Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent combined with surgical delivery system
Reexamination Certificate
2000-05-11
2001-09-04
Recla, Henry J. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent combined with surgical delivery system
Reexamination Certificate
active
06283990
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a combination of a balloon and a stent with specific sizes, wherein the stent is opened substantially to the maximum opening size by the balloon with substantially the same maximum opening size to provide an effective retaining or supporting ability to the stent in a vessel.
The most of the current stents on the market including coronary and peripheral stents are designed to have struts, and elbows or bending portions, wherein the struts in one strut section are bent at the elbows and arranged to have a zigzag shape as a whole. Some of the elbows in one strut section are connected to the elbows in the adjacent strut section. When the stent is in a closed condition, the struts are situated substantially parallel to the stent axis. As the stent begins to open by inflating a balloon on which the stent is mounted, an angle between two struts connected with each other through the elbow in between becomes wider.
In general, all the currently available stents are designed to cover all sizes by one or two stents in a coronary market. The range of the diameter when it is opened is between 2.5 mm and 4.0 mm.
There are two factors in determining the size of the stent in the open condition. One is the size of the balloon to be used, and the other is an inflating pressure applied to the balloon. For example, if a balloon with 3.0 mm in diameter is used, the stent will open to 3.0 mm in diameter. If a higher pressure is applied, the balloon may expand slightly more, so that the stent may become 3.2 mm in diameter.
The stents are generally sold in a package, so-called pre-mount stents. In the pre-mount stents, the stents are already mounted on various balloons, which respectively have various diameters, such as 2.5 mm, 3.0 mm, 3.5 mm, and 4.0 mm. Although the balloons are different in the pre-mount stents to equally open the stents in the various diameters, a common stent which opens to various diameters is mostly used for those balloons having different diameters.
More specifically, as shown in
FIG. 4
, a conventional stent
101
used for all types of the balloons has a cylindrical shape and a diameter D
101
in a closed condition, and mounted on a balloon
102
of a balloon catheter
103
, known in the art, as shown in FIG.
5
.
After the stent is delivered to a specific position by the balloon catheter
103
, an inflating pressure is applied inside the balloon
102
so that the balloon
102
is inflated to have an opening diameter D
102
as shown in FIG.
6
. Accordingly, the stent
101
mounted on the balloon
102
is opened by the balloon
102
to have the opening diameter D
102
. For example, the diameter D
102
is 2.5 mm. In the open stent shown in
FIG. 6
, an angle formed by a strut
104
and an axis A parallel to a central axis of the stent
101
is 40 degrees.
When the stent
101
is mounted on a balloon
102
′ of a balloon catheter
103
′ in which an opening diameter of the balloon
102
′ is larger than D
102
, the stent
101
is further opened to have a diameter D
103
which is larger than the diameter D
102
. For example, the diameter D
103
is 3 mm, and an angle formed by the strut
104
and the axis A of the stent
101
is 50 degrees as shown in FIG.
7
.
As described above, since the stent
101
having the same size, such as the diameter D
101
, in the closed condition is used for the various balloons
102
,
102
′ having various diameters D
102
, D
103
in the opened condition, the inflating pressures applied inside the balloons
102
,
102
′ are increased and the angles between the strut
104
and the axis of the stent
101
becomes larger as the diameter of the balloon becomes larger.
Namely, if the stent is opened to have a diameter close to the maximum opening diameter, the strut angles, as mentioned above, become obtuse. Thus, it requires more pressure to open the stent to have the maximum diameter. This is very desirable to the stent since it takes more pressure to close or collapse the stent. In other words, when the stent is opened to the maximum diameter, the stent has a high withstanding force against collapsing.
Thus, in the examples shown in
FIGS. 6 and 7
, the stent
101
shown in
FIG. 7
has the withstanding force against collapsing stronger than that shown in FIG.
6
. In this sense, although the same stent
101
is used, the ability for supporting is different according to the diameters of the balloons used in the blood vessel.
On the other hand, there is a prior art publication indicating that the struts are bent perpendicular to the stent axis, which is most desirable in supporting the blood vessel. Although this statement is true, it is almost impossible to expand the struts perpendicular to the axis of the stent by the balloon because it requires too high inflating pressure by the balloon. The relationship of the angle of the strut relative to the pressure applied to the strut is show below, wherein the angle is measured as in
FIGS. 6 and 7
.
Angle(degrees)
Pressure(ATM)
15
1.00
30
2.15
45
3.73
60
6.46
75
13.93
80
21.17
85
42.66
As shown above, it requires about 42 ATM to open the strut at 85 degrees. This is practically impossible to open the strut by the balloon. The balloon now available in the market can provide 12 to 20 ATM.
The present invention has been made in view of the above, and an object of the invention is to provide a combination of a specific size balloon and a specific size stent, wherein each stent is designed to open to the specific one size only to prevent collapsing of the stent after enlargement.
Another object of the invention is to provide a combination of the balloon and stent as stated above, wherein the stent is enlarged to the maximum size as designed to be used for a long time without trouble.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
In the present invention, a balloon having a predetermined maximum expandable size is combined with an expandable stent to be expanded by the balloon. The stent has a predetermined maximum expandable size equal to the maximum expandable size of the balloon.
The stent is formed of a plurality of rows of cylindrical strut sections situated side by side in a longitudinal direction to form the stent, and a plurality of connecting members for connecting two rows of the struts adjacent to each other. Each strut section in one row is formed of struts, and bending portions located at respective ends of the struts. A strut angle is defined by the strut and a line parallel to a central axis of the stent and extending through the bending portion. In the invention, the strut angle is at least 75 degrees, i.e. equal to or more than 75 degrees, and less than 90 degrees when the stent is fully expanded. Practically, the strut angle is between 75 and 80 degrees. When the stent is fully expanded by the balloon, the stent is not easily collapsed with less recoil. Thus, the stent can be used in a blood vessel or other portion for a long time without causing trouble.
In this respect, if the stent is expanded less than 75 degrees, the stent may be collapsed in a long usage or when a large collapsible force is applied to the stent for a long time. Also, the stent may recoil a lot. Thus, the strut angle is required at least 75 degrees.
In the invention, the balloon for the specific maximum expandable size is combined with the stent for the specific maximum expandable size. If the balloon for the large size is used for enlarging the small size stent, the stent may not be equally expanded at the maximum expanded condition. In order to fully and equally expand the stent, the balloon for the specific maximum expandable size must be used for the stent with the same specific maximum expandable size.
Preferably, the struts in the strut section are arranged side by side around the axis of the stent to form a zig-zag pattern. The struts in the strut section may be arranged substantially parallel to each other wh
Kanesaka & Takeuchi
Recla Henry J.
Truong Kevin
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