Abstract:
An improved ePTFE-based delivery graft is intended to dispense a bioactive agent such as a drug into the blood stream. A hollow tubing is infused with the agent from a source such as a drug delivery pump mechanism. The spiral hollow tubing is wrapped in a helical fashion around, or otherwise brought into contact with an outer wall of a porous ePTFE graft and adhered thereto. The agent is delivered to the lumen of the graft by infusing the agent through the porous interstices of the graft wall. Thus, the bioactive agent is conducted by the hollow tubing from a source to the outer surface of an ePTFE graft where it is released to diffuse into the graft to influence biological processes along both the inner and outer surfaces of the graft. The present invention allows the bioactive agent or drug to be renewed or changed after implant of the graft. In addition the present invention can be implanted in the same fashion as regular vascular grafts.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to medical devices, and more particularly, to an expanded polytetrafluoroethylene (ePTFE) based graft for delivering an agent into a natural tissue conduit, e.g., a blood vessel. 
     2. Description of Related Art 
     Providing frequent, direct delivery of bioactive agents to a natural tissue conduit has become a necessity for many medical treatments such as those requiring frequent intravenous administration of drugs. To meet this need, many types of devices including stents and vascular grafts have been used to deliver agents into natural tissue conduits. 
     Local delivery is advantageous in that the effective local concentration of a delivered drug can be much higher than can normally be achieved by systemic administration. Delivery of agents to vascular tissue to prevent restenosis is especially useful. U.S. Pat. No. 5,399,352 to Hanson discloses a device for delivering an effective concentration of a therapeutic agent locally at a target site within the body without producing unwanted systemic side effects. However, the device described in this reference differs considerably from existing vascular grafts. It would be especially advantageous to deliver drugs with a device more similar to currently used vascular grafts. 
     Stents and other existing devices are frequently coated with or impregnated with therapeutic agents for the treatment of diseases. A concern related to the use of stents and existing devices for drug delivery is that drug delivery may not be sustainable. Over time the concentration of drug on the stent or other similar delivery devices will diminish, through drug inactivation, degradation, or dilution. Thus, the therapeutic agent may need to be refreshed or even changed after implant of the device. Moreover, these existing devices are not capable of delivering drugs to an internal lumen along the entire length of the graft. 
     Accordingly, it would be desirable to provide a drug delivery graft capable of delivering a drug or any other agent to the internal lumen along the entire length of the graft, or restrict delivery to a finite area on the graft such that the agent may be renewed or altered after implant of the graft. Furthermore, a desirable drug delivery graft could be implanted in the same fashion as regular vascular grafts. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, an improved expanded polytetrafluoroethylene (ePTFE) drug delivery graft is provided. The invention can be used, for example, as a vascular graft providing sustained release of a selected bioactive or diagnostic agent directly into a blood or other fluid flow pathway. The graft is capable of delivering the bioactive or diagnostic agent to the internal lumen of a vascular graft along the entire length, or of restricting delivery to a finite area of the vascular graft. Various ePTFE grafts that are reinforced by external beading are well known in the art. However, unlike previous designs that utilize a solid beading for reinforcing purposes, the present design utilizes a hollow tubing as a drug conduit. Also, the hollow tubing behaves much like the existing low profile solid beading in that it has a small diameter and can be readily implanted into the body. The hollow tubing of the present invention serves as both a spiral support and drug conduit. 
     A simple tubular ePTFE graft is used, which is well known to be extremely porous. A hollow tubing of non-porous PTFE, fluoroethylene polymer (FEP) or other implantable polymer is wrapped around the graft and laminated or adhered in place. The hollow tubing may be wrapped helically; alternatively other arrangements (e.g., end to end loops) can be used. Before the wrapping occurs one surface of the hollow tubing is cut away (for example, laser cut), punctured repeatedly or otherwise rendered porous. When an agent such as a drug is injected into the hollow tubing, e.g., from an infusion pump or a subcutaneous access port, the drug flows through the hollow tubing and leaks through the cut or porous region and diffuses into the outer surface of the ePTFE graft. The drug diffuses into the graft where it mixes into the blood flowing therethrough and influences biological processes along the circulatory system. Depending on the drug used and the precise configuration of the device the dispensed material could have either systemic effect or have limited local effect. One particularly attractive use of the device is to dispense drugs to limit the restenosis that frequently occurs due to tissue proliferation at the site of anastimosis of an ePTFE graft to a blood vessel. 
     The invention takes advantage of the well-known porosity of an ePTFE graft. Impregnation of ePTFE grafts with therapeutic agents has been previously disclosed. However, the present invention allows the therapeutic agents to be renewed or altered following implant of the graft, something that is not possible with simple drug-impregnated graft materials. 
     A more complete understanding of the ePTFE drug delivery graft will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings that will first be described briefly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a drug delivery graft according to an embodiment of the present invention; 
     FIG. 2 is a side view of a hollow tubing according to an embodiment of the present invention; 
     FIG. 3 is a cross-sectional view of the drug delivery graft showing a cut portion of the hollow tubing according to an embodiment of the present invention. 
     FIG. 4 is a cross-sectional view of the drug delivery graft showing a porous hollow tubing according to an embodiment of the present invention. 
     FIG. 5 is a side view of an alternate embodiment of the drug delivery graft of the present invention. 
     FIG. 6 is a side view of another alternate embodiment of the drug delivery graft of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention satisfies the need for an improved drug delivery graft capable of delivering bioactive agents, including drugs, to an internal lumen of a graft, either along its entire length or in a localized area, through the use of hollow tubing on the outside of the graft. In the detailed description that follows, it should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
     Referring first to FIG. 1, a side view of a drug delivery graft  10  in accordance with an embodiment of the present invention is illustrated. The drug delivery graft  10  comprises a graft  2 , a hollow tubing  4 , and a drug source  6 . The hollow tubing  4  is wrapped (spiraled) in a helical fashion around an abluminal surface of the graft  2 . The drug source  6  is connected to one end  14  of the hollow tubing  4 . 
     The graft  2  may be a standard clinical vascular graft of any shape or size comprised preferably of expanded PTFE, which material consists of a porous network of nodes and fibrils created during the expansion process. This porous network provides a somewhat permeable wall for the graft  2 . The graft  2  can be constructed in a variety of sizes to allow a surgeon to select the appropriate size to accommodate a particular vascular application. Likewise, the porosity (internodal distance) of the graft can be varied to affect the rate of drug or agent release. 
     The drug delivery graft  10  injects a drug or other agent into the bore of the hollow tubing  4  from the drug source  6 . The drug source  6  can be any of a variety of commercially and technologically available systems that provide constant controlled rate delivery of an agent, such as a biologically activated mini pump that is either subcutaneously or extracorporeally located, an external mechanical pump, or an access port. For example, an open end  14  of the hollow tubing  4  may be connected via a micro-catheter to a subcutaneous or other drug source. 
     The agent delivered to the natural tissue conduit can be any substance, including any drug, and the device can be used for local or systemic delivery of such substances to prevent or treat a variety of disease syndromes or to promote or enhance desired activity within the body. A bioactive or diagnostic agent may include, for example, therapeutic or prophylactic agents, such as a drug, protein, enzyme, antibody or other agent, or cells that produce a drug, protein, enzyme, antibody, or other agent. The diagnostic material can include, for example, a radiolabeled antibody or antigen. 
     The natural tissue conduit into which the agent is ultimately delivered may include any structure of a body that functions to transport substances and includes, but is not limited to, e.g., blood vessels of the cardiovascular system (arteries and veins), the lymphatic system, the intestinal tract (esophagus, stomach, the small and large intestines, and colon), the portal system of the liver, the gall bladder and bile duct, the urinary system (bladder, and urethra), the respiratory system (trachea, bronchi and bronchioles), and ducts and ductules connecting endocrine organs to other areas of the body. The device of the present invention can be used in any mammal or in any animal in which natural tissue conduits are found. Suitable dosage requirements and treatment regimens for any agent delivered can be determined and will vary depending upon the tissue targeted for therapy and upon the particular agent utilized. 
     Referring now to FIG. 2, a side view of the hollow tubing  4  used in an embodiment of the present invention is illustrated. The hollow tubing  4  may be manufactured from a non-expanded or partially expanded small diameter PTFE tube or any other implantable polymer (e.g. FEP). The hollow tubing  4  may be manufactured in very small diameters (less than 1 mm) and long lengths (more than 10 feet) to accommodate all sizes of grafts. Whereas the prior art beading used solely for support purposes is a solid filament, the hollow tubing  4  has a bore to provide fluid delivery to the graft  2 . Preferably, the hollow tubing  4  has an uncut portion  16  and a partially cut portion  12  (or a porous and less or non-porous region arrange circumferentially) that allows communication between the lumen of the hollow tubing  4  and the outside surface of the graft  2 . Alternatively, communication between the lumen of the hollow tubing  4  and the outside surface of the graft  2  may be achieved by using a porous hollow tubing or a hollow tubing with mechanical or laser perforations. While the hollow tubing  4 , is shown generally cylindrical in shape, it should be appreciated that alternative designs are possible including a hollow tubing that is tapered along its length as well as one that has a stepped configuration or has other, non-circular cross-sections. Similarly the graft may be tapered or stepped or of a special shape, such as cuffed, as is known in the art. 
     In a preferred embodiment, to manufacture the hollow tubing  4 , a specified length of a tube made of PTFE, FEP or other any other implantable polymer may be loaded on a mandrel to secure the tube in a rigid fashion. The loaded tube may be placed in a cutting device where a defined portion of the tube is cut in the longitudinal direction. A semi-circular “half-tube” C-shaped section  12  may be created in the middle of the tube to create the hollow tubing  4 . The cutting device may comprise a LASER cutting device. Alternatively, the tube may be punctured repeatedly or otherwise rendered porous to allow release of the agent into the ePTFE of the graft. One end  18  of the hollow tubing  4  may be sealed mechanically, for example by a crimp, or by a heating process to terminate the lumen. The terminated end  18  may also be sealed with a silicon or other self-sealing material that can advantageously serve as a primer port for infusing an agent through, for example, a syringe. 
     Referring now to FIG. 3, a cross-sectional view of the drug delivery graft showing a cut portion of hollow tubing according to an embodiment of the present invention is illustrated. Hollow tubing  4  is wound spirally around the graft  2 . During the spiraling process, a cutaway portion  12  of the hollow tubing  4  is laminated and secured against the outer surface of the graft  2 , creating a drug outflow surface that communicates with the outer lumen of the graft  2 . Alternatively, FIG. 4 shows a cross-sectional view of the drug delivery graft showing a porous hollow tubing  24  according to an alternative embodiment of the present invention. The porous hollow tubing  24  comprises perforations or pores  22  through which an agent or drug is dispensed onto and into the graft  2 . The agent or drug is evenly distributed and diffuses into the graft  2  through the interstices of an agent infusion area  8 . The rate at which the drug or other agent penetrates the porous wall of the graft  2  is determined by several factors, including the size and number of the pores and the size of the drug molecule. The graft  2  is capable of delivering drugs or any other agents to the internal lumen along the entire length of the graft  2 , or of restricting delivery to a finite area on the graft  2 . In addition, it should be appreciated that the spacing of the hollow tubing  4  along the graft  2  can be varied to concentrate dosages in certain areas of need. Moreover, the spiraling of the hollow tubing  4  around the graft  2 , as shown in FIG. 1, could be combined with a traditional support beading spiraled around the graft  2  for additional support. 
     Turning now to FIG. 5, an alternate embodiment of the present invention is shown. Drug delivery graft  30  includes graft  32  and hollow tubing  34 . In this embodiment, the hollow tubing  34  is arranged longitudinally along the graft  32 , rather than wrapped around spirally as in FIG.  1 . The hollow tubing  34  is arranged in snake-like fashion, longitudinally along the outside of the graft  32 , and is connected to the drug source  6  at one end. The longitudinally arranged strips of hollow tubing  34  loop back at the ends of the graft so that a single continuous piece of hollow tubing is employed. In a second alternate embodiment illustrated in FIG. 6, hollow tubing  44  is arranged longitudinally along a graft  42  in a slightly different configuration to make up a drug delivery graft  40 . In this embodiment, the longitudinally arranged hollow tubing  44  is connected to manifolds  46  and  48  at each end. The manifold  46 , located at a proximal end of the graft  42 , is circumferentially arranged around the graft  42  and is also connected to the drug source  6 . The manifold  48 , located at a distal end of the graft  42  is cirumferentially arranged around the graft  42  in a closed loop. The drug provided from the drug source  6  flows into the manifold  46  where it is distributed to the longitudinally placed hollow tubing  44 , flowing through the hollow tubing  44  and along the manifold  48 , being distributed to the graft  42  in one of the above-mentioned methods shown in FIGS. 2-4. It should be appreciated that in both embodiments shown in FIGS. 5 and 6, the hollow tubing can be spaced equidistant or varied depending on the required application. 
     The spiraled or longitudinally-placed hollow tubing is sintered to the graft to adhere the hollow tubing to the graft in the same manner as existing standard grafts, adhering the cut (C-shaped) portion  12  and uncut hollow tubing portion  16  as shown in FIG. 3, or the porous hollow tubing  24  as shown in FIG. 4, along the length of the graft  2 . Alternatively, any of a number of known adhesive agents can be used to attach the hollow tubing. Further, the hollow tubing may be produced from a plastic material such as polypropylene, which can be adhered to the graft through a partial melting process. Thus, the design may use the existing low profile hollow tubing on existing grafts, for example IMPRAFlex® grafts, manufactured by IMPRA (Tempe, Ariz.), a Division of C.R. Bard, Inc., and can be implanted in the same fashion as regularly used existing vascular grafts. 
     The devices of the present invention can function as improved vascular grafts such that the agent or drug to be delivered prevents or treats complications associated with conventional vascular graft placement, including but not limited to platelet deposition, coagulation, thrombosis, neointimal hyperplasia and fibrosis. One particularly attractive use of the drug delivery graft would be to dispense drugs or any other agent to limit the stenosis that frequently occurs at the site of anastimosis of an ePTFE graft to a blood vessel. Examples of agents that prevent restenosis of a blood vessel include, but are not limited to, a growth factor, a growth factor inhibitor, growth factor receptor antagonist, transcriptional repressor, translational repressor, antisense DNA, antisense RNA, replication inhibitor, anti-microtubule agents, inhibitory antibodies, antibodies directed against growth factors or their receptors, bifunctional molecules comprising a growth factor and a cytotoxin, and bifunctional molecules comprising an antibody and a cytotoxin. 
     Having thus described a preferred embodiment of the expanded PTFE drug delivery graft, it should be apparent to those skilled in the art that certain advantages of the within system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims.