The assignee for this patent application is
Reporters obtained the following quote from the background information supplied by the inventors: "This invention relates to implantable medical devices and methods of fabricating implantable medical devices.
"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 The balloon may then be deflated and the catheter withdrawn.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 constraining member such as 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 When the stent is in a desired bodily location, the sheath may be withdrawn which allows the stent to self-expand.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.
"Potential problems with degradable polymers that may be suitable for use in stents include inadequate toughness and a degradation rate that is slower than is desirable for certain treatments."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "Various embodiments of the present invention include a stent comprising structural elements fabricated at least in part from a bioceramic/polymer composite, the composite having a plurality of bioceramic particles dispersed within a biodegradable polymer, the plurality of bioceramic particles comprising at least two types of bioceramic particles, at least two types having a different effect on the degradation rate of the polymer.
"Further embodiments of the present invention include a stent comprising structural elements fabricated from a bioceramic/polymer composite, the composite having a plurality of bioceramic particles dispersed within a biodegradable polymer, the plurality of bioceramic particles comprising acidic particles and basic particles, the acidic particles and basic particles having different particle size distributions.
"Additional embodiments of the present invention include a stent comprising structural elements fabricated from a bioceramic/polymer composite, the composite having a plurality of bioceramic particles dispersed within a biodegradable polymer, the plurality of bioceramic particles comprising at least two types of particles, wherein the degradation of a selected type of particle is reduced or prevented during a selected time frame by encapsulating some or all of the selected type of particles with a bioabsorbable polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1A depicts a three-dimensional view of a stent.
"FIG. 1B depicts a section of a structural element from the stent depicted in FIG. 2A.
"FIG. 2A depicts a schematic close-up view of the section depicted in FIG. 1B for a stent made from a polymer/bioceramic composite.
"FIG. 2B depicts a schematic close-up view of the section depicted in FIG. 1B made from a polymer blend/bioceramic composite.
"FIG. 3 depicts a schematic close-up view of an interface between a discrete polymer phase and a continuous polymer phase from FIG. 2B.
"FIG. 4 depicts a plot of the expected dependence of degradation rate the ratio of acidic to basic particles in a PLLA/modifier polymer/bioceramic composite stent.
"FIG. 5 depicts probability density functions of particle size distributions for two different types of particles.
"FIG. 6A depicts a synthesis scheme of a modifier polymer with a PLLA anchor segment.
"FIG. 6B depicts a synthesis scheme of a modifier polymer with a LPLG anchor segment."
For more information, see this patent application: WANG, Yunbing; GALE,
Keywords for this news article include: Surgery, Treatment, Cardiology, Restenosis, Heart Disease, Risk and Prevention, Surgical Technology,
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