JP4815057B2 - Stent - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stent for placement in a tubular tissue in the body.
[0002]
[Prior art]
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. A medical device that is a coil made of a single linear metal or polymer material, a metal tube cut out and processed by a laser, a linear member welded and assembled by a laser, There are things made by weaving multiple linear metals.
[0003]
These can be classified into those that are expanded by a balloon mounted with a stent and those that are expanded by removing a member that suppresses expansion from the outside. Among these, the stent expanded by the balloon is used by adjusting the expansion pressure according to the state of the tubular tissue to be expanded and the mechanical strength of the stent.
[0004]
In recent years, these stents have been frequently used especially for angioplasty of the heart and carotid artery.
[0005]
Japanese Patent Publication No. 4-6377 describes a stent that is expanded and then has a continuous diamond shape. This stent had the advantage that it was very resistant to the forces that the blood vessels were trying to contract. However, since this stent lacked axial flexibility when not expanded, it was very difficult to insert into a bent blood vessel, and the inside of the blood vessel could be damaged. In addition, since the axial flexibility is insufficient even after expansion, there is a problem in that when placed in a bent blood vessel, excessive stimulation is applied to the blood vessel to promote restenosis. In addition, the stent axial length contracts during expansion, causing problems such as difficulty in expanding the entire stenosis of the blood vessel and difficulty in positioning.
[0006]
Japanese Patent Publication No. 7-24688 describes a stent in which a wire is deformed in a zigzag shape and spirally wound so as to be further cylindrical. This stent was rich in axial flexibility and was excellent in insertion into a bent blood vessel. However, there is a problem that the resistance to the force with which the blood vessel attempts to contract is very small, and the blood vessel tends to contract due to the pressure with which the blood vessel attempts to contract.
[0007]
In addition, when a conventional stent is expanded to a target diameter, it is difficult to expand the strut of the stent uniformly. There was a problem that it was easy to do. If such uneven expansion is performed, the endothelial tissue of the tubular tissue protrudes greatly from the portion where the struts are largely opened, which may cause restenosis. In addition, when the non-uniform expansion is severe, it may become impossible to maintain a perfect circle in cross section. In order to solve this problem, a method of folding a balloon for mounting a stent has been devised, but it is still difficult to uniformly expand the balloon. In another method, attempts have been made to attach a member that easily expands uniformly to the surface of the balloon, but the balloon profile becomes large, making it difficult to deliver the stent to the target site. The problem of becoming.
[0008]
Also, most stents that are expanded by balloons have a problem that both ends of the stent warp to a larger diameter than the central portion during expansion, resulting in local overexpansion. When both ends of the stent are overexpanded, the endothelial cells of the tubular tissue are stimulated at the portions, which may cause restenosis due to cell proliferation.
[0009]
Furthermore, the conventional stent generally has a large gap formed between the stent struts when expanded, and the endothelial cells of the tubular tissue protrude beyond the gap, which may cause restenosis. . This is because the size of the basic cell constituting the stent is large, but in order to reduce this, it is necessary to reduce the width of the strut. However, the radial force obtained in that case, that is, the radial direction received from the outer periphery is required. There is a problem that the force that can withstand the stress is reduced.
[0010]
[Problems to be solved by the invention]
In view of these circumstances, the present invention intends to solve the problem of uniformly expanding and suppressing overexpansion, and further reducing the size of the basic cell constituting the stent to increase the inside of the stent of the endothelial cell of the tubular tissue. An object of the present invention is to provide a stent that suppresses the protrusion of the stent.
[0011]
[Means for Solving the Problems]
The present invention is a stent that is formed in a substantially tubular body and that can be extended radially outward of the substantially tubular body, and is placed in a tubular tissue in a body cavity, and is overexpanded beyond a target diameter. and have a structure that prevents, basic cells 2 constituting the stent, a main strut 5 of the straight shape arranged with its longitudinal stent longitudinally when not extended, when the folded between them extended The sub strut 6 supports the main strut 5 in the circumferential direction. When expanded, the main strut 5 and the sub strut 6 form an annular substantially polygonal shape having at least three sides, and a plurality of basic cells 2 are arranged in the circumferential direction. A band portion 3 is continuously formed, and a plurality of the band portions 3 are continuous in the longitudinal direction via link portions 4 having a structure that can be expanded and contracted in the longitudinal direction of the stent. The end is connected to the end of the main strut 5 of the basic cell 2 constituting the band unit 3, and the other end of the link unit 4 forms the other band unit 3 adjacent to the band unit 3. providing a stent, wherein Rukoto such is coupled to an end of the main strut 5 of the cell 2.
[0013]
Furthermore, the stent of the present invention has a total length of the sub struts 6 in one basic cell 2 folded between the main struts A, and one band in which a plurality of basic cells 2 are continuously formed in the circumferential direction. Satisfying the relationship of π × D = 0.5 × A × Sinθ × B and 60 ° ≦ θ <90 °, where B is the number of basic cells in section 3 and D is the target stent expansion diameter Furthermore, when the length of the main strut 5 in the longitudinal direction in the basic cell 2 when not expanded is L, it is desirable to satisfy the relationship of L ≦ A <2 × L. Moreover, it is more preferable to satisfy the relationship of 0.5 × W ≦ T ≦ 3 × W, where W is the width of the wire constituting the main strut 5 and the sub strut 6 and T is the thickness.
[0014]
The stent, the shape of the basic cell 2 during stent expansion, substantially triangular or substantially rectangular, or substantially trapezoidal, further, when the stent longitudinal length of the link portion 4 during unexpanded is C, It is preferable to satisfy the relationship of 0.3 × L ≦ C ≦ 2L.
[0015]
These stents are made of at least main strut 5 and sub-strut 6 made of one or more materials selected from stainless steel, superelastic metal, polymer material having a flexural modulus of 1 GPa or more, and biodegradable polymer material. Is preferred.
[0016]
Furthermore, the stent of the present invention is also provided as a structure in which a cylindrical thin film polymer film is formed on the outer peripheral surface of the stent.
[0017]
Moreover, it is desirable that these stents have an X-ray opaque marker that can confirm the position under X-ray contrast. Furthermore, a drug for preventing restenosis and suppressing thrombus formation and a therapeutic gene can be added or surface-treated.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a stent according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
[0019]
FIG. 1 is a development view of the stent 1 according to the present invention when not expanded. The stent 1 is formed in a substantially tubular body and is expandable radially outward of the tubular body, and a plurality of basic cells 2 expandable in the circumferential direction of the stent are continuously expanded in the circumferential direction. A band 3 that generates a force opposite to the force that the blood vessel tends to contract, that is, a radial force, is formed. Each band portion 3 is connected by a link portion 4 to give flexibility to a force from a direction perpendicular to the longitudinal direction of the stent 1 in order to advance in a bent lumen such as a blood vessel. The band part 3 and the link part 4 are continuous in the longitudinal direction by the length necessary for the stent.
[0020]
FIG. 2 is an enlarged view of the structure of the basic cell 2 of the stent 1. The basic cell 2 is composed of a main strut 5 disposed with its longitudinal direction oriented in the longitudinal direction of the stent and a sub strut 6 that is folded between them and supports the main strut 5 in the circumferential direction when expanded. When the stent 1 expands in the radial direction while being supported in the circumferential direction, it has a function of defining the diameter to be expanded. FIG. 3 shows the state of the basic cell 2 when the stent 1 is expanded. The main strut 5 and the sub strut 6 are continuously ring-shaped and form a substantially square shape.
[0021]
FIG. 4 schematically shows the basic cell 2 with line segments. Each dimension used in the present invention means a dimension when modeled with line segments. The present invention corresponds to the length of the basic cell 2 in the longitudinal direction, that is, the length of the main strut 5 is L, and corresponds to the total length of the sub struts 6 in one basic cell 2 folded between the main struts 5, that is, 6a + 6b + 6c + 6d. Π × D = 0, where A is the length to be performed, B is the number of basic cells 2 continuous in the circumferential direction in one band part 3 of the stent 1, and D is the expanded diameter of the intended stent. 5 × A × Sin θ × B, and θ satisfies a relationship of 60 ° ≦ θ <90 °. Here, π represents a circumference ratio. Further, θ is an angle formed between the line segment when the sub strut 6 is schematically illustrated at the time of expansion and the longitudinal axis of the stent, the angle on the side including the substantially polygonal internal angle, that is, an angle smaller than 90 °. In addition, in order for each basic cell 2 continuous in the circumferential direction to perform uniform expansion, it is important that θ is 60 ° or more, and if it is less than this, sufficient uniform expansion cannot be obtained. The value of θ is smaller than θ = 90 °, which is a theoretically expanded state. In the present invention, the greatest feature is that the sub strut 6 supports the main strut 5 at a large angle, and it is possible to suppress a large radial force and overexpansion of the stent. If the radial force can be strengthened, the width W of the wire constituting the main strut 5 and the sub strut 6 constituting the stent can be reduced, and the number of basic cells formed in one band can be increased. it can. As a result, the size of the basic cell can be reduced, and the opening area of the basic cell at the time of expansion can be reduced, so that the protrusion of the endothelial cells of the tubular tissue can be suppressed to a minimum. From the viewpoint of suppressing radial force and overexpansion, it is desirable that the angle formed between the sub strut 6 and the longitudinal axis of the stent is 70 ° ≦ θ ≦ 80 °.
[0022]
Further, in order to prevent the endothelial cells of the tubular tissue from protruding from the substantially square shape formed by the expanded main strut 5 and the sub strut 6, the length L of the main strut 5 and one of the sub struts 6 are suppressed. The relationship of the total length A in the basic cell is preferably L ≦ A <2 × L. If L> A, the expanded basic cell 2 has a substantially rectangular shape that is long in the longitudinal direction, but under such conditions, the radial force in the vicinity of the central portion of the main strut 5 cannot be sufficiently exhibited. On the other hand, when A ≧ 2 × L, the sub struts 6 folded between the main struts 5 overlap in the longitudinal direction, and the number of basic cells B continuous in the circumferential direction cannot be increased. . Under such conditions, the size of the substantially square formed by the expanded main strut 5 and sub strut 6 becomes large, and the endothelial cells of the tubular tissue are likely to protrude. Further, there is a problem that the radial radial force is weakened. The most ideal state is that the total length A in one basic cell of the sub strut 5 is smaller than 2 × L, the sub struts 6 do not overlap each other in one basic cell, and A is the maximum length. It is in such a state. At this time, the substantially quadrangle formed by the main strut 5 and the sub strut 6 has a shape close to a square. FIG. 5 shows a developed view when the stent 1 is expanded.
[0023]
FIG. 6 is a partial cross-sectional view of the stent 1. In the drawing, when the width of the wire constituting the main strut 5 and the sub strut 6 is W and the thickness is T, it is preferable to satisfy the condition of 0.5 × W ≦ T ≦ 3 × W. When the thickness T is smaller than 0.5 × W, a portion that undergoes a large plastic deformation when the stent is expanded, that is, a portion 7 where the main strut 5 and the sub strut 6 are connected and a folding tip portion 8 of the sub strut 6 are subjected to plastic deformation as shown in FIG. It turns up like this, and the problem that this part will bite into the inner surface of a tubular structure | tissue will arise. FIG. 8 shows an XX cross section of the turned up portion 8 of FIG. In order to suppress such deformation, the thickness T of each strut is preferably 0.5 × W or more, and more preferably 0.7 × W or more. Such a condition also applies to a self-expandable stent made of a superelastic metal or a part of a polymer material. When the stent is folded into a shape when the stent is not expanded, a portion that is greatly elastically deformed, that is, the main strut 5 As shown in FIG. 7, the connecting portion 7 of the sub strut 6 and the folded tip end portion 8 of the sub strut 6 folded in the main strut 5 are deformed. In general, a self-expanding stent is folded inside a sheath that suppresses the expansion of the stent when the stent is delivered into a target tubular tissue in the body, and a catheter inside the stent is inserted. In this method, the stent is self-expanded by removing the outer sheath while fixing the stent so that it does not shift at the target site. When the deformed portion as shown in FIG. 7 is formed when the stent is folded into the unexpanded shape, it becomes difficult to uniformly put the folded stent into the sheath, or the sheath is removed to expand the stent. At this time, the turned-up portion is caught by the sheath, and in the worst case, it may not be possible to release from the sheath. On the other hand, when the thickness T of the stent is larger than 3 × W, there is a problem that the processing accuracy when processing the stent pattern with a laser is lowered.
[0024]
FIG. 9 and FIG. 10 show another example, in which the basic cells 2 at the time of expansion each form a substantially triangular shape and a substantially trapezoidal shape. FIG. 11 and FIG. 12 show development views in the expanded state of these stents. In these examples, when each basic cell 2 is continuous in the circumferential direction, a shape that is targeted with respect to the longitudinal direction of the stent, that is, when the expanded basic cell forms a substantially triangular shape, a vertex of a substantially triangular shape When the basic cells at the time of expansion form a substantially trapezoid so that the bases are alternated, it is necessary to continue so that the upper base and the lower base of the trapezoid are alternately, and the number of basic cells in one circle That is, it is necessary that the number of basic cells existing in one band part is an even number. In this case, the diameter at the time of expansion of the target stent and the length of each strut of the basic cell can be realized by balancing in the above-described conditions. Further, when the basic cell 2 at the time of expansion forms a substantially triangular shape or a substantially trapezoidal shape as described above, if the angle formed between the main strut 5 and the longitudinal axis of the stent is large, the contraction in the longitudinal direction of the stent is large when the stent is expanded. As a result, positioning when placing the stent becomes difficult. In order to reduce the contraction in the longitudinal direction of the stent at the time of stent expansion, it is important to reduce the angle formed by the main strut 5 and the axis in the longitudinal direction of the stent. It is desirable to be. When the angle between the main strut 5 and the longitudinal axis of the stent is 0 °, the contraction in the longitudinal direction when the stent is expanded becomes zero, and the shape of the basic cell at that time forms a substantially square shape. When the shape of the basic cell at the time of stent expansion is substantially triangular, it is difficult to balance the radial force and the longitudinal contraction at the time of stent expansion, and the shape of the basic cell at the time of stent expansion is most preferably an equilateral triangle. At this time, the contraction rate in the longitudinal direction of the basic cell is about 15%.
[0025]
FIG. 13 is a view showing a link 9 in the link portion 4 that continuously connects the band portions 3 formed of the continuous basic cells 2 in the longitudinal direction. The link 9 desirably has a function of expanding and contracting in the longitudinal direction in order to follow the bent tubular tissue when the stent is transported to the target position through the bent tubular tissue. . FIGS. 14 to 17 show an example in which at least one bending portion 10 in the link 9 is provided so as to be able to follow such a bent tubular tissue, and a function of expanding and contracting in the longitudinal direction is added. .
[0026]
FIG. 18 is a diagram showing the relationship between the width of the band portion 3 in which the basic cells 2 are continuous, that is, the length L in the longitudinal direction of the basic cells 2 and the length C in the longitudinal direction of the link portion 4. In order to allow the stent to follow the bent tubular tissue, it is preferable that the length of the link portion is long because flexibility can be increased. However, since the link portion alone does not generate radial force, only the radial force is used. If considered, the shorter one is preferable. From these facts, the length C of the link part is preferably 0.3 × L ≦ C ≦ 2 × L. When C is smaller than 0.3 × L, sufficient flexibility cannot be obtained, and the ability to follow the bent tubular tissue is lowered. When C is larger than 2 × L, the radial force of the link portion becomes weak, and the problem that the expansion diameter of the link portion becomes small becomes remarkable.
[0027]
The above-described stents, in particular, the main strut 5 and the sub strut 6 can be made of a metal or a polymer material that can ensure a radial force. As the metal material, stainless steel typified by SUS316 or a superelastic metal such as a Ni-Ti alloy can be used. When these materials are used, the position of the stent processed by a computer is generally controlled. However, it is possible to process a stent pattern using a YAG laser. Further, as the polymer material, a thermoplastic polymer, a thermosetting polymer, a biodegradable molecule, or the like can be used, but a material having a flexural modulus of 1 GPa or more is preferable in order to function as a stent. . More preferably, the flexural modulus is desirably 2 GPa or more. The higher the flexural modulus, the smaller the strut width and thickness of the stent. Furthermore, as a stent, it may be desired that the stent is decomposed and absorbed after a certain period after being placed in a living body. In such a case, a biodegradable polymer material can be used. As a specific material of the biodegradable polymer that can be used as a stent, polylactic acid, polyglycolic acid, poly (ε-caprolactone), or the like can be used. When these polymer materials are used as raw materials for stents, if they are processed using YAG or a carbon dioxide laser, the laser irradiation part may be burned, or a melted part of the molten member may be generated near the laser irradiation part. Therefore, it is most ideal to use an excimer laser.
[0028]
When a stent is processed with these materials, the diameter of the tubular member serving as a raw material varies depending on whether the stent is of a type that is expanded by a balloon or a type that is expanded by itself. That is, if it is to be expanded with a balloon, generally a tubular member having a diameter larger than the folding diameter of the balloon on which the stent is mounted and smaller than the intended stent diameter is used as a raw material. Further, if it is of a type that expands itself, a tubular member having a diameter in the vicinity of the intended stent diameter may be processed as a raw material.
[0029]
In general, stents are used to expand the narrowed or occluded portion of tubular tissue in the body. However, unlike these purposes, if the tubular tissue has perforated, for example, the blood vessel has perforated. In such a case, as a first-aid treatment, a treatment in which the perforation is blocked may be performed using a stent having a thin film cover on the outer surface of the stent. Even in such cases, it is possible to use a thin film polymer material provided on the outer surface of the stent. As the polymer material for the thin film, a material having a large elongation such as a Teflon resin or a silicon resin can be used.
[0030]
Moreover, since these stents are normally used under X-ray contrast, it is preferable to have an X-ray opaque marker for grasping the position of the stent. Gold, platinum, a platinum rhodium alloy, etc. can be used as a radiopaque marker. The radiopaque marker is preferably present at both ends of the stent. However, in addition to fixing by a physical method, the marker can be applied by plating in the case of a stent made of a metal material. .
[0031]
Furthermore, a drug for preventing restenosis and suppressing thrombus formation and a therapeutic gene can be applied to these stents, or surface treatment can be performed.
[0032]
【The invention's effect】
According to the present invention, when the stent is expanded, the stent is uniformly expanded and overexpansion is suppressed, and further, the size of the basic cell constituting the stent is further reduced to suppress the protrusion of the endothelial cells of the tubular tissue to the inside of the stent. A stent can be provided and the restenosis of the tubular tissue can be reduced.
[Brief description of the drawings]
FIG. 1 shows a development before expansion of a stent 1 according to the present invention.
2 shows an enlarged view of a basic cell before expansion of the stent shown in FIG. 1. FIG.
3 shows an enlarged view of a basic cell after expansion of the stent shown in FIG. 1. FIG.
4 is a diagram schematically showing the struts of the basic cell before expansion of the stent shown in FIG. 1 with line segments. FIG.
FIG. 5 shows a development view after expansion of the stent shown in FIG. 1;
6 shows a part of a cross-sectional view of the stent 1 shown in FIG.
FIG. 7 shows an example of a shape change of a portion where plastic deformation occurs during stent expansion.
FIG. 8 is a cross-sectional view of a portion whose shape has changed as shown in FIG.
FIG. 9 is a development view before expansion in another example according to the present invention.
FIG. 10 is a development view before expansion in still another example of the present invention.
11 shows a development view after expansion of the stent shown in FIG. 9. FIG.
12 shows a development view after expansion of the stent shown in FIG. 10. FIG.
FIG. 13 shows an example of a stent link according to the present invention.
FIG. 14 shows an example of a stent link according to the present invention, which is flexible with respect to a force perpendicular to the longitudinal direction.
FIG. 15 shows an example of a stent link according to the present invention, which is flexible with respect to a force perpendicular to the longitudinal direction.
FIG. 16 shows an example of a stent link according to the present invention that is flexible with respect to a force perpendicular to the longitudinal direction.
FIG. 17 shows an example of a stent link according to the present invention that is flexible with respect to a force perpendicular to the longitudinal direction.
FIG. 18 shows an enlarged view of a band portion and a link portion of a stent according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Stent 2 Basic cell 3 Band part 4 Link part 5 Main strut 6 Sub strut 6a, 6b, 6c, 6d Each part of the sub strut in a basic cell 7 The part where the main strut and the sub strut are connected 8 The folding front end part 9 of the sub strut Link 10 Curved part in the link

Claims (9)

A stent that is formed in a substantially tubular body and that is extensible radially outward of the substantially tubular body, and is placed in a tubular tissue in a body cavity, and prevents a structure from over-expanding beyond a target diameter. and have a,
The basic cell 2 constituting the stent includes a main strut 5 having a straight shape arranged in the longitudinal direction of the stent when not expanded, and a sub that is folded between them and supports the main strut 5 in the circumferential direction when expanded. It consists of struts 6 and, when expanded, the main struts 5 and the sub struts 6 form an annular substantially polygonal shape consisting of at least three sides, and a plurality of basic cells 2 continuously form a band portion 3 in the circumferential direction. In addition, a plurality of the band portions 3 are continuous in the longitudinal direction via the link portions 4 having a structure that can expand and contract in the longitudinal direction of the stent,
One end of the link portion 4 is connected to the end portion of the main strut 5 of the basic cell 2 constituting the band portion 3, and the other end of the link portion 4 is adjacent to the band portion 3. the stent according to claim Rukoto such is coupled to an end of the main strut 5 of the basic cell 2 constituting the. The total length of the sub struts 6 in one basic cell 2 folded between the main struts 5 is A, and the number of basic cells in one band part 3 in which a plurality of basic cells 2 are continuously formed in the circumferential direction. the B, and satisfy the if the expanded diameter of the stent of interest was D, π × D = 0.5 × a × Sinθ × B and 60 ° ≦ θ <90 ° in relation claim 1 The described stent. 3. The stent according to claim 2, wherein when the length in the longitudinal direction of the main strut 5 in the basic cell 2 when not expanded is L, the relationship of L ≦ A <2 × L is satisfied. The main strut 5, the width of the wire constituting the sub-strut 6 W, the thickness is T, according to claim 1-3 characterized by satisfying the relationship of 0.5 × W ≦ T ≦ 3 × W The stent according to any one of the above. The stent according to any one of claims 1 to 4, wherein the shape of the basic cell 2 at the time of stent expansion is a substantially triangular shape, a substantially rectangular shape, or a substantially trapezoidal shape. When the length in the longitudinal direction of the stent of the link part 4 when not expanded is C and the length in the longitudinal direction of the main strut 5 when not expanded is L, the relationship of 0.3 × L ≦ C ≦ 2L is satisfied. The stent according to any one of claims 1 to 5, wherein: The main strut 5 and the sub strut 6 are made of one or more materials selected from stainless steel, superelastic metal, a polymer material having a flexural modulus of 1 GPa or more, and a biodegradable polymer material. 6. The stent according to any one of 6 . The stent according to any one of claims 1 to 7 , further comprising a cylindrical thin film polymer film on an outer peripheral surface of the stent. The stent according to any one of claims 1 to 8 , further comprising an X-ray opaque marker capable of confirming the position under X-ray contrast.

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