JP2013215487A - Laser processing method with skewered tube and stent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method which improves the yield of metal tubes for laser processing and maintains a deformation texture of a metal material, and also to provide a stent.SOLUTION: A core metal is inserted into the bores of a plurality of short tubes, and the tubes are subjected to dry laser processing and a laser processing method with a skewered tube in which a water column formed through a tube to be processed is used as a waveguide of a laser beam to form a stent. Because a tube shorter than in conventional methods is used in the method, industrial observation means can be used and credibility of observation of the inner and outer surfaces is secured.

Description

The present invention relates to a stent attached to the lumen of a human body or an animal, and a method for manufacturing the stent.

Stent treatment is a medical technology that is rapidly progressing in recent years. A stent is a mesh-like metal pipe placed in the body in order to prevent restenosis after expansion of a stenosis part such as a blood vessel. The stent accommodated in the reduced diameter at the distal end portion of the catheter is introduced into the stenosis portion and then attached to the inner wall of a blood vessel or the like by a release / expansion operation from the catheter. The stenosis of the coronary artery that causes myocardial infarction or the like is expanded along with the vasodilation operation by the expansion of the balloon set on the stent housing inner wall. This is called a balloon-expandable, and the metal is stainless steel or cobalt chrome alloy.

On the other hand, arteriosclerosis and stenosis are particularly prone to occur in blood vessels connected to the brain, and thrombus and plaque accumulated in the stenosis flow to the brain and cause cerebral infarction. In this case, the stent is self-expandable that is released from the catheter and expands by self-restoration, and the metal is a Ti-Ni superelastic alloy having excellent spring characteristics.

Also, as a recent trend, studies have been made on bioabsorbable materials as stent cores. That is, after the stent placement / restenosis prevention function period elapses, the core is absorbed by the living body and disappears. Candidates are likely to be polylactic acid resin-based, but the application of a metal material, Mg alloy, which has weak weakness in the essential stent retention force and is superior in expansion force, is advancing.

Ti-Ni alloy is one of the metal materials for stents that have many research and application examples.
It is well known that shape memory alloys such as Ti-Ni alloys exhibit remarkable shape memory accompanying the reverse transformation of the martensitic transformation. It is also well known that it exhibits good superelasticity with the stress-induced martensitic transformation caused by strong deformation in the matrix region after reverse transformation. The superelasticity is particularly apparent in Ti-Ni alloys and Ti-Ni-X alloys (X = V, Cr, Co, Nb, etc.) among many shape memory alloys.

The shape memory effect of the Ti—Ni alloy is disclosed in Patent Document 1, for example. Ti-Ni alloy superelasticity is characterized by the fact that it starts at the reverse transformation temperature start temperature (As temperature) of the alloy and is higher than the reverse transformation end temperature (Af temperature). The amount of recovery is about 7% in elongation strain. As temperature means shape recovery start temperature, and Af temperature means shape recovery end temperature (shape recovery temperature). A differential scanning calorimeter (DSC) is often used as an industrial transformation temperature measurement means. According to DSC, clear exothermic and endothermic peaks are seen before and after transformation.

Proposals for using a Ti—Ni superelastic alloy for a self-expanding stent are shown in Patent Documents 2, 3, 4 and the like. According to Patent Document 2, when a shape memory alloy is pulled in a matrix phase at an Af temperature or higher, stress initially increases linearly with strain. After that, stress-induced martensitic transformation occurs along with the addition of stress, and even if the strain increases, the stress flat region (Loading-Plato) is maintained up to about 7% strain. It is said that it is usual to have an area (Unload-Plato). That is, the application of superelasticity with a clear transformation. Patent Document 2 proposes a third element-added alloy Ti—Ni—X (X = Nb, Hf, Ta, W) in order to obtain a further highly elastic stent.

The characteristics of Ti-Ni alloys vary greatly depending on the cold work degree and heat treatment conditions, and do not show a clear transformation peak due to DSC, and there is no flat region where stress increases with increasing strain due to processing that suppresses transformation. Plato superelasticity can be provided. These elements are proposed as a high-strength Ti—Ni alloy core material that does not have a flat region in Patent Documents 5 and 6 in a guide wire.

U.S. Pat.No. 3,174,851 JP 07-112028 A Japanese Patent Laid-Open No. 08-000738 Japanese Unexamined Patent Publication No. 08-196642 JP-A-5-293175 Japanese Patent Laid-Open No. 2001-164348

(1) Material yield:
The stent is obtained by laser processing of a metal tube, and the tube to be processed is straight to improve the uniformity of the stent slot, and there is a distance of about 100 mm between the tube gripping portion of the laser processing apparatus and the laser beam portion, The tube in that area is not used for stent processing.

(2) Maintenance of processing texture:
In many cases, the metal material can obtain optimum characteristics by processing techniques (plastic processing, heat treatment) up to final dimensions. In the case of Ti-Ni alloy, it is possible to increase the strength of the material by the texture by cold strong working. However, straightening a laser-processed stent tube is generally performed by heat treatment and mechanical correction is difficult. For this reason, the folded texture is lost by heat treatment.
In addition, in the case where the optimum orientation of the material is dependent on the structure orientation and microcrystallization, it is necessary to impart characteristics in multi-axis forging / rolling with a block-shaped ingot and to preserve the structure by subsequent cutting.

(3) Inner surface observation of long tube:
Stents are mainly 0.1mm thick and 0.1mm slot processed products. For this reason, scratches and defects in the final processed tube cause breakage during indwelling, and observation of the inner and outer surfaces is important for ensuring reliability. However, there is no effective industrial observation means with long tubes, and it is necessary to rely on observation after stent processing.

As a result of a thorough examination of the laser processing method of the stent, the skewer tube laser processing method in which a water column formed by passing a cored bar through the tube inner diameter and forming the tube to be processed is a laser beam waveguide is effective. The headline, the present invention has been reached.

According to the laser processing method of the present invention, it is possible to provide a stent that can improve the yield of the tube and maintain the processed texture. In addition, since a short tube is used as compared with the conventional case, an industrial observation means is possible, and the reliability of the inner and outer surface observation can be ensured.

Stent processing development image Example of lad tube stent processing results DSC curve for each process

  Examples of the present invention will be described below. A pipe connection diagram in which a plurality of short tubes according to the present invention are inserted into a core material to form a skewered shape and an actual stent processing development example are shown in FIG.

Figure shows the results of stent processing of a clad tube with a steel alloy core inserted into a φ2.0mm, t0.2mm tube, dry laser processing, and water laser processing using a water column formed up to the tube to be processed as a laser beam waveguide. As shown in FIG. 2, although it can be said that a water laser is effective in the present invention, it is not an essential condition.

A Ti-51at% Ni alloy ingot was made into a 7 mm square section by hot forging → cold forging. The cold work rate applied to the material is about 50%. Thereafter, a thin tube for stent φ1.8 × φ1.4 mm × L50 mm was formed by cutting, and a plurality of them were attached to a steel core bar to form a skewered shape. Next, they were stented by the water laser shown in FIG.

Whether to introduce strain in each process was judged by DSC measurement of the material in each process. DSC can be divided into a type in which no clear exothermic peak and endothermic peak are observed in the cooling process and heating process, and a type in which the endothermic peak is not observed. It is well known that in the former, transformation is suppressed by the machining texture, and in the latter, transformation in the machining is released by the heat effect and the transformation appears. FIG. 3 shows the results of DSC curves and measured transformation temperatures for each process. It can be seen from FIG. 3 that the present invention can be processed into a stent with the strain introduced during forging fixed.

Claims (7)

Laser processing method for stents, characterized in that a cored bar is passed through the inner diameter of the processing tube, and a skewer tube laser processing method and its stent 2. The tube laser processing method according to claim 1, wherein one or a plurality of the tubes are arranged within a laser processing effective range. 2. The tube laser processing method according to claim 1, wherein the metal structure at the time of forming the material (rod, tube) is not destroyed by subsequent small diameter processing and slit processing. 2. The tube laser processing method according to claim 1, wherein the processed tube is subjected to inner surface treatment and dimension measurement. 5. The skewered tube laser processing method according to claim 1, wherein the core metal is secured with an adhesive or surface irregularities so that the outer tube is not partially or completely peeled off by stent processing. 6. The tube laser processing method according to claim 1, wherein the stent processing apparatus uses a water column formed up to a tube to be processed as a waveguide of laser light. 7. The tube laser processing method according to claim 1, wherein the outer diameter of the stent tube is 0.1 mm or more and 5 mm or less and the thickness of the tube is 0.001 mm or more and 1 mm or less.