Abstract:
A bifurcated stent that uses turning segments to reduce the strain at regions which bend at extreme angles. The turning segments can be placed on side branch petals or on connectors connecting the petals to the stent body. Combining the turning segments with connectors of different length and tethers provides for a stent with high flexibility that can accommodate various shaped body vessels. This design allows the bifurcation branch to extend easily, to a useful distance, and to be deployed along oblique angles. Best of all, this design avoids the problems of angularly strained side branch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Application No. 60/815,950, filed Jun. 23, 2006, the entire contents of which is incorporated herein by reference. 
     
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0003]    In some embodiments this invention relates to implantable medical devices, their manufacture, and methods of use. Some embodiments are directed to delivery systems, such as catheter systems of all types, which are utilized in the delivery of such devices. 
         [0004]    A stent is a medical device introduced to a body lumen and is well known in the art. Typically, a stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent in a radially reduced configuration, optionally restrained in a radially compressed configuration by a sheath and/or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. The introducer may enter the body from an access location outside the body, such as through the patient&#39;s skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. 
         [0005]    Stents, grafts, stent-grafts, vena cava filters, expandable frameworks, and similar implantable medical devices, collectively referred to hereinafter as stents, are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, fallopian tubes, coronary vessels, secondary vessels, etc. Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or a combination of self-expanding and balloon expandable (hybrid expandable). 
         [0006]    Stents may be created by methods including cutting or etching a design from a tubular stock, from a flat sheet which is cut or etched and which is subsequently rolled or from one or more interwoven wires or braids. 
         [0007]    Within the vasculature, it is not uncommon for stenoses to form at a vessel bifurcation. A bifurcation is an area of the vasculature or other portion of the body where a first (or parent) vessel is bifurcated into two or more branch vessels. Where a stenotic lesion or lesions form at such a bifurcation, the lesion(s) can affect only one of the vessels (i.e., either of the branch vessels or the parent vessel) two of the vessels, or all three vessels. Many prior art stents however are not wholly satisfactory for use where the site of desired application of the stent is juxtaposed or extends across a bifurcation in an artery or vein such, for example, as the bifurcation in the mammalian aortic artery into the common iliac arteries. 
         [0008]    The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists. 
         [0009]    All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety. 
         [0010]    Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below. 
         [0011]    A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims. 
         [0012]    All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    This invention contemplates a number of embodiments where any one, any combination of some, or all of the embodiments can be incorporated into a stent and/or a stent delivery system and/or a method of use. In the context of these embodiments, the term telescoping means to extend away from a stent wall in a direction different from that of the longitudinal axis of a stent. Telescoping includes but is not limited each or any combination of: extending along a linear, varied, or curved path; extending at an oblique angle from the longitudinal axis of the stent; as well as extending along a path parallel to the longitudinal axis of the stent. 
         [0014]    At least one embodiment is directed towards a stent having an unexpanded state and an expanded state. The stent comprises a generally tubular stent body defining a first circumferential plane. The stent body defines a first lumen with a first longitudinal axis extending therethrough and the body further defines at least one side opening having a center point. The at least one side opening is in fluid communication with the first lumen. The stent also comprises a side branch assembly, the side branch assembly comprising at least two petals engaged to the stent body adjacent to the side opening. In the unexpanded state, the at least two petals are positioned substantially within the first circumferential plane. In the expanded state the at least two petals extend above the first circumferential plane and define a second lumen with a second longitudinal axis extending therethrough and form an oblique angle with the first longitudinal axis. At least one of the petals has a base, a tip, and at least one length extending between the base and the tip. The tip is located closer to the center point than the base. In the unexpanded state there is at least one ductile bend along the at least one length. The ductile bend has a first end, a second end, and a curved region between the first and second ends. The second end is located at a position on the at least one length closer to the center point than the first end is to the center point. In the expanded state the petal assumes a twisted configuration and defines a generally rounded translational arc between the base and the tip. The portion of the length between the length base and the first end of the bend and the portion of the length between the second end of the bend and the length tip both generally correspond to the translational arc. The curved region of the bend is positioned at a location different from the translational arc as the petal is positioned out of the first circumferential plane. 
         [0015]    At least one embodiment is directed towards a stent in which there are at least four petals and the bent region of every other petal is located at the same relative position along the petal length. 
         [0016]    At least one embodiment is directed towards a stent in which at least one petal has two lengths which are connected by a summit and the bend extends between the two lengths. 
         [0017]    At least one embodiment is directed towards a stent in which at least one petal has a first length and a second length. Both of the lengths are connected by a summit. The first length has at least one bend and the second length has at least one more bend than the first length. 
         [0018]    At least one embodiment is directed towards a stent having at least a portion of at least one bend on the first length which extends between at least a portion of at least two bends of the second length. 
         [0019]    At least one embodiment is directed towards a stent having a petal which further comprises a first and a second side length each side length having first and second ends and a first and a second central length. Each central; length has first and second ends. The two side lengths extend the full length of the petal and are engaged to each other by their first ends. The two central lengths are engaged to each other by their first ends at a position farther from a center point of the side opening of than the first ends of the side lengths. The first central length and the first side length are engaged to each other at their second ends. The second central length and the first side length are engaged to each other at their second ends. The first side length also has at least one bend extending away from the petal. The first central length has at least one bend extending in the opposite direction of the bend in the first side length. The second side length has at least one bend extending away from the petal. The second central length has at least one bend extending in the opposite direction of the bend in the second side length. 
         [0020]    At least one embodiment is directed towards a stent having a second central length which has at least two bends and at least a portion of the at least one bend of the first central length extends in between the two bends. 
         [0021]    At least one embodiment is directed towards a stent further comprising a plurality of petals in which the second side length of each petal has at least two bends and at least a portion of at least one bend of the first side length of an adjacent petal extends in between the at least two bends of the second side length. 
         [0022]    At least one embodiment is directed towards a stent having an unexpanded state and an expanded state. The stent comprises a generally tubular stent body defining a first circumferential plane. The stent body defines a first lumen with a first longitudinal axis extending therethrough. The stent body further defines at least one side opening, the at least one side opening in fluid communication with the first lumen. The stent also has a side branch assembly comprising at least two connectors and at least two petals. The at least two connectors connect the at least two petals to the stent body adjacent to the side opening. In the unexpanded state, at least one of the at least two connectors has at least one ductile bend and the at least two petals are positioned substantially within the first circumferential plane. In the expanded state, the at least two petals extend above the first circumferential plane and define a second lumen with a second longitudinal axis extending therethrough. The second lumen forms an oblique angle with the first longitudinal axis. At least one of the petals also has at least one length. At least one of the connectors has a curved region between the stent body and the petal. The curved region is between a first end and a second end. The second end is located at a position on the connector closer to the center point than the first end. In the expanded state, the connector assumes a twisted configuration and defines an at least partially rounded translational arc between the stent body and the petal. The portion of the connector between the stent body and the first end of the bend and the portion of the connector between the second end of the bend and the petal both generally correspond to the translational arc. The curved region of the bend is positioned at a location different from the translational arc as the petal is positioned out of the first circumferential plane. 
         [0023]    At least one embodiment is directed towards a stent having the connector comprise a plurality of bends, the bends being longest closest to the stent body and progressively shortening as their proximity to the at least one petal increases. 
         [0024]    At least one embodiment is directed towards a stent in which there is a plurality of connectors. Each connector connects the stent body to one of a plurality of petals. At least two connectors have different numbers of bends. 
         [0025]    At least one embodiment is directed towards a stent having a plurality of connectors each connecting one of a plurality of petals to the stent body. In the expanded state one petal being an acute petal extending at a most acute angle relative to the first longitudinal axis and one being an obtuse petal extending at a most obtuse angle relative to the first longitudinal axis. The connector of the acute angle having more bends than a connector of the obtuse angle. 
         [0026]    At least one embodiment is directed towards a stent in which the side opening has a perimeter and further comprising a plurality of petals connected by connectors positioned along the perimeter at positions other than those of the obtuse and acute petal connectors. The plurality of connectors has more bends than the obtuse petal and fewer bends than the acute connector. The number of bends on the plurality of connectors increases progressively with proximity to the acute petal connector. 
         [0027]    At least one embodiment is directed towards a stent having at least one sidemost petal connector located at a position on the perimeter midway between the acute and obtuse petal connectors. The sidemost connector also has a highly twisted portion. The other connectors have progressively less twisted portions as they are positioned farther away from the sidemost connector. 
         [0028]    At least one embodiment is directed towards a stent in which there are a plurality of connectors each connecting one of a plurality of petals to the stent body. In the expanded state one is an acute petal and extends at a most acute angle relative to the first longitudinal axis. Also in the expanded state one is an obtuse petal and extends at a most obtuse angle relative to the first longitudinal axis. The connector of the acute petal has fewer bends than the connector of the obtuse petal. In the expanded state the obtuse petal is longer than the acute petal. 
         [0029]    At least one embodiment is directed towards a stent in which all of the connectors have bends and lengths between the bends which are positioned at a relatively perpendicular angle to an axis extending from the center of the side opening to the stent body. 
         [0030]    At least one embodiment is directed towards a stent having an unexpanded state and an expanded state. The stent comprises a generally tubular stent body which defines a first circumferential plane and a first lumen with a first longitudinal axis extending therethrough. The body further defines at least one side opening in fluid communication with the first lumen. The stent also comprises a side branch assembly having at least three connectors and at least three petals. The at least three connectors connect the at least three petals to the stent body adjacent to the side opening. In the unexpanded state, the at least three petals are positioned substantially within the first circumferential plane. In the expanded state the at least three petals extend above the first circumferential plane and define a second lumen with a second longitudinal axis extending therethrough. The second lumen in the expanded state forms an oblique angle with the first longitudinal axis. The plurality of petals comprises an acute petal, an obtuse petal, and at least one other petal. The acute petal extends at a most acute angle relative the first longitudinal axis. The obtuse petal extends at a most obtuse angle relative the first longitudinal axis. The obtuse petal connects to at least one other petal by a tether with a length. The acute petal is connected to at least one other petal by a tether with a length. 
         [0031]    At least one embodiment is directed towards a stent in which the length of the tether connected to the obtuse petal is longer than the length of the tether connected to the acute petal. 
         [0032]    At least one embodiment is directed towards a stent comprising at least four petals in which every petal is connected to an adjacent petal by a tether. The tether connected to the acute petal is the shortest tether. The tether connected to the obtuse petal is the longest. The tether lengths progressively increase in length by proximity to the obtuse petal. 
         [0033]    At least one embodiment is directed towards a stent in which the tether on the acute petal is connected at a point closer to the connector than in any other petal. The tether on the obtuse petal is connected at a point further away from the connector than in any other petal. The tether connection locations progressively get closer to the connector by proximity to the acute petal. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0034]    The invention is best understood from the following detailed description when read in connection with accompanying drawings, in which: 
           [0035]      FIG. 1  is a lateral view of an unexpanded bifurcated stent with a petal type side branch assembly in which the petals have turning segments. 
           [0036]      FIG. 2  is perspective view of the bifurcated stent after expansion. 
           [0037]      FIG. 3  is a lateral view of a side branch assembly having petals with turning segments. 
           [0038]      FIG. 4A  is a lateral view of a 2-dimensional image of a stent member undergoing high strain bending. 
           [0039]      FIG. 4B  is a perspective view of a stent member prior to undergoing high strain bending. 
           [0040]      FIG. 4C  is a perspective view of a stent member undergoing high strain bending. 
           [0041]      FIG. 5A  is a lateral view of a 2-dimensional image of a stent member undergoing low strain twisting. 
           [0042]      FIG. 5B  is a perspective view of a stent member prior to undergoing low strain twisting. 
           [0043]      FIG. 5C  is a perspective view of a stent member undergoing low strain twisting. 
           [0044]      FIG. 6  is a lateral view of a side branch assembly of petals which have an outer ring with turning segments. 
           [0045]      FIG. 7  is a lateral view of a side branch assembly of petals which have an outer ring with turning segments. 
           [0046]      FIG. 8  is a lateral view of a side branch assembly of petals which have an outer ring with progressively widening triangular turning segments. 
           [0047]      FIG. 9  is a lateral view of an expanded bifurcated stent in which a portion of the side branch assembly expands with high strain bending. 
           [0048]      FIG. 10  is a lateral view of an expanded bifurcated stent in which a portion of the side branch assembly expands with low strain twisting. 
           [0049]      FIG. 10B  is a lateral view a side branch assembly which expands with low strain twisting. 
           [0050]      FIG. 10C  is a lateral view of a side branch assembly which expands with low strain twisting. 
           [0051]      FIG. 11  is a lateral view of a stent side branch assembly having connectors with different numbers of bends. 
           [0052]      FIG. 12  is a lateral view of a stent side branch assembly having connectors with different numbers of bends and designed to accommodate rotational strain. 
           [0053]      FIGS. 13   a - 13   j  are images of different kinds of connectors. 
           [0054]      FIG. 14  is a lateral view of a side branch assembly having connectors with more than one number of turning segments. 
           [0055]      FIG. 15  is a lateral view of an expanded bifurcated stent which has a greater surface area on the high strain side of the side branch than on the low strain side. 
           [0056]      FIG. 16  is a lateral view of an unexpanded side branch assembly which will provide a greater surface area on the high strain side of the side branch than on the low strain side. 
           [0057]      FIG. 17  is a lateral view of an unexpanded side branch assembly which has longer tethers on the high strain side of the side branch than on the low strain side by. 
           [0058]      FIG. 18  is a lateral view of an unexpanded side branch assembly which has tethers positioned further away form the center point on the high strain side of the side branch than on the low strain side by. 
           [0059]      FIG. 19  is a perspective view of the stress levels of a side branch assembly connected to a main stent body by straight connectors when beginning expansion. 
           [0060]      FIG. 20  is a lateral view of the stress levels of a side branch assembly connected to a main stent body by straight connectors when beginning expansion. 
           [0061]      FIG. 21  is a lateral view of the stress levels of a side branch assembly connected to a main stent body by straight connectors when expanded. 
           [0062]      FIG. 22  is a close up lateral view of the stress levels of a straight connector connecting a side branch assembly to a main stent body when expanded. 
           [0063]      FIG. 23  is a perspective view of the stress levels of a side branch assembly connected to a main stent body by curved connectors when beginning expansion. 
           [0064]      FIG. 24  is a lateral view of the stress levels of a side branch assembly connected to a main stent body by curved connectors when beginning expansion. 
           [0065]      FIG. 25  is a lateral view of the stress levels of a side branch assembly connected to a main stent body by straight curved when expanded. 
           [0066]      FIG. 26  is a close up lateral view of the stress levels of a curved connector connecting a side branch assembly to a main stent body when expanded. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0067]    The invention will next be illustrated with reference to the figures wherein the same numbers indicate similar elements in all figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate the explanation of the apparatus of the present invention. 
         [0068]    For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated. 
         [0069]    Depicted in the figures are various aspects of the invention. Elements depicted in one figure may be combined with, or substituted for, elements depicted in another figure as desired. 
         [0070]    Referring now to  FIG. 1  there is shown an embodiment featuring an unexpanded substantially tubular bifurcated stent  1  which comprises a first stent body  10 , a side branch opening  30  along its surface, and a side branch assembly  30  adjacent to and covering at least a portion of the side branch opening  30 . Although in some embodiments the side branch opening is a circular or elliptical opening the opening can define any shape. The stent  1  is typically placed on a catheter shaft and is positioned within a bifurcated body vessel. The bifurcated body vessel will have at least two branching vessel lumens, one being a first vessel lumen and one being a second vessel lumen. When deployed (as illustrated in  FIG. 2 ), the stent  1  is oriented along a first longitudinal axis  16  through the first body vessel  3  and forms an angle oblique to a secondary longitudinal axis  36  running along the length of the second body vessel  2 . For the purposes of this application, the term “oblique” refers to an angle of greater than zero degrees, such as an angle of between about 1 and about 180 degrees. An oblique angle explicitly includes angles of about 90 degrees. 
         [0071]    When the stent is unexpanded, the side branch assembly  30  is positioned adjacent to the second vessel lumen and is engaged to the first stent body  10  by at least one connector  37  at an engagement region  93 . The surface of the first stent body  10  defines a first circumferential plane  12 . In the unexpanded state, the side branch assembly  30  is positioned substantially along the first circumferential plane  12 . 
         [0072]    Side branch assembly  30  in  FIG. 1  features two or more projecting members  33  which are sometimes referred to as petals or expansion petals which are connected by the connectors  37  to the first stent body  10 . Although  FIG. 1  shows twelve projecting members, embodiments of this invention can have two or more petals. When expanded, (as shown in  FIG. 2 ) the petals bend out of the first circumferential plane  12  and define the second lumen  34  which is in fluid communication with the first lumen  14  and extends into the second body vessel  2  along a second longitudinal axis  35  at an oblique angle. 
         [0073]    Referring now to  FIG. 3  there is shown one embodiment of an unexpanded side branch assembly  30  having at least one petal  33  with a length  32  generally extending towards a center point  31  of the side branch opening  18 . In some embodiments, there will be two or more petal lengths  32  connected by a petal summit  39 . The petal length  32  has a ductile turning segment or bend  53 . When the side branch assembly  30  expands, the turning segment  53  twists in addition to just bending, allowing the petal length  32  to deploy without high stress bending. Having one or more turning segments  53  positioned at various locations on the petal length  32  allows the petal  33  to assume additional non-linear configurations. 
         [0074]    As illustrated in  FIGS. 4A ,  4 B and  4 C, when a petal length  32  designed according to the PRIOR ART is bent at an oblique or extreme angle  90  to form the second lumen  34 , the bent petal will generally be congruent with a translational arc  27  defining a generally curved path starting from a point located at the beginning of the bend  55  and the end of the bend  56 . As used in this application, the term translational arc  27  is not a mathematical formula defining the vectors of the length  32  but instead is a general term used to describe a generally curved path or a generally rounded angular path drawn from the base  28  to the tip  29 .  FIG. 4B  shows the length prior to bending.  FIGS. 4A and 4C  show the length after bending. 
         [0075]    The beginning of the bend  45  and the end of the bend  46  are both located at positions along the length  32  between the base of the length  28  and the tip of the length  29 , the beginning of the bend  45  being closer to the base than the end of the bend  46 . When a petal length  32  bends along a translational arc  27 , the bending can be stressful and require significant energy to perform. This is the case in embodiments such as that illustrated in  FIG. 4  where the portion of the length closest to the base  28  remains parallel with the longitudinal axis  16  of the first lumen and the portion of the length closest to the tip remains parallel with the longitudinal axis  36  of the second lumen  34 . This is also the case in embodiments where the entire petal length  32  extends at least one angle relative to the first longitudinal axis  16 . This high energy description not only applies to petal lengths but also applies to straight connectors connecting petals or side branch assemblies to stent bodies. 
         [0076]    In contrast as shown in  FIGS. 5A ,  5 B, and  5 C, if at least one petal length  32  has at least one turning segment  53  between the base  28  and the tip  29  of the petal length  32 . The turning segment  53  can twist and function as a hinge point which allows the petal length  32  to bend at the same oblique or extreme angle  90  with less stress and requiring less energy than according to the PRIOR ART configurations of  FIGS. 4A ,  4 B and  4 C. Illustrated in  FIGS. 1 ,  3 , and  6 , is a view of an unexpanded petal  33  having at least one length  53  which spans from the tip  29  to the base  28  in which the turning segment  53  is a bend in the length  32  comprising a second end  56  closer to the center point  31 , a first end  55  first end closer to the base  28  and a curved region  57  between the two ends ( 55 ,  56 ).  FIG. 7  illustrates an unexpanded side branch assembly in which the connector has a turning segment.  FIG. 5B  shows the length prior to twisting.  FIGS. 5A and 5C  show the length after twisting. 
         [0077]    In  FIGS. 5A ,  5 B, and  5 C there are shown that as the side branch assembly deploys, the petal length  32  turns away from the first longitudinal axis  16  to form the second lumen  34  and the curved region  57  twists and pivots out of the translational arc  27 . Although in  FIGS. 5A-5C , the translational arc appears to follow the same path as the translational arc of  FIGS. 4A-4C , the path that any given translational arcs will assume is a function of the flexibility and torsional stress on the length  32  and can in places can deploy at more acute or obtuse angles and can be more angular or more rounded. 
         [0078]    The twisting and pivoting occurring during deployment relieves the torsion stress present in the petals illustrated in  FIGS. 4A-4C . This is the case in embodiments such as those illustrated in  FIGS. 5A-5C  where the portion of the length closest to the base  28  remains parallel with the longitudinal axis  16  of the first lumen and the portion of the length closest to the tip remains parallel with the longitudinal axis  36  the second lumen  34 . This is also the case in embodiments where the entire petal length  32  extends at least one angle relative to the first longitudinal axis  16 . This low energy description not only applies to petal lengths but also applies to connectors with turning segments which connect petals or side branch assemblies to stent bodies. As a rule, the lower the stress imposed on the petal length  32 , the less energy is required to bend the length  32 , the less likely the length is to break while bending, and the easier it is to deploy and form the second lumen  34 . Multiple turning segments on a given petal length allows for the deployment of second lumens with non-linear, curved, or irregular shapes and capable of having multiple turns and curves. 
         [0079]    In one embodiment, the turning segments are positioned along the petal length  32  at different distances from the center point  31 . In at least one embodiment, the positioning of the turning segments  53  alternate and are identical in every other petal length  32 . In at least one embodiment (as shown in  FIG. 3 ), the turning segments  53  are nested. For purposes of this application the term “nested” means that the end of at least one the turning segments  53  of at least one petal length  32  is positioned at a location on the length closer to the center point  31  than a turning segment  53 ′ on an adjacent petal length  32 ′ and is also positioned at a location on the length farther from the center point  31  than a turning segment  53 ″ on the same adjacent petal length  32 . In at least one embodiment at least two turning segments  53  have different lengths. And in at least one embodiment at least two turning segments  53  extend away from their respective petal length  32  at different angles. 
         [0080]    Referring now to  FIG. 6  there is shown an unexpanded side branch assembly  30  in which there are at least two concentric rings an inner ring and an outer ring  42 . The inner ring comprises that part of the petal length  32  which extends toward the center point  31  and is not within the outer ring  42 . As illustrated in  FIG. 6 , the inner ring can also comprise two or more pairs of petal lengths  32  extending towards the center point  31  which are connected by connected by a petal summit  39 . Connected to the end of the petal length furthest from the center point  31  is an outer ring  42  which comprises at least one outer length  40 . The outer ring has at least two outer lengths  40  which are connected by at least one outer summit  41 . In at least one embodiment, two petal lengths  32  are connected to one outer summit  41 . Some outer lengths  40  extend along the portion of the petal lengths  32  within the outer ring and some outer lengths  40  are on members which do not extend towards the petal summits  39 . Although  FIG. 6  illustrates a side branch assembly having two outer summits  41  for every one petal summit  39 , the ratio of petal summits  39  to outer summits  41  can be 1:1 or any other ratio. As illustrated in  FIG. 6 , not every outer summit  42  need be connected to the inner ring. 
         [0081]    At least one turning segment  53  can be located on none, some, or all of the petal lengths  32  and on some or all of the outer lengths  40 . The turning segments  53  can be nested, angled, and positioned along either the petal lengths  32  or outer lengths  40  in the same manner as described by  FIG. 3 . In one embodiment, every other outer length  40 ″ has two turning segments  53  and the adjacent outer length  40 ′ has one turning segment nested within the two segments of the adjacent outer length. 
         [0082]    The deployment of the petals  33  can also be facilitated by the presence of ductile turning segments  53  on the connectors  37  connecting the petal lengths  32  to the first stent body  10  as illustrated in  FIG. 7 . The presence of turning segments on connectors allow the connectors to undergo low strain twisting and pivoting in the same manner as described in the explanation of  FIGS. 5A-5C . The explanation of  FIGS. 5A-5C  when referring to turning segments on the connectors can be best understood by respectively substituting references to the end of the connector engaged to the petal with the tip of  FIGS. 5A-5C  and the end of the connector engaged to the stent body with the base of  FIGS. 5A-5C . 
         [0083]    Now referring again to  FIG. 7  it is shown that when all of the connectors surrounding the side branch assembly  30  have turning segments  53 , the connectors form a flex ring  50  which can flexibly accommodate the oblique angles formed by the side branch  30  deployment. As the side branch assembly  30  deploys, the connectors  37  twist instead of just bend and receive far less axial strain during side branch extension. In one embodiment, the lengths of the turning segments are oriented in a substantially perpendicular arrangement relative to an axis  60  drawn from the center point  31 . One embodiment is illustrated in  FIG. 8  where at least one connector  37  has a generally triangular shape comprising at least two turning segments  53  having progressively narrowing lengths on the segments positioned closer to the petals  33 . These narrowing turning segments  53  provide more conformability and flexibility at the ostium  38  of the resulting second lumen by twisting instead of bending during expansion. The longer turning segments  53  closest to the first stent body  10  are the most flexible and those closest to the petals  33  are the least flexible. This progression in flexibility allows the second lumen to be extended at angles extreme to the first longitudinal axis  16  and assures that the petals  33  project in the proper direction. The triangular shape of the connectors also is an efficient way of packaging mass which allows for a greater amount of solid surface area to be placed along the wall of the second lumen. The greater surface area allows for improved scaffolding properties and enhances the efficacy of drugs coatings on the stent. 
         [0084]    Different regions of the second lumen will have different bending stresses. Referring now to  FIG. 9 , there is shown a PRIOR ART standard stent assembly having a high strain carina  91  which is a location on the stent  1  where the second lumen  34  forms the most acute angle with the first lumen  14 . At the high strain carina  91 , the greatest amount of axial stress is formed by expanding the side branch assembly  30 . In contrast, the low strain carina  92  is a location on the stent  1  where the second lumen  34  forms the most obtuse angle with the first lumen  14 . At the low strain carina  92 , the least amount of axial stress formed by expanding the side branch assembly  30  occurs. In standard stent assemblies, the connector  37  connecting the petals  33  to the first stent body  10  have similar physical characteristics and do not efficiently address the different amounts of axial stress present at the two different carinas ( 91 ,  92 ). In contrast, as illustrated in  FIG. 10 , turning connectors  37  can address the high levels of axial strain at the carinas. By utilizing a number of different kinds of turning connectors  37 , the different physical requirements of the various carinas ( 91 ,  92 ) can be addressed. 
         [0085]    At least two embodiments of side branch assemblies  30  with turning connectors  37  capable of functioning within the stent of  FIG. 10  are shown in  FIGS. 10B and 10C . Although  FIGS. 10B and 10C  feature mounting rings  47  located at the ostium  38  for connecting the side branch assembly  30  to the main body of the stent, the mounting ring  47  is not an essential feature. Others embodiments of side branch assemblies with at least one turning connector are described below. 
         [0086]    In  FIG. 11 , there is shown a side branch assembly in which different kinds of turning connectors  37  are positioned at various carina points to accommodate the differing modes of bending action that occurs at different carinas. The connector at the high strain carina  91  has a greater number of bends than the connector at the low strain carina  92 . One embodiment of this concept has a steadily increasing number of bends progressively positioned from the lowest strain carina  92  to the highest strain carina  91 . 
         [0087]    Another embodiment is illustrated in  FIG. 12  where the connectors are designed to address both axial and rotational strain caused by side branch expansion. The connectors  37  connecting the 94 petals adjacent to the high strain carina  91  have bends designed to address both the axial stress and the rotational stress caused by the direction of the bending occurring at this location. The connectors located halfway between the two sides of the assembly  95  have connectors designed to accommodate the rotational twisting occurring at this region. The connectors located adjacent to the low strain carina  94  are designed to accommodate lower axial and rotational stress. 
         [0088]    Although  FIGS. 11 and 12  illustrate a side branch assembly having eight petals and eight connectors, there are embodiments with greater or fewer numbers of connectors. There are a number of designs that turning connectors can have some of which are illustrated in  FIGS. 13   a - 13   j  and are named as follows: 
         [0089]      13   a : single lateral turning connector.  13   b : double bilateral turning connector.  13   c : triple bilateral turning connector.  13   d : quadruple bilateral turning connector.  13   e : quintuple bilateral turning connector.  13   f : transverse bilateral turning connector.  13   g : diagonal bilateral turning connector.  13   h : double bilateral rotating connector.  13   i : double linear turning connector.  13   j : single arced turning connector. These turning connector configurations can also be used as the bend configurations for embodiments of the petal bends disclosed in  FIGS. 1-6 . 
         [0090]    Proper connector selection is governed by the following general rules: The higher the axial strain on the connector, the more bends the connector should have. The higher the rotational strain on the connector, the more of a rounded or curved shape the connector should have. The closer the connector is to the high strain carina  91  the higher the axial strain will be. The closer the connector is to the carina at the midpoint ( 95 ) between the high ( 91 ) and low ( 92 ) strain carinas, the greater the rotational strain will be. 
         [0091]    Referring now to  FIG. 14  there is shown at least one embodiment of a side branch assembly  30  for a bifurcated stent with more than one kind of turning connector  37 . At least one connector  37  has more than one grouping of curved regions  57 . At least some of these curved regions  57  can run in series with each other  59 ′ and  59 ″. Some of the connectors  37  can be connectors with a greater number of curving regions  58 ″ and some with a lesser numbers of curing regions  58 ′. The connectors  37  can also comprise a connector junction  61  where adjacent connectors can be engaged to each other. The connectors  37  can engage the petals  32  at an axis offset  62  which can be offset from a radial axis  60  extending along the path between the center point  31  and the base  28  where connector  37  is engaged to a mounting ring  47  or to the main body of the stent. 
         [0092]    In addition to those features explicitly illustrated in  FIG. 14 , there are at least some alternative embodiments described below.  FIG. 14  shows a side branch assembly  30  covering an opening in the stent main body that is generally elliptical. The opening can in fact be circular, rounded, angular, or in any conceivable shape.  FIG. 14  also illustrates the side branch assembly  30  having a mounting ring  47  suitable for engagement to the main body of the stent. The mounting ring is not an essential component and embodiments without mounting rings are possible.  FIG. 14  also shows a side branch assembly  30  having 6 connectors the greater number of curved regions  58 ″ of a connector having 8 curved regions and the lesser number of curved regions  58 ′ having 2 curved regions. Embodiments in which some of the connectors have none, greater, equal, or lesser number of curved regions are all contemplated.  FIG. 14  shows the connectors  37  having two curved region series  59 ′ and  59 ″ having generally parallel paths on each connector. Connectors can also have one or more than two curved region series and they can extend in generally non-parallel series as well. In addition, although  FIG. 14  shows all of the connectors having a connector junction  61  not all of the connectors need have one. 
         [0093]    Referring now to  FIG. 15  there is illustrated a bifurcated stent  1  which demonstrates that the area of the second body vessel  2 ′ adjacent to the petal length  32 ′ at the side of the low strain carina  92  is greater than the area of the second body vessel  2 ″ adjacent to the petal length  32 ″ at the high strain carina  91 . One embodiment (as shown in  FIG. 16 ) provides greater surface area to the portion of the second lumen  34  formed by the low strain petal length  32 ′ by increasing the length and the number of turns on the connector  37 ′ connecting the petal to the main stent body. In this embodiment, the low stress petal connector  37 ′ has the greatest number of turns, and the number of turns on each adjacent connector progressively decreases up to the high stress connector  37 ″. As the side branch assembly  30  expands, the increased number of turns in the connector  37 ″ increases the distance the expanded petal can extend which increases the area of the second body vessel  2  covered by the second stent lumen  34 . The number of turns in each connector  37  need not exactly match those in  FIG. 16  and can be adjusted to match the particular dimensions of the second body vessel. 
         [0094]    In at least one embodiment tethers can be used to control the expansion of different petals to adjust the resulting body vessel coverage. In  FIG. 17  there is shown at least one embodiment in which tethers  43  of differing lengths are attached to the petals lengths  32 . Long tethers  43 ′ are attached to the petals  32 ′ that will be on the low strain carina side  92 . The tethers progressively shorten between the petals  32 ′ closer to the high strain carina  91 . The shorter tethers  43 ″ reduce the degree to which the petal can extend during side branch expansion which reduces the overall length of that part of the second lumen  34 . 
         [0095]    In  FIG. 18  there is illustrated another embodiment utilizing tethers to properly adjust the lengths of the petals during side branch expansion. In this embodiment, the tether lengths are positioned at different points along the lengths of the petals  32 . Tethers  43 ′ are attached closer to the petal summit  39  on the petals  32 ′ that will be on the low strain carina side  92 . The tethers  43 ″ are positioned progressively further away from the petal summit  39  on the petals  32 ″ closer to the high strain carina  91 . The lower positioning reduces the degree to which the petal can extend during side branch expansion which reduces the overall length of that part of the second lumen  34 . 
         [0096]    Referring now to  FIGS. 19 and 20  there is shown a side branch assembly  30  over a side branch opening  18  in which the side branch assembly  30  is connected to the ostium  38  by straight connectors  37 . When an expansion force including but not limited to outward pressure from a balloon  20  or a self expansion mechanism pushes the side branch assembly to form the second lumen, levering stress becomes distributed unevenly along the side branch assembly  30 . In particular, the straight connector  37  undergoes significant levering stress. This stress both increases the energy needed to properly deploy the side branch assembly and increases the possibility that the connector will fail resulting in a stent that is not suitable for implantation.  FIG. 21  shows the same side branch assembly  30  in its expanded state and  FIG. 22  is a close up of the connector  37  connecting the side branch assembly  30  to the first stent body. 
         [0097]      FIGS. 23-26  show the same stress levels in an embodiment having curved connectors with turning segments. If contrasted with the stress diagrams of the straight connectors ( FIGS. 19-22 ), it can be shown that the curved connectors both reduce the highest magnitude of the stress as well as the overall distribution of the stress. This same stress reducing effect is present in turning segments located along a portion of a side branch projecting member. The stress reduction can best be illustrated with detailed comparisons of close up  FIGS. 22 and 26 . 
         [0098]      FIG. 22  shows a straight connector linking the side branch  30  to the ostium  38  of the stent. The stress levels extend along a range consisting of: none, low, medium, high, very high, and severe. In  FIG. 22 , as the connector  37  is bent along the translational arc  27 , extending from the base  28 , to the tip  29  are a number of sequential stress zones: first a short low stress zone  37   a , then: a long medium stress zone  37   b , a very long high stress zone  37   c , a medium length very high stress zone  37   d , and culminating in a high stress zone  37   e  at the tip  29 . 
         [0099]    In contrast  FIG. 26  shows that at least one turning segments  53  in the connector  37  reduces both the highest magnitude of stress experienced by the connector  37  as well as the overall stress distribution over the connector  37 . In  FIG. 26 , as the connector  37  is bent to partially follow the translational arc  27 , extending from the base  28  to the tip  29  are more sequential stress zones with lower stress magnitudes extending over a greater length of the connector. Specifically, there begins a medium length low stress zone  37   f  (longer than the short low stress zone  37   a  of  FIG. 22 ), followed by: a medium high stress zone  37   g , a short medium stress zone  37   h , a medium length low stress zone  37   i , a medium length high stress zone  37   j , a short low stress zone  37   k , a medium length low stress zone  371 , a medium high stress zone  37   m , a long medium stress zone  37   n  and culminating in a long low stress zone  37   o  at the tip  29 . 
         [0100]    Observation of  FIGS. 22 and 26  shows that a much greater proportion of the overall length of the curved connector  37  in  FIG. 26  undergoes medium or low stress than in the straight connector of  FIG. 22 . In particular, the very high zone  37   d  and high zone  37   e  close to the tip  29  in the straight connector correspond with the medium zone  37   n  and low zone  37   o  between the end of the bend  46  and the tip  29  of the curved connector. In addition, unlike in the straight connector, the curved connector has no very high stress zones. 
         [0101]    In some embodiments the stent, its delivery system, or other portion of an assembly may include one or more areas, bands, coatings, members, etc. that is (are) detectable by imaging modalities such as X-Ray, MRI, ultrasound, etc. In some embodiments at least a portion of the stent and/or adjacent assembly is at least partially radiopaque. 
         [0102]    In some embodiments at least a portion of the stent is configured to include one or more mechanisms for the delivery of a therapeutic agent. Often the agent will be in the form of a coating or other layer (or layers) of material placed on a surface region of the stent, which is adapted to be released at the site of the stent&#39;s implantation or areas adjacent thereto. 
         [0103]    A therapeutic agent may be a drug or other pharmaceutical product such as non-genetic agents, genetic agents, cellular material, etc. Some examples of suitable non-genetic therapeutic agents include but are not limited to: anti-thrombogenic agents such as heparin, heparin derivatives, vascular cell growth promoters, growth factor inhibitors, Paclitaxel, etc. Where an agent includes a genetic therapeutic agent, such a genetic agent may include but is not limited to: DNA, RNA and their respective derivatives and/or components; hedgehog proteins, etc. Where a therapeutic agent includes cellular material, the cellular material may include but is not limited to: cells of human origin and/or non-human origin as well as their respective components and/or derivatives thereof. Where the therapeutic agent includes a polymer agent, the polymer agent may be a polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS), polyethylene oxide, silicone rubber and/or any other suitable substrate. 
         [0104]    This completes the description of the preferred and alternate embodiments of the invention. The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. The various elements shown in the individual figures and described above may be combined, substituted, or modified for combination as desired. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. 
         [0105]    Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claims below.