Expandible stent
A stent has a tubular body with longitudinal struts interconnected by multi-bar linkages. The struts inhibit foreshortening of the body and relative rotation between the links in the linkages permits radial expansion. The links are plastically deformed as they are expanded to maintain the expanded diameter.
This application is a continuation of U.S. application Ser. No. 09/893,253 filed on Jun. 27, 2001 which is a continuation of U.S. application Ser. No. 09/063,496 filed on Apr. 20, 1998 which is a continuation-in-part of U.S. Ser. No. 08/687,223 filed on Jul. 25, 1996, which claims priority from U.K. application no. 9605486.1 filed on Mar. 15, 1996 and U.K. application no. 9515282.3 filed on Jul. 25, 1995 the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTIONExpandable stents are widely used to provide local reinforcement in fluid-carrying vessels within the human body. The stent is essentially a cylindrical member which may be expanded radially to dilate the vessel and to provide support for the wall of the vessel to maintain it in the dilated condition.
SUMMARY OF THE INVENTIONIn order to insert the stent, it has previously been proposed to place the stent into the vessel on an expandable or balloon catheter. With the stent positioned at the appropriate location, the catheter is inflated and the stent is caused to expand radially against the wall of the vessel. Once the stent is expanded to the required diameter, the catheter is deflated and may be removed, leaving the stent in position.
The stent must of course remain expanded against the wall or the vessel and should be capable of withstanding the forces imposed by the wall of the vessel. Moreover, the stent should be able to negotiate tight turns in the arterial system during placement while minimizing damnage to the arterial wall.
A number of different mechanisms have been proposed to permit the expansion of the stent, including devices which reorient the components forming the stent so that they may adopt a greater overall diameter.
In another class of stents, as typified by the stent shown in U.S. Pat. No. 4,733,665 to Palmaz, the stent is configured to be plastically deformable so that after expansion it retains the increased diameter. In the Palmaz stent, the plastic deformation is provided by means of an open-mesh diamond structure. As the catheter is expanded, the intersecting members of the mesh deform so that the stent adopts an increased diameter.
With the arrangements shown in the Palmaz stent and similar configurations, a radial expansion of the stent is accompanied by an axial foreshortening of the stent. The degree of foreshortening is predictable but the ultimate location of the stent along the vessel is not predictable. Thus, one end of the stent may remain stationary relative to the blood vessel so that the opposite end is subjected to the maximum axial displacement or there may be progressive foreshortening from both ends with an intermediate location remaining stationary. The foreshortening of the stent leads to an unpredictable location for the stent in its expanded condition and induces relative movement in an axial direction between the vessel wall and the stent which is generally undesirable.
It is therefore an object of the present invention to provide a stent in which the above disadvantages are obviated or mitigated.
In general terms, the present invention provides a stent in which a plurality of circumferentially-spaced longitudinal struts are interconnected by multibar linkages. Adjacent links of the linkages are angularly disposed to one another such that a radial force causes relative rotation between adjacent links to permit radial enlargement of the stent. The longitudinal struts inhibit foreshortening of the stent so that the final location of the stent can be predicted.
BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which
Referring therefore to
As can best be seen in
Each of the linkages 16 is similar and the relative dimensions between the links in each linkage determine the change in diameter for a given load. In a typical example, as shown in
The stent 10 is typically inserted into the vessel by using a balloon catheter 60. The stent 10 is mounted on the catheter 60 shown in
A protective sleeve 72 is located over the body 66 and is retained on a boss 74 on the head 64. The sleeve 72 thus protects the stent 10 from extraneous external forces with the body 66 providing support for the stent 10 in transit.
To transfer the stent to the catheter 60, the sleeve 72 is removed and the body 66 is aligned with the catheter 60. The stent may then be slid axially from the body 66 over the catheter 60 and the support and sleeve discarded. In this way, the stent is guided during transfer and the placement of the stent on the catheter facilitated.
The recess 68 assists in locating and aligning the catheter 60 during transfer and of course the wire, if present, may be fed through the bore 70.
The stent 10 is located on the body 66 such that the links 28 are closer to the boss 74 than the associated links 18. Transfer of the stent 10 to the catheter thus ensures that the stent 10 is oriented on the catheter 60 such that the connecting link 28 of the linkage 16 is in advance of the circumferential links 18 during insertion of the stent 10 into the vessel.
The catheter is inserted into the vessel in a conventional manner until it is located at the stenosis.
After placement within the vessel, the catheter is then inflated to apply a radially expanding force to the stent.
As shown in
By virtue of the relatively narrow links 20,22, the hinging at their junction to the larger links 18,22 exceeds the yield point of the material and causes a permanent deformation and increase in diameter. A pair of spaced hinge points is thus established and thus the total rotation required between the axial links 20 and circumferential link 28 is distributed between two locations.
The catheter is then deflated and removed, leaving the stent 10 in situ. It will be noted, however, that during inflation the struts 14 maintain the axial spacing between the circumferential links 18 so that the overall length of the stent remains the same with no relative axial movement between the vessel and the stent.
In tests with samples of the configuration of
An alternative embodiment of linkage 16 is shown in
In the embodiment of
In tests conducted with samples of the arrangements shown in
A further embodiment is seen in
The results of tests conducted on the embodiment shown in
A further embodiment is shown in
In the embodiment of
The unitary struts 40 alternate with linking struts 42 about the circumference of stent 10c and in the preferred embodiment an even number of each is provided so that the linking struts 42 are diametrically opposed. It is preferred that four linking struts 42 are provided and are circumferentially spaced at 90° intervals.
Each of the unitary struts 40 extend between two of the linkages 16c so as to interconnect them. The unitary struts are spaced apart from one another by a gap indicated at 44 so that each linkage 16c is connected to only one of the adjacent linkages 16c. By contrast, the linking struts 42 extend between four of the linkages 16c and are then spaced from the next of the linking struts 42 by a space indicated at 46.
The gaps 44 between the unitary struts are circumferentially aligned to provide annular bands 48 whereas spaces 46 are staggered between alternate linking struts 42. Each of the linking struts 42 has a waist 50 to provide a region of enhanced flexibility in a plane tangential to the surface of the stent 10c The waist 50 is aligned with one of the bands 48 and so provides the connection across the band 48 between the linkages 16c.
As can be seen in
This arrangement provides flexibility about mutually perpendicular axially spaced axes allowing relative pivotal movement between sections of the stent to conform to the vessel into which it is inserted.
The linkage 16c is shown in detail in
The circumferential link 28c is connected to axial link 20c by corner link 22c which is formed as a rectangular leg 24c.
It will be noted that the connection of each of the links 18c,20c,28c to the struts 134, nodes 32c and corner link 22c by radiused fillets 52 that reduce local stress concentrations.
In one preferred example, the relative dimensions are as follows:
The fillets 52 are each 0.125 and the thickness of the material between 0.0625 and 0.125. With this configuration, the application of a radial load results in the circumferential expansion shown in
Upon circumferential expansion, the linking struts 42 inhibit foreshortening as each band 48 has two axial struts that inhibit relative axial movement between adjacent linkages 16c. At the same time the relatively flexible waists 50 disposed at 90° to one another provides the requisite flexibility for insertion of the stent 10c.
Although the embodiment of
The following relative dimensions of linkage 16 have also been found to provide satisfactory performance:
EXAMPLE I
In each of these examples, the units are 0.001 inches and the thickness of the material used was 0.003 inches.
In Examples I and III, the width, ie. circumferential dimension, of the struts 14 was 5 units and the axial spacing between adjacent linkages 16 was 12 units.
In Example II the width of the struts 14 was 2.85 units and the axial spacing between adjacent linkages was 3 units.
In each case, the linkages repeated 4 times about the circumference. The diameter of the stent prior to expansion was 65 units and after expansion with a 45° rotation of the links 20c an outside diameter of 197 units was obtained with Example II and 152.3 units with Example III. The axial spacing between linkages 16 was sufficient to permit the bodily rotation of the corner links as the stent expands radially. The provision of the strut 14 inhibits foreshortening and therefore ensures that the linkages can rotate as required.
A further embodiment is shown in
A further embodiment is shown in
In the embodiment of
The radiused external corners inhibit interference between adjacent pairs of links 22e and nodes 3e as the stent 10c is expanded to ensure a uniform expansion of the inflating balloon. The fillets 82, 86 assist in stress distribution to effect the proper hinging action of the links.
The relative dimensions of the links may be adjusted to suit the requirements and in particular to suit the outside diameter of the balloon. Using the same nomenclature as used in
It will be seen that by varying the spacing between links 20e (dimension ‘c’) or the length of link 34 (dimension ‘a’) the spacing of the struts 40e and hence the circumference may be varied. Appropriate adjustment can be made to the length of link 20e (dimension ‘e’) to maintain an expanded diameter of 4 mm. In each of the above examples, the external corners and all fillets except those at opposite ends of the links 20 have a radius of 0.002 inches. The fillets at opposite ends of links 20e have a radius of 0.0015 inches.
A further embodiment is shown in
In the embodiment of
Circumferentially adjacent struts 40f are staggered relative to one another so as to provide an axial overlap and a gap 46f. Accordingly, diametrically opposed connections are established at spaced axial locations to facilitate flexure of the stent 10f.
Claims
1. A stent having a generally tubular body with a plurality of circumferentially spaced longitudinal struts extending parallel to a longitudinal axis of said body, circumferentially adjacent pairs of said struts being interconnected solely b)(a set) of linkages axially spaced from one another and defining a predetermined space between adjacent pairs of said struts, each of said linkages having a plurality of links angularly disposed relative to one another in an unexpanded condition such that when a radial force is exerted-on-said tubular body, relative rotation between adjacent links and plastic deformation occurs, thereby increasing said space between said adjacent pairs of said struts and permitting radial expansion of said stent, said struts inhibiting relative axial movement between said linkages and foreshortening of said body, each of said linkages having hinge points spaced apart along said linkage, said hinge points deforming upon radial expansion of said stent to facilitate relative rotation of said links, wherein said hinge points are provided by zones of relative weakness along said links.
2. A stent according to claim 1 wherein said zones of relative weakness are provided by a reduced cross-sectional area.
Type: Application
Filed: Jan 20, 2004
Publication Date: Mar 17, 2005
Inventors: J. Lee (Nova Scotia), Katherine Crewe (Etobicoke), Christine Mastrangelo (Etobicoke)
Application Number: 10/759,527