Abstract:
An expandable stent and delivery system are provided for treating body vessel defects, such as partially occluded blood vessels and aneurysms. The delivery system includes a core member having a threaded core member portion configured to interlock with a threaded strut member portion of the expandable stent. The expandable stent is mounted thusly onto the core member for movement within a delivery catheter and deployment to a body vessel defect. The deployment catheter is used to compress the interlocked threaded strut member portion into engagement with the threaded core member portion.

Description:
FIELD OF THE INVENTION  
       [0001]     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  
       [0002]     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.  
         [0003]     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.  
         [0004]     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  
       [0005]     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 threaded core member portion disposed about the distal portion. The delivery system also includes a deployment catheter. The stent is a tubular member having a thin wall and a strut member extending away from the thin wall. The strut member defines a threaded strut member portion. At least a portion of the threaded strut member is threadably engageable with at least a portion of the threaded core member portion, and the two are interlocked when received in a lumen of the deployment catheter.  
         [0006]     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 an expandable 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 strut member defining a threaded strut member portion and at least a portion of the threaded strut member portion is in threaded engagement with at least a portion of a threaded core member portion disposed at the distal portion of the elongated core member. The delivery system also includes a deployment catheter disposed about the stent to interlock the threaded strut member portion and the threaded core member portion. 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. Finally, the deployment catheter is moved further proximally with respect to the core member, which allows the stent to fully deploy.  
         [0007]     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 an expandable 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 strut member defining a threaded strut member portion and at least a portion of the threaded strut member portion is in threaded engagement with at least a portion of a threaded core member portion disposed at the distal portion of the elongated core member. The delivery system also includes a deployment catheter disposed about the stent to interlock the threaded strut member portion and the threaded core member portion. 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.  
         [0008]     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  
       [0009]     FIGS.  1  is a partial sectional view of an expandable stent and a delivery system in accordance with an embodiment of the present invention;  
         [0010]      FIG. 1A  is an enlarged detail view of the expandable stent of  FIG. 1  positioned within the delivery system;  
         [0011]      FIG. 2  is an enlarged detail view of an alternative expandable stent positioned within an alternative delivery system;  
         [0012]      FIG. 3A  is an enlarged perspective view of a strut member having an integral threaded strut member portion, according to an aspect of the present invention;  
         [0013]      FIG. 3B  is an enlarged perspective view of a strut member having an outer layer according to another aspect of the present invention;  
         [0014]      FIG. 4  is a cross sectional view of the stent and delivery system of  FIG. 1 , taken through the line  4 - 4  of  FIG. 1 ;  
         [0015]      FIG. 5  is a partial sectional view of the expandable stent and delivery system of  FIG. 1  in a body vessel;  
         [0016]      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  
         [0017]      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  
       [0018]     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.  
         [0019]      FIG. 1  illustrates an expandable stent  10  and delivery system  12 . The delivery system  12  includes a deployment catheter or microcatheter  14  which takes the form of an elongated tube having a lumen  16 . 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.  
         [0020]     A winged hub  22  may be coupled to the proximal section  18  of the deployment catheter  14 . Preferably formed from a polymer material, the winged hub  22  is used to insert the deployment catheter  14  into a body vessel, such as a blood vessel within the brain of a patient.  
         [0021]     The delivery system  12  also includes an elongated core member  24  which is formed of wire, preferably nitinol, but may also be formed from other metal alloys or a polymer material. The core member  24  is axially movable within the lumen  16  of the deployment catheter  14  and may be tapered so that a proximal portion  26  of the core member  24  has a greater diameter than an outer diameter D of a distal portion  28 .  
         [0022]     The distal portion  28  of the core member  24  includes at least one threaded core member portion  30 , as illustrated in  FIGS. 1 and 1 A. The threaded core member portion  30  preferably defines a helical thread, similar to a screw thread, and may have a root diameter R greater than the outer diameter D of the core member distal portion  28 , as illustrated in  FIG. 2 . In the embodiment of  FIG. 1 , the core member distal portion  2 B includes a second threaded core member portion  32  spaced distally from the first threaded core member portion  30 .  
         [0023]     As for the expandable stent  10 , it is removably mounted on the core member  24  for movement therewith through the deployment catheter  14 . 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.  
         [0024]     The illustrated stent  10  of  FIG. 1  is laser cut from a tubular piece of nitinol to form a skeletal tubular member  34 . The skeletal tubular member  34  has a thin wall, a small diameter, and when cut forms a plurality of cells which are created by a plurality of interconnected strut members. The nitinol is preferably treated so as to exhibit superelastic properties at body temperature.  
         [0025]     The stent  10  includes at least one strut member  36 , best illustrated in  FIG. 1A , extending away from the tubular member  34 . Preferably, the stent  10  includes a plurality of strut members  36  and  38  extending away from a proximal section  40  and a distal section  42 , respectively, of the tubular member  34 , as illustrated in  FIG. 1 . In one preferred embodiment, the stent  10  includes eight strut members, with four extending from each of the proximal and distal sections  40  and  42  of the stent tubular member  34 . Each strut member  36  and  38  defines a threaded strut member portion  44 , as described generally in U.S. Pat. No. 6,955,685 to Escamilla et al., which is hereby incorporated herein by reference.  
         [0026]     A strut member  36 , 38  with an integral threaded strut member portion  44  is illustrated in  FIG. 3A . As shown, the threaded strut member portion  44  is not a continuous helical thread, but has at least one row of teeth  46 . However, the threaded strut member portion  44  preferably defines a helical thread to interact with the core member  24 , as will be further described herein. Also, the threaded strut member portions  44  are preferably configured to generally occupy the space between the threaded core member portion  30 , 32  and the delivery catheter  14 , as best illustrated in  FIG. 4 .  
         [0027]     Depending on the material used to form the stent  10 , there are a number of different ways to form the threaded strut member portion  44 . For example, the threaded strut member portion  44  may be formed by cutting threads into the strut member  36 , 38  when the stent  10  is laser cut from a nitinol tubular member. Alternatively, a heat-molding technique may be used to form the threaded strut member portion  44  on the strut member  36 , 38 . Those of ordinary skill in the art will appreciated that the present invention may be practiced regardless of the method of forming the threaded strut member portion  44 .  
         [0028]     Additionally, as illustrated in  FIGS. 2 and 3 B, an outer layer  48  may be deposited or wound about at least a portion of the threaded strut member portion  44  in order to increase its diameter or to provide other performance characteristics. For example, in a preferred embodiment, the threaded strut member 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.  
         [0029]     The outer layer is preferably applied onto the threaded strut member portion  44  so as to maintain the integrity of the underlying thread. Alternatively, the outer layer itself may define a thread, such as a row of teeth or a helical coil, in which case the strut member  36 , 38  need not be formed with a threaded strut member portion  44 . This may be preferred, rather than forming the strut member itself with a thread. Accordingly, when used herein, the term “threaded strut member portion” refers to a configuration wherein a thread is provided by a threaded portion integrally formed in the strut member  36 , 38 , by an integral threaded portion covered by an outer layer that preserves the underlying thread, or by an unthreaded strut member covered by an outer layer that is itself arranged to provide a thread.  
         [0030]     In the case where an outer layer is applied to the strut member  36 , 38 , the outer layer is preferably secured to the strut member  36 , 38  using an adhesive material, such as a UV adhesive which is thermally cured. In addition to increasing the diameter of the strut member  36 , 38 , 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.  
         [0031]     As illustrated in  FIGS. 1 and 5 , the stent  10  is delivered to a body vessel V by the delivery catheter  14 . The stent  10  and associated core member  24  are axially movable together within the delivery catheter  14 . The stent  10  is removably locked onto the core member  24  by the interaction between the threaded strut member portion  44  and the threaded core member portion  30 , 32 . Preferably, the threaded strut member portion  44  and the threaded core member portion  30 , 32  are provided as mating helical threads, such that at least a portion of the two may be interlocked by rotation, similar to a nut and bolt. In order to reinforce the interlocking relationship between the threaded strut member portion  44  and the threaded core member portion  30 , 32 , an adhesive  50  may be applied therebetween, as illustrated in  FIG. 1A . Furthermore, the strut member  36 , 38  may be configured to simultaneously contact the delivery catheter  14  and the threaded core member portion  30 , 32  in order to prevent the strut member  36 , 38  from radially expanding and detaching from the threaded core member portion  30 , 32  As described above, the proper fit between the threaded core member portion  30 , 32 , the strut member  36 , 38 , and the delivery catheter  14  may be achieved by adjusting the size of the strut member  36 , 38  or by increasing the diameter of the threaded core member portion  30 , 32 , as illustrated in  FIG. 2 .  
         [0032]     If only one threaded core member portion is provided, then it is preferably located proximally of the stent tubular member  34  to interlock with one or more threaded strut member portions  44  extending from the proximal section  40  of the stent  10 . This is useful for retracting and repositioning the stent  10 , as will be described herein. It may be preferred, however, to provide threaded core member portions  30 , 32  at each end of the stent tubular member  34  to discourage the stent distal section  42  from clinging to the delivery catheter  14  and “bunching up” during deployment of the stent  10 .  
         [0033]     By the above-described configuration, the stent  10  is locked onto the core member  24  for axial movement through the delivery catheter  14 . In another embodiment, illustrated in  FIG. 2 , the interaction between the threaded strut member portion  44  and the threaded core member portion  30  is supplemented by provision of at least one cylindrical member associated with the distal portion  28   a  of the core member  24   a  and adjacent to the threaded core member portion  30 . The general configuration and function of such cylinders may be seen in U.S. Pat. No. 6,833,003 to Jones et ale, which is hereby incorporated herein by reference  
         [0034]     In the illustrated embodiment of  FIG. 2 , the distal portion  28   a  of the core member  24 a includes at least a first cylinder  52  and a second cylinder  54 , which are separated by the proximal threaded core member portion  30 . The cylindrical members  52  and  54  preferably have a greater diameter than the threaded core member portion  30 , such that they define a gap in which the threaded core member portion  30  resides. It will be appreciated that the cylinders  52  and  54  further prevent the stent  10  from moving axially along the core member  24 a while the threaded strut member portion  44  is interlocked with the threaded core member portion  30  and maintained within the gap.  
         [0035]     In addition to constraining the axial movement of the strut member  36 , the distal cylinder  54  is used to mount the expandable stent  10 . As the stent  10  is positioned and mounted on the second cylindrical member  54 , the strut members  36  extending away from the proximal section  40  of the tubular member  34  align with and are disposed within the gap, to interlock with the threaded core member portion  30 . Similarly, if provided, the strut members  38  extending from the distal section  42  of the tubular member  34  align with and are disposed within a second gap, not illustrated, formed by a space between the second cylindrical member  54  and a third cylindrical member, not illustrated. In this configuration, the stent  10  is locked in place and may be pushed or pulled through the deployment catheter  14  without damaging or deforming the stent  10 .  
         [0036]      FIG. 5  illustrates the expandable 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  24  by mating at least a portion of the threaded strut member portion  44  to at least a portion of the threaded core member portion  30 , 32 . The core member  24  is then slid into the deployment catheter  14  to thereby hold the stent  10  in its constrained configuration. Alternatively, the core member  24  may be positioned within the delivery catheter  14 , and then the stent  10  is compressed, fed into the catheter  14 , and interlocked onto the core member  24 . This may be preferred if the threaded core member portion  30 , 32  and the threaded strut member portion  44  are provided as mating helical threads. 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.  
         [0037]      FIG. 6  shows the deployment catheter  14  moved proximally, releasing the distal strut members  38  and allowing the distal section  42  of the expandable stent  10  to begin expanding. During expansion, the distal section  42  of the stent  10  comes in contact with the wall of the body vessel V. If adhesive is provided between the threaded strut member portion  44  and the threaded core member portion  32 , then it is preferably sufficiently weak so as to be overcome by the breakaway force of the expanding stent  10 .  
         [0038]     As illustrated in  FIG. 7 , the deployment catheter  14  is again moved proximally, releasing the proximal strut members  36  and allowing the stent  10  to fully expand Once the stent  10  is fully deployed within the body vessel V, the core member  24  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 .  
         [0039]     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  24  as described above with reference to  FIG. 6 , the proximal threaded strut member portion  44  will remain interlocked on the proximal threaded core member portion  30 . 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  24 , compressing the distal section  42  of the stent  10 , and forcing the distal strut members  38  into engagement with the distal threaded core member portion  32 . The stent  10  and delivery system  12  may then be withdrawn or repositioned to a different location within the body vessel V.  
         [0040]     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  24  are removed from the body.  
         [0041]     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.