referring now more particularly to the drawings , and those embodiments of the invention here presented by way of illustration , fig1 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 fig1 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 fig2 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 fig3 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 fig3 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 fig5 of the drawings . in fig5 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 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 fig5 the network 32 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 fig6 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 fig6 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 it 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 fig6 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 fig9 - 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 fig9 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 fig1 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 fig9 - 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 fig6 of the drawings . the catheter 36 and wire channel 46 would be the same , the specific stent being the only difference . fig1 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 fig1 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 fig5 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 , fig1 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 fig1 ; or , the stent 50 can be made of a relatively flaccid fabric or the like having spring filaments 60 embedded 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 re - stenosis 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 .
a prosthesis for use in preventing re - stenosis after angioplasty is formed of plastic or sheet metal , and is expandable and contractible 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 .