The present invention relates to a stent.

A stent is a medical device designed to be delivered to a lumen at a site in the human (or even animal) body, for instance a coronary artery, aorta or the oesophagus etc. The stent provides a medical treatment of some sort. Typical uses of a stent are to open blocked coronary arteries and large veins as caused for example by a disease such as stenosis or by cancer, to treat obstructions to breathing in the trachea and bronchus, to allow the passage of urine in the prostate and, more recently, to palliate cancer stenosis in the oesophagus. Stents preferably have a flexible structure allowing them to be collapsed to reduce their outer dimensions. This is to facilitate the passage of the stent into the site in the body where the stent is expanded for deployment. Stent therapy is now widely accepted for interventional treatment not only in the vascular system, but also the gastrointestinal, belier and urinary systems. Stent techniques have come to be regarded as simply, safe and effective in comparison to other surgical or non-surgical treatments.

The present invention has particular application to a stent for treating an intracranial aneurysm. Such an intracranial aneurysm is a weak region in the wall of an artery in the brain, where dilation or ballooning of the artery wall may be developed. Because the wall of the aneurysm is very thin, lacking the normal layer structure found in healthy arteries, it is easy to rupture and as a result to cause fatal haemorrhages in the brain. In the United States, about 27,000 people suffer from ruptures of intracranial aneurysms every year and of those, ten percent die before they reach the hospital.

Current methods for treating intracranial aneurysms include open surgical clipping and endosaccular coiling. In the surgical clipping method, the patient's skull is opened, and a surgical clip is placed across the neck of the aneurysm to stop blood from flowing into the aneurysm sac. The risk of this method is relatively high, especially for elderly or medically complicated patients. Compared to surgical clipping, endosaccular coiling is a less invasive method. In an endosaccular coiling procedure, one or more coils are delivered through a catheter into the aneurysm until the sac of the aneurysm is completely packed with coils, which will help to form a thrombus. Although endosaccular coiling is safer than surgical clipping, it has several limitations. First, after filled with the coils, the aneurysm will remain the same in size. As a result, the pressure on the surrounding tissue exerted by the aneurysm will not be removed. Second, this procedure is effective on the aneurysm that involves a well-formed sac with a small neck. When used to treat the wide-neck aneurysm, the coil is likely to protrude into the parent vessels, which remains a high risk. A possible solution to prevent coil protrusion is the use of the remodelling technique, in which a small balloon-occlusion microcatheter is used to protect the parent artery lumen during the insertion of the coil. However, this approach is helpless to keep the coil staying stably in the aneurysm that has a very large neck. Besides, a high rate of thromboembolism due to consecutive balloon occlusion of the parent artery associated with the method is a major problem in this approach.

A stent in combination with coiling embolization has been adopted to treat the wide-neck aneurysm. In a stent-assisted coiling procedure, a stent is first placed across the aneurysm neck, serving as a scaffold inside the lumen. Then, the coils are delivered into the sac of the aneurysm through the interstices of the stent. Although this method can solve some problems of purely coiling, it still has some drawbacks. First, a microcatheter through which the coils are sent into the aneurysm sac has to be navigated through the interstices of the stent. This process is difficult and time-consuming. Second, the coils are still used to fill the sac of the aneurysm in this method. As a result, the aneurysm size remains the same after the treatment. Furthermore, when it comes to the pseudoaneurysm where no fully-formed aneurysm sac can be identified, coiling methods are not applicable.

Using a stent alone to treat the aneurysm is a promising way to avoid the problems stated above. In this method, a stent with an area of coverage is placed across the aneurysm neck, blocking it sufficiently to restrain blood from flowing into the sac and finally to trigger a thrombus within the aneurysm. Because the aneurysm solidifies naturally on itself, there is no danger of its rupture. Furthermore, because no coil is involved in this method, the aneurysm will gradually shrink as the thrombus is absorbed. Consequently, the pressure applied on the surrounding tissue can be removed. Current stents made for the stent-assisted coiling, such as Neuroform stent (Boston Scientific), LEO stent (Bait) and Enterprise stent (Corids), have a very open design to allow the coils to pass through the interstices. Therefore, they are inadequate for direct treatment of the aneurysm.

A literature review shows that current stent designs aimed to direct treatment of the aneurysm fall into two categories.

The first category is characterized by having a helical design. WO-2004/1 12655 discloses a simple helical stent formed from a single thread of superelastic coiled wire.

US-6,063,1 1 1 also discloses a helical stent based on the coiled wire but suggests that the resilient wire of the stent can be sealed between two strips of film to provide more coverage to the aneurysm neck. US-6, 860,899 discloses a stent formed by a helically wound ribbon with gradient designs in the ribbon width and the size or number of the openings, as shown in Fig. 1.

US-2005/0033410 discloses a stent comprised of a helical body portion and an optional cylindrical distal portion, as shown in Fig. 2. The helical body portion comprises a series of cells that are inter-connected by hinges. The distal portion helps to anchor the stent at a desired location.

EP- 1,161,927 discloses a helical stent formed from a wound strip of a series of deformable cells, as shown in Fig. 3. Upon expansion, each cell expands, lengthening the strip in helical direction to allow the stent to expand without unwinding of the strip.

WO-2006/041638 discloses a stent formed by helically winding a ribbon, as shown in Fig. 4. Either the width or the length of the ribbon is variable so that the overall axial length of the stent can be the same before and after expansion.

The second category is the pleated stent design that provides a highly solid surface. WO-2005/044330 describes a cylindrical stent formed from a metal tube with fine patterns in its surface, as shown in Fig. 5 which shows the stent 1 in an artery 2 in which an aneurysm 3 is formed. The stent is pleated and assembled onto a balloon for delivery. US-2006/0155367 discusses a similar design to WO-2005/044330, except that US-

2006/0155367 increases the number of pleats when the stent is pleated. This is likely to improve the longitudinal flexibility of the stent. Besides, US-2006/0155367 involves a portion having a high area of coverage being provided in the vicinity of the aneurysm neck and leaves the rest of the stent with more open design to reduce the risk of blocking the side-branch arteries. The objective of direct treatment of the intracranial aneurysms with a stent alone is to prevent the blood from flowing into the aneurysm sac by blocking the neck of the aneurysm with a cover. For this reason, stents for this purpose desirably have a portion which can be arranged across an intracranial aneurysm having a sufficient area of coverage to block the intracranial aneurysm. Besides, the brain arteries are very tortuous. Therefore, stents used in the brain must have sufficient flexibility to prevent artery damage during delivery.

Use of a helical stent design, as in the first category discussed above, has the capability of providing a high degree of flexibility and can have a reasonable degree of coverage because the strip that is wound to form the helical stent can be relatively solid. However, packing and positioning of helical stents are difficult due to drastic shape changes upon expansion, such as unwinding or large amount of reduction in length. Besides, when a helical stent is bent, there can be large gaps between windings, which results in difficulty in positioning and a risk of failing to cover the aneurysm.

Use of a pleated stent design, as in the first category discussed above, can potentially provide easy positioning and good coverage of an aneurysm. But such a design has limited longitudinal flexibility which severely limits the ability to deliver them without causing arterial damage. Besides, due to the large deformation of the cylinder surface when these stents are pleated, they are not suitable to be constructed from a superelastic material which would assist delivery. It is therefore desirable to provide a stent which provides a good compromise between on one hand having a portion having a large area of coverage which is easily positioned, for example sufficient to block an intracranial aneurysm, and on the other hand having sufficient flexibility to prevent damage during delivery. In general terms these desirable characteristics compete with each other because in many stent designs flexibility is increased by making the structure more open and hence less rigid. Such characteristics would have particular, but not exclusive, application in a stent for treating an intracranial aneurysm.

According to a first aspect of the present invention, there is provided a stent arranged as a tube and configured to be deformable between an expanded state and a collapsed state in which the stent has a smaller radius than in the expanded state, wherein, over at least a portion of the stent, the stent comprises a plurality of plates and linkage members interconnecting the plates, the plates and the linkage members fitting between each other without overlapping in the expanded state of the stent, the linkage members being configured to be deformable in a manner causing the plurality of plates to slide over each other in a circumferential direction as the stent is deformed between the expanded state and the collapsed state, the plates being configured to retain their shape on deformation of the stent and to overlap in the collapsed state of the stent. Such a stent in accordance with the first aspect of the invention is capable of providing a good compromise between the desirable characteristics discussed above of having a portion having a large area of coverage which is easily positioned, for example to block an intracranial aneurysm, and on the other hand having sufficient flexibility to prevent damage during delivery. The use of the plates allows the stent to be provided with a high area of coverage in the expanded state without compromising the flexibility of the stent. As the plates are configured to retain their shape on deformation of the stent and to overlap in the collapsed state of the stent, the plates provide a high area of coverage in the expanded state without compromising the flexibility of the stent. This is because the plates are not required to fold or otherwise significantly deform. Instead, the plates simply slide over each other in a circumferential direction as the stent is deformed. Thus the area of the plates can be increased as compared to a part of the stent required to deform on collapse. Both the flexibility and the ability to collapse the portion of the stent including the plates are provided by the linkage members which need not have a high area of coverage in themselves in view of the plates.

In practice, this means that embodiments of the first aspect of the present invention designed for treating an intracranial aneurysm are capable of providing a sufficient area of coverage to block the intracranial aneurysm whilst having a good degree of flexibility to facilitate delivery without causing damage to the arteries, in particular having a higher degree of flexibility than the pleated stents discussed above.

The plates and the linkage members are designed to fit between each other without overlapping in the expanded state of the stent. This facilitates manufacture of the stent with a suitable design to achieve the desired properties discussed above. For example, the stent is capable of being manufactured from a sheet of material cut into the plurality of plates and the linkage members. This allows for relatively straightfoward manufacture, for example using laser cutting. In this case the entirety of the plates may be cut from that sheet of material.

In another type of construction, the plates may comprise a sheet of material different from the material of the linkage members. That different material may be more flexible than the material of the linkage members in order to increase the flexibility of the plates. The sheets of different material of the plates may be connected directly to the linkage members or may be supported by frames that are connected to the linkage members, for example by the frame containing at least one aperture across which said sheet of material extends or by the frame comprising a strut protruding from a linkage member and from which said sheet of material protrudes laterally. In this type of construction, the stent is capable of being manufactured from a sheet of material cut into the linkage members and, if present, the frames of the plates. The sheets of different material of the plates may be a coating on the sheet of material of the stent, the coating being itself cut into the individual plates. The stent may be made from a wide range of suitable biocompatible materials, for example a metal which may be a superelastic material. Use of a superelastic material provides particular advantages during delivery of a stent.

Desirably, to provide good coverage of typical intracranial aneurysms, in the expanded state of the stent, the plates encompass overall an area which is as high a proportion of said portion of the stent as possible, typically at least 50%, or more preferably at least 75%, although other areas might be provided for other applications.

Whilst the plurality of plates and linkage members may extend over the entirety of the stent, advantageously the plurality of plates and linkage members may extend over only a portion of the stent, the remainder of the stent comprising a deformable structure which is more open than said portion of the stent. This allows the flexibility of the stent as a whole to be increased, whilst still allowing the stent to be delivered with the portion including the plates covering a desired site such as an intracranial aneurysm. The provision of an open design outside the portion including the plates also limits the coverage of undesired areas of the lumen in which the stent is deployed, for example preventing blockage of the branch arteries adjacent an intracranial aneurysm. Advantageously, the stent is configured to have the same length in the collapsed state as in the expanded state. This assists delivery of the stent to a desired site, in contrast with, for example, a stent having an annular design in which the longitudinal expansion and collapse of the coils hinders accurate longitudinal positioning.

According to a second aspect of the present invention, there is provided a stent arranged as a tube and configured to be deformable between an expanded state and a collapsed state in which the stent has a smaller radius than in the expanded state, the stent comprising a plurality of rings each having a split, the rings being disposed in series along the stent and connected together by intermediate linkages having a lesser circumferential extent than the rings, the rings being configured to deform to reduce in radius when the stent is deformed from the expanded state to the collapsed state. Such a stent in accordance with the second aspect of the invention is capable of providing a good compromise between the desirable characteristics discussed above of having a portion having a large area of coverage which is easily positioned, for example to block an intracranial aneurysm, and on the other hand having sufficient flexibility to prevent damage during delivery. The rings may be arranged to be wide relative to the diameter of the stent in the expanded state and hence to provide a high area of coverage, typically being strips having a width longitudinally along the stent which is greater than their thickness radially. Nonetheless radial collapse is allowed by the split in the rings. The rings do not need a complicated structure such as folds to allow the stent to collapse as the rings may simply take on a tighter degree of curvature. For high degrees of radial collapse, the ends of the rings may overlap in the collapsed state of the stent. Flexibility of the stent is provided by the intermediate linkages having a lesser circumferential extent than the rings.

In practice this means that embodiments in accordance with the second aspect of the present invention designed for treating an intracranial aneurysm are capable of providing a sufficient area of coverage to block the intracranial aneurysm whilst having a good degree of flexibility to facilitate delivery without damage to the arteries, in particular having a higher degree of flexibility than the pleated stents discussed above.

Flexibility may be increased by arranging the intermediate linkages at different circumferential positions, for example arranged at circumferential positions disposed helically around the stent. Advantageously, the stent is capable of being manufactured from a sheet of material cut into the rings and the intermediate linkages. This allows for relatively straightfoward manufacture, for example using laser cutting.

The stent may be made from a wide range of suitable biocompatible materials, for example a metal or a superelastic material. Use of a superelastic material provides particular advantages during delivery of a stent.

To allow better understanding, embodiments of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:

Figs. l to 4 are perspective views of known stents; Fig. 5 is a side view of a known stent;

Fig. 6 is a perspective view of a stent having rings; Fig. 7 is an unwrapped plan view of the stent of Fig. 6;

Fig. 8 is a perspective view showing one of the rings of the stent of Fig. 6 collapsing;

Fig. 9 is a perspective view of a stent having rings;

Fig. 10 is an unwrapped plan view of the stent of Fig. 9; Fig. 11 is a plan view showing the collapse of a part of the structure of a first type of stent;

Figs. 12 to 20 are unwrapped plan views of modified designs of the first type of stent;

Fig. 21 is a plan view showing the collapse of a part of the structure of a second type of stent;

Figs. 22 to 25 are unwrapped plan views of modified designs of the second type of stent Fig. 26 is an unwrapped plan view of the stent of a modified design of the first type of stent;

Fig. 27 is an unwrapped plan view of the stent of a modified design of the second type of stent;

Figs. 28 to 30 are plan views of some alternative constructions of the plates of the stents; Fig. 31 is a plan view of a stent having an modified intermediate linkage; and

Fig. 32 is a plan view of part of the stent of Fig. 31 showing the collapsed and expanded states.

In the following description, for brevity and clarity like elements will be given the same reference numerals and a description thereof will not be repeated. A stent 10 which is an embodiment of the second aspect of the present invention is shown in Fig. 6 which is a perspective view and also in Fig. 7 which is a plan view of the stent shown notionally unwrapped from its actual tubular shape into a flat shape.

The stent 10 is arranged as a tube formed by a plurality of rings 1 1 disposed in series along the stent 10 and connected together by intermediate linkages 14. In general, the stent 10 may have any number of rings 1 1. The stent 10 is formed from a single sheet of material cut to define the rings 1 1 and the intermediate linkages 14. The rings 11 have a width longitudinally along the stent (corresponding to a horizontal width in Fig. 7) which is greater than their thickness radially.

The rings 1 1 are not completely annular but have a split defining each ring as a finite lengths of material having ends 12. In the expanded state shown in Fig. 6, the ends 12 of each ring 1 1 face each other so that each ring 1 1 has a gap 13 therebetween, the diameter of each ring 1 1 being approximately its length divided by π. Each ring 11 is deformable to reduce its radius so that the ends 11 of the ring overlap as viewed along a radial direction, as shown in Fig. 8. By such deformation of the individual rings 1 1, the stent 10 as a whole may be deformed between the expanded state and a collapsed state in which the stent 10 has a smaller radius than in the expanded state.

The intermediate linkages 14 have a lesser circumferential extent (corresponding to a vertical length in Fig. 7) than the rings 11. The intermediate linkages 14 are deformable to provide relative movement of the rings 11 and hence to provide flexibility of the stent 10 as a whole. The lower the circumferential extent of the intermediate linkages 14, the better the flexibility of the stents is. The intermediate linkages typically have a circumferential extent of at most π/8 radians. Conversely, the circumferential extent of the intermediate linkages 14 is chosen to be sufficiently large to make the stent 10 sufficiently durable for its intended use, this depending in part on the material of the stent 10.

In the stent 10 shown in Figs 6 and 7, the intermediate linkages 14 are arranged at the same circumferential position. However this limits the flexing of the stent 10 to a plane perpendicular to the intermediate linkages 14. An alternative which allows flexing in other planes and a greater overall radial strength is for the intermediate linkages 14 to be arranged at different circumferential positions. An example of this is the modified stent 10 shown in Figs 9 and 10, in which the intermediate linkages 14 are arranged at circumferential positions disposed helically around the stent 10. The stent 10 provides a good compromise between the desirable characteristics of, on one hand, having a large area of coverage which is easily positioned, for example to block an intracranial aneurysm, and, on the other hand, having sufficient flexibility to prevent damage during delivery. The rings 1 1 are designed to be wide relative to the diameter of the stent 10 in the expanded state thereby providing a high area of coverage. Nonetheless radial collapse is allowed by the split in the rings 1 1 without the need for a complicated structure such as folds. At the same time, the stent 10 is flexible due to the intermediate linkages 14.

The stent 10 may be designed to treat an intracranial aneurysm. In this case, the stent 10 is provided with sufficient flexibility to be delivered in a collapsed state to the intracranial aneurysm. Here, the stent 10 is deformed into the expanded state in which the rings 1 1 extend across the intracranial aneurysm. The rings 11 have sufficient width to block the intracranial aneurysm. In this context, the blocking is to a sufficient degree to restrain blood flow into the intracranial aneurysm and thereby treat it, rather than completely sealing off the intracranial aneurysm.

A stent 20 which is a first type of embodiment of the first aspect of the present invention will now be described.

There will first be described a portion of the stent 20 shown in Fig. 1 1. The stent 20 comprises a plurality of plates 21 interconnected by linkage members 22. In this case, the plates 21 and the linkage members 22 are connected together alternately in a chain. The stent 20 is formed from a single sheet of material cut to define the plates 21 and the linkage members 22. Thus the plates 21 and the linkage members 22 fit between each other without overlapping and are in the same tubular plane as each other, in the expanded state of the stent 20 (the plane being developed and shown flat in Fig. 11, but actually being tubular because the stent 20 is shaped as a tube). It should be noted that this is the fully expanded state of the stent 20, that is in the absence of any external constraint. In use, the stent 20 may be in a lumen that constrains the expansion so that in the expanded state in the lumen the stent 20 is partly contracted as compared to the fully expanded state shown in the drawings.

In this example, the plates 21 are trapezoid in outer shape having parallel sides extending in a circumferential direction C of the stent 20 perpendicular to a longitudinal direction L of the stent 20, successive plates 21 being arranged in alternating orientations. In this example, the plates 21 are solid plates. The entire stent 20 is shown in Fig. 12 which is a plan view of the stent 20 shown notionally unwrapped from its actual tubular shape into a flat shape. In this example the stent 20 comprises plural chains of plates 21 and linkage members 22 as shown in Fig. 11 interconnected together in the longitudinal direction L of the stent 20 by means of the plates 21 being connected by intermediate linkages 25 extending between the plates 21. In this example, there are three intermediate linkages 25 between each adjacent chain of six plates 21, the intermediate linkages 25 connecting in the middle the longer of the parallel sides of the plates 21. However, a variety of patterns can be obtained by changing the number and positions of the intermediate linkages 25. In general, the stent 20 may have any number of plates 21 in the circumferential direction C and any number of plates 21 in the longitudinal direction L. Referring back to Fig. 11 to illustrate the collapse of the stent 20 on deformation thereof, the linkage members 22 are strips of material which are narrow compared to the size of the plates 21 and which extend in alternating senses between opposite corners of adjacent plates 21. Thus, the linkage members 22 extend transversely to the circumferential direction C.

In the stent 20 of the first type of embodiment, the linkage members 22 are formed by straight arms 23 extending between two joint portions 24 which are curved. The joint portions 24 are each connected to a respective plate 21. The arms 23 extend parallel to the angled ends of the plates 21.

Each individual joint portion 24 is configured to deform to allow movement of the respective plates 21 connected thereto in the circumferential direction C, as shown in Fig. 11. In this example, the arm 23 remains straight with each joint portion 24 providing relative rotation between the arm 24 and a respective plate 21 , so that the arm 24 changes in orientation. Alternative designs could, however, provide flexing of the entire linkage element 22. As the linkage members 22 deform, the plates 21 move in the circumferential direction C, sliding over each other as shown in Fig. 1 1 , to move between the expanded state (uppermost in Fig. 11 ) in which they do not overlap and the collapsed state (lowermost in Fig. 11) in which they do overlap. During the deformation, the length of the chain of plates 21 and linkage members 22 in the circumferential direction C changes when the linkage members 22 deform, with a corresponding change in the radius of the stent 20, the stent 20 having a smaller radius in the collapsed state than in the expanded state. However, the length of the stent 20 in the longitudinal direction L does not change, as can be seen from Fig. 11. The plates 21 are configured to retain their shape on deformation of the stent 20, the linkage members 22 deforming preferentially due to their narrow width with respect to size of the plates 21. Thus the plates 21 do not contribute to the collapse of the stent 20 on deformation and have the primary purpose of providing an area of coverage in the expanded state of the stent 20. Nonetheless, the plates 21 do not hinder the collapse as they slide over each other. In this example, the arm 22 is inclined rearwardly with respect to the direction in which the orientation of the arm 23 changes when the joint portions 24 deform on deformation of the stent 20 from the expanded state to the collapsed state (that is the joint portions 24 are connected to the corners on the shorter parallel sides of the plates 21 in this example). This increases the degree of movement available between the expanded state and the collapsed state, as compared the arm 23 being instead inclined forwardly (that is with the joint portions 24 instead connected to the corners on the longer parallel sides of the plates 21 in this example).

The stent 20 provides a good compromise between the desirable characteristics of, on one hand, having a large area of coverage which is easily positioned, for example to block an intracranial aneurysm, and, on the other hand, having sufficient flexibility to prevent damage during delivery. The plates 21 provide the desired high area of coverage, whilst the linkage members 22 provide radial collapse. The linkage members 22 and intermediate linkages 25 together also provide a good degree of flexibility for the stent 20 as a whole. This is achieved without the need for a complicated structure such as folds.

Numerous modifications to the stent 20 are possible, for example as follows. Fig. 13 shows a modification to the example of Fig. 12 in which the plates 21, instead of being solid plates, comprise a frame 26 defining a central aperture 27. The plate 21 has the same shape as in the example of Fig. 12, but the central aperture 27 is cut out from the sheet of material forming the plates 21 to leave the frame 26 around the outer periphery of the plate 21. In this example the frame 26 forms a loop which increase the strength of the plate 21, but this is not essential.

In principle, the central aperture 27 could be left open, although this reduces the surface area of the plate 21. On the other hand, the frame 26 advantageously supports a material 28 extending across the central aperture 27 different from the material of the frame 26. The material 28 ensures the plate 21 including the central aperture 27 has the same areas as if it was a solid plate. However, the use of the central aperture 27 and material 28 allows the physical properties of the plate to be adapted. For example the material 28 may have a higher flexibility than the material of the frame 27, thereby increasing the flexibility of the plate 21 as compared to a solid plate. This can increase the ability of the plates 21 to deflect and slide over each other conformally.

Fig. 14 shows a modification to the example of Fig. 12 in which the plates 21 are modified to be formed as a primary platelet 29 which is connected to the linkage members 22 and two secondary platelets 30 each connected to the primary platelet by a respective joint 31. The primary platelet 29 and secondary platelets 30 are in this example each triangular in outer shape fitting together so that the overall outer shape of the plate 21 is generally trapezoid as in the example of Fig. 12. The joints 31 extends between one side of the primary platelet 29 and one side of a respective secondary platelet 30. In this example, there are two secondary platelets 30 having a single joint 31 in the middle thereof, but a variety of patterns can be obtained by changing the number and positions of the joints 31.

The joints 31 are narrower than the primary platelet 29 and secondary platelet 30 so as to allow radial deformation of the secondary platelet 30 with respect to the primary platelet 29. This assists in sliding of the secondary platelet 30 and hence the plate 21 as a whole over the adjacent plate 21.

Fig. 15 shows a modification to the example of Fig. 14 in which the plates 21 are modified so that the primary platelet 29 and secondary platelets 30 each comprise a frame 26 defining a central aperture 27, as described above with respect to the example of Fig. 13.

Fig. 16 shows a modification to the example of Fig. 12 in which each unit of two plates 21 interconnected by an intermediate linkage 25 is replaced by a single plate 32. The plate 32 is hexagonal in outer shape, this being equivalent to the outer shape of two adjacent plates 21 which are trapezoid in Fig. 12. Otherwise, the stent 20 has the same configuration is in Fig. 12, so that each plate 33 (except at the longitudinal ends of the stent 20) is connected by two intermediate linkages 25 to two plates 33, the plates 33 being arranged in a hexagonal lattice. Fig. 17 shows a modification to the example of Fig. 16 in which the plates 32 are modified to each comprise a frame 26 defining a central aperture 27, as described above with respect to the example of Fig. 13.

Fig. 18 shows a modification to the example of Fig. 14 in which each unit of two plates 21 interconnected by an intermediate linkage 25, is replaced by: a primary platelet 33 which replaces two adjacent primary platelets 29 in Fig. 14, and a secondary platelet which replaces tow adjacent secondary platelets in Fig. 14. The primary platelet 33 is rhomboid in outer shape, this being equivalent to the outer shape of two adjacent primary platelets 29 which are trapezoid in Fig. 12. The secondary platelet 34 is rhomboid in outer shape, this being equivalent to the outer shape of two adjacent secondary platelets 30 which are trapezoid in Fig. 12. The secondary platelet 34 is connected to two primary platelets 33 by respective joints 31 (except at the longitudinal ends of the stent 20) to allow radial deformation of the secondary platelet 34 with respect to the primary platelet 35, as in the example of Fig. 14 as described above.

Fig. 19 shows a modification to the example of Fig. 18 in which the primary platelets 29 and secondary platelets 34 are modified to each comprise a frame 26 defining a central aperture 27, as described above with respect to the example of Fig. 13. Fig. 20 shows a modification to the example of Fig. 12 in which the stent 20 has a slit 35 extending longitudinally along the stent 20. The slit 35 divides a plate 21 in each chain into two parts 21a and 21b. The slit 35 provides the stent 20 with and additional degree of freedom, in a similar manner to the stent 20 shown in Fig. 6. In particular the slit 35 increases the flexibility of the stent 20, albeit at the cost of reducing rigidity, and also allows collapse of the stent 20 to be accommodated in part by overlap of the parts of the stent 20 on each side of the slit 35, as well as by deformation of the type illustrated in Fig. 11.

Whilst a number of different configurations and patterns for the stent 20 have been illustrated, this is by no means limitative and indeed a large variety of patterns can be achieved by using different combinations of differently shaped plates, which need not be uniform over the stent 20.

A stent 40 which is a second type of embodiment of the first aspect of the present invention will now be described.

There will first be described a portion of the stent 40 shown in Fig. 21. The stent 40 comprises a plurality of plates 41 interconnected by linkage members 42. In this case, the linkage members 42 are connected together in a chain, with the plates 41 each connected thereto. The stent 40 is formed from a single sheet of material cut to define the plates 41 and the linkage members 42. Thus, the plates 41 and the linkage members 42 fit between each other without overlapping and are in the same tubular plane as each other, in the fully expanded state of the stent 40 shown in Fig. 21. In this example, the plates 41 are triangular in outer shape and arranged along a circumferential direction C of the stent 40 perpendicular to a longitudinal direction L of the stent 20. In the example of Fig. 21, the plates 41 are solid plates.

The entire stent 40 is shown in Fig. 22 which is a plan view of the stent 40 shown notionally unwrapped from its actual tubular shape into a flat shape. In this example, the plates 40 are modified as compared to the example of Fig. 21 to each comprise a frame 46 defining a central aperture 47, optionally supporting a material 48 that extends across the aperture 47, as described above with respect to the example of Fig. 13. Also, in this example the stent 40 comprises plural chains of linkage members 42 as shown in Fig. 21 interconnected together in the longitudinal direction L of the stent 40 by means of the linkage members 42 of each chain being connected by intermediate linkages 43 extending therebetween. The intermediate linkage 43 is formed as an arcuate member connected to the chains of linkage members 42 at the same circumferential position.

In this example, there are two intermediate linkages 43 between each adjacent chain of twelve linkage members 42 supporting six plates 41. However, a variety of patterns can be obtained by changing the number and positions of the intermediate linkages 43. By way of example, Fig. 23 illustrates a modification with three intermediate linkages 43 between each adjacent chain of twelve linkage members 42. In general, the stent 40 may have any number of plates 41 in the circumferential direction C and any number of plates 41 in the longitudinal direction L. The number of intermediate linkages 43 provided circumferentially, the shapes of the intermediate linkages 43 and the arrangement of the intermediate linkages 43 are changeable so that different mechanical performance can be achieved. For example, for better longitudinal flexibility, the number of intermediate linkages 43 circumferentially is reduced and also intermediate linkages 43 with longer nominal lengths are preferable. For smaller gaps, employing more intermediate linkages 43 circumferentially may help and also the intermediate linkages 43 can be arranged in helically progressing positions. Referring back to Fig. 21 to illustrate the collapse of the stent 40 on deformation thereof, the linkage members 42 are strips of material which are narrow compared to the size of the plates 41. Each linkage members 42 comprises two straight legs 44 connected together at their proximal ends by a joint portion 45 which is curved. The legs 44 are connected together at their distal ends to form the chain of linkage portions 42. Each leg 44 is also connected to a respective plate 41 at its distal end by an joint 49. The plates 41 are triangular in outer shape and the legs 42 extend parallel to the angled edges of the plates 41 in a zig-zag pattern in the expanded state of the stent 40. Thus the legs 42 extend transversely to the circumferential direction C. It is also noted that the legs 44 are each inclined rearwardly with respect to the direction in which the orientation of the legs 44 changes when the joint portions 45 deform on deformation of the stent 40 from the expanded state to the collapsed state.

Each individual joint portion 45 is configured to deform to allow movement of the respective plates 41 connected thereto in the circumferential direction C, as shown in Fig. 21. In this example, the legs 44 remain straight with each joint portion 45 providing relative rotation between the legs 44, so that the legs 44 change in orientation. Alternative designs could, however, provide flexing of the entire linkage member 42. As the linkage members 42 deform, the plates 41 move in the circumferential direction C, sliding over each other as shown in Fig. 21, to move between the expanded state (uppermost in Fig. 21) in which they do not overlap and the collapsed state (lowermost in Fig. 21) in which they do overlap. During the deformation, the length of the chain of linkage members 42 in the circumferential direction C changes when the linkage members 42 deform, with a corresponding change in the radius of the stent 40, the stent 40 having a smaller radius in the collapsed state than in the expanded state. However, the length of the stent 20 in the longitudinal direction L increases due to the change in orientation of the legs 44 increasing the distance between the joint portions 45, as can be seen from Fig. 21.

The plates 41 are configured to retain their shape on deformation of the stent 40. Thus the plates 41 do not contribute to the collapse of the stent 40 on deformation and have the primary purpose of providing an area of coverage in the expanded state of the stent 40. Nonetheless, the plates 41 do not hinder the collapse as they slide over each other. As a result of the joint 49 being narrower than the plate 41, the joint 49 is sufficiently deformable to allow the plates 41 to slide over one another. The joint 49 may deform during collapse of the stent 40 and/or be pre-deformed. Thus the stent 40 of the second type has a similar effect to the stent 20 of the first type, but in general terms has the advantage providing a more compact collapsed state, as well as being providing for more easy sliding of the plates 41 due to the plates 41 being connected to, and not within, the chain of linkage members 42.

As with the stent 20 of the first type, the stent 40 of the second type provides a good compromise between the desirable characteristics of, on one hand, having a large area of coverage which is easily positioned, for example to block an intracranial aneurysm, and, on the other hand, having sufficient flexibility to prevent damage during delivery. The plates 41 provide the desired high area of coverage, whilst the linkage members 42 provide radial collapse. The linkage members 42 and intermediate linkages 43 together also provide a good degree of flexibility for the stent 40 as a whole. This is achieved without the need for a complicated structure such as folds. Although in the examples of Figs. 22 and 23 each leg 44 is connected to a respective plate

41 by a single joint 49 at the distal end of the leg 44 this is not essential and in general the joints may be changed in number, location and size. By way of example, Figs. 24 and 25 each show a modification to the example of Fig. 22 in which the plate 41 is modified to be connected to the leg 44 by two joints 49 each connected to a leg 44 at a position shifted closer to the joint portion 45. Furthermore, the frame 46 extends only between the two joints 49, rather than in a complete loop, so that the plates 41 are effectively formed in part by the legs 44 (or similarly one may consider that the legs 44 are formed by an edge of the plate).

The example of Fig. 25 is further modified to include six intermediate linkages 43 between each adjacent chain of twelve linkage members 42, so that all the linkage members 42 between two adjacent chains are connected. On one hand, this arrangement can provide a more uniform change of shape when the stent 40 is bent, as compared to when less intermediate linkages 43 are provided. The length of the intermediate linkages 43 is also increased in this example to improve the longitudinal flexibility.

The stent 20 or 40 of either type may be designed to treat an intracranial aneurysm. In this case, the stent 20 or 40 is designed to have sufficient flexibility to allow delivery in a collapsed state to the intracranial aneurysm. Here, the stent 20 or 40 is deformed into the expanded state in which the plates 21 or 41 extend across the intracranial aneurysm. The plates 21 or 41 have sufficient area to block the intracranial aneurysm. In this context, the blocking is to a sufficient degree to restrain blood flow into the intracranial aneurysm and thereby treat it, rather than completely sealing off the intracranial aneurysm. Typically, this may be achieved by, in the expanded state of the stent 20 or 40, the plates 21 or 41 encompassing overall an area of the total area of the stent 20 or 40 (or the portion of the stent 20 or 40 in which they are formed) which is as high as possible, typically at least 50%, preferably at least 75%.

In the stents 20 and 40 described above, the plates 21, 32 or 41 and linkage members 22 or 42 extend over the entirety of the stent 20 or 40. As an alternative, the plates 21, 32 or 41 and linkage members 22 or 42 may extend over only a portion of the stent 20 or 40. The stent 20 shown in Fig. 26 and the stent 40 shown in Fig. 27 are examples of this.

In particular, Fig. 26 shows a modification of the stent 20 shown in Fig.17 in which a group of seven plates 32 are arranged in a hexagonal array extending over a central portion 36 of the stent 20. The remainder 37 of the stent 20 has a deformable structure which is more open than the central portion 36, whilst still being deformable between expanded and collapsed states. In particular, the remainder 37 of the stent 20 comprises a series of linkage rings 38 disposed in series longitudinally along the stent 20. Each linkage ring 38 comprises a strip of material with a zig-zag structure which on deformation can collapse and expand in the circumferential direction C with a corresponding change in the radius of the stent 20. The linkage rings 38 are interconnected by intermediate linkages 39. It is noted that the linkage rings 38 in this example have an identical structure to the chain of linkage members 42 in the stent 40 shown in Fig. 22. However this is not essential. The remainder 37 of the stent 20 in general have any structure capable of deformation between expanded and collapsed states, a wide variety of such structures being possible.

Similarly, Fig. 27 shows a modification of the stent 40 shown in Fig.23 in which a group of twenty eight plates 41 are arranged in an array extending over a central portion 49 of the stent 40. The remainder 50 of the stent 40 has the same deformable structure as the remainder 37 of the stent 20 described above, this being is more open than the central portion 36 whilst still being deformable between an expanded and collapsed state.

Such designs in which the plates 21, 32 or 41 and linkage members 22 or 42 extend over only a portion of the stent 20 or 40 have particular application for the treatment of an intracranial aneurysm. In this case, in use the stent 20 or 40 is delivered with the central portion 36 or 49 having a relatively high surface area covering the aneurysm. Although requiring greater accuracy in positioning, this modification to the stent 20 or 40 has the advantages that the stent 20 or 40 as a whole has greater flexibility and that the open design of the remainder of the stent 20 or 40 prevents blockage of branch arteries adjacent the aneurysm.

There are numerous possible variations to the construction of the plates. There follows some examples that may be applied to any of the stents described above.

The plates may be formed from the same material as the linkage members, as in some of the embodiments described above, for example the embodiments of Figs. 11 and 12. The plates may have various different shapes. The plates may, instead of being continuous, have an open structure. For example the plates may comprise strips of material with gaps therebetween.

Examples of this are shown in Figs. 29 and 30. In the example of Fig. 29, the plates 61 comprise a set of parallel strips 62 with gaps therebetween extending from a linkage member. In the example of Fig. 30, the plates 63 comprise a continuous strip 64 extending alternately back and forth so that sections thereof constitute a set of parallel strips 65 with gaps therebetween. As an alternative, the plates may comprise a sheet of different material from the material of the linkage members, for example a material that is less stiff than the linkage members in order to increase the flexibility of the plates.

Above there are described examples where the plates each comprise a frame supporting a sheet of different material extending across an aperture in the frame. The frame may take other shapes suitable for supporting such a sheet. For example as shown in Fig. 28, the plates 51 may comprise a strut 52 that protrudes from the linkage members and supports a sheet of material 53 extending laterally from the strut 52. Alternatively, the plates may be formed by a different sheet of material attached directly to the linkage members without any supporting frame.

The intermediate linkages 39 and 43 may also be modified. Fig. 31 shows an example of the stent 40 including an alternative intermediate linkage 70. The intermediate linkage 70 is connected directly to the plates 41 instead of the linkage members 42, but is connected at different circumferential positions to the plates 41 arranged at different longitudinal positions. As a result, the intermediate linkage 70 changes orientation on circumferential collapse as shown in Fig. 32, so that the relative longitudinal movement of the plates is taken up by the change in orientation of the intermediate linkage 70. As a result, the distance between two chains of plates in the longitudinal direction L does not experience much change in the collapsed and expanded states, minimising the overall change in the length of the stent 40 before and after collapse. The nominal length of each intermediate linkage 70 is maximized for good longitudinal flexibility. Meanwhile the stent 40 can have a uniform deformed shape under bending because the adjacent chains of plates 41 are fully connected by the intermediate linkage 70.

The stent 10, 20 or 40 may be manufactured from a sheet of material from which the structures described above are cut. The cutting may be performed, for example and without limitation, by laser cutting which can provide the desired accuracy in a straightforward manner. The cutting is performed to produce the stent 10, 20 or 40 in its fully expanded state. In the case of the stents 20 and 40, in this fully expanded state the plates 21, 32 or 41 and the linkage members 22 and 42 do not overlap. The sheet of material may initially be formed as a tube, for example by extrusion. In this case, the cutting is performed directly on the tube. Alternatively, the sheet of material may initially be formed as a flat sheet, which is subsequently curved into a tube and joined along the facing edges, for example by laser welding. In this case, the cutting may be performed on the flat sheet before joining or on the joined tube. When performed on the flat sheet before joining, the cutting may be performed, for example and without limitation, by chemical etching.

After cutting in the expanded state, the stent 10, 20 or 40 is crimped to collapse it into the collapsed state ready for delivery. The stent 10, 20 or 40 may be stored in a sheath to maintain the collapsed state. The material of the sheet may in general be any biocompatible material, for example a metal, for example 316L stainless steel. Generally, a biocompatible material is selected with appropriate mechanical properties for the site at which the stent 10, 20 or 40 is to be used. The sheet may be a unitary piece of material or a multi-layer material. The sheet may or may not be coated with a substance for adapting the physical properties of the stent 10, 20 or 40 and/or with a medicament which the stent 10, 20 or 40 thus delivers.

One advantageous type of material is a superelastic material, for example a shape memory alloy, for example Nitinol. One of the advantages of the design of the stent 10, 20 or 40 is that the maximum deformation of the material is within the limits allowing construction from such a superelastic material, e.g. Nitinol. The use of a superelastic material has the advantage that the stent 10, 20 or 40 may be self-expanding in situ. In particular, the material is selected so that it is in the superelastic state at the temperature in situ (body temperature). After manufacture, the stent 10, 20 or 40 is deformed into the collapsed state at a temperature at which the material is plastic, thereby facilitating the deformation. Thus, at body temperature, the phase change in the material causes deformation into the collapsed state, this being prevented in the interim by packaging the stent 10, 20 or 40 in a sheath.

In the case of stents 20 or 40 where the stent has plates comprising a different material from the linkage members, that different material may again in general be any biocompatible material. As discussed above, the material may be selected to have a higher degree of flexibilty than the sheet forming the main structure of the stent. The material may also or alternatively be selected to have other properties, for example to act as a carrier or a medicament. In many applications, the material may be a polymer. The material may be applied by any suitable method for example dip-coating. If the method results in the stent being encased in the material, it might be need to be cut away from the portions of the stent between the plates and the linkage members, for example by laser cutting. In the embodiments described above the plates and the linkage members fit between each other without overlapping and are in the same tubular plane as each other, in the expanded state of the stent. As already described, this facilitates manufacture. However, as an alternative, the stent 20 or 40 may be manufactured without the plates and the linkage members fitting between each other without overlapping and without being in the same tubular plane, for example by attaching plates to the outside of the linkage members, e.g. by welding.

The stent 10, 20 or 40 may be delivered in its compressed state enclosed in a sheath using conventional techniques, typically using a catheter. Once the stent 10, 20 or 40 has been delivered, the sheath is removed and the stent 10, 20 or 40 is deformed into an expanded state, either by using an inflatable balloon or by the phase change in the case of superelastic material as described above.