Patent Abstract:
The present invention relates to a system for delivering a medical prosthesis into a body lumen. A preferred embodiment of the invention utilizes a catheter having a stent mounted at the distal end that is released into the body lumen by movement of an outer sheath covering the stent in the proximal direction. The stent expands to conform to the inner wall of the lumen and the catheter is withdrawn.

Full Description:
RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/052,214 filed on Mar. 31, 1998, the entire teachings of which are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Implantable medical prostheses, such as stents, are placed within the body to maintain and/or treat a body lumen that has been impaired or occluded, for example, by a tumor The stent can be formed of strands of material formed into a tube and are usually delivered into the body lumen using a catheter. The catheter carries the stent to the desired site and the stent is released from the catheter and expands to engage the inner surface of the lumen.  
           [0003]    A self-expanding stent can be made of elastic materials. These are held in a compressed condition during catheter delivery by, for example, a sheath that covers the compressed stent. Upon reaching the desired site, the sheath constraining the stent is pulled proximally, while the stent is held in the desired position such that the stent expands.  
           [0004]    There are both self-expanding and non-self-expanding stents. The self-expanding type of device is made with a material having an elastic restoring force, whereas a non-self-expanding stent is often made with elastic, plastically deformable material. It is positioned over a mechanical expander, such as a balloon, which can be inflated to force the prosthesis radially outward once the desired site is reached.  
         SUMMARY OF THE INVENTION  
         [0005]    In a preferred embodiment, the invention features an implantable medical stent having a low profile during delivery. The stent is a tubular body with a body wall structure having a geometric pattern of cells defined by a series of elongated strands extending to regions of intersection. An example of a stent having a cell shape in accordance with the invention can be found in U.S. Pat. No. 5,800,519, which issued on Sep. 1, 1998, the entire contents of which is incorporated herein by reference. This stent cell structure utilized helically wrapped joints to connect the different strands to form a tubular body.  
           [0006]    A limitation on the use of the helically joined stent involved the minimum constrained diameter of the stent during delivery. Because of the helically wrapped joints abutting one another along a given circumference, the minimum constrained diameter of the stent was 9 French (3 mm). For example, the length of the helically wrapped joint for a strand having a diameter of 0.006 inches (0.15 mm) in the constrained position is 0.045 inches (1.1 mm). For a five cell structure having five helically twisted abutting joints, this results in a constrained circumference of 0.228 inches (5.79 mm) with a diameter of 0.072 inches (1.8 mm). However, there are many applications in which it is necessary to achieve a smaller constrained diameter to provide delivery, for example, through smaller lumens within the vascular system, to reduce trauma during percutaneous delivery, or to provide endoscopic delivery through small diameter channels of endoscopes.  
           [0007]    To achieve a smaller constrained diameter of 8 French or less, for example, a preferred embodiment of the invention replaces one or more of the helically wrapped joints along any given circumference with a simple crossed joint in which one strand crosses either above or below a second strand. Thus, the strands at a crossed joint can move more freely relative to each other, but this structure reduces the minimum circumference as the length of one or more helically twisted joints has been removed. This can reduce the constrained diameter by 50%.  
           [0008]    In another preferred embodiment of the invention, the stent can include a first tubular body made from a first group of strands and a second tubular body surrounding the first tubular body and made from a second group of strands. This type of structure can be used to fabricate a low-profile device having sufficient radial expansion force for a self-expanding stent without a substantial change in foreshortening. This embodiment can include, for example, three or four helically wrapped joints along any circumference of the first and second tubular bodies in which the joints of the two bodies are offset in the constrained state. This embodiment also significantly improves the ratio of the expanded diameter to the constrained diameter.  
           [0009]    The strands of the first group can have a different shape, diameter, or material from the strands of the second group such that the inner body has a larger radial restoring force than the outer body and can thereby impart the outward force to the outer body.  
           [0010]    In one embodiment, the strands of the inner body can be thicker than the strands of the outer body and can be interleaved with the outer body along the entire length of the stent. In another preferred embodiment, the inner and outer bodies can be interlocked at one or both ends. This can permit the use of a cover between the inner and outer bodies along a certain portion of the stent. The use of the cover can enhance epithialization between the wall of the lumen and the outer body, reduce migration of the stent in certain applications and can prevent tumor in-growth. The cover can also provide a supporting matrix for drug delivery.  
           [0011]    In one preferred embodiment, the strands of the stent are woven in a pattern with interlocking joints and skip joints as discussed above. In addition, the adjoining ends of the stent are aligned parallel to each other and laser-welded to secure the adjoining ends of the stent. The welded ends allow the stent to be compressed to a low profile.  
           [0012]    In one preferred delivery system, the stent is positioned over an inner shaft and is covered by a composite sheath. The composite sheath can comprise a plurality of materials to provide a variable property such as a graded stiffness along the length of the sheath. In one embodiment the sheath can Include a braid or coil between outer and inner sheath layers to provide the longitudinal stiffness and flexibility needed for particular applications. The sheath can have at least a ten percent variation in stiffness along its length and as much as a fifty percent variation with the stiffer section at the proximal end and the least stiff section at the distal end. The sheath can extend coaxially about the inner shaft from the handle connected to the proximal end of the catheter and can be connected to an actuator that is manually operated by the user to slide the sheath relative to the inner shaft.  
           [0013]    In one embodiment the inner shaft can include a braided tube, which extends from the proximal handle to a distal position of the delivery system. The inner shaft extends through a lumen of a catheter from the proximal handle to a distance short of the distal end where the catheter ends. The inner shaft can be free-floating within the lumen and receives the stent at the distal end. An outer sheath overlies the stent and the inner shaft and is moved to release the stent using a pull wire which is moved by the proximal handle using a conventional tooth strip attached to a pull wire.  
           [0014]    In a preferred embodiment, the inner shaft is formed of steel braided tube encased in a polyimide. For low profile stent delivery systems, where the smaller diameter of the body lumen or the smaller diameter of the endoscope delivery channel necessitate improvements in the Push (or pull) strength of the catheter, the use of a braided tube to maintain flexibility and pushability without kinking provides effective delivery of low profile stents.  
           [0015]    In the embodiments described above and in other embodiments, a mounting ring can be secured to the inner shaft or braided tube at the stent platform on which the stent is placed. The mounting ring has at least one radial member or ridge which projects towards the outer sheath. The ridge is located preferably at the proximal end of the stent. The ridges extend longitudinally, allowing the stent to be properly positioned while also allowing maximum compression of the stent for minimizing the diameter of the delivery system.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0017]    [0017]FIG. 1A is a flat layout view along the longitudinal axis of a stent;  
         [0018]    [0018]FIG. 1B is an enlarged portion of the stent taken at section  1 B- 1 B in FIG. 1A;  
         [0019]    [0019]FIG. 2A is a perspective view of a stent according to the invention;  
         [0020]    [0020]FIG. 2B is a flat layout view of an expanded low profile stent of FIG. 2A;  
         [0021]    [0021]FIG. 3 is an enlarged cross-sectional view of a delivery tube containing a low profile diamond metal stent;  
         [0022]    [0022]FIGS. 4A and 4B illustrate a mandrel for making a stent of FIGS. 2A, 2B, and  3 ;  
         [0023]    [0023]FIG. 4C is a sectional view of the strands attached with a ball-welding;  
         [0024]    [0024]FIG. 4D is a flat layout view of the joining ends of a low profile stent according to an alternative embodiment;  
         [0025]    [0025]FIG. 4E is a perspective view of the strand of the stent in a laser welding apparatus;  
         [0026]    [0026]FIG. 4F is a sectional view of the strands laser welded;  
         [0027]    [0027]FIG. 5A is a distal end view of an endoscope;  
         [0028]    [0028]FIG. 5B is a sectional view of the distal end of the endoscope;  
         [0029]    [0029]FIG. 6A is an “over-the-wire” delivery system;  
         [0030]    [0030]FIG. 6B is an enlarged view of the middle section of the “over-the-wire” delivery system;  
         [0031]    [0031]FIG. 7 is a rapid exchange delivery system;  
         [0032]    FIGS.  8 A- 8 E illustrate the operation of the delivery of the stent;  
         [0033]    [0033]FIG. 9 is a flat layout view of a double layer stent;  
         [0034]    [0034]FIG. 10 is a flat layout view of an alternative embodiment of a double layer stent;  
         [0035]    [0035]FIG. 11 is an enlarged cross sectional view of the double layer stent of FIG. 10 with an interposed cover in an artery;  
         [0036]    [0036]FIG. 12 is a cross sectional view of the double layer stent with the interposed cover taken along line  12 - 12  of FIG. 11;  
         [0037]    [0037]FIG. 13 illustrates a mandrel for making a stent of FIGS.  9  or  10  and  11 ;  
         [0038]    [0038]FIG. 14A is a perspective view of an alternative stent having six strands; and  
         [0039]    [0039]FIG. 14B is a flat layout view of the stent of FIG. 14A.  
         [0040]    [0040]FIG. 15A is a side view with portions broken away of an alternative embodiment of an “over-the-wire” delivery system;  
         [0041]    [0041]FIG. 15B is an enlarged view of a middle section of an “over-the-wire” delivery system;  
         [0042]    [0042]FIG. 15C is an enlarged view of the distal end of an “over-the-wire” delivery system;  
         [0043]    [0043]FIG. 16A is a sectional view taken along the line  16 A- 16 A of FIG. 15B;  
         [0044]    [0044]FIG. 16B is a sectional view taken along the line  16 B- 16 B of FIG. 15C;  
         [0045]    [0045]FIG. 17A is a side view of a portion of the catheter showing a locking ring;  
         [0046]    [0046]FIG. 17B is a sectional view taken along line  17 B- 17 B of FIG. 17A showing the interaction of the locking ring with the stent;  
         [0047]    [0047]FIG. 17C is an illustration of a partially deployed stent with a locking ring;  
         [0048]    [0048]FIG. 18 is a sectional view showing an alternative lock ring with the stent;  
         [0049]    [0049]FIG. 19A is a side view, with portions broken away, of an alternative embodiment of an “over-the-wire” delivery system;  
         [0050]    [0050]FIG. 19B is an enlarged view of the distal end of the “over-the-wire” delivery system of  19 A;  
         [0051]    [0051]FIG. 20A is an enlarged view of the distal end of an alternative embodiment of an “over-the-wire” delivery system;  
         [0052]    [0052]FIG. 20B is a similar view with the inner shaft removed;  
         [0053]    [0053]FIG. 20C is a sectional view of the distal end of an “over-the-wire” delivery system; and  
         [0054]    [0054]FIG. 21 is an enlarged view of an alternative embodiment of an “over-the-wire” delivery system;  
         [0055]    [0055]FIG. 22A is a flat layout view along the longitudinal axis of a stent;  
         [0056]    [0056]FIG. 22B is an enlarged portion of the stent taken at section  22 B- 22 B in FIG. 22A;  
         [0057]    [0057]FIG. 23A is a flat layout view of another embodiment of the stent according to the invention;  
         [0058]    [0058]FIG. 23B is a flat layout view of another embodiment of the stent according to the invention;  
         [0059]    [0059]FIGS. 24A and 24B are oblique views of the nodes of a stent;  
         [0060]    [0060]FIGS. 25A and 25B illustrate a mandrel for making a stent of FIGS.  22 A- 23 B;  
         [0061]    [0061]FIG. 26A is an enlarged cross-sectional view of a delivery tube containing an alternative embodiment of a low profile diamond metal stent;  
         [0062]    [0062]FIG. 26B is an enlarged portion of the stent taken at section  26 B- 26 B in FIG. 26A;  
         [0063]    [0063]FIG. 27A is a side view of a coaxial delivery system with portions broken away; and  
         [0064]    [0064]FIG. 27B is a sectional view taken along line  27 A- 27 A of FIG. 27A. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0065]    Referring to the drawings in detail, where like numerals indicate like elements there is illustrated an implantable prosthesis in accordance with the present invention designated generally as  10 .  
         [0066]    Medical prostheses, such as a stent  10  according to the invention, are placed within the body to treat a body lumen that has been impaired or occluded. Stents according to the invention are formed of wire configured into a tube and are usually delivered into the body lumen using a catheter The catheter carries the stent in a reduced-size form to the desired site. When the desired location is reached, the stent is released from the catheter and expanded so that it engages the lumen wall as explained below.  
         [0067]    A stent  20  is shown in a flat layout view in FIG. 1A. The stent  20  is formed of elongated strands  22  such as elastic metal wires. The wires  22  are woven to form a pattern of geometric cells  24 . The sides  26   a,    26   b,    26   c,  and  26   d  of each of the cells  24  are defined by a series of strand lengths  28   a,    28   b,    28   c,  and  28   d.  Each of the sides  26  are joined to the adjoining side at an intersection where the strands  22  are helically wrapped about each other to form interlocking joints  30 .  
         [0068]    Referring to FIGS. 1A and 1B, the interlocking joints  30  are loose and spaced from each other in the full expansion position. The cells  24  have a diamond shape. The strand angle is α. When the stent  20  is racially compressed, in certain instances, the interlocking joints  30  are in tight interference such that points  32  and  34  are in close proximity. In other Instances, the interlocking joints  30  separate. In addition, the interlocking joints  30  on the same circumference are in close contact, therefore establishing the compressed, reduced size which can be fit within a sleeve for delivery on a catheter. A medical prosthetic stent and method of manufacturing such a stent is described in U.S. patent application Ser. No. 08/743,395 which issued as U.S. Pat. No. 5,800,519 on Sep. 1, 1998 and which is incorporated herewith by reference.  
         [0069]    Referring to FIG. 2A, an isometric view of stent  10  according to the invention is shown in an expanded position. The stent  10  is formed from a plurality of strands  42 . In a preferred embodiment, there are five strands  42 , as seen in the layout view of FIG. 2B. The strands  42  are woven in a pattern starting at a proximal end  44 . The pattern forms a plurality of geometric cells  46 . Each strand  42  forms a pair of sides  48   a  and  48   b  of the most distal cell  46 . Each of the sides, with the exception of at least one as explained below, are joined to the adjoining side at an intersection  52  where the strands  42  are helically wrapped about each other to form interlocking joints  54 .  
         [0070]    While there are five intersections  52 , at least one of the intersections  52  is formed by strands  42  that cross forming a cross joint and are not twisted to form a wrap as indicated at point  56  in FIG. 2B. A preferred pattern of where the strands  42  just cross is spaced 1-½ cells  46  away, as seen in FIG. 2B.  
         [0071]    The strand angle α is increased in the compressed or constrained state of the stent in this embodiment. The strand angle can he in the range of 10°-80° depending upon the particular embodiment. Smaller strand angles between 10° and 45° often require a shortened cell side length L to maintain radial expansion force. Cell side lengths L in the range of 0.5 to 4 mm, for example, can be used with stent having these smaller strand angles. For stents with larger strand angles in the range of 3-8 mm can be used, depending on the expanded diameter of the stent, the number of cells and the desired radial expansion force.  
         [0072]    Referring to FIG. 3 the stent  10  is shown in the contracted position within the sleeve  58 . Similar to the embodiment shown in FIGS. 1A and 1B, the size to which the stent  10  can be constricted is limited by where the interlocking joints  54  engage each other. The elimination of one wrap joint allows for the stent  10  to be compressed to a smaller size.  
         [0073]    In a preferred embodiment, the strands  42  are formed of nitinol wire. The wires each have a diameter of 0.006 inches (0.15 mm) The diameter of the wires can vary depending on the number of cells and desired properties and generally in preferred embodiments range from 0.004 inches (0.10 mm) to 0.006 inches (0.15 mm). The stent  10  has an outside diameter when fully expanded of 10 millimeters. The stent  10  is capable of compressing into a sleeve  58  of an outside diameter of 8.0 French or less, and preferably 7.0 French (3 fr=1 mm). The stent shown in the FIGS. 1A and 1B, of similar material and dimension, is capable of compressing to a diameter of approximately 9 fr.  
         [0074]    In one preferred embodiment, the length of the legs or sides  48  of the cells  46  is similar to that of the embodiment shown in FIGS. 1A and 1B. The radial force is decreased from the elimination of one of the interlocking or wrap joints. The compressed stent  10  has a length of approximately 120 percent or less relative to the expanded stent. Therefore, for a 10 centimeter stent, the compressed length is 12 centimeters or less.  
         [0075]    In one preferred embodiment, the length of the legs or sides  48  of the cells  46  are reduced. The reduced length provides radial force and compensates for decreased radial force resulting from the elimination of one of the interlocking or wrap joints. In an alternative embodiment, the radial expansion force increased by varying the anneal cycle of the stent.  
         [0076]    The varying of the length of legs or sides  48  of the cell or the change in the angle α can effect foreshortening. While it is preferred to have foreshortening of 120 percent or less, in certain embodiments it may be desirable to have greater foreshortening, such as the compressed stent  10  has a length of approximately 150 percent of the expanded stent.  
         [0077]    In one preferred embodiment, a plurality of (ten shown) platinum-iridium radiopaque (R.O.) markers  60  are located on the stent  10 . The R.O. markers  60  are threaded onto the terminating cells; five on the proximal end and five on the distal end.  
         [0078]    A mandrel  62  for making the stent is shown in FIGS. 4A and 4B. The mandrel  62  has a plurality of pins  64  on the outer surface of the mandrel in a pattern that determines the geometric cell  46  pattern. The strands  42  are bent around the top portion  66  of each top anchoring pin  64  to form the proximal end  44  of the stent  10 . The strands  42  are then pulled diagonally downward to an adjacent anchoring pin  64  where the strands  42  are joined. The strands  42  are helically wrapped about each other to form the interlocking joint  54 , with each strand passing through a single 360 degree rotation. The two strands are pulled taught so that the interlocking joint  54  rests firmly against the bottom portion  68  of the anchoring pin  64  such that each strand  42  is maintained in tension.  
         [0079]    Each level of anchoring pins  64  is missing a pin  64  in a set order, such as to achieve the desired pattern in FIG. 2B. The stands  42  which pass the missing pin location simply cross to form the cross joint.  
         [0080]    In a preferred embodiment, the anchoring pins  64  are square. The square pins retain the helically wrap of the strands in a proper position. In a preferred embodiment, the pins have a width of 1 millimeter. The anchoring pins can have a smaller width such as 0.5 mm for use with narrower diameter strands, such as 0.005 inch diameter strands.  
         [0081]    The free ends of the strands  42  are then pulled downward to the next diagonally adjacent anchoring pin  64 . This process is continued until the desired length of the stent  10  is achieved.  
         [0082]    The stent  10  is then heat-treated. The strands  42  at the joining end  40  of the stent  10  are welded using a ball-welding technique. The strands  42  are twisted around each other for several twists of the strands as best seen in FIG. 2B. The strands having a diameter of 0.006 inches (0.15 mm) will form a diameter of 0.012 inches as seen in FIG. 4C. In addition, the ball-weld creates a weld ball  250  having a diameter of 0.018 inches (0.46 mm) to 0.020 inches (0.51 mm). Upon compression of the stent, the weld balls  250  may engage each other limiting the compression of the stent. The stent with these diameters can fit within an outer sheath having a 7 French inner diameter. The heat-treating and alternative finishing techniques are described in U.S. Pat. No. 5,800,519 on Sep. 1,1998, the entire contents is incorporated herein by reference.  
         [0083]    A layout view of the distal end of the stent  10  is shown in FIG. 4D. The strands  42  of the stent  10  are woven in a pattern as discussed above with respect to FIGS. 4A and 4B. The joining ends  40  of the stent  10  are aligned parallel to each other to form the end of the most distal cells  46 . The joining ends  40  of the strands  42  are held together by a pair of holding straps  268  onto a surface  270  as seen in FIG. 4E. A laser welder  272  moves along the joint  274  of the two adjoining strands  42 . A plurality of energy pulses are directed at the joint  274  as the laser welder  272  moves along the joint. After completing this initial weld, the laser welder  272  is moved back to a position  280 , to achieve a finished length and a higher energy pulse is directed at the point or position mark by dotted line  280  to cut the strands  42 .  
         [0084]    In a preferred embodiment, a 400 micron fiber is used with a spot size having a diameter of 3.9 to 4.1 millimeters. In one example, twenty pulses of energy are directed at the joint  274  as the laser welder  272  moves a distance of 1.3 millimeters (+/−0.5 mm). Each pulse has an energy level of 145 millijoules (+/−10 millijoules) and a duration of 0.1 milliseconds. The single higher energy pulse of one joule, and a duration of 2 milliseconds cuts the strands.  
         [0085]    Referring to FIG. 4F, an example of the cross-section of the strands  42  using the laser weld technique described above is shown. The laser welding forms a fill  276  on the top and a cut-off fill  278  on the bottom. The overall diameter of the strands  42  and weld is 0.012 inches (0.3 mm) therein for a five wire system the compression size is 4.57 French. Therein, a stent with the laser welded ends can compress to a smaller diameter than those with the ball welds.  
         [0086]    Another alternative to the R.O. markers  60  for locating the stent  10  using fluroscopy is to coat the stent with gold. The stent  10  can be either totally or partially coated. In a partially coated stent, only portions of the strands between the joints are coated. Coating of a stent is described in further detail in U.S. Pat. No. 5,201,901 which issued on Apr. 13, 1993, the entire contents is incorporated herein by reference. A clad composite stent is described in U.S. Pat. No. 5,630,840 which issued on May 20, 1997, the entire contents being incorporated herein by reference. A further embodiment of the invention utilizes a stent having a core as described in U.S. Pat. No. 5,725,570 which issued on Mar. 10, 1998, the entire contents is incorporated herein by reference.  
         [0087]    In one preferred embodiment, the stent  10  is installed using an endoscope  70  as seen in FIGS. 5A and 5B. The endoscope  70  has a channel  72  which is typically used for collecting biopsy samples or for suction. The stent  10  is passed through the channel  72  into the body as explained below. The endoscope  70  in addition has an air/water nozzle  74  for cleaning the area in front of the endoscope  70 . In addition, the endoscope  70  has a mechanism for the physician to see what is in front of the endoscope  70 ; this mechanism includes an objective lens  76 . A pair of illumination lenses  78  which are used in lighting the site are also shown.  
         [0088]    [0088]FIG. 5B illustrates a cross sectional view of the distal end of the endoscope  70 . An air/water tube  80  extends down to the air/water nozzle  74 . Both the viewing mechanism and the illumination mechanism have optical fiber bundles  82  leading to the respective lens  76  and  78   
         [0089]    Endoscopes come in various sizes and lengths depending on the purpose. The channel  72  likewise has different sizes. It is recognized that it may be desirable to use a smaller diameter scope to be less invasive or that a larger diameter scope will not fit the lumen. The following table is an example of various size endoscopes.  
                                                     Working Length   Distal Tip   Channel       (cm)   O.D. (mm)   Diameter (mm)                                 55   4.8   2.0        55   6.0   2.6        63   12.2   3.2       102   9.8   2.8       102   12.6   3.7       124   11.0   2.8       124   11.0   3.2       125   11.3   4.2       173   13.0   3.2                  
 
         [0090]    In a preferred embodiment, with the dimensions given above, the stent  10  as described in relation to FIGS.  2 A- 4 B can be used with channels of 3.2 mm or greater as described below. It is recognized that with other dimensions of the stent and/or laser weld of the ends, the stent catheter can fit in a smaller diameter channels such as 2.6 mm or 2.0 mm. For a 2.6 mm endoscope channel, a 2.3 mm outer shaft or catheter diameter is employed.  
         [0091]    In addition, the stent  10  can be introduced using a percutaneous insertion. In both the method using the endoscope  70  and the percutaneous procedure, an over the wire delivery system  86  as seen in FIG. 6A can be used. The over-the-wire delivery system  86  has an elongated catheter on inner shift  88  over which the stent  10  is positioned. The catheter  88  extends from a proximal handle  90  to a distal tip end  92 . The catheter  88  extends through an outer shaft  94  at the proximal end.  
         [0092]    An outer sheath  98  is located at the distal end of the over the wire delivery system  86 . The outer sheath  93  is moved towards the handle  90  using a pull wire  102  and a pull ring  104  as seen in FIG. 6B. A guidewire  103  extends through the catheter to the distal end tip  92 , as best seen in FIG. 6A.  
         [0093]    In a preferred embodiment, the outer sheath  98  has an outer diameter in the range of between 0.072 inches (1.8 mm) and 0.094 inches (2.4 mm). The inner diameter of the outer sheath  98  has a range of between 0.066 inches (1.7 mm) and 0.086 (2.2 mm)inches. The outer sheath tends to the lower portion of the range when the stent can contract to the 6 French size and towards the upper portion of the range when the stent can contract to the 7 French size.  
         [0094]    In one preferred embodiment, the outer sheath  98  is formed having several layers of material. The nominal outer diameter is 0.093 inches and a nominal inner diameter of between 0.078 and 0.081 inches. The inner layer is composed of polyethylene or TFE and has a nominal thickness of 0.001 inches. A layer of EVA or polyurethane of a nominal thickness of 0.0005 inches forms the second layer. A braid metal spring stainless or liquid crystal polymer (LCP) fiber having a thickness of 0.0015 to 0.0025 inches overlies the second layer and forms the core of the outer sheath  98 .  
         [0095]    In a preferred embodiment, the fourth layer varies in material composition as it extends from the proximal end to the distal end. The proximal end of the sheath is formed of Pebax or polyamide and the material varies to a polyamide or cristamid at the distal end. This layer has a nominal thickness of 0.002 inches. This varying of the material is for increased flexibility at the distal end to move through tortures easier and increased rigidity at the proximal end to give the catheter better push.  
         [0096]    The sheath  98  has a finish layer of a hydrophlic coating having a thickness of between 0.0005 and 0.001 inches. The coating is for increase lubricativity.  
         [0097]    The shaft has an outer diameter of 0.074 inches (1.88 mm) The shaft is formed of nylon  12 , cristamid, or cristamid.  
         [0098]    In a preferred embodiment, the tip extrusion has an outer diameter in the range of between 0.042 and 0.055 inches. The inner diameter of the tip extrusion has a range of between 0.036 and 0.040 inches.  
         [0099]    In one preferred embodiment, the tip extrusion or catheter has a nominal outer diameter of 0.047 inches and an inner diameter of 0.037 inches. The inner diameter defines the passage for he guidewire. In a preferred embodiment, the catheter is formed of Peek (Polyether ether ether Keetone) Peek Braid Peek, Polyimide or Polyimide Braid Polyimide. In a preferred embodiment, the guide wire  108  has a diameter of 0.035 inches. It is recognized that the guide wire can be larger or smaller as indicated below.  
         [0100]    An alternative method to the over-the-wire delivery system  86  shown in FIGS. 6A and 6B is a rapid exchange delivery system  112  shown in S  7 . The rapid exchange delivery system  112  has a shaft  114  that extends from a proximal handle  116 . A guidewire  118  extends from a two lumen transition zone  120  through an outer sheath  122  to a distal tip end  124 . In Contrast to the over the wire delivery system  86 , the guide wire  118  does not extend all the way back to the proximal handle  116 . Similar to the over the wire delivery system  86 , the outer sheath  122  of the rapid exchange delivery system  112  is moved towards the handle  116  using a pull wire  128  and a pull ring  130 .  
         [0101]    Referring to FIGS.  8 A- 8 F, the over-the-wire delivery system  86  of FIGS. 6A and 6B is shown for positioning a stent  10  in a bile duct. Stents are used in many uses including for treatment of an obstruction  134 , such as a tumor in the bile duct. The delivery system can position a prosthesis, such as a stent  10 , to move the obstruction out of the lumen  136 .  
         [0102]    Typically, the occlusion substantially closes off a lumen, such as a bile duct which has a healthy diameter of about 8-10 mm. The obstruction may be several centimeters in length. After the obstruction is located using one of several diagnostic techniques, the physician gains access to the lumen. Using ultrasound or fluoroscopy, the guidewire  108  such as seen in FIG. 8C, is positioned through the outer access sheath  98  so that it extends past the obstruction.  
         [0103]    Referring to FIG. 6A, the delivery system  86  is advanced axially and distally until the distal radiopaque marker  60  is positioned axially at a location at least about 1 cm distal of the occlusion  134 . This location substantially corresponds to the position at which the distal end  47  of the stent  10 , when expanded, will engage the lumen wall  136 . The location is selected so the stent  10  is positioned beyond the occlusion  134  but not too close to the end of the bile duct, for example. The marker  138  indicates the position of the proximal end  40  of the stent  10  in the expanded position and is such that the proximal end  40  of the prosthesis will engage healthy tissue over a length of at least 1 cm. Where possible the stent  10  is centered about the obstruction, based on the fully expanded length indicated by markers  138  and  140 . The marker  139  indicates the proximal end of the stent when the stent is in the fully compact form, which has an overall length of approximately 20 percent longer than in its expanded state. Therefore for a stent of 7.5 centimeters, the compressed state has a length of approximately 9 centimeters.  
         [0104]    The sheath  98  is retracted in one continuous motion as illustrated in FIG. 8B. With the sheath  98  partially withdrawn, (arrow  144 ), portions of the stent  10  expand (arrow  146 ) The lengthening of the stent  10  has a simultaneous effect of reducing the radial force the stent exerts on the wall of the sheath  98  and, therefore, reducing the frictional force between the inner wall of the sheath and the stent  10 , allowing a smoother retraction of the sheath  98  with less axial force.  
         [0105]    After sheath retraction continues but usually to a point less than the marker  138 , the proximal end  40  of the expanding and contracting prosthesis  10  exits the sheath  98  and engages the lumen wall  136 , forcing open the lumen  136  to its normal diameter and firmly anchoring the stent so that it resists axial motion, as illustrated in FIG. 8C.  
         [0106]    The stent is released entirely from the catheter body  88  by drawing the catheter body  88  proximally (arrow  152 ) as seen in FIG. 8D, which causes the end loops to be positioned at more distal positions along the members, until the radial force of the stent  10  causes the members to deflect outwardly (arrows  154 ).  
         [0107]    The catheter  88  is then removed from the body, leaving the prosthesis  10  properly positioned as Illustrated in FIG. 8E.  
         [0108]    An alternative embodiment of the low profile diamond stent is shown as a flat layout view in FIG. 9. The stent  160  has two separate layers  162  and  164 ; an inner layer  162  shown in hidden line and an outer layer  164 . Each layer  162  and  164  of the stent  160  has a plurality of strands  166 . In a preferred embodiment, each layer has four strands; this is in contrast to the five strands in the previous embodiment. While four and five strand embodiments are shown above, it is recognized that the number of strands and cells can vary, for example, from three to ten or higher, dependent on size, type of joint or the strands, use and other factors.  
         [0109]    The strands are woven in a pattern of geometric cells  169  starting at the distal end  170 . Each strand  166  forms a pair of legs  144  of the most distal opening on the cell  168 . The inner layer  162  and the outer layer  164  are intertwined at both the distal end  170  and the proximal end  172 .  
         [0110]    The sides  176   a,    176   b,    176   c,  and  176   d  of each of the cells  168  are defined by a series of strand lengths  178   a,    178   b,    178   c,  and  178   d.  Each of the sides  176  are joined to this adjoining side at an intersection where the strands are helically wrapped about each other to form interlocking joints  180 .  
         [0111]    Similar to the embodiment shown in FIGS. 1A and 1B and in contrast to the previous embodiment, every intersection has an interlocking joint  180 . Without the fifth strand  166 , the stent  160  can be contracted into a smaller diameter than that of the stent  20  shown in FIGS. 1A and 1B.  
         [0112]    In a preferred embodiment for use in a colon, both layers are formed of identical materials. Each strand is composed of nitinol and has a diameter of 0.010 inches (0.25 mm).  
         [0113]    Still referring to FIG. 9, the two separate layers  162  and  164  in the constricted position are off-set from each other so the interlocking joints of one layer do not engage with the interlocking joints of the other layer. The off-set between layers can be created by either an off-set during manufacturing as described below, or created by the related motion of the layers as the layers are constricted. The related motion can be the result of the constraints of the strands or the material properties. One property difference can be the thickness of the strands as described in the next embodiment.  
         [0114]    The stent can be coated with a silicon lubricant or suitable lubricant to ease the self-expanding of the stent.  
         [0115]    An alternative embodiment of the double layer stent  160  of FIG. 9 is shown in FIGS.  10 - 12 . In contrast to the double layer stent  160  of FIG. 9, the double layer stent  188  has a cover layer  190  interposed between an outer layer  192  and an inner layer  194 . The outer layer  192  is shown in hidden line and the cover layer  190  is shown in hidden line in FIG. 10. It is recognized that the cover layer  190  can be placed in other locations.  
         [0116]    Similar to the previous embodiment, the inner layer  194  and the outer layer  192  are intertwined at both the proximal end  170  and the distal end  172 . The intertwining of the layers  192  and  194  retains the cover layer  190  in position.  
         [0117]    In a preferred embodiment, each layer has four strands and are woven similar to the embodiment shown in FIG. 8 to define the geometric cells  198 . The strands of the two layers are formed of two different thickness wires in a preferred embodiment. The inner layer has a thicker wire.  
         [0118]    [0118]FIG. 11 shows the sent in an artery. The stent is moving an obstacle out of the passage. The cover prevents tumor in-growth, will seal fistulas and block aneurysms.  
         [0119]    One technique for placing a stent into the circulation system of a patient is to enter from the brachial artery located in the arm. This point of entry can be used for insertion into the vascular system including for example, peripheral locations such as the knee which require the flexibility of the diamond stent.  
         [0120]    A cross-sectional view of the stent  188  is shown in FIG. 12. The inner layer  194  having the thicker strands forces the cover  190  and the outer layer  192  outward. The cover  190  is in engagement with both the inner layer  194  and the outer layer  192 .  
         [0121]    In a preferred embodiment, the strands are formed of nitinol. The inner layer has strands having a diameter of 0.006 inches (0.15 mm). The strands of the outer layer have a diameter of 0.005 inches (0.13 mm). The radial expansion force of the thicker wire inner layer is transmitted to the outer layer. The radial expansion force can be altered by varying one or both layers.  
         [0122]    In another preferred embodiment, the stent has three strands on each layer. The inner layer has a diameter of 0.008 inches (0.02 mm). The strands of the outer layer have a diameter of 0.005 (0.13 mm) inches.  
         [0123]    The outer layer can be formed from a non self-expanding material. The outer layer can be chosen for its radiopaque characteristics. Materials that can be chosen for their radiopacity characteristics include tantalum, platinum, gold or other heavy atomic metal.  
         [0124]    In a preferred embodiment, a cover is interposed between the layers. The cover can be made of several types of material which allow the stent to be compressed to a small diameter and also be self-expanding. A preferred material is a woven carbon fiber, a metal mesh, a polymer such as a polyurethane, or a material treated with a drug for time release. Different agents can be employed on the inside and the outside. An electrical current can be applied to tissue using the stent. Different materials for the layers can be used than the interposed cover depending on the treatment site and the desired method of treatment.  
         [0125]    In one preferred embodiment, the layers  192  and  194  are interwoven for the entire stent without an interposed cover. Referring to FIG. 13, a mandrel  262  has a plurality of anchoring pins  264 . For a stent having two layers of four strands each, each row has eight (8) anchoring pins  264  at the same height. The top row, however, has the anchoring pins  264  for one strand positioned ½ millimeter higher than the other set. After the stent is woven, the distal end of each stent is pulled to the same position, therein resulting in the rest of the interlocking joints being offset.  
         [0126]    If there is no cover between the two layers, the two layers can be interwoven from the distal end to the proximal end.  
         [0127]    [0127]FIGS. 14A and 14B illustrate a single layer stent  210  having six strands. The stent  210  has four wrap joints  254  a pair of cross joints  256 .  
         [0128]    In one preferred embodiment, the stent  210  has a diameter of 14 millimeters in the expanded state. The stent has foreshortening in the range of 12 to 18 percent. With the strands having a diameter of 0.006 inches (0.15 mm), the stent with only four wrap joints 254 per row can compress to fit within a 7 French system.  
         [0129]    An alternative delivery system  286  is illustrated in FIG. 15A. The stent  10  is positioned over an inner shaft  288 , which is a braided tube, at a distal end  289  of the delivery system  286 . The inner shaft  288  extends to a proximal handle  290 . The delivery system  286  has an outer shaft  292  which extends from the proximal handle  290  to a point  294 , which is proximal the distal end  289 . The inner shaft  288  extends through a lumen  296  of the outer shaft  292  from the proximal handle  290  and projects out at the distal end of the outer shaft  292 . The inner shaft  288  secured to a luer fitting  298  housed in the proximal handle  290 , also referred to as an actuator housing or gun portion, of the delivery system  286 . The inner shaft  288  is free-floating with the lumen  296 .  
         [0130]    An outer sheath  300  overlies the inner shaft  288  and the outer shaft  292  from the distal end  289  of the inner shaft to a point  302  of the delivery system  286 . The outer sheath  300  is movable relative to the inner shaft  288  and the outer shaft  292  and is pulled from the distal end  289  of the inner shaft  288  using a pull wire  304  which extends in a second lumen  306  of the outer shaft  292 . The distal end of the second lumen  306  is proximal to the distal end of the lumen  296 . The outer sheath  300  and the pull wire  304  are pulled using an actuator  308  of the delivery system  286 . The pull wire  304  is attached to a toothed strip  310  that engages the actuator  308 . A guidewire  312  extends through the inner shaft  288  from the proximal handle  290  to the distal end  289 .  
         [0131]    In a preferred embodiment, the outer shaft  292  ends between 1.8 and 20.0 centimeters before the distal end  289 . The outer sheath  300  extends from the distal end  289 , in the range of 1 to 50 centimeters towards the proximal handle.  
         [0132]    Referring to FIG. 15B, an enlarged view of the delivery system where the inner shaft  288  extending from the outer shaft  292  is shown in FIG. 15A. The inner shaft  288  is shown projecting from the lumen  296  of the outer shaft  292 . The outer shaft  292  narrows at its distal end to minimize large discontinuities of material. The pull wire  304  is above the outer shaft  292  and can extend around the inner shaft  288 . The pull wire  304  is carried by the second lumen  306  of the outer shaft  292  to a point lust proximal to this location. The pull wire  304  extends down and is connected to the sheath  300  by a pull ring  305 . The pull ring  305  in a preferred embodiment is sintered to the outer sheath  300 . The inner shaft  288  is free to move within the lumen  296  of the outer shaft  292  at this point.  
         [0133]    The distal end  289  of the delivery system  286  is shown enlarged in FIG. 15C. At the end of the inner shaft  288  there is located a distal tip  318 . In a preferred embodiment, the tip is formed of a polymer which has been molded onto the inner shaft  288 . Overlying the inner shaft  288  is the stent  10 . The stent  10  is positioned by a reference locator/stop  321 . The outer sheath  300  overlies the inner shaft  288  and the stent  10 , and engages the distal tip  318 . A pair of radiopaque markers  328  are shown encircling the inner shaft  288 .  
         [0134]    Referring to FIG. 16A, a sectional view of the inner shaft  288  projecting from the lumen  296  of the outer shaft  292  is shown. The outer sheath  300  can be formed of various biocompatible polymers such as a polyamide with a center core of liquid crystal polymer (LCP). It is recognized that the outer sheath  300  can be formed of other compositions as discussed above and below in alternative embodiments. In a preferred embodiment, the outer sheath  300  has an outside diameter of 4-7 French. The wall thickness is typically 0.003 to 0.005 inches (0.076 mm to 0.13 mm).  
         [0135]    The outer shaft  292  has an outer diameter of 0.066 inches (1.7 mm), which allows the proximal end of the outer shaft  292  to fit within the outer sheath  300 . The outer shaft  292  in a preferred embodiment is made of polyamide or nylon, but can alternatively be made of other biocompatible polymers such as polyester, polyurethane, PVC or polypropylene. The lumen  296  of the outer shaft  292  has a diameter of 0.035 to 0.037 inches (0.89 to 0.94 mm), for example, and receives the inner shaft  288 . The outer shaft  292  in a preferred embodiment has a plurality of other lumens including the second lumen  306  which the pull wire  304  extends through. In a preferred embodiment, the second laden  306  has a diameter of slightly larger than the pull wire  304 . The pull wire  304  is typically a single stainless steel wire having a diameter of 0.012 inches (0.30 mm). However, the pull wire  304  can consist of a plurality of wires and can be formed of a different material.  
         [0136]    The inner shaft  288  is formed of a reinforced layer encased by an outer layer and an inner layer. In a preferred embodiment, the inner shaft  288  has as a center reinforcement layer comprising of a tubular woven steel braid  320 . The reinforcement layer is encased by the inner and outer layer of polyimide  322 . The tubular woven steel braid is formed of flat strands  324  having a thickness of 0.0015 to 0.003 inches (0.038 mm to 0.076 mm) and a width of 0.001 to 0.005 inches (0.025 to 0.13 mm) in a preferred embodiment. The inner diameter of the tubular woven steel braid is 0.015 to 0.038 inches (0.38 mm to 0.97 mm). The tubular steel braid is encased in the polyimide such that in a preferred embodiment the outer diameter of the inner shaft  288  0.021 to 0.041 inches (0.53 to 1.0 mm). The thickness of the wall of the inner shaft is typically between 0.003 to 0.008 inches.  
         [0137]    Within the single braided polymer tube  288  a guidewire  326  may extend as seen in FIG. 16A. The guidewire  326  in a preferred embodiment is formed of stainless steel. The guidewire  326  in a preferred embodiment has a diameter in the range of 0.014 to 0.037 inches (0.36 to 0.94 mm) and in a preferred embodiment 0.035 inches (0.89 mm).  
         [0138]    Referring to FIG. 16B, a sectional view of the distal end of the delivery system is shown. The sheath  300  is overlying the inner shaft  288  with the stent  10  being interposed. The pull wire  304  seen in FIG. 16A is secured to the sheath at a position proximal to that shown in FIG. 16B.  
         [0139]    The delivery system  286  can be used in numerous ways. One such way is by placing the delivery system&#39;s outer shaft  292  and inner shaft  288  through an endoscope  70  such as shown in FIGS. 5A and 5B. Alternatively, a percutaneous procedure can be used. In both procedures, the guidewire extending through the inner shaft  288  is extended beyond the inner shaft  288  and used to define the path. The inner shaft  288  is to be pushed a short distance along the guidewire. The guidewire and inner shaft  288  are moved until the distal tip is in position.  
         [0140]    The inner shaft  288  has sufficient strength that it is able to follow the guide wire and resist kinking Overlying the inner shaft  288  is the outer sheath  300  which gains its structural strength by engaging and forming a continuous structure with the distal tip  318  of the inner shaft. The sheath  300  is pulled in the proximal direction to expose the stent  10  as explained above and therefore does not have to slide over the distal tip  318  of the inner shaft  288 .  
         [0141]    The stent  10  is located between the outer sheath  300  and the inner shaft  288 . The inner shaft  288  is secured only at the luer fitting  298  housing the proximal handle  290  of the delivery system  286 . The inner shaft  288  floats freely and is not otherwise secured within the lumen  296  of the outer shaft  292 .  
         [0142]    When the distal tip is in the proper position in the artery, vessel or other desired location, the outer sheath  300  is pulled proximally by using the handle on the proximal handle  290  which engages an actuator  308  that moves the tooth strip  310 . The tooth strip  310  is connected to the pull wire  304  which extends through a lumen in the outer outer shaft to a point beyond the proximal end of the outer sheath and the pull wire extends from that point to the pull ring. With the outer sheath moved proximally, the stent  10  is able to self expand into proper position.  
         [0143]    Referring to FIGS. 17A and 17B, an alternative embodiment of a delivery system  330  is shown. The delivery system inner shaft  332  which is encircled by an inner ring  338  of a mounting ring  334 . The mounting ring  334  has at least one radial member or ridge  336 , which projects radially out from the inner ring  338  towards the outer sheath  300  In a preferred embodiment, the ring  334  has a pair of ridges  336  which project radially outward in opposite directions along a common axis, or in other words, at an angular separation of 180 degrees. Additional ridges  336  that can be evenly spaced around the circumference of the ring  334  to evenly distribute the load force on the stent and can extend longitudinally between 1 and 8 mm such that the proximal loops at one end of the stent grasp the ridges during mounting. The stent is then held in place by the outer sheath during delivery and release. For example, three members  336  are spaced 120 degrees apart round  334 .  
         [0144]    Cells of the stent  10  are placed around the protrusions  336 . With the strands  42  of the stent  10  encircling the tabs  336 , the stent  10  can compress while still being retained. Placement of the members at the proximal end of the stent  10  affords maximum extension and compression of the stent to within the needed diameters.  
         [0145]    An alternative method uses a solid mounting ring where the stent is held with a friction fit between the outer sheath and the ring to retain the stent in position in the delivery system The solid ring with the friction fit is further described in U.S. Pat. No. 5,702,418 which issued on Dec. 30, 1997, the entire contents of which is incorporated herewith by reference.  
         [0146]    Alternatively, as seen in FIG. 17C, the tabs or ridges  336  of the ring  334  retain the stent  10  as the stent  10  is deployed. If it is determined prior to the stent  10  being totally deployed that the stent is not in proper position, the stent can be retracted back into the delivery system.  
         [0147]    In a preferred embodiment, the inner ring  334  has an outer diameter of 0.05 inches (1.3 mm) The tabs  336  project such that the distance from the radial end of one tab  336  to the radial end of a tab on the other side of 0.07 inches. The tabs have a width of 0.01 inches. The ring  334  can have a length of 0.06 inches.  
         [0148]    [0148]FIG. 18 shows an alternative mounting ring  335 . The ring  335  is a solid ring with sections removed to define a plurality of grooves  337 . The grooves  337  receive the strands of the stent  10 , with the projections or ridges  339  located in the cells of the stent  10 .  
         [0149]    Similar to the previous “over-the-wire” delivery system shown, an “over-the-wire” delivery system  340  shown in FIG. 19A has an inner shaft  342  extending from a proximal handle  344  to a distal tip end  346 . The inner shaft  342  extends through an outer shaft  350  at the proximal end. An outer sheath  352  is located at the distal end of the “over-the-wire” delivery system  340 , overlying the exposed inner shaft  342  and a portion of the outer shaft  350 . The outer sheath  352  is moved toward the handle using a pull wire  354  and a pull ring  356 . The pull wire  354  extends through a lumen  348  of the outer shaft  350  from the proximal handle  344  to a point just proximal to where the inner shaft  342  extends from the outer shaft  350 .  
         [0150]    Referring to FIG. 19B, the outer sheath  352  is formed of several layers of material. An inner layer  360  can be formed of a nylon  12  which extends the entire length of the outer sheath  352 . Overlying the inner layer  360  is a braid  362  of either a metallic or fiberglass such as a stainless steel braid. The outer sheath  352  has an outer layer  364  formed of nylon  12  extending from the proximal end to a position proximal and adjacent to the distal end  346 . The last portion of the outer layer  364  is formed of another material which is less stiff, or softer, such as a PEBAX.  
         [0151]    In a preferred embodiment, the last portion of the outer sheath  352  which has the less stiff or softer material on the outer layer  364 , extends 36 centimeter (+/−one cm) and the entire length of the outer sheath is approximately 200 cm. In a preferred embodiment, the outer diameter of the sheath is 0.920 inches (+/−0.001 inches, or about 23.4 millimeters) with the wall thickness being 0.0070 inches (+/−0.0005 inches) (0.1778 millimeter +/−0.0127 millimeter). The braid  362  is formed of a stainless steel having a diameter of 0.0015 inches (0.038 millimeter).  
         [0152]    It is noted that the delivery systems shown can be used in various locations such as non-vascular systems and vascular systems. In the embodiment shown above, one of the application is endoscopic delivery in the gastric system which requires that the deliver, system be capable of taking a 90 degree bend. The inner shaft, sometimes referred to as the catheter, has an outer diameter that approximates the inner diameter of the outer sheath, for a segment near the distal end, just proximal to where the stent is positioned, as seen in FIG. 19B. This is in contrast to the embodiment shown in FIG. 16B.  
         [0153]    An alternative embodiment of an “over-the-wire” delivery system  370  is shown in FIGS. 20A and 20B. The delivery system  370  has an inner shaft  372  seen from the proximal handle  374  to a distal tip end  376 . The inner shaft  372  extends through an outer shaft  380  at the proximal end. An outer sheath  382  is located at the distal end of the “over-the-wire” delivery system  370 .  
         [0154]    This embodiment has the same elements as the previous embodiment. The outer sheath  382  has variable properties as explained below. As indicated above, it is recognized that the path the delivery system takes is almost never straight and usually has many bends between the insertion point into the body and the stricture or stent delivery site. In order to reach the delivery site, the delivery system including the outer sheath  382  must be flexible enough to negotiate the bends, but have sufficient strength and stiffness.  
         [0155]    The outer sheath  382  is formed of a plurality of layers. An inner layer  390  is formed of a fluorinated polymer such as PTFE or FEP, or polymer such as HDPE. A second layer  392  encases the first layer and consists of a polyurethane such as those sold underneath the name TECOFLEX™ or PLEXAR™. A third layer  394  consists of a polymer braiding, such as LCP fiber (Vectran), or a metal braided coil. In a preferred embodiment, the braiding is flat. However, it is recognized that a round braiding may also be used. A fourth layer  398 , an outer layer, of the outer sheath  382  material properties vary as it goes from the proximal end to the distal end.  
         [0156]    In a preferred embodiment, the properties of this fourth layer  398  are divided into two materials and a combination of these materials in the transition. For example, the first portion is a material/blend chosen for higher density, crush strength, relative high durometer and stiffness such as a polyamide sold under the trade name Cristamid or HDPE. The material at the distal end being selected for a higher flexibility, crease resistance, such as a polyamide with lower durometer or Pebax material (polyamid elastomer). In a transition area the material starts as a high 100 percent of the A property and transitions to 100 percent of the B property. This transition area in a preferred embodiment is less than one centimeter; however, the transition area can be up to lengths of 25 centimeters.  
         [0157]    [0157]FIG. 20B is an enlarged view of the outer sheath  382  extending from the distal end to the proximal end, with portions broken away. The inner shaft  372  and stent  10  have been removed from FIG. 20B to allow greater visibility of the metal braided coil. The metal braid is formed of a flat wire having a width of between 0.001 inches (0.025 mm) and 0.005 inches (0.13 mm) and a thickness of 0.001 inches (0.025 mm). For the LCP fiber braid, the width is 0.003 inches (0.076 mm) and a thickness of 0.0007 inches (0.018 mm) diameter. The stiff materials could also be polyester (PET), LCP (liquid crystal polymer), PEEK, PBT, etc. and the soft material could be polyester elastomer, Arnitel or Hytrel. Weave patterns can be one-over-ore or two-over-two. The pick density could be 20 pick/in or 120 pick/in, or vary in between.  
         [0158]    While the tailoring of the properties of the outer sheath  382  can be done for main purpose of ensuring sufficient strength and flexibility. For example, it is desirable that the distal end have sufficient flexibility and still have sufficient hoop or radial strength to prevent the self expanding stent from rupturing the sheath The tailoring of the properties can allow the overall wall thickness and therefore the outer diameter to be reduced.  
         [0159]    The dimensions given are for a preferred embodiment. It is recognized that the dimension and properties will vary depending on the intended use of the delivery system. For example, the overall outer diameter of the composite outer sheath  382  could vary from under 3 French (e.g. for a Radius™ (Coronary) delivery system) to 20 French or larger (e.g. For a colonic or aortic delivery system). The wall thickness can vary from as thin as 0.003 inches for example, for coronary use, to as thick as 0.050 inches, for example, for colonic or aortic use. In the preferred embodiment described here, the normal thickness is 0.005 inches. It is recognized that in addition to a seamless transition where the property of the outer layer, the fourth layer  398 , varies through a transition portion, the sections can vary more abruptly such as with lap joints.  
         [0160]    Referring to FIG. 20C, a sectional view of the distal end of the outer sheath is seen. The inner layer  390  has an inner diameter of for example between 0.078 inches to 0.081 inches (1.98 to 2.06 mm) for a 7 French delivery system. The outer diameter of the inner layer is between 0.082 to 0.083 inches (2.1 mm) The second layer  392 , which encases the first layer  390 , has an outer diameter of 0.084 inches (2.1 mm). The third layer with a fiber braid of 0.0007 inches has an outer diameter of 0.0868 inches (2.2 mm). The open area of the third layer is filled with material from both the fourth layer and the second layer. The fourth layer has an inner diameter of between 0.087 inches and 0.088 inches (2.21 mm to 2.23 mm) and an outer diameter of between 0.091 inches and 0.092 inches (2.31 mm and 2.34 mm).  
         [0161]    The third layer which consists of LCP fiber braid or metal braided coil could have variable pick density from proximal end to distal end. At the proximal end, the pick density is 20 pick/in for additional stiffness and tensile strength, and at the distal end, the pick density is 120 pick/in for additional flexibility and radial strength to restrain the stent in the delivery system. The transition length can be abrupt or gradual (1 cm to 25 cm).  
         [0162]    An alternative embodiment of an “over-the-wire” delivery system  400  is shown in FIG. 21. The delivery system  400  has an outer sheath  402  formed of a plurality of layers. The outer layer as its material properties vary as it goes from the proximal end to the distal end.  
         [0163]    In a preferred embodiment, the properties are divided into two materials and a combination of these materials in the transition area. For example, the first portion is a material/blend chosen for higher stiffness, crush-strength and having relative high durometer. The material at the distal end being selected for a higher flexibility, crease resistance and with a lower durometer.  
         [0164]    In a preferred embodiment, the outer sheath does not have a layer containing a polymer or metal braided coil.  
         [0165]    Referring to FIG. 22A, an alternative embodiment of a stent  410  is shown flat layout. The stent  410  is formed OF elongated strands  412  such as elastic metal wires. The wires  412  are woven to form a pattern of geometric cells  414 . The sides  416   a,    416   b,    416   c,  and  416   d  of each of the cells  414  are defined by a series of strand lengths  418   a,    418   b,    418   c,  and  418   d.  Each of the sides  416  are joined to the adjoining side at an intersection where the strands  412  in this embodiment are either helically wrapped about each other to form interlocking joints  420  or joined to form a box node  422 . The interlocking joints  420  are discussed above with respect to FIGS. 2A and 2B.  
         [0166]    Referring to FIG. 22E, the box node  422  is formed of a series of elements. The top of the box node  422  has an interlocking joint  420  where the strands  412  which extend from above cross each other. The strands  412  then extend down to form the sides of the box node  422 . The strands  412  then cross each other on the bottom of the box node  422  in another interlocking joint  420 . The respective strands therefore enter and exits the box node  422  from the same side. This is in contrast to the typical interlocking joint  420  or a cross joint, wherein the strands enter and exit at opposite corners of the joint. A cross joint is further explained above with respect to FIGS. 2A, 2B, and  3 . The strands  412  are shown representing their path in exploded perspective view. (The interlocking joint  420  does not allow the strands  412  to normally separate like this.)  
         [0167]    The box node constrains the displacement of the cell and introduces local stiffness. By varying the number of nodes and location of nodes the degree of stiffness can be controlled. With this approach, as required, the stent can have different local mechanical properties (radial strength, column strength, etc.) without compromising flexibility. For example, the ends of the stent can be significantly stiffer than the middle portion or vice versa. The node structure restricts dilation and foreshortening of the stent during flexing, bending, and extension.  
         [0168]    [0168]FIG. 23A is a flat layout view of another embodiment of the stent  410 ′. In this embodiment, the stent  410 ′ has a plurality of joints at the same level around the circumference of the tubular stents. The majority of the joints are interlocking Points  420 . In this embodiment, one of the joints of the plurality of the joints around the circumference is a box node joint  422 . The placement of the node joints  422  are located along a diagonal  426  of the stent  410 .  
         [0169]    [0169]FIG. 23B is a flat layout view of an alternative embodiment of the stent  410 ′. In this embodiment, generally two joints of the plurality of the joints around the circumference is a box node joint  422 . The placement of the box node joints are each along a diagonal. The diagonals are at any angle to each other, therefore in certain locations the box node joint for each diagonal is one in the same.  
         [0170]    [0170]FIG. 24A is a schematic of an oblique view of a stent. The strands have been removed from FIG. 24B for clarity. The position of the box nodes are shown. In a preferred embodiment, the nodes are on alternating oblique planes. The nodes are located on opposing oblique planes. Positioning of the oblique planes also constitutes a pattern. The nodes may be placed on both oblique planes, as illustrated in FIG. 24B, also with a repeating pattern.  
         [0171]    During deformation (bending, twisting, etc.) the oblique planes accommodate (dissipates) the transfer of forces and displacements instead of simply transmitting the deformation to the next region of the stent. Selecting the planes at opposing angles causes the stent to have a neutral response. Alternatively, the angle can be chosen to yield a preferred bending direction or plane. Locating the nodes on an oblique plane will cause the nodes to collapse in a staggered mariner. When the tent is in a loaded conformation, the nodes will not co-locate in the same perpendicular plane. This increases the packing efficiency when in its loaded conformation.  
         [0172]    A method of making the stent  410  is shown in FIGS. 25A and 25D. A mandrel  432  has a plurality of pins  434  on the outer surface of the mandrel in a pattern that determines the geometric cell  436  pattern. The strands  412  are bent around the top portion  438  of each top anchoring pin  434  to form the proximal end  440  of the stent  410 . The strands  412  are then pulled diagonally downward to an adjacent anchoring pin  434  where the strands  412  are joined. The strands  412  are helically wrapped about each other to form the interlocking joint  420 , with each strand passing through a single 360 degree rotation. The two strands are pulled taught so that the interlocking joint  420  rests firmly against the bottom portion  444  of the anchoring pin  434  such that each strand  412  is maintained in tension.  
         [0173]    Where a box node  422  is desired, the mandrel  432  has a pair of anchoring pins  434  for each box node  422 . The strands  412  are helically wrapped about each other to form an interlocking joint  420  and positioned between the anchoring pins  434 . The strands  412  extend down the sides of the lower anchoring pin  434 . The strands  412  are then helically wrapped about each other to form the interlocking joint  420 , with each strand passing through a single 360 degree rotation. The two strands are pulled taught so that the interlocking joint  420  rests firmly against the bottom portion  444  of the anchoring pin  434  such that each strand  412  is maintained in tension.  
         [0174]    In a preferred embodiment, the anchoring pins  434  are square with the edges having appropriate radii. The square pins retain the helically wrap of the strands in a proper position.  
         [0175]    The free ends of the strands  412  are then pulled downward to the next diagonally adjacent anchoring pin  434  This process is continued until the desired length of the stent  410  is achieved The stent  410  is then heat-treated. The strands  412  at the joining end of the stent  410  are attached, for example, by ball welding or laser welding the ends of the wires as discussed above.  
         [0176]    An alternative stent  450  is shown in a contracted position within the sleeve  452  in FIG. 26A. Similar to previous embodiment, the stent  450  is formed of elongated strands  22  such as elastic metal wires. The wires  22  are woven to form a pattern of geometric cells  24 . The sides  26   a,    26   b,    26   c,  and  26   d  of each of the cells  24  are defined by a series of strand lengths  28   a,    28   b,    28   c,  and  28   d.  Each of the sides  26  are joined to the adjoining side at an intersection where the strands  22  are helically wrapped about each other to form interlocking joints  460 . In contrast to the previous embodiments, the helically wrapped joints  460  extend longitudinal in contrast to radial. A medical prosthetic stent with longitudinal joints and method of manufacturing such a stent is described in U.S. Pat. No. 5,800,519 on Sep. 1, 1998 and which is incorporated herewith by reference.  
         [0177]    The strand angle a is increased in the compressed or constrained state of the stent in this embodiment. The strand angle can be in the range of 10°-80° depending upon the particular embodiment. Smaller strand angles between 10° and 45° often require a shortened cell side length L to maintain radial expansion force. Cell side lengths L in the range of 0.5 to 4 mm, for example, can be used with stent having these smaller strand angles. For stents with larger strand angles in the range of 3-8 mm can be used, depending on the expanded diameter of the stent, the number of cells and the desired radial expansion force.  
         [0178]    In addition to FIGS. 26A and 26B where the joints extend longitudinal, it is recognized that other embodiments such as the box node can extend longitudinal.  
         [0179]    Several delivery systems have been discussed above. It is recognized that an alternative delivery system  480 , that of a coaxial delivery system  480 , can be used. Referring to FIG. 27A, a stent  10  is positioned over an inner shaft  482 , which is a braided tube in a preferred embodiment at a distal end of the delivery system. The inner shaft  482  extends from a handle  484  located at the proximal end. The delivery system has an outer shaft  486  which extends from the proximal handle  484  to a point, which is proximal to the distal end  488 . The inner shaft  482  extends through a lumen  490  of the outer shaft from the proximal handle  484  and projects out the distal end of the outer shaft. The inner shaft  482  is free-floating within the lumen of the outer shaft  486 .  
         [0180]    An outer sheath  492  overlies the inner shaft  482  and the outer shaft  486  from the distal end  488  to the proximal handle  484 . This is in contrast to previous delivery systems discussed wherein the outer sheath  492  ends at a point distal to the handle. The outer sheath  492  is movable relative to the inner shaft  482  and the outer shaft  486  by pulling the outer sheath  492  at the proximal handle end. A guide wire  496  extends through the inner shaft from the proximal handle to the distal end.  
         [0181]    Referring to FIG. 27B, a sectional view of the inner shaft  482  protecting from the lumen  490  of the outer shaft  486  is shown. The outer sheath  492  is coaxial with the inner shaft  482  and the outer shaft  486 . The properties of the inner shaft  482 , outer shaft  486 , and outer sheath  492  can be similar to those discussed above with respect to other embodiments.  
         [0182]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Technology Classification (CPC): 0