APPARATUS AND METHOD FOR FORMATION OF FOIL-SHAPED STENT STRUTS
A device and method is disclosed for reducing turbulent blood flow over stent struts of an intravascular stent implanted in, for example, a coronary artery. An abrasive slurry is passed over the struts of an intravascular stent in order to remove a portion of the stent struts to form an airfoil shape. When the stent having airfoil-shaped struts is implanted in an artery, the flow of blood over the airfoil shape will reduce the likelihood of turbulent blood flow and thereby will reduce the likelihood of turbulent blood flow and thereby reduce the likelihood of a buildup in plaque or injury to the vessel wall.
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The invention relates generally to providing an apparatus for using an abrasive slurry for the removal of metal on products made from metals. More particularly, the invention relates to an apparatus for and method of using an abrasive slurry on medical devices made of titanium, stainless steel, tungsten, nickel-titanium, tantalum, cobalt-chromium-tungsten, cobalt-chromium, and the like to form a more hemodynamically compatible device.
While a wide range of products or devices can be made from the listed metal alloys for use with the present invention, medical devices are particularly suitable due to the biocompatible characteristics of these alloys. Thus, for example, implantable medical devices or devices that are used within the human body are particularly suitable and can be made from these alloys that have been treated in accordance with the present invention. More particularly, and as described in more detail herein, intravascular stents can be made from the listed alloys that have been treated according to the invention. Thus, while the description of prior art devices and of the invention herein refers mainly to intravascular stents, the invention is not so limited to medical products or intravascular stents.
Stents are generally metallic tube shaped intravascular devices which are placed within a blood vessel to structurally hold open the vessel. The device can be used to maintain the patency of a blood vessel immediately after intravascular treatments and can be used to reduce the likelihood of development of restenosis. Expandable stents are frequently used as they may travel in compressed form to the stenotic site generally either crimped onto an inflation balloon or compressed into a containment sheath in a known manner.
Metal stents can be formed in a variety of expandable configurations such as helically wound wire stents, wire mesh stents, weaved wire stents, metallic serpentine stents, or in the form of a chain of corrugated rings. Expandable stents, such as wire mesh, serpentine, and corrugated ring designs, for example, do not possess uniformly solid tubular walls. Although generally cylindrical in overall shape, the walls of such stents are perforated often in a framework design of wire-like elements or struts connected together or in a weave design of cross threaded wire.
Expandable stents formed from metal offer a number of advantages and are widely used. Metallic serpentine stents, for example, not only provide strength and rigidity once implanted they also are designed sufficiently compressible and flexible for traveling through the tortuous pathways of the vessel route prior to arrival at the stenotic site. Additionally, metallic stents may be radiopaque, thus easily visible by radiation illumination techniques such as x-ray film.
It is highly desirable for the surface of the stent to be extremely smooth so that it can be inserted easily and experience low-friction travel through the tortuous vessel pathway prior to implantation. A roughened outer surface may result in increased frictional obstruction during insertion and excess drag during travel to the stenotic site as well as damaging the endothelium lining of the vessel wall. A rough surface may cause frictional resistance to such an extent as to prevent travel to desired distal locations. A rough finish may also cause damage to the underlying inflation balloon. A less rough finish decreases thrombogenicity and increases corrosion resistance.
Stents have been formed from various metals including stainless steel, tantalum, titanium, tungsten, nickel-titanium which is commonly called Nitinol, and alloys formed with cobalt and chromium. Stainless steel has been extensively used to form stents and has often been the material of choice for stent construction. Stainless steel is corrosion resistant, strong, yet may be cut into very thin-walled stent patterns.
Cobalt-chromium alloy is a metal that has proven advantages when used in stent applications. Stents made from a cobalt-chromium alloy may be thinner and lighter in weight than stents made from other metallic materials, including stainless steel. Cobalt-chromium alloy is also a denser metal than stainless steel. Additionally, cobalt-chromium stents are nontranslucent to certain electromagnetic radiation waves, such as X-rays, and, relative to stainless steel stents, provide a higher degree of radiopacity, thus being easier to identify in the body under fluoroscopy.
Metal stents, however, suffer from a number of disadvantages. They often require processing to eliminate undesirable burrs, nicks, or sharp ends. Expandable metal stents are frequently formed by use of a laser to cut a framework design from a tube of metal. The tubular stent wall is formed into a lattice arrangement consisting of metal struts with gaps therebetween. Laser cutting, however, typically is at high temperature and often leaves debris and slag material attached to the stent. Such material, if left on a stent, would render the stent unacceptable for implantation. Treatment to remove the slag, burrs, and nicks is therefore required to provide a device suitable for use in a body lumen.
Descaling is a first treatment of the surface in preparation for further surface treatment such as electropolishing. Descaling may include, for example, scraping the stent with a diamond file, followed by dipping the stent in a hydrochloric acid or an HCl mixture, and thereafter cleaning the stent ultrasonically. A successfully descaled metal stent should be substantially slag-free in preparation for subsequent electropolishing.
Further finishing is often accomplished by the well known technique of electropolishing. Grinding, vibration, and tumbling techniques are often not suited to be employed on small detailed parts such as stents.
Electropolishing is an electrochemical process by which surface metal is dissolved. Sometimes referred to as “reverse plating,” the electropolishing process actually removes metal from the surface desired to be smoothed. The metal stent is connected to a power supply (the anode) and is immersed in a liquid electrolytic solution along with a metal cathode connected to the negative terminal of the power supply. Current is applied and flows from the stent, causing it to become polarized. The applied current controls the rate at which the metal ions of the anodic stent are generally removed and diffused through the solution to the cathode.
The rate of the electrochemical reaction is proportional to the current density. The positioning and thickness of the cathode in relation to the stent is important to make available an even distribution of current to the desired portion of the stent sought to be smoothed. For example, some prior art devices have a cathode in the form of a flat plate or a triangular or single wire loop configuration, which may not yield a stent or other medical device with a smooth surface on all exposed surfaces. For example, the prior art devices do not always provide a stent having a smooth surface on the inner tubular wall of the stent where blood flow will pass.
Most prior art stents are laser cut from a thin-walled metal tube leaving a mesh framework of stent struts. Typically, the stent struts have a rectangular transverse cross-section. When implanted in an artery, the rectangular-shaped cross-section of the stent struts may produce blood flow turbulence in the artery resulting in adverse vascular reactions such as the proliferation of restenosis.
What is needed is an apparatus and a process for treating a product or device made of a metal alloy to remove metal from the device to thereby reduce the likelihood of turbulent blood flow through the device. The present invention satisfies this need.
SUMMARY OF THE INVENTIONThe invention is directed to an improved apparatus and method for the treatment of an intravascular stent formed from a metal alloy. The invention is directed to an apparatus and method for passing an abrasive slurry over the struts of an intravascular stent in order to remove a portion of the stent struts to form an airfoil shape. More particularly, the transverse cross-section of one more struts of the stent have a shape that resembles an airfoil or a hydrofoil which will reduce turbulent blood flow in the vasculature in which the stent is implanted, thereby improving clinical outcome. In one embodiment, a chamber holds a stent stationary while an abrasive slurry flows through the inner lumen of the stent. As the abrasive slurry passes over the stent struts, metal is removed from a first edge and, to a lesser degree, metal is removed from a second edge of the strut. More metal is removed from the first edge than from the second edge, resulting in a cross-sectional shape resembling an airfoil.
The present invention stent improves on existing stents by providing a longitudinally flexible stent having a uniquely designed pattern and novel interconnecting members. In addition to providing longitudinal flexibility, the stent of the present invention also provides radial rigidity and a high degree of scaffolding of a vessel wall, such as a coronary artery. The present invention stent is processed so that it is more hemodynamically compatible and causes less blood flow turbulence when implanted in an artery.
Turning to the drawings,
Catheter assembly 12 as depicted in
As shown in
In a typical procedure to implant stent 10, the guide wire 18 is advanced through the patient's vascular system by well known methods so that the distal end of the guide wire is advanced past the plaque or diseased area 26. Prior to implanting the stent, the cardiologist may wish to perform an angioplasty procedure or other procedure (i.e., atherectomy) in order to open the vessel and remodel the diseased area. Thereafter, the stent delivery catheter assembly 12 is advanced over the guide wire so that the stent is positioned in the target area. The expandable member or balloon 22 is inflated by well known means so that it expands radially outwardly and in turn expands the stent radially outwardly until the stent is apposed to the vessel wall. The expandable member is then deflated and the catheter withdrawn from the patient's vascular system. The guide wire typically is left in the lumen for post-dilatation procedures, if any, and subsequently is withdrawn from the patient's vascular system. As depicted in
The stent 10 serves to hold open the artery after the catheter is withdrawn, as illustrated by
Referring to
Referring to
As shown in
Each cylindrical ring 40 defines a cylindrical plane 50 which is a plane defined by the proximal and distal ends 46,48 of the ring and the circumferential extent as the cylindrical ring travels around the cylinder. Each cylindrical ring includes cylindrical outer wall surface 52 which defines the outermost surface of the stent, and cylindrical inner wall surface 53 which defines the innermost surface of the stent. Cylindrical plane 50 follows the cylindrical outer wall surface.
An undulating link 54 is positioned within cylindrical plane 50. The undulating links connect one cylindrical ring 40 to an adjacent cylindrical ring 40 and contribute to the overall longitudinal flexibility to the stent due to their unique construction. The flexibility of the undulating links derives in part from curved portion 56 connected to straight portions 58 wherein the straight portions are substantially perpendicular to the longitudinal axis of the stent. Thus, as the stent is being delivered through a tortuous vessel, such as a coronary artery, the curved portions 56 and straight portions 58 of the undulating links will permit the stent to flex in the longitudinal direction which substantially enhances delivery of the stent to the target site. The number of bends and straight portions in a link can be increased or decreased from that shown, to achieve differing flexibility constructions. With the straight portions being substantially perpendicular to the stent longitudinal axis, the undulating link acts much like a hinge at the curved portion to provide flexibility. A straight link that is parallel to the stent axis typically is not flexible and does not add to the flexibility of the stent.
Referring to
As shown in
As shown in
In keeping with the invention, as shown in
As shown in
The longitudinal bore 84 has a diameter that is greater than the outer diameter of the stent 30. It is intended that different sized chamber 82 having different diameter longitudinal bores 84 be used for stents having different outer diameters. For example, a typical coronary artery stent in the manufactured configuration can have an outer diameter from between 2 mm to 3.5 mm, and have a length between 8 mm and 30 mm. More typically, a coronary stent has an outer diameter of 3 mm and length of 20 mm. The longitudinal bore 84 has a diameter that is greater than the outer diameter of the stent so that the stent can be easily inserted into the chamber 82 and into longitudinal bore 84 without scraping or damaging the stent struts. After the stent is inserted into the longitudinal bore 84, the end cap 86 is secured to the chamber 82 so that the end cap abuts one end of the stent 30 but does not force the stent against the flange 94 or ridge which is at the opposite end of the longitudinal bore from the end cap. Thus, after the end cap is secured to the chamber, the stent should have substantially no longitudinal movement within the longitudinal bore 84, and just have a slight amount of clearance between the diameter of the longitudinal bore and the outer diameter of the stent.
In further keeping with the invention, and referring to
More specifically, the strut radial thickness of stent 30 for a coronary artery stent typically is about 0.0032 inch. It will be appreciated, however, that the strut radial thickness can be thicker or thinner, depending on the stent design and where it is implanted. Thus, the strut radial thickness can be in the range from 0.060 inch to 0.002 inch. The present invention reduction in radial thickness of the struts can range from about 5% to about 20% at the first edge 106 and from about 3% to about 15% at the second edge 108. Preferably, the radial thickness of the first edge 106 is reduced by 20% and radial thickness of the second edge is reduced by 5%. As an example, for a stent strut that has a radial thickness of 0.0032 inch, the first edge 106 will be 20% thinner, or about 0.0026 inch and the second edge 108 will be 5% thinner, or about 0.003 inch. Further, the strut surface extending between the first edge 106 and second edge 108 may be straight or slightly curved and essentially form a taper, gradually getting thicker going from the first edge toward the second edge.
Referring to
The stent 30 of the present invention can be mounted on a balloon catheter similar to that shown in
It is important to note that the airfoil shape of the stent strut 102 as shown for example in
While the invention has been illustrated and described herein, in terms of its use as an intravascular stent, it will be apparent to those skilled in the art that the stent can be used in other body lumens. Other modifications and improvements may be made without departing from the scope of the invention.
Claims
1. A method for forming a stent, comprising:
- providing a metallic stent having a cylindrical shape and a pattern of stent struts;
- placing the stent in a chamber;
- injecting an abrasive slurry through the chamber and through a lumen of the stent;
- removing metal from an inner surface of at least one of the stent struts by the abrasive slurry flowing over the inner surface of the stent.
2. The method of claim 1, wherein as the abrasive slurry flows over the inner surface of the at least one stent strut, a transverse cross-section of the strut is transformed from a substantially rectangular shape into the shape of an airfoil.
3. The method of claim 1, wherein the abrasive slurry has a low viscosity so that it flows through the stent lumen without bending the stent struts.
4. (canceled)
5. The method of claim 1, wherein the abrasive slurry has a pressure range of 1500 psi to 3500 psi.
6. The method of claim 1, wherein the abrasive slurry contains abrasive particles having an average particle in the range of 12.0 microns (0.0005 inch) to 6.5 microns (0.0003 inch).
7. The method of claim 1, wherein the abrasive slurry contains a polymer.
8. The method of claim 1, wherein the airfoil-shaped cross-section of the at least one stent strut has a first edge that is thinner than a second edge.
9. The method of claim 7, wherein the at least one stent strut has a curved inner surface that extends between the first edge and the second edge.
10. The method of claim 7, wherein as the abrasive slurry flows over the inner surface of the at least one stent strut, the slurry flows in a direction from the first edge toward the second edge.
11. The method of claim 9, wherein the abrasive slurry removes more metal from the first edge than from the second edge.
12. The method of claim 2, wherein the transverse cross-sectional shape of the at least one stent strut before flowing the abrasive slurry over the inner surface is substantially rectangular with radiused corners.
13. The method of claim 1, wherein the metal removed from the at least one stent strut reduces the radial thickness of the first edge from about 5% to about 20% and the second edge from about 3% to about 15%.
14. The method of claim 1, wherein the stent has an outer surface and a radial thickness defined by the outer surface and the inner surface, the radial thickness being in a range of 0.002 inch to 0.060 inch.
Type: Application
Filed: Jun 30, 2011
Publication Date: Jan 3, 2013
Applicant: ABBOTT CARDIOVASCULAR SYSTEMS INC. (Santa Clara, CA)
Inventors: Randolf von Oepen (Aptos, CA), Kevin J. Ehrenreich (San Francisco, CA)
Application Number: 13/173,353
International Classification: B24C 1/00 (20060101);