Apparatus for crimping a stent

[0001] The present invention relates to an apparatus for crimping a stent down to a required profile for subsequent mounting of the stent onto a delivery system for use in medical applications.

[0002] Intraluminal stenting is useful in treating tubular vessels in the body that are narrowed or blocked and it is an alternative to surgical procedures that intend to bypass such a narrowing or blockage. When used in endovascular applications, the procedure involves inserting a prosthesis or stent into an artery and expanding it to prevent collapse if the vessel wall. Such stents are expanded by two well know methods. Either the stent is designed to be self-expanding or the stent is radially expanded with a balloon.

[0003] In particular the invention relates to a stent, which is mounted on the balloon of a balloon catheter for delivery to a body lumen in need thereof, the stent being radially expandable from a crimped state to an expanded state in which it provides support for the walls of the body lumen. Stents of the type referred to are manufactured with the stent in a partially or fully radially expanded condition. It is necessary to crimp the stent down by contracting it radially to enable it to pass through tortuous body vessels for delivery to the site in need thereof.

[0004] Heretofore, crimping of stents has been carried out manually. In the manual process, the stent is initially loaded onto a pin of a specified size and the stent is then crimped down uniformly, by hand, onto the pin. For some stents, it is necessary or desirable firstly to crimp the stent down onto an intermediate pin to ensure that the stent is crimped down uniformly. Due to the fact that the crimping is carried out manually, crimping can tend not to be completely uniform and consistent even with the help of the use of a pin.

[0005] Also known is a stent crimper having the form of an iris diaphragm, which can be closed down to an aperture size corresponding to a desired outer diameter crimped size. This is a relatively expensive device, which does not allow for a staged size reduction.

[0006] The present invention seeks to overcome the above disadvantages.

[0007] Accordingly, the present invention provides an apparatus for crimping down a radially expandable stent to a pre-determined profile, the apparatus comprising at least one set of rollers, each set including a first roller having at least a first groove and a second roller also having at least a first groove, the first groove on the first roller having the same dimensions and corresponding in relative location along the roller with the first groove on the second roller, each roller being rotatable about its transverse axis and the rollers being locatable in abutment with each other such that the first groove on the first roller is aligned with the corresponding first groove on the second roller so that the respective first grooves together define an aperture of substantially circular cross section and predetermined diameter whereby on rotation of the rollers, a stent advanced toward the rollers is drawn into the aperture thereby crimping down the stent to the pre-determined diameter.

[0008] Preferably, the stent is further crimped down to a desired final diameter suitable for delivery of the stent to the body vessel in need thereof by passing it successively through a series of said apertures provided by pairs of correspondingly dimensioned grooves provided on rollers with the successive grooves decreasing in dimension so that the stent is crimped down in stages.

[0009] The apparatus of this invention therefore has the advantage that it allows a stent to be easily crimped down in stages, enabling a smooth and even crimp to be achieved, avoiding any damage to or kinking or twisting of the stent which could affect its ability to be delivered or safely delivered to the body vessel in need thereof.

[0010] Conveniently, the apparatus may include a pin on which a stent is mountable.

[0011] A guide may also be included in the apparatus for guiding the stent towards the rollers and ensuring that it is held perpendicularly to the rollers as the stent is being advanced to the rollers and during crimping down.

[0012] In one embodiment, a series of pairs of correspondingly dimensioned grooves, arranged in order of decreasing dimensions are provided on each of the two rollers in the set.

[0013] Alternatively, a first pair of correspondingly dimensioned grooves may be provided on a first set of two rollers, and a second pair of correspondingly dimensioned grooves may be provided on a second set of two rollers with the stent being passed successively from the first set of rollers to the second set of rollers. A third pair of correspondingly dimensioned grooves may be provided on a third set of two rollers and further sets may also be provided with the stent being passed from one to the next set, crimping down further at each successive pass. The number of roller sets provided will depend on the crimp requirements of a particular stent and any number of sets of rollers from one upward may be provided as required.

[0014] In the case where two or more roller sets are used, it is advantageous that at least one set be disposed at right angles to an adjacent set. Where more than two sets are used, it is preferred that adjacent sets be disposed mutually perpendicular. This arrangement offers the advantage that any tendency to introduce an ovoid profile to the stent during crimping is reduced.

[0015] Whilst the groove defined by the pair of rollers of a set will be substantially circular in cross section, it is to be understood that the shape need not to be a perfect circle. In particular, in one advantageous arrangement, each groove of the pair has a chamfered edge which serves to protect the edges of the stent from damage during the crimping whilst not interfering with the purpose of crimping the stent down in an even fashion in the radially inwardly direction.

[0016] The apparatus of the invention has the advantage that it ensures that uniform crimping is achieved. Furthermore, crimping of stents using the apparatus of the invention ensures that overlapping of struts forming the stent, twisting of the stent or scratching of the stent material does not tend to occur.

[0017] The invention will now be described more particularly with reference to the accompanying drawings in which are shown three embodiments of an apparatus for crimping stents in accordance with the present invention.

[0018] In the drawings:

[0019] a. FIG. 1 is a perspective view of a first embodiment of an apparatus for crimping stents having two rollers mounted in a mounting frame;

[0020] b. FIG. 2 is a front view of the apparatus shown in the FIG. 1;

[0021] c. FIG. 3 is a perspective view of a second embodiment of an apparatus of the invention with the rollers located on a mounting block and with the set of two rollers having a series of pairs of correspondingly sized grooves, ranging from wider sized corresponding grooves to narrower sized corresponding grooves on each roller;

[0022] d. FIG. 4 is a perspective view of a third embodiment of an apparatus of the invention, in which a single pair of correspondingly sized grooves is provided on a first set of two rollers, in which embodiment a second and third set of rollers not shown are required, each roller in the set having correspondingly sized grooves ranging from relatively larger sized grooves on the first set of rollers, to relatively smaller sized grooves on the third set of rollers;

[0023] e. FIG. 5 is a perspective view of the embodiment of FIG. 4, showing three sets of roller pairs in sequence with their grooves aligned and with adjacent sets arranged in mutually perpendicular orientation;

[0024] f. FIG. 6 is a sectional view taken along the line A-A of FIG. 4; and

[0025] g. FIGS. 7 and 8 are enlarged views showing two different arrangement of the groove region circled in FIG. 6.

[0026] Referring initially to FIGS. 1 and 2 of the drawings, the first embodiment of the apparatus of the invention will now be described. In this embodiment, the apparatus is indicated generally by reference numeral 1 and includes one pair of rollers 2, 2 mounted on a mounting frame 3 on a base plate 4. Each roller 2, 2 has a series of pairs of correspondingly dimensioned grooves 5, 5; 6, 6; 7, 7 respectively, ranging from a pair of corresponding relatively large dimensioned grooves 5, 5 to a pair of medium dimensioned grooves 6, 6 to a pair of relatively small dimensioned grooves 7, 7. The respective corresponding pairs of grooves in the rollers are designed so that each corresponding groove on a roller lines up with that of the other roller to define an aperture, which is substantially circular in cross section.

[0027] Thus, for crimping to occur, the stent is firstly lined up perpendicular to the largest pair of grooves 5,5 on the rollers. The stent may or may not be located on a pin. The stent is then advanced so that one end thereof is in contact with the rollers. The rollers are then rotated together about the axes of rotation R in the directions shown by the arrows and this turning of the rollers draws the stent into the substantially circular aperture, which crimps it down to a diameter, which matches that of the groove pair. The stent is crimped down successively by passing it in turn through each of the pairs of grooves by rotation of the rollers. One or both of the rollers may be mechanically or manually driven.

[0028] If pins are used to support the stent during its passage through the apparatus, these may need to be changed depending on the size of the groove the stent is being passed into.

[0029] Typical pin sizes used for a three stage crimping down of a 4.0 mm diameter stent are as follows:

	1.3 mm	(0.051 inch)
	1.1 mm	(0.044 inch)
	0.85 mm	(0.0338 inch)

[0030] A guide may be used for ensuring that the stent is held perpendicular to the rollers as it is being crimped down.

[0031] Referring now to FIG. 3, the apparatus of the second embodiment is indicated generally by the reference numeral 20. Like parts have like numerals to those of the embodiment of FIGS. 1 and 2. The apparatus 20 operates in exactly the same manner as described above in relation to the first embodiment except that the rollers 22, 22 are mounted on a mounting block 21 rather than a mounting frame as in the first embodiment of the apparatus. As before, rollers 22, 22 have correspondingly dimensioned groove pairs 25, 25; 26, 26; 27, 27.

[0032] Referring now to FIGS. 4 to 8, the apparatus of the third embodiment is indicated generally by the reference numeral 30. The apparatus in this embodiment includes a series of sets of pairs of roller 33,33, 34,34, 35,35. The roller in the first pair of rollers 33, 33 have a single groove 36, 36 of relatively large dimensions cut in them. The succeeding sets of pairs of rollers have corresponding grooves of relatively medium dimensions on the second pair of rollers 34,34 and relatively small dimensions on a third pair of rollers 35,35. To crimp down the stent 50 on pin 52, it is passed successively from one set of a pair of rollers to the next in the series of sets of pairs of rollers with the stent being crimped down successively at each pair of rollers. In one arrangement of the third embodiment, the sets of pairs of rollers are mutually parallel. However, it is envisaged that adjacent pairs of rollers may be arranged mutually perpendicular as shown in FIG. 5 and this would have the benefit of enabling a uniform squeeze to be applied to a stent as it is undergoing crimping, thus eliminating any tendency for the stent to be crimped in an elliptical configuration.

[0033] It will be appreciated that the stent crimping apparatus of the invention may be used to crimp a stent irrespective of whether or not the stent is already assembled onto a balloon. Typically, the stent is slipped over the balloon prior to being crimped and therefore, it is important to ensure that in the course of crimping, the balloon does not become damaged rendering the final assembly useless for its purpose. For this reason, it is advantageous to provide a means for limiting the amount of force, which could be applied to the balloon-stent assembly, thereby reducing the risk of balloon damage. One way of achieving this end is to spring load one of the rollers at its central axis. Thus the force applied to the balloon/stent assembly can be limited by appropriate selection of the spring stiffness and preload. Other means of achieving this end will suggest themselves to the skilled person.

[0034] Beneficially, the edges of the grooves 37.37 of a roller pair will be formed with a chamfer as shown in FIG. 8 to ensure that they do not pinch or damage the stent. Likewise, the edge chamfering contributes to the avoidance of damage to the balloon in a case where the stent is being crimped onto the balloon. Alternatively, the grooves may define a substantially circular profile, as shown in FIG. 7.

[0035] Advantages of the Apparatus of the Present Invention:-

[0036] The apparatus of the present invention allows for uniform crimping of the stent, with the stent being crimped down more uniformly and more consistently than in the manual process of the prior art.

[0037] The apparatus enables the stent to be crimped down in defined stages. This can be of benefit in maintaining a uniform profile for the stent.

[0038] The apparatus can be used to crimp the stent either independent of the balloon on the delivery system or directly onto the balloon.

[0039] The apparatus of the invention provides a simple design for the process of crimping the stent down in stages.

[0040] The design of the apparatus means that the process is easy to automate. Furthermore, the process times are greatly reduced using the apparatus of the present invention and fewer stents are rejected for failing to meet quality control standards.

[0041] It will of course be understood that the present invention is not limited to the specific details described above, which are given by way of example only, and that various modifications and alterations are possible without departing from the scope of the invention.