MXPA99009850A - Covered stents expanding through gl - Google Patents

Abstract

The present invention relates to a stent (100) for deploying within a body lumen (501), the stent (100) comprises: a stent body (110) comprising an elastic material, the stent body has a cylindrical shape free having a free diameter (d), and a cover (102, 202, 302) in the stent body (110), characterized in that the cover is plastically deformable wherein the cover has a thickness (t) which substantially prevents the stent body (110) expands toward the free diameter when the stent body (110) is placed in a diameter smaller than the diameter of the stent

Description

COVERED STENTS EXPANDING THROUGH BALLOON FIELD OF THE INVENTION The present invention relates to implantable medical devices and covered implantable stents comprising an elastic or superelastic material.

BACKGROUND OF THE INVENTION Stents are support structures that are implanted in tubular organs, vessels, or other tubular body lumens to help keep said ducts open. Stents are usually used after balloon angioplasty to prevent restenosis and, more generally, can be used to repair any number of tubular body lumens, such as those in the vascular, biliary, genitourinary, gastrointestinal, respiratory and other systems systems. The materials used to make stents must be chemically and biologically inert to living tissue. The stents must also be able to remain in place and continue to support the tubular body lumens where they are implanted for extended periods. In addition, stents must have the ability to expand from a contracted state, which facilitates insertion into a body lumen, to an expanded diameter that is useful to support at least a portion of the body lumen. This expansion is achieved either mechanically, such as through the action of a balloon end catheter, or through self-expansion such as through shape memory effects or through the use of a restrained elastic stents. The above requirements limit the number of eligible stent materials. One of the most widely used metal alloy systems is the nickel-titanium system, the alloys of which are known as nitinol. Under certain conditions, nitinol is highly elastic, so that it is capable of undergoing extensive deformation and even returning to its original shape. Elastic stents are typically deployed in a body lumen by reducing the diameter of the stent through mechanical means, restraining the stent in reduced diameter during insertion into the body, and freeing the stent from restriction at a target site. Once released, the stent "self-expands" to its predetermined diameter, useful by virtue of its elastic properties. One of the advantages of elastic stents is that, after deployment, they are able to "bounce" back to their useful diameters after being deformed by external forces. The elastic nature of such stents not only makes them ideal for self-expansion after delivery to a target site, but also makes them desirable for use in body lumens that are usually subjected to external forces and time reductions corresponding in diameter or other deformations. For example, elastic stents are useful for placement in the carotid artery, which is often deformed by external forces since the vessel is very close to the surface of the body. However, there are some potential disadvantages associated with conventional elastic stents. For example, said self-expanding stents possess a predetermined individual diameter, thus limiting the use of a given stent and increasing the number of different stents required to cover a scale of useful diameters. When the predetermined diameter is greater than the lumen of the body in which the stent is placed, residual expansion forces generally occur in the undesired, gradual expansion of the surrounding lumen. The release of self-expanding stents usually does not exert sufficient force to open blocked body lumens containing hard plaque. In this way, it is sometimes necessary to perform the additional step of inserting a balloon into the partially deployed stent for additional dilation, thus adding cost, time and risk to the entire procedure.

COMPENDIUM OF THE INVENTION The present invention provides stents for deployment within tubular organs, blood vessels or other tubular body lumens. Said stents comprise a stent body having an elastic material, the stent body being characterized by a free cylindrical shape having a free diameter. The stent body is at least partially covered with a cover that substantially prevents the stent body from expanding to its free diameter when the stent body is placed in a diameter smaller than the free diameter. In addition, after the stent is expanded, the cover does not force the stent body to a diameter smaller than the diameter in which it is expanding. In one embodiment, the cover is a metal coating on the stent body. In another embodiment, the cover is a tube that surrounds the stent body. In yet another embodiment, the cover includes multiple rings around the body of the stent. The present invention also provides methods for deploying the stents of the present invention within tubular organs, blood vessels or other tubular body lumens. The method includes the steps of providing a stent comprising a stent body comprising an elastic material, the stent body being characterized by a free cylindrical shape having a free diameter; deform the stent to a diameter smaller than the free diameter; covering the stent with a cover that substantially prevents the stent body from expanding to the free diameter when the stent body is placed in a diameter smaller than the free diameter; insert the stent into the body while it is in the reduced diameter; and mechanically expand the stent. In one embodiment, the step of covering the stent comprises the step of coating the stent body. In another embodiment, the step of covering the stent comprises the step of placing a tube on the stent. In yet another embodiment, the step of covering the stent comprises the step of placing multiple rings on the stent. An advantage of the present invention is that it provides stents that are isothermally deployed in the body. Another advantage of the present invention is that it provides stents that resist loads exerted by a surrounding tubular member. Yet another advantage of the present invention is that it provides expanded stents that are bouncy and resilient along their longitudinal and radial axes, and thus resist deformation when exposed to longitudinal and radial forces. Yet another advantage of the present invention is that it provides stents that expand to desired, controlled dimensions, through balloon catheters, and each stent can be expanded to any diameter within a wide range of diameters.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A and 1B show planar and cross-sectional views, respectively, of one embodiment of the present invention, wherein a stent is covered with a metal coating. Figure 2 shows an embodiment of the present invention wherein a stent is covered with a tube. Figure 3 shows an embodiment of the present invention wherein multiple rings are located around a stent. Figures 4A to 4C show a cross-sectional view of a method for deploying a stent in a body lumen, according to the present invention.

DETAILED DESCRIPTION The present invention exhibits the advantages of conventional elastic stents, while minimizing the potential limitations and disadvantages of such stents. For example, the stents of the present invention are not limited to predetermined "learned" diameters and do not require dilation procedures after placement separate from the deployment stage. In addition, the stents of the present invention can each be expanded to a scale of useful diameters. In addition, when it expands to useful diameters in target sites within the body's lumens, the stents of the present invention are elastic so that they can rebound to their expanded diameters after being subjected to external forces that result in temporary reductions in diameter or other deformations. Generally, the stent of the present invention comprises a stent body comprising an elastic material, and a cover over the stent body. The cover substantially prevents the stent body from expanding to its free diameter when the stent body is placed in a slightly smaller diameter.

A stent of the present invention is deployed within a body lumen by deforming the stent to a diameter smaller than its free diameter, covering the stent with a cover that substantially prevents the stent from expanding to its free diameter by virtue of its properties elastic, inserting the stent into the body lumen, and mechanically expanding the stent such as through balloon inflation to a useful diameter, desired at a target site within the lumen of the body. According to one embodiment of the invention, as shown in Figure 1A, a stent 100 has a stent leather 110 having a free cylindrical shape of free diameter, d. The cylindrical shape and the diameter, d, of the stent body 110 are said to be "free" when the stent body 110 is not actuated after external forces. Although the stent 100 is in the form of a pattern tube, other suitable stent configurations (e.g., wire coil, ribbons, hexagons, nets, spiral strips, zig-zags, articulated stents, and the like) are also within the scope of the present invention. The stent body 110 comprises an elastic material that is capable of appreciable (elastic) recoverable deformation after the application of external forces without incurring extensive (plastic) permanent deformation. For example, the elastic material is preferably characterized by recoverable stresses greater than about 1%, most preferably greater than about 5%. The elastic material is, for example, a metallic or polymeric material. The elastic material includes so-called "superelastic" materials such as certain nitinol alloys, which are typically characterized by recoverable stresses greater than about 8%. The nitinoi is a preferred material for the stent body 110. Since the stent body 110 comprises an elastic material, it tends to spring back to its free configuration and free diameter after being deformed or compressed by external forces. However, the stent 100 includes a cover over the stent body 110 that substantially prevents the stent body 110 from expanding to its free diameter when it is placed in a diameter smaller than its free diameter. In addition, the cover keeps the stent body 110 in the diameter to which it expands once placed in a target site in the body. Therefore, according to the present invention, it is not required that the useful diameter at which the stent can be expanded is substantially equal to the free diameter of the stent body 110. In one embodiment, the cover on the stent body 110 is a liner 102 that preferably comprises a plastically deformable metal. The liner 102 optionally comprises an x-ray absorbing material, thereby making the stent 110 radiopaque. Preferred materials for coating 110 include gold, platinum, palladium and tantalum. The coating 112 is placed on the stent body 110 through any suitable method such as, for example, dipping, spraying, vapor deposition, chemical or electrochemical electrodeposition, cathodic deposition and the like. A preferred method for applying the coating 102 to the stent body 110 is through electrodeposition. The liner 102 is applied to a thickness, t (102), on the underlying stent body 110, the posts of which are characterized by a thickness, t (101), as shown in the cross-sectional view illustrated in Figure 1B. The stent body 110 is either partially or completely covered with the liner 102. When the diameter of the stent 100 is reduced such as when clamped in a balloon catheter, the thickness of the liner 102, t (102), is sufficient to provide the resistance necessary to maintain the stent body 110 in the reduced diameter, denying any tendency of the stent body 110 to expand to its free diameter, d, by virtue of its elastic properties. For example, when the liner 102 comprises a soft, foldable metal such as gold, and the stent body 110 comprises nitinol, the thickness of the liner 102 preferably approximates the transverse thickness of the posts of the stent body. Conversely, when the coating 102 comprises a stronger metal, its thickness need not be as thick as the posts of the underlying stent body. The liner 102 imparts desired properties to the stent 100. For example, when the coated stent 100 expands within the body, its compressive strength is a combination of the strength of the stent body 110 and the strength of the lining material, which plastically it deforms during the expansion of the stent 100. The radial resistance of the stent 100 against crushing and rewinding after deployment in this manner is greatly enhanced by the liner 102. When expanded, the coated stent of the present invention has the additional advantage of to be elastic in the longitudinal and radial directions, thus resisting permanent deformation by longitudinal and radial forces. In addition, since the addition of the liner 102 to the stent 100 substantially prevents the stent body 110 from expanding to its free diameter, it is not necessary to restrict the stent from expanding such as through a bay or other restraining means during insertion. in the body. Figure 2 shows another embodiment of the present invention wherein the stent 100 comprises a stent body 110 covered with a tube 202 in place of the liner 102 of the embodiment shown in Figure 1B. The tube 202 comprises any suitable biocompatible material having sufficient strength to substantially prevent the stent body 110 from expanding to its free diameter after the stent body 110 is placed in a diameter smaller than the free diameter. A preferred material for tube 202 is medical grade polyurethane implant. In the embodiment shown in Figure 2, the length of the tube 202 is substantially the length of the stent 100. The thickness of the tube 202 is sufficient to provide the strength necessary to maintain the stent body 110 in reduced diameter, thus negating any tendency of the stent body 110 to expand towards its free diameter, d, by virtue of its elastic properties. For example, when the stent body 110 comprises nitinol and the tube 202 comprises medical grade polyurethane implant, the tube 202 has a thickness of about 100 to 200 microns. The tube 202 has potentially multiple functions. For example, the tube 202 prevents the stent body 110 from expanding to its free diameter after the stent body 110 is placed in a diameter smaller than the free diameter. In addition, since the length of the tube 202 is substantially the length of the stent body 110, it serves to limit embolization and growth through the openings between the posts of the stent 100. As another example, the tube 202 is optionally used to maintain drug agents during delivery to a target site, after drug agents are released from tube 202. For example, tube 202 has drug agents embedded therein, which are subsequently released from tube 202 to the target site to avoid or limit neo-intimate proliferation. Another embodiment of the present invention is shown in Figure 3. This embodiment is similar to that shown in Figure 2 with the exception that the modality shown in Figure 3 includes multiple tubes or rings 302, each having a shorter length than that of stent body 110. This mode is preferred over the modality shown in Figure 2 in applications where the use of minimally covered stents is desired. The present invention provides methods for deploying the stent 100 within a body lumen. In one embodiment, the method includes the steps of providing a stent comprising a stent body comprising an elastic material, the stent body being characterized by a free cylindrical shape having a free diameter; deform the stent body to a diameter smaller than its free diameter; cover the stent with a cover that substantially prevents the stent body from expanding to its free diameter by virtue of its elastic properties; insert the stent into the body; and mechanically expanding the stent to a target site within the body lumen at a desired, desired diameter. The cover substantially prevents the stent from expanding during insertion into the body and placement at a target site within a body lumen. In addition, after the stent is deployed, the cover keeps the stent in the diameter to which it is expanded. Therefore, a stent of the present invention can be expanded to a wide range of diameters, and the useful diameter at which the stent is expanded is not required to be substantially equal to the free diameter of the stent body. A method for deploying a stent is described with reference to Figures 4A to 4C, which illustrate (in cross section) the deployment of a stent in an angioplasty procedure as a non-limiting example of the present invention. As shown in Figure 4A, a stent having a stent body 110 and a liner 102 on the stent body posts is mounted on a catheter 401 having an expandable portion 402. The diameter of the stent when mounted on the catheter 401 is smaller than its free diameter. Although the stent body 110 comprises an elastic material, the liner 102 is of sufficient strength to substantially prevent the stent body 110 from expanding to its free diameter by virtue of its elastic properties. The catheter 401 is placed within a body lumen 501 which has a blockage caused by the development of pest 502, for example, when it is inserted to the desired target site, the expandable portion 402 of the catheter 401 is expanded by known techniques of way that expands the stent to the useful dimension, desired as shown in Figure 4B. During said expansion, the metal coating 102 on the stent body 110 undergoes plastic deformation. Expandable portion 402 of catheter 401 is then deflated to facilitate removal of catheter 401 from body lumen 501, as shown in Figure 4C. The stent remains in place in an expanded configuration as shown in Figure 4C. The present invention is further described with reference to the following non-limiting examples.

EXAMPLE 1 Using known techniques, a standard tube stent was made from nitinol having an approximate composition of atomic 51% nickel, the rest being titanium. The thickness of the stent posts is approximately 100 microns. The stent has a free diameter of approximately 5 millimeters. The stent is electrodeposited with gold using conventional techniques at a thickness of approximately 100 microns. The stent is then deformed at room temperature, while the nitinol is in an austenitic phase, at a diameter of about 1 millimeter.

The gold coating keeps the stent at a diameter of approximately 1 millimeter. The coated stent is attached to the expandable portion of a conventional balloon catheter. Using known techniques, the balloon catheter is delivered to a target site within a body lumen having a diameter of approximately 5 millimeters. When the stent is placed at the target site, the balloon catheter is expanded to a diameter of between about 3 and about 5 millimeters. During such expansion, the stent is likewise expanded to a diameter of between about 3 to about 5 millimeters and the gold layer is plastically deformed, but remains as an intact coating. The balloon catheter is then deflated and removed from the body, leaving the expanded stent in place at the target site. The deployed stent has a high strength due to its austenitic phase and the additional imparted strength of the plastically deformed gold coating layer. In addition, the deployed stent has excellent resistance to rewinding and crushing, while maintaining its elasticity in the longitudinal direction (i.e., rebound capability).

EXAMPLE 2 Using known techniques, a standard tube stent was made from nitinol having an approximate composition of atomic 51% nickel, the remainder being titanium. The thickness of the stent posts is approximately 100 microns. The stent has a free diameter of approximately 5 millimeters. The stent is cooled in ice water to place the nitinol in a martensitic phase and deforms while cooling to a diameter of approximately one millimeter. A polyurethane tube, having a diameter of approximately 1.5 millimeters and a thickness of approximately 150 microns, is placed on the stent. Both the stent and the polyurethane tube have a length of approximately 1.5 centimeters. The polyurethane tube holds the stent to a diameter of approximately 1 millimeter. The covered stent is attached to the expandable portion of a conventional balloon catheter. Using known techniques, the balloon catheter is delivered to a target site within the lumen of a body having a diameter of approximately 5 millimeters. When the stent is placed in the target site, the balloon catheter is expanded to a diameter of between approximately 3 and 5 millimeters. During said expansion, both the stent and the polyurethane tube are likewise expanded to a diameter of between about 3 and 5 millimeters. The balloon catheter is then deflated and removed from the body, leaving the expanded stent and the polyurethane tube in place at the target site. The deployed stent has a high strength due to its austenitic phase and the additional imparted strength of the plastically deformed gold coating layer. In addition, the deployed stent has excellent resistance to rewinding and crushing, while maintaining its elasticity in the longitudinal direction (i.e., rebound capability). The present invention provides improved resistance stents that are isothermally deployed in the body without the need for restriction devices. When deployed in accordance with the present invention, the stents provide sufficient strength to resist rewinding and crushing, while maintaining elasticity in the longitudinal direction. It will be obvious to those skilled in the art, having considered this description, that other variations in this invention beyond those specifically illustrated can be made. However, such variations should be considered within the scope of this invention and be limited only by the following claims.

Claims (22)

1. - A stent to be deployed within the lumen of a body, said stent comprises: a stent body comprising an elastic material, said stent body being characterized by a free cylindrical shape having a free diameter; and a cover over the stent body, wherein said cover substantially prevents the stent body from expanding to the free diameter when the stent body is placed in a diameter smaller than the free diameter.

2. The stent according to claim 1, wherein the elastic material is nitinol.

3. The stent according to claim 2, wherein the nitinol is in a substantially austenitic phase when deployed in the body.

4. The stent according to claim 1, wherein the stent is a patterned stent.

5. The stent according to claim 1, wherein said cover is a metal coating.

6. The stent according to claim 5, wherein the thickness of said metal coating is approximately equal to the thickness of the stent body. 1.

The stent according to claim 6, wherein the thickness of the stent body is approximately 100 microns.

8. The stent according to claim 5, wherein the metal coating comprises a metal selected from the group consisting of gold, platinum, palladium, tantalum and alloys thereof.

9. The stent according to claim 5, wherein the metal coating is electrodeposited on the stent.

10. The stent according to claim 5, wherein the metal coating is radiopaque.

11. The stent according to claim 1, wherein the cover comprises a tube around the stent.

12. The stent according to claim 11, wherein the tube comprises a polymeric material.

13. The stent according to claim 12, wherein the polymeric material is polyurethane.

14. The stent according to claim 11, wherein the length of the tube is substantially the length of the stent.

15. The stent according to claim 11, wherein the stent of the tube is smaller than the length of the stent.

16. The stent according to claim 1, wherein the cover comprises multiple rings around the stent.

17. A method for deploying a stent within the lumen of a body, said method comprising the steps of: providing a stent comprising a stent body comprising an elastic material, the stent body being characterized by a free cylindrical shape having a free diameter; deforming the stent body to a diameter smaller than the free diameter; cover the stent with a cover while the stent body is in diameter smaller than the free diameter, the cover substantially preventing the stent body from expanding to the free diameter; insert the stent into the body lumen; and mechanically expand the stent.

18. The method according to claim 17, wherein the step of covering the stent comprises the step of electrodeposing a metal coating on the stent.

19. The method according to claim 17, wherein the step of covering the stent comprises the step of placing a polymer tube on the stent.

20. The method according to claim 17, wherein the step of covering the stent comprises the step of placing multiple rings around the stent.

21. The method according to claim 17, further comprising the step of mounting the stent on a balloon catheter before the step of inserting the stent into the body.

22. The method according to claim 21, wherein the step of mechanically expanding the stent comprises the step of inflating the balloon.