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Apparatus and method for formation of foil-shaped stent struts

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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.
Related Terms: Artery Implant Plaque Vascular Coronary Artery Struts Plaque Or Over The Air

Inventors: Randolf von Oepen, Kevin J. Ehrenreich
USPTO Applicaton #: #20130005218 - Class: 451 36 (USPTO) - 01/03/13 - Class 451 
Abrading > Abrading Process >Utilizing Fluent Abradant

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The Patent Description & Claims data below is from USPTO Patent Application 20130005218, Apparatus and method for formation of foil-shaped stent struts.

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BACKGROUND

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 INVENTION

The 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 an elevational view, partially in section, of a stent of the present invention mounted on a rapid exchange delivery catheter and positioned within an artery.

FIG. 2 is an elevational view, partially in section, similar to that in FIG. 1, wherein the stent is expanded within the artery, so that the stent embeds partially within the arterial wall.

FIG. 3 is an elevational view, partially in section, showing the expanded stent implanted within the artery after withdrawal of the rapid exchange delivery catheter.

FIG. 4 is a cross-sectional view of a prior art stent in which the stent struts have a rectangular cross-section thereby causing turbulent flow of blood through the artery.

FIG. 5 is a plan view of a flattened stent of one embodiment of the invention which illustrates a pattern of rings and links.

FIG. 6 is a partial plan view of the stent of FIG. 5 which has been expanded to approximately 4.0 mm inside diameter.



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stats Patent Info
Application #
US 20130005218 A1
Publish Date
01/03/2013
Document #
13173353
File Date
06/30/2011
USPTO Class
451 36
Other USPTO Classes
International Class
24C1/00
Drawings
8


Artery
Implant
Plaque
Vascular
Coronary Artery
Struts
Plaque Or
Over The Air


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