News Column

Patent Issued for Method of Fabricating an Implantable Medical Device to Reduce Chance of Late Inflammatory Response

June 25, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventors Huang, Bin (Pleasanton, CA); Gale, David C. (San Jose, CA), filed on May 31, 2006, was published online on June 10, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8747879 is assigned to Advanced Cardiovascular Systems, Inc. (Santa Clara, CA).

The following quote was obtained by the news editors from the background information supplied by the inventors: "This invention relates to a method of fabricating an implantable medical device by controlling crystalline structure.

"This invention relates generally to implantable medical devices having a range of mechanical and therapeutic requirements during use. In particular, the 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 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. 'Restenosis' refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been subjected to angioplasty or valvuloplasty.

"The stent must be able to satisfy several 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. This requires a sufficient degree of strength and rigidity or stiffness. In addition to having adequate radial 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 upon deployment which typically requires substantial deformation of portions of the stent. 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. Therefore, a stent must be capable of exhibiting relatively high toughness which corresponds to high strength and rigidity, as well as flexibility.

"A stent is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements or struts. The stent can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. A pattern can be formed in a tube, for example, by laser cutting. The scaffolding is designed to allow the stent to be radially expandable. The pattern is generally designed to maintain the longitudinal flexibility and radial rigidity required of the stent. Longitudinal flexibility facilitates delivery of the stent and radial rigidity is needed to hold open a bodily lumen upon deployment.

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

"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 after the clinical need for them has ended.

"One of the major problems associated with all types of stents is late inflammation caused by the stent after the stent begins to degrade and bioabsorb within the body. Inflammation may follow stent bioabsorption.

"What is needed in the art is an implantable medical device and method for making the device that reduces the likelihood for late inflammation during bioabsorption as well as maintains mechanical requirements during treatment."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The invention provides a method for fabricating an implantable medical device to increase biocompatibility of the device, the method comprising: heat setting a polymer construct, wherein the polymer construct is at a temperature range of from about Tg to about 0.6(Tm-Tg)+Tg such that the set polymer construct comprises a crystalline structure having crystals at a size less than about 2 microns; and fabricating an implantable medical device from the heat set polymer construct.

"The invention also provides a method for fabricating an implantable medical device to increase biocompatibility, the method comprising: maintaining a polymer construct at a temperature greater than Tg of the polymer at which the crystal nucleation rate of the polymer construct is greater than the crystal growth rate such that crystals of the polymer construct at a size less than about 2 microns is obtained; and fabricating an implantable medical device from the heat set polymer construct.

"The invention also provides an implantable medical device comprising: a plurality of crystalline domains having crystals dispersed within an amorphous domain, the majority of the crystals being less than about 2 microns.

"Finally, the invention provides a method of treating a bodily lumen with a degradable stent comprising: disposing a degradable semicrystalline polymeric stent within a bodily lumen, wherein a majority of the crystals in the polymer are of a crystal size less than about 2 microns; and radially expanding the device within the lumen."

URL and more information on this patent, see: Huang, Bin; Gale, David C.. Method of Fabricating an Implantable Medical Device to Reduce Chance of Late Inflammatory Response. U.S. Patent Number 8747879, filed May 31, 2006, 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=8747879.PN.&OS=PN/8747879RS=PN/8747879

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

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Source: Journal of Engineering


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