Stent

Abstract

A stent (1) comprising a tubular frame (2) comprising a first end (3) and a second end and a longitudinal axis (4) therebetween. The frame (2) comprises a plurality of struts (9) defining a generally cylindrical portion comprising a longitudinally extending helical fin (11) protruding radially inwardly and having a helix angle. The angle, relative to the longitudinal axis (4), of at least some of the struts (9) in the helical fin (11) is substantially aligned with the helix angle of the helical fin (11).

Claims

1. A stent having a crimped configuration of a first diameter to allow insertion into a vessel of a patient and an expanded configuration of a second diameter, said stent comprising a tubular frame comprising a first end and a second end and a longitudinal axis therebetween, wherein the frame comprises a plurality of struts defining a generally cylindrical portion having an internal radius, and wherein said frame comprises a longitudinally extending helical fin having a centre, said fin protruding radially inwardly for a distance equal to between 40% and 70% of the internal radius of the cylindrical portion, and said fin having a helix angle, and wherein the struts delineate a plurality of circumferential rings having a wave form, wherein the wave form comprises a plurality of peaks extending towards the first end of the frame and a plurality of troughs extending towards the second end of the frame, wherein: i) a trough-to-peak connecting strut connects each trough to a peak, and ii) within the helical fin each trough-to-peak connecting strut connecting to a peak located towards the centre of the helical fin has an angle which is substantially the same as the helix angle of the helical fin.

2. The stent of claim 1, wherein each successive trough on adjacent rings within the helical fin is aligned with the helical fin.

3. The stent of claim 1, wherein the cross-sectional shape of the helical fin is asymmetric.

4. The stent of claim 1, wherein the helical fin is formed by the deformation of at least a portion of a side wall of the frame.

5. The stent of claim 1, wherein the helix angle is selected from the group consisting of: between 5° and 50°, between 18° and 22° and between 20° and 40°.

6. The stent of claim 1, wherein the wave form is selected from the group consisting of a triangle wave form, a sine wave form and a square wave form.

7. The stent of claim 1, wherein the rings comprise a number of cells.

8. The stent of claim 7, wherein the shape of the cells is selected from the group consisting of: a diamond shape, an open cell configuration, a closed cell configuration, and a combination thereof.

9. The stent of claim 1, wherein the frame is composed of a material selected from the group consisting of: self-expanding material, nickel titanium (nitinol), stainless steel, and cobalt-chromium alloy.

10. The stent of claim 1, comprising at least one cover.

11. The stent of claim 10, wherein the at least one cover comprises polytetrafluoroethylene (PTFE).

12. The stent of claim 10, wherein the location of the at least one cover is selected from the group consisting of: (i) over the inner surface of the frame, (ii) over the outer surface of the frame, (iii) over the helical fin only, (iv) and a combination of (i) and (ii).

13. The stent of claim 10, wherein the at least one cover is heat sealed to the frame.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a perspective view of a stent of the invention having a helical fin and fitted on a mandrel.

(2) FIG. 2 is a view of a V-shaped bend from within the helical fin of the frame of FIG. 1.

(3) FIG. 3 is a perspective view of the stent of FIG. 1.

(4) FIG. 4 is a perspective view of the stent of FIG. 1.

(5) FIG. 5 is a view of the interior of the stent of FIG. 1 from the first end.

(6) FIG. 6 is a perspective view of the stent of FIG. 1.

(7) FIG. 7 is a perspective view of the stent of FIG. 1.

(8) FIG. 8 is a perspective view of a portion of the stent of FIG. 1, including a portion of the helical fin.

(9) FIG. 9 is a perspective view of the stent of FIG. 1.

(10) FIG. 10 is a perspective view of a stent in accordance with another embodiment of the present invention.

(11) FIG. 11 is a schematic side view of a stent in accordance with another embodiment of the present invention with some details omitted.

(12) FIG. 12 is a schematic side view of a stent in accordance with the embodiment of FIG. 11 from a different rotational angle with some details omitted.

(13) FIG. 13 is a schematic side view of a stent in accordance with the embodiment of FIG. 11 from a different rotational angle with some details omitted.

(14) FIG. 14 is a schematic view along the line A-A of FIG. 12.

(15) FIG. 15 is a close-up view of the circled area in FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

(16) Embodiments of the stent structures encompassed by the current invention are described below, although the invention is not intended to be limited by these examples.

(17) The current invention provides a stent having a tubular frame comprising a first (distal) and a second (proximal) end and a longitudinal axis therebetween. The frame comprises a plurality of struts defining a cylindrical portion comprising a longitudinally extending helical fin protruding radially inwardly and having a helix angle. The angle of some of the struts in the helical fin (relative to the longitudinal axis of the tubular frame) is substantially aligned with the helix angle of the helical fin. Aligning the angle of the struts with that of the helical fin imparts resistance against radial force and fatigue when within a patient vessel, thereby preventing the formation of fractures within the stent frame. The stent of the invention provides sufficient strength to resist compression, whilst maintaining desirable flexibility and the helical fin imparts spiral flow on fluid (e.g. blood) passing through the stent.

(18) The helix angle to achieve such flow depends on factors such as diameter of the stent, longitudinal and rotational velocity of the fluid and the viscosity of the fluid. Typically, the helical fin effects a rotational flow of fluid within the tubular stent when in use. The rotational flow may comprise a helical or spiral flow.

(19) FIG. 1 depicts a stent 1 of one embodiment of the present invention. The stent has a tubular frame 2 having a first end (distal) 3 and a second end (proximal; not shown) and a longitudinal axis 4 therebetween. The stent frame is depicted fitted on a mandrel 5 used to support the frame during the manufacturing of the stent but it is to be understood that the mandrel 5 is not present when the stent 1 is in use. The tubular frame 2 comprises a network of struts in the form of a series of undulating rings 13 disposed circumferentially along the longitudinal axis 4 of the frame. The rings are parallel to each other. The rings 13 are in a rounded triangle wave form having a plurality of peaks 6 extending towards the first end 3 and a plurality of troughs 7 extending towards the second end. Each peak 6 and trough 7 forms a V-shaped bend 8 in the same plane as the cylindrical surface defined by the tubular frame. The trough 7 of each V-shaped bend is connected to its respective peak 6 via a trough-to-peak connecting strut 9. Each ring is connected to its adjacent ring by a plurality of linker-struts 10 which extend between adjacent rings 13. Each linker-strut connects the trough of one V-shaped bend of a first ring to the peak of the adjacent V-shaped bend of an adjacent ring. Every fourth trough in each ring is connected to an adjacent peak on an adjacent ring.

(20) A portion of the side wall of the frame 2 is deformed radially inwardly to form a longitudinally extending helical fin 11. The helical fin defines an inducer path 12. As is shown in more detail in FIG. 2, the angle, relative to the longitudinal axis, of each trough-to-peak connecting strut 9a of each V-shaped bend 8 that extends towards the centre of the helical fin (i.e. that is present in the portion of one side wall that forms the helical fin) is substantially the same as the helix angle 14 of the inducer path 12. The angle, relative to the longitudinal axis, of each peak-to-trough connecting struts 9 of each V-shaped bend 8 that extends away from the centre of the helical fin (i.e. that are present in the portion of the other side wall that forms the helical fin) is the mirror angle of the helix angle (i.e. the helix angle 14 minus the angle 15 between the trough-to-peak connecting strut 9a and its adjacent peak-to-trough connecting strut 9b).

(21) The trough 7 of each V-shaped bend 8 that is within the helical fin 11 is aligned along the helical fin 11. This provides a substantially uniform geometry within the portion of the frame 2 forming the helical fin 11.

(22) FIG. 2 illustrates a V-shaped bend 8 from a wave form and from within the helical fin 11 of the frame 2 of FIG. 1. A trough 7 is connected to two peaks 6 by two connecting struts (9a, 9b). The first connecting strut (9a) extends to the peak towards the centre of the helical fin 11. The angle of this strut is substantially aligned with the helix angle 14 of the helical fin 11. The second connecting strut (9b) extends to the peak away from the centre of the helical fin 11. The angle of this connecting strut 9b is the mirror angle of the angle of the first connecting strut 9a.

(23) In the above-described embodiment, the tubular frame 2 comprises a network of struts in the form of a series of undulating rings 13. It is to be appreciated that each element in a ring comprising four peaks 6, four troughs 7 and one linker-strut may be considered to be a repeating element of the frame 2 and thus the struts that form the tubular frame 2 may be considered to be arranged as a series of repeating elements. In this regard, it will also be appreciated that the repeating elements are not strictly identical across the whole of the tubular frame 2 since the struts at the helical fin 11 are deformed in order to form the side walls of the helical fin 11. Nevertheless, it is possible to recognise that the repeating elements are present even in the struts of the helical fin 11, subject to some deformation thereof. It is to be understood that each repeating element within the tubular frame 2 comprises a certain strut length, that is to say the total length of each strut, and that in the tubular frame 2 outside of the helical fin 11, the fraction of the total strut length in each repeating element which is aligned with the helical fin 11 is relatively low (less than 10% of the total). On the other hand, within the helical fin 11, the fraction of the total strut length which is aligned with the helical fin 11 is almost 50%.

(24) In variants of this embodiment, the fraction of the total strut length aligned with the helical fin 11 of the repeating elements in the helical fin 11 can approach 50%. However, in other embodiments, the fraction of the total strut length aligned with the helical fin 11 in each repeating element in the helical fin 11 is lower and may, for example, be 10%, 20%, 30% or 40%. However, in these embodiments the fraction of the total strut length of the repeating elements in the helical fin 11 which is aligned with the helical fin is greater than in the repeating elements outside of the helical fin 11. For example, the repeating elements outside of the helical fin may have a fraction of the total strut length aligned with the helical fin of less than 5% whereas within the helical fin the fraction of the total strut length in each repeating element which is aligned with the helical fin may be at least 10%, at least 20%, at least 30%, at least 40% or 50%. In this regard, it is to be appreciated that in some embodiments, the repeating element is not a part of an undulating ring and may, instead, be a cell such as a diamond shape cell within the frame as will now be described.

(25) While the above-described embodiments of the stent 1 have a helical fin 11 which is not limited to any particular helix angle, a helix angle of between 5° and 50° with the longitudinal axis of the stent frame is typical. For example, the helical fin may have a helix angle of between 5° and 25°, preferably between 18° to 22°. It is preferred that the helix angle of the helical fin 11 is selected such that the helical fin 11 completes one whole turn around the longitudinal axis of the stent 1, within the length of the stent 1. In embodiments where the stent 1 is relatively short, it is desirable for the helix angle of the helical fin 11 to be relatively high in order to impart helical flow on the fluid passing therethrough, when implanted. As such, in some embodiments, the helix angle is typically between 20° and 40°.

(26) Referring to FIG. 10, a second embodiment of the present invention is shown. A stent 16 has a tubular frame 17 having a first end (distal) 18 and a second end (proximal) 19 and a longitudinal axis 20 therebetween. The tubular frame 17 comprises a network of struts 21 in the form of a series of rings 22 which each have a triangle wave form. The series of rings 22 is disposed circumferentially along the longitudinal axis 20 of the tubular frame 17 and the rings 22 are arranged parallel to each other. Each ring 22 comprises a plurality of peaks 23 extending towards the first end 18 of the tubular frame 17 and a plurality of troughs 24 extending towards the second end 19 of the tubular frame 17. Each peak 23 and trough 24 forms a V-shaped bend 25 in the same plane as the cylindrical surface defined by the tubular frame 17. Each trough 24 of each ring 23 abuts, and is connected to, a peak 23 in the adjacent ring 22 which is further towards the second end 19 of the tubular frame 17. The exception to this is the ring 22 at the second end 19 which only has an adjacent ring on its side closest to the first end 18.

(27) Each V-shaped bend 25 comprises a leading strut 26, which is angled to the left when viewed from the first end 18 to the second end 19 of the tubular frame 17, and a trailing strut 27, which is angled to the right when viewed from the first end 18 to the second end 19 of the tubular frame 17. Each leading strut 26 and its respective trailing strut 27 meet at the peak 23 of their V-shaped bend 25. It is to be appreciated that, owing to the alignment of adjacent rings 22, the leading strut 26 and the trailing strut 27 of each V-shaped bend 25 in a first ring 22 are aligned with the trailing strut 26′ and the trailing strut 27′ of a second and adjacent ring 22 to form a diamond-shaped cell 28.

(28) A portion of the side wall of the tubular frame 17 is deformed radially inwardly to form a longitudinally extending helical fin 29. The helical fin defines an inducer path 30. The angle of each trailing strut 27 within the helical fin 29, relative to the longitudinal axis 20 of the tubular frame 17 is aligned with the helix angle of the helical fin 29, itself. The angle of each leading strut 26 within the helical fin, relative to the longitudinal axis 20 of the tubular frame 17, is deformed in order to form the helical fin.

(29) Thus, in this embodiment, each V-shaped bend 25 can be considered to be a repeating element within the tubular frame 17. Within the helical fin, 50% of the strut length of each repeating element is aligned with the helix angle of the helical fin 29 since all trailing struts 27 are aligned with the helix angle of the helical fin 29 and the trailing struts 27 comprise 50% of each ring 22, with the remaining strut length comprising the leading struts 26.

(30) Located within the lumen defined by the tubular frame 17, is a cover 31 made from PTFE, which is positioned to lie flat against the inner surface of the lumen. The cover therefore separates the contents of the lumen from the tubular frame 17.

(31) The manufacture of embodiments the invention will now be described. In preferred embodiments of the present invention, the tubular frame 2, 17 is made from nitinol. Nitinol can be formed into a “memory” shape by constraining the material onto a mandrel or similar fixture and then performing a heat treatment. The treatment should be such that the temperature is reached through the entire cross section of the material. Once formed, the nitinol can be cooled and reshaped into its original shape. Once deformed, it will remain so until heated to its transformation temperature, the nitinol then expands to its stronger “memory” shape.

(32) An exemplary method of forming a stent of the present invention comprises preparing a stent blank (ie. a stent without a helical fin) of a preferred frame geometry, preferably by laser cutting said pattern in a nitinol tube. The frame is cut such that the angle of the struts that will form the helical formation is aligned with the desired helical angle. This step provides a stent blank having a frame comprising a first end and a second end and a longitudinal axis therebetween, wherein the frame comprises a plurality of struts. The stent blank comprises a helical element extending longitudinally along at least a portion of the length of the frame and having a helix angle. The angle of at least some of the struts along the helical element is substantially aligned with the angle of the helical element.

(33) It will be appreciated that the method of the invention can be used to introduce a helical fin into a stent of any frame geometry. In this exemplary method the frame is laser cut to provide a diameter of 2 mm. The frame is then supported on a mandrel of a 4 mm diameter. The frame is then heated at a temperature of between 400° C. and 600° C. for a time effective for the material to be exposed to the temperature. The laser frame is then expanded on a mandrel with a diameter of 6 mm and heat set at a temperature of between 400° C. and 600° C. for a time effective for the material to be exposed to the temperature. The expanded stent blank (i.e. a stent without a helical fin) is then further expanded by placing the frame onto a 8 mm customised mandrel having a female helical groove. The frame is then effectively clamped between the mandrel and a corresponding clamshell tool having a corresponding male ridge. This step creates the helical fin. The frame is then set at a temperature of between 400° C. and 600° C. to set the helical fin for a time effective for the material to be exposed to the temperature.

(34) The material is then removed from the mandrel and the finished frame can be used as the frame for a completed stent.

(35) It will be appreciated that any desired mandrel diameter can be used at each step of the process. The diameter used depends on the desired diameter of the finished stent. Typically, the first diameter is a quarter of the desired final diameter.

(36) The correct helix angle of the helical fin is the angle that provides the desired non-turbulent flow in the fluid that flows through the frame.

(37) In order to be used, the stent of the present invention is implanted into a patient, usually by a surgeon, by a method known in the art. In the process, the stent is crimped and inserted into the lumen of the blood vessel of the patient. Once positioned correctly, the stent is then expanded, either by balloon expansion or due to its self-expanding properties, thus compressing against the inner walls of the lumen. If expanded by a balloon catheter, the catheter is then removed by the surgeon. The stent substantially retains this expanded configuration. In vivo, the stent is under compression by the blood vessel. By virtue of the alignment of the connecting struts in the helical fin, the stent of the present invention resists radial compression and avoids fractures.

(38) In embodiments in which the stent is inserted into a narrowed or blocked blood vessel, the outer wall of the stent compacts any plaques present thereby reopening the vessel lumen and allowing normal blood flow to resume.

(39) It will be appreciated that in certain embodiments the stent is inserted as a precautionary measure, prior to any blockage or to provide support to weakened vessels.

(40) When in use, the radially inwardly extending helical fin 11, 29 generates desirable flow characteristics in blood flowing through the lumen of the stent, by imparting spiral flow on the blood.

(41) The helical fin 11, 29 extends radially inwardly for a distance equal to between 40% and 70% of the distance from the longitudinal axis of the frame to an internal side wall. Preferably, for a distance equal to between 40% and 60%, more preferably, for a distance equal to between 45% and 55%. Most preferably, the inwardly extending portion extends inwardly for a distance equal to substantially 50% of the distance from the longitudinal axis of the conduit to an internal side wall. Where the stent has a circular cross-section, the distance is as a percentage of the stent of the conduit.

(42) The helical fin 11, 29 may have a constant helix angle along at least a part of its length, or one which reduces or increases over at least part of its length. The fin may taper in the direction of the blood flow or in the opposite direction.

(43) The helical fin 11, 29 may have a V-shaped cross section, a square shaped cross section, a U-shaped cross section or a bell-shaped cross section. The fin may have a symmetrical cross section or an asymmetrical cross section.

(44) The stent of the present invention may also comprise a cover or sheath. The effect of the cover is to cushion the blood vessel or, if provided on the inner surface of the stent, the cover protects the bloodstream from the stent frame.

(45) While the above-described embodiments have related to vascular stents, it is to be understood that the present invention is not limited to any particular kind of vascular stent. Thus, in embodiments of the invention, the stent is a coronary stent, a peripheral arterial stent, a venous stent, a biliary stent, a ureteral stent or the like.

Example—Exemplification of Stent Structures

(46) A stent design, in accordance with embodiments of the present invention, is provided as is shown in accordance with FIGS. 11 to 15. (In FIGS. 11 to 15, the stent frame, and other details, are omitted with only the helical fin shown). The stent design comprises a helical fin having an asymmetric cross-section. Table 1 shows possible configurations for the dimensions of the stent design. The labels A to K in FIGS. 11 to 15 represent the following dimensions of the stent design.

(47) A represents the outer diameter of the stent in mm.

(48) B represents the overall length of the stent in mm.

(49) C represents the length of the main section of the helical fin along the longitudinal axis of the stent in mm.

(50) D represents the helix angle of the helical fin in degrees.

(51) E represents the length of the runout of the helical fin; that is the linear distance in mm along the longitudinal axis of the stent within which the helical fin terminates by the depth of the helical fin tapering to zero.

(52) F represents the height in mm of the helical fin measured internally.

(53) G represents the internal diameter of the stent in mm measured from one inside face to the perpendicular opposite inside face.

(54) H represents the distance in mm between the point 32 and the diameter which intersects the curved surface of the helical fin. A more detailed explanation of this measurement can be found in WO2005/004751 on page 6.

(55) I represents the angle between the following surface of the helical fin (i.e. the surface which is downstream in the fluid flow when the stent is implanted) and the vertical diameter described in reference to H above.

(56) J represents the angle between the leading surface of the helical fin (i.e. the surface which is upstream in the fluid flow when the stent is implanted) and the vertical diameter described in reference to H above.

(57) K represents the maximal thickness in mm of the tubular frame of the stent design.

(58) TABLE-US-00001 TABLE 1 Table showing exemplary values for the dimensions shown in the stent design of FIGS. 11 to 15 Dimensions Stent Size A B C D E F G H I J K 5 mm × 40 mm (V10) 5 40 32.21 26 2.5 1.25 4.6 1.15 38 10 0.197 5 mm × 60 mm (V11) 5 60 51.38 17 2.5 1.25 4.6 1.15 38 10 0.197 6 mm × 40 mm (V1) 6 40 32.65 30 2.5 1.5 5.6 1.4 38 10 0.197 6 mm × 60 mm (V4) 6 60 51.79 20 2.5 1.5 5.6 1.4 38 10 0.197 6 mm × 80 mm (V14) 6 80 70.35 15 2.5 1.5 5.6 1.4 38 10 0.197 6 mm × 100 mm (V15) 6 100 88.68 12 2.5 1.5 5.6 1.4 38 10 0.197 6 mm × 120 mm (V16) 6 120 106.9 10 2.5 1.5 5.6 1.4 38 10 0.197 7 mm × 40 mm (V2) 7 40 32.6 34 2.5 1.75 6.6 1.65 38 10 0.197 7 mm × 60 mm (V5) 7 60 51.81 29 2.5 1.75 6.6 1.65 38 10 0.197 7 mm × 80 mm (V17) 7 80 71.93 17 2.5 1.75 6.6 1.65 38 10 0.197 7 mm × 100 mm (V18) 7 100 88.2 14 2.5 1.75 6.6 1.65 38 10 0.197 7 mm × 120 mm (V19) 7 120 113.13 11 2.5 1.75 6.6 1.65 38 10 0.197 8 mm × 40 mm (V3) 8 40 32.17 38 2.5 2 7.6 1.9 38 10 0.197 8 mm × 60 mm (V6) 8 60 51.53 26 2.5 2 7.6 1.9 38 10 0.197 8 mm × 80 mm (V20) 8 80 72.99 19 2.5 2 7.6 1.9 38 10 0.197 8 mm × 100 mm (V21) 8 100 87.65 16 2.5 2 7.6 1.9 38 10 0.197 8 mm × 120 mm (V22) 8 120 108.86 13 2.5 2 7.6 1.9 38 10 0.197