Implanting stent and dilating device

A stent has a plurality of wavy annular members each formed of a narrow wavy element and arranged in the axial direction thereof; and a plurality of connection portions each connecting the adjacent wavy annular members to each other axially. The connection portion located in the vicinity of the axial center of the stent is weaker than other constituent parts of the stent and can be broken. That is, an inflating balloon catheter can be inserted into the stent such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent dilates radially. The connection portion can be broken by inflation of the balloon of the inflating balloon catheter.

BACKGROUND OF THE INVENTION

The present invention relates to a stent that is implanted in lumens such as the blood vessel, the bile duct, the trachea, the esophagus, the ureter, and the like so that it is used to improve a stenosed portion or a dosed portion generated in the lumens.

To cure various diseases that are caused when the blood vessel or other lumens are stenosed or dosed, the stent which is a tubular-shaped medical appliance generally is implanted at the stenosed portion or the dosed portion to expand them and secure the lumen thereof.

Because the stent is inserted into the body from outside, its diameter is small. The stent is dilated to make-its diameter large at the stenosed or dosed portions to keep the dilated state of the lumen.

The stent is classified into a self-expandable stent and a balloon expandable stent, depending on the function thereof and an implantation method. The balloon expandable stent which itself has no dilating function is secured at a desired portion. Then, a balloon provided in the stent is inflated to dilate (plastically deform) the stent so that the stent comes in dose contact with the inner surface of the desired lumen. That is, it is necessary to dilate the stent of this type in implanting it to the desired portion.

Balloon expandable stents are disclosed in Examined Japanese Patent Publication No. 4-6377 and Japanese Patent Application Laid-Open No. 2-174859. These stents are pipes having axial slots formed therein. The slots are arranged such that they may take inter-connected rhombus shapes when the stent is dilated.

The stent disclosed in Examined Japanese Patent Publication No. 4-6377 is superior in shape retention after dilation because slots take inter-connected rhombus shapes. That is, the stent is resistant to the contracting force of a blood vessel. In other words, the stent has a strong shape-holding force. Another advantage of the stent is that when increase in the diameter of the stent is desired in a dilated state, an additional balloon having an enlarged diameter may be inserted into the stent. The stent of this type is called tube type. The word tube type is derived from the fact that normally, the stent is manufactured by boring a hole on a metal tube (metal pipe) with a laser. The stent of this type has a structural characteristic that it consists of a large number of narrow members crossing each other.

In the stent disclosed in Examined Japanese Patent Publication No. 4-6377, supposing that one segment thereof consists of a long and narrow rectangle, one segment consists of long and narrow members crossing each other at six points. By dilating the long and narrow rectangle, the rectangle plastically deforms into a rhombic shape and maintains the deformed shape, thus being resistant to the contraction force of the blood vessel. The stent of the tube type has various shapes, in addition to the above configuration. But the stent of the tube type has a large number of cross points commonly, irrespective of configurations.

The stent disclosed in Japanese Patent Application Laid-Open No. 1-145076 is called coil-type stent consisting of one wire. The wire is deformed zigzag and wound spirally to form it into a cylindrical shape. Thus, the stent does not have any crossing points of wires.

When for example, the tube-type stent is implanted in a branched blood vessel, the long and narrow members are present at the branch portion, and the branch portion is always subjected to a blood stream. Thus, the tube-type stent may cause thrombus to arise at the branch portion. Another problem of the tube-type stent is that when the branch portion is stenosed again, it is impossible to expand the stenosed portion with a balloon or embed the stent therein, because the long and narrow member interferes with an operation.

On the other hand, the coil-type stent does not have crossing portions of wires. Therefore, it is possible to perform an operation of dilating the branch portion with the balloon. However, the coil-type stent does not have crossing portions of wires. Thus, it has a low force of keeping a dilated state. To increase the force of keeping a dilated state, it is necessary to thicken the wire. As a result, it is not easy to deliver the stent. Further, when the stent is caught by a blood vessel, the shape of the wire becomes out of order. That is, the coil-type stent is inferior to the tube-type stent in its function.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a tube-type stent which is implanted in the body and capable of reducing the degree of inhibition of a blood stream to a branched blood vessel and capable of curing a stenosed portion of the branched blood vessel. It is another object of the present invention to provide a blood vessel dilation device having the stent. The object of this invention is to provide a stent that is to be implanted in a body formed in a substantially tubular configuration, has a diameter so set that the stent is inserted into the body, and can be dilated radially outwardly upon application of a force acting radially outwardly from the interior thereof, the stent having a plurality of wavy annular members each formed of a wavy element and arranged in the axial direction thereof; and a plurality of connection portions each connecting the adjacent wavy annular members to each other axially, wherein the connection portion is weaker than other parts and can be broken.

The object of this invention is to provide a dilation device having a tubular shaft body; a foldable and expandable balloon provided to a front-end portion of the shaft body; and a stent installed on the folded balloon and dilating by expansion of the balloon, wherein the stent is the above mentioned stent; the shaft body has a balloon expansion lumen communicating with the inside of the balloon; and the dilation device has a radiographing member fixed to an outer surface of the shaft body such that a fixing position of the radiographing member is located at a center of the stent or has two radiographing members fixed to the outer surface of the shaft body such that the fixing positions of the radiographing members are located at one and other ends of a central region, of the stent, having a predetermined length.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the stent of the present invention will be described below with reference to the drawings.

A stent1of the present invention is a so-called balloon expandable stent. That is, the stent1is formed in a substantially tubular configuration and has a diameter so set that the stent1is inserted into the body. The stent1can be dilated radially outwardly upon application of a force acting radially outwardly from the interior of the tubular stent.

The stent1has a plurality of wavy annular members (wavy line-shaped annular member)2a,2beach formed of a narrow wavy element and arranged in the axial direction thereof; and a plurality of connection portions4each connecting the adjacent wavy annular members2a,2bto each other axially. The connection portion4located in the vicinity of the axial center of the stent1is weaker than the other constituent parts and can be broken. Owing to the construction, an inflating balloon catheter can be inserted into the stent1such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion4can be broken by the inflation of the balloon of the inflating balloon catheter.

Specifically, as shown inFIGS. 1 through 3, the stent1comprises a plurality of annular units31,32,33,34,35,36,37,38, and39and joining portions51,52,53,54,55,56,57, and58. The annular units31,32,33,34,35,36,37,38, and39each has the first wavy annular member2aformed of a narrow wavy element (preferably, having no edge); the second wavy annular member2bdisposed in the axial direction of the stent1such that a mountain of the second wavy annular member2bis proximate to a valley of the first wavy annular member2aand formed of a narrow wavy element (preferably, having no edge); and a plurality of narrow connection portions4(preferably, having no edge) each connecting the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bto each other. A plurality of annular units is arranged approximately linearly in the axial direction of the stent1. Each of the annular units has one of narrow joining portions51,52,53,54,55,56,57, and58(preferably, having no edge) each connecting the wavy elements of the adjacent annular units to each other. The connection portion4located in the vicinity of the axial center of the stent1is weaker than the other constituent parts and can be broken. In other words, the stent1is a tubular body comprising a large number of annular units connected to each other with the connection portions.

As shown inFIGS. 1 and 2which is a developed view ofFIG. 1, each of the annular members2a,2bhas five mountains and valleys spaced at almost the same intervals. Each of the annular members2a,2bis formed of a plurality of the wavy elements having no edge so that the wavy elements continue to become annular. It is preferable that the number of the mountains (valleys) of the annular member is four to seven. The second wavy annular member2bis disposed in the axial direction of the stent1such that the mountain thereof is proximate to the valley of the first wavy annular member2a. The valley of the first wavy annular member2aand the mountain of the second wavy annular member2bare connected to each other with a plurality of the short connection portions4to form one annular unit. In the embodiment, all the valleys of the first wavy annular member2aand all the mountains of the second wavy annular member2bare connected to each other with the connection portions4. One annular unit has five (number of mountains or valleys of annular member) connection portions4.

The stent1comprises the annular units31,32,33,34,35,36,37,38, and39(nine in the embodiment) constructed as described above and arranged in the axial direction of the stent1and a joining portion, respectively to connect the wavy annular members of the adjacent annular units to thereby form the cylindrical stent. Only one joining portion is formed between the adjacent annular units. The joining portions51,52,53,54,55,56,57, and58are so disposed that the adjacent ones are not continuous with each other. The inside of the mountain of the wavy annular member2blocated at the start point of the joining portion (for example, 51) is formed wider than the other mountains thereof.

The connection portion4located in the vicinity of the axial center of the stent1is weaker than other constituent parts of the stent1and can be broken. As shown inFIGS. 1 through 3, in the stent1of the embodiment, the sectional area of each connection portion4has a smaller (in other words, narrower) sectional area than that of each of the other parts of the stent1, namely, the wavy annular members2a,2band the joining portions51,52,53,54,55,56,57, and58. That is, the connection portion4is weaker than the other parts of the stent1. In particular, in the embodiment, the thickness of the connection portion4is almost equal to that of the other parts but the width thereof is smaller than that of the other parts.

The annular members2a,2bare formed not weakly but the connection portion4is formed weakly. A weak portion is not formed on the annular members2a,2b. If the weak portion is formed on the annular members2a,2b, the annular members2a,2bmay be naturally broken when the stent1is dilated. That is, if the annular members2a,2bhave the weak portion formed thereon, they may have a low dilating force. But even though the connection portion4is formed weakly, the connection portion4hardly deforms when the stent1is dilated. Thus, the connection portion4is hardly broken naturally when the stent1is dilated.

Although all the connection portions4are weak in the embodiment, it is possible to form a weak connection portion4aonly in the vicinity of the axial center of the stent50, as shown inFIG. 7showing another embodiment. The length of the region in which the weak connection portion is formed is preferably 30–60% of the entire length of the stent50. The region in which the weak connection portion is formed is so formed that the center thereof is located at approximately the center of the stent in the axial direction thereof. In the embodiment shown inFIG. 7, the connection portion4blocated in the vicinity of each axial end of the stent has a width equal to that of the wavy element of each of the annular members2a,2band does not have the weak portion.

Further, instead of making the entire connection portions4weak but as shown inFIGS. 8 through 12showing another embodiment, it is possible to form a weak portion on the connection portions4such that a portion having a smaller sectional area than the other constituent parts of the stent is formed on the connection portions4having the same sectional area as those of the other component parts. As the mode of the weak portion, for example, a nick is formed on each of the opposite side surfaces of the connection portion such that the nicks are axially spaced at a certain interval. As another example, one nick is formed on one side surface of the connection portion such that the nick extends to the widthwise center thereof. As still another example, two nicks are formed on both side surfaces of the connection portion such that the nicks extend to the widthwise center thereof and confront each other. As further example, a portion is formed on the connection portion such that the portion is shorter or thinner than other portions thereof. As still further example, a portion is formed on the connection portion such that the portion is shorter and thinner than other portions thereof.

An inflating balloon catheter can be inserted into each of the stents1,50such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion can be broken by the inflation of the balloon of the inflating balloon catheter, as shown inFIG. 19. As shown inFIG. 4, each annular member keeps a dilated configuration. Thus the entire stent1also keeps a dilated configuration. When the inflating balloon catheter is inserted into the dilated stent and passed the side wall of the stent1by guiding with a guide wire and the balloon is inflated, the connection portion of the stent is cut off by the inflated balloon. As a result, a hole having a diameter almost equal to an enlarged diameter of the inflated balloon is formed through the side wall. If the stent does not have the weak connection portion, the inflating balloon catheter cannot secure a hole (space) larger than the space formed of a deformation of the annular members to the maximum. Thus, if the balloon is inflated forcibly, it bursts. That is, because the stent has the weak connection portion, the stent is stable in its configuration in a blood vessel.

The joining portions51–58joining the wavy annular members of the adjacent annular units31–39remain unchanged substantially in their lengths when the stent1is dilated. Because the joining portions51–58and the connection portion4remain substantially unchanged in their lengths even when the stent1is dilated, the overall length of the stent1remains substantially unchanged before and after dilation. It never happens that the stent is reduced in length after dilation.

The joining portion51–58is so disposed that it connects the adjacent annular units31–39at only one position. Although the adjacent annular units31–39may be connected at two or more positions, it is preferable to connect them at only one position as embodied in the present invention so that the stent follows deformation of a blood vessel faithfully. Further in the embodiment, the joining portion51–58is so disposed that the adjacent ones are not continuous with each other. Therefore, it is possible to prevent a load generated by one annular unit that has followed the deformation of a blood vessel from being directly (or linearly) transmitted to the unadjacent annular units. Thus it is possible to allow the respective annular units to independently display their dilation function. Further, as inFIGS. 2 and 5showing one embodiment of the present invention, the joining portions51–58are so arranged that the odd joining portion and the even joining portion form 180 degrees therebetween at the axis of the stent. This construction is preferable because potential interactions between unadjacent annular units can be minimized.

To reduce the degree of damage to be applied to the inflated balloon when the connection portion4is broken, it is preferable that the edge of the wavy element of the stent is chamfered. As the method of chamfering the stent, after the stent is fabricated into a final shape, chemical polishing, electropolishing or mechanical polishing can be used. The chemical polishing is preferably carried out by dipping the stent in a chemical polishing solution for stainless steel. Any chemical polishing solution containing one capable of dissolving stainless steel may be used. For example, one preferable chemical polishing solution contains a mixture of hydrochloric acid and nitric acid serving as a base component and additives such as an organic sulfur compound for adjusting a dissolution rate, smoothing, and imparting luster and a surface active agent.

It is possible that the wavy element of the annular members2a,2blocated at the opposed ends of the stent1in the axial direction thereof has a sectional area, respectively smaller than that of the other wavy annular members. This construction causes the dilation force of the wavy annular members located at the opposed ends of the stent1in the axial direction thereof to be lower than those of the other wavy annular members when the stent1dilates, but allows the annular members2a,2blocated at the opposed ends of the stent1in the axial direction thereof to follow the bending of a blood vessel to a high extent. That is, the opposed ends of the stent1in the axial direction thereof have a high degree of affinity for the blood vessel. As the method of reducing the thickness of the annular members2a,2blocated at the opposed ends of the stent1in the axial direction thereof, after the stent is fabricated into the final shape, the annular members2a,2bis chemically polished or mechanically polished.

It is possible that the material of the annular unit (annular member) located at the axial center of the stent1have the maximum cross-sectional area and that the annular units (annular member) located nearer to the axial end of the stent have a smaller cross-sectional area than the annular units located nearer to the center of the stent. Specifically, the thickness of the annular units are so set that the thickness of the annular units34,35, and36located at the axial central part of the stent1have a largest thickness and the other annular units have small thicknesses decreasingly as they are nearer to both axial ends of the stent. This construction ensures that the stent1displays a sufficient dilating force at its central part and faithfully follows a bent portion of a blood vessel. That is, both axial ends of stent1have better affinity for the blood vessel. It is also possible that the annular unit located at the center of the stent1has a maximum width and the other annular units have small widths decreasingly as they are nearer to both axial ends of the stent.

In the stent1, a part of the wavy annular member2aof one annular unit is in penetration into the wavy space formed at the axial end (inner side of stent) of the other annular unit adjacent to the one annular unit. That is, a part of the mountain of the wavy annular member2aof one annular unit is in penetration into the concave portion of the wavy annular member2bformed in the vicinity of the connection portion of the other annular unit adjacent to the one annular unit. Therefore, the adjacent annular units overlap partially each other when the stent1is viewed in the axial direction thereof. Thus, when the constituent elements of the wavy annular members are reduced in their lengths in the axial direction of the stent upon dilation of the stent, gaps on the side surface of the stent increase to a small extent. Therefore, it is possible to dilate a stenosed portion of a blood vessel securely and holds an affected portion without a gap.

The mountain of the annular member2bhaving one of the joining portions51,52,53,54,55,56,57, and58formed therein is wider than the other mountains thereof, such that a part of the mountain is adjacent to the joining portion. Similarly, the valley of the annular member2ahaving one of the joining portions51,52,53,54,55,56,57, and58formed therein is wider than the other valleys thereof, such that a part of the valley is adjacent to the joining portion. In the embodiment, the joining portion is curved. The curved joining portions51,52,53,54,55,56,57, and58become approximately straight when the stent is dilated, as shown inFIGS. 4 and 5.

It is preferable that the material of the stent1has a certain degree of compatibility with an organism. For example, it is possible to use stainless steel, tantalum or tantalum alloys, platinum or platinum alloys, gold or gold alloys, cobalt base alloys and the like. It is preferable to plate the stent with a noble metal such as gold and platinum after the stent is fabricated into a final shape. As the stainless steel, SUS 316L most corrosion-resistant of the above metals can be preferably used.

It is preferable to anneal the stent1after it is fabricated into the final shape. Annealing improves the flexibility and plasticity of the entire stent so that the stent can be effectively implanted in a curved blood vessel. As compared with a non-annealed stent, the annealed stent has a lower force of restoring to an original state after it is dilated, and especially has a lower force of restoring to an original linear state when it is dilated at a curved portion of a blood vessel. This minimizes physical stimulation to the inner wall of the curved blood vessel, thus reducing the cause of a recurrence of stenosis. The stent is preferably annealed by heating it to 900 to 1200° C. in an inert gas atmosphere (e.g., a mixture gas of nitrogen and hydrogen) so that no oxide film is formed on the surface of the stent and then slowly cooling it.

The stent1has a diameter favorably 0.8 to 1.8 mm and more favorably 1.0 to 1.6 mm in an undilated state. The stent1has a length favorably 9 to 40 mm in an undilated state. The length of each of the wavy annular members2a,2bhas a length of 0.7 to 2.0 mm. The length of one of the annular units31through39is favorably 1.5–4.0 mm and more favorably 2.0–3.0 mm. The length of one connection portion4is favorably 0.01–0.5 mm. The number of the annular units is 3 to 50. The constituent elements (annular member) of the adjacent annular units have an axial overlap of about 0.5 to 1 mm. The distance between the center of one annular units and that of the annular unit adjacent thereto is preferably 1.3 to 2.5 mm. The length of each of the joining portions51,52,53,54,55,56,57, and58is preferably 1.4 to 2.7 mm. The angle of inclination (the angle of inclination of the joining portion relative to a longitudinal direction in a development view) of each of the joining portion51through58relative to the axis of the stent is favorably 0° to 30° and more favorably 5° to 25°.

The thickness of each of the wavy annular members2a,2bof the stent1and that of each of the joining portions51,52,53,54,55,56,57, and58are favorably 0.05 to 0.15 mm and more favorably 0.08 to 0.12 mm. The width of each of the wavy annular members2a,2band that of each of the joining portions51,52,53,54,55,56,57, and58are favorably 0.07 to 0.15 mm and more favorably 0.08 to 0.12 mm. The thickness of the connection portion4of the stent1is favorably 0.05–0.12 mm and more favorably 0.06–0.10 mm. The width of the connection portion4of the stent1is favorably 0.01–0.05 mm and more favorably 0.02 to 0.04 mm. The sectional area of the connection portion4is favorably 1/50 to ½ of that of the other parts (annular member and joining portion) and more favorably 1/20 to 1/10 of that of the other parts.

Another embodiment of the stent of the present invention is described below.

FIG. 8is a front view of a stent according to still another embodiment of the present invention.FIG. 9is a development view of the stent ofFIG. 8.FIG. 10is a partly enlarged front view of the stent ofFIG. 8.FIG. 11is a front view of the dilated stent ofFIG. 8.FIG. 12is a development view of the dilated stent ofFIG. 11.FIG. 13is a front view of a stent according to another embodiment of the present invention.

In a stent60of the embodiment, as shown inFIGS. 8 through 10, a plurality of wavy annular members62are adjacently formed such that mountains and valleys thereof are arranged approximately linearly, respectively in the axial direction of the stent60. A connection portion64connects mountains (valleys) of the adjacent wavy annular members62to each other. The connection portions64located in the vicinity of the axial center of the stent60have a weak portion65, respectively.

In other words, the stent60has a plurality of the annular members62made of a (endless) linear material connected to each other wavily (zigzag) and annularly. The annular member62serve as a means of keeping the stent60dilated. The connection portion (connector)64connects the adjacent annular members to each other to prevent them from separating from each other. A weak portion65(cutting point) is formed on the connection portion64. The weak portion65is formed not on the annular member62but on the connection portion64. In other words, the weak portion65is not formed on the annular member62. If the weak portion65is formed on the annular member62, the annular member may be naturally broken when the stent60is dilated. That is, if the annular member62has the weak portion65formed thereon, they may have a low dilating force when the stent60is dilated. But even though the weak portion65is formed on the connection portion64, the connection portion64hardly deforms when the stent60is dilated. Thus, the weak portion65is hardly broken naturally when the stent60is dilated. Although each connection portions64has the weak portion65in the embodiment, it is possible to form the weak portion65on only the connection portion located in the vicinity of the axial center of the stent60. The weak portion may be formed at any position of the connection portion64. In the embodiment, the weak portion is formed on the connection portion64such that the weak portion is located proximately to the mountain of the adjacent annular member62. However, the weak portion may be formed in the vicinity of the axial center of the connection portion64.

The weak portion65has a smaller than sectional area than the other constituent parts of the stent60. Specifically, a nick is formed on each of the opposite side surfaces of the connection portion64such that the nicks are axially spaced at a certain interval. In this manner, the weak portion65can be securely formed on the connection portion64. In addition to this construction, any construction of the weak portion65can be adopted so long as it can be destroyed when a force is applied thereto. As an example, one nick is formed on one side surface of the connection portion such that the nick extends to the widthwise center thereof. As another example, two nicks are formed on both side surfaces of the connection portion such that the nicks extend to the widthwise center thereof and confront each other. As still another example, a portion is formed on the connection portion such that the portion is shorter or thinner than other portions thereof. As still another example, a portion is formed on the connection portion such that the portion is shorter and thinner than other portions thereof.

An inflating balloon catheter can be inserted into the stent60of the embodiment such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The weak portion65of the connection portion64can be broken by the inflation of the balloon of the inflating balloon catheter. As shown inFIGS. 11 and 12, each annular member keeps a dilated configuration. Thus the entire stent60also keeps a dilated configuration. When the inflating balloon catheter is inserted into the dilated stent and passed the side wall of the stent60by guiding with a guide wire and the balloon is inflated, the connection portion64of the stent is cut off at the weak portion (cutting point)65by the inflated balloon. As a result, a hole having a diameter almost equal to an enlarged diameter of the inflated balloon is formed through the side wall. If the stent does not have the the weak portion (cutting point)65, the inflating-balloon catheter cannot secure a hole (space) larger than the space formed of a deformation of the annular members to the maximum. Thus, if the stent is dilated forcibly, the balloon bursts.

The stent is not limited to the above-described modes. For example, as shown inFIG. 13, the weak portion65may be formed on only the connection portion64located in the vicinity of the axial center of the stent. As another mode or construction of the stent, the valleys of the adjacent wavy annular members may be connected to each other (this construction can be formed by inverting the stent shown inFIG. 8axially). As still another example, the stent may be so constructed that connection portions located at odd-numbered positions in the axial direction of the stent connect the mountains to each other and connection portions located at even-numbered positions in the axial direction thereof connect the valleys to each other. Alternatively, the stent may be so constructed that connection portions located at odd-numbered positions in the axial direction of the stent connect the valleys to each other and connection portions located at even-numbered positions in the axial direction thereof connect the mountains to each other.

Similarly to the stent1, in the stent60, to reduce the degree of damage to be applied to the inflated balloon when the connection portion4is broken, it is preferable that the edge of the wavy element of the stent is chamfered. As the method of chamfering the stent, after the stent is fabricated into a final shape, chemical polishing, electropolishing or mechanical polishing can be used. Similarly to the stent1, in the stent60, it is possible that the wavy element of the annular members located at the opposed ends of the stent in the axial direction thereof has a sectional area, respectively smaller than that of the other wavy annular members. Further, similarly to the stent1, it is possible that the material of the annular unit located at the axial center of the stent1have the maximum cross-sectional area. It is also possible that the annular units located nearer to the axial end of the stent have a smaller cross-sectional area than the annular units located nearer to the axial center of the stent.

It is preferable that the material of the stent60has a certain degree of compatibility with an organism. For example, it is possible to use stainless steel, tantalum or tantalum alloys, platinum or platinum alloys, gold or gold alloys, cobalt base alloys and the like. It is preferable to plate the stent with a noble metal such as gold and platinum after the stent is fabricated into a final shape. As the stainless steel, SUS 316L most corrosion-resistant of the above metals can be preferably used. Similarly to the stent1, it is preferable to anneal the stent60after it is fabricated into the final shape.

The stent60has a diameter favorably 0.8 to 1.8 mm and more favorably 1.0 to 1.6 mm in an undilated state. The stent60has a length favorably 7 to 25 mm in an undilated state. The length of the wavy annular member62has a length of 0.7 to 2.0 mm. The length of one connection portion64is favorably 0.9–2.5 mm. The number of the wavy annular members62is four to seven. The distance between the center of one annular member62and that of the annular member adjacent thereto is preferably 0.9 to 2.5 mm.

The thickness of the wavy annular member62of the stent60and that of the connection portion64are favorably 0.05 to 0.15 mm and more favorably 0.08 to 0.12 mm. The width of the wavy annular member62and that of the connection portion64are favorably 0.07 to 0.15 mm and more favorably 0.08 to 0.12 mm. The length (width) of the narrowest portion (weak portion) of the connection portion64of the stent60is favorably 0.01–0.05 mm. The sectional area of the weak portion is favorably 1/50 to ½ of that of the other parts and more favorably 1/20 to 1/10 of that of the other parts.

Another embodiment of the present is described below with reference to the drawings.

FIG. 20is a front view of a stent according to another embodiment of the present invention.FIG. 21is a development view of the stent ofFIG. 20.FIG. 22is a partly enlarged front view of the dilated stent ofFIG. 20.FIG. 23is a partly enlarged front view of the dilated stent, ofFIG. 20, whose connection portion is broken.

A stent80of the present invention is a so-called balloon expandable stent. That is, the stent80is formed in a substantially tubular configuration and has a diameter so set that the stent80is inserted into the body. The stent80can be dilated radially outwardly upon application of a force acting radially outwardly from the interior of the tubular stent.

The stent80has a plurality of wavy annular members (wavy line-shaped annular member)2a,2beach formed of a narrow wavy element and arranged in the axial direction thereof; and a plurality of connection portions4each connecting the adjacent wavy annular members2a,2bto each other axially. The connection portion4located in the vicinity of the axial center of the stent80is weaker than the other constituent parts and can be broken. Owing to the construction, an inflating balloon catheter can be inserted into the stent80such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion4can be broken by the inflation of the balloon of the inflating balloon catheter.

Specifically, as shown inFIGS. 20 through 22, the stent80comprises a plurality of annular units31,32,33,34,35,36,37,38,39,40,41and42and joining portions181,182,183,184,185,186,187,188,189,190and191. The annular units3142consists of the first wavy annular member2aformed of a narrow wavy element (preferably, having no edge); the second wavy annular member2bdisposed in the axial direction of the stent80such that a mountain of the second wavy annular member2bis proximate to a valley of the first wavy annular member2aand formed of a narrow wavy element (preferably, having no edge); a plurality of connection portions4(preferably, having no edge) each connecting the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bto each other; and an integral portion (fused portion)81consisting of the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bintegrated (fused) therewith. A plurality of annular units is arranged approximately linearly in the axial direction of the stent80. Each of the annular units has one of narrow joining portions181–191(preferably, having no edge) each connecting the wavy elements (wavy annular member2a,2b) of the adjacent annular units to each other to thereby form the cylindrical stent. Each of the annular units has two integral portions. The two integral portions are so disposed that the adjacent ones are not continuous with each other. The joining portions181–191are so disposed that they connect the integral portions (fused portion)81to each other. Only one joining portion181–191is formed between the adjacent annular units. The joining portions181–191are so disposed that the adjacent ones are not continuous with each other. The joining portions181–191are so formed that they orient in different directions alternately in the axial direction of the stent.

The manner of disposing the integral portion (fused portion)81is not limited to the above-described one. Also, the configuration of the joining portion is not limited to the above-described one. For example, the integral portion (fused portion)81may be disposed spirally, and the joining portion connecting the integral portions (fused portion)81to each other may be disposed also spirally.

In the stent80, the connection portion4located in the vicinity of the axial center of the stent80is weaker than the other constituent parts and can be broken. In other words, the stent80is a tubular body comprising a large number of annular units connected to each other with the connection portions.

As shown inFIGS. 20 and 21which is a developed view ofFIG. 20, each of the annular members2a,2bof the stent80has six mountains and valleys spaced at almost the same intervals except the integral poritons. Each of the annular members2a,2bis formed of a plurality of the wavy elements having no edge. It is preferable that the number of the mountains (valleys) of the annular member is four to eight. The second wavy annular member2bis disposed in the axial direction of the stent80such that the mountain thereof is proximate to the valley of the first wavy annular member2a. The mountain of the second wavy annular member2band the valley of the first wavy annular member2aare integral with each other partly through the integral portion (fused portion)81. In the portions of the first and second wavy annular members2aand2bother than the integral portion (fused portion)81, the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bare connected to each other with a plurality of the short connection portions4to form one annular unit. In the embodiment, all the valleys of the first wavy annular member2aand all the mountains of the second wavy annular member2bare connected to each other with the connection portions4except the integral portion (fused portion)81. One annular unit has four (less by two than the number of mountains or valleys of annular member) connection portions4.

The connection portion4located in the vicinity of the axial center of the stent80is weaker than other constituent parts of the stent80and can be broken. As shown inFIGS. 20 through 22, in the stent80of the embodiment, the sectional area of each connection portion4has a smaller (in other words, narrower) sectional area than that of each of the other parts of the stent80, namely, the wavy annular members2a,2band the joining portions181–191. That is, the connection portion4is weaker than the other parts of the stent80. In particular, in the embodiment, the thickness of the connection portion4is almost equal to that of the other parts but the width thereof is smaller than that of the other parts.

The annular members2a,2bare formed not weakly but the connection portion4is formed weakly. A weak portion is not formed on the annular members2a,2b. If the weak portion is formed on the annular members2a,2b, the annular members2a,2bmay be naturally broken when the stent80is dilated. That is, if the annular members2a,2bhave the weak portion formed thereon, they may have a low dilating force. But even though the connection portion4is formed weakly, the connection portion4hardly deforms when the stent80is dilated. Thus, the connection portion4is hardly broken naturally when the stent80is dilated.

Although all the connection portions4of the stent80are weak, it is possible to form a weak connection portion4aonly in the vicinity of the axial center of the stent50, as in the case of the stent shown inFIG. 7. The length of the region in which the weak connection portion is formed is preferably 30–60% of the entire length of the stent50. The region in which the weak connection portion is formed is so formed that the center thereof is located at approximately the center of the stent in the axial direction thereof. In the embodiment shown inFIG. 7, the connection portion4blocated in the vicinity of each axial end of the stent has a width equal to that of the wavy element of each of the annular members2a,2band does not have the weak portion.

Further, instead of making the entire connection portions4weak, as in the case of the stent shown inFIGS. 8 through 12, it is possible to form a weak portion on the connection portions4such that a portion having a smaller sectional area than the other constituent parts of the stent is formed on the connection portions4having the same sectional area as those of the other component parts. As the mode of the weak portion, for example, a nick is formed on each of the opposite side surfaces of the connection portion such that the nicks are axially spaced at a certain interval. As another example, one nick is formed on one side surface of the connection portion such that the nick extends to the widthwise center thereof. As still another example, two nicks are formed on both side surfaces of the connection portion such that the nicks extend to the widthwise center thereof and confront each other. As further example, a portion is formed on the connection portion such that the portion is shorter or thinner than other portions thereof. As still further example, a portion is formed on the connection portion such that the portion is shorter and thinner than other portions thereof.

In the stent80of the present invention, an inflating balloon catheter can be inserted into each of the stents such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion can be broken by the inflation of the balloon of the inflating balloon catheter, as shown inFIG. 23. As shown inFIG. 23, each annular member keeps a dilated configuration. Thus the entire stent80also keeps a dilated configuration. When the inflating balloon catheter is inserted into the dilated stent and passed the side wall of the stent80by guiding with a guide wire and the balloon is inflated, the connection portion of the stent is cut off at the weak portion by the inflated balloon. As a result, a hole having a diameter almost equal to an enlarged diameter of the inflated balloon is formed through the side wall. If the stent does not have the the weak portion, the inflating balloon catheter cannot secure a hole (space) larger than the space formed of a deformation of the annular members to the maximum. Thus, if the stent is dilated forcibly, the balloon bursts. That is, because the stent has the weak connection portion, the stent is stable in its configuration in a blood vessel.

The joining portions181–191joining the wavy annular members of the adjacent annular units31–42remain unchanged substantially in their lengths when the stent80is dilated. Because the joining portions181–191and the connection portion4remain substantially unchanged in their lengths even when the stent80is dilated, the overall length of the stent80remains substantially unchanged before and after dilation. It never happens that the stent is reduced in length after dilation.

The joining portion181–191is so disposed that it connects the adjacent annular units31–42at only one position. Although the adjacent annular units31–42may be connected at two or more positions, it is preferable to connect them at only one position as embodied in the present invention so that the stent follows deformation of a blood vessel faithfully. Further in the embodiment, the joining portion181–191may be so disposed that the adjacent ones are continuous with each other.

To reduce the degree of damage to be applied to the inflated balloon when the connection portion4is broken, it is preferable that the edge of the wavy element of the stent is chamfered. As the method of chamfering the stent, after the stent is fabricated into a final shape, chemical polishing, electropolishing or mechanical polishing can be used. The chemical polishing is preferably carried out by dipping the stent in a chemical polishing solution for stainless steel. Any chemical polishing solution containing one capable of dissolving stainless steel may be used. For example, one preferable chemical polishing solution contains a mixture of hydrochloric acid and nitric acid serving as a base component and additives such as an organic sulfur compound for adjusting a dissolution rate, smoothing, and imparting luster and a surface active agent.

It is possible that the wavy element of the annular members2a,2blocated at the opposed ends of the stent80in the axial direction thereof has a sectional area, respectively smaller than that of the other wavy annular members. This construction causes the dilation force of the wavy annular members located at the opposed ends of the stent80in the axial direction thereof to be lower than those of the other wavy annular members when the stent80dilates, but allows the annular members2a,2blocated at the opposed ends of the stent80in the axial direction thereof to follow the bending of a blood vessel to a high extent. That is, the opposed ends of the stent80in the axial direction thereof have a high degree of affinity for the blood vessel. As the method of reducing the thickness of the annular members2a,2blocated at the opposed ends of the stent80in the axial direction thereof, after the stent is fabricated into the final shape, the annular members2a,2bis chemically polished or mechanically polished.

It is possible that the material of the annular unit (annular member) located at the axial center of the stent80have the maximum cross-sectional area and that the annular units (annular member) located nearer to the axial end of the stent have a smaller cross-sectional area than the annular units located nearer to the center of the stent. Specifically, the thickness of the annular units are so set that the thickness of the annular units34,35,36,37and38located at the axial central part of the stent80have a largest thickness and the other annular units have small thicknesses decreasingly as they are nearer to both axial ends of the stent. This construction ensures that the stent80displays a sufficient dilating force at its central part and faithfully follows a bent portion of a blood vessel. That is, both axial ends of stent80have better affinity for the blood vessel. It is also possible that the annular unit located at the center of the stent80has a maximum width and the other annular units have small widths decreasingly as they are nearer to both axial ends of the stent.

In the stent80, a part of the wavy annular member2aof one annular unit is in penetration into the wavy space formed at the axial end (inner side of stent) of the other annular unit adjacent to the one annular unit. That is, a part of the mountain of the wavy annular member2aof one annular unit is in penetration into the concave portion of the wavy annular member2bformed in the vicinity of the connection portion of the other annular unit adjacent to the one annular unit. Therefore, the adjacent annular units overlap partially each other when the stent80is viewed in the axial direction thereof. Thus, when the constituent elements of the wavy annular members are reduced in their lengths in the axial direction of the stent upon dilation of the stent, gaps on the side surface of the stent increase to a small extent. Therefore, it is possible to dilate a stenosed portion of a blood vessel securely and holds an affected portion without a gap.

The mountain of the annular member2bhaving one of the joining portions181–191formed therein is wider than the other mountains thereof, such that a part of the mountain is adjacent to the joining portion. Similarly, the valley of the annular member2ahaving one of the joining portions181–191formed therein is wider than the other valleys thereof, such that a part of the valley is adjacent to the joining portion. In the embodiment, the joining portion is approximately linear.

It is preferable that the material of the stent80has a certain degree of compatibility with an organism. For example, it is possible to use stainless steel, tantalum or tantalum alloys, platinum or platinum alloys, gold or gold alloys, cobalt base alloys and the like. It is preferable to plate the stent with a noble metal such as gold and platinum after the stent is fabricated into a final shape. As the stainless steel, SUS 316L most corrosion-resistant of the above metals can be preferably used.

It is preferable to anneal the stent80after it is fabricated into the final shape. Annealing improves the flexibility and plasticity of the entire stent so that the stent can be effectively implanted in a curved blood vessel. As compared with a non-annealed stent, the annealed stent has a lower force of restoring to an original state after it is dilated, and especially has a lower force of restoring to an original linear state when it is dilated at a curved portion of a blood vessel. This minimizes physical stimulation to the inner wall of the curved blood vessel, thus reducing the cause of a recurrence of stenosis. The stent is preferably annealed by heating it to 900 to 1200° C. in an inert gas atmosphere (e.g., a mixture gas of nitrogen and hydrogen) so that no oxide film is formed on the surface of the stent and then slowly cooling it.

The stent1has a diameter favorably 0.8 to 1.8 mm and more favorably 1.0 to 1.6 mm in an undilated state. The stent80has a length favorably 9 to 40 mm in an undilated state. The length of each of the wavy annular members2a,2bhas a length of 0.7 to 2.0 mm. The length of one of the annular units31through42is favorably 1.5–4.0 mm and more favorably 2.0–3.0 mm. The length of one connection portion4is favorably 0.01–0.5 mm. The number of the annular units is 3 to 50. The constituent elements (annular member) of the adjacent annular units have an axial overlap of about 0.5 to 1 mm. The distance between the center of one annular units and that of the annular unit adjacent thereto is preferably 1.3 to 2.5 mm. The length of each of the joining portions181–191is preferably 1.4 to 2.7 mm. The angle of inclination (the angle of inclination of the joining portion relative to a longitudinal direction in a development view) of each of the joining portion181through191relative to the axis of the stent is favorably 0° to 30° and more favorably 5° to 25°.

The thickness of each of the wavy annular members (wavy elements, wavy line-shaped elements)2a,2bof the stent80and that of each of the joining portions181–191are favorably 0.05 to 0.15 mm and more favorably 0.08 to 0.12 mm. The width of each of the wavy annular members2a,2band that of each of the joining portions181–191are favorably 0.07 to 0.15 mm and more favorably 0.08 to 0.12 mm. The thickness of the connection portion4of the stent80is favorably 0.05–0.12 mm and more favorably 0.06–0.10 mm. The width of the connection portion4of the stent80is favorably 0.01–0.05 mm and more favorably 0.02 to 0.04 mm. The sectional area of the connection portion4is favorably 1/50 to ½ of that of the other parts (annular member and joining portion) and more favorably 1/20 to 1/10 of that of the other parts.

Another embodiment of the present is described below with reference to the drawings.

FIG. 24is a front view of a stent according to another embodiment of the present invention.FIG. 25is a development view of the stent ofFIG. 24.FIG. 22is referred as a partly enlarged front view of the enlarged stent ofFIG. 24.FIG. 23is also referred as a partly enlarged front view of the dilated stent, ofFIG. 24, whose connection portion is broken.

A stent90of the present invention is a so-called balloon expandable stent. That is, the stent90is formed in a substantially tubular configuration and has a diameter so set that the stent90is inserted into the body. The stent90can be dilated radially outwardly upon application of a force acting radially outwardly from the interior of the tubular stent.

The stent90has a plurality of wavy annular members (wavy line-shaped annular member)2a,2beach formed of a narrow wavy element and arranged in the axial direction thereof; and a plurality of connection portions4each connecting the adjacent wavy annular members2a,2bto each other axially. The connection portion4located in the vicinity of the axial center of the stent80is weaker than the other constituent parts and can be broken. Owing to the construction, an inflating balloon catheter can be inserted into the stent80such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion4can be broken by the inflation of the balloon of the inflating balloon catheter.

Specifically, as shown inFIGS. 24 and 25, the stent90comprises a plurality of annular units31,32,33,34,35,36,37,38,39,40,41and42and joining portions181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201and202. The annular units31–42each have the first wavy annular member2aformed of a narrow wavy element (preferably, having no edge); the second wavy annular member2bdisposed in the axial direction of the stent90such that a mountain of the second wavy annular member2bis proximate to a valley of the first wavy annular member2aand formed of a narrow wavy element (preferably, having no edge); a plurality of narrow connection portions4(preferably, having no edge) each connecting the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bto each other; and an integral portion (fused portion)81consisting of the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bintegrated (fused) therewith. A plurality of annular units is arranged approximately linearly in the axial direction of the stent90. Each of the annular units has one of joining portions181–202(preferably, having no edge) each connecting the wavy elements of the adjacent annular units to each other. Thereby, the cylindrical stent is formed. One annular unit has three integral portions. The three integral portions are so formed that they are not adjacent to each other. The joining portions181–202are so formed that they connect the integral portions (fused portions)81to each other. The joining portions181–202are so formed that two of them are disposed between the adjacent annular units. The joining portions181–202are so arranged that those adjacent to each other are continuous with each other. However, the joining portions181–202are so arranged that two of them are continuous with each other and more than two of them are not continuous with each other. The joining portions181–202are so formed that they orient in different directions alternately in the axial direction of the stent. The joining portions connecting the adjacent annular units to each other orient in the same direction in the axial direction of the stent. As shown inFIGS. 24 and 25, the continuous joining portions are bent at a certain portion. The continuous joining portions can be called a joining portions-continuous member. For example, a joining portions-continuous member is consisted by the joining portions182and194. The joining portions-continuous member connects three annular units to each other. The joining portions-continuous member is bent at its center. For example, the joining portions-continuous member is bent between the joining portions182and194. More specifically, the joining portions-continuous member is bent at the integral portion of the central annular unit of the continuous three annular units. The adjacent joining portions-continuous members have different bending directions. The alternate joining portions-continuous members have the substantially same bending direction. Each joining portions-continuous member is disposed by forming an angle 120′ between the joining portions-continuous member and the axis of the stent. For example, the joining portions-continuous member consisting of the joining portions182and194is disposed by forming an angle 120′ between the joining portions-continuous member consisting of the joining portions183and184and the axis of the stent90. Further, the joining portions-continuous members are dislocated from each other by the length of one joining portion (half of joining portions-continuous member) in the rear-end direction of the stent. For example, the joining portions-continuous member consisting of the joining portions183and184is dislocated from the joining portions-continuous member consisting of the joining portions182and194by the length of the joining portion194.

Thus, the joining portions-continuous members are disposed spirally on the outer surface of the stent. In the adjacent annular units except the annular units31and42disposed at both axial ends of the stent90, there is disposed the rear side (rear half of joining portions-continuous member) of one joining portions-continuous member and the front side (front half of joining portions-continuous member) of the other joining portions-continuous member (located adjacent to the one joining portions-continuous member). Thus, one joining portion (half of joining portions-continuous member) of one joining portions-continuous member and one joining portion of the other joining portions-continuous member overlap each other in the axial direction of the stent. In other words, the joining portions-continuous members do not overlap each other entirely in the axial direction of the stent.

Owing to the arrangement of the joining portions (joining portions-continuous members), the stent has a cylindrical configuration-holding force to a high extent when the stent is dilated diametrically. Further, the joining portions arranged in this manner prevent the stent from being bent in a particular direction to a high extent.

The manner of disposing the integral portion (fused portion)81is not limited to the above-described one. Also, the configuration of the joining portion is not limited to the above-described one.

In the stent90, the connection portion4located in the vicinity of the axial center of the stent90is weaker than the other constituent parts and can be broken. In other words, the stent90is a tubular body comprising a large number of annular units connected to each other with the connection portions.

As shown inFIGS. 24 and 25which is a developed view ofFIG. 24, each of the annular members2a,2bof the stent90has six mountains and valleys spaced at almost the same intervals except the integral portions. Each of the annular members2a,2bis formed of a plurality of the wavy elements having no edge. It is preferable that the number of the mountains (valleys) of the annular member is four to eight. The second wavy annular member2bis disposed in the axial direction of the stent90such that the mountain thereof is proximate to the valley of the first wavy annular member2a. The mountain of the second wavy annular member2band the valley of the first wavy annular member2aare integral with each other partly through the integral portion (fused portion)81. In the portions of the first and second wavy annular members2aand2bother than the integral portion (fused portion)81, the valley of the first wavy annular member2aand the mountain of the second wavy annular member2bare connected to each other with a plurality of the short connection portions4to form one annular unit. In the embodiment, all the valleys of the first wavy annular member2aand all the mountains of the second wavy annular member2bare connected to each other with the connection portions4except the integral portion (fused portion)81. One annular unit has three (less by three than the number of mountains or valleys of annular member) connection portions4.

The connection portion4located in the vicinity of the axial center of the stent90is weaker than other constituent parts of the stent90and can be broken. As shown inFIGS. 24 and 25, in the stent90of the embodiment, the sectional area of each connection portion4has a smaller (in other words, narrower) sectional area than that of each of the other parts of the stent90, namely, the wavy annular members2a,2band the joining portions181–202. That is, the connection portion4is weaker than the other parts of the stent90. In particular, in the embodiment, the thickness of the connection portion4is almost equal to that of the other parts but the width thereof is smaller than that of the other parts.

The annular members2a,2bare formed not weakly but the connection portion4is formed weakly. A weak portion is not formed on the annular members2a,2b. If the weak portion is formed on the annular members2a,2b, the annular members2a,2bmay be naturally broken when the stent90is dilated. That is, if the annular members2a,2bhave the weak portion formed thereon, they may have a low dilating force. But even though the connection portion4is formed weakly, the connection portion4hardly deforms when the stent90is dilated. Thus, the connection portion4is hardly broken naturally when the stent90is dilated.

Although all the connection portions4of the stent90are weak, it is possible to form a weak connection portion4aonly in the vicinity of the axial center of the stent50, as in the case of the stent shown inFIG. 7. The length of the region in which the weak connection portion is formed is preferably 30–60% of the entire length of the stent50. The region in which the weak connection portion is formed is so formed that the center thereof is located at approximately the center of the stent in the axial direction thereof. In the embodiment shown inFIG. 7, the connection portion4blocated in the vicinity of each axial end of the stent has a width equal to that of the wavy element of each of the annular members2a,2band does not have the weak portion.

Further, instead of making the entire connection portions4weak, as in the case of the stent shown inFIGS. 8 through 12, it is possible to form a weak portion on the connection portions4such that a portion having a smaller sectional area than the other constituent parts of the stent is formed on the connection portions4having the same sectional area as those of the other component parts. As the mode of the weak portion, for example, a nick is formed on each of the opposite side surfaces of the connection portion such that the nicks are axially spaced at a certain interval. As another example, one nick is formed on one side surface of the connection portion such that the nick extends to the widthwise center thereof. As still another example, two nicks are formed on both side surfaces of the connection portion such that the nicks extend to the widthwise center thereof and confront each other. As further example, a portion is formed on the connection portion such that the portion is shorter or thinner than other portions thereof. As still further example, a portion is formed on the connection portion such that the portion is shorter and thinner than other portions thereof.

In the stent90of the present invention, an inflating balloon catheter can be inserted into each of the stents such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion can be broken by the inflation of the balloon of the inflating balloon catheter, as shown inFIG. 23. As shown inFIG. 23, each annular member keeps a dilated configuration. Thus the entire stent90also keeps a dilated configuration. When the inflating balloon catheter is inserted into the dilated stent and passed the side wall of the stent90by guiding with a guide wire and the balloon is inflated, the connection portion of the stent is cut off at the weak portion by the inflated balloon. As a result, a hole having a diameter almost equal to an enlarged diameter of the inflated balloon is formed through the side wall. If the stent does not have the the weak portion, the inflating balloon catheter cannot secure a hole (space) larger than the space formed of a deformation of the annular members to the maximum. Thus, if the balloon is inflated forcibly, it bursts. That is, because the stent has the weak connection portion, the stent is stable in its configuration in a blood vessel.

The joining portions181–202joining the wavy annular members of the adjacent annular units31–42remain unchanged substantially in their lengths when the stent90is dilated. Because the joining portions181–202and the connection portion4remain substantially unchanged in their lengths even when the stent90is dilated, the overall length of the stent90remains substantially unchanged before and after dilation. It never happens that the stent is reduced in length after dilation.

The joining portion181–202is so disposed that it connects the adjacent annular units31–42at two positions. In the embodiment, the joining portion181–202may be so disposed that the adjacent ones are continuous with each other.

To reduce the degree of damage to be applied to the inflated balloon when the connection portion4is broken, it is preferable that the edge of the wavy element of the stent is chamfered. As the method of chamfering the stent, after the stent is fabricated into a final shape, chemical polishing, electropolishing or mechanical polishing can be used. The chemical polishing is preferably carried out by dipping the stent in a chemical polishing solution for stainless steel. Any chemical polishing solution containing one capable of dissolving stainless steel may be used. For example, one preferable chemical polishing solution contains a mixture of hydrochloric acid and nitric acid serving as a base component and additives such as an organic sulfur compound for adjusting a dissolution rate, smoothing, and imparting luster and a surface active agent.

It is possible that the wavy element of the annular members2a,2blocated at the opposed ends of the stent90in the axial direction thereof has a sectional area, respectively smaller than that of the other wavy annular members. This construction causes the dilation force of the wavy annular members located at the opposed ends of the stent90in the axial direction thereof to be lower than those of the other wavy annular members when the stent90dilates, but allows the annular members2a,2blocated at the opposed ends of the stent90in the axial direction thereof to follow the bending of a blood vessel to a high extent. That is, the opposed ends of the stent90in the axial direction thereof have a high degree of affinity for the blood vessel. As the method of reducing the thickness of the annular members2a,2blocated at the opposed ends of the stent90in the axial direction thereof, after the stent is fabricated into the final shape, the annular members2a,2bis chemically polished or mechanically polished.

It is possible that the material of the annular unit (annular member) located at the axial center of the stent90have the maximum cross-sectional area and that the annular units (annular member) located nearer to the axial end of the stent have a smaller cross-sectional area than the annular units located nearer to the center of the stent. Specifically, the thickness of the annular units are so set that the thickness of the annular units34,35,36,37and38located at the axial central part of the stent90have a largest thickness and the other annular units have small thicknesses decreasingly as they are nearer to both axial ends of the stent. This construction ensures that the stent90displays a sufficient dilating force at its central part and faithfully follows a bent portion of a blood vessel. That is, both axial ends of stent90have better affinity for the blood vessel. It is also possible that the annular unit located at the center of the stent90has a maximum width and the other annular units have small widths decreasingly as they are nearer to both axial ends of the stent.

In the stent90, a part of the wavy annular member2aof one annular unit is in penetration into the wavy space formed at the axial end (inner side of stent) of the other annular unit adjacent to the one annular unit. That is, a part of the mountain of the wavy annular member2aof one annular unit is in penetration into the concave portion of the wavy annular member2bformed in the vicinity of the connection portion of the other annular unit adjacent to the one annular unit. Therefore, the adjacent annular units overlap partially each other when the stent90is viewed in the axial direction thereof. Thus, when the constituent elements of the wavy annular members are reduced in their lengths in the axial direction of the stent upon dilation of the stent, gaps on the side surface of the stent increase to a small extent. Therefore, it is possible to dilate a stenosed portion of a blood vessel securely and holds an affected portion without a gap.

The mountain of the annular member2bhaving one of the joining portions181–202formed therein is wider than the other mountains thereof, such that a part of the mountain is adjacent to the joining portion. Similarly, the valley of the annular member2ahaving one of the joining portions181–202formed therein is wider than the other valleys thereof, such that a part of the valley is adjacent to the joining portion. In the embodiment, the joining portion is approximately linear.

It is preferable that the material of the stent90has a certain degree of compatibility with an organism. For example, it is possible to use stainless steel, tantalum or tantalum alloys, platinum or platinum alloys, gold or gold alloys, cobalt base alloys and the like. It is preferable to plate the stent with a noble metal such as gold and platinum after the stent is fabricated into a final shape. As the stainless steel, SUS 316L most corrosion-resistant of the above metals can be preferably used.

It is preferable to anneal the stent90after it is fabricated into the final shape. Annealing improves the flexibility and plasticity of the entire stent so that the stent can be effectively implanted in a curved blood vessel. As compared with a non-annealed stent, the annealed stent has a lower force of restoring to an original state after it is dilated, and especially has a lower force of restoring to an original linear state when it is dilated at a curved portion of a blood vessel. This minimizes physical stimulation to the inner wall of the curved blood vessel, thus reducing the cause of a recurrence of stenosis. The stent is preferably annealed by heating it to 900 to 1200° C. in an inert gas atmosphere (e.g., a mixture gas of nitrogen and hydrogen) so that no oxide film is formed on the surface of the stent and then slowly cooling it.

The stent1has a diameter favorably 0.8 to 1.8 mm and more favorably 1.0 to 1.6 mm in an undilated state. The stent90has a length favorably 9 to 40 mm in an undilated state. The length of each of the wavy annular members2a,2bhas a length of 0.7 to 2.0 mm. The length of one of the annular units31through42is favorably 1.5–4.0 mm and more favorably 2.0–3.0 mm. The length of one connection portion4is favorably 0.01–0.5 mm. The number of the annular units31through42is 3 to 50. The constituent elements (annular member) of the adjacent annular units have an axial overlap of about 0.5 to 1 mm. The distance between the center of one annular units and that of the annular unit adjacent thereto is preferably 1.3 to 2.5 mm. The length of each of the joining portions181–202is preferably 1.4 to 2.7 mm. The angle of inclination (the angle of inclination of the joining portion relative to a longitudinal direction in a development view) of each of the joining portion181through202relative to the axis of the stent is favorably 0° to 30° and more favorably 5° to 25°.

The thickness of each of the wavy annular members2a,2b(wavy elements, wavy line-shaped elements) of the stent90and that of each of the joining portions181–202are favorably 0.05 to 0.15 mm and more favorably 0.08 to 0.12 mm. The width of each of the wavy annular members2a,2band that of each of the joining portions181–202are favorably 0.07 to 0.15 mm and more favorably 0.08 to 0.12 mm. The thickness of the connection portion4of the stent90is favorably 0.05–0.12 mm and more favorably 0.06–0.10 mm. The width of the connection portion4of the stent90is favorably 0.01–0.05 mm and more favorably 0.02 to 0.04 mm. The sectional area of the connection portion4is favorably 1/50 to ½ of that of the other parts (annular member and joining portion) and more favorably 1/20 to 1/10 of that of the other parts.

An embodiment of the blood vessel dilation device of the present invention is described below with reference to the drawings.

FIG. 14is a front view of a organ dilation device according to an embodiment of the present invention.FIG. 15is a partly enlarged sectional view showing a front end of the organ dilation device shown inFIG. 14.FIG. 16is a partly enlarged sectional view showing a rear end of the organ dilation device shown inFIG. 14.FIG. 17is a partly enlarged sectional view showing a front end of a organ dilation device according to another embodiment of the present invention.

A blood vessel dilation device100of the present invention has a tubular shaft body102, a foldable and expandable balloon103provided on a front end of the shaft body102; and a stent1installed on the folded balloon103so that the stent1covers the balloon103and dilated by expansion of the balloon103.

The stent1is formed in a substantially tubular configuration and has a diameter so set that it is inserted into the body. The stent1can be dilated when a force acting radially outwardly is applied thereto from the interior thereof. The stent1has a plurality of wavy annular members consisting of the wavy element and arranged in the axial direction of the stent1and a plurality of connection portions each connecting the adjacent wavy annular members to each other axially. The connection portion located in the vicinity of the axial center of the stent1is weaker than the other constituent parts thereof and can be broken.

The shaft body102of the blood vessel dilation device100of the present invention has a balloon expansion lumen communicating with the inside of the balloon103. The blood vessel dilation device100has a radiographing member105fixed to an outer surface of the shaft body102such that the fixing position of the radiographing member105is located at the center of the stent1or radiographing members105a,105bfixed to the outer surface of the shaft body102(in the embodiment, inner tube112) such that the fixing positions of the radiographing members105a,105bare located at one and other ends of the central region, of the stent1, having a predetermined length.

In the organ dilation device100of the embodiment, as shown inFIG. 14, the shaft body102has a guide wire lumen115whose one end is open at a front end of the shaft body102and other end is open at a rear end thereof.

The organ dilation device100of the present invention has the tubular shaft body102, the stent-dilating balloon103attached to the front end of the shaft body102; and the stent1installed on the balloon103. The shaft body102has an inner tube112, an outer tube113, and a branch hub110.

As shown inFIGS. 15 and 16, the inner tube112has a guide wire lumen115for inserting a guide wire thereinto. The length of the inner tube112is favorably 100 to 2000 mm and more favorably 150–1500 mm. The outer diameter of the inner tube112is favorably 0.1 to 1.0 mm and more favorably 0.3 to 0.7 mm. The thickness of the inner tube112is favorably 10 to 150 μm and more favorably 20 to 100 μm. The inner tube112is inserted into the outer tube113to such an extent that the front end of the inner tube112projects from the outer tube113. A balloon expansion lumen116is formed between the outer surface of the inner tube112and the inner surface of the outer tube113and has a large volume. The front end of the outer tube113into which the inner tube112is inserted is located a little rearward from the front end of the inner tube112.

The length of the outer tube113is favorably 100 to 2000 mm and more favorably 150–1500 mm. The outer diameter of the outer tube113is favorably 0.5 to 1.5 mm and more favorably 0.7 to 1.1 mm. The thickness of the outer tube113is favorably 25 to 200 μm and more favorably 50 to 100 μm.

In the organ dilation device100of the embodiment, the outer tube113consists of a front-end side outer tube113aand a shaft body side outer tube113bjoined with the front-end side outer tube113a. The diameter of the front-end side outer tube113adecreases in the region from the joining position at which the front-end side outer tube113aand the shaft body side outer tube113bare joined with each other to a position spaced at a certain interval forward from the joining position. Therefore, in the tapered region, the diameter of the front-end side outer tube113adecreases gradually. The diameter thereof except the tapered region is constant and smaller than that of the front end of the tapered region.

The outer diameter of the front-end side outer tube113aat its smaller-diameter portion is favorably 0.50 to 1.5 mm and more favorably 0.60 to 1.1 mm. The outer diameter of the front-end side outer tube113aat its rear end portion and that of the shaft body side outer tube113bare favorably 0.75 to 1.5 mm and more favorably 0.9 to 1.1 mm.

The balloon103has a front-end side bonding portion103aand a rear-end side bonding portion103b. The front-end side bonding portion103ais fixed to the inner tube112at a position a little rearward from the front end thereof. The rear-end side bonding portion103bis fixed to the front end of the outer tube113. The balloon103communicates with the balloon expansion lumen116at a position in the vicinity of the rear end of the balloon103.

A material having a certain degree of flexibility can be preferably used for the inner tube112and the outer tube113. It is favorable to use thermoplastic resins such as polyolefin (for example, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer), polyvinyl chloride, polyamide elastomer, and polyurethane; silicone rubber; latex rubber; and the like. It is more favorable to use the thermoplastic resins. Polyolefin is the most favorable of the thermoplastic resins.

As shown inFIG. 15, the balloon103is foldable. When the balloon103is not expanded, it can be folded over the outer surface of the inner tube112. The balloon103has a tubular (preferably, cylindrical) expandable portion having an approximately uniform diameter so that the stent1to be installed on the balloon103can be dilated. The expandable portion is not necessarily cylindrical but may be polygonal. As described above, the front-end side bonding portion103aof the balloon103is liquid-tightly bonded to the inner tube112, and the rear-end side bonding portion103bthereof is liquid-tightly bonded to the front end of the outer tube113with an adhesive agent or thermal fusion. The balloon103tapers between the expandable portion and each of the bonding portions103aand103b.

An expansion space103cis formed between the inner surface of the balloon103and the outer surface of the inner tube112. The entire circumference of the expansion space103ccommunicates with the balloon expansion lumen116at the rear end of the expansion space103c. Because the expansion space103ccommunicates with the balloon expansion lumen116having a comparatively large volume, it is easy to inject an expansion fluid into the balloon103through the balloon expansion lumen116.

A material having a certain degree of flexibility can be preferably used for the balloon103. It is favorable to use thermoplastic resins such as polyolefin (for example, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, cross link type of ethylene-vinyl acetate copolymer, polyvinyl chloride, polyamide elastomer, and polyurethane, polyester (for example, polyethylene terephthalate), polyarylane sulfide (for example, polyphenylene sulfide); silicone rubber; latex rubber and the like. It is particularly favorable to use extensible material. A biaxially oriented material can be preferably used for the balloon103because of its high degree of strength and expansion.

Regarding the size of the balloon103, the outer diameter of the dilated cylindrical portion (expandable portion) thereof is favorably 2 to 4 mm and more favorably 2.5 to 3.5 mm. The length of the balloon103is favorably 10 to 50 mm and more favorably 20 to 40 mm. The outer diameter of the front-end side bonding portion103ais favorably 0.9 to 1.5 mm and more favorably 1 to 1.3 mm. The length of the front-end side bonding portion103ais favorably 1 to 5 mm and more favorably 1 to 1.3 mm. The outer diameter of the rear-end side bonding portion103bis favorably 1 to 1.6 mm and more favorably 1.1 to 1.5 mm. The length of the rear-end side bonding portion103bis favorably 1 to 5 mm and more favorably 2 to 4 mm.

As shown inFIG. 15, the blood vessel dilation device100has radiographing members105a,105bfixed to the outer surface of the shaft body102(in the embodiment, inner tube112) such that the fixing positions of the radiographing members105a,105bare located at one and other ends of the central region, of the stent1, having a predetermined length. Therefore, in introducing the stent1into a branched blood vessel, it is easy to implant the stent1such that the central region thereof is disposed at the branch portion. The distance between the radiographing members105aand105bis preferably 2–5 mm and favorably 10–70% of the entire length of the stent1and more favorably 10–50% of the entire length thereof.

As shown inFIG. 17showing another embodiment, the blood vessel dilation device250may have a radiographing member105fixed to the outer surface of the shaft body such that the installing position of the radiographing member105is located at the center of the stent1. The blood vessel dilation device100has two radiographing members117,118fixed to the outer surface of the shaft body102such that the radiographing member117,118are located at one and other ends of the cylindrical portion (expandable portion) of the balloon103when the stent is dilated.

The radiographing members105,105a,105b,117, and118are preferably in the shape of a ring having a predetermined length, a coiled wire or the like. It is preferable that the radiographing members105,105a,105b,117, and118are made of gold, platinum, tungsten or alloys thereof or a silver-palladium alloy or the like.

As the stent1for use in the organ dilation devices100and250of the present invention, all of the above-described stents can be used.

As shown inFIG. 16, a linear reinforcement member133is inserted between the inner tube112and the outer tube113, namely, into the balloon expansion lumen116. The reinforcement member133prevents excess bending of the body of the organ dilation device100at bent portions of blood vessels without much deteriorating the flexibility of the organ dilation device100and facilitates the insertion of the frond end of the organ dilation device100into the bent portions of blood vessels. The diameter of the frond end of the reinforcement member133is set smaller than those of the other portions thereof by grinding or the like. It is preferable that front end of the small-diameter extends to the vicinity of the front end of the outer tube113of the body of the organ dilation device100. It is preferable that the reinforcement member133consists of a metal wire having a diameter 0.05 to 1.50 mm and more favorably 0.10 to 1.00 mm. The reinforcement member133is made of favorably an elastic metal such as stainless steel or a super elastic alloy and more favorably high-strength stainless steel for a spring or a super elastic alloy.

As shown inFIG. 16, the organ dilation device100of the embodiment has a branched hub110fixed to the rear end thereof.

The branched hub110consists of an inner-tube hub122fixed to the inner tube112and having a guide wire introducing opening109communicating with the guide wire lumen115and forming a guide wire port; and an outer-tube hub123fixed to the outer tube113and having an injection port111communicating with the balloon expansion lumen116. The outer-tube hub123and the inner-tube hub122are fixed to each other. As the material of the branched hub110, thermoplastic resin such as polycarbonate, polyamide, polysulfone, polyacrylate and methacrylate-butylene-stylene copolymer can be preferably used.

In the embodiment, the outer tube113has a bending-preventing tube150mounted on the rear end portion thereof. The bending-preventing tube150is formed of a heat-shrinkable material so that its inner diameter becomes a little smaller than the outer diameter of the outer tube113after the bending-preventing tube150shrinks with heat. The bending-preventing tube150thus formed is installed on the rear end portion of the outer tube113by fitting the bending-preventing tube150on the rear end portion of the outer tube113and heating (for example, with hot air) the bending-preventing tube150to shrink it. The bending-preventing tube150is fixed to the outer-tube hub123with a retaining pin152. The outer diameter of the cylindrical retaining pin152is approximately equal to the inner diameter of the outer tube113except the rear end portion thereof. That is, the outer diameter of the cylindrical retaining pin152at its rear end portion is larger than the outer diameter at the other portion thereof. Describing the method of installing the bending-preventing tube150on the outer-tube hub123in detail, the retaining pin152is inserted into the rear end of the outer tube113. Then, the outer tube113is inserted into the outer-tube hub123, with the front end thereof leading and pressed until the rear end of the retaining pin152passes a projection154formed on the inner surface of the outer-tube hub123. An adhesive agent may be applied to the contact surface of the outer-tube hub123and that of the bending-preventing tube150to secure the bending-preventing tube150to the outer-tube hub123.

The inner tube112has a bending-preventing tube160mounted on the rear end portion thereof. The bending-preventing tube160is formed of a heat-shrinkable material so that its inner diameter becomes a little smaller than the outer diameter of the inner tube112after the bending-preventing tube160shrinks with heat. The bending-preventing tube160thus formed can be easily installed on the rear end portion of the inner tube112by fitting the bending-preventing tube160on the rear end portion of the inner tube112and heating (for example, with hot air) the bending-preventing tube160to shrink it. The rear end of the reinforcement member133is fixed to the outer surface of the inner tube112with the bending-preventing tube160. The inner tube112on which the bending-preventing tube160has been installed is fixed to the inner-tube hub122. The bending-preventing tube160is fixed to the inner tube112with a retaining pin162. The outer diameter of the cylindrical retaining pin162is approximately equal to the inner diameter of the inner tube112except the rear end portion thereof. That is, the outer diameter of the cylindrical retaining pin162at its rear end portion is larger than the outer diameter at the other portion thereof. Describing the method of installing the bending-preventing tube160on the inner-tube hub122in detail, the retaining pin162is inserted into the rear end of the inner tube112. Then, the inner tube112is inserted into the inner-tube hub122, with the front end thereof leading and pressed until the rear end of the retaining pin162passes a projection164formed on the inner surface of the inner-tube hub122. An adhesive agent may be applied to the contact surface of the inner-tube hub122and that of the bending-preventing tube160to secure the inner tube112to the inner-tube hub122.

As the material of the outer-tube hub and the inner-tube hub, thermoplastic resin such as polycarbonate, polyamide, polysulfone, polyacrylate, and methacrylate-butylene-stylene copolymer can be preferably used.

The inner-tube hub122and the outer-tube hub123are fixed to each other by inserting the inner tube112into the rear end of the outer-tube hub123installed on the rear end of the outer tube113, with the front end of the inner tube112leading. The inner-tube hub122and the outer-tube hub123can be securely fixed to each other by applying an adhesive agent to the joining portion of each thereof.

The construction of the rear end portion of the organ dilation device100is not limited to the above-described one. For example, instead of the branched hub110, a tube having a port member forming an opening at its rear end may be liquid-tightly installed on the guide wire lumen115and the balloon expansion lumen116, respectively.

The method of using the stent of the present invention and the blood vessel dilation device of the present invention will be described below.FIGS. 18 and 19are explanatory views for describing the operation of the stent of the present invention and that of the blood vessel dilation device thereof.

The blood vessel dilation device100has the stent1and the balloon catheter for dilating the stent1in a blood vessel. The blood vessel dilation device100is inserted into a sheath, and a guide wire is introduced into the blood vessel dilation device. Then, under the guide of the guide wire, the blood vessel dilation device is introduced into a stenosed portion of a branched blood vessel. After the guide wire passes through the stenosed portion of the branched blood vessel, the blood vessel dilation device is progressed along the guide wire. After the blood vessel dilation device and the sheath are introduced into the stenosed portion, using a fluoroscope, the blood vessel dilation device is located in the stenosed portion such that the two radiographing members indicating the central portion of the stent straddles the branch portion. Then, the sheath is moved rearward. Then, a contrast medium is injected into the balloon under a high pressure to inflate the balloon. As a result of the inflation of the balloon, the stent1undergoes a plastic deformation, i.e., it dilates (inflates) radially outwardly, thus widening the stenosed portion. Then, the pressure of the balloon is removed to contract it. The stent does not contract owing to its plastic deformation caused dilation state-keeping force (configuration-keeping force) and thus stays at the stenosed portion, thereby keeping the blood vessel dilated and improving blood stream disorder.

To secure a favorable blood stream to the branched blood vessel and implant the stent therein, an operation of partly breaking a side wall of the stent positioned at an opened portion of the branch portion of the blood vessel is performed. In the operation of breaking the side wall of the stent partly, as shown inFIG. 18, initially, a guide wire171is introduced into a main blood vessel170. Then, the front end of the guide wire171is penetrated through the side wall of the stent1to insert the guide wire171into branched blood vessel172. Then, using the guide wire171, an dilating balloon catheter173(having an outer diameter allowing the catheter173) for use in the blood vessel dilation device and penetrable through the side wall of the stent is so guided that the front end of the catheter173reaches the interior of the branched blood vessel172and that the central portion of a balloon174of the catheter173crosses the side wall of the stent1. This state is shown inFIG. 18.

Then, the balloon is inflated to break the connection portion4that is the weak portion of the stent1, as shown inFIG. 19. As a result, an enlarged opening177larger than other portions of the stent1is formed on the side wall of the stent1. The enlarged opening177reduces the possibility that blood flowing from the main blood vessel170to the branched blood vessel172is blocked and allows insertion of another balloon catheters, blood vessel dilation device, and stent into the branched blood vessel172.

EXAMPLE

A metal pipe used in example 1 was made of stainless steel (SUS 316L) having a diameter of 1.4 mm, a thickness of 0.10 mm, and a length of 100 mm.

A stent was prepared by hollowing out a metal pipe to leave a stent skeleton. A stent skeleton can be hollowed out of a metal pipe in many ways. Exemplary processes include an etching process, known as photo-fabrication, using masks and chemicals, electric discharge machining, and mechanical machining. A laser machining processing method was used herein because it is simplest to operate and highest in precision.

A laser machining device used was a YAG laser model SL116E manufactured by NEC. The metal pipe was mounted on a jig equipped with a rotating motor and a fastening mechanism to prevent run-out of the metal pipe. The jig was set on a numerically controllable XY table. The XY table and the rotating motor were connected to a personal computer such that an output of the personal computer was transmitted to a numerical controller of the XY table and the rotating motor. A development drawing representing the stent having the structure shown inFIG. 2was inputted to the personal computer storing a design software.

The XY table and the rotating motor were driven in accordance with design data outputted from the personal computer. The pipe was irradiated with a laser beam to machine the pipe into a stent structure having the configuration shown inFIG. 1.

A mandrel was inserted into the pipe to prevent the laser beam from penetrating throughout the pipe. As the laser machining condition for the metal pipe, current value was 25 A, an output was 1.5 W, and a drive speed was 10 mm/min. The machine is not limited to the above-described system but it is possible to use a laser marker of the galvanometer system to be driven by a laser machining device.

A stent structure having the configuration shown inFIGS. 1 through 3was prepared in this manner. The stent structure was dipped in a stainless steel chemical polishing solution at about 98° C. for about 10 minutes to chamfer (deburr and chemically polish) the stent structure. The chemical polishing solution used in example 1 was a solution containing a mixture of hydrochloric acid and nitric acid serving as a main component, an organic sulfur compound, and a surface active agent. The chemical polishing solution is commercially available as Sunbit 505 from Sanshin Chemical Industry K.K.

In this manner, the stent of the present invention having the configuration shown inFIGS. 1 through 3was prepared. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting a wavy element (wavy annular member) and a joining portion was 0.12 mm. A connection portion had a width of 0.03 mm and a length of 0.1 mm. All the stent had a thickness of about 0.08 mm.

Similarly to example 1, a metal pipe made of stainless steel (SUS 316L) having a diameter of 1.4 mm, a thickness of 0.10 mm, and a length of 100 mm.

Using a method similar to that of example 1, a development drawing representing a stent having the construction shown inFIG. 5was inputted to the design software of the personal computer.

The stent of the present invention having the configuration shown inFIGS. 4 through 7was prepared. Similarly to example 1, the stent was chamfered. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member) and the connection portion was 0.12 mm, respectively. The narrowest portion of the slit-formed portion (weak portion) of the connection portion had a width of 0.02 mm. The connection portion had a length of 3 mm. All the stent had a thickness of about 0.08 mm.

Comparison Example 1

Using a method similar to that of example 1, a stent having the same configuration as that shown inFIGS. 1 through 3was prepared, but the connection portion was different from that shown inFIGS. 1 through 3. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member), the joining portion, and the connection portion was 0.12 mm, respectively. The connection portion had a length of 0.1 mm. All the stent had a thickness of about 0.08 mm.

Comparison Example 2

Using a method similar to that of example 2, a stent having the same configuration as that shown inFIGS. 4 through 7was prepared, but the weak portion was not formed on the connection portion. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member) and the connection portion was 0.12 mm, respectively. The connection portion had a length of 3 mm. The stent had a thickness of about 0.08 mm.

The stent of each of examples 1 and 2 and comparison examples 1 and 2 was mounted on a balloon of an expandable catheter (balloon catheter) for PTCA. Each stent was dilated to have a diameter of 3 mm. As a result, the stent of example 1 and that of comparison example 1 deformed as shown inFIG. 4, and the stent of example 2 and that of comparison example 2 deformed as shown inFIG. 11. The connection portion of each stent was not broken.

The expandable catheter (balloon catheter) for PTCA having an expanded diameter of 3 mm was inserted into the stent of each of examples 1 and 2 and comparison examples 1 and 2 from the lumen thereof such that the catheter penetrated through the side wall of the stent and the front end thereof projected to the outside. After the balloon crossed the side wall of the stent, the balloon was expanded. The result was that in the stent of each of examples 1 and 2, one connection portion was broken and the balloon could be expanded to a length of 3 mm. At the cutting point of the stent of example 1, the thickness was about 0.08 mm, the width was 0.03 mm, the sectional area was 0.0024 mm2. At the cutting point of the stent of example 2, the thickness was about 0.09 mm, the width was 0.02 mm, the sectional area was 0.0016 mm2. The stent of each of comparison examples 1 and 2 burst when the pressure of the balloon became about 16 atm when the balloon was inflated.

Similarly to example 1, a metal pipe made of stainless steel (SUS 316L) having a diameter of 1.4 mm, a thickness of 0.1 mm, and a length of 100 mm.

Using a method similar to that of example 1, a development drawing representing a stent having the construction shown inFIG. 21was inputted to the design software of the personal computer.

The stent of the present invention having the configuration shown inFIG. 20was prepared. Similarly to example 1, the stent was chamfered. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member) and the connection portion was 0.12 mm. The integral portion had a width of 0.20 mm. The connection portion had a width of 0.03 mm and a length of 0.05 mm. All the stent had a thickness of about 0.08 mm.

Similarly to example 1, a metal pipe made of stainless steel (SUS 316L) having a diameter of 1.4 mm, a thickness of 0.1 mm, and a length of 100 mm.

Using a method similar to that of example 1, a development drawing representing a stent having the construction shown inFIG. 25was inputted to the design software of the personal computer.

The stent of the present invention having the configuration shown inFIG. 24was prepared. Similarly to example 1, the stent was chamfered. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member) and the connection portion was 0.12 mm. The integral portion had a width of 0.20 mm. The connection portion had a width of 0.03 mm and a length of 0.05 mm. All the stent had a thickness of about 0.08 mm.

Comparison Example 3

Using a method similar to that of example 1, a stent having the same configuration as that shown inFIG. 20was prepared, but the connection portion was different from that shown inFIGS. 1 through 3. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member), the joining portion, and the connection portion was 0.12 mm, respectively. The integral portion had a width of 0.20 mm. The connection portion had a width of 0.10 mm and a length of 0.05 mm. All the stent had a thickness of about 0.08 mm.

Comparison Example 4

Using a method similar to that of example 1, a stent having the same configuration as that shown inFIG. 24was prepared, but the connection portion was different from that shown inFIGS. 1 through 3. The stent had an entire length of 20 mm and an outer diameter of 1.4 mm. The width of a portion constituting the wavy element (wavy annular member), the joining portion, and the connection portion was 0.12 mm, respectively. The integral portion had a width of 0.20 mm. The connection portion had a width of 0.10 and a length of 0.05 mm. All the stent had a thickness of about 0.08 mm.

The stent of each of examples 3 and 4 and comparison examples 3 and 4 was mounted on a balloon of an expandable catheter (balloon catheter) for PTCA. Each stent was dilated to have a diameter of 3 mm. As a result, the diameter of the stent of example 3 and 4 and that of comparison example 3 and 4 dilated. The connection portion of each stent was not broken.

The expandable catheter (balloon catheter) for PTCA having a diameter of 3 mm in an inflated state was inserted into the stent of example 3 and 4 and that of comparison example 3 and 4 from the lumen thereof such that the catheter penetrated through the side wall of the stent and the front end thereof projected to the outside. After the balloon crossed the side wall of the stent, the balloon was expanded. The result was that in the stent of example 3, one connection portion was broken and the balloon could be so inflated that it had an increased diameter of 3 mm. The cutting point of the stent of example 3 had a thickness of about 0.08 mm, a width of 0.03 mm, and a sectional area of 0.0024 mm2. The cutting point of the stent of example 4 had a thickness of about 0.08 mm, a width of 0.03 mm, and a sectional area of 0.0024 mm2. On the other hand, the stent of comparison examples 3 burst when the pressure of the balloon became about 16 atm when the balloon was inflated. The stent of comparison examples 4 burst when the pressure of the balloon became about 16 atm when the balloon was inflated.

The stent of the present invention is formed in a substantially tubular configuration and has a diameter so set that the stent is inserted into the body. The stent can be dilated radially outwardly upon application of a force acting radially outwardly from the interior of the tubular stent. The stent has a plurality of wavy annular members each formed of a narrow wavy element and arranged in the axial direction thereof; and a plurality of connection portions each connecting the adjacent wavy annular members to each other axially. The connection portion located in the vicinity of the axial center of the stent is weaker than the other constituent parts of the stent and can be broken. Owing to the construction, an inflating balloon catheter can be inserted into the stent such that the inflating balloon catheter penetrates through a side wall of the stent from its interior after the stent is dilated radially. The connection portion can be broken by the inflation of the balloon of the inflating balloon catheter.

In this construction, when the stent embedded in a visinity of a branch portion of a blood vessel, the connection portion of the stent can be partly broken, using the balloon catheter or the like. Consequently, it is possible to form an enlarged opening on the side wall of the stent located at an opened portion formed at the inlet of the branched blood vessel. The enlarged opening reduces the possibility that blood flowing from a main blood vessel to the branched blood vessel is blocked and prevents thrombus from arising at the branched portion. Further, using the enlarged opening formed on the side wall of the stent, it is possible to insert another balloon catheter, blood vessel dilation device and stent into the branched blood vessel.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.