Patent Publication Number: US-2010125325-A1

Title: Stent With Cathodic Protection and Stent Delivery System

Description:
TECHNICAL FIELD 
     The technical field of this disclosure is medical implant devices, particularly, stents with cathodic protection. 
     BACKGROUND OF THE INVENTION 
     Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a blood vessel or other anatomical lumen after implantation into the body lumen. Stents have been developed with coatings to deliver drugs or other therapeutic agents. 
     Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications including intravascular angioplasty. For example, a balloon catheter device is inflated during PTCA (percutaneous transluminal coronary angioplasty) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. After inflation, the pressurized balloon exerts a compressive force on the lesion thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels re-narrow. 
     To prevent restenosis, short flexible cylinders, or stents, constructed of metal or various polymers are implanted within the vessel to maintain lumen size. The stents acts as a scaffold to support the lumen in an open position. Various configurations of stents include a cylindrical tube defined by a mesh, interconnected stents or like segments. Some exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz and U.S. Pat. No. 5,421,955 to Lau. Balloon-expandable stents are mounted on a collapsed balloon at a diameter smaller than when the stents are deployed. Stents can also be self-expanding, growing to a final diameter when deployed without mechanical assistance from a balloon or like device. 
     Concern over the long-term effects of stents in the body has led to experimentation with bioabsorbable stents, i.e., stents that are absorbed by the body after deployment. Materials used for bioabsorbable stents have included bioabsorbable metals, such as highly reactive, corrodible magnesium. Unfortunately, the materials used to date have failed to produce satisfactory results. A bioabsorbable stent needs to seal any dissection and provide scaffolding to prevent wall recoil until such scaffolding is no longer needed. A bioabsorbable stent made of bare magnesium lasts a few weeks after deployment in a vessel, but should be present for several months to prevent wall recoil. With the stent gone prematurely, the vessel is reduced in diameter, making the treatment ineffective. 
     It would be desirable to have a stent with cathodic protection that would overcome the above disadvantages. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a stent delivery system including a catheter; a balloon operably attached to the catheter; and a stent disposed on the balloon. The stent includes a stent body having a first stent layer of an anodic stent material disposed about a second stent layer of a cathodic stent material; and a battery having a first battery layer of an anodic battery material and a second battery layer of a cathodic battery material. The first stent layer is electrically coupled to the first battery layer and the second stent layer is electrically coupled to the second battery layer. 
     Another aspect of the present invention provides a stent including a stent body having a first stent layer of an anodic stent material disposed about a second stent layer of a cathodic stent material; and a battery having a first battery layer of an anodic battery material and a second battery layer of a cathodic battery material. The first stent layer is electrically coupled to the first battery layer and the second stent layer is electrically coupled to the second battery layer. 
     Another aspect of the present invention provides a stent including a stent body having a first stent layer of an anodic stent material disposed about a second stent layer of a cathodic stent material; and means for establishing an electrical potential between the first stent layer and the second stent layer. 
     The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a stent delivery system made in accordance with the present invention. 
         FIG. 2  is a side view of a stent with cathodic protection made in accordance with the present invention. 
         FIG. 3  is a schematic diagram of a stent with cathodic protection made in accordance with the present invention. 
         FIG. 4  is a detail view of another embodiment of a stent with cathodic protection made in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS 
       FIG. 1  is a perspective view of a stent delivery system made in accordance with the present invention. The stent delivery system  100  includes a catheter  105 , a balloon  110  operably attached to the catheter  105 , and a stent  120  disposed on the balloon  110 . The balloon  110 , shown in an inflated state, can be any variety of balloons capable of expanding the stent  120 . The balloon  110  can be manufactured from a material such as polyethylene, polyethylene terephthalate (PET), nylon, Pebax® polyether-block co-polyamide polymers, or the like. In one embodiment, the stent delivery system  100  can include retention means  111 , such as mechanical or adhesive structures, for retaining the stent  120  on the balloon  110  until the stent  120  is deployed. The catheter  105  may be any variety of balloon catheters, such as a PTCA (percutaneous transluminal coronary angioplasty) balloon catheter, capable of supporting a balloon during angioplasty. The stent delivery system  100  can also include a sheath  102  through which the stent  120  is delivered to the deployment site. 
       FIG. 2  is a side view of a stent with cathodic protection made in accordance with the present invention. In this embodiment, the battery is external to the stent body to provide cathodic protection. 
     The stent  120  includes a stent body  130  and at least one battery  140  electrically coupled to the stent body  130 . The stent body  130  includes a number of stent body segments  132  made of stent segments  131 . The pattern of the stent body segments  132  can be W-shaped or can be a more complex shape with the elements of one segment continuing into the adjacent segment. The stent  120  can be installed in the stent delivery system of  FIG. 1  for implantation in a body lumen. 
     Referring to  FIG. 2 , the stent body  130  is conventional to stents generally and can be made of a wide variety of medical implantable materials. In one embodiment, the stent body  130  is bioabsorbable. The stent body  130  has a first stent layer of an anodic stent material disposed about and enclosing a second stent layer of a cathodic stent material. The stent body  130  can be welded, laser cut, molded, or consist of filaments or fibers which are wound or braided together in order to form a continuous structure. Depending on the material, the stent can be self-expanding, or be expanded by a balloon or some other device. In one embodiment, the stent body  130  can carry a coating, such as a polymer coating carrying one or more therapeutic agents, such as anti-inflammatory agents or anti-proliferative agents. In another embodiment, the stent body  130  can include one or more therapeutic agents within the stent material. 
     The battery  140  has a first battery layer of an anodic battery material and a second battery layer of a cathodic battery material to develop an electrical potential. The first stent layer of the stent body  130  is electrically coupled to the first battery layer and the second stent layer of the stent body  130  is electrically coupled to the second battery layer. The electrical potential prevents corrosion of the first stent layer until the battery  140  is depleted. An external battery  140  can be attached to the stent body  130  with welding, brazing, or the like, in the same manner of attachment as for the marker bands used to make points on the stent visible during fluoroscopy. In this embodiment, the battery is external to the stent body, i.e., the battery  140  is outside of the stent body  130 . 
       FIG. 3  is a schematic diagram of a stent with cathodic protection made in accordance with the present invention. A battery provides electrical potential at the stent body to prevent corrosion of the stent body by reversing the corrosion potential normally present when the stent is deployed in a vessel. 
     The strut segment  232  of the stent body in this example has a first stent layer  236  of an anodic stent material disposed about a second stent layer  234  of a cathodic stent material. The battery  240  has a number of first battery layers  246  of an anodic battery material alternating with a number of second battery layers  244  of a cathodic battery material. The outermost first battery layer  246  is electrically coupled to the first stent layer  236  and the outermost second battery layer  244  is electrically coupled to the second stent layer  234 . Thus, the cathodic battery material is electrically coupled to the cathodic stent material and the anodic battery material is electrically coupled to the anodic stent material. The cathodic materials are dissimilar from the anodic materials, so an electrical potential is generated when the materials are in contact. The electrical potential reverses the corrosion potential normally present when the stent is deployed in a vessel to provide cathodic protection. 
     The stent material and battery material can be selected as desired for a particular application. In one embodiment, the anodic stent material is the same as the anodic battery material and the cathodic stent material is the same as the cathodic battery material. In one embodiment, the anodic stent material and/or the anodic battery material is magnesium or a magnesium alloy (such as WE43 magnesium alloy). In one embodiment, the cathodic stent material and/or the cathodic battery material is iron, stainless steel (such as  316  stainless steel), copper, gold, or platinum. Gold or platinum in the battery  240  can also serve as marker bands to make points on the stent show up during fluoroscopy. 
     The battery  240  provides impressed current cathodic protection. In operation, the second stent layer  234  provides cathodic protection for the first stent layer  236 , which is exposed to fluid in the lumen in which the stent is implanted and subject to corrosion. The first stent layer  236  is protected until the sacrificial cathode second stent layer  234  is depleted. When the second stent layer  234  is depleted, there is no longer cathodic protection and the first stent layer  236  will corrode. The thickness of the second stent layer  234  and/or the amount of the cathodic stent material in the second stent layer  234  can be selected to determine a depletion time for the second stent layer  234 . As defined herein, the depletion time is the time at which cathodic protection is no longer provided by the second stent layer. When the first stent layer  236  is magnesium, the corrosion products are absorbed in the body. 
     The battery  240  can have the number of first battery layers  246  and second battery layers  244  required to provide a desired electrical potential. A number of batteries can be electrically coupled in series or parallel to provide the desired electrical potential or capacity, respectively. In one embodiment, the battery layers can be fabricated by depositing the layers using sputtering, vapor deposition, or the like. 
     The dual layer strut segment  232  of the stent body in this example includes a single second stent layer  234  having a circular cross section and a single first stent layer  236  having an annular cross section. The second stent layer  234  acts as a sacrificial cathode. Those skilled in the art will appreciate that the strut segments making up the stent body can have any cross section desired for a particular application. In another embodiment, the stent layers can have rectangular cross sections. In one embodiment, the strut segment  232  of the stent body can be fabricated by depositing layers using sputtering, vapor deposition, or the like. In another embodiment, the strut segment  232  of the stent body can be fabricated by co-extrusion of the anodic stent material and cathodic stent material into the stent layers. 
       FIG. 4  is a detail view of another embodiment of a stent with cathodic protection made in accordance with the present invention. The multi-layer strut segment  332  of the stent body in this example has a number of first stent layers  336  of an anodic stent material alternating with a number of second stent layers  334  of a cathodic stent material. The outermost first stent layer  336  can be electrically coupled to the first battery layer made of anodic battery material and the central innermost second stent layer  334  can be electrically coupled to the second battery layer made of cathodic battery material. 
     The strut segment  332  of the stent body can have the number of second stent layers  334  and first stent layers  336 . Those skilled in the art will appreciate that the strut segments making up the stent body can have any cross section desired for a particular application. In another embodiment, the stent layers can have rectangular cross sections. In one embodiment, the strut segment  332  of the stent body can be fabricated by depositing layers using sputtering, vapor deposition, or the like. In another embodiment, the strut segment  332  of the stent body can be fabricated by co-extrusion of the anodic stent material and cathodic stent material into the stent layers. 
     The strut segment  332  of the stent body can be used as a battery integral to the stent body. In one embodiment, the whole stent body can be made of strut segments  332  with internal electrical coupling as desired for a particular application. In another embodiment, the stent body can include a number of strut segments  332  interspersed with dual layer strut segments  232  as illustrated in  FIG. 3 . In one example, one or more multi-layer strut segment can be integrated as part of each stent body segment. 
     It is important to note that  FIGS. 1-4  illustrate specific applications and embodiments of the present invention, and are not intended to limit the scope of the present disclosure or claims to that which is presented therein. Upon reading the specification and reviewing the drawings hereof, it will become immediately obvious to those skilled in the art that myriad other embodiments of the present invention are possible, and that such embodiments are contemplated and fall within the scope of the presently claimed invention. 
     While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.