Patent Publication Number: US-2010125323-A1

Title: Coil Stent Delivery System and Method of Use

Description:
TECHNICAL FIELD 
     The technical field of this disclosure is delivery systems for medical implant devices, particularly, delivery systems for stents. 
     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. 
     One approach has been to develop coil stents in which the stent is a continuous helical coil. Coil stents can provide advantages over conventional stents in post-deployment flexibility and strength. Unfortunately, the relationship between coil diameter and the number of coil turns in crimped and deployed configurations complicates delivery of the coiled stents: the pitch change from the crimped to deployed configurations requires the coil stent to unwrap and unfurl. Coil stents exhibit a large degree of foreshortening, which requires the coil stent to be much longer in the crimped configuration than in the deployed configuration. This large length causes problems with pushability and column strength when the coil stent is advanced to the deployment site through a catheter. 
     Another problem with coil stents made of polymers, such as bioabsorbable polymers, is their tendency to creep and take a permanent set when held in constrained configurations for extended periods. This precludes pre-loading the polymer coil stents in a crimped configuration at the point of manufacture, and instead requires they be loaded into delivery systems just before implantation at the catheterization laboratory. This increases cost of procedures due to the need of trained staff to load the coil stent and increases the chance of mistakes. 
     It would be desirable to have a coil stent delivery system and method of use that would overcome the above disadvantages. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a stent delivery system including a coil stent; a housing, the housing having a receiver defining a receiver chamber and a sheath defining a sheath lumen, the receiver chamber being in communication with the sheath lumen; and a screw assembly, the screw assembly having a shaft, a helical screw disposed about a distal portion of the shaft, and a drive operably coupled to the shaft. The shaft is disposed in the receiver chamber and the sheath lumen, the helical screw is disposed in the sheath, and the coil stent is disposed about the shaft in the receiver chamber and engages the helical screw. Rotation of the drive moves the coil stent through the sheath lumen. 
     Another aspect of the present invention provides a delivery system for a coil stent including a housing, the housing having a receiver defining a receiver chamber and a sheath defining a sheath lumen, the receiver chamber being in communication with the sheath lumen; and a screw assembly, the screw assembly having a shaft, a helical screw disposed about a distal portion of the shaft, and a drive operably coupled to the shaft. The shaft is disposed in the receiver chamber and the sheath lumen, the helical screw is disposed in the sheath, and the coil stent is disposed about the shaft in the receiver chamber and engages the helical screw. Rotation of the drive moves the coil stent through the sheath lumen. 
     Another aspect of the present invention provides a method of delivering a coil stent including providing a coil stent delivery system, the coil stent delivery system having a sheath defining a sheath lumen and a shaft with a helical screw disposed about the shaft in the sheath lumen; advancing a distal end of the sheath to a deployment site; engaging the coil stent with the helical screw; and rotating the shaft to rotate the helical screw and urge the coil stent through the sheath toward the deployment site. 
     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 an exploded side view of a coil stent delivery system made in accordance with the present invention. 
         FIG. 2  is a cross section view of a coil stent delivery system made in accordance with the present invention. 
         FIGS. 3A-3D  are cross section views of deployment of a coil stent with a coil stent delivery system made in accordance with the present invention. 
         FIGS. 4A &amp; 4B  are cross section views of another deployment of a coil stent with a coil stent delivery system made in accordance with the present invention. 
         FIGS. 5A &amp; 5B  are cross section views of deployment of a coil stent with other embodiments of a coil stent delivery system made in accordance with the present invention. 
         FIG. 6  is a cross section view of yet another embodiment of a coil stent delivery system made in accordance with the present invention. 
         FIG. 7  is a cross section view of yet another embodiment of a coil stent delivery system made in accordance with the present invention. 
         FIG. 8  is a flow chart for a method of delivering a coil stent in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exploded cross section view of a coil stent delivery system made in accordance with the present invention. The stent delivery system  40  includes a coil stent  50 , a housing  60 , and a screw assembly  70 . The housing  60  has a receiver  62 , which defines a receiver chamber  64 , and a sheath  66 , which defines a sheath lumen  68 . The receiver chamber  64  is in communication with the sheath lumen  68 . The screw assembly  70  has a shaft  72 , a helical screw  74  disposed about a distal portion  76  of the shaft  72 , and a drive  78  operably coupled to the shaft  72 . When the stent delivery system  40  is assembled, the shaft  72  is disposed in the receiver chamber  64  and the sheath lumen  68 , the helical screw  74  is disposed in the sheath  66 , and the coil stent  50  is initially disposed about the shaft  72  in the receiver chamber  64  and engages the helical screw  74 . The drive  78  can rotate the shaft  72 , which rotates the helical screw  74 , to move the coil stent  50  through the sheath lumen  68 . As used herein, distal and proximal are from the viewpoint of the operator of the stent delivery system  40 , e.g., the receiver  62  is towards the proximal end of the housing  60  and the sheath  66  is towards the distal end. 
     The coil stent  50  can be any generally helical shaped stent. The coil stent  50  has a relaxed diameter when unconstrained and a delivery diameter when constrained within the sheath  66  during delivery. The diameter of the coil stent  50  as defined herein is the diameter across the central axis of the stent coil. The diameter of the receiver chamber  64  can be greater than or equal to the relaxed diameter of the coil stent  50  so the coil stent  50  is maintained in a relaxed configuration. The diameter of the sheath lumen  68  is the delivery diameter. In one embodiment, the coil stent  50  is sealed in the receiver chamber  64  at the time of manufacture to avoid having to load the coil stent  50  into the housing  60  at the catheterization laboratory. The coil stent  50  can have a cross section across the coil at the perimeter which is a circle, rectangle, ellipse, or any other cross section as desired for a particular application. The coil stent  50  can be the final length to be deployed at the deployment site, or can be a coil stent blank, which is longer than the desired final length and is cut to the desired length at the deployment site. 
     The coil stent  50  can be made of one or more biocompatible materials suitable for a particular application. In one embodiment, the coil stent  50  is bioabsorbable and can be made of a bioabsorbable material such as homopolymers and copolymers (including random and block polymers) of D-lactide, L-lactide, DL-lactide, caprolactone, trimethylenecarbonate, glycolide, caprolactone derivatives, P-Dioxanone, hydrolysable urethanes, and combinations thereof. Polyethylene oxide can be part of the polymer chain. Another exemplary material is degradable polyurethane. In one embodiment, the coil stent  50  is non-bioabsorbable and can be made of a non-bioabsorbable material such as homopolymers and copolymers of ethylene, propylene, amides, esters, acrylates, carbonates, imides, styrenes, non-hydrolysable urethanes, combinations thereof and the like. In another embodiment, at least an end portion of the coil stent  50  is made of a super-elastic material, such as nitinol or the like. In an exemplary coil stent  50  having an end portion of super-elastic material and a middle portion of a polymeric material, the super-elastic material end portion aids in deployment of the coil stent  50  since the super-elastic material is radially stronger than the polymeric material. One or both end portions of the coil stent  50  can be made of the super-elastic material. 
     In one embodiment, the coil stent  50  can be capable of carrying 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 coil stent  50  can include one or more therapeutic agents within the stent material. 
     The housing  60  is adapted to receive coil stent  50  and the screw assembly  70  in the receiver chamber  64  of the receiver  62  and the sheath lumen  68  of the sheath  66 . The screw assembly  70  is free to rotate within the housing  60 . The rotation of the screw assembly  70  moves the coil stent  50  axially from the receiver chamber  64  through the distal end of the sheath  66 , which is open, and out of the sheath  66  to the deployment site. In one embodiment, the sheath  66  can be rotated and moved axially relative to the screw assembly  70  without moving the screw assembly  70 , to assist in opening, sizing, and placement of the coil stent  50  at the deployment site. The sheath  66  can be flexible to allow advancement through a tortuous vasculature to a remote deployment site. The inner walls of the sheath  66  can be lubricated or have a lubricating coating to ease the passage of the coil stent  50  through the sheath  66 . In one embodiment, the sheath  66  can include a cutter, such as a radio frequency (RF) cutter, at the distal end to cut the coil stent  50  to the desired length at the deployment site. 
     The screw assembly  70  has a shaft  72 , a helical screw  74  disposed about a distal portion  76  of the shaft  72 , and a drive  78  operably coupled to the shaft  72 . The helical screw  74  acts like an Archimedes screw or a screw conveyor to move the coil stent  50  through the sheath  66  when the shaft  72  rotates the helical screw  74 . In one embodiment, the helical screw  74  is a continuous screw. In another embodiment, the helical screw  74  is a series of separate screw blades. In one embodiment, the surface of helical screw  74  in contact with the coil stent  50  is covered with a low-tack adhesive to assist in moving the coil stent  50  through the sheath  66 . 
     The shaft  72  can include a central shaft lumen. In one embodiment, the shaft lumen is operable to receive a guidewire. A guide wire is advanced through the vasculature to a deployment site and the stent delivery system  40  is advance over the guide wire in the shaft lumen of the shaft  72 . In another embodiment, coolant is disposed in the shaft lumen to cool the coil stent  50 , such as a coil stent made of a shape memory material, and prevent shape changes during deployment. 
     The shaft  72  can be flexible to allow advancement to a remote deployment site. In one embodiment, the shaft  72  can be a hypotube with grooves for increased flexibility. As defined herein, the grooves are cuts partially or completely through the thickness of the wall of the hypotube. The axial distribution of the grooves can be selected to tailor the flexibility of the shaft  72  as desired for a particular application. In one embodiment, the hypotube includes more grooves in a distal portion of the shaft  72  than in a proximal potion of the shaft  72 , so that the distal portion of the shaft  72  is more flexible. In one example, a 20 centimeter distal portion of the shaft  72  is more flexible and a 70 centimeter proximal potion of the shaft  72  is less flexible. 
     The drive  78  operably coupled to drive the shaft  72  can be a manual drive, such as a handle, or a motor. The drive  78  can rotate in one direction to move the coil stent  50  in an axial direction toward the deployment site and in the opposite direction to move the coil stent  50  in an axial direction away from the deployment site. The reverse rotation allows retraction of a coil stent  50  that is partially deployed at the deployment site when the operator determines that the placement of the coil stent  50  at the deployment site is not as desired. In one embodiment, a rotation counter can be operably connected to the helical screw to count rotations and determine the axial position of the coil stent  50  in the sheath  66  from the number of rotations. 
       FIG. 2 , in which like elements share like reference numbers with  FIG. 1 , is a cross section view of a coil stent delivery system made in accordance with the present invention. The shaft  72  is disposed in the receiver chamber  64  and the sheath lumen  68 , the helical screw  74  is disposed in the sheath  66 , and the coil stent  50  is disposed about the shaft  72  in the receiver chamber  64 . The distal end of the coil stent  50  engages the helical screw  74 . The helical screw  74  is shown schematically as a series of parallel lines along the shaft  72  for clarity of illustration. Rotation of the helical screw  74  moves the coil stent  50  axially through the sheath lumen  68 . The diameter of the receiver chamber  64  is greater than or equal to the relaxed diameter of the coil stent  50  to avoid stressing the coil stent  50  when disposed in the receiver chamber  64 . Since the coil stent  50  is not stressed, the coil stent  50  can be sealed in the receiver chamber  64  and the coil stent delivery system  40  delivered to the catheterization laboratory with the coil stent  50  pre-loaded. 
       FIGS. 3A-3D , in which like elements share like reference numbers with each other and with  FIG. 2 , are cross section views of deployment of a coil stent with a coil stent delivery system made in accordance with the present invention.  FIGS. 3A &amp; 3B  illustrate the transition of the coil stent from the receiver chamber to the sheath lumen at the proximal portion of the coil stent delivery system.  FIGS. 3C &amp; 3D  illustrate the transition of the coil stent from the sheath lumen to the vessel lumen at the deployment site. 
     Referring to  FIG. 3A , the distal tip  51  of the coil stent  50  is engaged with the proximal portion  71  of the helical screw  74 . The coil stent  50  is at a relaxed diameter. The operator rotates the driver  78 , which rotates the shaft  72  and the helical screw  74 . Referring to  FIG. 3B , the distal tip  51  of the stent coil  50  is drawn into the helical screw  74  and moves axially through the sheath lumen  68  toward the deployment site. The coil stent  50  is compressed to the delivery diameter by the sheath  66  to provide a small crossing profile. Further rotation of the driver  78  moves the coil stent  50  to the distal end of the sheath  66 . 
     Referring to  FIG. 3C , the distal tip  51  of the coil stent  50  emerges from the distal end  61  of the sheath  66  at the deployment site  82  in the vessel  80 . The coil stent  50  expands from the delivery diameter in the sheath  66  to the deployment diameter in the vessel  80 . Referring to  FIG. 3D , the rotation of the helical screw  74  continues to move the coil stent  50  from the sheath  66  to the vessel  80  until the whole coil stent  50  is in the vessel  80  at the deployment site  82 . In one embodiment, the sheath  66  and helical screw  74  are retracted as the coil stent  50  emerges from the sheath  66 . In another embodiment, the sheath  66  and helical screw  74  are held in a fixed axial position relative to the vessel  80  as the coil stent  50  emerges from the sheath  66 . The coil stent delivery system can be removed from the vasculature after the coil stent has been deployed. 
       FIGS. 4A &amp; 4B  are cross section views of another deployment of a coil stent with a coil stent delivery system made in accordance with the present invention.  FIGS. 4A &amp; 4B  show the transition of the coil stent from the sheath lumen to the vessel lumen at the deployment site. 
     Referring to  FIG. 4A , the distal tip  51  of the coil stent  50  emerges from the distal end  61  of the sheath  66  at the deployment site  82  in the vessel  80 . The coil stent  50  expands from the delivery diameter in the sheath  66  to the deployment diameter in the vessel  80 . Referring to  FIG. 4B , the rotation of the helical screw  74  continues to move the coil stent  50  from the sheath  66  to the vessel  80  until the whole coil stent  50  is in the vessel  80  at the deployment site  82 . In this example, the sheath  66  is retracted while the helical screw  74  is held in a fixed axial position relative to the vessel  80 . The coil stent  50  expands to the deployment diameter in the vessel  80  as the coil stent  50  becomes free of the sheath  66 . The coil stent delivery system can be removed from the vasculature after the coil stent has been deployed. 
       FIGS. 5A &amp; 5B  are cross section views of deployment of a coil stent with other embodiments of a coil stent delivery system made in accordance with the present invention. In this embodiment, the coil stent is cut to length at the deployment site. 
     Referring to  FIG. 5A , the distal tip  51  of the coil stent  50  emerges from the distal end  61  of the sheath  66  at the deployment site  82  in the vessel  80 . The coil stent  50  expands from the delivery diameter in the sheath  66  to the deployment diameter in the vessel  80 . In this embodiment, the coil stent  50  is a coil stent blank, which is longer than the desired final length and is cut to the desired length at the deployment site. The sheath  66  includes a cutter  90 , such as a radio frequency (RF) cutter, at the distal end  61  of the sheath  66 . Once the desired length of the coil stent  50  is located at the deployment site  82 , the cutter  90  is activated to cut the coil stent  50 . Referring to  FIG. 5B , the coil stent  50  has been cut from the coil stent blank and the coil stent remainder  92  remains in the sheath  66 . The rotation of the helical screw  74  can be reversed to draw the coil stent remainder  92  into the sheath  66 . The coil stent delivery system can then be removed from the vasculature. 
       FIG. 6  is a cross section view of yet another embodiment of a coil stent delivery system made in accordance with the present invention. In this embodiment, the helical screw  174  includes screw teeth  192  oriented to engage the coil stent  50 . The screw teeth  192  help grip the coil stent  50  and move it through the sheath  66 . 
       FIG. 7  is a cross section view of yet another embodiment of a coil stent delivery system made in accordance with the present invention. In this embodiment, the coil stent  150  has stent teeth  194  oriented to engage the screw teeth  192 . The stent teeth  194  can help move the coil stent  150  through the sheath  66 , anchor the coil stent  150  in the vessel, and/or prevent the coil stent  150  from slipping during deployment. The stent teeth  194  can be teeth and/or barbs as desired for a particular application. 
       FIG. 8  is a flow chart for a method of delivering a coil stent in accordance with the present invention. The method  200  includes providing a coil stent delivery system  202 , the coil stent delivery system having a sheath defining a sheath lumen and a shaft with a helical screw disposed about the shaft in the sheath lumen; advancing a distal end of the sheath to a deployment site  204 ; engaging the coil stent with the helical screw  206 ; and rotating the shaft  208  to rotate the helical screw and urge the coil stent through the sheath toward the deployment site. In one embodiment, the method  200  can further include rotating the shaft until the coil stent is free of the distal end of the sheath and deployed at the deployment site. In another embodiment, the method  200  can further include rotating the shaft until a portion of the coil stent is free of the distal end of the sheath, and retracting the sheath to deploy the coil stent at the deployment site. 
     In yet another embodiment, the method  200  can include rotating the shaft in a first direction until a portion of the coil stent is free of the distal end of the sheath; evaluating placement of the coil stent at the deployment site; and rotating the shaft in a second direction opposite the first direction to retract the portion of the stent into the sheath when the placement of the coil stent at the deployment site is not as desired. In yet another embodiment, the coil stent can be a coil stent blank, and the method  200  can include rotating the shaft until a desired length of the coil stent blank extends from the distal end of the sheath; and cutting the coil stent blank at the distal end of the sheath. In yet another embodiment, the method  200  can include counting rotations of the shaft to determine an axial location of the coil stent in the sheath. 
     It is important to note that  FIGS. 1-8  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.