Expandable stent

Background of the Invention and Related Art Statement

0001The invention relates to an expandable endoprosthesis device, generally called a stent, which is implanted into a patient's body lumen, such as a blood vessel, to maintain patency thereof. The stent is very useful in the treatment of atherosclerotic stenosis in blood vessels.

0002The stent is, generally, a tubular shaped device which functions to support a part of a blood vessel or another anatomical lumen from the inside thereof, and is particularly suitable for supporting and holding back a dissected arterial lining which can occlude a fluid passageway by collapse thereof. "Stent" here is defined as a prosthetic member used for reinforcing the blood vessel.

0003Various methods have been used to deliver and implant stents. In one of the methods frequently used for delivering a stent to a desired interlumenal location, an expandable stent is mounted on an expandable member, such as a balloon, provided on a distal end of an intravascular catheter, and the catheter is advanced to the desired location within the patient's body lumen. Then, the balloon on the catheter is inflated to expand the stent therearound into a permanent expanded condition, and the balloon is deflated for removing the catheter from the stent.

0004Therefore, advantages of the method of strengthening the blood vessel by the stent over the conventional vascular surgery include obviating the surgical exposing, incising, removing, replacing or bypassing a defective blood vessel required in the conventional vascular surgery.

0005The stents in the prior art can be categorized as a wire type stent or a coil stent and a tube stent. Further details of prior art stents can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,338 (Balko et al.); U.S. Pat. No. 4,553,545 (Masass et al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,120 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco) ; U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No. 4,886,062 (Wiktor) and U.S. Pat. No. 5,421,955 (Lau et al.).

0006When the stent is expanded as described above, it is important to maintain the stent in the expanded condition so that the body lumen expanded by the stent can be maintained open. The prior wire type stent or the coil stent is made by simply bending a wire having a flexibility so that the wire stent is easily expanded and shrunk. Therefore, the wire type stent had difficulties in maintaining the radially expanded condition for holding the body lumen open.

0007On the other hand, when the stent is delivered into the desirable site in the tortuous body lumens, it is also important that the stent is flexible and is bent easily to thereby facilitate the delivery of the stent in the narrow and meandering body lumen such as a blood vessel. Also, in view of expanding the stent in the body lumen for the treatment, it is important to expand the stent quickly so that the balloon catheter can be removed from the patient's body as quickly as possible.

0008In the tube type stent of the prior art, the tube stent has enough stiffness to maintain its expanded condition for holding the body lumen open at the desirable location. However, since the tube stent is not flexible as in the wire type stent, it is difficult to deliver the tube stent in the tortuous lumen to locate the stent in the desirable site.

0009Furthermore, when the radial force by the expandable member, such as a balloon, is applied from the inside of the stent, the forces applied at both ends of the stent are greater than the force applied to an inner portion of the stent. Therefore, both ends of the stent may be excessively expanded compared to the inner portion of the stent, so that the body lumen can not be equally expanded by such a stent.

0010Accordingly, one object of the invention is to provide a stent, which has a high degree of flexibility and expandability for advancing through passageways.

0011Another object of the invention is to provide a stent as stated above, which can be readily and equally expandable throughout the entire length thereof.

0012A further object of the invention is to provide a stent as stated above, which has a mechanical strength to hold the body lumen open equally, as well.

0013Further objects and advantages thereof will be apparent from the following description of the invention.

Summary of the Invention

0014To achieve the aforementioned objects of the invention, a stent of the invention is formed of an expandable tubular reinforcing member used for a body lumen, and includes a plurality of rows of expandable joint members and a plurality of rows of flexible elongated members. Each row of the joint members is spaced for a predetermined distance away from each other along the central axis of the reinforcing member, and each of the plural rows is formed of the joint members spaced apart from each other to form a circular shape around the central axis with a first diameter.

0015Each row of the elongated members is situated between adjacent two rows of the joint members. The elongated members extend diagonally to a central axis of the reinforcing member. Therefore, when a radial force is applied from an inside of the reinforcing member, the elongated members are bent relative to the joint members to thereby allow the tubular reinforcing member to have a second diameter larger than the first diameter.

0016In addition, since the elongated members are diagonally arranged and connected between the joint members spaced away from each other, the stent has enough flexibility to facilitate the delivery of the stent into the desirable site in the meandering body lumen.

0017The expandable tubular reinforcing member may include two rows of end portions disposed parallel to the rows of the joint members. Each row of the end portions is connected to a row of the joint members located at each longitudinal end of the reinforcing member, and is formed of a plurality of struts situated parallel to the central axis and connected to the joint members and a plurality of connecting portions. Each connecting portion connects a pair of struts situated adjacent to each other. In particular, each connecting portion has a thickness less than that of each strut. When the reinforcing member is expanded, each connecting portion is bent. Also, each strut has a length shorter than a length of each elongated member. Therefore, when the reinforcing member is expanded, the struts are equally bent at both ends at the same time.

0018In the invention, since the stent is provided with the end portions formed of the struts parallel to the stent and the connecting portions, the ends of the stent can be prevented from excessive expansion to equalize the expansion of the stent throughout the entire length thereof even though the expanding force at the ends of the stent is greater than the force at the inner portion of the stent.

0019Each joint member is preferably formed of two side portions and one middle portion for joining the two side portions. Two elongated members are connected to one side portion of one joint member in one row of the joint members, and are connected to two side portions of two joint members in another row of the joint members. The middle portion may be located at ends of the two side portions to have an open side in the joint member. The open sides in one row of the joint members are oriented in a same direction, and the open sides in adjacent two rows are directed in opposite directions.

0020Also, the elongated members may be formed of first and second elongated members alternately arranged to each other in one row of the elongated members. Each first elongated member is connected to the side portion near the open side in the joint member, and each second elongated member is connected to the side portion near the middle portion. When the reinforcing member is expanded, the first elongated members are bent first, and then the second elongated members are bent.

0021Preferably, the elongated members are integrally formed with the joint members and the end portions.

Brief Description of the Drawings

0022<ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a plan view of an expandable stent of the present invention, wherein the stent is cut along a longitudinal direction and is opened to show a flat condition;</li><li>Fig. 2 is an enlarged plan view of a part of the embodiment shown in Fig. 1;</li><li>Fig. 3 is an enlarged plan view of an end portion of the embodiment shown in Fig. 1;</li><li>Fig. 4 is a front view of the stent before it is expanded;</li><li>Fig. 5 is a side view of the stent before it is expanded; and</li><li>Fig. 6 is a side view of the stent after it is expanded.</li></ul>

Detailed Description of a Preferred Embodiment

0023Hereinafter, an embodiment of the present invention is explained by referring to the attached drawings.

0024In the embodiment of the present invention as shown in Figs. 1 through 6, a stent 1 situated in a human body lumen, such as a blood vessel, is formed of a plurality of flex joints 2, a plurality of elongated members 3, 4 connected to the flex joints 2, and a plurality of end portions 5. As shown in Fig. 1, i.e. a plan view cut into a flat form, plural rows of the flex joints 2 are disposed to be spaced away from each other along a longitudinal direction or central axis of the stent formed in a round shape. In each row, a plurality of flex joints is disposed to be spaced away from each other, and first and second elongated members 3, 4 connected in one joint 2 are connected to two flex joints 2 in the adjacent row, and extend diagonally to the central axis of the stent.

0025As shown in the magnified partial view of the stent of Fig. 2, the flex joint 2 has a semicircular shape and is formed of a pair of side portions 6, and a middle portion 7, wherein the side portions 6 are connected to both ends of the middle portion 7. The middle portion 7 and the two side portions 6 define an open side 8. Also, in adjacent two rows, the flex joints 2 orient in opposite directions. For example, the open sides 8 of one row of the flex joints 2 orient upwardly, while the open sides 8 of another row situated next to that row orient downwardly.

0026As shown in Fig. 1, each first elongated member 3 connects between the respective side portions 6 near the open sides 8 in two adjacent rows of the flex joints 2, and each second elongated member 4 connects between the respective side portions 6 near the middle portions 7 in the adjacent two rows.

0027As shown in Fig. 3, each end portion 5 is formed of a pair of struts 9, 10 arranged parallel to each other, and a connecting part 11. The connecting part 11 connects one strut 9 in one end portion 5 to one strut 10 in another end portion 5. Thus, the two flex joints 2 situated adjacent to each other are connected together by one end portion 5, respectively. The thickness of the connecting part 11 is thinner than the thickness of the struts 9, 10.

0028In the invention, the rows of the flex joints 2 and the elongated members 3, 4 are disposed perpendicularly to the central axis of the stent 1. The flex joints 2 situated in adjacent rows orient in the opposite directions, while the first and second elongated members 3, 4 located in the adjacent rows orient or incline in the opposite directions. Namely, the first and second elongated members 3, 4 in one row incline in one direction in the central axis, and the first and second elongated members in the adjacent row incline in the opposite direction in the central axis. Also, the rows of the end portions 5 are located at longitudinal ends of the stent 1, wherein the struts 9, 10 orient parallel to the central axis. When the stent is formed, the stent 1 has a first diameter D₁, as shown in Figs. 4 and 5.

0029The stent is preferably formed by etching. Namely, a pattern of the flex joints 2, elongated members 3, 4 and the end portions 5 are coated on a cylindrical metal member, which is etched in an acid liquid. Then, uncoated portions are removed. Other suitable methods may be used. For example, the stent can be formed by laser cutting.

0030When the stent 1 is used in the body lumen, such as a blood vessel, the stent 1 is delivered to the desired location in the body lumen by mounting it on an expandable member, such as a balloon, of a delivery catheter. When the stent 1 is delivered, since the elongated members 3, 4 diagonally extend between the flex joints 2, the elongated members 3, 4 can be bent easily along the body lumen. Accordingly, a stent catheter assembly is successfully pushed into the implantation site.

0031Then, when the expandable member, such as the balloon, is inflated for radially applying the force inside the stent 1, the stent 1 is expanded to have a second diameter D₂, as shown in Fig. 6, which is larger than the first diameter D₁. When the stent 1 is expanded, the first elongated members 3 are bent outwardly to expand the stent 1 first, and after the first elongated members 3 are bent, the second elongated members 4 are bent to further expand the stent 1.

0032The struts 9, 10 in the end portion 5 of the stent 1 have lengths shorter than that of the respective elongated members and extend parallel to the central axis of the stent. Also, the struts 9, 10 are connected to the connecting part 11 and the flex joints 2. Thus, when the expandable member is inflated, the struts 9, 10 are bent equally at the same time.

0033Since the first and second elongated members 3, 4 are arranged diagonally to the central axis of the stent 1, the first and second elongate members are easily expanded compared to the struts 9, 10 arranged parallel to the central axis of the stent 1. Since the force applied to the ends of the stent is greater than the force applied at the middle portion of the stent 1, the stent 1 can be expanded equally throughout the entire length thereof.

0034Also, the cylindrical design of the stent 1 may allow the plastic deformation of the metal (except with NiTi) when the stent is expanded. This plastic deformation can maintain the stent in its expanded position and resist collapsing in the body. With super elastic NiTi alloys, the expansion occurs when the stress of compression is removed so as to allow the phase transformation from austenite back to martensite as a result of the expansion of the stent 1.

0035The stent is formed of stainless steel, or may be formed of a NiTi alloy. Alteratively, the stent may be made of a radioactive material or irradiated with a radioactive isotope. The radioactive isotope may be a beta particle emitting radioisotope. By using the stent made of the radioactive material, cancer cells in and around the stent can be deactivated or killed.

0036Alternatively, the stent may be coated with an anticoagulating medication substance, such as heparin, and/or bio-absorbable material. Accordingly, when the stent is used in the blood vessel, blood clotting can be prevented.

0037Also, the stent may have pores or dents to absorb or retain a drug therein for slowly releasing the same. Thus, when the stent with a drug is implanted in the body lumen, the drug can be slowly released in the body lumen.

0038Preferably, as shown in Fig. 3, the thickness of the flex joint 2 is thinner than that of the elongated member to be bendable. The spacing of the flex joint 2, the respective length of the elongated members 3, 4, the thickness of the connecting part 11 and the like can be variable to allow the stent to have flexibility in various directions along its length without compromising the radial support for preventing the body lumen from collapsing. Therefore, the stent of the invention can support any dissection and flap in the body lumen.

0039Also, the number and location of the flex joints and the elongated members can be varied in order to develop the desired longitudinal flexibility in the stent structure both in the unexpanded stage and in the expanded stage.

0040While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.