U.S. patent application number 10/274943 was filed with the patent office on 2003-06-05 for stent to be implanted in human body and method of producing stent.
Invention is credited to Kudou, Takeshi, Moriuchi, Yousuke.
Application Number | 20030105513 10/274943 |
Document ID | / |
Family ID | 19140404 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030105513 |
Kind Code |
A1 |
Moriuchi, Yousuke ; et
al. |
June 5, 2003 |
Stent to be implanted in human body and method of producing
stent
Abstract
A stent, to be implanted in a human body, is made of a
super-elastic metal which is formed approximately cylindrically and
integrally and which shows super-elasticity before and after said
stent is inserted into said human body. The stent has a plurality
of annular parts (expansion element) deformable in a direction in
which an outer diameter thereof contracts, when a stress is applied
thereto and a plurality of connection parts (connection element)
each connecting said adjacent annular parts to each other, with
said annular parts arranged in an axial direction of said stent.
Each of said annular parts is elastically deformable owing to
super-elasticity thereof, whereas each of said connection parts is
substantially a plastically deformable part not super-elastic
entirely or partly.
Inventors: |
Moriuchi, Yousuke;
(Fujinomiya-shi, JP) ; Kudou, Takeshi;
(Fujinomiya-shi, JP) |
Correspondence
Address: |
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
19140404 |
Appl. No.: |
10/274943 |
Filed: |
October 22, 2002 |
Current U.S.
Class: |
623/1.15 |
Current CPC
Class: |
A61F 2002/91575
20130101; A61F 2/915 20130101; A61F 2002/91533 20130101; A61F 2/91
20130101; A61F 2002/91558 20130101; A61F 2230/0054 20130101; Y10T
29/53987 20150115 |
Class at
Publication: |
623/1.15 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2001 |
JP |
2001-323531 |
Claims
What is claimed is:
1. A stent, to be implanted in a human body, made of a
super-elastic metal which is formed approximately cylindrically and
integrally and which shows super-elasticity before and after said
stent is inserted into said human body; said stent having a
plurality of annular parts deformable in a direction in which an
outer diameter thereof contracts, when a stress is applied thereto
and a plurality of connection parts each connecting said adjacent
annular parts to each other, with said annular parts arranged in an
axial direction of said stent, wherein each of said annular parts
is elastically deformable owing to super-elasticity thereof,
whereas said connection part is substantially a plastically
deformable part not super-elastic entirely or partly or a normal
elastically deformable part not super-elastic entirely or
partly.
2. A stent according to claim 1, wherein said annular part is
composed of a wavy linear material.
3. A stent according to claim 1, wherein said annular part is
composed of a linear constituent having a plurality of notches and
a plurality of openings formed on a side surface thereof.
4. A stent according to claim 1, wherein said connection part is
curved or bent.
5. A stent according to claim 1, wherein said connection part is
curved or bent in a direction approximately orthogonal to an axial
direction of said stent.
6. A stent according to claim 1, wherein said stent has two or more
connection parts between said annular parts adjacent to each
other.
7. A stent according to claim 1, wherein said connection part is
substantially straight.
8. A stent according to claim 7, wherein said connection part is
substantially parallel with an axial direction of said stent.
9. A stent according to claim 7, wherein said connection part is
oblique to an axis of stent by a predetermined angle.
10. A method of producing a stent to be implanted in a human body,
comprising the steps of: forming a base material for said stent
having a plurality of annular parts deformable in a direction in
which an outer diameter thereof contracts, when a stress is applied
thereto and a plurality of connection parts each connecting said
adjacent annular parts to each other, with said annular parts
arranged in an axial direction of said stent, by partly removing a
side surface of a prepared approximately cylindrical pipe, made of
a super-elastic metal, having an outer diameter suitable for a
portion of the human body in which said stent is implanted; and
heat-treating a part or an entirety of said connection part of said
base material for said stent to substantially eliminate
super-elasticity of said connection part and impart plastic
deformability or normal elasticity thereto.
11. A method according to claim 10, wherein said heat-treating step
is performed by heat generation caused by a resistance of said
connection part owing to energization of both ends of said
connection part.
12. A method according to claim 10, wherein said heat treatment is
performed by laser beams emitted to said connection part.
13. A method of producing a stent to be implanted in a human body,
comprising the steps of: forming a base material for said stent
having a plurality of annular parts and a plurality of connection
parts each connecting said adjacent annular parts to each other,
with said annular parts arranged in an axial direction of said
stent by preparing an approximately cylindrical metal pipe having
an outer diameter smaller than an inner diameter of a portion in
which said stent is implanted and having super-elasticity or a
shape memory characteristic or to which said super-elasticity or
said shape memory characteristic can be imparted and by partly
removing a side surface of said pipe; forming an expanded mode of
said base material for said stent by expanding said base material
for said stent so that an outer diameter thereof becomes suitable
for said portion in which said stent is implanted and by
heat-setting said base material for said stent in an expanded state
to store a configuration of said expanded base material for said
stent and allow said super-elasticity to appear; and heat-treating
said expanded base material for said stent by heating an entirety
or a portion of said connection part to eliminate super-elasticity
thereof substantially and impart plastic deformability or normal
elasticity thereto.
14. A method according to claim 13, wherein said heat-treating step
is performed by disposing said expanded base material for said
stent on a heat sink on which said expanded base material for said
stent can be mounted and which has a plurality of concavities, with
each annular part of said base material for said stent in contact
with an outer surface of said heat sink and with said connection
parts, an entirety of a portion thereof or a portion thereof
disposed over said concavities of said heat sink and not in contact
with said outer surface of the heat sink and by energizing said
entire base material for said stent so that said base material for
said stent self-heats and said annular part in contact with said
outer surface of said heat sink radiates heat.
15. A method according to claim 7, wherein said heat-treating step
is performed by disposing said base material for said stent on a
heat sink on which said base material for said stent can be mounted
and which has a plurality of concavities, with each annular part of
said base material for said stent in contact with an outer surface
of said heat sink and with connection parts, an entirety of a
portion thereof or a portion thereof disposed over said concavities
of said heat sink and not in contact with said outer surface of
said heat sink and by energizing said entire base material for said
stent so that said base material for said stent self-heats and said
annular part in contact with said outer surface of said heat sink
radiates heat.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a stent that is implanted
in lumens such as the blood vessel, the bile duct, the trachea, the
esophagus, the ureter, and the like so that it is used to improve a
stenosed portion or a closed portion generated in the lumens.
[0002] To cure various diseases that are caused when the blood
vessel or lumens in the human body are stenosed or closed, the
stent which is a tubular medical appliance is implanted at the
stenosed portion or the closed portion to expand them and secure
the lumen thereof. Because the stent is inserted into the human
from outside, its diameter is small. The stent is dilated or
returned to its original shape to make its diameter large at the
stenosed or closed portions to keep the dilated state of the
lumen.
[0003] The stent is classified into a self-expandable stent and a
balloon expandable stent, depending on the function and dilating
mode thereof.
[0004] The balloon expandable stent which itself has no dilating
function is inserted into a desired portion. Then, a balloon
provided in the stent is inflated to dilate (plastically deform)
the stent so that the stent is fixed to the inner surface of the
desired lumen, with the stent in close contact therewith. That is,
it is necessary to dilate the stent of this type in implanting it
in the desired portion.
[0005] Fundamentally, the self-expandable stent is made of an
elastic material. The final size of the self-expandable stent is
set when it is expanded. In introducing the self-expandable stent
into the human body, it is folded into a small size and put into a
member (plastic tube in most cases) restricting its configuration.
Then the member, namely, the tube is introduced into the human
body. The self-expandable stent is discharged from the tube at the
desired portion. The self-expandable stent dilates itself owing to
its elasticity.
[0006] The dilating mode of the balloon expandable stent and that
of the self-expandable stent are different from each other. The
characteristic of the balloon expandable stent and that of the
self-expandable stent are also different from each other. These two
kinds of the stents have merits and demerits. The balloon
expandable stent dilates in the form of a plastic deformation in
conformity to the dilation of the balloon. Therefore the balloon
expandable stent can be embedded in a curved blood vessel, with the
balloon expandable stent curved plastically. However, in the case
where the balloon expandable stent is embedded in a sublimis blood
vessel (artery near the surface of human body such as carotid
arteries, femoral artery, and the like), there is a fear that the
balloon expandable stent is deformed plastically by an external
force. Generally, embedded into such a portion is the
self-expandable stent that is capable of returning to its original
configuration by its elasticity, even though it is deformed by an
external force applied thereto. The self-expandable stent has
property of returning to its original configuration. In most cases,
the stent is formed straight in its longitudinal direction. Thus
even though the self-expandable stent is so configured that it can
be curved at a light force, it will return to its original
(straight) configuration in the human body. Therefore when the
self-expandable stent is implanted in a curved blood vessel, the
force of the self-expandable stent of returning to its original
straight shape is always applied to both ends thereof.
[0007] The self-expandable stent is disclosed in U.S. Pat. No.
6,042,606 (WO99/16,387). The stent disclosed therein is formed
straight in its longitudinal direction. Thus even though the
self-expandable stent is so configured that it can be curved at a
light force, it will return to its original (straight)
configuration in the human body. Therefore when the self-expandable
stent is implanted in a curved blood vessel, the force of the
self-expandable stent of returning to its original straight shape
is always applied to both ends thereof.
SUMMARY OF THE INVENTION
[0008] Therefore, it is an object of the present invention to
provide a stent of a self-expandable type to which little stress is
applied to both ends thereof after it is implanted in the blood
vessel of the human body.
[0009] According to a first aspect of the invention, there is
provided a stent, to be implanted in a human body, made of a
super-elastic metal which is formed approximately cylindrically and
integrally and which shows super-elasticity before and after said
stent is inserted into said human body; said stent having a
plurality of annular parts deformable in a direction in which an
outer diameter thereof contracts, when a stress is applied thereto
and a plurality of connection parts each connecting said adjacent
annular parts to each other, with said annular parts arranged in an
axial direction of said stent, wherein each of said annular parts
is elastically deformable owing to super-elasticity thereof,
whereas said connection part is substantially a plastically
deformable part not super-elastic entirely or partly or a normal
elastically deformable part not super-elastic entirely or
partly.
[0010] According to a second aspect of the invention, there is
provided a method of producing a stent to be implanted in a human
body, comprising the steps of: forming a base material for said
stent having a plurality of annular parts deformable in a direction
in which an outer diameter thereof contracts, when a stress is
applied thereto and a plurality of connection parts each connecting
said adjacent annular parts to each other, with said annular parts
arranged in an axial direction of said stent, by partly removing a
side surface of a prepared approximately cylindrical pipe, made of
a super-elastic metal, having an outer diameter suitable for a
portion of the human body in which said stent is implanted; and
heat-treating a part or an entirety of said connection part of said
base material for said stent to substantially eliminate
super-elasticity of said connection part and impart plastic
deformability or normal elasticity thereto.
[0011] According to a third aspect of the invention, there is
provided a method of producing a stent to be implanted in a human
body, comprising the steps of: forming a base material for said
stent having a plurality of annular parts and a plurality of
connection parts each connecting said adjacent annular parts to
each other, with said annular parts arranged in an axial direction
of said stent by preparing an approximately cylindrical metal pipe
having an outer diameter smaller than an inner diameter of a
portion in which said stent is implanted and having
super-elasticity or a shape memory characteristic or to which said
super-elasticity or said shape memory characteristic can be
imparted and by partly removing a side surface of said pipe;
forming an expanded mode of said base material for said stent by
expanding said base material for said stent so that an outer
diameter thereof becomes suitable for said portion in which said
stent is implanted and by heat-setting said base material for said
stent in an expanded state to store a configuration of said
expanded base material for said stent and allow said
super-elasticity to appear; and heat-treating said expanded base
material for said stent by heating an entirety or a portion of said
connection part to eliminate super-elasticity thereof substantially
and impart plastic deformability or normal elasticity thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a front view showing a stent according to an
embodiment of the present invention.
[0013] FIG. 2 is a development view showing the stent shown in FIG.
1.
[0014] FIG. 3 is a partly enlarged view showing the stent shown in
FIG. 1.
[0015] FIG. 4 is an explanatory view showing a state in which a
connection part of the stent shown in FIG. 3 has been
stretched.
[0016] FIG. 5 is a front view showing a state in which the stent
shown in FIG. 1 has been contracted.
[0017] FIG. 6 is perspective view showing a stent according to
another embodiment of the present invention.
[0018] FIG. 7 is perspective view showing a stent according to
another embodiment of the present invention.
[0019] FIG. 8 is a front view showing a stent according to an
embodiment of the present invention.
[0020] FIG. 9 is a development view showing the stent shown in FIG.
8.
[0021] FIG. 10 is a partly enlarged view showing the stent shown in
FIG. 8.
[0022] FIG. 11 is a front view showing a stent according to an
embodiment of the present invention.
[0023] FIG. 12 is a development view showing the stent shown in
FIG. 11.
[0024] FIG. 13 is a partly enlarged view showing the stent shown in
FIG. 11.
[0025] FIG. 14 is an explanatory view for explaining an example of
a heat treatment apparatus to be used in a heat treatment step.
[0026] FIG. 15 shows a heat sink of the heat treatment apparatus
shown in FIG. 14.
[0027] FIG. 16 shows a state in which a base material for the stent
is mounted on the heat sink shown in FIG. 15.
[0028] FIG. 17 shows a heat sink according to another
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The stent of an embodiment of the present invention will be
described below with reference to the drawings.
[0030] A stent 1 of the present invention is implanted in a human
body. The stent 1 is made of a super-elastic metal formed
approximately cylindrically and integrally. The super-elastic metal
shows super-elasticity before and after the stent 1 is inserted
into the human body. The stent 1 has a plurality of annular parts 2
(in other words, expansion element) deformable in a direction in
which an outer diameter thereof contracts, when a stress is applied
thereto and a plurality of connection parts 3 (in other words,
connection element) each connecting the adjacent annular parts 2 to
each other, with the annular parts 2 arranged in the axial
direction of the stent 1. The annular part 2 is elastically
deformable owing to its super-elasticity. The connection part 3 is
substantially a plastically deformable part not super-elastic
entirely or partly or a normal elastically deformable part not
super-elastic entirely or partly.
[0031] The connection part 3 has a plastically deformable part or a
normal elastically deformable part.
[0032] The stent 1 of the embodiment is an integral product having
a plurality of the annular parts 2 arranged in the axial direction
of the stent 1 and a plurality of the connection parts 3 each
connecting the adjacent annular parts 2 to each other.
[0033] As shown in FIGS. 1 and 2, the annular parts 2 formed of the
super-elastic metal showing the super-elasticity are arranged
almost linearly. Each annular part 2 has a deformation assistant
function of assisting the deformation of the stent 1 in the
direction in which the outer diameter thereof contracts, when a
stress is applied to the stent 1. The adjacent annular parts 2 are
connected to each other with the connection parts 3 constituting
the plastically deformable part or having the plastically
deformable part. The connection parts 3 may constitutes the
plastically deformable part or has the plastically deformable part.
As shown in FIG. 5, the diameter of the stent 1 of the embodiment
contracts, when a load is applied radially inwardly to the entire
side (peripheral) surface thereof.
[0034] As shown in FIGS. 1, 2, and 3, the stent 1 of the embodiment
has a plurality of the annular parts 2 each composed of a linear
material 4 that is wavy (zigzag) and annular and functions to keep
the stent 1 expanded. The annular parts 2 are connected to one
another with the connection parts 3 (connector) in such a way that
the adjacent annular parts 2 do not separate from each other. A
plurality of the annular parts 2 are arranged almost linearly in
the axial direction of the stent 1, with valleys and mountains of
the axially adjacent wavy annular parts 2 proximate to each
other.
[0035] As described above, the annular part 2 is composed of the
linear material 4 wavy (zigzag) and annular. Thus the annular parts
2 has the deformation assistant function of assisting the
deformation of the stent 1 in the direction in which the outer
diameter thereof contracts, when a stress is applied to the stent
1. Further the annular part 2 is made of the super-elastic metal
showing the super-elasticity. Thus the annular part 2 returns to
the original configuration, when the stress is eliminated
therefrom.
[0036] Unlike the annular part 2, the connection part 3 is not
substantially super-elastic entirely or partly and is plastically
deformable or normal elastically deformable. Each of the connection
parts has a plastically deformable part or a normal elastically
deformable part. But some of he connection parts may have a
plastically deformable part or a normal elastically deformable
part. Thereby the stent 1 is capable of plastically deformable or
normal elastically deformable at the connection part 3. Further the
connection part 3 reduces a stress applied to a lumen such as a
blood vessel by both ends of the stent 1, when the stent 1 is
implanted therein. Since the connection part 3 is plastically
deformable or normal elastically deformable, the connection part 3
is curved in conformity to a curvature of the blood vessel and
keeps its curved configuration when the stent 1 is implanted in a
curved blood vessel or the like. Therefore little load is applied
to both ends of the stent 1. FIG. 3 is an enlarged view showing the
neighborhood of the connection part 3 of the stent 1. The
connection part 3 (portion shown with oblique lines) shown in FIG.
3 deforms plastically or normal elastically. When the stent 1 is
bent, with the connection part 3 (portion shown with oblique lines)
disposed radially outward, the connection part 3 is stretched and
deforms plastically as shown in FIG. 4. Consequently there is an
increase in the interval between the adjacent annular parts 2
because the adjacent annular parts 2 are connected to each other
with the stretched connection part 3. Since the connection part 3
deforms plastically, the connection part 3 keeps the stretched
state. The occupation percentage of the plastically deformable
portion (or normal elastically deformable portion) of the
connection part 3 is favorably in the range of 10 to 100 and more
favorably in the range of 40 to 100. The occupation percentage of
the plastically deformable portion (or normal elastically
deformable portion) of the connection part 3 is more favorably in
the range of 50 to 100 and most favorably in the range of 80 to
100.
[0037] The connection part 3 of the stent 1 of the embodiment
connects proximate valleys and mountains of the adjacent wavy
annular parts 2 to each other and is curved or bent. Therefore,
when a force is applied to the stent 1 in a curved direction after
the stent 1 is implanted in the lumen, the stent 1 is capable of
coping with the applied force without opposing thereto, because the
connection part 3 is disposed radially outward and thus capable of
stretching. Therefore little stress is applied to the lumen in
which the stent 1 has been implanted. In the stent 1 of the
embodiment, the connection part 3 is curved in the direction
orthogonal to the axial direction of the stent 1. Therefore the
connection part 3 is capable of reliably stretching, when the
connection part 3 is curved. The connection part 3 does not
necessarily have to be orthogonal to the axial direction of the
stent 1, but may be curved or bent at a predetermined angle with
respect to the axial direction of the stent 1. Although the
connection part 3 of the embodiment is U-shaped, it may be V-shaped
or S-shaped. In the case where the connection part 3 is bent or
curved, it is preferable that a bent portion thereof or a curved
portion thereof is essentially the plastically deformable portion
(or normal elastically deformable portion).
[0038] In the stent 1 of the embodiment, the adjacent annular parts
2 are connected to each other with a plurality of the connection
parts 3. It is preferable to connect the annular parts 2 to each
other by a plurality of the connection parts 3. In this case, it is
preferable to almost confront them at two positions of all the
positions where the valleys and the mountains of the adjacent
annular parts 2 confront each other. It is also preferable to
dispose three or more connection parts 3, with the connection parts
3 forming an almost equal angle with respect to the axis of the
stent 1. In the embodiment, valleys and mountains of the axially
adjacent wavy annular parts 2 are proximately formed, with the
valleys and the mountains connected to each other alternately by
the connection parts 3. In the stent 1 of the embodiment, the
connection part 3 is not disposed inside the annular part 2.
Therefore in the stent 1, the annular parts 2 and the connection
parts 3 are arranged in the axial direction thereof. In the stent 1
of this embodiment, a plurality of the annular parts 2 and a
plurality of the connection parts 3 are alternately arranged in the
axial direction thereof, with the annular parts 2 disposed at both
ends of the arrangement. When the connection parts 3 are viewed
from the side (peripheral) surface of the stent 1, the connection
parts 3 are not disposed inside the annular parts 2, but disposed
on an annular zone orthogonal to the axis of the stent 1. Therefore
it is possible to treat a change in properties of the connection
part 3 easily and reduce an influence given to the annular part 2
by the treatment of the change in properties of the connection part
3.
[0039] Although the outer diameter of the stent 1 is different
according to a portion where the stent 1 is implanted, the outer
diameter thereof is favorably in the range of 2.0 to 30 mm and more
favorably in the range of 2.5 to 20 mm. The thickness of the stent
1 is favorably in the range of 0.04 to 1.0 mm and more favorably in
the range of 0.06 to 0.5 mm. The length of the stent 1 is in the
range of 10 to 150 mm and favorably in the range of 15 to 100 mm.
In the case where the stent is implanted in a blood vessel, the
outer diameter thereof is favorably in the range of 2.0 to 14 mm
and more favorably in the range of 2.5 to 10 mm. The thickness of
the stent is favorably in the range of 0.04 to 0.3 mm and more
favorably in the range of 0.06 to 0.2 mm. The length of the stent
is in the range of 5 to 40 mm and favorably in the range of 10 to
30 mm.
[0040] As described above, in the stent 1 of the embodiment, the
annular part 2 is composed of a plurality of linear materials 4
wavy (zigzag) and annular. The number of waves is favorably in the
range of 6 to 36 and more favorably in the range of 8 to 24. The
length of the annular part 2 is favorably in the range of 1 to 10
mm and more favorably in the range of 1.5 to 5 mm. The number of
the annular parts 2 is favorably in the range of 3 to 30 and more
favorably in the range of 5 to 20. The distance between the
adjacent annular parts 2, in other words, the length of the
connection part 3 in the axial direction of the stent 1 is
favorably in the range of 0.1 to 5 mm and more favorably in the
range of 0.15 to 3 mm. It is favorable that the width of the linear
material 4 constituting the connection part 3 is small to allow the
linear material 4 to be bent at a small force. More specifically,
the width of the linear material 4 constituting the connection part
3 is favorably in the range of 0.03 to 0.2 mm and more favorably in
the range of 0.05 to 0.1 mm. The length of the connection part 3 is
favorably in the range of 0.15 to 8 mm and more favorably in the
range of 0.2 to 5 mm when the connection part 3 is straight.
[0041] The mode of the annular part of the stent is not limited to
the above-described one.
[0042] For example, the stent may have the annular part having a
form as shown in FIG. 6.
[0043] As in the case of the stent 1, a stent 20 of the embodiment
is implanted in the human body and made of a super-elastic metal
formed approximately cylindrically and integrally. The
super-elastic metal shows super-elasticity before and after the
stent 20 is inserted into the human body.
[0044] An annular part 21 of the stent 20 of the embodiment is
composed of a linear constituent which has a plurality of notches
and a plurality of openings formed on a side (peripheral) surface
thereof and is made of a metal showing super-elasticity.
[0045] The stent 20 of the embodiment is also an integral product
having a plurality of the annular parts 21 arranged in the axial
direction of the stent 20 and a plurality of the connection parts
27 each connecting the adjacent annular parts 21 to each other.
[0046] The annular part 21 has the notch at its ends 23a and 23b.
Thus the ends 23a and 23b of the annular part 21 are capable of
deforming easily. In particular, a partial deformation of the end
can be accomplished. Therefore the annular part 21 has a favorable
response to a deformation of a blood vessel in which the stent is
implanted. The end 23 is composed of ends of a plurality of frames
26a. Thus the end 23 has a sufficient strength and thus is not
easily broken. An opening 24 surrounded with frames 26a and 26b is
formed between both ends 23a and 23b of the annular part 21. The
opening 24 is deformed easily by a deformation of the frame 26a.
Therefore the annular part 21 deforms easily at its central portion
(central portion of frame).
[0047] In this embodiment, the opening 24 has the shape of a
hexagon long in the axial direction of the stent 20. The notch 25
has the shape of an isosceles triangle. A plurality of the notches
25 are formed at each end of the annular part 21. More
specifically, six notches 25 having almost the same configuration
are formed at each end of the annular part 21. A plurality of the
openings 24 are formed in such a way as to form the side surface of
the stent 20 or the peripheral surface thereof. More specifically,
six openings 24 are formed. Neither the configuration of each of
the notch and the opening is limited to the above-described one nor
the number of each of the notch and the opening is limited to the
above-described one. It is preferable that the number of the
notches is 3 to 10 and that the number of the openings is also 3 to
10.
[0048] In the stent 20 of the embodiment, a plurality of the
annular parts 21 are arranged in the axial direction thereof. The
adjacent annular parts 21 are connected to each other with the
connection parts 27. The connection part 27 is substantially a
plastically deformable part (or normal elastically deformable part)
not super-elastic entirely or partly. In other words, the
connection part 27 constitutes the substantially plastically
deformable part (or normal elastically deformable part) or has the
plastically deformable part (or normal elastically deformable
part).
[0049] In the stent 20 of the embodiment, three annular parts 21
are linearly arranged and connected to each other by the connection
parts 27. The connection part 27 connects proximate apexes of the
adjacent annular parts 21 to each other and is curved or bent.
Therefore, when a force is applied to the stent 20 in a curved
direction after the stent 20 is implanted in the lumen, the stent
20 is capable of coping with the applied force without opposing
thereto, because the connection part 27 is disposed radially
outward and thus capable of stretching. Therefore little stress is
applied to the lumen in which the stent 20 has been implanted. In
the stent 20 of the embodiment, the connection part 27 is curved in
the direction orthogonal to the axial direction of the stent 20.
Therefore the connection part 27 is capable of reliably stretching,
when the connection part 27 is curved. The connection part 27 does
not necessarily have to be orthogonal to the axial direction of the
stent 20, but may be curved or bent at a predetermined angle with
respect to the axial direction of the stent 20. Although the
connection part 27 of the embodiment is U-shaped, it may be
V-shaped or S-shaped. In the case where the connection part 27 is
bent or curved, it is preferable that a bent portion thereof or a
curved portion thereof is essentially the plastically deformable
portion. The occupation percentage of the plastically deformable
portion (or normal elastically deformable portion) of the
connection part 27 is favorably in the range of 10 to 100 and more
favorably in the range of 40 to 100. The occupation percentage of
the plastically deformable portion (or normal elastically
deformable portion) of the connection part 27 is more favorably in
the range of 50 to 100 and most favorably in the range of 80 to
100.
[0050] In the stent 20 of the embodiment, the adjacent annular
parts 21 are connected to each other with a plurality of the
connection parts 27. It is preferable to connect the annular parts
21 to each other with a plurality of the connection parts 27. In
this case, it is preferable to almost confront them at two
positions of all the positions where the adjacent annular parts 21
confront each other. It is also preferable to dispose three or more
connection parts 27, with the connection parts 27 forming an almost
equal angle with respect to the axis of the stent 20. In the
embodiment, the connection parts 27 are confronted at two positions
of all the positions where the adjacent annular parts 21 confront
each other.
[0051] In the stent 20 of the embodiment, the connection part 27 is
not disposed inside the annular part 21. Therefore in the stent 20,
the annular parts 21 and the connection parts 27 are arranged in
the axial direction thereof. In the stent 20 of this embodiment, a
plurality of the annular parts 21 and a plurality of the connection
parts 27 are alternately arranged in the axial direction thereof,
with the annular parts 21 disposed at both ends of the arrangement.
When the connection parts 27 are viewed from the side (peripheral)
surface of the stent 20, the connection parts 27 are not disposed
inside the annular parts 21, but disposed on an annular zone
orthogonal to the axis of the stent 20. Therefore it is possible to
treat a change in properties of the connection part 27 easily and
reduce an influence given to the annular part 21 by the treatment
of the change in properties of the connection part 27.
[0052] The length of the annular part 21 of the stent 20 of the
embodiment is favorably in the range of 2 to 4 mm and more
favorably in the range of 2.5 to 3.5 mm. The number of the annular
parts 21 is favorably in the range of 3 to 30 and more favorably in
the range of 5 to 20. The distance between the adjacent annular
parts 21, in other words, the length of the connection part 27 in
the axial direction of the stent 20 is favorably in the range of
0.1 to 5 mm and more favorably in the range of 0.15 to 3 mm. It is
favorable that the width of the linear material (frame)
constituting the annular part 21 is favorably in the range of 0.08
to 0.3 mm and more favorably in the range of 0.1 to 0.2 mm. The
length of the connection part 27 is favorably in the range of 0.15
to 8 mm and more favorably in the range of 0.2 to 5 mm when the
connection part 27 is straight. It is favorable that the width of
the linear material constituting the connection part 27 is small to
allow the linear material to be bent at a small force. More
specifically, the width of the linear material constituting the
connection part 27 is favorably in the range of 0.03 to 0.2 mm and
more favorably in the range of 0.05 to 0.1 mm.
[0053] As shown in FIG. 7, according to another embodiment of the
present invention, a stent 30 may have annular parts 31 each having
trapezoidal notches formed at its both ends and a plurality of
hexagonal openings formed at its central portion in the shape of a
honeycomb. As in the case of the above-described embodiments, a
connection part 27 is plastically deformable partly or
entirely.
[0054] The mode of the annular part is not limited to the above
described one.
[0055] FIG. 8 is a front view showing a stent according to an
embodiment of the present invention. FIG. 9 is a development view
showing the stent shown in FIG. 8. FIG. 10 is a partly enlarged
view showing the stent shown in FIG. 8.
[0056] As shown in FIGS. 8 and 9, a stent 50 of the embodiment has
a plurality of the annular parts 2 each composed of a linear
material 4 that is wavy (zigzag) and annular and functions to keep
the stent 50 expanded. The annular parts 2 are connected to each
other with the connection parts 53 (connector) in such a way that
the adjacent annular parts 2 do not separate from each other. A
plurality of the annular parts 2 are arranged almost linearly in
the axial direction of the stent 50, with valleys and mountains of
the axially adjacent wavy annular parts 2 confronting each
other.
[0057] The connection part 53 is not substantially super-elastic
entirely or partly and is plastically deformable or normal
elastically deformable. Thereby the stent 50 is capable of
plastically deformable or normal elastically deformable at the
connection part 53. Further the connection part 53 reduces a stress
applied to a lumen such as a blood vessel by both ends of the stent
50, when the stent 50 is implanted therein. Since the connection
part 53 is plastically deformable or normal elastically deformable,
the connection part 53 is curved in conformity to a curvature of
the blood vessel and keeps its curved configuration when the stent
50 is implanted in a curved blood vessel or the like. Therefore
little load is applied to both ends of the stent 50. FIG. 10 is an
enlarged view showing the neighborhood of the connection part 53 of
the stent 50. The connection part 53 (portion shown with oblique
lines) shown in FIG. 10 deforms plastically or has a normal elastic
deformation. When the stent 50 is bent, the connection part 53
deforms plastically or normal elastically. The occupation
percentage of the plastically deformable portion (or normal
elastically deformable portion) of the connection part 53 is
favorably in the range of 10 to 100 and more favorably in the range
of 40 to 100. The above-described normal elastic deformation means
an elastically deformed state not reaching the super-elastic.
[0058] The connection part 53 of the stent 50 of the embodiment
connects proximate valleys and mountains of the adjacent wavy
annular parts 2 to each other. The connection part 53 is straight.
In the stent of the embodiment, each connection part 53 connects
the valley of the annular part 2 to the mountain adjacent to the
mountain, of the adjacent annular part 2, nearest to the valley.
Thus the connection part 53 inclines. That is, the connection part
53 inclines at a predetermined angle to the axis of the stent
50.
[0059] In the stent 50 of the embodiment, the adjacent annular
parts 2 are connected to each other by a plurality of the
connection parts 53. It is preferable to connect the annular parts
2 to each other with a plurality of the connection parts 53. In the
case where the connection parts 53 are formed at two positions, it
is preferable to confront them at two positions of all the
positions where the valleys and the mountains of the adjacent
annular parts 2 almost confront each other. It is also preferable
to dispose three or more connection parts 53, with the connection
parts 53 forming an almost equal angle with the axis of the stent
50. In the embodiment, a plurality of valleys and mountains are
formed on the axially adjacent wavy annular parts 2, with the
valleys and the mountains proximate to each other. The valleys and
the mountains are connected to each other alternately by the
connection parts 53. The valley of the annular part 2 is connected
to the mountain adjacent to the mountain, of the adjacent annular
part 2, nearest to the valley. The connection parts 53 connecting
the same adjacent annular parts 2 to each other are parallel with
each other. The connection part 53 adjacent to each other in the
axial direction of the stent 50 connects the valleys to each other
alternately. The connection parts 53 adjacent to each other in the
axial direction of the stent 50 incline in different directions. As
shown in FIG. 9, the connection part 53 disposed uppermost incline
left downward, whereas the connection part 53 disposed below it
incline right downward. In the stent 50 of the embodiment, the
connection part 53 and the straight portion of the annular part 2
connected with the connection part 53 form a zigzag line in the
axial direction of the stent 50. In the stent 50 of the embodiment,
the connection part 53 is not disposed inside the annular part
2.
[0060] More specifically, in the stent 50 shown in FIGS. 8 and 9,
the number of the zigzag lines of each annular part 2 is 16. The
connection part 53 is formed at eight positions, with the
connection parts 53 forming an equal angle to the axis of the stent
50. In the stent 50, a plurality of the annular parts is formed,
with the mountains and the valleys adjacent to each other. Each
connection part is formed from the mountain of the annular part to
the valley of the adjacent annular part, with the connection part
oblique to the axis of the stent 50. The connection part is not
disposed inside the annular part.
[0061] The mode of the annular part is not limited to those
described above.
[0062] FIG. 11 is a front view showing a stent according to an
embodiment of the present invention. FIG. 12 is a development view
showing the stent shown in FIG. 11. FIG. 13 is a partly enlarged
view showing the stent shown in FIG. 11.
[0063] A stent 60 of this embodiment is almost the same as the
above-described stent 50 except that the connection part 53 is
substantially parallel with the axial direction (in other words,
axis) of the stent 60. As shown in FIGS. 11 and 12, the stent 60 of
the embodiment has a plurality of the annular parts 2 each composed
of a linear material 4 that is wavy (zigzag) and annular and
functions to keep the stent 60 expanded. The annular parts 2 are
connected to one another with the connection parts 53 (connector)
in such a way that the adjacent annular parts 2 do not separate
from each other. A plurality of the annular parts 2 are arranged
almost linearly in the axial direction of the stent 60, with
mountains of the axially adjacent wavy annular parts 2 are almost
straight. Similarly, plurality of the annular parts 2 are arranged
almost linearly in the axial direction of the stent 60, with
valleys of the axially adjacent wavy annular parts 2 are almost
straight. That is, the modes and dispositions of the annular parts
2 are identical to each other. The connection part 53 is not
substantially super-elastic entirely or partly and is plastically
deformable. FIG. 13 is an enlarged view showing the neighborhood of
the connection part 53 of the stent 60. The connection part 53
(portion shown with oblique lines) shown in FIG. 13 deforms
plastically or normal elastically. When the stent 60 is bent, with
the connection part 53 (portion shown with oblique lines) disposed
radially outward, the connection part 53 deforms plastically. The
occupation percentage of the plastically deformable portion (or
normal elastically deformable portion) of the connection part 53 is
favorably in the range of 10 to 100 and more favorably in the range
of 40 to 100.
[0064] The connection part 53 of the stent 60 of the embodiment
connects proximate valleys and valleys of the adjacent wavy annular
parts 2 to each other. The connection part 53 is straight. The
connection parts 53 are parallel with the axis of the stent 60.
[0065] In the stent 60 of the embodiment, the adjacent annular
parts 2 are connected to each other by a plurality of the
connection parts 53. It is preferable to connect the annular parts
2 to each other with a plurality of the connection parts 53. In the
case where there are two connection parts 53, it is preferable to
almost confront them at two positions of all the positions where
the valleys and the mountains of the adjacent annular parts 2
confront each other. It is also preferable to dispose three or more
connection parts 53, with the connection parts 53 forming an almost
equal angle to the axis of the stent 60. In the embodiment, a
plurality of valleys and mountains are formed on the axially
adjacent wavy annular parts 2, with the valleys and the mountains
proximate to each other. Valleys nearest to each other are
connected to each other by the connection parts 53 every three
valley. The connection parts 53 are parallel with each other. In
the stent 60 of the embodiment, a part of the connection part 53 is
disposed inside the annular part 2. The connection parts 53 are
formed in such a way that they are uncontinuous in the axial
direction of the stent 60. The connection parts 53 adjacent to each
other in the axial direction of the stent 60 connect the valleys to
each other alternately.
[0066] More specifically, in the stent 60 shown in FIGS. 11 and 12,
the number of the zigzag lines of each annular part 2 is 12, and
the connection part 53 is formed at three positions, with the
connection parts 53 forming an equal angle to the axis of the stent
60. In the stent 60, a plurality of the annular parts 53 are
formed, with the valleys adjacent to each other. The connection
parts are parallel with the axis of the stent 60. Each connection
part is formed from the valley of the annular part to the valley of
the adjacent annular part, with a part of the connection part
disposed between the adjacent annular part. By forming the stent 60
in the above-described configuration, it is possible to make the
length of the connection part larger than that of the zigzag
annular part and curve the stent easily at the connection part
thereof.
[0067] Although the outer diameter of each of the stents 50 and 60
is different according to a portion where they are implanted, the
outer diameter thereof is favorably in the range of 2.0 to 30 mm
and more favorably in the range of 2.5 to 20 mm. The thickness of
the stent is favorably in the range of 0.04 to 1.0 mm and more
favorably in the range of 0.06 to 0.5 mm. The length of the stent
is in the range of 10 to 150 mm and favorably in the range of 15 to
100 mm. In the case where the stent is implanted in a blood vessel,
the outer diameter thereof is favorably in the range of 2.0 to 14
mm and more favorably in the range of 2.5 to 10 mm. The thickness
of the stent is favorably in the range of 0.04 to 0.3 mm and more
favorably in the range of 0.06 to 0.2 mm. The length of the stent
is in the range of 5 to 80 mm and favorably in the range of 10 to
60 mm.
[0068] As described above, in the stents 50 and 60 of the
embodiment, the annular part 2 is composed of a plurality of linear
materials 4 wavy (zigzag) and annular. The number of waves is
favorably in the range of 6 to 36 and more favorably in the range
of 8 to 24. The length of the annular part 2 is favorably in the
range of 1 to 10 mm and more favorably in the range of 1.5 to 5 mm.
The number of the annular parts 2 is favorably in the range of 3 to
30 and more favorably in the range of 5 to 20. The distance between
the adjacent annular parts 2 is favorably in the range of 2 to 7
mm. The length of the connection part 53 is favorably in the range
of 2 to 10 mm. It is favorable that the width of the linear
material 4 constituting the connection part 53 is small to allow
the linear material 4 to be bent at a small force. More
specifically, the width of the linear material 4 constituting the
connection part 53 is favorably in the range of 0.03 to 0.2 mm and
more favorably in the range of 0.05 to 0.12 mm.
[0069] As shown in FIGS. 8, 9, 11, and 12, in the stents 50 and 60
of the above-described embodiments, it is preferable that an apex
55 of the bent portion forming the outermost end of each of the
annular parts 2 disposed at both ends of the stent has a bulged
configuration to reduce a load to be applied by the outermost end
of the stent to the inner wall of a lumen of the human body. It is
preferable that as shown in FIGS. 8 and 11, both ends of the stent
are approximately circular.
[0070] It is preferable to provide the stents 50 and 60 with a
marker 56 made of an X-ray-unpermeable material. It is favorable to
dispose the marker 56 at an end of the stent. It is more favorable
to dispose the marker 56 at both ends of the stent. More
specifically, as shown in FIGS. 8, 9, 11, and 12, it is preferable
to dispose a plurality of the markers 56 at both ends of the stent.
In the stents 50 and 60, the marker 56 is provided on the
connection part 53 disposed at one extreme end thereof, and also at
the other extreme end thereof.
[0071] The marker 56 made of the X-ray-unpermeable material is
fixed to the stent with the marker 56 sealing a small opening
formed on the stent. It is preferable to install the marker 56 on
the small opening formed on the stent by disposing a disk-shaped
member made of an X-ray contrast material a little smaller than the
small opening and pressing and caulking both surfaces thereof. The
form of the marker made of the X-ray-unpermeable material is not
limited to the above-described type. For example, it is possible to
apply the X-ray contrast material to the outer surface of the
stent, wind a wire material formed of the X-ray contrast material
around the stent or mount a ring-shaped member formed of the X-ray
contrast material on the stent. It is preferable to form the marker
56 of gold, platinum, tungsten, tantalum, alloy thereof or
silver-palladium alloy. The stents 1, 20, and 30 may be provided
with the marker 56 made of the X-ray-unpermeable material.
[0072] A super-elastic alloy can be preferably used as the
super-elastic metal forming the stent of each of the
above-described embodiments. Herein the super-elastic alloy means a
so-called shape memory alloy that shows super-elasticity
essentially at the temperature (in the vicinity of 37.degree. C.)
of the human body. The following super-elastic metals can be
preferably used: A Ti--Ni alloy of 49 to 53 atomic percent of Ni, a
Cu--Zn alloy of 38.5 to 41.5 wt % of Zn, a Cu--Zn--X alloy of 1 to
10 wt % of X (X.dbd.Be, Si, Sn, Al, Ga), and a Ni--Al alloy of 36
to 38 atomic percent of Al. The Ti--Ni alloy is most favorable. The
mechanical characteristic of the Ti--Ni alloy can be appropriately
changed by replacing a part of the Ti--Ni alloy with 0.01 to 10.0%
of X to obtain a Ti--Ni--X alloy (X.dbd.Co, Fe, Mn, Cr, V, Al, Nb,
W, B) or by replacing a part of the Ti--Ni alloy with 0.01 to 30.0
atomic percent of X to obtain a Ti--Ni--X alloy (X.dbd.Cu, Pb, Zr).
Further the mechanical characteristic of the Ti--Ni alloy can be
appropriately changed by selectively adopting a cold working ratio
or/and the condition of final heat treatment. In the case where the
Ti--Ni--X alloy is used, it is also possible to change its
mechanical characteristic appropriately by selectively adopting a
cold working ratio or/and the condition of final heat
treatment.
[0073] The buckling strength (yield stress when load is applied to
stent) of the super-elastic alloy to be used is favorably in the
range of 5 to 200 kg/mm.sup.2 (22.degree. C.) and more favorably in
the range of 8 to 150 kg/mm.sup.2. The restoring stress (yield
stress when load is eliminated from stent) of the super-elastic
alloy is favorably in the range of 3 to 180 kg/mm.sup.2 (22.degree.
C.) and more favorably in the range of 5 to 130 kg/mm.sup.2. The
super-elasticity means that when a metal is deformed (bent,
stretched, compressed) to a region in which it deforms plastically
at a service temperature, it returns to its original configuration
without heating it after the deformation is released.
[0074] The stent is formed by removing (for example, cutting,
dissolving) a part, of a pipe made of a super-elastic metal, not
constituting the stent. Thereby the stent is obtained as an
integral product.
[0075] The pipe made of the super-elastic metal to be used to form
the stent of the present invention can be produced by dissolving a
super-elastic alloy such as the Ti--Ni alloy in an inactive gas
atmosphere or a vacuum atmosphere to form an ingot thereof,
polishing the ingot mechanically, forming a pipe having a large
diameter by hot press and extrusion, repeating drawing step and
heat treatment step to adjust the diameter and thickness of the
pipe to a predetermined thickness and reduced diameter, and finally
polishing the surface of the pipe chemically or physically.
[0076] The pipe made of the super-elastic metal can be processed
into the base material for the stent by a cutting work such as
laser processing (for example, YAG laser), electrical discharge
machining, and the like or chemical etching or in combination
thereof.
[0077] The stent of the present invention may be coated with a
material suitable for the human body on its inner surface, outer
surface or inner and outer surfaces. As the material suitable for
the human body, synthetic resin and metal suitable for the human
body can be used. The following inactive metals are used to coat
the surface of the stent: gold by electroplating method, stainless
steel by evaporation method, silicon carbide by sputtering method,
plated titanium nitride by sputtering method, and plated gold by
sputtering method.
[0078] As the synthetic resin, the following thermoplastic resins
or thermosetting resins can be used: polyolefin (for example,
polyethylene, polypropylene, ethylene-propylene copolymer),
polyvinyl chloride, ethylene-vinyl acetate copolymer, polyamide
elastomer, polyurethane, polyester, fluorocarbon resin, silicone
rubber. Polyolefin, polyamide elastomer, polyester, and
polyurethane are favorable. A resin decomposable in the human body
(polylactic acid, polyglycolic acid, polylactic acid-polyglycolic
acid copolymer) is also favorable. It is preferable that the film
of the synthetic resin is soft to such an extent as not to prevent
frames constituting the stent from being curved. The thickness of
the film of the synthetic resin is favorably in the range of 5 to
300 .mu.m and more favorably in the range of 10 to 200 .mu.m.
[0079] As the method of thinly coating the surface of the stent
with the synthetic resin, it is possible to use a method of
inserting the pipe made of the super-elastic metal into the, melted
synthetic resin or into the synthetic resin dissolved in a
solution. It is also possible to use a chemical evaporation method
of polymerizing a monomer on the surface of the pipe made of the
super-elastic metal. In the case where the surface of the stent is
coated very thinly with the synthetic resin, the use of a dilute
solution or chemical evaporation method is preferable.
[0080] To improve the quality of the material suitable for the
human body to a higher extent, the resinous film may be coated with
an anti-thrombus material or the anti-thrombus material may be
fixed to the resinous film. As the anti-thrombus material, known
various resins can be used singly or as a mixture thereof. For
example, polyhydroxyethyl methacrylate, copolymer of
hydroxyethyl-methacrylate and styrene (for example, HEMA-St-HEMA
block copolymer) can be preferably used.
[0081] The method of producing the stent of the present invention
is described below.
[0082] There is provided a method of producing a stent to be
implanted in a human body, including the steps of forming a base
material for the stent having a plurality of annular parts
deformable in a direction in which an outer diameter thereof
contracts, when a stress is applied thereto and a plurality of
connection parts each connecting the adjacent annular parts to each
other, with the annular parts arranged in an axial direction of the
stent by partly removing a side surface of a prepared approximately
cylindrical pipe, made of a super-elastic metal, having an outer
diameter suitable for a portion of the human body in which the
stent is implanted; and heat-treating a part or an entirety of the
connection part of the base material for the stent to substantially
eliminate super-elasticity of each of the connection parts and
impart plastic deformability or normal elasticity thereto.
[0083] The pipe made of the super-elastic metal can be produced by
dissolving a super-elastic alloy such as the Ti--Ni alloy in an
inactive gas atmosphere or a vacuum atmosphere to form an ingot
thereof, polishing the ingot mechanically, forming a pipe having a
large diameter by hot press and extrusion, repeating drawing step
and heat treatment step to obtain a predetermined reduced thickness
and diameter of a semi-finished product of the stent, and finally
polishing the surface thereof chemically or physically.
[0084] A cutting work such as laser beam machining (for example,
YAG laser), electrical discharge machining, and mechanical
polishing or chemical etching can be used or in combination thereof
to perform the step of forming a base material for the stent having
a plurality of annular parts deformable in a direction in which an
outer diameter thereof contracts, when a stress is applied thereto
and a plurality of connection parts each connecting the adjacent
annular parts to each other, with the annular parts arranged in an
axial direction of the stent by partly removing a side surface of a
prepared approximately cylindrical pipe, made of a super-elastic
metal. Since the stent is formed by processing the pipe as
described above, the outer diameter of the processed pipe is equal
to that of the stent. Thus the stent formed in this manner has high
dimensional accuracy and returns to its original configuration when
it is implanted in the human body. Therefore it is possible to
securely improve a stenosed portion of the human body.
[0085] More specifically, in the step of forming the base material
for the stent, a primary processing step of initially processing
the base material for the stent into a predetermined configuration
is carried out. That is, initially electrical discharge machining
is conducted to fuse the portion, of the pipe made of the
super-elastic metal, not constituting the base material for the
stent. Thereby the portion of the pipe not constituting the base
material for the stent is removed. Thereafter a chamfering step
(secondary processing) of shaving the edge of the primarily
processed pipe for the stent is carried out. In the chamfering
step, blast treatment is conducted for removal of a burr and
chamfering by using hard fine particles. In the case where a
thermally modified portion is formed on the peripheral edge of the
primarily processed pipe, a step of treating the thermally modified
portion (tertiary step, chemical etching) may be conducted to
remove the thermally modified portion. The step of treating the
thermally modified portion is performed by immersing the primarily
processed pipe that has undergone the blast treatment in a
thermally modified portion-treating solution in which a mixture of
hydrofluoric acid and nitric acid is mixed with a small amount of
hydrogen peroxide solution. The chemical etching (thermally
modified portion-treating step) may be used to accomplish burr
removal and chamfering simultaneously. In this case, it is
unnecessary to carry out the blast treating step.
[0086] It is preferable that in the primary processing of the step
of forming the base material for the stent from the pipe made of
the super-elastic metal, the prepared pipe, made of the
super-elastic metal, having a predetermined outer diameter is
machined by using a laser apparatus (for example, YAG laser
apparatus).
[0087] The step of forming the base material for the stent from the
pipe made of the super-elastic metal may be performed by using
photo-fabrication technique, as described below.
[0088] In this method, initially, grease is removed from the inner
and outer surfaces of the pipe made of the super-elastic metal.
Then they are cleaned. The grease removal and cleaning are
conducted by immersing the pipe in a solution containing a
surface-active agent, immersing the pipe in an RO solution or
immersing the pipe in a cleaning organic solvent of hexane or the
like. After the pipe is dried, a photo-resist is applied to the
inner and outer surfaces of the pipe. As the photo-resist, both
positive type and negative type can be used. A UV resist, an
electron beam resist, and an X-ray resist may be used. The
thickness of the photo-resist is preferably in the range of 0.5 to
4 .mu.m. To enhance the adhesiveness of the photo-resist film to
the pipe, heat treatment (pre-baking) is performed at 80 to
90.degree. C.
[0089] Thereafter a masking film (different according to whether
photo-resist is of positive type or negative type) having a pattern
corresponding to the predetermined configuration of the base
material for the stent is wound around the outer surface of the
pipe made of the super-elastic metal to bring the masking film into
close contact with the outer surface of the pipe in a vacuum
atmosphere. Then an exposing work is performed. The exposing work
can be performed by using a super-high pressure mercury vapor lamp.
It is preferable to perform the exposing work by rotating the pipe
so that the pipe is entirely and securely irradiated. Then
developing treatment is performed. The developing treatment is
performed by immersing the pipe in a photo-resist developer.
Thereafter the developer is heated to 120 to 145.degree. C. to
perform post-baking treatment. Thereby the masking process
terminates.
[0090] In the pipe processed as described above, the photo-resist
is not present in the portion of the pipe not constituting the base
material for the stent, whereas the hardened photo-resist is
present in the portion of the pipe constituting the base material
for the stent. The semi-finished product for the stent is immersed
in an etching solution to dissolve the portion of the pipe not
constituting the base material for the stent therein. Thereby the
portion of the pipe not constituting the base material for the
stent is removed. The portion of the pipe not constituting the base
material for the stent is dissolved in the etching solution because
it contacts the etching solution. On the other hand, the hardened
photo-resist prevents the portion of the pipe constituting the base
material for the stent from contacting the etching solution.
Therefore the portion of the pipe constituting the base material
for the stent is not dissolved in the etching solution. The base
material for the stent having an outer configuration similar to
that of the stent is formed by the treatment conducted by using the
etching solution. Thereafter the hardened photo-resist that has
attached to the surface of the base material for the stent is
removed. This treatment is performed by immersing the base material
for the stent in a solution in which the hardened photo-resist
dissolves. Further, to remove the burr formed on the peripheral
edge of the base material for the stent and chamfer it, the blast
treatment is carried out, as described above. Then the base
material for the stent is immersed in the etching solution to
perform surface treatment. Thereby the base material for the stent
is formed.
[0091] As necessary, the step of plating the semi-finished product
for the stent with metal or forming a resinous film thereon is
performed. The semi-finished product for the stent is plated with
gold by electroplating method, stainless steel by evaporation
method, silicon carbide by sputtering method, titanium nitride or
gold.
[0092] It is favorable that the configuration of the base material
for the stent formed as described above is the same as that of any
of the stents 1, 20, 30, 50, and 60. It is most favorable that the
configuration of the base material for the stent is the same as
that of the stent 1. However, the configuration of the base
material for the stent is not limited to that of the stents 1, 20,
30, 50, and 60.
[0093] Thereafter heat treatment step is performed. The connection
part of the base material for the stent is heated to substantially
eliminate the super-elasticity of the connection part and impart
plastic deformability thereto.
[0094] The step of heat-treating the connection part is executed by
a heat developed by an electric resistance of each connection part
that is energized at both ends thereof (electric resistance
method), irradiating each connection part with a laser beam (laser
heating method) or pressing a highly heated tool such as a
soldering iron against each connection part (direct heating
method).
[0095] In the case where the electric resistance method is used, a
high-voltage electricity is applied to only both ends of the
connection part to heat the connection part by the electric
resistance of the super-elastic metal. This method is capable of
easily controlling heating because the connection part can be
heated to a high temperature by an instantaneous energization of
both ends thereof and because the connection part is cooled rapidly
by terminating the energization. When this method is used, it is
efficient that the connection part is comparatively long because
the resistance of the super-elastic metal is high.
[0096] In performing the laser heating method, it is preferable to
use YAG laser and semiconductor excitation laser as the laser. It
is possible to adjust heating energy by adjusting the output and
focal distance thereof.
[0097] In using the direct heating method, it is preferable to use
a soldering iron having a length equal to or longer than the
connection part.
[0098] In any of the above-described methods, it is preferable to
use the base material for the stent in which the connection part is
disposed in an annular portion (between adjacent annular parts)
orthogonal to the axis of the base material for the stent. By using
the base material for the stent in this mode, the heat treatment
process can be performed easily. More specifically, by
intermittently rotating the base material for the stent fixed to an
apparatus, heat treatment of the connection part disposed in one
annular portion can be accomplished. After the treatment of the
connection part in one annular portion terminates, the base
material for the stent or the base material to be heated is moved
axially to sequentially perform heat treatment of the connection
parts in other annular portions.
[0099] When the base material for the stent is stopped during its
intermittent rotation, the following operations are performed in
each heat treatment method: energizing contacts are brought into
contact with the connection part to heat it when the electric
resistance method is used; laser beams are emitted to each
connection part when the laser heating method is used; and the
connection part is allowed to contact a heat source when the direct
heating method is used.
[0100] Although the heating temperature in the heat treatment for
the connection part is different according to the metallic
composition of the super-elastic alloy and a temperature treatment
condition for imparting the super-elasticity thereto, the heating
temperature at a portion of the connection part where an elastic
deformation is eliminated favorably in the range of 400 to
600.degree. C. and more favorably in the range of 450 to
550.degree. C.
[0101] It is preferable that the step of heat-treating (heat
treatment step) is performed by disposing a base material for a
stent on a heat sink on which the base material for the stent can
be mounted and which has a plurality of concavities, with each
annular part of the base material for the stent in contact with an
outer surface of the heat sink and with the connection part, an
entirety of a portion thereof or a portion thereof over the
concavities of the heat sink, namely, not in contact with the outer
surface of the heat sink and by energizing the entire base material
for the stent so that the base material for the stent self-heats
and the annular part in contact with the outer surface of the heat
sink radiates heat.
[0102] This heat treatment step is the same as that of the method,
which will be described later, of producing the stent to be
implanted in the human body. Thus the description of the heat
treatment step is omitted herein.
[0103] It is preferable that the method, of the present invention,
of producing the stent to be implanted in the human body is as
follows:
[0104] The method of producing the stent to be implanted in the
human body comprises the steps of forming a base material for the
stent having a plurality of annular parts and a plurality of
connection parts each connecting the adjacent annular parts to each
other, with the annular parts arranged in an axial direction of the
stent by preparing an approximately cylindrical metal pipe having
an outer diameter smaller than an inner diameter of a portion in
which the stent is implanted and having super-elasticity or a shape
memory characteristic or to which the super-elasticity or the shape
memory characteristic can be imparted and by partly removing a side
surface of the pipe; forming an expanded mode of the base material
for the stent by expanding the base material for the stent so that
an outer diameter thereof becomes suitable for the portion in which
the stent is implanted and by heat-setting (heat-treating) the base
material for the stent in an expanded state to store a
configuration of the expanded base material for the stent and allow
the super-elasticity to appear; and heat-treating the expanded base
material for the stent by heating an entirety or a portion of the
connection parts to eliminate super-elasticity thereof
substantially and impart plastic deformability or normal elasticity
thereto.
[0105] Each step will be described below.
[0106] Initially the step of forming the base material for the
stent is carried out.
[0107] Prepared in the above step may be an approximately
cylindrical metal pipe which has an outer diameter smaller than an
inner diameter of a portion of the human body in which the stent is
implanted and to which super-elasticity or a shape memory
characteristic can be imparted.
[0108] The metal to be prepared may have the super-elasticity or
the shape memory characteristic. Otherwise, the super-elasticity or
the shape memory characteristic may be imparted to a metal pipe in
a processing step which will be described later.
[0109] The pipe can be produced by dissolving a
super-elasticity-impartabl- e alloy such as an Ti--Ni alloy in an
inactive gas atmosphere or a vacuum atmosphere to form an ingot
thereof, polishing the ingot mechanically, forming a pipe having a
large diameter by hot press and extrusion, repeating drawing step
and heat treatment step to adjust the diameter and thickness of the
pipe to a predetermined thickness and reduced diameter, and finally
polishing the surface of the pipe chemically or physically.
[0110] The side surface of the pipe is partly removed to form the
base material for the stent having a plurality of annular parts and
a plurality of connection parts each connecting the adjacent
annular parts to each other, with the annular parts arranged in an
axial direction of the stent. This step can be accomplished by a
cutting work such as laser processing (for example, YAG laser),
electrical discharge machining, mechanical polishing or chemical
etching or in combination thereof.
[0111] Thereafter the step of forming an expanded mode of the base
material for the stent is performed by expanding the outer diameter
of the base material for the stent prepared as described above so
that the diameter is suitable for a portion of the human body in
which it is implanted and by performing heat-setting in a base
material-expanded state to store the configuration of the base
material for the stent in the base material-expanded state and
allow the super-elasticity to appear.
[0112] The step of expanding the outer diameter of the base
material for the stent prepared as described above so that the
diameter is suitable for a portion of the human body in which it is
implanted can be accomplished by using a mandrel having a tapered
portion having a smaller diameter than that of the base material
for the stent at its one end thereof so that the one end thereof
can be inserted into the base material for the stent. The mandrel
has a large-diameter portion continuous with the tapered portion,
whose diameter is equal to the outer diameter of the stent in the
expanded state. The end of the tapered portion of the mandrel is
inserted into the base material for the stent, and the base
material for the stent is pressed into the large-diameter portion
of the mandrel. Thereby the base material for the stent is
expanded. The step of expanding the stent base material may be
performed stepwise. More specifically, a plurality of mandrels
different in the length of the outer diameter of the large-diameter
portion are prepared. The above-described expanding step (primary
expansion) is performed by using the mandrel having a small outer
diameter. Then an expanding step (secondary expansion) is performed
by using the mandrel having a large outer diameter. As necessary,
an expanding step (tertiary expansion) is performed by using the
mandrel having a larger outer diameter
[0113] In the step of heat-setting the base material for the stent
in an expanded state to store the configuration of the base
material for the stent in the expanded state and allow the
super-elasticity to appear, the base material for the stent is
heated by a heating means such as a heater, with the base material
for the stent disposed on the large-diameter portion of the mandrel
to store the configuration of the expanded base material for the
stent and impart the super-elasticity thereto. That is, by heating
the base material for the stent fitted on the mandrel, heat
treatment is performed in such a way that a stored configuration of
the stent is the outer diameter of the large-diameter portion of
the mandrel. It is preferable to heat-treat the base material for
the stent in an atmosphere of an inactive gas such as argon,
nitrogen or the like. Air can be also used as the atmosphere for
the heat treatment thereof.
[0114] The heating temperature and the heating time period at this
step (heat-setting step) is different according to a metal to be
used. It is preferable to heat the base material for the stent at
350 to 550.degree. C. for five to twenty minutes.
[0115] After the base material for the stent is cooled, it is
removed from the mandrel. It is preferable to air-cool it. More
specifically, it is preferable to cool it rapidly. The entire base
material for the stent, containing the connection part, obtained at
this step has the super-elasticity (or shape memory
characteristic).
[0116] Thereafter the entirety or a portion of the connection parts
expanded and having the super-elasticity is heated to substantially
eliminate the super-elasticity thereof and impart plastic
deformability or normal elasticity thereto.
[0117] The heat treatment is performed by disposing a base material
100 for the stent on a heat sink 80 on which the expanded base
material 100 for the stent can be mounted and which has a plurality
of concavities 81, with each annular part 2 of the base material
100 for the stent in contact with an outer surface of the heat sink
80 and with connection parts 53, an entirety of a portion thereof
or a portion thereof disposed over the concavities 81 of the heat
sink and not in contact with the outer surface of the heat sink and
by energizing the entire base material 100 for the stent so that
the base material 100 for the stent self-heats and the annular part
in contact with the outer surface of the heat sink 80 radiates
heat.
[0118] FIG. 14 is an explanatory view for explaining an example of
a heat treatment apparatus to be used in the heat treatment
step.
[0119] A heat treatment apparatus 70 has a stent-heating device 71,
a power supply device 72 for supplying electric current to the
stent-heating device 71, a heated state grasping device 73 for
grasping the heated state of the stent, a controller 74 for
controlling the operation of the power supply device 72 by using
information of the heated state grasped by the heated state
grasping device 73, and a cooling device 75 for cooling the
heat-treated stent.
[0120] The stent-heating device 71 has a heat sink 80 on which the
stent to be heat-treated is mounted, heat sink gripping portions
82a, 82b, electrodes 84a, 84b for energizing the stent, and a
connection terminal 85 for connecting the electrodes 84a, 84b to
the power supply device 72.
[0121] As shown in FIG. 15, the base material for the stent in the
expanded mode can be mounted on the heat sink 80. The heat sink 80
has a plurality of concavities 81. More specifically, the heat sink
80 has a base shaft 86 whose surface has been insulated,
electrode-mounting cylinders 87a, 87b made of a conductive material
and fixed to the base shaft 86, with a predetermined interval
spaced between each other, a plurality of ring-shaped member 88
made of a conductive material and disposed between the
electrode-mounting cylinders 87a and 87b in such a way that the
ring-shaped members 88 do not contact each other. The concavities
81 are formed between the ring-shaped members 88 and the
electrode-mounting cylinders 87a as well as 87b. As the base shaft
86, a metal pipe having preferable heat transfer property and a
insulated outer surfac is used in the embodiment. A cooling liquid
circulated by the cooling device flows through the pipe. As the
base shaft 86, an aluminum pipe whose surface has been insulated is
preferable. As the method of insulating the base shaft 86, it is
preferable to form an insulating film thereon. As the insulating
film, the following resins are suitable: fluorocarbon resin such as
PTFE and ETFE; and thermosetting resins such as epoxy resin,
silicone resin, phenol resin, polyimide resin, melamine resin, and
urea resin. The thickness of the film coating the surface of the
base shaft 86 is favorably in the range of 20 .mu.m to 50 .mu.m. In
the case where the aluminum pipe is used as the base shaft 86, it
is preferable to insulate its surface with anodized aluminum. In
this case, the thickness of the anodized aluminum is favorably in
the range of 15 .mu.m to 50 .mu.m.
[0122] It is preferable that the electrode-mounting cylinders 87a,
87b and the ring-shaped member 88 are made of metal such as copper
and brass.
[0123] The cooling device 75 has a cooling liquid tank 92, ducts
93, 94, a pump 95, and connectors 76a, 76b connected to the base
shaft 86. A cooling liquid 92a inside the cooling liquid tank 92 is
circulated by the pump 95 through the duct 93, the connectors 76b,
the base shaft 86, the connector 76a, the duct 94, and returned to
the cooling liquid tank 92. As the cooling liquid, water,
polyethylene glycol and the like are used. It is unnecessary to
provide the cooling liquid tank 92 with a cooling means because
heat is radiated naturally when the cooling liquid tank 92 contains
a large amount of cooling liquid. In the case where a small amount
of cooling liquid is used, it is preferable to provide the cooling
liquid tank 92 with a cooling means such as a chiller for cooling
the cooling liquid.
[0124] The cooling device does not necessarily have to be provided
with the cooling liquid, but may be provided with a cooling module.
In the case where the cooling module is used, it is installed on
the base shaft. In this case, it is preferable that the base shaft
is solid. As the cooling module, it is possible to use a thermo
module using a Peltier element, an electronic cooling module, and
the like.
[0125] As shown in FIG. 15, in the embodiment, each annular part 2
of the base material for the stent 100 contacts the outer surface
of the heat sink 80, and all of the connection parts 53 other than
both-end of the connection parts 53 are disposed over the
concavities 81 so that they do not contact the outer surface of the
heat sink 80.
[0126] As shown in FIGS. 14 and 15, the electrodes 84a, 84b are
mounted on the electrode-mounting cylinders 87a, 87b of the heat
sink 80. As shown in FIG. 14, both ends of the base shaft 86 are
gripped by the heat silk gripping portion 82a, 82b and fixed to a
base 71a. The electrodes 84a, 84b are connected to the connection
terminal 85 through lead wires 89a, 89b. It is preferable that the
electrodes 84a, 84b are reticulate, as shown in FIG. 15.
[0127] As the power supply device 72, a DC power supply device is
used. As the power supply device, a constant-current regulated
power is preferable. The power supply device 72 is connected to the
connection terminal 85 through lead wires 72a, 72b. The electrodes
84a, 84b may be connected directly to the power supply device 72
without providing the connection terminal.
[0128] As the heated state grasping device 73 for grasping the
heated state of the stent, a non-contact type such as a
thermography apparatus and a spot thermometer is used. When the
thermography apparatus is used, a lens 73a for observing the stent
enlargingly is provided. The thermography apparatus 73 grasps the
heated situation of the stent while it is heated and sends the
information thereof to the controller 74.
[0129] As the controller, a personal computer is used. The
controller 74 is connected to the power supply device directly or
indirectly. The controller 74 has a function of controlling the
operation of the power supply device. More specifically, the
controller 74 controls on and off of the power supply device or
electric current or a voltage so that the thermography apparatus 73
grasps the heated state of the connection part of the stent which
is heated to a desired temperature.
[0130] The base material 100 for the stent is disposed on the heat
sink 80 of the heat treatment apparatus having the above-described
construction, with each annular part 2 of the base material 100 for
the stent in contact with the outer surface of the heat sink 80 and
with at least the central portion of each connection part 2
disposed over the concavities 81 of the heat sink 80 and not in
contact with the outer surface of the heat sink. The controller 74
is operated to flow direct current between the electrodes 84a and
84b from the power supply device to thereby self-heat the base
material 100 for the stent. Further the cooling device is operated
to cool the base shaft and the heat sink 80. Thereby a self-heated
portion of the base material 100 for the stent in contact with the
heat sink 80 is cooled, whereas the connection part not in contact
with the heat sink 80 remain self-heated. A portion of the
connection part not in contact with the heat sink 80 but proximate
thereto is a little cooled and thus has a lower temperature than
that of the central portion thereof.
[0131] More specifically, with reference to FIG. 14, electric
current supplied from the power supply device 72 flows through the
electrode 82b, the electrode-mounting cylinder 87b, the right end
of the base material for the stent, the left end of the base
material for the stent, the electrode-mounting cylinder 87a, the
electrode 82a, and the power supply device 72. As shown in FIG. 16,
because the ring-shaped members 88 of the heat sink 80 and the base
shaft 86 are insulated from each other, the electric current flows
through the base material 100 for the stent collectively. Upon
application of the electric current to the base material 100 for
the stent, the base material 100 for the stent generates Joule
heat. Since the annular part 2 and a part of the connection part 53
contact the heat sink 80 (namely, ring-shaped members 88), the heat
escapes to the heat sink 80 (namely, ring-shaped members 88). Thus
the temperature of the stent does not rise. Because the portion
(central portion) of the connection part 53 corresponds to the
groove of the heat sink 80, the Joule heat generated in the central
portion of the connection part 53 does not escape to the heat sink.
Thus the central portion of the connection part 53 self-heats. The
self-heating temperature can be controlled by an amount of electric
current flowing through the base material 100 for the stent.
[0132] More specifically, data measured by the thermography
(non-contact type thermometer) is inputted to the personal computer
serving as the controller through a communication means such as a
GPIB or an RS-232C. The personal computer performs an appropriate
computation on measured data, based on the difference between a
predetermined target temperature and a measured temperature. The
result of the computation (data obtained by computation) is
inputted to the DC power supply device through the communication
means. Output electric current of the DC power supply device is
controlled so that the temperature of the connection part has the
target temperature. In this manner, based on the program stored by
the personal computer, the temperature of the connection part can
be maintained at a desired temperature for a desired period of
time.
[0133] According to this method, a plurality of stents having the
same configuration (designs, lengths, diameters are equal to each
other) can be heat-treated easily and simultaneously.
[0134] To this end, a plurality of annealing jigs are disposed,
with stents set thereon, and they are wired in such a way that
heating electric current are connected in series. The cooling
device (cooling liquid tank can be used commonly) and cooling
liquid pipes are arranged in parallel for each annealing jig. This
method allows electric current/voltage having the same value to be
applied to the stents and allows heat to escape to the heat sink in
the same manner. Therefore it is possible to heat-treat a plurality
of stents at the same time and in the same manner. In this case,
regarding the temperature of the connection part, monitoring
(measuring) of any one of the stents is sufficient.
[0135] A heat sink 90 having a mode shown in FIG. 17 is used for
the stent 60, shown in FIGS. 11 through 13, in which a portion of
the connection part 53 is disposed inside the annular part 2. The
heat sink 90 is different from the above-described heat sink in
that the ring-shaped member and the electrode-mounting cylinder are
provided with a groove for preventing contact between them and the
connection part. In particular, in the heat sink 90, a plurality of
grooves 88a are formed on the outer surface of the ring-shaped
member 88, and a plurality of grooves 91 are formed on the
electrode-mounting cylinder 87b. The width of each of the grooves
88a and 91 is set larger than that of the connection part.
[0136] It is possible to heat-treat the central portion of the
connection part and plasticize and soften it with the annular part
2 and both ends of the connection part 53 maintaining
super-elasticity. Although the percentage of the length of the
connection part to be plasticized depends on the design of the
stent, it is favorably in the range of 10% to 100% and more
favorably in the range of 40%-90%.
[0137] The examples of the present invention are described
below.
EXAMPLE 1
[0138] Cold working of a Ti--Ni alloy (51 atomic percent of Ni) was
performed to prepare a super-elastic metal pipe having an outer
diameter of about 8 mm, an inner diameter of about 7.6 mm, and a
length of about 34 mm. The super-elastic metal pipe was set on a
jig provided with a rotary motor having a fastening mechanism in
such a way as to prevent the pipe from being off-centered.
Thereafter the jig was set on an XY table capable of making a
numerical control. The XY table and the rotary motor were connected
to a personal computer. An output of the personal computer was
inputted to a numerical controller of the XY table and the rotary
motor. A development drawing representing the stent having the
structure shown in FIG. 2 was inputted to the personal computer
storing a design software.
[0139] The XY table and the rotary motor were driven in accordance
with design data outputted from the personal computer. The pipe was
irradiated with a laser beam to machine the pipe into a base
material for the stent having the configuration shown in FIG.
1.
[0140] As the laser machining condition for the metal pipe, current
value was set to 25 A, an output was set to 1.5 W, and a drive
speed was set to 10 mm/min. It is not limited to above-described
system as a laser marker. It may be a so-called laser
marker(Galvanometer system) the laser processing machine of which
drives.
[0141] The base material for the stent was dipped in a heated
chemical polishing solution for about two minutes to chamfer
(removal of burr and chemical polishing) it.
[0142] Thereafter energizing contacts were brought into contact
with each connection part to apply direct current thereto. Thereby
the portion between both the energizing contacts generated heat at
about 490 degrees for several seconds.
[0143] The stent prepared in this manner had an outer diameter of
about 8 mm, an entire length of 34 mm, and a thickness of 0.2 mm.
The width of the linear material constituting the annular part
(expansion element) was 0.12 mm. The connection part (connector
element) had a width of 0.06 mm. The entire connection part was
plastically deformable.
EXAMPLE 2
[0144] The entire surface of the stent of the example 1 was gold
plated. The stent of the example 1 was immersed in a sulfamic acid
plating bath (produced by Tokuriki Kabushiki Kaisha, trade name:
Auroflex T1) heated at 40.degree. C. Potassium cyanide was
dissolved in the plating bath. Thereby an unglossy gold-plated
layer having a thickness of 1.8 .mu.m was formed on the surface of
the stent.
COMPARISON EXAMPLE
[0145] A stent entirely showing super-elasticity having the
following size was obtained by carrying out a method similar to
that of the example 1 except that connection part was not
heat-treated. The stent had an outer diameter of about 8 mm, an
entire length of 34 mm, and a thickness of 0.2 mm. The width of the
linear material constituting the annular part (expansion element)
was 0.12 mm. The connection part (connector element) had a width of
0.06 mm.
EXPERIMENT
[0146] The stent of the example 1 and that of the comparison
example were wound around a rod having a diameter of 50 mm. Then an
operator's hand was released from the stents and the deformed state
of the stents was observed. The result was that the stent of the
comparison example was not deformed and had an original
configuration, whereas the stent of the example 1 was curved gently
at a radius of curvature of about 35 mm. This indicates that the
stents of the examples deform for a load applied thereto.
EXAMPLE 3
[0147] A super-elastic (or shape memory) Ti--Ni alloy pipe (for
example, outer diameter was about 1.6 mm, thickness was about 0.2
mm, and length was 1 m) was cut by laser beams to obtain a base
material for the stent. More specifically, the pipe was set on an
X.theta. table whose movement was controlled by a computer to which
a development drawing of the stent shown in FIG. 9 was inputted.
The outer surface of the pipe was convergently and intermittently
irradiated by laser beams. Thereby the base material for the stent
having a small diameter was prepared.
[0148] Thereafter the base material for the stent was chemically
polished to remove a burr therefrom. Then a core metal for
expanding the diameter of the base material for the stent was
inserted into the base material for the stent. Thereby the outer
diameter of the base material for the stent was increased to about
10 mm. Then the base material for the stent was heat-treated (and
then air-cooled), with the core metal disposed in the base material
for the stent. Thereby the expanded base material for the stent
entirely having super-elasticity was prepared.
[0149] The expanded base material for the stent was mounted on the
heat sink of the heat treatment apparatus having the construction
shown in FIG. 14 to perform a selective annealing (plasticizing) of
the connection parts.
[0150] A temperature control program was inputted to the computer
(PC) serving as the controller shown in FIG. 14. In accordance with
the program, an electric power was supplied from a DC power supply
device to a partial annealing device (and to base material for the
stent) through a lead wire. In dependence on a desired temperature
and time period, a current value is set appropriately by using the
program. Table 1 shows temperatures, time periods, and current
values used to anneal the connection part.
1TABLE 1 Time (minute) 0 (start of heating) 20 25 30 95 135 135
Finish of heating Temperature 410 410 400 390 260 190 190 Down to
room (.degree. C.) temperature Electric current 6.3 6.3 6.2 6.1 4.7
3.9 3.9 Air-cooling Where #: temperature dropped at the rate of
about -10.degree. C./5 minutes.
[0151] Electric current was applied to the base material for the
stent to selectively heat the connection parts by self-heating
(Joule heat). The temperature of the stent was kept at a high
temperature (410.degree. C.) for a certain period of time (20
minutes). The temperature dropped to 190.degree. C. (heating
current was gradually decreased) at the rate of about -10.degree.
C./5 minutes. Thereafter energizing was stopped to drop the
temperature to the room temperature. Then the heat treatment
finished.
[0152] As described above, the temperature of the connection part
was measured by a non-contact type thermometer such as a
thermography. The temperature is controlled by performing feed back
of the data. Therefore the fluctuation (difference between set
temperature and measured temperature) in the temperature during the
heat treatment could be within .+-.2.degree. C. This value is much
smaller than temperature accuracy required for annealing treatment.
Accordingly, the fluctuation in the temperature hardly affects the
annealing treatment. The value of electric current required for
heating is different according to various factors such as the
design of the stent and the temperature of the cooling water.
[0153] It was possible to selectively plasticize and soften only
the connection part of the base material for the stent by
performing the above-described partial annealing. The bent portion
of the zigzag line of the annular part was brought into contact
with the heat sink to prevent the temperature of the bent portion
of the zigzag line from rising. Therefore the bent portion of the
zigzag line maintained the super-elasticity and the base material
for the stent maintained its original expansion force and
self-expandability.
[0154] The stent of the present invention to be implanted in a
human body is made of a super-elastic metal formed approximately
cylindrically and integrally and showing super-elasticity before
and after the stent is inserted into the human body. The stent has
a plurality of annular parts deformable in a direction in which an
outer diameter thereof contracts, when a stress is applied thereto
and a plurality of connection parts each connecting the adjacent
annular parts to each other, with the annular parts arranged in an
axial direction of the stent. Each of the annular parts is
elastically deformable owing to super-elasticity thereof, whereas
each of the connection parts is substantially a plastically
deformable part (or a normal elastically deformable part) not
super-elastic entirely or partly.
[0155] In the stent of the present invention, the annular part
which is the expansion element is elastically deformable and
capable of reliably expanding a lumen in the human body by its
restoring force to its original diameter. Since only the connection
part has the plastically deformable portion, the lumen-expanding
function of the annular part is not inhibited. In conformity to a
curve of the lumen, the plastically deformable portion of the
connection part is plastically curved. Therefore a stress caused by
the force of the stent of returning to its original straight shape
is little applied to the lumen.
* * * * *