News Column

Patent Issued for Method for Attaching Radiopaque Markers to a Stent

June 25, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- Abbott Cardiovascular Systems Inc. (Santa Clara, CA) has been issued patent number 8745842, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventor is Wu, Patrick P. (Mountain View, CA).

This patent was filed on February 17, 2012 and was published online on June 10, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "This invention relates generally to implantable medical devices, such as stents, and, more particularly, to attaching radiopaque markers to polymeric stents.

"Expandable endoprostheses 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 blood 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 structure of stents is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements or struts. The scaffolding can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. In addition, a medicated stent may be fabricated by coating the surface of either a metallic or polymeric scaffolding with a polymeric carrier. The polymeric scaffolding may also serve as a carrier of an active agent or drug.

"The first step in treatment of a diseased site with a stent is locating a region that may require treatment such as a suspected lesion in a vessel, typically by obtaining an x-ray image of the vessel. To obtain an image, a contrast agent, which contains a radiopaque substance such as iodine is injected into a vessel. 'Radiopaque' refers to the ability of a substance to absorb x-rays. The x-ray image depicts the lumen of the vessel from which a physician can identify a potential treatment region. The treatment then involves both delivery and deployment of the stent. 'Delivery' refers to introducing and transporting the stent through a bodily lumen to a region 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 allowing the stent to self-expand.

"The stent must be able to simultaneously 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 lumen. In addition to having adequate radial strength or more accurately, hoop strength, the stent should be longitudinally flexible to allow it 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. The material from which the stent is constructed must allow the stent to undergo expansion, which typically requires substantial deformation of localized portions of the stent structure. Once expanded, the stent must maintain its size and shape throughout its service life despite the various forces that may come to bear thereon, including the cyclic loading induced by the beating heart. Finally, the stent must be biocompatible so as not to trigger any adverse vascular responses.

"In addition to meeting the mechanical requirements described above, it is desirable for a stent to be radiopaque, or fluoroscopically visible under x-rays. Accurate stent placement is facilitated by real time visualization of the delivery of a stent. A cardiologist or interventional radiologist can track the delivery catheter through the patient's vasculature and precisely place the stent at the site of a lesion. This is typically accomplished by fluoroscopy or similar x-ray visualization procedures. For a stent to be fluoroscopically visible it must be more absorptive of x-rays than the surrounding tissue. Radiopaque materials in a stent may allow for its direct visualization.

"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 may be configured to meet this additional clinical requirement since they may be designed to completely erode after the clinical need for them has ended. Stents fabricated from biodegradable polymers are particularly promising, in part because they may be designed to completely erode within a desired time frame.

"However, a significant shortcoming of biodegradable polymers (and polymers generally composed of carbon, hydrogen, oxygen, and nitrogen) is that they are radiolucent with no radiopacity. Biodegradable polymers tend to have x-ray absorption similar to body tissue.

"One way of addressing this problem is to attach radiopaque markers to structural elements of the stent. A radiopaque marker can be disposed within a structural element in such a way that the marker is secured to the structural element. However, the use of stent markers on polymeric stents entails a number of challenges. One challenge relates to the difficulty of insertion of markers.

"Another challenge pertains to the fact that some regions of polymeric struts tend to undergo significant deformation or strain during crimping and expansion. In particular, such changes are due to plastic deformation of polymers. Thus, during stent deployment, the portion of a stent containing an element may crack or stretch as stress is being applied to the expanding stent. As a result, the marker may become dislodged.

"Attachment of radiopaque markers to stents usually requires a significant amount of time to perform with reliability and uniformity. The amount of time required is increased when several markers must be attached at different locations on the stent. Also, conventionally-placed markers may project inward from the luminal surface of the stent to such a degree that blood flow is disrupted, or project outward from the abluminal surface of the stent to such a degree that the walls of the blood vessel are traumatized.

"Accordingly there is a need to for an apparatus and method of easily attaching radiopaque markers on stents. There is also a need for an apparatus and method of attaching radiopaque markers on stents such that the marker is retained in the stent during deformation of the stents during subsequent stent crimping and expansion. There is a further need for an apparatus and method of attaching a plurality of radiopaque markers to a stent with greater efficiency and uniformity. Also, there is a need to attach radiopaque markers such that the radiopaque markers do not overly protrude from the stent. The present invention satisfies these and other needs."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "Various embodiments of the present invention include a method of attaching a radiopaque marker onto a stent, the method comprising: placing a stent mounted on a mandrel into a gap between a first roller and a second roller, the stent including a radiopaque marker positioned at a surface of the stent, wherein both of the rollers are oriented such that their rotational axes are substantially parallel to the central axis of the stent; wherein the rollers rotate in the same direction, wherein the stent is rotated about its central axis in a direction opposite to the rollers thereby bringing the markers into contact with the first or second roller; and allowing the first or second roller to press the radiopaque marker in a manner that couples the radiopaque marker to the stent.

"Further embodiments of the present invention include a method of attaching a radiopaque marker onto a stent, the method comprising: placing a stent mounted on a mandrel into a gap between a first roller and a second roller, the stent including a radiopaque marker positioned at a surface of the stent, wherein both of the rollers are oriented such that their rotational axes are substantially parallel to the central axis of the stent, wherein the rollers are rotated about the central axis of the stent thereby bringing the rollers into contact with the markers, wherein the stent is rotated about its central axis in a direction opposite to the rollers; and as the rollers continue to rotate, allowing the rollers to press the radiopaque marker in a manner that couples the radiopaque marker to the stent.

"The features and advantages of the invention will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings."

For the URL and additional information on this patent, see: Wu, Patrick P.. Method for Attaching Radiopaque Markers to a Stent. U.S. Patent Number 8745842, filed February 17, 2012, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8745842.PN.&OS=PN/8745842RS=PN/8745842

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

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Source: Journal of Engineering


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