Wireworking – Article making or forming – Electric lamp or electric space discharge device electrode
Reexamination Certificate
2001-07-30
2003-05-27
Larson, Lowell A. (Department: 3725)
Wireworking
Article making or forming
Electric lamp or electric space discharge device electrode
C623S001190
Reexamination Certificate
active
06568432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for manufacturing a stent for treating internal tubular organs such as a blood vessel and more particularly for treating aneurysm.
2. Description of Related Art
Inside a body, there are many tubular organs, such as a blood vessel, a bile duct, a ureter, an esophagus, or the like; such organs bear a possibility of characteristic ailments such as stenosis or occlusion. For example, in respect of blood vessels, there are possibilities of ailments such as stenosis, occlusion, aneurysm, varicosity, and the like. More particularly, since aneurysm is a serious ailment where a rupture of a blood vessel causes excessive bleeding, prompt treatment is to be required, and various tools have been developed for treating thus ailment effectively.
Lately, the use of a metallic cylindrical tool called a stent is increasingly used for treating a portion of blood vessel stenosis or for treating aneurysm. For example, when treating aneurysm, a stentgraf, which covers the stent with an artificial blood vessel, is used; such stentgraf is positioned in place at the inner side of the aneurysm so that pressure of blood would not affect the aneurysm.
As for examples regarding the kinds of stents, there is a cylindrical stent made from a metal material (representatively from stainless steel) or a stent having a metal wire bent in a zigzag manner while at the same time having a cylindrical shape. Such stents are delivered to an affected portion internally through a blood vessel and positioned in place when reaching the affected portion.
In a case of positioning the stent at the affected portion, the stent is diametrally shrunk and confined within a long tubular delivery kit, in which the delivery kit has a guiding wire inserted therethrough; and then, starting from the guiding wire, the delivery kit is guided through a blood vessel from a portion such as the root of a leg till reaching the affected portion, and then, when reaching the affected portion, the delivery kit is retracted to release the stent from confinement. After being released from confinement, the stent diametrally self-expands, and is positioned in place at the affected portion in thus expanded state for protecting the blood vessel.
When the stent is released from confinement as mentioned above, it would be necessary for the stent to precisely return back to the original diameter (diameter before diametral shrinkage). If the return back to the original diameter lacks precision, preparation of a stent with a diameter anticipating the rate of returning back would become necessary and would cause the requirement of extra labor and material.
Meanwhile, as for zigzag shaped stents, various shapes thereof have been proposed as shown in
FIG. 5. A
stent
51
shown in FIG.
5
(
a
) is structured having numerous short members
51
a welded at the end portions thereof. Although the stent
51
has a characteristic of being easily diametrally shrunk, the material for the member
51
a
will be limited owing to the requirement of a welding procedure. A stent
52
shown in FIG.
5
(
b
) is structured with a single wire having a relatively large bending radius. Although the stent
52
has a characteristic of being resistant to fracture owing to a low degree of processing, the stent
52
has a difficulty of being diametrally shrunk, A stent
53
shown in FIG.
5
(
c
) is structured with a single wire having a relatively small bending radius. Although the stent
53
has a characteristic of being easily diametrally shrunk, thc stent has a problem of being easily fractured owing to a high degree of processing.
Although stainless steel is typically used as a material for the stent as mentioned above, a stainless steel stent raises a problem of not being able to sufficiently return back to the original diameter after being released from confinement, in a case when the elasticity limit for stainless steel is exceeded during diametral shrinkage.
Accordingly, it is preferable for a shape-memorizing alloy of Nickel (Ni) and Titanium (Ti) to be used as the material for the stent instead of stainless steel, since the alloy is: durable against repetitive force when in a range exceeding elasticity; corrosion-resistant; and safe upon the living body.
However, when attempting to manufacture the foregoing zigzag shaped stents
51
through
53
with use of a shape-memorizing alloy comprised of Nickel and Titanium, the stent
51
could not be applied upon, owing to the requirement of welding. Further, in respect of the stent
52
, owing to the large bending radius, a wire diameter could be thickened to allow high rigidity; nevertheless, containment into the delivery kit would be difficult since diametral shrinkage is difficult to be performed. Further, in respect of the stent
53
, owing to the high diametral shrinkage ability of the stent
53
, containment into the delivery kit could be performed easily, nevertheless, reduction of a bending radius during a bend-processing would heighten the degree of processing to raise the possibility of causing fracture.
Due to the foregoing problems, conventionally, it was difficult to manufacture a zigzag shaped stent using a wire made from a shape memorizing alloy of Nickel and Titanium which could satisfy the conditions of being able to diametrally shrink with ease and being difficult to become fractured.
It is an objet of this invention to provide a method of manufacturing a stent using a shape-memorizing alloy comprised of Nickel and Titanium, in which the stent is capable of reducing a bending radius and is therefore capable or enabling sufficient diametral shrinkage.
SUMMARY OF THE INVENTION
The present inventor has attempted various experiments for developing a method of manufacturing a stent by bend-processing a wire made from a shape-memorizing alloy of Nickel and Titanium. As a result, it has been found that the possibility of fracture during a process of bending the wire made from the Ni—Ti alloy depends on the difference in the past history of the wire.
An experiment have been performed where wires of equal thickness are bent into a same radius, in which one wire is made of a material being shape-memorized with a straight line shape, and the other wire is made of a material not having been shape-memorized. The experiment has tested whether or not fracture will occur during a process of detaching the wires from a jig and returning the wires back to the straight line shape after the wires have been shape-memorized into respective bending radiuses, under the conditions that: the datum for each item is 5; the bending radius ranges from 0.1 mm through 0.6 mm; and the thickness of the wire are respectively 0.3 mm, 0.4 mm, 0.5 mm. Thc result for the experiment is shown in chart 1. In chart 1, an X mark is applied when there is one or more fractured wires within datum 5, and a circle mark is applied when all of five are not fractured.
CHART 1
(*) fractured during forming R = 0.1
X: 1 or more wires of 5 wires fractured ◯: all 5 wires not fractured
Chart 1
N = 5
whether or not
whether or not
whether or not
fracture would
fracture would
fracture would
occur after being
occur after being
occur after being
heated, detached
heated, detached
heated, detached
from jig, and
from jig, and
from jig, and
&phgr;d-&phgr;0.3 mm
spread 180°
&phgr;d-&phgr;0.4 mm
spread 180°
&phgr;d-&phgr;0.5 mm
spread 180°
with
without
with
without
with
without
straight
straight
straight
straight
straight
straight
line
line
line
line
line
line
R (mm)
memory
memory
R (mm)
memory
memory
R (mm)
memory
memory
0.1
X (*)
◯
0.1
X
X
0.1
X
X
0.2
◯
◯
0.2
X
◯
0.2
X
X
0.3
◯
◯
0.3
◯
◯
0.3
X
◯
0.4
◯
◯
0.4
◯
◯
0.4
X
◯
0.5
◯
◯
0.5
◯
◯
0.5
◯
◯
0.6
◯
◯
0.6
◯
◯
0.6
◯
◯
As the results shown in chart 1, the wire already having been shape-memorized is more likely to fracture at a level of a larger radius compared to t
Fukuda Masatoshi
Fukuda Shoichi
Matsutani Masaaki
Larson Lowell A.
Mani, Inc.
Townsend & Banta
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