FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. STENT
2.
1. (A) NIPRO CORPORATION
(B) Japan
(C) 9-3, Honjo-nishi 3-chome, Kita-ku, Osaka-shi, Osaka 5318510 Japan
The following specification particularly describes the invention and the manner in which
it is to be performed.
2
TECHNICAL FIELD
[0001] The present invention relates to a medical stent to be used, for
example, to keep the inner diameter of the somatic lumen in an expanded state by
being expanded and implanted within the 5 somatic lumen such as blood vessels.
BACKGROUND ART
[0002] Conventionally, a stent has been used in the percutaneous
transluminal coronary angioplasty (PTCA), for example, to prevent a stenosis
10 portion of the coronary artery from restenosis due to recoil or the like after
dilation with a balloon. The stent has a peripheral wall portion in an approximate
shape of a cylinder, for example, and this peripheral wall portion is composed of a
line-shaped body that extends in a helical form in the circumferential direction
while reciprocating in the axial direction at a given amplitude. Then, the stent
15 inserted into the somatic lumen such as the coronary artery under a constricted
condition in the radial direction is expanded in the radial direction with a balloon
or by self-expansion using the shape-memory effect of the stent itself to be
implanted in close contact with the inner wall surface of the somatic lumen. This
prevents restenosis caused by recoiling and the like due to the stent’s rigidity in
20 the radial direction, thus maintaining the inner diameter of the somatic lumen in a
state of being expanded with a balloon.
[0003] Meanwhile, in the stent formed by coiling the line-shaped body in
a helical form, since the portions adjacent to each other in the axial direction are
not positioned against each other allowing them to move freely in the axial
25 direction, there is a risk of not expanding uniformly due to the density disparity in
the arrangement of the line-shaped body when the stent is expanded in the radial
direction with a balloon and the like. Therefore, in Japanese Domestic Publication
of International Patent Application No. JP-A-2011-502636 (Patent Document 1)
proposes a structure where a connecting part (connector 30) is provided to link the
30 adjacent portions of the line-shaped body to each other in the axial direction. This
allows the rigidity of the stent in the longitudinal direction to be enhanced to
achieve configuration stability.
[0004] However, once the line-shaped body is linked by the connecting
part in the axial direction, the stent’s rigidity not only in the longitudinal direction
35 but also in the radial direction is increased so that its conformability to the bend of
the somatic lumen and the like is degraded. As a result, there was a risk of
3
encountering stent fracture caused by the stent remaining in the bent portion for a
long time to be charged with repeated loads of blood flow and the like, which
caused a problem such as a higher rate of restenosis of the somatic lumen. In
addition, as the stent’s rigidity increases, the stent remaining in place gets less
susceptible to deformation in conformity to 5 the configuration of the somatic
lumen, which poses another risk of damaging the body tissues such as those of
blood-vessel walls by pressing the tip end of the stent against them.
BACKGROUND ART DOCUMENT
PATENT DOCUMENT
10 [0005]
Patent Document 1: JP-A-2011-502636
SUMMARY OF THE INVENTION
PROBLEM THE INVENTION ATTEMPTS TO SOLVE
15 [0006] The present invention was made against the background described
above and the problems to be solved are to provide a stent of a novel structure
with which deflection of the line-shaped body during expansion is prevented and a
substantially uniform expansion is achieved over the entire length thereof, and
with which, after implantation, stent fracture and any damage to the body tissues
20 can be prevented by the stent exhibiting a superior pliability and conformability to
the shape of the somatic lumen.
MEANS FOR SOLVING THE PROBLEM
[0007] In other words, a first aspect of the present invention provides a
stent comprising a cylindrical peripheral wall formed with a line-shaped body that
25 extends in a helical form in a circumferential direction while reciprocating in an
axial direction at a given amplitude, the stent being characterized in that at least
one connecting part is formed to link portions of the line-shaped body adjacent in
the axial direction, and a friable part is provided to rupture itself by being
implanted in a somatic lumen and release a link made by the connecting part.
30 [0008] In the stent with the structure according to the first aspect, relative
movement in the axial direction of adjacent portions of the line-shaped body in the
axial direction can be limited because of the connecting parts provided therein,
thus restricting density disparity in the axial direction due to deflection of the
line-shaped body. Therefore, the stent is expanded stably to its intended
35 configuration when the expansion (diameter enlarging deformation) is undertaken
by means of dilation with a balloon or by shape recoverability based on the
4
shape-memory effect and the like, thus preventing any rigidity disparity or
partially failed dilation caused by deflection of the line-shaped body.
[0009] Furthermore, the links made by the connecting parts are released
by the friable parts that are ruptured by implantation of the stent in the somatic
lumen, and after the rupture of the friable parts, 5 adjacent portions in the axial
direction of the line-shaped body is allowed to move relative to each other in the
axial direction to cancel any increase in the rigidity caused by provision of the
connecting parts. This enhances the conformability of the stent to the curvature of
the somatic lumen so that any stent fracture (buckling of the stent) and other
10 failures such as restenosis of the somatic lumen caused thereby is prevented from
occurring, while preventing any damage to the body tissues due to the contact
against the end tip of the stent.
[0010] The friable parts can be composed entirely of the connecting parts,
or can be provided partially with the connecting parts. Also, the friable parts are
15 ruptured not only by the stress acting on the connecting parts due to curving
deformation of the somatic lumen caused by changes in the body posture or the
pulsation of the blood vessel and the like in the somatic lumen after implantation
in the somatic lumen, but also by the stress acting on the friable parts due to the
expansion of the stent to the implanted condition, and these friable parts are
20 ruptured upon or after the implantation in the somatic lumen. In addition, the
friable parts are formed not only as parts with low mechanical strength but also
parts that chemically rupture itself. In other words, it is possible to form friable
parts using biodegradation or some materials susceptible to degradation over time.
[0011] A second aspect of the present invention provides the stent
25 according to the first aspect, wherein the friable part is configured by making a
cross sectional area extending perpendicular to a direction of linking of the
connecting part smaller than that extending perpendicular to a length direction of
the line-shaped body.
[0012] According to the second aspect, the friable parts are configured by
30 making the cross sectional area of the connecting parts smaller than that of the
line-shaped body, and concentrated stresses act on the friable parts upon
implantation (after dilation) and after implantation of the stent allowing the friable
parts to be ruptured in a stable manner. Therefore, pliability of the stent is
achieved by the rupture of the friable parts, thus avoiding failures such as
35 occurrence of stent fracture and any damage to the body tissues caused by the
contact therewith.
5
[0013] A third aspect of the present invention provides the stent according
to the first or second aspect, wherein a reciprocation amplitude of the line-shaped
body in the axial direction is made approximately constant over an entire length
thereof.
[0014] According to the third aspect, 5 since the entire stent is expanded
uniformly during expansion thereof, deflection of the line-shaped body in the
circumferential direction is restricted. Therefore, nonuniform strain is hard to be
caused during stent expansion to allow intended configuration of the stent to be
obtained after expansion, while the action of concentrated stresses due to the
10 rigidity disparity can be prevented, thus maintaining the durability of the stent.
[0015] A fourth aspect of the present invention provides the stent
according to the first or second aspect, wherein a helical inclination angle of the
line-shaped body relative to the axial direction is made to gradually increase
toward each end of the stent to get close to a vertical angle.
15 [0016] According to the fourth aspect, when the stent passes through a
bent portion of the blood vessel, for example, significant deformation of the tip
end of the stent in the axial direction floating up toward the outer periphery can be
prevented effectively. Also, since there is no need for locally providing any
portion with an excessively long or excessively short amplitude in the line-shaped
20 body, favorable effects of extension and flexion can be exerted by a stent over the
entire length thereof.
[0017] A fifth aspect of the present invention provides the stent according
to any one of the first to fourth aspects, wherein the at least one connecting part
comprises a plurality of connecting parts formed in the length direction of the
25 line-shaped body, and the friable part is provided in the connecting parts located
in a middle section of the line-shaped body in the length direction, whereas no
friable part is provided in the connecting parts located at each end of the
line-shaped body in the length direction, keeping the stent in a linked state after
implantation in the somatic lumen.
30 [0018] According to the fifth aspect, since the connecting parts are
provided in a linked state all the way through in the axial direction during
expansion of the stent, adjacent portions of the line-shaped body in the axial
direction are relatively positioned to each other to some extent, which prevents
deflection of the line-shaped body in the axial direction to have the stent expanded
35 to its intended configuration. Also, once the stent is implanted in the somatic
lumen, the friable parts are ruptured at the connecting parts located in the middle
6
section of the line-shaped body in the length direction, which enhances the stent’s
pliability. Meanwhile, in an implanted state, the stent is prevented from being
subject to deformation more than necessary by keeping the connecting parts
located at each end of the line-shaped body in the length direction in a linked state
so that the implanted stent is stably positioned in 5 place in the somatic lumen.
[0019] A sixth aspect of the present invention provides the stent according
to any one of the first to fifth aspects, wherein the connecting parts are provided at
a constant interval.
[0020] According to the sixth aspect, since portions with locally higher
10 rigidity due to the formation of the connecting parts are arranged in a uniform
manner, the stent is prevented from being subject to strain deformation during
expansion, thus making it possible to stably obtain the intended configuration of
the stent after expansion thereof.
[0021] A seventh aspect of the present invention provides the stent
15 according to any one of the first to sixth aspects, wherein the friable part is formed
by having the portions of the line-shaped body adjacent in the axial direction
welded to each other by laser.
[0022] According to the seventh aspect, the friable parts can be easily
formed only at given positions by laser welding. In addition, since the thickness,
20 width and cross sectional area and the like of the friable parts can be easily
adjusted by means of controlling the duration and intensity of the laser irradiation,
it is possible to control the rupture timing of the friable parts.
[0023] An eighth aspect of the present invention provides the stent
according to the seventh aspect, wherein proximal protrusions are provided in the
25 portions of the line-shaped body adjacent in the axial direction where the friable
part is formed by welding the proximal protrusions to each other by laser.
[0024] According to the eighth aspect, parts to be welded by laser can be
identified more easily by providing the proximal protrusions in advance on the
line-shaped body. In addition, linking by laser welding is made easier by
30 providing the proximal protrusions protruding in the direction of getting closer to
each other.
[0025] A ninth aspect of the present invention provides the stent according
to any one of the first to eighth aspects, wherein each end of the line-shaped body
in the length direction constitutes a widened disc portion.
35 [0026] According to the ninth aspect, by means of providing the disc
portion at each end of the line-shaped body that turns out to be a free end,
7
problems such as damaging the body tissues by either end of the line-shaped body
stuck in the somatic lumen can be avoided. Also, during angiography, both end
positions of the stent in the axial direction are made visually more identifiable due
to each broad disc portion working as a marker, thus making it easier to recognize
the position and conditions of the 5 stent within the somatic lumen.
[0027] A tenth aspect of the present invention provides the stent according
to any one of the first to ninth aspects, wherein an adherend made of a different
material is adhered to the line-shaped body, and the connecting part having the
friable part is formed by the adherend.
10 [0028] As evident from the tenth aspect, the friable parts are not
necessarily limited to those integrally formed with the line-shaped body, but can
be provided by adhering thereto an adherend formed with synthetic resin, for
example, integrally with the line-shaped body or adhering separately therefrom
upon or after the formation thereof.
15 [0029] An eleventh aspect of the present invention provides the stent
according to the tenth aspect, wherein the adherend is formed with a
biodegradable resin.
[0030] According to the eleventh aspect, since the adherent formed with a
biodegradable resin is degraded in the body after the implantation of the stent, the
20 linking of the line-shaped body at the connecting parts are easily and surely
released, thus avoiding any problems occurring such as stent fracture.
EFFECT OF THE INVENTION
[0031] According to the present invention, the line-shaped body extends in
a helical form along the circumference while reciprocating in the axial direction at
25 a given amplitude, whereas between the portions of the line-shaped body adjacent
to each other in the axial direction, connecting parts are provided to link those
adjacent portions to each other. This enhances the stent’s configuration stability
and prevents the line-shaped body from deflecting in the axial direction during
expansion to cause the stent to undergo strain deformation. Furthermore, since the
30 friable parts are provided that release the links at the connecting parts after being
ruptured due to the implantation of the stent in the somatic lumen, if
conformability of the stent to the shape of the somatic lumen is required, the
pliability of the stent is enhanced by the rupture of the friable parts, thus
enhancing the conformability of the stent to the shape of the somatic lumen.
35 This prevents occurrence of stent fracture as well as damage, infections or the like
to the body tissues caused by the somatic lumen being restricted by the stent.
8
BRIEF DESCRIPTION OF THE DRAWINGS
[0032]
FIG.1 is a side view of a stent as a first embodiment of the present
invention.
FIG.2 is a perspective view of a key 5 portion of the stent shown in FIG.1.
FIG.3 is a plan view of the key portion of the stent shown in FIG.2.
FIG.4 is an arrow view A in FIG.3.
FIG.5 is a cross sectional view taken along line 5-5 of FIG.3.
FIG.6 is a side view showing a shape of the stent of FIG.1 after expansion.
10 FIG.7 is a cross sectional view showing a key portion of a stent as a second
embodiment of the present invention.
FIG.8 is a cross sectional view showing a key portion of a stent as a third
embodiment of the present invention.
FIG.9 is a developed view of a stent as a fourth embodiment of the present
15 invention obtained by cutting the stent along a line on a circumference.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0033] Embodiments of the present invention will be described in
reference to the drawings as follows:
20 [0034] FIG.1 shows a stent 10 as a first embodiment of the present
invention. The stent 10 is provided with a peripheral wall 12 in an approximate
shape of a circular cylinder over the entire length thereof, the peripheral wall 12
being formed with a line-shaped body 14. In FIG.6 to be explained later and FIG.1,
a part of the stent 10 on the front surface side is illustrated, while the rear side
25 thereof is omitted for better understanding. In the following descriptions, the word
“axial direction” generally means the left-right direction in FIG.1, which is the
central axis direction of the peripheral wall 12.
[0035] More specifically, the line-shaped body 14 is a longitudinal
member extending with a cross section of an approximate rectangle that can be
30 formed with a biodegradable resin, synthetic resin and the like, but is preferably
formed with metal materials with superior biocompatibility such as stainless steel,
cobalt-chrome alloy, Ni-Ti alloy and the like (i.e. bioinert metals with no toxicity
to living tissues). Also, the line-shaped body 14 extends in a helical form in the
circumferential direction, in which a linear part 16 that extends in the axial
35 direction for a given length and a curved part 18a/18b that curves approximately
in a semi-circular shape are provided alternately in a continuous manner, making
9
wave forms by reciprocating in the axial direction at a given amplitude. For the
sake of explanation, the curved part with its convex facing one direction (leftward
in FIG.1) and the curved part with its convex facing the other direction (rightward
in FIG.1) are distinguished by labelling them 18a and 18b, respectively.
[0036] Especially in the present embodiment, 5 the reciprocation amplitude
of the line-shaped body 14 is made approximately constant over the entire length
thereof, making uniform wave forms nearly all across the peripheral wall 12. By
having the line-shaped body 14 extend in a helical form in the circumferential
direction while reciprocating in the axial direction, a band-shaped body is formed
10 extending in a helical form in the circumferential direction with a width
corresponding to the amplitude of the line-shaped body 14, and the band-shaped
bodies (curved parts 18a, 18b) arranged adjacent to each other in the axial
direction are separated at a given distance in the axial direction. The distance D in
the axial direction (see FIG.1) from the outer peripheral apex of the curved part
15 18a to the outer peripheral apex of the curved part 18b of this band-like body is
preferably set at 0.5mm  D  2.0mm, and more preferably at 0.9mm  D 
1.5mm.
[0037] Thus, by having the line-shaped body 14 extend in a helical form in
the circumferential direction while reciprocating in the axial direction at a given
20 amplitude, the peripheral wall 12 is formed in an approximate shape of a circular
cylinder over the entire length thereof. As described above, since the line-shaped
body 14 extends in a helical form in the circumferential direction while
reciprocating in the axial direction at a nearly constant amplitude over the entire
length thereof, as shown in FIG. 1, each end of the peripheral wall 12 in the axial
25 direction is located on a plane that extends at an angle to the axis-perpendicular
direction. In summary, the peripheral wall 12 is made in a shape of a circular
cylinder with each end cut off by an inclined plane. The peripheral wall 12 can be
obtained, for example, by forming the line-shaped body 14 in a given
configuration by means of cutting out from a metal member in an approximate
30 shape of a cylinder by laser.
[0038] Also, each end of the line-shaped body 14 in the length direction
constitutes a disc portion 20 in an approximate form of a circular disc partially
widened compared to the middle section. FIG.1 shows the disc portion 20 at one
end of the line-shaped body 14, but the same disc portion 20 is also provided at
35 the other unillustrated end.
[0039] Also, the line-shaped body 14 is provided with a plurality of
10
connecting parts 22 in the length direction. These connecting parts 22 are
provided so as to link the curved parts 18a and 18b adjacent in the axial direction
to each other, each formed per a given number of curved parts 18a, and
particularly in the present embodiment, each connecting part 22 is provided for
every six curved parts 18a. This allows the plurality 5 of connecting parts 22 to be
provided uniformly at a nearly constant interval in the length direction of the
line-shaped body 14.
[0040] More specifically, a friable part 24 is provided in the connecting
part 22 located in the middle section of the line-shaped body 14 in the length
10 direction. The friable part 24 is a part with less mechanical strength than the
line-shaped body 14, and in the present embodiment, each connecting part 22
located in the middle section in the length direction is entirely composed of the
friable part 24. Also, as shown in FIGS.2 to 5, the friable part 24 is provided
between the parts adjacent to each other in the axial direction (curved parts 18a,
15 18b adjacent to each other in the axial direction), and these curved parts 18a, 18b
are linked to each other by the friable part 24. The curved parts 18a, 18b adjacent
to each other in the axial direction are arranged to shift from each other in the
circumferential direction so that the direction of linking of the curved parts 18a,
18b by the friable part 24 is tilted against the axial direction. However, in cases
20 where the curved parts 18a, 18b adjacent to each other in the axial direction are
aligned with each other in the circumferential direction, for example, the direction
of linking of the curved parts 18a, 18b by the friable part 24 does not have to be
tilted against the axial direction, but instead can be parallel to the axial direction.
[0041] Furthermore, in the present embodiment, the friable part 24 is
25 formed by having the curved parts 18a, 18b adjacent to each other in the axial
direction in the line-shaped body 14 welded to each other by laser. This allows the
friable part 24 to be formed easily by after-processing, while making it possible to
form the friable part 24 in any shape and size by means of properly controlling the
duration and intensity of laser irradiation, thus enabling to easily control the
30 rupture timing of the friable part 24.
[0042] Moreover, the width w of the friable part 24 in the direction
perpendicular to the direction of linking of the curved parts 18a, 18b is made
smaller than the width W of the line-shaped body 14, and in the present
embodiment, the width w of the friable part 24 is made to be 0.2 to 0.5 times the
35 width W of the line-shaped body 14. In addition, the thickness h of the friable part
24 is made thinner than the thickness H of the line-shaped body 14 at 0.2 to 0.5
11
times the thickness thereof.
[0043] Thus, by making the friable part 24 narrower and thinner than the
line-shaped body 14, the cross sectional area of the friable part 24 (area of the
cross section extending perpendicular to the direction of linking) is made smaller
than that of the line-shaped body 14 (area 5 of the cross section extending
perpendicular to the length direction). The cross sectional area of the friable part
24 is preferably made 0.01 to 0.3 times as large as the cross sectional area of the
line-shaped body 14.
[0044] Also, the connecting part 22 located at each end of the line-shaped
10 body 14 in the length direction constitutes a linking part 26 without the friable
part 24. This linking part 26 is, as shown in FIG.1, provided for linking the curved
parts 18a, 18b that are adjacent to each other in the axial direction, and these
curved parts 18a, 18b are linked to each other by the linking part 26. In addition,
the linking part 26 is made thicker than the friable part 24 at about the same
15 thickness as the line-shaped body 14 as a part with high mechanical strength
compared to the friable part 24. Also, the linking part 26 preferably is formed at
each end of the line-shaped body 14 in the length direction in the number of about
one to ten. The linking part 26 can be formed integrally with the line-shaped body
14 by laser processing or can be formed later by laser welding in the same manner
20 as the friable part 24. Also, in the present embodiment, each end of the
line-shaped body 14 in the length direction forms a domain that goes one round
around the circumference from each end of the line-shaped body 14, and a single
linking part 26 is formed to link the curved part 18a or 18b located at the utmost
end of the line-shaped body 14 to the curved part 18b or 18a adjacent thereto in
25 the axial direction, respectively. However, each end of the line-shaped body 14 in
the length direction whereby the linking part 26 is formed can be defined as a
domain within a given range and should not be interpreted in a limited manner,
which refers to, for example, a domain that covers an area of three rounds in the
circumferential direction from each end of the line-shaped body 14. In other
30 words, each end of the line-shaped body 14 in the length direction means the area
in the line-shaped body 14 whereby the linking part 26 without the friable part 24
is formed.
[0045] The stent 10 with the connecting parts 22 described above are
externally fitted onto an unillustrated balloon of a balloon catheter for stent
35 expansion to be inserted into a stenosis portion of the somatic lumen. Then, by
dilating the balloon of the balloon catheter for stent expansion, the stent 10
12
externally fitted onto the balloon undergoes a diameter enlarging deformation to
get in close contact with the blood vessel wall. Thereafter, by means of
withdrawing the balloon from the stent 10 by contracting the balloon, the stent 10
is implanted at the stenosis portion of the blood vessel, thus preventing the
5 stenosis portion from restenosis.
[0046] During expansion of the stent 10 described above, the expanded
stent 10 keeps some of the curved parts 18a, 18b adjacent to each other in the
axial direction in linked conditions by the connecting parts 22, as shown in FIG.6.
[0047] Furthermore, since the stent 10 has the line-shaped body 14
10 extending in a helical form in the circumferential direction while reciprocating in
the axial direction at a given amplitude, the entire line-shaped body 14 undergoes
deformation in a stable manner during expansion of the stent 10. In addition, since
a plurality of connecting parts 22 are provided at equal intervals, a local increase
in rigidity by formation of one of the connecting parts 22 causes no strain
15 deformation in the stent 10. Therefore, the entire stent 10 undergoes a diameter
enlarging deformation in a stable manner to get in full and close contact with the
inner surface of the blood vessel, while avoiding problems such as partially
pressing too hard thereon.
[0048] Also, because of the stress caused by pulsation of the blood vessel
20 due to blood flow and curving movement of the blood vessel due to postural
changes acting on the stent 10 implanted in the blood vessel, the friable parts 24
are ruptured to release the links made by the connecting parts 22 between the
curved parts 18a, 18b adjacent to each other in the axial direction located in the
middle section of the stent 10 (peripheral wall 12). This allows a relative
25 displacement between the portions of the line-shaped body 14 adjacent to each
other in the axial direction, that is, the line-shaped body 14 in a helical form alone
is left in the middle of the peripheral wall 12 to make the stent 10 susceptible to
curving deformation, thereby improving the pliability of the stent 10. As a result,
the conformability of the stent 10 to the pulsation and curving of the blood vessel
30 is enhanced to prevent stent fracture caused by implantation and the like of the
stent at the curved part of the blood vessel so that a restrictive effect against
restenosis can be expected. In addition, since the configuration conformability of
the stent 10 is improved, during deformation of the blood vessel or during
implantation of the stent 10 at the curved part of the blood vessel, the end tip of
35 the axial direction of the stent 10 is prevented from being pressed hard on the
blood vessel wall, thus preventing damage, infections and the like of the blood
13
vessel caused by the abutment against the stent 10.
[0049] Since the main body of the stent 10 is composed of one line-shaped
body 14 that extends in a helical form, in addition to the fact that it is possible to
easily form the stent 10 with a few parts, the stent 10 does not get decomposed
into multiple parts even if all the friable parts 24 rupture, 5 thus effectively exerting
the stent’s intrinsic functions (e.g. maintaining the inner diameter of the blood
vessel in an expanded state).
[0050] The friable part 24 can be made to rupture from fatigue failure by
repeated action of stress caused by the pulsation of blood flow or the like, for
10 example, or to rupture from shear failure by significant stress acting thereon
caused by curving deformation of the blood vessel and the like. Furthermore, it
may also be ruptured chemically through decomposition or degradation after
implantation in the living body. In summary, the rupture mechanism of the friable
part 24 is not particularly limited as long as the friable part 24 ruptures
15 preferentially to the line-shaped body 14 by implantation of the stent 10 in the
somatic lumen (e.g. blood vessel).
[0051] The rupture of the friable part 24 after implantation of the stent 10
as described above is achieved by making the cross sectional area of the friable
part 24 smaller than that of the line-shaped body 14. In other words, when an
20 external force caused by pulsation of blood vessel acts on the stent 10,
concentrated stresses are applied to the friable part 24 with a smaller cross
sectional area than the line-shaped body 14 so that the friable part 24 ruptures
prior to the line-shaped body 14. Especially by setting the cross sectional area of
the friable part 24 at 0.01 to 0.3 times the cross sectional area of the line-shaped
25 body 14, the friable part 24 is maintained without rupture during expansion of the
stent 10, while the friable part 24 is easily ruptured by implantation of the stent 10,
thus maintaining the pliability of the stent 10.
[0052] Since the increase in the pliability of the stent 10 due to the rupture
of the friable part 24 enhances the configuration conformability of the stent 10 to
30 the deformation of the blood vessel caused by pulsation thereof and the like, the
stress acting on the stent 10 becomes smaller than that prior to the rupture of the
friable part 24, thereby leaving no chance of rupture for the line-shaped body 14
nor the linking part 26.
[0053] Meanwhile, at each end of the stent 10, the linking part 26 without
35 the friable part 24 never ruptures even after implantation of the stent 10 in the
blood vessel, keeping the curved parts 18a, 18b adjacent to each other in the axial
14
direction in a linked state by the connecting part 22. This secures the configuration
stability of the stent 10 to make it in close contact with the blood vessel walls at
least at each end. As a result, shifting of the implant position of the stent 10 is
prevented, thus stably maintaining the stenosis portion of the blood vessel in an
expanded state. Since the cross sectional area of the 5 linking part 26 is made larger
than that of the friable part 24 to rupture the friable part 24 prior to the linking part
26 under the action of stress resulting in the lowered rigidity of the stent 10, the
linking part 26 is maintained without rupturing under a condition of having the
curved parts 18a, 18b linked to each other.
10 [0054] In addition, since each end of the line-shaped body 14 is widened
to be the disc portion 20 in the stent 10 of the present embodiment, shifting of the
implant position of the stent 10 is prevented more effectively by means of making
the disc portion 20 in close contact with the blood vessel wall. Furthermore, since
the wide disc portion 20 in a shape of a circular disc is provided at each end of the
15 line-shaped body 14 in the stent 10 with a helical structure that turns out to be a
free end, problems such as damaging the blood vessels by either end of the
line-shaped body 14 stuck in the inner surface of the blood vessel can be avoided.
[0055] The disc portion 20 can also function as an angiographic marker
when the stent 10 is implanted at the stenosis portion of the blood vessel. In other
20 words, since the widened disc portion 20 with larger projected area than the
line-shaped body 14 in the side and plan views is superior in visibility during
angiography using X-rays and the like, provision of the disc portion 20 makes it
easier to identify the location of each end of the stent 10. As a result, it is also
made possible by angiography to more accurately determine whether the stent 10
25 is inserted in the intended site of implantation or whether the stent 10 is damaged
or deformed and the like.
[0056] FIG.7 shows a key portion of the stent as a second embodiment of
the present invention. In the following descriptions, substantially the same
members and parts as those of the above-described first embodiment are omitted
30 by assigning the same numerals to the equivalent components in each drawing.
Also, the parts omitted from the drawings are identical to those of the first
embodiment.
[0057] In other words, in the stent of the present embodiment, proximal
protrusions 30a, 30b are provided on the parts adjacent to each other in the axial
35 direction of the line-shaped body 14 (curved parts 18a, 18b adjacent to each other
in the axial direction). The proximal protrusions 30a, 30b are protrusions
15
protruding in the direction of facing of the curved parts 18a, 18b adjacent to each
other in the axial direction between the opposing surfaces thereof, and are formed
integrally with the respective curved parts 18a, 18b in the middle section in the
length direction thereof. Namely, the curved part 18a is formed with a proximal
protrusion 30a, while the curved part 18b adjacent to 5 18a in the axial direction is
formed with a proximal protrusion 30b, and the protrusion tips of these proximal
protrusions 30a, 30b are facing each other across a given distance in-between
without touching. These proximal protrusions 30a, 30b are formed only at the
intended site of the connecting part 22, which will be described later, and in the
10 present embodiment, the proximal protrusion 30a is formed at every sixth of the
plurality of curved parts 18a and the proximal protrusion 30b is formed at every
sixth of the plurality of curved parts 18b, which are similarly arranged in a helical
form in the circumferential direction.
[0058] Then, by irradiating laser beams at the protrusion tips of the
15 proximal protrusions 30a, 30b to weld them to each other, the friable part 24 is
formed between the protrusion tips of the proximal protrusions 30a, 30b that are
linked to each other. This allows the connecting part 22 to be formed by including
the proximal protrusions 30a, 30b and the friable part 24 in the middle section of
the line-shaped body 14 in the length direction, and the curved parts 18a, 18b are
20 linked to each other by the connecting part 22 restricting the relative displacement
of adjacent parts in the axial direction of the line-shaped body 14. In FIG.7, the
borders between the line-shaped body 14 and the proximal protrusions 30a, 30b as
well as the borders between the proximal protrusions 30a, 30b and the friable part
24 are each shown by two-dotted lines.
25 [0059] According to the stent of the present embodiment with the
proximal protrusions 30a, 30b described above, the location of the friable part 24
formed by laser welding is easily identifiable, thus enabling to perform the
forming work of the friable part 24 more easily and securely.
[0060] In addition, since the proximal protrusion 30a provided on the
30 curved part 18a and the proximal protrusion 30b provided on the curved part 18b
protrude in the direction of getting closer to each other, welding can be performed
easily and securely between the proximal protrusions 30a, 30b to obtain the
intended connecting part 22.
[0061] FIG.8 shows a key portion of the stent as a third embodiment of the
35 present invention. That is, the stent of the present embodiment has the line-shaped
body 14 with its surface covered by a coating layer 40 as an adherend. This
16
coating layer 40 is formed with a biodegradable resin (such as polylactic acid,
polycaprolactone or polyglycolic acid) and is deposited to cover the entire surface
of the line-shaped body 14 made of a metal material.
[0062] Then, the portions of the coating layer 40 that cover the curved
parts 18a and 18b of the line-shaped body 14 are 5 adjacent to each other in the
axial direction and are linked to each other by being integrated by laser welding.
This causes a connecting part 42 to be formed at the portion of the coating layer
40 adhered by laser welding and the like, and the curved parts 18a and 18b
adjacent to each other in the axial direction of the line-shaped body 14 are linked
10 to each other by the connecting part 42 formed with the coating layer 40.
[0063] Also, by forming the coating layer 40 with biodegradable resin, the
connecting part 42 is degraded and absorbed to rupture itself after implantation of
the stent in the somatic lumen. This causes a friable part 44, which releases the
linking of the line-shaped body 14 by the connecting part 42, to be formed with
15 the coating layer 40.
[0064] The friable part 44 can be provided as part of the coating layer 40
that is integrally adhered to the line-shaped body 14 in a complex structure as in
the case of the stent of the present embodiment. This allows the friable part 44 to
be formed with materials with different rupture strength, biodegradability and in
20 vivo degradation and so forth from those of the line-shaped body 14 or linking
part 26, thereby causing rupture of the friable part 44 preferentially over other
parts after implantation of the stent in the somatic lumen. Especially since the
friable part 44 is provided by use of the coating layer 40 formed with a
biodegradable resin, the rupture of the friable part 44 after implantation of the
25 stent is stably caused by in vivo degradation.
[0065] In the present embodiment, the entire surface of the line-shaped
body 14 is covered by the coating layer 40, part of which forms the friable part 44.
However, for example, the adherend formed with a biodegradable resin can be
adhered only to the curved part of the line-shaped body 14, all of which can form
30 the friable part 44. Also, the connecting part having the friable part can be formed
with the adherend by means of adhering later the adherend formed separately
from the line-shaped body 14.
[0066] FIG.9 shows a stent 46 as a fourth embodiment of the present
invention. The stent 46 of the present embodiment has basically the same shape as
35 that of the stent 10 of the first embodiment described above, and a developed view
obtained by cutting the stent 46 along a line on the circumference is shown in
17
FIG.9. Also, in FIG. 9, one end of the stent 46 is shown, and the other end is
omitted because of its approximate rotational symmetry with the shape in FIG.9.
[0067] In other words, in the first embodiment described above, each end
surface of the stent 10 in the axial direction is on a plane tilted against the axial
direction, but in the present embodiment, each 5 end surface of the stent 46 in the
axial direction is on a plane nearly perpendicular to the axial direction. Namely,
the position of each line-shaped body 14, that is, curved part 18a or 18b is
substantially lined up at each end of the stent 46 in the axial direction. Also, in the
stent 10 of the first embodiment described above, the line-shaped body 14 extends
10 in a helical form in the circumferential direction reciprocating in the axial
direction at a nearly constant amplitude over the entire length thereof, whereas in
the stent 46 of the present embodiment, the reciprocation amplitude of the
line-shaped body 14 in the axial direction gradually changes at each end of the
stent 46 in the axial direction. The structure of the stent 46 in the middle section in
15 the axial direction is equivalent to that of the first embodiment described above.
[0068] More specifically, in each end of the stent 46 in the axial direction,
at one location along the circumference of the line-shaped body 14, a widened
portion 48 is provided with its amplitude made larger than those of other portions
along the circumference. In FIG.9, the widened portion 48 is shown at the top of
20 the stent 46.
[0069] Under these circumstances, the dash lines in FIG.9 show both ends
of the width direction of the reciprocation amplitude of portions other than the
widened portion 48. In other words, the dash lines in FIG.9 show straight lines
connecting adjacent curved parts 18a, 18a or 18b, 18b at locations other than the
25 widened portion 48 of the line-shaped body 14. As shown in FIG.9, the size of the
amplitude of the widened portion 48 exceeds the separation distance between the
dash lines, and in the stent 46, the angle  of the helix that continues to extend
from each end of the widened portion 48 is varied thereby.
[0070] The reciprocation amplitude of the line-shaped body 14 of the
30 present embodiment is made nearly the same as that of the stent 46 in the middle
section in the axial direction even at the shortest portion located at the end of the
stent 46 in the axial direction. Especially in the present embodiment, the
reciprocation amplitude of the line-shaped body 14 particularly changes at the
widened portion 48, and the difference between the longest and shortest sizes of
35 the reciprocation amplitude of the line-shaped body 14 of the stent 46 is set at
0.5mm or smaller.
18
[0071] The helical inclination angles relative to the axial direction of the
line-shaped body 14 are made nearly equal to each other over the entire length
thereof in the stent 10 of the first embodiment described above, but in the stent 46
of the present embodiment, by use of the widened portion 48 described above, the
helical inclination angle relative to the axial 5 direction of the line-shaped body 14
is made to change gradually. More specifically, the helical inclination angle of the
line-shaped body 14 relative to the axial direction gradually increases toward each
end of the stent 46 in the axial direction, getting closer to the vertical (90 degrees).
Especially in the present embodiment, the helical inclination angle of the
10 line-shaped body 14 is made almost vertical around the end tip of the stent 46 in
the axial direction.
[0072] However, the helical inclination angle of the line-shaped body 14
does not have to reach the vertical at the end tip of the stent 46 in the axial
direction and can also reach an inclination angle slightly exceeding the vertical.
15 Preferably, the helical inclination angle of the line-shaped body 14 reaches at least
80 degrees at the end tip of the stent 46 in the axial direction, and more preferably,
the angle is set in the range of 85 to 90 degrees. In general, the inclination angle of
the middle section of the stent 46 is preferably set in the range of 50 to 75 degrees.
Also, the range of variation wherein the helical inclination angle of the
20 line-shaped body 14 gradually changes, that is, the setting range of the widened
portion 48 can be no less than one round in the circumferential direction of the
stent 46, but preferably set at no less than two rounds, and more preferably set to
vary in no less than three rounds. This makes it possible to avoid a rapid change of
the helical inclination angle of the line-shaped body 14, thus causing smoother
25 deformation and expansion of the stent 46 over the entire length thereof by means
of setting the variation in the inclination angle per one round at 5 degrees or less.
[0073] The helical inclination refers to the angle of the helix shown by
two-dotted lines in FIG.9 that connect the center point of each linear part 16 of the
line-shaped body 14 adjacent to each other in the middle section in the
30 axis-perpendicular direction (up-down direction) in FIG.9, and is represented by
the value of “90 degrees minus lead angle.” In FIG.9, the inclination angle of the
helix is indicated as an angle  relative to a central axis 50 that extends in the
axial direction shown by the one-dotted line (left-right direction in FIG.9).
[0074] In the stent 46 of the present embodiment with the structure
35 described above, each end surface of the stent 46 is made nearly perpendicular to
the axial direction, and the positions of the curved parts 18a, 18b of the
19
line-shaped body 14 are almost lined up at both ends so that the tip end of the
stent 46 in the axial direction can be effectively prevented from floating up locally
when the stent 46 passes through a bent portion of the blood vessel. In addition,
because the inclination relative to the axial direction is made at a right angle by
providing the widened portion 48 at each 5 end of the line-shaped body 14 to vary
the reciprocation amplitude, expansion and flexion of the stent 46 can be
performed effectively. In other words, by providing the widened portion 48, the
inclination angle at each end of the stent does not change rapidly, that is, there is
no need for providing any portion with an excessively long or excessively short
10 amplitude in the line-shaped body 14. This allows the stent 46 of the present
embodiment to exert favorable effects of expansion and flexion. Namely, if a
portion with an excessively short amplitude is provided at the end of the stent,
there is a risk of having difficulties in obtaining an expanding effect at the end
equivalent to that of the middle section. Also, if a portion with an excessively long
15 amplitude is provided at the end of the stent, the flexibility is lowered posing a
risk of having difficulties in achieving smooth deformation and expansion over
the entire length of the stent 46.
[0075] Embodiments of the present invention have been described in
detail above, but the present invention is not limited by those specific descriptions.
20 For example, in some of the embodiments described above, an example where the
friable part 24 is formed by laser welding of the line-shaped body 14 is shown, but
the friable part can also be formed integrally with the line-shaped body 14 in a
similar way of cut-out thereto when the line-shaped body 14 is cut out by laser
from a cylindrical metal member. According to this method, there is no need for
25 post-processing such as laser welding in order to form the friable part, thereby
reducing the number of manufacturing processes. In case of forming the friable
part integrally with the line-shaped body 14, the cross sectional area of the
connecting part is made smaller than that of the line-shaped body 14, which
causes preferential rupture of the connecting part over other parts.
30 [0076] Also, the friable part is not necessarily limited to the one formed
with metal materials, but for example, can be formed with a synthetic resin
material having biodegradability (which is degraded and discharged or absorbed
in the somatic lumen after implantation of the stent) or with a bonding agent and
the like. Thus, in cases where the friable part is formed with a material different
35 from that of the line-shaped body 14, it is not essential that the cross sectional area
of the friable part be smaller than that of the line-shaped body 14. In other words,
20
as long as the friable part is formed with a material with lower strength (more
susceptible to rupturing with the same shape) or a material easier to decompose or
erode in the living body than that of the line-shaped body 14 so that the friable
part ruptures before the line-shaped body 14 under the implanted condition, the
cross section of the friable part can be made the same 5 as or larger than that of the
line-shaped body 14. In summary, in the present invention, it is necessary for the
friable part to rupture preferentially over the line-shaped body under the implanted
condition, but it does not matter whether such a preferential rupturing of the
friable part is caused by differences in shape and size (cross sectional area) or a
10 difference in material between the friable part and the line-shaped body.
[0077] Also, the rupture timing of the friable part 24 can be after the
implantation of the stent 10 in the somatic lumen (e.g. blood vessel) or can be at
the time of expansion (during and upon completion of expansion) of the stent 10.
The rupture timing of the friable part 24 can be controlled by means of adjusting
15 the diameter enlargement rate (ratio of diameter after expansion to diameter
before expansion) of the stent 10 as well as adjusting the shape and size of the
friable part 24.
[0078] Also, the friable part 24 to be formed can be set in any number.
Furthermore, the friable part 24 does not necessarily have to be formed at every
20 sixth of the plurality of curved parts 18a but can be formed at any interval or at
every curved part 18a. Moreover, it is desirable that the friable part 24 be formed
at equal intervals in the line-shaped body 14 in order to secure the configuration
stability of the stent 10 during expansion, but in cases where the line-shaped body
is in an uneven shape in the length direction, for example, the configuration
25 stability can be rather enhanced by means of forming the friable part at unequal
intervals.
[0079] Also, the number of linking parts to be formed is not particularly
limited as long as they are provided at both ends of the line-shaped body 14, and
one or more, or even none of them can be formed. Furthermore, like the
30 connecting parts, the linking parts can be provided later by welding or adhesion of
other members formed with synthetic resin and the like, in addition to being
formed integrally with the line-shaped body 14.
[0080] Also, in some of the embodiments described above, the connecting
part 22 is formed to link the curved parts 18a and 18b arranged adjacent to each
35 other at the closest locations in the axial direction, but the formation locations of
the connecting parts are not particularly limited as long as they are provided to
21
have the adjacent segments in the axial direction linked to each other in the
line-shaped body. More specifically, the connecting parts can be provided so as to
link the linear parts 16, 16 of the line-shaped body 14 adjacent to each other in the
axial direction, or to link the linear part 16 and the curved part 18a/18b to each
other. Furthermore, the connecting parts can be 5 provided to link the curved parts
18a and 18b arranged far separated from each other in the axial direction.
[0081] Also, the line-shaped body 14 of the embodiments described above
has a structure where the linear part 16 and the curved part 18a/18b are provided
alternately in a continuous manner to extend in a helical form in the
10 circumferential direction while reciprocating in the axial direction, but the shape
of the line-shaped body is not limited to the one described in the embodiments
described above. In other words, the line-shaped body can extend in a helical form
in the circumferential direction while curving in waves (e.g. sine curve), for
example, over the entire length thereof, whereas the ones with linear configuration
15 that extend in a helical form in the circumferential direction while turning in
zigzags and reciprocating in the axial direction can also be adopted.
[0082] Furthermore, the line-shaped body can be obtained by processing
wires into a configuration that extend in a helical form in the circumferential
direction while reciprocating in the axial direction, in addition to being formed by
20 cutting out a cylindrical metal material by laser processing.
[0083] Also, the scope of application of the present invention is not
limited to stents to be expanded by a balloon (balloon expandable stents), but it is
applicable to those with a self-expansion function (self-expandable stents) by
forming the stents with materials that exert a shape-memory effect such as Ni-Ti
25 alloy, for example. More specifically, a stent that memorizes an expanded state,
for example, can recover its original expanded state based on the shape-memory
effect after insertion into the protection sheath in a contracted state to be
constrained therein, while constraints against the stent by the protection sheath is
released by removing the protection sheath from the stent at the implant position
30 in the somatic lumen. Even this type of stent with a self-expansion function can
achieve configuration stability in an expanded state as well as pliability in an
implanted state by the provision of the connecting parts 22 linking the line-shaped
body 14.
[0084] Moreover, in the fourth embodiment described above, the widened
35 portion 48 is provided at one location on the circumference, but it can be provided
at multiple locations along the circumference. Also in the fourth embodiment
22
described above, the helical inclination of the stent 46 is varied by providing a
stepped-variable portion in the axial direction such as the widened portion 48, but
it is not limited to such a configuration. For example, the helical inclination can be
varied by changing the reciprocation amplitude of the line-shaped body 14
gradually at an approximately constant rate. In such 5 a configuration as well, the
uniform expansion effect of the stent can be exerted sufficiently. Also, in this case,
the reciprocation amplitude can be changed gradually from the middle section
toward each end, or can be changed at each end, for example, within a range up to
the four rounds in the circumferential direction of the stent.
10 KEYS TO SYMBOLS
[0085]
10, 46: Stent, 12: Peripheral wall, 14: Line-shaped body,
18: Curved part (adjacent portions in the axial direction of the line-shaped body),
20: Disc portion, 22, 42: Connection part, 24, 44: Friable part,
15 26: Linking part (connecting part located at each end of the line-shaped body in
the length direction), 30: Proximal protrusion, 40: Coating layer (adherend)
23
We Claim:
1. A stent comprising a cylindrical peripheral wall formed with a line-shaped
body that extends in a helical form in a circumferential direction while
reciprocating in an axial direction at 5 a given amplitude, the stent being
characterized in that
at least one connecting part is formed to link portions of the line-shaped
body adjacent in the axial direction, and a friable part is provided to rupture itself
by being implanted in a somatic lumen and release a link made by the connecting
10 part.
2. The stent according to claim 1, wherein the friable part is configured by
making a cross sectional area extending perpendicular to a direction of linking of
the connecting part smaller than that extending perpendicular to a length direction
15 of the line-shaped body.
3. The stent according to claim 1 or 2, wherein a reciprocation amplitude of
the line-shaped body in the axial direction is made approximately constant over an
entire length thereof.
20
4. The stent according to claim 1 or 2, wherein a helical inclination angle of
the line-shaped body relative to the axial direction is made to gradually increase
toward each end of the stent to get close to a vertical angle.
25 5. The stent according to any one of claims 1-4, wherein the at least one
connecting part comprises a plurality of connecting parts formed in the length
direction of the line-shaped body, and the friable part is provided in the
connecting parts located in a middle section of the line-shaped body in the length
direction, whereas no friable part is provided in the connecting parts located at
30 each end of the line-shaped body in the length direction, keeping the stent in a
linked state after implantation in the somatic lumen.
6. The stent according to any one of claims 1-5, wherein the connecting parts
are provided at a constant interval.
35
7. The stent according to any one of claims 1-6, wherein the friable part is
24
formed by having the portions of the line-shaped body adjacent in the axial
direction welded to each other by laser.
8. The stent according to claim 7, wherein proximal protrusions are provided
in the portions of the line-shaped body adjacent in the 5 axial direction where the
friable part is formed by welding the proximal protrusions to each other by laser.
9. The stent according to any one of claims 1-8, wherein each end of the
line-shaped body in the length direction constitutes a widened disc portion.
10. The stent according to any one of claims 1-9, wherein an adherend made
of a different material is adhered to the line-shaped body, and the connecting part
having the friable part is formed by the adherend.
11. The stent according to claim 10, wherein the adherend is formed with a
biodegradable resin.