INTRAVASCULAR STENT

Abstract: A stent in a non-expanded state has a first and second expansion columns, each consisting of a plurality of expansion strut pairs. An expansion strut pair includes a first expansion strut, a second expansion strut and a joining strut that couples the first and second expansion struts at one end. Expansion strut pairs include expansion strut pair first and second corners formed where the joining strut couples the first and second expansion struts. A connecting strut column, formed of a plurality of connecting struts couples the first and second expansion columns. Connecting struts include a proximal section, a distal section and an intermediate section. The proximal section is coupled to the corner of an expansion strut pair of the first expansion column, and the distal section is coupled to the joining strut of an expansion strut pair of the second expansion column intermediate the expansion strut pair first corner and the expansion strut pair second corner.

Description: Intravascular Stent Cross-reference to Related Applications This application claims the benefit of Provisional Patent Application No 60/017,484 filed April 26, 1996, the disclosure of which is incorporated by reference This application is a continuation in part of U S Patent Application Serial No , (Attorney Docket No 17828 707), filed March 25, 1997, entitled "Intravascular StentX and a continuation in part of U S Patent Application Serial No , (Attorney Docket No 17828 708), filed March 25, 1997, entitled "Intravascular Stent", and a continuation in part of U S Patent Application Serial No , (Attorney Docket No 17828 709), filed March 25, 1997, entitled "Intravascular Stent" and is related to U S Patent Application Serial No , (Attorney Docket No 18461 709), filed April 25, 1997, entitled "Intravascular Stent" each having same named inventor G David Jang and being incorporated by reference BACKGROUND OF THE INVENTION Field ofthe Invention This invention relates to intravascular stents, and more particularly to an intravascular stent which provides easy introduction through tortuous sections of vessels Description ofthe Related Art Angioplasty, either coronary or general vascular, has advanced to become the most effective means for revascularization of stenosed vessels In the early 1980's, angioplasty first became available for clinical practice in the coronary artery, and has since proven an effective alterative to conventional bypass graft surgery Balloon catheter dependent angioplasty has consistently proven to be the most reliable and practical interventional procedure Other ancillary technologies such as laser based treatment, or directional or rotational arthrectomy, have proven to be either of limited effectiveness or dependent on balloon angioplasty for completion ofthe intended procedure. Restenosis following balloon-based angioplasty is the most serious drawback and is especially prevalent in the coronary artery system. Many regimens have been designed to combat restenosis, with limited success, including laser based treatment and directional or rotational arthrectomy. Intravascular stenting, however, noticeably reduces the restenosis rate following angioplasty procedures. The procedure for intravascular stent placement typically involves pre-dilation ofthe target vessel using balloon angioplasty, followed by deployment ofthe stent, and expansion ofthe stent such that the dilated vessel walls are supported from the inside. The intravascular stent functions as scaffolding for the lumen of a vessel. The scaffolding ofthe vessel walls by the stent serve to: (a) prevent elastic recoil ofthe dilated vessel wall, (b) eliminate residual stenosis ofthe vessel; a common occurrence in balloon angioplasty procedures, (c) maintain the diameter ofthe stented vessel segment slightly larger than the native unobstructed vessel segments proximal and distal the stented segment and (d) as indicated by the latest clinical data, lower the restenosis rate. Following an angioplasty procedure, the restenosis rate of stented vessels has proven significantly lower than for unstented or otherwise treated vessels; treatments include drug therapy and other methods mentioned previously. Another benefit of vessel stenting is the potential reduction of emergency bypass surgery arising from angioplasty procedures. Stenting has proven to be effective in some cases for treating impending closure of a vessel during angioplasty. Stenting can also control and stabilize an unstable local intimal tear of a vessel caused by normal conduct during an angioplasty procedure. In some cases, an incomplete or less than optimal dilatation of a vessel lesion with balloon angioplasty can successfully be opened up with a stent implant. Early in its development, the practice of stenting, especially in coronary arteries, had serious anticoagulation problems. However, anticoagulation techniques have since been developed and are becoming simpler and more effective. Better and easier to use regimens are continuously being introduced, including simple outpatient anticoagulation treatments, resulting in reduced hospital stays for stent patients. An example of a conventional stent patent is US 5,102,417 (hereafter the Palmaz Patent) The stent described in the Palmaz Patent consists of a series of elongated tubular members having a plurality of slots disposed substantially parallel to the longitudinal axis ofthe tubular members. The tubular members are connected by at least one flexible connector member The unexpanded tubular members ofthe Palmaz Patent are overly rigid so that practical application is limited to short lengths. Even with implementation ofthe multilink design with flexible connector members connecting a series of tubular members, longer stents can not navigate tortuous blood vessels. Furthermore, the rigidity ofthe unexpanded stent increases the risk of damaging vessels during insertion. Foreshortening ofthe stent during insertion complicates accurate placement ofthe stent and reduces the area that can be covered by the expanded stent. There is, further, no method of programming the stent diameter along its longitudinal axis to achieve a tapered expanded stent, and no method of reenforcement of stent ends or other regions is provided for. Another example of a conventional stent patent is WO 96/03092, the Brun patent. The stent described in the Brun patent is formed of a tube having a patterned shape, which has first and second meander patterns. The even and odd first meander patterns are 180 degrees out of phase, with the odd patterns occurring between every two even patterns The second meander patterns run perpendicular to the first meander patterns, along the axis of the tube Adjacent first meander patterns are connected by second meander patterns to form a generally uniform distributed pattern The symmetrical arrangement with first and second meander patterns having sharp right angled bends allows for catching and snagging on the vessel wall during delivery. Furthermore, the large convolutions in the second meander pattern are not fully straightened out during expansion reducing rigidity and structural strength of the expanded stent. There is, further, no method of programming the stent diameter along its longitudinal axis to achieve a tapering stent design, and no method of reenforcement of stent ends or other regions is provided for. These and other conventional stent designs suffer in varying degrees from a variety of drawbacks including: (a) inability to negotiate bends in vessels due to columnar rigidity ofthe unexpanded stent; (b) lack of structural strength, axio-lateral, ofthe unexpanded stent; (c) significant foreshortening ofthe stent during expansion; (d) limited stent length; (e) constant expanded stent diameter; (f) poor crimping characteristics; and (g) rough surface modulation ofthe unexpanded stent. There is a need for a stent with sufficient longitudinal flexibility in the unexpanded state to allow for navigation through tortuous vessels. There is a further need for a stent that is structurally strong in the unexpanded state such that risk of damage or distortion during delivery is minimal. A further need exists for a stent that maintains substantially the same longitudinal length during expansion to allow greater coverage at the target site and simplify proper placement ofthe stent. Yet a further need exists for a stent design with sufficient longitudinal flexibility that long stents of up to 100 mm can be safely delivered through tortuous vessels. There is a need for a stent that is configured to expand to variable diameters along its length, such that a taper can be achieved in the expanded stent to match the natural taper ofthe target vessel. A need exists for a stent which, (i) can be crimped tightly on the expansion balloon while maintaining a low profile and flexibility, (ii) has a smooth surface modulation when crimped over a delivery balloon, to prevent catching and snagging ofthe stent on the vessel wall during delivery or (iii) with reenforcement rings on the ends or middle or both to keep the ends ofthe stent securely positioned against the vessel walls ofthe target blood vessel. SUMMARY OF THE INVENTION Accordingly an object ofthe present invention is to provide a scaffold for an interior lumen of a vessel. Another object ofthe invention is to provide a stent which prevents recoil ofthe vessel following angioplasty. A further object ofthe invention is to provide a stent that maintains a larger vessel lumen compared to the results obtained only with balloon angioplasty. Yet another object ofthe invention is to provide a stent that reduces foreshortening of a stent length when expanded. Another object ofthe invention is to provide a stent with increased flexibility when delivered to a selected site in a vessel. A further object ofthe invention is to provide a stent with a low profile when crimped over a delivery balloon of a stent assembly. Yet a further object ofthe invention is to provide a stent with reduced tuliping of a stent frame. Another object ofthe invention is to provide a chain mesh stent that reduces vessel "hang up" in a tortuous vessel or a vessel with curvature A further object ofthe invention is to provide a chain mesh stent that increases radial and axio-lateral strength ofthe expanded stent. These and other objects ofthe invention are achieved in a stent in a non- expanded state. A first expansion column includes of a plurality of first expansion column strut pairs. A first expansion strut pair includes a first expansion strut adjacent to a second expansion strut and a first joining strut that couples the first and second expansion struts at a proximal end ofthe first expansion strut pair. A second expansion strut pair includes a third expansion strut adjacent to the second expansion strut and a second joining strut that couples the second and third expansion struts at a distal end ofthe second expansion strut pair. A third expansion strut pair includes a fourth expansion strut adjacent to the third expansion strut and a third joining strut that couples the third and fourth expansion struts at a proximal end ofthe third expansion strut pair. A fourth expansion strut pair includes a fifth expansion strut adjacent to the fourth expansion strut and a fourth joining strut that couples the fourth and fifth expansion struts at a distal end ofthe fourth expansion strut pair. A first expansion strut pair first corner is formed where the first joining strut is coupled to the first expansion strut, and a first expansion strut pair second corner is formed where the first joining strut is coupled to the second expansion strut. A second expansion strut pair first corner is formed where the second joining strut is coupled to the second expansion strut, and a second expansion strut pair second corner is formed where the second joining strut is coupled to the third expansion strut. A third expansion strut pair first corner is formed where the third joining strut is coupled to the third expansion strut, and a third expansion strut pair second corner is formed where the third joining strut is coupled to the fourth expansion strut. A fourth expansion strut pair first corner is formed where the fourth joining strut is coupled to the fourth expansion strut, and a fourth expansion strut pair second corner is formed where the fourth joimng strut is coupled to the fifth expansion strut. A second expansion column includes of a plurality of second expansion column strut pairs. A first expansion strut pair includes a first expansion strut adjacent to a second expansion strut and a first joining strut that couples the first and second expansion struts at a proximal end ofthe first expansion strut pair. A second expansion strut pair includes a third expansion strut adjacent to the second expansion strut and a second joining strut that couples the second and third expansion struts at a distal end ofthe second expansion strut pair. A third expansion strut pair includes a fourth expansion strut adjacent to the third expansion strut and a third joining strut that couples the third and fourth expansion struts at a proximal end ofthe third expansion strut pair. A fourth expansion strut pair includes a fifth expansion strut adjacent to the fourth expansion strut and a fourth joining strut that couples the fourth and fifth expansion struts at a distal end ofthe fourth expansion strut pair. A first expansion strut pair first corner is formed where the first joining strut is coupled to the first expansion strut, and a first expansion strut pair second comer is formed where the first joining strut is coupled to the second expansion strut. A second expansion strut pair first comer is formed where the second joining strut is coupled to the second expansion strut, and a second expansion strut pair second comer is formed where the second joining strut is coupled to the third expansion strut. A third expansion strut pair first comer is formed where the third joining strut is coupled to the third expansion strut, and a third expansion strut pair second comer is formed where the third joining strut is coupled to the fourth expansion strut. A fourth expansion strut pair first corner is formed where the fourth joining strut is coupled to the fourth expansion strut, and a fourth expansion strut pair second corner is formed where the fourth joining strut is coupled to the fifth expansion strut. A first connecting strut column is formed of a plurality of first connecting struts, each connecting strut ofthe first connecting strut column includes a connecting strut proximal section, a connecting strut distal section and a connecting strut intermediate section. A first connecting strut proximal section is coupled to the first corner ofthe second expansion stmt pair ofthe first expansion strut column, and a first connecting strut distal section is coupled to the first joining stmt ofthe first expansion stmt pair ofthe second expansion stmt column intermediate the first expansion stmt pair first corner and the first expansion stmt pair second comer. A second connecting stmt proximal section is coupled to the first comer ofthe fourth expansion stmt pair ofthe first expansion stmt column, and a second connecting stmt distal section is coupled to the third joining stmt ofthe third expansion stmt pair ofthe second expansion stmt column intermediate the third expansion stmt pair first corner and the third expansion stmt pair second corner. BRIEF DESCRIPTION OF THE DRAWINGS Fig. IA is a side elevation view ofthe pre-expansion mode of an embodiment ofthe stent ofthe present invention; Fig. IB is a cross sectional view of an embodiment ofthe stent ofthe present invention; Fig. IC is a longitudinal cross sectional view of an embodiment ofthe stent ofthe present invention; Fig. 2 A is a scale drawing ofthe stmt pattern of an embodiment ofthe stent ofthe present invention; Fig. 2B is an expanded view of a section ofthe pattern of Figure 2 A; Fig. 3 A is a schematic illustration of a pre-expansion mode of an embodiment ofthe stent ofthe present invention; Fig. 3B is a schematic illustration ofthe post-expansion mode of an embodiment ofthe stent ofthe present invention; Fig. 4A is a scale drawing including dimensions of an embodiment ofthe stent ofthe present invention; Fig. 4B is an enlarged section ofthe scale drawing of Figure 4 A; Fig. 5 is a scale drawing of an embodiment ofthe stent ofthe present invention with a tapered diameter in its post-expansion mode; Fig. 6A is a scale drawing of an embodiment ofthe stent ofthe present invention with reenforcement expansion columns, Fig. 6B is a perspective view ofthe embodiment of Figure 6A; Fig. 7A is a scale drawing of an embodiment ofthe stent ofthe present invention including relief notches at stmt joints to increase flexibility ofthe joints; Fig. 7B is an enlarged region ofthe embodiment of Figure 7A; Fig. 7C is an enlarged view of a single connecting stmt joining two expansion stmt pairs in accordance with the embodiment of Figure 7 A; Fig. 8A is a side elevation view of an embodiment ofthe stent ofthe present invention; Fig. 8B is a side elevation view of an embodiment ofthe stent ofthe present invention, shown as if the stent stmts and space there between were transparent; Fig. 8C is a scale drawing of an embodiment ofthe stent ofthe present invention; Fig. 8D is a variation ofthe embodiment ofthe stent of Fig. 8C; Fig. 8E is a perspective view ofthe embodiment of Figure 8D, Fig 8F is a drawing illustrating the post-expansion mode ofthe stent of the embodiment of Fig 8D ofthe present invention, Fig 8G is an enlarged view of a single connecting stmt joining two expansion stmt pairs in accordance with an embodiment ofthe present invention; Fig 9 A is a side elevation view of an embodiment ofthe stent ofthe present invention; Fig 9B is a perspective view ofthe embodiment of Fig 9 A, Fig 9C is a scale drawing ofthe embodiment of Fig 9 A, Fig 9D is an enlarged region ofthe drawing of Fig 9C, Fig 9E is a scale drawing of an embodiment ofthe stent ofthe present invention, Fig 9F is a scale drawing of an embodiment ofthe stent ofthe present invention, Fig 9G is an enlarged view of a single connecting stmt joining two expansion stmt pairs in accordance with an embodiment ofthe present invention, Fig 10 A is a drawing of an altemate geometry of connecting stmts and joining stmts m accord with the present invention, Fig 1 OB is a drawing of an alternate geometry of connecting stmts and joimng stmts in accord with the present invention, Fig IOC is a drawing of an alternate geometry of connecting stmts and joining stmts in accord with the present invention, Fig 10D is a drawing of an alternate geometry of connecting stmts and joining stmts in accord with the present invention, Fig 10E is a drawing of an alternate geometry of connecting stmts and joining stmts in accord with the present invention, Fig 1 OF is a drawing of an alternate geometry of connecting stmts and joining stmts in accord with the present invention, and Fig. 11 is a delivery balloon catheter, illustrating a method of deliver of a stent in accord with the present invention. DETAILED DESCRIPTION A first embodiment ofthe present invention is shown in Figures 1 A, IB, IC, 2 A and 2B. Referring to Figure 1 A, an elongate hollow tubular stent 10 in an unexpanded state is shown. A proximal end 12 and a distal end 14 define a longitudinal length 16 of stent 10. The longitudinal length 16 ofthe stent 10 can be as long as 100 mm or longer. A proximal opening 18 and a distal opening 20 connect to an inner lumen 22 of stent 10. Stent 10 can be a single piece, without any seams or welding joints or may include multiple pieces. Stent 10 is constructed of two to fifty or more expansion columns or rings 24 connected together by interspersed connecting stmt columns 26. The first column on the proximal end 12 and the last column on the distal end 14 of stent 10 are expansion columns 24. Expansion columns 24 are formed from a series of expansion stmts 28, and joining stmts 30. Expansion stmts 28 are thin elongate members arranged so that they extend at least in part in the direction ofthe longitudinal axis of stent 10. When an outward external force is applied to stent 10 from the inside by an expansion balloon or other means, expansion stmts 28 are reoriented such that they extend in a more circumferential direction, i e along the surface of cylindrical stent 10 and perpendicular to its longitudinal axis. Reorientation of expansion stmts 28 causes stent 10 to have an expanded circumference and diameter. In Figure 1 A, expansion stmts 28 of unexpanded stent 10 are seen to extend substantially parallel to the longitudinal axis of stent 10 Expansion stmts 28 are joined together by joining stmts 30 to form a plurality of expansion stmt pairs 32. Expansion stmt pairs have a closed end 34 and an open end 36. Additional joining stmts 30 join together expansion stmts 28 of adjacent expansion stmt pairs 32, such that expansion stmts 28 are joined alternately at their proximal and distal ends to adjacent expansion stmts 28 to form expansion columns 24. Each expansion column 24 contains a plurality, typically eight to twenty, twenty to sixty, or larger of expansion stmts 28. Expansion columns are preferably continuous unbroken ring stmctures extending around the circumference ofthe stent 10; however, broken stmctures in which individual stmts or pieces of stmts are removed from an otherwise continuous expansion column 24 can also be used. Connecting stmts 38 connect adjacent expansion columns 24 forming a series of interspersed connecting stmt columns 26 each extending around the circumference of stent 10. Each connecting stmt 38 joins a pair of expansion stmts 28 in an expansion column 24 to an adjacent pair of expansion stmts 28 in an adjacent expansion column 24. For stent 10 of Figure IA, the ratio of expansion stmts 28 in an expansion column 24 to connecting stmts 38 in a connecting stmt column 26 is two to one; however, this ratio in general can be x to 1 where x is greater or less than two. Furthermore, since the stent 10 of Figure 1 A begins with an expansion column 24 on the proximal end 12 and ends with an expansion column 24 on the distal end 14, if there are n expansion columns 24 with m expansion stmts 28 per column, there will be m-l connecting stmt columns 26, and n(m-l)/2 connecting stmts 38. The reduced number of connecting stmts 38 in each connecting stmt column 26, as compared to expansion stmts 28 in each expansion column 24, allows stent 10 to be longitudinally flexibility. Longitudinal flexibility can be further increased by using a narrow width connecting stmt, providing additional flexibility and suppleness to the stent as it is navigated around turns in a natural blood vessel. At least a portion ofthe open spaces between stmts in stent 10 form asymmetrical cell spaces 40. A cell space or geometric cell is an empty region on the surface of stent 10, completely surrounded by one or a combination of stent stmts, including expansion stmts 28, connecting stmts 38, or joining stmts 30. Asymmetrical cell spaces 40 are cell spaces which have no geometrical symmetry i.e. no rotation, reflection, combination rotation and reflection or other symmetry. Asymmetrical cell spaces 40 have an asymmetrical geometric configuration. Asymmetrical cell spaces 40 in Figure IA are surrounded by a first expansion stmt pair 32 in a first expansion column 24, a first connecting stmt 38, a second expansion stmt pair 32 in an adjacent expansion column 24, a first joining stmt 30, a second connecting stmt 38, and a second joining stmt 30. Furthermore, expansion stmt pairs 32 of asymmetrical cell space 40 may be circumferentially offset i e have longitudinal axes that are not collinear and have their open ends 36 facing each other. The space between two expansion stmts of an expansion stmt pair 32 is known as a loop slot 42. Figure IB shows inner lumen 22, radius 44 and stent wall 46 of stent 10 Stent wall 46 consists of stent stmts including expansion stmts 28, connecting stmts 38 and joining stmts 30 Figure IC shows, proximal end 12, distal end 14, longitudinal length 16, inner lumen 22, and stent wall 46 of stent 10 Inner lumen 22 is surrounded by stent wall 46 which forms the cylindrical surface of stent 10. Referring now to Figures 2A and 2B, joining stmts 30 of stent 10 are seen to extend at an angle to the expansion stmts 28, forming a narrow angle 48 with one expansion stmt 28 in an expansion stmt pair 32 and a wide angle 50 with the other expansion stmt 28 of an expansion stmt pair 32. Nanow angle 48 is less than ninety degrees, while wide angle 50 is greater than ninety degrees. Joining stmts 30 extend both longitudinally along the longitudinal axis of stent 10 and circumferentially, along the surface ofthe stent 10 perpendicular to its longitudinal axis. Expansion stmt spacing 52 between adjacent expansion stmts 28 in a given expansion column 24 are uniform in stent 10 of Figures 2 A and 2B, however, non-uniform spacings can also be used. Expansion stmt spacings 52 can be varied, for example, spacings 52 between adjacent expansion stmts 28 in an expansion column 24 can alternate between a narrow and a wide spacings Additionally, spacings 52 in a single expansion column 24 can differ from other spacings 52 in other columns 24 It is noted that varying expansion stmt spacings 52 which form the loop slots 42 results in variable loop slot widths Furthermore, the longitudinal axis ofthe loop slots 42 need not be collinear or even parallel with the longitudinal axis of loop slots 42 of an adjacent expansion column 24. Figures 2A and 2B show an arrangement of expansion stmts 28 such that collinear, parallel adjacent loop slots 42 are formed, but non-collinear and non-parallel loop slots 42 can also be used. Additionally the shape of loop slots 42 need not be the same among loop slots of a single or multiple expansion columns 24 The shape of loop slots 42 can be altered by changing the orientation or physical dimensions ofthe expansion stmts 28 and/or joining stmts 30 which connect expansion stmts 28 of expansion stmt pairs 32 defining the boundaries of loop slots 42. Connecting stmts 38 couple adjacent expansion columns 24, by connecting the distal end of an expansion stmt pair in one expansion column 24 to the proximal end of an adjacent expansion stmt pair 32 in a second expansion column 24 Connecting stmts 38 of Figures 2 A and 2B are formed from two linear sections, a first linear section 54 being joined at its distal end to a second linear section 56 at its proximal end to form a first slant angle 58 The first linear section 54 of a connecting stmt 38 is joined to expansion stmt 28 at the point where joining stmt 30 makes narrow angle 48 with expansion stmt 28 First linear section 54 extends substantially collinear to joining stmt 30 continuing the line of joining stmt 30 into the space between expansion columns 24. The distal end ofthe first linear section 54 is joined to the proximal end ofthe second linear section 56 forming slant angle 58 Second linear section 56 extends substantially parallel to expansion stmts 28 connecting at its distal end to joining stmt 30 in an adjacent expansion column 24 The distal end of second linear section 56 attaches to expansion stmt 28 at the point where joining stmt 30 makes narrow angle 48 with expansion stmt 28 Further, joining stmt 30 can have a second slant angle with a width that can be the same or different from the width ofthe first slant angle Figures 2A and 2B show connecting stmts 38 and joining stmts 30 slanted relative to the longitudinal axis of stent 10, with the circumferential direction ofthe slanted stmts alternating from column to adjacent column Circumferential direction refers to the handedness with which the slanted stmts wind about the surface ofthe stent 10 The circumferential direction ofthe slant of connecting stmt first linear sections 54 in a connecting stmt column 26 is opposite the circumferential direction ofthe slant of connecting stmt first linear sections 54 in an adjacent connecting stmt column 26 Similarly, the circumferential direction ofthe slant of joining stmts 30 in an expansion column 24 is opposite the circumferential direction ofthe slant of joining stmts 30 in an adjacent expansion column 24 Alternating circumferential slant directions of connecting stmts 38 and joining stmts 30 prevents axial warping of stent 10 during deliver and expansion Other non-alternating slant direction patterns can also be used for connecting stmts 38 or joining stmts 30 or both Figure 3 A and 3B show a schematic illustration of a stent design according to the present invention in an unexpanded and expanded state respectively The design is depicted as a flat projection, as if stent 10 were cut lengthwise parallel to its longitudinal axis and flattened out The connecting stmts 38 consist of first and second linear sections 54 and 56 forming slant angle 58 at pivot point 60 An asymmetrical cell space 40 is formed by expansion stmt pairs 32, connecting stmts 38 and joimng stmts 30 Multiple interlocking asymmetrical cell spaces 40 make up the design pattern As the stent is expanded, see Figure 3B, the expansion stmt pairs 32 spread apart at their open ends 36, shortening the length of expansion stmts 28 along the longitudinal axis ofthe cylindrical stent The longitudinal shortemng of expansion stmts 28 during expansion is countered by the longitudinal lengthening of connecting stmts 38 The widening of slant angle 58 during expansion straightens connecting stmts 38 and lengthens the distance between the coupled expansion stmt pairs 32 The widening ofthe slant angle of connecting stmts 38 substantially compensates for the longitudinal shortening of expansion stmts 28 Thus, the stent has substantially constant unexpanded and expanded longitudinal lengths When the stent is expanded, each expansion column 24 becomes circumferentially stretched, enlarging the space between stmts The interlinking through the expansion process gives the stent 10 a high radial support strength The entire stent 10 when expanded is unitized into a continuous chain mesh of stretched expansion columns 24 and connecting stmt columns 26 forming an asymmetrical interlocking cell geometry which resists collapse both axially and radially When the stent is expanded it has increased rigidity and fatigue tolerance In addition, efficient bending and straightening of connecting stmts 38 at pivot points 60 allows increased longitudinal flexibility ofthe stent For the stent to bend longitudinally, at least some of connecting stmts 38 are forced to bend in their tangent plane The tangent plane of a specific connecting stmt 38 refers to the plane substantially tangent to the cylindrical surface ofthe stent at that connecting stmt 38 The width of connecting stmts 38 can be twice as wide as a thickness Preferably, a one-to-one ratio is prefened However, pivot points 60 in connecting stmts 38 provide connecting stmts 38 a flexible joint about which to more easily bend increasing longitudinal flexibility ofthe stent Referring to Figures 4A and 4B, a variation ofthe first embodiment of stent 10 of the present invention is shown In this variation, stent 10 has a length 16 of 33 25 mm and an uncrimped and unexpanded circumference 88 of 5.26 mm Fifteen expansion columns 24 are interspersed with connecting stmt columns 26 Each expansion column 24 consists of twelve expansion stmts 28 joined alternately at their proximal and distal ends by joining stmts 30 forming six expansion stmt pairs 32 Expansion stmts 28 are aligned parallel to the longitudinal axis of cylindrical stent 10 Joining stmts 30 form a narrow angle 48 and a wide angle 50 with the respective expansion stmts 28 of expansion stmt pairs 32 Adjacent expansion columns 24 employ alternating circumferential slant directions of joining stmts 30 In this variation ofthe first embodiment, expansion stmt width 62 is 20 mm, expansion stmt length 64 is 1 51 mm, and connecting stmt width 66 is 13 mm Distance 68 from the outer edge of a first expansion stmt 28 to the outer edge of a second adjacent expansion stmt 28 in the same expansion column 24 is .64 mm, leaving a loop slot width 70 of .24 mm. In this variation ofthe first embodiment, connecting stmts 38 consist of a slanted first linear section 54 joined to a second linear section 56 at a slant angle 58. First linear section 54 is slightly longer than second linear section 56 and is attached at its proximal end to an expansion stmt 28 in an expansion column 24. The attachment ofthe proximal end of first linear section 54 to expansion stmt 28 is at the point where joining stmt 30 makes narrow angle 48 with expansion stmt 28. First linear section 54 extends substantially collinear to joining stmt 30 attaching at its distal end to the proximal end of second linear section 56 to form slant angle 58. Second linear section 56 extends substantially collinear to expansion stmts 28, attaching at its distal end to an expansion stmt 28 in an adjacent expansion column 24. The attachment occurs at the point where expansion stmt 28 forms narrow angle 48 with joining stmt 30. Joining stmts 30 and connecting stmt first linear sections 54 slant in alternating circumferential directions from column to adjacent column. The joining of connecting stmts 38 and expansion stmts 28 at the point where narrow angle 48 is formed aids smooth delivery of stent 10 by streamlining the surface ofthe unexpanded stent and minimizing possible catching points. Bare delivery of stent 10 to the target lesion in a vessel will thus result in minimal snagging or catching as it is navigated through turns and curvatures in the vessel. Stent 10 behaves like a flexible, tubular sled as it is moved forward or backward in the vessel on the delivery catheter, sliding through tortuous vessels and over irregular bumps caused by atherosclerotic plaques inside the vessel lumen. When fully expanded Stent 10 of Figures 4 A and 4B has an internal diameter of up to 5.0 mm, while maintaining an acceptable radial strength and fatigue tolerance. The crimped stent outer diameter can be as small as 1.0 mm or less depending on the condition ofthe underlying delivery balloon profile; A small crimped outer diameter is especially important if stent delivery is to be attempted without prediction ofthe target site. When the stent is optimally crimped over the delivery balloon, the surface ofthe crimped stent is smooth allowing for no snagging ofthe stent stmts during either forward or backward movement through a vessel. Figure 5 shows a second embodiment ofthe present invention in which the stent 10 in its expanded form has a gradual taper from proximal end 12 to distal end 14 The shaded segments 72, 74, 76, 78, 80, 82 and 84 of expansion stmts 28 represent regions of expansion stmts 28 to be removed. Removal of the shaded segments 72, 74, 76, 78, 80, 82 and 84 provides stent 10 with a gradual taper when expanded with distal end 14 having a smaller expanded diameter than proximal end 12 The degree of shortening ofthe expanded diameter ofthe stent 10 at a given expansion column 24 will be proportional to the length ofthe removed segment 72, 74, 76, 78, 80, 82, or 84 at that expansion column 24 In the expanded stent 10 the shortened expansion stmts 28 will have a shortened component along the circumference ofthe stent resulting in a shortened circumference and diameter The tapered diameter portion can be positioned anywhere along the length of stent 10, and the tapering can be made more or less gradual by removing appropriately larger or smaller portions ofthe expansion stmts 28 in a given expansion column 24 Tapering is especially important in long stents, longer than 12 mm, since tapering of blood vessels is more pronounced over longer lengths A long stent with a uniform stent diameter can only be matched to the target vessel diameter over a short region If the proximal vessel size is matched with the stent diameter, the expanded distal end ofthe stent will be too large for the natural vessel and may cause an intimal dissection ofthe distal vessel by stent expansion On the other hand, if the distal vessel size is matched with the stent diameter, the proximal end ofthe expanded stent will be too small to set inside the vessel lumen It is therefore desirable to have a stent with a tapered expanded diameter Another way achieve a tapered expanded stent is to change the stiffness ofthe stent stmts, expansion stmts, connecting stmts or joining stmts such that the stiffness ofthe stmts varies along the length of the stent The stiffness ofthe stmts can be changed by altering length, width or thickness, adding additional stiffening material, using a chemical or mechanical means to alter the physical properties ofthe stent material, or applying one or a series of elastic elements about the stent. Along with the use of a tapered diameter stent, a matching tapered balloon catheter would ideally be made for delivery and deployment ofthe tapered diameter stent. The method of using a tapered matching balloon catheter with a tapered diameter stent is within the scope ofthe present invention. Using a tapered balloon to expand a non-tapered stent will also achieve a tapered expanded stent; however, since no metal is removed from the stent, the stent is tapered as a result of incomplete expansion. The stent will therefore have increased metal fraction at the tapered end resulting in increased risk of acute thrombosis. Metal fraction is the proportion ofthe surface ofthe expanded stent covered by the stent stmt material. Shortening the expansion stmts as shown in Figure 5 allows for a tapered expanded stent with substantially constant metal fraction along its length. A third embodiment ofthe present invention shown in Figures 6 A and 6B has multiple reenforcement expansion columns 86 placed along the length of the stent 10. The Reenforcement columns 86 are placed along the stent length to provide additional localized radial strength and rigidity to stent 10. Additional strength and rigidity are especially important at the ends ofthe stent to prevent deformation ofthe stent both during delivery and after placement. During delivery the stent ends can catch on the vessel wall possibly deforming the unexpanded stent and altering its expansion characteristics. After the stent has been placed it is important that the stent ends are rigid so that they set firmly against the vessel wall; otherwise, during a subsequent catheter procedure, the catheter or guidewire can catch on the stent ends pulling the stent away from the vessel wall and possibly damaging and/or blocking the vessel. The specific variation ofthe third embodiment of stent 10 depicted in Figures 6A and 6B has a length 16 of 20.70 mm and an uncrimped and unexpanded circumference 88 of 5.26 mm. The stent 10 consists of six expansion columns 24 and three reenforcement expansion columns 86, each consisting respectively of twelve expansion stmts 28 or reenforcement expansion stmts 90. The reenforcement expansion columns 86 are positioned one at either end, and one along the length ofthe stent 10. The expansion stmt width 62 is .15 mm, reenforcement expansion stmt width 92 is .20 mm, and the connecting stmt width 66 is .10 mm. The narrow angle 48 formed by joining stmt 30 and expansion stmt 28 is 75 degrees, and the narrow angle 94 formed by reenforcement joining stmt 96 and reenforcement expansion stmt 90 is 60 degrees. Other arrangements of reenforcement expansion columns 86, such as providing reenforcement expansion columns 86 only on the ends of the stent, only on one end, or at multiple locations throughout the length ofthe stent can also be used and fall within the scope ofthe present invention. A taper can also be programmed into the reenforced stent 10 by shortening expansion stmts 28 and reenforcement expansion stmts 90 in appropriate expansion columns 24 and 86. A fourth embodiment ofthe present invention, shown in the Figures 7 A, 7B and 7C, is similar to the third embodiment but has the added feature of relief notches 98 and 100. A relief notch is a notch where metal has been removed from a stmt, usually at a joint where multiple stmts are connected. Relief notches increase flexibility of a stmt or joint by creating a thinned, narrow region along the stmt or joint. Relief notch 98 is formed at the joint formed between first linear section 54 of connecting stmt 38 and expansion stmt 28. Relief notch 100 is formed at the joint between second linear section 56 of connecting stmt 38 and expansion stmt 28. The positioning ofthe relief notches gives added flexibility to the unexpanded stent and prevents warping at the joints when the stent is expanded. This results in a smooth surface modulation to the expanded stent frame. Relief notches can be placed at other joints and can be included in any ofthe previously mentioned embodiments. Figures 8 A and 8B show a side elevation view of a variation ofthe fifth embodiment ofthe stent ofthe present invention. In this embodiment a four piece slanted connecting stmt 38 is used to couple the corner of an expansion stmt pair 32 in one expansion column 24 to the joining stmt 30 of a circumferentially offset expansion stmt pair 32 in an adjacent expansion column 24. The expansion stmts 28, joining stmts 30, expansion columns 24, reenforcement expansion stmts 90, reenforcement joining stmts 96, and reenforcement expansion columns 86 are substantially similar to the fourth embodiment of Figure 6 A. Connecting stmts 38 in connecting stmt columns 26, however, have an altered geometry and connectivity, described in more detail below. Figure 8 A shows only the stent stmts on the front half of the stent surface. The stent stmts on the rear half of the stent surface are not shown. The stent appears as it would if the stent stmts and space there between were opaque. Figure 8B shows all stent stmts from both the front and rear halves. The stent appears as it would if the stent stmts and the space there between were transparent. A first variation of a fifth embodiment ofthe present invention, shown in Figure 8C consists of a stent 10 with twelve expansion columns 24, four reenforcement expansion columns 86, and fifteen connecting stmt columns 26. In this variation, the stent 10 has a length 16 of 31.96 mm, and an unexpanded circumference 88 of 5.26 mm. Connecting stmts 38 shown in an enlarged view in Figure 8G are made up of four linear sections, a proximal end section 162, first and second intermediate sections 164 and 166 respectively and a distal end section 168 forming three slant angles 170, 172 and 174. The proximal end of proximal section 162 is attached to a corner 176 of an expansion stmt pair 32 of an expansion column 24. Corner 176 is formed where joining stmt 30 makes narrow angle 48 with expansion stmt 28. A second comer 178 of expansion stmt 32 is formed where joining stmt 30 makes wide angle 50 with expansion stmt 28. Comers 176 and 178 can have an angular shape formed by joining linear expansion stmts 28 and joining stmts 30, or preferably comers 176 and 178 are rounded to remove sharp edges and provide increased flexibility. Additionally rounded comers provide stent 10 with greater expandability and reduce stress in the stent stmt material at the comers in the expanded stent. Proximal end section 162 of connecting stmt 38 extends from comer 176 and is attached at its distal end to first intermediate section 164 forming slant angle 170. First intermediate section 164 extends from proximal end section 162 such that first intermediate section 164 is parallel to expansion stmts 28 and is connected at its distal end to the proximal end of second intermediate section 166 forming slant angie 172. Second intermediate section 166 extends in a slanted orientation relative to the longitudinal axis of stent 10, extending both longitudinally along and circumferentially about stent 10. Preferably, second intermediate section 166 is parallel to joining stmt 30 ofthe circumferentially offset expansion stmt pair 32 in adjacent expansion column 24. Second intermediate section 166 attaches at its distal end to the proximal end of distal end section 168 forming slant angie 174. Distal end section 168 extends from second intermediate section 166 attaching at its distal end to joining stmt 30 of circumferentially offset expansion stmt pair 32 of adjacent expansion column 24. The attachment is at a point intermediate comers 176 and 178, where joining stmt 30 forms narrow angle 48 and wide angle 50 respectively with expansion stmts 28. The connection point of distal end section 168 to joining stmt 30 is closer to comer 176 than comer 178. Preferably the connection point is one to two or more expansion stmt widths from comer 176. Offsetting the connection point of distal end section 168 to joining stmt 30 from corner 176 to a point intermediate comer 176 and corner 178 reduces warping ofthe expanded stent 10, resulting in a smooth surface modulation and reduced risk of thrombosis. Additionally, this design provides a longer total straightened length of connecting stmt 38, which further reduces foreshortening of stent 10 during expansion. A second variation of a fifth embodiment ofthe present invention, shown in an unexpanded form in Figures 8D, 8E and in an expanded form in Figure 8F consists of a stent 10 with six expansion columns 24, two reenforcement expansion columns 86, and seven connecting stmt columns 26. In this variation, the stent 10 has a length 16 of 15.04 mm, and an unexpanded circumference 88 of 5.26 mm. The stent design 10 is substantially similar to the design ofthe first variation ofthe fifth embodiment of Figure 8C with a reduced number of expansion columns, reenforcement expansion columns, and connecting stmt columns. Figure 8F illustrates a portion ofthe expanded stent 10 ofthe second variation ofthe fifth embodiment. After expansion of stent 10 by balloon or other means, the expansion stmts 28 are spread apart circumferentially, increasing the separation at the open end 36 of expansion stmt pairs 32 resulting in an increase in the circumference ofthe stent 10. The spreading ofthe expansion stmts 28 causes a longitudinal shortening ofthe expansion columns 24, which is compensated by a straightening ofthe connecting stmts 38. During the expansion process, the slant angles 170, 172 and 174 widen straightening the connection stmts 38, and causing an increase in the separation distance between adjacent expansion columns 24. The asymmetrical interlocking cell geometry ofthe expanded stent is illustrated in Figure 8F. Figures 9 A, 9B, 9C, 9D, 9E, 9F and 9G illustrate a sixth embodiment of the stent ofthe present invention. In this embodiment a three piece slanted connecting stmt 38 is used to couple the joining stmt 30 of an expansion stmt pair 32 in one expansion column 24 to the joining stmt 30 of a circumferentially offset expansion stmt pair 32 in an adjacent expansion column 24. The joints between segments of connecting stmt 38 are curved forming a smooth rounded shape. The expansion stmts 28, joining stmts 30, expansion columns 24, reenforcement expansion stmts 90, reenforcement joining stmts 96, and reenforcement expansion columns 86 are substantially similar to the fourth embodiment of Figure 8 A. Connecting stmts 38 in connecting stmt columns 26, however, have an altered geometry and connectivity, described in more detail below. A first variation of a sixth embodiment ofthe present invention, shown in Figure 9 A, 9B and 9C consists of a stent 10 with eight expansion columns 24, three reenforcement expansion columns 86, and ten connecting stmt columns 26. In this variation, the stent 10 has a length 16 of 20.32 mm. Relief notches 204 are utilized at the joints between reenforcement expansion stmts 90 and reenforcement joining stmts 96 in the reenforcement expansion columns 86 at the stent proximal end 12 and distal end 14. Relief notches 204 reduce the width of the joints between reenforcement expansion stmts 90 and reenforcement joining stmts 96, which reduces stress in the metal at the joints during and after expansion ofthe stent. Relief notches 204 are particularly important at the stent ends since the stent ends are especially susceptible to warping during and after expansion. Preferably relief notches 204 reduce the joint widths, such that the joint widths are substantially the same as the thickness of stent wall 46 (see Figures IB and IC). Connecting stmts 38 shown in an enlarged view in Figure 9D are made up of three linear sections, a proximal end section 194, an intermediate section 196 and a distal end section 198 forming two slant angles 200, 202. The connecting stmts 38 have wide radii of curvature at the joints between connecting stmt sections 194, 196 and 198. The shape of connecting stmt 38 is thus curved or wavy rather than jagged and angular. The slant angles 200 and 202 are defined by linearly extrapolating proximal end section 194, intermediate section 196 and distal end section 198, as shown by the dotted lines in Figure 9D. Figure 9E shows a variation ofthe connecting stmt design of the sixth embodiment ofthe present invention. The connecting stmt 38 of Figure 9E has smaller radii of curvature at the joints between proximal end section 194, intermediate section 196 and distal end section 198. Connecting stmt 38 of Figure 9E is thus more jagged and angular than that of Figure 9D Referring to the connecting stmts 38 of Figure 9D and 9E, the proximal end of proximal section 194 is attached to joining stmt 30 of expansion stmt pair 32 intermediate comers 176 and 178. Proximal end section 194 of connecting stmt 38 extends from joining stmt 30 and is attached at its distal end to intermediate section 196 forming slant angle 200. Intermediate section 196 extends from proximal end section 194 in a slanted orientation relative to the longitudinal axis of stent 10, extending both longitudinally along and circumferentially about stent 10. Intermediate section 196 is preferably parallel to joining stmts 30 of coupled expansion stmt pairs 32. Intermediate section 196 is connected at its distal end to the proximal end of distal end section 198 forming slant angle 202. Distal end section 198 extends from second intermediate section 196 attaching at its distal end to joining stmt 30 of circumferentially offset expansion stmt pair 32 of adjacent expansion column 24. The attachment is at a point intermediate comers 176 and 178, where joining stmt 30 forms narrow angle 48 and wide angle 50 respectively with expansion stmts 28. The connection point of proximal end section 194 and distal end section 198 to joining stmts 30 is closer to comer 176 than comer 178. Preferably the connection point is one to two or more expansion stmt widths from corner 176. Offsetting the connection point of distal end section 198 to joining stmt 30 from comer 176 to a point intermediate corner 176 and corner 178 reduces warping ofthe expanded stent 10, resulting in a smooth surface modulation and reduced risk of thrombosis. Additionally, this design provides a longer total straightened length of connecting stmt 38, which further reduces foreshortening of stent 10 during expansion. The connecting stmt 38 ofthe sixth embodiment has one hundred and eighty degree rotational symmetry about its center. The symmetry ofthe connecting stmt 38 does not, however, result in a symmetrical cell space as the width of loop slots 42 connected in each cell space are different. Adjacent loop slots 42 in each expansion column have alternating narrow and wide widths, preserving the asymmetry ofthe cell spaces. Introduction of one or many symmetrical cell spaces can be achieved in this design e.g. by providing uniform loop slot width to loop slots in adjacent expansion columns 24 contained in the same cell space. Additionally completely non-uniform cell space patterns utilizing symmetric or asymmetric cell spaces can be achieved e.g. by providing non-uniform variations in the widths of loop slots 42. A second variation of a sixth embodiment ofthe present invention, shown in an unexpanded form in Figures 9F consists of a stent 10 with six expansion columns 24, three reenforcement expansion columns 86, and eight connecting stmt columns 26. In this variation, the stent 10 has a length 16 of 16.00 mm, and an unexpanded circumference 88 of 5.26 mm. The stent design 10 is substantially similar to the design ofthe first variation ofthe sixth embodiment of Figures 9 A, 9B and 9C with a reduced number of expansion columns 24 and connecting stmt columns 26. A third variation of a sixth embodiment ofthe present invention, shown in an unexpanded form in Figures 9F consists of a stent 10 with twelve expansion columns 24, four reenforcement expansion columns 86, and fifteen connecting stmt columns 26. In this variation, the stent 10 has a length 16 of 30.01 mm, and an unexpanded circumference 88 of 5.26 mm. The stent design 10 is substantially similar to the design ofthe first variation ofthe sixth embodiment of Figures 9 A, 9B and 9C with an increased number of expansion columns 24 reenforcement expansion columns 86 and connecting stmt columns 26. Figures 10A, 10B, 10C, 10D, 10E and 10F illustrate some examples of alternate connecting stmt designs which can be used in any ofthe previously discussed embodiments. Figure 10A shows a rounded loop connecting stmt 38 which joins two circumferentially offset expansion stmt pairs 32 in adjacent expansion columns. Expansion stmts 28 in each expansion stmt pair 32 are joined by a joining stmt 30. Joining stmts 30 are slanted such as to form a narrow angle 48 and a wide angle 50 with the expansion stmts 28 they connect. The rounded loop connecting stmt 38 connects expansion stmts 28 at the point where narrow angle 48 is formed between expansion stmts 28 and joining stmts 30. The slopes ofthe rounded connecting stmt 38 at its proximal end 102 and distal end 104 substantially match the slopes of the joining stmts 30 connecting the pairs of expansion stmts 28. The rounded loop connecting stmt 38 thus blends smoothly into the joining stmts 30. Additionally the rounded loop connecting stmt 38 has a first radius of curvature 106 and a second radius of curvature 108. In the design of Figure 10B a rounded loop connecting stmt 38 joins two circumferentially offset expansion stmt pairs 32 in adjacent expansion columns. Expansion stmts 28 in each expansion stmt pair 32 are joined by a joining stmt 30. Joining stmts 30 are at right angles to the expansion stmts 28 they connect. The rounded loop connecting stmt 38 connects to expansion stmts 28 at the same point as joining stmts 30. The rounded connecting stmt 38 has a first radius of curvature 106 and a second radius of curvature 108 such that it connects circumferentially offset expansion stmt pairs 32. In the design of Figure 10C connecting stmt 38 joins two circumferentially offset expansion stmt pairs 32 in adjacent expansion columns. Expansion stmts 28 in each expansion stmt pair 32 are joined by a joining stmt 30. Joining stmts 30 are slanted such as to form a nanow angle 48 and a wide angle 50 with the expansion stmts 28 they connect. The connecting stmt 38 connects expansion stmts 28 at the point where narrow angle 48 is formed between expansion stmt 28 and joining stmt 30. The connecting stmt 38 is made up of three linear sections 110, 112, and 1 14 forming two slant angles 1 16 and 118. The proximal end of section 110 is attached to expansion stmt 28 at the point where joining stmt 30 forms nanow angle 48 with expansion stmt 28. Section 110 extends substantially collinear to joining stmt 30 and is attached at its distal end to intermediate section 112 forming slant angle 116. Intermediate section 112 extends at an angle to section 1 10 such that intermediate section 112 is substantially parallel to expansion stmts 28 and is connected at its distal end to the proximal end of distal section 114 forming slant angle 118. Distal section 114 extends at an angle such that it is substantially collinear to joining stmt 30 ofthe adjacent expansion stmt pair 32. Distal section 114 attaches at its distal end to expansion stmt 28 ofthe adjacent expansion stmt pair 32, at the point where joining stmt 30 forms nanow angle 48 with expansion stmt 28. In the design of Figures 10D and 10E a connecting stmt 38 joins two circumferentially offset expansion stmt pairs 32 in adjacent expansion columns. Expansion stmts 28 in each expansion stmt pair 32 are joined by a joining stmt 30. Joining stmts 30 are at right angles to the expansion stmts 28 they connect The connecting stmt 38 connects to expansion stmts 28 at the same point as joining stmts 30. The connecting stmts 38 of Figures 10D and 10E are made up of multiple connecting stmt sections connected end to end to form a jagged connecting stmt 38 with multiple slant angles, coupling expansion stmt pair 32 to adjacent expansion stmt pair 32. The connecting stmt of Figure 10D is made up of three connecting stmt sections, a proximal section 120, an intermediate section 122 and a distal section 124 defining two slant angles 126 and 128, while the connecting stmt of Figure 10E consists of four connecting stmt sections, a proximal section 130, intermediate sections 132 and 134, and a distal section 136 defining three slant angles 138, 140 and 142 In addition, connecting stmt section 134 can be modified by replacing connecting stmt section 136 by the dotted connecting stmt section 144 to give another possible geometry of connecting stmts 38. ln the design of Figures 10F connecting stmt 38 joins two circumferentially offset expansion stmt pairs 32 in adjacent expansion columns. Expansion stmts 28 in each expansion stmt pair 32 are joined by a joining stmt 30. Joining stmts 30 are slanted such as to form a narrow angle 48 and a wide angle 50 with the expansion stmts 28 they connect. Connecting stmt 38 is made up of four linear sections, a proximal end section 180, first and second intermediate sections 182 and 184 respectively and a distal end section 186 forming three slant angles 188, 190 and 192. The proximal end of section 180 is attached to comer 176 at the point where joining stmt 30 forms narrow angle 48 with expansion stmt 28. Proximal end section 180 extends at an angle to joining stmt 30 and is attached at its distal end to first intermediate section 182 forming slant angle 188. First intermediate section 182 extends at an angle to proximal end section 180 such that first intermediate section 182 is substantially parallel to expansion stmts 28 and is connected at its distal end to the proximal end of second intermediate section 184 forming slant angle 190 Second intermediate section 184 is substantially longer than the first intermediate section 182. Second intermediate section 184 extends at an angle such that it is substantially collinear to joining stmt 30 ofthe adjacent expansion stmt pair 32 Second intermediate section 184 attaches at its distal end to the proximal end of distal end section 186 forming slant angle 192 Distal end section 186 extends in a slightly sloping orientation relative to expansion stmts 28, attaching to comer 176 of expansion stmt pair 32 where joining stmt 30 forms narrow angle 48 with expansion stmt 28 Relief notches 206 are formed at the joint between distal end segment 186 of connecting stmt 38 and comer 176 of expansion stmt pair 32 to increase flexibility ofthe unexpanded stent and prevent warping when the stent is expanded One skilled in the art will recognize that there are many possible arrangements of connecting stmts and joining stmts consistent with the present invention, the above examples are not intended to be an exhaustive list, ln particular, it is noted that (a) connecting stmt sections need not be linear but may contain one or many radii of curvature, (b) connecting stmt sections may each have a different longitudinal axis, (c) the joint between connecting stmt sections need not be jagged or sharp, but rather can be smooth containing one or multiple radii of curvature, and (d) relief notches may be present at any ofthe stmt joints. The stent ofthe present invention is ideally suited for application in coronary vessels although versatility in the stent design allows for applications in non-coronary vessels, the aorta, and nonvascular tubular body organs Typical coronary vascular stents have expanded diameters that range from 2.5 to 5 O mm However, a stent with high radial strength and fatigue tolerance that expands to a 5 0 mm diameter may have unacceptably high stent metal fraction when used in smaller diameter vessels If the stent metal fraction is high, the chances of acute thrombosis and restenosis potential will increase Even with the same metal fraction a smaller caliber vessel is more likely than a larger one to have a high rate of thrombosis It is, therefore, prefened to have at least two different categories of stents for coronary application, for example, small vessels stents for use in vessels with diameters from 2.5 mm to 3 0 mm, and large vessel stents for use in vessels with diameters from 3 0 mm to 5 0 mm Thus, both small vessels and large vessels when treated with the appropriate sized stent will contain stents of similar idealized metal fraction The stent ofthe present invention can be made using a CAM-driven laser cutting system to cut the stent pattern from a stainless steel tube The rough-cut stent is preferably electro-polished to remove surface imperfections and sharp edges Other methods of fabricating the stent can also be used such as EDM, photo-electric etching technology, or other methods Any suitable material can be used for the stent including other metals and polymers so long as they provide the essential stmctural strength, flexibility, biocompatibility and expandability. The stent is typically at least partially plated with a radiopaque metal, such as gold, platinum, tantalum or other suitable metal It is preferred to plate only both ends ofthe stent by localized plating, however, the entire stent or other regions can also be plated When plating both ends, one to three or more expansion columns on each end ofthe stent are plated to mark the ends ofthe stent so they can be identified under fluoroscopy during the stenting procedure By plating the stent only at the ends, interference ofthe radiopaque plating material with performance characteristics or surface modulation ofthe stent frame is minimized. Additionally the amount of plating material required is reduced, lowering the material cost ofthe stent After plating, the stent is cleaned, typically with detergent, saline and ultrasonic means that are well-known in the art The stents are then inspected for quality control, assembled with the delivery balloon catheter, and properly packaged, labeled, and sterilized. Stent 10 can be marketed as stand alone or as a pre-mounted delivery balloon catheter assembly as shown in Figure 11. Referring to Figure 11, the stent 10 is crimped over a folded balloon 146 at the distal end 148 of a delivery balloon catheter assembly 150. The assembly 150 includes a proximal end adapter 152, a catheter shaft 154, a balloon channel 156, a guidewire channel 158, a balloon 146, and a guidewire 160. Balloon 146 can be tapered, curved, or both tapered and curved from a proximal end to a distal end in the expanded state. Additionally stent 10 can be non-tapered or tapered in the expanded state. Typically the guidewire 160 is inserted into the vein or artery and advanced to the target site. The catheter shaft 154 is then forwarded over the guidewire 160 to position the stent 10 and balloon 146 into position at the target site. Once in position the balloon 146 is inflated through the balloon channel 156 to expand the stent 10 from a crimped to an expanded state. In the expanded state, the stent 10 provides the desired scaffolding support to the vessel. Once the stent 10 has been expanded, the balloon 146 is deflated and the catheter shaft 154, balloon 146, and guidewire 160 are withdrawn from the patient. The stent ofthe present invention can be made as short as less than 10 mm in length or as long as 100 mm or more. If long stents are to be used, however, matching length or preferably slightly longer delivery catheter balloons will typically be needed to expand the stents into their deployed positions. Long stents, depending on the target vessel, may require curved long balloons, tapered long balloons or curved and tapered long balloons for deployment. Curved and/or tapered balloons which match the natural curve and taper of a blood vessel reduce stress on the blood vessel during and after stent deployment. This is especially important in many coronary applications which involve stenting in curved and tapered coronary vessels. The use of such curved and/or tapered balloons is within the scope ofthe present invention. The foregoing description of a preferred embodiment ofthe 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 ofthe invention be defined by the following claims and their equivalents. What is claimed is:

Claims: CLAIMS 1. A stent in a non-expanded state, comprising: a first expansion column formed of a plurality of first expansion column stmt pairs, a first expansion stmt pair including a first expansion stmt adjacent to a second expansion stmt and a first joining stmt that couples the first and second expansion stmts at a proximal end ofthe first expansion stmt pair, a second expansion stmt pair including a third expansion stmt adjacent to the second expansion stmt and a second joining stmt that couples the second and third expansion stmts at a distal end ofthe second expansion stmt pair, a third expansion stmt pair including a fourth expansion stmt adjacent to the third expansion stmt and a third joining stmt that couples the third and fourth expansion stmts at a proximal end ofthe third expansion stmt pair, a fourth expansion stmt pair including a fifth expansion stmt adjacent to the fourth expansion stmt and a fourth joining stmt that couples the fourth and fifth expansion stmts at a distal end ofthe fourth expansion stmt pair, a first expansion stmt pair first corner formed where the first joining stmt is coupled to the first expansion stmt, and a first expansion stmt pair second corner formed where the first joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair first corner formed where the second joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair second corner formed where the second joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair first corner formed where the third joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair second comer formed where the third joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair first corner formed where the fourth joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair second corner formed where the fourth joining stmt is coupled to the fifth expansion stmt; a second expansion column formed of a plurality of second expansion column stmt pairs, a first expansion stmt pair including a first expansion stmt adjacent to a second expansion stmt and a first joining stmt that couples the first and second expansion stmts at a proximal end ofthe first expansion stmt pair, a second expansion stmt pair including a third expansion stmt adjacent to the second expansion stmt and a second joining stmt that couples the second and third expansion stmts at a distal end ofthe second expansion stmt pair, a third expansion stmt pair including a fourth expansion stmt adjacent to the third expansion stmt and a third joining stmt that couples the third and fourth expansion stmts at a proximal end ofthe third expansion stmt pair, a fourth expansion stmt pair including a fifth expansion stmt adjacent to the fourth expansion stmt and a fourth joining stmt that couples the fourth and fifth expansion stmts at a distal end ofthe fourth expansion stmt pair, a first expansion stmt pair first comer formed where the first joining stmt is coupled to the first expansion stmt, and a first expansion stmt pair second corner formed where the first joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair first comer formed where the second joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair second comer formed where the second joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair first corner formed where the third joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair second comer formed where the third joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair first comer formed where the fourth joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair second comer formed where the fourth joining stmt is coupled to the fifth expansion stmt; and a first connecting stmt column formed of a plurality of first connecting stmts, each connecting stmt ofthe first connecting stmt column including a connecting stmt proximal section, a connecting stmt distal section and a connecting stmt intermediate section, a first connecting stmt proximal section is coupled to the first corner ofthe second expansion stmt pair ofthe first expansion stmt column, and a first connecting stmt distal section is coupled to the first joining stmt ofthe first expansion stmt pair ofthe second expansion stmt column intermediate the first expansion stmt pair first comer and the first expansion stmt pair second comer, and a second connecting stmt proximal section is coupled to the first comer ofthe fourth expansion stmt pair ofthe first expansion stmt column, and a second connecting stmt distal section is coupled to the third joining stmt ofthe third expansion stmt pair ofthe second expansion stmt column intermediate the third expansion stmt pair first comer and the third expansion stmt pair second comer. 2. The stent of claim 1, wherein each connecting stmt proximal section has a substantially linear geometry 3 The stent of claim 2, wherein each connecting stmt distal section has a substantially linear geometry 4 The stent of claim 3, wherein each connecting stmt intermediate section has a substantially linear geometry 5 The stent of claim 3, wherein each connecting stmt intermediate section includes a first linear section and a second linear section 6 The stent of claim 5, wherein the first linear section ofthe first connecting stmt intermediate section is shorter than the second linear section of the first connecting stmt intermediate section 7 The stent of claim 5, wherein each of a connecting stmt proximal section, distal section, first linear section ofthe intermediate section and second linear section ofthe intermediate section have a different longitudinal axis 8 The stent of claim 5, wherein a first slant angle is formed between the first linear section ofthe first connecting stmt intermediate section and the second linear section ofthe first connecting stmt intermediate section 9. The stent of claim 5, further including a radius of curvature formed at the first slant angle. 10. The stent of claim 5, wherein a radius of curvature is formed between the first linear section and the second linear section ofthe first connecting stmt intermediate section. 11. The stent of claim 5, wherein a second slant angle is formed between the second linear section ofthe first connecting stmt intermediate section and the distal section ofthe first connecting stmt. 12. The stent of claim 5, wherein a radius of curvature is formed between the second linear section ofthe first connecting stmt intermediate section and the distal section ofthe first connecting stmt. 13. The stent of claim 5, wherein a third slant angle is formed between the proximal section ofthe first connecting stmt and the first linear section ofthe first connecting stmt intermediate section. 14. The stent of claim 5, wherein a radius of curvature is formed between the proximal section of each connecting stmt and the first linear section of each connecting stmt intermediate section. 15. The stent of claim 1, wherein a ratio of a number of expansion stmts in an expansion stmt column to a number of connecting stmts in a connecting stmt column is 2 to 1. 16. The stent of claim 1, wherein the stent includes m first and second expansion columns, n connecting stmts per column and n (m-l)/2 connecting stmts. 17 The stent of claim 1, wherein the first and second expansion columns are each unbroken, continuous column stmctures 18. The stent of claim 1, wherein one ofthe first or second expansion column is a broken column stmcture 19 The stent of claim 1, further comprising: a plurality of first expansion columns, a plurality of second expansion columns, and a plurality of first connecting stmt columns, each first connecting stmt column coupling a first expansion column to a second expansion column 20 The stent of claim 19, wherein the plurality of first expansion columns, the plurality of second expansion columns and the plurality of first connecting stmt columns form an elongated stmcture 21 The stent of claim 1, wherein the first expansion column, the second expansion column, and the first connecting stmt column form a plurality of geometric cells and at least a portion ofthe plurality are symmetrical geometric cells 22 The stent of claim 1 , wherein the first expansion column, the second expansion column, and the first connecting stmt column form non- uniform cell space patterns 23 The stent of claim 1, wherein the first expansion stmt column, the second expansion stmt column and the first connecting stmt column form asymmetrical geometric configurations 24 The stent of claim 1 , further comprising a reenforcement expansion column made of a plurality of reenforcement expansion stmts, wherein each reenforcement expansion stmt has a width that is greater than a width of an expansion stmt in the first or second expansion columns. 25. The stent of claim 1, wherein the stent has a proximal end with a first reenforcement expansion column and a distal end with a second reenforcement expansion column. 26. The stent of claim 1, wherein the stent has a reenforcement expansion column between a proximal end and a distal end ofthe stent. 27. The stent of claim 1, further comprising: a third expansion column formed of a plurality of third expansion column stmt pairs, a first expansion stmt pair including a first expansion stmt adjacent to a second expansion stmt and a first joining stmt that couples the first and second expansion stmts at a proximal end ofthe first expansion stmt pair, a second expansion stmt pair including a third expansion stmt adjacent to the second expansion stmt and a second joining stmt that couples the second and third expansion stmts at a distal end ofthe second expansion stmt pair, a third expansion stmt pair including a fourth expansion stmt adjacent to the third expansion stmt and a third joining stmt that couples the third and fourth expansion stmts at a proximal end ofthe third expansion stmt pair, a fourth expansion stmt pair including a fifth expansion stmt adjacent to the fourth expansion stmt and a fourth joining stmt that couples the fourth and fifth expansion stmts at a distal end ofthe fourth expansion stmt pair, a first expansion stmt pair first corner formed where the first joining stmt is coupled to the first expansion stmt, and a first expansion stmt pair second corner formed where the first joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair first corner formed where the second joining stmt is coupled to the second expansion stmt, and a second expansion stmt pair second comer formed where the second joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair first corner formed where the third joining stmt is coupled to the third expansion stmt, and a third expansion stmt pair second comer formed where the third joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair first comer formed where the fourth joining stmt is coupled to the fourth expansion stmt, and a fourth expansion stmt pair second corner formed where the fourth joining stmt is coupled to the fifth expansion stmt; and a second connecting stmt column formed of a plurality of second connecting stmts, each connecting stmt ofthe second connecting stmt column including a connecting stmt proximal section, a connecting stmt distal section and a connecting stmt intermediate section, a first connecting stmt proximal section is coupled to the second corner ofthe second expansion stmt pair ofthe second expansion stmt column, and a first connecting stmt distal section is coupled to the first joining stmt ofthe first expansion stmt pair ofthe third expansion stmt column intermediate the first expansion stmt pair first comer and the first expansion stmt pair second comer, and a second connecting stmt proximal section is coupled to the second comer ofthe fourth expansion stmt pair ofthe second expansion stmt column, and a second connecting stmt distal section is coupled to the third joining stmt ofthe third expansion stmt pair of the third expansion stmt column intermediate the third expansion stmt pair first corner and the third expansion stmt pair second corner. 28. The stent of claim 1, wherein a width ofthe first connecting stmt is equal to or less than a width ofthe first expansion stmt ofthe first or second expansion columns. 29. The stent of claim 1, wherein a width of a connecting stmt ofthe first connecting stmt column is larger than a width of a first expansion stmt of the first or second expansion columns. 30 The stent of claim 1, wherein a width ofthe second expansion stmt ofthe first or second expansion columns is substantially the same as the width ofthe first expansion stmt ofthe first or second expansion columns 31 The stent of claim 1, wherein a space between the first and second expansion stmts ofthe first expansion column is equal to a space between the second and third expansion stmts ofthe first expansion column 32 The stent of claim 1, wherein a space between the first and second expansion stmts ofthe first expansion column is less than a space between the second and third expansion stmts ofthe first expansion column 33 The stent of claim 1, wherein a space between the first and second expansion stmts ofthe first expansion column is larger than a space between the second and third expansion stmts ofthe first expansion column 34 A stent in a non-expanded state, comprising a first column expansion stmt pair, a plurality ofthe first column expansion stmt pair forming a first expansion column, a second column expansion stmt pair, a plurality ofthe second column expansion stmt pair forming a second expansion column, and a first connecting stmt a plurality of first connecting stmts forming a first connecting stmt column, the plurality of first connecting stmts coupling the first expansion column to the second expansion column, and wherein the first expansion column, the second expansion column, and the first connecting stmt column provide a reduced tuliping

Inventors: JANG G DAVID, JANG, G., DAVID
Applicants: JANG G DAVID, JANG, G., DAVID
Application year: 1997
Main classification: A61F2
IPC codes: A61F2