Stent and stent delivery system

A stent and a stent delivery system are configured to exhibit good slip strength, flexibility, and expandability. The stent includes a plurality of wave-shaped struts positioned at intervals in the circumferential direction of the stent, and a plurality of connecting struts positioned between the wave-shaped struts. Each of the wave-shaped struts extends from one end to the other end in the axial direction, and has proximate portions that form portions in the vicinity of an adjacent wave-shaped strut, distant portions that form portions away from the adjacent wave-shaped strut, and straight portions that connect the proximate portions and the distant portions. The straight portions extend in the circumferential direction of the stent in a state in which the stent is mounted on the balloon. The connecting struts connect to each other the distant portions of adjacent wave-shaped struts.

TECHNICAL FIELD

The present invention generally relates to a stent and a stent delivery system.

BACKGROUND DISCUSSION

A stent delivery system, which is a medical device used to improve a stenosis or occlusion generated in the lumen in vivo, is provided with a dilatable balloon positioned on the outer periphery of the distal portion of a hollow shaft portion, and a stent positioned on the outer periphery of the balloon and having wave-shaped struts that are expanded by the dilatation of the balloon. After reaching a target region (stenosis or occlusion), the stent, which is mounted on the balloon by caulking with its diameter being reduced, is plastically deformed by the dilatation of the balloon and is indwelled in a state of being in close contact with the inner surface of the target region.

The wave-shaped struts of a conventional stent extend in the circumferential direction of the stent and are multiply positioned at intervals in the axial direction of the stent, each of the wave-shaped struts including proximate portions that form portions in the vicinity of an adjacent wave-shaped strut, distant portions that form portions away from the adjacent wave-shaped strut, and straight portions that connect the proximate and distant portions. The proximate portions of adjacent wave-shaped struts are connected by connecting portions.

Since the straight portions of the wave-shaped strut extend in the axial direction of the stent in a state in which the stent is mounted on the balloon, the above-described stent has the problem of being prone to slip along the axial direction of the balloon. The entire stent also has the problem of insufficient flexibility (compliance with the curvature of the lumen in vivo) due to a large difference in stiffness between the wave-shaped struts and the connecting portions.

In view of the improvement in flexibility, extension of the wave-shaped struts in the axial direction of the stent may, for example, reduce the difference in stiffness in the axial direction of the stent (for example, see Japanese PCT National Publication No. 2008-516668, the contents of which are hereby incorporated by reference.)

However, since the proximate portions of adjacent wave-shaped struts in the stent described in Japanese PCT National Publication No. 2008-516668 are directly connected to each other, the proximate portions are hardly deformed even if the stent is expanded by a balloon, and thus the stent may not be expanded well.

SUMMARY

An aspect of the disclosure here involves a stent mounted on an outer periphery of a dilatable balloon and configured to be expanded by dilatation of the balloon, the stent including a plurality of wave-shaped struts positioned at intervals in a circumferential direction of the stent, and a plurality of connecting struts positioned between the wave-shaped struts. Each of the wave-shaped struts extends from one end to the other end in an axial direction of the stent, and has proximate portions that form portions in the vicinity of an adjacent wave-shaped strut, distant portions that form portions away from the adjacent wave-shaped strut, and straight portions that connect the proximate and distant portions. The straight portions extend in the circumferential direction of the stent in a state in which the stent is mounted on the balloon, and the connecting struts connect the distant portions of the adjacent wave-shaped struts to each other.

Another aspect of the disclosure involves a stent delivery system that includes a balloon catheter having a hollow shaft portion and a dilatable balloon positioned on an outer periphery of a distal portion of the shaft portion, and the stent mounted on the balloon and configured to be expanded by the dilatation of the balloon.

According to the disclosure here, the wave-shaped struts, which extend from one end to the other end in the axial direction of the stent, reduce a difference in stiffness in the axial direction of the stent, and improve flexibility of the entire stent. The straight portions of the wave-shaped strut, which extend in the circumferential direction in a state in which the stent is mounted on the balloon, suppress the occurrence of a slip of the stent along the axial direction relative to the balloon. In addition, since the distant portions of adjacent wave-shaped struts are connected indirectly through the connecting struts, the adjacent straight portions or the adjacent proximate portions in the axial direction of each of the wave-shaped struts hardly come into contact with each other when the balloon is dilated, and the stent is expanded well. Thus, a stent and a stent delivery system having good slip strength, flexibility, and expandability can be provided.

The connecting struts preferably extend straight in the circumferential direction of the stent. In this case, slippage of the stent along the axial direction relative to the balloon can be more reliably suppressed. The distant portions connected by the connecting struts are preferably disposed at one end and/or the other end of the stent. Hence, since the connecting struts extending in the circumferential direction of the stent are located at the ends of the stent and a separation of the ends of the stent from the balloon decreases, the occurrence of the ends of the stent curling away from the balloon is suppressed while passing through a path to a target region.

The connecting strut is preferably connected in the center of each of the distant portions with respect to the axial direction of the stent, and only parts of the distant portions are more preferably connected by the connecting struts. With respect to the axial direction of the stent, the length of the distant portion connected by the connecting strut is particularly preferably greater than the length of the distant portion that is not connected by the connecting strut. In this case, the distant portions in addition to the proximate portions are easily deformed based on the dilatation of the balloon, and thus the stent is more easily expanded.

The straight portion is preferably extended such that a crossing angle relative to the axial direction of the stent is 45 degrees or more and 90 degrees or less, more preferably the crossing angle is 60 degrees or more and 90 degrees or less, and particularly more preferably the crossing angle is 90 degrees. In this case, the occurrence of a slip of the stent along the axial direction relative to the balloon can be more effectively suppressed.

The stent and a stent delivery system disclosed here exhibits good slip strength, flexibility, and expandability.

Other features, characteristics and aspects of the stent and a stent delivery system will become apparent from the following detailed description considered with reference to the accompanying drawings.

DETAILED DESCRIPTION

As illustrated inFIG. 1, a stent delivery system100according to one embodiment disclosed by way of example, which is used to improve a stenosis (or occlusion)182in a lumen180in vivo (seeFIG. 2), includes a hollow shaft tube (shaft portion)160, a balloon130positioned on the outer periphery of the distal portion of the shaft tube160, a stent120mounted on the balloon130, and a hub140located at the proximal end of the shaft tube160.

The lumen180in vivo is, for example, a coronary artery of the heart, and one of the purposes of indwelling the stent120is to prevent restenosis after percutaneous transluminal coronary angioplasty (PTCA).

The stent120, which is mounted on the outer periphery of the balloon130, has a good “slip strength”, “flexibility” and “expandability”. With respect to stent120, “slip strength” means that there is sufficient difficulty in the occurrence of a slip along the axial direction of the stent relative to the balloon, “flexibility” means that there is compliance with the curvature of the lumen180, and “expandability” means the ease of expansion by the dilatation of the balloon. The stent120is used to maintain the patency of the lumen180by being indwelled on the inner surface of the stenosis182in close contact therewith.

The balloon130, which is dilatable, is configured to expand the stent120mounted on the outer periphery thereof to increase its diameter. The stent120is mounted on the balloon130by caulking (engaging) with its diameter in a reduced state, and this thereby suppresses slip of the stent120relative to the balloon130and its “peeling” (i.e., separation) away from the balloon130.

The hub140has an injection port142and a guide wire port144. The injection port142is used, for example, to introduce and discharge pressurized fluid to dilate the balloon130. The pressurized fluid is a liquid such as saline or an angiographic contrast agent. The guide wire port144is used to insert a guide wire150into the shaft tube160to protrude the guide wire150beyond the distal end portion of the shaft tube160.

The stent120is indwelled, for example, in the following manner:

The distal end portion of the stent delivery system100is first inserted into the lumen180of a patient, and is positioned at the stenosis182, i.e. a target region, with the guide wire150therein that has already been protruded in advance beyond the distal end portion of the shaft tube160. Introducing the pressurized fluid through the injection port142then dilates the balloon130, and causes the expansion and plastic deformation of the stent120to bring the stent120into close contact with the stenosis182(seeFIG. 2). The balloon130is next depressurized to release the engagement between the stent120and the balloon130, and the stent120is separated from the balloon130. The stent120is thus indwelled in the stenosis182while being plastically deformed. The stent delivery system100, from which the stent120has been separated, is finally moved backward and removed from the lumen180.

One skilled in the art will appreciate that the stent delivery system100is not limited to the disclosed embodiment as being applied to a stenosis generated in a coronary artery of the heart, and that the stent delivery system100can also be applied to a stenosis generated in other blood vessels, bile duct, trachea, esophagus, urethra and the like.

The distal portion of the stent delivery system100will now be described in detail.

FIG. 3is a sectional view illustrating the distal portion of the stent delivery system illustrated inFIG. 1.

The balloon130is positioned on the outer periphery of the distal portion of the shaft tube160along its axial direction A in a folded state (or contracted state), and is dilatable. Since the stent120is mounted on the outer periphery of the balloon130, strut bodies122(shown inFIG. 4) of the stent120are expanded by the dilatation of the balloon130.

The material forming the balloon130is preferably one of those having flexibility, such as polyolefin, polyvinyl chloride, polyamide, polyamide elastomer, polyurethane, polyesters such as polyethylene terephthalate, polyarylene sulfide such as polyphenylene sulfide, silicone rubber, and latex rubber. Examples of the polyolefin include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and cross-linked ethylene-vinyl acetate copolymer.

The shaft tube160includes an inner tube162and an outer tube164into which the inner tube162is inserted. The inner tube162, which is in communication with the guide wire port144of the hub140, extends through the balloon130to a distal end. Thus, the guide wire150inserted into the guide wire port144is protrudable beyond the distal end of the stent delivery system100, and the interior of the inner tube162constitutes a lumen161for the guide wire.

The outer periphery of the inner tube162, disposed within the interior of the balloon130as shown inFIG. 3, is provided with cylindrical markers170. The cylindrical markers170, which are made of a radiopaque material, provide a clear angiogram under X-ray fluoroscopy, and thus allow the positions of the balloon130and the stent120to be easily confirmed. Examples of the radiopaque material include platinum, gold, tungsten, iridium, and an alloy thereof.

The outer tube164is disposed outside the inner tube162. A lumen163, which is defined by a space between the inner peripheral surface of the outer tube164and the outer peripheral surface of the inner tube162, is in communication with the injection port142of the hub140. The balloon130is fixed in a liquid-tight manner on the outer periphery of the distal end portion of the outer tube164, and the interior of the balloon130is in communication with the lumen163. Thus, the pressurized fluid introduced from the injection port142passes through the lumen163and is introduced into the balloon130, thereby allowing the balloon130to be dilated. A method of fixing the balloon130to the outer periphery of the distal end portion of the outer tube164is not particularly limited, and for example, an adhesive or heat-sealing may be applied thereto.

The material constituting the outer tube164is preferably one having flexibility, for example, polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, a mixture of two or more of these, thermoplastic resin such as soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyester, polyester elastomer, polyurethane, fluorine resin, silicone rubber, and latex rubber.

The material constituting the inner tube162may be the same material as the outer tube164or a metallic material. The metallic material may be, for example, stainless steel or Ni—Ti alloy.

In addition, the material constituting the hub140(seeFIG. 1) may be, for example, thermoplastic resin such as polycarbonate, polyamide, polysulfone, polyarylate, and methacrylate-butylene-styrene copolymer.

The stent120will now be described in detail.

FIG. 4is a developed view illustrating an initial state of the stent illustrated inFIG. 3.FIG. 5is a developed view illustrating an expanded state of the stent.FIG. 6is an explanatory view illustrating the deformation of the stent from the initial state to the expanded state.

In a state (initial state) of being mounted on the balloon130, the stent120includes, as illustrated inFIG. 4, a plurality of wave-shaped strut bodies (wave-shaped struts)122positioned at intervals in the circumferential direction C, and a plurality of connecting struts128positioned between the strut bodies122. The strut bodies122extend from one end120A to the other end120B in the axial direction A, each of the strut bodies122having proximate portions123, distant portions124,125and straight portions126.

The proximate portions123and the distant portions124,125are portions that are in the vicinity of and away from an adjacent strut body122, respectively. The straight portions126connect the proximate portions123with the distant portions124,125and extend in the circumferential direction C. The proximate portions123and the distant portions124,125, which are turning portions of the straight portions126, have curved (bent) shapes.

The connecting strut128extends straight in the circumferential direction C, and connects the distant portions124of adjacent strut bodies122to each other. Thus, the strut bodies122and the connecting struts128constitute an annular body as a unit. Note that the proximate portions123of adjacent strut bodies122are not connected to each other at all.

As described above, the strut bodies122extend from the one end120A to the other end120B in the axial direction A. This reduces the difference in stiffness in the axial direction A, and improves flexibility of the entire stent120.

The straight portions126of the strut body122, which as described above extend in the circumferential direction C in a state in which the stent120is mounted on the balloon130, suppress the occurrence of slippage of the stent120along the axial direction A relative to the balloon130such that it exhibits good slip strength. This inhibits the stent120from dropping-off of the balloon130, for example, while the distal end portion of the stent delivery system100passes through a stenosis.

Since the distant portions124of adjacent strut bodies122are indirectly connected to each other via the connecting struts128, the straight portions126and the proximate portions123that are adjacent in the axial direction A of each of the strut bodies122have minimal contact and thus do not interfere with each other when the balloon130is dilated. As a result, the stent120expands well.

The distant portions124connected by the straight connecting struts128are disposed at the one end120A and the other end120B of the stent. That is, since the connecting struts128extending straight in the circumferential direction C are located at the ends of the stent, separation (curling) away from the balloon130decreases. The occurrence of curling away from the balloon130at the ends of the stent is thus suppressed while passing through a path to a target region. For example, difficulty when the distal end portion of the stent delivery system100passes through bent and meandering blood vessels is reduced. A risk that the stent120is caught, for example, in the stenosis182and drops off is also reduced.

This configuration is also advantageous to manufacture the stent delivery system100: The occurrence of curling away from the balloon130at the ends of the stent is suppressed when the stent120is mounted on the balloon130. The distant portions124connected by the connecting struts128may be disposed only at the one end120A of the stent, if necessary.

The connecting struts128connect only part of the distant portions124(connected to every third portion in the configuration illustrated inFIG. 4), and the strut body122has the distant portions125that are not connected by the connecting struts128. Accordingly, the distant portions125that are not connected by the connecting struts128, in addition to the proximate portions123, are also easily deformed by the dilatation of the balloon130and thus the stent is easily expanded.

The connecting strut128is connected to the center of the distant portion124with respect to the axial direction A, and a length L1 of the distant portion124connected by the connecting strut128is greater than a length L0 of the distant portion125that is not connected by the connecting strut128. Accordingly, the distant portions124connected by the connecting struts128are also deformed by the dilatation of the balloon130, and thus the stent is easily expanded.

The connection position of the connecting strut128is not limited to the center. The ratio between the respective lengths L1 and L0 of the distant portions124and125is not particularly limited, but preferably in the range of L0:L1=1:1.5 to 1:4.0. The shape of the connecting strut128is not limited to being straight, and it may also have a bent or wavy shape.

In order to effectively suppress the occurrence of a slip of the stent120along the axial direction A relative to the balloon130, the straight portion126and the connecting strut128are preferably extended such that a crossing angle relative to the axial direction A is 45 degrees or more and 90 degrees or less, i.e., between 45-90 degrees, and more preferably the crossing angle is 60 degrees or more and 90 degrees or less, i.e., between 60-90 degrees, and particularly more preferably the crossing angle is 90 degrees.

When the stent120is indwelled on, for example, the inner surface of the stenosis182in close contact therewith, the stent120is expanded (its diameter is increased) by the dilatation of the balloon, and the shape changes from the shape illustrated inFIG. 4to the shape illustrated inFIG. 5.

In this case, the expansion direction is consistent with the extending direction of the connecting struts128, while the expansion direction intersects the extending direction of the proximate portions123and the distant portions124of the strut body122. Therefore, the connecting struts128are difficult to deform, but the proximate portions123and the distant portions124are easily deformed. Also, as shown inFIG. 5, the straight portions126and the proximate portions123adjacent in the axial direction A minimally contact or interfere with each other when they are expanded by the balloon.

More specifically, as illustrated inFIG. 6, the shapes of the connecting struts128(128A to128H) before and after the expansion are nearly the same and without significant change, while the strut bodies122(122A to122H) disposed between the connecting struts128, which strut bodies122include the proximate portions123, the distant portions124,125and the straight portions126, are significantly distorted and, for example, the straight portions126become inclined in the axial direction A. As a result, the length in the axial direction A of the stent120is reduced according to the amount of expansion of the stent diameter. Whether the entire stent120can be expanded uniformly may be studied using, for example, the finite element method (FEM).

FIGS. 7 and 8are developed views illustrating first and second modifications according to further embodiments of the disclosure, respectively.

The position of connection between the distant portions124using the connecting struts128is not limited to every third distant portion illustrated inFIG. 4. For example, the connecting struts128may connect every fifth distant portion124(seeFIG. 7) or all the distant portions124(seeFIG. 8).

A method of forming the strut body122and the connecting strut128is not particularly limited. For example, based on a strut pattern, e.g., the patterns of the strut body122and the connecting strut128, the strut body122and the connecting strut128may be formed by laser-cutting the outer periphery of a stent material, or by placing a masking material corresponding to the strut pattern on the outer periphery of the stent material and performing etching.

According to the exemplary embodiments as described above, a stent and a stent delivery system having good slip strength, flexibility, and expandability can thus be provided.

The disclosure here is not limited to the above-described exemplary embodiments, and may be variously modified within the scope of the claims. For example, a balloon catheter is not limited to the over-the-wire (OTW) type, and the rapid exchange (RX) type may also be applied thereto.

The stent may be made of a biodegradable polymer that is decomposed and absorbed over time in vivo, or may be coated on its surface with a drug such as a physiologically active substance. The biodegradable polymer is, for example, polylactic acid, polyglycolic acid, or copolymer of lactic acid and glycolic acid. The physiologically active substance is, for example, an anti-cancer agent, immunosuppressive agent, antibiotics, or antithrombotics. Furthermore, the marker may be positioned on the proximal side of the shaft tube.

The detailed description above describes a stent and stent delivery system disclosed by way of example. The disclosure is not limited, however, to the precise embodiment and variations described. Various changes, modifications and equivalents can effected by one skilled in the art without departing from the spirit and scope of the invention as defined in the accompanying claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims.