Abstract:
A radially expandable segmented stent, the stent including annular metallic stent segments and connectors interconnecting each segment, the interconnectors are formed from a biodegradable polymer material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of copending U.S. patent application Ser. No. 10/171,199, filed Jun. 12, 2002, now allowed, which is a continuation of U.S. patent application Ser. No. 09/346,826, filed Jul. 2, 1999, now issued as U.S. Pat. No. 6,409,754. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to multiple interconnected stents or stent segments, the interconnections being comprised of lengths of a plastic material. The term “plastic” is used herein to refer to materials which are capable of being deformed permanently without rupture. 
     In the prior art, stents are well known for use in opening and reinforcing the interior wall of blood vessels and other body conduits. 
     Stents are generally tubular, radially expandable and may be of the self-expanding type or may be expandable with an outward pressure applied to the stent, typically by expansion of an interiorly positioned balloon. Stents are made of various materials such as plastic or metal, metal usually being preferred. 
     Since stents must be of somewhat rigid design to provide reinforcement support and may be required to be of considerable length in order to extend over a lengthy area, it is difficult to resolve this need for rigidity with the need of having a flexible stent which is readily implanted by inserting it through a sometimes tortuous curving path as is often encountered in the percutaneous insertion technique typically used for implantation of stents. This is further complicated by the fact that stents must be readily expandable upon implantation to provide a support structure. 
     It is known that a plurality of stent elements can be loosely interconnected together by filaments or the like to provide a lengthy flexible stent arrangement. Such arrangements are shown in the following patents for example: 
     U.S. Pat. No. 5,405,377 to Cragg 
     U.S. Pat. No. 5,665,115 to Cragg 
     U.S. Pat. No. 5,755,781 to Jayaraman 
     U.S. Pat. No. 5,443,476 to Schwartz et al. 
     U.S. Pat. No. 5,135,536 to Hillstead 
     U.S. Pat. No. 5,035,706 to Gianturco et al. 
     WO 93/13825 (PCT) to Maeda et al. 
     The following technical literature is also of interest in this regard:
           Tracheobronchial Tree: Expandable Metallic Stents Used in Experimental and Clinical Applications, Work in Progress; Radiology , February 1986, pp 309-312.     Experimental intrahepatic Portacaval Anastomosis: Use of Expandable Gianturco Stents; Radiology , February 1987, 162: 481-485.     Gianturco Expandable Wire Stents in the Treatment of Superior Vena Cava Syndrome Recurring After Maximum - Tolerance Radiation; Cancer , September 1987, Vol. 60, pp 1243-1246.     Modified Gianturco Expandable Wire Stents in Experimental And Clinical Use; Cerise, Porto Cervo , May 1987, pp 100-103.       

     BRIEF SUMMARY OF THE INVENTION 
     This invention is directed to an improvement in the general concept of joined stents or stent segments (hereinafter referred to collectively as “stent segments”) in which a “plastic” material (capable of exhibiting permanent deformation) extends between stents or stent segments (hereinafter referred to collectively as stent segments) to interconnect them with a somewhat constrained freedom of motion relative to each other, i.e., not loosely connected but flexibly connected. The stent segments are preferably of closed cell design and even more preferably of the self-expanding type. More precisely, the interconnecting elements are of a material different than the stent material and are plastically deformable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1  is a schematic showing of a stent according to the invention; 
         FIG. 2  is a schematic showing of a closed cell stent; 
         FIG. 3  shows the stent of  FIG. 2  expanded in a fragmentary view; 
         FIG. 4  is a schematic showing of an open cell stent; 
         FIG. 5  shows the stent of  FIG. 4  expanded, and 
         FIG. 6  is a showing of a preferred connection arrangement for a stent of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a schematic drawing of a flexible segmented stent  10  according to the invention is shown. It is preferably comprised of a plurality of closed cell stents or stent segments  12  interconnected by plastic connectors  14 . 
     Stents  12  are most preferably of closed cell construction and of the self-expandable type such as NITINOL stents which are cut or etched from tubular stock or rolled from cut or etched flat sheet or other shape memory metals which do not themselves exhibit permanent deformation. 
     Generally speaking, a self-expanding stent tends to return to its unconstrained or expanded condition. Also, in this type of stent it is generally preferred that it be of a closed cell construction. In accordance with this invention it has been found to be particularly advantageous to use self-expanding elastic material for the stent or stent segment, i.e., a material which is not “plastic” or “deformable” and to use a “plastic” “deformable” material for the connector elements. Such materials as plastic, i.e., polymeric, which may be biodegradable, metals such as gold, or viscoelastic polymers such as polyethylene may be used. Such connectors provide constrained motion yet some flexibility of the stent portions relative to each other and allow for permanent expansion of the combination as needed. 
     Alternatively, the stents may be of the type which are expandable with an outward radial pressure as is known in the art and may be of closed cell or open cell construction. Such stents may be of metal such as stainless steel, titanium, nickel or any other metal compatible with the body. However, in this type of combination, the connector elements will, according to the invention, be of a different material than the stents or stent segments yet the connector elements will be of a “plastic”, i.e., deformable material such as a polymer or the like as pointed out above. 
     In use, these stent combinations will allow for the provisions of relatively long stents which may be trimmed to any desired length at the time of the procedure. 
       FIG. 2  is a specific example of one type of closed cell construction in a stent  14 .  FIG. 3  shows the closed cells of stent  14  when expanded. 
       FIG. 4  is an example of open cell construction in a stent  16 .  FIG. 5  shows the open cells of stent  16  when expanded. 
     In one embodiment of the invention, it relates to self expanding stents or stent segments interconnected by connector elements of a different material exhibiting permanent deformation, i.e., “plastic behavior” upon expansion, the stents preferably being of closed cell construction. 
     In another embodiment of the invention it relates to balloon expandable or the like stents or stent segments rigidly interconnected by structural connector elements of a different “plastic” material than the stents or stent segments, preferably polymeric plastic, most preferably biodegradable, although in the case of a metal stent, the connector may be of a different metal exhibiting different permanent deformation characteristics, i.e., plastic behavior. 
     Connector elements may be of any of the variety of implantable grade metals or polymeric plastics such as polytetrafluoroethylene, polyethylene, polypropylene, nylon, polyester, polyurethane and others exhibiting permanent deformation and of a material different from that of the stent or stent segment per se. 
     The connector elements may also be of biodegradable material such as polycaprolactone, polyglycolic acid, polylactic acid and the like, so long as the material exhibits permanent deformation and form a structural part of the stent combination. 
     If the stents are of metal they may be coated with a biocompatible material such as polyurethane, polyethylene, polytetrafluorethylene, silicone, block copolymers of polyurethane, polyethylene and silicone, biodegradable polymers such as polylactic acid, polyglycolic acid and/or hydroxy butyrate or valerate copolymer. 
     In such an instance, the connectors may be fused to the coating on each stent segment to interconnect them. 
     Most preferably however, interconnection between stents is accomplished as shown in  FIG. 6 . In such an arrangement, a raised portion  18  is formed on connector  20  and an opening  22  is formed in stent  24 , the opening  22  being shaped to receive portion  18  and interfit therewith. Of course, the reverse arrangement may be used in which the received portion  18  is on stent  22  and the opening  22  is on the connector  20 . 
     The connectors are preferably flat and elongated but may be of various configurations such as straight, S-shaped, U-shaped, etc., and of different cross-section. 
     The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.