JP5355972B2 - Stent manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a stent. More specifically, the present invention relates to a method for manufacturing a self-expanding stent based on a NiTi alloy.

Traditionally, stents have been used to expand stenosis or occlusions in biological or body cavities such as blood vessels, bile ducts, esophagus, trachea, urethra, gastrointestinal tract, and other organs, and maintain the lumen in an open state. It has been.
Stents include balloon expandable stents and self-expandable stents depending on the function and placement method.

The balloon expandable stent does not have an expansion function. The balloon is expanded by placing the stent directly on the deflated balloon, the balloon is positioned at the target site, and the stent is expanded (plastically deformed) by the expansion force of the balloon. Fix it in close contact with the inner surface of the target part.
In this type of stent, the expansion diameter can be adjusted by a balloon. However, when the stent is placed in a blood vessel having a lot of movement such as a blood vessel of a lower limb, it may be plastically deformed by the external force.

On the other hand, the self-expanding stent has an expansion function. In order to place the stent in the target site, the stress applied to maintain the contracted state is removed after the stent is inserted into the target site in the contracted state. For example, the stent is contracted and stored in a sheath having an outer diameter smaller than the inner diameter of the target site, and after the distal end of the sheath reaches the target site, the stent is pushed out of the sheath. The extruded stent is released from the sheath to release the stress load, and restores and expands to the shape before contraction. Thereby, it adheres and fixes to the inner surface of the target part.
This type of stent has elastic force that is an expansion function of the stent itself, so even if it is placed in a blood vessel with a lot of movement, such as a blood vessel in the lower limbs, it can follow the movement, so it will be damaged by plastic deformation. Less is.

  As self-expanding stents, those based on NiTi alloys, which are shape-memory alloys having biocompatibility, are currently the mainstream. Here, the NiTi-based alloy includes a wide range of alloys mainly composed of nickel and titanium, and a representative one is a NiTi alloy containing 43 to 57 wt% of Ni and the balance being Ti and inevitable impurities. . A small amount of other metals such as cobalt, iron, palladium, platinum, boron, aluminum, silicon, vanadium, niobium, copper, and the like may be added to such a NiTi alloy.

  For a stent based on a NiTi alloy, for example, a NiTi alloy pipe having an outer diameter suitable for an in-vivo site to be placed is prepared, and the side surface of the pipe is processed by cutting (for example, , Mechanical cutting, laser cutting), chemical etching, or the like, and a plurality of notches or a plurality of openings are formed on the side surface.

In order to make the stent surface smooth after the formation of the notch or opening on the side surface, specifically, the surface roughness Ra of the stent surface is 1.5 μm or less, the stent surface is usually polished. As a method for polishing a stent surface having a complicated shape, electrolytic polishing is generally used (see Patent Document 1).
However, electropolishing deteriorates each time the electropolishing liquid is polished, and the polishing power changes, which is inconvenient to manage and the electrolyte processing is complicated, so the stent surface can be uniformly polished more easily. There is a need for a way to do this.

As a method for uniformly polishing a hard material having high hardness, polishing by electron beam irradiation has been proposed as polishing of a mold material (see Patent Document 2). Further, a surface processing method using electron beam irradiation has been proposed as a surface processing method for dentures made of metal materials (see Patent Document 3).
As described above, a polishing method by electron beam irradiation has been proposed as a polishing method for a somewhat large surface such as a mold or a denture, but as a method for polishing a stent having a very small surface to be polished, polishing by electron beam irradiation is not possible. Not proposed.

JP-A-11-332998 JP 2004-1086 A JP-A-8-224297

  An object of this invention is to provide the manufacturing method of the stent based on a NiTi type alloy using the novel grinding | polishing method which can grind | polish the stent surface simply and uniformly.

  The inventors of the present application tried to apply a polishing method by electron beam irradiation to the surface polishing of a stent based on a NiTi alloy, and were able to polish the stent surface uniformly. It was confirmed that the fatigue life was significantly reduced. As a result of earnestly examining the irradiation conditions of the electron beam and the processing performed before and after the electron beam irradiation, the inventors of the present application can suppress a decrease in fatigue life by applying a specific processing before and after the electron beam irradiation. I found out that I can do it.

The present invention is based on the above findings by the present inventors, and is a method for manufacturing a stent,
Preparing a stent based on a NiTi-based alloy;
Removing the outermost layer on the surface of the stent;
Polishing the surface of the stent by electron beam irradiation;
And a step of heat-treating the stent.

  In the stent manufacturing method of the present invention, the step of removing the outermost layer on the surface of the stent preferably includes acid treatment of the surface of the stent.

  In the stent manufacturing method of the present invention, it is preferable that the step of heat-treating the stent includes annealing the stent.

  According to the present invention, the stent surface can be polished easily and uniformly. According to the present invention, a stent having excellent fatigue life and corrosion resistance can be manufactured.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[Stent of the present invention]
FIG. 1 is a front view showing the shape of a preferred configuration example of the stent of the present invention. FIG. 2 is a development view of the stent shown in FIG. FIG. 3 is a development view of the stent in a state where the diameter of the stent shown in FIG. 1 is reduced. FIG. 4 is a partially enlarged view of the stent shown in FIG.

The stent 301 is a stent including a plurality of wavy annular bodies 302 in the axial direction, and the wavy annular body 302 includes a plurality of one-end-side bent portions having a vertex 302a on one end side in the axial direction of the stent 301 and the stent 301. The wavy line-shaped annular body 302 having a plurality of other end side bent portions having apexes 302b on the other end side in the axial direction and adjacent in the axial direction of the stent 301 is a wavy line on one end side in the axial direction of the stent 301. A shared linear portion having a start end 322 at or near one apex 302b of the other end side bent portion of the annular body 302, and a terminal end 323 between the apex 302b of the other end bend portion and the apex 302a of the one end bend portion. 321 and adjacent wavy annular bodies are integrated by the shared linear portion 321.
The stent 301 is composed of a plurality of annular bodies in which adjacent wavy annular bodies are integrated by having a partially shared portion, and does not include a portion provided only as a so-called connection portion, and all of them are expanded. It is composed only of parts that exert power.

The stent 301 is a so-called self-expanding stent that is formed in a substantially cylindrical shape, is reduced in diameter when inserted into a living body, and can be restored to a shape before being reduced in diameter when placed in the living body. FIG. 1 shows the external shape of the stent 301 when it is expanded.
The number of wavy annular bodies 302 forming the stent 301 is 11 in the case shown in FIG. The number of wavy annular bodies 302 varies depending on the length of the stent, but is preferably 2 to 150, and more preferably 5 to 100.
Each wavy-line annular body 302 has a plurality of one end side bent portions having apexes on one end side in the axial direction of the stent 301 and a plurality of other end side bent portions having apexes on the other end side in the axial direction of the stent 301. And an endless wavy body that is continuous in an annular shape. The one end side bent portion and the other end side bent portion in the annular body 302 are alternately formed, and the numbers thereof are the same. The number of one-end-side bent portions (other-end-side bent portions) in one wavy annular body 302 is nine in the case shown in FIG. The number of one-end-side bent portions (other-end-side bent portions) is preferably 4 to 20, and particularly preferably 6 to 12. And the linear body which forms the wavy-line annular body 302 in this stent is always curved, and there are very few linear portions. For this reason, since the linear body which forms the annular body 302 has a sufficient length, it exhibits a high expansion force during expansion. Further, the axial length of the wavy annular body 302 is preferably 1 to 10 mm, and particularly preferably 1.5 to 5 mm.

In the stent 301, as shown in FIGS. 1, 2, 3, and 4, each wavy-line annular body 302 has a protruding one end side vertex 302 a 1 that protrudes from the other end side bent portion apex 302 a to one end side. And a large wave portion that forms a protruding other end apex (in this embodiment, coincides with the starting point) 322 that protrudes from the other end bend apex. Furthermore, in this stent, the wavy annular body includes a plurality of large wave portions. In this stent, one annular body includes nine one-end-side bent portions, and three large wave portions are provided in one annular body. The three large wave portions are formed so as to be substantially equiangular with respect to the central axis of the stent 301.
The wavy annular body 302 adjacent to the proximal end side in the axial direction of the stent 301 has a start end 322 at or near one vertex 302b of the other end side bent portion of the wavy annular body 302 on one end side in the axial direction of the stent 301. And has a shared linear portion 321 having a terminal end 323 between the apex 302b of the other-end-side bent portion and the apex 302a of the one-end-side bent portion, and the adjacent wavy annular bodies are integrated by the shared linear portion 321. ing.

Specifically, the shared linear portion 321 has one apex 302b of the bent portion on the other end side of the wavy annular body 302 on one end side in the axial direction of the stent 301 as the start end 322, and the start end 322 and the apex 302b. Are the same. Further, the shared linear portion 321 has a terminal end 323 between the apex 302a of the one end side bent portion that is continuous with the apex 302b (also the start end 322). In particular, in the illustrated stent 301, the shared linear portion 321 has a terminal end in the vicinity of the middle point between the apex 302b (also the start end 322) and the apex 302a of the one end side bent portion. . The end 323 is preferably located at the midpoint, but is 1/100 to 49/49 of the total length between the apex 302b (which is also the start end 322) and the apex 302a of the one end side bent portion. The position may be on the apex side of about 100. In this case, it is preferable that the position of the end 323 is shifted from the middle point toward the vertex 302a.
Since the stent 301 has the above-described configuration, the stent 301 includes a start end branch portion formed by the start end portion of the shared linear portion 321 and a terminal branch portion formed by the end portion of the shared linear portion 321. Specifically, the start end branching portion is bifurcated toward the one end side with the start end 322 as a branch point, and the end branch portion is directed toward the other end side with the end point 323 as a branch point. It has a form that branches into two.

Furthermore, in this stent 301, the length between the projecting one end apex 302a1 and the projecting other end apex (matching the start end 322) in the large wave section is a long linear section that is longer than the linear section connecting the other apexes. . And the other end side end of this long linear part is the start end of a shared linear part as mentioned above. And in this stent 301, the shared linear part 321 is formed in a part of large wave part.
Moreover, in this stent 301, as shown in FIG. 2, each wavy-line annular body 302 has a short line-shaped portion 326 that connects between the terminal end 323 of the shared line-shaped portion 321 and the apex 302a of the one end side bent portion. Yes. Further, the annular body 302 integrated with the annular body 302 having the short linear portion 326 and the shared linear portion 321 has a structure in which the start end 322 and the other end side bent portion of the shared linear portion 321 are arranged as shown in FIG. It has the short line part 325 which connects between the vertices 302b, and the long line part 324 which connects between the terminal end 323 of the shared line part 321 and the other vertex 302b of the other end side bent part.
Therefore, a long linear portion is formed between the protruding one end vertex (matching with the terminal end 323) and the protruding other end vertex (matching with the annular body adjacent to the other end side and the starting end 322 of the shared linear portion) in the large wave portion. ing. That is, in the stent 301, the shared linear portion 321 adjacent in the axial direction has a long linear shape when the end 323 of the shared linear portion 321 and the start end 322 of the adjacent shared linear portion 321 are viewed from one end side in the axial direction. It is a form connected by the section 324. For this reason, as shown in FIG. 2, in this stent 301, the zigzag configuration formed by repeating the long linear portion 324 and the shared linear portion 321 forms a spiral from one end of the stent toward the other end. It is supposed to be.

In this stent, there is no so-called connection portion, and there is no bending failure and expansion force reduction due to the connection portion, and the entire stent exhibits a uniform expansion holding force.
The stent 301 includes a plurality of shared linear portions 321 between adjacent wavy annular bodies. Specifically, three shared linear portions 321 are provided between adjacent wavy annular bodies. The three shared linear portions 321 are formed so as to be substantially equiangular with respect to the central axis of the stent 301.
In the stent 301, the short linear portion 325 that connects the start end 322 of the shared linear portion 321 and the apex 302 b of the bent portion on the other end side is not continuous in the axial direction of the stent 301, and a plurality of short linear portions 325 are connected. However, it is formed so as to be substantially linear. Further, in this stent 301, as shown in FIG. 4, the linear portions (long linear portions and other linear portions) excluding the short linear portions 325 and 326 described above have the traveling direction of the linear body in the vicinity of the intermediate portion. A bending portion 332 that is substantially parallel and slightly changes is provided. By having this bending part 332, the linear part length becomes long and expansion force also becomes high.

Further, in this stent 301, the length of the long linear portion 324 (that is, the length between the terminal end 323 of the shared linear portion 321 and the start end 322 of the shared linear portion 321), the shared linear portion 321 and the short linear portion. Comparing the total length of 325 (that is, the length from the end 323 of the shared linear portion 321 to the vertex 302b beyond the start end 322), the long linear portion 324 is slightly longer. By doing this, the vertex 302b is connected to the adjacent linear portion 333 (specifically, a normal linear portion that connects the vertex 302a and the vertex 302b and has no linear sharing portion or branching portion). Excessive proximity can be prevented and the width in the closed space formed by the linear body (as shown in FIG. 2, this stent 301 has a closed space connecting the V and M shapes). It is possible to reduce the number of letters, and exhibits high expansion maintenance power.
Further, as shown in FIG. 2, the apex 302a of the one-end-side bent portion of the wavy annular body 302 enters the space formed between the apexes 302b of the other-end bent portion of one adjacent wavy-shaped annular body. The vertex 302b of the other end side bent portion of the wavy annular body 302 penetrates into the space formed between the apexes 302a of the one end side bent portion of the other adjacent wavy annular body. By doing so, the length of the linear body constituting the stent can be increased, and a closed space formed by the linear body (as shown in FIG. The area of the connected closed space is formed), and a high expansion maintaining force is exhibited.

  Furthermore, in this stent 301, in the contracted state shown in FIG. 3, there are almost no gaps in the circumferential direction, and the elements are arranged. For this reason, it has high coverage.

  Since the stent 301 has the shape as described above, the stent 301 is not broken by the large deformation and is excellent in durability (fatigue life) even after being placed in a highly deformed blood vessel such as the lower limb.

Although the size of the stent 301 varies depending on the indwelling target site, generally, the outer diameter at the time of expansion (at the time of non-contraction, at the time of restoration) is 2.0 to 30 mm, preferably 2.5 to 20 mm, and the length is It is 5-250 mm, More preferably, it is 15-200 mm. In particular, in the case of an intravascular stent, the outer diameter is 2.0 to 14 mm, preferably 2.5 to 12 mm, and the length is 5 to 100 mm, more preferably 10 to 80 mm.
The wall thickness is 0.04 to 0.3 mm, preferably 0.06 to 0.22 mm.

  As mentioned above, although the shape of the stent of this invention was demonstrated using drawing, the shape of the stent of this invention is not limited to what was illustrated. Examples of other configurations of the stent of the present invention include the stents described in JP 2008-161475 A, JP 2007-144108 A, and JP 2005-279076 A, for example.

The stent of the present invention is based on a NiTi alloy. NiTi-based alloys widely include alloys mainly composed of nickel and titanium. NiTi-based alloys are generally called shape memory alloys, and some of them show superelasticity at least at a living body temperature (around 37 ° C.). Superelasticity here means that even if it is deformed (bending, pulling, compressing) to a region where normal metal is plastically deformed at the operating temperature, it will recover to its almost uncompressed shape without the need for heating after the deformation is released. It means to do.
As a typical NiTi alloy, there is a NiTi alloy containing 43 to 57 wt% of Ni and the balance being Ti and inevitable impurities. A small amount of other metals such as cobalt, iron, palladium, platinum, boron, aluminum, silicon, vanadium, niobium, copper, and the like may be added to such a NiTi alloy.
The NiTi-based alloy used as the base material of the stent of the present invention preferably contains 54.5 to 57 wt% of Ni and the balance is made of Ti and inevitable impurities. In such a NiTi alloy, in addition to Ti and Ni, C is 0.070 wt% or less, Co is 0.050 wt% or less, Cu is 0.010 wt% or less, Cr is 0.010 wt% or less, and H is 0.00. You may contain 005 wt% or less, Fe 0.050 wt% or less, Nb 0.025 wt% or less, and O 0.050 wt% or less.

The surface of the stent of the present invention is polished by electron beam irradiation. Although details of the polishing by electron beam irradiation will be described later, there is a layer formed on the surface of the stent by melting and solidifying the NiTi alloy constituting the base material of the stent at the time of electron beam irradiation. FIGS. 5A and 5B are views for explaining changes in the NiTi-based alloy constituting the base material of the stent due to electron beam irradiation. FIG. 5A shows the time of electron beam irradiation, and FIG. 5B shows the state after electron beam irradiation.
As shown in FIG. 5B, a layer 20 having a crystal structure different from that of the remaining part of the base material is formed on the surface of the base material by melting and solidifying the NiTi-based alloy upon electron beam irradiation. Has been. Specifically, the NiTi-based alloy constituting the layer 20 has a crystal grain size smaller than that of the NiTi-based alloy constituting the remaining portion of the substrate 10.
The crystal grain size of the NiTi-based alloy constituting the layer 20 is smaller than that of the NiTi-based alloy constituting the remaining part of the base material 10 because the surface of the base material is irradiated by electron beam irradiation. This is because the crystal grains are refined by heating to about 3000K and then cooling.
The formation of the layer 20 improves the corrosion resistance of the stent. This is presumably because the crystal grains of the NiTi-based alloy constituting the layer 20 become finer due to electron beam irradiation.
The crystal grains of the NiTi alloy can be confirmed with a transmission electron microscope (TEM).
The thickness of the layer 20 varies depending on the electron beam irradiation conditions, but is about 5 to 6 μm when implemented under the conditions described later.

[Method for producing stent of the present invention]
The above-described stent of the present invention can be preferably produced by the procedure described below.
The stent manufacturing method of the present invention includes a step of preparing a stent based on a NiTi alloy, a step of removing the outermost layer on the surface of the stent, and a step of polishing the surface of the stent by electron beam irradiation. And heat-treating the stent.

[Step of preparing a stent based on a NiTi alloy]
This step can be performed according to a normal procedure for manufacturing a stent based on a NiTi alloy. For example, in the case of the stent 301 shown in FIGS. 1-4, it can produce by removing (for example, cutting, melt | dissolving) a stent non-component part using the pipe which consists of a NiTi type alloy. Thereby, it is an integrally formed product.

[Step of removing outermost layer of stent surface]
In the NiTi-based alloy constituting the stent, there may be inclusions generated during the production of the alloy material. In addition, when creating a stent by the above procedure, foreign matter may adhere to the stent surface.
In this step, the outermost layer on the stent surface where these inclusions and foreign substances may be present is removed.

The inventors of the present application have found that the fatigue life of the stent is reduced when polishing by electron beam irradiation is performed.
The inventors of the present application have found that by reducing the outermost layer of the stent surface where inclusions and foreign matters may be present and then performing polishing by electron beam irradiation, it is possible to suppress a decrease in fatigue life. It was.

The method used to remove the outermost layer on the stent surface is not particularly limited, but there is little risk of generating new foreign substances, and the acid used to remove the outermost layer from the surface of the stent having a fine and complicated shape is as follows: There is no particular limitation as long as it has the effect of dissolving the NiTi alloy. Examples thereof include nitric acid, hydrofluoric acid, hydrogen peroxide acid, and mixed acids thereof. Among these, a mixed acid of nitric acid and hydrofluoric acid is preferable because it has a strong action of dissolving the NiTi alloy.
Commercially available etching solutions can also be used. For example, Fujiseclean FE-17 (Fuji Acetylene Industry Co., Ltd.) is mentioned.
The method of bringing the acid into contact with the stent surface is not particularly limited. For example, the acid may be sprayed onto the stent surface. However, a method of immersing the stent in a predetermined acid is preferable because it is suitable for bringing the acid into contact with the surface of the stent having a fine and complicated shape. Although the temperature of the acid at the time of immersion and the immersion time differ depending on the acid to be used, in the examples described later, it was immersed in Fujiseclean FE-17 diluted to 25 vol% with water at room temperature for 30 seconds.

[Step of polishing the surface of the stent by electron beam irradiation]
In this step, in order to smooth the surface of the stent after removing the non-stent component, specifically, the surface roughness Ra of the stent surface is 1.5 μm or less, preferably 0.32 μm or less, more preferably 0. In order to make it 15 μm or less, polishing by electron beam irradiation is performed.
The conditions for electron beam irradiation preferably satisfy, for example, the following.
Energy density: about 1 J / cm ² or more, preferably about 1 J / cm ² or more 20 J / cm ² or less, more preferably, about 2J / cm ² or more 15 J / cm ² or less, more preferably, from about 4J / cm ² or more 12 J / cm ² or less, and most preferably from about 5 J / cm ² or more 9J / cm ² or less.
Pulse width: 1 μs or more.
Number of irradiation (number of pulses): about 5 times or more, more preferably about 20 to 40 times.

[Process for heat-treating the stent]
As described above, when the polishing by electron beam irradiation is performed, the fatigue life of the stent is reduced. The inventors of the present application have found that the fatigue life of the stent can be recovered by heat-treating the stent after polishing by electron beam irradiation.
The cause-and-effect relationship in which the fatigue life of the stent is recovered by heat treatment is not necessarily clear, but the reason is that (1) the strain introduced into the NiTi alloy constituting the substrate by electron beam irradiation is recovered, (2) Superelastic heat treatment effect (effect in which the material in which the M transformation is suppressed by electron beam irradiation is restored to a material that can easily undergo the M transformation and its reverse transformation by the heat treatment), (3) The NiTi alloy is treated by the heat treatment. Examples thereof include those obtained by changing the physical properties of the NiTi-based alloy by being partly melted and then recrystallized.

An annealing treatment is preferable as the heat treatment performed for the above purpose. The reason is that the annealing treatment has a superelastic heat treatment effect. That is, since it is possible to recover the strain introduced into the NiTi alloy by electron beam irradiation by annealing, a material in which the M transformation is suppressed by the electron beam irradiation is a material that is easily subjected to the M transformation and its reverse transformation. It is because it can be recovered.
The annealing treatment is performed at 300 to 1100 ° C., preferably 450 to 700 ° C., more preferably 500 to 600 ° C. for 1 minute to 10 hours, preferably 5 minutes to under vacuum or a rare gas atmosphere such as argon or helium. What is necessary is just to implement for 1 hour, More preferably 5 minutes-30 minutes time.

  The stent obtained by the above procedure may be further processed as necessary. For example, for the purpose of supporting a biological physiologically active substance such as an immunosuppressive agent or an anticancer agent on the stent surface, a treatment for forming a layer containing the biological physiologically active substance on the stent surface may be performed. The stent surface may be covered with a cylindrical cover.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to the following Example.
In the following examples, reference examples, and comparative examples, a NiTi alloy (Ti: 49 atomic% (43.94 wt%), Ni: 51 atomic% (56.06 wt%) was not formed into a stent shape. )) A wire (φ0.5 mm) made of 20 cm in length was used, and the treatment described below was performed. In Comparative Example 1, acid treatment and heat treatment were not performed. In Comparative Example 2, acid treatment and heat treatment were not performed, and electrolytic polishing was performed instead of polishing by electron beam irradiation. In Reference Example 1, acid treatment was not performed. In Reference Example 2, no heat treatment was performed.
[Acid treatment]
FUJI SECLEAN FE-17 (HNO ₃ : 53.8%, HF: 8.0%, H ₂ O: 38.2%) was diluted with water to a concentration of 25 vol%, and the sample wire was placed at room temperature for 30 seconds. Soaked.
[Polishing by electron beam irradiation]
The sample wire was irradiated with an electron beam under the following conditions.
Anode voltage: 20 kV
Energy density: about 7 J / cm ²
Distance between electron gun end and sample wire: 20mm
Number of pulses: 100 shots for Example 1 and Reference Examples 1 and 2
Except for the above, a 10-shot sample wire was irradiated with three electron beams at intervals of 35 mm in the longitudinal direction.
[Electrolytic polishing]
In Comparative Example 2, a mixture of sulfuric acid, phosphoric acid and water was used as the electrolytic solution, and electropolishing was performed at a voltage of 15V.
[Heat treatment]
The sample wire after electron beam irradiation was heat-treated under the following conditions.
Example 1: Annealing treatment was performed at 600 ° C. for 1 hour in an argon stream (100 ml / min), and then allowed to cool.
Example 2: Annealing treatment was performed at 875 ° C. for 1 hour in a vacuum (pressure 8 × 10 ⁻³ Pa), followed by ice quenching.
Example 3: Annealing treatment was performed at 650 ° C. for 1 hour in an argon stream (100 ml / min), and then ice quenching was performed.
Example 4: Annealing was performed at 650 ° C. for 1 hour in a vacuum (pressure 8 × 10 ⁻³ Pa), and then ice quenching was performed.
Example 5, Reference Example 1: Annealing treatment was performed at 300 ° C. for 1 hour in vacuum (pressure 8 × 10 ⁻³ Pa), and then allowed to cool.
Example 6: Annealing treatment was performed at 500 ° C. for 1 hour in a vacuum (pressure 8 × 10 ⁻³ Pa), and then allowed to cool.
Example 7: Annealing treatment was performed at 500 ° C. for 10 hours in a vacuum (pressure 8 × 10 ⁻³ Pa), and then allowed to cool.

[Fatigue life evaluation]
A rotating bending test was performed on the sample wire after each treatment under the following conditions to evaluate the fatigue life.
Water bath temperature for dipping the wire: 37 ° C, 45 ° C, 50 ° C
Wire holding length: 80mm
Rotation speed: 3600 rpm
In addition, in order to make the load stress in a rotation bending test into an equivalent level, the center distance (center distance) was adjusted about each sample.
[3-point bending test]
In addition, a three-point bending test was performed under the following conditions.
Test speed: 2 mm / min
Support point distance: 25mm
Push-in amount: 0 → 2 → 0mm

FIG. 6 is a graph comparing changes in fatigue life due to electrolytic polishing or polishing by electron beam (EB) irradiation on an untreated sample wire. The electrolytic polishing data is the data of Comparative Example 2, and the polishing data by electron beam irradiation is the data of Comparative Example 1.
As is clear from FIG. 6, it was confirmed that the fatigue life was lowered when polishing by electron beam irradiation was performed without the acid treatment as the pretreatment and the heat treatment as the posttreatment.

FIG. 7 is a graph comparing changes in fatigue life depending on the presence or absence of acid treatment as a pretreatment for the sample wire subjected to polishing by electron beam (EB) irradiation. Data without acid treatment (only EB) is data of Comparative Example 1, and data with acid treatment (acid treatment + EB) is data of Reference Example 2.
As is clear from FIG. 7, it was confirmed that the decrease in fatigue life was significantly suppressed by performing the acid treatment as the pretreatment. However, although not shown, the fatigue life was inferior to that of an untreated sample wire. Suppression of the decrease in fatigue life due to the acid treatment as a pretreatment is caused by inclusion of solid-containing particles, particularly TiC, on the surface, causing stress concentration, but the outermost layer containing these by acid treatment. This can be explained as an effect obtained by removing.
FIG. 7 also compares the change in fatigue life due to the presence or absence of heat treatment. Data without acid treatment (only EB) and heat treatment (300 ° C.) are the data of Reference Example 1, data with acid treatment (only acid treatment + EB) and data with heat treatment (300 ° C.) are the data of Example 5. is there. From these data, it was confirmed that the fatigue life was improved by performing the heat treatment.

FIG. 8 is a graph comparing changes in fatigue life depending on the presence or absence of heat treatment as a post-treatment for sample wires that have been polished by electron beam (EB) irradiation. Data without heat treatment (only EB) is data of Comparative Example 1, data with heat treatment (EB + 500 ° C., 1 h) is data of Example 6, and data with heat treatment (EB + 500 ° C., 10 h) is Example 7. It is data of. Note that FIG. 8 also shows unprocessed data.
As is clear from FIG. 8, it was confirmed that the fatigue life is improved by performing the heat treatment as compared with the untreated one. Compared to the sample irradiated only with electron beam, the fatigue life is greatly improved.

9 to 11 are graphs showing the results of a three-point bending test for Examples 1 and 2 and an untreated sample wire.
As is apparent from FIGS. 9 to 11, Examples 1 and 2 subjected to heat treatment were not inferior to untreated ones in the results of the three-point bending test.

The results of the rotary bending test for Example 1, Comparative Example 1, and the untreated sample wire are shown in the following table. In the rotary bending test, the following table and FIGS. 7 and 8 were carried out under the same conditions.
As is clear from the table, the fatigue life of Example 1 was significantly recovered as compared with Comparative Example 1, and was not inferior to the untreated one.

FIG. 1 is a front view showing the shape of a preferred configuration example of the stent of the present invention. FIG. 2 is a development view of the stent shown in FIG. FIG. 3 is a development view of the stent in a state where the diameter of the stent shown in FIG. 1 is reduced. FIG. 4 is a partially enlarged view of the stent shown in FIG. FIGS. 5A and 5B are views for explaining changes in the NiTi-based alloy constituting the base material of the stent due to electron beam irradiation. FIG. 5A shows the time of electron beam irradiation, and FIG. 5B shows the state after electron beam irradiation. FIG. 6 is a graph comparing changes in fatigue life due to electrolytic polishing or polishing by electron beam (EB) irradiation on an untreated sample wire. FIG. 7 is a graph comparing changes in fatigue life depending on the presence or absence of acid treatment as a pretreatment for the sample wire subjected to polishing by electron beam (EB) irradiation. FIG. 8 is a graph comparing changes in fatigue life depending on the presence or absence of heat treatment as a post-treatment for sample wires that have been polished by electron beam (EB) irradiation. FIG. 9 is a graph showing the results of a three-point bending test of the sample wire of Example 1. FIG. 10 is a graph showing the results of a three-point bending test of the sample wire of Example 2. It is the graph which showed the result of the three-point bending test of an untreated sample wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Base material 20 Surface layer 301 Stent body part 302 Annular body 321 Shared linear part 324 Long linear part

Claims (3)

A method for manufacturing a stent, comprising:
Preparing a stent based on a NiTi-based alloy;
Removing the outermost layer on the surface of the prepared stent;
A step of polishing by electron beam irradiation of the surface of the stent to remove the outermost layer,
And a step of heat-treating the polished stent.   The method for manufacturing a stent according to claim 1, wherein the step of removing the outermost layer on the surface of the stent includes acid treatment of the surface of the stent. The step of heat-treating the stent includes:
The manufacturing method of the stent of Claim 1 or 2 including annealing the said stent.