Patent Publication Number: US-2005143801-A1

Title: Systems and methods for overcoming or preventing vascular flow restrictions

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of PCT Patent Application Serial No. PCT/US02/32016, filed Oct. 5, 2002 and published on Apr. 17, 2003 as WO 03/030964 A2 which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      I. Field of the Invention  
      This invention generally relates to overcoming or preventing vascular flow restrictions for improved blood flow. More specifically, this invention relates to systems and methods which involve: (1) providing at least one structural element within or about a vessel having a vascular flow restriction; and (2) equipping the structural element with bio-lining such that it restores blood flow and minimizes, if not eliminates, the interface between blood and non-biological materials to thereby prevent restenosis.  
      II. Discussion of the Prior Art  
      Vascular stenosis is a major problem in health care worldwide, and is characterized as the narrowing (and potential blocking) of blood vessels as a result of the deposition of fatty materials, cellular debris, calcium, and/or blood clots (collectively referred to as “vascular flow restrictions”). Current treatments to overcome vascular flow restrictions include the administration of thombolytics (clot-dissolving drugs), interventional devices, and/or bypass surgery. As will be demonstrated below, these state-of-the-art techniques and devices all fail to adequately answer the vexing problem of maintaining blood flow through blood vessels.  
      Thrombolytics are typically administered in high doses. However, even with aggressive therapy, thrombolytics fail to restore blood flow in the affected vessel in about 30% of patients. In addition, these drugs can also dissolve beneficial clots or injure healthy tissue causing potentially fatal bleeding complications.  
      Interventional procedures include angioplasty, atherectomy, and laser ablation. However, the use of such devices to remove flow-restricting deposits may leave behind a wound that heals by forming a scar. The scar itself may eventually become a serious obstruction in the blood vessel (a process known as restenosis). Also, diseased blood vessels being treated with interventional devices sometimes develop vasoconstriction (elastic recoil), a process by which spasms or abrupt reclosures of the vessel occur, thereby restricting the flow of blood and necessitating further intervention. Approximately 40% of treated patients require additional treatment for restenosis resulting from scar formation occurring over a relatively long period, typically 4 to 12 months, while approximately 1-in-20 patients require treatment for vasoconstriction, which typically occurs from 4 to 72 hours after the initial treatment.  
      Percutaneous transluminal coronary angioplasty (PTCA), also known as balloon angioplasty, is a treatment for coronary vessel stenosis. In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient and advanced through the aorta until the distal end is in the ostium of the desired coronary artery. Using fluoroscopy, a guide wire is then advanced through the guiding catheter and across the site to be treated in the coronary artery. A balloon catheter is advanced over the guide wire to the treatment site. The balloon is then expanded to reopen the artery. The increasing popularity of the PTCA procedure is attributable to its relatively high success rate, and its minimal invasiveness compared with coronary by-pass surgery.  
      The benefit of balloon angioplasty, especially of the coronary arteries, has been amply demonstrated over the past decade. Angioplasty is effective to open occluded vessels that would, if left untreated, result in myocardial infarction or other cardiac disease or dysfunction. These benefits are diminished, however, by restenosis rates approaching 50% of the patient population that undergo the procedure. Restenosis is believed to be a natural healing reaction to the injury of the arterial wall that is caused by angioplasty procedures. The healing reaction begins with the clotting of blood at the site of the injury. The final result of the complex steps of the healing process is intimal hyperplasia, the migration and proliferation of medial smooth muscle cells (in a mechanism analogous to wound healing and scar tissue), until the artery is again stenotic or occluded. Such reocclusion may even exceed the clogging that prompted resort to the original angioplasty procedure. Accordingly, a huge number of patients experiencing a successful primary percutaneous transluminal coronary angioplasty (PTCA) procedure are destined to require a repeat procedure. The patient faces an impact on his or her tolerance and well being, as well as the considerable cost associated with repeat angioplasty.  
      To reduce the likelihood of reclosure of the vessel, it has become common practice for the physician to implant a stent in the patient at the site of the angioplasty or artherectomy procedure, immediately following that procedure, as a prophylactic measure. A stent is typically composed of a biologically compatible material (biomaterial) such as a biocompatible metal wire of tubular shape or metallic perforated tube. The stent should be of sufficient strength and rigidity to maintain its shape after deployment, and to resist the elastic recoil of the artery that occurs after the vessel wall has been stretched. The deployment procedure involves advancing the stent on a balloon catheter to the designated site of the prior (or even contemporaneous) procedure under fluoroscopic observation. When the stent is positioned at the proper site, the balloon is inflated to expand the stent radially to a diameter at or slightly larger than the normal unobstructed inner diameter of the arterial wall, for permanent retention at the site. The stent implant procedure from the time of initial insertion to the time of retracting the balloon is relatively brief, and certainly far less invasive than coronary bypass surgery. In this fashion, the use of stents has constituted a beacon in avoidance of the complication, risks, potential myocardial infarction, need for emergency bypass operation, and repeat angioplasty that would be present without the stenting procedure.  
      Despite its considerable benefits, coronary stenting alone is not a panacea, as studies have shown that about 30% of the patient population subjected to that procedure will still experience restenosis (referred to hereinafter as “in-stent restenosis”). While this percentage is still quite favorable compared to the approximate 50% recurrence rate for patients who have had a PTCA procedure without stent insertion at the angioplasty site, improvement is nonetheless needed to reduce the incidence of in-stent restenosis. In the past few years, considerable research has been devoted worldwide to studying the mechanisms of in-stent restenosis. It has been shown that the very presence of the stent in the blood stream may induce a local or even systemic activation of the patient&#39;s hemostase coagulation system, resulting in local thrombus formation which, over time, may restrict the flow of blood.  
      To avoid this problem, various efforts have been undertaken to coat or treat the surface of the stent to prevent or minimize thrombus formation. One approach to reducing in-stent restenosis involves coating the stent with a biocompatible, non-foreign body-inducing, biodegradable polylactic acid of thin paint-like thickness in a range below 100 microns, and preferably about 10 microns thick. Animal research has shown that a 30% reduction in in-stent restenosis may be achieved using this technique. This thin coating on a metallic stent may be used to release drugs incorporated therein, such as hirudin and/or a platelet inhibitor such as prostacyclin (PGI.sub.2), a prostaglandin. Both of these drugs are effective to inhibit proliferation of smooth muscle cells, and decrease the activation of the intrinsic and extrinsic coagulation system. Therefore, the potential for a very significant reduction in restenosis has been demonstrated in these animal experiments.  
      Other coating techniques involve coating the stent with a biodegradable substance or composition which undergoes continuous degradation in the presence of body fluids such as blood, to self-cleanse the surface as well as to release thrombus inhibitors incorporated in the coating. Disintegration of the carrier occurs slowly through hydrolytic, enzymatic or other degenerative processes. The biodegradable coating acts to prevent the adhesion of thrombi to the biomaterial or the coating surface, especially as a result of the inhibitors in the coating, which undergo slow release with the controlled degradation of the carrier. Blood components such as albumin, adhesive proteins, and thrombocytes can adhere to the surface of the biomaterial, if at all, for only very limited time because of the continuous cleansing action along the entire surface that results from the ongoing biodegradation.  
      Materials used for the biodegradable coating and the slow, continuous release of drugs incorporated therein include synthetic and naturally occurring aliphatic and hydroxy polymers of lactic acid, glycolic acid, mixed polymers and blends. Alternative materials for those purposes include biodegradable synthetic polymers such as polyhydroxybutyrates, polyhydroxyvaleriates and blends, and polydioxanon, modified starch, gelatine, modified cellulose, caprolactaine polymers, acrylic acid and methacrylic acid and their derivatives. It is important that the coating have tight adhesion to the surface of the biomaterial, which can be accomplished by applying the aforementioned thin, paint-like coating of the biodegradable material that may have coagulation inhibitors blended therein, as by dipping or spraying, followed by drying, before implanting the coated biomaterial device.  
      Anti-proliferation substances may be incorporated into the coating carrier to slow proliferation of smooth muscle cells at the internal surface of the vascular wall. Such substances include corticoids and dexamethasone, which prevent local inflammation and further inducement of clotting by mediators of inflammation. Substances such as taxol, tamoxifen and other cytostatic drugs directly interfere with intimal and medial hyperplasia, to slow or prevent restenosis, especially when incorporated into the coating carrier for slow release during biodegradation. Local relaxation of a vessel can be achieved by inclusion of nitrogen monoxide (NO) or other drugs that release NO, such as organic nitrates or molsidomin, or SIN1, its biologically effective metabolite.  
      The amount and dosage of the drug or combination of drugs incorporated into and released from the biodegradable carrier material is adjusted to produce a local suppression of the thrombotic and restenotic processes, while allowing systemic clotting of the blood. The active period of the coated stent may be adjusted by varying the thickness of the coating, the specific type of biodegradable material selected for the carrier, and the specific time release of incorporated drugs or other substances selected to prevent thrombus formation or attachment, subsequent restenosis and inflammation of the vessel.  
      The biodegradable coating may also be applied to the stent in multiple layers, either to achieve a desired thickness of the overall coating or a portion thereof for prolonged action, or to employ a different beneficial substance or substances in each layer to provide a desired response during a particular period following implantation of the coated stent. For example, at the moment the stent is introduced into the vessel, thrombus formation will commence, so that a need exists for a top layer if not the entire layer of the coating to be most effective against this early thrombus formation, with a relatively rapid release of the incorporated, potent anticoagulation drug to complement the self-cleansing action of the disintegrating carrier. For the longer term of two weeks to three months after implantation, greater concern resides in the possibility of intimal hyperplasia that can again narrow or fully obstruct the lumen of the vessel. Hence, the same substance as was present or a different substance from that in the top layer might be selected for use in the application of the coating to meet such exigencies. Hirudin, for example, can be effective against both of these mechanisms or phenomena.  
      A still further technique for preventing restenosis involves the use of radiation. U.S. Pat. No. 4,768,507 to Fischell et al. proposes in the use of a special percutaneous insertion catheter for purposes of enhancing luminal dilatation, preventing arterial restenosis, and preventing vessel blockage resulting from intimal dissection following balloon and other methods of angioplasty. U.S. Pat. No. 4,779,641 and co-pending European patent application No. 92309580.6 disclose the use of an interbiliary duct stent, wherein radioactive coils of a wire are embedded into the interior wall of the bile duct to prevent restenotic processes from occurring. U.S. Pat. No. 4,448,691 and co-pending European patent application No. 90313433.6 disclose a helical wire stent, provided for insertion into an artery following balloon angioplasty or atherectomy, which incorporates or is plated with a radioisotope to decrease the proliferation of smooth muscle cells. The disclosure teaches that the stent may be made radioactive by irradiation or by incorporating a radioisotope into the material of which the stent is composed. Another solution would be to locate the radioisotope at the core of the tubular stent or to plate the radioisotope onto the surface of the stent. The patent also teaches, aside from the provision of radioactivity of the stent, that an outer coating of anti-thrombogenic material might be applied to the stent.  
      U.S. Pat. No. 5,059,166 to Fischell et al. discloses a helical coil spring stent composed of a pure metal which is made radioactive by irradiation. Alternative embodiments disclosed in summary fashion in the patent include a steel helical stent which is alloyed with a metal that can be made radioactive, such as phosphorus (14.3 day half life); or a helical coil which has a radioisotope core and a spring material covering over the core; or a coil spring core plated with a radioisotope such as gold 198 (Au.sup.198, which has a half life of 2.7 days), which may be coated with an anti-thrombogenic layer of carbon.  
      Clinical basic science reports such as “Inhibition of neointimal proliferation with low dose irradiation from a beta particle emitting stent” by John Laird et al published in Circulation (93: 529-536, 1996) describe creating a beta particle-emitting stent by bombarding the outside of a titanium wire with phosphorus. The implantation of phosphorus into the titanium wire was achieved by placing the P.sup.31 into a special vacuum apparatus, and then vaporizing, ionizing and, accelerating the ions with a higher voltage so that the P.sup.31 atoms become buried beneath the surface of the titanium wire in a thickness of about ⅓ micron. After exposing the wire together with the phosphorus radioisotope for several hours to a flux of slow neutrons part of the P.sup.31 atoms were converted into a P.sup.32, a pure beta particle emitter with a maximum energy of 1.709 megaelectron-volts, an average of 0.695 megaelectron-volts, and a half-life of 14.6 days.  
      Despite the convincing clinical results obtained by this method, practical application of the method in human patients raises considerable concerns. First, it is difficult to create a pure beta emitter from phosphorus if a stent is exposed to a flux of slow neutrons. In addition to converting phosphorus from P.sup.31 to P.sup.32, the metallic structure of the titanium wire will become radioactive. Therefore, about 20 days are needed to allow the radiation to decay, especially gamma radiation which originates from the titanium wire. Even worse is the situation where a metal such as stainless steel undergoes radioactive irradiation, resulting in production of unwanted .gamma. radiation and a wide range of short and long term radionuclei such as cobalt.sup.57, iron.sup.55, zinc.sup.65, molybdenum.sup.99, cobalt.sup.55. A pure beta radiation emitter with a penetration depth of about 3 millimeters is clearly superior for a radioactive stent for purposes of local action, side effects, and handling.  
      Reports have indicated that good results have been obtained with a radioactive wire inserted into the coronary arteries or into arteriosclerotic vessels of animals. Results obtained with a gamma radiation source from a wire stems from the deeper penetration of gamma radiation, which is about 10 mm. Assuming that the vessel is 3 to 4 mm in diameter, a distance of 2 to 4 mm depending on the actual placement of the wire toward a side wall has to be overcome before the radiation acts. Therefore, the clinical results that have been obtained with radioactive guide wires that have been inserted into the coronary arteries for a period ranging from about 4 to 20 minutes for delivery of a total dosage of about 8 to 18 Gray (Gy) have shown that gamma radiation has a beneficial effect while beta radiation from a wire is less favorable. On the other hand, gamma radiation which originates from a stainless steel stent such as composed of 316 L is less favorable since the properties of .beta. radiation such as a short half-life and a short penetration depth are superior to .gamma. radiation originating from radioactive 316 L with a long half-life and a deeper penetration since the proliferative processes of smooth muscle cell proliferation occur within the first 20 to 30 days and only in the very close vicinity of the stent.  
      In addition, a half-life which is too short such as one to two days considerably impacts on logistics if a metallic stent needs to be made radioactive. That is, by the time the stent is ready for use, its radioactivity level may have decayed to a point which makes it unsuitable for the intended purpose.  
      Another technique for preventing in-stent restenosis involves providing stents seeded with endothelial cells (Dichek, D. A. et al Seeding of Intravascular Stents With Genetically Engineered Endothelial Cells; Circulation 1989; 80: 1347-1353). In that experiment, sheep endothelial cells that had undergone retrovirus-mediated gene transfer for either bacterial beta-galactosidase or human tissue-type plasmogen activator were seeded onto stainless steel stents and grown until the stents were covered. The cells were therefore able to be delivered to the vascular wall where they could provide therapeutic proteins. Other methods of providing therapeutic substances to the vascular wall by means of stents have also been proposed such as in international patent application WO 91/12779 “Intraluminal Drug Eluting Prosthesis” and international patent application WO 90/13332 “Stent With Sustained Drug Delivery”. In those applications, it is suggested that antiplatelet agents, anticoagulant agents, antimicrobial agents, antimetabolic agents and other drugs could be supplied in stents to reduce the incidence of restenosis.  
      In the vascular graft art, it has been noted that fibrin can be used to produce a biocompatible surface. For example, in an article by Soldani et al., “Bioartificial Polymeric Materials Obtained from Blends of Synthetic Polymers with Fibrin and Collagen” International Journal of Artificial Organs, Vol. 14, No. 5, 1991, polyurethane is combined with fibrinogen and cross-linked with thrombin and then made into vascular grafts. In vivo tests of the vascular grafts reported in the article indicated that the fibrin facilitated tissue ingrowth and was rapidly degraded and reabsorbed. Also, in published European Patent Application 0366564 applied for by Terumo Kabushiki Kaisha, Tokyo, Japan, discloses a medical device such as an artificial blood vessel, catheter or artificial internal organ is made from a polymerized protein such as fibrin. The fibrin is said to be highly nonthrombogenic and tissue compatible and promotes the uniform propagation of cells that regenerates the intima. Also, in an article by Gusti et al., “New Biolized Polymers for Cardiovascular Applications”, Life Support Systems, Vol. 3, Suppl. 1, 1986, “biolized” polymers were made by mixing synthetic polymers with fibrinogen and cross-linking them with thrombin to improve tissue ingrowth and neointima formation as the fibrin biodegrades. Also, in an article by Haverich et al., “Evaluation of Fibrin Seal in Animal Experiments”, Thoracic Cardiovascular Surgeon, Vol. 30, No. 4, pp. 215-22, 1982, the authors report the successful sealing of vascular grafts with fibrin. However, none of these teach that the problem of restenosis could be addressed by the use of fibrin and, in fact, conventional treatment with anticoagulant drugs following angioplasty procedures is undertaken because the formation of blood clots (which include fibrin) at the site of treatment is thought to be undesirable.  
      As evidenced by the foregoing, the prior art is replete with attempts at solving the problem of vascular flow restrictions. Notwithstanding these efforts, the prior art systems and methods all suffer significant drawbacks which inhibit widespread adoption and success, as evidenced by the multitude of attempts in this area. The present invention is directed at overcoming, or at least reducing the effects of, one or more of the problems set forth above.  
     SUMMARY OF THE INVENTION  
      The present invention helps overcome the drawbacks of the prior art by providing systems and methods for overcoming or preventing vascular flow restrictions. More specifically, the present invention includes systems and methods which involve solve the problems in the prior art by: (1) providing at least one structural element within or about a vessel having a vascular flow restriction; and (2) equipping the structural element with bio-lining such that it restores blood flow and minimizes, if not eliminates, the interface between blood and non-biological materials. By reducing or eliminating this “blood-device” interface, the present invention prevents (or at the very least lessens) the re-formation of vascular flow restrictions within the diseased vessel (otherwise known as “vascular restenosis”). The various systems and methods described below all address the goal of overcoming vascular flow restrictions for improved blood flow.  
      In one broad aspect, the present invention overcomes or prevents vascular flow restrictions by providing a bio-lined structural element for placement within a diseased or occluded blood vessel. The structural element may comprise any number of devices or components capable of providing sufficient structural support to maintain the lumen of a blood vessel in a sufficiently open and unrestricted state once deployed within or about the blood vessel. Such devices or components may include, but are not necessarily limited to, any number of stent or stent-like devices of generally tubular, meshed construction. The bio-lining provided within the structural element may comprise any number of lining materials having characteristics which prevent or reduce the formation of vascular flow restrictions when deployed within a blood vessel. Such lining materials may include, but are not necessarily limited to, autologous vessel (harvested from the patient), tissue-engineered vessel (preferably based on the patient&#39;s own DNA), or synthetic vessel, or combination of any or all above-mentioned tissue.  
      Still other broad aspects of the present invention involve preparing the bio-lined structural element for use in overcoming vascular flow restrictions. One such aspect involves harvesting autologous tissue from the patient for use as the bio-lining according to the present invention. A more particular aspect involves implanting the structural element over a blood vessel within the patient for a sufficient duration such that the blood vessel actually grows into (and becomes imbedded within) the structural element and can be thereafter harvested and used in the patient. A still further aspect involves harvesting a length of autologous blood vessel for immediate affixation within the structural element, such as through the use of cutting devices and/or cutting catheters. Yet another aspect involves equipping a structural element with a bio-lining created through tissue-engineering techniques.  
      Further broad aspects of the present invention involve overcoming vascular flow restrictions by disposing a structural element about some or all of the periphery of a native vessel suffering from a vascular flow restriction and thereafter affixing the structural element to the native vessel. By buttressing the vessel in this fashion, the lumen of the vessel suffering the vascular flow restriction may become “opened” or otherwise widened to increase the inner diameter, thereby producing improved blood flow.  
      Still other broad aspects of the present invention involve overcoming vascular flow restrictions by providing a pair of bio-lined structural elements disposed a distance from one another and connected by a length of bio-lining. In this fashion, each of the bio-lined structural elements may be deployed on either side of a vascular flow restriction such that flow is restored through the length of bio-lining that extends there between.  
      Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The following description of the preferred embodiments of the present invention will be better understood in conjunction with the appended drawings, in which:  
       FIG. 1  is a cross-sectional view of a bio-lined structural element according to one aspect of the present invention;  
       FIG. 2  is a cross-sectional view of a bio-lined structural element according to one aspect of the present invention;  
       FIG. 3  is a cross-sectional view of a bio-lined structural element according to one aspect of the present invention;  
       FIG. 4  is an enlarged view of a coupling member according to one aspect of the present invention;  
       FIG. 5  is a cross-sectional view of a deployment catheter according to one aspect of the present invention;  
       FIG. 6  is an enlarged view of a catheter body of the deployment catheter shown in  FIG. 5 ;  
       FIG. 7  is a cross-sectional view of the catheter body taken through lines  7 - 7  in  FIG. 6 ;  
       FIG. 8  is an enlarged view of a coupling member disposed within the wall of the balloon of the deployment catheter of  FIG. 5 ;  
       FIG. 9  is an enlarged view showing a plurality of alternate coupling members for use in the present invention;  
       FIG. 10  is a cross-sectional view of a bio-lined structural element employing an inner structural element according to one aspect of the present invention;  
       FIG. 11  is a side view of an inner structural according to one aspect of the present invention;  
       FIG. 12  is a top view of an inner structural element according to one aspect of the present invention;  
       FIG. 13  is a side view of an inner structural element according to one aspect of the present invention;  
       FIG. 14  is a side view of an inner structural element according to one aspect of the present invention;  
       FIG. 15  is a side view of the inner structural element shown in  FIG. 14 ;  
       FIG. 16  is a cross-sectional view illustrating the method of implanting a structural element over a length of autologous blood vessel to prepare a bio-lined structural element according to the present invention;  
       FIG. 17  is a perspective view of a structural element for implanting over a length of autologous blood vessel to produce a bio-lined structural element according to one aspect of the present invention;  
       FIG. 18  is a perspective view of a structural element for implanting over a length of autologous blood vessel to produce a bio-lined structural element according to one aspect of the present invention;  
       FIG. 19  is a cross-sectional view of a structural element immediately upon implantation according to one aspect of the present invention;  
       FIG. 20  is a cross-sectional view of a structural element after a period of implantation according to one aspect of the present invention;  
       FIG. 21  is a cross-sectional view illustrating a step of harvesting the bio-lined structural element according to one aspect of the present invention;  
       FIG. 22  is a cross-sectional view illustrating a step of harvesting the bio-lined structural element according to one aspect of the present invention;  
       FIG. 23  is a cross-sectional view illustrating the method of implanting a structural element over two lengths of autologous blood vessel to prepare a bio-lined structural element according to the present invention;  
       FIG. 24  is a partial cross-sectional view of a cutting catheter according to one aspect of the present invention;  
       FIGS. 25-27  are cross-sectional views illustrating the introduction of a guidewire and preparation of a target vessel for harvesting autologous bio-lining according to one aspect of the present invention;  
       FIG. 28  is a partial cross-sectional view illustrating a dilator and introducer positioned within the target vessel following the steps shown in  FIGS. 25-27  according to one aspect of the present invention;  
       FIG. 29  is a partial cross-sectional view illustrating the advancement of the cutting catheter shown in  FIG. 24  over the dilator and introducer according to one aspect of the present invention;  
       FIG. 30  is a partial cross-sectional view illustrating the cutting catheter advanced to extricate the target autologous bio-lining from surrounding tissue and a deployment catheter of the type shown in  FIGS. 5-8  disposed within the introducer according to one aspect of the present invention;  
       FIG. 31  is a partial cross-sectional view illustrating the deployment catheter in use (deploying coupling members into autologous bio-lining within a patient) after being advanced through the end of the introducer and past the cutting catheter according to one aspect of the present invention;  
       FIG. 32  is a partial cross-sectional view illustrating the cutting catheter in use after the deployment has been employed to deploy the coupling members into the autologous bio-lining according to one aspect of the present invention;  
       FIG. 33  is a partial cross-sectional view illustrating the step of severing the distal end of the autologous bio-lining for withdrawal from the patient according to one aspect of the present invention;  
       FIG. 34  is a partial cross-sectional view illustrating the step of severing the distal end of the autologous bio-lining for withdrawal from the patient according to one aspect of the present invention;  
       FIGS. 35-39  are partial cross-sectional views illustrating alternate embodiments of the cutting catheter according to several aspects of the present invention;  
       FIG. 40  is a partial cross-sectional view of a holding catheter according to one aspect of the present invention;  
       FIG. 41  is a partial cross-sectional view of the holding catheter shown in  FIG. 40  in use according to one aspect of the present invention;  
       FIG. 42  is a side view of a windowed cutting catheter according to one aspect of the present invention;  
       FIGS. 43-44  are cross-sectional views of a bio-lined structural element according to one aspect of the present invention;  
       FIGS. 45-46  are cross-sectional views of a bio-lined structural element according to one aspect of the present invention;  
       FIGS. 47-48  are cross-sectional views of a bio-lined structural element according to one aspect of the present invention;  
       FIGS. 49-52  are cross-sectional views illustrating a connector assembly and its use for connecting the two lengths of bio-lining to form the bio-lined structural element shown in  FIGS. 47-48  according to one aspect of the present invention;  
       FIGS. 53-55  are cross-sectional views illustrating a connector assembly and its use for connecting the two lengths of bio-lining to form the bio-lined structural element shown in  FIGS. 47-48  according to one aspect of the present invention;  
       FIGS. 56-57  are cross-sectional views illustrating the manner in which structural elements of the type shown in  FIGS. 47-48  are coupled to the bio-lining according to one aspect of the present invention;  
       FIG. 58  is a cross-sectional view illustrating the manner in which structural elements of the type shown in  FIGS. 47-48  are coupled to the bio-lining according to one aspect of the present invention;  
       FIGS. 59-60  are cross-sectional views illustrating the manner in which structural elements of the type shown in  FIGS. 47-48  are coupled to the bio-lining according to one aspect of the present invention;  
       FIGS. 61-62  are cross-sectional views illustrating the manner in which structural elements of the type shown in  FIGS. 47-48  are coupled to the bio-lining according to one aspect of the present invention;  
       FIG. 63 a  cross-sectional view of a bio-lined structural element according to one aspect of the present invention;  
       FIGS. 64-68  are side views illustrating a manner of introducing a self-expanding bio-lined structural element within a blood vessel according to one aspect of the present invention;  
       FIG. 69  is side view illustrating a constricting device and self-expanding structural element according to one aspect of the present invention;  
       FIG. 70  is an enlarged view of the self-expanding structural element according to one aspect of the present invention;  
       FIG. 71  is a top view of the constricting device of the type shown in  FIG. 69  according to one aspect of the present invention; and  
       FIG. 72  is a side view of the handle member of the constriction device according to one aspect of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Illustrative embodiments of the present invention are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with business-related constraints, which may vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
      The present invention provides systems and methods for overcoming or preventing vascular flow restrictions which involve minimizing (if not eliminating) the extent to which blood interfaces with a structural element deployed within or about a diseased vessel to restore blood flow. By reducing or eliminating this “blood-device” interface, the present invention prevents (or at the very least lessens) the re-formation of vascular flow restrictions within the diseased vessel (otherwise known as “vascular restenosis”). The various systems and methods described below all address the goal of overcoming vascular flow restrictions for improved blood flow. Although set forth individually, it will be appreciated that the various features of any given design or system disclosed herein may be combined with those of other designs or systems disclosed herein without departing from the scope of the present invention.  
      I. Bio-Lined Structural Element  
      In one broad aspect, the present invention overcomes the problems of the prior art by providing a bio-lined structural element for placement within a diseased blood vessel. The structural element may comprise any number of devices or components capable of providing sufficient structural support to maintain the lumen of a blood vessel in a sufficiently open and unrestricted state once deployed within or about the blood vessel. Such devices or components may include, but are not necessarily limited to, any number of stent or stent-like devices of generally tubular, meshed construction. The bio-lining provided within the structural element may comprise any number of lining materials having characteristics which prevent or reduce the formation of vascular flow restrictions when deployed within a blood vessel. Such lining materials may include, but are not necessarily limited to, autologous vessel (harvested from the patient), tissue-engineered vessel (preferably based on the patient&#39;s own DNA), or synthetic vessel, or combination of any or all above-mentioned tissue. The structural element and/or bio-lining may also be equipped with a therapeutic agent capable of inhibiting smooth muscle cell proliferation and/or proliferation or migration of fibroblast cells, including but not limited to a combination of therapeutic agents, such as a first agent of paclitaxel and a second therapeutic agent of camptothecin, colchicine or dexamethasone.  
      A. Bio-Lined Structural Element Design(s)  
       FIG. 1  illustrates a bio-lined structural element  10  according to a first broad aspect of the present invention. The bio-lined structural element  10  includes a structural element  12  having a length of bio-lining  14  disposed therein. The bio-lining  14  may be adhered, affixed, or otherwise coupled to the interior of the structural element  12  using any number of different methods, manners, compositions, or devices (several of which will be discussed below by way of example only). The structural element  12  is preferably of a radially expandable construction such that it can be introduced into a diseased or occluded blood vessel while in a contracted state of minimal diameter and thereafter deployed into an expanded state of increased diameter. Deploying the bio-lined structural element  10  is this fashion serves to maintain or restore blood flow therethrough the diseased or occluded vessel. In an important aspect, the bio-lining  14  prevents the blood from interfacing or contacting the structural element  12  or the diseased wall of the vessel (i.e. coronary artery). In this fashion, the bio-lined structural element  10  of the present invention prevents or minimizes restenosis within the diseased blood vessel.  
      In one embodiment, the structural element  12  comprises a stent having a generally tubular, meshed construction and the bio-lining  14  comprises a length of autologous vessel harvested from the patient. It will be appreciated, however, these choices are set forth by way of example only and are in no way limiting on the broad scope of the present invention. When provided as a stent, the structural element  12  may be of self-expanding or balloon-expandable construction. Structural element  12  may be composed of any number of different biocompatible materials, including but not limited to biocompatible metals (such as stainless steel, titanium, tungsten, tantalum, gold, platinum, cobalt, iridium, alloys thereof, and shape-memory alloys) and biocompatible polymers or plastics (such as polytetra-fluoroethylene (PTFE), polyamides, polyimides, silicones, acrylates, methacrylates, fluorinated polymers, homo-polymers, copolymers or polymer blends. By way of example only, the structural element  12  may be a stent composed of a copolymer of acrylate and methacrylate, such as that described in U.S. Pat. No. 5,163,952 (the contents of which is incorporated by reference in its entirety).  
      The structural element  12  and bio-lining  14  may have a selected axial length and maximum diameter determined according to the size of the lesion or treatment area within the blood vessel and the diameter of the blood vessel. Although not shown, the bio-lining  14  may be sized slightly longer than the structural element  12  in order to fold or dispose the ends of the bio-lining  14  over the ends of the structural element  12 . This effectively covers the ends of the structural element  12  to further reduce the blood-device interface once deployed within a treatment site. Although not shown, the structural element  12  may also be equipped with an outer sleeve or element (of biocompatible polymeric and/or metallic construction) capable of being positioned over the structural element  12 . Such an outer sleeve or element may be useful in bolstering the strength of the structural element  12 , covering any sharp edges on the structural element  12 , and/or preventing the protrusion of any diseased vessel through the structural element  12  that may otherwise contact the exterior surface of the bio-lining and possibly affect the form or function of the bio-lined structural element.  
      Any of a variety of techniques may be employed to affix or otherwise couple the bio-lining  14  within the structural element  12  according to the present invention, including mechanical or adhesive technology. Such mechanical coupling may be accomplished, for example, via barbed coupling members, ultrasonic welding, resistive heating and laser irradiation. Such adhesive coupling may be accomplished, for example, via fluorinated thermoplastic polymer adhesives such as fluorinated ethylene/propylene copolymers, perfluoroalkoxy fluoro-carbons, ethylene/tetrafluoroethylene copolymers, fluoroacrylates, and fluorinated polyvinyl ethers.  
      Still other techniques involve the use of bio-compatible adhesives. That is, any of a variety of suitable bio-compatible adhesives (including but not limited to UV-activated bio-glue and/or fibrin) may be employed to affix the bio-lining  14  within the structural element  12 . This can be accomplished (by way of example only) via the following method: (a) applying adhesive to the exterior of the bio-lining  14  and/or interior surface of the structural element  12 ; (b) advancing the bio-lining  14  into the structural element  12 ; (c) bringing the exterior surface of the bio-lining  14  into contact with the interior surface of the structural element  12 ; and (d) curing the glue. In one embodiment, step (c) may be accomplished by introducing an instrument through the lumen of the bio-lining  14 , wherein the instrument is dimensioned to expand the bio-lining  14  such that it is brought into abutting relation with the interior surface of the structural element  12 . When employing UV-activated bio-glue, step (d) may be accomplished by subjecting the bio-lining  14  and structural element  12  to ultra-violet light in an amount and/or duration sufficient to cure the bio-glue.  
       FIG. 2  illustrates, by way of example only, one manner of coupling the bio-lining  14  to the structural element  12 . Namely, a plurality of sutures  24  may be provided to physically couple or attach the bio-lining  14  to the interior of the structural element  12 . To create the sutures  24 , a surgeon may simply advance a needle (not shown) through the structural element  12  such that the suture material extends into the bio-lining  14  and returns through the structural element  12  to be tied off. By creating a plurality of such sutures  24 , the bio-lining  14  will be effectively coupled to the interior of the structural element  12  such that the combination may thereafter be contracted, introduced into a treatment site, and deployed for improved blood flow according to the present invention.  
      The sutures  24  may comprise any number of bio-compatible suture or devices which perform suture-like functions, including but not limited to sutures, thread-like materials, and/or surgical staples. Sutures  24  may also comprise any of a variety of bio-degradable materials, including but not limited to fibrin and/or collagen-based materials. In this fashion, the sutures  24  will be able to maintain the bio-lining  14  securely within the structural element  12  for a sufficient period to promote the ingrowth of the bio-lining  14  into the structural element  12 . At some point after such ingrowth, the sutures  24  will deteriorate according to their bio-degradable characteristics, thereby removing any “dimples” on the interior of the bio-lining  14  that may sometimes occur due to the sutures  24 . Removal of such “dimples” advantageously makes the interior of the bio-lining  14  as smooth as possible for improved laminar blood flow past the treatment site.  
       FIG. 3  illustrates, by way of example only, yet another manner of coupling the bio-lining  14  to the structural element  12 . Namely, a plurality of coupling members  16  are provided to physically couple or attach the bio-lining  14  to the interior of the structural element  12 . With combined reference to  FIGS. 3 and 4 , each coupling member  16  includes a shaft  18  having a penetrating tip  20  at the distal end and an enlarged base  22  at the proximal end. As will be discussed in greater detail below, the coupling members  16  are designed such that, upon deployment, the penetrating tips  20  pass through the bio-lining  14  and engage with the structural element  12 , while the enlarged bases  22  abut against the interior of the bio-lining  14 . In this fashion, deployment of the coupling members  16  draws the bio-lining  14  into contact with the interior of the structural element  12  and thereby affixes the bio-lining  14  within the structural element  12 .  
       FIGS. 5-8  illustrate one manner of deploying the coupling members  16  according to the present invention. Referring initially to  FIG. 5 , a deployment catheter  30  is provided having a catheter body  36  with an inflatable balloon  32  disposed on the distal end thereof. With reference to  FIGS. 5-7 , the catheter body  36  is preferably of multi-lumen construction, having a centrally located guide-wire lumen  38  and an inflation lumen  40 . Referring to  FIGS. 5 and 8 , the balloon  32  is designed to receive a plurality of coupling members  16 . This may be accomplished, for example, by encapsulating the coupling members  16  (at least partially) within the wall of the balloon  32  during manufacture of the balloon  32  (such as through injection molding). Another possible fabrication method entails dipping in urethane or silicone a cylinder that is holding several coupling members  16  in an appropriate position.  
      In either case (as shown most clearly in  FIG. 8 ), a cavity  34  will result for each coupling member  16  to envelop the base  22  and, if desired, a portion of the shaft  18 . This effectively maintains each coupling member  16  in an appropriate position for proper deployment. In a preferred embodiment, this “appropriate position” is one in which the coupling members  16  are disposed within the wall of the balloon  32  such that the penetrating tips  20  are pointing in a generally radially outward manner. Upon inflation and expansion of balloon  32 , the coupling members  16  will be driven outwardly such that the penetrating tips  20  pierce through the bio-lining  14  and become engaged with the structural element  12 . The inflation of the balloon  32  will simultaneously serve to loosen or dislodge the bases  22  from within the balloon cavities  34 . The balloon  32  may thereafter be deflated and removed along with the rest of the catheter  30 , leaving the bio-lining  14  securely coupled within the structural element  12 .  
      Although shown in a specific configuration in  FIGS. 3-8 , it will be appreciated that coupling members  16  may be arranged in any number of different fashions and provided in varying quantities and/or dimensions depending upon the application. For example, although shown in  FIG. 3  deployed in a plurality of rows, it will be appreciated that the coupling members  16  may be deployed in any number of different configurations, including but not limited to spiral, criss-cross, or randomly disposed. Coupling members  16  may also be provided in any number of different designs, such as those shown by way of example in  FIG. 9 .  
      Coupling members  16  may comprise any number of suitable biocompatible materials, including but not limited to polytetrafluoroethylene (PTFE), stainless steel, polyamides, polyimides, silicones, acrylates, methacrylates, fluorinated polymers, homopolymers, copolymers or polymer blends. Coupling members  16  may also comprise any of a variety of bio-degradable materials. An advantageous aspect of constructing coupling members  16  from bio-degradable material is that the (albeit modest) blood-device interface due to the bases  22  will be eliminated once the bio-degradation process is complete. Elimination of the bases  22  will also result in improved laminar blood flow, as described above with reference to the bio-degradable sutures  24  of  FIG. 2 .  
      Although the coupling members  16  shown in  FIGS. 3-9  are separate and distinct from each other (i.e. not interconnected), it is contemplated as part of the present invention to provide the coupling members  16  as part of a unitary structure such that the coupling members  16  are interconnected. For example, with reference to  FIG. 10 , the coupling members  16  can be formed as part of an inner structural element  42 . Structural element  42  is preferably constructed according to the same principles set forth above with regard to structural element  12 . That is, structural element  42  is preferably of a radially expandable construction such that it can be introduced within the bio-lining  14  while in a contracted state of minimal diameter and thereafter be deployed into an expanded state of increased diameter.  
      In one embodiment, the structural element  42  may comprise a stent having a generally tubular, meshed construction. Structural element  42  may comprise any number of suitable biocompatible materials, including but not limited to those enumerated above with reference to structural element  12 . Although a blood-device interface does exist once the bio-lined structural element  10  is deployed within a treatment site, the meshed nature of such a stent-type structural element  42  minimizes the extent to which blood interfaces with the structural element  42 . This, in turn, reduces the likelihood of restenosis within the treatment site. With reference to  FIG. 11 , this blood-device interface may be further reduced by providing the stent-type structural element  42  having a spiral construction.  
       FIGS. 12-14  illustrate (by way of example only) various manners of constructing the stent-type structural element  42  according to a still further aspect of the present invention. For clarity, these stent designs are shown as if each stent-type structural element  42  were longitudinally cut and opened so as to lie flat within the plane of the paper. It will be appreciated, however, that each stent-type structural element  42  has a generally tubular shape in practice. Each stent-type structural element  42  is constructed having a plurality of interconnected “V” shaped elements  44 ,  46 ,  48  (and straight element  50  in  FIG. 14 ). Whether balloon-expandable or self-expanding, each stent-type structural element  42  is constructed such that the coupling members  16  have a low-profile prior to deployment. That is, the coupling members  16  lie within the same general plane as the “V” shaped elements  44 - 50  prior to deployment.  
      Upon deployment, the “V” shaped elements  44 - 48  forming the stent-type structural element  42  will distend and become generally straightened. In an important aspect, this straightening of the “V” shaped elements  44 - 48  causes the coupling members  16  to extend generally perpendicularly from the generally cylindrical shape of the fully deployed stent-type structural element  42 . In this fashion, each coupling member  16  will extend through the bio-lining  14  and engage with the mesh of the outer stent-type structural element  12  as shown in  FIG. 10 . The coupling members  16  may be provided in any number of different configurations, including but not limited to the “arrow-type” design shown in  FIGS. 12-13  and the “hook-type” design shown in  FIGS. 14-15 .  
      B. Bio-Lining Preparation  
      As noted above, the bio-lining  14  may comprise any number of lining materials having characteristics that prevent or reduce the formation of vascular flow restrictions when deployed within a blood vessel. These materials include, but are not limited to, autologous vessel (harvested from the patient), tissue-engineered vessel (preferably based on the patient&#39;s own DNA), or synthetic vessel, or combination of any or all above-mentioned tissue. The following discussion sets forth, by way of example only, various manners of harvesting autologous tissue from the patient for use as the bio-lining  14  according to the present invention. It will be readily appreciated, therefore, that any number of different techniques for bio-lining preparation (i.e. using synthetic vessel and/or tissue-engineered vessel) may be employed without departing from the scope of the present invention. Moreover, it is to be readily understood that the following systems and methods of bio-lining preparation involving autologous tissue are set forth by way of example only.  
      1. Structural Element Implantation  
       FIG. 16  illustrates one manner of preparing autologous bio-lining which involves implanting the structural element  12  over a blood vessel  14  within the patient for a sufficient duration such that the blood vessel  14  actually grows into (and becomes imbedded within) the structural element  12 . This process may be undertaken in any number of different methods. One such method involves: (a) gaining access to a suitable blood vessel within the patient; (b) implanting the structural element  12  over the blood vessel; and (c) removing the structural element  12  from the patient after a sufficient duration has elapsed for the blood vessel  14  to have grown into (and become imbedded within) the structural element  12 .  
      Step (a) of gaining access to a suitable blood vessel may be performed in any number of fashions, including but not limited to surgically cutting away various tissues or muscles in order to gain direct access to the given blood vessel. The blood vessel itself may include any number of suitable vessels within the patient, including but not limited to the radial artery and/or the internal mammary artery.  
      Step (b) of implanting the structural element  12  may be performed in any number of fashions, including but not limited to those involving severing the target blood vessel during implantation and those which leave the blood vessel undisturbed until the entire system (bio-lined structural element  10 ) is removed from the patient. The method involving severing the blood vessel may comprise the following steps: (i) severing the blood vessel at a single point along its exposed length; (ii) passing the structural element  12  over the severed blood vessel; and (iii) re-connecting (such as by suturing, surgical stapling, or other coupling devices) the ends of the severed blood vessel such that the structural element  12  is implanted over the blood vessel.  
      The method of implantation which leaves the blood vessel undisturbed (that is, non-severed) until eventual harvest may be accomplished in any number of different fashions. These include, but are not necessarily limited to, providing the structural element  12  such that it has a “placeable” design. As used herein, “placeable” is defined as any design that allows the structural element  12  to be positioned entirely or partially around the target blood vessel without first cutting or severing the target blood vessel. Such “placeable” structural elements  12  may include, but are not necessarily limited to, rollable stent devices of the type shown in U.S. Pat. No. 5,833,707 and stents or stent-type devices constructed from shape-memory materials such as Nitinol or shape-memory polymers described in U.S. Pat. No. 5,163,952 (the disclosures of both are hereby expressly incorporated by reference into this disclosure).  
       FIGS. 17-18  illustrate a still further manner of providing the structural element  12 , featuring a semi-circular cross section comprised of (in  FIG. 17 ) a plurality of arcuate members  25  and/or (in  FIG. 18 ) a single coil-type arcuate member  25 . According to one aspect of the present invention, the arcuate members  25  may be hinged (as in  FIG. 17 ) or otherwise deformable (such as a coil-type arrangement in  FIG. 18 ) such that they can be manipulated into position about the target vessel. The arcuate members  25  may also be dimensioned such that, when fully positioned about the target vessel, a channel or slot  26  is created between the ends of the arcuate members  25 . Such a slot or channel  26  may be particularly advantageous in ensuring uninterrupted blood flow into side branches during the implantation period. That is, the structural element  12  may be positioned such that the side branches from the blood vessel extend through the slot  26 . In so doing, the side branches will be free from impingement or crimping by the structural element  12 , thereby ensuring uninterrupted blood flow.  
       FIGS. 19-22  further illustrate the implantation and harvesting process according to the present invention.  FIG. 19  shows the structural element  12  immediately upon implantation over the target vessel  14  (such as the radial artery).  FIG. 20  shows the structural element  12  after the passage of time, wherein the target vessel  14  has grown into (and becomes imbedded within) the structural element  12 . For clarity, the structural element  12  is shown with such tissue ingrowth  28  extending between the arcuate members  25 . It will be appreciated, however, that such ingrowth will also take place into the actual arcuate members  25 , particularly where the structural element  12  is provided as a stent or stent-type structure.  FIGS. 21-22  shows two exemplary manners of removing the structural element  12  after tissue ingrowth has occurred. Namely, as shown in  FIG. 21 , scissors  54  may be employed to cut the blood vessel  14  on either side of the structural element  12 . As shown in  FIG. 22 , this may also be accomplished through the use of surgical stapling devices capable of sealing off the blood vessel on either side of the structural element  12  with staples  56 .  
      Although shown and described above with reference to a single structural element  12  for implantation, it is to be readily understood that the present invention clearly contemplates and covers the use of a plurality of structural elements  12  to overcome vascular flow restrictions. For example, as shown in  FIG. 23 , two separate structural elements  12  may be implanted over the target vessel  14  such that the structural elements  12  are separated by a predetermined distance. Following sufficient ingrowth, the structural elements  12  may be harvested from the patient such that a length of unsupported blood vessel  14  extends therebetween. One advantage of such a configuration is that, upon deployment into a region of vascular flow restriction, the unsupported region of the vessel  14  may be positioned within an existing structural device within the patient (such as a previously implanted stent).  
      With the autologous bio-lined structural element  10  harvested from the patient (regardless of the number of structural elements  12 ), the bio-lined structural element  10  may be implanted into a vessel experiencing restricted blood flow (such as a coronary artery). In this fashion, the blood flowing through the bio-lined structural element  10  will only contact the interior of the autologous bio-lining  14  within the structural element  12  and not the structural element  12  itself. This is a significant advantage over the prior art techniques for restoring blood flow in that it eliminates the interface between the blood and the diseased portion of the vessel or any foreign elements, thereby eliminating (or drastically reducing) the likelihood for restenosis.  
      2. Autologous Vessel Harvesting  
      The bio-lined structural element  10  of the present invention may also be prepared by harvesting a length of autologous blood vessel for immediate affixation within the structural element (as opposed to the longer duration implantation method described above). One such manner involves the use of a cutting catheter according to a still further aspect of the present invention. As will be described in greater detail below, the cutting catheter of the present invention may take any number of different forms. The common denominator between all these forms, however, is the inclusion of a cutting element that can be advanced over a length of autologous blood vessel and thereafter employed to harvest the autologous vessel for affixation within a structural element according to the present invention.  
       FIG. 24  illustrates, broadly, one such cutting catheter  60  according to the present invention. The cutting catheter  60  includes a catheter body  62  having a cutting element  64  disposed at or near the distal end. The catheter body  62  and cutting element  64  are dimensioned to be advanced over a length of autologous target vessel  14  such that the cutting element  64  progressively extricates the exterior surface of the blood vessel  14  from the surrounding tissues (not shown) within the patient. Following such extrication, the target vessel  14  may thereafter be harvested from the patient for use according to the present invention.  
      Various manners of positioning the cutting catheter  60  over the autologous tissue  14  will now be described. Referring to  FIG. 25 , a guide wire  66  may be employed to locate an area along the autologous blood vessel  14 . The guide wire  66  may be introduced by advancing it through the layers of tissue surrounding the patient&#39;s target blood vessel  14  and onward through the wall of the blood vessel  14  for advancement into the interior lumen. The guide wire  66  is helpful in that it can be used to aid in the insertion of the cutting catheter  60  or other devices to the targeted vessel section  14 .  
      With the guide wire  66  in place, a clip applicator  70  may then be employed to seal off the proximal end of the target vessel  14  as shown in  FIGS. 26-27 . The clip applicator  70  (shown by way of example only) may include a proximal clip applicator head  72  and a distal clip applicator head  74  for the purpose of applying proximal and distal clips  76 ,  78 , respectively. A scissors (not shown) or similar cutting element on the applicator  70  may be employed to sever the target vessel  14  following the application of clips  76 ,  78  ( FIG. 27 ).  
      After locating the target vessel  25  and the placement of guide wires  20 , an introducer  80  and a dilator  82  may then be advanced over the guide wire  66  into target vessel  14  as shown in  FIG. 28 . The introducer  80  comprises a generally tubular structure which, when positioned with its distal end within blood vessel  14 , creates a port or lumen through which access may be gained into the interior of the blood vessel  14 . The dilator  82  serves to expand the aperture formed by the guide wire  66  such that the introducer  80  may be passed into the interior of the blood vessel  14 . Both the introducer  80  and dilator  82  may comprise any number of known or commercially available devices.  
      With reference to  FIG. 29 , the cutting catheter  60  may now be advanced over the introducer  80  to progressively extricate the exterior surface of the target vessel  14  from the surrounding tissue (not shown) according to the present invention. The cutting catheter  60  is advanced such that the cutting element  64  engages introducer  80  closely and follows its path. A small clearance exists between the cutting catheter  60  and introducer  80  which allows cutting catheter  60  to slide past introducer  80  while exerting minimal force on the cutting catheter  60 . Cutting element  64  preferably contains a sharp blade portion  84  (such as the angled portion shown in  FIG. 24 ) at or near its distal end. The angled nature of the blade portion  84  allows the cutting element  64  to closely follow the contour of the introducer  80  without cutting into or snagging on the exterior surface of the introducer  30 .  
      As the cutting catheter  60  is advanced along the introducer  80 , it will eventually force the cutting element  64  to cut through the wall of the blood vessel  14  as shown in  FIG. 30 . Once this occurs and the cutting catheter element  64  is positioned over the targeted vessel  14 , dilator  82  may then be removed while keeping introducer  80  and guide wire  66  in place. A deployment catheter  30  may then be advanced over the guide wire  66  for the purpose of deploying a plurality of coupling members  16  maintained on the balloon  32  according to the same principles discussed above with reference to  FIGS. 5-8 . A protective sheath  90  may be employed to cover the coupling members  16  during advancement of the deployment catheter  30  within the target vessel  14 . In this fashion, the coupling members  16  will not engage or impinge upon the interior of the blood vessel  14  until deployment.  
      The deployment catheter  30  (preferably with protective sheath  90  in place) is thereafter advanced to a predetermined location within the blood vessel  14 . With the deployment catheter  30  at this advanced location, the protective sheath  90  may be withdrawn and the balloon  32  inflated to thereby deploy the coupling members  16  as shown in  FIG. 31 . The cutting catheter  60  may then be advanced along the exterior surface of the blood vessel  14  to progressively cut the target vessel  14  from the surrounding tissue as shown in  FIG. 32 . In a beneficial aspect, this advancement is facilitated through the use of the penetrating tips  20 , which preferably extend past the exterior periphery of the blood vessel  14  following deployment (best seen in  FIG. 31 ). More specifically, the height of the penetrating tips  20  causes the cutting element  64  to “ride” over the penetrating tips  20 , rather than on the exterior surface of the blood vessel  14  itself. This advantageously protects the exterior surface of the blood vessel  14  from being damaged, cut, or otherwise impinged by the cutting element  64 . As will be appreciated, the angled nature of the blade portion  84  facilitates the progression along the penetrating tips  20 .  
      With the coupling members  16  deployed into the blood vessel  14 , and the blood vessel  14  extricated from the surrounding tissue, the distal end of the blood vessel  14  must then be cut or otherwise severed such that the blood vessel  14  may be withdrawn for use in lining a structural element  12  according to the present invention. Several illustrative cutting devices will be described below for accomplishing this task. At this point, however, it should be pointed out that any number of different manners, methods, or mechanisms may be employed to withdraw the blood vessel  14  from the patient, including but not limited to the deployment catheter  30  disclosed above, without departing from the scope of the present invention.  
      For example, with reference to  FIGS. 40-41 , a holding catheter  110  may be provided for temporarily holding the blood vessel  14  to accomplish such withdrawal. Holding catheter  110  may be constructed similarly to the deployment catheter  30 , with a deployment balloon  32  disposed on the end of a catheter body  36  (preferably having a centrally disposed lumen for slideably receiving the guide wire  66 ). Unlike the deployment catheter  30 , however, the coupling members  16  are fixedly attached to the balloon  32  such that they will not become physically removed or detached from the balloon  32  upon inflation. Moreover, the coupling members  16  are essentially straight and do not include any type of engagement tip (such as tip  20  disclosed above). An optional guide catheter  114  may be provided having apertures  112  suitable to pass and guide the coupling members  16  during expansion and contraction of the balloon  32 .  
      Upon inflation, the coupling members  16  extend into the wall of the blood vessel  14  to thereby hold the blood vessel  14  in place (and at the same time protect the exterior surface of the blood vessel  14 ) while the cutting catheter  60  is employed as shown in  FIG. 41 . Once extricated from the surrounding tissue, the blood vessel  14  may be cut or severed in a manner to be described below, allowing the holding catheter  110  to be withdrawn from the patient with the blood vessel  14  temporarily maintained on the balloon  32 . Once harvested, the blood vessel  14  may be removed or otherwise released by simply deflating the balloon  32  (causing the coupling members  16  to retract). The blood vessel  14  may thus be harvested from the patient in a quick and easy fashion for later affixation within a structural element  12  according to the present invention.  
      It should be readily appreciated that the features of the holding catheter  110  may be accomplished in any number of suitable fashions without departing from the scope of the present invention. For example, although shown disposed within the optional guide catheter  114 , it will be appreciated that the feature of temporarily deploying the coupling members  16  may be accomplished without employing the guide catheter  114 . That is, the guide catheter  114  need not be included if holding catheter  110  (via the expansion of balloon  32 ) is capable, by itself, of temporarily holding the blood vessel  14  according to the present invention.  
      With the blood vessel  14  extricated from the surrounding tissue according to the present invention, the next step involves cutting the distal end of the targeted vessel  14  such that it can be physically removed from the patient for use as bio-lining within a structural element  12  according to the present invention. More specifically, cutting the end of the blood vessel  14  will allow the withdrawal of the entire harvesting assembly. This cutting step may be performed in any number of suitable fashions. One such method (shown generally in  FIG. 33 ) involves inserting a cutting device  86  directly through the tissue above the distal end of the cutting catheter  60 . By introducing the cutting device  86  in this fashion, and thereafter manipulating its cutting elements (shown generally at  88 ), the distal end of the blood vessel  14  may be severed for graft removal. Other methods may be employed which involve equipping the cutting catheter  60  with additional cutting features capable of severing the distal end of the blood vessel  14 . For example, the cutting catheter  60  may be equipped with one or more apertures near its distal end capable of being employed to position an electrocautery snare (not shown) around the blood vessel  14 . Once positioned around the blood vessel  14 , the electrocautery snare may be selectively energized to sever or otherwise cut of the blood vessel  14  such that it can be removed from the patient.  
      In a still further aspect of the present invention, the cutting catheter  60  may be equipped with one or more retractable cutting element(s)  94  as shown in  FIGS. 34-37 . Each retractable cutting element  94  is preferably hingedly disposed (via, for example, pivot pin  96 ) within a recessed portion along the interior of the catheter body  62 . This positioning allows each retractable cutting element  94  to remain flush along the interior of the catheter body  62  as the cutting catheter  60  is advanced along the blood vessel  14 . The hinged nature of each retractable cutting element  94  allows it to pivot between a retracted position during forward displacement (left to right in  FIGS. 35-37 ) and a deployed position during backward displacement (right to left in  FIGS. 35-37 ). In the deployed position, the retractable cutting element  94  extends inwardly toward the center of the cutting catheter  60  and serves to cut the blood vessel  14  as the cutting catheter  60  is moved backwards and/or rotated. Although not shown, the cutting catheter  60  may include one or more inwardly protruding, fixed cutting element(s) extending from the interior surface of the catheter body  62  near the cutting element  64 .  
      The cutting catheter  60  as shown in  FIG. 35  is set forth by way of example only, and it is to be readily understood that various modifications or alterations may be undertaken without departing from the scope of the present invention. For example, with reference to  FIG. 36 , the cutting catheter  60  may further include the cutting element  64  of the type shown and described above. Moreover, although not shown, it is contemplated as part of the present invention to provide the retractable cutting element  94  and the cutting element  64  on two separate cutting catheters.  
       FIG. 37  illustrates yet another aspect of the cutting catheter  60  of the present invention. Namely, each retractable cutting element  94  is equipped with a locking groove or lumen  98  capable of receiving a wire (not shown) for the purpose of locking the cutting element  94  within the recessed portion of the catheter body  62 . In this case, the catheter body  62  will need a corresponding groove or lumen  100  in order to receive the aforementioned wire for engagement within the locking groove  98  of the retractable cutting element  94 . In order to deploy each cutting element  94 , the wire must first be withdrawn from the locking groove  98 . Thereafter, the cutting catheter  60  may be pulled backwards to deploy the cutting element  94  for cutting the blood vessel  14 . It is also contemplated as part of the present invention to provide the cutting element  94  with a bias to extend inwardly when the wire is withdrawn from the locking groove  98 . This may be accomplished through the use of springs in conjunction with the pivot pins  96 , as well as via material selection (i.e. using nitinol or other shape-memory materials to construct the cutting element  94 ).  
       FIG. 38  illustrates a still further aspect of the cutting catheter  60  of the present invention. The cutting catheter  60  may be manufactured such that the main portion of the catheter body  62  and the cutting element  64  are of different diameter. One manner of accomplishing this is to provide the catheter body  62  with a tapered portion  102  extending between the main portion and the cutting element  64 . A beneficial aspect of this design is that it minimizes (if not eliminates) the amount of drag experienced between the interior of the catheter body  62  and the exterior of the blood vessel  14 . This reduction in drag improves the ease with which the cutting catheter  60  may be advanced over the blood vessel  14 . This, once again, is based on the fact that the cutting element  64  is the only significant segment of the catheter  60  that contacts the blood vessel  14  during advancement. This is in contradistinction to cutting catheters of constant diameter (as shown above), which experience a dragging force along their entire length as they are advanced to cut the blood vessel  14  from surrounding tissue.  
      The cutting element  64  shown and described above with reference to  FIGS. 24-38  may also take a number of different configurations without departing from the scope of the present invention. For example, the cutting element  64  may take any number of different shapes other than the angled configuration shown and described above (forming blade portion  84 ). The cutting element  64  may also comprise any number of different types of cutting instrumentation. For example, with reference to  FIG. 39 , the cutting element  64  may comprise a cauterization tip or a harmonic scalpel activated electrically through an electric wire  104  disposed within the catheter body  62 . When provided as a cauterization element, the cutting element  64  may be selectively activated to cauterize as it is advanced along the exterior of the blood vessel  14 , thereby preventing or minimizing any bleeding that may otherwise result from the extrication of the blood vessel  14  from surrounding tissue. When provided as a harmonic scalpel, the cutting element  64  may be selectively activated to harmonically cut the blood vessel  14  away from surrounding tissue during advancement of the cutting catheter  60 .  
      The foregoing manners and mechanisms for harvesting a length of blood vessel  14  are set forth by way of example only. For example, with reference to  FIG. 42 , a windowed cutting catheter  120  according to a still further aspect of the present invention is provided for extricating and cutting a length of blood vessel  14  from the surrounding tissue. The windowed cutting catheter  120  includes a catheter body  122  and an anvil assembly  124 . The catheter body  122  is elongated, hollow and includes a cutting base  126  at its distal end and an access window  128  disposed a predetermined distance from the distal end. The lumen extending through the catheter body  122  and cutting base  126  is dimensioned such that a proximal portion  118  of the blood vessel  14  may be passed through the cutting base  126  and manipulated to exit out the access window  128  as shown. The catheter body  122  may be flexible but should preferably be of sufficient rigidity such that it can advance the cutting base  126  over the blood vessel  14 . The cutting base  126  is preferably configured such that it extricates the blood vessel  14  from surrounding tissue during this advancement process. The windowed cutting catheter  120  is particularly suited for minimally invasive access. That is, a small incision may be made over a target blood vessel such that the target vessel can be cut, creating an open proximal end. The cutting base  126  may then be advanced over the proximal end of the blood vessel  14  until it exits the access window  128 . At that point, the cutting base  126  may be advanced to “burrow” through the tissue surrounding the exterior of the blood vessel  14  to extricate the blood vessel  14  from surrounding tissue.  
      With the length of blood vessel  14  thus extricated, the anvil assembly  124  may then be employed to cut the distal end of the blood vessel  14  such that the blood vessel  14  may be removed for use in preparing a bio-lined structural element  10  according to the present invention. The anvil assembly  124  includes a handle member  130 , a shaft  132  extending from the handle member  130 , and an anvil member  134  disposed on the distal end of the shaft  132 . In use, the anvil member  134  is introduced into the open proximal end  118  of the blood vessel  14  and advanced through the interior of the blood vessel  14  until it comes into contact with the cutting base  126 . The cutting base  126  and anvil member  134  are dimensioned such that, when such contact is caused, the exterior of the anvil member  134  and the interior of the cutting base  126  cooperatively act to sever or cut the distal end of the blood vessel  14 . With the distal end of the blood vessel  14  cut or severed, the anvil assembly  124  may be withdrawn from the catheter body  122  (such as by pulling it through the access window  128 ). The blood vessel  14  may then be removed from its position over the shaft  132  and employed to form the bio-lined structural element  10  according to the present invention.  
      3. Tissue Engineering  
      The bio-lined structural element  10  of the present invention may also be produced by equipping a structural element  12  with a bio-lining created through tissue-engineering techniques. Such tissue-engineering techniques are described, among other places, by L&#39;Heureux et al. in “A Human Tissue-Engineered Vascular Media: A New Model for Pharmacological Studies of Contractile Responses” (FASEB J. 2001 February; 15(2): 515-24), Michel et al. in “Characterization of a New Tissue-Engineered Human Skin Equivalent with Hair” (In Vitro Cell Dev. Biol. Anim. 1999 June; 35(6): 318-26), and L&#39;Hereux et al. in “In Vitro Construction of a Human Blood Vessel from Cultured Vascular Cells: A Morphologic Study” (J Vasc Surg 1993 March; 17(3): 499-509, the contents of which are hereby incorporated by reference as if set forth fully herein.  
      These tissue-engineering techniques may be used according to the following method of the present invention: (a) obtaining a tissue sample from a patient; (b) growing a length of tissue-engineered bio-lining based on the sample; and (c) equipping a structural element  12  with the tissue-engineered bio-lining to produce the bio-lined structural element  10 . Step (c) may be performed by affixing or otherwise securing the tissue-engineered bio-lining within the structural element  12  in any number of suitable fashions, including but not limited to those described herein.  
      One advantage of this method is that the patient may undergo the tissue sample retrieval during an initial visit and thereafter have the complete bio-lined structural element  10  implanted during a later, subsequent visit. That is to say, the tasks of growing the tissue-engineered bio-lining  14  and securing it within the structural element  12  may be performed “off-line” such that the patient need only be present for tissue-sample retrieval and implantation of the completed bio-lined structural element  10 . This advantageously minimizes the amount of time the patient will need to be hospitalized or present in a clinic for treatment of a vascular flow restriction.  
      II. Vessel Buttress  
      A bio-lined structural element according to the present invention may also be produced by disposing a structural element about some or all of the periphery of a vessel suffering from a vascular flow restriction and thereafter affixing the structural element to the native vessel. By buttressing the vessel in this fashion, the lumen of the vessel suffering the vascular flow restriction may become “opened” or otherwise widened to increase the inner diameter, thereby producing improved blood flow. This concept of overcoming vascular flow restrictions according to the present invention may be accomplished in any of a variety of suitable fashions, including but not limited to the following exemplary configurations described below.  
      A. Semi-Arcuate Structural Element  
       FIGS. 43-44  illustrate one such exemplary system for overcoming vascular flow restrictions according to the present invention. Namely, a semi-arcuate structural element  12  is provided over the exposed portion of the periphery of a blood vessel  14  which, in this case (by way of example only) is a coronary artery. Once the semi-arcuate structural element  12  is disposed in this position, a plurality of coupling members  16  may be employed to pierce through the coronary artery  14  such that the base  22  of each coupling member  16  is within the lumen of the coronary artery  14  and each penetrating tip  20  is disposed on the exterior surface of the arcuate member  12 . As one skilled in the art will appreciate, the coupling members  16  may be deployed in this fashion using a deployment balloon  32  similar to, if not identical, to that shown and described above with reference to  FIGS. 5-8 . That is, the deployment balloon  32  may be introduced into the target site via percutaneous techniques. Once positioned under the structural element  12 , the coupling members  16  may be deployed to thereby expand the inner diameter of the blood vessel  14  and, moreover, to maintain it in this expanded state (by affixing it to the interior of the structural element  12 ) for improved blood flow.  
      The structural element  12  may take the form of any number of suitable materials and shapes. For example, the structural element  12  may be essentially straight or curved and have a length suitable to cover some or all of the length of the vascular flow restriction. Those skilled in the art will also appreciate that the manner of expanding and affixing the coronary vessel  14  to the structural element  12  may be accomplished in any number of suitable fashions, rather than through the use of coupling members  16 , without departing from the scope of the present invention. For example, any number of adhesives could be employed along the exterior surface of the vessel wall such that, when brought into contact with the inner surface of the structural element  12 , the vessel wall may be caused to remain in this expanded position. That, for example, may occur through the use of an expansion balloon  32  within the lumen of the vessel  14  to maintain the vessel wall in contact with the interior surface of the structural element  12  for a sufficient duration to effect curing of the adhesive (such as through the use of UV-activated adhesive).  
      B. Generally Cylindrical, Hinged Structural Element  
       FIGS. 45-46  illustrate a still further exemplary system for overcoming vascular flow restrictions according to the present invention. In this case, a generally cylindrical structural element  12  of hinged construction is disposed over a vascular treatment site of, for example, a coronary artery  14 . More specifically, the generally cylindrical structural element  12  comprises a pair of arcuate members  12 A,  12 B which are hingedly coupled via at least one hinge element  140  and optionally locked or otherwise closed together via a clasp member  142 . The hinged coupling allows the arcuate members  12 A,  12 B to be temporarily separated or “opened” such that the free end of one of the arcuate members (i.e.  12 B in  FIG. 45 ) may be passed or burrowed under the lower or non-exposed periphery of the coronary artery. Once arcuate member  12 B is passed under the coronary artery  14 , the arcuate member  12 A may be “closed” or brought into contact with arcuate member  12 B, thereby encompassing the target area of the coronary artery  14  within the generally cylindrical structural element  12  (as shown in  FIG. 45 ). As will be appreciated, the clasp member  142  may be omitted, particularly if the structural elements  12 A,  12 B are biased into a normally closed position.  
      With the generally cylindrical structural element  12  disposed in this position, a plurality of coupling members  16  may be employed to pierce through the coronary artery  14  such that the base  22  of each coupling member  16  is within the lumen of the coronary artery  14  and each penetrating tip  20  is disposed on the exterior surface of the arcuate members  12 A,  12 B (as shown in  FIG. 46 ). As one skilled in the art will appreciate, the coupling members  16  may be deployed in this fashion using a deployment balloon  32  similar to, if not identical, to that shown and described above with reference to  FIGS. 5-8 . That is, the deployment balloon  32  may be introduced into the target site via percutaneous techniques. Once positioned under the structural element  12 , the coupling members  16  may be deployed to thereby expand the inner diameter of the blood vessel  14  and, moreover, to maintain it in this expanded state (by affixing it to the interior of the structural element  12 ) for improved blood flow.  
      As with the structural element  12  in  FIGS. 43-44 , the generally cylindrical structural element  12  may take the form of any number of suitable materials and shapes. For example, the structural element  12  may be essentially straight or curved and have a length suitable to cover some or all of the length of the vascular flow restriction.  
      Although shown going from “inside-out” in  FIG. 46 , it will be appreciated that the coupling members  16  may be deployed from “outside-in” such that the base members  22  rest against the exterior surface of the structural element  12  and the penetrating tips  20  are disposed on the inside of the blood vessel  14 . This manner of deployment may be facilitated by positioning an “anvil member” or similarly solid structure within the blood vessel  14  such that the penetrating tips  20  will become expanded or bent upon contact therewith, thus aiding to secure the blood vessel  14  to the structural element  12 .  
      Any number of adhesives may be employed along the exterior surface of the vessel wall  14  such that, when brought into contact with the inner surface of the structural element  12 , the vessel wall  14  may be caused to remain in this expanded position. These adhesives may include, but are not necessarily limited to, UV-activated adhesives.  
      A still further manner of coupling or otherwise affixing the blood vessel to the generally cylindrical structural element  12  involves the use of coupling members  16  formed as part of a unitary structure, such as an inner structural element  42  of the type shown and described with reference to  FIG. 10-15 . In such an arrangement, the inner structural element  42  may be selectively positioned within the target area within the vessel and thereafter deployed (such as by balloon expansion) such that the coupling members  16  pierce through the wall of the blood vessel  14  and into the generally cylindrical structural element  12 . In this fashion, the blood vessel  14  will be secured within the interior surface of the structural element  12  in an expanded state for improved blood flow.  
      III. Bio-Lining with Structural Element Terminations  
      Vascular flow restrictions may also be overcome according to the present invention by providing a pair of bio-lined structural elements disposed a distance from one another and connected by a length of bio-lining. In this fashion, each of the bio-lined structural elements may be deployed on either side of a vascular flow restriction such that flow is restored through the length of bio-lining that extends therebetween. This concept of overcoming vascular flow restrictions according to the present invention may be accomplished in any of a variety of suitable fashions, including but not limited to the following exemplary configurations described below.  
      A. Two Piece Bio-Lining  
       FIGS. 47-48  illustrate one such exemplary system for overcoming vascular flow restrictions according to the present invention. Namely, a pair of bio-lined structural elements  10  are provided, each having a length of bio-lining  14  extending therefrom. The structural elements  10  are preferably dimensioned to be introduced into an incision  150  formed through the wall of a vessel  152  suffering from a vascular flow restriction. Thereafter, each structural element  12  may be deployed in order to secure each bio-lined structural element  10  on either side of the incision  150 . The structural elements  12  may comprise any number of suitable structures, including those described above and, most preferably, of balloon-deployable construction such that they may be introduced through the incision via a balloon catheter, which may thereafter be used to deploy the structural element  12 . Once deployed in the target vessel  152 , the free end of each length of bio-lining  14  may be connected together (as will be explained below) in order to provide a continuous lumen between the bio-lined structural elements  10  as shown in  FIG. 48 . As will be appreciated, this system advantageously provides direct access to remove the vascular flow restriction (through the incision  152 ) and thereafter provides the ability to quickly and easily restore a path of fluid communication for improved blood flow.  
      The free ends of each length of bio-lining  14  may be coupled together or otherwise connected in any of a variety of suitable fashions without departing from the scope of the present invention. For example, with reference to  FIGS. 49-52 , a lap joint assembly  160  may be employed according to one aspect of the present invention. Lap joint assembly  160  includes a connector member  162  and a ring member  164 . The connector member  162  has a groove  166  formed between a ridged portion  168  and an angled portion  170 . The ring member  164  is generally elastic and dimensioned to engage within the groove  166  of the connector  162  to secure the free ends of the bio-lining  14 . As shown in  FIG. 49 , both the connector  162  and ring member  164  have an inner lumen dimensioned to pass a respective free end of bio-lining  14  therethrough. As shown in  FIG. 50 , each free end is thereafter rolled back over the respective portion of the lap joint assembly  160 . From this point, as shown in  FIG. 51 , the ring member  164  and connector  162  are brought into close proximity and the free end from the ring member  164  is rolled off and extended over the free end residing over the connector  162 . The ring member  164  may thereafter be rolled over the angled portion  170  of the connector  162  and, in so doing, come to rest within the groove  166 . coupling the bio-linings  14  in this fashion thus advantageously restores blood flow and minimizes, if not eliminates, any blood-device interface.  
      A still further exemplary manner of coupling or otherwise connecting the free ends of the bio-lining  14  is shown with reference to  FIGS. 53-55 . A butt joint assembly  172  is provided having a pair of connector bases  174 ,  176  and a connector shell  178 . Each connector base  174 ,  176  includes a groove  180  formed between a pair of ridged portions  182 . The connector shell  178  includes a pair of ridged portions  184  which are capable of being lodged within the groove portion  180  of a respective connector base  174 ,  176 . As shown in  FIG. 53 , each connector base  174 ,  176  includes an inner lumen dimensioned to pass a respective free end of the bio-lining  14  therethrough. Each free end is thereafter rolled over the respective connector base  174 ,  176 , preferably such that the free end is disposed at least partially within the respective groove  180  as shown in  FIG. 54 . At that point, each connector base  174 ,  176  may be urged or otherwise advanced into the connector shell  178  such that the ridged portions  184  of the connector shell  178  engage within the groove  180  of the respective connector base  174 ,  176  as shown in  FIGS. 54 and 55 . Once again, the resulting lumen of bio-lining  14  thus advantageously restores blood flow and minimizes, if not eliminates, any blood-device interface.  
      As mentioned above, each structural element  12  forming part of the embodiment shown in  FIGS. 47-55  is preferably of balloon-expandable construction.  FIGS. 56-62  illustrate exemplary manners of securing bio-lining  14  to each balloon-expandable structural element  12  according to the present invention. In one aspect, the free end of each length of bio-lining  14  (only one shown for clarity) may be passed through the lumen of structural element  12  ( FIG. 56 ) and thereafter rolled over the structural element  12  ( FIG. 57 ). For added purchase, a second (outer) structural element  190  may be placed over the first structural element  12  so as to sandwich the free end of the bio-lining  14  therebetween as shown in  FIG. 58 . Alternatively, each structural element  12  may be constructed having additional features for securing the free ends of the bio-lining  14 . For example, with reference to  FIGS. 59-60 , each structural element  12  may be equipped with a plurality of members or extensions  192  capable of being bent inwardly towards the main body  194  of the structural element  12  to thereby close upon the bio-lining  14 . In similar fashion, as shown in  FIGS. 61-62 , the structural element  12  may be provided with a plurality of members or extensions  192  capable of being folded over towards the main body  194  of the structural element  12  to thereby close upon the bio-lining  14 .  
      B. One Piece Bio-Lining  
       FIG. 63  illustrates a still further exemplary system for overcoming vascular flow restrictions according to the present invention. In this embodiment, a pair of bio-lined structural elements  10  are provided, this time having a single length of bio-lining  14  extending between them. In order to provide a single lumen (as opposed to two separate lengths of bio-lining  14  as shown in  FIGS. 47-55 ), at least one of the structural elements  12  must be of self-expanding construction. By way of example only, the proximal structural element  12  (on left in  FIG. 63 ) may be of balloon-expandable construction and the distal structural element  12  (on right in  FIG. 63 ) may be of self-expanding construction. Under this scenario, the proximal structural element  12  would be secured to the proximal free end of the bio-lining  14  in one of the manners described above with reference to  FIGS. 56-62  and introduced into the incision  150  over a balloon catheter (not shown) for deployment upstream from the vascular restriction.  
      The distal structural element  12  may be secured to the distal free end of the bio-lining  14  and deployed downstream from the vascular restriction in any number of suitable fashions without departing from the scope of the present invention. One exemplary manner, by way of example only, is shown with reference to  FIGS. 64-68 . A needle  200  having a retractable snare  202  may be employed to encompass the distal bio-lined structural element  10  ( FIGS. 64-65 ). At this point, the distal free end of the bio-lining  14  is wrapped over the distal structural element  12  (akin to the wrap-over described above with reference to  FIGS. 56-57 ) and the snare  202  is sandwiching the bio-lining  14  against the exterior surface of the structural element  12 . The snare  202  may then be closed (as shown in  FIG. 66 ) such that the needle  200  may be passed through the incision and advanced to a location downstream from the vascular restriction as shown in  FIG. 67 . The snare  202  may then be released and the needle  200  withdrawn in order to permit the self-expanding distal structural element  12  to automatically deploy as shown in  FIG. 68 .  
      A still further manner of deploying the self-expanding structural element  12  according to the present invention will now be described with reference to  FIGS. 69-72 . A constricting device  210  is provided which, in conjunction with eyelets or apertures  212  formed in the self-expanding structural element  12 , allows the structural element  12  to be constricted into a reduced diameter to facilitate introduction into a vascular incision  150 . More specifically, the constriction device  210  includes a handle member  214  and a retractable string or thread-like element  216 . The retractable thread-like element  216  is dimensioned to be advanced through the eyelets or apertures  212  (best seen in  FIG. 70 ). The handle member  214  may be equipped to pass the thread-like element  216  therethrough such that the thread-like element  216  may be easily withdrawn to constrict (and thereby reduce the diameter of) the self-expanding structural element  12 . As shown in  FIG. 72 , the tensioning of the thread-like element  216  may be augmented by providing the handle member  214  with a spring-loaded portion  218 . Once the self-expanding structural element  12  is positioned as desired within the blood vessel, the thread-like element  216  may then be released or otherwise cut such that the structural element  12  is able to self-expand.  
      As evidenced by the foregoing, the various systems and methods of the present invention address the goal of overcoming vascular flow restrictions for improved blood flow. More specifically, the present invention provides systems and methods for overcoming vascular flow restrictions which involve minimizing (if not eliminating) the extent to which blood interfaces with a structural element deployed within or about a diseased vessel to restore blood flow. These inventive systems and methods accomplish this by: (1) providing at least one structural element within or about a vessel having a vascular flow restriction; and (2) equipping the structural element with bio-lining such that it restores blood flow and minimizes, if not eliminates, the interface between blood and non-biological materials.  
      By reducing or eliminating this “blood-device” interface, the present invention prevents (or at the very least lessens) the reformation of vascular flow restrictions within the diseased vessel.  
      Many alterations or modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention. The illustrated embodiments have been shown only for purposes of clarity and examples should not be taken as limiting the invention as defined by the following claims, which includes all equivalents, whether now or later devised.