Abstract:
A stent delivery system is provided with an inner elongate shaft having a proximal portion and a distal portion and an outer elongate shaft having a lumen extending at least partially therethrough, wherein the proximal portion of the inner elongate shaft is at least partially movably disposed within the lumen. The system also includes a stent positionable about the inner elongate shaft having collapsed and expanded configurations. The system includes a proximal restraining member removably engaged with the outer elongate shaft and attached the stent, and a distal restraining member removably engaged with the inner elongate shaft and attached to the stent. The system also has a proximal biasing member operatively engaged with a distal portion of the outer elongate shaft, a distal biasing member operatively engaged with the distal portion of the inner elongate shaft, and an outer tube with a lumen movably disposed over the inner elongate shaft.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a medical device and, in particular to a device for delivering and deploying a self-expanding stent and a method of delivering and deploying the stent into a body lumen. 
       BACKGROUND 
       [0002]    Self-expanding stents are medical devices used to treat diseased areas of a variety of body lumens, including, but not limited to: veins, esophagi, bile ducts, colons, and ureters. Generally, self-expanding stents are used to support a weak point in the body lumen or to bypass it completely. A self-expanding stent is a tubular structure with at least one lumen that runs through it. Self-expanding stents are often made of a wire or mesh material that can elastically contract and expand. 
         [0003]    A self-expanding stent is typically introduced into the body using a delivery device that includes an outer sheath coaxially disposed and slidable over an inner catheter. The stent is disposed at the distal end of the device between the inner catheter and the outer sheath and held in a compressed position by the outer sheath. The inner catheter and the outer sheath move coaxially with respect to each other. The stent may be deployed by proximally pulling the outer sheath relative to the inner catheter until the stent is exposed. The self-expanding stent then expands from the stent distal end to the stent proximal end as the sheath is proximally withdrawn. 
         [0004]    Several problems may occur with the sheathed delivery device described above. Sheath release delivery devices are difficult to reposition or remove and slow to operate. Often, the stent is first partially deployed to determine whether the stent is properly positioned within the body lumen. Partial deployment is achieved by withdrawing the outer sheath so that only a portion of the self-expanding stent is exposed. The stent may then be reconstrained by pushing the outer sheath back over the entire length of the stent, thus allowing the stent to be repositioned or removed. However, once the stent is fully deployed, i.e. radially expanded, the sheath cannot reconstrain the stent. For example, utilizing a conventional outer sheath/inner catheter delivery device may cause the physician to inadvertently use excessive force and pull back the outer sheath too far, thereby prematurely deploying the stent in an incorrect position within a body lumen. At this step in the procedure, repositioning of the stent becomes difficult, if not impossible, because the stent has already radially self-expanded in the body lumen. Additionally, retraction of the outer sheath with controlled movement may not be achieved because the physician is manually retracting the outer sheath which may lead to uneven or inadvertent movement of the outer sheath that can lead to improper positioning of the stent. 
         [0005]    Additionally, in a typical sheath release device where the outer sheath is proximally withdrawn, the first portion of the self-expanding stent to make contact with the body vessel is the most distal portion of the stent. This type of release may cause difficulty in accurately placing the proximal portion of the stent because the distal end of the stent is positioned first while the proximal portion of the stent is still covered by the outer sheath. Accurate placement of the proximal portion of the stent and/or the stent body may be important in certain applications such as to prevent stent migration. Additionally, conventional sheathed stent delivery systems may cause problems where direct visualization of the stent is required. For example, in endoscopically placed stents, the sheath tends to prevent or obscure the location of the stent, making accurate placement of the stent more difficult. 
         [0006]    Further potential drawbacks for the conventional sheathed stent delivery system involve the stent placement within the system prior to use within a patient. Loading and anchoring of a conventional sheathed stent delivery device is an involved process that may require preloading the stent into the device so that the stent remains compressed within the sheath during shipment and storage prior to use in the patient. Extended compression of the stent may lead to an alteration in the stent mechanical properties. 
         [0007]    Conventional sheathed stent delivery devices also require a high force to overcome the friction between the stent and the sheath that may also be a problem for proper stent placement within the patient. The introducer must be mechanically strong enough to overcome the frictional forces between the sheath and the stent to avoid undesirable frictional consequences such as stretching of the introducer catchers and hysterics in the movement of the stent. The sheathed stent delivery device also requires more space within an endoscope compared to a sheathless device and also adds additional expense to the delivery system. 
         [0008]    Accordingly, in view of the drawbacks of current technology, there is a desire for a delivery system that can increase the control, accuracy and ease of placement of a stent during deployment of the stent within a lumen within a patient. The delivery system would ideally reduce the risk of malfunction while providing for a smoother, more accurate and quicker deployment of the entire stent. The delivery system also would provide the ability to recollapse, recapture, reposition and/or remove the stent after expansion of the stent. 
       BRIEF SUMMARY 
       [0009]    In one aspect of the present invention, a stent delivery system is provided. The stent delivery system comprises an inner elongate shaft comprising a proximal portion and a distal portion and an outer elongate shaft comprising a lumen extending at least partially therethrough, wherein the proximal portion of the inner elongate shaft is at least partially movably disposed within the lumen. The system further comprises a stent positionable about the inner elongate shaft having a collapsed configuration and an expanded configuration. The system also comprises at least one proximal restraining member removably engaged with the outer elongate shaft, wherein the at least one proximal restraining member is also attached to the stent and at least one distal restraining member removably engaged with the inner elongate shaft, wherein the at least one distal restraining member is also attached to the stent. The system further comprises a proximal biasing member operatively engaged with at least a distal portion of the outer elongate shaft, the proximal biasing member configured to prevent unintentional disengagement of the proximal restraining member from the outer elongate shaft, and a distal biasing member operatively engaged with the distal portion of the inner elongate shaft, the distal biasing member configured to prevent unintentional disengagement of the distal restraining member from the inner elongate shaft. Additionally, the system comprises an outer tube comprising a lumen extending at least partially therethrough, wherein the distal portion of the inner elongate shaft is at least partially movably disposed within the lumen of the outer tube, wherein the outer tube is disposed between the proximal biasing member and the distal biasing member. Additionally, movement of the inner elongate shaft relative to the outer elongate shaft in a first direction releases tension to the proximal and distal restraining members to move the stent to the expanded configuration. 
         [0010]    The stent delivery system may further comprise a first position and a second position, wherein the inner elongate shaft is moved proximally with respect to the outer elongate shaft to move the stent delivery system from the first position to the second position and the stent is in the expanded configuration in the second position and the stent is in the collapsed configuration in the first position. The stent delivery system may also further comprise a third position, wherein the inner elongate shaft is moved proximally with respect to the outer elongate shaft to move the stent delivery system from the second position to the third position, wherein in the third position the at least one proximal restraining member is released from the outer elongate shaft and the at least one distal restraining member is released from the inner elongate shaft, thus releasing the stent from about the inner elongate shaft. In another embodiment, a proximal portion of the proximal biasing member is fixedly secured to the outer elongate shaft and a distal portion of the distal biasing member is fixedly secured to the inner elongate shaft, wherein when the stent delivery system is moved from the second position to the third position the outer tube pushes a distal portion of the proximal biasing member in a proximal direction and a proximal portion of the distal biasing member in a distal direction. The stent delivery system may additionally comprise at least one proximal restraining member removably engaged with the outer elongate shaft by a proximal hook fixedly attached to the outer elongate shaft, and the at least one distal restraining member removably engaged with the inner elongate shaft by a distal hook fixedly attached to the inner elongate shaft, wherein the distal hook is attached to the inner elongate shaft at a point distal to the proximal hook. Further, in the first and second position the at least one proximal restraining member is engaged with the proximal hook and the at least one distal restraining member is engaged with the distal hook, wherein in the third position the at least one proximal restraining member is released from the proximal hook and the at least one distal restraining member is released from the distal hook. 
         [0011]    The stent delivery system may also comprise a proximal end stop fixedly attached to a distal portion of the outer elongate shaft and a distal end stop fixedly attached to the distal portion of the inner elongate shaft. It may also comprise a proximal pusher sleeve slidably disposed about the proximal portion of the inner elongate shaft and a distal portion of the outer elongate shaft and disposed between the proximal end stop and the outer tube, and a distal pusher sleeve slidably disposed about the distal portion of the inner elongate shaft and disposed between the distal end stop and the outer tube. Further, the distal biasing member is disposed between the distal end stop and the distal pusher sleeve and the proximal biasing member is disposed between the proximal end stop and the proximal pusher sleeve and when the stent delivery system is moved from the second position to the third position the outer tube pushes the proximal pusher sleeve and the proximal biasing member in a proximal direction and the distal pusher sleeve and the distal biasing member in a distal direction. In another embodiment, the proximal restraining member may be removably engaged with the outer elongate shaft by a proximal hook fixedly attached to the outer elongate shaft and the distal restraining member may be removably engaged with the inner elongate shaft by a distal hook fixedly attached to the inner elongate shaft, wherein the distal hook is attached to the inner elongate shaft at a point distal to the proximal hook. Further, in the first and second position the at least one proximal restraining member may be engaged with the proximal hook and the at least one distal restraining member may be engaged with the distal hook, wherein in the third position the at least one proximal restraining member is released from the proximal hook and the at least one distal restraining member is released from the distal hook. 
         [0012]    In another aspect of the invention, a method of delivering a stent is provided. The method comprises inserting a distal portion of a stent delivery system into a body lumen of a patient. The stent delivery system comprises an inner elongate shaft comprising a proximal portion and a distal portion, an outer elongate shaft comprising a lumen extending at least partially therethrough, wherein the proximal portion of the inner elongate shaft is at least partially movably disposed within the lumen, a stent positionable about the inner elongate shaft, the stent having a collapsed configuration and an expanded configuration, at least one proximal restraining member removably engaged with the outer elongate shaft, wherein the at least one proximal restraining member is also attached to the stent, at least one distal restraining member removably engaged with the inner elongate shaft, wherein the at least one distal restraining member is also attached to the stent, a proximal biasing member operatively engaged with at least a distal portion of the outer elongate shaft, the proximal biasing member configured to prevent unintentional disengagement of the proximal restraining member from the outer elongate shaft, a distal biasing member operatively engaged with the distal portion of the inner elongate shaft, the distal biasing member configured to prevent unintentional disengagement of the distal restraining member from the inner elongate shaft, and an outer tube comprising a lumen extending at least partially therethrough, wherein the distal portion of the inner elongate shaft is at least partially movably disposed within the lumen of the outer tube, wherein the outer tube is disposed between the proximal biasing member and the distal biasing member. The method further comprises maintaining the stent in the collapsed configuration with the inner and outer elongate shafts in a first position and tension applied to the at least one proximal and at least one distal restraining members for delivery of the stent to an implant site, and positioning the stent at the implant site. The method also comprises expanding the stent to the expanded configuration by moving the inner and outer elongate shafts relative to each other to a second position, thereby releasing tension on the proximal and distal restraining members so that the stent moves to the expanded configuration. The method may also comprise returning the inner and elongate shafts to the first position to move the stent from the expanded configuration to the collapsed configuration. In another contemplation, the method may further comprise releasing the stent from about the outer elongate shaft at the implant site by moving the inner and outer elongate shafts relative to each other to a third position so that the proximal restraining member is released from the outer elongate shaft and the distal restraining members is released from the inner elongate shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of distal portion a stent delivery system in a first position according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a detailed view of the hook system of the stent delivery system in a first position; 
           [0015]      FIG. 3  is a detailed view of the hook system of the stent delivery system in a second position; 
           [0016]      FIG. 4  is a detailed view of the hook system of the stent delivery system in a first position; 
           [0017]      FIG. 5  is a side view of distal portion a stent delivery system in a second position; 
           [0018]      FIG. 6  is a side view of distal portion a stent delivery system in a third position; 
           [0019]      FIG. 7  is a detailed view of the hook system of the stent delivery system in a third position; and 
           [0020]      FIG. 8  is a detailed view of a handle of the stent delivery system. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings. It should also be understood that the drawings are not to scale and in certain instances details have been omitted, which are not necessary for an understanding of the present invention, such as conventional details of fabrication and assembly. 
         [0022]    As used in the specification, the terms proximal and distal should be understood as being in the terms of a physician using the delivery system. Hence the term distal means the portion of the delivery system which is farthest from the physician and the term proximal means the portion of the delivery system which is nearest to the physician. 
         [0023]      FIG. 1  illustrates a distal end of a stent delivery system  10  in accordance with embodiments of the present invention. The stent delivery system  10  may include an inner cannula  12  and an outer cannula  14 . The outer cannula  14  (or outer elongate shaft) may be an elongate shaft with a lumen within which a portion of the inner cannula  12  (or inner elongate shaft) is movably disposed. The inner cannula  12  may optionally have a lumen for a wire guide. An outer tube  16  may be movably disposed over a distal portion of the inner cannula  12 . A proximal end stop  18  may be fixedly secured to a distal portion of the outer cannula  14 . A distal end stop  20  may be fixedly secured to the distal end of the inner cannula  12  or a tip  22  of the stent delivery system  10 . A proximal pusher sleeve  24  may be positioned between the outer tube  16  and the proximal end stop  18 . The proximal pusher sleeve  24  may be freely slidable over both the inner cannula  12  and outer cannula  14 . A distal pusher sleeve  26  may be positioned between the outer tube  16  and the distal end stop  20 . The distal pusher sleeve  26  may be freely slidable over the inner cannula  12 . Positioned between the proximal end stop  18  and the proximal pusher sleeve  24  is a proximal spring  28 . The one end of the proximal spring  28  may be fixedly secured to the proximal end stop  18 , while the other end may be optionally secured to the proximal pusher sleeve  24 . A distal spring  30  may be positioned between the distal end stop  20  and the distal pusher sleeve  26 . One end of the distal spring  30  may be fixedly secured to the distal end stop  20 , while the other end may be optionally secured to the distal pusher sleeve  26 . While in this embodiment, springs are used, any other biasing member may be used in place of the proximal and distal springs  28 ,  30 . A proximal hook  32  may be attached to the outer cannula  14  at a point distal the proximal end stop  18 , while a distal hook  34  may be attached to the inner cannula  12  at a point proximal the distal end stop  20 . A stent (not shown) may be loaded over the inner cannula  12 , outer cannula  14 , and outer tube  16 . The stent may be attached to the stent delivery system  10  at the proximal and distal hooks  32 ,  34 . 
         [0024]      FIGS. 2, 3, and 4  show detailed views of the stent  36  and how it may be attached to the stent delivery system  10 . As shown in  FIG. 2 , when the stent delivery system  10  is in its natural state without any external forces applied, the proximal spring  28  covers the proximal hook  32 . To expose the proximal hook  32 , the proximal pusher sleeve  24  is advanced proximally, thus contracting the proximal spring  28  until the proximal hook  32  is exposed. Once the proximal hook  32  is exposed, as shown in  FIG. 3 , one or multiple suture loops  38 , or restraining members, are looped around the proximal hook  32  at one end, and attached to the stent  36  at the other end. The proximal pusher sleeve  24  is then released and the proximal spring  28  pushes the proximal pusher sleeve  24  distally to its original, natural position. The proximal spring  28  covers a portion of the suture loops  38  while applying a distal force to them, thus securing them and, by extension, the stent  36  to the proximal hook  32  and the stent delivery system  10 . The same process is repeated at the distal end of the stent delivery system  10 , thus securing the distal end of the stent  36  to the distal hook  34  with additional suture loops  38 . While suture loops  38  are used in the present embodiment, any other similar restraining members may be used instead. 
         [0025]      FIG. 1  shows the stent delivery system  10  in a first position; however, the stent delivery system  10  may also have at least a second position ( FIG. 5 ). The operator may alternate between the two positions by moving the inner cannula  12  relative to the outer cannula  14 . To move the stent delivery system  10  from the first position to the second position, the inner cannula  12  is moved proximally relative to the outer cannula  14 . The stent  36  (not shown in  FIGS. 1 and 5 ) may be movable between a collapsed and an expanded configuration. In the collapsed configuration, the stent  36  is longitudinally extended along the stent delivery system  10 , which causes the stent  36  to correspondingly collapse in an axial direction. In the expanded configuration, the stent  36  is longitudinally contracted along the stent delivery system  10 , which causes the stent  36  to correspondingly expand axially. When the stent  36  is attached to the stent delivery system  10 , the first position of the stent delivery system  10  corresponds to the collapsed configuration of the stent  36 , while the second position of the stent delivery system  10  corresponds to the expanded configuration of the stent  36 . The proximal hook  32  is located at a fixed position on the outer cannula  14 , while the distal hook  34  is located at a fixed position on the inner cannula  12 . Thus, as the inner cannula  12  and outer cannula  14  are moved longitudinally with respect to each other, the distance between the distal and proximal hooks  32 ,  34  either increases or decreases. Since one end of the stent  36  is attached to the distal hook  34  and the other end is attached to the proximal hook  32 , as the inner cannula  12  and outer cannula  14  are moved with respect to each other, a tension is applied or released to the stent  36  through the suture loops  38 , thus causing the stent  36  to correspondingly collapse or expand. When the stent delivery system  10  is in the first position, the proximal hook  32  and distal hook  34  are at distance that causes a tension to be applied to the stent  36 , thus maintaining the stent  36  in the collapsed configuration. As the stent delivery system  10  is moved to the second position, the distance between the proximal and distal hooks  32 ,  34  decreases, therefore releasing the tension on the stent  36  and thus allowing the stent  36  to longitudinally contract and axially expand into the expanded configuration. 
         [0026]    As shown in  FIGS. 6 and 7 , the stent delivery system  10  may also have a third position. To move the stent delivery system from the second position to the third position, the inner cannula  12  is again moved proximally relative to the outer cannula  14 . As the inner cannula  12  continues to be moved in a proximal direction, an increasing amount of the distal portion of the inner cannula  12  will be pulled into the lumen of the outer cannula  14 . Because of this movement, eventually one end of the outer tube  16  will contact the proximal pusher sleeve  24  and the other end of the outer tube  16  will contact the distal pusher sleeve  26 . At this point, any further proximal movement of the inner cannula  12  will cause the outer tube  16  to force the proximal pusher sleeve  24  in a proximal direction against the proximal spring  28  and the distal pusher sleeve  26  in a distal direction against the distal spring  30 . As both pusher sleeves  24 ,  26  are forced in their respective directions, their respective springs  28 ,  30  will contract. As shown in detail in  FIG. 7 , (and as is similarly happening on the distal end of the stent delivery system  10 ) once the outer tube  16 , due to the motion of the inner cannula  12 , pushes the proximal pusher sleeve  24  proximally to the third position, the proximal hook  32  is exposed and the proximal pusher sleeve  24  pushes the suture loops  38  off the proximal hook  32 , thus releasing the suture loops  38 , and by extension the stent  36 , from about the stent delivery system  10 . Once the stent  36  is released from about the stent delivery system  10 , the stent  36  is fully deployed in the target body lumen. Because the operator must apply a deliberate directional force to the stent delivery system to deploy the stent  36 , accidental or premature deployment of the stent  36  is unlikely. For example, the chance of accidental deployment while the stent  36  is being delivered to the diseased site is lessened. 
         [0027]    In this embodiment, both pusher sleeves  24 ,  26  have a U-shaped design, with prongs  40 . The prongs  40  of the pusher sleeves  24 ,  26  are designed to contact and push the springs  28 ,  30 , thus leaving a gap between the prongs  40  where the hooks  32 ,  34  can be exposed. Thus, when the suture loops  38  are pushed off the hooks  32 ,  34  by the pusher sleeves  24 ,  26 , there is a gap that allows them to freely release from the stent delivery system  10  without getting caught on the springs  28 ,  30 . However, a design omitting the pusher sleeves  24 ,  26  altogether is possible. By omitting the pusher sleeves  24 ,  26 , the outer tube  16  may directly contact the springs  28 ,  30  and push them in their respective directions. The outer tube  16  may also include integral prongs  40  on each end, thus eliminating the need for the pusher sleeves  24 ,  26  altogether. Additionally, while hooks  32 ,  34  are used to secure the suture loops  38  to the stent delivery system  10 , any structure or method capable of removably securing the suture loops  38  to the stent delivery system  10  may be used. Also, while single hooks  32 ,  34  are used on each end of the stent delivery system  10 , multiple hooks can be used at each end. For example, the proximal hook  32  may be replaced with two or more hooks with individual suture loops  38  attached to each hook and the stent  38 . 
         [0028]    The stent  36  is ideally a self-expandable woven or braided stent, thus allowing the stent  36  to automatically expand once freed from about the stent delivery system  10 . By way of non-limiting example, the stent  36  may be formed as a woven or braided mesh formed from a metal or polymer or a laser cut pattern formed in a metal stent. The stent delivery system  10  uses the axial elongation of compressed woven, braided, or laser cut stents, normally considered a disadvantage, as an advantage to eliminate the need for a delivery sheath. The stent may also be formed from a bioabsorbable material. One example of a woven stent is the EVOLUTION® stent (Wilson-Cook Medical, Inc.). 
         [0029]    The suture loops  38  may each be attached to the stent  36  at single points, or they may be woven through the respective ends of the stent  36 . Thus, when tension is applied to the suture loops  38 , the ends of the stent  36  will radially close in addition the stent  36  elongating and collapsing, thus allowing a more uniformly collapsed profile. 
         [0030]    As shown in  FIG. 8 , a handle  50  attached to the proximal end of the stent delivery system  10  may be used to assist the operator in manipulating the inner cannula  12  relative to the outer cannula  14 . A hinge  52  allows the left arm  54  and right arm  56  of the handle  50  to pivot with respect to each other, thus allowing the outer cannula  14  and inner cannula  12  to move correspondingly. Thus, the operator may use the handle  50  to easily move the stent delivery system  10  between the first, second, and third positions. The handle  50  may also include a spring  58  or other biasing member to bias the handle  50  in a certain position. In one embodiment, the spring  58  may bias the stent delivery system  10  towards the first position, thus requiring deliberate manipulation of the handle by the physician to move the stent delivery system  10  into the second and third positions. Alternatively, the spring  58  may bias the stent delivery system  10  towards the second, or even third, positions. In some embodiments, a lock  60  may be used to releasably lock the handle  50  in any longitudinal position, such as the first, second, or third positions. Alternatively, separate handles may be used for the inner cannula  12  and the outer cannula  14 , with a lock  60  between them. Also alternatively, handles may be omitted altogether and the operator may directly manipulate the inner and outer cannulas  12 ,  14 . 
         [0031]    The design of the stent delivery system  10  may be altered to achieve various desirable characteristics. For example, the stent delivery system  10  may be designed such that the outer tube  16  is in contact with the proximal and distal pusher sleeves  24 ,  26  when the stent deployment system  10  is in the first position. Thus, the proximal and distal springs  28 ,  30  will apply a resistive force to any attempted movement of the stent delivery system  10  to the second position, and further to the third position. Therefore the default, natural state of the stent deployment system  10  will be in the first position, which allows easier maneuverability within a body lumen without having to ensure the stent  36  remains collapsed. Similarly, the stent delivery system  10  may be designed such that the outer tube  16  initially contacts the proximal and distal pusher sleeves  24 ,  26  when the stent delivery system  10  is in the second position. Thus, the stent delivery system  10  is freely movable between the first and second positions; but when moving the stent delivery system  10  from the second position to the third position, the proximal and distal springs  28 ,  30  will provide a resistive force. This resistive force may provide a cue to the operator that any further movement towards the third position may result in premature or accidental deployment of the stent  36 . Thus, the operator may freely move the stent delivery system  10  between the first and second positions without fear of accidental deployment, and will have to apply a greater, deliberate force to move the stent delivery system  10  to the third position and deploy the stent  36 . 
         [0032]    In accordance with the alternative design choices discussed above, the proximal and distal springs  28 ,  30  may also be altered to achieve various desirable results. For example, it is often desirable to control which portion of the stent  36  is deployed first. To achieve this controlled deployment, the distal spring  30  may be shorter in length than the proximal spring  28  or have a lower requisite force to compress the distal spring  30  a certain distance. Thus, when the outer tube  16  is pushing against and compressing both the proximal and distal springs  28 ,  30 , the shorter length of the distal spring  30  or reduced requisite force to compress the distal spring  30  will cause the distal hook  34  to be exposed prior to exposure of the proximal hook  32 , thus causing the distal end of the stent  36  to release from about the stent deployment system  10  first. Alternatively, the proximal spring  28  may be designed to allow the proximal end of the stent  36  to deploy first. As an alternative to changing the design of the springs  28 ,  30 , the location of the proximal and distal hooks  32 ,  34  may be altered to achieve the same results. 
         [0033]    While not necessary, the stent delivery system  10  may include a standard delivery sheath slidably positionable over a portion of the stent delivery system  10  to cover the stent  36 . The optional delivery sheath may form a smooth outer surface to facilitate a smoother delivery of the stent  36  to the desired location. For example, the smooth outer surface may prevent damage to the walls of the body lumen or damage to the stent  36  while the stent delivery system  10  is being inserted into the body lumen. When present, the delivery sheath may provide some compressive force to the stent  36 . Once the stent delivery system  10  is at the desired location, the delivery sheath may be removed by sliding the delivery sheath proximally with respect to the stent delivery system  10  until the delivery sheath has been withdrawn from the patient&#39;s body lumen. Once the delivery sheath is removed, the stent delivery system  10  may be used as previously described. 
         [0034]    While the embodiment discussed above makes use of certain components to achieve the desired functionality of the stent delivery system  10 , other components that perform the same functions may be used. For example, the proximal end stop  18  may be replaced with any structure capable of preventing the proximal end of the proximal spring  28  from sliding along the stent delivery system  10  in a proximal direction. Alternatively, the proximal end stop  18  may be removed entirely and the proximal spring  28  may be fixedly secured to the outer cannula  14 . Similar substitutions may be made for the distal end stop  20 . 
         [0035]    In some embodiments, the suture loops  38  may remain attached to the stent  36  after the stent delivery system  10  is withdrawn. The suture loops  38  may be designed to be biodegradable. Additionally, while this embodiment utilizes suture loops  38  to secure the stent  36  to the stent delivery system  10 , any type of mechanism that can releaseably hold the stent  36  in an expanded and collapsed configuration may be used. By way of non-limiting example, the suture loops  38  may be substituted with releasable bands, hooks, adhesives, wires, and the like. 
         [0036]    The materials used to manufacture the components of the stent delivery systems described herein may be any materials known to one skilled in the art that are suitable for use in patients. By way of non-limiting example, the inner cannula, outer cannula and delivery sheath may be formed from polytetrafluoroethylene (PTFE) particularly when a low friction delivery sheath is desirable. Nylon and HDPE may also be used for clarity. Additional possible materials include, but are not limited to the following, polyethylene ether ketone (PEEK), fluorinated ethylene propylene (FEP), perfluoroalkoxy polymer resin (PFA), polyamide, polyurethane, high density or low density polyethylene, and nylon including multi-layer or single layer structures and the like and may also include reinforcement wires, braid wires, coils, coil springs and or filaments. 
         [0037]    The stent may be formed from but is not limited to the following materials: Nickel titanium alloys, for example, nitinol, stainless steel, cobalt alloys and titanium alloys. The wires may be made from a metallic alloy such as stainless steel or nickel titanium. In some embodiments, the restraining members may be made from polymers having sufficient strength to hold the stent in the collapsed configuration. The restraining members may be single, multiple, braided or twisted. In some embodiments, the restraining members or segments thereof may be coated, for example with a coating such as PTFE. In some embodiments, the stent and/or the restraining members may be made from biodegradable materials. A number of bioabsorbable homopolymers, copolymers, or blends of bioabsorbable polymers are known in the medical arts. These include, but are not necessarily limited to, polyesters including poly-alpha hydroxy and poly-beta hydroxy polyesters, polycaprolactone, polyglycolic acid, polyether-esters, poly(p-dioxanone), polyoxaesters; polyphosphazenes; polyanhydrides; polycarbonates including polytrimethylene carbonate and poly(iminocarbonate); polyesteramides; polyurethanes; polyisocyanates; polyphosphazines; polyethers including polyglycols, polyorthoesters; epoxy polymers including polyethylene oxide; polysaccharides including cellulose, chitin, dextran, starch, hydroxyethyl starch, polygluconate, hyaluronic acid; polyamides including polyamino acids, polyester-amides, polyglutamic acid, polylysine, gelatin, fibrin, fibrinogen, casein, collagen. 
         [0038]    Other suitable biocompatible materials may also be used for any of the components described herein. 
         [0039]    Operation of the stent delivery system  10  of the present invention is described with reference to the stent delivery system  10  by way of non-limiting example. Alternative methods of operating the system may also be used. The stent delivery system  10  may be provided in a sterile packaging. The stent  36  may be provided in the expanded configuration or collapsed configuration within the packaging. For example, some stent materials may weaken or otherwise deform when stored in a collapsed configuration during shipping and storage. The stent  36  may be provided in the expanded configuration and be moved to the collapsed configuration to the first position prior to delivery into the patient. 
         [0040]    The delivery system  10  may be delivered to the patient using an endoscope that may be positioned within the body lumen so the operator can view a proximal side of the diseased area to be treated with the stent  36 . The operator inserts the stent delivery system  10  into the patient&#39;s body lumen with the stent  36  in the collapsed configuration. A wire guide may be inserted first to assist in navigating the endoscope to the diseased site and the system  10  is then delivered through the working channel of the endoscope over the wire guide to the diseased site. The inner cannula  12  may have a lumen that receives the wire guide, or the inner cannula may be a solid elongate shaft. Alternatively, the stent delivery system  10  may be inserted into the patient&#39;s lumen without the use of an endoscope, depending on the size and location of the lumen. 
         [0041]    The collapsed stent  36  may be moved within the body lumen to correctly position the stent  36  at the diseased site. The stent delivery system  10  is moved to the second position and the stent  36  is correspondingly moved to the expanded configuration by proximal movement of the inner cannula  12  relative to the outer cannula  14 . The position of the expanded stent  36  can be monitored through fluoroscopy or other methods well known in the art. If necessary, such as if the stent  36  is incorrectly positioned, the physician may return the stent delivery system  10  to the first position and thus the stent  36  to the collapsed configuration by moving the inner cannula  12  distally with respect to the outer cannula  14 . The stent delivery system  10  may be moved from the first position to the second position, and thus the stent  36  from the collapsed configuration to the expanded configuration, as many times as needed. 
         [0042]    Once proper position for the stent  16  is achieved within the patient&#39;s body lumen, the stent delivery system  10  may then be moved to the third position, therefore causing the stent  36  to release from about the stent delivery system  10  and fully expand in the body lumen. The delivery system  10  may then be withdrawn proximally from the patient. 
         [0043]    The above Figures and disclosure are intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in the art. All such variations and alternatives are intended to be encompassed within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the attached claims.