Abstract:
There is disclosed a stent for implanting in the body. The stent is formed of a tube having a patterned shape which has first and second meander patterns having axes extending in first and second directions. The first meander patterns can be formed into even and odd first meander patterns. The even and odd first meander patterns are 180° out of phase with each other and the odd patterns occur between every two even patterns. The second meander patterns are intertwined with the first meander patterns. The first and second directions can be orthogonal to each other. The second meander patterns can also be formed of even and odd patterns.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to stents for implanting into a living body.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various stents 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 stent expands, thereby widening the orifice. Other mechanical devices which cause expansion of the stent are also utilized.  
           [0003]    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. Stents 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.  
           [0004]    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.  
           [0005]    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  
         [0006]    It is therefore an object of the present invention to provide a flexible stent which minimally shrinks, in the longitudinal direction, during expansion.  
           [0007]    The stent of the present invention is formed of a tube having a patterned shape which has first and second meander patterns having axes extending in first and second directions wherein the second meander patterns are intertwined with the first meander patterns. The first and second directions can be orthogonal to each other.  
           [0008]    In accordance with one embodiment of the present invention, the first meander patterns are formed into even and odd first meander patterns. The even and odd first meander patterns are 180° out of phase with each other and the odd patterns occur between every two even patterns. The second meander patterns can also be formed of even and odd patterns.  
           [0009]    Additionally, in accordance with a preferred embodiment of the present invention, the second meander patterns have two loops per period and the even and odd first meander patterns are connected on first and second sides, respectively, of each loop of the second meander patterns.  
           [0010]    Alternatively or in addition, the second meander patterns are formed of even and odd second meander patterns. In this embodiment, the even and odd first meander patterns have loops and the even and odd second meander patterns are connected to the even and odd first meander patterns so as to leave one full loop between each pair of even and odd second meander patterns.  
           [0011]    Moreover, in accordance with a preferred embodiment of the present invention, the first and second meander patterns are formed from flat metal. Alternatively, they can be cut from wire. Further, they can be imbedded or covered with any body-compatible material.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:  
         [0013]    [0013]FIG. 1 is an illustration of a patterned stent, constructed and operative in accordance with a first preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is an illustration of the pattern of the stent of FIG. 1;  
         [0015]    [0015]FIG. 3 is an illustration of the stent of FIG. 1 in a bent position;  
         [0016]    [0016]FIG. 4 is an illustration of the stent of FIG. 1 in an expanded format;  
         [0017]    [0017]FIGS. 5A and 5B are illustrations of the changes in the patterns of the stent of FIG. 1 due to expansion;  
         [0018]    [0018]FIG. 6 is a schematic illustration of a second embodiment of the pattern for a stent;  
         [0019]    [0019]FIG. 7 is an illustration of a third embodiment of the pattern for the stent; and  
         [0020]    [0020]FIG. 8 is an illustration of the pattern of FIG. 7 in an expanded format.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    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.  
         [0022]    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 and “orthogonal meander patterns” are patterns whose center lines are orthogonal to each other.  
         [0023]    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 .  
         [0024]    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.  
         [0025]    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 patters  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.    
         [0026]    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.    
         [0027]    Returning to FIG. 1, the pattern of FIG. 2 is formed into a tube  30  of an easily deformable material, such as 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.  
         [0028]    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.  
         [0029]    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.  
         [0030]    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.  
         [0031]    [0031]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 right 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.    
         [0032]    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.  
         [0033]    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 b 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.  
         [0034]    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 unexpanded stent of to 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.  
         [0035]    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.  
         [0036]    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 .  
         [0037]    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.  
         [0038]    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.    
         [0039]    [0039]FIG. 8 illustrates the pattern of FIG. 7 in 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.  
         [0040]    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: