Abstract:
The present invention is directed at a removable stent for providing reinforcement to a selected region of a selected body lumen including a resilient cylindrical layer, including at least one bioresorbable extrusion exterior from the resilient cylindrical layer for resisting migration of the removable stent when the removable stent is positioned in the selected region of the selected body lumen. The present invention also includes a temporary implantable endoprosthesis which includes a tubular, radially compressible and axially flexible structure, including at least one bioresorbable extrusion exterior from the resilient cylindrical layer for resisting migration of the removable stent when the removable stent is positioned in the selected region of the selected body lumen.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation and claims priority of U.S. patent application Ser. No. 10/219,979 filed Aug. 16, 2002 and is related to an application entitled “Disintegrating Stent and Method of Making Same,” Ser. No. 09/592,413, by Jonathan Stinson, filed Jun. 13, 2000, the entire contents of both applications being hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to implantable medical prostheses which incorporate an anchoring mechanism to reduce or eliminate migration of the prostheses. 
         [0004]    2. Description of Related Art 
         [0005]    Medical prostheses frequently referred to as stents are well known and commercially available. These devices are used within body vessels of humans for a variety of medical applications. Examples include intravascular stents for treating stenoses, stents for maintaining openings in the urinary biliary, tracheobronchial, esophageal, and renal tracts, and vena cava filters. Stents may also be used by physicians for malignant tumors. Benign tumors are seldom stented with metal platforms. 
         [0006]    Typically, a stent is delivered into position at a treatment site in a compressed state using a delivery device. After the stent is positioned at the treatment site, the delivery device is actuated to release the stent. Following release of the stent, self-expanding stents are allowed to self-expand within the body vessel. Alternatively, a balloon may be used to expand other types of stents. This expansion of the stent in the body vessel helps to retain the stent in place and prevent movement or migration of the stent. Stents are typically composed of stent filaments. 
         [0007]    Stents may be categorized as permanent, removable or bioresorbable. Permanent stents are retained in place and incorporated into the vessel wall. Removable stents are removed from the body vessel when the stent is no longer needed. A bioresorbable stent may be composed of, or include, biogradable material or bioresorbable material which is broken down by the body and absorbed or passed from the body when it is no longer needed. 
         [0008]    Commonly used materials for known stent filaments include Elgiloy(R) and Phynox(R) metal spring alloys. Other metallic materials that may be used for stents filaments are  316  stainless steel, MP35N alloy and superelastic Nitinol nickel-titanium Another stent, available from Schneider (USA) Inc. of Minneapolis, Minn., has a radiopaque clad composite structure such as shown in U.S. Pat. No. 5,630,840 to Mayer. Stents can also be made of a titanium alloy as described in U.S. Pat. No. 5,888,201. 
         [0009]    Bioabsorbable implantable endoprostheses such as stents, stent-grafts, grafts, filters, occlusive devices, and valves may be made of poly(alpha-hydroxy acid) such as poly-L-lactide (PLLA), poly-D-lactide (PDLA), polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(aminoacides), or related coploymers materials, each of which have a characteristic degradation rate in the body. For example, PGA and polydioxanone are relatively fast-bioabsorbing materials (weeks to months) and PLA and polycaprolactone are a relatively slow-bioabsorbing material (months to years). 
         [0010]    Stents may also be covered with various materials to encourage or inhibit tissue attachment to the stent. Covered stents are gaining, favor for biliary applications because they more effectively inhibit tissue attachment, intrusion, and constriction of the tract than bare stents. For example, polytetrafluoroethylene (PTFE) covered stents are desirable for removable stents because tissue attachment or in-growth is reduced in comparison to bare stent or a stent covered with textile (polyester) material. Laminated ePTFE may also be used to cover stents. 
         [0011]    As stents are covered with material to aid in their removal, stent migration from the treatment site increases. There remains a continuing need for covered stents which include characteristics to maintain the stent in position at the treatment site. For example, stents covered with ePTFE, such as Precedent, are easily removed after a given time period, such as six months, but may not provide sufficient fixation to prevent the risk of migration during the six month period. 
       SUMMARY 
       [0012]    The present invention relates to a removable stent for providing reinforcement to a selected region of a selected body lumen including a resilient cylindrical layer. The improvement to the stent is the inclusion of at least one bioresorbably extrusion exterior from the resilient cylindrical layer for resisting migration of the stent when the stent is positioned in the selected region of the selected body lumen. 
         [0013]    Another embodiment of the present invention includes at least one bioresorbable extrusion exterior from a resilient cylindrical layer of a temporary implantable endoprosthesis. The bioresorbable extrusion exterior to the resilient cylindrical layer resists migration of the stent when the stent is positioned in a selected region of a selected body lumen. 
         [0014]    The present invention also includes a method of reducing migration of a removable stent which includes the steps of constructing a removable stent including a resilient cylindrical layer and placing at least one bioresorbable extrusion exterior from the resilient cylindrical layer on the stent. The removable stent is then positioned and expanded within a body lumen. Migration of the stent is resisted by the interaction between the at least one biosorbable extrusion and the body lumen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    We first briefly describe the drawings. 
           [0016]      FIG. 1  is an isometric view of an example of a braided nitinol stent, comprised of 0.25 mm single filament strands that incorporates bioresorbable extrusions of the present invention; 
           [0017]      FIG. 2  is a simplified representation of a braided tubular stent of the type illustrated in  FIG. 1  incorporating bioresorbable extrusions of the present invention; 
           [0018]      FIG. 3  illustrates another stent incorporating another bioresorbable extrusion of the present invention; 
           [0019]      FIG. 4  is an isometric view of an example of a metal spring alloy stent comprised of a single helical coil that a bioresorbable extrusion of the present invention may be used in connection with; 
           [0020]      FIG. 5  is an isometric view of a rolled film or sheet-type bioabsorbable stent that may be used in connection with the bioresorbable extrusion of the present invention; 
           [0021]      FIG. 6  is an isometric view of a solid extruded or molded tube-type stent that may be used in connection with the bioresorbable extrusion of the present invention; 
           [0022]      FIG. 7  is an isometric view of a knitted or woven polymer filament-type stent that may be used in connection with bioresorbable extrusion of the present invention; 
           [0023]      FIG. 8  is a side view of a delivery device with the sent shown in  FIG. 1  loaded thereon; 
           [0024]      FIG. 9  is a detailed view of the portion of the delivery device encircled at “FIG.  9 ” in  FIG. 8 ; 
           [0025]      FIG. 10  is a detailed view of the portion of the delivery device encircled at “FIG.  10 ” in  FIG. 8 ; 
           [0026]      FIGS. 11-14  are partial cross-sectional side views of the distal portion of the delivery device and stent shown in  FIG. 8  at various stages during a stent deployment operation in a body vessel; and 
           [0027]      FIG. 15  is a side view of a pusher-type delivery device. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The present invention improves the fixation characteristics of removable stents by incorporating bioresorbable or bioabsorbable barbs onto the removable stent or a covered stent to anchor the stent during the service life of the stent. 
         [0029]    An implantable prosthesis or stent  101  according to a preferred embodiment of the present invention is illustrated generally in  FIGS. 1 through 3 . Each of these figures includes a removable stent body with bioresorbable exterior extrusions added which, when placed in a body lumen, resist migration of the stent.  FIG. 4  shows an alternative embodiment of the invention according to which the removable stent is comprised of a single helical coil of a metal spring alloy and the bioresorbable exterior extrusion is in the shape of a barb, angled to prevent migration of the stent once placed in a body lumen.  FIG. 5  shows an alternative embodiment of the invention according to which the removable stent is comprised of a rolled film or sheet and the bioresorbable exterior extrusions are positioned circumferentially around the exterior of the stent.  FIG. 6  shows an alternative embodiment of the invention according to which the removable stent is comprised of a solid extruded or molded tube and the bioresorbable exterior extrusions are triangular in shape to resist migration of the stent in any direction.  FIG. 7  shows an alternative embodiment of the invention according to which the removable stent is comprised of knitted or woven metal filaments and the bioresorbable exterior extrusions are in the shape of barbs curved towards the ends of the stent. Removable stent bodies of the type illustrated in  FIGS. 4-7 , (without the bioresorbable exterior extrusions) are generally well-known in the art and may be manufactured according to well-known methods. The bioresorbable exterior extrusions may be added to the removable stents after the body of the removable stent is constructed or may be manufactured as part of the removable stent body. Any of the removable stents according to the embodiments of  FIGS. 1-7  may be made using biostable material such as Elgiloy(R) or Phynox(R) metal spring alloys,  316  stainless steel, MP35N alloy, superelastic Nitinol nickel-titanium or similar non-bioresorbable materials. 
         [0030]    Referring again to the preferred embodiment of  FIGS. 1 through 3 , removable stent  101  is a tubular device formed from two sets of oppositely-directed, parallel, spaced-apart and helically wound elongated strands or filaments  102 . The removable stent body of  FIGS. 1 and 2  is described in more detail in U.S. patent application Ser. No. 08/904,967, filed Aug. 1, 1997. In particular, the sets of filaments  102  are interwoven in an over and under braided configuration intersecting at points such as  103  to form an open mesh or weave construction. Methods for fabricating the body of removable stents  101  are generally known and disclosed, for example, in the Wallsten U.S. Pat. No. 4,655,771 and the Wallsten, et al. U.S. Pat. No. 5,061,275. 
         [0031]    Removable stent  101  is shown in its expanded or relaxed state in  FIGS. 1 and 2 , i.e., in the configuration it assumes when subject to no external loads or stresses. The filaments  102  are resilient, permitting the radial compression of removable stent  101  into a reduced-radius, extended-length configuration or state suitable for delivery to the desired placement or treatment site through a body vessel (i.e., transluminally). Removable stent  101  may also be self-expandable from the compressed state, and axially flexible. Bioresorbable exterior extrusions  104  are also resilient permitting bioresorbable exterior extrusions  104  to be contained within a delivery device when removable stent  101  is in a compressed state but expanded to the relaxed state as shown in  FIGS. 1 and 2 . Bioresorbable exterior extrusions  104  are also inflexible enough, so that when in the expanded state in a body lumen, bioresorbable exterior extrusions  104  prevent migration of removable stent  101  within body lumen. According to one embodiment of the invention, at least one and preferably all bioresorbable extrusions is composed of one or more commercially available grades of polylactide, poly-L-lactide (PLLA), poly-D-lactide (PDLA), polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), poly(alpha-hydroxy acid) or related copolymers materials. 
         [0032]    According to one embodiment of the invention, removable stent  101  may be a radially and axially flexible tubular body having a predetermined diameter that is variable under axial movement of the ends of the body relative to each other. Removable stent  101  may be composed of a plurality of individually rigid but flexible and elastic thread elements or filaments  102 , each of which may extend in a helix configuration along a longitudinal center line of the body as a common axis. The filaments  102  may define a radially self-expanding body. The body may be provided by a first number of filaments  102  having a common direction of winding but axially displaced relative to each other, and crossing a second number of filaments  102  also axially displaced relative to each other but having an opposite direction of winding. Bioresorbable exterior extrusions  104  are flexible in the axially direction of removable stent  101 , but rigid in the longitudinal direction. The flexibility of bioresorbable exterior extrusions  104  in the axial direction allows removable stent  101 , including bioresorbable exterior extrusions  104  to be compressed into a delivery device. The center line common axis or longitudinal direction of removable stent  101  and the axial (or axially) direction are different and not parallel. Axial (or axially) directions are situated around an axis, in this case the longitudinal direction. Therefore, by including both compression of bioresorbable exterior extrusions  104  in an axial (or axially) direction along with compression of removable stent  101  has each flexible bioresorbable exterior extrusion  104  wrapped in a non-longitudinal direction around the compressed removable stent  101 . The rigidity of bioresorbable exterior extrusions  104  in the longitudinal direction of removable stent  101  ensures that, once removable stent  101  is positioned in a body lumen, bioresorbable exterior extrusions  104  will resist migration of removable stent  101  within the body lumen. 
         [0033]    Bioresorbable exterior extrusions  104  may take a variety of shapes. Bioresorbable exterior extrusions  104  of  FIG. 1  are in the shape of a barb with the concave surface of the barb towards the center of removable stent  101 . Alternatively, bioresorbable exterior extrusions  201  of  FIG. 2  may be triangular in shape and rigid in the longitudinal direction of removable stent  202  to resist migration in a longitudinal direction once removable stent  202  is positioned within a body lumen. 
         [0034]    Removable stent  301  of  FIG. 3  includes a plurality of individually rigid but flexible and elastic thread elements or filaments  302 , each of which may extend in a helix configuration along a longitudinal center line of the body as a common axis. The filaments  302  may define a radially self-expanding body. The body may be provided by a first number of filaments  302  having a common direction of winding but axially displaced relative to each other, and crossing a second number of filaments  305  also axially displaced relative to each other but having an opposite direction of winding. Bioresorbable exterior extrusions  304  are flexible in the axially direction of removable stent  301 , but rigid in the longitudinal direction. The flexibility of bioresorbable exterior extrusions  304  in the axial direction allows removable stent  301 , including bioresorbable exterior extrusions  304  to be compressed into a delivery device. Filaments  302  and filaments  305  may be configured to alternate at intersections. For example, at one intersection filament  302  may be exterior to filament  305  as shown at  303 . Alternatively, filament  305  may be exterior to filament  302  at other intersections as shown at  306 .  FIG. 3  also shows that a number of bioresorbable exterior extrusions may be included in an embodiment to further resist migration of removable stent  301  when placed within a body lumen. 
         [0035]      FIGS. 3 through 7  show other embodiments of the placement of bioresorbable exterior extrusions on various removable stent configurations. Notably,  FIG. 5  depicts bioresorbable exterior extrusions  502  along an outer circumference of removable stent  501 . Note that many orientations and configurations of bioresorbable exterior extrusions may be configured to resist migration of the stent within a body lumen. 
         [0036]    Note also that bioresorbable exterior extrusions of the present invention may be used to resist migration of other types of removable stents. Other stent structures and features may be include, for example, stents having features which enhance or cooperate with the tubular and self-expandable structure or which facilitate the implantation of the structure. One example is the inclusion of radiopaque markers on the structure which are used to visualize the position of the stent through fluoroscopy during implantation. Other examples include collapsing threads or other structures to facilitate repositioning of the stent. 
         [0037]    Note that the use of bioresorbable exterior extrusions on a removable stent would help ensure the proper position of the removable stent during its in service, or in the lumen, time. By selection of the proper bioresorbable materials, when the time to remove the removable stent has arrived, the bioresorbable exterior extrusions have been absorbed into, or broken down by the body, allowing for easy removal. 
         [0038]    Note also that a non-bioresorbable exterior extrusion attached to the removable stent body with bioabsorbable material may also be used in the implementation of the present invention. 
         [0039]      FIGS. 8 through 10  are illustrations of a delivery device  801  for delivering removable stent  101  to a treatment site in a body vessel. As shown, removable stent  101  is carried by the distal portion  809  of delivery device  801 , and is placed on the delivery device in a radially contracted or compressed state. The proximal portion of delivery device  801  generally remains outside of the body for manipulation by the operator. 
         [0040]    Delivery device  801  includes an elongated, inner tube  802 , preferably having an axially extending lumen therethrough. The distal portion  809  of inner tube  801  is flexible and can be made from nylon or other suitably flexible biocompatible polymeric material. At its distal end, inner tube  801  is provided with a head  805 . Head  805  serves to facilitate the insertion of delivery device  801  through a narrow opening in a body vessel. The proximal portion of inner tube  802  is preferably formed from stainless steel or other suitably rigid metal alloy. The proximal end of the distal portion of inner tube  802  is bonded to the distal end of the proximal portion of the inner tube in any conventional manner such as by using a standard adhesive. 
         [0041]    A proximal tube  804  surrounds the proximal portion of inner tube  802  in coaxial fashion. Proximal tube  804  is preferably formed from polyurethane. The proximal end of tube  804  is connected to a valve body  803  having a side port  806 . An extension tube  807  extends from side port  806  to an opening  808 . This arrangement allows fluid to be injected through extension tube  807  and between proximal tube  804  and inner tube  802 . 
         [0042]    A moveable hose  901  surrounds the distal portion of inner tube  802 . Hose  901  is rolled over itself to form a double-walled section. The proximal end of inner wall  1001  of a double-walled section is connected directly to inner tube  802 . The proximal end of the outer wall  1002  of the double-walled section is connected to the outer surface of the distal portion of proximal tube  804 . These connections can be achieved by any conventional means such as by a standard adhesive. This arrangement allows hose  901  to be rolled off removable stent  101  and placed on the distal portion of inner tube  802 . By moving valve body  803  in the proximal direction, outer wall  1002  of hose  901  slides proximally over inner wall  1001 . This causes inner wall  1001  to “roll back” off of removable stent  101 . To facilitate movement of hose  901  off of removable stent  101 , at least that portion of inner wall  1001  that contacts outer wall  1002  in the area where hose  901  is rolled over to form the double-walled section should be lubricious. The lubricious characteristic can be achieved by adding a lubricious substance to this surface of hose  901 , injecting a lubricious liquid between inner wall  1001  and outer wall  1002  or forming hose  901  from a naturally slippery material such as Teflon coating. 
         [0043]    At least the surfaces of inner wall  1001  and outer wall  1002  that face each other in the double-walled section are coated with a lubricious hydrophilic coating. In one embodiment the hydrophilic coating is  2018 -M material available from Hydromer Inc. of Whitehouse, N.J. Other materials that can be used are polyethylene oxide and hyaluronic acid. When wet, the hydrophilic coating becomes lubricious and thus reduces friction between inner wall  1001  and outer wall  1002  of the double-walled section of hose  901  as outer wall  1002  moves past inner wall  1001 . This facilitates the removal of the double-walled section of hose  901  from removable stent  101 . Hydrophilic material may be added to hose  901  during the assembly of delivery device  801 . To enable the hydrophilic material to adequately bond to hose  901 , the material used to manufacture hose  901  should be matched to the hydrophilic material used. It has been found that polyurethane works well as a material for hose  901 . In particular, a blend of  65 D and  75 D polyurethane provides sufficient flexibility to allow hose  901  to roll over itself yet still be soft enough and compatible with the hydrophilic material that it can be properly coated. In one embodiment, the blend is formed of 50% 65D polyurethane and 50% 75D polyurethane. During the assembly of delivery device  801 , one side of hose  901  is coated with the hydrophilic material after the outer wall  1002  of the hose has been connected to proximal tube  804 . Isopropyl alcohol is first applied to one side of hose  901  to clean the surface and remove the waxy film resulting from the plasticizers in the polyurethane. The same side of hose  901  is then coated with the hydrophilic material. The surface of hose  901  should be flushed with alcohol for about thirty seconds. Similarly, the surface of hose  901  should be flushed with the hydrophilic coating for about thirty seconds. It has been found that this technique deposits sufficient hydrophilic material on inner wall  1001  and outer wall  1002  to allow hose  901  to be rolled back with minimal friction when the hydrophilic material is wet. 
         [0044]    After delivery device  801  has been assembled and is ready for use, the hydrophilic coating is wetted with physiological saline solution by injecting the solution through extension tube  807 , past proximal tube  804  and into the space between inner wall  1001  and outer wall  1002  of the double-walled section of hose  901 . Excess fluid exits from the hole  902  formed toward the distal end of the double-walled section of hose  901 . In this same manner, a lubricious fluid such as polyethylene glycol can be injected into the space between inner wall  1001  and outer wall  1002  of the double-walled section to provide the lubricious characteristic of hose  901  in place of adding a lubricious hydrophilic material through hose  901  as described above. 
         [0045]    The manner by which delivery device  801  is operated to deliver removable stent  101  to a treatment site in a body vessel or lumen including curved sections is illustrated in  FIGS. 11-14 . As shown, removable stent  101  is placed in a radially compressed state in a surrounding relationship to the outer distal end of inner tube  802 . Removable stent  101  is constrained on inner tube  802  by the double-walled section of hose  901 . It is important that removable stent  101  not be confined too tightly on inner tube  802 . Hose  901  should apply just enough force to removable stent  101  to hold removable stent  101  in place. The double-walled section of hose  901  can be removed from around removable stent  101  by pulling valve body  803  and proximal tube  804  in a proximal direction. The double-walled section “rolls” off removable stent  101 . No sliding movements take place between removable stent  101  and inner wall  1001  which contacts removable stent  101 . Along with the movement of the double-walled section in a proximal direction, the distal end of removable stent  101  will be exposed in a radial direction to engagement against the wall of the body vessel. As the double-walled section of hose  901  continues moving proximally, more of removable stent  101  expands in a radial direction until the entire length of removable stent  101  is exposed and engages the wall of a body. 
         [0046]    A lumen is used to enable delivery device  801  to follow a guide wire (not shown) previously inserted percutaneously into the body vessel. The lumen of inner tube  802  can also be used to introduce a contrast fluid to the area around the distal end of delivery device  801  so the position of delivery device  801  can be detected (e.g., through the use fluoroscopy or X-ray techniques). 
         [0047]    In  FIG. 15  there is shown another embodiment of a delivery device which may be used to position stents including the present invention within a body lumen. 
         [0048]    This assembly constitutes a flexible instrument intended to introduce the tubular body in contracted state into for example a blood vessel and then to expand the body when located therein. The parts of the instrument consist of an outer flexible tube  1501  and a concentric also flexible inner tube  1502 . At one end of the outer tube an operational member  1503  is arranged. Another operational member  1504  is attached to the free end of inner tube  1502 . In this manner the inner tube  1502  is axially displaceable in relation to the outer tube  1501 . At the other end of inner tube  1502  a piston  1505  is attached which when moving runs along the inner wall of outer tube  1501 . 
         [0049]    When the instrument is to be used the tubular expansible body  1506  in contracted state is first placed inside tube  1501 , the inner tube  1502  with the piston  1505  being located in the rear part  1507  of outer tube  1501 . The starting position of piston  1505  is shown by dashed lines at  1508  in  FIG. 15 . In this manner part of tube  1501  is filled with the contracted tubular body  1506  in the starting position. 
         [0050]    During implantation the flexible tubular part of the device is inserted to the location of a blood vessel intended for implantation. Member  1504  is then moved in the direction of arrow  1509 , the contracted body  1506  being pushed out through end  1510  of tube  1501 , the part of the tubular body  1506  leaving tube end  1510  expanding until in its expanded position  1511  it is brought to engagement with the interior of vascular wall  1512 . The tubular body  1506 ,  1511  is for sake of simplicity shown in  FIG. 15  as two sinus-shaped lines. To the extent that the expanded body  1506  comes into engagement with vascular wall  1512  tube end  1510  is moved by moving member  1503  in the direction of arrow  1513 . The contracted body  1506  is moved by the piston  1505  pushing against one end of the body. Thus, the implantation takes place by simultaneous oppositely directed movements of members  1504  and  1503 , the displacement of member  1504  being larger than that of member  1503 . When the contracted body  1506  has been fully removed from the tube  1501  the expansion is terminated and the instrument can be removed from the location of the operation. 
         [0051]    The delivery system according to  FIG. 15  has the great advantage that the constructional details are quite simple and can be operated with high reliability. The instrument shown is also suitable for implantation of helices with very small diameters. As an example there may be mentioned that experiments have been performed with a tubular expansible body consisting of crossing thread elements, the contracted diameter of the body being only 2 mms and the expanded diameter 6 mms. It is also fully conceivable to implant expanded bodies with even smaller diameter. The instrument according to  FIG. 15  may also advantageously be used for implantation of bodies in the form of grafts of a very large diameter. 
         [0052]    In implantation of long bodies it is conceivable that the resistance in displacing same in tube  1501  becomes too high. In this case it may be suitable to replace piston  1505  at the front end of tube  1502  with movable jaws or latches which operate in such a manner that when tube  1502  is brought forward in the direction of arrow  1509  the latches engage the inner side of body  1506 , the body being brought forward. When tube  1502  is brought back in the direction of arrow  1513  the latches are released. In this manner body  1506  can be moved forwardly by a pump-like motion of tube  1502 . 
         [0053]    Many embodiments of the different members shown in  FIG. 15  are, of course, conceivable. Thus, it is possible for example to simplify implantation for the surgeon by controlling the relative motion between members  1503  and  1504  in a mechanical manner. 
         [0054]    The stents of the present invention may be delivered by alternative methods or using alternative devices. For instance, the device described in Heyn et al. U.S. Pat. No. 5,201,757 may be utilized. 
         [0055]    Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. 
         [0056]    It will be evident from considerations of the foregoing that the devices of the present invention may be constructed using a number of methods and materials, in a wide variety of sizes and styles for the greater efficiency and convenience of a user. 
         [0057]    The above described embodiments of the invention are merely descriptive of its principles and are not to be considered limiting. Further modifications of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the following claims.