Abstract:
An expandable stent and delivery system is provided for treating body vessel defects, such as partially occluded blood vessels and aneurysms. The delivery system includes a core member having a non-cylindrical retraction member with extending portions configured to extend between struts of the stent. The stent includes enlarged anchor members that cooperate with the retraction member to secure the stent to the core member for movement within a delivery catheter and deployment to a body vessel defect. The extending portions provide a greater contact area than would be possible with a cylindrical retraction member, which is especially beneficial when retracting a partially deployed stent into the catheter.

Description:
FIELD OF THE INVENTION 
     The disclosed invention relates to intraluminal therapeutic devices and delivery systems therefor, and more particularly, to expandable stents and delivery systems which may be used in the treatment of body vessel defects. This invention also relates to the deployment and repositioning of expandable stents within body vessels, especially those within the brain. 
     DESCRIPTION OF RELATED ART 
     On a worldwide basis, nearly one million balloon angioplasties are performed annually to treat vascular diseases such as blood vessels that are clogged or narrowed by a lesion or stenosis. The objective of this procedure is to increase the inner diameter of the partially occluded blood vessel lumen. In an effort to prevent restenosis without requiring surgery, short flexible cylinders or scaffolds, referred to as stents, are often placed into the body vessel at the site of the stenosis or defect. Stents are typically made of metal or polymers and are widely used for reinforcing diseased body vessels. Stents are also useful in treating aneurysms by providing an internal lumen to cover an aneurysm and thus reduce the flow of blood and the pressure within the aneurysm. 
     Some stents are expanded to their proper size using a balloon catheter. Such stents are referred to as “balloon expandable” stents. Other stents, referred to as “self-expanding” stents, are designed to elastically resist compression in a self-expanding manner. Balloon expandable stents and self-expanding stents are compressed into a small diameter cylindrical form and deployed within a body vessel using a catheter-based delivery system. 
     Stents have been developed with radiopaque markers to aid in the visualization of the stent upon deployment. Radiopaque markers facilitate the positioning of the stent within a body vessel by allowing a physician to determine the exact location, size, and orientation of the stent under x-ray or fluoroscopy. These markers are typically formed of a radiopaque material such as tantalum, zirconium, titanium, or platinum. Published U.S. Patent Application No. 2002/0082683 to Stinson et al., which is hereby incorporated herein by reference, discloses one such radiopaque marker comprised of a pigtail, knot, or ring, of tantalum wire wrapped around a crossing point of struts within a stent. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, an expandable stent and a stent delivery system are provided. The delivery system includes an elongated core member with a distal portion and a non-cylindrical retraction member disposed about the distal portion. The stent is a tubular member having a thin wall and an anchor member extending away from the thin wall. An extending portion of the retraction member is engageable with a distal portion of the anchor member when the stent is compressed onto the core member by a deployment catheter of the delivery system. A radius of the extending portion of the retraction member is greater than a compressed inner radius of the tubular member when the stent is compressed onto the core member. 
     In accordance with another aspect of the present invention, a method of deploying an expandable stent within a body vessel is provided. The method involves providing a self-expanding stent and delivery system. The stent is mounted about a distal portion of an elongated core member of the delivery system. The stent has a thin wall and an anchor member extending away from the thin wall. An extending portion of the retraction member is engageable with a distal portion of the anchor member when the stent is compressed onto the core member by a deployment catheter of the delivery system. A radius of the extending portion of the retraction member is greater than a compressed inner radius of the tubular member when the stent is compressed onto the core member. The stent and at least a portion of the delivery system are inserted into a body vessel, and then the stent is positioned adjacent to a defect of the body vessel. When the stent is properly positioned, the deployment catheter is moved proximally with respect to the core member, which allows the stent to begin expanding within the body vessel. Finally, the deployment catheter is moved further proximally with respect to the core member, which allows the stent to fully deploy. 
     In accordance with yet another aspect of the present invention, a method of resheathing an expandable stent within a body vessel is provided. The method involves providing a self-expanding stent and delivery system. The stent is mounted about a distal portion of an elongated core member of the delivery system. The stent has a thin wall and an anchor member extending away from the thin wall. An extending portion of the retraction member is engageable with a distal portion of the anchor member when the stent is compressed onto the core member by a deployment catheter of the delivery system. A radius of the extending portion of the retraction member is greater than a compressed inner radius of the tubular member when the stent is compressed onto the core member. The expandable stent and at least a portion of the delivery system are inserted into a body vessel, and then the stent is positioned adjacent to a defect of the body vessel. When the stent is properly positioned, the deployment catheter is moved proximally with respect to the core member, which allows the stent to begin expanding within the body vessel. If it is determined that the stent should be moved to a different position within the body vessel, then the deployment catheter is moved distally with respect to the core member, which forces the stent back into the cathether. When the stent is back in the cathether, the delivery system can be relocated. 
     Other aspects, objects and advantages of the present invention, including the various features used in various combinations, will be understood from the following description according to preferred embodiments of the present invention, taken in conjunction with the drawings in which certain specific features are shown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view of an expandable stent and a delivery system in accordance with an embodiment of the present invention; 
         FIG. 1A  is a cross sectional view of the retraction member of  FIG. 1 , taken through the line  1 A- 1 A of  FIG. 1 ; 
         FIG. 1B  is a plan view of an alternative retraction member profile; 
         FIG. 2  is a partial sectional view of an expandable stent and a delivery system in accordance with another embodiment of the present invention; 
         FIG. 3  is a cross sectional view of the stent and delivery system of  FIG. 2 , with anchor members having an outer layer; 
         FIG. 4A  is an enlarged perspective view of an anchor member having an integral threaded portion, according to an aspect of the present invention; 
         FIG. 4B  is an enlarged perspective view of an anchor member having an outer layer according to another aspect of the present invention; 
         FIG. 5  is a partial sectional view of the expandable stent and delivery system of  FIG. 1  in a body vessel; 
         FIG. 6  is a partial sectional view of the delivery system with the deployment catheter moved proximally, allowing the distal section of the expandable stent to expand within the body vessel, while the proximal section of the expandable stent remains interlocked within the deployment catheter; and 
         FIG. 7  is a partial sectional view of the delivery system with the deployment catheter moved proximally and the expandable stent fully expanded within the body vessel. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner. 
       FIG. 1  illustrates an expandable stent  10  and delivery system  12 . The delivery system  12  includes a deployment catheter or microcatheter (not shown in  FIG. 1 ), which takes the form of an elongated tube having a lumen  16 , and an introducer  13 . A proximal section  18  of the deployment catheter  14  is sufficiently flexible to traverse a body vessel, typically a blood vessel, but is sufficiently rigid so that it can be pushed distally through the body vessel. A distal section  20  of the deployment catheter  14  is preferably formed of a material that is more flexible than the proximal section  18 , for enhanced maneuverability through a tortuous stretch of a body vessel. For example, the proximal section  18  may be substantially comprised of stainless steel, while the distal section  20  may be substantially comprised of a nitinol material in a superelastic state at body temperature. 
     The delivery system  12  also includes an elongated core member  22  which is formed of wire, preferably nitinol, but may also be formed from other metal alloys or a polymer material. The core member  22  is axially movable within the lumen  16  of the deployment catheter  14  and can have a varying diameter, as will be described in greater detail herein. 
     A distal portion  24  of the core member  22  includes a non-cylindrical retraction member  26 , as illustrated in  FIGS. 1-3 . The shape of the retraction member  26  depends on the configuration of the associated stent  10 , but as illustrated in  FIG. 1A , it includes at least one extending portion  28  that extends between adjacent struts  30  of the stent  10 , thereby achieving a larger radius R than a compressed inner radius r of the stent  10  when the same is compressed onto the core member  22 . In the embodiment of  FIG. 1A , the retraction member  26  has a gear- or spur-shaped profile with a plurality of extending portions  28  arranged in a symmetrical configuration, which may be preferred to maintain the core member  22  centered within the deployment catheter  14 .  FIG. 1B  shows an alternative retraction member  26   a  that uses a polygonal profile to provide a plurality of extending portions  28   a . Other profiles are possible and the scope of the present invention is not limited to the particular geometries of the illustrated retraction members  26  and  26   a.    
     The retraction member  26  may be integrally formed with the core member  22 , but it typically is a separate piece, such as a collar or ring, that is rigidly affixed to the core member  22 . The means for affixing the retraction member  26  to the core member  22  may vary according to a number of factors, such as the materials of the surfaces to be joined, but suitable means may include welding, spot welding, brazing, soldering, and thermal interference fitting. Rather than providing a single collar or ring, each extending portion  28  may be separately affixed to the core member  22 , but such an operation typically is not preferred because it is labor intensive and may result in misaligned or staggered extending portions. 
     As for the self-expanding stent  10 , it is removably mounted on the core member  22  for movement therewith through the deployment catheter  14 . Examples of suitable core members are illustrated in  FIGS. 1 ,  2 , and  3 . The expandable stent  10  may take on many different patterns or configurations, such as those disclosed in U.S. Pat. Nos. 6,673,106 and 6,818,013, both to Mitelberg et al. and both of which are hereby incorporated herein by reference. The stent  10  may be coated with an agent, such as heparin or rapamycin, to prevent stenosis or restenosis of the vessel. Examples of such coatings are disclosed in U.S. Pat. No. 5,288,711 to Mitchell et al.; U.S. Pat. No. 5,516,781 to Morris et al.; U.S. Pat. No. 5,563,146 to Morris et al.; and U.S. Pat. No. 5,646,160 to Morris et al., all of which are hereby incorporated herein by reference. 
     The illustrated stent  10  of  FIGS. 1 ,  2 , and  3  is laser cut from a tubular piece of nitinol to form a skeletal tubular member  32 . The skeletal tubular member  32  has a thin wall, a small diameter, and when cut forms a plurality of cells which are created by a plurality of interconnected struts  30 . The nitinol is preferably treated so as to exhibit superelastic properties at body temperature. 
     The stent  10  includes at least one anchor member  34 , an example of which is illustrated in detail in  FIG. 4A , extending away from the tubular member  32 . Preferably, the stent  10  includes a plurality of anchor members  34  and  36  extending away from a proximal section  38  and a distal section  40 , respectively, of the tubular member  32 , as illustrated in  FIGS. 1 ,  2 , and  3 . In one preferred embodiment, the stent  10  includes eight anchor members, with four extending from each of the proximal and distal sections  38  and  40  of the stent tubular member  32 . 
     If anchor members  34 ,  36  are provided at both sides of the stent  10 , then a second retraction member  42  can be provided for engagement with the distal anchor members  36 . Each retraction member preferably has a plurality of separate extending members  28 , each one adapted for engagement with one or more of the anchor members. Typically, a one-to-one engagement is preferred. For example,  FIG. 1A  shows a stent  10  with four proximal anchor members  34 , each of which is engageable by a separate extending member  28  of the proximal retraction member  26 . 
     The illustrated anchor members  34 ,  36  include a threaded portion  44 , as described generally in U.S. Pat. No. 6,955,685 to Escamilla et al., which is hereby incorporated herein by reference. An anchor member with an integral threaded portion  44  is illustrated in  FIG. 4A . Depending on the material used to form the stent  10 , there are a number of different ways to form the threaded portion  44 . For example, the threaded portion  44  may be formed by cutting threads into the anchor member  34 ,  36  when the stent  10  is laser cut from a nitinol tubular member. Alternatively, a heat-molding technique may be used to form the threaded portion  44  on the anchor member  34 ,  36 . Those of ordinary skill in the art will appreciate that the present invention may be practiced regardless of the method of forming the threaded portion  44 , if one is provided. 
     Additionally, as illustrated in  FIGS. 3 and 4B , an outer layer  46  may be deposited or wound about at least a portion of the anchor member  34 ,  36  or threaded portion  44  in order to increase its diameter or to provide other performance characteristics. For example, in a preferred embodiment, the threaded portion  44  is wound with a radiopaque material defining a marker coil. The marker coil may be formed of a metallic or polymeric material that exhibits the characteristic of being radiopaque, such as tantalum or tantalum alloy. The marker coil may also be comprised of gold, gold alloy, platinum, platinum alloy, titanium, zirconium, bromine, iodine, barium, bismuth, or any combination thereof. In addition to increasing the diameter of the anchor member  34 ,  36 , an outer layer provided as a marker coil serves as a radiopaque marker for improved visualization during the deployment of the stent within a body vessel. 
     In the case where an outer layer is applied to the anchor member  34 ,  36 , the outer layer is preferably secured to the anchor member  34 ,  36  using an adhesive material, such as a UV adhesive which is thermally cured. 
     Regardless of the geometry of the anchor member  34 ,  36  and whether it includes an outer layer  46 , it preferably is thicker than the thin wall of the stent  10 , as illustrated in  FIGS. 1A and 2 . The proximal anchor members  34  interacts with the proximal retraction member  26  in order to retract a partially deployed stent, as will be described herein, so it should be reinforced for improved retractability. 
     As illustrated in  FIGS. 1 ,  2  and  3 , the stent  10  is delivered to a body vessel by the delivery catheter  14 . The stent  10  and associated core member  22  are axially movable together within the delivery catheter  14 . The stent  10  is preferably removably locked onto the core member  22  by axially trapping the proximal anchor members  34  between the extending portions  28  of the proximal retraction member  26  and a cylindrical member  48  disposed about the distal portion  24  of the core member  22 . The general configuration and function of such a cylinder may be seen in U.S. Pat. No. 6,833,003 to Jones et al., which is hereby incorporated herein by reference. 
     As illustrated in  FIGS. 1 ,  2 , and  3 , the cylindrical member  48  may be spaced from the extending portions  28  of the retraction member  26  to define a gap that receives the anchor members  34 . Preferably, the length of the anchor members  34  is substantially equal to the length of the gap in order to prevent the anchor members  34 , and hence the stent  10 , from shifting position along the core member  22 . In the embodiment of  FIGS. 2 and 3 , a second retraction member  42  and a second cylindrical member  50  are provided distally of the first retraction member  26  in order to define a second gap for securing the distal anchor members  36 . If only one retraction member  26  is provided, then it is preferably located proximally of the stent tubular member  32  to interlock with the proximal anchor members  34 . This is useful for retracting and repositioning the stent  10 , as will be described herein. 
     In a preferred embodiment, an intermediate cylindrical member  52  is provided on which to mount the stent  10 .  FIG. 1  shows the proximal retraction member  26  spaced from the intermediate cylinder  52 , while  FIGS. 2 and 3  show the retraction member  26  extending from the intermediate cylinder  52 . If the core member  22  is provided with an intermediate cylindrical member  52 , but without a distal retraction member, then any distal anchor members  36  may be trapped in a gap defined between the intermediate cylindrical member  52  and the distal cylindrical member  50 . It is preferred to have at least some means for removably locking the distal anchor members  36  to the core member  22  in order to discourage the stent distal section  40  from clinging to the delivery catheter  14  and “bunching up” during deployment of the stent  10 . 
       FIG. 5  illustrates the self-expanding stent  10  and delivery system  12  of  FIG. 1  positioned within a body vessel V. Initially, the stent  10  is interlocked to the core member  22  by positioning the proximal anchor members  34  within the gap defined between the proximal cylinder  48  and the retraction member  26 . If a core member means for receiving the distal anchor members  36  is provided, then the distal anchor members  36  may be similarly secured. The core member  22  is then slid into the deployment catheter  14  to thereby compress the thin wall of the stent  10  into a compressed condition against the core member  22 . When the stent  10  is positioned within the delivery catheter  14 , the delivery system  12  is inserted into the body vessel V and advanced distally until the stent  10  is aligned with a vessel defect S. Although the delivery system  12  is illustrated in use with a stenosed body vessel, it will be appreciated that it may be used with any other vessel defect treatable with a stent, such as an aneurysm. 
       FIG. 6  shows the deployment catheter  14  moved proximally, releasing the distal anchor members  36  and allowing the distal section  40  of the expandable stent  10  to begin expanding. During expansion, the distal section  40  of the stent  10  comes in contact with the wall of the body vessel V. 
     As illustrated in  FIG. 7 , the deployment catheter  14  is again moved proximally, releasing the proximal anchor members  34  and allowing the stent  10  to fully expand. Once the stent  10  is fully deployed within the body vessel V, the core member  22  remains extended through the stent  10  and thus acts as a guide wire, providing a physician with easier access to locations within the body vessel distal of the stent  10 . 
     If, during the deployment process, it is determined that the stent  10  should be relocated or realigned, the deployment catheter  14  may be used to resheath the stent  10 . With the stent  10  positioned on the core member  22  as described above with reference to  FIG. 6 , the proximal anchor members  34  will remain interlocked in the gap between the proximal cylindrical member  48  and the proximal retraction member  26 . In this configuration, the stent  10  may be resheathed. To resheath the stent  10 , the deployment catheter  14  is moved distally, thereby forcing the stent  10  back into the catheter  14  and onto the core member  22 , compressing the distal section  40  of the stent  10 , and forcing the distal anchor members  36  into engagement with the core member  22 . The stent  10  and delivery system  12  may then be withdrawn or repositioned to a different location within the body vessel V. 
     It will be appreciated that, during the retraction step, a distal portion  54  of the proximal anchor members  34 , best illustrated in  FIG. 1A , will contact the extending portions  28  of the proximal retraction member  26 . The extending portions  28  pass between adjacent struts  30  of the stent  10 , thereby allowing the radii R of the extending portions  28  of the retraction member  26  to exceed a compressed inner radius r of the stent wall or tubular member  32 . In contrast, a cylindrical retraction member, similar to the intermediate cylinder  52  described previously, has a definite size limitation because the cylinder is necessarily bounded by the inner surface of the stent. Thus, it will be appreciated that the provision of a retraction member  26  that is non-cylindrical in transverse cross-section or end profile (examples being shown in  FIG. 1A  and  FIG. 1B ) allows for a greater contact area with a distal portion  54  of the proximal anchor members  34 , which increased contact area improves the retractability of the stent  10 . 
     When the expandable stent  10  has been properly positioned and fully expanded within the blood vessel V, as illustrated in  FIG. 7 , the delivery catheter  14  and the core member  22  are removed from the body. 
     It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention, including those combinations of features that are individually disclosed or claimed herein.