Abstract:
A prosthesis for use in preventing restenosis after angioplasty is formed of plastic or sheet metal, and is expandable and contractable for placement. The prosthesis can be inserted while in a collapsed position, then expanded and locked at the larger diameter. Spring force can be provided by the material itself, or metal springs can be embedded within the walls of the prosthesis. Preferably, the walls have holes therethrough to promote tissue growth; and, in one embodiment, the holes are in the form of slots so that the prosthesis is segmented and can bend longitudinally.

Description:
INFORMATION DISCLOSURE STATEMENT 
     There has been considerable use of balloon angioplasty due to stenosis in arteries having atherosclerotic plaque and the like in an effort to enlarge the lumen and to provide adequate blood flow. While such angioplasty has been successful, it has been found that in many cases re-stenosis requires that the procedure be repeated. 
     More recently, there have been efforts at following the balloon angioplasty with placement of a stent, the stent being in the nature of a sleeve that will mechanically maintain some minimum lumen diameter. 
     It will be obvious that, in order to place a stent utilizing the balloon angioplasty technology, the stent must necessarily have a sufficiently small external diameter to be moved into the desired area by some means such as a catheter, then to be expanded, both to be held in place by the arterial elasticity and to provide the minimum lumen diameter. Prior stents have generally taken the form of wire mesh that is collapsed for placement into the artery, then expanded, either by means of a balloon or by its own elasticity. The stent is generally held in place simply by the arterial elasticity in the first instance, and it has been found that epithelialization takes place throughout the stent so that the entire stent becomes effectively imbedded in the vessel wall. 
     The prior art stents, being woven stainless steel wire or the like tend not to be very flexible longitudinally so that their primary use is in straight portions of vessels. Also, inflation of the balloon is required to expand the wire mesh to its desired size in some cases, while other wire mesh stents tend to take a particular size, and must be held by a sleeve or the like during placement. 
     SUMMARY OF THE INVENTION 
     This invention relates generally to prostheses, and is more particularly concerned with a prosthesis in the form of a stent to be placed in a vessel for mechanically maintaining an opening. 
     This invention provides a stent for maintaining a minimum opening through an artery or the like, the stent being in the form of a sleeve having a discontinuity so the sleeve has a collapsed position to be assumed during placement of the stent, and an expanded position for use in its final location for maintaining the desired opening. In one embodiment of the invention, the stent may be carried by one catheter while a second coaxial catheter in the nature of a conventional balloon catheter is carried therein. This arrangement allows use of the balloon catheter to provide a mechanical opening in the vessel, then to allow the stent to be slipped into place over the balloon. The balloon can then be used to manipulate the stent for any necessary opening of the stent and disengagement of the stent from the coaxial catheter. It is also contemplated that the stent of the present invention can be carried by a single, generally conventional balloon catheter. 
     The stent of the present invention may selectively be biased towards a closed position and lockable in an open position, or biased in an open position and lockable in a closed position. In the former case, the stent will be put into place in its collapsed condition, then forcibly expanded by a balloon or the like to the desired locked condition. In the latter case, the stent may be held by a pin or the like in its collapsed condition, and the pin removed to allow the stent to assume its open position. 
     The stent of the present invention may be made from any of numerous materials, including metal or the like, and also including various plastic materials. The plastic materials may be simply homogeneous molded plastics, or may comprise a plastic covering over a knit or woven mesh. The knit or woven mesh may, in turn, be metal or plastic. The precise material can be selected to achieve the desired features of the stent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will become apparent from consideration of the following specification when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view showing one form of stent made in accordance with the present invention and carried by a coaxial catheter; 
         FIG. 2  is an enlarged cross-sectional view taken substantially along the line  2 — 2  in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a slightly modified form of stent shown in its open and locked position; 
         FIG. 4  is a fragmentary view showing the stent of  FIG. 3  after expansion beyond its maximum, open position; 
         FIG. 5  is a fragmentary perspective view, partially in cross-section, showing one form of material for use in constructing the stents of the present invention; 
         FIG. 6  is an elevational view showing another modified form of stent made in accordance with the present invention, the stent being carried on a catheter; 
         FIG. 7  is a cross-sectional view taken substantially along the line  7 — 7  in  FIG. 6 ; 
         FIG. 8  is a fragmentary view showing the stent of  FIG. 7  after expansion; 
         FIG. 9  is a top plan view of another modified form of stent made in accordance with the present invention, the stent being shown without the carrying catheter; 
         FIG. 10  is a bottom plan view of the device shown in  FIG. 9 ; 
         FIG. 11  is an enlarged cross-sectional view taken substantially along the line  11 — 11  in  FIG. 9 ; and, 
         FIG. 12  is a view similar to  FIG. 11  but showing the stent in its expanded condition. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now more particularly to the drawings, and those embodiments of the invention here presented by way of illustration,  FIG. 1  shows a stent generally indicated at  15 , the stent  15  being carried by a catheter  16 . The catheter  16  is one of two coaxial catheters, the other catheter  18  being a generally conventional balloon catheter having the balloon  19  at its distal end. 
     It will be understood by those skilled in the art that, in conventional balloon angioplasty, a catheter such as the catheter  18  is threaded through the arterial system to place the balloon at the location of the stenosis. The balloon  19  is then inflated to urge the arterial wall outwardly and open the lumen in the artery. This same technique will be utilized with the arrangement shown in  FIG. 1  of the drawings, the balloon  19  acting to perform the angioplasty; however, after the vessel is sufficiently open by means of the balloon  19 , the coaxial catheter  16  will be manipulated to urge the stent  15  in place over the balloon  19 . After the stent  15  is over the balloon  19 , the balloon  19  will be inflated to urge the stent outwardly to its opened condition. 
     Referring to  FIG. 2  of the drawings, it will be seen that the stent  15  includes a wall  20 , the wall  20  having sufficient memory that the stent as a whole tends to maintain its collapsed condition. One end of the wall  20  is provided with a hook  21  for engagement with one of a plurality of complementary hook means  22 . The hook  21  will necessarily be biased outwardly sufficiently that, as the hook  21  is urged past the plurality of hook means  22 , the hook  21  will engage each of the hooks  22 . Because of this arrangement, when the balloon  19  is not further inflated, the hook  21  will remain engaged with one of the hooks  22  to prevent collapse of the stent  15 . 
     It will also be noticed that the stent  15  contains a plurality of generally circumferential ribs  24 . It is contemplated that the ribs  24  will engage the arterial walls sufficiently to prevent inadvertent movement of the stent after placement and removal of the catheter  16 . As will be discussed hereinafter, the stent  15  may also contain a plurality of openings to allow tissue to grow therethrough and further hold the stent  15  in place. 
     Looking now at  FIGS. 3 and 4  of the drawings, it will be seen that the stent  25  is a slightly modified form of the stent  15 . The stent  25  includes the wall  26  which will be biased towards collapse as is the wall  20  of the stent  15 . Once the stent  25  is urged to its expanded condition, the interlocking hook means  28  will become engaged as shown in  FIG. 3  to prevent collapse of the stent  25  and maintain the stent in its maximum, open condition. 
     It will be understood that there may be times when the stent is improperly placed, or for other reasons must be removed. With the stent  25 , the ends  29  and  30  of the wall  26  are so biased that, when the stent  25  is expanded so far that the ends  29  and  30  are released from engagement, the end  29  will move inwardly and the end  30  will move outwardly. On subsequent release of the stent  25 , the walls  29  and  30  have exchanged places so that the hook means  28  cannot now engage. As a result, the stent  25  will collapse to its minimum external diameter. 
     Though many different materials may be utilized in forming the stents of the present invention, one form of material is illustrated in  FIG. 5  of the drawings. In  FIG. 5  there is a woven network indicated at  31 . This woven network may be metal such as stainless steel or the like, or may be a knit or woven plastic material such as polyester filaments. If the network  31  is made of metal, the intersections of the materials can be soldered or spot welded, and if the network is polyester or other thermoplastic, the intersections can be sonically welded or otherwise heat sealed to one another. 
     Following provision of the network  31 , the network  31  is covered by a plastic material indicated at  32 . The material  32  can again be any of numerous materials, so long as the material is implantable. Nevertheless, numerous plastic materials including polyethylene, polyester, polytetraflouroethylene and others can be utilized. 
     As illustrated in  FIG. 5 , the network  31  is simply coated with the material  32  so that openings  34  are distributed throughout the material. While the openings  34  are not necessarily so uniformly distributed, it will be understood that the use of a plurality of openings  34  promotes epithelialization to promote incorporation of the stent into the vessel wall. 
     Turning now to  FIG. 6  of the drawings, there is a stent indicated at  35  carried at the end of a catheter  36 . The catheter  36  includes a balloon  38  as is known in the art. 
     While the above described stents have been biased inwardly and have been forced outwardly, the stent  35  is biased outwardly and is forced inwardly and retained by means of a pin  39 . For a full understanding of the stent  35 , attention is directed to  FIGS. 6 ,  7  and  8  of the drawings which show both plan view and cross-sectional views of the stent  35 . 
     The stent  35  is here shown as having a generally smooth wall  40  having a plurality of openings  43  in accordance with the foregoing discussion. The wall  40  is biased outwardly towards its maximum diameter; however, for placement by means of the catheter  36 , the stent  35  is urged inwardly to its minimum diameter, and the stent is provided with a first pair of lugs  41  carried on the end  42  of the wall  40 , and second pair of lugs  44  carried generally towards the opposite end  45  of the wall  40 . When the wall  40  is urged inwardly to collapse the stent  35 , appropriate openings in the lugs  41  and  44  are aligned, and the pin  39  is placed therethrough to hold the stent  35  in its collapsed position. 
     As is shown in  FIG. 6  of the drawings, it is contemplated that the pin  39  will be in the form of a wire that extends along the catheter  36 , contained within a channel  46 . With this arrangement, the pin  39  will extend to the lug  44  at the distal end of the stent  35 , and it will be understood that the distal end lug  44  may have a hole that does not extend completely through the lug in order to cover the end of the pin  39 . The pin  39  then extends the full length of the stent  35  and into the channel  46 . While not here illustrated, it will be understood that the pin  39  extends completely along the length of the catheter  36  so the pin  39  can be manipulated externally of the body so that, at the appropriate moment, the pin  39  can be removed from the lugs  41  and  44  and allow the stent  35  to expand. 
     As here shown, when the stent  35  expands, the ends  42  and  45  will remain overlapped to some extent. If desired, interlocking grooves  48  and  49  can be provided so the stent  35  has a relatively fixed expanded diameter. 
     Attention is next directed to  FIGS. 9–12  of the drawings which show another modified form of stent. The stent  50  is similar to the stent  35  in that it is biased outwardly and is forcibly held inward by a pin; however, the stent  50  is considerably different from the stent  35  in that the stent  50  is of a somewhat segmented construction to allow longitudinal flexibility. 
     In the top plan view shown in  FIG. 9  of the drawings, it will be seen that the stent  50  includes a plurality of segments  51 , each segment  51  having a lug  52  thereon for receipt of a pin  54 . The segments  51  are interspersed with segments  56  on the opposite side of the pin  54 , the segments  56  having lugs  58  thereon. As is better shown in  FIG. 10  of the drawings, there is a generally continuous spine  59  extending along the bottom of the stent  50  and interconnecting all of the segments  51  and  56 . Because of this construction, it will be seen that the stent  50  will be readily bendable along its longitudinal axis, the bending being resisted only by the relatively narrow spine  59 . Furthermore, it will be understood that the individual segments  51  and  56  can be made much shorter to provide for tighter radii, or relatively long in the event the stent is not intended to be very flexible. 
     Though the stent  50  in  FIGS. 9–12  of the drawings is not shown in conjunction with a catheter, it will be understood by those skilled in the art that the stent will be put into place using an arrangement such as that shown in  FIG. 6  of the drawings. The catheter  36  and wire channel  46  would be the same, the specific stent being the only difference. 
       FIG. 11  of the drawings shows the cross-sectional shape of the stent  50  while the stent is held in its closed, or collapsed, condition by the pin  54 . When the pin  54  is removed, the stent  50  will expand to the condition shown in  FIG. 12  of the drawings. It will of course be recognized that a balloon, such as the balloon  38 , may be utilized to assist in urging the walls of the stent outwardly to the desired position. 
     The material from which the stent  50  is made may be any of the numerous materials previously mentioned, including the material shown in  FIG. 5  of the drawings. Because the stent  50  is made up of a plurality of individual segments  51  and  56 , there is no particular need for additional openings in the wall of the stent, the spaces between the segments providing adequate openings for initial fluid drainage and subsequent epithelialization. 
     Simply by way of example,  FIGS. 10 and 12  illustrate the inclusion of a filament  60  in the wall of the stent. The purpose of the filament  60  is to show that the stent  50  can be made of a plastic material having sufficient memory to be urged to the open condition as shown in  FIG. 12 ; or, the stent  50  can be made of a relatively flaccid fabric or the like having spring filaments  60  imbedded therein for urging the stent  50  to its open position. Also, the stent  50  can be made entirely of metal, including well known alloys of platinum and gold, or chromium and cobalt. 
     From the foregoing discussion it will be understood that the present invention provides an arterial stent and a method for placing the stent for preventing restenosis following angioplasty or other mechanical opening of the lumen in an artery. While several specific designs and materials have been disclosed, those skilled in the art will recognize that the materials must be implantable, and all portions of the stent must be sufficiently smooth to prevent trauma during placement. Further, all corners and the like should be well rounded to promote epithelialization without subsequent trauma due to the presence of sharp edges during natural body motions. 
     It will of course be understood by those skilled in the art that the particular embodiments of the invention here presented are by way of illustration only, and are meant to be in no way restrictive; therefore, numerous changes and modifications may be made, and the full use of equivalents resorted to, without departing from the spirit or scope of the invention as outlined in the appended claims.