Abstract:
A stent for implanting in the body to hold open a blood vessel includes cells with facing loops and the curved flexible links disposed and adapted to cooperate so that, when unexpended, the stent can flex as it is moved through curved blood vessels to a site where it is to be expanded and so that, when the stent is expanded in a curved vessel, at that site, as compared to each other, cells on the outside of the curve are open in length, but narrow in width as compared to cells on the inside of the curve which are short in length but increased in width to result in a more constant stent cell area between the inside and the outside of the curve than would otherwise occur causing the stent, when coated with a medicine, to apply a more even dose to the inside wall of the lumen, avoiding the possibility that a toxic dose is supplied at one area while a less than effective dose is applied to another area.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation of Ser. No. 09/337,629 filed Jun. 21, 1999, which is a continuation of Ser. No. 09/026,099 filed Feb. 19, 1998 (now U.S. Pat. No. 5,972,018), which is a continuation of Ser. No. 08/881,594 filed Jun. 24, 1997 (now U.S. Pat. No. 5,843,120), which is a continuation of Ser. No. 08/782,467 filed Jan. 10, 1997, now abandoned, which is a continuation of Ser. No. 08/457,354, filed May 31, 1995 (now U.S. Pat. No. 5,733,303), which is a continuation of Ser. No. 08/282,181 filed Jul. 28, 1994 (now abandoned) and a continuation-in-part of Ser. No. 08/213,272, filed Mar. 17, 1994 (now U.S. Pat. No. 5,449,373). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to stents for implanting into a living body.  
         BACKGROUND OF THE INVENTION  
         [0003]    Various stems are known in the art wherein, for the present application, the term “stent” indicates a device, made of body-compatible material, which is utilized to widen a blood vessel, or other orifice in the body, and to maintain the resultant size of the lumen. Typically, the stent is delivered to the desired location in the body with an inflatable balloon and, when the balloon is inflated, the stem expands, thereby widening the orifice. Other mechanical devices which cause expansion of the stent are also utilized.  
           [0004]    Exemplary patents in the field of stents formed of wire are: U.S. Pat. No. 5,019,090 to Pinchuk, U.S. Pat. No. 5,161,547 to Tower, U.S. Pat. No. 4,950,227 to Savin, et al., U.S. Pat. No. 5,314,472 to Fontaine, U.S. Pat. No. 4,886,062 and U.S. Pat. No. 4,969,458 to Wiktor and U.S. Pat. No. 4,856,516 to Hillstead. Stems formed of cut stock metal are described in: U.S. Pat. No. 4,733,665 to Palmaz, U.S. Pat. No. 4,762,128 to Rosenbluth, U.S. Pat. No. 5,102,417 to Palmaz and Schatz, U.S. Pat. No. 5,195,984 to Schatz and WO 91FR013820 to Meadox.  
           [0005]    The stents described in U.S. Pat. No. 5,102,417 to Palmaz and Schatz have expandable tubular grafts connected together with a flexible connector. The grafts are formed of a plurality of slots disposed parallel to the longitudinal axis of the tube. The flexible connectors are helical connectors. Since the tubular grafts are relatively rigid, the flexible connectors are needed so that the stents can bend when being fed through a curved blood vessel. When the stents of U.S. Pat. No. 5,102,417 expand, the grafts expand radially and, consequently, shrink longitudinally. However, at the same time, the helical connectors twist. The twisting motion is most probably harmful to the blood vessel.  
           [0006]    U.S. Pat. No. 5,195,984 to Schatz describes a similar stent but with one straight connector, parallel to the longitudinal axis of the tubular grafts, between tubular grafts. The straight member removes the twisting motion; however, it is not a very strong connector.  
         SUMMARY OF THE PRESENT INVENTION  
         [0007]    In accordance with embodiments of the present invention, a stent for implanting in the body to hold open a blood vessel, includes a body-compatible metal mesh defining a tube having adjacent contiguous cells, the cells having walls which are also the walls of adjacent cells. Each of the plurality of cells includes a pair of facing loops, each facing loop having a curved apex generally aligned along the longitudinal axis. Each facing loop has a first end and a second end that are generally aligned along the circumferential axis, each of the facing loops adapted to open further upon radial expansion of the stent which tends to foreshorten the stent longitudinally. Each of the plurality of cells further includes a pair of curved flexible links which connect the adjacent ends of the pair of facing loops to complete each of the plurality of cells, the pair of curved flexible links made of a metal which, upon expansion of the stent, bend to substantially offset foreshortening along the longitudinal axis.  
           [0008]    The pair of facing loops and the curved flexible links are disposed and adapted to cooperate so that the tube, when unexpended, can flex as it is moved through curved blood vessels to a site where it is to be expanded and so that, when the stent is expanded in a curved vessel, at that site, as compared to each other, cells on the outside of the curve are open in length, but narrow in width as compared to cells on the inside of the curve which are short in length but increased in width. This results in a more constant stent cell area between the inside and the outside of the curve than would otherwise occur. Consequently, when the stent is coated with a medicine the compensation results in a more even dose being applied to the inside wall of the lumen, avoiding the possibility that a toxic dose is supplied at one area while a less than effective dose is applied to another area 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:  
         [0010]    [0010]FIG. 1 is an illustration of a patterned stent, constructed and operative in accordance with a first preferred embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is an illustration of the pattern of the stent of FIG. 1;  
         [0012]    [0012]FIG. 3 is an illustration of the stent of FIG. 1 in a bent position;  
         [0013]    [0013]FIG. 4 is an illustration of the stent of FIG. 1 in an expanded format;  
         [0014]    [0014]FIGS. 5A and 5B are illustrations of the changes in the patterns of the stent of FIG. 1 due to expansion;  
         [0015]    [0015]FIG. 6 is a schematic illustration of a second embodiment of the pattern for a stent;  
         [0016]    [0016]FIG. 7 is an illustration of a third embodiment of the pattern for the stent; and  
         [0017]    [0017]FIG. 8 is an illustration of the pattern of FIG. 7 in an expanded format. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    Reference is now made to FIGS.  1 - 4  which illustrate a first embodiment of a stent, constructed and operative in accordance with the principles of the present invention. FIG. 1 illustrates the stent in its non-expanded form, FIG. 2 illustrates the pattern of the stent, FIG. 3 illustrates it in a partially bent position and FIG. 4 illustrates it in an expanded form. As shown in FIG. 3, the stent  30  defines a longitudinal aperture  80  having a longitudinal axis or longitudinal extension  79 .  
         [0019]    The stent of the present invention is a tube whose sides are formed into a plurality of each of two orthogonal meander patterns which patterns are intertwined with each other. The term “meander pattern” is taken herein to describe a periodic pattern about center line and “orthogonal meander patterns” are patterns whose center lines are orthogonal to each other.  
         [0020]    In the stent of FIGS.  1 - 4 , the two meander patterns are labeled  11  and  12  and they are most easily seen in FIG. 2. Meander pattern  11  is a vertical sinusoid having a vertical center line  9 . Meander pattern  11  has two loops  14  and  16  per period wherein loops  14  open to the right while loops  16  open to the left. Loops  14  and  16  share common members  15  and  17 , where member  15  connects from one loop  14  to its following loop  16  and member  15  connects from one loop  16  to its following loop  14 .  
         [0021]    Meander pattern  12  is an horizontal pattern having an horizontal center line  13 . Meander pattern  12  also has loops, labeled  18  and  20 , but between loops of a period is an extended straight section labeled  22 . Loops  18  open downwards and loops  20  open upwards.  
         [0022]    Vertical meander pattern  11  is provided in odd and even (o and e) versions which are 180° out of phase with each other. Thus, each left opening loop  16  of meander pattern  11   o  faces a right opening loop  14  of meander pattern  11   e  and a right opening loop  14  of meander pattern  11   o  faces a left opening loop  16  of meander pattern  11   e.    
         [0023]    Horizontal meander pattern  12  is also provided in odd and even forms. The straight sections  22  of horizontal meander pattern  12   e  intersect with every third common member  17  of vertical meander pattern  11   e . The straight sections  22  of horizontal meander pattern  12   o  intersect with every third common member  15  of vertical meander pattern  11   e , beginning with the common member  15  two after an intersected common member  17 . The result is a full loop  14  between meander patterns  12   e  and  12   o  and a full loop  16  between meander patterns  12   o  and  12   e.    
         [0024]    Returning to FIG. 1, the pattern of FIG. 2 is formed into a tube  30  of an easily deformable material, such as a metal. Due to the two meander patterns, the stent of FIG. 1, when attached over a catheter balloon, is flexible and can therefore be easily dragged through curved blood vessels. An example of the way in which the stent of FIG. 1 bends is illustrated in FIG. 3.  
         [0025]    In FIG. 3, the stent begins to bend at the point marked A in the direction marked by arrow  40 . As the stent begins to curve, the section marked I becomes the inside of the curve while the section marked O becomes the outside of the curve. The inside of the curve I is shortened vis-a-vis the outside of the curve O.  
         [0026]    During bending, the loops  14 - 20  to the right of the point A change shape in order to compensate for the differences in length between the inside and outside curves. For example, loops  18   i  and  20   i  near the inside of the curve are closer together than loops  18   o  and  20   o  on the outside of the curve, which expand. Loops  14   i  and  16   i  near the inside I are compressed while the loops  14   o  and  16   o  closer to the outside O of the curve are expanded.  
         [0027]    As can be seen, both meander patterns  11  and  12  are involved in the bending. Although not shown, it will be appreciated that the stent of FIGS.  1 - 4  can bend in any direction and in more than one direction at any time.  
         [0028]    [0028]FIG. 4 illustrates the stent of FIG. 1 in its expanded form. When the stent expands, both meander patterns  11  and  12  expand (i.e. all loops  14 - 20  open up). As can be seen, the expanded stent has two types of enclosed spaces, a large space  42  between meander patterns  12   o  and  12   e  and a small space  44  between meander patterns  12   e  and  12   o . As can also be seen, each large space  42  has two loops  14  on its left side and two loops  16  on its fight side. The large spaces between vertical meander patterns  11   e  and  11   o , which are labeled  42   a , have loops  18  at their tops and bottoms while the large spaces between vertical meander patterns  11   o  and  11   e , which are labeled  42   b , have loops  20  at their tops and bottoms. Similarly for small spaces  44   a  and  44   b.    
         [0029]    It is noted that, due to the orthogonal meander patterns  11  and  12 , the stent of FIG. 1 does not significantly shrink during expansion. This is illustrated in detail in FIGS. 5A and 5B to which reference is now made. FIG. 5A illustrates the movement, during expansion, of one vertical meander pattern  11  and FIG. 5B illustrates the movement, during expansion, of one horizontal meander pattern  12 . The original patterns are shown with solid lines and the expanded patterns are shown with dashed lines.  
         [0030]    The vertical meander pattern  11  of FIG. 5A expands by widening its loops  14  and  16 . As a result, the vertical meander pattern  11  grows vertically by an amount 2*h 1  per loop. However, it also shrinks horizontally, by an amount 2*d 1 . Similarly, the horizontal meander pattern  12  of FIG. 5B expands by widening its loops  18  and  20 . As a result, the horizontal meander pattern  12  grows horizontally by an amount 2*d 2  per loop. However, it also shrinks vertically, by an amount h 2 . Thus, the vertical growth of the vertical meander pattern  11  compensates, at least partially, for the vertical shrinkage of the horizontal meander pattern  12 , and vice versa. It is noted that the end portions of any stent are only partially compensated and therefore, may shrink somewhat.  
         [0031]    It will be appreciated that the two orthogonal meander patterns  11  and  12  and the compensation they provide to each other provides flexibility to the unexpended stent of FIG. 1 However, when the stent is expanded, the changes in each of loops  14  and  16  provide rigidity to the resultant stent and thus, enable the stent to maintain a blood vessel at a desired inner diameter.  
         [0032]    The stent of the present invention can be manufactured from flat metal which is etched into the pattern of FIG. 2. The etched metal is then bent to form the tube  30 . Alternatively, the pattern of FIG. 2 can be manufactured from welded or twisted wire.  
         [0033]    It will be appreciated that the stent of the present invention can be made from metal and/or wire. Additionally, it can be plated with a protective material, embedded with a medicine, and/or covered with a material which can fill in the spaces  42  and  44 .  
         [0034]    It will be appreciated that the present invention encompasses all stents manufactured with a pattern formed of two meander patterns, orthogonal or otherwise. Another exemplary pattern, also with orthogonal meander patterns, is provided herein wherein FIG. 6 is a schematic version and FIG. 7 is a more rounded version. FIG. 8 shows the pattern of FIG. 7 in an expanded format. The pattern of FIGS. 6 and 7 is similar to that shown in FIG. 2 except that it has more horizontal meander patterns  12  and they are of one kind, rather than being even and odd as in FIG. 2.  
         [0035]    As can be seen in both FIGS. 6 and 7, there are two types of vertical meander patterns  11   e  and  11   o  which are 180° out of phase with each other. The horizontal meander patterns  12  connect with every line  15  of vertical meander pattern  11   e.    
         [0036]    [0036]FIG. 8 illustrates the pattern of FIG. 7 is an expanded format. Since there are no even and odd horizontal meander patterns, in the expanded format of FIG. 8, there are no large and small spaces. Instead, all spaces are of the same size, i.e., the stent is comprised of a plurality of spaces or cells  50  defining a uniform cellular structure.  
         [0037]    As shown in FIGS. 3, 7 and  8 , Applicants&#39; invention can also be described as an expandable stent defining a longitudinal aperture  80  having a longitudinal axis or extension  79  and a circumferential axis or extension  105 , including a plurality of flexible connected cells  50  with each of the flexible cells  50  having a first longitudinal end  77  and a second longitudinal end  78  Each cell  50  also is provided with a first longitudinal apex  100  disposed at the first longitudinal end  77  and a second longitudinal apex  104  disposed at the second longitudinal end  78 . Each cell  50  also includes a first member  51  having a longitudinal component having a first end  52  and a second end  53 ; a second member  54  having a longitudinal component having a first end  55  and a second end  56 ; a third member  57  having a longitudinal component having a first end  58  and a second end  59 ; and a fourth member  60  having a longitudinal component having a first end  61  and a second end  62 . The stent also includes a first loop  63  defining a first angle  64  disposed between the first end  52  of the first member  51  and the first end  55  of the second member  54 .  
         [0038]    A second loop  65  defining a second angle  66  is disposed between the second end  59  of the third member  57  and the second end  62  of the fourth member  60  and is disposed generally opposite to the first loop  63 . A first flexible compensating member or flexible link  67  having a first end  68  and a second end  69  is disposed between the first member  51  and the third member  57  with the first end  68  of the first flexible compensating member or flexible link  67  communicating with the second end  53  of the first member  51  and the second end  69  of the first flexible compensating member or flexible link  67  communicating with the first end  58  of the third member  57 . The first end  68  and the second end  69  are disposed a variable longitudinal distance  70  from each other.  
         [0039]    A second flexible compensating member  71  having a first end  72  and a second end  73  is disposed between the second member  54  and the fourth member  60 . The first end  72  of the second flexible compensating member or flexible link  71  communicates with the second end  56  of the second member  54  and the second end  73  of the second flexible compensating member or flexible link  71  communicates with the first end  61  of the fourth member  60 . The first end  72  and the second end  73  are disposed a variable longitudinal distance  74  from each other.  
         [0040]    In a preferred embodiment, the first and second flexible compensating member or flexible links  67  and  71  are arcuate. The fist and second flexible compensating member or flexible links  67  and  71  are differentially extendable or compressible when the stent is bent in a curved direction away from the longitudinal axis  79  of the aperture  80 . (Shown in FIG. 3.) The first member  51 , second member  54 , third member  57 , and fourth member  60  and the first loop  63  and the second loop  65  and the first flexible compensating member or flexible link  67  and the second flexible compensating member or flexible link  71  are disposed so that as the stent is expanded the distance between the first flexible compensating member or flexible link  67  and the second flexible compensating member or flexible link  71  increases and the longitudinal component of the first member  51 , second member  54 , third member  57  and fourth member  60  decreases while the first loop  63  and the second loop  65  remain generally opposite to one another, the ends  68  and  69  of the first flexible compensating member or flexible link  67  and the ends  72  and  73  of the second flexible compensating member or flexible link  71  open so as to increase the variable longitudinal distance  70  between the first end  68  and the second end  69  of the first flexible compensating member or flexible link  67  and so as to increase the variable longitudinal distance  74  between the first end  72  and the second end  73  of the second flexible compensating member or flexible link  71 . This compensates for the decreasing of the longitudinal component of the first member  51 , second member  54 , third member  57 , and fourth member  60  and substantially lessens the foreshortening of the stent upon its expansion.  
         [0041]    In a preferred embodiment, and as shown in FIG. 5A, the flexible compensating member or flexible links  67  and  71  compensate in an amount that is substantially equal to the amount that the stent foreshortens. As shown in FIGS. 7 and 8, the first flexible compensating member or flexible link  67  and the second flexible compensating member or flexible link  71  in each cell  50  of each row or band of cells  101 ,  102  and  103 , serve to flexibly connect other cells  50  in adjacent rows or bands  102 ,  103 , and  104  which themselves have first and second compensating members  67  and  71 .  
         [0042]    As shown in FIG. 7, the first flexible compensating member or flexible links  67  and  71  in row or band  101  serve to flexibly connect the cells  50  in adjacent rows or bands  102  and  103 . As shown in FIGS. 7 and 8, a portion of the flexible member  67  or  71  disposed between the first ends  68  and  72  and the second ends  69  and  73  may be provided with a width that is smaller than the width of the apices  100  and  104  to which they are attached.  
         [0043]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the claims which follow: