Patent Issued for Stents with Enhanced Fracture Toughness

By a News Reporter-Staff News Editor at Journal of Engineering -- Advanced Cardiovascular Systems, Inc. (Santa Clara, CA) has been issued patent number 8323329, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Gale, David C. (Kennesaw, GA); Huang, Bin (Pleasanton, CA); Limon, Timothy (Cupertino, CA); Gueriguian, Vincent J. (San Francisco, CA).

This patent was filed on May 3, 2010 and was cleared and issued on December 4, 2012.

From the background information supplied by the inventors, news correspondents obtained the following quote: "This invention relates to methods of fabricating stents having selected mechanical properties.

"This invention relates to radially expandable endoprostheses, which are adapted to be implanted in a bodily lumen. An 'endoprosthesis' corresponds to an artificial device that is placed inside the body. A 'lumen' refers to a cavity of a tubular organ such as a blood vessel.

"A stent is an example of such an endoprosthesis. Stents are generally cylindrically shaped devices, which function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen such as urinary tracts and bile ducts. Stents are often used in the treatment of atherosclerotic stenosis in blood vessels. 'Stenosis' refers to a narrowing or constriction of the diameter of a bodily passage or orifice. In such treatments, stents reinforce body vessels and prevent restenosis following angioplasty in the vascular system. 'Restenosis' refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty, stenting, or valvuloplasty) with apparent success.

"The treatment of a diseased site or lesion with a stent involves both delivery and deployment of the stent. 'Delivery' refers to introducing and transporting the stent through a bodily lumen to a region, such as a lesion, in a vessel that requires treatment. 'Deployment' corresponds to the expanding of the stent within the lumen at the treatment region. Delivery and deployment of a stent are accomplished by positioning the stent about one end of a catheter, inserting the end of the catheter through the skin into a bodily lumen, advancing the catheter in the bodily lumen to a desired treatment location, expanding the stent at the treatment location, and removing the catheter from the lumen.

"In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter. Mounting the stent typically involves compressing or crimping the stent onto the balloon. The stent is then expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be secured to the catheter via a retractable sheath or a sock. When the stent is in a desired bodily location, the sheath may be withdrawn which allows the stent to self-expand.

"The stent must be able to satisfy a number of mechanical requirements. First, the stent must be capable of withstanding the structural loads, namely radial compressive forces, imposed on the stent as it supports the walls of a vessel. Therefore, a stent must possess adequate radial strength. Radial strength, which is the ability of a stent to resist radial compressive forces, is due to strength and rigidity around a circumferential direction of the stent. Radial strength and rigidity, therefore, may also be described as, hoop or circumferential strength and rigidity.

"Once expanded, the stent must adequately maintain its size and shape throughout its service life despite the various forces that may come to bear on it, including the cyclic loading induced by the beating heart. For example, a radially directed force may tend to cause a stent to recoil inward. Generally, it is desirable to minimize recoil.

"In addition, the stent must possess sufficient flexibility to allow for crimping, expansion, and cyclic loading. Longitudinal flexibility is important to allow the stent to be maneuvered through a tortuous vascular path and to enable it to conform to a deployment site that may not be linear or may be subject to flexure. Finally, the stent must be biocompatible so as not to trigger any adverse vascular responses.

"The structure of a stent is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements often referred to in the art as struts or bar arms. The scaffolding can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. The scaffolding is designed so that the stent can be radially compressed (to allow crimping) and radially expanded (to allow deployment). A conventional stent is allowed to expand and contract through movement of individual structural elements of a pattern with respect to each other.

"Additionally, a medicated stent may be fabricated by coating the surface of either a metallic or polymeric scaffolding with a polymeric carrier that includes an active or bioactive agent or drug. Polymeric scaffolding may also serve as a carrier of an active agent or drug.

"Furthermore, it may be desirable for a stent to be biodegradable. In many treatment applications, the presence of a stent in a body may be necessary for a limited period of time until its intended function of, for example, maintaining vascular patency and/or drug delivery is accomplished. Therefore, stents fabricated from biodegradable, bioabsorbable, and/or bioerodable materials such as bioabsorbable polymers should be configured to completely erode only after the clinical need for them has ended.

"However, there are potential shortcomings in the use of polymers as a material for implantable medical devices, such as stents. There is a need for a manufacturing process for a stent that addresses such shortcomings so that a polymeric stent can meet the clinical and mechanical requirements of a stent."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Certain embodiments of the present invention include a stent comprising a cylindrically aligned bending element formed by a first bar arm and a second bar arm, the angle between the bar arms being greater than about 90.degree., wherein the stent is fabricated from a tube radially expanded by at least about 400%.

"Further embodiments of the present invention include a stent comprising a cylindrically aligned bending element formed by a first bar arm and a second bar arm, an angle between each of the bar arms and the circumferential direction being less than about 45.degree., wherein the stent is fabricated from a tube radially expanded by at least 500%.

"Additional embodiments of the present invention include a stent comprising a plurality of cylindrically aligned bending elements, the angles between the bending elements being greater than about 90.degree..

"Other embodiments of the present invention include a method of fabricating a stent comprising: radially expanding a tube to at least about 400%; and cutting a pattern comprising a cylindrically aligned bending element formed by a first bar arm and a second bar arm, the angle between the bar arms being greater than about 90.degree., wherein the stent is fabricated from a tube radially expanded by at least about 400%.

"Some embodiments of the present invention include a method for fabricating a stent comprising: conveying a gas into a poly(L-lactide) tube disposed within a cylindrical mold to increase a pressure inside the tube, wherein the increased pressure radially expands the polymeric tube to conform to the inside surface of the mold; applying tension along the axis of the tube to axially extend the tube; and fabricating a stent from the radially expanded and axially extended tube.

"Certain embodiment of the present invention include a method for fabricating a stent comprising: processing a polymer form to increase the Tg of the polymer at least about 10.degree. C.; and fabricating a stent from the processing form.

"Additional embodiments of the present invention include a method for fabricating a stent comprising: processing a polymer form so as to increase the Tg of the polymer to at least about 40.degree. C. above ambient temperature to allow storage of the processed polymer at the ambient temperature; and fabricating a stent from the processed polymer.

"Other embodiments of the present invention include a method for fabricating a stent comprising: processing a polymer form so as to increase the Tg of the polymer to at least about 20.degree. C. above a crimping temperature."

For the URL and additional information on this patent, see: Gale, David C.; Huang, Bin; Limon, Timothy; Gueriguian, Vincent J.. Stents with Enhanced Fracture Toughness. U.S. Patent Number 8323329, filed May 3, 2010, and issued December 4, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=91&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4540&f=G&l=50&co1=AND&d=PTXT&s1=20121204.PD.&OS=ISD/20121204&RS=ISD/20121204

Keywords for this news article include: Advanced Cardiovascular Systems Inc.

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