Abstract:
The present invention generally relates to medical devices, particularly to a SDS (stent delivery system) that incorporates a spring stent stop. The delivery system, owing to a novel stent stop construction, can be assembled, with the crimped stent in place within the outer sheath of the device, to enable the device to be assembled with considerably greater efficiency by eliminating processes and component(s).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to medical devices, particularly to a SDS (stent delivery system) that incorporates a spring stent stop. The delivery system, owing to a novel stent stop construction, can be assembled, through the crimped stent in place within the outer sheath of the device, enabling the device to be assembled with considerably greater efficiency by eliminating process steps and component(s). 
       BACKGROUND OF THE INVENTION 
       [0002]    A stent is a generally longitudinal tubular device formed of biocompatible material(s) that is useful in the treatment of stenoses, strictures or aneurysms in blood vessels and other body vessels. Stents can be implanted within an unhealthy vessel to reinforce collapsing, partially occluded, weakened, or abnormally dilated sections of the vessel. Typically, stents are employed after angioplasty of a blood vessel to maintain vessel patency of the diseased lesion of the vessel. While stents are most notably used in blood vessels, stents may also be implanted in other body vessels such as the urogenital tract and the bile duct. A stent may exhibit flexibility to allow it to be inserted through curved vessels. Furthermore, Nitinol (self expanding) stents are often compressed radially, such as by crimping, to facilitate placement into the delivery system in preparation for deployment using intraluminal catheter implantation. 
         [0003]    Stents are akin to scaffoldings in their support of the passageway. Structurally, a stent may have two or more struts or wire support members connected together into a lattice-like frame. As indicated, stents may be in a compressed state prior to delivery and deployment, as compression facilitates insertion through small cavities. Stents can be delivered to the desired implantation site percutaneously in a catheter or similar transluminal device. With a lattice-like structure, a portion of the stent surface area is open, such openings defined by the struts that form the stent. 
         [0004]    Typically, during delivery of self-expanding stents, the delivery device encloses the stent within the distal sheath. The stent and sheath can be advanced to a site within the patient&#39;s vessel through a guide catheter. A self-expanding stent possesses chronic outward force (COF) when warmed above the martensitic transition temperature for the nitinol alloy (e.g., above 30° C.), which causes the stent to expand to a pre-determined diameter following its deployment in the vessel when the encasing sheath is retracted from the compressed stent. 
         [0005]    Stent delivery systems (SDS) for self-expanding stents are generally comprised of an inner shaft or shafts terminating distally in a stop, from which a separate wire lumen extends further distally, and at the end of such wire lumen is provided a distal tip. The inner shaft of stent delivery systems disclosed in the art may have a proximal portion made from a flexible coiled member, akin to a compressed or closed coil spring, and a distal wire lumen that may be polymeric in constitution, such as a construct formed of a coextrusion of high density polyethylene and nylon. The stent resides within the distal outer sheath of the device. The outer sheath is comprised of various segments joined together by any number of means known to those of ordinary skill in the art including heat fusing, adhesive bonding, chemical bonding or mechanical attachment. The prior art further shows that a stop is fixed to the inner shaft in the vicinity of where the flexible coiled member and distal shaft portion converge. The diameter of the stop should provide sufficient surface area to maintain relative position of the stent during deployment, that is, the stop should provide a counterforce against stent movement as the outer shaft is pulled in the proximal direction as part of the stent deployment process. 
         [0006]    The stent is crimped and loaded into an outer sheath. The stent has to be loaded into the outer sheath, a process that renders the construction and assembly of the delivery device highly complex. Furthermore typical construction of the distal region of a delivery device is complicated because the outer sheath is typically a component separate from the inner shaft member. Thus, the inner shaft and the outer sheath must be assembled in a specific order in order to have the stop proximal of the stent. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a stop for use in a stent delivery system, which exhibits spring-like characteristics. The stop of the present invention is compressible preferably in a radially inward direction when a sufficient compressive force is applied, yet expands to its original non-compressed state when such force is removed. When in the desired position on the axially extending member of the medical implant delivery device, the stop provides a rigid surface positioned to contact the proximal stent end. That is, when the stent is positioned upon the axially extending member, such as the inner shaft of the medical implant delivery device, the rigid surface of the stop contacts the stent, maintaining the position of the stent during deployment. This function is advantageous as the outer sheath is retracted proximally during deployment, an action that but for the presence of the stop, could cause the stent to be deployed outside the target site. This configuration allows the inner sheath assembly (with stop affixed) to be assembled by passing the proximal end of the inner sheath assembly through the distal outer member and have the loaded stent already in place. The inner sheath could eliminate the need for a separate guidewire sheath, as the tip of the device can be over-molded directly on the inner sheath prior to assembly. 
         [0008]    The stent stop of the present invention can be constructed of elements arrayed to define a through hole sized to receive the inner shaft of the medical implant delivery device. 
         [0009]    In one aspect of the invention, the spring stent is provided with elements having a first base end from which a plurality of fingers distally project. The fingers are radially compressible inward, in a direction extending towards the inner shaft member, yet biased to project radial openness at the distal end of the spring stent stop, which radial openness at the distal end is relatively greater than the radial openness of the base end (proximal end) of the device. 
         [0010]    In yet another aspect, the spring stent stop of the present invention is sized and dimensioned so that when compressed, the stop has sufficiently reduced outer diameter to allow it to pass through a crimped stent as it moves proximally through the stent, and then into the desired position proximal to the stent. The particular aspect simplifies the preparation of the delivery device that employs the present spring stent stop in that the stop can be installed on the device after installation of the stent. 
         [0011]    In a further aspect of the invention, the stop possesses memory, so that upon compression, the stop returns to its original uncompressed dimensions once a compressive force is no longer applied to it. In the uncompressed state, the diameter of the distal end of the stop as manifested in the degree of openness of the fingers of the stop is substantially the same as the inner diameter of the outer member. Such memory can be provided by a biasing component, or material property of the material used in constructing the stop. 
         [0012]    The spring stent stop is affixed to the target location of residence upon the axially extending member by, for example, crimping, welding, or bonding it to the inner member. The stop member, ordinarily constructed of a relatively rigid material, can provide the inner member with an additional degree of column strength, preventing the inner sheath from collapsing and facilitating deployment of the stent while maintaining stent position at the target lesion. In a further embodiment, the present invention is a delivery device comprising the aforedescribed spring stent stop. In a specific embodiment, the stent delivery system requires no separate wire lumen distal to the stop, and further, construction of the inventive delivery system is simplified, as the distal tip is affixed to the inner member assembly subsequent to stent crimping and loading. That is, after the stent is loaded into the outer sheath, the inner member assembly, with the spring stent stop and tip previously affixed, can be moved into position so that the stent stop engages the proximal edge of the stent and the tip engages the distal outer sheath. 
         [0013]    A further embodiment of the present invention is a method of assembling and preparing a medical device delivery system for use in implanting a medical device in the body of a patient comprising the steps of loading the device (e.g., a stent), crimping the stent, loading crimped stent into the outer member, passing a spring stent stop, such as described above, proximally through the stent, positioning the spring stent stop, aligning the distal tip to the outer sheath of the device, and then fixing the aligned inner member to proximal handle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an elevational view of a stent delivery system in that can be modified in accordance with the present invention; 
           [0015]      FIG. 2  is a perspective view of a spring stent stop of the present invention passing through a stent; and 
           [0016]      FIG. 3  is a second perspective view of a spring stent stop of the present invention positioned for delivery and deployment of the stent. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The structural attributes of the present invention may be incorporated into existing stent delivery systems. For that reason, the features of the stent delivery systems disclosed in U.S. Pat. Nos. 6,773,446 and 6,939,352, each of which share the assignee with the present application, are incorporated herein by reference as an examples of stent delivery systems that can be modified to include the attributes within the ambit of this disclosure. However, the present invention need not be bound to the specific features and embodiments of these particular patent disclosures. In any event,  FIG. 1  illustrates a conventional stent delivery system of the kind disclosed in U.S. Pat. No. 6,773,446. 
         [0018]      FIG. 2  presents a perspective view of the present invention, in which spring stent stop  10  is shown at a position along the inner shaft member  100  of a stent delivery device. Specifically, the spring stent stop  10  is depicted at a position on the inner shaft member  100  that is proximal to distal tip  115  of delivery system. Here, the distal tip is shown in  FIGS. 1 and 2 , though upon consideration of the entirety of the disclosure, it shall be evident that the affixing of the distal tip  115  to the inner shaft member  100  can take place prior to assembly or affixed after the spring stent stop is positioned proximal of the stent. 
         [0019]    The spring stent stop  10  is constructed of finger elements  30 , wherein the whole or part of such elements can be seen in  FIGS. 2 and 3 . The finger elements  30  extend distally from base portion  20 . 
         [0020]    Stop  10  can be made from any number of materials known in the art, including metals such as nitinol, stainless steel, or highly radio-opaque material such as platinum, gold, tantalum or polymers, including radio-opaque filled polymers. Providing a radio-opaque stop is advantageous and can aide in positioning the stent within the target lesion during deployment within a vessel. 
         [0021]    The stop of the present invention is compressible preferably in a radially inward direction when a sufficient compressive force is applied, and will expand to its original non-compressed state when such force is removed. The stop provides a rigid surface  110  located at the distal end of the stop that is positioned to contact the proximal stent end when the stop is deployed on the inner shaft. In other words, when the stent is positioned upon the inner shaft of the stent delivery system during deployment of the stent, the rigid surface of the stop contacts the stent, maintaining the position of the stent during deployment. This function is advantageous as the outer sheath  200  is refracted (i.e., moved proximally) during deployment, an action that but for the presence of the stop, could urge the stent to also move proximally. 
         [0022]    In assembling the device, the spring stent stop and distal tip, which previously are affixed to the inner member, is loaded through the crimped stent within the outer member and positioned proximal of the stent. 
         [0023]    Upon passing through the crimped stent, the spring stop takes its position proximal to the crimped stent. Thus the crimped stent, and outer sheath portion of the shaft, reside between the spring stop and the distal tip. 
         [0024]    After the spring stop  10  passes through the crimped stent, the spring like features of the stent, and biasing action associated therewith, cause the fingers  30  to open to a diameter that is substantially the same as the inside diameter of the outer member  200 . 
         [0025]    The spring like action of the stop creates a frictional engagement to shaft  10 . When the distal fingers of the spring stop expand after passing through the crimped stent, the diameter of stop  10  is large enough to make sufficient contact with the proximal end of stent  50 . The frictional contact with the outer sheath  200  does not adversely affect stent deployment. As explained above, stop  10  helps to maintain the relative position during deployment, by preventing the stent from being deployed proximal of target lesion. The radio-opaque stop  10  also aides in positioning the stent within the target lesion during deployment within a vessel, as is described below. 
         [0026]    One of the advantages provided by the present invention is that the separate distal component in the form of a wire lumen can be eliminated. That is, the delivery device can instead be constructed of only one inner shaft, thereby eliminating a separate wire lumen assembly as the tip can be affixed onto the inner member distal sheath, and therefore, the inner shaft can extend further than in heretofore known arrangements. Thus, the distal tip can be overmolded to the inner shaft with the spring stent stop already in place, which is yet another advantage offered by the present inventive stop construction. 
         [0027]    To illustrate the advantages of the inventions disclosed herein, consider that with the present spring stop arrangement, the stent is crimped and loaded into the outer sheath. The inner shaft assembly is then slid through the crimped stent and outer sheath and positioned with the spring stent stop proximal of the crimped stent and the distal tip engaging the distal end of the outer sheath. The spring stent stop is moved to its location proximal to the crimped stent by passing the spring stent stop through the crimped stent, possibly by riding a tube, as explained above. The stent fingers, exhibiting spring-like movement in the radially inward direction (yet biased radially outward), are thus moved radially inward and retained in that position as the stop passes through the crimped stent. After the entire spring stop passes through the crimped stent, the fingers spring radially outward to their uncompressed position, with the fingers extending into a position that substantially abuts the proximal end of the crimped stent. Completing the delivery system construction, the distal tip is positioned to engage the distal outer member and the proximal inner member is joined (for example, by overmolding or adhesive bonding) to the handle to maintain alignment of the spring stent and distal tip relative to the stent. 
         [0028]    It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.