Abstract:
An endoprosthesis cover may be attached to the distal end of a delivery device. The cover may be generally cylindrical in shape and may have a lumen through it. An endoprosthesis may then be covered as it is delivered to a treatment site.

Description:
RELATED APPLICATION DATA 
     This application is a continuation of U.S. application Ser. No. 11/036,028, filed Jan. 14, 2005, now U.S. Pat. No. 8,021,416, which is a continuation of application Ser. No. 10/001,538, filed Nov. 14, 2001, now U.S. Pat. No. 6,846,316, which is a continuation of application Ser. No. 09/459,143, filed Dec. 10, 1999, now U.S. Pat. No. 6,331,184. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to devices implanted within the human body and further to coverings about those devices. Specifically, the present invention relates to a detachable system for covering an implantable devices as it is delivered into the human body. Those skilled in the art will recognize the benefits of applying the present invention to similar fields not discussed herein. 
     BACKGROUND OF THE INVENTION 
     A variety of devices are now commercially available for implantation through minimally invasive techniques. These devices include stents and stent-grafts used to maintain patent flow in blood vessels, the endo-biliary system or the urinary system. These stents and stent grafts have several different forms. Some are in the form of coiled wires while others are made from slotted tubes. Stents are also generally self-expanding or balloon expandable. Typically, they are made from metal and have a few important characteristics. These characteristics include expanded hoop strength, expansion force, expanded and unexpanded diameter, and the amount of foreshortening during expansion. Obviously the art of stent design is to work with these conflicting characteristics in such a way as to form the ideal stent. That stent would require very little force to expand, start with a very small unexpanded diameter and reliably expand to whatever diameter desired and the stent would not foreshorten when expanded. 
     Another important characteristic of a stent or stent-graft is the amount of expanded stent material that comes into contact with the vessel. Having the surface of the stent in contact with the stent is important because of in-stent restenosis. In-stent restenosis is a phenomenon where, for some reason, the vessel grows through the struts or between the coils and thereby obstructs fluid flow in the vessel. Where the stent is in direct contact with the vessel, the vessel can not impinge on the fluid flow. There is, therefore, a need for a stent which maximizes all of the characteristics above and has as close to 100% vessel contact in the area that is stented as possible. 
     Another type of device may generally be characterized as aneurysm repair devices. Depending upon where in the body the aneurysm is located, a ruptured aneurysm may be fatal. Typically aneurysm repair devices are used to prevent the aneurysm from getting larger and ultimately bursting. Exemplary types of aneurysm repair devices include those which protect the aneurysm from getting larger by shielding the aneurysm from fluid pressure, covering the neck of an aneurysm, or filling the aneurysm with some sort of packing material. Similar to stents, aneurysm repair devices have a variety of conflicting material characteristics which make them perform better, most notably surface contact or sealing capability. In addition, present coil-shaped repair devices have a potential for the leading edge of the coil to corkscrew into the vessel wall. There is therefore a need for an aneurysm repair device that has good sealing characteristics and one which would be less likely to corkscrew into the vessel wall. 
     U.S. Pat. No. 5,334,210 describes a prior art vascular occlusion assembly and is depicted in  FIG. 1  of the current application. The assembly comprises a foldable material occlusion bag which is filled with a flexible filler. Because the material is not non-compliant, it must be folded and must therefore disadvantageously increase the profile of the device. This bag may be positioned in a blood vessel and is intended to stop fluid from flowing through the vessel. There is therefore no lumen in the device. 
     Overall there is need for a prosthesis which has nearly complete vessel wall contact while maintaining a patent fluid channel. This prosthesis and its accompanying delivery system would be highly advantageous. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the deficiencies of the prior art by providing a sheath attached to the distal end of a delivery device. The sheath may be generally cylindrical in shape and have a lumen therethrough. The sheath may be expandable such that, as an endoprosthesis is delivered into the lumen of the sheath, the sheath will take on the exterior configuration of the endoprosthesis. The endoprosthesis is thereby covered while maintaining a patent fluid lumen. The sheath may further be detachable from the delivery device and may have holes or slots to enhance blood porosity and to enhance its distensability. The endoprosthesis may include stents, coils, stent grafts, aneurysm repair devices or any other endoprosthesis known in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a prior art device. 
         FIG. 2  illustrates a first embodiment of the delivery system. 
         FIG. 3  depicts a partially deployed coil with the delivery system. 
         FIG. 4  depicts a fully deployed stent in a body lumen. 
         FIG. 5  illustrates a second endoprosthesis. 
         FIG. 6  illustrates a third endoprosthesis. 
         FIG. 7  depicts the third endoprosthesis partially deployed. 
         FIG. 8  illustrates the third endoprosthesis fully deployed in an aneurysm neck. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings in which like elements in different drawing are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. 
     Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those skilled in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that may also be used. 
     Turning now to  FIG. 1 . Delivery system  15  includes tube  10 . Tube  10  may be a micro-catheter, guide catheter, hypotube or any other type of tube commonly known in the art. Depending on the application, the inner diameter or tube  10  may be 0.008-0.39 inches. Tube  10  may be formed of a polymer or a combination of polymers, metal, a metal polymer composite, a combination of polymers and metallic braid (not shown). Surrounding a distal portion of tube  10  is sheath  20 . Sheath  20  may preferably be made of an elastomer or other highly compliant polymer. Such polymers may include latex, styrenic block copolymers such as SBS and SEBS made by Shell under trade name of Kraton, polyether-ester block copolymers (COPE) for co-polyesters made by DuPont under the trade name of Hytrel, thermoplastic polyamide elastomers (PEBA) made by Atochem under the trade name of Pebax, and thermoplastic polyurethane elastomer (TPUR) made by Dow under the trade name Pellathane, or thermoplastic polyolefin elastomers (TPOs). 
     Sheath  20  may further include a proximal opening  25  and a distal opening  27 . In its non-distended configuration, sheath  20  may generally form a cylinder. Sheath  20  may have a ridge (not shown) on its interior near distal opening  27  which may be configured to better capture the distal end of a prosthesis. In an alternative embodiment, sheath  20  my have slots or holes (not shown) which would enhance the porosity of sheath  20  and provide better flexibility. 
     Sheath  20  may be frictionally fit about the distal end of tube  10 . In a preferred embodiment, an adhesive bond  30  binds sheath  20  to tube  10 . Sheath  20  may detach from tube  10  in a variety of ways. Where sheath  20  is frictionally fit over tube  10 , detachment may be achieved simply by overcoming the frictional forces between sheath  20  and tube  10 , pushing a prosthesis out of the distal end of tube  10 . Where sheath  20  is attached to tube  10  by adhesive bond  30 , the adhesive may be engineered to detach at any desired force. Adhesive bond  30  may be formed with any medically approved adhesive. In an alternative embodiment, sheath  20  may have a circumferential perforation distal of adhesive bond  30  and thereby provide sheath  20  with a tear away detachment mechanism. 
     Turning now to  FIG. 3 . Delivery system  15  is shown with a partially deployed self expanding coil  35 . Coil  35  may be attached to pusher wire  40 . When pusher wire  40  is moved distally relative to tube  10 , the distal portion of coil  35  engages the distal portion of sheath  20 . Sheath  20  then distends distally has coil  35  is advanced further out of tube  10 . Once the entire coil  35  has been pushed out of tube  10 , pusher wire  40  may be electrolytically detached. Methods of electrolytic detach are describe in U.S. Pat. No. 5,122,136 which is hereby incorporated by reference. It may further be appreciated that a variety of detach mechanisms are available to serve this function and furthermore that pusher wire  40  does not need to be attached to coil  35 . 
       FIG. 4  depicts delivery system  15  in use in the vasculature. In this embodiment, a self-expanding stent  45  has been introduced into a blood vessel. Pusher  40  has been advanced such that stent  45  was forced out of tube  10  and into contact with the interior of sheath  20 . After sheath  20  detached from tube  10 , sheath  20  remains in place about stent  45  and prevents any incursion by the surrounding tissue into the lumen of stent  45  and thereby maintains a patent fluid lumen for blood to flow through. Another embodiment is depicted in  FIG. 5  where a tulip shaped coil  50  is placed in a body lumen. 
       FIG. 6  illustrates yet another embodiment where wire  55  is advanced through tube  10 . Wire  55  may be formed of any suitable medically approved metal such as stainless steel or alloys of nickel such as Nitinol. Wire  55  has a pre-curved shape and is only forced out of that shape by placing wire  55  into tube  10 . Care should be taken to choose a material for sheath  20  which will conform to the pre-curved shape of wire  55  without deforming wire  55 . 
     As can readily be appreciated from  FIG. 7 , as wire  55  emerges from tube  10  it enters sheath  20  and resumes its pre-curved shape. In this embodiment, wire  55  is pre-curved into a flat disc-like shape but could be any of a variety of shapes known in the art. As described above, further advancement of wire  55  eventually detaches sheath  20  from tube  10  and thereby delivers pre-curved wire  55  into a desired location with sheath  20  surrounding wire  55 .  FIG. 8  depicts a particular use of pre-curved wire  55 . In this embodiment wire  55  forms into a disc-like shape suitable for covering an aneurysm neck. Wire  55  may be delivered without any other structure being placed into aneurysm  60 . Alternatively, wire  55  may be delivered after particles or other embolic materials (not shown) have been deployed into aneurysm  60 . In another embodiment wire  55  may be delivered into aneurysm  60  and particles may be delivered through wire  55  thereby filling aneurysm  60  and capping it with wire  55 . 
     While the specification describes the preferred designs, materials, methods of manufacture and methods of use, those skilled in the art will appreciate the scope and spirit of the invention with reference to the appended claims.