Abstract:
An intra-coronary stent provides intraluminal-scaffolding support of a vascular wall after percutaneous angioplasty in which a balloon catheter is used to expand a stenotic vascular lesion. The flexible stent substantially fully covers a vessel surface inside a vascular lumen. The improved stent easily delivers a delivery balloon to a selected vascular lumen site. The flexible stent has a smooth surface and sufficient radiopacity in the delivery and post delivery phase.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of Provisional Patent Application No. 60/235,164 filed Sep. 23, 2000, the disclosure of which is incorporated by reference. 
     
    
     
       FIELD OF INVENTION  
         [0002]    This invention relates generally to intravascular stents, and more particularly to intra-coronary stents that provide intraluminal-scaffolding support of a vascular wall after percutaneous angioplasty in which a balloon catheter is used to expand a stenotic vascular lesion.  
         DESCRIPTION OF THE RELATED ART  
         [0003]    By the year 2000, the percutaneous balloon angioplasty and stent implant procedures have become the dominant non-surgical revascularization method of the atherosclerotic stenosis, or obstruction, of the vascular lumen, and particularly in the coronary vascular system of the heart. With balloon angioplasty alone, without use of stent, the restenosis rate after angioplasty has been as high as 25-45% in the first time coronary cases. With use of stents after balloon angioplasty, the restenosis has been reduced significantly. Even so, the restenosis rate after stent implant is reported to be 15-25% range in coronary arteries, depending on the condition of the vessel stented or what specific stent was used. An ideal coronary stent is still elusive in the current state of the art commercial products.  
           [0004]    Some of the best selling current, second generation, stents can be divided into two categories. One category is a stent with flexibility and the other with good vessel coverage. The flexible current stents generally have poor vessel coverage, tissue prolapse, rough surface modulation and increased restenosis rate. On the other hand, a good vessel coverage stent in the current state of art has better vessel coverage but not flexible enough for easy delivery and efficient procedure. This means that an ideal stent that has good flexibility and good vessel coverage remains as the gold standard that has not yet been reached.  
           [0005]    To further reduce the restenosis rate after stent implant, numerous means has been tried, including laser, atherectomy, high frequency ultrasound, radiation device, local drug delivery, etc. Although the brachytherapy (radiation treatment) has proved to be reasonably effective in further reducing restenosis after stent implant, using brachytherpy is very cumbersome, inconvenient and costly. Mainly because it is radioactive device and radiation therapy specialist from another department has to be involved with the interventional cardiologist in the cardiac catheterization laboratory. The laser and atherectomy devices proved to be marginally useful in this purpose with added costs. Even if these measures would reduce the restenosis rate in theory or in real terms, an ideal stent that has good vessel coverage and flexibility would produce even better outcomes.  
           [0006]    The local drug therapy appears to be a very promising method for the future, as better pharmaceutical, chemical or biogenetic agents are developed and became available. Some research data, both from animal tests and human clinical studies, indicate that there are evidences of suppressing restenosis after stent implant when certain growth blocking pharmaceutical agents available today are used to coat the stent. In another instances, it has been speculated that certain surface modifying materials coated on the surface of the stent may be beneficial by it alone or in combination with growth suppressing agent, in reducing restenosis rate. In either instance, the drug or substance should be locally attached or coated on the stent and in sufficient amounts. However, attaching or coating a sufficient amount of a substance or drug on the coronary stent is not so easy a proposition, because coating enough volume of the drug on the small surface area of the stent is an elusive dream. If and when stent coating becomes practical, an ideally designed stent would still have better outcomes than a poorly designed stent, when used with substance coating.  
           [0007]    There is a need for an improved stent that is very flexible and substantially fully covers a vessel surface inside a vascular lumen.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, an object of the present invention is to provide a stent that is very flexible and substantially fully covers vessel surfaces inside a vascular lumen.  
           [0009]    Another object of the present invention is to provide an improved stent that is easily delivered with a delivery balloon to a selected vascular lumen site.  
           [0010]    Still another object of the present invention is to provide a stent that provides good flexibility, a smooth surface modulation without tulips and sufficient radiopacity during the delivery phase of the stent.  
           [0011]    A further object of the present invention is to provide a stent with good flexibility, a smooth surface modulation without tulips and sufficient radiopacity in the delivery and post delivery phase to the selected vascular site.  
           [0012]    These and other objects of the present invention are achieved in a stent, in a non-expanded state, that includes a first expansion column with individual expansion struts which form a plurality of expansion strut pairs. Each two adjacent expansion strut pairs in the first expansion column share a common strut. A second expansion column has individual expansion struts that form a plurality of expansion strut pairs. Each two adjacent expansion strut pairs in the second expansion column share a common strut. A first connecting strut column includes a plurality of individual connecting struts. Each individual connecting strut is an extension arm of an individual expansion strut from the first expansion column, and an extension arm of an individual expansion strut of the second expansion column.  
           [0013]    In another embodiment of the present invention, a stent, in a non-expanded state, has a first expansion column with individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops couple adjacent individual expansion struts. Each two adjacent expansion strut pairs in the first expansion column share a common strut. A second expansion column includes individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops couple adjacent individual expansion struts. Each two adjacent expansion strut pairs of the second expansion column share a common strut. A first connecting strut column has a plurality of individual connecting struts. Each end of an individual connecting strut extends from ipsi-lateral sides of expansion strut pair loops of the first and second expansion columns.  
           [0014]    In another embodiment of the present invention, a stent, in a non-expanded state, has a first expansion column with individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops couple adjacent individual expansion struts. Each two adjacent expansion strut pairs in the first expansion column share a common strut. A second expansion column includes individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops couple adjacent individual expansion struts. Each two adjacent expansion strut pairs of the second expansion column share a common strut. A first connecting strut column has a plurality of individual connecting struts. Each end of an individual connecting strut extends from contra-lateral sides of expansion strut pair loops of the first and second expansion columns.  
           [0015]    In another embodiment of the present invention, a stent, in a non-expanded state, a first expansion column includes individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops form first and second bifurcated expansion strut arms at expansion strut bifurcation points. Each two adjacent expansion strut pairs in the first expansion column share a common strut. A second expansion column includes individual expansion struts that form a plurality of expansion strut pair loops. The expansion strut pair loops form first and second bifurcated expansion strut arms at expansion strut bifurcation points. Each two adjacent expansion strut pairs share a common strut. A first connecting strut column has a plurality of individual connecting struts. One of the expansion strut arms forms a portion of a connecting strut. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0016]    [0016]FIG. 1 is a side-elevation view of one embodiment of an unexpanded stent of the present invention.  
         [0017]    [0017]FIG. 2 is an isometric view of the FIG. 1 stent drawn in scale for a 15 mm length.  
         [0018]    [0018]FIG. 3 is a close up view of the first and second expansion columns.  
         [0019]    [0019]FIG. 4 is a close up view of the FIG. 1 stent.  
         [0020]    [0020]FIG. 5 illustrates one embodiment of the connecting struts of the first connecting strut column.  
         [0021]    [0021]FIG. 6 illustrates one embodiment of the connecting struts that form the second connecting strut column.connector structs joining the expansion struts of FIG. 4.  
         [0022]    [0022]FIG. 7 is a close up view of closed cells created by adjacent expansion columns and their associated connecting strut colums.  
         [0023]    [0023]FIG. 8 is illustrates the alignment of two adjacent expansion columns. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring now to FIGS. 1 and 2, one embodiment of a stent  10  of the present invention is illustrated in a non-expanded state. Stent  10  includes a first expansion column  12  with individual expansion struts  14  that form a plurality of expansion strut pairs  16 . Adjacent expansion strut pairs  16  in first expansion column  12  share a common strut, indicated as  18 . A second expansion column  20  also has individual expansion struts  22  that form a plurality of expansion strut pairs  22 . Adjacent expansion strut pairs  22  in second expansion column  20  share a common strut, indicated as  24 . Stent  10  is configured to provide easy delivery that is achieved with a sufficient level of flexibility in combination with a delivery balloon, a smooth surface modulation without tulips and a reasonable radiopacity during the delivery phase of stent  10 .  
         [0025]    Stent  10  provides enhanced flexibility and conformability while maintaining a full vessel coverage with optimal metal fraction. Additionally, stent  10  has, (i) substantially evenly expanding stent struts, (ii) excellent radial strength and radiopacity and (iii) smooth surface modulations in both the delivery and deployed phases of the stent life cycle. Stent  10  has a continuous, unbroken cylindrical form without any break or de-linking around the circumference and along its length.  
         [0026]    As illustrated in FIG. 3, expansion strut pairs  16  and  24  form loops that couple adjacent individual expansion struts  14  and  22 . In one embodiment, the loops of expansion strut pairs  16  and  24  are aligned in a peak to valley geometry. In another embodiment, the loops of expansion strut pairs  16  and  24  are aligned in a peak to peak geometry.  
         [0027]    Expansion strut pairs  16  and  24  are jointed by a joining strut segment on distal and proximal ends and form the loops to form a “zigzig” pattern that continues for a selected number of cycles without a break around a circumference of stent  10 . The number of cycles can be any number but in one embodiment the number is six or less.  
         [0028]    Expansion struts  14  and  22  have first and second segments. At least a portion of the first segment of expansion struts  14  is positioned in close proximity in front of the loop of an expansion strut pair  16 . At least a portion of the second section of expansion struts  22  is positioned in close proximity in front of the loop of an expansion strut pair  24 . In one embodiment, close proximity is a distance of at least 0.001 inch. In another embodiment, close proximity is a distance less than 0.04 inch. At least one expansion strut  14  and  22  of expansion strut pairs  16  and  24  can have a stair-step segment at its proximal end and, the other expansion strut of the expansion strut pairs  16  and  24  has a stair-step segment at its distal end. In various embodiments, expansion struts  14  and  22  can have a, (i) short stepped-down segment at the proximal end, (ii) short stepped-down segment at the distal end, (iii) short stepped-up segment at the proximal end and short stepped-up segment at a the distal end. In all of these embodiments, expansion struts  14  and  22  have a short sloped transitional segment of that can have the same length between the long and short parts in expansion struts  14  and  22 .  
         [0029]    As illustrated in FIG. 4, stent  10  includes a first connecting strut column  26  with a plurality of individual connecting struts  28 . Each connecting strut  28  is an extension arm  30  of an expansion strut  14  from first expansion column  12 , and an extension arm  32  of an expansion strut  22  of second expansion column  20 .  
         [0030]    In the FIG. 4 embodiment, expansion columns  12 ,  20 ,  34 , and the others in stent  10 , have six zigzag cycles. Each six cycle expansion column includes twelve horizontally arranged expansion struts Connecting columns  26 ,  40  and the others do not have a zigzag cycle, but have doulbe stair-step connecting struts that are arranged in a paralleling alignment. For every one pair of expansion struts, there is only one associated connecting strut and the ratio of expansion struts to connecting struts is two-one.  
         [0031]    Stent  10  also includes additional expansion and connecting strut columns. Stent  10  includes a third expansion column  34  with expansion struts  36  that form expansion strut pairs  38 . A second connecting strut column  40  is made of a plurality of individual connecting struts  42 . Each connecting strut  42  is an extension arm  43  of an expansion strut  22  from second expansion column  20  and an extension arm  44  of an expansion strut  36  of third expansion column  34 .  
         [0032]    In various embodiments, one or both extension arms  30  and  32  extend from contra-lateral sides or ipsi-lateral sides of two opposing expansion strut pairs  16  and  24  (FIG. 5); and one or both extension arms  32  and  46  extend from contra-lateral sides or ipsi-lateral sides of two opposing expansion strut pairs  24  and  38  respectively. Extension from contra-lateral sides provides a diagonal link pathway and multiple angled pivot points of a connecting strut  28  and  42  provides enhanced flexibility, conformability and excellent crimping characteristics to stent  10 .  
         [0033]    Connecting struts  28  in first connecting strut column  26  have a longitudinal axis  46  (FIG. 5) and connecting struts  42  in second connecting strut column  40  have a longitudinal axis  48  (FIG. 6) that is non-parallel to longitudinal axis  46 . In various embodiments, longitudinal axis  46  and  48  can be, (i) non-perpendicular to a longitudinal axis  50  of stent  10 , (ii) substantially perpendicular to longitudinal axis  50 , (iii) substantially diagonal in angle with respect to longitudinal axis  50  and (iv) substantially parallel to longitudinal axis  50 .  
         [0034]    Longitudinal axis  46  extends in one direction  52  while longitudinal axis  48  extends in an opposite direction  54 . Longitudinal axis  46  and  48  each have a diagonal angle  56  with respect to a longitudinal axis of stent  10 . Diagonal angle  56  of longitudinal axis  46  extends in direction  52  in any number of different patterns, while diagonal angle  56  of longitudinal axis  48  extends in direction  54  in any number of different patterns. Substantially all of the connecting struts  28  in first connecting strut column  26  have a parallel longitudinal axi  46 . The same is true with every connecting strut  42  in second connecting strut column  40 , as well as other connecting struts in other connecting strut columns. Preferablly, every connecting strut  42  in first connecting strut column  26  has the same diagonal angle  56  with respect to longitudinal axis  50 . The same is true of all other connecting struts in the other connecting strut columns of stent  10 . Each longitudinal axis  46  and  48  has a slant angle vertical configuration, e.g., with diagonal angle  56 , relative to longiduinal axis  50  of stent  10 . This slant angle vertical configuration enhances the flexibility of stent  10  and is crimping characteristics on a balloon.  
         [0035]    In various embodiments of the present invention, connecting struts  28 ,  42 , and any other connecting struts in additional connecting strut columns form a, (i) single stair-step pattern, (ii) double stair-step pattern (FIGS. 5 and 6), (iii) multiple stair-step pattern, (iv) a stair-step pattern that includes at least one substantially horizontal segment  58  and at least one substantially slant-angled segment  60  and (v) at least one substantially horizontal segment  58 , at least one substantially slant-angled segment  60  and a curved section  62  that joins substantially horizontal segment  58  with substantially slant angled segment  60  (vi) first segment  58  and a second segment  64 , with at least a portion of first segment  58  is positioned in close proximity to a loop of an expansion strut pair  16  in first expansion column  12 . Curved section  62  can have one radius of curvature, multiple radii of curvature, variabel degrees radius or radii or curvature, a wide or a narrow radius of curvature.  
         [0036]    In the FIGS. 5 and 6 embodiments, expansion struts  14  and  22  have double stair-step patterns with multiple angled pivot points  65 . Pivot points  65  also enhance the flexibility of stent  10 . Additionally, linking first and second expansion columns  12  and  20  in a diagonally manner relative to longitudianl axis  50  provides further flexibility to stent  10 .  
         [0037]    Adjacent expansion columns and their associated connecting strut columns define a plurality of cells  66  that are illustrated in FIG. 7. Cells  66  have asymmetrical or symmetrical geometries. Cells  66  can have evenly spaced geometric shapes throughout stent  10 . In one embodiment, cells  66  have substantially six sides when stent  10  is in a nominally expanded state. In another embodiment, cells  66  have substantially hexagonal geometric configurations when stent  10  is in a nominally expanded state. Optionally included are strain relief notches  67  that relieve the strain caused by metal deformation when stent  10  is expanded in the deployment phase.  
         [0038]    [0038]FIG. 8 illustrates one embodiment of the spacing and alignment characteristics of expansion columns  12  and  20  without illustrating first connecting strut column  26 . In this embodiment, the width of first connecting strut column  26  is narrower than the width of expansion columns  12  and  20 . However, the width of first connecting strut column  26  can be narrower, the same as or wider than the width of expansion columns  12  and  20 . Additionally, the width of any connecting strut column in stent  10  can be variable and different from one or more of the other connecting strut columns of stent  10 . Further, the width of any expansion column in stent  10  can be different and variable from one or more other expansion columns in stent  10 .  
         [0039]    First, second and third expansion columns  12 ,  20  and  34  can each form a corrugated expansion ring.  
         [0040]    In another embodiment, expansion strut pair  16  loops and expansion strut pair  24  loops form first and second bifurcated expansion strut arms  68  at expansion strut bifurcation points.  
         [0041]    The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.