Patent Publication Number: US-2006004436-A1

Title: Stent having arcuate struts

Description:
RELATED APPLICATIONS  
      The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. patent application Ser. No. 60/584,994, filed Jul. 2, 2004, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to medical devices generally used percutaneously and in particular to stents.  
     BACKGROUND  
      Minimally invasive surgical stent technology has become popular since stents were introduced to the medical device market in the United States in the early 1990s. For more than a decade, stents have proven to provide an excellent means for maintaining vessel patency, and have become widely accepted in the medical field.  
      By way of background, these stents are configured to be implanted into body vessels when a vessel passageway, which may have become partially narrowed, occluded, or otherwise diseased, needs reinforcement, support, repair, or otherwise improved performance to restore or increase blood flow through that diseased section. The term “passageway” is understood to be any lumen, chamber, channel, opening, bore, orifice, flow passage, duct, or cavity for conveying, regulating, flowing, or moving bodily fluids and/or gases in an animal. As an example, stents have been used in many passageways in a body, including a heart, blood vessel, artery, vein, capillary, bronchiole, trachea, esophagus, aorta, intestine, bile duct, ureter, urethra, fallopian tube, and other locations in a body (collectively, “vessel”) to name a few.  
      Stents come in many different configurations. In general, a stent may comprise a ring, or stack of rings, each ring being formed from struts and apices connecting the struts, whereby the stent defines an approximately tube-like configuration. Furthermore, the stent surface may not define a truly round cylinder if the struts are straight, because the struts follow a straight line from the apex on one end of the strut to the apex on the other end of the strut.  
      In addition, the stent may assume a collapsed tubular configuration having a smaller diameter and an expanded tubular configuration having a larger diameter. In its collapsed smaller diameter configuration, the stent can be constrained with a delivery system (e.g., a sheath, cannula, catheter, or introducer) that helps to position the stent in the vessel passageway at a desired location. After deployment from the delivery system, the stent expands to its larger diameter.  
      Expandable stents are normally evaluated according to four performance criteria: the radially outward expansile force that the stent exerts on a vessel&#39;s interior surface; the small diameter to which the stent is capable of being compressed for the insertion procedure; the stent&#39;s ability to traverse curved passageways; and the stability in not migrating from its originally implanted position. Among their many types, expandable stents may be self-expanding, balloon-expandable, or a combination thereof as when the stent is partially self-expandable and partially balloon-expandable.  
      Generally stated, a balloon-expandable stent is mounted on an expandable member, such as a balloon, provided on the distal end of a delivery system, such as catheter. In operation, a physician, operator, or other healthcare professional (collectively, “physician”) advances the catheter to a desired location within the vessel passageway in a patient, and then withdraws the sheath or other covering member from the stent. Next, inflating the balloon plastically deforms the stent into an expanded condition. After deflating the balloon, the physician removes the catheter from the patient&#39;s body.  
      For a self-expanding stent, the stent is resiliently compressed into a collapsed smaller diameter and carried by the delivery system. Due to its construction and/or material properties, the stent expands to its second, larger diameter upon deployment. In its expanded configuration, the stent exhibits sufficient stiffness such that it will remain expanded in the vessel passageway and exert a radially outward force on the vessel&#39;s interior surface.  
      One particularly useful self-expanding stent is the Z-Stent, which Cook Incorporated introduced and made available to the market, due to the Z-Stent&#39;s ease of manufacturing, high radial force, and self-expanding properties. Examples of the Z-stent design are found in U.S. Pat. Nos. 5,507,771; 5,035,706; and 4,580,568. By way of example only, stents have utilized this design for applications involving the bronchioles, trachea, thoracic aortic aneurysms (stent-graft), abdominal aortic aneurysms (stent-graft), intestines (biliary tract), and venous valves. The stent is capable of being compressed, inserted into a sheath, pushed out into the passageway of a vessel, and then- self-expanded to help keep the vessel passageway in an open state at the stent location. A few devices using embodiments of the Z-stent design include the self-expanding Zilver® biliary stent, the Zilver® 518 biliary stent, the Zilver®D 635 biliary stent, and the Zenith® AAA Endovascular Graft, which are available from Cook Incorporated.  
      It would be desirable to have an additional choice for stents that includes the advantages of the conventional stents and the modifications, as taught herein, that would provide alternative improved clinical performance.  
     SUMMARY OF THE INVENTION  
      A stent for implantation in a body vessel is provided. In one embodiment, the device includes a circumferential element having first and second longitudinal ends. The circumferential element comprises a plurality (i.e., two or more) of arcuate struts and a plurality of strut connections.  
      In another embodiment, the stent for implantation in a body vessel comprises a tubular main body having first and second longitudinal ends and defining a lumen in communication with openings at or near the first and second ends. The main body is capable of having a radially compressed first diameter configuration and a radially expanded second diameter configuration. Pluralities of circumferential elements are disposed along a longitudinal axis of the main body. Each circumferential element comprises a plurality of arcuate struts, a plurality of strut connections, and one or more link members joining the circumferential elements together.  
      A method of maintaining vessel patency is also provided. In one embodiment, a method according to the invention comprises providing a delivery system with a distal end portion containing a compressed stent having first and second longitudinal ends, arcuate struts, and strut connections. The distal end portion is inserted into a body and delivered through the body until the unexpanded stent is located where desired. The stent is deployed from the distal end portion of the delivery system and expanded to a second, larger diameter configuration.  
      In another method of maintaining vessel patency, a stent comprising a circumferential element is provided. The stent inserted into a distal end portion of a stent delivery catheter. The catheter distal end portion is delivered into an internal region of a body to a location where desired. The stent is deployed from the catheter distal end portion and to the expanded configuration.  
      In another method of using a stent for implantation in a body vessel, a stent is provided comprising a circumferential element. An endoscope is provided that comprises a flexible distal insertion portion and a working channel having a distal opening. Another step comprises providing an elongate stent delivery catheter having a distal end portion configured to be inserted into the endoscope working channel and further having a stent mounting region configured for detachably and releasably securing the stent in a radially compressed configuration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a perspective view of a medical device according to one embodiment of the invention having concave struts.  
       FIG. 1B  is a perspective view of  FIG. 1A  with an alternative embodiment of the strut connections.  
       FIG. 2A  is a perspective view of a medical device according to one embodiment of the invention having convex struts.  
       FIG. 2B  is a perspective view of  FIG. 2A  with an alternative embodiment of the strut connections.  
       FIG. 3  is a perspective view of convex struts according to one embodiment of the invention.  
       FIG. 3A  is a perspective view of a convex strut spaced arcuately relative to a plane including a longitudinal axis of the stent.  
       FIG. 3B  shows another convex strut arcing relative to a longitudinal axis.  
       FIG. 3C  is a view of the convex-strut according to  FIG. 3B  spaced arcuately relative to a plane including the longitudinal axis.  
       FIG. 4  is a perspective view of concave struts according to another embodiment of the invention.  
       FIG. 4A  is a perspective view of a concave strut spaced arcuately relative to a plane including a longitudinal axis of the stent.  
       FIG. 4B  shows another concave strut arcing relative to a longitudinal axis.  
       FIG. 4C  is a view of the concave strut according to  FIG. 4B  spaced arcuately relative to a plane including the longitudinal axis.  
       FIG. 5A  is a perspective view of  FIG. 1A  shown in a schematic partial perspective view of a body vessel.  
       FIG. 5B  is a perspective view of  FIG. 1B  shown in a schematic partial perspective view of a body vessel.  
       FIG. 6A  is a perspective view of  FIG. 2A  shown in a schematic partial perspective view of a body vessel.  
       FIG. 6B  is a perspective view of  FIG. 2B  shown in a schematic partial perspective view of a body vessel.  
       FIG. 7A  is a schematic perspective view of a medical device according to a tubular embodiment of the invention having concave struts.  
       FIG. 7B  is a schematic partial perspective view of an alternative embodiment of  FIG. 7A  having convex struts.  
       FIG. 8A  is a partial view of a sutured link member according to an embodiment of the invention.  
       FIG. 8B  is a detailed partial view of an alternative embodiment of a sutured link member.  
       FIG. 8C  is a perspective view of a link member according to another alternative embodiment of the invention.  
       FIG. 9A  is a perspective view of a strut connection in accordance with one embodiment of the invention.  
       FIG. 9B  is a perspective view of an alternative embodiment of the strut connection of  FIG. 9A .  
       FIG. 10  is a perspective view of an alternative embodiment of a strut connection used with an embodiment of the invention.  
       FIG. 11  is a perspective view of an alternative embodiment of a strut connection.  
       FIG. 12  is a perspective view of an alternative embodiment of a strut connection.  
       FIG. 13  is a perspective view of an alternative embodiment of the strut connection of  FIG. 12 .  
       FIG. 14  is a block diagram illustrating a method of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      The present invention relates to medical devices and, in particular, to stent devices for implanting into vessel passageways, and methods of using stents to maintain vessel patency. To promote the principles that help in understanding the invention, the following provides a detailed description of several embodiments of the invention as illustrated by the drawings as well as the language used to describe various aspects relating to the invention. The description is not intended to limit the invention in any manner, but rather serves to enable those skilled in the art to make and use the invention. As used in this specification, the terms comprise(s), include(s), having, has, with, contain(s) and variants of those terms are all intended to be open ended transitional phrases, terms, or words that do not preclude the possibility that other steps or structure may be added.  
      Embodiments of tubular stents according to the present invention comprise “arcuate” struts, which is more fully described below and illustrated in the figures. Briefly stated, the term “arcuate” is used to indicate that the stents bend (i.e., arc) outwardly or inwardly of a cylindrical envelop—as opposed to being straight and lying on a cylindrical envelope. In one embodiment, an arcuate strut is “concave,” while an alternate embodiment may have an arcuate strut that is “convex,” where the terms “concave” and “convex” are defined relatively as viewed from within the stent, as more fully explained later. Furthermore, the arcuate struts are joined end-to-end by strut connections and formed into a ring or band (i.e., circumferential elements) to form a tubular shape. The circumferential element may be zigzag, serpentine, undulating, Z-shaped, and the like (collectively, “zigzag”). Stent embodiments may have one circumferential element (N−1), or they may comprise more than one circumferential element (N&gt;1) joined together.  
      Stents may be made of any suitable biocompatible material, or material that is capable of being made biocompatible such as with a coating, chemical treatment, or the like. Examples of suitable materials include, without limitation, stainless steel, nitinol, titanium, nickel titanium, other shape memory and/or superelastic alloys, polymers, polyether block amide, and composite materials, cobalt-chrome alloys, and amorphous metal alloys. Stainless steel and nitinol are biocompatible and particularly shapeable, although nitinol is less stiff than is stainless steel and, thereby, will not produce the same radial force in a similarly-sized stent. The stent may also be made of a degradable polymer, such as a homopolymer, blend, or copolymer of Poly-alpha Hydroxy Acids (e.g., Polyactic Acid or Polyglycolic Acid), Trimethylene Carbonate, Polycaprolactone, Poly-beta Hydroxy Acids (e.g., Polyhydroxybutyrate, Polyhydroxyvalerate), Polyphosphazines, Polyorganophosphazines, Polyanhydrides, Polyesteramides, Polyorthoesters, Polyethylene oxide, Polyester-ethers (e.g., Polydioxanone), and/or Polyamino acids (e.g., Poly-L-glutamic acid or Poly-L-lysine). The term “material” shall include any one or more material(s) from this list used individually or in combination in a stent embodiment according to the invention.  
      In addition, a stent can be formed from the material in many different ways. By way of illustration and not by way of limitation, the wire for use as or in a stent or stent component may be formed from extrusion or may be purchased as wire that is commercially available. Then, the wire may be turned or bent to form strut connections, and the wire with strut connections may be placed and shaped between two blocks with complementary curved interfaces corresponding to the desired shape of the arcuate struts. Strut connections and arcuate struts are discussed below. With its strut connections and arcuate struts, the length of wire may then be wrapped around, molded, and shaped onto a mandrel. Alternatively, the stent pattern may be cut from a tube or sheet of material, laser cut, chemical etched, stamped, electric discharge machined, or formed by other known processes.  
       FIGS. 1A, 1B ,  2 A, and  2 B illustrate several embodiments of stents  10  in accordance with the invention, and show each stent in a radially expanded configuration. The stent  10  has first and second longitudinal ends  11 ,  12  defining a lumen  13 . The terms “first” and “second” as used to describe the embodiments are terms used as a convention that merely distinguishes elements in the embodiment, and not as terms supplying a numerical limit, serial limit, spatial location, or any differences in the ends unless expressly and unequivocally stated otherwise. In one embodiment, for example, the first end  11  may be located at or near a proximal portion of the stent while the second end  12  is located at or near a distal portion, although the first end does not necessarily need to appear before the second end, and the second end does not necessarily appear after the first end. As is conventional, “distal” means the end that is directed or oriented away from the physician when the device is inserted into a patient while “proximal” means the end that is closer to or toward the physician relative to the distal end.  
      Also, the lumen  13  defines a longitudinal axis  14 . The term “longitudinal” and its variants are intended to mean, in a broad sense, running longitudinally (lengthwise). The longitudinal axis  14  need not necessarily be straight, and could in fact curve as in a tangent to a referenced segment or point on or contained within a stent lumen  13 . Indeed, given the flexibility of a stent, the “longitudinal” axis may be straight at some portions of the lumen and bent or curved at other portions.  
      In their expanded configurations and when viewed end-on, a stent  10  generally exhibits a tubular cross-section containing the lumen  13 . Furthermore, in the expanded configuration the tubular cross-section of the stent need not be constant between its proximal and distal ends  11 ,  12 , respectively, and may be straight or curved, because the stent is configured for placement in a vessel passageway. In one embodiment, the stent may be modified for a bifurcated vessel or a passageway that brachiates, and the stent has side tubular branches or has a portion that contains two tubular stent bodies side-by-side of equal or unequal length, which is particularly suited in the field of cardiology. Furthermore, the specific dimensions of a particular stent according to the invention will depend on numerous factors, including the type of vessel in which the device is to be implanted, the axial length of the treatment site, the inner diameter of the vessel, the delivery method for placing the stent, and others. Those skilled in the art can determine an appropriately sized and dimensioned stent based on these various factors.  
      In essence, the body of a stent contains one or more circumferential elements  15 . Generally stated, a circumferential element comprises strut connections  30  at the first and second ends  11 ,  12 , respectively, and struts  20  intermediate the first and second ends  11 ,  12  of the stent  10 . The term “intermediate” is intended to mean between, though not necessarily equidistant to, the distal most tip of the second end  12  and the proximal most tip of the first end  11 .  
      Struts  
      As generally stated, a stent  10  includes at least one circumferential element  15 .  FIGS. 1A through 2B  show views of embodiments each having one (N=1) circumferential element  15 , whereby the circumferential elements (shown in an expanded state) comprise struts  20  and strut connections  30 . More particularly, a circumferential element comprises, for example, a “zigzag” pattern (as previously described) that contains a series of concave  24  or convex  25  struts, whereby strut connections  30  (described later) join adjacent struts  20 .  FIGS. 1A and 1B  show circumferential elements  15  according to two illustrative embodiments whereby the struts  20  are concave  24 . In contrast,  FIGS. 2A and 2B  show circumferential elements  15  according to two illustrative embodiments whereby the struts  20  are convex  25 .  
      Referring to an arcuate strut  20  as concave  24  or convex  25  is largely a matter of perspective as well as the frame of reference used in describing embodiments according to the invention.  FIGS. 3 and 4  show, for example, enlarged schematic views of embodiments of struts  20 , which optionally can be utilized in  FIGS. 1A, 1B ,  2 A, and  2 B, in order to assist in explaining concave and convex as used in this specification to describe embodiments of the invention, and not as any lexicographic definition. As shown in  FIGS. 3 and 4 , a strut  20  comprises a wire member  21 , and the strut has first and second end portions  22 ,  23  corresponding, respectively, to proximal and distal ends  11 ,  12  of the stent  10 . The wire member  21  arcs (e.g., follows an arc-shaped course) intermediate the first and second end portions  22 ,  23 , and the arc may be either concave  24  or convex  25 . The longitudinal axis  14  helps to provide a frame of reference for labeling a strut as either concave or convex, whereby  FIG. 3  depicts a convex strut  25  while  FIG. 4  depicts a concave strut  24  in reference to the longitudinal axis  14  of those figures. The arcuate struts  20  are spaced arcuately relative to a plane  14 ′ including the longitudinal axis  14 . In other words, the struts bend (i.e., arc) outwardly or inwardly of a cylindrical envelop-as opposed to being straight and lying on a cylindrical envelope.  
       FIGS. 3A, 3B , and  3 C illustrate convex struts  25  spaced arcuately relative to a plane  14 ′ including the longitudinal axis  14 .  FIG. 3A  shows a convex strut  25  according to the embodiment in  FIG. 3 , whereby the first and second end portions  22 ,  23 , respectively, will be spaced at distances  60 ,  62 , respectively, from the plane  14 ′ greater than the distance  64  from an intermediate portion  26  of the strut  25  to the plane  14 ′. The distances compare as follows:  64 &lt; 60  and  64 &lt; 62 . In other words, the intermediate portion  26  in a convex strut  25  is closer to the longitudinal axis  14  than the first and second end portions  22 ,  23  are to the longitudinal axis  14 .  FIG. 3B  shows another convex strut  25  arcing relative to the longitudinal axis  14 . Expanded struts  20  may not be parallel to the longitudinal axis  14  but instead be angled relative to the axis  14  when viewed radially in order for the struts  20 , when joined end-to-end by strut connections, to encircle the axis and to form a tubular cross-section containing a lumen. In order to better explain an arcuate strut, therefore, it should be understood that a plane  14 ′ along the length and width of the stent (e.g., generally bisects the stent lengthwise) the longitudinal axis  14  such that the arcuate struts are spaced arcuately relative to the plane  14 ′, whereby the intermediate portion  26  in a convex strut  25  is closer to the plane  14 ′ than the first and second end portions  22 ,  23 , respectively, are to the plane  14 ′.  FIG. 3C  shows  FIG. 3B  from the perspective of the plane  14 ′, whereby the first and second ends  22 ,  23  are spaced arcuately at distances  60 ,  62  relative to the plane  14 ′, and the intermediate portion  26  spaced arcuately at a distance  64  relative to the plane  14 ′.  
       FIGS. 4A, 4B , and  4 C illustrate concave struts  24  spaced arcuately relative to a plane  14 ′ including the longitudinal axis  14 .  FIG. 4A  shows a concave strut  24  according to the embodiment in  FIG. 4 , whereby the first and second end portions  22 ,  23 , respectively, will be spaced at distances  70 ,  72 , respectively, from the plane  14 ′ greater than the distance  74  from an intermediate portion  26 ′ of the strut  24  to the plane  14 ′. The distances compare as follows:  74 &lt; 70  and  74 &lt; 72 . In other words, the intermediate portion  26  in a concave strut  24  is farther from the longitudinal axis  14  than the first and second end portions  22 ,  23  are to the longitudinal axis  14 .  FIG. 4B  shows another concave strut  24  arcing relative to the longitudinal axis  14 . As previously explained, expanded struts  20  may be angled relative to the longitudinal axis  14  when viewed radially. Therefore, a plane  14 ′, as previously described, includes the longitudinal axis  14  such that the arcuate struts are spaced arcuately relative to the plane  14 ′. In the case of concave struts  24 , the first and second end portions  22 ,  23 , respectively, are closer to the plane  14 ′ than the intermediate portion  26  is to the plane  14 ′.  FIG. 4C  shows  FIG. 4B  from the perspective of the plane  14 ′, whereby the first and second ends  22 ,  23  are spaced arcuately at distances  70 ,  72  relative to the plane  14 ′, and the intermediate portion  26 ′ spaced arcuately at a distance  74 , relative to the plane  14 ′.  
      A strut may vary in length depending on the overall desired length of the expanded circumferential element  15 . In addition, the cross-sectional profile of a strut may be, for example only and not by way of limitation, a generally solid tubular shape or a flat rectangular design.  
      Turning to  FIGS. 5A, 5B ,  6 A, and  6 B, alternative embodiments of circumferential elements  15  are shown. These Figures show a perspective of a passageway  41  of a vessel  40 . Furthermore,  FIGS. 5A through 6B  provide a perspective view of the circumferential element  15  as deployed such that the circumferential element  15  has radially expanded in an abutting relationship to the interior surface  42  of the vessel passageway.  FIGS. 5A and 5B  show embodiments with a circumferential element  15  having concave struts  24 , while  FIGS. 6A and 6B  depict embodiments with a circumferential element having convex struts  25 .  
      As shown in  FIGS. 7A and 7B , embodiments may have more than one circumferential element  15  (N&gt;1). For example, circumferential elements  15  may be stackable via link members  16  (e.g.,  FIGS. 8A-8C ) into a main body  110  that is tubular and having first and second ends  111 ,  112 . The circumferential elements  15 , as previously described, have first and second longitudinal ends  11 ,  12 , respectively. The tubular main body  110  first and second ends  111 ,  112  defining a lumen  13  along a longitudinal axis  14 , whereby the lumen is in communication with openings  17 ,  18 , respectively, at or near the first and second ends  111 ,  112 , respectively. The main body has, on the one hand, a radially compressed first diameter configuration (not shown) that is self-expandable, balloon-expandable, or a combination thereof, and has, on the other hand, a radially expanded second diameter configuration. The circumferential elements have a “zigzag” pattern (previously described) containing a series of concave ( FIG. 7A ) or convex ( FIG. 7B ) struts interconnected by strut connections as in  FIGS. 1A-2B ,  5 A- 6 B, and  9 A- 13 .  
      For instance,  FIG. 7A  is an embodiment of a main body  110  having concave struts  24  in a radially expanded second diameter configuration. The main body of  FIG. 7A  has more than one circumferential element  15  joined by a link member  16  (e.g.,  FIGS. 8A-8C ) in order to form a column of circumferential elements  15  with concave struts  24 .  FIG. 7B  is an embodiment of a main body  110  having convex struts  25  in a radially expanded second diameter configuration, whereby more than one circumferential element  15  is joined by a link member  16  (e.g.,  FIGS. 8A-8C ) to form a column of linked circumferential elements  15  with convex struts  25 .  
       FIGS. 8A, 8B , and  8 C are alternative embodiments of link members  16  for connecting circumferential elements  15  to form a column of linked circumferential elements  15  as in  FIGS. 7A and 7B , by way of illustration only and not be way of limitation. Thus, a strut connection  30  located at a first end portion  22  corresponding to a distal end  12  of a circumferential element  15  may be secured to a strut connection  30  located at a second end portion  23  corresponding to a proximal end  11  of an adjacent circumferential element  15 . In  FIGS. 8A and 8B , the link member  16  comprises a suture, whereby the suture is threaded through the strut connections (described below) of one circumferential element to corresponding adjacent strut connections of a second circumferential element.  FIG. 8C  utilizes a link member  16  formed from material, whereby the link member  16  connects a portion of a strut (or strut connection) of one circumferential element  15  to a portion of a strut (or strut connection) of a second circumferential element  15 . Indeed, the entire stent can be formed integral as, for example, by laser cutting a tube. Alternatively, a link member or struts themselves on adjacent circumferential elements may be joined by sutures, welds, solder, glue, or additional wires.  
      Against the foregoing backdrop, an aspect of the utility of the arcuate struts is that concave and convex struts  24 ,  25 , respectively, produce improved clinical results in the vessel passageway. An embodiment is pressed into the interior surface  42  of a vessel passageway  41  so as to not interfere with the fluid flow through the passageway. Also, the stent, being pressed into the interior surface  42  of the vessel passageway, may eventually be covered with endothelial cell growth that further minimizes fluid flow interference.  
      In addition, concave and convex struts provide additional unique results. A circumferential element  15  or a column of circumferential elements  15  having convex struts  25  (as shown in  FIGS. 2A, 2B ,  6 A,  6 B, and  7 B) provides improved tacking characteristics to prevent stent migration within the vessel passageway. In particular, convex struts  25  provide discrete points of attachment to the interior surface  42  of the vessel passageway  41  to tack up and better hold the stent in place and minimize migration, which is beneficial in many applications, such as bronchiole or tracheal applications, for example. Thus, when a stent with convex struts  25  is expandably deployed in the passageway  41  of a vessel  40 , the strut connections  30  (discussed below) located at the first and second ends  22 ,  23 , respectively, of the struts make good contact with the interior vessel wall.  
      A circumferential element  15  or a column of circumferential elements  15  having concave struts  24  (as shown in  FIGS. 1A, 1B ,  5 A,  5 B, and  7 A) provides improved radial force and decreases trauma to the interior surface  42  of the passageway  41  of a vessel  40 , which is preferred in circulatory applications. Thus, an expanded stent having concave struts  24  more closely models a cylinder than does a conventional stent, and a cylindrical stent is advantageous in the case of large stents, especially stent grafts. For instance, stented grafts (which are commonly used to bypass aneurysms) preferably form a seal against the interior vessel wall  42  in order to isolate the aneurysm from blood pressure. This challenge is addressed today by significantly oversizing the stent graft, which essentially stretches the vessel wall to the point of making a seal all the way around the periphery of the stent. By giving struts a concave arc shape  24 , each strut provides an arcuate attachment to the interior surface  42  of the vessel passageway  41  and better fits the curve of the vessel wall, thereby leaving fewer and smaller gaps between the graft material and the vessel wall into which blood can leak, and without oversizing the stent or overstretching the vessel wall.  
      Strut Connections  
      Arcuate struts  20  for a circumferential element  15  are joined together end-to-end by strut connections  30  in alternating fashion. Otherwise stated, a strut connection  30  links an end portion  22  or  23  of one strut and an end portion  22  or  23  of a second strut. Therefore, when formed into a ring-like tubular structure, the successively joined struts and strut connections together form the circumferential elements  15  depicted in  FIGS. 1A through 2B  and in  FIGS. 5A through 7B  and formed at first and/or second longitudinal ends  11 ,  12  of the stent  10 , although other structure may be added. The words “formed at” an end include a location that is at or within a short distance of the distal most (or proximal most, respectively) tip of that end.  
      More specifically, strut connections  30  comprise a bend of material (as described above) having a cross-sectional profile that, for example only and not by way of limitation, may be generally tubular shaped or have a rectangular design. Furthermore, strut connections  30  are capable of being compressible to a compressed configuration. In a self-expandable stent, strut connections may be biased to expand radially to an expanded configuration. When expanded (via a balloon, self-expanding properties, or a combination thereof) to their radially expanded configuration, the strut connections  30  of a circumferential element  15  provide discrete points of attachment.  
       FIGS. 9 through 13  show enlarged views of embodiments of strut connections  30  in their expanded configurations. When compressed, a strut connection  30  may be expanded by a balloon. Alternatively, a strut connection  30  may be biased to an expanded configuration due to the material&#39;s elastic memory, which results in a spring-like effect when a stent has been compressed to a collapsed diameter configuration. Furthermore, the strut connection in  FIGS. 9A and 9B  are a “coiled” structure. The term “coiled” and variants thereof, as used to describe embodiments of the invention and not used as any lexicographic definition, means that a length of the material comprises at least one turn as when the length of material is rolled or twisted into a shape that is looped, circular, spiral, bent, curled, or headed.  
      With reference to  FIG. 9A , the coiled strut connection  31  comprises a turn that includes about 1½ turns of wire, although the turns may range from about 1¼ turns to about 1¾ turns. The turns from the strut connection  31  connect a first end portion  22  of a first strut and a second end portion  23  of a second strut. The strut connection  31 , due to its turn, forms a closed eyelet  32  that appears as a 360 degree bend or more. In the embodiment illustrated in  FIG. 9A , the strut connection  31  goes through a turn θ in the range of about 480 and 540 degrees, and is shown in  FIG. 9A  at about 520 degrees, and forms a closed eyelet  32 . The strut connection  31 , due to its turn, distributes the stress over a longer length of strut than would be the case in a simple sharp bend. This is an advantage for stents that utilize large diameter struts requiring high radial force. Such a case would be, for instance, an esophageal stent in the case of tumor invasion.  FIG. 9B  is an alternative embodiment of  FIG. 9A , whereby the strut connection  31 ′ goes through an additional turn θ′ of roughly 360 degrees and forms a closed eyelet  32 ′.  
       FIG. 10  illustrates a strut connection  33  comprising an open-ended ogee arch-like compound-curved structure generally having a turn a that resembles a head-neck-shoulder design (a “head strut connection”). The head strut connection  33  connects a first end portion  22  of a first strut and a second end portion  23  of a second strut. The bend of material of a head strut connection  33  extends through a turn σ that is in the range of about 200 and 270 degrees to form an open eyelet  34 . The strut connection  33  distributes stress over a longer length of strut than would be the case in a sharp bend, but distributes stress over a shorter length of strut than a strut connection  31 . By ending the turn a at less than 360 degrees, the strut connection  33  occupies less space and can be compressed into a smaller delivery system.  
      In addition, strut connections of  FIGS. 9A, 9B , and  10  have convenient eyelets  32 ,  32 ′, and  34 , respectively, in which suture material can be laced or tied in order to form a stent having a stackable (column) configuration of circumferential elements. Thus, the suture material may be threaded though eyelets  32  ( FIG. 8A ) or tied to eyelets  34  ( FIG. 8B ) to form the link members  16  of  FIGS. 8A and 8B . In the embodiment of a stent  10  that comprises a column of circumferential elements as in  FIGS. 7A and 7B , a link member  16  may at properly spaced intervals replace a strut connection  30  so as to join adjacently positioned struts  20  as shown in  FIG. 8C .  
      Even in an embodiment having a single circumferential element  15 , the embodiment may include a strut connection position whereby a strut connection occasionally may be skipped or replaced, as when adjacent strut ends are joined by other means. For example, ends  22  or  23  of two adjacent struts may be joined by a radiopaque gold marker for the purpose of visualization during placement of the stent. Alternatively, the ends  22  or  23  of adjacent struts may be joined by any other suitable means, such as sewing, adhesives, wires, weld, solder, glue, chemical cross-linking, heat source, light source, radiofrequency, laser, or other energy source.  
      The strut connections  31 ,  31 ′, and  33  of  FIGS. 9 and 10  are capable of compression and expansion without plastic deformation. In contrast, a V-shaped strut connection would be limited by mechanical failure and plastic deformation, whereby compression results in work hardening, kinking, or even snapping.  
      Alternative embodiments of coiled strut connections  35 ,  36 ,  38  are shown with bends in  FIGS. 11 through 13 .  FIG. 11  shows a strut connection  35  that has a “U-shaped” or tombstone profile and open eyelet  34 ′, and connects a first end portion  22  of a first strut and a second end portion  23  of a second strut. The strut connection  38  of  FIG. 12  has a modified, rounded V-shaped vertex σ having an open eyelet  37 ′ and joining first and second end portions  22 ,  23  of first and second struts, respectively.  FIG. 13  illustrates a strut connection  36  having a modified, sharp V-shaped vertex σ″ profile having an open eyelet  37  and connecting first and second end portions  22 ,  23  of first and second struts, respectively.  
      Compressed Stent  
      Strut connections in the compressed (collapsed) configuration compete for and take up space. Therefore, a medium-sized or a larger introducer system might be preferred to accommodate a stent, because the strut connections essentially have to occupy the same space in the introducer system. A medium-sized or larger delivery system is fine for esophageal stenting, as one non-limiting example. However, it may be difficult to deliver a larger stent percutaneously into a vessel passageway having a smaller inner diameter, as in the vascular system. As a result, when the need to have a smaller introducer system becomes important, such as for the introduction of stents into the coronary arteries or cranial vessels, the strut connections are preferably smaller so as to occupy even less space.  
      The actual ratio of expanded to collapsed size is a function of the material elasticity or how much deflection the material can absorb before being plastically deformed. For example, a strut in AISI type 304 stainless steel might allow a 15 or 20% deflection while Nitinol in the superelastic condition might allow a 30 to 40% deflection. It is also a function of the number of struts around the periphery of the stent.  
      The stents are formed of wire arranged in a closed configuration that includes a series of struts that are joined by an equal number of joints. The ends of the wire can be closed in a variety of ways, including the use of a sleeve which is welded or crimped against the ends of the wire to produce a continuous or endless configuration.  
      Methods  
      The invention also comprises a method of using arcuate stents for implantation in a body vessel in order to maintain vessel patentcy.  
      In practice, the stent is compressed into a reduced first diameter size for insertion into, and possible removal from, a body passageway. After being properly positioned within a body passageway, the stent is allowed to expand to an expanded second diameter shape.  
      In an alternative embodiment, a sleeve is utilized with the stent for implantation. The stent compressed into a reduced first diameter size for insertion into the sleeve. The sleeve is positioned in a body passageway and removed so as to allow the stent to expand to an expanded second diameter shape. The sleeve may be made of any suitable material (natural, synthetic, or combination thereof) such as a plastic that is pliable, strong, resilient, elastic, and flexible. The sleeve material should be biocompatible, or should be able to be made biocompatible, such as by coating, chemical treatment, or the like.  
       FIG. 14  shows a method  100 , an embodiment that comprises providing a delivery system (such as a catheter, endoscope, other endoscope accessory, or the like) with a distal end portion containing a compressed stent having a circumferential element  15  moveable between radially compressed and radially expanded configurations, the circumferential element  15  further having first and second longitudinal ends  11 ,  12 , respectively, and a longitudinal axis  14  and arcuate struts  20  being joined at the first and second ends by strut connections  30 ,  31 ,  31 ′,  33 ,  35 ,  36 ,  38  and where the struts in the expanded configuration are spaced  60 ,  62 ,  64 ,  70 ,  72 ,  74  arcuately relative to a plane  14 ′ that includes the longitudinal axis (step  101 ). The distal end portion is inserted into a body through a mouth, orifice, or incision (step  102 ). The distal end portion is positioned in an internal region of a body until the compressed (unexpanded stent) is located where desired (step  103 ). The stent is deployed from the distal end portion of the delivery system and to an expanded configuration (step  104 ).  
      Another method of maintaining vessel patency comprises providing a stent having a circumferential element  15  moveable between radially compressed and expanded configurations, the circumferential element  15  further having first and second longitudinal ends  11 ,  12 , respectively, and a longitudinal axis  14  and arcuate struts  20  being joined at the first and second ends by strut connections  30 ,  31 ,  31 ′,  33 ,  35 ,  36 ,  38  and wherein the struts in the expanded configuration are spaced  60 ,  62 ,  64 ,  70 ,  72 ,  74  arcuately relative to a plane  14 ′ that includes the longitudinal axis. The stent while in a compressed configuration is inserted into a distal end portion of a stent delivery catheter. The distal end portion of the stent delivery catheter is delivered into an internal region of a body until the compressed stent is located where desired. The stent is deployed from the distal end portion of the delivery system and to the expanded configuration.  
      In another method of using a stent for implantation in a body vessel, a stent is provided in one step, whereby the stent comprises a circumferential element  15  moveable between radially compressed and radially expanded configurations, the circumferential element  15  further having first and second longitudinal ends  11 ,  12 , respectively, and a longitudinal axis  14  and arcuate struts  20  being joined at the first and second ends by strut connections  30 ,  31 ,  31 ′,  33 ,  35 ,  36 ,  38  and where the struts in the expanded configuration are spaced  60 ,  62 ,  64 ,  70 ,  72 ,  74  arcuately relative to a plane  14 ′ that includes the longitudinal axis. In another step, an endoscope is provided that comprises a flexible distal insertion portion with a distal light and lens for visualizing the interior of an internal region of a body and a working channel having a distal opening for passing a medical device into the observation field and working space of the endoscope, and further configured to provide suction for drawing target tissue toward the distal end of the flexible distal insertion portion. Another step comprises providing an elongate stent delivery catheter having a distal end portion configured to be inserted into the endoscope working channel, the distal end portion further having a stent mounting region configured for detachably and releasably securing the stent in a radially compressed configuration. In addition to those steps, one step comprises positioning the endoscope distal insertion portion to a designated site within a vessel for implantation. Still another step comprises disposing the compressed stent within the catheter stent mounting region, then in another step inserting the catheter distal end portion into the endoscope working channel, and in another step deploying the stent from the catheter distal end portion wherein the circumferential element first end  11  is expelled from the catheter distal end portion to a radially expanded configuration at the designated site and wherein the circumferential element second end  12  is expelled from the catheter distal end portion to a radially expanded configuration at the designated site. One the disposing, inserting, and deploying steps with a second stent having a circumferential element  15  moveable between radially compressed and radially expanded configurations, the circumferential element  15  further having first and second longitudinal ends  11 ,  12 , respectively, and a longitudinal axis  14  and arcuate struts  20  being joined at the first and second ends by strut connections  30 ,  31 ,  31 ′,  33 ,  35 ,  36 ,  38  and where the struts in the expanded configuration are spaced  60 ,  62 ,  64 ,  70 ,  72 ,  74  arcuately relative to a plane  14 ′ that includes the longitudinal axis. A further step comprises withdrawing the endoscope containing catheter from the vessel. Steps for the forgoing methods need not be performed sequentially. For example only, an endoscope, stent, and catheter may be provided in any order.  
      It is intended that the foregoing detailed description of the medical devices and method of maintaining vessel patency be regarded as illustrative rather than limiting. It should be understood that it is the following claims, including all equivalents that are intended to define the spirit and scope of this invention. Terms are to be given their reasonable meaning and like terms may be used interchangeably in the broadest sense to achieve a particular result. Therefore, the embodiment of any figure and features thereof may be combined with the embodiments depicted in other figures. Other features known in the art and not inconsistent with the structure and function of the present invention may be added to the embodiments.  
      While particular elements, drawings, embodiments, and applications of the present invention have been shown, illustrated, and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Therefore, it is therefore contemplated by the appended claims to cover such modifications as incorporate those features which come within the spirit and scope of the invention.