Abstract:
The present invention consists of an implantable structural element for in vivo delivery of bioactive active agents to a situs in a body. The implantable structural element may be configured as an implantable prosthesis, such as an endoluminal stent, cardiac valve, osteal implant or the like, which serves a dual function of being prosthetic and a carrier for a bioactive agent. Alternatively, the implantable structural element may simply be an implantable article that serves the single function of acting as a time-release carrier for the bioactive agent.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 10/258,087, filed Aug. 19, 2003, which is a U.S. national stage of PCT/U.S. 2001/44642, filed Nov. 19, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/716,146, filed Nov. 17, 2000, which are all herein incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to an implantable device for in vivo delivery of bioactive compounds. The present invention provides an implantable structural material having a three-dimensional conformation suitable for loading a bioactive agent into the structural material, implanting the structural material in vivo and releasing the bioactive agent from the structural agent to deliver a pharmacologically acceptable level of the bioactive agent to an internal region of a body. More particularly, the present invention relates to an implantable medical device, such as an endoluminal stent, stent-graft, graft, valves, filters, occluders, osteal implant or the like, having cavitated regions incorporated within the material of the device with micropores that communicate a bioactive agent from the cavity to an area external the device. 
         [0003]    The present invention may be used for any indication where it is desirable to deliver a bioactive agent to a local situs within a body over a period of time. For example, the present invention may be used in treating vascular occlusive disease, disorders or vascular injury, as an implantable contraceptive for delivery of a contraceptive agent delivered intrauterine or subcutaneously, to carry an anti-neoplastic agent or radioactive agent and implanted within or adjacent to a tumor, such as to treat prostate cancer, for time-mediated delivery of immunosuppresents, antiviral or antibiotic agents for treating of autoimmune disorders such as transplantation rejection or acquired immune disorders such as HIV, or to treat implant or non-implant-related inflammation or infections such as endocarditis. 
         [0004]    Occlusive diseases, disorders or trauma cause patent body lumens to narrow and restrict the flow or passage of fluid or materials through the body lumen. One example of occlusive disease is arteriosclerosis in which portions of blood vessels become occluded by the gradual build-up of arteriosclerotic plaque, this process is also known as stenosis. When vascular stenosis results in the functional occlusion of a blood vessel the vessel must be returned to its patent condition. Conventional therapies for treatment of occluded body lumens include dilatation of the body lumen using bioactive agents, such as tissue plasminogen activator (TPA) or vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers which have improved blood flow and collateral development in ischemic limb and myocardium (S. Yla-Herttuala,  Cardiovascular Gene Therapy , Lancet, Jan. 15, 2000), surgical intervention to remove the blockage, replacement of the blocked segment with a new segment of endogenous or exogenous graft tissue, or the use of a catheter-mounted device such as a balloon catheter to dilate the body lumen or an artherectomy catheter to remove occlusive material. The dilation of a blood vessel with a balloon catheter is called percutaneous transluminal angioplasty. During angioplasty, a balloon catheter in a deflated state is inserted within an occluded segment of a blood vessel and is inflated and deflated a number of times to expand the vessel. Due to the inflation of the balloon catheter, the plaque formed on the vessel walls cracks and the vessel expands to allow increased blood flow through the vessel. 
         [0005]    In approximately sixty percent of angioplasty cases, the blood vessel remains patent. However, the restenosis rate of approximately forty percent is unacceptably high. Endoluminal stents of a wide variety of materials, properties and configurations have been used post-angioplasty in order to prevent restenosis and loss of patency in the vessel. 
         [0006]    While the use of endoluminal stents has successfully decreased the rate of restenosis in angioplasty patients, it has been found that a significant restenosis rate continues to exist even with the use of endoluminal stents. It is generally believed that the post-stenting restenosis rate is due, in major part, to a failure of the endothelial layer to regrow over the stent and the incidence of smooth muscle cell-related neointimal growth on the luminal surfaces of the stent. Injury to the endothelium, the natural nonthrombogenic lining of the arterial lumen, is a significant factor contributing to restenosis at the situs of a stent. Endothelial loss exposes thrombogenic arterial wall proteins, which, along with the generally thrombogenic nature of many prosthetic materials, such as stainless steel, titanium, tantalum, 
         [0007]    Nitinol, etc. customarily used in manufacturing stents, initiates platelet deposition and activation of the coagulation cascade, which results in thrombus formation, ranging from partial covering of the luminal surface of the stent to an occlusive thrombus. Additionally, endothelial loss at the site of the stent has been implicated in the development of neointimal hyperplasia at the stent situs. Accordingly, rapid re-endothelialization of the arterial wall with concomitant endothelialization of the body fluid or blood contacting surfaces of the implanted device is considered critical for maintaining vasculature patency and preventing low-flow thrombosis. To prevent restenosis and thrombosis in the area where angioplasty has been performed, anti-thrombosis agents and other biologically active agents can be employed. 
         [0008]    It has been found desirable to deliver bioactive agents to the area where a stent is placed concurrently with stent implantation. Many stents have been designed to delivery bioactive agents to the anatomical region of stent implantation. Some of these stents are biodegradable stents which are impregnated with bioactive agents. Examples of biodegradable impregnated stents are those found in U.S. Pat. Nos. 5,500,013, 5,429,634, and 5,443,458. Other known bioactive agent delivery stents include a stent disclosed in U.S. Pat. No. 5,342,348 in which a bioactive agent is impregnated into filaments which are woven into or laminated onto a stent. U.S. Pat. No. 5,234,456 discloses a hydrophilic stent that may include a bioactive agent adsorbed which can include a biologically active agent disposed within the hydrophilic material of the stent. Other bioactive agent delivery stents disclosed in U.S. Pat. Nos. 5,201,778, 5,282,823, 5,383,927; 5,383,928, 5,423,885, 5,441,515, 5,443,496, 5,449,382, 4,464,450, and European Patent Application No. 0 528 039. Other devices for endoluminal delivery of bioactive agents are disclosed in U.S. Pat. Nos. 3,797,485, 4,203,442, 4,309,776, 4,479,796, 5,002,661, 5,062,829, 5,180,366, 5,295,962, 5,304,121, 5,421,826, and International Application No. WO 94/18906. A directional release bioactive agent stent is disclosed in U.S. Pat. No. 6,071,305 in which a stent is formed of a helical member that has a groove in the abluminal surface of the helical member. A bioactive agent is loaded into the groove prior to endoluminal delivery and the bioactive agent is therefore in direct apposition to the tissue that the bioactive agent treats. Finally, International Application No. WO 00/18327 discloses a drug delivery stent in which a tubular conduit is wound into a helical stent. The tubular conduit has either a single continuous lumen or dual continuous lumens that extend the entire length of the conduit. The tubular conduit has regions or segments thereof that has pores to permit drug “seepage” from the conduit. One end of the tubular conduit is in fluid flow communication with a fluid delivery catheter, which introduces a fluid, such as drug into the continuous lumen and through the pores. Where biodegradable or non-biodegradable polymer-based or polymer-coated stents have been used, the polymers cause an immune inflammatory response once the drug is eluted out of the polymer. Where a polymer is employed as the bioactive agent carrier, it is, therefore, desirable to isolate the polymer from body tissues in order to limit the immune inflammatory response after the bioactive agent has eluted as can be accomplished with the present invention. 
       SUMMARY OF THE INVENTION 
       [0009]    As used herein the term “bioactive agent” is intended to include one or more pharmacologically active compounds which may be in combination with pharmaceutically acceptable carriers and, optionally, additional ingredients such as antioxidants, stabilizing agents, permeation enhancers, and the like. Examples of bioactive agents which may be used in the present invention include but are not limited to hydrophilic agents, hydrophilic agents, antiviral drugs, antibiotic drugs, steroids, fibronectin, anti-clotting drugs, anti-platelet function drugs, drugs which prevent smooth muscle cell growth on inner surface wall of vessel, heparin, heparin fragments, aspirin, coumadin, tissue plasminogen activator (TPA), urokinase, hirudin, streptokinase, antiproliferatives (methotrexate, cisplatin, fluorouracil, 
         [0010]    Adriamycin), antioxidants (ascorbic acid, beta carotene, vitamin E), antimetabolites, thromboxane inhibitors, non-steroidal and steroidal anti-inflammatory drugs, immunosuppresents, such as rapomycin, beta and calcium channel blockers, genetic materials including DNA and RNA fragments, complete expression genes, antibodies, lymphokines, growth factors (vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)), prostaglandins, leukotrienes, laminin, elastin, collagen, nitric oxide (NO) and integrins. 
         [0011]    The inventive structural material has a three dimensional conformation having a geometry and construction in which there is an internal cavity or a plurality of internal cavities within the structural material and a conduit or opening or plurality of conduits or openings which communicate between the internal cavity and external the structural material. The three dimensional conformation of the structural material may assume a cylindrical, tubular, planar, spherical, curvilinear or other general shape which is desired and suited for a particular implant application. For example, in accordance with the present invention there is provided an endoluminal stent that is made of a plurality of structural members that define a generally tubular shape for the endoluminal stent. At least some of the plurality of structural members are comprised of the inventive structural material and have at least one internal cavity and at least one conduit or opening which communicates between the internal cavity and external the stent. Alternate types of implantable devices contemplated by the present invention include, without limitation, stent-grafts, grafts, heart valves, venous valves, filters, occlusion devices, catheters, osteal implants, implantable contraceptives, implantable anti-tumor pellets or rods, or other implantable medical devices. 
         [0012]    The inventive stent for delivery of bioactive agents consists generally of a plurality of structural elements, at least some of which have internal cavities that retain the bioactive agents, and openings that pass between the internal cavities and the surface of the structural elements to communicate the bioactive agent from the internal cavity external the stent. Other than described herein, the present invention does not depend upon the particular geometry, material, material properties or configuration of the stent. 
         [0013]    Because of their use as a structural scaffold and the requirement that stents be delivered using transcatheter approaches, stents necessarily are delivered in a reduced diametric state and are expanded or allowed to expand in vivo to an enlarged diametric state. Thus, all stents have certain structural regions that are subject to higher stress and strain conditions than other structural regions of the stent. Thus, it may be advantageous to position the internal cavities that retain the bioactive agents in structural regions of the stent that are subjected to relatively lower stress and strain during endoluminal delivery and deployment. Alternatively, where delivery of a bolus of a bioactive agent is desired, internal cavities may be positioned in regions that undergo large deformation during delivery and deployment thereby forcing the bioactive agent out of the internal cavity under the positive pressure exerted by the deformation. Diffusion forces, then, elute remaining bioactive agent present in either the region of large deformation or the regions of lower stress and strain. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of an implantable member in accordance with the present invention. 
           [0015]      FIG. 2  is a perspective view of an endoluminal stent having a plurality of structural members in accordance with the present invention. 
           [0016]      FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 . 
           [0017]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 2 . 
           [0018]      FIG. 5  is a fragmentary perspective view of an alternative embodiment of the inventive endoluminal stent in accordance with the present invention. 
           [0019]      FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 5 . 
           [0020]      FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 5 . 
           [0021]      FIG. 8  is a perspective view of a planar structural element for delivery of a bioactive agent in accordance with the present invention. 
           [0022]      FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8 . 
           [0023]      FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 8 . 
           [0024]      FIG. 11  is a plan view of an alternative embodiment of the endoluminal stent in accordance with the present invention. 
           [0025]      FIG. 12  is a photomicrographic cross-sectional view taken along line  12 - 12  of  FIG. 11 . 
           [0026]      FIGS. 13A-13F  are sequential diagrams illustrating the inventive method for fabricating the inventive endoluminal stent. 
           [0027]      FIG. 14  are side-by-side photomicrographs illustrating selective formation of an internal cavity within the inventive endoluminal stent. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    As noted above, the term “bioactive agent” is intended to encompass one or more pharmacologically active compounds which may be in combination with pharmaceutically acceptable carriers and, optionally, additional ingredients such as antioxidants, stabilizing agents, permeation enhancers, and the like. Examples of bioactive agents which may be used in the present invention include but are not limited to antibiotic drugs, antiviral drugs, neoplastic agents, steroids, fibronectin, anti-clotting drugs, anti-platelet function drugs, drugs which prevent smooth muscle cell growth on inner surface wall of vessel, heparin, heparin fragments, aspirin, coumadin, tissue plasminogen activator (TPA), urokinase, hirudin, streptokinase, antiproliferatives (methotrexate, cisplatin, fluorouracil, Adriamycin), antioxidants (ascorbic acid, beta carotene, vitamin E), antimetabolites, thromboxane inhibitors, non-steroidal and steroidal anti-inflammatory drugs, immunosuppresents, such as rapomycin, beta and calcium channel blockers, genetic materials including DNA and RNA fragments, complete expression genes, antibodies, lymphokines, growth factors (vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)), prostaglandins, leukotrienes, laminin, elastin, collagen, nitric oxide (NO), and integrins. 
         [0029]    With particular reference to  FIG. 1 , the present invention consists generally of a body element  10  having a three-dimensional conformation defining X, Y and Z-axes of the body element  10  and at least one of a plurality of interior cavities  12  defined within the body element  10 , and at least one of a plurality of passages or pores  14  which communicate between the at least one of a plurality of interior cavities  12  and exterior to the body element  10 . While the body element  10  depicted in  FIG. 1  is of a generally cylindrical three dimensional conformation, alternative three dimensional conformations, such as planar, spherical, ovular, tetrahedral, curvilinear or virtually any other three dimensional conformation suitable for implantation into a living body is contemplated by the present invention. The plurality of passages  14  have dimensions sufficient to permit the bioactive agent to elute by diffusion, osmotic pressure or under the influence of a positive pressure applied by cellular in-growth into the plurality of interior cavities  12 . 
         [0030]    The location of the plurality of passages  14  is dependent upon the particular application for which the body element  10  is intended. For example, with particular reference to  FIGS. 2-5 , where the body element  10  is a tubular body  20  made of a plurality of interconnected structural elements  21 , such as a stent, stent-graft or graft, which defines a central lumen  22  and has openings  24  at opposing proximal and distal ends of the tubular body  20 , the plurality of passages  14  are formed in at least some of the plurality of interconnected structural elements  21  and may be disposed on only the luminal surface  26  or only on the abluminal surface  28  of the tubular body  20 , or both. Pores  14  on the luminal surface  26  only will communicate the bioactive agent into the lumen and any body fluid, such as blood, flowing through the central lumen of the tubular body, while pores  14  on only the abluminal surface  26  will communicate the bioactive agent to the abluminal surface of the tubular body. At least a portion of some of the plurality of interior cavities  12  may communicate with either the proximal or distal ends of at least some of the plurality of interconnected structural elements  21 . In this case, the proximal and/or distal ends of at least some of the plurality of interconnected structural elements may be tapered such as to self-cannulating into body tissue during delivery and deployment. The bioactive agent retained with the internal cavity  12  which communicates with the proximal and/or distal ends of at least some of the plurality of interconnected structural elements will then pass out of the proximal and/or distal ends in much the same manner as fluid flowing through an injection needle. 
         [0031]    In addition to the foregoing positioning of the pores  14 , both the plurality of internal cavities  12  and the plurality of pores  14  may be positioned to be discontinuous and in different circumferential or different longitudinal regions of the tubular body  20 . Within a single one of the plurality of interconnected structural elements  21 , the internal cavities  12  may be separated by a separation member  25 , which completely subtends the internal cavity  12 , divides it into discrete discontinuous internal cavities  12 . The advantage of forming a plurality of discontinuous internal cavities  12  is that it permits loading of different bioactive agents into different regions of the body member  10  or tubular member  20  to isolate different regions for delivery of different bioactive agents to different sites within a body. For example, a first grouping of a plurality of internal cavities  12  and associated plurality of pores  14  may be located at a proximal end of the tubular body  20 , and a second grouping of a plurality of internal cavities  12  and associated plurality of pores  14  may be located at an intermediate region of the tubular body  20 , and a third grouping of a plurality of internal cavities  12  and associated plurality of pores  14  may be located at a distal end of the tubular body  20 . A first bioactive agent may be loaded into the first and third grouping of a plurality of internal cavities  12 , while a second bioactive agent may be loaded into the second grouping of a plurality of internal cavities  12 . Where, for example, the tubular body  20  is an endoluminal stent, stent-graft or graft which is implanted post-angioplasty, the proximal and distal ends of the tubular body  20  are anchored adjacent to healthy tissue while the intermediate region of the tubular body  20  are positioned adjacent to the diseased or injured tissue. In this configuration, a first bioactive agent, such as an endothelial growth factor and/or contrast medium to impart enhanced radioopacity to the tubular body  20  may be carried in the first and third groups of a plurality of internal cavities  12  and associated pores  14 , while an anticoagulant, such as heparin, may be carried in the second group of a plurality of internal cavities  12  and associated pores  14 . In this manner, the tubular body has enhanced radioopacity to aid in delivery and deployment and endothelial growth factors to enhance endothelialization of the tubular body  20 , while delivering an anticoagulant directly to the site of the tissue lesion. 
         [0032]    Moreover, where the internal cavities  12  are discontinuous, the plurality of pores  14  may be configured to include degradable plugs which degrade at different rates to expose different bioactive agents in the internal cavities  12  to the body at different points in time. Alternatively or additionally, the degradable plugs may degrade at different to expose the same bioactive agent in different internal cavities  12  at different periods of time to effectively elongate the period of time during which the bioactive agent is delivered. Alternatively, the plurality of pores  14  may be dimensioned to permit different elution rates of the bioactive agent and provide for a more protracted or time-release of the bioactive agent from the internal cavities  12 . Moreover, by adjusting the carriers of the bioactive agent, e.g., to provide more or less capacity to elute in vivo, in combination with alternate dimensions and orientations of the plurality of pores  14 , e g , luminal or abluminally oriented, both the time of elution and the duration of elution may be adjusted. 
         [0033]    The body element  10  is preferably formed of a metal such as titanium, vanadium, aluminum, nickel, tantalum, zirconium, chromium, silver, gold, silicon, magnesium, niobium, scandium, platinum, cobalt, palladium, manganese, molybdenum and alloys thereof, such as zirconium-titanium-tantalum alloys, nitinol, or stainless steel. 
         [0034]    Turning to  FIGS. 5-7  there is illustrated an alternative embodiment of the inventive endoluminal stent fabricated from a plurality of tubular structural elements  31  formed into a tubular stent and having a desired geometry. It will be appreciated that the generally hexagonal cell geometric pattern illustrated in  FIG. 5  is merely exemplary and a myriad of different geometries of different geometric complexities are contemplated by the invention. Each of the tubular structural elements  31  has a central lumen  37  that forms the internal cavity within each structural element  31 . A plurality of separation member  38  may be provided to subdivide the internal cavity  37  into a plurality of discontinuous internal cavities  37 . Each of the tubular structural elements  31  has a plurality of openings  36  which communicate between the internal cavity  37  and one or both of a luminal surface  33  or an abluminal surface  35  of each of the plurality of tubular structural elements  31 . The tubular structural elements  31  may assume any transverse cross-sectional configuration having a central lumen. 
         [0035]    Those of ordinary skill in the stent forming arts will understand that in order to form a tubular endoluminal stent of tubular elements  31 , it is necessary to join at least some of the plurality of tubular elements  31 . Conventionally, a plurality of spot-welds  34  which serve to interconnect sections of individual tubular elements  31  in juxtaposed relationship to one and other. The plurality of spot welds  34  may also be employed to seal the internal cavity  37  at the position of the spot weld, thereby creating a separation member  38  within the internal cavity  37  of each individual tubular element  31  and forming a discontinuous internal cavity  37 . 
         [0036]    As noted above, the plurality of openings  36  are dimensioned to permit the bioactive agent to elute from the at least one of a plurality of internal cavities  37  and through the associated plurality of openings  36  by diffusion, osmotic pressure or under the influence of a positive pressure applied by cellular in-growth into the plurality of internal cavities  37  or under positive pressure applied by stress and/or strain exerted on the plurality of internal cavities  37  due to deformation of the individual tubular structural elements  31 . Additionally, the positioning of the plurality of openings  36  relative to the individual tubular structural elements  31  and to the endoluminal stent as a whole may be adapted to deliver varying quantities of or different bioactive agents from different regions of the tubular structural elements  31  or different regions of the endoluminal stent  30 . Moreover, proximal and/or distal ends of individual tubular structural elements  31  may be tapered so as to form self-cannulating ends of the individual tubular structural elements  31  which penetrate body tissue and permit the bioactive agent to be communicated from the internal cavity  37  out the proximal or distal end of the tubular structural element  31  in a manner similar to a hypodermic needle. 
         [0037]    In accordance with another embodiment of the present invention, and as illustrated in  FIGS. 8-10 , there is provided an implantable device  40  which consists of a structural body  42  having a three-dimensional conformation extending in the X-axis, Y-axis and Z-axis dimensionally. While the illustrated embodiment of the structural body  42  is planar, those of ordinary skill in the medical device fabrication art will understand that it is within the skill of the artisan to fabricate the structural body  42  of any desired three-dimensional conformation depending upon the desired use and indication of the implantable device  40 . The three-dimensional conformation of the structural body  42  may be cylindrical, tubular, quadrilinear, planar, spherical, ovular, tetrahedral, curvilinear or virtually any other three-dimensional conformation suitable for implantation into a living body. 
         [0038]    Like the above-described embodiments, the structural body  42  has at least one of a plurality of internal cavities  47 , each of which carry a bioactive agent  47 , and a plurality of openings  44  which pass from at least one upper  46 , lower  48  or lateral  45  surface of the structural body  42 , through the Z-axis thickness of the body and communicate with the at least one of a plurality of internal cavities  47  in the structural body  42 . Where a plurality of internal cavities  47  are provided within the structural body  42 , a plurality of bioactive agents  49  may be loaded into the structural body  42  with one or more bioactive agents  49  being loaded into each of the plurality of internal cavities  47 . 
         [0039]    Each of the above-described preferred embodiments of the present invention may be fabricated by a number of methods. In accordance with present invention, it is contemplated that either forming wrought metal parts, such as capillary tubing, into the implantable device or forming the implantable devices by vacuum deposition techniques are the preferred method of making the implantable structural elements of the present invention. Where an implantable device is to be fabricated of a plurality of individual tubular elements, such as depicted in  FIGS. 5-7 , pre-existing microtubular members having an outer diameter, for example, between 60 and 400 μm and a wall thickness of between 10 and 350 μm, may be employed to fabricate extremely small dimensioned devices suitable for intracranial or coronary artery applications. The microtubular members may be formed into a cylindrical endoluminal device, such as by braiding or bending and joining microtubular members together by spot welding. Where ends of the microtubular members are formed to be self-cannulating, the self-cannulating ends may be exposed on the abluminal surface of an endoluminal device at any point along the longitudinal axis thereof. The plurality of openings passing through the wall of each of the individual tubular elements may be formed by microdrilling the openings through the wall and into the internal cavity or lumen of the individual tubular members. The plurality of openings may be laser cut, etched or formed by EDM methods, and may be formed either pre- or post-formation of the tubular elements into the three-dimensional conformation of the implantable device. Where an implantable device is to be formed from non-preexisting structural elements, vacuum deposition techniques may be employed to form the implantable structural body, such as sputtering, reactive ion etching, chemical vapor deposition, plasma vapor deposition, or the like, as are known in the microelectronics fabrication arts and are more fully described in co-pending, commonly assigned U.S. patent application Ser. No. 09/443,929, filed Nov. 19, 1999, which is hereby incorporated by reference. Because, the internal cavities and openings must be formed during deposition, the vacuum deposition techniques must be modified to deposit requisite patterns of sacrificial material to form the regions of the internal cavities and openings, over a base layer of structural material, then depositing a second layer of structural material over the sacrificial material and the base layer. The sacrificial material may then be removed, such as by etching, to leave the internal cavities and plurality of openings formed within the deposited bulk material. 
         [0040]    An alternative embodiment of the present invention is illustrated in  FIGS. 11 and 12 , in which an endoluminal stent configuration is depicted for example only. Those of ordinary skill in the art will understand and recognize that alternative device designs and geometries are also contemplated by the present invention. In accordance with the alternate embodiment of the invention there is illustrated an endoluminal stent  50  comprised of a plurality of structural elements  52  interconnected at a plurality of hinge regions  54  and defining a plurality of interstices  59  bounded by the plurality of structural elements and the plurality of hinge regions  54 . As described above, the material used to fabricate the inventive device has a Z-axis wall thickness in the device material. The inventive device incorporates at least one of a plurality of internal cavities  56  within the wall thickness of the material used to form the implantable device or endoluminal stent  50 . A plurality of micropores  58  are provided and communicate between a external surface of the device  50  and one of the plurality of internal cavities  56 . As noted above, the plurality of micropores  58  are dimensioned to permit the bioactive agent to elute from the at least one of a plurality of internal cavities  56  and through the associated plurality of micropores  58  by diffusion, osmotic pressure or under the influence of a positive pressure applied by cellular in-growth into the plurality of internal cavities  56  or under positive pressure applied by stress and/or strain exerted on the plurality of internal cavities  56  due to deformation of the individual structural elements  52 . The plurality of micropores  58  may furthermore be provided to communicate between an internal cavity  56  and either a luminal or abluminal surface of the inventive endoluminal stent, such as to expose the bioactive agent retained within the plurality of internal cavities  56  either to the blood stream, in the case of luminal micropores  58 , and/or to adjacent tissue, in the case of abluminal micropores  58 . 
         [0041]    The at least one of a plurality of internal cavities  56  may be continuous or discontinuous throughout the inventive device  50 . Specifically, in accordance with one preferred embodiment of the invention, the plurality of internal cavities  56  is discontinuous and each of the plurality of discontinuous internal cavities  56  reside within regions of the device  50  that are substantially non-load bearing regions of the device. In the particular embodiment illustrated in  FIG. 11 , the plurality of hinge regions  54  are devoid of internal cavities  56  because they are load bearing regions of the stent. It is contemplated, however, that regions of the inventive device  50  that are deformed or that are load bearing may include either continuous internal cavities  56  or discontinuous internal cavities within their wall thickness and provide for elution of a bioactive agent retained within the internal cavity positioned at the load bearing region under the influence of a positive motivating pressure exerted on the bioactive agent by deformation or load stress transferred by the device geometry to the internal cavity and to the bioactive agent. By providing regions of continuous and discontinuous internal cavities  56 , a plurality of bioactive agents may be loaded into different internal cavities  56  for achieving different elution rates and pharmacological effects.  FIG. 12  is a photomicrograph illustrating a transverse cross-sectional view through an individual structural element  52  illustrating the internal cavity  56 . 
         [0042]    Turning now to  FIGS. 13A-F  and  14  there is depicted a method for fabricating the inventive devices for delivery of bioactive agents. In  FIG. 13A  a first layer  64  of a device-forming metal, such as titanium, vanadium, aluminum, nickel, tantalum, zirconium, chromium, silver, gold, silicon, magnesium, niobium, scandium, platinum, cobalt, palladium, manganese, molybdenum and alloys thereof, such as zirconium-titanium-tantalum alloys, nitinol, or stainless steel is formed onto a sacrificial substrate material  62 . A sacrificial layer  66  is formed of a sacrificial material capable of being selectively removed without removing the underlying first layer  64 . The next step involves selective removal of portions of the sacrificial layer  66  to leave cavity-forming portions  68  of the first sacrificial layer  66 . A second layer  70  of a device forming metal, such as those enumerated above, is then formed onto the first layer  62  of the device forming metal and covers the cavity-forming portions  68 . 
         [0043]    In the next step, depicted in  FIG. 13D , the plurality of micropores  72  are formed and pass through the second layer  70  and communicate with the cavity-forming portions  68 . The plurality of micropores  72  may be formed by selective removal of the second layer  70  such as by laser or chemical etching. Alternatively, the second layer  70  of the device forming metal may be selectively formed such as to form the plurality of micropores  70  during forming of the second layer  70 . In the next step, depicted in  FIG. 13E , the sacrificial material of the cavity-forming portions  68  is selectively removed, such as by chemical etching of the cavity-forming portions  68 , without removing or effecting the material properties of either the first layer  64  or the second layer  70  of the device material, thereby leaving a plurality of internal cavities  74  defined within the second layer  70  and bounded by the first layer  64  of device material, with the plurality of micropores  70  communicating between the plurality of internal cavities  74  and an external surface of the device material  70 . Finally, in step  13 F, the sacrificial substrate material  62  is selectively removed thereby obtaining the inventive implantable device.  FIG. 14  is a photomicrograph illustrating a device formed in Step  13 E at the left panel and in Step  13 F in the right panel. 
         [0044]    In accordance with a preferred embodiment of the present invention, the above method is performed by vacuum deposition techniques to form the inventive implantable device. Suitable processed, include, for example, sputtering, reactive ion etching, chemical vapor deposition, plasma vapor deposition, or the like, as are known in the microelectronics fabrication arts and are more fully described in co-pending, commonly assigned U.S. patent application Ser. No. 09/443,929, filed Nov. 19, 1999, which is hereby incorporated by reference. 
         [0045]    It will be understood by those of ordinary skill in the art that alternative designs of implantable devices, for example grafts, patches, shunts, valves, filters or occluders, that do not require structural elements  52 , hinge regions  54  or interstices  56  of an endoluminal stent, yet have a device material with a Z-axis thickness that is suitable for incorporation of the internal cavities and micro-openings or micropores of the present invention to elute a bioactive agent. 
         [0046]    Regardless of which fabrication method is employed, the bioactive agent must be loaded into the internal cavities of the implantable device. Loading of the bioactive agent may be accomplished by flowing a liquid or semi-liquid state of the bioactive agent through the plurality of openings and into the internal cavities, either throughout the entire device or in regions of the implantable device. Flow loading may be facilitated by applying positive pressure, temperature change or both, such as is used in hot isostatic pressing (HIP). In HIP the pressurizing medium is typically a gas, and the process is carried out at elevated temperatures for specific time periods. While HIP is typically utilized to densify materials, to heal casting defects and voids, or to bond similar or dissimilar materials it may be used to drive a fluid or semi-fluid from external the implantable device into the internal cavities of the implantable device. Alternative, diffusion-mediated loading, osmotic loading or vacuum loading may be employed to load the bioactive agent into the internal cavities. 
         [0047]    While the present invention has been described with reference to its preferred embodiments, those of ordinary skill in the art will understand and appreciate that variations in structural materials, bioactive agents, fabrication methods, device configuration or device indication and use may be made without departing from the invention, which is limited in scope only by the claims appended hereto.