Patent Publication Number: US-2005143803-A1

Title: Protective sheath for drug coated stent

Description:
RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Patent Application 60/532,797 filed Dec. 24, 2003. 
    
    
     FIELD OF THE INVENTION  
      This invention relates generally to protective sheaths for biomedical stents. More specifically, the invention relates to a protective sheath for biomedical drug coated stents to be used in packaging for shipping.  
     BACKGROUND OF THE INVENTION  
      Drug coated stents can improve the overall effectiveness of angioplasty and stenotic procedures performed on the cardiovascular system and other vessels within the body by delivering potent therapeutic compounds at the point of infarction. Drugs such as anti-inflammatants and anti-thrombogenics may be dispersed within the drug-polymer coating and released after insertion and deployment of the stent. These drugs and coatings can reduce the trauma to the local tissue bed, aid in the healing process, and significantly reduce the narrowing or constriction of the blood vessel that can reoccur where the stent is placed.  
      However, if the drug coated stents are packaged to ship to a medical practitioner, without a protective sheath, some of the drug on the stent may rub off of the stent while it is in the package. In a majority of cases, the drug coated stent attached to a catheter is covered with a protective sleeve and then inserted inside a hollow shipping tube. The shipping tube is then configured into a hoop to fit within a shipping box. During the bending of the hoop some of the drug may rub off into the protective sleeve as the stent and sleeve contact the side of the hoop.  
      In other cases, the drug coated stent attached to a catheter is placed within a protective sleeve and then pushed through the length of the looped shipping hoop, so that at least one point of the stent rubs against an inner surface of the hollow tube and the drug on the stent is removed from that point by friction. If the catheter is twisted upon insertion into the hollow tube, multiple points on the stent may have the drug removed by friction.  
      Sometimes the drug coated stent attached to a catheter is placed in a protective cover. The catheter with attached stent is then wrapped into a plurality of loops and connected to a tray. The stent may rub against the tray during the process of shipping on at least one point and the drug may be removed from that point by friction between the stent and the tray.  
      In all these packaging systems the protective sleeve is not always sufficient to prevent a quantity of drug from being rubbed off the stent. In a case when the drug is rubbed off, the drug intended for release to aid a patient is then reduced by an unknown and variable amount. This will result in variable aid for the patient with variable healing effects. It is desirable to package drug coated stents in a manner which prevents any reduction in the amount of drug on the stent.  
     SUMMARY OF THE INVENTION  
      It is an object of this invention to provide a sheath to be used in a packaging system to prevent friction on a drug coated stent from removing the drug applied on the stent by overcoming the deficiencies and limitations described above.  
      One aspect of the present invention provides a system for packaging a drug coated stent, including a transport package body with an arcuate catheter guide. The system also includes a catheter attached to the drug coated stent and received in the catheter guide. A sheath is disposed on the catheter and encloses the drug coated stent. The sheath includes at least one reduced thickness region to increase flexibility of the sheath.  
      A second aspect of the present invention provides a sheath for protecting a drug coated stent, including a body portion including a central lumen for receiving a drug coated stent. The body portion includes at least one reduced thickness region to increase flexibility of the sheath.  
      A third aspect of this invention provides a method for packaging a catheter mounted drug coated stent. The method includes sliding a proximal end of a sheath including at least one reduced thickness region over a distal end of the drug coated stent and contacting a tapered distal end of the sheath with the catheter. The method also includes flexing the sheath about the reduced thickness regions while inserting the catheter mounted drug coated stent into an arcuate guide of a transport package.  
      The present invention is illustrated by the accompanying drawings of various embodiments and the detailed description given below. The drawings should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding. 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. The foregoing aspects and other attendant advantages of the present invention will become more readily appreciated by the detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Various embodiments of the present invention are illustrated by the accompanying figures, wherein:  
       FIG. 1  is an illustration of a sheath, in accordance with a first embodiment of the current invention;  
       FIG. 2  is an illustration of the sheath of  FIG. 1 , in a flexed position;  
       FIG. 3  is an illustration of a prior art drug coated stent;  
       FIG. 4  is an illustration of a drug coated stent inside the sheath of  FIG. 1 ;  
       FIG. 5  is an illustration of a drug coated stent flexed inside the flexed sheath of  FIG. 2 ;  
       FIG. 6  is an illustration of a stent delivery catheter inserted to different positions within an arcuate catheter guide;  
       FIG. 7  is an illustration of a transport package;  
       FIG. 8  is an illustration of a sheath, in accordance with a second embodiment of the current invention;  
       FIG. 9  is an illustration of a sheath, in accordance with a third embodiment of the current invention;  
       FIG. 10  is an illustration of a sheath, in accordance with a fourth embodiment of the current invention;  
       FIG. 11  is an illustration of a stylet inserted into the sheath of  FIG. 1 ; and  
       FIG. 12  is an illustration of a sheath, in accordance with a fifth embodiment of the current invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS  
      The invention is based on the observation that the drug on drug coated stents was removed by varying amounts from the stent by friction between the drug coated stent and the shipping hoop in a packaging system used to ship the drug coated stents to medical practitioners. When the drug is removed by varying amounts the quality of care to a patient is degraded by varying and unknown amounts. Thus in accordance with the invention, a sheath prevents friction on a drug coated stent when the stent attached to a catheter is threaded into the shipping hoop. In this manner the sheath ensures that all the drug on a drug coated stent remains on the stent after shipment to a medical professional.  
      The following description should be read with reference to the drawings in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, are not intended to limit the scope of the invention.  
       FIG. 1  shows one embodiment of a sheath  100 . The body portion of sheath  100  has a sheath proximal end  120  with a proximal central lumen  125  and a sheath distal end  130 , which tapers down from a main body portion  110  to a sheath distal closed region  135 . The proximal end tapers up to the proximal end of the main body portion  110 . The sheath distal closed region  135  and opposing proximal central lumen  125  are both centered upon the central axis  105  of the sheath  100 .  
      The sheath  100  has a reduced thickness region forming a spiral configuration which encircles the main body portion  110  of the sheath  100 . The reduced thickness region in this embodiment is a spiral cut  140 . The spiral cut  140  begins at cut section  141  circles around the back side (not shown) of the main body portion  110  and is visible again at cut section  142 . After a second pass around the back of the main body portion  110  the cut is seen at cut section  143 . The cut sections  142  and  143  isolate the body section  145 . Body sections  146  and  147  are on either side of body section  145  and they are all separated by spiral cut  140 . The spiral cut  140  continues to diagonally encircle the main body portion  110  until it nears the end of main body portion  110  at cut section  144 , where the spiral cut  140  ends. The diameter of the main body portion  110  is larger than the diameter of proximal central lumen  125  and the diameter of sheath distal closed region  135 . The sheath  100  can be made out of plastics, such as polyethylene, polytrifluoroethlylene, polyurethane, polyelefin, vinyl derivatives, thermoplastics, thermosets, thermoplastic rubbers, and combinations thereof. The sheath  100  can be injected molded with the cuts  141 ,  142 ,  143 ,  144  or reduced thickness regions in place. In an alternate embodiment, sheath  100  is molded and then cuts are made in the main body portion  110 . Reduced thickness areas may be used in place of cuts when the remaining material is flexible enough to stretch and buckle as required when the sheath  100  is flexed.  
      The spiral cut  140  permits the main body portion  110  to be flexed, as shown in  FIG. 2 , in which like elements share like reference numbers with  FIG. 1 . The flexed sheath  200  has a curved axis  205 , which is centered in the proximal central lumen  125  and the sheath distal closed region  135  and has at least one radius of curvature. The spiral cut  140  inserted in the sheath  100  of  FIG. 1  changes shape to that of cut  240  when the sheath  100  is flexed to form flexed sheath  200 . The cut sections  242 ,  243  and  244  are now wider than cuts  142 ,  143  and  144  of  FIG. 1  on the side opposite the radius of curvature of curved axis  205 . At the top of the main body portion  210  the flexing has separated the edges of the cuts  242 ,  243  and  244 . Additionally, the cut sections  241 ,  242  and  243  are narrower than cut sections  141 ,  142  and  143  of  FIG. 1  on the side towards the radius of curvature of curved central axis  205 . At the bottom of the main body portion  210  the flexing has brought the edges of the cuts  241 ,  242  and  243  close together. On the inside of the radius of curvature of curved central axis  205  the body section  145  touches adjacent body section  146  on its proximal edge and body section  145  touches adjacent body section  147  on its distal edge. On the outside of the radius of curvature of curved central axis  205  the body section  145  does not touch either body section  146  or body section  147 .  
       FIG. 3  shows a stent delivery assembly  250  to be inserted into sheath  100  for shipping to a medical practitioner. The main components of the stent delivery system  250  include an undeployed stent  270  and a stent delivery catheter  260  including a catheter proximal end  261  and a catheter distal end  262  and an central lumen  263 , which is a tubular component. The use of stents and stent delivery systems is well known in the art. The stent may be deployed once in position within a lesion by expanding a balloon (not shown) folded under the stent  170  or by retracting a stent covering (not shown) that allows expansion of a self expanding stent. Once deployed the drug on the stent  270  is eluted to aid in the healing process.  
       FIG. 4  shows a stent delivery assembly  250  after it has been inserted into a sheath  100 . The outer diameter of the catheter distal end  262  is slightly larger than or just equal to the inner diameter of the sheath distal end  130  to provide an interference fit for the distal end  262  of the stent delivery catheter  260 . The stent  270  is axially aligned with the central axis  105  within the main body portion  110  of the sheath  100 . The catheter proximal end  261  is held within the opening  125  of the sheath  100 . The diameter of the main body portion  110  is larger than the diameter of the sheath proximal end  120  and the diameter of sheath distal end  130 . The diameter of the main body portion  110  is also larger than the undeployed stent  270  thus the undeployed stent  270  is not contacting any surface. The largest diameter of the stent delivery assembly  250  is smaller than the proximal central lumen  125  of the stent  100  to allow the proximal end of the sheath to slide over the distal portion of the stent delivery assembly  250 .  
       FIG. 5  shows the stent delivery assembly  250  after it has been inserted into a sheath  100  and flexed. The catheter distal end  262  of the flexed stent delivery catheter  260  maintains the interference fit in the sheath distal end  130  as stent delivery catheter  260  is flexed within flexed sheath  200 . The catheter distal end  262  and the catheter proximal end  261  of the stent delivery catheter  260  hold the flexed undeployed stent  290  in a position which prevents the stent  270  from contacting any surface of the flexed sheath  200 .  
       FIG. 6  is an illustration of a stent delivery catheter  260  inserted to different positions within an arcuate catheter guide  330 . As a stent delivery catheter  260  is threaded into the input opening  335  of the arcuate catheter guide  330  it is in a first position shown by first inserted stent delivery catheter  265 . The sheath  100 , which holds the undeployed stent  270 , is unflexed in this first position, since the sheath  100  has just entered the tubing of the arcuate catheter guide  330 . In this position the central axis  105  of sheath  100  is about tangential to arcuate catheter guide  330 . As the stent delivery catheter  260  continues to be threaded into the tube of the arcuate catheter guide  330  the sheath  100  moves to a second position shown by second inserted stent delivery catheter  266 . Since the sheath  100  is now forced against the curved inner surface of the arcuate catheter guide  330  and sheath  100  is now flexed into the position of flexed sheath  200 . If the flexed sheath  200  did not cover the stent  270  at least a portion of drug coated stent  270  would rub against the curved inner surface of the arcuate catheter guide  330 . Some of the drug on the drug coated stent  270  would be left on the inner surface of the arcuate catheter guide  330  due to the friction with drug coated stent  270 .  
      Once the stent delivery catheter  260  is completely threaded into the arcuate catheter guide  330  it placed in the shipping box  310 , as shown in  FIG. 7  where it is held in place with a plurality of attachment clips  320 . Only a proximal portion of the catheter proximal end  261  of the stent delivery assembly  250  is visible outside the arcuate catheter guide  330 . The sheath  200  will be in the flexed position while inside the arcuate catheter guide  330 . If the transport package body  300  is shaken or dropped during shipping the stent  270  will remain untouched by any surface as it is securely held inside the main body portion  210  by the interference fit of the catheter distal end  262  within the sheath distal end  130 .  
      The method for packaging a stent delivery catheter  260  mounted with a drug coated stent  270  begins by sliding proximal central lumen  125  of sheath  100  over the catheter distal end  262  of the stent delivery catheter  260 . Then the catheter distal end  262  contacts the tapered sheath distal end  130  and is guided towards the sheath distal closed region  135 . Next the central lumen  263  in centered within the sheath distal end  130  which holds catheter distal end  262  with an interference fit. The sheath  100  is flexed about the cuts  141 ,  142 ,  143  and  144  while the stent delivery catheter  260  mounted with drug coated stent  270  is inserted to the arcuate catheter guide  330  of a transport package body  300 .  
      Once the transport package body  300  is delivered, the medical practitioner pulls the exposed end of the catheter proximal end  261  away from the input opening  335  of the arcuate catheter guide  330  to un-thread the stent delivery catheter  260 . The flexed sheath  200  will continue to prevent friction between the drug coated stent  270  and the inner surface of the arcuate catheter guide  330  as the stent deliver catheter  260  is removed. The flexed sheath  200  will experience friction with the inner surface of the arcuate catheter guide  330  while protecting the stent  270 . When the stent is to be delivered to the cardiovascular system or other vessels within the body of a patient the medical practitioner removes the sheath  100  by pulling the catheter proximal end  261  and the sheath distal closed region  135  in opposite directions.  
       FIG. 8 , in which like elements share like reference numbers with  FIG. 1 , shows a second embodiment of a sheath  400 . Several circumferential cuts including  442 ,  443 ,  446 ,  447  provide the flexibility to sheath  400 . The circumferential cut  446  is in between circumferential cuts  442  and  443  and on the opposite side of the main body portion  110  of the sheath  400 . Main body section  445  is between circumferential cuts  442  and  443 . The circumferential cuts including  442 ,  443 ,  446 ,  447  may extend the length of the main body portion  110 . The spacing between cuts  442 ,  443 ,  446 ,  447  and the length and width of cuts  442 ,  443 ,  446 ,  447  may vary according the dimensions of the sheath  400 .  
       FIG. 9 , in which like elements share like reference numbers with  FIG. 1 , shows a third embodiment of a sheath  500 . Several circumferential cuts including  542 ,  543 ,  546 ,  547  and  548  provide the flexibility to sheath  500 . The circumferential cut  542  is directly opposed to circumferential cut  546 , which is on the opposite side of the main body portion  110  of the sheath  500 . The circumferential cut  543  is directly opposed to circumferential cut  547 , which is on the opposite side of the main body portion  110  of the sheath  500 . Main body section  545  is between circumferential cuts  542  and  543 . Circumferential cut  548  is disposed between the opposing pairs of cuts  542 ,  546 ,  545  and  547  and within a portion of the body section  545 . The center of the arc of the cut  548  is about right angle with the center of the arc of the cuts  542 ,  543 ,  546  and  547 . A cut directly opposing cut  548  and about the same length as cut  548  is on the back side of the main body portion  110 . The circumferential cuts including  542 ,  543 ,  546 ,  547  and  548  extend the length of the main body portion  110 .  
      The circumferential cuts including  542 ,  543 ,  546 ,  547  and  548  may extend the length of the main body portion  110 . The spacing between cuts  542 ,  543 ,  546 ,  547  and  548  and the length and width of cuts  542 ,  543 ,  546 ,  547  and  548  may vary according the dimensions of the sheath  400 .  
       FIG. 10 , in which like elements share like reference numbers with  FIG. 1 , shows a fourth embodiment of a sheath  600 . Several staggered cuts including  642 ,  643  and  644  provide the flexibility to sheath  600 . Each cut on sheath  600  comprises two circumferential cut sections  650  offset and connected by an axial cut section  660 . Thus at least a portion of cut regions including  642 ,  643  and  644  are along at least a portion of a circumference of a main body portion  110  of the sheath  100 . Axial cut section  660  is parallel the central axis  105  of the main body portion  110  of the sheath  100 .  
      The cuts  642 ,  643  and  644  are located in a staggered relation to each other. For example, cut  643  is over and down from  642  while cut  644  is over and down from cut  643  and so forth. All the cuts including  642 ,  643  and  644  form a spiral pattern around the main body portion  110 .  
      The cuts including  642 ,  643  and  644  may extend the length of the main body portion  110 . The spacing between cuts  642 ,  643  and  644  and the length and width of cuts  642 ,  643  and  644  may vary according the dimensions of the sheath  600 .  
      In an alternative embodiment, an alternating pattern of circumferential cut sections  650  and axial cut sections  660  may form one continuous cut spiraling around main body portion  110 .  
       FIG. 11 , in which like elements share like reference numbers with  FIG. 4 , shows how sheath  700  can accommodate a stylet  710 , which comprises a stylet head  720  and a stylet pin  730 . The stent delivery catheter  260  of  FIG. 3  is not shown inserted in the sheath  700  in  FIG. 11  for ease of viewing.  
      The function and use of stylets  710  is known in the art. A stylet pin  710  may be inserted into the central lumen  263  of a catheter distal end  262  during sterilization of the stent delivery catheter  260  to prevent the shrinkage of the inner diameter of the central lumen  263  in the catheter distal end  262 . This is important if the catheter is designed with tight tolerances. Additionally, a stylet prevents kinking of the stent delivery catheter  260  around the stent  270  area, which may happen if the stent delivery catheter  260  is handled roughly when being removed from the arcuate catheter guide  330 .  
      Stylets  710  are made from metal, such as stainless steel and plastics, such as polyethylene, polytrifluoroethlylene, polyurethane, polyelefin, vinyl derivatives, thermoplastics, thermosets, thermoplastic rubbers, and combinations thereof. Stylets come in various lengths dependant upon the stent length and may protrude from the protective sheath.  
      In  FIG. 11 , the stylet  710  is a separate piece from the sheath  700 . The sheath distal closed region  135  of sheath  100  is replaced with a sheath distal opening  131  having a diameter larger than the diameter of the stylet pin  730  and smaller than the diameter of the stylet head  720 . The inner diameter of the central lumen  263  of the catheter distal end  262  is larger than the outer diameter of the stylet pin  710 . This fit provides the interference fit to hold the catheter distal end  262  in place in the sheath  700  when stylet  710  is inserted into the sheath  700  with the catheter distal end  262  positioned in the sheath distal opening  131 . An interference fit is obtained by making the outer diameter of stylet pin  730  slightly larger than the inner diameter of central lumen  263 . In an alternative embodiment, a rough surface finish on the stylet pin  730  provides the interference fit. In an alternative embodiment, a slight S curvature is added to the stylet pin  730  for the interference fit.  
      The method for packaging a stent delivery catheter  260  mounted with a drug coated stent  270  begins by sliding the proximal central lumen  125  of sheath  700  over the catheter distal end  262  of the stent delivery catheter  260 . Then the catheter distal end  262  contacts the tapered sheath distal end  130  and is guided towards the sheath distal opening  131  so the central lumen  263  in centered within the sheath distal opening  131 . Next the stylet pin  730  is inserted into the central lumen  263  of the catheter distal end  262 . The sheath  700  is flexed about the cuts  141 ,  142 ,  143  and  144  while the stent delivery catheter  260  mounted with drug coated stent  270  is inserted to the arcuate catheter guide  330  of a transport package body  300 .  
      In an alternative embodiment, the stylet  710  may be inserted into the sheath  700  and then the distal end of the stent delivery catheter  260  is inserted into the sheath  700 . The tapering of the sheath distal end  130  guides the catheter distal end  262  towards the stylet pin  730 . As the stylet pin  730  enters the central lumen  263  an interference fit is provided.  
      In  FIG. 12 , a stylet  810  is an integral piece with the sheath  800 . The stent delivery catheter  260  of  FIG. 3  is not shown inserted in the sheath  800  in  FIG. 12  for ease of viewing. The sheath distal closed region  135  of sheath  100  in  FIG. 4  is now shaped as a pin  830  and a tab  820 . Tab  820  may have a shape similar to that of stylet head  720 . The pin  830  has a diameter smaller than the inner diameter of the central lumen  263  of the catheter distal end  262 . This fit provides the interference fit to hold the catheter distal end  262  in place in the sheath  800 . Stylet pin  830  may have a diameter, which is slightly more than the inner diameter of central lumen  263 . In this case, an interference fit to hold the catheter distal end  262  in place in the sheath  800  is provided. In an alternative embodiment, a rough surface finish on the stylet pin  730  provides the interference fit. In an alternative embodiment, a slight S curvature is added to the stylet pin  830  for the interference fit.  
      When the stent delivery catheter  260  is inserted into the sheath  800 , catheter distal end  262  has an outer diameter smaller than the inner diameter of the sheath distal region  130 . The central lumen  263  of the catheter distal end  262  will be positioned over pin  830  as the catheter distal end  262  is inserted into the sheath  800 . The tapering of the sheath distal end  130  guides the inner lumen  263  over the pin  830 .  
      The sheaths  100 ,  400 ,  500 ,  600 ,  700  and  800  can be made out of plastics, such as polyethylene, polytrifluoroethlylene, polyurethane, polyelefin, vinyl derivatives, thermoplastics, thermosets, thermoplastic rubbers, and combinations thereof. The sheaths  100 ,  400 ,  500 ,  600 ,  700  and  800  can be injected molded with the cuts or reduced thickness regions. In an alternative embodiment, sheaths  100 ,  400 ,  500 ,  600 ,  700  and  800  can be molded and then the main body portion  110  will be cut with the required pattern of cuts.  
      Reduced thickness regions may be used in place of some or all the cuts in the sheaths  100 ,  400 ,  500 ,  600 ,  700  and  800 . For example, the cut sections  140 ,  141 ,  142 ,  143 ,  144  may be reduced thickness areas in sheath  100 , which buckle and stretch as required when the sheath  100  is flexed. Various exemplary embodiments of cuts are presented but any cut or thickness reduction with allows for the main body portion  110  to flex without touching a stent  270  held within the sheaths  100 ,  400 ,  500 ,  600  and  700  is within the scope of the invention.  
      The stent delivery assembly  250  may be inserted in a flexible protective covering, such as a transparent plastic covering, to maintain sterility of the stent delivery assembly  250  prior to insertion into the arcuate catheter guide  330 . In this case the sheaths  100 ,  400 ,  500 ,  600 ,  700  and  800  prevent the drug from being rubbed off of the drug coated stent  270  into the flexible protective covering.  
      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.