News Column

Researchers Submit Patent Application, "Biodegradable Polymeric Stents", for Approval

September 4, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Gale, David C. (Kennesaw, GA); Huang, Bin (Pleasanton, CA); Abbate, Anthony J. (Santa Clara, CA); Limon, Timothy A. (Cupertino, CA); Kleine, Klaus (Los Gatos, CA), filed on April 17, 2014, was made available online on August 21, 2014.

The patent's assignee is Abbott Cardiovascular Systems Inc.

News editors obtained the following quote from the background information supplied by the inventors: "This invention relates to methods of manufacturing polymeric stents.

"This invention relates to radially expandable endoprostheses, that 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 that 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 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.

"Stents are typically composed of scaffolding that includes a pattern or network of interconnecting structural elements or struts, formed from wires, tubes, or sheets of material rolled into a cylindrical shape. This scaffolding gets its name because it physically holds open and, if desired, expands the wall of the passageway. Typically, stents are capable of being compressed or crimped onto a catheter so that they can be delivered to and deployed at a treatment site.

"Delivery includes inserting the stent through small lumens using a catheter and transporting it to the treatment site. Deployment includes expanding the stent to a larger diameter once it is at the desired location. Mechanical intervention with stents has reduced the rate of restenosis as compared to balloon angioplasty. Yet, restenosis remains a significant problem. When restenosis does occur in the stented segment, its treatment can be challenging, as clinical options are more limited than for those lesions that were treated solely with a balloon.

"Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy uses medicated stents to locally administer a therapeutic substance. Effective concentrations at the treated site require systemic drug administration which often produces adverse or even toxic side effects. Local delivery is a preferred treatment method because it administers smaller total medication levels than systemic methods, but concentrates the drug at a specific site. Local delivery thus produces fewer side effects and achieves better results.

"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.

"The stent must be able to satisfy a number of mechanical requirements. 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. In addition, the stent must possess sufficient flexibility to allow for crimping, expansion, and cyclic loading.

"Some treatments with implantable medical devices require the presence of the device only for a limited period of time. Once treatment is complete, which may include structural tissue support and/or drug delivery, it may be desirable for the stent to be removed or disappear from the treatment location. One way of having a device disappear may be by fabricating the device in whole or in part from materials that erode or disintegrate through exposure to conditions within the body. Thus, erodible portions of the device can disappear or substantially disappear from the implant region after the treatment regimen is completed. After the process of disintegration has been completed, no portion of the device, or an erodible portion of the device will remain. In some embodiments, very negligible traces or residue may be left behind. Stents fabricated from biodegradable, bioabsorbable, and/or bioerodable materials such as bioabsorbable polymers can be designed 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."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Certain embodiments of the invention include a method of fabricating a stent delivery device comprising forming a polymeric tube using extrusion, the tube being drawn during extrusion so that a diameter of the formed tube is less than a target diameter; radially deforming the formed tube so that the deformed tube comprises the target diameter; forming a stent from the deformed tube, wherein forming the stent includes laser machining a stent pattern in the deformed tube with an ultra-short pulse laser; and crimping the stent on a support element, wherein a temperature of the stent during crimping is above an ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 depicts a stent.

"FIG. 2 depicts an axial cross-section of a polymer tube positioned within an annular member or mold.

"FIG. 3 depicts a deformed polymer tube in a mold.

"FIG. 4 depicts a schematic plot of the crystal nucleation rate and the crystal growth rate, and the overall rate of crystallization.

"FIG. 5 depicts a mathematical representation of a Gaussian laser beam profile.

"FIG. 6 depicts a collimated two-dimensional representation of a laser beam.

"FIG. 7 depicts an overhead view of the surface of a substrate.

"FIG. 8 illustrates a kerf machined by a laser.

"FIG. 9 depicts an exemplary stent pattern.

"FIG. 10A depicts an exemplary bending element of a stent pattern.

"FIG. 10B depicts the strain distribution along a line offset from the neutral axis of the bending element depicted in FIG. 10B.

"FIG. 11 is a schematic plot of the specific volume of an amorphous polymer vs. temperature."

For additional information on this patent application, see: Gale, David C.; Huang, Bin; Abbate, Anthony J.; Limon, Timothy A.; Kleine, Klaus. Biodegradable Polymeric Stents. Filed April 17, 2014 and posted August 21, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4802&p=97&f=G&l=50&d=PG01&S1=20140814.PD.&OS=PD/20140814&RS=PD/20140814

Keywords for this news article include: Surgery, Cardiology, Restenosis, Heart Disease, Risk and Prevention, Surgical Technology, Abbott Cardiovascular Systems Inc..

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Source: Politics & Government Week


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