Patent Publication Number: US-2021161693-A1

Title: Short Stent

Description:
PRIORITY 
     This application is a division of U.S. patent application Ser. No. 15/423,391, filed Feb. 2, 2017, now U.S. Pat. No. 10,905,578, which is incorporated by reference into this application. 
    
    
     BACKGROUND 
     Intraluminal prostheses used to maintain, open, or dilate blood vessels are commonly known as stents. Stents have been used in various body lumens, including, e.g., the biliary tree, venous system, peripheral arteries, and coronary arteries. Stent generally include cylindrical frames that define a plurality of openings. 
     There are two broad classes of stents: self-expanding stents and balloon-expandable stents. Self-expanding stents expand intraluminally when a constraining cover is removed, such as a sheath of a stent delivery system. Other forms respond to elevated temperatures (due to the stent&#39;s material properties). Self-expanding stents are generally loaded into a delivery system by collapsing the stent from an expanded configuration at a first, larger diameter to a collapsed configuration at a second, smaller diameter. Balloon-expandable stents are typically characterized by intraluminal expansion using an inflation force, such as a balloon catheter. Balloon-expandable stents are generally loaded onto a balloon catheter using a crimping process to collapse the stent, and are plastically deformed when the balloon is inflated in the body vessel to the expanded configuration. 
     There are two basic architectures for stents, circumferential and helical. Circumferential architectures generally include a series of cylindrical rings, formed by a series of struts, connected by elements or bridges along a stent longitudinal axis. Helical configurations include a helical structure along the longitudinal axis of the stent, formed by a series of struts, connected by connecting elements or bridges. 
     Arterial and venous system stents can be made by machining a pattern of struts and connecting elements from a metal tube, typically by laser machining the pattern into the tube. The pattern of struts and connecting elements can be configured depending on the desired attributes, e.g. flexibility and bendability. The pattern can facilitate uniform expansion and curtail stent foreshortening upon expansion. 
     SUMMARY 
     Invention embodiments comprise a stent with butterfly-shaped cells and pinched-ellipsoid-shaped cells. In some embodiments, these cells contribute to a stent with a ring comprising two crown-shaped moieties having a multiplicity of vertexes disposed between struts and these moieties connect to each other crown bottom to crown bottom. In some embodiments, in addition to vertexes disposed between struts, the stents have a strut-vertex-bridge-vertex-strut sequence. 
     In these or other embodiments, the stent has a ring comprising first and second crown-shaped moieties having a multiplicity of vertexes wherein the vertexes are disposed between struts; one or more struts disposed between a crown-bottom vertex on the first ring and a crown-bottom vertex on the second ring; and one or more markers connected to a crown-top vertex. Sometimes these stents or the rings of these stents comprise a radiopaque insert disposed in the marker. And in some embodiments, the stent is adapted for balloon expansion. 
     In these or other embodiments, a stent comprises a first ring with two first moieties having a multiplicity of sections comprising a vertex disposed between struts; a first, type-I bridge disposed between the first moieties crown bottom to crown bottom; a second ring with two second moieties having a multiplicity of sections comprising a vertex disposed between struts; a second, type-I bridge disposed between the second moieties crown bottom to crown bottom; and a type-II bridge disposed between the rings crown top to crown top. In some embodiments, the stent had a sequence of struts, vertexes, and bridges of strut, vertex, type-I bridge, vertex, strut, vertex, type-II bridge, vertex, strut, vertex, type-I bridge, vertex, strut. In some embodiments, the first-ring struts and vertexes are arranged in a first butterfly-shaped cell and a first pinched-ellipsoid-shaped cell; and another ring has struts and vertexes arranged in a second butterfly-shaped cell and a second pinched-ellipsoid-shaped cell. Sometimes the first butterfly-shaped cell is different from the second butterfly-shaped cell and the first pinched-ellipsoid-shaped cell is different from the second pinched-ellipsoid-shaped cell. These embodiments can comprise markers, as well. 
     In these or other embodiments, a system comprising an inner catheter with a distal stent bed; and a stent disposed on the distal bed is disclosed. In some embodiments, the system also has a stent anchor disposed on the inner catheter proximal to the stent, in which the stent anchor comprises a receiver having a shape complementary to a stent component, such as a marker. Self-expanding or other versions of the system can have an outer sheath disposed over the stent and the stent anchor. Sometimes the stent anchor has one or more fingers and a finger or these fingers can contain a receiver or the receiver is disposed across fingers. In some embodiments, a finger is biased outward. 
     In these or other embodiments, the system has a stent with a compressed configuration and an expanded configuration and the diameter of the expanded configuration is greater than the diameter of the stent anchor. In some embodiments, the stent has struts, vertexes, and bridges in a sequence of strut, vertex, type-I bridge, vertex, strut, vertex, type-II bridge, vertex, strut, vertex, type-I bridge, vertex, strut. The system can have first-ring struts and vertexes that are arranged in a first butterfly-shaped cell and a first pinched-ellipsoid-shaped cell and second-ring struts and vertexes that are arranged in a second butterfly-shaped cell and a second pinched-ellipsoid-shaped cell. In some embodiments, the first butterfly-shaped cell is different from the second butterfly-shaped cell and the first pinched-ellipsoid-shaped cell is different from the second pinched-ellipsoid-shaped cell. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG. 1A  is a stent embodiment shown in a laid-out configuration. 
         FIG. 1B  is a stent, similar to that of  FIG. 1A , but shown in a perspective view. 
         FIG. 1C  shows two cells of the stent of  FIG. 1A . 
         FIG. 2  shows an embodiment of a stent anchor. 
         FIG. 3A  shows a locked arrangement of a stent-anchor embodiment comprising fingers. 
         FIG. 3B  shows an unlocked arrangement of the stent-anchor embodiment of  FIG. 3A . 
         FIG. 4A  is a perspective view of another stent anchor embodiment comprising fingers. 
         FIG. 4B  is a side-view of the stent-anchor embodiment of  FIG. 4A . 
         FIG. 5  is a view of a stent anchor interacting with a crimped stent. 
         FIG. 6A  is a view of an embodiment of a delivery system containing a stent anchor and a stent bed. 
         FIG. 6B  is a view of an embodiment of the delivery system of  FIG. 6A  also containing a crimped stent. 
         FIG. 7A  is a laid out view of a longer stent embodiment. 
         FIG. 7B  is a view of stent cell from the stent of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 stent cell A 
                  12 
               
               
                 stent cell B 
                  14 
               
               
                 stent cell C 
                  16 
               
               
                 stent cell D 
                  18 
               
               
                 stent 
                 100, 700 
               
               
                 vertex, v2 
                 102 
               
               
                 vertex, v1 
                 104 
               
               
                 vertex, v4 
                 108 
               
               
                 vertex, v3 
                 110 
               
               
                 bridge, b1, type-I 
                 114 
               
               
                 bridge, b2, type-II 
                 118 
               
               
                 curved strut, c2 
                 120 
               
               
                 curved strut, c3 
                 126 
               
               
                 curved strut, c1 
                 130 
               
               
                 stent anchor 
                 500, 500a, 500b 
               
               
                 finger 
                 504 
               
               
                 slit 
                 506 
               
               
                 receiver 
                 508 
               
               
                 marker 
                 512 
               
               
                 insert 
                 514 
               
               
                 stent delivery system 
                 600 
               
               
                 stent delivery system distal end 
                 601 
               
               
                 stent bed 
                 602 
               
               
                 proximal-most end of stent 
                 603 
               
               
                 distal tip 
                 604 
               
               
                 outer sheath 
                 606 
               
               
                 distal-most end of outer sheath 
                 607 
               
               
                 tube 
                 608 
               
               
                 inner catheter 
                 610 
               
               
                 stent 
                 700, 100 
               
               
                   
               
            
           
         
       
     
     The following description and accompanying figures describe and show certain embodiments to demonstrate, in a non-limiting manner, several possible stent frame and stent holder configurations. The patterns can be incorporated into any intraluminal prosthesis, such as a self-expanding stent or a balloon-expandable stent, without limitation. In some embodiments, the disclosed pattern may be machined (e.g., laser machined) from a seamless metal or polymer tube. Non-limiting examples of metal tubes include stainless steel (e.g., AISI 316 SS), titanium, cobalt-chromium alloys, and nickel titanium alloys (nitinol). In other embodiments, the pattern may be formed into a metal or polymer sheet rolled into a tubular shape. The tubes or sheets may be heat-treated, annealed, or electropolished. Other known treatments are also contemplated. 
     The term “stent architecture” means the various stent features that contribute to its form, including the stent wall pattern. The term “stent cell” means a portion of the pattern that repeats along a circumferential or longitudinal path. 
     Extensive foreshortening, the stent getting shorter as it expands, can lead to inaccurate stent deployment. In certain embodiments, the stent architecture is designed to prevent excessive foreshortening. Other design considerations include in vivo stent flexibility and patency. Other designs minimize the profile of the collapsed stent. In certain embodiments, the stent architecture prevents excessive foreshortening. 
     Some of the drawings show stents in an expanded configuration, but laid-flat. These are but one possible configuration. Depending on the target vessel size, the stent can be over expanded, which could slightly alter the element&#39;s shape or their relationship to one another (e.g., elements parallel to the stent longitudinal axis may be oblique at over expanded diameters). Some drawings show the stents in an as-cut configuration and are top views of the stent. In some embodiments, the stents are formed in a tube having a diameter of about 4.8 mm. In some embodiments, the stents are formed in a tube having a diameter of about 6.4 mm. These are non-limiting tube diameter examples. In general, the tube diameters are based on target vessel diameters with larger tube diameters being selected for larger target vessels). Various stent embodiments have a longitudinal length, indicated as l in the figures, in the range from about 3 mm to about 20 mm or about 6 mm to about 12 mm, although longer lengths are also contemplated without limitation, depending on the particular application. 
     Referring to  FIGS. 1A-C , stent  100  is shown, including a repeating pattern of two types of stent cells: stent cell A  12  and stent cell B  14  aligned along circumferences of circles perpendicular to longitudinal axis,  . The pattern can be arranged on one or more circumferences, depending on various stent dimensions including, e.g., stent length, stent cell length, connector length, etc. Stent cells  12  and  14  are formed from struts repeating along the circumferences. This pattern can have 3 to 8 repetitions. In some embodiments, this pattern repeats 4 times. 
     Beginning from the top left side of  FIG. 1A , a repeating series of stent elements is shown extending from line  16 . The struts form M-shaped and V-shaped sections. Generally, the M-shaped sections include a first c1-curved strut  130 , followed by a v1-vertex  104 , followed by a mirrored pair of c2-curved struts  120 , and joined by a v2-vertex  102 . Generally, the V-shaped stent elements include a mirrored pair of c3-curved struts  126 , joined by a v3-vertex  110 . 
     The struts forming M-shaped sections contribute to the perimeter around stent cell  12 . The struts forming V-shaped sections contribute to the perimeter around stent cell  14 . 
     Moving circumferentially around the stent ring, the M-shaped sections join to an adjacent inverted-V-shaped section through a first v4-vertex  108 . The V-shaped section joins to an adjacent M-shaped section through a v4-vertex mirrored from that of the first v4-vertex  108 , and so on. 
     V-shaped and M-shaped sections alternate around the ring until returning to the first M-shaped section. These alternating sections form a first, r1-ring. The shortest stent embodiments also comprise a second, r2-ring, which is a mirror image of the r1-ring. The two rings join through b1-bridges  114 . The b1-bridges  114  join the rings by bridging corresponding v4-vertexes  108 , one v4-vertex  108  lying in an r1-ring and another v4-vertex  108  lying in an adjacent r2-ring. An r1-ring and an r2-ring joined in this fashion yield an r3-ring. (The previous discussion neglects m1-markers  512 .) 
     The stent ends comprise m1-markers  512  extending substantially longitudinally from one or more v1-vertexes  104 . 
     Depending on the length of the stent embodiment, 1 to 100 instances of an r3-ring join to form the stent. Two adjacent instances of r3-rings connect through one or more b2-bridges  118  ( FIG. 7 ), extending between adjacent v1-vertexes  104 . A b2-bridge  118  joins r3-rings by bridging corresponding v4-vertexes  104  lying in adjacent r3-rings. 
     Some embodiments use an r1-ring comprising motif A. Stepping around r1-ring, motif A begins with a first c1-curved strut. Next, a v1-vertex connects a first c2-curved strut to the first c1-curved strut. A v2-vertex connects a second c2-curved strut to the first c2-curved strut. A v1-vertex connects a second c1-curved strut to the second c2-curved strut. 
     After that, a v4-vertex connects a first c3-curved strut to the second c1-curved strut. Next, a v3-vertex connects a second c3-curved strut to the first c3-curved strut. And a v2-vertex connects the first c1-curved strut to the second c3-curved strut. In some embodiments, any combination of curved struts c1, c2, and c3 can be substantially straight. 
     An alternative description of motif a follows. A v1-vertex connects a c1-curved strut to a c2-curved strut. A second v2-vertex connects two c2-curved struts. A third v3-vertex connects two, c3-curved struts. And a v4-vertex connects a c3-curved strut to a c1-curved strut. 
     In some embodiments having motif A, a c1-curved strut connects a v1-vertex and a v4-vertex. A c2-curved strut connects a v2-vertex to a v1-vertex. And a c3-curved strut connects a v3-vertex to a v4-vertex. 
     In some embodiments, the order of curved struts in motif A is c1, c2, c2, c1, c3, c3. And the order of vertexes in motif A is v1, v2, v1, v4, v3, v4. This does not take into account m1-markers. 
     Motif A can be repeated based on the desired circumference of the r1-ring; one or more repetitions of motif A exist in r1-ring, and one or more repetitions of motif A exist in r2-ring. In some embodiments, r1-ring comprises 4 instances of motif A. 
       FIG. 1C  depicts cell  12  and cell  14 . Alternatively, the stent pattern can be described as comprising two motifs x and y. Motif x comprises cell  12 , which resembles a butterfly. Motif y comprises cell  14 , which resembles an ellipsoid pinched on the ends of the major axis. Butterfly motif x alternates with ellipsoid motif y around r3-ring. For longer stents, r3-ring repeats one or more times. Adjacent rings, r3, join wing-tip-to-wing-tip through v4-vertexes. 
     Similarly,  FIG. 1B  depicts a perspective view of stent  100  in an expanded configuration. Stent  100  comprises two crown-shaped moieties that are mirror images of each other with the mirror plane perpendicular to stent  100 &#39;s longitudinal axis. This is a crown-bottom-to-crown-bottom arrangement. Stent  100  comprises three types of curved struts  120 ,  126 ,  130  joined by four types of vertexes  104 ,  102 ,  108 ,  110 . 
     The crown shapes connect to each other, having b1-bridge  114  connecting vertex  108  on one crown to its mirror image on the other crown. 
     The crown-shaped moieties comprise various curved-strut-vertex-curved-strut parts: strut  120 , vertex  102 , strut  120 ; strut  120 , vertex  104 , strut  130 ; strut  130 , vertex  108 , strut  126 ; strut  126 , vertex  110 , strut  126 ; strut  126 , vertex  108 , strut  130 ; and strut  130 , vertex  104 , strut  120 . In some embodiments, this pattern repeats. 
     Neglecting m1-markers  512 , stent  100  has a mirror plane perpendicular to the longitudinal axis, longitudinal mirror planes bisecting the v2-vertexes  102 , longitudinal mirror planes bisecting the v3-vertexes  110 , and a 4-fold longitudinal axis of rotation. 
     The following definition of strut length is used. A “strut length” is the length of a strut from a center of the radius of curvature of the vertex at one end of the strut to another center of the radius of curvature of the vertex at the other end of the strut. “c1” represents the strut length of a c1-curved strut; “c2” represents the strut length of a c2-curved strut; “c3” represents the strut length of a c3-curved strut; “b1” represents the strut length of a b1-bridge; “b2” represents the strut length of a b2-bridge. 
     In some embodiments, c1/b2=2.3-3.1; c2/b2=2.7-3.5; c3/b2=1.8-2.6; b1/b2=1.1-1.9; c1/b2=2.5-2.9; c2/b2=2.9-3.3; c3/b2=2.0-2.4; b1/b2=1.3-1.7; c1/b2=2.6-2.8; c2/b2=3.0-3.3.1; c3/b2=2.1-2.3; b1/b2=1.4-1.6. 
     A vertex angle is the smallest angle at a strut intersection. “v1” represents the angle of a v1-vertex; “v2” represents the angle of a v2-vertex; “v3” represents the angle of a v3-vertex; “v4” represents the angle of a v4-vertex. 
     In some embodiments, a v1-vertex occurs at the intersection of two struts, a v2-vertex occurs at the intersection two struts, a v3-vertex occurs at the intersection of two struts, a v4-vertex occurs at the intersection of two struts and a bridge; or any combination of these. Sometimes, a v1-vertex occurs at the intersection of two struts and a bridge. 
     In some embodiments v1 ranges from about 21-41, 26-36, or 30-32 degrees. In some embodiments v2 ranges from about 48-68, 53-63, or 57-59 degrees. In some embodiments v3 ranges from about 57-77, 62-72, or 66-68 degrees. In some embodiments v4 ranges from about 29-49, 34-44, or 28-40 degrees. 
       FIG. 7A  depicts a longer stent embodiment. In the figure, stent  700  has been cut and rolled flat. Longer versions of stent  100  comprise two or more bottom-to-bottom pairs or r3-rings, as described above. One bottom-to-bottom pair connects to an adjacent bottom-to-bottom pair through crown-top-to-crown-top b2-bridges  118  extending between a vertex  104  and its mirror-image counterpart. In some embodiments not all of vertexes  104  connect to their mirror-image counterparts.  FIG. 7A  also depicts b2-unbridged gap  118   a  between corresponding vertexes  104 . 
     In some embodiments, every other vertex  104  attaches to its mirror image counterpart on an adjacent ring. In some embodiments, less than 90, 80, 70, 60, 50, 40, 30, 20, 10 percent of vertexes  104  connect to their mirror image counterparts. In some embodiments, smaller percentages of vertex  104  connections favor more flexible stents all other things being equal. 
     Alternatively, as shown in  FIG. 7B , stent  700  comprises four types of stent cells: stent cell a  12 , stent cell B  14 , stent cell C  16 , and stent cell D  18 . Cells  12  and  16  are butterfly shaped, but not equivalent. Cells  14  and  18  have the shape of an ellipse pinched at both ends of the major axis, but are not equivalent 
     Stent  700  comprises a ring perpendicular to the longitudinal axis that comprises alternating cells  12  and  14 . In some embodiments, this ring has 4-8 pairs of alternating cells  12  and  14 . The stent comprises another ring perpendicular to the longitudinal axis and fused with the first ring that comprises alternating cell  16  and cell  18 . In some embodiments, this ring has 4-6 pairs of alternating cells  16  and  18 . Depending upon the desired stent length, more or fewer pairs of alternating rings are lined up in particular embodiments. 
     Cell  12  comprises two bridges  114 , four struts  130 , four struts  120 , two vertexes  102 , four vertexes  104 , and four vertexes  108 . These components are arranged in a butterfly shape. Taking these components in groups, cell  12  comprises: strut  130 , vertex  104 , strut  120 ; strut  120 , vertex  102 , stent  120 ; strut  120 , vertex  104 , strut  130 ; strut  130 , vertex  108 , bridge  114 ; bridge  114 , vertex  108 , strut  130 ; strut  130 , vertex  104 , strut  120 ; strut  120 , vertex  102 , strut  120 ; strut  120 , vertex  104 , strut  130 ; strut  130 , vertex  108 , bridge  114 ; and bridge  114 , vertex  108 , strut  130 . 
     Cell  14  comprises two bridges  114 , four struts  126 , four vertexes  108 , and two vertexes  110  arranged in a pinched-ellipsoid shape. Taking the components in groups, Cell  14  comprises: strut  126 , vertex  110 , strut  126 ; strut  126 , vertex  108 , bridge  114 ; bridge  114 , vertex  108 , strut  126 ; strut  126 , vertex  110 , strut  126 ; strut  126 , vertex  108 , bridge  114 ; and bridge  114 , vertex  108 , strut  126 . 
     Cells  16  and  18  will be described as being completely bridged. But various embodiments exist having fewer than the total number of possible bridges. 
     Cell  16  comprises two bridges  118 , four struts  126 , four struts  130 , four vertexes  104 , two vertexes  110 , and four vertexes  108 , arranged in a butterfly shape. 
     Taking the components in groups, cell  16  comprises: strut  130 , vertex  108 , strut  126 ; strut  126 , vertex  110 , strut  126 ; strut  126 , vertex  108 , strut  130 ; strut  130 , vertex  104 , bridge  118 ; bridge  118 , vertex  104 , strut  130 ; strut  130 , vertex  108 , strut  126 ; strut  126 , vertex  110 , strut  126 ; strut  126 , vertex  108 , strut  130 ; strut  130 , vertex  104 , bridge  118 ; and bridge  118 , vertex  104 , strut  130 . 
     Cell  18  has two bridges  118 , four struts  126 , two vertexes  102 , and four vertexes  104  arranged in a pinched-ellipsoid shape. Taking these components in groups, cell  18  comprises: strut  120 , vertex  102 , strut  120 ; strut  120 , vertex  104 , bridge  118 ; bridge  118 , vertex  104 , strut  120 ; strut  120 , vertex  102 , strut  120 ; strut  120  vertex  104 , bridge  118 ; and bridge  118 , vertex  104 , strut  120 . 
     Returning to  FIGS. 1A and 1B , the stents comprise substantially straight regions. One such region has the following sequence: strut  130 , vertex  108 , bridge  114 , vertex  108 , and strut  130 . “Substantially straight,” in some embodiments, means as straight as the elements of the sequence joined together as in  FIG. 1A . In these or other embodiments, “substantially straight” regions comprise struts with a total distance, d. In some embodiments, “Substantially straight” means that the total deviation from linear is less than 10, 9, 8, 7, 6, 5, 4, 3, or 2 times d. Straight regions contribute to the stent&#39;s ability to resist foreshortening. 
     Returning to stent  700  of  FIG. 7A , stent  700  has substantially straight regions substantially the same as stent  100 . These straight regions join to other, similar, straight regions by bridges  118 , in some embodiments. Since the number of bridges  118  is sometimes variable based on the desired stiffness of the stent, the length of joined, substantially straight regions varies. In some embodiments, the total length of the joined region exceeds 10, 20, 30, 40, 50, 60, 70, 80, 90, or 99 percent of the total length of the stent. 
     Described in another way, the substantially straight regions have struts, vertexes, and bridges in a sequence of strut, vertex, type-I bridge, vertex, strut, vertex, type-II bridge, vertex, strut, vertex, type-I bridge, vertex, strut. 
     In some embodiments, the substantially straight regions cause the stents to exhibit no foreshortening or to exhibit less foreshortening than stents with similar lengths exhibit upon expansion. In some embodiments, the total length of a substantially straight region is 6 mm. 
       FIG. 2  depicts a perspective view of stent holder  500  and receivers  508  formed from tube  608 . Stent anchor  500  has a tubular structure and comprises any one or any combination of metal, ceramic, polymer, and glass. Stent holder  500  has an outer diameter similar to that of stent  100  when stent  100  is in its un-expanded configuration. When stent  100  assumes its expanded configuration, its diameter is greater than stent holder  500 &#39;s diameter. Outer sheath  606  restrains stent  100 . 
       FIG. 3A  depicts a perspective view of stent anchor  500   a . Stent anchor  500   a  has a tubular structure and comprises any one or any combination of metal, ceramic, polymer, and glass. The stent anchor comprises one or more fingers  504   a  and  504   b , which in this embodiment are formed by cutting tube  608  creating slits  506 . Two or more adjacent fingers  504  comprise cut outs that align to form receiver  508 , which is designed to interact with stent  100  (or stent  700 ). In some embodiments, receiver  508  holds the stent. In some embodiments receiver  508  serves as a locking mechanism;  FIG. 3A  depicts stent anchor  500   a  in the locked position. 
       FIG. 3B  depicts stent anchor  500   a  in the unlocked position. In this embodiment, finger  504   a  is substantially fixed and finger  504   b  is movable. In some embodiments, during the manufacture of stent anchor  500   a , finger  504   b  is bent or biased such that finger  504   b  has a relaxed position as shown in  FIG. 3B . This position operates as the unlocked position because the cutouts in fingers  504   a  and  504   b  do not align to create receiver  508  when the anchor is in this position. 
     But in some embodiments, fingers  504   a  and  504   b  are both bent or biased inwardly or outwardly. 
     Stent anchor  500   a  has an outer diameter that is substantially the same as the inner diameter of outer sheath  606  (depicted in  FIG. 6B ). That is, stent anchor  500   a  fits inside of and touches the inner surface of outer sheath  606 . Likewise, due to its self-expanding nature, stent  100  touches the inner surface of outer sheath  606 . 
     Outer sheath  606  restrains stent anchor  500   a  similarly to the way it restrains stent  100 . Outer sheath  606  also restrains fingers  504   a  and  504   b . When mounted on the delivery system, fingers  504   a  and  504   b  holding them in the locked position. 
       FIG. 4A  depicts a perspective view of another embodiment of stent anchor  500   b.    
     Stent anchor  500   b  comprises four fingers  504  cut from tube  608  with receiver  508  formed in fingers  504 .  FIG. 4B  is a side view of the stent anchor of  FIG. 4A . Stent anchor  500   b  has an outer diameter that is substantially the same as the inner diameter of outer sheath  606 . That is, stent anchor  500   b  fits inside of and touches the inner surface of outer sheath  606 . Likewise, due to its self-expanding nature, stent  100  touches the inner surface of outer sheath  606 . Since markers  512  lie inside of receiver  508 , stent  100  is held in place. Stent  100  is held in place by the capture of marker  512  inside of receiver  508  (as shown in  FIG. 5 ). 
     Additionally, similar to those of  FIGS. 3A and 3B , stent anchor  500   b  has at least two configurations.  FIG. 4A  illustrates stent anchor  500   b  in a locked configuration. The embodiments in these figures can also have one or more bent or biased fingers. 
     Outer sheath  606  restrains stent anchor  500   b  similarly to the way it restrains stent  100  and stent anchor  500   a . The unlocked configuration comprises at least one of fingers  504  extends radially inward or outward because finger  504  is bent or biased that way. 
       FIG. 5  depicts stent anchor  500   a  engaged with stent  100 . As discussed above, stent  100  can have two arrangements: compressed and expanded.  FIG. 5  depicts stent  100  in the compressed arrangement. Stent  100  comprises at least one vertex  104 , as described above. ( FIG. 1B  depicts stent  100  in the expanded state.) 
     Stent  100  engages stent anchor  500   a  through the interaction between receiver  508  and marker  512 . In some embodiments, marker  512  comprises radiopaque insert  514 , which provides the stent with increased visibility under fluoroscopy. 
       FIG. 6A  depicts a stent delivery system  600  having distal end  601  and inner catheter  610 . Stent bed  602  is proximal of distal tip  604 . Stent anchor  500   a  is proximal of stent bed  602 , coaxially around inner catheter  610 . Stent anchor  500   a  comprises one or more fingers  504 . These fingers are shaped to create stent receiver  508  situated at the distal end of stent anchor  500   a.    
       FIG. 6B  depicts a stent delivery system  600  similar to that of  FIG. 6A , but additionally including outer sheath  606  and compressed stent  100 . 
     Stent delivery system  600  comprises a distal end  601  which comprises stent bed  602  located in a distal region of distal end  601 . Stent bed  602  has a smaller diameter than adjacent portions of the stent delivery system in some embodiments. 
     Stent  100  is clamped or crimped onto stent delivery system  600  at stent bed  602 . In some embodiments, the inner surface of stent  100  interacts with stent bed  602 . 
     An outer sheath  606  extends over stent  100  constraining stent  100  in a radially compressed deliver configuration that has a small enough diameter to fit coaxially into outer sheath  606 . 
     In some self-expanding embodiments, the expansion halts when stent  100  expands out to the inner surface of outer sheath  606 . The outer sheath can retract or move proximally relative to stent  100  and stent anchor  500   a  to a retracted position in which distal-most end  607  of retractable sheath  606  lies proximally of proximal most end  603  of stent  100 . 
     Delivery system  600  also comprises distal tip  604  which aids delivery system  600  in traveling through the vasculature and protects stent  100  during this transit. While stent  100  is mounted on stent bed  602 , stent anchor  500   a  holds stent  100  in place, resisting proximal or distal motion, because receiver  508  captures marker  512 . 
     The  FIG. 6  embodiments depict receiver  508  and marker  512  as circular. But any pair of cooperative or complementary shapes is useful for these components. 
     In operation, a physician threads stent delivery system  600  through a patient&#39;s vasculature until it reaches the intended delivery site. This insertion is typically monitored by fluoroscopy with insert  514  providing a more intense image because it has higher radiopacity than surrounding substances. The physician initiates delivery of stent  100  by beginning to retract outer sheath  606  using any one of a number of suitable retraction mechanisms. As outer sheath  606  uncovers stent  100 , the uncovered portion begins to automatically expand. As stent  100  expands, the capture of marker  512  in receiver  508  prevents any tendency towards distal movement. Once distal-most end  607  is proximal of marker  512 , marker  512  releases from receiver  508 . Releasing marker  512  releases stent  100 . 
     In embodiments with stent anchor  500  as shown in  FIG. 2 , stent  100  releases from stent anchor  500  by expansion. Proximal retraction of outer sheath  606  uncovers all of stent  100  and allows it to expand. But expansion of the region of stent  100  that contains captured marker  512  does not occur until stent  100  is mostly uncovered, i.e. retraction completes. Then, stent  100  finishes moving radially outward, which causes marker  512  to also move radially outward. Once the inner diameter of stent  100  exceeds the outer diameter of stent anchor  500 , marker  512  clears receiver  508  and marker  512  is no longer held in place. 
     And retraction frees stent  100 , allowing it to radially expand from the delivery configuration to the delivered or expanded configuration. 
     In embodiments with stent anchor  500   a  or  500   b  as shown in  FIGS. 3A, 3B, 4A, and 4B . Stent  100  releases from stent anchor  500   a  or  500   b  by expansion, as described above for stent anchor  500 . Retraction of outer sheath  600  allows stent  100  to expand into its expanded state. The expansion of the region of stent  100  that contains the captured marker does not occur until that portion becomes uncovered during retraction. But in these embodiments, retraction does not complete until fingers  504   a  and  504   b  are uncovered. 
     At that time, finger  504   b  springs back to its unlocked position. So, in these embodiments, stent  100  is released by marker  512  moving out of receiver  508 , as with stent anchor  500 , and by finger  504   b  moving such that receiver  508  no longer exists. Having two release mechanisms provides redundancy in case one of the mechanisms does not fully release stent  100 . Some embodiments of stent anchor  500   b  release in this way, as well. 
     The stents or any portion of the stents can be bare, coated, covered, encapsulated, or bio-resorbable. 
     Bio-active agents can be added to the stent (e.g., either by a coating or via a carrier medium such as resorbable polymers) for delivery to the host vessel or duct. The bio-active agents can also be used to coat the entire stent. A coating can include one or more non-genetic therapeutic agents, genetic materials and cells and combinations thereof as well as other polymeric coatings. Non-genetic therapeutic agents include anti-thrombogenic agents such as heparin, heparin derivatives, urokinase, and PPack (dextrophenylalanine pro line arginine chloromethylketone); anti-proliferative agents such as enoxaprin, angio-peptin, or monoclonal antibodies capable of blocking smooth muscle cell proliferation, hirudin, and acetylsalicylic acid; anti-inflammatory agents such as dexamethasone, predniso-lone, corticosterone, budesonide, estrogen, sulfasalazine, and mesalamine; antineoplastic/antiproliferative/antimiotic agents such as paclitaxel, 5-fluorouracil, cisplatin, vinblas-tine, vincristine, epothilones, endostatin, angiostatin and thy-midine kinase inhibitors; anesthetic agents such as lidocaine, bupivacaine, and ropivacaine; anti-coagulants, an RGD pep-tide-containing compound, heparin, antithrombin compounds, platelet receptor antagonists, antithrombin antibodies, anti-platelet receptor antibodies, aspirin, prostaglandin inhibitors, platelet inhibitors and tick antiplate-let peptides; vascular cell growth promotors such as growth factor inhibitors, growth factor receptor antagonists, tran-scriptional activators, and translational promotors; vascular cell growth inhibitors such as growth factor inhibitors, growth factor receptor antagonists, transcriptional repressors, trans-lational repressors, replication inhibitors, inhibitory antibodies, antibodies directed against growth factors, bifunctional molecules consisting of a growth factor and a cytotoxin, bifunctional molecules consisting of an antibody and a cytotoxin; cholesterol-lowering agents; vasodilating agents; and agents which interfere with endogenous vascoactive mechanisms. Genetic materials include anti-sense DNA and RNA, DNA coding for, anti-sense RNA, tRNA or rRNA to replace defec-tive or deficient endogenous molecules, angiogenic factors including growth factors such as acidic and basic fibroblast growth factors, vascular endothelial growth factor, epidermal growth factor, transforming growth factor alpha and beta, platelet-derived endothelial growth factor, platelet-derived growth factor, tumor necrosis factor alpha, hepatocyte growth  15  factor and insulin like growth factor, cell cycle inhibitors including CD inhibitors, thymidine kinase (“TK”) and other agents useful for interfering with cell proliferation the family of bone morphogenic proteins (“BMPs”), BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7 (OP-1), BMP-8, BMP-9, BMP-10, BMP-1, BMP-12, BMP-13, BMP-14, BMP-15, and BMP-16. Desirable BMP&#39;s are any of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 and BMP-7. These dimeric proteins can be provided as homodimers, heterodimers, or combinations thereof, alone or together with other molecules. 25 Alternatively or, in addition, molecules capable of inducing an upstream or downstream effect of a BMP can be provided. Such molecules include any of the “hedgehog” proteins, or the DNAs encoding them. Cells can be of human origin (autologous or allogeneic) or from an animal source (xenogeneic), genetically engineered if desired to deliver proteins of interest at the deployment site. The cells can be provided in a delivery media. The delivery media can be formulated as needed to maintain cell function and viability. 35 Suitable polymer coating materials include polycarboxylic acids, cellulosic polymers, including cellulose acetate and cellulose nitrate, gelatin, polyvinylpyrrolidone, cross-linked polyvinylpyrrolidone, polyanhydrides including maleic anhydride polymers, polyamides, polyvinyl alcohols, copolymers of vinyl monomers such as EVA, polyvinyl ethers, polyvinyl aromatics, polyethylene oxides, glycosaminoglycans, polysaccharides, polyesters including polyethylene terephthalate, polyacrylamides, polyethers, polyether sulfone, polycarbonate, polyalkylenes including polypropy-45-lene, polyethylene and high molecular weight polyethylene, halogenated polyalkylenes including polytetrafluoroethylene, polyurethanes, polyorthoesters, proteins, polypeptides, silicones, siloxane polymers, polylactic acid, polyglycolic acid, polycaprolactone, polyhydroxybutyrate valerate and blends and copolymers thereof, coatings from polymer dispersions such as polyurethane dispersions (for example, BAYHDROL® fibrin, collagen and derivatives thereof, polysaccharides such as celluloses, starches, dextrans, algi-nates and derivatives, hyaluronic acid, squalene emulsions. 55 Polyacrylic acid, available as HYDRO PLUS® (from Boston Scientific Corporation of Natick, Mass.), and described in U.S. Pat. No. 5,091,205, the disclosure of which is hereby incorporated herein by reference, is particularly desirable. Even more desirable is a copolymer of poly lactic acid and polycaprolactone.