Patent Publication Number: US-7220275-B2

Title: Stent with protruding branch portion for bifurcated vessels

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 60/404,756, filed Aug. 21, 2002, U.S. Provisional Application No. 60/487,226, filed Jul. 16, 2003, and U.S. Provisional Application No. 60/488,006, filed Jul. 18, 2003, the entire contents of which are incorporated herein by reference. 
     The present application is a continuation-in-part of now abandoned U.S. patent application Ser. No. 09/668,687, filed Sep. 22, 2000, which was a continuation-in-part of U.S. patent application Ser. No. 09/326,445, filed Jun. 4, 1999, which issued as U.S. Pat. No. 6,325,826. The present application is also a continuation-in-part of U.S. patent application Ser. No. 10/440,401, filed May 19, 2003 which is a continuation of U.S. patent application Ser. No. 09/750,372, filed Dec. 27, 2000, which issued as U.S. Pat. No. 6,599,316. The present application is also a continuation-in-part of U.S. patent application Ser. No. 09/963,114, filed Sep. 24, 2001, which issue as U.S. Pat. No. 6,706,062, and which is a continuation of U.S. patent application Ser. No. 09/326,445, filed Jun. 4, 1999, now U.S. Pat. No. 6,325,826. U.S. patent application Ser. No. 09/326,445 is continuation-in-part of PCT Application No. US99/00835, filed Jan. 13, 1999, which claims the benefit of U.S. patent application Ser. No. 09/007,265, filed Jan. 14, 1998, which issued as U.S. Pat. No. 6,210,429, which is a continuation-in-part of now abandoned of U.S. patent application Ser. No. 08/744,002, filed Nov. 4, 1996. The entire contents of all of the above references are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of medical stents and, more particularly, to a stent for the treatment of lesions and other problems in or near a vessel bifurcation. 
     BACKGROUND OF THE INVENTION 
     A stent is an endoprosthesis scaffold or other device that typically is intraluminally placed or implanted within a vein, artery, or other tubular body organ for treating an occlusion, stenosis, aneurysm, collapse, dissection, or weakened, diseased, or abnormally dilated vessel or vessel wall, by expanding the vessel or by reinforcing the vessel wall. In particular, stents are quite commonly implanted into the coronary, cardiac, pulmonary, neurovascular, peripheral vascular, renal, gastrointenstinal and reproductive systems, and have been successfully implanted in the urinary tract, the bile duct, the esophagus, the tracheo-bronchial tree and the brain, to reinforce these body organs. Two important current widespread applications for stents are for improving angioplasty results by preventing elastic recoil and remodeling of the vessel wall and for treating dissections in blood vessel walls caused by balloon angioplasty of coronary arteries, as well as peripheral arteries, by pressing together the intimal flaps in the lumen at the site of the dissection. Conventional stents have been used for treating more complex vascular problems, such as lesions at or near bifurcation points in the vascular system, where a secondary artery branches out of a larger, main artery, with limited success rates. 
     Conventional stent technology is relatively well developed. Conventional stent designs typically feature a straight tubular, single type cellular structure, configuration, or pattern that is repetitive through translation along the longitudinal axis. In many stent designs, the repeating structure, configuration, or pattern has strut and connecting members that impede blood flow at bifurcations. Furthermore, the configuration of struts and connecting members may obstruct the use of post-operative devices to treat a branch vessel in the region of a vessel bifurcation. For example, deployment of a first stent in the main lumen may prevent a physician from inserting a branch stent through the ostium of a branch vessel of a vessel bifurcation in cases where treatment of the main vessel is suboptimal because of displaced diseased tissue (for example, due to plaque shifting or “snow plowing”), occlusion, vessel spasm, dissection with or without intimal flaps, thrombosis, embolism, and/or other vascular diseases. As a result, the physician may choose either to insert a stent into the branch in cases in which such additional treatment may otherwise be unnecessary, or alternatively the physician may elect not to treat, or to “sacrifice”, such side lumen. Accordingly, the use of regular stents to treat diseased vessels at or near a vessel bifurcation may create a risk of compromising the benefit of stent usage to the patient after the initial procedure and in future procedures on the main vessel, branch vessels, and/or the bifurcation point. 
     A regular stent is designed in view of conflicting considerations of coverage versus access. For example, to promote coverage, the cell structure size of the stent may be minimized for optimally supporting a vessel wall, thereby preventing or reducing tissue prolapse. To promote access, the cell size may be maximized for providing accessibility of blood flow and of a potentially future implanted branch stent to branch vessels, thereby preventing “stent jailing”, and minimizing the amount of implanted material. Regular stent design has typically compromised one consideration for the other in an attempt to address both. Problems the present inventors observed involving side branch jailing, fear of plaque shifting, total occlusion, and difficulty of the procedure are continuing to drive the present inventors&#39; into the development of novel, non-conventional or special stents, which are easier, safer, and more reliable to use for treating the above-indicated variety of vascular disorders. 
     Although conventional stents are routinely used in clinical procedures, clinical data shows that these stents are not capable of completely preventing in-stent restenosis (ISR) or restenosis caused by intimal hyperplasia. In-stent restenosis is the reoccurrence of the narrowing or blockage of an artery in the area covered by the stent following stent implantation. Patients treated with coronary stents can suffer from in-stent restenosis. 
     Many pharmacological attempts have been made to reduce the amount of restenosis caused by intimal hyperplasia. Many of these attempts have dealt with the systemic delivery of drugs via oral or intravascular introduction. However, success with the systemic approach has been limited. 
     Systemic delivery of drugs is inherently limited since it is difficult to achieve constant drug delivery to the inflicted region and since systemically administered drugs often cycle through concentration peaks and valleys, resulting in time periods of toxicity and ineffectiveness. Therefore, to be effective, anti-restenosis drugs should be delivered in a localized manner. 
     One approach for localized drug delivery utilizes stents as delivery vehicles. For example, stents seeded with transfected endothelial cells expressing bacterial beta-galactosidase or human tissue-type plasminogen activator were utilized as therapeutic protein delivery vehicles. See, e.g., Dichek, D. A. et al., “Seeding of Intravascular Stents With Genetically Engineered Endothelial Cells”,  Circulation , 80: 1347–1353 (1989). 
     U.S. Pat. No. 5,679,400, International Patent Application WO 91/12779, entitled “Intraluminal Drug Eluting Prosthesis,” and International Patent Application WO 90/13332, entitled “Stent With Sustained Drug Delivery” disclose stent devices capable of delivering antiplatelet agents, anticoagulant agents, antimigratory agents, antimetabolic agents, and other anti-restenosis drugs. 
     U.S. Pat. Nos. 6,273,913, 6,383,215, 6,258,121, 6,231,600, 5,837,008, 5,824,048, 5,679,400 and 5,609,629 teach stents coated with various pharmaceutical agents such as Rapamycin, 17-beta-estradiol, Taxol and Dexamethasone. 
     Although prior art references disclose numerous stents configurations coated with one or more distinct anti-restenosis agents, they do not disclose the inventive stent design of the present application. There is, therefore, a need for a stent design that can effectively provide ostial branch support in a vessel bifurcation and effectively act as a delivery vehicle for drugs useful in preventing restenosis. This is particularly true in complicated cases, such as lesions located at a bifurcation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a stent for use in a bifurcated body lumen having a main branch and a side branch. The stent comprises a radially expandable generally tubular stent body having proximal and distal opposing ends with a body wall having a surface extending therebetween. The surface has a geometrical configuration defining a first pattern, and the first pattern has first pattern struts and connectors arranged in a predetermined configuration. The stent also comprises a branch portion comprised of a second pattern, wherein the branch portion is at least partially detachable from the stent body. 
     In one embodiment, the second pattern is configured according to the first pattern having at least one absent connector, and in another embodiment, the second pattern has a plurality of absent connectors. The second pattern may have second pattern struts, and the second pattern struts can be more densely packed than the first pattern struts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the invention may be embodied in practice. 
       In the drawings: 
         FIG. 1  is an illustration of a blood vessel bifurcation having an obstruction; 
         FIGS. 2–4  are illustrations of prior art stents implemented at a blood vessel bifurcation; 
         FIG. 5  is a flat view of an embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 6  is an enlarged view of a portion of the unexpanded stent shown in  FIG. 5 ; 
         FIG. 7  is a perspective view of the expandable branch portion of the stent of  FIG. 5  in the expanded configuration; 
         FIG. 8  is an enlarged view of a portion of another embodiment of a stent according to the present invention; 
         FIG. 9  is an enlarged view of a portion of an alternative embodiment of a stent according to the present invention; 
         FIG. 10  is a perspective view of the expandable branch portion of the stent of  FIG. 9  in the expanded configuration; 
         FIG. 11  is a schematic view of the stent of  FIG. 5  in the expanded state implemented at a blood vessel bifurcation; 
         FIG. 12  is a schematic view of the stent of  FIG. 9  in the expanded state implemented at a blood vessel bifurcation; 
         FIG. 13  is an enlarged view of a portion of another embodiment of a stent according to the present invention; 
         FIG. 14  is a flat view of another embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 15  is an enlarged view of a portion of the unexpanded stent shown in  FIG. 14 ; 
         FIG. 16  is a view of a portion of another embodiment of a stent according to the present invention; 
         FIG. 17  is a flat view of another embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 18  is a perspective view of the expandable branch portion of the stent of  FIG. 17  in the expanded configuration; 
         FIG. 19  is a flat view of another embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 20  is an enlarged view of a portion of the stent of  FIG. 19 ; 
         FIG. 21  is a view of the expandable branch portion of the stent of  FIG. 19  in the expanded configuration; 
         FIG. 22  is a flat view of another embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 23  is a flat view of another embodiment of an unexpanded stent in accordance with the present invention; 
         FIG. 24  is a view of an expandable branch portion of the stent of  FIG. 23  in the expanded condition; 
         FIGS. 25–28  are illustrations of the steps for a method of inserting a stent of the present invention, according to one embodiment. 
         FIGS. 29–31  are illustrations of the steps for another method of inserting a stent of the present invention. 
         FIG. 32  is a view of a herniated balloon for use with the method of  FIGS. 29–31 ; and 
         FIG. 33  is a view of another stent delivery system for inserting a stent in accordance with another method of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to stents for placement at vessel bifurcations and are generally configured to at least partially cover a portion of a branch vessel as well as a main vessel. Referring to  FIG. 1 , an exemplary blood vessel bifurcation  1  is shown, having a main vessel  2  extending along a main vessel axis  3  and a branch vessel  4  extending along a branch vessel axis  5 . Main vessel  2  and branch vessel  4  are disposed at an angle  11  of less than 90 degrees. An obstruction  6  is located within bifurcation  1 , spanning or at least partially obstructing main vessel  2  and a proximal portion branch vessel  4 . 
     Prior attempts at relieving main vessel  2  and branch vessel  4  from obstruction  6 , such as the one depicted in  FIG. 1 , have been problematic. Referring to  FIGS. 2–4 , examples of prior methods and structures for stenting an obstructed bifurcation are shown. As shown in  FIG. 2 , a first stent  8  is introduced into main vessel  2  and an access hole or side opening in the wall of stent  8  is usually created with a balloon to provide access to branch vessel  4  and unobstructed blood flow thereto. Typically, the access hole is created by deforming the struts and connectors of the main stent pattern, which may also deform the area of the stent surrounding the created opening and lead to undesirable results. Also, if stent  8  is used alone, at least a portion of obstruction  6  located within branch vessel  4  is left without stent coverage. Referring to  FIGS. 3 and 4 , one prior solution has been to introduce a second stent  10  into branch vessel  4 , for example via a second catheter inserted through a side opening of first stent  8 . As can be seen in  FIGS. 3 and 4 , such a configuration may introduce additional problems. For example, as shown in  FIG. 3 , second stent  10  may not provide full coverage of the portion of obstruction  6  in branch vessel  4  due to the angle  11  of the side branch vessel  4  with respect to main vessel  2  and the fact that the ends of the stent typically define a right angle to the longitudinal axis of the lumen. Alternatively, second stent  10  may extend beyond the bifurcation into main vessel  2 , as shown in  FIG. 4 , and cause potential obstruction of blood flow in main vessel  2  and/or cause problems at the overlapping portions of stents  8  and  10 . 
     Referring now to  FIGS. 5–7 , a stent  12  according to one embodiment of the present invention comprises stent body or wall  14  extending along a longitudinal axis  16  from a proximal end  20  to a distal end  22  and defining a lumen  18  therein. Stent  12  may have a three-dimensional geometrical configuration having variable dimensions (length, width, height, depth, thickness, etc.). In a preferred embodiment, stent body  14  is a generally tubular structure. As defined herein, “tubular” can include an elongate structure that has varied cross-sections and does not require that the cross-section be circular. For example, the cross-section of stent wall  14  may be generally oval. In an alternate embodiment, stent body  14  is generally cylindrical. Also, the stent body  14  may have varied cross-sectional shapes along the longitudinal axis  16  of the stent. For example, the circumferences in the proximal and distal parts of the stent may be different. This may occur, for example, if during stent delivery the delivery system causes the stent to distend. Lumen  18  represents the inner volumetric space bounded by stent body  14 . In a preferred embodiment, stent  12  is radially expandable from an unexpanded state to an expanded state to allow the stent to expand radially and support the main vessel. In the unexpanded state, stent body  14  defines a lumen  18  having a first volume, and in the expanded state, stent body  14  defines a lumen  18  having a second volume larger than the first volume. 
       FIG. 5  shows stent  12  in an unexpanded state in a flattened elevational view. As shown in  FIG. 5 , stent body  14  has a generally cellular configuration and comprises a generally repeatable series of struts  24  and connectors  26  configured in a predetermined general, overall, or main pattern along the length of stent  12 . Struts  24  comprise a pair of longitudinal strut portions  25  joined by a curved portion  27  at the proximal ends. Struts  24  are interconnected by curved portion  29  at the distal ends and formed into rings  28  that extend about the circumference of stent  12 . A series of the circumferential rings  28  are spaced apart from one another longitudinally along the entire length of stent  12 , and connectors  26  connect rings  28  to each other longitudinally. Connectors  26  extend generally longitudinally between adjacent circumferential rings  28  and connect to the respective curved portions  27 ,  29  of longitudinally adjacent struts  24  of adjacent rings  28 . In a preferred embodiment, connectors  26  are generally S-shaped or zigzag-shaped, although other patterns may also be used. Details of patterns that may be used for stent  12  are described more fully in co-pending PCT application IL02/00840, filed Oct. 20, 2002, incorporated herein by reference in its entirety. Furthermore, many other strut and connector patterns may be used, and the present pattern is shown for illustration purposes only. 
     Stent  12  further includes a branch portion  30  located at some point along the length of stent  12 . Branch portion  30  comprises a section or portion of stent wall  14  that is configured to extend into a branch vessel in a vessel bifurcation. In general, branch portion  30  is configured to be movable from an unextended position to an extended position. In the unextended position, branch portion  30  is disposed in the volume defined by the unexpanded stent  12 , that is, the branch portion  30  does not protrude radially from stent wall  14 . In the extended position, the branch portion  30  extends outwardly from stent wall  14  and branch portion  30  is extended into the branch vessel. As best seen in  FIG. 6 , branch portion  30  comprises a stent wall section of stent body  14  that is initially flush, coplanar, or cocylindrical with the remainder of stent body  14  and may extend outwardly with respect to the remainder of stent body  14 . In this regard, branch portion  30  is generally adjacent an opening, slit, space, void, or other incongruity in the overall or main pattern of stent body  14 . This configuration allows for access into a branch vessel, and at the same time allows for circumferential alignment of the stent within the vessel prior to deployment. In other embodiments, multiple branch portions can be incorporated into the stent to permit multiple access to one or more vessels. In a preferred embodiment, branch portion  30  may be positioned in the midsection of stent  12 . In alternate embodiments, branch portion  30  may be positioned anywhere along the length of stent  12 . 
     As best seen in  FIG. 6 , in a first embodiment, branch portion  30  comprises a portion of branch ring  32  and is positioned adjacent and proximal to an opening  34 . Upon extension of branch portion  30 , the portion of branch ring  32  adjacent opening  34  extends into the branch vessel, whereas the circumferential ring  28  adjacent branch ring  32  does not extend into the branch vessel. Opening  34  is formed by an absence of at least one connector  26  adjoining branch ring  32  with a branch opposing ring  33 . In some embodiments, four adjacent connectors are absent; however, in alternate embodiments any number of connectors may be absent to create opening  34 . In this embodiment, branch ring  32  is substantially similar geometrically to circumferential rings  28  and comprises branch ring struts  36  substantially similar to struts  24 ; however, a plurality of adjacent struts are free from connectors  26  adjacent opening  34 . In this regard, branch ring  32  is at least partially detachable from stent body  14  to facilitate at least a portion of branch ring  32  to extend outwardly with respect to stent body  14 . In some embodiments, the geometry of branch ring  32  may vary with respect to circumferential rings  28 , and branch ring struts  36  may have different configurations than struts  24 . 
     When stent  12  is expanded, as shown in  FIG. 7 , branch portion  30  is extended into the branch vessel, causing a portion of branch ring  32  to at least partially cover the inner surface of the branch vessel  4 . Thus, in a preferred embodiment, the stent coverage in the branch vessel includes at least partial coverage of the proximal side of the inner branch vessel wall. 
     Various alternative embodiments provide varying geometries of branch portion  30 . For example, branch ring  32  may vary with respect to circumferential rings  28 , and branch ring struts  36  may have different configurations than struts  24 . In one alternate embodiment, branch ring struts  36  are longer than struts  24 . In another embodiment, branch ring struts  36  are more closely packed circumferentially, resulting in a greater number of branch ring struts  36  per area within branch ring  32  as compared to circumferential rings  28 . In another embodiment, branch ring struts  36  may be thinner than struts  24 . In yet another embodiment, branch ring struts  36  may be made of a different material than struts  24 . 
     Referring to  FIG. 8 , another alternate embodiment of stent  19  is shown wherein a branch portion  30  comprises a branch ring  32  having branch ring struts  36  that are longer than struts  24  and a greater number of branch ring struts  36  provided as compared to the number of struts  24  in circumferential rings  28 , resulting in a more closely packed branch ring  32 . Furthermore, the number of branch ring connectors  38  on both sides of branch ring  32  is lower per branch strut  36  than the number of connectors  26  per strut  24 . Opening  34  is adjacent branch ring  32  on a distal side thereof, and the distal ends  46  of at least one, and preferably a plurality, of branch ring struts  40 ,  42 ,  44  are free from connectors and detachable from stent body  14 . In this embodiment, two branch ring struts  48  and  50  positioned laterally adjacent struts  40 ,  42 , and  44  have proximal ends  52  free from connectors. In this regard, free proximal ends  52  provide less resistance to movement of branch ring  32  during outward expansion with respect to stent body  14 . This same procedure can be used to provide one, two, three or more proximal ends in the ring free of connectors. Additionally, the shape and configuration of branch ring connectors  38  is different than those of connectors  26 . For example branch ring connectors along the proximal side of branch ring  32  are longer than connectors  26  to facilitate greater expansion of branch portion  30  into a vessel side branch. Also, branch ring connectors along the distal side of branch ring  32  are shaped and oriented differently than connectors  26  to facilitate greater expansion of branch portion  30  into the branch vessel. In alternate embodiments, branch ring connectors  38  may also differ among themselves. Also, the longer branch ring struts  36  are generally more flexible than comparable shorter struts because the added length permits more deflection. Also, the added length permits greater coverage vessel wall coverage due to deeper penetration into the branch vessel during extension. In alternate embodiments, different geometries and orientations of branch ring connectors  38  may be used. 
     Referring to  FIG. 9 , another alternate embodiment of stent  29  is shown having a branch portion  30  similar to that of the embodiment of  FIG. 8 , except branch ring struts  40 ,  42 , and  44  are longer than the other branch ring struts  36 , and the distal ends thereof define an arcuate profile to the proximal side of opening  34 . Also, central strut  42  is longer than struts  40 ,  44  adjacent to strut  42 . In this regard, when branch portion  30  is extended, struts  40 ,  42 , and  44  extend further into the branch vessel and provide more coverage of the vessel wall than the embodiment depicted in  FIG. 8 . In this regard, this embodiment may more readily cover an obstruction in a bifurcation vessel such as the one depicted in  FIG. 1  and, therefore, may provide better blood flow to a branch vessel. Furthermore, as described in more detail below, this embodiment facilitates the use of a second stent in the branch vessel. 
     Referring to  FIG. 10 , stent  29  of  FIG. 9  is shown in an expanded state with branch portion  30  extended into the branch vessel, causing branch ring  32  to at least partially cover the inner surface of the branch vessel on the proximal side. The distal end of strut  42  of branch ring  32  extends further into the branch vessel than the distal ends of struts  40 ,  44  because strut  42  is longer in this embodiment than adjacent struts  40 ,  44 . In this regard, a generally tapered, straight or linear profile along the distal perimeter of branch portion  30  is created when branch portion  30  is expanded into the branch vessel. 
     Referring to  FIGS. 11 and 12 , schematic views are shown of stents  12 ,  29  of  FIGS. 5 and 9 , respectively, in the expanded state as implemented at a blood vessel bifurcation. As shown in  FIG. 11 , stent  19  of the embodiment of  FIG. 8  has a generally curved or radial profile along the distal perimeter  45  of branch portion  30  as it extends into branch vessel  4 . The generally curved or radial profile is due to the particular geometry of branch portion  30  of stent  19  of the embodiment of  FIG. 8 . In particular, because all of the branch ring struts  36  of branch ring  32  are of equal length in this embodiment, the distal ends of struts  36  radially expand equidistantly into branch vessel  4 , thereby creating a generally curved or radial profile along the distal perimeter  45  of branch portion  30 . Referring to  FIG. 12 , stent  29  of the embodiment of  FIG. 9  has a generally tapered, straight or linear profile along the distal perimeter  47  of the branch portion  30  of the stent as it extends into branch vessel  4 . The generally straight or linear profile in  FIG. 12  is a result of the particular geometry of branch portion  30  of stent  29  of the embodiment of  FIG. 9 . In particular, because central strut  42  of branch ring  32  is longer in this embodiment than struts  40 ,  44  adjacent to strut  42 , the distal end of strut  42  extends further into branch vessel  4  than the distal ends of struts  40 ,  44 , as best seen in  FIG. 10 , thus creating a generally tapered, straight or linear profile along the distal perimeter of branch portion  30 . In a preferred embodiment, the linear profile is at a right angle with respect to the axis of branch vessel  4 . In alternative embodiments, however, the linear profile may be at any angle with respect to the axis of branch vessel  4 . One advantageous feature of the linear profile along the distal perimeter of branch portion  30  shown in  FIG. 12  is that if a second stent  51  were to be used in branch vessel  4 , the linear profile facilitates better alignment with the second stent and permits coverage of a larger surface area of the branch vessel wall. For example, if a second stent  51  were to be used in combination with stent  12  of  FIG. 11 , gaps may exist between the two stents at the interface between the radial distal perimeter  45  and an abutting straight or linear edge of a second stent, whereas a close abutting interface may be achieved with stent  29  of  FIG. 12 . 
     Referring to  FIG. 13 , another embodiment of stent  39  is shown having an alternative embodiment of a branch portion  30  similar to that of the embodiment of  FIG. 9 , except lateral branch ring struts  48  and  50  are longer than the other branch ring struts  36 , and the proximal ends  52  of branch ring struts  48 ,  50  extend proximally beyond the other branch ring struts into a space between the branch ring  32  and the adjacent circumferential ring  28 . Branch ring struts  48 ,  50  have proximal ends  52  free from connectors and provide less resistance to movement of branch ring  32  during outward expansion with respect to stent body  14 . In this regard, the longer lateral branch ring struts  48 ,  50  function similar to a hinge and further facilitate extension of branch ring portion  30  outwardly, which may accommodate a branch vessel disposed at a greater angle  11  ( FIG. 1 ) as compared to stent  29  of the embodiment of  FIG. 9 . Again, since struts  40 ,  42 , and  44  are longer than branch ring struts  36 , they are more flexible and provide more coverage of a vessel wall than the embodiment depicted in  FIG. 8 . 
     Referring now to  FIGS. 14 and 15 , another embodiment of stein  49  is shown having a stent body  14  that has a Longitudinal section  53  that has a different pattern than main pattern  54 . Longitudinal section  53  comprises a generally repeatable series of struts  56  and connectors  58  that are smaller in dimension than struts  24  and connectors  26 , but are formed into a similar geometrical pattern as main pattern  54 . In this regard, the struts  56  are more numerous per area within rings  28 , and rings  28  are more numerous per area in section  53  because the length of struts  56  is shorter than the length of struts  24  and the length of connectors  58  is shorter than the length of connectors  26 . In a preferred embodiment, the same number of connectors  58  extend between adjacent rings  28 ; however, because the struts are more numerous in longitudinal section  53 , connectors  58  extend longitudinally between every other strut of adjacent rings  28 . As shown in  FIG. 15 , stent  49  Thither includes a branch portion  30  positioned within section  53 . Branch portion  30  comprises a branch ring  32  adjacent an opening  34 . Opening  34  is formed by an absence of at least one connector  58  adjoining branch ring  32  with branch opposing ring  33 . In a preferred embodiment, two adjacent connectors are absent; however, in alternate embodiments any number of connectors maybe absent to create opening  34 . In this embodiment, branch ring  32  is substantially similar geometrically to circumferential rings  28  and comprises branch ring struts  36  substantially similar to struts  56 ; however, a plurality of adjacent struts are free from a connectors  58  adjacent opening  34  and branch ring  32  is at least partially detachable from stent body  14  at opening  34  to facilitate at least a portion of branch ring  32  to extend outwardly with respect to stent body  14 . The generally smaller struts and connectors of longitudinal section  53  provide for freer movement of the strut and connector material and facilitate conformance to a vessel wall. The smaller struts and connectors also provide for a relatively more dense surface area coverage of the branch vessel wall, which may be advantageous in achieving a more uniform coverage around the ostium. In particular, this embodiment may provide particularly advantageous coverage of a geometrically complex obstruction in a bifurcation vessel since the relatively small pattern may flex or contour around the obstruction and provide coverage therefor. Also, this embodiment is advantageous for relatively small obstructions as the smaller pattern may cover more surface area of obstruction. 
     Referring to  FIG. 16 , another embodiment of stent  59  is shown and includes an alternate branch portion  30  comprising a portion of three adjacent branch ring sections  60 ,  62 ,  64  connected and extending circumferentially from two adjacent circumferential rings  28 . Branch ring sections  60 ,  62 ,  64  each includes a plurality of branch struts  66  and are connected in the longitudinal direction by branch connectors  68 . Struts  66  are shorter longitudinally than struts  24  of rings  28  and connectors  68  are smaller than connectors  26 . The distal ring  60  is adjacent opening  34  and the distal ends of struts  66  of ring  60  are detachable from stent body  14  at opening  34  to permit extension of at least a portion of branch ring sections  60 ,  62 ,  64  to expand outwardly with respect to stent body  14 . In this embodiment, the three branch ring sections  60 ,  62 ,  64  may extend outwardly in a more radial fashion and this branch portion  30  may be particularly advantageous for adapting or conforming to the shape of the proximal side of the ostium. Furthermore, the branch portion of this embodiment may more readily extend or flex around an obstruction in a bifurcation vessel such as the one depicted in  FIG. 1  while providing branch wall coverage and better blood flow to the branch vessel. 
     Referring to  FIGS. 17 and 18 , an alternate embodiment of stent  69  is shown and includes an alternate branch portion  30 . In this particular embodiment, branch portion  30  comprises support struts  70  and an expandable ring  72 . Branch portion  30  defines at least one side opening  74 . In one embodiment, the dimensions of the cell defining side opening  74  are such that the side opening  74  (prior to expansion of the stent) is larger than other openings in stent body  14 . The presence of side opening  74  is generally configured to accommodate a side sheath therethrough and allow a physician to access a branch vessel during or after a procedure. In a particular embodiment, as shown in  FIG. 17 , side opening  74  is surrounded by expandable ring  72  of continuous material. In alternative embodiments, expandable ring  72  comprises unattached portions, or one portion that only partially covers side opening  74 . A series of support struts  70  connect expandable ring  72  with struts  24  and connectors  26 . Support struts  70  preferably comprise patterns in a folded or wrap-around configuration that at least partially straighten out during expansion, allowing expandable ring  72  to protrude into the branch vessel. 
     In this embodiment, when stent  69  is expanded, as shown in  FIG. 18 , branch portion  30  is extended into the branch vessel, causing expandable ring  72  to at least partially cover the inner surface of the branch vessel. Thus, in a preferred embodiment, the stent coverage in a portion the branch vessel includes the full circumference of the inner branch vessel wall. In alternative embodiments, partial coverage or several sections of coverage are present. 
     Referring to  FIGS. 19–21 , another embodiment of a stent  79  is shown having a main stent body  14  and another embodiment of a branch portion  30 .  FIGS. 19 and 20  show stent  79  in the unexpanded condition where branch portion  30  has not been deployed.  FIG. 21  shows the stent  79  in the expanded configuration where the branch portion  30  has been expanded. As shown, main stent body  14  includes a main stent pattern having a generally repeatable ring  28  and connector  26  pattern. Branch portion  30  and the surrounding midsection  80  interrupt the repeatable ring  28  and connector  26  pattern of stent  79 . In this embodiment, branch portion  30  is configured to be both radially expandable and longitudinally extendable into the branch vessel and relative to its longitudinal axis  83  so that, in a preferred embodiment, the branch portion  30  contacts the entire periphery or circumference of the inner wall of the branch vessel in the expanded configuration. In this regard, branch portion  30  preferably provides 360° coverage of the wall of the branch vessel. That is, branch portion  30  can be extended outward with respect to longitudinal axis  81  of stent  79 , and can also be expanded radially about axis  83  so as to contact the vessel (thereby allowing it to be adjustable with respect to vessel size). 
     Referring to  FIG. 20 , an enlarged view of section  80  of stent  79  is shown. In a preferred embodiment, a structural support member  84  may be provided as a transition between the main stent body  14  and branch portion  30 . In one aspect of a preferred embodiment, structural support member  84  may be elliptical to accommodate branch vessels extending at an angle to the main vessel. In alternate embodiment, other shapes of support member  84  can be used to accommodate the vasculature. The structural support member  84  may include a continuous ring. In this embodiment, structural support member  84  is a full, non-expandable ring and it does not expand radially beyond a particular circumference. 
     As shown in  FIGS. 19 and 20 , two concentric rings, inner ring  86  and outer ring  88 , are positioned within structural support member  84  and surround a generally circular central branch opening  34  to provide access to the side branch vessel when stent  79  is in the unexpanded condition. Rings  86  and  88  are interconnected by a plurality of inner connectors  90 . Outer ring  88  is connected to structural support member  84  by a plurality of outer connectors  92 . Rings  86  and  88  are generally curvilinear members. For example, rings  86 ,  88  can be defined by undulation petals, prongs, or peaks  94 . In a preferred embodiment, each ring  86 ,  88  have the same number of undulation peaks  94 , but the inner ring may be more closely or tightly arranged, as shown. In another preferred embodiment, each ring  86 ,  88  has eight pedals or undulation peaks  94 , although in alternate embodiments each ring can have any number of undulation peaks, and the number of peaks need not be equal for each ring. The undulation peaks  94  generally include a pair of strut portions  96  interconnected by curved portions  98 , and the strut portions themselves are connected to adjacent strut portions by another curved portion. In a preferred embodiment, eight outer connectors  92  extend between structural support member  84  and outer ring  88 , and each outer connector  92  is attached at one end to approximately the middle of a strut portion  96  of outer ring  88  and the structural support member  84  at the other end. As shown, outer connectors  92  may also have an undulated shape, although in alternate embodiments outer connectors  92  may have differing shapes. In another aspect of the preferred embodiment, outer connectors  92  may be evenly or symmetrically spaced about the structural support member  84 . The inner ring  86  is attached to the outer ring  88  by a plurality of inner connectors  90  and, in a preferred embodiment, eight inner connectors  90  connect the rings. Inner connectors  90  extend from curved portion  98  of outer ring  88  to curved portion of inner ring  86 . As shown in  FIG. 20 , in a preferred embodiment, inner connectors  90  have a simple curved shape. Other quantities, configurations, sizes and arrangements of connectors, rings and spacing can be used depending upon the desired results. Varying the connectors can provide for different amounts of flexibility and coverage. The type of configuration of rings and connectors shown addresses the need for radial and longitudinal expansion of branch portion  30 , as well as branch vessel coverage. Other configurations and arrangements for the branch portion can be used in accordance with the invention. 
     Referring again to  FIGS. 19 and 20 , the stent pattern surrounding branch portion  30  may be modified with a different pattern to accommodate branch portion  30 , as can all of the aforementioned embodiments. In particular, the rings  28  in the midsection  80  may be configured and dimensioned to be denser to provide sufficient coverage and flexibility to compensate for the area occupied by branch portion  30 . 
     Referring now to  FIG. 21 , stent  79  is shown in the expanded configuration, with branch portion  30  deployed. Upon expansion of branch portion  30 , the inner and outer rings  86 ,  88  shift about the longitudinal branch axis  83  and expand laterally away from the main stent body  14  and into the branch vessel to form a branch coverage portion. Upon expansion, the outer connectors  92  can move outwardly and the inner connectors  90  can straighten to a position substantially parallel to longitudinal branch axis  83 . In a preferred embodiment, the expanded rings  86 ,  88  have substantially the same expanded diameter, although in alternate embodiments rings  86 ,  88  could also have different diameters to accommodate a tapered vessel, if, for example a tapered balloon is used. The branch portion  30  can be extended at different angles to the longitudinal axis  81  of the stent depending upon the geometry of the branch vessel being treated. In this embodiment, the branch portion  30  may preferably extend into the branch vessel about 1.5–3 mm. 
     Referring now to  FIG. 22 , another embodiment of a stent  89  is shown having a main stent body  14  and another embodiment of a branch portion  30 . Stent  89  is substantially similar to stent  79 , except stent  89  has a discontinuous support member  104  surrounding a two concentric ring  86 ,  88  structure. Support member  104  has a generally elliptical shape and includes a plurality of discontinuities  106  along the perimeter. The configuration of the discontinuous support member facilitates additional flexibility of the branch portion during expansion and generally provides for accommodating a greater range of branch vessel geometries. In one aspect of a preferred embodiment, structural support member  104  may be elliptical to accommodate branch vessels extending at an angle to the main vessel. 
     Referring to  FIGS. 23 and 24 , another embodiment of a stent  99  is shown in the unexpanded and expanded states, respectively. Stent  99  comprises a main stent body  14  and another embodiment of a branch portion  30 . Stent  99  is substantially similar to stent  79 , except stent  99  has a branch portion  30  including a support member  108  surrounding three concentric rings: a first ring  110 , a second ring  112 , and a third ring  114  instead of two. First ring  114  is connected to the support member  108  by an outer or first connector  92 . The first ring  114  defines a complete circuit which extends without interruption from the first side or clockwise side  92 ′ of the first connector to the second side or counterclockwise side  92 ″ of the first connector  92 . The second ring  112  is connected to the first ring  114  by an inner or second connector  90 . As with the first ring  114 , the second ring  112  defines a complete circuit which extends without interruption from the first side or clockwise side  90 ′ of the second connector  90  to the second side or counterclockwise side  90 ″ of the second connector  90 . As can be seen in  FIG. 24 , when stent  99 is expanded the three concentric ring structure of this embodiment facilitates additional branch wall support because a generally more dense pattern is created in branch portion  30  wit the addition of another concentric ring. 
     In all of the above embodiments, the branch portion  30  protrudes into the branch vessel when the stent is fully expanded. The branch portion upon expansion can extend into the branch vessel in different lengths depending upon the application. The amount of extension may vary in a range between about 0.1–10.0 mm. In one preferred embodiment, the length of extension is 1–3 mm. In another preferred embodiment, the length of extension is approximately 2 mm. In alternative embodiments, the amount of extension into the branch vessel may be variable for different circumferential segments of branch portion  30 . As shown in each of the embodiments, the branch portion is approximately 2.5 mm in width and about 2.5–3.0 mm in length. However, the branch portion can be dimensioned to accommodate varying size branch vessels. The branch portion can be formed of any tubular shape to accommodate the branch vessel, including, oval or circular, for example. 
     In general, a wide variety of delivery systems and deployment methods may be used with the aforementioned stent embodiments. For example, a catheter system may be used for insertion and the stent may be balloon expandable or self-expandable, or the stent may be balloon expandable and the branch portion self-expandable, or vice versa. Once the stent is in position in the main vessel and the branch portion is aligned with the side branch the stent can be expanded. If the stent is balloon expandable, the stent may be expanded with a single expansion or multiple expansions. In particular, the stent can be deployed on a stent delivery system having a balloon catheter and side sheath as described, for example, in U.S. Pat. Nos. 6,325,826 and 6,210,429, the entire contents of which are incorporated herein by reference. In one preferred embodiment, a kissing balloon technique may be used, whereby one balloon is configured to expand the stent and the other balloon is configured to extend branch portion  30 . After the main portion of the stent is expanded in the main vessel, the stent delivery system may be removed and a second balloon may be passed through the side hole in the branch portion and expanded to expand the branch portion of the stent. In an alternate embodiment, the same balloon may be inserted in the main vessel inflated, deflated, retracted and inserted into the branch vessel, and then reinflated to expand branch portion  30  and cause it to protrude into the branch vessel. Alternatively, the stent can be delivered on two balloons and the main portion and the branch portion can be expanded simultaneously. As needed, the branch portion can be further expanded with another balloon or balloons. Yet another alternative is to use a specially shaped balloon that is capable of expanding the main and branch portions simultaneously. The stent can also be deployed with other types of stent delivery systems. Alternatively, the stent, or portions of the stent, can be made of a self-expanding material, and expansion may be accomplished by using self-expanding materials for the stent or at least branch portion  30  thereof, such as Nitinol, Cobalt Chromium, or by using other memory alloys as are well known in the prior art. 
     The construction and operation of catheters suitable for the purpose of the present invention are further described in U.S. patent application Ser. No. 09/663,111, filed Sep. 15, 2000, which is a continuation-in-part of U.S. patent application Ser. No. 09/614,472, filed Jul. 11, 2000, which is a continuation-in-part of U.S. patent application Ser. No. 09/325,996, filed Jun. 4, 1999, and Ser. No. 09/455,299, filed Dec. 6, 1999, the disclosures of all of which are incorporated herein by reference. It should be noted that the catheters taught in the above applications are exemplary, and that other catheters that are suitable with the stents of the subject application are included within the scope of the present application. In alternative embodiments, catheters without balloons may be used. For example, if the stent is comprised of memory alloy such as Nitinol or Cobalt Chromium, or is a mechanically self-expanding stent, balloons are not necessarily included on the catheters. Furthermore, any other catheter, including ones that are not disclosed herein, may be used to position stents according to the present invention. 
     Referring now to  FIGS. 25–28 , illustrations of the steps of one example of a method for employing a stent according to the invention are shown. By way of example, the method is depicted utilizing stent  12 . Methods for positioning such a catheter system within a vessel and positioning such a system at or near a bifurcation are described more fully in co-pending U.S. patent application Ser. No. 10/320,719 filed on Dec. 17, 2002, which is incorporated herein by reference in its entirety. As shown in  FIG. 25 , a catheter system  120  is positioned proximal to a bifurcation, using any known method. A branch guidewire  122  is then advanced through an opening in the stent and into the branch vessel  4 , as shown in  FIG. 26 . In a preferred embodiment, the opening may be a designated side branch opening, such as an opening formed by the absence of some connectors  26 , as described above. Branch portion  30  is adjacent the opening. As shown in  FIG. 27 , if the side sheath  124  is attached to the main catheter  120 , the main catheter  120  is advanced along with the side catheter  124 . Alternatively, if the side sheath  124  is separate from to the main catheter  120 , the second catheter or side sheath  124  is then advanced independently through the opening in the stent and into the branch vessel. Branch portion  30  is positioned over a portion of the lumen of the branch vessel  4  as the side sheath  124  is inserted into branch vessel  4 . Referring to  FIG. 28 , a first balloon  126  located on main catheter  120  is then expanded, causing expansion of the stent body, and a second balloon  128  located on the second catheter or side sheath  124  is also expanded, causing branch portion  30  to be pushed outward with respect to the stent body, thus providing stent coverage of at least a portion of the branch vessel. The balloons are then deflated and the catheter system and guidewires are then removed. 
     Referring now to  FIGS. 29–31 , illustrations of the steps of another method for employing a stent of the present invention is shown. By way of example, the method is depicted utilizing stent  12 . The depicted method may be accomplished using a catheter system having a main catheter  131  including a herniated balloon  135  ( FIG. 32 ). In particular, the stent can be deployed on a stent delivery system having a herniated balloon as described, for example, in U.S. Patent Application No. 60/488,006, filed Jul. 18, 2003, the entire contents of which are incorporated herein by reference. As shown in  FIG. 29 , the catheter  131  includes a balloon  135  that has a protruding portion  137  that protrudes outwardly from the cylindrical outer surface  134  of the balloon. 
     Referring to  FIG. 32 , the herniated balloon  135 , shown in an expanded state, has a generally cylindrical shape and the protruding portion  137  can be any appendage or integral portion of the balloon that moves outwardly from the outer surface  134  of the balloon upon inflation, in accordance with the principles of the invention. In a preferred embodiment, the protruding portion  137  is a portion of the balloon wall that has greater expandability than other portions of the balloon wall that retain a generally cylindrical shape. In another embodiment, protruding portion  137  may be a solid structure attached to the balloon wall. The protruding portion  137  can have any shape desirable to effect deployment of branch portion  30 . In one preferred embodiment, protruding portion  137  has a hemispherical shape. In another preferred embodiment, protruding portion  137  has an ovoid shape. In use, the stent  12  is crimped onto the balloon  135  so that the protruding portion  137  is positioned at the branch portion. As shown, the protruding portion  137  is positioned adjacent or alongside the radially inward side of branch portion  30 . The herniated balloon  135  is used to expand the branch portion  30  and/or deploy the outwardly deployable structure of stent  12  by applying a force in the laterally outward direction to the expandable elements by deflecting these elements toward the side branch  4 . The protruding portion  137  may be located at any position along the length of the balloon. For example, it can be located on the middle ⅓ of the stent. 
     In one embodiment, the balloon may be constructed of composite materials. For example, a combination of elastomeric and semi to non compliant materials such as urethane, silicone, and latex, (Elastomeric) polyethylene hytrel pebax polyarylethertherketone, polyoxymethylene, polyamide, polyester thermoplastic polyetheretherketone and polypropylene (semi to non compliant), may be used. The balloon may also be constructed by combining the above-mentioned materials with woven textiles such as Kevlar, silk cotton, wool, etc. In this construction, a textile is wound or woven onto a rod that has the shape of the desired herniated balloon and the polymer is then extruded or dip coated over the rod. The composite is cured, heat set or adhesively fused together. The rod is then removed and the remaining shape is a herniated balloon. The balloon can also be constructed by adding an appendage to a conventional balloon by using a molded collar or adhesively attaching an object to the surface of the balloon or by using a mound of adhesive to create the herniation or protruding portion. In an alternate embodiment, the balloon can be constructed by molding three small balloons and attaching them in tandem with the center balloon being round in shape. The balloon would share a common inflation port. When the balloon is inflated the center balloon becomes the herniation. 
     Referring again to  FIGS. 29–32 , protruding portion  137  may be configured to fit directly into an opening in the stent. As shown in  FIG. 29 , catheter  131  is advanced over a guidewire  133  and positioned proximal to the bifurcation. As shown in  FIG. 30 , the catheter is advanced until the protruding portion  137  of the balloon is positioned at the bifurcation. In one embodiment, protruding portion  137  protrudes outwardly from catheter  131  enough so that it actually comes into contact with the bifurcation, thus providing a method of alignment wit the branch vessel  4 .  FIG. 31  shows that as the balloon  135  is expanded, it simultaneously causes the stent to expand and branch portion  30  to be pushed toward the branch vessel  4 . Upon inflation of the balloon, the herniated portion  137  expands and extends through the branch portion  30  toward the side branch to open the entrance of the occluded side branch artery.  FIG. 32  shows a perspective view of the herniated balloon  135  extending along a main vessel axis  136 . 
     In an alternative method, the stent can be delivered using a herniated balloon and a dual lumen delivery system. This system can include a main catheter defining a first lumen with concentric guidewire lumen and balloon inflation lumen, a herniated balloon, as described above, on the main catheter, a side sheath with a guidewire lumen, and a stent. The stent is crimped over the main catheter, balloon and side sheath with the side sheath exiting the stent through a branch opening or side hole. The distal end of the side sheath is used for aligning the stent branch opening with the branch vessel  4 . 
     In another embodiment, the appendage or herniation may be located on a second catheter or side sheath of the delivery system, such as the system  138  depicted in  FIG. 33 . In this case, the system is a two-balloon system. The smaller balloon  140  can be positioned in the stent in a similar manner as the herniation. The appendage or herniation may have an inflation lumen  141  and a lumen for receiving a guidewire  142  for locating the branch vessel  4 . 
     One particular application for the use of a stent with a branch portion  30  such as the one described above is for localized drug delivery. As was discussed hereinabove, restenosis, including in-stent restenosis, is a common problem associated with medical procedures involving the vasculature. Pharmaceutical agents have been found to be helpful in treating and/or preventing restenosis, and these are best delivered locally to the site of potential or actual restenosis, rather than systemically. 
     As used herein, the term “preventing” includes stopping or reducing the occurrence or severity of a disease or condition or the symptoms of the disease or condition. 
     As used herein, the term “treating” includes substantially reducing the severity of a disease or condition or the symptoms of the disease or condition, or substantially reducing the appearance of a disease or condition or the symptoms of the disease or condition. The term “treating” includes substantially completely abolishing a disease or condition or the symptoms of the disease or condition. The term “treating” also encompasses preventing, stopping, or reducing the occurrence or severity of a disease or condition or the symptoms of the disease or condition. 
     When—as with anti-restenosis drugs, for example—a drug is useful primarily at a particular body site, systemic administration is not necessary and is often undesirable. For instance, systemic administration of drugs often results in undesirable side effects. Also, it is difficult to achieve constant drug delivery to a site needing treatment using systemic delivery methods. Drugs administered systemically often cycle through concentration peaks and valleys, resulting in time periods of toxicity and ineffectiveness. In contrast, drugs delivered in a localized manner can be delivered at a high concentration at the site(s) where treatment is needed, while minimizing the systemic concentration of the drug, thus minimizing or eliminating side effects. Additionally, localized delivery facilitates the maintenance of appropriate drug levels at the treatment site, with minimal undesired fluctuation. 
     Stents according to the present invention may have one or more drug depots on and/or in the stent wall. As used herein, the term “depot” describes a store of at least one drug designed to retain and thereafter release the drug(s). According to current technology, materials incorporating drug(s) are often associated with stents by coating the drug-containing material(s) onto the walls of the stents. Thus, “coating” is referred to and used herein in describing the depot(s), but this use is solely for convenience of explanation and is in no way limiting, and other methods of associating drug(s) with stents that are currently available or that may become available are specifically contemplated. As another non-limiting example, as is discussed further hereinbelow, stents may be “seeded” with genetically engineered cells that secrete or otherwise release drug(s). As yet another non-limiting example, biocompatible polymers incorporating drug(s) may be molded into a solid mass of a desired size and shape and attached to the stent using pharmaceutically acceptable methods. 
     The term “depot” refers generally to an area of a stent that is coated or otherwise associated with drug(s) or a material incorporating drug(s). Any given depot is generally discrete from other depots. For example, in certain embodiments, a depot may consist of a discrete mass of material incorporating drug(s). As another example, because the walls of stents according to the present invention comprise open spaces, a depot may also include spaces. A depot may include open spaces, for example, in embodiments where drug(s) or a material incorporating drug(s) is coated or seeded onto a stent to form the depot. One depot may abut, or be adjacent to a second depot, but the second depot will generally have different drug(s) and/or different concentration(s) of drug(s), as is discussed in further depth hereinbelow. 
     It will be understood that depot(s) of stents according to the present invention can be “on” or “in” the stent walls. For example, where it is desired to release drugs(s) primarily to the cells of the vessel walls at the site of placement of a stent, it may be desirable to coat, attach a drug-containing mass, or otherwise associate drug(s) with only the outer side of the stent wall. As another example, when it is desired to deliver drug(s) to an organ, tissue, or region of the body downstream from a stent, it may be desirable to coat, attach a drug-containing mass, or otherwise associate drug(s) with only the inner side of the stent wall. In still other embodiments, it may be desirable to coat, attach a drug-containing mass, or otherwise associate drug(s) with the inner side of the stent wall, the outer side of the stent wall, and/or the portions of the stent wall that face inward to the open spaces within the wall. 
     The terms “drug,” “drug compound,” and “pharmaceutical agents” are used interchangeably herein, unless stated otherwise. These terms are meant to be construed broadly, to mean pharmaceutically acceptable substances (i.e., substances that are safe for use in the body of a mammal such as a human) and that have some biological effect on cells of the body. The terms also include substances that are being tested for safety for use in the body of a mammal such as a human and/or to determine whether (or what) biological effect they have on cells of the body. Examples of types of molecules that may be drugs as the term is defined herein include, but are not limited to, proteins and peptides, small molecules, antibodies, multi-cyclical molecules, macrolides, and nucleic acids. The general and specific examples provided herein, as well as similar substances, are included in the term “drugs” according to the present invention. 
     Depots of stents according to the present invention are capable releasing, or eluting, the stored drug(s). Hence, the depots of the present invention can be made of any material that can entrap, encapsulate, adhere, or otherwise retain and thereafter release the stored drug(s). Depots of stents according to the present invention are preferably capable of controllably releasing drug(s). Hence, the depots of the present invention are preferably made of any material that can entrap, encapsulate, adhere or otherwise retain and controllably release the stored drug(s). 
     The phrases “controllably release”, “controllable release,” and “controllably releasing” are used herein to describe a release of drug(s) at a predetermined rate and duration under selected conditions. Slow release is one form of controllable release. 
     In certain preferable embodiments, depots of the present invention comprise one or more biocompatible polymer(s) loaded with drug(s). In certain embodiments, the biocompatible polymer utilized minimizes irritation to the wall of the lumen where the stent is implanted. Methods for incorporating biocompatible polymers loaded with drug(s) into or onto stents generally involve coating the stent with the polymer(s) and are well known in the art. See, e.g., U.S. Pat. No. 5,679,400. 
     Several configurations for loading drug(s) into biocompatible polymers are envisaged by the present invention. The drug(s) may be, for example, molded into the polymer, entrapped or encapsulated within the polymer, covalently attached to the polymer, physically adhered to the polymer, or otherwise incorporated into the biocompatible polymer. 
     The biocompatible polymer may be, for example, either a biostable polymer or a biodegradable polymer, depending on factors such as the desired rate of release or the desired degree of polymer stability under physiological conditions. 
     Biodegradable polymers that are usable in the context of the present invention include, without limitation, poly(L-lactic add), polycaprolactone, poly(lactide-co-glycolide), poly(hydroxybutyrate), poly(hydroxybutyrate-co-valerate), polydioxanone, polyorthoester, polyanhydride, poly(glycolic acid), poly(D,L-lactic acid), poly(glycolic acid-co-trimethylene carbonate), polyphosphoester, polyphosphoester urethane, poly(amino acids), cyanoacrylates, poly(trimethylene carbonate), poly(iminocarbonate), copoly(ether-esters) (e.g. PEO/PLA), polyalkylene oxalates, polyphosphazenes and biomolecules such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronic acid. 
     Biostable polymers that are usable in the context of the present invention include, without limitation, polyurethanes, silicones, polyesters, polyolefins, polyisobutylene, ethylene-alphaolefin copolymers; acrylic polymers and copolymers, vinyl halide polymers and copolymers, such as polyvinyl chloride; polyvinyl ethers, such as polyvinyl methyl ether; polyvinylidene halides, such as polyvinylidene fluoride and polyvinylidene chloride; polyacrylonitrile, polyvinyl ketones; polyvinyl aromatics, such as polystyrene, polyvinyl esters, such as polyvinyl acetate; copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and ethylene-vinyl acetate copolymers; polyamides, such as Nylon 66 and polycaprolactam; alkyd resins; polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins; polyurethanes; rayon; rayon-triacetate; cellulose, cellulose acetate, cellulose butyrate; cellulose acetate butyrate; cellophane; cellulose nitrate; cellulose propionate; cellulose ethers; and carboxymethyl cellulose. 
     In certain other embodiments, depot(s) on or in stents according to the present invention comprise liposomes into which drug(s) have been encapsulated or entrapped. Methods for incorporating liposomes loaded with drug(s) into or onto stents generally involve coating the stent with the polymer(s) and are known in the art. See, e.g., Kallinteri P. et al. “Dexamethasone incorporating liposomes: an in vitro study of their applicability as a slow releasing delivery system of dexamethasone from covered metallic stents,”  Biomaterials  23(24): 4819–26 (2002). In yet other embodiments, depot(s) depot(s) on or in stents according to the present invention comprise genetically engineered cells that secrete or otherwise release desired drug(s), e.g., therapeutic protein(s). Methods for incorporating genetically engineered cells into or onto stents generally involve seeding the cells onto the stent and are known in the art. See, e.g., Dichek, D. A. et al., “Seeding of Intravascular Stents With Genetically Engineered Endothelial Cells”,  Circulation , 80: 1347–1353 (1989); Flugelman M. Y. et al., “Genetically engineered endothelial cells remain adherent and viable after stent deployment and exposure to flow in vitro,”  Circ Res ., 70: 348–54 (1992). 
     One or more depots may be present at any location in or on the walls of stents according to the present invention. Depot(s) may be utilized with any and all stents according to the present invention. Depot(s) may be present in or on the wall of the main vessel portion of stents according to the present invention. Similarly, depot(s) may be present in or on the wall of the branch portion of stents according to the present invention. The position of depot(s) depends on desired site(s) of highest concentration of drug delivery. 
     The size of depot(s) on or in stents of the present invention depends on various parameters, such as the material of which the stent body is fabricated, the permeability of the stent body and the depot, the efficacy of the depot in retaining the drug(s), the concentration of the drug(s), and the desired rate and duration of release of the drug(s). Depot(s) may extend around the entire, or only a portion of, the circumference of main vessel portions of stents according to the present invention. Likewise, depot(s) may extend longitudinally for all or only a portion of the length of main vessel portions of stents according to the present invention. With regard to branch portions of stents according to the present invention, depot(s) may cover all or only a portion of the walls, or may be in all or only a portion of the walls. 
     When it is desired to increase the overall volume of a depot, it may often be preferable to increase the length and/or width of the depot, rather than its thickness, or depth. In other words, it may often be preferable to increase the size of a depot along or within the wall of a stent, rather than extending the depot farther into the lumen of the stent. Depot(s) that extend too far into the lumen of a stent may impede fluid flow through the stent, and depots that are too thick on the outside wall may deform the stent into the vessel, also impeding fluid flow. However, it may be desirable to concentrate a large volume of depot in a small surface area, to maximize drug concentration to a small section of vessel. Contrariwise, it may in other instances be desirable to have drug(s) released along a large section of vessel, in which cases it may be desirable to use a depot that has a large surface area along or within a wall of the stent. 
     Thus, the length, width, and thickness of a depot are variables that can be tailored according to the desired drug distribution and the size of the main and branch vessels to be treated. For example, a depot that is thick enough to impede fluid flow in a narrow vessel may be an optimal thickness for a larger vessel. 
     Additionally, the concentration of drug(s) in a depot can be varied according to the desired rate of elution of the drug from the depot and the desired concentration of the drug in the local area of the depot. Thus, the parameters of depot length, width, and thickness and drug concentration can be varied to tailor depots to elute the desired concentration of drug(s) to the desired area(s) in vessels of varying sizes. 
     Non-limiting examples of anti-restenosis drugs that may be incorporated into depot(s) in or on stents according to the present invention include anticoagulant agents, antiproliferative agents, antimigratory agents, antimetabolic agents, anti-inflammatory agents, and immunosuppressive substances, and combinations thereof. Particularly useful anti-restenosis drugs include paclitaxel, rapamycin, and HDAC inhibitors. Examples of histone deacetylase (HDAC) inhibitors, which are efficient inhibitors of smooth muscle cell (SMC) proliferation, include, without limitation, hydroxamic acids such as trichostatin A (TSA), suberoyl anilide hydroxamic acid (SAHA), oxamflatin, m-carboxycinnamic acid bishydroxamide (CBHA), cyclic hydroxamic acid-containing peptide 1 (CHAP1), cyclic hydroxamic acid-containing peptide 31 (CHAP31), suberic bishydroxamate (SBHA), pyroxamide, and scriptaid. Further details pertaining to an HDAC inhibitors, their use, and stents incorporating same are disclosed in a U.S. Provisional Patent Application No. 60/397,780 assigned to a common assignee of the present invention, filed Jul. 24, 2002, entitled “STENTS CAPABLE OF CONTROLLABLY RELEASING HISTONE DEACETYLASE INHIBITORS,” incorporated by reference herein in its entirety. 
     In addition to anti-restenosis drugs, stents according to the present invention can also be used as vehicles for localized delivery of other drugs. As a non-limiting example, stents of the present invention are particularly useful in for localized delivery of anti-thrombotic drugs. Thrombosis (the formation of a thrombus, or blot clot) sometimes occurs in association with medical procedures involving the vasculature. For example, thrombosis may result from physical injury of an arterial wall by a vascular interventional procedure such as percutaneous transluminal coronary angioplasty (“PTCA”; a type of balloon angioplasty) or coronary bypass surgery. Although thrombosis can result in death, the procedures which may have thrombosis as a side effect are themselves are life-saving and widely used. Additionally, thrombosis may also result from progression of a natural disease, such as atherosclerosis. Accordingly, administration of anti-thrombotic drugs to patients who have undergone vascular procedures is often desirable. 
     Many anti-thrombotic drugs are known in the art. Non-limiting examples include aspirin (acetylsalicylic acid), prostaglandin E 1 , selective thromboxane A 2  inhibitors, selective thrombin inhibitors, platelet receptor GPIIb/IIIa blockers, tissue plasminogen activator, streptokinase, heparin, hirudin, bivalirudin, and kistrin and other platelet and/or thrombin inhibitors. As with anti-restenosis drugs, administration of anti-thrombotics locally to the site of potential thrombosis is usually vastly preferable to systemic administration. 
     Additional, non-limiting examples of types of drugs that may be incorporated into depot(s) in or on stents according to the present invention include antineoplastic, antimitotic, antiplatelet, antifibrin, antithrombin, antibiotic, antioxidant, and antiallergic substances as well as combinations thereof. 
     Depots for use in accordance with the present invention may include one or more different drug(s). For example, it will often be desirable to include two or more drugs that have additive, or even synergistic effects. Where more than one drug is incorporated into a single depot, it will be generally preferred to incorporate drugs that will not interfere with, degrade, destabilize, or otherwise interfere with one another. However, in some cases in may be desirable to include a first drug along with a second drug that reduces or alters the activity of the first drug in a desired manner. In the same manner, different depots may include different drugs, or different concentrations of the same drug. The many possible permutations allow for great flexibility in treatment. 
     Stents according to the present invention can be used as vehicles for localized delivery of drugs to cells of the walls of both the main and branch vessels at the location of the stent. Drugs that are particularly suitable for treatment of cells in the immediate area of the stent include anti-restenosis and anti-thrombotic drugs. If desired, different concentrations of drugs, or different drugs, may be included in depot(s) located in or on different areas of the stent walls. For example, it may be desirable to treat the cells of the main vessel with a first drug, combination of drugs, and/or concentration of drug(s) and to treat the cells of the branch vessel with a second, different, drug, combination of drugs, and/or concentration of drug(s). As another example, it may be desirable to maintain a high concentration of anti-restenosis drug(s) near the bifurcation of the vessels. As yet another non-limiting example, it may be desirable to maintain a high concentration of anti-restenosis drug(s) at the three open ends (two on the main portion and one on the branch portion) of the stent. It will be appreciated by one skilled in the art upon reading the present disclosure that many combinations of two or more depots are possible within the spirit and scope of the present invention. 
     Stents according to the present invention can be used as vehicles to deliver drug(s) to an organ, tissue, or region of the body downstream from the stent. For example, stents according to the present invention may be positioned in an artery that supplies blood to an organ, such as the heart, in a location close to that organ. Drug(s) that elute from the depot(s) in or on the stent may be carried by the blood flow to the organ. In this way, localized delivery to tissues, organs, and body regions can be achieved. Using stents according to the present invention, a first drug, combination of drugs, and/or concentration of drug(s), may be delivered to an organ, tissue, or region downstream from the main portion of the stent while a second, different, drug, combination of drugs, and/or concentration of drug(s) is delivered to an organ, tissue, or region downstream from the branch portion of the stent. This differential delivery can be accomplished by locating a depot having a first drug, combination of drugs, and/or concentration of drug(s) in or on an area of the main portion of the stent that is not contacted by blood flowing through the branch vessel, and locating a second depot having a second, different, drug, combination of drugs, and/or concentration of drug(s) in or on the branch portion of the stent. It will be appreciated by one skilled in the art upon reading the present disclosure that many combinations of two or more depots are possible within the spirit and scope of the present invention. 
     Specific, and non-limiting, examples of drugs that may be incorporated into depot(s) in or on stents according to the present invention include the following drugs. Examples of antineoplastic and/or antimitotic drugs include docetaxel (e.g., Taxotere® from Aventis S. A., Frankfurt, Germany) methotrexate, azathioprine, vincristine, vinblastine, fluorouracil, doxorubicin hydrochloride (e.g., Adriamycin® from Pharmacia &amp; Upjohn, Peapack N.J.), and mitomycin (e.g., Mutamycin® from Bristol-Myers Squibb Co., Stamford, Conn.). Examples of antiplatelet, anticoagulant, antifibrin, and antithrombin drugs include sodium heparin, low molecular weight heparins, heparinoids, hirudin, argatroban, forskolin, vapiprost, prostacyclin and prostacyclin analogues, dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor antagonist antibody, recombinant hirudin, and thrombin inhibitors such as Angiomax™ (Biogen, Inc., Cambridge, Mass.). Examples of cytostatic or antiproliferative drugs include angiopeptin, angiotensin converting enzyme inhibitors such as captopril (e.g., Capoten® and Capozide® from Bristol-Myers Squibb Co., Stamford, Conn.), cilazapril or lisinopril (e.g., Prinivil® and Prinzide® from Merck &amp; Co., Inc., Whitehouse Station, N.J.); calcium channel blockers (such as nifedipine), colchicine, fibroblast growth factor (FGF) antagonists, histamine antagonists, lovastatin (an HMG-CoA reductase inhibitor, brand name Mevacor® from Merck &amp; Co., Inc., Whitehouse Station, N.J.), monoclonal antibodies (such as those specific for Platelet-Derived Growth Factor (PDGF) receptors), nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitors, suramin, serotonin blockers, steroids, thioprotease inhibitors, triazolopyrimidine (a PDGF antagonist), and nitric oxide. An example of an antiallergic agent is permirolast potassium. Other therapeutic substances or agents that may be used include alpha-interferon and dexamethasone. The preventative and treatment properties of the foregoing therapeutic substances or agents are well-known to those of ordinary skill in the art. 
     The present invention also provides kits comprising a stent or stents according to the present invention. In addition to a stent or stents, a kit according to the present invention may include, for example, delivery catheter(s), balloon(s), and/or instructions for use. In kits according to the present invention, the stent(s) may be mounted in or on a balloon or catheter. Alternatively, the stent(s) may be separate from the balloon or catheter and may be mounted therein or thereon prior to use. 
     A stent for use in a bifurcated body lumen having a main branch and a side branch. The stent comprises a radially expandable generally tubular stent body having proximal and distal opposing ends with a body wall having a surface extending therebetween. The surface has a geometrical configuration defining a first pattern, and the first pattern has first pattern struts and connectors arranged in a predetermined configuration. The stent also comprises a branch portion comprised of a second pattern, wherein the branch portion is at least partially detachable from the stent body.