JP5267457B2 - Stent - Google Patents

Description

  The present invention relates to a stent for implantation in a living body.

  Stents are used to treat various diseases caused by stenosis or occlusion of blood vessels or other in-vivo lumens, to expand the stenosis or occlusion site and to maintain the size of the lumen. Is a medical device. A stent is a coil made of a single linear metal or polymer material, a metal tube cut and processed by a laser, a linear member welded and assembled by a laser, a plurality of wires There are things made by weaving metal like metal.

  From the point of expansion mechanism, it can be expanded by a balloon with a stent mounted (balloon expandable type), and can be expanded by removing a member that suppresses expansion (self-expandable type). And can be classified.

  The balloon expandable type is attached to the balloon portion of an expandable member (balloon catheter) attached to the vicinity of the distal end of the intravascular catheter (balloon catheter), and advances the catheter to the treatment site in the body lumen of the patient. The balloon is inflated at the treatment site, and the stent is expanded and indwelled accordingly. The balloon is then deflated and the catheter is removed. When the balloon is expanded, the expansion pressure is adjusted according to the state of the tubular tissue to be expanded and the mechanical strength of the stent.

  The stent is required to have pulsation durability that suppresses the occurrence of stress concentration in the stent due to a large movement of the blood vessel due to the pulsation of the heart when placed in the blood vessel. When stress concentration occurs in the stent, problems such as fracture and breakage of the stent occur. These problems are very serious problems that have a great impact on stent failure after stent placement.

In addition, the stent is strong enough to withstand the tubular tissue to be expanded, flexible enough to advance through the severely bent tubular tissue to the target site without problems, and when placed in the tubular tissue. Various stent designs are required, such as post-expansion flexibility to prevent damage to the tubular tissue as much as possible, expansion uniformity and fineness of design to cover the tubular tissue more evenly, etc. Has been proposed. These are disclosed in, for example, Patent Documents 1 to 2.
Japanese Patent Application Laid-Open No. 6-181993 No. 11-501551

  In a stent having a coating layer such as a stent coated with a drug, when the stent is expanded with a balloon catheter, there is a problem that the coating layer is cracked or peeled off at a portion having a large strain accompanying expansion of the stent. These problems are very large problems that affect the therapeutic effect after stent placement.

  In general, the inner curvature and the outer curvature of the bent portion in the stent cell are the same in the center of the circle forming the mutual curvature, and the width of the bent portion is the width of the strut in order to ensure radial rigidity. The inner radius of curvature is determined so as to be the same. However, in actual use, a large movement of the blood vessel due to the pulsation of the heart causes stress concentration in the bent portion of the cell, and the possibility of breakage increases. In addition, since the strain associated with the expansion of the stent increases and the coating layer is cracked or peeled off, a stent design with less stress concentration at the bent portion and less strain is currently required. In order to reduce the stress concentration and distortion of the bent part, increasing the curvature inside the strut can be considered as one countermeasure.

  However, there is a limit to increasing the curvature inside the strut in order to improve the pulsation durability of the stent and to suppress the cracking and peeling of the coating layer. If the curvature on the inner side of the strut is increased, the width of the bent portion is narrowed and the rigidity in the radial direction is lowered.

  In view of these circumstances, the present invention intends to solve the problem by providing a stent that reduces the stress concentration generated in the stent due to a large blood vessel movement caused by the pulsation of the heart when placed in the body. Another object of the present invention is to provide a stent having high pulsation durability after stent placement.

  The present invention has one or more of the following features.

One feature of the present invention is a stent that is formed into a generally tubular body and is radially expandable from a compressed first diameter to a second expanded diameter.
The stent has a generally undulating component that is extensible in a circumferential direction;
The center position of the circle forming the inner curvature of the bent portion and the center position of the circle forming the outer curvature of the substantially corrugated component are the center position of the circle forming the inner curvature of the bent portion and the circle forming the outer curvature. Arranged at different positions with respect to the stent longitudinal axis direction so that the line connecting the central positions is parallel to the stent longitudinal axis direction ,
The width of the bent portion formed by the inner curvature and the outer curvature is larger than the width of the strut of the straight portion disposed between the bent portions in the substantially corrugated component,
The length of the arc of the inner curvature at the bent portion is 50% or more of the circumference of a circle drawn with the inner curvature,
The stent is characterized in that an inner radius of curvature of the bent portion is larger than a value obtained by subtracting the strut width of the straight portion from the outer radius of curvature .

  Another feature of the present invention is that the inner radius of curvature and the outer radius of curvature of the bent portion are different.

  Another feature of the present invention is that the center position of the circle forming the inner curvature of the bent portion is disposed farther from the bent portion in the longitudinal direction of the stent than the center position of the circle forming the outer curvature. That is.

  In an embodiment of the present invention, the stent material can be formed of at least one material selected from the group consisting of stainless steel, nickel alloy, and cobalt chromium alloy.

  In an embodiment of the present invention, it is possible to immobilize a drug that suppresses vascular occlusion on the outer surface of the stent.

  The above and other features of the present invention and their effects will become apparent from the following description and drawings.

  According to the present invention, it is possible to reduce stress concentration caused by a large movement of a blood vessel due to the pulsation of the heart when placed in the body. Furthermore, it becomes possible to suppress the cracking and peeling of the coating layer due to the strain accompanying the expansion of the stent. Furthermore, it becomes possible to improve the expansion uniformity after stent expansion. Thereby, the pulsation durability after placement of the stent is high, cracking and peeling of the coating layer when the stent is expanded can be suppressed, and a stent with excellent expansion uniformity after the stent expansion can be provided.

FIG. 2 is a development view of the stent 1. It is the elements on larger scale which show the substantially waveform component 2 which can be expand | extended in the circumferential direction. It is the elements on larger scale which show the substantially waveform component 3 which can be expand | extended in the circumferential direction. FIG. 5 is a partial view showing a portion 4 composed of a substantially waveform component 2. FIG. 5 is a partial view showing a portion 5 made up of a substantially waveform component 3. It is an expanded view of the stent of the comparative example 1. It is the elements on larger scale which show the substantially waveform component 7 which can be expand | extended in the circumferential direction. It is the elements on larger scale which show the substantially waveform component 8 which can be expand | extended in the circumferential direction. FIG. 6 is a partial view showing a portion 9 composed of a substantially waveform component 7. A portion BR>} showing a portion 10 composed of a substantially waveform component 8. 10 is a schematic diagram for explaining a configuration section of a stent of Comparative Example 1. FIG.

101 first end section 102 second end section 103 third central section 104 fourth section 105 fifth section 201 center of outer radius of curvature 202 center of inner radius of curvature 203 outer radius of curvature 204 inner radius of curvature 205 strut width 206 Bending width 301 Center of outer curvature radius 302 Center of inner curvature radius 303 Outer curvature radius 304 Inner curvature radius 305 Strut width 306 Bending width 701 Outer curvature radius 702 Inner curvature radius 703 Strut width 801 Outer curvature radius 802 Inner curvature Radius 803 strut width 1101 first end section 1102 second end section 1103 third central section 1104 fourth section 1105 fifth section

  Hereinafter, embodiments of the stent according to the present invention will be described, but the present invention is not limited thereto.

1. Stent Shape FIG. 1 is a development view of a stent 1 according to an embodiment of the present invention. The stent 1 shown in FIG. 1 is a substantially tubular body and is a radially expandable stent from a compressed first diameter to an enlarged second diameter, wherein the stent extends in the circumferential direction. And a center position of a circle that forms the inner curvature of the bent portion and a center position of the circle that forms the outer curvature are different from each other in the longitudinal direction of the stent. A stent characterized by being. By adopting such a configuration, it is possible to reduce stress concentration generated in the stent due to pulsation of the heart and the like, and it is possible to obtain a stent with high pulsation durability.

  In the present invention, in particular, the line connecting the center position of the circle forming the inner curvature of the bent portion and the center position of the circle forming the outer curvature needs to be arranged so as to be parallel to the stent longitudinal axis direction. However, the stent 1 is an example of being arranged in parallel. By arranging the lines connecting the central positions in this way so as to be parallel to the stent longitudinal axis direction (including the case where they are substantially parallel), the struts extending on both sides across the bent portion are the same. It is easy to balance the both sides and design is easy.

  In addition, the stent 1 includes end sections (first end section 101, second end section 102), a third center section 103, and the first end section 101 and the third center section 103. A fourth section 104, and a fifth section 105 between the second end section 102 and the third central section 103. The rigidity of the fourth section 104 is such that the first end section 101, The rigidity of the third section 103 is smaller than that of the third central section 103, and the rigidity of the fifth section 105 is smaller than that of the second end section 102 and the third central section 103. The present invention does not particularly require such a configuration, but by adopting such a configuration, it is possible to improve the flexibility in the stent long axis direction as described later.

  FIG. 2 is a partially enlarged view of the substantially waveform component 2 that can be extended in the circumferential direction. FIG. 3 is a partially enlarged view of the substantially waveform component 3 that can be extended in the circumferential direction. Element 3 is a substantially corrugated component in the fourth section 104 or the fifth section 105 of the stent 1. Element 2 is a substantially corrugated component in the first end section 101, the second end section 102, or the third central section 103 of the stent 1. In the stent 1, the element 3 has a larger number of substantially corrugated components that can extend in the circumferential direction than the element 2, and the strut width, the bent strut width, the outer curvature radius, and the inner curvature radius are small. (It is also possible to select one or more of these factors to form the rigid element 3). Therefore, the element 3 functions as a highly movable part during delivery and expansion of the stent, and has an effect of improving the flexibility in the long axis direction.

  In order to reduce the stress concentration caused by the large movement of the blood vessel due to the heart beat when the stent is placed, the center position of the circle forming the inner curvature of the substantially corrugated component and the circle forming the outer curvature Is preferably 25 μm to 60 μm. Particularly in the substantially corrugated component 2 in the stent 1, the center 202 of the circle that forms the inner curvature and the circle that forms the outer curvature are preferable. The distance from the center 201 is 30 μm to 60 μm (see FIG. 2). In the substantially waveform component 3 or the like, the distance between the center 302 of the circle that forms the inner curvature and the center 301 of the circle that forms the outer curvature. The distance is preferably 25 μm to 55 μm (see FIG. 3).

  In the conventional stent, the center position of the circle that forms the inner curvature of the bent portion and the center position of the circle that forms the outer curvature are substantially the same for securing rigidity in the radial direction. When the center positions are the same, strain concentrates at a predetermined portion of the bent portion between the struts during stent expansion, and as a result, stress concentrates. Although it is conceivable to increase the inner radius of curvature from the viewpoint of reducing the stress concentration on the inner portion of the bent portion, in the conventional shape stent, the increase of the inner radius of curvature will simultaneously reduce the width of the bent portion, As a result, a stent with excellent pulsation durability cannot be obtained.

  In this regard, the inventor of the present application reduced the inner curvature radius (204 or 304) of the bent portion and the strut width (205 or 305) from the outer curvature radius (203 or 303) as shown in FIG. 2 or FIG. By making it larger than the center position (202 or 302) of the circle forming the inner curvature, the center position (201, 301) of the circle forming the outer curvature is slightly to the right of the figure (what is the stent connecting portion)? Displacement to the bending direction (near 206 in FIG. 2 or near 306 in FIG. 3) when the stent is expanded by shifting in a direction away from the bending direction, in other words, by disposing it at a position farther from the bending portion with respect to the longitudinal direction of the stent. Has been found uniquely to disperse the stress as a result. By adopting such a structure, it is possible to reduce the stress concentration inside the bent portion and to prevent the width of the bent portion from being reduced, and to provide a stent with excellent pulsation durability of the present invention. It is what has come to obtain.

  In addition, the bending part said here is from the position of the start of the circular arc of inner curvature to the position of the end. Further, in the embodiment, “the length of the arc of the inner curvature at the bent portion” refers to the length of the inner arc of the bent portion, that is, the straight portion inside the portion sandwiched between the struts in FIG. The length (distance) from the start point to the end point of the arc. In the embodiment, “the length of the circumference of the circle drawn with the inner curvature” is the length of the circumference of the circle drawn by virtually extending the arc inside the portion sandwiched between the struts in FIG. 2. Say it.

  In an embodiment, the arc length of the inner curvature in the bent portion is 50% or more, 55% or more, or 60% or more as the lower limit of the circumference of the circle drawn with the inner curvature, and the upper limit Is preferably 65% or less, or 60% or less.

  In the present invention, it is preferable that the inner radius of curvature of the bent portion of the substantially corrugated component is 0.3 to 0.5 times the outer radius of curvature. The inner radius of curvature 204 is 0.35 to 0.5 times the outer radius of curvature 203 (see FIG. 2). In the substantially corrugated component 3, the inner radius of curvature 304 at the bent portion is 0.3 to 0.3 of the outer radius of curvature 303. It is preferably 0.45 times (see FIG. 3). As a result, it is possible to balance the improvement in durability by reducing the stress concentration and the rigidity in the radial direction, which is a characteristic necessary for supporting the blood vessel, in a balanced manner.

  For example, in the case of a stent subjected to laser cutting and electrolytic polishing treatment, the radius of curvature defined here is measured after measuring a stent after cutting a metal cylindrical tube as a raw material into a stent design by laser cutting and performing electrolytic polishing. Say the radius of curvature.

  In addition, when the stent is placed, the width of the bent portion formed by the inner curvature and the outer curvature in the substantially corrugated component is arranged between the bent portions in order to increase resistance to the force that the blood vessel tends to contract. It is preferable that the width is larger than the width of the strut of the straight portion, and it is particularly preferable that the value is 1.05 to 1.35 times the width of the strut of the straight portion. Further, in the substantially waveform component 2, the width 206 of the bent portion that forms the inner curvature radius 204 and the outer curvature radius 203 is 1.05 to 1.35 times the strut width 205. The width 306 of the bent portion that forms the inner radius of curvature 304 and the outer radius of curvature 303 is preferably 1.05 to 1.35 times the width 305 of the strut.

2. Stent Forming Method As a stent forming method, a laser processing method, an electric discharge processing method, a mechanical cutting method, an etching method, and the like that are generally known as methods for producing a stent can be used. It is also possible to chamfer the end portions of the struts in various types of polishing such as electrolytic polishing after forming the stent.

  The “compressed first diameter” varies depending on the target disease, but is usually about 1.2 mm or less, preferably about 0.9 mm or less, and can be set to be 0.5 mm or more. preferable. The “expanded second diameter” is selected in accordance with the inner diameter of the patient body lumen, and differs depending on the lumen to be treated. For example, taking the cardiac coronary artery as an example, the diameter is set to about 2.0 mm to 5.0 mm.

  The length of the stent depends on the length of the site of the patient's body lumen to be treated. For example, in the vascular system, those with a total length of about 7 mm to 100 mm are mainly used, and when the heart coronary artery is taken as an example, those with a total length of about 7 to 40 mm are mainly used.

  Metallic materials useful for the structural material forming the stent of the present invention include stainless steel, titanium, nickel, iridium, iridium magnesium oxide, niobium, platinum, tantalum, gold, and alloys thereof, as well as gold-plated alloy iron, Examples thereof include platinum-plated alloy iron, cobalt chromium alloy, and titanium nitride-coated stainless steel. Preferably, from the viewpoint of having appropriate rigidity and elasticity, the stent according to the present invention is made of stainless steel, nickel alloy such as Ni—Ti alloy, metal such as Cu—Al—Mn alloy, Co—Cr alloy, or the like. For example, a metal specified in JIS-G4303 or a metal specified in ISO5832-5, ISO5832-6, ISO5832-7, or the like can be used.

  The diameter, length, material, and the like of the stent described above are merely examples, and do not limit the present invention.

  Hereinafter, examples of the stent according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  One example of a method for placing a stent is to compress and secure it to the balloon portion at the tip of the catheter, advance it to the treatment site in the patient lumen, and expand the balloon to place the stent in place. It is done by pulling out. Therefore, the stent has two modes, a compressed state and an expanded state. The stent is delivered in a compressed state and placed in the patient's lumen in an expanded state. The stents of the comparative examples and examples shown below were produced by a manufacturing method known to those skilled in the art in which a metal cylindrical tube as a raw material was cut into a stent design by laser cutting and subjected to electrolytic polishing.

In addition, for each stent, the ratio of the distance between the center of the circle forming the outer curvature and the center of the circle forming the inner curvature with respect to the outer curvature radius is defined as the curvature center eccentricity, and is calculated by the following formula 1. did.
(Formula 1) Curvature center eccentricity = Distance between the center position of the circle forming the outer curvature and the center position of the circle forming the inner curvature / outer radius of curvature (Comparative Example 1)
The stent of the comparative example 1 shows the typical example of the stent by a prior art. FIG. 6 and FIG. 11 are developed views of an elongated tubular body having both ends. The stent of Comparative Example 1 is formed from a plurality of cylindrically shaped elements, the cylindrically shaped elements being formed from generally corrugated components, the cylindrically shaped elements being radially expandable and with a common longitudinal axis, The crests of the substantially waveform components are partially connected to each other so that they are interconnected so as to be substantially matched. The stent of Comparative Example 1 includes two different substantially waveform components, ie, a substantially waveform component 7 and a substantially waveform component 8 (see FIG. 6). The first end section 1101, the second end section 1102 and the third central section 1103 are composed of a substantially corrugated component 7, and the fourth section 1104 and the fifth section 1105 are composed of a generally corrugated component 8 ( FIG. 11).

  In the stent of Comparative Example 1, the substantially corrugated component 7 has the strut width 703 of FIG. 7 of 130 μm, the inner radius of curvature 702 of 55 μm, the outer radius of curvature 701 of 185 μm, and the curvature center eccentricity of 0% (ie, the outer curvature). The center distance between the radius center and the inner radius of curvature is zero). On the other hand, the substantially corrugated component 8 has a strut width 803 of 110 μm, an inner curvature radius 802 of 40 μm, an outer curvature radius 801 of 150 μm, and a curvature center eccentricity of 0% (that is, the center of the outer curvature radius and the inner curvature). The distance between the center and the radius is zero). Regarding the evaluation described later, the evaluation was carried out for each substantially waveform component. Specifically, a portion 9 made up of a substantially waveform component 7 and a portion 10 made up of a substantially waveform component 8 were evaluated.

  The stent length was 18.4 mm, the outer diameter of the stent was 1.80 mm, and the thickness was 75 μm. In the first end section 1101, the second end section 1102, and the third central section 1103, the number of waves per round is 8, and in the fourth section 1104 and the fifth section 1105, the number of waves per round is The number was made as 10. The metal used as a raw material was manufactured using the metal prescribed | regulated to ISO5832-7.

(Example)
Regarding the following Examples 1 to 3, since the stents of Examples 1 to 3 have two different substantially waveform components, ie, a substantially waveform component 2 and a substantially waveform component 3 (see FIG. 1), Evaluation was performed for each substantially waveform component. Specifically, evaluation was made on a portion 4 consisting of a substantially waveform component 2 and a portion 5 consisting of a substantially waveform component 3.

Example 1
Example 1 is formed from a plurality of cylindrically-shaped elements, said cylindrically-shaped elements being formed from substantially corrugated components, these cylindrically-shaped elements being radially expandable and having a common longitudinal axis and substantially corrugated The peak portions of the components are partially connected to each other so that they are interconnected so as to be substantially aligned.

  The substantially corrugated component 2 of the first end section 101, the second end section 102, and the third central section 103 has a strut width 205 of FIG. 2 of 130 μm, an inner radius of curvature 204 of 80 μm, and an outer radius of curvature 203 of The width 206 of the bent portion forming the inner curvature radius 204 and the outer curvature radius 203 is 185 μm, the distance between the center 202 of the inner curvature radius and the center 201 of the outer curvature radius is 45 μm, and the curvature center eccentricity is 24.3%. The substantially corrugated component 3 of the fourth section 104 and the fifth section 105 includes a strut width 305 of 110 μm, an inner radius of curvature 304 of 60 μm, an outer radius of curvature 303 of 150 μm, an inner radius of curvature 304 and an outer radius of curvature 303 of FIG. The width 306 of the bend forming the inner curvature radius is 130 μm, the distance between the inner curvature radius center 302 and the outer curvature radius center 301 is 40 μm, and the curvature center eccentricity is 26.7%. The stent length was 18.4 mm, the outer diameter of the stent was 1.80 mm, and the thickness was 75 μm.

  In the first end section 101, the second end section 102, and the third central section 103, the number of waves per round is 8, and in the fourth section 104 and the fifth section 105, the number of waves per round. 10 was produced. The metal used as a raw material was manufactured using the metal prescribed | regulated to ISO5832-7.

(Example 2)
Example 2 is given as an example of a stent according to the present invention. In the second embodiment, compared with the first embodiment, the inner curved radii of the substantially waveform components 2 and 3 are small, the width of the bent portion is small, and the distance between the centers of the curvature radii is small.

  Example 2 is formed from a plurality of cylindrically shaped elements, said cylindrically shaped elements being formed from substantially corrugated components, these cylindrically shaped elements being radially expandable and having a common longitudinal axis and substantially corrugated configurations The peak portions of the elements are partially connected to each other so as to be substantially aligned.

  The substantially corrugated component 2 of the first end section 101, the second end section 102, and the third central section 103 has a strut width 205 of 130 μm, an inner radius of curvature 201 of 75 μm, and an outer radius of curvature 203 of FIG. The width 206 of the bent portion forming the inner curvature radius 204 and the outer curvature radius 203 is 145 μm, the distance between the inner curvature radius center 202 and the outer curvature radius center 201 is 35 μm, and the curvature center eccentricity is 18.9%.

  The substantially corrugated component 3 of the fourth section 104 and the fifth section 105 has a strut width 305 of 110 μm, an inner radius of curvature 304 of 55 μm, an outer radius of curvature 303 of 150 μm, an inner radius of curvature 304 and an outer radius of curvature 303 of FIG. The width 306 of the bend forming the inner curvature radius is 125 μm, the distance between the inner curvature radius center 302 and the outer curvature radius center 301 is 30 μm, and the curvature center eccentricity is 20.0%. The stent length was 18.4 mm, the outer diameter of the stent was 1.80 mm, and the thickness was 75 μm.

  In the first end section 101, the second end section 102, and the third central section 103, the number of waves per round is 8, and in the fourth section 104 and the fifth section 105, the number of waves per round. 10 was produced. The metal used as a raw material was manufactured using the metal prescribed | regulated to ISO5832-7.

(Example 3)
Example 3 is given as an example of a stent according to the present invention. In Example 3, compared with Example 1, the width of the bent portions of the substantially waveform components 2 and 3 is large, and the distance at the center of the radius of curvature is large.

  Example 3 is formed from a plurality of cylindrically-shaped elements, said cylindrically-shaped elements being formed from generally corrugated components, these cylindrically-shaped elements being radially expandable and having a common longitudinal axis and being generally corrugated The peak portions of the components are partially connected to each other so that they are interconnected so as to be substantially aligned.

  The substantially corrugated component 2 of the first end section 101, the second end section 102, and the third central section 103 has a strut width 205 of FIG. 2 of 130 μm, an inner radius of curvature 204 of 80 μm, and an outer radius of curvature 203 of The width 306 of the bent portion forming the inner curvature radius 204 and the outer curvature radius 203 is 160 μm, the distance between the center of the inner curvature radius 204 and the center of the outer curvature radius 203 is 55 μm, and the curvature center eccentricity is 29.7%.

  The substantially corrugated component 3 of the fourth section 104 and the fifth section 105 includes a strut width 305 of 110 μm, an inner radius of curvature 304 of 60 μm, an outer radius of curvature 303 of 150 μm, an inner radius of curvature 304 and an outer radius of curvature 303 of FIG. The width 306 of the bent portion forming the inner curvature radius is 140 μm, the distance between the inner curvature radius center 302 and the outer curvature radius center 301 is 50 μm, and the curvature center eccentricity is 33.3%. The stent length was 18.4 mm, the outer diameter of the stent was 1.80 mm, and the thickness was 75 μm. In the first end section 1101, the second end section 102, and the third central section 103, the number of waves per circuit is 8, and in the fourth section 104 and the fifth section 105, the number of waves per circuit. 10 was produced. The metal used as a raw material was manufactured using the metal prescribed | regulated to ISO5832-7.

  In Examples 1 to 3, the circumference of the inner curvature between the struts was about 52% of the circumference of the circle drawn with the inner radius of curvature. On the other hand, in Comparative Example 1, the circumference of the inner curvature between the struts was about 44% of the circumference of the circle drawn with the inner curvature radius.

(Evaluation)
The following evaluation was implemented regarding the said comparative example 1 and Examples 1-3.

(1) Maximum equivalent stress In order to compare the maximum equivalent stress after compression and expansion of the stent, finite element analysis was performed. For finite element analysis, general-purpose finite element analysis software ANSYS (ANSYS) was used. The stent model was created as an 8-node solid model, and two layers of mesh were cut in the thickness direction. As the material characteristics, the numerical values of metals specified in ISO5832-7 were used. First, the stent was compressed to an outer diameter of 1.1 mm, and then expanded to an outer diameter of 4.4 mm. The maximum equivalent stress generated in the stent when expanded was examined, and the maximum equivalent stress is shown in Tables 1 and 2 below.

  (Evaluation results)

  As shown in Tables 1 and 2, the maximum equivalent stress after compression and expansion of the stent is the best in Example 1, and even when compared with Comparative Example 1, Examples 1-3 according to the present invention are good. The result was.

  Further, when evaluated from the viewpoint of the curvature radius eccentricity, the curvature radius eccentricity of the portion 4 made of the substantially waveform component 2 is in the range of 23 to 26%, and the curvature radius eccentricity of the portion 5 made of the substantially waveform component 3 is. Example 1 in which the rate was in the range of 25 to 28% gave the best results.

  Next, evaluations such as in vitro evaluation experiments were performed after drug coating described below with respect to Comparative Example 1 and Examples 1 to 3.

(2) Drug coating Lactic acid-glycolic acid copolymer (product number: 85DG065, Absorbable Polymers International, lactic acid / glycolic acid = 85/15, weight average molecular weight 85,000) as a polymer, tacrolimus (Astellas Pharmaceutical Co., Ltd.) Company) was dissolved in chloroform (Wako Pure Chemical Industries, Ltd.) to prepare a solution having a drug concentration / polymer concentration = 0.5 wt% / 0.5 wt%. A stainless steel wire having a diameter of 100 μm was fixed to one end of the stent, and the other end was connected to a stirrer to hold the stent vertically in the length direction. While rotating the stirrer at 100 rpm, the solution prepared using a spray gun having a nozzle diameter of 0.3 mm was sprayed onto the stent, and the solution was attached to the stent. The distance from the spray gun nozzle to the stent was 75 mm, and the air pressure during spraying was 0.15 MPa. After spraying, it was vacuum dried at room temperature for 1 hour. The spray time was adjusted to form an inner layer (drug / polymer weight ratio = 1.0) having a polymer weight of 100 μg and a drug weight of 100 μg per stent.

  Lactic acid-glycolic acid copolymer (product number: 85DG065, Absorbable Polymers International, lactic acid / glycolic acid = 85/15, weight average molecular weight 85,000) as the polymer, and tacrolimus (Astellas Pharma Inc.) as chloroform ( Wako Pure Chemical Industries, Ltd.) to prepare a solution having a drug concentration / polymer concentration = 0.13 wt% / 0.5 wt%. A stainless steel wire having a diameter of 100 μm was fixed to one end of the stent on which the inner layer was formed, and the other end was connected to a stirrer to hold the stent vertically in the length direction. While rotating the stirrer at 100 rpm, the solution prepared using a spray gun having a nozzle diameter of 0.3 mm was sprayed onto the stent, and the solution was attached to the stent. The distance from the spray gun nozzle to the stent was 75 mm, and the air pressure during spraying was 0.15 MPa. After spraying, it was vacuum dried at room temperature for 1 hour. The spray time was adjusted to form an outer layer (drug / polymer weight ratio = 0.26) having a polymer weight of 192 μg and a drug weight of 50 μg per stent.

  The obtained polymer has a weight of 292 μg and a drug weight of 150 μg per stent.

  Table 3 shows the amount of drug and high molecular weight applied to Comparative Example 1 and Examples 1 to 3.

(In vitro evaluation experiment)
First, the stent was compression-fixed to the balloon part of the balloon catheter. Here, the balloon catheter used was a rapid exchange type balloon catheter having a balloon diameter of 3.0 mm at a rated expansion pressure and a balloon portion length of 20 mm. The stent was expanded by a procedure in which the balloon was expanded at a pressure of 9 atm and maintained for 30 seconds, the pressure in the balloon was removed, and the balloon was removed from the stent. The expanded stent was fixed on an electron microscope observation sample stage, and after depositing a Pt—Pd alloy, the surface was observed with a scanning electron microscope (S-3000N, Hitachi High-Technologies Corporation). Tables 4 and 5 show the results of preparing five samples for each stent and evaluating the frequency of occurrence of cracking and peeling of the coating layer.

  (Evaluation results)

  As shown in Tables 4 and 5, cracks in the coating layer of the portion 4 composed of the substantially corrugated component 2 and the portion 5 composed of the substantially corrugated component 3 accompanying the expansion of the stents of Examples 1 to 3 according to the present invention. The occurrence frequency of peeling and peeling was low, and it was confirmed that the surface properties were good. On the other hand, with the expansion of the stent of Comparative Example 1, the frequency of occurrence of cracking and peeling of the coating layer of the portion 9 consisting of the substantially waveform component 7 and the portion 10 consisting of the substantially waveform component 8 was high.

  Further, when evaluated from the viewpoint of the radius of curvature eccentricity, the radius of curvature of the portion 4 consisting of the substantially waveform component 2 is within the range of 23 to 26%, and the radius of curvature of the portion 5 consisting of the waveform component 3 is substantially the same. Example 1 in which the eccentricity ratio was in the range of 25 to 28% was the best result.

(Load per unit length)
Next, the following “load per unit length” was evaluated for Comparative Example 1 and Examples 1 to 3. First, the stent was compression-fixed to the balloon part of the balloon catheter. Here, the balloon catheter used was a rapid exchange type balloon catheter having a balloon diameter of 3.0 mm at a rated expansion pressure and a balloon portion length of 20 mm. The stent was expanded by a procedure in which the balloon was expanded at a pressure of 9 atm and maintained for 30 seconds, the pressure in the balloon was removed, and the balloon was removed from the stent. Next, the radial stiffness of the expanded stent was evaluated. For the evaluation, the expanded stent was subjected to a compression test using Ez-Test (Shimadzu Corporation), and evaluation was performed based on the load per unit length when 30% of the outer diameter of the expanded stent was compressed. Three samples were prepared for each stent, and the average load per unit length in each section is shown in Tables 6 and 7 below.

  (Evaluation results)

  As shown in Tables 6 and 7, in Examples 1 to 3 according to the present invention, the load per unit length was hardly changed in spite of the fact that the inner radius of curvature was increased as compared with Comparative Example 1. It became.

(Extended uniformity)
Next, the following evaluation was implemented regarding the comparative example 1 and Examples 1-3. First, all the stents to be evaluated were compressed and fixed to the balloon portion of the balloon catheter. Here, the balloon catheter used was a rapid exchange type balloon catheter having a balloon diameter of 3.0 mm at a rated expansion pressure and a balloon portion length of 20 mm. The stent was expanded in a 37 ° C. water bath by expanding the balloon at a pressure of 9 atm and maintaining it for 30 seconds, then removing the pressure in the balloon and removing the balloon from the stent. Next, 3 parts along the longitudinal direction of the stent (ends, _{Central: OD A, OD B, OD} C) was measured, and further the outside diameter of the third portion of the stent circumferentially rotated 90 ° ( both ends, the _center: OD _D, OD E, was measured in OD _F), it was evaluated extended uniformity. In the examples, both ends are positions of 0.5 mm in the direction from the respective ends of the stent to the center of the stent, and the center is the length of the expanded stent in the long axis direction. It is a position that is half the length of the value.

The expansion uniformity was calculated by the following formula 2. For evaluation of expansion uniformity, three samples were prepared for each stent, and the average value in each section was obtained. The expansion uniformity of each stent is shown in Table 8 and Table 9 below.
(Expression 2) Extended uniformity (%) = [(OD _x −OD _AV ) / OD _AV ] × 100
* OD _x is the circumferential angle of each circumference, the outer diameter at the part * OD _AV = (OD _A + OD _B + OD _C + OD _D + OD _E + OD _F ) / 6
(Evaluation results)

  As shown in Table 8 and Table 9, the expansion uniformity was the best in Example 1, and even when compared with Comparative Example 1, the results of Examples 1 to 3 according to the present invention were good.

  Further, when evaluated from the viewpoint of the curvature radius eccentricity, the curvature radius eccentricity of the portion 4 made of the substantially waveform component 2 is in the range of 23 to 26%, and the curvature radius eccentricity of the portion 5 made of the substantially waveform component 3 is. Example 1 in which the rate was in the range of 25 to 28% gave the best results.

Claims (5)

A stent that is formed into a generally tubular body and is radially expandable from a compressed first diameter to an expanded second diameter,
The stent has a generally corrugated component extensible in a circumferential direction;
The center position of the circle forming the inner curvature of the bent portion and the center position of the circle forming the outer curvature of the substantially corrugated component are the center position of the circle forming the inner curvature of the bent portion and the circle forming the outer curvature. Arranged at different positions with respect to the stent longitudinal axis direction so that the line connecting the central positions is parallel to the stent longitudinal axis direction ,
The width of the bent portion formed by the inner curvature and the outer curvature is larger than the width of the strut of the straight portion disposed between the bent portions in the substantially corrugated component,
The length of the arc of the inner curvature at the bent portion is 50% or more of the circumference of a circle drawn with the inner curvature,
The stent according to claim 1, wherein an inner radius of curvature of the bent portion is larger than a value obtained by subtracting a width of a strut of the straight portion from an outer radius of curvature . Claim 1 Symbol placement of the stent, characterized in that the inner curvature radius and an outer radius of curvature of the bent portion are different. The center position of the circle forming the inner curvature of the bent portion is arranged at a position farther from the bent portion in the longitudinal direction of the stent than the center position of the circle forming the outer curvature. Or the stent according to 2 . The stent according to any one of claims 1 to 3 , wherein the material of the stent is formed of at least one material selected from the group consisting of stainless steel, nickel alloy, and cobalt chromium alloy. The stent according to any one of claims 1 to 4 , wherein a drug that suppresses vascular occlusion is immobilized on an outer surface of the stent.

Images