Field of the invention

This invention relates to a transluminal delivery system for a self-expanding luminal prosthesis, the system comprising an inner catheter component and a retractable sheath to surround the component thereby to define an angular space to receive the prosthesis, the component exhibiting an anti-sliding component, for abutting a luminal surface portion of the prosthesis to restrain the prosthesis from sliding with the sheath, and relative to the inner catheter, while the sheath retracts relative to the prosthesis to release the prosthesis progressively into the target bodily lumen.

The invention also relates to a method of connecting a radially inwardly compressed self-expanding stent to an inner catheter within the lumen of the stent so that when the stent is delivered to a stenting site, the stent is retained against axial movement, relative to the inner catheter, while a sheath disposed radially outside the stent and imposing a radially inwardly compressive effect on the stent is retracted proximally along the length of the stent, to release the stent radially outwardly, distal of the distal end of the sheath.

The invention also relates to a method of building an assembly of a transluminal delivery system and a self- expanding prosthesis for a bodily lumen, the system comprising an inner catheter and a retractable sheath that surrounds the prosthesis and may be retracted to release the prosthesis, progressively, into the bodily lumen, the inner catheter including an anti-sliding component that occupies a lumen of the prosthesis and restrains the prosthesis from sliding with the sheath while the sheath retracts.

State of the art

Transluminal delivery systems for self-expanding stents are disclosed in Applicant's WO2005/030092, in WO2000/71058 of Scimed Life Systems Inc. and in WO2009/033066 of Cook Inc. These WO publications show components within the lumen of the stent that inhibit sliding of the stent with the sheath when the sheath is retracted, relative to the inner catheter, progressively to release the stent from the delivery system. Further disclosures of structures that engage with the luminal surface of a stent housed in a catheter delivery system are to be found in US-B2-7172618, US 5702418, US-B2- 6576006, US-B1-6620191, US-B2-7473271 and US-B2-7241308

With stent delivery systems being required to deliver ever more sophisticated stents to ever more challenging locations within the body of a patient, the engineering demands on the delivery systems have never been higher. The ideal delivery system inner catheter restrains the stent from sliding proximally with the sheath surrounding the stent without imposing any local stress concentrations on any particular part of the stent. Ideally, the inner catheter pushes evenly, all over the maximum possible surface area of the stent being restrained. Good inner catheters are therefore those that can accommodate local variations in inside diameter of the compressed stent within its sheath, and which abut the luminal surface of the sheath throughout the length of the sheath. There should be minimal likelihood of any damage to the stent during the assembly of the stent with its delivery system and the delivery system as such should be simple and economical in construction and operation. To an extent, these design objectives are incompatible. The present invention aims to bring to an unprecedentedly high level the successful compromise of the conflicting design objectives. Summary of the invention

In a nutshell, the underlying concept of the present invention is to provide on the inner catheter an anti-sliding component that can be slid axially into position in the lumen of the stent and which has a capacity to swell radially so that the radial thickness during the building of the assembly may be less than the radial thickness of the anti-sliding component during retraction of the sheath. In one simple realisation of the inventive concept, an anti-sliding component in the form of a sleeve is stretched axially, to reduce its radial thickness while the stent is crimped down onto the reduced thickness anti-sliding component. A sheath is introduced around the crimped stent and then, after that, the axial tension on the anti-sliding component is released, allowing the material of the anti-sliding component to relax, and the length to reduce, with consequent swelling of the radial thickness of the anti-sliding component. Any such swelling can vary locally, being at its greatest where the internal diameter of the annular stent is locally larger than average. Analogously, where the internal diameter of the stent is somewhat smaller than average, the capacity for local radially outwardly swelling of the anti-sliding component is rather more confined and occurs to a rather lesser extent. The consequence is that the anti-sliding component presses against more or less the entire axial length of the luminal surface of the stent, regardless of whether that luminal surface exhibits local variations in luminal diameter.

There are, however, other embodiments. Consider, for example, an inner catheter that carries, coaxially on its abluminal surface, a cylindrical braid with a very small radial thickness and which is bonded to the inner catheter within its lumen, but only at one end of the braid. This composite inner catheter is then introduced axially into the lumen of the stent, with the braid entering the stent lumen with the bonded portion of its length at the leading end, that enters the stent lumen first. Thus, as the inner catheter is advanced along the length of the stent lumen, the bonded leading end of the braided cylinder pulls the remaining length of the braid cylinder Into the stent lumen. The braid is under mild lengthwise tension, to the extent there is any frictional drag, as the inner catheter is advanced into the stent lumen. Much later, when the stent is being deployed, if the bonded portion of the braid is more proximal in relation to the stent than the unbonded remainder of the length of the braid, then any friction-induced tendency of the stent to slide proximally relative to the inner catheter will impose an endwise compressive stress on the braid cylinder, with the consequence that It will tend to "ruck up" or assume a crumpled form, which thereby "locks up" the gap between the inner catheter and the stent and resists any further proximal movement of the stent relative to the inner catheter shaft.

A striking technical effect of such a "lock up" concept is that, the more shear stress is imposed on the anti-sliding element by the stent, the more the element locks up, to resist that stress. In other words, the stresses imposed by the anti-sliding element on the stent are only as high as they need to be, to stop the stent sliding relative to the inner catheter.

A similar effect can be engineered, by endowing the abluminal surface of the inner catheter with a plurality of cantilevered filaments with good column strength that extend radially outwardly from the inner catheter shaft to give it a velvet or flock appearance. When one advances the flocked inner catheter into the stent lumen, from one end of the stent lumen, then the end of the stent first encountered by the filaments will push the filaments back so that they trail each from a leading end fixed to the inner catheter that is advancing into the lumen of the stent. Later, when the sheath is retracted to release the stent, and the stent tends to be entrained and carried proximally with the sheath, the free ends of the filaments will press against the luminal surface of the stent and the anchorage of the respective opposite ends of each filament, on the inner catheter, proximally of the free ends of the filaments pressing against the stent, will restrain any further proximal movement of the stent relative to the inner catheter. One can imagine each of the filaments functioning as a miniature pawl, with a tendency to resist sliding of the stent relative to the inner catheter that benefits from a high column strength in each filament.

Preferably, the anti-sliding component should be arranged so that it works to greatest effect near the distal end of the stent, as the sheath surrounding the stent is pulled back proximally, so that the stent, in general, suffers a degree of lengthwise axial tension during such withdrawal. Such preferential effect at the distal end might be engineered by arranging for the anti-sliding component to have an inherently larger diameter near the distal end of the stent than it exhibits closer to the proximal end of the stent.

The invention may be applied in a wide variety of delivery systems where it is desired to deliver an implant such as a stent, filter, stent graft or stent with an integrated heart valve via a catheter with a high deployment accuracy.

Brief description of the drawings

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Fig. 1 is a longitudinal diametral section through a "classic" delivery system to release a self- expanding stent; Fig. 2 is a longitudinal diametral section through a delivery system as in Fig. 1, but including an inner catheter with an anti-sliding component;

Fig. 3, 5, 6 and 8 to 12 are longitudinal diametral sections like Figs. 1 and 2, with an inner catheter that exhibits an anti-sliding component in accordance with the present invention; and

Figs. 4 and 7 are longitudinal diametral sections like Figs. 1 and 2, with an inner catheter that exhibits anti- sliding filaments.

Detailed description

The schematic drawing of Fig. 1 shows a stent 10 that has been radially crimped to a small diameter for advancement along a lumen to a stenting site within the body of a patient. To release the stent into the bodily lumen a sheath 12 that surrounds the stent and confines it radially is pulled back proximally in the direction of arrow 14 using a pulling device 16 such as a pull tube or pull wire that runs all the way back to the hand unit (not shown) at the proximal end of the transluminal catheter delivery system. Typically, there is some sort of bond, such as with a collar 18, that connects the pulling element 16 with the sheath 12 that surrounds the stent.

Absent any other structure, then any proximal movement of the sheath 12 will carry the stent with it because the stent is a self-expanding stent and so is continuously pressing on the luminal surface of the sheath 12. To stop the stent 10 moving proximally with the sheath 12, it has been conventional to employ an annular element 20 that can conveniently be termed a "stopper". The stopper element 20 also runs back to the not-shown hand unit, through a shaft 22 that will of course be in endwise compressive stress during the time period when the sheath 12 is being retracted and the stopper 20 is required to stop the stent moving proximally with the sheath 12. By contrast, the pulling element 16 during this time period will be in endwise tensile stress.

One can see immediately from Fig. 1 that the stopper annulus 20 carries all of the load that the stent 10 imposes on the catheter shaft element 22 that finds itself in endwise compressive stress during stress deployment. Thus, portions of the structure of the stent 10 that are immediately distal of the stopper annulus 20 are liable to suffer greater concentrations of stress than portions of the stent 10 up near the distal end of the stent, remote from the stopper annulus 20. This is not ideal. Ideally, the stresses imposed on the stent during release of the stent should be shared homogeneously and equally by all portions of the structure of the stent .

Turning to Fig. 2, the stent 10 is the same and the outer sheath 12 is the same and the pulling element 16 is the same but the inner catheter that will be in compressive stress while the stent is being released is in the form of an elongate tube 30 that extends through the lumen of the stent 10. On the abluminal surface of the inner catheter tube 30 there is provided a plurality of protuberances 32 that can engage with the luminal surface of the crimped stent 10. Contemplated is to place the inner catheter with the protuberances inside the lumen of the stent 10 before crimping the stent down onto the protuberances and surrounding the crimped stent with the sheath 12.

Clearly, this assembly technique can bring advantages relative to the basic system of Fig. 1, especially in the case of stents of great length and great flexibility. Looking now at drawing Fig. 3, we see the same arrangement of stent 10, sheath 12 and pulling element 16, but inside the lumen of the stent is an inner catheter 30 moving from left to right in the drawing as indicated by arrow F. In fact, the inner catheter 30 is being installed in the lumen of the stent 10, to create an assembly of inner catheter, stent and sheath 12 for incorporation in the catheter system for delivering the stent 10.

The inner catheter 30 has an abluminal surface to which is bonded in length portion 33 an end portion 34 of a cylindrical braided element 36 that fits snugly around the external diameter of the inner catheter shaft 30. Most of the length of the braid 36 is free to slide on the abluminal surface of the inner catheter 30, the exception being in the end zone 33. It will be appreciated that when one pulls the inner catheter 30 from left to right in Fig. 3, through the lumen of the stent 10, in the direction of arrow F, the leading portion 34 of the braid 36 can be pulled to a position adjacent the proximal end of the stent and the collar 18 between the stent sheath and the pulling member 16. This will leave the sliding portion of the length 36 of the braid inside the stent lumen, and it is arranged for the braid to be a relatively snug fit between the inner catheter 30 and the luminal surface of the stent 10.

Now, turning to Fig. 6, we can see what happens when it is time to deploy the stent and the pulling member 16 is pulled proximally, in the direction of arrow G relative to the inner catheter 30. The stent 10 at first follows the proximal movement of the sheath 12 but this will have the effect of "rucking" the slidable braid 36 which, in consequence, will tend to "pile up" in any interstices available to it, within the luminal surface of the stent 10. Any such piling up, or departure from a cylindrical abluminal surface of the braid 36, will have a braking effect on the incipient proximal movement of the stent 10, because the braid 36 cannot slide proximally to any extent, blocked as it is by the fixation of the proximal end of the braid 36, to the inner catheter 30, in length portion 33. In this way, the stent 10 can be released without any significant proximal sliding relative to the inner catheter 30.

Although Fig. 6 shows the length portion 33 of the inner catheter at the proximal end of the stent, it is also contemplated to provide it up near the distal end of the stent lumen. Indeed, it is contemplated to provide a plurality of short lengths of braid, spaced along the inner catheter in the stent lumen, each tethered to the inner catheter at the proximal end of each such braid length.

It is conventional to use a cylindrical braid when a degree of "springiness" is desired, such as in the child's toy called the "Chinese Finger" or a self-expanding stent after Wallsten. Here, however, one is looking for a braid that has some capability to crumple or concertina, which is almost the opposite of the quality of springiness.

As ever, materials and dimensions are chosen deliberately on the basis of optimising fitness for purpose. Here, one will contemplate the ideal number of filament crossing points per unit of axial length of the cylindrical braid and the possibility to blend different materials in the filament weave. One possibility is to incorporate filaments of polyurethane as damping filaments. A homogeneous or heterogeneous mixture of filaments selected from steel, nitinol or other alloys may form the braid, and heat-treating of some or all of these materials may be used to desirably tune the mechanical properties of the braid. The braid itself may be enclosed in a very thin polymer matrix, for example polyurethane. Possibly, it will be effective to use filaments of non-circular cross section, rough-surfaced or with corners (square or hexagon cross-section, for example) to enhance frictional engagement with the stent and inner catheter during stent release. It may be effective to roughen the abluminal surface of the inner catheter beneath the braid.

The inventor contemplates that braid lengths of as little as 5 mm (or even less) may be fully effective to accomplish the desired effect. That is to say that the axial length of the unbonded portion of the braid (not including the portion which is bonded to the inner catheter 30) need only be 5mm in length, possibly even shorter, depending on the particular application for which it is being used. The same will apply to other non-braided tubular anti-sliding components and sleeves, such as the sleeve 50 of Figure 8.

Indeed, as the length of such braided and non-braided sleeves is increased, so too is the extent to which the sleeves will ruck up or crumple, as well as the extent to which their thickness will increase, as the unbonded portions slide along the abluminal surface of the inner catheter 30. In certain circumstances, where the anti-sliding sleeve is of significant length, this can generate undesirably large radial forces acting radially inwardly on the inner catheter 30 and radially outwardly on the surrounding stent 10 and sheath 12. Where the radial forces are too large, retraction of the sheath 12 and proper positioning and placement of stent 10 may be inhibited, and there is a risk of damaging one or more of the inner catheter 30, stent 10 or sheath 12. Such consequences are counter to the objective of spreading the compressive forces which hold the stent 10 in position on the inner catheter 30 along the axial length of the stent 10, rather than having concentrated forces at the location of a stopper annulus 20 as described in relation to Figure 1 above, when the sheath 12 is retracted.

To this end, a shorter length of anti-sliding sleeve is preferred, and it is furthermore proposed to provide two or more of the anti-sliding sleeves along the length of the inner catheter 30 within the lumen of the stent 10, depending on the length of the stent 10 to be delivered and the forces involved. Currently, the use of two or three anti-sliding sleeves is preferred, for most stent delivery applications. Of course, the anti-sliding sleeves may all be of the same configuration, or different lengths and types of sleeves may be used at different positions along the length of the inner catheter 30 within the lumen of stent 10. For example, a mixture of braided and non-braided sleeves may be used in the same transluminal catheter delivery system. Different materials or combinations of materials may be selected for use in each individual anti-sliding sleeve, as appropriate.

Turning to Fig. 4, there is shown an alternative way of reducing the likelihood of the stent 10 sliding on the abluminal surface of the inner catheter 30, whereby the abluminal surface of the inner catheter 30 is equipped with a multitude of filaments 40 that extend radially outwardly from a fixed end 42 of each of the filaments 40, respectively fixed to the abluminal surface of the inner catheter 30. As the catheter 30 is pulled through the lumen of the stent 10, as described above in relation to Fig. 3, and as indicated again by arrow F, the distal end 44 of the stent will press against each of the arriving filaments 42 and will cause them to lie down more parallel to the length direction of the inner catheter, with the cantilevered free end 46 of each filament located distally of the fixed end 42 by the length of the filament 40.

Turning to Fig. 7 , we see how a tensile stress on the pulling element 16, causing it to move in the direction of arrow G, and tending to drag the stent 10 with it, will prompt engagement (in the manner of a pawl) between the free end 46 of many, or most, or all of the filaments 40 with a surface portion of the luminal surface of the stent 10. Any such abutment will have the natural effect of resisting any proximal sliding of the stent 10 relative to the inner catheter 30. Any such resistance to sliding, however, will have no inhibitory effect on the radial expansion of the distal end of the stent 10, as the sheath 12 slides progressively and proximally away from the stent 10. Furthermore, once the stent is deployed, the filaments 40 present no obstacle to proximal withdrawal of the inner catheter from the deployed stent 10 and the bodily lumen in which the delivery catheter has been advanced to the stenting site.

Turning now to a third embodiment, as shown in Fig. 5, the inner catheter 30 is provided with a sleeve 50 that is, in general, freely slidable on the abluminal surface of the inner catheter 30. As an exception, in a small portion 52 of the length of the inner catheter 30, there is an adhesive bond between the catheter 30 and the slidable jacket/sleeve 50. In this embodiment, an endwise tensile stress, represented by arrows H, is imposed on the sleeve 50 prior to any pulling of the inner catheter 30 through the lumen of the stent 10, as represented by arrow F. The imposition of the endwise tensile stress has the effect of reducing the radial thickness t of the sleeve 50. This reduced radial thickness facilitates progress of the inner catheter shaft 30 axially through the lumen of the stent 10. The catheter is advanced until the short length portion 52, where the sleeve 50 is bonded to the catheter 30, arrives at a position adjacent to the proximal end of the stent 10. Once the tensioned sleeve 50 lies within the stent lumen, and the stent is safely confined within the sheath 12, the endwise tension can be released, allowing the radial thickness t of the sleeve 50 to increase and any such thickness increase will manifest itself as an expansion, locally, of portions of the sleeve, into interstices of the luminal surface of the stent 10. See Fig. 8. Any such form fit between the abluminal surface of the sleeve 50 and the luminal surface of the stent 10, allied to the bonding of the sleeve 50 to the inner catheter 30, will have the effect of acting as a brake on any tendency of the stent 10 to move proximally with the sleeve 12, relative to the inner catheter 30.

If desired, the abluminal surface of the inner catheter of the third embodiment (and even the abluminal surface of the braid of the first embodiment) could be rendered filamentous, to take advantage of the idea of the second embodiment as well .

Another embodiment of the invention is shown in Figure 9. This embodiment is somewhat similar to that of Figure 3, in that the inner catheter 30 has an abluminai surface to which is bonded a proximal end portion 64 of a cylindrical element 66, The cylindrical element 66 is made of a flexible tubing and fits loosely around the external diameter of the inner catheter shaft 30. It is again bonded at a distal end portion 65. However, the locations at which end portions 64 and 66 are bonded to the inner catheter 30 are selected such that an intermediate unbonded length of the cylindrical element 66 lying between the end portions is greater than the distance between the locations at which the end portions 64 and 66 are bonded, so that the unbonded length is to a certain extent free to slide on the abluminal surface of the inner catheter 30.

It will be appreciated that the arrangement of Figure 9 allows the cylindrical element 66 to ruck up in either direction, meaning that the inner catheter 30 can be used for urging a surrounding stent 10 in both directions. This effect can be utilised to advantage both in manufacturing and use of a transluminal catheter delivery system.

Although it has been proposed to crimp the stent 10 and load the stent 10 into a sheath 12, prior to then drawing the inner catheter 30 axially into the delivery system within the lumen of the stent 10 (as denoted by arrows F in Figures 3, 4 and 5) , such a method presents additional complexity. Specifically, after crimping the stent 10 to its reduced diameter, one has first to load the stent 10 into the sheath 12. One way to do this is to push the stent 10 axially from within the crimping device into an adjacently disposed and aligned sheath, for example using a pusher configured like the inner catheter 30 of Figure 2. Such a pusher then has to be withdrawn from inside the lumen of the stent 10 so that the inner catheter 30 having the anti-sliding component can be inserted proximally (in the direction of arrows F) into the lumen of stent 10 within sheath 12.

It would be preferable, instead, to crimp the stent 10 down directly onto the inner catheter 30 having the anti-sliding component. The inner catheter 30 with the anti-sliding component may then be used to push the crimped stent 10 into the sheath 12, without needing to use a separate pusher or to carry out a separate step of inserting the inner catheter 30 with the anti-sliding sleeve into the lumen of stent 10 after it has been installed in the sheath 12.

Although this is possible with the inner catheters 30 of Figures 3 to 8, there is a drawback in that the stent 10 then has to be pushed distally, from the proximal opening of the sheath 12, along the whole length of the sheath 12, until the distal end of the stent 10 is at or near to the distal end of the sheath 12, ready for deployment by proximally retracting the sheath 12 (in a transluminal catheter delivery system in which the stent to be deployed is located near the distal end of the catheter and the sheath is retracted proximally) . This is necessary, since the inner catheters 30 of these Figures have only one-directional pushing ability. Such a process is impractical, however, in many systems in which the retractable restraining sheath is significantly longer than the stent to be deployed. In some systems, the retractable sheath extends along substantially the whole length of the catheter, rather than having a separate pulling element 16, whereas the stent is located only along a relatively short distal portion of the catheter.

It is therefore contemplated to use the inner catheter 30 of Figure 9 so that, in manufacture of the transluminal catheter delivery system, the stent 10 can be crimped down onto the inner catheter 30, and the inner catheter 30 can then be used to pull the stent 10 into the aligned sheath 12 from the distal end of the sheath 12, only for a distance substantially equal to the length of the stent, even if the sheath 12 is significantly longer than the stent 10 to be deployed. This is possible as the anti-sliding sleeve 66 is fixed at both ends, and so will crumple (ruck up) towards the bonded distal end portion 65 of the sleeve 66, thereby engaging with the inner lumen of the crimped stent to enable the inner catheter 30 to urge the stent proximally into the distal end of an aligned sheath 12. The inner catheter then remains within the lumen of the stent 10 and the sheath 12, as the inner catheter of the delivery system.

In order to deploy the stent 10 using such a system, the sheath 12 is then retracted proximally by pulling on pulling element 16, which places the inner catheter 30 in compression. The sheath 12 tends to draw the stent 10 proximally, which in turn causes the sleeve 66 to ruck up towards the bonded proximal end portion 64 of the sleeve 66. The sleeve 66 thereby engages the inner lumen of the stent 10, as in the embodiments already described, to effectively push the stent 10 against the sheath retraction force and hold the stent 10 in place as it expands upon release from the sheath 12. In this way, as the stent 10 is deployed, the interaction between the rucked zone and the luminal surface of the stent 10 prevents significant proximal sliding relative to the inner catheter 30, and allows precise deployment. In this embodiment, the cylindrical element 66 is advantageously PET tubing so that the end portions 64 and 65 may be secured on the inner catheter by heat-shrinking while the sliding portion remains free to translate and crumple (ruck up) as required.

Regarding the engagement between the anti-sliding sleeve component 66 and the inner lumen of the surrounding stent 10, as with the anti-sliding sleeves 36, 50, 76 of the other embodiments disclosed herein, it has been contemplated that where the anti-sliding sleeve is rucked up the sleeve material or braids may inter-engage with the interstices of the sent 10. However, for many stents, the interstices are not sufficiently open, with the stent in the crimped configuration, to allow for such inter-engagement. Indeed, for stents which are laser cut from a Nitinol tube, there are virtually no interstices in the stent structure in the crimped, reduced-diameter configuration. The engagement between the anti-sliding components and the stent inner luminal surface is, therefore, in most cases, simply a frictional engagement. By selecting suitable materials for the anti-sliding sleeves, a secure frictional engagement can be achieved. Moreover, by selecting a suitable material for the anti-sliding sleeve, the anti-sliding sleeve can present a "soft" bed onto which the stent 10 can be crimped, without damaging the stent 10 or any stent coating. By using a suitably pliable (soft) material, the frictional engagement between the anti-sliding component and the stent luminal surface can also be enhanced. If desired, an outer polymeric sleeve could be incorporated in or provided on the outside of a braided sleeve, the braided sleeve providing the material resilience to present a crumpling action and the sleeve improving the frictional engagement between the braided sleeve and the stent luminal surface (as compared to the frictional engagement between only a braided layer and the stent luminal surface) . Incorporating a braided sleeve in a thin PUR matrix is contemplated. A further embodiment of the invention is now described with reference to Figures 10, 11 and 12. This embodiment may be useful in situations where it is desired to have separate control of motion of the stent and the anti-sliding action of the anti-sliding component. This embodiment is also advantageous in that it allows the anti-sliding sleeve to be engaged with the inner lumen of the stent 10 without any initial retraction or movement of the stent 10 with the sheath 12, which is needed to a small but generally insignificant degree with the above-described embodiments. It is, though, preferred to avoid any positional variation of the stent 10 relative to the inner catheter 30 during deployment as far as possible, as this improves precision of stent placement.

In this embodiment, as shown in Figure 10, a loose sleeve 76 is positioned about the inner catheter 30 and bonded to the inner catheter 30 at a proximal portion 74. The sleeve may be flexible tubing, braided wire or a composite structure of either. The distal portion is attached to an annular slider

75, which is centred on but also free to slide on the inner catheter 30. The intermediate portion between proximal and distal portions is otherwise unattached to the inner catheter. Running proximally from the slider 75 underneath sleeve 76 is a pull element 77 which is also free to slide and traverses bonded portion 74 without impedance, for example by means of an aperture or slit.

Stent 10 may be loaded onto inner catheter 30 by crimping the stent 10 down onto the inner catheter 30 slider 75 and sleeve

76, as for the embodiments described above. The stent remains at this stage substantially freely movable relative to the inner catheter. Such a configuration may be seen in Figure 11. When, during deployment of the stent 10, the correct position of the stent 10 is reached for it to be released from the sheath 12, proximal tension is applied to the pull element 77 causing the slider 75 to travel proximally relative to stent, catheter and bonded proximal portion 74 of the sleeve 76. As the sleeve 76 is compressed longitudinally between slider 75 and bonded proximal portion 74, it will expand in radial extent, for example by rucking up or crumpling, as explained with reference to the embodiments described above, to engage with the luminal surface of the stent 10. The more tension that is applied to the pull element 77, the closer the slider 75 approaches bonded proximal portion 74, and the greater the degree of interaction between the sleeve 76 and the luminal surface of the stent 10. Motion of the stent relative to the catheter will tend to strengthen this interaction further, in analogous ways to those described above with reference to the other embodiments. In this way, the stent 10 can be restrained on demand from motion relative to the catheter 30 by actuation of the pull element 77. Such a configuration may be seen in Figure 12.

In some applications, it may even be desirable to make the process reversible, and allow the pull element 77 to have sufficient column strength to translate the slider 75 in the distal direction, returning the sleeve 76 to its previous un- crumpled configuration and relieving the stent 10 from the radial restraining force.

In this embodiment, the sleeve 76 is advantageously PET tubing while the slider can be constructed as a PEBAX tube riding on an inner PI tube. Alternatively, a metal braid may be used as a sleeve, as in the embodiment of Figure 3. In general, It may be useful to include features that increase levels of friction between the abluminal surface of the inner catheter and any portion of an anti-slidlng component that is slldable on that surface. That might take the form of a roughening of that abluminal surface, a roughening of any luminal surface of the slidable component, or both.

In connection with the embodiments described above, a stent receiving element may be provided on a portion of the unbonded sliding portion of the sleeve. Such is shown at the distal end of the sleeve 76 in Figure 11, in which the slider or slide ring 75 is provided with an enlarged diameter as compared to the diameter of the sleeve 76. An enlarged diameter element of this kind may also be provided to the anti-sliding sleeves of the other embodiments, regardless of whether they include a sliding ring. The enlarged diameter element is preferably of a relatively soft material, to avoid damaging the stent 10 or inner catheter 30. The receiving element serves to first receive the inner lumen of the stent 10, as stent 10 is crimped down onto the inner catheter 30 and anti-sliding sleeve 76. As such, the stent 10 is fist crimped down onto the receiving element before coming into engagement with the anti-sliding sleeve 76. After the stent 10 engages with the receiving element 75, the stent 10 may be moved towards a bonded portion of the anti-sliding sleeve 76, here proximally in the direction of arrow F in Figure 10. This causes the unbonded portion of the anti-sliding sleeve 76 to crumple between the receiving element 75 and the bonded portion 74, ensuring a uniform rucking up along the length of the unbonded portion of the anti-sliding sleeve. The stent 10 may then be further crimped onto the inner catheter to further reduce its diameter and bring it into engagement with the rucked up anti-sliding sleeve. Although described as a two-stage crimping process, the procedure may be completed in a single movement using an appropriate crimping device and effecting a longitudinal movement of the inner catheter 30 relative to the stent 10, once the stent is engaged with the receiving element 75.

Such receiving elements are also useful, even if the above steps are not taken during the manufacturing and assembly process, as they allow the rucking or crumpling behaviour of the anti-sliding sleeve to be more accurately predicted and controlled, by guaranteeing that the sleeve 76 will crumple in the region between the receiving element 75 and the fixed portion 74 of the anti-sliding sleeve 76. Without a receiving element 75, portions of the anti-sliding sleeve 76 which were not in good contact with the stent 10 may not get rucked up during retraction of the sheath 12 (in the embodiments not using a pull element 77), or may not get rucked up evenly or uniformly along the length of the anti- sliding sleeve. Receiving element 75 is therefore useful in these respects.

An important part of the routine work of stent delivery system designers is to select optimum materials for individual component parts of stent delivery systems. The present invention is no exception to this general rule. For the skilled reader of this specification, choice of materials is a matter of background knowledge and routine expertise. The skilled reader will be able readily to appreciate how the present inventive concept allows assembly of a catheter-type, transluminal stent delivery system that has minimal passing diameter and maximal management of the movement of the stent during release of the stent from the system, with minimal occurrence of unpredictable stress overloading of any part of the material of the stent being deployed.