Abstract:
The present invention relates to tissue-supporting medical devices and drug delivery systems, and more particularly to tubular flexible stents that are implanted within a body lumen of a living animal or human to support the organ, maintain patency and/or deliver drugs or agents. The tubular flexible stent has a cylindrical shape defining a longitudinal axis and includes a helical section having of a plurality of longitudinally oriented strut members and a plurality of circumferentially oriented hinge members connecting circumferentially adjacent strut members to form a band. The band is wrapped about the longitudinal axis in a substantially helical manner to form a plurality of helical windings. At least one connector member extends between longitudinally adjacent helical windings of the band.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. Ser. No. 12/698,717, filed Feb. 2, 2010, which claims the benefit of U.S. Provisional Application, Ser. No. 61/149,244, filed Feb. 2, 2009, both of which are incorporated by reference in their entirety herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to tissue-supporting medical devices and drug delivery systems, and more particularly to expandable devices that are implanted within a body lumen of a living animal or human to support the organ, maintain patency and/or deliver drugs or agents. 
         [0004]    2. Summary of the Related Art 
         [0005]    In the past, permanent or biodegradable devices have been developed for implantation within a body passageway to maintain patency of the passageway and/or locally deliver drug or agent. These devices are typically introduced percutaneously, and transported transluminally until positioned at a desired location. These devices are then expanded either mechanically, such as by the expansion of a mandrel or balloon positioned inside the device, or expand themselves by releasing stored energy upon actuation within the body. Once expanded within the lumen, these devices, typically referred to as stents, become encapsulated within the body tissue and remain a permanent implant. 
         [0006]    Known stent designs include monofilament wire coil stents (U.S. Pat. No. 4,969,458); welded metal cages (U.S. Pat. Nos. 4,733,665 and 4,776,337); and, most prominently, thin-walled metal cylinders with axial slots formed around the circumference (U.S. Pat. Nos. 4,733,665, 4,739,762, and 4,776,337). Known construction materials for use in stents include polymers, organic fabrics and biocompatible metals, such as, stainless steel, gold, silver, tantalum, titanium, cobalt chromium and shape memory alloys such as Nitinol. 
         [0007]    U.S. Pat. Nos. 4,733,665, 4,739,762, and 4,776,337 disclose expandable and deformable interluminal vascular grafts in the form of thin-walled tubular members with axial slots allowing the members to be expanded radially outwardly into contact with a body passageway. After insertion, the tubular members are mechanically expanded beyond their elastic limit and thus permanently fixed within the body. The force required to expand these tubular stents is proportional to the thickness of the wall material in a radial direction. To keep expansion forces within acceptable levels for use within the body (e.g., 5-10 atm), these designs must use very thin-walled materials (e.g., stainless steel tubing with 0.0025 inch thick walls). However, materials this thin are not visible on conventional fluoroscopic and x-ray equipment and it is therefore difficult to place the stents accurately or to find and retrieve stents that subsequently become dislodged and lost in the circulatory system. 
         [0008]    Further, many of these thin-walled tubular stent designs employ networks of long, slender struts whose width in a circumferential direction is two or more times greater than their thickness in a radial direction. When expanded, these struts are frequently unstable, that is, they display a tendency to buckle, with individual struts twisting out of plane. Excessive protrusion of these twisted struts into the bloodstream has been observed to increase turbulence, and thus encourage thrombosis. Additional procedures have often been required to attempt to correct this problem of buckled struts. For example, after initial stent implantation is determined to have caused buckling of struts, a second, high-pressure balloon (e.g., 12 to 18 atm) would be used to attempt to drive the twisted struts further into the lumen wall. These secondary procedures can be dangerous to the patient due to the risk of collateral damage to the lumen wall. 
         [0009]    In addition, many of the known stents display a large elastic recovery, known in the field as “recoil,” after expansion inside a lumen. Large recoil necessitates over-expansion of the stent during implantation to achieve the desired final diameter. Over-expansion is potentially destructive to the lumen tissue. Known stents of the type described above experience recoil of up to about 6 to 12% from maximum expansion. 
         [0010]    Large recoil also makes it very difficult to securely crimp most known stents onto delivery catheter balloons. As a result, slippage of stents on balloons during interlumenal transportation, final positioning, and implantation has been an ongoing problem. Many ancillary stent securing devices and techniques have been advanced to attempt to compensate for this basic design problem. Some of the stent securing devices include collars and sleeves used to secure the stent onto the balloon. 
         [0011]    Another problem with known stent designs is non-uniformity in the geometry of the expanded stent. Non-uniform expansion can lead to non-uniform coverage of the lumen wall creating gaps in coverage and inadequate lumen support. Further, over expansion in some regions or cells of the stent can lead to excessive material strain and even failure of stent features. This problem is potentially worse in low expansion force stents having smaller feature widths and thicknesses in which manufacturing variations become proportionately more significant. In addition, a typical delivery catheter for use in expanding a stent includes a balloon folded into a compact shape for catheter insertion. The balloon is expanded by fluid pressure to unfold the balloon and deploy the stent. This process of unfolding the balloon causes uneven stresses to be applied to the stent during expansion of the balloon due to the folds causing the problem non-uniform stent expansion. 
         [0012]    It is desirable to provide flexibility in stents to facilitate introduction of the stent into vessels that are difficult to reach. Often, however, characteristics of the stent that provide longitudinal flexibility, which is desirable when introducing the stent into the vessel, can be disadvantageous in terms of keeping the stent in an expanded condition. For example, stents formed from interconnected rings with closed cell structures or generally diamond-shaped cells are typically less flexible than stents formed from one or more helices, but are usually more uniformly and consistently expandable than helical stents. It is desirable to provide a stent with substantial flexibility that is adapted to be expanded in a uniform and consistent fashion. 
         [0013]    In WO 03/015664, which is incorporated by reference, a stent having interconnected struts with openings for drug delivery is disclosed. However, elements for bridging the struts are generally thinner and spaced further apart than the struts. Thus, for such drug-eluting stents, the bridging element can provide an area of reduced or less consistent drug delivery. It is desirable to provide a drug-eluting stent in which areas of reduced or less consistent drug delivery can be reduced. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention relates to tissue-supporting medical devices and drug delivery systems, and more particularly to expandable, devices that are implanted within a body lumen of a living animal or human to support the organ, maintain patency and/or deliver drugs or agents. 
         [0015]    In one embodiment of the invention the flexible stent has proximal and distal end portions and a cylindrical shape, with luminal and abluminal surfaces and a thickness there between. The cylindrical shape defines a longitudinal axis. The flexible stent comprises a helical section having of a plurality of longitudinally oriented strut members and a plurality of circumferentially oriented hinge members connecting circumferentially adjacent strut members to form a band. The band is wrapped about the longitudinal axis in a substantially helical manner to form a plurality of helical windings. Each strut member has a substantially rectangular shape with opposing longitudinally oriented long sides and opposing circumferentially oriented short sides. Each hinge member is connected to the strut members along the short side of each strut member. At least one connector member extends between longitudinally adjacent helical windings of the band and is attached on each end to the short side of a strut member. The connector member not attached to the hinge members. 
         [0016]    In another embodiment of the invention the tubular flexible stent has a cylindrical shape with proximal and distal end portions and defining a longitudinal axis. The flexible stent comprises a helical section having of a plurality of longitudinally oriented strut members and a plurality of circumferentially oriented hinge members connecting circumferentially adjacent strut members to form a band. The band is wrapped about the longitudinal axis in a substantially helical manner to form a plurality of helical windings. The helical section comprises a proximal transition zone, a distal transition zone, and a central zone there between, each having a pitch and an incident angle, wherein the pitch and incident angle of the proximal and distal transition zones are different than the central zone. 
         [0017]    In still another embodiment of the present invention, the tubular flexible stent has a cylindrical shape with proximal and distal end portions and defining a longitudinal axis. The flexible stent comprises a helical section having of a plurality of longitudinally oriented strut members and a plurality of circumferentially oriented hinge members connecting circumferentially adjacent strut members to form a band. The band is wrapped about the longitudinal axis in a substantially helical manner to form a plurality of helical windings. The helical section further comprises strings formed from groups of contiguous strut members and hinge members organized to form a string pattern, wherein contiguous strings along the band have different string patterns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  is a perspective view of a flexible stent in the expanded (deployed) state according to one embodiment of the present invention. 
           [0019]      FIG. 1B  is a perspective view of a flexible stent in the crimped state according to one embodiment of the present invention. 
           [0020]      FIG. 1C  is a perspective view of a flexible stent in the “as cut” (manufactured) state according to one embodiment of the present invention. 
           [0021]      FIG. 2  is plan view of a flexible stent according to one embodiment of the present invention. 
           [0022]      FIG. 3  is an exploded plan view of the flexible stent of  FIG. 2 . 
           [0023]      FIG. 4A  is a close-up plan view of a strut from a flexible stent according to one embodiment of the present invention. 
           [0024]      FIG. 4B  is a close-up plan view of a strut from a flexible stent according to one embodiment of the present invention. 
           [0025]      FIG. 4C  is a close-up plan view of a strut from a flexible stent according to one embodiment of the present invention. 
           [0026]      FIG. 4D  is a close-up plan view of an organically optimized strut from a flexible stent according to one embodiment of the present invention. 
           [0027]      FIG. 5A  is a close-up plan view of a ductile hinge from a flexible stent according to one embodiment of the present invention. 
           [0028]      FIG. 5B  is a close-up plan view of a ductile hinge from a flexible stent according to one embodiment of the present invention. 
           [0029]      FIG. 6A  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0030]      FIG. 6B  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0031]      FIG. 6C  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0032]      FIG. 6D  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0033]      FIG. 6E  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0034]      FIG. 6F  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0035]      FIG. 6G  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0036]      FIG. 6H  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0037]      FIG. 6I  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0038]      FIG. 6J  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0039]      FIG. 6K  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0040]      FIG. 6L  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0041]      FIG. 6M  is a close-up plan view of a circular hinge region from a flexible stent according to one embodiment of the present invention. 
           [0042]      FIG. 7  is a close-up plan view of an index hinge from a flexible stent according to one embodiment of the present invention. 
           [0043]      FIG. 8  is a close-up plan view of the central zone depicted in  FIG. 3  to illustrate the incident angle of the helical band (wrap). 
           [0044]      FIG. 9A  is a close-up plan view of a connector strut string that is part of the repeating pattern that forms the central zone of the flexible stent illustrated in  FIG. 2  according to one embodiment of the present invention. 
           [0045]      FIG. 9B  is a close-up plan view of a free strut string that is part of the repeating pattern that forms the central zone of the flexible stent illustrated in  FIG. 2  according to one embodiment of the present invention. 
           [0046]      FIG. 10  is plan view of a flexible stent according to one embodiment of the present invention. 
           [0047]      FIG. 11  is an exploded plan view of the flexible stent of  FIG. 10 . 
           [0048]      FIG. 12  is plan view of a flexible stent according to one embodiment of the present invention. 
           [0049]      FIG. 13  is an exploded plan view of the flexible stent of  FIG. 12 . 
           [0050]      FIG. 14  is plan view of a flexible stent according to one embodiment of the present invention. 
           [0051]      FIG. 15  is an exploded plan view of the flexible stent of  FIG. 14 . 
           [0052]      FIG. 16  is a close-up plan view of the free strut string and the connector strut string that are part of the repeating pattern that form the central zone of the flexible stent illustrated in  FIG. 14  according to one embodiment of the present invention. 
           [0053]      FIG. 17  is a close-up plan view of the free strut string and the connector strut string that are part of the repeating pattern that form the central zone of the flexible stent illustrated in  FIG. 12  according to one embodiment of the present invention. 
           [0054]      FIG. 18  is a close-up plan view of the free strut string and the connector strut string that are part of the repeating pattern that form the central zone of the flexible stent illustrated in  FIG. 10  according to one embodiment of the present invention. 
           [0055]      FIG. 19  is a plan view of a flexible stent without depots according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0056]    The stent of the present invention is very flexible and deliverable, while still providing sufficient radial strength to maintain vessel patency. The stent can be formed in any suitable manner, such as by laser cutting a tube made from a suitable material, including cobalt chromium alloys, stainless steel alloys or nickel titanium alloys. Although coronary flexible stents of the present invention are disclosed to illustrate one embodiment of the present invention, one of ordinary skill in the art would understand that the disclosed invention can be equally applied to other locations and lumens in the body, such as, for example, vascular, non-vascular and peripheral vessels, ducts, and the like. 
         [0057]    In accordance with one aspect of the present invention, the flexible stent is designed to be crimped down to a reduced diameter and percutaneously delivered through a body lumen to a target site by a delivery catheter. The target site may be, for example, a cardiac artery. Once deployed the flexible stent functions to maintain vessel patency and, if desired, deliver controlled amounts of drug or agent. 
         [0058]    Perspective views of a flexible stent  100  in the expanded (deployed), crimped, and “as cut” or manufactured state according to one embodiment of the present invention are illustrated in  FIGS. 1A ,  1 B and  1 C respectively. The stent  100  has an “as cut” diameter when first manufactured of D 3 , as illustrated in  FIG. 10 . The stent  100  is crimped down to a first diameter D 1 , illustrated in  FIG. 1B , for insertion into a patient and navigation through the vessels, and a second diameter D 2 , illustrated in  FIG. 1A , for deployment into the target area of a vessel, with the second diameter being greater than the first diameter. 
         [0059]    The flexible stent  100  is cylindrical with a tubular configuration of structural elements having luminal and abluminal surfaces,  101 ,  102  respectively, and thickness (wall thickness) “T” there between. The cylindrical shape of the stent defines a longitudinal axis  103  and has proximal and distal ends portions  104 ,  105  respectively. 
         [0060]    The terms proximal and distal are typically used to connote a direction or position relative to a human body. For example, the proximal end of a bone may be used to reference the end of the bone that is closer to the center of the body. Conversely, the term distal can be used to refer to the end of the bone farthest from the body. In the vasculature, proximal and distal are sometimes used to refer to the flow of blood to the heart, or away from the heart, respectively. Since the flexible stent described in this invention can be used in many different body lumens, including both the arterial and venous system, the use of the terms proximal and distal in this application are used to describe relative position in relation to the direction of delivery. For example, the use of the term distal end portion in the present application describes the end portion of the stent first introduced into the vasculature and farthest from the entry point into the body relative to the delivery path. Conversely, the use of the term proximal end portion is used to describe the back end portion of the stent that is closest to the entry point into the body relative to the delivery path. 
         [0061]      FIGS. 2 and 3  are plan views of the stent  100  in a partially expanded condition according to one embodiment of the present invention. As used herein, the term plan view is understood to be a two-dimensional ( 2 -D) view of a stent that has been cut along the longitudinal axis and laid out flat, such that the bottom edge could be wrapped around a cylinder and connected to the top edge. 
         [0062]    The stent  100  architecture generally includes ring-like end sections  106 ,  107  along the proximal and distal ends,  104 ,  105  respectively, and a helical interior section  108  there between. The helical interior section  108  further includes a central zone  111  and proximal and distal transition zones  109 ,  110  respectively. The transition zones  109 ,  110  transition between the central zone  111  and the proximal and distal ring-like end sections  106 ,  107 .  FIG. 3  is an exploded plan view of the stent  100  illustrating the different sections and zones. 
         [0063]    The stent  100  includes a plurality of longitudinally oriented struts  113  connected by a series of circumferentially oriented ductile hinges  114 . Circumferentially adjacent struts  113  are connected at opposite ends by the hinges  114  in a substantially S or Z shaped sinusoidal-like pattern to form a band. Flexible connectors  112  are distributed throughout the stent  100  architecture for structural stability under a variety of loading conditions. The stent design illustrated in  FIGS. 1 through 3  have a flexible connector geometry, however, a wide variety of connector geometries are contemplated. See generally  FIGS. 6B through 6H . 
         [0064]    The region in the stent  100  where the interior helical section  108  is first connected to the ring-like end sections  106 ,  107  is referred to as an anchor point, and the hinge  114  at that location is referred to as an “anchor hinge”. This “take off” point may vary based on design constraints. Additionally the incident angle, strut thickness, strut width, hinge width, hinge length, depot position and size, and connection length may vary based on optimization and design constraints. 
         [0065]    As used herein the terms longitudinally, circumferentially and radially oriented are known to denote a particular direction relative to the stent  100  and the longitudinal axis  103 . A longitudinally oriented member is directed, end to end (along its axis), generally in the direction of the longitudinal axis  103 . It obvious after reviewing the figures that the longitudinal direction of the strut  113  is closer to being parallel to the longitudinal axis when the stent  100  is in the crimped state as illustrated in  FIG. 1B , then when the stent  100  is in the expanded, deployed state as illustrated in  FIG. 1A . Regardless, in each case, the strut  113  is considered to be longitudinally oriented as the axis of the strut  113  is substantially oriented in the same direction as the longitudinal axis. A circumferentially oriented member, such as hinge  114 , is directed substantially along the circumference of the tubular stent  100 . Similarly, a radial direction or radially oriented is along a radius that extends generally from the longitudinal axis outward to the circumference of the tubular stent  100  in cross-section. 
         [0066]      FIGS. 4A ,  4 B and  4 C illustrate typical struts  113  according to various embodiments of the present invention. Each strut  113  is a substantially rectangular shaped member having longitudinally extending long sides  115  and circumferentially extending short sides  116 . Opposing long sides  115  and short sides  116  may be substantially parallel to one another forming a near perfect rectangular as depicted by the strut  113  illustrated in  FIG. 4A , or may be canted or angled to form a tapered strut  113  as depicted by the strut  113  illustrated in  FIG. 4B . As can be seen in  FIGS. 4A and 4B , the hinges  114  attached to the strut  113  along the short sides  116  of the strut, however the width of the strut (length of the short side  116 ) is greater than the width of the hinge  114  in a preferred embodiment of the invention. As illustrated in  FIG. 4B , the flexible connectors  112  connect to the struts  113  along the short sides  116  of the struts  113 , but do not connect to the hinges  114 . 
         [0067]      FIG. 4C  represents a unique strut  113  that may be found in some embodiments of the stent  100  design. The strut  113  depicted in  FIG. 4C  is characterized by two connection points to circular hinges  114  (as hereinafter described) and two connection points to flexible connectors  112 . This strut  113  is widest at the proximal and distal ends (at the connection points of the hinges  114  and flexible connectors  112 ) and tapers to its minimum width near the mid-point in the longitudinal strut  113  length. That is to say the length of the short side  116  of the strut  113  depicted in  FIG. 4C  is greater than the width near the longitudinal center point of the strut  113 . 
         [0068]    The struts  113  may have one or more depots  117  for containing at least one agent. The depots  117  may be any form of recess, channel, hole or cavity capable of holding an agent, but are preferably through holes precisionly formed through the stent  100 . In a preferred embodiment, the through hole passes through the strut from the luminal to abluminal surface. This preferred configuration may allow an agent or agents to be delivered both in a radially inward and outward direction along the luminal and abluminal sides of the stent  100 . In addition, the depots  117  may be filled with a polymer inlay, either alone or containing one or more agents in solution or otherwise. Various depots  117  in the same stent may be filled with the same or different agents, and may have the same or different concentrations of agents. Any individual depot  117  may be filed with one or multiple agents, and the agents may be separated by a barrier layer. The barrier layer may be position in various configurations in the depot  117  as need to separate the agents. In a preferred embodiment, the barrier layer is oriented parallel to the luminal stent surface. 
         [0069]    The struts  113  may have symmetrically sized depots  117  as illustrated in  FIGS. 4A-4C , or may include organically optimized depots  117  as illustrated in  FIG. 4D . Organically optimized depots  117  are designed to maximize the depot  117  volume for any given strut  113  size, while reducing the stress state of the entire feature through the addition or removal of material critical to maintaining structural integrity upon stent  100  expansion. 
         [0070]    As the term is used herein, the agent can be any therapeutic or pharmaceutic agent or drug, including the following: antiproliferative/antimitotic agents including natural products such as vinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine), paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin and idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin (mithramycin) and mitomycin, enzymes (L-asparaginase which systemically metabolizes L-asparagine and deprives cells which don&#39;t have the capacity to synthesize their own asparagine; antiproliferative/antimitotic alkylating agents such as nitrogen mustards (mechlorethamine, cyclophosphamide and analogs, melphalan, chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan, nitrosoureas (carmustine (BCNU) and analogs, streptozocin), trazenes-dacarbazinine (DTIC); antiproliferative/antimitotic antimetabolites such as folic acid analogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine, and cytarabine), purine analogs and related inhibitors (mercaptopurine, thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine}); platinum coordination complexes (cisplatin, carboplatin), procarbazine, hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen); Anticoagulants (heparin, synthetic heparin salts and other inhibitors of thrombin); fibrinolytic agents (such as tissue plasminogen activator, streptokinase and urokinase), aspirin, dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory; antisecretory (breveldin); anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone, fludrocortisone, prednisone, prednisolone, 6α-methylprednisolone, triamcinolone, betamethasone, and dexamethasone), non-steroidal agents (salicylic acid derivatives i.e. aspirin; para-aminophenol derivatives i. e. acetominophen; Indole and indene acetic acids (indomethacin, sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac, and ketorolac), arylpropionic acids (ibuprofen and derivatives), anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids (piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds (auranofin, aurothioglucose, gold sodium thiomalate); immunosuppressive: (cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenic: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF); nitric oxide donors; anti-sense oligo nucleotides and combinations thereof. 
         [0071]    One or more agents may be distributed in one or more of the depots  117 , along at least a portion of the luminal or abluminal stent  100  surfaces, or any combination of depots and/or stent surfaces. In a preferred embodiment, the agent is distributed in the depots  117  only, such that the exposed agent surface area is limited to the cross-sectional area of the depot opening in the stent  100  surface (luminal, abluminal or both). This design allows for agent delivery from the stent  100  having a surface area upon insertion into the patient that is substantially bare metal. In a preferred embodiment, the exposed bare metal surface area of the stent  100  is between 40 and 95 percent upon insertion of the stent  100  into a patient, and is most preferably approximately 75 percent bare metal upon insertion of the stent  100  into a patient. That is, the surface area of the stent  100  is approximately 25 percent agent and approximately 75 percent bare metal. As the agent is released, the stent  100  becomes a purely bare metal stent. 
         [0072]    In a preferred embodiment, the depots  117  are distributed nearly uniformly throughout the strut pattern to provide a consistent agent dosage per unit surface area of the deployed stent  100  independent of the diameter or length of the stent used. The struts  113  may be of varying lengths, incident angle, depot configuration, and widths as needed to meet the product design. 
         [0073]    Ductile hinges  114  are used as the connection element between two circumferentially adjacent struts  113 . There are two types of ductile hinges  114  found in stent  100 .  FIGS. 5A and 5B  illustrate the two typical ductile hinges found in one embodiment of the present invention.  FIG. 5A  represents a single “free hinge”  114   a  that connects two circumferentially adjacent struts  113 . In a preferred embodiment, this free hinge  114   a  is “C” shaped and is substantially symmetric about reference line “A” drawn though the apex point on the curved section.  FIG. 5B  represents a ductile hinge  114   b  that connects two circumferentially adjacent struts  113 , where one of the struts is further connected to a flexible connector  112 . This ductile hinge  114   b  is more circular in shape than the “C” shaped free hinge  114   a  disclosed in  FIG. 5A , and is sometimes referred hereto as a “circular hinge”  14   b . Although free hinges  114   a  and connector hinges  114   b  are identified separately here, they are sometimes generally both referred to as ductile hinges  114 . The regions surrounding the circular hinge  14   b  is referred to as a circular hinge region. While the flexible connector  112  and circular ductile hinge  114   b  both connect to the same short side  116  of the strut  113  in the circular hinge region, they are not connected to one another. 
         [0074]      FIG. 6A  provides greater detail of the “circular hinge region”  118  that serves as a connection point between two strut pairs on adjacent windings of the helical section  108 . This hinge region  118  includes several components, and provides a ductile region in between circumferentially adjacent struts  113  that form a strut pair, while providing the necessary connectivity between longitudinally adjacent strut pairs by the flexible connector  112 . When combined, the longitudinally adjacent strut pairs and interconnecting flexible connector  112  create regions known as “quad hinge regions”. These regions are comprised of four struts that are directly or indirectly connected through the circular hinges  114   b  and flexible connectors  112 . The incident angle, hinge  114   b  width, degree of taper, length, and hole pattern are subject to change based on the stents intended design, the location of the feature and stent performance optimization.  FIGS. 6B through 6M  illustrated various connectors  112  that can be use to connect adjacent strut pairs in the circular hinge region  118 . 
         [0075]      FIG. 7  illustrates another key stent attribute important during the manufacturing process of the stent  100 . The encircled ductile hinge  114  is known as the “index hinge”. This “index hinge” is characterized by longer strut  113  lengths, which causes the ductile hinge or strut  113  head to protrude beyond the plane of the strut  113  heads on the remaining struts within the sinusoidal end ring. For ease of illustration, reference line A has been drawn perpendicular to the longitudinal axis  103  and tangent to the curved surfaces of both the hinges  114  above and below the index hinge. Reference line B has been drawn perpendicular to the longitudinal axis  103  and tangent to the curved surface of the hinge  114  representing the index hinge. The distance between reference lines A and B along the longitudinal axis is the offset provided by the index. This offset serves as a reference point to help determine the orientation of the stent  100 . The “index hinge” may occur at any location along the proximal and distal ring-like end sections  106 ,  107 . 
         [0076]    Generally speaking, the ductile hinges  114  are deformable elements that are substantially thinner in width than the surrounding struts  113 . This allows the ductile hinges  114  to sustain plastic deformation while still remaining flexible in the deformed state. The struts  113  are therefore much stiffer than the ductile hinges  114 , and thus do not experience any plastic deformation during stent expansion. The struts  113  essentially rotate as rigid bodies, while the ductile hinges  114  are designed to the bear the plastic strains associated with stent expansion. As a result, the depots  117  in the struts  113  are shielded from undue stress during expansion that may cause damage or dislodgement of the agents and/or polymer inlays. The depots  117  are ideally in a stress-free state throughout the stent deployment process. 
         [0077]    In a preferred embodiment of the present invention, the ductile hinges  114  are optimized, through the use of width tapering, such that they offer sufficient radial stiffness to the stent  100  while simultaneously ensuring that peak plastic strains at full expansion do not exceed the strain carrying capability of the material. This width tapering is optimized, for each hinge  114  type, to achieve a smooth and uniform distribution of plastic strains along the length of the ductile hinge  114 . By smoothing the strain distribution and thus eliminating strain concentrations in the ductile hinge  114 , the width, and thereby stiffness, is maximized. Maximizing the stiffness of the ductile hinge  114  is advantageous in providing radial stiffness and fatigue durability for the stent  100 . 
         [0078]    In general the width of the tapered ductile hinge  114  gradually increases while approaching the root of the hinge  114 , where the hinge  114  meets an abrupt transition into the wider strut  113  (or stiffer structure). This prevents plastic strains from concentrating at the roots of the hinges since the tapered hinge root is stiffer and therefore distributes plastic strain to the central portion of the hinge  114 . The central portion of the ductile hinge  114 , which encompasses the apex of the curve, generally has a uniform width. 
         [0079]    Turning again to  FIGS. 2 and 3 , the ring-like end sections  106 ,  107  include a plurality of circumferentially arranged, longitudinally oriented strut members  113  connected at opposite ends by a plurality of circumferentially oriented ductile hinges  114  in a substantially sinusoidal S or Z shaped pattern so as to form the band into an endless ring. In the illustrated embodiment, the end sections  106 ,  107  are formed from struts  113  of varying length as needed optimize the stent design and provide the necessary geometry for the connection at the anchor point where the interior helical section  108  is first connected to the ring-like end sections  106 ,  107 . 
         [0080]    Between the ring-like end sections  106 ,  107  lies the interior helical section  108  of the stent  100 , where the band of sinusoidally arranged struts  113  and hinges  114  follow a helical path. The helical band of the interior section  108  is achieved by arranging the struts  113  in a repeating pattern of alternating short and long lengths. The helical interior section  108  may be further divided into proximal and distal transition zone  109 ,  110  respectively, and a central zone  111 . 
         [0081]    The central zone  111  comprises strings (collections of elements) formed from groups of contiguous strut members  113  and hinge members  114  organized to form a string pattern. In one embodiment of the invention, contiguous strings have different string patterns and repeating strings are geometrically symmetric to form a repeating central pattern. In a preferred embodiment of the invention, the repeating central pattern consists of two different repeating strings. The central zone  111  therefore has a constant pitch and incident angle. 
         [0082]    As used herein the term pitch is understood to mean the number of sinusoidal turns over a given area. This is similar nomenclature to the diametral pitch of a gear. The greater the pitch, the greater the number of sinusoidal turns, i.e. the greater number of struts  113  and ductile hinges  114 , will be found per wrap as the sinusoidal band winds about the longitudinal axis  103 . This creates a very dense pattern of struts  113  and hinges  114 . Conversely, the smaller the pitch, the smaller number of sinusoidal turns, and thus the smaller number of struts  113  and hinges  114  will be found per wrap as the sinusoidal band winds about the longitudinal axis  103 . The term incident angle refers specifically to the helical winding section of the stent  100  and is understood to mean the angle at which the sinusoidal band makes (wraps) with the longitudinal axis. 
         [0083]      FIG. 8  is a close up 2 dimensional view of the central zone  111  depicted in  FIG. 3 . A first reference line “A” has been drawn parallel to the longitudinal axis  103 . A second reference line “B” has been drawn to represent the direction of the sinusoidal band. The incident angle (a) is the angle between reference line A and reference line B. 
         [0084]      FIGS. 9A and 9B  illustrate the two strut strings that are part of the repeating pattern that form the central zone  111  of the stent  100  according to one embodiment of the present invention. Referring to  FIGS. 3 ,  8 ,  9 A and  9 B, the central zone  111  starts at the proximal end of the distal transition zone  110  with a free strut string  119  illustrated in  FIG. 9B . The illustrated free strut string  119  includes a long three depot strut  113  connected on each end to a short two depot strut  113  by a free hinge  114   a . The free strut string  119  is attached on its proximal end to the distal end of a connector strut string  120 . The connector strut string  120  includes a connector hinge  114   b  at its proximal and distal ends, and an alternating arrangement of three long (three depot) struts  113  and two short (two depot) struts  113  connected by free hinges  114   a . This pattern of alternating free strut strings  119  and connector strut strings  120  continue until the central zone  111  meets the proximal transition zone  109 . The embodiment illustrated in  FIG. 3  has a central zone that includes five free strut strings  119  and four connector strut strings  120 . The length of the stent  100  can be changed by adding or shortening the central zone  111 , i.e. by adding or removing free strut strings  119  or connector strut strings  120  as necessary to maintain the repeating pattern, while maintaining the proximal and distal transition zones  109 ,  110 , and proximal and distal ring-like end section  106 ,  107  as disclosed. 
         [0085]    The proximal and distal transition zones  109 ,  110  are sections of variable pitch, and in which there is no repeatability or symmetry. The proximal and distal transition zones  109 ,  110  are constructed so as to afford a gradual decrease in pitch in transitioning between the central zone  111  and the proximal and distal ring-like end sections  105 ,  107 . The proximal and distal transition zones  109 ,  110  are connected to the proximal and distal ring-like end section  106 ,  107 , respectively, by a connecting geometry called an anchor hinge. 
         [0086]    The stent  100  designs depicted in the aforementioned figures are known as an open cell design, meaning that connectors between longitudinally adjacent windings of sinusoidal elements occur only intermittently through the structure rather than spanning every longitudinally adjacent hinge  114  or strut  113 . A design in which every longitudinally adjacent hinge or strut is connected is known as a closed cell design. An open-celled architecture is generally more flexible than a closed-cell architecture. 
         [0087]    As previously described, the general architecture of the stent  100  includes a helical interior section  108  with ring-like end sections  106 ,  107  at each end, and connectors  112  distributed through the architecture for structural stability under a variety of loading conditions. The helical interior section  108  may be further separated into a central zone  111  having a constant pitch and incident angle, and proximal and distal transition zones  109 ,  110  respectively. This general architecture remains the same for various stents of different sizes; however, the geometry and pattern of the elements (struts, hinges and flex connectors) may change as need to adapt to various desired stent diameters. 
         [0088]      FIGS. 10 through 15  illustrate various embodiments of the stent designs for different diametrically size stents.  FIGS. 10 ,  12  and  14  are two-dimensional plan views, similar to  FIG. 2 , illustrating stents  200 ,  300 ,  400 , respectively, of different sizes and patterns.  FIGS. 11 ,  13  and  15  are exploded plan views, similar to  FIG. 3 , of the stents  200 ,  300 ,  400 , respectively, illustrating the different sections and zones. For ease of illustration, like reference numerals have been assigned to like elements of the stent  100 , and it is understood that the description of elements related to stent  100  applies equally to like elements in stents  200 ,  300  and  400 . 
         [0089]    Each stent pattern design is customized to target optimal results based on the treatment of the stent&#39;s intended target vessel.  FIGS. 10 and 11  represents one embodiment of a stent  200  intended for extra small diameter target vessel lesions. The extra small diameter stent family has been optimized for very small vessel diameters via several design features, and is meant to be fabricated from a smaller diameter tubing material. 
         [0090]    The current embodiment for an extra small stent includes sinusoidal proximal and distal ring-like end sections  206 ,  207  comprised of ten struts  213  in each ring-like end sections  206 ,  207 . Between the ring-like end sections  206 ,  207  lies the interior helical section  208  of the stent  200 , where the sinusoidal arrangement of struts  213  and hinges  214  follow a helical path. The helical path of the interior section  208  is achieved by arranging the struts  213  in a repeating pattern of alternating short and long lengths to form a band. There are nine struts  213  per winding in each the interior bands. The fewer number of struts allows for increased stent performance while maintaining critical processing parameters. The helical interior section  208  may be further divided into proximal and distal transition zones  209 ,  210  respectively and a central zone  211  as illustrated in  FIG. 11 . 
         [0091]    The central zone  211  consists of repeating strut strings, or collections of struts, which are geometrically symmetric to form a repeating pattern in the band. The central zone  211  therefore has a constant pitch and incident angle. The repeating interior pattern is comprised of two 3-strut patterns that alternate to form the 9-strut repeating interior pattern. 
         [0092]      FIG. 18  illustrates the two strut strings  219 ,  220  that are part of the repeating pattern from the central zone  211  of the stent  200  according to one embodiment of the present invention. Referring to  FIGS. 10 ,  11  and  18 , the central zone  211  starts at the distal end of the proximal transition zone  209  with a free strut string  219  illustrated in  FIG. 18 . The illustrated free strut string  219  includes a long (four depot) strut  213  connected on each end to a short (two depot) strut  213  by a free hinge  214   a . The free strut string  219  is attached on its distal end to the proximal end of a connector strut string  220 . The connector strut string  220  includes a connector hinge  214   b  at its proximal and distal ends, and an alternating arrangement of two long (four depot) struts  213  and one short (two depot) strut  213  connected by free hinges  214   a . This pattern of alternating free strut strings  219  and connector strut strings  220  continue until the central zone  211  meets the distal transition zone  210 . The embodiment illustrated in  FIGS. 10 and 11  have a central zone that includes six free strut strings  219  and six connector strut strings  220 . 
         [0093]    The current embodiment for a medium sized stent includes sinusoidal proximal and distal ring-like end sections  306 ,  307  comprised of twelve strut  313  end rings. Between the ring-like end sections  306 ,  307  lies the interior helical section  308  of the stent  300 , where the sinusoidal arrangement of struts  313  and hinges  314  in the band follow a helical path. The helical path of the interior section  308  is achieved by arranging the struts  313  in a repeating pattern of alternating short and long lengths to form the band. There are thirteen struts  313  per band winding in the interior helical section  108 . The increased number of struts allows for increased stent performance while maintaining critical processing parameters. The helical interior section  308  may be further divided into proximal and distal transition zones  309 ,  310  respectively and a central zone  311  as illustrated in  FIG. 13 . 
         [0094]    The central zone  311  consists of repeating strut strings, or collections of struts, which are geometrically symmetric to form a repeating pattern. The central zone  311  therefore has a constant pitch and incident angle. The repeating interior pattern is comprised of one 3-strut pattern and one 5-strut pattern that alternate to form the 13-strut repeating interior pattern. 
         [0095]      FIG. 17  illustrates the two strut strings  319 ,  320  that are part of the repeating pattern forming the central zone  311  of the stent  300  according to one embodiment of the present invention. Referring to  FIGS. 12 ,  13  and  17 , the central zone  311  starts at the distal end of the proximal transition zone with a connector strut string  320  illustrated in  FIG. 17 . The illustrated connector strut string  720  includes a connector hinge  314   b  at its proximal and distal ends, and an arrangement of three long (three depot) struts  313  connected by free hinges  314   a . The free strut string  319  is attached on its proximal end to the distal end of the connector strut string  320 . The illustrated free strut string  319  includes a series of three long (three depot) struts  313  interconnected by a free hinge  314   a . The three, three depot struts  313  are connected on each end to a short two depot strut  313  by free hinges  314   a . The pattern of alternating connector strut strings  320  and free strut strings  319  continue until the central zone  311  meets the distal transition zone  310 . The embodiment illustrated in  FIGS. 12 and 13  has a central zone that includes three connector strut strings  320  and two free strut strings  319 . The length of the stent  300  can be changed by adding or shortening the central zone  311 , i.e. by adding or removing connector strut strings  320  or free strut strings  319  as necessary to maintain the repeating pattern, while maintaining the proximal and distal transition zones  309 ,  310  and proximal and distal ring-like end section  306 ,  307  as disclosed. 
         [0096]      FIGS. 14 and 15  represents one embodiment of a stent  400  intended for a large diameter target vessel lesions. The large diameter stent family has been optimized for larger vessels via several design features. Like previous designs, the current embodiment contains sinusoidal proximal and distal ring-like end sections  406 ,  407  comprised of twelve struts  413 . The struts  413  in said end sections  406 ,  407  are of varying length; however, on the whole they are longer in the large diameter stent design than the typical strut of an equivalent smaller nominal stent design. The end sections  406 ,  407  are connected via several points to the proximal and distal transition zones  409 ,  410  as illustrated in  FIG. 15 . 
         [0097]      FIG. 16  illustrates the two strut strings that are part of the repeating pattern from the central zone  411  of the stent  400  according to one embodiment of the present invention. Referring to  FIGS. 14 ,  15  and  16 , the central zone  411  starts at the proximal end of the distal transition zone  410  with a free strut string  419  illustrated in  FIG. 16 . The illustrated free strut string  419  includes an alternating arrangement of short (three depot) struts  113  and long (four depot) struts interconnected on each end by a free hinge  414   a . The free strut string  419  is attached on its proximal end to the distal end of a connector strut string  420 . The connector strut string  420  is three struts  413  long, and includes a connector hinge  414   b  at its proximal and distal ends. The three struts in the connector string  420  include an alternating arrangement of long (four depot) struts  413  and a short (three depot) strut  413  connected by free hinges  414   a . This pattern of alternating free strut strings  419  and connector strut strings  420  continue until the central zone  411  meets the proximal transition zone  409 . The embodiment illustrated in  FIG. 15  has a central zone that includes three free strut strings  419  and two connector strut strings  420 . 
         [0098]    The present invention also contemplates the use of solid struts in similar strut/hinge orientations as those disclosed in  FIGS. 2 ,  10 ,  12 , and  14 .  FIG. 19  illustrates a stent  500  having similar design architecture without depots along the struts  513 . Stent  500  can be used as a bare metal stent or can be partially or completely coated with an agent and/or appropriate carrier as is known in the art.