      FIG. 3A  is a cross-sectional view of a strut, taken along line  3 A- 3 A of  FIG. 2 ; and  FIG. 3B  is a cross-sectional view of a strut, taken along line  3 B- 3 B of  FIG. 2 . 
           [0022]      FIG. 4  illustrates a portion of a method of making a stent. 
           [0023]      FIG. 5  illustrates a method of making a stent. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring to  FIG. 1 , a method  20  of making a stent  100  is illustrated. Method  20  is capable of providing a stent that includes electrically conductive portions that are unable to carry an electrical current in a closed loop, e.g., around the circumference of the stent. Consequently, as described more below, the visibility of material, such as blood or a stenosis, present in the lumen of stent  100  during magnetic resonance imaging (MRI) can be enhanced. 
         [0025]    Method  20  provides a mechanically strong stent having at least one electrically conductive portion (e.g., layer) interrupted by an electrical insulator. Method  20  includes providing an electrically conductive inner tubular member  22 . Inner tubular member  22  has a non-centric lumen  24  such that along a radial cross section, the inner tubular member has a relatively thin portion  25  and a relatively thick portion  27 . Next, a layer of electrically insulating material  26  is formed over inner tubular member  22  (step  28 ), and subsequently, an electrically conductive outer tubular member  30  is formed or placed over layer  26  (step  32 ) to yield a three-layer tubular member  34 . As shown, three-layer tubular member  34  is formed such that inner tubular member  22  and layer  26  are non-centric with respect to outer tubular member  30 , e.g., diametrically opposed to lumen  24 . As a result, similar to inner tubular member  22 , outer tubular member  30  has a relatively thin portion  36  and a relatively thick portion  37 . 
         [0026]    Next, in step  38 , portions of inner tubular member  22  and outer tubular member  30  are removed. As shown, thin portions  25  and  36 , are removed to reveal an inner portion  40  and an outer portion  42  of electrically insulative layer  26 , respectively. The result is a tubular member  44  having inner tubular member  22  and outer tubular member  30  separated by electrically insulative layer  26 , and each member  22  and  30  is interrupted by the electrically insulative layer at portions  40  and  42 , respectively. As a result, neither inner tubular member  22  nor outer tubular member  30  can carry an electrical current circumferentially (arrow A) around tubular member  44 . 
         [0027]    Tubular member  44  is then formed, e.g., by laser cutting, into stent  100  having bands  46  and struts  48  connecting the bands (step  50 ). In particular, referring to  FIGS. 2 and 3 , struts  48  are formed at selected locations of bands  46  such that there is no electrical continuity between the bands for an electrical current to flow in a closed loop. As shown, one strut  48  is formed at portion  42  ( FIG. 2 ). Starting at any starting reference point of inner tubular member  22  of band  46   a , electrical current can flow to inner tubular member  22  of band  46   b  via a section of tubular member  22  in strut  48  ( FIG. 3A ). However, the electrical current cannot flow back to the starting point to close a loop because inner tubular member  22  of band  46   b  is interrupted by insulative layer  26  at portion  40 . Electrical current also cannot flow from outer tubular member  30  of bands  46   a  or  46   b  through strut  48  because the strut does not include a portion of the outer tubular member. Similarly, alternatively or in addition to strut  48  shown in  FIG. 2 , a strut including a portion of insulative layer  26  and a portion of outer tubular member  30  can be formed at portion  40  (as exemplified by strut  48 ′ between band  46   b  and  46   c ). Current cannot flow to form a loop because outer tubular member  30  of bands  46   b  and  46   c  are interrupted by insulative layer  26  at portion  42 . 
         [0028]    Thus, electrical current cannot flow in a loop within a band because conductive tubular members  22  and  30  are interrupted by insulative layer  26 . Current also cannot form a closed loop by flowing between bands because struts  48  are formed at selected positions to prevent an electrical current loop from forming. 
         [0029]    The lack of electrical continuity within a band and between bands  46  can enhance the MRI visibility of material in the lumen of stent  100 . Without wishing to be bound by theory, during MRI, an incident electromagnetic field is applied to a stent. The magnetic environment of the stent can be constant or variable, such as when the stent moves within the magnetic field (e.g., from a beating heart) or when the incident magnetic field is varied. When there is a change in the magnetic environment of the stent, which can act as a coil or a solenoid, an induced electromotive force (emf) is generated, according to Faraday&#39;s Law. The induced emf in turn can produce an eddy current that induces a magnetic field that opposes the change in magnetic field. The induced magnetic field can interact with the incident magnetic field to reduce (e.g., distort) the visibility of material in the lumen of the stent. A similar effect can be caused by a radiofrequency pulse applied during MRI. 
         [0030]    By forming stent  100  to include electrically conductive portions that cannot form a closed current loop, the occurrence of an eddy current is reduced (e.g., eliminated). Accordingly, the occurrence of an induced magnetic field that can interact with the incident magnetic field is also reduced. As a result, the visibility of material in the lumen of stent  100  during MRI can be enhanced. 
         [0031]    Method  20  is described in more detail below. 
         [0032]    Referring again to  FIG. 1 , inner tubular member  22  can be formed of any biocompatible material suitable for MRI, e.g., non-ferromagnetic materials. The biocompatible material can be suitable for use in a self-expandable stent, a balloon-expandable stent, or both. For self-expandable stents, inner tubular member  22  can be formed of a continuous solid mass of a relatively elastic biocompatible material, such as a superelastic or pseudo-elastic metal alloy. Examples of superelastic materials include, for example, a Nitinol (e.g., 55% nickel, 45% titanium), silver-cadmium (Ag—Cd), gold-cadmium (Au—Cd), gold-copper-zinc (Au—Cu—Zn), copper-aluminum-nickel (Cu—Al—Ni), copper-gold-zinc (Cu—Au—Zn), copper-zinc/(Cu—Zn), copper-zinc-aluminum (Cu—Zn—Al), copper-zinc-tin (Cu—Zn—Sn), copper-zinc-xenon (Cu—Zn—Xe), indium-thallium (In—Tl), nickel-titanium-vanadium (Ni—Ti—V), and copper-tin (Cu—Sn). See, e.g., Schetsky, L. McDonald, “Shape Memory Alloys”, Encyclopedia of Chemical Technology (3rd ed.), John Wiley &amp; Sons, 1982, vol. 20. pp. 726-736 for a full discussion of superelastic alloys. Other examples of materials suitable for inner tubular member  22  include one or more precursors of superelastic alloys, i.e., those alloys that have the same chemical constituents as superelastic alloys, but have not been processed to impart the superelastic property under the conditions of use. Such alloys are further described in PCT application US91/02420. 
         [0033]    In other embodiments, inner tubular member  22  can include one or more materials that can be used for a balloon-expandable stent. Suitable examples of materials include noble metals, such as platinum, gold, and palladium, refractory metals, such as tantalum, tungsten, molybdenum and rhenium, and alloys thereof. Suitable materials include radiopaque materials, such as metallic elements having atomic numbers greater than 26, e.g., greater than 43, and/or those materials having a density greater than about 9.9 g/cc. In certain embodiments, the radiopaque material is relatively absorptive of X-rays, e.g., having a linear attenuation coefficient of at least 25 cm −1 , e.g., at least 50 cm −1 , at 100 keV. Some radiopaque materials include tantalum, platinum, iridium, palladium, tungsten, gold, ruthenium, and rhenium. The radiopaque material can include an alloy, such as a binary, a ternary or more complex alloy, containing one or more elements listed above with one or more other elements such as iron, nickel, cobalt, or titanium. Other examples of stent materials include titanium, titanium alloys (e.g., alloys containing noble and/or refractory metals), stainless steels, stainless steels alloyed with noble and/or refractory metals, nickel-based alloys (e.g., those that contained Pt, Au, and/or Ta), iron-based alloys (e.g., those that contained Pt, Au, and/or Ta), and cobalt-based alloys (e.g., those that contained Pt, Au, and/or Ta). 
         [0034]    Inner tubular member  22  can include a mixture of two or more materials listed above, in any arrangement or combination. 
         [0035]    Inner tubular member  22  including non-concentric lumen  24  can be formed by conventional techniques. For example, inner tubular member  22  can be formed from a solid rod of a selected material, and lumen  24  can be mechanically formed, e.g., by drilling. Alternatively, inner tubular member  22  can be extruded to include a non-concentric lumen. The size of lumen  24  can be determined, for example, by the final thickness desired for inner tubular member  22  after thin portion  25  is removed (step  38 ). 
         [0036]    Next, insulative layer  26  is formed on inner tubular member  22  (step  32 ). Insulative layer  26  can include any electrically non-conductive and MRI compatible material. Suitable materials include polymers, such as thermoplastics or thermosetting materials. The polymer can enhance the flexibility of stent  100 . Examples of polymers include polyolefins, polyesters, polyethers, polyamides and nylons, polyvinyl chlorides, copolymers and terpolymers thereof, or mixtures thereof. Other suitable materials include ceramics, such as titanium oxides, hafnium oxides, iridium oxides, chromium oxides, aluminum oxides (e.g., α-Al 2 O 3  or yttria-stabilized alumina), glass ceramic (e.g., Macor™, a blend of fluorophlogopite mica and borosilicate glass from Corning, or Bioglass™ from USBiomaterials), calcium phosphate (e.g., hydroxylapatite), zirconium oxide (e.g., transformation toughened zirconia, fully stabilized zirconia, or partially stabilized zirconia with magnesium or yttrium), feldspathic porcelain, and silicon nitride. Other suitable materials include cements. Examples include glass ionomers (e.g., Glasscor™ or Glassbase™ available from Pulpdent), resin reinforced glass ionomers (e.g., Vitrebond™ from 3M), polycarboxylates (e.g., TylokPlus™ from L. D. Caulk), cyanoacrylates, zinc phosphates, resin composite cements (e.g., filled bisphenol-A-glycidyldimethacrylate resin combined with methacrylics, or RelyX ARC from 3M), and cements used in the field of dentistry. Insulative layer  26  can include a mixture of two or more materials listed above, in any arrangement or combination. 
         [0037]    In some embodiments, insulative layer  26  can include an insulating form of the material of inner tubular member  22 . For example, inner tubular member  22  can include tantalum or tungsten, and insulative layer  26  can include tantalum oxide or tungsten oxide, respectively. Such embodiments can have relatively low interfacial differences (e.g., stress), which can provide good adhesion between the materials. 
         [0038]    The thickness of insulative layer  26  can vary. Generally, insulative layer  26  is sufficiently thick to electrically isolate inner tubular member  22  from outer tubular member  30 , and/or to prevent members  22  and  30  from carrying a continuous loop of electrical current. Insulative layer  26  is preferably sufficiently thick to withstand processing tolerances, e.g., handling during manufacturing or removal of portions  25  and  36  without damage. In some embodiments, the thickness of insulative layer  26  can range from about 5 to about 200 nanometers for ceramics or cements, or about 0.1 to about 50 micrometers for polymers. 
         [0039]    Insulative layer  26  can be formed on inner tubular member  22  according to a variety of techniques. In some cases, the choice of technique is a function of the materials of insulative layer  26  and/or inner tubular member  22 . For example, in embodiments in which insulative layer  26  includes a polymer, an adhesive can be used to bond the polymer to inner tubular member  22 . In embodiments in which insulative layer  26  includes an insulating form of a material of inner tubular member  22 , techniques, such as plasma ion implantation or heating the inner tubular member in an appropriate (e.g., oxidizing) atmosphere, can be used. Other suitable techniques include thermal spraying techniques, such as plasma arc spraying, chemical vapor deposition, physical vapor deposition, or dipping. In certain embodiments, inner and outer tubular members  22  and  30  can be co-drawn, and insulative layer  26 , for example, a polymer, can be formed, e.g., by pouring the liquid or molten polymer into the space defined between the members. 
         [0040]    After insulative layer  26  is formed, outer tubular member  30  is formed over the insulative layer to form three-layer tubular member  34  (step  32 ). In general, materials suitable for inner tubular member  22  are also suitable materials for outer tubular member  30 . Outer tubular member  30  can be provided as described above for inner tubular member  22 . Stent  100  can include the same or different materials for inner and outer tubular members  22  and  30 . 
         [0041]    Outer tubular member  30  can be joined to inner tubular member  22  and insulative layer  26  using a variety of methods. For example, similar to inner tubular member  22 , outer tubular member  30  can include a non-concentric lumen (not shown) into which inner tubular member  22  and insulative layer  26  are inserted. Members  22  and  30  can be joined together by co-drawing the members. Alternatively or in addition, members  22  and  30  can be joined together using magnetic pulse forming or welding. The use of magnetic forces to deform a work piece is described, for example, in Batygin Yu et al., “The Experimental Investigations of the Magnetic Pulse Method Possibilities for Thin-walled Metal Plates Deformation”, Technical Electro-dynamics, 1990, #5, p. 15-19; and commonly assigned U.S. Ser. No. 10/192,253, filed Jul. 10, 2002. In some embodiments, an adhesive can be applied between insulative layer  26  and outer tubular member  30 . 
         [0042]    As shown in  FIG. 1 , tubular member  34  is formed such that lumen  24  of inner tubular member  22  and the lumen defined by outer tubular member  30  are offset (as shown, diametrically offset) relative to the circumference of tubular member  34 . Expressed another way, thin portions  25  and  36  are about 180 degrees apart about the circumference of tubular member  34 . By offsetting the lumens of inner and outer tubular members  22  and  30 , when thin portions  25  and  36  are removed to form tubular member  44  (described below), tubular member  44  can be formed with relatively uniform wall thickness and good structural integrity. In other embodiments, lumen  24  and the lumen defined by outer tubular member  30  (or thin portions  25  and  36 ) are less than about 180 degrees, e.g., between zero and 180 degrees, apart about the circumference of tubular member  34 . 
         [0043]    After tubular member  34  is formed, portions of inner and outer tubular members  22  and  30  are removed to prevent the members from carrying an electrical current circumferentially around tubular member  34  (step  38 ). In certain embodiments, thin portions  25  and  36  are removed such that inner and outer tubular members  22  and  30 , respectively, are interrupted by insulative layer  26 . Since lumen  24  and the lumen of outer tubular member  30  are offset, the portion of inner tubular member  22  that is removed (e.g., thin portion  25 ) is compensated by relatively thick portion  37  of the outer tubular member. Similarly, the portion of outer tubular member  30  that is removed (e.g., thin portion  36 ) is compensated by relatively thick portion  27  of inner tubular member  22 . As a result, tubular member  44  has relatively uniform wall thickness and good strength. 
         [0044]    Portions of inner and outer tubular members  22  and  30  can be removed by a variety of methods. For example, portions of inner and outer tubular members  22  and  30  can be removed by electropolishing, in which both portions can be removed simultaneously. Since thin portions  25  and  36  are thinner than other portions of members  22  and  30 , respectively, techniques, such as electropolishing, that uniformly remove layers of members  22  and  30  will eliminate the thin portions first to expose insulative layer  26 . Electropolishing is described, for example, in U.S. Pat. No. 6,375,826. Other suitable methods for removing portions of inner and outer tubular members  22  and  30  include laser cutting, mechanical machining (e.g., drilling), and/or chemical etching combined with a suitable masking technique. 
         [0045]    Subsequently, tubular member  44  is formed into stent  100  (step  50 ). For example, selected portions of tubular member  44  can be removed for the tubular member to define bands  46  and struts  48 . The portions can be removed by laser cutting, for example, using an excimer laser and/or an ultrashort pulse laser. Laser cutting is described, for example, in U.S. Pat. Nos. 5,780,807 and 6,517,888. In certain embodiments, during laser cutting, a liquid carrier, such as a solvent or an oil, is flowed through lumen  24 . The carrier can prevent dross formed on one portion of tubular member  44  from re-depositing on another portion (possibly providing electrical continuity), and/or reduce formation of recast material on the tubular member. Other methods of removing portions of tubular member  44  include mechanical machining (e.g., micro-machining), electrical discharge machining (EDM), photoetching (e.g., acid photoetching), and/or chemical etching. 
         [0046]    In some cases, tubular member  34  can be formed into a stent before portions of inner and outer tubular members  22  and  30  are removed. For example, laser cutting tubular member  34  into a stent can precede electropolishing tubular member  34 . 
         [0047]    Stent  100  can further be finished, e.g., electropolished to a smooth finish, according to conventional methods. In some embodiments, about 0.0001 inch of material can be removed from the interior and/or exterior surfaces by chemical milling and/or electropolishing. Stent  100  can be annealed at predetermined stages of method  20  to refine the mechanical and physical properties of the stent. 
         [0048]    In use, stent  100  can be used, e.g., delivered and expanded, according to conventional methods. Suitable catheter systems are described in, for example, Wang U.S. Pat. No. 5,195,969, and Hamlin U.S. Pat. No. 5,270,086. Suitable stents and stent delivery are also exemplified by the Radius® or Symbiot® systems, available from Boston Scientific Scimed, Maple Grove, Minn. 
         [0049]    Generally, stent  100  can be of any desired shape and size (e.g., coronary stents, aortic stents, peripheral vascular stents, gastrointestinal stents, urology stents, and neurology stents). Depending on the application, stent  100  can have a diameter of between, for example, 1 mm to 46 mm. In certain embodiments, a coronary stent can have an expanded diameter of from about 2 mm to about 6 mm. In some embodiments, a peripheral stent can have an expanded diameter of from about 4 mm to about 24 mm. In certain embodiments, a gastrointestinal and/or urology stent can have an expanded diameter of from about 6 mm to about 30 mm. In some embodiments, a neurology stent can have an expanded diameter of from about 1 mm to about 12 mm. An abdominal aortic aneurysm (AAA) stent and a thoracic aortic aneurysm (TAA) stent can have a diameter from about 20 mm to about 46 mm. Stent  100  can be balloon-expandable, self-expandable, or a combination of both (e.g., U.S. Pat. No. 5,366,504). Stent  100  can be delivered by other actuating mechanisms, such as those that include an electroactive polymer or a pneumatic action. 
         [0050]    Stent  100  can also be a part of a stent-graft. In other embodiments, stent  100  can include and/or be attached to a biocompatible, non-porous or semi-porous polymer matrix made of polytetrafluoroethylene (PTFE), expanded PTFE, polyethylene, urethane, or polypropylene. The endoprosthesis can include a releasable therapeutic agent, drug, or a pharmaceutically active compound, such as described in U.S. Pat. Nos. 5,674,242 and 6,517,888; U.S. Ser. No. 09/895,415, filed Jul. 2, 2001; and U.S. Ser. No. 10/232,265, filed Aug. 30, 2002. The therapeutic agents, drugs, or pharmaceutically active compounds can include, for example, anti-thrombogenic agents, antioxidants, anti-inflammatory agents, anesthetic agents, anti-coagulants, and antibiotics. 
         [0051]    Still numerous other embodiments are possible. 
         [0052]    For example, while described above as tubular, inner member  22 , insulative layer  26 , and/or outer member  30  can have non-circular cross sections, e.g., non-circular inner and/or outer perimeters. The cross sections can be oval, elliptical, or regularly or irregularly polygonal, having three or more sides. The lumens of inner member  22 , insulative layer  26 , and/or outer member  30  can be relatively concentric. Furthermore, other arrangements of struts  48  are possible. 
         [0053]    For example, referring to  FIG. 4 , three-layer member  34   a  (similar to member  34 ) includes an inner member  22   a , an insulative layer  26   a , and an outer member  30   a , each having an oval cross section. Inner member  22   a , insulative layer  26   a , and outer member  30   a  are generally the same as member  22 , layer  26 , and member  30 , respectively. Three-layer member  34   a  can be processed as described above (step  38 ) to remove portions of members  22   a  and  30   a  and to prevent members  22   a  and  30   a  from carrying a closed loop of electrical current. As a result, a member  44   a  is formed having member  22   a  interrupted by insulative layer  26   a  at two locations (A and B), and member  30   a  interrupted by the insulative layer at two locations (C and D). Member  44   a  can be formed into a stent as described above. Struts  48  can be formed in any arrangement at locations A, B, C, and/or D. 
         [0054]    While stent  100  is shown including wide, substantially solid bands  46 , in other embodiments, bands  46  include a wire shaped in an undulating pattern (as described, e.g., U.S. Pat. No. 6,419,693). 
         [0055]    Stent  100  can have fewer or more than the three layers shown in  FIG. 1 . For example, stent  100  can include insulative layer  26 , and inner member  22  or outer member  30 . 
         [0056]    In some embodiments, stent  100  includes a protective coating on the exterior surface and/or on the interior surface. The coating can be used to enhance the biocompatibility of the stent and/or to protect the stent from corrosion if, for example, the stent includes two different metals. The protective coating can include one or more of the ceramic, polymer, and/or cement described above. More than one protective coatings can be applied. 
         [0057]    Other methods for making a stent unable to carry electrical current in a closed loop are possible. Referring to  FIG. 5 , method  60  includes starting with a first sheet  62  of electrically conductive material having an insulative layer  64  on the sheet and on the edges  66  of the sheet. First sheet  62  is then rolled (e.g., around a mandrel) to form a tube  68  having edges  66  spaced apart (step  70 ). A second sheet  72  (similar to first sheet  62 ) is formed into a tube and placed over tube  68  to form tubular member  76  (step  74 ). As shown, the edges  78  of second sheet  72  are spaced apart from each other, and spaced from edges  66 , e.g., about 180 degrees. Next, tubular member  76  is reduced in sized (e.g., by drawing) to join edges  66  together, edges  78  together, and sheets  62  and  72  together (step  80 ). The result is tubular member  82 , which can be used to form a stent, as described above (e.g., step  50 ). Struts  48  can be formed where edges  66  and  78  meet. Sheets  62  and  72  can include the same materials as member  22 , and insulative layer  64  can include the same materials as layer  26 . 
         [0058]    In other embodiments, edges  66  and  78  can be joined together (e.g., by welding) to form tubular member  76  having two seams. After tubular member  76  is reduced in sized (e.g., drawn) to form tubular member  82 , the seams can be preferentially removed, e.g., by chemical etching. The removed material can be subsequently replaced with an insulative material. Tubular member  82  can then be formed into a stent as described above. 
         [0059]    Method  20  and the embodiments described above can be used to form medical devices other than stents and stent-grafts. For example, method  20  can be used to form filters, such as removable thrombus filters described in Kim et al., U.S. Pat. No. 6,146,404; in intravascular filters such as those described in Daniel et al., U.S. Pat. No. 6,171,327; and in vena cava filters such as those described in Soon et al., U.S. Pat. No. 6,342,062. Method  20  can be used to form guidewires, such as a Meier steerable guidewire, catheters, and hypotubes. Method  20  can be used to form vaso-occlusive devices, e.g., coils, used to treat intravascular aneurysms, as described, e.g., in Bashiri et al., U.S. Pat. No. 6,468,266, and Wallace et al., U.S. Pat. No. 6,280,457. Method  20  can also be used in surgical instruments, such as forceps, needles, clamps, and scalpels. 
         [0060]    All publications, applications, references, and patents referred to in this application are herein incorporated by reference in their entirety. 
         [0061]    Other embodiments are within the claims.